Deactivation of hepatic stellate cells during liver fibrosis resolution in mice.
ABSTRACT Activated hepatic stellate cells (HSCs), the main fibrogenic cell type in the liver, undergo apoptosis after cessation of liver injury, which contributes to resolution of fibrosis. In this study, we investigated whether HSC deactivation constitutes an additional mechanism of liver fibrosis resolution.
HSC activation and deactivation were investigated by single-cell PCR and genetic tracking in transgenic mice that expressed a tamoxifen-inducible CreER under control of the endogenous vimentin promoter (Vimentin-CreER).
Single-cell quantitative polymerase chain reaction demonstrated activation of almost the entire HSC population in fibrotic livers, and a gradual decrease of HSC activation during fibrosis resolution, indicating deactivation of HSCs. Vimentin-CreER marked activated HSCs, demonstrated by a 6- to 16-fold induction of a membrane-bound green fluorescent protein (mGFP) Cre-reporter after injection of carbon tetrachloride, in liver and isolated HSCs, and a shift in localization of mGFP-marked HSCs from peri-sinusoidal to fibrotic septa. Tracking of mGFP-positive HSCs revealed the persistence of 40%-45% of mGFP expression in livers and isolated HSCs 30-45 days after carbon tetrachloride was no longer administered, despite normalization of fibrogenesis parameters; these findings confirm reversal of HSC activation. After fibrosis resolution, mGFP expression was observed again in desmin-positive peri-sinusoidal HSCs; no mGFP expression was detected in hepatocytes or cholangiocytes, excluding mesenchymal-epithelial transition. Notably, reverted HSCs remained in a primed state, with higher levels of responsiveness to fibrogenic stimuli.
In mice, reversal of HSC activation contributes to termination of fibrogenesis during fibrosis resolution, but results in higher responsiveness of reverted HSCs to recurring fibrogenic stimulation.
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ABSTRACT: We examined the effect of parasitologic cure of S. mansoni infection on liver fibrosis in mice. Praziquantel, 250 mg/kg body weight, was administered orally to mice 8 weeks after infection with 50 S. mansoni cercariae. We assessed liver fibrosis by chemical measurement of collagen content as measured by the estimation of hydroxyproline and by histologic examination at the time of treatment, and at 10 and 20 weeks post-treatment, in comparison with the same measurements in untreated S. mansoni-infected mice and age-matched normal control mice. The extent of infection was monitored by liver egg counts. Compared to normal uninfected mice, mice with untreated S. mansoni infection showed steady accumulation of liver collagen at the 3 measurement periods, reaching an average level of 15-fold greater than that found in normal mice at 28 weeks after infection. Mice treated with praziquantel showed a prompt decrease in S. mansoni liver egg load with no viable eggs 10 weeks after treatment. Liver fibrosis was modestly diminished in treated mice compared to untreated controls 10 weeks after treatment; fibrosis was arrested and liver collagen content had diminished to normal levels by 20 weeks after treatment. No praziquantel toxicity was noted. The survival of treated mice was markedly greater than that of untreated infected animals. We conclude that parasitologic cure of murine S. mansoni infection is followed by arrest and eventual partial reversal of liver fibrosis under the conditions employed.The American journal of tropical medicine and hygiene 04/1985; 34(2):314-21. · 2.53 Impact Factor
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ABSTRACT: Chemokines may be involved in the tissue response to injury regulating the influx of leukocytes, and modulating a number of other critical biologic actions, including angiogenesis, neoplastic growth, myo-fibroblast activation, and the response to viral infections. In the liver, up-regulated expression of different members of the chemokine system may be induced by almost all types of injury, and there is often a clear relation between the chemokine pattern activated by different types of injury and the predominant subclasses of leukocytes which infiltrate the liver. Neutralization of specific chemokines by passive immunization or the use of animals deficient in specific chemokines or chemokine receptors has indicated a causal relation between up-regulation of chemokines and leukocyte infiltration. Inflammation is part of the liver wound healing response, that in chronic conditions leads to the development of fibrosis and cirrhosis. Hepatic stellate cells, which play a leading role in the development of fibrosis following their transition to myofibroblasts, express different chemokines. Chemokine expression by stellate cells is regulated by soluble mediators, in particular pro-inflammatory cytokines, as well as growth factors, proteases, and products of oxidative stress. In addition, stellate cells also respond to chemokines with biologic actions relevant for tissue repair, such as cell migration or induction of other chemokines. These data indicate that chemokines in the liver may modulate the progression of liver fibrosis through actions on hepatic stellate cells.Frontiers in Bioscience 10/2002; 7:d1899-914. · 3.29 Impact Factor
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ABSTRACT: The myofibroblastic differentiation of hepatic stellate cells (HSC) is a critical event in liver fibrosis and is part of the final common pathway to cirrhosis in chronic liver disease from all causes. The molecular mechanisms driving HSC differentiation are not fully understood. Because macroscopic tissue stiffening is a feature of fibrotic disease, we hypothesized that mechanical properties of the underlying matrix are a principal determinant of HSC activation. Primary rat HSC were cultured on inert polyacrylamide supports of variable but precisely defined shear modulus (stiffness) coated with different extracellular matrix proteins or poly-L-lysine. HSC differentiation was determined by cell morphology, immunofluorescence staining, and gene expression. HSC became progressively myofibroblastic as substrate stiffness increased on all coating matrices, including Matrigel. The degree rather than speed of HSC activation correlated with substrate stiffness, with cells cultured on supports of intermediate stiffness adopting stable intermediate phenotypes. Quiescent cells on soft supports were able to undergo myofibroblastic differentiation with exposure to stiff supports. Stiffness-dependent differentiation required adhesion to matrix proteins and the generation of mechanical tension. Transforming growth factor-β treatment enhanced differentiation on stiff supports, but was not required. HSC differentiate to myofibroblasts in vitro primarily as a function of the physical rather than the chemical properties of the substrate. HSC require a mechanically stiff substrate, with adhesion to matrix proteins and the generation of mechanical tension, to differentiate. These findings suggest that alterations in liver stiffness are a key factor driving the progression of fibrosis.AJP Gastrointestinal and Liver Physiology 04/2011; 301(1):G110-8. · 3.65 Impact Factor