Elucidating the effects of Olfactory Receptor 78 on blood pressure and renin release

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Project Summary Recent studies in our laboratory have demonstrated that olfactory receptor 78 (Olfr78) is a short chain fatty acid (SCFA) receptor that plays a critical role in the modulation of blood pressure. Olfr78 modulates renin release in response to SCFA’s such as propionate, which are produced by the gut microbiota. To date we have shown that Olfr78 is expressed in the renal juxtaglomerular apparatus (JGA), and that Olfr78KO mice are defective in their ability to release renin in response to SCFAs. In addition however, Olfr78 is also expressed in vascular smooth muscle cells of the peripheral vasculature; where it could also contribute to blood pressure control. Full body Olfr78 null mice exhibit lowered blood pressure at baseline, and we hypothesize that this hypotension is primarily mediated by Olfr78 signaling in the JGA. To definitively identify the Olfr78-expressing cell type which is primarily responsible for the hypotensive phenotype, we will use a recently created mouse model where Olfr78 is selectively knocked out in the JGA using a Cre-lox system (Olfr78 JGA KO). Characterization of these tissue specific knockout mice will determine the contribution of JGA-localized Olfr78 to the hypotensive phenotype observed in the full body knockout, as well as expand upon Olfr78’s role in the kidney. Furthermore, while it is known that Olfr78 is a G-protein coupled receptor, the precise signaling pathway linking SCFA binding and renin release has not yet been shown. Prior studies show that cAMP production leads to renin release in the JGA, and that this release is inhibited by the elevation of cytosolic calcium levels. To establish the link between Olfr78 and cAMP mediated renin release, plan to utilize a stably expressing Olfr78 immortalized JGA cell line. This cell line will be a valuable tool in probing the mechanism underlying Olfr780mediated renin secretion in vitro. The subsequent findings can then be applied back to the in vivo model to better understand how a single OR can impact the complex process of blood pressure regulation. I hypothesize that Olfr78 in the JGA plays a significant role in the regulation of blood pressure via renin release, and that this release is mediated via a Gsα dependent cAMP pathway. To address this hypothesis, I propose the following aims. Aim 1: To identify which Olfr78 expressing cell type is responsible for baseline hypotension seen in the full body Olfr78 knockout. I will characterize a mouse model where Olfr78 has been selectively knocked out in the JGA using cre-lox technology, looking specifically at renin levels and blood pressure at baseline and under hypertensive stress. Aim 2: To determine how Olfr78 activation leads to renin release in vivo, we will elucidate the mechanism of renin release using an in vitro model. Using an immortalized mouse kidney cell line, we will use various pharmacological inhibitors to probe the necessary components of the signaling cascade required for Olfr78 mediated renin release. Together, these studies will reveal new insights into a novel pathway of blood pressure regulation.