Lymphocyte calcium signaling from membrane to nucleus

A multiple-oscillator mechanism underlies antigen-induced Ca2+ oscillations in Jurkat T-cells

T-cell receptor stimulation triggers cytosolic Ca2+ signaling by inositol-1,4,5-trisphosphate (IP3)-mediated Ca2+ release from the endoplasmic reticulum (ER) and Ca2+ entry through Ca2+ release-activated Ca2+ (CRAC) channels gated by ER-located stromal-interacting molecules (STIM1/2). Physiologically, cytosolic Ca2+ signaling manifests as regenerative Ca2+ oscillations, which are critical for nuclear factor of activated T-cells-mediated transcription. In most cells, Ca2+ oscillations are thought to originate from IP3 receptor-mediated Ca2+ release, with CRAC channels indirectly sustaining them through ER refilling. Here, experimental and computational evidence support a multiple-oscillator mechanism in Jurkat T-cells whereby both IP3 receptor and CRAC channel activities oscillate and directly fuel antigen-evoked Ca2+ oscillations, with the CRAC channel being the major contributor. KO of either STIM1 or STIM2 significantly reduces CRAC channel activity. As such, STIM1 and STIM2 synergize for optimal Ca2+ oscillations and activation of nuclear factor of activated T-cells 1 and are essential for ER refilling. The loss of both STIM proteins abrogates CRAC channel activity, drastically reduces ER Ca2+ content, severely hampers cell proliferation and enhances cell death. These results clarify the mechanism and the contribution of STIM proteins to Ca2+ oscillations in T-cells.

The Lysosomal Calcium Channel TRPML1 Maintains Mitochondrial Fitness in NK Cells through Interorganelle Cross-Talk

Cytotoxic lymphocytes eliminate cancer cells through the release of lytic granules, a specialized form of secretory lysosomes. This compartment is part of the pleomorphic endolysosomal system and is distinguished by its highly dynamic Ca2+ signaling machinery. Several transient receptor potential (TRP) calcium channels play essential roles in endolysosomal Ca2+ signaling and ensure the proper function of these organelles. In this study, we examined the role of TRPML1 (TRP cation channel, mucolipin subfamily, member 1) in regulating the homeostasis of secretory lysosomes and their cross-talk with mitochondria in human NK cells. We found that genetic deletion of TRPML1, which localizes to lysosomes in NK cells, led to mitochondrial fragmentation with evidence of collapsed mitochondrial cristae. Consequently, TRPML1-/- NK92 (NK92ML1-/-) displayed loss of mitochondrial membrane potential, increased reactive oxygen species stress, reduced ATP production, and compromised respiratory capacity. Using sensitive organelle-specific probes, we observed that mitochondria in NK92ML1-/- cells exhibited evidence of Ca2+ overload. Moreover, pharmacological activation of the TRPML1 channel in primary NK cells resulted in upregulation of LC3-II, whereas genetic deletion impeded autophagic flux and increased accumulation of dysfunctional mitochondria. Thus, TRPML1 impacts autophagy and clearance of damaged mitochondria. Taken together, these results suggest that an intimate interorganelle communication in NK cells is orchestrated by the lysosomal Ca2+ channel TRPML1.

Clinical Staphylococcus aureus inhibits human T-cell activity through interaction with the PD-1 receptor

IMPORTANCE

Therapies that target and aid the host immune defense to repel cancer cells or invading pathogens are rapidly emerging. Antibiotic resistance is among the largest threats to human health globally. Staphylococcus aureus (S. aureus) is the most common bacterial infection, and it poses a challenge to the healthcare system due to its significant ability to develop resistance toward current available therapies. In long-term infections, S. aureus further adapt to avoid clearance by the host immune defense. In this study, we discover a new interaction that allows S. aureus to avoid elimination by the immune system, which likely supports its persistence in the host. Moreover, we find that blocking the specific receptor (PD-1) using antibodies significantly relieves the S. aureus-imposed inhibition. Our findings suggest that therapeutically targeting PD-1 is a possible future strategy for treating certain antibiotic-resistant staphylococcal infections.

Spatiotemporal characteristics of P-selectin-induced β2 integrin activation of human neutrophils under flow

Activation of integrins is crucial for recruitment of flowing leukocytes to inflammatory or injured vascular sites, but their spatiotemporal characteristics are incompletely understood. We discovered that β2-integrin activation over the entire surface of neutrophils on immobilized P-selectin occurred via mitogen-activated protein kinase (MAPK) or non-MAPK signaling with a minute-level timescale in a force-dependent manner. In flow, MAPK signaling required intracellular Ca2+ release to activate integrin within 2 min. Integrin activation via non-MAPK signaling occurred first locally in the vicinity of ligated P-selectin glycoprotein ligand-1 (PSGL-1) within sub-seconds, and then over the entire cell surface within 1 min in an extracellular Ca2+ influx-dependent manner. The transition from a local (but rapid) to global (but slow) activation mode was triggered by ligating the freshly activated integrin. Lipid rafts, moesin, actin, and talin were involved in non-MAPK signaling. Fluid loads had a slight effect on local integrin activation with a second-level timescale, but served as enhancers of global integrin activation.

Orai1 Inhibitors as Potential Treatments for Pulmonary Arterial Hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH) is characterized by progressive distal pulmonary artery (PA) obstruction, leading to right ventricular hypertrophy and failure. Exacerbated intracellular calcium (Ca²⁺) signaling contributes to abnormalities in PA smooth muscle cells (PASMCs), including aberrant proliferation, apoptosis resistance, exacerbated migration, and arterial contractility. Store-operated Ca²⁺ entry is involved in Ca²⁺ homeostasis in PASMCs, but its properties in PAH are unclear.

METHODS

Using a combination of Ca²⁺ imaging, molecular biology, in vitro, ex vivo, and in vivo approaches, we investigated the roles of the Orai1 SOC channel in PA remodeling in PAH and determined the consequences of pharmacological Orai1 inhibition in vivo using experimental models of pulmonary hypertension (PH).

RESULTS

Store-operated Ca²⁺ entry and Orai1 mRNA and protein were increased in human PASMCs (hPASMCs) from patients with PAH (PAH-hPASMCs). We found that MEK1/2 (mitogen-activated protein kinase kinase 1/2), NFAT (nuclear factor of activated T cells), and NFκB (nuclear factor-kappa B) contribute to the upregulation of Orai1 expression in PAH-hPASMCs. Using small interfering RNA (siRNA) and Orai1 inhibitors, we found that Orai1 inhibition reduced store-operated Ca²⁺ entry, mitochondrial Ca²⁺ uptake, aberrant proliferation, apoptosis resistance, migration, and excessive calcineurin activity in PAH-hPASMCs. Orai1 inhibitors reduced agonist-evoked constriction in human PAs. In experimental rat models of PH evoked by chronic hypoxia, monocrotaline, or Sugen/hypoxia, administration of Orai1 inhibitors (N-{4-[3,5-bis(Trifluoromethyl)-1H-pyrazol-1-yl]phenyl}-4-methyl-1,2,3-thiadiazole-5-carboxamide [BTP2], 4-(2,5-dimethoxyphenyl)-N-[(pyridin-4-yl)methyl]aniline [JPIII], or 5J4) protected against PH.

CONCLUSIONS

In human PAH and experimental PH, Orai1 expression and activity are increased. Orai1 inhibition normalizes the PAH-hPASMCs phenotype and attenuates PH in rat models. These results suggest that Orai1 should be considered as a relevant therapeutic target for PAH.

