Telomere length is a critical determinant for survival in multiple myeloma

The variable clinical outcomes of Multiple Myeloma (MM) patients are incompletely defined by current prognostication tools. We examined the clinical utility of high‐resolution telomere length analysis as a prognostic marker in MM. Cohort stratification, using a previously determined length threshold for telomere dysfunction, revealed that patients with short telomeres had a significantly shorter overall survival (P < 0·0001; HR = 3·4). Multivariate modelling using forward selection identified International Staging System (ISS) stage as the most important prognostic factor, followed by age and telomere length. Importantly, each ISS prognostic subset could be further risk‐stratified according to telomere length, supporting the inclusion of this parameter as a refinement of the ISS.     

Telomere length is reset during early mammalian embryogenesis

The enzyme telomerase is active in germ cells and early embryonic development and is crucial for the maintenance of telomere length. Whereas the different length of telomeres in germ cells and somatic cells is well documented, information on telomere length regulation during embryogenesis is lacking. In this study, we demonstrate a telomere elongation program at the transition from morula to blastocyst in mice and cattle that establishes a specific telomere length set point during embryogenesis. We show that this process restores telomeres in cloned embryos derived from fibroblasts, regardless of the telomere length of donor nuclei, and that telomere elongation at this stage of embryogenesis is telomerase-dependent because it is abrogated in telomerase-deficient mice. These data demonstrate that early mammalian embryos have a telomerase-dependent genetic program that elongates telomeres to a defined length, possibly required to ensure sufficient telomere reserves for species integrity.     

Telomere length is paternally inherited and is associated with parental lifespan

Telomere length (TL) is emerging as a biomarker for aging and survival. To evaluate factors influencing this trait, we measured TL in a large homogeneous population, estimated the heritability (h(2)), and tested for parental effects on TL variation. Our sample included 356 men and 551 women, aged 18-92 years, from large Amish families. Mean TL in leukocytes was measured by quantitative PCR (mean: 6,198 +/- 1,696 bp). The h(2) of TL was 0.44 +/- 0.06 (P < 0.001), after adjusting for age, sex, and TL assay batch. As expected, TL was negatively correlated with age (r = -0.40; P < 0.001). There was no significant difference in TL between men and women, consistent with our previous findings that Amish men lived as long as Amish women. There was a stronger and positive correlation and association between TL in the offspring and paternal TL (r = 0.46, P < 0.001; beta = 0.22, P = 0.006) than offspring and maternal TL (r = 0.18, P = 0.04; beta = -0.02, P = 0.4). Furthermore, we observed a positive correlation and association between daughter's TL and paternal lifespan (r = 0.20, P < 0.001; beta = 0.21, P = 0.04), but not between daughter's TL and maternal lifespan (r = -0.01, beta = 0.04; both P = not significant). Our data, which are based on one of the largest family studies of human TL, support a link between TL and aging and lifespan and suggest a strong genetic influence, possibly via an imprinting mechanism, on TL regulation.     

Telomere length regulation in mice is linked to a novel chromosome locus

Little is known about the mechanisms that regulate species-specific telomere length, particularly in mammalian species. The genetic regulation of telomere length was therefore investigated by using two inter-fertile species of mice, which differ in their telomere length. Mus musculus (telomere length >25 kb) and Mus spretus (telomere length 5–15 kb) were used to generate F1 crosses and reciprocal backcrosses, which were then analyzed for regulation of telomere length. This analysis indicated that a dominant and trans-acting mechanism exists capable of extensive elongation of telomeres in somatic cells after fusion of parental germline cells with discrepant telomere lengths. A genome wide screen of interspecific crosses, using M. spretus as the recurrent parent, identified a 5-centimorgan region on distal chromosome 2 that predominantly controls the observed species-specific telomere length regulation. This locus is distinct from candidate genes encoding known telomere-binding proteins or telomerase components. These results demonstrate that an unidentified gene(s) mapped to distal chromosome 2 regulates telomere length in the mouse.     

