Lipopolysaccharide Reverses Hepatic Stellate Cell Activation In Vitro and In Vivo via Modulation of c‐Myb and SMAD7

Abstract

BackgroundDuring liver injury, the perisinusoidal quiescent hepatic stellate cells (HSCs) become activated and transdifferentiate into highly proliferative myofibroblastic phenotype (aHSCs) that expresses α‐smooth muscle actin (αSMA) and platelet‐derived growth factor β receptor (PDGFβR). aHSCs are the major fibrogenic cell type regardless of etiology of chronic liver disease. Their interactions with gut‐derived bacterial lipopolysaccharide (LPS), a potent inflammatory mediator, are implicated in hepatic fibrogenesis. However, evidence also indicates that LPS can attenuate fibrogenic characteristics of aHSCs. We examined molecular mechanisms of anti‐fibrogenic effects of LPS on aHSCs in vitro and in vivo.MethodsCulture‐activated rat HSCs were exposed to 1–100 ng/ml LPS for 24h and parameters of fibrosis and inflammatory cytokines/chemokines were determined by q‐RT‐PCR, Western and immunohistochemical analyses. In vivo, HSC activation and liver fibrosis were induced in rats by CCl4 administration for 3 weeks, after which LPS (5 mg/kg; ip) or vehicle‐PBS was administered. HSCs were isolated 24h later and fibrogenic/inflammatory parameters were analyzed.ResultsLPS, concentration‐dependently, induced phenotypic changes in aHSCs as illustrated by reduction in cell size and rounded shape. LPS strongly down‐regulated mRNA and protein expressions of αSMA, as well as PDGFβR, TGFβRI, Col1α1 and fibronectin. These effects of LPS were prevented by its inhibitor polymyxin B. The LPS‐induced size/shape change of aHSCs was associated with loss of proliferation (Ki67 staining) and down‐regulation of PDGFβR, without any effect on viability, or lipid accumulation (typical of quiescent HSCs). Mechanistically, LPS significantly down‐regulated mRNA and protein expression of c‐Myb, a transcription factor for αSMA, and up‐regulated Smad7 that inhibits Smad2/3–4‐induced transcription of Col1α1. Furthermore, HSCs isolated from in vivo LPS‐treated CCl4‐fibrotic rats demonstrated reduced proliferation, and down‐regulation of αSMA, PDGFβR, TGFβRI and c‐Myb expression, and increased expression of SMAD7. Additionally, in vitro exposure of HSCs isolated from CCl4 and CCl4+LPS‐treated rats to LPS induced further phenotypic change, inhibition of proliferation, and down‐regulation of αSMA, c‐Myb and PDGFβR expression suggesting that the in vivo LPS‐treated HSCs are not desensitized to the subsequent LPS challenge. Interestingly, LPS elicited powerful pro‐inflammatory response (increased TNFα, IL6 and CXCL1 expression) but also strongly up‐regulated expression of anti‐inflammatory IL10 in HSCs.ConclusionLPS limits fibrosis by modulation of c‐Myb and SMAD7 thus down‐regulating the key fibrogenic mechanisms in aHSCs that may have important implication in chronic liver disease.Support or Funding InformationSupported by VA Merit Review Award 1IO1BX001174‐01 and Department of Defense W81XWH‐14.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.