Bone Morphogenetic Protein Receptor Research Articles

Loss of Type 2 Bone Morphogenetic Protein Receptor Activates NOD-Like Receptor Family Protein 3/Gasdermin E-Mediated Pyroptosis in Pulmonary ArterialHypertension.

Pulmonary arterial hypertension (PAH) is an incurable disease initiated by endothelial dysfunction, secondary to vascular inflammation and occlusive pulmonary arterial vascular remodeling, resulting in elevated pulmonary arterial pressure and right heart failure. Previous research has reported that dysfunction of type 2 bone morphogenetic protein receptor (BMPR2) signaling pathway in endothelium is inclined to prompt inflammation in PAH models, but the underlying mechanism of BMPR2 deficiency-mediated inflammation needs further investigation. This study was designed to investigate whether BMPR2 deficiency contributes to pulmonary arterial hypertension via the NLRP3 (NOD-like receptor family protein 3)/GSDME (gasdermin E)-mediated pyroptosis pathway. NLRP3 knockout or short hairpin RNA interference of GSDME was performed in PAH animal models to investigate its effect on PAH progression. In addition, the effects of BMPR2 deficiency and restoration of BMPR2 by BMP9 (bone morphogenetic protein 9) or FK506 on pyroptosis were explored both in animal and cell models. Knockout of NLRP3 or short hairpin RNA interference of GSDME in animal models can alleviate the development of pyroptosis, accompanied with improved endothelial integrity, vascular remodeling, and right ventricular systolic pressure. Blocking BMPR2 is sufficient to induce NLRP3 upregulation and release of inflammatory factor IL-1β (interleukin-1β) in pulmonary arterial endothelial cells. Moreover, BMPR2 deficiency can induce GSDME-mediated pyroptosis through NLRP3 activation in 2 animal models, whereas activation of BMPR2 signaling by FK506 or BMP9 can reverse these phenotypes. These findings provide evidence that loss of BMPR2 signaling promotes endothelial cell pyroptosis by enhancing NLRP3/GSDME signaling in PAH. Our findings may provide new insights to explore the inflammatory mechanism of PAH treatment.

Sotatercept in pulmonary hypertension and beyond.

Sotatercept binds free activins by mimicking the extracellular domain of the activin receptor type IIA (ACTRIIA). Additional ligands are BMP/TGF-beta, GDF8, GDF11 and BMP10. The binding with activins leads to the inhibition of the signalling pathway and the deactivation of the bone morphogenic protein (BMP) receptor type 2. In this way, sotatercept activates an antiproliferative signalling to the cells of the pulmonary arteries and arterioles with the aim of rebalancing the proliferative and antiproliferative pathway that characterizes the pulmonary arterial hypertension (PAH). Sotatercept is indicated for the treatment of group 1 PAH in combination with drugs that act through the endothelin receptor, nitric oxide or prostacyclin. Its effects, demonstrated in the STELLAR study, are the improvement of exercise capacity and the FC-WHO functional class, together with the reduction of the risk of clinical worsening events. In addition to its antiremodeling effects on the pulmonary circulation, sotatercept has several haematological effects that could suggest its use in the treatment of some blood disorders other than PAH. In this review, we will discuss the effects of the drug on PAH and in parallel provide an in-depth overview of its application in haematological disorders, focusing on clinical and preclinical studies.

BMP and STRA8 act collaboratively to ensure correct mitotic-to-meiotic transition in the fetal mouse ovary.

A successful mitosis-to-meiosis transition in germ cells is essential for fertility in sexually reproducing organisms. In mice and humans, it is established that expression of STRA8 is critical for meiotic onset in both sexes. Here we show that BMP signalling is also essential, not for STRA8 induction but for correct meiotic progression in female mouse fetal germ cells. Largely in agreement with evidence from primordial germ cell-like cells (PGCLCs) in vitro, germ cell-specific deletion of BMP receptor 1A (BMPR1A; ALK3) caused aberrant retention of pluripotency marker OCT4 and meiotic progression was compromised; however, the timely onset of Stra8/STRA8 expression was unaffected. Comparing the transcriptomes of Bmpr1a-cKO and Stra8-null models, we reveal interplay between the effects of BMP signalling and STRA8 function. Our results verify a role for BMP signalling in instructing germ cell meiosis in female mice in vivo, and shed light on the regulatory mechanisms underlying fetal germ cell development.

