Abstract 20812: TRPM7 Contributes to Atrial Fibrogenesis via Regulating Fibrotic Factors in Human AF
Background: Atrial fibrosis is an important factor causing atrial fibrillation (AF). However, the mechanisms of fibrogenesis are not fully understood. We recently demonstrated that TRPM7, a major Ca2+-permeable channel in fibroblasts, contributes to fibrogenesis in AF patients. Here we investigated the mechanisms by which TRPM7-mediated Ca2+ regulates atrial fibrogenesis.
Methods: With informed consent, right atrial biopsies were obtained from AF or sinus rhythm (SR) patients undergoing cardiac surgery. Fibroblasts were dissociated from biopsy samples. The freshly isolated or cultured fibroblasts were used for current recording, Ca2+-imaging, qPCR, western blot, and other experiments.
Results: Fibroblasts from AF patients displayed higher basal level of differentiation as indicated by increased α-SMA expression. Besides the increased TRPM7 current and TRPM7-mediated Ca2+ influx in AF fibroblasts versus SR fibroblasts, there was a higher expression level of fibrosis related factors, including PDGF, TGFβ1, collagen-I, TGFβ activating kinase 1 (TAK1) in AF versus SR fibroblasts. TRPM7 current and Ca2+ influx in human atrial fibroblasts can be reduced by 70% by TRPM7 specific shRNA. Importantly, knock-down of TRPM7 by TRPM7-shRNA in AF fibroblasts reduced more than 50% of the levels of pro-fibrotic factors, including TGFβ1, TAK1, and PDGF. Fibroblast differentiation and expression of collagen-I were also significantly decreased by TRPM7-shRNA in AF fibroblasts. Conversely, over-expression of TRPM7 by infecting fibroblasts with TRPM7-adenovirus markedly enhanced expression of TGFβ1, phosphorylationed TAK1 and Smad2/3.
Conclusions: Fibroblasts from AF patients showed increased levels of fibroblast differentiation, TGFβ1, PDGF, α-SMA, collagen, TRPM7, and TRPM7-mediated Ca2+ influx as compared to fibroblasts from SR subjects. Knock-down of TRPM7 decreased expression levels of TGFβ1, TAK1, and PDGF; and inhibited fibroblast differentiation. Over-expression of TRPM7 in fibroblasts enhanced expression of TGFβ1 and PDGF, and increased phosphorylated TAK1 and Smad2/3. These results indicate that TRPM7 contributes to fibrogenesis in AF patients by promoting the levels of fibrotic factors and stimulating their downstream pathways.
- © 2010 by American Heart Association, Inc.