Immunological Disorders: Regulation of Ca(2+) Signaling in T Lymphocytes

Immunization of recombinant NS3 protein (protease region) of dengue virus induces high levels of CTLA-4 and apoptosis in splenocytes of BALB/c mice

DENV infection outcomes depend on the host's variable expression of immune receptors and mediators, leading to either resolution or exacerbation. While the NS3 protein is known to induce robust immune responses, the specific impact of its protease region epitopes remains unclear. This study investigated the effect of recombinant NS3 protease region proteins from all four DENV serotypes on splenocyte activation in BALB/c mice (n = 5/group). Mice were immunized with each protein, and their splenocytes were subsequently stimulated with homologous antigens. We measured the expression of costimulatory molecules (CD28, CD80, CD86, CD152) by flow cytometry, along with IL-2 production, CD25 expression, and examined the antigen-specific activation of CD4 + and CD8 + T cells. Additionally, the expression of IL-1, IL-10, and TGF-β1 in splenocytes from immunized animals was assessed. Apoptosis was evaluated using Annexin V/PI staining and DNA fragmentation analysis. Stimulation of splenocytes from immunized mice triggered apoptosis (phosphatidylserine exposure and caspase 3/7 activation) and increased costimulatory molecule expression, particularly CD152. Low IL-2 production and low CD25 expression, as well as sustained expression of the IL-10 gene. These results suggest that these molecules might be involved in mechanisms by which the NS3 protein contributes to viral persistence and disease pathogenesis.

Synthetic Biology Meets Ca2+ Release-Activated Ca2+ Channel-Dependent Immunomodulation

Many essential biological processes are triggered by the proximity of molecules. Meanwhile, diverse approaches in synthetic biology, such as new biological parts or engineered cells, have opened up avenues to precisely control the proximity of molecules and eventually downstream signaling processes. This also applies to a main Ca2+ entry pathway into the cell, the so-called Ca2+ release-activated Ca2+ (CRAC) channel. CRAC channels are among other channels are essential in the immune response and are activated by receptor-ligand binding at the cell membrane. The latter initiates a signaling cascade within the cell, which finally triggers the coupling of the two key molecular components of the CRAC channel, namely the stromal interaction molecule, STIM, in the ER membrane and the plasma membrane Ca2+ ion channel, Orai. Ca2+ entry, established via STIM/Orai coupling, is essential for various immune cell functions, including cytokine release, proliferation, and cytotoxicity. In this review, we summarize the tools of synthetic biology that have been used so far to achieve precise control over the CRAC channel pathway and thus over downstream signaling events related to the immune response.

Inborn Errors of Immunity and Cytokine Storm Syndromes

Inborn errors of immunity (IEI) are a diverse and growing category of more than 430 chronic disorders that share susceptibilities to infections. Whether the result of a genetic lesion that causes defective granule-dependent cytotoxicity, excessive lymphoproliferation, or an overwhelming infection represents a unique antigenic challenge, IEIs can display a proclivity for cytokine storm syndrome (CSS) development. This chapter provides an overview of CSS pathophysiology as it relates to IEIs. For each IEI, the immunologic defect and how it promotes or discourages CSS phenomena are reviewed. The IEI-associated molecular defects in pathways that are postulated to be critical to CSS physiology (i.e., toll-like receptors, T regulatory cells, the IL-12/IFNγ axis, IL-6) and, whenever possible, review strategies for treating CSS in IEI patients with molecularly directed therapies are highlighted.

