Gao Mei Hua, Lai Ngai Chin, Tang Tong, Guo Tracy, Tang Ruoying, Chun Byeong Jo, Wang Hong, Dalton Nancy N, Suarez Jorge, Dillmann Wolfgang H, Hammond H Kirk
VA San Diego Healthcare System and Department of Medicine, University of California San Diego, San Diego, California, United States of America.
PLoS One. 2013 Sep 16;8(9):e72151. doi: 10.1371/journal.pone.0072151. eCollection 2013.
So many clinical trials of positive inotropes have failed, that it is now axiomatic that agents that increase cAMP are deleterious to the failing heart. An alternative strategy is to alter myocardial Ca(2+) handling or myofilament response to Ca(2+) using agents that do not affect cAMP. Although left ventricular (LV) function is tightly linked to adenylyl cyclase (AC) activity, the beneficial effects of AC may be independent of cAMP and instead stem from effects on Ca(2+) handling. Here we ask whether an AC mutant molecule that reduces LV cAMP production would have favorable effects on LV function through its effects on Ca(2+) handling alone.
We generated transgenic mice with cardiac-directed expression of an AC6 mutant (AC6mut). Cardiac myocytes showed impaired cAMP production in response to isoproterenol (74% reduction; p<0.001), but LV size and function were normal. Isolated hearts showed preserved LV function in response to isoproterenol stimulation. AC6mut expression was associated with increased sarcoplasmic reticulum Ca(2+) uptake and the EC50 for SERCA2a activation was reduced. Cardiac myocytes isolated from AC6mut mice showed increased amplitude of Ca(2+) transients in response to isoproterenol (p = 0.0001). AC6mut expression also was associated with increased expression of LV S100A1 (p = 0.03) and reduced expression of phospholamban protein (p = 0.01).
LV AC mutant expression is associated with normal cardiac function despite impaired cAMP generation. The mechanism appears to be through effects on Ca(2+) handling - effects that occur despite diminished cAMP.
众多正性肌力药物的临床试验均告失败，以至于目前已成为公理的是，增加环磷酸腺苷（cAMP）的药物对衰竭心脏有害。一种替代策略是使用不影响cAMP的药物来改变心肌钙（Ca2+）处理或肌丝对Ca2+的反应。尽管左心室（LV）功能与腺苷酸环化酶（AC）活性紧密相关，但AC的有益作用可能独立于cAMP，而是源于对Ca2+处理的影响。在此，我们探讨一种降低LV cAMP生成的AC突变分子是否仅通过其对Ca2+处理的影响就对LV功能产生有利影响。
我们构建了心脏定向表达AC6突变体（AC6mut）的转基因小鼠。心肌细胞对异丙肾上腺素的反应显示cAMP生成受损（降低74%；p<0.001），但LV大小和功能正常。离体心脏对异丙肾上腺素刺激显示LV功能得以保留。AC6mut表达与肌浆网Ca2+摄取增加相关，且SERCA2a激活的半数有效浓度（EC50）降低。从AC6mut小鼠分离的心肌细胞对异丙肾上腺素的反应显示Ca2+瞬变幅度增加（p = 0.0001）。AC6mut表达还与LV S100A1表达增加（p = 0.03）和受磷蛋白表达降低（p = 0.01）相关。
尽管cAMP生成受损，但LV AC突变体表达与正常心脏功能相关。其机制似乎是通过对Ca2+处理的影响——尽管cAMP减少，但这些影响仍会发生。
