Therapeutic doses of hydroxyurea cause telomere dysfunction and reduce TRF2 binding to telomeres

Telomere attrition and genomic instability in unexplained recurrent pregnancy loss in humans: A preliminary study

Genome instability is defined as an elevated rate of DNA damage and mutations as a result of exposure to potential direct and indirect mutagens. This current investigation was designed to elucidate the genomic instability among couples experiencing unexplained recurrent pregnancy loss (uRPL). A cohort of 1272 individuals with history of unexplained RPL with normal karyotype was retrospectively screened for levels of intracellular ROS production, baseline genomic instability and telomere functionality. The experimental outcome was compared with 728 fertile control individuals. In this study, it was perceived that individuals with uRPL exhibited higher intracellular oxidative stress, along with higher basal levels of genomic instability as compared with the fertile controls. This observation elucidates the role of genomic instability as well as involvement of telomeres in cases of uRPL. It was also observed that higher oxidative stress might be associated with DNA damage and telomere dysfunction resulting in genomic instability among subjects with unexplained RPL. This study highlighted the assessment of genomic instability status in individuals experiencing uRPL.

Telomere length and telomere repeat-binding protein in children with sickle cell disease

BACKGROUND

This study aimed to assess the telomere length and plasma telomere repeat-binding factor 2 (TRF2) levels in addition to other inflammatory markers in children with sickle cell disease (SCD).

METHODS

We enrolled 106 children (90 SCD and 26 controls) aged 1-15 years from the Hematology unit of King Fahad Medical City (KFMC), Saudi Arabia. Genomic DNA extracted from blood and leukocyte TL was determined using quantitative reverse transcription PCR, whereas TRF2, C-reactive protein, interleukin-6, and DNA oxidative damage were determined by using respective commercially available assays.

RESULTS

Leukocyte TL was inversely correlated with age in the SCD patients (r = -0.24, P = 0.02) and the controls (r = -0.68, P < 0.0001). In addition, SCD patients had significantly shorter TL (7.74 ± 0.81 kb) (P = 0.003) than controls (8.28 ± 0.73 kb). In contrast, no significant difference in TL among the SCD genotypes (HbSS and HbSβ0) has been observed. A modest, positive correlation was seen between TL and reticulocyte % (r = 0.21; P = 0.06). There were no significant differences in the TL and TRF2 concentrations between subjects with HbSS and HbSβ⁰ genotypes.

CONCLUSIONS

Short leukocyte TL was significantly associated with SCD. An inverse association was observed between TL and hemoglobin. Hydroxyurea treatment revealed no impact on TL.

IMPACT

This study explored the TL and plasma TRF2 in Saudi children with SCD. This is the first documentation that SCD children have shorter TL than their healthy counterparts, and no association between TL and TRF2 has been observed. Hydroxyurea treatment showed no impact on TL in children with SCD. This study is the first of its kind in children with SCD. It will pave the way for another study with a larger sample size in a diverse population to scrutinize these findings better.

Therapeutic Dose of Hydroxyurea-Induced Synaptic Abnormalities on the Mouse Spermatocyte

Hydroxyurea (HU) is a widely used pharmacological therapy for sickle cell disease (SCD). However, replication stress caused by HU has been shown to inhibit premeiotic S-phase DNA, leading to reproductive toxicity in germ cells. In this study, we administered the therapeutic doses of HU (i.e., 25 and 50 mg/kg) to male mice to explore whether replication stress by HU affects pachytene spermatocytes and causes the abnormalities of homologous chromosomes pairing and recombination during prophase I of meiosis. In comparison with the control group, the proportions of spermatocyte gaps were significantly different in the experimental groups injected with 25 mg/kg (p < 0.05) and 50 mg/kg of HU (p < 0.05). Moreover, the proportions of unrepaired double-stranded breaks (DSBs) observed by γH2AX staining also corresponded to a higher HU dose with a greater number of breaks. Additionally, a reduction in the counts of recombination foci on the autosomal SCs was observed in the pachytene spermatocytes. Our results reveal that HU has some effects on synaptonemal complex (SC) formation and DSB repair which suggest possible problems in fertility. Therefore, this study provides new evidence of the mechanisms underlying HU reproductive toxicity.

Mapping replication timing domains genome wide in single mammalian cells with single-cell DNA replication sequencing

Replication timing (RT) domains are stable units of chromosome structure that are regulated in the context of development and disease. Conventional genome-wide RT mapping methods require many S-phase cells for either the effective enrichment of replicating DNA through bromodeoxyuridine (BrdU) immunoprecipitation or the determination of copy-number differences during S-phase, which precludes their application to non-abundant cell types and single cells. Here, we provide a simple, cost-effective, and robust protocol for single-cell DNA replication sequencing (scRepli-seq). The scRepli-seq methodology relies on whole-genome amplification (WGA) of genomic DNA (gDNA) from single S-phase cells and next-generation sequencing (NGS)-based determination of copy-number differences that arise between replicated and unreplicated DNA. Haplotype-resolved scRepli-seq, which distinguishes pairs of homologous chromosomes within a single cell, is feasible by using single-nucleotide polymorphism (SNP)/indel information. We also provide computational pipelines for quality control, normalization, and binarization of the scRepli-seq data. The experimental portion of this protocol (before sequencing) takes 3 d.

