Stress-associated premature senescence (SAPS) has been implicated in diabetes-induced vascular dysfunction. We have shown that microRNA34a (miR-34a) is involved in promoting senescence of the retinal microvasculature. Loss of nicotinamide phosphoribosyltransferase (NAMPT), a rate-limiting enzyme of NAD+ biosynthesis from nicotinamide mononucleotide (NMN), has been implicated in aging and metabolic diseases. Interestingly NAMPT is a target of miR34a, therefore, herein, we investigated the role and reciprocal relationship of miR34a and NAMPT on diabetes-induced senescence of the retinal vasculature. NAMPT expression and NAD+ content were significantly reduced in retina of streptozotocin-induced diabetic rats (STZ-rats, 8-12 weeks of hyperglycemia) and in human postmortem diabetic retinas. On the contrary, miR34a expression was found increased and positively correlated with augmented levels of senescence markers. Exposure of human retinal endothelial cells (HuREC) to glucidic stress (25mM) also decreased NAMPT and NAD+ levels while augmented the expression of miR34a and of senescence markers. Transfection of HuREC with miR-34a mimic, but not a scramble construct, in normal glucose conditions inhibited the expression of NAMPT and reduced NAD+ levels while promoting the expression of senescence markers. These effects of miR34a mimic on HuREC were halted by supplementation with NMN (0.05-1mM), but without modifying NAMPT expression. Lastly, NMN supplementation also prevented high glucose-induced loss of NAD+ and elevation of senescence markers. Our data show that high glucose/diabetes-induced SAPS in the retinal microvasculature involves miR34a-mediated blockade of NAMPT and consequent loss of NAD+. Moreover, our data suggest that NMN supplementation could be a viable therapeutic strategy to improve endothelial dysfunction in diabetic retinopathy.
M. Bartolli: None. R. Jadeja: None. M. Thounaojam: None. D. Gutsaeva: None. P. Martin: None.
National Institutes of Health (EY022416, EY028714)