Loss of Hepatocyte-Specific PPARγ Expression Ameliorates Early Events of Steatohepatitis in Mice Fed the Methionine and Choline-Deficient Diet

Hepatic HKDC1 deletion alleviates western diet-induced MASH in mice

The global prevalence of Metabolic Dysfunction-Associated Steatohepatitis (MASH) has been rising sharply, closely mirroring the increasing rates of obesity and metabolic syndrome. MASH exhibits a strong sexual dimorphism where females are affected with more severe forms after menopause. Hexokinase domain-containing protein 1 (HKDC1) has recently been recognized for its role in liver diseases, where its expression is minimal under normal conditions but significantly increases in response to metabolic stressors like obesity and liver injury. This selective upregulation suggests HKDC1's potential specialization in hepatic glucose and lipid dysregulation, linking it closely to the progression of MASH. This study aims to clarify the role of HKDC1 in Western diet-induced MASH in female mice by examining its impact on hepatic glucose and lipid metabolism, offering insights into its potential as a therapeutic target and addressing the need for sex-specific research in liver disease. This study reveals that HKDC1 expression is elevated in obese women with MASH and correlates with liver pathology. In a mouse model, liver-specific HKDC1 knockout (HKDC1LKO) protected against Western diet-induced obesity, glucose intolerance, and MASH features, including steatosis, inflammation, and fibrosis. Transcriptomic analysis showed that HKDC1 deletion reduced pro-inflammatory and pro-fibrotic gene expression, while gut microbiome analysis indicated a shift toward MASH-protective bacteria. These findings suggest that HKDC1 may exacerbate MASH progression through its role in metabolic and inflammatory pathways, making it a potential therapeutic target.

Fructus arctii mitigates diabetic nephropathy via the Apoh/PPAR-γ pathway

BACKGROUND

Diabetic nephropathy (DN) is characterized by renal fibrosis and functional decline. Apolipoprotein H (Apoh) and Fructus arctii, a traditional medicinal plant, have demonstrated potential in treating metabolic and fibrotic disorders. This study Focused on revealing the roles of Apoh and Fructus arctii in mitigating DN.

METHODS

Db/db mice served as an in vivo DN model, and mouse glomerular mesangial cells (mMCs) and renal tubular epithelial cells (mTECs) were treated with high glucose (HG) to simulate DN in vitro. Apoh silencing and overexpression were performed using shRNA and pcDNA3.1 vectors. Fructus arctii was administered to both cellular and animal models to assess its therapeutic potential. Cellular proliferation was measured using CCK-8 and EdU assays, while fibrosis markers were analyzed by Western blot, IHC and RT-qPCR. PPAR-γ pathway involvement was confirmed through treatment with the antagonist GW9662. Renal structural changes were evaluated with histological staining including H&E, PAS, Masson's trichrome, and picrosirius red staining.

RESULTS

Apoh expression was markedly reduced in HG-treated cells and the kidneys of db/db mice. Overexpression of Apoh suppressed HG-induced proliferation in mMCs and mTECs by downregulating cyclin D1 and PCNA. Additionally, Apoh overexpression alleviated fibrosis by reducing Fibronectin, Collagen I, and α-SMA levels, effects mediated through the PPAR-γ pathway. Treatment with the PPAR-γ antagonist GW9662 reversed these protective effects. In db/db mice, Fructus arctii administration improved renal function by reducing blood glucose, proteinuria, and renal collagen deposition. It also alleviated fibrosis and enhanced Apoh and PPAR-γ expression. Silencing Apoh nullified the protective effects of Fructus arctii on cell proliferation and fibrosis, confirming its reliance on the Apoh/PPAR-γ pathway.

CONCLUSION

Fructus arctii alleviated DN progression by modulating cell proliferation and renal fibrosis via the Apoh/PPAR-γ pathway.

