Sildenafil inhibits chronically hypoxic upregulation of canonical transient receptor potential expression in rat pulmonary arterial smooth muscle

Sodium Houttuyfonate Alleviates Monocrotaline-induced Pulmonary Hypertension by Regulating Orai1 and Orai2

An increased intracellular Ca2+ concentration ([Ca2+]i) is a key trigger for pulmonary arterial smooth muscle cell (PASMC) proliferation and contributes greatly to pulmonary hypertension (PH). Extracellular Ca2+ influx via a store-operated Ca2+ channel, termed store-operated Ca2+ entry (SOCE), is a crucial mechanism for [Ca2+]i increase in PASMCs. Calcium release-activated calcium modulator (Orai) proteins, consisting of three members (Orai1-3), are the main components of the store-operated Ca2+ channel. Sodium houttuyfonate (SH) is a product of the addition reaction of sodium bisulfite and houttuynin and has antibacterial, antiinflammatory, and other properties. In this study, we assessed the contributions of Orai proteins to monocrotaline (MCT)-enhanced SOCE, [Ca2+]i, and cell proliferation in PASMCs and determined the effect of SH on MCT-PH and the underlying mechanism, focusing on Orai proteins, SOCE, and [Ca2+]i in PASMCs. Our results showed that: 1) Orai1 and Orai2 were selectively upregulated in the distal pulmonary arteries and the PASMCs of MCT-PH rats; 2) knockdown of Orai1 or Orai2 reduced SOCE, [Ca2+]i, and cell proliferation without affecting their expression in PASMCs in MCT-PH rats; 3) SH significantly normalized the characteristic parameters in a dose-dependent manner in the MCT-PH rat model; and 4) SH decreased MCT-enhanced SOCE, [Ca2+]i, and PASMC proliferation via Orai1 or Orai2. These results indicate that SH likely exerts its protective role in MCT-PH by inhibiting the Orai1,2-SOCE-[Ca2+]i signaling pathway.

Exploring the pathogenesis of pulmonary vascular disease

Pulmonary hypertension (PH) is a complex cardiopulmonary disorder impacting the lung vasculature, resulting in increased pulmonary vascular resistance that leads to right ventricular dysfunction. Pulmonary hypertension comprises of 5 groups (PH group 1 to 5) where group 1 pulmonary arterial hypertension (PAH), results from alterations that directly affect the pulmonary arteries. Although PAH has a complex pathophysiology that is not completely understood, it is known to be a multifactorial disease that results from a combination of genetic, epigenetic and environmental factors, leading to a varied range of symptoms in PAH patients. PAH does not have a cure, its incidence and prevalence continue to increase every year, resulting in higher morbidity and mortality rates. In this review, we discuss the different pathologic mechanisms with a focus on epigenetic modifications and their roles in the development and progression of PAH. These modifications include DNA methylation, histone modifications, and microRNA dysregulation. Understanding these epigenetic modifications will improve our understanding of PAH and unveil novel therapeutic targets, thus steering research toward innovative treatment strategies.

Role of transient receptor potential channels in the regulation of vascular tone

Vascular tone is a major element in the control of hemodynamics. Transient receptor potential (TRP) channels conducting monovalent and/or divalent cations (e.g. Na+ and Ca2+) are expressed in the vasculature. Accumulating evidence suggests that TRP channels participate in regulating vascular tone by regulating intracellular Ca2+ signaling in both vascular smooth muscle cells (VSMCs) and endothelial cells (ECs). Aberrant expression/function of TRP channels in the vasculature is associated with vascular dysfunction in systemic/pulmonary hypertension and metabolic syndromes. This review intends to summarize our current knowledge of TRP-mediated regulation of vascular tone in both physiological and pathophysiological conditions and to discuss potential therapeutic approaches to tackle abnormal vascular tone due to TRP dysfunction.

Small molecules targeting canonical transient receptor potential channels: an update

Transient receptor potential canonical (TRPC) channels belong to an important class of non-selective cation channels. This channel family consists of multiple members that widely participate in various physiological and pathological processes. Previous studies have uncovered the intricate regulation of these channels, as well as the spatial arrangement of TRPCs and the binding sites for various small molecule compounds. Multiple small molecules have been identified as selective agonists or inhibitors targeting different subtypes of TRPC, including potential preclinical drug candidates. This review covers recent advancements in the understanding of TRPC regulation and structure and the discovery of TRPC small molecules over the past few years, with the aim of facilitating research on TRPCs and small-molecule drug discovery.

The Xanthine Derivative KMUP-1 Inhibits Hypoxia-Induced TRPC1 Expression and Store-Operated Ca2+ Entry in Pulmonary Arterial Smooth Muscle Cells

Exposure to hypoxia results in the development of pulmonary arterial hypertension (PAH). An increase in the intracellular Ca2+ concentration ([Ca2+]i) in pulmonary artery smooth muscle cells (PASMCs) is a major trigger for pulmonary vasoconstriction and proliferation. This study investigated the mechanism by which KMUP-1, a xanthine derivative with phosphodiesterase inhibitory activity, inhibits hypoxia-induced canonical transient receptor potential channel 1 (TRPC1) protein overexpression and regulates [Ca2+]i through store-operated calcium channels (SOCs). Ex vivo PASMCs were cultured from Sprague-Dawley rats in a modular incubator chamber under 1% O2/5% CO2 for 24 h to elucidate TRPC1 overexpression and observe the Ca2+ release and entry. KMUP-1 (1 μM) inhibited hypoxia-induced TRPC family protein encoded for SOC overexpression, particularly TRPC1. KMUP-1 inhibition of TRPC1 protein was restored by the protein kinase G (PKG) inhibitor KT5823 (1 μM) and the protein kinase A (PKA) inhibitor KT5720 (1 μM). KMUP-1 attenuated protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA, 1 μM)-upregulated TRPC1. We suggest that the effects of KMUP-1 on TRPC1 might involve activating the cyclic guanosine monophosphate (cGMP)/PKG and cyclic adenosine monophosphate (cAMP)/PKA pathways and inhibiting the PKC pathway. We also used Fura 2-acetoxymethyl ester (Fura 2-AM, 5 μM) to measure the stored calcium release from the sarcoplasmic reticulum (SR) and calcium entry through SOCs in hypoxic PASMCs under treatment with thapsigargin (1 μM) and nifedipine (5 μM). In hypoxic conditions, store-operated calcium entry (SOCE) activity was enhanced in PASMCs, and KMUP-1 diminished this activity. In conclusion, KMUP-1 inhibited the expression of TRPC1 protein and the activity of SOC-mediated Ca2+ entry upon SR Ca2+ depletion in hypoxic PASMCs.

Down-regulation of connexin 43 contributes to structure and function of pulmonary artery in nicotine-administered mice

Dysregulated connexin signaling is implicated in the pathophysiology of pulmonary artery hypertension (PAH). Nicotine affects pulmonary vascular remodeling. However, the potential mechanistic link between connexin signaling and nicotine-induced pulmonary artery remodeling remains unclear. We aimed to investigate the role of connexin 43 (Cx43) in pulmonary artery remodeling in nicotine-administered C57BL/6 J wild-type (WT) and Cx43 heterozygous (Cx43^+/-) mice. Hemodynamic parameters and right ventricle pathology were assessed in the mice. Serum biochemical indices of hepatic and renal function were measured. The RT-PCR, immunofluorescence, and western blotting were conducted to evaluate Cx43 mRNA and protein levels. We performed histological staining to identify pulmonary arteries. Wire myography was used to examine contraction and relaxation responses in the pulmonary arteries. Pulmonary vascular permeability was assessed through Evans blue staining. Compared with the WT group, the Cx43^+/- group showed lower Cx43 mRNA and protein expression in the pulmonary arteries (P < 0.01). Nicotine treatment significantly increased Cx43 expression (P < 0.01) and induced morphological changes in the pulmonary arteries (P < 0.01). Our findings suggest that Cx43 plays a crucial role in pulmonary artery reactivity and permeability in mice. Furthermore, downregulation of Cx43 expression may contribute to alterations in pulmonary artery structure and function.

Sildenafil protects against pulmonary hypertension induced by hypoxia in neonatal rats via activation of PPARγ‑mediated downregulation of TRPC

Persistent pulmonary hypertension of the newborn (PPHN) is a common pulmonary vascular disease during the neonatal period, and it is associated with a high clinical mortality rate and a poor prognosis. At present, the treatment of PPHN is based mainly on inhaled nitric oxide (iNO), high‑frequency ventilation, and pulmonary vasodilators. Sildenafil has gradually begun to be used in recent years for the treatment of PPHN and has exhibited some success; however, its detailed mechanism of action requires further elucidation. An animal model of neonatal pulmonary hypertension (neonatal rats, 48 h after birth, 10% O2, 14 days) as well as a cell model [human pulmonary artery smooth muscle cells (PASMCs), 4% O2, 60 h] were established. The effects of sildenafil on pulmonary hypertension in neonatal rats were evaluated by hematoxylin and eosin staining, immunofluorescence analysis, western blotting and PCR, and the changes in peroxisome proliferator‑activated receptor γ (PPARγ), transient receptor potential canonical (TRPC)1, TRPC6 and Ki67 expression levels were detected under hypoxic conditions. The results revealed that sildenafil reversed the increases in the right ventricular mean pressure and right ventricular hypertrophy index induced by hypoxia, and attenuated pulmonary arterial remodeling as well as PASMC proliferation. The inhibitory effects of sildenafil on TRPC expression and PASMC proliferation were attenuated by GW9662 and PPARγ small interfering RNA. In conclusion, sildenafil protects against hypoxia‑induced pulmonary hypertension and right ventricular hypertrophy in neonatal rats by upregulating PPARγ expression and downregulating TRPC1 and TRPC6 expression.

