MECHANISM OF RETINAL ISCHEMIA

Yeshiva University, New York NY

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Abstract

Visual loss secondary to retinal ischemia is a serious and common clinical problem. It may occur as a result of acute vascular occlusion or of other ocular diseases whose pathogenetic mechanisms may involve retinal ischemia such as acute glaucoma, diabetic retinopathy and hypertensive vascular disease. Our long range goal is to enhance our understanding of the fundamental mechanisms responsible for ischemic retinal damage. Based upon the knowledge acquired, strategies to improve retinal viability in in vivo animal models resembling human disease will be developed. The pathophysiology of ischemic retinal damage is complex and appears to involve several mechanisms of cell death. Based upon our findings in the retina, as well as our findings in cerebral ischemia, we now propose to focus on the role of apoptotic cell death in retinal ischemia. The specific aims of this project are to test the following hypotheses: 1) Apoptosis plays a role in the cascade of events leading to retinal degeneration following ischemia: a) In vivo ischemia followed by reperfusion induces apoptosis as determined by established morphologic (ultrastructural, cresyl violet), biochemical (DNA 'ladder') and immunohistochemical (TUNEL) parameters; b) Differential expression of apoptosis related genes accounts for the selective vulnerability of the inner retinal layers that occurs a result of transient ischemia. 2) Retinal ischemic injury may be prevented or attenuated by agents which inhibit apoptosis: a) Agents that inhibit apoptosis afford protection in an in vivo model of retinal ischemia; b) Overexpression of the bcl-2 gene product (a protein which inhibits apoptosis in a variety of other systems) results in less ischemic damage to the retina; c) Attenuation of the p53 gene product (a protein which promotes apoptosis in a variety of other systems) results in less ischemic damage to the retina. These hypothesis will be tested utilizing an in vivo model of transient retinal ischemia followed b reperfusion. Specific therapy for retinal ischemia may therefore be designed by obtaining a better understanding of basic mechanisms. The retina offers a unique situation, where these agents, all of which have significant systemic effects, may be utilized by injecting directly into the vitreous and thereby minimizing systemic effects. Utilized in this manner, agents that inhibit apoptosis or gene therapy that modifies the cells response to apoptosis may be exciting new approaches to the treatment of retinal ischemia.