Nutritional and Pharmacological Targeting of the Calcium-Sensing Receptor Influences Chemically Induced Colitis in Mice

Estrogen receptor β activation alleviates inflammatory bowel disease by suppressing NLRP3-dependent IL-1β production in macrophages via downregulation of intracellular calcium level

INTRODUCTION

Although several estrogen receptor β (ERβ) agonists have been reported to alleviate IBD, the pivotal mechanism remains obscure.

OBJECTIVES

To examine the effects and mechanisms of ERβ activation on cytokine/chemokine networks in colitis mice.

METHODS

Dextran sulfate sodium salt (DSS) and trinitro-benzene-sulfonic acid (TNBS) were used to induce mouse colitis model. Multiple molecular biological methods were employed to evaluate the severity of mouse colitis and the level of cytokine and/or chemokine.

RESULTS

Bioinformatics analysis, ELISA and immunofluorescence results showed that the targeted cytokines and/or chemokines associated with ERβ expression and activation is IL-1β, and the anti-colitis effect of ERβ activation was significantly attenuated by the overexpression of AAV9-IL-1β. Immunofluorescence analysis indicated that ERβ activation led to most evident downregulation of IL-1β expression in colonic macrophages as compared to monocytes and neutrophils. Given the pivotal roles of NLRP3, NLRC4, and AIM2 inflammasome activation in the production of IL-1β, we examined the influence of ERβ activation on inflammasome activity. ELISA and WB results showed that ERβ activation selectively blocked the NLRP3 inflammasome assembly-mediated IL-1β secretion. The calcium-sensing receptor (CaSR) and calcium signaling play crucial roles in the assembly of the NLRP3 inflammasome. WB and immunofluorescence results showed that ERβ activation reduced intracellular CaSR expression and calcium signaling in colonic macrophages. Combination with CaSR overexpression plasmid reversed the suppressive effect of ERβ activation on NLRP3 inflammasome assembly, and counteracting the downregulation of IL-1β secretion.

CONCLUSION

Our research uncovers that the anti-colitis effect of ERβ activation is accomplished through the reduction of IL-1β levels in colonic tissue, achieved by specifically decreasing CaSR expression in macrophages to lower intracellular calcium levels and inhibit NLRP3 inflammasome assembly-mediated IL-1β production.

The calcium-sensing receptor: a comprehensive review on its role in calcium homeostasis and therapeutic implications

The calcium-sensing receptor (CaSR), a key member of the family C G protein-coupled receptors (GPCRs), plays a crucial role in regulating calcium homeostasis and parathyroid hormone (PTH) secretion. It responds to various physiological ligands, including calcium ions and amino acids, activating multiple signaling pathways through interactions with different G proteins and β-arrestin. This review focuses on the structural features of CaSR, emphasizing recent advances in understanding its activation mechanisms via agonists and allosteric modulators. CaSR holds significant therapeutic potential, particularly in treating calcitropic disorders such as hyperparathyroidism and hypoparathyroidism. Current pharmacological agents, including calcimimetics such as cinacalcet and etelcalcetide, have proven effective in managing secondary hyperparathyroidism (SHPT); however, they are associated with side effects such as hypocalcemia. Emerging investigational drugs, including palopegteriparatide and other small molecules, show promise in addressing various calcium-related conditions. Despite challenges that have led to the discontinuation of some drug developments, ongoing research is focused on refining CaSR-targeted therapies to improve efficacy, reduce adverse effects, and enhance patient outcomes.

Targeting the Calcium-Sensing Receptor in Chemically Induced Medium-Grade Colitis in Female BALB/C Mice

BACKGROUND/OBJECTIVES

The extracellular calcium-sensing receptor (CaSR) is a multifunctional receptor proposed as a possible drug target for inflammatory bowel disease. We showed previously that CaSR inhibition with NPS 2143, a negative allosteric modulator of the CaSR, somewhat ameliorated the symptoms of chemically induced severe colitis in mice. However, it was unclear whether the potential of CaSR inhibition to reduce colitis may have been overshadowed by the severity of the induced inflammation in our previous study. Therefore, we tested if CaSR inhibition could prevent medium-grade colitis.

