Atrial natriuretic peptide-dependent modulation of hypoxia-induced pulmonary vascular remodeling

Hypoxic stress upsets the balance in the normal relationships between mitogenic and growth inhibiting pathways in lung, resulting in pulmonary vascular remodeling characterized by hyperplasia of pulmonary arterial smooth muscle cells (PASMCs) and fibroblasts and enhanced deposition of extracellular matrix. Atrial natriuretic peptide (ANP) reduces pulmonary vascular resistance and attenuates hypoxia-induced pulmonary hypertension in vivo and PASMC proliferation and collagen synthesis in vitro. The current study utilized an ANP null mouse model (Nppa-/-) to test the hypothesis that ANP modulates the pulmonary vascular and alveolar remodeling response to normobaric hypoxic stress. Nine-10 wk old male ANP null (Nppa-/-) and wild type nontransgenic (NTG) mice were exposed to chronic hypoxia (10% O(2), 1 atm) or air for 6 wks. Measurement: pulmonary hypertension, right ventricular hypertrophy, and pulmonary arterial and alveolar remodeling were assessed. Hypoxia-induced pulmonary arterial hypertrophy and muscularization were significantly increased in Nppa-/- mice compared to NTG controls. Furthermore, the stimulatory effects of hypoxia on alveolar myofibroblast transformation (8.2 and 5.4 fold increases in Nppa-/- and NTG mice, respectively) and expression of extracellular matrix molecule (including osteopontin [OPN] and periostin [PN]) mRNA in whole lung were exaggerated in Nppa-/- mice compared to NTG controls. Combined with our previous finding that ANP signaling attenuates transforming growth factor (TGF)-beta-induced expression of OPN and PN in isolated PASMCs, the current study supports the hypothesis that endogenous ANP plays an important anti-fibrogenic role in the pulmonary vascular adaptation to chronic hypoxia.     

Determinants of an elevated pulmonary arterial pressure in patients with pulmonary arterial hypertension

Given the difficulty of diagnosing early-stage pulmonary arterial hypertension (PAH) due to the lack of signs and symptoms, and the risk of an open lung biopsy, the precise pathological features of presymptomatic stage lung tissue remain unknown. It has been suggested that the maximum elevation of the mean pulmonary arterial pressure (P_pa) is achieved during the early symptomatic stage, indicating that the elevation of the mean P_pa is primarily driven by the pulmonary vascular tone and/or some degree of pulmonary vascular remodeling completed during this stage. Recently, the examination of a rat model of severe PAH suggested that the severe PAH may be primarily determined by the presence of intimal lesions and/or the vascular tone in the early stage. Human data seem to indicate that intimal lesions are essential for the severely increased pulmonary arterial blood pressure in the late stage of the disease.However, many questions remain. For instance, how does the pulmonary hemodynamics change during the course of the disease, and what drives the development of severe PAH? Although it is generally acknowledged that both pulmonary vascular remodeling and the vascular tone are important determinants of an elevated pulmonary arterial pressure, which is the root cause of the time-dependent progression of the disease? Here we review the recent histopathological concepts of PAH with respect to the progression of the lung vascular disease.     

