Resistin mediates the hepatic stellate cell phenotype.

AIM: To describe the role of resistin in liver fibrosis. METHODS: For the in vivo animal study, Sprague Dawley rats were subjected to bile duct ligation (BDL) for 4 wk. Rat liver, adipose tissue (epididymal fat) and serum were analyzed for resistin expression. For the in vitro experiment, rat primary hepatic stellate cells (HSCs) and Kupffer cells (KCs) were used. HSCs were exposed to recombinant resistin, and collagen  I, transforming growth factor ß1, α smooth muscle actin, tissue inhibitor of metalloproteinase 1 and connective tissue growth factor expression were analyzed. Resistin gene and protein expression was quantified as was the expression of pro-inflammatory cytokines including tumor necrosis factor α (TNFα), interleukin (IL)-1, IL-6, IL-8 and monocyte chemotactic protein-1 (MCP-1). The effects of resistin on HSC proliferation, migration and apoptosis were determined. The effects of resistin on KCs were also investigated. RESULTS: Following BDL, rat epididymal fat and serum rather than liver showed higher resistin expression compared to control rats. In liver, resistin was expressed in quiescent HSCs and KCs. Resistin treatment resulted in enhancement of TNFα, IL-6, IL-8 and MCP-1 gene expression and increased IL-6 and MCP-1 protein in HSCs. Resistin activated HSC phospho-MAPK/p38, and p38 inhibition diminished IL-6 and MCP-1 expression. Furthermore, resistin facilitated HSC proliferation and migration, but decreased apoptosis which was via an IL-6 and MCP-1 mechanism. Finally, resistin-induced transforming growth factor ß1 from KCs enhanced HSC collagen  I expression. CONCLUSION: Resistin directly and indirectly modulates HSC behavior towards a more pro-fibrogenic phenotype.

Leptin and acetaldehyde synergistically promotes αSMA expression in hepatic stellate cells by an interleukin 6-dependent mechanism.

BACKGROUND: The mechanisms whereby patients with obesity/overweight are more susceptible to alcohol-associated liver fibrosis are unclear. Leptin, a peptide hormone secreted by white adipose tissue is increased in association with overweight/obesity and is recognized as mediator of liver fibrosis. We sought to assess whether leptin contributes to alcoholic liver fibrosis by in vitro studies in hepatic stellate cells (HSC). METHODS: Rat HSCs in second or third passage were utilised. Leptin, Acetaldehyde or combination with leptin and acetaldehyde were incubated for specific periods in cultured HSCs. Profibrogenic gene and protein expression were determined and associated-signalling pathways were assessed. Interleukin 6 (IL-6) antibody neutralization was used to evaluate the role of IL-6. RESULTS: Leptin did not promote acetaldehyde-induced gene expression of collagen I, transforming growth factor ß1 (TGFß1) and tissue inhibitor of metalloproteinase 1 (TIMP1) in vitro. However, combined treatment of leptin with acetaldehyde synergistically enhanced the protein expression of smooth muscle actin (αSMA), an activation marker of HSCs, and of Interleukin-6 (IL-6). The combination of leptin and acetaldehyde also augmented MAPK/p38 and MAPK/ERK1/2 phosphoprotein expression. IL-6 neutralization down-regulated protein expression of pp38, pERK1/2 and αSMA, while exogenous rat recombinant IL-6 administration up-regulated αSMA. Similarly, MAPK/p38 and MAPK/ERK1/2 inhibition attenuated αSMA expression. H(2)O(2) induction by acetaldehyde was not potentiated by co-treatment with leptin nor did IL-6 neutralization reduce acetaldehyde-induced H(2)O(2) production. CONCLUSIONS: We conclude that leptin potentiates acetaldehyde-induced HSC activation and αSMA expression by an IL-6-dependent mechanism.

Kupffer cells mediate leptin-induced liver fibrosis.

BACKGROUND & AIMS: Leptin has profibrogenic effects in liver, although the mechanisms of this process are unclear. We sought to elucidate the direct and indirect effects of leptin on hepatic stellate cells (HSCs). METHODS: HSCs from Sprague-Dawley rats were exposed to leptin and expression of collagen-I, tissue inhibitor of matrix metalloproteinases-1 (TIMP1), transforming growth factor beta1 (TGF-beta1), and connective tissue growth factor (CTGF/CCN2) was assessed. The effects of medium from Kupffer cells (KCs) and sinusoidal endothelial cells (SECs) following leptin were evaluated in HSCs; alpha-smooth muscle actin (alphaSMA) production and KC signaling were analyzed. RESULTS: HSCs were not activated by incubation with leptin. However, HSCs cultured with medium taken from KCs that were incubated with leptin had increased expression of collagen I, TIMP1, TGF-beta1, and CTGF/CCN2, as well as alphaSMA protein levels and proliferation. These effects were leptin receptor dependent because conditioned medium from KCs isolated from leptin receptor-deficient Zucker (fa/fa) rats did not activate HSCs. In KCs incubated with leptin, messenger RNA and protein expression of TGF-beta1 and CTGF/CCN2 increased. Leptin potentiated signal transducer and activator of transcription 3, AKT, and extracellular signal-related kinase 1/2 phosphorylation in KCs and increased AP-1 and nuclear factor-kappaB DNA binding. Finally, addition of anti-TGF-beta to KC-conditioned medium inhibited HSC expression of collagen I, TIMP1, and CTGF/CCN2, whereas signal transducer and activator of transcription 3 inhibitor attenuated TGF-beta1 production by KC. CONCLUSIONS: Leptin mediates HSC activation and liver fibrosis through indirect effects on KC; these effects are partly mediated by TGF-beta1.

Roles of adipokines in liver injury and fibrosis.

Adipose tissue is now recognized as the largest endocrine organ in the body, secreting over 100 proteins termed adipokines that influence energy homeostasis, lipid physiology, inflammation, immune function and wound healing. Some of these proteins, such as TNFalpha, have important proinflammatory effects, but during hepatic injury are principally secreted at a local level within the liver. Their role in liver injury and fibrosis is beyond the scope of this review. However, circulating adipose-derived proteins such as leptin, adiponectin and resistin have important systemic effects, including the modulation of injury and fibrosis. The activities of these adipokines in the pathogenesis of liver injury and fibrosis will be the topic of this review.