Capacitative Calcium Entry Research Articles

The Physiopathologic Roles of Calcium Signaling in Podocytes.

Calcium (Ca2+) plays a critical role in podocyte function. The Ca2+-sensitive receptors on the cell surface can sense changes in Ca2+ concentration, and Ca2+ flow into podocytes, after activation of Ca2+ channels (such as transient receptor potential canonical (TRPC) channels and N-type calcium channels) by different stimuli. In addition, the type 2 ryanodine receptor (RyR2) and the voltage-dependent anion channel 1 (VDAC1) on mitochondrial store-operated calcium channels (SOCs) on the endoplasmic reticulum maintain the Ca2+ homeostasis of the organelle. Ca2+ signaling is transmitted through multiple downstream signaling pathways and participates in the morphogenesis, structural maintenance, and survival of podocytes. When Ca2+ is dysregulated, it leads to the occurrence and progression of various diseases, such as focal segmental glomerulosclerosis, diabetic kidney disease, lupus nephritis, transplant glomerulopathy, and hypertensive renal injury. Ca2+ signaling is a promising therapeutic target for podocyte-related diseases. This review first summarizes the role of Ca2+ sensing, Ca2+ channels, and different Ca2+-signaling pathways in the biological functions of podocytes, then, explores the status of Ca2+ signaling in different podocyte-related diseases and its advances as a therapeutic target.

Molecular action mechanisms of two novel and selective calcium release-activated calcium channel antagonists

The prototypical calcium release-activated calcium (CRAC) channel, composed of STIM1 and Orai1, is a sought-after drug target for treating autoimmune disorders. Herein, we identified two novel and selective CRAC channel inhibitors, the indole-like compound C63368 and pyrazole core-containing compound C79413, potently and reversibly inhibiting the CRAC channel with low micromolar IC50s and sparing various off-target ion channels. These two compounds did not inhibit STIM1 activation or its coupling with Orai1, nor did they affect the channel's calcium-dependent fast inactivation. Instead, they directly acted on the Orai1 protein, with the channel's pore geometry profoundly affecting their potencies. In vitro, C63368 and C79413 effectively inhibited Jurkat cell proliferation and cytokines production in human T lymphocytes. Intragastric administration of C63368 and C79413 to mice yielded great therapeutic benefits in psoriasis and colitis animal models of autoimmune disorders, reducing serum cytokines production and significantly relieving pathological symptoms. It's worth noting, that this study provided the first insight into the characterization and mechanistic investigation of an indole-like CRAC channel antagonist. Altogether, the identification of these two highly selective CRAC channel antagonists, coupled with the elucidation of their action mechanisms, not only provides valuable template molecules but also offers profound insights for drug development targeting the CRAC channel.

Robust expression of the TRPC1 channel associated with photoreceptor loss in the rat retina

Baseline intracellular calcium levels are significantly higher in neuronal and glial cells of rat retinas with retinitis pigmentosa (RP). Although this situation could initiate multiple detrimental pathways that lead to cell death, we considered the possibility of TRPC1 being involved in maintaining calcium homeostasis in the retina by acting as a component of store-operated calcium (SOC) channels with special relevance during photoreceptor degeneration. In this study, we examined by Western blot the expression of TRPC1 in healthy control rat retinas (Sprague-Dawley, SD) and retinas with RP (P23H-1 rats). We also analyzed its specific cellular distribution by immunofluorescence to recognize changes during neurodegeneration and to determine whether its presence is consistent with high basal calcium levels and cellular survival in degenerating retinas. We found that TRPC1 immunostaining was widely distributed across the retina in both rat strains, SD and P23H, and its expression levels significantly increased in the retinas with advanced degeneration compared to the age-control SD rats. In the outer retina, TRPC1 immunoreactivity was distributed in pigment epithelium cells, the photoreceptor inner segments of older animals, and the outer plexiform layer. In the inner retina, TRPC1 labeling was detected in horizontal cells, specific somata of bipolar and amacrine cells, and cellular processes in all the strata of the inner plexiform layer. Somata and processes were also highly immunoreactive in the ganglion cell layer and astrocytes in the nerve fiber layer in all animals. In the P23H rat retinas, the TRPC1 distribution pattern changed according to advancing photoreceptor degeneration and the gliosis reaction, with TRPC1 immunoreactive Müller cells mainly in advanced stages of disease. The cellular TRPC1 immunoreactivity found in this work suggests different mechanisms of activation of these channels depending on the cell type. Furthermore, the results support the idea that photoreceptor loss due to RP is associated with robust TRPC1 protein expression in the rat inner retina and raise the possibility of TRPC1 channels contributing to maintain high basal calcium levels during neurodegeneration and/or maintenance processes of the inner retina.