Exosome-equipped TNF antisense oligodeoxynucleotide or 2-deoxy-D-glucose ameliorated nonalcoholic steatohepatitis by modulating superoxide dismutase 1 in mice

Inflammatory mediators tumor necrosis factor (TNF) and interleukin 1 beta (IL1β), primarily derived from hepatic macrophages in the liver, play a crucial role in the progression of nonalcoholic steatohepatitis (NASH). Meanwhile, intravenously injected exosomes are mainly distributed in the liver and predominantly taken up by hepatic macrophage. Herein, we aimed to evaluate the feasibility of targeted inhibition of TNF and IL1β expression in hepatic macrophages via exosomes as a potential therapeutic strategy for NASH. In this study, we demonstrated that antisense oligodeoxynucleotide targeting TNF (ASO-TNF) or 2-deoxy-d-glucose (2DG) effectively suppressed the expression of TNF and/or IL1β in macrophages. Exosomes loaded with ASO-TNF or 2DG were able to suppress the expression of TNF and/or IL1β in macrophages in vitro or in vivo. Furthermore, infusion of Exo/ASO-TNF or Exo/2DG significantly attenuated experimental steatohepatitis in choline deficient amino acid-defined (CDAA) or methionine and choline deficient (MCD) diet-fed mice. RNA-seq results showed that treatment with Exo/ASO-TNF or Exo/2DG significantly inhibited pro-inflammatory signaling pathways. Mechanistically, we observed that administration of Exo/ASO-TNF or Exo/2DG could attenuate NASH progression by up-regulating the expression of superoxide dismutase 1 (Sod1). Combined, our findings demonstrated that infusion of exosomes loaded with ASO-TNF or 2DG alleviated experimental steatohepatitis in murine models. Thus, infusion of exosomes loaded with anti-inflammatory agents holds promise as a potential therapeutic strategy for NASH treatment.

Hepatic HKDC1 Deletion Alleviates Western Diet-Induced MASH in Mice

The global prevalence of Metabolic dysfunction-associated steatohepatitis (MASH) has been rising sharply, closely mirroring the increasing rates of obesity and metabolic syndrome. MASH exhibits a strong sexual dimorphism where females are affected with more severe forms after menopause. Hexokinase domain-containing protein 1 (HKDC1) has recently been recognized for its role in liver diseases, where its expression is minimal under normal conditions but significantly increases in response to metabolic stressors like obesity and liver injury. This selective upregulation suggests HKDC1s potential specialization in hepatic glucose and lipid dysregulation, linking it closely to the progression of MASLD and MASH. This study aims to clarify the role of HKDC1 in Western diet-induced MASH in female mice by examining its impact on hepatic glucose and lipid metabolism, offering insights into its potential as a therapeutic target and addressing the need for sex-specific research in liver disease. This study reveals that HKDC1 expression is elevated in obese women with MASH and correlates with liver pathology. In a mouse model, liver-specific HKDC1 knockout (HKDC1LKO) protected against Western diet-induced obesity, glucose intolerance, and MASH features, including steatosis, inflammation, and fibrosis. Transcriptomic analysis showed that HKDC1 deletion reduced pro-inflammatory and pro-fibrotic gene expression, while gut microbiome analysis indicated a shift toward MASH-protective bacteria. These findings suggest that HKDC1 may exacerbate MASH progression through its role in metabolic and inflammatory pathways, making it a potential therapeutic target.

The deubiquitinase USP28 maintains the expression of PPARγ and its inactivation protects mice from diet-induced MASH and hepatocarcinoma

Metabolic dysfunction-associated steatohepatitis (MASH), a progressive form of metabolic dysfunction-associated fatty liver disease (MAFLD), is a leading cause of liver disease worldwide and can progress to cirrhosis and cancer. Despite its prevalence, the pathogenesis of MASH remains poorly understood, and there is only one U.S. Food and Drug Administration-approved treatment, highlighting the need for new therapeutic strategies. Peroxisome proliferator-activated receptor (PPAR)γ is activated in the liver under high-fat or obese conditions, promoting lipid storage and contributing to MASH progression. We found that USP28 expression is elevated in the livers of MAFLD/MASH patients. Through dietary induction, including a methionine-choline deficient (MCD) diet and a western diet (WD) combined with carbon tetrachloride (CCl4) injections, we established two severe mouse models of MASH to explore the role of USP28. Mechanistically, the hepatic deubiquitinase (DUB) USP28 directly binds to PPARγ, preventing its ubiquitination and subsequent degradation, thereby maintaining the integrity of the PPARγ signaling pathway. In the absence of Usp28 or if the DUB is inhibited, PPARγ is downregulated, and the PPAR signaling pathway is inhibited, enhancing cellular defenses against excess fat. Both genetic and pharmacological inactivation of Usp28 significantly reduced MASH severity induced by the MCD diet or WD-CCl4 regimen, as well as WD-CCl4-induced hepatocellular carcinoma in mice.

