Leptin induces increased alpha2(I) collagen gene expression in cultured rat hepatic stellate cells

Maternal obesity driven changes in collagen linearity of breast extracellular matrix induces invasive mammary epithelial cell phenotype

Obesity has been linked with numerous health issues as well as an increased risk of breast cancer. Although effects of direct obesity in patient outcomes is widely studied, effects of exposure to obesity-related systemic influences in utero have been overlooked. In this study, we investigated the effect of multigenerational obesity on epithelial cell migration and invasion using decellularized breast tissues explanted from normal female mouse pups from a diet induced multigenerational obesity mouse model. We first studied the effect of multigenerational diet on the mechanical properties, adipocyte size, and collagen structure of these mouse breast tissues, and then, examined the migration and invasion behavior of normal (KTB-21) and cancerous (MDA-MB-231) human mammary epithelial cells on the decellularized matrices from each diet group. Breast tissues of mice whose dams had been fed with high-fat diet exhibited larger adipocytes and thicker and curvier collagen fibers, but only slightly elevated elastic modulus and inflammatory cytokine levels. MDA-MB-231 cancer cell motility and invasion were significantly greater on the decellularized matrices from mice whose dams were fed with high-fat diet. A similar trend was observed with normal KTB-21 cells. Our results showed that the collagen curvature was the dominating factor on this enhanced motility and stretching the matrices to equalize the collagen fiber linearity of the matrices ameliorated the observed increase in cell migration and invasion in the mice that were exposed to a high-fat diet in utero. Previous studies indicated an increase in serum leptin concentration for those children born to an obese mother. We generated extracellular matrices using primary fibroblasts exposed to various concentrations of leptin. This produced curvier ECM and increased breast cancer cell motility for cells seeded on the decellularized ECM generated with increasing leptin concentration. Our study shows that exposure to obesity in utero is influential in determining the extracellular matrix structure, and that the resultant change in collagen curvature is a critical factor in regulating the migration and invasion of breast cancer cells.

Conditional knockout of leptin receptor in the female reproductive tract reduces fertility due to parturition defects in mice

Leptin is required for fertility, including initiation of estrous cycles. It is therefore challenging to assess the role of leptin signaling during pregnancy. While neuron-specific transgene approaches suggest that leptin signaling in the central nervous system is most important, experiments with pharmacologic inhibition of leptin in the uterus or global replacement of leptin during pregnancy suggest leptin signaling in the reproductive tract may be required. Here, conditional leptin receptor knockout (Lepr cKO) with a progesterone receptor-driven Cre recombinase was used to examine the importance of leptin signaling in pregnancy. Lepr cKO mice have almost no leptin receptor in uterus or cervix, and slightly reduced leptin receptor levels in corpus luteum. Estrous cycles and progesterone concentrations were not affected by Lepr cKO. Numbers of viable embryos did not differ between primiparous control and Lepr cKO dams on days 6.5 and 17.5 of pregnancy, despite a slight reduction in the ratio of embryos to corpora lutea, showing that uterine leptin receptor signaling is not required for embryo implantation. Placentas of Lepr cKO dams had normal weight and structure. However, over four parities, Lepr cKO mice produced 22% fewer live pups than controls, and took more time from pairing to delivery by their fourth parity. Abnormal birth outcomes of either dystocia or dead pups occurred in 33% of Lepr cKO deliveries but zero control deliveries, and the average time to deliver each pup after crouching was significantly increased. Thus, leptin receptor signaling in the reproductive tract is required for normal labor and delivery. Summary sentence. Mice lacking leptin receptor in the reproductive tract produce fewer live pups and have more adverse labor outcomes than controls, but normal numbers of embryos near term, showing that leptin receptor signaling is required for normal parturition.

Superoxide-induced Type I collagen secretion depends on prolyl 4-hydroxylases

Reactive oxygen species (ROS) including superoxide (O₂^•-) play an important role in a variety of diseases, including Alzheimer's Disease, cancer, and atherosclerosis. Early reports showed that O₂^•- is a stimulant for collagen synthesis. However, the mechanism remains incompletely understood. Here we showed that LY83583 (6-anilinoquinoline-5,8-quinone), a substance known to induce O₂^•- production by smooth muscle cell (SMC), increases Type I collagen secretion. This effect could be blocked by treating the cells with Tiron, a scavenger for O₂^•-. LY83583-induced Type I collagen secretion required P4HA1 and P4HA2. Knockout of either P4ha1 or P4ha2 greatly reduced LY83583-stimulated Type I collagen maturation whereas silencing of both P4ha1 and P4ha2 completely blocked LY83583-induced Type I collagen maturation. Although significantly more hydroxyproline on purified Type I collagen was detected from LY83583 treated mouse embryonic fibroblast (MEF) cells by mass spectrometry, the level of prolyl 4-hydroxylases was not altered. Thus, LY83583 might increase the enzymatic activity of prolyl 4-hydroxylases to increase Type I collagen maturation. In addition, we found that LY83583 activated prolyl 4-hydrolases differed from ascorbate-activated prolyl 4-hydroxylase in two aspects: (1) LY83583 activated both P4HA1 and P4HA2 involved in collagen maturation whereas ascorbate mainly stimulated P4HA1 in collagen maturation; (2) LY83583 did not induce N259 glycosylation on P4HA1 as ascorbate did. The mechanisms remain to be investigated.

The Association of leptin with severity of non-alcoholic fatty liver disease: A population-based study

Background/Aims

Leptin is associated with metabolic disorders, which predispose one to non-alcoholic fatty liver disease (NAFLD). The role of leptin in NAFLD pathogenesis is not fully understood. We aim to investigate the association between serum leptin level and severity of NAFLD using U.S. nationally representative data.

Methods

Data were obtained from the United States Third National Health and Nutrition Examination Survey. NAFLD was defined by ultrasound detection and severity of hepatic steatosis in the absence of other liver diseases. The severity of hepatic fibrosis was determined by NAFLD fibrosis score (NFS). We used multivariate survey-weighted generalized logistic regression to evaluate the association between leptin level and the degree of NAFLD. We also performed subgroup analyses by body mass index (lean vs. classic NAFLD).

Results

Among 4,571 people, 1,610 (35%) had NAFLD. By ultrasound findings, there were 621 people with mild, 664 with moderate, and 325 with severe steatosis. There were 885 people with low NFS (<-1.455, no significant fibrosis), 596 with intermediate NFS, and 129 with high NFS (>0.676, advanced fibrosis). Leptin levels for normal, mild, moderate and severe steatosis were 10.7±0.3 ng/mL, 12.1±0.7 ng/mL, 15.6±0.8 ng/mL, 16±1.0 ng/mL, respectively (trend P-value<0.001). Leptin levels for low, intermediate, and high NFS were 11.8±0.5 ng/mL, 15.6±0.8 ng/mL, 28.5±3.5ng/mL, respectively (trend P-value<0.001). This association remained significant even after adjusting for known demographic and metabolic risk factors. In the subgroup analysis, this association was only prominent in classic NAFLD, but not in lean NAFLD.

Conclusions

Serum leptin level is associated with the severity of NAFLD, especially in classic NAFLD patients.

Expression patterns of STAT3, ERK and estrogen-receptor α are associated with development and histologic severity of hepatic steatosis: a retrospective study

BACKGROUND

Hepatic steatosis renders hepatocytes vulnerable to injury, resulting in the progression of preexisting liver disease. Previous animal and cell culture studies implicated mammalian target of rapamycin (mTOR), signal transducer and activator of transcription-3 (STAT3), extracellular signal-regulated kinase (ERK) and estrogen-receptor α in the pathogenesis of hepatic steatosis and disease progression. However, to date there have been few studies performed using human liver tissue to study hepatic steatosis. We examined the expression patterns of mTOR, STAT3, ERK and estrogen-receptor α in liver tissues from patients diagnosed with hepatic steatosis.