Role of Orai-family channels in the activation and regulation of transcriptional activity

Store operated Ca²⁺ entry (SOCE) is a cornerstone for the maintenance of intracellular Ca²⁺ homeostasis and the regulation of a variety of cellular functions. SOCE is mediated by STIM and Orai proteins following the activation of inositol 1,4,5-trisphosphate receptors. Then, a reduction of the endoplasmic reticulum intraluminal Ca²⁺ concentration is sensed by STIM proteins, which undergo a conformational change and activate plasma membrane Ca²⁺ channels comprised by Orai proteins. STIM1/Orai-mediated Ca²⁺ signals are finely regulated and modulate the activity of different transcription factors, including certain isoforms of the nuclear factor of activated T-cells, the cAMP-response element binding protein, the nuclear factor κ-light chain-enhancer of activated B cells, c-fos, and c-myc. These transcription factors associate SOCE with a plethora of signaling events and cellular functions. Here we provide an overview of the current knowledge about the role of Orai channels in the regulation of transcription factors through Ca²⁺ -dependent signaling pathways.

The GABA and GABA-Receptor System in Inflammation, Anti-Tumor Immune Responses, and COVID-19

GABA and GABA_A-receptors (GABA_A-Rs) play major roles in neurodevelopment and neurotransmission in the central nervous system (CNS). There has been a growing appreciation that GABA_A-Rs are also present on most immune cells. Studies in the fields of autoimmune disease, cancer, parasitology, and virology have observed that GABA-R ligands have anti-inflammatory actions on T cells and antigen-presenting cells (APCs), while also enhancing regulatory T cell (Treg) responses and shifting APCs toward anti-inflammatory phenotypes. These actions have enabled GABA_A-R ligands to ameliorate autoimmune diseases, such as type 1 diabetes (T1D), multiple sclerosis (MS), and rheumatoid arthritis, as well as type 2 diabetes (T2D)-associated inflammation in preclinical models. Conversely, antagonism of GABA_A-R activity promotes the pro-inflammatory responses of T cells and APCs, enhancing anti-tumor responses and reducing tumor burden in models of solid tumors. Lung epithelial cells also express GABA-Rs, whose activation helps maintain fluid homeostasis and promote recovery from injury. The ability of GABA_A-R agonists to limit both excessive immune responses and lung epithelial cell injury may underlie recent findings that GABA_A-R agonists reduce the severity of disease in mice infected with highly lethal coronaviruses (SARS-CoV-2 and MHV-1). These observations suggest that GABA_A-R agonists may provide off-the-shelf therapies for COVID-19 caused by new SARS-CoV-2 variants, as well as novel beta-coronaviruses, which evade vaccine-induced immune responses and antiviral medications. We review these findings and further advance the notions that (1) immune cells possess GABA_A-Rs to limit inflammation in the CNS, and (2) this natural "braking system" on inflammatory responses may be pharmacologically engaged to slow the progression of autoimmune diseases, reduce the severity of COVID-19, and perhaps limit neuroinflammation associated with long COVID.

Biological insights into systemic lupus erythematosus through an immune cell-specific transcriptome-wide association study

OBJECTIVE

Genome-wide association studies (GWAS) have identified >100 risk loci for systemic lupus erythematosus (SLE), but the disease genes at most loci remain unclear, hampering translation of these genetic discoveries. We aimed to prioritise genes underlying the 110 SLE loci that were identified in the latest East Asian GWAS meta-analysis.

METHODS

We built gene expression predictive models in blood B cells, CD4+ and CD8+ T cells, monocytes, natural killer cells and peripheral blood cells of 105 Japanese individuals. We performed a transcriptome-wide association study (TWAS) using data from the latest genome-wide association meta-analysis of 208 370 East Asians and searched for candidate genes using TWAS and three data-driven computational approaches.

RESULTS

TWAS identified 171 genes for SLE (p<1.0×10-5); 114 (66.7%) showed significance only in a single cell type; 127 (74.3%) were in SLE GWAS loci. TWAS identified a strong association between CD83 and SLE (p<7.7×10-8). Meta-analysis of genetic associations in the existing 208 370 East Asian and additional 1498 cases and 3330 controls found a novel single-variant association at rs72836542 (OR=1.11, p=4.5×10-9) around CD83. For the 110 SLE loci, we identified 276 gene candidates, including 104 genes at recently-identified SLE novel loci. We demonstrated in vitro that putative causal variant rs61759532 exhibited an allele-specific regulatory effect on ACAP1, and that presence of the SLE risk allele decreased ACAP1 expression.

