COL18A1 and pulmonary arterial hypertension: Interesting candidates among these are SPARC, which was found at increased levels in lung of IPAH patients and is involved in the regulation of PASMC proliferation (21), ECE1, which is involved in the cleavage/transformation of Endothelin 1 to its active form (22), PECAM-1, which plays a role in the adaptation of endothelium to shear stress (23) and COL18A1, which when cleaved produces Endostatin, a protein whose serum levels are correlated with disease severity and survival in PAH (24).