Calcium-sensing receptor and calcium kidney stones

Functional analysis reveals calcium-sensing receptor gene regulating cell-cell junction in renal tubular epithelial cells

PURPOSE

Calcium-sensing receptor (CASR) influences the expression pattern of multiple genes in renal tubular epithelial cells. The objective of this inquiry was to explore the molecular mechanisms of CASR in renal tubular epithelial cells and nephrolithiasis.

METHODS

HK-2 cells were transfected with lentiviruses carrying either CASR (named CASR) or an empty vector negative control (named NC), as well as shRNA intended to target CASR (named shCASR) or its corresponding negative control (named shNC). CCK-8 assay was used to detect the effect of CASR on the proliferation of HK-2 cells. RNA-Sequencing was applied to explore potential pathways regulated by CASR in HK-2 cells.

RESULTS

PCR and western blot results showed that CASR expression was significantly increased in CASR cells and was decreased in shCASR cells when compared to their corresponding negative control, respectively. CCK-8 assay revealed that CASR inhibited the proliferation of HK-2 cells. RNA-Sequencing results suggested that the shCASR HK-2 cells exhibited a significant up-regulation of 345 genes and a down-regulation of 366 genes. These differentially expressed genes (DEGs) were related to cell apoptosis and cell development. In CASR HK-2 cells, 1103 DEGs primarily functioned in mitochondrial energy metabolism, and amino acid metabolism. With the Venn diagram, 4 DEGs (Clorf116, ENPP3, IL20RB, and CLDN2) were selected as the hub genes regulated by CASR. Enrichment analysis revealed that these hub genes were involved in cell-cell junction, and epithelial cell development.

CONCLUSIONS

In summary, our investigation has the potential to offer novel perspectives on CASR regulating cell-cell junction in HK-2 cells.

In vivo treatment with calcilytic of CaSR knock-in mice ameliorates renal phenotype reversing downregulation of the vasopressin-AQP2 pathway

High concentrations of urinary calcium counteract vasopressin action via the activation of the Calcium-Sensing Receptor (CaSR) expressed in the luminal membrane of the collecting duct cells, which impairs the trafficking of aquaporin-2 (AQP2). In line with these findings, we provide evidence that, with respect to wild-type mice, CaSR knock-in (KI) mice mimicking autosomal dominant hypocalcaemia, display a significant decrease in the total content of AQP2 associated with significantly higher levels of AQP2 phosphorylation at Ser261, a phosphorylation site involved in AQP2 degradation. Interestingly, KI mice also had significantly higher levels of phosphorylated p38MAPK, a downstream effector of CaSR and known to phosphorylate AQP2 at Ser261. Moreover, ATF1 phosphorylated at Ser63, a transcription factor downstream of p38MAPK, was significantly higher in KI. In addition, KI mice had significantly higher levels of AQP2-targeting miRNA137 consistent with a post-transcriptional downregulation of AQP2. In vivo treatment of KI mice with the calcilytic JTT-305, a CaSR antagonist, increased AQP2 expression and reduced AQP2-targeting miRNA137 levels in KI mice. Together, these results provide direct evidence for a critical role of CaSR in impairing both short-term vasopressin response by increasing AQP2-pS261, as well as AQP2 abundance, via the p38MAPK-ATF1-miR137 pathway. KEY POINTS: Calcium-Sensing Receptor (CaSR) activating mutations are the main cause of autosomal dominant hypocalcaemia (ADH) characterized by inappropriate renal calcium excretion leading to hypocalcaemia and hypercalciuria. Current treatments of ADH patients with parathyroid hormone, although improving hypocalcaemia, do not improve hypercalciuria or nephrocalcinosis. In vivo treatment with calcilytic JTT-305/MK-5442 ameliorates most of the ADH phenotypes of the CaSR knock-in mice including hypercalciuria or nephrocalcinosis and reverses the downregulation of the vasopressin-sensitive aquaporin-2 (AQP2) expression, providing direct evidence for a critical role of CaSR in impairing vasopressin response. The beneficial effect of calcilytic in reducing the risk of renal calcification may occur in a parathyroid hormone-independent action through vasopressin-dependent inhibition of cAMP synthesis in the thick ascending limb and in the collecting duct. The amelioration of most of the abnormalities in calcium metabolism including hypercalciuria, renal calcification, and AQP2-mediated osmotic water reabsorption makes calcilytic a good candidate as a novel therapeutic agent for ADH.

Children With Type 1 Spinal Muscular Atrophy Are at Increased Risk for Nephrolithiasis

BACKGROUND

Nephrolithiasis is not a well-documented condition in children with spinal muscular atrophy (SMA). It is possible that this condition was underestimated before the era of nusinersen because of a much shorter life expectancy. We present our observational data on nephrolithiasis and its possible risk factors in children with type 1 SMA.

METHODS

We retrospectively reviewed the charts of 20 children with genetically confirmed type 1 SMA. Thirteen patients (aged 9 to 55 months) who underwent urinary tract ultrasonography were included in the study. Medical records were retrospectively reviewed for demographic and clinical characteristics, ultrasound results, and metabolic abnormalities.

