Stim1- and Orai1-mediated store-operated calcium entry is critical for angiotensin II-induced vascular smooth muscle cell proliferation

Inositol 1,4,5-Trisphosphate Receptors Regulate Vascular Smooth Muscle Cell Proliferation and Neointima Formation in Mice

BACKGROUND

Vascular smooth muscle cell (VSMC) proliferation is involved in many types of arterial diseases, including neointima hyperplasia, in which Ca2+ has been recognized as a key player. However, the physiological role of Ca2+ release via inositol 1,4,5-trisphosphate receptors (IP3Rs) from endoplasmic reticulum in regulating VSMC proliferation has not been well determined.

METHODS AND RESULTS

Both in vitro cell culture models and in vivo mouse models were generated to investigate the role of IP3Rs in regulating VSMC proliferation. Expression of all 3 IP3R subtypes was increased in cultured VSMCs upon platelet-derived growth factor-BB and FBS stimulation as well as in the left carotid artery undergoing intimal thickening after vascular occlusion. Genetic ablation of all 3 IP3R subtypes abolished endoplasmic reticulum Ca2+ release in cultured VSMCs, significantly reduced cell proliferation induced by platelet-derived growth factor-BB and FBS stimulation, and also decreased cell migration of VSMCs. Furthermore, smooth muscle-specific deletion of all IP3R subtypes in adult mice dramatically attenuated neointima formation induced by left carotid artery ligation, accompanied by significant decreases in cell proliferation and matrix metalloproteinase-9 expression in injured vessels. Mechanistically, IP3R-mediated Ca2+ release may activate cAMP response element-binding protein, a key player in controlling VSMC proliferation, via Ca2+/calmodulin-dependent protein kinase II and Akt. Loss of IP3Rs suppressed cAMP response element-binding protein phosphorylation at Ser133 in both cultured VSMCs and injured vessels, whereas application of Ca2+ permeable ionophore, ionomycin, can reverse cAMP response element-binding protein phosphorylation in IP3R triple knockout VSMCs.

CONCLUSIONS

Our results demonstrated an essential role of IP3R-mediated Ca2+ release from endoplasmic reticulum in regulating cAMP response element-binding protein activation, VSMC proliferation, and neointima formation in mouse arteries.

Control of CDH1/E-Cadherin Gene Expression and Release of a Soluble Form of E-Cadherin in SARS-CoV-2 Infected Caco-2 Intestinal Cells: Physiopathological Consequences for the Intestinal Forms of COVID-19

COVID-19 is the biggest pandemic the world has seen this century. Alongside the respiratory damage observed in patients with severe forms of the disease, gastrointestinal symptoms have been frequently reported. These symptoms (e.g., diarrhoea), sometimes precede the development of respiratory tract illnesses, as if the digestive tract was a major target during early SARS-CoV-2 dissemination. We hypothesize that in patients carrying intestinal SARS-CoV-2, the virus may trigger epithelial barrier damage through the disruption of E-cadherin (E-cad) adherens junctions, thereby contributing to the overall gastrointestinal symptoms of COVID-19. Here, we use an intestinal Caco-2 cell line of human origin which expresses the viral receptor/co-receptor as well as the membrane anchored cell surface adhesion protein E-cad to investigate the expression of E-cad after exposure to SARS-CoV-2. We found that the expression of CDH1/E-cad mRNA was significantly lower in cells infected with SARS-CoV-2 at 24 hours post-infection, compared to virus-free Caco-2 cells. The viral receptor ACE2 mRNA expression was specifically down-regulated in SARS-CoV-2-infected Caco-2 cells, while it remained stable in HCoV-OC43-infected Caco-2 cells, a virus which uses HLA class I instead of ACE2 to enter cells. It is worth noting that SARS-CoV-2 induces lower transcription of TMPRSS2 (involved in viral entry) and higher expression of B0AT1 mRNA (that encodes a protein known to co-express with ACE2 on intestinal cells). At 48 hours post-exposure to the virus, we also detected a small but significant increase of soluble E-cad protein (sE-cad) in the culture supernatant of SARS-CoV-2-infected Caco-2 cells. The increase of sE-cad release was also found in the intestinal HT29 cell line when infected by SARS-CoV-2. Beside the dysregulation of E-cad, SARS-CoV-2 infection of Caco-2 cells also leads to the dysregulation of other cell adhesion proteins (occludin, JAMA-A, zonulin, connexin-43 and PECAM-1). Taken together, these results shed light on the fact that infection of Caco-2 cells with SARS-CoV-2 affects tight-, adherens-, and gap-junctions. Moreover, intestinal tissues damage was associated to the intranasal SARS-CoV-2 infection in human ACE2 transgenic mice.

STIM and Orai Mediated Regulation of Calcium Signaling in Age-Related Diseases

Tight spatiotemporal regulation of intracellular Ca²⁺ plays a critical role in regulating diverse cellular functions including cell survival, metabolism, and transcription. As a result, eukaryotic cells have developed a wide variety of mechanisms for controlling Ca²⁺ influx and efflux across the plasma membrane as well as Ca²⁺ release and uptake from intracellular stores. The STIM and Orai protein families comprising of STIM1, STIM2, Orai1, Orai2, and Orai3, are evolutionarily highly conserved proteins that are core components of all mammalian Ca²⁺ signaling systems. STIM1 and Orai1 are considered key players in the regulation of Store Operated Calcium Entry (SOCE), where release of Ca²⁺ from intracellular stores such as the Endoplasmic/Sarcoplasmic reticulum (ER/SR) triggers Ca²⁺ influx across the plasma membrane. SOCE, which has been widely characterized in non-excitable cells, plays a central role in Ca²⁺-dependent transcriptional regulation. In addition to their role in Ca²⁺ signaling, STIM1 and Orai1 have been shown to contribute to the regulation of metabolism and mitochondrial function. STIM and Orai proteins are also subject to redox modifications, which influence their activities. Considering their ubiquitous expression, there has been increasing interest in the roles of STIM and Orai proteins in excitable cells such as neurons and myocytes. While controversy remains as to the importance of SOCE in excitable cells, STIM1 and Orai1 are essential for cellular homeostasis and their disruption is linked to various diseases associated with aging such as cardiovascular disease and neurodegeneration. The recent identification of splice variants for most STIM and Orai isoforms while complicating our understanding of their function, may also provide insight into some of the current contradictions on their roles. Therefore, the goal of this review is to describe our current understanding of the molecular regulation of STIM and Orai proteins and their roles in normal physiology and diseases of aging, with a particular focus on heart disease and neurodegeneration.

Role of Store-Operated Ca2+ Entry in the Pulmonary Vascular Remodeling Occurring in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a severe and multifactorial disease. PAH pathogenesis mostly involves pulmonary arterial endothelial and pulmonary arterial smooth muscle cell (PASMC) dysfunction, leading to alterations in pulmonary arterial tone and distal pulmonary vessel obstruction and remodeling. Unfortunately, current PAH therapies are not curative, and therapeutic approaches mostly target endothelial dysfunction, while PASMC dysfunction is under investigation. In PAH, modifications in intracellular Ca2+ homoeostasis could partly explain PASMC dysfunction. One of the most crucial actors regulating Ca2+ homeostasis is store-operated Ca2+ channels, which mediate store-operated Ca2+ entry (SOCE). This review focuses on the main actors of SOCE in human and experimental PASMC, their contribution to PAH pathogenesis, and their therapeutic potential in PAH.

