Conclusions
Slc25a51 is a fasting-induced gene that is needed for hepatic SIRT3 functions.
Methods
We examined Slc25a51 expression in the liver of fasted mice, and examined its circadian rhythm in wild-type mice and those with liver-specific deletion of the clock gene BMAL1 (LKO). We suppressed Slc25a51 expression in hepatocytes and the mouse liver using shRNA-mediated knockdown, and then examined mitochondrial NAD+ levels, SIRT3 activities, and acetylation levels of SIRT3 target proteins (IDH2 and ACADL). We measured mitochondrial oxygen consumption rate using Seahorse analysis in hepatocytes with reduced Slc25a51 expression.
Objective
SLC25A51 is a recently discovered mitochondrial NAD+ transporter. We tested the hypothesis that, during fasting, increased expression of SLC25A51 is needed for enhanced mitochondrial NAD+ uptake to sustain SIRT3 activity. Because the fasting-fed cycle and circadian rhythm are closely linked, we further tested the hypothesis that SLC25A51 is a circadian regulated gene.
Results
We found that fasting induced the hepatic expression of Slc25a51, and its expression showed a circadian rhythm-like pattern that was disrupted in LKO mice. Reduced expression of Slc25a51 in hepatocytes decreased mitochondrial NAD+ levels and SIRT3 activity, reflected by increased acetylation of SIRT3 targets. Slc25a51 knockdown reduced the oxygen consumption rate in intact hepatocytes. Mice with reduced Slc25a51 expression in the liver manifested reduced hepatic mitochondrial NAD+ levels, hepatic steatosis and hypertriglyceridemia. Conclusions: Slc25a51 is a fasting-induced gene that is needed for hepatic SIRT3 functions.