Harvesting and culturing of primary cardiac fibroblasts were conducted as previously described 27 (link). For immunoblotting, cells were grown to 80–90% confluence. Cells were then washed three times with PBS to remove residual FBS before being serum starved in DMEM supplemented with 10 μg/ml TGFβ (R&D), 100 μg/ml L-ascorbic acid (Sigma), and 40 μg/ml soybean trypsin inhibitor (Sigma). Twenty-four hours post starvation; conditioned media were collected, and concentrated by centrifugation filters (Millipore).