PI-3 K/AKT and ERK signaling pathways mediate leptin-induced inhibition of PPARgamma gene expression in primary rat hepatic stellate cells. Mol Cell Biochem. 2009;325:131-139. [PMID: 19191008 DOI: 10.1007/s11010-009-0027-3]

Harnessing nuclear receptors to modulate hepatic stellate cell activation for liver fibrosis resolution

With the recent approval of Resmetirom as the first drug targeting nuclear receptors for metabolic dysfunction-associated steatohepatitis (MASH), there is promising way to treat MASH-associated liver fibrosis. However, liver fibrosis can arise from various pathogenic factors, and effective treatments for fibrosis due to other causes remain elusive. The activation of hepatic stellate cells (HSCs) represents a central link in the pathogenesis of hepatic fibrosis. Therefore, harnessing nuclear receptors to modulate HSC activation may be an effective approach to resolving the complex liver fibrosis caused by various factors. In this comprehensive review, we systematically explore the structure and physiological functions of nuclear receptors, shedding light on their multifaceted roles in HSC activation. Recent advancements in drug development targeting nuclear receptors are discussed, providing insights into their potential as rational and effective therapeutic targets for modulating HSC activation in the context of liver fibrosis. By elucidating the intricate interplay between nuclear receptors and HSC activation, this review contributes to the discovery of new nuclear receptor targets in HSCs for resolving hepatic fibrosis.

Genomics and metabolomics of early-stage thioacetamide-induced liver injury: An interspecies study between guinea pig and rat

To study the complex processes involved in liver injuries, researchers rely on animal investigations, using chemically or surgically induced liver injuries, to extrapolate findings and infer human health risks. However, this presents obvious challenges in performing a detailed comparison and validation between the highly controlled animal models and development of liver injuries in humans. Furthermore, it is not clear whether there are species-dependent and -independent molecular initiating events or processes that cause liver injury before they eventually lead to end-stage liver disease. Here, we present a side-by-side study of rats and guinea pigs using thioacetamide to examine the similarities between early molecular initiating events during an acute-phase liver injury. We exposed Sprague Dawley rats and Hartley guinea pigs to a single dose of 25 or 100 mg/kg thioacetamide and collected blood plasma for metabolomic analysis and liver tissue for RNA-sequencing. The subsequent toxicogenomic analysis identified consistent liver injury trends in both genomic and metabolomic data within 24 and 33 h after thioacetamide exposure in rats and guinea pigs, respectively. In particular, we found species similarities in the key injury phenotypes of inflammation and fibrogenesis in our gene module analysis for liver injury phenotypes. We identified expression of several common genes (e.g., SPP1, TNSF18, SERPINE1, CLDN4, TIMP1, CD44, and LGALS3), activation of injury-specific KEGG pathways, and alteration of plasma metabolites involved in amino acid and bile acid metabolism as some of the key molecular processes that changed early upon thioacetamide exposure and could play a major role in the initiation of acute liver injury.

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.

Gene Expression and Histochemical Analyses in the Fatty Livers of Rats Fed a Histidine-Excess Diet

Triglyceride (TG) and cholesterol accumulation are known to occur in the liver of rats fed a histidine-excess (5%) diet, but there are few studies reporting histochemical and molecular biological analyses of the rat liver. The aim of this study was to elucidate the molecular basis of this lipid-accumulation mechanism. Lipid accumulations, tissue section images, and gene expression levels were compared in the livers of rats fed a control or histidine-excess diet for 5 wk (n=8/group). Serum levels of TGs, free fatty acids, total cholesterol, high-density lipoprotein cholesterol, glucose, albumin, and the enzyme activities of aspartate aminotransferase and alanine aminotransferase were also analyzed. In the livers of rats fed a histidine-excess diet, histochemical analyses showed what appeared to be a preliminary stage of nonalcoholic fatty liver, characterized by lipid accumulation around the central vein area and minor fibrosis. However, there were no changes in serum TG or free fatty acid levels. Quantitative PCR analyses showed the up-regulation of FAT/CD36, which is related to the uptake of fatty acids into cells, and the downregulation of two apolipoprotein genes, ApoC3 and ApoE. The mRNA levels of PPARγ, LXRα, and AMPKα in the liver were also reduced by excess histidine intake. The results of this study suggest that steatosis caused by excess histidine intake may be the result of an imbalance between lipid transport from the liver and the uptake of free fatty acids into hepatocytes.

PNPLA3 I148M Up-Regulates Hedgehog and Yap Signaling in Human Hepatic Stellate Cells

Liver fibrosis represents the wound healing response to sustained hepatic injury with activation of hepatic stellate cells (HSCs). The I148M variant of the PNPLA3 gene represents a risk factor for development of severe liver fibrosis. Activated HSCs carrying the I148M variant display exacerbated pro-inflammatory and pro-fibrogenic features. We aimed to examine whether the I148M variant may impair Hedgehog and Yap signaling, as key pathways implicated in the control of energy expenditure and maintenance of myofibroblastic traits. First, we show that TGF-β rapidly up-regulated the PNPLA3 transcript and protein and Yap/Hedgehog target gene expression. In addition, HSCs overexpressing PNPLA3 I148M boosted anaerobic glycolysis, as supported by higher lactate release and decreased phosphorylation of the energy sensor AMPK. These cells displayed higher Yap and Hedgehog signaling, due to accumulation of total Yap protein, Yap promoter activity and increased downstream targets expression, compared to WT cells. HSCs exposed to TGF-β and leptin rapidly increased total Yap, together with a reduction in its inhibited form, phosphorylated Yap. In line, Yap-specific inhibitor Verteporfin strongly abolished Yap-mediated genes expression, at baseline as well as after TGF-β and leptin treatments in HSCs with I148M PNPLA3. Finally, Yap transcriptional activity was strongly reduced by a combination of Verteporfin and Rosiglitazone, a PPARγ synthetic agonist. In conclusion, HSCs carrying the PNPLA3 variant show activated Yap/Hedgehog pathways, resulting in altered anaerobic glycolysis and enhanced synthesis of Hedgehog markers and sustained Yap signaling. TGF-β and leptin exacerbate Yap/Hedgehog-related fibrogenic genes expression, while Yap inhibitors and PPARγ agonists abrogate these effects in PNPLA3 I148M carrying HSCs.

