Experiments proposed here offer key training and significant elements in a path toward Dr. Paola Rosas’ career goals with focus on the understanding of the relations among gender, obesity and heart failure with preserved ejection fraction (HFpEF, EF>50%). HFpEF is more frequently seen in postmenopausal women (2:1) vs men and in obese patients. Moreover, obesity and extreme obesity are higher in women than men. However, the cause of these differences are unclear. Proposed studies build on preliminary evidence of localization of p21-activated kinase 1 (PAK1) in adipose tissue and its involvement in female fat accumulation that accentuates with aging. Aged female global PAK1 knock-out (PAK1-/-) mice exhibit significantly increased visceral adiposity, similar to post-menopausal women. Furthermore, with aging, unlike male PAK1-/- mice, female PAK1-/- mice show diastolic dysfunction. PAK1 is a pleiotropic serine/threonine protein kinase demonstrated to be cardio-protective against different stressors. There is evidence, in other organs, that PAK1 is involved in estrogen signaling pathways; however, these processes have not yet been studied in the heart or in the adipose tissue. These discoveries led to the hypothesis that PAK1 is regulated by estrogens, and that dysregulation of PAK1 due to lack of estrogens, contributes to obesity and HFpEF. With these findings in mind, I propose the following aims. Aim #1: Investigate the mechanisms by which estrogens regulate PAK1 in the heart and the adipose tissue. I will study how PAK1 is activated by estrogens in the heart and the adipose tissue and how this activation involves estrogen receptor α (ERα) and/or G protein-coupled estrogen receptor (GPER). Aim #2: Investigate the mechanisms by which PAK1 regulates cardiac function in female mice. I will study how the absence of PAK1 in a PAK1-cardiac specific knock-out mouse model, affects intracellular Ca2+ kinetics and the response of myofilaments to Ca2+, thereby affecting cardiac relaxation. Aim #3: Investigate the mechanisms by which PAK1 regulates adipose tissue homeostasis in female mice and the effect of its dysregulation on cardiac function. I will examine how lack of PAK1 in adipose tissue promotes increased visceral adiposity leading to obesity which subsequently affects diastolic function in the female heart. Impact: Addressing these aims will significantly advance our understanding of the role of PAK1 on the regulation of cardiac and adipose tissue function in females, by exploring the relation between estrogens and PAK1 signaling in the heart and the adipose tissue. Furthermore, these contributions will explain, at least in part, the higher incidence of HFpEF and obesity in post-menopausal women. Results are expected to bring novel alternatives and open new horizons in the treatment of HFpEF and obesity in women. This research will also form the basis for Dr. Rosas’ first R01 application to conduct further studies on the role of PAK1 as an anti-obesit...