A Recombinant Antibody Against ALK2 Promotes Tissue Iron Redistribution and Contributes to Anemia Resolution in a Mouse Model of Anemia of Inflammation.

Patients with chronic inflammation are burdened with anemia of inflammation (AI), where inflammatory cytokines inhibit erythropoiesis, impede erythropoietin production, and limit iron availability by inducing the iron regulator hepcidin. High hepcidin hinders iron absorption and recycling, thereby worsening the impaired erythropoiesis by restricting iron availability. AI management is important as anemia impacts quality of life and potentially affects morbidity and mortality. The bone morphogenetic protein (BMP)-SMAD pathway is crucial for hepcidin regulation. Here, we characterized a research antibody against BMP receptor ALK2, RKER-216, and investigated its mechanism in suppressing hepcidin and improving anemia in acute/chronic inflammation. Additive effects of RKER-216 and recombinant human erythropoietin (rhEPO) on erythropoiesis and iron utilization were also explored. We showed that RKER-216 neutralized ALK2 activity by competing with the binding of BMP6. RKER-216 reduced hepcidin transcription in Hep3B cells, and a subcutaneous dose of RKER-216 at 3 mg/kg suppressed serum hepcidin and increased circulating iron for 3-4 days in wildtype mice. Moreover, RKER-216 decreased hepcidin by inhibiting SMAD1/5/9 signaling in lipopolysaccharide-mediated inflammation and liberated iron from the recycling pathway to alleviate anemia in mice with adenine-induced chronic kidney disease (CKD), a mouse model of AI. Finally, RKER-216 reversed iron-restricted erythropoiesis in CKD mice and supplied the iron requirement for complete resolution of anemia when coupled with rhEPO in addressing AI. Our data support that ALK2 is a key hepcidin regulator and that a neutralizing ALK2 antibody has the potential to restore iron homeostasis as monotherapy or in combination with rhEPO to ameliorate AI.

Endothelial tip-cell position, filopodia formation and biomechanics require BMPR2 expression and signaling

Blood vessel formation relies on biochemical and mechanical signals, particularly during sprouting angiogenesis when endothelial tip cells (TCs) guide sprouting through filopodia formation. The contribution of BMP receptors in defining tip-cell characteristics is poorly understood. Our study combines genetic, biochemical, and molecular methods together with 3D traction force microscopy, which reveals an essential role of BMPR2 for actin-driven filopodia formation and mechanical properties of endothelial cells (ECs). Targeting of Bmpr2 reduced sprouting angiogenesis in zebrafish and BMPR2-deficient human ECs formed fewer filopodia, affecting cell migration and actomyosin localization. Spheroid assays revealed a reduced sprouting of BMPR2-deficient ECs in fibrin gels. Even more strikingly, in mosaic spheroids, BMPR2-deficient ECs failed to acquire tip-cell positions. Yet, 3D traction force microscopy revealed that these distinct cell behaviors of BMPR2-deficient tip cells cannot be explained by differences in force-induced matrix deformations, even though these cells adopted distinct cone-shaped morphologies. Notably, BMPR2 positively regulates local CDC42 activity at the plasma membrane to promote filopodia formation. Our findings reveal that BMPR2 functions as a nexus integrating biochemical and biomechanical processes crucial for TCs during angiogenesis.

Enhancement of Differentiation and Mineralization of Human Dental Pulp Stem Cells via TGF-β Signaling in Low-Level Laser Therapy Using Er:YAG Lasers.