AKAP79 Orchestrates a Cyclic AMP Signalosome Adjacent to Orai1 Ca2+ Channels

To ensure specificity of response, eukaryotic cells often restrict signalling molecules to sub-cellular regions. The Ca²⁺ nanodomain is a spatially confined signal that arises near open Ca²⁺ channels. Ca²⁺ nanodomains near store-operated Orai1 channels stimulate the protein phosphatase calcineurin, which activates the transcription factor NFAT1, and both enzyme and target are initially attached to the plasma membrane through the scaffolding protein AKAP79. Here, we show that a cAMP signalling nexus also forms adjacent to Orai1. Protein kinase A and phosphodiesterase 4, an enzyme that rapidly breaks down cAMP, both associate with AKAP79 and realign close to Orai1 after stimulation. PCR and mass spectrometry failed to show expression of Ca²⁺-activated adenylyl cyclase 8 in HEK293 cells, whereas the enzyme was observed in neuronal cell lines. FRET and biochemical measurements of bulk cAMP and protein kinase A activity consistently failed to show an increase in adenylyl cyclase activity following even a large rise in cytosolic Ca²⁺. Furthermore, expression of AKAP79-CUTie, a cAMP FRET sensor tethered to AKAP79, did not report a rise in cAMP after stimulation, despite AKAP79 association with Orai1. Hence, HEK293 cells do not express functional active Ca²⁺-activated adenylyl cyclases including adenylyl cyclase 8. Our results show that two ancient second messengers are independently generated in nanodomains close to Orai1 Ca²⁺ channels.

Bioactivity-guided isolation of immunomodulatory compounds from the fruits of Ligustrum lucidum

ETHNOPHARMACOLOGICAL RELEVANCE

The fruits of Ligustrum lucidum (FLL) W.T. Aiton (Oleaceae) is included in the 2020 "Chinese Pharmacopoeia" and is widely used in traditional Chinese medicine as a tonic. In recent years, FLL has been reported to improve immune function, but the bioactive compounds and mechanisms of FLL remain poorly characterized.

AIM OF THE STUDY

To identify FFL compounds with strong immune activity and explore their molecular mechanisms.

MATERIALS AND METHODS

The phagocytic activity of RAW264.7 macrophages and proliferation activity of spleen lymphocytes were used to guide the isolation of bioactive compounds from FLL extracts. Lymphocyte subpopulations, Ca²⁺ concentrations, and surface molecule expression were analyzed using flow cytometry. Cytokine secretion was examined using ELISA. FITC-OVA uptake was observed using fluorescence microscopy. NF-κB activation was analyzed using western blotting.

RESULTS

The extraction and isolation produced ten compounds, namely oleuropeinic acid, nuezhenide, isonuezhenide, salidroside, isoligustrosidic acid, ligulucidumosides A, 8(E)-nuezhenide, hydroxytyrosol, oleuropein, and p-hydroxyphenethyl 7-β-D-glucosideelenolic acid ester were isolated and identified from FLL-Bu-30%. Immunoactivity experiments showed that hydroxytyrosol had the strongest macrophage phagocytotic and lymphocyte proliferation-promoting activities. Further studies showed that hydroxytyrosol could significantly enhance lymphocyte subsets CD3⁺, CD4⁺/CD8⁺, and CD3⁺CD4^-CD8^-, promote IL-4, IFN-γ, and TNF-α secretion, and increase intracellular Ca²⁺ concentrations. In addition, the results from RAW264.7 macrophages showed that hydroxytyrosol increased FITC-OVA uptake, induced TNF-α and IL-1β production, upregulated MHC-II, CD80, and CD86 expression, promoted cytoplasmic IκB-α degradation, and increased nuclear NF-κB p65 levels.

CONCLUSION

Our study provides substantial evidence regarding the mechanism of the immunomodulatory effects of compounds from FLL.

The N terminus of Orai1 couples to the AKAP79 signaling complex to drive NFAT1 activation by local Ca2+ entry

To avoid conflicting and deleterious outcomes, eukaryotic cells often confine second messengers to spatially restricted subcompartments. The smallest signaling unit is the Ca2+ nanodomain, which forms when Ca2+ channels open. Ca2+ nanodomains arising from store-operated Orai1 Ca2+ channels stimulate the protein phosphatase calcineurin to activate the transcription factor nuclear factor of activated T cells (NFAT). Here, we show that NFAT1 tethered directly to the scaffolding protein AKAP79 (A-kinase anchoring protein 79) is activated by local Ca2+ entry, providing a mechanism to selectively recruit a transcription factor. We identify the region on the N terminus of Orai1 that interacts with AKAP79 and demonstrate that this site is essential for physiological excitation-transcription coupling. NMR structural analysis of the AKAP binding domain reveals a compact shape with several proline-driven turns. Orai2 and Orai3, isoforms of Orai1, lack this region and therefore are less able to engage AKAP79 and activate NFAT. A shorter, naturally occurring Orai1 protein that arises from alternative translation initiation also lacks the AKAP79-interaction site and fails to activate NFAT1. Interfering with Orai1-AKAP79 interaction suppresses cytokine production, leaving other Ca2+ channel functions intact. Our results reveal the mechanistic basis for how a subtype of a widely expressed Ca2+ channel is able to activate a vital transcription pathway and identify an approach for generation of immunosuppressant drugs.

Ca2+ Microdomains, Calcineurin and the Regulation of Gene Transcription

Ca²⁺ ions function as second messengers regulating many intracellular events, including neurotransmitter release, exocytosis, muscle contraction, metabolism and gene transcription. Cells of a multicellular organism express a variety of cell-surface receptors and channels that trigger an increase of the intracellular Ca²⁺ concentration upon stimulation. The elevated Ca²⁺ concentration is not uniformly distributed within the cytoplasm but is organized in subcellular microdomains with high and low concentrations of Ca²⁺ at different locations in the cell. Ca²⁺ ions are stored and released by intracellular organelles that change the concentration and distribution of Ca²⁺ ions. A major function of the rise in intracellular Ca²⁺ is the change of the genetic expression pattern of the cell via the activation of Ca²⁺-responsive transcription factors. It has been proposed that Ca²⁺-responsive transcription factors are differently affected by a rise in cytoplasmic versus nuclear Ca²⁺. Moreover, it has been suggested that the mode of entry determines whether an influx of Ca²⁺ leads to the stimulation of gene transcription. A rise in cytoplasmic Ca²⁺ induces an intracellular signaling cascade, involving the activation of the Ca²⁺/calmodulin-dependent protein phosphatase calcineurin and various protein kinases (protein kinase C, extracellular signal-regulated protein kinase, Ca²⁺/calmodulin-dependent protein kinases). In this review article, we discuss the concept of gene regulation via elevated Ca²⁺ concentration in the cytoplasm and the nucleus, the role of Ca²⁺ entry and the role of enzymes as signal transducers. We give particular emphasis to the regulation of gene transcription by calcineurin, linking protein dephosphorylation with Ca²⁺ signaling and gene expression.

Sodium Transporters in Human Health and Disease

Sodium (Na+) electrochemical gradients established by Na+/K+ ATPase activity drives the transport of ions, minerals, and sugars in both excitable and non-excitable cells. Na+-dependent transporters can move these solutes in the same direction (cotransport) or in opposite directions (exchanger) across both the apical and basolateral plasma membranes of polarized epithelia. In addition to maintaining physiological homeostasis of these solutes, increases and decreases in sodium may also initiate, directly or indirectly, signaling cascades that regulate a variety of intracellular post-translational events. In this review, we will describe how the Na+/K+ ATPase maintains a Na+ gradient utilized by multiple sodium-dependent transport mechanisms to regulate glucose uptake, excitatory neurotransmitters, calcium signaling, acid-base balance, salt-wasting disorders, fluid volume, and magnesium transport. We will discuss how several Na+-dependent cotransporters and Na+-dependent exchangers have significant roles in human health and disease. Finally, we will discuss how each of these Na+-dependent transport mechanisms have either been shown or have the potential to use Na+ in a secondary role as a signaling molecule.

