Fatty acid-induced endoplasmic reticulum stress promoted lipid accumulation in calf hepatocytes, and endoplasmic reticulum stress existed in the liver of severe fatty liver cows

Expression of hepatic genes involved in bile acid metabolism in dairy cows with fatty liver

Bile acids are cholesterol-derived molecules that are primarily produced in the liver. In nonruminants with fatty liver, overproduction of bile acids is associated with liver injury. During the transition period, fatty liver is a metabolic disorder that can affect up to 50% of high-producing dairy cows. The purpose of this study was to provide a comprehensive evaluation on hepatic bile acid metabolism in dairy cows with fatty liver by assessing expression changes of genes involved in bile acid synthesis, export and uptake. The serum activities of aspartate aminotransferase, alanine aminotransferase and glutamate dehydrogenase and concentration of total bile acids were all greater, whereas serum concentration of total cholesterol was lower in cows with fatty liver than in healthy cows. Content of total bile acids was higher but total cholesterol was slightly lower in liver tissues from fatty liver cows than from healthy cows. The hepatic mRNA abundance of cholesterol 7a-hydroxylase (CYP7A1), hydroxy-delta-5-steroid dehydrogenase, 3 β- and steroid delta-isomerase 7 (HSD3B7) and sterol 12α-hydroxylase (CYP8B1), enzymes involved in the classic pathway of bile acid synthesis, was higher in fatty liver cows than in healthy cows. Compared with healthy cows, the hepatic mRNA abundance of alternative bile acid synthesis pathway-related genes sterol 27-hydroxylase (CYP27A1) and oxysterol 7α-hydroxylase (CYP7B1) did not differ in cows with fatty liver. The protein and mRNA abundance of bile acid transporter bile salt efflux pump (BSEP) were lower in the liver of dairy cow with fatty liver. Compared with healthy cows, the hepatic mRNA abundance of bile acid transporters solute carrier family 51 subunit α (SLC51A), ATP binding cassette subfamily C member 1 (ABCC1) and 3 (ABCC3) was greater in cows with fatty liver, whereas the solute carrier family 51 subunit β (SLC51B) did not differ. The expression of genes involved in bile acid uptake, including solute carrier family 10 member 1 (NTCP), solute carrier organic anion transporter family member 1A2 (SLCO1A2) and 2B1 (SLCO2B1) was upregulated in dairy cows with fatty liver. Furthermore, the hepatic protein and mRNA abundance of bile acid metabolism regulators farnesoid X receptor (FXR) and small heterodimer partner (SHP) were lower in cows with fatty liver than in healthy cows. Overall, these data suggest that inhibition of FXR signaling pathway may lead to the increased bile acid synthesis and uptake and decreased secretion of bile acids from hepatocytes to the bile, which elevates hepatic bile acids content in dairy cows with fatty liver. As the hepatotoxicity of bile acids has been demonstrated on nonruminant hepatocytes, it is likely that the liver injury is induced by increased hepatic bile acids content in dairy cows with fatty liver.

Fatty acids promote M1 polarization of monocyte-derived macrophages in healthy or ketotic dairy cows and a bovine macrophage cell line via impairing mTOR-mediated autophagy

Excessive concentrations of free fatty acids (FFA) are the main factors causing immune dysfunction and inflammation in dairy cows with ketosis. Polarization of macrophages (the process of macrophages freely switching from one phenotype to another) into M1 or M2 phenotypes is an important event during inflammation induced by environmental stimuli. In non-ruminants, mammalian target of rapamycin (mTOR)-mediated autophagy (a major waste degradation process) regulates macrophage polarization. Thus, the objective was to unravel the role of mTOR-mediated autophagy on macrophage polarization in ketotic dairy cows. Four experiments were performed as follows: (1) In vitro differentiated monocyte-derived macrophages from healthy dairy cows or dairy cows with clinical ketosis (CK) were treated with 100 ng/mL lipopolysaccharide (LPS) and 100 ng/mL interferon-γ (IFN-γ) or 10 ng/mL interleukin-4 (IL4) and 10 ng/mL interleukin-10 (IL10) for 24 h; (2) Immortalized bovine macrophages were treated with 0, 0.3, 0.6, 1.2 mM FFA and LPS and IFN-γ or IL4 and IL10 for 24 h; (3) Macrophages were pretreated with 2 μM 4,6-dimorpholino-N-(4-nitrophenyl)-1,3,5-triazin-2-amine (MHY1485) for 30 min before treatment with LPS and IFN-γ or IL4 and IL10; (4) Macrophages were pretreated with 100 nM rapamycin (RAPA) for 2 h before treatment with LPS and IFN-γ or IL4 and IL10. Compared with healthy cows, cows with CK had a greater mean fluorescence intensity (MFI) of CD86+, but lower MFI of CD206+ and lower number of autophagosomes and autolysosomes in macrophages. Exogenous FFA treatment upregulated protein abundance of inducible nitric oxide synthase (iNOS) and mean fluorescence intensity of CD86, whereas it downregulated the protein abundance of arginase 1 (ARG1) and mean fluorescence intensity of CD206. In addition, FFA increased the p-p65/p65 protein abundance and tumor necrosis factor α (TNFA), interleukin-1B (IL1B), and interleukin-6 (IL6) mRNA abundance, but decreased LC3-phosphatidylethanolamine conjugate (LC3-II) protein abundance and autophagosomes and autolysosomes number. Pretreatment with MHY1485 promoted macrophage M1 polarization and inhibited macrophage M2 polarization via decreased mTOR-mediated autophagy. Activation of mTOR-mediated autophagy by pretreatment with RAPA attenuated the upregulation of inflammation in M1 macrophages that was induced by FFA. These data revealed that high concentrations of FFA promote macrophage M1 polarization in ketotic dairy cows via impairing mTOR-mediated autophagy.

Inositol-requiring enzyme 1α and c-Jun N-terminal kinase axis activation contributes to intracellular lipid accumulation in calf hepatocytes

During the perinatal period, dairy cows undergo negative energy balance, resulting in elevated circulating levels of nonesterified fatty acids (NEFA). Although increased blood NEFA concentrations are a physiological adaptation of early lactation, excessive NEFA in dairy cows is a major cause of fatty liver. Aberrant lipid metabolism leads to hepatic lipid accumulation and subsequently the development of fatty liver. Both inositol-requiring enzyme 1α (IRE1α) and c-Jun N-terminal kinase (JNK) have been validated for their association with hepatic lipid accumulation, including their regulatory functions in calf hepatocyte insulin resistance, oxidative stress, and apoptosis. Meanwhile, both IRE1α and JNK are involved in lipid metabolism in nonruminants. Therefore, the aim of this study was to investigate how IRE1α and JNK regulate lipid metabolism in bovine hepatocytes. An experiment was conducted on randomly selected 10 healthy cows (hepatic triglyceride [TG] content <1%) and 10 cows with fatty liver (hepatic TG content >5%). Liver tissue and blood samples were collected from experimental cows. Serum concentrations of NEFA and β-hydroxybutyrate (BHB) were greater, whereas serum concentrations of glucose and milk production were lower in cows with fatty liver. The western blot results revealed that dairy cows with fatty liver had higher phosphorylation levels of JNK, c-Jun, and IRE1α in the liver tissue. Three in vitro experiments were conducted using primary calf hepatocytes isolated from 5 healthy calves (body weight: 30-40 kg; 1 d old). First, hepatocytes were treated with NEFA (1.2 mM) for 0.5, 1, 2, 3, 5, 7, 9, or 12 h, which showed that the phosphorylated levels of JNK, c-Jun, and IRE1α increased in both linear and quadratic effects. In the second experiment, hepatocytes were treated with high concentrations of NEFA (1.2 mM) for 12 h with or without SP600125, a canonical inhibitor of JNK. Western blot results showed that SP600125 treatment could decrease the expression of lipogenesis-associated proteins (PPARγ and SREBP-1c) and increase the expression of fatty acid oxidation (FAO)-associated proteins (CPT1A and PPARα) in NEFA-treated hepatocytes. The perturbed expression of lipogenesis-associated genes (FASN, ACACA, and CD36) and FAO-associated gene ACOX1 were also recovered by JNK inhibition, indicating that JNK reduced excessive NEFA-induced lipogenesis and FAO dysregulation in calf hepatocytes. Third, short hairpin RNA targeting IRE1α (sh-IRE1α) was transfected into calf hepatocytes to silence IRE1α, and KIRA6 was used to inhibit the kinase activity of IRE1α. The blockage of IRE1α could at least partially suppressed NEFA-induced JNK activation. Moreover, the blockage of IRE1α downregulated the expression of lipogenesis genes and upregulated the expression of FAO genes in NEFA-treated hepatocytes. In conclusion, these findings indicate that targeting the IRE1α-JNK axis can reduce NEFA-induced lipid accumulation in bovine hepatocytes by modulating lipogenesis and FAO. This may offer a prospective therapeutic target for fatty liver in dairy cows.

Role of diacylglycerol O-acyltransferase 1 (DGAT1) in lipolysis and autophagy of adipose tissue from ketotic dairy cows

High-yielding dairy cows in early lactation often encounter difficulties in meeting the energy requirements essential for maintaining milk production. This is primarily attributed to insufficient dry matter intake, which consequently leads to sustained lipolysis of adipose tissue. Fatty acids released by lipolysis can disrupt metabolic homeostasis. Autophagy, an adaptive response to intracellular environmental changes, is considered a crucial mechanism for regulating lipid metabolism and maintaining a proper cellular energy status. Despite its close relationship with aberrant lipid metabolism and cyto-lipotoxicity in animal models of metabolic disorders, the precise function of diacylglycerol o-acyltransferase 1 (DGAT1) in bovine adipose tissue during periods of negative energy balance (NEB) is not fully understood. Particularly regarding its involvement in lipolysis and autophagy. The objective of the present study was to assess the impact of DGAT1 on both lipolysis and autophagy in bovine adipose tissue and isolated adipocytes. Adipose tissue and blood samples were collected from cows diagnosed as clinically ketotic (n = 15) or healthy (n = 15) following a veterinary evaluation based on clinical symptoms and serum concentrations of BHB, which were 3.19 mM (interquartile range = 0.20) and 0.50 mM (interquartile range = 0.06), respectively. Protein abundance of DGAT1 and phosphorylation levels of unc-51-like kinase 1 (ULK1), were greater in adipose tissue from cows with ketosis, whereas phosphorylation levels of phosphoinositide 3-kinase (PI3K), protein kinase B (AKT), and mammalian target of rapamycin (mTOR) were lower. Furthermore, when adipocytes isolated from the harvested adipose tissue of 15 healthy cows were transfected with DGAT1 overexpression adenovirus or DGAT1 small interfering RNA followed by exposure to epinephrine (EPI), it led to greater ratios and protein abundance of phosphorylated hormone-sensitive triglyceride lipase (LIPE) to total LIPE and adipose triglyceride lipase (ATGL), while inhibiting the protein phosphorylation levels of ULK1, PI3K, AKT and mTOR. Overexpression of DGAT1 in EPI-treated adipocytes reduced lipolysis and autophagy, whereas silencing DGAT1 further exacerbated EPI-induced lipolysis and autophagy. Taken together, these findings indicate that upregulation of DGAT1 may function as an adaptive response to suppress adipocytes lipolysis, highlighting the significance of maintaining metabolic homeostasis in dairy cows during periods of NEB.

HFD-exacerbated Metabolic Side Effects of Olanzapine Are Suppressed by ER Stress Inhibitor

OBJECTIVE

Numerous schizophrenic patients are suffering from obesity primarily attributed to antipsychotic medication and poor dietary habits. This study investigated the progressive deterioration of olanzapine-induced metabolic disorders in the presence of a high-fat diet (HFD) and explored the involvement of endoplasmic reticulum (ER) stress.

METHODS

Female Sprague-Dawley rats fed on a standard chow diet or HFD were treated with olanzapine (3 mg/kg/day) and the ER stress inhibitor 4-phenylbutyric acid (4-PBA, 1 and 0.5 g/kg/day) for 8 days. Changes in body weight, food intake, and plasma lipids were assessed. Hepatic fat accumulation was evaluated using oil red O staining. Western blotting and immunofluorescence assays were employed to examine the expression of ER stress markers, NOD-like receptor pyrin domain-containing protein 3 (NLRP3), and proopiomelanocortin (POMC) in the hypothalamus or liver.

RESULTS

Compared to olanzapine alone, olanzapine+HFD induced greater weight gain, increased hyperlipidemia, and enhanced hepatic fat accumulation (P<0.05). Co-treatment with 4-PBA exhibited a dose-dependent inhibition of these effects (P<0.05). Further mechanistic investigations revealed that olanzapine alone activated ER stress, upregulated NLRP3 expression in the hypothalamus and liver, and downregulated hypothalamic POMC expression. The HFD exacerbated these effects by 50%-100%. Moreover, co-administration of 4-PBA dose-dependently attenuated the olanzapine+HFD-induced alterations in ER stress, NLRP3, and POMC expression in the hypothalamus and liver (P<0.05).

