WRN gene 1367 Arg allele protects against development of type 2 diabetes mellitus

Studying Werner syndrome to elucidate mechanisms and therapeutics of human aging and age-related diseases

Aging is a natural and unavoidable part of life. However, aging is also the primary driver of the dominant human diseases, such as cardiovascular disease, cancer, and neurodegenerative diseases, including Alzheimer's disease. Unraveling the sophisticated molecular mechanisms of the human aging process may provide novel strategies to extend 'healthy aging' and the cure of human aging-related diseases. Werner syndrome (WS), is a heritable human premature aging disease caused by mutations in the gene encoding the Werner (WRN) DNA helicase. As a classical premature aging disease, etiological exploration of WS can shed light on the mechanisms of normal human aging and facilitate the development of interventional strategies to improve healthspan. Here, we summarize the latest progress of the molecular understandings of WRN protein, highlight the advantages of using different WS model systems, including Caenorhabditis elegans, Drosophila melanogaster and induced pluripotent stem cell (iPSC) systems. Further studies on WS will propel drug development for WS patients, and possibly also for normal age-related diseases.

Allelic interaction effects of DNA damage and repair genes on the predisposition to age-related cataract

Purpose

Age-related cataract (ARC) is a leading cause of visual impairment and blindness worldwide. DNA damage and malfunction of DNA repair are believed to contribute to the pathogenesis of ARC. Aside from increasing age, the risk factors for ARC appear to be rather complex, and one or more gene variations could play critical roles in the diverse processes of ARC progression. This study aimed to investigate the combined effects of different genetic variants on ARC risk.

Methods

A cohort of 789 ARC patients and 531 normal controls from the Jiangsu Eye Study was included in this study. Genotyping of 18 single-nucleotide polymorphisms (SNPs) in 4 DNA damage/repair genes was performed using TaqMan SNP assays. SNP-SNP interactions were analyzed via multifactor dimensionality reduction (MDR), classification and regression tree (CART) and genetic risk score (GRS) analyses.

Results

Based on single-locus analyses of the 18 SNPs examined, WRN-rs11574311 (T>C) was associated with ARC risk. However, in MDR, the gene-gene interaction among the five SNPs (WRN-rs4733220 (G>A), WRN-rs1801195 (T>G), OGG1-rs2072668 (G>C) and OGG1-rs2304277 (A>G)) on ARC risk was significant (OR = 5.03, 95% CI: 3.54~7.13). CART analyses also revealed that the combination of five SNPs above was the best polymorphic signature for discriminating between the cases and the controls. The overall odds ratio for CART ranged from 4.56 to 7.90 showing an incremental risk for ARC. This result indicated that these critical SNPs participate in complex interactions. The GRS results showed an increased risk for ARC among individuals with the SNPs in this polymorphic signature.

Conclusion

The use of multifactorial analysis (or an integrated approach) rather than a single methodology could be an improved strategy for identifying complex gene interactions. The multifactorial approach used in this study has the potential to identify complex biological relationships among ARC-related genes and processes. This approach will lead to the discovery of novel biological information, ultimately improving ARC risk management.

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.

Catalytic activities of Werner protein are affected by adduction with 4-hydroxy-2-nonenal

4-Hydroxy-2-nonenal (HNE) is a reactive α,β-unsaturated aldehyde generated during oxidative stress and subsequent peroxidation of polyunsaturated fatty acids. Here, Werner protein (WRN) was identified as a novel target for modification by HNE. Werner syndrome arises through mutations in the WRN gene that encodes the RecQ DNA helicase which is critical for maintaining genomic stability. This hereditary disease is associated with chromosomal instability, premature aging and cancer predisposition. WRN appears to participate in the cellular response to oxidative stress and cells devoid of WRN display elevated levels of oxidative DNA damage. We demonstrated that helicase/ATPase and exonuclease activities of HNE-modified WRN protein were inhibited both in vitro and in immunocomplexes purified from the cell extracts. Sites of HNE adduction in human WRN were identified at Lys577, Cys727, His1290, Cys1367, Lys1371 and Lys1389. We applied in silico modeling of the helicase and RQC domains of WRN protein with HNE adducted to Lys577 and Cys727 and provided a potential mechanism of the observed deregulation of the protein catalytic activities. In light of the obtained results, we postulate that HNE adduction to WRN is a post-translational modification, which may affect WRN conformational stability and function, contributing to features and diseases associated with premature senescence.

