Gao Mei Hua, Lai N Chin, Giamouridis Dimosthenis, Kim Young Chul, Guo Tracy, Hammond H Kirk
VA San Diego Healthcare System, Department of Medicine, Division of Cardiology, San Diego CA, United States of America.
University of California, San Diego, Department of Medicine, Division of Cardiology, La Jolla CA, United States of America.
PLoS One. 2017 Aug 2;12(8):e0181282. doi: 10.1371/journal.pone.0181282. eCollection 2017.
Increased expression of adenylyl cyclase type 6 (AC6) has beneficial effects on the heart through cyclic adenosine monophosphate (cAMP)-dependent and cAMP-independent pathways. We previously generated a catalytically inactive mutant of AC6 (AC6mut) that has an attenuated response to β-adrenergic receptor stimulation, and, consequently, exhibits reduced myocardial cAMP generation. In the current study we test the hypothesis that cardiac-directed expression of AC6mut would protect the heart from sustained β-adrenergic receptor stimulation, a condition frequently encountered in patients with heart failure.
AC6mut mice and transgene negative siblings received osmotic mini-pumps to provide continuous isoproterenol infusion for seven days. Isoproterenol infusion caused deleterious effects that were attenuated by cardiac-directed AC6mut expression. Both groups showed reduced left ventricular (LV) ejection fraction, but the reduction was less in AC6mut mice (p = 0.047). In addition, AC6mut mice showed superior left ventricular function, manifested by higher values for LV peak +dP/dt (p = 0.03), LV peak -dP/dt (p = 0.008), end-systolic pressure-volume relationship (p = 0.003) and cardiac output (p<0.03). LV samples of AC6mut mice had more sarco/endoplasmic reticulum Ca2+-ATPase (SERCA2a) protein (p<0.01), which likely contributed to better LV function. AC6mut mice had lower rates of cardiac myocyte apoptosis (p = 0.016), reduced caspase 3/7 activity (p = 0.012) and increased B-cell lymphoma 2 (Bcl2) expression (p = 0.0001).
Mice with cardiac-directed AC6mut expression weathered the deleterious effects of continuous isoproterenol infusion better than control mice, indicating cardiac protection.
6型腺苷酸环化酶（AC6）表达增加通过环磷酸腺苷（cAMP）依赖性和非依赖性途径对心脏产生有益作用。我们之前构建了一种AC6催化失活突变体（AC6mut），其对β-肾上腺素能受体刺激的反应减弱，因此心肌cAMP生成减少。在本研究中，我们检验了以下假设：心脏定向表达AC6mut可保护心脏免受持续的β-肾上腺素能受体刺激，这种情况在心力衰竭患者中经常出现。
AC6mut小鼠和转基因阴性同窝小鼠接受渗透微型泵，持续输注异丙肾上腺素7天。输注异丙肾上腺素会产生有害影响，而心脏定向表达AC6mut可减轻这些影响。两组的左心室（LV）射血分数均降低，但AC6mut小鼠的降低幅度较小（p = 0.047）。此外，AC6mut小鼠表现出更好的左心室功能，表现为LV峰值 +dP/dt（p = 0.03）、LV峰值 -dP/dt（p = 0.008）、收缩末期压力-容积关系（p = 0.003）和心输出量（p<0.03）更高。AC6mut小鼠的LV样本中肌浆网/内质网Ca2+-ATP酶（SERCA2a）蛋白更多（p<0.01），这可能有助于改善LV功能。AC6mut小鼠的心肌细胞凋亡率较低（p = 0.016），半胱天冬酶3/7活性降低（p = 0.012），B细胞淋巴瘤2（Bcl2）表达增加（p = 0.0001）。
心脏定向表达AC6mut的小鼠比对照小鼠更能耐受持续输注异丙肾上腺素的有害影响，表明具有心脏保护作用。
