Allelic variants of human calcitonin receptor: distribution and association with bone mass in postmenopausal Italian women

Characterization of signalling and regulation of common calcitonin receptor splice variants and polymorphisms

The calcitonin receptor (CTR) is a class B G protein-coupled receptor that is a therapeutic target for the treatment of hypercalcaemia of malignancy, Paget's disease and osteoporosis. In primates, the CTR is subject to alternative splicing, with a unique, primate-specific splice variant being preferentially expressed in reproductive organs, lung and kidney. In addition, humans possess a common non-synonymous single-nucleotide polymorphism (SNP) encoding a proline/leucine substitution in the C-terminal tail. In low power studies, the leucine polymorphism has been associated with increased risk of osteoporosis in East Asian populations and, independently, with increased risk of kidney stone disease in a central Asian population. The CTR is pleiotropically coupled, though the relative physiological importance of these pathways is poorly understood. Using both COS-7 and HEK293 cells recombinantly expressing human CTR, we have characterized both splice variant and polymorphism dependent response to CTs from several species in key signalling pathways and competition binding assays. These data indicate that the naturally occurring changes to the intracellular face of CTR alter ligand affinity and signalling, in a pathway and agonist dependent manner. These results further support the potential for these primate-specific CTR variants to engender different physiological responses. In addition, we report that the CTR exhibits constitutive internalization, independent of splice variant and polymorphism and this profile is unaltered by peptide binding.

Association between calcitonin receptor AluI gene polymorphism and bone mineral density: A meta-analysis

The association between calcitonin receptor (CTR) AluI gene polymorphism and bone mineral density (BMD) remains unclear. In order to elucidate this association, a meta-analysis was performed to provide a comprehensive assessment of the studies carried out to date. PubMed, the Cochrane Library, Web of Science and the China National Knowledge Infrastructure database were searched to identify eligible studies. The data were extracted independently by two authors using a standard form, the studies were meta-analyzed and disagreements were resolved through discussion. Fifteen eligible studies involving 3,093 females and 654 males were included for analysis. Overall, the male subjects with the CC genotype had non-statistically different lumbar spine and femoral neck BMD compared to subjects with the CT/TT and CT genotypes. The BMD of female subjects with the CC genotype was similar to that of patients with the CT or CT/TT genotypes. In Chinese male subjects, those with the CC genotype had almost the same BMD as those with the CT and CT/TT genotypes. The results also demonstrated that Chinese female subjects with the CC genotype had similar BMD at the lumbar spine and femoral neck to subjects with the CT and CT/TT genotypes. Furthermore, Southern Chinese subjects with CC genotypes did not have a different BMD at the lumbar spine and femoral neck compared to patients with CT and CT/TT genotypes. Notably, Northern Chinese subjects with the CC genotype had a higher BMD at the lumbar spine compared to subjects with CT/TT genotypes and a lower BMD at the femoral neck compared to subjects with CT/TT genotypes. Among Northern Chinese females, those with CC genotypes also had a higher BMD at the lumbar spine compared to those with CT/TT genotypes, while no difference was observed in the BMD of the lumbar spine and femoral neck between patients with CC and CT genotypes. In Southern Chinese females, no significant difference was found in the BMD at the lumbar spine and femoral neck between those with CC and those with CT or CT/TT genotypes. In conclusion, the AluI gene polymorphism may have an association with BMD in Northern Chinese subjects and the CC genotype may have a protective effect on spine BMD; however, the CC genotype may be a risk factor for low femoral neck BMD in Northern Chinese subjects. Further studies are required to fully investigate the potential association between AluI gene polymorphism and BMD.

Calcitonin receptor gene polymorphism in cCinese Xinjiang Han and Uygur women with primary osteoporosis

CONTEXT

Osteoporosis is a systemic disease with a strong genetic component. Calcitonin receptors (CTR) are involved in maintaining calcium homeostasis. There is no consensus whether CTR gene polymorphism plays a role in affecting pathogenesis of osteoporosis.

OBJECTIVE

The objective of this study was to investigate genetic susceptibility of calcitonin receptor gene polymorphism (genotypes and allele frequencies) to primary osteoporosis between Han and Uygur patients and healthy controls in the Chinese Xinjiang region.

