SIRT1 selectively exerts the metabolic protective effects of hepatocyte nicotinamide phosphoribosyltransferase

Calorie restriction abates aging and cardiometabolic disease by activating metabolic signaling pathways, including nicotinamide adenine dinucleotide (NAD(+)) biosynthesis and salvage. Nicotinamide phosphoribosyltransferase (NAMPT) is rate-limiting in NAD(+) salvage, yet hepatocyte NAMPT actions during fasting and metabolic duress remain unclear. We demonstrate that hepatocyte NAMPT is upregulated in fasting mice, and in isolated hepatocytes subjected to nutrient withdrawal. Mice lacking hepatocyte NAMPT exhibit defective FGF21 activation and thermal regulation during fasting, and are sensitized to diet-induced glucose intolerance. Hepatocyte NAMPT overexpression induced FGF21 and adipose browning, improved glucose homeostasis, and attenuated dyslipidemia in obese mice. Hepatocyte SIRT1 deletion reversed hepatocyte NAMPT effects on dark-cycle thermogenesis, and hepatic FGF21 expression, but SIRT1 was dispensable for NAMPT insulin-sensitizing, anti-dyslipidemic, and light-cycle thermogenic effects. Hepatocyte NAMPT thus conveys key aspects of the fasting response, which selectively dissociate through hepatocyte SIRT1. Modulating hepatocyte NAD(+) is thus a potential mechanism through which to attenuate fasting-responsive disease. NAD + metabolism is potential target to treat metabolic disorders, in part due to the effects of the NAD + dependent enzyme Sirt1. Here the authors report that hepatic nicotinamide phosphoribosyltransferase, a rate-limiting step in the NAD + salvage pathway, regulates dark-cycle thermogenesis in a Sirt1-dependent but light-cycle thermogenesis and glucose homeostasis in a Sirt1-independent manner.

Automated summary

This study demonstrates the upregulation of hepatocyte NAMPT during fasting, which plays a role in regulating FGF21 activation and glucose homeostasis. Moreover, hepatic NAMPT can improve dyslipidemia and induce adipose browning in obese mice. Modulating hepatocyte NAD(+) may be a potential mechanism to attenuate fasting-responsive disease.