Abstract 11340: The Plasma Membrane Calcium ATPase 4 Signaling in Cardiac Fibroblasts Mediates Cardiomyocyte Hypertrophy (Best of Basic Science Abstract)

Abstract

Plasma membrane calcium ATPase 4 (PMCA4) is a ubiquitously expressed Ca 2+ pump that is important in mediating molecular signaling in the heart. Here we show a novel role of PMCA4 in cardiac fibroblasts in controlling cardiac hypertrophy. We generated three PMCA4 knockout mouse strains: i) PMCA4 global knockout (PMCA4 -/- ); ii) PMCA4 cardiomyocyte-specific knockout (PMCA4 cko ); iii) PMCA4 fibroblast-specific knockout (PMCA4 fko ). Following transverse aortic constriction (TAC) for 5 weeks, PMCA4 -/- and PMCA4 fko mice displayed a significantly reduced hypertrophy compared to control mice. In contrast, the PMCA4 cardiac specific knockout (PMCA4 cko ) mice did not show any protective effect following TAC, prompting us to hypothesise that the protective effect might be due to PMCA4 ablation in fibroblasts. Microarray analysis revealed a ~100 fold upregulation of secreted frizzled-related protein 2 (sFRP2) in PMCA4 -/- fibroblasts, which was further confirmed by qRT-PCR and Western blot. sFRP2 is a potent inhibitor of the Wnt/β-catenin pathway. We then cultured wild type (WT) cardiomyocytes with conditioned medium from either PMCA4 -/- or WT fibroblasts. In response to phenylephrine stimulation, cardiomyocytes cultured in PMCA4 -/- fibroblast–conditioned medium displayed 88% less hypertrophy than those cultured in WT fibroblast–conditioned medium (P<0.01). Mechanistically, PMCA4 -/- fibroblasts showed a significant elevation in NFκB activity, a transcription factor that regulates sFRP2 expression. Inhibition of NFκB activity significantly reduced the sFRP2 expression in PMCA4 -/- fibroblasts to a level comparable to WT expression. A chemical library screen identified a novel PMCA4 inhibitor, aurintricarboxylic acid (ATA). ATA treatment enhanced sFRP2 expression in the mouse heart. Importantly, ATA inhibited and reversed TAC-induced cardiac hypertrophy in mice, demonstrating its efficacy in both preventive and therapeutic strategies. In conclusion, PMCA4-mediated signaling in cardiac fibroblasts plays a key role in controlling cardiac hypertrophy. Cardiac fibroblasts lacking PMCA4 produce higher levels of sFRP2, which protects the neighbouring cardiomyocytes. Finally, PMCA4 is a potential target for cardiac hypertrophy treatment.