Erich and Hanna Klessmann Institute for Cardiovascular Research & Development (EHKI), Heart and Diabetes Center NRW, University Hospital of the Ruhr-University Bochum, Georgstrasse 11, 32545 Bad Oeynhausen, Germany.
Institute for Clinical Biochemistry and Pathobiochemistry, Cellular Morphology, German Diabetes Center, Auf'm Hennekamp 65, 40225 Düsseldorf, Germany.
J Mol Cell Cardiol. 2020 Apr;141:17-29. doi: 10.1016/j.yjmcc.2020.03.006. Epub 2020 Mar 19.
We aimed to unravel the genetic, molecular and cellular pathomechanisms of DSC2 truncation variants leading to arrhythmogenic cardiomyopathy (ACM).
We report a homozygous 4-bp DSC2 deletion variant c.1913_1916delAGAA, p.Q638LfsX647 causing a frameshift carried by an ACM patient. Whole exome sequencing and comparative genomic hybridization analysis support a loss of heterozygosity in a large segment of chromosome 18 indicating segmental interstitial uniparental isodisomy (UPD). Ultrastructural analysis of the explanted myocardium from a mutation carrier using transmission electron microscopy revealed a partially widening of the intercalated disc. Using qRT-PCR we demonstrated that DSC2 mRNA expression was substantially decreased in the explanted myocardial tissue of the homozygous carrier compared to controls. Western blot analysis revealed absence of both full-length desmocollin-2 isoforms. Only a weak expression of the truncated form of desmocollin-2 was detectable. Immunohistochemistry showed that the truncated form of desmocollin-2 did not localize at the intercalated discs. In vitro, transfection experiments using induced pluripotent stem cell derived cardiomyocytes and HT-1080 cells demonstrated an obvious absence of the mutant truncated desmocollin-2 at the plasma membrane. Immunoprecipitation in combination with fluorescence measurements and Western blot analyses revealed an abnormal secretion of the truncated desmocollin-2.
In summary, we unraveled segmental UPD as the likely genetic reason for a small homozygous DSC2 deletion. We conclude that a combination of nonsense mediated mRNA decay and extracellular secretion is involved in DSC2 related ACM.
我们旨在揭示导致心律失常性心肌病（ACM）的 DSC2 截断变异的遗传、分子和细胞发病机制。
我们报告了一个纯合的 4 个碱基对 DSC2 缺失变异 c.1913_1916delAGAA，p.Q638LfsX647，由 ACM 患者携带。全外显子组测序和比较基因组杂交分析支持大片段 18 号染色体的杂合性丢失，提示部分片段性染色体间单亲二体性（UPD）。使用透射电子显微镜对突变携带者的心脏移植组织进行超微结构分析显示，闰盘部分变宽。使用 qRT-PCR，我们证明与对照组相比，纯合子携带者心脏移植组织中的 DSC2mRNA 表达显著降低。Western blot 分析显示两种全长的桥粒蛋白 2 同工型均不存在。仅检测到桥粒蛋白 2 截断形式的微弱表达。免疫组织化学显示，截短形式的桥粒蛋白 2 不在闰盘处定位。在体外，使用诱导多能干细胞衍生的心肌细胞和 HT-1080 细胞进行转染实验表明，突变的截短型桥粒蛋白 2 明显不存在于质膜上。免疫沉淀结合荧光测量和 Western blot 分析显示截短的桥粒蛋白 2 异常分泌。
总之，我们发现部分 UPD 可能是导致小的 DSC2 纯合缺失的遗传原因。我们得出结论，无意义介导的 mRNA 衰变和细胞外分泌的结合可能与 DSC2 相关的 ACM 有关。
