Store-Operated Calcium Channels

CRAC channel activity pulsates during cytosolic Ca2+ oscillations

Intracellular Ca2+ ions are used as second messengers throughout the phylogenetic tree. They are indispensable for diverse biological processes ranging from fertilization to cell death. In Metazoans, signaling information is conveyed via the amplitude, frequency and spatial profile of cytosolic Ca2+ oscillations. In non-excitable cells, these oscillations generally arise from regenerative release of Ca2+ from inositol 1,4,5-trisphosphate (InsP3)-sensitive intracellular stores, which are refilled by entry of Ca2+ through Ca2+ release-activated Ca2+ (CRAC) channels in the plasma membrane. However, the precise contribution of these store-operated CRAC channels to Ca2+ oscillations has remained controversial for decades. One view proposes that CRAC channels remain open throughout stimulation, functioning as the pacemaker in setting Ca2+ oscillation frequency. An alternative hypothesis is that channel activity oscillates in parallel with InsP3-driven regenerative Ca2+ release. Here, by tethering a genetically encoded Ca2+ indicator to the pore- forming subunit of the CRAC channel, Orai1, we distinguish between these hypotheses and demonstrate that CRAC channel activity fluctuates in phase with cytosolic Ca2+ oscillations during physiological levels of stimulation. We also find that spatially distinct CRAC channel clusters fire in a coordinated manner, revealing that CRAC channels are not independent units but might function in a synchronized manner to provide pulses of Ca2+ signal at the same time.

Magnetite Nanodiscs Activate Mechanotransductive Calcium Signaling in Diverse Cell Types

Remote magnetomechanical stimulation using magnetic nanomaterials has emerged as a robust and minimally invasive technique for modulating neuronal activity. However, despite the presence of machinery to convert mechanical force into biochemical signals in many types of cells, magnetomechanical stimulation of non-neuronal tissue remains largely unexplored. Here, we demonstrate that in the presence of weak magnetic fields (12-56 mT) with frequencies 5-125 Hz, magnetite nanodiscs (MNDs) activate ubiquitous mechano-sensitive calcium signaling pathways, including transmembrane calcium entry, the release of intracellular calcium reserves, and store-operated calcium signaling. MNDs mediate calcium transients in cells with disparate calcium signaling machinery, such as cardiomyocytes and hippocampal astrocytes. The characteristics of these calcium responses depend on the protein machinery available in each cell type. These findings expand the reach of cellular modulation strategies using magnetic nanoparticles to non-neuronal cells and thereby open new applications probing endocrine, immune, and circulatory functions and related disorders with remote magnetic approaches.

Anxa10 and neuropathic pain: Insights into dysregulation of endoplasmic reticulum-mitochondria contact tethering complex and therapeutic potential

The stability of membrane contact sites is critically dependent on Endoplasmic Reticulum mitochondria contact tethering complexes (EMCTCs), and dysregulation of these sites has been implicated in neuropathic diseases. In this study, we examined the role of Annexin A10 (Anxa10), a calcium-dependent protein, in neuropathic pain by investigating its influence on EMCTCs dysregulation. Using RNA sequencing, western blotting, and behavioral assays, we observed that spared nerve injury (SNI)-induced neuropathic pain significantly increased Anxa10 expression levels within the spinal dorsal horn (SDH) of mice. By employing cell-specific gene regulation via the Cre/loxp system, we utilized loxp-modified adeno-associated virus vectors to modulate Anxa10 expression in GAD2-Cre (inhibitory neurons), vGlut2-Cre (excitatory neurons), and Fos-Cre (activity-induced neurons) transgenic mice. Our results demonstrated that specific down-regulation of Anxa10 in excitatory neurons within the SDH alleviated neuropathic pain, whereas up-regulation of Anxa10, regardless of cell type, induced spontaneous pain in mice. Ultrastructural analysis of the endoplasmic reticulum (ER) and mitochondria, as well as double immunofluorescence staining, revealed that downregulation of Anxa10 mitigated the SNI-induced reduction in ER-mitochondrial distance. Additionally, it attenuated the SNI-induced upregulation of key components of EMCTCs, including IP3R, GRP75, and VDAC1, while preventing the SNI-induced downregulation of NCX3 expression. Furthermore, we formulated and validated the hypothesis that SGK1 and PI3K are positioned downstream of Anxa10. The up-regulation of Anxa10 compromised mitochondrial integrity and disrupted mitochondrial networks, ultimately leading to elevated oxidative stress. Collectively, these findings suggest that Anxa10 represents a promising therapeutic target for correcting EMCTCs dysregulation and mitigating neuropathic pain.

Chitosan-based biomaterials for bone tissue engineering

Common critical size bone defects encountered in clinical practice often result in inadequate bone regeneration,primarily due to the extent of damage surpassing the inherent capacity of the body for self-healing. Bone tissue engineering scaffolds possess the desirable characteristics of biomimetic bone structure, simulated extracellular matrix, optimal mechanical strength, and biological functionality, rendering them the preferred option for the treatment of bone defects. Chitosan demonstrates favorable biocompatibility, plasticity, and a range of biological activities, rendering it a highly appealing material. Chitosan and its derivatives have been found to exert an impact on bone repair through their ability to modulate macrophage polarization, angiogenesis, and the delicate equilibrium of bone remodeling. However, the efficacy of pure chitosan is constrained, necessitating its combination with other bioactive substances to achieve an optimal biomimetic scaffold that is compatible with the specific bone defect site. Chitosan is commonly utilized in the field of bone repair in four different application forms: rigid scaffold, hydrogel, membranes, and microspheres. In order to enhance comprehension of the benefits and constraints associated with chitosan, this review provides a comprehensive overview of the structure and biological properties of chitosan, the molecular mechanisms by which chitosan promotes osteogenic differentiation, the diverse methods of chitosan preparation for various applications, and the impacts of chitosan when loaded with bioactive substances.

Altered Mitochondrial Bioenergetics and Calcium Kinetics in Young-Onset PLA2G6 Parkinson's Disease iPSCs

Parkinson's disease (PD) has emerged as a multisystem disorder affecting multiple cellular and organellar systems in addition to the dopaminergic neurons. Disease-specific induced pluripotent stem cells (iPSCs) model early developmental changes and cellular perturbations that are otherwise inaccessible from clinical settings. Here, we report the early changes in patient-derived iPSCs carrying a homozygous recessive mutation, R741Q, in the PLA2G6 gene. A gene-edited R747W iPSC line mirrored these phenotypes, thus validating our initial findings. Bioenergetic dysfunction and hyperpolarization of mitochondrial membrane potentials were hallmarks of the PD iPSCs. Further, a concomitant increase in glycolytic activity indicated a possible compensation for mitochondrial respiration. Elevated basal reactive oxygen species (ROS) and decreased catalase expression were also observed in the disease iPSCs. No change in autophagy was detected. These inceptive changes could be potential targets for early intervention of prodromal PD in the absence of disease-modifying therapies. However, additional investigations are crucial to delineate the cause-effect relationships of these observations.

On-demand treatment of metabolic diseases by a synthetic drug-inducible exocytosis system

Here, we present StimExo as a rational design strategy allowing various user-defined control signals to trigger calcium-dependent exocytosis and mediate on-demand protein secretion in cell-therapy settings. Using a modular framework incorporating inducible protein-protein interactions into an engineered bipartite activator of calcium release-activated calcium (CRAC) channels, Ca2+ influx mediated by the STIM/Orai1 machinery was flexibly adjusted to depend on different user-defined input signals. Application of StimExo to various endocrine cells enables instant secretion of therapeutic hormones upon administration of safe and patient-compliant trigger compounds. StimExo also mediated insulin exocytosis using a cell-based gene delivery strategy in vivo, accounting for real-time control of blood glucose homeostasis in male diabetic mice in response to the FDA-approved drug grazoprevir. This study achieves true "sense-and-respond" cell-based therapies and provides a platform for remote control of in vivo transgene activities using various trigger signals of interest.

