CINC-2 and miR-199a-5p in exosomes secreted by transplanted Thy1+ cells activate hepatocytic progenitor cell growth in rat liver regeneration

Abstract Background Small hepatocyte-like progenitor cells (SHPCs) are hepatocytic progenitor cells that transiently form clusters in rat livers treated with retrorsine and with 70% partial hepatectomy (PH). We previously reported that transplantation of Thy1 + cells derived from d-galactosamine-treated livers promotes SHPC expansion, resulting in the acceleration of liver regeneration. Extracellular vesicles (EVs) produced by Thy1 + cells act on sinusoidal endothelial cells (SECs) and Kupffer cells to secrete IL17B and IL25, respectively, resulting in SHPC activation through IL17 receptor B (RB) signaling. Our aim is to identify factors in Thy1-EVs that activate IL17RB signaling. Methods Thy1 + cells isolated from rats with d-galactosamine-induced liver injury were cultured for one week. Although some liver stem/progenitor cells proliferated into colonies, others maintained as mesenchymal cells (MCs). Thy1-MCs or Thy1-liver stem/progenitor cells were transplanted into retrorsine/PH-treated livers to examine their effects on SHPCs. SHs isolated from adult rat livers were used to validate factors regulating growth induction. Results The number and size of SHPCs remarkably increased in livers transplanted with Thy1-MCs. Comprehensive analysis of Thy1-MC-EVs revealed that miR-199a-5p , CINC-2, and MCP-1 are candidates for stimulating SHPC growth. Administration of the miR-199a-5p mimic, and not CINC-2, promoted SH growth. SECs treated with CINC-2 induced IL17b expression and their conditioned medium promoted SH growth. Conclusion Thy1-MC transplantation may accelerate liver regeneration due to SHPCs expansion, which is stimulated by CINC-2/IL17RB signaling and miR-199a-5p .