METHODS

We reviewed the clinical and histomorphological features of 29 patients diagnosed with hepatic steatosis: 18 with non-alcoholic fatty liver disease (NAFLD), 11 with alcoholic fatty acid disease (AFLD), and a control group (16 biliary cysts and 22 hepatolithiasis). Immunohistochemistry was performed on liver tissue using an automated immunostainer. The histologic severity of hepatic steatosis was evaluated by assessing four key histomorphologic parameters common to NAFLD and AFLD: steatosis, lobular inflammation, ballooning degeneration and fibrosis.

RESULTS

mTOR, phosphorylated STAT3, phosphorylated pERK, estrogen-receptor α were found to be more frequently expressed in the hepatic steatosis group than in the control group. Specifically, mTOR was expressed in 78% of hepatocytes, and ERK in 100% of hepatic stellate cells, respectively, in patients with NAFLD. Interestingly, estrogen-receptor α was diffusely expressed in hepatocytes in all NALFD cases. Phosphorylated (active) STAT3 was expressed in 73% of hepatocytes and 45% of hepatic stellate cells in patients with AFLD, and phosphorylated (active) ERK was expressed in hepatic stellate cells in all AFLD cases. Estrogen-receptor α was expressed in all AFLD cases (focally in 64% of AFLD cases, and diffusely in 36%). Phosphorylated STAT3 expression in hepatocytes and hepatic stellate cells correlated with severe lobular inflammation, severe ballooning degeneration and advanced fibrosis, whereas diffusely expressed estrogen-receptor α correlated with a mild stage of fibrosis.

CONCLUSIONS

Our data indicate ERK activation and estrogen-receptor α may be relevant in the development of hepatic steatosis. However, diffuse expression of estrogen-receptor α would appear to impede disease progression, including hepatic fibrosis. Finally, phosphorylated STAT3 may also contribute to disease progression.

The pattern of IL-24/mda-7 and its cognate receptors expression following activation of human hepatic stellate cells

Activation of hepatic stellate cells (HSCs) is the pivotal event during liver fibrosis. Interleukin (IL)-24/melanoma differentiation-associated gene-7 (mda-7) has attracted attention in the pathophysiology of some diseases, while its role in activation/suppression of human HSCs is still unclear. It is important to elucidate whether the expression levels of the IL-24/mda-7 protein and its receptors in HSC cells are changed following activation. LX-2 cells, a human hepatic stellate cell line were activated by a combination of leptin and serum starvation. The activation state was evaluated through measuring the mRNA expression of profibrotic molecules, collagen-I, TIMP metalloproteinase inhibitor-1 and transforming growth factor-β. The expression of IL-24/mda-7 was assessed in mRNA and protein levels by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and ELISA methods, respectively. Hence, the amount of IL-22R1 and IL-20R2 subunit expression was also compared in activated and normal LX-2 cells by RT-qPCR. The expression level of IL-24/mda-7 and its cognate receptors was detectable both in the normal and activated LX-2 cell line. Furthermore, in activated LX-2, a significant increase of IL24 expression either on IL-22R1 and IL-20R2 subunits was also noticeable in comparison to normal cells. The activation state of LX-2 cells caused significant changes of IL-24/mda-7 and its receptors expression. In addition, the elevation in IL-24/mda-7 during LX-2 cell activation, suggested that IL-24/mda-7 and its cognate receptors serve a possible role in the development of the fibrosis process. Therefore, IL-24/mda-7 and relevant signaling pathways may be employed as a target for fibrosis treatment.

STAT3 Inhibition Suppresses Hepatic Stellate Cell Fibrogenesis: HJC0123, a Potential Therapeutic Agent for Liver Fibrosis

Hepatic Stellate Cells (HSCs) are the major source of the excessive extracellular matrix (ECM) production that replaces liver parenchyma with fibrous tissue during liver fibrosis. The signal transducer and activator of transcription 3 (STAT3) promotes HCSs survival, proliferation, and activation contributing to fibrogenesis. We have previously used a fragment-based drug design approach and have discovered a novel STAT3 inhibitor, HJC0123. Here, we explored the biological effects of HJC0123 on the fibrogenic properties of HSCs. HJC0123 treatment resulted in the inhibition of HSCs proliferation at submicromolar concentrations. HJC0123 reduced the phosphorylation, nuclear translocation, and transcriptional activity of STAT3. It decreased the expression of STAT3-regulated proteins, induced cell cycle arrest, promoted apoptosis and downregulated SOCS3. HJC0123 treatment inhibited HSCs activation and downregulated ECM protein fibronectin and type I collagen expression. In addition, HJC0123 increased IL-6 production and decreased TGF-β induced Smad2/3 phosphorylation. These results demonstrate that HJC0123 represents a novel STAT3 inhibitor that suppresses the fibrogenic properties of HSCs, suggesting its therapeutic potential in liver fibrosis.

Galanin receptor 2 mediates antifibrogenic effects of galanin on hepatic stellate cells

Galanin is an endogenous factor involved in the negative regulation of the biological effects of leptin in bioenergetic metabolism. Leptin promotes fibrogenic effects in hepatic stellate cells (HSCs), however, little is known about the effects of galanin on HSCs. In the present study, the biological functions of galanin and its receptors (GalRs) in HSCs were investigated using cell culture in vitro. It was found that galanin and GalR3 mRNA are expressed in quiescent and activated HSCs. GalR2 expression was undetectable in quiescent HSCs but was markedly induced in activated HSCs. In the HSC-T6 cell line, which is an activated rat HSC cell line, treatment with 100 nmol/l galanin significantly inhibited cell proliferation. It also inhibited transforming growth factor (TGF)-β1 and α-smooth muscle actin (SMA) expression and upregulated peroxisome proliferator-activated receptor (PPAR)-γ expression. Following the knockdown of GalR2 by specific small interfering RNA, the activation of GalR3 by galanin does not influence these effects of galanin on HSCs. However, activation of GalR2 alone by galanin following the knockdown of GalR3 inhibits HSC proliferation and TGF-β1 and α-SMA expression, in addition to inducing PPAR-γ expression. These data suggest that galanin inhibits HSC activation and suppresses the profibrogenic features of these cells, and these effects might be mediated by GalR2. Thus, galanin is a potential endogenous factor in the inhibition of liver fibrosis.

Purinergic receptor X7 mediates leptin induced GLUT4 function in stellate cells in nonalcoholic steatohepatitis

Metabolic oxidative stress via CYP2E1 can act as a second hit in NASH progression. Our previous studies have shown that oxidative stress in NASH causes higher leptin levels and induces purinergic receptor X7 (P2X7r). We tested the hypothesis that higher circulating leptin due to CYP2E1-mediated oxidative stress induces P2X7r. P2X7r in turn activates stellate cells and causes increased proliferation via modulating Glut4, the glucose transporter, and increased intracellular glucose. Using a high fat diet-fed NAFLD model where bromodichloromethane (BDCM) was administered to induce CYP2E1-mediated oxidative stress, we show that P2X7r expression and protein levels were leptin and CYP2E1 dependent. P2X7r KO mice had significantly decreased stellate cell proliferation. Human NASH livers showed marked increase in P2X7r, and Glut4 in α-SMA positive cells. NASH livers had significant increase in Glut4 protein and phosphorylated AKT, needed for Glut4 translocation while leptin KO and P2X7r KO mice showed marked decrease in Glut4 levels primarily in stellate cells. Mechanistically stellate cells showed increase in phosphorylated AKT, Glut4 protein and localization in the membrane following administration of P2X7r agonist or leptin+P2X7r agonist, while use of P2X7r antagonist or AKT inhibitor attenuated the response suggesting that leptin-P2X7r axis in concert but not leptin alone is responsible for the Glut4 induction and translocation. Finally P2X7r-agonist and leptin caused an increase in intracellular glucose and consumption by increasing the activity of hexokinase. In conclusion, the study shows a novel role of leptin-induced P2X7r in modulating Glut4 induction and translocation in hepatic stellate cells, that are key to NASH progression.

