The Calcium-Sensing Receptor in Health and Disease

Thiazolium salt mimics the non-coenzyme effects of vitamin B1 in rat synaptosomes

Long-term studies have confirmed a causal relationship between the development of neurodegenerative processes and vitamin B1 (thiamine) deficiency. However, the biochemical mechanisms underlying the high neurotropic activity of thiamine are not fully understood. At the same time, there is increasing evidence that vitamin B1, in addition to its coenzyme functions, may have non-coenzyme activities that are particularly important for neurons. To elucidate which effects of vitamin B1 in neurons are due to its coenzyme function and which are due to its non-coenzyme activity, we conducted a comparative study of the effects of thiamine and its derivative, 3-decyloxycarbonylmethyl-5-(2-hydroxyethyl)-4-methyl-1,3-thiazolium chloride (DMHT), on selected processes in synaptosomes. The ability of DMHT to effectively compete with thiamine for binding to thiamine-binding sites on the plasma membrane of synaptosomes and to participate as a substrate in the thiamine pyrophosphokinase reaction was demonstrated. In experiments with rat brain synaptosomes, unidirectional effects of DMHT and thiamine on the activity of the pyruvate dehydrogenase complex (PDC) and on the incorporation of radiolabeled [2-14C]pyruvate into acetylcholine were demonstrated. The observed effects of thiamine and DMHT on the modulation of acetylcholine synthesis can be explained by suggesting that both compounds, which interact in cells with enzymes of thiamine metabolism, are phosphorylated and exert an inhibitory/activating effect (concentration-dependent) on PDC activity by affecting the regulatory enzymes of the complex. Such effects were not observed in the presence of structural analogues of thiamine and DMHT without a 2-hydroxyethyl substituent at position 5 of the thiazolium cycle. The effect of DMHT on the plasma membrane Ca-ATPase was similar to that of thiamine. At the same time, DMHT showed high cytostatic activity against neuroblastoma cells.

New insights into renal calcium-sensing receptor activation

PURPOSE OF REVIEW

Activation of the calcium-sensing receptor (CASR) in the parathyroid gland suppresses the release of parathyroid hormone (PTH). Furthermore, activation of the renal CASR directly increases the urinary excretion of calcium, by inhibiting transepithelial calcium transport in the nephron. Gain-of-function mutations in the CASR gene lead to autosomal dominant hypocalcemia 1 (ADH1), with inappropriately low PTH levels and hypocalcemia, indicative of excessive activation of the parathyroid CASR. However, hypercalciuria is not always observed. The reason why the manifestation of hypercalciuria is not uniform among ADH1 patients is not well understood.

RECENT FINDINGS

Direct activation of the CASR in the kidney has been cumbersome to study, and an indirect measure to effectively estimate the degree of CASR activation following chronic hypercalcemia or genetic gain-of-function CASR activation has been lacking. Studies have shown that expression of the pore-blocking claudin-14 is strongly stimulated by the CASR in a dose-dependent manner. This stimulatory effect is abolished after renal Casr ablation in hypercalcemic mice, suggesting that claudin-14 abundance may gauge renal CASR activation. Using this marker has led to unexpected discoveries regarding renal CASR activation.

SUMMARY

These new studies have informed on renal CASR activation thresholds and the downstream CASR-regulated calcium transport mechanisms.

Hypercalcemia in Cancer: Causes, Effects, and Treatment Strategies

Calcium plays central roles in numerous biological processes, thereby, its levels in the blood are under strict control to maintain homeostatic balance and enable the proper functioning of living organisms. The regulatory mechanisms ensuring this balance can be affected by pathologies such as cancer, and as a result, hyper- or hypocalcemia can occur. These states, characterized by elevated or decreased calcium blood levels, respectively, have a significant effect on general homeostasis. This article focuses on a particular form of calcium metabolism disorder, which is hypercalcemia in neoplasms. It also constitutes a summary of the current knowledge regarding the diagnosis of hypercalcemia and its management. Hypercalcemia of malignancy is estimated to affect over 40% of cancer patients and can be associated with both solid and blood cancers. Elevated calcium levels can be an indicator of developing cancer. The main mechanism of hypercalcemia development in tumors appears to be excessive production of parathyroid hormone-related peptides. Among the known treatment methods, bisphosphonates, calcitonin, steroids, and denosumab should be mentioned, but ongoing research promotes progress in pharmacotherapy. Given the rising global cancer prevalence, the problem of hypercalcemia is of high importance and requires attention.

G protein-coupled receptors (GPCRs): advances in structures, mechanisms, and drug discovery

G protein-coupled receptors (GPCRs), the largest family of human membrane proteins and an important class of drug targets, play a role in maintaining numerous physiological processes. Agonist or antagonist, orthosteric effects or allosteric effects, and biased signaling or balanced signaling, characterize the complexity of GPCR dynamic features. In this study, we first review the structural advancements, activation mechanisms, and functional diversity of GPCRs. We then focus on GPCR drug discovery by revealing the detailed drug-target interactions and the underlying mechanisms of orthosteric drugs approved by the US Food and Drug Administration in the past five years. Particularly, an up-to-date analysis is performed on available GPCR structures complexed with synthetic small-molecule allosteric modulators to elucidate key receptor-ligand interactions and allosteric mechanisms. Finally, we highlight how the widespread GPCR-druggable allosteric sites can guide structure- or mechanism-based drug design and propose prospects of designing bitopic ligands for the future therapeutic potential of targeting this receptor family.

Calcium sensing receptor: A promising therapeutic target in pulmonary hypertension

Pulmonary hypertension (PH) is characterized by elevation of pulmonary arterial pressure and pulmonary vascular resistance. The increased pulmonary arterial pressure and pulmonary vascular resistance due to sustained pulmonary vasoconstriction and pulmonary vascular remodeling can lead to right heart failure and eventual death. A rise in intracellular Ca2+ concentration ([Ca2+]i) and enhanced pulmonary arterial smooth muscle cells (PASMCs) proliferation contribute to pulmonary vasoconstriction and pulmonary vascular remodeling. Recent studies demonstrated that extracellular calcium sensing receptor (CaSR) as a G-protein coupled receptor participates in [Ca2+]i increase induced by hypoxia in the experimental animals of PH and in PH patients. Pharmacological blockade or gene knockout of CaSR significantly attenuates the development of PH. This review will aim to discuss and update the pathogenicity of CaSR attributed to onset and progression in PH.

Calcium-sensing Receptor, a Potential Biomarker Revealed by Large-scale Public Databases and Experimental Verification in Metastatic Breast Cancer

INTRODUCTION

Breast cancer (BC) is a common cancer characterized by a high molecular heterogeneity. Therefore, understanding its biological properties and developing effective treatments for patients with different molecular features is imperative. Calcium-sensing receptor (CaSR) has been implicated in several regulatory functions in various types of human cancers. However, its underlying pathological mechanism in BC progression remains elusive.

METHODS

We utilized The Cancer Genome Atlas and Gene Expression Omnibus databases to explore the function of CaSR in the metastasis of BC. Gene ontology analysis, Kyoto Encyclopedia of Genes and Genomes analysis, and Gene Set Enrichment Analysis of biological processes and cell signaling pathways revealed that CaSR could be activated or inhibited. Importantly, quantitative reverse transcriptase-polymerase chain reaction and western blotting were used to verify the gene expression of the CaSR. Wound healing and transwell assays were conducted to assess the effect of CaSR on the migration of BC cells.

RESULTS

We demonstrated that CaSR expression in metastatic BC was higher than that in non-metastatic BC. It is the first time that database information has been used to reveal the biological process and molecular mechanism of CaSR in BC. Moreover, the CaSR expression in normal breast epithelial cells was notably less compared to that in BC cells. The activation of CaSR by Cinacalcet (a CaSR agonist) significantly enhanced the migration of BC cells, whereas NPS-2143 (a CaSR antagonist) treatment dramatically inhibited these effects.

CONCLUSION AND FUTURE PERSPECTIVE

Bioinformatics techniques and experiments demonstrated the involvement of CaSR in BC metastasis. Our findings shed new light on the receptor therapy and molecular pathogenesis of BC, and emphasize the crucial function of CaSR, facilitating the metastasis of BC.

