Adrenomedullin: angiogenesis and gene therapy

Adrenomedullin (AM) is a potent, long-lasting vasodilator peptide that was originally isolated from human pheochromocytoma. AM signaling is of particular significance in endothelial cell biology since the peptide protects cells from apoptosis, promotes angiogenesis, and affects vascular tone and permeability. The angiogenic effect of AM is mediated by activation of Akt, mitogen-activated protein kinase/extracellular signal-regulated kinase 1/2, and focal adhesion kinase in endothelial cells. Both AM and its receptor, calcitonin receptor-like receptor, are upregulated through a hypoxia-inducible factor-1-dependent pathway under hypoxic conditions. Thus AM signaling plays an important role in the regulation of angiogenesis in hypoxic conditions. Recently, we have developed a nonviral vector, gelatin. Positively charged gelatin holds negatively charged plasmid DNA in its lattice structure. DNA-gelatin complexes can delay gene degradation, leading to efficient gene transfer. Administration of AM DNA-gelatin complexes induces potent angiogenic effects in a rabbit model of hindlimb ischemia. Thus gelatin-mediated AM gene transfer may be a new therapeutic strategy for the treatment of tissue ischemia. Endothelial progenitor cells (EPCs) play an important role in endothelial regeneration. Interestingly, EPCs phagocytose ionically linked DNA-gelatin complexes in coculture, which allows nonviral gene transfer into EPCs. AM gene transfer into EPCs inhibits cell apoptosis and induces proliferation and migration, suggesting that AM gene transfer strengthens the therapeutic potential of EPCs. Intravenous administration of AM gene-modified EPCs regenerate pulmonary endothelium, resulting in improvement of pulmonary hypertension. These results suggest that in vivo and in vitro transfer of AM gene using gelatin may be applicable for intractable cardiovascular disease.     

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

Several recent papers have shown that both familial primary pulmonary hypertension (FPPH) and sporadic primary pulmonary hypertension (PPH) may have a common etiology that is associated with the inheritance and/or spontaneous development of germline mutations in the bone morphogenetic protein receptor (BMPR) type II gene. Because BMPR-II is a ubiquitously expressed receptor for a family of secreted growth factors known as the bone morphogenetic proteins (BMPs), these findings suggest that BMPs play an important role in the maintenance of normal pulmonary vascular physiology. In the present commentary we discuss the implications of these findings in the context of BMP receptor biology, and relate these data to the genetics and pulmonary pathophysiology of patients with PPH.     

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.     

BMPR2 haploinsufficiency as the inherited molecular mechanism for primary pulmonary hypertension

Primary pulmonary hypertension (PPH) is a potentially lethal disorder, because the elevation of the pulmonary arterial pressure may result in right-heart failure. Histologically, the disorder is characterized by proliferation of pulmonary-artery smooth muscle and endothelial cells, by intimal hyperplasia, and by in situ thrombus formation. Heterozygous mutations within the bone morphogenetic protein type II receptor (BMPR-II) gene (BMPR2), of the transforming growth factor beta (TGF-beta) cell-signaling superfamily, have been identified in familial and sporadic cases of PPH. We report the molecular spectrum of BMPR2 mutations in 47 additional families with PPH and in three patients with sporadic PPH. Among the cohort of patients, we have identified 22 novel mutations, including 4 partial deletions, distributed throughout the BMPR2 gene. The majority (58%) of mutations are predicted to lead to a premature termination codon. We have also investigated the functional impact and genotype-phenotype relationships, to elucidate the mechanisms contributing to pathogenesis of this important vascular disease. In vitro expression analysis demonstrated loss of BMPR-II function for a number of the identified mutations. These data support the suggestion that haploinsufficiency represents the common molecular mechanism in PPH. Marked variability of the age at onset of disease was observed both within and between families. Taken together, these studies illustrate the considerable heterogeneity of BMPR2 mutations that cause PPH, and they strongly suggest that additional factors, genetic and/or environmental, may be required for the development of the clinical phenotype.     