CONCLUSION

HFD worsened olanzapine-induced weight gain and lipid metabolic disorders, possibly through ER stress-POMC and ER stress-NLRP3 signaling. ER stress inhibitors could be effective in preventing olanzapine+HFD-induced metabolic disorders.

Low abundance of insulin-induced gene 1 contributes to SREBP-1c processing and hepatic steatosis in dairy cows with severe fatty liver

Fatty liver is a major metabolic disorder of high-producing dairy cows during the transition period. In nonruminants, it is well established that insulin-induced gene 1 (INSIG1) plays a crucial role in regulating hepatic lipogenesis by controlling the anchoring of sterol regulatory element-binding protein 1 (SREBP-1) on the endoplasmic reticulum along with SREBP cleavage-activating protein (SCAP). Whether the INSIG1-SCAP-SREBP-1c transport axis is affected in cows experiencing fatty liver is unknown. Thus, the aim of this study was to investigate the potential role of INSIG1-SCAP-SREBP-1c axis in the progression of fatty liver in dairy cows. For in vivo experiments, 24 dairy cows at the start of their fourth lactation (median; range 3-5) and 8 d in milk (median; range 4-12 d) were selected into a healthy group [n = 12; triglyceride (TG) content <1%] and a severe fatty liver group (n = 12; TG content >10%) according to their hepatic TG content. Blood samples were collected for detecting serum concentrations of free fatty acids, β-hydroxybutyrate, and glucose. Compared with healthy cows, cows with severe fatty liver had higher serum concentrations of β-hydroxybutyrate and free fatty acids and lower concentration of glucose. Liver biopsies were used to detect the status of INSIG1-SCAP-SREBP-1c axis, and the mRNA expression of SREBP-1c-target lipogenic genes acetyl-CoA carboxylase α (ACACA), fatty acid synthase (FASN), and diacylglycerol acyltransferase 1 (DGAT1). Cows with severe fatty liver had lower protein expression of INSIG1 in the hepatocyte endoplasmic reticulum fraction, greater protein expression of SCAP and precursor SREBP-1c in the hepatocyte Golgi fraction, and greater protein expression of mature SREBP-1c in the hepatocyte nuclear fraction. In addition, the mRNA expression of SREBP-1c-target lipogenic genes ACACA, FASN, and DGAT1 was greater in the liver of dairy cows with severe fatty liver. In vitro experiments were conducted on hepatocytes isolated from 5 healthy 1-d-old female Holstein calves, and hepatocytes from each calf were run independently. First, hepatocytes were treated with 0, 200, or 400 μM palmitic acid (PA) for 12 h. Exogenous PA treatment decreased INSIG1 protein abundance, enhanced the endoplasmic reticulum to Golgi export of SCAP-precursor SREBP-1c complex and the nuclear translocation of mature SREBP-1c, all of which was associated with increased transcriptional activation of lipogenic genes and TG synthesis. Second, hepatocytes were transfected with INSIG1-overexpressing adenovirus for 48 h and treated with 400 μM PA 12 h before the end of transfection. Overexpressing INSIG1 inhibited PA-induced SREBP-1c processing, upregulation of lipogenic genes, and TG synthesis in hepatocytes. Overall, the present in vivo and in vitro results indicated that the low abundance of INSIG1 contributed to SREBP-1c processing and hepatic steatosis in dairy cows. Thus, the INSIG1-SCAP-SREBP-1c axis may be a novel target for treatment of fatty liver in dairy cows.

AdipoRon alleviates fatty acid-induced lipid accumulation and mitochondrial dysfunction in bovine hepatocytes by promoting autophagy

During the transition period in dairy cows, high circulating concentrations of nonesterified fatty acids (NEFA) increase hepatic lipid deposits and are considered a major pathological factor for liver damage. We investigated whether AdipoRon, a synthetic small-molecule agonist of adiponectin receptors 1 and 2 shown to prevent liver lipid accumulation in nonruminants, could alleviate NEFA-induced lipid accumulation and mitochondrial dysfunction. Bovine hepatocytes were isolated from 5 healthy Holstein female newborn calves (1 d of age, 30-40 kg, fasting), and independently isolated hepatocytes from at least 3 different calves were used for each subsequent experiment. The composition and concentration of NEFA used in this study were selected according to hematological criteria of dairy cows with fatty liver or ketosis. First, hepatocytes were cultured with various concentrations of NEFA (0, 0.6, 1.2, or 2.4 mM) for 12 h. In a second experiment, hepatocytes were treated with AdipoRon at different concentrations (0, 5, 25, or 50 μM for 12 h) and times (25 μM for 0, 6, 12, or 24 h) with or without NEFA (1.2 mM) treatment. In the last experiment, hepatocytes were treated with AdipoRon (25 μM), NEFA (1.2 mM), or both for 12 h after treatment with or without the autophagy inhibitor chloroquine. Hepatocytes treated with NEFA had increased protein abundance of sterol regulatory element-binding protein 1c (SREBP-1c) and mRNA abundance of acetyl-CoA carboxylase 1 (ACACA), and decreased protein abundance of peroxisome proliferator-activated receptor α (PPARA), proliferator-activated receptor gamma coactivator-1 α (PGC-1α), mitofusin 2 (MFN2), cytochrome c oxidase subunit IV (COX IV), and mRNA abundance of carnitine palmitoyltransferase 1A (CPT1A), along with lower ATP concentrations. AdipoRon treatment reversed these effects, suggesting this compound had a positive effect on lipid metabolism and mitochondrial dysfunction during the NEFA challenge. In addition, upregulated expression of microtubule-associated protein 1 light chain 3-II (LC3-II, encoded by MAP1LC3) and downregulated expression of sequestosome-1 (SQSTM1, also called p62) indicated that AdipoRon enhanced autophagic activity in hepatocytes. The fact that chloroquine impeded the beneficial effects of AdipoRon on lipid accumulation and mitochondrial dysfunction suggested a direct role for autophagy during NEFA challenge. Our results suggest that autophagy is an important cellular mechanism to prevent NEFA-induced lipid accumulation and mitochondrial dysfunction in bovine hepatocytes, which is consistent with other studies. Overall, AdipoRon may represent a promising therapeutic agent to maintain hepatic lipid homeostasis and mitochondrial function in dairy cows during the transition period.

Liver fibrosis is a common pathological change in the liver of dairy cows with fatty liver

Fatty liver (i.e., hepatic lipidosis) is a prevalent metabolic disorder in dairy cows during the transition period, characterized by excess hepatic accumulation of triglyceride (TG), tissue dysfunction, and cell death. Detailed pathological changes, particularly hepatic fibrosis, during fatty liver remain to be determined. Liver fibrosis occurs as a consequence of liver damage, resulting from the excessive accumulation of extracellular matrix, which distorts the architecture of the normal liver, compromising its normal synthetic and metabolic functions. Thus, we aimed to investigate liver fibrosis status and its potential causal factors including oxidative stress, hepatocyte apoptosis, and production of inflammatory cytokines in the liver of cows with fatty liver. Forty-five dairy cows (parity, 3-5) were selected, and liver biopsy and blood were collected on the second week postpartum (days in milk, 10-14 d). On the basis of the degree of lipid accumulation in liver, selected cows were categorized into normal (n = 25; TG <1% wet wt), mild fatty liver (n = 15; 1% ≤ TG <5% wet wt), and moderate fatty liver (n = 5; 5% ≤ TG <10% wet wt). Compared with normal cows, blood concentrations of nonesterified fatty acids and β-hydroxybutyrate, along with alanine aminotransferase and aspartate aminotransferase activities, were greater in the cows with fatty liver (mild and moderate). Hepatic extracellular matrix deposition, as indicated by Picrosirius red staining, was greater in cows with fatty liver than those with normal ones. In addition, we observed an increased proportion of collagen type I fiber in extracellular matrix with increased lipid accumulation in the liver. Compared with normal cows, the area of α-smooth muscle actin (α-SMA)-positive staining along with the mRNA abundance of collagen type I α 1 (COL1A1), ACTA2 (gene encoding α-SMA), and transforming growth factor-β (TGFB) were greater in cows with fatty liver. Compared with normal cows, hepatic contents of malondialdehyde, glutathione disulfide, and 8-isoprostane were greater, whereas total antioxidant capacity, the hepatic content of glutathione, and activities of antioxidant indicators, including superoxide dismutase, glutathione peroxidase, and catalase, were lower in cows with fatty liver. The number of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling-positive cells and abundance of apoptosis-related molecules BAX, CASP3, CASP8, and CASP9 were greater in cows with fatty liver. However, mRNA abundance of the anti-apoptotic gene BCL2 did not differ. The mRNA abundance of pro-inflammatory cytokines including tumor necrosis factor-α (TNFA), interleukin-1β (IL1B), and interleukin-6 (IL6) was greater in the liver of cows with fatty liver. Overall, the present study indicated that fibrosis is a common pathological response to liver damage and is associated with oxidative stress, hepatocyte death, and inflammation.

Performance and Metabolic, Inflammatory, and Oxidative Stress-Related Parameters in Early Lactating Dairy Cows with High and Low Hepatic FGF21 Expression

Induction of FGF21 expression in the liver and a significant increase in plasma FGF21 concentration have been demonstrated in cows during early lactation, but knowledge about the function of FGF21 in dairy cows remains limited. In order to improve the understanding of the physiological role of FGF21 in dairy cows, the present study aimed to investigate differences in metabolic pathways between dairy cows with high and low hepatic expression of FGF21 at week 1 of lactation (n = 8/group) by liver transcriptomics, targeted plasma metabolomics, and analysis of inflammatory and oxidative stress-related parameters. Dry matter intake, energy balance, milk yield, and energy-corrected milk yield at days 8−14 postpartum did not differ between cows with high and low hepatic FGF21 expression. However, cows with high FGF21 expression showed an upregulation of genes involved in endoplasmic reticulum stress, inflammation, and nuclear factor E2-related factor 2 (Nrf2)-dependent cytoprotection compared to cows with low FGF21 expression at week 1 postpartum (p < 0.05). Concentrations of important antioxidants (tocopherols, β-carotene, and glutathione) in the liver and plasma, trolox equivalent antioxidant capacity in plasma, concentrations of oxidative stress-related compounds (thiobarbituric acid-reactive substances and protein carbonyls), and levels of most acute phase proteins at week 1 postpartum did not differ between cows with high or low FGF21 expression. Moreover, among a total of >200 metabolites assayed in the plasma, concentrations of only 7 metabolites were different between cows with high or low FGF21 expression (p < 0.05). Overall, the results showed that cows with high and low FGF21 hepatic expression had only moderate differences in metabolism, but FGF21 might be important in the adaptation of dairy cows to stress conditions during early lactation.

NFATc1 signaling drives chronic ER stress responses to promote NAFLD progression

OBJECTIVES

Non-alcoholic fatty liver disease (NAFLD) can persist in the stage of simple hepatic steatosis or progress to steatohepatitis (NASH) with an increased risk for cirrhosis and cancer. We examined the mechanisms controlling the progression to severe NASH in order to develop future treatment strategies for this disease.

DESIGN

NFATc1 activation and regulation was examined in livers from patients with NAFLD, cultured and primary hepatocytes and in transgenic mice with differential hepatocyte-specific expression of the transcription factor (Alb-cre, NFATc1^c.a . and NFATc1^Δ/Δ ). Animals were fed with high-fat western diet (WD) alone or in combination with tauroursodeoxycholic acid (TUDCA), a candidate drug for NAFLD treatment. NFATc1-dependent ER stress-responses, NLRP3 inflammasome activation and disease progression were assessed both in vitro and in vivo.

RESULTS

NFATc1 expression was weak in healthy livers but strongly induced in advanced NAFLD stages, where it correlates with liver enzyme values as well as hepatic inflammation and fibrosis. Moreover, high-fat WD increased NFATc1 expression, nuclear localisation and activation to promote NAFLD progression, whereas hepatocyte-specific depletion of the transcription factor can prevent mice from disease acceleration. Mechanistically, NFATc1 drives liver cell damage and inflammation through ER stress sensing and activation of the PERK-CHOP unfolded protein response (UPR). Finally, NFATc1-induced disease progression towards NASH can be blocked by TUDCA administration.

CONCLUSION

NFATc1 stimulates NAFLD progression through chronic ER stress sensing and subsequent activation of terminal UPR signalling in hepatocytes. Interfering with ER stress-responses, for example, by TUDCA, protects fatty livers from progression towards manifest NASH.

