GRP78 expression inhibits insulin and ER stress-induced SREBP-1c activation and reduces hepatic steatosis in mice

Modulation of liver lipid metabolic pathways by central nervous system ER stress

Metabolic dysfunction-associated steatotic liver disease (MASLD), considered as the hepatic manifestation of metabolic syndrome, can increase the risk for cardiometabolic diseases. Accumulating reports have implicated the central nervous system in MASLD pathogenesis, specifically endoplasmic reticulum (ER) stress in subfornical organ (SFO) to hypothalamic paraventricular nucleus (PVN) projecting neurons (SFO→PVN). Here, we investigated how ER stress in this neural circuit influences hepatic lipid regulatory pathways that may contribute to MASLD development during obesity. Hepatic steatosis was elicited by feeding C57BL/6J male mice a high-fat diet for 11 wk. Intersectional viral targeting was used to inhibit ER stress in SFO→PVN neurons to examine the contribution of ER stress in this circuit to hepatic lipid acquisition and disposal genes during obesity. Inhibition of ER stress in SFO→PVN neurons of obese mice resulted in a reduction in hepatic triglycerides and lipid acquisition genes that was paralleled by a reduction in liver tyrosine hydroxylase, the rate-limiting enzyme in catecholamine synthesis. Moreover, hepatic tyrosine hydroxylase expression was positively correlated with lipid acquisition but not disposal pathways. These results indicate that ER stress in SFO→PVN neurons may contribute to MASLD through sympathetic nervous system influences, primarily on hepatic lipid acquisition.NEW & NOTEWORTHY Endoplasmic reticulum stress in SFO→PVN neurons modulates hepatic lipid acquisition and disposal pathways during obesity-induced hepatic steatosis. Hepatic tyrosine hydroxylase levels are positively correlated with liver triglyceride levels and lipid acquisition pathway-related genes in diet-induced obese animals.

Therapeutic potential of fisetin in hepatic steatosis: Insights into autophagy pathway regulation and endoplasmic reticulum stress alleviation in high-fat diet-fed mice

Non-alcoholic fatty liver disease (NAFLD) is a common condition with limited FDA-approved treatments due to its complex pathogenesis. Metabolic stress-induced lipotoxicity triggers the unfolded protein response, leading to the development of NAFLD through inflammation and apoptosis. Moreover, metabolic dysregulation compromises autophagic capacity, impairing effective ERphagy and lipophagy in the liver. Fisetin (FSN), a flavonoid present in various fruits and vegetables, has demonstrated the ability to regulate the processes mentioned above and possesses a range of biological properties. In this study using a high-fat diet-induced NAFLD mouse model, treatment with FSN at a dosage of 80 mg/kg per day for eight weeks resulted in reduced hepatic lipid accumulation. This effect was mediated by modulating ER stress through enhancing autophagic activity, as indicated by decreased expression of GRP78, elf2a, ATF4, and CHOP genes, along with increased AMPK phosphorylation, decreased mTOR expression, and elevated levels of ULK1, ATG5, and Beclin1. Additionally, there was an increase in the LCII/LC3I ratio and a reduction in p62 levels in hepatic tissue. Our findings suggest that FSN exerts its effects by activating the AMPK/mTOR signaling pathway and its downstream targets, underscoring its potential therapeutic advantages in managing NAFLD by targeting autophagy and ER stress pathways.

Lipogenesis and MASLD: re-thinking the role of SREBPs

Metabolic dysfunction-associated steatotic liver disease (MASLD) is the most common chronic liver disease worldwide and a major risk factor for hepatocellular carcinoma (HCC). Lipid metabolism, particularly de novo lipogenesis (DNL) regulated by sterol regulatory element-binding proteins (SREBPs), plays a key role in MASLD progression. While excessive SREBP activation contributes to hepatic steatosis, our recent findings indicate that strong SREBP inhibition paradoxically exacerbates liver injury and accelerates carcinogenesis in murine MASLD models. Mechanistically, SREBP dysfunction disrupts phospholipid homeostasis, leading to impaired endoplasmic reticulum (ER) membrane fluidity, ER stress, and hepatocyte injury. Transcriptomic analysis of clinical samples revealed a dynamic shift in SREBP activity, with upregulation in early MASLD but significant downregulation in advanced, burned-out MASH. This suggests that SREBP dysfunction in advanced disease may contribute to fibrosis progression and increased HCC risk. Given these findings, therapeutic strategies targeting lipid metabolism in MASLD must be carefully tailored to disease stage. This review provides an updated perspective on the biphasic role of SREBP in MASLD, emphasizing the need to re-think lipid metabolism-targeted therapies and develop personalized interventions to mitigate disease progression and HCC development.

Understanding the Link Between Sterol Regulatory Element Binding Protein (SREBPs) and Metabolic Dysfunction Associated Steatotic Liver Disease (MASLD)

PURPOSE OF THE REVIEW

This review aims to summarize the current scientific understanding on the complex interplay between sterol regulatory element-binding proteins (SREBPs) and metabolic dysfunction associated steatotic liver disease (MASLD) by critically examining a few significant molecular pathways. Additionally, the review explores the potential of both natural and synthetic SREBP inhibitors as promising therapeutic candidates for MASLD.

RECENT FINDINGS

SREBPs are central regulators of lipid homeostasis, with SREBP-1c primarily controlling fatty acid synthesis and SREBP-2 regulating cholesterol metabolism. Dysregulation of SREBP activity, often triggered by excessive caloric intake, insulin resistance, or endoplasmic reticulum (ER) stress, contributes to the development of metabolic syndrome and MASLD. SREBP-1c overexpression leads to increased de novo lipogenesis (DNL), hepatic lipid accumulation, and insulin resistance, while SREBP-2 modulates cholesterol metabolism via miRNA-33 and ABCA1 regulation leading to the pathogenesis of MASLD. The PI3K-Akt-mTORC1 pathway plays a critical role in SREBP activation, linking nutrient availability to lipid synthesis. Synthetic SREBP inhibitors, such as fatostatin and 25-hydroxycholesterol, and natural compounds, including kaempferol and resveratrol, show promise in modulating SREBP activity in vivo.

CONCLUSION

While targeting SREBP pathways presents a promising avenue for mitigating MASLD, further scientific investigation is imperative to identify and validate potential molecular targets. Although current studies on synthetic and natural SREBP inhibitors demonstrate encouraging results, rigorous pre-clinical and clinical research is warranted to translate these findings into effective MASLD treatments.

Effect of midlife exercise on lipid metabolism in aging mice: comparable to lifelong exercise, better than ceasing midlife exercise

This study examines the effects of continuous versus interrupted lifelong exercise on lipid metabolism in naturally aging male BALB/c mice. Five-week-old male BALB/c mice were randomly assigned to five groups: young control group (YC), natural ageing control group (AC), exercise cessation group (DE), middle-aged commencing exercise group (ME), and lifelong exercise group (LE). Moderate Intensity Continuous Training exercise sessions were conducted three times per week, with each session lasting 50 min; after exercise interventions until 72 weeks of age, the following parameters were measured: body morphology, exercise capacity, blood lipid, liver fat content, liver function, expression of liver lipid metabolism-related genes and endoplasmic reticulum stress-related genes, and activities of liver metabolism enzymes. The results suggest that advancing age leads to disrupted lipid processing, reduced hepatic performance, and increased endoplasmic reticular tension. Compared with the AC group, the ME and LE cohorts showed reduced serum lipids, whereas the LE group exhibited elevated high-density lipoprotein cholesterol (HDL-C) levels (P < 0.05). Post-exercise reductions were observed in hepatic total cholesterol and free fatty acid (FFA). Moreover, the exercises mitigated age-related hepatic impairments and diminished susceptibility towards cirrhosis despite higher aspartate aminotransferase (AST) and lower albumin (ALB) levels being evident within the DE cohort (P < 0.05). Exercise demonstrates the potential to mitigate age-related abnormalities in lipid metabolism. Middle-aged commencing and lifelong exercise interventions are more effective in alleviating lipid abnormalities than exercise cessation in middle age. This disparity in efficacy can be attributed to differences in regulating endoplasmic reticulum stress, enhancing liver lipid oxidation capacity, and reducing lipid synthesis ability. Notably, middle-aged individuals commencing exercise yield similar outcomes in regulating aging-associated abnormal lipid metabolism compared to the lifelong exercise group. This highlights the importance of initiating exercise in middle age, as it remains beneficial even if lifelong commitment is unfeasible, so exercise initiation in midlife is still beneficial. However, to prevent liver lipid metabolism disorders later in life, the earlier exercise initiation, the better.

HSF1 Mediates Palmitic Acid-Disrupted Lipid Metabolism and Inflammatory Response by Maintaining Endoplasmic Reticulum Homeostasis in Fish

Fish oil (FO) is being progressively replaced by palm oil (PO), which is rich in palmitic acid (PA). However, our understanding of the effects of PA on fish and the underlying molecular mechanisms remains limited. Heat shock transcription factor 1 (HSF1) is a critical transcription factor involved in stress response, but whether it responds to the effects of PA in fish remains unknown. In this study, in vitro and in vivo experiments were combined to investigate the molecular mechanisms by which HSF1 responds to PA. Our results indicated that PA induced fat accumulation, inflammation, and activation of protein processing in the endoplasmic reticulum (PPER) in the PaL cells. Moreover, the nuclear translocation of HSF1 was significantly increased by PA. After HSF1 was disrupted using small molecules (HSF1A and KRIBB11) or through HSF1A knockout, the PA-induced fat accumulation and expression levels of key genes related to PPER, lipid metabolism, and inflammation were significantly altered. Additionally, the analysis of CUT&Tag sequencing and dual-luciferase reporter showed that HSF1 protein can directly bind to the promoters of genes involved in PPER, lipid metabolism, and inflammatory response, thereby activating their transcriptional activity, especially HSC70, HSP90α, and HSP90β. Eicosapentaenoic acid (EPA) supplementation significantly improved the survival rate and growth performance of juvenile silver pomfret and reduced PA-induced adverse effects by inhibiting the activation of HSF1 in the liver. This study proves that HSF1 protein may respond to PA-induced lipid metabolism disorder and inflammatory response by maintaining endoplasmic reticulum stability in fish. Furthermore, EPA supplementation effectively counteracts PA-induced adverse effects.

