A polymorphic variant at the Werner helicase (WRN) gene is associated with bone density, but not spondylosis, in postmenopausal women

A comprehensive overview on osteoporosis and its risk factors

Osteoporosis is a bone disorder with remarkable changes in bone biologic material and consequent bone structural distraction, affecting millions of people around the world from different ethnic groups. Bone fragility is the worse outcome of the disease, which needs long term therapy and medical management, especially in the elderly. Many involved genes including environmental factors have been introduced as the disease risk factors so far, of which genes should be considered as effective early diagnosis biomarkers, especially for the individuals from high-risk families. In this review, a number of important criteria involved in osteoporosis are addressed and discussed.

Werner syndrome (WRN) gene variants and their association with altered function and age-associated diseases

Werner syndrome (WS) is a heritable autosomal recessive human disorder characterized by the premature onset of several age-associated pathologies including cancer. The protein defective in WS patients, WRN, is encoded by a member of the human RECQ gene family that contains both a DNA exonuclease and a helicase domain. WRN has been shown to participate in several DNA metabolic pathways including DNA replication, recombination and repair, as well as telomere maintenance and transcription modulation. Here we review base pair-level genetic variation that has been documented in WRN, with an emphasis on non-synonymous coding single nucleotide polymorphisms (SNPs) and their associations with anthropomorphic features, longevity and disease risk. These associations have been challenging to identify, as many reported WRN SNP associations appear to be further conditioned upon ethnic, age, gender or other environmental co-variables. The WRN variant phenotypic associations identified to date are intriguing, and several are of clear clinical import. Consequently, it will be important to extend these initial associations and to identify the mechanisms and conditions under which specific WRN variants may compromise WRN function to drive cellular and organismal phenotypes as well as disease risk.

Homozygosity for the WRN Helicase-Inactivating Variant, R834C, does not confer a Werner syndrome clinical phenotype

Loss-of-function mutations in the WRN helicase gene cause Werner syndrome- a progeroid syndrome with an elevated risk of cancer and other age-associated diseases. Large numbers of single nucleotide polymorphisms have been identified in WRN. We report here the organismal, cellular, and molecular phenotypes of variant rs3087425 (c. 2500C > T) that results in an arginine to cysteine substitution at residue 834 (R834C) and up to 90% reduction of WRN helicase activity. This variant is present at a high (5%) frequency in Mexico, where we identified 153 heterozygous and three homozygous individuals among 3,130 genotyped subjects. Family studies of probands identified ten additional TT homozygotes. Biochemical analysis of WRN protein purified from TT lymphoblast cell lines confirmed that the R834C substitution strongly and selectively reduces WRN helicase, but not exonuclease activity. Replication track analyses showed reduced replication fork progression in some homozygous cells following DNA replication stress. Among the thirteen TT homozygotes, we identified a previously unreported and statistically significant gender bias in favor of males (p = 0.0016), but none of the clinical findings associated with Werner syndrome. Our results indicate that WRN helicase activity alone is not rate-limiting for the development of clinical WS.

Association of the rs1346044 Polymorphism of the Werner Syndrome Gene RECQL2 with Increased Risk and Premature Onset of Breast Cancer

Like other RECQ helicases, WRN/RECQL2 plays a crucial role in DNA replication and the maintenance of genome stability. Inactivating mutations in RECQL2 lead to Werner syndrome, a rare autosomal disease associated with premature aging and an increased susceptibility to multiple cancer types. We analyzed the association of two coding single-nucleotide polymorphisms in WRN, Cys1367Arg (rs1346044), and Arg834Cys (rs3087425), with the risk, age at onset, and clinical subclasses of breast cancer in a hospital-based case-control study of an Austrian population of 272 breast cancer patients and 254 controls. Here we report that the rare homozygous CC genotype of rs1346044 was associated with an approximately two-fold elevated breast cancer risk. Moreover, patients with the CC genotype exhibited a significantly increased risk of developing breast cancer under the age of 55 in both recessive and log-additive genetic models. CC patients developed breast cancer at a mean age of 55.2 ± 13.3 years and TT patients at 60.2 ± 14.7 years. Consistently, the risk of breast cancer was increased in pre-menopausal patients in the recessive model. These findings suggest that the CC genotype of WRN rs1346044 may contribute to an increased risk and a premature onset of breast cancer.

