CCAAT/enhancing binding protein beta deletion in mice attenuates inflammation, endoplasmic reticulum stress, and lipid accumulation in diet-induced nonalcoholic steatohepatitis

EMC10 modulates hepatic ER stress and steatosis in an isoform specific manner

BACKGROUND & AIMS

Endoplasmic reticulum (ER) membrane protein complex subunit 10 (EMC10) has been implicated in obesity. Here we investigated the roles of the two isoforms of EMC10, including a secreted isoform (scEMC10) and an ER membrane-bound isoform (mEMC10), in MASLD.

METHODS

Manifold steatotic mouse models and HepG2 cells were employed to investigate the role of EMC10 in the regulation of hepatic PERK-eIF2α-ATF4 signaling and hepatosteatosis. The therapeutic effect of scEMC10-neutralizing antibody on mouse hepatosteatosis was explored. Associations of MASLD with serum scEMC10 and hepatic mEMC10 were determined in two cohorts of participants with MASLD.

RESULTS

scEMC10 promoted, while mEMC10 suppressed the activation of hepatocytic PERK-eIF2α-ATF4 signaling. Emc10 gene knockout exacerbated, while hepatic overexpression of mEMC10 ameliorated hepatic ER stress and steatosis in mice challenged with either a MCD diet or tunicamycin, highlighting a direct, suppressive role of mEMC10 in MASLD via modulation of hepatic ER stress. Overexpression of scEMC10 promoted, whereas neutralization of circulating scEMC10 prevented hepatosteatosis in mice with fatty liver, suggesting a progressive role of scEMC10 in MASLD. Clinically, serum scEMC10 increased, while hepatic mEMC10 decreased in participants with MASLD. Correlative analysis indicated serum scEMC10 positively, whereas hepatic mEMC10 negatively correlated with liver fat content and serum ALT, AST, and GGT.

CONCLUSIONS

These findings demonstrate a novel, isoform specific role for EMC10 in the pathogenesis of MASLD and identify the secreted isoform as a tractable therapeutic target for MASLD via antibody-based neutralization.

IMPACT AND IMPLICATIONS

We have shown the role of EMC10 in the regulation of energy homeostasis and obesity. In this study, we determine the distinct roles of the two isoforms of EMC10 in the regulation of hepatic ER stress and steatosis in mice, and associations of MASLD with different EMC10 isoforms in humans. Our findings delineate a novel regulatory axis for hepatosteatosis and identify EMC10 as a modulator of the PERK-eIF2α-ATF4 signaling cascade that may be of broad physiological significance. Moreover, our pre-clinical and clinical studies clearly provide the foundations for translation of scEMC10 modulation for the treatment of MASLD.

C/EBPβ: The structure, regulation, and its roles in inflammation-related diseases

Inflammation, a mechanism of the human body, has been implicated in many diseases. Inflammatory responses include the release of inflammatory mediators by activating various signaling pathways. CCAAT/enhancer binding protein β (C/EBPβ), a transcription factor in the C/EBP family, contains the leucine zipper (bZIP) domain. The expression of C/EBPβ is mediated at the transcriptional and post-translational levels, such as phosphorylation, acetylation, methylation, and SUMOylation. C/EBPβ has been involved in inflammatory responses by mediating several signaling pathways, such as MAPK/NF-κB and IL-6/JAK/STAT3 pathways. C/EBPβ plays an important role in the pathological development of inflammation-related diseases, such as osteoarthritis, pneumonia, hepatitis, inflammatory bowel diseases, and rheumatoid arthritis. Here, we comprehensively discuss the structure and biological effects of C/EBPβ and its role in inflammatory diseases.

Effects of oleoylethanolamide supplementation on the expression of lipid metabolism-related genes and serum NRG4 levels in patients with non-alcoholic fatty liver disease: A randomized controlled trial

BACKGROUND

This study investigated the effects of oleoylethanolamide (OEA) supplementation on the expression levels of SIRT1, AMPK, PGC-1α, PPAR-γ, CEBP-α and CEBP-β genes and serum neuregulin 4 (NRG4) levels in patients with non-alcoholic fatty liver diseases (NAFLD).

METHODS

Sixty obese patients with NAFLD were equally allocated into either OEA or placebo group for 12 weeks. The mRNA expression levels of genes were determined using the reverse transcription polymerase chain reaction (RT-PCR) technique. Serum NRG4 level was also assessed using an enzyme-linked immunosorbent assay (ELISA) kit.

RESULTS

At the endpoint, mRNA expression levels of SIRT1(p = 0.001), PGC-1α (p = 0.011) and AMPK (p = 0.019) were significantly higher in the OEA group compared to placebo group. However, no significant differences were observed in the expression levels of PPAR-γ, CEBP-α and CEBP-β between the two groups. Serum NRG4 levels significantly increased in the OEA group compared with the placebo group after controlling for confounders (p = 0.027). In the OEA group, significant relationships were found between percent of changes in the expression levels of the SIRT1, AMPK and PGC-1α as well as serum NRG4 level with percent of changes in some anthropometric measures. Moreover, in the intervention group, percent of changes in high-density lipoprotein cholesterol was positively correlated with percent of changes in the expression levels of the SIRT1 and AMPK. While, percent of changes in triglyceride was inversely correlated with percent of changes in the expression levels of SIRT1.

CONCLUSION

OEA could beneficially affect expression levels of some lipid metabolism-related genes and serum NRG4 level. "REGISTERED UNDER IRANIAN REGISTRY OF CLINICAL TRIALS IDENTIFIER NO: IRCT20090609002017N32".

UPR-Induced miR-616 Inhibits Human Breast Cancer Cell Growth and Migration by Targeting c-MYC

C/EBP homologous protein (CHOP), also known as growth arrest and DNA damage-inducible protein 153 (GADD153), belongs to the CCAAT/enhancer-binding protein (C/EBP) family. CHOP expression is induced by unfolded protein response (UPR), and sustained CHOP activation acts as a pivotal trigger for ER stress-induced apoptosis. MicroRNA-616 is located within an intron of the CHOP gene. However, the regulation of miR-616 expression during UPR and its function in breast cancer is not clearly understood. Here we show that the expression of miR-616 and CHOP (host gene of miR-616) is downregulated in human breast cancer. Both miR-5p/-3p arms of miR-616 are expressed with levels of the 5p arm higher than the 3p arm. During conditions of ER stress, the expression of miR-616-5p and miR-616-3p arms was concordantly increased primarily through the PERK pathway. Our results show that ectopic expression of miR-616 significantly suppressed cell proliferation and colony formation, whereas knockout of miR-616 increased it. We found that miR-616 represses c-MYC expression via binding sites located in its protein coding region. Furthermore, we show that miR-616 exerted growth inhibitory effects on cells by suppressing c-MYC expression. Our results establish a new role for the CHOP locus by providing evidence that miR-616 can inhibit cell proliferation by targeting c-MYC. In summary, our results suggest a dual function for the CHOP locus, where CHOP protein and miR-616 can cooperate to inhibit cancer progression.

Endoplasmic reticulum stress-mediated cell death in liver injury

The endoplasmic reticulum is an important intracellular organelle that plays an important role in maintaining cellular homeostasis. Endoplasmic reticulum stress (ERS) and unfolded protein response (UPR) are induced when the body is exposed to adverse external stimuli. It has been established that ERS can induce different cell death modes, including autophagy, apoptosis, ferroptosis, and pyroptosis, through three major transmembrane receptors on the ER membrane, including inositol requirement enzyme 1α, protein kinase-like endoplasmic reticulum kinase and activating transcription factor 6. These different modes of cell death play an important role in the occurrence and development of various diseases, such as neurodegenerative diseases, inflammation, metabolic diseases, and liver injury. As the largest metabolic organ, the liver is rich in enzymes, carries out different functions such as metabolism and secretion, and is the body's main site of protein synthesis. Accordingly, a well-developed endoplasmic reticulum system is present in hepatocytes to help the liver perform its physiological functions. Current evidence suggests that ERS is closely related to different stages of liver injury, and the death of hepatocytes caused by ERS may be key in liver injury. In addition, an increasing body of evidence suggests that modulating ERS has great potential for treating the liver injury. This article provided a comprehensive overview of the relationship between ERS and four types of cell death. Moreover, we discussed the mechanism of ERS and UPR in different liver injuries and their potential therapeutic strategies.