METHODS

Female BALB/c mice were treated with NPS 2143 or a vehicle prior to the induction of colitis with 2.5% DSS. On the day of sacrifice, colons and plasma were collected. The histology score was determined based on hematoxylin-eosin-stained sections. Mucin content, proliferation (Ki67), and immune cell infiltration (CD3 and CD20) were quantified based on immunostainings. Gene expression was measured by RT-qPCR.

RESULTS

Treatment with NPS 2143 had no effect on the clinical symptom score of the mice. However, the colons of the mice in the treated group were significantly longer (p < 0.05), and NPS 2143 significantly reduced colon ulceration (p < 0.05). The treatment also significantly reduced the expression of COX2 in the proximal colon and IL-22 in the distal colon. The proliferation of cells in the lymph nodes was significantly lower after the treatment, but no difference was observed in the epithelial cells.

CONCLUSIONS

In summary, while NPS 2143 had an anti-inflammatory effect on medium-grade colitis, this effect appeared to be milder than in severe colitis, as observed previously, indicating that the effectiveness of CaSR inhibition as an anti-inflammatory measure in the colon is proportional to disease severity.

Ophthalmate is a new regulator of motor functions via CaSR: implications for movement disorders

Dopamine's role as the principal neurotransmitter in motor functions has long been accepted. We broaden this conventional perspective by demonstrating the involvement of non-dopaminergic mechanisms. In mouse models of Parkinson's disease, we observed that L-DOPA elicited a substantial motor response even when its conversion to dopamine was blocked by inhibiting the enzyme aromatic amino acid decarboxylase (AADC). Remarkably, the motor activity response to L-DOPA in the presence of an AADC inhibitor (NSD1015) showed a delayed onset, yet greater intensity and longer duration, peaking at 7 h, compared to when L-DOPA was administered alone. This suggests an alternative pathway or mechanism, independent of dopamine signalling, mediating the motor functions. We sought to determine the metabolites associated with the pronounced hyperactivity observed, using comprehensive metabolomics analysis. Our results revealed that the peak in motor activity induced by NSD1015/L-DOPA in Parkinson's disease mice is associated with a surge (20-fold) in brain levels of the tripeptide ophthalmic acid (also known as ophthalmate in its anionic form). Interestingly, we found that administering ophthalmate directly to the brain rescued motor deficits in Parkinson's disease mice in a dose-dependent manner. We investigated the molecular mechanisms underlying ophthalmate's action and discovered, through radioligand binding and cAMP-luminescence assays, that ophthalmate binds to and activates the calcium-sensing receptor (CaSR). Additionally, our findings demonstrated that a CaSR antagonist inhibits the motor-enhancing effects of ophthalmate, further solidifying the evidence that ophthalmate modulates motor functions through the activation of the CaSR. The discovery of ophthalmate as a novel regulator of motor function presents significant potential to transform our understanding of brain mechanisms of movement control and the therapeutic management of related disorders.

Chronic Cinacalcet improves skin flap survival in rats: the suggested role of the nitric oxide pathway

Cinacalcet is a calcimimetic medicine that has been used to treat secondary hyperparathyroidism and parathyroid cancer. Various studies have proposed the positive role of calcium and its receptor in skin wound healing. Furthermore, Cinacalcet interacts with other skin repair-related mechanisms, including inflammation and nitric oxide pathways. The present study evaluated the effect of Cinacalcet on the random-pattern skin flap survival. Eighty-four Wistar male rats were used. Multiple doses of Cinacalcet (30, 3, 1, 0.3, and 0.05 mg/kg) were used in 3 different routes of administration before the surgery. Histopathological evaluations, quantitative assessment of IL-6, TNF-α, and nitric oxide (NO), and the expression of calcium-sensing receptor (CaSR) and E-cadherin were evaluated in the skin tissue. To assess the role of NO, a NO synthase inhibitor, N-nitro-L-arginine methyl ester hydrochloride (L-NAME), was used, and histopathological effects were investigated. Cinacalcet pretreatment at the IP chronic 1 mg/kg dose significantly increased the skin flap survival rate and enhanced the NO tissue level compared to the control. However, the administration of L-NAME abolished its protective effects. IP Chronic 1 mg/kg of Cinacalcet could also decline the levels of IL-6 and TNF-α and also increase the expression of CaSR and E-cadherin in the flap tissue compared with the control group. Chronic Cinacalcet at 1 mg/kg could improve skin flap survival, probably mediated by the CaSR, NO, and inflammation-related pathways.