Role of calcitonin gene-related peptide (CGRP) in chronic hypoxia-induced pulmonary hypertension in the mouse. Influence of gene transfer in vivo

Calcitonin gene-related peptide (CGRP) is believed to play an important role in maintaining low pulmonary vascular resistance (PVR) and may be involved in modulating the pulmonary vascular response to chronic hypoxia. In the present study, an adenoviral vector encoding CGRP (AdRSVCGRP) was used to examine the effects of in vivo gene transfer of CGRP to the lung on increases in PVR, right ventricular mass, and pulmonary vascular remodeling that occurs in chronic hypoxia in the mouse. Following intratracheal administration of AdRSVCGRP or reporter gene mice were exposed to 16 days of chronic hypoxia (FIO(2) 0.10). The increase in pulmonary arterial pressure (PAP), PVR, right ventricular mass, and pulmonary vascular remodeling in response to chronic hypoxia was attenuated in animals overexpressing CGRP, whereas systemic arterial pressure was not altered. Following exposure to hypoxia, a subgroup of mice were treated with capsaicin, which did not significantly alter CGRP expression in the mouse lung. These data show that in vivo transfer of the CGRP gene to the lung attenuates the increase in PVR, right ventricular mass, and pulmonary vascular remodeling in chronically hypoxic mice with little effect on the systemic circulation. Moreover, these data suggest that adenoviral gene transfer of CGRP to the lung results in expression of the gene product in non-neural tissue.     

The prostacyclin analogue treprostinil blocks NFkappaB nuclear translocation in human alveolar macrophages

Primary pulmonary hypertension (PPH) is characterized by increased pulmonary arterial pressure and vascular resistance. We and others have observed that inflammatory cytokines and infiltrates are present in the lung tissue, but the significance is uncertain. Treprostinil (TRE), a prostacyclin analogue with extended half-life and chemical stability, has shown promise in the treatment of PPH. We hypothesize that TRE might exert beneficial effects in PPH by antagonizing inflammatory cytokine production in the lung. Here we show that TRE dose-dependently inhibits inflammatory cytokine (tumor necrosis factor-alpha, interleukin-1beta, interleukin-6, and granulocyte macrophage colony-stimulating factor) secretion and gene expression by human alveolar macrophages. TRE blocks NFkappaB activation, but IkappaB-alpha phosphorylation and degradation are unaffected. Moreover, TRE does not affect the formation of the NFkappaB.DNA complex but blocks nuclear translocation of p65. These results are the first to illustrate the anti-cytokine actions of TRE in down-regulating NFkappaB, not through its inhibitory component or by direct binding but by blocking nuclear translocation. These data indicate that inflammatory mechanisms may be important in the pathogenesis of PPH and cytokine antagonism by blocking NFkappaB may contribute to the efficacy of TRE therapy in PPH.     

Hemodynamic effects of exogenous adrenomedullin in healthy and endotoxemic sheep

Adrenomedullin (AM) is a vasodilatory peptide hormone, playing a key role in the regulation of cardiovascular homeostasis. In view of the circulatory failure in sepsis, it is still debated as to whether the occurrence of vascular hyporeactivity against AM plays a causative or protective role. This study was designed as a prospective, controlled trial to elucidate the hemodynamic response following a titrating infusion of human AM in healthy and endotoxemic sheep. ANOVA demonstrated that AM infusion produced hypotension and tachycardia, and increased cardiac index in a dose-dependent manner, both in healthy and endotoxemic sheep. In addition, AM application reduced pulmonary vascular resistance index in ovine endotoxemia (P=0.02). These findings confirm that AM produces a hyperdynamic circulation, in the presence and absence of systemic inflammation. Further, exogenous AM could possibly be a useful adjunct in the common setting of sepsis-associated pulmonary hypertension.     

Impaired release of ATP from red blood cells of humans with primary pulmonary hypertension

Previously, we reported that in the isolated perfused rabbit lung, red blood cells (RBCs) obtained from either rabbits or healthy humans were a required component of the perfusate to unmask evidence of nitric oxide (NO) participation in regulation of the pulmonary circulation. In addition, we found that mechanical deformation of rabbit and healthy human RBCs released ATP, a known agonist for enhanced NO synthesis. In contrast, RBCs obtained from patients with cystic fibrosis (CF) did not release ATP in response to mechanical deformation. The coexistence of airway disease and alveolar hypoxia in patients with CF precluded the drawing of conclusions relating a defect in RBC ATP release with the pulmonary hypertension associated with CF. Airway disease and alveolar hypoxia are not, however, features of primary pulmonary hypertension (PPH), a human condition of unknown etiology. We postulated that a defect in NO generation might contribute to the increased pulmonary vascular resistance in PPH, and as a first step, we hypothesized that RBCs obtained from patients with PPH would not release ATP. In contrast to RBCs of healthy humans, when RBCs of PPH patients were passed through filters (average pore size 12, 8, or 5 microm), ATP was not released and the RBCs exhibited reduced deformability. Moreover, when incubated with the active cAMP analogue, Sp-cAMP (100 microM), an activator of the CF transmembrane conductance regulator, ATP was not released. These results demonstrate that RBCs obtained from patients with PPH fail to release ATP whether the stimulus is mechanical or pharmacological. Thus, failure of RBCs to release ATP in patients with PPH might be a major pathogenetic factor that accounts for the heretofore unknown etiology of their pulmonary hypertension.     

