AVE-1231

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.

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.

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.

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.

The ascending brainstem transmitter acetylcholine depolarizes thalamocortical relay neurons while it induces hyperpolarization in local circuit inhibitory interneurons.Sustained K+ currents are modulated in thalamic neurons to control their activity modes; for the interneurons the molecular nature of the underlying ion channels is as yet unknown.Activation of TASK‐1 K+ channels results in hyperpolarization of interneurons and suppression of their action potential firing.The modulation cascade involves a non‐receptor tyrosine kinase, c‐Src.The present study identifies a novel pathway for the activation of TASK‐1 channels in CNS neurons that resembles cholinergic signalling and TASK‐1 current modulation during hypoxia in smooth muscle cells.

The dorsal part of the lateral geniculate nucleus (dLGN) is the main thalamic site for state‐dependent transmission of visual information. Non‐retinal inputs from the ascending arousal system and inhibition provided by γ‐aminobutyric acid (GABA)ergic local circuit interneurons (INs) control neuronal activity within the dLGN. In particular, acetylcholine (ACh) depolarizes thalamocortical relay neurons by inhibiting two‐pore domain potassium (K2P) channels. Conversely, ACh also hyperpolarizes INs via an as‐yet‐unknown mechanism. By using whole cell patch‐clamp recordings in brain slices and appropriate pharmacological tools we here report that stimulation of type 2 muscarinic ACh receptors induces IN hyperpolarization by recruiting the G‐protein βγ subunit (Gβγ), class‐1A phosphatidylinositol‐4,5‐bisphosphate 3‐kinase, and cellular and sarcoma (c‐Src) tyrosine kinase, leading to activation of two‐pore domain weakly inwardly rectifying K+ channel (TWIK)‐related acid‐sensitive K+ (TASK)‐1 channels. The latter was confirmed by the use of TASK‐1‐deficient mice. Furthermore inhibition of phospholipase Cβ as well as an increase in the intracellular level of phosphatidylinositol‐3,4,5‐trisphosphate facilitated the muscarinic effect. Our results have uncovered a previously unknown role of c‐Src tyrosine kinase in regulating IN function in the brain and identified a novel mechanism by which TASK‐1 channels are activated in neurons.