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The calcium-sensing receptor (CaS, provisional nomenclature as recommended by NC-IUPHAR [47] and subsequently updated [77]) responds to multiple endogenous ligands, including extracellular calcium and other divalent/trivalent cations, polyamines and polycationic peptides, L-amino acids (particularly L-Trp and L-Phe), glutathione and various peptide analogues, ionic strength and extracellular pH (reviewed in [78]). While divalent/trivalent cations, polyamines and polycations are CaS receptor agonists [14, 110], L-amino acids, glutamyl peptides, ionic strength and pH are allosteric modulators of agonist function [36, 47, 61, 108, 109]. Indeed, L-amino acids have been identified as "co-agonists", with both concomitant calcium and L-amino acid binding required for full receptor activation [149, 54]. The sensitivity of the CaS receptor to primary agonists is increased by elevated extracellular pH [18] or decreased extracellular ionic strength [109] while sensitivity is decreased by pathophysiological phosphate concentrations [20]. This receptor bears no sequence or structural relation to the plant calcium receptor, also called CaS.

This set contains class C 'orphan' G protein coupled receptors where the endogenous ligand(s) is not known.

The calcium-sensing receptor (CaS, provisional nomenclature as recommended by NC-IUPHAR [47] and subsequently updated [77]) responds to multiple endogenous ligands, including extracellular calcium and other divalent/trivalent cations, polyamines and polycationic peptides, L-amino acids (particularly L-Trp and L-Phe), glutathione and various peptide analogues, ionic strength and extracellular pH (reviewed in [78]). While divalent/trivalent cations, polyamines and polycations are CaS receptor agonists [14, 110], L-amino acids, glutamyl peptides, ionic strength and pH are allosteric modulators of agonist function [36, 47, 61, 108, 109]. Indeed, L-amino acids have been identified as "co-agonists", with both concomitant calcium and L-amino acid binding required for full receptor activation [148, 54]. The sensitivity of the CaS receptor to primary agonists is increased by elevated extracellular pH [18] or decreased extracellular ionic strength [109]. This receptor bears no sequence or structural relation to the plant calcium receptor, also called CaS.

The calcium-sensing receptor (CaS, provisional nomenclature as recommended by NC-IUPHAR [46] and subsequently updated [76]) responds to multiple endogenous ligands, including extracellular calcium and other divalent/trivalent cations, polyamines and polycationic peptides, L-amino acids (particularly L-Trp and L-Phe), glutathione and various peptide analogues, ionic strength and extracellular pH (reviewed in [77]). While divalent/trivalent cations, polyamines and polycations are CaS receptor agonists [14, 109], L-amino acids, glutamyl peptides, ionic strength and pH are allosteric modulators of agonist function [35, 46, 60, 107, 108]. Indeed, L-amino acids have been identified as "co-agonists", with both concomitant calcium and L-amino acid binding required for full receptor activation [147, 53]. The sensitivity of the CaS receptor to primary agonists is increased by elevated extracellular pH [17] or decreased extracellular ionic strength [108]. This receptor bears no sequence or structural relation to the plant calcium receptor, also called CaS.

Context\ud While therapy with immune checkpoint inhibitors such as nivolumab have substantially improved survival in several types of cancer, increased attention has been given to adverse immune events associated with their use, including the development of endocrine autoimmunity.\ud \ud Objectives\ud First, to describe a patient with a two-year history of metastatic small cell lung cancer who had been treated with nivolumab a few months prior to presentation with the signs and symptoms of severe hypocalcemia and hypoparathyroidism. Second, to investigate the etiology of the patient’s hypoparathyroidism, including the presence of activating autoantibodies against the calcium-sensing receptor (CaSR), since humoral and cellular immune responses against the CaSR have been reported in patients with autoimmune hypoparathyroidism.\ud \ud Case and Results\ud A 61-year-old female was admitted with persistent nausea, vomiting, epigastric pain, constipation, and generalized weakness. Laboratory analyses showed low total serum calcium, ionized calcium, and parathyroid hormone (PTH). The patient was diagnosed with severe hypocalcemia as a result of autoimmune hypoparathyroidism after testing positive for CaSR-activating autoantibodies. She was treated with intravenous calcium gluconate infusions followed by a transition to oral calcium carbonate plus calcitriol which normalized her serum calcium. Her serum PTH remained low0 during her hospitalization and initial outpatient follow-up despite adequate repletion of magnesium.\ud \ud Conclusions\ud This case illustrates autoimmune hypoparathyroidism induced by immune checkpoint inhibitor-blockade. As immune checkpoint inhibitors are now used to treat many cancers, clinicians should be aware of the potential risk for hypocalcemia that may be associated with their use.

This set contains class C 'orphan' G protein coupled receptors where the endogenous ligand(s) is not known.

The calcium-sensing receptor (CaS, provisional nomenclature as recommended by NC-IUPHAR [44]) responds to multiple endogenous ligands, including extracellular calcium and other divalent/trivalent cations, polyamines and polycationic peptides, L-amino acids (particularly L-Trp and L-Phe), glutathione and various peptide analogues, ionic strength and extracellular pH (reviewed in [74]). While divalent/trivalent cations, polyamines and polycations are CaS receptor agonists [14, 106], L-amino acids, glutamyl peptides, ionic strength and pH are allosteric modulators of agonist function [34, 44, 58, 104, 105]. Indeed, L-amino acids have been identified as "co-agonists", with both concomitant calcium and L-amino acid binding required for full receptor activation [143, 51]. The sensitivity of the CaS receptor to primary agonists is increased by elevated extracellular pH [17] or decreased extracellular ionic strength [105]. This receptor bears no sequence or structural relation to the plant calcium receptor, also called CaS.

Hypoparathyroidism is a disorder characterized by hypocalcemia due to insufficient secretion of PTH. Pseudohypoparathyroidism is a less common disorder due to target organ resistance to PTH. This report summarizes the results of the findings and recommendations of the Working Group on Epidemiology and Diagnosis of Hypoparathyroidism.Each contributing author reviewed the recent published literature regarding epidemiology and diagnosis of hypoparathyroidism using PubMed and other medical literature search engines.The prevalence of hypoparathyroidism is an estimated 37 per 100 000 person-years in the United States and 22 per 100 000 person-years in Denmark. The incidence in Denmark is approximately 0.8 per 100 000 person-years. Estimates of prevalence and incidence of hypoparathyroidism are currently lacking in most other countries. Hypoparathyroidism increases the risk of renal insufficiency, kidney stones, posterior subcapsular cataracts, and intracerebral calcifications, but it does not appear to increase overall mortality, cardiovascular disease, fractures, or malignancy. The diagnosis depends upon accurate measurement of PTH by second- and third-generation assays. The most common etiology is postsurgical hypoparathyroidism, followed by autoimmune disorders and rarely genetic disorders. Even more rare are etiologies including parathyroid gland infiltration, external radiation treatment, and radioactive iodine therapy for thyroid disease. Differentiation between these different etiologies is aided by the clinical presentation, serum biochemistries, and in some cases, genetic testing.Hypoparathyroidism is often associated with complications and comorbidities. It is important for endocrinologists and other physicians who care for these patients to be aware of recent advances in the epidemiology, diagnosis, and genetics of this disorder.