Picrosides-rich fraction from Picrorhiza kurroa attenuates steatohepatitis in zebrafish and mice by modulating lipid metabolism and inflammation

BACKGROUND

Non-alcoholic steatohepatitis (NASH) has become a serious public health concern with high global prevalence. The lack of safe and efficient treatment for the condition demands exploring new therapeutic solutions.

PURPOSE

In the present study, we investigated the protective efficacy of picrosides-rich fraction (PF) from Picrorhiza kurroa against steatohepatitis and revealed the molecular mechanism of action.

METHODS

PF was prepared and characterized using UPLC analysis. Initially, the efficacy of PF was studied on the zebrafish model of NASH. Further, a Methionine and Choline-Deficient (MCD) diet-induced NASH model in mice was employed to evaluate the hepatoprotective efficacy of PF by utilizing biochemical, histopathological and molecular studies.

RESULTS

The UPLC analysis revealed the presence of 29.11% and 29.86% picroside I and II in the PF, respectively. In the zebrafish model of NASH, PF treatment reduced the hepatic lipid accumulation and modulated the expressions of lipogenic, inflammatory, oxidative, and cellular stress genes. Further, in MCD diet-induced NASH in mice, PF treatment showed a significant improvement in body weights and serum liver injury markers. Reduced degenerative changes and fibrous tissue was observed in the PF-treated groups. The downregulated expression of Srebp1c, Cd36, Fas, Chrebp, Pparγ, and Hnf4α showed anti-lipogenic potential of PF treatment. NASH development followed oxidative stress, mitochondrial dysfunction, and inflammation in the liver of mice. However, PF treatment encouraged mitochondrial biogenesis by upregulating Pgc1α, Tfam, and Nrf2 expressions. The elevated levels of NFκB, TNFα, IL6, TGFβ, and αSMA were also restored by PF, advocating its anti-inflammatory and anti-fibrogenic effect.

CONCLUSION

The present study revealed that PF ameliorate the progression of NASH by increasing mitochondrial biogenesis and decreasing lipogenesis, hepatic inflammation, and fibrosis.

CD36 in liver diseases

Cluster of differentiation 36 (CD36) is a transmembrane glycoprotein with the ability to bind to multiple ligands and perform diverse functions. Through the recognition of long-chain fatty acids, proteins containing thrombospondin structural homology repeat domains such as thrombospondin-1, and molecules with molecular structures consistent with danger- or pathogen-associated molecular patterns, CD36 participates in various physiological and pathological processes of the body. CD36 is widely expressed in various cell types, including hepatocytes and KCs in the liver, where it plays a pivotal role in lipid metabolism, inflammation, and oxidative stress. Accumulating evidence suggests that CD36 plays a complex role in the development of nonalcoholic simple fatty liver disease and NASH and contributes to the pathogenesis of inflammatory liver injury, hepatitis B/hepatitis C, liver fibrosis, and liver cancer. This review summarizes the current understanding of the structural properties, expression patterns, and functional mechanisms of CD36 in the context of liver pathophysiology. Furthermore, the potential of CD36 as a therapeutic target for the prevention and treatment of liver diseases is highlighted.

Daphnetin ameliorates hepatic steatosis by suppressing peroxisome proliferator-activated receptor gamma (PPARG) in ob/ob mice

Non-alcoholic fatty liver disease (NAFLD) is the predominant metabolic liver disorder and currently lacks effective and safe pharmaceutical interventions. Daphnetin (DA), a natural coumarin derivative with anti-inflammatory and antioxidant activities, is a promising agent for NAFLD treatment. In this study, we evaluated the effects and mechanisms of DA on hepatic lipid metabolism in ob/ob mice. Our results showed that DA effectively ameliorates glucose metabolism and hepatic lipid accumulation in ob/ob mice. Metabolomics and RNA sequencing (RNA-seq), combined with GEO data analysis, suggest that DA primarily modulates the peroxisome proliferator-activated receptor gamma (PPARG) pathway, as validated in vivo in ob/ob mice. Mechanistically, DA selectively targets PPARG in hepatic cells by inhibiting PPARG promoter activity and downregulating its expression, resulting in decreased transcription of downstream lipid metabolism-related genes, including fatty acid binding protein 4 (Fabp4), cluster of differentiation 36 (Cd36), and fatty acid synthase (Fasn). This effect was abolished in PPARG-deficient HepG2 cells subjected to palmitic acid (PA) insult. Our findings provide evidence that DA acts as a selective suppressor of hepatic PPARG, suggesting an attractive strategy by targeting PPARG for the prevention of hepatic steatosis.

