Bone morphogenetic proteins, genetics and the pathophysiology of primary pulmonary hypertension

Total flavonoids of rhizoma drynariae ameliorates bone formation and mineralization in BMP-Smad signaling pathway induced large tibial defect rats

Osteogenesis and angiogenesis acts as an essential role in repairing large tibial defects (LTDs). Total flavonoids of rhizoma drynariae (TFRD), a traditional Chinese medicinal herb, is reported to show anabolic effects on fracture healing. However, whether TFRD could improve the bone formation and angiogenesis in LTDs remains unknown. The purpose of this study was to evaluate the effect of TFRD on bone formation and angiogenesis in LTDs in distraction osteogenesis (DO). Using a previously established fracture model, LTD rats was established with circular external fixator (CEF). All rats then randomly divided into TFRD low dosage group (with DO), TFRD medium dosage group (with DO), TFRD high dosage group (with DO), model group (with DO) and blank group (without DO). Twelve weeks after treatment, according to X-ray and Micro-CT, TFRD groups (especially in medium dosage group) can significantly promote the formation of a large number of epiphyses and improve new bone mineralization compared with model group, and the results of HE and Masson staining and in vitro ALP level of BMSC also demonstrated the formation of bone matrix and mineralization in the TFRD groups. Also, angiographic imaging suggested that total flavonoids of TFRD was able to promote angiogenesis in the defect area. Consistently, TFRD significantly increased the levels of BMP-2, SMAD1, SMAD4, RUNX-2, OSX and VEGF in LTD rats based on ELISA and Real-Time PCR. In addition, we found that ALP activity of TFRD medium dosage group reached a peak after 10 days of induction through BMSC cell culture in vitro experiment. TFRD promoted bone formation in LTD through activation of BMP-Smad signaling pathway, which provides a promising new strategy for repairing bone defects in DO surgeries.

Role of SMURF1 ubiquitin ligase in BMP receptor trafficking and signaling

Heterozygous germline mutations in the bone morphogenetic protein type II receptor gene (BMPRII) are associated with hereditary pulmonary arterial hypertension (HPAH). Missense mutations, both in the extracellular ligand-binding and cytoplasmic kinase domains, mostly involve substitution of conserved Cys residues. Singular substitution at any of those Cys residues causes cytoplasmic, perinuclear localization of BMPR with reduced cell surface expression and BMP signaling. The present study examined the effect of Cys residue substitution on BMPR endocytic trafficking and lysosome degradation. We demonstrate that endocytosis/lysosomal degradation of BMPR occurs by two distinct pathways. SMURF1 ubiquitin ligase induces lysosomal degradation of BMPR, while ligase-inactive SMURF1 maintains BMPR protein level and cell surface expression. Substitution of BMPR Cys residues increases lysosomal degradation which is blocked by ligase-inactive SMURF1, elevating protein levels of Cys-substituted BMPRs. Expression of Cys-substituted BMPR suppresses basal BMP signaling activity which is also up-regulated by ligase-inactive SMURF1. Cys-residue substitution thus appears to cause BMPR endocytosis to lysosomes in a SMURF1 ubiquitin ligase-associated pathway. Kinase-activated BMPR undergoes endocytic/lysosomal degradation by a pathway with certain unique properties. Therefore, our results describe a novel mechanism whereby SMURF1 ubiquitin ligase regulates constitutive endocytosis of BMPR which may be mediated by its conserved Cys residues.

Effect of Total Flavonoids of Rhizoma drynariae on Tibial Dyschondroplasia by Regulating BMP-2 and Runx2 Expression in Chickens

Tibial dyschondroplasia (TD) is an abnormality of the growth cartilage that occurs in chickens and other rapidly growing avian species. This disease not only cause huge economic losses, but also greatly affects animal welfare. The total flavonoids of Rhizoma drynariae (TFRD) has been used to cure wide variety of diseases including bone fractures and osteoarthritis and osteoporosis. However, less information is available about the using of TFRD against the TD. The aim of this study was to determine the effect of TFRD on TD by regulating BMP-2 and Runx2 in chickens. A total of 200 birds were randomly divided into control, TD, TD recovery (TDR), and TFRD groups. All the groups were given standard diet with an addition of thiram (50 mg/kg) from days 3 to 7 in TD, TDR, and TFRD groups in order to induce TD in chickens. After the induction of TD, the birds of TFRD group were fed standard diet with the addition of TFRD at 20 mg/kg. Clinical results conveyed that TFRD can improve the growth performance of the TD chickens and recover normal activity, and it is more obvious than TDR. Gene expressions of BMP-2 and Runx2 were down-regulated during the development of the disease and were up-regulated obviously after TFRD treatment. In conclusion, TFRD not only decreased the mortality rate but also increased the growth performance of TD in chickens. In conclusion, TFRD plays important role in improving the growth performance, adjusting the relevant physiological indicators, and regulating BMP-2 and Runx2 in chickens.

Aucubin suppresses Titanium particles‑mediated apoptosis of MC3T3‑E1 cells and facilitates osteogenesis by affecting the BMP2/Smads/RunX2 signaling pathway

Aucubin represents an iridoid glucoside separated from multiple Chinese herbs, which has been demonstrated to possess numerous pharmacological activities. In the present study, the aim was to investigate the roles and mechanisms of aucubin in the suppression of mouse MC3T3-E1 osteoblast apoptosis induced by Titanium particles and the promotion of bone formation. MTT assay and flow cytometry were performed to analyze cell viability and apoptosis, respectively. ELISA and para-nitrophenyl phosphate colorimetry were carried out to evaluate the oxidative stress markers and alkaline phosphatase (ALP). Western blotting and reverse transcription-quantitative polymerase chain reaction assays were used to evaluate the associated mRNA and protein expression. The results revealed that aucubin enhanced the cell activity of MC3T3-E1 cells treated with Ti particles. Aucubin suppressed the apoptosis of Ti particles-induced MC3T3-E1 cells and facilitated osteogenesis by affecting the B-cell lymphoma-2 (Bcl-2), Bcl-2 associated X protein, ALP and associated osteogenic factors expression. Aucubin reduced the oxidative stress in Ti particles-induced MC3T3-E1 cells. In addition, aucubin upregulated the bone morphogenetic protein 2 (BMP2)/Smads/runt related transcription factor 2 (RunX2) pathway in Ti particles-induced MC3T3-E1 cells. In conclusion, the present study confirmed that aucubin suppressed the Ti particles-mediated apoptosis of MC3T3-E1 cells and facilitated osteogenesis by affecting the BMP2/Smads/RunX2 signaling pathway.

Baicalein attenuates monocrotaline-induced pulmonary arterial hypertension by inhibiting endothelial-to-mesenchymal transition

AIMS

Endothelial-to-mesenchymal transition (EndoMT) was shown to lead to endothelial cell (EC) dysfunction in pulmonary arterial hypertension (PAH). Baicalein was reported to inhibit epithelial-to-mesenchymal transition (EMT), a biological process that has many regulatory pathways in common with EndoMT. Whether it can attenuate PAH by inhibiting EndoMT remains obscure.

MAIN METHODS

PAH was induced by a single subcutaneous injection of MCT (60 mg/kg) in male Sprague Dawley rats. Two weeks after MCT administration, the rats in the treatment groups received baicalein orally (50 or 100 mg/kg/day) for an additional 2 weeks. Hemodynamic changes and right ventricular hypertrophy (RVH) were evaluated on day 28. Cardiopulmonary interstitial fibrosis was detected using Masson's trichrome, Picrosirius-red, and immunohistochemical staining. The reactivity of pulmonary arteries (PAs) was examined ex vivo. The protein expresson of EndoMT molecules, bone morphogenetic protein receptor 2 (BMPR2), and nuclear factor-κB (NF-κB) was examined to explore the mechanism of protective action of baicalein.

