Project Summary: A large body of experimental and clinical evidence has demonstrated that dysregulation of the renin angiotensin system (RAS), resulting in elevated concentrations of Angiotensin II (Ang II), contributes to increased inflammation, oxidative stress, and development of metabolic syndrome, obesity, diabetes and its complications including DR. In addition to circulating RAS, components of RAS are also expressed in different tissues including the eye. Local RAS dysfunction contributes to tissue pathophysiology and end-organ damage in diabetes. However, the exact mechanisms by which ocular RAS contribute to retinal pathophysiology in diabetes are still not well-understood. Prorenin, a precursor of the active renin, the rate-limiting enzyme in RAS cascade, is highly elevated plasma of diabetic patients and ocular fluid of DR patients. The discovery of its receptor, pro/renin receptor (PRR), provided a mechanistic link of elevated prorenin in pathogenesis of DR. Activation of this pathway has been shown to increase Ang II production at tissue level, as well as direct activation of downstream signaling independent of Ang II action, both of which contribute to end-organ damage. In addition to function as a crucial component of RAS, PRR is an integral component of vacuolar H+-ATPase (V-ATPase), which plays central roles in the acidification of intracellular compartments and cellular pH homeostasis. PRR also acts an adaptor protein between the Wnt signaling complex and V-ATPase. Moreover, a soluble form of PRR (sPRR) is produced by protease-mediated cleavage and is elevated under various pathological conditions including DR. Increasing evidence implicates a pathological role of elevated sPRR; however, the mechanisms by which sPRR contribute to pathogenesis of these conditions are still not fully understood. We hypothesize that elevated prorenin, PRR and its soluble form (sPRR) contribute to pathogenesis of DR by multiple pathways, leading to local RAS activation, as well as signaling events independent of Ang II action. The goal of this proposal is to (1) determine the mechanisms of prorenin-induced, PRR-mediated signaling pathways in pathogenesis of DR; (2) determine whether elevated sPRR mediate prorenin-stimulated effects and activates Ang II-dependent pathways in the retina; and (3) determine the effects and mechanisms of prorenin and sPRR on V-ATPase function and associated cellular processes. Collectively, the proposed studies will determine the mechanism(s) and signaling pathways by which prorenin, pro/renin receptor, and its soluble form contribute to retinal neurovascular dysfunction in diabetes. Knowledge of the mechanisms and relationship between these pathways will drive the development of more effective therapies for diabetic retinopathy.