Effects of diacylglycerol O-acyltransferase 1 (DGAT1) on endoplasmic reticulum stress and inflammatory responses in adipose tissue of ketotic dairy cows

Adipose tissue of ketotic dairy cows exhibits greater lipolytic rate and signs of inflammation, which further aggravate the metabolic disorder. In nonruminants, the endoplasmic reticulum (ER) is a key organelle coordinating metabolic adaptations and cellular functions; thus, disturbances known as ER stress lead to inflammation and contribute to metabolic disorders. Enhanced activity of diacylglycerol O-acyltransferase 1 (DGAT1) in murine adipocytes undergoing lipolysis alleviated ER stress and inflammation. The aim of the present study was to investigate the potential role of DGAT1 on ER stress and inflammatory response of bovine adipose tissue in vivo and in vitro. Adipose tissue and blood samples were collected from cows diagnosed as clinically ketotic (n = 15) or healthy (n = 15) following a veterinary evaluation based on clinical symptoms and serum concentrations of β-hydroxybutyrate, which were 4.05 (interquartile range = 0.46) and 0.52 mM (interquartile range = 0.14), respectively. Protein abundance of DGAT1 was greater in adipose tissue of ketotic cows. Among ER stress proteins measured, ratios of phosphorylated PKR-like ER kinase (p-PERK) to PERK and phosphorylated inositol-requiring enzyme 1 (p-IRE1) to IRE1, and protein abundance of cleaved ATF6 protein were greater in adipose tissue of ketotic cows. Furthermore, ratios of phosphorylated RELA subunit of NF-κB (p-RELA) to RELA and phosphorylated c-jun N-terminal kinase (p-JNK) to JNK were greater, whereas protein abundance of NF-κB inhibitor α (NFKBIA) was lower in adipose tissue of ketotic cows. In addition, mRNA abundance of proinflammatory cytokines including TNF and IL-6 was greater in adipose tissue of ketotic cows. To better address mechanistic aspects of these responses, primary bovine adipocytes isolated from the harvested adipose tissue of healthy cows were subjected to lipolysis-stimulating conditions via incubation with 1 μM epinephrine (EPI) for 2 h. In another experiment, adipocytes were cultured with DGAT1 overexpression adenovirus and DGAT1 small interfering RNA for 48 h, respectively, followed by EPI (1 μM) exposure for 2 h. Treatment with EPI led to greater ratios of p-PERK to PERK, p-IRE1 to IRE1, p-RELA to RELA, p-JNK to JNK, and cleaved ATF6 protein, whereas EPI stimulation inhibited protein abundance of NFKBIA. Furthermore, treatment with EPI upregulated the secretion of proinflammatory cytokines into culture medium, including TNF-α and IL-6. Overexpression of DGAT1 in EPI-treated adipocytes attenuated ER stress, the activation of NF-κB and JNK signaling pathways, and the secretion of inflammatory cytokines. In contrast, silencing DGAT1 further aggravated EPI-induced ER stress and inflammatory responses. Overall, these data indicated that activation of DGAT1 may act as an adaptive mechanism to dampen metabolic dysregulation in adipose tissue. As such, it contributes to relief from ER stress and inflammatory responses.

Targeting IRE1α and PERK in the endoplasmic reticulum stress pathway attenuates fatty acid-induced insulin resistance in bovine hepatocytes

Endoplasmic reticulum (ER) stress can be induced by various stimuli and triggers the unfolded protein response to activate intracellular signaling pathways that are mediated by 3 ER-resident sensors: inositol requiring protein-1α (IRE1α), PKR-like ER kinase (PERK), and activating transcription factor-6 (ATF6). In nonruminants, ER stress plays a critical role in hepatic insulin resistance. However, whether ER stress plays a role in nonesterified fatty acid (NEFA)-induced hepatic insulin resistance in dairy cows is still unknown. Experiments were conducted using primary bovine hepatocytes isolated from 5 healthy calves (body weight: 30-40 kg; 1 d old). First, hepatocytes were treated with NEFA (1.2 mM) for 0.5, 1, 2, 3, 5, 7, 9, or 12 h. Treatment with NEFA elevated abundance of phosphorylated IRE1α and PERK, and cleavage of ATF6, along with the ER stress-associated genes XBP1, ATF4, and DNAJC3, resulting in both linear and quadratic effects. Furthermore, ER Tracker red staining and transmission electron microscopy results indicated that ER was dilated and degranulated in response to NEFA treatment, suggesting that ER stress was induced by NEFA treatment in bovine hepatocytes. Second, to assess the effect of ER stress on NEFA-induced insulin resistance, hepatocytes were treated with different concentrations of NEFA (0, 0.6, 1.2, or 2.4 mM) for 5 h with or without tauroursodeoxycholic acid (TUDCA, a canonical inhibitor of ER stress). Here, NEFA induced insulin resistance by increasing the abundance of insulin receptor substrate-1 (IRS1) phosphorylation at the inhibitory residue Ser 307 (S307) and decreasing the abundance of phosphorylated protein kinase B (AKT) and glycogen synthase kinase-3β (GSK3β) in a dose-dependent manner. This was accompanied by upregulation of an abundance of gluconeogenic genes [phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6-Pase)]. These detrimental effects of NEFA on insulin signaling could be reversed with TUDCA treatment, indicating a mechanistic link between ER stress and NEFA-induced insulin resistance. In a third experiment, pGPU6/GFP/Neo vectors containing short hairpin RNA targeting IRE1α were used to silence IRE1α transcription, and GSK2656157 (PERK phosphorylation inhibitor) and 4-(2-aminoethyl) benzenesulfonyl fluoride (AEBSF; an inhibitor of ATF6) were used to block PERK and ATF6 branches, respectively. Notably, the silencing of the IRE1α branch improved NEFA-induced insulin resistance by decreasing phosphorylation of IRS1 (S307) and increasing phosphorylation of AKT and GSK3β, and reducing PEPCK and G6-Pase mRNA abundance, which was likely dependent on IRE1α kinase activity. Similarly, blockage of the PERK branch increased phosphorylation of AKT and GSK3β, and reduced PEPCK and G6-Pase mRNA abundance, but had no effect on phosphorylation of IRS1 (S307). However, results showed that inhibition of the ATF6 branch had no effects on phosphorylation of IRS1, AKT, and GSK3β, and instead found increasing PEPCK and G6-Pase mRNA abundance. Taken together, data in the present study found that impeding IRE1α and PERK signaling might aid in relieving hepatic insulin resistance. However, the more detailed mechanisms of how IRE1α and PERK signaling contribute to hepatic insulin resistance in dairy cows remain to be determined.

Peroxisome Proliferator-Activated Receptor Activation in Precision-Cut Bovine Liver Slices Reveals Novel Putative PPAR Targets in Periparturient Dairy Cows

Metabolic challenges experienced by dairy cows during the transition between pregnancy and lactation (also known as peripartum), are of considerable interest from a nutrigenomic perspective. The mobilization of large amounts of non-esterified fatty acids (NEFA) leads to an increase in NEFA uptake in the liver, the excess of which can cause hepatic accumulation of lipids and ultimately fatty liver. Interestingly, peripartum NEFA activate the Peroxisome Proliferator-activated Receptor (PPAR), a transcriptional regulator with known nutrigenomic properties. The study of PPAR activation in the liver of periparturient dairy cows is thus crucial; however, current in vitro models of the bovine liver are inadequate, and the isolation of primary hepatocytes is time consuming, resource intensive, and prone to errors, with the resulting cells losing characteristic phenotypical traits within hours. The objective of the current study was to evaluate the use of precision-cut liver slices (PCLS) from liver biopsies as a model for PPAR activation in periparturient dairy cows. Three primiparous Jersey cows were enrolled in the experiment, and PCLS from each were prepared prepartum (−8.0 ± 3.6 DIM) and postpartum (+7.7± 1.2 DIM) and treated independently with a variety of PPAR agonists and antagonists: the PPARα agonist WY-14643 and antagonist GW-6471; the PPARδ agonist GW-50156 and antagonist GSK-3787; and the PPARγ agonist rosiglitazone and antagonist GW-9662. Gene expression was assayed through RT-qPCR and RNAseq, and intracellular triacylglycerol (TAG) concentration was measured. PCLS obtained from postpartum cows and treated with a PPARγ agonist displayed upregulation of ACADVL and LIPC while those treated with PPARδ agonist had increased expression of LIPC, PPARD, and PDK4. In PCLS from prepartum cows, transcription of LIPC was increased by all PPAR agonists and NEFA. TAG concentration tended to be larger in tissue slices treated with PPARδ agonist compared to CTR. Use of PPAR isotype-specific antagonists in PCLS cultivated in autologous blood serum failed to decrease expression of PPAR targets, except for PDK4, which was confirmed to be a PPARδ target. Transcriptome sequencing revealed considerable differences in response to PPAR agonists at a false discovery rate-adjusted p-value of 0.2, with the most notable effects exerted by the PPARδ and PPARγ agonists. Differentially expressed genes were mainly related to pathways involved with lipid metabolism and the immune response. Among differentially expressed genes, a subset of 91 genes were identified as novel putative PPAR targets in the bovine liver, by cross-referencing our results with a publicly available dataset of predicted PPAR target genes, and supplementing our findings with prior literature. Our results provide important insights on the use of PCLS as a model for assaying PPAR activation in the periparturient dairy cow.

Effects of Naltrexone on Expression of Lipid Metabolism-Related Proteins in Liver Steatosis Induced by Endoplasmic Reticulum Stress in Mice

This study aimed to explore the effect of naltrexone on the expression of lipid metabolism-related proteins in liver steatosis induced by endoplasmic reticulum stress in mice. Thirty inbred mice (C57BL/6J) were divided into three groups: group A (normal control group), group B (model control), and group C (naltrexone group). The male mice in group A were fed a regular diet, and the mice in groups B and C were fed a high-fat diet. Liver steatosis was observed by histopathological sections. Mouse liver (alanine aminotransferase (ALT) and triglyceride (TC)) content (glucose regulatory protein (GRP78), endoplasmic reticulum transmembrane protein kinase-1α (IRE-1α), C/EBP source protein (CHOP), cysteine-containing aspartate proteolytic enzyme 12 (caspase-12), B lymphoma-2 (Bcl-2), and cell death mediator (Bim)) was detected. Compared with group A, bodyweight, fat weight, ALT, TG, and hepatic steatosis were significantly increased in B and C groups (P < 0.05); compared with group B, group C showed a significant decrease in bodyweight, fat weight, ALT, TG, and hepatic steatosis (P < 0.05). Compared with group A, the expression levels of GRP78, IRE-1α, CHOP, caspase-12, and Bim in liver tissue of groups B and C mice were increased. Bcl-2 decreased (P < 0.05). Compared with group B and group C after naltrexone intervention, the expression levels of GRP78, IRE-1α, CHOP, caspase-12, and Bim decreased significantly, and Bcl-2 increased significantly (P < 0.05). Naltrexone can effectively reduce bodyweight and adipose tissue accumulation, reduce liver fat lesions, improve the expression of lipid metabolism-related proteins and endoplasmic reticulum stress, reduce liver lipid synthesis, and protect liver cells.

Inhibitory Antibodies against PCSK9 Reduce Surface CD36 and Mitigate Diet-Induced Renal Lipotoxicity

Background

PCSK9 modulates the uptake of circulating lipids through a range of receptors, including the low-density lipoprotein receptor (LDLR) and CD36. In the kidney, CD36 is known to contribute to renal injury through pro-inflammatory and -fibrotic pathways. In this study, we sought to investigate the role of PCSK9 in modulating renal lipid accumulation and injury through CD36 using a high fat diet (HFD)-induced murine model.

Methods

The effect of PCSK9 on the expression of CD36 and intracellular accumulation of lipid was examined in cultured renal cells and in the kidneys of male C57BL/6J mice. The effect of these findings was subsequently explored in a model of HFD-induced renal injury in Pcsk9 ^-/- and Pcsk9 ^+/+ littermate control mice on a C57BL/6J background.

Results

In the absence of PCSK9, we observed heightened CD36 expression levels, which increased free fatty acid (FFA) uptake in cultured renal tubular cells. As a result, PCSK9 deficiency was associated with an increase in long-chain saturated FFA-induced ER stress. Consistent with these observations, Pcsk9^-/- mice fed a HFD displayed elevated ER stress, inflammation, fibrosis, and renal injury relative to HFD-fed control mice. In contrast to Pcsk9^-/- mice, pretreatment of WT C57BL/6J mice with evolocumab, an anti-PCSK9 monoclonal antibody (mAb) that binds to and inhibits the function of circulating PCSK9, protected against HFD-induced renal injury in association with reducing cell surface CD36 expression on renal epithelia.