DESIGN

This was a cross-sectional study conducted in an academic hospital.

SUBJECTS

Between 2010 and 2012 a total of 404 female patients with primary osteoporosis (200 Han and 204 Uygur) and 316 healthy control subjects (160 Han and 156 Uygur) were recruited to determine the distribution of C/T single nucleotide polymorphism of the CTR gene. PCR-restriction fragment length polymorphism was used at the 1377-bp site.

RESULTS

The frequency of polymorphic C/T alleles of the calcitonin receptor gene in each group fit the Hardy-Weinberg equilibrium model. There was no statistically significant difference in genotypes (P = 0.922) or allele frequency (P = 0.654) between the Xinjiang Han postmenopausal osteoporosis patients and the controls. Similarly, there was no difference in genotypes (P = 0.897) or allele frequency (P = 0.825) between Xinjiang Uygur postmenopausal osteoporosis patients and the controls. Moreover, there was no significant difference (P = 0.86) between the combination of both ethnic groups and controls. In contrast, compared to these two ethnic groups, Han CC type accounted for 67.8%, CT 30.0%, and TT 2.2%, whereas Uighur CC type accounted for 55.6%, CT 33.3%, and TT 11.2%, which is statistically significant between Han and Uygur CTR genotypes (P = 0.006). Allele frequency of C accounted for 82.8% and T for 17.2% in Han, whereas C accounted for 72.2% and T for 27.8% in Uygur (P = 0.001).

CONCLUSION

There was no statistically significant difference in CTR gene nucleotide sequence polymorphisms at 1377-bp between Chinese Xinjiang Han and Uygur patients with primary osteoporosis, suggesting that this CTR gene polymorphism may not affect incidence of osteoporosis. However, there was a significant difference in CTR gene nucleotide sequence polymorphism at the 1377-bp site between Chinese Xinjiang Han and Uygur, but the importance of this difference needs further study.

Genetic and environmental factors affecting peak bone mass in premenopausal Japanese women

The purpose of this study was to examine the relationships between peak bone mass and genetic and environmental factors. We measured whole-body bone mineral density (BMD), lumbar spine BMD, and radius BMD with dual-energy X-ray absorptiometry (DXA) and analyzed eight genetic factors: vitamin D receptor (VDR)-3', VDR-5', estrogen receptor (ER), calcitonin receptor (CTR), parathyroid hormone (PTH), osteocalcin (OC), apolipoprotein E (ApoE), and fatty acid binding protein 2 (FABP2) allelic polymorphisms using polymerase chain reaction-restriction fragment length polymorphisms (PCR-RFLPs). We also surveyed menstrual history, food intake, and history of physical activity using questionnaires.After adjusting for age, body mass index (BMI), current smoking status, current Ca intake, alcohol intake, menoxenia, and physical activity, the mean BMD in subjects with the HH/Hh genotype was significantly higher than that of subjects with the hh genotype for whole-body BMD (mean±SD, 1.20±0.10 vs. 1.18±0.09 g/cm(2); HH/Hh vs. hh, p=0.04) and at lumbar spine BMD (mean±SD, 1.18±0.14 vs. 1.14±0.12 g/cm(2); HH/Hh vs. hh, p=0.02) in OC allelic polymorphism. Furthermore, the results of multiple regression analyses taking the 8 genetic factors plus the 7 environmental factors listed above into account showed that the strongest factor contributing to BMD was BMI at any site (whole-body and lumbar BMD p<0.0001, radius BMD p=0.0029). In addition, OC polymorphism (p=0.0099), physical activity (p=0.0245), menoxenia (p=0.0384), and PTH polymorphism (p=0.0425) were independent determinants for whole-body BMD, and OC polymorphism (p=0.0137) and physical activity (p=0.0421) were independent determinants for lumbar BMD and radius BMD, respectively.