The crosstalk between cardiomyocyte calcium and inflammasome signaling pathways in atrial fibrillation

Atrial fibrillation (AF) is the most frequent arrhythmia in adults. The prevalence and incidence of AF is going to increase substantially over the next few decades. Because AF increases the risk of stroke, heart failure, dementia, and others, it severely impacts the quality of life, morbidity, and mortality. Although the pathogenesis of AF is multifaceted and complex, focal ectopic activity and reentry are considered as the fundamental proarrhythmic mechanisms underlying AF development. Over the past 2 decades, large amount of evidence points to the key role of intracellular Ca²⁺ dysregulation in both initiation and maintenance of AF. More recently, emerging evidence reveal that NLRP3 (NACHT, LRR, PYD domain-containing 3) inflammasome pathway contributes to the substrate of both triggered activity and reentry, ultimately promoting AF. In this article, we review the current state of knowledge on Ca²⁺ signaling and NLRP3 inflammasome activity in AF. We also discuss the potential crosstalk between these two quintessential contributors to AF promotion.

New Insights on the Role of TRP Channels in Calcium Signalling and Immunomodulation: Review of Pathways and Implications for Clinical Practice

Calcium is the most abundant mineral in the human body and is central to many physiological processes, including immune system activation and maintenance. Studies continue to reveal the intricacies of calcium signalling within the immune system. Perhaps the most well-understood mechanism of calcium influx into cells is store-operated calcium entry (SOCE), which occurs via calcium release-activated channels (CRACs). SOCE is central to the activation of immune system cells; however, more recent studies have demonstrated the crucial role of other calcium channels, including transient receptor potential (TRP) channels. In this review, we describe the expression and function of TRP channels within the immune system and outline associations with murine models of disease and human conditions. Therefore, highlighting the importance of TRP channels in disease and reviewing potential. The TRP channel family is significant, and its members have a continually growing number of cellular processes. Within the immune system, TRP channels are involved in a diverse range of functions including T and B cell receptor signalling and activation, antigen presentation by dendritic cells, neutrophil and macrophage bactericidal activity, and mast cell degranulation. Not surprisingly, these channels have been linked to many pathological conditions such as inflammatory bowel disease, chronic fatigue syndrome and myalgic encephalomyelitis, atherosclerosis, hypertension and atopy.

K+ and Ca2+ Channels Regulate Ca2+ Signaling in Chondrocytes: An Illustrated Review

An improved understanding of fundamental physiological principles and progressive pathophysiological processes in human articular joints (e.g., shoulders, knees, elbows) requires detailed investigations of two principal cell types: synovial fibroblasts and chondrocytes. Our studies, done in the past 8–10 years, have used electrophysiological, Ca²⁺ imaging, single molecule monitoring, immunocytochemical, and molecular methods to investigate regulation of the resting membrane potential (E_R) and intracellular Ca²⁺ levels in human chondrocytes maintained in 2-D culture. Insights from these published papers are as follows: (1) Chondrocyte preparations express a number of different ion channels that can regulate their E_R. (2) Understanding the basis for E_R requires knowledge of (a) the presence or absence of ligand (ATP/histamine) stimulation and (b) the extraordinary ionic composition and ionic strength of synovial fluid. (3) In our chondrocyte preparations, at least two types of Ca²⁺-activated K⁺ channels are expressed and can significantly hyperpolarize E_R. (4) Accounting for changes in E_R can provide insights into the functional roles of the ligand-dependent Ca²⁺ influx through store-operated Ca²⁺ channels. Some of the findings are illustrated in this review. Our summary diagram suggests that, in chondrocytes, the K⁺ and Ca²⁺ channels are linked in a positive feedback loop that can augment Ca²⁺ influx and therefore regulate lubricant and cytokine secretion and gene transcription.

Calcium-responsive liposomes: Toward ion-mediated targeted drug delivery

Liposomes are clinically approved supramolecular drug delivery platforms due to their ability to enhance the pharmacokinetic properties of encapsulated therapeutic agents. A key point for advancing liposomal drug delivery would be to control the timing and location of cargo release to maximize drug potency and minimize side effects. Toward this end, triggered release approaches have been developed that exploit either pathophysiological stimuli (passive release) including pH or external stimuli (active release) such as light. Here, we present a novel approach for triggering release of contents from liposomes driven by increased calcium at target sites, which plays an important role in biology related to certain diseases. In this chapter, we provide detailed experimental procedures for this project, including synthesis of calcium-responsive lipid switch 1, evaluation of dye release properties and selectivity via fluorescence-based release assays as well as studies of morphology changes during release process by dynamic light scattering (DLS) and scanning transmission electron microscopy (STEM).

Beyond the CRAC: Diversification of ion signaling in B cells

Although calcium signaling and the important role of calcium release–activated calcium channels is well recognized in the context of immune cell signaling, there is a vast diversity of ion channels and transporters that regulate the entry of ions beyond calcium, including magnesium, zinc, potassium, sodium, and chloride. These ions play a critical role in numerous metabolic and cellular processes. The importance of ions in human health and disease is illustrated by the identification of primary immunodeficiencies in patients with mutations in genes encoding ion channels and transporters, as well as the immunological defects observed in individuals with nutritional ion deficiencies. Despite progress in identifying the important role of ions in immune cell development and activation, we are still in the early stages of exploring the diversity of ion channels and transporters and mechanistically understanding the role of these ions in immune cell biology. Here, we review the biology of ion signaling in B cells and the identification of critical ion channels and transporters in B‐cell development, activation, and differentiation into effector cells. Elucidating the role of ion channels and transporters in immune cell signaling is critical for expanding the repertoire of potential therapeutics for the treatment of immune disorders. Moreover, increased understanding of the role of ions in immune cell function will enhance our understanding of the potentially serious consequences of ion deficiencies in human health and disease.

Creating a New Cancer Therapeutic Agent by Targeting the Interaction between Bcl-2 and IP3 Receptors

Bcl-2 is a member of a family of proteins that regulate cell survival. Expression of Bcl-2 is aberrantly elevated in many types of cancer. Within cells of the immune system, Bcl-2 has a physiological role in regulating immune responses. However, in cancers arising from cells of the immune system Bcl-2 promotes cell survival and proliferation. This review summarizes discoveries over the past 30 years that have elucidated Bcl-2's role in the normal immune system, including its actions in regulating calcium (Ca²⁺) signals necessary for the immune response, and for Ca²⁺-mediated apoptosis at the end of an immune response. How Bcl-2 modulates the release of Ca²⁺ from intracellular stores via inositol 1,4,5-trisphosphate receptors (IP₃R) is discussed, and in particular, the role of Bcl-2/IP₃R interactions in promoting the survival of cancer cells by preventing Ca²⁺-mediated cell death. The development and usage of a peptide, referred to as TAT-Pep8, or more recently, BIRD-2, that induces death of cancer cells by inhibiting Bcl-2's control over IP₃R-mediated Ca²⁺ elevation is discussed. Studies aimed at discovering a small molecule that mimics BIRD-2's anticancer mechanism of action are summarized, along with the prospect of such a compound becoming a novel therapeutic option for cancer.

Novel findings of 18β-glycyrrhetinic acid on sRAGE secretion through inhibition of transient receptor potential canonical channels in high-glucose environment

Enhancing soluble receptor for advanced glycation endproducts (sRAGE) is considered as a potent strategy for diabetes therapy. sRAGE secretion is regulated by calcium and transient receptor potential canonical (TRPC) channels. However, the role of TRPC channels in diabetes remains unknown. 18β-Glycyrrhetinic acid (18β-GA), produced from liquorice, has shown antidiabetic properties. This study was aimed to investigate the effect of 18β-GA on sRAGE secretion via TRPC channels in high glucose (HG)-induced THP-1 cells. HG treatment enhanced TRPC3 and TRPC6 expression and consequently caused reactive oxygen species (ROS) accumulation mediated through p47 nicotinamide-adenine dinucleotide phosphate oxidase and inducible nitric oxide synthase (iNOS) associated with uncoupling protein 2 (UCP2) decline and lower sRAGE secretion. Interestingly, 18β-GA showed the dramatic effects similar to Pyr3 or 2-aminoethyl diphenyl borinate inhibitors and effectively reversed HG-elicited mechanisms including that blocking TRPC3 and TRPC6 protein expressions, suppressing intracellular [Ca2+] concentration, decreasing expressions of ROS, p47s, and iNOS, but increasing UCP2 level and promoting sRAGE secretion. Therefore, 18β-GA provides a potential implication to diabetes mellitus and its complications.