Leptin promotes methionine adenosyltransferase 2A expression in hepatic stellate cells by the downregulation of E2F-4 via the β-catenin pathway

Most obese patients develop hyperleptinaemia. Leptin, mainly produced by adipocytes, demonstrates a promotional role in liver fibrosis. Hepatic stellate cell (HSC) activation, a key step in liver fibrogenesis, requires global reprogramming of gene expression. The remodeling of DNA methylation is a mechanism of the epigenetic regulation of gene expression. The biosynthesis of S-adenosylmethionine, a principle biological methyl donor, is catalyzed by methionine adenosyltransferase (MAT) such as MATⅡ which has been shown to promote HSC activation in vitro. This study was mainly aimed to determine the effect of leptin on MAT2A expression (the catalytic subunit of MATⅡ) in HSCs. Results showed that MAT2A knockdown reduced leptin-induced HSC activation and liver fibrosis in the leptin-deficient mouse model. Leptin promoted MAT2A expression in HSCs and increased MAT2A promoter activity. The axis of the β-catenin pathway/E2F-4 mediated the effect of leptin on MAT2A expression. Leptin-induced β-catenin signaling reduced E2F-4 expression and thus abated E2F-4 binding to MAT2A promoter at a site around -2779 bp, leading to an increase in the MAT2A promoter activity. These data might shed more light on the mechanisms responsible for liver fibrogenesis in obese patients with hyperleptinaemia.

The protective effect of Zataria multiflora Boiss essential oil on CCl4 induced liver fibrosis in rats

Activation of hepatic stellate cells by free radicals is an initial step in the development of liver fibrosis. Zataria multiflora Boiss (ZM) essential oil as a natural product has antioxidant activity and maybe a suitable candidate for treatment or prevention of the disease. Thus, this study aims to evaluate the protective effect of ZM oil in CCl₄ induced liver fibrosis. Male rats were divided into 5 groups, group C: control rats; CO: vehicle control group; CE: rats that received essential oil (500 µl/kg); F: fibrosis group, rat were intraperitoneally injected with CCl₄ (1 mL/kg); FE: fibrosis rats that received both CCl₄ and ZM essential oil as mentioned above. At the end of the 11th week, serum samples and liver tissues were collected for the evaluation of fibrosis markers, liver enzymes, oxidative stress parameters and histopathological studies. The results showed a significant increase in the activity of serum AST, ALT, total bilirubin, TGF-β1, hyaluronan, and hydroxyproline levels in serum and liver tissues in F group. Also, an abnormality in lipid profile and the existence of oxidative stress was found in serum and liver tissues in F group compared to the control groups. Our study showed that ZM essential oil could ameliorate mentioned parameters. Histopathological examinations confirmed the results of biochemical evaluations.

Respective roles of the mitogen-activated protein kinase (MAPK) family members in pancreatic stellate cell activation induced by transforming growth factor-β1 (TGF-β1)

Activated pancreatic stellate cells (PSCs) play a crucial role in the progression of pancreatic fibrosis. Transforming growth factor-β (TGF-β) is one of the strongest stimulator inducing fibrosis. The mitogen-activated protein kinase (MAPK) proteins (including ERK, JNK and p38 MAPK) are known to contribute to PSC activation and pancreatic fibrosis. Previous studies have identified PSC activation induced by TGF-β1 is related to MAPK pathway, but the respective role of MAPK family members in PSC activation still unclear, and which family member may be the key mediator in mice PSC activation still controversial. In this study, we investigated the influence of different MAPK family member (JNK, ERK, and p38 MAPK) on mice PSC activation using an in vivo and in vitro model. The results showed p-JNK, p-ERK and p-p38 MAPK were all over-expressed in CP group, and p-JNK, p-ERK, and p-p38 MAPK were co-expressed with activated PSC. In vitro, TGF-β1 induced JNK and ERK over-expression in PSCs. In contrast, p38 MAPK expression in PSC showed only a very weak increase. JNK- and ERK-specific inhibitors inhibited FN and α-SMA mRNA expression in PSCs, and a p38 MAPK inhibitor had no effect on PSC activation. These findings indicate that JNK and ERK were directly involved in the PSCs activation induced by TGF-β1 and the development of pancreatic fibrosis. p38 MAPK participate in the progression of CP, but it does not respond to TGF-β1 directly and may not be regarded as the target of TGF-β1 induced PSC activation.

Leptin up-regulates microRNA-27a/b-3p level in hepatic stellate cells

Obese patients, often accompanied by hyperleptinemia, are prone to liver fibrogenesis. Leptin is an adipocyte-derived hormone and plays a promotion role in liver fibrosis. Sterol regulatory element binding protein-1c (SREBP1c) exerts a crucial role in inhibiting hepatic stellate cell (HSC) activation, a key step in liver fibrogenesis. Our previous studies indicated that leptin inhibited SREBP1c expression, contributing to leptin-induced HSC activation and liver fibrosis. microRNAs (miR) have emerged as important layers of regulatory control and regulate gene expression, and are implicated in numerous diseases. The present study revealed leptin up-regulation of miR-27a/b-3p levels in HSCs in vitro and in vivo. Three signaling pathways were required for leptin regulation of miR-27a/b-3p levels. miR-27a/b-3p could reduce SREBP1c and liver x receptor α (LXRα) levels, increased α-smooth muscle actin (α-SMA, a marker for HSC activation) and α1(I)collagen levels in cultured HSCs. miR-27a/b-3p regulation of SREBP1c and LXRα were independent of 3'-untranslated region of SREBP1c and LXRα mRNA. In vivo experiments further demonstrated the miR-27a/b-3p involved in leptin-associated decrease in SREBP1 level in HSCs, HSC activation, and liver fibrosis. These data might have potential implications for our understanding of molecular mechanisms underlying leptin roles in liver fibrogenesis of obese patients with hyperleptinaemia.

Egr-1 mediates leptin-induced PPARγ reduction and proliferation of pulmonary artery smooth muscle cells

Loss of peroxisome proliferator-activated receptor γ (PPARγ) has been found to contribute to pulmonary artery smooth muscle cell (PASMC) proliferation and pulmonary arterial remodeling therefore the development of pulmonary hypertension (PH). Yet, the molecular mechanisms underlying PPARγ reduction in PASMC remain poorly understood. Here, we demonstrated that leptin dose- and time-dependently inducued PPARγ down-regulation and proliferation of primary cultured rat PASMC, this was accompanied with the activation of extracellular regulated kinase1/2 (ERK1/2) signaling pathway and subsequent induction of early growth response-1 (Egr-1) expression. The presence of MEK inhibitors U0126 or PD98059, or prior silencing Egr-1 with small interfering RNA suppressed leptin-induced PPARγ reduction. In addition, activation of PPARγ by pioglitazone or targeting ERK1/2/Egr-1 suppressed leptin-induced PASMC proliferation. Taken together, our study indicates that ERK1/2 signaling pathway-mediated leptin-induced PPARγ reduction and PASMC proliferation through up-regulation of Egr-1 and suggests that targeting leptin/ERK1/2/Egr-1 pathway might have potential value in ameliorating vascular remodeling and benefit PH.

