15-HETE mediates sub-acute hypoxia-induced TRPC1 expression and enhanced capacitative calcium entry in rat distal pulmonary arterial myocytes

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.

Transient receptor potential channels in the vasculature

The mammalian genome encodes 28 distinct members of the transient receptor potential (TRP) superfamily of cation channels, which exhibit varying degrees of selectivity for different ionic species. Multiple TRP channels are present in all cells and are involved in diverse aspects of cellular function, including sensory perception and signal transduction. Notably, TRP channels are involved in regulating vascular function and pathophysiology, the focus of this review. TRP channels in vascular smooth muscle cells participate in regulating contractility and proliferation, whereas endothelial TRP channel activity is an important contributor to endothelium-dependent vasodilation, vascular wall permeability, and angiogenesis. TRP channels are also present in perivascular sensory neurons and astrocytic endfeet proximal to cerebral arterioles, where they participate in the regulation of vascular tone. Almost all of these functions are mediated by changes in global intracellular Ca(2+) levels or subcellular Ca(2+) signaling events. In addition to directly mediating Ca(2+) entry, TRP channels influence intracellular Ca(2+) dynamics through membrane depolarization associated with the influx of cations or through receptor- or store-operated mechanisms. Dysregulation of TRP channels is associated with vascular-related pathologies, including hypertension, neointimal injury, ischemia-reperfusion injury, pulmonary edema, and neurogenic inflammation. In this review, we briefly consider general aspects of TRP channel biology and provide an in-depth discussion of the functions of TRP channels in vascular smooth muscle cells, endothelial cells, and perivascular cells under normal and pathophysiological conditions.

MicroRNA-190 regulates hypoxic pulmonary vasoconstriction by targeting a voltage-gated K⁺ channel in arterial smooth muscle cells

Pulmonary arterial hypertension (PAH) is associated with sustained vasoconstriction, profound structural remodeling of vasculatures and alterations in Ca(2+) homeostasis in arterial smooth muscle cells (SMCs), while the underlying mechanisms are still elusive. By regulating the expression of proteins, microRNAs (miRNAs) are known to play an important role in cell fates including differentiation, apoptosis and proliferation, and may be involved in the development of PAH. Based on our previous study, hypoxia produced a significant increase of the miR-190 level in the pulmonary artery (PA), here, we used synthetic miR-190 to mimic the increase in hypoxic conditions and showed evidence for the effects of miR-190 on pulmonary arterial vasoconstriction and Ca(2+) influx in arterial SMCs. Synthetic miR-190 remarkably enhanced the vasoconstriction responses to phenylephrine (PE) and KCl. The voltage-gated K(+) channel subfamily member, Kcnq5, mRNA was shown to be a target for miR-190. Meanwhile, miR-190 antisense oligos can partially reverse the effects of miR-190 on PASMCs and PAs. Therefore, these results suggest that miR-190 appears to be a positive regulator of Ca(2+) influx, and plays an important role in hypoxic pulmonary vascular constriction.

MicroRNA-138 plays a role in hypoxic pulmonary vascular remodelling by targeting Mst1

Unbalanced apoptosis is a major cause of structural remodelling of vasculatures associated with PAH (pulmonary arterial hypertension), whereas the underlying mechanisms are still elusive. miRNAs (microRNAs) regulate the expression of several proteins that are important for cell fate, including differentiation, proliferation and apoptosis. It is possible that these regulatory RNA molecules play a role in the development of PAH. To test this hypothesis, we studied the effect of several miRNAs on the apoptosis of cultured PASMCs (pulmonary artery smooth muscle cells) and identified miR-138 to be an important player. miR-138 was expressed in PASMCs, and its expression was subjected to regulation by hypoxia. Expression of exogenous miR-138 suppressed PASMC apoptosis, prevented caspase activation and disrupted Bcl-2 signalling. The serine/threonine kinase Mst1, an amplifier of cell apoptosis, seemed to be a target of miR-138, and the activation of the Akt pathway was necessary for the anti-apoptotic effect of miR-138. Therefore the results of the present study suggest that miR-138 appears to be a negative regulator of PASMC apoptosis, and plays an important role in HPVR (hypoxic pulmonary vascular remodelling).