A missense single nucleotide polymorphism, V114I of the Werner syndrome gene, is associated with risk of osteoporosis and femoral fracture in the Japanese population

Werner syndrome is a rare autosomal recessive disorder caused by mutations in the human WRN gene and characterized by the early onset of normal aging symptoms. Given that patients with this disease exhibit osteoporosis, the present study aimed to determine whether the WRN gene contributes to the etiology of osteoporosis. A genetic association study of eight non-synonymous polymorphisms in the WRN gene and the incidence of femoral fracture was undertaken in 1,632 consecutive Japanese autopsies in which 140 patients had experienced the fracture during their lifetime. The results were validated in 251 unrelated postmenopausal Japanese women with osteoporosis and 269 non-institutionalized, community-dwelling Japanese adults. A statistically significant association was observed between rs2230009 (c.340G > A)--which results in a Val to Ile substitution--and fracture risk; the incidence of femoral fracture increased dose-dependently with the number of A alleles (p = 0.0120). Femoral neck bone and whole bone densities were lower among postmenopausal women with osteoporosis and community-dwelling adults, respectively, if they were of the AG instead of the GG genotype. The results suggest that Japanese subjects bearing at least one A allele of rs2230009 of the WRN gene are at a significantly higher risk of femoral fracture, possibly due to decreased bone density.

WRN Cys1367Arg polymorphism is not associated with skull base chordoma

Skull base chordoma is a rare tumor with unknown risk factors. Werner syndrome, which is caused by a mutation in the WRN gene, is a disease of progeria, resembling the pathological process of aging. The present study aimed to provide data on the possible association between skull base chordoma and the single-nucleotide polymorphism (SNP) rs1346044 of the WRN gene. Between July, 2010 and September, 2012, a total of 65 patients with pathologically confirmed skull base chordoma and 65 control subjects were enrolled in this case-control study. The clinical data of the skull base chordoma patients were documented and the rs1346044 site in all the enrolled subjects was analyzed by sequencing and statistically compared using SPSS software. The A allele was the dominant allele of the rs1346044. The comparisons of genotype distributions and allele frequencies did not reveal any significant difference between the groups [P=0.383, 95% confidence interval (CI): 0.346-1.505]. The clinicopathological factors were assessed and no statistically significant difference was observed. In conclusion, the present study suggested that there is no association between rs1346044 SNP and skull base chordomas, at least in the population analyzed.

Polymorphisms of the WRN gene and DNA damage of peripheral lymphocytes in age-related cataract in a Han Chinese population

Werner syndrome is caused by mutations in the DNA repair Werner helicase (WRN) gene and characterized by accelerated aging including cataracts. Age-related cataract (ARC) cases (N = 504) and controls (N = 244) were recruited from a population-based study to evaluate the association of single-nucleotide polymorphisms (SNPs) of WRN and another DNA repair gene (human 8-oxoguanine DNA N-glycosylase 1) with ARC. Among the five SNPs tested, only WRN rs1346044 was found to be significantly associated between cases and controls before multiple-testing adjustment. The minor C allele of rs1346044 was associated with ARC with an odds ratio (OR) of 0.66, suggesting a protective role of the C allele for developing ARC. The stratification analysis on the subtypes of ARC showed that rs1346044 was significantly associated with cortical cataract, but not with nuclear, posterior subcapsular, and mixed types after multiple-testing adjustment (OR = 0.51, p< 0.01). The genetic model analysis showed that the results fit the dominant model (OR = 0.44, p < 0.001). The comet assay used to assess the extent of DNA damage in peripheral lymphocytes of ARC cases found that the DNA damage in lymphocytes from patients with CC genotype was significantly less than that in patients with TT genotype. We concluded that the C allele of rs1346044, a non-synonymous SNP resulting in the conversion of Cys to Arg at amino acid position 1367 of WRN, alters susceptibility to ARC, especially the cortical type of the disease, in the Han Chinese. The underlying mechanism of its protective role might be related to the improved DNA repair function.