Embelin Elevates Endoplasmic Reticulum Calcium Levels and Blocks the Sterol Regulatory Element-Binding Protein 2 Mediated Proprotein Convertase Subtilisin/Kexin Type 9 Expression and Improves the Low-Density Lipoprotein Receptor Mediated Lipid Clearance on Hepatocytes

Cardiovascular diseases (CVDs) continue to be one of the leading causes of morbidity and mortality worldwide, with a significant increase in recent years. Atherosclerosis, the pathological basis and prime reason for CVDs is primarily driven by dysregulated lipid metabolism and inflammation. Recently, proprotein convertase subtilisin kexin9 (PCSK9) has been evolved to be highly implicated in the circulatory low-density lipoprotein cholesterol levels by its modulatory effects on the low-density lipoprotein receptor (LDLR) mediated clearance. Even though not economical, the therapies targeting PCSK9 demonstrated appreciable levels of efficiency in managing hyperlipidaemic conditions. Embelin (2,5-dihydroxy-3-undecyl-1,4-benzoquinone) is a naturally occurring para-benzoquinone isolated from dried berries of Embelia ribes, which possess several effects in maintaining the cholesterol homeostasis. In this study, we have analysed the role of embelin in sterol regulatory element-binding protein 2 (SREBP2) mediated PCSK9 expression in cultured hepatocytes. The study showed that the embelin treatment attenuates the endoplasmic reticulum (ER) stress-induced reactive oxygen species levels and ER stress markers on cultured hepatocytes. The treatment of embelin modulates the mRNA and protein level expression of SREBP2 and its downstream targets like PCSK9, LDLR, and HMG-CoA reductase (HMGCR). Interestingly the Ca2+ levels and the calcium binding protein of ER were significantly increased with embelin treatment. The work revealed a putative mechanism of embelin in lowering PCSK9 levels by boosting ER Ca2+ levels, thereby blocking SREBP2 nuclear translocation. Further, this reduces LDLR degradation and increases receptor-mediated circulatory lipid clearance. The study summarized the potential clinical applications of embelin in addressing the cardio vascular diseases.

Intermittent Fasting Improves Social Interaction and Decreases Inflammatory Markers in Cortex and Hippocampus

Autism spectrum disorder (ASD) is a psychiatric condition characterized by reduced social interaction, anxiety, and stereotypic behaviors related to neuroinflammation and microglia activation. We demonstrated that maternal exposure to Western diet (cafeteria diet or CAF) induced microglia activation, systemic proinflammatory profile, and ASD-like behavior in the offspring. Here, we aimed to identify the effect of alternate day fasting (ADF) as a non-pharmacologic strategy to modulate neuroinflammation and ASD-like behavior in the offspring prenatally exposed to CAF diet. We found that ADF increased plasma beta-hydroxybutyrate (BHB) levels in the offspring exposed to control and CAF diets but not in the cortex (Cx) and hippocampus (Hpp). We observed that ADF increased the CD45 + cells in Cx of both groups; In control individuals, ADF promoted accumulation of CD206 + microglia cells in choroid plexus (CP) and increased in CD45 + macrophages cells and lymphocytes in the Cx. Gestational exposure to CAF diet promoted defective sociability in the offspring; ADF improved social interaction and increased microglia CD206 + in the Hpp and microglia complexity in the dentate gyrus. Additionally, ADF led to attenuation of the ER stress markers (Bip/ATF6/p-JNK) in the Cx and Hpp. Finally, biological modeling showed that fasting promotes higher microglia complexity in Cx, which is related to improvement in social interaction, whereas in dentate gyrus sociability is correlated with less microglia complexity. These data suggest a contribution of intermittent fasting as a physiological stimulus capable of modulating microglia phenotype and complexity in the brain, and social interaction in male mice.

Bletilla striata polysaccharides alleviate metabolic dysfunction-associated steatotic liver disease through enhancing hepatocyte RelA/ HNF1α signaling

BACKGROUND

Bletilla striata polysaccharides (BSP) have antioxidant, immune regulation, and anti-fibrotic activities. However, the therapeutic effect and mechanisms underlying the action of BSP in metabolic dysfunction-associated steatotic liver disease (MASLD) have not been fully understood.

AIM

To investigate the therapeutic effects and mechanisms of BSP on MASLD by centering on the hepatocyte nuclear factor kappa B p65 (RelA)/hepatocyte nuclear factor-1 alpha (HNF1α) signaling.

METHODS

A mouse model of MASLD was induced by feeding with a high-fat-diet (HFD) and a hepatocyte model of steatosis was induced by treatment with sodium oleate (SO) and sodium palmitate (SP). The therapeutic effects of BSP on MASLD were examined in vivo and in vitro. The mechanisms underlying the action of BSP were analyzed for their effect on lipid metabolism disorder, endoplasmic reticulum (ER) stress, and the RelA/HNF1α signaling.

RESULTS

HFD feeding reduced hepatocyte RelA and HNF1α expression, induced ER stress, lipid metabolism disorder, and necroptosis in mice, which were significantly mitigated by treatment with BSP. Furthermore, treatment with BSP or BSP-containing conditional rat serum significantly attenuated the sodium oleate/sodium palmitate (SO/SP)-induced hepatocyte steatosis by decreasing lipid accumulation, and lipid peroxidation, and enhancing the expression of RelA, and HNF1α. The therapeutic effects of BSP on MASLD were partially abrogated by RELA silencing in mice and RELA knockout in hepatocytes. RELA silencing or knockout significantly down-regulated HNF1α expression, and remodeled ER stress and oxidative stress responses during hepatic steatosis.

CONCLUSION

Treatment with BSP ameliorates MASLD, associated with enhancing the RelA/HNF1α signaling, remodeling ER stress and oxidative stress responses in hepatocytes.

Caveolin 1 in bovine liver is associated with fatty acid-induced lipid accumulation and the endoplasmic reticulum unfolded protein response: Role in fatty liver development

Disruption of endoplasmic reticulum (ER) homeostasis (i.e., ER stress) is intrinsically linked with lipid metabolism disorders in dairy cows. Caveolin 1 (CAV1) is a ubiquitously expressed membrane-associated scaffolding protein involved in regulating the secretory pathway within the ER. Whether inhibiting the activity of CAV1 affects the ER and its potential role in hepatic lipid deposition in dairy cows is unknown. Biopsies of liver tissue from Holstein cows (median DIM = 13 d, range = 5-21 d) diagnosed as healthy (n = 6; hepatic triacylglycerol (TAG) levels <1%; median milk production = 38.9 kg/d, interquartile range = 38.0-40.8 kg/d) or suffering from fatty liver (n = 6; hepatic TAG levels >5%; median milk production = 36.6 kg/d, interquartile range = 35.7-38.1 kg/d) revealed that fatty liver was associated with lower abundance of the CAV1 gene and protein, higher phosphorylation (p) levels of PERK and IRE1α, and increased abundance of the ATF6, GRP78, and CHOP proteins, and several unfolded protein response (UPR) genes (ATF4, sXBP1, and GRP78). Proteins related to de novo fatty acid synthesis, including ACC1, SREBP-1c, PPARγ, and downstream targets genes of SREBP1 (ACACA and FASN) also had greater abundance. This in vivo analysis highlighted a mechanistic link between CAV1 protein abundance, ER stress, and lipid metabolism in fatty liver. A mechanistic study was then performed in vitro with primary hepatocytes isolated from 5 healthy calves (weight = 40-45 kg; 1 d old). Initially, hepatocytes were treated with free fatty acid (FFA; 1.2 mM) for 1, 3, 6, or 12 h. Treatment with FFA reduced CAV1 protein abundance linearly while reducing abundance of ER stress-related proteins, phosphorylated [p-] IRE1α, p-PERK, GRP78, ATF6, and CHOP. Proteins related to de novo fatty acid synthesis (ACC1, SREBP-1c, PPARγ) also increased linearly, and lipid droplets accumulated progressively over time following FFA treatment. Subsequently, to assess the role of CAV1 in FFA-induced ER stress and de novo fatty acid synthesis, hepatocytes were transfected with pCMV-CAV1 (cattle)-3 × FLAG-Neo (plasmid construct [pc-]CAV1) plasmid to overexpress CAV1 or with siRNA to silence CAV1 (siCAV1) transcription. Overexpression of CAV1 alleviated ER stress by reducing levels of p-PERK and p-IRE1α, as well as protein abundance of ATF6, GRP78, CHOP, and several UPR genes (GRP78, ATF4, and sXBP1). Similarly, CAV1 overexpression decreased protein abundance of ACC1, SREBP-1c, PPARγ, and downstream targets genes of SREBP1 (ACACA and FASN). Conversely, silencing CAV1 exacerbated FFA-induced ER stress and de novo fatty acid synthesis. Considering the negative role of FFA-induced ER stress on lipid accumulation in hepatocytes, a second in vitro experiment involved hepatocytes treated with 0.5 μg/mL tunicamycin (TM; a typical ER stress inducer) for 24 h with or without overexpressing CAV1 (pc-CAV1). Overexpressing CAV1 reversed TM-induced increases in mRNA and protein associated with ER stress and de novo fatty acid synthesis. Furthermore, use of hepatocytes transfected with pc-CAV1 for 48 h and subjected to co-immunoprecipitation revealed that CAV1 interacts with IRE1α and ATF6. Overall, the data suggest that CAV1 may help reduce hepatic ER stress and mitigate fatty acid synthesis by binding to and inhibiting IRE1α and ATF6 signaling.