Conclusions

We report that circulating PCSK9 modulates renal lipid uptake in a manner dependent on renal CD36. In the context of increased dietary fat consumption, the absence of circulating PCSK9 may promote renal lipid accumulation and subsequent renal injury. However, although the administration of evolocumab blocks the interaction of PCSK9 with the LDLR, this evolocumab/PCSK9 complex can still bind CD36, thereby protecting against HFD-induced renal lipotoxicity.

An evaluation of maternal serum dynamic thiol-disulfide homeostasis and ischemia modified albumin changes in pregnant women with COVID-19

Objective:

It is thought that oxidative stress, free radicals, reactive oxygen species and reactive nitrogen species affect the pathophysiology of coronavirus disease-2019 (COVID-19). This study aimed to evaluate the oxidative status in pregnant patients with COVID-19 infection according to the changes seen in the levels of maternal serum thiol-disulfide and ischemia-modified albumin (IMA).

Materials and Methods:

A study group was formed of 40 pregnant women with confirmed COVID-19 infection (study group) and a control group of 40 healthy pregnant women with no risk factors determined. In this prospective, case-controlled study, analyses were made of the maternal serum native thiol, total thiol, disulfide, IMA, and disulfide/native thiol concentrations.

Results:

The maternal serum native thiol and total thiol concentrations in the study group were determined to be statistically significantly lower (p=0.007 and p=0.006, respectively), and the disulfide/native thiol ratio was higher but not to a level of statistical significance (p=0.473). There was no difference between the two groups regarding IMA levels (p=0.731).

Conclusion:

The thiol-disulfide balance was seen to shift in the oxidant direction in pregnancies with COVID-19, which might support the view that ischemic processes play a role in the etiopathogenesis of this novel disease.

The Role of Tea Tree Oil in Alleviating Palmitic Acid-Induced Lipid Accumulation in Bovine Hepatocytes

Tea tree oil (TTO) plays an important role in lipid metabolism, alleviating the inflammatory responses. Fatty liver is associated with lipid accumulation in hepatocytes, leading to inflammation. However, there is very limited information on the effects of TTO on lipid accumulation, and inflammation in bovine hepatocytes. This study aimed to evaluate whether TTO alleviates palmitic acid (PA)-induced lipid accumulation in bovine hepatocytes. Hepatocytes isolated from mid-lactating Holstein cows were pretreated with 100 μM PA for 72 h. Cells were either pretreated with PA alone (PA group) or with PA followed by 0.00625% TTO treatment for 12 h (PT group). Expression of fatty acid oxidant genes increased (P < 0.05) while fatty acid synthesis genes decreased (P < 0.05) in the PT group compared with the PA group. PA treatment resulted in increased (P < 0.05) expression of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6), but these increases were less in the PT group (P < 0.05). Compared to the PA group, expression of phosphorylated (p)-p65 and p-inhibitor κBα (p-IκBα) was suppressed (P < 0.05) by TTO treatment. TTO treatment limited (P < 0.05) the increase in intracellular reactive oxygen species (ROS) and prevented (P < 0.05) a reduction in mitochondrial membrane potential observed in response to PA treatment. Expression of endoplasmic reticulum (ER) stress genes was reduced (P < 0.05) in the PT group compared with the PA group. Our results suggest that TTO treatment attenuates the effects of PA in hepatocytes, leading to fatty acid oxidation, decreased fatty acid synthesis, suppressed inflammatory response, and reduced ER stress. Taken together, the results of this study suggest that TTO treatment may be a promising therapeutic approach to imbalanced lipid homeostasis, inflammation and ER stress in dairy cows shortly before and after calving.

Increased adipose tissue lipolysis in dairy cows with fatty liver is associated with enhanced autophagy activity

Lipolysis is increased in adipose tissue of cows with fatty liver during the transition period. Autophagy, a major cellular degradation process, plays a critical role in adipose tissue homeostasis. The objective of this study was to explore the relationship between lipolysis and autophagy in adipose tissue of cows with fatty liver. Using a nested case-control design, we compared blood and adipose tissue samples from 10 control cows [parity: median = 3, range = 2-4; days in milk: median = 8 d, range = 5-10 d; hepatic triacylglycerol content: median = 0.55% liver wt, range = 0.48-0.61% liver wt] and 10 lactation stage-matched cows with fatty liver (parity: median = 3, range = 2-4; days in milk: median = 9 d, range = 5-11 d; hepatic triacylglycerol content: median = 6.28% liver wt, range = 2.86-7.75% liver wt). Data were analyzed using paired t-tests. Serum concentrations of free fatty acids and β-hydroxybutyrate were greater and glucose concentration was lower in cows with fatty liver, which we determined by using commercially-available kits. Furthermore, western blotting showed that increased protein abundance of ATGL (adipose triglyceride lipase), ATG5 (autophagy-related gene 5), and ATG7; ratio of phosphorylated (p)-HSL (hormone-sensitive lipase) to HSL and MAP1LC3 (microtubule-associated protein 1 light chain 3, also called LC3-II) to LC3-I along with decreased abundance of PLIN1 (perilipin 1), SQSTM1 (sequestosome-1, also called p62), and the ratio of p-mTOR (phosphorylated mechanistic target of rapamycin) to mTOR in cows with fatty liver. Quantitative reverse-transcription PCR revealed an increase in abundance of MAP1LC3 mRNA and a decrease in SQSTM1 mRNA in cows with fatty liver. These findings were replicated using an adipocyte model. Primary cultures of calf adipocytes isolated from the adipose tissue of the peritoneal omentum and mesentery were treated with 10 mM 3-methyladenine (3-MA), 5 nM rapamycin, 1 µM isoproterenol (ISO), and 1 µM ISO + 10 mM 3-MA. Comparisons among groups were analyzed using one-way ANOVA. Compared with the control, the 1 µM ISO treatment upregulated the abundance of ATGL, the ratio of p-HSL to HSL and LC3-II to LC3-I, and the glycerol content, whereas it downregulated the abundance of PLIN1 and p62 in calf adipocytes. Compared with the 1 μM ISO treatment group, 1 µM ISO + 10 mM 3-MA downregulated the abundance of ATGL, the ratio of p-HSL to HSL and LC3-II to LC3-I, and the glycerol content, whereas it upregulated the abundance of PLIN1 and p62. Compared with the control, the 5 nM rapamycin treatment upregulated the abundance of ATGL, the ratio of p-HSL to HSL and LC3-II to LC3-I, and the glycerol content, whereas it downregulated the abundance of PLIN1 and p62 in calf adipocytes. Overall, these data indicated that increased lipolysis in adipose tissue of cows with fatty liver was associated with enhanced autophagy. However, the specific molecular mechanisms that link lipolysis and autophagy need to be further investigated.

NEFA Promotes Autophagosome Formation through Modulating PERK Signaling Pathway in Bovine Hepatocytes

During the perinatal period, the abnormally high plasma non-esterified fatty acids (NEFA) concentration caused by the negative energy balance (NEB) can impose a significant metabolic stress on the liver of dairy cows. Endoplasmic reticulum (ER) stress is an important adaptive response that can serve to maintain cell homeostasis in the event of stress. The protein kinase R-like endoplasmic reticulum kinase (PERK) pathway is the most rapidly activated cascade when ER stress occurs in cells and has an important impact on the regulation of hepatic lipid metabolism and autophagy modulation. However, it is unknown whether NEFA can affect autophagy through modulating the PERK pathway, under NEB conditions. In this study, we provide evidence that NEFA treatment markedly increased lipid accumulation, the phosphorylation level of PERK and eukaryotic initiation factor 2α (eIF2α), and the expression of glucose-regulated protein 78 (Grp78), activating transcription factor 4 (ATF4), and C/EBP homologous protein (CHOP). More importantly, NEFA treatment can cause a substantial increase in the protein levels of autophagy-related gene 7 (ATG7), Beclin-1 (BECN1), sequestosome-1 (p62), and microtubule-associated protein 1 light chain 3 (LC3)-II, and in the number of autophagosomes in primary bovine hepatocytes. The addition of GSK2656157 (PERK phosphorylation inhibitor) can significantly inhibit the effect of NEFA on autophagy and can further increase lipid accumulation. Overall, our results indicate that NEFA could promote autophagy via the PERK pathway in bovine hepatocytes. These findings provide novel evidence about the potential role of the PERK signaling pathway in maintaining bovine hepatocyte homeostasis.

Endoplasmic reticulum stress as a key mechanism in stunted growth of seawater rainbow trout (Oncorhynchus mykiss)

BACKGROUND

Rainbow trout (Oncorhynchus mykiss) is a salmonid species with a complex life-history. Wild populations are naturally divided into freshwater residents and sea-run migrants. Migrants undergo an energy-demanding adaptation for life in seawater, known as smoltification, while freshwater residents display these changes in an attenuated magnitude and rate. Despite this, in seawater rainbow trout farming all fish are transferred to seawater. Under these circumstances, weeks after seawater transfer, a significant portion of the fish die (around 10%) or experience growth stunting (GS; around 10%), which represents an important profitability and welfare issue. The underlying causes leading to GS in seawater-transferred rainbow trout remain unknown. In this study, we aimed at characterising the GS phenotype in seawater-transferred rainbow trout using untargeted and targeted approaches. To this end, the liver proteome (LC-MS/MS) and lipidome (LC-MS) of GS and fast-growing phenotypes were profiled to identify molecules and processes that are characteristic of the GS phenotype. Moreover, the transcription, abundance or activity of key proteins and hormones related to osmoregulation (Gill Na+, K + -ATPase activity), growth (plasma IGF-I, and liver igf1, igfbp1b, ghr1 and ctsl) and stress (plasma cortisol) were measured using targeted approaches.

RESULTS

No differences in Gill Na+, K + -ATPase activity and plasma cortisol were detected between the two groups. However, a significant downregulation in plasma IGF-I and liver igf1 transcription pointed at this growth factor as an important pathomechanism for GS. Changes in the liver proteome revealed reactive-oxygen-species-mediated endoplasmic reticulum stress as a key mechanism underlying the GS phenotype. From the lipidomic analysis, key observations include a reduction in triacylglycerols and elevated amounts of cardiolipins, a characteristic lipid class associated with oxidative stress, in GS phenotype.

CONCLUSION

While the triggers to the activation of endoplasmic reticulum stress are still unknown, data from this study point towards a nutritional deficiency as an underlying driver of this phenotype.

Factors associated with negative energy balance in periparturient dairy cows raised under tropical climate of Thailand-A mini-review

This review attempted to explain factors associated with negative energy balance (NEB) occurring during the periparturient period in dairy cows raised under tropical climatic conditions. The NEB has long been proven as an inevitable event in periparturient dairy cows. This condition had negative effects on the overall performances of dairy cows, including milk production, reproduction, and health condition. Therefore, periparturient management to overcome the NEB problem is vital for optimizing profit in dairy farming. In most tropical countries such as Thailand, dairy cows have been predominantly kept by small-holder farmers. Consequently, baseline milk yields, feed availability, feeding management, and general farming practices are different from typical commercial dairy farming. Heat stress also plays a crucial role in NEB conditions, and elevated temperature-humidity indexes above-normal conditions are recorded throughout the year. These factors influence the NEB in tropical dairy cows, which could result in different outcomes and consequences. Understanding the affecting components of NEB in dairy cows would help alleviate the severity of the NEB and its consequences, optimizing the dairy cow’s performance.

