Date Published: November 3, 2012
Publisher: Impact Journals LLC
Author(s): Chung-Wah Siu, Yee-Ki Lee, Jenny Chung-Yee Ho, Wing-Hon Lai, Yau-Chi Chan, Kwong-Man Ng, Lai-Yung Wong, Ka-Wing Au, Yee-Man Lau, Jinqiu Zhang, Kenneth Weijian Lay, Alan Colman, Hung-Fat Tse.
We identified an autosomal dominant non-sense mutation (R225X) in exon 4 of the lamin A/C (LMNA) gene in a Chinese family spanning 3 generations with familial dilated cardiomyopathy (DCM). In present study, we aim to generate induced pluripotent stem cells derived cardiomyocytes (iPSC-CMs) from an affected patient with R225X and another patient bearing LMNA frame-shift mutation for drug screening.
Higher prevalence of nuclear bleb formation and micronucleation was present in LMNAR225X/WT and LMNAFramshift/WT iPSC-CMs. Under field electrical stimulation, percentage of LMNA-mutated iPSC-CMs exhibiting nuclear senescence and cellular apoptosis markedly increased. shRNA knockdown of LMNA replicated those phenotypes of the mutated LMNA field electrical stress. Pharmacological blockade of ERK1/2 pathway with MEK1/2 inhibitors, U0126 and selumetinib (AZD6244) significantly attenuated the pro-apoptotic effects of field electric stimulation on the mutated LMNA iPSC-CMs.
LMNA-related DCM was modeled in-vitro using patient-specific iPSC-CMs. Our results demonstrated that haploinsufficiency due to R225X LMNA non-sense mutation was associated with accelerated nuclear senescence and apoptosis of iPSC- CMs under electrical stimulation, which can be significantly attenuated by therapeutic blockade of stress-related ERK1/2 pathway.
Lamins A and C are intermediate filament proteins encoded by lamin A/C gene (LMNA) and constitute major components of nuclear lamina . Mutations in LMNA have been shown to cause a wide range of human diseases collectively referred to as “laminopathies,”[2-6] from Hutchinson Gilford Progeria (premature aging syndrome), muscular dystrophy, to familial dilated cardiomyopathy (DCM). LMNA-related DCM is characterized by early onset of atrial fibrillation and conduction system disease, and subsequent progression to sudden cardiac death and heart failure [7, 8]. Indeed, LMNA mutations are the most common cause of familial DCM, accounting for 5-10% of overall familial DCM and up to 30-45% families with DCM and conduction system disease [9, 10]. Although the age of presentation in LMNA-related DCM can range from the first to sixth decade of life, almost all patients become symptomatic after age 60 [7, 11, 12]. Furthermore, LMNA-related DCM, especially in those associated with conductive system disease have a more malignant clinical course than other familial DCM due to a high rates of progressive heart failure and sudden cardiac death due to ventricular tachyarrhythmias [12-15]. Despite our increasing awareness on the importance of LMNA-relatedDCM, the mechanism of the disease as well as the therapeutic strategies to prevent the onset and progression of disease remain unclear.
LMNA-related DCM is the most common form of familial DCM encountered in clinical practice. Affected individuals are often asymptomatic at early stage except with typical ECG findings of low amplitude P waves, prolonged PR intervals, but relatively normal QRS complexes. As the disease progresses with age, patients develop atrial fibrillation, progressive conduction block and left ventricular dysfunction, and sudden cardiac death due to life-threatening ventricular tachyarrhythmias [7, 12, 15]. Since the first description of isolated DCM related to LMNA mutations by Fatkin et al in 1999, there are more than 40 LMNA mutations related to familial DCM have been reported. Despite of numerous clinical reports, the pathogenic mechanisms by which a defect in nuclear envelope link to the clinical DCM remain elusive.