A novel fatty acid mimetic with pan-PPAR partial agonist activity inhibits diet-induced obesity and metabolic dysfunction-associated steatotic liver disease

OBJECTIVE

The prevalence of metabolic diseases is increasing globally at an alarming rate; thus, it is essential that effective, accessible, low-cost therapeutics are developed. Peroxisome proliferator-activated receptors (PPARs) are transcription factors that tightly regulate glucose homeostasis and lipid metabolism and are important drug targets for the treatment of type 2 diabetes and dyslipidemia. We previously identified LDT409, a fatty acid-like compound derived from cashew nut shell liquid, as a novel pan-active PPARα/γ/δ compound. Herein, we aimed to assess the efficacy of LDT409 in vivo and investigate the molecular mechanisms governing the actions of the fatty acid mimetic LDT409 in diet-induced obese mice.

METHODS

C57Bl/6 mice (6-11-month-old) were fed a chow or high fat diet (HFD) for 4 weeks; mice thereafter received once daily intraperitoneal injections of vehicle, 10 mg/kg Rosiglitazone, 40 mg/kg WY14643, or 40 mg/kg LDT409 for 18 days while continuing the HFD. During treatments, body weight, food intake, glucose and insulin tolerance, energy expenditure, and intestinal lipid absorption were measured. On day 18 of treatment, tissues and plasma were collected for histological, molecular, and biochemical analysis.

RESULTS

We found that treatment with LDT409 was effective at reversing HFD-induced obesity and associated metabolic abnormalities in mice. LDT409 lowered food intake and hyperlipidemia, while improving insulin tolerance. Despite being a substrate of both PPARα and PPARγ, LDT409 was crucial for promoting hepatic fatty acid oxidation and reducing hepatic steatosis in HFD-fed mice. We also highlighted a role for LDT409 in white and brown adipocytes in vitro and in vivo where it decreased fat accumulation, increased lipolysis, induced browning of WAT, and upregulated thermogenic gene Ucp1. Remarkably, LDT409 reversed HFD-induced weight gain back to chow-fed control levels. We determined that the LDT409-induced weight-loss was associated with a combination of increased energy expenditure (detectable before weight loss was apparent), decreased food intake, increased systemic fat utilization, and increased fecal lipid excretion in HFD-fed mice.

CONCLUSIONS

Collectively, LDT409 represents a fatty acid mimetic that generates a uniquely favorable metabolic response for the treatment of multiple abnormalities including obesity, dyslipidemia, metabolic dysfunction-associated steatotic liver disease, and diabetes. LDT409 is derived from a highly abundant natural product-based starting material and its development could be pursued as a therapeutic solution to the global metabolic health crisis.

Proanthocyanidin Alleviates Liver Ischemia/Reperfusion Injury by Suppressing Autophagy and Apoptosis via the PPARα/PGC1α Signaling Pathway

Background and Aims

Hepatic ischemia-reperfusion injury (IRI) is a common pathophysiological phenomenon in clinical practice, which usually occurs in liver transplantation, liver resection, severe trauma, and hemorrhagic shock. Proanthocyanidin (PC), exerted from various plants with antioxidant, antitumor, and antiaging activity, were administrated in our study to investigate the underlying mechanism of its protective function on IRI.

Methods

Two doses of PC (50 mg/kg, 100 mg/kg) were given to BALB/c mice by intragastric administration for 7 days before partial (70%) warm IR surgery. Serum and liver tissues were collected 2, 8, and 24 h after reperfusion for relevant experiments.

Results

The results of transaminase and hematoxylin and eosin staining indicated that PC pretreatment significantly alleviated IRI in mice. Serum total superoxide dismutase increased and malondialdehyde decreased in PC pretreatment groups. Enzyme-linked immunosorbent assays, western blotting, quantitative real-time polymerase chain reaction, and immunohistochemistry showed that inflammation, apoptosis, and autophagy in PC preprocessing groups were significantly inhibited and were dose-dependent. The protein, mRNA expression, and immunohistochemical staining results of peroxisome proliferator-activated receptor alpha (PPARα) and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) in the PC pretreatment groups were significantly upregulated compared with the IR group in a dose-dependent manner.