CONCLUSIONS

Cell-level TWAS in six types of immune cells complemented SLE gene discovery and guided the identification of novel genetic associations. The gene findings shed biological insights into SLE genetic associations.

Omnitemporal choreographies of all five STIM/Orai and IP3Rs underlie the complexity of mammalian Ca2+ signaling

Stromal-interaction molecules (STIM1/2) sense endoplasmic reticulum (ER) Ca²⁺ depletion and activate Orai channels. However, the choreography of interactions between native STIM/Orai proteins under physiological agonist stimulation is unknown. We show that the five STIM1/2 and Orai1/2/3 proteins are non-redundant and function together to ensure the graded diversity of mammalian Ca²⁺ signaling. Physiological Ca²⁺ signaling requires functional interactions between STIM1/2, Orai1/2/3, and IP₃Rs, ensuring that receptor-mediated Ca²⁺ release is tailored to Ca²⁺ entry and nuclear factor of activated T cells (NFAT) activation. The N-terminal Ca²⁺-binding ER-luminal domains of unactivated STIM1/2 inhibit IP₃R-evoked Ca²⁺ release. A gradual increase in agonist intensity and STIM1/2 activation relieves IP₃R inhibition. Concomitantly, activated STIM1/2 C termini differentially interact with Orai1/2/3 as agonist intensity increases. Thus, coordinated and omnitemporal functions of all five STIM/Orai and IP₃Rs translate the strength of agonist stimulation to precise levels of Ca²⁺ signaling and NFAT induction, ensuring the fidelity of complex mammalian Ca²⁺ signaling.

Calcium Signaling in T Cells and Chronic Inflammatory Disorders of the Oral Cavity

Acute immune responses to microbial insults in the oral cavity often progress to chronic inflammatory diseases such as periodontitis and apical periodontitis. Chronic oral inflammation causes destruction of the periodontium, potentially leading to loss of the dentition. Previous investigations have demonstrated that the composition of oral immune cells, rather than the overall extent of cellular infiltration, determines the pathological development of chronic inflammation. The role of T lymphocyte populations, including Th1, Th2, Th17, and Treg cells, has been extensively described. Studies now propose pathogenic Th17 cells as a distinct subset, uniquely classifiable from traditional Th17 populations. In situ differentiation of pathogenic Th17 cells has been verified as a source of destructive inflammation, which critically drives pathogenesis in chronic inflammatory diseases such as diabetes, rheumatoid arthritis, and inflammatory bowel disease. Pathogenic Th17 cells resemble a Th1 penotype and produce not only interleukin 17 (IL-17) but also γ-interferon (IFN-γ) and granulocyte-macrophage colony-stimulating factor (GM-CSF). The proinflammatory cytokine-specific mechanisms known to induce IL-17 expression in Th17 cells are well characterized; however, differentiation mechanisms that lead to pathogenic Th17 cells are less understood. Recently, Ca2⁺ signaling through Ca²⁺ release-activated Ca²⁺ channels (CRAC) in T cells has been uncovered as a major signaling axis involved in the regulation of T-cell-mediated chronic inflammation. In particular, pathogenic Th17 cell-mediated immunological diseases appear to be effectively targeted via such Ca²⁺ signaling pathways. Pathogenic plasticity of Th17 cells has been extensively illustrated in autoimmune and chronic inflammatory diseases. Although their specific causal relationship to oral infection-induced chronic inflammatory diseases is not fully established, pathogenic Th17 cells may be involved in the underlining mechanism. This review highlights the current understanding of T-cell phenotype regulation, calcium signaling pathways in this event, and the potential role of pathogenic Th17 cells in chronic inflammatory disorders of the oral cavity.