Telomere length is age-dependent and reduced in monocytes of Alzheimer patients

Telomeres are regions of repetitive DNA at the end of eukaryotic chromosomes, which prevent chromosomal instability. Telomere shortening is linked to age-related disease including Alzheimer's disease (AD) and has been reported to be reduced in leukocytes of AD patients. The aim of the present study was to measure telomere length in monocytes of patients with AD or mild cognitive impairment (MCI) compared to healthy subjects. Our data show significant shorter telomere length in AD patients (6.6±0.2kb; p=0.05) compared to controls (7.3±0.2kb). Telomere length of MCI patients did not differ compared to healthy subjects (7.0±0.2kb). We observe a strong correlation between telomere length and age (p=0.01, r=-0.38), but no association between telomere length and Mini-Mental State Examination score. In conclusion, the telomere length is age-dependent in monocytes and decreased in AD patients, which could mean that the AD pathology may contribute to telomere length shortening. The high variability of telomere lengths in individuals suggests that it will not be useful as a general biomarker for AD. However, it could become a biomarker in personalized long-term monitoring of an individuals' health.     

Telomere length inversely correlates with pulse pressure and is highly familial

There is evidence that telomeres, the ends of chromosomes, serve as clocks that pace cellular aging in vitro and in vivo. In industrialized nations, pulse pressure rises with age, and it might serve as a phenotype of biological aging of the vasculature. We therefore conducted a twin study to investigate the relation between telomere length in white blood cells and pulse pressure while simultaneously assessing the role of genetic factors in determining telomere length. We measured by Southern blot analysis the mean length of the terminal restriction fragments (TRF) in white blood cells of 49 twin pairs from the Danish Twin Register and assessed the relations of blood pressure parameters with TRF. TRF length showed an inverse relation with pulse pressure. Both TRF length and pulse pressure were highly familial. We conclude that telomere length, which is under genetic control, might play a role in mechanisms that regulate pulse pressure, including vascular aging.     

rDNA array length is a major determinant of replicative lifespan in budding yeast

The complex processes and interactions that regulate aging and determine lifespan are not fully defined for any organism. Here, taking advantage of recent technological advances in studying aging in budding yeast, we discovered a previously unappreciated relationship between the number of copies of the ribosomal RNA gene present in its chromosomal array and replicative lifespan (RLS). Specifically, the chromosomal ribosomal DNA (rDNA) copy number (rDNA CN) positively correlated with RLS and this interaction explained over 70% of variability in RLS among a series of wild-type strains. In strains with low rDNA CN, SIR2 expression was attenuated and extrachromosomal rDNA circle (ERC) accumulation was increased, leading to shorter lifespan. Suppressing ERC formation by deletion of FOB1 eliminated the relationship between rDNA CN and RLS. These data suggest that previously identified rDNA CN regulatory mechanisms limit lifespan. Importantly, the RLSs of reported lifespan-enhancing mutations were significantly impacted by rDNA CN, suggesting that changes in rDNA CN might explain the magnitude of some of those reported effects. We propose that because rDNA CN is modulated by environmental, genetic, and stochastic factors, considering rDNA CN is a prerequisite for accurate interpretation of lifespan data.