Comparative transcriptomic analysis of mammary gland tissues reveals the critical role of GPR110 in palmitic acid-stimulated milk protein and fat synthesis

The G protein-coupled receptors (GPCR) sensing nutritional signals (amino acids, fatty acids, glucose, etc.) are not fully understood. In this research, we used transcriptome sequencing to analyse differentially expressed genes (DEG) in mouse mammary gland tissues at puberty, lactation and involution stages, in which eight GPCR were selected out and verified by qRT-PCR assay. It was further identified the role of GPR110-mediating nutrients including palmitic acid (PA) and methionine (Met) to improve milk synthesis using mouse mammary epithelial cell line HC11. PA but not Met affected GPR110 expression in a dose-dependent manner. GPR110 knockdown decreased milk protein and fat synthesis and cell proliferation and blocked the stimulation of PA on mechanistic target of rapamycin (mTOR) phosphorylation and sterol-regulatory element binding protein 1c (SREBP-1c) expression. In summary, these experimental results disclose DEG related to lactation and reveal that GPR110 mediates PA to activate the mTOR and SREBP-1c pathways to promote milk protein and fat synthesis.

Evidence that pyrophosphate acts as an extracellular signalling molecule to exert direct functional effects in primary cultures of osteoblasts and osteoclasts

Extracellular pyrophosphate (PPi) is well known for its fundamental role as a physiochemical mineralisation inhibitor. However, information about its direct actions on bone cells remains limited. This study shows that PPi decreased osteoclast formation and resorptive activity by ≤50 %. These inhibitory actions were associated with reduced expression of genes involved in osteoclastogenesis (Tnfrsf11a, Dcstamp) and bone resorption (Ctsk, Car2, Acp5). In osteoblasts, PPi present for the entire (0-21 days) or latter stages of culture (7-21/14-21 days) decreased bone mineralisation by ≤95 %. However, PPi present for the differentiation phase only (0-7/0-14 days) increased bone formation (≤70 %). Prolonged treatment with PPi resulted in earlier matrix deposition and increased soluble collagen levels (≤2.3-fold). Expression of osteoblast (RUNX2, Bglap) and early osteocyte (E11, Dmp1) genes along with mineralisation inhibitors (Spp1, Mgp) was increased by PPi (≤3-fold). PPi levels are regulated by tissue non-specific alkaline phosphatase (TNAP) and ecto-nucleotide pyrophosphatase/phosphodiesterase 1 (NPP1). PPi reduced NPP1 expression in both cell types whereas TNAP expression (≤2.5-fold) and activity (≤35 %) were increased in osteoblasts. Breakdown of extracellular ATP by NPP1 represents a key source of PPi. ATP release from osteoclasts and osteoblasts was decreased ≤60 % by PPi and by a selective TNAP inhibitor (CAS496014-12-2). Pertussis toxin, which prevents Gαi subunit activation, was used to investigate whether G-protein coupled receptor (GPCR) signalling mediates the effects of PPi. The actions of PPi on bone mineralisation, collagen production, ATP release, gene/protein expression and osteoclast formation were abolished or attenuated by pertussis toxin. Together these findings show that PPi, modulates differentiation, function and gene expression in osteoblasts and osteoclasts. The ability of PPi to alter ATP release and NPP1/TNAP expression and activity indicates that cells can detect PPi levels and respond accordingly. Our data also raise the possibility that some actions of PPi on bone cells could be mediated by a Gαi-linked GPCR.

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.

Inhibition of Calcium-Sensing Receptor Alleviates Chronic Intermittent Hypoxia-Induced Cognitive Dysfunction via CaSR-PKC-ERK1/2 Pathway

Obstructive sleep apnea-hypopnea syndrome (OSAHS) is typically characterized by chronic intermittent hypoxia (CIH), associated with cognitive dysfunction in children. Calcium-sensing receptor (CaSR) mediates the apoptosis of hippocampal neurons in various diseases. However, the effect of CaSR on OSAHS remains elusive. In the present study, we investigated the role of CaSR in CIH-induced memory dysfunction and underlying mechanisms on regulation of PKC-ERK1/2 signaling pathway in vivo and in vitro. CIH exposures for 4 weeks in mice, modeling OSAHS, contributed to cognitive dysfunction. CIH accelerated apoptosis of hippocampal neurons and resulted in the synaptic plasticity deficit via downregulated synaptophysin (Syn) protein level. The mice were intraperitoneally injected with CaSR inhibitor (NPS2143) 30 min before CIH exposure and the results demonstrated CaSR inhibitor alleviated the apoptosis and synaptic plasticity deficit in the hippocampus of CIH mice. We established intermittent hypoxia PC12 cell model and found that the activation of CaSR accelerated CIH-induced PC12 apoptosis and synaptic plasticity deficit by upregulated p-ERK1/2 and PKC. Overall, our findings revealed that CaSR held a critical function on CIH-induced cognitive dysfunction in mice by accelerating hippocampal neuronal apoptosis and reducing synaptic plasticity via augmenting CaSR-PKC-ERK1/2 pathway; otherwise, inhibition of CaSR alleviated CIH-induced cognitive dysfunction.

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 role of calcium-sensitive receptor in ovalbumin-induced airway inflammation and hyperresponsiveness in juvenile mice with asthma

The role of the calcium-sensitive receptor (CaSR) was assessed in a juvenile mouse model of asthma induced by ovalbumin (OVA). The experiment was divided into normal control, OVA, and OVA +2.5/5 mg/kg NPS2143 (a CaSR antagonist) groups. OVA induction was performed in all groups except the normal control, followed by assessing airway hyperresponsiveness (AHR) and lung pathological changes. Serum OVA-specific IgE and IgG1 were detected with an enzyme-linked immunosorbent assay (ELISA), and inflammatory cells were counted in bronchoalveolar lavage fluid (BALF). Real-time quantitative polymerase chain reaction, ELISA, and western blotting were performed to detect gene and protein expression. NPS2143 improved the OVA-induced AHR in mice, and AHR was higher in the OVA +2.5 mg/kg NPS2143 group than in the OVA +5 mg/kg NPS2143 group. Furthermore, NPS2143 reduced the production of OVA-specific IgE and IgG1 in serum and the number of eosinophils and lymphocytes in BALF in OVA mice with reduced CaSR expression in lung tissues. Besides, OVA-induced mice exhibited peribronchial and perivascular inflammatory cell infiltration, which was accompanied by severe goblet cell hyperplasia/hyperplasia and airway mucus hypersecretion. Furthermore, these mice exhibited increased levels of Interleukin (IL)-5, IL-13, MCP-1, and eotaxin, which were alleviated by NPS2143. The 5 mg/kg NPS2143 showed more effective than the 2.5 mg/kg treatment. CaSR expression was elevated in the lung tissues of OVA-induced asthmatic juvenile mice, whereas the CaSR antagonist NPS2143 reduced AHR and attenuated the inflammatory response in OVA-induced juvenile mice, possibly exerting therapeutic effects on childhood asthma.

[Diagnostic trap: Lithium neurotoxicity with normal lithemia]

We describe here the case of a 54-year-old bipolar woman, followed in psychiatry and treated with lithium and a selective serotonin reuptake inhibitor (escitalopram) and lamotrigine, presenting a lithium poisoning with an altered state of consciousness caused by a supposed mismanagement of her treatment. Lithium poisoning was suggested based on neurological clinical features, but the blood test brought out a lithium concentration within the therapeutic values at 1,2 mmol/L (N: 0,6-1,2 mmol/L). The classic biological complications related to lithium poisoning (hypercalcemia, diabetes insipidus) confirmed the diagnosis. The patient has been transferred to our nephrology department where she got two hemodialysis sessions conducting to clinical and biological improvement, confirming the diagnosis of lithium poisoning despite the normal blood levels. Later, she was transferred to the psychiatry department for follow-up and for treatment adjustment.