The effects of iloprost and beta3 receptor agonist on TRPA1 and TRPC1 immunreactivity in an experimental lower extremty ischemia-reperfusion injury model

BACKGROUND

In this study, we aimed to investigate the effects of antioxidant iloprost (ILO) and ß3 adrenergic receptor agonist (BRL) on transient receptor potential ankyrin 1 (TRPA1) and transient receptor potential canonical 1 (TRPC1) ion channels on an experimental ischemia and reperfusion injury model in 30 male Wistar albino rats aged 8-10 weeks.

METHODS

Wistar Albino rats aged were divided into 5 equal groups. Group I Sham operation, Group II IR (ischemiareperfusion) procedure, Group III IR + intravenous ILO administration, Group IV IR + intraperitoneal BRL administration, and Group V IR + intravenous ILO + intraperitoneal BRL administration group. Two ng/kg/min ILO intravenous infusion was applied to the ILO group. A single dose of 5 mcg/kg BRL intraperitoneal was applied to BRL group. TOS (total oxidant status), TRPA1, and TRPC1 levels were measured with ELISA (enzyme linked immunosorbent assay) in serum, immunohistochemical staining in musculus quadriceps femoris tissue.

RESULTS

Compared with the sham group, the IR group had a statistically significant increase in serum levels of TOS (p = 0.004), TRPA1 (p = 0.002), and TRPC1 (p = 0.008) along with TRPA1- and TRPC1-immunoreactivity (p = 0.005, each) in the tissue. When compared with the IR group in terms of serum levels of TRPA1 and tissue TRPA1-immunoreactivity, although there was no statistically significant difference in the IR+Ilo (p = 0.257 and p = 0.429, respectively), IR+Brl (p = 0.024 and p = 0.177, respectively), and IR+Ilo+Brl (p = 0.024 and p = 0.329, respectively) groups, serum levels of TOS and TRPC1 along with tissue TRPC1-immunoreactivity were statistically significantly reduced in the IR+Ilo (p = 0.002, p = 0.008, and p = 0.004, respectively), IR+Brl (p = 0.004, p = 0.008, and p = 0.004, respectively), and IR+Ilo+Brl groups (p = 0.002, p = 0.008, and p = 0.004, respectively).

DISCUSSION

In IR group serum TOS, TRPA1 and TRPC1 levels ,and tissue TRPA1 and TRPC1 immunoreactivity were statistically significant increase when compared to the sham group. In IR+ILO, IR+BRL and IR+ILO+BRL groups serum TRPA1 and tissue TRPA1 immunoreactivity did not change when compared to IR group. Serum TOS and TRPC1 levels, tissue TRPC1 immunoreactivty were statistically significant decreased when compared to IR group. More detailed and expanded population studies are needed to discuss our results.

Mechanosensitivity in Pulmonary Circulation: Pathophysiological Relevance of Stretch-Activated Channels in Pulmonary Hypertension

A variety of cell types in pulmonary arteries (endothelial cells, fibroblasts, and smooth muscle cells) are continuously exposed to mechanical stimulations such as shear stress and pulsatile blood pressure, which are altered under conditions of pulmonary hypertension (PH). Most functions of such vascular cells (e.g., contraction, migration, proliferation, production of extracellular matrix proteins, etc.) depend on a key event, i.e., the increase in intracellular calcium concentration ([Ca²⁺]_i) which results from an influx of extracellular Ca²⁺ and/or a release of intracellular stored Ca²⁺. Calcium entry from the extracellular space is a major step in the elevation of [Ca²⁺]_i, involving a variety of plasmalemmal Ca²⁺ channels including the superfamily of stretch-activated channels (SAC). A common characteristic of SAC is that their gating depends on membrane stretch. In general, SAC are non-selective Ca²⁺-permeable cation channels, including proteins of the TRP (Transient Receptor Potential) and Piezo channel superfamily. As membrane mechano-transducers, SAC convert physical forces into biological signals and hence into a cell response. Consequently, SAC play a major role in pulmonary arterial calcium homeostasis and, thus, appear as potential novel drug targets for a better management of PH.

Hypoxia and the integrated stress response promote pulmonary hypertension and preeclampsia: Implications in drug development

Chronic hypoxia is a common cause of pulmonary hypertension, preeclampsia, and intrauterine growth restriction (IUGR). The molecular mechanisms underlying these diseases are not completely understood. Chronic hypoxia may induce the generation of reactive oxygen species (ROS) in mitochondria, promote endoplasmic reticulum (ER) stress, and result in the integrated stress response (ISR) in the pulmonary artery and uteroplacental tissues. Numerous studies have implicated hypoxia-inducible factors (HIFs), oxidative stress, and ER stress/unfolded protein response (UPR) in the development of pulmonary hypertension, preeclampsia and IUGR. This review highlights the roles of HIFs, mitochondria-derived ROS and UPR, as well as their interplay, in the pathogenesis of pulmonary hypertension and preeclampsia, and their implications in drug development.

Chronic hypoxia promoted pulmonary arterial smooth muscle cells proliferation through upregulated calcium-sensing receptorcanonical transient receptor potential 1/6 pathway

OBJECTIVES

Although both calcium-sensing receptor (CaSR) and canonical transient receptor potential (TRPC) proteins contribute to chronic hypoxia (CH)-induced pulmonary arterial smooth muscle cells (PASMCs) proliferation, the relationship between CaSR and TRPC in hypoxic PASMCs proliferation remains poorly understood. The goal of this study was to identify that CH promotes PASMCs proliferation through CaSR-TRPC pathway.

METHODS

Rat PASMCs were isolated and treated with CH. Cell proliferation was assessed by cell counting, CCK-8 assay, and EdU incorporation. CaSR and TRPC expressions were determined by qPCR and Western blotting. Store-operated Ca²⁺ entry (SOCE) was assessed by extracellular Ca²⁺ restoration.

RESULTS

In PASMCs, CH enhanced the cell number, cell viability and DNA synthesis, which is accompanied by upregulated expression of CaSR, TRPC1 and TRPC6. Negative CaSR modulators (NPS2143, NPS2390) inhibited, whereas positive modulators (spermine, R568) enhanced, the CH-induced increases in cell number, cell viability and DNA synthesis in PASMCs. Knockdown of CaSR by siRNA inhibited the CH-induced upregulation of TRPC1 and TRPC6 and enhancement of SOCE and attenuated the CH-induced enhancements of cell number, cell viability and DNA synthesis in PASMCs. However, neither siTRPC1 nor siTRPC6 had an effect on the CH-induced CaSR upregulation, although both significantly attenuated the CH-induced enhancements of cell number, cell viability and DNA synthesis in PASMCs.

CONCLUSION

These results demonstrate that upregulated CaSR-TRPC1/6 pathway mediating PASMCs proliferation is an important pathogenic mechanism under hypoxic conditions.

Canonical transient receptor potential channels and their modulators: biology, pharmacology and therapeutic potentials

Canonical transient receptor potential channels (TRPCs) are nonselective, high calcium permeability cationic channels. The TRPCs family includes TRPC1, TRPC2, TRPC3, TRPC4, TRPC5, TRPC6, and TRPC7. These channels are widely expressed in the cardiovascular and nervous systems and exist in many other human tissues and cell types, playing several crucial roles in the human physiological and pathological processes. Hence, the emergence of TRPCs modulators can help investigate these channels’ applications in health and disease. It is worth noting that the TRPCs subfamilies have structural and functional similarities, which presents a significant difficulty in screening and discovering of TRPCs modulators. In the past few years, only a limited number of selective modulators of TRPCs were detected; thus, additional research on more potent and more selective TRPCs modulators is needed. The present review focuses on the striking desired therapeutic effects of TRPCs modulators, which provides intel on the structural modification of TRPCs modulators and further pharmacological research. Importantly, TRPCs modulators can significantly facilitate future studies of TRPCs and TRPCs related diseases.

TRPC and TRPV Channels' Role in Vascular Remodeling and Disease

Transient receptor potentials (TRPs) are non-selective cation channels that are widely expressed in vascular beds. They contribute to the Ca²⁺ influx evoked by a wide spectrum of chemical and physical stimuli, both in endothelial and vascular smooth muscle cells. Within the superfamily of TRP channels, different isoforms of TRPC (canonical) and TRPV (vanilloid) have emerged as important regulators of vascular tone and blood flow pressure. Additionally, several lines of evidence derived from animal models, and even from human subjects, highlighted the role of TRPC and TRPV in vascular remodeling and disease. Dysregulation in the function and/or expression of TRPC and TRPV isoforms likely regulates vascular smooth muscle cells switching from a contractile to a synthetic phenotype. This process contributes to the development and progression of vascular disorders, such as systemic and pulmonary arterial hypertension, atherosclerosis and restenosis. In this review, we provide an overview of the current knowledge on the implication of TRPC and TRPV in the physiological and pathological processes of some frequent vascular diseases.

