Characterization of the bone morphogenetic protein (BMP) system in human pulmonary arterial smooth muscle cells isolated from a sporadic case of primary pulmonary hypertension: roles of BMP type IB receptor (activin receptor-like kinase-6) in the mitotic action

Endothelin-1 Alters BMP Signaling to Promote Proliferation of Pulmonary Artery Smooth Muscle Cells

Pulmonary arterial hypertension (PAH) is characterized by abnormal outgrowth of pulmonary artery smooth muscle cells (PASMCs) of the media. Abundant expression of endothelin-1 (ET-1) and activated p38 mitogen-activated protein kinase (p38MAPK) has been observed in PAH patients. p38MAPK has been implicated in cell proliferation. An unspecified disturbance in bone morphogenetic protein (BMP) signaling may be involved in the development of PAH. Type I receptors (BMPR1A and BMPR1B) and type II receptors (BMPR2) transduce signals via two distinct pathways, i.e., canonical and non-canonical pathways, activating Smad1/5/8 and p38MAPK, respectively. BMPR1B expression was previously reported to be enhanced in the PASMCs of patients with idiopathic PAH. BMP15 binds specifically to BMPR1B. We assessed the effects of ET-1 on BMP receptor expression and cell proliferation. BMP2 increased BMPR1B expression in human PASMCs after pretreatment with ET-1 in vitro. Although BMP2 alone did not affect PASMC proliferation, BMP2 treatment after ET-1 pretreatment significantly accelerated PASMC proliferation. PH-797804, a selective p38MAPK inhibitor, abrogated this proliferation. Similarly, after ET-1 pretreatment, BMP15 significantly accelerated the proliferation of PASMCs, whereas stimulation with BMP15 alone did not. In conclusion, in PASMCs, ET-1 exposure under pathological conditions alters BMP signaling to activate p38MAPK, resulting in cell proliferation.

Identifying Potential Mutations Responsible for Cases of Pulmonary Arterial Hypertension

Pulmonary Arterial Hypertension (PAH) is a progressive and devastating disease for which there is an escalating body of genetic and related pathophysiological information on disease pathobiology. Nevertheless, the success to date in identifying susceptibility genes, genetic variants and epigenetic processes has been limited due to PAH clinical multi-faceted variations. A number of germline gene candidates have been proposed but demonstrating consistently the association with PAH has been problematic, at least partly due to the reduced penetrance and variable expressivity. Although the data for bone morphogenetic protein receptor type 2 (BMPR2) and related genes remains undoubtedly the most extensive, recent advanced gene sequencing technologies have facilitated the discovery of further gene candidates with mutations among those with and without familial forms of PAH. An in depth understanding of the multitude of biologic variations associated with PAH may provide novel opportunities for therapeutic intervention in the coming years. This knowledge will irrevocably provide the opportunity for improved patient and family counseling as well as improved PAH diagnosis, risk assessment, and personalized treatment.

Optogenetic Control of the BMP Signaling Pathway

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor β (TGFβ) superfamily and have crucial roles during development; including mesodermal patterning and specification of renal, hepatic, and skeletal tissues. In vitro developmental models currently rely upon costly and unreliable recombinant BMP proteins that do not enable dynamic or precise activation of the BMP signaling pathway. Here, we report the development of an optogenetic BMP signaling system (optoBMP) that enables rapid induction of the canonical BMP signaling pathway driven by illumination with blue light. We demonstrate the utility of the optoBMP system in multiple human cell lines to initiate signal transduction through phosphorylation and nuclear translocation of SMAD1/5, leading to upregulation of BMP target genes including Inhibitors of DNA binding ID2 and ID4. Furthermore, we demonstrate how the optoBMP system can be used to fine-tune activation of the BMP signaling pathway through variable light stimulation. Optogenetic control of BMP signaling will enable dynamic and high-throughput intervention across a variety of applications in cellular and developmental systems.

Common Genetic Variants on Bone Morphogenetic Protein Receptor Type IB (BMPR1B) Gene Are Predictive for Carotid Intima-Media Thickness

BACKGROUND

Bone morphogenetic proteins (BMP) 2 and 4 are implicated in the development of atherosclerosis. However, the relationships between the proteins, their main receptors and carotid intima-media thickness (cIMT), a predictive preclinical phenotype of atherosclerosis, have not been established. Methods and Results: We screened and validated the relationships of single-nucleotide polymorphisms (SNPs) on BMP2, BMP4, BMPR1A, BMPR1B, and BMPR2 with thicker cIMT by 2 independent case-control studies that used different subject selection methods. Among 200 screened SNPs, 12 on BMPR1B were regarded as candidate genetic markers (P-value <5.0×10^-4). After combining the discovery and validation studies and adjusting for traditional cardiovascular risk factors, rs4456963*G, rs4235438*T, rs2522530*T, and rs3796433*C showed significant higher odds ratios (ORs) of having thicker cIMT (adjusted ORs: 1.50-1.56; all P-values <2.5×10^-4). Multivariate analyses showed that rs4456963 and rs3796433 were significantly independent determinants of cIMT thickening. The corresponding multivariate-adjusted ORs for rs4456963*G and rs3796433*C alleles were 1.50 (95% confidence interval (CI): 1.22-1.84) and 1.50 (95% CI: 1.23-1.82), respectively. Interaction between rs4456963 and rs3796433 was evident by the significantly higher OR (8.16, 95% CI: 3.12-21.3) for subjects with the GG-CC genotype. The rs4456963*G and rs3796433*C showed positively linear trends with severity of carotid atherosclerosis.

CONCLUSIONS

We identified 2 SNPs on BMPR1B showing significantly independent correlations with thicker cIMT. The study provides invaluable evidence supporting that BMPR1B is closely related to carotid atherosclerosis and a potential target for the development of therapeutic agents for atherosclerotic disease.

