Project Summary Cardiovascular disease (CVD) is the leading cause of death in the world. Current therapies for CVD aim to treat the symptoms rather than the underlying cause of the disease, thus we desperately need novel insights into the molecular mechanisms of CVD to develop new therapies. Calcium (Ca2+) ions play critical roles in fundamental physiological processes in the cardiovascular system that underlie tissue homeostasis and pump function. A universal characteristic of the failing heart is impaired Ca2+ cycling through the sarco/endoplasmic reticulum (S/ER), the major internal store of Ca2+ in cardiomyocytes. Ca2+ re-sequestration into the S/ER is mediated by a Ca2+-ATPase pump (SERCA), whose activity is regulated by phospholamban (PLN) and sarcolipin (SLN). In the past 3 years, we have identified 4 additional conserved small proteins that regulate SERCA activity in myocytes and non-myocyte cell types, consisting of myoregulin (MLN), endoregulin (ELN), anotheregulin (ALN) and dwarf open reading frame (DWORF). This proposal outlines a comprehensive plan to dissect the function of these peptides to provide critical insights into the complex mechanism of SERCA regulation and Ca2+ homeostasis. To accomplish this, I will employ the following 3 specific aims: 1. To examine the role of ELN and ALN as nodal regulators of SERCA activity, 2. To analyze the in vivo function of the cardiac expressed SERCA-regulins in health and disease, and 3. To investigate the role of Ca2+ dysregulation and SERCA dysfunction in the development of metabolic disorders and cardiovascular disease. The K99 portion of this proposal will be carried out in the lab of the renowned molecular biologist, Dr. Eric Olson. Under Dr. Olson’s guidance, I will functionally characterize the phenotype of ALN and ELN loss-of-function mice and elucidate their mechanism of action (Aim 1). Aims 2a and 2b, which are dedicated to characterizing the cardiomyocyte expressed peptides (ALN, PLN and DWORF), will be initiated under Dr. Olson’s supervision and continued during the independent phase. Finally, the techniques to evaluate systemic metabolism detailed in Aim 3 represent new research experiences for me and will require extensive training during the K99 phase of my award. The knowledge and skills that I acquire during this time will serve as critical components of the foundation of my own independent lab. In summary, the comprehensive plan proposed in this Pathway to Independence Award application will provide me with the opportunity to continue to develop an independent research program that will be instrumental in my success as a scientist. Importantly, the collective body of work generated through the completion of the proposed Aims will make major contributions to the field of cardiovascular science and will set the tone for my career.