Abstract 17773: Cardiac Myocyte-specific Expression of LMNAD300N Activates MMP2 and Induces Severe Interstitial Fibrosis and Cardiac Systolic Dysfunction Leading to Premature Death in Mice
Mutations in the LMNA, encoding lamin A/C, cause a wide range of diseases, collectively known as laminopathies. In the heart, LMNA mutations cause dilated cardiomyopathy (DCM), conduction defect and sudden death. We recently identified a p.D300N mutation in LMNA in a patient with restrictive cardiomyopathy, conduction defect, atrial fibrillation and premature death. To delineate the molecular mechanism(s) responsible for cardiac phenotype caused by the p.D300N mutation, we generated a Doxycycline (DOX)-inducible (Tet-off) bigenic mice and expressed LmnaD300N or a wild type (WT) Lmna (LmnaWT), under the transcriptional regulation of Myh6 promoter. Expression of LmnaD300N was associated with severe interstitial fibrosis (6-fold increase compared with LmnaWT, p<0.05), cardiac dilatation, dysfunction and premature death, with ∼80% mortality at 4 weeks of age. Increased interstitial fibrosis was associated with a dramatic increase in p-SMAD2 level, a downstream target of TGF-β. To determine whether the induced phenotype could be prevented upon shutting down expression of the transgene, we treated the bigenic mice with DOX (100¼g/ml in drinking water) soon after birth. Treatment with DOX prevented fibrosis, cardiac dilation and dysfunction and normalized survival. However, despite prevention of the phenotype, LmnaD300N expression was unchanged, indicating transgene-independent effects of DOX. Because MMP2 and MMP9 are known to cleave and activate latent TGF-β and because DOX is known to inhibit MMPs, we assessed expression level of MMP-2 and MMP-9 in the LmnaD300N bigenic mice by immunoblotting. MMP-2 but MMP-9 level was increased significantly in the LmnaD300N mice and were normalized upon treatment with DOX. Thus, cardiac myocyte-specific expression of LmnaD300N activates MMP2, by yet-to-be-defined mechanism(s) and induces cardiac fibrosis and dysfunction, which are reversed upon inhibiting MMP-2 with DOX. The findings suggest that inhibition of MMP-2 might have preventive and therapeutic implications in laminopathies
- © 2012 by American Heart Association, Inc.