Molecular mechanisms of telomere biology disorders

Dyskeratosis congenita associated with a novel missense variant in TERT: Approach for the dermatologists

Dyskeratosis congenita (DC) is a telomeropathy presenting diagnostic and therapeutic challenges across multiple specialties; yet, subtle dermatological signs enable early detection, altering patient prognosis. A specific DC genetic sequencing was performed according to the clinical criteria of our patient in study. Subsequently, cross-checked information in the main genetic databases was carried out. Additionally, an extensive review of the literature was made to organize the main dermatological aspects in DC. We report a novel variant of DC. Additionally, we share 10 useful and practical messages for dermatologists and any specialist caring for this group of patients.

Replication stress as a driver of cellular senescence and aging

Replication stress refers to slowing or stalling of replication fork progression during DNA synthesis that disrupts faithful copying of the genome. While long considered a nexus for DNA damage, the role of replication stress in aging is under-appreciated. The consequential role of replication stress in promotion of organismal aging phenotypes is evidenced by an extensive list of hereditary accelerated aging disorders marked by molecular defects in factors that promote replication fork progression and operate uniquely in the replication stress response. Additionally, recent studies have revealed cellular pathways and phenotypes elicited by replication stress that align with designated hallmarks of aging. Here we review recent advances demonstrating the role of replication stress as an ultimate driver of cellular senescence and aging. We discuss clinical implications of the intriguing links between cellular senescence and aging including application of senotherapeutic approaches in the context of replication stress.

Clinical mutations in the TERT and TERC genes coding for telomerase components induced oxidative stress, DNA damage at telomeres and cell apoptosis besides decreased telomerase activity

Telomeres are nucleoprotein structures at the end of chromosomes that maintain their integrity. Mutations in genes coding for proteins involved in telomere protection and elongation produce diseases such as dyskeratosis congenita or idiopathic pulmonary fibrosis known as telomeropathies. These diseases are characterized by premature telomere shortening, increased DNA damage and oxidative stress. Genetic diagnosis of telomeropathy patients has identified mutations in the genes TERT and TERC coding for telomerase components but the functional consequences of many of these mutations still have to be experimentally demonstrated. The activity of twelve TERT and five TERC mutants, five of them identified in Spanish patients, has been analyzed. TERT and TERC mutants were expressed in VA-13 human cells that express low telomerase levels and the activity induced was analyzed. The production of reactive oxygen species, DNA oxidation and TRF2 association at telomeres, DNA damage response and cell apoptosis were determined. Most mutations presented decreased telomerase activity, as compared to wild-type TERT and TERC. In addition, the expression of several TERT and TERC mutants induced oxidative stress, DNA oxidation, DNA damage, decreased recruitment of the shelterin component TRF2 to telomeres and increased apoptosis. These observations might indicate that the increase in DNA damage and oxidative stress observed in cells from telomeropathy patients is dependent on their TERT or TERC mutations. Therefore, analysis of the effect of TERT and TERC mutations of unknown function on DNA damage and oxidative stress could be of great utility to determine the possible pathogenicity of these variants.

The function of Bazhen decoction in rescuing progeroid cell senescence via facilitating G-quadruplex resolving and telomere elongation

ETHNOPHARMACOLOGICAL RELEVANCE

The Bazhen decoction is one of the most extensively used Traditional Chinese medicine (TCM) prescriptions for treatment of aging related diseases. However, due to the complexity of the components, the pharmacological mechanism of Bazhen decoction is still limited.

AIM OF THE STUDY

In this study, with the aim of helping the clinical precision medicine of TCM, we try out a systematic analysis for dissecting the molecular mechanism of complicated TCM prescription: Bazhen decoction. We identify the pharmacological mechanism of Bazhen decoction in telomere elongation as revealed by systematic analysis.

MATERIALS AND METHODS

By RNA sequencing and transcriptome analysis of Bazhen decoction treated wild type cells, we reveal the transcriptome profile induced by Bazhen decoction. We utilized the cells derived from Werner syndrome (WS) mice, which is known to be dysfunctional in telomere elongation due to the deficiency of DNA helicase Wrn. By Western blot, qPCR, Immunofluorescence, flow cytometry, telomere FISH, and SA-β-Gal staining, we verify the transcriptome data and confirm the pharmacological function of Bazhen decoction and its drug containing serum in telomere elongation and reversing progeroid cell senescence.

