In the sinus node in PAH, we also observed widespread upregulation of fibrosis transcripts: in vimentin mRNA (fibroblast marker), in mRNA for components of the extracellular matrix (collagen 1, elastin, fibronectin), in mRNA for receptors that mediate attachment between myocytes and the extracellular matrix (integrin α5, integrin β1), in TIMP1 mRNA, and in mRNA for the fibrotic agent, TGFβ1 (electronic supplementary material, table S2). Here, TIMP1 is linked to pulmonary arterial hypertension.