Ca2+-Dependent Processes of Innate Immunity in IBD

IBD is an uncontrolled inflammatory condition of the gastrointestinal tract, which mainly manifests in two forms: ulcerative colitis (UC) and Crohn's disease (CD). The pathogenesis of IBD appears to be associated with an abnormal response of innate and adaptive immune cells. Innate immunity cells, such as macrophages, mast cells, and granulocytes, can produce proinflammatory (e.g., TNF-α) and oxidative stress (ROS) mediators promoting intestinal damage, and their abnormal responses can induce an imbalance in adaptive immunity, leading to the production of inflammatory cytokines that increase innate immune damage, abate intestinal barrier functions, and aggravate inflammation. Considering that Ca2+ signalling plays a key role in a plethora of cellular functions, this review has the purpose of deepening the potential Ca2+ involvement in IBD pathogenesis.

Comparative analysis of calcium-sensing receptor (CaSR) expression and function in normal and abnormal human sperm and spermatogenic cells

The calcium-sensing receptor (CaSR) is a critical mediator of calcium homeostasis in various tissues. Its role in human reproduction, especially in sperm function and male fertility, remains not fully elucidated. This study investigates the expression patterns of CaSR in normal and abnormal sperm and spermatogenic cells and evaluates its potential effect on sperm motility and morphology. Using immunohistochemistry (IHC), quantitative PCR (qPCR), we assessed the expression levels of CaSR in normal sperm, spermatogonia, and cases of asthenozoospermia, oligozoospermia, and teratozoospermia. In vitro functional assays were performed to analyze the effects of CaSR modulation on sperm motility under varying conditions, including the presence of specific CaSR agonists and antagonists. Our study revealed distinct patterns of CaSR expression in normal sperm and spermatogonia compared with those in abnormal sperm samples, particularly in cases of asthenozoospermia, oligozoospermia, and teratozoospermia. A marked decrease in CaSR expression was evident in these abnormal samples, highlighting its significance in normal sperm functionality. Functional assays further elucidated the role of CaSR in sperm motility. Activation of CaSR through specific agonists enhanced sperm motility, while inhibition by antagonists led to reduced motility. Our findings suggest that CaSR plays a significant role in maintaining sperm functionality and that changes in its expression may be associated with male infertility. These insights into the molecular underpinnings of sperm physiology highlight CaSR as a potential therapeutic target for treating certain forms of male infertility.

The Effects of Artificial Sweeteners on Intestinal Nutrient-Sensing Receptors: Dr. Jekyll or Mr. Hyde?

The consumption of artificial and low-calorie sweeteners (ASs, LCSs) is an important component of the Western diet. ASs play a role in the pathogenesis of metabolic syndrome, dysbiosis, inflammatory bowel diseases (IBDs), and various inflammatory conditions. Intestinal nutrient-sensing receptors act as a crosstalk between dietary components, the gut microbiota, and the regulation of immune, endocrinological, and neurological responses. This narrative review aimed to summarize the possible effects of ASs and LCSs on intestinal nutrient-sensing receptors and their related functions. Based on the findings of various studies, long-term AS consumption has effects on the gut microbiota and intestinal nutrient-sensing receptors in modulating incretin hormones, antimicrobial peptides, and cytokine secretion. These effects contribute to the regulation of glucose metabolism, ion transport, gut permeability, and inflammation and modulate the gut-brain, and gut-kidney axes. Based on the conflicting findings of several in vitro, in vivo, and randomized and controlled studies, artificial sweeteners may have a role in the pathogenesis of IBDs, functional bowel diseases, metabolic syndrome, and cancers via the modulation of nutrient-sensing receptors. Further studies are needed to explore the exact mechanisms underlying their effects to decide the risk/benefit ratio of sugar intake reduction via AS and LCS consumption.

Role of micronutrients in inflammatory bowel disease

Inflammatory bowel disease (IBD) is an autoimmune intestinal disease that includes ulcerative colitis, Crohn's disease, and indeterminate colitis. Patients with IBD are often at risk for malnutrition, including micronutrient deficiencies, due to dietary restrictions and poor intestinal absorption. Micronutrients, including vitamins and minerals, play an important role in the human body's metabolism and maintenance of tissue functions. This article reviews the role of micronutrients in IBD. Micronutrients can affect the occurrence and progression of IBD by regulating immunity, intestinal flora, oxidative stress, intestinal barrier function, and other aspects. Monitoring and timely supplementation of micronutrients are important to delay progression and improve clinical symptoms in IBD patients.