Differences between basal lung levels of select eicosanoids in rat and mouse

Metabolites of arachidonic acid play an important role in mediating inflammation, cell proliferation, and oxidative stress that contribute to many pulmonary diseases. We hypothesized that the substantial differences between rats and mice in their responses to experimental pulmonary hypertensive stimuli would be associated with parallel differences in their basal eicosanoid profile. Rat and mouse lung extracts were subjected to liquid chromatography tandem mass spectrometry that was optimized for simultaneous separation and rapid quantification of the major hydroxyeicosatetraenoic acids (HETEs) and prostaglandins (PGs). Basal levels (pg/μg protein) of arachidonic acid metabolites differed significantly between rat and mouse lungs. Median values of the following major eicosanoids were significantly higher in mouse than in rat lungs: 5-HETE, 8-HETE, 12-HETE, 15-HETE, PGE₂, and PGI₂, as well as isoprostane-E₂ and -F_2α. In addition, the PGI₂/TXB₂ ratio was increased in mouse relative to rat lungs. On the basis of the important roles that these compounds play in determining pulmonary vascular tone, the differences in select eicosanoid profiles, especially the PGI₂/TXB₂ ratio, between rat and mouse lungs may underlie the interspecies differences in susceptibility to the development of pulmonary hypertension.

Role of 15-lipoxygenase/15-hydroxyeicosatetraenoic acid in hypoxia-induced pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a rare disease with a complex aetiology characterized by elevated pulmonary artery resistance, which leads to right heart ventricular afterload and ultimately progressing to right ventricular failure and often death. In addition to other factors, metabolites of arachidonic acid cascade play an important role in the pulmonary vasculature, and disruption of signaling pathways of arachidonic acid plays a central role in the pathogenesis of PAH. 15-Lipoxygenase (15-LO) is upregulated in pulmonary artery endothelial cells and smooth muscle cells of PAH patients, and its metabolite 15-hydroxyeicosatetraenoic acid (15-HETE) in particular seems to play a central role in the contractile machinery, and in the initiation and propagation of cell proliferation via its effects on signal pathways, mitogens, and cell cycle components. Here, we focus on our important research into the role played by 15-LO/15-HETE, which promotes a proliferative, antiapoptotic, and vasoconstrictive physiological milieu leading to hypoxic pulmonary hypertension.

Integration of transient receptor potential canonical channels with lipids

Transient receptor potential canonical (TRPC) channels are the canonical (C) subset of the TRP proteins, which are widely expressed in mammalian cells. They are thought to be primarily involved in determining calcium and sodium entry and have wide-ranging functions that include regulation of cell proliferation, motility and contraction. The channels are modulated by a multiplicity of factors, putatively existing as integrators in the plasma membrane. This review considers the sensitivities of TRPC channels to lipids that include diacylglycerols, phosphatidylinositol bisphosphate, lysophospholipids, oxidized phospholipids, arachidonic acid and its metabolites, sphingosine-1-phosphate, cholesterol and some steroidal derivatives and other lipid factors such as gangliosides. Promiscuous and selective lipid sensing have been detected. There appear to be close working relationships with lipids of the phospholipase C and A₂ enzyme systems, which may enable integration with receptor signalling and membrane stretch. There are differences in the properties of each TRPC channel that are further complicated by TRPC heteromultimerization. The lipids modulate activity of the channels or insertion in the plasma membrane. Lipid microenvironments and intermediate sensing proteins have been described that include caveolae, G protein signalling, SEC14-like and spectrin-type domains 1 (SESTD1) and podocin. The data suggest that lipid sensing is an important aspect of TRPC channel biology enabling integration with other signalling systems.

15-Hydroxyeicosatetraenoic acid (15-HETE) protects pulmonary artery smooth muscle cells from apoptosis via inducible nitric oxide synthase (iNOS) pathway

15-Hydroxyeicosatetraenoic acid (15-HETE), one of many important metabolic products of arachidonic acid (AA) catalyzed by 15-lipoxygenase, plays an important role in pulmonary vascular smooth muscle remodeling. We have previously shown its unsubstituted effects on the apoptotic responses of pulmonary artery smooth muscle cells (PASMCs), but the underlying mechanisms are still poorly manifested. Previous studies have shown that inducible nitric oxide synthase (iNOS) plays an important protective role against sepsis-induced pulmonary apoptosis. Therefore, the purpose of this study is to determine whether 15-HETE anti-apoptotic process is mediated through the iNOS pathway in rat PASMCs. To test this hypothesis, we studied the contribution of iNOS to the 15-HETE induced anti-apoptotic responses using cell viability measurement, Western blot, mitochondrial potential analysis, nuclear morphology determination and TUNEL assay. Our results showed that both exogenous and endogenous 15-HETE up-regulated iNOS protein and mRNA expression and 15-HETE enhanced the cell survival, attenuated mitochondrial depolarization, up-regulated the expression of Bcl-2 and procaspase-3 in PASMCs under serum-deprived condition. These effects were reversed by iNOS inhibitor SMT or l-canavanine. Taken together, our data indicates that iNOS is a novel signaling transduction pathway, which is necessary for the effects of 15-HETE in protection PASMCs from apoptosis and may be an important mechanism underlying the treatment of pulmonary artery hypertension and also provides a novel therapeutic insight in future.