Exploring the regulatory roles of circular RNAs in the pathogenesis of atherosclerosis

Circular RNAs (circRNAs) are a class of noncoding RNAs with a covalently closed loop structure. Recent evidence has shown that circRNAs can regulate gene transcription, alternative splicing, microRNA (miRNA) "molecular sponges", RNA-binding proteins and protein translation. Atherosclerosis is one of the leading causes of death worldwide, and more studies have indicated that circRNAs are related to atherosclerosis pathogenesis, including vascular endothelial cells, vascular smooth muscle cells, inflammation and lipid metabolism. In this review, we systematically summarize the biogenesis, characteristics and functions of circRNAs with a focus on their roles in the pathogenesis of atherosclerosis.

Effect of miRNA-223-3p Targeting Stromal Interaction Molecule 1 on Proliferation and Apoptosis of Hypoxia/Reoxygenation-Applied H9c2 Cardiomyocytes

This study was established to determine the effect of miRNA-223-3p on the proliferation and apoptosis of hypoxia/reoxygenation-applied H9c2 cardiomyocytes and the associated mechanisms. A hypoxia/reoxygenation (H/R) model was established, with normal cells also used as a control. miRNA-NC, miRNA-223-3p, anti-miRNA-NC, and anti-miRNA-223-3p plasmids were transfected into normally cultured cardiomyocytes, defined as the miRNA-NC, miRNA-223-3p, anti-miRNA-NC, and anti-miRNA-223-3p groups. In addition, miRNA-223-3p was co-transfected into normally cultured cardiomyocytes with pcDNA3.1 and pcDNA3.1-STIM1 plasmids, followed by treatment with H/R for cells in the miR-NC and miR-223-3p groups, defined as the H/R+miRNA-NC, H/R+miRNA-223-3p, H/R+miRNA-223-3p+pcDNA3.1, and H/R+miRNA-223-3p+pcDNA3.1-STIM1 groups. A liposome method was adopted for assessing transfection. qRT-PCR was used to detect miRNA-223-3p expression, while western blotting was used to detect protein expression. MTT assay was used to detect cell viability, flow cytometry to detect apoptosis, and dual luciferase reporter gene assay to detect fluorescence activity. After H/R treatment, miR-223-3p, cyclin D1, and Bcl-2 expression of cardiomyocytes decreased, p21 and Bax expression significantly increased, cell activity decreased, and the apoptosis rate increased. miRNA-223-3p achieved the targeted regulation of STIM1 expression. miRNA-223-3p overexpression promoted the H/R-induced cardiomyocyte proliferation and inhibited cardiomyocyte apoptosis. STIM1 overexpression reversed the proliferation-promoting and apoptosis-inhibiting effects of miRNA-223-3p on cardiomyocytes treated with H/R. The findings show that miRNA-223-3p overexpression promotes H/R-induced cell proliferation, inhibits apoptosis, and protects H/R-induced cardiomyocytes from injury, via a mechanism probably associated with STIM1 expression. miRNA-223-3p thus provides a new target for treating cardiomyocyte injury.

ORAI1 Ca2+ Channel as a Therapeutic Target in Pathological Vascular Remodelling

In the adult, vascular smooth muscle cells (VSMC) are normally physiologically quiescent, arranged circumferentially in one or more layers within blood vessel walls. Remodelling of native VSMC to a proliferative state for vascular development, adaptation or repair is driven by platelet-derived growth factor (PDGF). A key effector downstream of PDGF receptors is store-operated calcium entry (SOCE) mediated through the plasma membrane calcium ion channel, ORAI1, which is activated by the endoplasmic reticulum (ER) calcium store sensor, stromal interaction molecule-1 (STIM1). This SOCE was shown to play fundamental roles in the pathological remodelling of VSMC. Exciting transgenic lineage-tracing studies have revealed that the contribution of the phenotypically-modulated VSMC in atherosclerotic plaque formation is more significant than previously appreciated, and growing evidence supports the relevance of ORAI1 signalling in this pathologic remodelling. ORAI1 has also emerged as an attractive potential therapeutic target as it is accessible to extracellular compound inhibition. This is further supported by the progression of several ORAI1 inhibitors into clinical trials. Here we discuss the current knowledge of ORAI1-mediated signalling in pathologic vascular remodelling, particularly in the settings of atherosclerotic cardiovascular diseases (CVDs) and neointimal hyperplasia, and the recent developments in our understanding of the mechanisms by which ORAI1 coordinates VSMC phenotypic remodelling, through the activation of key transcription factor, nuclear factor of activated T-cell (NFAT). In addition, we discuss advances in therapeutic strategies aimed at the ORAI1 target.

Angiotensin-Converting Enzyme 2 Gene Expression in Breast Tissue

OBJECTIVE

Binding to angiotensin-converting enzyme 2 (ACE2) receptor is a critical step for severe acute respiratory syndrome coronavirus 2 (SARSCoV- 2) to mediate its entry into target cells. ACE2 is expressed in many human tissues, including the lungs. However, no research has demonstrated that SARS-CoV-2 can infect human breast tissue. This study aimed to investigate ACE2 gene expression in human breast tissue using a public database.

MATERIALS AND METHODS

A search of a public gene expression database was performed to investigate ACE2 gene expression in in human breast tissue.

RESULTS

The gene expression profile demonstrated that ACE2 gene expression was higher in human breast tissue than human lung tissue.

CONCLUSION

Our knowledge about coronavirus disease-2019 (COVID-19) is expanding rapidly. Clinicians are eager for vetted information regarding all aspects of this new illness, and this study demonstrates that the level of ACE2 expression in human breast tissue is higher than that in the lung tissue, a major target tissue affected by SARS-CoV-2 infection. This finding strongly suggests that SARS-CoV-2 infection causes breast pathology.

Circular RNA in cardiovascular disease: Expression, mechanisms and clinical prospects

Circular RNAs (circRNAs) are a group of covalently closed, endogenous, non‐coding RNAs, which exist widely in human tissues including the heart. Increasing evidence has shown that cardiac circRNAs play crucial regulatory roles in cardiovascular diseases (CVDs). In this review, we aimed to provide a systemic understanding of circRNAs with a special emphasis on the cardiovascular system. We have summarized the current research on the classification, biogenesis and properties of circRNAs as well as their participation in the pathogenesis of CVDs. CircRNAs are conserved, stable and have specific spatiotemporal expression; thus, they have been accepted as a potential diagnostic marker or an incremental prognostic biomarker for CVDs.

Upregulation of Orai1 and increased calcium entry contribute to angiotensin II-induced human coronary smooth muscle cell proliferation: Running Title: Angiotensin II-induced human coronary smooth muscle cells proliferation

Angiotensin II (Ang II) is an oligopeptide of the renin-angiotensin system, and Ang II-induced vascular smooth muscle cell (VSMC) proliferation is an important pathophysiological process involved in atherosclerosis; however, the underlying mechanism remains unclear. Orai1 and Stim1 are the main components of store-operated Ca²⁺ entry (SOCE), which has an important effect on VSMC proliferation. In the present study, we showed that Ang II-induced human coronary smooth muscle cell (HCSMC) proliferation was associated with increased calcium entry. The expression of Orai1, but not that of Stim1, was significantly upregulated in Ang II-treated HCSMCs. However, knockdown of Orai1 or Stim1 decreased HCSMC proliferation and SOCE activity in Ang II-treated HCSMCs. Orai1 was significantly downregulated in HCSMCs transfected with short interfering RNA (siRNA) against NOX2 or NF-κB. Transfection with siRNA against NOX2 or p65 also decreased Ang II-induced HCSMCs SOCE activation and proliferation. These findings suggested that Ang II upregulated Orai1 via the NF-κB and NOX2 pathways, leading to increased SOCE and HCSMC proliferation. The molecular factors mediating Ang II-induced SOCE upregulation are potential therapeutic targets for the prevention of Ang II-sensitive or Ang II-dependent HCSMC proliferation.