Dual nuclear magnetic resonance for probing intrinsic bone structure and a potential gut-bone axis in ovariectomized rats

Currently, the existence of a gut-bone axis receives massive attention, and while sound premises and indirect proofs exist for the gut-bone axis concept, few studies have provided actual data linking the gut and bone physically. This study aimed to exploit the versatile nature of nuclear magnetic resonance (NMR) to link NMR relaxometry data on bone mineralization with NMR spectroscopic profiling of gut metabolites. For this purpose, sample material was obtained from a 6-week intervention study with ovariectomized (OVX) rats (n = 49) fed with seven different diets varying in calcium content (0.2-6.0 mg/kg) and prebiotic fiber content (0-5.0% w/w). This design ensured a span in (i) calcium available for bone mineralization and (ii) metabolic activity in the gut. After termination of the intervention, longitudinal (T₁ ), transverse (T₂ ) relaxation, and mechanical bone strength were measured on the excised femur bones. A PLS model with high predictability (Q²  = 0.86, R²  = 0.997) was demonstrated between T₂ decay curves and femur mechanical strength. Correlations were established between bone T₂ populations and gut short-chain fatty acids. In conclusion, the present dual NMR approach showed strong correlation between T₂ relaxation and mechanical strength of the bone, and when metabolic activity in the gut was modulated by inulin, the potential existence of a gut-bone axis was demonstrated.

Autosomal dominant hypocalcemia with a novel CASR mutation: a case study and literature review

Autosomal dominant hypocalcemia type 1 (ADH1) is a rare inherited disorder characterized by hypocalcemia with low parathyroid hormone (PTH) levels and high urinary calcium. Its clinical presentation varies from mild asymptomatic to severe hypocalcemia. It is caused by gain-of-function mutations in the calcium-sensing receptor gene (CASR) which affect PTH secretion from the parathyroid gland and calcium resorption in the kidney. Here, we describe a case who presented with symptoms of recurrent seizure caused by hypocalcemia with a novel CASR variant. We comprehensively analyzed the phenotypic features of this presentation and reviewed the current literature to better understand clinical manifestations and the genetic spectrum.

Strategy for sodium-salt substitution: On the relationship between hypertension and dietary intake of cations

Chronic diseases, especially cardiovascular diseases (CVD), have become one of the main causes affecting human health. Hypertension is a prominent representative of CVD. The formation and development of hypertension is closely related to people's daily diet. A large number of studies have shown that excessive intake of salt (NaCl) could increase the risk of hypertension. In recent years, more and more investigations have focused on other cations that may be contained in edible salt, exploring whether they have an effect on hypertension and the underlying mechanism. This article focuses on the relationship between four metal elements (potassium, calcium, magnesium, and zinc) and hypertension, by discussing the main metabolic pathway, the impact of diet intake on blood pressure, and especially the regulation mechanisms on blood pressure in detail. At the same time, some opinions and suggestions are put forward, combined with the current hot topics "salt reduction" and "salt substitution".

Astrocyte Dysregulation and Calcium Ion Imbalance May Link the Development of Osteoporosis and Alzheimer’s Disease

The typical symptoms of patients with Alzheimer’s disease (AD) are amyloid-β (Aβ) plaques and tau hyperphosphorylation. However, recent studies show that these symptoms are not the cause of the disease but are generated after the pathogenesis. Compared with other types of dementia, AD has the obvious features of pineal gland calcification and decreased melatonin production. The pineal gland is mainly composed of pinealocytes that release melatonin and astrocytes. Astrocytes function to maintain a balanced concentration of calcium ions, provide nerve cell nutrients, and migrate nutrients in vivo. Calcium ions are among the most important neurotransmitters. Once triggered, a calcium wave can be formed between astrocytes to activate other astrocytes to transmit information. Most calcium is stored in the skeleton. Bone tissue is composed mainly of osteocytes, osteoblasts, and osteoclasts. Of these, osteocyte is a kind of astrocyte which regulates the activity of osteoclasts and osteoblasts. The pineal gland is composed mainly of astrocytes; osteocytes are also a kind of astrocyte. Therefore, we conclude that when astrocytes are gradually disabled, calcium may be lost from the bones, prompting osteoporosis. The calcium ions then released into the blood may accumulate and cause ectopic calcification in the pineal gland, which promotes the occurrence of AD. Finally, this study used aspects of drugs and hormones (bone and calcium metabolism hormones and melatonin) to infer the hypothesis, which proposes that astrocyte dysregulation promotes the long-term imbalance of calcium ions in vivo and leads to osteoporosis and AD.

Differential parathyroid and kidney Ca2+-sensing receptor activation in autosomal dominant hypocalcemia 1

Background

Parathyroid Ca²⁺-sensing receptor (CaSR) activation inhibits parathyroid hormone (PTH) release, while activation of renal CaSRs attenuates Ca²⁺ transport and increases expression of the pore-blocking claudin-14. Patients with autosomal dominant hypocalcemia 1 (ADH1), due to activating CASR mutations, exhibit hypocalcemia but not always hypercalciuria (elevated Ca²⁺ in urine). The latter promotes nephrocalcinosis and renal insufficiency. Although CaSRs throughout the body including the kidney harbor activating CASR mutations, it is not understood why only some ADH1 patients display hypercalciuria.

Methods

Activation of the CaSR was studied in mouse models and a ADH1 patient. In vitro CaSR activation was studied in HEK293 cells.

Findings

Cldn14 showed blood Ca²⁺ concentration-dependent regulation, which was absent in mice with kidney-specific Casr deletion, indicating Cldn14 is a suitable marker for chronic CaSR activation in the kidney. Mice with a gain-of-function mutation in the Casr (Nuf) were hypocalcemic with low plasma PTH levels. However, renal CaSRs were not activated at baseline but only after normalizing blood Ca²⁺ levels. Similarly, significant hypercalciuria was not observed in a ADH1 patient until blood Ca²⁺ was normalized. In vitro experiments indicate that increased CaSR expression in the parathyroid relative to the kidney could contribute to tissue-specific CaSR activation thresholds.

Interpretation

Our findings suggest that parathyroid CaSR overactivity can reduce plasma Ca²⁺ to levels insufficient to activate renal CaSRs, even when an activating mutation is present. These findings identify a conceptually new mechanism of CaSR-dependent Ca²⁺ balance regulation that aid in explaining the spectrum of hypercalciuria in ADH1 patients.

Funding

Erasmus+ 2018/E+/4458087, the Canadian Institutes for Health research, the Novo Nordisk Foundation, the Beckett Foundation, the Carlsberg Foundation and Independent Research Fund Denmark.

Parathyroid hormone (PTH) regulation of metabolic homeostasis: An old dog teaches us new tricks

BACKGROUND

Late in the nineteenth century, it was theorized that a circulating product produced by the parathyroid glands could negatively impact skeletal homeostasis. A century later, intermittent administration of that protein, namely parathyroid hormone (PTH), was approved by the FDA and EMA as the first anabolic agent to treat osteoporosis. Yet, several unanswered but important questions remain about the skeletal actions of PTH.

SCOPE OF REVIEW

Current research efforts have focused on improving the efficacy of PTH treatment by designing structural analogs and identifying other targets (e.g., the PTH or the calcium sensing receptor). A unique but only recently described aspect of PTH action is its regulation of cellular bioenergetics and metabolism, namely in bone and adipose tissue but also in other tissues. The current review aims to provide a brief background on PTH's previously described actions on bone and highlights how PTH regulates osteoblast bioenergetics, contributing to greater bone formation. It will also shed light on how PTH could alter metabolic homeostasis through its actions in other cells and tissues, thereby impacting the skeleton in a cell non-autonomous manner.

MAJOR CONCLUSIONS

PTH administration enhances bone formation by targeting the osteoblast through transcriptional changes in several pathways; the most prominent is via adenyl cyclase and PKA. PTH and its related protein, PTHrP, also induce glycolysis and fatty acid oxidation in bone cells and drive lipolysis and thermogenic programming in adipocytes; the latter may indirectly but positively influence skeletal metabolism. While much work remains, alterations in cellular metabolism may also provide a novel mechanism related to PTH's temporal actions. Thus, the bioenergetic impact of PTH can be considered another of the myriad anabolic effects of PTH on the skeleton. Just as importantly from a translational perspective, the non-skeletal metabolic effects may lead to a better understanding of whole-body homeostasis along with new and improved therapies to treat musculoskeletal conditions.

