PKM2 Drives Lactate-mediated Fibrosis in Liver Transplantation

Background. Pyruvate kinase M2 (PKM2) is a key enzyme in glycolysis and plays a crucial role in regulating lactate levels, which promotes hepatic stellate cell activation, leading to fibrosis. Sirtuin 3 (SIRT3) regulates the acetylation level of PKM2 as a deacetylase, thereby mediating the glycolysis process in the liver. Methods. Mice underwent orthotopic liver transplantation. Immunoprecipitation was used to assess the acetylation levels of PKM2 and the interaction between PKM2 and Sirtuins and Western blot (WB) was performed to assess protein level of PKM2 and Sirtuins. Liver fibrosis was detected by immunohistochemistry, WB, Sirius Red staining, and Masson staining. Results. Overexpression of SIRT3 alleviates fibrosis following nonalcoholic fatty liver disease donor liver transplantation by enhancing PKM2 deacetylation, thereby reducing lactate levels in hepatic macrophages. Mechanistically, the deacetylation of PKM2 by SIRT3 in hepatic macrophages was identified as a potential therapeutic target for intrahepatic lactate accumulation through bioinformatics analysis combined with in vivo and in vitro experiments. These findings were further confirmed by immunoprecipitation and WB. Finally, in our in vitro nonalcoholic fatty liver disease model, SIRT3 overexpression reduced lactate levels in hepatic macrophages, with K367 identified as the critical deacetylation site on PKM2 that modulates its lactate-metabolizing function. Conclusions. PKM2 acetylation-mediated high lactate level, which leads to liver fibrosis, is driven by low SIRT3 expression. This finding may represent a potential therapeutic target in clinical fatty liver transplantation.