Context Activating antibodies directed at the extracellular calcium‐sensing receptor (CaSR) have been described in autoimmune hypoparathyroidism in the setting of isolated hypoparathyroidism or autoimmune polyglandular syndrome type 1. Materials and methods A 34‐year‐old female presented with hypocalcemia (6.0 mg/dL) and hypomagnesemia (1.1 mg/dL) accompanied by low serum PTH (2.4 pg/mL) as well as urinary calcium and magnesium wasting. She was diagnosed with hypoparathyroidism, which was refractory to standard therapy. She was started on 60 mg prednisone and 150 mg azathioprine treatment daily on suspicion of an autoimmune aetiology. The patient was tested for CaSR antibodies. Results The patient was positive for CaSR antibodies of the IgG1 subtype, which stimulated phosphorylation of extracellular signal‐regulated kinases 1 and 2 (ERK1/2) and inositol phosphate (IP) accumulation. Post‐treatment with prednisone and azathioprine, her serum calcium and magnesium normalised, as did her CaSR antibody titre and antibody‐mediated stimulation of ERK1/2 phosphorylation and IP accumulation. Conclusion This is the first demonstration of CaSR antibody‐mediated hypoparathyroidism responsive to immunosuppressive therapy, adding to the evidence that autoimmune hypoparathyroidism can be, in some cases, reversible and not the result of autoimmune parathyroid destruction.

The pathogenesis of parathyroid gland hyperplasia is poorly understood, and a better understanding is essential if there is to be improvement over the current strategies for prevention and treatment of secondary hyperparathyroidism. Here we investigate the specific role of Klotho expressed in the parathyroid glands (PTGs) in mediating parathyroid hormone (PTH) and serum calcium homeostasis, as well as the potential interaction between calcium-sensing receptor (CaSR) and Klotho. We generated mouse strains with PTG-specific deletion of Klotho and CaSR and dual deletion of both genes. We show that ablating CaSR in the PTGs increases PTH synthesis, that Klotho has a pivotal role in suppressing PTH in the absence of CaSR, and that CaSR together with Klotho regulates PTH biosynthesis and PTG growth. We utilized the tdTomato gene in our mice to visualize and collect PTGs to reveal an inhibitory function of Klotho on PTG cell proliferation. Chronic hypocalcemia and ex vivo PTG culture demonstrated an independent role for Klotho in mediating PTH secretion. Moreover, we identify an interaction between PTG-expressed CaSR and Klotho. These findings reveal essential and interrelated functions for CaSR and Klotho during parathyroid hyperplasia.

The extracellular calcium ( C a o 2 + )-sensing receptor (CaSR) plays key roles in maintaining C a o 2 + homeostasis by regulating the functions of parathyroid and kidney in response to perturbations in C a o 2 + so as to maintain a nearly constant level of blood calcium. The cloning of the CaSR made it feasible to rapidly identify several disorders arising from inactivating or activating mutations of the receptor. More than 300 such mutations of the CaSR have been reported, the majority of which cause familial hypocalciuric hypercalcemia, type 1 (FHH1), a generally benign hypercalcemic and hypocalciuric condition. Recently, inactivating mutations in genes downstream of the CaSR that also participate in C a o 2 + sensing, namely the G protein, Gα 11 , and the σ-1 subunit of the adaptor-related protein complex 2 (AP2S1), have been identified, which cause FHH2 and FHH3, respectively. These syndromes are similar to those caused by mutations of the CaSR, but with some interesting differences. In contrast to FHH, homozygous inactivating mutations of the CaSR in many cases cause neonatal severe hyperparathyroidism (NSHPT). It is a severe, sometimes life-threatening form of hyperparathyroidism, although it has become increasingly apparent that there is a wide range of severity associated with homozygous inactivating CaSR mutations. Patients with FHH1 and FHH2 generally do not need parathyroid surgery, while total parathyroidectomy is not uncommonly necessary to control hyperparathyroidism and hypercalcemia in NSHPT. Patients with FHH3 can have a somewhat more severe phenotype than in FHH1 or FHH2, and their optimal management requires further study. Activating mutations of the CaSR produce autosomal dominant hypocalcemia (now called ADH1), rarely with features of Bartter’s syndrome (so called type V), because the CaSR is too sensitive to its ligand, C a o 2 + . ADH2, with a similar or perhaps milder phenotype, is caused by heterozygous activating mutations of Gα 11 . As additional hyper- and hypocalcemic patients with CASR , GNA11 , or AP2S1 mutations have been studied, the clinical presentations of the various forms of FHH, ADH, and NSHPT have broadened to the point where their biochemical findings overlap significantly, leading to new diagnostic and therapeutic challenges for the clinician and patient.

A major manifestation of autoimmune polyendocrine syndrome type 1 (APS1) is hypoparathyroidism, which is suggested to result from aberrant immune responses against the parathyroid glands. The calcium-sensing receptor (CaSR), which plays a pivotal role in maintaining calcium homeostasis by sensing blood calcium levels and regulating release of parathyroid hormone (PTH), is an autoantibody target in APS1. In this study, the aim was to characterize the binding sites, specificity, functional affinity, IgG subclass, and functional effects of CaSR autoantibodies using phage-display technology, ELISA, and bioassays. The results indicated that CaSR autoantibody binding sites were at aa 41–69, 114–126, 171–195, and 260–340 in the extracellular domain of the receptor. Autoantibodies against CaSR epitopes 41–69, 171–195, and 260–340 were exclusively of the IgG1 subclass. Autoantibody responses against CaSR epitope 114–126 were predominantly of the IgG1 with a minority of the IgG3 subclass. Only autoantibodies recognizing CaSR epitopes 114–126 and 171–195 affected receptor activity; inositol-phosphate accumulation was increased significantly in HEK293-CaSR cells, and PTH secretion from PTH-C1 cells was reduced significantly when either were incubated with purified Ab and Ca2+ compared with Ca2+ alone. In conclusion, although the majority of APS1 patients do not have CaSR-stimulating autoantibodies, the hypoparathyroid state in a small minority of patients is the result of functional suppression of the parathyroid glands.

By the 1840s French psychiatrists had abandoned Moral Treatment as an individual psychological therapy, as opposed to an institutional practice. One advocate of Moral Treatment, however, would not go along with this movement. In three books and several papers published between 1834 and 1846, François Leuret (1797–1851) advocated aggressive psychological treatment. Recent commentators have understandably concentrated on the controversies surrounding Leuret’s practices. What such an approach has failed to make clear, however, is that Leuret had a complex, systematic psychological theory supporting his clinical judgements. In addition to reviewing the controversies that surrounded Leuret, this paper spells out Leuret’s psychological theory and shows how he used this theory to think about the individual psychotherapy he provided for his patients.

