Differential Downregulation of Subcellular Specific adrenoceptor Signaling in The Heart

Objective: Recent studies have shown that intracellular b1- adrenoceptors (b1ARs) are associated with the (Sarco)endoplasmic reticulum calcium ATPase 2a (SERCA2a) on the sarcoplasmic reticulum (SR) membrane. However, the mechanism of how this plasma membrane- and SR-associated pool of b1ARs signals downregulation under chronic sympathetic stimulation is not well understood. We aim to study these subcellular β1AR signals in different cellular compartments in a heart failure (HF) mouse model with chronic infusion of isoproterenol (ISO). Results and Methods: We investigated the association of b1AR with L-type calcium channel (LTCC), ryanodine receptor 2 (RyR2), and SERCA2a by utilizing proximity ligation assay (PLA) and confocal imaging in HF induced by chronic ISO infusion (30 mg/kg/day, 2 weeks). Chronic ISO infusion resulted in a downregulation of b1AR, and decreased receptor association with LTCC and RyR2 at the tubular membrane. In comparison, the b1AR association with SERCA2a was increased; however, the local cAMP-PKA mediated phospholamban phosphorylation is downregulated. Using Förster Resonance Energy Transfer (FRET) with genetically encoded biosensors to probe subcellular β1AR-PKA signaling, we observed reduced local ISO-induced PKA signaling at the RyR2 but not the SERCA2a nanodomains. Meanwhile, the expression of phosphodiesterases (PDEs) was altered including the downregulation of PDE4D and PDE3A and the upregulation of PDE2A, PDE4A, and PDE4B, which alters the local PKA activities in individual subcellular nanodomains. Interestingly, the localized PKA signal induced by endogenous norepinephrine at the SERCA2a nanodomain was impaired. Inhibition of monoamine oxidase A rescued the norepinephrine-induced local PKA signaling at the SERCA2a nanodomain and myocyte sarcomere shortening. Conclusion: We have uncovered distinct remodeling of b1AR signaling at the RyR2 and SERCA2a nanodomains in mouse HF after a chronic infusion of ISO. Our study offers strategies to restore the subcellular nanodomain cardiac b1AR signaling and contractile function in HF associated with chronic adrenergic stress, pointing toward potential therapeutic targets. National Institutes of Health grants R01-HL147263 and HL162825, Veteran Affair Merit grants IK6BX005753, 01BX002900 and BX005100. This is the full abstract presented at the American Physiology Summit 2024 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.