Shaping human telomeres: from shelterin and CST complexes to telomeric chromatin organization

Regulation of cellular senescence in tumor progression and therapeutic targeting: mechanisms and pathways

Cellular senescence, a stable state of cell cycle arrest induced by various stressors or genomic damage, is recognized as a hallmark of cancer. It exerts a context-dependent dual role in cancer initiation and progression, functioning as a tumor suppressor and promoter. The complexity of senescence in cancer arises from its mechanistic diversity, potential reversibility, and heterogeneity. A key mediator of these effects is the senescence-associated secretory phenotype (SASP), a repertoire of bioactive molecules that influence tumor microenvironment (TME) remodeling, modulate cancer cell behavior, and contribute to therapeutic resistance. Given its intricate role in cancer biology, senescence presents both challenges and opportunities for therapeutic intervention. Strategies targeting senescence pathways, including senescence-inducing therapies and senolytic approaches, offer promising avenues for cancer treatment. This review provides a comprehensive analysis of the regulatory mechanisms governing cellular senescence in tumors. We also discuss emerging strategies to modulate senescence, highlighting novel therapeutic opportunities. A deeper understanding of these processes is essential for developing precision therapies and improving clinical outcomes.

Genomic Profiling of Cardiac Angiosarcoma Reveals Novel Targetable KDR Variants, Recurrent MED12 Mutations, and a High Burden of Germline POT1 Alterations

PURPOSE

Cardiac angiosarcoma is a rare, aggressive malignancy with limited treatment options. Both sporadic and familial cases occur, with recent links to germline POT1 mutations. The genomic landscape of this disease is poorly understood.

EXPERIMENTAL DESIGN

We conducted comprehensive genomic profiling of cardiac angiosarcoma to assess the burden of germline predisposition and identify other recurrent genomic alterations of clinical significance.

RESULTS

Six patients were female, and four were male. The median age at presentation was 40 years (range, 21-69 years). All cases with available follow-up exhibited an aggressive clinical course (6/8 patients died of disease). KDR alterations, including novel structural variants, were found in 9/11 cases at a rate significantly higher than that in noncardiac angiosarcomas. POT1 mutations were present in 45.5% of cardiac angiosarcoma cases. In three of five POT1-mutant cases, the germline status was confirmed through testing of normal tissue, and in one additional case, the germline status was inferred with high probability through allele frequency analysis. Additionally, we identified novel recurrent MED12 exon 2 mutations in POT1 wild-type cardiac angiosarcoma, suggesting an alternative path to cardiac angiosarcoma oncogenesis.

CONCLUSIONS

Cardiac angiosarcoma demonstrates a unique genetic profile, distinct from noncardiac angiosarcoma. This study highlights the role of germline POT1 burden on cardiac angiosarcoma development and demonstrates recurrent MED12 alterations for the first time. The reported KDR variants provide a potential avenue for the treatment of this aggressive disease. Given the prevalence of germline POT1 mutations reported in this study, germline genetic testing should be considered in patients diagnosed with cardiac angiosarcoma.

The relationship between telomere length and aging-related diseases

The intensifying global phenomenon of an aging population has spurred a heightened emphasis on studies on aging and disorders associated with aging. Cellular senescence and aging are known to be caused by telomere shortening. Telomere length (TL) has emerged as a biomarker under intense scrutiny, and its widespread use in investigations of diseases tied to advancing age. This review summarizes the current knowledge of the association between telomeres and aging-related diseases, explores the important contribution of dysfunctional telomeres to the development and progression of these diseases, and aims to provide valuable insights for the development of novel therapeutic strategies.

Unraveling aging from transcriptomics

Research into aging constitutes a pivotal endeavor aimed at elucidating the underlying biological mechanisms governing aging and age-associated diseases, as well as promoting healthy longevity. Recent advances in transcriptomic technologies, such as bulk RNA sequencing (RNA-seq), single-cell transcriptomics, and spatial transcriptomics, have revolutionized our ability to study aging at unprecedented resolution and scale. These technologies present novel opportunities for the discovery of biomarkers, elucidation of molecular pathways, and development of targeted therapeutic strategies for age-related disorders. This review surveys recent breakthroughs in different types of transcripts on aging, such as mRNA, long noncoding (lnc)RNA, tRNA, and miRNA, highlighting key findings and discussing their potential implications for future studies in this field.

Canonical and non-canonical functions of the non-coding RNA component (TERC) of telomerase complex

The telomerase complex consists of a protein component (TERT), which has reverse transcriptase activity, and an RNA component (TERC), which serves as a template for telomere synthesis. Evidence is rapidly accumulating regarding the non-canonical functions of these components in both normal or diseased cells. An oligonucleotide-based drug, the first telomerase inhibitor, secured FDA approval in June 2024. We recently summarized the non-canonical functions of TERT in viral infections and cancer. In this review, we expand on these non-canonical functions of TERC beyond telomere maintenance. Specifically, we explore TERC's roles in cellular aging and senescence, immune regulation, genetic diseases, human cancer, as well as involvement in viral infections and host interactions. Finally, we discuss a transcription product of telomere repeats, TERRA, and explore strategies for targeting TERC as a therapeutic approach.

Beyond interacting with Rap1: Dissecting the roles of Rif1

Rap1 interacting factor 1 (Rif1), an evolutionarily conserved protein discovered in budding yeast, is crucial for controlling telomere length when it interacts with Rap1. Recent research, however, has shown that Rif1 not only controls telomere length and homeostasis, but also plays a role in transcriptional silencing, DNA replication timing, DNA replication fork protection, DNA damage repair and chromatin architecture. In this review, we summarize the current understanding of Rif1 in structure, function, and regulation, especially its relevance to cancer hallmarks. Also, we discuss its role as a regulator in the pathogenesis of disease.

Rapid dynamics allow the low-abundance RTEL1 helicase to promote telomere replication

Regulator of telomere length 1 (RTEL1) helicase facilitates telomere replication by disassembling DNA secondary structures, such as G-quadruplexes and telomeric loops (t-loops), at the ends of the chromosomes. The recruitment of RTEL1 to telomeres occurs during the S-phase of the cell cycle, but the dynamics of the process has not been studied. Here, we utilized CRISPR genome editing and single-molecule imaging to monitor RTEL1 movement within human cell nuclei. RTEL1 utilizes rapid three-dimensional diffusion to search for telomeres and other nuclear targets. Only 5% of the chromatin-bound RTEL1 is associated with telomeres at any time in the S-phase, but the telomere-bound RTEL1 has much more extended associations. This binding is enhanced by the interaction between RTEL1 and the telomeric protein TRF2 but is largely independent of RTEL1 ATPase activity. The absence of RTEL1 catalytic activity leads to severe defects in cell proliferation, slow progression out of S-phase, and chromosome end-to-end fusion events. We propose that the rapid diffusion of RTEL1 allows this low-abundance protein to explore the nucleus, bind TRF2, and be recruited to telomeres.

Zbtb48 is a regulator of Mtfp1 expression in zebrafish

ZBTB48 (also known as TZAP) is a transcription factor that has previously been reported to bind to telomeres and act as a negative regulator of telomere length in human cell lines. To explore whether transcription factor activity and telomere length regulation are conserved at the organismal level in vertebrates, we generate a zbtb48-/- zebrafish line via CRISPR‒Cas genome editing. The zbtb48-/- mutants display no obvious physical or behavioral abnormalities in the first two generations. We find no statistically significant changes in telomere length in first-generation adults. However, for the gene regulatory aspect of Zbtb48, similar to that in human cancer cell lines, we observe downregulation of mtfp1 at both the mRNA and protein levels in the zbtb48-/- mutants. This suggests that mtfp1 is an evolutionarily conserved regulatory target of Zbtb48. Further investigation of the spatiotemporal expression of zbtb48 in previously published zebrafish data reveals low transcript expression in diverse tissues, except in germline stem cells and gametocytes of the gonads. Notably, Mtfp1 protein downregulation is detected in the ovaries of 40 dpf zbtb48-/- mutants and in the testes of both 40 dpf and 10.5-month-old zbtb48-/- mutants.

