Association of a polymorphic variant of the Werner helicase gene with myocardial infarction in a Japanese population

WRN helicase expression in Werner syndrome cell lines

Mutations in the chromosome 8p WRN gene cause Werner syndrome (WRN), a human autosomal recessive disease that mimics premature aging and is associated with genetic instability and an increased risk of cancer. All of the WRN mutations identified in WRN patients are predicted to truncate the WRN protein with loss of a C-terminal nuclear localization signal. However, many of these truncated proteins would retain WRN helicase and/or nuclease functional domains. We have used a combination of immune blot and immune precipitation assays to quantify WRN protein and its associated 3'-->5' helicase activity in genetically characterized WRN patient cell lines. None of the cell lines from patients harboring four different WRN mutations contained detectable WRN protein or immune-precipitable WRN helicase activity. Cell lines from WRN heterozygous individuals contained reduced amounts of both WRN protein and helicase activity. Quantitative immune blot analyses indicate that both lymphoblastoid cell lines and fibroblasts contain approximately 6 x 10(4)WRN molecules/cell. Our results indicate that most WRN mutations result in functionally equivalent null alleles, that WRN heterozygote effects may result from haploinsufficiency and that successful modeling of WRN pathogenesis in the mouse or in other model systems will require the use of WRN mutations that eliminate WRN protein expression.

Werner helicase expression in human fetal and adult aortas

Werner syndrome is a human progeroid syndrome caused by mutations at the Werner helicase locus (WRN). Progeroid features and diseases associated with aging (including arteriosclerosis) do not become apparent until after puberty. We entertained two alternative hypotheses to explain the post-pubertal onset: 1) WRN expression is induced at the time of puberty, its earlier functions being satisfied by another member of that family of helicases; and 2) it is expressed at all ages, but the phenotype of deficiency becomes apparent only after puberty. We report initial experiments consistent with the second hypothesis. Steady-state levels of WRN mRNA in aortic tissues were determined by semiquantitative reverse transcription-polymerase chain reaction. WRN mRNA was detectable as early as 49 days of gestation (the earliest available material). There was no statistically significant change in these levels between fetal and adult tissues. The presence of the WRN protein in fetal aorta was confirmed by Western analysis. This rules out the possibility that Werner syndrome phenotypes manifest after the puberty because of peripubertal induction of WRN expression.

Gene expression profile of aging and its retardation by caloric restriction

The gene expression profile of the aging process was analyzed in skeletal muscle of mice. Use of high-density oligonucleotide arrays representing 6347 genes revealed that aging resulted in a differential gene expression pattern indicative of a marked stress response and lower expression of metabolic and biosynthetic genes. Most alterations were either completely or partially prevented by caloric restriction, the only intervention known to retard aging in mammals. Transcriptional patterns of calorie-restricted animals suggest that caloric restriction retards the aging process by causing a metabolic shift toward increased protein turnover and decreased macromolecular damage.

Lipoprotein-genotype associations in Trinidadian neonates

OBJECTIVES

We hypothesized that common variation in the angiotensinogen (AGT), beta-3-adrenergic receptor, intestinal fatty acid-binding protein, serum paraoxonase, paraoxonase-2, hepatic lipase, apolipoprotein E (APOE), and Werner helicase (WRN) genes would be associated with variation in biochemical phenotypes in a previously unstudied neonatal sample.

DESIGN AND METHODS

We examined associations of both nongenetic and genetic variables with plasma lipoprotein traits in neonates from Trinidad.

RESULTS

Among nongenetic variables, we found significant associations between plasma concentrations of: 1) lipoprotein(a) [Lp(a)] and both ethnicity (p = 0.037) and birth weight (p = 0.001); 2) total cholesterol and gender (p = 0.010); 3) triglyceride and birth weight (p = 0.035); and 4) apolipoprotein AI and gender (p = 0.016). Among genetic variables, we found that: 1) common variation on chromosome 1q in AGT codon 235 was significantly associated with variation in plasma apolipoproteins AI (p<0.0001) and B (p = 0.013); 2) common variation in WRN at codon 1367 was significantly associated with variation in plasma Lp(a) (p<0.0001); and 3) common variation in APOE at codons 112 and 158 was significantly associated with variation in plasma triglycerides (p = 0.013).