Conclusions

PC pretreatment suppressed inflammation, apoptosis, and autophagy via the PPAR-α signaling pathway to protect against IRI of the liver in mice.

The anti-fibrotic efficacy of adelmidrol depends on hepatic PPARγ levels

Adelmidrol, an anti-inflammatory small-molecule compound, can treat inflammatory diseases like arthritis and colitis in a PPARγ-dependent manner. Effective anti-inflammatory therapy is beneficial in delaying the progression of liver fibrosis. This study aimed to investigate the effect and underlying mechanisms of adelmidrol on hepatic fibrosis induced by CCl4 and CDAA-HFD. In the CCl4 model, adelmidrol (10 mg/kg) significantly reduced the incidence of liver cirrhosis from 76.5% to 38.9%, with a reduction of ALT, AST, and extracellular matrix deposition. RNA-seq revealed adelmidrol markedly inhibited the activation of hepatic scar-associated Trem2+ macrophages and PDGFRα+ stellate cells. Adelmidrol exhibited a limited anti-fibrotic effect in CDAA-HFD-induced fibrosis. Further, inconsistencies were observed in the expression trends in liver PPARγ in both models. CCl4 injury led to the continuous decrease in hepatic PPARγ levels, adelmidrol treatment up-regulated hepatic PPARγ expression and down-regulated the expression of pro-inflammatory factor NF-κB and pro-fibrotic factor TGF-β1. Adelmidrol also inhibited the activation of macrophages and HSCs in a PPARγ-dependent manner in vitro. GW9662, a specific PPARγ antagonist, counteracted the anti-fibrotic effect of adelmidrol. In CDAA-HFD-induced model, hepatic PPARγ expression gradually increased with the progress of modeling. Adelmidrol enhanced steatosis in hepatocytes by the activation of the PPARγ/CD36 pathway in the CDAA-HFD model and FFA-treated HepG2, showing a limited anti-fibrotic effect. GW9662 reversed the pro-steatotic effect of adelmidrol and improved fibrosis. The anti-fibrotic outcomes of adelmidrol were related to hepatic PPARγ levels, which depends on the synergistic effect of PPARγ agonism caused by adelmidrol on hepatocytes, macrophages, and HSCs in different pathological states.

Role of hepatic peroxisome proliferator-activated receptor γ in non-alcoholic fatty liver disease

Peroxisome proliferator-activated receptor γ (PPARγ) belongs to a family of nuclear receptors that could serve as lipid sensors. PPARγ is the target of a group of insulin sensitizers called thiazolidinediones (TZDs) which regulate the expression of genes involved in glucose and lipid metabolism as well as adipokines that regulate metabolic function in other tissues. Non-alcoholic fatty liver disease (NAFLD) has a high prevalence worldwide and is even higher in patients with obesity and insulin resistance. TZD-mediated activation of PPARγ could serve as a good treatment for NAFLD because TZDs have shown anti-fibrogenic and anti-inflammatory effectsin vitro and increase insulin sensitivity in peripheral tissues which improves liver pathology. However, mechanistic studies in mouse models suggest that the activation of PPARγ in hepatocytes might reduce or limit the therapeutic potential of TZD against NAFLD. In this review, we briefly describe the short history of PPAR isoforms, the relevance of their expression in different tissues, as well as the pathogenesis and potential therapeutics for NAFLD. We also discuss some evidence derived from mouse models that could be useful for endocrinologists to assess tissue-specific roles of PPARs, complement reverse endocrinology approaches, and understand the direct role that PPARγ has in hepatocytes and non-parenchymal cells.

