Abstract 9889: Novel Mechanisms of Cardiac Macrophage-Mast Cell Interactions in Radiation-Induced Myocardial Fibrosis

Abstract

Introduction: Both galectin-3 (gal3) and macrophages are implicated in myocardial fibrotic remodeling. Macrophages express gal3 on their surface, whereas mast cells express a high-affinity gal3 receptor, FcεRI. Understanding the mechanisms of their interactions will lead to highly targeted therapeutic approaches. Hypothesis: We hypothesize that a macrophage-expressed pro-fibrotic molecule, gal3, is a mediator of macrophage-mast cell interactions in a pre-clinical model of radiation-induced myocardial fibrosis. Methods: We studied myocardial fibrosis, cardiac macrophage-mast cell infiltration, and gal3 expression in a rodent model of thoracic radiation. We performed long-term culture of the bone-marrow cells isolated from gal3 KO (gal3 -/- ) and gal3 overexpression (gal3 +/+ ) mice. Recombinant M-CSF co-cultured cells transformed to macrophages (F4/80 + /CD11B + ), whereas IL-3-treated cells transformed to mast cells (FCεR1 + /c-kit + ). Then, we used microfluidic and transwell systems to examine the gal3-dependent macrophage-mast cell interactions in the live cell culture. Results: Thoracic radiation exposure induced myocardial fibrosis (% fibrosis, radiation: 5±2, controls: 2±0.6; p=0.01, N=5-8), which was also associated with macrophage (cells/cm 3 , radiation: 114±28, controls: 81±0.3; p=0.05, N=8) and mast cell (cells/cm 3 , radiation: 14±5, controls: 9±0.3; p=0.05, N=5-8) infiltration, and cardiac gal3 expression (pg/ng, radiation: 85±15, controls: 14±8; p=0.001, N=7). Exogenous gal3 treatment led to increased mast cell tryptase activity confirming their activation [tryptase (ng/ml), untreated: 291±46, gal3: 494±191; p<0.01, N=3-8]. Quantitative macrophage-mast cell activity in a microfluidic system showed 7.5-fold increased macrophage-mast cell adhesion in gal3 +/+ cells suggesting increased interactions with gal3 overexpression [cell adhesion (cells/mm 2 ), WT: 23±5.8, Gal3 +/+ :175±38; p<0.01, N=4]. Conclusion: In a pre-clinical model of radiation-induced myocardial fibrosis, gal3 can mediate crucial macrophage-mast cell interactions. Our data provide possible mechanistic evidence of gal3 involvement in macrophage-mast cell interactions en route to myocardial fibrosis after radiation exposure.