Perturbing Organelle-Level K+/Ca2+ Homeostasis by Nanotherapeutics for Enhancing Ion-Mediated Cancer Immunotherapy

Intracellular ions are involved in numerous pivotal immune processes, but the precise regulation of these signaling ions to achieve innovative immune therapeutic strategies is still a huge challenge. Here, an ion-mediated immunotherapy agent (IMIA) is engineered to achieve precise spatiotemporal control of perturbing K+/Ca2+ homeostasis at the organelle-level, thereby amplifying antitumor immune responses to achieve high-performance cancer therapy. By taking in intracellular K+ and supplying exogenous Ca2+ within tumor cells, K+/Ca2+ homeostasis is perturbed by IMIA. In parallel, perturbing K+ homeostasis induced endoplasmic reticulum (ER) stress triggers the release of Ca2+ from ER and causes a decreased concentration of Ca2+ in ER, which further accelerates ER-mitochondria Ca2+ flux and the influx of extracellular Ca2+ (store-operated Ca2+ entry (SOCE)) via opening Ca2+ release-activated Ca2+ (CRAC) channels, thus creating a self-amplifying ion interference loop to perturb K+/Ca2+ homeostasis. In this process, the elevated immunogenicity of tumor cells would evoke robust antitumor immune responses by driving the excretion of damage-associated molecular patterns (DAMPs). Importantly, this ion-immunotherapy strategy reshapes the immunosuppressive tumor microenvironment (TME), and awakens the systemic immune response and long-term immune memory effect, thus effectively inhibiting the growth of primary/distant tumors, orthotopic tumors as well as metastatic tumors in different mice models.

STIM Proteins: The Gas and Brake of Calcium Entry in Neurons

Stromal interaction molecules (STIM)s are Ca2+ sensors in internal Ca2+ stores of the endoplasmic reticulum. They activate the store-operated Ca2+ channels, which are the main source of Ca2+ entry in non-excitable cells. Moreover, STIM proteins interact with other Ca2+ channel subunits and active transporters, making STIMs an important intermediate molecule in orchestrating a wide variety of Ca2+ influxes into excitable cells. Nevertheless, little is known about the role of STIM proteins in brain functioning. Being involved in many signaling pathways, STIMs replenish internal Ca2+ stores in neurons and mediate synaptic transmission and neuronal excitability. Ca2+ dyshomeostasis is a signature of many pathological conditions of the brain, including neurodegenerative diseases, injuries, stroke, and epilepsy. STIMs play a role in these disturbances not only by supporting abnormal store-operated Ca2+ entry but also by regulating Ca2+ influx through other channels. Here, we review the present knowledge of STIMs in neurons and their involvement in brain pathology.

Hippocampal dendritic spines store-operated calcium entry and endoplasmic reticulum content is dynamic microtubule dependent

One of the mechanisms of calcium signalling in neurons is store-operated calcium entry (SOCE), which is activated when the calcium concentration in the smooth endoplasmic reticulum (ER) decreases and its protein-calcium sensor STIM (stromal interacting molecule) relocate to the endoplasmic reticulum and plasma membrane junctions, forms clusters and induces calcium entry. In electrically non-excitable cells, STIM1 is coupled with the positive end of a tubulin microtubule through interaction with EB1 (end-binding) protein, which controls its oligomerization, SOCE and participates in ER movement. STIM2 homologue, which is specific for mature hippocampal dendritic spines, is known to interact with EB3 protein, however, not much is known about the role of this interaction in STIM2 clustering or ER trafficking in neurons. Intriguingly, in neurons, reducing the expression of EB3 protein or disrupting the interaction of STIM2 protein with EB proteins results in decreased SOCE, in contrast to experiments with STIM1 in non-excitable cells. In this study, these two homologues are compared side-by-side in HEK-293T, and it is shown for the first time that their clustering and SOCE is oppositely regulated by dynamic tubulin microtubules. In particular, for STIM2, the interaction with dynamic microtubule cytoskeleton is required for clustering and is shown to potentiate SOCE, while for STIM1 this interaction restricts clustering, resulting in SOCE decrease. After store depletion in primary hippocampal neurons, the wild type STIM2 is redistributed from the necks to the heads of dendritic spines, while the STIM2 variant with a mutation that disrupts the interaction with EB proteins is excluded from dendritic spines. In addition, overexpression of the mutant variant leads to ER reorganization in neuronal soma and reduction of ER presence in spines. It also leads to a reduction in the number of spines containing the spine apparatus formed by ER cisternae, as well as a reduction in dendritic spines SOCE. These effects are opposite of those detected during overexpression of the wild type STIM2. Considered together, these findings underline the important role of dynamic microtubules in regulation of neuronal SOCE and ER morphology.

The genetically encoded calcium indicator GCaMP3 reveals spontaneous calcium oscillations at asexual stages of the human malaria parasite Plasmodium falciparum

Most protocols used to study the dynamics of calcium (Ca2+) in the malaria parasite are based on dyes, which are invasive and do not allow discrimination between the signal from the host cell and the parasite. To avoid this pitfall, we have generated a parasite line expressing the genetically encoded calcium sensor GCaMP3. The PfGCaMP3 parasite line is an innovative tool for studying spontaneous intracellular Ca2+ oscillations without external markers. Using this parasite line, we demonstrate the occurrence of spontaneous Ca2+ oscillations in the ring, trophozoite, and schizont stages in Plasmodium falciparum. Using the Fourier transform to fluorescence intensity data extracted from different experiments, we observe cytosolic Ca2+ fluctuations. These spontaneous cytosolic Ca2+ oscillations occur in the three intraerythrocytic stages of the parasite, with most oscillations occurring in the ring and trophozoite stages. A control parasite line expressing only a GFP control did not reveal such fluctuations, demonstrating the specificity of the observations. Our results clearly show dynamic, spontaneous Ca2+ oscillations during the asexual stage in P. falciparum, independent from external stimuli.

Discovery of selective Orai channel blockers bearing an indazole or a pyrazole scaffold

The calcium release activated calcium (CRAC) channel is highly expressed in T lymphocytes and plays a critical role in regulating T cell proliferation and functions including activation of the transcription factor nuclear factor of activated T cells (NFAT), cytokine production and cytotoxicity. The CRAC channel consists of the Orai pore subunit and STIM (stromal interacting molecule) endoplasmic reticulum calcium sensor. Loss of CRAC channel mediated calcium signaling has been identified as an underlying cause of severe combined immunodeficiency (SCID), leading to drastically weakened immunity against infections. Gain-of-function mutations in Orai and STIM have been associated with tubular aggregated myopathy (TAM), a skeletal muscle disease. While a number of small molecules have shown activity in inhibiting the CRAC signaling pathway, the usefulness of those tool compounds is limited by their off-target activity against TRPM4 and TRPM7 ion channels, high lipophilicity, and a lack of understanding of their mechanism of action. We report structure-activity relationship (SAR) studies that resulted in the characterization of compound 4k [1-(cyclopropylmethyl)-N-(3-fluoropyridin-4-yl)-1H-indazole-3-carboxamie] as a fast onset, reversible, and selective CRAC channel blocker. 4k fully blocked the CRAC current (IC50: 4.9 μM) and the nuclear translocation of NFAT at 30 and 10 μM, respectively, without affecting the electrophysiological function of TRPM4 and TRPM7 channels. Computational modeling appears to support its direction binding to Orai proteins that form the transmembrane CRACchannel.

House dust mite allergens, store-operated Ca2+ channels and asthma

The house dust mite is the principal source of aero-allergen worldwide. Exposure to mite-derived allergens is associated with the development of asthma in susceptible individuals, and the majority of asthmatics are allergic to the mite. Mite-derived allergens are functionally diverse and activate multiple cell types within the lung that result in chronic inflammation. Allergens activate store-operated Ca2+ release-activated Ca2+ (CRAC) channels, which are widely expressed in multiple cell types within the lung that are associated with the pathogenesis of asthma. Opening of CRAC channels stimulates Ca2+-dependent transcription factors, including nuclear factor of activated T cells and nuclear factor-κB, which drive expression of a plethora of pro-inflammatory cytokines and chemokines that help to sustain chronic inflammation. Here, I describe drivers of asthma, properties of mite-derived allergens, how the allergens are recognized by cells, the signalling pathways used by the receptors and how these are transduced into functional effects, with a focus on CRAC channels. In vivo experiments that demonstrate the effectiveness of targeting CRAC channels as a potential new therapy for treating mite-induced asthma are also discussed, in tandem with other possible approaches.