KEY FINDINGS

Baicalein (50 and 100 mg/kg) significantly alleviated MCT-induced PAH and cardiopulmonary interstitial fibrosis. Furthermore, baicalein treatment enhanced PA responsiveness to acetylcholine (ACh) in PAH rats. The upregulation of EndoMT molecules (N-cadherin, vimentin, Snail, and Slug) strongly suggest that EndoMT participates in MCT-induced PAH, which was reversed by baicalein (50 and 100 mg/kg) treatment. Moreover, baicalein partially reversed MCT-induced reductions in BMPR2 and NF-κB activation in the PAs.

SIGNIFICANCE

Baicalein attenuated MCT-induced PAH in rats by inhibiting EndoMT partially via the NF-κB-BMPR2 pathway. Thus, baicalein might be considered as a promising treatment option for PAH.

TGF-β1 inhibits the apoptosis of pulmonary arterial smooth muscle cells and contributes to pulmonary vascular medial thickening via the PI3K/Akt pathway

Previous studies have highlighted that the transforming growth factor‑β1 (TGF‑β1) pathway may be activated by hypoxic conditions. TGF‑β1 also participates in the regulation of proliferation, differentiation, migration and apoptosis of various cell types. Furthermore, TGF‑β1 has been reported to participate in the regulation of the progression of pulmonary arterial hypertension (PAH). However, the effect of TGF‑β1 on pulmonary arterial smooth muscle cells (PASMCs) and the corresponding molecular mechanisms remain unclear. The present study aimed to determine whether TGF‑β1 protects against cell apoptosis in PASMCs, and identify the underlying molecular mechanisms. Western blotting, MTT and lactate dehydrogenase activity assays were performed, and the activity of caspase‑3 and caspase‑9 was detected in order to investigate the hypothesis. It was determined that TGF‑β1 may facilitate cell growth in a dose‑dependent manner in serum‑starved PASMCs. Furthermore, it was observed that apoptosis in serum‑starved PASMCs was inhibited by TGF‑β1 via regulation of the expression levels of mitochondrial membrane proteins. Additionally, the phosphatidylinositol 3‑kinase/protein kinase B (PI3K/Akt) pathway was found to be activated by TGF‑β1 in PASMCs, while the inhibition of PI3K/Akt signaling also prevented the apoptosis‑limiting effects of TGF‑β1. These observations suggest that TGF‑β1 protects PASMCs from apoptosis and contributes to pulmonary vascular medial thickening via the PI3K/Akt pathway.

Hepatic Shunting of Eggs and Pulmonary Vascular Remodeling in Bmpr2(+/-) Mice with Schistosomiasis

RATIONALE

Schistosomiasis is a major cause of pulmonary arterial hypertension (PAH). Mutations in the bone morphogenetic protein type-II receptor (BMPR-II) are the commonest genetic cause of PAH.

OBJECTIVES

To determine whether Bmpr2(+/-) mice are more susceptible to schistosomiasis-induced pulmonary vascular remodeling.

METHODS

Wild-type (WT) and Bmpr2(+/-) mice were infected percutaneously with Schistosoma mansoni. At 17 weeks postinfection, right ventricular systolic pressure and liver and lung egg counts were measured. Serum, lung and liver cytokine, pulmonary vascular remodeling, and liver histology were assessed.

MEASUREMENTS AND MAIN RESULTS

By 17 weeks postinfection, there was a significant increase in pulmonary vascular remodeling in infected mice. This was greater in Bmpr2(+/-) mice and was associated with an increase in egg deposition and cytokine expression, which induced pulmonary arterial smooth muscle cell proliferation, in the lungs of these mice. Interestingly, Bmpr2(+/-) mice demonstrated dilatation of the hepatic central vein at baseline and postinfection, compared with WT. Bmpr2(+/-) mice also showed significant dilatation of the liver sinusoids and an increase in inflammatory cells surrounding the central hepatic vein, compared with WT. This is consistent with an increase in the transhepatic passage of eggs.

CONCLUSIONS

This study has shown that levels of BMPR-II expression modify the pulmonary vascular response to chronic schistosomiasis. The likely mechanism involves the increased passage of eggs to the lungs, caused by altered diameter of the hepatic veins and sinusoids in Bmpr2(+/-) mice. Genetically determined differences in the remodeling of hepatic vessels may represent a new risk factor for PAH associated with schistosomiasis.

Functional changes in pulmonary arterial endothelial cells associated with BMPR2 mutations

Pulmonary arterial hypertension (PAH) is a devastating disease characterized by abnormal remodeling of small, peripheral pulmonary arteries. Germline mutations in the bone morphogenetic protein receptor type 2 (BMPR2) gene are a major risk factor for developing PAH. At present, the correlation between the BMPR2 mutation and the patient's prognosis remains controversial despite several investigations. In this study, we explored the functional effects of four BMPR2 mutations to dissect the functional significance of the BMPR2 gene defect. Cellular immunofluorescence assay of four mutants (Tyr67Cys, Thr268fs, Ser863Asn, and Gln433X) revealed that the BMPR2 protein containing Thr268fs, Ser863Asn, or Gln433X exhibited abnormal subcellular localization. The BrdU incorporation and TUNEL assay suggested that any of the BMPR2 mutations Thr268fs, Ser863Asn, or Gln433X could improve endothelial cell apoptosis and decrease cell proliferation. All of the four mutants could inhibit nitric oxide (NO) synthesis in HLMVE cells, and ET-1 levels increased in the cells transfected with mutant Ser863Asn. Our results will improve the understanding of the genotype-phenotype correlations and mechanisms associated with BMPR2 mutations.

BMP4 protects rat pulmonary arterial smooth muscle cells from apoptosis by PI3K/AKT/Smad1/5/8 signaling

Bone morphogenetic protein-4 (BMP4), a member of the transforming growth factor β (TGF-β) family of growth factors, is activated and increased under hypoxic conditions, which plays an important role in the progression of pulmonary arterial hypertension (PAH). Previous studies have shown that BMP4 is involved in the regulation of proliferation, differentiation, migration and apoptosis of various cell types. However, the precise mechanisms involved in the regulation of pulmonary artery smooth muscle cells (PASMCs) in PAH are still incompletely understood. It has been reported that AKT is a critical regulator of cell survival and vascular remodeling. Therefore, there may be crosstalk between BMP4 anti-apoptotic processes and PI3K/AKT survival effect in rat PASMCs. To test this hypothesis, we performed confocal, cell viability measurement, mitochondrial potential, real-time polymerase chain reaction (PCR), and Western blot analysis to determine the role of BMP4 on cell survival and apoptosis. We found that hypoxia up-regulated the expression of BMP4. BMP4 promoted cell survival, reduced mitochondrial depolarization, and increased the expression of Bcl-2 and procaspase-3 in PASMCs under serum-deprived condition. These effects were reversed by PI3K/AKT inhibitors (LY294002 and wortmannin). Thus, these findings indicate that BMP4 protects PASMCs from apoptosis at least in part, mediated via the PI3K/AKT pathway.

