Conditional, cell-type-specific transgenic mouse lines are of high value in cardiovascular research. A standard tool for cardiomyocyte-restricted DNA editing is the αMHC-MerCreMer/loxP system. However, there is an ongoing debate on the occurrence of cardiac side effects caused by unspecific Cre activity or related to tamoxifen/oil overload. Here, we investigated potential adverse effects of DNA editing by the αMHC-MerCreMer/loxP system in combination with a low-dose treatment protocol with the tamoxifen metabolite 4-hydroxytamoxifen (OH-Txf). αMHC-MerCreMer mice received intraperitoneally OH-Txf (20 mg/kg) for 5 or 10 days. These treatment protocols were highly efficient to induce DNA editing in adult mouse hearts. Multi-parametric magnetic resonance imaging revealed neither transient nor permanent effects on cardiac function during or up to 19 days after 5 day OH-Txf treatment. Furthermore, OH-Txf did not affect cardiac phosphocreatine/ATP ratios assessed by in vivo ³¹P MR spectroscopy, indicating no Cre-mediated side effects on cardiac energy status. No MRI-based indication for the development of cardiac fibrosis was found as mean T1 relaxation time was unchanged. Histological analysis of myocardial collagen III content after OH-Txf confirmed this result. Last, mean T2 relaxation time was not altered after Txf treatment suggesting no pronounced cardiac lipid accumulation or tissue oedema. In additional experiments, cardiac function was assessed for up to 42 days to investigate potential delayed side effects of OH-Txf treatment. Neither 5- nor 10-day treatment resulted in a depression of cardiac function. Efficient cardiomyocyte-restricted DNA editing that is free of unwanted side effects on cardiac function, energetics or fibrosis can be achieved in adult mice when the αMHC-MerCreMer/loxP system is activated by the tamoxifen metabolite OH-Txf.

条件性、细胞类型特异性转基因小鼠系在心血管研究中具有很高的价值。用于心肌细胞限制性 DNA 编辑的标准工具是 αMHC-MerCreMer/loxP 系统。然而，关于非特异性 Cre 活性或与他莫昔芬/油过载相关的心脏副作用的发生一直存在争议。在这里，我们研究了 αMHC-MerCreMer/loxP 系统与使用他莫昔芬代谢物 4-羟基他莫昔芬 (OH-Txf) 的低剂量治疗方案相结合的 DNA 编辑的潜在不利影响。αMHC-MerCreMer 小鼠腹腔内接受 OH-Txf (20 mg/kg) 5 或 10 天。这些治疗方案对于诱导成年小鼠心脏中的 DNA 编辑非常有效。多参数磁共振成像显示，在 OH-Txf 治疗 5 天期间或长达 19 天后，对心脏功能的影响既没有短暂也没有永久性影响。此外，OH-Txf 不影响体内评估的心脏磷酸肌酸/ATP 比率³¹P MR 光谱，表明没有 Cre 介导的对心脏能量状态的副作用。由于平均 T1 弛豫时间未发生变化，因此未发现基于 MRI 的心脏纤维化发展指征。OH-Txf 后心肌胶原 III 含量的组织学分析证实了这一结果。最后，Txf 治疗后平均 T2 弛豫时间没有改变，表明没有明显的心脏脂质积累或组织水肿。在另外的实验中，心脏功能被评估长达 42 天，以研究 OH-Txf 治疗的潜在延迟副作用。5 天和 10 天的治疗均未导致心脏功能下降。有效的心肌细胞限制性 DNA 编辑，不会对心脏功能产生不良副作用，