Non-Additive Effects of Combined NOX1/4 Inhibition and Calcimimetic Treatment on a Rat Model of Chronic Kidney Disease-Mineral and Bone Disorder (CKD-MBD)

Chronic kidney disease-mineral and bone disorder (CKD-MBD) increases cardiovascular calcification and skeletal fragility in part by increasing systemic oxidative stress and disrupting mineral homeostasis through secondary hyperparathyroidism. We hypothesized that treatments to reduce reactive oxygen species formation and reduce parathyroid hormone (PTH) levels would have additive beneficial effects to prevent cardiovascular calcification and deleterious bone architecture and mechanics before end-stage kidney disease. To test this hypothesis, we treated a naturally progressive model of CKD-MBD, the Cy/+ rat, beginning early in CKD with the NADPH oxidase (NOX1/4) inhibitor GKT-137831 (GKT), the preclinical analogue of the calcimimetic etelcalcetide, KP-2326 (KP), and their combination. The results demonstrated that CKD animals had elevated blood urea nitrogen, PTH, fibroblast growth factor 23 (FGF23), and phosphorus. Treatment with KP reduced PTH levels compared with CKD animals, whereas GKT treatment increased C-terminal FGF23 levels without altering intact FGF23. GKT treatment alone reduced aortic calcification and NOX4 expression but did not alter the oxidative stress marker 8-OHdG in the serum or aorta. KP treatment reduced aortic 8-OHdG and inhibited the ability for GKT to reduce aortic calcification. Treatments did not alter heart calcification or left ventricular mass. In the skeleton, CKD animals had reduced trabecular bone volume fraction and trabecular number with increased trabecular spacing that were not improved with either treatment. The cortical bone was not altered by CKD or by treatments at this early stage of CKD. These results suggest that GKT reduces aortic calcification while KP reduces aortic oxidative stress and reduces PTH, but the combination was not additive. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Renal cell markers: lighthouses for managing renal diseases

Kidneys, one of the vital organs in our body, are responsible for maintaining whole body homeostasis. The complexity of renal function (e.g., filtration, reabsorption, fluid and electrolyte regulation, and urine production) demands diversity not only at the level of cell types but also in their overall distribution and structural framework within the kidney. To gain an in depth molecular-level understanding of the renal system, it is imperative to discern the components of kidney and the types of cells residing in each of the subregions. Recent developments in labeling, tracing, and imaging techniques have enabled us to mark, monitor, and identify these cells in vivo with high efficiency in a minimally invasive manner. In this review, we summarize different cell types, specific markers that are uniquely associated with those cell types, and their distribution in the kidney, which altogether make kidneys so special and different. Cellular sorting based on the presence of certain proteins on the cell surface allowed for the assignment of multiple markers for each cell type. However, different studies using different techniques have found contradictions in cell type-specific markers. Thus, the term "cell marker" might be imprecise and suboptimal, leading to uncertainty when interpreting the data. Therefore, we strongly believe that there is an unmet need to define the best cell markers for a cell type. Although the compendium of renal-selective marker proteins presented in this review is a resource that may be useful to researchers, we acknowledge that the list may not be necessarily exhaustive.

CircHIPK3 Plays Vital Roles in Cardiovascular Disease

Circular RNAs (circRNAs) are covalently closed RNAs that function in various physiological and pathological processes. CircRNAs are widely involved in the development of cardiovascular disease (CVD), one of the leading causes of morbidity and mortality worldwide. CircHIPK3 is generated from the second exon of the HIPK3 gene, a corepressor of homeodomain transcription factors. As an exonic circRNA (ecRNA), circHIPK3 is produced through intron-pairing driven circularization facilitated by Alu elements. In the past 5 years, a growing number of studies have revealed the multifunctional roles of circHIPK3 in different diseases, such as cancer and CVD. CircHIPK3 mainly participates in CVD pathogenesis through interacting with miRNAs. This paper summarizes the current literature on the biogenesis and functions of circHIPK3, elucidates the role of circHIPK3 in different CVD patterns, and explores future perspectives.

Novel pharmacological therapies for the treatment of bronchial asthma

Asthma has long been recognised as a chronic inflammatory disease of the airways, often in response to inhaled allergens prompting inappropriate activation of the immune response. involving a range of cells including mast cells, Th2 lymphocytes and eosinophils and a wide range of inflammatory mediators. First-line therapy for treatment of persistent asthma involves the use of inhaled corticosteroids (ICS) in combination with inhaled β2-agonists enabling both the control of the underlying airways inflammation and a reduction of airway hyperresponsiveness. However, many patients remain symptomatic despite high-dose therapy. There is therefore a continued unmet clinical need to develop specifically new anti-inflammatory therapies for patients with asthma, either as an add-on therapy to ICS or as replacement monotherapies. The success of fixed dose combination inhalers containing both a bronchodilator and an anti-inflammatory drug has also led to the development of "bifunctional" drugs which are molecules specifically designed to have two distinct pharmacological actions based on distinct pharmacophores. In this review we will discuss these different pharmacological approaches under development for the treatment of bronchial asthma and the available pre-clinical and clinical data.

The calcium sensing receptor (CaSR) promotes Rab27B expression and activity to control secretion in breast cancer cells

Chemotactic and angiogenic factors secreted within the tumor microenvironment eventually facilitate the metastatic dissemination of cancer cells. Calcium-sensing receptor (CaSR) activates secretory pathways in breast cancer cells via a mechanism driven by vesicular trafficking of this receptor. However, it remains to be elucidated how endosomal proteins in secretory vesicles are controlled by CaSR. In the present study, we demonstrate that CaSR promotes expression of Rab27B and activates this secretory small GTPase via PI3K, PKA, mTOR and MADD, a guanine nucleotide exchange factor, also known as DENN/Rab3GEP. Active Rab27B leads secretion of various cytokines and chemokines, including IL-6, IL-1β, IL-8, IP-10 and RANTES. Expression of Rab27B is stimulated by CaSR in MDA-MB-231 and MCF-7 breast epithelial cancer cells, but not in non-cancerous MCF-10A cells. This regulatory mechanism also occurs in HeLa and PC3 cells. Our findings provide insightful information regarding how CaSR activates a Rab27B-dependent mechanism to control secretion of factors known to intervene in paracrine communication circuits within the tumor microenvironment.

Role of the calcium-sensing receptor (CaSR) in cancer metastasis to bone: Identifying a potential therapeutic target

Cancer is a major cause of morbidity and mortality worldwide due to its ability to evade immune surveillance and metastasize from its origin to a secondary point of contact. Though several treatment techniques have been developed to suppress or manage cancer spread, a strategy for total control over the disease continues to evade researchers. In considering ways to control or prevent cancer from metastasizing to the bone, we analyze the impact of the calcium-sensing receptor (CaSR), whose primary role is to maintain calcium (Ca²⁺) homeostasis in cellular and systemic physiological processes. CaSR is a pleiotropic receptor capable of enhancing the proliferation of some cancers such as breast, lung, prostate and kidney cancers at its primary site(s) and stimulating bone metastasis, while exerting a suppressive effect in others such as colon cancer. The activity of CaSR not only increases cancer cell proliferation, migration and suppression of apoptosis in the organs indicated, but also increases the secretion of parathyroid hormone-related protein (PTHrP) and epiregulin, which induce osteolytic activity and osteoblastic suppression. In addition, released cytokines and Ca²⁺ from bone resorption are critical factors that further promote cancer proliferation. In this review, we seek to highlight previous viewpoints on CaSR, discuss its role in a new context, and consider its potential clinical application in cancer treatment.