Transforming growth factor-β stimulates Smad1/5 signaling in pulmonary artery smooth muscle cells and fibroblasts of the newborn mouse through ALK1

The intracellular signaling mechanisms through which TGF-β regulates pulmonary development are incompletely understood. Canonical TGF-β signaling involves Smad2/3 phosphorylation, Smad2/3·Smad4 complex formation and nuclear localization, and gene regulation. Here, we show that physiologically relevant TGF-β1 levels also stimulate Smad1/5 phosphorylation, which is typically a mediator of bone morphogenetic protein (BMP) signaling, in mouse pup pulmonary artery smooth muscle cells (mPASMC) and lung fibroblasts and other interstitial lung cell lines. This cross-talk mechanism likely has in vivo relevance because mixed Smad1/5/8·Smad2/3 complexes, which are indicative of TGF-β-stimulated Smad1/5 activation, were detected in the developing mouse lung using a proximity ligation assay. Although mixed Smad complexes have been shown not to transduce nuclear signaling, we determined that TGF-β stimulates nuclear localization of phosphorylated Smad1/5 and induces the expression of prototypical BMP-regulated genes in the mPASMC. Small-molecule kinase inhibitor studies suggested that TGF-β-regulated Smad1/5 phosphorylation in these cells is mediated by TGF-β-type I receptors, not BMP-type I receptors, but possibly the accessory activin-like kinase (ALK1) receptor. Although work by others suggested that ALK1 is expressed exclusively in endothelial cells in the vasculature, we detected ALK1 mRNA and protein expression in mPASMC in vitro and in mouse pup lungs. Moreover, using an antimurine ALK1 antibody and mPASMC, we determined that ALK1 regulates Smad1/5 phosphorylation by TGF-β. Together, these studies characterize an accessory TGF-β-stimulated BMP R-Smad signaling mechanism in interstitial cells of the developing lung. They also indicate the importance of considering alternate Smad pathways in studies directed at determining how TGF-β regulates newborn lung development.

The role of genetics in pulmonary arterial hypertension

Group 1 pulmonary hypertension or pulmonary arterial hypertension (PAH) is a rare disease characterized by proliferation and occlusion of small pulmonary arterioles, leading to progressive elevation of pulmonary artery pressure and pulmonary vascular resistance, and right ventricular failure. Historically, it has been associated with a high mortality rate, although, over the last decade, treatment has improved survival. PAH includes idiopathic PAH (IPAH), heritable PAH (HPAH), and PAH associated with certain medical conditions. The aetiology of PAH is heterogeneous, and genetics play an important role in some cases. Mutations in BMPR2, encoding bone morphogenetic protein receptor 2, a member of the transforming growth factor-β superfamily of receptors, have been identified in 70% of cases of HPAH, and in 10-40% of cases of IPAH. Other genetic causes of PAH include mutations in the genes encoding activin receptor-like type 1, endoglin, SMAD9, caveolin 1, and potassium two-pore-domain channel subfamily K member 3. Mutations in the gene encoding T-box 4 have been identified in 10-30% of paediatric PAH patients, but rarely in adults with PAH. PAH in children is much more heterogeneous than in adults, and can be associated with several genetic syndromes, congenital heart disease, pulmonary disease, and vascular disease. In addition to rare mutations as a monogenic cause of HPAH, common variants in the gene encoding cerebellin 2 increase the risk of PAH by approximately two-fold. A PAH panel of genes is available for clinical testing, and should be considered for use in clinical management, especially for patients with a family history of PAH. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

BMP4 increases the expression of TRPC and basal [Ca2+]i via the p38MAPK and ERK1/2 pathways independent of BMPRII in PASMCs

Multiple abnormalities of bone morphogenetic protein (BMPs) signaling are implicated in the process of pulmonary arterial hypertension (PAH). BMP4 plays an important role during the process of pulmonary arterial remodeling and mutant of the principle BMP4 receptor, BMP receptors II (BMPRII), is found to associate with the development of PAH. However, the likely mechanism defining the contribution of BMPRII to BMP4 mediated signaling in pulmonary arterial smooth muscle cells (PASMCs) remains comprehensively unclear. We previously found that enhanced store operated calcium entry (SOCE) and basal intracellular calcium concentration [Ca2+]i were induced by BMP4 via upregulation of TRPC1, 4 and 6 expression in PASMCs, and that BMP4 modulated TRPC channel expression through activating p38MAPK and ERK1/2 signaling pathways. In this study, BMPRII siRNA was used to knockdown BMPRII expression to investigate whether BMP4 upregulates the expression of TRPC and activating Smad1/5/8, ERK1/2 and p38MAPK pathway via BMPRII in distal PASMCs. Our results showed that knockdown of BMPRII: 1) attenuated BMP4 induced activation of P-Smad1/5/8, without altering BMP4 induced P-p38MAPK and P-ERK1/2 activation in PASMCs; 2) did not attenuate the BMP4-induced TRPC1, 4 and 6 expression; 3) did not affect BMP4-enhanced SOCE and basal [Ca2+]i. Thus, we concluded that BMP4 activated Smad1/5/8 pathway is BMPRII-dependent, while the BMP4 - ERK/p-P38 - TRPC - SOCE signaling axis are likely mediated through other receptor rather than BMPRII.

Whole-exome sequencing reveals TopBP1 as a novel gene in idiopathic pulmonary arterial hypertension

RATIONALE

Idiopathic pulmonary arterial hypertension (IPAH) is a life-threatening disorder characterized by progressive loss of pulmonary microvessels. Although mutations in the bone morphogenetic receptor 2 (BMPR2) are found in 80% of heritable and ∼15% of patients with IPAH, their low penetrance (∼20%) suggests that other unidentified genetic modifiers are required for manifestation of the disease phenotype. Use of whole-exome sequencing (WES) has recently led to the discovery of novel susceptibility genes in heritable PAH, but whether WES can also accelerate gene discovery in IPAH remains unknown.

OBJECTIVES

To determine whether WES can help identify novel gene modifiers in patients with IPAH.

METHODS

Exome capture and sequencing was performed on genomic DNA isolated from 12 unrelated patients with IPAH lacking BMPR2 mutations. Observed genetic variants were prioritized according to their pathogenic potential using ANNOVAR.

MEASUREMENTS AND MAIN RESULTS

A total of nine genes were identified as high-priority candidates. Our top hit was topoisomerase DNA binding II binding protein 1 (TopBP1), a gene involved in the response to DNA damage and replication stress. We found that TopBP1 expression was reduced in vascular lesions and pulmonary endothelial cells isolated from patients with IPAH. Although TopBP1 deficiency made endothelial cells susceptible to DNA damage and apoptosis in response to hydroxyurea, its restoration resulted in less DNA damage and improved cell survival.

