Background: Monoallelic mutations in the gene encoding bone morphogenetic protein receptor 2 ( Bmpr2 ) are the main genetic risk factor for heritable pulmonary arterial hypertension (PAH) with incomplete penetrance. Several Bmpr2 transgenic mice have been reported to develop mild spontaneous PAH. In this study, we examined whether rats with the Bmpr2 mutation were susceptible to developing more severe PAH. Methods: The zinc finger nuclease method was used to establish rat lines with mutations in the Bmpr2 gene. These rats were then characterized at the hemodynamic, histological, electrophysiological, and molecular levels. Results: Rats with a monoallelic deletion of 71 bp in exon 1 (Δ 71 rats) showed decreased BMPRII expression and phosphorylated SMAD1/5/9 levels. Δ 71 Rats develop age-dependent spontaneous PAH with a low penetrance (16%–27%), similar to that in humans. Δ 71 Rats were more susceptible to hypoxia-induced pulmonary hypertension than wild-type rats. Δ 71 Rats exhibited progressive pulmonary vascular remodeling associated with a proproliferative phenotype and showed lower pulmonary microvascular density than wild-type rats. Organ bath studies revealed severe alteration of pulmonary artery contraction and relaxation associated with potassium channel subfamily K member 3 (KCNK3) dysfunction. High levels of perivascular fibrillar collagen and pulmonary interleukin-6 overexpression discriminated rats that developed spontaneous PAH and rats that did not develop spontaneous PAH. Finally, detailed assessments of cardiomyocytes demonstrated alterations in morphology, calcium (Ca ²⁺ ), and cell contractility specific to the right ventricle; these changes could explain the lower cardiac output of Δ 71 rats. Indeed, adult right ventricular cardiomyocytes from Δ 71 rats exhibited a smaller diameter, decreased sensitivity of sarcomeres to Ca ²⁺ , decreased [Ca ²⁺ ] transient amplitude, reduced sarcoplasmic reticulum Ca ²⁺ content, and short action potential duration compared with right ventricular cardiomyocytes from wild-type rats. Conclusions: We characterized the first Bmpr2 mutant rats and showed some of the critical cellular and molecular dysfunctions described in human PAH. We also identified the heart as an unexpected but potential target organ of Bmpr2 mutations. Thus, this new genetic rat model represents a promising tool to study the pathogenesis of PAH.

Mutations in the KCNK3 gene, which encodes for an outward-rectifier K⁺ channel, have been identified in patients suffering from pulmonary arterial hypertension (PAH), and constitute the first described channelopathy in PAH. In human PAH and experimental pulmonary hypertension (PH), we demonstrated that KCNK3 expression and function are severely reduced in pulmonary vascular cells, promoting PH-like phenotype at the morphologic and haemodynamic levels. Since KCNK3 channel is also expressed in both the human and rodent heart, we aimed to elucidate the pathophysiological role of KCNK3 channel in right ventricular (RV) hypertrophy (RVH) related to PH. Using whole-cell Patch-clamp technique, we demonstrated that KCNK3 is predominantly expressed in adult rat RV cardiomyocytes compared to the left ventricle cardiomyocytes and participates in the repolarizing phase of the RV action potential. We revealed a reduction in KCNK3 function prior to development of RVH and the rise of pulmonary vascular resistance. KCNK3 function is severely reduced in RV cardiomyocytes during the development of RVH in several rat models of PH (exposure to monocrotaline, chronic hypoxia, and Sugen/hypoxia) and chronic RV pressure overload (pulmonary artery banding). In experimental PH, we revealed a reduction in KCNK3 function before any rise in pulmonary vascular resistance and the development of RVH. KCNK3 mRNA level is also reduced in human RV tissues from PAH patients compared to non-PAH patients. In line with these findings, chronic inhibition of KCNK3 in rats with the specific inhibitor (A293) induces RV hypertrophy which is associated with the re-expression of foetal genes, RV fibrosis, RV inflammation, and subsequent loss of RV performance as assessed by echocardiography. Our data indicate that loss of KCNK3 function and expression is a hallmark of the RV hypertrophy/dysfunction associated with PH.

Pulmonary arterial hypertension (PAH) is a severe cardiovascular disease that is caused by the progressive occlusion of the distal pulmonary arteries, eventually leading to right heart failure and death. Almost 40% of patients with PAH are iron deficient. Although widely studied, the mechanisms linking between PAH and iron deficiency remain unclear. Here we review the mechanisms regulating iron homeostasis and the preclinical and clinical data available on iron deficiency in PAH. Then we discuss the potential implications of iron deficiency on the development and management of PAH.

Pulmonary arterial hypertension (PAH), the most serious chronic disorder of the pulmonary circulation, is characterized by pulmonary vasoconstriction and remodeling, resulting in increased afterload on the right ventricle (RV). In fact, RV function is the main determinant of prognosis in PAH. The most frequently used experimental models of PAH include monocrotaline- and chronic hypoxia-induced PAH, which primarily affect the pulmonary circulation. Alternatively, pulmonary artery banding (PAB) can be performed to achieve RV overload without affecting the pulmonary vasculature, allowing researchers to determine the RV-specific effects of their drugs/interventions. In this work, using two different degrees of pulmonary artery constriction, we characterize, in full detail, PAB-induced adaptive and maladaptive remodeling of the RV at 3 wk after PAB surgery. Our results show that application of a mild constriction resulted in adaptive hypertrophy of the RV, with preserved systolic and diastolic function, while application of a severe constriction resulted in maladaptive hypertrophy, with chamber dilation and systolic and diastolic dysfunction up to the isolated cardiomyocyte level. By applying two different degrees of constriction, we describe, for the first time, a reliable and short-duration PAB model in which RV adaptation can be distinguished at 3 wk after surgery. We characterize, in full detail, structural and functional changes of the RV in its response to moderate and severe constriction, allowing researchers to better study RV physiology and transition to dysfunction and failure, as well as to determine the effects of new therapies.