SARS-CoV-2 spike protein receptor-binding domain perturbates intracellular calcium homeostasis and impairs pulmonary vascular endothelial cells

Exposure to the spike protein or receptor-binding domain (S-RBD) of SARS-CoV-2 significantly influences endothelial cells and induces pulmonary vascular endotheliopathy. In this study, angiotensin-converting enzyme 2 humanized inbred (hACE2 Tg) mice and cultured pulmonary vascular endothelial cells were used to investigate how spike protein/S-RBD impacts pulmonary vascular endothelium. Results show that S-RBD leads to acute-to-prolonged induction of the intracellular free calcium concentration ([Ca2+]i) via acute activation of TRPV4, and prolonged upregulation of mechanosensitive channel Piezo1 and store-operated calcium channel (SOCC) key component Orai1 in cultured human pulmonary arterial endothelial cells (PAECs). In mechanism, S-RBD interacts with ACE2 to induce formation of clusters involving Orai1, Piezo1 and TRPC1, facilitate the channel activation of Piezo1 and SOCC, and lead to elevated apoptosis. These effects are blocked by Kobophenol A, which inhibits the binding between S-RBD and ACE2, or intracellular calcium chelator, BAPTA-AM. Blockade of Piezo1 and SOCC by GsMTx4 effectively protects the S-RBD-induced pulmonary microvascular endothelial damage in hACE2 Tg mice via normalizing the elevated [Ca2+]i. Comparing to prototypic strain, Omicron variants (BA.5.2 and XBB) of S-RBD induces significantly less severe cell apoptosis. Transcriptomic analysis indicates that prototypic S-RBD confers more severe acute impacts than Delta or Lambda S-RBD. In summary, this study provides compelling evidence that S-RBD could induce persistent pulmonary vascular endothelial damage by binding to ACE2 and triggering [Ca2+]i through upregulation of Piezo1 and Orai1. Targeted inhibition of ACE2-Piezo1/SOCC-[Ca2+]i axis proves a powerful strategy to treat S-RBD-induced pulmonary vascular diseases.

Role of Nitric Oxide in the Altered Calcium Homeostasis of Platelets from Rats with Biliary Cirrhosis.

Previously, we found that intracellular calcium (Ca2+) homeostasis is altered in platelets from an experimental model of liver cirrhosis, namely the bile-duct-ligated (BDL) rat. These alterations are compatible with the existence of a hypercoagulable state. In the present study, we analyzed the role of nitric oxide in the abnormal calcium signaling responses of an experimental cirrhosis model, the bile duct-ligated rat. Chronic treatment with L-NAME was used to inhibit NO production in a group of control and BDL animals, and the responses compared to those obtained in a control and BDL untreated group (n = 6 each). The experiments were conducted on isolated platelets loaded with fura-2, using fluorescence spectrometry. Chronic treatment with L-NAME increased thrombin-induced Ca2+ release from internal stores in both control and BDL rats. However, the effect was significantly greater in the BDL rats (p < 0.05). Thrombin-induced calcium entry from the extracellular space was also elevated but at lower doses and, similarly in both control and BDL platelets, treated with the NO synthesis inhibitor. Capacitative calcium entry was also enhanced in the control platelets but not in platelets from BDL rats treated with L-NAME. Total calcium in intracellular stores was elevated in untreated platelets from BDL rats, and L-NAME pretreatment significantly (p < 0.05) elevated these values both in controls and in BDL but significantly more in the BDL rats (p < 0.05). Our results suggest that nitric oxide plays a role in the abnormal calcium signaling responses observed in platelets from BDL rats by interfering with the mechanism that releases calcium from the internal stores.

