Genetic and ultrastructural studies in dilated cardiomyopathy patients: a large deletion in the lamin A/C gene is associated with cardiomyocyte nuclear envelope disruption

Abstract

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.

Lamin A/C mutations in dilated cardiomyopathy

“…The structural hypothesis states that mutations within lamin A/C lead to disorganization of the proteinaceous meshwork, instability of the nuclear envelope and disorganization of chromatin, which in turn leads to the overall inability of the cell to properly function in contracting tissue environment such as striated muscles [46,47]. Building on this hypothesis, recent studies identified repetitive disruptions of the nuclear envelope in the presence of lamin A/C mutations [17,48]. These disruptions impaired protein distribution into cell compartments.…”

“…These disruptions impaired protein distribution into cell compartments. Translocations of large amounts of protein into the cytoplasm could trigger aggresome formation or even induce cell apoptosis [48]. On the other hand, translocation of transcription factors into the cytoplasm might impair gene expression.…”

A Complex Double Deletion in LMNA Underlies Progressive Cardiac Conduction Disease, Atrial Arrhythmias, and Sudden Death

“…The mutation that we describe is the first complex deletion in this gene reported. A large deletion encompassing exon 3 to 12 was described by Gupta et al 34 in a 39-year-old woman with ventricular arrhythmias and mild dilatation and normal function. PCR analysis for the 566-bp fragment specific for our deletion on genomic DNA from this woman did not result in an amplification product, suggesting that although the mutation encompassed the same region, a different mutational event could underlie the disorder (Fré-dérique Tesson, personal communication).…”

“…29 Laminopathies result primarily from missense mutations. 10,22 Nonsense 30 mutations, splice-site 31 mutations, small insertions 32 /deletions, 33 as well as large deletions 28,34 are less common. The mutation that we describe is the first complex deletion in this gene reported.…”

Global transcriptional changes caused by an EDMD mutation correlate to tissue specific disease phenotypes inC. elegans

“…Cardiomyocytes of these patients demonstrate nuclear envelope abnormalities, changes in lamins expression and mitochondria miss-localization. 28,29 C. elegans pharynx is often used as a model of the function and muscular composition of the human heart. 30 In our analysis, we detected down regulation of several genes involved in the proper function and structure of the pharyngeal muscle; abu-6, abu-7, abu-8 and abu-15 (homologs of Keratinassociated protein 10-4) have a role in protecting against miss-folded protein stress, as well as proper pharyngeal grinder function; act-1 is required for pharyngeal muscle structures and myo-2 (human myosin heavy chain ortholog) encodes a muscle pharynx specific myosin heavy chain isoform.…”