Project Summary It is well-established that premenopausal females have blood pressure that is ~10mmHg lower than that of males. We previously reported that an evolutionarily conserved olfactory receptor, OLFR558, is expressed in the kidney; we have now uncovered that OLFR558 is required for sex differences in blood pressure. OLFR558 localizes to renin-containing juxtaglomerular cells in the kidney, and to vascular smooth muscle cells. KO females exhibit increased blood pressure (and increased pulse wave velocity), whereas KO males exhibit decreased blood pressure (and decreased renal expression of renin, and, decreased plasma renin activity). As a result, blood pressure is similar in KO males and females. Our understanding of OLFR558’s role is currently hindered by our poor understanding of OLFR558 ligands. The central Aim of this proposal is to advance our understanding of OLFR558 ligands in order to better develop our understanding of OLFR558 physiology. In Aim 1, we will work to better understand putative endogenous ligands of OLFR558. To date, we have identified 18 ligands which activate OLFR558 in vitro; however, it is unclear how many of these ligands circulate at levels that activate OLFR558 in vivo (Aim 1a). Of note, several of these ligands modulate additional pathways; thus, we will measure blood pressure responses to each ligand in both OLFR558 WT and KO mice to define the OLFR558-mediated response (Aim 1b). Several of the best ligands for OLFR558 are produced by microbiota; in Aim 2 we will determine if the commensal microbiome influences OLFR558 signaling. Finally, in Aim 3, we will leverage our recent success in discovering novel synthetic OLFR558 agonists with high potency and selectivity, as well as a novel OLFR558 antagonist. These novel probes will be used as research tools to selectively manipulate OLFR558 activity in vivo; at the same time, this Aim will explore the therapeutic potential of these novel ligands.