Loss Of Telomere Length Research Articles

Short Telomeres in Hatchling Snakes: Erythrocyte Telomere Dynamics and Longevity in Tropical Pythons

BackgroundTelomere length (TL) has been found to be associated with life span in birds and humans. However, other studies have demonstrated that TL does not affect survival among old humans. Furthermore, replicative senescence has been shown to be induced by changes in the protected status of the telomeres rather than the loss of TL. In the present study we explore whether age- and sex-specific telomere dynamics affect life span in a long-lived snake, the water python (Liasis fuscus).Methodology/Principal FindingsErythrocyte TL was measured using the Telo TAGGG TL Assay Kit (Roche). In contrast to other vertebrates, TL of hatchling pythons was significantly shorter than that of older snakes. However, during their first year of life hatchling TL increased substantially. While TL of older snakes decreased with age, we did not observe any correlation between TL and age in cross-sectional sampling. In older snakes, female TL was longer than that of males. When using recapture as a proxy for survival, our results do not support that longer telomeres resulted in an increased water python survival/longevity.Conclusions/SignificanceIn fish high telomerase activity has been observed in somatic cells exhibiting high proliferation rates. Hatchling pythons show similar high somatic cell proliferation rates. Thus, the increase in TL of this group may have been caused by increased telomerase activity. In older humans female TL is longer than that of males. This has been suggested to be caused by high estrogen levels that stimulate increased telomerase activity. Thus, high estrogen levels may also have caused the longer telomeres in female pythons. The lack of correlation between TL and age among old snakes and the fact that longer telomeres did not appear to affect python survival do not support that erythrocyte telomere dynamics has a major impact on water python longevity.

Genetic association study of selected candidate genes (ApoB, LPL, Leptin) and telomere length in obese and hypertensive individuals

BackgroundA genetic study was carried out among obese and hypertensive individuals from India to assess allelic association, if any, at three candidate loci: Apolipoprotein B (ApoB) minisatellite and two tetranucleotide repeat loci; LPL (Lipoprotein lipase) and Leptin. Attempt has also been made to find out whether telomere length attrition is associated with hypertension and obese individuals.MethodsVenous blood samples were collected from 37 normal, 35 obese and 47 hypertensive individuals. Genomic DNA was extracted from peripheral blood mononuclear cells (PBMC) and PCR amplifications were achieved using locus specific primers. Genotyping of ApoB minisatellite was performed using 4% polyacrylamide gel electrophoresis (PAGE) followed by silver staining, whereas LPL and Leptin loci were genotyped using ALF Express™ DNA sequencer. Telomere length was determined using a recently developed real time based quantitative PCR, where the relative telomere length was determined by calculating the relative ratio of telomere (T) and single copy gene (S) PCR products which is expressed as T/S ratio.ResultsAll the three loci are highly polymorphic, display high heterozygosity and conform to Hardy-Weinberg's equilibrium expectations. ApoB minisatellite displayed 14 alleles, whereas LPL and Leptin tetranucleotide loci were having 9 and 17 alleles, respectively. Interestingly two new alleles (9 and 11 repeats) were detected at ApoB locus for the first time. The alleles at Leptin locus were classified as Class I (lower alleles: 149-200 bp) and Class II alleles (higher alleles: >217 bp). Higher alleles at ApoB (>39 repeats), predominant allele 9 at LPL and alleles 164 bp and 224 bp at Leptin loci have shown allelic association with hypertensive individuals. After adjusting the influence of age and gender, the analysis of co-variance (ANCOVA) revealed the relative telomere length (T/S ratio) in hypertensive individuals to be (1.01 ± 0.021), which was significantly different (P < 0.001) from obese (1.20 ± 0.023) and normal (1.22 ± 0.014) individuals. However, no significant difference in the relative telomere length was observed among male and female individuals, although age related decrease in telomere length was observed in these limited sample size.ConclusionThe present study revealed that allelic association at ApoB, LPL, Leptin loci and loss of telomere length may have strong genetic association with hypertensive individuals. However, further study on larger sample size is needed to draw firm conclusions.