Downregulation of stromal interaction molecule-1 is implicated in the age-associated vasoconstriction dysfunction of aorta, intrarenal, and coronary arteries

The contractile function of vascular smooth muscle cells (VSMCs) typically undergoes significant changes with advancing age, leading to severe vascular aging-related diseases. The precise role and mechanism of stromal interaction molecule-1 (STIM1) in age-mediated Ca2+ signaling and vasocontraction remain unclear. The connection between STIM1 and age-related vascular dysfunction was investigated using a multi-myograph system, immunohistochemical analysis, protein blotting, and SA-β-gal staining. Results showed that vasoconstrictor responses in the thoracic aorta, intrarenal artery, and coronary artery decreased with age. STIM1 knockdown in the intrarenal and coronary arteries reduced vascular tone in young mice, while no change was observed in the thoracic aorta. A significant reduction in vascular tone occurred in the STIM1 knockout group with nifedipine. In the thoracic aorta, vasoconstriction significantly decreased with age following the use of nifedipine and thapsigargin and almost disappeared after STIM1 knockdown. The proportion of senescent VSMCs increased significantly in aged mice and further increased in sm-STIM1 KO aged mice. Moreover, the expression of senescence markers p21, p16, and IL-6 significantly increased with age, with p21 expression further increased in the STIM1 knockdown aged group, but not p16 or IL-6. These findings indicate that different arteries exhibit distinct organ-specific features and that STIM1 downregulation may contribute to age-related vasoconstrictive dysfunction through activation of the p21 pathway.

Purinergic agonists increase [Ca2+]i in rat conjunctival goblet cells through ryanodine receptor type 3

ATP and benzoylbenzoyl-ATP (BzATP) increase free cytosolic Ca2+ concentration ([Ca2+]i) in conjunctival goblet cells (CGCs) resulting in mucin secretion. The purpose of this study was to investigate the source of the Ca2+i mobilized by ATP and BzATP. First-passage cultured rat CGCs were incubated with Fura-2/AM, and [Ca2+]i was measured under several conditions with ATP and BzATP stimulation. The following conditions were used: 1) preincubation with the Ca2+ chelator EGTA, 2) preincubation with the SERCA inhibitor thapsigargin (10-6 M), which depletes ER Ca2+ stores, 3) preincubation with phospholipase C (PLC) or protein kinase A (PKA) inhibitor, or 4) preincubation with the voltage-gated calcium channel antagonist nifedipine (10-5 M) and the ryanodine receptor (RyR) antagonist dantrolene (10-5 M). Immunofluorescence microscopy (IF) and quantitative reverse transcription polymerase chain reaction (RT-qPCR) were used to investigate RyR presence in rat and human CGCs. ATP-stimulated peak [Ca2+]i was significantly lower after chelating Ca2+i with 2 mM EGTA in Ca2+-free buffer. The peak [Ca2+]i increase in CGCs preincubated with thapsigargin, the PKA inhibitor H89, nifedipine, and dantrolene, but not the PLC inhibitor, was reduced for ATP at 10-5 M and BzATP at 10-4 M. Incubating CGCs with dantrolene alone decreased [Ca2+]i and induced CGC cell death at a high concentration. RyR3 was detected in rat and human CGCs with IF and RT-qPCR. We conclude that ATP- and BzATP-induced Ca2+i increases originate from the ER and that RyR3 may be an essential regulator of CGC [Ca2+]i. This study contributes to the understanding of diseases arising from defective Ca2+ signaling in nonexcitable cells.NEW & NOTEWORTHY ATP and benzoylbenzoyl-ATP (BzATP) induce mucin secretion through an increase in free cytosolic calcium concentration ([Ca2+]i) in conjunctival goblet cells (CGCs). The mechanisms through which ATP and BzATP increase [Ca2+]i in CGCs are unclear. Ryanodine receptors (RyRs) are fundamental in [Ca2+]i regulation in excitable cells. Herein, we find that ATP and BzATP increase [Ca2+]i through the activation of protein kinase A, voltage-gated calcium channels, and RyRs, and that RyRs are crucial for nonexcitable CGCs' Ca2+i homeostasis.

Adaptation of STIM1 structure-function relationships for optogenetic control of calcium signaling

In cellular contexts, the oscillation of calcium ions (Ca2+) is intricately linked to various physiological processes, such as cell proliferation, metabolism, and survival. Stromal interaction molecule 1 (STIM1) proteins form a crucial regulatory component in the store-operated calcium entry process. The structural attributes of STIM1 are vital for its functionality, encompassing distinct domains situated in the endoplasmic reticulum lumen and the cytoplasm. The intraluminal domain enables the timely detection of diminishing Ca2+ concentrations, prompting structural modifications that activate the cytoplasmic domain. This activated cytoplasmic domain undergoes conformational alterations and engages with membrane components, opening a channel that facilitates the influx of Ca2+ from the extracellular environment. Given its multiple domains and interaction mechanisms, STIM1 plays a foundational role in cellular biology. This review focuses on the design of optogenetic tools inspired by the structure and function of STIM1. These tools offer a groundbreaking approach for studying and manipulating intracellular Ca2+ signaling with precise spatiotemporal control. We further explore the practical applications of these tools, spanning fundamental scientific research, clinical studies, and their potential for translational research.

Non-voltage-gated Ca2+ channel signaling in glomerular cells in kidney health and disease

Positioned at the head of the nephron, the renal corpuscle generates a plasma ultrafiltrate to initiate urine formation. Three major cell types within the renal corpuscle, the glomerular mesangial cells, podocytes, and glomerular capillary endothelial cells, communicate via endocrine- and paracrine-signaling mechanisms to maintain the structure and function of the glomerular capillary network and filtration barrier. Ca2+ signaling mediated by several distinct plasma membrane Ca2+ channels impacts the functions of all three cell types. The past two decades have witnessed pivotal advances in understanding of non-voltage-gated Ca2+ channel function and regulation in the renal corpuscle in health and renal disease. This review summarizes the current knowledge of the physiological and pathological impact of non-voltage-gated Ca2+ channel signaling in mesangial cells, podocytes and glomerular capillary endothelium. The main focus is on transient receptor potential and store-operated Ca2+ channels, but ionotropic N-methyl-d-aspartate receptors and purinergic receptors also are discussed. This update of Ca2+ channel functions and their cellular signaling cascades in the renal corpuscle is intended to inform the development of therapeutic strategies targeting these channels to treat kidney diseases, particularly diabetic nephropathy.

Nanomaterial-Based Repurposing of Macrophage Metabolism and Its Applications

Macrophage immunotherapy represents an emerging therapeutic approach aimed at modulating the immune response to alleviate disease symptoms. Nanomaterials (NMs) have been engineered to monitor macrophage metabolism, enabling the evaluation of disease progression and the replication of intricate physiological signal patterns. They achieve this either directly or by delivering regulatory signals, thereby mapping phenotype to effector functions through metabolic repurposing to customize macrophage fate for therapy. However, a comprehensive summary regarding NM-mediated macrophage visualization and coordinated metabolic rewiring to maintain phenotypic equilibrium is currently lacking. This review aims to address this gap by outlining recent advancements in NM-based metabolic immunotherapy. We initially explore the relationship between metabolism, polarization, and disease, before delving into recent NM innovations that visualize macrophage activity to elucidate disease onset and fine-tune its fate through metabolic remodeling for macrophage-centered immunotherapy. Finally, we discuss the prospects and challenges of NM-mediated metabolic immunotherapy, aiming to accelerate clinical translation. We anticipate that this review will serve as a valuable reference for researchers seeking to leverage novel metabolic intervention-matched immunomodulators in macrophages or other fields of immune engineering.