CONCLUSIONS

WES led to the discovery of TopBP1, a gene whose deficiency may increase susceptibility to small vessel loss in IPAH. We predict that use of WES will help identify gene modifiers that influence an individual's risk of developing IPAH.

Downregulation of bone morphogenetic protein receptor axis during HIV-1 and cocaine-mediated pulmonary smooth muscle hyperplasia: implications for HIV-related pulmonary arterial hypertension

OBJECTIVE

Our previous findings support an additive effect of cocaine to HIV infection in the development of pulmonary arteriopathy through enhanced proliferation of human pulmonary smooth muscle cells. We now examined the role of antiproliferative bone morphogenetic protein receptor (BMPR) axis in HIV protein and cocaine-mediated pulmonary smooth muscle hyperplasia.

APPROACH AND RESULTS

Stimulation of BMPR axis resulted in attenuation of synergistic increase in the proliferation of human pulmonary arterial smooth muscle cells in response to cocaine and HIV protein, transactivator of transcription (Tat). Interestingly, an increase in mRNA but decrease in protein levels of BMPR with correlated decrease in the activation of Sma- and MAD-related family protein 1/5/8 and Id1 gene expression was observed on combined treatment with cocaine and Tat when compared with the untreated cells at all time points tested. Although longer exposure to either cocaine or Tat alone also resulted in a significant decrease in the BMPR protein expression, the abrogation on combined treatment was still significantly more when compared with that of the monotreatments. Significant increase in mRNA but downmodulation of BMPR protein expression was also observed in the lung extracts from HIV-infected intravenous drug users (HIV+IVDU) when compared with that from HIV-infected non-IVDUs (HIV) or uninfected IVDUs (IVDU). Furthermore, significant decrease in BMPR protein expression was also observed in HIV or IVDUs when compared with normal controls that correlated with in vitro findings on chronic exposure to cocaine or HIV protein alone.

CONCLUSIONS

Simultaneous exposure of pulmonary smooth muscle cells to viral protein(s) and cocaine exacerbates downregulation of BMPR axis that may result in enhanced pulmonary vasculature aberrations in HIV+IVDUs.

Pro-apoptotic effects of imatinib on PDGF-stimulated pulmonary artery smooth muscle cells from patients with idiopathic pulmonary arterial hypertension

BACKGROUND

Remodeling of the pulmonary artery by an inappropriate increase of pulmonary artery smooth muscle cells (PASMCs) is problematic in the treatment of idiopathic pulmonary arterial hypertension (IPAH). Effective treatment that achieves reverse remodeling is required. The aim of this study was to assess the pro-apoptotic effects of imatinib, a platelet-derived growth factor (PDGF)-receptor tyrosine kinase inhibitor, on PASMCs obtained from patients with IPAH.

METHODS

PASMCs were obtained from 8 patients with IPAH undergoing lung transplantation. Cellular proliferation was assessed by (3)H-thymidine incorporation. Pro-apoptotic effects of imatinib were examined using TUNEL and caspase-3,7 assays and using transmission electron microscopy.

RESULTS

Treatment with imatinib (0.1 to 10 μg/mL) significantly inhibited PDGF-BB (10 ng/mL)-induced proliferation of PASMCs from IPAH patients. Imatinib (1 μg/mL) did not induce apoptosis in quiescent IPAH-PASMCs, but it had a pro-apoptotic effect on IPAH-PASMCs stimulated with PDGF-BB. Imatinib did not induce apoptosis in normal control PASMCs with or without PDGF-BB stimulation. PDGF-BB induced phosphorylation of Akt at 15 min, and Akt phosphorylation was inhibited by imatinib in IPAH-PASMCs. Akt-I-1/2 (1 μmol/L), an Akt inhibitor, in the presence of PDGF-BB significantly increased apoptotic cells compared with the control condition. Thus, Akt-I-1/2 could mimic the effects of imatinib on PASMCs.

CONCLUSION

Imatinib has anti-proliferative and pro-apoptotic effects on IPAH-PASMCs stimulated with PDGF. The inhibitory effect of imatinib on Akt phosphorylation induced by PDGF plays an important role in the pro-apoptotic effect.

BMP signaling in vascular development and disease

Genetic and functional studies indicate that common components of the bone morphogenetic protein (BMP) signaling pathway play critical roles in regulating vascular development in the embryo and in promoting vascular homeostasis and disease in the adult. However, discrepancies between in vitro and in vivo findings and distinct functional properties of the BMP signaling pathway in different vascular beds, have led to controversies in the field that have been difficult to reconcile. This review attempts to clarify some of these issues by providing an up to date overview of the biology and genetics of BMP signaling relevant to the intact vasculature.

Inhibitory effects of simvastatin on platelet-derived growth factor signaling in pulmonary artery smooth muscle cells from patients with idiopathic pulmonary arterial hypertension

Idiopathic pulmonary arterial hypertension (IPAH) is a progressive disease characterized by inappropriate increase of pulmonary artery smooth muscle cells (PASMCs) leading to occlusion of pulmonary arterioles. Inhibition of platelet-derived growth factor (PDGF) signaling is starting to garner attention as a targeted therapy for IPAH. We assessed the inhibitory effects of simvastatin, a 3-hydroxy-3-methylglutanyl coenzyme A reductase inhibitor, on PDGF-induced proliferation and migration of PASMCs obtained from 6 patients with IPAH who underwent lung transplantation. PDGF stimulation caused a significantly higher growth rate of PASMCs from patients with IPAH than that of normal control PASMCs as assessed by (3)H-thymidine incorporation. Simvastatin (0.1 micromol/L) significantly inhibited PDGF-induced cell proliferation of PASMCs from patients with IPAH but did not inhibit proliferation of normal control cells at the same concentration. Western blot analysis revealed that simvastatin significantly increased the expression of cell cycle inhibitor p27. PDGF significantly increased the migration distance of IPAH-PASMCs compared with that of normal PASMCs, and simvastatin (1 micromol/L) significantly inhibited PDGF-induced migration. Immunofluorescence staining revealed that simvastatin (1 micromol/L) inhibited translocation of Rho A from the cytoplasm to membrane and disorganized actin fibers in PASMCs from patients with IPAH. In conclusion, simvastatin had inhibitory effects on inappropriate PDGF signaling in PASMCs from patients with IPAH.