RESULTS

Seven children (54%) had nephrolithiasis; 5 had multiple stones and two had a single stone. Two patients had microlithiasis (<3 mm), three had a stone in the size of 3 to 5 mm, and one had a stone in the size of more than 8 mm. Two patients with nephrolithiasis had urinary tract abnormalities. Patients with nephrolithiasis were more likely to have a history of urinary tract infections (UTIs) (P = 0.048) and higher urine specific gravity (P = 0.014) than patients without nephrolithiasis. Five of seven children with nephrolithiasis had a urine metabolic evaluation; all had hypercalciuria, three had hyperuricosuria, but none had hyperoxaluria, hypocitraturia, or hypomagnesemia.

CONCLUSION

Children with SMA type 1 are at an increased risk for nephrolithiasis. Hypercalciuria and high urine specific gravity appear to be the most common risk factors for the occurrence of nephrolithiasis. In addition, UTI is more common in patients with type 1 SMA with nephrolithiasis.

Hypomagnesemia: a potential underlooked cause of persistent vitamin D deficiency in chronic kidney disease

Magnesium and vitamin D play important roles in most cells of the body. These nutrients act in a coordinated fashion to maintain physiologic functions of various organs, and their abnormal balance could adversely affect these functions. Therefore, deficient states of both nutrients may lead to several chronic medical conditions and increased cardiovascular and all-cause mortality. Chronic kidney disease (CKD) patients have altered metabolism of both magnesium and vitamin D. Some studies indicate that magnesium could have a role in the synthesis and metabolism of vitamin D, and that magnesium supplementation substantially reversed the resistance to vitamin D treatment in some clinical situations. Recent observational studies also found that magnesium intake significantly interacted with vitamin D status and, particularly with the risk of cardiovascular mortality. It is therefore essential to ensure adequate levels of magnesium to obtain the optimal benefits of vitamin D supplementation in CKD patients. In this review, we discuss magnesium physiology, magnesium and vitamin D metabolism in CKD, potential metabolic interactions between magnesium and vitamin D and its clinical relevance, as well as the possible role of magnesium supplementation to assure adequate vitamin D levels.

Haplotype of CaSR gene is associated with risk of renal stone disease in West Indian population

Calcium is the most abundant metabolite involved in the stone matrix. The CaSR gene controls calcium homeostasis, and genetic variation in the CaSR gene could lead to the development of renal stone disease. Therefore, the current study has been designed to assess the association of genetic variants of CaSR gene polymorphisms with renal stone disease. A single-centric prospective study has been carried out on a total of 300 participants (150 cases and 150 controls). Serum levels of calcium, creatinine, parathyroid hormone, and 24 h urine metabolites were measured. Two polymorphisms, rs1801725 and rs1042636, of the CaSR gene, have been genotyped for each participant. T test, binary logistic regression, and Chi-square analysis were used for statistical analysis. Renal stone patients had significantly higher levels of serum parathyroid hormone, creatinine, and 24-h urine metabolites in comparison to the controls. CaSR gene variants, rs1801725 (GG) and rs1042636 (AA), both have shown significant association with renal stone disease. In addition, individuals having specific genotypes along with metabolic abnormalities such as hypercalcemia and hyperparathyroidism are found to be at a higher significant risk of developing the renal stone disease. In the present study, the haplotype of the CaSR gene has shown an association with renal stone disease. Individuals with hyperparathyroidism and hypercalcemia and risk genotype have a higher susceptibility to developing renal stone disease.

miR-103a-3p Silencing Ameliorates Calcium Oxalate Deposition in Rat Kidney by Activating the UMOD/TRPV5 Axis

Maintaining the balance of calcium (Ca2+) metabolism in the kidney is crucial in preventing the formation of kidney stones. Functionally, the microRNA (miRNA) participating in this process needs to be unveiled. We induced NRK-52E cell injury by oxalate treatment. The role of transient receptor potential cation channel subfamily V member 5 (TRPV5) in oxalate-induced cells was studied by TRPV5 overexpression transfection, qRT-PCR, Western blot, MTT, and crystal adhesion detection. After identifying uromodulin (UMOD) expression in injured cells, we confirmed the interaction between TRPV5 and UMOD by coimmunoprecipitation (CoIP) and cell-surface biotinylation assays. The validation of UMOD-regulating TRPV5 in viability, crystal adhesion, and Ca2+ concentration of oxalate-induced cells was performed. Bioinformatics analysis and luciferase assay were used to identify the miRNA-targeting UMOD. The role of the miR-103a-3p-regulating UMOD/TRPV5 axis was detected by rescue experiments. We constructed a rat model with treatment of ethylene glycol (EG) to investigate the miR-103a-3p/UMOD/TRPV5 axis in vivo by hematoxylin-eosin (H&E) staining, Western blot, and immunohistochemistry (IHC). Upregulation of TRPV5 protected NRK-52E cells from oxalate-induced injury by enhancing cell viability and inhibiting CaOx adhesion. UMOD was depleted in oxalate-induced cells and positively interacted with TRPV5. UMOD silencing reversed the effect of TRPV overexpression on oxalate-induced cells. miR-103a-3p targeted UMOD and was mediated in the regulation of the UMOD/TRPV5 axis in oxalate-induced cells. Downregulating miR-103a-3p mitigated EG-induced CaOx deposition in kidney tissues in vivo by activating the UMOD/TRPV5 axis. miR-103a-3p silencing ameliorated CaOx deposition in the rat kidney by activating the UMOD/TRPV5 axis.