The A-kinase anchoring protein Yotiao decrease the ER calcium content by inhibiting the store operated calcium entry

The meticulous regulation of ER calcium (Ca2+) homeostasis is indispensable for the proper functioning of numerous cellular processes. Disrupted ER Ca2+ balance is implicated in diverse diseases, underscoring the need for a systematic exploration of its regulatory factors in cells. Our recent genomic-scale screen identified a scaffolding protein A-kinase anchoring protein 9 (AKAP9) as a regulator of ER Ca2+ levels, but the underlying molecular mechanisms remain elusive. Here, we reveal that Yotiao, the smallest splicing variant of AKAP9 decreased ER Ca2+ content in animal cells. Additional testing using a combination of Yotiao truncations, knock-out cells and pharmacological tools revealed that, Yotiao does not require most of its interactors, including type 1 inositol 1,4,5-trisphosphate receptors (IP3R1), protein kinase A (PKA), protein phosphatase 1 (PP1), adenylyl cyclase type 2 (AC2) and so on, to reduce ER Ca2+ levels. However, adenylyl cyclase type 9 (AC9), which is known to increases its cAMP generation upon interaction with Yotiao for the modulation of potassium channels, plays an essential role for Yotiao's ER-Ca2+-lowering effect. Mechanistically, Yotiao may work through AC9 to act on Orai1-C terminus and suppress store operated Ca2+ entry, resulting in reduced ER Ca2+ levels. These findings not only enhance our comprehension of the interplay between Yotiao and AC9 but also contribute to a more intricate understanding of the finely tuned mechanisms governing ER Ca2+ homeostasis.

Regulation of anti-tumor immunity by metal ion in the tumor microenvironment

Metal ions play an essential role in regulating the functions of immune cells by transmitting intracellular and extracellular signals in tumor microenvironment (TME). Among these immune cells, we focused on the impact of metal ions on T cells because they can recognize and kill cancer cells and play an important role in immune-based cancer treatment. Metal ions are often used in nanomedicines for tumor immunotherapy. In this review, we discuss seven metal ions related to anti-tumor immunity, elucidate their roles in immunotherapy, and provide novel insights into tumor immunotherapy and clinical applications.

Insights into the dynamics of the Ca2+ release-activated Ca2+ channel pore-forming complex Orai1

An important calcium (Ca2+) entry pathway into the cell is the Ca2+ release-activated Ca2+ (CRAC) channel, which controls a series of downstream signaling events such as gene transcription, secretion and proliferation. It is composed of a Ca2+ sensor in the endoplasmic reticulum (ER), the stromal interaction molecule (STIM), and the Ca2+ ion channel Orai in the plasma membrane (PM). Their activation is initiated by receptor-ligand binding at the PM, which triggers a signaling cascade within the cell that ultimately causes store depletion. The decrease in ER-luminal Ca2+ is sensed by STIM1, which undergoes structural rearrangements that lead to coupling with Orai1 and its activation. In this review, we highlight the current understanding of the Orai1 pore opening mechanism. In this context, we also point out the questions that remain unanswered and how these can be addressed by the currently emerging genetic code expansion (GCE) technology. GCE enables the incorporation of non-canonical amino acids with novel properties, such as light-sensitivity, and has the potential to provide novel insights into the structure/function relationship of CRAC channels at a single amino acid level in the living cell.

Periparturient Mineral Metabolism: Implications to Health and Productivity

Mineral metabolism, in particular Ca, and to a lesser extent phosphorus (P) and magnesium (Mg), is altered with the onset of lactation because of extensive irreversible loss to synthesize colostrum and milk. The transient reduction in the concentration of Ca in blood, particularly when it lasts days, increases the risk of mineral-related disorders such as hypocalcemia and, to a lesser extent, hypophosphatemia. Although the incidence of clinical hypocalcemia can be reduced by prepartum dietary interventions, subclinical hypocalcemia remains prevalent, affecting up to 60% of the dairy cows in the first 3 d postpartum. More importantly, strong associations exist between hypocalcemia and increased susceptibility to other peripartum diseases and impaired reproductive performance. Mechanistic experiments have demonstrated the role of Ca on innate immune response in dairy cows, which presumably predisposes them to other diseases. Hypocalcemia is not related to inadequate Ca intake as prepartum diets marginal to deficient in Ca reduce the risk of the disease. Therefore, the understanding of how Ca homeostasis is regulated, in particular how calciotropic hormones such as parathyroid hormone and 1,25-dihydroxyvitamin D3, affect blood Ca concentrations, gastrointestinal Ca absorption, bone remodeling, and renal excretion of Ca become critical to develop novel strategies to prevent mineral imbalances either by nutritional or pharmacological interventions. A common method to reduce the risk of hypocalcemia is the manipulation of the prepartum dietary cation-anion difference. Feeding acidogenic diets not only improves Ca homeostasis and reduces hypocalcemia, but also reduces the risk of uterine diseases and improves productive performance. Feeding diets that induce a negative Ca balance in the last weeks of gestation also reduce the risk of clinical hypocalcemia, and recent work shows that the incorporation of mineral sequestering agents, presumably by reducing the absorption of P and Ca prepartum, increases blood Ca at calving, although benefits to production and health remain to be shown. Alternative strategies to minimize subclinical hypocalcemia with the use of vitamin D metabolites either fed prepartum or as a pharmacological agent administered immediately after calving have shown promising results in reducing hypocalcemia and altering immune cell function, which might prove efficacious to prevent diseases in early lactation. This review summarizes the current understanding of Ca homeostasis around parturition, the limited knowledge of the exact mechanisms for gastrointestinal Ca absorption in bovine, the implications of hypocalcemia on the health of dairy cows, and discusses the methods to minimize the risk of hypocalcemia and their impacts on productive performance and health in dairy cows.

Activation mechanisms and structural dynamics of STIM proteins

The family of stromal interaction molecules (STIM) includes two widely expressed single-pass endoplasmic reticulum (ER) transmembrane proteins and additional splice variants that act as precise ER-luminal Ca2+ sensors. STIM proteins mainly function as one of the two essential components of the so-called Ca2+ release-activated Ca2+ (CRAC) channel. The second CRAC channel component is constituted by pore-forming Orai proteins in the plasma membrane. STIM and Orai physically interact with each other to enable CRAC channel opening, which is a critical prerequisite for various downstream signalling pathways such as gene transcription or proliferation. Their activation commonly requires the emptying of the intracellular ER Ca2+ store. Using their Ca2+ sensing capabilities, STIM proteins confer this Ca2+ content-dependent signal to Orai, thereby linking Ca2+ store depletion to CRAC channel opening. Here we review the conformational dynamics occurring along the entire STIM protein upon store depletion, involving the transition from the quiescent, compactly folded structure into an active, extended state, modulation by a variety of accessory components in the cell as well as the impairment of individual steps of the STIM activation cascade associated with disease.

Calcium signaling in endothelial and vascular smooth muscle cells: sex differences and the influence of estrogens and androgens

Calcium signaling in vascular endothelial cells (ECs) and smooth muscle cells (VSMCs) is essential for the regulation of vascular tone. However, the changes to intracellular Ca2+ concentrations are often influenced by sex differences. Furthermore, a large body of evidence shows that sex hormone imbalance leads to dysregulation of Ca2+ signaling and this is a key factor in the pathogenesis of cardiovascular diseases. In this review, the effects of estrogens and androgens on vascular calcium-handling proteins are discussed, with emphasis on the associated genomic or nongenomic molecular mechanisms. The experimental models from which data were collected were also considered. The review highlights 1) in female ECs, transient receptor potential vanilloid 4 (TRPV4) and mitochondrial Ca2+ uniporter (MCU) enhance Ca2+-dependent nitric oxide (NO) generation. In males, only transient receptor potential canonical 3 (TRPC3) plays a fundamental role in this effect. 2) Female VSMCs have lower cytosolic Ca2+ levels than males due to differences in the activity and expression of stromal interaction molecule 1 (STIM1), calcium release-activated calcium modulator 1 (Orai1), calcium voltage-gated channel subunit-α1C (CaV1.2), Na+-K+-2Cl- symporter (NKCC1), and the Na+/K+-ATPase. 3) When compared with androgens, the influence of estrogens on Ca2+ homeostasis, vascular tone, and incidence of vascular disease is better documented. 4) Many studies use supraphysiological concentrations of sex hormones, which may limit the physiological relevance of outcomes. 5) Sex-dependent differences in Ca2+ signaling mean both sexes ought to be included in experimental design.

Wound Repair and Ca2+ Signalling Interplay: The Role of Ca2+ Channels in Skin

The process of wound healing is intricate and tightly controlled, involving a number of different cellular and molecular processes. Numerous cellular functions, especially those related to wound healing, depend critically on calcium ions (Ca2+). Ca2+ channels are proteins involved in signal transduction and communication inside cells that allow calcium ions to pass through cell membranes. Key Ca2+ channel types involved in wound repair are described in this review.

