BMPR2 acts as a gatekeeper to protect endothelial cells from increased TGFß responses and altered cell mechanics.

Balanced transforming growth factor-beta (TGFß)/bone morphogenetic protein (BMP)-signaling is essential for tissue formation and homeostasis. While gain in TGFß signaling is often found in diseases, the underlying cellular mechanisms remain poorly defined. Here we show that the receptor BMP type 2 (BMPR2) serves as a central gatekeeper of this balance, highlighted by its deregulation in diseases such as pulmonary arterial hypertension (PAH). We show that BMPR2 deficiency in endothelial cells (ECs) does not abolish pan-BMP-SMAD1/5 responses but instead favors the formation of mixed-heteromeric receptor complexes comprising BMPR1/TGFßR1/TGFßR2 that enable enhanced cellular responses toward TGFß. These include canonical TGFß-SMAD2/3 and lateral TGFß-SMAD1/5 signaling as well as formation of mixed SMAD complexes. Moreover, BMPR2-deficient cells express genes indicative of altered biophysical properties, including up-regulation of extracellular matrix (ECM) proteins such as fibrillin-1 (FBN1) and of integrins. As such, we identified accumulation of ectopic FBN1 fibers remodeled with fibronectin (FN) in junctions of BMPR2-deficient ECs. Ectopic FBN1 deposits were also found in proximity to contractile intimal cells in pulmonary artery lesions of BMPR2-deficient heritable PAH (HPAH) patients. In BMPR2-deficient cells, we show that ectopic FBN1 is accompanied by active ß1-integrin highly abundant in integrin-linked kinase (ILK) mechano-complexes at cell junctions. Increased integrin-dependent adhesion, spreading, and actomyosin-dependent contractility facilitates the retrieval of active TGFß from its latent fibrillin-bound depots. We propose that loss of BMPR2 favors endothelial-to-mesenchymal transition (EndMT) allowing cells of myo-fibroblastic character to create a vicious feed-forward process leading to hyperactivated TGFß signaling. In summary, our findings highlight a crucial role for BMPR2 as a gatekeeper of endothelial homeostasis protecting cells from increased TGFß responses and integrin-mediated mechano-transduction.

PPARγ is a gatekeeper for extracellular matrix and vascular cell homeostasis: beneficial role in pulmonary hypertension and renal/cardiac/pulmonary fibrosis.

PURPOSE OF REVIEW: Pulmonary arterial hypertension (PAH) is characterized by pulmonary arterial endothelial cell (PAEC) dysfunction and apoptosis, pulmonary arterial smooth muscle cell (PASMC) proliferation, inflammation, vasoconstriction, and metabolic disturbances that include disrupted bone morphogenetic protein receptor (BMPR2)-peroxisome proliferator-activated receptor gamma (PPARγ) axis and DNA damage. Activation of PPARγ improves many of these mechanisms, although erroneous reports on potential adverse effects of thiazolidinedione (TZD)-class PPARγ agonists reduced their clinical use in the past decade. Here, we review recent findings in heart, lung, and kidney research related to the pathobiology of vascular remodeling and tissue fibrosis, and also potential therapeutic effects of the PPARγ agonist pioglitazone. RECENT FINDINGS: Independent of its metabolic effects (improved insulin sensitivity and fatty acid handling), PPARγ activation rescues BMPR2 dysfunction, inhibits TGFß/Smad3/CTGF and TGFß/pSTAT3/pFoxO1 pathways, and induces the PPARγ/apoE axis, inhibiting vascular remodeling. PPARγ activation dampens mtDNA damage via PPARγ/UBR5/ATM pathway, improves function of endothelial progenitor cells (EPCs), and decrease renal fibrosis by repressing TGFß/pSTAT3 and TGFß/EGR1. SUMMARY: Pharmacological PPARγ activation improves many hallmarks of PAH, including dysfunction of BMPR2-PPARγ axis, PAEC, PASMC, EPC, mitochondria/metabolism, and inflammation. Recent randomized controlled trials, including IRIS (Insulin Resistance Intervention After Stroke Trial), emphasize the beneficial effects of PPARγ agonists in PAH patients, leading to recent revival for clinical use.

