Telomere length analysis in monocytes and lymphocytes from patients with systemic lupus erythematosus using multi-color flow-FISH

Telomere length and its association with systemic lupus erythematosus in an Asian population: A Mendelian randomization study

OBJECTIVES

To investigate whether shorter telomere length is a causal risk factor for systemic lupus erythematosus (SLE) in the Asian population.

METHODS

We applied the two-sample Mendelian randomization (MR) method to the pooled statistics from a genome-wide association study (GWAS) of 6,707 SLE cases and 16,047 controls. We selected nine single-nucleotide polymorphisms (SNPs) with genome-wide significance as instrumental variables for telomere length. The main analysis was carried out by the random-effects inverse-variance weighted (IVW) method. Horizontal pleiotropy was evaluated by the intercept of MR-Egger regression.

RESULTS

A potentially causal relationship between longer genetically predicted telomere length and increased risk of systemic lupus erythematosus (OR = 1.72, 95%CI: 1.21, 2.46, p = 0.01) was observed. The MR-Egger regression demonstrated an intercept proximal to zero (intercept = 0.017, p = 0.69), which does not provide evidence of the presence of horizontal pleiotropy.

CONCLUSIONS

Our findings provided evidence supporting a potential causal relationship between longer telomere length and increased risk of systemic lupus erythematosus.

Mendelian randomization as a tool to gain insights into the mosaic causes of autoimmune diseases

Autoimmune diseases (ADs) are a broad range of disorders which are characterized by long-term inflammation and tissue damage arising from an immune response against one's own tissues. It is now widely accepted that the causes of ADs include environmental factors, genetic susceptibility and immune dysregulation. However, the exact etiology of ADs has not been fully elucidated to date. Because observational studies are plagued by confounding factors and reverse causality, no firm conclusions can be drawn about the etiology of ADs. Over the years, Mendelian randomization (MR) analysis has come into focus, offering unique perspectives and insights into the etiology of ADs and promising the discovery of potential therapeutic interventions. In MR analysis, genetic variation (alleles are randomly dispensed during meiosis, usually irrespective of environmental or lifestyle factors) is used instead of modifiable exposure to explore the link between exposure factors and disease or other outcomes. Therefore, MR analysis can provide a valuable method for exploring the causal relationship between different risk factors and ADs when its inherent assumptions and limitations are fully considered. This review summarized the recent findings of MR in major ADs, including systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), multiple sclerosis (MS), and type 1 diabetes mellitus (T1DM), focused on the effects of different risk factors on ADs risks. In addition, we also discussed the opportunities and challenges of MR methods in ADs research.

Telomere dysfunction promotes small vessel vasculitis via the LL37-NETs-dependent mechanism

Background

Small vessel vasculitis (SVV) is a group of systemic autoimmune diseases that are mediated by neutrophil extracellular traps (NETs) in response to cathelicidin LL37, an aging molecular marker, which could be induced by telomere dysfunction. Therefore, in this study, we evaluated the hypothesis that telomere dysfunction in neutrophils may promote SVV via an LL37-NETs-dependent mechanism.

Methods

We contrasted the release of neutrophil NETs from mice with telomere dysfunction, mice with DNA damage and wide-type mice. Neutrophil telomere length, the expression of LL37, and the formation of NETs were measured in SVV patients and healthy controls (HCs). The co-expression of γH2AX, LL37, and NETs were detected in SVV patients to evaluate the association of the immune aging of neutrophils and pro-inflammatory conditions. LL37 inhibitor was used to verify its key role in NETs release in SVV patients and DNA damage mice.

Results

We found that NETs were over-induced by telomere dysfunction and DNA damage in mice, which may be associated with a marked increase in LL37. For patients with SVV, telomeres in neutrophils were significantly shortened, which was also associated with higher levels of LL37 and NETs. Inhibition of LL37 reduced the NETs released from neutrophils.