Involvement of the bone morphogenetic protein system in endothelin- and aldosterone-induced cell proliferation of pulmonary arterial smooth muscle cells isolated from human patients with pulmonary arterial hypertension

Recent genetic studies have uncovered a link between familial and idiopathic pulmonary arterial hypertension (PAH) and germline mutations in the bone morphogenetic protein type-II receptor (BMPRII). The pathology of PAH is characterized by remodeling of the pulmonary arteries due to pulmonary artery smooth muscle cell (PASMC) hyperproliferation. Although increased endothelial injury and impaired suppression of PASMC proliferation are both critical for the cellular pathogenesis of PAH, a detailed molecular mechanism underlying PAH has yet to be elucidated. In the present study, we investigated the roles of the BMP system and other vasoactive factors associated with PAH (including endothelin (ET), angiotensin II (Ang II) and aldosterone) in the mitotic actions of PASMCs isolated from idiopathic and secondary PAH lungs. ET1 and aldosterone stimulated PASMC proliferation of idiopathic PAH more effectively than secondary PAH, whereas Ang II and ET3 failed to activate mitosis in either of the PASMC cell type. The effects of ET1 and aldosterone were blocked by bosentan, an ET type-A/B receptor (ETA/BR) antagonist, and eplerenone, a selective mineralocorticoid receptor (MR) blocker, respectively. Among the BMP ligands examined, BMP-2 and BMP-7, but not BMP-4 or BMP-6, significantly increased cell mitosis in both PASMC cell types. Notably, ET1- and aldosterone-induced mitosis and mitogen-activated protein kinase phosphorylation were significantly increased in the presence of BMP-2 and BMP-7 in PASMCs isolated from idiopathic PAH, although additive effects were not observed in PASMCs isolated from secondary PAH. Inhibition of extracellular signal-regulated kinase 1 (ERK1)/ERK2 signaling suppressed basal-, ET1- and aldosterone-induced PASMC mitosis more potently than that of stress-activated protein kinase/c-Jun NH2-terminal kinase inhibition. Given the fact that BMP-2 and BMP-7 upregulated ETA/BR and MR expression and that BMP-2 decreased 11betaHSD2 (11beta-hydroxysteroid dehydrogenase type 2) levels in PASMCs isolated from idiopathic PAH, BMPR-Smad signaling may have a key role in amplifying the ETA/BR and/or MR-ERK signaling in PASMCs of the PAH lung. Collectively, the functional link between BMP and ET and/or the MR system may be involved in the progress of PASMC mitosis, ultimately leading to the development of clinical PAH.

Multiple endocrine regulation by bone morphogenetic protein system

Bone morphogenetic proteins (BMPs) were originally identified with regard to their actions to regulate ectopic formation of bone and cartilage and early embryonic development. Subsequently, our research program has investigated a BMP system that exists in the mammalian ovary and plays roles in regulating numerous granulosa cell functions. BMP ligands including BMP-2, -4, -6, -7 and -15 were found to inhibit gondotropin-dependent progesterone synthesis by granulosa cells, which led to the hypothesis that BMPs are a physiological luteinization inhibitor in growing ovarian follicles during the follicular phase of the ovarian cycle. The physiological importance of the BMP system for normal mammalian reproduction has been further recognized by the discovery of aberrant reproductive phenotypes of female sheep and humans having mutated genes encoding BMP-15. Physiological roles of BMPs in the pituitary, hypothalamus, adrenal and other tissues have also been discovered. Here we discuss recent advances in the understanding of autocrine/paracrine actions of BMPs in the systemic regulation of endocrine function.

Bmp2 and Bmp4 exert opposing effects in hypoxic pulmonary hypertension

The bone morphogenetic protein (BMP) type 2 receptor ligand, Bmp2, is upregulated in the peripheral pulmonary vasculature during hypoxia-induced pulmonary hypertension (PH). This contrasts with the expression of Bmp4, which is expressed in respiratory epithelia throughout the lung. Unlike heterozygous null Bmp4 mice (Bmp4(LacZ/+)), which are protected from the development of hypoxic PH, mice that are heterozygous null for Bmp2 (Bmp2(+/-)) develop more severe hypoxic PH than their wild-type littermates. This is associated with reduced endothelial nitric oxide synthase (eNOS) expression and activity in the pulmonary vasculature of hypoxic Bmp2(+/-) but not Bmp4(LacZ/+) mutant mice. Furthermore, exogenous BMP2 upregulates eNOS expression and activity in intrapulmonary artery and pulmonary endothelial cell preparations, indicating that eNOS is a target of Bmp2 signaling in the pulmonary vasculature. Together, these data demonstrate that Bmp2 and Bmp4 exert opposing roles in hypoxic PH and suggest that the protective effects of Bmp2 are mediated by increasing eNOS expression and activity in the hypoxic pulmonary vasculature.

Prostate cancer cells modulate osteoblast mineralisation and osteoclast differentiation through Id-1

Background:

Id-1 is overexpressed in and correlated with metastatic potential of prostate cancer. The role of Id-1 in this metastatic process was further analysed.

Methods:

Conditioned media from prostate cancer cells, expressing various levels of Id-1, were used to stimulate pre-osteoclast differentiation and osteoblast mineralisation. Downstream effectors of Id-1 were identified. Expressions of Id-1 and its downstream effectors in prostate cancers were studied using immunohistochemistry in a prostate cancer patient cohort (N=110).

Results:

We found that conditioned media from LNCaP prostate cancer cells overexpressing Id-1 had a higher ability to drive osteoclast differentiation and a lower ability to stimulate osteoblast mineralisation than control, whereas conditioned media from PC3 prostate cancer cells with Id-1 knockdown were less able to stimulate osteoclast differentiation. Id-1 was found to negatively regulate TNF-β and this correlation was confirmed in human prostate cancer specimens (P=0.03). Furthermore, addition of recombinant TNF-β to LNCaP Id-1 cell-derived media blocked the effect of Id-1 overexpression on osteoblast mineralisation.