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.

Variation in DNA repair gene XRCC3 affects susceptibility to astrocytomas and glioblastomas

The gene XRCC3 (X-ray cross complementing group 3) has the task of repairing damage that occurs when there is recombination between homologous chromosomes. Repair of recombination between homologous chromosomes plays an important role in maintaining genome integrity, although it is known that double-strand breaks are the main inducers of chromosomal aberrations. Changes in the XRCC3 protein lead to an increase in errors in chromosome segregation due to defects in centrosomes, resulting in aneuploidy and other chromosomal aberrations, such as small increases in telomeres. We examined XRCC3 Thr241Met polymorphism using PCR-RFLP in 80 astrocytoma and glioblastoma samples. The individuals of the control group (N = 100) were selected from the general population of the São Paulo State. Odds ratio and 95%CI were calculated using a logistic regression model. Patients who had the allele Met of the XRCC3 Thr241Met polymorphism had a significantly increased risk of tumor development (odds ratio = 3.13; 95% confidence interval = 1.50-6.50). There were no significant differences in overall survival of patients. We suggest that XRCC3 Thr241Met polymorphism is involved in susceptibility for developing astrocytomas and glioblastomas.

Analysis of the polymorphisms XRCC1Arg194Trp and XRCC1Arg399Gln in gliomas

XRCC genes (X-ray cross-complementing group) were discovered mainly for their roles in protecting mammalian cells against damage caused by ionizing radiation. Studies determined that these genes are important in the genetic stability of DNA. Although the loss of some of these genes does not necessarily confer high levels of sensitivity to radiation, they have been found to represent important components of various pathways of DNA repair. To ensure the integrity of the genome, a complex system of DNA repair was developed. Base excision repair is the first defense mechanism of cells against DNA damage and a major event in preventing mutagenesis. Repair genes may play an important role in maintaining genomic stability through different pathways that are mediated by base excision. In the present study, we examined XRCC1Arg194Trp and XRCC1Arg399Gln polymorphism using PCR-RFLP in 80 astrocytoma and glioblastoma samples. Patients who had the allele Trp of the XRCC1Arg194Trp polymorphism had an increased risk of tumor development (OR = 8.80; confidence interval at 95% (95%CI) = 4.37-17.70; P < 0.001), as did the allele Gln of XRCC1Arg399Gln (OR = 1.01; 95%CI = 0.53-1.93; P = 0.971). Comparison of overall survival of patients did not show significant differences. We suggest that XRCC1Arg194Trp and XRCC1Arg399Gln polymorphisms are involved in susceptibility for developing astrocytomas and glioblastomas.

Aging is accompanied by a progressive decrease of expression of the WRN gene in human blood mononuclear cells

The WRN gene encodes DNA helicase participating in genome maintenance. We looked for associations of natural aging with expression and methylation of this gene in blood mononuclear cells and with its common polymorphisms. Analyses were performed in ethnically homogenous Polish Caucasians. The mean level of the WRN messenger RNA was significantly lower in long-living individuals than in young and middle-aged controls (p < .001 and p = .025, respectively). Analysis of the 361 bp WRN promoter CpG island showed that aging might be accompanied by a slight increase of its methylation status; however, it seems to be biologically insignificant. Finally, analysis of the WRN R834C, L1074F, and C1367R polymorphisms showed that the frequencies of the L1074F and C1367R polymorphisms were similar in all age groups tested, whereas the R834C polymorphism was absent from Polish Caucasians. We suggest that age-related decrease of the WRN expression but not its common genetic variants might contribute to human immunosenescence.