Telomemore enables single-cell analysis of cell cycle and chromatin condensation

Single-cell RNA-seq methods can be used to delineate cell types and states at unprecedented resolution but do little to explain why certain genes are expressed. Single-cell ATAC-seq and multiome (ATAC + RNA) have emerged to give a complementary view of the cell state. It is however unclear what additional information can be extracted from ATAC-seq data besides transcription factor binding sites. Here, we show that ATAC-seq telomere-like reads counter-inituively cannot be used to infer telomere length, as they mostly originate from the subtelomere, but can be used as a biomarker for chromatin condensation. Using long-read sequencing, we further show that modern hyperactive Tn5 does not duplicate 9 bp of its target sequence, contrary to common belief. We provide a new tool, Telomemore, which can quantify nonaligning subtelomeric reads. By analyzing several public datasets and generating new multiome fibroblast and B-cell atlases, we show how this new readout can aid single-cell data interpretation. We show how drivers of condensation processes can be inferred, and how it complements common RNA-seq-based cell cycle inference, which fails for monocytes. Telomemore-based analysis of the condensation state is thus a valuable complement to the single-cell analysis toolbox.

TERRA and the alternative lengthening of telomeres: a dangerous affair

Eukaryotic telomeres are transcribed into the long noncoding RNA TERRA. A fraction of TERRA remains associated with telomeres by forming RNA:DNA hybrids dubbed telR-loops. TERRA and telR-loops are essential to promote telomere elongation in human cancer cells that maintain telomeres through a homology-directed repair pathway known as alternative lengthening of telomeres or ALT. However, TERRA and telR-loops compromise telomere integrity and cell viability if their levels are not finely tuned. The study of telomere transcription in ALT cells will enormously expand our understanding of the ALT mechanism and of how genome integrity is maintained. Moreover, telomere transcription, TERRA and telR-loops are likely to become exceptionally suited targets for the development of novel anti-cancer therapies.

TRF1 and TRF2 form distinct shelterin subcomplexes at telomeres

The shelterin complex protects chromosome ends from the DNA damage repair machinery and regulates telomerase access to telomeres. Shelterin is composed of six proteins (TRF1, TRF2, TIN2, TPP1, POT1 and RAP1) that can assemble into various subcomplexes in vitro. However, the stoichiometry of the shelterin complex and its dynamic association with telomeres in cells is poorly defined. To quantitatively analyze the shelterin function in living cells we generated a panel of cancer cell lines expressing HaloTagged shelterin proteins from their endogenous loci. We systematically determined the total cellular abundance and telomeric copy number of each shelterin subunit, demonstrating that the shelterin proteins are present at telomeres in equal numbers. In addition, we used single-molecule live-cell imaging to analyze the dynamics of shelterin protein association with telomeres. Our results demonstrate that TRF1-TIN2-TPP1-POT1 and TRF2-RAP1 form distinct subcomplexes that occupy non-overlapping binding sites on telomeric chromatin. TRF1-TIN2-TPP1-POT1 tightly associates with chromatin, while TRF2-RAP1 binding to telomeres is more dynamic, allowing it to recruit a variety of co-factors to chromatin to protect chromosome ends from DNA repair factors. In total, our work provides critical mechanistic insight into how the shelterin proteins carry out multiple essential functions in telomere maintenance and significantly advances our understanding of macromolecular structure of telomeric chromatin.

New insights into methods to measure biological age: a literature review

Biological age is a concept that reflects the physiological state of an individual rather than the chronological time since birth. It can help assess the risk of age-related diseases and mortality and the effects of interventions to slow down or reverse aging. However, there is no consensus on measuring biological age best, and different methods may yield different results. In this paper, which includes 140 relevant pieces of literature, out of 33,000, we review some new methods to measure biological age based on recent advances in biotechnology and data science. We discussed some novel biomarkers and algorithms that can capture the dynamic and multidimensional aspects of aging at different levels. We evaluate their performance and validity using various datasets and criteria and compare them with existing methods. We also discuss their potential applications and implications for aging research and clinical practice. We conclude that the new methods offer more accurate and reliable estimates of biological age and open new avenues for understanding and modulating the aging process.

Beginning at the ends: telomere and telomere-based cancer therapeutics

Telomeres, which are situated at the terminal ends of chromosomes, undergo a reduction in length with each cellular division, ultimately reaching a critical threshold that triggers cellular senescence. Cancer cells circumvent this senescence by utilizing telomere maintenance mechanisms (TMMs) that grant them a form of immortality. These mechanisms can be categorized into two primary processes: the reactivation of telomerase reverse transcriptase and the alternative lengthening of telomeres (ALT) pathway, which is dependent on homologous recombination (HR). Various strategies have been developed to inhibit telomerase activation in 85-95% of cancers, including the use of antisense oligonucleotides such as small interfering RNAs and endogenous microRNAs, agents that simulate telomere uncapping, expression modulators, immunotherapeutic vaccines targeting telomerase, reverse transcriptase inhibitors, stabilization of G-quadruplex structures, and gene therapy approaches. Conversely, in the remaining 5-15% of human cancers that rely on ALT, mechanisms involve modifications in the chromatin environment surrounding telomeres, upregulation of TERRA long non-coding RNA, enhanced activation of the ataxia telangiectasia and Rad-3-related protein kinase signaling pathway, increased interactions with nuclear receptors, telomere repositioning driven by HR, and recombination events between non-sister chromatids, all of which present potential targets for therapeutic intervention. Additionally, combinatorial therapy has emerged as a strategy that employs selective agents to simultaneously target both telomerase and ALT, aiming for optimal clinical outcomes. Given the critical role of anti-TMM strategies in cancer treatment, this review provides an overview of the latest insights into the structure and function of telomeres, their involvement in tumorigenesis, and the advancements in TMM-based cancer therapies.

The Quest for Eternal Youth: Hallmarks of Aging and Rejuvenating Therapeutic Strategies

The impressive achievements made in the last century in extending the lifespan have led to a significant growth rate of elderly individuals in populations across the world and an exponential increase in the incidence of age-related conditions such as cardiovascular diseases, diabetes mellitus type 2, and neurodegenerative diseases. To date, geroscientists have identified 12 hallmarks of aging (genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, impaired macroautophagy, mitochondrial dysfunction, impaired nutrient sensing, cellular senescence, stem cell exhaustion, defective intercellular communication, chronic inflammation, and gut dysbiosis), intricately linked among each other, which can be targeted with senolytic or senomorphic drugs, as well as with more aggressive approaches such as cell-based therapies. To date, side effects seriously limit the use of these drugs. However, since rejuvenation is a dream of mankind, future research is expected to improve the tolerability of the available drugs and highlight novel strategies. In the meantime, the medical community, healthcare providers, and society should decide when to start these treatments and how to tailor them individually.