Atrial natriuretic peptide clearance receptor agonist lowers pulmonary pressure in hypoxic rats

We demonstrated previously that intravenous administration of exogenous atrial natriuretic peptide (ANP) lowers mean pulmonary arterial pressure (MPAP) in hypoxia-adapted rats. To test the hypothesis that endogenous ANP may also lower MPAP in this model, C-ANP-(4-23), a ring-deleted analogue of ANP that binds to the biologically silent ANP clearance receptor (C-ANP receptor) but not to the ANP biological receptor (B-ANP receptor), was administered intravenously as a bolus injection (10 micrograms/kg) followed by an infusion (1 micrograms.kg-1.min-1 for 60 min) to rats adapted to hypoxia (10% O2) for 4 wk and to air control rats. C-ANP-(4-23) significantly lowered MPAP in hypoxic rats but not in air controls. A statistically insignificant reduction in mean systemic arterial pressure was found in both groups after C-ANP-(4-23) administration. C-ANP-(4-23) significantly (two- to threefold) increased endogenous plasma ANP levels in both groups; the increase was not significantly different between groups. Both basal and post-C-ANP-(4-23) levels of plasma ANP were greater in hypoxia-adapted animals than in air controls; the C-ANP-induced increase in plasma ANP was not significantly different between groups. These results suggest that the endogenous ANP may modulate pulmonary vascular tone in rats with hypoxic pulmonary hypertension.     

Inhaled nitric oxide-induced rebound pulmonary hypertension: role for endothelin-1

Clinically significant increases in pulmonary vascular resistance have been noted on acute withdrawal of inhaled nitric oxide (NO). Endothelin (ET)-1 is a vasoactive peptide produced by the vascular endothelium that may participate in the pathophysiology of pulmonary hypertension. The objectives of this study were to determine the effects of inhaled NO on endogenous ET-1 production in vivo in the intact lamb and to determine the potential role of ET-1 in the rebound pulmonary hypertension associated with the withdrawal of inhaled NO. Seven 1-mo-old vehicle-treated control lambs and six PD-156707 (an ET(A) receptor antagonist)-treated lambs were mechanically ventilated. Inhaled NO (40 parts per million) was administered for 24 h and then acutely withdrawn. After 24 h of inhaled NO, plasma ET-1 levels increased by 119.5 +/- 42.2% (P < 0.05). Western blot analysis revealed that protein levels of preproET-1, endothelin-converting enzyme-1alpha, and ET(A) and ET(B) receptors were unchanged. On acute withdrawal of NO, pulmonary vascular resistance (PVR) increased by 77.8% (P < 0.05) in control lambs but was unchanged (-5.5%) in PD-156707-treated lambs. Inhaled NO increased plasma ET-1 concentrations but not gene expression in the intact lamb, and ET(A) receptor blockade prevented the increase in PVR after NO withdrawal. These data suggest a role for ET-1 in the rebound pulmonary hypertension noted on acute withdrawal of inhaled NO.     

Platelet-derived growth factor (PDGF) induces pulmonary vascular remodeling through 15-LO/15-HETE pathway under hypoxic condition