Evaluation of ATM Kinase Inhibitor KU-55933 as Potential Anti-Toxoplasma gondii Agent

Toxoplasma gondii is an apicomplexan protozoan parasite with a complex life cycle composed of multiple stages that infect mammals and birds. Tachyzoites rapidly replicate within host cells to produce acute infection during which the parasite disseminates to tissues and organs. Highly replicative cells are subject to Double Strand Breaks (DSBs) by replication fork collapse and ATM, a member of the phosphatidylinositol 3-kinase (PI3K) family, is a key factor that initiates DNA repair and activates cell cycle checkpoints. Here we demonstrate that the treatment of intracellular tachyzoites with the PI3K inhibitor caffeine or ATM kinase-inhibitor KU-55933 affects parasite replication rate in a dose-dependent manner. KU-55933 affects intracellular tachyzoite growth and induces G1-phase arrest. Addition of KU-55933 to extracellular tachyzoites also leads to a significant reduction of tachyzoite replication upon infection of host cells. ATM kinase phosphorylates H2A.X (γH2AX) to promote DSB damage repair. The level of γH2AX increases in tachyzoites treated with camptothecin (CPT), a drug that generates fork collapse, but this increase was not observed when co-administered with KU-55933. These findings support that KU-55933 is affecting the Toxoplasma ATM-like kinase (TgATM). The combination of KU-55933 and other DNA damaging agents such as methyl methane sulfonate (MMS) and CPT produce a synergic effect, suggesting that TgATM kinase inhibition sensitizes the parasite to damaged DNA. By contrast, hydroxyurea (HU) did not further inhibit tachyzoite replication when combined with KU-55933.

Second malignancies in hydroxyurea and interferon-treated Philadelphia-negative myeloproliferative neoplasms

OBJECTIVE

In an era of controversy in regard to 'hydroxyurea-leukaemogenicity' and when interferon-alfa2 (IFN) is being revived in the treatment of Philadelphia-negative myeloproliferative neoplasms (MPNs), we aim in this single-centre observational study to describe the frequencies of second malignancies in a cohort of MPN patients treated with hydroxyurea (HU) or IFN monotherapy or the combination of these agents.

PATIENTS AND METHODS

Records of a MPN cohort of 196 patients were reviewed, and a retrospective analysis was performed on 90 patients treated with HU, 38 patients treated with IFN and 68 patients treated with both IFN and HU. Logistic regression was used to compare frequencies in second malignancies.

RESULTS

Patients treated with HU had a significantly higher risk of developing all second malignancies compared with patients treated with IFN [HU vs. IFN: OR of 4.01 (95%CI: 1.12-14.27, P-value: 0.023) and HU-IFN vs. IFN: OR 5.58 (95%CI: 1.55-20.15, P-value: 0.004)].

CONCLUSION

We have found an increased risk of second malignancies in MPN patients treated with HU compared with patients treated with IFN.

Precipitating factors and targeted therapies in combating the perils of sickle cell disease--- A special nutritional consideration

Nutritional research in sickle cell disease has been the focus in recent times owing to not only specific nutritional deficiencies, but also the improvements associated with less painful episodes. Though hydroxyurea remains the drug of choice, certain adverse health effects on long term supplementation makes room for researches of different compounds. Macro and micro nutrient deficiencies, along with vitamins, play an important role in not only meeting the calorific needs, but also reducing clinical complications and growth abnormalities. Symptoms of hyper protein metabolism, increased cell turnover, increased cardiac output, and appetite suppression due to enhanced cytokine production, might give us leads for better understanding of the mechanisms involved. Different nutritional approaches comprising of traditional herbal therapies, antioxidants, flavonoids, vitamins, minerals etc., reducing oxidative stress and blood aggregation, have been tried out to increase the health potential. Nutritional therapies may also serve complementary to the newer therapies using ozone, hematopoietic stem cell transplantation, antifungal medications, erythropoietin etc. Herein we try to present a holistic picture of the different patho-physiological mechanisms, and nutritional strategies adopted.

Telomeric impact of conventional chemotherapy

The increased level of chromosome instability in cancer cells, leading to aneuploidy and gross chromosomal rearrangements, is not only a driving force for oncogenesis but also can be the Achille's heel of the disease since many chemotherapies (CT) kill cells by inducing a non-tolerable rate of DNA damage. A wealth of published evidence showed that telomere stability can be more affected than the bulk of the genome by several conventional antineoplasic drugs. These results raise the interesting possibility that CT with genotoxic drugs preferentially target telomeres. In agreement with this view, accelerated shortening of telomere length has been described in blood lineage cells following high-dose CT (stem cell transplantation) or non-myeloablative CT. However, almost nothing is known on the consequences of this shortening in terms of telomere stability, senescence and on the development of second cancers or post-treatment aging-like syndromes in cancer survivors (cognitive defect, fertility impairment, etc.). In this article, we propose: (1) telomeres of cancer cells are preferential genomic targets of chemotherapies altering chromosome maintenance; (2) telomere functional parameters can be a surrogate marker of chemotherapy sensitivity and toxicity; (3) the use of anti-telomere molecule could greatly enhance the sensitivity to standards chemotherapies.