Rosiglitazone attenuates hypoxia-induced pulmonary arterial remodeling

Thiazolidinediones (TZDs) are insulin-sensitizing agents that also decrease systemic blood pressure, attenuate the formation of atherosclerotic lesions, and block remodeling of injured arterial walls. Recently, TZDs were shown to prevent pulmonary arterial (PA) remodeling in rats treated with monocrotaline. Presently we report studies testing the ability of the TZD rosiglitazone (ROSI) to attenuate pathological arterial remodeling in the lung and prevent the development of pulmonary hypertension (PH) in rats subjected to chronic hypoxia. PA remodeling was reduced in ROSI-treated animals exposed to hypoxia compared with animals exposed to hypoxia alone. ROSI treatment blocked muscularization of distal pulmonary arterioles and reversed remodeling and neomuscularization in lungs of animals previously exposed to chronic hypoxia. Decreased PA remodeling in ROSI-treated animals was associated with decreased smooth muscle cell proliferation, decreased collagen and elastin deposition, and increased matrix metalloproteinase-2 activity in the PA wall. Cells expressing the c-Kit cell surface marker were observed in the PA adventitia of untreated animals exposed to hypoxia but not in ROSI-treated hypoxic rats. Right ventricular hypertrophy and cardiomyocyte hypertrophy were also blunted in ROSI-treated hypoxic animals. Interestingly, mean PA pressures were elevated equally in the untreated and ROSI-treated groups, indicating that ROSI had no effect on the development of PH. However, mean PA pressure was normalized acutely in both groups of hypoxia-exposed animals by Fasudil, an agent that inhibits RhoA/Rho kinase-mediated vasoconstriction. We conclude that ROSI can attenuate and reverse PA remodeling and neomuscularization associated with hypoxic PH. However, this agent fails to block the development of PH, apparently because of its inability to repress sustained Rho kinase-mediated arterial vasoconstriction.     

The hypoxia-induced microRNA-130a controls pulmonary smooth muscle cell proliferation by directly targeting CDKN1A

Excessive proliferation of human pulmonary artery smooth muscle cells (HPASMC) is one of the major factors that trigger vascular remodeling in hypoxia-induced pulmonary hypertension. Several studies have implicated that hypoxia inhibits the tumor suppressor p21 (CDKN1A). However, the precise mechanism is unknown.The mouse model of hypoxia-induced PH and in vitro experiments were used to assess the impact of microRNAs (miRNAs) on the expression of CDKN1A. In these experiments, the miRNA family miR-130 was identified to regulate the expression of CDKN1A. Transfection of HPASMC with miR-130 decreased the expression of CDKN1A and, in turn, significantly increased smooth muscle proliferation. Conversely, inhibition of miR-130 by anti-miRs and seed blockers increased the expression of CDKN1A. Reporter gene analysis proved a direct miR-130–CDKN1A target interaction. Exposure of HPASMC to hypoxia was found to induce the expression of miR-130 with concomitant decrease of CDKN1A. These findings were confirmed in the mouse model of hypoxia-induced pulmonary hypertension showing that the use of seed blockers against miR-130 restored the expression of CDKN1A.These data suggest that miRNA family miR-130 plays an important role in the repression of CDKN1A by hypoxia. miR-130 enhances hypoxia-induced smooth muscle proliferation and might be involved in the development of right ventricular hypertrophy and vascular remodeling in pulmonary hypertension.     

MMP-10 from M1 macrophages promotes pulmonary vascular remodeling and pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is characterized by muscularized pulmonary blood vessels, leading to right heart hypertrophy and cardiac failure. However, state-of-the-art therapeutics fail to target the ongoing remodeling process. Here, this study shows that matrix metalloproteinases (MMP)-1 and MMP-10 levels are increased in the medial layer of vessel wall, serum, and M1-polarized macrophages from patients with PAH and the lungs of monocrotaline- and hypoxia-induced PAH rodent models. MMP-10 regulates the malignant phenotype of pulmonary artery smooth muscle cells (PASMCs). The overexpression of active MMP-10 promotes PASMC proliferation and migration via upregulation of cyclin D1 and proliferating cell nuclear antigen, suggesting that MMP-10 produced by infiltrating macrophages contributes to vascular remodeling. Furthermore, inhibition of STAT1 inhibits hypoxia-induced MMP-10 but not MMP-1 expression in M1-polarized macrophages from patients with PAH. In conclusion, circulating MMP-10 could be used as a potential targeted therapy for PAH.     