Among 125,954 new users of osteoporosis (OP) medications, 77 % of subjects stopped OP medications, and 23 % of subjects added or started a new OP medication during follow-up, with the first addition or start of a new OP medication occurring in a mean of 739 days after original OP treatment.We described patterns and predictors of OP medication use, focusing on treatment changes over time.We analyzed health and pharmacy insurance claims for a large cohort of low-income Medicare beneficiaries with a drug benefit for the years 1998-2008. Study subjects had documented Medicare claims and no receipt of OP medications (i.e., bisphosphonate, raloxifene, calcitonin, teriparatide, or hormonal therapy) during a baseline of 180 days. Subjects were then required to start an OP medication. Baseline patient and prescriber characteristics were assessed in multivariable Cox regression models to identify correlates of adding or starting a new OP medication. Fractures, bone mineral density testing, and visits with endocrinologists or rheumatologists occurring after baseline were also examined as correlates.We included 125,954 new users of OP medications with a mean age of 78 years, 97 % female, and 92 % white. OP medication prescribers included specialists (i.e., endocrinologists or rheumatologists) (6.2 %), orthopedic surgeons (1.0 %), primary care providers (64.9 %), other physicians (3.7 %), and missing (24.1 %). Seventy-seven percent of subjects stopped OP medications, and 23 % of subjects added or started a new OP medication during follow-up, with the first addition or start of a new OP medication occurring in a mean of 739 days after original OP treatment; 4 % added or started a new OP medication more than once. In fully adjusted models, many baseline variables correlated with starting a second OP medication. Post-baseline fractures [hazard ratio (HR) 1.76, 95 % confidence interval (CI) 1.71-1.82] and bone mineral density testing (HR 2.94, 95 % CI 2.86-3.03) were strong predictors.Approximately one quarter of patients starting an OP medication added or started a new OP medication during follow-up. Long-term sequential treatment strategy trials would inform optimal medication treatment for OP.

Metabotropic glutamate receptor 1α (mGluR1α), a member of the family C G protein-coupled receptors, is emerging as a potential drug target for various disorders, including chronic neuronal degenerative diseases. In addition to being activated by glutamate, mGluR1α is also modulated by extracellular Ca(2+). However, the underlying mechanism is unknown. Moreover, it has long been challenging to develop receptor-specific agonists due to homologies within the mGluR family, and the Ca(2+)-binding site(s) on mGluR1α may provide an opportunity for receptor-selective targeting by therapeutics. In the present study, we show that our previously predicted Ca(2+)-binding site in the hinge region of mGluR1α is adjacent to the site where orthosteric agonists and antagonists bind on the extracellular domain of the receptor. Moreover, we found that extracellular Ca(2+) enhanced mGluR1α-mediated intracellular Ca(2+) responses evoked by the orthosteric agonist l-quisqualate. Conversely, extracellular Ca(2+) diminished the inhibitory effect of the mGluR1α orthosteric antagonist (S)-α-methyl-4-carboxyphenylglycine. In addition, selective positive (Ro 67-4853) and negative (7-(hydroxyimino)cyclopropa[b]chromen-1a-carboxylate ethyl ester) allosteric modulators of mGluR1α potentiated and inhibited responses to extracellular Ca(2+), respectively, in a manner similar to their effects on the response of mGluR1α to glutamate. Mutations at residues predicted to be involved in Ca(2+) binding, including E325I, had significant effects on the modulation of responses to the orthosteric agonist l-quisqualate and the allosteric modulator Ro 67-4853 by extracellular Ca(2+). These studies reveal that binding of extracellular Ca(2+) to the predicted Ca(2+)-binding site in the extracellular domain of mGluR1α modulates not only glutamate-evoked signaling but also the actions of both orthosteric ligands and allosteric modulators on mGluR1α.

We present a case of an 82-year-old woman with elevated parathyroid hormone (PTH) levels, hypocalciuria, hypercalcemia, and stage 3 chronic kidney disease. Hypocalciuria initially was attributed to chronic kidney disease, and hypercalcemia was attributed to primary hyperparathyroidism. Subsequent laboratory studies showed autoantibodies in the patient's serum directed against the calcium-sensing receptor (CaSR). Functional testing in a CaSR-transfected human embryonic kidney-293 cell line showed that the patient's antibodies inhibited CaSR-mediated intracellular signaling that ordinarily would have been stimulated by extracellular calcium ions. Her serum calcium and PTH levels were normalized by treatment with the calcimimetic cinacalcet. We advise consideration of the presence of inhibitory autoantibodies directed at the CaSR in patients with hypercalcemic hyperparathyroidism and unexplained hypocalciuria or with confounding conditions affecting interpretation of urinary calcium measurement. A calcimimetic is an effective treatment for the hypercalcemia and elevated PTH levels in acquired hypocalciuric hypercalcemia caused by inhibitory anti-CaSR autoantibodies.

Maintaining a constant level of blood Ca(2+) is essential because of calcium's myriad intracellular and extracellular roles. The CaSR plays key roles in maintaining [Formula: see text] homeostasis by detecting small changes in blood Ca(2+) and modulating the production/secretion of the Ca(2+)-regulating hormones, PTH, CT, FGF23 and 1,25(OH)2D3, so as to appropriately regulate Ca(2+) transport into or out of blood via kidney, intestine, and/or bone. When Ca(2+) is high, the CaSR suppresses PTH synthesis and secretion, promotes its degradation, and inhibits parathyroid cellular proliferation. It has just the opposite effects on the C-cell, stimulating CT when [Formula: see text] is high. In bone, Ca(2+), acting via the CaSR, stimulates recruitment and proliferation of preosteoblasts, their differentiation to mature osteoblasts, and synthesis and mineralization of bone proteins. Conversely, [Formula: see text] inhibits the formation and activity and promotes apoptosis of osteoclasts, likely via the CaSR. These actions tend to mobilize skeletal Ca(2+) during [Formula: see text] deficiency and retain it when Ca(2+) is plentiful.

The mechanisms by which parathyroid hormone (PTH) produces anemia are unclear. Parathyroid hormone secretion is regulated by the extracellular Ca2+ -sensing receptor. We investigated the effects of ablating PTH on hematological indices and erythrocytes volume regulation in wild-type, PTH-null, and Ca2+ -sensing receptor-null/PTH-null mice. The erythrocyte parameters were measured in whole mouse blood, and volume regulatory systems were determined by plasma membrane K+ fluxes, and osmotic fragility was measured by hemoglobin determination at varying osmolarities. We observed that the absence of PTH significantly increases mean erythrocyte volume and reticulocyte counts, while decreasing erythrocyte counts, hemoglobin, hematocrit, and mean corpuscular hemoglobin concentration. These changes were accompanied by increases in erythrocyte cation content, a denser cell population, and increased K+ permeability, which were in part mediated by activation of the K+ /Cl- cotransporter and Gardos channel. In addition we observed that erythrocyte osmotic fragility in PTH-null compared with wild-type mice was enhanced. When Ca2+ -sensing receptor gene was deleted on the background of PTH-null mice, we observed that several of the alterations in erythrocyte parameters of PTH-null mice were largely rescued, particularly those related to erythrocyte volume, K+ fluxes and osmotic fragility, and became similar to those observed in wild-type mice. Our results demonstrate that Ca2+ -sensing receptor and parathyroid hormone are functionally coupled to maintain erythrocyte homeostasis.