Timeless preserves telomere length by promoting efficient DNA replication through human telomeres

A variety of telomere protection programs are utilized to preserve telomere structure. However, the complex nature of telomere maintenance remains elusive. The Timeless protein associates with the replication fork and is thought to support efficient progression of the replication fork through natural impediments, including replication fork block sites. However, the mechanism by which Timeless regulates such genomic regions is not understood. Here, we report the role of Timeless in telomere length maintenance. We demonstrate that Timeless depletion leads to telomere shortening in human cells. This length maintenance is independent of telomerase, and Timeless depletion causes increased levels of DNA damage, leading to telomere aberrations. We also show that Timeless is associated with Shelterin components TRF1 and TRF2. Timeless depletion slows telomere replication in vitro, and Timeless-depleted cells fail to maintain TRF1-mediated accumulation of replisome components at telomeric regions. Furthermore, telomere replication undergoes a dramatic delay in Timeless-depleted cells. These results suggest that Timeless functions together with TRF1 to prevent fork collapse at telomere repeat DNA and ensure stable maintenance of telomere length and integrity.

Genetic modifiers of HbF and response to hydroxyurea in sickle cell disease

Fetal hemoglobin (HbF) levels are generally inversely proportional to severity of sickle cell disease (SCD) for given sickle phenotypes. Molecular regulation of HbF occurs through complex interactions cis and trans to the beta globin gene locus. Novel insights made through population-based genetic epidemiologic studies of non-anemic populations were replicated in SCD groups, despite large differences in HbF levels. Identification of the lymphoid transcription factor BCL11A as a key suppressor of HbF expression validates approaches using population genetics to study HbF expression. We review these methods and findings, and speculate on applying pharmaco-genetics to optimize hydroxyurea therapy aimed at increasing HbF.

Regulation of Epstein-Barr virus origin of plasmid replication (OriP) by the S-phase checkpoint kinase Chk2

The Epstein-Barr virus (EBV) origin of plasmid replication (OriP) is required for episome stability during latent infection. Telomere repeat factor 2 (TRF2) binds directly to OriP and facilitates DNA replication and plasmid maintenance. Recent studies have found that TRF2 interacts with the DNA damage checkpoint protein Chk2. We show here that Chk2 plays an important role in regulating OriP plasmid stability, chromatin modifications, and replication timing. The depletion of Chk2 by small interfering RNA (siRNA) leads to a reduction in DNA replication efficiency and a loss of OriP-dependent plasmid maintenance. This corresponds to a change in OriP replication timing and an increase in constitutive histone H3 acetylation. We show that Chk2 interacts with TRF2 in the early G(1)/S phase of the cell cycle. We also show that Chk2 can phosphorylate TRF2 in vitro at a consensus acceptor site in the amino-terminal basic domain of TRF2. TRF2 mutants with a serine-to-aspartic acid phosphomimetic substitution mutation were reduced in their ability to recruit the origin recognition complex (ORC) and stimulate OriP replication. We suggest that the Chk2 phosphorylation of TRF2 is important for coordinating ORC binding with chromatin remodeling during the early S phase and that a failure to execute these events leads to replication defects and plasmid instability.

Genetic modifiers of the severity of sickle cell anemia identified through a genome-wide association study

We conducted a genome-wide association study (GWAS) to discover single nucleotide polymorphisms (SNPs) associated with the severity of sickle cell anemia in 1,265 patients with either "severe" or "mild" disease based on a network model of disease severity. We analyzed data using single SNP analysis and a novel SNP set enrichment analysis (SSEA) developed to discover clusters of associated SNPs. Single SNP analysis discovered 40 SNPs that were strongly associated with sickle cell severity (odds for association >1,000); of the 32 that we could analyze in an independent set of 163 patients, five replicated, eight showed consistent effects although failed to reach statistical significance, whereas 19 did not show any convincing association. Among the replicated associations are SNPs in KCNK6 a K(+) channel gene. SSEA identified 27 genes with a strong enrichment of significant SNPs (P < 10(-6)); 20 were replicated with varying degrees of confidence. Among the novel findings identified by SSEA is the telomere length regulator gene TNKS. These studies are the first to use GWAS to understand the genetic diversity that accounts the phenotypic heterogeneity sickle cell anemia as estimated by an integrated model of severity. Additional validation, resequencing, and functional studies to understand the biology and reveal mechanisms by which candidate genes might have their effects are the future goals of this work.