SECOND MESSENGERS IN THE RETINA

Summary

Principal Investigator: RAJU VS RAJALA
Abstract: DESCRIPTION (provided by applicant): The overall goal of our research program is to gain a greater understanding of the intracellular signaling pathways that provide neuroprotection of both rod and cone photoreceptor cells. The specific objective of this renewal application is to investigate the role of phosphoinositides (PI), particularly those produced by phosphoinositide 3-kinase (PI3K), in this process. The PI Cycle describes a series of biochemical reactions that occur on the inner leaflet of the plasma membrane of cells in response to receptor activation by extracellular stimuli. Studies from our laboratory over the past two decades have shown that the retina and rod outer segments (ROS) have an active PI metabolism. Biochemical studies revealed that the ROS contain the enzymes necessary for phosphorylation of PIs. Interestingly, conditional deletion of p85[unreadable], which regulates class IA PI3K, from cones resulted in an age-related cone degeneration. The phenotype was not rescued by healthy rods, suggesting that rod-derived cone survival factors may signal through cone PI3K. Furthermore, deletion of p85[unreadable] in rods did not exhibit any degeneration phenotype, suggesting a functional redundancy. We link several previously independent areas of inquiry by testing the novel hypotheses that 1) endogenous signaling molecules mediate their protective effect on cones through cone PI3K, 2) cone cell death in cone PI3K knockout mice is due to decreased phospholipid synthesis, decreased ribosomal protein synthesis and decreased antioxidant defense metabolism, and 3) Rod CNG channels can be regulated by class 1B PI3K. These three hypotheses are novel and have emerged from our work over the last four years on the PI3K/Akt pathway in the retina. They are also innovative in that we integrated our novel findings with those of other groups to develop new ideas about mechanisms by which retinas are protected from the daily stress caused by light, polyunsaturated fatty acids, and reactive oxygen species. We will utilize a combination of genetic, molecular, and biochemical approaches to test the proposed hypotheses. In humans, age-related macular degeneration and diabetic retinopathy are the most common disorders affecting cones. Cones also are affected indirectly in diseases such as retinitis pigmentosa and directly in cone and cone-rod dystrophies. Understating the mechanism of PI3K mediated functions in rods and cones may have important ramifications for the treatment of rod and cone dystrophies. PUBLIC HEALTH RELEVANCE: The retina is one of the most susceptible tissues to oxidant stress. To survive daily stress challenges, the retina has developed remarkable protective mechanisms. Our long-term goal is to understand these mechanisms as a foundation on which novel drug therapies can be designed to protect retinal function in patients who suffer from retinal degenerations.
Funding Period: 1995-02-01 - 2014-08-31
more information: NIH RePORT