| Diabetes affects more than 382 million people worldwide and can lead to vision loss as a result of progressive degeneration of the neurovascular unit in the retina, a condition known as diabetic retinopathy (DR). Early stage DR is characterized by microangiopathies including microaneurysms, microhemorrhages, and hyperpermeability. Analyses of postmortem human retinal tissue and retinas from animal models indicate that degeneration of the pericytes, the cells that make up the outer layer of capillaries, is an early event in DR; however, the relative contribution of specific cellular components to DR pathobiology has been difficult to dissect due to the complexity of existing models.;To directly assess the consequences of pericyte death on retinal microvascular integrity, I used a mouse model (iDTR; M-Cre) conditionally expressing a simian diphtheria toxin receptor (DTR) controlled by the smooth muscle myosin heavy chain Cre (M-Cre) promoter. Upon induction of Cre, the simian DTR is expressed in pericytes and smooth muscle cells, which therefore become diphtheria toxin (DT) sensitive. Administration of DT to these mice causes mural cell loss. Five days after the first DT injection, iDTR; MCre mice developed microaneurysms, acellular capillaries, and increased vascular permeability, vascular changes that are characteristic of background DR.;To measure pericyte loss and acellular capillaries and to avoid bias and ambiguities associated with manual analysis, automated techniques were established to reliably quantify pericytes and endothelial cells, as well as acellular capillaries in the mouse retina. Using these algorithms, DT-treated iDTR; M-Cre mice were shown to have a 7-15% decrease in pericytes compared to controls. Furthermore, there were twice as many acellular capillaries detected in the iDTR; M-Cre mice as compared to controls.;Using a mouse model of inducible mural cells loss, I have demonstrated a direct role for pericyte loss in the development of microangiopathies observed in DR without the confounding metabolic factors present in existing DR models. These results suggests that preventing or delaying pericyte dropout will avert or attenuate the retinal pathology associated with diabetes and highlight a potential for future novel therapies. |
