CXCL12 and pulmonary arterial hypertension: This is relevant, because CXCL12 and its receptor CXC chemokine receptor 4 (CXCR4) are present in complex lesions in PAH [10,11] and CXCL12 promotes aberrant angiogenesis, endothelial proliferation and PH [23,24,39–44] while others have found Wnt1 to be protective from aberrant tumor angiogenesis [45].