Vascular damage in a mouse model of diabetic retinopathy: Relation to neuronal and glial changes

PURPOSE. Lack of information about the development of diabetic retinopathy in mice has greatly hindered the use of genetic mouse models for the study of disease mechanisms and the development of therapeutic strategies. The objective of this study was to characterize the occurrence and pathologic progression of diabetic retinopathy in C57Bl/6J mice. METHODS. Diabetes was induced with five consecutive injections of streptozotocin (STZ). The retinas were collected at different time points ( 2 weeks to 22 months) after the induction of diabetes and examined by using molecular, histologic, and immunohistochemical techniques and morphometric analysis. RESULTS. There was transient induction of cell apoptosis and caspase-3 activation in retinal neurons of C57Bl/6 mice within days of diabetes induction. Glial fibrillary acidic protein (GFAP), a marker of glial activation, likewise was transiently upregulated, seemingly in astrocytes but not in Muller cells. These abnormalities quickly returned to normal; ultimately, no detectable loss of retinal ganglion cells (RGCs) was noted by any of three independent methods ( number of cells in ganglion cell layer of retinal cross-sections, retrograde labeling of retinal ganglion cells with fluorescent dye, or TUNEL staining) after up to a 1-year duration of diabetes. Despite this apparent lack of evidence for progressive damage in neurons and glial cells, diabetic mice developed vascular disease characteristic of the early stage of diabetic retinopathy beginning at 6 months after the onset of disease. The vascular damage - formation of acellular capillaries and pericyte ghosts - continued to increase through the 18 months examined. CONCLUSIONS. Diabetic C57Bl/6J mice develop capillary lesion that are characteristic of the early stages of diabetic retinopathy in patients. The data suggest that diabetes-induced degeneration of retinal capillaries can develop independent of neuronal loss or chronic GFAP upregulation in glial cells.