Lophatherum gracile Brongn. attenuates neutrophilic inflammation through inhibition of JNK and calcium

ETHNOPHARMACOLOGICAL RELEVANCE

Lophatherum gracile Brongn. (L. gracile) has been long used in traditional herbal medicine to clinically clear heat, disinhibit dampness, and treat inflammation. However, the effect of L. gracile on the activation of human neutrophils remains unclear.

AIM OF THE STUDY

The aim of current study is to investigate the anti-inflammatory properties of L. gracile extract (LGE) in N-formyl-methionyl-leucyl-phenylalanine (fMLF)-induced activation of human neutrophils.

MATERIALS AND METHODS

Superoxide anion generation and elastase release were estimated by spectrophotometry. A series of signaling pathways including mitogen-activated protein kinases (MAPKs) and protein kinase B (Akt), as well as calcium mobilization were studied by Western blot analysis and spectrofluorometry.

RESULTS

Our experimental results indicated that the nontoxic dosage of LGE does-dependently inhibited the fMLF-induced superoxide anion (O₂^•-) generation, elastase release, CD11b expression, adhesion, and chemotactic migration in human neutrophils. LGE selectively inhibited the fMLF-induced phosphorylation of JNK but not p38, ERK, or Akt in human neutrophils. LGE also decreased the intracellular Ca²⁺ levels ([Ca²⁺]_i) in fMLF-activated human neutrophils. However, a specific JNK inhibitor inhibited the fMLF-induced O₂^•- generation and CD11b expression, but it had no effect on [Ca²⁺]_i in human neutrophils.

CONCLUSIONS

LGE exhibited anti-inflammatory activities in fMLF-activated human neutrophils. The pharmacological mechanisms of LGE-repressed neutrophilic inflammation were through two independent pathways, JNK signaling and calcium mobilization. Our results suggested that LGE holds the potential to be developed as an anti-inflammatory botanical medicine.

Altered Ca2+ Homeostasis in Immune Cells during Aging: Role of Ion Channels

Aging is an unstoppable process and begins shortly after birth. Each cell of the organism is affected by the irreversible process, not only with equal density but also at varying ages and with different speed. Therefore, aging can also be understood as an adaptation to a continually changing cellular environment. One of these very prominent changes in age affects Ca²⁺ signaling. Especially immune cells highly rely on Ca²⁺-dependent processes and a strictly regulated Ca²⁺ homeostasis. The intricate patterns of impaired immune cell function may represent a deficit or compensatory mechanisms. Besides, altered immune function through Ca²⁺ signaling can profoundly affect the development of age-related disease. This review attempts to summarize changes in Ca²⁺ signaling due to channels and receptors in T cells and beyond in the context of aging.

Gardenia jasminoides extract and its constituent, genipin, inhibit activation of CD3/CD28 co-stimulated CD4+ T cells via ORAI1 channel

Gardenia jasminoides (GJ) is a widely used herbal medicine with anti-inflammatory properties, but its effects on the ORAI1 channel, which is important in generating intracellular calcium signaling for T cell activation, remain unknown. In this study, we investigated whether 70% ethanolic GJ extract (GJ_EtOH) and its subsequent fractions inhibit ORAI1 and determined which constituents contributed to this effect. Whole-cell patch clamp analysis revealed that GJ_EtOH (64.7% ± 3.83% inhibition at 0.1 mg/ml) and all its fractions showed inhibitory effects on the ORAI1 channel. Among the GJ fractions, the hexane fraction (GJ_HEX, 66.8% ± 9.95% at 0.1 mg/ml) had the most potent inhibitory effects in hORAI1-hSTIM1 co-transfected HEK293T cells. Chemical constituent analysis revealed that the strong ORAI1 inhibitory effect of GJ_HEX was due to linoleic acid, and in other fractions, we found that genipin inhibited ORAI1. Genipin significantly inhibited I_ORAI1 and interleukin-2 production in CD3/CD28-stimulated Jurkat T lymphocytes by 35.9% ± 3.02% and 54.7% ± 1.32% at 30 μM, respectively. Furthermore, the same genipin concentration inhibited the proliferation of human primary CD4⁺ T lymphocytes stimulated with CD3/CD28 antibodies by 54.9% ± 8.22%, as evaluated by carboxyfluorescein succinimidyl ester assay. Our findings suggest that genipin may be one of the active components of GJ responsible for T cell suppression, which is partially mediated by activation of the ORAI1 channel. This study helps us understand the mechanisms of GJ in the treatment of inflammatory diseases.