Cholecalciferol Supplementation Induced Up-Regulation of SARAF Gene and Down-Regulated miR-155-5p Expression in Slovenian Patients with Multiple Sclerosis.

Multiple sclerosis is a common immune-mediated inflammatory and demyelinating disease. Lower cholecalciferol levels are an established environmental risk factor in multiple sclerosis. Although cholecalciferol supplementation in multiple sclerosis is widely accepted, optimal serum levels are still debated. Moreover, how cholecalciferol affects pathogenic disease mechanisms is still unclear. In the present study, we enrolled 65 relapsing-remitting multiple sclerosis patients who were double-blindly divided into two groups with low and high cholecalciferol supplementation, respectively. In addition to clinical and environmental parameters, we obtained peripheral blood mononuclear cells to analyze DNA, RNA, and miRNA molecules. Importantly, we investigated miRNA-155-5p, a previously published pro-inflammatory miRNA in multiple sclerosis known to be correlated to cholecalciferol levels. Our results show a decrease in miR-155-5p expression after cholecalciferol supplementation in both dosage groups, consistent with previous observations. Subsequent genotyping, gene expression, and eQTL analyses reveal correlations between miR-155-5p and the SARAF gene, which plays a role in the regulation of calcium release-activated channels. As such, the present study is the first to explore and suggest that the SARAF miR-155-5p axis hypothesis might be another mechanism by which cholecalciferol supplementation might decrease miR-155 expression. This association highlights the importance of cholecalciferol supplementation in multiple sclerosis and encourages further investigation and functional cell studies.

22. The Role of Orai1 in Osteogenic Differentiation Induced by Nanoparticulate Mineralized Collagen Glycosaminoglycan Materials

PURPOSE: Development of synthetic regenerative materials inspired by the extracellular matrix (ECM) has been a topic of significant interest due to the known properties of the ECM to direct cell fate determination via tunable material composition and biomechanical properties. Nanoparticulate mineralized collagen glycosaminoglycan (MC-GAG) is a low density, open-cell foam that has been evaluated in our laboratory to induce osteogenic differentiation of primary osteoprogenitors in vitro as well as regeneration of rabbit skull defects in vivo without pre-seeding with progenitor cells or addition of exogenous growth factors, which was not observed in non-mineralized collagen glycosaminoglycan (Col-GAG) materials. Given that the critical difference between MC-GAG and Col-GAG is the mineral content, the spatial concentration of inorganic ions on MC-GAG may be critical to its osteogenic properties. This is supported by prior research demonstrating that high calcium concentrations in the bone microenvironment stimulate osteoblastic differentiation. How these biochemical cues are transmitted to cells and activate downstream osteogenic signaling pathways should be further elucidated. Orai1 is a critical subunit of store-operated calcium release-activated calcium channels (CRAC) that has been implicated to be involved in bone homeostasis. In this work, we evaluated the contribution of Orai1 to MC-GAG-mediated osteogenesis. METHODS: To examine the role of extracellular calcium signaling through store-operated calcium channels, such as Orai1, on osteogenic differentiation of primary bone marrow-derived human mesenchymal stem cells (hMSCs), we treated 2D cell cultures with a small molecule inhibitor of store-operated calcium entry (SOCE), MRS1845, for 14 days. hMSCs were subsequently seeded on MC-GAG or Col-GAG for 7 days with or without MRS1845. Baseline Orai1 gene and protein expression was evaluated. Next, small interfering RNAs (siRNAs) targeting ORAI1 and a scrambled control were used to specifically knockdown ORAI1 expression in hMSCs cultured on Col-GAG and MC-GAG. Osteogenic gene and protein expression were measured using quantitative RT-PCR and western blot analyses, respectively. Mineralization was evaluated by Alizarin Red staining. RESULTS: To understand whether store-operated calcium entry was essential to osteogenic differentiation, we treated hMSCs in 2D cultures with a small molecule inhibitor of SOCE, MRS1845, and found a reduction in calcium depositions visualized with Alizarin Red staining when compared to untreated hMSCs. In 3D cultures, MRS1845 downregulated the gene expression of early osteogenic marker ALP and protein expression of the intracellular osteogenic mediator Runx2 specifically on MC-GAG compared to controls. As small molecule inhibitors lack channel specificity, we knocked down ORAI1 expression through siRNA transfection. When MC-GAG was compared with Col-GAG, baseline ORAI1 gene expression was 1.8-fold higher (p=0.02) and Orai1 protein expression was upregulated (p=0.003). ORAI1 knockdown reduced the protein expression of Runx2 and gene expression of late osteogenic marker BSP2 specifically on MC-GAG compared to scrambled control siRNA. Mineralization significantly diminished on MC-GAG with ORAI1 knockdown, whereas no effects were evident on Col-GAG as demonstrated by Alizarin Red staining. CONCLUSIONS: ORAI1-mediated calcium ion signaling was required for MC-GAG-induced osteogenic differentiation. Further elucidation of the osteogenic mechanisms and refinement of calcium levels on MC-GAG may facilitate its clinical application in the reconstruction of osseous defects.