Tetramethylpyrazine: A promising drug for the treatment of pulmonary hypertension

BACKGROUND AND PURPOSE

Tetramethylpyrazine (TMP) was originally isolated from the traditional Chinese herb ligusticum and the fermented Japanese food natto and has since been synthesized. TMP has a long history of beneficial effects in the treatment of many cardiovascular diseases. Here we have evaluated the therapeutic effects of TMP on pulmonary hypertension (PH) in animal models and in patients with pulmonary arterial hypertension (PAH) or chronic thromboembolic pulmonary hypertension (CTEPH).

EXPERIMENTAL APPROACH

Three well-defined models of PH -chronic hypoxia (10% O₂ )-induced PH (HPH), monocrotaline-induced PH (MCT-PH) and Sugen 5416/hypoxia-induced PH (SuHx-PH) - were used in Sprague-Dawley rats, and assessed by echocardiography, along with haemodynamic and histological techniques. Primary cultures of rat distal pulmonary arterial smooth muscle cells (PASMCs) were used to study intracellular calcium levels. Western blots and RT-qPCR assays were also used. In the clinical cohort, patients with PAH or CTEPH were recruited. The effects of TMP were evaluated in all systems.

KEY RESULTS

TMP (100 mg·kg^-1 ·day^-1 ) prevented rats from developing experimental PH and ameliorated three models of established PH: HPH, MCT-PH and SuHx-PH. The therapeutic effects of TMP were accompanied by inhibition of intracellular calcium homeostasis in PASMCs. In a small cohort of patients with PAH or CTEPH, oral administration of TMP (100 mg, t.i.d. for 16 weeks) increased the 6-min walk distance and improved the 1-min heart rate recovery.

CONCLUSION AND IMPLICATIONS

Our results suggest that TMP is a novel and inexpensive medication for treatment of PH. Clinical trial is registered with www.chictr.org.cn (ChiCTR-IPR-14005379).

TRPC channels: Structure, function, regulation and recent advances in small molecular probes

Transient receptor potential canonical (TRPC) channels constitute a group of receptor-operated calcium-permeable nonselective cation channels of the TRP superfamily. The seven mammalian TRPC members, which can be further divided into four subgroups (TRPC1, TRPC2, TRPC4/5, and TRPC3/6/7) based on their amino acid sequences and functional similarities, contribute to a broad spectrum of cellular functions and physiological roles. Studies have revealed complexity of their regulation involving several components of the phospholipase C pathway, G_i and G_o proteins, and internal Ca²⁺ stores. Recent advances in cryogenic electron microscopy have provided several high-resolution structures of TRPC channels. Growing evidence demonstrates the involvement of TRPC channels in diseases, particularly the link between genetic mutations of TRPC6 and familial focal segmental glomerulosclerosis. Because TRPCs were discovered by the molecular identity first, their pharmacology had lagged behind. This is rapidly changing in recent years owning to great efforts from both academia and industry. A number of potent tool compounds from both synthetic and natural products that selective target different subtypes of TRPC channels have been discovered, including some preclinical drug candidates. This review will cover recent advancements in the understanding of TRPC channel regulation, structure, and discovery of novel TRPC small molecular probes over the past few years, with the goal of facilitating drug discovery for the study of TRPCs and therapeutic development.

Transplantation of Mesenchymal Stem Cells Attenuates Pulmonary Hypertension by Normalizing the Endothelial-to-Mesenchymal Transition

For decades, stem cell therapies for pulmonary hypertension (PH) have progressed from laboratory hypothesis to clinical practice. Promising preclinical investigations have laid both a theoretical and practical foundation for clinical application of mesenchymal stem cells (MSCs) for PH therapy. However, the underlying mechanisms are still poorly understood. We sought to study the effects and mechanisms of MSCs on the treatment of PH. For in vivo experiments, the transplanted GFP+ MSCs were traced at different time points in the lung tissue of a chronic hypoxia-induced PH (CHPH) rat model. The effects of MSCs on PH pathogenesis were evaluated in both CHPH and sugen hypoxia-induced PH models. For in vitro experiments, primary pulmonary microvascular endothelial cells were cultured and treated with the MSC conditioned medium. The specific markers of endothelial-to-mesenchymal transition (EndMT) and cell migration properties were measured. MSCs decreased pulmonary arterial pressure and ameliorated the collagen deposition, and reduced the thickening and muscularization in both CHPH and sugen hypoxia-induced PH rat models. Then, MSCs significantly attenuated the hypoxia-induced EndMT in both the lungs of PH models and primary cultured rat pulmonary microvascular endothelial cells, as reflected by increased mesenchymal cell markers (fibronectin 1 and vimentin) and decreased endothelial cell markers (vascular endothelial cadherin and platelet endothelial cell adhesion molecule-1). Moreover, MSCs also markedly inhibited the protein expression and degradation of hypoxia-inducible factor-2α, which is known to trigger EndMT progression. Our data suggest that MSCs successfully prevent PH by ameliorating pulmonary vascular remodeling, inflammation, and EndMT. Transplantation of MSCs could potentially be a powerful therapeutic approach against PH.

A novel function of calcium sensing receptor in chronic hypoxia-induced pulmonary venous smooth muscle cells proliferation

Chronic hypoxia (CH) causes remodeling not only in pulmonary arteries but also in pulmonary veins. Pulmonary vascular remodeling stems from increased pulmonary vascular myocyte proliferation. However, the pathogenesis of CH-induced proliferation of pulmonary venous smooth muscle cells (PVSMCs) remains unknown. The present study aimed to explore the mechanisms by which CH affects PVSMCs proliferation. PVSMCs were isolated from rat distal pulmonary veins and exposed to CH (4% O₂ for 60 h). The expression of calcium sensing receptor (CaSR) was determined by immunofluorescence, real-time quantitative PCR and Western blotting. Cell proliferation was assessed by cell counting, CCK-8 assay, and BrdU incorporation. Apoptosis analysis was examined by flow cytometry. In rat distal PVSMCs, CH increased the cell number and cell viability and enhanced DNA synthesis, which is accompanied by upregulated mRNA and protein expression levels of CaSR. Two negative CaSR modulators (NPS2143, NPS2390) not only attenuated CH-induced CaSR upregulation but also inhibited CH-induced increases in cell number, cell viability and the proliferation index of PVSMCs, whereas two positive modulators (spermine, R568) not only amplified CH-induced CaSR upregulation but also intensified CH-induced increases in cell number, cell viability and the proliferation index of PVSMCs. Silencing CaSR with siRNA similarly attenuated the CH-induced enhancement of cell number, cell viability and DNA synthesis in PVSMCs. Neither CH nor downregulation of CaSR with siRNA had an effect on apoptosis in PVSMCs. These results suggest that CaSR mediating excessive proliferation is a new pathogenic mechanism involved in the initiation and progression of distal PVSMCs proliferation under CH conditions.

Inactivation of carboxyl terminus of Hsc70-interacting protein prevents hypoxia-induced pulmonary arterial smooth muscle cells proliferation by reducing intracellular Ca2+ concentration

Carboxyl terminus of Hsc70-interacting protein (CHIP) is a 35-kDa cytoplasmic protein expressed in human striated muscle, brain, aortic smooth muscle, endothelial cells, and other tissues. Studies have confirmed that CHIP regulates cell growth, apoptosis, cell phenotype, metabolism, neurodegeneration, etc. However, whether CHIP is involved in pulmonary artery smooth muscle cell (PASMC) proliferation, a vital contributor to chronic hypoxia-induced pulmonary hypertension (CHPH), remains unknown. In this study, we first evaluated CHIP expression in the pulmonary arteries (PAs) of CHPH model rats. Subsequently, by silencing CHIP, we investigated the effect of CHIP on hypoxia-induced PASMC proliferation and the underlying mechanism. Our results showed that CHIP expression was upregulated in the PAs of CHPH model rats. Silencing CHIP significantly suppressed the hypoxia-triggered promotion of proliferation, [Ca²⁺]_i, store-operated Ca²⁺ entry (SOCE), and some regulators of SOCE such as TRPC1 and TRPC6 in cultured PASMCs. These results indicate that CHIP likely contributes to hypoxia-induced PASMC proliferation by targeting the SOCE-[Ca²⁺]_i pathway through the regulation of TRPC1 and TRPC6 in the PASMCs. In conclusion, the findings of the current study clarify the role of CHIP in hypoxia-induced PASMC proliferation.

Chloroquine is a potent pulmonary vasodilator that attenuates hypoxia-induced pulmonary hypertension

BACKGROUND AND PURPOSE

Sustained pulmonary vasoconstriction and excessive pulmonary vascular remodelling are two major causes of elevated pulmonary vascular resistance in patients with pulmonary arterial hypertension. The purpose of this study was to investigate whether chloroquine induced relaxation in the pulmonary artery (PA) and attenuates hypoxia-induced pulmonary hypertension (HPH).

