Location of Thesis Examination

Room H 410 Health Sciences Addition

Degree

Doctor of Philosophy

Program

Pathology

Supervisor

Dr. Subrata Chakrabarti

Delay of Publication

1

Abstract

Chronic complications are the leading cause of the mortality and morbidity in diabetic patients. Endothelial cell dysfunction plays an important role in the pathogenesis of chronic diabetic complications. Extracellular signal-regulated kinase 5 (ERK5) is essential for maintaining normal endothelial function and vascular integrity. This project investigated the role of ERK5 in the pathogenesis of diabetic retinopathy. Since increased endothelin-1 (ET-1), vascular endothelial growth factor (VEGF) and fibronectin (FN) are important features of diabetic complications, we examined the regulatory role of ERK5 on ET-1, VEGF and FN production in diabetes. We also studied the mechanism of ERK5 activation in this context.

We examined expression of ERK5, ET-1, VEGF and FN in endothelial cells as well as in retinal tissues of diabetic rats. Results showed that ET-1, VEGF and FN expression were increased in endothelial cells treated with high levels of glucose as well as in retinal tissues of diabetic rats. These changes were associated with decreased ERK5 activation. We used constitutively active MEK5 (CAMEK5) recombinant adenovirus to upregulate ERK5 signaling and showed that ET-1, VEGF and FN expression were significantly inhibited in endothelial cells in both basal and glucose conditions. In contrast, ERK5 gene silencing stimulates ET-1, VEGF and FN expression. Dominant negative MEK5 (DNMEK5) transduction resulted in increase of glucose-induced ET-1, VEGF and FN synthesis. In vitro angiogenesis assay showed a markedly increased tube formation angiogenesis after ERK5 gene knockdown, indicating that elevated VEGF by siERK5 may contribute to the angiogenesis in diabetic retinopathy. Retinal tissue from the diabetic animals also showed reduced ERK5. We also demonstrated that ERK5 is regulated by neurotrophins.

Taken together, this study shows that ERK5 signaling may be involved in the pathogenesis of diabetic vasculopathy. ERK5 may lend itself as a potential target for the treatment of diabetic microangiopathy.