The native ORAI channel trio underlies the diversity of Ca2+ signaling events

The essential role of ORAI1 channels in receptor-evoked Ca2+ signaling is well understood, yet little is known about the physiological activation of the ORAI channel trio natively expressed in all cells. The roles of ORAI2 and ORAI3 have remained obscure. We show that ORAI2 and ORAI3 channels play a critical role in mediating the regenerative Ca2+ oscillations induced by physiological receptor activation, yet ORAI1 is dispensable in generation of oscillations. We reveal that ORAI2 and ORAI3 channels multimerize with ORAI1 to expand the range of sensitivity of receptor-activated Ca2+ signals, reflecting their enhanced basal STIM1-binding and heightened Ca2+-dependent inactivation. This broadened bandwidth of Ca2+ influx is translated by cells into differential activation of NFAT1 and NFAT4 isoforms. Our results uncover a long-sought role for ORAI2 and ORAI3, revealing an intricate control mechanism whereby heteromerization of ORAI channels mediates graded Ca2+ signals that extend the agonist-sensitivity to fine-tune transcriptional control.

The polyphenol ellagic acid exerts anti-inflammatory actions via disruption of store-operated calcium entry (SOCE) pathway activators and coupling mediators

Ellagic acid, a naturally occurring phenol found in a variety of fruits and nuts has been shown to possess anti-inflammatory properties. However, the mechanism of action behind its anti-inflammatory action is unclear. Using human Jurkat T cells, our study examined the effects of ellagic acid (EA) on Ca²⁺ handling, in particular, store-operated Ca²⁺ entry (SOCE), a process critical to proper T cell function. We observed that the acute addition of EA-induced Ca²⁺ release with an EC₅₀ of 63 μM. The Ca²⁺ release was significantly attenuated by Xestospongin C, a known inhibitor of the Inositol 1,4,5-trisphosphate receptor (IP₃R) channel and was unaffected by the phospholipase C (PLC) inhibitor, U73122. Furthermore, chronic incubation of Jurkat T cells with EA not only decreased the ATP-induced Ca²⁺ release but also diminished the SOCE-mediated Ca²⁺ influx in a dose-dependent manner. This inhibition was confirmed by reduced Mn²⁺ entry rates in the EA-treated cells. The ATP-induced Ca²⁺ entry was also attenuated in EA-treated HEK293 cells transiently transfected with SOCE channel Orai1-myc and ER-sensor stromal interaction molecule (STIM1) (HEK^STIM/Orai). Moreover, EA treatment interfered with the Orai1 and STIM1 coupling by disrupting STIM1 puncta formation in the HEK^STIM/Orai cells. We observed that EA treatment reduced cytokine secretion and nuclear factor of activated T-cell transcriptional activity in stimulated T cells. Hence, by inhibiting SOCE mediated Ca²⁺ influx, EA decreased downstream activation of pro-inflammatory mediators. These results suggest a novel target for EA-mediated effects and provide insight into the mechanisms underlying EA-mediated anti-inflammatory effects.

