NAD+ Anabolism Disturbance Causes Glomerular Mesangial Cell Injury in Diabetic Nephropathy
Xue Li, Yankun Li, Fengxia Li, Qi Chen, Zhonghua Zhao, Xueguang Liu, Nong Zhang, Hui Li
Abstract
The homeostasis of NAD+ anabolism is indispensable for maintaining the NAD+ pool. In mammals, the mainly synthetic pathway of NAD+ is the salvage synthesis, a reaction catalyzed by nicotinamide mononucleotide adenylyltransferase (NAMPT) and nicotinamide mononucleotide adenylyltransferase (NMNATs) successively, converting nicotinamide (NAM) to nicotinamide mononucleotide (NMN) and NMN to NAD+, respectively. However, the relationship between NAD+ anabolism disturbance and diabetic nephropathy (DN) remains elusive. Here our study found that the disruption of NAD+ anabolism homeostasis caused an elevation in both oxidative stress and fibronectin expression, along with a decrease in Sirt1 and an increase in both NF-κB P65 expression and acetylation, culminating in extracellular matrix deposition and globular fibrosis in DN. More importantly, through constitutively overexpressing NMNAT1 or NAMPT in human mesangial cells, we revealed NAD+ levels altered inversely with NMN levels in the context of DN and, further, their changes affect Sirt1/NF-κB P65, thus playing a crucial role in the pathogenesis of DN. Accordingly, FK866, a NAMPT inhibitor, and quercetin, a Sirt1 agonist, have favorable effects on the maintenance of NAD+ homeostasis and renal function in db/db mice. Collectively, our findings suggest that NMN accumulation may provide a causal link between NAD+ anabolism disturbance and diabetic nephropathy (DN) as well as a promising therapeutic target for DN treatment.