Coupling of store-operated calcium entry to vasoconstriction is acid-sensing ion channel 1a dependent in pulmonary but not mesenteric arteries

Although voltage-gated Ca²⁺ channels (VGCC) are a major Ca²⁺ entry pathway in vascular smooth muscle cells (VSMCs), several other Ca²⁺-influx mechanisms exist and play important roles in vasoreactivity. One of these is store-operated Ca²⁺ entry (SOCE), mediated by an interaction between STIM1 and Orai1. Although SOCE is an important mechanism of Ca²⁺ influx in non-excitable cells (cells that lack VGCC); there is debate regarding the contribution of SOCE to regulate VSMC contractility and the molecular components involved. Our previous data suggest acid-sensing ion channel 1a (ASIC1a) is a necessary component of SOCE and vasoconstriction in small pulmonary arteries. However, it is unclear if ASIC1a similarly contributes to SOCE and vascular reactivity in systemic arteries. Considering the established role of Orai1 in mediating SOCE in the systemic circulation, we hypothesize the involvement of ASIC1a in SOCE and resultant vasoconstriction is unique to the pulmonary circulation. To test this hypothesis, we examined the roles of Orai1 and ASIC1a in SOCE- and endothelin-1 (ET-1)-induced vasoconstriction in small pulmonary and mesenteric arteries. We found SOCE is coupled to vasoconstriction in pulmonary arteries but not mesenteric arteries. In pulmonary arteries, inhibition of ASIC1a but not Orai1 attenuated SOCE- and ET-1-induced vasoconstriction. However, neither inhibition of ASIC1a nor Orai1 altered ET-1-induced vasoconstriction in mesenteric arteries. We conclude that SOCE plays an important role in pulmonary, but not mesenteric, vascular reactivity. Furthermore, in contrast to the established role of Orai1 in SOCE in non-excitable cells, the SOCE response in pulmonary VSMCs is largely mediated by ASIC1a.

Kindlin-2 deficiency induces fatal intestinal obstruction in mice

Rationale: Smooth muscle-motility disorders are mainly characterized by impaired contractility and functional intestinal obstruction. Some of these cases are caused by genetic mutations of smooth muscle genes ACTA2, ACTG2, MYH11, MYLK and LMOD1. Still the etiology is complex and multifactorial and the underlying pathology is poorly understood. Integrin interaction protein Kindlin-2 is widely expressed in striated and smooth muscle cells (SMC). However, the function of Kindlin-2 in the smooth muscle remains elusive.

Methods: We generated two mouse models using different cre promoter transgenic mice, Kindlin-2^fl/fl SM22α-cre+ (cKO mice) and Kindlin-2^fl/fl; MYH-cre+ (iKO mice). Embryos and adult tissues were prepared for hematoxylin and eosin (H&E) staining, immunohistochemistry (IHC) and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) apoptosis assay. We investigated ultrastructure changes of mouse smooth muscle using transmission electron microscopy (TEM) and measured smooth muscle contractile force in mounting aortic and intestinal rings using the multiwire myograph system (DMT 620M). In addition, cell traction force microscopy (CTFM) was applied to observe the functional change of primary SMC after Kindlin-2 depletion by RNAi.

Results: Depletion of Kindlin-2 encoding gene Fermt2 in embryonic smooth muscles leads to apoptosis, downregulates the key components of SMC, impairs smooth muscle development, and finally causes embryonic death at E14.5. Tamoxifen-induced Kindlin-2-specific knockout in adult mouse smooth muscle showed decreased blood pressure, intestinal hypoperistalsis, and eventually died of intestinal obstruction. Kindlin-2 depletion also leads to downregulated Myh11, α-SMA, and CNN, shortened myofilament, broken myofibrils, and impaired contractility of the smooth muscles in iKO mice. Mechanistically, loss of Kindlin-2 decreases Ca2⁺ influx in primary vascular smooth muscle cells (PVSMC) by downregulating the expression of calcium-binding protein S100A14 and STIM1.

Conclusion: We demonstrated that Kindlin-2 is essential for maintaining the normal structure and function of smooth muscles. Loss of Kindlin-2 impairs smooth muscle formation during embryonic development by inducing apoptosis and jeopardizes the contraction of adult smooth muscle by blocking Ca²⁺ influx that leads to intestinal obstruction. Mice with Kindlin-2 depletion in adult smooth muscle could be a potent animal model of intestinal obstruction for disease research, drug treatment and prognosis.

Pathophysiological Significance of Store-Operated Calcium Entry in Cardiovascular and Skeletal Muscle Disorders and Angiogenesis

Store-Operated Ca²⁺ Entry (SOCE) is an important Ca²⁺ influx pathway expressed by several excitable and non-excitable cell types. SOCE is recognized as relevant signaling pathway not only for physiological process, but also for its involvement in different pathologies. In fact, independent studies demonstrated the implication of essential protein regulating SOCE, such as STIM, Orai and TRPCs, in different pathogenesis and cell disorders, including cardiovascular disease, muscular dystrophies and angiogenesis. Compelling evidence showed that dysregulation in the function and/or expression of isoforms of STIM, Orai or TRPC play pivotal roles in cardiac hypertrophy and heart failure, vascular remodeling and hypertension, skeletal myopathies, and angiogenesis. In this chapter, we summarized the current knowledge concerning the mechanisms underlying abnormal SOCE and its involvement in some diseases, as well as, we discussed the significance of STIM, Orai and TRPC isoforms as possible therapeutic targets for the treatment of angiogenesis, cardiovascular and skeletal muscle diseases.

TRPP2 associates with STIM1 to regulate cerebral vasoconstriction and enhance high salt intake-induced hypertensive cerebrovascular spasm

Cerebrovascular spasm is a life-threatening event in salt-sensitive hypertension. The relationship between store-operated calcium entry (SOCE) and vasoconstriction in hypertension has not been fully clarified. This study investigated the changes in cerebrovascular contractile responses in high salt intake-induced hypertension and the functional roles of the main components of SOCE, namely, polycystin-2 (TRPP2), stromal interaction molecule 1 (STIM1), and Orai3. Polycystic kidney disease 2 (which encodes TRPP2) knockout mice displayed decreased cerebrovascular SOCE-induced contraction. The blood pressure of age-matched rats fed a normal or high-salt diet for 4 weeks was monitored weekly using noninvasive tail-cuff plethysmography. The systolic blood pressure of the rats fed a high-salt diet was significantly higher than that of controls. Western blotting and immunohistochemical results showed that these hypertensive rats expressed higher levels of cerebrovascular TRPP2, STIM1, and Orai3 than controls. Cerebrovascular tension measurements of the basilar artery indicated that SOCE-mediated contraction was significantly increased in hypertensive rats compared with control rats. In addition, SOCE-mediated contraction was decreased in the basilar arteries of rats pretreated with the SOCE inhibitor BTP-2 (10 μM) or transfected with TRPP2-specific or STIM1-specific small interfering RNA. Staining with 2,3,5-triphenyltetrazolium chloride (TTC) was used to quantify the infarcted brain area 24 h after middle cerebral artery occlusion, a model of ischemic stroke, in rodents. The infarcted brain area was significantly greater in hypertensive rats and significantly lower in BTP-2-treated rats than in controls. Taken together, these findings indicate that SOCE-induced contraction may be overactive in the basilar arteries of salt-sensitive hypertensive rats, suggesting the dysregulation of TRPP2 and SOCE and its other components.