Effects of Dietary Colostrum Basic Protein on Bone Growth and Calcium Absorption in Mice

Colostrum basic protein (CBP) is a trace protein extracted from bovine colostrum. Previous studies have shown that CBP can promote bone cell differentiation and increase bone density. However, the mechanism by which CBP promotes bone activity remains unclear. This study investigated the mechanism of the effect of CBP on bone growth in mice following dietary supplementation of CBP at doses that included 0.015%, 0.15%, 1.5%, and 5%. Compared with mice fed a normal diet, feeding 5% CBP significantly enhanced bone rigidity and improved the microstructure of bone trabeculae. Five-percent CBP intake triggered significant positive regulation of calcium metabolism in the direction of bone calcium accumulation. The expression levels of paracellular calcium transport proteins CLDN2 and CLDN12 were upregulated nearly 1.5-fold by 5% CBP. We conclude that CBP promotes calcium absorption in mice by upregulating the expression of the calcium-transporting paracellular proteins CLND2 and CLND12, thereby increasing bone density and promoting bone growth. Overall, CBP contributes to bone growth by affecting calcium metabolism.

Photo-Controlled Calcium Overload from Endogenous Sources for Tumor Therapy

Designing reactive calcium-based nanogenerators to produce excess calcium ions (Ca2+ ) in tumor cells is an attractive tumor treatment method. However, nanogenerators that introduce exogenous Ca2+ are either overactive incapable of on-demand release, or excessively inert incapable of an overload of calcium rapidly. Herein, inspired by inherently diverse Ca2+ -regulating channels, a photo-controlled Ca2+ nanomodulator that fully utilizes endogenous Ca2+ from dual sources was designed to achieve Ca2+ overload in tumor cells. Specifically, mesoporous silica nanoparticles were used to co-load bifunctional indocyanine green as a photodynamic/photothermal agent and a thermal-sensitive nitric oxide (NO) donor (BNN-6). Thereafter, they were coated with hyaluronic acid, which served as a tumor cell-targeting unit and a gatekeeper. Under near-infrared light irradiation, the Ca2+ nanomodulator can generate reactive oxygen species that stimulate the transient receptor potential ankyrin subtype 1 channel to realize Ca2+ influx from extracellular environments. Simultaneously, the converted heat can induce BNN-6 decomposition to generate NO, which would open the ryanodine receptor channel in the endoplasmic reticulum and allow stored Ca2+ to leak. Both in vitro and in vivo experiments demonstrated that the combination of photo-controlled Ca2+ influx and release could enable Ca2+ overload in the cytoplasm and efficiently inhibit tumor growth.

Mitochondrial malfunction mediates impaired cholinergic Ca2+ signalling and submandibular salivary gland dysfunction in diabetes

Xerostomia (dry-mouth syndrome) is a painful and debilitating condition that frequently occurs in individuals with diabetes and is associated with impaired saliva production and salivary gland hypofunction. Saliva fluid production relies on Ca2+-coupled secretion driven by neurotransmitter stimulation of submandibular acinar cells. Although impairments in intracellular Ca2+ signalling have been reported in various xerostomia models, the specific Ca2+-dependent mechanisms underlying saliva fluid hypofunction in diabetes remain unclear. In this study, we show that diabetic animals exhibit severe xerostomia, evident by reduced saliva flow rate, diminished total protein content, and decreased amylase activity in the saliva secreted by submandibular glands. These impairments remained resistant to exogenous cholinergic stimulation. In submandibular acinar cells, the intracellular Ca2+ signals evoked by cholinergic stimulation were reduced and delayed in diabetes, caused by malfunctioning mitochondria. Upon initiation of cholinergic-evoked Ca2+ signals, mitochondria accumulate higher Ca2+ and fail to redistribute Ca2+ influx and facilitate the store-operated Ca2+ entry effectively. Structural damage to mitochondria was evident in the acinar cells in diabetes. These findings provide insights into the potential targeting of malfunctioning mitochondria for the treatment of diabetic xerostomia as an alternative strategy to the existing pharmacotherapeutic approaches. This article is part of the Special Issue on "Ukrainian Neuroscience".

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.

Regulatory mechanisms controlling store-operated calcium entry

Calcium influx through plasma membrane ion channels is crucial for many events in cellular physiology. Cell surface stimuli lead to the production of inositol 1,4,5-trisphosphate (IP3), which binds to IP3 receptors (IP3R) in the endoplasmic reticulum (ER) to release calcium pools from the ER lumen. This leads to the depletion of ER calcium pools, which has been termed store depletion. Store depletion leads to the dissociation of calcium ions from the EF-hand motif of the ER calcium sensor Stromal Interaction Molecule 1 (STIM1). This leads to a conformational change in STIM1, which helps it to interact with the plasma membrane (PM) at ER:PM junctions. At these ER:PM junctions, STIM1 binds to and activates a calcium channel known as Orai1 to form calcium release-activated calcium (CRAC) channels. Activation of Orai1 leads to calcium influx, known as store-operated calcium entry (SOCE). In addition to Orai1 and STIM1, the homologs of Orai1 and STIM1, such as Orai2/3 and STIM2, also play a crucial role in calcium homeostasis. The influx of calcium through the Orai channel activates a calcium current that has been termed the CRAC current. CRAC channels form multimers and cluster together in large macromolecular assemblies termed "puncta". How CRAC channels form puncta has been contentious since their discovery. In this review, we will outline the history of SOCE, the molecular players involved in this process, as well as the models that have been proposed to explain this critical mechanism in cellular physiology.

How Merkel cells transduce mechanical stimuli: A biophysical model of Merkel cells

Merkel cells combine with Aβ afferents, producing slowly adapting type 1(SA1) responses to mechanical stimuli. However, how Merkel cells transduce mechanical stimuli into neural signals to Aβ afferents is still unclear. Here we develop a biophysical model of Merkel cells for mechanical transduction by incorporating main ingredients such as Ca2+ and K+ voltage-gated channels, Piezo2 channels, internal Ca2+ stores, neurotransmitters release, and cell deformation. We first validate our model with several experiments. Then we reveal that Ca2+ and K+ channels on the plasma membrane shape the depolarization of membrane potentials, further regulating the Ca2+ transients in the cells. We also show that Ca2+ channels on the plasma membrane mainly inspire the Ca2+ transients, while internal Ca2+ stores mainly maintain the Ca2+ transients. Moreover, we show that though Piezo2 channels are rapidly adapting mechanical-sensitive channels, they are sufficient to inspire sustained Ca2+ transients in Merkel cells, which further induce the release of neurotransmitters for tens of seconds. Thus our work provides a model that captures the membrane potentials and Ca2+ transients features of Merkel cells and partly explains how Merkel cells transduce the mechanical stimuli by Piezo2 channels.

SMDT1 variants impair EMRE-mediated mitochondrial calcium uptake in patients with muscle involvement

Ionic calcium (Ca2+) is a key messenger in signal transduction and its mitochondrial uptake plays an important role in cell physiology. This uptake is mediated by the mitochondrial Ca2+ uniporter (MCU), which is regulated by EMRE (essential MCU regulator) encoded by the SMDT1 (single-pass membrane protein with aspartate rich tail 1) gene. This work presents the genetic, clinical and cellular characterization of two patients harbouring SMDT1 variants and presenting with muscle problems. Analysis of patient fibroblasts and complementation experiments demonstrated that these variants lead to absence of EMRE protein, induce MCU subcomplex formation and impair mitochondrial Ca2+ uptake. However, the activity of oxidative phosphorylation enzymes, mitochondrial morphology and membrane potential, as well as routine/ATP-linked respiration were not affected. We hypothesize that the muscle-related symptoms in the SMDT1 patients result from aberrant mitochondrial Ca2+ uptake.

