Doctor of Philosophy
Dr. Subrata Chakrabarti
Chronic diabetic complications are significant causes of morbidity. In diabetes, as the cellular changes are similar to aging, we investigated the role of sirtuins (SIRTs) in chronic diabetic complications.
We examined glucose and aging-induced changes in the endothelial cells (ECs), the primary targets of chronic diabetic complications. ECs in high glucose showed evidences of early senescence, being more pronounced in microvascular ECs in association with decreased SIRT1 and FOXO1-dependent reduction in antioxidant gene expressions. A regulatory relationship of deacetylator SIRT1 and histone acetylator p300 was identified. Renal and retinal tissues of diabetic animals showed similar results.
Having established such changes, we investigated microRNA-mediated regulation of glucose-induced SIRT1 alteration. We examined the effect of miRNA-195 (miR-195), a SIRT1-targeting miRNA, on the development of diabetes-induced changes in the ECs and retina. High glucose caused increased miR-195 levels and decreased SIRT1 expression in the ECs. We showed that miR-195 binds to the 3′ untranslated region of SIRT1 and transfection with miR-195 antagomir or over-expression of SIRT1 prevented above changes, whereas transfection with miR-195 mimic produced glucose-like effects. miR-195 expression was upregulated in retinas of diabetic rats and intravitreal injection of miR-195 antagomir ameliorated reduction of SIRT1 and associated changes in diabetes. These studies identified a novel mechanism whereby miR-195 regulates SIRT1-mediated tissue damage.
Based on results above, we examined whether in diabetes, SIRT1 alteration mediate specific effects in the target organs affected in diabetic complications. We focused on endothelin1 (ET-1) and transforming growth factor beta 1 (TGF-β1), two key mediators of increased extracellular matrix protein production. In ECs exposed to high glucose, there were increased ET-1, TGF-β1, p300 and collagen Iα(I) along with SIRT1 downregulation. Such changes were corrected by knockdown of p300 or SIRT1 overexpression. In the kidneys and retina of diabetic mice, similar biochemical alterations were seen along with increased vascular permeability in retina and microalbuminuria of the kidney. In the transgenic animals with SIRT1 overexpression, such diabetes-induced abnormalities were prevented.
Overall these studies identified SIRT1-mediated accelerated aging phenomena in diabetes causing cellular injuries leading to renal and retinal injury. SIRT1 may lend itself as a target to prevent organ damages in diabetes.
Mortuza, Rokhsana, "Role of SIRT1 in Vascular Complications of Diabetes" (2014). Electronic Thesis and Dissertation Repository. 2457.