CONCLUSIONS

The associations with AGT and WRN are novel and may have resulted either from a direct influence of the genetic variants or through linkage disequilibrium with other functional loci, such as the familial combined hyperlipidemia locus on chromosome 1q in the case of AGT. Despite the fact that there are some limitations in making determinations from cord blood, the results suggest that there may be genetic determinants of plasma lipoproteins in neonates.

ACE, PAI-1, decorin and Werner helicase genes are not associated with the development of renal disease in European patients with type 1 diabetes

BACKGROUND

Genetic factors are involved in the development of diabetic nephropathy in Type 1 diabetes. We have examined the association of four candidate genes, angiotensin converting enzyme (ACE): insertion/deletion (I/D) polymorphism, plasminogen activator inhibitor-1 (PAI-1): 4G/5G polymorphism, decorin: 179/183/185 polymorphism and Werner syndrome helicase: C/R polymorphism, with the presence of diabetic nephropathy in Type 1 diabetic patients.

METHODS

175 Type 1 diabetic patients with albuminuria (59 with microalbuminuria and 116 with macroalbuminuria) were compared with 136 Type 1 diabetic patients with normoalbuminuria and duration of disease longer than 15 years (mean+/-SD: 25+/-8 years). 200 non-diabetic subjects were also studied as background population.

RESULTS

We found no association in the polymorphism of the four genes examined between patients with and without diabetic nephropathy and the control subjects.

CONCLUSIONS

The genes studied are unlikely to be involved in the susceptibility to nephropathy in Type 1 diabetic patients.

Transcriptional activation by the Werner syndrome gene product in yeast

Werner syndrome (WS) is characterized by the premature occurrence of many age-related features. Before the cloning of the gene for WS (WRN), several reports suggested that transcriptional defects of genes may relate to the mechanisms of the occurrence of WS and natural aging. Because WRN, which encodes a helicase (WRN-H), has been cloned, we are attempting to clarify the mechanism of the transcriptional abnormalities found in WS cells, using WRN and WRN-H. In this article, we studied transcriptional activation of a promoter by WRN-H in a yeast assay system as a first step. The results showed that WRN-H functions as a transcriptional activator in the system. Furthermore, we performed additional transcriptional assays using various parts of WRN to define the critical region of WRN-H for transcriptional activation in yeast. The results revealed the critical region for the activation most likely mapped to the region of 315 to 403 aa. The region of 404 to 1309 aa may also effect activation in the presence of the critical region. The two regions contain an acidic domain, and the region of 404 to 1309 aa also contains a helicase domain. If this transcriptional activation by WRN-H occurs also in human cells in vivo, direct activation of the promoters by WRN-H could explain the results of somatic cell hybrid studies as well as the overexpressed genes detected in WS cells. However, our results should be interpreted with caution, because thus far, the transcriptional activation by WRN-H were only demonstrated using one promoter in a yeast system.

Genetics of longevity

Recent studies on the genetics of aging in the yeast Saccharomyces cerevisiae, the roundworm Caenorhabditis elegans, and the fruit fly Drosophila melanogaster have converged revealing the central role of metabolic capacity and resistance to stress in determining life span. Signal transduction has emerged from these studies as an important molecular mechanism underlying longevity. In their broad features, the results obtained in these genetic models are applicable to the dietary restriction paradigm in mammals, suggesting a general significance. It will be of interest to determine whether many of the molecular details will also pertain. The examination of centenarian populations for the frequency of certain alleles of pertinent genes may provide insights into the relevance of the conclusions of studies in invertebrates to human aging. These population genetic studies can be augmented by mechanistic studies in transgenic mice.

