PECAM1 and pulmonary arterial hypertension: Findings in PAH diverge from these observations: co-expression of CD31 with α-SMA is common in the endothelial, layer as well as the neointima.24 Other key markers of EndMT have also been observed in PAH lungs, including Twist-1 and p120-catenin, indicating that evidence of intermediate phases of this process are detectable even in end-stage disease.