Low-level laser therapy (LLLT) using an erbium-doped yttrium aluminum garnet (Er:YAG) laser provides a non-invasive approach applicable to various dental treatments. Here, we investigated the effects of Er:YAG laser irradiation on human dental pulp stem cells (hDPSCs) in an in vitro experiment. The hDPSCs were categorized into four groups: laser-irradiated with activators (VLT: activated vitamin D3, bone morphogenetic protein receptor inhibitor, and transforming growth factor-beta (TGF-β)) (LLLT(+)VLT), laser-irradiated without activators (LLLT(+)-only), non-irradiated with activators (LLLT(-)VLT), and non-irradiated without activators (control). Cell proliferation, hard tissue differentiation, TGF-β signaling pathway activity, mineralization induction, and gene expression levels were assessed using several approaches, including cell proliferation assays, ALP assays, western blotting, Alizarin Red S staining, X-ray diffraction, and quantitative polymerase chain reaction. Cell proliferation was similar between the LLLT(+)-only and control groups. The ALP activity was significantly higher in LLLT(+)VLT group than in LLLT(-)VLT group (p < 0.05); however, it was suppressed by TGF-β signaling inhibitors. Western blotting showed enhanced SMAD3 phosphorylation in the LLLT(+)VLT group. The mineralization nodules and mRNA levels of matrix vesicle marker genes were significantly higher in LLLT(+)VLT group, and the nodules were partially composed of hydroxyapatite. The hard tissue formation marker gene expression in LLLT(+)VLT group was significantly higher (p < 0.05) than that in the LLLT(+)-only and control groups; however, it was unchanged or suppressed compared with that in LLLT(-)VLT group. LLLT using an Er:YAG laser, combined with VLT, may promote the differentiation of hDPSCs into hard tissue-forming cells and enhance mineralization.

High Shear Stress Reduces ERG Causing Endothelial-Mesenchymal Transition and Pulmonary Arterial Hypertension.

Computational modeling indicated that pathological high shear stress (HSS; 100 dyn/cm2) is generated in pulmonary arteries (PAs; 100-500 µm) in congenital heart defects causing PA hypertension (PAH) and in idiopathic PAH with occlusive vascular remodeling. Endothelial-to-mesenchymal transition (EndMT) is a feature of PAH. We hypothesize that HSS induces EndMT, contributing to the initiation and progression of PAH. We used Ibidi perfusion system to determine whether HSS applied to human PA endothelial cells (ECs) induces EndMT when compared with physiological laminar shear stress (15 dyn/cm2). The mechanism was investigated and targeted to prevent PAH in a mouse with HSS induced by an aortocaval shunt. EndMT, a feature of PAH not previously attributed to HSS, was observed. HSS did not alter the induction of transcription KLF (Krüppel-like factor) 2/4, but an ERG (ETS-family transcription factor) was reduced, as were histone H3 lysine 27 acetylation enhancer-promoter peaks containing ERG motifs. Consequently, there was reduced interaction between ERG and KLF2/4, a feature important in tethering KLF and the chromatin remodeling complex to DNA. In PA ECs under laminar shear stress, reducing ERG by siRNA caused EndMT associated with decreased BMPR2 (bone morphogenetic protein receptor 2), CDH5 (cadherin 5), and PECAM1 (platelet and EC adhesion molecule 1) and increased SNAI1/2 (Snail/Slug) and ACTA2 (smooth muscle α2 actin). In PA ECs under HSS, transfection of ERG prevented EndMT. HSS was then induced in mice by an aortocaval shunt, causing progressive PAH over 8 weeks. An adeno-associated viral vector (AAV2-ESGHGYF) was used to replenish ERG selectively in PA ECs. Elevated PA pressure, EndMT, and vascular remodeling (muscularization of peripheral arteries) in the aortocaval shunt mice were markedly reduced by ERG delivery. Pathological HSS reduced lung EC ERG, resulting in EndMT and PAH. Agents that upregulate ERG could reverse HSS-mediated PAH and occlusive vascular remodeling resulting from high flow or narrowed PAs.

The modulatory role of bone morphogenetic protein signaling in cerebellar synaptic plasticity.

