Calcilytics enhance sildenafil-induced antiproliferation in idiopathic pulmonary arterial hypertension

Corosolic acid attenuates platelet-derived growth factor signaling in macrophages and smooth muscle cells of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a progressive and life-threatening disease that is characterized by vascular remodeling of the pulmonary artery. Pulmonary vascular remodeling is primarily caused by the excessive proliferation and migration of pulmonary arterial smooth muscle cells (PASMCs), which are facilitated by perivascular inflammatory cells including macrophages. Corosolic acid (CRA) is a natural pentacyclic triterpenoid that exerts anti-inflammatory effects. In the present study, the effects of CRA on the viability of macrophages were examined using monocrotaline (MCT)-induced PAH rats and human monocyte-derived macrophages. Although we previously reported that CRA inhibited signal transducer and activator of transcription 3 (STAT3) signaling and ameliorated pulmonary vascular remodeling in PAH, the inhibitory mechanism remains unclear. Therefore, the underlying mechanisms were investigated using PASMCs from idiopathic PAH (IPAH) patients. In MCT-PAH rats, CRA inhibited the accumulation of macrophages around remodeled pulmonary arteries. CRA reduced the viability of human monocyte-derived macrophages. In IPAH-PASMCs, CRA attenuated cell proliferation and migration facilitated by platelet-derived growth factor (PDGF)-BB released from macrophages and PASMCs. CRA also downregulated the expression of PDGF receptor β and its signaling pathways, STAT3 and nuclear factor-κB (NF-κB). In addition, CRA attenuated the phosphorylation of PDGF receptor β and STAT3 following the PDGF-BB simulation. The expression and phosphorylation levels of PDGF receptor β after the PDGF-BB stimulation were reduced by the small interfering RNA knockdown of NF-κB, but not STAT3, in IPAH-PASMCs. In conclusion, CRA attenuated the PDGF-PDGF receptor β-STAT3 and PDGF-PDGF receptor β-NF-κB signaling axis in macrophages and PASMCs, and thus, ameliorated pulmonary vascular remodeling in PAH.

Calcium sensing receptor: A promising therapeutic target in pulmonary hypertension

Pulmonary hypertension (PH) is characterized by elevation of pulmonary arterial pressure and pulmonary vascular resistance. The increased pulmonary arterial pressure and pulmonary vascular resistance due to sustained pulmonary vasoconstriction and pulmonary vascular remodeling can lead to right heart failure and eventual death. A rise in intracellular Ca2+ concentration ([Ca2+]i) and enhanced pulmonary arterial smooth muscle cells (PASMCs) proliferation contribute to pulmonary vasoconstriction and pulmonary vascular remodeling. Recent studies demonstrated that extracellular calcium sensing receptor (CaSR) as a G-protein coupled receptor participates in [Ca2+]i increase induced by hypoxia in the experimental animals of PH and in PH patients. Pharmacological blockade or gene knockout of CaSR significantly attenuates the development of PH. This review will aim to discuss and update the pathogenicity of CaSR attributed to onset and progression in PH.

Sildenafil Improves Pulmonary Vascular Remodeling in a Rat Model of Persistent Pulmonary Hypertension of the Newborn

ABSTRACT

Persistent pulmonary hypertension of the newborn (PPHN) is characterized by pulmonary arterial remodeling mainly because of apoptosis resistance and excessive proliferation of pulmonary artery smooth muscle cells (PASMCs). Sildenafil is a phosphodiesterase-5 inhibitor. Some reports have shown that sildenafil exerts protective effects against PPHN. However, the function of sildenafil in PPHN and the underlying molecular mechanisms is not clear. Here, we revealed that sildenafil effectively suppressed hypoxia-induced PASMC proliferation and apoptosis inhibition ( P < 0.05). Also, sildenafil obviously reduced ventricular hypertrophy, and inhibited pulmonary vascular remodeling in the PPHN model ( P < 0.05). Moreover, sildenafil treatment significantly attenuated the induction of Notch3 and Hes1 induced by hypoxia treatment ( P < 0.05). Furthermore, overexpression of Notch3 abolished the reduction of PASMC proliferation and promotion of PASMC apoptosis induced by sildenafil under hypoxia ( P < 0.05), whereas knockdown of Notch3 had an opposite effect ( P < 0.05). Together, our study demonstrates that sildenafil shows a potential benefit against the development of PPHN by inhibiting Notch3 signaling, providing a strategy for treating PPHN in the future.