Association of ORAI1 Genetic Polymorphism with Serum Calcium and Phosphorus Levels in Non-dialysis Chronic Kidney Disease Patients: A Case-control Study

Background

As chronic kidney disease (CKD) is a silent killer, it is now a global concern to find out the possible causes by genetic and biological markers. In the earlier stages of CKD, serum calcium and phosphorus levels fall down later on turned into hypercalcemia and hyperphosphatemia contributing high mortality in CKD. This study aimed to examine the serum calcium and phosphorus levels in non-dialysis CKD patients and healthy controls to find out their association with ORAI1 genetic polymorphism.

Methods

The present study recruited 96 non-dialysis CKD patients and 100 control subjects matched by age, gender, and body mass index (BMI). Measurement of serum calcium levels was performed with atomic absorption spectrophotometer (HITACHI, 170-30) and phosphorus levels were determined by UV VIS spectrophotometer (Analytik Jena SPEKOL 2000). PCR-RFLP technique was applied to determine the genetic polymorphism of ORAI1 (rs12313273 and rs6486795) gene.

Results

The mean values of serum calcium and phosphorus levels were 2.53 ± 0.50 mg/dL and 3.77 ± 0.42 mg/dL for the patient group and 3.67 ± 2.37 mg/dL and 13.66 ± 6.34 mg/dL for the control group, respectively. We observed significantly reduced serum calcium and phosphorus levels in non-dialysis CKD patients compared with control subjects (p < 0.001). No significant polymorphism of ORAI1 (rs12313273 and rs6486795) was found with declined serum calcium and phosphorus levels.

Conclusions

The present study suggested that there is no linear correlation between ORAI1 genetic polymorphism with serum calcium and phosphorus levels in non-dialysis CKD patients.

TRPM8 channel inhibitor AMTB suppresses murine T-cell activation induced by T-cell receptor stimulation, concanavalin A, or external antigen re-stimulation

Transient receptor potential (TRP) channels are a family of non-selective cation channels that are functionally expressed in various organs and cells. Among them, transient receptor potential vanilloid (TRPV) 1 and TRPV4 channels are expressed in T cells, where they serve as Ca²⁺ channels for T-cell receptor signaling [Bertin et al., 2014, Majhi et al., 2015]. Here, we show that not only TRPV1 and TRPV4 channel inhibitors, but also a transient receptor potential melastatin (TRPM) 8 channel inhibitor can suppress murine T-cell activation. Mouse splenic lymphocytes pretreated with N-(3-aminopropyl)-2-[(3-methylphenyl)methoxy]-N-(2-thienylmethyl)benzamide hydrochloride (AMTB), a TRPM8 channel-selective inhibitor, showed significantly reduced IL-2 and IL-6 release from T cells after stimulation with anti-CD3ε/anti-CD28 antibodies or concanavalin A. AMTB also suppressed IL-2 mRNA expression and activation of extracellular signal-regulated kinase 1/2, which is involved in IL-2 production. Further, the increase of CD25 (IL-2 receptor alpha chain) expression after T-cell activation was suppressed by AMTB. TRPM8 channel was expressed in CD4⁺ T cells isolated from splenocytes, and we confirmed that the release of IL-2 from isolated CD4⁺ T cells was significantly suppressed by AMTB. In vitro re-stimulation of splenocytes from external antigen-immunized mice with the same antigen induced IL-2 and IL-6 production, which was significantly suppressed by AMTB. Thus, the TRPM8 channel inhibitor AMTB suppresses T-cell activation induced by various stimulants.

Targeting Bcl-2-IP3 receptor interaction to treat cancer: A novel approach inspired by nearly a century treating cancer with adrenal corticosteroid hormones

Bcl-2 inhibits cell death by at least two different mechanisms. On the one hand, its BH3 domain binds to pro-apoptotic proteins such as Bim and prevents apoptosis induction. On the other hand, the BH4 domain of Bcl-2 binds to the inositol 1,4,5-trisphosphate receptor (IP₃R), preventing Ca²⁺ signals that mediate cell death. In normal T-cells, Bcl-2 levels increase during the immune response, protecting against cell death, and then decline as apoptosis ensues and the immune response dissipates. But in many cancers Bcl-2 is aberrantly expressed and exploited to prevent cell death by inhibiting IP₃R-mediated Ca²⁺ elevation. This review summarizes what is known about the mechanism of Bcl-2's control over IP₃R-mediated Ca²⁺ release and cell death induction. Early insights into the role of Ca²⁺ elevation in corticosteroid-mediated cell death serves as a model for how targeting IP₃R-mediated Ca²⁺ elevation can be a highly effective therapeutic approach for different types of cancer. Moreover, the successful development of ABT-199 (Venetoclax), a small molecule targeting the BH3 domain of Bcl-2 but without effects on Ca²⁺, serves as proof of principle that targeting Bcl-2 can be an effective therapeutic approach. BIRD-2, a synthetic peptide that inhibits Bcl-2-IP₃R interaction, induces cell death induction in ABT-199 (Venetoclax)-resistant cancer models, attesting to the value of developing therapeutic agents that selectively target Bcl-2-IP₃R interaction, inducing Ca²⁺-mediated cell death.

Guanine and inosine nucleotides/nucleosides suppress murine T cell activation

Damaged tissues and cells release intracellular purine nucleotides, which serve as intercellular signaling factors. We previously showed that exogenously added adenine nucleotide (250 μM ATP) suppressed the activation of murine splenic T lymphocytes. Here, we examined the effects of other purine nucleotides/nucleosides on mouse T cell activation. First, we found that pretreatment of mouse spleen T cells with 250 μM GTP, GDP, GMP, guanosine, ITP, IDP, IMP or inosine significantly reduced the release of stimulus-inducible cytokine IL-2. This suppression of IL-2 release was not caused by induction of cell death. Further studies with GTP, ITP, guanosine and inosine showed that pretreatment with these nucleotides/nucleosides also suppressed release of IL-6. However, these nucleotides/nucleosides did not suppress stimulus-induced phosphorylation of ERK1/2, suggesting that the suppression of the release of inflammatory cytokines does not involve inhibition of ERK1/2 signaling. In contrast to ATP pretreatment at the same concentration, guanine or inosine nucleotides/nucleosides did not attenuate the expression of CD25. Our findings indicate that exogenous guanine or inosine nucleotides/nucleosides can suppress inflammatory cytokine release from T cells, and may be promising candidates for use as supplementary agents in the treatment of T cell-mediated immune diseases.

Calcium-Responsive Liposomes via a Synthetic Lipid Switch

Liposomal drug delivery would benefit from enhanced control over content release. Here, we report a novel avenue for triggering release driven by chemical composition using liposomes sensitized to calcium-a target chosen due to its key roles in biology and disease. To demonstrate this principle, we synthesized calcium-responsive lipid switch 1, designed to undergo conformational changes upon calcium binding. The conformational change perturbs membrane integrity, thereby promoting cargo release. This was shown through fluorescence-based release assays via dose-dependent response depending on the percentage of 1 in liposomes, with minimal background leakage in controls. DLS experiments indicated dramatic changes in particle size upon treatment of liposomes containing 1 with calcium. In a comparison of ten naturally occurring metal cations, calcium provided the greatest release. Finally, STEM images showed significant changes in liposome morphology upon treatment of liposomes containing 1 with calcium. These results showcase lipid switches driven by molecular recognition principles as an exciting avenue for controlling membrane properties.