Heritable forms of pulmonary arterial hypertension

Tremendous progress has been made in understanding the genetics of heritable pulmonary arterial hypertension (HPAH) since its description in the 1950s. Germline mutations in the gene coding bone morphogenetic receptor type 2 (BMPR2) are detectable in the majority of cases of HPAH, and in a small proportion of cases of idiopathic pulmonary arterial hypertension (IPAH). Recent advancements in gene sequencing methods have facilitated the discovery of additional genes with mutations among those with and without familial PAH (CAV1, KCNK3). HPAH is an autosomal dominant disease characterized by reduced penetrance, variable expressivity, and female predominance. These characteristics suggest that genetic and nongenetic factors modify disease expression, highlighting areas of active investigation. The reduced penetrance makes genetic counseling complex, as the majority of carriers of PAH-related mutations will never be diagnosed with the disease. This issue is increasingly important, as clinical testing for BMPR2 and other mutations is now available for the evaluation of patients and their at-risk kin. The possibilities to avoid mutation transmission, such as the rapidly advancing field of preimplantation genetic testing, highlight the need for all clinicians to understand the genetic features of PAH risk.

Pulmonary arterial hypertension (ascites syndrome) in broilers: a review

Pulmonary arterial hypertension (PAH) syndrome in broilers (also known as ascites syndrome and pulmonary hypertension syndrome) can be attributed to imbalances between cardiac output and the anatomical capacity of the pulmonary vasculature to accommodate ever-increasing rates of blood flow, as well as to an inappropriately elevated tone (degree of constriction) maintained by the pulmonary arterioles. Comparisons of PAH-susceptible and PAH-resistant broilers do not consistently reveal differences in cardiac output, but PAH-susceptible broilers consistently have higher pulmonary arterial pressures and pulmonary vascular resistances compared with PAH-resistant broilers. Efforts clarify the causes of excessive pulmonary vascular resistance have focused on evaluating the roles of chemical mediators of vasoconstriction and vasodilation, as well as on pathological (structural) changes occurring within the pulmonary arterioles (e.g., vascular remodeling and pathology) during the pathogenesis of PAH. The objectives of this review are to (1) summarize the pathophysiological progression initiated by the onset of pulmonary hypertension and culminating in terminal ascites; (2) review recent information regarding the factors contributing to excessively elevated resistance to blood flow through the lungs; (3) assess the role of the immune system during the pathogenesis of PAH; and (4) present new insights into the genetic basis of PAH. The cumulative evidence attributes the elevated pulmonary vascular resistance in PAH-susceptible broilers to an anatomically inadequate pulmonary vascular capacity, to excessive vascular tone reflecting the dominance of pulmonary vasoconstrictors over vasodilators, and to vascular pathology elicited by excessive hemodynamic stress. Emerging evidence also demonstrates that the pathogenesis of PAH includes characteristics of an inflammatory/autoimmune disease involving multifactorial genetic, environmental, and immune system components. Pulmonary arterial hypertension susceptibility appears to be multigenic and may be manifested in aberrant stress sensitivity, function, and regulation of pulmonary vascular tissue components, as well as aberrant activities of innate and adaptive immune system components. Major genetic influences and high heritabilities for PAH susceptibility have been demonstrated by numerous investigators. Selection pressures rigorously focused to challenge the pulmonary vascular capacity readily expose the genetic basis for spontaneous PAH in broilers. Chromosomal mapping continues to identify regions associated with ascites susceptibility, and candidate genes have been identified. Ongoing immunological and genomic investigations are likely to continue generating important new knowledge regarding the fundamental biological bases for the PAH/ascites syndrome.

Epigenetic regulation of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is diagnosed as a sustained elevation of pulmonary arterial pressure to more than 25 mm Hg at rest or to more than 30 mm Hg with exercise. PAH is an intrinsic disease of the pulmonary vascular smooth muscle and endothelial cells in association with plexiform lesions, medial thickening, concentric laminar intimal fibrosis and thrombotic lesions. Pulmonary vascular remodeling is the characteristic pathological change of PAH. The pathogenesis of PAH has been studied at the level of smooth muscle and endothelial cells. Existing research does not adequately explain susceptibility to the disease, and recent evidence reveals that epigenetic alterations may be involved in PAH. Epigenetics refers to all heritable changes in phenotype or in gene expression states, including chromatin remodeling, DNA methylation, histone modification and RNA interference, which are not involved in the DNA sequence itself. This review will focus on recent advances in epigenetics related to PAH, including epigenetic changes of superoxide dismutase, endothelial nitric oxide synthase and the bone morphogenetic protein signaling pathway. This will provide new insight for improved treatment and prevention of PAH. Future work aimed at specific epigenetic treatments may prove to be an effective therapy for patients with PAH.

Trapping of BMP receptors in distinct membrane domains inhibits their function in pulmonary arterial hypertension

Bone morphogenetic proteins (BMPs) are pleiotrophic growth factors that influence diverse processes such as skeletal development, hematopoiesis, and neurogenesis. They play crucial roles in diseases such as pulmonary arterial hypertension (PAH). In PAH, mutants of the BMP type II receptors (BMPR2) were detected, and their functions were impaired during BMP signaling. It is thought that expression levels of these receptors determine the fate of BMP signaling, with low levels of expression leading to decreased Smad activation in PAH. However, our studies demonstrate, for the first time, that the localization of receptors on the plasma membrane, in this case BMPR2, was misdirected. Three BMPR2 mutants, D485G, N519K, and R899X, which are known to be involved in PAH, were chosen as our model system. Our results show that all three BMPR2 mutants decreased BMP-dependent Smad phosphorylation and Smad signaling. Although the three mutants reached the cell membrane and their expression was lower than that of BMPR2, they formed smaller clusters and associated differently with membrane domains, such as caveolae and clathrin-coated pits. The disruption of these domains restored the Smad signaling of D485G and N519K to the level of wild-type BMPR2, showing that these mutants were trapped in the domains, rather than just expressed at a lower level on the surface. Therefore, new treatment options for PAH should also target receptor localization, rather than just expression level.

Smad3-mediated myocardin silencing: a novel mechanism governing the initiation of smooth muscle differentiation

Both TGF-β and myocardin (MYOCD) are important for smooth muscle cell (SMC) differentiation, but their precise role in regulating the initiation of SMC development is less clear. In TGF-β-induced SMC differentiation of pluripotent C3H10T1/2 progenitors, we found that TGF-β did not significantly induce Myocd mRNA expression until 18 h of stimulation. On the other hand, early SMC markers such as SM α-actin, SM22α, and SM calponin were detectable beginning 2 or 4 h after TGF-β treatment. These results suggest that Myocd expression is blocked during the initiation of TGF-β-induced SMC differentiation. Consistent with its endogenous expression, Myocd promoter activity was not elevated until 18 h following TGF-β stimulation. Surprisingly, Smad signaling was inhibitory to Myocd expression because blockade of Smad signaling enhanced Myocd promoter activity. Overexpression of Smad3, but not Smad2, inhibited Myocd promoter activity. Conversely, shRNA knockdown of Smad3 allowed TGF-β to activate the Myocd promoter in the initial phase of induction. Myocd was activated by PI3 kinase signaling and its downstream target Nkx2.5. Interestingly, Smad3 did not affect PI3 kinase activity. However, Smad3 physically interacted with Nkx2.5. This interaction blocked Nkx2.5 binding to the Myocd promoter in the early stage of TGF-β induction, leading to inhibition of Myocd mRNA expression. Moreover, Smad3 inhibited Nkx2.5-activated Myocd promoter activity in a dose-dependent manner. Taken together, our results reveal a novel mechanism for Smad3-mediated inhibition of Myocd in the initiation phase of SMC differentiation.