Silencing of circHIPK3 Inhibits Pressure Overload-Induced Cardiac Hypertrophy and Dysfunction by Sponging miR-185-3p

Background

Cardiac hypertrophy is induced by diverse patho-physiological stimuli and indicates an increase in cardiomyocyte size. Circular RNAs (circRNAs) and microRNAs (miRNAs), members of noncoding RNAs, are involved in several biological processes and cardiovascular diseases (CVD). Here, we investigated the potential role of circHIPK3, which is produced by the third exon of the HIPK3 gene in cardiac hypertrophy.

Methods

qRT-PCR and Sanger sequencing were conducted to identify the expression and characteristics (head-to-tail structure, stability, and location) of circHIPK3 in cardiac hypertrophy; Immunostaining of α-SMA was performed to evaluate the size of the cardiomyocytes; Transverse aortic constriction (TAC) induced hypertrophy models of mice were established to investigate the effect of circHIPK3 in vivo. Bioinformatics analysis and luciferase reporter assays, RNA immunoprecipitation, and fluorescence in situ hybridization (FISH) experiments were conducted to investigate the mechanism of circHIPK3-mediated cardiac hypertrophy.

Results

circHIPK3 is circular, more stable, and mainly located in the cytoplasm. Silencing of circHIPK3 inhibited the TAC induced cardiac hypertrophy, and reversed the effect of TAC on the echocardiograph parameters, such as left ventricular end-diastolic pressure (LVEDPS), left ventricular fraction shortening (LVFS), left ventricular ejection fraction (LVEF), and left ventricular systolic dysfunction (LVSD), and also the heart weight to tibial length (HW/TL). Angiotensin II (Ang II) Ang II-treated cardiomyocytes showed larger size of cardiomyocyte and upregulation of fetal genes, biomarkers of cardiac hypertrophy, peptide hormones, atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), and myofilament protein, β-myosin heavy chain (β-MHC). These effects were reversed by circHIPK3 knockdown. Mechanically, circHIPK3 sponges miR-185-3p. In addition, miR-185-3p targets CASR. The rescue experiments confirmed the interaction between circHIPK3 and miR-185-3p as well as miR-185-3p and CASR.

Discussion

Our data suggested that circHIPK3 serve as a miR-185-3p sponge to regulate cardiac hypertrophy revealing a potential new target for the prevention of TAC- and Ang-II induced cardiac hypertrophy.

Calcium physiology, metabolism and supplementation: a glance at patients with ankylosing spondylitis

The aim of this review is to describe the metabolism of calcium in ankylosing spondylitis compared to physiologic conditions, and to present the current evidence on the benefits and disadvantages of calcium supplementation in these patients. A narrative review of the literature was conducted using the PubMed database and a total of 65 articles were selected. Calcium is involved in many physiopathological processes, including inflammation, bone loss and bone formation, all of which occur in ankylosing spondylitis. Many ankylosing spondylitis patients suffer from concomitant osteopenia or osteoporosis, which represent indications for calcium supplementation. Conversely, there are still concerns about the use of calcium salts for the prevention of bone fragility in non-osteoporotic or non-osteopenic patients. In these cases, biologic agents may indirectly normalize calcium dysmetabolism by rebalancing the cytokine milieu, in turn associated with bone remodeling. Calcium supplements may be disadvantageous for entheseal calcifications, but so far there are no clear data confirming that such an association exists.

Calcium-Sensing Receptor Mediates β-Amyloid-Induced Synaptic Formation Impairment and Cognitive Deficits via Regulation of Cytosolic Phospholipase A2/Prostaglandin E2 Metabolic Pathway

Calcium-sensing receptor (CaSR) is a G protein-coupled receptor (GPCRs). Soluble β-amyloid peptide (Aβ) is one of the orthosteric modulators of CaSR, while, the role and underlying mechanism of CaSR in cognitive decline in Alzheimer’s disease (AD) is unclear. In this study, molecular technology such as live-cell imaging combined with behavioral tests were used to explore the role and the underlying mechanism of CaSR in the cognitive deficits in AD mice. The expression levels of CaSR were increased both in AD mice and Aβ_1–42 (β-amyloid protein)-treated primary cultured neurons. Pharmacological inhibition of CaSR ameliorated recognitive and spatial memory deficits of Aβ_1–42-oligomer-treated mice in a dose-dependent manner. Pharmacological inhibition of CaSR or down-regulation of the expression of CaSR by CaSR-shRNA-lentivirus prevented the impairment of filopodia, and the synapse induced by oligomeric Aβ_1–42. The contents of cytosolic phospholipase A2 (cPLA2) and prostaglandin E2 (PGE2) in hippocampal neurons and tissue were increased after treatment with Aβ_1–42 oligomers. Inhibition or down-regulation of CaSR mediates Aβ-induced synapse formation and cognitive deficits partially, through the activation of the cPLA2/PGE2 pathway. This study provides novel insights on CaSR, which is a promising therapeutic target for AD.

Class C GPCRs in the airway

Understanding and targeting of GPCRs remain a critical aspect of airway pharmacology and therapeutics for diseases such as asthma or COPD. Most attention has been on the large Class A GPCRs towards improved bronchodilation and blunting of remodeling. Better known in the central or peripheral nervous system, there is increasing evidence that Class C GPCRs which include metabotropic glutamate and GABA receptors, the calcium sensing receptor, sweet/umami taste receptors and a number of orphan receptors, can contribute to airway structure and function. In this review, we will summarize current state of knowledge regarding the pharmacology of Class C GPCRs, their expression and potential functions in the airways, and the application of pharmacological agents targeting this group in the context of airway diseases.

Biomarkers of vascular calcification in serum

Over the last decades, the association between vascular calcification (VC) and all-cause/cardiovascular mortality, especially in patients with high atherogenic status, such as those with diabetes and/or chronic kidney disease, has been repeatedly highlighted. For over a century, VC has been noted as a passive, degenerative, aging process without any treatment options. However, during the past decades, studies confirmed that mineralization of the arteries is an active, complex process, similar to bone genesis and formation. The main purpose of this review is to provide an update of the existing biomarkers of VC in serum and develop the various pathogenetic mechanisms underlying the calcification process, including the pivotal roles of matrix Gla protein, osteoprotegerin, bone morphogenetic proteins, fetuin-a, fibroblast growth-factor-23, osteocalcin, osteopontin, osteonectin, sclerostin, pyrophosphate, Smads, fibrillin-1 and carbonic anhydrase II.

Calcium sensing receptor activation in THP-1 macrophages triggers NLRP3 inflammasome and human preadipose cell inflammation

Excess adipose tissue (AT) associates with inflammation and obesity-related diseases. We studied whether calcium-sensing receptor (CaSR)-mediated NLRP3 inflammasome activation in THP-1 macrophages elevates inflammation in LS14 preadipocytes, modeling deleterious AT cell crosstalk. THP-1 macrophages exposed to cinacalcet (CaSR activator, 2 μM, 4 h) showed elevated proinflammatory marker and NLRP3 inflammasome mRNA, pro-IL-1β protein and caspase-1 activity, whereas preincubation with CaSR negative modulators prevented these effects. The key NLRP3 inflammasome component ASC was silenced (siRNA) in THP-1 cells, and inflammasome activation was evaluated (qPCR, Western blot, caspase-1 activity) or they were further cultured to obtain conditioned medium (CoM). Exposure of LS14 preadipocytes to CoM from cinacalcet-treated THP-1 elevated LS14 proinflammatory cytokine expression, which was abrogated by THP-1 inflammasome silencing. Thus, CaSR activation elevates THP-1-induced inflammation in LS14 preadipocytes, via macrophage NLRP3 inflammasome activation. Modulating CaSR activation may prevent deleterious proinflammatory cell crosstalk in AT, a promising approach in obesity-related metabolic disorders.

A NOVEL MUTATION IN CALCIUM-SENSING RECEPTOR PRESENTING AS FAMILIAL HYPOCALCIURIC HYPERCALCEMIA IN A YOUNG MAN

Objective

Familial hypocalciuric hypercalcemia (FHH) is considered a relatively benign condition characterized by elevated serum calcium with relatively low urinary calcium excretion. It typically results from an altered set point in calcium homeostasis originating from mutations in the calcium-sensing receptor (CASR), AP2S1, or GNA11 genes, which encode for the calcium-sensing receptor (CaSR), adaptor-related protein complex 2, and G-protein alpha-11 subunit, respectively. Despite numerous reports of novel variants in these genes associated with FHH, new variants continue to be discovered.

