Wnt-11 Signaling in Cardiomyocytes

Abstract

The Wnt/frizzled signalling pathways play a key role in cardiogenesis and in adult hearts during cardiac remodelling. We investigated whether the expression of Wnt-11 and its anticipated downstream signalling components is altered in human failing hearts and whether Wnt-11 acutely affects Ca2+ transients in adult murine cardiomyocytes.Left ventricles (LV) homogenates of human non-failing hearts (NF, n=4) and end-stage failing hearts with ischemic (ICM, n=5) and dilated (DCM, n=5) cardiomyopathy were used for western blotting with antibodies against Wnt-11, Fzd-4 and Fzd-7 (Wnt receptors) and Dvl-1 (downstream cytoplasmic regulator). Expression of proteins was normalized to GAPDH and is given as a fraction of average protein expression in NF. Ca2+ transients were measured during confocal line scan imaging with Fluo-4 in isolated murine adult cardiomyocytes after 5 (ncells=20) and 25 minutes (ncells=18) incubation with recombinant Wnt-11 (2 µg/ml). Untreated cells served as controls (ncells=27).Wnt-11 expression in LV in ICM (0.85 ± 0.05) and DCM (0.91 ± 0.34) was not significantly changed when compared to NF. However, the expression of Wnt-11 receptors was highly increased: Fzd-4 in ICM (6.25 ± 1.23; p<0.005) and in DCM (4.81 ± 0.82; p<0.005) as well Fzd-7 in ICM (4.48 ± 0.63; p<0.001) and in DCM (4.45 ± 0.76; p<0.001). The expression of Dvl-1 tended to be decreased in ICM (0.63 ± 0.15; p=0.15) and DCM (0.64 ± 0.29; p=0.17). The amplitude of Ca2+ transients (F/F0), time to peak, and time to 50 % decay (RT50) were not altered during 5 and 25 minutes incubation with Wnt-11 when compared to untreated control cells.The expression of the Wnt-receptors, Fzd-4 and Fzd-7 is significantly increased in human end-stage failing hearts, suggesting their regulation in cardiac remodelling and/or dysfunction. Wnt-11 did not acutely alter cardiomyocyte Ca2+ transients in non-diseased cardiomyocytes.