Micro-RNA 21 inhibition of SMAD7 enhances fibrogenesis via leptin-mediated NADPH oxidase in experimental and human nonalcoholic steatohepatitis

Hepatic fibrosis in nonalcoholic steatohepatitis (NASH) is the common pathophysiological process resulting from chronic liver inflammation and oxidative stress. Although significant research has been carried out on the role of leptin-induced NADPH oxidase in fibrogenesis, the molecular mechanisms that connect the leptin-NADPH oxidase axis in upregulation of transforming growth factor (TGF)-β signaling have been unclear. We aimed to investigate the role of leptin-mediated upregulation of NADPH oxidase and its subsequent induction of micro-RNA 21 (miR21) in fibrogenesis. Human NASH livers and a high-fat (60% kcal) diet-fed chronic mouse model, where hepatotoxin bromodichloromethane was used to induce NASH, were used for this study. To prove the role of the leptin-NADPH oxidase-miR21 axis, mice deficient in genes for leptin, p47phox, and miR21 were used. Results showed that wild-type mice and human livers with NASH had increased oxidative stress, increased p47phox expression, augmented NF-κB activation, and increased miR21 levels. These mice and human livers showed increased TGF-β, SMAD2/3-SMAD4 colocalizations in the nucleus, increased immunoreactivity against Col1α, and α-SMA with a concomitant decrease in protein levels of SMAD7. Mice that were deficient in leptin or p47phox had decreased activated NF-κB and miR21 levels, suggesting the role of leptin and NADPH oxidase in inducing NF-κB-mediated miR21 expression. Further miR21 knockout mice had decreased colocalization events of SMAD2/3-SMAD4 in the nucleus, increased SMAD7 levels, and decreased fibrogenesis. Taken together, the studies show the novel role of leptin-NADPH oxidase induction of miR21 as a key regulator of TGF-β signaling and fibrogenesis in experimental and human NASH.

Upregulation of miR21 and repression of Grhl3 by leptin mediates sinusoidal endothelial injury in experimental nonalcoholic steatohepatitis

Sinusoidal endothelial dysfunction (SED) has been found to be an early event in nonalcoholic steatohepatitis (NASH) progression but the molecular mechanisms underlying its causation remains elusive. We hypothesized that adipokine leptin worsens sinusoidal injury by decreasing functionally active nitric oxide synthase 3 (NOS)3 via miR21. Using rodent models of NASH, and transgenic mice lacking leptin and leptin receptor, results showed that hyperleptinemia caused a 4-5 fold upregulation of hepatic miR21 as assessed by qRTPCR. The upregulation of miR21 led to a time-dependent repression of its target protein Grhl3 levels as shown by western blot analyses. NOS3-p/NOS3 ratio which is controlled by Grhl3 was significantly decreased in NASH models. SED markers ICAM-1, VEGFR-2, and E-selectin as assessed by immunofluorescence microscopy were significantly up regulated in the progressive phases of NASH. Lack of leptin or its receptor in vivo, reversed the upregulation of miR21 and restored the levels of Grhl3 and NOS3-p/NOS3 ratio coupled with decreased SED dysfunction markers. Interestingly, leptin supplementation in mice lacking leptin, significantly enhanced miR21 levels, decreased Grhl3 repression and NOS3 phosphorylation. Leptin supplementation in isolated primary endothelial cells, Kupffer cells and stellate cells showed increased mir21 expression in stellate cells while sinusoidal injury was significantly higher in all cell types. Finally miR21 KO mice showed increased NOS3-p/NOS3 ratio and reversed SED markers in the rodent models of NASH. The experimental results described here show a close association of leptin-induced miR21 in aiding sinusoidal injury in NASH.

Loss of vitamin D receptor signaling from the mammary epithelium or adipose tissue alters pubertal glandular development

Vitamin D₃ receptor (VDR) signaling within the mammary gland regulates various postnatal stages of glandular development, including puberty, pregnancy, involution, and tumorigenesis. Previous studies have shown that vitamin D₃ treatment induces cell-autonomous growth inhibition and differentiation of mammary epithelial cells in culture. Furthermore, mammary adipose tissue serves as a depot for vitamin D₃ storage, and both epithelial cells and adipocytes are capable of bioactivating vitamin D₃. Despite the pervasiveness of VDR in mammary tissue, individual contributions of epithelial cells and adipocytes, as well as the VDR-regulated cross-talk between these two cell types during pubertal mammary development, have yet to be investigated. To assess the cell-type specific effect of VDR signaling during pubertal mammary development, novel mouse models with mammary epithelial- or adipocyte-specific loss of VDR were generated. Interestingly, loss of VDR in either cellular compartment accelerated ductal morphogenesis with increased epithelial cell proliferation and decreased apoptosis within terminal end buds. Conversely, VDR signaling specifically in the mammary epithelium modulated hormone-induced alveolar growth, as ablation of VDR in this cell type resulted in precocious alveolar development. In examining cellular cross-talk ex vivo, we show that ligand-dependent VDR signaling in adipocytes significantly inhibits mammary epithelial cell growth in part through the vitamin D₃-dependent production of the cytokine IL-6. Collectively, these studies delineate independent roles for vitamin D₃-dependent VDR signaling in mammary adipocytes and epithelial cells in controlling pubertal mammary gland development.

Curcumin eliminates the effect of advanced glycation end-products (AGEs) on the divergent regulation of gene expression of receptors of AGEs by interrupting leptin signaling

Non-alcoholic steatohepatitis (NASH) is a major risk factor for hepatic fibrogenesis. NASH is often found in diabetic patients with hyperglycemia. Hyperglycemia induces non-enzymatic glycation of proteins, yielding advanced glycation end-products (AGEs). Effects of AGEs are mainly mediated by two categories of cytoplasmic membrane receptors. Receptor for AGEs (RAGE) is associated with increased oxidative stress and inflammation, whereas AGE receptor-1 (AGE-R1) is involved in detoxification and clearance of AGEs. Activation of hepatic stellate cells (HSC) is crucial to the development of hepatic fibrosis. We recently reported that AGEs stimulated HSC activation likely by inhibiting gene expression of AGE-R1 and inducing gene expression of RAGE in HSC, which were eliminated by the antioxidant curcumin. This study is to test our hypothesis that curcumin eliminates the effects of AGEs on the divergent regulation of the two receptors of AGEs in HSC by interrupting the AGE-caused activation of leptin signaling, leading to the inhibition of HSC activation. We observed herein that AGEs activated leptin signaling by inducing gene expression of leptin and its receptor in HSC. Like AGEs, leptin differentially regulated gene expression of RAGE and AGE-R1. Curcumin eliminated the effects of AGEs in HSC by interrupting leptin signaling and activating transcription factor NF-E2 p45-related factor 2 (Nrf2), leading to the elevation of cellular glutathione and the attenuation of oxidative stress. In conclusions, curcumin eliminated the effects of AGEs on the divergent regulation of gene expression of RAGE and AGE-R1 in HSC by interrupting the AGE-caused activation of leptin signaling, leading to the inhibition of HSC activation.

Leptin and adiponectin: emerging therapeutic targets in breast cancer

Obesity is a recognized risk factor for breast cancer development and poorer response to therapy. Two major fat tissue-derived adipokines, leptin and adiponectin have been implicated in mammary carcinogenesis. Leptin appears to promote breast cancer progression through activation of mitogenic, antiapoptotic, and metastatic pathways, while adiponectin may restrict tumorigenic processes primarily by inhibiting cell metabolism. Furthermore, adiponectin is known to counteract detrimental leptin effects in breast cancer models. Thus, therapeutic inhibition of pro-neoplastic leptin pathways and reactivation of anti-neoplastic adiponectin signaling may benefit breast cancer patients, especially the obese subpopulation. This review focuses on current experimental strategies aiming at leptin and adiponectin pathways in breast cancer models. Novel leptin receptor antagonists and adiponectin receptor agonists as well as other compounds for therapeutic modulation of adipokine pathways are discussed in detail, including potential pharmacological advantages and limitations of these approaches.