Calcium-Sensitive Receptors Alters Intestinal Microbiota Metabolites Especially SCFAs and Ameliorates Intestinal Barrier Damage in Neonatal Rat Endotoxemia

Purpose

The calcium-sensing receptor (CaSR) acts as a major modulator of tissue responses related to calcium homeostasis and expresses highly in the mammalian intestine. Endotoxemia tends to impair intestinal barrier function and poses significant obstacles in clinical treatment. This work is designed to decipher whether CaSR can protect lipopolysaccharide (LPS)-induced intestinal barrier dysfunction in neonatal rats by targeting intestinal metabolites.

Patient and Methods

In this study, we utilized gas chromatography (GC) combined with liquid chromatography-mass spectrometry (LC-MS) to quantitatively analyze SCFAs and metabolites in fecal samples of 24 neonatal rats with LPS induced endotoxemia.

Results

Our results showed that CaSR alleviated endotoxin damage to the intestinal tight junction structure and upregulated the levels of butyric acid, propionic acid, valeric acid, and isovaleric acid in short-chain fatty acids (SCFAs). Non-targeted metabolomics analysis indicated that CaSR improved intestinal metabolic disorders by regulating glycerophospholipid metabolism, α-linolenic acid metabolism, as well as sphingolipids metabolism.

Conclusion

CaSR can alter intestinal microbiota metabolites, especially SCFAs, and improve intestinal barrier damage in neonatal rat endotoxemia.

The calcium-sensing receptor modulates the prostaglandin E2 pathway in intestinal inflammation

Introduction: The prostaglandin E2 (PGE2) pathway is one of the main mediators of intestinal inflammation. As activation of the calcium-sensing receptor (CaSR) induces expression of inflammatory markers in the colon, we assessed the impact of the CaSR on the PGE2 pathway regulation in colon cancer cells and the colon in vitro and in vivo. Methods and Results: We treated CaSR-transfected HT29 and Caco-2 colon cancer cell lines with different orthosteric ligands or modulators of the CaSR and measured gene expression and PGE2 levels. In CaSR-transfected HT29CaSR-GFP and Caco-2CaSR-GFP cells, the orthosteric CaSR ligand spermine and the positive allosteric CaSR modulator NPS R-568 both induced an inflammatory state as measured by IL-8 gene expression and significantly increased the expression of the PGE2 pathway key enzymes cyclooxygenase (COX)-2 and/or prostaglandin E2 synthase 1 (PGES-1). Inhibition of the CaSR with the calcilytic NPS 2143 abolished the spermine- and NPS R-568-induced pro-inflammatory response. Interestingly, we observed cell-line specific responses as e.g. PGES-1 expression was affected only in HT29CaSR-GFP but not in Caco-2CaSR-GFP cells. Other genes involved in the PGE2 pathway (COX-1, or the PGE2 receptors) were not responsive to the treatment. None of the studied genes were affected by any CaSR agonist in GFP-only transfected HT29GFP and Caco-2GFP cells, indicating that the observed gene-inducing effects of spermine and R-568 were indeed mediated by the CaSR. In vivo, we had previously determined that treatment with the clinically approved calcimimetic cinacalcet worsened symptoms in a dextran sulfate sodium (DSS)-induced colitis mouse model. In the colons of these mice, cinacalcet significantly induced gene expression of PGES-2 and the EP3 receptor, but not COX-2; while NPS 2143 increased the expression of the PGE2-degrading enzyme 15-hydroxyprostaglandin dehydrogenase (15-PGDH). Importantly, neither treatment had any effect on the colons of non-DSS treated mice. Discussion: Overall, we show that activation of the CaSR induces the PGE2 pathway, albeit with differing effects in vitro and in vivo. This may be due to the different microenvironment in vivo compared to in vitro, specifically the presence of a CaSR-responsive immune system. Since calcilytics inhibit ligand-mediated CaSR signaling, they may be considered for novel therapies against inflammatory bowel disease.