RESULTS

We reveal that Bazhen decoction may systematically regulate multiple anti-aging pathways, including stem cell regulation, protein homeostasis, cardiovascular function, neuronal function, anti-inflammation, anti-DNA damage induced stress, DNA helicase activity and telomere lengthening. We find that Bazhen decoction and its drug containing serum could up-regulate multiple DNA helicases and telomere regulating proteins. The increased DNA helicases promote the resolving of G-quadruplex (G4) structures, and facilitate DNA replication and telomere elongation. These improvements also endow the cellular resistance to DNA damages induced by replication stress, and rescue the WS caused cellular senescence.

CONCLUSIONS

Together these data suggest that Bazhen decoction up-regulate the expression of DNA helicases, thus facilitate G4 resolving and telomere maintenance, which rescue the progeroid cellular senescence and contribute to its anti-aging properties. Our data reveal a new molecular mechanism of Bazhen decoction in anti-aging related diseases via elongating telomere, this may shed light in the application of Bazhen decoction in multiple degenerative diseases caused by telomere erosion.

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.

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.

Linking Gene Fusions to Bone Marrow Failure and Malignant Transformation in Dyskeratosis Congenita

Dyskeratosis Congenita (DC) is a multisystem disorder intrinsically associated with telomere dysfunction, leading to bone marrow failure (BMF). Although the pathology of DC is largely driven by mutations in telomere-associated genes, the implications of gene fusions, which emerge due to telomere-induced genomic instability, remain unexplored. We meticulously analyzed gene fusions in RNA-Seq data from DC patients to provide deeper insights into DC's progression. The most significant DC-specific gene fusions were subsequently put through in silico assessments to ascertain biophysical and structural attributes, including charge patterning, inherent disorder, and propensity for self-association. Selected candidates were then analyzed using deep learning-powered structural predictions and molecular dynamics simulations to gauge their potential for forming higher-order oligomers. Our exploration revealed that genes participating in fusion events play crucial roles in upholding genomic stability, facilitating hematopoiesis, and suppressing tumors. Notably, our analysis spotlighted a particularly disordered polyampholyte fusion protein that exhibits robust higher-order oligomerization dynamics. To conclude, this research underscores the potential significance of several high-confidence gene fusions in the progression of BMF in DC, particularly through the dysregulation of genomic stability, hematopoiesis, and tumor suppression. Additionally, we propose that these fusion proteins might hold a detrimental role, specifically in inducing proteotoxicity-driven hematopoietic disruptions.

Genetically determined telomere length and its association with chronic obstructive pulmonary disease and interstitial lung disease in biobank Japan: A Mendelian randomization study

Importance

Chronic obstructive pulmonary disease (COPD) and interstitial lung disease (ILD) have been linked to shorter telomere length (TL). While understanding this association has critical clinical implications for respiratory diseases, previous studies exploring these associations were conducted in European populations. The present study aims to investigate this relationship in an Asian population.

Objective

To examine the causal relationship between leukocyte TL and COPD and ILD in an Asian population.

Design

Setting, and Participants: We used a genome-wide association study summary statistics-based two-sample Mendelian randomization (MR) design to investigate the association between leukocyte TL, genetically predicted by nine single-nucleotide polymorphisms and the risk of COPD and ILD. Participants were Japanese individuals enrolled in the Biobank Japan Project, including 3315 COPD patients and 806 ILD patients.

Exposure

Leukocyte TL was genetically predicted by nine single-nucleotide polymorphisms.

Results

The inverse-variance weighted estimates showed a significant inverse association between leukocyte TL and COPD (odds ratio [OR] = 0.78; 95 % confidence interval [CI]: 0.64, 0.95; P = 0.01) and ILD (OR = 0.29; 95 % CI: 0.14, 0.61; P = 0.001), respectively. All sensitivity analyses yielded consistent results. The MR-Egger regression intercept test showed no evidence of horizontal pleiotropy (Pintercept: COPD, 0.56; ILD: 0.70).

Conclusion

and Relevance: Our findings suggest that leukocyte telomere shortening may causally increase the risk of COPD and ILD. These results highlight the potential importance of TL for these respiratory diseases.