Translating an understanding of the pathogenesis of hepatic fibrosis to novel therapies

The response to injury is one of wound healing and fibrogenesis, which ultimately leads to fibrosis. The fibrogenic response to injury is a generalized one across virtually all organ systems. In the liver, the injury response, typically occurring over a prolonged period of time, leads to cirrhosis (although it should be pointed out that not all patients with liver injury develop cirrhosis). The fact that many different diseases result in cirrhosis suggests a common pathogenesis. The study of hepatic fibrogenesis over the past 2 decades has been remarkably active, leading to a considerable understanding of this process. It clearly has been shown that the hepatic stellate cell is a central component in the fibrogenic process. It also has been recognized that other effector cells are important in the fibrogenic process, including resident fibroblasts, bone marrow-derived cells, fibrocytes, and even perhaps cells derived from epithelial cells (ie, through epithelial to mesenchymal transition). A key aspect of the biology of fibrogenesis is that the fibrogenic process is dynamic; thus, even advanced fibrosis (or cirrhosis) is reversible. Together, an understanding of the cellular basis for liver fibrogenesis, along with multiple aspects of the basic pathogenesis of fibrosis, have highlighted many exciting potential therapeutic opportunities. Thus, although the most effective antifibrotic therapy is simply treatment of the underlying disease, in situations in which this is not possible, specific antifibrotic therapy is likely not only to become feasible, but will soon become a reality. This review highlights the mechanisms underlying fibrogenesis that may be translated into future antifibrotic therapies and to review the current state of clinical development.

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.

Sp1 and Sp3 transcription factors mediate leptin-induced collagen α1(I) gene expression in primary culture of male rat hepatic stellate cells

Mechanisms by which leptin stimulates collagen α(1)(I) [Col1a(I)] gene expression are unclear. The purposes of this study were to identify the trans-acting factors and cis-acting elements in Col1a(I) promoter involved in this effect as well as the pathways that are implicated. In primary cultures of rat hepatic stellate cells (HSCs), we measured the effects of leptin on Col1a(I) gene and protein expression and on the binding of nuclear proteins to the Col1a(I) promoter. We found that leptin increased Col1a(I) gene and protein expression in activated HSCs. Transient transfections showed that leptin exerted its effects through elements located between -220 and -112 bp of the Col1a(I) promoter. Gel retardation assays demonstrated that leptin induced the binding of transcription factors specific protein (Sp)-1 and Sp3 to two elements located between -161 and -110 bp of the Col1a(I) promoter. Leptin-induced Sp1/Sp3 phosphorylation, but this effect was suppressed by inhibiting or silencing Janus kinase-2, phosphatidylinositol-3-kinase, nonphagocytic adenine dinucleotide phosphate (NADPH) oxidase, or ERK1/2, by the use of antioxidants or catalase, or by preventing protein-aldehyde adduct formation. Leptin provoked oxidative stress, aldehyde-protein adduct formation, and increased gene expression of some components of the NADPH oxidase complex. In conclusion, in HSCs, leptin up-regulates Col1a(I) gene expression after activating NADPH oxidase, inducing oxidative stress, aldehyde-protein adduct formation, and ERK1/2 phosphorylation, which in turn activates Sp1/Sp3 and provokes the binding of these two factors to regulatory elements located between -161 and -110 bp of the Col1a(I) promoter. These findings may contribute to a better understanding of mechanisms involved in the leptin-induced liver fibrosis.

Glutathione synthesis

BACKGROUND

Glutathione (GSH) is present in all mammalian tissues as the most abundant non-protein thiol that defends against oxidative stress. GSH is also a key determinant of redox signaling, vital in detoxification of xenobiotics, and regulates cell proliferation, apoptosis, immune function, and fibrogenesis. Biosynthesis of GSH occurs in the cytosol in a tightly regulated manner. Key determinants of GSH synthesis are the availability of the sulfur amino acid precursor, cysteine, and the activity of the rate-limiting enzyme, glutamate cysteine ligase (GCL), which is composed of a catalytic (GCLC) and a modifier (GCLM) subunit. The second enzyme of GSH synthesis is GSH synthetase (GS).

SCOPE OF REVIEW

This review summarizes key functions of GSH and focuses on factors that regulate the biosynthesis of GSH, including pathological conditions where GSH synthesis is dysregulated.

MAJOR CONCLUSIONS

GCL subunits and GS are regulated at multiple levels and often in a coordinated manner. Key transcription factors that regulate the expression of these genes include NF-E2 related factor 2 (Nrf2) via the antioxidant response element (ARE), AP-1, and nuclear factor kappa B (NFκB). There is increasing evidence that dysregulation of GSH synthesis contributes to the pathogenesis of many pathological conditions. These include diabetes mellitus, pulmonary and liver fibrosis, alcoholic liver disease, cholestatic liver injury, endotoxemia and drug-resistant tumor cells.

GENERAL SIGNIFICANCE

GSH is a key antioxidant that also modulates diverse cellular processes. A better understanding of how its synthesis is regulated and dysregulated in disease states may lead to improvement in the treatment of these disorders. This article is part of a Special Issue entitled Cellular functions of glutathione.

Adiponectin inhibits leptin signalling via multiple mechanisms to exert protective effects against hepatic fibrosis

Adiponectin is protective against hepatic fibrosis, whereas leptin promotes fibrosis. In HSCs (hepatic stellate cells), leptin signals via a JAK2 (Janus kinase 2)/STAT3 (signal transducer and activator of transcription 3) pathway, producing effects that enhance ECM (extracellular matrix) deposition. SOCS-3 (suppressor of cytokine signalling-3) and PTP1B (protein tyrosine phosphatase 1B) are both negative regulators of JAK/STAT signalling, and recent studies have demonstrated a role for adiponectin in regulating SOCS-3 expression. In the present study we investigate mechanisms whereby adiponectin dampens leptin signalling and prevents excess ECM production. We treated culture-activated rat HSCs with recombinant adiponectin, leptin, both or neither, and also treated adiponectin knockout (Ad-/-) and wild-type mice with leptin and/or carbon tetrachloride (CCl4) or saline. We analyse JAK2 and Ob-Rb (long form of the leptin receptor) phosphorylation, and PTP1B expression and activity. We also explore potential mechanisms through which adiponectin regulates SOCS-3-Ob-Rb association. Adiponectin inhibits leptin-stimulated JAK2 activation and Ob-Rb phosphorylation in HSCs, whereas both were increased in Ad-/- mice. Adiponectin stimulates PTP1B expression and activity in vitro, whereas PTP1B expression was lower in Ad-/-mice than in wild-type mice. Adiponectin also promotes SOCS-3-Ob-R association and blocks leptin-stimulated formation of extracellular TIMP-1 (tissue inhibitor of metalloproteinases-1)-MMP-1 (matrix metalloproteinase-1) complexes in vitro. These results suggest two novel mechanisms whereby adiponectin inhibits hepatic fibrosis: (i) by promoting binding of SOCS-3 to Ob-Rb, and (ii) by stimulating PTP1B expression and activity, thus inhibiting JAK2/STAT3 signalling at multiple points.

Clinicopathological features of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is the most common form of chronic liver disease worldwide and its incidence is increasing concomitantly with the increase in the prevalence of metabolic syndrome. Fatty liver encompasses a broad pathological spectrum of disease, from relatively benign accumulation of fat (simple steatosis) to progressive non-alcoholic steatohepatitis (NASH), which is associated with necroinflammation and fibrosis. Approximately 20-30% of the Japanese population is estimated to have NAFLD, 10% of which is suggested to have NASH. The most worrisome feature of NASH is the potential progression to cirrhosis, hepatocellular carcinoma (HCC), and finally, mortality. Several factors, such as insulin resistance, adipokines, endotoxins and oxidative stress, are involved in the pathogenesis of NASH. However, the precise etiological mechanism of NAFLD/NASH has yet to be elucidated. This article reviews the clinical background, pathogenesis, new diagnostic approaches and future directions regarding NAFLD/NASH.