Correlation between osteoporosis and degeneration of intervertebral discs in aging rats

This study examined the correlation between osteoporosis and the degeneration of intervertebral discs. Sprague-Dawley rats were maintained up to 22 or 28 months. The femoral bone, tibial bone and lumbar vertebra were histologically studied and the expression of collagen type II and X in intervertebral discs was immunohistochemiscally determined. Several indices for the degeneration of intervertebral discs and osteoporosis and the correlation among them were then analyzed. Close correlations were found among the indices for the degeneration of intervertebral discs, including the relative area of the vascular bud, the ratio of the uncalcified and the calcified layers, the expression of collagen type II and X. The correlation with collagen type X was negative. There existed positive correlations among the indices for osteoporosis, including the thickness ratio of cortical bone, the relative area of bone trabecula, the density of femoral and vertebral body bones, and the maximum stress and strain on bone. Analysis on the relationship of osteoporosis and the disease on disc showed that the indices of osteoporosis were negatively correlated with the indices of the degeneration of intervertebral discs but the expression of collagen type X was positively correlated, with the density of vertebral body bones having the strongest dependence on collagen type X. The maximum stress and strain bore no correlation with the degeneration of intervertebral discs. These results suggest that osteoporosis was negatively correlated with the degeneration of intervertebral discs.

Genetic aspects of osteoporosis

The multiple factors contributing to the pathogenesis of osteoporosis include genetic and environmental factors. Because decrease in bone mineral density (BMD) is the major clinical indicator and a useful quantitative trait, many association and linkage studies of BMD have been conducted. Although the series of studies showed apparently significant associations, the genes have not been found that can be utilized in clinical practice. Several genes identified in robust genome-wide association studies will be the new cutting edge in genetic studies of osteoporosis. Our recent reports of functional single nucleotide polymorphism in the tissue-nonspecific alkaline phosphatase gene and gamma-carboxylase gene are presented in this review to discuss the future prospects in the genetic research of osteoporosis from the point of view of genome-nutrition interaction.

Delineation of WRN helicase function with EXO1 in the replicational stress response

The WRN gene defective in the premature aging disorder Werner syndrome encodes a helicase/exonuclease. We examined the ability of WRN to rescue DNA damage sensitivity of a yeast mutant defective in the Rad50 subunit of Mre11-Rad50-Xrs2 nuclease complex implicated in homologous recombination repair. Genetic studies revealed WRN operates in a yEXO1-dependent pathway to rescue rad50 sensitivity to methylmethane sulfonate (MMS). WRN helicase, but not exonuclease, is required for MMS resistance. WRN missense mutations in helicase or RecQ C-terminal domains interfered with the ability of WRN to rescue rad50 MMS sensitivity. WRN does not rescue rad50 ionizing radiation (IR) sensitivity, suggesting that WRN, in collaboration with yEXO1, is tailored to relieve replicational stress imposed by alkylated base damage. WRN and yEXO1 are associated with each other in vivo. Purified WRN stimulates hEXO1 nuclease activity on DNA substrates associated with a stalled or regressed replication fork. We propose WRN helicase operates in an EXO1-dependent pathway to help cells survive replicational stress. In contrast to WRN, BLM helicase defective in Bloom's syndrome failed to rescue rad50 MMS sensitivity, but partially restored IR resistance, suggesting a delineation of function by the human RecQ helicases.