Transmembrane protein 66 attenuates neointimal hyperplasia after carotid artery injury by SOCE inactivation

Neointimal hyperplasia could be one of the most important complications after balloon angioplasty. Since calcium signaling has several physiologic effects on the regulation of the proliferation and migration of vascular smooth muscle cells (VSMCs), it was hypothesized that transmembrane protein 66 (TMEM66), a store operated calcium entry (SOCE)‑associated regulatory factor, possesses vascular protection against balloon injury. The rat balloon‑induced carotid artery injury model was performed. Histological analysis was used to check neointimal hyperplasia. TMEM66 expression was measured by PCR and immunoblotting. The results revealed that TMEM66 was expressed in the medial and neointimal layers of the injured artery, and the expression of TMEM66 was markedly decreased. TMEM66 overexpression attenuated neointimal hyperplasia via VSMC proliferation/migration inhibition, and restored expression of VSMC phenotypic markers. Moreover, TMEM66 overexpression reduced the increased expression of Stim1 and Orai1 and PDGF‑BB treatment‑enhanced [Ca2+]i. In conclusion, TMEM66 protects against balloon injury‑induced neointimal hyperplasia, and may be a pharmacological target for the treatment of restenosis.

Rab7‑mediated autophagy regulates phenotypic transformation and behavior of smooth muscle cells via the Ras/Raf/MEK/ERK signaling pathway in human aortic dissection

Autophagy regulates the metabolism, survival and function of numerous types of cell, including cells that comprise the cardiovascular system. The dysfunction of autophagy has been demonstrated in atherosclerosis, restenotic lesions and hypertensive vessels. As a member of the Ras GTPase superfamily, Rab7 serves a significant role in the regulation of autophagy. The present study evaluated how Rab7 affects the proliferation and invasion, and phenotypic transformations of aortic dissection (AD) smooth muscle cells (SMCs) via autophagy. Rab7 was overexpressed in AD tissues and the percentage of synthetic human aortic SMCs (HASMCs) was higher in AD tissues compared with NAD tissues. Downregulation of Rab7 decreased cell growth, reduced the number of invasive cells and decreased the percentage cells in the G1 phase. Autophagy of HASMCs was inhibited following Rab7 knockdown. Inhibition of autophagy with 3‑methyladenine or Rab7 knockdown suppressed the phenotypic conversion of contractile to synthetic HASMCs. The action of Rab7 may be mediated by inhibiting the Ras/Raf/mitogen‑activated protein kinase (MAPK) kinase (MEK)/extracellular signal related kinase (ERK) signaling pathway. In conclusion, the results revealed that Rab7‑mediated autophagy regulated the behavior of SMCs and the phenotypic transformations in AD via activation of the Ras/Raf/MEK/ERK signaling pathway. The findings of the present study may improve understanding of the role Rab7 in the molecular etiology of AD and suggests the application of Rab7 as a novel therapeutic target in the treatment of human AD.

ORAI channels in cellular remodeling of cardiorespiratory disease

Cardiorespiratory disease, which includes systemic arterial hypertension, restenosis, atherosclerosis, pulmonary arterial hypertension, asthma, and chronic obstructive pulmonary disease (COPD) are highly prevalent and devastating diseases with limited therapeutic modalities. A common pathophysiological theme to these diseases is cellular remodeling, which is contributed by changes in expression and activation of ion channels critical for either excitability or growth. Calcium (Ca²⁺) signaling and specifically ORAI Ca²⁺ channels have emerged as significant regulators of smooth muscle, endothelial, epithelial, platelet, and immune cell remodeling. This review details the dysregulation of ORAI in cardiorespiratory diseases, and how this dysregulation of ORAI contributes to cellular remodeling.

Methylglyoxal evokes acute Ca2+ transients in distinct cell types and increases agonist-evoked Ca2+ entry in endothelial cells via CRAC channels

Methylglyoxal (MG) is a by-product of glucose metabolism and its accumulation has been linked to the development of diabetic complications such as retinopathy and nephropathy by affecting multiple signalling pathways. However, its influence on the intracellular Ca²⁺ homeostasis and particularly Ca²⁺ entry, which has been reported to be mediated via TRPA1 channels in DRG neurons, has not been studied in much detail in other cell types. In this study, we report the consequences of acute and long-term MG application on intracellular Ca²⁺ levels in endothelial cells. We showed that acute MG application doesn't evoke any instantaneous changes in the intracellular Ca²⁺ concentration in immortalized mouse cardiac endothelial cells (MCECs) and murine microvascular endothelial cells (muMECs). In contrast, an MG-induced rise in intracellular Ca²⁺ level was observed in primary mouse mesangial cells within 30 s, indicating that the modulation of Ca²⁺ homeostasis by MG is strictly cell type specific. The formation of the MG-derived advanced glycation end product (AGE) MG-H1 was found to be time and concentration-dependent in MCECs. Likewise, MG pre-incubation for 6 h increased the angiotensin II-evoked Ca²⁺ entry in MCECs and muMECs which was abrogated by inhibition of Calcium release activated calcium (CRAC) channels with GSK-7975A, but unaffected by an inhibitor specific to TRPA1 channels. Quantitative PCR analysis revealed that MG pre-treatment did not affect expression of the genes encoding the angiotensin receptors AT1R (Agtr 1a & Agtr 1b), Trpa1 nor Orai1, Orai2, Orai3, Stim1, Stim2 and Saraf which operate as constituents or regulators of CRAC channels and store-operated Ca²⁺ entry (SOCE) in other cell types. Together, our results show that long-term MG stimulation leads to the formation of glycation end products, which facilitates the agonist-evoked Ca²⁺ entry in endothelial cells, and this could be a new pathway that might lead to MG-evoked vasoregression observed in diabetic vasculopathies.

Ca2+ Entry Through Reverse Mode Na+/Ca2+ Exchanger Contributes to Store Operated Channel-Mediated Neointima Formation After Arterial Injury

BACKGROUND

Na⁺/Ca²⁺ exchange (NCX) reversal-mediated Ca²⁺ entry is a critical pathway for stimulating proliferation in many cell lines. However, the role of reverse-mode NCX1 in neointima formation and atherosclerosis remains unclear. The aims of the present study were to investigate the functional role of NCX1 in the pathogenesis of atherosclerosis and vascular smooth muscle cell (VSMC) proliferation, and to determine the interaction between NCX1 and store depletion in VSMCs.

METHODS

A rat balloon injury model was established to examine the effect of the knockdown of NCX1 on neointima formation after injury. VSMCs were cultured to verify that NCX1 knockdown suppressed serum-induced VSMC proliferation.

RESULTS

The results showed that balloon injury induced neointima formation and upregulated NCX1 expression at 7 and 14 days after injury in rat carotid arteries (1.18- and 1.45-fold, respectively). A lentivirus vector expressing short hairpin (sh)RNA against rat NCX1 dramatically downregulated NCX1, proliferating cell nuclear antigen (PCNA) and Ki-67 expression, and suppressed neointima formation in vivo (62% at 7 days and 70% at 14 days). KB-R7943 (an inhibitor of reverse-mode NCX1) and NCX1 knockdown significantly inhibited serum-induced VSMC proliferation (65% at 72 hours and 41% at 72 hours, respectively), determined according to PCNA and Ki-67 expression and cell counting in vitro, and markedly suppressed store depletion-mediated Ca²⁺ entry and peripheral cytosolic Na⁺ transients in VSMCs.

CONCLUSIONS

Reverse-mode NCX1 is activated by store depletion and is required for proliferative VSMC proliferation and neointima formation after arterial injury.

