Abstract
Purpose:
Microglia activation during diabetes is linked to the pathogenesis of diabetic retinopathy. Here we determined whether expression of CX3CR1 in microglia is essential for retinal vascular rarefaction associated with ER stress, neuronal toxicity, and diabetes.
Methods:
Eight week old wild-type or Cx3cr1 GFP/GFP mice received a single intravitreal injection of NMDA (40 nmol/eye) or tunicamycin (0.1μg/eye). Two weeks after injection the mice were sacrificed and eyes were enucleated. Microglia activation in wholemount retinas were observed under the microscope. Acellular capillaries were evaluated in trypsin digested retinas. Diabetes was induced in 8-week-old Thbs1-/- or Cx3cr1 GFP/GFP; Thbs1-/- mice with a single injection of streptozotocin (STZ; 180 mg/kg in citrate buffer, pH 4.2 by ip injection). Three days later, blood glucose levels were determined. The mice included the diabetic group when glucose level was above 250 mg/dl. After 3 month of diabetes, the mice were sacrificed. The retinas were examined by GFP fluorescence for microglia activation and trypsin digestion for evaluation of acellular capillaries.
Results:
The microglia activation occurred in both NMDA and tunicamycin injected wild-type and Cx3cr1 GFP/GFP mice. This was associated with changes in morphology and distribution of microglial cells detected by GFP fluorescence. The mean numbers of acellular capillaries were decreased by 10-fold in NMDA and 15-fold in tunicamycin injected Cx3cr1 GFP/GFP mice compared with corresponding controls. Thbs1-/- mice develop increased numbers of acellular capillaries compared to wild-type mice when made diabetic by a single injection of STZ. A 30-fold increase in mean number of acellular capillaries was observed in Thbs1-/- mice after 3 months of diabetes compared to wild-type mice. The formation of acellular capillaries was attenuated in Cx3cr1 GFP/GFP; Thbs1-/- mice after 3 month of diabetes. We observed a significant increase in GFP fluorescence and altered localization of microglia as well as a 10-fold decrease in the mean number of acellular capillaries in diabetic Cx3cr1 GFP/GFP; Thbs1-/- mice compared to diabetic Thsbs1-/- mice.
Conclusions:
Lack of Cx3cr1 expression protected the retina from vascular rarefaction in response to ER stress, neurotoxicity, and diabetes. Thus, antagonism of Cx3cr1 may provide a suitable target for prevention of early diabetic retinopathy.
Keywords: 499 diabetic retinopathy •
595 microglia •
688 retina