Calcium and phosphorus homeostasis are highly interrelated and share common regulatory hormones, including FGF23. However, little is known about calcium's role in the regulation of FGF23. We sought to investigate the regulatory roles of calcium and phosphorus in FGF23 production using genetic mouse models with targeted inactivation of PTH (PTH KO) or both PTH and the calcium-sensing receptor (CaSR; PTH-CaSR DKO). In wild-type, PTH KO, and PTH-CaSR DKO mice, elevation of either serum calcium or phosphorus by intraperitoneal injection increased serum FGF23 levels. In PTH KO and PTH-CaSR DKO mice, however, increases in serum phosphorus by dietary manipulation were accompanied by severe hypocalcemia, which appeared to blunt stimulation of FGF23 release. Increases in dietary phosphorus in PTH-CaSR DKO mice markedly decreased serum 1,25-dihydroxyvitamin D3[1,25(OH)2D3] despite no change in FGF23, suggesting direct regulation of 1,25(OH)2D3synthesis by serum phosphorus. Calcium-mediated increases in serum FGF23 required a threshold level of serum phosphorus of about 5 mg/dl. Analogously, phosphorus-elicited increases in FGF23 were markedly blunted if serum calcium was less than 8 mg/dl. The best correlation between calcium and phosphorus and serum FGF23 was found between FGF23 and the calcium × phosphorus product. Since calcium stimulated FGF23 production in the PTH-CaSR DKO mice, this effect cannot be mediated by the full-length CaSR. Thus the regulation of FGF23 by both calcium and phosphorus appears to be fundamentally important in coordinating the serum levels of both mineral ions and ensuring that the calcium × phosphorus product remains within a physiological range.

Ca2+-sensing receptors (CaSRs) play a central role in regulating extracellular calcium concentration ([Ca2+]o) homeostasis and many (patho)physiological processes in multiple organs. This regulation is orchestrated by a cooperative response to extracellular stimuli such as small changes in Ca2+, Mg2+, amino acids, and other ligands. In addition, CaSR is a pleiotropic receptor regulating several intracellular signaling pathways, including calcium mobilization and intracellular calcium oscillation. Nearly 200 mutations and polymorphisms have been found in CaSR in relation to a variety of human disorders associated with abnormal Ca2+ homeostasis. In this review, we summarize efforts directed at identifying binding sites for calcium and amino acids. Both homotropic cooperativity among multiple calcium binding sites and heterotropic cooperativity between calcium and amino acid were revealed using computational modeling, predictions, and site-directed mutagenesis coupled with functional assays. The hinge region of the bilobed Venus flytrap (VFT) domain of CaSR plays a pivotal role in coordinating multiple extracellular stimuli, leading to cooperative responses from the receptor. We further highlight the extensive number of disease-associated mutations that have also been shown to affect CaSR's cooperative action via several types of mechanisms. These results provide insights into the molecular bases of the structure and functional cooperativity of this receptor and other members of family C of the G protein-coupled receptors (cGPCRs) in health and disease states, and may assist in the prospective development of novel receptor-based therapeutics.

BACKGROUND: The calcium-sensing receptor regulates the secretion of parathyroid hormone in response to changes in extracellular calcium concentrations, and mutations that result in a loss of function of the receptor are associated with familial hypocalciuric hypercalcemia. Mutations involving a gain of function have been associated with hypocalcemia in two kindreds. We examined the possibility that the latter type of mutation may result in a phenotype of familial hypocalcemia with hypercalciuria. METHODS: We studied six kindreds given a diagnosis of autosomal dominant hypoparathyroidism on the basis of their hypocalcemia and normal serum parathyroid hormone concentrations, a combination that suggested a defect of the calcium-sensing receptor. The hypocalcemia was associated with hypercalciuria, and treatment with vitamin D resulted in increased hypercalciuria, nephrocalcinosis, and renal impairment. Mutations in the calcium-sensing-receptor gene were identified by DNA-sequence analysis and expressed in human embryonic kidney cells (HEK-293). RESULTS: Five heterozygous missense mutations (Asn118Lys, Phe128Leu, Thr151Met, Glu191Lys, and Phe612Ser) were detected in the extracellular domain of the calcium-sensing-receptor gene and shown to cosegregate with the disease. Analysis of the functional expression of three of the mutant receptors in HEK-293 cells demonstrated shifts in the dose-response curves so that the extracellular calcium concentrations needed to produce half-maximal increases in total inositol phosphate in the cells were significantly (P=0.02 to P

Structural and functional characterization of the extracellular domain of the human CaSR with bound Mg2+ and a tryptophan derivative., Ca2+-sensing receptors (CaSRs) modulate calcium and magnesium homeostasis and many (patho)physiological processes by responding to extracellular stimuli, including divalent cations and amino acids. We report the first crystal structure of the extracellular domain (ECD) of human CaSR bound with Mg2+ and a tryptophan derivative ligand at 2.1 Å. The structure reveals key determinants for cooperative activation by metal ions and aromatic amino acids. The unexpected tryptophan derivative was bound in the hinge region between two globular ECD subdomains, and represents a novel high-affinity co-agonist of CaSR. The dissection of structure-function relations by mutagenesis, biochemical, and functional studies provides insights into the molecular basis of human diseases arising from CaSR mutations. The data also provide a novel paradigm for understanding the mechanism of CaSR-mediated signaling that is likely shared by the other family C GPCR [G protein (heterotrimeric guanine nucleotide–binding protein)–coupled receptor] members and can facilitate the development of novel CaSR-based therapeutics.

Hypocalcemia secondary to hypoparathyroidism is a rare cause of congestive heart failure. However, its early recognition and treatment lead to significant improvement in cardiac function. We report a middle-aged woman presenting with symptoms of heart failure with a serum calcium level of 3.7 mg/dl and a serum inorganic phosphate level of 17.6 mg/dl 22 years after subtotal thyroidectomy. Besides calcium and calcitriol supplementation, she was the first patient with severe hypocalcemic cardiomyopathy to be given off-label recombinant human parathyroid hormone (PTH) because of an elevated serum calcium–phosphate product. We discuss the management and outcome of the patient and then present a brief review of similar previously reported cases. We also describe the pivotal role of calcium ion and the potential role of PTH in maintaining myocardial contractility, effective natriuresis, and possible pathogenic mechanisms contributing to heart failure secondary to hypocalcemia and hypoparathyroidism.

Objective To discuss the unusual occurrence of both familial hypocalciuric hypercalcemia (FHH) and primary hyperparathyroidism in the same patient and to explore potential mechanisms of association and issues related to clinical management. Methods We discuss the diagnosis, compare the clinical presentations of FHH and primary hyperparathyroidism, review the literature regarding patients who have presented with both disorders, and discuss management considerations. We also describe 2 patients who have both FHH (confirmed by genetic testing for a mutation in the gene encoding the calcium-sensing receptor [CASR]) and primary hyperparathyroidism. Results The occurrence of both FHH and primary hyperparathyroidism in the same patient has been reported in a few cases, including 2 patients described here, one of whom was documented to have a novel CASR mutation. In those with clinical sequelae of hyperparathyroidism, parathyroidectomy has led to reduction, but not normalization, of serum calcium levels. Conclusions The coexistence of FHH and primary hyperparathyroidism should be considered in patients with hypercalcemia, hypophosphatemia, frankly elevated parathyroid hormone levels, and low urinary calcium excretion. Genetic testing for inactivating CASR gene mutations can confirm the diagnosis of FHH. Although surgical intervention does not resolve hypercalcemia, it may be beneficial by reducing the degree of hypercalcemia, alleviating the symptoms, and preventing potential complications of hyperparathyroidism. (Endocr Pract. 2012;18:412-417)

The calcium-sensing receptor (CaSR) is a G-protein-coupled receptor that has an extracellular bilobed venus flytrap domain (VFTD) predicted to contain five calcium (Ca(2+))-binding sites. To elucidate the structure-function relationships of the VFTD, we investigated 294 unrelated probands with familial hypocalciuric hypercalcaemia (FHH), neonatal severe primary hyperparathyroidism (NSHPT) or autosomal dominant hypocalcaemic hypercalciuria (ADHH) for CaSR mutations and performed in vitro functional expression studies and three-dimensional modelling of mutations involving the VFTD. A total of 70 different CaSR mutations were identified: 35 in FHH, 10 in NSHPT and 25 in ADHH patients. Furthermore, a CaSR variant (Glu250Lys) was identified in FHH and ADHH probands and demonstrated to represent a functionally neutral polymorphism. NSHPT was associated with a large proportion of truncating CaSR mutations that occurred in the homozygous or compound heterozygous state. Thirty-four VFTD missense mutations were identified, and 18 mutations were located within 10 Å of one or more of the predicted Ca(2+)-binding sites, particularly at the VFTD cleft, which is the principal site of Ca(2+) binding. Mutations of residues 173 and 221, which are located at the entrance to the VFTD cleft binding site, were associated with both receptor activation (Leu173Phe and Pro221Leu) and inactivation (Leu173Pro and Pro221Gln), thereby highlighting the importance of these residues for entry and binding of Ca(2+) by the CaSR. Thus, these studies of disease-associated CaSR mutations have further elucidated the role of the VFTD cleft region in Ca(2+) binding and the function of the CaSR.

