Abstract 74: Naturally Occurring Human α1a-Adrenergic Receptor Genetic Variant Induces Transformation of Cardiomyoblasts to Fibroblast-Like Phenotype

Hypertensive heart disease is a progressive condition leading to myocardial remodeling, alterations in cardiomyocytes and fibrosis. Three α1 adrenergic receptor (AR) subtypes are expressed in human heart (α1a, α1b, α1d). Recently, we reported that human α1aAR with the naturally occurring G247R SNP (247R), originally identified in a hypertensive patient, constitutively couples to EGFR-transactivation pathway in fibroblasts and leads to hyperproliferation. We hypothesized that expression of 247R in cardiomyoblasts plays an important role in their remodeling. We demonstrate that constitutive expression of 247R in H9C2 cardiomyoblasts changes the morphology of myoblasts to fibroblast-like cells (transformed, tr247R); higher 247R expression results in earlier onset of transformation. Expression of α1aAR-WT does not affect cell morphology. Tr247R cells exhibit 2-3 fold increased constitutive proliferation compared to control or WT cells as determined by cell counts and thymidine incorporation assays; pERK is upregulated in tr247R cells as determined by Western blot analyses. Treatment with AraC, a DNA replication inhibitor, eliminates the 247R cells but not the H9C2 myoblasts. Expression of cell-specific markers is being evaluated in tr247R and control cells. RT-PCR and zymograms revealed increased MMP2 mRNA and protein levels in tr247R cells compared to control or WT cells and are comparable to MMP2 levels in fibroblasts. Increased proliferation of tr247R cells is reduced by EGFR specific inhibitor AG1478 but not general MMP inhibitor GM6001. Agonist stimulation of tr247R results in hypertrophy as determined by leucine incorporation. Interestingly, hypertrophy but not cell proliferation is inhibited by prazosin, an α1aAR inverse agonist, suggesting that increased proliferation and hypertrophy observed in transformed cells are two independent pathways triggered by 247R. Our data demonstrate that expression of α1aAR genetic variant triggers alterations in cardiomyoblasts via distinct signaling pathways leading to hyperproliferation, transformation of the cells to fibroblast-like phenotype and hypertrophy. Consequently, these changes may lead to fibrosis in human heart, extracellular matrix remodeling and heart failure.