Genotype‐Phenotype Effects of Bmpr2 Mutations on Disease Severity in Mouse Models of Pulmonary Hypertension

Abstract

More than 350 mutations in the type-2 BMP (bone morphogenetic protein) receptor, BMPR2, have been identified in patients with heritable pulmonary arterial hypertension (HPAH). However, only 30% of BMPR2 mutation carriers develop PAH, and we cannot predict which of these carriers will develop clinical disease. One possibility is that the nature of the BMPR2 mutation affects disease severity. This hypothesis has been difficult to test clinically, given the rarity of HPAH and the complexity of the confounding genetic and environmental risk factors. To test this hypothesis, therefore, we evaluated the susceptibility to experimental pulmonary hypertension (PH) of mice carrying different HPAH-associated Bmpr2 mutations on otherwise identical genetic backgrounds. Mice with Bmpr2ΔEx4-5 mutations (Bmpr2 +/− ), in which the mutant protein is not expressed, develop less severe PH in response to hypoxia or hypoxia with vascular endothelial growth factor receptor inhibition than mice with an extracellular-domain Bmpr2ΔEx2 mutation (Bmpr2 ΔEx2/+ ), in which the mutant protein is expressed. This was associated with a marked decrease in stabilizing phosphorylation of threonine 495 endothelial nitric oxide synthase (pThr495 eNOS) in Bmpr2ΔEx2/+ compared to wild-type and Bmpr2 +/− mouse lungs. These findings provide the first experimental evidence that BMPR2 mutation types influence the severity of HPAH and suggest that patients with BMPR2 mutations who express mutant BMPR2 proteins by escaping non-sense-mediated messenger RNA decay (NMD− mutations) will develop more severe disease than HPAH patients with NMD+ mutations who do not express BMPR2 mutant proteins. Since decreased levels of pThr495 eNOS are associated with increased eNOS uncoupling, our data also suggest that this effect may result from defects in eNOS function.Keywords: bone morphogenetic protein type 2 receptor mutations, experimental pulmonary hypertension, hereditary pulmonary arterial hypertension, disease severity, non-sense-mediated messenger RNA decay, endothelial nitric oxide synthase. Patients with heritable pulmonary arterial hypertension (HPAH) inherit heterozygous mutations in the bone morphogenetic protein (BMP) type 2 receptor (BMPR2) locus.1 BMPR2 mutations account for about 75% of patients with family histories of PAH and 25% of patients with sporadic disease. This establishes BMPR2 mutations as the major genetic determinant of HPAH. 2 BMPR2 mutation carriers with PAH tend to have an earlier age of diagnosis and more severe pulmonary hemodynamic parameters and are less likely to demonstrate vasoreactivity than noncarriers. 3-6 However, less than 30% of BMPR2 mutation carriers develop clinical disease, 7 and while the disease is known to have a sex bias and a number of candidate disease-modifying genetic variants at other loci have been shown to influence disease penetrance, 2 we are still unable to predict which patients carrying BMPR2 mutations will develop overt disease or, if they do, how severe their disease will be. One possibility is ...

BMPR2 mutations and endothelial dysfunction in pulmonary arterial hypertension (2017 Grover Conference Series)

“…2 c–e). 27 These findings demonstrated for the first time that there is a genotype–phenotype relationship between the type of Bmpr2 mutation and PH susceptibility. While limited to experimental models of PH that do not recapitulate the structural changes seen in the pulmonary vasculature of patients with established PAH, these studies suggest that different BMPR2 mutations types could have distinct effects on PAH severity in HPAH.…”

“…To address this question, therefore, we have taken an alternative, experimental approach by evaluating the PH susceptibility of mice carrying two different germline Bmpr2 mutations. 27 For this, we used two established mouse lines: Bmpr2 ΔEx4-5/+ mice in which there is an out of frame deletion of the fourth and fifth exons of Bmpr2 ( Bmpr2 +/− mice), 28 and Bmpr2 ΔEx2/+ mice in which there is an in-frame deletion of the second exon of Bmpr2 ( Fig. 1 a).…”

“…2 e). 27 Furthermore, while changes in endothelial eNOS and Src kinase activation could account for some of the early events associated with the development of PAH in patients carrying BMPR2 mutations, they are unlikely to account for the obstructive vascular remodeling that occurs in patients with PAH. For example, while mice with eNOS deficiency develop mild PH associated with muscularization of peri-acinar pulmonary vessels, they do not develop severe obliterative pulmonary vascular remodeling.…”

CrossTalk opposing view: The mouse SuHx model is not a good model of pulmonary arterial hypertension

“…Fortunately, the quest for better mouse models of PAH has continued and several recently reported genetically modified mouse models have spontaneous PAH (Dai & Zhao, ) or more severe PAH when combined with SuHx (Frump et al . ). For example, mice with Tie2‐Cre‐mediated disruption of the gene encoding PHD2 in endothelial and haematopoetic cells has spontaneous, severe, progressive PH with vascular lesions that mirror those in human PAH (Dai et al .…”

CrossTalk proposal: The mouse SuHx model is a good model of pulmonary arterial hypertension

“…Responses to SuHx have also been demonstrated to vary depending on BMPR2 mutations (Frump et al . ), indicating a genetic role in the PH pathophysiology. Nevertheless, it is unclear how precisely these models reflect molecular and biochemical derangements in clinical PAH since, of course, rodents have a different genetic constitution and the pathophysiological responses may differ from those in humans.…”