Restoration of Autophagic Flux Improves Endothelial Function in Diabetes Through Lowering Mitochondrial ROS-mediated eNOS Monomerization

<a>Endothelial nitric oxide synthase (eNOS) monomerization and uncoupling play crucial roles in mediating vascular dysfunction in diabetes mellitus although the underlying mechanisms are still incompletely understood. Growing evidence indicates that autophagic dysregulation is involved in the pathogenesis of diabetic endothelial dysfunction, however, whether autophagy regulates eNOS activity through controlling eNOS monomerization/dimerization remains elusive. The present study shows that autophagic flux was impaired in the endothelium of diabetic <i>db/db</i> mice and in human endothelial cells exposed to advanced glycation end products or oxidized low-density lipoprotein. Inhibition of autophagic flux by chloroquine or bafilomycin A1 were sufficient to induce eNOS monomerization and lowers nitric oxide bioavailability through raising mitochondrial reactive oxygen species (mtROS). Restoration of autophagic flux by overexpressing transcription factor EB (TFEB), a master regulator of autophagy and lysosomal biogenesis, decreased endothelial cell oxidative stress, increased eNOS dimerization and improved endothelium-dependent relaxations (EDR) in <i>db/db</i> mouse aortas. Inhibition of mammalian target of rapamycin kinase (mTOR) increased TFEB nuclear localization, reduced mtROS accumulation, facilitated eNOS dimerization, and enhanced EDR in <i>db/db</i> mice. Moreover, calorie restriction also elevated TFEB expression, improved autophagic flux, and restored EDR in the aortas of <i>db/db</i> mice. Taken together, the present study reveals that mtROS-induced eNOS monomerization is closely associated with the impaired TFEB-autophagic flux axis leading to endothelial dysfunction in diabetic mice.</a>