Methods

We describe a 20-year-old man with a family history of hypercalcemia who had clinical findings compatible with FHH and no evidence of multiple endocrine neoplasia who underwent CASR gene sequencing for evaluation of hypercalcemia. Parathyroid gland single-photon emission computerized tomography scan was normal.

Results

CASR gene sequencing revealed a previously unreported heterozygous intronic variant at position 1608+3A>G (chromosome 3: 121994892) resulting in a 77-residue deletion. His mother has a history of bipolar disorder and hyperparathyroidism with an adenoma found on imaging, yet our patient had no evidence of adenoma and therefore no surgical intervention was recommended. Given that CaSR plays a role in parathyroid growth, some variants in CASR may ultimately lead to parathyroid hypertrophy and be mistaken for primary hyperparathyroidism.

Conclusion

Long-term clinical follow up will be helpful in understanding the ultimate effects of specific CASR mutations on parathyroid growth or progression to significant hypercalcemia.

The future of bronchodilation: looking for new classes of bronchodilators

Available bronchodilators can satisfy many of the needs of patients suffering from airway disorders, but they often do not relieve symptoms and their long-term use raises safety concerns. Therefore, there is interest in developing new classes that could help to overcome the limits that characterise the existing classes.At least nine potential new classes of bronchodilators have been identified: 1) selective phosphodiesterase inhibitors; 2) bitter-taste receptor agonists; 3) E-prostanoid receptor 4 agonists; 4) Rho kinase inhibitors; 5) calcilytics; 6) agonists of peroxisome proliferator-activated receptor-γ; 7) agonists of relaxin receptor 1; 8) soluble guanylyl cyclase activators; and 9) pepducins. They are under consideration, but they are mostly in a preclinical phase and, consequently, we still do not know which classes will actually be developed for clinical use and whether it will be proven that a possible clinical benefit outweighs the impact of any adverse effect.It is likely that if developed, these new classes may be a useful addition to, rather than a substitution of, the bronchodilator therapy currently used, in order to achieve further optimisation of bronchodilation.

Design and Preclinical Development of TransCon PTH, an Investigational Sustained-Release PTH Replacement Therapy for Hypoparathyroidism

Hypoparathyroidism (HP) is a condition of parathyroid hormone (PTH) deficiency leading to abnormal calcium and phosphate metabolism. The mainstay of therapy consists of vitamin D and calcium supplements, as well as adjunct Natpara (PTH(1-84)). However, neither therapy optimally controls urinary calcium (uCa) or significantly reduces the incidence of hypercalcemia and hypocalcemia. TransCon PTH, a sustained-release prodrug of PTH(1-34) in development for the treatment of HP, was designed to overcome these limitations. To determine the pharmacokinetics and pharmacodynamics of TransCon PTH, single and repeat s.c. dose studies were performed in rats and monkeys. TransCon PTH demonstrated a half-life of 28 and 34 hours in rats and monkeys, respectively. After repeated dosing, an infusion-like profile of the released PTH, characterized by low peak-to-trough levels, was obtained in both species. In intact rats and monkeys, daily subcutaneous administration of TransCon PTH was associated with increases in serum calcium (sCa) levels and decreases in serum phosphate levels (sP). In monkeys, at a single dose of TransCon PTH that increased sCa levels within the normal range, a concurrent decrease in uCa excretion was observed. In 4-week repeat-dose studies in intact rats and monkeys, uCa excretion was comparable to controls across all dose levels despite increases in sCa levels. Further, in a rat model of HP, TransCon PTH normalized sCa and sP levels 24 hours per day. This was in contrast to only transient trends toward normalization of sCa and sP levels with an up to 6-fold higher molar dose of PTH(1-84). After repeated dosing to HP rats, uCa excretion transiently increased, corresponding to increases in sCa above normal range, but at the end of the treatment period, uCa excretion was generally comparable to sham controls. TransCon PTH was well tolerated and the observed pharmacokinetics and pharmacodynamics were in line with the expected action of physiological replacement of PTH. © 2019 American Society for Bone and Mineral Research.

Microcalcifications, calcium-sensing receptor, and cancer

Calcium stones and calculi are observed in numerous human tissues. They are the result of deposition of calcium salts and are due to high local calcium concentrations. Prostatic calculi are usually classified as endogenous or extrinsic stones. Endogenous stones are commonly caused by obstruction of the prostatic ducts around an enlarged prostate resulting from benign prostatic hyperplasia or from chronic inflammation. The latter occurs mainly around the urethra and is generally caused by reflux of urine into the prostate. Calcium concentrations higher than in the plasma at sites of infection may induce the chemotactic response that eventually leads to recruitment of inflammatory cells. The calcium sensing receptor (CaSR) may be crucial for this recruitment as its expression and activity are increased by cytokines such as IL-6 and high extracellular calcium concentrations, respectively. The links between calcium calculi, inflammation, calcium supplementation, and CaSR functions in prostate cancer patients will be discussed in this review.

Signaling pathways involved in vascular smooth muscle cell calcification during hyperphosphatemia

Medial vascular calcification has emerged as a putative key factor contributing to the excessive cardiovascular mortality of patients with chronic kidney disease (CKD). Hyperphosphatemia is considered a decisive determinant of vascular calcification in CKD. A critical role in initiation and progression of vascular calcification during elevated phosphate conditions is attributed to vascular smooth muscle cells (VSMCs), which are able to change their phenotype into osteo-/chondroblasts-like cells. These transdifferentiated VSMCs actively promote calcification in the medial layer of the arteries by producing a local pro-calcifying environment as well as nidus sites for precipitation of calcium and phosphate and growth of calcium phosphate crystals. Elevated extracellular phosphate induces osteo-/chondrogenic transdifferentiation of VSMCs through complex intracellular signaling pathways, which are still incompletely understood. The present review addresses critical intracellular pathways controlling osteo-/chondrogenic transdifferentiation of VSMCs and, thus, vascular calcification during hyperphosphatemia. Elucidating these pathways holds a significant promise to open novel therapeutic opportunities counteracting the progression of vascular calcification in CKD.

Live-Cell Imaging of Physiologically Relevant Metal Ions Using Genetically Encoded FRET-Based Probes

Essential biochemical reactions and processes within living organisms are coupled to subcellular fluctuations of metal ions. Disturbances in cellular metal ion homeostasis are frequently associated with pathological alterations, including neurotoxicity causing neurodegeneration, as well as metabolic disorders or cancer. Considering these important aspects of the cellular metal ion homeostasis in health and disease, measurements of subcellular ion signals are of broad scientific interest. The investigation of the cellular ion homeostasis using classical biochemical methods is quite difficult, often even not feasible or requires large cell numbers. Here, we report of genetically encoded fluorescent probes that enable the visualization of metal ion dynamics within individual living cells and their organelles with high temporal and spatial resolution. Generally, these probes consist of specific ion binding domains fused to fluorescent protein(s), altering their fluorescent properties upon ion binding. This review focuses on the functionality and potential of these genetically encoded fluorescent tools which enable monitoring (sub)cellular concentrations of alkali metals such as K⁺, alkaline earth metals including Mg²⁺ and Ca²⁺, and transition metals including Cu⁺/Cu²⁺ and Zn²⁺. Moreover, we discuss possible approaches for the development and application of novel metal ion biosensors for Fe²⁺/Fe³⁺, Mn²⁺ and Na⁺.