Serum matrix metalloproteinase-1 level represents disease activity as opposed to fibrosis in patients with histologically proven nonalcoholic steatohepatitis

Background/Aims

Nonalcoholic steatohepatitis (NASH) is prevalent in both economically developed and developing countries. Twenty percent of NASH progresses to cirrhosis with/without hepatocellular carcinoma, and there is an urgent need to find biomarkers for early diagnosis and monitoring progression of the disease. Using immunohistochemical and immunoelectron microscopic examination we previously reported that expression of matrix metalloproteinase-1 (MMP-1) increased in monocytes, Kupffer cells and hepatic stellate cells in early stage NASH. The present study investigated whether serum MMP-1 levels reflect disease activity and pharmaceutical effects in NASH patients.

Methods

We measured the serum levels of MMPs, tissue inhibitors of metalloproteinases (TIMPs), and several cytokines/chemokines in patients with histologically proven early and advanced stages of NASH and compared them with those in healthy controls.

Results

Serum MMP-1 levels in stage 1 fibrosis, but not in the more advanced fibrosis stages, were significantly higher than in healthy controls (P=0.019). There was no correlation between serum MMP-1 level and fibrosis stage. Serum MMP- 1 levels in NASH patients represented disease activity estimated by serum aminotransferase values during the follow-up period. In contrast, MMP-2, MMP-9 and TIMPs did not change with disease activity. Consistent with the finding that MMP-1 is expressed predominantly in monocytes and Kupffer cells, serum levels of monocyte chemotactic protein-1 and granulocyte-colony stimulating factor were significantly increased in NASH with stage 1 fibrosis.

Conclusions

These results suggest that serum MMP-1 levels represent disease activity and may serve as a potential biomarker for monitoring the progression of NASH.

Leptin reduces microRNA-122 level in hepatic stellate cells in vitro and in vivo

Obese patients, often accompanied by hyperleptinemia, are more likely to develop liver fibrosis. Leptin, an adipocyte-derived hormone, augments inflammatory in liver and promotes hepatic stellate cell (HSC) activation (a key step for liver fibrogenesis) and liver fibrosis. microRNA-122 (miR-122) is the most abundant liver-specific miRNA and can attenuate liver fibrosis. This study examined the effect of leptin on miR-122 level in HSCs in vivo and in vitro. Results demonstrated that leptin reduced the levels of both miR-122 (mature miR-122) and primary miR-122 (pri-miR-122). The effects of leptin on the levels of miR-122 and pri-miR-122 were through at least hedgehog pathway. Leptin-induced decrease in sterol regulatory element-binding protein-1c (SREBP-1c) has been shown to contribute to leptin-induced HSC activation. We revealed a mutual promotional effect between SREBP-1c and miR-122. Further experiments indicated that miR-122 inhibited leptin-induced liver fibrosis in leptin-deficient mouse model. These data have potential implications for clarifying the mechanisms of hepatic fibrogenesis associated with elevated leptin level in human such as obese patients.

GATA binding protein 3 is correlated with leptin regulation of PPARγ1 in hepatic stellate cells

Accumulating evidence reveals that hormone leptin, mainly produced by adipocyte, plays a unique role in promotion of liver fibrosis. Hepatic stellate cell (HSC) activation is a key step in liver fibrosis and peroxisome‐proliferator activated receptor γ (PPARγ) exerts a crucial role in inhibition of HSC activation. Our previous researches demonstrated that leptin reduced PPARγ1 (a major subtype of PPARγ in HSCs) expression through GATA binding protein 2 (GATA2) binding to a site around −2323 in PPARγ1 promoter. The present researches aimed to examine the effect of GATA3 on leptin‐induced inhibition of PPARγ1 and elucidate the relationship between GATA3 and GATA2. Gene expressions were analysed by real‐time PCR, western blot, luciferase assay and immunostaining. C57BL/6J ob/ob mouse model of thioacetamide‐induced liver injury was used in vivo. Results demonstrate that leptin significantly induces GATA3 expression in HSCs by multiple signalling pathways including NADPH oxidase pathway. There exist crosstalks between NADPH oxidase pathway and the other pathways. GATA3 can bind to GATA2‐binding site in PPARγ1 promoter and interacts with GATA2, contributing to leptin inhibition of PPARγ1 expression in HSCs. These data demonstrated novel molecular events for leptin inhibition of PPARγ1 expression in HSCs and thus might have potential implications for clarifying the detailed mechanisms underlying liver fibrosis in diseases in which circulating leptin levels are elevated such as non‐alcoholic steatohepatitis in obese patients.

Sex-determining region Y-box 9 acts downstream of NADPH oxidase to influence the effect of leptin on PPARγ1 expression in hepatic stellate cells

Leptin, an adipocyte-derived hormone, promotes liver fibrogenesis and inhibits the expression of peroxisome-proliferator activated receptor γ (PPARγ), a key transcription factor in inhibition of hepatic stellate cell (HSC) activation, in HSCs. This research aimed to further investigate the mechanisms underlying leptin regulation of PPARγ1 in HSCs in vivo and in vitro. Results demonstrated that sex-determining region Y-box 9 (Sox9) could bind to a site around -2275 within leptin response region of PPARγ1 promoter and inhibited PPARγ1 expression. Sox9 upregulated the expressions of α1(I)collagen and alpha-smooth muscle actin in HSCs. Leptin stimulated Sox9 expression and Sox9 binding to PPARγ1 promoter. The signaling pathways of NADPH oxidase, β-catenin, and delta-like homolog1 (DLK1) mediated leptin upregulation of Sox9 expression. Moreover, there existed crosstalk between NADPH oxidase pathway and β-catenin or DLK1 signaling pathway. Human liver specimens of cirrhosis were shown to be of a large number of the positive HSCs for p47phox (playing a central role in NADPH oxidase activity), 4-hydroxynonenal (a lipid peroxidation product), Sox9, and α-smooth muscle actin whereas PPARγ-positive HSCs were rarely detected. These results might deepen understanding of the molecular mechanisms for leptin inhibition of PPARγ1 expression in HSCs and for the liver fibrosis associated with leptin.