Reducing hepatic endoplasmic reticulum stress ameliorates the impairment in insulin signaling induced by high levels of β-hydroxybutyrate in bovine hepatocytes

Ketotic dairy cows exhibit a state of negative energy balance (NEB) characterized by elevated circulating levels of β-hydroxybutyrate (BHB) and fatty acids. Impaired hepatic insulin signaling in dairy cows occurs frequently during the transition into lactation, but its role on liver function during this period is not well known. In nonruminants, endoplasmic reticulum (ER) stress is a causal factor contributing to impaired insulin signaling in the liver. Thus, the aim of this study was to investigate the status of hepatic insulin and ER stress signaling and whether ER stress contributes to impaired insulin signaling in dairy cows with ketosis. Healthy (control cows, n = 10, BHB ≤0.6 mM) and ketotic (ketotic cows, n = 10, BHB ≥1.2 mM) cows at 3 to 10 d in milk were selected for liver biopsy and blood sampling before feeding. In vitro experiments were conducted with isolated hepatocytes from 5 healthy calves (1 d old, fasted female, 30-40 kg of body weight). Treatments included BHB (0, 0.9, 1.8, 3.6 mM), tauroursodeoxycholic acid (TUDCA, a canonical inhibitor of ER stress), and different incubation times (0.5, 1, 2, 3, 5, 7, 9, or 12 h). Ketotic cows had lower daily milk yield (median: 29.50 vs. 23.00 kg), higher plasma nonesterified fatty acid (NEFA) (median: 0.33 vs. 1.17 mM), BHB (median: 0.43 vs. 3.22 mM), aspartate aminotransferase (median: 70.58 vs. 155.70 U/L), alanine aminotransferase (median: 18.31 vs. 37.90 U/L), lower plasma glucose (median: 4.32 vs. 2.37 mg/dL), and revised quantitative insulin sensitivity check index (median: 0.39 vs. 0.37) compared with healthy cows. Increased abundance of phosphorylated insulin receptor substrate-1 (IRS1) and decreased abundance of phosphorylated protein kinase B (AKT) and glycogen synthase kinase-3β (GSK3β) in ketotic cows indicated a state of insulin resistance. In addition, abundance of phosphorylated protein kinase RNA-like ER kinase (PERK) and inositol requiring protein-1α (IRE1α), and cleavage of activating transcription factor-6 (ATF6) were greater in the liver of ketotic cows. In vitro, at the early stages of incubation, treatment with BHB upregulated abundance of phosphorylated of IRE1α, PERK, and the cleavage of ATF6, as well as several unfolded protein response genes [X-box-binding protein-1 (XBP1), 78 kDa glucose-regulated protein (GRP78), and C/EBP homologous protein (CHOP)]. Furthermore, in response to increasing doses of BHB, the phosphorylation level of PERK, IRE1α, and the cleavage of ATF6, and the abundance of XBP1, GRP78, and CHOP increased. In addition, BHB treatment increased phosphorylation of IRS1 and decreased phosphorylation of AKT and GSK3β, and upregulated abundance of gluconeogenic genes (phosphoenolpyruvate carboxykinase and glucose-6-phosphatase). Importantly, these changes were reversed by inhibiting ER stress with TUDCA treatment. Overall, the present study indicated that reversing ER stress during ketosis might help alleviate hepatic insulin resistance. Targeting ER stress may represent a potential therapeutic target for controlling the negative aspects of ketosis on liver function.

Effects of starvation-induced negative energy balance on endoplasmic reticulum stress in the liver of cows

Objective

Endoplasmic reticulum (ER) stress engages the unfolded protein response (UPR) that serves as an important mechanism for modulating hepatic fatty acid oxidation and lipogenesis. Chronic fasting in mice induced the UPR activation to regulate lipid metabolism. However, there is no direct evidence of whether negative energy balance (NEB) induces ER stress in the liver of cows. This study aimed to elucidate the relationship between the NEB attributed to feed deprivation and ER stress in bovine hepatocytes.

Methods

Blood samples and liver biopsy tissues were collected from 6 non-lactating cows before and after their starvation for 48 h. The blood non-esterified fatty acids (NEFA), β-hydroxybutyric acid (BHBA) and glucose level were analyzed. Real-time quantitative polymerase chain reaction and Western blotting were used to explore the regulation of genes associated with UPR and lipid metabolism.

Results

The starvation increased the plasma BHBA and NEFA levels and decreased the glucose level. Additionally, the starvation caused significant increases in the mRNA expression level of spliced X-box binding protein 1 (XBP1s) and the protein level of phosphorylated inositol-requiring kinase 1 alpha (p-IRE1α; an upstream protein of XBP1) in the liver. The mRNA expression levels of peroxisome proliferator-activated receptor alpha and its target fatty acid oxidation- and ketogenesis-related genes were significantly upregulated by the starvation-mediated NEB. Furthermore, we found that the mRNA expression levels of lipogenic genes were not significantly changed after starvation.

Conclusion

These findings suggest that in the initial stage of NEB in dairy cows, the liver coordinates an adaptive response by activating the IRE1 arm of the UPR to enhance ketogenesis, thereby avoiding a fatty liver status.

Elucidation of the mechanism of NEFA-induced PERK-eIF2α signaling pathway regulation of lipid metabolism in bovine hepatocytes

During the periparturient transition period, negative energy balance (NEB) characterized by high concentrations of non-esterified fatty acids (NEFA) may cause fatty liver and ketosis in dairy cows. Previous studies have shown that the protein kinase R-like endoplasmic reticulum kinase (PERK) branch of the endoplasmic reticulum stress (ERS) response plays an important role in lipid metabolism in hepatocytes. This study, therefore, investigated the role of the PERK-branch in NEFA-induced fatty liver. Different concentrations of NEFA or GSK2656157 (a novel catalytic inhibitor of PERK) were used to treat hepatocytes isolated from calves. The NEFA treatment significantly increased the triacylglycerol (TG) content, the phosphorylation level of PERK and eukaryotic initiation factor 2α (eIF2α), and the abundance of glucose-regulated protein 78 (Grp78), C/EBP homologous protein (CHOP), sterol regulatory element-binding protein 1c (SREBP-1c), fatty acid synthase (FASN), peroxisome proliferator-activated receptor-α (PPARα), carnitine palmitoyltransferase 1A (CPT1A), apolipoprotein B (APOB), and the low-density lipoprotein receptor (LDLR). Compared with the 1.2 mM NEFA group, inhibition of PERK activity further increased the TG content in hepatocytes, the very-low-density lipoprotein (VLDL) content in the supernatant and the protein abundance of APOB while reducing the expression and nuclear levels of SREBP-1c and PPARα, as well as the expression of CPT1A and CPT2. In conclusion, the results showed that the NEFA-induced PERK-eIF2α signaling pathway promotes lipid synthesis, lipid oxidation, but inhibits the assembly and secretion of VLDL. Therefore, during the transition period, the activation of the PERK-eIF2α signaling pathway in the liver of dairy cows could defeat the acid-induced lipotoxicity and provide energy to alleviate NEB.

Intracellular Ca2+ signaling and ORAI calcium release-activated calcium modulator 1 are associated with hepatic lipidosis in dairy cattle

Fatty liver is a common metabolic disorder afflicting dairy cows during the periparturient period and is closely associated with endoplasmic reticulum (ER) stress. The onset of ER stress in humans and mice alters hepatic lipid metabolism, but it is unknown if such event contributes to fatty liver in dairy cows soon after parturition. ORAI calcium release-activated calcium modulator 1 (ORAI1) is a key component of the store-operated Ca2+ entry mechanism regulating cellular Ca2+ balance. The purpose of this study was to investigate the role of ORAI1 on hepatic lipidosis via ER stress in dairy cows. Liver tissue biopsies were collected from Holstein cows diagnosed as healthy (n = 6) or with hepatic lipidosis (n = 6). Protein and mRNA abundance of ER stress-related targets, lipogenic targets, or the transcription regulator SREBP1 and ORAI1 were greater in cows with lipidosis. In vitro, hepatocytes were isolated from four healthy female calves and used for culture with a 1.2 mM mixture of fatty acids (oleic, linoleic, palmitic, stearic, and palmitoleic acid) for various times (0, 3, 6, 9, or 12 h). As incubation time progressed, increases in concentration of Ca2+ and abundance of protein kinase RNA-like ER kinase (PERK), inositol-requiring protein 1α (IRE1α), and activating transcription factor-6 (ATF6) protein in response to exogenous fatty acids underscored a mechanistic link among Ca2+, fatty acids, and ER stress. In a subsequent study, hepatocytes were transfected with small interfering RNA (siORAI1) or the ORAI1 inhibitor BTP2 for 48 h or 2 h followed by a challenge with the 1.2 mM mixture of fatty acids for 6 h. Compared with control group, silencing or inhibition of ORAI1 led to decreased abundance of fatty acid synthesis (FASN, SREBP1, and ACACA) and ER stress-related proteins in bovine hepatocytes. Overall, data suggested that NEFA through ORAI1 regulate intracellular Ca2+ signaling, induce ER stress, and lead to lipidosis in isolated hepatocytes.

Propionate alleviates palmitic acid-induced endoplasmic reticulum stress by enhancing autophagy in calf hepatic cells

Negative energy balance-induced high blood concentrations of free fatty acids during the early postpartum period in dairy cows is a major cause of liver injury. Cows in severe negative energy balance often have suboptimal intakes of feed, which contributes to shortfalls in production of ruminal propionate and circulating glucose. Although increasing propionate production by the rumen through feed additives such as propylene glycol is effective in helping cows alleviate the shortfall in dietary energy supply, mechanisms whereby propionate affects liver function beyond gluconeogenesis are unknown. Therefore, the objective of this study was to investigate whether propionate could protect calf hepatic cells from palmitic acid (PA)-induced lipotoxicity and the underlying mechanisms. Calf hepatic cells were isolated from 5 healthy calves (1 d old, female, 30-40 kg, fasting) and treated with various concentrations of PA (0, 100, 200, or 400 μM) and propionate (0, 1, 2, or 4 mM) after being administered with or without autophagic inhibitor. Propionate enhanced autophagic activity in calf hepatic cells, as indicated by elevated expression of autophagy markers LC3-II (microtubule-associated protein 1 light chain 3-II, encoded by MAP1LC3) and decreased expression of SQSTM1 (sequestosome-1, also called p62). Conversely, PA suppressed autophagic activity and decreased cell viability, which was improved by propionate in calf hepatic cells. In addition, propionate decreased the phosphorylation of proteins EIF2AK3 (kinase R/PKR like ER kinase) and ERN1 (inositol-requiring enzyme 1α) and cleaved ATF6 (activating transcription factor 6) in PA-treated calf hepatic cells, indicating the suppression effect of propionate on endoplasmic reticulum (ER) stress. However, inhibition of autophagic activity by chloroquine or bafilomycin A1 impede the beneficial effects of propionate on ER stress and cell viability. These results demonstrated that propionate alleviates ER stress and elevates cell viability in PA-treated calf hepatic cells by enhancing autophagy, which implies that autophagy may be a promising target in improving liver injury of dairy cows during transition period.

Disruption of endoplasmic reticulum homeostasis exacerbates liver injury in clinically ketotic cows

Disruption of endoplasmic reticulum (ER) homeostasis, a condition termed "ER stress," contributes to the development of liver injury in nonruminants. Because liver injury is a prominent pathological feature associated with overproduction of ketone bodies in dairy cows with ketosis, understanding the ER stress state and its functional consequences on liver injury is of particular interest. Here, 30 multiparous cows (within 3 wk postpartum) classified based on blood β-hydroxybutyrate (BHB) as healthy (n = 15, BHB <0.6 mM) or clinically ketotic (n = 15, BHB >3.0 mM) were used. Compared with healthy cows, ketotic cows had greater levels of serum fatty acids and activities of serum aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, γ-glutamyl transferase, and glutamate dehydrogenase but lower serum glucose. Furthermore, dairy cows with ketosis had greater protein abundance of ER stress markers in liver tissue, including protein kinase RNA-like ER kinase (PERK), inositol-requiring protein-1α (IRE1α), and cleaved activating transcription factor-6 (ATF6). Cows with ketosis also had higher mRNA levels of hepatic 78-kDa glucose-regulated protein (GRP78) and spliced X-box binding protein 1 (sXBP1). These data confirmed an enhanced ER stress state in clinically ketotic cows. To explore whether enhanced hepatic ER stress was induced by elevated ketone bodies and the possible contribution of ER stress to liver injury, in vitro experiments were then performed using isolated primary calf hepatocytes treated with incremental concentrations of BHB (0, 0.6, 1.2, 3.0, and 4.8 mM) for 12 h with or without overexpression of GRP78 (the master regulator of unfolded protein response). Phosphorylation levels of PERK and IRE1α proteins, level of cleaved ATF6 protein, and mRNA abundance of GRP78 and sXBP1 in hepatocytes increased after treatment with high (3.0 and 4.8 mM) BHB, indicating a mechanistic link between excessive BHB and enhanced hepatic ER stress. Furthermore, treatment with 3.0 and 4.8 mM BHB markedly elevated activities of aspartate aminotransferase and alanine aminotransferase in cell supernatant, indicating exacerbated hepatocyte damage after ER stress was enhanced. Overexpression of GRP78 attenuated both BHB-induced ER stress and the ensuing cellular damage, suggesting that hepatocyte damage caused by excessive BHB can be mediated via enhanced ER stress. Overall, the present study revealed that ER stress may exacerbate liver injury development in clinically ketotic cows, underscoring the biological relevance of this pathway in the context of liver injury.