Calcium sensitive receptor and claudin-14 expression in kidney tissues of two kidney stone models

INTODUCTION

The differences in protein expression of calcium sensitive receptor (CaSR) and claudin-14 in a kidney stone model established by nanobacteria (NB) and ethylene glycol (EG) were compared.

MATERIAL AND METHODS

Ninety Wistar male rats were randomly divided into the NB group, the EG group, and the blank control group (NC group), with 30 rats in each group. Three rats of each group were sacrificed every week after injection. Histopathology was used to evaluate the stone formation of each group. The expression of CaSR and claudin-14 protein was detected by immunohistochemistry every week.

RESULTS

There was formation of bright crystals in the kidneys of the EG group and the NB group, but not the NC group. At the 3rd week, the expression of CaSR and claudin-14 in the kidney tissue of the EG group began to increase while that in the NB group increased at the 4^th week. The expression of CaSR and claudin-14 protein in the EG group was stronger than that in the NB group. Meanwhile, CaSR was expressed in the NC group but did not change significantly. Claudin-14 was not expressed in the NC group.

CONCLUSIONS

Our results indicate that the traditional EG kidney stone modeling method is more rapid than the NB kidney stone modeling method, with a high stone formation rate, and the CaSR and claudin-14 protein expression levels are higher. Meanwhile, the NB used to establish the kidney stone model was isolated from patients with kidney stones, which may imitate the process of natural formation of kidney stones of patients. Therefore, the results of our research are more conducive to related research on the etiology of stones.

Cinacalcet may suppress kidney enlargement in hemodialysis patients with autosomal dominant polycystic kidney disease

A massively enlarged kidney can impact quality of life of autosomal dominant polycystic kidney disease (ADPKD) patients. A recent in vitro study demonstrated that an allosteric modulator of the calcium sensing receptor decreases adenosine-3′,5′-cyclic monophosphate, an important factor for kidney enlargement in ADPKD. Therefore, the present study was performed to determine whether cinacalcet, a calcium sensing receptor agonist, suppresses kidney enlargement in hemodialysis patients with ADPKD. Alteration of total kidney volume together with clinical parameters was retrospectively examined in 12 hemodialysis patients with ADPKD treated at a single institution in Japan. In the non-cinacalcet group with longer hemodialysis duration (n = 5), total kidney volume had an annual increase of 4.19 ± 1.71% during an overall period of 877 ± 494 days. In contrast, the annual rate of increase in total kidney volume in the cinacalcet group (n = 7) was significantly suppressed after cinacalcet treatment, from 3.26 ± 2.87% during a period of 734 ± 352 days before the start of cinacalcet to − 4.71 ± 6.42% during 918 ± 524 days after initiation of treatment (p = 0.047). The present findings showed that cinacalcet could be a novel therapeutic tool for suppression of kidney enlargement in hemodialysis patients with ADPKD.

Calcium Transport in the Kidney and Disease Processes

Calcium is a key ion involved in cardiac and skeletal muscle contractility, nerve function, and skeletal structure. Global calcium balance is affected by parathyroid hormone and vitamin D, and calcium is shuttled between the extracellular space and the bone matrix compartment dynamically. The kidney plays an important role in whole-body calcium balance. Abnormalities in the kidney transport proteins alter the renal excretion of calcium. Various hormonal and regulatory pathways have evolved that regulate the renal handling of calcium to maintain the serum calcium within defined limits despite dynamic changes in dietary calcium intake. Dysregulation of renal calcium transport can occur pharmacologically, hormonally, and via genetic mutations in key proteins in various nephron segments resulting in several disease processes. This review focuses on the regulation transport of calcium in the nephron. Genetic diseases affecting the renal handling of calcium that can potentially lead to changes in the serum calcium concentration are reviewed.

Vitamin D and Kidney Stones

This review explores the relationship between vitamin D supplementation and lithogenesis. A causal relationship has been assumed despite myriad studies demonstrating that therapeutic doses of vitamin D do not increase lithogenic risk. Select stone formers may be at increased risk for recurrence with vitamin D supplementation, possibly from CYP24A1 gene mutations. Additionally, the evidence for who is vitamin D deficient, and the benefits of supplementation in those not at risk for rickets, is sparse. Concerns may be avoidable as vitamin D screening appears unnecessary in most patients, and superior pharmacology is available which increases bone density, while decreasing stone formation.

Association between calcium-sensing receptor (CaSR) R990G, CaSR A986S, and CaSR Q1011E gene polymorphisms and the risk of urolithiasis: a meta-analysis

Backgrounds

In the last two decades, studies have been widely carried out to assess the association between single-nucleotide polymorphisms (SNPs) of calcium-sensing receptor (CaSR) gene in exon 7 and the risk of urolithiasis. However, inconsistency across the studies was reported. Therefore, our current study aimed to perform a meta-analysis concerning the association between the risk of urolithiasis and the gene polymorphisms of CaSR R990G, CaSR A986S, and CaSR Q1011E.

