Abstract
Purpose: :
Retinopathies are major causes of visual impairment. We used a model of ischemic retinopathy to examine the role of CD40 in the pathogenesis of retinal injury.
Methods: :
Ischemia / reperfusion of the retina was induced by transient elevation of the intra-ocular pressure. Histological changes in the retina were assessed using PASH staining and immunohistochemistry. Real time PCR was used to examine expression of mRNA of pro-inflammatory molecules. Flow cytometry was used to study expression of CD40 and ICAM-1. Production of KC/CXCL1 was assessed by ELISA. Bone marrow transplants were performed by administration of bone marrow cells to lethally irradiated mice.
Results: :
Retinal inflammation, loss of ganglion cells and capillary degeneration were markedly attenuated in ischemic retinas of CD40 knock-out mice. Upregulation of NOS2 and COX2 after retinal ischemia were blunted in CD40 knock-out mice. NOS2/COX-2 upregulation in ischemic retinas from wild-type mice was at least in part explained by recruitment of NOS2+/COX-2+ leukocytes. Upregulation of KC/CXCL1 and ICAM-1 also required CD40. Primary retinal endothelial and Muller cells expressed CD40. Stimulation of these cells through CD40 caused ICAM-1 upregulation and KC/CXCL1 production. Bone marrow transplant experiments revealed that leukocyte infiltration, ganglion cell loss and upregulation of pro-inflammatory molecules after retinal ischemia were dependent on CD40 expression in the retina and not peripheral blood leukocytes.
Conclusions: :
These studies identified CD40 as a regulator of retinal inflammation and neuro-vascular degeneration after retinal ischemia. They support a model where CD40 stimulation of endothelial and Muller cells triggers adhesion molecule upregulation and chemokine production promoting the recruitment of leukocytes that express NOS2/COX-2, molecules linked to neuro-vascular degeneration.
Keywords: ischemia • nitric oxide • Muller cells