Adenosine 5'-monophosphate-activated protein kinase ameliorates bovine adipocyte oxidative stress by inducing antioxidant responses and autophagy

Adipose tissue concentration of reactive oxygen species (ROS) increases in dairy cows with ketosis, suggesting that the tissue experiences oxidative stress. Autophagy, an adaptive response to cellular stress, has been shown to promote survival and plays a critical role in antioxidant responses. Dysregulation of adenosine 5'-monophosphate-activated protein kinase (AMPK) is closely related to antioxidant responses and autophagy of adipocytes in animal models of metabolic disorders, but its role in bovine adipose tissue during periods of stress is unknown. We hypothesized that AMPK may play important roles in the regulation of oxidative stress in adipose tissue of ketotic cows. Specific objectives were to evaluate autophagy status and AMPK activity in adipose tissue of ketotic cows, and their link with oxidative stress in isolated bovine adipocytes. Selection of 15 healthy and 15 clinically ketotic Holstein cows at 17 (±4) d postpartum was performed after a thorough veterinary evaluation for clinical symptoms and also based on serum β-hydroxybutyrate concentrations before collection of subcutaneous adipose tissue samples. Primary cultures of bovine adipocytes isolated from the harvested adipose tissue were stimulated with varying concentrations of H₂O₂ (0, 50, 100, 200, or 400 μM) for 2 h. In another experiment, adipocytes were cultured with the AMPK activator A769662 or adenovirus-containing small interfering RNA (ad-AMPKα-siRNA) for 3 or 48 h, respectively, followed by H₂O₂ exposure (200 μM) for 2 h. Compared with healthy cows, clinical ketosis led to increased abundance of AMPK and nuclear factor erythroid-derived 2-like 2 (NFE2L2), but lower abundance of Kelch-like ECH-associated protein 1 (KEAP1) in adipose tissue. Abundance of the key proautophagy proteins Beclin1, sequestosome 1 (SQSTM1), autophagy-related gene 7 (ATG7), ATG5, and ratio of microtubule-associated protein light chain 3 (LC3) II to LC3I were greater in adipose tissue of ketotic cows. In bovine adipocytes, treatment with H₂O₂ induced accumulation of ROS and malondialdehyde (MDA), whereas H₂O₂ stimulation inhibited activities of the antioxidant enzymes glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD). Addition of AMPK activator A769662 increased antioxidant response via activating NFE2L2 and its downstream targets heme oxygenase 1 (HMOX1), superoxide dismutase 1 (SOD1), catalase (CAT), and glutathione-S-transferase (GST) to improve H₂O₂-induced oxidative stress in adipocytes. Simultaneously, activation of AMPK increased abundance of Beclin1, SQSTM1, ATG7, ATG5, and ratio of LC3II to LC3I. In contrast, inhibition of AMPK downregulated abundance of NFE2L2, HMOX1, SOD1, CAT, Beclin1, SQSTM1, ATG7, ATG5, and ratio of LC3II to LC3I, and further aggravated H₂O₂-induced oxidative stress. Overall, these data indicate that activation of AMPK, as an adaptive mechanism for acute metabolic regulation of adipose tissue homeostasis, can induce antioxidant responses and autophagy, and further reduce oxidative stress in bovine adipocytes.

Apigenin Ameliorates Insulin Resistance and Lipid Accumulation by Endoplasmic Reticulum Stress and SREBP-1c/SREBP-2 Pathway in Palmitate-Induced HepG2 Cells and High-Fat Diet-Fed Mice

Insulin resistance (IR) is the common basis of diabetes and cardiovascular diseases, and its development is closely associated with lipid metabolism disorder. Flavonoids have definite chemical defense effects, including anti-inflammatory effects, anticancer effects, and antimutation effects. However, the function and mechanism of apigenin (AP, a kind of flavonoid) in IR are still unclear. In our study, intracellular fat accumulation model cells and high-fat diet (HFD)-fed model mice were established using palmitate (PA) and HFD. Mechanistically, we first demonstrated that AP could notably downregulate sterol regulatory element-binding protein 1c (SREBP-1c), sterol regulatory element-binding protein 2 (SREBP-2), fatty acid synthase, stearyl-CoA desaturase 1, and 3-hydroxy-3-methyl-glutaryl-CoA reductase in PA-induced hyperlipidemic cells and mice. Functionally, we verified that AP could markedly reduce lipid accumulation in PA-induced hyperlipidemic cells and decrease the body weight, visceral fat weight, IR, and lipid accumulation in HFD-induced hyperlipidemic mice. Besides, we showed that PA could significantly downregulate endoplasmic reticulum stress (ERS)-related proteins and inhibit ERS. Furthermore, we proved that AP could reduce blood lipids by inhibiting ERS in PA-induced hyperlipidemic cells. Meanwhile, 4-phenyl butyric acid (also called ERS alleviator), like AP, could significantly reduce blood lipids and alleviate IR in HFD-fed model mice. Therefore, we concluded that AP could substantially improve the disorder of lipid metabolism, and its mechanism might be related to the decrease of SREBP-1c, SREBP-2, and downstream genes, the inhibition of ERS, and the reduction of blood lipids and IR. SIGNIFICANCE STATEMENT: Apigenin, a nontoxic and naturally sourced flavonoid, has antihyperlipidemic properties in mice and hepatocyte. This study highlights a new mechanism of apigenin and proposes that these hypolipidemic effects are associated with the mitigation of endoplasmic reticulum stress and insulin resistance in diet-induced obesity. This study might provide translational insight into the prevention and treatment of apigenin in hyperlipidemia-related diseases.

Supplementation with beta-1,3-glucan improves productivity, immunity and antioxidative status in transition Holstein cows

Dairy cows undergo dramatic physiological changes during the transition from late pregnancy to early lactation, which make them vulnerable to metabolic stress and immune dysfunction. The objective of this study was to evaluate the effects of a commercial beta-1,3-glucan product (Aleta™, containing 50% beta-1,3-glucan) on productivity, immunity and antioxidative status in transition cows. Fifty-four multiparous Holstein cows received a control diet or a diet supplemented with 5 or 10 g of beta-1,3-glucan per cow per day from 21 days before expected calving to 21 days after parturition. Blood samples were collected at day -21, 1, and 21 relative to calving. Colostrum and milk were collected at day 1 and 21 after calving, respectively. Data showed that supplementation with beta-1,3-glucan had no effect on milk composition, but increased milk production. Beta-1,3-glucan treatment also improved the milk quality, as shown by reduced milk somatic cell count and increased immunoglobulin levels in colostrum. Notably, beta-1,3-glucan markedly reduced serum levels of pro-inflammatory cytokines and C-reactive protein, while elevated serum immunoglobulin levels, indicating its immunity enhancement in transition cows. Moreover, beta-1,3-glucan addition reduced the serum malondialdehyde level and enhanced the activities of serum superoxide dismutase and catalase, which enhanced the antioxidative capacity in transition cows. In summary, supplementation with beta-1,3-glucan improves productivity, immunity and antioxidative status in transition dairy cows.

Effects of late-gestation heat stress independent of reduced feed intake on colostrum, metabolism at calving, and milk yield in early lactation of dairy cows

The objective of this study was to differentiate the effects of acute heat stress (HS) from those of decreased dry matter intake (DMI) during the prepartum period on metabolism, colostrum, and subsequent production of dairy cows. Holstein dairy cows (n = 30) with similar parity and body weight were randomly assigned to 1 of 3 treatments on 45 d before calving: (1) cooled (CL, n = 10) conditions with ad libitum feed intake, (2) HS conditions with ad libitum feed intake (n = 10), and (3) pair-fed cooled (CLPF, n = 10) with reduced DMI similar to the HS group while housed under cooled conditions. The reduction in the amount of feed offered to the CLPF cows was calculated daily as the percentage decrease from the average DMI of HS cows relative to the CL cows. For CLPF and CL cows, barns provided shade, sprinklers, and fans, whereas the HS cows were provided only with shade. Cows in all groups received individually the same total mixed ration. Cows were dried off 60 d before the expected calving. Cows in the HS group and, by design, the CLPF cows had reduced DMI (~20%) during the experiment. Heat stress decreased gestation length, first colostrum yield, and calf birth weight compared with CL and CLPF cows. Milk yield decreased 21% (5 kg) in the HS and 8% (2 kg) in CLPF cows, indicating that reduced feed intake during late gestation accounted for 60% of the total reduced milk yield. The CLPF cows exhibited an elevated NEFA concentration compared with the CL and HS cows. The HS cows had a greater mRNA abundance of HSP70 in the peripheral blood leukocytes at 21 d prepartum compared with the other groups. At calving, the mRNA abundance of HSP70 was greater in HS cows, followed by CLPF, compared with the CL cows. In conclusion, HS during the late gestation period caused metabolism and production differences, which were only partially attributed to reduced feed intake in dairy cows.

Advances in fatty acids nutrition in dairy cows: from gut to cells and effects on performance

High producing dairy cows generally receive in the diet up to 5-6% of fat. This is a relatively low amount of fat in the diet compared to diets in monogastrics; however, dietary fat is important for dairy cows as demonstrated by the benefits of supplementing cows with various fatty acids (FA). Several FA are highly bioactive, especially by affecting the transcriptome; thus, they have nutrigenomic effects. In the present review, we provide an up-to-date understanding of the utilization of FA by dairy cows including the main processes affecting FA in the rumen, molecular aspects of the absorption of FA by the gut, synthesis, secretion, and utilization of chylomicrons; uptake and metabolism of FA by peripheral tissues, with a main emphasis on the liver, and main transcription factors regulated by FA. Most of the advances in FA utilization by rumen microorganisms and intestinal absorption of FA in dairy cows were made before the end of the last century with little information generated afterwards. However, large advances on the molecular aspects of intestinal absorption and cellular uptake of FA were made on monogastric species in the last 20 years. We provide a model of FA utilization in dairy cows by using information generated in monogastrics and enriching it with data produced in dairy cows. We also reviewed the latest studies on the effects of dietary FA on milk yield, milk fatty acid composition, reproduction, and health in dairy cows. The reviewed data revealed a complex picture with the FA being active in each step of the way, starting from influencing rumen microbiota, regulating intestinal absorption, and affecting cellular uptake and utilization by peripheral tissues, making prediction on in vivo nutrigenomic effects of FA challenging.

Lipid Accumulation and Injury in Primary Calf Hepatocytes Challenged With Different Long-Chain Fatty Acids

Fatty liver disease is one of the most common disorders afflicting dairy cows during the postpartum period, and is associated with increased blood non-esterified fatty acid (NEFA) uptake by the liver. Major long-chain fatty acids (LCFA) in NEFA are palmitic (PA), palmitoleic (POA), stearic (SA), oleic (OA), and linoleic (LA) acid. In order to investigate the characteristics of lipid accumulation and injury caused by these NEFA, primary calf hepatocytes were isolated and challenged for 12 h with 1.2 mmol/L PA, POA, SA, OA, LA, or a mixture of these LCFA (NEFA). Compared with POA, OA, and LA, culture with PA and SA led to greater abundance of CCAAT-enhancer binding protein, glucose-regulated protein 78 mRNA, and stearoyl-CoA desaturase 1 mRNA along with greater concentrations of H₂O₂, malondialdehyde and reactive oxygen species (ROS). Although culture with POA, OA, and LA led to lower very low density lipoprotein (VLDL) concentration in cell culture medium, POA and OA led to greater concentrations of triacylglycerol, protein abundance of sterol regulatory element-binding protein 1c, fatty acid synthase, acetyl coenzyme A carboxylase 1, ApoB100, and sortilin 1 (SORT1). Compared with individual fatty acids, culture with NEFA led to an intermediate degree of lipid accumulation and hepatocytes damage. Overall, the data suggest that saturated fatty acids cause more severe oxidative and ER stress. However, unsaturated fatty acids cause serious lipid accumulation. Furthermore, a fatty acid balanced nutrient regulation was suggested useful improve liver health of transition period dairy cows.

Selenium Deficiency in Chickens Induces Intestinal Mucosal Injury by Affecting the Mucosa Morphology, SIgA Secretion, and GSH-Px Activity

The small intestine is one of the target organs of dietary selenium (Se) deficiency. Our objective was to investigate the effects of Se deficiency on small intestinal mucosa morphology and function in chickens. In the present study, 1-day (d)-old chickens were fed either a commercial diet with 0.15 mg/kg Se (control group) or a Se-deficient diet with 0.016 mg/kg Se (Se-group). The average daily weight gain, Se content in the blood, secretory immunoglobulin A (SIgA) secretion, and glutathione peroxidase (GSH-Px) activity in the small intestine in chickens were examined after 10, 20, 30, and 40 days of feeding. We also observed the morphology of the small intestine and recorded the number of intraepithelial lymphocytes (IELs). The average daily weight gain decreased; the level of Se in the blood decreased significantly; and SIgA secretion and GSH-Px activity in the duodenum, jejunum, and ileum decreased to different degrees. Histological analysis showed that the villus length, crypt depth, mucosal thickness, and number of IELs in the small intestine decreased to different extents in different periods. In the Se-group, longer feeding times were associated with more severe injury to physiological structure and function in the intestinal mucosa in chickens. In conclusion, Se deficiency induced injury of the mucosal immune barrier and physical barrier of the small intestine, and decreased the growth performance and antioxidant capacity in chickens.