Chronic hyperglycemia induces hepatocyte pyroptosis via Gα12/Gα13-associated endoplasmic reticulum stress: Effect of pharmacological intervention

AIMS

Hyperglycemia induces pathophysiological changes. Endoplasmic reticulum (ER) stress with Gα12 overexpression may promote hepatocyte death. This study investigated whether sustained hyperglycemia triggers ER stress-associated pyroptosis and fibrosis in the liver alongside an overexpression of Gα12, and examined the potential link with VEGF-A levels.

MAIN METHODS

Mice were subjected to a high-fat diet (60 kcal% fat) with streptozotocin (50 mg/kg body weight, three consecutive times, between 12-13th weeks). AZ2 (a functional Gα12 inhibitor) was treated at 10 mg/kg body weight (5 times/week, 3 weeks). Immunoblotting and immunohistochemistry analyses were performed.

KEY FINDINGS

Hepatic Gα12/Gα13 were overexpressed in the diabetic mice. The following proteins downstream from the Gα12 axis were upregulated: PGC1α, PPARα, and SIRT1. Sustained hyperglycemia promoted ER stress marker levels. Histopathological and biochemical assays showed large-sized lipid droplet accumulation, hepatocyte degeneration, and damage as blood transaminase activities increased. Moreover, the diabetic condition increased IL-1β, caspase-1, and NLRP3 levels, which were supportive of pyroptosis. Consistently, the intensities of Masson's trichrome, collagen-1A1, α-SMA, vimentin, and fibronectin all increased. VEGF-A and VEGFR2 levels also increased in the liver and/or sera. The levels of hepatic pigment epithelial-derived factor (PEDF), a physiological antagonist of VEGF-A, decreased with its reciprocal increase in serum. These events were reversed by AZ2 treatment, supporting the role of Gα12 in hyperglycemic stress in the liver.

SIGNIFICANCE

Chronic hyperglycemia causes hepatic pyroptosis and fibrosis related to ER stress with Gα12/Gα13 and VEGF overexpression, which may be overcome by AZ2 treatments.

Roles of X-box binding protein 1 in liver pathogenesis

The prevalence of drug-induced liver injury (DILI) and viral liver infections presents significant challenges in modern healthcare and contributes to considerable morbidity and mortality worldwide. Concurrently, metabolic dysfunctionassociated steatotic liver disease (MASLD) has emerged as a major public health concern, reflecting the increasing rates of obesity and leading to more severe complications such as fibrosis and hepatocellular carcinoma. X-box binding protein 1 (XBP1) is a distinct transcription factor with a basic-region leucine zipper structure, whose activity is regulated by alternative splicing in response to disruptions in endoplasmic reticulum (ER) homeostasis and the unfolded protein response (UPR) activation. XBP1 interacts with a key signaling component of the highly conserved UPR and is critical in determining cell fate when responding to ER stress in liver diseases. This review aims to elucidate the emerging roles and molecular mechanisms of XBP1 in liver pathogenesis, focusing on its involvement in DILI, viral liver infections, MASLD, fibrosis/cirrhosis, and liver cancer. Understanding the multifaceted functions of XBP1 in these liver diseases offers insights into potential therapeutic strategies to restore ER homeostasis and mitigate liver damage.

6-Gingerol, a Bioactive Compound of Zingiber officinale, Ameliorates High-Fat High-Fructose Diet-Induced Non-Alcoholic Related Fatty Liver Disease in Rats

Purpose

Endoplasmic reticulum (ER) stress has a prominent role in the pathogenesis of high-fat diet-induced non-alcohol related fatty liver disease (NAFLD). The aim of this study is to investigate the effects of 6-G on the reduction of ER stress-induced NAFLD in metabolic syndrome (MetS) rats.

Methods

Twenty-five male Sprague-Dawley rats were fed with a high-fat high-fructose (HFHF) diet for 16 weeks. The rats were treated orally with 6-G (50,100, and 200 mg/kgBW) once daily for eight weeks. At Week 16, all animals were sacrificed, and serum and liver tissue were harvested for biochemical and structural analysis.

Results

NAFLD liver rats were shown to have elevated protein expression of GRP78, and ER-associated apoptotic protein, such as IRE1, TRAF2, p-JNK, and p-NF-κB, which were considerably reduced by the 6-G at three doses treatment. Furthermore, a significant increase in liver apoptosis and non-alcoholic steatohepatitis (NAS) score were observed in the NAFLD rat liver and which were also attenuated by the 6-G treatment at three doses. 6-G treatment also reduced ALT, AST, and ALP serum levels.

Conclusion

Considering all the findings, it is suggested that the 6-G treatment could be a potential candidate therapy in treating ER stress-induced NAFLD in rats.

The Influence of Aging on the Unfolded Protein Response in Human Skeletal Muscle at Rest and after Acute Exercise

BACKGROUND

The unfolded protein response (UPR) is a proteostatic process that is activated in response to endoplasmic reticulum stress. It is currently unclear how aging influences the chronic and adaptive UPR in human skeletal muscle. Here we determined the effect of aging on UPR activation at rest, in response to exercise, and the associations with muscle function.

METHODS

Thirty young (20-35 yr) and 50 older (65-85 yr) individuals were enrolled. Vastus lateralis biopsies were performed at rest and 3 and 48 h after a single bout of resistance exercise. The abundance of UPR-related transcripts and proteins was measured by RNA sequencing and Western blotting, respectively. Fractional synthetic rates of muscle protein were determined by mass spectrometry after intravenous infusion of 13 C 6 phenylalanine.

RESULTS

Older adults demonstrated elevated transcriptional and proteomic markers of UPR activation in resting muscle. Resting UPR gene expression was negatively associated with muscle strength and power in older adults. The UPR is similarly activated by acute resistance exercise in young and older adults and positively associated with muscle function but not the anabolic response to exercise.

CONCLUSIONS

Skeletal muscle from older adults exhibits chronically activated UPR, which accompanies functional decline. The adaptive UPR is a proteostatic mechanism that is upregulated in response to exercise in young and older adults and positively associated with muscle function.

The lipid side of unfolded protein response

Although our current knowledge of the molecular crosstalk between the ER stress, the unfolded protein response (UPR), and lipid homeostasis remains limited, there is increasing evidence that dysregulation of either protein or lipid homeostasis profoundly affects the other. Most research regarding UPR signaling in human diseases has focused on the causes and consequences of disrupted protein folding. The UPR itself consists of very complex pathways that function to not only maintain protein homeostasis, but just as importantly, modulate lipid biogenesis to allow the ER to adjust and promote cell survival. Lipid dysregulation is known to activate many aspects of the UPR, but the complexity of this crosstalk remains a major research barrier. ER lipid disequilibrium and lipotoxicity are known to be important contributors to numerous human pathologies, including insulin resistance, liver disease, cardiovascular diseases, neurodegenerative diseases, and cancer. Despite their medical significance and continuous research, however, the molecular mechanisms that modulate lipid synthesis during ER stress conditions, and their impact on cell fate decisions, remain poorly understood. Here we summarize the current view on crosstalk and connections between altered lipid metabolism, ER stress, and the UPR.

2-Deoxy-D-Glucose Downregulates Fatty Acid Synthase Gene Expression Via an Endoplasmic Reticulum Stress-Dependent Pathway in HeLa Cells

Fatty acid synthase (FASN) catalyzes the rate-limiting step of cellular lipogenesis. FASN expression is upregulated in various types of cancer cells, implying that FASN is a potential target for cancer therapy. 2-Deoxy-D-glucose (2-DG) specifically targets cancer cells by inhibiting glycolysis and glucose metabolism, resulting in multiple anticancer effects. However, whether the effects of 2-DG involve lipogenic metabolism remains to be elucidated. We investigated the effect of 2-DG administration on FASN expression in HeLa human cervical cancer cells. 2-DG treatment for 24 h decreased FASN mRNA and protein levels and suppressed the activity of an exogenous rat Fasn promoter. The use of a chemical activator or inhibitors or of a mammalian expression plasmid showed that neither AMPK nor the Sp1 transcription factor is responsible for the inhibitory effect of 2-DG on FASN expression. Administration of thapsigargin, an endoplasmic reticulum (ER) stress inducer, or 4-(2-aminoethyl) benzenesulfonyl fluoride (AEBSF), a site 1 protease inhibitor, mimicked the inhibitory effect of 2-DG on FASN expression. 2-DG did not further decrease FASN expression in the presence of thapsigargin or AEBSF. Site 1 protease mediates activation of ATF6, an ER stress mediator, as well as sterol regulatory element-binding protein 1 (SREBP1), a robust transcription factor for FASN. Administration of 2-DG or thapsigargin for 24 h suppressed activation of ATF6 and SREBP1, as did AEBSF. We speculated that these effects of 2-DG or thapsigargin are due to feedback inhibition via increased GRP78 expression following ER stress. Supporting this, exogenous overexpression of GRP78 in HeLa cells suppressed SREBP1 activation and Fasn promoter activity. These results suggest that 2-DG suppresses FASN expression via an ER stress-dependent pathway, providing new insight into the molecular basis of FASN regulation in cancer.