Besides an ITIM/SHP-1-dependent pathway, CD22 collaborates with Grb2 and plasma membrane calcium-ATPase in an ITIM/SHP-1-independent pathway of attenuation of Ca2+i signal in B cells

CD22 is a surface immunoglobulin implicated in negative regulation of B cell receptor (BCR) signaling; particularly inhibiting intracellular Ca2+ (Ca2+i)signals. Its cytoplasmic tail contains six tyrosine residues (Y773/Y783/Y817/Y828/Y843/Y863, designated Y1~Y6 respectively), including three (Y2/5/6) lying within immunoreceptor tyrosine-based inhibitory motifs (ITIMs) that serve to recruit the protein tyrosine phosphatase SHP-1 after BCR activation-induced phosphorylation. The mechanism of inhibiting Ca2+i by CD22 has been poorly understood. Previous study demonstrated that CD22 associated with plasma membrane calcium-ATPase (PMCA) and enhanced its activity (Chen, J. et al. Nat Immunol 2004;5:651-7). The association is dependent on BCR activation-induced cytoplasmic tyrosine phosphorylation, because CD22 with either all six tyrosines mutated to phenylalanines or cytoplasmic tail truncated loses its ability to associate with PMCA. However, which individual or a group of tyrosine residues determine the association and how CD22 and PMCA interacts, are still unclear. In this study, by using a series of CD22 tyrosine mutants, we found that ITIM Y2/5/6 accounts for 34.3~37.1% Ca2+i inhibition but is irrelevant for CD22/PMCA association. Non-ITIM Y4 and its YEND motif contribute to the remaining 69.4~71.7% Ca2+i inhibition and is the binding site for PMCA-associated Grb2. Grb2, independently of BCR cross-linking, is constitutively associated with and directly binds to PMCA in both chicken and human B cells. Knockout of Grb2 by CRISPR/Cas9 completely disrupted the CD22/PMCA association. Thus, our results demonstrate for the first time that in addition to previously-identified ITIM/SHP-1-dependent pathway, CD22 holds a major pathway of negative regulation of Ca2+i signal, which is ITIM/SHP-1-independent, but Y4/Grb2/PMCA-dependent.

Adenine Nucleotides Attenuate Murine T Cell Activation Induced by Concanavalin A or T Cell Receptor Stimulation

Extracellular ATP and its metabolites affect various cellular immune responses, including T cell function, but there are apparently conflicting reports concerning the effects of adenine nucleotides on T cells. For example, it has been reported that ATP-mediated activation of P2 receptor is involved in T cell activation; activation of adenosine receptors suppresses T cell function; and 1 mM ATP induces T cell death via activation of P2X7 receptor. Therefore, in this work we investigated in detail the effects of 100–250 μM ATP, ADP, or AMP on murine T cell activation. First, an in vitro study showed that pretreatment of murine splenic T cells with 100–250 μM ATP, ADP, or AMP significantly suppressed the concanavalin A (ConA)-induced release of cytokines, including IL-2. This suppression was not due to induction of cell death via the P2X7 receptor or to an immunosuppressive effect of adenosine. ATP attenuated the expression of CD25, and decreased the cell proliferation ability of activated T cells. The release of IL-2 by ConA-stimulated lymphocytes was suppressed by post-treatment with ATP, as well as by pretreatment. These results suggest that exogenous ATP suppresses the activation of T cells. Secondly, we evaluated the effect of ATP in a ConA-treated mice. Treatment with ATP attenuated the increase of IL-2 concentration in the blood. Overall, these results suggest that adenine nucleotides might have potential as supplemental therapeutic agents for T cell-mediated immune diseases, by suppressing T cell activation.

Store-operated Ca2+ channels in airway epithelial cell function and implications for asthma

The epithelial cells of the lung are at the interface of a host and its environment and are therefore directly exposed to the inhaled air-borne particles. Rather than serving as a simple physical barrier, airway epithelia detect allergens and other irritants and then help organize the subsequent immune response through release of a plethora of secreted signals. Many of these signals are generated in response to opening of store-operated Ca²⁺ channels in the plasma membrane. In this review, we describe the properties of airway store-operated channels and their role in regulating airway epithelial cell function.

This article is part of the themed issue ‘Evolution brings Ca²⁺ and ATP together to control life and death’.

Imaging early embryonic calcium activity with GCaMP6s transgenic zebrafish

Intracellular Ca²⁺ signaling regulates cellular activities during embryogenesis and in adult organisms. We generated stable Tg[βactin2:GCaMP6s]^stl351 and Tg[ubi:GCaMP6s]^stl352 transgenic lines that combine the ubiquitously-expressed Ca²⁺ indicator GCaMP6s with the transparent characteristics of zebrafish embryos to achieve superior in vivo Ca²⁺ imaging. Using the Tg[βactin2:GCaMP6s]^stl351 line featuring strong GCaMP6s expression from cleavage through gastrula stages, we detected higher frequency of Ca²⁺ transients in the superficial blastomeres during the blastula stages preceding the midblastula transition. Additionally, GCaMP6s also revealed that dorsal-biased Ca²⁺ signaling that follows the midblastula transition persisted longer during gastrulation, compared with earlier studies. We observed that dorsal-biased Ca²⁺ signaling is diminished in ventralized ichabod/β-catenin2 mutant embryos and ectopically induced in embryos dorsalized by excess β-catenin. During gastrulation, we directly visualized Ca²⁺ signaling in the dorsal forerunner cells, which form in a Nodal signaling dependent manner and later give rise to the laterality organ. We found that excess Nodal increases the number and the duration of Ca²⁺ transients specifically in the dorsal forerunner cells. The GCaMP6s transgenic lines described here enable unprecedented visualization of dynamic Ca²⁺ events from embryogenesis through adulthood, augmenting the zebrafish toolbox.

Coronins and their role in immunological phenomena

Coronins are a large family of proteins occurring in many eukaryotes. In mammals, seven coronin genes have been identified, evidencing that coronins 1 to 6 present classic coronin structure, while coronin 7 is a tandem coronin particle, without a spiral domain, although the best characterised coronin, in terms of both structure and function, is the mammalian coronin 1. It has been proven that they are related to regulation of actin dynamics, e.g. as a result of interaction with the complex of proteins Arp2/3. These proteins also modulate the activity of immune system cells, including lymphocyte T and B cells, neutrophils and macrophages. They are involved in bacterial infections with Mycobacterium tuberculosis, M. leprae and Helicobacter pylori and participate in the response to viral infections, e.g. infections of lymphocytic choriomeningitis virus (LCMV) and vesicular stomatitis Indiana virus (VSV). Also their involvement in autoimmune diseases such as lupus erythematosus has been recorded.

Acetylcholine released from T cells regulates intracellular Ca2+, IL-2 secretion and T cell proliferation through nicotinic acetylcholine receptor

AIMS

T lymphocytes synthesize acetylcholine (ACh) and express muscarinic and nicotinic ACh receptors (mAChR and nAChR, respectively) responsible for increases in the intracellular Ca²⁺ concentration ([Ca²⁺]_i). Our aim in the present study was to assess whether autocrine ACh released from T lymphocytes regulates their physiological functions.

MAIN METHODS

MOLT-3 human leukemic cell line and murine splenocytes were loaded with fura-2 to monitor [Ca²⁺]_i changes in the absence or presence of several AChR antagonists, including mecamylamine, methyllycaconitine and scopolamine. Real-time PCR and ELISA were performed to measure interleukin-2 (IL-2) mRNA and protein levels.

KEY FINDINGS

T lymphocytes constitutively produce sufficient amounts of ACh to elicit autocrine changes in [Ca²⁺]_i. These autocrine ACh-evoked [Ca²⁺]_i transients were mediated by nAChRs and then influx of extracellular Ca²⁺. Mecamylamine, a nAChR inhibitor, suppressed not only these [Ca²⁺]_i transients, but also IL-2 release and T cell proliferation.