Bone morphogenetic proteins (BMPs), regulators of bone formation, have been implicated in embryogenesis and morphogenesis of various tissues and organs. BMP signaling plays a role in the formation of appropriate synaptic connections and development of normal neural circuits in the brain. However, physiological roles of BMP signaling in postnatal neural functions, including synaptic plasticity, remain largely unknown. Long-term depression (LTD) of synaptic transmission at parallel fiber (PF)-Purkinje cell (PC) synapses in the cerebellum has been suggested one neuronal mechanism underlying cerebellar functions. Here, we explored the contribution of BMP signaling to the induction of mouse cerebellar LTD. We first demonstrated that BMP2 and/or 4 were expressed in GABAergic neurons in mature networks of the cerebellar cortex. mRNA encoding BMP receptor type 1B (Bmpr1b) was expressed in the PC layer. Exogenous application of noggin, a BMP ligand inhibitor, suppressed the induction of cerebellar LTD by conjunctive stimulation, which caused normal LTD under control condition. Furthermore, mice deficient in BMPR1B exhibited attenuation of the extent of LTD induction, whereas they showed normal excitatory synaptic transmission at PF-PC synapses. These results suggest that after postnatal development, BMP signaling activated by BMPR1B, expressed in the PC layer, plays a crucial role in the facilitation of cerebellar LTD, leading to the modulation of cerebellar functions and behaviors.

RANK drives structured intestinal epithelial expansion during pregnancy.

During reproduction, multiple species such as insects and all mammals undergo extensive physiological and morphological adaptions to ensure health and survival of the mother and optimal development of the offspring. Here we report that the intestinal epithelium undergoes expansion during pregnancy and lactation in mammals. This enlargement of the intestinal surface area results in a novel geometry of expanded villi. Receptor activator of nuclear factor-κΒ (RANK, encoded by TNFRSF11A) and its ligand RANKL were identified as a molecular pathway involved in this villous expansion of the small intestine in vivo in mice and in intestinal mouse and human organoids. Mechanistically, RANK-RANKL protects gut epithelial cells from cell death and controls the intestinal stem cell niche through BMP receptor signalling, resulting in the elongation of villi and a prominent increase in the intestinal surface. As a transgenerational consequence, babies born to female mice that lack Rank in the intestinal epithelium show reduced weight and develop glucose intolerance after metabolic stress. Whereas gut epithelial remodelling in pregnancy/lactation is reversible, constitutive expression of an active form of RANK is sufficient to drive intestinal expansion followed by loss of villi and stem cells, and prevents the formation of Apcmin-driven small intestinal stem cell tumours. These data identify RANK-RANKL as a pathway that drives intestinal epithelial expansion in pregnancy/lactation, one of the most elusive and fundamental tissue remodelling events in mammalian life history and evolution.

Therapeutic Resolution of Pulmonary Arterial Hypertension (PAH) Using Natural Products

Pulmonary arterial hypertension (PAH) is a progressive and rare condition characterised by the occlusion of pulmonary arterioles, with clinical manifestations resulting from the cross-sectional area reduction of the small pulmonary arteries. The disease is driven by a combination of factors including vasoconstriction, thrombosis, inflammation, proliferation, and the obstructive remodelling of the pulmonary artery walls. Heterozygous mutations in the type II bone morphogenetic protein receptor (BMPR2) underlie the majority of the inherited and familial forms of PAH. Current evidence indicates that in PAH, the BMPR2-mediated-signalling is diminished and the TGFβ signalling is heightened. Even when managed with current therapeutic approaches, the disease eventually results in increased pulmonary vascular resistance, right heart failure, and premature death. Natural products act as vascular disease treatment agents and have been used in clinical practice following compelling clinical trials. The rationale for the selection of natural compounds derives from their multi-targeted approach and synergistic effects. Although novel medicines licenced by the FDA (USA) between 1981 and 2010, constitute approximately 34% natural products or derivatives of natural products, their potentials for the treatment of PAH are not fully explored. The objective of this review is to emphasise the significance of natural products in the therapeutic resolution of PAH.

Functional effects of BMPR1B in porcine endometrium provides novel insights into the high fecundity of Taihu pigs.

