Genistein enhances NAD⁺ biosynthesis by upregulating nicotinamide phosphoribosyltransferase in adipocytes

A decrease in the NAD⁺ level in adipocytes causes adipose-tissue dysfunction, leading to systemic glucose, and lipid metabolism failure. Therefore, it is necessary to develop small molecules and nutraceuticals that can increase NAD⁺ levels in adipocytes. Genistein, a nutraceutical derived from soybeans, has various physiological activities and improves glucose and lipid metabolism. In this study, we aimed to unravel the effects of genistein on the NAD⁺ level in adipocytes and the underlying molecular mechanisms. Genistein enhanced NAD⁺ biosynthesis by increasing the expression of nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme in NAD⁺ biosynthesis. A pull-down assay using genistein-immobilized beads revealed prohibitin 1 (PHB1) as a target protein of genistein. The knockdown of Phb1 suppressed the genistein-induced increase in NAMPT expression and NAD⁺ level in adipocytes. Genistein-bound PHB1 contributed to the stabilization of the transcription factor CCAAT/enhancer-binding protein β through the activation of extracellular signal-regulated kinase, resulting in increased NAMPT expression at the transcriptional level. Genistein induced the dephosphorylation of peroxisome proliferator-activated receptor at serine 273 and increased the level of the insulin-sensitizing adipokine adiponectin in adipocytes, whereas the knockdown of Nampt and Phb1 abolished these genistein-mediated effects. Our results proved the potential efficacy of genistein in increasing the NAD⁺ level and restoring metabolic function in adipocytes. Furthermore, we identified PHB1, localized to the plasma membrane, as a novel candidate target protein for increased expression of NAMPT in adipocytes. Overall, these findings will assist in developing NAD⁺-boosting nutraceuticals to alleviate metabolic dysfunctions in adipose tissues.