Abstract
We had previously reported that exchange protein for cAMP 1 (Epac1) reduced inflammatory mediators in the retina of mice and in retinal endothelial cells (REC). Since ischemia can induce retinal damage potentially through activation of inflammatory cascades, we hypothesized that Epac1 would protect the retina against neuronal and vascular damage after exposure to ischemia/reperfusion (I/R). We used Epac1 floxed and endothelial cell specific Epac1 knockout mice for this work. We exposed them to ischemia for 90 minutes followed by reperfusion. One day after I/R, some mice were used for fluorescein angiography imaging or Evan’s blue measurements of permeability. Mice were sacrificed at 2 days for neuronal measurements and at 10 days for measurements of degenerate capillaries. Data show increased leakage in the Epac1 Cre-Lox (Epac1 EC-KO) mice exposed to I/R when compared to Epac1 floxed mice with the same treatment. I/R also increased numbers of degenerate capillaries and cell loss in all retinal layers of Epac1 EC-KO mice. Retinal thickness was reduced more significantly in the Epac1 EC-KO mice compared to Epac1 floxed mice after I/R. Taken together, the data suggest that Epac1 is protective against both neuronal and vascular damage to the retina after exposure to I/R.
Highlights
Rates of diabetes are reaching epidemic levels
We have reported that Epac1 can reduce both toll-like receptor 4 (TLR4) and high mobility group box 1 (HMGB1) in retinal endothelial cells (REC)[11]
A number of studies have shown that key inflammatory pathways can induce retinal damage in response to ischemia, including TLR4 and HMGB1 [4, 5, 7]
Summary
Rates of diabetes are reaching epidemic levels. Other retinal diseases are highly clinically relevant, as the loss of sight is one feared most by patients. One animal model used to mimic retinal ischemia damage is ischemia/reperfusion [1,2,3]. Studies have reported that toll-like receptor 4 (TLR4) contributes to retinal I/R injury [4, 5]. TLR4 was responsible for cardiac damage in response to I/R [6]. In addition to TLR4, others reported that high mobility group box 1 (HMGB1) mediates retinal injury in response to I/R [7]. Work has shown that inhibition of HMGB1 by glycyrrhizin blocked I/R injury to the brain and retina [8]
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