Hepatocyte PPARγ contributes to the progression of non-alcoholic steatohepatitis in male and female obese mice

Non-alcoholic steatohepatitis (NASH) is associated with obesity and increased expression of hepatic peroxisome proliferator-activated receptor γ (PPARγ). However, the relevance of hepatocyte PPARγ in NASH associated with obesity is still poorly understood. In this study, hepatocyte PPARγ was knocked out (PpargΔHep) in male and female mice after the development of high-fat diet-induced obesity. The diet-induced obese mice were then maintained on their original diet or switched to a high fat, cholesterol, and fructose (HFCF) diet to induce NASH. Hepatic PPARγ expression was mostly derived from hepatocytes and increased by high fat diets. PpargΔHep reduced HFCF-induced NASH progression without altering steatosis, reduced the expression of key genes involved in hepatic fibrosis in HFCF-fed male and female mice, and decreased the area of collagen-stained fibrosis in the liver of HFCF-fed male mice. Moreover, transcriptomic and metabolomic data suggested that HFCF-diet regulated hepatic amino acid metabolism in a hepatocyte PPARγ-dependent manner. PpargΔHep increased betaine-homocysteine s-methyltransferase expression and reduced homocysteine levels in HFCF-fed male mice. In addition, in a cohort of 102 obese patients undergoing bariatric surgery with liver biopsies, 16 cases were scored with NASH and were associated with increased insulin resistance and hepatic PPARγ expression. Our study shows that hepatocyte PPARγ expression is associated with NASH in mice and humans. In male mice, hepatocyte PPARγ negatively regulates methionine metabolism and contributes to the progression of fibrosis.

Myeloid- and hepatocyte-specific deletion of group VIA calcium-independent phospholipase A2 leads to dichotomous opposing phenotypes during MCD diet-induced NASH

Polymorphisms of phospholipase A2VIA (iPLA2β or PLA2G6) are associated with body weights and blood C-reactive protein. The role of iPLA2β/PLA2G6 in non-alcoholic steatohepatitis (NASH) is still elusive because female iPla2β-null mice showed attenuated hepatic steatosis but exacerbated hepatic fibrosis after feeding with methionine- and choline-deficient diet (MCDD). Herein, female mice with myeloid- (MPla2g6^-/-) and hepatocyte- (LPla2g6^-/-) specific PLA2G6 deletion were generated and phenotyped after MCDD feeding. Without any effects on hepatic steatosis, MCDD-fed MPla2g6^-/- mice showed further exaggeration of liver inflammation and fibrosis as well as elevation of plasma TNFα, CCL2, and circulating monocytes. Bone-marrow-derived macrophages (BMDMs) from MPla2g6^-/- mice displayed upregulation of PPARγ and CEBPα proteins, and elevated release of IL6 and CXCL1 under LPS stimulation. LPS-stimulated BMDMs from MCDD-fed MPla2g6^-/- mice showed suppressed expression of M1 Tnfa and Il6, but marked upregulation of M2 Arg1, Chil3, IL10, and IL13 as well as chemokine receptors Ccr2 and Ccr5. This in vitro shift was associated with exaggeration of hepatic M1/M2 cytokines, chemokines/chemokine receptors, and fibrosis genes. Contrarily, MCDD-fed LPla2g6^-/- mice showed a complete protection which was associated with upregulation of Ppara/PPARα and attenuated expression of Pparg/PPARγ, fatty-acid uptake, triglyceride synthesis, and de novo lipogenesis genes. Interestingly, LPla2g6^-/- mice fed with chow or MCDD displayed an attenuation of blood monocytes and elevation of anti-inflammatory lipoxin A4 in plasma and liver. Thus, PLA2G6 inactivation specifically in myeloid cells and hepatocytes led to opposing phenotypes in female mice undergoing NASH. Hepatocyte-specific PLA2G6 inhibitors may be further developed for treatment of this disease.

Current insights in molecular characterization of non-alcoholic fatty liver disease and treatment

There is a continuously rising incidence of non-alcoholic fatty liver disease (NAFLD) around the world, which parallels the increasing incidence of metabolic diseases. NAFLD is a range of liver conditions that contains simple non-alcoholic fatty liver and advanced non-alcoholic steatohepatitis. In serious cases, NAFLD may develop into cirrhosis or even liver cancer. NAFLD has an intense relationship with metabolic syndrome, type 2 diabetes mellitus. It is known that gut microbiota, and functional molecules such as adenosine monophosphate-activated protein kinase JNK, and peroxisome proliferator-activated receptors (PPARs) in progressing and treating NAFLD. Traditionally, the conventional and effective therapeutic strategy is lifestyle intervention. Nowadays, new medicines targeting specific molecules, such as farnesoid X receptor, PPARs, and GLP-1 receptor, have been discovered and shown beneficial effects on patients with NAFLD. In this article, we focus on the molecular mechanisms and therapeutic approaches to NAFLD.

