Telomere length and risk of stroke in Chinese.

BACKGROUND AND PURPOSE: Accumulating evidence suggests that telomere length is a maker for biological aging of the cardiovascular system. Whether stroke is associated with accelerated biological aging as measured by telomere length has not been conclusively demonstrated. Our aim was to determine whether mean leukocyte telomere length is a predictor for the development of stroke. METHODS: The relative telomere length of leukocytes was determined by quantitative polymerase chain reaction in 1309 stroke patients and 1309 age- and sex-matched control subjects as well as 858 stroke patients followed prospectively for 5 years. For each measure, the study sample was divided into quartiles. The associations between the telomere length and risk of stroke as well as poststroke adverse outcomes were determined. RESULTS: Mean telomere length was significantly shorter in stroke patients than in control subjects. Shorter telomere length levels were directly associated with a higher risk of stroke in the case/control sample. As compared with the fourth (longest) quartile, the odd ratios [OR] (and 95% confidence intervals [CI]) for ischemic stroke risk were as follows: third quartile, 1.37 (1.04-1.82); second quartile, 1.53 (1.17-2.02); and first quartile, 2.12 (1.62-2.77). Follow-up of the patients from the prospective cohort also showed that shorter telomere length levels were associated with mortality from all causes but not with recurrence of stroke. CONCLUSIONS: Shorter telomere length was associated with ischemic stroke and was a strong predictor of poststroke death.

Telomere dysfunction in peripheral lymphocytes as a potential predisposition factor for renal cancer.

PURPOSE: Genetic integrity is maintained in part by the architecture of telomeres. We previously developed a laser scanning cytometry based quantitative fluorescence in situ hybridization assay to assess telomere length in peripheral blood lymphocytes. In this study we modified the assay by incorporating 9 control cell lines to normalize telomere length. MATERIALS AND METHODS: We applied this assay to 65 patients with renal cell carcinoma, and 65 age, sex and ethnicity matched controls. For each subject we measured telomere length in CD4+ T cells, CD8+ T cells and overall peripheral blood lymphocytes. RESULTS: For cases vs controls mean normalized telomere length +/- SD was 0.84 +/- 0.15 vs 0.95 +/- 0.18 for CD4+ T cells, 0.80 +/- 0.21 vs 0.95 +/- 0.22 for CD8+ T cells and 0.88 +/- 0.25 vs 0.99 +/- 0.22 for overall peripheral blood lymphocytes (each p <0.05). After adjustment for patient age, sex, ethnicity and smoking status, and using 75% of telomere length in controls as a cutoff point, short telomere length in CD4+ T cells was associated with a significantly increased risk of renal cell carcinoma (OR 3.08, 95% CI 1.14-8.34). Compared to individuals within the highest quartile of telomere length the OR for those within the 3rd, 2nd and 1st quartiles was 1.81 (95% CI 0.54-6.08), 2.15 (95% CI 0.67-6.91) and 5.41 (95% CI 1.78-16.4), respectively (p for trend <0.01). Similar trends were observed in CD8+ T cells and overall peripheral blood lymphocytes. In controls there was no significant difference among the telomere lengths of CD4+ T cells, CD8+ T cells and overall PBLs. CONCLUSIONS: Our data argue against the possibility that telomere length difference between cancer cases and controls may be due to the variations of lymphocyte subpopulation or clonal expansion. Our data strongly support the hypothesis that telomere shortening in peripheral blood lymphocytes is a genetic predisposing factor for cancer.

Identification and functional characterization of 2 variant alleles of the telomerase RNA template gene (TERC) in a patient with dyskeratosis congenita.

Heterozygous mutations of the human telomerase RNA template gene (TERC) have been described in patients with acquired aplastic anemia and the autosomal dominant form of dyskeratosis congenita (DKC). Patients with mutations in both TERC alleles have not yet been reported. Here, we report a patient with DKC who inherited 2 distinct TERC sequence variants from her parents; a deletion (216_229del) in one and a point mutation (37A>G) in the other allele of the TERC gene. Her marrow was hypocellular and showed an abnormal clone [46, XX t(7;21)(q34;q22)]. The telomere lengths in leukocytes of the patient and her relatives were shorter than those of the age-matched controls and were progressively shorter in subsequent generations of family members with the 216_229del allele. Telomerase enzymatic levels in lymphocytes from the patient were approximately half of those measured in healthy controls. The 216_229del mutation failed to reconstitute telomerase activity in transfected cells, but, when coexpressed with the 37A>G variant, telomerase activity was only modestly suppressed. These clinical and laboratory findings support the concept that telomerase levels in human hematopoietic stem cells are tightly controlled as even moderately reduced levels result in accelerated telomere shortening and eventual marrow failure.