Protease-activated receptor-1 mediated calcium oscillations in renal mesangial cells

INTRODUCTION. Mesangial cells provide structural support to the glomerular tuft and modulate the glomerular capillary flow via their contractile properties. Mesangial cells undergo phenotypic changes into myofibroblast-like cells, such as proliferation, mesangial expansion, abnormal glomerular tuft formation, and reduced numbers of capillary loops, are present in several glomerular diseases, including diabetic nephropathy and glomerulonephritis. In addition, thrombin-induced mesangial remodeling was found in diabetic patients, and expression of the corresponding protease-activated receptors (PARs) in the renal mesangium was reported. However, the functional PAR-mediated signaling and mechanisms in mesangial cells were not examined. This study aims to investigate protease-activated mechanisms regulating mesangial cell contraction and glomerular capillary flow. METHODS. We used primary human renal mesangial cells (HRMC) to determine the signaling mechanisms mediated by PAR1 thrombin-activated receptors. Confocal fluorescent microscopy was utilized to detect changes in intracellular Ca 2+ response to specific PAR1 modulators. Pharmacology and patch clamp electrophysiology was further applied to reveal downstream signaling mechanisms responsible for intracellular Ca 2+ oscillations. RESULTS. PAR1-mediated Ca 2+ response displayed high sensitivity to specific agonist (TFLLR-NH 2 ) with EC 50 values of 3 and 6.3 nM for male and female-derived cultured cells, respectively (the competition of a ligand for receptor binding fit converged; adj. R 2 =0.98). The response to PAR1 activation promoted initial cytosolic Ca 2+ increase followed by synchronized, damped Ca 2+ oscillations with a lag of 6.74±0.84 min between peaks. The pre-application of a specific inhibitor (RWJ56110) eliminated PAR1-mediated response, and oscillations were blocked by the changes of an extracellular solution to zero Ca 2+ . The specific inhibitors for store-operated calcium (SOCs) (Pyr6) and TRPC3 (GSK 2833503A) channels strongly attenuated oscillation behavior (up to 40% when added separately and up to 65% when both were applied; two-way ANOVA, * p&lt;0.0001). In addition, the effect of a specific inhibitor of TRPC6 channels (BI-749327) had a minimal impact on Ca 2+ flux. Further single-channel electrophysiology experiments in HRMC cells confirmed the involvement of SOC and TRPC3 channels in PAR1-mediated GPCR activation. CONCLUSION. Our results indicate that coagulation proteases like thrombin may strongly regulate mesangial cell contraction and corresponding glomerular capillary flow by PAR1 GPCRs-related activation. The contraction mechanism is mediated presumably through SOCs entry and TRPC3 channels. Since high thrombin levels are linked to poor diabetic control, the described signaling may play a crucial role in the development of diabetic glomerular disease. DK126720 (to OP), DK129227 (to AS and OP), Veterans Affairs Support Veterans Affairs (Merit Award I01 BX000820 to JL), research grant from Dialysis Clinic, Inc (to JL). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Accessory cells precondition naive T cells and regulatory T cells for cytokine-mediated proliferation

