Department of Clinical Research, University of Bern, Murtenstrasse 35, 3010 Bern, Switzerland.
Cardiovasc Res. 2011 Feb 1;89(2):320-8. doi: 10.1093/cvr/cvq326. Epub 2010 Oct 14.
Duchenne muscular dystrophy (DMD) is a severe striated muscle disease due to the absence of dystrophin. Dystrophin deficiency results in dysfunctional sodium channels and conduction abnormalities in hearts of mdx mice. Disease progression in the mdx mouse only modestly reflects that of DMD patients, possibly due to utrophin up-regulation. Here, we investigated mice deficient in both dystrophin and utrophin [double knockout (DKO)] to assess the role of utrophin in the regulation of the cardiac sodium channel (Na(v)1.5) in mdx mice.
Co-immunoprecipitation studies in HEK293 cells showed that utrophin interacts with Na(v)1.5 via syntrophin proteins, an interaction abolished by deletion of the PDZ (PSD-95, Dlg, and Zona occludens) domain-binding motif of Na(v)1.5. We also provide evidence for such interaction in mouse heart using Na(v)1.5 C-terminus fusion proteins. In hearts of DKO mice, Na(v)1.5 protein levels were decreased by 25 ± 8%, together with a 42 ± 12% reduction of syntrophins compared with mdx, where utrophin was up-regulated by 52 ± 9% compared with C57BL/10 control mice. Sodium current was found to be reduced by 41 ± 5% in DKO cardiomyocytes compared with mdx, representing a loss of 63 ± 3% when compared with C57BL/10 wild-type control mice. Decreased Na(v)1.5 protein and current in DKO were reflected in a significant slowing of 27 ± 6% of maximal upstroke velocity of the cardiac action potential compared with mdx.
Utrophin plays a central role in the regulation of Na(v)1.5 in mdx mice. These findings provide support for therapeutic strategies aimed at overexpressing utrophin in the hopes of reducing cardiac pathology in DMD patients.
杜氏肌营养不良症（DMD）是一种严重的横纹肌疾病，其病因是抗肌萎缩蛋白（dystrophin）缺失。肌萎缩蛋白缺失导致 mdx 小鼠心脏中的钠离子通道功能障碍和传导异常。mdx 小鼠的疾病进展仅能适度反映 DMD 患者的情况，这可能是由于肌联蛋白（utrophin）上调所致。在这里，我们研究了同时缺乏肌萎缩蛋白和肌联蛋白的小鼠[双敲除（DKO）]，以评估肌联蛋白在调节 mdx 小鼠心脏钠离子通道（Na(v)1.5）中的作用。
在 HEK293 细胞中的共免疫沉淀研究表明，肌联蛋白通过连接蛋白（syntrophin）蛋白与 Na(v)1.5 相互作用，这种相互作用可被 Na(v)1.5 的 PDZ（PSD-95、Dlg 和 Zona occludens）结构域结合基序缺失所消除。我们还使用 Na(v)1.5 C 端融合蛋白为心脏中的这种相互作用提供了证据。在 DKO 小鼠的心脏中，Na(v)1.5 蛋白水平下降了 25%±8%，与 mdx 相比，连接蛋白减少了 42%±12%，而 mdx 中的肌联蛋白与 C57BL/10 对照组相比上调了 52%±9%。与 mdx 相比，DKO 心肌细胞中的钠离子电流减少了 41%±5%，与 C57BL/10 野生型对照组相比减少了 63%±3%。在 DKO 中，Na(v)1.5 蛋白和电流的减少反映在心脏动作电位最大上升速度的显著减慢，与 mdx 相比减慢了 27%±6%。
肌联蛋白在 mdx 小鼠中对 Na(v)1.5 的调节起着核心作用。这些发现为旨在过度表达肌联蛋白以减少 DMD 患者心脏病理学的治疗策略提供了支持。
