BMP7 and atrial fibrillation: Self-renewal (inactive WNT signaling) is maintained by elevated expression of the renal progenitor markers SIX2, WT1 and CD133 (stem cell proliferation marker) and downregulated expression of BMP7. In contrast, upon activation of canonical WNT signaling by GSK3β inhibition with CHIR99021, AF-MSCs exit self-renewal and differentiate as a consequence of elevated BMP7 expression and downregulation of SIX2, WT1 and CD133 respectively.