Abstract 4364208: Sweet Taste Receptors Alter Contractility and Calcium Handling in Cardiomyocytes

Abstract

GPCR-based taste receptors are expressed in taste buds where they mediate perception of bitter, umami, and sweet taste qualities. Bitterness is recognized by type II taste GPCRs (TAS2R), while umami and sweetness are detected by type I taste GPCRs (TAS1R). There are three TAS1Rs which heterodimerize to form umami (TAS1R1/TAS1R3) and sweet (TAS1R2/TAS1R3) receptors. Recently, extra-oral taste receptors were found in tissues such as the airways, brain, and pancreas where they function as toxin (bitter) and nutrient (umami/sweet) sensors. Studies also show cardiac TAS1R mRNA expression, including tas1r1 and tas1r3. However, whether sweet taste receptor (STR) proteins are expressed in the heart is not yet known. Here, using immunoblotting and immunofluorescence, we show that TAS1R2 and TAS1R3 are expressed in human and mouse myocardia, localized to the plasma membrane. To investigate cardiac STR function, we stimulated hiPSC-derived engineered heart tissue (EHT) and adult mouse cardiomyocytes with aspartame, a STR agonist, resulting in positive inotropy and accelerated Ca 2+ handling. To assess the pathway by which STR signaling alters excitation-contraction coupling, we acutely stimulated neonatal rat ventricular myocytes (NRVMs) with aspartame-treated growth media. Subsequently, we fractionated the membrane from the cytosol and evaluated proteomic changes by mass spectrometry. This revealed membrane enrichment of Gqα, a G-protein implicated in IP 3 -mediated Ca 2+ efflux from the sarcoplasmic reticulum. Further, localization of kinases (CAMKIID, SPEG, PKC) was altered. We gauged phosphorylation changes following aspartame treatment in unfractionated NRVMs. Interestingly, phospholemman was dephosphorylated, which is implicated in modulating contractility via NKA inhibition, indirectly affecting NCX activity. High sugar diets are associated with higher arrhythmia susceptibility. To evaluate if this results from cardiac STR overstimulation, we prolonged aspartame treatment of adult mouse cardiomyocytes, resulting in a higher frequency of irregular Ca 2+ transients. Using RNAseq and immunoblotting, we show expression of type I and II taste GPCRs is altered in human heart failure. Specifically, TAS1R2 is upregulated in heart failure. We show that TAS1R2 overexpression is associated with functional changes in EHTs when exposed to aspartame. Together, these results uncover a novel GPCR pathway altering cardiac physiology in response to extracellular nutrient detection.