Smurf1 ubiquitin ligase causes downregulation of BMP receptors and is induced in monocrotaline and hypoxia models of pulmonary arterial hypertension

Reduced bone morphogenetic protein (BMP) receptor (BMPR) expression and BMP signaling have been implicated in vascular cell proliferation and remodeling associated with pulmonary arterial hypertension (PAH). The low penetrance of the BMPR II disease gene in familial PAH suggests that additional genetic or environmental factors are involved in clinical manifestation of PAH. Smurf1 ubiquitin ligase, together with inhibitory SMAD 6/7, forms a negative feedback loop for the attenuation of BMP signals by downregulating BMPR and signaling molecules and, in addition, functions in the integration of MAPK/Ras mitogenic pathways. The present study found that Smurf1 was significantly elevated in pulmonary arteries of monocrotaline and hypoxia-induced PAH rats. In the pulmonary artery of hypoxia-exposed mice, elevation of Smurf1 and SMAD7 was correlated with reduced expression of BMPR II protein. Over-expression of Smurf1 in cultured cells induced ubiquitination and degradation of BMPR I and II whereas ligase-inactive Smurf1 reduced ubiquitination and elevated their protein levels, thus serving a dominant-negative function. Smurf1-induced receptor degradation was inhibited by both proteasomal and lysosomal inhibitors. Thus, Smurf1 reduces steady-state levels of BMPRs by ubiquitination and subsequent degradation involving proteasomes and lysosomes. Therefore, these results show that Smurf1 induction could be a key event for triggering downregulation of BMP signaling and causing vascular cell proliferation and remodeling in PAH and that abrogating Smurf1 function could be a strategy for PAH therapeutics.

Microtubule stabilization by bone morphogenetic protein receptor-mediated scaffolding of c-Jun N-terminal kinase promotes dendrite formation

Neuronal outgrowth occurs via coordinated remodeling of the cytoskeleton involving both actin and microtubules. Microtubule stabilization drives the extending neurite, yet little is known of the molecular mechanisms whereby extracellular cues regulate microtubule dynamics. Bone morphogenetic proteins (BMPs) play an important role in neuronal differentiation and morphogenesis, and BMP7 in particular induces the formation of dendrites. Here, we show that BMP7 induces stabilization of microtubules in both a MAP2-dependent neuronal cell culture model and in dendrites of primary cortical neurons. BMP7 rapidly activates c-Jun N-terminal kinases (JNKs), known regulators of microtubule dynamics, and we show that JNKs associate with the carboxy terminus of the BMP receptor, BMPRII. Activation and binding of JNKs to BMPRII is required for BMP7-induced microtubule stabilization and for BMP7-mediated dendrite formation in primary cortical neurons. These data indicate that BMPRII acts as a scaffold to localize and coordinate cytoskeletal remodeling and thereby provides an efficient means for extracellular cues, such as BMPs, to control neuronal dendritogenesis.

Genetics of pulmonary arterial hypertension

Tremendous progress has been made in understanding the genetics of hereditable pulmonary arterial hypertension (HPAH) since its description in the 1950s. Germline mutations in the gene coding bone morphogenetic receptor type 2 ( BMPR2) are detectable in the majority of cases of HPAH, and in a small proportion of cases of idiopathic pulmonary arterial hypertension (IPAH). HPAH is an autosomal dominant disease characterized by reduced penetrance, variable expressivity, female predominance, and genetic anticipation. These characteristics suggest that endogenous and exogenous factors modify disease expression and areas of emphasis for future investigation. The variable clinical expression makes genetic counseling complex because the majority of carriers of a BMPR2 mutation will not be diagnosed with the disease. This issue will become increasingly important, as clinical testing for BMPR2 mutations is now available for the evaluation of patients and family members with HPAH and IPAH.

Serotonin induces Rho/ROCK-dependent activation of Smads 1/5/8 in pulmonary artery smooth muscle cells

Serotonin (5-HT) stimulates pulmonary artery smooth muscle cell proliferation and has been associated with pulmonary arterial hypertension (PAH). Bone morphogenetic protein receptor 2 (BMPR2) mutations similarly have been linked to PAH. However, possible crosstalk between 5-HT and BMPR signaling remains poorly characterized. We report here that 5-HT activates Smads 1/5/8 in bovine and human pulmonary artery smooth muscle cells (SMCs) and causes translocation of these Smads from cytoplasm to the nucleus. DN BMPR1A blocked 5-HT activation of Smads 1/5/8 by 5-HT and BMPR1A overexpression enhanced it. Activation of Smads by 5-HT occurred through the 5-HT 1B/1D receptor as it was blocked with the inhibitor GR 55562 but unaffected by inhibitors of the 5-HT transporter and a variety of 5-HT receptors. Activation of the Smads by 5-HT depended on Rho/Rho kinase signaling as it was blocked by Y27632, but unaffected by inhibitors of PI3K or MAPK. Transfection of cells with BMPR1A and ligation of the BMP receptor with BMP-2 also activated GTP-Rho A of these SMCs, while DN BMPR1A blocked the activation. 5-HT stimulated an increase in serine/threonine phosphorylation of BMPR1A, supporting the activation of BMPR1A by 5-HT in SMCs. Infusion of 5-HT into mice with miniosmotic infusion pumps caused activation of Smads 1/5/8 in lung tissue, demonstrating the effect in vivo. The studies support a unique concept that 5-HT transactivates the serine kinase receptor, BMPR 1A, to activate Smads 1/5/8 via Rho and Rho kinase in pulmonary artery SMCs. Rho and Rho kinase also participate in the activation of Smads by BMP.

Induction of microRNA-221 by platelet-derived growth factor signaling is critical for modulation of vascular smooth muscle phenotype

The platelet-derived growth factor (PDGF) signaling pathway is a critical regulator of animal development and homeostasis. Activation of the PDGF pathway leads to neointimal proliferative responses to artery injury; it promotes a switch of vascular smooth muscle cells (vSMC) to a less contractile phenotype by inhibiting the SMC-specific gene expression and increasing the rate of proliferation and migration. The molecular mechanism for these pleiotropic effects of PDGFs has not been fully described. Here, we identify the microRNA-221 (miR-221), a small noncoding RNA, as a modulator of the phenotypic change of vSMCs in response to PDGF signaling. We demonstrate that miR-221 is transcriptionally induced upon PDGF treatment in primary vSMCs, leading to down-regulation of the targets c-Kit and p27Kip1. Down-regulation of p27Kip1 by miR-221 is critical for PDGF-mediated induction of cell proliferation. Additionally, decreased c-Kit causes inhibition of SMC-specific contractile gene transcription by reducing the expression of Myocardin (Myocd), a potent SMC-specific nuclear coactivator. Our study demonstrates that PDGF signaling, by modulating the expression of miR-221, regulates two critical determinants of the vSMC phenotype; they are SMC gene expression and cell proliferation.

Human herpesvirus-8 infection of primary pulmonary microvascular endothelial cells

Human herpesvirus-8 (HHV-8) is the causative agent of Kaposi's sarcoma and is associated with the angioproliferative disorders primary effusion lymphoma and multicentric Castleman's disease. Evidence of HHV-8 infection within the pulmonary vasculature of patients with idiopathic pulmonary arterial hypertension (IPAH) has been described. We hypothesize that HHV-8 infection of pulmonary microvascular endothelial cells results in an apoptotic-resistant phenotype characteristic of severe pulmonary arterial hypertension. Our objective was to investigate the ability of HHV-8 to infect human pulmonary microvascular endothelial cells in vitro and characterize the phenotypic effect of this infection. Human pulmonary microvascular endothelial cells were exposed to HHV-8 using two methods (direct virus and co-culture technique). The presence of lytic and latent infection was confirmed. Changes in endothelial cell gene and protein expression and effects on cellular apoptosis were measured. HHV-8 can both lytically and latently infect primary human pulmonary microvascular endothelial cells in vitro. HHV-8 infection results in significant changes in gene expression, including alterations of pathways important to cellular apoptosis. HHV-8 infection also alters expression of genes integral to the bone morphogenic protein pathway, including down-regulation of bone morphogenic protein-4. Other genes previously implicated in the development of PAH are affected by HHV-8 infection, and cells infected with HHV-8 are resistant to apoptosis.