Identification of the calcitonin receptor in osteoarthritic chondrocytes

Background

Preclinical and clinical studies have shown that salmon calcitonin has cartilage protective effects in joint degenerative diseases, such as osteoarthritis (OA). However, the presence of the calcitonin receptor (CTR) in articular cartilage chondrocytes is yet to be identified. In this study, we sought to further investigate the expression of the CTR in naïve human OA articular chondrocytes to gain further confirmation of the existents of the CTR in articular cartilage.

Methods

Total RNA was purified from primary chondrocytes from articular cartilage biopsies from four OA patients undergoing total knee replacement. High quality cDNA was produced using a dedicated reverse transcription polymerase chain reaction (RT-PCR) protocol. From this a nested PCR assay amplifying the full coding region of the CTR mRNA was completed. Western blotting and immunohistochemistry were used to characterize CTR protein on protein level in chondrocytes.

Results

The full coding transcript of the CTR isoform 2 was identified in all four individuals. DNA sequencing revealed a number of allelic variants of the gene including two potentially novel polymorphisms: a frame shift mutation, +473del, producing a shorter form of the receptor protein, and a single nucleotide polymorphism in the 3' non coding region of the transcript, +1443 C>T. A 53 kDa protein band, consistent with non-glycosylated CTR isoform 2, was detected in chondrocytes with a similar size to that expressed in osteoclasts. Moreover the CTR was identified in the plasma membrane and the chondrocyte lacuna of both primary chondrocytes and OA cartilage section.

Conclusions

Human OA articular cartilage chondrocytes do indeed express the CTR, which makes the articular a pharmacological target of salmon calcitonin. In addition, the results support previous findings suggesting that calcitonin has a direct anabolic effect on articular cartilage.

Genetic predisposition for femoral neck stress fractures in military conscripts

BACKGROUND

Stress fractures are a significant problem among athletes and soldiers and may result in devastating complications or even permanent handicap. Genetic factors may increase the risk, but no major susceptibility genes have been identified. The purpose of this study was to search for possible genetic factors predisposing military conscripts to femoral neck stress fractures.

RESULTS

Eight genes involved in bone metabolism or pathology (COL1A1, COL1A2, OPG, ESR1, VDR, CTR, LRP5, IL-6) were examined in 72 military conscripts with a femoral neck stress fracture and 120 controls. The risk of femoral neck stress fracture was significantly higher in subjects with low weight and body mass index (BMI). An interaction between the CTR (rs1801197) minor allele C and the VDR C-A haplotype was observed, and subjects lacking the C allele in CTR and/or the C-A haplotype in VDR had a 3-fold higher risk of stress fracture than subjects carrying both (OR = 3.22, 95% CI 1.38-7.49, p = 0.007). In addition, the LRP5 haplotype A-G-G-C alone and in combination with the VDR haplotype C-A was associated with stress fractures through reduced body weight and BMI.

CONCLUSIONS

Our findings suggest that genetic factors play a role in the development of stress fractures in individuals subjected to heavy exercise and mechanical loading. The present results can be applied to the design of future studies that will further elucidate the genetics of stress fractures.

Genetic determinants of osteoporosis: common bases to cardiovascular diseases?

Osteoporosis is the most common and serious age-related skeletal disorder, characterized by a low bone mass and bone microarchitectural deterioration, with a consequent increase in bone fragility and susceptibility to spontaneous fractures, and it represents a major worldwide health care problem with important implications for health care costs, morbidity and mortality. Today is well accepted that osteoporosis is a multifactorial disorder caused by the interaction between environment and genes that singularly exert modest effects on bone mass and other aspects of bone strength and fracture risk. The individuation of genetic factors responsible for osteoporosis predisposition and development is fundamental for the disease prevention and for the setting of novel therapies, before fracture occurrence. In the last decades the interest of the Scientific Community has been concentrated in the understanding the genetic bases of this disease but with controversial and/or inconclusive results. This review tries to summarize data on the most representative osteoporosis candidate genes. Moreover, since recently osteoporosis and cardiovascular diseases have shown to share common physiopathological mechanisms, this review also provides information on the current understanding of osteoporosis and cardiovascular diseases common genetic bases.