Leptin regulates MMP-2, TIMP-1 and collagen synthesis via p38 MAPK in HL-1 murine cardiomyocytes

A clear association between obesity and heart failure exists and a significant role for leptin, the product of the obese gene, has been suggested. One aspect of myocardial remodeling which characterizes heart failure is a disruption in the balance of extracellular matrix synthesis and degradation. Here we investigated the effects of leptin on matrix metalloproteinase (MMP) activity, tissue inhibitor of metalloproteinase (TIMP) expression, as well as collagen synthesis in HL-1 cardiac muscle cells. Gelatin zymographic analysis of MMP activity in conditioned media showed that leptin enhanced MMP-2 activity in a dose- and time-dependent manner. Leptin is known to stimulate phosphorylation of p38 MAPK in cardiac cells and utilization of the p38 MAPK inhibitor, SB203580, demonstrated that this kinase also plays a role in regulating several extracellular matrix components, such that inhibition of p38 MAPK signaling prevented the leptin-induced increase in MMP-2 activation. We also observed that leptin enhanced collagen synthesis determined by both proline incorporation and picrosirius red staining of conditioned media. Pro-collagen type-I and pro-collagen type-III expression, measured by real-time PCR and Western blotting were also increased by leptin, effects which were again attenuated by SB203580. In summary, these results demonstrate the potential for leptin to play a role in mediating myocardial ECM remodeling and that the p38 MAPK pathway plays an important role in mediating these effects.

Adiponectin activation of AMPK disrupts leptin-mediated hepatic fibrosis via suppressors of cytokine signaling (SOCS-3)

Adiponectin is an adipocytokine that was recently shown to be anti-fibrogenic in hepatic fibrosis. Leptin, on the other hand, promotes hepatic fibrosis. The purpose of the present study was to elucidate a mechanism (or mechanisms) whereby adiponectin dampens leptin signaling in activated hepatic stellate cells (HSCs), and prevents excess extracellular matrix production. Activated HSCs, between passages 2 and 5, were cultured and exposed to recombinant human adiponectin and recombinant leptin. Immunoblot analysis for SOCS-3, TIMP-1, and the phosphorylated species of Stat3 and adenosine monophosphate-activated protein kinase (AMPK) were conducted. We also examined MMP-1 activity by immunosorbant fluorimetric analysis. In HSCs, adiponectin-induced phosphorylation of AMPK, and subsequently suppressed leptin-mediated Stat3 phosphorylation and SOCS-3 induction. Adiponectin also blocked leptin-stimulated secretion of TIMP-1, and significantly increased MMP-1 activity, in vitro. To extend this study, we treated adiponectin knockout mice (Ad-/-) daily with 5 mg/kg recombinant leptin and/or carbon tetrachloride (2 ml/kg) for 6 weeks. Post-necropsy analysis was performed to examine for inflammation, and histological changes in the Ad-/- and wild-type mice. There was no significant difference in inflammation, or aminotransferases, between mice receiving carbon tetrachloride and leptin versus carbon tetrachloride alone. As anticipated, the combination of leptin and CCl(4) enhanced hepatic fibrosis in both wild-type and Ad-/- mice, as estimated by amount of collagen in injured livers, but wild-type mice had significantly higher levels of SOCS-3 and significantly lower levels of TIMP-1 mRNA and protein than did adiponectin KO mice exposed to both CCl(4) and leptin. We therefore conclude that the protective effects of adiponectin against liver fibrosis require AMPK activation, and may occur through inhibition of the Jak-Stat signal transduction pathway.

Leptin-based therapeutics

Leptin, a pluripotent adipokine, has been discovered as a hormone controlling energy balance in hypothalamic neuroendocrine centers. In addition, recent studies provided ample evidence that leptin can be produced by cells other than adipocytes, and that the hormone can regulate many physiological processes other than energy balance and appetite. In this context, it is not surprising that both leptin excess as well as leptin insufficiency have been implicated in various pathologies. Consequently, despite initially disappointing results with recombinant leptin as the drug for obesity management, new leptin receptor modifiers have been developed and emerged as potential treatment modalities for numerous metabolic, immunological and neoplastic diseases. The major focus of this paper is a systematic review of current experimental leptin-based therapies, including pharmacological advantages and limitations of each prodrug category.

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.

Changes in the expression of methionine adenosyltransferase genes and S-adenosylmethionine homeostasis during hepatic stellate cell activation

Hepatic stellate cell (HSC) activation is an essential event during liver fibrogenesis. Methionine adenosyltransferase (MAT) catalyzes biosynthesis of S-adenosylmethionine (SAMe), the principle methyl donor. SAMe metabolism generates two methylation inhibitors, methylthioadenosine (MTA) and S-adenosylhomocysteine (SAH). Liver cell proliferation is associated with induction of two nonliver-specific MATs: MAT2A, which encodes the catalytic subunit alpha2, and MAT2beta, which encodes a regulatory subunit beta that modulates the activity of the MAT2A-encoded isoenzyme MATII. We reported that MAT2A and MAT2beta genes are required for liver cancer cell growth that is induced by the profibrogenic factor leptin. Also, MAT2beta regulates leptin signaling. The strong association of MAT genes with proliferation and leptin signaling in liver cells led us to examine the role of these genes during HSC activation. MAT2A and MAT2beta are induced in culture-activated primary rat HSCs and HSCs from 10-day bile duct ligated (BDL) rat livers. HSC activation led to a decline in intracellular SAMe and MTA levels, a drop in the SAMe/SAH ratio, and global DNA hypomethylation. The decrease in SAMe levels was associated with lower MATII activity during activation. MAT2A silencing in primary HSCs and MAT2A or MAT2beta silencing in the human stellate cell line LX-2 resulted in decreased collagen and alpha-smooth muscle actin (alpha-SMA) expression and cell growth and increased apoptosis. MAT2A knockdown decreased intracellular SAMe levels in LX-2 cells. Activation of extracellular signal-regulated kinase and phosphatidylinositol-3-kinase signaling in LX-2 cells required the expression of MAT2beta but not that of MAT2A.

CONCLUSION

MAT2A and MAT2beta genes are induced during HSC activation and are essential for this process. The SAMe level falls, resulting in global DNA hypomethylation.

Transcriptional regulation of hepatic stellate cells

Hepatic stellate cell (HSC) activation is a process of cellular transdifferentiation in which, upon liver injury, the quiescent vitamin A storing perisinusoidal HSC is converted into a wound-healing myofibroblast and acquires potent pro-inflammatory and pro-fibrogenic activities. This remarkable phenotypic transformation is underpinned by changes in the expression of a vast number of genes. In this review we survey current knowledge of the transcription factors that either control HSC activation or which regulate specific fibrogenic functions of the activated HSC such as collagen expression, proliferation and resistance to apoptosis.

Roles of adipocytokines in the pathogenesis of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is closely associated with obesity, abnormal lipid metabolism and insulin resistance. Adipocytokines, which secrete leptin, adiponectin, tumor necrosis factor, peroxisome proliferator-activated receptor, resistin, interleukin-6 (IL-6), interleukin-8 (IL-8), visfatin, plasminogen activator inhibitor-1, play important roles in the pathogenesis and development of NAFLD. This paper tries to further discuss the roles of adipocytokines in the purpose of providing new ideas and methods for clinical research.

Competitive inhibition of leptin signaling results in amelioration of liver fibrosis through modulation of stellate cell function

Leptin signaling is involved in T-cell polarization and is required for profibrotic function of hepatic stellate cells (HSCs). Leptin-deficient ob/ob mice do not develop liver fibrosis despite the presence of severe long-standing steatohepatitis. Here, we blocked leptin signaling with our recently generated mouse leptin antagonist (MLA), and examined the effects on chronic liver fibrosis in vivo using the chronic thioacetamide (TAA) fibrosis model, and in vitro using freshly-isolated primary HSCs. In the chronic TAA fibrosis model, leptin administration was associated with significantly enhanced liver disease and a 100% 5-week to 8-week mortality rate, while administration or coadministration of MLA markedly improved survival, attenuated liver fibrosis, and reduced interferon gamma (IFN-gamma) levels. No significant changes in weight, serum cholesterol, or triglycerides were noted. In vitro administration of rat leptin antagonist (RLA), either alone or with leptin, to rat primary HSCs reduced leptin-stimulated effects such as increased expression of alpha-smooth muscle actin (alpha-SMA), and activation of alpha1 procollagen promoter.