15-lipoxygenase (15-LO) is known to play an important role in chronic pulmonary hypertension. Accumulating evidence for its down-stream participants in the vasoconstriction and remodeling processes of pulmonary arteries, while how hypoxia regulates 15-LO/15-hydroxyeicosatetraenoic acid (15-HETE) to mediate hypoxic pulmonary hypertension is still unknown. Platelet-derived growth factor (PDGF) is an important vascular regulator whose concentration increases under hypoxic condition in the lungs of both humans and mice with pulmonary hypertension. The present study was carried out to determine whether hypoxia advances the pulmonary vascular remodeling through the PDGF/15-LO/15-HETE pathway. We found that pulmonary arterial medial thickening caused by hypoxia was alleviated after a treatment of the hypoxic rats with imatinib, which was associated with down-regulations of 15-LO-2 expression and 15-HETE production. Moreover, the increases in cell proliferation and endogenous 15-HETE content by hypoxia were attenuated by the inhibitors of PDGF-β receptor in pulmonary artery smooth muscle cells (PASMCs). The effects of PDGF-BB on cell proliferation and survival were weakened after the administration of 15-LO inhibitors or 15-LO RNA interference. These results suggest that hypoxia promotes PASMCs proliferation and survival, contributing to pulmonary vascular medial hypertrophy, which is likely to be mediated via the PDGF-BB/15-LO-2/15-HETE pathway.     

Adrenomedullin and adrenomedullin binding protein-1 protect endothelium-dependent vascular relaxation in sepsis

Downregulation of vascular endothelial constitutive nitric oxide synthase (ecNOS) contributes to the vascular hyporesponsiveness in sepsis. Although coadministration of the potent vasodilatory peptide adrenomedulin (AM) and the newly discovered AM binding protein (AMBP-1) maintains cardiovascular stability and reduces mortality in sepsis, it remains unknown whether AM/AMBP-1 prevents endothelial cell dysfunction. To investigate this possibility, we subjected adult male rats to sepsis by cecal ligation and puncture (CLP), with or without subsequent intravenous administration of the combination of AM (12 microg/kg) and AMBP-1 (40 microg/kg). Thoracic aortae were harvested 20 h after CLP (i.e., the late stage of sepsis) and endothelium-dependent vascular relaxation was determined by the addition of acetylcholine (ACh) in an organ bath system. In addition, ecNOS gene and protein expression was assessed by RT-PCR and immunohistochemistry, respectively. The results indicate that ACh-induced (i.e., endothelium-dependent) vascular relaxation was significantly reduced 20 h after CLP. Administration of AM/AMBP-1 prevented the reduction of vascular relaxation. In addition, ecNOS gene expression in aortic and pulmonary tissues was downregulated 20 h after CLP and AM/AMBP-1 attenuated such a reduction. Moreover, the decreased ecNOS staining in thoracic aortae of septic animals was prevented by the treatment with AM/AMBP-1. These results, taken together, indicate that AM/AMBP-1 preserves ecNOS and prevents reduced endothelium-dependent vascular relaxation (i.e., endothelial cell dysfunction) in sepsis. In light of our recent finding that AM/AMBP-1 improves organ function and reduces mortality in sepsis, it is most likely that the protective effect of these compounds on ecNOS is a mechanism responsible for the salutary effect of AM/AMBP-1 in sepsis.     

Oxidant stress but not thromboxane decreases with epoprostenol therapy

Epoprostenol has improved the outcome of patients with primary pulmonary hypertension (PPH); however, its mechanism of action remains poorly understood. Isoprostanes are easily measured markers of oxidant stress and can activate platelets leading to increased thromboxane A2 (TxA2) production. We hypothesized that oxidant stress is associated with increased TxA2 synthesis and that epoprostenol decreases oxidant stress and TxA2 production in patients with PPH. Morning urine samples were obtained from 19 patients with PPH. We measured urinary metabolites of the isoprostane, 8-iso-PGF2alpha (F2-IsoP-M), and of TxA2 (Tx-M) before and after treatment with epoprostenol in patients with PPH. Mean (+/-SE) levels of F2-IsoP-M were elevated at baseline in our patients, 863 +/- 97 pg/mg creatinine. During treatment with epoprostenol, values decreased to 636 +/- 77 pg/mg creatinine (P = 0.011), and there was a strong correlation between the change in F2-IsoP-M and follow-up pulmonary vascular resistance (R2 = 0.69, P < 0.001). Tx-M levels were markedly elevated at baseline and were unchanged with therapy. These results indicate that oxidant stress decreases with epoprostenol therapy and is associated with hemodynamic and clinical improvement. The failure of Tx-M to decrease with therapy suggests that epoprostenol does not exert a beneficial effect through inhibition of TxA2 production in patients with PPH.     

