To profile the changes in the expression pattern of class I HDAC isoforms (Fig. 1A) in IPAH, we characterized the gene and protein expression levels of HDAC1, HDAC2, HDAC3 and HDAC8 in different human tissues including heart, lung and pulmonary arteries (PA) obtained from IPAH and donor lungs. Here, HDAC1 is linked to idiopathic pulmonary arterial hypertension.