Werner syndrome gene variants in human sarcomas

Werner syndrome is an autosomal inherited disease that is characterized by premature aging. The gene mutated in Werner syndrome (WS), WRN, encodes both a 3' --> 5' DNA helicase and a 3' --> 5' DNA exonuclease. Among the WS phenotypes is an exceptionally high incidence of sarcomas. We asked whether spontaneous sarcomas, not known to be associated with WS, also harbor mutations or unreported single nucleotide polymorphisms (SNPs) in WRN. We analyzed RNA or DNA sequences within the helicase and exonuclease domains from 51 and 69 matched sarcoma and adjacent normal tissues, respectively. Among a total of 13 nucleotide variants detected, we identified three novel nonsynonymous substitutions: c.611C>T, c.809_810insT, and c.1882C>G. We further characterized one, c.611C>T, which results in substitution of an evolutionarily conserved proline at amino acid 204 in the exonuclease domain with leucine. We show that P204L WRN exhibits a reduction of WRN exonuclease activity; the specific activity is approximately 10-fold lower than that of wild-type WRN. In contrast, the helicase activity of P204L WRN is reduced less than twofold.

WRN Cys1367Arg SNP is not associated with risk and prognosis of gliomas in Southeast Brazil

Werner syndrome (WS) is a premature aging disorder characterized by early onset of symptoms related to normal aging and by a high predisposition to various types of cancer, including gliomas. WS is caused by inherited recessive mutations in the WRN gene, which encodes a helicase considered a caretaker of the genome. Aiming to study the role of WRN Cys1367Arg in glioma susceptibility and oncologic prognosis of patients, we investigated the genotype distribution of this single nucleotide polymorphism in 94 glioma patients and 100 healthy subjects. Comparisons of genotype distributions and allele frequencies did not reveal any significant difference between the groups. Overall and disease-free survival rates were calculated, but no statistically significant difference was observed. Our data suggest that WRN Cys1367Arg SNP is not involved either in susceptibility to developing gliomas or in patient survival, at least in the Brazilian population.

Association of a missense single nucleotide polymorphism, Cys1367Arg of the WRN gene, with the risk of bone and soft tissue sarcomas in Japan

Bone and soft tissue sarcomas (BSTSs) are rare malignant tumors of mesenchymal origin. Although BSTSs frequently occur in some hereditary cancer syndromes with germline mutations of DNA repair genes, genetic factors responsible for sporadic cases have not been determined. In the present study we undertook a case-control study and analyzed possible associations between the susceptibility to BSTS and the single nucleotide polymorphisms (SNPs) in DNA repair genes. Genomic DNAs extracted from case and control peripheral blood leukocytes were genotyped by pyrosequencing. For candidate polymorphisms, we chose 50 non-synonymous missense SNPs, which we have previously been identified by resequencing 36 DNA repair genes among the Japanese population. In the first screening, we analyzed 240 cases and 685 controls and selected six SNPs at the significance level of P < 0.1 (Fisher's exact test). The six SNPs were further analyzed in the second genotyping on an additional set of 304 cases and 834 controls. In the joint analysis (the first and second genotyping combined) of 544 cases and 1378 controls, Cys1367Arg of the WRN gene was found to be a protective factor of BSTS (odds ratio = 0.66, 95% confidence interval = 0.49-0.88, P = 0.005). An exploratory subgroup analysis without multiple comparison adjustment suggested that the WRN-Cys1367Arg SNP is associated with soft tissue sarcomas, sarcomas with reciprocal chromosomal translocations and malignant fibrous histiocytoma.

Effects of alfacalcidol alone or in combination with elcatonin on incidence of osteoporotic vertebral fractures in postmenopausal women with spondylosis