3D-Q-FISH/Telomere/TRF2 Nanotechnology Identifies a Progressively Disturbed Telomere/Shelterin/Lamin AC Complex as the Common Pathogenic, Molecular/Spatial Denominator of Classical Hodgkin Lymphoma

The bi- or multinucleated Reed-Sternberg cell (RS) is the diagnostic cornerstone of Epstein-Barr Virus (EBV)-positive and EBV-negative classical Hodgkin lymphoma (cHL). cHL is a germinal center (GC)-derived B-cell disease. Hodgkin cells (H) are the mononuclear precursors of RS. An experimental model has to fulfill three conditions to qualify as common pathogenic denominator: (i) to be of GC-derived B-cell origin, (ii) to be EBV-negative to avoid EBV latency III expression and (iii) to support permanent EBV-encoded oncogenic latent membrane protein (LMP1) expression upon induction. These conditions are unified in the EBV-, diffuse large B-Cell lymphoma (DLBCL) cell line BJAB-tTA-LMP1. 3D reconstructive nanotechnology revealed spatial, quantitative and qualitative disturbance of telomere/shelterin interactions in mononuclear H-like cells, with further progression during transition to RS-like cells, including progressive complexity of the karyotype with every mitotic cycle, due to BBF (breakage/bridge/fusion) events. The findings of this model were confirmed in diagnostic patient samples and correlate with clinical outcomes. Moreover, in vitro, significant disturbance of the lamin AC/telomere interaction progressively occurred. In summary, our research over the past three decades identified cHL as the first lymphoid malignancy driven by a disturbed telomere/shelterin/lamin AC interaction, generating the diagnostic RS. Our findings may act as trailblazer for tailored therapies in refractory cHL.

Overexpression of protection of telomeres 1 (POT1), a single-stranded DNA-binding proteins in alfalfa (Medicago sativa), enhances seed vigor

Extensive bodies of research are dedicated to the study of seed aging with a particular focus on the roles of reactive oxygen species (ROS), and the ensuing oxidative damage during storage, as a primary cause of seed vigor decreasing. ROS diffuse to the nucleus and damage the telomeres, resulting in a loss of genetic integrity. Protection of telomeres 1 (POT1) is a telomeric protein that binds to the telomere region, and plays an essential role in maintaining genomic stability in plants. In this study, there were totally four MsPOT1 genes obtained from alfalfa genome. Expression analysis of four MsPOT1 genes in germinated seed presented the different expressions. Four MsPOT1 genes displayed high expression levels at the early stage of seed germination, Among the four POT1 genes, it was found that MS. gene040108 was significantly up-regulated in the early germination stage of CK seeds, but down-regulated in aged seeds. RT-qPCR assays and RNA-seq data revealed that MsPOT1-X gene was significantly induced by seed aging treatment. Transgenic seeds overexpressing MsPOT1-X gene in Arabidopsis thaliana and Medicago trunctula exhibited enhanced seed vigor, telomere length, telomerase activity associated with reduced H2O2 content. These results would provide a new way to understand aging stress-responsive MsPOT1 genes for genetic improvement of seed vigor. Although a key gene regulating seed vigor was identified in this study, the specific mechanism of MsPOT1-X gene regulating seed vigor needs to be further explored.

Inherited Telomere Biology Disorders: Pathophysiology, Clinical Presentation, Diagnostics, and Treatment

Background

Telomeres are the end-capping structures of all eukaryotic chromosomes thereby protecting the genome from damage and degradation. During the aging process, telomeres shorten continuously with each cell division until critically short telomeres prevent further proliferation whereby cells undergo terminal differentiation, senescence, or apoptosis. Premature aging due to critically short telomere length (TL) can also result from pathogenic germline variants in the telomerase complex or related genes that typically counteract replicative telomere shortening in germline and certain somatic cell populations, e.g., hematopoetic stem cells. Inherited diseases that result in altered telomere maintenance are summarized under the term telomere biology disorder (TBD).

Summary

Since TL both reflects but more importantly restricts the replicative capacity of various human tissues, a sufficient telomere reserve is particularly important in cells with high proliferative activity (e.g., hematopoiesis, immune cells, intestinal cells, liver, lung, and skin). Consequently, altered telomere maintenance as observed in TBDs typically results in premature replicative cellular exhaustion in the respective organ systems eventually leading to life-threatening complications such as bone marrow failure (BMF), pulmonary fibrosis, and liver cirrhosis.

Key Messages

The recognition of a potential congenital origin in approximately 10% of adult patients with clinical BMF is of utmost importance for the proper diagnosis, appropriate patient and family counseling, to prevent the use of inefficient treatment and to avoid therapy-related toxicities including appropriate donor selection when patients have to undergo stem cell transplantation from related donors. This review summarizes the current state of knowledge about TBDs with particular focus on the clinical manifestation patterns in children (termed early onset TBD) compared to adults (late-onset TBD) including typical treatment- and disease course-related complications as well as their prognosis and adequate therapy. Thereby, it aims to raise awareness for a disease group that is currently still highly underdiagnosed particularly when it first manifests itself in adulthood.

Dysfunction of Telomeric Cdc13-Stn1-Ten1 Simultaneously Activates DNA Damage and Spindle Checkpoints

Telomeres, the ends of eukaryotic linear chromosomes, are composed of repeated DNA sequences and specialized proteins, with the conserved telomeric Cdc13/CTC1-Stn1-Ten1 (CST) complex providing chromosome stability via telomere end protection and the regulation of telomerase accessibility. In this study, SIZ1, coding for a SUMO E3 ligase, and TOP2 (a SUMO target for Siz1 and Siz2) were isolated as extragenic suppressors of Saccharomyces cerevisiae CST temperature-sensitive mutants. ten1-sz, stn1-sz and cdc13-sz mutants were isolated next due to being sensitive to intracellular Siz1 dosage. In parallel, strong negative genetic interactions between mutants of CST and septins were identified, with septins being noticeably sumoylated through the action of Siz1. The temperature-sensitive arrest in these new mutants of CST was dependent on the G2/M Mad2-mediated and Bub2-mediated spindle checkpoints as well as on the G2/M Mec1-mediated DNA damage checkpoint. Our data suggest the existence of yet unknown functions of the telomeric Cdc13-Stn1-Ten1 complex associated with mitotic spindle positioning and/or assembly that could be further elucidated by studying these new ten1-sz, stn1-sz and cdc13-sz mutants.

Searching for Beauty and Health: Aging in Women, Nutrition, and the Secret in Telomeres

Women typically outlive men, yet they often experience greater frailty and a higher incidence of chronic diseases as they age. By exploring the biological foundations of aging, with a particular focus on telomere dynamics, this manuscript aims to describe how dietary and lifestyle choices can significantly influence the aging process. The review comprehensively examines current research, underscoring the power of nutrition to counteract age-related changes, support healthy aging, and maintain vitality and beauty in women. The exploration of telomeres-the protective caps at the ends of chromosomes-reveals how they serve as markers of cellular aging and are potential targets for interventions aimed at enhancing women's longevity and quality of life. This study also emphasizes the importance of sex-specific approaches and precision medicine in understanding the unique health challenges women face as they age. By proposing targeted strategies, the review seeks to address these challenges, offering insights into preventive measures that can foster resilience, promote well-being, and extend healthy life expectancy in women. Ultimately, this work provides a sophisticated understanding of the aging process in women, highlighting the pivotal role of tailored interventions in preserving both health and beauty.

