7, Supporting Table 1). These results are consistent with the observation that these double knockout mice maintain high SAMe levels with a concurrent increased flux from PE to PC, but do not develop liver steatosis. It has recently been suggested that PC made via PEMT
may be an important source of hepatic TG. Herein we investigated the role of SAMe on TG homeostasis and found that activation of PEMT by an excess of hepatic SAMe leads to increased TG synthesis and ultimately to liver steatosis. For these studies we used Gnmt−/− mice, a model we developed which is characterized by the high hepatic content of SAMe, and the rapid development of fatty liver. We initially observed that hepatocytes from Gnmt−/− animals maintained on a normal diet this website present with normal lipogenesis and FA β-oxidation but with increased TG secretion. This is consistent with recent observations showing that low SAMe stimulates de novo lipogenesis in the liver, while impairing VLDL GSK126 nmr assembly and TG secretion. We subsequently observed that the flux from PE to PC via PEMT was markedly stimulated in Gnmt−/− hepatocytes, which is in perfect agreement with the observation that this model is characterized by a 40-fold increase in hepatic SAMe concentration. Concurrent with
PEMT’s cellular localization, we observed a reduction in microsomal PE concomitant with an increase in PC in the Gnmt−/− mice. Whereas the mass of PE in whole liver was reduced 2-fold, PC content was only slightly increased, suggesting an increase in PC catabolism and/or secretion in HDL in mutant mice. Accordingly, both the mass of hepatic DG and TG and the serum HDL-PC levels increased in Gnmt−/− mice compared to WT animals. These results are consistent with recent findings showing that membrane
PC can be an important precursor of liver TG under normal physiological conditions. Administration of an MDD to Gnmt−/− mice normalized hepatic SAMe content, Ibrutinib molecular weight which is fully consistent with our understanding of the function of GNMT in methionine catabolism. More important, in addition to lowering hepatic SAMe, placing the Gnmt−/− mice on an MDD also served to restore normal hepatic lipid metabolism, indicating that SAMe is the rate-limiting substrate linking PE with TG via PC and DG. The observation that PEMT inhibition with DZA in Gnmt−/− hepatocytes resulted in decreased TG levels further supports the role of PEMT in this process. These results demonstrate for the first time that PEMT is an unexpected source of hepatic TG, particularly in cases of SAMe excess. We conclude that stimulation of the PEMT pathway induced by high SAMe can explain hepatic steatosis in Gnmt mutant mice. This finding is clearly relevant to human disease, as children with GNMT mutations were recently identified to suffer from liver injury.