EXPERIMENTAL APPROACH

Isometric tension was measured in rat PA rings pre-constricted with phenylephrine or high K⁺ solution. PA pressure was measured in mouse isolated, perfused and ventilated lungs. Fura-2 fluorescence microscopy was used to measure cytosolic free Ca²⁺ concentration levels in PA smooth muscle cells (PASMCs). Patch-clamp experiments were performed to assess the activity of voltage-dependent Ca²⁺ channels (VDCCs) in PASMC. Rats exposed to hypoxia (10% O₂ ) for 3 weeks were used as the model of HPH or Sugen5416/hypoxia (SuHx) for in vivo experiments.

KEY RESULTS

Chloroquine attenuated agonist-induced and high K⁺ -induced contraction in isolated rat PA. Pretreatment with l-NAME or indomethacin and functional removal of endothelium failed to inhibit chloroquine-induced PA relaxation. In PASMC, extracellular application of chloroquine attenuated store-operated Ca²⁺ entry and ATP-induced Ca²⁺ entry. Furthermore, chloroquine also inhibited whole-cell Ba²⁺ currents through VDCC in PASMC. In vivo experiments demonstrated that chloroquine treatment ameliorated the HPH and SuHx models.

CONCLUSIONS AND IMPLICATIONS

Chloroquine is a potent pulmonary vasodilator that may directly or indirectly block VDCC, store-operated Ca²⁺ channels and receptor-operated Ca²⁺ channels in PASMC. The therapeutic potential of chloroquine in pulmonary hypertension is probably due to the combination of its vasodilator, anti-proliferative and anti-autophagic effects.

Canonical Transient Receptor Potential Channels and Their Link with Cardio/Cerebro-Vascular Diseases

The canonical transient receptor potential channels (TRPCs) constitute a series of nonselective cation channels with variable degrees of Ca²⁺ selectivity. TRPCs consist of seven mammalian members, TRPC1, TRPC2, TRPC3, TRPC4, TRPC5, TRPC6, and TRPC7, which are further divided into four subtypes, TRPC1, TRPC2, TRPC4/5, and TRPC3/6/7. These channels take charge of various essential cell functions such as contraction, relaxation, proliferation, and dysfunction. This review, organized into seven main sections, will provide an overview of current knowledge about the underlying pathogenesis of TRPCs in cardio/cerebrovascular diseases, including hypertension, pulmonary arterial hypertension, cardiac hypertrophy, atherosclerosis, arrhythmia, and cerebrovascular ischemia reperfusion injury. Collectively, TRPCs could become a group of drug targets with important physiological functions for the therapy of human cardio/cerebro-vascular diseases.

Inhibition of phosphodiesterase-5 suppresses calcineurin/NFAT- mediated TRPC6 expression in pulmonary artery smooth muscle cells

The up-regulation of transient receptor potential channel 6 (TRPC6) has been found to contribute to the proliferation of pulmonary artery smooth muscle cells (PASMCs), and inhibition of phosphodiesterase-5 (PDE5) has been shown to suppress TRPC6 expression in PASMCs. However, the molecular mechanisms underlying the up-regulation of TRPC6 expression and PDE5 modulation of TRPC6 expression in PASMCs remain largely unclear. The aim of this study is to address these issues. Endothelin-1 (ET-1) dose and time-dependently up-regulated TRPC6 expression in primary cultured rat PASMCs, and this was accompanied with the activation of calcineurin and subsequent translocation of NFATc4 to the nucleus. Further study indicated that inhibition of calcineurin by cyclosporine A or knockdown of NFATc4 using small interfering RNA suppressed ET-1-induced TRPC6 up-regulation. In addition, luciferase reporter assay showed that NFATc4 directly regulated the expression of TRPC6 in PASMCs. Inhibition of PDE5 by sildenafil suppressed ET-1-induced activation of calcineurin/NFATc4 signaling pathway and consequent TRPC6 up-regulation in PASMCs, while these inhibitory effects of sildenafil were abolished by PKG inhibitor Rp-8Br-cGMPs. Taken together, our study indicates that ET-1 stimulates TRPC6 expression by activation of calcineurin/NFATc4 signaling pathway, and inhibition of PDE5 suppresses calcineurin/NFATc4- mediated TRPC6 expression in PASMCs in a cGMP-PKG-dependent manner.

The Role of Transient Receptor Potential Channel 6 Channels in the Pulmonary Vasculature

Canonical or classical transient receptor potential channel 6 (TRPC6) is a Ca²⁺-permeable non-selective cation channel that is widely expressed in the heart, lung, and vascular tissues. The use of TRPC6-deficient (“knockout”) mice has provided important insights into the role of TRPC6 in normal physiology and disease states of the pulmonary vasculature. Evidence indicates that TRPC6 is a key regulator of acute hypoxic pulmonary vasoconstriction. Moreover, several studies implicated TRPC6 in the pathogenesis of pulmonary hypertension. Furthermore, a unique genetic variation in the TRPC6 gene promoter has been identified, which might link the inflammatory response to the upregulation of TRPC6 expression and ultimate development of pulmonary vascular abnormalities in idiopathic pulmonary arterial hypertension. Additionally, TRPC6 is critically involved in the regulation of pulmonary vascular permeability and lung edema formation during endotoxin or ischemia/reperfusion-induced acute lung injury. In this review, we will summarize latest findings on the role of TRPC6 in the pulmonary vasculature.

Hydrogen peroxide is a critical regulator of the hypoxia-induced alterations of store-operated Ca2+ entry into rat pulmonary arterial smooth muscle cells

To investigate the association between store-operated Ca2+ entry (SOCE) and reactive oxygen species (ROS) during hypoxia, this study determined the changes of transient receptor potential canonical 1 (TRPC1) and Orai1, two candidate proteins for store-operated Ca2+ (SOC) channels and their gate regulator, stromal interaction molecule 1 (STIM1), in a hypoxic environment and their relationship with ROS in pulmonary arterial smooth muscle cells (PASMCs). Exposure to hypoxia caused a transient Ca2+ spike and subsequent Ca2+ plateau of SOCE to be intensified in PASMCs when TRPC1, STIM1, and Orai1 were upregulated. SOCE in cells transfected with specific short hairpin RNA (shRNA) constructs was almost completely eliminated by the knockdown of TRPC1, STIM1, or Orai1 alone and was no longer affected by hypoxia exposure. Hypoxia-induced SOCE enhancement was further strengthened by PEG-SOD but was attenuated by PEG-catalase, with correlated changes to intracellular hydrogen peroxide (H2O2) levels and protein levels of TRPC1, STIM1, and Orai1. Exogenous H2O2 could mimic alterations of the interactions of STIM1 with TRPC1 and Orai1 in hypoxic cells. These findings suggest that TRPC1, STIM1, and Orai1 are essential for the initiation of SOCE in PASMCs. Hypoxia-induced ROS promoted the expression and interaction of the SOC channel molecules and their gate regulator via their converted product, H2O2.

Isolation, culture and identification of pulmonary arterial smooth muscle cells from rat distal pulmonary arteries

The culture of pulmonary arterial smooth muscle cells (PASMCs) is one of the most powerful tools for exploring the mechanisms of pulmonary hypertension (PH). Both pulmonary vasoconstriction and remodeling occur predominantly in distal pulmonary arteries (PA). In this study, we provide our detailed and standardized protocol for easy isolation and culture of PASMCs from rat distal PA to supply every investigator with a simple, economical and useful method in studying PH. The protocol can be divided into four stages: isolation of distal PA, isolation of cells, growth in culture and passage of cells. Rat distal PASMCs were characterized by morphological activity and by immunostaining for smooth muscle α-actin and smooth muscle myosin heavy chain, but not for CD90/Thy-1 or von Willebrand factor. Furthermore, functional assessments were performed, confirming the presence of voltage-dependent Ca²⁺ channels and physiological characteristic of response to hypoxia. In conclusion, we have developed a detailed and simple protocol for obtaining rat distal PASMCs. These PASMCs exhibit features consistent with vascular smooth muscle cells, and they could subsequently be used to further explore the pathophysiological mechanisms of PH.

Sildenafil Prevents Podocyte Injury via PPAR-γ-Mediated TRPC6 Inhibition

Transient receptor potential channel C6 (TRPC6) gain-of-function mutations and increased TRPC6 expression in podocytes induce glomerular injury and proteinuria. Sildenafil reduces TRPC6 expression and activity in nonrenal cell types, although the mechanism is unknown. Peroxisome proliferator-activated receptor γ (PPAR-γ) is a downstream target of sildenafil in the cyclic guanosine monophosphate (cGMP)-activated protein kinase G (PKG) axis. PPAR-γ agonists, like pioglitazone, appear antiproteinuric. We hypothesized that sildenafil inhibits TRPC6 expression in podocytes through PPAR-γ-dependent mechanisms, thereby counteracting podocyte injury and proteinuria. Treatment with sildenafil, the cGMP derivative 8-bromoguanosine 3',5'-cyclic monophosphate sodium salt (8-Br-cGMP), or pioglitazone dose-dependently downregulated podocyte injury-induced TRPC6 expression in vitro Knockdown or application of antagonists of PKG or PPAR-γ enhanced TRPC6 expression in podocytes and counteracted effects of sildenafil and 8-Br-cGMP. We observed similar effects on TRPC6 promoter activity and TRPC6-dependent calcium influx. Chromatin immunoprecipitation showed PPAR-γ binding to the TRPC6 promoter. Sildenafil or pioglitazone treatment prevented proteinuria and the increased TRPC6 expression in rats with adriamycin-induced nephropathy and mice with hyperglycemia-induced renal injury. Rats receiving PPAR-γ antagonists displayed proteinuria and increased podocyte TRPC6 expression, as did podocyte-specific PPAR-γ knockout mice, which were more sensitive to adriamycin and not protected by sildenafil. Thus, sildenafil ameliorates podocyte injury and prevents proteinuria through cGMP- and PKG-dependent binding of PPAR-γ to the TRPC6 promoter, which inhibits TRPC6 promoter activity, expression, and activity. Because sildenafil is approved for clinical use, our results suggest that additional clinical study of its antiproteinuric effect in glomerular disease is warranted.

