In contrast, although some cell proliferation genes were down-regulated in PAH cluster 4, 23 genes in angiogenesis, migration and adhesion pathways were up-regulated, such as (claudin 4 (cldn5), pgf, cxcr4, nidogen 2 (nid2), and ccl14). This evidence concerns the gene CLDN5 and pulmonary arterial hypertension.