Inflammation induces endothelial-to-mesenchymal transition and promotes vascular calcification through downregulation of BMPR2.

Endothelial-to-mesenchymal transition (EndMT) has been unveiled as a common cause for a multitude of human pathologies, including cancer and cardiovascular disease. Vascular calcification is a risk factor for ischemic vascular disorders and slowing calcification may reduce mortality in affected patients. The absence of early biomarkers hampers the identification of patients at risk. EndMT and vascular calcification are induced upon cooperation between distinct stimuli, including inflammatory cytokines and transforming growth factor beta (TGF-ß) family members. However, how these signaling pathways interplay to promote cell differentiation and eventually vascular calcification is not well understood. Using in vitro and ex vivo analysis in animal models and patient-derived tissues, we have identified that the pro-inflammatory cytokines tumor necrosis factor alpha (TNF-α) and interleukin-1 beta (IL-1ß) induce EndMT in human primary aortic endothelial cells, thereby sensitizing them for BMP-9-induced osteogenic differentiation. Downregulation of the BMP type II receptor BMPR2 is a key event in this process. Rather than compromising BMP canonical signal transduction, loss of BMPR2 results in decreased JNK signaling in ECs, thus enhancing BMP-9-induced mineralization. Altogether, our results point at the BMPR2-JNK signaling axis as a key pathway regulating inflammation-induced EndMT and contributing to calcification. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Mechanisms of Lipid Accumulation in the Bone Morphogenetic Protein Receptor Type 2 Mutant Right Ventricle.

RATIONALE: In heritable pulmonary arterial hypertension with germline mutation in the bone morphogenetic protein receptor type 2 (BMPR2) gene, right ventricle (RV) dysfunction is associated with RV lipotoxicity; however, the underlying mechanism for lipid accumulation is not known. OBJECTIVES: We hypothesized that lipid accumulation in cardiomyocytes with BMPR2 mutation occurs owing to alterations in lipid transport and impaired fatty acid oxidation (FAO), which is exacerbated by a high-lipid (Western) diet (WD). METHODS: We used a transgenic mouse model of pulmonary arterial hypertension with mutant BMPR2 and generated a cardiomyocyte cell line with BMPR2 mutation. Electron microscopy and metabolomic analysis were performed on mouse RVs. MEASUREMENTS AND MAIN RESULTS: By metabolomics analysis, we found an increase in long-chain fatty acids in BMPR2 mutant mouse RVs compared with controls, which correlated with cardiac index. BMPR2-mutant cardiomyocytes had increased lipid compared with controls. Direct measurement of FAO in the WD-fed BMPR2-mutant RV showed impaired palmitate-linked oxygen consumption, and metabolomics analysis showed reduced indices of FAO. Using both mutant BMPR2 mouse RVs and cardiomyocytes, we found an increase in the uptake of (14)C-palmitate and fatty acid transporter CD36 that was further exacerbated by WD. CONCLUSIONS: Taken together, our data suggest that impaired FAO and increased expression of the lipid transporter CD36 are key mechanisms underlying lipid deposition in the BMPR2-mutant RV, which are exacerbated in the presence of dietary lipids. These findings suggest important features leading to RV lipotoxicity in pulmonary arterial hypertension and may point to novel areas of therapeutic intervention.

Pulmonary arterial hypertension: the clinical syndrome.

Pulmonary arterial hypertension is a progressive disorder in which endothelial dysfunction and vascular remodeling obstruct small pulmonary arteries, resulting in increased pulmonary vascular resistance and pulmonary pressures. This leads to reduced cardiac output, right heart failure, and ultimately death. In this review, we attempt to answer some important questions commonly asked by patients diagnosed with pulmonary arterial hypertension pertaining to the disease, and aim to provide an explanation in terms of classification, diagnosis, pathophysiology, genetic causes, demographics, and prognostic factors. Furthermore, important molecular pathways that are central to the pathogenesis of pulmonary arterial hypertension are reviewed, including nitric oxide, prostacyclin, endothelin-1, reactive oxygen species, and endothelial and smooth muscle proliferation.