Compromised COPII vesicle trafficking leads to glycogenic hepatopathy

Being a vital cellular process, coat protein complex II (COPII) vesicle trafficking has been found to play a crucial role in liver metabolism. However, its functions and the underlying mechanisms in systemic metabolic homeostasis have not been fully understood. Here, with a newly identified gene trap zebrafish line (sec31anju221), we show that compromised COPII vesicle trafficking leads to biphasic abnormal hepatic metabolism. During the larval stage, deficiency of COPII-mediated trafficking leads to activation of the unfolded protein response and the development of hepatic steatosis. By using epistasis analysis, we found that the eIF2α-ATF4 pathway serves as the primary effector for liver steatosis. In adult sec31anju221 fish, the hepatosteatosis was reversed and the phenotype switched to glycogenic hepatopathy. Proteomic profiling and biochemical assays indicate that sec31anju221 fish are in a state of hypothyroidism. Moreover, our study shows that thyroid hormone treatment alleviates the metabolic defects. This study provides insights into processes of liver diseases associated with vesicle trafficking impairments and expands our understanding of the pathological interplay between thyroid and liver.

Influence of Lipid Class Used for Omega-3 Fatty Acid Supplementation on Liver Fat Accumulation in MASLD

Metabolic dysfunction-associated steatotic liver disease (MASLD) occurs in subjects with obesity and metabolic syndrome. MASLD may progress from simple steatosis (i.e., hepatic steatosis) to steatohepatitis, characterized by inflammatory changes and liver cell damage, substantially increasing mortality. Lifestyle measures associated with weight loss and/or appropriate diet help reduce liver fat accumulation, thereby potentially limiting progression to steatohepatitis. As for diet, both total energy and macronutrient composition significantly influence the liver's fat content. For example, the type of dietary fatty acids can affect the metabolism of lipids and hence their tissue accumulation, with saturated fatty acids having a greater ability to promote fat storage in the liver than polyunsaturated ones. In particular, polyunsaturated fatty acids of n-3 series (omega-3), such as docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), have been intensively studied for their antisteatotic effects, both in preclinical animal models of obesity and hepatic steatosis and in overweight/obese patients. Their effects may depend not only on the dose and duration of administration of omega-3, or DHA/EPA ratio, but also on the lipid class used for their supplementation. This review summarizes the available evidence from recent comparative studies using omega-3 supplementation via different lipid classes. Albeit the evidence is mainly limited to preclinical studies, it suggests that phospholipids and possibly wax esters could provide greater efficacy against MASLD compared to traditional chemical forms of omega-3 supplementation (i.e., triacylglycerols, ethyl esters). This cannot be attributed solely to improved EPA and/or DHA bioavailability, but other mechanisms may be involved. Keywords: MASLD • Metabolic dysfunction-associated steatotic liver disease • NAFLD • Non-alcoholic fatty liver disease • n-3 polyunsaturated fatty acids.

Obesity disrupts the pituitary-hepatic UPR communication leading to NAFLD progression

Obesity alters levels of pituitary hormones that govern hepatic immune-metabolic homeostasis, dysregulation of which leads to nonalcoholic fatty liver disease (NAFLD). However, the impact of obesity on intra-pituitary homeostasis is largely unknown. Here, we uncovered a blunted unfolded protein response (UPR) but elevated inflammatory signatures in pituitary glands of obese mice and humans. Furthermore, we found that obesity inflames the pituitary gland, leading to impaired pituitary inositol-requiring enzyme 1α (IRE1α)-X-box-binding protein 1 (XBP1) UPR branch, which is essential for protecting against pituitary endocrine defects and NAFLD progression. Intriguingly, pituitary IRE1-deletion resulted in hypothyroidism and suppressed the thyroid hormone receptor B (THRB)-mediated activation of Xbp1 in the liver. Conversely, activation of the hepatic THRB-XBP1 axis improved NAFLD in mice with pituitary UPR defect. Our study provides the first evidence and mechanism of obesity-induced intra-pituitary cellular defects and the pathophysiological role of pituitary-liver UPR communication in NAFLD progression.

TXNDC5 Plays a Crucial Role in Regulating Endoplasmic Reticulum Activity through Different ER Stress Signaling Pathways in Hepatic Cells

The pathogenesis of non-alcoholic fatty liver disease (NAFLD) is influenced by a number of variables, including endoplasmic reticulum stress (ER). Thioredoxin domain-containing 5 (TXNDC5) is a member of the protein disulfide isomerase family and acts as an endoplasmic reticulum (ER) chaperone. Nevertheless, the function of TXNDC5 in hepatocytes under ER stress remains largely uncharacterized. In order to identify the role of TXNDC5 in hepatic wild-type (WT) and TXNDC5-deficient (KO) AML12 cell lines, tunicamycin, palmitic acid, and thapsigargin were employed as stressors. Cell viability, mRNA, protein levels, and mRNA splicing were then assayed. The protein expression results of prominent ER stress markers indicated that the ERN1 and EIF2AK3 proteins were downregulated, while the HSPA5 protein was upregulated. Furthermore, the ATF6 protein demonstrated no significant alterations in the absence of TXNDC5 at the protein level. The knockout of TXNDC5 has been demonstrated to increase cellular ROS production and its activity is required to maintain normal mitochondrial function during tunicamycin-induced ER stress. Tunicamycin has been observed to disrupt the protein levels of HSPA5, ERN1, and EIF2AK3 in TXNDC5-deficient cells. However, palmitic acid has been observed to disrupt the protein levels of ATF6, HSPA5, and EIF2AK3. In conclusion, TXNDC5 can selectively activate distinct ER stress pathways via HSPA5, contingent on the origin of ER stress. Conversely, the absence of TXNDC5 can disrupt the EIF2AK3 cascade.

Exercise enhances hepatic mitochondrial structure and function while preventing endoplasmic reticulum stress and metabolic dysfunction-associated steatotic liver disease in mice fed a high-fat diet

Metabolic dysfunction-associated steatotic liver disease (MASLD) has attracted increasing attention from the scientific community because of its severe but silent progression and the lack of specific treatment. Glucolipotoxicity triggers endoplasmic reticulum (ER) stress with decreased beta-oxidation and enhanced lipogenesis, promoting the onset of MASLD, whereas regular physical exercise can prevent MASLD by preserving ER and mitochondrial function. Thus, the hypothesis of this study was that high-intensity interval training (HIIT) could prevent the development of MASLD in high-fat (HF)-fed C57BL/6J mice by maintaining insulin sensitivity, preventing ER stress, and promoting beta-oxidation. Forty male C57BL/6J mice (3 months old) comprised 4 experimental groups: the control (C) diet group, the C diet + HIIT (C-HIIT) group, the HF diet group, and the HF diet + HIIT (HF-HIIT) group. HIIT sessions lasted 12 minutes and were performed 3 times weekly by trained mice. The diet and exercise protocols lasted for 10 weeks. The HIIT protocol prevented weight gain and maintained insulin sensitivity in the HF-HIIT group. A chronic HF diet increased ER stress-related gene and protein expression, but HIIT helped to maintain ER homeostasis, preserve mitochondrial ultrastructure, and maximize beta-oxidation. The increased sirtuin-1/peroxisome proliferator-activated receptor-gamma coactivator 1-alpha expression implies that HIIT enhanced mitochondrial biogenesis and yielded adequate mitochondrial dynamics. High hepatic fibronectin type III domain containing 5/irisin agreed with the antilipogenic and anti-inflammatory effects observed in the HF-HIIT group, reinforcing the antisteatotic effects of HIIT. Thus, we confirmed that practicing HIIT 3 times per week maintained insulin sensitivity, prevented ER stress, and enhanced hepatic beta-oxidation, impeding MASLD development in this mouse model even when consuming high energy intake from saturated fatty acids.

Platelets induce endoplasmic reticulum stress in macrophages in vitro

BACKGROUND

Endoplasmic reticulum (ER) stress is a key feature of lipid-laden macrophages and contributes to the development of atherosclerotic plaques. Blood platelets are known to interact with macrophages and fine-tune effector functions such as inflammasome activation and phagocytosis. However, the effect of platelets on ER stress induction is unknown.

OBJECTIVES

The objective of this study is to elucidate the potential of platelets in regulating ER stress in macrophages in vitro.

METHODS

Bone marrow-derived macrophages and RAW 264.7 cells were incubated with isolated murine platelets, and ER stress and inflammation markers were determined by reverse transcription-quantitative polymerase chain reaction, Western blotting, and enzyme-linked immunosorbent assay. ER morphology was investigated by electron microscopy. Cell viability, lipid accumulation, and activation were measured by flow cytometry. To gain mechanistic insights, coincubation experiments were performed with platelet decoys/releasates as well as lipopolysaccharide, blocking antibodies, and TLR4 inhibitors.

RESULTS

Coincubation of platelets and macrophages led to elevated levels of ER stress markers (BIP, IRE1α, CHOP, and XBP1 splicing) in murine and human macrophages, which led to a pronounced enlargement of the ER. Macrophage ER stress was accompanied by increased release of proinflammatory cytokines and intracellular lipid accumulation, but not cell death. Platelet decoys, but not platelet releasates or lysate from other cells, phenocopied the effect of platelets. Blocking TLR4 inhibited inflammatory activation of macrophages but did not affect ER stress induction by platelet coincubation.

CONCLUSION

To our knowledge, this study is the first to demonstrate that platelets induce ER stress and unfolded protein response in macrophages by heat-sensitive membrane proteins, independent of inflammatory activation of macrophages.

