PP2Acα positively regulates the termination of liver regeneration in mice through the AKT/GSK3β/Cyclin D1 pathway

Background & Aims: Liver injury triggers a highly organized and ordered liver regeneration (LR) process. Once regeneration is complete, a stop signal ensures that the regenerated liver is an appropriate functional size. The inhibitors and stop signals that regulate LR are unknown, and only limited information is available about these mechanisms. Methods: A 70% partial hepatectomy (PH) was performed in hepatocyte-specific PP2Ac alpha-deleted (PP2Ac alpha(-/-)) and control (PP2Ac alpha(+/+)) mice. LR was estimated by liver weight, serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels and cell proliferation, and the related cellular signals were analyzed. Results: We found that the catalytic subunit of PP2A was markedly upregulated during the late stage of LR. PP2Ac alpha(-/-) mice showed prolonged LR termination, an increased liver size compared to the original mass and lower levels of serum ALT and AST compared with control mice. In these mice, cyclin D1 protein levels, but not mRNA levels, were increased. Mechanistically, AKT activated by the loss of PP2Ac alpha inhibited glycogen synthase kinase 3 beta (GSK3 beta) activity, which led to the accumulation of cyclin D1 protein and accelerated hepatocyte proliferation at the termination stage. Treatment with the PI3K inhibitor wortmannin at the termination stage was sufficient to inhibit cyclin D1 accumulation and hepatocyte proliferation. Conclusions: PP2Ac alpha plays an essential role in the proper termination of LR via the AKT/GSK3 beta/Cyclin D1 pathway. Our findings enrich the understanding of the molecular mechanism that controls the termination of LR and provides a potential therapeutic target for treating liver injury. (C) 2015 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.