Immune cell C/EBPβ deficiency is associated with hepatic mononuclear defects and spontaneous hepatitis but not steatohepatitis induced liver fibrosis

BACKGROUND

CCAAT/enhancer-binding protein β (C/EBPβ) is a transcription factor known to be involved in macrophage differentiation and function, steatohepatitis and liver fibrosis.

METHODS

Immune restricted C/EBPβ deficient and control mice were investigated in steady-state and in the CDA-HFD steatohepatitis model. Mice were assessed for weight change, liver biochemical profile, histology and hepatic phagocytes composition.

RESULTS

Flow cytometry analysis of hepatic nonparenchymal cells revealed reduced numbers of hepatic monocytes and Kupffer cells and an increase in hepatic MHC class II positive myeloid cells in immune cells restricted C/EBPβ deficient mice. Immune-restricted C/EBPβ deficiency resulted in decreased weight gain and appearance of mild spontaneous liver inflammation. Nevertheless, In the CDA-HFD steatohepatitis model, immune restricted C/EBPβ deficient and proficient mice exhibit similar grade of hepatic steatosis, liver enzymes levels and fibrosis stage.

CONCLUSIONS

Immune-restricted C/EBPβ deficiency leads to significant alteration in hepatic mononuclear phagocytes composition associated with spontaneous mild hepatitis. Steatohepatitis associated fibrosis is not dependent on C/EBPβ expression by immune cells.

Dehydrocostus lactone ameliorates lipid accumulation, insulin resistance, and endoplasmic reticulum stress in palmitate-treated hepatocytes

Fatty liver disease is caused by lipid accumulation in the liver, insulin resistance (IR), reactive oxygen species (ROS), and endoplasmic reticulum (ER) stress. Dehydrocostus lactone (DHE) has anticancer, anti-inflammatory, and anti-ulcer effects. However, its effects on hepatic steatosis and IR remain unclear. In this study, we investigated whether DHE has antisteatotic effect on fatty liver in vitro. Hepatocytes HepG2 and SNU-449 cells were exposed to 0.25 mM palmitate (PA), and then antisteatotic effect was evaluated by treatment with 10 μM DHE. DHE treatment reduced lipid accumulation and lipogenesis factor protein levels, compared with PA-treated hepatocytes. DHE treatment also decreased gluconeogenesis marker expression and recovered IR in PA-treated hepatocytes, and promoted glucose uptake in PA-treated HepG2 cells. Additionally, the levels of ROS and ER stress factors in PA-treated HepG2 cells were reduced by DHE treatment, compared with PA-treated HepG2 cells. Overall, DHE decreased lipid accumulation and lipogenesis factors as well as recovered IR, gluconeogenesis, and glucose uptake by reducing ER stress and ROS levels in PA-treated hepatocytes. Thus, DHE is a potential antisteatotic agent.

A type IV Autotaxin inhibitor ameliorates acute liver injury and nonalcoholic steatohepatitis

The lysophosphatidic acid (LPA) signaling axis is an important but rather underexplored pathway in liver disease. LPA is predominantly produced by Autotaxin (ATX) that has gained significant attention with an impressive number of ATX inhibitors (type I-IV) reported. Here, we evaluated the therapeutic potential of a (yet unexplored) type IV inhibitor, Cpd17, in liver injury. We first confirmed the involvement of the ATX-LPA signaling axis in human and murine diseased livers. Then, we evaluated the effects of Cpd17, in comparison with the classic type I inhibitor PF8380, in vitro, where Cpd17 showed higher efficacy. Thereafter, we characterized the mechanism-of-action of both inhibitors and found that Cpd17 was more potent in inhibiting RhoA-mediated cytoskeletal remodeling, and phosphorylation of MAPK/ERK and AKT/PKB. Finally, the therapeutic potential of Cpd17 was investigated in CCl₄ -induced acute liver injury and diet-induced nonalcoholic steatohepatitis, demonstrating an excellent potential of Cpd17 in reducing liver injury in both disease models in vivo. We conclude that ATX inhibition, by type IV inhibitor in particular, has an excellent potential for clinical application in liver diseases.

C/EBPβ/AEP signaling couples atherosclerosis to the pathogenesis of Alzheimer's disease

Atherosclerosis (ATH) and Alzheimer's disease (AD) are both age-dependent inflammatory diseases, associated with infiltrated macrophages and vascular pathology and overlapping molecules. C/EBPβ, an Aβ or inflammatory cytokine-activated transcription factor, and AEP (asparagine endopeptidase) are intimately implicated in both ATH and AD; however, whether C/EBPβ/AEP signaling couples ATH to AD pathogenesis remains incompletely understood. Here we show that C/EBPβ/AEP pathway mediates ATH pathology and couples ATH to AD. Deletion of C/EBPβ or AEP from primary macrophages diminishes cholesterol load, and inactivation of this pathway reduces foam cell formation and lesions in aorta in ApoE-/- mice, fed with HFD (high-fat-diet). Knockout of ApoE from 3xTg AD mouse model augments serum LDL and increases lesion areas in the aorta. Depletion of C/EBPβ or AEP from 3xTg/ApoE-/- mice substantially attenuates these effects and elevates cerebral blood flow and vessel length, improving cognitive functions. Strikingly, knockdown of ApoE from the hippocampus of 3xTg mice decreases the cerebral blood flow and vessel length and aggravates AD pathologies, leading to cognitive deficits. Inactivation of C/EBPβ/AEP pathway alleviates these events and restores cognitive functions. Hence, our findings demonstrate that C/EBPβ/AEP signaling couples ATH to AD via mediating vascular pathology.

Exogenous administration of unacylated ghrelin attenuates hepatic steatosis in high-fat diet-fed rats by modulating glucose homeostasis, lipogenesis, oxidative stress, and endoplasmic reticulum stress

Low levels of unacylated ghrelin (UAG) and a higher ratio of acylated ghrelin (AG)/UAG in obesity are associated with non-alcoholic fatty liver disease (NAFLD). This study tested the potential protective effect of increased circulatory levels of UAG by exogenous UAG administration on hepatic steatosis in high-fat diet (HFD)-fed rats and investigated some possible mechanisms. Rats were divided (n = 6/group) as low fat diet (LFD), LFD + UAG (200 mg/kg), HFD, HFD + UAG (50, 100, or 200 mg/kg). Treatments were given for 8 weeks. Increasing the dose of UAG increased circulatory levels of UAG and normalized the ratio of AG/UAG at the dose of 200 mg/kg. With no change in insulin levels, and in a dose-dependent manner, treatment with UAG to HFD rats attenuated the gain in food intake, body weights, and liver weights, lowered fasting glucose levels, prevented hepatic cytoplasmic vacuolization, and reduced serum and hepatic levels of cholesterol, triglycerides, and free fatty acids. They also progressively reduced levels of reactive oxygen species, lipid peroxides, tumor necrosis factor-α, and interleukin-6, as well as mRNA levels of Bax and caspase-3 but increased levels of glutathione and superoxide dismutase and mRNA levels of Bcl2. In concomitant, UAG, in a dose-response manner, significantly reduced hepatic mRNA levels of SREBP1, SREBP2, ATF-6, IRE-1, and eIF-2α but increased those of PPARα. In conclusion, reducing the circulatory ratio of AG/UAG ratio by exogenous administration of UAG attenuates HFD-induced hepatic steatosis by suppressing lipogenesis, stimulating FAs oxidation, preventing oxidative stress, inflammation, ER stress, and apoptosis.

CHOP-ASO Ameliorates Glomerular and Tubular Damage on Top of ACE Inhibition in Diabetic Kidney Disease

BACKGROUND

Maladaptive endoplasmic reticulum stress signaling in diabetic kidney disease (DKD) is linked to increased glomerular and tubular expression of the cell-death-promoting transcription factor C/EBP homologous protein (CHOP). Here, we determined whether locked nucleic acid (LNA)-modified antisense oligonucleotides (ASOs) targeting CHOP ameliorate experimental DKD.

METHODS

We determined the efficacy of CHOP-ASO in the early and late stages of experimental DKD (in 8- or 16-week-old db/db mice, respectively) alone or with an angiotensin-converting enzyme inhibitor (ACEi), after an in vivo dose-escalation study. We used renal functional parameters and morphologic analyses to assess the effect of CHOP-ASO and renal gene-expression profiling to identify differentially regulated genes and pathways. Several human CHOP-ASOs were tested in hyperglycemia-exposed human kidney cells.