Conclusions

Taken together, the results of these studies suggest that dysfunction of telomeres may promote SVV through the mechanism of LL37-dependent NETs. Thus, targeting the LL37-NETs may be a novel therapy for SVV.

Telomeres, Telomerase and Ageing

Telomeres are specialised structures at the end of linear chromosomes. They consist of tandem repeats of the hexanucleotide sequence TTAGGG, as well as a protein complex called shelterin. Together, they form a protective loop structure against chromosome fusion and degradation. Shortening or damage to telomeres and opening of the loop induce an uncapped state that triggers a DNA damage response resulting in senescence or apoptosis.Average telomere length, usually measured in human blood lymphocytes, was thought to be a biomarker for ageing, survival and mortality. However, it becomes obvious that regulation of telomere length is very complex and involves multiple processes. For example, the "end replication problem" during DNA replication as well as oxidative stress are responsible for the shortening of telomeres. In contrast, telomerase activity can potentially counteract telomere shortening when it is able to access and interact with telomeres. However, while highly active during development and in cancer cells, the enzyme is down-regulated in most human somatic cells with a few exceptions such as human lymphocytes. In addition, telomeres can be transcribed, and the transcription products called TERRA are involved in telomere length regulation.Thus, telomere length and their integrity are regulated at many different levels, and we only start to understand this process under conditions of increased oxidative stress, inflammation and during diseases as well as the ageing process.This chapter aims to describe our current state of knowledge on telomeres and telomerase and their regulation in order to better understand their role for the ageing process.

Telomere shortening correlates with leukemic stem cell burden at diagnosis of chronic myeloid leukemia

Telomere length (TL) in peripheral blood (PB) cells of patients with chronic myeloid leukemia (CML) has been shown to correlate with disease stage, prognostic scores, response to therapy, and disease progression. However, due to considerable genetic interindividual variability, TL varies substantially between individuals, limiting its use as a robust prognostic marker in individual patients. Here, we compared TL of BCR-ABL^-, nonleukemic CD34⁺CD38^- hematopoietic stem cells (HSC) in the bone marrow of CML patients at diagnosis to their individual BCR-ABL⁺ leukemic stem cell (LSC) counterparts. We observed significantly accelerated telomere shortening in LSC compared with nonleukemic HSC. Interestingly, the degree of LSC telomere shortening was found to correlate significantly with the leukemic clone size. To validate the diagnostic value of nonleukemic cells as internal controls and to rule out effects of tyrosine kinase inhibitor (TKI) treatment on these nontarget cells, we prospectively assessed TL in 134 PB samples collected in deep molecular remission after TKI treatment within the EURO-SKI study (NCT01596114). Here, no significant telomere shortening was observed in granulocytes compared with an age-adjusted control cohort. In conclusion, this study provides proof of principle for accelerated telomere shortening in LSC as opposed to HSC in CML patients at diagnosis. The fact that the degree of telomere shortening correlates with leukemic clone's size supports the use of TL in leukemic cells as a prognostic parameter pending prospective validation. TL in nonleukemic myeloid cells seems unaffected even by long-term TKI treatment arguing against a reduction of telomere-mediated replicative reserve in normal hematopoiesis under TKI treatment.

Assessment of Telomere Length, Phenotype, and DNA Content

Telomere sequences at the end of chromosomes control somatic cell division; therefore, telomere length in a given cell population provides information about its replication potential. This unit describes a method for flow cytometric measurement of telomere length in subpopulations using fluorescence in situ hybridization of fluorescently-labeled probes (Flow-FISH) without prior cell separation. After cells are stained for surface immunofluorescence, antigen-antibody complexes are covalently cross-linked onto cell membranes before FISH with a telomere-specific probe. Cells with long telomeres are included as internal standards. Addition of a DNA dye permits exclusion of proliferating cells during data analysis. DNA ploidy measurements of cells of interest and internal standard are performed on separate aliquots in parallel to Flow-FISH. Telomere fluorescence of G0/1 cells of subpopulations and internal standards obtained from Flow-FISH are normalized for DNA ploidy, and telomere length in subsets of interest is expressed as a fraction of the internal standard telomere length. © 2017 by John Wiley & Sons, Inc.