Bortezomib alleviates experimental pulmonary hypertension by regulating intracellular calcium homeostasis in PASMCs

The ubiquitin-proteasome system is considered to be the key regulator of protein degradation. Bortezomib (BTZ) is the first proteasome inhibitor approved by the US Food and Drug Administration for treatment of relapsed multiple myeloma and mantle cell lymphoma. Recently, BTZ treatment was reported to inhibit right ventricular hypertrophy and vascular remodeling in hypoxia-exposed and monocrotaline-injected rats. However, the underlying mechanisms remain poorly understood. We previously confirmed that hypoxia-elevated basal intracellular Ca(2+) concentration ([Ca(2+)]i) and store-operated Ca(2+) entry (SOCE) in pulmonary artery smooth muscle cells (PASMCs) are involved in pulmonary vascular remodeling. In this study we aim to determine whether BTZ attenuates the hypoxia-induced elevation of [Ca(2+)] in PASMCs and the signaling pathway involved in this mechanism. Our results showed that 1) in hypoxia- and monocrotaline-induced rat pulmonary hypertension (PH) models, BTZ markedly attenuated the development and progression of PH, 2) BTZ inhibited the hypoxia-induced increase in cell proliferation, basal [Ca(2+)]i, and SOCE in PASMCs, and 3) BTZ significantly normalized the hypoxia-upregulated expression of hypoxia-inducible factor-1α, bone morphogenetic protein 4, canonical transient receptor potential isoforms 1 and 6, and the hypoxia-downregulated expression of peroxisome proliferator-activated receptor-γ in rat distal pulmonary arteries and PASMCs. These results indicate that BTZ exerts its protective role in the development of PH potentially by inhibiting the canonical transient receptor potential-SOCE-[Ca(2+)]i signaling axis in PASMCs.

Sodium tanshinone IIA sulfonate inhibits hypoxia-induced enhancement of SOCE in pulmonary arterial smooth muscle cells via the PKG-PPAR-γ signaling axis

Our laboratory previously showed that sodium tanshinone IIA sulfonate (STS) inhibited store-operated Ca(2+) entry (SOCE) through store-operated Ca(2+) channels (SOCC) via downregulating the expression of transient receptor potential canonical proteins (TRPC), which contribute to the formation of SOCC (Wang J, Jiang Q, Wan L, Yang K, Zhang Y, Chen Y, Wang E, Lai N, Zhao L, Jiang H, Sun Y, Zhong N, Ran P, Lu W. Am J Respir Cell Mol Biol 48: 125-134, 2013). The detailed molecular mechanisms by which STS inhibits SOCE and downregulates TRPC, however, remain largely unknown. We have previously shown that, under hypoxic conditions, inhibition of protein kinase G (PKG) and peroxisome proliferator-activated receptor-γ (PPAR-γ) signaling axis results in the upregulation of TRPC (Wang J, Yang K, Xu L, Zhang Y, Lai N, Jiang H, Zhang Y, Zhong N, Ran P, Lu W. Am J Respir Cell Mol Biol 49: 231-240, 2013). This suggests that strategies targeting the restoration of this signaling pathway may be an effective treatment strategy for pulmonary hypertension. In this study, our results demonstrated that STS treatment can effectively prevent the hypoxia-mediated inhibition of the PKG-PPAR-γ signaling axis in rat distal pulmonary arterial smooth muscle cells (PASMCs) and distal pulmonary arteries. These effects of STS treatment were blocked by pharmacological inhibition or specific small interfering RNA knockdown of either PKG or PPAR-γ. Moreover, targeted PPAR-γ agonist markedly enhanced the beneficial effects of STS. These results comprehensively suggest that STS treatment can prevent hypoxia-mediated increases in intracellular calcium homeostasis and cell proliferation, by targeting and restoring the hypoxia-inhibited PKG-PPAR-γ signaling pathway in PASMCs.

NSFC spurs significant basic research progress of respiratory medicine in China

Over the years, research in respiratory medicine has progressed rapidly in China. This commentary narrates the role of the National Natural Science Foundation of China (NSFC) in supporting the basic research of respiratory medicine, summarizes the major progress of respiratory medicine in China, and addresses the main future research directions sponsored by the NSFC.

Noggin inhibits hypoxia-induced proliferation by targeting store-operated calcium entry and transient receptor potential cation channels

Abnormally elevated bone morphogenetic protein 4 (BMP4) expression and mediated signaling play a critical role in the pathogenesis of chronic hypoxia-induced pulmonary hypertension (CHPH). In this study, we investigated the expression level and functional significance of four reported naturally occurring BMP4 antagonists, noggin, follistatin, gremlin1, and matrix gla protein (MGP), in the lung and distal pulmonary arterial smooth muscle cell (PASMC). A 21-day chronic hypoxic (10% O2) exposure rat model was utilized, which has been previously shown to successfully establish experimental CHPH. Among the four antagonists, noggin, but not the other three, was selectively downregulated by hypoxic exposure in both the lung tissue and PASMC, in correlation with markedly elevated BMP4 expression, suggesting that the loss of noggin might account for the hypoxia-triggered BMP4 signaling transduction. Then, by using treatment of extrogenous recombinant noggin protein, we further found that noggin significantly normalized 1) BMP4-induced phosphorylation of cellular p38 and ERK1/2; 2) BMP4-induced phosphorylation of cellular JAK2 and STAT3; 3) hypoxia-induced PASMC proliferation; 4) hypoxia-induced store-operated calcium entry (SOCE), and 5) hypoxia-increased expression of transient receptor potential cation channels (TRPC1 and TRPC6) in PASMC. In combination, these data strongly indicated that the hypoxia-suppressed noggin accounts, at least partially, for hypoxia-induced excessive PASMC proliferation, while restoration of noggin may be an effective way to inhibit cell proliferation by suppressing SOCE and TRPC expression.

YM155, a selective survivin inhibitor, reverses chronic hypoxic pulmonary hypertension in rats via upregulating voltage-gated potassium channels

To test the hypothesis that chronic hypoxic pulmonary hypertension (CH-PH) is associated with increased survivin and decreased voltage-gated potassium (KV) channels expression in pulmonary arteries, rats were randomized as: normoxia (N); normoxia + YM155, survivin suppressor (NY); hypoxia (H); hypoxia + YM155 (HY). HY group had significantly reduced pulmonary arterial pressure, right ventricular weight and right ventricular hypertrophy compared with H group. Survivin mRNA and protein were detected in pulmonary arteries of rats with CH-PH, but not rats without CH-PH. YM155 downregulated survivin protein and mRNA. KV channel expression and activity were upregulated after YM155 treatment. Survivin may play a role in the pathogenesis of CH-PH.

Hypoxia inducible factor-1-dependent up-regulation of BMP4 mediates hypoxia-induced increase of TRPC expression in PASMCs

AIMS

Previously we demonstrated that both hypoxia inducible factor-1 (HIF-1) and bone morphogenetic protein-4 (BMP4) up-regulate transient receptor potential canonical (TRPC) 1 and TRPC6, resulting in increased basal intracellular Ca(2+) concentration ([Ca(2+)]i) in pulmonary arterial smooth muscle cells (PASMCs), driving development of chronic hypoxia (CH)-induced pulmonary hypertension (CHPH). This study aims to determine whether HIF-1 regulates BMP4, and whether BMP4 mediates TRPC and basal [Ca(2+)]i increases in hypoxic PASMCs.

METHODS AND RESULTS

The level of BMP4 mature protein was increased for ∼183% in distal pulmonary arterial smooth muscle (PA) from CH (10% O2 for 21 days; CH) exposed rats, and 143% in PASMCs cultured under prolonged hypoxia (4% O2 for 60 h). In rat PASMCs, HIF-1α overexpression up-regulated, whereas HIF-1α knockdown under hypoxia decreased BMP4 expression; site-mutation identified two functional HIF-1-binding sites in Bmp4 gene promoter; noggin or BMP4 siRNA treatment blocked hypoxia-induced increases of TRPC1 and TRPC6 expression and basal [Ca(2+)]i. Likewise, in mice, exposure to CH increased BMP4 expression in distal PA for ∼80%, which was absent in HIF-1α heterozygous mutant mice. Comparing with wild-type littermates, BMP4 heterozygous mutant mice exposed to CH displayed lower BMP4 and TRPC levels in PA, decreased basal [Ca(2+)]i in PASMCs, and attenuated CHPH. In human PASMCs, HIF-1α knockdown attenuated hypoxia-induced BMP4 expression and knockdown of either HIF-1α or BMP4 abolished hypoxia-induced TRPC expression and basal [Ca(2+)]i.

