Microglia-mediated inflammation plays a significant role in neuronal and vascular damage in diabetic retinopathy (DR), but the mechanism linking inflammation, neurodegeneration, and impaired vascular integrity is still unclear. Previous studies from diabetic mouse models showed accumulation of fibrinogen at vessel lesions surrounded by perivascular microglial clusters. The purpose of this study was to evaluate whether the pathological hallmarks of gliosis and vascular aberrations characterized in diabetic animal models are consistent with those in diabetic human retinas, and to assess the effects of the defibrinogenating agent ancrod in retinal pathology and visual acuity in a two-hit inflammatory diabetic mouse model. Post-mortem human eyes were assessed for retinal and inflammatory gene expression by quantitative PCR. Immunohistochemical analyses in human and murine retinas were performed using markers of gliosis, vascular integrity, and fibrinogen deposition. An inflammatory microenvironment, with microgliosis and microaneurysms, was found in the diabetic human eye. Microglial activation, fibrinogen deposition, and axonal loss were also observed in the diabetic murine retina. Ancrod treatment correlated with reduced microgliosis, less fibrinogen deposition, and reduced pro-inflammatory cytokine levels in diseased retinal tissues. Together, these data suggest that fibrinogen contributes to microglia-mediated inflammation in the diabetic retina. Since retinal microgliosis, vascular pathology, and vision deficits manifest in diabetic mice irrespective of CX3CR1 genotype, our results indicate that defibrinogenation can dampen systemic neuroinflammation and vascular insults, thereby improving vision at early stages of diabetes. Summary Statement Diabetic human and murine retinas revealed pronounced microglial morphological activation and vascular abnormalities associated with inflammation. Pharmacological fibrinogen depletion using ancrod dampened microglial morphology alterations, resolved fibrinogen accumulation, rescued axonal integrity, and reduced inflammation in the diabetic murine retina.

Microglia-mediated inflammation plays a significant role in neuronal and vascular damage in diabetic retinopathy, but the mechanism linking inflammation, neurodegeneration, and impaired vascular integrity is still unclear. Our previous studies from diabetic mouse models showed accumulation of fibrinogen, at vessel lesions surrounded by perivascular microglial clusters. In this study, we evaluated whether the pathological hallmarks of gliosis and vascular aberrations characterized in diabetic animal models are consistent with those in diabetic human retinas. Postmortem human retinas were analyzed by immunohistochemistry for markers of gliosis, vascular integrity, and fibrinogen deposition. Immunohistochemical and gene expression analyses of human postmortem retinas revealed evidence of an inflammatory microenvironment, with microgliosis and impaired vasculature. To define the therapeutic potential of reducing fibrinogen in DR, the defibrinogenating agent ancrod was administered in a two-hit inflammatory diabetic mouse model, after which retinal pathology and visual acuity were assessed. Histopathological analyses revealed microglial activation, vascular aberrations, and fibrinogen deposition in the diabetic murine retina. Notably, after treatment with ancrod, diabetic mice appeared to improve visual acuity, which was associated with reduced microglia activation and less fibrinogen deposition in the retina. This study shows that fibrinogen-mediated microglial activation, blood-retinal barrier damage, and vision loss, can be ameliorated by reducing fibrinogen levels. Overall, these findings suggest that that fibrinogen contributes to microglia-mediated inflammation in the diabetic retina. Supported by R01 EY029913