Association between shortened telomere length and systemic lupus erythematosus: a meta-analysis

Objective We aimed to evaluate the relationship between telomere length and systemic lupus erythematosus (SLE). Methods PUBMED and EMBASE databases were searched; meta-analyses were performed comparing telomere length in SLE patients and healthy controls, and on SLE patients in subgroups based on ethnicity, sample type, assay method and data type. Results Eight studies including 472 SLE patients and 365 controls were ultimately selected which showed that telomere length was significantly shorter in the SLE group than in the control group (standardized mean difference (SMD) = -0.835, 95% confidence interval (CI) = -1.291 to -0.380, p = 3.3 × 10^-4). Stratification by ethnicity showed significantly shortened telomere length in the SLE group in Caucasian, Asian and mixed populations (SMD = -0.455, 95% CI = -0.763 to -0.147, p = 0.004; SMD = -0.887, 95% CI = -1.261 to -0.513, p = 3.4 × 10^-4; SMD = -0.535, 95% CI = -0.923 to -0.147, p = 0.007; respectively). Furthermore, telomere length was significantly shorter in the SLE group than in the control group in whole blood and peripheral blood mononuclear cell groups (SMD = -0.361, 95% CI = -0.553 to -0.169, p = 2.3 × 10^-4; SMD = -1.546, 95% CI = -2.583 to -0.510, p = 0.003; respectively); a similar trend was observed in leukocyte groups (SMD = -0.699, 95% CI = -1.511 to -0.114, p = 0.092). Meta-analyses based on assay method or data type revealed similar associations. Conclusions Our meta-analysis demonstrated that telomere length was significantly shorter in patients with SLE, regardless of ethnicity, sample type or assay method evaluated.

Rps14 haploinsufficiency causes a block in erythroid differentiation mediated by S100A8 and S100A9

Impaired erythropoiesis in the deletion 5q (del(5q)) subtype of myelodysplastic syndrome (MDS) has been linked to heterozygous deletion of RPS14, which encodes the ribosomal protein small subunit 14. We generated mice with conditional inactivation of Rps14 and demonstrated an erythroid differentiation defect that is dependent on the tumor suppressor protein p53 (encoded by Trp53 in mice) and is characterized by apoptosis at the transition from polychromatic to orthochromatic erythroblasts. This defect resulted in age-dependent progressive anemia, megakaryocyte dysplasia and loss of hematopoietic stem cell (HSC) quiescence. As assessed by quantitative proteomics, mutant erythroblasts expressed higher levels of proteins involved in innate immune signaling, notably the heterodimeric S100 calcium-binding proteins S100a8 and S100a9. S100a8--whose expression was increased in mutant erythroblasts, monocytes and macrophages--is functionally involved in the erythroid defect caused by the Rps14 deletion, as addition of recombinant S100a8 was sufficient to induce a differentiation defect in wild-type erythroid cells, and genetic inactivation of S100a8 expression rescued the erythroid differentiation defect of Rps14-haploinsufficient HSCs. Our data link Rps14 haploinsufficiency in del(5q) MDS to activation of the innate immune system and induction of S100A8-S100A9 expression, leading to a p53-dependent erythroid differentiation defect.

