FRZB and atrial fibrillation: Specific proteins were identified in AF-MSCs differentiated to neurogenic lineage, including selenium binding protein 1 (SBP1), which is exclusively located at the growing tips of neurites; secreted frizzled related protein 1 (SFRP1), involved in downregulation of Wnt signalling; metalloproteinase inhibitor 3 (TIMP3), which complexes with metalloproteinase (such as collagenases) and irreversibly inactivates them; integrator complex subunit 4-like protein 2 (IN4L2) of unknown function (Supplementary Table 1).