Corosolic acid ameliorates vascular remodeling in pulmonary arterial hypertension via the downregulation of STAT3 signaling

Pulmonary arterial hypertension (PAH) is a progressive and fatal disease that is characterized by vascular remodeling of the pulmonary artery. PAH remodeling is primarily caused by the excessive proliferation of pulmonary arterial smooth muscle cells (PASMCs). Therefore, an inhibitory mechanism is expected as a target for the treatment of PAH. Corosolic acid (CRA) is a pentacyclic triterpenoid extracted from the leaves of Banaba (Lagerstroemia speciosa) that exerts anti-diabetic, anti-inflammatory, and anti-tumor effects. In the present study, the effects of CRA on PAH remodeling were examined using PASMCs from idiopathic pulmonary arterial hypertension (IPAH) patients and monocrotaline (MCT)-induced pulmonary hypertensive (PH) rats. CRA inhibited the excessive proliferation of IPAH-PASMCs in a concentration-dependent manner (IC₅₀ = 14.1 μM). It also reduced the migration of IPAH-PASMCs. The CRA treatment downregulated the expression of signal transducer and activator of transcription 3 (STAT3) in IPAH-PASMCs. In MCT-PH rats, the administration of CRA (1 mg/kg/day) attenuated increases in right ventricular systolic pressure, pulmonary vascular remodeling, and right ventricular hypertrophy. CRA also decreased the expression of STAT3 in pulmonary arterial smooth muscles from MCT-PH rats. In conclusion, the anti-proliferative and anti-migratory effects of CRA in PASMCs ameliorated PAH remodeling by downregulating STAT3 signaling pathways.

WNT5B promotes vascular smooth muscle cell dedifferentiation via mitochondrial dynamics regulation in chronic thromboembolic pulmonary hypertension

Chronic thromboembolic pulmonary hypertension (CTEPH) is characterized by proliferative vascular remodeling. Abnormal vascular smooth muscle cell (VSMC) phenotype switching is crucial to this process, highlighting the need for VSMC metabolic changes to cover cellular energy demand in CTEPH. We report that elevated Wnt family member 5B (WNT5B) expression is associated with vascular remodeling and promotes VSMC phenotype switching via mitochondrial dynamics regulation in CTEPH. Using primary culture of pulmonary artery smooth muscle cells, we show that high WNT5B expression activates VSMC proliferation and migration and results in mitochondrial fission via noncanonical Wnt signaling in CTEPH. Abnormal VSMC proliferation and migration were abolished by mitochondrial division inhibitor 1, an inhibitor of mitochondrial fission. Secreted frizzled-related protein 2, a soluble scavenger of Wnt signaling, attenuates VSMC proliferation and migration by accelerating mitochondrial fusion. These findings indicate that WNT5B is an essential regulator of mitochondrial dynamics, contributing to VSMC phenotype switching in CTEPH.

Calcium-sensing receptor in the development and treatment of pulmonary hypertension

Calcium-sensing receptor (CaSR) is widely involved in the cell proliferation, differentiation, migration, adhesion and apoptosis, which can affect the vascular remodeling in the humanbody. The main ligand of CaSR is extracellular Ca²⁺. CaSR has the physiological significance in Ca²⁺ homeostasis. Pulmonary vascular remodeling is one of the main histopathological changes of pulmonary hypertension (PH). The abnormal proliferation of pulmonary artery smooth muscle cells (PASMCs) results in the pulmonary vascular remodeling. CaSR is an important regulator of [Ca²⁺]_i. [Ca²⁺]_i is the main cause of the excessive pulmonary vascular remodeling in patients with PH. In this review, it was conclued that the structure of CaSR was prone to explore the devolopment or the treatment of PH. It was found that the regulation of CaSR with some miRNA could inhibit the proliferation of PASMCs, and that CaSR could affect the occurrence of autophagy in PH. Therefore, CaSR would become a new therapeutic target to PH.

A Novel Mechanism of Sildenafil Improving the Excessive Proliferation and H2S Production in Pulmonary Arterial Smooth Muscle Cells

The dysregulation of pulmonary arterial vasoactive mediators or excessive proliferation of pulmonary arterial smooth muscle cells (PASMCs) might result in contraction or remodeling of pulmonary blood vessels, leading to related lung diseases. Recent studies suggest that hydrogen sulfide (H2S), a gaseous vasodilator generated in the blood vessels by the enzymes cystathionine γ-lyase (CSE) and cystathionine-β-synthase (CBS), could induce the vasodilation, thus improving contraction or remodeling-induced lung diseases. In this study, we hypothesized that PASMCs could produce H2S and relax the pulmonary artery, and its mechanism is related to CSE, CBS, and TRPV4 channels by affecting both the excessive proliferation and pulmonary vasoconstriction in PASMCs. We found that the sildenafil treatment could remarkably promote H2S production and control the proliferation in PASMCs; meanwhile, the protein levels of CSE and CBS and the intracellular concentration of calcium could also be increased by sildenafil. Moreover, the effects of sildenafil could be reversed by a CBS inhibitor or a CSE inhibitor, indicating that sildenafil could affect CSE and CBS to modulate the production of H2S and the proliferation in rat PASMCs. Together, we demonstrated a new mechanism for sildenafil to modulate the synthesis of H2S and cell proliferation in PASMCs by affecting CSE and CBS. TRPV4-dependent Ca events and BMP4 may also be involved.