Abstract Naïve T cells and regulatory T cells, when purified, do not proliferate to the common cytokine receptor γ-chain family cytokines interleukin (IL)-2, IL-7 or IL-15, despite their expression of cognate cytokine receptors. Cell-to-cell contact with dendritic cells (DCs) enabled proliferation of the T cell to these cytokines, independent of antigen recognition or T cell receptor stimulation. This effect lasted after separation of T cells from DCs, enabling enhanced proliferation of the T cells in mice depleted of DCs. We propose calling this a “preconditioning effect”. Interestingly, IL-2 alone was sufficient to induce phosphorylation and nuclear translocation of STAT5 in T cells, but could not activate MAPK and AKT pathways and failed to induce transcription of IL-2-target genes. Preconditioning was necessary to activate these two pathways, and induced weak Ca 2+mobilization independent of calcium release-activated channels. When preconditioning was combined with IL-2, full activation of downstream mTOR, 4E-BP1 hyperphosphorylation and prolonged S6 phosphorylation occurred, and T cells underwent proliferation. Collectively, accessory cells provide T cell preconditioning, a unique activation mechanism, controlling cytokine-mediated proliferation of T cells.

Neuronal Store-Operated Calcium Channels.

The endoplasmic reticulum (ER) is the major intracellular calcium (Ca2+) storage compartment in eukaryotic cells. In most instances, the mobilization of Ca2+ from this store is followed by a delayed and sustained uptake of Ca2+ through Ca2+-permeable channels of the cell surface named store-operated Ca2+ channels (SOCCs). This gives rise to a store-operated Ca2+ entry (SOCE) that has been thoroughly investigated in electrically non-excitable cells where it is the principal regulated Ca2+ entry pathway. The existence of this Ca2+ route in neurons has long been a matter of debate. However, a growing body of experimental evidence indicates that the recruitment of Ca2+ from neuronal ER Ca2+ stores generates a SOCE. The present review summarizes the main studies supporting the presence of a depletion-dependent Ca2+ entry in neurons. It also addresses the question of the molecular composition of neuronal SOCCs, their expression, pharmacological properties, as well as their physiological relevance.

Accessory cells precondition naïve T cells and regulatory T cells for cytokine-mediated proliferation

Naïve Tcells and regulatory Tcells, when purified, do not proliferate to the γc-cytokines IL-2, IL-7, or IL-15, despite their expression of cognate cytokine receptors. Dendritic cells (DCs) enabled the Tcell proliferation to these cytokines, through cell-to-cell contact, but independent of Tcell receptor stimulation. This effect lasted after separation of Tcells from DCs, enabling enhanced proliferation of the Tcells in DC-depleted hosts. We propose calling this a "preconditioning effect". Interestingly, IL-2 alone was sufficient to induce phosphorylation and nuclear translocation of STAT5 in Tcells, but could not activate MAPK and AKT pathways and failed to induce transcription of IL-2 target genes. "Preconditioning" was necessary to activate these two pathways and induced weak Ca2+ mobilization independent of calcium release-activated channels. When preconditioning was combined with IL-2, full activation of downstream mTOR, 4E-BP1 hyperphosphorylation, and prolonged S6 phosphorylation occurred. Collectively, accessory cells provide Tcell preconditioning, a unique activation mechanism, controlling cytokine-mediated proliferation of Tcells.

The pair ceramide 1-phosphate/ceramide kinase regulates intracellular calcium and progesterone-induced human sperm acrosomal exocytosis.

Before fertilization, spermatozoa must undergo calcium-regulated acrosome exocytosis in response to physiological stimuli such as progesterone and zona pellucida. Our laboratory has elucidated the signaling cascades accomplished by different sphingolipids during human sperm acrosomal exocytosis. Recently, we established that ceramide increases intracellular calcium by activating various channels and stimulating the acrosome reaction. However, whether ceramide induces exocytosis on its own, activation of the ceramide kinase/ceramide 1-phosphate (CERK/C1P) pathway or both is still an unsolved issue. Here, we demonstrate that C1P addition induces exocytosis in intact, capacitated human sperm. Real-time imaging in single-cell and calcium measurements in sperm population showed that C1P needs extracellular calcium to induce [Ca2+]i increase. The sphingolipid triggered the cation influx through voltage-operated calcium (VOC) and store-operated calcium (SOC) channels. However, it requires calcium efflux from internal stores through inositol 3-phosphate receptors (IP3R) and ryanodine receptors (RyR) to achieve calcium rise and the acrosome reaction. We report the presence of the CERK in human spermatozoa, the enzyme that catalyzes C1P synthesis. Furthermore, CERK exhibited calcium-stimulated enzymatic activity during the acrosome reaction. Exocytosis assays using a CERK inhibitor demonstrated that ceramide induces acrosomal exocytosis, mainly due to C1P synthesis. Strikingly, progesterone required CERK activity to induce intracellular calcium increase and acrosome exocytosis. This is the first report, implicating the bioactive sphingolipid C1P in the physiological progesterone pathway leading to the sperm acrosome reaction.