Single nucleotide polymorphisms in the P2X7 gene are associated to fracture risk and to effect of estrogen treatment

OBJECTIVES

The purinergic P2RX7 receptor (P2RX7) has been shown to play a role in the regulation of osteoblast and osteoclast activity. The aim of this study was to determine the presence of polymorphisms in exon 13 of the P2X7 gene and the association with osteoclast apoptosis in vitro and bone status in vivo.

METHODS

A total of 1764 postmenopausal women were genotyped for three single nucleotide polymorphisms detected after sequencing of exon 13 of P2X7. Bone markers, bone mineral density of the hip and lumbar spine were determined at baseline and after 10 years, and vertebral fracture incidence after 10 years. In-vitro ATP-induced caspase-1 determinations were performed on osteoclasts from the different genotypes.

RESULTS

Three polymorphisms were detected (Gln460Arg, Glu496Ala, and Ile568Asn). None of the polymorphisms was related to bone mineral density or changes in bone mineral density over 10 years in hormone replacement therapy naïve women. The Ile568Asn polymorphism was however, associated with effect of hormone replacement therapy. Furthermore, the 10-year fracture incidence was significantly associated with both the Glu496Ala and the Ile568Asn. The Glu496Ala polymorphism was closely related to ATP-induced osteoclast apoptosis in vitro, as osteoclasts from individuals homozygous for the C allele had significantly decreased apoptotic activity.

CONCLUSION

The P2X7 Glu496Ala and the Ile568Asn single nucleotide polymorphisms are associated with 10-year fracture risk in postmenopausal women and response to hormone replacement therapy treatment. Further, the Glu496Ala polymorphism is strongly influencing osteoclast apoptosis in vitro, which could contribute to increased fracture risk.

Leptin receptor genotype at Gln223Arg is associated with body composition, BMD, and vertebral fracture in postmenopausal Danish women

Leptin is emerging as a key regulator of bone remodeling. In a population-based study of 1306 postmenopausal Danish women, nonsynonymous LEPR SNPs were associated with risk of adiposity, BMD, and vertebral fracture. Smoking exacerbates this LEPR-associated fracture risk.

INTRODUCTION

Nonsynonymous single nucleotide polymorphisms (SNPs) in the human LEPR gene have been associated with adiposity in a number of studies, but there have been no large-scale studies of their implications for BMD and osteoporotic fracture risk in postmenopausal women.

MATERIALS AND METHODS

We carried out a population-based study of 1430 women. Three well-known nonsynonymous leptin receptor (LEPR) SNPs (Lys109Arg, Gln223Arg, and Lys656Asn) were genotyped for qualitative and quantitative association analysis. Phenotype characteristics of main interest were DXA measures of body fat and lean tissue mass, BMD, and radiographic vertebral fractures.

RESULTS

Gln223Arg associated with risk of vertebral fracture (overall OR = 1.76; OR in smokers = 2.31; p = 0.0004), in addition to BMD of the femoral neck and total hip (p = 0.036 and 0.008, respectively). Heterozygote carriers showed lower BMD at both sites. Gln223Arg was also associated with adiposity (p = 0.001 for total fat mass). For adiposity, the at-risk allele was G (resulting in an arginine at position 223).

CONCLUSIONS

Variation in LEPR seemed to contribute to the variation in BMD and fracture risk in Danish postmenopausal women; the heterozygous genotype was associated with increased risk of manifest osteoporosis. Further studies are needed to replicate these data and to clarify the mechanisms involved.

Association between an AluI polymorphism in the calcitonin receptor gene and quantitative ultrasound parameters in Korean men

OBJECTIVE

The purpose of this study was to investigate the association between an AluI RFLP of the calcitonin receptor (CTR) gene and quantitative ultrasound (QUS) parameters in Korean men, and the interaction with nutrition as a lifestyle factor.

MATERIALS AND METHODS

Broadband ultrasound attenuation, speed of sound and stiffness index of the calcaneus were measured using an ultrasound bone densitometer in 201 Korean men (mean age +/- SD: 51.6 +/- 11.7 years). The PCR-RFLP method was used to analyze an AluI polymorphism in the CTR gene.

