In PAH PAECs, however, an enhancer of HTR1BRC shows reduced H3K27ac signal, and seems to prime the cells against the induction of HTR1BRC mRNA and protein after serotonin stimulation, thus offering another way in which angiogenesis is subverted in PAH, that is consistent with the reduction in NOS3 in response to serotonin. Here, NOS3 is linked to pulmonary arterial hypertension.