Methods

Published papers from PubMed, Embase, Cohcrane, and Web of science were included for the study, and they were analyzed using fixed or random effect model.

Results

A total of 11 papers consisting of eight papers evaluating CaSR R990G, nine papers evaluating CaSR A986S, and five papers evaluating CaSR Q1011E were included in our analysis. Our pooled calculation found that protective effect against urolithiasis was observed in R allele and RR genotype of CaSR R990G and A allele and AA genotype of CaSR A986S. Conversely, increased susceptibility to urolithiasis was found in G allele and RG genotype of CaSR R990G and S allele of CaSR A986S. Interestingly, our findings in sub-group analysis confirmed that the correlation between CaSR R990G and urolithiasis was found in Caucasian population. Meanwhile, in Asian population, the association was observed in CaSR A986S.

Conclusions

CaSR R990G and CaSR A986S, but not CaSR Q1011E, are associated with the risk of urolithiasis.

Impaired kidney structure and function in spinal muscular atrophy

Objective

To determine changes in serum profiles and kidney tissues from patients with spinal muscular atrophy (SMA) type 1 compared with age- and sex-matched controls.

Methods

In this cohort study, we investigated renal structure and function in infants and children with SMA type 1 in comparison with age- and sex-matched controls.

Results

Patients with SMA had alterations in serum creatinine, cystatin C, sodium, glucose, and calcium concentrations, granular casts and crystals in urine, and nephrocalcinosis and fibrosis. Nephrotoxicity and polycystic kidney disease PCR arrays revealed multiple differentially expressed genes, and immunoblot analysis showed decreased calcium-sensing receptors and calbindin and increased insulin-like growth factor-binding proteins in kidneys from patients with SMA.

Conclusions

These findings demonstrate that patients with SMA type 1, in the absence of disease-modifying therapies, frequently manifest impaired renal function as a primary or secondary consequence of their disease. This study provides new insights into systemic contributions to SMA disease pathogenesis and the need to identify coadjuvant therapies.

A Twin Study of Genetic Influences on Nephrolithiasis in Women and Men

BACKGROUND

Nephrolithiasis is a complex phenotype influenced by both genetic and environmental factors. Previously we found a genetic component to stone disease using a sample of male twin pairs. We now report on the genetic contribution to stones in a sample of female and male twin pairs.

METHODS

We conducted a classic twin study of kidney stones using the Washington State Twin Registry. Data were collected by questionnaire to obtain self-reported history of kidney stones. Univariate structural equation modeling was used to determine the relative contributions of additive genetics, common environment, and unique environment.

RESULTS

There were 7053 same-sex pairs with kidney stone data. The mean age of the sample was 39 years, similar in women and men. The prevalence of stones was 4.9% of women and 6.2% of men. We found significant contributions from genetics and the unique environment (P < 0.05 for both) for the risk for stone disease in women and men. There was no significant contribution of the common environment for either sex. After adjusting for age, heritability was 46% (95% confidence interval 0.36-0.56) in women and 57% (0.46-0.68) in men, which was significantly different (P < 0.05).

CONCLUSIONS

Nephrolithiasis in women has a heritable component less than that we again demonstrate in men. This finding may in part explain why more stone formers are men than women. Women twins demonstrated a greater effect of the unique environment on stone prevalence. The specific environmental risk factors that account for this effect are not currently known.

Calcium-sensing receptor (CaSR) modulates vacuolar H+-ATPase activity in a cell model of proximal tubule

BACKGROUND

The calcium-sensing receptor (CaSR) is localized in the apical membrane of proximal tubules in close proximity to the transporters responsible for proton secretion. Therefore, the aim of the present study was to analyze the effects of CaSR stimulation on the biochemical activity of the vacuolar H⁺-ATPase in a cellular model of proximal tubule cells, OKP cells.

METHODS

Biochemical activity of H⁺-ATPase was performed using cell homogenates, and the inorganic phosphate released was determined by a colorimetric method. Changes in cytosolic ionized calcium [Ca²⁺]_i were also determined using Fluo-4.

RESULTS

A significant increase of vacuolar H⁺-ATPase activity was observed when the CaSR was stimulated with agonists such as Gd³⁺ (300 µM) and neomycin (200 µM). This activity was also stimulated in a dose-dependent fashion by changes in extracellular Ca²⁺ (Ca²⁺_o) between 10^-4 and 2 mM. Gd³⁺ and neomycin produced a sustained rise of [Ca²⁺]_i, an effect that disappears when extracellular calcium was removed in the presence of 0.1 µM thapsigargin. Inhibition of phospholipase C (PLC) activity with U73122 (5 × 10^-8 M) reduced the increase in [Ca²⁺]_i induced by neomycin.