RESULTS

CHOP-ASOs efficiently reduced renal CHOP expression in diabetic mice and reduced markers of DKD at the early and late stages. Early combined intervention (CHOP-ASO and ACEi) efficiently prevented interstitial damage. At the later timepoint, the combined treatment reduced indices of both glomerular and tubular damage more efficiently than either intervention alone. CHOP-ASO affected a significantly larger number of genes and disease pathways, including reduced sodium-glucose transport protein 2 (Slc5a2) and PROM1 (CD133). Human CHOP-ASOs efficiently reduced glucose-induced CHOP and prevented death of human kidney cells in vitro .

CONCLUSIONS

The ASO-based approach efficiently reduced renal CHOP expression in a diabetic mouse model, providing an additional benefit to an ACEi, particularly at later timepoints. These studies demonstrate that ASO-based therapies efficiently reduce maladaptive CHOP expression and ameliorate experimental DKD.

From quiescence to repair: C/EBPβ as a regulator of muscle stem cell function in health and disease

CCAAT/Enhancer Binding protein beta (C/EBPβ) is a transcriptional regulator involved in numerous physiological processes. Herein, we describe a role for C/EBPβ as a regulator of skeletal muscle stem cell function. In particular, C/EBPβ is expressed in muscle stem cells in healthy muscle where it inhibits myogenic differentiation. Downregulation of C/EBPβ expression at the protein and transcriptional level allows for differentiation. Persistence of C/EBPβ promotes stem cell self-renewal and C/EBPβ expression is required for mitotic quiescence in this cell population. As a critical regulator of skeletal muscle homeostasis, C/EBPβ expression is stimulated in pathological conditions such as cancer cachexia, which perturbs muscle regeneration and promotes myofiber atrophy in the context of systemic inflammation. C/EBPβ is also an important regulator of cytokine expression and immune response genes, a mechanism by which it can influence muscle stem cell function. In this viewpoint, we describe a role for C/EBPβ in muscle stem cells and propose a functional intersection between C/EBPβ and NF-kB action in the regulation of cancer cachexia.

The Interplay between Insulin Resistance, Inflammation, Oxidative Stress, Base Excision Repair and Metabolic Syndrome in Nonalcoholic Fatty Liver Disease

One of the most common chronic liver disorders, affecting mainly people in Western countries, is nonalcoholic fatty liver disease (NAFLD). Unfortunately, its pathophysiological mechanism is not fully understood, and no dedicated treatment is available. Simple steatosis can lead to nonalcoholic steatohepatitis and even to fibrosis, cancer, and cirrhosis of the liver. NAFLD very often occurs in parallel with type 2 diabetes mellitus and in obese people. Furthermore, it is much more likely to develop in patients with metabolic syndrome (MS), whose criteria include abdominal obesity, elevated blood triacylglycerol level, reduced high-density lipoprotein cholesterol level, increased blood pressure, and high fasting glucose. An important phenomenon in MS is also insulin resistance (IR), which is very common in NAFLD. Liver IR and NAFLD development are linked through an interaction between the accumulation of free fatty acids, hepatic inflammation, and increased oxidative stress. The liver is particularly exposed to elevated levels of reactive oxygen species due to a large number of mitochondria in hepatocytes. In these organelles, the main DNA repair pathway is base excision repair (BER). The present article will illustrate how impairment of BER may be related to the development of NAFLD.

Ethyl pyruvate supplemented in drinking water ameliorates experimental nonalcoholic steatohepatitis

Inflammation and oxidative stress play a significant role in the pathogenesis of nonalcoholic steatohepatitis (NASH). Ethyl pyruvate (EP) is a novel anti-inflammatory agent and a potent reactive oxygen species (ROS) scavenger. Therefore, EP supplemented in drinking water may alleviate experimental NASH in this study (even though 0.3% of EP cannot attenuate the simple non-aggressive fatty liver). The methionine-choline-deficient (MCD) diet was given to the C57BL/6 male mice for 3 weeks to induce NASH. The NASH animals were randomized into 3 treatment groups: animals in the MCD alone group were treated with normal drinking water alone; animals in the delayed EP group were given 3% (v/v) of EP supplemented in normal drinking water, the treatment started 10 days after MCD diet feeding; animals in the early EP therapy group were treated the same as the delayed EP group except that EP treatment started the same day when MCD diet was given; the control mice were fed with normal chow and treated with normal drinking water (n = 10 for each group). Compared to MCD group with normal drinking water, early EP treatment significantly decreased serum ALT and improved NASH histopathology; delayed EP therapy only attenuated NASH in 50% (5/10) of the animals. The beneficial effects were associated with decreased hepatic TNF-a and IL-6 mRNA expression on early 5 days, inhibited NF-kB activation, reduced liver tissue malondialdehyde levels, and decreased intestinal bacterial translocation (BT). In conclusion: EP supplemented in drinking water attenuates experimental NASH.

Glucagon Like Peptide-1 Receptor Agonists Alters Pancreatic and Hepatic Histology and Regulation of Endoplasmic Reticulum Stress in High-fat Diet Mouse Model

BACKGROUND

Obesity is a major health problem worldwide, and non-alcoholic fatty pancreas disease (NAFPD) and non-alcoholic fatty liver disease (NAFLD) are obesity-associated complications. Liraglutide, a glucagon-like peptide-1 (GLP-1) agonist, has been approved for treatment of obesity. We aimed to evaluate the therapeutic effects of liraglutide on the complications through its regulation of endoplasmic reticulum (ER) stress.

METHODS

A high-fat diet mouse model was established in C57BL/6J mice. Two groups of mice were fed a high-fat diet with 60% fat for 16 weeks and control mice were fed standard chow. A four-week 0.6 mg/kg/day liraglutide treatment was started in one high-fat diet group after 12 weeks of the high-fat diet. After sacrificing the mice, pancreatic and hepatic tissues were prepared for western blot and immunohistochemistry for ER stress proteins, including activating transcription factor 4 (ATF4), caspase 12, C/EBP homologous protein (CHOP) eukaryotic initiation factor 2 α (eIF2α), glucose regulated protein (GRP) 78 and protein kinase RNA-like endoplasmic reticulum kinase (PERK).

RESULTS

Liraglutide significantly decreased body weight gained by mice consuming a high-fat diet (27.6 g vs. 34.5 g, P<0.001), and levels of all ER proteins increased significantly in both the pancreas and liver (all P<0.05). Expression of most ER stress proteins in pancreatic tissue correlated with disease scores of NAFLD (all P<0.05). However, no significant differences were found in pancreatic ATF 4 expression between mice without NAFLD, and those with early non-alcoholic steatohepatitis (NASH) and fibrotic NASH (P=0.122).

CONCLUSION

Liraglutide reduces the severity of NAFPD and NAFLD may through regulating the ER stress pathway and downstream apoptosis signaling.

Si-Wu-Tang Alleviates Nonalcoholic Fatty Liver Disease via Blocking TLR4-JNK and Caspase-8-GSDMD Signaling Pathways

Background

Nonalcoholic fatty liver disease (NAFLD) has high global prevalence; however, the treatments of NAFLD are limited due to lack of approved drugs.

Methods

Mice were randomly assigned into three groups: Control group, NAFLD group, NAFLD plus Si-Wu-Tang group. A NAFLD mice model was established by feeding with a methionine- and choline-deficient (MCD) diet for four weeks. Si-Wu-Tang was given orally by gastric gavage at the beginning of 3rd week, and it lasted for two weeks. The treatment effects of Si-Wu-Tang were confirmed by examining the change of body weight, serum alanine aminotransferase (ALT) and aspartate transaminase (AST) levels, Oil Red O staining, and hematoxylin and eosin (H&E) staining of the liver samples and accompanied by steatosis grade scores. The expression and activation of the possible signaling proteins involved in the pathogenesis of NAFLD were determined by western blotting.

Results

Mice fed with four weeks of MCD diet displayed elevated serum levels of ALT and AST, while there was decreased body weight. The hepatic Oil Red O staining and H&E staining showed severe liver steatosis with high steatosis grade scores. All these can be improved by treating with Si-Wu-Tang for two weeks. Mechanistically, the increased hepatic TLR4 expression and its downstream JNK phosphorylation induced by MCD diet were suppressed by Si-Wu-Tang. Moreover, the upregulations of Caspase-8, gasdermin D (GSDMD), and cleaved-GSDMD in liver mediated by MCD diet were all inhibited by Si-Wu-Tang.