Hypoxia selectively upregulates cation channels and increases cytosolic [Ca2+] in pulmonary, but not coronary, arterial smooth muscle cells

Ca²⁺ signaling, particularly the mechanism via store-operated Ca²⁺ entry (SOCE) and receptor-operated Ca²⁺ entry (ROCE), plays a critical role in the development of acute hypoxia-induced pulmonary vasoconstriction and chronic hypoxia-induced pulmonary hypertension. This study aimed to test the hypothesis that chronic hypoxia differentially regulates the expression of proteins that mediate SOCE and ROCE [stromal interacting molecule (STIM), Orai, and canonical transient receptor potential channel TRPC6] in pulmonary (PASMC) and coronary (CASMC) artery smooth muscle cells. The resting cytosolic [Ca²⁺] ([Ca²⁺]_cyt) and the stored [Ca²⁺] in the sarcoplasmic reticulum were not different in CASMC and PASMC. Seahorse measurement showed a similar level of mitochondrial bioenergetics (basal respiration and ATP production) between CASMC and PASMC. Glycolysis was significantly higher in PASMC than in CASMC. The amplitudes of cyclopiazonic acid-induced SOCE and OAG-induced ROCE in CASMC are slightly, but significantly, greater than in PASMC. The frequency and the area under the curve of Ca²⁺ oscillations induced by ATP and histamine were also larger in CASMC than in PASMC. Na⁺/Ca²⁺ exchanger-mediated increases in [Ca²⁺]_cyt did not differ significantly between CASMC and PASMC. The basal protein expression levels of STIM1/2, Orai1/2, and TRPC6 were higher in CASMC than in PASMC, but hypoxia (3% O₂ for 72 h) significantly upregulated protein expression levels of STIM1/STIM2, Orai1/Orai2, and TRPC6 and increased the resting [Ca²⁺]_cyt only in PASMC, but not in CASMC. The different response of essential components of store-operated and receptor-operated Ca²⁺ channels to hypoxia is a unique intrinsic property of PASMC, which is likely one of the important explanations why hypoxia causes pulmonary vasoconstriction and induces pulmonary vascular remodeling, but causes coronary vasodilation.

STIM-1 and ORAI-1 channel mediate angiotensin-II-induced expression of Egr-1 in vascular smooth muscle cells

An upregulation of Egr-1 expression has been reported in models of atherosclerosis and intimal hyperplasia and, various vasoactive peptides and growth promoting stimuli have been shown to induce the expression of Egr-1 in vascular smooth muscle cells (VSMC). Angiotensin-II (Ang-II) is a key vasoactive peptide that has been implicated in the pathogenesis of vascular diseases. Ang-II elevates intracellular Ca2+ through activation of the store-operated calcium entry (SOCE) involving an inositol-3-phosphate receptor (IP3R)-coupled depletion of endoplasmic reticular Ca2+ and a subsequent activation of the stromal interaction molecule 1 (STIM-1)/Orai-1 complex. However, the involvement of IP3R/STIM-1/Orai-1-Ca2+ -dependent signaling in Egr-1 expression in VSMC remains unexplored. Therefore, in the present studies, we have examined the role of Ca2+ signaling in Ang-II-induced Egr-1 expression in VSMC and investigated the contribution of STIM-1 or Orai-1 in mediating this response. 2-aminoethoxydiphenyl borate (2-APB), a dual non-competitive antagonist of IP3R and inhibitor of SOCE, decreased Ang-II-induced Ca2+ release and attenuated Ang-II-induced enhanced expression of Egr-1 protein and mRNA levels. Egr-1 upregulation was also suppressed following blockade of calmodulin and CaMKII. Furthermore, RNA interference-mediated depletion of STIM-1 or Orai-1 attenuated Ang-II-induced Egr-1 expression as well as Ang-II-induced phosphorylation of ERK1/2 and CREB. In addition, siRNA-induced silencing of CREB resulted in a reduction in the expression of Egr-1 stimulated by Ang-II. In summary, our data demonstrate that Ang-II-induced Egr-1 expression is mediated by STIM-1/Orai-1/Ca2+ -dependent signaling pathways in A-10 VSMC.

Resveratrol attenuates high glucose-induced endothelial cell apoptosis via mediation of store-operated calcium entry

The aim of this study was to evaluate the influence of resveratrol on HG-induced calcium entry in islet microvascular (MS-1) endothelial cells. MS-1 cells were pretreated with resveratrol or 2-APB (an inhibitor of store-operated calcium entry) and then incubated with high glucose. Cell viability was determined using the cell counting kit-8 method. Reactive oxygen species, endothelial apoptosis, and NO production were detected by DHE probe, TUNEL detection, and nitrate reductase assay kit. Protein levels of SOCE were detected by western blotting. Pretreatment with resveratrol significantly attenuated HG-induced endothelial apoptosis and improved cell viability. However, pretreatment with resveratrol and 2-APB abolished this effect, suggesting that the attenuation of HG-induced apoptosis by resveratrol may be associated with SOCE. Subsequent analyses indicated that HG induced the SOCE-related proteins, including TRPC1, Orai1, and Stim1. These results suggest that resveratrol pretreatment is associated with relieved HG-induced endothelial apoptosis at least partly via inhibition of SOCE-related proteins.

Cardiovascular and Hemostatic Disorders: Role of STIM and Orai Proteins in Vascular Disorders

Store-operated Ca²⁺ entry (SOCE) mediated by STIM and Orai proteins is a highly regulated and ubiquitous signaling pathway that plays an important role in various cellular and physiological functions. Endoplasmic reticulum (ER) serves as the major site for intracellular Ca²⁺ storage. Stromal Interaction Molecule 1/2 (STIM1/2) sense decrease in ER Ca²⁺ levels and transmits the message to plasma membrane Ca²⁺ channels constituted by Orai family members (Orai1/2/3) resulting in Ca²⁺ influx into the cells. This increase in cytosolic Ca²⁺ in turn activates a variety of signaling cascades to regulate a plethora of cellular functions. Evidence from the literature suggests that SOCE dysregulation is associated with several pathophysiologies, including vascular disorders. Interestingly, recent studies have suggested that STIM proteins may also regulate vascular functions independent of their contribution to SOCE. In this updated book chapter, we will focus on the physiological role of STIM and Orai proteins in the vasculature (endothelial cells and vascular smooth muscle cells). We will further retrospect the literature implicating a critical role for these proteins in vascular disease.

Aristoyunnolin H attenuates extracellular matrix secretion in cardiac fibroblasts by inhibiting calcium influx

Aristoyunnolin H is a novel aristophyllene sesquiterpenoid isolated from the traditional Chinese medicine Aristolochia yunnanensis Franch. The present research was designed to explore the anti-fibrotic effects of aristoyunnolin H in adult rat cardiac fibroblasts (CFs) stimulated with angiotensin II (Ang II). Western blot analysis data showed that aristoyunnolin H reduced the upregulation of fibronectin (FN), connective tissue growth factor and collagen I(Col I) production induced by Ang II in CFs. By studying the dynamic intracellular changes of Ca²⁺, we further found that while aristoyunnolin H relieved the calcium influx, it has no effect on intracellular calcium store release. Meanwhile, aristoyunnolin H also inhibited the Ang II-stimulated phosphorylation of Ca²⁺/calmodulin-dependent protein kinase II. In conclusion, aristoyunnolin H may attenuate extracellular matrix secretion in vitro by inhibiting Ang II-induced calcium signaling.

Essential Role of Smooth Muscle STIM1 in Hypertension and Cardiovascular Dysfunction

OBJECTIVES

Chronic hypertension is the most critical risk factor for cardiovascular disease, heart failure, and stroke.

