The Na+/H+ exchanger contributes to increased smooth muscle proliferation and migration in a rat model of pulmonary arterial hypertension

Aquaporin 1 confers apoptosis resistance in pulmonary arterial smooth muscle cells from the SU5416 hypoxia rat model

Pulmonary hypertension (PH) arises from increased pulmonary vascular resistance due to contraction and remodeling of the pulmonary arteries. The structural changes include thickening of the smooth muscle layer from increased proliferation and resistance to apoptosis. The mechanisms underlying apoptosis resistance in PH are not fully understood. In cancer cells, high expression of aquaporin 1 (AQP1), a water channel, is associated with apoptosis resistance. We showed AQP1 protein was expressed in pulmonary arterial smooth muscle cells (PASMCs) and upregulated in preclinical PH models. In this study, we used PASMCs isolated from control male rats and the SU5416 plus hypoxia (SuHx) model to test the role of AQP1 in modulating susceptibility to apoptosis. We found the elevated level of AQP1 in PASMCs from SuHx rats was necessary for resistance to apoptosis and that apoptosis resistance could be conferred by increasing AQP1 in control PASMCs. In exploring the downstream pathways involved, we found AQP1 levels influence the expression of Bcl-2, with enhanced AQP1 levels corresponding to increased Bcl-2 expression, reducing the ratio of BAX to Bcl-2, consistent with apoptosis resistance. These results provide a mechanism by which AQP1 can regulate PASMC fate.

Fatty acid metabolism promotes TRPV4 activity in lung microvascular endothelial cells in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a morbid disease characterized by significant lung endothelial cell (EC) dysfunction. Prior work has shown that microvascular endothelial cells (MVECs) isolated from animals with experimental PAH and patients with PAH exhibit significant abnormalities in metabolism and calcium signaling. With regards to metabolism, we and others have shown evidence of increased aerobic glycolysis and evidence of increased utilization of alternate fuel sources (such as fatty acids) in PAH EC. In the realm of calcium signaling, our prior work linked increased activity of the transient receptor potential vanilloid-4 (TRPV4) channel to increased proliferation of MVECs isolated from the Sugen/Hypoxia rat model of PAH (SuHx-MVECs). However, the relationship between metabolic shifts and calcium abnormalities was not clear. Specifically, whether shifts in metabolism were responsible for increasing TRPV4 channel activity in SuHx-MVECs was not known. In this study, using human data, serum samples from SuHx rats, and SuHx-MVECs, we describe the consequences of increased MVEC fatty acid oxidation in PAH. In human samples, we observed an increase in long-chain fatty acid levels that was associated with PAH severity. Next, using SuHx rats and SuHx-MVECs, we observed increased intracellular levels of lipids. We also show that increasing intracellular lipid content increases TRPV4 activity, whereas inhibiting fatty acid oxidation normalizes basal calcium levels in SuHx-MVECs. By exploring the fate of fatty acid-derived carbons, we observed that the metabolite linking increased intracellular lipids to TRPV4 activity was β-hydroxybutyrate (BOHB), a product of fatty acid oxidation. Finally, we show that BOHB supplementation alone is sufficient to sensitize the TRPV4 channel in rat and mouse MVECs. Returning to humans, we observe a transpulmonary BOHB gradient in human patients with PAH. Thus, we establish a link between fatty acid oxidation, BOHB production, and TRPV4 activity in MVECs in PAH. These data provide new insight into metabolic regulation of calcium signaling in lung MVECs in PAH.NEW & NOTEWORTHY In this paper, we explore the link between metabolism and intracellular calcium levels in microvascular endothelial cells (MVECs) in pulmonary arterial hypertension (PAH). We show that fatty acid oxidation promotes sensitivity of the transient receptor potential vanilloid-4 (TRPV4) calcium channel in MVECs isolated from a rodent model of PAH.

