Abstract
Purpose::
Apoptosis is believed to be a crucial step in the development of diabetic retinopathy, and Bcl-2 has been found to regulate cellular susceptibility to apoptosis. We studied (1) the effect of diabetes and hyperglycemia on expression of Bcl-2 in retina and retinal endothelial cells, (2) the ability of Bcl-2 to inhibit hyperglycemia-induced death of retinal endothelial cells and degeneration of retinal capillaries in diabetes, and (3) the roles of nitric oxide, cyclooxygenase-2 (COX-2) and caspases on hyperglycemia-induced alterations in Bcl-2 expression.
Methods::
Nondiabetic and diabetic wildtype mice and transgenic mice overexpressing Bcl-2 selectively in endothelium (using the preproendothelin promoter) were used. For in vitro experiments, primary bovine retinal endothelial cells (BREC) were incubated in 5mM and 25 mM glucose.
Results::
In vivo, diabetes decreased Bcl-2 expression in whole retina, increased the rate of endothelial cell death in retinal capillaries, and caused degeneration of retinal capillaries (resulting in acellular capillaries). Diabetes-induced degeneration of retinal capillaries over an 8 month period was inhibited in animals overexpressing Bcl-2 in the endothelium. In vitro findings were consistent with the in vivo studies. Elevated glucose decreased Bcl-2 expression in BREC, and death of BREC in elevated glucose was significantly inhibited by incubating the cells with a peptide containing a cell-permeable, BH4 (anti-apoptotic) domain of Bcl-2. Inhibition of NO production (with L-NAME), COX-2 (with NS-398), or caspases (with BD-FMK) inhibited the decrease in Bcl-2 and increase in cell death due to elevated glucose in vitro.
Conclusions::
Diabetes-induced increase in retinal capillary cell death can be inhibited by over-expression of the anti-apoptotic protein Bcl-2. We postulate that Bcl-2 downregulation contributes to the process of retinal vascular cell death and development of retinopathy in diabetes, and that therapies that preserve Bcl-2 will help inhibit the development of diabetic retinopathy.
Keywords: apoptosis/cell death • diabetic retinopathy