Susan L. Rook

Extracellular carbonic anhydrase mediates hemorrhagic retinal and cerebral vascular permeability through prekallikrein activation

Excessive retinal vascular permeability contributes to the pathogenesis of proliferative diabetic retinopathy and diabetic macular edema, leading causes of vision loss in working-age adults. Using mass spectroscopy–based proteomics, we detected 117 proteins in human vitreous and elevated levels of extracellular carbonic anhydrase-I (CA-I) in vitreous from individuals with diabetic retinopathy, suggesting that retinal hemorrhage and erythrocyte lysis contribute to the diabetic vitreous proteome. Intravitreous injection of CA-I in rats increased retinal vessel leakage and caused intraretinal edema. CA-I–induced alkalinization of vitreous increased kallikrein activity and its generation of factor XIIa, revealing a new pathway for contact system activation. CA-I–induced retinal edema was decreased by complement 1 inhibitor, neutralizing antibody to prekallikrein and bradykinin receptor antagonism. Subdural infusion of CA-I in rats induced cerebral vascular permeability, suggesting that extracellular CA-I could have broad relevance to neurovascular edema. Inhibition of extracellular CA-I and kallikrein-mediated innate inflammation could provide new therapeutic opportunities for the treatment of hemorrhage-induced retinal and cerebral edema.

Suppression of Fas-FasL-induced endothelial cell apoptosis prevents diabetic blood–retinal barrier breakdown in a model of streptozotocin-induced diabetes

Diabetic macular edema, resulting from increased microvascular permeability, is the most prevalent cause of vision loss in diabetes. The mechanisms underlying this complication remain poorly understood. In the current study, diabetic vascular permeability (blood‐retinal barrier breakdown) is demonstrated to result from a leukocyte‐mediated Fas‐FasL‐dependent apoptosis of the retinal vasculature. Following the onset of streptozotocin‐induced diabetes, FasL expression was increased in rat neutrophils (P<0.005) and was accompanied by a simultaneous increase in Fas expression in the retinal vasculature. Static adhesion assays demonstrated that neutrophils from diabetic, but not control, rats induced endothelial cell apoptosis in vitro (P<0.005). The latter was inhibited via an antibody‐based FasL blockade (P<0.005). In vivo, the inhibition of FasL potently reduced retinal vascular endothelial cell injury, apoptosis, and blood‐retinal barrier breakdown (P<0.0001) but did not diminish leukocyte adhesion to the diabetic retinal vasculature. Taken together, these data are the first to identify leukocyte‐mediated FasFasL‐dependent retinal endothelial cell apoptosis as a major cause of blood‐retinal barrier breakdown in early diabetes. These data imply that the targeting of the Fas‐FasL pathway may prove beneficial in the treatment of diabetic retinopathy.