Cinacalcet corrects biased allosteric modulation of CaSR by AHH autoantibody

Biased agonism is a paradigm that may explain the selective activation of a signaling pathway via a GPCR that activates multiple signals. The autoantibody-induced inactivation of the calcium-sensing receptor (CaSR) causes acquired hypocalciuric hypercalcemia (AHH). Here, we describe an instructive case of AHH in which severe hypercalcemia was accompanied by an increased CaSR antibody titer. These autoantibodies operated as biased allosteric modulators of CaSR by targeting its Venus flytrap domain near the Ca2+-binding site. A positive allosteric modulator of CaSR, cinacalcet, which targets its transmembrane domain, overcame this autoantibody effect and successfully corrected the hypercalcemia in this patient. Hence, this is the first study to our knowledge that identifies the interaction site of a disease-causing GPCR autoantibody working as its biased allosteric modulator and demonstrates that cinacalcet can correct the AHH autoantibody effects both in vitro and in our AHH patient. Our observations provide potentially new insights into how biased agonism works and how to design a biased allosteric modulator of a GPCR. Our observations also indicate that the diagnosis of AHH is important because the severity of hypercalcemia may become fatal if the autoantibody titer increases. Calcimimetics may serve as good treatment options for some patients with severe AHH.

[Electrhopysiological Effect of the Polyamine Spermine in Normoxic and Ischemic Ventricular Myocardium]

Cytoplasmic polyamines (PA) are involved in control of many cellular functions and are well known as regulators of so called inward-rectifier potassium ion channels. Nevertheless, functional significance of extracellular PA in the heart is poorly elucidated. Aim of this study was to study effects of endogenous PA spermine in the ventricular myocardium. Effects of the extracellular spermine were investigated in isolated multicellular preparations of rabbit and rat ventricular myocardium. Langendorff-perfused  isolated rat and rabbit hearts were also used. Action potential (APs) duration and pattern of excitation in ventricular myocardium were estimated using standard microelectrode technique and optical mapping. Functional refractory periods were assessed in Langendorff perfused hearts with the help of programmedelectrical stimulation of the ventricle. In this study extracellular PA spermine (0.1-5 mM) induced shortening of the APs in multicellular preparations of rat ventricular myocardium registered using sharp microelectrode technique. However, spermine caused only weak effect in preparations of ventricular myocardium from rabbit heart: highest tested concentration of spermine (5 mM) induced 4.7 % APs shortening. Similarly, 0.1-1 mM of spermine was unable to alter substantially ventricular effective refractory periods in isolated perfused rabbit hearts. In two animal species tested (rat and rabbit) 0.1-1 mM of spermine failed to affect conduction velocity and activation pattern in ventricles of isolated Langendorff-perfused hearts under normoxia. However, in the rat no-flow model of ischemia-reperfusion extracellular spermine improved conduction of excitation in ventricles. Our results allow suggesting that extracellular spermine can prevent ischemia-induced proarrhythmic changes in ventricular myocardium probably due to reduction of calcium accumulation, but this effect is significant only when PA is applied in millimolar concentrations. Also, potential anti-ischemic effect of the PA may be species specific.

Antagonism of Ca2+-sensing receptors by NPS 2143 is transiently masked by p38 activation in mouse brain bEND.3 endothelial cells

Ca²⁺-sensing receptors (CaSR) are G protein-coupled receptors which are activated by a rise in extracellular Ca²⁺. CaSR activation has been known to inhibit parathyroid hormone release and stimulate calcitonin release from parathyroid glands and thyroid parafollicular C cells, respectively. The roles of CaSR in other cell types including endothelial cells (EC) are much less understood. In this work, we demonstrated protein and functional expression of CaSR in mouse cerebral EC (bEND.3). Unexpectedly, CaSR response (high Ca²⁺-elicited cytosolic [Ca²⁺] elevation) was unaffected by edelfosine or U73122 but strongly suppressed by SK&F 96365, ruthenium red, and 2-aminoethoxydiphenyl borate (2-APB), suggesting involvement of TRPV and TRPC channels but not Gq-phospholipase C. Acute application of NPS2143, a negative allosteric modulator of CaSR, suppressed CaSR response. However, a 40-min NPS2143 pre-treatment surprisingly enhanced CaSR response. After 4-24 h of application, this enhancement faded away and suppression of CaSR response was observed again. Similar results were obtained when La³⁺ and Sr²⁺ were used as CaSR agonists. The transient NPS 2143 enhancement effect was abolished by SB203580, a p38 inhibitor. Consistently, NPS 2143 triggered a transient p38 activation. Taken together, results suggest that in bEND.3 cells, NPS 2143 caused acute suppression of CaSR response, but then elicited a transient enhancement of CaSR response in a p38-dependent manner. NPS 2143 effects on CaSR in bEND.3 cells therefore depended on drug exposure time. These findings warrant cautious use of this agent as a CaSR modulator and potential cardiovascular drug.

Astragaloside IV Suppresses High Glucose-Induced NLRP3 Inflammasome Activation by Inhibiting TLR4/NF-κB and CaSR

Long-term exposure to high glucose induces vascular endothelial inflammation that can result in cardiovascular disease. Astragaloside IV (As-IV) is widely used for anti-inflammatory treatment of cardiovascular diseases. However, its mechanism of action is still not fully understood. In this study, we investigated the effect of As-IV on high glucose-induced endothelial inflammation and explored its possible mechanisms. In vivo, As-IV (40 and 80 mg/kg/d) was orally administered to rats for 8 weeks after a single intraperitoneal injection of streptozotocin (STZ, 65 mg/kg). In vitro, human umbilical vein endothelial cells (HUVECs) were treated with high glucose (33 mM glucose) in the presence or absence of As-IV, NPS2143 (CaSR inhibitor), BAY 11-7082 (NF-κB p65 inhibitor), and INF39 (NLRP3 inhibitor), and overexpression of CaSR was induced by infection of CaSR-overexpressing lentiviral vectors to further discuss the anti-inflammatory property of As-IV. The results showed that high glucose increased the expression of interleukin-18 (IL-18), interleukin-1β (IL-1β), NLRP3, caspase-1, and ASC, as well as the protein level of TLR4, nucleus p65, and CaSR. As-IV can reverse these changes in vivo and in vitro. Meanwhile, NPS2143, BAY 11-7082, and INF39 could significantly abolish the high glucose-enhanced NLRP3, ASC, caspase-1, IL-18, and IL-1β expression in vitro. In addition, both NPS2143 and BAY 11-7082 attenuated high glucose-induced upregulation of NLRP3, ASC, caspase-1, IL-18, and IL-1β expression. In conclusion, this study suggested that As-IV could inhibit high glucose-induced NLRP3 inflammasome activation and subsequent secretion of proinflammatory cytokines via inhibiting TLR4/NF-κB signaling pathway and CaSR, which provides new insights into the anti-inflammatory activity of As-IV.

Novel homozygous inactivating mutation of the calcium-sensing receptor gene in neonatal severe hyperparathyroidism responding to cinacalcet therapy: A case report and literature review

RATIONALE

Calcium-sensing receptor (CaSR) mutations can cause life-threatening neonatal severe hyperparathyroidism (NSHPT). The medical management of NSHPT is often challenging and complex. Here, we present a case of NSHPT caused by a novel homozygous CaSR mutation.

PATIENT CONCERNS

A Chinese female infant presented with poor feeding, constipation, severe hypotonia, and periodic bradycardia. Biochemistry tests revealed markedly elevated serum levels of Ca and parathyroid hormone (PTH).

DIAGNOSES

Genetic sequencing revealed a previously undescribed CaSR mutation in exon 3 (c.242T>A; p.I81K). A diagnosis of NSHPT secondary to homozygously inherited familial hypocalciuric hypercalcemia syndrome was established.

INTERVENTIONS

Cinacalcet was administered after the common treatments (low-calcium intake, hydration, and furosemide), calcitonin, and pamidronate therapy all failed.

OUTCOMES

Serum Ca decreased and stabilized with cinacalcet therapy. During a 10-month follow-up, total calcium was maintained within the high-normal range and PTH was normalized.

LESSONS

A trial of cinacalcet therapy might be undertaken in cases of NSHPT while definitive results of the genetic analysis are awaited.