Telomere Disfunction Is Not An Early Genetic Event in Adult T-Cell Leukemia/Lymphoma

Adult T-cell leukemia/lymphoma (ATL) is a mature T-cell neoplasm of post-thymic lymphocytes linked to human T-cell lymphotropic virus type I (HTLV-I). ATL develops in 3–5% of HTLV-I carriers after a long period of clinical latency and presents chromosomes abnormalities resulting in aneuploidy usually seem in telomere dysfunction disease. We were interested whether the abnormalities of the telomere regulation in ATL and if its abnormalities are correlated with ATL pathogenesis. The telomere length of TCD4 and TCD8 lymphocytes in samples from HTLV-I carriers (n= 52) with median age of 49.5 years (18–71 years) and ATL patients (n= 6) with median of 39 years (18–59 years) were assessed by fluorescence in situ hybridization and flow cytometry (Flow-FISH) and compared with healthy subjects (n = 58) matched for gender and age. We did not detected significant difference the telomere length of the TCD4 and TCD8 lymphocytes between HTLV-I carriers and health subjects. However we showed an accentuated loss in telomere length of the malignant T lymphocyte in ATL disease and values closed to those ageexpected in non-malignant T lymphocyte in ATL disease. We concluded that these results do not support a major role of telomere disfunction as an early event in pathogenesis of the ATL.

Premature Aging of Hematopoietic Cells in Long Term Survivors after HSCT with Chronic GVHD and a Female Donor.

The establishment of donor-derived hematopoiesis in recipients of hematopoietic stem cell (HSC) transplantation (HSCT) involves extensive proliferation of HSCs and might lead to “premature aging” of hematopoietic cells. Telomere shortening as indicator of cell proliferation has been described after HSCT. The telomere attrition has mainly been observed during the first year after allogeneic HSCT. Thereafter, telomere length dynamics of recipients appeared not to differ from their donors. The aim of our cross-sectional study was to evaluate the telomere attrition in leukocyte subsets of very long term survivors (LTS) after HSCT in relation to donor/recipient age, sex, cell counts in peripheral blood, number of transplanted nucleated cells (NTNC), and occurrence of acute and chronic graft versus host disease (GVHD). Automated multicolour flow-FISH was used to measure the telomere length in granulocytes, naive T-cells, B-cells and NK/NKT-cells of 44 LTS and their HLA-identical sibling donors. At HSCT the median age of donors and recipients was 25.8 (2–46) and 26.8 years (5–50). The median follow-up after HSCT was 17.5 years (11–26). Four patients received HSCT for aplastic anemia, 40 for hematological malignancies. All patients received bone marrow as source of HSC and TBI was part of the conditioning in 39 (89%). Acute GVHD was observed in 31 (70%), and chronic GVHD in 22 (50%) patients. The age-matched and cell-type specific absolute telomere length values for recipients and donors fell between the 1st-99th percentile of the normal distribution. The telomere length (mean ± std) was significantly shorter in recipients as compared to their donors (p<0.01) for granulocytes (6.5±0.9 vs 7.1±0.9), T-cells (5.7±1.2 vs 6.6±1.2), B-cells (7.1±1.1 vs 7.8±1.1) and NK/NKT-cells (4.8±1.0 vs 5.6±1.3). The mean difference between recipients and donors for each subset of cells was between 0.6–0.9 kb. The mean telomere length of all subsets of cells was significantly shorter for males compared to females even though this difference was small. Age, sex of recipient, NTNC, and acute GVHD had no impact on telomere attrition. In all cell types except NK/NKT-cells we found a significant telomere shortening in recipients transplanted with a female donor (p<0.04) and in those with chronic GVHD (p<0.04). The telomere length difference between donor/recipient was most pronounced for recipients with the combination of a female donor and chronic GVHD (Figure 1). The loss in telomere length is more than twice for patients with a female donor and chronic GVHD compared to those with a male donor without chronic GVHD. In summary, our data reveal chronic GVHD and a female donor to be predictors for higher telomere attrition in LTS after HSCT. The more pronounced telomere attrition with a female donor and chronic GVHD corresponds to approximately 30–60 years of cell aging and raises once more the question of cellular immuno-senescence and its consequences in LTS of HSCT. [Display omitted]