Low molecular weight hyaluronan inhibits lung epithelial ion channels by activating the calcium-sensing receptor

Herein, we tested the hypothesis that low molecular weight hyaluronan (LMW-HA) inhibits lung epithelial ions transport in-vivo, ex-vivo, and in-vitro by activating the calcium-sensing receptor (CaSR). Twenty-four hours post intranasal instillation of 50-150 µg/ml LMW-HA to C57BL/6 mice, there was a 75% inhibition of alveolar fluid clearance (AFC), a threefold increase in the epithelial lining fluid (ELF) depth, and a 20% increase in lung wet/dry (W/D) ratio. Incubation of human and mouse precision cut lung slices with 150 µg/ml LMW-HA reduced the activity and the open probability (Po) of epithelial sodium channel (ENaC) in alveolar epithelial type 2 (ATII) cells, and in mouse tracheal epithelial cells (MTEC) monolayers as early as 4 h. The Cl- current through cystic fibrosis transmembrane conductance regulator (CFTR) and the activity of Na,K-ATPase were both inhibited by more than 66% at 24 h. The inhibitory effects of LMW-HA on ion channels were reversed by 1 µM NPS-2143, or 150 µg/ml high molecular weight hyaluronan (HMW-HA). In HEK-293 cells expressing the calcium-sensitive Cl- channel TMEM16-A, CaSR was required for the activation of the Cl- current by LMW-HA. This is the first demonstration of lung ions and water transport inhibition by LMW-HA, and its mediation through the activation of CaSR.

The calcium-sensing receptor in inflammation: Recent updates

The Calcium-Sensing Receptor (CaSR) is a member of the class C of G-proteins coupled receptors (GPCRs), it plays a pivotal role in calcium homeostasis by directly controlling calcium excretion in the kidneys and indirectly by regulating parathyroid hormone (PTH) release from the parathyroid glands. The CaSR is found to be ubiquitously expressed in the body, playing a plethora of additional functions spanning from fluid secretion, insulin release, neuronal development, vessel tone to cell proliferation and apoptosis, to name but a few. The present review aims to elucidate and clarify the emerging regulatory effects that the CaSR plays in inflammation in several tissues, where it mostly promotes pro-inflammatory responses, with the exception of the large intestine, where contradictory roles have been recently reported. The CaSR has been found to be expressed even in immune cells, where it stimulates immune response and chemokinesis. On the other hand, CaSR expression seems to be boosted under inflammatory stimulus, in particular, by pro-inflammatory cytokines. Because of this, the CaSR has been addressed as a key factor responsible for hypocalcemia and low levels of PTH that are commonly found in critically ill patients under sepsis or after burn injury. Moreover, the CaSR has been found to be implicated in autoimmune-hypoparathyroidism, recently found also in patients treated with immune-checkpoint inhibitors. Given the tight bound between the CaSR, calcium and vitamin D metabolism, we also speculate about their roles in the pathogenesis of severe acute respiratory syndrome coronavirus-19 (SARS-COVID-19) infection and their impact on patients' prognosis. We will further explore the therapeutic potential of pharmacological targeting of the CaSR for the treatment and management of aberrant inflammatory responses.

AOM/DSS Induced Colitis-Associated Colorectal Cancer in 14-Month-Old Female Balb/C and C57/Bl6 Mice-A Pilot Study

Colitis is a major risk factor for the development of colorectal cancer, leading to colitis-associated colorectal cancer (CAC). The most commonly used animal model to study CAC is the azoxymethane-dextran sulphate-sodium (AOM/DSS) model. The ideal experimental conditions of this model depend on several factors, including the used mouse strain. No data on feasibility and conditions for older mice, e.g., for aging studies, have yet been reported. Thus, we conducted a descriptive, observational pilot study where CAC was induced in 14-month-old female Balb/C and C57/Bl6 mice using 12.5 mg/kg AOM i.p. and three different concentrations of DSS (1, 2, and 3%) in drinking water (ad. lib.). The mice were monitored regularly during the three-month experimental phase. After euthanasia, the colons of the mice were evaluated macroscopically and microscopically. Both the mouse strains showed a DSS-concentration-dependent induction of CAC. Carcinomas were only observed at 3% DSS. The DSS dose was found to be significantly correlated with the histology score and % Ki67 positive cells only in C57/Bl6 mice but not in Balb/C mice, which showed a variable response to the CAC induction. No differences in colon length, weight, or mucin content were observed. Optimal conditions for CAC induction in these aged animals are thus considered to be 3% DSS, as carcinomas did not develop when 2% DSS was used. On the other hand, Balb/C mice reacted severely to 3% DSS, indicating that 2.5% DSS may be the "sweet spot" for future experiments comparing CAC in aged Balb/C and C57/Bl6 mice. This model will allow investigation of the effect of aging on CAC development and therapy.

