Invited Lecture(JSH)
Thu. November 5th   14:30 - 15:10   Room 5: Portopia Hotel South Wing Ohwada A
Invited Lecture8
 Fibrosis in Nonalcoholic steatohepatitis (NASH)
David Brenner
University of California, San Diego School of Medicine
In the normal liver, hepatic stellate cells (HSCs) have a quiescent phenotype in which they function as pericytes and as the major storage site of vitamin A. In metabolic and hepatotoxic injury, the HSCs activate to become myofibroblasts and secrete extracellular matrix, producing the fibrous scar of liver fibrosis. Upon removal of the etiological agent, experimental and clinical liver fibrosis can regress, and the myofibroblasts are eliminated either by apoptosis or reversion to an inactivated phenotype. Although hepatic stellate cell phenotypes have been extensively studied in experimental carbon tetrachloride, bile duct ligation, and alcoholic liver disease, the role of HSCs in clinical and experimental NASH is largely unknown.
Foz/foz mice have a mutation in the ALMS1 gene that results on hyperphagia. C57b6 foz/foz mice on a Western diet for 12 weeks develop NASH with fibrosis. Switching back to a chow diet results in regression of NASH. In this study, we purified HSCs on a chow diet, after 12 weeks on a Western diet, and after 8 weeks back on a chow diet. These HSCs were subjected to single cell RNA-seq, analyzed into clusters, and compared to the well-characterized HSC phenotypes (quiescent, activated, and inactivated) in the chronic CCl4-induced model of liver fibrosis. As expected, the chow fed mice exclusively expressed quiescent HSCs. On the Western diet, the quiescent HSC clusters disappeared and were replaced by clusters of activated HSCs. On return to the chow diet, the activated HSCs resolved nearly completely with the emergence of new clusters. One cluster closely matched the inactivated HSC phenotype. The inactivated HSCs were similar to, but distinct from, quiescent HSCs.
We have also analyzed human HSCs purified from normal and NASH livers that have been declined for liver transplantation. The HSCs were purified using methodology of perfusion and gradient centrifugation adopted from rodent HSCs. Because of contamination with fatty hepatocytes, the HSCs were cultured to obtain human HSCs with high purity. Despite the culture on plastic, human HSCs from NASH and normal livers maintained significant differences in gene expression. In particular, the gene expression of IRS2 and N4BP2 decreased on activation, and the gene expression of CD14 and SLC5A12 increased on activation. Thus, epigenetic changes determining gene expression are maintained in culture of human HSCs.
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