HDAC1 and idiopathic pulmonary arterial hypertension: Contrary to the confined nuclear HDAC1 expression in endothelial cells (PAEC) lining the lumen of normal PAs, the remodeled PAs in IPAH-lungs displayed strong nuclear immunoreactivity for HDAC1 protein in all resident vascular cell types, including PAECs, smooth muscle cells (PASMC) and PAAFs (Fig. 2A).