Gkongensin A, an HSP90β inhibitor, improves hyperlipidemia, hepatic steatosis, and insulin resistance

The prevalence of obesity and its primary associated comorbidities, such as type 2 diabetes and fatty liver disease, has reached epidemic proportions, with no successful treatment available at present. Heat shock protein 90 (HSP90), a crucial chaperone, plays a key role in de novo lipogenesis (DNL) by stabilizing and maintaining sterol regulatory element binding protein (SREBP) activity. Kongensin A (KA), derived from Croton kongensis, inhibits RIP3-mediated necrosis, showing promise as an anti-necrotic and anti-inflammatory agent. It is not yet clear if KA, acting as an HSP90 inhibitor, can enhance hyperlipidemia, hepatic steatosis, and insulin resistance in obese individuals by controlling lipid metabolism. In this study, we first found that KA can potentially decrease lipid content at the cellular level. C57BL/6J mice were given a high-fat diet (HFD) and received KA and lovastatin through oral administration for 7 weeks. KA improved hyperlipidemia, fatty liver, and insulin resistance, as well as reduced body weight in diet-induced obese (DIO) mice, with no significant alteration in food intake. In vitro, KA suppressed DNL and reduced the amounts of mSREBPs. KA promoted mSREBP degradation via the FBW7-mediated ubiquitin-proteasome pathway. KA decreased the level of p-Akt Ser308, and p-GSK3β Ser9 by inhibiting the interaction between HSP90β and Akt. Overall, KA enhanced hyperlipidemia, hepatic steatosis, and insulin resistance by blocking SREBP activity, thereby impacting the FBW7-controlled ubiquitin-proteasome pathway.

Adipose tissue peroxisomal lipid synthesis orchestrates obesity and insulin resistance through LXR-dependent lipogenesis

OBJECTIVE

Adipose tissue mass is maintained by a balance between lipolysis and lipid storage. The contribution of adipose tissue lipogenesis to fat mass, especially in the setting of high-fat feeding, is considered minor. Here we investigated the effect of adipose-specific inactivation of the peroxisomal lipid synthetic protein PexRAP on fatty acid synthase (FASN)-mediated lipogenesis and its impact on adiposity and metabolic homeostasis.

METHODS

To explore the role of PexRAP in adipose tissue, we metabolically phenotyped mice with adipose-specific knockout of PexRAP. Bulk RNA sequencing was used to determine transcriptomic responses to PexRAP deletion and 14C-malonyl CoA allowed us to measure de novo lipogenic activity in adipose tissue of these mice. In vitro cell culture models were used to elucidate the mechanism of cellular responses to PexRAP deletion.

RESULTS

Adipose-specific PexRAP deletion promoted diet-induced obesity and insulin resistance through activation of de novo lipogenesis. Mechanistically, PexRAP inactivation inhibited the flux of carbons to ethanolamine plasmalogens. This increased the nuclear PC/PE ratio and promoted cholesterol mislocalization, resulting in activation of liver X receptor (LXR), a nuclear receptor known to be activated by increased intracellular cholesterol. LXR activation led to increased expression of the phospholipid remodeling enzyme LPCAT3 and induced FASN-mediated lipogenesis, which promoted diet-induced obesity and insulin resistance.

CONCLUSIONS

These studies reveal an unexpected role for peroxisome-derived lipids in regulating LXR-dependent lipogenesis and suggest that activation of lipogenesis, combined with dietary lipid overload, exacerbates obesity and metabolic dysregulation.

Endoplasmic reticulum stress PERK-ATF4-CHOP pathway is involved in non-alcoholic fatty liver disease in type 1 diabetic rats: The rescue effect of treatment exercise and insulin-like growth factor I

Endoplasmic Reticulum Stress (ERS) is a key factor in the development of Non-Alcoholic Fatty Liver Disease (NAFLD) in diabetes. The current study aimed to examine the effects of exercise and IGF-I on ERS markers in liver tissue. Rats were divided into five groups (n = 8 per group), including control (CON), diabetes (DIA), diabetes + exercise (DIA + EX), diabetes + IGF-I (DIA + IGF-I), and diabetes + exercise + IGF-I (DIA + EX + IGF-I). Type 1 diabetes was induced by an I.P. injection of streptozotocin (60 mg/kg). After 30 days of treatment with exercise or IGF-I alone or in combination, liver tissue was assessed for caspase 12, 8, and CHOP protein levels, and expression of ERS markers (ATF-6, PERK, IRE-1A) and lipid metabolism-involved genes (FAS, FXR, SREBP-1c) by western immunoblotting. In addition, for the evaluation of histopathological changes in the liver, Hematoxylin - Eosin and Masson's Trichrome staining were done. Compared to the control group, diabetes significantly caused liver fibrosis, induced ERS, increased caspase 12 and 8 levels in the liver, and changed expression levels of genes associated with lipid metabolism, including FAS, FXR, and SREBP-1c. Treatment with either exercise or IGF-I reduced fibrosis levels suppressed ER stress markers and apoptosis, and improved expression of genes associated with lipid metabolism. In addition, simultaneous treatment with exercise and IGF-I showed a synergistic effect compared to DIA + E and DIA + IGF-I. The results suggest that IGF-1 and exercise reduced liver fibrosis possibly by reducing ERS, creating adaptive ER stress status, and improving protein folding.

Loss of mitogen-activated protein kinase phosphate-5 aggravates islet dysfunction in mice with type 1 and type 2 diabetes

Impaired functionality and loss of islet β-cells are the primary abnormalities underlying the pathogenesis of both type 1 and 2 diabetes (T1DM and T2DM). However, specific therapeutic and preventive mechanisms underlying these conditions remain unclear. Mitogen-activated protein kinase phosphatase-5 (MKP-5) has been implicated in carcinogenesis, lipid metabolism regulation, and immune cell activation. In a previous study, we demonstrated the involvement of exogenous MKP-5 in the regulation of obesity-induced T2DM. However, the role of endogenous MKP-5 in the T1DM and T2DM processes is unclear. Thus, mice with MKP-5 knockout (KO) were generated and used to establish mouse models of both T1DM and T2DM. Our results showed that MKP-5 KO exacerbated diabetes-related symptoms in mice with both T1DM and T2DM. Given that most phenotypic studies on islet dysfunction have focused on mice with T2DM rather than T1DM, we specifically aimed to investigate the role of endoplasmic reticulum stress (ERS) and autophagy in T2DM KO islets. To accomplish this, we performed RNA sequence analysis to gain comprehensive insight into the molecular mechanisms associated with ERS and autophagy in T2DM KO islets. The results showed that the islets from mice with MKP-5 KO triggered 5' adenosine monophosphate-activated protein kinase (AMPK)-mediated autophagy inhibition and glucose-regulated protein 78 (GRP-78)-dominated ERS. Hence, we concluded that the autophagy impairment, resulting in islet dysfunction in mice with MKP-5 KO, is mediated through GRP-78 involvement. These findings provide valuable insights into the molecular pathogenesis of diabetes and highlight the significant role of MKP-5. Moreover, this knowledge holds promise for novel therapeutic strategies targeting MKP-5 for diabetes management.

Integrated traditional Chinese and Western medicine in the prevention and treatment of non-alcoholic fatty liver disease: future directions and strategies

Traditional Chinese medicine (TCM) has been widely used for several centuries for metabolic diseases, including non-alcoholic fatty liver disease (NAFLD). At present, NAFLD has become the most prevalent form of chronic liver disease worldwide and can progress to non-alcoholic steatohepatitis (NASH), cirrhosis, and even hepatocellular carcinoma. However, there is still a lack of effective treatment strategies in Western medicine. The development of NAFLD is driven by multiple mechanisms, including genetic factors, insulin resistance, lipotoxicity, mitochondrial dysfunction, endoplasmic reticulum stress, inflammation, gut microbiota dysbiosis, and adipose tissue dysfunction. Currently, certain drugs, including insulin sensitizers, statins, vitamin E, ursodeoxycholic acid and betaine, are proven to be beneficial for the clinical treatment of NAFLD. Due to its complex pathogenesis, personalized medicine that integrates various mechanisms may provide better benefits to patients with NAFLD. The holistic view and syndrome differentiation of TCM have advantages in treating NAFLD, which are similar to the principles of personalized medicine. In TCM, NAFLD is primarily classified into five types based on clinical experience. It is located in the liver and is closely related to spleen and kidney functions. However, due to the multi-component characteristics of traditional Chinese medicine, its application in the treatment of NAFLD has been considerably limited. In this review, we summarize the advances in the pathogenesis and treatment of NAFLD, drawn from both the Western medicine and TCM perspectives. We highlight that Chinese and Western medicine have complementary advantages and should receive increased attention in the prevention and treatment of NAFLD.

Tri-ortho-cresyl phosphate induces hepatic steatosis by mTOR activation and ER stress induction

Tri-ortho-cresyl phosphate (TOCP), an organophosphorus compound (OP), which is widely used as plasticizer, flame retardant and other industrial products, has been reported to cause multiple toxicities including neurotoxicity and reproductive toxicity. However, it remains to be elusive whether TOCP induces hepatotoxicity. The purpose of this study was to investigate the effect of TOCP on hepatocytes and the lipid metabolism in particular. The adult mice were given a single dose of TOCP (800 mg/kg, p.o.) and the histological changes in liver tissue and lipid content in serum were determined. The results showed that more vacuoles and lipid droplets were observed in the liver of the mice exposed to TOCP. And triglyceride concentrations in serum and liver tissue significantly increased. However, the histopathological changes of the liver and the elevated triglyceride levels in the exposed mice can be reversed by endoplasmic reticulum (ER) stress inhibitor 4-phenylbutyric acid and mTOR signal inhibitor rapamycin. It was also found that the changes of expression levels of the biomarkers of ER stress and mTOR signaling pathway, such as GRP78, CHOP, and p-mTOR, in the exposed mice were consistent with those observed in the cultured primary hepatocytes treated with the same chemicals. These results showed that TOCP activated mTOR signal and ER stress to induce de novo lipid synthesis, which led to the hepatic steatosis in mouse.