Budding yeast, Saccharomyces cerevisiae, has been a foundational model organism for the study of cellular aging. Cells divide asymmetrically and the mother cell undergoes a limited number of divisions, which defines the cell’s replicative lifespan (RLS). Measuring RLS is technically challenging and only recent advances have enabled more efficient screening for lifespan-modulating factors (1–5).A number of processes, pathways, and mechanisms have been implicated in yeast aging (reviewed in ref. 6), with regulators of the ribosomal RNA gene array (rDNA) representing perhaps the best-characterized group of lifespan modulators. Proteins that act at the rDNA locus modify rDNA stability and the formation of extrachromosomal rDNA circles (ERCs), a known aging factor in S. cerevisiae (7). Sir2, the defining member of the Sirtuin family of histone deacetylases, silences the rDNA locus and suppresses formation of ERCs (8). Conversely, the protein Fob1 binds to a replication fork barrier site in the rDNA locus, decreases rDNA stability, and thus promotes the production of ERCs (9, 10). Since the accumulation of ERCs in the mother cell limits its RLS, sir2Δ and fob1Δ strains are short and long lived, respectively (8, 11).The rDNA locus is highly repetitive and dynamic. While 150 repeats are considered a normal copy number (CN) for the strain background used in this study, the number of repeats commonly ranges from 100 to 250 copies (12). And while the size of the rDNA array is relatively stable for a limited number of divisions, rDNA CN can change on a timescale faster than the estimated mutation rate (13). Thus, it may be considered a type of “contingency locus,” which is characterized by environmentally responsive genetic variation that results in distinct phenotypic outcomes (14–16).The rDNA copy number varies significantly in strains found in the wild and those used in the laboratory (12, 13, 17–19). This variation can occur spontaneously, but can also be introduced by standard laboratory DNA transformation protocols or changes in growth environment (12, 13, 20). In addition, there are Sir2- and Fob1-dependent feedback mechanisms in place by which a “normal” rDNA CN is maintained through modulation of Sir2 expression levels (21). Interestingly, rDNA array size is anticorrelated with ERC abundance in young cells, suggesting that chromosomal and extrachromosomal rDNA are in an equilibrium (13). Despite this known connection between rDNA array size and Sir2 and ERC levels, no evidence for array size impacting lifespan has been found (12, 15, 18).Yet, significant variability exists within reported lifespans of S. cerevisiae. A metastudy found that the RLS of the same wild-type strains varied between 20 and 40, depending on the study in which it was reported (22). This variability was attributed to a reporting bias and small sample sizes. However, these findings are also consistent with uncontrolled genetic or environmental factors contributing to the variability. In addition, a genome-wide screen measuring the RLS of deleted nonessential genes found a significant discrepancy between strains with opposing mating types carrying the same gene deletion (23). This discrepancy was mostly attributed to statistical error due to a low number of cells analyzed, but was not fully explored. Given this large degree of variability, which likely impacts the interpretation of any lifespan measurement, we wanted to address the underlying cause. Here we show that the chromosomal rDNA copy number is an important determinant of replicative lifespan in yeast and can explain a large part of the reported variability in lifespan.     

Telomere length in myelodysplastic syndromes

We have studied telomere length in the bone marrow cells or the granulocyte and lymphocyte cell fractions of 54 patients with myelodysplastic syndromes (MDS) by Southern blot hybridization using the (TTAGGG)₄ probe. The average telomere length expressed as the peak telomere repeat array (TRA) in the peripheral blood, or bone marrow samples obtained from a group of 21 healthy age-matched controls (26–89 years old, mean age 55), ranged between 7.5 and 9.5 kb (mean peak TRA 8.6 kb). Twenty-four patients with refractory anemia (RA) were studied; 10/24 (42%) had telomere reduction (<7.5 kb) relative to age-matched controls and the mean peak TRA was 7.5 kb (range 4.0–9.0 kb). Eleven patients with RA with excess blasts (RAEB) were studied; 5/11 (45%) had reduced telomeres relative to age-matched controls and the mean peak TRA was 7.1 kb (range 5.0–9.0 kb). Eighteen patients with MDS in transformation to AML, comprising 15 with RAEB in transformation (RAEBt) and 3 with CMML in transformation (CMMLt), were also studied. Thirteen of eighteen patients (72%) had telomere reduction relative to age-matched controls and the mean peak TRA was 6.1 kb (range 3.5–9.0 kb). Thirty-six patients included in the study had either a normal karyotype or a simple karyotype (1 karyotypic change) and 20/36 (55%) of these had telomere reduction and the mean peak TRA was 7.1 kb (range 4.3–9.0 kb); 8 patients had a complex karyotype (3 or more karyotypic changes) and 5/8 (62%) of these had telomere reduction and the mean peak TRA was 6.1 kb (range 3.5–9.0 kb). We conclude, firstly that there is heterogeneity of telomere length in MDS and that this is observed throughout the spectrum of FAB-subtypes. Secondly, these data show that a marked reduction in telomere length in MDS if often associated with leukemic transformation and with the presence of complex karyotypic abnormalities. Am. J. Hematol. 56:266–271, 1997. © 1997 Wiley-Liss, Inc.     