Conclusions

Treatment with Si-Wu-Tang improves MCD diet-induced NAFLD in part via blocking TLR4-JNK and Caspase-8-GSDMD signaling pathways, suggesting that Si-Wu-Tang has potential for clinical application in treating NAFLD.

Hepatic E4BP4 induction promotes lipid accumulation by suppressing AMPK signaling in response to chemical or diet-induced ER stress

Prolonged ER stress has been known to be one of the major drivers of impaired lipid homeostasis during the pathogenesis of non-alcoholic liver disease (NAFLD). However, the downstream mediators of ER stress pathway in promoting lipid accumulation remain poorly understood. Here, we present data showing the b-ZIP transcription factor E4BP4 in both the hepatocytes and the mouse liver is potently induced by the chemical ER stress inducer tunicamycin or by high-fat, low-methionine, and choline-deficient (HFLMCD) diet. We showed that such an induction is partially dependent on CHOP, a known mediator of ER stress and requires the E-box element of the E4bp4 promoter. Tunicamycin promotes the lipid droplet formation and alters lipid metabolic gene expression in primary mouse hepatocytes from E4bp4^flox/flox but not E4bp4 liver-specific KO (E4bp4-LKO) mice. Compared with E4bp4^flox/flox mice, E4bp4-LKO female mice exhibit reduced liver lipid accumulation and partially improved liver function after 10-week HFLMCD diet feeding. Mechanistically, we observed elevated AMPK activity and the AMPKβ1 abundance in the liver of E4bp4-LKO mice. We have evidence supporting that E4BP4 may suppress the AMPK activity via promoting the AMPKβ1 ubiquitination and degradation. Furthermore, acute depletion of the Ampkβ1 subunit restores lipid droplet formation in E4bp4-LKO primary mouse hepatocytes. Our study highlighted hepatic E4BP4 as a key factor linking ER stress and lipid accumulation in the liver. Targeting E4BP4 in the liver may be a novel therapeutic avenue for treating NAFLD.

Transcriptional Regulation in Non-Alcoholic Fatty Liver Disease

Obesity is the primary risk factor for the pathogenesis of non-alcoholic fatty liver disease (NAFLD), the worldwide prevalence of which continues to increase dramatically. The liver plays a pivotal role in the maintenance of whole-body lipid and glucose homeostasis. This is mainly mediated by the transcriptional activation of hepatic pathways that promote glucose and lipid production or utilization in response to the nutritional state of the body. However, in the setting of chronic excessive nutrition, the dysregulation of hepatic transcriptional machinery promotes lipid accumulation, inflammation, metabolic stress, and fibrosis, which culminate in NAFLD. In this review, we provide our current understanding of the transcription factors that have been linked to the pathogenesis and progression of NAFLD. Using publicly available transcriptomic data, we outline the altered activity of transcription factors among humans with NAFLD. By expanding this analysis to common experimental mouse models of NAFLD, we outline the relevance of mouse models to the human pathophysiology at the transcriptional level.

Osteopontin acts as a negative regulator of autophagy accelerating lipid accumulation during the development of nonalcoholic fatty liver disease

Accumulating evidence links osteopontin (OPN), a pro-fibrogenic extracellular matrix protein, to the pathogenesis of non-alcoholic fatty liver disease (NAFLD). In this study, liver tissues isolated from non-alcoholic steatohepatitis (NASH) patients expressed higher OPN than those of controls. However, the exact mechanism(s) for this phenomenon is yet to be clarified. Autophagy is the natural, regulated degradation and recycling of a cell's dysfunctional components, in order to maintain homeostasis. Increasing evidence supports that autophagy can constitute an effective Defence mechanism against NAFLD conditions. Herein, we constructed NAFLD mice model by high-fat (HF) and methionine-choline-deficient (MCD) diet and found that OPN is upregulated in livers of NAFLD mice. Besides, secreted OPN inhibited autophagosome-lysosome fusion via binding with its receptors integrin αVβ3 and αVβ5 in HepG2 cells supplemented with free fatty acids (FFA) and the livers of NAFLD mice. Silencing of OPN attenuated autophagy impairment and reduced lipid accumulation, while supplementation of OPN exhibited the opposite effect. Furthermore, treatment with anti-OPN Ab significantly attenuated steatosis as well as autophagy impairment in the liver. Our findings indicated that OPN plays a vital role in the pathogenesis of the development of NAFLD via autophagy impairment, which might represent a potential new therapeutic target for the treatment of NAFLD.

Novel Combinatorial Regimen of Garcinol and Curcuminoids for Non-alcoholic Steatohepatitis (NASH) in Mice

Non-alcoholic steatohepatitis (NASH) is a progressive form of Non-alcoholic fatty liver disease (NAFLD), a chronic liver disease with a significant unmet clinical need. In this study, we examined the protective effects of Garcinia indica extract standardized to contain 20% w/w of Garcinol (GIE) and 95% Curcuminoids w/w from Curcuma longa (Curcuminoids) in a Stelic animal model (STAM) of NASH. The STAM mice developed steatosis, hepatocyte ballooning, and inflammation, which were significantly reduced by the combination of GIE and Curcuminoids, resulting in a lower NAFLD activity score. The treatment reduced fibrosis as observed by Sirius red staining, liver hydroxyproline content and mRNA levels of TGF- β and collagen in the liver. Immunostaining with alpha-smooth muscle actin (α SMA) revealed a significant reduction in hepatic stellate cells. Intriguingly, the combination regimen markedly decreased the mRNA levels of MCP1 and CRP and both mRNA and protein levels of TNF-α. NF-kB, reduced the hepatic and circulating FGF21 levels and altered the nonenzymatic (glutathione) and enzymatic antioxidant markers (Glutathione peroxidase, and superoxide dismutase). Our results suggest that the combination of GIE and Curcuminoids can reduce the severity of NASH by reducing steatosis, fibrosis, oxidative stress, and inflammation. The results suggest that the combinatorial regimen could be an effective supplement to prevent the progression of liver steatosis to inflammation and fibrosis in NASH.

NADPH and Glutathione Redox Link TCA Cycle Activity to Endoplasmic Reticulum Homeostasis

Many metabolic diseases disrupt endoplasmic reticulum (ER) homeostasis, but little is known about how metabolic activity is communicated to the ER. Here, we show in hepatocytes and other metabolically active cells that decreasing the availability of substrate for the tricarboxylic acid (TCA) cycle diminished NADPH production, elevated glutathione oxidation, led to altered oxidative maturation of ER client proteins, and attenuated ER stress. This attenuation was prevented when glutathione oxidation was disfavored. ER stress was also alleviated by inhibiting either TCA-dependent NADPH production or Glutathione Reductase. Conversely, stimulating TCA activity increased NADPH production, glutathione reduction, and ER stress. Validating these findings, deletion of the Mitochondrial Pyruvate Carrier-which is known to decrease TCA cycle activity and protect the liver from steatohepatitis-also diminished NADPH, elevated glutathione oxidation, and alleviated ER stress. Together, our results demonstrate a novel pathway by which mitochondrial metabolic activity is communicated to the ER through the relay of redox metabolites.

Vitamin D Receptor Activation in Liver Macrophages Protects Against Hepatic Endoplasmic Reticulum Stress in Mice

BACKGROUND AND AIMS

Hepatic endoplasmic reticulum (ER) stress, whether triggered by intrinsic or extrinsic factors, can be resolved by the unfolded protein response (UPR). Sustained UPR activation leads to cell death and inflammatory response and contributes to liver disease progression. Hepatic tissue macrophages are key players in orchestrating liver inflammation, and ER stress can enhance macrophage activation. However, it is not well defined how the interplay between ER stress and inflammation is regulated during hepatic stress response.

APPROACH AND RESULTS

Here we demonstrate that vitamin D receptor (VDR) activation mitigates hepatic ER stress response, whereas VDR knockout mice undergo persistent UPR activation and apoptosis in response to chemical ER stress inducer. Moreover, VDR deficiency promotes hepatic macrophage infiltration and increases gene expression and systematic levels of proinflammatory cytokines, including interleukin (IL)-1β, IL-6, and tumor necrosis factor α. VDR expression is induced in hepatic macrophages by ER stress, and VDR plays a dual regulatory role in macrophages by protecting against ER stress and promoting anti-inflammatory polarization. Co-culture with VDR-activated bone marrow-derived macrophages suppresses UPR target genes in primary hepatocytes treated with ER stress inducers. Thus, the immunomodulatory functions of VDR in macrophages are critical in hepatic ER stress resolution in mice.