Protection of the Telomeric Junction by the Shelterin Complex

Shelterin serves critical roles in suppressing superfluous DNA damage repair pathways on telomeres. The junction between double-stranded telomeric tracts (dsTEL) and single-stranded telomeric overhang (ssTEL) is the most accessible region of the telomeric DNA. The shelterin complex contains dsTEL and ssTEL binding proteins and can protect this junction by bridging the ssTEL and dsTEL tracts. To test this possibility, we monitored shelterin binding to telomeric DNA substrates with varying ssTEL and dsTEL lengths and quantified its impact on telomere accessibility using single-molecule fluorescence microscopy methods in vitro. We identified the first dsTEL repeat nearest the junction as the preferred binding site for creating the shelterin bridge. Shelterin requires at least two ssTEL repeats, while the POT1 subunit of shelterin that binds to ssTEL requires longer ssTEL tracts for stable binding to telomeres and effective protection of the junction region. The ability of POT1 to protect the junction is significantly enhanced by the 5'-phosphate at the junction. Collectively, our results show that shelterin enhances the binding stability of POT1 to ssTEL and provides more effective protection compared with POT1 alone by bridging single- and double-stranded telomeric tracts.

TRF2-RAP1 represses RAD51-dependent homology-directed telomere repair by promoting BLM-mediated D-loop unwinding and inhibiting BLM-DNA2-dependent 5'-end resection

Inappropriate homology-directed repair (HDR) of telomeres results in catastrophic telomere loss and aberrant chromosome fusions, leading to genome instability. We have previously shown that the TRF2-RAP1 heterodimer protects telomeres from engaging in aberrant telomere HDR. Cells lacking the basic domain of TRF2 and functional RAP1 display HDR-mediated telomere clustering, resulting in the formation of ultrabright telomeres (UTs) and massive chromosome fusions. Using purified proteins, we uncover three distinct molecular pathways that the TRF2-RAP1 heterodimer utilizes to protect telomeres from engaging in aberrant HDR. We show mechanistically that TRF2-RAP1 inhibits RAD51-initiated telomeric D-loop formation. Both the TRF2 basic domain and RAP1-binding to TRF2 are required to block RAD51-mediated homology search. TRF2 recruits the BLM helicase to telomeres through its TRFH domain to promote BLM-mediated unwinding of telomere D-loops. In addition, TRF2-RAP1 inhibits BLM-DNA2-mediated 5' telomere end resection, preventing the generation of 3' single-stranded telomere overhangs necessary for RAD51-dependent HDR. Importantly, cells expressing BLM mutants unable to interact with TRF2 accumulate telomere D-loops and UTs. Our findings uncover distinct molecular mechanisms coordinated by TRF2-RAP1 to protect telomeres from engaging in aberrant HDR.

Germline variants in acquired aplastic anemia: current knowledge and future perspectives

Aplastic anemia (AA) is a disease characterized by failure of hematopoiesis, bone marrow aplasia, and pancytopenia. It can be inherited or acquired. Although acquired AA is believed to be immune-mediated and random, new evidence suggests an underlying genetic predisposition. Besides confirmed genomic mutations that contribute to inherited AA (such as pathogenic mutations of TERT and TERC), germline variants, often in heterozygous states, also play a not negligible role in the onset and progression of acquired AA. These variants, associated with inherited bone marrow failure syndromes and inborn errors of immunity, contribute to the disease, possibly through mechanisms including gene homeostasis, DNA repair, and immune injury. This article explores the nuanced association between acquired AA and germline variants, detailing the clinical significance of germline variants in diagnosing and managing this condition. More work is encouraged to better understand the role of immunogenic pathogenic variants and whether somatic mutations participate as secondary "hits" in the development of bone marrow failure.

The Clinical and Genetic Landscape of Hereditary Cancer: Experience from a Single Clinical Diagnostic Laboratory

BACKGROUND/AIM

The application of next-generation sequencing (NGS) technology in the genetic investigation of hereditary cancer is important for clinical surveillance, therapeutic approach, and reducing the risk of developing new malignancies. The aim of the study was to explore genetic predisposition in individuals referred for hereditary cancer.

MATERIALS AND METHODS

A total of 8,261 individuals were referred for multigene genetic testing, during the period 2020-2023, in the laboratory, and underwent multigene genetic testing using NGS. Among the examined individuals, 56.17% were diagnosed with breast cancer, 6.77% with ovarian cancer, 2.88% with colorectal cancer, 1.91% with prostate cancer, 6.43% were healthy with a significant family history of cancer, while 3.06% had a different type of cancer and 0.21% had not provided any information. Additionally, in 85 women with breast cancer we performed whole exome sequencing analysis.

RESULTS

20% of the examined individuals carried a pathogenic variant. Specifically, 54.8% of the patients had a pathogenic variant in a clinically significant gene (BRCA1, BRCA2, PALB2, RAD51C, PMS2, CDKN2A, MLH1, MSH2, TP53, MSH6, APC, RAD51D, PTEN, RET, CDH1, MEN1, and VHL). Among the different types of pathogenic variants detected, a significant percentage (6.52%) represented copy number variation (CNV). With WES analysis, the following findings were detected: CTC1: c.880C>T, p.(Gln294*); MLH3: c.405del, p.(Asp136Metfs*2), PPM1D: c.1426_1430del, p.(Glu476Leufs*3), and SDHB: c.395A>G, p.(His132Arg).

CONCLUSION

Comprehensive multigene genetic testing is necessary for appropriate clinical management of pathogenic variants' carriers. Additionally, the information obtained is important for determining the risk of malignancy development in family members of the examined individuals.

RIOK2 transcriptionally regulates TRiC and dyskerin complexes to prevent telomere shortening

Telomere shortening is a prominent hallmark of aging and is emerging as a characteristic feature of Myelodysplastic Syndromes (MDS) and Idiopathic Pulmonary Fibrosis (IPF). Optimal telomerase activity prevents progressive shortening of telomeres that triggers DNA damage responses. However, the upstream regulation of telomerase holoenzyme components remains poorly defined. Here, we identify RIOK2, a master regulator of human blood cell development, as a critical transcription factor for telomere maintenance. Mechanistically, loss of RIOK2 or its DNA-binding/transactivation properties downregulates mRNA expression of both TRiC and dyskerin complex subunits that impairs telomerase activity, thereby causing telomere shortening. We further show that RIOK2 expression is diminished in aged individuals and IPF patients, and it strongly correlates with shortened telomeres in MDS patient-derived bone marrow cells. Importantly, ectopic expression of RIOK2 alleviates telomere shortening in IPF patient-derived primary lung fibroblasts. Hence, increasing RIOK2 levels prevents telomere shortening, thus offering therapeutic strategies for telomere biology disorders.

Protection of the Telomeric Junction by the Shelterin Complex

Shelterin serves critical roles in suppressing superfluous DNA damage repair pathways on telomeres. The junction between double-stranded telomeric tracts (dsTEL) and single-stranded telomeric overhang (ssTEL) is the most accessible region of the telomeric DNA. The shelterin complex contains dsTEL and ssTEL binding proteins and can protect this junction by bridging between the ssTEL and dsTEL tracts. To test this possibility, we monitored shelterin binding to telomeric DNA substrates with varying ssTEL and dsTEL lengths and quantified its impact on telomere accessibility using single-molecule fluorescence microscopy methods in vitro. We identified the first dsTEL repeat nearest to the junction as the preferred binding site for creating the shelterin bridge. Shelterin requires at least two ssTEL repeats while the POT1 subunit of shelterin that binds to ssTEL requires longer ssTEL tracts for stable binding to telomeres and effective protection of the junction region. The ability of POT1 to protect the junction is significantly enhanced by the 5'-phosphate at the junction. Collectively, our results show that shelterin enhances the binding stability of POT1 to ssTEL and provides more effective protection compared to POT1 alone by bridging single- and double-stranded telomeric tracts.