LOXL2 inhibition ameliorates pulmonary artery remodeling in pulmonary hypertension

Background

Conduit pulmonary arterial stiffening and the resultant increase in pulmonary vascular impedance has emerged as an important underlying driver of pulmonary arterial hypertension (PAH). Given that matrix deposition is central to vascular remodeling, we evaluated the role of the collagen crosslinking enzyme lysyl oxidase like 2 (LOXL2) in this study.

Methods and Results

Human pulmonary artery smooth muscle cells (PASMCs) subjected to hypoxia showed increased LOXL2 secretion. LOXL2 activity and expression were markedly higher in primary PASMCs isolated from pulmonary arteries of the rat Sugen 5416 + hypoxia (SuHx) model of severe PH. Similarly, LOXL2 protein and mRNA levels were increased in pulmonary arteries (PA) and lungs of rats with PH (SuHx and monocrotaline (MCT) models). Pulmonary arteries (PAs) isolated from rats with PH exhibited hypercontractility to phenylephrine and attenuated vasorelaxation elicited by acetylcholine, indicating severe endothelial dysfunction. Tensile testing revealed a a significant increase in PA stiffness in PH. Treatment with PAT-1251, a novel small-molecule LOXL2 inhibitor, improved active and passive properties of the PA ex vivo. There was an improvement in right heart function as measured by right ventricular pressure volume loops in-vivo with PAT-1251. Importantly PAT-1251 treatment ameliorated PH, resulting in improved pulmonary artery pressures, right ventricular remodeling, and survival.

Conclusion

Hypoxia induced LOXL2 activation is a causal mechanism in pulmonary artery stiffening in PH, as well as pulmonary artery mechanical and functional decline. LOXL2 inhibition with PAT-1251 is a promising approach to improve pulmonary artery pressures, right ventricular elastance, cardiac relaxation, and survival in PAH.

New & Noteworthy

Pulmonary arterial stiffening contributes to the progression of PAH and the deterioration of right heart function. This study shows that LOXL2 is upregulated in rat models of PH. LOXL2 inhibition halts pulmonary vascular remodeling and improves PA contractility, endothelial function and improves PA pressure, resulting in prolonged survival. Thus, LOXL2 is an important mediator of PA remodeling and stiffening in PH and a promising target to improve PA pressures and survival in PH.

Pathophysiology and pathogenic mechanisms of pulmonary hypertension: role of membrane receptors, ion channels, and Ca2+ signaling

The pulmonary circulation is a low-resistance, low-pressure, and high-compliance system that allows the lungs to receive the entire cardiac output. Pulmonary arterial pressure is a function of cardiac output and pulmonary vascular resistance, and pulmonary vascular resistance is inversely proportional to the fourth power of the intraluminal radius of the pulmonary artery. Therefore, a very small decrease of the pulmonary vascular lumen diameter results in a significant increase in pulmonary vascular resistance and pulmonary arterial pressure. Pulmonary arterial hypertension is a fatal and progressive disease with poor prognosis. Regardless of the initial pathogenic triggers, sustained pulmonary vasoconstriction, concentric vascular remodeling, occlusive intimal lesions, in situ thrombosis, and vascular wall stiffening are the major and direct causes for elevated pulmonary vascular resistance in patients with pulmonary arterial hypertension and other forms of precapillary pulmonary hypertension. In this review, we aim to discuss the basic principles and physiological mechanisms involved in the regulation of lung vascular hemodynamics and pulmonary vascular function, the changes in the pulmonary vasculature that contribute to the increased vascular resistance and arterial pressure, and the pathogenic mechanisms involved in the development and progression of pulmonary hypertension. We focus on reviewing the pathogenic roles of membrane receptors, ion channels, and intracellular Ca2+ signaling in pulmonary vascular smooth muscle cells in the development and progression of pulmonary hypertension.