Immunosuppressive Activity of Artemisia argyi Extract and Isolated Compounds

The need for novel drugs for the treatment of autoimmune diseases is high, since available pharmaceuticals often have substantial side effects and limited efficacy. Natural products are a good starting point in the development of immunosuppressive leads. Since enhanced T cell proliferation is a common feature of autoimmune diseases, we investigated the T cell proliferation inhibitory potential of an extract library of plants used in traditional Chinese medicine. Using a newly established cell-based screening platform, an ethyl acetate extract of Artemisia argyi H.Lév. & Vaniot (Asteraceae, A. argyi) was found to suppress the proliferation of human primary T lymphocytes in vitro in an IL-2-dependent manner. Flow cytometry- and ELISA-based techniques further demonstrated that the A. argyi extract reduced the activation and function of T cells. Transcription factor analysis and flow cytometric calcium influx investigations indicated that the immunomodulatory effect was based on specific modification of T cell signaling in a non-cytotoxic manner which is mediated via the NFAT pathway and a non-sequestrant inhibition of the calcium influx. A series of guaianolide and seco-guaianolide sesquiterpene lactones, as well as a flavonoid, were identified in a previous study as the bioactive compounds in the A. argyi extract. The effects of these bioactive compounds were compared to those of the crude extract. The tested sesquiterpene lactones act via the transcription factor NFAT and NF-κB, thereby exhibiting their immunosuppressive potential, but have an overall effect on T cell biology on a more-downstream level than the crude A. argyi extract.

Exploring the impact of a naturally occurring sapogenin diosgenin on underlying mechanisms of Ca2+ movement and cytotoxicity in human prostate cancer cells

Literature has shown that diosgenin, a naturally occurring sapogenin, inducedcytotoxic effects in many cancer models. This study investigated the effect of diosgenin on intracellular Ca²⁺ concentration ([Ca²⁺ ]i) and cytotoxicity in PC3 human prostate cancer cells. Diosgenin (250-1000 μM) caused [Ca²⁺ ]i rises which was reduced by Ca²⁺ removal. Treatment with thapsigargin eliminated diosgenin-induced [Ca²⁺ ]i increases. In contrast, incubation with diosgeninabolished thapsigargin-caused [Ca²⁺ ]i increases. Suppression of phospholipase C with U73122 eliminated diosgenin-caused [Ca²⁺ ]i increases. Diosgenin evoked Mn²⁺ influx suggesting that diosgenin induced Ca²⁺ entry. Diosgenin-induced Ca²⁺ influx was suppressed by PMA, GF109203X, and nifedipine, econazole, or SKF96365. Diosgenin (250-600 μM) concentration-dependently decreased cell viability. However, diosgenin-induced cytotoxicity was not reversed by chelation of cytosolic Ca²⁺ with BAPTA/AM. Together, diosgenin evoked [Ca²⁺ ]i increases via Ca²⁺ release and Ca²⁺ influx, and caused Ca²⁺ -non-associated deathin PC3 cells. These findings reveal a newtherapeutic potential of diosgenin for human prostate cancer.

Calcium signalling in T cells

Calcium (Ca²⁺) signalling is of paramount importance to immunity. Regulated increases in cytosolic and organellar Ca²⁺ concentrations in lymphocytes control complex and crucial effector functions such as metabolism, proliferation, differentiation, antibody and cytokine secretion and cytotoxicity. Altered Ca²⁺ regulation in lymphocytes leads to various autoimmune, inflammatory and immunodeficiency syndromes. Several types of plasma membrane and organellar Ca²⁺-permeable channels are functional in T cells. They contribute highly localized spatial and temporal Ca²⁺ microdomains that are required for achieving functional specificity. While the mechanistic details of these Ca²⁺ microdomains are only beginning to emerge, it is evident that through crosstalk, synergy and feedback mechanisms, they fine-tune T cell signalling to match complex immune responses. In this article, we review the expression and function of various Ca²⁺-permeable channels in the plasma membrane, endoplasmic reticulum, mitochondria and endolysosomes of T cells and their role in shaping immunity and the pathogenesis of immune-mediated diseases.

