Abstract P233: Cardiac Regulator Of G Protein Signaling-4 Upregulation Protects Against FFAR3-mediated Inflammation And Sympathetic Hyperactivity

Abstract

Background: Free fatty acid receptor (FFAR)-3 is a Gi/o protein-coupled receptor (GPCR) mediating many cellular effects of short-chain fatty acids like propionate. It inhibits cyclic 3’,5’-adenosine monophosphate (cAMP) synthesis and promotes sympathetic nervous system (SNS) activity and norepinephrine (NE) release. 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. Study objective: We examined whether RGS4 regulates FFAR3 signaling and function in cardiac myocytes and sympathetic neurons in vitro, as well as in mice post-pressure overload in vivo. Methods & Results: siRNA-mediated RGS4 depletion in H9c2 cardiomyocytes enhances propionate-induced cAMP lowering, Giα protein subunit activation, and upregulation of pro-inflammatory mediators [p38 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 (increased afterload), 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. 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). Conclusions: RGS4 inhibits cardiac propionic acid/FFAR3 pro-inflammatory, and neuronal propionic acid/FFAR3 NE release-stimulating signaling. Pressure overload upregulates cardiac RGS4 in vivo to protect the heart against FFAR3-mediated inflammation and elevated SNS activity/NE release. Thus, cardiac RGS4 upregulation might represent a cardioprotective mechanism against the chronically increased afterload imposed by systemic hypertension.