This proposal focuses on development of new potential treatments for patients with heart failure and preserved ejection fraction (HFpEF). Among symptomatic patients with HF, approximately half have preserved ejection fraction, and their mortality is similar to those with HF with reduced EF (HFrEF). However, unlike the case with HFrEF, there is currently no treatment for HFpEF that prolongs life, and few that reduce hospitalization rates for heart failure. We need new therapies to address this unmet medical need. Discovering and developing such an approach is the purpose of this proposal. Cardiovascular gene transfer is conceptually an attractive method for treating heart failure, but difficulty in obtaining high yield transgene expression in the heart in a manner that can be easily and safely applied has been challenging. However, we recently have demonstrated the effectiveness of intravenous (IV) delivery of a long-term expression vector encoding a peptide, urocortin-2 (UCn2), with favorable cardiovascular effects through its paracrine action. A single intravenous injection in normal mice of an adeno-associated virus vector (AAV8) encoding murine UCn2 (AAV8.UCn2) has favorable effects on Tau and LV peak -dP/dt, two measures of left ventricular (LV) diastolic function. This approach solves the problem of attaining high yield cardiac gene transfer and ultimately would enable patients to be treated by intravenous injection during an office visit, and provides a novel means to increase diastolic function. The goal of this proposal is to test the safety and efficacy of this method of therapy in animal models of HFpEF. In the 4-year tenure of our present VA Merit, we have published three papers on the effectiveness of gene transfer of UCn2: one in normal mice, a second in mice with HFrEF, and a third that focuses on the safety and metabolic effects of UCn2 gene transfer. Gene transfer of AAV8 encoding UCn2 yielded persistent increases in plasma UCn2 (18 months following a single IV injection) and improved LV function in severe HF induced by myocardial infarction. In these studies, we noted that UCn2 gene transfer increased LV peak -dP/dt (p<0.0001) and reduced Tau (p=0.05). We now propose to test the safety and efficacy of IV delivery of AAV8.UCn2 in two models of HFpEF: 1) trans-aortic constriction (TAC), which imposes a LV pressure stress and HFpEF in the early phase; and 2) aged mice (18-months-old) many of which have diastolic dysfunction and meet criteria for HFpEF. Although our primary goal is to improve LV diastolic function and to test this in physiological studies after gene transfer, we also will determine mechanisms for the anticipated increase in diastolic function. In the final year, we will initiate testing in rabbits as a segue to an eventual Investigational New Drug (IND) application to initiate a clinical trial using AAV8.UCn2 to treat patients with HFpEF, a transition we have made in our laboratory twice previously (ClinicalTrials.go...