Store-Operated Calcium Entry Increases Nuclear Calcium in Adult Rat Atrial and Ventricular Cardiomyocytes

Store-operated calcium entry (SOCE) in cardiomyocytes may be involved in cardiac remodeling, but the underlying mechanisms remain elusive. We hypothesized that SOCE may increase nuclear calcium, which alters gene expression via calcium/calmodulin-dependent enzyme signaling, and elucidated the underlying cellular mechanisms. An experimental protocol was established in isolated adult rat cardiomyocytes to elicit SOCE by re-addition of calcium following complete depletion of sarcoplasmic reticulum (SR) calcium and to quantify SOCE in relation to the electrically stimulated calcium transient (CaT) measured in the same cell before SR depletion. Using confocal imaging, calcium changes were recorded simultaneously in the cytosol and in the nucleus of the cell. In ventricular myocytes, SOCE was observed in the cytosol and nucleus amounting to ≈15% and ≈25% of the respective CaT. There was a linear correlation between the SOCE-mediated calcium increase in the cytosol and nucleus. Inhibitors of TRPC or Orai channels reduced SOCE by ≈33-67%, whereas detubulation did not. In atrial myocytes, SOCE with similar characteristics was observed in the cytosol and nucleus. However, the SOCE amplitudes in atrial myocytes were ≈two-fold larger than in ventricular myocytes, and this was associated with ≈1.4- to 3.6-fold larger expression of putative SOCE proteins (TRPC1, 3, 6, and STIM1) in atrial tissue. The results indicated that SOCE in atrial and ventricular myocytes is able to cause robust calcium increases in the nucleus and that both TRPC and Orai channels may contribute to SOCE in adult cardiomyocytes.

Impaired intracellular Ca2+ signaling contributes to age-related cerebral small vessel disease in Col4a1 mutant mice

Humans and mice with mutations in COL4A1 and COL4A2 manifest hallmarks of cerebral small vessel disease (cSVD). Mice with a missense mutation in Col4a1 at amino acid 1344 (Col4a1+/G1344D) exhibit age-dependent intracerebral hemorrhages (ICHs) and brain lesions. Here, we report that this pathology was associated with the loss of myogenic vasoconstriction, an intrinsic vascular response essential for the autoregulation of cerebral blood flow. Electrophysiological analyses showed that the loss of myogenic constriction resulted from blunted pressure-induced smooth muscle cell (SMC) membrane depolarization. Furthermore, we found that dysregulation of membrane potential was associated with impaired Ca2+-dependent activation of large-conductance Ca2+-activated K+ (BK) and transient receptor potential melastatin 4 (TRPM4) cation channels linked to disruptions in sarcoplasmic reticulum (SR) Ca2+ signaling. Col4a1 mutations impair protein folding, which can cause SR stress. Treating Col4a1+/G1344D mice with 4-phenylbutyrate, a compound that promotes the trafficking of misfolded proteins and alleviates SR stress, restored SR Ca2+ signaling, maintained BK and TRPM4 channel activity, prevented loss of myogenic tone, and reduced ICHs. We conclude that alterations in SR Ca2+ handling that impair ion channel activity result in dysregulation of SMC membrane potential and loss of myogenic tone and contribute to age-related cSVD in Col4a1+/G1344D mice.

Diuretic hormone 31 activates two G protein-coupled receptors with differential second messengers for diuresis in Drosophila suzukii

Diuretic hormones (DHs) bind to G protein-coupled receptors (GPCRs), regulating water and ion balance to maintain homeostasis in animals. Two distinct DHs are known in insects: calcitonin (CT)-like DH31 and corticotropin-releasing factor (CRF)-like DH44. In this study, we identified and characterized DH31 and two DH31 GPCR variants, DH31-Ra and DH31-Rb, from spotted-wing drosophila, Drosophila suzukii, a globally prevalent vinegar fly causing severe damage to small fruits. Both GPCRs are active, but DH31-Ra is the dominant receptor based on gene expression analyses and DH31 peptide binding affinities. A notable difference between the two variants lies in 1) the GPCR structures of their C-termini and 2) the utilization of second messengers, and the amino acid sequences of the two variants are identical. DH31-Ra contains 12 additional amino acids, providing different intracellular C-terminal configurations. DH31-Ra utilizes both cAMP and Ca2+ as second messengers, whereas DH31-Rb utilizes only cAMP; this is the first time reported for an insect CT-like DH31 peptide. DH31 stimulated fluid secretion in D. suzukii adults, and secretion increased in a dose-dependent manner. However, when the fly was injected with a mixture of DH31 and CAPA, an anti-diuretic hormone, fluid secretion was suppressed. Here, we discuss the structures of the DH31 receptors and the differential signaling pathways, including second messengers, involved in fly diuresis. These findings provide fundamental insights into the characterization of D. suzukii DH31 and DH31-Rs, and facilitate the identification of potential biological targets for D. suzukii management.

A bibliometric analysis: Ca2+ fluxes and inflammatory phenotyping by flow cytometry in peripheral blood mononuclear cells

Background

The immune system, composed of organs, tissues, cells, and proteins, is the key to protecting the body from external biological attacks and inflammation. The latter occurs in several pathologies, such as cancers, type 1 diabetes, and human immunodeficiency virus infection. Immunophenotyping by flow cytometry is the method of choice for diagnosing these pathologies. Under inflammatory conditions, the peripheral blood mononuclear cells (PBMCs) are partially activated and generate intracellular pathways involving Ca2+-dependent signaling cascades leading to transcription factor expression. Ca2+ signaling is typically studied by microscopy in cell lines but can present some limitations to explore human PBMCs, where flow cytometry can be a good alternative.

Objective

In this review, we dived into the research field of inflammation and Ca2+ signaling in PBMCs. We aimed to investigate the structure and evolution of this field in a physio-pathological context, and then we focused our review on flow cytometry analysis of Ca2+ fluxes in PBMCs.

Methods

From 1984 to 2022, 3865 articles on inflammation and Ca2+ signaling in PBMCs were published, according to The Clarivate Web of Science (WOS) database used in this review. A bibliometric study was designed for this collection and consisted of a co-citation and bibliographic coupling analysis.

Results

The co-citation analysis was performed on 133 articles: 4 clusters highlighted the global context of Ca2+ homeostasis, including chemical probe development, identification of the leading players in Ca2+ signaling, and the link with chemokine production in immune cell function. Next, the bibliographic coupling analysis combined 998 articles in 8 clusters. This analysis outlined the mechanisms of PBMC activation, from signal integration to cellular response. Further explorations of the bibliographic coupling network, focusing on flow cytometry, revealed 21 articles measuring cytosolic Ca2+ in PBMCs, with only 5 since 2016. This final query showed that Ca2+ signaling analysis in human PBMCs using flow cytometry is still underdeveloped and investigates mainly the cytosolic Ca2+ compartment.

Conclusion

Our review uncovers remaining knowledge gaps of intracellular players involved in Ca2+ signaling in PBMCs, such as reticulum and mitochondria, and presents flow cytometry as a solid option to supplement gold-standard microscopy studies.

Orai3 Calcium Channel Contributes to Oral/Oropharyngeal Cancer Stemness through the Elevation of ID1 Expression

Emerging evidence indicates that intracellular calcium (Ca2+) levels and their regulatory proteins play essential roles in normal stem cell proliferation and differentiation. Cancer stem-like cells (CSCs) are subpopulations of cancer cells that retain characteristics similar to stem cells and play an essential role in cancer progression. Recent studies have reported that the Orai3 calcium channel plays an oncogenic role in human cancer. However, its role in CSCs remains underexplored. In this study, we explored the effects of Orai3 in the progression and stemness of oral/oropharyngeal squamous cell carcinoma (OSCC). During the course of OSCC progression, the expression of Orai3 exhibited a stepwise augmentation. Notably, Orai3 was highly enriched in CSC populations of OSCC. Ectopic Orai3 expression in non-tumorigenic immortalized oral epithelial cells increased the intracellular Ca2+ levels, acquiring malignant growth and CSC properties. Conversely, silencing of the endogenous Orai3 in OSCC cells suppressed the CSC phenotype, indicating a pivotal role of Orai3 in CSC regulation. Moreover, Orai3 markedly increased the expression of inhibitor of DNA binding 1 (ID1), a stemness transcription factor. Orai3 and ID1 exhibited elevated expression within CSCs compared to their non-CSC counterparts, implying the functional importance of the Orai3/ID1 axis in CSC regulation. Furthermore, suppression of ID1 abrogated the CSC phenotype in the cell with ectopic Orai3 overexpression and OSCC. Our study reveals that Orai3 is a novel functional CSC regulator in OSCC and further suggests that Orai3 plays an oncogenic role in OSCC by promoting cancer stemness via ID1 upregulation.