Transpulmonary amino acid metabolism in the sugen hypoxia model of pulmonary hypertension

In pulmonary artery hypertension (PAH), emerging evidence suggests that metabolic abnormalities may be contributing to cellular dysfunction in PAH. Metabolic abnormalities such as glycolytic shift have been observed intracellularly in several cell types in PAH, including microvacular endothelial cells (MVECs). Concurrently, metabolomics of human PAH samples has also revealed a variety of metabolic abnormalities; however the relationship between the intracellular metabolic abnormalities and the serum metabolome in PAH remains under investigation. In this study, we utilize the sugen/hypoxia (SuHx) rodent model of PAH to examine the RV, LV and MVEC intracellular metabolome (using targeted metabolomics) in normoxic and SuHx rats. We additionally validate key findings from our metabolomics experiments with data obtained from cell culture of normoxic and SuHx MVECs, as well as metabolomics of human serum samples from two different PAH patient cohorts. Taken together, our data, spanning rat serum, human serum and primary isolated rat MVECs reveal that: (1) key classes of amino acids (specifically, branched chain amino acids-BCAA) are lower in the pre-capillary (i.e., RV) serum of SuHx rats (and humans); (2) intracellular amino acid levels (in particular BCAAs) are increased in SuHx-MVECs; (3) there may be secretion rather than utilization of amino acids across the pulmonary microvasculature in PAH and (4) an oxidized glutathione gradient is present across the pulmonary vasculature, suggesting a novel fate for increased glutamine uptake (i.e., as a source of glutathione). in MVECs in PAH. In summary, these data reveal new insight into the shifts in amino acid metabolism occurring across the pulmonary circulation in PAH.

Mechanism of Hypoxia-Mediated Smooth Muscle Cell Proliferation Leading to Vascular Remodeling

Vascular remodeling refers to changes in the size, contraction, distribution, and flow rate of blood vessels and even changes in vascular function. Vascular remodeling can cause cardiovascular and cerebrovascular diseases. It can also lead to other systemic diseases, such as pulmonary hypertension, pulmonary atherosclerosis, chronic obstructive pulmonary disease, stroke, and ascites of broilers. Hypoxia is one of the main causes of vascular remodeling. Prolonged hypoxia or intermittent hypoxia can lead to loss of lung ventilation, causing respiratory depression, irregular respiratory rhythms, and central respiratory failure. Animals that are unable to adapt to the highland environment are also prone to sustained constriction of the small pulmonary arteries, increased resistance to pulmonary circulation, and impaired blood circulation, leading to pulmonary hypertension and right heart failure if they live in a highland environment for long periods of time. However, limited studies have been found on the relationship between hypoxia and vascular remodeling. Therefore, this review will explore the relationship between hypoxia and vascular remodeling from the aspects of endoplasmic reticulum stress, mitochondrial dysfunction, abnormal calcium channel, disordered cellular metabolism, abnormal expression of miRNA, and other factors. This will help to understand the detailed mechanism of hypoxia-mediated smooth muscle cell proliferation and vascular remodeling for the better treatment and management of diseases due to vascular remodeling.

Hypotension in hereditary cardiomyopathy

It is well accepted that hypertension may lead to the development of heart failure (HF). However, little is known about the development of hypotension that may contribute to the onset of hereditary cardiomyopathy (HCM), thus promoting heart failure and early death. The purpose of this study is to verify whether a decrease in blood pressure takes place during different phases of HCM (asymptomatic, necrosis, hypertrophy, and heart failure). Using the well-known animal model, the UM-X7.1 hamster strain of HCM (HCMH), our results showed the absence of a change in mean arterial pressure (MAP) during the asymptomatic phase preceding the development of necrosis in HCMHs when compared to age-matched normal hamster (NH). However, there was a progressive decrease in MAP that reached its lowest level during the heart failure phase. The MAP during the development of the necrosis phase of HCM was accompanied by a significant increase in the level of the sodium-hydrogen exchanger, NHE1. Treatments with the potent NHE1 inhibitor, EMD 87580 (rimeporide), did not affect MAP of NH. However, treatments with EMD 87580 during the three phases of the development of HCM significantly reversed the hypotension associated with HCM.Our results showed that the development of HCM is associated with hypotension. These results suggest that a decrease in blood pressure could be a biomarker signal for HCM leading to HF and early death. Since the blockade of NHE1 significantly but partially prevented the reduction in MAP, this suggests that other mechanisms can contribute to the development of hypotension in HCM.