Mitochondrial dysfunction and endoplasmic reticulum stress in calf hepatocytes are associated with fatty acid-induced ORAI calcium release-activated calcium modulator 1 signaling

The store-operated Ca²⁺ entry (SOCE) moiety ORAI calcium release-activated calcium modulator 1 (ORAI1) located in the endoplasmic reticulum (ER) participates in key cellular functions such as protein folding, transport, and secretion, and lipid metabolism. We used an in vitro approach to test whether exogenous fatty acids alter ORAI1 signaling and to explore potential consequences on mitochondrial dysfunction and ER stress. First, hepatocytes isolated from 4 healthy female calves (1 d old, 40-50 kg) were challenged with a 1.2 mM mixture of oleic, linoleic, palmitic, stearic, and palmitoleic acids for 0.5, 1, 3, 6, 9, and 12 h to measure oxidative stress [intracellular reduced glutathione (GSH), superoxide dismutase (SOD), malondialdehyde (MDA), and hydrogen peroxide] and ER stress (protein abundance of PERK, IRE, ATF6, and GRP78). Concentrations of GSH and SOD decreased at 0.5 h, and MDA and hydrogen peroxide increased at 1 h; ER stress proteins increased at 6 h. To determine whether ER stress was caused by oxidative stress, primary calf hepatocytes were treated with the same 1.2 mM fatty acid mix or the reactive oxygen species (ROS) inhibitor N-acetylcysteine (NAC) for 6 h. We found that NAC prevented an increase in ER stress protein abundance. Next, the role of ORAI1 on ER stress was measured by transfecting hepatocytes with small interfering (si)ORAI1 or the ORAI1 inhibitor BTP2, followed by a challenge with 1.2 mM fatty acids for 3 h. Without inhibiting ORAI1, exogenous fatty acids upregulated ORAI1 mRNA and protein abundance, oxidative stress, ER stress proteins, and protein abundance of marker indicators of an opened mitochondrial permeability transition pore (mPTP). Inhibition with BPT2 or silencing via siORAI1 abrogated oxidative stress, including increased GSH concentration and SOD activity, decreased MDA, hydrogen peroxide, and ROS concentration; ER stress protein abundance was downregulated, and mitochondrial function was restored. Last, changes in markers of mPTP opening were evaluated by culturing hepatocytes for 6 h with the sarcoendoplasmic Ca²⁺ ATPase inhibitor thapsigargin or the calcium ionophore ionomycin. We detected an increase in VDAC1, CLPP, and CypD protein abundance, all of which indicated opening of the mPTP. Overall, data from these in vitro studies suggest that ORAI1 mediates ER stress induced by high concentrations of fatty acids, in part through alleviating mitochondrial dysfunction caused by oxidative stress.

Choline and methionine regulate lipid metabolism via the AMPK signaling pathway in hepatocytes exposed to high concentrations of nonesterified fatty acids

High concentrations of nonesterified fatty acids (NEFAs) and β-hydroxybutyric acid (BHBA) induce lipid peroxidation, resulting in liver damage. Choline and methionine (Met) can promote energy balance and benefit liver health in transition dairy cows; however, the regulating mechanism remains unclear. In the present study, we established the hepatocyte damage model by 1.5 mM NEFAs or BHBA treatment, and examined lipid metabolism in hepatocytes. The results showed that 1.5 mM NEFAs and 1.5 mM BHBA significantly decreased the messenger RNA (mRNA) expression of AMP-activated protein kinase (AMPK)-α as well as its target genes carnitine palmitoyltransferase-1α (CPT-1α), acetyl-CoA carboxylase, fatty acid synthetase, and Apolipoprotein B100 (ApoB100). Choline and Met upregulated the phosphorylation level of AMPK-α, which was blocked by BML (an AMPK-α inhibitor). The mRNA expression level of peroxisome proliferator-activated receptor-α (PPAR-α), CPT-1α, and ApoB100 showed a similar trend. The expressions of liver X recptoer α (LXR-α) and sterol regulatory element-binding protein 1c (SREBP-1c) were decreased by choline and Met, while only the decrease of LXR-α was blocked by BML. These findings indicate that the high-level NEFAs and BHBA weaken the lipid metabolism by impairing the fatty acid oxidation, synthesis, and transport proteins. Choline and Met regulate PPAR-α and LXR-α transcriptional activity through AMPK-α phosphorylation and regulate SREBP-1c independently of AMPK-α to promote lipid oxidation and transport in NEFAs-treated hepatocytes.

Sodium butyrate reduces bovine mammary epithelial cell inflammatory responses induced by exogenous lipopolysaccharide, by inactivating NF-κB signaling

Exogenous molecules derived from catabolic states (e.g., fatty acids, β-hydroxybutyrate) during periods of stress such as the periparturient period or pathogen challenges [e.g., lipopolysaccharide (LPS)] can trigger an inflammatory response in tissues such as the liver and the mammary gland. Butyrate is one of the major short-chain fatty acids produced in the rumen, and work with non-ruminants has demonstrated that it can alter inflammatory processes. The primary objective of this study was to explore the preventive effect of sodium butyrate (SB) on LPS-induced inflammation in bovine mammary epithelial cells along with underlying molecular mechanisms. Immortalized bovine mammary epithelial cells (MAC-T) were treated with SB (0.1, 0.25, 0.5, 1, 2, or 5 mM) or with the histone deacetylase inhibitor trichostatin A (TSA; 6.25, 12.5, 25, or 50 nM) for 18 h, followed by a challenge with 1 µg/mL LPS for an additional 6 h. Pretreatment with SB prevented increase in apoptosis of LPS-challenged MAC-T cells in a dose-dependent manner. The LPS treatment upregulated mRNA abundance of tumor necrosis factor α (TNFA), interleukin-6 (IL6), and interleukin-1B (IL1B), whereas inhibition of histone deacetylase with TSA dampened this effect. More importantly, SB had clear dose-dependent effects on the inflammatory response by preventing upregulation of TNFA, IL6, and IL1B. Furthermore, pretreatment with TSA or SB attenuated the downregulation of histone H3 acetylation protein abundance induced by LPS. The greater ratio of p-IκB α/IκB α and p-p65/p65 protein abundance and the increase in nuclear localization of NF-κB p65 protein in response to LPS were attenuated by pretreatment with SB. Overall, the data indicated that exogenous SB alleviates mammary cell pro-inflammatory responses partly through post-translational mechanisms that diminish NF-κB signaling. Thus, the cytoprotective effect of SB against an inflammatory challenge might represent a preventive tool to help the mammary gland against pathogens such as those causing mastitis.

Effects of beta-1,3-glucan supplementation on concentrations of serum metabolites in transition Holstein cows

Objectives of this study were to evaluate the alleviating effects of a commercial beta-1,3-glucan product (Aleta, containing 50% beta-1,3-glucan, Kemin Industries) on metabolic stress in transition Holstein cows as reflected by circulating metabolites and enzymes. Fifty-four multiparous Holstein cows were randomly allocated to three groups with 18 cows each. Cows in each group received a commercial basal diet or the basal diet supplemented with Aleta calculated to supply 5 or 10 g of Aleta per cow per day. Blood samples were collected at day -21, 1, and 21 relative to calving for determination of serum triglyceride (TG), total cholesterol (TC), low density lipoprotein cholesterol (LDL-C), high density lipoprotein cholesterol (HDLC), very low density lipoprotein (VLDL), glucose, insulin, β-hydroxybutyric acid (BHBA), aspartate aminotransferase (AST), alanine aminotransferase (ALT), glutamyl transpeptidase (GGT), and non-esterified fatty acid (NEFA). Supplementation with Aleta markedly elevated serum concentrations of TG, TC, HDLC, LDL-C and VLDL, implying its positive effect on lipid metabolism in transition dairy cows. Aleta treatment significantly decreased the serum concentrations of NEFA and BHBA, but markedly elevated the serum concentrations of glucose and insulin. Also, Aleta treatment significantly elevated the dry matter intake and milk production in postpartum cows, indicating the alleviating effect of Aleta on negative energy balance in transition cows. Moreover, Aleta treatment significantly reduced the serum activities of AST, ALT and GGT, indicating its hepatoprotective effect on transition cows. These results suggest that Aleta supplementation may help to improve fat metabolism disorder initiated by negative energy balance in transition dairy cows.

Non-esterified Fatty Acid Induce Dairy Cow Hepatocytes Apoptosis via the Mitochondria-Mediated ROS-JNK/ERK Signaling Pathway

Elevated plasma non-esterified fatty acid (NEFA) levels and hepatocytes damage are characteristics of ketosis in dairy cows. Oxidative stress is associated with the pathogenesis of NEFA-induced liver damage. However, the exact mechanism by which oxidative stress mediates NEFA-induced hepatocytes apoptosis and liver injury remains poorly understood. The results of the present study demonstrated that NEFA contribute to reactive oxygen species (ROS) generation, resulting in an imbalance between oxidative and antioxidant species, transcriptional activation of p53, transcriptional inhibition of nuclear factor E2-related factor 2 (Nrf2), loss of mitochondria membrane potential (MMP) and release of apoptosis-inducing factor (AIF) and cytochrome c (cyt c) into the cytosol, leading to hepatocytes apoptosis. Besides, NEFA triggered apoptosis in dairy cow hepatocytes via the regulation of c-Jun N-terminal kinase (JNK), extracellular signal-regulated protein kinases 1 and 2 (ERK1/2), Bcl-2-associated X protein (Bax), B-cell lymphoma gene 2 (Bcl-2), caspase 9 and poly (ADP-ribose) polymerase (PARP). Pretreatment with the inhibitor SP600125 or PD98059 or the antioxidant N-acetylcysteine (NAC) revealed that NEFA-ROS-JNK/ERK-mediated mitochondrial signaling pathway plays a crucial role in NEFA-induced hepatocytes apoptosis. Moreover, the results suggested that the transcription factors p53 and Nrf2 function downstream of this NEFA-ROS-JNK/ERK pathway and are involved in NEFA-induced hepatocytes apoptosis. In conclusion, these findings indicate that the NEFA-ROS-JNK/ERK-mediated mitochondrial pathway plays an important role in NEFA-induced dairy cow hepatocytes apoptosis and strongly suggests that the inhibitors SP600125 and PD98059 and the antioxidant NAC may be developed as therapeutics to prevent hyperlipidemia-induced apoptotic damage in ketotic dairy cows.

Leucine improves α-amylase secretion through the general secretory signaling pathway in pancreatic acinar cells of dairy calves

The present study aimed to elucidate the mechanisms by which leucine impacts the secretion of pancreatic enzymes, especially amylase, by studying the proteomics profiles of pancreatic acinar (PA) cells from dairy cows. PA cells, the experimental model, were treated with four concentrations of leucine (0, 0.23, 0.45, and 0.90 mM). The abundance of different proteins in the four leucine treatment groups was detected. Label-free proteomic analysis enabled the identification of 1,906 proteins in all four treatment groups, and 1,350 of these proteins showed common expression across the groups. The primary effects of leucine supplementation were increased (P < 0.05) citrate synthase and ATPase activity, which enlarged the cytosolic ATP pool, and the upregulation of secretory protein 61 (Sec61) expression, which promoted protein secretion. In summary, these results suggest that leucine increases citrate synthase in the TCA cycle and ATPase activity and promotes the Sec signaling pathway to increase the exocrine function of PA cells.

Mitochondrial membrane protein mitofusin 2 as a potential therapeutic target for treating free fatty acid-induced hepatic inflammation in dairy cows during early lactation

Inflammation is critical in the progression from benign hepatic lipidosis to pathological hepatic steatosis. The objective of this study was to examine the potential role of the outer mitochondrial membrane protein mitofusin 2 (MFN2) in the etiology of hepatic steatosis in dairy cows during early lactation. Using a nested case-control design, we compared blood and liver samples from 10 healthy cows and 10 age-matched cows with moderate fatty liver. Cows with moderate fatty liver had high liver triacylglycerols, elevated plasma concentrations of free fatty acids (FFA) and β-hydroxybutyrate, and low concentrations of glucose. Cows with moderate fatty liver had overactivated inflammatory pathways in the liver, as indicated by increased abundance of phosphorylated nuclear factor κB (NF-κB) p65, NLR family pyrin domain containing 3 (NLRP3) and caspase-1 inflammasome protein, and elevated plasma concentrations and hepatic mRNA abundance of their molecular targets IL-1β, IL-6, and tumor necrosis factor α (TNF-α). In the cell culture model, we were able to replicate our findings in cows with moderate fatty liver: 1.2 mM exogenous FFA decreased the abundance of MFN2 and upregulated phosphorylation levels of the inhibitor of NF-κB (IκB) α and NF-κB p65, the IκB kinase β activity, and the abundance of NLRP3, caspase-1, IL-1β, IL-6, and TNF-α. Whereas MFN2 knockdown potentiated the FFA-induced activation of these inflammatory pathways, overexpression of MFN2 attenuated the detrimental effect of excess exogenous FFA by improving mitochondrial function and decreasing the release of reactive oxygen species, suggesting that MFN2 may be a potential therapeutic target for FFA-induced hepatic inflammation in dairy cows during early lactation.

