Abstract 16914: Expression of Lamin Mutation p.R644C, The Most Common Known Cause of Cardiolaminopathies, Causes Cardiac Fibroblasts Senescence
Background: Mutations in LMNA, encoding lamin A/C (LMNA), cause a diverse array of distinct phenotypes, including progeroid syndromes. The phenotype in the heart, referred to as cardiolaminopathies, typically manifests as early onset and progressive dilated cardiomyopathy (DCM), atrial bradyarrhythmias and conduction defects. The most commonly reported mutation in cardiolaminopathies is the p.R644C, which is located in the C-terminus. The domain is involved in progeroid syndromes. We posit that cardiolaminopathies caused by the p.R644C mutation represent non-syndromic premature cardiac aging.
Methods and Results: We expressed wild type and mutant LMNA (LMNA-WT and LMNA-R644C, respectively) in cardiac fibroblasts isolated from adult mouse hearts using recombinant adenoviruses. Expression of LMNA-R644C was associated with blebbing of the nuclear membrane, a characteristic of progeroid syndromes. Co-immunopreciptation studies showed reduced binding of LMNA-R644C to its interactome proteins, namely retinoblastoma (Rb), lamin-associated protein 2α and protein phosphatase 2A, leading to reduced inactivation of Rb by hyperphosphorylation. Consequently, levels of Cdkn1a (P19) and Cdkn2d (P21), well-established inhibitors of cell cycle progression were increased and levels of Cyclin A2 and Cyclin B1, markers of cell cycle progression to mitosis, were reduced. In accord with cell cycle inhibition, proliferation rate of cardiac fibroblasts was decreased, as indicated by increased cell doubling time and reduced BrdU incorporation, while expression level of senescence-associated β-galactosidase, a marker for cell senescence was increased.
Conclusions: Expression of LMNA-R644C mutation, the most common mutation found in cardiolaminopathies, impairs interactions among constituents of the LMNA/Rb/LAP2α/PP2A complex leading to hypophosphorylation of Rb, suppression of cell cycle progression and senescence of cardiac fibroblasts. We conclude that cardiolaminopathies represent non-syndromic premature cardiac senescence.
- © 2011 by American Heart Association, Inc.