Regulation of store-operated Ca2+ entry by IP3 receptors independent of their ability to release Ca2

Loss of endoplasmic reticular (ER) Ca2+ activates store-operated Ca2+ entry (SOCE) by causing the ER localized Ca2+ sensor STIM to unfurl domains that activate Orai channels in the plasma membrane at membrane contact sites (MCS). Here, we demonstrate a novel mechanism by which the inositol 1,4,5 trisphosphate receptor (IP3R), an ER-localized IP3-gated Ca2+ channel, regulates neuronal SOCE. In human neurons, SOCE evoked by pharmacological depletion of ER-Ca2+ is attenuated by loss of IP3Rs, and restored by expression of IP3Rs even when they cannot release Ca2+, but only if the IP3Rs can bind IP3. Imaging studies demonstrate that IP3Rs enhance association of STIM1 with Orai1 in neuronal cells with empty stores; this requires an IP3-binding site, but not a pore. Convergent regulation by IP3Rs, may tune neuronal SOCE to respond selectively to receptors that generate IP3.

Adhesion to laminin-1 and collagen IV induces the formation of Ca2+ microdomains that sensitize mouse T cells for activation

During an immune response, T cells migrate from blood vessel walls into inflamed tissues by migrating across the endothelium and through extracellular matrix (ECM). Integrins facilitate T cell binding to endothelial cells and ECM proteins. Here, we report that Ca²⁺ microdomains observed in the absence of T cell receptor (TCR)/CD3 stimulation are initial signaling events triggered by adhesion to ECM proteins that increase the sensitivity of primary murine T cells to activation. Adhesion to the ECM proteins collagen IV and laminin-1 increased the number of Ca²⁺ microdomains in a manner dependent on the kinase FAK, phospholipase C (PLC), and all three inositol 1,4,5-trisphosphate receptor (IP₃R) subtypes and promoted the nuclear translocation of the transcription factor NFAT-1. Mathematical modeling predicted that the formation of adhesion-dependent Ca²⁺ microdomains required the concerted activity of two to six IP₃Rs and ORAI1 channels to achieve the increase in the Ca²⁺ concentration in the ER-plasma membrane junction that was observed experimentally and that required SOCE. Further, adhesion-dependent Ca²⁺ microdomains were important for the magnitude of the TCR-induced activation of T cells on collagen IV as assessed by the global Ca²⁺ response and NFAT-1 nuclear translocation. Thus, adhesion to collagen IV and laminin-1 sensitizes T cells through a mechanism involving the formation of Ca²⁺ microdomains, and blocking this low-level sensitization decreases T cell activation upon TCR engagement.

Neural stem cell self-renewal stimulation by store-operated calcium entries in adult mouse area postrema: influence of leptin

Neural stem cells (NSCs) persist in specific brain germinative niches and sustain neurogenesis throughout life in adult mammals. In addition to the two major stem cell niches in the subventricular zone and the hippocampal dentate gyrus, the area postrema located in the brainstem has been identified as a neurogenic zone as well. NSCs are regulated by signals from the microenvironment that adjust stem cell response to the needs of the organism. Evidence accumulated over the past decade indicates that Ca²⁺ channels play pivotal functions in NSC maintenance. In this study, we explored in area postrema NSCs the presence and roles of a subset of Ca²⁺ channels, the store-operated Ca²⁺ channels (SOCs) that have the capacity to transduce extracellular signals into Ca²⁺ signals. Our data show that NSCs derived from the area postrema express TRPC1 and Orai1, known to form SOCs, as well as their activator STIM1. Ca²⁺ imaging indicated that NSCs exhibit store-operated Ca²⁺ entries (SOCEs). Pharmacological blockade of SOCEs with SKF-96365, YM-58483 (also known as BTP2) or GSK-7975A resulted in decreased NSC proliferation and self-renewal, indicating a major role for SOCs in maintaining NSC activity within the area postrema. Furthermore, our results show that leptin, an adipose tissue-derived hormone whose ability to control energy homeostasis is dependent on the area postrema, decreased SOCEs and reduced self-renewal of NSCs in the area postrema. As aberrant SOC function has been linked to an increasing number of diseases, including brain disorders, our study opens new perspectives for NSCs in brain pathophysiology.

Ca2+ release or Ca2+ entry, that is the question: what governs Ca2+ oscillations in pancreatic β cells?

The standard model for Ca2+ oscillations in insulin-secreting pancreatic β cells centers on Ca2+ entry through voltage-activated Ca2+ channels. These work in combination with ATP-dependent K+ channels, which are the bridge between the metabolic state of the cells and plasma membrane potential. This partnership underlies the ability of the β cells to secrete insulin appropriately on a minute-to-minute time scale to control whole body plasma glucose. Though this model, developed over more than 40 years through many cycles of experimentation and mathematical modeling, has been very successful, it has been challenged by a hypothesis that calcium-induced calcium release from the endoplasmic reticulum through ryanodine or inositol trisphosphate (IP3) receptors is instead the key driver of islet oscillations. We show here that the alternative model is in fact incompatible with a large body of established experimental data and that the new observations offered in support of it can be better explained by the standard model.

Post-injury Inhibition of Endothelin-1 Dependent Renal Vasoregulation Mitigates Rhabdomyolysis-Induced Acute Kidney Injury

In patients with rhabdomyolysis, the overwhelming release of myoglobin into the circulation is the primary cause of kidney injury. Myoglobin causes direct kidney injury as well as severe renal vasoconstriction. An increase in renal vascular resistance (RVR) results in renal blood flow (RBF) and glomerular filtration rate (GFR) reduction, tubular injury, and acute kidney injury (AKI). The mechanisms that underlie rhabdomyolysis-induced AKI are not fully understood but may involve the local production of vasoactive mediators in the kidney. Studies have shown that myoglobin stimulates endothelin-1 (ET-1) production in glomerular mesangial cells. Circulating ET-1 is also increased in rats subjected to glycerol-induced rhabdomyolysis. However, the upstream mechanisms of ET-1 production and downstream effectors of ET-1 actions in rhabdomyolysis-induced AKI remain unclear. Vasoactive ET-1 is generated by ET converting enzyme 1 (ECE-1)-induced proteolytic processing of inactive big ET to biologically active peptides. The downstream ion channel effectors of ET-1-induced vasoregulation include the transient receptor potential cation channel, subfamily C member 3 (TRPC3). This study demonstrates that glycerol-induced rhabdomyolysis in Wistar rats promotes ECE-1-dependent ET-1 production, RVR increase, GFR decrease, and AKI. Rhabdomyolysis-induced increases in RVR and AKI in the rats were attenuated by post-injury pharmacological inhibition of ECE-1, ET receptors, and TRPC3 channels. CRISPR/Cas9-mediated knockout of TRPC3 channels attenuated ET-1-induced renal vascular reactivity and rhabdomyolysis-induced AKI. These findings suggest that ECE-1-driven ET-1 production and downstream activation of TRPC3-dependent renal vasoconstriction contribute to rhabdomyolysis-induced AKI. Hence, post-injury inhibition of ET-1-mediated renal vasoregulation may provide therapeutic targets for rhabdomyolysis-induced AKI.

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.

Phosphatidylinositol 4,5-bisphosphate and calcium at ER-PM junctions - Complex interplay of simple messengers

Endoplasmic reticulum-plasma membrane contact sites (ER-PM MCS) are a specialised domain involved in the control of Ca²⁺ dynamics and various Ca²⁺-dependent cellular processes. Intracellular Ca²⁺ signals are broadly supported by Ca²⁺ release from intracellular Ca²⁺ channels such as inositol 1,4,5-trisphosphate receptors (IP₃Rs) and subsequent store-operated Ca²⁺ entry (SOCE) across the PM to replenish store content. IP₃Rs sit in close proximity to the PM where they can easily access newly synthesised IP₃, interact with binding partners such as actin, and localise adjacent to ER-PM MCS populated by the SOCE machinery, STIM1-2 and Orai1-3, to possibly form a locally regulated unit of Ca²⁺ influx. PtdIns(4,5)P₂ is a multiplex regulator of Ca²⁺ signalling at the ER-PM MCS interacting with multiple proteins at these junctions such as actin and STIM1, whilst also being consumed as a substrate for phospholipase C to produce IP₃ in response to extracellular stimuli. In this review, we consider the mechanisms regulating the synthesis and turnover of PtdIns(4,5)P₂ via the phosphoinositide cycle and its significance for sustained signalling at the ER-PM MCS. Furthermore, we highlight recent insights into the role of PtdIns(4,5)P₂ in the spatiotemporal organization of signalling at ER-PM junctions and raise outstanding questions on how this multi-faceted regulation occurs.