RESULTS

In all subjects, the distribution of CC, CT and TT genotypes occurred with frequencies of 87.1, 12.4 and 0.5%, respectively. When stratified by omnivore and vegetarian groups, there was a significant association between an AluI polymorphism in the CTR gene and QUS parameters such as speed of sound and stiffness index in only vegetarian subjects.

CONCLUSION

Our data suggest that the AluI polymorphism of the CTR gene can be useful as a genetic marker in the interindividual susceptibility of QUS parameters by the interaction with nutritional status as a lifestyle factor.

Association of vitamin-D and calcitonin receptor gene polymorphism in paediatric nephrolithiasis

We investigated the role of vitamin-D receptor gene (VDR) and calcitonin receptor (CTR) gene polymorphism in childhood nephrolithiasis in the north Indian population. A control group of 60 healthy paediatric individuals (age range 4-16 years) and 50 paediatric patients (age range 2-14 years) with kidney stones were examined. Polymorphism in both genes (VDR and CTR) was detected by using PCR-based restriction analysis. There was a statistically significant difference between the two groups for the genotypes of the VDR gene Fok-I polymorphism (P =0.007) and the CTR gene (P =0.048) polymorphism. The odds ratio (95% Confidence Interval) for the C allele in those at risk of stone disease was 1.83 (0.82-4.09) in VDR gene polymorphism and 1.99 (0.90-4.39) in the case of CTR gene polymorphism. Our results suggest that the effects of VDR (Fok-I) and CTR gene polymorphism contribute to the understanding of the pathogenesis of urinary calculi. It is also suggestive of a potential candidate gene in the search for genetic causes of paediatric calcium oxalate nephrolithiasis.

Postmenopausal serum androstenedione levels are associated with the calcitonin receptor gene polymorphism T1377c. A pilot study

We tested the hypothesis that homeostasis of sex-steroids is related to the calcitonin receptor (CALCR) genotype. To determine the CALCR genotype PCR amplification followed by digestion with Alul restriction enzyme were carried out according to Nakamura et al. Indeed, a single nucleotide difference at position 1377 of cDNA generates two alleles (CC genotype or TT genotype). Serum estradiol, testosterone and their precursors androstendione (AD) and DHEA levels were estimated in a cohort of 113 postmenopausal women. While serum DHEA levels did not differ between the individual allele combinations, AD levels as well as AD/DHEA ratio were higher in carriers of TC and CC genotypes than those with TT genotype (p<0.05 and p<0.02, respectively, ANCOVA). We postulate that the 3beta-hydroxysteroid dehydrogenase activity is associated with C allele at least in C19 steroids. The data correspond with the functionality of CALCR.

In vitro characterization of a human calcitonin receptor gene polymorphism

Calcitonin is a 32 amino acid peptide hormone that inhibits bone resorption by stimulating calcitonin receptors (CTR) located on the surfaces of osteoclasts. A polymorphism at nucleotide 1340 of the human calcitonin receptor gene (CALCR) lies within the coding region and has the potential to change the amino acid at codon 447 from leucine to proline. In the present study, we scanned the coding region, portions of the 5'-flanking and 3'-flanking sequences, and the intron-exon boundaries of the human CALCR gene for additional polymorphisms, and determined the frequency of the codon 447 polymorphism in several ethnic groups. Because a leucine to proline change has the potential for significant structural alteration, receptor genes encoding either leucine or proline at residue 447 were transiently expressed in COS-7 cells to determine the binding and functional consequences of this polymorphism. Our complete polymorphism scan of the CALCR gene identified 11 polymorphic sites in the gene and confirmed the presence of the previously identified nucleotide T1340C (codon 447) polymorphism. Ten of the 11 polymorphisms were single nucleotide polymorphisms (SNPs). For the codon 447 polymorphism, the prevalence of the TT genotype (leucine) was 59% in Caucasians, 27% in African-Americans, 0% in Asians, and 20% in Hispanics. The presence of this SNP appears to have no statistically significant difference with the receptor's ability to bind calcitonin or signal when activated with the hormone.