Telomere length study in celiac disease

OBJECTIVES: Telomeres are important structures that are critical for maintaining chromosomal integrity and cell surveillance. The aim of this study was to analyze telomere length in patients with celiac disease (CD), a multifactorial disorder with a strong genetic component that exhibits genomic instability and cancer predisposition, particularly T-cell lymphomas. METHODS: Telomere length measured by telomere restriction fragments (TRF) was studied in small intestinal biopsy (SIB) samples and peripheral blood lymphocytes (PBL) from 20 untreated CD patients, distributed according to the clinical form as four asymptomatic, five monosymptomatic, and 11 polysymptomatic individuals. We also analyzed TRF from normal peripheral blood lymphocytes and normal biopsy samples as normal controls. RESULTS: TRF evaluation showed a significant telomere shortening in SIB samples from CD patients (4.21 +/- 0.29 Kb) compared to PBL from the same individuals (9.17 +/- 0.35 Kb) (p < 0.0001), independently of clinical form. Mean TRF peak values from normal biopsy samples were significantly higher (8.33 +/- 0.38 Kb) than those observed in CD biopsy samples (p < 0.001). No differences between TRF values in CD-PBL and normal peripheral blood lymphocytes (8.89 +/- 0.37Kb) were found. CONCLUSIONS: Our findings in patients with CD, a disorder in which the gluten-induced mucosal injury could accelerate telomere shortening, would increase the process of end-to-end fusions resulting in chromosomal changes, supports the hypothesis that genomic instability and telomere reduction may play a role in the cancer predisposition observed in these patients.     

Telomere length in human liver diseases

Abstract: To determine the role of telomere-mediated gene stability in hepatocarcinogenesis, we examined the telomere length of human liver with or without chronic liver diseases and hepatocellular carcinomas (HCC). The mean telomere restriction fragment (TRF) length of normal liver (n=13), chronic hepatitis (n=11), liver cirrhosis (n=24) and HCC (n=24) was 7.8±0.2, 7.1±0.3, 6.4±0.2 and 5.2±0.2 kb, respectively (mean±standard error). TRF length decreased with a progression of chronic liver diseases and that in HCC was significantly shorter than that in other chronic liver diseases (p<0.05). The ratios of TRF length of HCC to that of corresponding surrounding liver of well differentiated (n=7), moderately differentiated (n=10) and poorly differentiated (n=4) HCCs were 0.83±0.06, 0.75±0.05 and 0.98±0.09, respectively. The ratio of poorly differentiated HCC was significantly higher than that of moderately differentiated HCC (p<0.05). A comparison between the size and telomere length ratio of moderately differentiated HCCs revealed a decrease of the ratio with size until it reached 50 mm in diameter. In contrast, the ratio increased as the size enlarged over 50 mm. These findings suggest that the gene stability of the liver cells mediated by the telomere is reduced as chronic liver disease progresses and that telomerase is activated in poorly differentiated HCC and moderately differentiated HCC over 50 mm in diameter.     

Telomere length shortening is associated with disease evolution in chronic myelogenous leukemia.

