Dissertation
Investigating the pathogenesis of pre-clinical diabetic retinopathy: transcription factor Sp1 glycosylation upregulates VEGF-A
Doctor of Philosophy (Ph.D.), Drexel University
Jan 2019
DOI:
https://doi.org/10.17918/xbzs-cg87
Abstract
Diabetes mellitus is a devastating metabolic disease. One of the earliest diabetic complications involves damage to the retina, known as diabetic retinopathy (DR). DR is indolent and progressively damages the tissue parenchyma and microvasculature, leading to blindness. Intermittent retinal exposure to hyperglycemia initiates a durable cascade of molecular consequences including upregulation of the pro-angiogenic factor vascular endothelial growth factor A (VEGF-A). This factor is central to DR pathogenesis, but initiation of VEGF-A upregulation is not well understood. In Müller glia and retinal pigment epithelium, transcription factor Sp1 and glucose-driven post-translational modification by O-GlcNAc were required for VEGF-A promoter stimulation and upregulation. The role for Sp1-specific O-GlcNAcylation was evaluated using a series of Sp1 point mutants. This analysis revealed that VEGF-A upregulation and secretion required modification of zinc finger Ser698 and 702. Glucose-driven upregulation of plasminogen activator inhibitor 1 (PAI-1) and transforming growth factor [beta]1 (TGF[beta]1) were also O-GlcNAc-dependent, but Sp1-independent. VEGF-A expression is negatively regulated through Sp1 sequestration by the anti-angiogenic tumor suppressor von Hippel Lindau (VHL) protein. The Sp1-VHL interaction was interrupted by hyperglycemia and restored by inhibition of PKC[zeta]. PKC[zeta] inhibition also abrogated glucose-driven VEGF-A and TGF[beta]1. As PKC[zeta] is an Sp1 kinase, the complex interplay between Sp1 modifications remains to be resolved. This investigation reveals a novel mechanism by which glucose drives pathological expression of VEGF-A. We report for the first time that Sp1-VHL complexes form in retinal cells and are dissociated by hyperglycemia. Inhibition of O-GlcNAc effectively prevented VEGF-A, PAI-1, and TGF[beta]1 upregulation, making it a compelling therapeutic target. Overall, these data contribute to our understanding of pre-clinical DR pathogenesis, as well as identify novel aspects of disease for future study.
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Details
- Title
- Investigating the pathogenesis of pre-clinical diabetic retinopathy
- Creators
- Kelly Rose Donovan - DU
- Contributors
- Jane Clifford (Advisor) - Drexel University (1970-)
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- x, 239 pages
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- Biochemistry and Molecular Biology; College of Medicine; Drexel University
- Other Identifier
- 9635; 991014632823304721