CONCLUSIONS

VDR signaling in macrophages regulates a shift between proinflammatory and anti-inflammatory activation during ER stress-induced inflammation to promote hepatic ER stress resolution.

Sulforaphene Suppresses Adipocyte Differentiation via Induction of Post-Translational Degradation of CCAAT/Enhancer Binding Protein Beta (C/EBPβ)

Adipocyte differentiation (adipogenesis) is a crucial process that determines the total number and size of mature adipocytes that will develop. In this study, the anti-adipogenic effect of sulforaphene (SFEN), a dietary isothiocyanate (ITC) derived from radish, is investigated both in 3T3-L1 pre-adipocytes and in human adipose tissue-derived stem cells. The results revealed that SFEN significantly inhibit adipogenic cocktail-induced adipocyte differentiation and lipid accumulation at the early stage of adipogenesis. Additionally, the effects are more potent compared to those of other ITCs derived from various cruciferous vegetables. As a related molecular mechanism of action, SFEN promotes the post-translational degradation of CCAAT/enhancer-binding protein (C/EBP) β by decreasing the stability of C/EBPβ, which is responsible for decreasing the expression of master regulatory proteins such as peroxisome proliferator-activated receptor γ and C/EBPα. Collectively, these results suggest that the intake of SFEN-enriched natural materials could be helpful as a strategy for preventing obesity.

Human antigen R: A potential therapeutic target for liver diseases

Human antigen R (HuR), also known as HuA and embryonic lethal abnormal vision-like 1 (ELAVL1), is a ubiquitously expressed RNA binding protein and functions as an RNA regulator and mediates the expression of various proteins by diverse post-transcriptional mechanisms. HuR has been well characterized in the inflammatory responses and in the development of various cancers. The importance of HuR-mediated roles in cell signaling, inflammation, fibrogenesis and cancer development in the liver has attracted a great deal of attention. However, there is still a substantial gap between the current understanding of the potential roles of HuR in the progression of liver disease and whether HuR can be targeted for the treatment of liver diseases. In this review, we introduce the function and mechanistic characterization of HuR, and then focus on the physiopathological roles of HuR in the development of different liver diseases, including hepatic inflammation, alcoholic liver diseases, non-alcoholic fatty liver diseases, viral hepatitis, liver fibrosis and liver cancers. We also summarize existing approaches targeting HuR function. In conclusion, although characterizing the liver-specific HuR function and demonstrating the multi-level regulative networks of HuR in the liver are still required, emerging evidence supports the notion that HuR represents a potential therapeutic target for the treatment of chronic liver diseases.

Metabolic impairment in response to early induction of C/EBPβ leads to compromised cardiac function during pathological hypertrophy

Chronic pressure overload-induced left ventricular hypertrophy in heart is preceded by a metabolic perturbation that prefers glucose over lipid as substrate for energy requirement. Here, we establish C/EBPβ (CCAAT/enhancer-binding protein β) as an early marker of the metabolic derangement that triggers the imbalance in fatty acid (FA) oxidation and glucose uptake with increased lipid accumulation in cardiomyocytes during pathological hypertrophy, leading to contractile dysfunction and endoplasmic reticulum (ER) stress. This is the first study that shows that myocardium-targeted C/EBPβ knockdown prevents the impaired cardiac function during cardiac hypertrophy led by maladaptive metabolic response with persistent hypertrophic stimuli, whereas its targeted overexpression in control increases lipid accumulation significantly compared to control hearts. A new observation from this study was the dual and opposite transcriptional regulation of the alpha and gamma isoforms of Peroxisomal proliferator activated receptors (PPARα and PPARγ) by C/EBPβ in hypertrophied cardiomyocytes. Before the functional and structural remodeling sets in the diseased myocardium, C/EBPβ aggravates lipid accumulation with the aid of the increased FA uptake involving induced PPARγ expression and decreased fatty acid oxidation (FAO) by suppressing PPARα expression. Glucose uptake into cardiomyocytes was greatly increased by C/EBPβ via PPARα suppression. The activation of mammalian target of rapamycin complex-1 (mTORC1) during increased workload in presence of glucose as the only substrate was prevented by C/EBPβ knockdown, thereby abating contractile dysfunction in cardiomyocytes. Our study thus suggests that C/EBPβ may be considered as a novel cellular marker for deranged metabolic milieu before the heart pathologically remodels itself during hypertrophy.

The serum amyloid A3 promoter-driven luciferase reporter mice is a valuable tool to image early renal fibrosis development and shows the therapeutic effect of glucosyl-hesperidin treatment

Tubulointerstitial fibrosis is a progressive process affecting the kidneys, causing renal failure that can be life-threatening. Thus, renal fibrosis has become a serious concern in the ageing population; however, fibrotic development cannot be diagnosed early and assessed noninvasively in both patients and experimental animal models. Here, we found that serum amyloid A3 (Saa3) expression is a potent indicator of early renal fibrosis; we also established in vivo Saa3/C/EBPβ-promoter bioluminescence imaging as a sensitive and specific tool for early detection and visualization of tubulointerstitial fibrosis. Saa3 promoter activity is specifically upregulated in parallel with tumor necrosis factor α (TNF-α) and fibrotic marker collagen I in injured kidneys. C/EBPβ, upregulated in injured kidneys and expressed in tubular epithelial cells, is essential for the increased Saa3 promoter activity in response to TNF-α, suggesting that C/EBPβ plays a crucial role in renal fibrosis development. Our model successfully enabled visualization of the suppressive effects of a citrus flavonoid derivative, glucosyl-hesperidin, on inflammation and fibrosis in kidney disease, indicating that this model could be widely used in exploring therapeutic agents for fibrotic diseases.

Breed, Diet, and Interaction Effects on Adipose Tissue Transcriptome in Iberian and Duroc Pigs Fed Different Energy Sources

In this study, we analyzed the effects of breed, diet energy source, and their interaction on adipose tissue transcriptome in growing Iberian and Duroc pigs. The study comprised 29 Iberian and 19 Duroc males, which were kept under identical management conditions except the nutritional treatment. Two isoenergetic diets were used with 6% high oleic sunflower oil (HO) or carbohydrates (CH) as energy sources. All animals were slaughtered after 47 days of treatment at an average live weight of 51.2 kg. Twelve animals from each breed (six fed each diet) were employed for ham subcutaneous adipose tissue RNA-Seq analysis. The data analysis was performed using two different bioinformatic pipelines. We detected 837 and 1456 differentially expressed genes (DEGs) according to breed, depending on the pipeline. Due to the strong effect of breed on transcriptome, the effect of the diet was separately evaluated in the two breeds. We identified 207 and 57 DEGs depending on diet in Iberian and Duroc pigs, respectively. A joint analysis of both effects allowed the detection of some breed–diet interactions on transcriptome, which were inferred from RNA-Seq and quantitative PCR data. The functional analysis showed the enrichment of functions related to growth and tissue development, inflammatory response, immune cell trafficking, and carbohydrate and lipid metabolism, and allowed the identification of potential regulators. The results indicate different effects of diet on adipose tissue gene expression between breeds, affecting relevant biological pathways.

An interaction between MKL1, BRG1, and C/EBPβ mediates palmitate induced CRP transcription in hepatocytes

Non-alcoholic steatohepatitis (NASH) is one of the most predominant disorders in metabolic syndrome. Induction of pro-inflammatory mediators in hepatocytes exposed to free fatty acids represents a hallmark event during NASH pathogenesis. C-reactive protein (CRP) is a prototypical pro-inflammatory mediator. In the present study, we investigated the mechanism by which megakaryocytic leukemia 1 (MKL1) mediates palmitate (PA) induced CRP transcription in hepatocytes. We report that over-expression of MKL1, but not MKL2, activated the CRP promoter whereas depletion or inhibition of MKL1 repressed the CRP promoter. MKL1 potentiated the induction of the CRP promoter activity by PA treatment. Importantly, MKL1 knockdown by siRNA or pharmaceutical inhibition by CCG-1423 attenuated the induction of endogenous CRP expression in hepatocytes. Similarly, primary hepatocytes isolated from wild type (WT) mice produced more CRP than those isolated from MKL1 deficient (KO) mice when stimulated with PA. Mechanistically, the sequence-specific transcription factor CCAAT-enhancer-binding protein (C/EBPβ) interacted with MKL1 and recruited MKL1 to activate CRP transcription. Reciprocally, MKL1 modulated C/EBPβ activity by recruiting the chromatin remodeling protein BRG1 to the CRP promoter to alter histone modifications. In conclusion, our data delineate a novel epigenetic mechanism underlying augmented hepatic inflammation during NASH pathogenesis.