CONCLUSIONS

BMP4 acts downstream of HIF-1 and mediates hypoxia-induced up-regulation of TRPC, leading to increased basal [Ca(2+)]i in PASMCs, promoting CHPH pathogenesis.

BMP4 increases the expression of TRPC and basal [Ca2+]i via the p38MAPK and ERK1/2 pathways independent of BMPRII in PASMCs

Multiple abnormalities of bone morphogenetic protein (BMPs) signaling are implicated in the process of pulmonary arterial hypertension (PAH). BMP4 plays an important role during the process of pulmonary arterial remodeling and mutant of the principle BMP4 receptor, BMP receptors II (BMPRII), is found to associate with the development of PAH. However, the likely mechanism defining the contribution of BMPRII to BMP4 mediated signaling in pulmonary arterial smooth muscle cells (PASMCs) remains comprehensively unclear. We previously found that enhanced store operated calcium entry (SOCE) and basal intracellular calcium concentration [Ca2+]i were induced by BMP4 via upregulation of TRPC1, 4 and 6 expression in PASMCs, and that BMP4 modulated TRPC channel expression through activating p38MAPK and ERK1/2 signaling pathways. In this study, BMPRII siRNA was used to knockdown BMPRII expression to investigate whether BMP4 upregulates the expression of TRPC and activating Smad1/5/8, ERK1/2 and p38MAPK pathway via BMPRII in distal PASMCs. Our results showed that knockdown of BMPRII: 1) attenuated BMP4 induced activation of P-Smad1/5/8, without altering BMP4 induced P-p38MAPK and P-ERK1/2 activation in PASMCs; 2) did not attenuate the BMP4-induced TRPC1, 4 and 6 expression; 3) did not affect BMP4-enhanced SOCE and basal [Ca2+]i. Thus, we concluded that BMP4 activated Smad1/5/8 pathway is BMPRII-dependent, while the BMP4 - ERK/p-P38 - TRPC - SOCE signaling axis are likely mediated through other receptor rather than BMPRII.

Peroxisome proliferator-activated receptor γ inhibits pulmonary hypertension targeting store-operated calcium entry

In this study, we investigated the role of peroxisome proliferator-activated receptor γ (PPARγ) on store-operated calcium entry (SOCE) and expression of the main store-operated calcium channel (SOCCs) components, canonical transient receptor potential (TRPC) in chronic hypoxia (CH)-induced pulmonary hypertension (CHPH) rat models. Small interfering RNA (siRNA) knockdown and adenoviral overexpression strategies were constructed for loss-of-function and gain-of-function experiments. PPARγ agonist rosiglitazone attenuates the pathogenesis of CHPH and suppresses Hif-1α, TRPC1, TRPC6 expression in the distal pulmonary arteries (PA), and SOCE in freshly isolated rat distal pulmonary arterial smooth muscle cells (PASMCs). By comprehensive use of knockdown and overexpression studies, and bioinformatical analysis of the TRPC gene promoter and luciferase reporter assay, we demonstrated that PPARγ exerts roles of anti-proliferation, anti-migration, and pro-apoptosis in PASMCs, likely by inhibiting the elevated SOCE and TRPC expression. These effects were inhibited under the conditions of hypoxia or Hif-1α accumulation. We also found that under hypoxia, accumulated Hif-1α protein acts as upstream of suppressed PPARγ level; however, targeted PPARγ rescue acts as negative feedback on suppressing Hif-1α level and Hif-1α mediated signaling pathway. PPARγ inhibits CHPH by targeting SOCE and TRPC via inhibiting Hif-1α expression and signaling transduction.

KEY MESSAGES

Rosiglitazone protects PH by normalizing RVSP but not right ventricle hypotrophy. PPARγ inhibits PASMCs proliferation via targeting SOCE and TRPC by suppressing Hif-1α. PPARγ and Hif-1α share mutual inhibitory regulation in PASMCs. PPARγ restoration might be a beneficial strategy for PH treatment.

Chronic hypoxia increases TRPC6 expression and basal intracellular Ca2+ concentration in rat distal pulmonary venous smooth muscle

BACKGROUND

Hypoxia causes remodeling and contractile responses in both pulmonary artery (PA) and pulmonary vein (PV). Here we explore the effect of hypoxia on PV and pulmonary venous smooth muscle cells (PVSMCs).

METHODS

Chronic hypoxic pulmonary hypertension (CHPH) model was established by exposing rats to 10% O2 for 21 days. Rat distal PVSMCs were isolated and cultured for in vitro experiments. The fura-2 based fluorescence calcium imaging was used to measure the basal intracellular Ca2+ concentration ([Ca2+]i) and store-operated Ca2+ entry (SOCE). Quantitative RT-PCR and western blotting were performed to measure the expression of mRNA and levels of canonical transient receptor potential (TRPC) protein respectively.

RESULTS

Hypoxia increased the basal [Ca2+]i and SOCE in both freshly dissociated and serum cultured distal PVSMCs. Moreover, hypoxia increased TRPC6 expression at mRNA and protein levels in both cultured PVSMCs exposed to prolonged hypoxia (4% O2, 60 h) and distal PV isolated from CHPH rats. Hypoxia also enhanced proliferation and migration of rat distal PVSMCs.

CONCLUSIONS

Hypoxia induces elevation of SOCE in distal PVSMCs, leading to enhancement of basal [Ca2+]i in PVSMCs. This enhancement is potentially correlated with the increased expression of TRPC6. Hypoxia triggered intracellular calcium contributes to promoted proliferation and migration of PVSMCs.

Ion channels and transporters as therapeutic targets in the pulmonary circulation

Pulmonary circulation is a low pressure, low resistance, high flow system. The low resting vascular tone is maintained by the concerted action of ion channels, exchangers and pumps. Under physiological as well as pathophysiological conditions, they are targets of locally secreted or circulating vasodilators and/or vasoconstrictors, leading to changes in expression or to posttranslational modifications. Both structural changes in the pulmonary arteries and a sustained increase in pulmonary vascular tone result in pulmonary vascular remodeling contributing to morbidity and mortality in pediatric and adult patients. There is increasing evidence demonstrating the pivotal role of ion channels such as K(+) and Cl(-) or transient receptor potential channels in different cell types which are thought to play a key role in vasoconstrictive remodeling. This review focuses on ion channels, exchangers and pumps in the pulmonary circulation and summarizes their putative pathophysiological as well as therapeutic role in pulmonary vascular remodeling. A better understanding of the mechanisms of their actions may allow for the development of new options for attenuating acute and chronic pulmonary vasoconstriction and remodeling treating the devastating disease pulmonary hypertension.

Phosphodiesterase 5 inhibition ameliorates angiontensin II-induced podocyte dysmotility via the protein kinase G-mediated downregulation of TRPC6 activity

The emerging role of the transient receptor potential cation channel isotype 6 (TRPC6) as a central contributor to various pathological processes affecting podocytes has generated interest in the development of therapeutics to modulate its function. Recent insights into the regulation of TRPC6 have revealed PKG as a potent negative modulator of TRPC6 conductance and associated signaling via its phosphorylation at two highly conserved amino acid residues: Thr(69)/Thr(70) (Thr(69) in mice and Thr(70) in humans) and Ser(321)/Ser(322) (Ser(321) in mice and Ser(322) in humans). Here, we tested the role of PKG in modulating TRPC6-dependent responses in primary and conditionally immortalized mouse podocytes. TRPC6 was phosphorylated at Thr(69) in nonstimulated podocytes, but this declined upon ANG II stimulation or overexpression of constitutively active calcineurin phosphatase. ANG II induced podocyte motility in an in vitro wound assay, and this was reduced 30-60% in cells overexpressing a phosphomimetic mutant TRPC6 (TRPC6T70E/S322E) or activated PKG (P < 0.05). Pretreatment of podocytes with the PKG agonists S-nitroso-N-acetyl-dl-penicillamine (nitric oxide donor), 8-bromo-cGMP, Bay 41-2772 (soluble guanylate cyclase activator), or phosphodiesterase 5 (PDE5) inhibitor 4-{[3',4'-(methylenedioxy)benzyl]amino}[7]-6-methoxyquinazoline attenuated ANG II-induced Thr(69) dephosphorylation and also inhibited TRPC6-dependent podocyte motility by 30-60%. These data reveal that PKG activation strategies, including PDE5 inhibition, ameliorate ANG II-induced podocyte dysmotility by targeting TRPC6 in podocytes, highlighting the potential therapeutic utility of these approaches to treat hyperactive TRPC6-dependent glomerular disease.