Ageing and the telomere connection: An intimate relationship with inflammation

Telomeres are the heterochromatic repeat regions at the ends of eukaryotic chromosomes, whose length is considered to be a determinant of biological ageing. Normal ageing itself is associated with telomere shortening. Here, critically short telomeres trigger senescence and eventually cell death. This shortening rate may be further increased by inflammation and oxidative stress and thus affect the ageing process. Apart from shortened or dysfunctional telomeres, cells undergoing senescence are also associated with hyperactivity of the transcription factor NF-κB and overexpression of inflammatory cytokines such as TNF-α, IL-6, and IFN-γ in circulating macrophages. Interestingly, telomerase, a reverse transcriptase that elongates telomeres, is involved in modulating NF-κB activity. Furthermore, inflammation and oxidative stress are implicated as pre-disease mechanisms for chronic diseases of ageing such as neurodegenerative diseases, cardiovascular disease, and cancer. To date, inflammation and telomere shortening have mostly been studied individually in terms of ageing and the associated disease phenotype. However, the interdependent nature of the two demands a more synergistic approach in understanding the ageing process itself and for developing new therapeutic approaches. In this review, we aim to summarize the intricate association between the various inflammatory molecules and telomeres that together contribute to the ageing process and related diseases.

Shortened telomere length in patients with systemic lupus erythematosus

OBJECTIVE

Patients with systemic lupus erythematosus (SLE) have a higher rate of premature death compared to the general population, suggesting a phenotype of premature senescence in SLE. Telomere length can be used to assess overall biologic aging. This study was undertaken to address the hypothesis that patients with SLE have reduced telomere length.

METHODS

Telomere length was measured cross-sectionally in whole blood from SLE patients and age-matched healthy female controls, using real-time quantitative polymerase chain reaction. SLE-related and cardiovascular risk factors were assessed.

RESULTS

We compared telomere length in 63 SLE patients and 63 matched controls with a median age of 50.8 years (interquartile range [IQR] 37-59 years) and 49.9 years (IQR 32-60 years), respectively. The median relative telomere length in SLE patients was 0.97 (IQR 0.47-1.57), compared to 1.53 (IQR 0.82-2.29) in controls (P = 0.0008). We then extended our cohort to measure telomere length in 164 SLE patients. Shorter telomere length was associated with Ro antibodies (β ± SE -0.36 ± 0.16; P = 0.023), and longer telomere length was associated with steroid therapy (0.29 ± 0.14; P = 0.046). We also noted an association of longer telomere length with increasing body mass index (β ± SE 0.07 ± 0.01; P < 0.0001) and tobacco smoking (0.64 ± 0.26; P = 0.016), as well as with the presence of carotid plaque (0.203 ± 0.177; P = 0.032).

CONCLUSION

Telomere length is shortened in SLE patients compared to controls and does not appear to be a reflection of disease activity or immune cell turnover. Subsets of patients such as those positive for Ro antibodies may be particularly susceptible to premature biologic aging. The predictive value of telomere length as a biomarker of future risk of damage/mortality in SLE requires longitudinal evaluation.

Systemic lupus erythematosus and vitamin D deficiency are associated with shorter telomere length among African Americans: a case-control study

Systemic lupus erythematosus (SLE) is a chronic systemic autoimmune disease that disproportionately affects African American females. The causes of SLE are unknown but postulated to be a combination of genetic predisposition and environmental triggers. Vitamin D deficiency is one of the possible environmental triggers. In this study we evaluated relationships between vitamin D status, cellular aging (telomere length) and anti-telomere antibodies among African American Gullah women with SLE. The study population included African American female SLE patients and unaffected controls from the Sea Island region of South Carolina. Serum 25-hydroxyvitamin D levels were measured using a nonchromatographic radioimmunoassay. Telomere length was measured in genomic DNA of peripheral blood mononuclear cells (PBMCs) by monochrome multiplex quantitative PCR. Anti-telomere antibody levels were measured by enzyme-linked immunosorbent assay (ELISA). Patients with SLE had significantly shorter telomeres and higher anti-telomere antibody titers compared to age- and gender-matched unaffected controls. There was a positive correlation between anti-telomere antibody levels and disease activity among patients and a significant correlation of shorter telomeres with lower 25-hydroxyvitamin D levels in both patients and controls. In follow-up examination of a subset of the patients, the patients who remained vitamin D deficient tended to have shorter telomeres than those patients whose 25-hydroxyvitamin D levels were repleted. Increasing 25-hydroxyvitamin D levels in African American patients with SLE may be beneficial in maintaining telomere length and preventing cellular aging. Moreover, anti-telomere antibody levels may be a promising biomarker of SLE status and disease activity.