Adrenomedullin binding protein-1 modulates vascular responsiveness to adrenomedullin in late sepsis

Adrenomedullin (AM), a potent vasodilatory peptide, plays an important role in initiating the hyperdynamic response during the early stage of sepsis. Moreover, the reduced vascular responsiveness to AM appears to be responsible for the transition from the early, hyperdynamic to the late, hypodynamic phase of sepsis. Although the novel specific AM binding protein-1 (AMBP-1) enhances AM-mediated action in a cultured cell line, it remains to be determined whether AMBP-1 plays any role in modulating vascular responsiveness to AM during sepsis. To study this, adult male rats were subjected to sepsis by cecal ligation and puncture (CLP). The thoracic aorta was harvested for determination of AM-induced vascular relaxation. Aortic levels of AMBP-1 were determined by Western blot analysis, and AM receptor gene expression in the aortic tissue was assessed by RT-PCR. The results indicate that AMBP-1 significantly enhanced AM-induced vascular relaxation in aortic rings from sham-operated animals. Although vascular responsiveness to AM decreased at 20 h after CLP (i.e., the late, hypodynamic stage of sepsis), addition of AMBP-1 in vitro restored the vascular relaxation induced by AM. Moreover, the aortic level of AMBP-1 decreased significantly at 20 h after CLP. In contrast, AM receptor gene expression was not altered under such conditions. These results, taken together, suggest that AMBP-1 plays an important role in modulating vascular responsiveness to AM, and the reduced AMBP-1 appears to be responsible for the vascular AM hyporesponsiveness observed during the hypodynamic phase of sepsis.     

The role of endogenous lung neuropeptides in regulation of the pulmonary circulation

Vascular resistance in the mammalian pulmonary circulation is affected by many endogenous agents that influence vascular smooth muscle, right ventricular myocardium, endothelial function, collagen and elastin deposition, and fluid balance. When the balance of these agents is disturbed, e.g. by airway hypoxia from high altitude or pulmonary obstructive disorders, pulmonary hypertension ensues, as characterized by elevated pulmonary artery pressure (P(PA)). Among neuropeptides with local pulmonary artery pressor effects are endothelin-1 (ET-1), angiotensin II (AII), and substance P, and among mitigating peptides are calcitonin gene-related peptide (CGRP), adrenomedullin (ADM), atrial natriuretic peptide (ANP), vasoactive intestinal peptide (VIP) and ET-3. Moreover, somatostatin28 (SOM28) exacerbates, whereas SOM14 decreases P(PA) in hypoxic rats, with lowering and increasing of lung CGRP levels, respectively. Pressure can also be modulated by increasing or decreasing plasma volume (VIP and ANP, respectively), or by induction or suppression of vascular tissue remodeling (ET-1 and CGRP, respectively). Peptide bioavailability and potency can be regulated through hypoxic up- and down- regulation of synthesis or release, activation by converting enzymes (ACE for AII and ECE for ET-1), inactivation by neutral endopeptidase and proteases, or by interaction with nitric oxide (NO). Moreover, altered receptor density and affinity can account for changed peptide efficacy. For example, upregulation of ET(A) receptors and ET-1 synthesis occurs in the hypoxic lung concomitantly with reduced CGRP release. Also, receptor activity modifying protein 2 (RAMP2) has been shown to confer ADM affinity to the pulmonary calcitonin-receptor-like receptor (CRLR). We recently detected the mRNA encoding for RAMP2, CRLR, and the CGRP receptor RDC-1 in rat lung. The search for an effective, lung selective treatment of pulmonary hypertension will likely benefit from exploring the imbalance and restoring the balance between these native modulators of intrapulmonary pressure. For example, blocking of the ET-1 receptor ET(A) and vasodilation by supplemental CGRP delivered i. v. or via airway gene transfer, have proven to be useful experimentally.     