Effects of chronic exposure to cigarette smoke on canonical transient receptor potential expression in rat pulmonary arterial smooth muscle

To clarify the possible mechanism of cigarette smoke (CS)-induced pulmonary hypertension and furthermore provide effective targets for prevention and treatment, the effects of chronic CS on rat pulmonary arterial smooth muscle in vivo and nicotine treatment on rat pulmonary arterial smooth muscle cells (PASMCs) in vitro were investigated. In this study, we demonstrated that chronic CS exposure led to rat weight loss, right ventricular hypertrophy, and pulmonary arterial remodeling. A fluorescence microscope was used to measure intracellular calcium concentration ([Ca(2+)]i) in rat distal PASMCs. Results showed that basal [Ca(2+)]i and store-operated calcium entry (SOCE) levels in PASMCs from 3- and 6-mo CS-exposed rats were markedly higher than those in cells from the unexposed control animals (the increases in 6-mo CS group were more significant than that in 3-mo group), accompanied with increased canonical transient receptor potential 1 (TRPC1) and TRPC6 expression at both mRNA and protein levels in isolated distal PA. Simultaneously, in vitro study showed that nicotine treatment (10 nM) significantly increased basal [Ca(2+)]i and SOCE and upregulated TRPC1 and TRPC6 expression in cultured rat distal PASMCs. TRPC siRNA knockdown strategies revealed that the elevations of basal [Ca(2+)]i and SOCE induced by nicotine in PASMCs were TRPC1 and TRPC6 dependent. These results suggested that chronic CS-induced changes in vascular tone and structure in PA and the development of pulmonary hypertension might be largely due to upregulation of TRPC1 and TRPC6 expression in PASMCs, in which nicotine played an important role.

Acute hypoxia activates store-operated Ca(2+) entry and increases intracellular Ca(2+) concentration in rat distal pulmonary venous smooth muscle cells

RATIONALE

Exposure to acute hypoxia causes vasoconstriction in both pulmonary arteries (PA) and pulmonary veins (PV). The mechanisms on the arterial side have been studied extensively. However, bare attention has been paid to the venous side.

OBJECTIVES

To investigate if acute hypoxia caused the increase of intracellular Ca(2+) concentration ([Ca(2+)]i), and Ca(2+) influx through store-operated calcium channels (SOCC) in pulmonary venous smooth muscle cells (PVSMCs).

METHODS

Fluorescent microscopy and fura-2 were used to measure effects of 4% O2 on [Ca(2+)]i and store-operated Ca(2+) entry (SOCE) in isolated rat distal PVSMCs.

MEASUREMENTS AND MAIN RESULTS

In PVSMCs perfused with Ca(2+)-free Krebs Ringer bicarbonate solution (KRBS) containing cyclopiazonic acid to deplete Ca(2+) stores in the sarcoplasmic reticulum (SR) and nifedipine to prevent Ca(2+) entry through L-type voltage-depended Ca(2+) channels (VDCC), hypoxia markedly enhanced both the increase in [Ca(2+)]i caused by restoration of extracellular [Ca(2+)] and the rate at which extracellular Mn(2+) quenched fura-2 fluorescence. Moreover, the increased [Ca(2+)]i in PVSMCs perfused with normal salt solution was completely blocked by SOCC antagonists SKF-96365 and NiCl2 at concentrations that SOCE >85% was inhibited but [Ca(2+)]i responses to 60 mM KCl were not altered. On the contrary, L-type VDCC antagonist nifedipine inhibited increase in [Ca(2+)]i to hypoxia by only 50% at concentrations that completely blocked responses to KCl. The increased [Ca(2+)]i caused by hypoxia was completely abolished by perfusion with Ca(2+)-free KRBS.

CONCLUSIONS

These results suggest that acute hypoxia enhances SOCE via activating SOCCs, leading to increased [Ca(2+)]i in distal PVSMCs.

Classical transient receptor potential 1 and 6 contribute to hypoxic pulmonary hypertension through differential regulation of pulmonary vascular functions

Hypoxic pulmonary hypertension is characterized by increased vascular tone, altered vasoreactivity, and vascular remodeling, which are associated with alterations in Ca(2+) homeostasis in pulmonary arterial smooth muscle cells. We have previously shown that classical transient receptor potential 1 and 6 (TRPC1 and TRPC6) are upregulated in pulmonary arteries (PAs) of chronic hypoxic rats, but it is unclear whether these channels are essential for the development of pulmonary hypertension. Here we found that pulmonary hypertension was suppressed in TRPC1 and TRPC6 knockout (Trpc1(-/-) and Trpc6(-/-)) mice compared with wild-type after exposure to 10% O(2) for 1 and 3 weeks. Muscularization of pulmonary microvessels was inhibited, but rarefaction was unaltered in hypoxic Trpc1(-/-) and Trpc6(-/-) mice. Small PAs of normoxic wild-type mice exhibited vasomotor tone, which was significantly enhanced by chronic hypoxia. Similar vasomotor tone was found in normoxic Trpc1(-/-) PAs, but the hypoxia-induced enhancement was blunted. In contrast, there was minimal vascular tone in normoxic Trpc6(-/-) PAs, but the hypoxia-enhanced tone was preserved. Chronic hypoxia caused significant increase in serotonin-induced vasoconstriction; the augmented vasoreactivity was attenuated in Trpc1(-/-) and eliminated in Trpc6(-/-) PAs. Moreover, the effects of 3-week hypoxia on pulmonary arterial pressure, right ventricular hypertrophy, and muscularization of microvessels were further suppressed in TRPC1-TRPC6 double-knockout mice. Our results, therefore, provide clear evidence that TRPC1 and TRPC6 participate differentially in various pathophysiological processes, and that the presence of TRPC1 and TRPC6 is essential for the full development of hypoxic pulmonary hypertension in the mouse model.

Sildenafil inhibits hypoxia-induced transient receptor potential canonical protein expression in pulmonary arterial smooth muscle via cGMP-PKG-PPARγ axis

Transient receptor potential canonical (TRPC) proteins play important roles in chronically hypoxic pulmonary hypertension (CHPH). Previous results indicated that sildenafil inhibited TRPC1 and TRPC6 expression in rat distal pulmonary arteries (PAs). However, the underlying mechanisms remain unknown. We undertook this study to investigate the downstream signaling of sildenafil's regulation on TRPC1 and TRPC6 expression in pulmonary arterial smooth muscle cells (PASMCs). Hypoxia-exposed rats (10% O2 for 21 d) and rat distal PASMCs (4% O2 for 60 h) were taken as models to mimic CHPH. Real-time PCR, Western blotting, and Fura-2-based fluorescent microscopy were performed for mRNA, protein, and Ca(2+) measurements, respectively. The cellular cyclic guanosine monophosphate (cGMP) analogue 8-(4-chlorophenylthio)-guanosine 3',5'-cyclic monophosphate sodium salt (CPT-cGMP) (100 μM) inhibited TRPC1 and TRPC6 expression, store-operated Ca(2+) entry (SOCE), and the proliferation and migration of PASMCs exposed to prolonged hypoxia. The inhibition of CPT-cGMP on TRPC1 and TRPC6 expression in PASMCs was relieved by either the inhibition or knockdown of cGMP-dependent protein kinase (PKG) and peroxisome proliferator-activated receptor γ (PPARγ) expression. Under hypoxic conditions, CPT-cGMP increased PPARγ expression. This increase was abolished by the PKG antagonists Rp8 or KT5823. PPARγ agonist GW1929 significantly decreased TRPC1 and TRPC6 expression in PASMCs. Moreover, hypoxia exposure decreased, whereas sildenafil treatment increased, PKG and PPARγ expression in PASMCs ex vivo, and in rat distal PAs in vivo. The suppressive effects of sildenafil on TRPC1 and TRPC6 in rat distal PAs and on the hemodynamic parameters of CHPH were inhibited by treatment with the PPARγ antagonist T0070907. We conclude that sildenafil inhibits TRPC1 and TRPC6 expression in PASMCs via cGMP-PKG-PPARγ-dependent signaling during CHPH.

BMP4 increases canonical transient receptor potential protein expression by activating p38 MAPK and ERK1/2 signaling pathways in pulmonary arterial smooth muscle cells

Abnormal bone morphogenetic protein (BMP) signaling has been implicated in the pathogenesis of pulmonary hypertension. We previously found that BMP4 elevated basal intracellular Ca(2+) ([Ca(2+)]i) concentrations in distal pulmonary arterial smooth muscle cells (PASMCs), attributable in large part to enhanced store-operated Ca(2+) entry through store-operated Ca(2+) channels (SOCCs). Moreover, BMP4 up-regulated the expression of canonical transient receptor potential (TRPC) proteins thought to compose SOCCs. The present study investigated the signaling pathways through which BMP4 regulates TRPC expression and basal [Ca(2+)]i in distal PASMCs. Real-time quantitative PCR was used for the measurement of mRNA, Western blotting was used for the measurement of protein, and fluorescent microscopic for [Ca(2+)]i was used to determine the involvement of p38 and extracellular regulated kinase (ERK)-1/2 mitogen-activated protein kinase (MAPK) signaling in BMP4-induced TRPC expression and the elevation of [Ca(2+)]i in PASMCs. We found that the treatment of BMP4 led to the activation of both p38 MAPK and ERK1/2 in rat distal PASMCs. The induction of TRPC1, TRPC4, and TRPC6 expression, and the increases of [Ca(2+)]i caused by BMP4 in distal PASMCs, were inhibited by treatment with either SB203580 (10 μM), the selective inhibitor for p38 activation, or the specific p38 small interfering RNA (siRNA). Similarly, those responses induced by BMP4 were also abolished by treatment with PD98059 (5 μM), the selective inhibitor of ERK1/2, or by the knockdown of ERK1/2 using its specific siRNA. These results indicate that BMP4 participates in the regulation of Ca(2+) signaling in PASMCs by modulating TRPC channel expression via activating p38 and ERK1/2 MAPK pathways.

