Leptin Stimulates Tissue Inhibitor of Metalloproteinase-1 in Human Hepatic Stellate Cells

Abstract

Leptin is recognized as a profibrogenic hormone in the liver, but the mechanisms involved have not been clarified. The tissue inhibitor of metalloproteinase (TIMP)-1, which acts through inhibition of collagen degradation, is synthesized by activated hepatic stellate cells (HSC) in response to fibrogenic substances. The capacity of leptin to induce TIMP-1 and its signaling molecules were investigated in a human HSC cell line, LX-2. Leptin stimulated TIMP-1 protein, mRNA, and promoter activity. JAK1 and -2, as well as STAT3 and -5, were activated. After leptin, there was increased expression of tyrosine 1141-phosphorylated leptin receptor, which may contribute to STAT3 activation. AG 490, a JAK inhibitor, blocked JAK phosphorylation with concomitant inhibition of STAT activation, TIMP-1 mRNA expression, and promoter activity. Leptin also induced an oxidative stress, which was inhibited by AG 490, indicating a JAK mediation process. ERK1/2 MAPK and p38 were activated, which was prevented by catalase, indicating an H 2 O 2 -dependent mechanism. Catalase treatment resulted in total suppression of TIMP-1 mRNA expression and promoter activity. SB203580, a p38 inhibitor, prevented p38 activation and reduced TIMP-1 message half-life with down-regulation of TIMP-1 mRNA. These changes were reproduced by overexpression of the dominant negative p38␣ and p38␤ mutants. PD098059, an ERK1/2 inhibitor, opposed ERK1/2 activation and TIMP-1 promoter activity, leading to TIMP-1 mRNA down-regulation. Thus, leptin has a direct action on liver fibrogenesis by stimulating TIMP-1 production in activated HSC. This process appears to be mediated by the JAK/STAT pathway via the leptin receptor long form and the H 2 O 2 -dependent p38 and ERK1/2 pathways via activated JAK.

Cellular and molecular mechanisms in liver fibrogenesis

“…Moreover, leptin has been shown to up-regulate type I procollagen expression, to potentiate TGFβ1-mediated effects [53], to induce tissue inhibitor of metalloproteinase-1 (TIMP1) expression [54] as well as to stimulate HSC proliferation and survival [55], and up-regulate expression of chemokines (like CCL2) in a NF-kB-dependent way [52]. Although leptin may stimulate multiple signaling pathways, literature data suggest that its pro-fibrogenic effects are mainly NADPH oxidase and ROS dependent [56] and may also be mediated by inhibition of the expression and activity of peroxisome proliferator-activated receptor- (PPAR-), which maintains HSC quiescence and reverses HSC trans-differentiation to MFs.…”

Modulation of Liver Fibrosis by Adipokines

“…Like for many other cytokine receptors, expression of ObRb is low in quiescent HSCs, and increases during the activation process [17]. As far as the induction of fibrosis is concerned, exposure of culture-activated HSCs to leptin has been shown to upregulate type I procollagen expression, potentiate the effects of TGF-β1 [17,18] and induce the expression of tissue inhibitor of metalloproteinase-1 [19]. In addition, leptin increases HSC proliferation and survival [20], and upregulates the expression of chemokines such as monocyte chemoattractant protein-1 via NF-ĸB activation [16].…”

Cytochrome P4502E1 primes macrophages to increase TNF-α production in response to lipopolysaccharide

“…This was assessed by the addition of cis-parinaric acid (Molecular Probes) to the macrophage culture at a final concentration of 5 M. Subsequent to peroxidative stress, cis-parinaric acid is degraded, resulting in decreased fluorescence intensity. The loss of fluorescence is proportional to the lipid peroxidation process (6,27,31,37). Cis-parinaric acid fluorescence was measured at 325 nm for excitation and 413 nm for emission.…”

“…This was determined by the addition of hydroethidine (Molecular Probes) to the macrophage culture at a final concentration 10 M. Hydroethidine is oxidized by O 2 Ϫ produced in the cells. The loss of fluorescence in the cells is proportional to the superoxide anion generated (6,7,37). Hydroethidine fluorescence was measured at 352 nm for excitation and 434 nm for emission.…”

“…The DPIinhibitable rate of NADPH consumption was used to measure NADPH oxidase activity (47). NADPH consumption was measured by the decrease in absorbance at 340 nm in a Carey Bio100 spectro- (6,7). DCF fluorescence was measured at 488 nm for excitation and 525 nm for emission.…”