Phospholipase modulators have been shown to affect the topology of lipid bilayers and the formation of tubulo-vesicular structures, but the specific endogenous phospholipases involved have yet to be identified. Here we show that TRPML1 (MLN1), a Ca(2+)-permeable channel, contributes to membrane remodeling through a serine lipase consensus domain, and thus represents a novel type of bifunctional protein. Remarkably, this serine lipase active site determines the ability of MLN1 to generate tubulo-vesicular extensions in mucolipin-1-expressing oocytes, human fibroblasts and model membrane vesicles. Our demonstration that MLN1 is involved in membrane remodeling and the formation of extensions suggests that it may play a role in the formation of cellular processes linked to the late endosome/lysosome (LE/L) pathway. MLN1 is absent or mutated in patients with mucolipidosis IV (MLIV), a lysosomal disorder with devastating neurological and other consequences. This study provides potential insight into the pathophysiology of MLIV.

Autoantibodies directed against the calcium-sensing receptor (CaSR) have been reported in several individuals with various autoimmune disorders and PTH-mediated hypercalcemia. Previously, glucocorticoid treatment has been shown to decrease the CaSR autoantibody titers and normalize the hypercalcemia in a patient with autoimmune hypocalciuric hypercalcemia (AHH).The objective of the study was to evaluate a patient with AHH for the presence of blocking autoantibodies against the CaSR and to monitor her biochemical and serological responses to a trial of glucocorticoid therapy.Glucocorticoid treatment had no effect on serum total or ionized calcium concentration or serum PTH levels, all of which remained at higher than normal levels. In contrast, on prednisone, urinary calcium excretion increased from overtly hypocalciuric levels to normal values. Anti-CaSR autoantibodies were detected at similar levels in the patient's serum before, during, and after glucocorticoid treatment. Functional testing of these antibodies showed that they inhibited the stimulatory effect of extracellular Ca(2+) on ERK1/2 but did not suppress the calcium-induced accumulation of inositol-1-phosphate.We report a patient with AHH with frankly elevated PTH levels who was found to have autoantibodies against the CaSR. The hypercalcemia and CaSR autoantibody titers failed to respond to glucocorticoid therapy, unlike a previously reported patient with similar clinical and biochemical features. The anti-CaSR antibody-mediated inhibition of CaSR-stimulated ERK1/2 activity, but not of inositol-1-phosphate accumulation, suggests that ERK1/2 may mediate, at least in part, the regulation of PTH secretion and urinary calcium excretion by the CaSR.

The National Lung Screening Trial (NLST) is a randomized multicenter study comparing low-dose helical computed tomography (CT) with chest radiography in the screening of older current and former heavy smokers for early detection of lung cancer, which is the leading cause of cancer-related death in the United States. Five-year survival rates approach 70% with surgical resection of stage IA disease; however, more than 75% of individuals have incurable locally advanced or metastatic disease, the latter having a 5-year survival of less than 5%. It is plausible that treatment should be more effective and the likelihood of death decreased if asymptomatic lung cancer is detected through screening early enough in its preclinical phase. For these reasons, there is intense interest and intuitive appeal in lung cancer screening with low-dose CT. The use of survival as the determinant of screening effectiveness is, however, confounded by the well-described biases of lead time, length, and overdiagnosis. Despite previous attempts, no test has been shown to reduce lung cancer mortality, an endpoint that circumvents screening biases and provides a definitive measure of benefit when assessed in a randomized controlled trial that enables comparison of mortality rates between screened individuals and a control group that does not undergo the screening intervention of interest. The NLST is such a trial. The rationale for and design of the NLST are presented.

We have investigated, in neonates, whether the calcium-sensing receptor (CaR) mediates the effects of dietary calcium on bone turnover and/or modulates parathyroid hormone (PTH)–induced bone turnover. Wild-type (WT) pups and pups with targeted deletion of the Pth (Pth–/–) gene or of both Pth and CaR (Pth–/–CaR–/–) genes were nursed by dams on a normal or high-calcium diet. Pups nursed by dams on a normal diet received daily injections of vehicle or of PTH(1–34) (80 µg/kg) for 2 weeks starting from 1 week of age. In pups receiving vehicle and fed by dams on a normal diet, trabecular bone volume, osteoblast number, type 1 collagen–positive area, and mineral apposition rate, as well as the expression of bone-formation-related genes, all were reduced significantly in Pth–/– pups compared with WT pups and were decreased even more dramatically in Pth–/–CaR–/– pups. These parameters were increased in WT and Pth–/– pups but not in Pth–/–CaR–/– pups fed by dams on a high-calcium diet compared with pups fed by dams on a normal diet. These parameters also were increased in WT, Pth–/–, and Pth–/–CaR–/– pups following exogenous PTH treatment; however, the percentage increase was less in Pth–/–CaR–/– pups than in WT and Pth–/– pups. In vehicle-treated pups fed by dams on either the normal or high-calcium diet and in PTH-treated pups fed by dams on a normal diet, the number and surfaces of osteoclasts and the ratio of RANKL/OPG were reduced significantly in Pth–/– pups and less significantly in Pth–/–CaR–/– pups compared with WT pups. These parameters were further reduced significantly in WT and Pth–/– pups from dams fed a high-calcium diet but did not decrease significantly in similarly treated Pth–/–CaR–/– pups, and they increased significantly in PTH-treated pups compared with vehicle-treated, genotype-matched pups fed by dams on the normal diet. These results indicate that in neonates, the CaR mediates alterations in bone turnover in response to changes in dietary calcium and modulates PTH-stimulated bone turnover. © 2011 American Society for Bone and Mineral Research.