Mapping of a major locus that determines telomere length in humans.

Telomere length is a crucial factor for both normal chromosomal function and senescence. Mean telomere length in humans shows considerable interindividual variation and strong genetic determination. To see if a locus (or loci) affecting telomere length in humans could be mapped, we performed a quantitative-trait linkage analysis of mean leukocyte telomere-restriction-fragment (TRF) lengths, measured by Southern blotting, in 383 adult subjects comprising 258 sib pairs. Heritability of mean (+/-SE) TRF was 81.9%+/-11.8%. There was significant linkage (LOD score 3.20) of mean TRF length to a locus on chromosome 12, which explained 49% of the overall variability in mean TRF length. We present preliminary analysis of a strong candidate gene in the region, the DNA helicase DDX11. In conclusion, we report mapping of the first locus that determines mean telomere length in humans. Identification of the gene involved and elucidation of its mechanism of action could have important implications for our understanding of chromosomal assembly, telomere biology, and susceptibility to age-related diseases.

In situ analyses of genome instability in breast cancer.

Transition through telomere crisis is thought to be a crucial event in the development of most breast carcinomas. Our goal in this study was to determine where this occurs in the context of histologically defined breast cancer progression. To this end, we assessed genome instability (using fluorescence in situ hybridization) and other features associated with telomere crisis in normal ductal epithelium, usual ductal hyperplasia, ductal carcinoma in situ and invasive cancer. We modeled this process in vitro by measuring these same features in human mammary epithelial cell cultures during ZNF217-mediated transition through telomere crisis and immortalization. Taken together, the data suggest that transition through telomere crisis and immortalization in breast cancer occurs during progression from usual ductal hyperplasia to ductal carcinoma in situ.

Telomere attrition and accumulation of senescent cells in cultured human endothelial cells.

The human umbilical vein endothelial cell (HUVEC) is an important model of the human endothelium that is widely used in vascular research. HUVECs and the adult endothelium share many characteristics including progression into senescence as the cells age. Despite this, the shortening of telomeres and its relationship to the progression into senescence are poorly defined in HUVECs. In this study of several HUVEC lines we show notable consistency in their growth curves. There is a steady decline in the growth rate of HUVECs grown continually in culture and we estimate complete cessation of growth after approximately 70 population doublings. The HUVECs lose telomeric DNA at a consistent rate of 90 base pairs/population doubling and show a progressive accumulation of shortened telomeres (below 5 kilobases). This telomeric loss correlates with the accumulation of senescent HUVECs in culture as assessed by staining for beta-galactosidase activity at pH 6. Although the telomere length of a large population of cells is a relatively crude measure, we suggest that in HUVECs a mean telomere length (as measured by terminal restriction fragment length) of 5 kilobases is associated with entry into senescence. These data demonstrate the strong relationship between telomere attrition and cell senescence in HUVECs. They suggest that DNA damage and subsequent telomere attrition are likely to be key mechanisms driving the development of endothelial senescence in the pathogenesis of vascular disease.

Telomere shortening in cultured autografts of patients with burns.

In extensive third-degree burns, donor sites for conventional split thickness skin grafts are limited. In such cases, cultured epithelial (keratinocyte) grafts are prepared from small samples of the patient's own skin and expanded in tissue culture, a process that may incur very many cell divisions. Telomeres shorten with each cell division, and are markers of cellular proliferative history. We therefore measured telomere length in healed cultured epithelial autografts from four patients with burns, and noted that their telomeres were shorter than those in non-cultured skin from the same individuals, and than those in skin of healthy donors older than 80 years. Such great loss of telomeric DNA suggests that engrafted cells might have a shortened lifespan, which could have negative repercussions on the long-term viability of these grafts.