Osteoporosis and spondylosis often occur simultaneously. However, there are no previous reports about the effects of osteoporosis medication on incidence of vertebral fractures in people with spondylosis. In this study, we conducted a retrospective investigation of the effects of alfacalcidol alone or in combination with elcatonin on incidence of osteoporotic vertebral fractures in women with spondylosis. The present subjects were 101 postmenopausal women with osteoporosis aged >60 years, divided into three groups: D group (n = 45), treated for >5 years with alfacalcidol; D+ECT group (n = 26), treated for >5 years with alfacalcidol plus elcatonin; control group (n = 30), who received no medications for >5 years. Over the 5-year treatment period, bone mineral density (BMD) of the lumbar spine and proximal femur did not significantly change in the D and D+ECT groups, but they significantly decreased in the control group (P < 0.05). The number of incident vertebral fractures per patient was significantly higher in the control group (2.9) than in the D group (1.2) and D+ECT group (1.5) (P < 0.01). There was no significant difference in BMD or incident vertebral fractures between the D and D+ECT groups. In all three groups, the number of incident vertebral fractures positively correlated with the number of prevalent vertebral fractures (0.303 </= r </= 0.434), and negatively correlated with baseline BMD (-0.703 </= r </= -0.326) and the osteophyte score representing the degree of spondylosis (-0.769 </= r </= -0.365). Further multiple regression analysis revealed that the medication (D or D+ECT, P < 0.001) and the osteophyte score (P < 0.001) were the most significant contributors for the number of incident vertebral fractures. In conclusion, elcatonin had no additive effects on BMD or prevention of vertebral fractures in postmenopausal women receiving alfacalcidol. Presence of spondylosis (indicated by a high osteophyte score) appears to have an effect on prevention of vertebral fractures.

A polymorphic marker in the first intron of the Werner gene associates with cognitive function in aged Danish twins

Werner's syndrome is a premature aging syndrome with many features common to normal aging. The possible association between phenotypic markers for normal aging and SNP's in the WRN gene was investigated in 426 dizygotic, Danish twins age 70-90 years. All participants were scored every second year using a number of physical and cognitive tests. In addition their self-rated health was registered as well as self reported status with regards to nine diseases. Blood was drawn from all participants and purified DNA was typed for four SNP's in the WRN gene. The four SNP's were located in intron 1, exon 6, exon 9 and exon 34. In an unpaired analysis of this material a significant association between the intron 1 SNP and cognitive function was demonstrated. Our finding, which will need corroboration in independent samples, therefore may suggest that the t-allele of the intron 1 SNP is beneficial to cognitive function. However, since the t-allele of this SNP is very rare, we did not encounter any tt-homozygous individuals for this allele.

The enzymatic activities of the Werner syndrome protein are disabled by the amino acid polymorphism R834C

The Werner syndrome protein, WRN, is a member of the RecQ family of DNA helicases. It possesses both 3'-->5' DNA helicase and 3'-->5' DNA exonuclease activities. Mutations in WRN are causally associated with a rare, recessive disorder, Werner syndrome (WS), distinguished by premature aging and genomic instability; all are reported to result in loss of protein expression. In addition to WS-linked mutations, single nucleotide polymorphisms, with frequencies that exceed those of WS-associated mutations, are also present in WRN. We have initiated studies to determine if six of these polymorphisms affect the enzymatic activities of WRN. We show that two common polymorphisms, F1074L and C1367R, and two infrequent polymorphisms, Q724L and S1079L, exhibit little change in activity relative to wild-type WRN; the polymorphism, T172P, shows a small but consistent reduction of activity. However, an infrequent polymorphism, R834C, located in the helicase domain dramatically reduces WRN helicase and helicase-coupled exonuclease activity. The structure of the E. coli helicase core suggests that R834 may be involved in interactions with ATP. As predicted, substitution of Arg with Cys interferes with ATP hydrolysis that is absolutely required for unwinding DNA. R834C thus represents the first missense amino acid polymorphism in WRN that nearly abolishes enzymatic activity while leaving expression largely unaffected.

Inverse relation between osteoporosis and spondylosis in postmenopausal women as evaluated by bone mineral density and semiquantitative scoring of spinal degeneration

STUDY DESIGN

The relation between bone mineral density and severity of spondylosis was evaluated in postmenopausal women.

OBJECTIVE

To examine the possible inverse relation between osteoporosis and spondylosis by evaluating the association between bone mineral density and osteophyte formation or intervertebral disc narrowing using a semiquantitative scoring system.

