Abstract 412: Galectin-3 Promotes Pro-Hypertrophic Communication Between Fibroblasts and Cardiomyocytes

Abstract

Galectin-3 (gal-3) is a β-galactoside-binding protein used as a prognostic biomarker in chronic heart failure (CHF) patients. Genetic and pharmacologic studies show that gal-3 is required for cardiac remodeling in animal models of CHF, suggesting an active role for gal-3 in the progression of the disease, but the mechanism involved is largely unknown. We assessed the hypothesis that gal-3 induces cardiac remodeling, causing both cardiomyocyte hypertrophy and fibroblasts activation through a mechanism involving intercellular communication. As a model, we used neonatal rat ventricular cardiomyocytes (NRVM), and fibroblasts (NRVF) stimulated with recombinant gal-3. We assessed cell death and proliferation by flow cytometry and MTT assays. To elucidate the signaling pathways involved, we quantified relative changes in protein levels by Western blot. To determine cell size and sarcomerization, we used confocal microscopy. Changes in mRNA and microRNA expression were analyzed by qPCR. Our results show that gal-3 does not induce hypertrophy or sarcomerization on isolated NRVM culture. On the other hand, NRVF treated with gal-3 exhibit an increase in ERK1/2 (n=3, p<0.05) and AKT (n=3, p<0.05) phosphorylation, as well as a marked increase in cell proliferation (n=4, p<0.05), without changes in αSMA and collagen. Interestingly, gal-3 increased tgfb1 expression in cardiac fibroblasts (n=5, p<0.05) and induced an increase of miR-21 and miR-23a levels in the culture media (15- and 6-folds over basal, respectively, n=4, p<0.05). To test a possible paracrine communication between cardiomyocytes and fibroblasts, we stimulated NRVM with fibroblast-derived, gal-3-stimmulated conditioned medium. Our results show that in this condition there is an increase in both cardiac remodeling markers (Nppa and Myh7), as well as cardiomyocyte area. In conclusion, gal-3 activates pro-survival and proliferation signaling pathways in cardiac fibroblasts without a direct effect on cardiomyocytes. However, gal-3 can induce cardiomyocyte hypertrophy by a mechanism involving paracrine communication between fibroblasts and myocytes, which likely includes TGFβ1 and the hypertrophy-related miR-21 and miR-23a.