Differential proinflammatory and prooxidant effects of bone morphogenetic protein-4 in coronary and pulmonary arterial endothelial cells

There is increasing evidence that TGF-beta family member cytokine bone morphogenetic protein (BMP)-4 plays different pathophysiological roles in the pulmonary and systemic circulation. Upregulation of BMP-4 has been linked to atherosclerosis and hypertension in the systemic circulation, whereas disruption of BMP-4 signaling is associated with the development of pulmonary hypertension. To test the hypothesis that BMP-4 elicits differential effects in the pulmonary and systemic circulation, we compared the prooxidant and proinflammatory effects of BMP-4 in cultured human coronary arterial endothelial cells (CAECs) and pulmonary arterial endothelial cells (PAECs). We found that BMP-4 (from 0.3 to 10 ng/ml) in CAECs increased O(2)(*-) and H(2)O(2) generation, induced NF-kappaB activation, upregulated ICAM-1, and induced monocyte adhesiveness to ECs. In contrast, BMP-4 failed to induce oxidative stress or endothelial activation in PAECs. Also, BMP-4 treatment impaired acetylcholine-induced relaxation and increased O(2)(*-) production in cultured rat carotid arteries, whereas cultured rat pulmonary arteries were protected from these adverse effects of BMP-4. Thus, we propose that BMP-4 exerts prooxidant, prohypertensive, and proinflammatory effects only in the systemic circulation, whereas pulmonary arteries are protected from these adverse effects of BMP-4. The vascular bed-specific endothelial effects of BMP-4 are likely to contribute to its differential pathophysiological role in the systemic and pulmonary circulation.

Genetics and mediators in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is an uncommon disorder of the pulmonary vasculature characterized by remodeling of the smallest pulmonary arteries, leading to a progressive increase in pulmonary vascular resistance. Various forms of PAH exist, including familial (FPAH) and idiopathic (IPAH) forms and associated conditions. FPAH transmits as an autosomal dominant trait that exhibits genetic anticipation but also markedly reduced penetrance (20%). The primary genetic defect of FPAH, identifiable in more than 70% of cases of FPAH, is a mutation in the gene encoding bone morphogenetic protein receptor type 2 (BMPR2), a member of the transforming growth factor beta superfamily. The true prevalence of BMPR2 mutations in IPAH is unknown, with reports ranging from 10% to 40% of patients. The cause of the variable phenotypic expression of PAH among carriers of mutated BMPR2 genes and patients is unclear, and likely related to environmental and genetic modifiers of disease not yet fully elucidated. Although BMPR2-related pathways seem to be pivotal, many other mediator pathways participate in the pathogenesis of different forms of PAH and are being actively investigated, both independently and in combination. As understanding of the molecular basis of this devastating disease improves, opportunities for earlier diagnosis, additional therapeutic regimens, and perhaps disease prevention will emerge.

Pulmonary Arterial Hypertension

The first description of the circulation of blood through the lungs has been attributed to Ibn Nafis (1210–1288).1 The concept was rediscovered by Michael Servetus, a Spanish physician during the Renaissance (1511–1553) and recorded, oddly enough, in two pages of his religious treatise, Christianismi Restitutio (1553).2 The definitive exposition of the pulmonary circulation was made by William Harvey in DeMotu Cordis (1628).3 The first observation of the pulmonary capillaries was first reported by Marcellus Malpighi (1661).4 Heart catheterization in humans, driven by a desire to obtain the perfect mixed venous specimen and measure cardiac output, was first performed in 1929 by the German urologist Forssmann,5 using a ureteral catheter to access his own right atrium. Over a decade later, Cournand and Richards at Columbia University in New York subsequently used right heart catheterization to record pulmonary artery pressure (PAP) in patients with shock and secondary forms of pulmonary hypertension (PHT). For these accomplishments, which were inspired by an interest in the pulmonary circulation and PHT related to mitral stenosis, Forssmann, Cournand, and Richards received the Nobel Prize in 1956.

Role of NADPH oxidases in disturbed flow- and BMP4- induced inflammation and atherosclerosis

Atherosclerosis is an inflammatory disease, occurring preferentially in branched or curved arterial regions exposed to disturbed flow conditions including oscillatory shear stress (OS). In contrast, straight portions exposed to undisturbed laminar shear stress (LS) are relatively lesion free. The opposite effects of atheroprotective LS and proatherogenic OS are likely to be determined by differential expression of genes and proteins, including redox regulating factors. OS induces inflammation via mechanisms involving increased reactive oxygen species (ROS) production from the NADPH oxidases. Through a transcript profiling study and subsequent verification and functional studies, the authors discovered that OS induces inflammation by producing bone morphogenic protein 4 (BMP4) in endothelial cells. BMP4 stimulates expression and activity of NADPH oxidase requiring p47phox and Nox-1 in an autocrine-like manner. The NADPH oxidase activation by BMP4 then leads to ROS production, NF-kappaB activation, intercellular adhesion molecule 1 (ICAM-1) expression, and subsequent increased monocyte adhesivity of endothelial cells. It is proposed that endothelial NADPH oxidases play a critical role in disturbed flow- and BMP4-dependent inflammation, which is the critical early atherogenic response occurring in atheroprone areas. This emerging field of shear stress, BMP4, NADPH oxidases, inflammation, and atherosclerosis is reviewed.

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 morphogenetic protein-2 induces proinflammatory endothelial phenotype

The transforming growth factor-beta superfamily member bone morphogenetic protein-2 (BMP-2) is up-regulated in atherosclerotic arteries; however, its effects on the endothelium are not well characterized. Using microdissected coronary arterial endothelial cells (CAECs) and cultured primary CAECs, we demonstrated endothelial mRNA expression of BMP-2 and BMP-4. The proinflammatory cytokine tumor necrosis factor-alpha and H2O2 significantly increased endothelial expression of BMP-2 but not BMP-4. In organ culture, BMP-2 substantially decreased relaxation of rat carotid arteries to acetylcholine and increased production of reactive oxygen species, events inhibited by pharmacologically blocking protein kinase C (PKC) or NAD(P)H oxidase. BMP-2 activated nuclear factor-kappaB in CAECs, and BMP-2 and BMP-4 substantially increased adhesion of monocytic THP-1 cells, which was reduced by pharmacologically inhibiting p42/44 MAP kinase pathway (also by siRNA down-regulating ERK-1/2) or PKC. Incubation of rat carotid arteries with BMP-2 ex vivo also increased adhesion of mononuclear cells to the endothelium, requiring p42/44 MAP kinase and PKC. Western blotting showed that in CAECs and carotid arteries BMP-2 elicited phosphorylation of p42/44 MAP kinase, which was reduced by blocking MAP kinase kinase and PKC. Collectively, expression of BMP-2 is regulated by proinflammatory stimuli, and increased levels of BMP-2 induce endothelial dysfunction, oxidative stress, and endothelial activation. Thus, the proinflammatory effects of BMP-2 may play a role in vascular pathophysiology.