The Degree of Telomere Loss in Hematopoietic Cells Correlates with the Risk of Secondary Myelodysplasia/Acute Leukemia Development Following Autologous Stem Cell Transplantation.

Introduction: Secondary myelodysplastic syndrome and acute myelogenous leukemia (sMDS/AML) may occur following autologous stem cell transplantation (ASCT). The molecular pathogenesis of sMDS/AML is uncertain; moreover, no suitable indicators able to define the risk of sMDS/AML development have been identified so far. A marked though variable telomere loss has been observed in hematopoietic cells following ASCT; meanwhile, shortening of telomere length has been observed to be associated with several neoplasias, including haematological malignancies. Thus, telomere dynamics has been investigated in a series of patients who received ASCT, in order to verify whether the degree of telomere loss in hematopoietic cells might be associated with the risk of sMDS/AML development.Methods: Telomere length (TL) was retrospectively evaluated in bone marrow (BM) cells from 38 lymphoma patients (M/F=24/14; median age=51 years, range 24–68) long-term survivors following ASCT and from 51 healthy donors (M/F=31/20; median age=53 years, range 18–82). Median follow-up since ASCT was 6 years (range 1–10). All patients were in continuous complete remission and displayed normal haematological values at the time of TL assessment. Among 38 autografted patients, 7 developed sMDS/AML (3 AML, 3 sMDS, 1 persistent pancitopenia with cytogenetic abnormalities), at a median of 5 years (range 1–10) following transplant. There were no significant differences in terms of demographical and clinical features not even for the amount of CD34+ve cells reinfused (median values: 5.2 vs 6.8 × 106 CD34+ cells/kg, respectively), between patients developing sMDS/AML and the remaining autografted patients. Samples for TL analysis were obtained and stored at a median of 12 months (range 6–24) before clinical development of sMDS/AML. TL was evaluated by Southern blot analysis.Results: TL of autografted patients was found to be significantly shorter compared to that of age-matched healthy donors, consistently with previous reports (see Figure 1, squares=healthy controls, circles=autografted subjects). A further TL loss was observed in all the 7 patients who subsequently developed sMDS/AML; their TL (Figure 1, black circles) was significantly shorter compared to both healthy subjects and sMDS/AML-free autografted patients (Figure 1, grey circles) (p<0.0005 and p<0.01, respectively).Conclusions. A marked telomere loss seems to be a predictive marker of the development of sMDS/AML following ASCT; TL analysis can now be considered among follow-up assays, in order to early identify patients at high-risk of sMDS/AML occurrence following autograft. [Display omitted]

Prolonged exposure of naïve CD8+ T cells to interleukin‐7 or interleukin‐15 stimulates proliferation without differentiation or loss of telomere length

Interleukin (IL)-7 and IL-15 are cytokines implicated in homeostatic control of the peripheral CD8 T-cell pool. We compared the effects of IL-7 and IL-15 on survival and proliferation of purified human CD8+ T-cell subsets. Low concentrations of either cytokine reduced the spontaneous apoptosis of all subsets, and enhancement of survival corresponded to the extent of Bcl-2 up-regulation. Surprisingly, although minimal proliferation of naïve CD8+ T cells was observed during the first week of culture with cytokines, a marked expansion of these cells occurred at later time points, particularly in response to IL-15. This occurred largely without phenotypic change or acquisition of effector function, indicating a dissociation of differentiation from proliferation. Notably, progression of naïve CD8+ T cells through several cell divisions resulted in up-regulation of telomerase and the maintenance of telomere length. These data show that IL-7 and IL-15 induce cell proliferation and rescue from apoptosis in a concentration, time and subset-dependent manner, and have implications for the homeostatic expansion of the naïve CD8+ T-cell pool.