Upregulation of Aquaporin 1 Mediates Increased Migration and Proliferation in Pulmonary Vascular Cells From the Rat SU5416/Hypoxia Model of Pulmonary Hypertension

Pulmonary arterial hypertension (PAH) is a progressive disorder characterized by exuberant vascular remodeling leading to elevated pulmonary arterial pressure, maladaptive right ventricular remodeling, and eventual death. The factors controlling pulmonary arterial smooth muscle cell (PASMC) and endothelial cell hyperplasia and migration, hallmark features of the vascular remodeling observed in PAH, remain poorly understood. We previously demonstrated that hypoxia upregulates the expression of aquaporin 1 (AQP1), a water channel, in PASMCs, and that this upregulation was required for hypoxia-induced migration and proliferation. However, whether the same is true in a model of severe PAH and in pulmonary microvascular endothelial cells (MVECs) is unknown. In this study, we used the SU5416 plus hypoxia (SuHx) rat model of severe pulmonary hypertension, which mimics many of the features of human PAH, to determine whether AQP1 levels were altered in PASMCs and MVECs and contributed to a hyperproliferative/hypermigratory phenotype. Rats received a single injection of SU5416 (20 mg/kg) and then were placed in 10% O2 for 3 weeks, followed by a return to normoxic conditions for an additional 2 weeks. We found that AQP1 protein levels were increased in both PASMCs and MVECs from SuHx rats, even in the absence of sustained hypoxic exposure, and that in MVECs, the increase in protein expression was associated with upregulation of AQP1 mRNA levels. Silencing of AQP1 had no significant effect on PASMCs from control animals but normalized enhanced migration and proliferation observed in cells from SuHx rats. Loss of AQP1 also reduced migration and proliferation in MVECs from SuHx rats. Finally, augmenting AQP1 levels in MVECs from control rats using forced expression was sufficient to increase migration and proliferation. These results demonstrate a key role for enhanced AQP1 expression in mediating abnormal migration and proliferation in pulmonary vascular cells from a rodent model that reflects many of the features of human PAH.

The mechanism of ions in pulmonary hypertension

Pulmonary hypertension（PH）is a kind of hemodynamic and pathophysiological state, in which the pulmonary artery pressure (PAP) rises above a certain threshold. The main pathological manifestation is pulmonary vasoconstriction and remodelling progressively. More and more studies have found that ions play a major role in the pathogenesis of PH. Many vasoactive substances, inflammatory mediators, transcription-inducing factors, apoptosis mediators, redox substances and translation modifiers can control the concentration of ions inside and outside the cell by regulating the activity of ion channels, which can regulate vascular contraction, cell proliferation, migration, apoptosis, inflammation and other functions. We all know that there are no effective drugs to treat PH. Ions are involved in the occurrence and development of PH, so it is necessary to clarify the mechanism of ions in PH as a therapeutic target for PH. The main ions involved in PH are calcium ion (Ca2+), potassium ion (K+), sodium ion (Na+) and chloride ion (Cl-). Here, we mainly discuss the distribution of these ions and their channels in pulmonary arteries and their role in the pathogenesis of PH.