Sex affects bone morphogenetic protein type II receptor signaling in pulmonary artery smooth muscle cells.

RATIONALE: Major pulmonary arterial hypertension (PAH) registries report a greater incidence of PAH in women; mutations in the bone morphogenic protein type II receptor (BMPR-II) occur in approximately 80% of patients with heritable PAH (hPAH). OBJECTIVES: We addressed the hypothesis that women may be predisposed to PAH due to normally reduced basal BMPR-II signaling in human pulmonary artery smooth muscle cells (hPASMCs). METHODS: We examined the BMPR-II signaling pathway in hPASMCs derived from men and women with no underlying cardiovascular disease (non-PAH hPASMCs). We also determined the development of pulmonary hypertension in male and female mice deficient in Smad1. MEASUREMENTS AND MAIN RESULTS: Platelet-derived growth factor, estrogen, and serotonin induced proliferation only in non-PAH female hPASMCs. Female non-PAH hPASMCs exhibited reduced messenger RNA and protein expression of BMPR-II, the signaling intermediary Smad1, and the downstream genes, inhibitors of DNA binding proteins, Id1 and Id3. Induction of phospho-Smad1/5/8 and Id protein by BMP4 was also reduced in female hPASMCs. BMP4 induced proliferation in female, but not male, hPASMCs. However, small interfering RNA silencing of Smad1 invoked proliferative responses to BMP4 in male hPASMCs. In male hPASMCs, estrogen decreased messenger RNA and protein expression of Id genes. The estrogen metabolite 4-hydroxyestradiol decreased phospho-Smad1/5/8 and Id expression in female hPASMCs while increasing these in males commensurate with a decreased proliferative effect in male hPASMCs. Female Smad1(+/-) mice developed pulmonary hypertension (reversed by ovariectomy). CONCLUSIONS: We conclude that estrogen-driven suppression of BMPR-II signaling in non-PAH hPASMCs derived from women contributes to a pro-proliferative phenotype in hPASMCs that may predispose women to PAH.

Impaired bone morphogenetic protein receptor II signaling in a transforming growth factor-ß-dependent mouse model of pulmonary hypertension and in systemic sclerosis.

RATIONALE: Up to 10% of patients with systemic sclerosis (SSc) develop pulmonary arterial hypertension (PAH). This risk persists throughout the disease and is time dependent, suggesting that SSc is a susceptibility factor. Outcome for SSc-PAH is poor compared with heritable or idiopathic forms, despite clinical and pathological similarities. Although susceptibility in heritable PAH and idiopathic PAH is strongly associated with gene mutations leading to reduced expression of bone morphogenetic protein receptor (BMPR) II, these mutations have not been observed in SSc-PAH. OBJECTIVES: To explore BMPRII expression and function in a mouse model of SSc (TßRIIΔk-fib) that is susceptible to developing pulmonary hypertension and in SSc lung. METHODS: BMPRII and downstream signaling pathways were profiled in lung tissue and fibroblasts from the TßRIIΔk-fib model, which develops pulmonary vasculopathy with pulmonary hypertension that is exacerbated by SU5416. Complementary studies examined SSc or control lung tissue and fibroblasts. MEASUREMENTS AND MAIN RESULTS: Our study shows reduced BMPRII, impaired signaling, and altered receptor turnover activity in a transforming growth factor (TGF)-ß-dependent mouse model of SSc-PAH. Similarly, a significant reduction in BMPRII expression is observed in SSc lung tissue and fibroblasts. Increased proteasomal degradation of BMPRII appears to underlie this and may result from heightened TGF-ß activity. CONCLUSIONS: We found reduced BMPRII protein in patients with SSc-PAH and a relevant mouse model associated with increased proteasomal degradation of BMPRII. Collectively, these results suggest that impaired BMP signaling, resulting from TGF-ß-dependent increased receptor degradation, may promote PAH susceptibility in SSc and provide a unifying mechanism across different forms of PAH.

