Cardiac fibroblasts isolated from adult (WT and Mac-2 knockout) mice were exposed to radiation (9 Gy) and incubated for 72 hours in CO2 incubator; mRNA was isolated and qPCR was performed. Radiation exposure increased collagen I (panel A), collagen III (panel B) and TGFβ1 (panel C) gene expression in wild type cardiac fibroblast but not in Mac-2 null cells. Data are expressed as fold change of control. N = 3 each group, presented as a pooled mean of two independent experiments performed in duplicates. *, P<0.001 wild type vs. KO, knock out post-radiation. Panel D represents chronic myocardial TGFβ1 mRNA expression levels in rat hearts upon completion of in vivo studies, i.e., after 18-weeks of radiation. P = not significant.