Litter size in pigs is affected by factors such as ovulation number, embryonic survival, and uterine environment conditions. Endometrial epithelial and stromal cells represent the first site of contact between the embryo and sows; therefore, dynamic changes in the growth and development of these cells are among the major factors affecting the intrauterine environment and implantation. Bone morphogenetic protein receptor type-1B (BMPR1B) is a receptor of the bone morphogenetic protein (BMP) family that has been identified as a candidate gene for reproductive traits in pigs. In our previous study, we used whole-genome resequencing to identify BMPR1B as a candidate gene affecting sow litter size in Taihu pigs and revealed the transcriptional regulation of BMPR1B in the endometrium. However, the functional role of BMPR1B in the growth and development of the endometrium in pigs has not been comprehensively elucidated. In this study, we isolated, characterized, and immortalized Meishan pig endometrial cells, and systematically explored the biological function of BMPR1B using a cell model. BMPR1B promoted cell proliferation and migration of endometrial stromal cells but inhibited that of endometrial epithelial cells. Transcriptome sequencing revealed potential pathways through which BMPR1B influences the growth and development of endometrial cells, including vascular system development, gland morphology, cell migration and adhesion, and reproductive system development. Moreover, the outstanding uterine function of Meishan pigs from endometrial genomic aspects was performed elucidated through CUT&Tag experiments. Most biological process, including reproductive system development, embryonic morphogenesis, and angiogenesis, were enriched by genes that were differentially bound by enhancer markers. These findings provide a valuable resource for future research on the mechanisms underlying the excellent uterine function in Meishan pigs.

Hemodynamic and Genetic Associations with the Risk of Idiopathic Pulmonary Arterial Hypertension Development in an Ethnic Cohort of Kazakhs.

Idiopathic pulmonary arterial hypertension (IPAH) is a progressive and fatal disease. The aim of this study was to evaluate the association of polymorphism of the type 2 bone morphogenetic protein receptor gene (BMPR2) with the risk of IPAH development in an ethnic group of Kazakhs. We also describe the clinical and hemodynamic characteristics and outcomes of patients with and without carriers of BMPR2 gene mutations in IPAH. No available research highlights this problem in an ethnic group of Kazakhs. A total of 53 patients of only Kazakh nationality with IPAH participated in the study. Clinical, functional, and hemodynamic characteristics, as well as the outcome of the disease, were compared among carriers and non-carriers of the BMPR2 mutation. When receiving IPAH diagnosis, the average age of patients was 40.0 (32.0-48.0) years. Women predominated among the patients (86.8%). Of these, 17 (32.0%) were carriers of the gene mutation, and 36 (68.0%) did not have this mutation. The results of our research demonstrate that the Rs17199249 variant in BMPR2 contributed to increased susceptibility to IPAH. The T allele was associated with an increased risk of IPAH, with T = 75 (70.75%), G = 31 (29.24%), MAF-0.2925, x2-0.001, and HWE p-0.975. Carriers of the BMPR2 mutation were predominantly women (80.0%), and they had higher pulmonary vascular resistance (8.7-14.9 vs. 5.9-12.6 WU; p = 0.038), a low cardiac index (1.9-2.6 vs. 2.3-3.1 L/min per m2; p = 0.027), and a shorter time to death (p = 0.022). This is the first study of the genetic causes of IPAH that demonstrates the genetic polymorphism of BMPR2 is associated with an increased risk of IPAH developing with worse hemodynamic parameters and clinical outcomes.

Adaptation of ACMG/AMP guidelines for clinical classification of BMPR2 variants in Pulmonary Arterial Hypertension resolves variants of unclear pathogenicity in ClinVar.

Pulmonary arterial hypertension (PAH) is a rare disease that can be caused by pathogenic variants, most frequently in the bone morphogenetic protein receptor type 2 ( BMPR2 ) gene. We formed a ClinGen variant curation expert panel to devise guidelines for the clinical interpretation of BMPR2 variants identified in PAH patients. The general ACMG/AMP variant classification criteria were refined for PAH and adapted to BMPR2 following ClinGen procedures. Subsequently, these specifications were tested independently by three members of the curation expert panel on 28 representative BMPR2 variants selected from ClinVar, and then presented and discussed in the plenum. Application of the final BMPR2 variant specifications resolved 6 of 9 variants (66%) where multiple ClinVar classifications included a Variant of Uncertain Significance, with all six being reclassified as Benign or Likely Benign. Four splice site variants underwent clinically consequential reclassifications based on the presence or absence of supporting mRNA splicing data. The variant specifications provide an international framework and a useful tool for BMPR2 variant classification and can be applied to increase confidence and consistency in BMPR2 interpretation for diagnostic laboratories, clinical providers, and patients.