Rosiglitazone Requires Hepatocyte PPARγ Expression to Promote Steatosis in Male Mice With Diet-Induced Obesity

Thiazolidinediones (TZD) are peroxisome proliferator-activated receptor γ (PPARγ) agonists that may reduce hepatic steatosis through their effects in adipose tissue and therefore have been assessed as potential therapies to treat nonalcoholic fatty liver disease (NAFLD) in humans. However, some studies suggest that expression and activation of hepatocyte PPARγ promotes steatosis and that would limit the benefits of TZD as a NAFLD therapy. To further explore this possibility, we examined the impact of short-term rosiglitazone maleate treatment after the development of moderate or severe diet-induced obesity, in both control and adult-onset hepatocyte-specific PPARγ knockout (PpargΔHep) mice. Independent of the level of obesity and hepatic PPARγ expression, the TZD treatment enhanced insulin sensitivity, associated with an increase in white adipose tissue (WAT) fat accumulation, consistent with clinical observations. However, TZD treatment increased hepatic triglyceride content only in control mice with severe obesity. Under these conditions, PpargΔHep reduced diet-induced steatosis and prevented the steatogenic effects of short-term TZD treatment. In these mice, subcutaneous WAT was enlarged and associated with increased levels of adiponectin, while hepatic levels of phosphorylated adenosine 5'-monophosphate-activated protein kinase were also increased. In addition, in mice with severe obesity, the expression of hepatic Cd36, Cidea, Cidec, Fabp4, Fasn, and Scd-1 was increased by TZD in a PPARγ-dependent manner. Taken together, these results demonstrate that hepatocyte PPARγ expression offsets the antisteatogenic actions of TZD in mice with severe obesity. Therefore, in obese and insulin resistant humans, TZD-mediated activation of hepatocyte PPARγ may limit the therapeutic potential of TZD to treat NAFLD.

The Agonists of Peroxisome Proliferator-Activated Receptor-γ for Liver Fibrosis

Liver fibrosis is a common link in the transformation of acute and chronic liver diseases to cirrhosis. It is of great clinical significance to study the factors associated with the induction of liver fibrosis and elucidate the method of reversal. Peroxisome proliferator-activated receptors (PPARs) are a class of nuclear transcription factors that can be activated by peroxisome proliferators. PPARs play an important role in fibrosis of various organs, especially the liver, by regulating downstream targeted pathways, such as TGF-β, MAPKs, and NF-κB p65. In recent years, the development and screening of PPAR-γ ligands have become a focus of research. The PPAR-γ ligands include synthetic hypolipidemic and antidiabetic drugs. In addition, microRNAs, lncRNAs, circRNAs and nano new drugs have attracted research interest. In this paper, the research progress of PPAR-γ in the pathogenesis and treatment of liver fibrosis was discussed based on the relevant literature in recent years.

Crosstalk between PPARs and gut microbiota in NAFLD

Nonalcoholic fatty liver disease (NAFLD) has become the most common liver disorder in both China and worldwide. It ranges from simple steatosis and progresses over time to nonalcoholic steatohepatitis (NASH), advanced liver fibrosis, cirrhosis, or hepatocellular carcinoma(HCC). Furthermore, NAFLD and its complications impose a huge health burden to society. The microbiota is widely connected and plays an active role in human physiology and pathology, and it is a hidden 'organ' in determining the state of the host, in terms of homeostasis, or disease. Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptorsuperfamily and can regulate multiple pathways involved in metabolism, and serve as effective targets forthe treatment of many types of metabolic syndromes, including NAFLD. The purpose of this review is to integrate related articles on gut microbiota, PPARs and NAFLD, and present a balanced overview on how the microbiota can possibly influence the development of NAFLD through PPARs.

Hepatocyte-Specific Loss of PPARγ Protects Mice From NASH and Increases the Therapeutic Effects of Rosiglitazone in the Liver

BACKGROUND & AIMS

Nonalcoholic steatohepatitis (NASH) is commonly observed in patients with type 2 diabetes, and thiazolidinediones (TZD) are considered a potential therapy for NASH. Although TZD increase insulin sensitivity and partially reduce steatosis and alanine aminotransferase, the efficacy of TZD on resolving liver pathology is limited. In fact, TZD may activate peroxisome proliferator-activated receptor gamma (PPARγ) in hepatocytes and promote steatosis. Therefore, we assessed the role that hepatocyte-specific PPARγ plays in the development of NASH, and how it alters the therapeutic effects of TZD on the liver of mice with diet-induced NASH.

