The morphological and functional assessment of FAP+ and -SMA+-cells in different times of rat toxic liver fibrosis

Qualitative study of the source of the fibro-genic cell population in relation to the etiology and stage of fibrosis, as well as an understanding of the molecular mechanisms that regulate changes in the phenotype of hepatic fibroblasts, are of paramount importance in the development of pharmacological drugs. The purpose of the study was a morphological and functional assessment of activated portal fibroblasts (FAP+) and fat-accumulating cells (α-SMA+) of the liver at various stages of toxic liver fibrosis in rats. Liver fibrosis and cirrhosis in male Wistar rats were induced with thioacetamide solution for 17 weeks. Morphological examination of the liver was carried out on paraffin sections stained with hematoxylin and eosin using the Mallory method; immunohistochemical examination was carried out using polyclonal rabbit antibodies to the portal fibroblast antigen FAP and using monoclonal mouse antibodies to the α-SMA+ cell antigen. Before the onset of liver fibrosis stage F3/F4, from weeks 3 to 7, the number of FAP+ and α-SMA+ cells increased alternately. During the stages of transformation of fibrosis into cirrhosis from 7 to 11 weeks, their number increased slightly. At the stage of incomplete (F5) and before the onset of significant cirrhosis (F6) from weeks 11 to 15, the number of FAP+ and α-SMA+ cells were inconsistent and there was an alternating increase and decrease in their number. α-SMA+ cells before the start of the process of transformation of fibrosis into cirrhosis (F4/F5) were observed in sinusoids and foci of necrosis. Then they were detected both in sinusoids and in connective tissue trabeculae. FAP+ cells at the stage of portal fibrosis (F1) were localized near the interlobular vessels and interlobular bile ducts of the portal zones, and from the F2/F3 period they were detected in connective tissue trabeculae and sinusoids. In quantitative terms, α-SMA+ cells predominated at all stages of fibrosis. Based on the results obtained, it can be assumed that FAP+ cells make a major contribution to the development of the portal and initial stages of bridging fibrosis. They should be considered as one of the myofibroblast populations in thioacetamide-induced liver fibrogenesis.