GDF7 and atrial fibrillation: Growth factor mRNA was also elevated in MSC co-cultures, epidermal growth factor (EGF) insulin-like growth factor (IGF)-1, osteogenic protein (OP)-1, growth and differentiation factor (GDF)-7 and transforming growth factor (TGF)-β were all up-regulated by NP cells and IGF-1, OP-1 and GDF-7 by AF cells.