An N-terminal-truncated isoform of FAM134B (FAM134B-2) regulates starvation-induced hepatic selective ER-phagy

This study has identified a novel truncated isoform of FAM134B (FAM134B-2) that regulates starvation-induced selective ER-phagy of secretory proteins such as ApoCIII through the activation of C/EBPβ.

Autophagy is a conserved system that adapts to nutrient starvation, after which proteins and organelles are degraded to recycle amino acids in response to starvation. Recently, the ER was added to the list of targets of autophagic degradation. Autophagic degradation pathways of bulk ER and the specific proteins sorted through the ER are considered key mechanisms in maintaining ER homeostasis. Four ER-resident proteins (FAM134B, CCPG1, SEC62, and RTN3) have been identified as ER-resident cargo receptors, which contain LC3-interacting regions. In this study, we identified an N-terminal–truncated isoform of FAM134B (FAM134B-2) that contributes to starvation-induced ER-related autophagy. Hepatic FAM134B-2 but not full-length FAM134B (FAM134B-1) is expressed in a fed state. Starvation drastically induces FAM134B-2 but no other ER-resident cargo receptors through transcriptional activation by C/EBPβ. C/EBPβ overexpression increases FAM134B-2 recruitment into autophagosomes and lysosomal degradation. FAM134B-2 regulates lysosomal degradation of ER-retained secretory proteins such as ApoCIII. This study demonstrates that the C/EBPβ-FAM134B-2 axis regulates starvation-induced selective ER-phagy.

Asking the Right Questions With Animal Models: Methionine- and Choline-Deficient Model in Predicting Adverse Drug Reactions in Human NASH

In the past few decades, great conceptual and technological advances have been made in the field of toxicology, but animal model-based research still remains one of the most widely used and readily available tools for furthering our current knowledge. However, animal models are not perfect in predicting all systemic toxicity in humans. Extrapolating animal data to accurately predict human toxicities remains a challenge, and researchers are obligated to question the appropriateness of their chosen animal model. This paper provides an assessment of the utility of the methionine- and choline-deficient (MCD) diet fed animal model in reflecting human nonalcoholic steatohepatitis (NASH) and the potential risks of adverse drug reactions and toxicities that are associated with the disease. As a commonly used NASH model, the MCD model fails to exhibit most metabolic abnormalities in a similar manner to the human disease. The MCD model, on the other hand, closely resembles human NASH histology and reflects signatures of drug transporter alterations in humans. Due to the nature of the MCD model, it should be avoided in studies of NASH pathogenesis, metabolic parameter evaluation, and biomarker identification. But it can be used to accurately predict altered drug disposition due to NASH-associated transporter alterations.

Hydrogen sulfide and hepatic lipid metabolism - a critical pairing for liver health

Hydrogen sulfide (H₂ S) is the most recently recognized gasotransmitter, influencing a wide range of physiological processes. As a critical regulator of metabolism, H₂ S has been suggested to be involved in the pathology of many diseases, particularly obesity, diabetes and cardiovascular disorders. Its involvement in liver health has been brought to light more recently, particularly through knockout animal models, which show severe hepatic lipid accumulation upon ablation of H₂ S metabolic pathways. A complex relationship between H₂ S and lipid metabolism in the liver is emerging, which has significant implications for liver disease establishment and/or progression, regardless of the disease-causing agent. In this review, we discuss the critical importance of H₂ S in hepatic lipid metabolism. We then describe the animal models so far related with H₂ S and lipid-associated liver disease, as well as H₂ S-based treatments available. Finally, we highlight important considerations for future studies and identify areas in which much still remains to be determined. LINKED ARTICLES: This article is part of a themed section on Hydrogen Sulfide in Biology & Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.4/issuetoc.

Association between endoplasmic reticulum stress and risk factors of diabetic retinopathy

Diabetic retinopathy (DR) is one of the most common and challenging ocular complications of diabetes mellitus. As a chronic, progressive ocular disease that poses a serious threat to vision, DR has gradually become a leading cause of blindness worldwide. Emerging evidence points to an important role of endoplasmic reticulum (ER) stress in not only maintaining the steady-state equilibrium in the body, but also in intracellular synthesis, protein folding, and other essential functions. Recent studies have demonstrated clear associations between ER stress-related physiological functions and the pathogenesis of DR. When cells are stimulated by external stimuli, UPR pathway is activated firstly to protect it. However, long-term harmful factors can induce ER stress. which interferes with the physiological metabolism of retinal cells and participates in the occurrence of DR via the ATF6 pathway, PERK pathway and IRE1 pathway. At present, ER stress blocker is expected to become a new anti-DR therapy. Thus, understanding the relationship between ER stress and DR will help to develop new effective preventative treatments. In this review, we summarize the risk factors of DR pathogenesis induced by ER stress toward revealing potentially new therapeutic targets.

Therapeutic inhibition of spleen tyrosine kinase in inflammatory macrophages using PLGA nanoparticles for the treatment of non-alcoholic steatohepatitis

Non-alcoholic steatohepatitis (NASH) is the leading cause of cirrhosis worldwide and the most rapidly growing indication for liver transplantation. Macrophages are the important cellular component in the inflammatory milieu in NASH. Inflammatory and pro-fibrotic mediators produced by macrophages causes significant tissue injury in many inflammatory diseases. Therefore, inhibition of the inflammatory macrophages would be a promising approach to attenuate NASH. In this study, we studied the implication of SYK pathway in NASH, and investigated PLGA nanoparticles-based delivery of SYK pathway inhibitor as an effective and promising therapeutic approach for the treatment of NASH. We found positive correlation between SYK expression with the pathogenesis of NASH and alcoholic hepatitis in patients. Importantly, SYK expression was significantly induced in M1-differentiated inflammatory macrophages. To inhibit SYK pathway specifically, we used a small-molecule inhibitor R406 that blocks Fc-receptor signaling pathway and reduces immune complex-mediated inflammation. R406 dose-dependently inhibited nitric-oxide release and M1-specific markers in M1-differentiated macrophages. Thereafter, we synthesized PLGA nanoparticles to deliver R406 to increase the drug pharmacokinetics for the efficient treatment of NASH. We investigated the therapeutic efficacy of R406-PLGA in-vitro in differentiated macrophages, and in-vivo in Methionine-Choline-deficient (MCD)-diet induced NASH mouse model. R406-PLGA inhibited M1-specific differentiation markers in RAW and bone-marrow-derived macrophages. In-vivo, R406 and more strongly R406-PLGA ameliorated fibrosis, inflammation and steatosis in mice. R406 and more significantly R406-PLGA reduced ALT, AST, cholesterol and triglyceride plasma levels. These results suggest that delivery of SYK inhibitor using PLGA nanoparticles can be a potential therapeutic approach for the treatment of Non-alcoholic steatohepatitis.

HCBP6 upregulates human SREBP1c expression by binding to C/EBPβ-binding site in the SREBP1c promoter

Sterol regulatory element-binding protein-1c (SREBP1c) plays an important role in triglyceride (TG) homeostasis. Although our previous study showed that hepatitis C virus core-binding protein 6 (HCBP6) regulates SREBP1c expression to maintain intracellular TG homeostasis, the mechanism underlying this regulation is unclear. In the present study, we found that HCBP6 increased intracellular TG levels by upregulating SREBP1c expression. HCBP6 increased SREBP1c transcription by directly binding to the SREBP1c promoter (at the −139- to +359-bp region). Moreover, we observed that HCBP6 interacted with C/EBPβ-binding site in the SREBP1c promoter both in vitro and in vivo. These results indicate that HCBP6 upregulates human SREBP1c expression by binding to the C/EBPβ-binding site in the SREBP1c promoter.

