Abstract
Purpose :
Post-translational modification of proteins by O-linked N-Acetylglucosamine (O-GlcNAcylation) is enhanced by diabetes and obesity. O-GlcNAcylation has recently emerged as a critical regulator of mitochondrial function. The aim of this study was to investigate the hypothesis that the renin-angiotensin system regulates retinal protein O-GlcNAcylation and mitochondrial function.
Methods :
Mice fed a high fat diet were treated chronically with the angiotensin converting enzyme inhibitor captopril or captopril plus the Mas receptor antagonist A779. Western blotting and qPCR were used to analyze retinal homogenates. Similar analyses were performed on lysates from human MIO-M1 retinal Müller cell cultures exposed to media supplemented with Angiotensin-(1-7). Culture conditions were manipulated to influence the hexosamine biosynthetic pathway (HBP) and/or signaling downstream of the Mas receptor.
Results :
Captopril attenuated the increase in retinal protein O-GlcNAcylation that was observed in obese mice in a manner dependent on Mas receptor activation. In MIO-M1 cells, Angiotensin-(1-7) enhanced cAMP levels and inhibited O-GlcNAcylation. The repressive effect on O-GlcNAcylation was dependent on exchange protein activated by cAMP (EPAC), but not protein kinase A, and was recapitulated by a constitutively active variant of the small GTPase Rap1. Angiotensin-(1-7) suppressed O-GlcNAcylation by inhibition of O-GlcNAc Transferase (OGT) activity. O-GlcNAcylation enhanced cellular respiration and promoted mitochondrial superoxide levels in cells in culture and in the retina, whereas Angiotensin-(1-7) signaling prevented the effect.
Conclusions :
These studies identify a novel molecular link between Angiotensin-(1-7), O-GlcNAcylation, and oxidative stress in the retina. Thus, targeted activation of Angiotensin-(1-7) signaling may be beneficial in addressing the abnormally elevated O-GlcNAcylation and mitochondrial dysfunction that is associated with diabetic retinal complications.
This is a 2020 ARVO Annual Meeting abstract.