Abstract 16782: Autocrine/Paracrine ATP/Adenosine-Mediated Regulation of Cardiac Fibroblasts
Cardiac fibroblasts (CFs) maintain the extracellular matrix (ECM) in the heart, contributing to both basal ECM and remodeling after injury. Pathologic activation of CFs results in cardiac fibrosis through excessive deposition of collagens and other ECM proteins. Cellular stress releases nucleotides via connexin (Cx) hemichannels. The nucleotides activate pro-fibrotic P2Y receptors. CFs likely also “basally” release nucleotides via Cx hemichannels. We hypothesized that basal activation of P2Y receptors by nucleotides regulates CF phenotype and in addition, that hydrolysis of released nucleotides by nucleotide diphosphohydrolases (ENTPDs) blunts nucleotide-P2Y receptor-promoted responses. We isolated CFs from adult rats and assayed mRNA (quantitative real-time PCR), protein (immunoblotting), [3H]proline incorporation into collagen and collagen gel contraction. We found that hydrolysis of basal extracellular ATP and UTP by apyrase (1 U/ml) markedly reduces CF activation, decreasing α-smooth muscle actin (α-SMA) gene and protein expression (>90%, p<0.001 and 80%, p<0.05, respectively) and inhibiting collagen gel contraction. Conversely, inhibition of ENTPDs by sodium polyoxotungstate (POM-1, 50 µM) increased α-SMA gene and protein expression and collagen accumulation (by 200%; p<0.001) and POM-1 stimulated collagen gel contraction (by 25%; p<0.001). Inhibition of nucleotide degradation thus enhances pro-fibrotic responses. Hydrolysis of ATP also generates adenosine, which is anti-fibrotic in CFs via P1 receptors. Treatment of CFs with adenosine deaminase (ADA, 1 U/ml) to remove extracellular adenosine increased basal collagen accumulation by 67% (p<0.01). Thus, basal nucleotide signaling is pro-fibrotic in CFs but is blunted by ENTPDs that generate adenosine. Thus, “resting” adult CFs undergo autocrine/paracrine regulation by ATP/P2Y receptors and adenosine/P1 receptors that are, respectively, pro-and anti-fibrotic (Figure).
- © 2012 by American Heart Association, Inc.