Methyl-Beta-Cyclodextrin Restores Aberrant Bone Morphogenetic Protein 2-Signaling in Bone Marrow Stromal Cells Obtained from Aged C57BL/6 Mice.

During aging, disruptions in various signaling pathways become more common. Some older patients will exhibit irregular bone morphogenetic protein (BMP) signaling, which can lead to osteoporosis (OP)-a debilitating bone disease resulting from an imbalance between osteoblasts and osteoclasts. In 2002, the Food and Drug Administration (FDA) approved recombinant human BMP-2 (rhBMP-2) for use in spinal fusion surgeries as it is required for bone formation. However, complications with rhBMP-2 arose and primary osteoblasts from OP patients often fail to respond to BMP-2. Although patient samples are available for study, previous medical histories can impact results. Consequently, the C57BL/6 mouse line serves as a valuable model for studying OP and aging. We find that BMP receptor type Ia (BMPRIa) is upregulated in the bone marrow stromal cells (BMSCs) of 15-month-old mice, consistent with prior data. Furthermore, conjugating BMP-2 with Quantum Dots (QDot®s) allows effective binding to BMPRIa, creating a fluorescent tag for BMP-2. Furthermore, after treating BMSCs with methyl-β-cyclodextrin (MβCD), a disruptor of cellular endocytosis, BMP signaling is restored in 15-month-old mice, as shown by von Kossa assays. MβCD has the potential to restore BMPRIa function, and the BMP signaling pathway offers a promising avenue for future OP therapies.

LncRNA MYOSLID contributes to PH via targeting BMPR2 signaling in pulmonary artery smooth muscle cell

Background/objectiveThe pathogenesis and vascular remodeling during pulmonary hypertension (PH) have been associated with dysregulation of bone morphogenetic protein receptor type 2 (BMPR2) and transforming growth factor-β (TGF-β) signaling in pulmonary artery smooth muscle cells (PASMCs). Evidence suggests that the human-specific lncRNA MYOSLID is a transcriptional target of the TGF-β/SMAD pathway. In this study, we investigated the involvement of MYOSLID in the pathogenesis of PH. MethodsLung tissues from PH patients and rat PH models were analyzed to assess clinical relevance. RNA-Seq was performed to identify target genes. Pulmonary artery smooth muscle cells (PASMCs) were used to evaluate function and underlying mechanisms. ResultsRNA-Seq analysis of PASMCs stimulated by TGF-β1 revealed significantly dysregulated lncRNAs. MYOSLID expression was markedly elevated in lung tissues from PH patients and in PASMCs stimulated with TGF-β1. Mechanistically, loss of MYOSLID inhibited the TGF-β pathway by reducing SMAD2/3 PHosphorylation and activated the BMPR2 pathway by enhancing SMAD1/5/9 phosphorylation and increasing ID genes expression in PASMCs. DAZAP2, a target gene of MYOSLID, functions as an inhibitor of BMPR2 signaling. Moreover, DAZAP2 expression was significantly elevated in lung tissues from PH patients and rat PH models. Functionally, knockdown of MYOSLID and DAZAP2 reduced proliferation, migration, and apoptosis resistance in PASMCs. ConclusionThe activation of the MYOSLID-DAZAP2-BMPR2 axis contributes to pulmonary vascular remodeling, and targeting MYOSLID and DAZAP2 may represent novel therapeutic strategies for PH treatment.

Abstract 4136605: Effect Of A Bone Morphogenetic Protein Receptor Type 2 Mutation On The Cardiomyocyte Response To Pressure Overload