Sildenafil for Pulmonary Arterial Hypertension

Pulmonary hypertension is a life-threatening illness with debilitating physical and emotional consequences. The progression of this devastating disease is characterized by a continuous increase in pulmonary vascular resistance, which results in elevated pulmonary artery pressure and leads to right heart failure. Treatment is focused on targeting the underlying complex etiology via the endothelin, prostacyclin, and nitric oxide (NO) pathways. Emergence of new treatments over the past 2 decades has led to improvement in the functional status and time to clinical worsening. Even with recent advances, outcomes remain suboptimal. Phosphodiesterase-5 (PDE-5) inhibitors, such as sildenafil, were approved for treatment of pulmonary arterial hypertension (PAH) by the Food and Drug Administration (FDA) in 2005, which holds promise in improving quality of life and therefore making this class of medications effective palliative therapy agents. In this review, we summarize the emergence of sildenafil as a treatment for PAH and its role as palliative therapy.

Platelet-derived growth factor up-regulates Ca2+-sensing receptors in idiopathic pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a progressive and fatal disease associated with remodeling of the pulmonary artery. We previously reported that the Ca²⁺-sensing receptor (CaSR) is up-regulated in pulmonary arterial smooth muscle cells (PASMCs) from patients with idiopathic PAH (IPAH) and contributes to enhanced Ca²⁺ responses and excessive cell proliferation. However, the mechanisms underlying the up-regulation of CaSR have not yet been elucidated. We herein examined involvement of platelet-derived growth factor (PDGF) on CaSR expression, Ca²⁺ responses, and proliferation in PASMCs. The expression of PDGF receptors was higher in PASMCs from patients with IPAH than in PASMCs from normal subjects. In addition, PDGF-induced activation of PDGF receptors and their downstream molecules [ERK1/2, p38, protein kinase B, and signal transducer and activator of transcription (STAT) 1/3] were sustained longer in PASMCs from patients with IPAH. The PDGF-induced CaSR up-regulation was attenuated by small interfering RNA knockdown of PDGF receptors and STAT1/3, and by the treatment with imatinib. In monocrotaline-induced pulmonary hypertensive rats, the up-regulation of CaSR was reduced by imatinib. The combination of NPS2143 and imatinib additively inhibited the development of pulmonary hypertension. These results suggest that enhanced PDGF signaling is involved in CaSR up-regulation, leading to excessive PASMC proliferation and vascular remodeling in patients with IPAH. The linkage between CaSR and PDGF signals is a novel pathophysiological mechanism contributing to the development of PAH.-Yamamura, A., Nayeem, M. J., Al Mamun, A., Takahashi, R., Hayashi, H., Sato, M. Platelet-derived growth factor up-regulates Ca²⁺-sensing receptors in idiopathic pulmonary arterial hypertension.

Calcium sensing receptor expression and signalling in cardiovascular physiology and disease

Initially identified in the parathyroidea, the calcium sensing receptor (CaSR) is now recognized as an ubiquitously expressed receptor that exerts specific functions in multiple organs including the cardiovascular system. This review will focus on the role that CaSR plays in vascular and cardiac tissues. In the vasculature, CaSR is expressed in endothelial and smooth muscle cells. CaSR of endothelial cells participates in part to the regulation of local perfusion by linkage of CaSR activation to endothelial hyperpolarization and nitric oxide release. CaSR of smooth muscle cells is involved in the control of proliferation. In the pulmonary vasculature, however, CaSR participates in the onset of pulmonary hypertension, making CaSR antagonism a therapeutic option in this case. In the heart, CaSR is expressed in cardiac fibroblasts and myoyctes, contributing to normal cardiac function and composition of extracellular matrix. More important, activation of CaSR may participate in the cardiac protective effects of ischaemic pre-conditioning. In conclusion, CaSR plays an important physiological role in many regulatory pathways of the cardiovascular system, but due to the complex interaction between various cardiovascular cells and cell-specific effects, use of activators or inhibitors of CaSR for treatment of specific disease forms is yet not on the way.

