Background:
Pulmonary arterial hypertension (PAH) is a lethal vasculopathy characterized by remodelling of distal pulmonary arteries associated with inflammation, endothelial cells (EC) dysfunction and a pro-proliferative/anti-apoptotic phenotype in pulmonary arterial smooth muscle cells (PASMC). Tet methylcytosine dioxygenase 2 (Tet2) is a key enzyme in cytosine demethylation that is crucial for epigenetic control of gene expression. Deficiency of Tet2 expression in myeloid cellsresults in increased inflammatory cytokine levels. Moreover, impaired Tet2 expression in EC has also been associated with decreased autophagy, as well as EC dysfunction. In addition, Tet2 silencing contributes to pro-proliferative phenotype of SMC. Thus, we hypothesized that Tet2 deletion would contribute to PAH by upregulation of inflammation and induction of PASMC proliferation and EC dysfunction.
Methods and Results:
To assess the ability of Tet2 deficiency to induce PAH we assessed cardiopulmonary hemodynamics in a conditional hematopoietic and endothelial cells Tet2
-/-
mouse model. Tet2
-/-
mice developed PAH associated with significant increases of right ventricular systolic pressure (RVSP), elevation of total pulmonary resistance (TPR) and increased vascular wall thickness of distal pulmonary arteries. Tet2
-/-
lung tissue as well as macrophages and EC sorted from the lung displayed aberrant inflammatory cytokine signalling with robust overexpression of IL1βnoted on a Nanostring immune gene expression panel. In vitro IL1βincreased PASMC proliferation measured using EDU. Downregulation of TET2 in PASMC using siRNA resulted in a similar PAH-like phenotype. Moreover, lung from Tet2
-/-
mice exhibited an alteration of vasoactive mediator gene expression (increased endothelin-1 (ET1), Arginase 2 (Arg2) and decreased eNOS). Finally we showed that downregulation of Tet2 (achieved by nebulization of si-Tet2) in rats with monocrotaline-induced PAH exacerbated disease severity (increasing TPR adverse pulmonary vascular remodelling).This phenotype was independent of the sex, was associated with a moderate decrease in RV function but had no significant effect on LV hemodynamic parameters.
Conclusions:
Tet2 is a protective epigenetic regulator that when conditionally downregulated in hematopoietic and endothelial cells leads toPAH by inducing a state of inflammation that contributes to PASMC proliferation and EC dysfunction which drives adverse pulmonary vascular remodelling.