SIGNIFICANCE

Here, we confirmed that T lymphocytes utilize ACh as a tool to interact with each other and that autocrine ACh-activated nAChRs are involved in cytokine release and cell proliferation. These findings suggest the possibility that nAChR agonists and antagonists and smoking are able to modulate immune function, which in turn suggests the therapeutic potential of immune activation or suppression using nAChR agonists or antagonists.

TRP channels and traffic-related environmental pollution-induced pulmonary disease

Environmental pollutant exposures are major risk factors for adverse health outcomes, with increased morbidity and mortality in humans. Diesel exhaust (DE) is one of the major harmful components of traffic-related air pollution. Exposure to DE affects several physiological systems, including the airways, and pulmonary diseases are increased in highly populated urban areas. Hence, there are urgent needs to (1) create newer and lesser polluting fuels, (2) improve exhaust aftertreatments and reduce emissions, and (3) understand mechanisms of actions for toxic effects of both conventional and cleaner diesel fuels on the lungs. These steps could aid the development of diagnostics and interventions to prevent the negative impact of traffic-related air pollution on the pulmonary system. Exhaust from conventional, and to a lesser extent, clean fuels, contains particulate matter (PM) and more than 400 additional chemical constituents. The major toxic constituents are nitrogen oxides (NOx) and polycyclic aromatic hydrocarbons (PAHs). PM and PAHs could potentially act via transient receptor potential (TRP) channels. In this review, we will first discuss the associations between DE from conventional as well as clean fuel technologies and acute and chronic airway inflammation. We will then review possible activation and/or potentiation of TRP vanilloid type 1 (TRPV1) and ankyrin 1 (TRPA1) channels by PM and PAHs. Finally, we will discuss and summarize recent findings on the mechanisms whereby TRPs could control the link between DE and airway inflammation, which is a primary determinant leading to pulmonary disease.

Quantitation of Gingerols in Human Plasma by Newly Developed Stable Isotope Dilution Assays and Assessment of Their Immunomodulatory Potential

In a pilot study with two volunteers, the main pungent and bioactive ginger (Zingiber officinale Roscoe) compounds, the gingerols, were quantitated in human plasma after ginger tea consumption using a newly established HPLC-MS/MS(ESI) method on the basis of stable isotope dilution assays. Limits of quantitation for [6]-, [8]-, and [10]-gingerols were determined as 7.6, 3.1, and 4.0 nmol/L, respectively. The highest plasma concentrations of [6]-, [8]-, and [10]-gingerols (42.0, 5.3, and 4.8 nmol/L, respectively) were reached 30-60 min after ginger tea intake. Incubation of activated human T lymphocytes with gingerols increased the intracellular Ca(2+) concentration as well as the IFN-γ secretion by about 20-30%. This gingerol-induced increase of IFN-γ secretion could be blocked by the specific TRPV1 antagonist SB-366791. The results of the present study point to an interaction of gingerols with TRPV1 in activated T lymphocytes leading to an augmentation of IFN-γ secretion.

Up-regulation of Store-operated Ca2+ Entry and Nuclear Factor of Activated T Cells Promote the Acinar Phenotype of the Primary Human Salivary Gland Cells

The signaling pathways involved in the generation and maintenance of exocrine gland acinar cells have not yet been established. Primary human salivary gland epithelial cells, derived from salivary gland biopsies, acquired an acinar-like phenotype when the [Ca(2+)] in the serum-free medium (keratinocyte growth medium, KGM) was increased from 0.05 mm (KGM-L) to 1.2 mm (KGM-H). Here we examined the mechanism underlying this Ca(2+)-dependent generation of the acinar cell phenotype. Compared with cells in KGM-L, those in KGM-H display enhancement of Orai1, STIM1, STIM2, and nuclear factor of activated T cells 1 (NFAT1) expression together with an increase in store-operated Ca(2+) entry (SOCE), SOCE-dependent nuclear translocation of pGFP-NFAT1, and NFAT-dependent but not NFκB-dependent gene expression. Importantly, AQP5, an acinar-specific protein critical for function, is up-regulated in KGM-H via SOCE/NFAT-dependent gene expression. We identified critical NFAT binding motifs in the AQP5 promoter that are involved in Ca(2+)-dependent up-regulation of AQP5. These important findings reveal that the Ca(2+)-induced switch of salivary epithelial cells to an acinar-like phenotype involves remodeling of SOCE and NFAT signaling, which together control the expression of proteins critically relevant for acinar cell function. Our data provide a novel strategy for generating and maintaining acinar cells in culture.

T Cell Receptor Mediated Calcium Entry Requires Alternatively Spliced Cav1.1 Channels

The process of calcium entry in T cells is a multichannel and multi-step process. We have studied the requirement for L-type calcium channels (Ca_v1.1) α1S subunits during calcium entry after TCR stimulation. High expression levels of Ca_v1.1 channels were detected in activated T cells. Sequencing and cloning of Ca_v1.1 channel cDNA from T cells revealed that a single splice variant is expressed. This variant lacks exon 29, which encodes the linker region adjacent to the voltage sensor, but contains five new N-terminal exons that substitute for exons 1 and 2, which are found in the Ca_v1.1 muscle counterpart. Overexpression studies using cloned T cell Ca_v1.1 in 293HEK cells (that lack TCR) suggest that the gating of these channels was altered. Knockdown of Ca_v1.1 channels in T cells abrogated calcium entry after TCR stimulation, suggesting that Ca_v1.1 channels are controlled by TCR signaling.

TCR Signal Strength Alters T-DC Activation and Interaction Times and Directs the Outcome of Differentiation

The ability of CD4+ T cells to differentiate into effector subsets underpins their ability to shape the immune response and mediate host protection. During T cell receptor-induced activation of CD4+ T cells, both the quality and quantity of specific activatory peptide/MHC ligands have been shown to control the polarization of naive CD4+ T cells in addition to co-stimulatory and cytokine-based signals. Recently, advances in two--photon microscopy and tetramer-based cell tracking methods have allowed investigators to greatly extend the study of the role of TCR signaling in effector differentiation under in vivo conditions. In this review, we consider data from recent in vivo studies analyzing the role of TCR signal strength in controlling the outcome of CD4+ T cell differentiation and discuss the role of TCR in controlling the critical nature of CD4+ T cell interactions with dendritic cells during activation. We further propose a model whereby TCR signal strength controls the temporal aspects of T-DC interactions and the implications for this in mediating the downstream signaling events, which influence the transcriptional and epigenetic regulation of effector differentiation.

Transient Receptor Potential (TRP) channels in T cells

The transient receptor potential (TRP) family of ion channels is widely expressed in many cell types and plays various physiological roles. Growing evidence suggests that certain TRP channels are functionally expressed in the immune system. Indeed, an increasing number of reports have demonstrated the functional expression of several TRP channels in innate and adaptive immune cells and have highlighted their critical role in the activation and function of these cells. However, very few reviews have been entirely dedicated to this subject. Here, we will summarize the recent findings with regards to TRP channel expression in T cells and discuss their emerging role as regulators of T cell activation and functions. Moreover, these studies suggest that beyond their pharmaceutical interest in pain management, certain TRP channels may represent potential novel therapeutic targets for various immune-related diseases.