Regulation of mitochondrial fragmentation in microvascular endothelial cells isolated from the SU5416/hypoxia model of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a morbid disease characterized by progressive right ventricle (RV) failure due to elevated pulmonary artery pressures (PAP). In PAH, histologically complex vaso-occlusive lesions in the pulmonary vasculature contribute to elevated PAP. However, the mechanisms underlying dysfunction of the microvascular endothelial cells (MVECs) that comprise a significant portion of these lesions are not well understood. We recently showed that MVECs isolated from the Sugen/hypoxia (SuHx) rat experimental model of PAH (SuHx-MVECs) exhibit increases in migration/proliferation, mitochondrial reactive oxygen species (ROS; mtROS) production, intracellular calcium levels ([Ca2+]i), and mitochondrial fragmentation. Furthermore, quenching mtROS with the targeted antioxidant MitoQ attenuated basal [Ca2+]i, migration and proliferation; however, whether increased mtROS-induced [Ca2+]i entry affected mitochondrial morphology was not clear. In this study, we sought to better understand the relationship between increased ROS, [Ca2+]i, and mitochondrial morphology in SuHx-MVECs. We measured changes in mitochondrial morphology at baseline and following inhibition of mtROS, with the targeted antioxidant MitoQ, or transient receptor potential vanilloid-4 (TRPV4) channels, which we previously showed were responsible for mtROS-induced increases in [Ca2+]i in SuHx-MVECs. Quenching mtROS or inhibiting TRPV4 attenuated fragmentation in SuHx-MVECs. Conversely, inducing mtROS production in MVECs from normoxic rats (N-MVECs) increased fragmentation. Ca2+ entry induced by the TRPV4 agonist GSK1017920A was significantly increased in SuHx-MVECs and was attenuated with MitoQ treatment, indicating that mtROS contributes to increased TRPV4 activity in SuHx-MVECs. Basal and maximal respiration were depressed in SuHx-MVECs, and inhibiting mtROS, but not TRPV4, improved respiration in these cells. Collectively, our data show that, in SuHx-MVECs, mtROS production promotes TRPV4-mediated increases in [Ca2+]i, mitochondrial fission, and decreased mitochondrial respiration. These results suggest an important role for mtROS in driving MVEC dysfunction in PAH.

Carbonic Anhydrase Inhibition Ameliorates Inflammation and Experimental Pulmonary Hypertension

Inflammation and vascular smooth muscle cell (VSMC) phenotypic switching are causally linked to pulmonary arterial hypertension (PAH) pathogenesis. Carbonic anhydrase inhibition induces mild metabolic acidosis and exerts protective effects in hypoxic pulmonary hypertension. Carbonic anhydrases and metabolic acidosis are further known to modulate immune cell activation. To evaluate if carbonic anhydrase inhibition modulates macrophage activation, inflammation, and VSMC phenotypic switching in severe experimental pulmonary hypertension, pulmonary hypertension was assessed in Sugen 5416/hypoxia (SU/Hx) rats after treatment with acetazolamide or ammonium chloride (NH4Cl). We evaluated pulmonary and systemic inflammation and characterized the effect of carbonic anhydrase inhibition and metabolic acidosis in alveolar macrophages and bone marrow-derived macrophages (BMDMs). We further evaluated the treatment effects on VSMC phenotypic switching in pulmonary arteries and pulmonary artery smooth muscle cells (PASMCs) and corroborated some of our findings in lungs and pulmonary arteries of patients with PAH. Both patients with idiopathic PAH and SU/Hx rats had increased expression of lung inflammatory markers and signs of PASMC dedifferentiation in pulmonary arteries. Acetazolamide and NH4Cl ameliorated SU/Hx-induced pulmonary hypertension and blunted pulmonary and systemic inflammation. Expression of carbonic anhydrase isoform 2 was increased in alveolar macrophages from SU/Hx animals, classically (M1) and alternatively (M2) activated BMDMs, and lungs of patients with PAH. Carbonic anhydrase inhibition and acidosis had distinct effects on M1 and M2 markers in BMDMs. Inflammatory cytokines drove PASMC dedifferentiation, and this was inhibited by acetazolamide and acidosis. The protective antiinflammatory effect of acetazolamide in pulmonary hypertension is mediated by a dual mechanism of macrophage carbonic anhydrase inhibition and systemic metabolic acidosis.