Conclusion:

In prostate cancer cells, the ability of Id-1 to modulate bone cell differentiation favouring metastatic bone disease is partially mediated by TNF-β, and Id-1 could be a potential therapeutic target for prostate cancer to bone metastasis.

Bone morphogenetic protein signalling in heritable versus idiopathic pulmonary hypertension

Mutations in the gene encoding bone morphogenetic protein (BMP) receptor type 2 (BMPR-2) have been reported in pulmonary arterial hypertension (PAH), but their functional relevance remains incompletely understood. BMP receptor expression was evaluated in human lungs and in cultured pulmonary artery smooth muscle cells (PASMCs) isolated from 19 idiopathic PAH patients and nine heritable PAH patients with demonstrated BMPR-2 mutations. BMP4-treated PASMCs were assessed for Smad and p38 mitogen-activated protein kinase (MAPK) signalling associated with mitosis and apoptosis. Lung tissue and PASMCs from heritable PAH patients presented with decreased BMPR-2 expression and variable increases in BMPR-1A and BMPR-1B expression, while a less important decreased BMPR-2 expression was observed in PASMCs from idiopathic PAH patients. Heritable PAH PASMCs showed no increased phosphorylation of Smad1/5/8 in the presence of BMP4, which actually activated the p38MAPK pathway. Individual responses varied from one mutation to another. PASMCs from PAH patients presented with an in vitro proliferative pattern, which could be inhibited by BMP4 in idiopathic PAH but not in heritable PAH. PASMCs from idiopathic PAH and more so from heritable PAH presented an inhibition of BMP4-induced apoptosis. Most heterogeneous BMPR-2 mutations are associated with defective Smad signalling compensated for by an activation of p38MAPK signalling, accounting for PASMC proliferation and deficient apoptosis.

Altered nano/micro-order elasticity of pulmonary artery smooth muscle cells of patients with idiopathic pulmonary arterial hypertension

BACKGROUND

Idiopathic pulmonary arterial hypertension (IPAH) is a disease characterized by progressively increased resistance of pulmonary arteries. In this study, we evaluated the mechanical property of single pulmonary artery smooth muscles cells (PASMC) from patients with IPAH and tested whether the PASMC showed abnormal response to a vasodilator by use of an atomic force microscope (AFM).

METHODS

PASMC were isolated and cultured from explanted lungs of 7 patients with IPAH (IPAH-PASMC). Normal vascular specimens from 3 patients with bronchogenic carcinoma were used as normal controls (normal PASMC). The nano/micro-order elasticity of five to ten living PASMC in each sample was measured by parabolic force curves of cantilever deflection/indentation obtained by using an AFM. The elasticity measurements were performed under control conditions and under condition of nitric oxide (NO) treatment (190 and 380 nmol/L).

RESULTS

There was no significant difference between nano/micro-order elasticity of normal PASMC and that of IPAH-PASMC under the control conditions. In normal PASMC, NO (190 and 380 nmol/L) significantly reduced (i.e., softened) the nano/micro-order elasticity. However, NO did not reduce elasticity in IPAH-PASMC, indicating higher vasodilator-resistive nano/micro-order rigidity in IPAH-PASMC.

CONCLUSION

Nano/micro-order elasticity change in PASMC in response to vasodilation induced by NO is reduced in patients with IPAH.

Increased susceptibility to hypoxic pulmonary hypertension in Bmpr2 mutant mice is associated with endothelial dysfunction in the pulmonary vasculature

Patients with familial pulmonary arterial hypertension inherit heterozygous mutations of the type 2 bone morphogenetic protein (BMP) receptor BMPR2. To explore the cellular mechanisms of this disease, we evaluated the pulmonary vascular responses to chronic hypoxia in mice carrying heterozygous hypomorphic Bmpr2 mutations (Bmpr2 delta Ex2/+). These mice develop more severe pulmonary hypertension after prolonged exposure to hypoxia without an associated increase in pulmonary vascular remodeling or proliferation compared with wild-type mice. This is associated with defective endothelial-dependent vasodilatation and enhanced vasoconstriction in isolated intrapulmonary artery preparations. In addition, there is a selective decrease in hypoxia-induced, BMP-dependent, endothelial nitric oxide synthase expression and Smad signaling in the intact lungs and in cultured pulmonary microvascular endothelial cells from Bmpr2 delta Ex2/+ mutant mice. These findings indicate that the pulmonary endothelium is a target of abnormal BMP signaling in Bmpr2 delta Ex2/+ mutant mice and suggest that endothelial dysfunction contributes to their increased susceptibility to hypoxic pulmonary hypertension.

Synergistic effects of Nell-1 and BMP-2 on the osteogenic differentiation of myoblasts

Osteogenesis is synergistically enhanced by the combined effect of complimentary factors. This study showed that Nell-1 and BMP-2 synergistically enhanced osteogenic differentiation of myoblasts and phosphorylated the JNK MAPK pathway. The findings are important because of the osteochondral specificity of Nell-1 signaling and the potential therapeutic effects of coordinated BMP-2 and Nell-1 delivery.

INTRODUCTION

BMPs play an important role in the migration and proliferation of mesenchymal cells and have a unique ability to alter the differentiation of mesenchymal cells toward chondrogenic and osteogenic lineages. Signaling upstream of Cbfa1/Runx2, BMPs effects are not limited to cells of the osteoblast lineage. Thus, additional osteoblast-specific factors that could synergize with BMP-2 would be advantageous for bone regeneration procedures. NELL-1 (NEL-like molecule-1; NEL [a protein strongly expressed in neural tissue encoding epidermal growth factor like domain]) is a novel growth factor believed to preferentially target cells committed to the osteochondral lineage.

MATERIALS AND METHODS

C2C12 myoblasts were transduced with AdLacZ, AdNell-1, AdBMP-2, or AdNell-1+AdBMP-2 overexpression viruses. Effects were studied by cell morphology, alkaline phosphatase activity, osteopontin production, and MAPK signaling. Additionally, in a nude mouse model, viruses were injected into leg muscles, and new bone formation was examined after 2 and 8 wk.