Cinacalcet Targets the Neurokinin-1 Receptor and Inhibits PKCδ/ERK/P65 Signaling to Alleviate Dextran Sulfate Sodium-Induced Colitis

Objective: Inflammatory bowel disease is an immune-mediated chronic inflammatory disease of the gastrointestinal tract for which curative drugs are currently not available. This study was performed to assess the therapeutic effects of cinacalcet on dextran sulfate sodium (DSS)-induced colitis. Methods: Primary macrophages obtained from bone marrow and the macrophage cell line RAW264.7 were used to examine the inhibitory effect of cinacalcet on cytokine production, the PKCδ/ERK/P65 signaling pathway, and NF-κB P65 translocation. Colitis was induced using DSS to assess the treatment effect of cinacalcet. Bioinformatics approaches were adopted to predict potential targets of cinacalcet, and a drug affinity responsive target stability (DARTs) assay was performed to confirm binding between cinacalcet and potential target. Results: In vivo analysis showed that cinacalcet reduced the disease activity score, prevented shortening of the colon, diminished inflammatory cell infiltration, and protected the structural integrity of the intestinal wall. Cinacalcet also reduced production of the inflammatory cytokines TNFα, IL-1β, and IL-6 in the colon and sera of mice with DSS-induced colitis. In vitro studies revealed that cinacalcet suppressed the translocation of P65 and inhibited production of the inflammatory cytokines IL-1β and IL-6. Mechanistic studies revealed that the target of cinacalcet was neurokinin-1 receptor (NK1R) and their binding was confirmed by a DARTs assay. Furthermore, the inhibition of NK-κB P65 activation was found to occur via the suppression of PKCδ/ERK/P65 signaling mediated by cinacalcet. Conclusion: Cinacalcet inhibits the activation of NF-κB and reduces the production of inflammatory cytokines by suppressing the PKCδ/ERK/P65 signaling pathway via targeting NK1R, suggesting that it can be used to treat inflammatory diseases, particularly colitis.

Stereo-Specific Modulation of the Extracellular Calcium-Sensing Receptor in Colon Cancer Cells

Pharmacological allosteric agonists (calcimimetics) of the extracellular calcium-sensing receptor (CaSR) have substantial gastro-intestinal side effects and induce the expression of inflammatory markers in colon cancer cells. Here, we compared the effects of both CaSR-specific (R enantiomers) and -unspecific (S enantiomers) enantiomers of a calcimimetic (NPS 568) and a calcilytic (allosteric CaSR antagonists; NPS 2143) to prove that these effects are indeed mediated via the CaSR, rather than via off-target effects, e.g., on β-adrenoceptors or calcium channels, of these drugs. The unspecific S enantiomer of NPS 2143 and NPS S-2143 was prepared using synthetic chemistry and characterized using crystallography. NPS S-2143 was then tested in HEK-293 cells stably transfected with the human CaSR (HEK-CaSR), where it did not inhibit CaSR-mediated intracellular Ca2+ signals, as expected. HT29 colon cancer cells transfected with the CaSR were treated with both enantiomers of NPS 568 and NPS 2143 alone or in combination, and the expression of CaSR and the pro-inflammatory cytokine interleukin 8 (IL-8) was measured by RT-qPCR and ELISA. Only the CaSR-selective enantiomers of the calcimimetic NPS 568 and NPS 2143 were able to modulate CaSR and IL-8 expression. We proved that pro-inflammatory effects in colon cancer cells are indeed mediated through CaSR activation. The non-CaSR selective enantiomer NPS S-2143 will be a valuable tool for investigations in CaSR-mediated processes.