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.

Roles of Werner syndrome protein in protection of genome integrity

Werner syndrome protein (WRN) is one of a family of five human RecQ helicases implicated in the maintenance of genome stability. The conserved RecQ family also includes RecQ1, Bloom syndrome protein (BLM), RecQ4, and RecQ5 in humans, as well as Sgs1 in Saccharomyces cerevisiae, Rqh1 in Schizosaccharomyces pombe, and homologs in Caenorhabditis elegans, Xenopus laevis, and Drosophila melanogaster. Defects in three of the RecQ helicases, RecQ4, BLM, and WRN, cause human pathologies linked with cancer predisposition and premature aging. Mutations in the WRN gene are the causative factor of Werner syndrome (WS). WRN is one of the best characterized of the RecQ helicases and is known to have roles in DNA replication and repair, transcription, and telomere maintenance. Studies both in vitro and in vivo indicate that the roles of WRN in a variety of DNA processes are mediated by post-translational modifications, as well as several important protein-protein interactions. In this work, we will summarize some of the early studies on the cellular roles of WRN and highlight the recent findings that shed some light on the link between the protein with its cellular functions and the disease pathology.

The clinical characteristics of Werner syndrome: molecular and biochemical diagnosis

Werner syndrome (WS) is an adult onset segmental progeroid syndrome caused by mutations in the WRN gene. The WRN gene encodes a 180 kDa nuclear protein that possesses helicase and exonuclease activities. The absence of WRN protein leads to abnormalities in various DNA metabolic pathways such as DNA repair, replication and telomere maintenance. Individuals with WS generally develop normally until the third decade of life, when premature aging phenotypes and a series of age-related disorders begin to manifest. In Japan, where a founder effect has been described, the frequency of Werner heterozygotes appears to be as high as 1/180 in the general population. Due to the relatively non-specific nature of the symptoms and the lack of awareness of the condition, this disease may be under-diagnosed in other parts of the world. Genetic counseling of WS patients follows the path of other autosomal recessive disorders, with special attention needed for cancer surveillance in relatives. Molecular diagnosis of WS is made by nucleotide sequencing and, in some cases, protein analysis. It is also of potential interest to measure WRN activities in WS patients. More than 50 different disease-causing mutations in the WRN gene have been identified in WS patients from all over the world. All but one of these cases has mutations that result in the premature termination of the protein. Here we describe the clinical, molecular and biochemical characteristics of WS for use by medical professionals in a health care setting. Additional information is available through the International Registry of WS (http://www.wernersyndrome.org).

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.

WRN polymorphisms affect expression levels of plasminogen activator inhibitor type 1 in cultured fibroblasts

BACKGROUND

Recessive mutations in WRN gene eliminate WRN protein function (helicase) and cause Werner syndrome. One of the most important clinical features of Werner syndrome patients are the premature onset and accelerated atherosclerosis process. Studies carried out on polymorphic WRN locus have shown that the alleles 1367R and 1074L confer protection for cardiovascular disease. Given that the levels of plasminogen activator inhibitor type 1 (PAI-1) were found to be significantly increased in Werner syndrome patients, is quiet possible that PAI-1 expression could be under regulation of WRN helicase. Therefore the purpose of this work was to evaluate the role of WRN polymorphism in modulating the expression of PAI-1.

METHODS

In order to accomplish our aim, an array of primary cultured fibroblasts from normal adult donors was genotyped for polymorphisms of both the WRN and PAI-1 loci. In addition, steady state levels of WRN and PAI-1 were measured by semi-quantitative RT-PCR assays in such cultures. To search for the potential relationship between the lack of WRN protein and PAI-1 expression, heterozygous cultures of fibroblasts (1367RC/1074LF; WRN genotype) were treated with a molecule of interference RNA against WRN messenger RNA (mRNA).