CONCLUSION

Inhibition of leptin-enhanced hepatic fibrosis may hold promise as a future antifibrotic therapeutic modality.

Liver diseases and metabolic syndrome

Emerging attention has been paid to metabolic syndrome, which comprises several metabolic disorders including visceral obesity, diabetes mellitus, dyslipidemia, and hypertension. Whether the severity of each disease is mild to moderate, the comorbidity of these metabolic disorders has a serious impact on the development of atherosclerosis. Nonalcoholic fatty liver disease (NAFLD) is the major hepatic disorder in patients with metabolic syndrome, and indeed it is the most common cause of abnormal liver function tests in the working population in industrialized countries. In recent years, it has become recognized that NAFLD is no longer just a trivial disease, and a rather considerable proportion of the patients develop liver cirrhosis. Furthermore, chronic infection of hepatitis C virus also develops a pathological feature of steatohepatitis, and extended hepatic steatosis has a serious impact not only on the progression of hepatic fibrosis but also on the antiviral efficacy of interferon therapy. Emerging lines of studies indicated that insulin resistance, abnormal lipid metabolism, and dysregulation of cytokines/adipokines (e.g., tumor necrosis factor-alpha, adiponectin, and leptin) are profoundly involved in the pathogenesis of NAFLD. This review aims to integrate the reported evidence and to provide the current point of view for comprehensive understanding of the pathophysiology of steatohepatitis.

Disease-specific mechanisms of fibrosis: hepatitis C virus and nonalcoholic steatohepatitis

Our mechanistic understanding of liver fibrosis has increased dramatically in recent years for all liver diseases and for hepatitis C and nonalcoholic steatohepatitis (NASH) in particular. Hepatitis C causes liver injury and fibrosis through direct cytopathic means, direct and indirect interactions with hepatic stellate cells, and activation of the immune system. Steatosis and insulin resistance, which are intrinsic deficits in NASH, are also of great importance in hepatitis C and may be induced by viral or host metabolic factors. For NASH, the key mediators of damage include oxidative stress, fat compartmentalization, visceral fat, apoptosis, and adipokine derangement. This article explores in depth the disease-specific mechanisms of fibrosis in hepatitis C and NASH, with a focus on recent developments.

Oxidative and nitrosative stress and fibrogenic response

Uncontrolled production of collagen I is the main feature of liver fibrosis. Following a fibrogenic stimulus such as alcohol, hepatic stellate cells (HSC) transform into an activated collagen-producing cell. In alcoholic liver disease, numerous changes in gene expression are associated with HSC activation, including the induction of several intracellular signaling cascades, which help maintain the activated phenotype and control the fibrogenic and proliferative state of the cell. Detailed analyses for understanding the molecular basis of the collagen I gene regulation have revealed a complex process involving reactive oxygen species (ROS) as key mediators. Less is known, however, about the contribution of reactive nitrogen species (RNS). In addition, a series of cytokines, growth factors, and chemokines, which activate extracellular matrix (ECM)-producing cells through paracrine and autocrine loops, contribute to the fibrogenic response.

Prevention of hepatic fibrosis in a murine model of metabolic syndrome with nonalcoholic steatohepatitis

The endocannabinoid pathway plays an important role in the regulation of appetite and body weight, hepatic lipid metabolism, and fibrosis. Blockade of the endocannabinoid receptor CB1 with SR141716 promotes weight loss, reduces hepatocyte fatty acid synthesis, and is antifibrotic. D-4F, an apolipoprotein A-1 mimetic with antioxidant properties, is currently in clinical trials for the treatment of atherosclerosis. C57BL/6J mice were fed a high-fat diet for 7 months, followed by a 2.5-month treatment with either SR141716 or D-4F. SR141716 markedly improved body weight, liver weight, serum transaminases, insulin resistance, hyperglycemia, hypercholesterolemia, hyperleptinemia, and oxidative stress, accompanied by the significant prevention of fibrosis progression. D-4F improved hypercholesterolemia and hyperleptinemia without improvement in body weight, steatohepatitis, insulin resistance, or oxidative stress, and yet, there was significant prevention of fibrosis. D-4F prevented culture-induced activation of stellate cells in vitro. In summary, C57BL/6J mice given a high-fat diet developed features of metabolic syndrome with nonalcoholic steatohepatitis and fibrosis. Both SR141716 and D-4F prevented progression of fibrosis after onset of steatohepatitis, ie, a situation comparable to a common clinical scenario, with D-4F seeming to have a more general antifibrotic effect. Either compound therefore has the potential to be of clinical benefit.

Identification of leptin gene expression in sinusoidal endothelial rat liver cells

Sinusoidal endothelial liver cells (SECs) have a key role in the pathophysiology of chronic liver disease. Leptin is an important profibrogenic and proinflammatory cytokine whose expression in sinusoidal endothelial liver has not been documented. The authors studied the potential of rat SECs to express the leptin and leptin receptor genes. Two cell lines of rat SECs were generated from a male rat liver by pronase-collagenase perfusion and dilution cloning. They were characterized according to morphology, ploidy, von Willebrand antigen immunoreactivity, CD31 transcription, matrix metalloproteinase secretion, and pseudocapillary formation. Expression of the leptin and leptin receptor genes was studied using qualitative reverse transcriptase-polymerase chain reaction. Both cell lines fulfilled the accepted criteria for consideration as being derived from the liver sinusoidal endothelium. Confluent monolayers of both cell lines transcribed leptin and leptin receptor genes. This work demonstrated that SECs can transcribe the leptin gene in vitro, cotranscribing with the leptin receptor gene. Leptin production and signaling at this level could be of paramount importance in liver physiopathology; further studies of this issue are warranted because it represents a potential intervention point during chronic liver diseases.

Participation of reactive oxygen species generated by NADPH oxidase in regulating signal transduction in hepatic stellate cells

Reactive oxygen species (ROS) are established molecules that are injurious to such biomolecules as DNA and protein, and that can induce lipid peroxidation. However, it is now held that Nox/Duox family of NADPH oxidases generate ROS in a carefully regulated manner, which can act as second messengers influencing signal transduction in various cells including hepatic stellate cells (HSCs). This paper focused on mechanism of ROS generated by NOX/Duox regulating signal transduction, and then reviewed signal transduction of ROS-mediated liver profibrogenic factors, e.g., transforming growth factor-β (TGF-β), platelet-derived growth factor (PDGF), Angiotensin II (Ang II) and leptin, et al in HSCs.

Nonalcoholic steatohepatitis and the metabolic syndrome

Nonalcoholic fatty liver disease (NAFLD) is a major form of chronic liver disease in adults and children. It is one of the consequences of the current obesity epidemic, and can progress to nonalcoholic steatohepatitis (NASH), characterized by steatosis, inflammation, and progressive fibrosis, ultimately leading to cirrhosis and end-stage liver disease. The factors implicated in this progression are poorly understood. NASH is closely associated with obesity and the metabolic syndrome. Recent studies emphasize the role of insulin resistance, oxidative stress, lipid peroxidation, and cytokine release in the development of NASH. This review summarizes the current knowledge on the etiology and pathomechanism of NASH and the role of the metabolic syndrome in NASH development.