A calcium/cAMP signaling loop at the ORAI1 mouth drives channel inactivation to shape NFAT induction

ORAI1 constitutes the store-operated Ca²⁺ release-activated Ca²⁺ (CRAC) channel crucial for life. Whereas ORAI1 activation by Ca²⁺-sensing STIM proteins is known, still obscure is how ORAI1 is turned off through Ca²⁺-dependent inactivation (CDI), protecting against Ca²⁺ toxicity. Here we identify a spatially-restricted Ca²⁺/cAMP signaling crosstalk critical for mediating CDI. Binding of Ca²⁺-activated adenylyl cyclase 8 (AC8) to the N-terminus of ORAI1 positions AC8 near the mouth of ORAI1 for sensing Ca²⁺. Ca²⁺ permeating ORAI1 activates AC8 to generate cAMP and activate PKA. PKA, positioned by AKAP79 near ORAI1, phosphorylates serine-34 in ORAI1 pore extension to induce CDI whereas recruitment of the phosphatase calcineurin antagonizes the effect of PKA. Notably, CDI shapes ORAI1 cytosolic Ca²⁺ signature to determine the isoform and degree of NFAT activation. Thus, we uncover a mechanism of ORAI1 inactivation, and reveal a hitherto unappreciated role for inactivation in shaping cellular Ca²⁺ signals and NFAT activation.

ORAI1 constitutes the store-operated Ca²⁺ release-activated Ca²⁺ (CRAC) channel, but how this channel is turned off through Ca²⁺-dependent inactivation (CDI) remained unclear. Here the authors identify a spatially-restricted Ca²⁺/cAMP signaling crosstalk critical for mediating CDI which in turn regulates cellular Ca²⁺ signals and NFAT activation.

The Ca2+ sensor STIM1 regulates the type I interferon response by retaining the signaling adaptor STING at the endoplasmic reticulum

Stimulator of interferon genes (STING) is an endoplasmic reticulum (ER) signaling adaptor that is essential for the type I interferon response to DNA pathogens. Aberrant activation of STING is linked to the pathology of autoimmune and autoinflammatory diseases. The rate-limiting step for the activation of STING is its translocation from the ER to the ER-Golgi intermediate compartment. Here, we found that deficiency in the Ca2+ sensor stromal interaction molecule 1 (STIM1) caused spontaneous activation of STING and enhanced expression of type I interferons under resting conditions in mice and a patient with combined immunodeficiency. Mechanistically, STIM1 associated with STING to retain it in the ER membrane, and coexpression of full-length STIM1 or a STING-interacting fragment of STIM1 suppressed the function of dominant STING mutants that cause autoinflammatory diseases. Furthermore, deficiency in STIM1 strongly enhanced the expression of type I interferons after viral infection and prevented the lethality of infection with a DNA virus in vivo. This work delineates a STIM1-STING circuit that maintains the resting state of the STING pathway.

The TRPC6 intronic polymorphism, associated with the risk of neurological disorders in systemic lupus erythematous, influences immune cell function

Patients with systemic lupus erythematosus (SLE) carrying a TT genotype for the rs7925662 single nucleotide polymorphism (SNP) in the transient receptor potential canonical channel 6 (TRPC6) gene are more likely to develop neuropsychiatric manifestations (NPSLE). We functionally characterised the effects of TRPC6 on peripheral blood mononuclear cells from 18 patients with SLE and 8 healthy controls with a known genotype. TRPC6 influenced calcium currents, apoptosis rates and cytokine secretion in a disease- and genotype-dependent manner. Cells from TT patients with NPSLE were more dependent on TRPC6 for the generation of calcium currents.

Pro-inflammatory role of transient receptor potential canonical channel 6 in the pathogenesis of chronic rhinosinusitis with nasal polyps

BACKGROUND

The pathogenesis of chronic rhinosinusitis with nasal polyps (CRSwNP) has not been fully elucidated. This study sought to explore the role and mechanism of transient receptor potential canonical channel 6 (TRPC6) in the pathogenesis of CRSwNP.

