Abstract
Diabetic retinopathy (DR) is a leading cause of blindness worldwide, and its prevalence is growing. Current therapies for DR address only the later stages of the disease, are invasive, and have limited effectiveness. Retinal pericyte death is an early pathologic feature of DR. Although it has been observed in diabetic patients and in animal models of DR, the cause of pericyte death remains unknown. A novel pro-apoptotic pathway initiated by the interaction between glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and the E3 ubiquitin ligase, seven in absentia homolog 1 (Siah1), was recently identified in ocular tissues. In this article we examined the involvement of the GAPDH/Siah1 interaction in human retinal pericyte (hRP) apoptosis. HRP were cultured in 5 mm normal glucose, 25 mm l- or d-glucose for 48 h (osmotic control and high glucose treatments, respectively). Siah1 siRNA was used to down-regulate Siah1 expression. TAT-FLAG GAPDH and/or Siah1-directed peptides were used to block GAPDH and Siah1 interaction. Co-immunoprecipitation assays were conducted to analyze the effect of high glucose on the association of GAPDH and Siah1. Apoptosis was measured by Annexin V staining and caspase-3 enzymatic activity assay. High glucose increased Siah1 total protein levels, induced the association between GAPDH and Siah1, and led to GAPDH nuclear translocation. Our findings demonstrate that dissociation of the GAPDH/Siah1 pro-apoptotic complex can block high glucose-induced pericyte apoptosis, widely considered a hallmark feature of DR. Thus, the work presented in this article can provide a foundation to identify novel targets for early treatment of DR.
Highlights
Pericyte cell death occurs early in diabetic retinopathy, but the cause remains unknown
High Glucose Causes Human Retinal Pericyte Apoptosis by a glyceraldehyde-3-phosphate dehydrogenase (GAPDH)/seven in absentia homolog 1 (Siah1)-dependent Pathway—HRP were treated with normal glucose, L-glucose, or high glucose for 48 –72 h
It is widely recognized that high glucose results in retinal cell apoptosis, but the specific molecular mechanisms responsible for cell death remains under active investigation
Summary
Pericyte cell death occurs early in diabetic retinopathy, but the cause remains unknown. Results: High glucose-induced retinal pericyte apoptosis is mediated, in part, by the association of GAPDH and Siah. Because there is abundant evidence suggesting a role for retinal pericyte death in the pathogenesis of diabetic retinopathy, it is desirable to elucidate pro-apoptotic pathways in these cells under diabetes-relevant conditions. If these pathways can be identified and characterized, rational therapeutic strategies can be developed to block retinal pericyte death and retinal vasoregression.
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