LAUSR

Free fatty acid receptor (FFAR)-3 (also known as GPR41) is a Gi/o protein-coupled receptor (GPCR) mediating many cellular effects of short-chain fatty acids (SCFAs) like propionate and butyrate. It inhibits cyclic 3’,5’-adenosine monophosphate (cAMP) synthesis and promotes sympathetic nervous system (SNS) activity and norepinephrine (NE) release. It is also blocked by ketone bodies, such as beta-hydroxybutyrate. Regulator of G protein Signaling (RGS)-4 deactivates (terminates) Gi/o- and Gq-protein signaling. Cardiac RGS4 protects the heart against arrhythmogenesis via calcium signaling attenuation and against pressure overload-induced hypertrophy. In the present study, we examined whether RGS4 regulates SCFA signaling and function (through FFAR3) in cardiac myocytes and sympathetic neurons in vitro, as well as in mice post-pressure overload in vivo. We found that siRNA-mediated RGS4 depletion in H9c2 cardiomyocytes enhances propionate-induced cAMP lowering, Giα protein subunit activation, and upregulation of pro-inflammatory mediators [p38 mitogen activated protein kinase (MAPK), interleukin (IL)-6 & IL-1β, transforming growth factor (TGF)-β]. On the other hand, RGS4 overexpression in sympathetic neuron-like Neuro-2A cells significantly reduces propionate/FFAR3-mediated NE release. In vivo, in C57/B6 mice undergoing transverse aortic constriction (TAC) to induce pressure overload, cardiac RGS4 was found upregulated, at both the mRNA and protein levels, in post-TAC mice compared to sham-operated controls. This was accompanied by markedly reduced propionic acid-dependent FFAR3 signaling in isolated membranes from the post-TAC hearts. 3-hydroxybutyrate exerts the same effect in vitro in HEK293T cells overexpressing human FFAR3, i.e., inhibits Gi/o protein signaling by FFAR3. Finally, although initially (24 hours post-TAC) elevated, compared to sham (6.6+0.4 nmol/g of tissue vs. 4.1+0.7 nmol/g of tissue, respectively; n=5), cardiac NE levels were markedly suppressed at 7 days post-TAC (5.4+0.3 nmol/g of heart tissue, n=5). In conclusion, RGS4 inhibits SCFA/FFAR3 pro-inflammatory signaling in the myocardium, and neuronal SCFA/FFAR3 signaling that promotes NE release. Pressure overload upregulates cardiac RGS4 in vivo to protect the heart against FFAR3-mediated inflammation and elevated catecholamine toxicity. Thus, RGS4 actions on FFAR3 or pharmacological blockade of this receptor with a ketone body may protect the heart against pathological stimuli (e.g., hypertension) that precipitate heart disease via increased sympathetic activity and elevated catecholaminergic toxicity. 1) NIH (NHLBI); 2) NSU‘s President‘s Faculty Research & Development Grant (PFRDG). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.