Sulforaphane prevents chromium-induced lung injury in rats via activation of the Akt/GSK-3β/Fyn pathway

Chromium (Cr) is an internationally recognized carcinogenic hazard that causes serious pulmonary toxicity. However, Cr-induced pulmonary toxicity lacks effective treatment to date. Sulforaphane (SFN), a well-known organosulfur compound, has gained increasing attention because of its unique biological function. This study investigates if SFN could decrease K₂Cr₂O₇-induced pulmonary toxicity and a potential mechanism involved using a rat 35-day Cr-induced pulmonary toxicity model and the mouse alveolar type II epithelial cell line (MLE-12). The results showed that SFN prevented Cr-induced oxidative stress, histopathological lesions, inflammation, apoptosis, and changes in protein kinase B (Akt) and glycogen synthase kinase 3 beta (GSK-3β) levels in vivo and in vitro. However, SFN can not play the protective effect against K₂Cr₂O₇-induced cell injury after treating by an Akt-specific inhibitor (MK-2206 2HCl) in MLE-12 cells. Furthermore, SFN increased the expression of nuclear factor-E2-related factor-2 (Nrf2) phase II detoxification enzymes. Collectively, this study demonstrates that SFN prevents K₂Cr₂O₇-induced lung toxicity in rats through enhancing Nrf2-mediated exogenous antioxidant defenses via activation of the Akt/GSK-3β/Fyn signaling pathway. SFN may be a novel natural substance to cure Cr-induced lung toxicity.

Low Expression of Sirtuin 1 in the Dairy Cows with Mild Fatty Liver Alters Hepatic Lipid Metabolism

Simple Summary

Sirtuin 1 (SIRT1), a NAD-dependent histone deacetylase, is involved in oxidative stress and lipid metabolism regulation. Limited studies exist regarding the role of SIRT1 in lipid metabolism disorder in periparturient dairy cows. This study explores the effect of hepatic steatosis on the expression of the SIRT1 gene and protein and the proteins encoded by the genes downstream to it, all of which are involved in lipid metabolism in the liver. Control cows (n = 6, parity 3.0 ± 2.0, milk production 28 ± 47 kg/d) and mild fatty liver cows (n = 6, parity 2.3 ± 1.5, milk production 20 ± 6 kg/d) were retrospectively selected based on liver triglycerides (TG) content (% wet liver). The present study indicates that low SIRT1 expression caused by hepatic steatosis promotes hepatic fatty acid synthesis and inhibits fatty acid β-oxidation. We believe that our study makes a significant contribution to the literature because it demonstrates that hepatic steatosis is associated with increased hepatic fatty acid synthesis, inhibited fatty acid β-oxidation and reduced lipid transport.

Abstract

Dairy cows usually experience negative energy balance coupled with an increased incidence of fatty liver during the periparturient period. The purpose of this study was to investigate the effect of hepatic steatosis on the expression of the sirtuin 1 (SIRT1), along with the target mRNA and protein expressions and activities related to lipid metabolism in liver tissue. Control cows (n = 6, parity 3.0 ± 2.0, milk production 28 ± 7 kg/d) and mild fatty liver cows (n = 6, parity 2.3 ± 1.5, milk production 20 ± 6 kg/d) were retrospectively selected based on liver triglycerides (TG) content (% wet liver). Compared with the control group, fatty liver cows had greater concentrations of cholesterol and TG along with the typically vacuolated appearance and greater lipid droplets in the liver. Furthermore, fatty liver cows had greater mRNA and protein abundance related to hepatic lipid synthesis proteins sterol regulatory element binding proteins (SREBP-1c), long-chain acyl-CoA synthetase (ACSL), acyl-CoA carbrolase (ACC) and fatty acid synthase (FAS) and lipid transport proteins Liver fatty acid binding protein (L-FABP), apolipoprotein E (ApoE), low density lipoprotein receptor (LDLR) and microsomal TG transfer protein (MTTP) (p < 0.05). However, they had lower mRNA and protein abundance associated with fatty acid β-oxidation proteins SIRT1, peroxisome proliferator-activated receptor co-activator-1 (PGC-1α), peroxisome proliferator–activated receptor-α (PPARα), retinoid X receptor (RXRα), acyl-CoA 1 (ACO), carnitine palmitoyltransferase 1 (CPT1), carnitine palmitoyltransferase 2 (CPT2) and long- and medium-chain 3-hydroxyacyl-CoA dehydrogenases (LCAD) (p < 0.05). Additionally, mRNA abundance and enzyme activity of enzymes copper/zinc superoxide dismutase (Cu/Zn SOD), catalase (CAT), glutathione peroxidase (GSH-Px) and manganese superoxide dismutase (Mn SOD) decreased and mRNA and protein abundance of p45 nuclear factor-erythroid 2 (p45 NF-E2)-related factor 1 (Nrf1), mitochondrial transcription factor A (TFAM) decreased (p < 0.05). Lower enzyme activities of SIRT1, PGC-1α, Cu/Zn SOD, CAT, GSH-Px, SREBP-1c and Mn SOD (p < 0.05) and concentration of reactive oxygen species (ROS) were observed in dairy cows with fatty liver. These results demonstrate that decreased SIRT1 associated with hepatic steatosis promotes hepatic fatty acid synthesis and inhibits fatty acid β-oxidation. Hence, SIRT1 may represent a novel therapeutic target for the treatment of the fatty liver disease in dairy cows.

Imidacloprid-induced liver fibrosis in quails via activation of the TGF-β1/Smad pathway

Imidacloprid (IMI) is one of the most frequently used neonicotinoid insecticide, and its potential toxicity and environmental hazards have gradually attracted people's attention. Liver fibrosis caused by long-term inflammation or oxidative stress can lead to cirrhosis and liver failure, even death. However, the mechanism of liver fibrosis induced by neonicotinoid insecticide remains unclear. This study investigates whether IMI could induce liver fibrosis in quails and a potential mechanism. Our study used a quail 90-day IMI-induced liver fibrosis model. The results showed that IMI induced histopathological lesions, oxidative stress, inflammation, fibrosis, and changes in nuclear factor-kappa B (NF-κB), nuclear factor-E2-related factor-2 (Nrf2), and transforming growth factor (TGF-β1) levels. Furthermore, IMI enhanced the expression of liver fibrosis marker proteins, including collagen I, α-smooth muscle actin (α-SMA), and fibronectin 1 (FN-1), by activating the TGF-β1/Smad signaling pathway. In conclusion, our study demonstrated that IMI exposure induces liver fibrosis via activation of the TGF-β1/Smad signaling pathway in quails.

Green tea polyphenols decrease weight gain, ameliorate alteration of gut microbiota, and mitigate intestinal inflammation in canines with high-fat-diet-induced obesity

Green tea polyphenols (GTPs) exhibit beneficial effects towards obesity and intestinal inflammation; however, the mechanisms and association with gut microbiota are unclear. We examined the role of the gut microbiota of GTPs treatment for obesity and inflammation. Canines were fed either a normal diet or high-fat diet with low (0.48% g/kg), medium (0.96% g/kg), or high (1.92% g/kg), doses of GTPs for 18 weeks. GTPs decreased the relative abundance of Bacteroidetes and Fusobacteria and increased the relative abundance of Firmicutes as revealed by 16S rRNA gene sequencing analysis. The relative proportion of Acidaminococcus, Anaerobiospirillum, Anaerovibrio, Bacteroides, Blautia, Catenibactetium, Citrobacter, Clostridium, Collinsella, and Escherichia were significantly associated with GTPs-induced weight loss. GTPs significantly (P<.01) decreased expression levels of inflammatory cytokines, including TNF-α, IL-6, and IL-1β, and inhibited induction of the TLR4 signaling pathway compared with high-fat diet. We show that the therapeutic effects of GTPs correspond with changes in gut microbiota and intestinal inflammation, which may be related to the anti-inflammatory and anti-obesity mechanisms of GTPs.

Identification for Exploring Underlying Pathogenesis and Therapy Strategy of Oral Squamous Cell Carcinoma by Bioinformatics Analysis

BACKGROUND Oral squamous cell carcinoma (OSCC), one of the most common cavity-associated cancers, has a high incidence and worldwide mortality. However, the cause and underlying molecular mechanisms of OSCC remain unclear. MATERIAL AND METHODS Three microarray datasets (GSE23558, GSE34105, and GSE74530) from the Gene Expression Omnibus (GEO) database were downloaded and then integrated to gain differentially expressed genes (DEGs). We performed Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichments of DEGs in order to elucidate DEGs' biological roles. Protein-protein interaction (PPI) networks were established in order to identify hub genes. To validate the gene markers for OSCC, the data of TCGA OSCC were also assessed. RESULTS Together, 651 DEGs containing 288 upregulated genes and 363 downregulated genes were screened out, which could completely distinguish between OSCC and normal control tissues by principal component analysis (PCA). The GO analysis indicated the DEGs were enriched in chemokine activity in the biological process group. The molecular functions of DEGs included growth factor activity. The molecular functions included oxidoreductase activity. The main DEG-associated cellular components included extracellular exosome. The KEGG pathway analysis indicated the DEGs were mainly participated in the cytokine-cytokine receptor interaction, metabolism of xenobiotics by cytochrome P450 and glutathione metabolism signal pathway. The co-expression network identified core genes from the PPI network. Additionally, Kaplan-Meier survival analysis showed that CSF2 and EGF genes were significantly correlated with OSCC patients' overall survival. CONCLUSIONS Our study using an integrated bioinformatics analysis might provide valuable information for exploring potential new molecular biomarkers and therapeutic targets for OSCC.

The Gut-Liver Axis in the Control of Energy Metabolism and Food Intake in Animals

Recent research has convincingly demonstrated a bidirectional communication axis between the gut and liver that enables the gut microbiota to strongly affect animals' feeding behavior and energy metabolism. As such, the gut-liver axis enables the host to control and shape the gut microbiota and to protect the intestinal barrier. Gut microbiota-host communication is based on several gut-derived compounds, such as short-chain fatty acids, bile acids, methylamines, amino acid-derived metabolites, and microbial-associated molecular patterns, which act as communication signals, and multiple host receptors, which sense the signals, thereby stimulating signaling and metabolic pathways in all key tissues of energy metabolism and food intake regulation. Disturbance in the microbial ecosystem balance, or microbial dysbiosis, causes profound derangements in the regulation of appetite and satiety in the hypothalamic centers of the brain and in key metabolic pathways in peripheral tissues owing to intestinal barrier disruption and subsequent induction of hepatic and hypothalamic inflammation.

Leucine Regulates the Exocrine Function in Pancreatic Tissue of Dairy Goats In Vitro

This study aimed to investigate the effects of leucine (Leu) on the synthesis and secretion of digestive enzymes in cultured pancreatic tissue of dairy goats and on the signaling molecules. Fresh pancreatic tissue from dairy goats was cut into approximately 2 mm × 2 mm pieces and incubated in oxygenated Krebs-Ringer bicarbonate buffer containing 0 (the control), 0.40, 0.80, or 1.60 mM Leu at 39°C in a CO₂ incubator for 180 min. The results showed that Leu increased the release of α-amylase, trypsin, and chymotrypsin in the buffer and tissue, as well as the total activity (P < 0.05), especially at 0.40 and 0.80 mM. Compared with the control, 1.60 mM Leu increased the release of α-amylase and the total activity of trypsin and chymotrypsin (P < 0.05) but had no effect on the tissue concentration of α-amylase, trypsin, and chymotrypsin or the total activity of α-amylase (P > 0.05). Leu improved the mRNA expression of α-amylase, trypsin, and chymotrypsin (P < 0.05), especially at 0.80 and 1.60 mM. The activity and mRNA expression of lipase were not affected (P > 0.05). Compared with the control, 0.40 and 0.80 mM Leu increased the expression of the γ isoform of 4EBP1 (P < 0.05), implying increased phosphorylation of 4EBP1. Leu increased the phosphorylation of S6K1 (P < 0.05). Compared with the control, 0.40 and 0.80 mM Leu decreased the eEF2 phosphorylation level (P < 0.05). Conclusively, these results suggested that Leu could regulate the synthesis of pancreatic enzymes by increasing the mRNA expression and phosphorylation level of protein factors in the mammalian target of rapamycin pathway and the optimal Leu level in this experiment was 0.80 mM.