Guangdong Key Laboratory of Genome Stability and Human Disease Prevention, Guangdong Key Laboratory of Regional Immunity and Diseases, Department of Pathophysiology (W.L., G.W., W.C., Y.L., J.L.), School of Medicine, Shenzhen University, China.
Prenatal Diagnosis Center, The Women and Children Hospital of Guangdong Province, Guangzhou, China (C.Z.).
Circulation. 2019 Apr 30;139(18):2142-2156. doi: 10.1161/CIRCULATIONAHA.118.029413.
KChIP2 (K channel interacting protein) is the auxiliary subunit of the fast transient outward K current ( I) in the heart, and insufficient KChIP2 expression induces I downregulation and arrhythmogenesis in cardiac hypertrophy. Studies have shown muscle-specific mitsugumin 53 (MG53) has promiscuity of function in the context of normal and diseased heart. This study investigates the possible roles of cardiac MG53 in regulation of KChIP2 expression and I, and the arrhythmogenic potential in hypertrophy.
MG53 expression is manipulated by genetic ablation of MG53 in mice and adenoviral overexpression or knockdown of MG53 by RNA interference in cultured neonatal rat ventricular myocytes. Cardiomyocyte hypertrophy is produced by phenylephrine stimulation in neonatal rat ventricular myocytes, and pressure overload-induced mouse cardiac hypertrophy is produced by transverse aortic constriction.
KChIP2 expression and I density are downregulated in hearts from MG53-knockout mice and MG53-knockdown neonatal rat ventricular myocytes, but upregulated in MG53-overexpressing cells. In phenylephrine-induced cardiomyocyte hypertrophy, MG53 expression is reduced with concomitant downregulation of KChIP2 and I, which can be reversed by MG53 overexpression, but exaggerated by MG53 knockdown. MG53 knockout enhances I remodeling and action potential duration prolongation and increases susceptibility to ventricular arrhythmia in mouse cardiac hypertrophy. Mechanistically, MG53 regulates NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) activity and subsequently controls KChIP2 transcription. Chromatin immunoprecipitation demonstrates NF-κB protein has interaction with KChIP2 gene. MG53 overexpression decreases, whereas MG53 knockdown increases NF-κB enrichment at the 5' regulatory region of KChIP2 gene. Normalizing NF-κB activity reverses the alterations in KChIP2 in MG53-overexpressing or knockdown cells. Coimmunoprecipitation and Western blotting assays demonstrate MG53 has physical interaction with TAK1 (transforming growth factor-b [TGFb]-activated kinase 1) and IκBα (nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha), critical components of the NF-κB pathway.
These findings establish MG53 as a novel regulator of KChIP2 and I by modulating NF-κB activity and reveal its critical role in electrophysiological remodeling in cardiac hypertrophy.
KChIP2（K 通道相互作用蛋白）是心脏中快速瞬时外向 K 电流（I）的辅助亚基，KChIP2 表达不足会导致 I 下调和心脏肥厚中的心律失常发生。研究表明，肌肉特异性的 Mitsugumin 53（MG53）在正常和患病心脏中具有混杂功能。本研究探讨了心脏 MG53 在调节 KChIP2 表达和 I 以及肥厚中的心律失常潜能方面的可能作用。
通过在小鼠中基因敲除 MG53 或通过腺病毒过表达或 RNA 干扰敲低 MG53，来操纵 MG53 的表达，并用苯肾上腺素刺激培养的新生大鼠心室肌细胞来产生心肌细胞肥大，通过横主动脉缩窄来产生压力超负荷诱导的小鼠心脏肥厚。
MG53 敲除小鼠和 MG53 敲低的新生大鼠心室肌细胞中的 KChIP2 表达和 I 密度下调，但在 MG53 过表达的细胞中上调。在苯肾上腺素诱导的心肌细胞肥大中，MG53 表达减少，同时 KChIP2 和 I 下调，这可以通过 MG53 过表达逆转，但通过 MG53 敲低加剧。MG53 敲除增强了 I 的重构和动作电位时程延长，并增加了小鼠心脏肥厚中的室性心律失常易感性。机制上，MG53 调节 NF-κB（核因子 kappa 轻链增强子的激活 B 细胞）活性，随后控制 KChIP2 转录。染色质免疫沉淀实验表明 NF-κB 蛋白与 KChIP2 基因相互作用。MG53 过表达减少，而 MG53 敲低增加 KChIP2 基因 5'调控区的 NF-κB 富集。正常化 NF-κB 活性可逆转 MG53 过表达或敲低细胞中 KChIP2 的改变。共免疫沉淀和 Western blot 分析表明，MG53 与 TAK1（转化生长因子-β[ TGFb]-激活激酶 1）和 IκBα（核因子κ轻链增强子 B 细胞抑制剂，α）具有物理相互作用，这是 NF-κB 途径的关键组成部分。
这些发现确立了 MG53 通过调节 NF-κB 活性成为 KChIP2 和 I 的新型调节剂，并揭示了其在心脏肥厚中电生理重构中的关键作用。