Bone morphogenetic protein receptor-2 signaling promotes pulmonary arterial endothelial cell survival: implications for loss-of-function mutations in the pathogenesis of pulmonary hypertension

Mutations in the bone morphogenetic protein (BMP) receptor-2 (BMPR2) have been found in patients with idiopathic pulmonary arterial hypertension (IPAH); however, the mechanistic link between loss of BMPR2 signaling and the development of pulmonary arterial hypertension is unclear. We hypothesized that, contrary to smooth muscle cells, this pathway promotes survival in pulmonary artery endothelial cells (ECs) and loss of BMPR2 signaling will predispose to EC apoptosis. ECs were treated with BMP-2 or BMP-7 (200 ng/mL) for 24 hours in regular or serum-free (SF) medium, with and without addition of tumor necrosis factor alpha, and apoptosis was assessed by flow cytometry (Annexin V), TUNEL, or caspase-3 activity. Treatment for 24 hours in SF medium increased apoptosis, and both BMP-2 and BMP-7 significantly reduced apoptosis in response to serum deprivation to levels not different from serum controls. Transfection with 5 microg of small interfering RNAs for BMPR2 produced specific gene silencing assessed by RT-PCR and Western blot analysis. BMPR2 gene silencing increased apoptosis almost 3-fold (P=0.0027), even in the presence of serum. Circulating endothelial progenitor cells (EPCs) isolated from normal subjects or patients with IPAH were differentiated in culture for 7 days and apoptosis was determined in the presence and absence of BMPs. BMP-2 reduced apoptosis induced by serum withdrawal in EPCs from normal subjects but not in EPCs isolated from patients with IPAH. These results support the hypothesis that loss-of-function mutations in BMPR2 could lead to increased pulmonary EC apoptosis, representing a possible initiating mechanism in the pathogenesis of pulmonary arterial hypertension.

HIV-1 TAT represses transcription of the bone morphogenic protein receptor-2 in U937 monocytic cells

The bone morphogenetic protein receptor-2 (BMPR2) is a member of the transforming growth factor-beta receptor family and is expressed on the surface of several cell types including endothelial cells and macrophages. Recently, a cause for familial primary pulmonary hypertension (FPPH) has been identified as mutations in the gene encoding BMPR2. Three forms of pulmonary hypertension (PH) exist, including PPH, FPPH, and PH secondary to other etiologies (sporadic PH) such as drug abuse and human immunodeficiency virus (HIV) infection. It is interesting that these subtypes are histologically indistinguishable. The macrophage is a key target cell for HIV-1, significantly altering macrophage cell function upon infection. HIV-1 trans-activator of transcription (Tat), an immediate-early product of the HIV-1 lifecycle, plays an important role in mediating HIV-induced modulation of host cell function. Our laboratory has previously shown that Tat represses mannose receptor transcription in macrophages. In the current study, we examined activity from the BMPR2 promoter in the macrophage cell line U937 and potential regulation by Tat. Transfection of U937 cells with BMPR2 promoter-reporter constructs revealed dose-dependent repression of BMPR2 promoter activity in the presence of Tat. Experiments using truncations of the BMPR2 promoter localized Tat-mediated repression to the first 208 bases of the promoter. Decreased BMPR2 transcription resulted in altered downstream signaling. Similar to mothers against decapentaplegics (SMAD) phosphorylation and SMAD6 expression, in response to BMP2 treatment, were down-regulated after Tat treatment. Finally, HIV-1 infection and treatment with Tat protein of the U937 human monocytic cell line resulted in a decreased, endogenous BMPR2 transcript copy number.

Génétique de l’hypertension artérielle pulmonaire: données récentes et applications pratiques

INTRODUCTION

Pulmonary arterial hypertension (PAHT) is defined as an increase of mean pulmonary artery pressure above 25 mmHg at rest, or 30 mmHg on exercise, due to obliteration of small calibre pulmonary arteries by proliferation of endothelial cells and smooth muscle. Beside idiopathic PAHT and that associated with other conditions, a familial form has been identified.

STATE OF THE ART

Family studies have shown an association between mutations of the BMPR2 gene and PAHT phenotypes. The products of this gene appear to be involved in vascular homeostasis and its mutations are the basis of a loss this function and, in consequence, proliferation of pulmonary vascular cells.

PERSPECTIVES

Certain characteristics, such as incomplete penetrance and genetic anticipation, lead to a complex relationship between genotype and phenotype and make genetic counselling difficult. Other members of the extended family of TGF-beta receptors are implicated in the development of the Osler-Rendu syndrome, but may also be associated with the development of PAHT.

CONCLUSION

Progress in genetics allows better understanding of the pathophysiology of this disease and could lead to new therapeutic possibilities.

Bone morphogenetic protein 2 (BMP-2) and induction of tumor angiogenesis

PURPOSE

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor-beta family and play an important role in the regulation of embryonic vasculogenesis but their role in postnatal angiogenesis remains to be clarified. In this study we investigated a possible role of BMP-2 in the promotion of tumor angiogenesis.

METHODS

We studied the effect of BMP-2 on human dermal microvascular endothelial cells (HDMECs) and examined a possible angiogenic activity of BMP-2 with the mouse sponge assay. The effect of BMP-2 overexpression on tumor vascularization was also analyzed in xenografts of human BMP-2 transfected MCF-7 breast cancer cells (MCF-7/BMP2) in mice.

RESULTS

BMP receptor activation selectively induced the phosphorylation of p38 mitogen-activated protein kinase (MAPK) in contrast to the ERK1/2 MAP kinases. In keeping with this finding, BMP-2 had no significant effect on endothelial cell proliferation but promoted HDMEC tube formation in the matrigel assay. The transcription factor inhibitor of differentiation 1 (Id1), which is known to play an important role in neovascularization of tumors, was confirmed as a BMP target in HDMECs. Immunohistochemical analysis of sponge sections revealed that BMP-2 induced vascularization and showed an additive enhancement of angiogenesis with VEGF. In the murine breast cancer xenograft model, human MCF-7 cells with stable overexpression of BMP-2 developed vascularized tumors while empty vector control MCF-7 cells failed to form tumors.

CONCLUSIONS

We conclude that activation of the BMP pathway by BMP-2 can promote vascularization and might be involved in tumor angiogenesis possibly by stimulating the Id1 and p38 MAPK pathway.

Regulation of Bone Morphogenetic Protein-2 Expression in Endothelial Cells

Background— Recent studies suggest that bone morphogenetic protein-2 (BMP-2), a transforming growth factor-β superfamily member cytokine, plays an important role both in vascular development and pathophysiological processes, including endothelial activation that is likely to contribute to the development of coronary atherosclerosis, yet the factors that regulate arterial expression of BMP-2 are completely unknown. We tested the hypothesis that BMP-2 expression in endothelial cells is governed by an H 2 O 2 and nuclear factor (NF)-κΒ–dependent pathway that can be activated by both proinflammatory and mechanical stimuli.

Methods and Results— The proinflammatory cytokine tumor necrosis factor (TNF)-α induced NF-κΒ activation and elicited significant increases in BMP-2 mRNA and protein in primary coronary arterial endothelial cells and human umbilical vein endothelial cells that were prevented by NF-κΒ inhibitors (pyrrolidine dithiocarbamate and SN-50), silencing of p65 (siRNA), or catalase. Administration of H 2 O 2 also elicited NF-κΒ activation and BMP-2 induction. In organ culture, exposure of rat arteries to high pressure (160 mm Hg) elicited H 2 O 2 production, nuclear translocation of NF-κΒ, and upregulation of BMP-2 expression. Although high pressure upregulated TNF-α, it appears that it directly regulates BMP-2 expression, because upregulation of BMP-2 was also observed in vessels of TNF-α knockout mice.

Conclusions— Vascular BMP-2 expression can be regulated by H 2 O 2 -mediated activation of NF-κΒ both by inflammatory stimuli and by high intravascular pressure.

Unilateral acheiria and fatal primary pulmonary hypertension in a girl with incontinentia pigmenti

We describe a newborn girl with incontinentia pigmenti (IP, MIM308300), unilateral acheiria, and fatal primary pulmonary hypertension. Limb deficiency has not been described previously in IP and pulmonary hypertension only on two previous occasions. A review of the cause of IP shows that these rare manifestations may not be unexpected, given the many roles of the underlying gene product.

