Cardiac fibrosis is a pathological feature commonly found in hearts exposed to haemodynamic orneurohormonal stress. Elevated levels of arginine vasopressin (AVP) are closely associated with the progression of heart failure and could be an underlying cause of cardiac fibrosis. The aim of this study is to characterize the effect of AVP on neonatal rat cardiac fibroblasts (NRCFs) and to illustrate its signalling mechanism. The proliferative effect of AVP was assessed by methylthiazolyldiphenyl-tetrazolium assay and 5-bromo-2'-deoxyuridine (BrdU) incorporation assay, and the amounts of cellular signalling proteins α-smooth muscle actin (α-SMA), matrix metalloproteinase (MMP) 2, MMP9, and phosphorylated ERK were determined by western blotting. AVP, in a time- and concentration-dependent manner, promoted NRCF proliferation and the expression of MMP2 and MMP9. Inhibition of G protein-coupled receptor kinase2 (GRK2) by the inhibitory peptide GRK2-Ct or knock-down of GRK2 suppressed AVP-induced BrdU incorporation and the expression of MMP2 and α-SMA in NRCFs. Moreover, shRNA-mediated silencing of β-arrestin1 or β-arrestin 2 abolished AVP-induced BrdU incorporation and MMP2 expression. AVP-induced NRCF proliferation depended on the phosphorylation of ERK , and inhibition of GRK2 or silencing of β-arrestins blocked AVP-induced ERK phosphorylation. The effects of AVP on NRCF proliferation and α-SMA expression were blocked by SR45059, a vasopressin receptor type1A (V R) selective antagonist. In conclusion, AVP promotes NRCF proliferation through V R-mediated GRK2/β-arrestin/ERK signalling.

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Ca(2+)/calmodulin-dependent calcineurin (CaN) plays an important role in various Ca(+2) signaling pathways, among which are those involved in cardiac diseases. It has also been shown that a heightened sympathetic tone accelerates the development of heart failure. The present study investigates whether the CaN-mediated nuclear factor of activated T-cells (NFAT) pathway is involved in cultured neonatal rat cardiac fibroblast proliferation induced by phenylephrine. CF proliferation was assessed by a cell survival assay and cell counts. Green fluorescent protein-tagged NFAT3 was used to determine the cellular location of NFAT3. CaN activity and protein levels were also determined by an activity assay kit and Western blotting, respectively. Results showed that phenylephrine promoted CF proliferation, which was abolished by α1-adrenergic receptor antagonist (prazosin), a blocker of Ca(+2) influx (nifedipine), an intracellular Ca(2+) buffer (BAPTA-AM), CaN inhibitors (cyclosporin A and FK506), and over-expression of dominant negative CaN. Phenylephrine activated CaN and evoked NFAT3 nuclear translocation, both of which were blocked by cyclosporine A (CsA) or over-expression of dominant negative CaN. These results suggest that the Ca(2+)/CaN/NFAT pathway mediates PE-induced CF proliferation, and this pathway might be a possible therapeutic target in cardiac fibrosis.