Aims Despite massive efforts, we remain far behind in our attempts to identify effective therapies to treat heart failure with preserved ejection fraction (HFpEF). Diastolic function is critically regulated by sarcoplasmic/endoplasmic reticulum (SR) calcium ATPase 2a (SERCA2a) which forms a functional cardiomyocyte (CM) microdomain where 3’,5’-cyclic adenosine monophosphate (cAMP) produced upon β-adrenoceptor (β-AR) stimulation leads to phospholamban (PLN) phosphorylation and facilitated Ca2+ reuptake. Methods and Results To visualise real time cAMP dynamics in the direct vicinity of SERCA2a in healthy and diseased myocytes, we generated a novel mouse model on the leprdb background that stably expresses the Epac1-PLN Förster resonance energy transfer (FRET) biosensor. Mice homozygous for the leprdb mutation (db/db), developed obesity and type 2 diabetes and presented with a HFpEF phenotype, evident by mild left ventricular hypertrophy and elevated left atria filling pressures. Live cell imaging uncovered a substantial β2-AR subtype stimulated cAMP response within the PLN/SERCA2a microdomain of db/db but not healthy control (db/+) CMs, that was accompanied by increased PLN phosphorylation and accelerated calcium re-uptake. Importantly, db/db CMs also exhibited a desensitisation to β1-AR stimulated cAMP pools within the PLN/SERCA2a microdomain which was accompanied by a blunted lusitropic effect, suggesting the increased β2-AR control is an intrinsic compensatory mechanism to maintain PLN/SERCA2a mediated calcium dynamics and cardiac relaxation. Mechanistically, this was due to a local loss of cAMP degrading phosphodiesterase 4 (PDE4) associated specifically with the PLN/SERCA2a complex. Conclusions These newly identified alterations of cAMP dynamics at the subcellular level in HFpEF should provide mechanistic understanding of microdomain remodelling and pave the way towards new therapies.

中文翻译：

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肥胖和 2 型糖尿病引起的射血分数保留的心力衰竭中 SERCA2a 微域内 cAMP 动态的重塑


目标 尽管付出了巨大的努力，我们在寻找有效疗法来治疗射血分数保留的心力衰竭（HFpEF）方面仍然远远落后。舒张功能受到肌浆/内质网 (SR) 钙 ATP 酶 2a (SERCA2a) 的严格调节，该酶形成功能性心肌细胞 (CM) 微域，其中 3',5'-环磷酸腺苷 (cAMP) 在 β-肾上腺素受体 (β-AR) 上产生) 刺激会导致受磷蛋白 (PLN) 磷酸化并促进 Ca2+ 再摄取。方法和结果为了可视化健康和患病肌细胞中 SERCA2a 附近的实时 cAMP 动态，我们在 leprdb 背景上生成了一种新型小鼠模型，该模型稳定表达 Epac1-PLN Förster 共振能量转移 (FRET) 生物传感器。 leprdb 突变 (db/db) 纯合的小鼠出现肥胖和 2 型糖尿病，并呈现 HFpEF 表型，表现为轻度左心室肥大和左心房充盈压升高。活细胞成像发现，db/db 的 PLN/SERCA2a 微域内有大量 β2-AR 亚型刺激 cAMP 反应，但健康对照 (db/+) CM 则不然，伴随着 PLN 磷酸化增加和钙再摄取加速。重要的是，db/db CM 还表现出对 PLN/SERCA2a 微域内 β1-AR 刺激的 cAMP 池的脱敏，并伴有减弱的松弛效应，表明增加的 β2-AR 控制是维持 PLN/SERCA2a 介导的内在补偿机制钙动力学和心脏舒张。从机制上讲，这是由于与 PLN/SERCA2a 复合物特异性相关的 cAMP 降解磷酸二酯酶 4 (PDE4) 的局部丢失所致。 结论 这些新发现的 HFpEF 亚细胞水平 cAMP 动态变化应该提供对微区重塑的机制理解，并为新疗法铺平道路。