C1q/TNF–Related Protein-3 attenuates endothelial dysfunction in diabetic retinopathy via the Nitric Oxide signaling pathway

Abstract

Background Diabetic retinopathy (DR) is a severe microvasculature complication of diabetes. Restoration of dysfunctional endothelial cells represents a promising approach to treatment of DR. It has been demonstrated that a number of CTRP (C1q/tumor necrosis factor-related protein) members improves vascular endothelial function of the aortic vasculature. However, the role of CTRPs in the treatment of DR remains largely unresolved. Therefore, the aim of this study was to determine whether members of the CTRP family improve diabetes-induced endothelial dysfunction of retinal vasculature, thus exhibiting a protective effect against diabetic injury of retina. Methods The vasoactivity of currently identified murine CTRP family members was assessed in vascular rings and the underlying molecular mechanisms elucidated in human retinal microvascular endothelial cells. We then mimicked diabetic retinopathy both in vitro and in vivo, after which they were treated with CTRP3, and the vasoactivity, apoptotic cell death and vascular leakage in the retina were evaluated. Discovery-drive approaches followed by cause-effect analysis were used to uncover the molecular mechanisms of CTRP3. Results Our results demonstrate that CTRP3, CTRP5, and CTRP9 exert vasorelaxant effects on macro- and micro-vessels, with CTRP3 being the most potent in micro-vessels. The effects of CTRP3 were found to be endothelium-dependent via the AdipoR1/AMPK/eNOS/Nitric Oxide (NO) pathway. In in vitro microvascular reactivity studies, CTRP3 successfully improved high glucose/high lipid-induced impairment of endothelium-dependent vasodilatation. Blockade of either AMPK or eNOS completely abolished the previously observed effects of CTRP3. In addition, in the murine diabetic retinopathy model, CTRP3 treatment increased endothelium-dependent relaxation and NO levels in microvessels, and inhibited apoptotic cell death and vascular leakage in the retina. Finally,blockade of NO synthesis completely abolished the effects of CTRP3 that had been measured previously. Conclusion Taken together, our findings reveal that the AdipoR1/AMPK/eNOS/NO signaling pathway, through which CTRP3 reverses endothelial dysfunction of the microvasculature by normalization of impaired vasodilatation, represents a novel intervention effective against diabetic injury of retina.