APPROACH AND RESULTS

Here we show that wild-type mice infused with angiotensin II develop hypertension, cardiac hypertrophy, perivascular fibrosis, and endothelial dysfunction with enhanced stromal interaction molecule 1 (STIM1) expression in heart and vessels. All these pathologies were significantly blunted in mice lacking STIM1 specifically in smooth muscle (Stim1(SMC-/-)). Mechanistically, STIM1 upregulation during angiotensin II-induced hypertension was associated with enhanced endoplasmic reticulum stress, and smooth muscle STIM1 was required for endoplasmic reticulum stress-induced vascular dysfunction through transforming growth factor-β and nicotinamide adenine dinucleotide phosphate oxidase-dependent pathways. Accordingly, knockout mice for the endoplasmic reticulum stress proapoptotic transcriptional factor, CCAAT-enhancer-binding protein homologous protein (CHOP(-/-)), were resistant to hypertension-induced cardiovascular pathologies. Wild-type mice infused with angiotensin II, but not Stim1(SMC-/-) or CHOP(-/-) mice showed elevated vascular nicotinamide adenine dinucleotide phosphate oxidase activity and reduced phosphorylated endothelial nitric oxide synthase, cGMP, and nitrite levels.

CONCLUSIONS

Thus, smooth muscle STIM1 plays a crucial role in the development of hypertension and associated cardiovascular pathologies and represents a promising target for cardiovascular therapy.

Differential expression of store-operated calcium- and proliferation-related genes in hepatocellular carcinoma cells following TRPC1 ion channel silencing

TRPC1 and store-operated Ca²⁺ (SOC) entry have previously been associated with hepatocellular carcinoma cell proliferation. The aim of the study was to determine genes and processes associated with TRPC1 down-regulation and the resulting increase of SOC entry and decrease in hepatocellular carcinoma cell proliferation. For this purpose, transcriptome analysis was performed to determine differentially expressed genes in TRPC1-silenced Huh7 cells. SOC entry- and proliferation-related genes correlated with TRPC1 down-regulation were also examined. Changes in SOC entry and cell proliferation were monitored in the TRPC1-silenced and parental cells and found to be significantly increased and decreased, respectively, in TRPC1-silenced cells. A total of 71 genes were significantly differentially expressed (40 up- and 31 down-regulated), including four mitogen-activated protein kinase (MAPK) signalling-associated genes. STIM1 levels were significantly up-regulated and negatively correlated with TRPC1 levels. In addition, expression of two cell cycle regulation genes, CDK11A/11B and URGCP, was observed to decrease, whereas ERBB3 and FGFR4, pro-survival genes, increased significantly in TRPC1-silenced cells. In conclusion, these results suggest reciprocal alterations in TRPC1 and STIM1 levels and a role for STIM1 in the regulation of SOC entry in TRPC1-silenced Huh7 cells. In addition to TRPC1, STIM1 may participate in Huh7 cell proliferation by regulating SOC entry. Alterations in MAPK signalling genes may be involved in diminished cell proliferation in TRPC1-silenced Huh7 cells. Similarly, changes in cell cycle regulating genes in TRPC1-silenced cells indicate possible cell cycle arrest along with compensatory up-regulation of ERBB3 growth factor receptor—amongst others—to maintain hepatocellular carcinoma cell proliferation.

Downregulation of ACE2/Ang-(1-7)/Mas axis promotes breast cancer metastasis by enhancing store-operated calcium entry

The renin-angiotensin system (RAS) is an important component of the tumor microenvironment and plays a key role in promoting cancer cell proliferation, angiogenesis, metabolism, migration and invasion. Meanwhile, the arm of angiotensin-converting enzyme (ACE)2/angiotensin-(1-7) [Ang-(1-7)]/Mas axis in connection with RAS is associated with anti-proliferative, vasodilatory and anti-metastatic properties. Previous studies have shown that Ang-(1-7) reduces the proliferation of orthotopic human breast tumor growth by inhibiting cancer-associated fibroblasts. However, the role of ACE/Ang-(1-7)/Mas axis in the metastasis of breast cancer cells is still unknown. In the present study, we found that ACE2 protein level is negatively correlated with the metastatic ability of breast cancer cells and breast tumor grade. Upregulation of ACE2/Ang-(1-7)/Mas axis inhibits breast cancer cell migration and invasion in vivo and in vitro. Mechanistically, ACE2/Ang-(1-7)/Mas axis activation inhibits store-operated calcium entry (SOCE) and PAK1/NF-κB/Snail1 pathways, and induces E-cadherin expression. In summary, our results demonstrate that downregulation of ACE2/Ang-(1-7)/Mas axis stimulates breast cancer metastasis through the activation of SOCE and PAK1/NF-κB/Snail1 pathways. These results provide new mechanisms by which breast cancer develop metastasis and shed light on developing novel anti-metastasis therapeutics for metastatic breast cancer by modulating ACE2/Ang-(1-7)/Mas axis.

Orai channel-mediated Ca2+ signals in vascular and airway smooth muscle

Orai (Orai1, Orai2, and Orai3) proteins form a family of highly Ca(2+)-selective plasma membrane channels that are regulated by stromal-interacting molecules (STIM1 and STIM2); STIM proteins are Ca(2+) sensors located in the membrane of the endoplasmic reticulum. STIM and Orai proteins are expressed in vascular and airway smooth muscle and constitute the molecular components of the ubiquitous store-operated Ca(2+) entry pathway that mediate the Ca(2+) release-activated Ca(2+) current. STIM/Orai proteins also encode store-independent Ca(2+) entry pathways in smooth muscle. Altered expression and function of STIM/Orai proteins have been linked to vascular and airway pathologies, including restenosis, hypertension, and atopic asthma. In this review we discuss our current understanding of Orai proteins and the store-dependent and -independent signaling pathways mediated by these proteins in vascular and airway smooth muscle. We also discuss the current studies linking altered expression and function of Orai proteins with smooth muscle-related pathologies.

Roles of store-operated Ca2+ channels in regulating cell cycling and migration of human cardiac c-kit+ progenitor cells

Cardiac c-kit(+) progenitor cells are important for maintaining cardiac homeostasis and can potentially contribute to myocardial repair. However, cellular physiology of human cardiac c-kit(+) progenitor cells is not well understood. The present study investigates the functional store-operated Ca(2+) entry (SOCE) channels and the potential role in regulating cell cycling and migration using confocal microscopy, RT-PCR, Western blot, coimmunoprecipitation, cell proliferation, and migration assays. We found that SOCE channels mediated Ca(2+) influx, and TRPC1, STIM1, and Orai1 were involved in the formation of SOCE channels in human cardiac c-kit(+) progenitor cells. Silencing TRPC1, STIM1, or Orai1 with the corresponding siRNA significantly reduced the Ca(2+) signaling through SOCE channels, decreased cell proliferation and migration, and reduced expression of cyclin D1, cyclin E, and/or p-Akt. Our results demonstrate the novel information that Ca(2+) signaling through SOCE channels regulates cell cycling and migration via activating cyclin D1, cyclin E, and/or p-Akt in human cardiac c-kit(+) cells.

Scavenger receptor class A member 5 (SCARA5) and suprabasin (SBSN) are hub genes of coexpression network modules associated with peripheral vein graft patency

OBJECTIVE

Approximately 30% of autogenous vein grafts develop luminal narrowing and fail because of intimal hyperplasia or negative remodeling. We previously found that vein graft cells from patients who later develop stenosis proliferate more in vitro in response to growth factors than cells from patients who maintain patent grafts. To discover novel determinants of vein graft outcome, we have analyzed gene expression profiles of these cells using a systems biology approach to cluster the genes into modules by their coexpression patterns and to correlate the results with growth data from our prior study and with new studies of migration and matrix remodeling.

