PROJECT SUMMARY Cyclic nucleotide phosphodiesterases (PDEs) are a class of enzymes ubiquitously expressed in the human body, and they play a critical role in a broad range of physiological processes, including regulation of the immune system, cardiovascular function, metabolism, reproduction, neurobiological processes of learning and memory, and vision. PDEs function enzymatically to hydrolyze intracellular cyclic nucleotide second messengers (cAMP and cGMP), thereby affecting various downstream cellular signaling pathways that control homeostatic processes. These include repair mechanisms that promote cell survival (somatic maintenance), as well as pro- apoptotic mechanisms that result in cell death. In aging and disease, dysregulation of these signaling networks can lead to a reduced investment in somatic maintenance, resulting in pathophysiological states of disease. However, as key regulatory nodes that modulate intracellular and subcellular concentrations of second messenger signaling molecules, it is conceivable that PDEs could be pharmacologically targeted in order to upregulate pathways that improve cellular viability in disease states. By integrating recent advances in PDE biology with high-throughput methods, this proposal aims to identify new PDE-targeting agents and further characterize the pathways through which they alleviate pathophysiology in chronic, debilitating disease. Specifically, our focus will be on the application of newly identified therapeutic agents to ameliorating disease in a mouse model of retinal degeneration. Our long-term goal is to obtain a better understanding of the role played by PDE-dependent signaling pathways in the pathogenesis of retinal degeneration and to develop interventions that stop the progression of human blinding diseases. Accordingly, we propose three thematically and experimentally linked Specific Aims, to: 1) identify novel PDE- modulating compounds through in silico screening, 2) evaluate the therapeutic efficacy of PDE-selective inhibitors in preventing retinal degeneration, and 3) validate a systems pharmacology approach to optimizing PDE inhibitor therapy. Successful completion of Aim 1 will result in the discovery of novel compounds that circumvent the limitations of existing PDE inhibitors and exhibit superior targeting selectivity with enhanced potential for clinical utility. Through completion of Aim 2, we intend to demonstrate a statistically significant therapeutic effect conferred by PDE inhibition that is robustly conserved across different mouse models of retinal degeneration. Lastly, successful completion of Aim 3 will dissect the underlying molecular mechanisms of cytoprotection in the context of stress-induced retinal degeneration, thereby providing innovative systems biology insights on the synergism between intersecting networks involving crosstalk among the many different cell types in the retina. Indeed, these insights will facilitate a more unified perspective to attain o...