Comparison of lung proteome profiles in two rodent models of pulmonary arterial hypertension

We studied the lung proteome changes in two widely used models of pulmonary arterial hypertension (PAH): monocrotaline (MCT) injection and chronic hypoxia (CH); untreated rats were used as controls (n = 6/group). After 28 days, invasive right ventricular systolic pressure (RVSP) was measured. Lungs were immunostained for alpha-smooth muscle actin (alphaSMA). 2-DE (n = 4/group) followed by nano-LC-MS/MS was applied for protein identification. Western blotting was used additionally if possible. RVSP was significantly increased in MCT- and CH-rats (MCT 62.5 +/- 4.4 mmHg, CH 62.2 +/- 4.1 mmHg, control 25.0 +/- 1.7 mmHg, p<0.001). This was associated with an increase of alphaSMA positive vessels. In both groups, there was a significantly increased expression of proteins associated with the contractile apparatus (diphosphoHsp27 (p<0.001), Septin2 (p<0.001), F-actin capping protein (p<0.01), and tropomyosin beta (p<0.02)). In CH, proteins of the nitric oxide (Hsc70; p = 0.002), carbon monoxide (biliverdin reductase; p = 0.005), and vascular endothelial growth factor (VEGF) pathway (annexin 3; p<0.001) were significantly increased. In MCT, proteins involved in serotonin synthesis (14-3-3; p = 0.02), the enhanced unfolded protein response (ERp57; p = 0.02), and intracellular chloride channels (CLIC 1; p = 0.002) were significantly elevated. Therefore, MCT- and CH-induced vasoconstriction and remodeling seemed to be mediated via different signaling pathways. These differences should be considered in future studies using either PAH model.     

Cellular mechanosignaling in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a vasculopathy characterized by sustained elevated pulmonary arterial pressures in which the pulmonary vasculature undergoes significant structural and functional remodeling. To better understand disease mechanisms, in this review article we highlight recent insights into the regulation of pulmonary arterial cells by mechanical cues associated with PAH. Specifically, the mechanobiology of pulmonary arterial endothelial cells (PAECs), smooth muscle cells (PASMCs) and adventitial fibroblasts (PAAFs) has been investigated in vivo, in vitro, and in silico. Increased pulmonary arterial pressure increases vessel wall stress and strain and endothelial fluid shear stress. These mechanical cues promote vasoconstriction and fibrosis that contribute further to hypertension and alter the mechanical milieu and regulation of pulmonary arterial cells.     

Characterization of hypoxia-induced [Ca2+]i rise in rabbit pulmonary arterial smooth muscle cells

We have investigated the effects of hypoxia on the intracellular Ca2+ concentration ([Ca2+]i) in rabbit pulmonary (PASMCs) and coronary arterial smooth muscle cells with fura-2. Perfusion of a glucose-free and hypoxic (PO2<50 mmHg) external solution increased [Ca2+]i in cultured as well as freshly isolated PASMCs. However it had no effect on [Ca2+]i in freshly isolated coronary arterial myocytes. In the absence of extracellular Ca2+, hypoxic stimulation elicited a transient [Ca2+]i increase in cultured PASMCs which was abolished by the simultaneous application of cyclopiazonic acid and ryanodine, suggesting the involvement of sarcoplasmic reticulum (SR) Ca2+ store. Pretreatment with the mitochondrial protonophore, carbonyl cyanide m-chlorophenyl-hydrazone (CCCP) enhanced the [Ca2+]i rise in response to hypoxia. A short application of caffeine gave a transient [Ca2+]i rise which was prolonged by CCCP. Decay of the caffeine-induced [Ca2+]i transients was significantly slowed by treatment of CCCP or rotenone. After full development of the hypoxia-induced [Ca2+]i rise, nifedipine did not decrease [Ca2+]i. These data suggest that the [Ca2+]i increase in response to hypoxia may be ascribed to both Ca2+ release from the SR and the subsequent activation of nifedipine-insensitive capacitative Ca2+ entry. Mitochondria appear to modulate hypoxia induced Ca2+ release from the SR.     