AntagomiR directed against miR-20a restores functional BMPR2 signalling and prevents vascular remodelling in hypoxia-induced pulmonary hypertension.

AIMS: Dysregulation of the bone morphogenetic protein receptor type 2 (BMPR2) is a hallmark feature that has been described in several forms of pulmonary hypertension. We recently identified the microRNA miR-20a within a highly conserved pathway as a regulator of the expression of BMPR2. To address the pathophysiological relevance of this pathway in vivo, we employed antagomiR-20a and investigated whether specific inhibition of miR-20a could restore functional levels of BMPR2 and, in turn, might prevent pulmonary arterial vascular remodelling. METHODS AND RESULTS: For specific inhibition of miR-20a, cholesterol-modified RNA oligonucleotides (antagomiR-20a) were synthesized. The experiments in mice were performed by using the hypoxia-induced mouse model for pulmonary hypertension and animal tissues were analysed for right ventricular hypertrophy and pulmonary arterial vascular remodelling. Treatment with antagomiR-20a enhanced the expression levels of BMPR2 in lung tissues; moreover, antagomiR-20a significantly reduced wall thickness and luminal occlusion of small pulmonary arteries and reduced right ventricular hypertrophy. To assess BMPR2 signalling and proliferation, we performed in vitro experiments with human pulmonary arterial smooth muscle cells (HPASMCs). Transfection of HPASMCs with antagomiR-20a resulted in activation of downstream targets of BMPR2 showing increased activation of Id-1 and Id-2. Proliferation of HPASMCs was found to be reduced upon transfection with antagomiR-20a. CONCLUSION: This is the first report showing that miR-20a can be specifically targeted in an in vivo model for pulmonary hypertension. Our data emphasize that treatment with antagomiR-20a restores functional levels of BMPR2 in pulmonary arteries and prevents the development of vascular remodelling.

Cadherin-6B stimulates an epithelial mesenchymal transition and the delamination of cells from the neural ectoderm via LIMK/cofilin mediated non-canonical BMP receptor signaling.

We previously provided evidence that cadherin-6B induces de-epithelialization of the neural crest prior to delamination and is required for the overall epithelial mesenchymal transition (EMT). Furthermore, de-epithelialization induced by cadherin-6B was found to be mediated by BMP receptor signaling independent of BMP. We now find that de-epithelialization is mediated by non-canonical BMP signaling through the BMP type II receptor (BMPRII) and not by canonical Smad dependent signaling through BMP Type I receptor. The LIM kinase/cofilin pathway mediates non-canonical BMPRII induced de-epithelialization, in response to either cadherin-6B or BMP. LIMK1 induces de-epithelialization in the neural tube and dominant negative LIMK1 decreases de-epithelialization induced by either cadherin-6B or BMP. Cofilin is the major known LIMK1 target and a S3A phosphorylation deficient mutated cofilin inhibits de-epithelialization induced by cadherin-6B as well as LIMK1. Importantly, LIMK1 as well as cadherin-6B can trigger ectopic delamination when co-expressed with the competence factor SOX9, showing that this cadherin-6B stimulated signaling pathway can mediate the full EMT in the appropriate context. These findings suggest that the de-epithelialization step of the neural crest EMT by cadherin-6B/BMPRII involves regulation of actin dynamics via LIMK/cofilin.

Altered expression and signal transduction of endothelin-1 receptors in heritable and idiopathic pulmonary arterial hypertension.

