Humans with Pulmonary Arterial Hypertension display a global hypermethylation signature that worsens in patients who have a mutation in the gene encoding the methylation eraser, Tet Methylcytosine Dioxygenase 2 (TET2).

Epigenetic changes in gene expression due to DNA methylation are important physiologic and pathologic regulators of pulmonary vascular structure and function. Genetic or acquired alterations in DNA methylation or demethylation have been associated with the development and progression of pulmonary arterial hypertension (PAH). However, the DNA methylome signature of human PAH and its consequences on the PAH transcriptome are unknown. Reduced Representation Bisulfite Sequencing (RRBS) was used for epigenome-wide mapping of DNA methylation in whole peripheral blood of 10 healthy people and 20 age/sex matched PAH patients. RNA deep sequencing was performed in parallel on the same samples. We used whole-exome sequencing to identify two PAH cohorts, one free of mutations in the genes know to be associated with PAH patients and the second had mutations of TET2, a newly identified PAH gene that encodes an enzyme that mediates DNA demethylation. We report an increased in global DNA methylation in the blood of PAH patients compared to healthy controls. Patients carrying the TET2 mutation had a further increase in DNA compared to mutation free PAH patients. We identified 1,069 unique Differentially Methylated Regions (DMR) in the blood of PAH patients with a TET2 mutation. When organized into functional groups, we observed an enrichment of genes involved in immune, cell differentiation, or metabolic. When we compared these genes to publicly available data from an independent study on blood from PAH patients compared to controls, we identified 218 mRNA transcripts that align with our data (e.g. are hypermethylated blood genes that are downregulated in PAH blood), and functional analysis of these genes reveals common enriched terms in immune, cell differentiation, or metabolic function. We characterized DNA methylation changes associated with TET2 mutation in the blood of patients with PAH compared to controls. This data demonstrates that epigenetic regulation of genes by methylation is involved in altered immune function, cell differentiation and metabolism in PAH.