Evaluation of telomerase in non-melanoma skin cancer.

Telomerase, a ribonucleoprotein, is capable of adding telomeric sequences (TTAGGG hexameric repeats) to the ends of chromosomes and, thereby, halting the erosion of chromosome at each cell division. Whereas most normal somatic cells contain minimal or no detectable telomerase activity, most immortal and tumour cells exhibit significant levels of telomerase activity and show no net loss of telomere length during proliferation. The evaluation of telomerase has been proposed for diagnostic and therapeutic purposes in human cancer. Skin cancer is the most common cancer in humans; the precise molecular events in skin carcinogenesis are numerous and complicated and not yet completely clarified. In this study, we evaluated telomerase in 35 basal cell carcinomas and in 14 squamous cell carcinomas in order to determine if activation of the telomerase enzyme was a pivotal step in the development of skin cancer and whether telomerase activity levels were different between the two histotypes. A higher enzymatic level was shown to be associated with squamous cell carcinomas, while low levels were mainly detected in the basal cell histotype (chi2 test; p=0.02). Telomerase complex activity is dependent on its catalytic subunit, telomerase reverse transcriptase hTERT. By reverse transcription-PCR, using primers within the reverse transcriptase domain of hTERT, we observed a significant correlation between hTERT expression and telomerase activity in our skin tumour samples (p=0.0003). We detected the presence of multiple, alternately spliced transcripts, corresponding to full-length messages as well as spliced messages with critical reverse transcriptase motifs deleted. A higher telomerase messenger level was shown to be associated with squamous cell carcinomas (chi2 test; p<0.0001), as for telomerase activity. Our results provide arguments supporting the role of telomerase in skin cancer and suggest RT-PCR of telomerase RNA as a tool easier and faster than TRAP assay to identify more aggressive malignancies among non-melanoma skin specimens.

Decrease of telomere length in thyroid adenomas without telomerase activity.

In somatic cells, telomeres shorten with population doubling, thus limiting their capacity to divide. Telomerase, which synthesizes telomeric repeats, can compensate for such shortening. Telomerase activity is known to be absent from most somatic differentiated cells but is present in germline cells, immortal cell lines, or a large majority of malignant tumors. Autonomous thyroid adenomas are benign tumors composed of highly differentiated cells characterized by TSH-independent function and growth. Telomere length and telomerase activity were measured in autonomous and hypofunctioning adenomas and their surrounding tissues. A significant decrease of 3.8+/-1.0 kilobases (kb) was observed in the length of the terminal restriction fragments (TRF) in 12 autonomous adenomas (8.6+/-1.1 kb), compared with the TRF length of their surrounding tissues (12.4+/-1.6 kb). The same kind of decrease, 3.5+/-1.2 kb, was also observed in 16 hypofunctioning adenomas (12.3+/-1.7 kb in surrounding tissue and 8.8+/-1.6 kb in the adenomas). No telomerase activity was detected either in the 12 autonomous adenomas studied or in most of the quiescent tissues (10 of 12). Most of the hypofunctioning adenomas tested (15 of 16) did not display telomerase activity. These results suggest that the cells have undergone a higher number of cell divisions in the adenomas than in the surrounding tissue. Moreover, there is a larger spread of the TRF length distribution in autonomous adenomas than in the collateral tissue. This could reflect the heterogeneity in proliferation status of the cells in the nodule, some of which have reached the end of their life span, whereas others are still proliferating (but with no malignant potential for the autonomous adenomas). In conclusion, benign adenomas exhibit a shorter and more variable telomere length than the normal collateral quiescent tissue, with no telomerase activity to compensate this loss in telomere length.