Exercise, heat shock proteins and insulin resistance

Best known as chaperones, heat shock proteins (HSPs) also have roles in cell signalling and regulation of metabolism. Rodent studies demonstrate that heat treatment, transgenic overexpression and pharmacological induction of HSP72 prevent high-fat diet-induced glucose intolerance and skeletal muscle insulin resistance. Overexpression of skeletal muscle HSP72 in mice has been shown to increase endurance running capacity nearly twofold and increase mitochondrial content by 50%. A positive correlation between HSP72 mRNA expression and mitochondrial enzyme activity has been observed in human skeletal muscle, and HSP72 expression is markedly decreased in skeletal muscle of insulin resistant and type 2 diabetic patients. In addition, decreased levels of HSP72 correlate with insulin resistance and non-alcoholic fatty liver disease progression in livers from obese patients. These data suggest the targeted induction of HSPs could be a therapeutic approach for preventing metabolic disease by maintaining the body's natural stress response. Exercise elicits a number of metabolic adaptations and is a powerful tool in the prevention and treatment of insulin resistance. Exercise training is also a stimulus for increased HSP expression. Although the underlying mechanism(s) for exercise-induced HSP expression are currently unknown, the HSP response may be critical for the beneficial metabolic effects of exercise. Exercise-induced extracellular HSP release may also contribute to metabolic homeostasis by actively restoring HSP72 content in insulin resistant tissues containing low endogenous levels of HSPs.This article is part of the theme issue 'Heat shock proteins as modulators and therapeutic targets of chronic disease: an integrated perspective'.

Liver function and dysfunction - a unique window into the physiological reach of ER stress and the unfolded protein response

The unfolded protein response (UPR) improves endoplasmic reticulum (ER) protein folding in order to alleviate stress. Yet it is becoming increasingly clear that the UPR regulates processes well beyond those directly involved in protein folding, in some cases by mechanisms that fall outside the realm of canonical UPR signaling. These pathways are highly specific from one cell type to another, implying that ER stress signaling affects each tissue in a unique way. Perhaps nowhere is this more evident than in the liver, which-beyond being a highly secretory tissue-is a key regulator of peripheral metabolism and a uniquely proliferative organ upon damage. The liver provides a powerful model system for exploring how and why the UPR extends its reach into physiological processes that occur outside the ER, and how ER stress contributes to the many systemic diseases that involve liver dysfunction. This review will highlight the ways in which the study of ER stress in the liver has expanded the view of the UPR to a response that is a key guardian of cellular homeostasis outside of just the narrow realm of ER protein folding.

Pathogenesis of NASH: How Metabolic Complications of Overnutrition Favour Lipotoxicity and Pro-Inflammatory Fatty Liver Disease

Overnutrition, usually with obesity and genetic predisposition, lead to insulin resistance, which is an invariable accompaniment of nonalcoholic fatty liver disease (NAFLD). The associated metabolic abnormalities, pre- or established diabetes, hypertension and atherogenic dyslipidemia (clustered as metabolic syndrome) tend to be worse for nonalcoholic steatohepatitis (NASH), revealing it as part of a continuum of metabolic pathogenesis. The origins of hepatocellular injury and lobular inflammation which distinguish NASH from simple steatosis have intrigued investigators, but it is now widely accepted that NASH results from liver lipotoxicity. The key issue is not the quantity of liver fat but the type(s) of lipid molecules that accumulate, and how they are "packaged" to avoid subcellular injury. Possible lipotoxic mediators include free (unesterified) cholesterol, saturated free fatty acids, diacylglycerols, lysophosphatidyl-choline, sphingolipids and ceramide. Lipid droplets are intracellular storage organelles for non-structural lipid whose regulation is influenced by genetic polymorphisms, such as PNPLA3. Cells unable to sequester chemically reactive lipid molecules undergo mitochondrial injury, endoplasmic reticulum (ER) stress and autophagy, all processes of interest for NASH pathogenesis. Lipotoxicity kills hepatocytes by apoptosis, a highly regulated, non-inflammatory form of cell death, but also by necrosis, necroptosis and pyroptosis; the latter involve mitochondrial injury, oxidative stress, activation of c-Jun N-terminal kinase (JNK) and release of danger-associated molecular patterns (DAMPs). DAMPs stimulate innate immunity by binding pattern recognition receptors, such as Toll-like receptor 4 (TLR4) and the NOD-like receptor protein 3 (NLRP3) inflammasome, which release a cascade of pro-inflammatory chemokines and cytokines. Thus, lipotoxic hepatocellular injury attracts inflammatory cells, particularly activated macrophages which surround ballooned hepatocytes as crown-like structures. In both experimental and human NASH, livers contain cholesterol crystals which are a second signal for NLRP3 activation; this causes interleukin (IL)-1β and IL18 secretion to attract and activate macrophages and neutrophils. Injured hepatocytes also liberate plasma membrane-derived extracellular vesicles; these have been shown to circulate in NASH and to be pro-inflammatory. The way metabolic dysfunction leads to lipotoxicity, innate immune responses and the resultant pattern of cellular inflammation in the liver are likely also relevant to hepatic fibrogenesis and hepatocarcinogenesis. Pinpointing the key molecules involved pharmacologically should eventually lead to effective pharmacotherapy against NASH.

Attenuation of hepatic steatosis by purple sweet potato colour is associated with blocking Src/ERK/C/EBPβ signalling in high-fat-diet–treated mice

Our previous work showed that purple sweet potato colour (PSPC), a class of naturally occurring anthocyanins, effectively improved hepatic glucose metabolic dysfunction in high-fat-diet (HFD)–treated mice. This study investigated the effects of PSPC on HFD-induced hepatic steatosis and the signalling events associated with these effects. Mice were divided into 4 groups: control group, HFD group, HFD+PSPC group, and PSPC group. PSPC was administered daily for 20 weeks at oral doses of 700 mg/(kg·day)−1). Our results showed that PSPC significantly improved obesity and related metabolic parameters, as well as liver injury in HFD-treated mice. Moreover, PSPC dramatically attenuated hepatic steatosis in HFD-treated mice. PSPC markedly prevented oxidative stress-mediated Src activation in HFD-treated mouse livers. Furthermore, PSPC feeding remarkably suppressed mitogen-activated protein kinase kinase/extracellular-signal-regulated kinase (MEK/ERK) signalling and consequent CCAAT/enhancer binding protein β (C/EBPβ) activation and restored AMPK activation in HFD-treated mouse livers, which was confirmed by U0126 treatment. Ultimately, PSPC feeding dramatically reduced protein expression of FAS and CD36 and the activation of ACC, and increased the protein expression of CPT1A in the livers of HFD-treated mice, indicating decreased lipogenesis and fatty acid uptake and enhanced fatty acid oxidation. In conclusion, PSPC exhibited beneficial effects on hepatic steatosis, which were associated with blocking Src and C/EBPβ activation.

miR-212-5p suppresses lipid accumulation by targeting FAS and SCD1

MicroRNAs, a class of small noncoding RNAs, are implicated in controlling a variety of biological processes. We have shown that leucine deprivation suppresses lipogenesis by inhibiting fatty acid synthase (FAS) expression in the liver previously; the aim of our current study is to investigate which kind of microRNA is involved in the regulation of FAS expression in response to leucine deprivation. Here, we indicated that microRNA-212-5p specifically binds to mouse FAS 3'UTR and inhibits its activity. Leucine deficiency significantly increased the mRNA levels of miR-212-5p in the livers of mice. Further studies proved that miR-212-5p also directly binds to the 3'UTR of stearoyl-CoA desaturase-1 (SCD1) to inhibit its activity. Overexpression of miR-212-5p decreases the protein levels of FAS and SCD1 in vitro and in vivo, and silencing of miR-212-5p has the opposite effects in mouse primary hepatocytes. Moreover, overexpression of miR-212-5p significantly decreases triglyceride (TG) accumulation in primary hepatocytes and in the livers of mice injected with adenovirus-mediated overexpressing of miR-212-5p (Ad-miR-212). Interestingly, inhibition of miR-212-5p reverses the suppressive effects of leucine deficiency on FAS and SCD1 expression, as well as TG accumulation in mouse primary hepatocytes. Finally, we demonstrate that leucine deficiency induces the expression of miR-212-5p in a GCN2/ATF4-dependent manner. Taken together, our results demonstrate a novel function of hepatic miR-212-5p in the regulation of lipid metabolism which represents a potential therapeutic target for the treatment of non-alcohol fatty liver diseases (NAFLD).