CONCLUSION

CaSR stimulation induces an increase in the vacuolar H⁺-ATPase activity of OKP cells, an effect that involves an increase in [Ca²⁺]_i and require phospholipase C activity. The consequent decrease in intratubular pH could lead to increase ionization of luminal calcium, potentially enhancing its reabsorption in distal tubule segments and reducing the formation of calcium phosphate stones.

Association between vitamin D receptor gene polymorphisms and idiopathic hypocitraturia in a Chinese Bai population

Idiopathic hypocitraturia (IH) is a risk factor for urolithiasis. IH is associated with vitamin D receptor (VDR) gene single nucleotide polymorphisms (SNPs) in a Chinese Han population. However, this association between VDR SNPs and IH has not been recapitulated in a Chinese Bai population. The aim of this study is to investigate the association between VDR SNPs and IH in a Chinese Bai population. A total of 320 participants comprising of 200 Chinese Bai patients with IH and 120 Chinese Bai control participants with normal urinary citrate level were enrolled for this study. The VDR SNPs rs7975232, rs2228570, rs731236 and rs1544410 were detected by Sanger sequencing, and the association between these SNPs and the presence of IH in the Chinese Bai population was analyzed. The prevalence of VDR SNPs rs7975232 allele A and rs2228570 genotype TT was significantly higher in patients than in controls (p < 0.0125, after Bonferroni correction). The haplotype TCGC was a protective factor in the Chinese Bai population who otherwise might suffer from IH, while the haplotype TTGA was a risk factor. VDR SNPs rs731236 and rs1544410 have a linkage disequilibrium value of 0.811. VDR SNPs rs7975232, rs2228570, and haplotypes TCGC, TTGA are associated with IH in a Chinese Bai population.

Activation of Calcium-Sensing Receptor increases intracellular calcium and decreases cAMP and mTOR in PKD1 deficient cells

Clinical and fundamental research suggest that altered calcium and cAMP signaling might be the most proximal events in ADPKD pathogenesis. Cells from ADPKD cysts have a reduced resting cytosolic calcium [Ca²⁺]_i and increased cAMP levels. CaSR plays an essential role in regulating calcium homeostasis. Its activation is associated with [Ca²⁺]_i increase and cAMP decrease, making CaSR a possible therapeutic target. Human conditionally immortalized Proximal Tubular Epithelial cells (ciPTEC) with stable knockdown of PKD1 (ciPTEC-PC1KD) and ciPTEC generated from an ADPKD1 patient (ciPTEC-PC1Pt) were used as experimental tools. CaSR functional expression was confirmed by studies showing that the calcimimetic NPS-R568 induced a significant increase in [Ca²⁺]_i in ciPTEC-PC1KD and ciPTEC-PC1Pt. Resting [Ca²⁺]_i were significantly lower in ciPTEC-PC1KD with respect to ciPTECwt, confirming calcium dysregulation. As in native cyst cells, significantly higher cAMP levels and mTOR activity were found in ciPTEC-PC1KD compared to ciPTECwt. Of note, NPS-R568 treatment significantly reduced intracellular cAMP and mTOR activity in ciPTEC-PC1KD and ciPTEC-PC1Pt. To conclude, we demonstrated that selective CaSR activation in human ciPTEC carrying PKD1 mutation increases [Ca²⁺]_i, reduces intracellular cAMP and mTOR activity, reversing the principal dysregulations considered the most proximal events in ADPKD pathogenesis, making CaSR a possible candidate as therapeutic target.

Epidemiology of stone disease across the world

Nephrolithiasis is a highly prevalent disease worldwide with rates ranging from 7 to 13% in North America, 5-9% in Europe, and 1-5% in Asia. Due to high rates of new and recurrent stones, management of stones is expensive and the disease has a high level of acute and chronic morbidity. The goal of this study is to review the epidemiology of stone disease in order to improve patient care. A review of the literature was conducted through a search on Pubmed^®, Medline^®, and Google Scholar^®. This review was presented and peer-reviewed at the 3rd International Consultation on Stone Disease during the 2014 Société Internationale d'Urologie Congress in Glasgow. It represents an update of the 2008 consensus document based on expert opinion of the most relevant studies. There has been a rising incidence in stone disease throughout the world with a narrowing of the gender gap. Increased stone prevalence has been attributed to population growth and increases in obesity and diabetes. General dietary recommendations of increased fluid, decreased salt, and moderate intake of protein have not changed. However, specific recommended values have either changed or are more frequently reported. Geography and environment influenced the likelihood of stone disease and more information is needed regarding stone disease in a large portion of the world including Asia and Africa. Randomized controlled studies are lacking but are necessary to improve recommendations regarding diet and fluid intake. Understanding the impact of associated conditions that are rapidly increasing will improve the prevention of stone disease.