Calcimimetics, which activate the extracellular calcium (Ca(o)(2+))-sensing receptor in the parathyroid and other tissues participating in Ca(o)(2+) homeostasis, were the first described allosteric activators of a G-protein-coupled receptor. Cinacalcet, the only calcimimetic currently approved for human use, is used clinically for treating secondary hyperparathyroidism (e.g., overactivity of parathyroid glands) in patients being dialyzed for chronic kidney disease. By sensitizing the parathyroids to Ca(o)(2+), cinacalcet lowers the circulating parathyroid hormone (PTH) level. It also reduces serum calcium and phosphate, changes increasing the percentage of patients achieving the guidelines recommended by the National Kidney Foundation (NKF) for these minerals. Studies are underway addressing whether better adherence to these guidelines in patients receiving cinacalcet reduces cardiovascular disease and related mortality, which are both common is the dialysis population. The second approved use of cinacalcet is for treating hypercalcemia in patients with inoperable parathyroid carcinoma. In this setting, it provides the first medical therapy chronically lowering serum calcium concentration in this condition, albeit not to normal in most patients. Its effect on the long-term prognosis of these patients, if any, is presently unclear. "Off-label" administration of cinacalcet [i.e., not yet approved by the US Food and Drug Administration (FDA)] effectively lowers serum calcium and/or PTH in various other forms of hyperparathyroidism and increases serum phosphate in renal phosphate-wasting syndromes by reducing PTH-induced phosphaturia. In the future, the drug could conceivably be utilized to modulate the activity of the CaSR in other tissues (i.e., kidney, colon) in therapeutically desirable ways.

The extracellular calcium-sensing receptor (CaSR) plays a major role in the maintenance of a physiological serum ionized calcium (Ca2+) concentration by regulating the circulating levels of parathyroid hormone. It was molecularly identified in 1993 by Brown et al. in the laboratory of Dr. Steven Hebert with an expression cloning strategy. Subsequent studies have demonstrated that the CaSR is highly expressed in the kidney, where it is capable of integrating signals deriving from the tubular fluid and/or the interstitial plasma. Additional studies elucidating inherited and acquired mutations in the CaSR gene, the existence of activating and inactivating autoantibodies, and genetic polymorphisms of the CaSR have greatly enhanced our understanding of the role of the CaSR in mineral ion metabolism. Allosteric modulators of the CaSR are the first drugs in their class to become available for clinical use and have been shown to treat successfully hyperparathyroidism secondary to advanced renal failure. In addition, preclinical and clinical studies suggest the possibility of using such compounds in various forms of hypercalcemic hyperparathyroidism, such as primary and lithium-induced hyperparathyroidism and that occurring after renal transplantation. This review addresses the role of the CaSR in kidney physiology and pathophysiology as well as current and in-the-pipeline treatments utilizing CaSR-based therapeutics.

We examined parathyroid and skeletal function in 3-month-old mice expressing the null mutation for 25-hydroxyvitamin D-1alpha-hydroxylase [1alpha(OH)ase(-/-)] and in mice expressing the null mutation for both the 1alpha(OH)ase and the calcium-sensing receptor [Casr(-/-)1alpha(OH)ase(-/-)] genes. On a normal diet, all mice were hypocalcemic, with markedly increased parathyroid hormone (PTH), increased trabecular bone volume, increased osteoblast activity, poorly mineralized bone, enlarged and distorted cartilaginous growth plates, and marked growth retardation, especially in the compound mutants. Osteoclast numbers were reduced in the Casr(-/-)1alpha(OH)ase(-/-) mice. On a high-lactose, high-calcium, high-phosphorus "rescue" diet, serum calcium and PTH were normal in the 1alpha(OH)ase(-/-) mice but increased in the Casr(-/-)1alpha(OH)ase(-/-) mice with reduced serum phosphorus. Growth plate architecture and mineralization were improved in both mutants, but linear growth of the double mutants remained abnormal. Mineralization of bone improved in all mice, but osteoblast activity and trabecular bone volume remained elevated in the Casr(-/-)1alpha(OH)ase(-/-) mice. These studies support a role for calcium-stimulated maturation of the cartilaginous growth plate and mineralization of the growth plate and bone and calcium-stimulated CaSR-mediated effects on bone resorption. PTH-mediated bone resorption may require calcium-stimulated CaSR-mediated enhancement of osteoclastic activity. (c) 2010 American Society for Bone and Mineral Research.

Serum calcium levels are tightly regulated. We performed genome-wide association studies (GWAS) in population-based studies participating in the CHARGE Consortium to uncover common genetic variations associated with total serum calcium levels. GWAS of serum calcium concentrations was performed in 20 611 individuals of European ancestry for similar to 2.5 million genotyped and imputed single-nucleotide polymorphisms (SNPs). The SNP with the lowest P-value was rs17251221 (P = 2.4 * 10(-22), minor allele frequency 14%) in the calcium-sensing receptor gene (CASR). This lead SNP was associated with higher serum calcium levels [0.06 mg/dl (0.015 mmol/l) per copy of the minor G allele] and accounted for 0.54% of the variance in serum calcium concentrations. The identification of variation in CASR that influences serum calcium concentration confirms the results of earlier candidate gene studies. The G allele of rs17251221 was also associated with higher serum magnesium levels (P = 1.2 * 10(-3)), lower serum phosphate levels (P = 2.8 * 10(-7)) and lower bone mineral density at the lumbar spine (P = 0.038), but not the femoral neck. No additional genomic loci contained SNPs associated at genome-wide significance (P < 5 * 10(-8)). These associations resemble clinical characteristics of patients with familial hypocalciuric hypercalcemia, an autosomal-dominant disease arising from rare inactivating mutations in the CASR gene. We conclude that common genetic variation in the CASR gene is associated with similar but milder features in the general population.

Previously, we have demonstrated the presence of anti-calcium-sensing receptor (CaSR) antibodies in patients with autoimmune polyglandular syndrome type 1 (APS1), a disease that is characterized in part by hypoparathyroidism involving hypocalcemia, hyperphosphatemia, and low serum levels of parathyroid hormone. The aim of this study was to define the binding domains on the CaSR of anti-CaSR antibodies found in APS1 patients and in one patient suspected of having autoimmune hypocalciuric hypercalcemia (AHH). A phage-display library of CaSR peptides was constructed and used in biopanning experiments with patient sera. Selectively enriched IgG-binding peptides were identified by DNA sequencing, and subsequently, immunoreactivity to these peptides was confirmed in ELISA. Anti-CaSR antibody binding sites were mapped to amino acid residues 41–69, 114–126, and 171–195 at the N-terminal of the extracellular domain of the receptor. The major autoepitope was localized in the 41–69 amino acid sequence of the CaSR with antibody reactivity demonstrated in 12 of 12 (100%) APS1 patients with anti-CaSR antibodies and in 1 AHH patient with anti-CaSR antibodies. Minor epitopes were located in the 114–126 and 171–195 amino acid domains, with antibody reactivity shown in 5 of 12 (42%) and 4 of 12 (33%) APS1 patients, respectively. The results indicate that epitopes for anti-CaSR antibodies in the AHH patient and in the APS1 patients who were studied are localized in the N-terminal of the extracellular domain of the receptor. The present work has demonstrated the successful use of phage-display technology in the discovery of CaSR-specific epitopes targeted by human anti-CaSR antibodies. © 2010 American Society for Bone and Mineral Research.