Rho kinase and Na+ /H+ exchanger mediate endothelin-1-induced pulmonary arterial smooth muscle cell proliferation and migration

Excessive production of endothelin‐1 (ET‐1) has been observed in almost all forms of pulmonary hypertension. ET‐1, a highly potent vasoconstrictor, can also potentiate pulmonary arterial smooth muscle cell (PASMC) growth and migration, both of which contribute to the vascular remodeling that occurs during the development of pulmonary hypertension. Increasing evidence indicates that alkalinization of intracellular pH (pH_i), typically due to activation of Na⁺/H⁺ exchange (NHE), is associated with enhanced PASMC proliferation and migration. We recently demonstrated that application of exogenous ET‐1 increased NHE activity in murine PASMCs via a mechanism requiring Rho kinase (ROCK). However, whether ROCK and/or increased NHE activity mediate ET‐1‐induced migration and proliferation in PASMCs remains unknown. In this study, we used fluorescent microscopy in transiently cultured PASMCs from distal pulmonary arteries of the rat and the pH‐sensitive dye, BCECF‐AM, to measure changes in resting pH_i and NHE activity induced by exposure to exogenous ET‐1 (10⁻⁸ mol/L) for 24 h. Cell migration and proliferation in response to ET‐1 were also measured using Transwell assays and BrdU incorporation, respectively. We found that application of exogenous ET‐1 had no effect on NHE1 expression, but increased pH_i, NHE activity, migration, and proliferation in rat PASMCs. Pharmacologic inhibition of NHE or ROCK prevented the ET‐1‐induced changes in cell function (proliferation and migration). Our results indicate that ET‐1 modulates PASMC migration and proliferation via changes in pH_i homeostasis through a pathway involving ROCK.

Exosome-Mediated Transfer of ACE (Angiotensin-Converting Enzyme) From Adventitial Fibroblasts of Spontaneously Hypertensive Rats Promotes Vascular Smooth Muscle Cell Migration

Migration of vascular smooth muscle cells (VSMCs) is pivotal for vascular remodeling in hypertension. Vascular adventitial fibroblasts (AFs) are important in the homeostasis of vascular structure. This study is designed to investigate the roles of AF exosomes (AFE) in VSMC migration and underling mechanism. Primary VSMCs and AFs were obtained from the aorta of spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. VSMC migration was evaluated with Boyden chamber assay and wound healing assay. AFE from WKY rats and SHR were isolated and identified. AFE from SHR promoted but AFE from WKY rats had no significant effect on VSMC migration. The effects of AFE on VSMC migration were prevented by an exosome inhibitor GW4869, an AT₁R (Ang II [angiotensin II] type 1 receptor) antagonist losartan, or an inhibitor of ACE (angiotensin-converting enzyme) captopril. ACE contents and activity were much higher in AFE from SHR than those from WKY rats. There were no significant difference in Ang II and AT₁R mRNA and protein levels between AFE from SHR and AFE from WKY rats. AFE from SHR increased Ang II and ACE contents and ACE activity in VSMCs of WKY rats and SHR. The changes of Ang II contents and ACE activity were prevented by captopril. ACE knockdown in AFs reduced ACE contents and activity in AFE from SHR and inhibited AFE-induced migration of VSMCs of WKY rats and those of SHR. These results indicate that exosomes from AFs of SHR transfer ACE to VSMCs, which increases Ang II levels and activates AT₁R in VSMCs and thereby promotes VSMC migration.