RESULTS

We found that, carriers of 1367R and 1074L alleles of WRN shown to have low amounts of PAI-1 in plasma (7.56 +/- 5.02), as compared with carriers of 1367C and 1074F alleles (16.09 +/- 6.03). Moreover, fibroblasts from carriers with these alleles had low expression levels of PAI-1 mRNA. The treatment of heterozygous primary fibroblast cultures (1367RC/1074LF; WRN genotype) with iRNA against WRN mRNA caused PAI-1 overexpression. Treatment with normal PAI-1 inducers (TGFbeta, TNFalpha, or insulin) in these cultures and from those with genotypes 1367CC/1074FF and 1367RR/1074FL resulted in a genotype-dependent PAI-1 expression level.

CONCLUSION

Our results suggest that polymorphisms in the WRN gene might have a significant role regulating PAI-1 levels in healthy individuals and "normal states" as well as acute or chronic stress, obesity, aging, acute inflammation, among others, where characteristic high levels of insulin, TNF alpha and TGFbeta, could favor PAI-1 high levels in carriers with polymorphic variants (C and F alleles), beyond the levels reached by carriers with other alleles (R and L alleles).

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.

Hyperinsulinemia and insulin resistance in Wrn null mice fed a diabetogenic diet

Werner syndrome (WS) is an autosomal recessive progeroid syndrome caused by mutations in the Werner (Wrn) gene. WS patients have increased incidence of a number of chronic conditions including insulin resistance and type 2 diabetes. Since ingestion of foods that are high in fat and sugar is associated with increased incidence of diabetes, we examined if Wrn mutations might affect metabolic response to a diabetogenic diet. Four-month-old mice with a null mutation for the Wrn gene were fed a diet consisting of 36% fat (lard), 33% table sugar, and 20% protein plus balanced vitamins and minerals. Wrn null mice had significantly increased body weights, increased serum insulin levels, impaired glucose tolerance, and insulin resistance during 4 months of eating the diabetogenic diet. Diffuse fatty infiltration of the liver and pancreatic islet hyperplasia was characteristic morphological features. These observations suggest that Wrn null mice have impaired glucose homeostasis and fat metabolism, and may be a useful model to investigate metabolic conditions associated with aging.

Genetic determinants of exceptional human longevity: insights from the Okinawa Centenarian Study

Centenarians represent a rare phenotype appearing in roughly 10-20 per 100,000 persons in most industrialized countries but as high as 40-50 per 100,000 persons in Okinawa, Japan. Siblings of centenarians in Okinawa have been found to have cumulative survival advantages such that female centenarian siblings have a 2.58-fold likelihood and male siblings a 5.43-fold likelihood (versus their birth cohorts) of reaching the age of 90 years. This is indicative of a strong familial component to longevity. Centenarians may live such extraordinarily long lives in large part due to genetic variations that either affect the rate of aging and/or have genes that result in decreased susceptibility to age-associated diseases. Some of the most promising candidate genes appear to be those involved in regulatory pathways such as insulin signaling, immunoinflammatory response, stress resistance or cardiovascular function. Although gene variants with large beneficial effects have been suggested to exist, only APOE, an important regulator of lipoproteins has been consistently associated with a longer human lifespan across numerous populations. As longevity is a very complex trait, several issues challenge our ability to identify its genetic influences, such as control for environmental confounders across time, the lack of precise phenotypes of aging and longevity, statistical power, study design and availability of appropriate study populations. Genetic studies on the Okinawan population suggest that Okinawans are a genetically distinct group that has several characteristics of a founder population, including less genetic diversity, and clustering of specific gene variants, some of which may be related to longevity. Further work on this population and other genetic isolates would be of significant interest to the genetics of human longevity.