Ohnuki Yoshiki, Suita Kenji, Ishikawa Misao, Mototani Yasumasa, Nariyama Megumi, Ito Aiko, Matsuo Ichiro, Hayakawa Yoshio, Morii Akinaka, Mitsubayashi Takao, Saeki Yasutake, Ishikawa Yoshihiro, Okumura Satoshi
Department of Physiology, Tsurumi University School of Dental Medicine, Yokohama, Japan.
Cardiovascular Research Institute, Yokohama City University Graduate School of Medicine, Yokohama, Japan.
PLoS One. 2025 Jun 17;20(6):e0325986. doi: 10.1371/journal.pone.0325986. eCollection 2025.
β-Adrenergic receptor (β-AR) stimulation of the heart, leading to increased cardiac output, is mediated by cyclic AMP (cAMP), which induces protein kinase A (PKA)-mediated phosphorylation of the myofilament proteins troponin I (TnI) and myosin binding protein-C (MyBP-C). The aim of this study was to investigate the contribution of the exchange protein activated by cAMP (Epac1), a PKA-independent cAMP effector, to the response of cardiac myofilaments to β-AR stimulation. The calcium sensitivity of force and ATPase activity, and the tension cost (ATPase activity/force) were significantly greater in skinned myocardium from transgenic mice specifically overexpressing Epac1 in the heart (Epac1TG) and wild-type (WT) mice treated with 8CPT-AM, an Epac-selective cAMP analogue, as compared with non-transgenic (NTG) or control mice, respectively. In addition, myosin regulatory light chain (RLC) phosphorylation was significantly greater in Epac1TG and WT mice treated with 8CPT-AM than in NTG or control mice via phospholipase C/phosphokinase C, without any change in the phosphorylation of TnI or MyBP-C. We also examined the effects of chronic β-AR stimulation on cardiac function in Epac1TG. The left ventricular ejection fraction was significantly decreased from baseline in both NTG and Epac1TG after isoproterenol infusion (60 mg/kg/day for 1 week), but the magnitude of the decrease was much greater in Epac1TG. Our results suggest that Epac1 activation might induce an imbalance between force-generating capacity and ATPase activity in skinned myocardium. This could increase oxygen consumption and the energetic cost of contraction in living myocardium under conditions of chronic β-AR stimulation, leading to the development of heart failure.
心脏的β-肾上腺素能受体（β-AR）刺激会导致心输出量增加，这是由环磷酸腺苷（cAMP）介导的，cAMP会诱导蛋白激酶A（PKA）介导的肌丝蛋白肌钙蛋白I（TnI）和肌球蛋白结合蛋白C（MyBP-C）的磷酸化。本研究的目的是探讨cAMP激活的交换蛋白（Epac1），一种不依赖PKA的cAMP效应器，对心肌肌丝对β-AR刺激反应的贡献。与非转基因（NTG）或对照小鼠相比，在心脏中特异性过表达Epac1的转基因小鼠（Epac1TG）以及用Epac选择性cAMP类似物8CPT-AM处理的野生型（WT）小鼠的皮肤心肌中，力和ATP酶活性的钙敏感性以及张力成本（ATP酶活性/力）显著更高。此外，通过磷脂酶C/磷酸激酶C，用8CPT-AM处理的Epac1TG和WT小鼠中的肌球蛋白调节轻链（RLC）磷酸化显著高于NTG或对照小鼠，而TnI或MyBP-C的磷酸化没有任何变化。我们还研究了慢性β-AR刺激对Epac1TG心脏功能的影响。异丙肾上腺素输注（60mg/kg/天，持续1周）后，NTG和Epac1TG的左心室射血分数均较基线显著降低，但Epac1TG的降低幅度要大得多。我们的结果表明，Epac1激活可能会导致皮肤心肌中力产生能力和ATP酶活性之间失衡。这可能会增加慢性β-AR刺激条件下活体心肌的耗氧量和收缩的能量成本，导致心力衰竭的发生。