The Role of SCAP/SREBP as Central Regulators of Lipid Metabolism in Hepatic Steatosis

The prevalence of metabolic dysfunction-associated steatotic liver disease (MASLD) is rapidly increasing worldwide at an alarming pace, due to an increase in obesity, sedentary and unhealthy lifestyles, and unbalanced dietary habits. MASLD is a unique, multi-factorial condition with several phases of progression including steatosis, steatohepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma. Sterol element binding protein 1c (SREBP1c) is the main transcription factor involved in regulating hepatic de novo lipogenesis. This transcription factor is synthesized as an inactive precursor, and its proteolytic maturation is initiated in the membrane of the endoplasmic reticulum upon stimulation by insulin. SREBP cleavage activating protein (SCAP) is required as a chaperon protein to escort SREBP from the endoplasmic reticulum and to facilitate the proteolytic release of the N-terminal domain of SREBP into the Golgi. SCAP inhibition prevents activation of SREBP and inhibits the expression of genes involved in triglyceride and fatty acid synthesis, resulting in the inhibition of de novo lipogenesis. In line, previous studies have shown that SCAP inhibition can resolve hepatic steatosis in animal models and intensive research is going on to understand the effects of SCAP in the pathogenesis of human disease. This review focuses on the versatile roles of SCAP/SREBP regulation in de novo lipogenesis and the structure and molecular features of SCAP/SREBP in the progression of hepatic steatosis. In addition, recent studies that attempt to target the SCAP/SREBP axis as a therapeutic option to interfere with MASLD are discussed.

SREBPs as the potential target for solving the polypharmacy dilemma

The phenomenon of polypharmacy is a common occurrence among older people with multiple health conditions due to the rapid increase in population aging and the popularization of clinical guidelines. The prevalence of metabolic syndrome is growing quickly, representing a serious threat to both the public and the worldwide healthcare systems. In addition, it enhances the risk of cardiovascular disease as well as mortality and morbidity. Sterol regulatory element binding proteins (SREBPs) are basic helix-loop-helix leucine zipper transcription factors that transcriptionally modulate genes that regulate lipid biosynthesis and uptake, thereby serving an essential role in biological systems regulation. In this article, we have described the structure of SREBPs and explored their activation and regulation of signals. We also reveal that SREBPs are intricately involved in the modulation of metabolic diseases and thus have tremendous potential as the novel target for single-drug therapy for multiple diseases.

Optimization of Phloretin-loaded Nanospanlastics for Targeting of FAS/SREBP1c/AMPK/ OB-Rb Signaling Pathway in HFD-induced Obesity

OBJECTIVES

Obese patients are at increased risk for CVD, which is the main cause of premature death and has been a major cause of disability and ill health in recent years. PTN, a natural dihydrochalcone flavonoid, has a variety of pharmacological characteristics. This article aimed to prepare PTN-NSLs to evaluate their anti-obesity activity.

METHODS

Morphology, Particle size, zeta potential, UV-vis, entrapment efficiency, FT-IR spectra, and an in vitro release study of PTN-NSLs were described. PTN-NSLs were also tested for their anti-obesity properties in obese rats. The LD50 of PTN-NSLs was calculated, as was the 1/20 LD50 prepared for the treatment of obese rats. Also, the level of glycemic, oxidative stress and inflammatory biomarkers were estimated in the obese rat's model.

RESULTS

The synthesized PTN-NSLs were uniform, spherically shaped, and well dispersed with no aggregation noted, with a size range of 114.06 ± 8.35 nm. The measured zeta potential value of PTN-NSLs was -32.50.8 mv. Also, the UV spectra of PTN and PTN-NSLs have strong absorption at 225 and 285 nm. Also, the LD50 of PTN-NSLs was found to be 2750 mg/kg.b.w. Moreover, administrating obese rats with PTN-NSLs resulted in improved glycemic features as well as GSH, SOD, GPx, GR, IL10, TBARs, and IL-6 levels, as well as attenuated FAS, SREBP1c, AMPK, ACO, CPT1, and OB-Rb gene expression.

CONCLUSION

Administration of PTN-NSLs significantly attenuated the levels of glycemic, oxidative stress, and inflammatory biomarkers. The biochemical and PCR findings are aided by histological investigations. Also, the present findings imply that PTN-NSLs might be a promising pharmacological tool for the treatment of obesity-related diseases.

Endoplasmic Reticulum Stress and Obesity

In recent years, the world has seen an alarming increase in obesity and is closely associated with insulin resistance, which is a state of low-grade inflammation, the latter characterized by elevated levels of proinflammatory cytokines in blood and tissues. A shift in energy balance alters systemic metabolic regulation and the important role that chronic inflammation, endoplasmic reticulum (ER) dysfunction, and activation of the unfolded protein response (UPR) plays in this process.Why obesity is so closely associated with insulin resistance and inflammation is not understood well. This suggests that there are probably many causes for obesity-related insulin resistance and inflammation. One of the faulty mechanisms is protein homeostasis, protein quality control system included protein folding, chaperone activity, and ER-associated degradation leading to endoplasmic reticulum (ER) stress.The ER is a vast membranous network responsible for the trafficking of a wide range of proteins and plays a central role in integrating multiple metabolic signals critical in cellular homeostasis. Conditions that may trigger unfolded protein response activation include increased protein synthesis, the presence of mutant or misfolded proteins, inhibition of protein glycosylation, imbalance of ER calcium levels, glucose and energy deprivation, hypoxia, pathogens, or pathogen-associated components and toxins. Thus, characterizing the mechanisms contributing to obesity and identifying potential targets for its prevention and treatment will have a great impact on the control of associated conditions, particularly T2D.

Epigenetic Network in Immunometabolic Disease

Although a large amount of data consistently shows that genes affect immunometabolic characteristics and outcomes, epigenetic mechanisms are also heavily implicated. Epigenetic changes, including DNA methylation, histone modification, and noncoding RNA, determine gene activity by altering the accessibility of chromatin to transcription factors. Various factors influence these alterations, including genetics, lifestyle, and environmental cues. Moreover, acquired epigenetic signals can be transmitted across generations, thus contributing to early disease traits in the offspring. A closer investigation is critical in this aspect as it can help to understand the underlying molecular mechanisms further and gain insights into potential therapeutic targets for preventing and treating diseases arising from immuno-metabolic dysregulation. In this review, the role of chromatin alterations in the transcriptional modulation of genes involved in insulin resistance, systemic inflammation, macrophage polarization, endothelial dysfunction, metabolic cardiomyopathy, and nonalcoholic fatty liver disease (NAFLD), is discussed. An overview of emerging chromatin-modifying drugs and the importance of the individual epigenetic profile for personalized therapeutic approaches in patients with immuno-metabolic disorders is also presented.

Circumventricular organ-hypothalamic circuit endoplasmic reticulum stress drives hepatic steatosis during obesity

OBJECTIVE

Nonalcoholic fatty liver disease (NAFLD), characterized by excess liver triglyceride accumulation (hepatic steatosis), leads to an increased risk for cardiometabolic diseases and obesity-related mortality. Emerging evidence points to endoplasmic reticulum (ER) stress in the central nervous system as critical in NAFLD pathogenesis. Here, we tested the contribution of ER stress in a circumventricular organ-hypothalamic circuit in NAFLD development during obesity.

METHODS

C57BL/6J male mice were fed a high-fat diet (HFD) or normal chow. A combination of histological, viral tracing, intersectional viral targeting, and in vivo integrative physiological approaches were used to examine the role of ER stress in subfornical organ to hypothalamic paraventricular nucleus projecting neurons (SFO➔PVN) in NAFLD during diet-induced obesity.

RESULTS

Immunohistochemical analysis revealed marked unfolded protein response activation in the SFO, particularly in excitatory SFO➔PVN neurons of HFD-fed animals. Moreover, intersectional viral inhibition of ER stress in SFO➔PVN neurons resulted in a reduction in hepatomegaly, hepatic steatosis, and a blunted increase in body weight gain during diet-induced obesity, independent of changes in food intake, substrate partitioning, energy expenditure, and ambulatory activity.

CONCLUSIONS

These results indicate that ER stress in an SFO➔PVN neural circuit contributes to hepatic steatosis during obesity.

Lipid Metabolism Regulators Are the Possible Determinant for Characteristics of Myopic Human Scleral Stroma Fibroblasts (HSSFs)

The purpose of the current investigation was to elucidate what kinds of responsible mechanisms induce elongation of the sclera in myopic eyes. To do this, two-dimensional (2D) cultures of human scleral stromal fibroblasts (HSSFs) obtained from eyes with two different axial length (AL) groups, <26 mm (low AL group, n = 2) and >27 mm (high AL group, n = 3), were subjected to (1) measurements of Seahorse mitochondrial and glycolytic indices to evaluate biological aspects and (2) analysis by RNA sequencing. Extracellular flux analysis revealed that metabolic indices related to mitochondrial and glycolytic functions were higher in the low AL group than in the high AL group, suggesting that metabolic activities of HSSF cells are different depending the degree of AL. Based upon RNA sequencing of these low and high AL groups, the bioinformatic analyses using gene ontology (GO) enrichment analysis and ingenuity pathway analysis (IPA) of differentially expressed genes (DEGs) identified that sterol regulatory element-binding transcription factor 2 (SREBF2) is both a possible upstream regulator and a causal network regulator. Furthermore, SREBF1, insulin-induced gene 1 (INSIG1), and insulin-like growth factor 1 (IGF1) were detected as upstream regulators, and protein tyrosine phosphatase receptor type O (PTPRO) was detected as a causal network regulator. Since those possible regulators were all pivotally involved in lipid metabolisms including fatty acid (FA), triglyceride (TG) and cholesterol (Chol) biosynthesis, the findings reported here indicate that FA, TG and Chol biosynthesis regulation may be responsible mechanisms inducing AL elongation via HSSF.