METHODS

Immunohistochemistry (IHC) was employed to evaluate TRPC6 immunolabeling. Real-time polymerase chain reaction (PCR) was conducted to assay TRPC6, stromal interaction molecule 1 (STIM1), and calcium release-activated calcium channel protein 1 (Orai1) messenger RNA (mRNA) levels in 70 patients with CRSwNP, including eosinophilic CRSwNP (ECRSwNP) or non-eosinophilic CRSwNP (nECRSwNP), and 28 control subjects. The concentrations of inflammatory mediators, including interleukin (IL)-1β, IL-5, and IL-25, were assayed by enzyme-linked immunosorbent assay (ELISA). In experiments on human nasal epithelial cell (HNEC) culture and stimulation, the mean fluorescence intensity (MFI) of intracellular Ca²⁺ was assayed by flow cytometry. Western blotting, real-time PCR, and ELISA were also conducted to assess the effects and mechanisms of TRPC6 activator 1-oleoyl-2-acetyl-glycerol (OAG) and TRPC6 inhibitor 1-[2-(4-methoxyphenyl)-2-[3-(4-methoxyphenyl) propoxy]ethyl-1H-imidazole (SKF-96365) on HNECs.

RESULTS

Upregulation of TRPC6, STIM1, and Orai1 levels was found in CRSwNP patients, particularly in those with ECRSwNP. TRPC6-positive cells correlated positively with the numbers of eosinophils and neutrophils, respectively. Moreover, TRPC6 mRNA was positively correlated with STIM1 and Orai1 mRNA levels. The concentrations of inflammatory mediators, including IL-1β, IL-5, and IL-25, were elevated in CRSwNP, especially in ECRSwNP. In cultured HNECs, TRPC6, STIM1, Orai1, Ca²⁺ MFI levels, and inflammatory mediators were upregulated by lipopolysaccharide (LPS) and OAG but were inhibited by SKF-96365.

CONCLUSION

TRPC6 plays a pro-inflammatory role in the pathogenesis of CRSwNP via regulating Ca²⁺ flow.

CRACR2A-Mediated TCR Signaling Promotes Local Effector Th1 and Th17 Responses

Ca2+ release-activated Ca2+ channel regulator 2A (CRACR2A) is expressed abundantly in T cells and acts as a signal transmitter between TCR stimulation and activation of the Ca2+/NFAT and JNK/AP1 pathways. CRACR2A has been linked to human diseases in numerous genome-wide association studies and was shown to be one of the most sensitive targets of the widely used statin drugs. However, the physiological role of CRACR2A in T cell functions remains unknown. In this study, using transgenic mice for tissue-specific deletion, we show that CRACR2A promotes Th1 responses and effector function of Th17 cells. CRACR2A was abundantly expressed in Th1 and Th17 cells. In vitro, deficiency of CRACR2A decreased Th1 differentiation under nonpolarizing conditions, whereas the presence of polarizing cytokines compensated this defect. Transcript analysis showed that weakened TCR signaling by deficiency of CRACR2A failed to promote Th1 transcriptional program. In vivo, conditional deletion of CRACR2A in T cells alleviated Th1 responses to acute lymphocytic choriomeningitis virus infection and imparted resistance to experimental autoimmune encephalomyelitis. Analysis of CNS from experimental autoimmune encephalomyelitis-induced mice showed impaired effector functions of both Th1 and Th17 cell types, which correlated with decreased pathogenicity. Collectively, our findings demonstrate the requirement of CRACR2A-mediated TCR signaling in Th1 responses as well as pathogenic conversion of Th17 cells, which occurs at the site of inflammation.

GRAM marks the spot for STIM. Commentary on "GRAM domain proteins specialize functionally distinct ER-PM contact sites in human cells"

GRAM domain proteins were reported as novel ER-PM tethers defining specific membrane contact sites (MCS) subdomains. GRAMD2a pre-marks the sites occupied by STIM1 at MCS and its ablation impairs STIM1 translocation, but not store-operated Ca²⁺ entry. We discuss these apparently counterintuitive findings in the context of STIM/ORAI signaling at MCS.