Adipocytokines and hepatic fibrosis

Obesity and metabolic syndrome pose significant risk for the progression of many types of chronic illness, including liver disease. Hormones released from adipocytes, adipocytokines, associated with obesity and metabolic syndrome, have been shown to control hepatic inflammation and fibrosis. Hepatic fibrosis is the final common pathway that can result in cirrhosis, and can ultimately require liver transplantation. Initially, two key adipocytokines, leptin and adiponectin, appeared to control many fundamental aspects of the cell and molecular biology related to hepatic fibrosis and its resolution. Leptin appears to act as a profibrogenic molecule, while adiponectin has strong-antifibrotic properties. In this review, we emphasize pertinent data associated with these and other recently discovered adipocytokines that may drive or halt the fibrogenic response in the liver.

Hepatic stellate cells activated by acidic tumor microenvironment promote the metastasis of hepatocellular carcinoma via osteopontin

Extracellular pH of solid tumor is generally acidic due to excessive glycolysis and poor perfusion. But whether acidic tumor microenvironment influenced the stromal cells infiltrating in tumor remains unknown. As the predominant progenitor of stromal cells in liver, the number of activated hepatic stellate cells (HSCs) was found positively correlated to the acidification level in the tumor tissues of HCC patients in our study. Whereas, in vitro acidic culture condition and in vivo co-implanting xenograft model were adopted to study the response of HSCs and its influence on HCC progression. HSCs were activated under acidic culture condition depending on the phosphorylation of cellular signal-regulated kinase (ERK). Acidity-activated HSCs promoted HCC metastasis in vitro and in vivo. Osteopontin (OPN) excretion from HSCs was increased under acidic condition and proved to promote the migration of HCC cells. Furthermore, the expression level of OPN was significantly associated with myofibroblasts and the combination of α-SMA with OPN was a powerful predictor for poor prognosis of HCC patients. Activation of HSCs in acidic tumor microenvironment represents a novel mechanism for HCC metastasis and provides a potential therapeutic strategy for HCC.

Use of mesenchymal stem cells to treat liver fibrosis: Current situation and future prospects

Progressive liver fibrosis is a major health issue for which no effective treatment is available, leading to cirrhosis and orthotopic liver transplantation. However, organ shortage is a reality. Hence, there is an urgent need to find alternative therapeutic strategies. Cell-based therapy using mesenchymal stem cells (MSCs) may represent an attractive therapeutic option, based on their immunomodulatory properties, their potential to differentiate into hepatocytes, allowing the replacement of damaged hepatocytes, their potential to promote residual hepatocytes regeneration and their capacity to inhibit hepatic stellate cell activation or induce their apoptosis, particularly via paracrine mechanisms. The current review will highlight recent findings regarding the input of MSC-based therapy for the treatment of liver fibrosis, from in vitro studies to pre-clinical and clinical trials. Several studies have shown the ability of MSCs to reduce liver fibrosis and improve liver function. However, despite these promising results, some limitations need to be considered. Future prospects will also be discussed in this review.

Curcumin regulates peroxisome proliferator-activated receptor-γ coactivator-1α expression by AMPK pathway in hepatic stellate cells in vitro

Curcumin exerts an inhibitory effect on hepatic stellate cell (HSC) activation, a key step for liver fibrogenesis, and on liver fibrosis by up-regulation of peroxisome proliferator-activated receptor-γ (PPARγ) expression. PPARγ plays a crucial role in suppression of HSC activation. Peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) functions as a co-activator for PPARγ. Therefore, researches on the effect of curcumin on PGC-1α might contribute to understanding of the mechanisms underlying curcumin inhibition of HSC activation and liver fibrosis through PPARγ. The present study aimed to investigate the effect of curcumin on PGC-1α expression in HSCs in vitro and examine the underlying molecular mechanisms by western blot, reat-time PCR, and transfection. Our results showed that curcumin stimulation increased PGC-1α expression and the effects of curcumin on PGC-1α expression were correlated with the activation of adenosine monophosphate-activated protein kinase (AMPK). Curcumin increased superoxide dimutase-2 (SOD2) transcription and activity by AMPK/PGC-1α axis. Moreover, PGC-1α was demonstrated to inhibit α1(I) collagen (a marker for liver fibrosis) transcription in cultured HSCs. These results demonstrated the promotion effect of curcumin on PGC-1α expression through AMPK pathway, which led to the increases in PPARγ activity and in SOD-2 transcription and activity. These data might suggest a possible new explanation for the inhibitory effect of curcumin on HSC activation and on liver fibrogenesis.

High-fat diet-induced changes in liver thioredoxin and thioredoxin reductase as a novel feature of insulin resistance

High-fat diet (HFD) can induce oxidative stress. Thioredoxin (Trx) and thioredoxin reductase (TrxR) are critical antioxidant proteins but how they are affected by HFD remains unclear. Using HFD-induced insulin-resistant mouse model, we show here that liver Trx and TrxR are significantly decreased, but, remarkably, the degree of their S-acylation is increased after consuming HFD. These HFD-induced changes in Trx/TrxR may reflect abnormalities of lipid metabolism and insulin signaling transduction. HFD-driven accumulation of 4-hydroxynonenal is another potential mechanism behind inactivation and decreased expression of Trx/TrxR. Thus, we propose HFD-induced impairment of liver Trx/TrxR as major contributor to oxidative stress and as a novel feature of insulin resistance.

GATA binding protein 2 mediates leptin inhibition of PPARγ1 expression in hepatic stellate cells and contributes to hepatic stellate cell activation

Hepatic stellate cell (HSC) activation is a crucial step in the development of liver fibrosis. Peroxisome-proliferator activated receptor γ (PPARγ) exerts a key role in the inhibition of HSC activation. Leptin reduces PPARγ expression in HSCs and plays a unique role in promoting liver fibrosis. The present studies aimed to investigate the mechanisms underlying leptin regulation of PPARγ1 (a major subtype of PPARγ) in HSCs in vivo and in vitro. Results revealed a leptin response region in mouse PPARγ1 promoter and indicated that the region included a GATA binding protein binding site around position -2323. GATA binding protein-2 (GATA-2) could bind to the site and inhibit PPARγ1 promoter activity in HSCs. Leptin induced GATA-2 expression in HSCs in vitro and in vivo. GATA-2 mediated leptin inhibition of PPARγ1 expression by its binding site in PPARγ1 promoter in HSCs and GATA-2 promoted HSC activation. Leptin upregulated GATA-2 expression through β-catenin and sonic hedgehog pathways in HSCs. Leptin-induced increase in GATA-2 was accompanied by the decrease in PPARγ expression in HSCs and by the increase in the activated HSC number and liver fibrosis in vivo. Our data might suggest a possible new explanation for the promotion effect of leptin on liver fibrogenesis.