METHODS

Hepatocyte-specific PPARγ expression was knocked out in adult mice before and after the development of NASH induced with a high fat, cholesterol, and fructose (HFCF) diet.

RESULTS

HFCF diet increased PPARγ expression in hepatocytes, and rosiglitazone further activated PPARγ in hepatocytes of HFCF-fed mice in vivo and in vitro. Hepatocyte-specific loss of PPARγ reduced the progression of HFCF-induced NASH in male mice and increased the benefits derived from the effects of TZD on extrahepatic tissues and non-parenchymal cells. RNAseq and metabolomics indicated that HFCF diet promoted inflammation and fibrogenesis in a hepatocyte PPARγ-dependent manner and was associated with dysregulation of hepatic metabolism. Specifically, hepatocyte-specific loss of PPARγ plays a positive role in the regulation of methionine metabolism, and that could reduce the progression of NASH.

CONCLUSIONS

Because of the negative effect of hepatocyte PPARγ in NASH, inhibition of mechanisms promoted by endogenous PPARγ in hepatocytes may represent a novel strategy that increases the efficiency of therapies for NAFLD.

GH directly inhibits steatosis and liver injury in a sex-dependent and IGF1-independent manner

A reduction in hepatocyte growth hormone (GH)-signaling promotes non-alcoholic fatty liver disease (NAFLD). However, debate remains as to the relative contribution of the direct effects of GH on hepatocyte function vs indirect effects, via alterations in insulin-like growth factor 1 (IGF1). To isolate the role of hepatocyte GH receptor (GHR) signaling, independent of changes in IGF1, mice with adult-onset, hepatocyte-specific GHR knockdown (aHepGHRkd) were treated with a vector expressing rat IGF1 targeted specifically to hepatocytes. Compared to GHR-intact mice, aHepGHRkd reduced circulating IGF1 and elevated GH. In male aHepGHRkd, the shift in IGF1/GH did not alter plasma glucose or non-esterified fatty acids (NEFA), but was associated with increased insulin, enhanced systemic lipid oxidation and reduced white adipose tissue (WAT) mass. Livers of male aHepGHRkd exhibited steatosis associated with increased de novo lipogenesis, hepatocyte ballooning and inflammation. In female aHepGHRkd, hepatic GHR protein levels were not detectable, but moderate levels of IGF1 were maintained, with minimal alterations in systemic metabolism and no evidence of steatosis. Reconstitution of hepatocyte IGF1 in male aHepGHRkd lowered GH and normalized insulin, whole body lipid utilization and WAT mass. However, IGF1 reconstitution did not reduce steatosis or eliminate liver injury. RNAseq analysis showed IGF1 reconstitution did not impact aHepGHRkd-induced changes in liver gene expression, despite changes in systemic metabolism. These results demonstrate the impact of aHepGHRkd is sexually dimorphic and the steatosis and liver injury observed in male aHepGHRkd mice is autonomous of IGF1, suggesting GH acts directly on the adult hepatocyte to control NAFLD progression.

Bergenin Attenuates Hepatic Fibrosis by Regulating Autophagy Mediated by the PPAR-γ/TGF-β Pathway

Liver fibrosis is a pathological process involving diffuse extracellular matrix (ECM) deposition in the liver. It is typical of many chronic liver diseases, including cirrhosis, and effective drugs are needed. In this study, we explored the protective effect of bergenin on liver fibrosis induced by carbon tetrachloride and bile duct ligation. A variety of molecular biological methods (qRT-PCR, western blotting, and immunohistochemistry) were employed to confirm the increased degree of hepatocyte injury and ECM formation in the disease model, consistent with autophagy and activation of the TGF-β pathway. Bergenin activated PPAR-γ and inhibited TGF-β and autophagy and decreased liver fibrosis by inhibiting hepatocyte necrosis and ECM formation in a dose-dependent manner. The results suggest that bergenin may be a promising drug candidate for the treatment of liver fibrosis.