Small molecule telomerase inhibitors are also potent inhibitors of telomeric C-strand synthesis

Telomere replication is essential for continued proliferation of human cells, such as stem cells and cancer cells. Telomerase lengthens the telomeric G-strand, while C-strand replication is accomplished by CST-polymerase α-primase (CST-PP). Replication of both strands is inhibited by formation of G-quadruplex (GQ) structures in the G-rich single-stranded DNA. TMPyP4 and pyridostatin (PDS), which stabilize GQ structures in both DNA and RNA, inhibit telomerase in vitro, and in human cells they cause telomere shortening that has been attributed to telomerase inhibition. Here, we show that TMPyP4 and PDS also inhibit C-strand synthesis by stabilizing DNA secondary structures and thereby preventing CST-PP from binding to telomeric DNA. We also show that these small molecules inhibit CST-PP binding to a DNA sequence containing no consecutive guanine residues, which is unlikely to form GQs. Thus, while these "telomerase inhibitors" indeed inhibit telomerase, they are also robust inhibitors of telomeric C-strand synthesis. Furthermore, given their binding to GQ RNA and their limited specificity for GQ structures, they may disrupt many other protein-nucleic acid interactions in human cells.

Telomeres and telomerase in Sarcoma disease and therapy

Sarcoma is a rare tumor derived from the mesenchymal tissue and mainly found in children and adolescents. The outcome for patients with sarcoma is relatively poor compared with that for many other solid malignant tumors. Sarcomas have a highly heterogeneous pathogenesis, histopathology and biological behavior. Dysregulated signaling pathways and various gene mutations are frequently observed in sarcomas. The telomere maintenance mechanism (TMM) has recently been considered as a prognostic factor for patients with sarcomas, and alternative lengthening of telomeres (ALT) positivity has been correlated with poor outcomes in patients with several types of sarcomas. Therefore, telomeres and telomerases may be useful targets for treating sarcomas. This review aims to provide an overview of telomere and telomerase biology in sarcomas.

Understanding the molecular mechanisms of human diseases: the benefits of fission yeasts

The role of model organisms such as yeasts in life science research is crucial. Although the baker's yeast (Saccharomyces cerevisiae) is the most popular model among yeasts, the contribution of the fission yeasts (Schizosaccharomyces) to life science is also indisputable. Since both types of yeasts share several thousands of common orthologous genes with humans, they provide a simple research platform to investigate many fundamental molecular mechanisms and functions, thereby contributing to the understanding of the background of human diseases. In this review, we would like to highlight the many advantages of fission yeasts over budding yeasts. The usefulness of fission yeasts in virus research is shown as an example, presenting the most important research results related to the Human Immunodeficiency Virus Type 1 (HIV-1) Vpr protein. Besides, the potential role of fission yeasts in the study of prion biology is also discussed. Furthermore, we are keen to promote the uprising model yeast Schizosaccharomyces japonicus, which is a dimorphic species in the fission yeast genus. We propose the hyphal growth of S. japonicus as an unusual opportunity as a model to study the invadopodia of human cancer cells since the two seemingly different cell types can be compared along fundamental features. Here we also collect the latest laboratory protocols and bioinformatics tools for the fission yeasts to highlight the many possibilities available to the research community. In addition, we present several limiting factors that everyone should be aware of when working with yeast models.

The Role of Glia Telomere Dysfunction in the Pathogenesis of Central Nervous System Diseases

Maintaining the telomere length is decisive for the viability and homeostasis process of all the cells of an organism, including human glial cells. Telomere shortening of microglial cells has been widely associated with the onset and progression of neurodegenerative diseases such as Parkinson's and Alzheimer's disease. Additionally, traumatic brain injury appears to have a positive correlation with the telomere-shortening process of microglia, and telomere length can be used as a non-invasive biomarker for the clinical management of these patients. Moreover, telomere involvement through telomerase reactivation and homologous recombination also known as the alternative lengthening of telomeres (ALT) has been described in gliomagenesis pathways, and particular focus has been given in the translational significance of these mechanisms in gliomas diagnosis and prognostic classification. Finally, glia telomere shortening is implicated in some psychiatric diseases. Given that telomere dysfunction of glial cells is involved in the central nervous system (CNS) disease pathogenesis, it represents a promising drug target that could lead to the incorporation of new tools in the medicinal arsenal for the management of so far incurable conditions.

Mendelian randomization identifies causal effects of major depressive disorder on accelerated aging

BACKGROUND

Evidence links major depressive disorder (MDD) with aging, but it's unclear if MDD accelerates aging and what factors mediate this transition.

METHODS

Two-sample Mendelian randomization (MR) analyses were applied to estimate the causal association between MDD and frailty index (FI), telomere length (TL), and appendicular lean mass (ALM) from available genome-wide association studies in populations of European ancestry. Furthermore, we conducted mediation MR analyses to assess the mediating effects of 31 lifestyle factors or diseases on the causal relationship between MDD and aging.

RESULTS

MDD was significantly causally associated with increased FI (βIVW = 0.23, 95 % CI = 0.18 to 0.28, p = 1.20 × 10-17), shorter TL (βIVW = -0.04, 95 % CI = -0.07 to -0.01, p = 0.01), and decreased ALM (βIVW = -0.07, 95 % CI = -0.11 to -0.03, p = 3.54 × 10-4). The mediation analysis through two-step MR revealed smoking initiation (9.09 %), hypertension (6.67 %) and heart failure (5.36 %) mediated the causal effect of MDD on FI. Additionally, alcohol use disorders and alcohol dependence on the causal relationship between MDD and TL were found to be 17.52 % and 17.13 % respectively.

LIMITATIONS

Confounding, statistical power, and Euro-centric focus limit generalization.

CONCLUSION

Overall, individuals with MDD may be at a higher risk of experiencing premature aging, and this risk is partially influenced by the pathways involving smoking, alcohol use, and cardiovascular health. It underscores the importance of early intervention and comprehensive health management in individuals with MDD to promote healthy aging and overall well-being.

Targeting shelterin proteins for cancer therapy

As a global health challenge, cancer prompts continuous exploration for innovative therapies that are also based on new targets. One promising avenue is targeting the shelterin protein complex, a safeguard for telomeres crucial in preventing DNA damage. The role of shelterin in modulating ataxia-telangiectasia mutated (ATM) and ataxia-telangiectasia and Rad3-related (ATR) kinases, key players in the DNA damage response (DDR), establishes its significance in cancer cells. Disrupting these defence mechanisms of shelterins, especially in cancer cells, renders telomeres vulnerable, potentially leading to genomic instability and hindering cancer cell survival. In this review, we outline recent approaches exploring shelterins as potential anticancer targets, highlighting the prospect of developing selective molecules to exploit telomere vulnerabilities toward new innovative cancer treatments.

Binding of the TRF2 iDDR motif to RAD50 highlights a convergent evolutionary strategy to inactivate MRN at telomeres

Telomeres protect chromosome ends from unscheduled DNA repair, including from the MRN (MRE11, RAD50, NBS1) complex, which processes double-stranded DNA breaks (DSBs) via activation of the ATM kinase, promotes DNA end-tethering aiding the non-homologous end-joining (NHEJ) pathway, and initiates DSB resection through the MRE11 nuclease. A protein motif (MIN, for MRN inhibitor) inhibits MRN at budding yeast telomeres by binding to RAD50 and evolved at least twice, in unrelated telomeric proteins Rif2 and Taz1. We identify the iDDR motif of human shelterin protein TRF2 as a third example of convergent evolution for this telomeric mechanism for binding MRN, despite the iDDR lacking sequence homology to the MIN motif. CtIP is required for activation of MRE11 nuclease action, and we provide evidence for binding of a short C-terminal region of CtIP to a RAD50 interface that partly overlaps with the iDDR binding site, indicating that the interaction is mutually exclusive. In addition, we show that the iDDR impairs the DNA binding activity of RAD50. These results highlight direct inhibition of MRN action as a crucial role of telomeric proteins across organisms and point to multiple mechanisms enforced by the iDDR to disable the many activities of the MRN complex.