Human pulmonary arterial smooth muscle cells (PASMC) were isolated from elastic pulmonary arteries dissected from lungs of individuals with and without pulmonary arterial hypertension (PAH). Reflecting increased smooth muscle constriction in cells from PAH subject, Ca(2+) influx in response to endothelin-1 (ET-1) increased in all the PAH PASMC populations relative to the normal donor control cells. The ETA receptor mRNA levels remained unchanged, whereas the ETB receptor mRNA levels decreased in both heritable and idiopathic PAH-derived PASMC. All the PASMC populations expressed considerably higher ETA compared to ETB receptor number. Both ETA and ETB receptor numbers were reduced in bone morphogenetic protein receptor type II (BMPR2) mutation PAH. ETB receptors showed a particular reduction in number. Phospho-antibody array analysis of normal and BMPR2 deletion PASMC illustrated ERK and Akt activation to be the most prominent and to be taking place principally through ETB receptors in normal PASMC, but primarily through ETA receptors in PASMC from BMPR2 PAH subjects. Additionally in the PAH cells the total relative ET-1 signal response was markedly reduced. Western analysis from the BMPR2 PASMC duplicated the array results, whereas PASMC from iPAH subjects showed variability with most samples continuing to signal through ETB. In sum, these results indicate that generally both receptors are reduced in PAH particularly ETB, and that ETB signaling through protein kinases becomes markedly reduced in BMPR2 PASMC, while it continues in IPAH. Importantly, the data suggest that caution must be taken when applying ET-1 receptor antagonist therapy to PAH patients.

Bone morphogenetic protein receptor II regulates pulmonary artery endothelial cell barrier function.

Mutations in bone morphogenetic protein receptor II (BMPR-II) underlie most heritable cases of pulmonary arterial hypertension (PAH). However, less than half the individuals who harbor mutations develop the disease. Interestingly, heterozygous null BMPR-II mice fail to develop PAH unless an additional inflammatory insult is applied, suggesting that BMPR-II plays a fundamental role in dampening inflammatory signals in the pulmonary vasculature. Using static- and flow-based in vitro systems, we demonstrate that BMPR-II maintains the barrier function of the pulmonary artery endothelial monolayer suppressing leukocyte transmigration. Similar findings were also observed in vivo using a murine model with loss of endothelial BMPR-II expression. In vitro, the enhanced transmigration of leukocytes after tumor necrosis factor α or transforming growth factor ß1 stimulation was CXCR2 dependent. Our data define how loss of BMPR-II in the endothelial layer of the pulmonary vasculature could lead to a heightened susceptibility to inflammation by promoting the extravasation of leukocytes into the pulmonary artery wall. We speculate that this may be a key mechanism involved in the initiation of the disease in heritable PAH that results from defects in BMPR-II expression.

Attenuation of leukocyte recruitment via CXCR1/2 inhibition stops the progression of PAH in mice with genetic ablation of endothelial BMPR-II.

Previous studies from our group have demonstrated that bone morphogenetic protein receptor-II (BMPR-II), expressed on pulmonary artery endothelial cells, imparts profound anti-inflammatory effects by regulating the release of proinflammatory cytokines and promoting barrier function by suppressing the transmigration of leukocytes into the pulmonary vessel wall. Here we demonstrate that, in mice with endothelial-specific loss of BMPR-II expression (L1Cre(+);Bmpr2(f/f)), reduction in barrier function and the resultant pulmonary hypertension observed in vivo are the result of increased leukocyte recruitment through increased CXCR1/2 signaling. Loss of endothelial expressed BMPR-II leads to elevated plasma levels of a wide range of soluble mediators important in regulating leukocyte migration and extravasation, including the CXCR1/2 ligand, KC. Treatment of L1Cre(+);Bmpr2(f/f) mice with the CXCR1/2 antagonist SCH527123 inhibits leukocyte transmigration into lung and subsequently reverses the pulmonary hypertension. Our data have uncovered a previously unrecognized regulatory function of BMPR-II, which acts to regulate the expression of CXCR2 on endothelial cells, suggesting that increased CXCR2 signaling may also be a feature of the human pathology and that CXCR1/2 pathway antagonists may represent a novel therapeutic approach for treating pulmonary hypertension because of defects in BMPR-II expression.

A pair of transmembrane receptors essential for the retention and pigmentation of hair.