A newly developed calcium-sensitive dye, Fura-2, was employed in dispersed bovine parathyroid cells to study the effects of extracellular calcium and magnesium on cytosolic calcium concentration and parathyroid hormone (PTH) release. In comparison with control cells, Fura-2-loaded parathyroid cells showed the same maximal rate of PTH release, set-point for extracellular Ca++ (the calcium concentration producing half of the maximal inhibition of PTH release), and maximal inhibition of PTH release (71.6%) by high extracellular Ca++. At an extracellular Mg++ concentration of 0.5 mM, raising extracellular Ca++ in a stepwise fashion from 0.5 mM to 2.0 mM produced a dose-dependent, statistically significant (p < 0.01) increase in cytosolic Ca++ from 198 ± 24 nM (0.5 mM Ca++) to 411 ± 21 nM (2.0 mM Ca++) which closely paralleled the concomitant decrease in PTH release. An elevation of extracellular Mg++ from 0.5 mM to 5 mM, at an extracellular Ca++ of 0.5 mM, resulted in a transient spike of cytosolic Ca++ which lasted for approximately 30 seconds, followed by a small but stable increase in the cytosolic Ca++ concentration (174 ± 7 nM vs. 237 ± 10 nM, n = 4, p < 0.01). Prior removal of extracellular calcium by addition of an excess of EGTA did not abolish the transient spike induced by high extracellular magnesium concentrations in Fura-2-loaded cells, suggesting that this rapid increase in cytosolic Ca++ arises, at least in part, from intracellular stores of Ca++. This is supported by the observation that pretreating cells with ionomycin resulted in disappearance of the magnesium-induced spike. In parallel experiments, the values for cytosolic calcium concentration at high and low extracellular calcium and magnesium concentrations in cells loaded with Fura-2 were comparable to those in cells loaded with Quin-2. These results show that Fura-2 may be employed to measure the cytosolic Ca++ concentration in dispersed bovine parathyroid cells and that extracellular Ca++ and Mg++ produced sustained increases in cytosolic Ca++ in cells loaded with this dye which are comparable to those seen with Quin-2-loaded cells. In addition, however, probably because of the lower loading concentrations possible with Fura-2, cells loaded with this dye show Mg++-induced spikes in intracellular Ca++, resulting, in part, from release of intracellular Ca++. These Ca++ transients support other data suggesting the possibility of an extracellular divalent cation receptor on parathyroid cells, which may produce some of its effects on parathyroid function by mobilizing intracellular Ca++.

We examined the effects of TPA on the high Ca2+-stimulated accumulation of inositol phosphates in bovine parathyoid cells to determine whether protein kinase C modulates phosphoinositide turnover in a fashion similar to that observed in other cell types stimulated by more classic Ca2+ mobilizing hormones. Following exposure of parathyroid cells to TPA (10−6 M) for 10 or 30 minutes, there was a time- and dose-dependent inhibition of the accumulation of inositol monophosphate (IP), inositol bisphosphate (IP2), and inositol trisphosphate (IP3) stimulated by 3 mM Ca2+. Half the maximal observed inhibition took place at 1–10 nM TPA, with 50–60% inhibition of high Ca2+-stimulated accumulation of inositol phosphates at 10−6 M TPA. The active phorbol ester, 4β-phorbol didecanoate, produced similar effects; the inactive derivative, 4α-phorbol didecanoate, was without effect. When parathyroid cells were exposed to TPA (10−6 M) for varying times and were then incubated with high (3 mM) Ca2+, inhibition of inositol phosphate accumulation was observed with 10 or 30 minutes preincubation. In contrast, preincubation of cells with TPA for 3 or 18 h markedly enhanced the high (3 mM) Ca2+-induced increase in inositol phosphates. In cells preincubated with TPA for 18 h, binding sites for [3H]phorbol dibutyrate and total protein kinase C (PKC) activity were reduced by greater than 95% and by 71%, respectively, consistent with downregulation of the enzyme. These results suggest that the high extracellular Ca2+-stimulated increase in accumulation of inositol phosphates in parathyroid cells, which has been postulated to result from a receptorlike process, can be modulated by agonists of protein kinase C in a fashion similar to that observed with more classic Ca2+ mobilizing hormones. Activators of kinase C initially inhibit the generation of inositol phosphates, presumably as a result of reduced turnover of phosphoinositides, but subsequently enhance inositol phosphate accumulation, probably because of down-regulation of protein kinase C.

Serum autoantibodies directed toward antigenic determinants on the surface of human parathyroid cells (PTAb-CS) have been demonstrated in a subset (8 of 23) of adult patients with idiopathic hypoparathyroidism (IHP). In sera from 3 of 8 patients with PTAb-CS, binding of these autoantibodies to their respective parathyroid cell surface antigen(s) resulted in marked inhibition of parathyroid hormone (PTH) secretion in an in vitro dispersed human parathyroid cell (dPTC) system. In 1 subject evaluated longitudinally, circulating levels of PTAb-CS, and the magnitude of the inhibitory effect on PTH secretion, temporally correlated with the clinical course of the hypoparathyroidism. These findings suggest a causative role for antibodies directed against cell surface antigens in parathyroid dysfunction in some cases of "autoimmune" hypoparathyroidism.

We previously showed that high extracellular calcium (Ca2+) concentrations raise the levels of inositol phosphates in bovine parathyroid cells, presumably via the G protein-coupled, "receptor-like" mechanism through which Ca2+ is thought to regulate these cells. To date, however, there are limited data showing Ca(2+)-evoked hydrolysis of phosphoinositides with attendant increases in the levels of the biologically active 1,4,5 isomer of inositol trisphosphate (IP3) that would be predicted to arise from such a receptor-mediated process. In the present studies we used HPLC and TLC, respectively, to quantify the high Ca(2+)-induced changes in various inositol phosphates, including the isomers of IP3, and phosphoinositides in bovine parathyroid cells prelabeled with [3H]inositol. In the absence of lithium, high Ca2+ dose dependently elevated the levels of inositol-1,4,5-trisphosphate [I(1,4,5)P3], with a maximal, 4- to 5-fold increase within 5 s; the levels of inositol 1,3,4-trisphosphate [I(1,3,4)P3] first rose significantly at 5-10 s and remained 5- to 10-fold elevated for at least 30 minutes. These changes were accompanied by reciprocal 29-36% decreases in PIP2 (within 5-10 s, the earliest time points examined), PIP (within 60 s), and PI (within 60 s). These results document that, as in other cells responding to more classic "Ca(2+)-mobilizing" hormones, the high Ca(2+)-evoked increases in inositol phosphates in bovine parathyroid cells arise from the hydrolysis of phosphoinositides, leading to the rapid accumulation of the active isomer of IP3. The latter presumably underlies the concomitant spike in the cytosolic calcium concentration (Ca(i)) in parathyroid cells.

The parathyroid glands are an infrequent target for autoimmunity; the exception being in the autoimmune polyglandular syndrome type 1, where autoimmune hypoparathyroidism is the rule. Antibodies that are directed against the parathyroid cell-surface calcium-sensing receptor (CaSR) have recently been recognised to be present in the serum of patients with autoimmune hypoparathyroidism. In some individuals, these anti-CaSR antibodies have also been shown to produce functional activation of the receptor, suggesting a direct pathogenic role in hypocalcemia. Additionally, a few hypercalcemic patients with autoimmune hyperparathyroidism owing to anti-CaSR antibodies that inhibit receptor activation have now been identified. Other novel parathyroid autoantigens are starting to be elucidated. These findings suggest that new approaches to treatment, such as CaSR antagonists or agonists (calcilytics/calcimimetics) may be worthwhile.