We studied telomere length in the peripheral blood leukocyte samples of a large group of patients with chronic myelogenous leukemia (CML) by Southern blot hybridization using the (TTAGGG)4 probe. The average telomere length expressed as the peak telomere repeat array (TRA) of the peripheral blood samples obtained from a group of 34 healthy age-matched controls ranged between 7.6 and 10.0 kb and the mean peak TRA was 8.7 kb. Forty-one patients in the chronic phase of CML were studied; 32/41 (78%) showed telomere reduction (<7.6 kb) relative to age-matched controls and the mean peak TRA was 6.4 kb (range 4.0-10.6 kb). Serial samples were analysed from 12 patients at both chronic phase and during disease progression. The leukocyte DNA of all 12 patients in accelerated phase and/or blast crisis showed telomere reduction relative to age-matched controls and the mean peak TRA was 4.1 kb (range 3.0-5.4 kb). The peak TRA in the accelerated or blast phase was reduced compared with the corresponding paired sample in the chronic phase in all cases studied. These data show that a marked reduction in telomere length is associated with disease progression in CML.     

The brain-specific factor FEZ1 is a determinant of neuronal susceptibility to HIV-1 infection

Neurons are one of the few cell types in the human body that do not support HIV type-1 (HIV-1) replication. Although the lack of key receptors is a major obstacle to infection, studies suggest that additional functions inhibit virus replication to explain the exquisite resistance of neurons to HIV-1. However, specific neuronal factors that may explain this resistance remain to be discovered. In a screen for antiviral factors using a fibroblast line chemically mutagenized and selected for resistance to retroviral infection, we recently identified induction of rat FEZ1 (fasciculation and elongation protein zeta-1), a brain-specific protein, as the cause of this resistance. When exogenously expressed in nonneuronal cell lines rat FEZ1 blocked nuclear entry of retroviral DNA. Here, we demonstrate that among human brain cells, neurons naturally express high levels of FEZ1 compared to astrocytes or microglia cells and are correspondingly less susceptible to infection with pseudotyped HIV-1 that bypasses receptor-mediated viral entry. Demonstrating that endogenous FEZ1 was functionally important in the resistance of neurons to HIV-1 infection, siRNA-mediated knockdown of endogenous FEZ1 increased the infectivity of neurons while sensitive brain cell types like microglia became more resistant upon FEZ1 overexpression. In addition, FEZ1 expression was not induced in response to IFN treatment. As such, in contrast to other widely expressed, IFN-inducible antiviral factors, FEZ1 appears to represent a unique neuron-specific determinant of cellular susceptibility to infection in a cell type that is naturally resistant to HIV-1.The brain is a major target organ for HIV-1 infection. HIV-1 enters the central nervous system (CNS) in ≈80% of infected individuals early after infection and can cause a wide range of neurological disorders including cognitive motor impairment and HIV-associated dementia (HAD; also known as AIDS dementia complex) (1). Although the incidence of HAD has markedly reduced with the introduction of highly active antiretroviral therapy (HAART), the overall prevalence of HAD is rising as the number of treated subjects with chronic HIV infection increases (1). Notably, HIV-1 infects a restricted number of cell types in the brain. While perivascular macrophages and microglia appear to be the major target cells of the CNS for the virus, HIV-1 is less abundant in astrocytes and rarely seen in oligodendrocytes, brain microvascular endothelia cells (BMVECs) and neurons (1), although recent reports have suggested that neuronal progenitor brain cells can be infected with HIV-1 (2, 3). The block to viral infection is at least in part at the receptor level as, in contrast to both macrophages and microglia cells, the major receptor for HIV-1 entry, CD4 is not expressed in astrocytes, oligodendrocytes, BMVECs, or neuronal cells. Although still not clear today, the limited infection in astrocytes has been linked to inefficient entry of HIV by endocytosis (4, 5) as highly productive infection can be detected using viruses pseudotyed with envelope glycoproteins of either vesicular stomatitis virus (VSV-G) or amphotropic murine leukemia virus (MuLV), which efficiently enter CD4-negative cells (6, 7). On the other hand, an unidentified intrinsic intracellular restriction to efficient HIV-1 replication has been shown in astrocytes in which a cytoplasmic activity interferes with nuclear uptake of the nucleoplasmic shuttle protein Rev (8, 9). Additionally, APOBEC3G-mediated intrinsic immunity has also been suggested to block HIV-1 replication in the CNS (10–12). Therefore, regardless of the route of entry there are likely to be additional postentry blocks to infection in brain cell types that do not support HIV-1 infection, particularly in highly restrictive cell types such as neurons.In an attempt to discover cellular genes with antiviral activity, we recently screened the rat fibroblast line R3–2 (13), generated by chemical mutagenesis and selection for resistance to retroviral infection, and identified the causal factor as the brain specific protein FEZ1 (14). A mammalian homolog of the Caenorhabditis elegans UNC −76 protein, FEZ1 is a direct target of protein kinase C (PKC)ζ-dependent signaling (15) and a microtubule motor associated-protein (16) essential for synaptic vesicle transport and axonal outgrowth (17, 18). We showed that expression of rat FEZ1 blocked nuclear entry of retroviral DNA in various mammalian cells (14), suggesting that it functioned in the intracellular transport of viral cargos into the nucleus. In support of these findings the interaction of FEZ1 with microtubules was recently shown to promote neurite extension and block intracellular trafficking of the human polyomavirus JC virus (JCV) (19). Although FEZ1 is extensively expressed in the brain (17, 20) and in situ hybridization suggests that it may be preferentially expressed in neurons of the developing rat brain (21) there has been little comparative analysis of its'' expression in different brain cell types. Here, we determined the expression of FEZ1 in neurons, astrocytes, and microglia and examined its potential function as a natural determinant of neuronal susceptibility to HIV-1 infection.     