S-acylation of SARAF regulates store-operated calcium entry.

The endoplasmic reticulum (ER) is the primary intracellular calcium storage site. Upon cellular stimulation by an agonist, the production of inositol 1,4,5-trisphosphate (IP3) leads to activation of IP3 receptor channels on the ER membrane and calcium efflux from ER lumen. This leads to ER calcium store depletion. Upon store depletion, the ER-resident calcium sensor STIM1 and plasma membrane calcium channel Orai1 bind to each other to form the calcium release-activated calcium (CRAC) channel. These channels lead to calcium entry from extracellular milieu. This entry is known as store-operated calcium entry (SOCE). Previously, we have shown that Orai1 and STIM1 are S-acylated upon store-depletion and this process is crucial for CRAC channel formation and SOCE. TMEM66, also known as SARAF, is a ER transmembrane protein that is known to associate with STIM1 in resting conditions, and subsequently with Orai1 after store-depletion. This binding of SARAF with Orai1 upon store-depletion is important for the inactivation of CRAC currents. We hypothesize S-acylation of SARAF is required for the inactivation of SOCE. Here we show that SARAF is S-acylated in Jurkat T cells upon activation of the T cell receptor (TCR) and subsequent store-depletion. We also show the residue where SARAF undergoes this S-acylation. Importantly, a C320S mutant version of SARAF that cannot undergo S-acylation has deficits in CRAC channel formation and SOCE. Put together, these data suggest SARAF is a crucial component of SOCE.

Plasma membrane curvature promotes ER-PM contact formation mediated by junctophilin.

The endoplasmic reticulum (ER) forms close membrane-membrane contact with the plasma membrane (PM), which is essential for lipid biosynthesis and transfer, as well as calcium release and retrieval. The spatial distribution and the abundance of ER-PM contact vary greatly within cells both spatially and temporally, while the spatial determinant for contact formation is still unclear. Cardiomyocytes (CMs), form curvature-enriched PM structures named transverse tubules (T-Tubules), acting as a hub for ER-PM contact formation. Loss of T-tubule structures in vitro culture is accompanied by decreased ER-PM contact. This suggests a potential role of membrane curvatures in ER-PM contact formation. Using nanofabricated quartz nanopillars of the same dimension as T-tubules, we showed that nano-curvatures could recruit ER-PM contact mediator junctophilin (JPH) and subsequently establish ER-PM contact in both CMs and non-muscle cells. JPH interacts with the PM through a positively charged low complexity region and senses the curvature through its interaction with caveolae on the PM. Calcium depletion assay reveals that calcium release-activated channel (CRAC) gets recruited to the curvature-driven ER-PM contacts upon activation. The measurement of intracellular calcium propagation in CMs reveals that PM curvatures could also promote voltage-gated calcium channel (VGCC) mediated calcium transients. Thus, PM curvature recruits ER through the interaction between caveolae and JPH and promotes the formation of functional ER-PM contact in excitable cells.

ORAI Calcium Channels: Regulation, Function, Pharmacology, and Therapeutic Targets.