The calcium-sensing receptor (CaR) is responsive to changes in the extracellular Ca(2+) (Ca(2+)(o)) concentration. It is a member of the largest family of cell surface receptors, the G protein-coupled receptors, and it has been shown to be involved in Ca(2+)(o) homeostasis. Apart from its primary role in Ca(2+)(o) homeostasis, the CaR may be involved in phenomena that allow for the development of many types of benign or malignant tumors, from parathyroid adenomas to breast, prostate, and colon cancers. For example, whereas the CaR is expressed in both normal and malignant breast tissue, increased CaR levels have been reported in highly metastatic primary breast cancer cells and breast cancer cell lines, possibly contributing to their malignancy and associated alterations in their biological properties. In these settings the CaR exhibits oncogenic properties. Enhanced CaR expression and altered proliferation of prostate cancer cells in response to increased Ca(2+)(o) have also been described. In contrast, colon and parathyroid cancers often present with reduced or absent CaR expression, and activation of this receptor decreases cell proliferation, suggesting a role for the CaR as a tumor suppressor gene. Thus, the CaR may play an important role in the development of many types of neoplasia. Herein, we review the role of the CaR in various benign and malignant tumors in further detail, describing its contribution to parathyroid tumors, breast, prostate, and colon cancers, and we evaluate how pharmacological manipulations of this receptor may be of interest for the treatment of certain cancers in the future.

Background: At the Third International Workshop on Asymptomatic Primary Hyperparathyroidism (PHPT) in May 2008, recent data on the disease were reviewed. We present the results of a literature review on issues arising from the clinical presentation and natural history of PHPT. Methods: Questions were developed by the International Task Force on PHPT. A comprehensive literature search for relevant studies was reviewed, and the questions of the International Task Force were addressed by the Consensus Panel. Conclusions: 1) Data on the extent and nature of cardiovascular involvement in those with mild disease are too limited to provide a complete picture. 2) Patients with mild PHPT have neuropsychological complaints. Although some symptoms may improve with surgery, available data remain inconsistent on their precise nature and reversibility. 3) Surgery leads to long-term gains in spine, hip, and radius bone mineral density (BMD). Because some patients have early disease progression and others lose BMD after 8–10 yr, regular monitoring (serum calcium and three-site BMD) is essential in those followed without surgery. Patients may present with normocalcemic PHPT (normal serum calcium with elevated PTH concentrations; no secondary cause for hyperparathyroidism). Data on the incidence and natural history of this phenotype are limited. 4) In the absence of kidney stones, data do not support the use of marked hypercalciuria (>10 mmol/d or 400 mg/d) as an indication for surgery for patients. 5) Patients with bone density T-score −2.5 or less at the lumbar spine, hip, or distal one third radius should have surgery.

Strontium ranelate exerts both an anti-catabolic and an anabolic effect on bone cells. To further investigate the molecular mechanism whereby strontium ranelate inhibits bone resorption, we focused our attention on the effects of strontium ranelate on osteoclast apoptosis and on the underlying mechanism(s). Using primary mature rabbit osteoclasts, we demonstrated that strontium (Sro2+) dose-dependently stimulates the apoptosis of mature osteoclasts. As shown previously for calcium (Cao2+), the Sro2+-induced effect on mature osteoclasts is mediated by the Cao2+-sensing receptor, CaR, which in turn stimulates a phospholipase C-dependent signaling pathway and nuclear translocation of NF-kappaB. Unlike Cao2+, however, Sro2+-induced osteoclast apoptosis was shown to depend on PKCbetaII activation and to be independent of inositol 1,4,5-trisphosphate action. As a consequence of these differences in their intracellular signaling pathways, Sro2+ and Cao2+ in combination were shown to exert a greater effect on mature osteoclast apoptosis than did either divalent cation by itself. Altogether, our results show that Sro2+ acts through the CaR and induces osteoclast apoptosis through a signaling pathway similar to but different in certain respects from that of Cao2+. This difference in the respective signaling cascades enables Sro2+ to potentiate Cao2+-induced osteoclast apoptosis and vice versa. In this manner, it is conceivable that Sro2+ and Cao2+ act together to inhibit bone resorption in strontium ranelate-treated patients.

Oligodendrocytes develop from oligodendrocyte progenitor cells (OPCs), which in turn arise from a subset of neuroepithelial precursor cells during midneurogenesis. Development of the oligodendrocyte lineage involves a plethora of cell-intrinsic and -extrinsic signals. A cell surface calcium-sensing receptor (CaR) has been shown to be functionally expressed in immature oligodendrocytes. Here, we investigated the expression and function of the CaR during oligodendrocyte development. We show that the order of CaR mRNA expression as assessed by quantitative polymerase chain reaction is mature oligodendrocyte > neuron > astrocyte. We next determined the rank order of CaR expression on inducing specification of neural stem cells to the neuronal, oligodendroglial, or astrocytic lineages and found that the relative levels of CaR mRNA expression are OPC > neuron > astrocytes. CaR mRNA expression in cells at various stages of development along the oligodendrocyte lineage revealed that its expression is robustly up-regulated during the OPC stage and remains high until the premyelinating stage, decreasing thereafter by severalfold in the mature oligodendrocyte. In OPCs, high Ca2+ acting via the CaR promotes cellular proliferation. We further observed that high Ca2+ stimulates the mRNA levels of myelin basic protein in preoligodendrocytes, which is also CaR mediated. Finally, myelin basic protein levels were significantly reduced in the cerebellum of CaR-null mice during development. Our results show that CaR expression is up-regulated when neural stem cells are specified to the oligodendrocyte lineage and that activation of the receptor results in OPC expansion and differentiation. We conclude that the CaR may be a novel regulator of oligodendroglial development and function. © 2008 Wiley-Liss, Inc.

The calcium-sensing receptor (CaR) is a G protein-coupled receptor that “senses” extracellular calcium ions (Ca2+o) as an extracellular first messenger. In this report, we have shown that the CaR is expressed in primary cultures of microglial cells derived from rat brain as assessed by RT-PCR using four CaR-specific primer pairs followed by sequencing of the amplified products, by northern blot analysis using a CaR-specific probe, as well as by immunocytochemistry and western analysis utilizing a specific polyclonal anti-CaR antiserum. In addition, raising Ca2+, from 0.75 to 3.0 mM or addition of the polycationic CaR agonist neomycin or a “calcimimetic” CaR activator (R-467; NPS Pharmaceuticals) increased the open state probability (Po) of a Ca+-activated Kf channel having a unitary conductance of 84 ± 4 pS, indicating that the channel is modulated by the CaR. Therefore, our data strongly suggest that a functional CaR is expressed in cultured rat microglia, similar to that in parathyroid gland and kidney, which could potentially play an important role(s) in regulating microglial function.

The extracellular calcium (Ca 2+ o )-sensing receptor (CaSR) enables the parathyroid glands and other CaSR-expressing cells involved in calcium homeostasis, such as the kidney and bone, to sense alterations in the level of Ca 2+ o and to respond with changes in function that are directed at normalizing the blood calcium concentration. Several disorders of Ca 2+ o sensing arise from inherited or acquired abnormalities that ‘reset' the serum calcium concentration upwards or downwards. Heterozygous inactivating mutations of the CaSR produce a benign form of hypercalcaemia, termed ‘familial hypocalciuric hypercalcaemia', while homozygous mutations produce a much more severe hypercalcaemic disorder resulting from marked hyperparathyroidism, called ‘neonatal severe hyperparathyroidism'. Activating mutations cause a hypocalcaemic syndrome of varying severity, termed ‘autosomal-dominant hypocalcaemia or hypoparathyroidism' as well as Bartter's syndrome type V. Calcimimetic CaSR activators and calcilytic CaSR antagonists have also been developed with potential for use in the treatment of these disorders.