RESULTS

C2C12 myoblasts co-transduced with AdNell-1+AdBMP-2 showed a synergistic effect on osteogenic differentiation as detected by alkaline phosphatase activity and osteopontin production. Nell-1 stimulation on AdNell-1 + AdBMP-2 preconditioned C2C12 cells revealed significant activation of the non-BMP-2 associated c-Jun N-terminal kinase (JNK) MAPK signaling pathway, but not the p38 or extracellular signal-regulated kinase (ERK1/2) MAPK pathways. Importantly Nell-1 alone did not induce osteogenic differentiation of myoblasts. In a nude mouse model, injection of AdNell-1 alone stimulated no bone formation within muscle; however, injection of AdNell-1+AdBMP-2 stimulated a synergistic increase in bone formation compared with AdBMP-2 alone.

CONCLUSIONS

These findings are important because of the confirmed osteochondral specificity of Nell-1 signaling and the potential therapeutic effects of enhanced BMP-2 action with coordinated Nell-1 delivery.

Antagonistic effects of bone morphogenetic protein-4 and -7 on renal mesangial cell proliferation induced by aldosterone through MAPK activation

Aldosterone and angiotensin II (ANG II) contribute to the development and progression of renal damage. Here we investigated the effects of bone morphogenetic proteins (BMPs) on renal cell proliferation evoked by aldosterone and ANG II with mouse mesangial cells, which express mineralocorticoid receptors (MR), ANG II type 1 receptors, and BMP signaling molecules. Aldosterone and ANG II stimulated mesangial cell mitosis and activated ERK1/2 and SAPK/JNK signaling. These aldosterone effects were neutralized by the MR antagonist eplerenone and inhibition of transcription or translation, suggesting the involvement of genomic activation via MR. BMP-4 and BMP-7 stimulated Smad1, -5, -8 signaling more potently than BMP-2 and BMP-6, leading to suppression of mesangial cell mitosis and MR expression. MAPK inhibitors including U-0126 and SP-600125, but not SB-203580, suppressed aldosterone-induced cellular DNA synthesis, implying that ERK1/2 and SAPK/JNK pathways play crucial roles in mesangial cell proliferation. BMP-4 and BMP-7 inhibited phosphorylation of ERK1/2 and SAPK/JNK induced by aldosterone while activating p38 pathway, resulting in inhibition of aldosterone-induced cell mitosis. In contrast, aldosterone modulated the mesangial BMP system by decreasing expression of ALK-3, BMP-4, and BMP-7 while increasing inhibitory Smad6 expression. Thus novel functional cross talk between the mesangial BMP system and aldosterone signaling was uncovered, in which inhibition of MAPK signaling and MR expression by BMP-4 and BMP-7 may be involved in ameliorating renal damage due to mesangial proliferation caused by aldosterone.

Carvedilol inhibits proliferation of cultured pulmonary artery smooth muscle cells of patients with idiopathic pulmonary arterial hypertension

Idiopathic pulmonary arterial hypertension (IPAH) is associated with proliferation of smooth muscle cells (SMCs) in small pulmonary arteries. Inhibition of proliferation of pulmonary artery smooth muscle cells (PASMCs) may be an effective treatment of patients with idiopathic pulmonary arterial hypertension. Recent studies have shown that carvedilol, an alpha- and beta-blocker with antioxidant and calcium channel blocking properties, inhibits the proliferation of cultured normal human pulmonary artery smooth muscle cells. In this study, we tested the hypothesis that carvedilol has antiproliferative effects on pulmonary artery smooth muscle cells of patients with idiopathic pulmonary arterial hypertension. Pulmonary artery smooth muscle cells from six idiopathic pulmonary arterial hypertension patients who had undergone lung transplantation were cultured. To determine cell proliferation, H-thymidine incorporation was measured. Platelet-derived growth factor-induced proliferation of IPAH-PASMCs was significantly greater than that of normal control pulmonary artery smooth muscle cells. Carvedilol (0.1 microM to 10 microM) inhibited the proliferation of idiopathic pulmonary arterial hypertension-pulmonary artery smooth muscle cells in a concentration-dependent manner. Prazosin (an alpha-blocker) and N-acetyl L cysteine (an antioxidant agent) (0.1 microM to 10 microM) did not inhibit their proliferation, but the high concentration of propranolol (a beta-blocker) and nifedipine (a calcium channel blocker) (10 microM) inhibited the proliferation. The combination of propranolol and nifedipine inhibited the proliferation but only at a high concentration (10 microM) combination. Cell cycle analysis revealed that carvedilol (10 microM) significantly decreased the number of cells in S and G2/M phases. These results indicate that carvedilol inhibits the exaggerated proliferation of pulmonary artery smooth muscle cells of patients with idiopathic pulmonary arterial hypertension partially via its beta-blocking [corrected] and calcium channel blocking effects in vitro.

Bone morphogenetic protein-2 upregulates expression and function of voltage-gated K+ channels in human pulmonary artery smooth muscle cells

Activity of voltage-gated K(+) (K(V)) channels in pulmonary artery smooth muscle cells (PASMC) plays an important role in control of apoptosis and proliferation in addition to regulating membrane potential and pulmonary vascular tone. Bone morphogenetic proteins (BMPs) inhibit proliferation and induce apoptosis in normal human PASMC, whereas dysfunctional BMP signaling and downregulated K(V) channels are involved in pulmonary vascular medial hypertrophy associated with pulmonary hypertension. This study evaluated the effect of BMP-2 on K(V) channel function and expression in normal human PASMC. BMP-2 (100 nM for 18-24 h) significantly (>2-fold) upregulated mRNA expression of KCNA5, KCNA7, KCNA10, KCNC3, KCNC4, KCNF1, KCNG3, KCNS1, and KCNS3 but downregulated (at least 2-fold) KCNAB1, KCNA2, KCNG2, and KCNV2. The most dramatic change was the >10-fold downregulation of KCNG2 and KCNV2, two electrically silent gamma-subunits that form heterotetramers with functional K(V) channel alpha-subunits (e.g., KCNB1-2). Furthermore, the amplitude and current density of whole cell K(V) currents were significantly increased in PASMC treated with BMP-2. It has been demonstrated that K(+) currents generated by KCNB1 and KCNG1 (or KCNG2) or KCNB1 and KCNV2 heterotetramers are smaller than those generated by KCNB1 homotetramers, indicating that KCNG2 and KCNV2 (2 subunits that were markedly downregulated by BMP-2) are inhibitors of functional K(V) channels. These results suggest that BMP-2 divergently regulates mRNA expression of various K(V) channel alpha-, beta-, and gamma-subunits and significantly increases whole cell K(V) currents in human PASMC. Finally, we present evidence that attenuation of c-Myc expression by BMP-2 may be involved in BMP-2-mediated increase in K(V) channel activity and regulation of K(V) channel expression. The increased K(V) channel activity may be involved in the proapoptotic and/or antiproliferative effects of BMP-2 on PASMC.