Adrenomedullin release in the rat mesenteric resistance artery

Adrenomedullin (AM) is a potent vasodilator peptide whose major source is the vascular wall. In the present study, the mechanism of release of AM was investigated in the rat mesenteric resistance artery. The isolated mesenteric vascular bed was perfused with Krebs solution at a constant flow rate (5 ml/min) and AM in the perfusate was measured by a highly sensitive enzyme immunoassay (Immunoenzymometric assay; IEMA) method. In preparations without endothelium, spontaneous release of AM was detected in the perfusate (68.7+/-5.8 fmol/ml, n=45). Periarterial nerve stimulation (PNS, 4 and 8 Hz) caused 11.4+/-3.9% (4 Hz) and 9.1+/-3.5% (8 Hz) decreases in the spontaneous release of AM. Removal of Ca2+ from the medium did not affect the spontaneous AM release, but abolished the PNS-induced inhibition of spontaneous AM release. Perfusion of 10nM calcitonin gene-related peptide (CGRP) or 0.1 microM capsaicin (inducer of CGRP release) inhibited significantly the spontaneous AM release. PNS (8 Hz)-induced inhibition of spontaneous AM release was antagonized by CGRP(8-37) (CGRP receptor antagonist). These results suggest that AM is mainly released from vascular smooth muscle cells of the rat mesenteric artery and endogenous or exogenous CGRP inhibits AM release.     

L-NAME enhances responses to atrial natriuretic peptide in the pulmonary vascular bed of the cat.

This study investigated the hypothesis that atrial natriuretic peptide (ANP) responses are mediated by particulate guanylate cyclase in the pulmonary vascular bed of the cat. When tone in the pulmonary vascular bed was raised to a high steady level with the thromboxane mimic U-46619, injections of ANP caused dose-related decreases in lobar arterial pressure. After administration of HS-142-1, an ANP-A- and ANP-B-receptor antagonist, vasodilator responses to ANP were reduced. The nitric oxide (NO) synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) enhanced ANP vasodilator responses, suggesting that inhibition of NO modulates ANP responses. L-NAME administration with constant 8-bromo-cGMP infusion attenuated the increased vasodilator response to ANP, suggesting that supersensitivity to ANP occurs upstream to activation of a cGMP-dependent protein kinase. In pulmonary arterial rings, ANP produced concentration-related vasorelaxant responses with and without endothelium. Methylene blue, L-NAME, or N(omega)-monomethyl-L-arginine did not alter ANP vasorelaxant responses. These data show that ANP supersensitivity observed in the intact pulmonary vascular bed is not seen in isolated pulmonary arterial segments, suggesting that it may only occur in resistance vessel elements. These results suggest that ANP responses occur through activation of ANP-A and/or -B receptors in an endothelium-independent manner and are modulated by NO in resistance vessel elements in the pulmonary vascular bed of the cat.     

Functional heterogeneity of bone morphogenetic protein receptor-II mutants found in patients with primary pulmonary hypertension

Germline mutations in the BMPR2 gene encoding bone morphogenetic protein (BMP) type II receptor (BMPR-II) have been reported in patients with primary pulmonary hypertension (PPH), but the contribution of various types of mutations found in PPH to the pathogenesis of clinical phenotypes has not been elucidated. To determine the biological activities of these mutants, we performed functional assays testing their abilities to transduce BMP signals. We found that the reported missense mutations within the extracellular and kinase domains of BMPR-II abrogated their signal-transducing abilities. BMPR-II proteins containing mutations at the conserved cysteine residues in the extracellular and kinase domains were detected in the cytoplasm, suggesting that the loss of signaling ability of certain BMPR-II mutants is due at least in part to their altered subcellular localization. In contrast, BMPR-II mutants with truncation of the cytoplasmic tail retained the ability to transduce BMP signals. The differences in biological activities among the BMPR-II mutants observed thus suggest that additional genetic and/or environmental factors may play critical roles in the pathogenesis of PPH.     

The possible role of hydrogen sulfide on the pathogenesis of spontaneous hypertension in rats

Hydrogen sulfide (H(2)S) is a newly found modulator in vascular system. This work showed that gene expression of cystathionine gamma-lyase (CSE), a H(2)S generating enzyme, and the activity of CSE in thoracic aorta were suppressed in hypertension rats. The plasma level of H(2)S also decreased in those rats. Exogenous administration of H(2)S could increase the plasma level of H(2)S and enhance the CSE activity of aorta. Exogenous administration of H(2)S also attenuated the elevation of pressure and lessened the aorta structural remodeling during the development of hypertension. In WKY rats, the gene expression and activity of CSE also decreased when the endogenous production of H(2)S was deprived by administration of DL-propargylglycine (specific inhibitor of CSE), accompanying the elevated pressure and the development of vascular remodeling. The results showed that endogenous H(2)S system was involved in both the maintenance of basal blood pressure and the development of hypertension. Exogenous H(2)S could exert beneficial effect on the pathogenesis of spontaneous hypertension.