Progress in Understanding the Genetics of Calcium-Containing Nephrolithiasis

Renal stone disease is a frequent condition, causing a huge burden on health care systems globally. Calcium-based calculi account for around 75% of renal stone disease and the incidence of these calculi is increasing, suggesting environmental and dietary factors are acting upon a preexisting genetic background. The familial nature and significant heritability of stone disease is known, and recent genetic studies have successfully identified genes that may be involved in renal stone formation. The detection of monogenic causes of renal stone disease has been made more feasible by the use of high-throughput sequencing technologies and has also facilitated the discovery of novel monogenic causes of stone disease. However, the majority of calcium stone formers remain of undetermined genotype. Genome-wide association studies and candidate gene studies implicate a series of genes involved in renal tubular handling of lithogenic substrates, such as calcium, oxalate, and phosphate, and of inhibitors of crystallization, such as citrate and magnesium. Additionally, expression profiling of renal tissues from stone formers provides a novel way to explore disease pathways. New animal models to explore these recently-identified mechanisms and therapeutic interventions are being tested, which hopefully will provide translational insights to stop the growing incidence of nephrolithiasis.

Associations of the calcium-sensing receptor gene CASR rs7652589 SNP with nephrolithiasis and secondary hyperparathyroidism in haemodialysis patients

Nephrolithiasis, secondary hyperparathyroidism (sHPT), and cardiovascular complications are associated with disturbances in Ca handling and contribute to morbidity/mortality during haemodialysis (HD). Calcimimetics, activators of the calcium-sensing receptor (CaSR), provide an effective means of reducing parathyroid hormone (PTH) secretion in sHPT. Polymorphism in CaSR gene (CASR) influences Ca-related parameters, however it was not shown in HD patients for CASR rs7652589. The minor allele at this polymorphism modifies the binding sites of transcription factors and CaSR expression. We hypothesized that CASR rs7652589 variants may also influence CaSR in end stage renal disease (ESRD). We aimed to determine the associations of rs7652589 with nephrolithiasis-related ESRD, Ca, P, ALP, PTH, response to treatment with cinacalcet, prevalence of coronary artery disease, and all-cause/cardiovascular mortality in HD patients (n = 1162). Healthy individuals (n = 918) were controls. This study shows that the A allele of rs7652589 is a risk allele for nephrolithiasis-related ESRD. The AA genotype is associated with more severe sHPT (higher Ca and PTH concentrations). The A allele is associated with reduced CaSR transcript level in peripheral blood mononuclear cells. According to computational analysis, potential binding sites for GLI3, AHR and TP53 are removed by the A allele, whereas binding sites for SOX18 and TP63 are created.

Polymorphisms of CASR gene increase the risk of primary hyperparathyroidism

OBJECTIVE

To evaluate correlations between polymorphisms of calcium-sensing receptor (CASR) gene [A986S (rs1081725), R990G (rs1042636) and Q1011E (rs1801726)] and the risk of primary hyperparathyroidism (PHPT) among human population.

METHODS

Relevant studies were retrieved from online databases using computer-based search strategies, which were then supplemented by manual search strategies. Case-control studies related to our topic were identified based on strict inclusion and exclusion criteria. Statistical analyses were conducted using the Comprehensive Meta-analysis 2.0 (Biostat Inc., Englewood, NJ, USA).

RESULTS

We retrieved 202 studies from online databases and other sources initially and eventually enrolled six studies into our meta-analysis. These six studies contained a sum of 693 PHPT patients and 1252 healthy controls. Our meta-analysis results showed that single nucleotide polymorphisms (SNPs) of CASR gene A986S (rs1081725) and R990G (rs1042636), but not Q1011E (rs1801726), may increase the risk of PHPT [A986S (rs1081725): allele model: P = 0.013; dominant model: P = 0.044; R990G (rs1042636): allele model: P = 0.023; dominant model: P = 0.026)]. Subgroup analyses based on ethnicity showed that among Asians, A986S (rs1081725) increased the PHPT risk (P = 0.04) under the allele model, but not under the dominant model. Among Caucasians, there was no association between gene frequencies and PHPT under both the allele and dominant model. In Asians, no significant association was observed between R990G (rs1042636) and PHPT risk, but in Caucasians, R990G (rs1042636) significantly increased the incidence of PHPT [R990G (rs1042636): allele model: P = 0.015; dominant model: P = 0.009)].

CONCLUSION

Our results indicate that SNPs of CASR gene A986S (rs1081725) and R990G (rs1042636) may increase the risk of PHPT, and the polymorphisms can potentially be used as important biological markers for early diagnosis of PHPT.

Common and rare variants associated with kidney stones and biochemical traits

Kidney stone disease is a complex disorder with a strong genetic component. We conducted a genome-wide association study of 28.3 million sequence variants detected through whole-genome sequencing of 2,636 Icelanders that were imputed into 5,419 kidney stone cases, including 2,172 cases with a history of recurrent kidney stones, and 279,870 controls. We identify sequence variants associating with kidney stones at ALPL (rs1256328[T], odds ratio (OR)=1.21, P=5.8 × 10⁻¹⁰) and a suggestive association at CASR (rs7627468[A], OR=1.16, P=2.0 × 10⁻⁸). Focusing our analysis on coding sequence variants in 63 genes with preferential kidney expression we identify two rare missense variants SLC34A1 p.Tyr489Cys (OR=2.38, P=2.8 × 10⁻⁵) and TRPV5 p.Leu530Arg (OR=3.62, P=4.1 × 10⁻⁵) associating with recurrent kidney stones. We also observe associations of the identified kidney stone variants with biochemical traits in a large population set, indicating potential biological mechanism.