Reactive oxygen species induced Ca2+ influx via TRPV4 and microvascular endothelial dysfunction in the SU5416/hypoxia model of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a lethal disease characterized by elevations in pulmonary arterial pressure, in part due to formation of occlusive lesions in the distal arterioles of the lung. These complex lesions may comprise multiple cell types, including endothelial cells (ECs). To better understand the molecular mechanisms underlying EC dysfunction in PAH, lung microvascular endothelial cells (MVECs) were isolated from normoxic rats (N-MVECs) and rats subjected to SU5416 plus hypoxia (SuHx), an experimental model of PAH. Compared with N-MVECs, MVECs isolated from SuHx rats (SuHx-MVECs) appeared larger and more spindle shaped morphologically and expressed canonical smooth muscle cell markers smooth muscle-specific α-actin and myosin heavy chain in addition to endothelial markers such as Griffonia simplicifolia and von Willebrand factor. SuHx-MVEC mitochondria were dysfunctional, as evidenced by increased fragmentation/fission, decreased oxidative phosphorylation, and increased reactive oxygen species (ROS) production. Functionally, SuHx-MVECs exhibited increased basal levels of intracellular calcium concentration ([Ca2+]i) and enhanced migratory and proliferative capacity. Treatment with global (TEMPOL) or mitochondria-specific (MitoQ) antioxidants decreased ROS levels and basal [Ca2]i in SuHx-MVECs. TEMPOL and MitoQ also decreased migration and proliferation in SuHx-MVECs. Additionally, inhibition of ROS-induced Ca2+ entry via pharmacologic blockade of transient receptor potential vanilloid-4 (TRPV4) attenuated [Ca2]i, migration, and proliferation. These findings suggest a role for mitochondrial ROS-induced Ca2+ influx via TRPV4 in promoting abnormal migration and proliferation in MVECs in this PAH model.

Effects of FHL1 and P21 on hypoxia-induced pulmonary vascular remodeling in neonatal rats

Numerous studies have demonstrated that altered expression levels of four and a half LIM domains 1 (FHL1) and P21 are necessary for hypoxia-induced pulmonary vascular remodeling in both adult rats and human patients with idiopathic pulmonary arterial hypertension. However, whether FHL1 and P21 are present in the pulmonary artery and whether these proteins affect pulmonary vascular remodeling in hypoxia-induced pulmonary hypertension (HPH) in neonatal rats remain unknown. The present study investigated the effects of altered FHL1 and P21 expression on pulmonary vascular remodeling in neonatal rats with HPH. A total of 32 newborn Sprague-Dawley rats were exposed to hypoxia or room air for 7 or 14 days (n=8/subgroup). Parameters including the percentage of medial wall thickness (WT%), the percentage of medial wall area (WA%), right ventricular (RV) mean pressure, RV hypertrophy index (RVHI) and RV systolic pressure (RVSP) were measured to evaluate the development of HPH. Additionally, the expressions of FHL1 and P21 in the pulmonary artery smooth muscle cells (PASMCs) were measured by reverse transcription-quantitative polymerase chain reaction, western blot analysis and immunohistochemical staining. WA%, WT%, RV mean pressure, RVHI and RVSP were significantly increased in the HPH model group when compared with the control group (P<0.01). The protein expression levels of FHL1 were significantly increased in the HPH group (P<0.05), while the mRNA and protein expression levels of P21 were significantly reduced (P<0.05). Pearson correlation analysis indicated that the protein expressions of FHL1 and P21 were correlated with WA% and WT% (all P<0.001), and that the protein expression of P21 was negatively correlated with that of FHL1 (P<0.01). The results indicated that the expressions of FHL1 and P21 were altered in the PASMCs of newborn rats with HPH. Furthermore, FHL1 and P21 may serve important roles in pulmonary vascular remodeling.

Opsin 3 and 4 mediate light-induced pulmonary vasorelaxation that is potentiated by G protein-coupled receptor kinase 2 inhibition