Bone Morphogenic Protein-4 Induces Hypertension in Mice

Background— Recent in vitro studies have shown that disturbed flow and oxidative conditions induce the expression of bone morphogenic proteins (BMPs 2 and 4) in cultured endothelial cells. BMPs can stimulate superoxide production and inflammatory responses in endothelial cells, raising the possibility that BMPs may play a role in vascular diseases such as hypertension and atherosclerosis. In this study, we examined the hypothesis that BMP4 would induce hypertension in intact animals by increasing superoxide production from vascular nicotinamide adenine dinucleotide phosphate (NADPH) oxidases and an impairment of vasodilation responses.

Methods and Results— BMP4 infusion by osmotic pumps increased systolic blood pressure in a time- and dose-dependent manner in both C57BL/6 mice (from 101 to 125 mm Hg) and apolipoprotein E–null mice (from 107 to 146 mm Hg) after 4 weeks. Cotreatment with the BMP antagonist noggin or the NADPH oxidase inhibitor apocynin completely blocked the BMP4 effect. In addition, BMP4 infusion stimulated aortic NADPH oxidase activity and impaired vasorelaxation, both of which were prevented either by coinfusing noggin or by treating the isolated aortas with apocynin. BMP4, however, did not cause significant changes in maximum relaxation induced by the endothelium-independent vasodilator nitroglycerin. Remarkably, BMP4 infusion failed to stimulate aortic NADPH oxidases, increase blood pressure, and impair vasodilation responses in p47phox-deficient mice.

Conclusions— These results suggest that BMP4 infusion induces hypertension in mice in a vascular NADPH oxidase–dependent manner and the subsequent endothelial dysfunction. We suggest that BMP4 is a novel mediator of endothelial dysfunction and hypertension and that noggin and its analogs could be used as therapeutic agents for treating vascular diseases.

Bone morphogenetic protein 4: potential regulator of shear stress-induced graft neointimal atrophy

OBJECTIVE

Placement in baboons of a distal femoral arteriovenous fistula increases shear stress through aortoiliac polytetrafluoroethylene (PTFE) grafts and induces regression of a preformed neointima. Atrophy of the neointima might be controlled by shear stress-induced genes, including the bone morphogenetic proteins (BMPs). We have investigated the expression and function of BMPs 2, 4, and 5 in the graft neointima and in cultured baboon smooth muscle cells (SMCs).

METHODS

Baboons received bilateral aortoiliac PTFE grafts and 8 weeks later, a unilateral femoral arteriovenous fistula.

RESULTS

Quantitative polymerase chain reaction showed that high shear stress increased BMP2, 4, and 5 messenger RNA (mRNA) in graft intima between 1 and 7 days, while noggin (a BMP inhibitor) mRNA was decreased. BMP4 most potently (60% inhibition) inhibited platelet-derived growth factor-stimulated SMC proliferation compared with BMP2 and BMP5 (31% and 26%, respectively). BMP4 also increased SMC death by 190% +/- 10%. Noggin reversed the antiproliferative and proapoptotic effects of BMP4. Finally, Western blotting confirmed BMP4 protein upregulation by high shear stress at 4 days. BMP4 expression demonstrated by in situ hybridization was confined to endothelial cells.

CONCLUSIONS

Increased BMPs (particularly BMP4) coupled with decreased noggin may promote high shear stress-mediated graft neointimal atrophy by inhibiting SMC proliferation and increasing SMC death.

Regulatory roles of bone morphogenetic proteins and glucocorticoids in catecholamine production by rat pheochromocytoma cells

We here report a new physiological system that governs catecholamine synthesis involving bone morphogenetic proteins (BMPs) and activin in the rat pheochromocytoma cell line, PC12. BMP type I receptors, including activin receptor-like kinase-2 (ALK-2) (also referred to as ActRIA) and ALK-3 (BMPRIA), both type II receptors, ActRII and BMPRII, as well as the ligands BMP-2, -4, and -7 and inhibin/activin subunits were expressed in PC12 cells. PC12 cells predominantly secrete dopamine, whereas noradrenaline and adrenaline production is negligible. BMP-2, -4, -6, and -7 and activin A each suppressed dopamine and cAMP synthesis in a dose-dependent fashion. The BMP ligands also decreased 3,4-dihydroxyphenylalanine decarboxylase mRNA expression, whereas activin suppressed tyrosine hydroxylase expression. BMPs induced both Smad1/5/8 phosphorylation and Tlx2-Luc activation, whereas activin stimulated 3TP-Luc activity and p38 MAPK phosphorylation. ERK signaling was not affected by BMPs or activin. Dexamethasone enhanced catecholamine synthesis, accompanying increases in tyrosine hydroxylase and 3,4-dihydroxyphenylalanine decarboxylase transcription without cAMP accumulation. In the presence of dexamethasone, BMPs and activin failed to reduce dopamine as well as cAMP production. In addition, dexamethasone modulated mitotic suppression of PC12 induced by BMPs in a ligand-dependent manner. Furthermore, intracellular BMP signaling was markedly suppressed by dexamethasone treatment and the expression of ALK-2, ALK-3, and BMPRII was significantly inhibited by dexamethasone. Collectively, the endogenous BMP/activin system plays a key role in the regulation of catecholamine production. Controlling activity of the BMP system may be critical for glucocorticoid-induced catecholamine synthesis by adrenomedullar cells.