POT1 recruits and regulates CST-Polα/primase at human telomeres

Telomere maintenance requires the extension of the G-rich telomeric repeat strand by telomerase and the fill-in synthesis of the C-rich strand by Polα/primase. At telomeres, Polα/primase is bound to Ctc1/Stn1/Ten1 (CST), a single-stranded DNA-binding complex. Like mutations in telomerase, mutations affecting CST-Polα/primase result in pathological telomere shortening and cause a telomere biology disorder, Coats plus (CP). We determined cryogenic electron microscopy structures of human CST bound to the shelterin heterodimer POT1/TPP1 that reveal how CST is recruited to telomeres by POT1. Our findings suggest that POT1 hinge phosphorylation is required for CST recruitment, and the complex is formed through conserved interactions involving several residues mutated in CP. Our structural and biochemical data suggest that phosphorylated POT1 holds CST-Polα/primase in an inactive, autoinhibited state until telomerase has extended the telomere ends. We propose that dephosphorylation of POT1 releases CST-Polα/primase into an active state that completes telomere replication through fill-in synthesis.

Structural and functional insights into yeast Tbf1 as an atypical telomeric repeat-binding factor

Telomeric repeat-binding factor 1 (Tbf1) has a similar architecture as the TRF family of telomeric proteins and plays important roles in both telomere homeostasis and ribosome regulation. However, the molecular basis of why Tbf1 has such different functions compared to other TRFs remains unclear. Here, we present the crystal structures of the TRF homology (TRFH) and Myb-L domains from Schizosaccharomyces pombe Tbf1 (spTbf1). TRFH-mediated homodimerization is essential for spTbf1 stability. Importantly, spTbf1TRFH lacks the conserved docking motif for interactions with telomeric proteins, explaining why spTbf1 does not participate in the assembly of the shelterin complex. Finally, structural and biochemical analyses demonstrate that TRFH and Myb-L domains as well as the loop region of spTbf1 coordinate to recognize S. pombe telomeric double-stranded DNA. Overall, our findings provide structural and functional insights into how fungi Tbf1 acts as an atypical telomeric repeat-binding factor, which helps to understand the evolution of TRFH-containing telomeric proteins.

Current and Future Trends of Colorectal Cancer Treatment: Exploring Advances in Immunotherapy

Cancer of the colon and rectum (CRC) has been identified among the three most prevalent types of cancer and cancer-related deaths for both sexes. Even though significant progress in surgical and chemotherapeutic techniques has markedly improved disease-free and overall survival rates in contrast to those three decades ago, recent years have seen a stagnation in these improvements. This underscores the need for new therapies aiming to augment patient outcomes. A number of emerging strategies, such as immune checkpoint inhibitors (ICIs) and adoptive cell therapy (ACT), have exhibited promising outcomes not only in preclinical but also in clinical settings. Additionally, a thorough appreciation of the underlying biology has expanded the scope of research into potential therapeutic interventions. For instance, the pivotal role of altered telomere length in early CRC carcinogenesis, leading to chromosomal instability and telomere dysfunction, presents a promising avenue for future treatments. Thus, this review explores the advancements in CRC immunotherapy and telomere-targeted therapies, examining potential synergies and how these novel treatment modalities intersect to potentially enhance each other's efficacy, paving the way for promising future therapeutic advancements.

Genetic polymorphisms affecting telomere length and their association with cardiovascular disease in the Heinz-Nixdorf-Recall study

Short telomeres are associated with cardiovascular disease (CVD). We aimed to investigate, if genetically determined telomere-length effects CVD-risk in the Heinz-Nixdorf-Recall study (HNRS) population. We selected 14 single-nucleotide polymorphisms (SNPs) associated with telomere-length (p<10-8) from the literature and after exclusion 9 SNPs were included in the analyses. Additionally, a genetic risk score (GRS) using these 9 SNPs was calculated. Incident CVD was defined as fatal and non-fatal myocardial infarction, stroke, and coronary death. We included 3874 HNRS participants with available genetic data and had no known history of CVD at baseline. Cox proportional-hazards regression was used to test the association between the SNPs/GRS and incident CVD-risk adjusting for common CVD risk-factors. The analyses were further stratified by CVD risk-factors. During follow-up (12.1±4.31 years), 466 participants experienced CVD-events. No association between SNPs/GRS and CVD was observed in the adjusted analyses. However, the GRS, rs10936599, rs2487999 and rs8105767 increase the CVD-risk in current smoker. Few SNPs (rs10936599, rs2487999, and rs7675998) showed an increased CVD-risk, whereas rs10936599, rs677228 and rs4387287 a decreased CVD-risk, in further strata. The results of our study suggest different effects of SNPs/GRS on CVD-risk depending on the CVD risk-factor strata, highlighting the importance of stratified analyses in CVD risk-factors.

Human CST complex restricts excessive PrimPol repriming upon UV induced replication stress by suppressing p21

DNA replication stress, caused by various endogenous and exogenous agents, halt or stall DNA replication progression. Cells have developed diverse mechanisms to tolerate and overcome replication stress, enabling them to continue replication. One effective strategy to overcome stalled replication involves skipping the DNA lesion using a specialized polymerase known as PrimPol, which reinitiates DNA synthesis downstream of the damage. However, the mechanism regulating PrimPol repriming is largely unclear. In this study, we observe that knockdown of STN1 or CTC1, components of the CTC1/STN1/TEN1 complex, leads to enhanced replication progression following UV exposure. We find that such increased replication is dependent on PrimPol, and PrimPol recruitment to stalled forks increases upon CST depletion. Moreover, we find that p21 is upregulated in STN1-depleted cells in a p53-independent manner, and p21 depletion restores normal replication rates caused by STN1 deficiency. We identify that p21 interacts with PrimPol, and STN1 depletion stimulates p21-PrimPol interaction and facilitates PrimPol recruitment to stalled forks. Our findings reveal a previously undescribed interplay between CST, PrimPol and p21 in promoting repriming in response to stalled replication, and shed light on the regulation of PrimPol repriming at stalled forks.

Pharmacodynamic and Toxicity Studies of 6-Isopropyldithio-2'-guanosine Analogs in Acute T-Lymphoblastic Leukemia

(1) Background: The research group has developed a new small molecule, 6-Isopropyldithio-2'-deoxyguanosine analogs-YLS004, which has been shown to be the most sensitive in acute T-lymphoblastic leukemia cells. Moreover, it was found that the structure of Nelarabine, a drug used to treat acute T-lymphoblastic leukemia, is highly similar to that of YLS004. Consequently, the structure of YLS004 was altered to produce a new small molecule inhibitor for this study, named YLS010. (2) Results: YLS010 has exhibited potent anti-tumor effects by inducing cell apoptosis and ferroptosis. A dose gradient was designed for in vivo experiments based on tentative estimates of the toxicity dose using acute toxicity in mice and long-term toxicity in rats. The study found that YLS010 at a dose of 8 mg/kg prolonged the survival of late-stage acute T-lymphoblastic leukemia mice in the mouse model study. (3) Conclusions: YLS010 has demonstrated specific killing effects against acute T-lymphoblastic leukemia both in vivo and in vitro. Preclinical studies of YLS010 offer a new opportunity for the treatment of patients with acute T-lymphoblastic leukemia in clinical settings.