Identification of a Novel Small Molecule That Enhances the Release of Extracellular Vesicles with Immunostimulatory Potency via Induction of Calcium Influx

Extracellular vesicles (EVs) transfer antigens and immunomodulatory molecules in immunologic synapses as a part of intracellular communication, and EVs equipped with immunostimulatory functions have been utilized for vaccine formulation. Hence, we sought small-molecule compounds that increase immunostimulatory EVs released by antigen-presenting dendritic cells (DCs) for enhancement of vaccine immunogenicity. We previously performed high-throughput screening on a 28K compound library using three THP-1 reporter cell lines with CD63 Turbo-Luciferase, NF-κB, and interferon-sensitive response element (ISRE) reporter constructs, respectively. Because intracellular Ca2+ elevation enhances EV release, we screened 80 hit compounds and identified compound 634 as a Ca2+ influx inducer. 634 enhanced EV release in murine bone marrow-derived dendritic cells (mBMDCs) and increased costimulatory molecule expression on the surface of EVs and the parent cells. EVs isolated from 634-treated mBMDCs induced T cell proliferation in the presence of antigenic peptides. To assess the roles of intracellular Ca2+ elevation in immunostimulatory EV release, we performed structure-activity relationship (SAR) studies of 634. The analogues that retained the ability to induce Ca2+ influx induced more EVs with immunostimulatory properties from mBMDCs than did those that lacked the ability to induce Ca2+ influx. The levels of Ca2+ induction of synthesized analogues correlated with the numbers of EVs released and costimulatory molecule expression on the parent cells. Collectively, our study presents that a small molecule, 634, enhances the release of EVs with immunostimulatory potency via induction of Ca2+ influx. This agent is a novel tool for EV-based immune studies and vaccine development.

S417 in the CC3 region of STIM1 is critical for STIM1-Orai1 binding and CRAC channel activation

Store-operated Ca2+ entry (SOCE) is a universal Ca2+ influx pathway that is important for the function of many cell types. SOCE is controlled by the interaction of the ER Ca2+ sensor STIM1 with the plasma membrane Ca2+ channel Orai1. S417 is located in the third coiled-coil (CC3) domain of the C-terminus of STIM1. We found that single-point mutation of this residue (S417G) abolished STIM1 C-terminus interactions with Orai1. Mutation of S417 also abolished CAD-Orai1 binding and Orai1 channel activation, eliminated STIM1 puncta formation, and co-localization with Orai1 and SOCE. 2-APB was found to restore the binding of the STIM1 C-terminus mutant (S417G) to Orai1 and dose-dependently activate Orai1 channel. Both CBD and NBD of Orai1 are required for 2-APB-induced coupling between the Orai1 and STIM1 C-terminus mutant (S417G) and CRAC channel activation. We also demonstrated that 2-APB led to delayed activation of Orai1-K85E channel, although Orai1-K85E obviously impairs 2-APB-induced STIM1 C-terminus mutant (S417G)-Orai1 coupling. Our results suggest S417 in the CC3 domain of STIM1 is essential for STIM1-Orai1 binding and CRAC channel activation.

The Molecular Heterogeneity of Store-Operated Ca2+ Entry in Vascular Endothelial Cells: The Different roles of Orai1 and TRPC1/TRPC4 Channels in the Transition from Ca2+-Selective to Non-Selective Cation Currents

Store-operated Ca²⁺ entry (SOCE) is activated in response to the inositol-1,4,5-trisphosphate (InsP₃)-dependent depletion of the endoplasmic reticulum (ER) Ca²⁺ store and represents a ubiquitous mode of Ca²⁺ influx. In vascular endothelial cells, SOCE regulates a plethora of functions that maintain cardiovascular homeostasis, such as angiogenesis, vascular tone, vascular permeability, platelet aggregation, and monocyte adhesion. The molecular mechanisms responsible for SOCE activation in vascular endothelial cells have engendered a long-lasting controversy. Traditionally, it has been assumed that the endothelial SOCE is mediated by two distinct ion channel signalplexes, i.e., STIM1/Orai1 and STIM1/Transient Receptor Potential Canonical 1(TRPC1)/TRPC4. However, recent evidence has shown that Orai1 can assemble with TRPC1 and TRPC4 to form a non-selective cation channel with intermediate electrophysiological features. Herein, we aim at bringing order to the distinct mechanisms that mediate endothelial SOCE in the vascular tree from multiple species (e.g., human, mouse, rat, and bovine). We propose that three distinct currents can mediate SOCE in vascular endothelial cells: (1) the Ca²⁺-selective Ca²⁺-release activated Ca²⁺ current (I_CRAC), which is mediated by STIM1 and Orai1; (2) the store-operated non-selective current (I_SOC), which is mediated by STIM1, TRPC1, and TRPC4; and (3) the moderately Ca²⁺-selective, I_CRAC-like current, which is mediated by STIM1, TRPC1, TRPC4, and Orai1.

Celastrol inhibits store operated calcium entry and suppresses psoriasis

Introduction: Psoriasis is an inflammatory autoimmune skin disease that is hard to cure and prone to relapse. Currently available global immunosuppressive agents for psoriasis may cause severe side effects, thus it is crucial to identify new therapeutic reagents and druggable signaling pathways for psoriasis. Methods: To check the effects of SOCE inhibitors on psoriasis, we used animal models, biochemical approaches, together with various imaging techniques, including calcium, confocal and FRET imaging. Results and discussion: Store operated calcium (Ca²⁺) entry (SOCE), mediated by STIM1 and Orai1, is crucial for the function of keratinocytes and immune cells, the two major players in psoriasis. Here we showed that a natural compound celastrol is a novel SOCE inhibitor, and it ameliorated the skin lesion and reduced PASI scores in imiquimod-induced psoriasis-like mice. Celastrol dose- and time-dependently inhibited SOCE in HEK cells and HaCaT cells, a keratinocyte cell line. Mechanistically, celastrol inhibited SOCE via its actions both on STIM1 and Orai1. It inhibited Ca²⁺ entry through constitutively-active Orai1 mutants independent of STIM1. Rather than blocking the conformational switch and oligomerization of STIM1 during SOCE activation, celastrol diminished the transition from oligomerized STIM1 into aggregates, thus locking STIM1 in a partially active state. As a result, it abolished the functional coupling between STIM1 and Orai1, diminishing SOCE signals. Overall, our findings identified a new SOCE inhibitor celastrol that suppresses psoriasis, suggesting that SOCE pathway may serve as a new druggable target for treating psoriasis.

Ion channels and channelopathies in glomeruli

An essential step in renal function entails the formation of an ultrafiltrate that is delivered to the renal tubules for subsequent processing. This process, known as glomerular filtration, is controlled by intrinsic regulatory systems and by paracrine, neuronal, and endocrine signals that converge onto glomerular cells. In addition, the characteristics of glomerular fluid flow, such as the glomerular filtration rate and the glomerular filtration fraction, play an important role in determining blood flow to the rest of the kidney. Consequently, disease processes that initially affect glomeruli are the most likely to lead to end-stage kidney failure. The cells that comprise the glomerular filter, especially podocytes and mesangial cells, express many different types of ion channels that regulate intrinsic aspects of cell function and cellular responses to the local environment, such as changes in glomerular capillary pressure. Dysregulation of glomerular ion channels, such as changes in TRPC6, can lead to devastating glomerular diseases, and a number of channels, including TRPC6, TRPC5, and various ionotropic receptors, are promising targets for drug development. This review discusses glomerular structure and glomerular disease processes. It also describes the types of plasma membrane ion channels that have been identified in glomerular cells, the physiological and pathophysiological contexts in which they operate, and the pathways by which they are regulated and dysregulated. The contributions of these channels to glomerular disease processes, such as focal segmental glomerulosclerosis (FSGS) and diabetic nephropathy, as well as the development of drugs that target these channels are also discussed.