The changes in intracellular free calcium (Ca2+) levels are one of the most widely regulators of cell function; therefore, calcium as a universal intracellular mediator is involved in very important human diseases and disorders. In many cells, Ca2+ inflow is mediated by store-operated calcium channels, and it is recognized that the store-operated calcium entry (SOCE) is mediated by the two partners: the pore-forming proteins Orai (Orai1-3) and the calcium store sensor, stromal interaction molecule (STIM1-2). Importantly, the Orai/STIM channels are involved in crucial cell signalling processes such as growth factors, neurotransmitters, and cytokines via interaction with protein tyrosine kinase coupled receptors and G protein-coupled receptors. Therefore, in recent years, the issue of Orai/STIM channels as a drug target in human diseases has received considerable attention. This review summarizes and highlights our current knowledge of the Orai/STIM channels in human diseases and disorders, including immunodeficiency, myopathy, tubular aggregate, Stormorken syndrome, York platelet syndrome, cardiovascular and metabolic disorders, and cancers, as well as suggesting these channels as drug targets for pharmacological therapeutic intervention. Moreover, this work will also focus on the pharmacological modulators of Orai/STIM channel complexes. Together, our thoughtful of the biology and physiology of the Orai/STIM channels have grown remarkably during the past three decades, and the next important milestone in the field of store-operated calcium entry will be to identify potent and selective small molecules as a therapeutic agent with the purpose to target human diseases and disorders for patient benefit.

A Genome-Wide Functional Screen Identifies Enhancer and Protective Genes for Amyloid Beta-Peptide Toxicity.

Alzheimer's disease (AD) is known to be caused by amyloid β-peptide (Aβ) misfolded into β-sheets, but this knowledge has not yet led to treatments to prevent AD. To identify novel molecular players in Aβ toxicity, we carried out a genome-wide screen in Saccharomyces cerevisiae, using a library of 5154 gene knock-out strains expressing Aβ1-42. We identified 81 mammalian orthologue genes that enhance Aβ1-42 toxicity, while 157 were protective. Next, we performed interactome and text-mining studies to increase the number of genes and to identify the main cellular functions affected by Aβ oligomers (oAβ). We found that the most affected cellular functions were calcium regulation, protein translation and mitochondrial activity. We focused on SURF4, a protein that regulates the store-operated calcium channel (SOCE). An in vitro analysis using human neuroblastoma cells showed that SURF4 silencing induced higher intracellular calcium levels, while its overexpression decreased calcium entry. Furthermore, SURF4 silencing produced a significant reduction in cell death when cells were challenged with oAβ1-42, whereas SURF4 overexpression induced Aβ1-42 cytotoxicity. In summary, we identified new enhancer and protective activities for Aβ toxicity and showed that SURF4 contributes to oAβ1-42 neurotoxicity by decreasing SOCE activity.

Icaritin inhibits oxidative stress in murine astrocytes by binding to Orai1 to block store-operated calcium channel.

Previous study has shown that icaritin (ICT) has meaningful protective effect on cerebral ischemic stroke, and this study aimed to investigate its mechanism from the aspect of protecting astrocytes from oxidative stress. Murine primary astrocytes were pretreated by ICT and exposed to H2 O2 to induce oxidative stress. The results indicated that ICT inhibited H2 O2 -induced astrocytes apoptosis, decreased Bax and cleaved caspase-3, and increased Bcl-2. In addition, ICT inhibited H2 O2 -induced oxidative stress, increased mitochondrial membrane potential (ΔΨm ), and maintained mitochondrial morphology. ICT decreased the synthesis of malondialdehyde and increased the activity of glutathione peroxidase, catalase, and superoxide dismutase. Moreover, ICT suppressed the transient and resting intracellular Ca2+ overload. Further investigation revealed that ICT could target the combination with Orai1 to block store-operated calcium channel induced by H2 O2 . However, ICT did not enhance the protective effect of RO2959, a selective blocker of Orai1. These results indicate that ICT can play a neuroprotective role against oxidative stress injury by binding to Orai1 to block SOCC.

Contribution of calcium dysregulation to impaired coronary artery contraction in Zucker diabetic fatty rats.