Effects of leptin deficiency on postnatal lung development in mice

Leptin modulates energy metabolism and lung development. We hypothesize that the effects of leptin on postnatal lung development are volume dependent from 2 to 10 wk of age and are independent of hypometabolism associated with leptin deficiency. To test the hypotheses, effects of leptin deficiency on lung maturation were characterized in age groups of C57BL/6J mice with varying Lep(ob) genotypes. Quasi-static pressure-volume curves and respiratory impedance measurements were performed to profile differences in respiratory system mechanics. Morphometric analysis was conducted to estimate alveolar size and number. Oxygen consumption was measured to assess metabolic rate. Lung volume at 40-cmH(2)O airway pressure (V(40)) increased with age in each genotypic group, and V(40) was significantly (P < 0.05) lower in leptin-deficient (ob/ob) mice beginning at 2 wk. Differences were amplified through 7 wk of age relative to wild-type (+/+) mice. Morphometric analysis showed that alveolar surface area was lower in ob/ob compared with +/+ and heterozygote (ob/+) mice beginning at 2 wk. Unlike the other genotypic groups, alveolar size did not increase with age in ob/ob mice. In another experiment, ob/ob at 4 wk received leptin replacement (5 microg.g(-1) x day(-1)) for 8 days, and expression levels of the Col1a1, Col3a1, Col6a3, Mmp2, Tieg1, and Stat1 genes were significantly increased concomitantly with elevated V(40). Leptin-induced increases in V(40) corresponded with enlarged alveolar size and surface area. Gene expression suggested a remodeling event of lung parenchyma after exogenous leptin replacement. These data support the hypothesis that leptin is critical to postnatal lung remodeling, particularly related to increased V(40) and enlarged alveolar surface area.

Identification of proteins secreted from leptin stimulated MCF-7 breast cancer cells: a dual proteomic approach

Leptin is an adipocyte-derived hormone that regulates energy expenditure and food intake. A significant role for leptin in breast cancer has also been indicated by the resistance of leptin knockout mice in development of mammary tumors. In vitro, leptin induces proliferation of MCF-7 cells by activating cellular signaling pathways (1, 11, 12, 16, 17, 56). As leptin is emerging as an important factor for tumor growth, and hormones can exert their actions via autocrine/paracrine mechanisms, we hypothesized leptin may act by regulating epithelial-derived proteins. To test this hypothesis, leptin-regulated proteins secreted from MCF-7 mammary tumor cells were identified using proteomics techniques. Treatment of MCF-7 cells with 500 ng/ml leptin for 24 hours resulted in a 40% increase in cell number and a 5-fold increase in protein secretion as compared to controls. Establishing the significance of leptin-induced secreted factors, the addition of conditioned media from leptin-treated MCF-7 cells to synchronized MCF-7 cells resulted in 40% increase in cell number. Identification of leptin-regulated secreted proteins was done by 2D gel electrophoresis coupled with MALDI-TOF mass spectrometry. Proteins identified using Pro Found software and NCBI database included KF10 Collagen Precursor, Serologically Defined Breast Cancer Antigen NY-BR-62 and Cortactin Isoform a. A Human Cytokine Antibody Array system was used to identify low abundant proteins in the media of control and 500 ng/ml leptin-stimulated MCF-7 cells. In leptin treated cells, levels of FGF-9 were increased while IGFBP-3 and TGF-beta3 levels were decreased. Many previous studies have focused on the regulation of distinct cellular proteins by leptin during mammary tumor cell proliferation. However, ours is the first study to identify leptin-regulated secreted proteins, many of which are known to play important roles in cancer. Our data support that leptin can influence mammary tumor growth and progression through regulation of autocrine/paracrine factors and by modulating the extracellular matrix composition.

Leptin stimulates alpha1(I) collagen expression in human hepatic stellate cells via the phosphatidylinositol 3-kinase/Akt signalling pathway

BACKGROUND/AIMS

Leptin has been recognized as a profibrogenic hormone in the liver and is involved in collagen type I formation by activated hepatic stellate cells (HSCs) in response to fibrogenic substances, but the molecular signal mechanisms by which leptin promotes liver fibrogenesis through upregulation of collagen type I expression is not clear. We investigated whether leptin-induced collagen type I is mediated by the Janus kinase-phosphatidylinositol 3-kinase-Akt (JAKs-PI3K-Akt) pathway in a human HSC cell line, LX-2.

METHODS

LX-2 cells were treated with or without various inhibitors in the presence of leptin.

RESULTS

Leptin increased alpha1(I) collagen mRNA and protein. JAK1, PI3K and Akt were activated after leptin stimulation. AG490, a JAK inhibitor, blocked JAK1 phosphorylation accompanied by inhibition of PI3K and Akt activation as well as alpha1(I) collagen mRNA expression, indicating a JAK1-dependent mechanism. Wortmannin, a PI3K inhibitor, prevented PI3K and Akt activation and resulted in suppression of alpha1(I) collagen mRNA expression, suggesting a PI3K-mediated process. These changes were reproduced by overexpression of the dominant-negative p85alpha mutant. A443654.3, an Akt inhibitor, opposed Akt activation, leading to downregulation of alpha1(I) collagen mRNA. Overexpression of the dominant-negative Akt mutant led to similar alterations.

CONCLUSION

Leptin has a direct action on liver fibrogenesis by stimulating alpha1(I) collagen production in activated HSC. The process appears to be mediated by the PI3K/Akt pathway through activated JAK1.

Association between leptin, metabolic factors and liver histology in patients with chronic hepatitis C

BACKGROUND

Steatosis is common in hepatitis C virus (HCV)-infected patients and likely accelerates fibrosis progression. Leptin, the peptide product of the obesity gene (ob), has been implicated in hepatic fibrogenesis; circulating levels of leptin correlate with body fat mass. The objective of the present study was to determine the clinical and histological correlates of serum leptin in HCV-infected patients, and to determine its utility in predicting liver histological lesions.

PATIENTS AND METHODS

In 62 patients with chronic HCV, serum leptin was measured using a commercially available immunoassay. Associations between leptin, metabolic parameters, and severe hepatic fibrosis (stages 2 to 4) and steatosis (30% or greater) were determined. The utility of leptin in predicting liver histology was determined using receiver operating characteristic (ROC) curves.

RESULTS

The median body mass index (BMI) was 23.2 kg/m2 (range 17.7 kg/m2 to 35.6 kg/m2); 16% of patients (n=10) had HCV genotype 3. Severe fibrosis and steatosis were present in 23% and 13% of patients, respectively. Leptin was strongly correlated with the BMI, and its levels were higher in women. BMI-corrected leptin levels were not independently associated with severe fibrosis but were significantly associated with steatosis (OR of 1.07; 95% CI 1.01 to 1.04). On it own, leptin was poorly predictive of severe steatosis (area under the ROC curve was 0.64; 95% CI 0.42 to 0.87). However, its accuracy improved with the addition of HCV genotype (area under the ROC curve was 0.86; 95% CI 0.72 to 1.00; P=0.07).

CONCLUSIONS

As observed in the non-HCV setting, serum leptin correlates with BMI; higher leptin levels are found in women than men with chronic HCV. Serum leptin is a poor predictor of HCV-related fibrosis but may play a role in predicting steatosis when combined with HCV genotype.

Metabolic liver disease of obesity and role of adipose tissue in the pathogenesis of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is an increasingly recognized cause of liver-related morbidity and mortality. It can develop secondary to numerous causes but a great majority of NAFLD cases occur in patients who are obese or present with other components of metabolic syndrome (hypertension, dyslipidemia, diabetes). This is called primary NAFLD and insulin resistance plays a key role in its pathogenesis. Obesity is characterized by expanded adipose tissue, which is under a state of chronic inflammation. This disturbs the normal storage and endocrine functions of adipose tissue. In obesity, the secretome (adipokines, cytokines, free fatty acids and other lipid moieties) of fatty tissue is amplified, which through its autocrine, paracrine actions in fat tissue and systemic effects especially in the liver leads to an altered metabolic state with insulin resistance (IR). IR leads to hyperglycemia and reactive hyperinsulinemia, which stimulates lipid-accumulating processes and impairs hepatic lipid metabolism. IR enhances free fatty acid delivery to liver from the adipose tissue storage due to uninhibited lipolysis. These changes result in hepatic abnormal fat accumulation, which may initiate the hepatic IR and further aggravate the altered metabolic state of whole body. Hepatic steatosis can also be explained by the fact that there is enhanced dietary fat delivery and physical inactivity. IR and NAFLD are also seen in various lipodystrophic states in contrary to popular belief that these problems only occur due to excessive adiposity in obesity. Hence, altered physiology of adipose tissue is central to development of IR, metabolic syndrome and NAFLD.