METHODS

RNA from 4-hour serum- or platelet-derived growth factor (PDGF)-BB-stimulated human saphenous vein cells obtained from the outer vein wall (20 cell lines) was used for microarray analysis of gene expression, followed by weighted gene coexpression network analysis. Cell migration in microchemotaxis chambers in response to PDGF-BB and cell-mediated collagen gel contraction in response to serum were also determined. Gene function was determined using short-interfering RNA to inhibit gene expression before subjecting cells to growth or collagen gel contraction assays. These cells were derived from samples of the vein grafts obtained at surgery, and the long-term fate of these bypass grafts was known.

RESULTS

Neither migration nor cell-mediated collagen gel contraction showed a correlation with graft outcome. Although 1188 and 1340 genes were differentially expressed in response to treatment with serum and PDGF, respectively, no single gene was differentially expressed in cells isolated from patients whose grafts stenosed compared with those that remained patent. Network analysis revealed four unique groups of genes, which we term modules, associated with PDGF responses, and 20 unique modules associated with serum responses. The "yellow" and "skyblue" modules, from PDGF and serum analyses, respectively, correlated with later graft stenosis (P = .005 and P = .02, respectively). In response to PDGF, yellow was also associated with increased cell growth. For serum, skyblue was also associated with inhibition of collagen gel contraction. The hub genes for yellow and skyblue (ie, the gene most connected to other genes in the module), scavenger receptor class A member 5 (SCARA5) and suprabasin (SBSN), respectively, were tested for effects on proliferation and collagen contraction. Knockdown of SCARA5 increased proliferation by 29.9% ± 7.8% (P < .01), whereas knockdown of SBSN had no effect. Knockdown of SBSN increased collagen gel contraction by 24.2% ± 8.6% (P < .05), whereas knockdown of SCARA5 had no effect.

CONCLUSIONS

Using weighted gene coexpression network analysis of cultured vein graft cell gene expression, we have discovered two small gene modules, which comprise 42 genes, that are associated with vein graft failure. Further experiments are needed to delineate the venous cells that express these genes in vivo and the roles these genes play in vein graft healing, starting with the module hub genes SCARA5 and SBSN, which have been shown to have modest effects on cell proliferation or collagen gel contraction.

Ca2+ signaling in cytoskeletal reorganization, cell migration, and cancer metastasis

Proper control of Ca²⁺ signaling is mandatory for effective cell migration, which is critical for embryonic development, wound healing, and cancer metastasis. However, how Ca²⁺ coordinates structural components and signaling molecules for proper cell motility had remained elusive. With the advance of fluorescent live-cell Ca²⁺ imaging in recent years, we gradually understand how Ca²⁺ is regulated spatially and temporally in migrating cells, driving polarization, protrusion, retraction, and adhesion at the right place and right time. Here we give an overview about how cells create local Ca²⁺ pulses near the leading edge, maintain cytosolic Ca²⁺ gradient from back to front, and restore Ca²⁺ depletion for persistent cell motility. Differential roles of Ca²⁺ in regulating various effectors and the interaction of roles of Ca²⁺ signaling with other pathways during migration are also discussed. Such information might suggest a new direction to control cancer metastasis by manipulating Ca²⁺ and its associating signaling molecules in a judicious manner.

Leukotriene-C4 synthase, a critical enzyme in the activation of store-independent Orai1/Orai3 channels, is required for neointimal hyperplasia

Leukotriene-C4 synthase (LTC4S) generates LTC4 from arachidonic acid metabolism. LTC4 is a proinflammatory factor that acts on plasma membrane cysteinyl leukotriene receptors. Recently, however, we showed that LTC4 was also a cytosolic second messenger that activated store-independent LTC4-regulated Ca(2+) (LRC) channels encoded by Orai1/Orai3 heteromultimers in vascular smooth muscle cells (VSMCs). We showed that Orai3 and LRC currents were up-regulated in medial and neointimal VSMCs after vascular injury and that Orai3 knockdown inhibited LRC currents and neointimal hyperplasia. However, the role of LTC4S in neointima formation remains unknown. Here we show that LTC4S knockdown inhibited LRC currents in VSMCs. We performed in vivo experiments where rat left carotid arteries were injured using balloon angioplasty to cause neointimal hyperplasia. Neointima formation was associated with up-regulation of LTC4S protein expression in VSMCs. Inhibition of LTC4S expression in injured carotids by lentiviral particles encoding shRNA inhibited neointima formation and inward and outward vessel remodeling. LRC current activation did not cause nuclear factor for activated T cells (NFAT) nuclear translocation in VSMCs. Surprisingly, knockdown of either LTC4S or Orai3 yielded more robust and sustained Akt1 and Akt2 phosphorylation on Ser-473/Ser-474 upon serum stimulation. LTC4S and Orai3 knockdown inhibited VSMC migration in vitro with no effect on proliferation. Akt activity was suppressed in neointimal and medial VSMCs from injured vessels at 2 weeks postinjury but was restored when the up-regulation of either LTC4S or Orai3 was prevented by shRNA. We conclude that LTC4S and Orai3 altered Akt signaling to promote VSMC migration and neointima formation.

Altered calcium signaling in cancer cells

It is the nature of the calcium signal, as determined by the coordinated activity of a suite of calcium channels, pumps, exchangers and binding proteins that ultimately guides a cell's fate. Deregulation of the calcium signal is often deleterious and has been linked to each of the 'cancer hallmarks'. Despite this, we do not yet have a full understanding of the remodeling of the calcium signal associated with cancer. Such an understanding could aid in guiding the development of therapies specifically targeting altered calcium signaling in cancer cells during tumorigenic progression. Findings from some of the studies that have assessed the remodeling of the calcium signal associated with tumorigenesis and/or processes important in invasion and metastasis are presented in this review. The potential of new methodologies is also discussed. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

Stromal interaction molecule 1 is essential for normal cardiac homeostasis through modulation of ER and mitochondrial function

The endoplasmic reticulum (ER) Ca(2+) sensor stromal interaction molecule 1 (STIM1) has been implicated as a key mediator of store-dependent and store-independent Ca(2+) entry pathways and maintenance of ER structure. STIM1 is present in embryonic, neonatal, and adult cardiomyocytes and has been strongly implicated in hypertrophic signaling; however, the physiological role of STIM1 in the adult heart remains unknown. We, therefore, developed a novel cardiomyocyte-restricted STIM1 knockout ((cr)STIM1-KO) mouse. In cardiomyocytes isolated from (cr)STIM1-KO mice, STIM1 expression was reduced by ∼92% with no change in the expression of related store-operated Ca(2+) entry proteins, STIM2, and Orai1. Immunoblot analyses revealed that (cr)STIM1-KO hearts exhibited increased ER stress from 12 wk, as indicated by increased levels of the transcription factor C/EBP homologous protein (CHOP), one of the terminal markers of ER stress. Transmission electron microscopy revealed ER dilatation, mitochondrial disorganization, and increased numbers of smaller mitochondria in (cr)STIM1-KO hearts, which was associated with increased mitochondrial fission. Using serial echocardiography and histological analyses, we observed a progressive decline in cardiac function in (cr)STIM1-KO mice, starting at 20 wk of age, which was associated with marked left ventricular dilatation by 36 wk. In addition, we observed the presence of an inflammatory infiltrate and evidence of cardiac fibrosis from 20 wk in (cr)STIM1-KO mice, which progressively worsened by 36 wk. These data demonstrate for the first time that STIM1 plays an essential role in normal cardiac function in the adult heart, which may be important for the regulation of ER and mitochondrial function.