Heteroclitic Peptides Increase Proliferation and Reduce Evidence of Human Immunodeficiency Virus-Specific CD8⁺ T Cell Dysfunction

Human immunodeficiency virus (HIV)-specific CD8(+) T cell dysfunction parallels disease progression; therefore, restoring potent HIV-specific CD8(+) T cell responses is a key therapeutic goal. Certain CD8(+) T cell peptide epitope variants, termed heteroclitic, enhance cytokine production by the HIV-specific CD8(+) T cells of some individuals. In this study, we investigated whether heteroclitic peptides that enhance cytokine production by HIV-specific CD8(+) T cells also reduce functional and phenotypic evidence of HIV-specific CD8(+) T cell exhaustion in those instances. Twenty-four variant peptides of human histocompatibility-linked leukocyte antigen (HLA)-A2-restricted reference HIV peptide epitopes designated as A2-7; Nef 83→91, A2-8; Nef 135→143, A2-Gag; Gag 77→85 and A2-9; Gag 433→440 were synthesized with conservative and semiconservative amino acid substitutions at positions 3, 5, and 7 or 3, 5, and 8 of Gag 433→440. Variants that enhanced interferon-gamma (IFN-γ) and/or interleukin-2 (IL-2) production in enzyme-linked immunospot assays (29 cases overall) were subsequently tested by 7-day in vitro peptide stimulation for their effects on HIV-specific CD8(+) T cell proliferation and programmed death-1 (PD-1) expression. Heteroclitic variants enhanced HIV-specific CD8(+) T cell proliferation by >20% in 13/29 cases tested, reduced PD-1 expression on proliferating cells by 15-50% in 10 cases, and reduced PD-1 expression on proliferating cells by >50% in 3 cases. In five cases, the same heteroclitic peptide increased proliferation by >20% and reduced PD-1 expression by >15%. These data demonstrate that heteroclitic peptides can alter the magnitude and character of HIV-specific CD8(+) cell responses relative to reference peptides and may have a unique immunotherapeutic value in therapeutic vaccines.

Signaling in lymphocyte activation

The fate of T and B lymphocytes, the key cells that direct the adaptive immune response, is regulated by a diverse network of signal transduction pathways. The T- and B-cell antigen receptors are coupled to intracellular tyrosine kinases and adaptor molecules to control the metabolism of inositol phospholipids and calcium release. The production of inositol polyphosphates and lipid second messengers directs the activity of downstream guanine-nucleotide-binding proteins and protein and lipid kinases/phosphatases that control lymphocyte transcriptional and metabolic programs. Lymphocyte activation is modulated by costimulatory molecules and cytokines that elicit intracellular signaling that is integrated with the antigen-receptor-controlled pathways.

A high-throughput chemical screen reveals that harmine-mediated inhibition of DYRK1A increases human pancreatic beta cell replication

Types 1 and 2 diabetes affect some 380 million people worldwide. Both ultimately result from a deficiency of functional pancreatic insulin-producing beta cells. Beta cells proliferate in humans during a brief temporal window beginning around the time of birth, with a peak percentage (∼2%) engaged in the cell cycle in the first year of life. In embryonic life and after early childhood, beta cell replication is barely detectable. Whereas beta cell expansion seems an obvious therapeutic approach to beta cell deficiency, adult human beta cells have proven recalcitrant to such efforts. Hence, there remains an urgent need for antidiabetic therapeutic agents that can induce regeneration and expansion of adult human beta cells in vivo or ex vivo. Here, using a high-throughput small-molecule screen (HTS), we find that analogs of the small molecule harmine function as a new class of human beta cell mitogenic compounds. We also define dual-specificity tyrosine-regulated kinase-1a (DYRK1A) as the likely target of harmine and the nuclear factors of activated T cells (NFAT) family of transcription factors as likely mediators of human beta cell proliferation and differentiation. Using three different mouse and human islet in vivo-based models, we show that harmine is able to induce beta cell proliferation, increase islet mass and improve glycemic control. These observations suggest that harmine analogs may have unique therapeutic promise for human diabetes therapy. Enhancing the potency and beta cell specificity of these compounds are important future challenges.

The toll-like receptor family protein RP105/MD1 complex is involved in the immunoregulatory effect of exopolysaccharides from Lactobacillus plantarum N14

The radioprotective 105 (RP105)/MD1 complex is a member of the Toll-like receptor (TLR) family. It was reported that RP105/MD1 cooperates with the lipopolysaccharide (LPS) receptor TLR4/MD2 complex and plays a crucial role in the response of immune cells to LPS. This work evaluated whether RP105, TLR4 or TLR2 were involved in the immunoregulatory capacities of Lactobacillus plantarum N14 (LP14) or its exopolysaccharides (EPS). EPS from LP14 were fractionated into neutral (NPS) and acidic (APS) EPS by anion exchange chromatography. Experiments with transfectant HEK(RP105/MD1) and HEK(TLR2) cells demonstrated that LP14 strongly activated NF-κB via RP105 and TLR2. When we studied the capacity of APS to activate NF-κB pathway in HEK(RP105/MD1) and HEK(TLR4) cells; we observed that APS strongly stimulated both transfectant cells. Our results also showed that LP14 and APS were able to decrease the production of pro-inflammatory cytokines (IL-6, IL-8 and MCP-1) in porcine intestinal epithelial (PIE) cells in response to enterotoxigenic Escherichia coli (ETEC) challenge. In order to confirm the role of TLR2, TLR4 and RP105 in the immunoregulatory effect of APS from LP14, we used small interfering RNA (siRNA) to knockdown these receptors in PIE cells. The capacity of LP14 and APS to modulate pro-inflammatory cytokine expression was significantly reduced in PIE(RP105-/-) cells. It was also shown that LP14 and APS were capable of upregulating negative regulators of the TLR signaling in PIE cells. This work describes for the first time that a Lactobacillus strain and its EPS reduce inflammation in intestinal epithelial cells in a RP105/MD1-dependend manner.

The ion channel TRPV1 regulates the activation and proinflammatory properties of CD4⁺ T cells

TRPV1 is a Ca(2+)-permeable channel studied mostly as a pain receptor in sensory neurons. However, its role in other cell types is poorly understood. Here we found that TRPV1 was functionally expressed in CD4(+) T cells, where it acted as a non-store-operated Ca(2+) channel and contributed to T cell antigen receptor (TCR)-induced Ca(2+) influx, TCR signaling and T cell activation. In models of T cell-mediated colitis, TRPV1 promoted colitogenic T cell responses and intestinal inflammation. Furthermore, genetic and pharmacological inhibition of TRPV1 in human CD4(+) T cells recapitulated the phenotype of mouse Trpv1(-/-) CD4(+) T cells. Our findings suggest that inhibition of TRPV1 could represent a new therapeutic strategy for restraining proinflammatory T cell responses.

Bcl-2 regulation of the inositol 1,4,5-trisphosphate receptor and calcium signaling in normal and malignant lymphocytes: potential new target for cancer treatment

The anti-apoptotic protein Bcl-2 is a versatile regulator of cell survival. Its interactions with its own pro-apoptotic family members are widely recognized for their role in promoting the survival of cancer cells. These interactions are thus being targeted for cancer treatment. Less widely recognized is the interaction of Bcl-2 with the inositol 1,4,5-trisphosphate receptor (InsP3R), an InsP3-gated Ca(2+) channel located on the endoplasmic reticulum. The nature of this interaction, the mechanism by which it controls Ca(2+) release from the ER, its role in T-cell development and survival, and the possibility of targeting it as a novel cancer treatment strategy are summarized in this review. This article is part of a Special Issue entitled: Calcium signaling in health and disease. Guest Editors: Geert Bultynck, Jacques Haiech, Claus W. Heizmann, Joachim Krebs, and Marc Moreau.

Lactobacillus delbrueckii TUA4408L and its extracellular polysaccharides attenuate enterotoxigenic Escherichia coli-induced inflammatory response in porcine intestinal epitheliocytes via Toll-like receptor-2 and 4

SCOPE

Immunobiotics are known to modulate intestinal immune responses by regulating Toll-like receptor (TLR) signaling pathways, which are responsible for the induction of cytokines and chemokines in response to microbial-associated molecular patterns. However, little is known about the immunomodulatory activity of compounds or molecules from immunobiotics.

