Death of retinal neurons in streptozotocin-induced diabetic mice

PURPOSE. Neuronal cell death has been reported in retinas of humans with diabetic retinopathy and in diabetic rat models. Little is known about neuronal cell death in mouse models of diabetic retinopathy. This study was designed to determine whether neurons are lost in diabetic mouse retinas and whether the loss involves an apoptotic process. METHODS. Three-week-old C57Bl/6 mice were made diabetic with streptozotocin. They were studied over the course of 14 weeks after onset of diabetes. Eyes were processed for morphometric analysis and detection of apoptotic cells by TUNEL analysis and activated caspase-3 and were subjected to electron microscopy. RESULTS. Morphometric analysis of retinal cross sections of mice that had been diabetic 14 weeks showed similar to 20% to 25% fewer cells in the ganglion cell layer compared with age-matched control mice. There was a modest, but significant, decrease in the thickness of the whole retina and the inner and outer nuclear layers in mice that had been diabetic for 10 weeks. TUNEL analysis and detection of active caspase-3 revealed that cells of the ganglion cell layer were dying by apoptosis. Electron microscopic analysis detected morphologic features characteristic of apoptosis, including margination of chromatin and crenated nuclei of cells in the ganglion cell layer. CONCLUSIONS. The data suggest that in diabetic mouse retinas, neurons in the ganglion cell layer die, and this death occurs through an apoptotic pathway. Diabetic mice may be appropriate and valuable models for studies of neuronal cell death in diabetes.