Comparative Application of Terminal Restriction Fragment Analysis Tools to Large-Scale Genomic Assays

The analysis of telomere length is an important component of many studies aiming to characterize the role of telomere maintenance mechanisms in cellular lifespan, disease, or in general chromosome protection and DNA replication pathways. Several powerful methods to accurately measure the telomere length from Southern blots have been developed, but their utility for large-scale genomic studies has not been previously evaluated. Here, we performed a comparative analysis of two recently developed programs, TeloTool and WALTER, for the extraction of mean telomere length values from Southern blots. Using both software packages, we measured the telomere length in two extensive experimental datasets for the model plant Arabidopsis thaliana, consisting of 537 natural accessions and 65 T-DNA (transfer DNA for insertion mutagenesis) mutant lines in the reference Columbia (Col-0) genotype background. We report that TeloTool substantially overestimates the telomere length in comparison to WALTER, especially for values over 4500 bp. Importantly, the TeloTool- and WALTER-calculated telomere length values correlate the most in the 2100-3500 bp range, suggesting that telomeres in this size interval can be estimated by both programs equally well. We further show that genome-wide association studies using datasets from both telomere length analysis tools can detect the most significant SNP candidates equally well. However, GWAS analysis with the WALTER dataset consistently detects fewer significant SNPs than analysis with the TeloTool dataset, regardless of the GWAS method used. These results imply that the telomere length data generated by WALTER may represent a more stringent approach to GWAS and SNP selection for the downstream molecular screening of candidate genes. Overall, our work reveals the unanticipated impact of the telomere length analysis method on the outcomes of large-scale genomic screens.

Germline Predisposition to Myeloid Neoplasms: Diagnostic Concepts and Classifications

Molecular and sequencing advances have led to substantial breakthroughs in the discovery of new genes and inherited mutations associated with increased risk of developing myeloid malignancies. Many of the same germline mutated genes are also drivers of malignancy in sporadic cancer. Recognition of myeloid malignancy associated with germline mutations is essential for proper therapy, disease surveillance, informing related donor selection for hematopoietic stem cell transplantation, and genetic counseling of the patient and affected family members. Some germline mutations are associated with syndromic features that precede the development of malignancy; however, penetrance may be highly variable leading to masking of the syndromic phenotype and/or inherited etiology.

Implementation of a prospective screening strategy to identify adults with a telomere biology disorder among those undergoing lung transplant evaluation for interstitial lung disease

INTRODUCTION

Patients with interstitial lung disease (ILD) secondary to telomere biology disorders (TBD) experience increased morbidity after lung transplantation. Identifying patients with TBD may allow for personalized management to facilitate better outcomes. However, establishing a TBD diagnosis in adults is challenging.

METHODS

A TBD screening questionnaire was introduced prospectively into the lung transplant evaluation. Patients with ILD screening positive were referred for comprehensive TBD phenotyping and concurrent telomere length measurement and germline genetic testing.

RESULTS

Of 98 patients, 32 (33%) screened positive. Eight patients (8% of total; 25% of patients with a positive screen) met strict TBD diagnostic criteria, requiring either critically short lymphocyte telomeres (<1st percentile) (n = 4), a pathogenic variant in a TBD-associated gene (n = 1), or both (n = 3) along with a TBD clinical phenotype. Additional patients not meeting strict diagnostic criteria had histories consistent with TBD along with telomere lengths <10th percentile and/or rare variants in TBD-associated genes, highlighting a critical need to refine TBD diagnostic criteria for this patient population.

CONCLUSION

A TBD phenotype screening questionnaire in patients with ILD undergoing lung transplant evaluation has a diagnostic yield of 25%. Additional gene discovery, rare variant functional testing, and refined TBD diagnostic criteria are needed to realize the maximum benefit of testing for TBD in patients undergoing lung transplantation.

Pediatric Bone Marrow Failure: A Broad Landscape in Need of Personalized Management

Irreversible severe bone marrow failure (BMF) is a life-threatening condition in pediatric patients. Most important causes are inherited bone marrow failure syndromes (IBMFSs) and (pre)malignant diseases, such as myelodysplastic syndrome (MDS) and (idiopathic) aplastic anemia (AA). Timely treatment is essential to prevent infections and bleeding complications and increase overall survival (OS). Allogeneic hematopoietic stem cell transplantation (HSCT) provides a cure for most types of BMF but cannot restore non-hematological defects. When using a matched sibling donor (MSD) or a matched unrelated donor (MUD), the OS after HSCT ranges between 60 and 90%. Due to the introduction of post-transplantation cyclophosphamide (PT-Cy) to prevent graft versus host disease (GVHD), alternative donor HSCT can reach similar survival rates. Although HSCT can restore ineffective hematopoiesis, it is not always used as a first-line therapy due to the severe risks associated with HSCT. Therefore, depending on the underlying cause, other treatment options might be preferred. Finally, for IBMFSs with an identified genetic etiology, gene therapy might provide a novel treatment strategy as it could bypass certain limitations of HSCT. However, gene therapy for most IBMFSs is still in its infancy. This review summarizes current clinical practices for pediatric BMF, including HSCT as well as other disease-specific treatment options.