Kidney stone formation is influenced by genetic factors and recurrent stone formation places a significant burden on health care systems. Here Oddsson et al. perform a large-scale genome-wide association study and uncover new genetic variants associated with kidney stone susceptibility and associated biochemical traits.

Conditionally immortalized human proximal tubular epithelial cells isolated from the urine of a healthy subject express functional calcium-sensing receptor

The calcium-sensing receptor (CaSR) is a G protein-coupled receptor, which plays an essential role in regulating Ca(2+) homeostasis. Here we show that conditionally immortalized proximal tubular epithelial cell line (ciPTEC) obtained by immortalizing and subcloning cells exfoliated in the urine of a healthy subject expresses functional endogenous CaSR. Immunolocalization studies of polarized ciPTEC revealed the apical localization of the receptor. By Western blotting of ciPTEC lysates, both monomeric and dimeric forms of CaSR at 130 and ∼250 kDa, respectively, were detected. Functional studies indicated that both external calcium and the positive CaSR allosteric modulator, NPS-R568, induced a significant increase in cytosolic calcium, proving a high sensitivity of the endogenous receptor to its agonists. Calcium depletion from the endoplasmic reticulum using cyclopiazonic acid abolished the increase in cytosolic calcium elicited by NPS-R568, confirming calcium exit from intracellular stores. Activation of CaSR by NPS-R significantly reduced the increase in cAMP elicited by forskolin (FK), a direct activator of adenylate cyclase, further confirming the functional expression of the receptor in this cell line. CaSR expressed in ciPTEC was found to interact with Gq as a downstream effector, which in turn can cause release of calcium from intracellular stores via phospholipase C activation. We conclude that human proximal tubular ciPTEC express functional CaSR and respond to its activation with a release of calcium from intracellular stores. These cell lines represent a valuable tool for research into the disorder associated with gain or loss of function of the CaSR by producing cell lines from patients.

The G allele of CaSR R990G polymorphism increases susceptibility to urolithiasis and hypercalciuria: evidences from a comprehensive meta-analysis

Background. The calcium-sensing receptor gene (CaSR) is a candidate to explain urolithiasis. A number of case-control studies were conducted to investigate associations between CaSR polymorphisms with risks of hypercalciuria and urolithiasis in humans. But the results were still inconsistent. Methods. A meta-analysis was performed to address this issue. Crude odds ratios (ORs) with 95% confidence intervals (CIs) were calculated to estimate the strength of associations between CaSR polymorphisms and the risk of urolithiasis. The pooled standardized mean difference (SMD) with 95% CI was used for the meta-analysis of CaSR polymorphisms and urine calcium concentration. Results. For urolithiasis association, the SS genotype of A986S polymorphism was a risk factor for urolithiasis in Asians and PHPT patients, but a protective factor in Caucasians. The GG genotype of R990 polymorphism was associated with an increased risk of urolithiasis, especially in Caucasians and healthy population. Regarding urine calcium concentration association, individuals with the G allele had a higher level of urine calcium than the noncarriers. Conclusions. This meta-analysis revealed that the G allele of CaSR R990G polymorphism increases susceptibility to urolithiasis and hypercalciuria. The A986S and Q1011E polymorphisms were associated with urolithiasis and hypercalciuria in specific populations.

Calcium-sensing receptor gene polymorphisms in patients with calcium urolithiasis: a systematic review

BACKGROUND

Calcium-sensing receptor gene (CaSR) might be a strong component of the complex genetic background regulating calcium excretion and stone formation in kidney. The polymorphisms in different parts of the gene could be associated with calcium stone formation.

OBJECTIVE

The individual studies indicate a correlation between CaSR gene polymorphisms and urolithiasis but not sufficient to draw a precise result. We aimed to search literature to come to a reliable conclusion through a systematic review.

MATERIALS AND METHODS

We have serached individiual studies regarding the issue and high quality reviews. We assessed all the studies to draw a conclusion.

CONCLUSION

The genetic background of the neprolithiasis is an interesting issue deserving to be disscussed on. Regading genes of which, CaSR gene polymorphisms is the leading one, are studied in many individual studies but they are not sufficient to have a precise conclusion. Well-oriented and documented, phenotypically homogenous large cohort studies are needed for further evaluation.

Stimulation of calcium-sensing receptor increases biochemical H⁺-ATPase activity in mouse cortex and outer medullary regions