The first junior European Calcium Society meeting: calcium research across scales, Kingdoms and countries

The first junior European Calcium Society online meeting, held October 20-21, 2020, aimed to promote junior researchers in the Ca²⁺ community. The meeting included four scientific sessions, covering Ca²⁺ research from molecular detail to whole organisms. Each session featured one invited speaker and three speakers selected based on submitted abstracts, with the overall aim of actively involving early-career researchers. Consequently, the meeting underlined the diversity of Ca²⁺ physiology, by showcasing research across scales and Kingdoms, as presented by a correspondingly diverse speaker panel across career stages and countries. In this meeting report, we introduce the visions of the junior European Calcium Society board and summarize the meeting content.

Effects of pharmacological calcimimetics on colorectal cancer cells over-expressing the human calcium-sensing receptor

The calcium-sensing receptor (CaSR) is a ubiquitously expressed multifunctional G protein-coupled receptor. Several studies reported that the CaSR plays an anti-inflammatory and anti-tumorigenic role in the intestine, and that it is down-regulated during colorectal carcinogenesis. We hypothesized that positive allosteric CaSR modulators (type II calcimimetics) selectively targeting the intestinal cells could be used for the treatment of intestinal pathologies. Therefore, the aim of this study was to determine the effect of pharmacological stimulation of CaSR on gene expression in vitro and on tumor growth in vivo. We stably transduced two colon cancer cell lines (HT29 and Caco2) with lentiviral vectors containing either the CaSR fused to GFP or GFP only. Using RNA sequencing, RT-qPCR experiments and ELISA, we determined that CaSR over-expression itself had generally little effect on gene expression in these cells. However, treatment with 1 μM of the calcimimetic NPS R-568 increased the expression of pro-inflammatory factors such as IL-23α and IL-8 and reduced the transcription of various differentiation markers in the cells over-expressing the CaSR. In vivo, neither the presence of the CaSR nor p.o. treatment of the animals with the calcimimetic cinacalcet affected tumor growth, tumor cell proliferation or tumor vascularization of murine HT29 xenografts. In summary, CaSR stimulation in CaSR over-expressing cells enhanced the expression of inflammatory markers in vitro, but was not able to repress colorectal cancer tumorigenicity in vivo. These findings suggest potential pro-inflammatory effects of the CaSR and type II calcimimetics in the intestine.

International Union of Basic and Clinical Pharmacology. CVIII. Calcium-Sensing Receptor Nomenclature, Pharmacology, and Function

The calcium-sensing receptor (CaSR) is a class C G protein-coupled receptor that responds to multiple endogenous agonists and allosteric modulators, including divalent and trivalent cations, L-amino acids, γ-glutamyl peptides, polyamines, polycationic peptides, and protons. The CaSR plays a critical role in extracellular calcium (Ca2+ o) homeostasis, as demonstrated by the many naturally occurring mutations in the CaSR or its signaling partners that cause Ca2+ o homeostasis disorders. However, CaSR tissue expression in mammals is broad and includes tissues unrelated to Ca2+ o homeostasis, in which it, for example, regulates the secretion of digestive hormones, airway constriction, cardiovascular effects, cellular differentiation, and proliferation. Thus, although the CaSR is targeted clinically by the positive allosteric modulators (PAMs) cinacalcet, evocalcet, and etelcalcetide in hyperparathyroidism, it is also a putative therapeutic target in diabetes, asthma, cardiovascular disease, and cancer. The CaSR is somewhat unique in possessing multiple ligand binding sites, including at least five putative sites for the "orthosteric" agonist Ca2+ o, an allosteric site for endogenous L-amino acids, two further allosteric sites for small molecules and the peptide PAM, etelcalcetide, and additional sites for other cations and anions. The CaSR is promiscuous in its G protein-coupling preferences, and signals via Gq/11, Gi/o, potentially G12/13, and even Gs in some cell types. Not surprisingly, the CaSR is subject to biased agonism, in which distinct ligands preferentially stimulate a subset of the CaSR's possible signaling responses, to the exclusion of others. The CaSR thus serves as a model receptor to study natural bias and allostery. SIGNIFICANCE STATEMENT: The calcium-sensing receptor (CaSR) is a complex G protein-coupled receptor that possesses multiple orthosteric and allosteric binding sites, is subject to biased signaling via several different G proteins, and has numerous (patho)physiological roles. Understanding the complexities of CaSR structure, function, and biology will aid future drug discovery efforts seeking to target this receptor for a diversity of diseases. This review summarizes what is known to date regarding key structural, pharmacological, and physiological features of the CaSR.