METHODS AND RESULTS

We evaluated whether Lactobacillus delbrueckii subsp. delbrueckii TUA4408L (Ld) or its extracellular polysaccharide (EPS): acidic EPS (APS) and neutral EPS (NPS), modulated the response of porcine intestinal epitheliocyte (PIE) cells against Enterotoxigenic Escherichia coli (ETEC) 987P. The roles of TLR2, TLR4, and TLR negative regulators in the immunoregulatory effects were also studied. ETEC-induced inflammatory cytokines were downregulated when PIE cells were prestimulated with both Ld or EPSs. Ld, APS, and NPS inhibited ETEC mediated mitogen-activated protein kinase (MAPK) and nuclear factor-κB (NF-κB) activation by upregulating TLR negative regulators. The capability of Ld to suppress inflammatory cytokines was diminished when PIE cells were blocked with anti-TLR2 antibody, while APS failed to suppress inflammatory cytokines when cells were treated with anti-TLR4 antibody. Induction of Ca²⁺ fluxes in TLR knockdown cells confirmed that TLR2 plays a principal role in the immunomodulatory action of Ld, while the activity of APS is mediated by TLR4. In addition, NPS activity depends on both TLR4 and TLR2.

CONCLUSION

Ld and its EPS have the potential to be used for the development of anti-inflammatory functional foods to prevent intestinal diseases in both humans and animals.

Modulation of T Cell Metabolism and Function through Calcium Signaling

As a vital second messenger in the activation of lymphocytes, the divalent cation Ca(2+) plays numerous roles in adaptive immune responses. Importantly, Ca(2+) signaling is essential for T cell activation, tolerance of self-antigens, and homeostasis. Supporting the essential role of Ca(2+) signaling in T cell biology, the Ca(2+) regulated protein phosphatase calcineurin is a key target of pharmacologic inhibition for preventing allograft rejection and for autoimmune therapy. Recent studies have highlighted the unique role of Stim1 and Orai1/2 proteins in the regulation of store-operated/calcium release activated calcium (CRAC) channels in the context of T cells. While Ca(2+) is known to modulate T cell activation via effects on calcineurin and its target, nuclear factor of activated T cells (NFAT), this second messenger also regulates other pathways, including protein kinase C, calmodulin kinases, and cytoskeletal proteins. Ca(2+) also modulates the unique metabolic changes that occur during in distinct T cell stages and subsets. Herein, we discuss the means by which Ca(2+) mobilization modulates cellular metabolism following T cell receptor ligation. Further, we highlight the crosstalk between mitochondrial metabolism, reactive oxygen species (ROS) generation, and CRAC channel activity. As a target of mitochondrial ROS and Ca(2+) regulation, we describe the involvement of the serine/threonine kinase DRAK2 in the context of these processes. Given the important roles for Ca(2+) dependent signaling and cellular metabolism in adaptive immune responses, the crosstalk between these pathways is likely to be important for the regulation of T cell activation, tolerance, and homeostasis.

Emerging roles of L-type voltage-gated and other calcium channels in T lymphocytes

In T lymphocytes, calcium ion controls a variety of biological processes including development, survival, proliferation, and effector functions. These distinct and specific roles are regulated by different calcium signals, which are generated by various plasma membrane calcium channels. The repertoire of calcium-conducting proteins in T lymphocytes includes store-operated CRAC channels, transient receptor potential channels, P2X channels, and L-type voltage-gated calcium (Ca_v1) channels. In this paper, we will focus mainly on the role of the Ca_v1 channels found expressed by T lymphocytes, where these channels appear to operate in a T cell receptor stimulation-dependent and voltage sensor independent manner. We will review their expression profile at various differentiation stages of CD4 and CD8 T lymphocytes. Then, we will present crucial genetic evidence in favor of a role of these Ca_v1 channels and related regulatory proteins in both CD4 and CD8 T cell functions such as proliferation, survival, cytokine production, and cytolysis. Finally, we will provide evidence and speculate on how these voltage-gated channels might function in the T lymphocyte, a non-excitable cell.

FRET imaging of calcium signaling in live cells in the microenvironment

The microenvironment has been shown to regulate cellular functions including cell growth, differentiation, proliferation, migration, cancer development and metastasis. However, the underlying molecular mechanism remains largely unclear. We have integrated micro-pattern technology and molecular biosensors based on fluorescence resonance energy transfer (FRET) to visualize calcium responses in cells constrained to grow on a micro-patterned surface. Upon ATP stimulation, human umbilical vein endothelial cells (HUVECs) cultured on different surface micro-patterns had a shorter decay time and a reduced peak of a transient intracellular calcium rise compared to control cells without constraints. The decay time is regulated by the plasma membrane and the membrane calcium channels, while the peak by endoplasmic reticulum (ER) calcium release. Further results revealed that voltage operated channels (VOCs), coupling the plasma membrane and ER, can affect both the decay time and the peak of calcium response. The inhibition of VOCs can eliminate the effect of different micro-patterns on calcium signals. When two connected HUVECs were constrained to grow on a micro-pattern, drastically distinct calcium responses upon ATP stimulation can be observed, in contrast to the similar responses of two connected cells cultured without patterns. Interestingly, the inhibition of VOCs also blocked this difference of calcium responses between two connected cells on micro-patterns. These results indicate that a micro-patterned surface can have a profound effect on the calcium responses of HUVECs under ATP stimulation, largely mediated by VOCs. Therefore, our results shed new light on the molecular mechanism by which HUVECs perceive the microenvironment and regulate intracellular calcium signals.

The calcium feedback loop and T cell activation: how cytoskeleton networks control intracellular calcium flux

During T cell activation, the engagement of a T cell with an antigen-presenting cell (APC) results in rapid cytoskeletal rearrangements and a dramatic increase of intracellular calcium (Ca(2+)) concentration, downstream to T cell antigen receptor (TCR) ligation. These events facilitate the organization of an immunological synapse (IS), which supports the redistribution of receptors, signaling molecules and organelles towards the T cell-APC interface to induce downstream signaling events, ultimately supporting T cell effector functions. Thus, Ca(2+) signaling and cytoskeleton rearrangements are essential for T cell activation and T cell-dependent immune response. Rapid release of Ca(2+) from intracellular stores, e.g. the endoplasmic reticulum (ER), triggers the opening of Ca(2+) release-activated Ca(2+) (CRAC) channels, residing in the plasma membrane. These channels facilitate a sustained influx of extracellular Ca(2+) across the plasma membrane in a process termed store-operated Ca(2+) entry (SOCE). Because CRAC channels are themselves inhibited by Ca(2+) ions, additional factors are suggested to enable the sustained Ca(2+) influx required for T cell function. Among these factors, we focus here on the contribution of the actin and microtubule cytoskeleton. The TCR-mediated increase in intracellular Ca(2+) evokes a rapid cytoskeleton-dependent polarization, which involves actin cytoskeleton rearrangements and microtubule-organizing center (MTOC) reorientation. Here, we review the molecular mechanisms of Ca(2+) flux and cytoskeletal rearrangements, and further describe the way by which the cytoskeletal networks feedback to Ca(2+) signaling by controlling the spatial and temporal distribution of Ca(2+) sources and sinks, modulating TCR-dependent Ca(2+) signals, which are required for an appropriate T cell response. This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters. Guest Editor: Jean Claude Hervé.

On guard: coronin proteins in innate and adaptive immunity

Recent work has implicated members of the evolutionarily conserved family of coronin proteins - in particular coronin 1 - in immune homeostasis. Coronins are involved in processes as diverse as pathogen survival in phagocytes and homeostatic T cell signalling. Notably, in both mice and humans, coronin mutations are associated with immune deficiencies and resistance to autoimmunity. In this article, we review what is currently known about these conserved molecules and discuss a potential common mechanism that underlies their diverse activities, which seem to involve cytoskeletal interactions as well as calcium-calcineurin signalling.