Hair follicles are simple, accessible models for many developmental processes. Here, using mutant mice, we show that Bmpr2, a known receptor for bone morphogenetic proteins (Bmps), and Acvr2a, a known receptor for Bmps and activins, are individually redundant but together essential for multiple follicular traits. When Bmpr2/Acvr2a function is reduced in cutaneous epithelium, hair follicles undergo rapid cycles of hair generation and loss. Alopecia results from a failure to terminate hair development properly, as hair clubs never form, and follicular retraction is slowed. Hair regeneration is rapid due to premature activation of new hair-production programs. Hair shafts differentiate aberrantly due to impaired arrest of medullary-cell proliferation. When Bmpr2/Acvr2a function is reduced in melanocytes, gray hair develops, as melanosomes differentiate but fail to grow, resulting in organelle miniaturization. We conclude that Bmpr2 and Acvr2a normally play cell-type-specific, necessary roles in organelle biogenesis and the shutdown of developmental programs and cell division.

Functional redundancy of type II BMP receptor and type IIB activin receptor in BMP2-induced osteoblast differentiation.

Signaling pathways for bone morphogenetic proteins (BMPs) are important in osteoblast differentiation. Although the precise function of type I BMP receptors in mediating BMP signaling for osteoblast differentiation and bone formation has been characterized previously, the role of type II BMP receptors in osteoblasts is to be well clarified. In this study, we investigated the role of type II BMP receptor (BMPR-II) and type IIB activin receptor (ActR-IIB) in BMP2-induced osteoblast differentiation. While osteoblastic 2T3 cells expressed BMPR-II and ActR-IIB, loss-of-function studies, using dominant negative receptors and siRNAs, showed that BMPR-II and ActR-IIB compensated each other functionally in mediating BMP2 signaling and BMP2-induced osteoblast differentiation. This was evidenced by two findings. First, unless there was loss of function of both type II receptors, isolated disruption of either BMPR-II or ActR-IIB did not remove BMP2 activity. Second, in cells with loss of function of both receptors, restoration of function of either BMPR-II or ActR-IIB by transfection of the wild-type forms, restored BMP2 activity. These findings suggest a functional redundancy between BMPR-II and ActR-IIB in osteoblast differentiation. Results from experiments to test the effects of transforming growth factor ß (TGF-ß), activin, and fibroblast growth factor (FGF) on osteoblast proliferation and differentiation suggest that inhibition of receptor signaling by double-blockage of BMPR-II and ActR-IIB is BMP-signaling specific. The observed functional redundancy of type II BMP receptors in osteoblasts is novel information about the BMP signaling pathway essential for initiating osteoblast differentiation.

BMP signaling pathway is required for commitment of C3H10T1/2 pluripotent stem cells to the adipocyte lineage.

Obesity is accompanied by an increase in both adipocyte number and size. The increase in adipocyte number is the result of recruitment to the adipocyte lineage of pluripotent stem cells present in the vascular stroma of adipose tissue. These pluripotent cells have the potential to undergo commitment and then differentiate into adipocytes, as well as myocytes, osteocytes, and chondrocytes. In this article, we show that both bone morphogenetic protein (BMP)2 and BMP4 can induce commitment of C3H10T1/2 pluripotent stem cells into adipocytes. After treatment of C3H10T1/2 stem cells with these BMPs during proliferation followed by exposure to differentiation inducers at growth arrest, nearly all cells enter the adipose development pathway, express specific adipocyte markers, and acquire the adipocyte phenotype. Overexpression of constitutively active BMP receptor (CA)-BMPr1A or CA-BMPr1B induces commitment in the absence of BMP2/4, whereas overexpression of a dominant-negative receptor dominant-negative-BMPr1A suppresses commitment induced by BMP. Also, knockdown of the expression of Smad4 (coregulator in the BMP/Smad signaling pathway) with RNAi disrupts commitment by the BMPs. However, knockdown of expression of p38 MAPK (an intermediary in the BMP/MAPK signaling pathway) with RNAi had little effect on BMP-induced commitment. Together, these findings indicate that the BMP/Smad signaling pathway has a dominant role in adipocyte lineage determination. Proteomic analysis identified lysyl oxidase (LOX), a bona fide downstream target gene of the BMP signaling pathway. Expression of LOX is induced by BMP2/4 during adipocyte lineage commitment, and knockdown of its expression disrupts the commitment process.

Molecular pathogenesis of pulmonary arterial hypertension.