The β-catenin pathway contributes to the effects of leptin on SREBP-1c expression in rat hepatic stellate cells and liver fibrosis

BACKGROUND AND PURPOSE

Liver fibrosis is commonly associated with obesity and most obese patients develop hyperleptinaemia. The adipocytokine leptin has a unique role in the development of liver fibrosis. Activation of hepatic stellate cells (HSCs) is a key step in hepatic fibrogenesis and sterol regulatory element-binding protein-1c (SREBP-1c) can inhibit HSC activation. We have shown that leptin strongly inhibits SREBP-1c expression in rat HSCs. Hence, we aimed to clarify whether the β-catenin pathway, the crucial negative regulator of adipocyte differentiation, mediates the effects of leptin on SREBP-1c expression in HSCs and in mouse liver fibrosis.

EXPERIMENTAL APPROACH

HSCs were prepared from rats and mice. Gene expressions were analysed by real-time PCR, Western blot analysis, immunostaining and transient transfection assays.

KEY RESULTS

Leptin increased β-catenin protein but not mRNA levels in cultured HSCs. Leptin induced phosphorylation of glycogen synthase kinase-3β at Ser(9) and subsequent stabilization of β-catenin protein was mediated, at least in part, by ERK and p38 MAPK pathways. The leptin-induced β-catenin pathway reduced SREBP-1c expression and activity but did not affect protein levels of key regulators controlling SREBP-1c activity, and was not involved in leptin inhibition of liver X receptor α. In a mouse model of liver injury, the β-catenin pathway was shown to be involved in leptin-induced liver fibrosis.

CONCLUSIONS AND IMPLICATIONS

The β-catenin pathway contributes to leptin regulation of SREBP-1c expression in HSCs and leptin-induced liver fibrosis in mice. These results have potential implications for clarifying the mechanisms of liver fibrogenesis associated with elevated leptin levels.

Chronic hepatitis C and liver fibrosis

Chronic infection with hepatitis C virus (HCV) is a leading cause of liver-related morbidity and mortality worldwide and predisposes to liver fibrosis and end-stage liver complications. Liver fibrosis is the excessive accumulation of extracellular matrix proteins, including collagen, and is considered as a wound healing response to chronic liver injury. Its staging is critical for the management and prognosis of chronic hepatitis C (CHC) patients, whose number is expected to rise over the next decades, posing a major health care challenge. This review provides a brief update on HCV epidemiology, summarizes basic mechanistic concepts of HCV-dependent liver fibrogenesis, and discusses methods for assessment of liver fibrosis that are routinely used in clinical practice. Liver biopsy was until recently considered as the gold standard to diagnose and stage liver fibrosis. However, its invasiveness and drawbacks led to the development of non-invasive methods, which include serum biomarkers, transient elastography and combination algorithms. Clinical studies with CHC patients demonstrated that non-invasive methods are in most cases accurate for diagnosis and for monitoring liver disease complications. Moreover, they have a high prognostic value and are cost-effective. Non-invasive methods for assessment of liver fibrosis are gradually being incorporated into new guidelines and are becoming standard of care, which significantly reduces the need for liver biopsy.

Cellular and molecular mechanisms in the pathogenesis of liver fibrosis: An update

There have been considerable recent advances towards a better understanding of the complex cellular and molecular network underlying liver fibrogenesis. Recent data indicate that the termination of fibrogenic processes and the restoration of deficient fibrolytic pathways may allow the reversal of advanced fibrosis and even cirrhosis. Therefore, efforts have been made to better clarify the cellular and molecular mechanisms that are involved in liver fibrosis. Activation of hepatic stellate cells (HSCs) remains a central event in fibrosis, complemented by other sources of matrix-producing cells, including portal fibroblasts, fibrocytes and bone marrow-derived myofibroblasts. These cells converge in a complex interaction with neighboring cells to provoke scarring in response to persistent injury. Defining the interaction of different cell types, revealing the effects of cytokines on these cells and characterizing the regulatory mechanisms that control gene expression in activated HSCs will enable the discovery of new therapeutic targets. Moreover, the characterization of different pathways associated with different etiologies aid in the development of disease-specific therapies. This article outlines recent advances regarding the cellular and molecular mechanisms involved in liver fibrosis that may be translated into future therapies. The pathogenesis of liver fibrosis associated with alcoholic liver disease, non-alcoholic fatty liver disease and viral hepatitis are also discussed to emphasize the various mechanisms involved in liver fibrosis.

Curcumin affects β-catenin pathway in hepatic stellate cell in vitro and in vivo

OBJECTIVES

Emerging evidence indicates that Wnt/β-catenin pathway is linked to the fibrosis of different organs including liver fibrosis. β-Catenin promotes hepatic stellate cells (HSCs) activation, a key event in the development of liver fibrosis, and has emerged as a novel mediator of fibrosis. Curcumin, a natural active ingredient derived from turmeric, possesses an inhibitory effect on liver fibrosis. This study is aimed to examine whether curcumin affects β-catenin expression/activity in HSCs and explores the underlying mechanisms.

METHODS

The researchers used Western blot, real-time PCR, transfection assay and electrophoretic mobility shift assay and employed cultured HSCs and rat model of liver injury.

KEY FINDINGS

Results showed that curcumin could reduce β-catenin protein level in HSCs in vitro and in vivo. Both β-catenin transactivation activity and DNA-binding activity were suppressed by curcumin. Moreover, nuclear β-catenin protein level was decreased by curcumin treatment. Further experiments suggested that delta-like homologue 1 contributed to curcumin inhibition of β-catenin transactivation activity in cultured HSCs.

CONCLUSIONS

Curcumin affects β-catenin pathway in HSCs and might suggest a possible new explanation for the effects of curcumin on HSC activation and liver fibrosis.

F‑actin cytoskeleton reorganization is associated with hepatic stellate cell activation

The activation of hepatic stellate cells (HSCs) is involved in the development of hepatic fibrosis. Previous studies have indicated that the acquisition of certain properties by activated HSCs is highly dependent on the reorganization of the actin cytoskeleton. However, direct evidence showing that the reorganization of the actin cytoskeleton is responsible for HSC activation is lacking. The aim of the present study was to investigate the role of cytoskeletal reorganization during HSC activation and to clarify the underlying mechanism. HSC-T6 cells were treated either with the F-actin stabilizer jasplakinolide (Jas) or the depolymerizer cytochalasin D (Cyto D). The actin cytoskeleton was evaluated via assessment of stress fiber formation. Furthermore, the activation properties of HSCs, including proliferation, adhesion, migration and the expression of α-smooth muscle actin (α-SMA) and collagen 1, were investigated in vitro. The results showed that Jas and Cyto D affected the actin distribution in HSC-T6 cells. Treatment with Jas resulted in thick actin bundles and a patchy appearance in the cytoplasm in HSC-T6 cells. In parallel, polymerization of actin microfilaments induced by Jas upregulated the expression of α-SMA and collagen 1, and also enhanced the migration and adhesion properties of HSC-T6 cells. Furthermore, the activation of HSC-T6 cells induced by the reorganization of the actin cytoskeleton was associated with the p38 mitogen-activated protein kinase (p38 MAPK) pathway. In conclusion, the present study suggests that the reorganization of the F-actin cytoskeleton is associated with HSC activation and that the p38 MAPK pathway is involved in this process. The inhibition of F-actin reorganization may thus be a potential key factor or molecular target for the control of liver fibrosis or cirrhosis.