Familial hypocalciuric hypercalcemia and related disorders

Familial hypocalciuric hypercalcemia (FHH) causes hypercalcemia by three genetic mechanisms: inactivating mutations in the calcium-sensing receptor, the G-protein subunit α₁₁, or adaptor-related protein complex 2, sigma 1 subunit. While hypercalcemia in other conditions causes significant morbidity and mortality, FHH generally follows a benign course. Failure to diagnose FHH can result in unwarranted treatment or surgery for the mistaken diagnosis of primary hyperparathyroidism (PHPT), given the significant overlap of biochemical features. Determinations of urinary calcium excretion greatly aid in distinguishing PHPT from FHH, but overlap still exists in certain cases. It is important that 24-h urine calcium and creatinine be included in the initial workup of hypercalcemia. FHH should be considered if low or even low normal urinary calcium levels are found in what is typically an asymptomatic hypercalcemic patient. The calcimimetic cinacalcet has been used to treat hypercalcemia in certain symptomatic causes of FHH.

A curious case of growth failure and hypercalcemia: Answers

BACKGROUND

Sarcoidosis is a multisystem granulomatous disease of unknown etiology that rarely presents in childhood. Here, we report a case of pediatric sarcoidosis, presenting with renal failure and hypercalcemia.

CASE DIAGNOSIS/TREATMENT

A previously well 14-year-old Caucasian boy was admitted to the Hospital for Sick Children, Canada, for hypertension and renal failure following work-up by his family physician for initial concerns of growth failure. On admission, his weight was 35 kg (<3rd percentile), his height was 148 cm (<<3rd percentile), and his blood pressure was 154/116 mmHg (>99th percentile for height). Laboratory findings showed elevated creatinine (218 umol/L), hypercalcemia (3.21 mmol/L), and normocytic anemia (hemoglobin 105 g/L). His further assessment showed a urinary concentrating defect with hypercalciuria (calcium/creatinine 1.76 mmol/mmol) and nephrocalcinosis on ultrasound. His eye examination showed uveitis with conjunctival biopsy remarkable for granulomas, which led to pursuit of a diagnosis of possible sarcoidosis. Angiotensin Angiotensin-converting enzyme was found to be high at 96 U/L, and he had a renal biopsy that was consistent with interstitial nephritis with granulomas. Treatment was started with prednisone leading to resolution of his hypercalcemia but persistence of his mild chronic kidney disease.

CONCLUSIONS

This case represents an atypical presentation of a rare pediatric disease and highlights the spectrum of renal manifestations and treatment options in sarcoidosis.

Bioinformatics-Based Identification of Methylated-Differentially Expressed Genes and Related Pathways in Gastric Cancer

BACKGROUND AND AIMS

The aim of the study was to identify methylated-differentially expressed genes (MDEGs) in gastric cancer and investigate their potential pathways.

METHODS

Expression profiling (GSE13911 and GSE29272) and methylation profiling (GSE25869 and GSE30601) data were obtained from GEO DataSets. Differentially expressed genes and differentially methylated genes were identified using GEO2R. Gene ontology and pathway enrichment analyses were performed for the MDEGs. Protein-protein interaction (PPI) networks were established by STRING and Cytoscape. Analysis of modules in the PPI networks was performed using MCODE. Further, the hub genes derived from the PPI networks were verified by The Cancer Genome Atlas (TCGA) database and human tissues, with methylation-specific PCR for genes methylation and real-time qPCR for genes expression.

RESULTS

A total of 445 genes were identified as hypermethylated, lowly expressed genes (Hyper-LGs), which were enriched in the regulation of system process and channel activity. A total of 129 genes were identified as hypomethylated, highly expressed genes (Hypo-HGs), which were involved in cell adhesion, cell proliferation, and protein binding. Pathway analysis showed that Hyper-LGs were associated with neuroactive ligand-receptor interaction and calcium signaling pathway, while Hypo-HGs were enriched in pathways in cancer. In the PPI networks, after verification by TCGA analysis and human tissue detection, CASR, CXCL12, and SST were identified as significantly different hub genes.

CONCLUSIONS

MDEG analysis helps to understand the epigenetic regulation mechanisms involved in the development and progression of gastric cancer. The hub genes have predictive and prognostic value as methylation-based biomarkers for the precise diagnosis and treatment of gastric cancer.

Tumor expression of calcium sensing receptor and colorectal cancer survival: Results from the nurses' health study and health professionals follow-up study

Although experimental evidence suggests calcium-sensing receptor (CASR) as a tumor-suppressor, the prognostic role of tumor CASR expression in colorectal carcinoma remains unclear. We hypothesized that higher tumor CASR expression might be associated with improved survival among colorectal cancer patients. We evaluated tumor expression levels of CASR by immunohistochemistry in 809 incident colorectal cancer patients within the Nurses' Health Study and the Health Professionals Follow-up Study. We used Cox proportional hazards regression models to estimate multivariable hazard ratio (HR) for the association of tumor CASR expression with colorectal cancer-specific and all-cause mortality. We adjusted for potential confounders including tumor biomarkers such as microsatellite instability, CpG island methylator phenotype, LINE-1 methylation level, expressions of PTGS2, VDR and CTNNB1 and mutations of KRAS, BRAF and PIK3CA. There were 240 colorectal cancer-specific deaths and 427 all-cause deaths. The median follow-up of censored patients was 10.8 years (interquartile range: 7.2, 15.1). Compared with patients with no or weak expression of CASR, the multivariable HRs for colorectal cancer-specific mortality were 0.80 [95% confidence interval (CI): 0.55-1.16] in patients with moderate CASR expression and 0.50 (95% CI: 0.32-0.79) in patients with intense CASR expression (p-trend = 0.003). The corresponding HRs for overall mortality were 0.85 (0.64-1.13) and 0.81 (0.58-1.12), respectively. Higher tumor CASR expression was associated with a lower risk of colorectal cancer-specific mortality. This finding needs further confirmation and if confirmed, may lead to better understanding of the role of CASR in colorectal cancer progression.

NPS 2143, a selective calcium-sensing receptor antagonist inhibits lipopolysaccharide-induced pulmonary inflammation

NPS 2143, a novel and selective antagonist of calcium-sensing receptor (CaSR) has been reported to possess anti-inflammatory activity. In the present study, we examined the protective effect of NPS 2143 on lipopolysaccharide (LPS)-induced acute lung injury (ALI). NPS 2143 pretreatment significantly inhibited the influx of inflammatory cells and the expression of monocyte chemoattractant protein-1 (MCP-1) in the lung of mice with LPS-induced ALI. NPS 2143 decreased the levels of neutrophil elastase (NE) and protein concentration in the bronchoalveolar lavage fluid (BALF). NPS 2143 also reduced the production of inflammatory cytokines such as tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in the BALF and serum. In addition, NPS 2143 attenuated the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), and increased the activation of AMP-activated protein kinase (AMPK) in the lung. NPS 2143 also downregulated the activation of nuclear factor-kappa B (NF-κB) in the lung. In LPS-stimulated H292 airway epithelial cells, NPS 2143 attenuated the releases of IL-6 and MCP-1. Furthermore, NPS 2143 upregulated the activation of AMPK and downregulated the activation of NF-κB. These results suggest that NPS 2143 could be potential agent for the treatment of inflammatory diseases including ALI.

RETRACTED: Effects of lentivirus-mediated silencing of Periostin on tumor microenvironment and bone metastasis via the integrin-signaling pathway in lung cancer

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief. Concern was raised about the reliability of the Western blot results in Figures 1B, 3B, 5B, and 8A which appear to have a similar phenotype as seen in many other publications, as detailed here: https://pubpeer.com/publications/E266A07D28435DB334E8777CAC97E3; and here: https://docs.google.com/spreadsheets/d/1r0MyIYpagBc58BRF9c3luWNlCX8VUvUuPyYYXzxWvgY/edit#gid=262337249. In addition, a portion of Figure 6B, ‘NC’ group appears to contain image similarities with Figure 6B, ‘si-Integrin-αvβ3’ group, and a portion of Figure 6B, ‘Blank’ group appears to contain image similarities with Figure 6B, ‘NC’ group. The journal requested that the corresponding author comment on these concerns and provide the raw data. However, the authors were not able to satisfactorily fulfill this request and therefore the Editor-in-Chief decided to retract the article.