Candidate genes for osteoporosis. Therapeutic implications

Osteoporosis, which afflicts 10 million Americans, is a complex disease characterized by decreased bone mass, microarchitectural deterioration of bone tissue, and an increase in fracture risk. Family and twin studies have established a genetic contribution to the etiology of osteoporosis. The biological candidate genes of osteoporosis can be ordered into 5 categories: (i) calcium homeostasis; (ii) hormonal dysfunction; (iii) osteoblast and osteoclast development and regulation; (vi) cartilage matrix metabolism; and (v) lipoprotein metabolism. In addition, genome-wide scans have identified a number of chromosomal regions harboring genes that influence bone mineral density. Moreover, the drug responses to various treatments of osteoporosis are reported to be modulated by DNA polymorphisms of the vitamin D receptor gene, the estrogen receptor 1 gene, and the transforming growth factor beta 1 gene. With the rapid advancement of the Human Genome Project and biotechnology, it will be possible to carry out parallel analyses of large numbers of candidate genes for osteoporosis and to calculate a patient's individual fracture risk in the context of specific environmental influences. This will eventually lead to more advanced diagnostic methods and more efficacious drugs targeting osteoporosis.

Mouse models of abnormal skeletal development and homeostasis

Studies of a number of mouse mutations with skeletal defects have contributed significantly to the understanding of bone development and homeostasis. In many cases, such mutants are also genetic models of disorders in humans, characterized by reduced bone mass (osteoporosis), increased bone mass (osteopetrosis), or abnormalities in endochondral ossification (chondrodysplasias).

Loss of calcitonin binding in rat is not related to calcitonin receptor gene abnormality

C-cell tumors occur frequently (50%) in old WAG/Rij rats. Interestingly, genetically transmitted loss of CT binding sites in the kidney has also been demonstrated in WAG/Rij rats. To determine if these issues are resulted from mutation of calcitonin receptor (CTR), we analyzed the CTR genomic abnormality in WAG/Rij rat. We demonstrated that both Wistar and WAG/Rij rats expressed type-C1a CTR by RT-PCR analysis and their mRNA expressions were approximately equal by Northern blotting analysis. Direct sequence of RT-PCR products for CTR showed no different nucleotide sequences between the two strains. There were three polymorphisms at the first transmembrane domain and the fourth intracellular membranes, which are different from Sprague-Dawley rat. We concluded that the loss of CT binding in WAG/Rij rat is not related to CTR gene abnormality. Abnormal system of CTR amino acid modification may be occurred in WAG/Rij rat.

Genetic markers of osteoarticular disorders: facts and hopes

Osteoarthritis and osteoporosis are the two most common age-related chronic disorders of articular joints and skeleton, representing a major public health problem in most developed countries. Apart from being influenced by environmental factors, both disorders have a strong genetic component, and there is now considerable evidence from large population studies that these two disorders are inversely related. Thus, an accurate analysis of the genetic component of one of these two multifactorial diseases may provide data of interest for the other. However, the existence of confounding factors must always be borne in mind in interpreting the genetic analysis. In addition, each patient must be given an accurate clinical evaluation, including family history, history of drug treatments, lifestyle, and environment, in order to reduce the background bias. Here, we review the impact of recent work in molecular genetics suggesting that powerful molecular biology techniques will soon make possible both a rapid accumulation of data on the genetics of both disorders and the development of novel diagnostic, prognostic, and therapeutic approaches.

Calcitonin and calcitonin receptors: bone and beyond

Calcitonin (CT), a 32 amino acid peptide hormone produced primarily by the thyroid, and its receptor (CTR) are well known for their ability to regulate osteoclast mediated bone resorption and enhance Ca2+ excretion by the kidney. However, recent studies now suggest that CT and CTRs may play an important role in a variety of processes as wide ranging as embryonic/foetal development and sperm function/physiology. In this review article, CT and CTR gene transcription, signal transduction and function are addressed. The effects of CT on the physiology of a variety of organ systems are discussed and the relationship between polymorphisms in the CTR gene and bone mineral density (BMD)/osteoporosis is examined. Recent studies demonstrating the ability of receptor activity modifying proteins (RAMPs) to post-translationally modify the calcitonin receptor-like receptor (CRLR) are detailed and studies employing transgenic mouse technology to determine the temporal and tissue specific transcriptional activity of the CTR gene in vivo are discussed.