SUMMARY OF BACKGROUND DATA

The literature contains studies demonstrating an inverse relation between osteoporosis and spondylosis as well as those documenting insufficient support for such a relation. However, in these studies, only limited-range grading systems (e.g., Grades 1-4) were used to evaluate the severity of spondylosis.

METHODS

In this study, 104 postmenopausal women older than 60 years underwent bone mineral density measurement of the lumbar spine (anteroposterior, lateral, and midlateral) and proximal femur (femoral neck, trochanter, and Ward's triangle) using dual-energy x-ray absorptiometry. Raw data representing the semiquantitative osteophyte score and disc score as well as the number of vertebral fractures were obtained using spinal radiograph. Correlations between bone mineral density and the radiographic variable were then analyzed.

RESULTS

Significant negative correlations were found between all bone mineral density data and the number of vertebral fractures (-0.524 < or r= r < or = -0.347; P < 0.05). Marginal/moderate positive correlations were observed between the osteophyte score and the bone mineral density data (0.263 < or = r < or = 0.580, P < 0.05), and between the disc score and the bone mineral density data (0.233 < or = r < or = 0.570, P < 0.05).CONCLUSIONS On the basis of the finding that spondylotic changes in postmenopausal women exhibit positive correlations not only with the lumbar bone mineral density, but also with the remote-site bone mineral density, this study supports the view that osteoporosis has an inverse relation with spondylosis.

A comparison of bone mineral density in elderly female patients with COPD and bronchial asthma

BACKGROUND

A recent study has shown that osteoporosis and vertebral fractures are quite common in patients with advanced COPD and showed a significant relationship to the mortality of these patients. These results suggested that management of osteoporosis in advanced COPD is an important intervention. But whether patients with COPD who had never received chronic systemic corticosteroids have a high incidence of osteoporosis and whether these patients require treatment strategies to decrease osteoporotic fracture is not yet known. Furthermore, it is unclear whether there are differences in terms of the degree of osteoporosis between patients with COPD and patients with bronchial asthma.

OBJECTIVES

To compare the degree of osteoporosis and bone metabolism markers between elderly women with COPD and those with bronchial asthma who had never received chronic systemic corticosteroids, and to determine the factors influencing bone metabolism in these patients.

DESIGN

Cross-sectional medical survey.

PATIENTS

A total of 44 elderly female patients with COPD (n = 20) or bronchial asthma (n = 24) who had not received chronic systemic corticosteroids were enrolled (mean +/- SEM age, 74.6 +/- 1.0 years).

MEASUREMENTS

Total body and lumbar bone mineral density (BMD) were measured by dual-energy x-ray absorptiometry, and the data were compared between the two groups. In addition, the association between bone mass and clinical variables was determined.

RESULTS

When lumbar BMD was expressed as a Z score, the Z scores of patients with COPD were significantly lower than those of patients with bronchial asthma (p < 0.01). The prevalence of osteoporosis was also significantly higher in patients with COPD (50% vs 21%, p < 0.05). In patients with COPD, body mass index was positively correlated with BMD in the lumbar spine (r = 0.55, p = 0.02) and total body (r = 0.49, p = 0.03). Other clinical, biochemical, and anthropometric variables were not correlated with BMD.

CONCLUSIONS

In elderly female patients, osteoporosis is more common in cases of COPD than in bronchial asthma, even if these patients had not received long-term systemic corticosteroids. The explanation for the higher prevalence of osteoporosis in COPD is still not known, but preventive strategies to decrease osteoporotic fractures should be added to the management of elderly patients with COPD.

Roles of the Werner syndrome protein in pathways required for maintenance of genome stability

Werners syndrome is a disease of premature aging where the patients appear much older than their chronological age. The gene codes for a protein that is a helicase and an exonuclease, and recently we have learned about some of its protein interactions. These interactions are being discussed as they shed light on the molecular pathways in which Werner protein participates. Insight into these pathways brings insight into the aging process.