Suppression of Akt1 phosphorylation by adenoviral transfer of the PTEN gene inhibits hypoxia-induced proliferation of rat pulmonary arterial smooth muscle cells

Recent findings identify the role of proliferation of pulmonary artery smooth muscle cells (PASMCs) in pulmonary vascular remodeling. Phosphoinositide 3 kinase (PI3K) and serine/threonine kinase (Akt) proteins are expressed in vascular smooth muscle cells. In addition, phosphatase and tensin homolog deleted on chromosome 10 (PTEN) has been identified as a negative regulator of cytokine signaling that inhibits the PI3K-Akt pathway. However, little is known about the role of PTEN/Akt signaling in hypoxia-associated vascular remodeling. In this study, we found that hypoxia-induced the expression of Akt1 mRNA and phosphorylated protein by at least twofold in rat PASMCs. Phospho-PTEN significantly decreased in the nuclei of PASMCs after hypoxic stimulation. After forcing over-expression of PTEN by adenovirus-mediated PTEN (Ad-PTEN) transfection, the expression of phospho-Akt1 was significantly suppressed in PASMCs at all time-points measured. Additionally, we showed here that hypoxia increased proliferation of PASMCs by nearly twofold and over-expression of PTEN significantly inhibited hypoxia-induced PASMCs proliferation. These findings suggest that phospho-PTEN loss in the nuclei of PASMCs under hypoxic conditions may be the major cause of aberrant activation of Akt1 and may, therefore, play an important role in hypoxia-associated pulmonary arterial remodeling. Finally, the fact that transfection with Ad-PTEN inhibits the phosphorylation of Akt1 in PASMCs suggests a potential therapeutic effect on hypoxia-associated pulmonary arterial remodeling.     

Adiponectin ameliorates angiotensin II-induced vascular endothelial damage

Adiponectin is an adipocyte-specific adipocytokine that possesses anti-atherogenic and anti-diabetic properties. It has been shown to have a beneficial effect on the cardiovascular system, but it remains to be elucidated whether adiponectin has a therapeutic effect on vascular damage induced by the potential vasoactive substance angiotensin II (Ang II). In this study, the effects of adiponectin on Ang II-induced vascular endothelial damage were investigated. In cultured human umbilical vein endothelium cells, Ang II stimulation increased generation of ROS and 4-hydroxy-2-nonenal, both of which were clearly restored by administration of adiponectin. In addition, administration of adiponectin was found to increase cell viability and prevent apoptosis. Our results also demonstrate that the protective effects of adiponectin against Ang II-induced vascular endothelial damage are dependent on the binding of adiponectin to its cell surface receptor 1. Importantly, we found that adiponectin treatment modulates the apoptotic pathway by reducing the expression of LOX-1, up-regulating both cIAP-1 and the ratio of Bcl-2/Bax. Finally, our data displayed that the protective effects of adiponectin against Ang II cytotoxicity depend on AMPK activation mediated by the endosomal adaptor protein, adaptor protein with phosphotyrosine binding, pleckstrin homology domains, and leucine zipper motif.     

Compensatory roles of Protein Related to DAN and Cerberus (PRDC) decrease in pulmonary arterial hypertension

Bone morphogenetic protein (BMP) signaling is commonly suppressed in patients with pulmonary arterial hypertension (PAH), but the compensatory mechanism of BMP signaling suppression is incompletely elucidated. This study aimed to investigate the role of PRDC, an antagonist of BMPs, in PAH and the underlying mechanism. Human lungs were collected and rat PAH was induced (monocrotaline, 60 mg/kg). BMP cascade and PRDC were detected in lungs and distal pulmonary artery smooth muscle cells (dPASMCs). In vitro cell experiments and in vivo supplementation of PRDC in hypertensive rats were subsequently performed. PRDC and BMP cascade all decreased in human and rat hypertensive lungs. Cell experiments confirmed that BMP2/4 inhibited dPASMCs proliferation by increasing cell cycle inhibitors (p21, p27), prevented dPASMCs migration by down-regulating MMP2/9 and up-regulating TIMP1/2 expression, and promoted dPASMCs apoptosis by up-regulating Bax, caspase3/9 and down-regulating Bcl-2 expression, as well as enhancing caspase3/7 activity, while, PRDC reversed the effects of BMP2/4 on dPASMCs proliferation, migration and apoptosis. In vivo trial found that PRDC supplementation deteriorated rat PAH in terms of pulmonary hemodynamics, vasculopathies and right ventricle hypertrophy. Taken together, compensatory decrease of PRDC in hypertensive lungs theoretically slow down the natural course of PAH, suggesting its therapeutic potential in PAH.     