Proteomic analysis reveals that proteasome subunit beta 6 is involved in hypoxia-induced pulmonary vascular remodeling in rats

Background

Chronic hypoxia (CH) is known to be one of the major causes of pulmonary hypertension (PH), which is characterized by sustained elevation of pulmonary vascular resistance resulting from vascular remodeling. In this study, we investigated whether the ubiquitin proteasome system (UPS) was involved in the mechanism of hypoxia-induced pulmonary vascular remodeling. We isolated the distal pulmonary artery (PA) from a previously defined chronic hypoxic pulmonary hypertension (CHPH) rat model, performed proteomic analyses in search of differentially expressed proteins belonging to the UPS, and subsequently identified their roles in arterial remodeling.

Results

Twenty-two proteins were differently expressed between the CH and normoxic group. Among them, the expression of proteasome subunit beta (PSMB) 1 and PSMB6 increased after CH exposure. Given that PSMB1 is a well-known structural subunit and PSMB6 is a functional subunit, we sought to assess whether PSMB6 could be related to the multiple functional changes during the CHPH process. We confirmed the proteomic results by real-time PCR and Western blot. With the increase in quantity of the active subunit, proteasome activity in both cultured pulmonary artery smooth muscle cells (PASMCs) and isolated PA from the hypoxic group increased. An MTT assay revealed that the proteasome inhibitor MG132 was able to attenuate the hypoxia-induced proliferation of PASMC in a dose-dependent manner. Knockdown of PSMB6 using siRNA also prevented hypoxia-induced proliferation.

Conclusion

The present study revealed the association between increased PSMB6 and CHPH. CH up-regulated proteasome activity and the proliferation of PASMCs, which may have been related to increased PSMB6 expression and the subsequently enhanced functional catalytic sites of the proteasome. These results suggested an essential role of the proteasome during CHPH development, a novel finding requiring further study.

Bone morphogenetic protein 2 decreases TRPC expression, store-operated Ca(2+) entry, and basal [Ca(2+)]i in rat distal pulmonary arterial smooth muscle cells

Recent studies indicate that multiple bone morphogenetic protein (BMP) family ligands and receptors are involved in the development of pulmonary arterial hypertension, yet the underlying mechanisms are incompletely understood. Although BMP2 and BMP4 share high homology in amino acid sequence, they appear to exert divergent effects on chronic hypoxic pulmonary hypertension (CHPH). While BMP4 promotes vascular remodeling, BMP2 prevents CHPH. We previously demonstrated that BMP4 upregulates the expression of canonical transient receptor potential channel (TRPC) proteins and, thereby, enhances store-operated Ca(2+) entry (SOCE) and elevates intracellular Ca(2+) concentration ([Ca(2+)]i) in pulmonary arterial smooth muscle cells (PASMCs). In this study, we investigated the effects of BMP2 on these variables in rat distal PASMCs. We found that treatment with BMP2 (50 ng/ml, 60 h) inhibited TRPC1, TRPC4, and TRPC6 mRNA and protein expression. Moreover, BMP2 treatment led to reduced SOCE and decreased basal [Ca(2+)]i in PASMCs. These alterations were associated with decreased PASMC proliferation and migration. Conversely, knockdown of BMP2 with specific small interference RNA resulted in increased cellular levels of TRPC1, TRPC4, and TRPC6 mRNA and protein, enhanced SOCE, elevated basal [Ca(2+)]i, and increased proliferation and migration of PASMCs. Together, these results indicate that BMP2 participates in regulating Ca(2+) signaling in PASMCs by inhibiting TRPC1, TRPC4, and TRPC6 expression, thus leading to reduced SOCE and basal [Ca(2+)]i and inhibition of cell proliferation and migration.

Vascular remodeling in pulmonary hypertension

Pulmonary hypertension is a complex, progressive condition arising from a variety of genetic and pathogenic causes. Patients present with a spectrum of histologic and pathophysiological features, likely reflecting the diversity in underlying pathogenesis. It is widely recognized that structural alterations in the vascular wall contribute to all forms of pulmonary hypertension. Features characteristic of the remodeled vasculature in patients with pulmonary hypertension include increased stiffening of the elastic proximal pulmonary arteries, thickening of the intimal and/or medial layer of muscular arteries, development of vaso-occlusive lesions, and the appearance of cells expressing smooth muscle-specific markers in normally non-muscular small diameter vessels, resulting from proliferation and migration of pulmonary arterial smooth muscle cells and cellular transdifferentiation. The development of several animal models of pulmonary hypertension has provided the means to explore the mechanistic underpinnings of pulmonary vascular remodeling, although none of the experimental models currently used entirely replicates the pulmonary arterial hypertension observed in patients. Herein, we provide an overview of the histological abnormalities observed in humans with pulmonary hypertension and in preclinical models and discuss insights gained regarding several key signaling pathways contributing to the remodeling process. In particular, we will focus on the roles of ion homeostasis, endothelin-1, serotonin, bone morphogenetic proteins, Rho kinase, and hypoxia-inducible factor 1 in pulmonary arterial smooth muscle and endothelial cells, highlighting areas of cross-talk between these pathways and potentials for therapeutic targeting.

Sodium tanshinone IIA sulfonate inhibits canonical transient receptor potential expression in pulmonary arterial smooth muscle from pulmonary hypertensive rats

Danshen, the dried root of Salvia miltiorrhiza, is widely used in clinics in China for treating various diseases, including cardiovascular diseases. Sodium tanshinone IIA sulfonate (STS), a water-soluble derivative of tanshinone IIA isolated as the major active component from Danshen, was recently reported to be effective in attenuating the characteristic pulmonary vascular changes associated with chronically hypoxic pulmonary hypertension (CHPH); however, the underlying detailed mechanisms are poorly understood. In this study, we investigated the effects of STS on basal intracellular Ca(2+) concentration ([Ca(2+)](i)) and store-operated Ca(2+) entry (SOCE) in distal pulmonary arterial smooth muscle cells (PASMCs) exposed to prolonged hypoxia or isolated from CHPH rats. SOCE measured by Mn(2+) quenching of Fura-2 fluorescence in PASMCs from rats exposed to chronic hypoxia (10% O(2), 21 d) was increased by 59%, and basal [Ca(2+)](i) was increased by 119%; this effect was inhibited by intraperitoneal injection of STS. These inhibitory effects of STS on hypoxic increases of SOCE and basal [Ca(2+)](i) were associated with reduced expression of canonical transient receptor potential (TRPC)1 and TRPC6 in distal pulmonary arterial smooth muscle and decreases on right ventricular pressure, right ventricular hypertrophy, and peripheral pulmonary vessel thickening. In ex vivo cultured distal PASMCs from normoxic rats, STS (0-25 μM) dose-dependently inhibited hypoxia-induced cell proliferation and migration, paralleled with attenuation in increases of basal [Ca(2+)](i), SOCE, mRNA, and protein expression of TRPC1 and TRPC6. STS also relieved right ventricular systolic pressure, right ventricular hypertrophy, and TRPC1 and TRPC6 protein expression in distal pulmonary arteries in a monocrotaline-induced rat model of pulmonary arterial hypertension. These results indicate that STS prevents pulmonary arterial hypertension development likely by inhibiting TRPC1 and TRPC6 expression, resulting in normalized basal [Ca(2+)](i) and attenuated proliferation and migration of PASMCs.

Pathogenic role of store-operated and receptor-operated ca(2+) channels in pulmonary arterial hypertension

Pulmonary circulation is an important circulatory system in which the body brings in oxygen. Pulmonary arterial hypertension (PAH) is a progressive and fatal disease that predominantly affects women. Sustained pulmonary vasoconstriction, excessive pulmonary vascular remodeling, in situ thrombosis, and increased pulmonary vascular stiffness are the major causes for the elevated pulmonary vascular resistance (PVR) in patients with PAH. The elevated PVR causes an increase in afterload in the right ventricle, leading to right ventricular hypertrophy, right heart failure, and eventually death. Understanding the pathogenic mechanisms of PAH is important for developing more effective therapeutic approach for the disease. An increase in cytosolic free Ca²⁺ concentration ([Ca²⁺]_cyt) in pulmonary arterial smooth muscle cells (PASMC) is a major trigger for pulmonary vasoconstriction and an important stimulus for PASMC migration and proliferation which lead to pulmonary vascular wall thickening and remodeling. It is thus pertinent to define the pathogenic role of Ca²⁺ signaling in pulmonary vasoconstriction and PASMC proliferation to develop new therapies for PAH. [Ca²⁺]_cyt in PASMC is increased by Ca²⁺ influx through Ca²⁺ channels in the plasma membrane and by Ca²⁺ release or mobilization from the intracellular stores, such as sarcoplasmic reticulum (SR) or endoplasmic reticulum (ER). There are two Ca²⁺ entry pathways, voltage-dependent Ca²⁺ influx through voltage-dependent Ca²⁺ channels (VDCC) and voltage-independent Ca²⁺ influx through store-operated Ca²⁺ channels (SOC) and receptor-operated Ca²⁺ channels (ROC). This paper will focus on the potential role of VDCC, SOC, and ROC in the development and progression of sustained pulmonary vasoconstriction and excessive pulmonary vascular remodeling in PAH.