Activation of LIMK1 by binding to the BMP receptor, BMPRII, regulates BMP-dependent dendritogenesis

The growth and morphological differentiation of dendrites are critical events in the establishment of proper neuronal connectivity and neural function. One extrinsic factor, BMP7, has been shown to specifically affect dendritic morphogenesis; however, the underlying mechanism by which this occurs is unknown. Here we show that LIM kinase 1 (LIMK1), a key downstream effector of Rho GTPases, colocalizes with the BMP receptor, BMPRII, in the tips of neurites and binds to BMPRII. This interaction is required for BMP-dependent induction of the dendritic arbor in cortical neurons. Furthermore, we demonstrate that the physical interaction of LIMK1 with BMPRII synergizes with the Rho GTPase, Cdc42, to activate LIMK1 catalytic activity. These studies thus define a Smad-independent pathway that directly links the BMP receptor to regulation of actin dynamics and provides insights into how extracellular signals modulate LIMK1 activity to permit fine spatial control over cytoskeletal remodelling during dendritogenesis.

The transforming growth factor-beta superfamily of receptors

The transforming growth factor-beta (TGF-beta) superfamily of receptors comprises two groups of transmembrane serine-threonine kinase receptors, so called type I, and type II receptors, that are activated following engagement by members of the TGF-beta superfamily of ligands. These events specify diverse downstream responses that are differentially regulated by controlling access and activation of the ligands, their receptors and downstream substrates in different cell types. The purpose of this review is to describe the biochemical properties of these receptors, focusing specifically on the mechanisms regulating receptor/ligand interactions and activation in mammalian cells.

Increased sympathetic nerve activity in pulmonary artery hypertension

BACKGROUND

This study tested the hypothesis that sympathetic nerve activity is increased in pulmonary artery hypertension (PAH), a rare disease of poor prognosis and incompletely understood pathophysiology. We subsequently explored whether chemoreflex activation contributes to sympathoexcitation in PAH.

METHODS AND RESULTS

We measured muscle sympathetic nerve activity (MSNA) by microneurography, heart rate (HR), and arterial oxygen saturation (Sao(2)) in 17 patients with PAH and 12 control subjects. The patients also underwent cardiac echography, right heart catheterization, and a 6-minute walk test with dyspnea scoring. Circulating catecholamines were determined in 8 of the patients. Chemoreflex deactivation by 100% O(2) was assessed in 14 patients with the use of a randomized, double-blind, placebo-controlled, crossover study design. Compared with the controls, the PAH patients had increased MSNA (67+/-4 versus 40+/-3 bursts per minute; P<0.0001) and HR (82+/-4 versus 68+/-3 bpm; P=0.02). MSNA in the PAH patients was correlated with HR (r=0.64, P=0.006), Sao(2) (r=-0.53, P=0.03), the presence of pericardial effusion (r=0.51, P=0.046), and NYHA class (r=0.52, P=0.033). The PAH patients treated with prostacyclin derivatives had higher MSNA (P=0.009), lower Sao(2) (P=0.01), faster HR (P=0.003), and worse NYHA class (P=0.04). Plasma catecholamines were normal. Peripheral chemoreflex deactivation with hyperoxia increased Sao(2) (91.7+/-1% to 98.4+/-0.2%; P<0.0001) and decreased MSNA (67+/-5 to 60+/-4 bursts per minute; P=0.0015), thereby correcting approximately one fourth of the difference between PAH patients and controls.

CONCLUSIONS

We report for the first time direct evidence of increased sympathetic nerve traffic in advanced PAH. Sympathetic hyperactivity in PAH is partially chemoreflex mediated and may be related to disease severity.

Suv39h histone methyltransferases interact with Smads and cooperate in BMP-induced repression

Smad proteins transduce signals from transforming growth factor-beta (TGF-beta) superfamily ligands to regulate the expression of target genes. In order to identify novel partners of Smad proteins in transcriptional regulation, we performed a two-hybrid screen using Smad5, a protein that is activated predominantly by bone morphogenetic protein (BMP) signaling. We identified an interaction between Smad5 and suppressor of variegation 3-9 homolog 2 (Suv39h2), a chromatin modifier enzyme. Suv39h proteins are histone methyltransferases that methylate histone H3 on lysine 9, resulting in transcriptional repression or silencing of target genes. Biochemical studies in mammalian cells demonstrated that Smad5 binds to both known mammalian isoforms of Suv39h proteins, and that Smad proteins activated by the TGF-beta signaling pathway, Smad2 and Smad3, do not bind with significant affinity. Functional studies using the muscle creatine kinase (MCK) promoter, which is suppressed by BMP signaling, demonstrate that Suv39h proteins and Smads cooperate to repress promoter activity. These data suggest a model where association of Smad proteins with Suv39h methyltransferases can repress or silence genes involved in developmental processes, and argues that inefficient gene repression may result in the alteration of the differentiated phenotype. Thus, examination of the Smad-Suv interaction may provide insight into the mechanism of phenotypic determination mediated by BMP signaling.

Smads as intracellular mediators of airway inflammation

Transforming growth factor-beta (TGF-beta) plays an important role in the pathogenesis of allergic asthma and other airway diseases. Signals from the activated TGF-beta receptor complex are transduced to the nucleus of airway cells by Smad proteins, which represent a family of transcription factors that have recently been implicated to play a major role as intracellular mediators of inflammation. The Smad family consists of the receptor-regulated Smads, a common pathway Smad, and inhibitory Smads. Receptor-regulated Smads (R-Smads) are phosphorylated by the TGF-beta type Ireceptor. They include Smad2 and Smad3, which are recognized by TGF-beta and activin receptors, and Smads 1, 5, 8, and 9, which are recognized by bone morphogenetic protein (BMP) receptors. Smad4 is a common pathway Smad, which is also defined as cooperating Smad (co-Smad) and is not phosphorylated by the TGF-beta type I receptor. Inhibitory Smads(anti-Smads) include Smad6 and Smad7, which down-regulate TGF-beta signaling. To date, the Smads are the only TGF-beta receptor substrates with a demonstrated ability to propagate signals and with regard to the growing number of investigations of Smad-mediated effects in the airways, Smads may prove to be an important target for future development of new therapeutic strategies for asthma and chronic obstructive pulmonary disease.

Gene microarray analysis of peripheral blood cells in pulmonary arterial hypertension

The importance of genetic predisposition, inflammation, and autoimmune mechanisms in the development of pulmonary arterial hypertension (PAH) is becoming increasingly clear. We hypothesized that the analysis of gene expression profiles from peripheral blood mononuclear cells would distinguish patients with PAH from normal volunteers. We also hypothesized that a subset of genes would discriminate between patients with idiopathic PAH and pulmonary hypertension related to secondary causes. Mononuclear cells were isolated from 15 patients diagnosed with PAH and 6 normal control subjects. Microarray expression was performed, and the expression profiles were analyzed for consistent and predictive differences in gene expression. We identified a signature set of 106 genes that discriminated with high certainty (p < or = 0.002) between patients with PAH and normal individuals. The results of the microarray analysis were retrospectively and prospectively confirmed by quantitative polymerase chain reaction for 2 of the 106 genes. Supervised clustering analysis generated a list of differentially expressed genes between patients with idiopathic and secondary causes of pulmonary hypertension. Microarray expression profiling of peripheral blood cells can discriminate between patients with PAH and normal volunteers. These findings may have important implications toward diagnosis, screening, and pathogenesis of this disease.