Quantitative models of the rat pulmonary arterial tree morphometry applied to hypoxia-induced arterial remodeling.

Little is known about the constituent hemodynamic consequences of structural changes that occur in the pulmonary arteries during the onset and progression of pulmonary arterial remodeling. Many disease processes are known to be responsible for vascular remodeling that leads to pulmonary arterial hypertension, cor pulmonale, and death. Histology has been the primary tool for evaluating pulmonary remodeling, but it does not provide information on intact vascular structure or the vessel mechanical properties. This study is an extension of our previous work in which we developed an alternative imaging technique to evaluate pulmonary arterial structure. The lungs from Sprague-Dawley rats were removed, perfusion analysis was performed on the isolated lungs, and then an X-ray contrast agent was used to fill the arterial network for imaging. The lungs were scanned over a range of intravascular pressures by volumetric micro-computed tomography, and the arterial morphometry was mapped and measured in the reconstructed isotropic volumes. A quantitative assessment of hemodynamic, structural, and biomechanical differences between rats exposed for 21 days to hypoxia (10% O(2)) or normoxia (21.0% O(2)) was performed. One metric, the normalized distensibility of the arteries, is significantly (P < 0.001) larger [0.025 +/- 0.0011 (SE) mmHg(-1)] (n = 9) in normoxic rats compared with hypoxic [0.015 +/- 0.00077 (SE) mmHg(-1)] (n = 9). The results of the study show that these models can be applied to the Sprague-Dawley rat data and, specifically, can be used to differentiate between the hypoxic and the control groups.     

MiR-20a regulates the PRKG1 gene by targeting its coding region in pulmonary arterial smooth muscle cells

Chronic hypoxia triggers pulmonary vascular remodeling, which is associated with de-differentiation of pulmonary artery smooth muscle cells (PASMC). Here, we show that miR-20a expression is up-regulated in response to hypoxia in both mouse and human PASMC. We also observed that miR-20a represses the protein kinase, cGMP-dependent, type I (PRKG1) gene and we identified two crucial miR-20a binding sites within the coding region of PRKG1. Functional studies showed that miR-20a promotes the proliferation and migration of human PASMC, whereas it inhibits their differentiation. In summary, we provided a possible mechanism by which hypoxia results in decreased PRKG1 expression and in the phenotypic switching of PASMC.     

Wnt5a attenuates hypoxia-induced pulmonary arteriolar remodeling and right ventricular hypertrophy in mice

Hypoxic pulmonary hypertension (HPH), which is characterized by pulmonary arteriolar remodeling and right ventricular hypertrophy, is still a life-threatening disease with the current treatment strategies. The underlying molecular mechanisms of HPH remain unclear. Our previously published study showed that Wnt5a, one of the ligands in the Wnt family, was critically involved in the inhibition of hypoxia-induced pulmonary arterial smooth muscle cell proliferation by downregulation of β-catenin/cyclin D1 in vitro. In this study, we investigated the possible functions and mechanisms of Wnt5a in HPH in vivo. Recombinant mouse Wnt5a (rmWnt5a) or phosphate buffered saline (PBS) was administered to male C57/BL6 mice weekly from the first day to the end of the two or four weeks after exposed to hypoxia (10% O₂). Hypoxia-induced pulmonary hypertension was associated with a marked increase in β-catenin/cyclin D1 expression in lungs. Right ventricular systolic pressure and right ventricular hypertrophy index were reduced in animals treated with rmWnt5a compared with PBS. Histology showed less pulmonary vascular remodeling and right ventricular hypertrophy in the group treated with rmWnt5a than with PBS. Treatment with rmWnt5a resulted in a concomitant reduction in β-catenin/cyclin D1 levels in lungs. These data demonstrate that Wnt5a exerts its beneficial effects on HPH by regulating pulmonary vascular remodeling and right ventricular hypertrophy in a manner that is associated with reduction in β-catenin/cyclin D1 signaling. A therapy targeting the β-catenin/cyclin D1 signaling pathway might be a potential strategy for HPH treatment.     