Multiple Roles of dXNP and dADD1-Drosophila Orthologs of ATRX Chromatin Remodeler

The Drosophila melanogaster dADD1 and dXNP proteins are orthologues of the ADD and SNF2 domains of the vertebrate ATRX (Alpha-Thalassemia with mental Retardation X-related) protein. ATRX plays a role in general molecular processes, such as regulating chromatin status and gene expression, while dADD1 and dXNP have similar functions in the Drosophila genome. Both ATRX and dADD1/dXNP interact with various protein partners and participate in various regulatory complexes. Disruption of ATRX expression in humans leads to the development of α-thalassemia and cancer, especially glioma. However, the mechanisms that allow ATRX to regulate various cellular processes are poorly understood. Studying the functioning of dADD1/dXNP in the Drosophila model may contribute to understanding the mechanisms underlying the multifunctional action of ATRX and its connection with various cellular processes. This review provides a brief overview of the currently available information in mammals and Drosophila regarding the roles of ATRX, dXNP, and dADD1. It discusses possible mechanisms of action of complexes involving these proteins.

A novel mutation of CTC1 leads to telomere shortening in a chinese family with interstitial lung disease

Interstitial lung diseases (ILDs), or diffuse pulmonary lung disease, are a subset of lung diseases that primarily affect lung alveoli and the space around interstitial tissue and bronchioles. It clinically manifests as progressive dyspnea, and patients often exhibit a varied decrease in pulmonary diffusion function. Recently, variants in telomere biology-related genes have been identified as genetic lesions of ILDs. Here, we enrolled 82 patients with interstitial pneumonia from 2017 to 2021 in our hospital to explore the candidate gene mutations of these patients via whole-exome sequencing. After data filtering, a novel heterozygous mutation (NM_025099: p.Gly131Arg) of CTC1 was identified in two affected family members. As a component of CST (CTC1-STN1-TEN1) complex, CTC1 is responsible for maintaining telomeric structure integrity and has also been identified as a candidate gene for IPF, a special kind of chronic ILD with insidious onset. Simultaneously, real-time PCR revealed that two affected family members presented with short telomere lengths, which further confirmed the effect of the mutation in the CTC1 gene. Our study not only expanded the mutation spectrum of CTC1 and provided epidemiological data on ILDs caused by CTC1 mutations but also further confirmed the relationship between heterozygous mutations in CTC1 and ILDs, which may further contribute to understanding the mechanisms underlying ILDs.

Canine sperm motility is associated with telomere shortening and changes in expression of shelterin genes

BACKGROUND

Motion quality is a critical property for essential functions. Several endogenous and exogenous factors are involved in sperm motility. Here, we measured the relative telomere length and evaluated the gene expression of its binding-proteins, shelterin complex (TRF1, TRF2, RAP1, POT1, TIN2, and TPP1) in sperm of dogs using relative quantitative real-time PCR. We compared them between two sperm subpopulations with poor and good motion qualities (separated by swim-up method). Telomere shortening and alterations of shelterin gene expression result from ROS, genotoxic insults, and genetic predisposition.

RESULTS

Sperm kinematic parameters were measured in two subpopulations and then telomeric index of each parameter was calculated. Telomeric index for linearity, VSL, VCL, STR, BCF, and ALH were significantly higher in sperms with good motion quality than in sperms with poor quality. We demonstrated that poor motion quality is associated with shorter telomere, higher expression of TRF2, POT1, and TIN2 genes, and lower expression of the RAP1 gene in dog sperm. The levels of TRF1 and TPP1 gene expression remained consistent despite variations in sperm quality and telomere length.

CONCLUSION

Data provided evidence that there are considerable changes in gene expression of many shelterin components (TRF2, TIN2, POT1and RAP1) associated with shortening telomere in the spermatozoa with poor motion quality. Possibly, the poor motion quality is the result of defects in the shelterin complex and telomere length. Our data suggests a new approach in the semen assessment and etiologic investigations of subfertility or infertility in male animals.