Urotensin-II promotes vascular smooth muscle cell proliferation through store-operated calcium entry and EGFR transactivation

AIMS

Urotensin-II (UII) is a vasoactive peptide that promotes vascular smooth muscle cells (VSMCs) proliferation and is involved in the pathogenesis of atherosclerosis, restenosis, and vascular remodelling. This study aimed to determine the role of calcium (Ca(2+))-dependent signalling and alternative signalling pathways in UII-evoked VSMCs proliferation focusing on store-operated Ca(2+) entry (SOCE) and epithelium growth factor receptor (EGFR) transactivation.

METHODS AND RESULTS

We used primary cultures of VSMCs isolated from Wistar rat aorta to investigate the effects of UII on intracellular Ca(2+) mobilization, and proliferation determined by the 5-bromo-2-deoxyuridine (BrdU) assay. We found that UII enhanced intracellular Ca(2+) concentration ([Ca(2+)]i) which was significantly reduced by classical SOCE inhibitors and by knockdown of essential components of the SOCE such as stromal interaction molecule 1 (STIM1), Orai1, or TRPC1. Moreover, UII activated a Gd(3+)-sensitive current with similar features of the Ca(2+) release-activated Ca(2+) current (ICRAC). Additionally, UII stimulated VSMCs proliferation and Ca(2+)/cAMP response element-binding protein (CREB) activation through the SOCE pathway that involved STIM1, Orai1, and TRPC1. Co-immunoprecipitation experiments showed that UII promoted the association between Orai1 and STIM1, and between Orai1 and TRPC1. Moreover, we determined that EGFR transactivation, extracellular signal-regulated kinase (ERK) and Ca(2+)/calmodulin-dependent kinase (CaMK) signalling pathways were involved in both UII-mediated Ca(2+) influx, CREB activation and VSMCs proliferation.

CONCLUSION

Our data show for the first time that UII-induced VSMCs proliferation and CREB activation requires a complex signalling pathway that involves on the one hand SOCE mediated by STIM1, Orai1, and TRPC1, and on the other hand EGFR, ERK, and CaMK activation.

Emerging roles of store-operated Ca²⁺ entry through STIM and ORAI proteins in immunity, hemostasis and cancer

Store-operated Ca(2+) entry (SOCE) is an important Ca(2+) influx pathway, which is defined by the fact that depletion of intracellular Ca(2+) stores, mainly the endoplasmic reticulum (ER), triggers the opening of Ca(2+) channels in the plasma membrane. The best characterized SOC channel is the Ca(2+) release-activated Ca(2+) (CRAC) channel, which was first described in cells of the immune system but has since been reported in many different cell types. CRAC channels are multimers of ORAI family proteins, of which ORAI1 is the best characterized. They are activated by stromal interaction molecules (STIM) 1 and 2, which respond to the depletion of intracellular Ca(2+) stores with oligomerization and binding to ORAI proteins. The resulting SOCE is critical for the physiological function of many cell types including immune cells and platelets. Recent studies using cell lines, animal models and primary cells from human patients with defects in SOCE have highlighted the importance of this Ca(2+) entry mechanism in a variety of pathophysiological processes. This review focuses on the role of SOCE in immunity to infection, allergy, hemostasis and cancer.

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.

Calcium-dependent deceleration of the cell cycle in muscle cells by simulated microgravity

Of all our mechanosensitive tissues, skeletal muscle is the most developmentally responsive to physical activity. Conversely, restricted mobility due to injury or disease results in muscle atrophy. Gravitational force is another form of mechanical input with profound developmental consequences. The mechanical unloading resulting from the reduced gravitational force experienced during spaceflight results in oxidative muscle loss. We examined the early stages of myogenesis under conditions of simulated microgravity (SM). C2C12 mouse myoblasts in SM proliferated more slowly (2.23× less) as a result of their being retained longer within the G2/M phase of the cell cycle (2.10× more) relative to control myoblasts at terrestrial gravity. Blocking calcium entry via TRP channels with SKF-96365 (10-20 μM) accumulated myoblasts within the G2/M phase of the cell cycle and retarded their proliferation. On the genetic level, SM resulted in the reduced expression of TRPC1 and IGF-1 isoforms, transcriptional events regulated by calcium downstream of mechanical input. A decrease in TRPC1-mediated calcium entry thus appears to be a pivotal event in the muscle atrophy brought on by gravitational mechanical unloading. Hence, relieving the constant force of gravity on cells might prove one valid experimental approach to expose the underlying mechanisms modulating mechanically regulated developmental programs.

Knockdown of stromal interaction molecule 1 (STIM1) suppresses store-operated calcium entry, cell proliferation and tumorigenicity in human epidermoid carcinoma A431 cells

Store-operated calcium (Ca(2+)) entry (SOCE) is important for cellular activities such as gene transcription, cell cycle progression and proliferation in most non-excitable cells. Stromal interaction molecule 1 (STIM1), a newly identified Ca(2+)-sensing protein, monitors the depletion of endoplasmic reticulum (ER) Ca(2+) stores and activates store-operated Ca(2+) channels at the plasma membrane to induce SOCE. To investigate the possible roles of STIM1 in tumor growth in relation to SOCE, we established STIM1 knockdown (KD) clones of human epidermoid carcinoma A431 cells by RNA interference. Thapsigargin, an inhibitor of ER Ca(2+)-ATPase, -induced and phospholipase C-coupled receptor agonist-induced SOCEs were reduced in two STIM1 KD clones compared to a negative control clone. Re-expression of a KD-resistant full-length STIM1, but not a Ca(2+) release-activated Ca(2+) channel activation domain (CAD)-deleted STIM1 mutant, in the KD clone restored the amplitude of SOCE, suggesting the specificity of the STIM1 knockdown. The cell growth of the STIM1 KD clones was slower than that of the negative control clone. DNA synthesis assessed by BrdU incorporation, as well as EGF-stimulated EGF receptor activation, decreased in the STIM1 KD clones. Xenograft growth of the STIM1 KD clones was significantly retarded compared with that of the negative control. Cell migration was attenuated in the STIM1 KD clone and the STIM1 silencing effect was reversed by transient re-expression of the full-length STIM1 but not CAD-deletion mutant. These results indicate that STIM1 plays an important role in SOCE, cell-growth and tumorigenicity in human epidermoid carcinoma A431cells, suggesting the potential use of STIM1-targeting agents for treating epidermoid carcinoma.

Orai1 calcium channels in the vasculature

Orai1 was discovered in T cells as a calcium-selective channel that is activated by store depletion. Recent studies suggest that it is expressed and functionally important also in blood vessels, not only because haematopoietic cells can incorporate in the vascular wall but also because Orai1 is expressed and functional in vascular smooth muscle cells and endothelial cells. This article summarises the arising observations in this new area of vascular research and debates underlying issues and challenges for future investigations. The primary focus is on vascular smooth muscle cells and endothelial cells. Specific topics include Orai1 expression; Orai1 roles in store-operated calcium entry and ionic currents of store-depleted cells; blockade of Orai1-related signals by Synta 66 and other pharmacology; activation or regulation of Orai1-related signals by physiological substances and compartments; stromal interaction molecules and the relationship of Orai1 to other ion channels, transporters and pumps; transient receptor potential canonical channels and their contribution to store-operated calcium entry; roles of Orai1 in vascular tone, remodelling, thrombus formation and inflammation; and Orai2 and Orai3. Overall, the observations suggest the existence of an additional, previously unrecognised, calcium channel of the vascular wall that is functionally important particularly in remodelling but probably also in certain vasoconstrictor contexts.