MD-1对心力衰竭小鼠室性心律失常的影响及其机制研究

Ventricular arrhythmia is the most common cause of sudden cardiac death in patients with heart failure (HF). Structural and electrical remodeling is the key mechanism underlying ventricular arrhythmia after HF. Toll-like receptor 4 (TLR4)-mediated signal transduction pathway plays an important regulatory role in cardiac structural and electrical remodeling. Myeloid differentiation protein-1 (MD-1), a member of lipid-recognition family, negatively regulates TLR4 signaling pathway by forming a complex with TLR4 homologue RP105. Our preliminary study showed the expression of MD-1 was significantly down-regulated in failing hearts. Furthermore, MD-1 deficiency augmented pressure overload-induced cardiac remodeling, whereas cardiac-specific MD-1 overexpression exhibited the opposite phenotype. These findings suggest that MD-1 may play an critical role in ventricular arrhythmia after HF. However, the effects and the underlying mechanisms of MD-1 on ventricular arrhythmia after HF have not yet been investigated. Therefore, the present proposal, using MD-1 knockout mice and transgenic mice with cardiac-specific overexpression of MD-1, will identify the effects of MD-1 on ventricular arrhythmia after HF and explore the underlying mechanisms from structural and electrical remodeling perspectives by electrophysiological, pathological and molecular examinations. We aim to provide new molecular target for treatment and prevention of ventricular arrhythmia after HF.

室性心律失常是心力衰竭（心衰）患者猝死的主要原因。组织重构和电重构是心衰后室性心律失常发生的关键机制。Toll样受体4（TLR4）信号转导通路在心脏组织重构和电重构中具有重要调节作用。髓样分化蛋白-1（MD-1）是脂类识别家族成员之一，通过与TLR4同源分子RP105形成复合物而负性调节TLR4信号转导通路。我们的前期研究发现，心衰心脏组织中MD-1表达显著降低，MD-1基因敲除恶化压力负荷诱导的心脏重构，而心脏特异性MD-1过表达则呈现相反表型，提示MD-1可能对心衰后室性心律失常有重要调控作用。然而，目前尚无研究报道MD-1对心衰后室性心律失常的影响。本项目拟运用MD-1基因敲除小鼠和心脏特异性MD-1转基因小鼠，通过电生理研究、组织形态学研究和分子生物学研究，阐明MD-1对心衰后室性心律失常的影响，并从电重构和组织重构的角度探讨其机制，以期发现防治心衰后室性心律失常的新靶点。

室性心律失常是心力衰竭（心衰）患者猝死的主要原因。组织重构和电重构是心衰后室性心律失常发生的关键机制。心衰心脏组织中MD-1表达显著降低，MD-1基因敲除恶化压力负荷诱导的心脏重构，而心脏特异性MD-1过表达则呈现相反表型，提示MD-1可能对心衰后室性心律失常有重要调控作用。然而，MD-1在其中机制尚不明确。本项目主要内容包括：（1）采用MD-1基因敲除小鼠、心脏特异性MD-1转基因小鼠和野生型小鼠，通过主动脉缩窄术（Aortic Banding, AB）建立小鼠心衰模型，观察MD-1 对心衰后心脏组织重构的影响。结果显示：与野生型小鼠相比，MD-1敲除加重了小鼠心衰后心功能的恶化以及心肌肥厚和纤维化，而MD1过表达小鼠则呈现相反效应。（2）应用MD-1基因敲除小鼠，建立心衰模型，通过在体心脏电生理研究、离体心脏电生理研究和心肌细胞电生理研究，探讨MD-1对心衰后心脏电重构和室性心律失常发生的影响。结果显示：MD1基因敲除促进心脏复极化延长和舒张期SR钙渗漏，从而增加左室电生理不稳定性，这与钾、钠通道蛋白和钙调蛋白的变化相关。（3）应用MD-1基因敲除小鼠和心脏特异性MD-1转基因小鼠，建立心衰模型，通过分子生物学研究，阐明MD-1影响心脏组织重构和电重构的分子机制。结果显示：MD1可调控TLR4及其下游的MEK-ERK1/2和NF-κB信号通路、AKT信号通路，以及CaMKII信号通路进而调节心肌肥厚、心肌细胞离子通道和心肌钙处理蛋白，从而影响心衰后心室组织重构和电重构。本项目研究结果提示MD1通过调控TLR4及其下游的MEK-ERK1/2和NF-κB信号通路、AKT信号通路，以及CaMKII信号通路，从而影响心脏重构的发生发展，这为深入认识心衰后心脏重构提供了理论依据，也为临床防治心衰后心脏重构和室性心律失常提供了新靶点。