Structural Motifs at the Telomeres and Their Role in Regulatory Pathways

Telomeres are specialized structures, found at the ends of linear chromosomes in eukaryotic cells, that play a crucial role in maintaining the stability and integrity of genomes. They are composed of repetitive DNA sequences, ssDNA overhangs, and several associated proteins. The length of telomeres is linked to cellular aging in humans, and deficiencies in their maintenance are associated with various diseases. Key structural motifs at the telomeres serve to protect vulnerable chromosomal ends. Telomeric DNA also has the ability to form diverse complex DNA higher-order structures, including T-loops, D-loops, R-loops, G-loops, G-quadruplexes, and i-motifs, in the complementary C-rich strand. While many essential proteins at telomeres have been identified, the intricacies of their interactions and structural details are still not fully understood. This Perspective highlights recent advancements in comprehending the structures associated with human telomeres. It emphasizes the significance of telomeres, explores various telomeric structural motifs, and delves into the structural biology surrounding telomeres and telomerase. Furthermore, telomeric loops, their topologies, and the associated proteins that contribute to the safeguarding of telomeres are discussed.

Kinesin Family Member-18A (KIF18A) Promotes Cell Proliferation and Metastasis in Hepatocellular Carcinoma

BACKGROUND & AIMS

Kinesin family member 18A (KIF18A) is notable for its aberrant expression across various cancer types and its pivotal role is driving cancer progression. In this study, we aim to investigate the intricate molecular mechanisms underlying the impact of KIF18A on the progression of HCC.

METHODS

Western blotting assays, a quantitative real-time PCR and immunohistochemical analyses were performed to quantitatively assess KIF18A expression in HCC tissues. We then performed genetic manipulations within HCC cells by silencing endogenous KIF18A using short hairpin RNA (shRNA) and introducing exogenous plasmids to overexpress KIF18A. We monitored cell progression, analyzed cell cycle and cell apoptosis and assessed cell migration and invasion both in vitro and in vivo. Moreover, we conducted RNA-sequencing to explore KIF18A-related signaling pathways utilizing Reactome and KEGG enrichment methods and validated these critical mediators in these pathways.

RESULTS

Analysis of the TCGA-LIHC database revealed pronounced overexpression of KIF18A in HCC tissues, the finding was subsequently confirmed through the analysis of clinical samples obtained from HCC patients. Notably, silencing KIF18A in cells led to an obvious inhibition of cell proliferation, migration and invasion in vitro. Furthermore, in subcutaneous and orthotopic xenograft models, suppression of KIF18A sgnificantly redudce tumor weight and the number of lung metastatic nodules. Mechanistically, KIF18A appears to facilitate cell proliferation by upregulating MAD2 and CDK1/CyclinB1 expression levels, with the activation of SMAD2/3 signaling contributing to KIF18A-driven metastasis.

CONCLUSION

Our study elucidates the molecular mechanism by which KIF18A mediates proliferation and metastasis in HCC cells, offering new insights into potential therapeutic targets.

Methods that shaped telomerase research

Telomerase, the ribonucleoprotein (RNP) responsible for telomere maintenance, has a complex life. Complex in that it is made of multiple proteins and an RNA, and complex because it undergoes many changes, and passes through different cell compartments. As such, many methods have been developed to discover telomerase components, delve deep into understanding its structure and function and to figure out how telomerase biology ultimately relates to human health and disease. While some old gold-standard methods are still key for determining telomere length and measuring telomerase activity, new technologies are providing promising new ways to gain detailed information that we have never had access to before. Therefore, we thought it timely to briefly review the methods that have revealed information about the telomerase RNP and outline some of the remaining questions that could be answered using new methodology.

Starting DNA Synthesis: Initiation Processes during the Replication of Chromosomal DNA in Humans

The initiation reactions of DNA synthesis are central processes during human chromosomal DNA replication. They are separated into two main processes: the initiation events at replication origins, the start of the leading strand synthesis for each replicon, and the numerous initiation events taking place during lagging strand DNA synthesis. In addition, a third mechanism is the re-initiation of DNA synthesis after replication fork stalling, which takes place when DNA lesions hinder the progression of DNA synthesis. The initiation of leading strand synthesis at replication origins is regulated at multiple levels, from the origin recognition to the assembly and activation of replicative helicase, the Cdc45-MCM2-7-GINS (CMG) complex. In addition, the multiple interactions of the CMG complex with the eukaryotic replicative DNA polymerases, DNA polymerase α-primase, DNA polymerase δ and ε, at replication forks play pivotal roles in the mechanism of the initiation reactions of leading and lagging strand DNA synthesis. These interactions are also important for the initiation of signalling at unperturbed and stalled replication forks, "replication stress" events, via ATR (ATM-Rad 3-related protein kinase). These processes are essential for the accurate transfer of the cells' genetic information to their daughters. Thus, failures and dysfunctions in these processes give rise to genome instability causing genetic diseases, including cancer. In their influential review "Hallmarks of Cancer: New Dimensions", Hanahan and Weinberg (2022) therefore call genome instability a fundamental function in the development process of cancer cells. In recent years, the understanding of the initiation processes and mechanisms of human DNA replication has made substantial progress at all levels, which will be discussed in the review.

The translational potential of studying bat immunity

Molecular studies in bats have led to the discovery of antiviral adaptations that may explain how some bat species have evolved enhanced immune tolerance towards viruses. Accumulating data suggest that some bat species have also evolved remarkable features of longevity and low rates of cancer. Furthermore, recent research strongly suggests that discovering immune adaptations in bat models can be translated to develop immune modulators and recognize alternate therapeutic strategies for diseases affecting humans. We posit that research in bat immunology will lead to discoveries that can potentially be translated to improve health outcomes in humans.

CST-polymerase α-primase solves a second telomere end-replication problem

Telomerase adds G-rich telomeric repeats to the 3' ends of telomeres1, counteracting telomere shortening caused by loss of telomeric 3' overhangs during leading-strand DNA synthesis ('the end-replication problem'2). Here we report a second end-replication problem that originates from the incomplete duplication of the C-rich telomeric repeat strand (C-strand) by lagging-strand DNA synthesis. This problem is resolved by fill-in synthesis mediated by polymerase α-primase bound to Ctc1-Stn1-Ten1 (CST-Polα-primase). In vitro, priming for lagging-strand DNA replication does not occur on the 3' overhang and lagging-strand synthesis stops in a zone of approximately 150 nucleotides (nt) more than 26 nt from the end of the template. Consistent with the in vitro data, lagging-end telomeres of cells lacking CST-Polα-primase lost 50-60 nt of telomeric CCCTAA repeats per population doubling. The C-strands of leading-end telomeres shortened by around 100 nt per population doubling, reflecting the generation of 3' overhangs through resection. The measured overall C-strand shortening in the absence of CST-Polα-primase fill-in is consistent with the combined effects of incomplete lagging-strand synthesis and 5' resection at the leading ends. We conclude that canonical DNA replication creates two telomere end-replication problems that require telomerase to maintain the G-rich strand and CST-Polα-primase to maintain the C-strand.

Guardians of the Genome: How the Single-Stranded DNA-Binding Proteins RPA and CST Facilitate Telomere Replication

Telomeres act as the protective caps of eukaryotic linear chromosomes; thus, proper telomere maintenance is crucial for genome stability. Successful telomere replication is a cornerstone of telomere length regulation, but this process can be fraught due to the many intrinsic challenges telomeres pose to the replication machinery. In addition to the famous "end replication" problem due to the discontinuous nature of lagging strand synthesis, telomeres require various telomere-specific steps for maintaining the proper 3' overhang length. Bulk telomere replication also encounters its own difficulties as telomeres are prone to various forms of replication roadblocks. These roadblocks can result in an increase in replication stress that can cause replication forks to slow, stall, or become reversed. Ultimately, this leads to excess single-stranded DNA (ssDNA) that needs to be managed and protected for replication to continue and to prevent DNA damage and genome instability. RPA and CST are single-stranded DNA-binding protein complexes that play key roles in performing this task and help stabilize stalled forks for continued replication. The interplay between RPA and CST, their functions at telomeres during replication, and their specialized features for helping overcome replication stress at telomeres are the focus of this review.