We recently demonstrated that blue light induces vasorelaxation in the systemic mouse circulation, a phenomenon mediated by the nonvisual G protein-coupled receptor melanopsin (Opsin 4; Opn4). Here we tested the hypothesis that nonvisual opsins mediate photorelaxation in the pulmonary circulation. We discovered Opsin 3 (Opn3), Opn4, and G protein-coupled receptor kinase 2 (GRK2) in rat pulmonary arteries (PAs) and in pulmonary arterial smooth muscle cells (PASMCs), where the opsins interact directly with GRK2, as demonstrated with a proximity ligation assay. Light elicited an intensity-dependent relaxation of PAs preconstricted with phenylephrine (PE), with a maximum response between 400 and 460 nm (blue light). Wavelength-specific photorelaxation was attenuated in PAs from Opn4^-/- mice and further reduced following shRNA-mediated knockdown of Opn3. Inhibition of GRK2 amplified the response and prevented physiological desensitization to repeated light exposure. Blue light also prevented PE-induced constriction in isolated PAs, decreased basal tone, ablated PE-induced single-cell contraction of PASMCs, and reversed PE-induced depolarization in PASMCs when GRK2 was inhibited. The photorelaxation response was modulated by soluble guanylyl cyclase but not by protein kinase G or nitric oxide. Most importantly, blue light induced significant vasorelaxation of PAs from rats with chronic pulmonary hypertension and effectively lowered pulmonary arterial pressure in isolated intact perfused rat lungs subjected to acute hypoxia. These findings show that functional Opn3 and Opn4 in PAs represent an endogenous "optogenetic system" that mediates photorelaxation in the pulmonary vasculature. Phototherapy in conjunction with GRK2 inhibition could therefore provide an alternative treatment strategy for pulmonary vasoconstrictive disorders.

Sodium-Hydrogen-Exchanger expression in human sperm and its relationship with semen parameters

PURPOSE

Sperm-specific sodium-hydrogen exchanger (sNHE) is essential to maintain sperm normal function in mice; however, its role in human sperm has not been clarified to date. The aim of this study is to investigate the expression pattern of sNHE in human spermatozoa and its relationship with sperm functional parameters.

METHOD

Semen samples from 68 asthenozoospermic and 61 normozoospermic men were analyzed for sperm concentration, motility, and acrosome reaction, and high motile spermatozoa were collected by swim-up method. The expression of sNHE in spermatozoa was detected by Western blot and immunofluorescence staining. The relationship between sNHE expression and sperm parameters was assessed.

RESULTS

We identified sNHE is mainly localized to the principal piece of the human sperm tail. The expression of sNHE was positively correlated with sperm concentration, total number, and progressive motility. Moreover, sNHE expression was upregulated in swim-up sperm and associated with most of sperm motility parameters including straight line velocity and curvilinear velocity. Our results also showed that sNHE expression is decreased in sperm from patients with asthenozoospermia compared with that from normal controls. However, no correlation was found between sNHE expression and acrosome reaction in spermatozoa.

CONCLUSIONS

The expression pattern of sNHE suggested that this protein may be involved in the regulation of sperm motility, and aberration of its expression in sperm may contribute to the pathogenesis of asthenozoospermia.

The Na+/H+ exchanger contributes to increased smooth muscle proliferation and migration in a rat model of pulmonary arterial hypertension

Increased muscularity of small pulmonary vessels, involving enhanced proliferation and migration of pulmonary arterial smooth muscle cells (PASMCs), is a key component of the vascular remodeling underlying the development of pulmonary hypertension (PH). Stimuli such as growth factors and hypoxia induce PASMC alkalinization, proliferation, and migration through upregulation of the Na⁺/H⁺ exchanger (NHE), inhibition of which prevents the development of hypoxia‐induced vascular remodeling and PH. We wanted to explore whether NHE was also necessary for pathologic PASMC proliferation and migration in a model of pulmonary arterial hypertension (PAH), a severe form of PH not associated with persistent hypoxia. PASMCs were isolated from rats exposed to SU5416‐hypoxia (SuHx) followed by return to normoxia and from vehicle controls. We measured resting intracellular pH (pH_i) and NHE activity using the pH‐sensitive fluorescent dye BCECF‐AM. PASMC proliferation and migration were assessed using BrdU incorporation and transwell filters, respectively. NHE activity was increased in SuHx PASMCs, although resting pH_i was unchanged. SuHx PASMCs also exhibited increased proliferation and migration relative to controls, which was attenuated in the setting of pharmacologic inhibition of NHE. Our findings suggest that increased NHE activity contributes to pathologic PASMC function in the SuHx model of PAH, although this effect does not appear to be mediated by global changes in pH_i homeostasis.