Immunopathogenesis of primary biliary cirrhosis: an old wives' tale

Primary biliary cirrhosis (PBC) is a cholestatic liver disease characterised by the autoimmune destruction of the small intrahepatic bile ducts. The disease has an unpredictable clinical course, but may progress to fibrosis and cirrhosis. Although medical treatment with urseodeoxycholic acid is largely successful, some patients may progress to liver failure requiring liver transplantation. PBC is characterised by the presence of disease specific anti-mitochondrial (AMA) antibodies, which are pathognomonic for PBC development. The disease demonstrates an overwhelming female preponderance and virtually all women with PBC present in middle age. The reasons for this are unknown; however several environmental and immunological factors may be involved. As the immune systems ages, it become less self tolerant, and mounts a weaker response to pathogens, possibly leading to cross reactivity or molecular mimicry. Some individuals display immunological changes which encourage the development of autoimmune disease. Risk factors implicated in PBC include recurrent urinary tract infection in females, as well as an increased prevalence of reproductive complications. These risk factors may work in concert with and possibly even accelerate, immune system ageing, contributing to PBC development. This review will examine the changes that occur in the immune system with ageing, paying particular attention to those changes which contribute to the development of autoimmune disease with increasing age. The review also discusses risk factors which may account for the increased female predominance of PBC, such as recurrent UTI and oestrogens.

Telomere length measurement-caveats and a critical assessment of the available technologies and tools

Studies of telomeres and telomere biology often critically rely on the detection of telomeric DNA and measurements of the length of telomere repeats in either single cells or populations of cells. Several methods are available that provide this type of information and it is often not clear what method is most appropriate to address a specific research question. The major variables that need to be considered are the material that is or can be made available and the accuracy of measurements that is required. The goal of this review is to provide a comprehensive summary of the most commonly used methods and discuss the advantages and disadvantages of each. Methods that start with genomic DNA include telomere restriction fragment (TRF) length analysis, PCR amplification of telomere repeats relative to a single copy gene by Q-PCR or MMQPCR and single telomere length analysis (STELA), a PCR-based approach that accurately measures the full spectrum of telomere lengths from individual chromosomes. A different set of methods relies on fluorescent in situ hybridization (FISH) to detect telomere repeats in individual cells or chromosomes. By including essential calibration steps and appropriate controls these methods can be used to measure telomere repeat length or content in chromosomes and cells. Such methods include quantitative FISH (Q-FISH) and flow FISH which are based on digital microscopy and flow cytometry, respectively. Here the basic principles of various telomere length measurement methods are described and their strengths and weaknesses are highlighted. Some recent developments in telomere length analysis are also discussed. The information in this review should facilitate the selection of the most suitable method to address specific research question about telomeres in either model organisms or human subjects.

The telomere/telomerase system in autoimmune and systemic immune-mediated diseases

Telomeres are specialized nucleoproteic structures that cap and protect the ends of chromosomes. They can be elongated by the telomerase enzyme, but in telomerase negative cells, telomeres shorten after each cellular division because of the end replicating problem. This phenomenon leads ultimately to cellular senescence, conferring to the telomeres a role of biological clock. Oxidative stress, inflammation and increased cell renewal are supplementary environmental factors that accelerate age-related telomere shortening. Similar to other types of DNA damage, very short/dysfunctional telomeres activate a DNA response pathway leading to different outcomes: DNA repair, cell senescence or apoptosis. During the last 10 years, studies on the telomere/telomerase system in autoimmune and/or systemic immune-mediated diseases have revealed its involvement in relevant physiopathological processes. Here, we present a literature review of telomere and telomerase homeostasis in systemic inflammatory diseases including systemic lupus erythematosus, rheumatoid arthritis and granulomatous diseases. The available data indicate that both telomerase activity and telomere length are modified in various systemic immune-mediated diseases and appear to be connected with premature immunosenescence. Studies on the telomere/telomerase system open new research avenues for the basic understanding and for therapeutic approaches of these pathologies.