The aim of this project was to investigate the interaction between the calcium-sensing receptor (CaSR) and proton extrusion by the V-ATPase and gastric-like isoform of the H(+)/K(+)-ATPase in the mouse nephron. Biochemical activity of H(+)- ATPases was analysed using a partially purified membrane fraction of mouse cortex and outer medullary region. The V-ATPase activity (sensitive to 10(-7) mol·L(-1) bafilomycin) from the cortical and outer medullary region was significantly stimulated by increasing the [Formula: see text] (outside Ca(2+)), in a dose-dependent pattern. Gastric H(+)/K(+)-ATPase activity (sensitive to 10(-5) mol·L(-1) Schering 28080) was also sensitive to changes in [Formula: see text] levels. A significant increase in V-ATPase activity was also observed when CaSR was stimulated with agonists such as 300 μmol·L(-1) Gd(3+) and 200 μmol·L(-1) neomycin, both in the cortex and outer medulla. The cortical and outer medullary gastric H(+)/K(+)-ATPase activity was also stimulated by Gd(3+) and neomycin. Finally, cortical V-ATPase activity was significantly stimulated by 10(-9) mol·L(-1) angiotensin II, and the stimulation of CaSR in the presence of angiotensin significantly enhanced this effect, suggesting that an interaction in the intracellular signaling pathways is involved. In summary, CaSR stimulation enhances the biochemical activity of V-ATPase and gastric H(+)/K(+)-ATPase in both the cortical and outer medullary region of mouse kidney.

Catechin prevents the calcium oxalate monohydrate induced renal calcium crystallization in NRK-52E cells and the ethylene glycol induced renal stone formation in rat

BACKGROUND

Reactive oxygen species play important roles in renal calcium crystallization. In this study, we examined the effects of catechin, which have been shown to have antioxidant properties on the renal calcium crystallization.

METHODS

In the vitro experiment, the changes of the mitochondrial membrane potential, expression of superoxide dismutase (SOD), 4-hydroxynonenal (4-HNE), cytochrome c, and cleaved caspase 3 were measured to show the effects of catechin treatment on the NRK-52E cells induced by calcium oxalate monohydrate (COM). In the vivo study, Sprague-Dawley rats were administered 1% ethylene glycol (EG) to generate a rat kidney stone model and then treated with catechin (2.5 and 10 mg/kg/day) for 14 days. The urine and serum variables were dected on 7 and 14 days after EG administration. The expression of cytochrome c, cleaved caspase 3, SOD, osteopontin (OPN), malondialdehyde (MDA), 8-hydroxy-2'-deoxyguanosine (8-OHdG) in kidney were measured. Furthermore, the mitochondrial microstructure in the kidney was also examined by transmission electron microscopy.

RESULTS

Catechin treatment could prevent the changes in mitochondrial membrane potential and expression of SOD, 4-HNE, cytochrome c, and cleaved caspase 3 in NRK-52E cells induced by the COM. For the in vivo experiments, the EG administration induced renal calcium crystallization was also prevented by the catechin. The expression of SOD, OPN, MDA, OPN and 8-OHdG, were increased after EG administration and this increase was diminished by catechin. Moreover, catechin also prevented EG induced mitochondrial collapse in rat.

CONCLUSIONS

Catechin has preventive effects on renal calcium crystallization both in vivo and in vitro, and provide a potential therapeutic treatment for this disease.

Minireview: the intimate link between calcium sensing receptor trafficking and signaling: implications for disorders of calcium homeostasis

The calcium-sensing receptor (CaSR) regulates organismal Ca(2+) homeostasis. Dysregulation of CaSR expression or mutations in the CASR gene cause disorders of Ca(2+) homeostasis and contribute to the progression or severity of cancers and cardiovascular disease. This brief review highlights recent findings that define the CaSR life cycle, which controls the cellular abundance of CaSR and CaSR signaling. A novel mechanism, termed agonist-driven insertional signaling (ADIS), contributes to the unique hallmarks of CaSR signaling, including the high degree of cooperativity and the lack of functional desensitization. Agonist-mediated activation of plasma membrane-localized CaSR increases the rate of insertion of CaSR at the plasma membrane without altering the constitutive endocytosis rate, thereby acutely increasing the maximum signaling response. Prolonged CaSR signaling requires a large intracellular ADIS-mobilizable pool of CaSR, which is maintained by signaling-mediated increases in biosynthesis. This model provides a rational framework for characterizing the defects caused by CaSR mutations and the altered functional expression of wild-type CaSR in disease states. Mechanistic dissection of ADIS of CaSR should lead to optimized pharmacological approaches to normalize CaSR signaling in disorders of Ca(2+) homeostasis.

A woman with recurrent calcium phosphate kidney stones

Kidney stones composed predominantly (50% or more) of calcium phosphate constitute up to 10% of all stones and 15%-20% of calcium stones, 80% of which are composed of calcium oxalate. Calcium phosphate is a minor component of up to 30% of calcium oxalate stones as well. The cause of calcium phosphate stones is often obscure but most often related to a high urine pH. Some patients with calcium phosphate stones may have incomplete renal tubular acidosis. Others have distal renal tubular acidosis characterized by hyperchloremic acidosis, hypocitraturia, and high urine pH. The use of carbonic anhydrase inhibitors such as acetazolamide, topiramate, and zonisamide leads to a similar picture. Treatment options to specifically prevent calcium phosphate stone recurrence have not been tested in clinical trials. Increases in urine volume and restriction of sodium intake to limit calcium excretion are important. Citrate supplementation is probably effective, although the concomitant increase in urine pH may increase calcium phosphate supersaturation and partially offset the inhibition of crystallization resulting from the increased urine citrate excretion and the alkali-associated reduction in urine calcium excretion. Thiazides lower urine calcium excretion and may help ensure the safety of citrate supplementation.