SREBP Regulation of Lipid Metabolism in Liver Disease, and Therapeutic Strategies

Sterol regulatory element-binding proteins (SREBPs) are master transcription factors that play a crucial role in regulating genes involved in the biogenesis of cholesterol, fatty acids, and triglycerides. As such, they are implicated in several serious liver diseases, including non-alcoholic fatty liver disease (NAFLD), non-alcoholic steatohepatitis (NASH), fibrosis, and hepatocellular carcinoma (HCC). SREBPs are subject to regulation by multiple cofactors and critical signaling pathways, making them an important target for therapeutic interventions. In this review, we first introduce the structure and activation of SREBPs, before focusing on their function in liver disease. We examine the mechanisms by which SREBPs regulate lipogenesis, explore how alterations in these processes are associated with liver disease, and evaluate potential therapeutic strategies using small molecules, natural products, or herb extracts that target these pathways. Through this analysis, we provide new insights into the versatility and multitargets of SREBPs as factors in the modulation of different physiological stages of liver disease, highlighting their potential targets for therapeutic treatment.

High-fat diet alters intestinal microbiota and induces endoplasmic reticulum stress via the activation of apoptosis and inflammation in blunt snout bream

The primary organ for absorbing dietary fat is the gut. High dietary lipid intake negatively affects health and absorption by causing fat deposition in the intestine. This research explores the effect of a high-fat diet (HFD) on intestinal microbiota and its connections with endoplasmic reticulum stress and inflammation. 60 fish (average weight: 45.84 ± 0.07 g) were randomly fed a control diet (6% fat) and a high-fat diet (12 % fat) in four replicates for 12 weeks. From the result, hepatosomatic index (HSI), Visceralsomatic index (VSI), abdominal fat (ADF), Intestosomatic index (ISI), mesenteric fat (MFI), Triglycerides (TG), total cholesterol (TC), non-esterified fatty acid (NEFA) content were substantially greater on HFD compared to the control diet. Moreover, fish provided the HFD significantly obtained lower superoxide dismutase (SOD) and glutathione peroxidase (GPX) activities. In contrast, an opposite result was seen in malondialdehyde (MDA) content in comparison to the control. HFD significantly altered intestinal microbiota in blunt snout bream, characterized by an increased abundance of Aeromonas, Plesiomonas proteobacteria, and firmicutes with a reduced abundance of Cetobacterium and ZOR0006. The transcriptional levels of glucose-regulated protein 78 (grp78), inositol requiring enzyme 1 (ire1), spliced X box-binding protein 1 (xbp1), DnaJ heat shock protein family (Hsp40) member B9 (dnajb9), tumor necrosis factor alpha (tnf-α), nuclear factor-kappa B (nf-κb), monocyte chemoattractant protein-1 (mcp-1), and interleukin-6 (il-6) in the intestine were markedly upregulated in fish fed HFD than the control group. Also, the outcome was similar in bax, caspases-3, and caspases-9, ZO-1, Occludin-1, and Occludin-2 expressions. In conclusion, HFD could alter microbiota and facilitate chronic inflammatory signals via activating endoplasmic reticulum stress.

In-depth analysis of de novo lipogenesis in non-alcoholic fatty liver disease: Mechanism and pharmacological interventions

Non-alcoholic fatty liver disease (NAFLD) is characterized by the abnormal buildup of lipids in the liver tissue. Non-alcoholic fatty liver (NAFL) may progress to non-alcoholic steatohepatitis. Triglycerides in the liver can originate from various sources, including de novo lipogenesis (DNL). Research indicates that DNL significantly escalates in NAFLD, worsening steatosis. However, the precise regulatory mechanism of DNL in the development of this disease is not fully understood. Therefore, the targeted reduction of DNL could be a crucial therapeutic strategy. Currently, numerous pharmaceutical agents targeting DNL have been developed, attracting significant attention. This review examines the mechanism of DNL upregulation in NAFLD, assessing its potential as a therapeutic target for hepatic steatosis. Furthermore, we thoroughly examine hepatocellular lipotoxicity and provide an extensive review of the application and limitations of relevant therapeutic drugs, with a focus on key enzymes involved in DNL. The implementation of these pharmacological strategies is expected to significantly improve the management and overall outcomes for patients with NAFLD.

Exploring the role of SWI/SNF complex subunit BAF60c in lipid metabolism and inflammation in fish

Chromatin remodeling plays an important role in regulating gene transcription, in which chromatin remodeling complex is a crucial aspect. Brg1/Brm-associated factor 60c (BAF60c) subunit forms a bridge between chromatin remodeling complexes and transcription factors in mammals; hence, it has received extensive attention. However, the roles of BAF60c in fish remain largely unexplored. In this study, we identified BAF60c-interacting proteins by using HIS-pull-down and LC-MS/MS analysis in fish. Subsequently, the RNA-seq analysis was performed to identify the overall effects of BAF60c. Then, the function of BAF60c was verified through BAF60c knockdown and overexpression experiments. We demonstrated for the first time that BAF60c interacts with glucose-regulated protein 78 (GRP78) and regulates lipid metabolism, endoplasmic reticulum (ER) stress, and inflammation. Knockdown of BAF60c reduces fatty acid biosynthesis, ER stress, and inflammation. In conclusion, the results enriched BAF60c-interacting protein network and explored the function of BAF60c in lipid metabolism and inflammation in fish.

Endoplasmic reticulum stress in the pathogenesis of alcoholic liver disease

The endoplasmic reticulum (ER) plays a pivotal role in protein synthesis, folding, and modification. Under stress conditions such as oxidative stress and inflammation, the ER can become overwhelmed, leading to an accumulation of misfolded proteins and ensuing ER stress. This triggers the unfolded protein response (UPR) designed to restore ER homeostasis. Alcoholic liver disease (ALD), a spectrum disorder resulting from chronic alcohol consumption, encompasses conditions from fatty liver and alcoholic hepatitis to cirrhosis. Metabolites of alcohol can incite oxidative stress and inflammation in hepatic cells, instigating ER stress. Prolonged alcohol exposure further disrupts protein homeostasis, exacerbating ER stress which can lead to irreversible hepatocellular damage and ALD progression. Elucidating the contribution of ER stress to ALD pathogenesis may pave the way for innovative therapeutic interventions. This review delves into ER stress, its basic signaling pathways, and its role in the alcoholic liver injury.

The role of heat shock proteins (HSPs) in type 2 diabetes mellitus pathophysiology

Type 2 diabetes mellitus (T2DM) is a metabolic disorder characterized by sustained hyperglycemia caused by impaired insulin signaling and secretion. Metabolic stress, caused by an inappropriate diet, is one of the major hallmarks provoking inflammation, endoplasmic reticulum (ER) stress, and mitochondrial dysfunction. Heat shock proteins (HSPs) are a group of highly conserved proteins that have a crucial role in chaperoning damaged and misfolded proteins to avoid disruption of cellular homeostasis under stress conditions. To do this, HSPs interact with diverse intra-and extracellular pathways among which are the insulin signaling, insulin secretion, and apoptosis pathways. Therefore, HSP dysfunction, e.g. HSP70, may lead to disruption of the pathways responsible for insulin secretion and uptake. Consistently, the altered expression of other HSPs and genetic polymorphisms in HSP-producing genes in diabetic subjects has made HSPs hot research in T2DM. This paper provides a comprehensive overview of the role of different HSPs in T2DM pathogenesis, affected cellular pathways, and the potential therapeutic strategies targeting HSPs in T2DM.

The Lipid Metabolism as Target and Modulator of BOLD-100 Anticancer Activity: Crosstalk with Histone Acetylation

The leading first-in-class ruthenium-complex BOLD-100 currently undergoes clinical phase-II anticancer evaluation. Recently, BOLD-100 is identified as anti-Warburg compound. The present study shows that also deregulated lipid metabolism parameters characterize acquired BOLD-100-resistant colon and pancreatic carcinoma cells. Acute BOLD-100 treatment reduces lipid droplet contents of BOLD-100-sensitive but not -resistant cells. Despite enhanced glycolysis fueling lipid accumulation, BOLD-100-resistant cells reveal diminished lactate secretion based on monocarboxylate transporter 1 (MCT1) loss mediated by a frame-shift mutation in the MCT1 chaperone basigin. Glycolysis and lipid catabolism converge in the production of protein/histone acetylation substrate acetyl-coenzymeA (CoA). Mass spectrometric and nuclear magnetic resonance analyses uncover spontaneous cell-free BOLD-100-CoA adduct formation suggesting acetyl-CoA depletion as mechanism bridging BOLD-100-induced lipid metabolism alterations and histone acetylation-mediated gene expression deregulation. Indeed, BOLD-100 treatment decreases histone acetylation selectively in sensitive cells. Pharmacological targeting confirms histone de-acetylation as central mode-of-action of BOLD-100 and metabolic programs stabilizing histone acetylation as relevant Achilles' heel of acquired BOLD-100-resistant cell and xenograft models. Accordingly, histone gene expression changes also predict intrinsic BOLD-100 responsiveness. Summarizing, BOLD-100 is identified as epigenetically active substance acting via targeting several onco-metabolic pathways. Identification of the lipid metabolism as driver of acquired BOLD-100 resistance opens novel strategies to tackle therapy failure.

Human skin stem cell-derived hepatic cells as in vitro drug discovery model for insulin-driven de novo lipogenesis

Metabolic dysfunction-associated steatotic liver disease (MASLD), formerly known as non-alcoholic fatty liver disease (NAFLD), is characterized by intrahepatic triglyceride accumulation and can progress to metabolic dysfunction-associated steatohepatitis (MASH) and liver fibrosis. Hepatic de novo lipogenesis (DNL), activated by glucose and insulin, is a central pathway contributing to early-stage development of MASLD. The emerging global prevalence of MASLD highlights the urgent need for pharmaceutical intervention to combat this health threat. However, the identification of novel drugs that could inhibit hepatic DNL is hampered by a lack of reliable, insulin-sensitive, human, in vitro, hepatic models. Here, we report human skin stem cell-derived hepatic cells (hSKP-HPC) as a unique in vitro model to study insulin-driven DNL (iDNL), evidenced by both gene expression and lipid accumulation readouts. Insulin-sensitive hSKP-HPC showed increased sterol regulatory element-binding protein 1c (SREBP-1c) expression, a key transcription factor for DNL. Furthermore, this physiologically relevant in vitro human steatosis model allowed both inhibition and activation of the iDNL pathway using reference inhibitors and activators, respectively. Optimisation of the lipid accumulation assay to a high-throughput, 384-well format enabled the screening of a library of annotated compounds, delivering new insights on key players in the iDNL pathway and MASLD pathophysiology. Together, these results establish the value of the hSKP-HPC model in preclinical development of antisteatotic drugs to combat MASLD.