脂肪干细胞移植对野百合碱诱发的肺动脉高压大鼠肺动脉压的量效和时效作用

目的探索脂肪干细胞（ADSC）移植治疗野百合碱（MCT）诱导的肺动脉高压（PAH）大鼠的适宜细胞数和干预时间。 方法（1）MCT的建模时效和量效：雄性SD大鼠48只分为正常对照组,20 mg/kg、30 mg/kg、40 mg/kg MCT组分别予腹腔注射生理盐水、MCT 20 mg/kg、30 mg/kg、40 mg/kg,4和8周后,右心室插管法检测平均肺动脉压（mPAP）,称重法计算右心室肥厚指数（RVHI）。（2）ADSC的治疗量效作用：雄性SD大鼠分别予腹腔注射MCT（30只）和生理盐水（30只）,1周后通过颈静脉注射分别移植0.5×10⁶、1.0×10⁶、3.0×10⁶、5.0×10⁶ADSC,其他组予等量生理盐水。移植3周后检测mPAP和RVHI。（3）ADSC的治疗时效作用：雄性SD大鼠30只,分别注射40 mg/kg MCT（24只）和生理盐水（6只）。MCT腹腔注射1 d,1、2周后分别移植1.0×10⁶个ADSC。MCT注射4周后检测mPAP和RVHI。多组间比较采用单因素或双因素方差分析,两两比较采用LSD检验。 结果（1）腹腔注射4周后,30 mg/ kg或40 mg/kg MCT组mPAP和RVHI均升高[mPAP值（24.89±3.31）mmHg,（27.19±2.11）mmHg比（15.80±0.42）mmHg,差异有统计学意义（P均< 0.05）;RVHI值0.42±0.06,0.47±0.04比0.25±0.02,差异有统计学意义（P均< 0.05）]。8周后,20 mg/kg或30 mg/ kg MCT组mPAP和RVHI均恢复正常,而40 mg/kg MCT组大鼠全部死亡。（2）40 mg/ kg MCT诱导的PAH大鼠mPAP和RVHI均升高。移植1.0×10⁶个ADSC可降低PAH大鼠的mPAP[（17.24±0.66）mmHg比（27.19±1.73）mmHg,P < 0.05]。移植0.5×10⁶、3.0×10⁶、5.0× 10⁶个ADSC不能降低PAH大鼠的mPAP和RVHI。（3）MCT腹腔注射1周和2周后,移植1.0×10⁶个ADSC可降低PAH大鼠的mPAP。 结论40 mg/kg MCT造模4周可建立稳定的PAH大鼠模型;造模1或2周后移植1.0×10⁶个ADSC能有效降低PAH大鼠的mPAP。     

Adiponectin ameliorates doxorubicin-induced cardiotoxicity through Akt protein-dependent mechanism

Accumulating evidence shows that obesity is associated with doxorubicin cardiac toxicity in the heart, but the molecular mechanisms that contribute to this pathological response are not understood. Adiponectin is an adipose-derived, cardioprotective factor that is down-regulated in obesity. Here, we investigated the effect of adiponectin on doxorubicin (DOX)-induced cardiotoxicity and assessed the mechanisms of this effect. A single dose of DOX was intraperitoneally injected into the abdomen of adiponectin knock-out (APN-KO) and wild-type (WT) mice. APN-KO mice had increased mortality and exacerbated contractile dysfunction of left ventricle compared with WT mice. APN-KO mice also showed increased apoptotic activity and diminished Akt signaling in the failing myocardium. Systemic delivery of adenoviral vector expressing adiponectin improved left ventricle dysfunction and myocardial apoptosis following DOX injection in WT and APN-KO mice but not in Akt1 heterozygous KO mice. In cultured rat neonatal cardiomyocytes, adiponectin stimulated Akt phosphorylation and inhibited DOX-stimulated apoptosis. Treatment with sphingosine kinase-1 inhibitor or sphingosine 1-phosphate receptor antagonist diminished adiponectin-induced Akt phosphorylation and reversed the inhibitory effects of adiponectin on myocyte apoptosis. Pretreatment with anti-calreticulin antibody reduced the binding of adiponectin to cardiac myocytes and blocked the adiponectin-stimulated increase in Akt activation and survival in cardiomyocytes. Interference of the LRP1/calreticulin co-receptor system by siRNA or blocking antibodies diminished the stimulatory actions of adiponectin on Akt activation and myocyte survival. These data show that adiponectin protects against DOX-induced cardiotoxicity by its ability to promote Akt signaling.     