Telomere length is key to hepatocellular carcinoma diversity and telomerase addiction is an actionable therapeutic target

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Telomere length of circulating leukocytes is decreased in patients with chronic heart failure.

OBJECTIVES: This study sought to test the hypothesis that patients with chronic heart failure (CHF) have shorter telomeres compared with age-balanced and gender-balanced healthy individuals. BACKGROUND: Telomere length is considered to be a marker of biological aging. Chronic heart failure might be viewed as a condition associated with accelerated biological aging. METHODS: The telomere length ratio of leukocytes was determined prospectively by a quantitative polymerase chain reaction-based method in a case-control setting involving 803 participants: 183 healthy individuals and 620 CHF patients, ages 40 to 80 years, New York Heart Association functional class II to IV, and left ventricular ejection fraction of 0.40 or less. RESULTS: The median telomere length ratio was 0.64 (interquartile range [IQR] 0.47 to 0.88) in CHF patients compared with 1.05 (IQR 0.86 to 1.29) in control patients (p < 0.001). The telomere length ratio in CHF patients related to severity of disease (median value [IQR] of patients with New York Heart Association class II, III, or IV function was 0.67 [0.48 to 0.92], 0.63 [0.46 to 0.86], and 0.55 [0.46 to 0.75], respectively; p for trend <0.05). In addition, telomeres were shorter in patients with an ischemic compared with a nonischemic etiology of CHF. Patients with none, 1 (coronary, cerebral, or peripheral vascular disease), 2 (any combination of the previous), or 3 atherosclerotic manifestations had a median (IQR) telomere length of 0.72 (0.51 to 1.01), 0.65 (0.48 to 0.87), 0.48 (0.39 to 0.72), and 0.43 (0.27 to 0.67), respectively (p for trend <0.001). CONCLUSIONS: Telomere length is shorter in patients with CHF compared with age-balanced and gender-balanced control patients, and related to the severity of disease. In addition, telomere length was incrementally shorter according to the presence and extent of atherosclerotic disease manifestations.