The nucleolar protein NML regulates hepatic ATP levels during liver regeneration after partial hepatectomy

We previously identified a novel protein complex, eNoSC, which senses intracellular energy status and epigenetically regulates the rDNA locus by changing the ratio between the numbers of active and silent gene clusters. eNoSC contains a novel nucleolar protein, Nucleomethylin (NML), which has a methyltransferase-like domain and binds to Lys9-dimethylated histone H3 at the rDNA locus, along with the NAD⁺-dependent deacetylase SIRT1 and the histone methyltransferase SUV39H. The aim of this study was to determine the role of NML in liver after partial hepatectomy (PHx). We assessed liver regeneration and lipid metabolism after PHx in wild-type (WT) and NML transgenic (NML-TG) mice. Survival rates of NML-TG mice were reduced after PHx. We found that hepatic triglyceride content in NML-TG mice remained elevated 48 h after PHx, but not delayed liver regeneration. Moreover, hepatic ATP levels in NML-TG mice were higher than that in WT 48 h after PHx. These observations suggest that NML may regulate consumption of hepatic triglyceride in liver regeneration after PHx due to storage of excess ATP. The delayed consumption of hepatic triglyceride may be the cause of reduced survival rate in NML-TG mice.