Role of adipocytokines in hepatic fibrogenesis

Obesity and insulin resistance are the key factors for progression of hepatic fibrosis in various chronic liver diseases including non-alcoholic steatohepatitis (NASH). Recently it has been shown that leptin plays a pivotal role in development of hepatic fibrosis. Leptin promotes hepatic fibrogenesis through upregulation of transforming growth factor-beta in Kupffer cells and sinusoidal endothelial cells. Further, leptin facilitates proliferation and prevents apoptosis of hepatic stellate cells. There is a paradox, however, in that ob/ob mice and Zucker rats, which are the obese and diabetic strains, had minimal profibrogenic responses in the liver, most likely because they lack leptin and its receptors. To establish a more clinically relevant model to study the mechanism of fibrogenesis under steatohepatitis, fatty changes and profibrogenic responses in the liver caused by methionine-choline deficiency (MCD) were investigated in the KK-A(y) mouse, which is an obese and diabetic strain. KK-A(y) mice developed more severe hepatic steatosis, inflammation and fibrosis induced by an MCD diet as compared to C57Bl/6 controls. Importantly, KK-A(y) mice lack physiological upregulation of adiponectin levels, suggesting that adiponectin plays a pivotal role not only in regulation of insulin sensitivity but also in modulation of inflammatory and profibrogenic responses in dietary steatohepatitis. Collectively, these findings support the hypothesis that the balance of adipocytokine expression is a key regulator for the progression of hepatic fibrosis in the setting of steatohepatitis.

Correlation of serum TNF-alpha levels and histologic liver injury scores in pediatric nonalcoholic fatty liver disease

We tested the power of tumor necrosis factor (TNF)-alpha and/or leptin in predicting the degree of liver involvement in children with nonalcoholic fatty liver disease (NAFLD). We measured serum levels of TNF-alpha and leptin and computed NAFLD activity score (NAS) (NAS >or= 5, diagnostic of nonalcoholic steatohepatitis [NASH]) in 72 consecutive biopsy-proven NAFLD cases (training and validation sets, 36 cases each). Univariate analysis evaluated variables significantly associated with a diagnostic NAS. Receiver operating characteristic (ROC) curve analysis assessed the diagnostic value of selected variables in predicting a NAS of 5 or more.TNF-alpha (P < .0001), leptin (P = .001); triglycerides (P = .013), and alkaline phosphatase (P = .046) levels were significantly associated with a NAS of 5 or more. TNF-alpha and leptin levels predicted the risk of NAS of 5 or more. ROC analyses defined cutoff values for TNF-alpha, leptin, and risk score. They identified 90%, 83%, and 83% of the cases, respectively, with a NAS of 5 or more (true-positive cases) from the validation set.TNF-alpha alone or combined with leptin in a simple risk score can accurately predict a NAS of 5 or more. TNF-alpha seems to be a specific laboratory marker of NASH.

Nonlinear optical imaging to evaluate the impact of obesity on mammary gland and tumor stroma

Obesity is an established risk factor for breast cancer incidence and mortality. However, the mechanism that links obesity to tumorigenesis is not well understood. Here we combined nonlinear optical imaging technologies with an early-onset diet-induced obesity breast cancer animal model to evaluate the impact of obesity on the composition of mammary gland and tumor stroma. Using coherent anti-Stokes Raman scattering and second harmonic generation on the same platform, we simultaneously imaged mammary adipocytes, blood capillaries, collagen fibrils, and tumor cells without any labeling. We observed that obesity increases the size of lipid droplets of adipocytes in mammary gland and collagen content in mammary tumor stroma, respectively. Such impacts of obesity on mammary gland and tumor stroma could not be analyzed using standard two-dimensional histologic evaluation. Given the importance of mammary stroma to the growth and migration of tumor cells, our observation provides the first imaging evidence that supports the relationship between obesity and breast cancer risk.

A peroxisome-proliferator activated receptor-gamma ligand could regulate the expression of leptin receptor on human hepatic stellate cells

Leptin is a peptide known to play a profibrogenic role in hepatic stellate cells (HSCs). Peroxisome-proliferator activated receptor (PPAR)-gamma ligands are suggested to have an anti-fibrogenic effect on HSCs. Since the association of these two factors in HSC activation has not been demonstrated, we hypothesized that PPAR-gamma ligands would suppress leptin-induced HSC activation and regulate leptin receptor expression. Immortalized human HSCs were activated by either leptin or platelet-derived growth factor (PDGF) in one group. In another group, ciglitazone, a PPAR-gamma ligand, was treated before the leptin or PDGF stimulation. Proliferation of human HSCs was achieved by both PDGF and leptin, and this could be suppressed by ciglitazone. PPAR-gamma mRNA expression was diminished in activated HSCs either by PDGF or leptin, and this was reversed by ciglitazone in both cases. Leptin receptor (OB-R) mRNA expression increased in activated HSCs either by PDGF or leptin, and the expression was inhibited by ciglitazone. Another adipogenic transcription factor, sterol regulatory element-binding protein-1c (SREBP-1c) mRNA expression was decreased either by PDGF or leptin. However, this effect was not reversed by ciglitazone pre-treatment. The inhibitory effect of ciglitazone on leptin-induced HSC proliferation was associated with the reversion of extracellular factor-regulated kinases (ERKs) activation. HSCs were OB-R expressing cells, and ciglitazone could regulate the expression of OB-R mRNA.

Signal transduction and activation of hepatic stellate cells

Liver fibrosis, which leads to cirrhosis, occurs as a result of various injurious processes and it is the common pathologic basis of all the chronic hepatic diseases. At present, a good many researches demonstrate that the activation of hepatic stellate cells play a critical role in fibrogenesis. Prolonged liver injury results in hepatocyte damages and secretion of many fibrogenic cytokines such as transforming growth factor-beta 1, angiotensin, and leptin, which triggers the activation of hepatic stellate cells through different intracellular signal transduction pathways. In this article, we reviewed the research advancement in the signal transduction pathway of nuclear receptor and membrane receptor during the activation of hepatic stellate cells.

Repeated whiskey binges promote liver injury in rats fed a choline-deficient diet

BACKGROUND/AIMS

Alcoholic liver disease is associated with nutritional deficiency and it may aggravate within the context of fatty liver. We investigated the relationship between alcohol intake (whiskey binge drinking) and a choline-deficient diet (CD) and assessed whether stellate cells could contribute to liver injury in this model.

RESULTS

Rats fed the CD diet plus whiskey showed increased liver damage compared to rats fed the CD diet, as demonstrated by H&E staining, elevated transaminases, steatosis, TNF-alpha levels, enhanced CYP2E1 activity, impaired antioxidant defense, elevated lipid peroxidation, and protein carbonyls. The combined treatment triggered an apoptotic response as determined by elevated Bax, caspase-3 activity, cytochrome-c release, and decreased Bcl-2 and Bcl-XL. Stellate cells were activated as increased expression of alpha-Sma was observed over that by the CD diet alone. The combined treatment shifted extracellular matrix remodeling towards a pro-fibrogenic response due to up-regulation of collagen I, TIMP1, and Hsp47 proteins, along with down-regulation of MMP13, MMP2, and MMP9 expression, proteases which degrade collagen I. These events were accompanied by increased phosphorylation of p38, a kinase that elevates collagen I.

CONCLUSIONS

Repeated alcohol binges in the context of mild steatosis may promote activation of stellate cells and contribute to liver injury.