Telomere dynamics and oxidative stress in Arabidopsis grown in lunar regolith simulant

NASA envisions a future where humans establish a thriving colony on the Moon by 2050. Plants will be essential for this endeavor, but little is known about their adaptation to extraterrestrial bodies. The capacity to grow plants in lunar regolith would represent a major step towards this goal by minimizing the reliance on resources transported from Earth. Recent studies reveal that Arabidopsis thaliana can germinate and grow on genuine lunar regolith as well as on lunar regolith simulant. However, plants arrest in vegetative development and activate a variety of stress response pathways, most notably the oxidative stress response. Telomeres are hotspots for oxidative damage in the genome and a marker of fitness in many organisms. Here we examine A. thaliana growth on a lunar regolith simulant and the impact of this resource on plant physiology and on telomere dynamics, telomerase enzyme activity and genome oxidation. We report that plants successfully set seed and generate a viable second plant generation if the lunar regolith simulant is pre-washed with an antioxidant cocktail. However, plants sustain a higher degree of genome oxidation and decreased biomass relative to conventional Earth soil cultivation. Moreover, telomerase activity substantially declines and telomeres shorten in plants grown in lunar regolith simulant, implying that genome integrity may not be sustainable over the long-term. Overcoming these challenges will be an important goal in ensuring success on the lunar frontier.

Club cell-specific telomere protection protein 1 (TPP1) protects against tobacco smoke-induced lung inflammation, xenobiotic metabolic dysregulation, and injurious responses

Inhaling xenobiotics, such as tobacco smoke is a major risk factor for pulmonary diseases, e.g., COPD/emphysema, interstitial lung disease, and pre-invasive diseases. Shelterin complex or telosome provides telomeric end protection during replication. Telomere protection protein 1 (TPP1) is one of the main six subunits of the shelterin complex supporting the telomere stability and genomic integrity. Dysfunctional telomeres and shelterin complex are associated as a disease mechanism of tobacco smoke-induced pulmonary damage and disease processes. The airway epithelium is critical to maintaining respiratory homeostasis and is implicated in lung diseases. Club cells (also known as clara cells) play an essential role in the immune response, surfactant production, and metabolism. Disrupted shelterin complex may lead to dysregulated cellular function, DNA damage, and disease progression. However, it is unknown if the conditional removal of TPP1 from Club cells can induce lung disease pathogenesis caused by tobacco smoke exposure. In this study, conditional knockout of Club-cell specific TPP1 demonstrated the instability of other shelterin protein subunits, such as TRF1, dysregulation of cell cycle checkpoint proteins, p53 and downstream targets, and dysregulation of telomeric genes. This was associated with age-dependent senescence-associated genes, increased DNA damage, and upregulated RANTES/IL13/IL33 mediated lung inflammation and injury network by cigarette smoke (CS). These phenomena are also associated with alterations in cytochrome P450 and glutathione transferases, upregulated molecular pathways promoting lung lesions, bronchial neoplasms, and adenocarcinomas. These findings suggest a pivotal role of TPP1 in maintaining lung homeostasis and injurious responses in response to CS. Thus, these data TPP1 may have therapeutic value in alleviating telomere-related chronic lung diseases.

Genome stability from the perspective of telomere length

Telomeres and their associated proteins protect the ends of chromosomes to maintain genome stability. Telomeres undergo progressive shortening with each cell division in mammalian somatic cells without telomerase, resulting in genome instability. When telomeres reach a critically short length or are recognized as a damage signal, cells enter a state of senescence, followed by cell cycle arrest, programmed cell death, or immortalization. This review provides an overview of recent advances in the intricate relationship between telomeres and genome instability. Alongside well-established mechanisms such as chromosomal fusion and telomere fusion, we will delve into the perspective on genome stability by examining the role of retrotransposons. Retrotransposons represent an emerging pathway to regulate genome stability through their interactions with telomeres.

The C-terminal extension of dyskerin is a dyskeratosis congenita mutational hotspot that modulates interaction with telomerase RNA and subcellular localization

Dyskerin is a component of the human telomerase complex and is involved in stabilizing the human telomerase RNA (hTR). Many mutations in the DKC1 gene encoding dyskerin are found in X-linked dyskeratosis congenita (X-DC), a premature aging disorder and other related diseases. The C-terminal extension (CTE) of dyskerin contributes to its interaction with the molecular chaperone SHQ1 during the early stage of telomerase biogenesis. Disease mutations in this region were proposed to disrupt dyskerin-SHQ1 interaction and destabilize dyskerin, reducing hTR levels indirectly. However, biochemical evidence supporting this hypothesis is still lacking. In addition, the effects of many CTE disease mutations on hTR have not been examined. In this study, we tested eight dyskerin CTE variants and showed that they failed to maintain hTR levels. These mutants showed slightly reduced but not abolished interaction with SHQ1, and caused defective binding to hTR. Deletion of the CTE further reduced binding to hTR, and perturbed localization of dyskerin to the Cajal bodies and the nucleolus, and the interaction with TCAB1 as well as GAR1. Our findings suggest impaired dyskerin-hTR interaction in cells as a previously overlooked mechanism through which dyskerin CTE mutations cause X-DC and related telomere syndromes.

Protein-Protein Interactions of Seryl-tRNA Synthetases with Emphasis on Human Counterparts and Their Connection to Health and Disease

Seryl-tRNA synthetases (SerRSs), members of the aminoacyl-tRNA synthetase family, interact with diverse proteins, enabling SerRSs to enhance their role in the translation of the genetic message or to perform alternative functions in cellular processes beyond translation. Atypical archaeal SerRS interacts with arginyl-tRNA synthetase and proteins of the ribosomal P-stalk to optimize translation through tRNA channeling. The complex between yeast SerRS and peroxin Pex21p provides a connection between translation and peroxisome function. The partnership between Arabidopsis SerRS and BEN1 indicates a link between translation and brassinosteroid metabolism and may be relevant in plant stress response mechanisms. In Drosophila, the unusual heterodimeric mitochondrial SerRS coordinates mitochondrial translation and replication via interaction with LON protease. Evolutionarily conserved interactions of yeast and human SerRSs with m3C32 tRNA methyltransferases indicate coordination between tRNA modification and aminoacylation in the cytosol and mitochondria. Human cytosolic SerRS is a cellular hub protein connecting translation to vascular development, angiogenesis, lipogenesis, and telomere maintenance. When translocated to the nucleus, SerRS acts as a master negative regulator of VEGFA gene expression. SerRS alone or in complex with YY1 and SIRT2 competes with activating transcription factors NFκB1 and c-Myc, resulting in balanced VEGFA expression important for proper vascular development and angiogenesis. In hypoxia, SerRS phosphorylation diminishes its binding to the VEGFA promoter, while the lack of nutrients triggers SerRS glycosylation, reducing its nuclear localization. Additionally, SerRS binds telomeric DNA and cooperates with the shelterin protein POT1 to regulate telomere length and cellular senescence. As an antitumor and antiangiogenic factor, human cytosolic SerRS appears to be a promising drug target and therapeutic agent for treating cancer, cardiovascular diseases, and possibly obesity and aging.