Recent investigations have suggested that it might be possible to reverse the pathology of pulmonary arterial hypertension (PAH), a disorder that can be rapidly progressive and fatal despite current treatments including i.v. prostacyclin. This review will address the cellular and molecular processes implicated in clinical, genetic, and experimental studies as underlying the pulmonary vascular abnormalities associated with PAH. Emerging treatments are aimed at inducing apoptosis of abnormal vascular cells that obstruct blood flow and at promoting regeneration of "lost" distal vasculature.

Sex Differences in Pulmonary Hypertension.

Pulmonary arterial hypertension (PAH) occurs in women more than men whereas survival in men is worse than in women. In recent years, much research has been carried out to understand these sex differences in PAH. This article discusses clinical and preclinical studies that have investigated the influences of sex, serotonin, obesity, estrogen, estrogen synthesis, and estrogen metabolism on bone morphogenetic protein receptor type II signaling, the pulmonary circulation and right ventricle in both heritable and idiopathic pulmonary hypertension.

PERK inhibition attenuates vascular remodeling in pulmonary arterial hypertension caused by BMPR2 mutation.

Pulmonary arterial hypertension (PAH) is a fatal disease characterized by excessive pulmonary vascular remodeling. However, despite advances in therapeutic strategies, patients with PAH bearing mutations in the bone morphogenetic protein receptor type 2 (BMPR2)-encoding gene present severe phenotypes and outcomes. We sought to investigate the effect of PER-like kinase (PERK), which participates in one of three major pathways associated with the unfolded protein response (UPR), on PAH pathophysiology in BMPR2 heterozygous mice. BMPR2 heterozygosity in pulmonary artery smooth muscle cells (PASMCs) decreased the abundance of the antiapoptotic microRNA miR124-3p through the arm of the UPR mediated by PERK. Hypoxia promoted the accumulation of unfolded proteins in BMPR2 heterozygous PASMCs, resulting in increased PERK signaling, cell viability, cellular proliferation, and glycolysis. Proteomic analyses revealed that PERK ablation suppressed PDGFRß-STAT1 signaling and glycolysis in hypoxic BMPR2 heterozygous PASMCs. Furthermore, PERK ablation or PERK inhibition ameliorated pulmonary vascular remodeling in the Sugen/chronic hypoxia model of PAH, irrespective of BMPR2 status. Hence, these findings suggest that PERK inhibition is a promising therapeutic strategy for patients with PAH with or without BMPR2 mutation.

BMP type II receptor regulates positioning of outflow tract and remodeling of atrioventricular cushion during cardiogenesis.

Signaling of bone morphogenetic protein (BMP) via type I and type II receptors is involved in multiple processes contributing to cardiogenesis. To investigate the role of the BMP type II receptor (BMPRII) in heart development, the BMPRII gene was deleted throughout the embryo during gastrulation using a Mox2-Cre transgene. BMPRII(flox/-);Mox2-Cre mice exhibited cardiac defects including double-outlet right ventricle, ventricular septal defect (VSD), atrioventricular (AV) cushion defects, and thickened valve leaflets. To characterize the tissue-specific functions of BMPRII in cardiogenesis, a series of Cre transgenes (alphaMHC-, Tie2-, Wnt1-, and SM22alpha-Cre) was employed. Interestingly, myocardial development was normal when the BMPRII gene was deleted in myocardial cells using Mox2-Cre, alphaMHC-Cre, or SM22alpha-Cre transgenes, suggesting that signaling by other BMP type II receptors may compensate for the absence of BMPRII in the myocardial cells. AV cushion defects including atrial septal defect, membranous VSD, and thickened valve leaflets were found in BMPRII(flox/-);Tie2-Cre mice. Abnormal positioning of the aorta was observed in BMPRII(flox/-);Wnt1-Cre and BMPRII(flox/-);SM22alpha-Cre mice. Taken together, these results demonstrate that endocardial BMPRII expression is required for septal formation and valvulogenesis. Moreover, mesenchymal BMPRII expression in the outflow tract cushion is required for proper positioning of the aorta.