Novel Mutations and Decreased Expression of the Epigenetic Regulator <i>TET2</i> in Pulmonary Arterial Hypertension.

Abstract

Pulmonary arterial hypertension (PAH) is a lethal vasculopathy. Hereditary cases are associated with germline mutations in <i>BMPR2</i> and 16 other genes; however, these mutations occur in <25% of patients with idiopathic PAH and are rare in PAH associated with connective tissue diseases. Preclinical studies suggest epigenetic dysregulation, including altered DNA methylation, promotes PAH. Somatic mutations of Tet-methylcytosine-dioxygenase-2 (<i>TET2</i>), a key enzyme in DNA demethylation, occur in cardiovascular disease and are associated with clonal hematopoiesis, inflammation, and adverse vascular remodeling. The role of <i>TET2</i> in PAH is unknown. To test for a role of <i>TET2</i>, we used a cohort of 2572 cases from the PAH Biobank. Within this cohort, gene-specific rare variant association tests were performed using 1832 unrelated European patients with PAH and 7509 non-Finnish European subjects from the Genome Aggregation Database (gnomAD) as control subjects. In an independent cohort of 140 patients, we quantified <i>TET2</i> expression in peripheral blood mononuclear cells. To assess causality, we investigated hemodynamic and histological evidence of PAH in hematopoietic <i>Tet2</i>-knockout mice. We observed an increased burden of rare, predicted deleterious germline variants in <i>TET2</i> in PAH patients of European ancestry (9/1832) compared with control subjects (6/7509; relative risk=6; <i>P</i>=0.00067). Assessing the whole cohort, 0.39% of patients (10/2572) had 12 <i>TET2</i> mutations (75% predicted germline and 25% somatic). These patients had no mutations in other PAH-related genes. Patients with <i>TET2</i> mutations were older (71±7 years versus 48±19 years; <i>P</i><0.0001), were more unresponsive to vasodilator challenge (0/7 versus 140/1055 [13.2%]), had lower pulmonary vascular resistance (5.2±3.1 versus 10.5±7.0 Wood units; <i>P</i>=0.02), and had increased inflammation (including elevation of interleukin-1β). Circulating <i>TET2</i> expression did not correlate with age and was decreased in >86% of PAH patients. <i>Tet2</i>-knockout mice spontaneously developed PAH, adverse pulmonary vascular remodeling, and inflammation, with elevated levels of cytokines, including interleukin-1β. Long-term therapy with an antibody targeting interleukin-1β blockade resulted in regression of PAH. PAH is the first human disease related to potential <i>TET2</i> germline mutations. Inherited and acquired abnormalities of <i>TET2</i> occur in 0.39% of PAH cases. Decreased <i>TET2</i> expression is ubiquitous and has potential as a PAH biomarker.