Prednisolone inhibits proliferation of cultured pulmonary artery smooth muscle cells of patients with idiopathic pulmonary arterial hypertension

BACKGROUND

Idiopathic pulmonary arterial hypertension (IPAH) is associated with proliferation of smooth muscle cells (SMCs) in small pulmonary arteries. There is no therapy that specifically inhibits SMC proliferation. Recent studies reported that prednisolone (PSL) inhibits the postangioplasty proliferation of SMCs in atherosclerotic arteries. In this study, we tested the hypothesis that PSL has antiproliferative effects on pulmonary artery SMCs of patients with IPAH.

METHODS AND RESULTS

Pulmonary artery SMCs were harvested from the pulmonary arteries of 6 patients with IPAH who underwent lung transplantation. Control SMCs were obtained from 5 patients with bronchogenic carcinoma who underwent lung lobectomy. After incubation in the presence of platelet-derived growth factor (PDGF), PSL was added at different concentrations and cell proliferation was assessed by 3H-thymidine incorporation. PSL (2x10(-4) and 2x10(-3) mol/L) significantly inhibited PDGF-stimulated proliferation (P<0.05) of SMCs from patients with IPAH but did not affect cell viability of SMCs, as confirmed by trypan blue staining. In cell cycle analysis using a microscope-based multiparameter laser scanning cytometer, PSL inhibited the progression of SMCs from G(0)/G1 to the S phase. This inhibition was associated with increased p27 expression level. PSL (2x10(-4) mol/L) also inhibited PDGF-induced SMC migration.

CONCLUSIONS

Our results indicate that PSL has an antiproliferative effect on cultured SMCs of pulmonary arteries from patients with IPAH and suggest that PSL may be potentially useful therapeutically in patients with IPAH.

Bone Morphogenetic Protein 4 Promotes Pulmonary Vascular Remodeling in Hypoxic Pulmonary Hypertension

We show that 1 of the type II bone morphogenetic protein (BMP) receptor ligands, BMP4, is widely expressed in the adult mouse lung and is upregulated in hypoxia-induced pulmonary hypertension (PH). Furthermore, heterozygous null Bmp4 lacZ/+ mice are protected from the development of hypoxia-induced PH, vascular smooth muscle cell proliferation, and vascular remodeling. This is associated with a reduction in hypoxia-induced Smad1/5/8 phosphorylation and Id1 expression in the pulmonary vasculature. In addition, pulmonary microvascular endothelial cells secrete BMP4 in response to hypoxia and promote proliferation and migration of vascular smooth muscle cells in a BMP4-dependent fashion. These findings indicate that BMP4 plays a dominant role in regulating BMP signaling in the hypoxic pulmonary vasculature and suggest that endothelium-derived BMP4 plays a direct, paracrine role in promoting smooth muscle proliferation and remodeling in hypoxic PH.

Bone Morphogenetic Protein (BMP) Type II Receptor Deletion Reveals BMP Ligand-specific Gain of Signaling in Pulmonary Artery Smooth Muscle Cells

Bone morphogenetic protein (BMP) ligands signal by binding the BMP type II receptor (BMPR2) or the activin type II receptors (ActRIIa and ActRIIb) in conjunction with type I receptors to activate SMADs 1, 5, and 8, as well as members of the mitogen-activated protein kinase family. Loss-of-function mutations in Bmpr2 have been implicated in tumorigenesis and in the etiology of primary pulmonary hypertension. Because several different type II receptors are known to recognize BMP ligands, the specific contribution of BMPR2 to BMP signaling is not defined. Here we report that the ablation of Bmpr2 in pulmonary artery smooth muscle cells, using an ex vivo conditional knock-out (Cre-lox) approach, as well as small interfering RNA specific for Bmpr2, does not abolish BMP signaling. Disruption of Bmpr2 leads to diminished signaling by BMP2 and BMP4 and augmented signaling by BMP6 and BMP7. Using small interfering RNAs to inhibit the expression of other BMP receptors, we found that wild-type cells transduce BMP signals via BMPR2, whereas BMPR2-deficient cells transduce BMP signals via ActRIIa in conjunction with a set of type I receptors distinct from those utilized by BMPR2. These findings suggest that disruption of Bmpr2 leads to the net gain of signaling by some, but not all, BMP ligands via the activation of ActRIIa.

Functional roles of the bone morphogenetic protein system in thyrotropin signaling in porcine thyroid cells

We uncovered a new regulation of thyrocyte function by bone morphogenetic protein (BMP) under the influence of thyrotropin (TSH) using primary culture of porcine thyrocytes. The BMP type I receptors, ALK-2 (ActRIA), -3 (BMPRIA), and -6 (BMPRIB), were expressed in porcine thyrocytes, while ALK-6 was not detected in human thyroid. Treatment with BMP-2, -4, -6, -7, and TGF-beta1 exhibited a dose-dependent suppression of DNA synthesis by porcine thyrocytes. BMP-2, -4, -6, -7, and TGF-beta1 suppressed TSH receptor mRNA expression on thyrocytes, which was consistent with their suppressive effect on TSH-induced cAMP synthesis and TSH-induced insulin-like growth factor-1 expression. Activin exhibited minimal suppression of thyrocyte DNA synthesis and did not exhibit suppressive effects on TSH receptor mRNA expression. Phosphorylated Smad1/5/8 was detected in the lysates of porcine thyrocytes treated with BMP-2, -4, -6, and -7. However, in the presence of TSH, BMP-6 and -7 failed to activate Smad1/5/8 phosphorylation and 3TP-reporter activity, whereas BMP-2 and -4 maintained clear activation of the BMP signaling regardless of the presence of TSH. This diverged regulation of thyroid BMP system by TSH is most likely due to the reduction of ALK-6 expression caused by TSH. Thus, the thyroid BMP system is functionally linked to TSH actions through modulating TSH receptor expression and TSH, in turn, selectively inhibits BMP signaling. Given that BMP system is present in human thyroid and the expression pattern of ALK-2 and BMPRII is different between follicular adenomas and normal thyroid tissues, the endogenous BMP system may be involved in regulating thyrocyte growth and TSH sensitivity of human thyroid adenomas.