Ahnak depletion accelerates liver regeneration by modulating the TGF-β/Smad signaling pathway

Abstract

Ahnak, a large protein first identified as an inhibitor of TGF-B signaling in human neuroblastoma, was recently shown to pro-mote TGF-B in some cancers. The TGF-B signaling pathway re-gulates cell growth, various biological functions, and cancer growth and metastasis. In this study, we used Ahnak knockout (KO) mice that underwent a 70% partial hepatectomy (PH) to investigate the function of Ahnak in TGF-B signaling during liver regeneration. At the indicated time points after PH, we analyzed the mRNA and protein expression of the TGF -B/Smad signaling pathway and cell cycle-related factors, evaluated the cell cycle through proliferating cell nuclear antigen (PCNA) immunostai-ning, analyzed the mitotic index by hematoxylin and eosin staining. We also measured the ratio of liver tissue weight to body weight. Activation of TGF-B signaling was confirmed by analyzing the levels of phospho-Smad 2 and 3 in the liver at the indicated time points after PH and was lower in Ahnak KO mice than in WT mice. The expression levels of cyclin B1, D1, and E1; proteins in the Rb/E2F transcriptional pathway, which regulates the cell cycle; and the numbers of PCNA-positive cells were increased in Ahnak KO mice and showed tendencies op-posite that of TGF-B expression. During postoperative regene-ration, the liver weight to body weight ratio tended to increase faster in Ahnak KO mice. However, 7 days after PH, both groups of mice showed similar rates of regeneration, following which their active regeneration stopped. Analysis of hepatocytes under-going mitosis showed that there were more mitotic cells in Ahnak KO mice, consistent with the weight ratio. Our findings suggest that Ahnak enhances TGF-B signaling during postoper-ative liver regeneration, resulting in cell cycle disruption; this highlights a novel role of Ahnak in liver regeneration. These results provide new insight into liver regeneration and poten-tial treatment targets for liver diseases that require surgical treatment. [BMB Reports 2022; 55(8): 401-406]