NAMPT-Mediated NAD⁺ Biosynthesis in Adipocytes Regulates Adipose Tissue Function and Multi-organ Insulin Sensitivity in Mice

Obesity is associated with adipose tissue dysfunction and multi-organ insulin resistance. However, the mechanisms of such obesity-associated systemic metabolic complications are not clear. Here, we characterized mice with adipocyte-specific deletion of nicotinamide phosphoribosyltransferase (NAMPT), a rate-limiting NAD⁺ biosynthetic enzyme known to decrease in adipose tissue of obese and aged rodents and people. We found that adipocyte-specific Nampt knockout mice had severe insulin resistance in adipose tissue, liver, and skeletal muscle and adipose tissue dysfunction, manifested by increased plasma free fatty acid concentrations and decreased plasma concentrations of a major insulin-sensitizing adipokine, adiponectin. Loss of Nampt increased phosphorylation of CDK5 and PPARγ (serine-273) and decreased gene expression of obesity-linked phosphorylated PPARγ targets in adipose tissue. These deleterious alterations were normalized by administering rosiglitazone or a key NAD⁺ intermediate, nicotinamide mononucleotide (NMN). Collectively, our results provide important mechanistic and therapeutic insights into obesity-associated systemic metabolic derangements, particularly multi-organ insulin resistance.