Osteogenic regulation of vascular calcification: an early perspective

Cardiovascular calcification is a common consequence of aging, diabetes, hypercholesterolemia, mechanically abnormal valve function, and chronic renal insufficiency. Although vascular calcification may appear to be a uniform response to vascular insult, it is a heterogenous disorder, with overlapping yet distinct mechanisms of initiation and progression. A minimum of four histoanatomic variants-atherosclerotic (fibrotic) calcification, cardiac valve calcification, medial artery calcification, and vascular calciphylaxis-arise in response to metabolic, mechanical, infectious, and inflammatory injuries. Common to the first three variants is a variable degree of vascular infiltration by T cells and macrophages. Once thought benign, the deleterious clinical consequences of calcific vasculopathy are now becoming clear; stroke, amputation, ischemic heart disease, and increased mortality are portended by the anatomy and extent of calcific vasculopathy. Along with dystrophic calcium deposition in dying cells and lipoprotein deposits, active endochondral and intramembranous (nonendochondral) ossification processes contribute to vascular calcium load. Thus vascular calcification is subject to regulation by osteotropic hormones and skeletal morphogens in addition to key inhibitors of passive tissue mineralization. In response to oxidized lipids, inflammation, and mechanical injury, the microvascular smooth muscle cell becomes activated. Orthotopically, proliferating stromal myofibroblasts provide osteoprogenitors for skeletal growth and fracture repair; however, in valves and arteries, vascular myofibroblasts contribute to cardiovascular ossification. Current data suggest that paracrine signals are provided by bone morphogenetic protein-2, Wnts, parathyroid hormone-related polypeptide, osteopontin, osteoprotegerin, and matrix Gla protein, all entrained to endocrine, metabolic, inflammatory, and mechanical cues. In end-stage renal disease, a "perfect storm" of vascular calcification often occurs, with hyperglycemia, hyperphosphatemia, hypercholesterolemia, hypertension, parathyroid hormone resistance, and iatrogenic calcitriol excess contributing to severe calcific vasculopathy. This brief review recounts emerging themes in the pathobiology of vascular calcification and highlights some fundamental deficiencies in our understanding of vascular endocrinology and metabolism that are immediately relevant to human health and health care.

Activation of K+ channels: an essential pathway in programmed cell death

Cell apoptosis and proliferation are two counterparts in sharing the responsibility for maintaining normal tissue homeostasis. In recent years, the process of the programmed cell death has gained much interest because of its influence on malignant cell growth and other pathological states. Apoptosis is characterized by a distinct series of morphological and biochemical changes that result in cell shrinkage, DNA breakdown, and, ultimately, phagocytic death. Diverse external and internal stimuli trigger apoptosis, and enhanced K+ efflux has been shown to be an essential mediator of not only early apoptotic cell shrinkage, but also of downstream caspase activation and DNA fragmentation. The goal of this review is to discuss the role(s) played by K+ transport or flux across the plasma membrane in the regulation of the apoptotic volume decrease and apoptosis. Attention has also been paid to the role of inner mitochondrial membrane ion transport in the regulation of mitochondrial permeability and apoptosis. We provide specific examples of how deregulation of the apoptotic process contributes to pulmonary arterial medial hypertrophy, a major pathological feature in patients with pulmonary arterial hypertension. Finally, we discuss the targeting of K+ channels as a potential therapeutic tool in modulating apoptosis to maintain the balance between cell proliferation and cell death that is essential to the normal development and function of an organism.

Bone morphogenetic proteins induce apoptosis in human pulmonary vascular smooth muscle cells

Pulmonary vascular medial hypertrophy in primary pulmonary hypertension (PPH) is mainly caused by increased proliferation and decreased apoptosis in pulmonary artery smooth muscle cells (PASMCs). Mutations of the bone morphogenetic protein (BMP) receptor type II (BMP-RII) gene have been implicated in patients with familial and sporadic PPH. The objective of this study was to elucidate the apoptotic effects of BMPs on normal human PASMCs and to examine whether BMP-induced effects are altered in PASMCs from PPH patients. Using RT-PCR, we detected six isoforms of BMPs (BMP-1 through -6) and three subunits of BMP receptors (BMP-RIa, -RIb, and -RII) in PASMCs. Treatment of normal PASMCs with BMP-2 or -7 (100-200 nM, 24-48 h) markedly increased the percentage of cells undergoing apoptosis. The BMP-2-mediated apoptosis in normal PASMCs was associated with a transient activation or phosphorylation of Smad1 and a marked downregulation of the antiapoptotic protein Bcl-2. In PASMCs from PPH patients, the BMP-2- or BMP-7-induced apoptosis was significantly inhibited compared with PASMCs from patients with secondary pulmonary hypertension. These results suggest that the antiproliferative effect of BMPs is partially due to induction of PASMC apoptosis, which serves as a critical mechanism to maintain normal cell number in the pulmonary vasculature. Inhibition of BMP-induced PASMC apoptosis in PPH patients may play an important role in the development of pulmonary vascular medial hypertrophy in these patients.

Bone morphogenic protein 4 produced in endothelial cells by oscillatory shear stress stimulates an inflammatory response

Atherosclerosis is now viewed as an inflammatory disease occurring preferentially in arterial regions exposed to disturbed flow conditions, including oscillatory shear stress (OS), in branched arteries. In contrast, the arterial regions exposed to laminar shear (LS) are relatively lesion-free. The mechanisms underlying the opposite effects of OS and LS on the inflammatory and atherogenic processes are not clearly understood. Here, through DNA microarrays, protein expression, and functional studies, we identify bone morphogenic protein 4 (BMP4) as a mechanosensitive and pro-inflammatory gene product. Exposing endothelial cells to OS increased BMP4 protein expression, whereas LS decreased it. In addition, we found BMP4 expression only in the selective patches of endothelial cells overlying foam cell lesions in human coronary arteries. The same endothelial patches also expressed higher levels of intercellular cell adhesion molecule-1 (ICAM-1) protein compared with those of non-diseased areas. Functionally, we show that OS and BMP4 induced ICAM-1 expression and monocyte adhesion by a NFkappaB-dependent mechanism. We suggest that BMP4 is a mechanosensitive, inflammatory factor playing a critical role in early steps of atherogenesis in the lesion-prone areas.

Alterations in TGF-beta1 expression in lambs with increased pulmonary blood flow and pulmonary hypertension

The mechanisms responsible for pulmonary vascular remodeling in congenital heart disease with increased pulmonary blood flow remain unclear. We developed a lamb model of congenital heart disease and increased pulmonary blood flow utilizing an in utero placed aortopulmonary vascular graft (shunted lambs). Morphometric analysis of barium-injected pulmonary arteries indicated that by 4 wk of age, shunts had twice the pulmonary arterial density of controls (P < 0.05), and their pulmonary vessels showed increased muscularization and medial thickness at both 4 and 8 wk of age (P < 0.05). To determine the potential role of TGF-beta1 in this vascular remodeling, we investigated vascular changes in expression and localization of TGF-beta1 and its receptors TbetaRI, ALK-1, and TbetaRII in lungs of shunted and control lambs at 1 day and 1, 4, and 8 wk of life. Western blots demonstrated that TGF-beta1 and ALK-1 expression was elevated in shunts compared with control at 1 and 4 wk of age (P < 0.05). In contrast, the antiangiogenic signaling receptor TbetaRI was decreased at 4 wk of age (P < 0.05). Immunohistochemistry demonstrated shunts had increased TGF-beta1 and TbetaRI expression in smooth muscle layer and increased TGF-beta1 and ALK-1 in endothelium of small pulmonary arteries at 1 and 4 wk of age. Moreover, TbetaRI expression was significantly reduced in endothelium of pulmonary arteries in the shunt at 1 and 4 wk. Our data suggest that increased pulmonary blood flow dysregulates TGF-beta1 signaling, producing imbalance between pro- and antiangiogenic signaling that may be important in vascular remodeling in shunted lambs.