miR-146a impedes the anti-aging effect of AMPK via NAMPT suppression and NAD+/SIRT inactivation

Nicotinamide adenine dinucleotide (NAD+) is indispensable for the anti-aging activity of the sirtuin (SIRT) family enzymes. AMP-activated protein kinase (AMPK) upregulates NAD+ synthesis and SIRT activity in a nicotinamide phosphoribosyltransferase (NAMPT)-dependent manner. However, the molecular mechanisms that affect AMPK-driven NAMPT expression and NAD+/SIRT activation remain unclear. In this study, we tried to identify senescence-associated microRNAs (miRNAs) that negatively regulate the cascade linking AMPK and NAMPT expression. miRNA-screening experiments showed that the expression of miR-146a increased in senescent cells but decreased following AMPK activation. Additionally, miR-146a overexpression weakened the metformin-mediated upregulation of NAMPT expression, NAD+ synthesis, SIRT activity, and senescence protection, whereas treatment with the miR-146a inhibitor reversed this effect. Importantly, these findings were observed both in vitro and in vivo. Mechanistically, miR-146a directly targeted the 3'-UTR of Nampt mRNA to reduce the expression of NAMPT. AMPK activators metformin and 5-aminoimidazole-4-carboxamide (AICAR) hindered miR-146a expression at the transcriptional level by promoting IκB kinase (IKK) phosphorylation to attenuate nuclear factor-kappaB (NF-κB) activity. These findings identified a novel cascade that negatively regulates the NAD+/SIRT pathway by suppressing miR-146a-mediated NAMPT downregulation. Furthermore, our results showed that miR-146a impedes the anti-aging effect of AMPK. This mutual inhibitory relationship between miR-146a and AMPK enriches our understanding of the molecular connections between AMPK and SIRT and provides new insight into miRNA-mediated NAD+/SIRT regulation and an intervention point for the prevention of aging and age-related diseases.