The potential role of leptin in the vascular remodeling associated with obesity

BACKGROUND/OBJECTIVES

Extracellular matrix (ECM) participates in the vascular remodeling associated with obesity. We investigated the effects of leptin on the production of ECM components in primary cultured vascular smooth muscle cells (VSMCs) and whether leptin could be a mediator of obesity-induced vascular remodeling.

METHODS

T he effects of leptin (100 ng ml(-1)) on ECM components and superoxide anion production (O(2)(.-)) were evaluated in presence or absence of the antioxidant melatonin (10(-)(3) mmol l(-1)) or the inhibitor of phosphatidylinositol 3'-kinase (PI3K), LY294002 (2 × 10(-)(4) mmol l(-1)) in VSMCs from adult rats in order to explore the role of both oxidative stress and the participation of PI3K/Akt pathway in the effects of leptin. ECM components and O(2)(.-) were quantified in the aortic media of male Wistar rats fed a high-fat diet (HFD; 33.5% fat), or a standard diet (CT; 3.5% fat) for 6 weeks.

RESULTS

In VSMCs, leptin enhanced gene and protein levels of collagen I, fibronectin, transforming growth factor (TGF)-β and connective tissue growth factor (CTGF) but did not change those of collagen III and galectin-3. Leptin also increased O(2)(.-) and Akt phosphorylation in VSMCs. These effects were prevented by the presence of either melatonin or LY294002, except O(2)(.-) production in the case of PI3K inhibition. The increase in body weight in HFD rats was accompanied by aorta thickening due to an increase in media area. The aortic fibrosis observed in HFD rats was associated with high levels of leptin, collagen type I, fibronectin, TGF-β, CTGF, phosphorylated Akt and O(2)(.-). Aortic leptin levels were positively correlated with total collagen, collagen I, TGF-β and CTGF levels. No differences were observed in the levels of collagen III, elastin or galectin-3 between both the groups.

CONCLUSIONS

Leptin could participate in the vascular remodeling and stiffness associated with obesity by ECM production in VSMCs through the activation of oxidative stress-PI3K/Akt pathway and the production of the profibrotic factors TGF-β and CTGF.

Hepatitis C virus core protein stimulates fibrogenesis in hepatic stellate cells involving the obese receptor

Hepatitis C virus core protein (HCVcp), which is secreted by infected cells, is reported as an immunomodulator in immune cells. However, the effects of HCVcp on hepatic stellate cells (HSCs), the key cells in liver fibrosis, still remain unclear. In this study, we investigated the effects of HCVcp on obese receptor (ObR) related downstream signaling pathways and fibrogenic gene expression in HSCs. LX-2, a human HSC line, was incubated with HCVcp. Inhibitors and short interfering RNAs were used to interrogate the mechanisms of HCVcp action on HSCs. HCVcp (20-100 ng/ml) concentration-dependently stimulated α-smooth muscle actin (α-SMA) protein expression and mRNA expression of α-SMA, procollagen α2(I) and TGF-β1 genes, with a plateau of 220% of controls at 100 ng/ml. HCVcp induced mRNA and protein expression of ObR. Blocking of Ob-Rb with a neutralizing antibody inhibited phosphorylation of signal transducer and activator of transcription 3 (STAT3) and AMPKα stimulated by HCVcp. Furthermore, knockdown of Ob-Rb down-regulated HCVcp-induced STAT3, AKT, and AMPKα phosphorylation, and reversed HCVcp-suppressed mRNA expression of matrix metalloproteinase (MMP)-1, peroxisome proliferator-activated receptor (PPAR)γ and sterol regulatory element binding protein-1c (SREBP-1c) genes. AMPKα signaling blockade reversed HCVcp-suppressed SREBP-1c mRNA expression. HCVcp stimulated reactive oxygen species formation and gp91(phox) (a component of NADPH oxidase) protein expression, together with AKT phosphorylation, leading to suppression of PPARγ and SREBP-1c genes. Our results provide a new finding that HCVcp induced ObR-dependent Janus Kinase (JAK) 2-STAT3, AMPKα, and AKT signaling pathways and modulated downstream fibrogenetic gene expression in HSCs.

Stat3 pathway correlates with the roles of leptin in mouse liver fibrosis and sterol regulatory element binding protein-1c expression of rat hepatic stellate cells

Leptin, the adipocyte-derived hormone, plays an unique role in promoting liver fibrosis. Hepatic stellate cell (HSC) activation is the key step in liver fibrogenesis and sterol regulatory element binding protein-1c (SREBP-1c, a pivotal transcription factor for adipocyte differentiation) exerts a critical function in inhibition of HSC activation. Stat3 pathway is the main pathway induced by leptin and its role in liver fibrogenesis is controversial. Our previous results demonstrated the inhibitory effect of leptin on SREBP-1c expression in HSCs. The present study aimed to explore the role of Stat3 pathway in leptin-induced liver fibrogenesis in mouse model, focusing on examining the effect of leptin-induced Stat3 pathway on SREBP-1c expression in HSCs in vitro and in vivo. Results suggested that Stat3 pathway mediated the promotional role of leptin in liver fibrosis in mouse and was involved in leptin inhibition of SREBP-1c expression in HSCs. Leptin-induced Stat3 activation was, at least partially, ERK pathway-dependent in cultured HSCs and was correlated positively with β-catenin activity and negatively with liver X receptor α expression and activity which influenced SREBP-1c expression in HSCs. The decrease in SREBP-1c expression by leptin-induced Stat3 pathway led to the increase in the marker for HSC activation and in α1(I) collagen expression in HSCs. In summary, the effect of leptin-induced Stat3 pathway on SREBP-1c expression in HSCs might contribute to the role of leptin in liver fibrosis in mouse, thus advancing understanding of the mechanisms of liver fibrogenesis associated with leptin.