[Telomeres and telomerase: relevance and future prospects in systemic lupus erythematosus]

Telomeres are specialized structures that cap and protect the end of chromosomes. Telomeres progressively shorten after each cellular division unless an enzyme, the telomerase, counteracts. Telomeres are implicated in cellular senescence, acting like a biological clock. Telomere length and telomerase activity are important in the physiopathology of cancer. In the past years, research has focused on them in order to find new therapeutic targets. Yet, oxidative stress, inflammation and increased leucocytes renewal are major environmental factors associated with telomeres shortening acceleration and thus in concordance with biological age. Thus, telomeric erosion induces cell apoptosis; indeed, apoptotic cell clearance is impaired in systemic lupus. Considering these elements and data resulting from oncology, telomere/telomerase couple was studied during the last decade in systemic lupus erythematosus. The objective was to know if this couple could have an implication in the physiopathology of this disease. A systematic review of literature is proposed about telomere and/or telomerase in systemic lupus erythematosus in order to discuss their physiopathological implication. Among 273 tested patients, telomere seems to be eroded and telomerase activity insufficiently increased but correlated to the activity of the disease. The analysis of telomere length and telomerase activity could be useful as prognosis factor or disease activity index. Telomere erosion could reflect an accelerated replicative senescence of the immune system. The role of the regulator T lymphocytes has not yet been precised. Standardized studies on larger population could be realized in systemic lupus and open new avenues of research and/or therapy based upon the telomere/telomerase biology.

Telomeres and immunological diseases of aging

A defining feature of the eukaryotic genome is the presence of linear chromosomes. This arrangement, however, poses several challenges with regard to chromosomal replication and maintenance. To prevent the loss of coding sequences and to suppress gross chromosomal rearrangements, linear chromosomes are capped by repetitive nucleoprotein structures, called telomeres. Each cell division results in a progressive shortening of telomeres that, below a certain threshold, promotes genome instability, senescence, and apoptosis. Telomeric erosion, maintenance, and repair take center stage in determining cell fate. Cells of the immune system are under enormous proliferative demand, stressing telomeric intactness. Lymphocytes are capable of upregulating telomerase, an enzyme that can elongate telomeric sequences and, thus, prolong cellular lifespan. Therefore, telomere dynamics are critical in preserving immune function and have become a focus for studies of immunosenescence and autoimmunity. In this review, we describe the role of telomeric nucleoproteins in shaping telomere architecture and in suppressing DNA damage responses. We summarize new insights into the regulation of telomerase activity, hereditary disorders associated with telomere dysfunction, the role of telomere loss in immune aging, and the impact of telomere dysfunction in chronic inflammatory disease.

Assessment of telomere length, phenotype, and DNA content

Telomere sequences at the end of chromosomes control somatic cell division; therefore, telomere length in a given cell population provides information about its replication potential. This unit describes a method for flow cytometric measurement of telomere length in subpopulations using fluorescence in situ hybridization of fluorescently-labeled probes (Flow-FISH) without prior cell separation. After cells are stained for surface immunofluorescence, antigen-antibody complexes are covalently cross-linked onto cell membranes before FISH with a telomere-specific probe. Cells with long telomeres are included as internal standards. Addition of a DNA dye permits exclusion of proliferating cells during data analysis. DNA ploidy measurements of cells of interest and internal standard are performed on separate aliquots in parallel to Flow-FISH. Telomere fluorescence of G(0/1) cells of subpopulations and internal standards obtained from Flow-FISH are normalized for DNA ploidy and telomere length in subsets of interest is expressed as a fraction of the internal standard telomere length.