Amelioration of late-onset hepatic steatosis in IDH2-deficient mice

Nonalcoholic fatty liver disease (NAFLD) has a high prevalence in the general population and can evolve into nonalcoholic steatohepatosis (NASH), cirrhosis, and complications such as liver failure and hepatocellular carcinoma. Recently, we reported that mitochondrial NADP⁺-dependent isocitrate dehydrogenase, encoded by the IDH2, plays an important role in the regulation of redox balance and oxidative stress levels, which are tightly associated with intermediary metabolism and energy production. In the present study, we showed that in mice targeted disruption of IDH2 attenuates age-associated hepatic steatosis by the activation of p38/cJun NH2-terminal kinase (JNK) and p53, presumably induced by the elevation of mitochondrial reactive oxygen species (ROS), which in turn resulted in the suppression of hepatic lipogenesis and inflammation via the upregulation of fibroblast growth factor 21 (FGF21) and the inhibition of NFκB signaling pathways. Our finding uncovers a new mechanism involved in hepatocellular steatosis and IDH2 may be a valuable therapeutic target for the management of NAFLD.

Aristolochia manshuriensis Kom ethyl acetate extract protects against high-fat diet-induced non-alcoholic steatohepatitis by regulating kinase phosphorylation in mouse

Aristolochia manshuriensis Kom (AMK) is an herb used as a traditional medicine; however, it causes side effects such as nephrotoxicity and carcinogenicity. Nevertheless, AMK can be applied in specific ways medicinally, including via ingestion of low doses for short periods of time. Non-alcoholic steatohepatitis (NASH) induced the hepatocyte injury and inflammation. The protective effects of AMK against NASH are unclear; therefore, in this study, the protective effects of AMK ethyl acetate extract were investigated in a high-fat diet (HFD)-induced NASH model. We found decreased hepatic steatosis and inflammation, as well as increased levels of lipoproteins during AMK extract treatment. We also observed decreased hepatic lipid peroxidation and triglycerides, as well as suppressed hepatic expression of lipogenic genes in extract-treated livers. Treatment with extract decreased the activation of c-jun N-terminal kinase 1/2 (JNK1/2) and increased the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2). These results demonstrate that the protective effect of the extract against HFD-induced NASH occurred via reductions in reactive oxygen species production, inflammation suppression, and apoptosis related to the suppression of JNK1/2 activation and increased ERK1/2 phosphorylation. Taken together, these results indicate that that ethyl acetate extract of AMK has potential therapeutic effects in the HFD-induced NASH mouse model.

Cystathionine beta-synthase deficiency alters hepatic phospholipid and choline metabolism: Post-translational repression of phosphatidylethanolamine N-methyltransferase is a consequence rather than a cause of liver injury in homocystinuria

Classical homocystinuria (HCU) due to inactivating mutation of cystathionine β-synthase (CBS) is a poorly understood life-threatening inborn error of sulfur metabolism. A previously described cbs-/- mouse model exhibits a semi-lethal phenotype due to neonatal liver failure. The transgenic HO mouse model of HCU exhibits only mild liver injury and recapitulates multiple aspects of the disease as it occurs in humans. Disruption of the methionine cycle in HCU has the potential to impact multiple aspect of phospholipid (PL) metabolism by disruption of both the Kennedy pathway and phosphatidylethanolamine N-methyltransferase (PEMT) mediated synthesis of phosphatidylcholine (PC). Comparative metabolomic analysis of HO mouse liver revealed decreased levels of choline, and choline phosphate indicating disruption of the Kennedy pathway. Alterations in the relative levels of multiple species of PL included significant increases in PL degradation products consistent with enhanced membrane PL turnover. A significant decrease in PC containing 20:4n6 which primarily formed by the methylation of phosphatidylethanolamine to PC was consistent with decreased flux through PEMT. Hepatic expression of PEMT in both the cbs-/- and HO models is post-translationally repressed with decreased levels of PEMT protein and activity that inversely-correlates with the scale of liver injury. Failure to induce further repression of PEMT in HO mice by increased homocysteine, methionine and S-adenosylhomocysteine or depletion of glutathione combined with examination of multiple homocysteine-independent models of liver injury indicated that repression of PEMT in HCU is a consequence rather than a cause of liver injury. Collectively, our data show significant alteration of a broad range of hepatic PL and choline metabolism in HCU with the potential to contribute to multiple aspects of pathogenesis in this disease.

Serum Amyloid A3 Gene Expression in Adipocytes is an Indicator of the Interaction with Macrophages

The infiltration of macrophages into adipose tissue and their interaction with adipocytes are essential for the chronic low-grade inflammation of obese adipose tissue. In this study, we identified the serum amyloid A3 (Saa3) gene as a key adipocyte-derived factor that is affected by interaction with macrophages. We showed that the Saa3 promoter in adipocytes actually responds to activated macrophages in a co-culture system. Decreasing C/EBPβ abundance in 3T3-L1 adipocytes or point mutation of C/EBPβ elements suppressed the increased promoter activity in response to activated macrophages, suggesting an essential role of C/EBPβ in Saa3 promoter activation. Bioluminescence based on Saa3 promoter activity in Saa3-luc mice was promoted in obese adipose tissue, showing that Saa3 promoter activity is most likely related to macrophage infiltration. This study suggests that the level of expression of the Saa3 gene could be utilized for the number of infiltrated macrophages in obese adipose tissue.

The role of TRIB1 in lipid metabolism; from genetics to pathways

The plasma concentration of lipids is a heritable risk factor for the development of atherosclerosis and related coronary artery diseases (CAD). Mammalian tribbles homologue 1 (TRIB1) is a human locus, the downstream linkage disequilibrium (LD) block of which affects plasma low-density lipoprotein (LDL)-associated cholesterol, triglyceride (TG) levels and CAD across multiple ethnic groups. In addition, association of TRIB1 with non-alcoholic fatty liver disease (NAFLD) has also been shown. A regulatory sequence that enhances TRIB1 promoter activity was identified in the LD block and the minor allele of a single nt polymorphism (SNP, rs6982502) in this regulatory sequence reduces the activity of the TRIB1 promoter. The minor allele of rs6982502 is a risk allele for increasing plasma lipid levels and NAFLD. Trib1 deficiency increases plasma cholesterol and TGs in mice and overexpression of TRIB1 in mouse liver reduces these factors. Expression of rate-limiting lipogenic enzymes is increased in Trib1-knockout mouse liver and decreased with overexpression. Recently, carbohydrate-responsive element-binding protein (ChREBP) emerged as a novel binding partner of TRIB1. Furthermore, novel binding partner, Sin3A (Swi-independent 3A)-associated protein, 18 kDa, was identified, which activates microsomal TG transfer protein (MTTP) expression by binding with MTTP regulatory elements in co-ordination with mSin3A and TRIB1. Very recently, a small molecular compound that up-regulates TRIB1 expression in HepG2 cells has been discovered. Further exploration of the binding partners of TRIB1 and their involvement in lipid metabolism may aid discovery of novel pharmacological targets for the management of dyslipidaemia and steatosis.

C/EBPβ in bone marrow is essential for diet induced inflammation, cholesterol balance, and atherosclerosis

BACKGROUND AND OBJECTIVE

Atherosclerosis is both a chronic inflammatory disease and a lipid metabolism disorder. C/EBPβ is well documented for its role in the development of hematopoietic cells and integration of lipid metabolism. However, C/EBPβ's role in atherosclerotic progression has not been examined. We assessed the impact of hematopoietic CEBPβ deletion in ApoE(-/-) mice on hyperlipidemia, inflammatory responses and lesion formation in the aorta.

METHODS AND RESULTS

ApoE(-/-) mice were reconstituted with bone marrow cells derived from either WT or C/EBPβ(-/-) mice and placed on low fat or high fat/high cholesterol diet for 11 weeks. Hematopoietic C/EBPβ deletion in ApoE(-/-) mice reduced blood and hepatic lipids and gene expression of hepatic stearoyl CoA desaturase 1 and fatty acid synthase while expression of ATP binding cassette transporter G1, cholesterol 7-alpha-hydroxylase, and liver X receptor alpha genes were significantly increased. ApoE(-/-) mice reconstituted with C/EBPβ(-/-) bone marrow cells also significantly reduced blood cytokine levels and reduced lesion area in aortic sinuses compared with ApoE(-/-) mice reconstituted with WT bone marrow cells. Silencing of C/EBPβ in RAW264.7 macrophage cells prevented oxLDL-mediated foam cell formation and inflammatory cytokine secretion in conditioned medium.

CONCLUSION

C/EBPβ in hematopoietic cells is crucial to regulate diet-induced inflammation, hyperlipidemia and atherosclerosis development.