Introduction: A mutation in the Bone Morphogenetic Protein Receptor Type 2 ( BMPR2 ) gene is in 70% of hereditary pulmonary arterial hypertension (hPAH) patients the causative mutation of the disease. Previous work demonstrated that right ventricular function is more impaired in hPAH patients with a BMPR2 mutation. However, the underlying mechanism remains elusive. Moreover, natriuretic peptides, such as N-terminal Brain Natriuretic Peptides (NTproBNP) and Mid Regional proAtrial Natriuretic Peptides (MRproANP), are secreted from cardiomyocytes upon stretch as adaptation to increased pressure overload. We hypothesize that the BMPR2 mutation impairs the response to increased pressure overload. For this purpose, we make use of ventricular induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) of hPAH patients carrying a BMPR2 mutation and their isogenic controls in which the mutation was corrected. Aim: To study the effect of a BMPR2 mutation on the response to pressure overload in vitro . Methods: iPSCs from 2 hPAH patients and its isogenic controls were used. iPSCs were differentiated into ventricular iPSC-CMs and stretched 10% equiaxially for 24h at 1Hz on the Flexcell FX-6000 system. Natriuretic peptides gene expressions were quantified via RT-PCR. NTproBNP and MRproANP release were measured on cell supernatants throughout specific immunoassays. Normality of the data was checked, and statistics were performed accordingly. Results: No differences were observed on natriuretic peptides gene expression on static and stretched iPSC-CMs. There is a clear correlation between NTproBNP and MRproANP release (R 2 =0.83, p&lt;0.0001, Figure 1A). Interestingly, hPAH iPSC-CMs showed higher baseline values for NTproBNP release compared to isogenic iPSC-CMs (p&lt;0.01, Figure 1B). Furthermore, stretching resulted in increased NTproBNP and MRproANP secretion in both hPAH and isogenic iPSC-CMs (Figure 1B-C). Conclusions: Secretion of NTproBNP and MRproANP was closely correlated in iPSC-CMs. iPSC-CMs of hPAH patients with a BMPR2 mutation showed higher baseline values of NTproBNP. Increased secretion of NTproBNP and MRproANP upon mechanical stimulation was similar between hPAH and isogenic iPSC-CMs. Experiments in atrial iPSC-CMs are currently ongoing to test potential differences in natriuretic peptide secretion between ventricular and atrial cardiomyocytes as the right atrium is also under stretch in PAH.

Stepwise release of Activin-A from its inhibitory prodomain is modulated by cysteines and requires furin coexpression to promote melanoma growth

The Activin-A precursor dimer can be cleaved by furin, but how this proteolytic maturation is regulated in vivo and how it facilitates access to signaling receptors is unclear. Here, analysis in a syngeneic melanoma grafting model shows that without furin coexpression, Activin-A failed to accelerate tumor growth, correlating with failure of one or both subunits to undergo cleavage in signal-sending cells, even though compensatory processing by host cells nonetheless sustained elevated circulating Activin-A levels. In reporter assays, furin-independent cleavage of one subunit enabled juxtacrine Activin-A signaling, whereas completion of proteolytic maturation by coexpressed furin or by recipient cells stimulated contact-independent activity, crosstalk with BMP receptors, and signal inhibition by follistatin. Mechanistically, Activin-A processing was modulated by allosteric disulfide bonds flanking the furin site. Disruption of these disulfide linkages with the prodomain enabled Activin-A binding to cognate type II receptors independently of proteolytic maturation. Stepwise proteolytic maturation is a novel mechanism to control Activin-A protein interactions and signaling.

BMP3b regulates bone mass by inhibiting BMP signaling

Bone morphogenetic protein 3b (BMP3b), also known as growth differentiation factor 10 (GDF10), is a non-osteogenic BMP highly expressed in the skeleton. Although in vitro studies have shown that BMP3b suppresses osteoblast differentiation, the physiological role of BMP3b in regulating bone mass in vivo remains unknown. Here, we show that BMP3b deletion in mice leads to a high bone mass phenotype via an unexpected novel mechanism involving de-repression of canonical BMP/Smad signaling. BMP3b null mice were viable, and exhibited no significant difference in body size compared to wildtype control. Trabecular bone parameters assessed by histomorphometry and μCT, revealed a significant increase in bone volume and bone mineral density. Expression of osteoblast-differentiation genes were elevated in bone tissue of BMP3b null mice, whereas expression of osteoclast-related genes remained unchanged. Consistent with this, Bmp3b was highly expressed in osteoblasts relative to osteoclast cells. Ex-vivo culture of primary bone marrow mesenchymal stem cells (BMSCs) and primary bone marrow-derived osteoclasts revealed that inactivation of BMP3b enhances osteogenesis without affecting osteoclastogenesis. Mechanistically, we found that BMP3b suppressed BMP4-induced Smad1/5 phosphorylation and inhibited the activity of a BMP4-driven Id-1 luciferase reporter. Protein-protein interaction assays revealed that BMP3b competitively interfered with the association of BMP4 and BMP type I receptors. These findings suggest that BMP3b regulates bone mass by acting as a BMP receptor antagonist. Thus, maintenance of bone mass involves antagonism of canonical BMP/Smad signaling by a member of the BMP family.