Effects of hydrogen sulfide on hypoxic pulmonary vascular structural remodeling

To study the role of hydrogen sulfide (H2S) in hypoxic pulmonary vascular structural remodeling (HPVSR), a total of 24 Wistar rats were randomly divided into three groups: control group (n = 8), hypoxia group (n = 8) and hypoxia with sodium hydrosulfide (hy + NaHS) group (n = 8). The mean pulmonary artery pressure (mPAP), plasma H2S and the percentage of muscularized arteries (MA), partially muscularized arteries (PMA) and nonmuscularized arteries (NMA) in small pulmonary vessels were measured. Collagen I and III, elastin, transforming growth factor-beta3 (TGF-beta3), proliferative cell nuclear antigen (PCNA) and human urotensin II(U-II) expressions were detected by immunohistochemical assay. The mRNA expressions of procollagen I and III, matrix metalloproteinase-1 (MMP-1) and tissue inhibitor of metalloproteinease-1 (TIMP-1) were detected by in situ hybridization. The results showed that NaHS significantly increased plasma H2S, decreased mPAP and the percentage of MA and PMA of small pulmonary vessels in rats under hypoxia. Meanwhile, NaHS inhibited the proliferation of pulmonary artery smooth muscle cells (PASMCs) represented by a decrease in the expressions of PCNA and human U-II in pulmonary artery wall. NaHS reduced the expression of collagen I and III, elastin and TGF-beta3 protein and decreased the expressions of procollagen I and III mRNA in pulmonary arteries of rats under hypoxia, but it did not impact the ratio of TIMP-1 mRNA to MMP-1mRNA in pulmonary arteries of rats under hypoxia. These data suggested that H2S played an important role in the development of HPVSR.     

Loss of alveolar membrane diffusing capacity and pulmonary capillary blood volume in pulmonary arterial hypertension

Background

Reduced gas transfer in patients with pulmonary arterial hypertension (PAH) is traditionally attributed to remodeling and progressive loss of pulmonary arterial vasculature that results in decreased capillary blood volume available for gas exchange.

Methods

We tested this hypothesis by determination of lung diffusing capacity (DL) and its components, the alveolar capillary membrane diffusing capacity (D_m) and lung capillary blood volume (V_c) in 28 individuals with PAH in comparison to 41 healthy individuals, and in 19 PAH patients over time. Using single breath simultaneous measure of diffusion of carbon monoxide (DL_CO) and nitric oxide (DL_NO), DL and D_m were respectively determined, and V_c calculated. D_m and V_c were evaluated over time in relation to standard clinical indicators of disease severity, including brain natriuretic peptide (BNP), 6-minute walk distance (6MWD) and right ventricular systolic pressure (RVSP) by echocardiography.

Results

Both DL_CO and DL_NO were reduced in PAH as compared to controls and the lower DL in PAH was due to loss of both D_m and V_c (all p < 0.01). While DL_CO of PAH patients did not change over time, DL_NO decreased by 24 ml/min/mmHg/year (p = 0.01). Consequently, D_m decreased and V_c tended to increase over time, which led to deterioration of the D_m/V_c ratio, a measure of alveolar-capillary membrane functional efficiency without changes in clinical markers.

Conclusions

The findings indicate that lower than normal gas transfer in PAH is due to loss of both D_m and V_c, but that deterioration of D_m/V_c over time is related to worsening membrane diffusion.