Current Trends and Future Perspectives in the Treatment of Pulmonary Arterial Hypertension

Pulmonary hypertension continues to be a life-threatening illness with debilitating physical and emotional consequences affecting around 1% of global population. The progression of this devastating disease is characterized by increase in pulmonary vascular resistance resulting in elevated pulmonary pressure, eventually leading to right heart failure and death. Better understanding of pathophysiology has led to substantial improvements in terms of availability of treatment options. The purpose of this review is to summarize the currently available treatment options along with pertinent trials and possible future therapies of pulmonary arterial hypertension.

Tadalafil induces antiproliferation, apoptosis, and phosphodiesterase type 5 downregulation in idiopathic pulmonary arterial hypertension in vitro

Idiopathic pulmonary arterial hypertension (IPAH) is a fatal disease of the pulmonary artery resulting from a currently unidentified etiology. IPAH is pathologically characterized as sustained vasoconstriction and vascular remodeling of the pulmonary artery. Vascular remodeling is mediated by enhanced proliferation and reduced apoptosis in pulmonary arterial smooth muscle cells (PASMCs). Based on its pathological mechanism, specific phosphodiesterase type 5 (PDE5) inhibitors have been used in the treatment of IPAH. In addition to sildenafil, tadalafil has been approved for the treatment of IPAH. However, the effects of tadalafil on excessive proliferation of IPAH-PASMCs currently remain unknown. In the present study, the in vitro pharmacological profiles of tadalafil for cell proliferation and apoptosis were assessed in IPAH-PASMCs using MTT, BrdU incorporation, and caspase 3/7 assays. Expression analyses revealed that PDE5 mRNA and protein expression levels were markedly higher in IPAH-PASMCs than in normal-PASMCs. The treatment with tadalafil inhibited the excessive proliferation of IPAH-PASMCs in a concentration-dependent manner with an IC₅₀ value of 4.5μM. On the other hand, tadalafil (0.03-100μM) did not affect cell growth of PASMCs from normal subjects and patients with chronic thromboembolic pulmonary hypertension (CTEPH). In addition, tadalafil induced apoptosis in IPAH-PASMCs. The antiproliferative and apoptotic effects of tadalafil were markedly stronger than those of sildenafil and vardenafil. The upregulated expression of PDE5 in IPAH-PASMCs was significantly attenuated by a long-term treatment with tadalafil. Taken together, these results indicate that tadalafil attenuates vascular remodeling by inhibiting cell proliferation, promoting apoptosis, and downregulating PDE5 in IPAH-PASMCs, thereby ameliorating IPAH.

Sildenafil attenuates hypoxic pulmonary remodelling by inhibiting bone marrow progenitor cells

The recruitment of bone marrow (BM)-derived progenitor cells to the lung is related to pulmonary remodelling and the pathogenesis of pulmonary hypertension (PH). Although sildenafil is a known target in PH treatment, the underlying molecular mechanism is still elusive. To test the hypothesis that the therapeutic effect of sildenafil is linked to the reduced recruitment of BM-derived progenitor cells, we induced pulmonary remodelling in rats by two-week exposure to chronic hypoxia (CH, 10% oxygen), a trigger of BM-derived progenitor cells. Rats were treated with either placebo (saline) or sildenafil (1.4 mg/kg/day ip) during CH. Control rats were kept in room air (21% oxygen) with no treatment. As expected, sildenafil attenuated the CH-induced increase in right ventricular systolic pressure and right ventricular hypertrophy. However, sildenafil suppressed the CH-induced increase in c-kit⁺ cells in the adventitia of pulmonary arteries. Moreover, sildenafil reduced the number of c-kit⁺ cells that colocalize with tyrosine kinase receptor 2 (VEGF-R2) and CD68 (a marker for macrophages), indicating a positive effect on moderating hypoxia-induced smooth muscle cell proliferation and inflammation without affecting the pulmonary levels of hypoxia-inducible factor (HIF)-1α. Furthermore, sildenafil depressed the number of CXCR4⁺ cells. Collectively, these findings indicate that the improvement in pulmonary haemodynamic by sildenafil is linked to decreased recruitment of BM-derived c-kit⁺ cells in the pulmonary tissue. The attenuation of the recruitment of BM-derived c-kit⁺ cells by sildenafil may provide novel therapeutic insights into the control of pulmonary remodelling.