StratosPHere 2: study protocol for a response-adaptive randomised placebo-controlled phase II trial to evaluate hydroxychloroquine and phenylbutyrate in pulmonary arterial hypertension caused by mutations in BMPR2

BackgroundPulmonary arterial hypertension is a life-threatening progressive disorder characterised by high blood pressure (hypertension) in the arteries of the lungs (pulmonary artery). Although treatable, there is no known cure for this rare disorder, and its exact cause is unknown. Mutations in the bone morphogenetic protein receptor type-2 (BMPR2) are the most common genetic cause of familial pulmonary arterial hypertension. This study represents the first-ever trial of treatments aimed at directly rescuing the BMPR2 pathway, repurposing two drugs that have shown promise at restoring levels of BMPR2 signalling: hydroxychloroquine and phenylbutyrate.MethodsThis three-armed phase II precision medicine study will investigate BMPR2 target engagement and explore the efficacy of two repurposed therapies in pulmonary arterial hypertension patients with BMPR2 mutations. Patients will be stratified based on two BMPR2 mutation classes: missense and haploinsufficient mutations. Eligible subjects will be randomised to one of the three arms (two active therapy arms and a placebo arm, all plus standard of care) following a Bayesian response-adaptive design implemented independently in each stratum and updated in response to a novel panel of primary biomarkers designed to assess biological modification of the disease.DiscussionThe results of this trial will provide the first randomised evidence of the efficacy of these therapies to rescue BMPR2 function and will efficiently explore the potential for a differential response of these therapies per mutation class to address causes rather than consequences of this rare disease.Trial registrationThe study has been registered with ISRCTN (ISRCTN10304915, 22/09/2023).

Case of Bone Morphogenetic Protein Receptor Type 2 (BMPR2) Mutation Complicated by Pulmonary Hypertension Encountered at Autopsy

Abstract Introduction/Objective Bone morphogenetic protein receptor type 2 is a protein encoded by the BMPR2 gene which regulates cell division and apoptosis. BMPR2 mutations result in monoclonal plexiform lesions of proliferating endothelial cells in pulmonary arterioles, which leads to elevated pulmonary artery pressures, right ventricular failure, and death. Here, we present the case of a 12-year-old male with a known history of pulmonary hypertension secondary to BMPR2 mutation referred for medical autopsy after suffering cardiac arrest and passing away. Methods/Case Report This 12-year-old male was diagnosed with pulmonary hypertension in December 2022 after suffering a syncopal episode while running at recess. Genetic testing was obtained, and he was found to have a BMPR2 mutation. His father was tested and also harbored this mutation, but did not clinically have pulmonary hypertension. The decedent was initiated on ambrisentan, tadalafil, and spironolactone, but continued to present to the Emergency Department periodically for syncopal episodes. In April 2024, he presented to the Medical University of South Carolina in cardiac arrest which began while playing outside. A complete autopsy was performed, including gross and microscopic examination of tissues and postmortem vitreous electrolyte analysis. Gross examination revealed the decedent’s heart was enlarged to 350 grams (normal mean for age = 181 grams). Both cardiac ventricles were dilated and the right ventricle was markedly hypertrophic with a thickness of 1.2 cm. Microscopic sections are pending but will presumptively show significant cardiac myocyte hypertrophy and pulmonary arteriole thickening. Cause of death is pending certification but is presumed to be sudden cardiac death resulting from BMPR2 mutation- related pulmonary hypertension. Results (if a Case Study enter NA) NA Conclusion This case highlights a common genetic presentation of pulmonary arterial hypertension, with approximately 80% of familial cases of pulmonary arterial hypertension harboring BMPR2 mutations. Further research should be done to investigate treatment options and management of this genetic presentation.