Diabetic coronary artery injury is closely associated with Ca2+ dysregulation, although the underlying mechanism remains unclear. This study explored the role and mechanism of Ca2+ handling in coronary artery dysfunction in type 2 diabetic rats. Zucker diabetic fatty (ZDF) rats were used as the type 2 diabetes mellitus model. The contractility of coronary artery rings induced by KCl, CaCl2 , 5-HT and U46619 was significantly lower in ZDF rats than in Zucker lean rats. Vasoconstriction induced by 5-HT and U46619 was greatly inhibited by nifedipine. However, in the presence of 1μM nifedipine or in the Ca2+ -free KH solution containing 1μM nifedipine, there was no difference in the vasoconstriction between Zucker lean and ZDF rats. Store-operated calcium channels (SOCs) were not involved in coronary vasoconstriction. The downregulation of contractile proteins and the upregulation of synthesized proteins were in coronary artery smooth muscle cells (CASMCs) from ZDF rats. Metformin reversed the reduction of vasoconstriction in ZDF rats. Taken together, L-type calcium channel is important for regulating the excitation-contraction coupling of VSMCs in coronary arteries, and dysregulation of this channel contributes to the decreased contractility of coronary arteries in T2DM.

Store-operated calcium channels in skin.

The skin is a complex organ that acts as a protective layer against the external environment. It protects the internal tissues from harmful agents, dehydration, ultraviolet radiation and physical injury as well as conferring thermoregulatory control, sensation, immunological surveillance and various biochemical functions. The diverse cell types that make up the skin include 1) keratinocytes, which form the bulk of the protective outer layer; 2) melanocytes, which protect the body from ultraviolet radiation by secreting the pigment melanin; and 3) cells that form the secretory appendages: eccrine and apocrine sweat glands, and the sebaceous gland. Emerging evidence suggests that store-operated Ca2+ entry (SOCE), whereby depletion of intracellular Ca2+ stores triggers Ca2+ influx across the plasma membrane, is central to the normal physiology of these cells and thus skin function. Numerous skin pathologies including dermatitis, anhidrotic ectodermal dysplasia, hyperhidrosis, hair loss and cancer are now linked to dysfunction in SOCE proteins. Principal amongst these are the stromal interaction molecules (STIMs) that sense Ca2+ depletion and Orai channels that mediate Ca2+ influx. In this review, the roles of STIM, Orai and other store-operated channels are discussed in the context of keratinocyte differentiation, melanogenesis, and eccrine sweat secretion. We explore not only STIM1-Orai1 as drivers of SOCE, but also independent actions of STIM, and emerging signal cascades stemming from their activities. Roles are discussed for the elusive transient receptor potential canonical channel (TRPC) complex in keratinocytes, Orai channels in Ca2+-cyclic AMP signal crosstalk in melanocytes, and Orai isoforms in eccrine sweat gland secretion.

AKT Regulation of ORAI1-Mediated Calcium Influx in Breast Cancer Cells.

Simple SummaryA remodeling in calcium homeostasis and the protein kinase AKT signaling pathway often promotes tumorigenic traits in cancer cells. Changes in calcium signaling can be mediated through altered expression or activity of calcium channels and pumps, which constitute a class of targetable therapeutic targets. Currently, the interplay between the two signaling pathways in breast cancer cells is unclear. A better understanding of the association between calcium and AKT signaling, and the molecular players involved may identify novel therapeutic strategies for breast cancers with abnormal AKT signaling. Using fluorescence calcium imaging and gene silencing/knockout techniques, we showed that increased AKT activation results in increased calcium entry, and that this is mediated through ORAI1 calcium channels. Future studies exploring therapeutic strategies to target PTEN-deficient or hyperactivated AKT cancers should consider this novel correlation between AKT activation and ORAI1-mediated calcium influx.Although breast cancer cells often exhibit both abnormal AKT signaling and calcium signaling, the association between these two pathways is unclear. Using a combination of pharmacological tools, siRNA and CRISPR/Cas9 gene silencing techniques, we investigated the association between PTEN, AKT phosphorylation and calcium signaling in a basal breast cancer cell line. We found that siRNA-mediated PTEN silencing promotes AKT phosphorylation and calcium influx in MDA-MB-231 cells. This increase in AKT phosphorylation and calcium influx was phenocopied by the pharmacological AKT activator, SC79. The increased calcium influx associated with SC79 is inhibited by silencing AKT2, but not AKT1. This increase in calcium influx is suppressed when the store-operated calcium channel, ORAI1 is silenced. The results from this study open a novel avenue for therapeutic targeting of cancer cells with increased AKT activation. Given the association between ORAI1 and breast cancer, ORAI1 is a possible therapeutic target in cancers with abnormal AKT signaling.