Nucleolar localization of the Werner syndrome protein in human cells

Werner Syndrome (WS) is a human genetic disorder with many features of premature aging. The gene defective in WS (WRN) has been cloned and encodes a protein homologous to several helicases, including Escherichia coli RecQ, the human Bloom syndrome protein (BLM), and Saccharomyces cerevisiae Sgs1p. To better define the function of WRN protein we have determined its subcellular localization. Indirect immunofluorescence using polyclonal anti-human WRN shows a predominant nucleolar localization. Studies of WRN mutant cells lines confirmed the specificity of antibody recognition. No difference was seen in the subcellular localization of the WRN protein in a variety of normal and transformed human cell lines, including both carcinomas and sarcomas. The nucleolar localization of human WRN protein was supported by the finding that upon biochemical subcellular fractionation, WRN protein is present in an increased concentration in a subnuclear fraction enriched for nucleolar proteins. We have also determined the subcellular localization of the mouse WRN homologue (mWRN). In contrast to human WRN protein, mWRN protein is present diffusely throughout the nucleus. Understanding the function of WRN in these organisms of vastly differing lifespan may yield new insights into the mechanisms of lifespan determination.

Genetics and the pathobiology of ageing

Genetics offers a powerful approach to the elucidation of mechanisms underlying specific components of the senescent phenotype of our species. Perhaps thousands of gene variations have escaped the force of natural selection and thus play roles in the genesis of different patterns of ageing in man. It is possible that a subset of these genes may be of particular importance in how most people age. While variations at the Werner helicase locus could be one such example, several lines of evidence suggest that mutation at that locus leads to a 'private' mechanism of ageing. It will be important, however, to investigate polymorphisms underlying the regulation of expression of this gene in the general population. Polymorphisms (normally occurring variants of a gene, or sequence of DNA), rather than mutations, may also prove to be more relevant to our understanding of the differing susceptibilities of people to common disorders such as late onset Alzheimer's disease. Polymorphic forms of the Apolipoprotein E gene is a good example. It remains to be seen if the pathogenetic framework (beta amyloidosis) derived from studies of the several rare mutations responsible for early onset familial forms of the disease proves relevant to the pathogenesis of the vastly more prevalent sporadic forms of the disorder. In contrast to the satisfying progress on the genetics of the diseases of ageing, research on the genetic basis for unusually robust retention of structure and function in old age has been neglected and requires a higher priority for the future. Such research should include studies of environmental agents and should address mechanisms of 'sageing', a stage in the life course characterized by an extensive utilization of behavioural and physiological adaptations to compensate for functional declines. For the genetics of longevity, we have to turn to genetically tractable organisms such as nematodes and fruit flies. Such studies have provided significant support for the oxidative stress theory of ageing. It will be important to learn more about the age-related pathologies and pathophysiologies of these organisms.

Molecular and epidemiological studies of Werner syndrome in the Japanese population

Werner syndrome (WS) is an autosomal recessive genetic disease characterized by many age-related features. The gene responsible for WS (WRN) has been isolated and contains a helicase domain, but its function is unknown. Six different mutations throughout the WRN gene have been reported in the Japanese population. We have studied whether patients with a specific mutation exhibit distinct phenotypes from others. Fourteen patients with different mutations showed almost the same signs and symptoms and, therefore, the C terminal part of the product appears to be crucial for its functions, although other parts may be important as well. Haplotype analyses using 13 microsatellites covering the 2.8-3.0 cM WRN region showed that two out of six different mutations had founder chromosomes. These two founder chromosomes may be evenly distributed throughout the western part of Japan, suggesting that these mutations go back to a time earlier than 1400 years ago.

Genetics of aging

The role of genetics in determining life-span is complex and paradoxical. Although the heritability of life-span is relatively minor, some genetic variants significantly modify senescence of mammals and invertebrates, with both positive and negative impacts on age-related disorders and life-spans. In certain examples, the gene variants alter metabolic pathways, which could thereby mediate interactions with nutritional and other environmental factors that influence life-span. Given the relatively minor effect and variable penetrance of genetic risk factors that appear to affect survival and health at advanced ages, life-style and other environmental influences may profoundly modify outcomes of aging.