β-Catenin pathway is required for TGF-β1 inhibition of PPARγ expression in cultured hepatic stellate cells

Hepatic stellate cell (HSC) activation is a key step in process of liver fibrosis. Transforming growth factor-β1 (TGF-β1) is the most powerful mediator of HSC activation and plays a central role in liver fibrosis. Peroxisome proliferator-activated receptor-γ (PPARγ) is an important regulator of adipocyte differentiation and has been proposed as a crucial factor for inhibition of HSC activation. The effect of TGF-β1 on PPARγ in HSCs is largely unknown. This study is aimed to examine whether TGF-β1 can influence PPARγ expression, focusing on the role of β-catenin pathway, a key pathway linked to adipogenesis, in TGF-β1 regulation of PPARγ in cultured HSCs. Our results demonstrated that TGF-β1 evidently inhibited PPARγ expression and activity in cultured HSCs, which were mediated through β-catenin pathway. TGF-β1 promoted β-catenin expression and also increased the stability of β-catenin protein through ERK1/2/glycogen synthase kinase-3β (GSK-3β) axis in cultured HSCs. Moreover, TGF-β1 inhibition of PPARγ expression by β-catenin pathway caused the increase in alpha1(1) collagen and tissue inhibitor of matrix metalloproteinase expression. These results indicated for the first time that TGF-β1 could down-regulate PPARγ expression through β-catenin pathway and subsequently contributed to the increase in alpha1(1) collagen level in cultured HSCs.

p38 mitogen-activated protein kinase and liver X receptor-α mediate the leptin effect on sterol regulatory element binding protein-1c expression in hepatic stellate cells

Leptin, a key hormone in regulating energy homeostasis, is mainly produced by adipocytes. Cogent evidence indicates a unique role of leptin in the promotion of liver fibrosis. Hepatic stellate cell (HSC) activation is a pivotal step in the process of liver fibrosis. Sterol regulatory element binding protein (SREBP)-1c, a critical transcription factor for lipid synthesis and adipocyte differentiation, functions as a key transcription factor in inhibition of HSC activation. SREBP-1c is highly expressed in quiescent HSCs and downregulated upon HSC activation. The aim of this study is to examine the effect of leptin on SREBP-1c gene expression in HSCs in vitro and in vivo and elucidate the underlying mechanisms. The results of the present study demonstrated that leptin strongly inhibited SREBP-1c expression in HSCs in vivo and in vitro. p38 MAPK was involved in leptin regulation of SREBP-1c expression in cultured HSCs. Leptin-induced activation of p38 MAPK led to the decreases in liver X receptor (LXR)-α protein level, activity and its binding to the SREBP-1c promoter, which caused the downregulation of SREBP-1c expression. Moreover, leptin inhibition of SREBP-1c expression via p38 MAPK increased the expression of alpha1(I) collagen in HSCs. Our results might provide new insights into the mechanisms of the unique role of leptin in the development of liver fibrosis and might have potential implications for clarifying the molecular mechanisms underlying liver fibrosis in diseases in which circulating leptin levels are elevated such as nonalcoholic steatohepatitis, type 2 diabetes mellitus and alcoholic cirrhosis.

Peroxisome proliferator-activated receptor-γ cross-regulation of signaling events implicated in liver fibrogenesis

Peroxisome proliferator-activated receptor-γ (PPARγ) is a nuclear receptor with transcriptional activity controlling multiple physical and pathological processes. Recently, PPARγ has been implicated in the pathogenesis of liver fibrosis. Its depleted expression has strong associations with the activation and transdifferentiation of hepatic stellate cells, the central event in liver fibrogenesis. Studies over the past decade demonstrate that PPARγ cross-regulates a number of signaling pathways mediated by growth factors and adipokines, and cellular events including apoptosis and senescence. These signaling and cellular events and their molecular interactions with PPARγ system are profoundly involved in liver fibrogenesis. We critically summarize these mechanistic insights into the PPARγ regulation in liver fibrogenesis based on the updated findings in this area. We conclude with a discussion of the impacts of these discoveries on the interpretation of liver fibrogenesis and their potential therapeutic implications. PPARγ activation could be a promising strategy for antifibrotic therapy.

Adipokines and redox signaling: impact on fatty liver disease

Adipokines (adipose tissue cytokines) are polypeptide factors secreted by adipose tissue in a highly regulated manner. The 'classical' adipokines (leptin, adiponectin, and resistin) are expressed only by adipocytes, but other adipokines have been shown to be released by resident and infiltrating macrophages, as well as by components of the vascular stroma. Indeed, adipose tissue inflammation is known to be associated with a modification in the pattern of adipokine secretion. Several studies indicate that adipokines can interfere with hepatic injury associated with fatty infiltration, differentially modulating steatosis, inflammation, and fibrosis. Moreover, plasma levels of adipokines have been investigated in patients with nonalcoholic fatty liver disease in order to establish correlations with the underlying state of insulin resistance and with the type and severity of hepatic damage. In this Forum article, we provide a review of recent data that suggest a significant role for oxidative stress, reactive oxygen species, and redox signaling in mediating actions of adipokines that are relevant in the pathogenesis of nonalcoholic fatty liver disease, including hepatic insulin resistance, inflammation, and fibrosis.

Mechanisms of hepatic fibrogenesis

Multiple etiologies of liver disease lead to liver fibrosis through integrated signaling networks that regulate the deposition of extracellular matrix. This cascade of responses drives the activation of hepatic stellate cells (HSCs) into a myofibroblast-like phenotype that is contractile, proliferative and fibrogenic. Collagen and other extracellular matrix (ECM) components are deposited as the liver generates a wound-healing response to encapsulate injury. Sustained fibrogenesis leads to cirrhosis, characterized by a distortion of the liver parenchyma and vascular architecture. Uncovering the intricate mechanisms that underlie liver fibrogenesis forms the basis for efforts to develop targeted therapies to reverse the fibrotic response and improve the outcomes of patients with chronic liver disease.

Saccharomyces cerevisiae modulates immune gene expressions and inhibits ETEC-mediated ERK1/2 and p38 signaling pathways in intestinal epithelial cells

BACKGROUND

Enterotoxigenic Escherichia coli (ETEC) infections result in large economic losses in the swine industry worldwide. ETEC infections cause pro-inflammatory responses in intestinal epithelial cells and subsequent diarrhea in pigs, leading to reduced growth rate and mortality. Administration of probiotics as feed additives displayed health benefits against intestinal infections. Saccharomyces cerevisiae (Sc) is non-commensal and non-pathogenic yeast used as probiotic in gastrointestinal diseases. However, the immuno-modulatory effects of Sc in differentiated porcine intestinal epithelial cells exposed to ETEC were not investigated.