The effect of heat-killed Lactobacillus brevis SBL88 on improving selective hepatic insulin resistance in non-alcoholic fatty liver disease mice without altering the gut microbiota

BACKGROUND AND AIM

There have been several reports that some probiotics improve non-alcoholic fatty liver disease (NAFLD); however, many studies have involved cocktail therapies. We evaluated whether heat-killed Lactobacillus brevis SBL88 (L. brevis SBL88) monotherapy improves the clinical features of NAFLD.

METHODS

The NAFLD model was induced in mice fed a high-fat diet (HFD) (HFD mice) or HFD + 1% heat-killed L. brevis SBL88 (SBL mice) for 16 weeks. Histopathological liver findings were analyzed. To evaluate the gut microbiota, a modified terminal restriction fragment length polymorphism analysis of the feces was performed. RNA sequencing in the liver was performed with Ion Proton™. To investigate the direct effects of heat-killed L. brevis SBL88, an in vitro study was performed.

RESULTS

Histopathological findings revealed that fat droplets in the liver were significantly reduced in SBL mice; however, terminal restriction fragment length polymorphism did not show alterations in the gut microbiota between HFD mice and SBL mice. RNA sequencing and pathway analysis revealed that the regulation of lipid and insulin metabolism was affected. The mRNA expression of insulin receptor substrate 2 (IRS-2) was significantly higher in SBL mice, whereas the expression of IRS-1 was not significantly different. Phospho-IRS-2 expression was also significantly increased in SBL mice. In addition, an in vitro study revealed significant alterations in IRS-2 and forkhead box protein O1 expression levels.

CONCLUSION

SBL mice exhibited partially improved selective hepatic insulin resistance. Our data suggest that heat-killed L. brevis SBL88 could attenuate the clinical features of NAFLD that are not mediated by alterations in the gut microbiota.

Unfolded Protein Response Signaling in Liver Disorders: A 2023 Updated Review

Endoplasmic reticulum (ER) is the site for synthesis and folding of secreted and transmembrane proteins. Disturbance in the functioning of ER leads to the accumulation of unfolded and misfolded proteins, which finally activate the unfolded protein response (UPR) signaling. The three branches of UPR-IRE1 (Inositol requiring enzyme 1), PERK (Protein kinase RNA-activated (PKR)-like ER kinase), and ATF6 (Activating transcription factor 6)-modulate the gene expression pattern through increased expression of chaperones and restore ER homeostasis by enhancing ER protein folding capacity. The liver is a central organ which performs a variety of functions which help in maintaining the overall well-being of our body. The liver plays many roles in cellular physiology, blood homeostasis, and detoxification, and is the main site at which protein synthesis occurs. Disturbance in ER homeostasis is triggered by calcium level imbalance, change in redox status, viral infection, and so on. ER dysfunction and subsequent UPR signaling participate in various hepatic disorders like metabolic (dysfunction) associated fatty liver disease, liver cancer, viral hepatitis, and cholestasis. The exact role of ER stress and UPR signaling in various liver diseases is not fully understood and needs further investigation. Targeting UPR signaling with drugs is the subject of intensive research for therapeutic use in liver diseases. The present review summarizes the role of UPR signaling in liver disorders and describes why UPR regulators are promising therapeutic targets.

Tauroursodeoxycholic Acid Supplementation in In Vitro Culture of Indicine Bovine Embryos: Molecular and Cellular Effects on the In Vitro Cryotolerance

During embryo development, the endoplasmic reticulum (ER) acts as an important site for protein biosynthesis; however, in vitro culture (IVC) can negatively affect ER homeostasis. Therefore, the aim of our study was to evaluate the effects of the supplementation of tauroursodeoxycholic acid (TUDCA), an ER stress inhibitor, in the IVC of bovine embryos. Two experiments were carried out: Exp. 1: an evaluation of blastocyst rate, hatching kinetics, and gene expression of hatched embryos after being treated with different concentrations of TUDCA (50, 200, or 1000 μM) in the IVC; Exp. 2: an evaluation of the re-expansion, hatching, and gene expression of hatched embryos previously treated with 200 µM of TUDCA at IVC and submitted to vitrification. There was no increase in the blastocyst and hatched blastocyst rates treated with TUDCA in the IVC. However, embryos submitted to vitrification after treatment with 200 µM of TUDCA underwent an increased hatching rate post-warming together with a down-regulation in the expression of ER stress-related genes and the accumulation of lipids. In conclusion, this work showed that the addition of TUDCA during in vitro culture can improve the cryotolerance of the bovine blastocyst through the putative modulation of ER and oxidative stress.

Association Between Sensitivity to Thyroid Hormones and Metabolic Dysfunction-Associated Fatty Liver Disease in Euthyroid Subjects: A Cross-Sectional Study

Objective

Thyroid hormones (THs) exert instrumental effects in regulating lipids metabolism. Whereas, research investigating the relationship between sensitivity indices to THs and metabolic dysfunction-associated fatty liver disease (MAFLD) have contradicted this. This study was designed to approach the correlation between sensitivity indices to THs and MAFLD in euthyroid subjects.

Methods

An overall sample of 6356 euthyroid participants were enrolled in a Chinese hospital. Free triiodothyronine to free thyroxine ratio (FT3/FT4), thyrotropin triiodothyronine resistance index (TT3RI), thyrotropin thyroxine resistance index (TT4RI), thyroid stimulating hormone index (TSHI) and thyroid feedback quantile-based indices (TFQIFT3 and TFQIFT4) were collected as sensitivity indicators to THs. Participants were split into two groups based on whether they suffered with MAFLD or not. And participants were categorized into quartiles based on sensitivity indicators to THs. The effects of sensitivity indices to THs on MAFLD were analyzed using regression analysis. Bootstrap was performed to assess the mediation effect of triglyceride glucose (TyG) index on the relationship between sensitivity parameters to THs and MAFLD.

Results

The incidence of MAFLD in euthyroid subjects was 34.47%. As FT3/FT4, TT3RI and TFQIFT3 levels rose, so did the MAFLD prevalence. After adjustment for confounders, logistic regression analyses indicated that the high-level FT3/FT4 and TFQIFT3 still remained risk factors for MAFLD. The relevance of FT3/FT4 and MAFLD was stronger among those whose age ≤ 40 years and had non-visceral obesity. And the interrelation between TFQIFT3 and MAFLD was stronger in subjects whose age ≤ 40 years. Mediation analyses suggested that TyG index had a noteworthy indirect impact on the relationship between FT3/FT4, TFQIFT3 and MAFLD.

Conclusion

Increased FT3/FT4 and TFQIFT3 were significantly related to MAFLD prevalence in populations with normal thyroid function. TyG index partly mediated the relevance between FT3/FT4, TFQIFT3 and MAFLD.

Non-Alcoholic Fatty Liver Disease: Translating Disease Mechanisms into Therapeutics Using Animal Models

Nonalcoholic fatty liver disease (NAFLD) is a range of pathologies arising from fat accumulation in the liver in the absence of excess alcohol use or other causes of liver disease. Its complications include cirrhosis and liver failure, hepatocellular carcinoma, and eventual death. NAFLD is the most common cause of liver disease globally and is estimated to affect nearly one-third of individuals in the United States. Despite knowledge that the incidence and prevalence of NAFLD are increasing, the pathophysiology of the disease and its progression to cirrhosis remain insufficiently understood. The molecular pathogenesis of NAFLD involves insulin resistance, inflammation, oxidative stress, and endoplasmic reticulum stress. Better insight into these molecular pathways would allow for therapies that target specific stages of NAFLD. Preclinical animal models have aided in defining these mechanisms and have served as platforms for screening and testing of potential therapeutic approaches. In this review, we will discuss the cellular and molecular mechanisms thought to contribute to NAFLD, with a focus on the role of animal models in elucidating these mechanisms and in developing therapies.

Erigeron annuus Extract Alleviates Insulin Resistance via Regulating the Expression of Mitochondrial Damage and Endoplasmic Reticulum Stress-Related Genes

Diabetes is a prevalent and debilitating metabolic disorder affecting a large population worldwide. The condition is characterized by insulin resistance and impaired function of pancreatic β-cells, leading to elevated blood glucose levels. In this study, the antidiabetic effects of Erigeron annuus extract (EAE) on zebrafish with damaged pancreatic islets caused by insulin resistance were investigated. The study utilized the zebrafish model to monitor live pancreatic islets. RNA sequencing was also conducted to determine the mechanism by which EAE exerts its antidiabetic effect. The results showed that EAE was effective in recovering reduced islets in excess insulin-induced zebrafish. The effective concentration at 50% (EC₅₀) of EAE was determined to be 0.54 μg/mL, while the lethal concentration at 50% (LC₅₀) was calculated as 202.5 μg/mL. RNA sequencing indicated that the mode of action of EAE is related to its ability to induce mitochondrial damage and suppress endoplasmic reticulum stress. The findings of this study demonstrate the efficacy and therapeutic potential of EAE in treating insulin resistance in zebrafish. The results suggest that EAE may offer a promising approach for the management of diabetes by reducing mitochondrial damage and suppressing endoplasmic reticulum stress. Further research is required to establish the clinical application of EAE in diabetic patients.