| Neurotrophic factors play central roles in the developing and mature nervous system by promoting neuronal survival. The discovery in 1990 that an exogenously supplied neurotrophic factor could slow the progression of photoreceptor loss in an animal model of retinal degeneration has given rise to an active field of research whose ultimate goal is to develop neuroprotective therapy for patients with blinding diseases. At the same time, a growing body of evidence suggests that endogenously expressed neurotrophic factors maintain retinal health and mediate retinal responses to stress throughout life. This thesis investigates both the requirement for retinal expression of neurotrophic factors in a model of endogenous neuroprotection, and the activity of exogenous factors in a clinically relevant new model of retinal injury.; Several types of sublethal stress precondition the retina to withstand an otherwise lethal injury. These preconditioning protocols are associated with the upregulation of endogenously expressed neurotrophic factors. However, there are as yet no loss-of-function data demonstrating that these factors actually mediate the endogenous neuroprotective effect. The investigation of this issue has been hampered by the fact that preconditioning is robust in rats, but largely ineffective in mice, preventing the use of mouse knockouts. To test the requirement for endogenous neuroprotective factors in preconditioning in rats, we turned to a relatively new approach, the use of RNA interference (RNAi). We developed RNAi constructs that successfully knocked down expression of the strongest candidate for endogenous neuroprotection, basic fibroblast growth factor (bFGF), in cultured cells. We delivered these constructs to the retina in vivo using viral vectors, but observed no weakening of preconditioning as a result. In a complementary approach with greater potential to account for the possibility of multiple neurotrophic factors acting together in vivo, we used pharmacologic inhibitors to attempt to block signal transduction pathways that function downstream of the candidate factors. While we did not ultimately succeed in implicating specific factors in endogenous neuroprotection, the methods we developed can be applied to a wide variety of basic and therapeutic studies in retinal biology.; We also examined the activity of neurotrophic factors in a new model of retinal injury. Photodynamic therapy (PDT) is widely used for the treatment of age-related macular degeneration, the most common cause of blindness in elderly Americans. PDT reduces vision loss by closing neovascular channels that arise from the choroid, but also damages the overlying retina, perhaps contributing to the disappointing results seen in many patients. We developed a highly reproducible rat model of retinal injury from PDT and demonstrated structural and functional preservation of the retina by exogenously supplied brain-derived neurotrophic factor (BDNF). Other factors protected photoreceptors in this model, but without improving retinal function. In the course of these studies, we used multifocal electroretinography (mfERG) to demonstrate a therapeutic effect in a rodent model for the first time, improving the discriminatory power of studies involving rodent models of retinal diseases with localized pathology. |