The calcilytics Calhex-231 and NPS 2143 and the calcimimetic Calindol reduce vascular reactivity via inhibition of voltage-gated Ca2+ channels

The present study investigates the effect of commonly used negative and positive allosteric modulators of the calcium-sensing receptor (CaSR) on vascular reactivity. In wire myography studies, increasing [Ca2+]o from 1mM to 6mM induced concentration-dependent relaxations of methoxamine-induced pre-contracted rabbit mesenteric arteries, with 6mM [Ca2+]o producing almost complete relaxation. [Ca2+]o-induced relaxations were attenuated in the presence of the calcilytics Calhex-231 and NPS 2143, and abolished by the removal of the endothelium. In addition to their calcilytic effects, Calhex-231 and NPS 2143 also produced concentration-dependent inhibitions of methoxamine- or KCl-induced precontracted tone, which were unaffected by removal of the endothelium and unopposed in the presence of the calcimimetic Calindol. In vessels with depleted Ca2+ stores, contractions mediated by Ca2+ influx via voltage-gated Ca2+ channels (VGCCs) were inhibited by Calhex231. In freshly isolated single rabbit mesenteric artery smooth muscle cells, Calhex-231 and NPS 2143 inhibited whole-cell VGCC currents. Application of Calindol also inhibited methoxamine- and KCl-induced pre-contracted tone, and inhibited whole-cell VGCC currents. In conclusion, in addition to their CaSR-mediated actions in the vasculature, Calhex-231, NPS 2143 and Calindol reduce vascular contractility via direct inhibition of VGCCs.

Calcium-Sensing Receptor Regulates Cytosolic [Ca 2+ ] and Plays a Major Role in the Development of Pulmonary Hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease characterized by elevated pulmonary vascular resistance (PVR) leading to right heart failure and premature death. The increased PVR results in part from pulmonary vascular remodeling and sustained pulmonary vasoconstriction. Excessive pulmonary vascular remodeling stems from increased pulmonary arterial smooth muscle cell (PASMC) proliferation and decreased PASMC apoptosis. A rise in cytosolic free Ca²⁺ concentration ([Ca²⁺]_cyt) in PASMC is a major trigger for pulmonary vasoconstriction and a key stimulus for PASMC proliferation and migration, both contributing to the development of pulmonary vascular remodeling. PASMC from patients with idiopathic PAH (IPAH) have increased resting [Ca²⁺]_cyt and enhanced Ca²⁺ influx. Enhanced Ca²⁺ entry into PASMC due to upregulation of membrane receptors and/or Ca²⁺ channels may contribute to PASMC contraction and proliferation and to pulmonary vasoconstriction and pulmonary vascular remodeling. We have shown that the extracellular Ca²⁺-sensing receptor (CaSR), which is a member of G protein-coupled receptor (GPCR) subfamily C, is upregulated, and the extracellular Ca²⁺-induced increase in [Ca²⁺]_cyt is enhanced in PASMC from patients with IPAH in comparison to PASMC from normal subjects. Pharmacologically blockade of CaSR significantly attenuate the development and progression of experimental pulmonary hypertension in animals. Additionally, we have demonstrated that dihydropyridine Ca²⁺ channel blockers (e.g., nifedipine), which are used to treat PAH patients but are only effective in 15–20% of patients, activate CaSR resulting in an increase in [Ca²⁺]_cyt in IPAH-PASMC, but not normal PASMC. Our data indicate that CaSR functionally couples with transient receptor potential canonical (TRPC) channels to mediate extracellular Ca²⁺-induced Ca²⁺ influx and increase in [Ca²⁺]_cyt in IPAH-PASMC. Upregulated CaSR is necessary for the enhanced extracellular Ca²⁺-induced increase in [Ca²⁺]_cyt and the augmented proliferation of PASMC in patients with IPAH. This review will highlight the pathogenic role of CaSR in the development and progression of PAH.

Emerging concepts in smooth muscle contributions to airway structure and function: implications for health and disease

Airway structure and function are key aspects of normal lung development, growth, and aging, as well as of lung responses to the environment and the pathophysiology of important diseases such as asthma, chronic obstructive pulmonary disease, and fibrosis. In this regard, the contributions of airway smooth muscle (ASM) are both functional, in the context of airway contractility and relaxation, as well as synthetic, involving production and modulation of extracellular components, modulation of the local immune environment, cellular contribution to airway structure, and, finally, interactions with other airway cell types such as epithelium, fibroblasts, and nerves. These ASM contributions are now found to be critical in airway hyperresponsiveness and remodeling that occur in lung diseases. This review emphasizes established and recent discoveries that underline the central role of ASM and sets the stage for future research toward understanding how ASM plays a central role by being both upstream and downstream in the many interactive processes that determine airway structure and function in health and disease.