Faculty of Health Sciences, University of Ottawa, Ottawa, ON, K1H 8M5, Canada.
Basic Res Cardiol. 2010 May;105(3):365-77. doi: 10.1007/s00395-010-0085-4. Epub 2010 Feb 3.
Major nuclear envelope abnormalities, such as disruption and/or presence of intranuclear organelles, have rarely been described in cardiomyocytes from dilated cardiomyopathy (DCM) patients. In this study, we screened a series of 25 unrelated DCM patient samples for (a) cardiomyocyte nuclear abnormalities and (b) mutations in LMNA and TMPO as they are two DCM-causing genes that encode proteins involved in maintaining nuclear envelope architecture. Among the 25 heart samples investigated, we identified major cardiomyocyte nuclear abnormalities in 8 patients. Direct sequencing allowed the detection of three heterozygous LMNA mutations (p.D192G, p.Q353K and p.R541S) in three patients. By multiplex ligation-dependant probe amplification (MLPA)/quantitative real-time PCR, we found a heterozygous deletion encompassing exons 3-12 of the LMNA gene in one patient. Immunostaining demonstrated that this deletion led to a decrease in lamin A/C expression in cardiomyocytes from this patient. This LMNA deletion as well as the p.D192G mutation was found in patients displaying major cardiomyocyte nuclear envelope abnormalities, while the p.Q353K and p.R541S mutations were found in patients without specific nuclear envelope abnormalities. None of the DCM patients included in the study carried a mutation in the TMPO gene. Taken together, we found no evidence of a genotype-phenotype relationship between the onset and the severity of DCM, the presence of nuclear abnormalities and the presence or absence of LMNA mutations. We demonstrated that a large deletion in LMNA associated with reduced levels of the protein in the nuclear envelope suggesting a haploinsufficiency mechanism can lead to cardiomyocyte nuclear envelope disruption and thus underlie the pathogenesis of DCM.
主要核膜异常，如核膜破裂和/或核内细胞器的存在，在扩张型心肌病（DCM）患者的心肌细胞中很少被描述。在这项研究中，我们筛选了 25 名无关的 DCM 患者样本，以研究（a）心肌细胞核异常和（b）LMNA 和 TMPO 突变，因为这两个基因是导致 DCM 的基因，编码参与维持核膜结构的蛋白质。在研究的 25 个心脏样本中，我们在 8 名患者中发现了主要的心肌细胞核异常。直接测序检测到 3 名患者存在三种杂合性 LMNA 突变（p.D192G、p.Q353K 和 p.R541S）。通过多重连接依赖性探针扩增（MLPA）/实时定量 PCR，我们发现一名患者的 LMNA 基因外显子 3-12 存在杂合性缺失。免疫染色表明，这种缺失导致该患者心肌细胞中 lamin A/C 的表达减少。这种 LMNA 缺失以及 p.D192G 突变存在于表现出主要心肌细胞核膜异常的患者中，而 p.Q353K 和 p.R541S 突变存在于没有特定核膜异常的患者中。研究中纳入的 DCM 患者均未携带 TMPO 基因突变。综上所述，我们没有发现 DCM 的发病和严重程度、核异常的存在以及 LMNA 突变的存在或缺失之间存在基因型-表型关系的证据。我们证明了 LMNA 中的大片段缺失与核膜中蛋白质水平降低相关，提示存在杂合不足机制，可导致心肌细胞核膜破裂，从而成为 DCM 的发病机制基础。