METHODOLOGY/PRINCIPAL FINDINGS

We reported that the yeast Sc (strain CNCM I-3856) modulates transcript and protein expressions involved in inflammation, recruitment and activation of immune cells in differentiated porcine intestinal epithelial IPEC-1 cells. We demonstrated that viable Sc inhibits the ETEC-induced expression of pro-inflammatory transcripts (IL-6, IL-8, CCL20, CXCL2, CXCL10) and proteins (IL-6, IL-8). This inhibition was associated to a decrease of ERK1/2 and p38 MAPK phosphorylation, an agglutination of ETEC by Sc and an increase of the anti-inflammatory PPAR-γ nuclear receptor mRNA level. In addition, Sc up-regulates the mRNA levels of both IL-12p35 and CCL25. However, measurement of transepithelial electrical resistance displayed that Sc failed to maintain the barrier integrity in monolayer exposed to ETEC suggesting that Sc does not inhibit ETEC enterotoxin activity.

CONCLUSIONS

Sc (strain CNCM I-3856) displays multiple immuno-modulatory effects at the molecular level in IPEC-1 cells suggesting that Sc may influence intestinal inflammatory reaction.

Mechanisms of hepatic fibrogenesis

Multiple etiologies of liver disease lead to liver fibrosis through integrated signaling networks that regulate the deposition of extracellular matrix. This cascade of responses drives the activation of hepatic stellate cells (HSCs) into a myofibroblast-like phenotype that is contractile, proliferative and fibrogenic. Collagen and other extracellular matrix (ECM) components are deposited as the liver generates a wound-healing response to encapsulate injury. Sustained fibrogenesis leads to cirrhosis, characterized by a distortion of the liver parenchyma and vascular architecture. Uncovering the intricate mechanisms that underlie liver fibrogenesis forms the basis for efforts to develop targeted therapies to reverse the fibrotic response and improve the outcomes of patients with chronic liver disease.

Mechanisms of hepatic fibrogenesis

Multiple etiologies of liver disease lead to liver fibrosis through integrated signaling networks that regulate the deposition of extracellular matrix. This cascade of responses drives the activation of hepatic stellate cells (HSCs) into a myofibroblast-like phenotype that is contractile, proliferative and fibrogenic. Collagen and other extracellular matrix (ECM) components are deposited as the liver generates a wound-healing response to encapsulate injury. Sustained fibrogenesis leads to cirrhosis, characterized by a distortion of the liver parenchyma and vascular architecture. Uncovering the intricate mechanisms that underlie liver fibrogenesis forms the basis for efforts to develop targeted therapies to reverse the fibrotic response and improve the outcomes of patients with chronic liver disease.

Double antioxidant activities of rosiglitazone against high glucose-induced oxidative stress in hepatocyte

Chronic hyperglycemia is the hallmark of diabetes and its complication. High glucose-induced excessive reactive oxygen species (ROS) production has been considered to play an important role in the development of diabetes. However, the influence of high glucose on the liver remains to be clarified. Rosiglitazone (RSG) is a member of thiazolidinediones (TDZs) family, which is the ligand of the of nuclear transcription factor peroxisome proliferator-activated receptor-γ (PPARγ), being used clinically for the treatment of type 2 diabetic patients through their insulin-sensitizing effect. In the present study, we investigated the cytotoxicity of high glucose in QZG hepatocytes and evaluated the protective effect of RSG. The results showed that high glucose significantly reduced cell viability through generation of ROS via activation of PKC, which was inhibited by RSG. On the one hand, RSG notably inhibited the activation of PKC induced by high glucose independent of PPARγ, leading to the decrease of ROS generation. On the other hand, RSG notably increased the expression of key antioxidant transcription factor Nrf2 and antioxidant enzyme HO-1 in a PPARγ-dependent manner, leading to the elimination of excessive ROS. In addition, RSG also inhibited the decrease of COX-2 expression induced by high glucose through activating PPARγ. Furthermore, the activation of Akt and MAPKs was involved in the effect of RSG on Nrf2, HO-1 and COX-2. In summary, our study supports the hypothesis that RSG protect hepatocytes from high glucose-induced toxicity through PPARγ-dependent and PPARγ-independent pathways.

Daily genetic profiling indicates JAK/STAT signaling promotes early hepatic stellate cell transdifferentiation

AIM

To identify signaling pathways and genes that initiate and commit hepatic stellate cells (HSCs) to transdifferentiation.

METHODS

Primary HSCs were isolated from male Sprague-Dawley rats and cultured on plastic for 0-10 d. Gene expression was assessed daily (quiescent to day 10 culture-activation) by real time polymerase chain reaction and data clustered using AMADA software. The significance of JAK/STAT signaling to HSC transdifferentiation was determined by treating cells with a JAK2 inhibitor.

RESULTS

Genetic cluster analyses, based on expression of these 21 genes, showed similar expression profiles on days 1-3, days 5 and 6, and days 7-10, while freshly isolated cells (day Q) and day 4 cells were genotypically distinct from any of the other days. Additionally, gene expression clustering revealed strong upregulation of interleukin-6, JAK2 and STAT3 mRNA in the early stages of activation. Inhibition of the JAK/STAT signaling pathway impeded the morphological transdifferentiation of HSCs which correlated with decreased mRNA expression of several profibrotic genes including collagens, α-SMA, PDGFR and TGFβR.

CONCLUSION

These data demonstrate unique clustered genetic profiles during the daily progression of HSC transdifferentiation and that JAK/STAT signaling may be critical in the early stages of transdifferentiation.

Leptin inhibits PPARgamma gene expression in hepatic stellate cells in the mouse model of liver damage

Hepatic stellate cell (HSC) activation is a key cellular event in the development of liver fibrosis. Peroxisome proliferator-activated receptor-gamma (PPARgamma) has been shown to function as a key transcription regulator linked to suppressing HSC activation. Compelling evidence indicates that leptin plays a unique role in the development of liver fibrosis. The aim of this study is to investigate the in vivo impact of leptin on PPARgamma expression in HSCs in the model of TAA-induced liver damage. The results of the present study provide the first in vivo evidence that leptin might exert an inhibitory effect on PPARgamma protein expression in HSCs, which is mediated at least through leptin-induced ERK1/2 activation. Long-form leptin receptor is involved in leptin-induced ERK1/2 activation and the subsequent decline in PPARgamma expression in HSCs in the model. Furthermore, the inhibitory effect of leptin on PPARgamma protein expression enhances HSC activation and proliferation in this model. The in vivo findings from this report might provide additional insights into the mechanisms underlying the profibrogenic action of leptin in liver.