Neonatal administration of fenofibrate had no developmental programming effect on the lipid profile and relative leucocyte telomere lengths of adolescent rats fed a high-fructose diet postnatally

Telomere length, a marker of ageing, is susceptible to developmental programming that may cause its accelerated attrition. Metabolic syndrome triggers telomere attrition. Fenofibrate, a peroxisome proliferator-activated receptor-alpha agonist, is protective against telomere attrition. We investigated the impact of fenofibrate administered during suckling on the lipid profile and leucocyte telomere lengths of rats fed a high-fructose diet post-weaning. Suckling Sprague-Dawley pups (n = 119) were allocated to four groups and gavaged with either 10 mL·kg-1 body mass 0.5% dimethyl sulfoxide, 100 mg·kg-1 body mass fenofibrate, fructose (20%, w / v), or a combination of fenofibrate and fructose for 15 days. Upon weaning, each of the initial groups was split into two subgroups: one had plain water while the other had fructose solution (20%, w / v) to drink for 6 weeks. Blood was collected for DNA extraction and relative leucocyte telomere length determination by real-time PCR. Plasma triglycerides and cholesterol were also quantified. The treatments had no effect (p > 0.05) on body mass, cholesterol concentration, and relative leucocyte telomere lengths in both sexes. Post-weaning fructose increased triglyceride concentrations (p < 0.05) in female rats. Fenofibrate administered during suckling did not affect ageing nor did it prevent high fructose-induced hypertriglyceridaemia in female rats.

Telomouse-a mouse model with human-length telomeres generated by a single amino acid change in RTEL1

Telomeres, the ends of eukaryotic chromosomes, protect genome integrity and enable cell proliferation. Maintaining optimal telomere length in the germline and throughout life limits the risk of cancer and enables healthy aging. Telomeres in the house mouse, Mus musculus, are about five times longer than human telomeres, limiting the use of this common laboratory animal for studying the contribution of telomere biology to aging and cancer. We identified a key amino acid variation in the helicase RTEL1, naturally occurring in the short-telomere mouse species M. spretus. Introducing this variation into M. musculus is sufficient to reduce the telomere length set point in the germline and generate mice with human-length telomeres. While these mice are fertile and appear healthy, the regenerative capacity of their colonic epithelium is compromised. The engineered Telomouse reported here demonstrates a dominant role of RTEL1 in telomere length regulation and provides a unique model for aging and cancer.

Telomere biology and ribosome biogenesis: structural and functional interconnections

Telomeres are nucleoprotein structures that play a pivotal role in the protection and maintenance of eukaryotic chromosomes. Telomeres and the enzyme telomerase, which replenishes telomeric DNA lost during replication, are important factors necessary to ensure continued cell proliferation. Cell proliferation is also dependent on proper and efficient protein synthesis, which is carried out by ribosomes. Mutations in genes involved in either ribosome biogenesis or telomere biology result in cellular abnormalities and can cause human genetic diseases, defined as ribosomopathies and telomeropathies, respectively. Interestingly, recent discoveries indicate that many of the ribosome assembly and rRNA maturation factors have additional noncanonical functions in telomere biology. Similarly, several key proteins and enzymes involved in telomere biology, including telomerase, have unexpected roles in rRNA transcription and maturation. These observations point to an intriguing cross-talk mechanism potentially explaining the multiple pleiotropic symptoms of mutations in many causal genes identified in various telomeropathy and ribosomopathy diseases. In this review, we provide a brief summary of eukaryotic telomere and rDNA loci structures, highlight several universal features of rRNA and telomerase biogenesis, evaluate intriguing interconnections between telomere biology and ribosome assembly, and conclude with an assessment of overlapping features of human diseases of telomeropathies and ribosomopathies.

Research progress of small-molecule drugs in targeting telomerase in human cancer and aging

Telomeres are unique structures located at the ends of linear chromosomes, responsible for stabilizing chromosomal structures. They are synthesized by telomerase, a reverse transcriptase ribonucleoprotein complex. Telomerase activity is generally absent in human somatic cells, except in stem cells and germ cells. Every time a cell divides, the telomere sequence is shortened, eventually leading to replicative senescence and cell apoptosis when the telomeres reach a critical limit. However, most human cancer cells exhibit increased telomerase activity, allowing them to divide continuously. The importance of telomerase in cancer and aging has made developing drugs targeting telomerase a focus of research. Such drugs can inhibit cancer cell growth and delay aging by enhancing telomerase activity in telomere-related syndromes or diseases. This review provides an overview of telomeres, telomerase, and their regulation in cancer and aging, and highlights small-molecule drugs targeting telomerase in these fields.

Bioinformatic analysis of the effect of SNPs in the pig TERT gene on the structural and functional characteristics of the enzyme to develop new genetic markers of productivity traits

BACKGROUND

Telomerase reverse transcriptase (TERT) plays a crucial role in synthesizing telomeric repeats that safeguard chromosomes from damage and fusion, thereby maintaining genome stability. Mutations in the TERT gene can lead to a deviation in gene expression, impaired enzyme activity, and, as a result, abnormal telomere shortening. Genetic markers of productivity traits in livestock can be developed based on the TERT gene polymorphism for use in marker-associated selection (MAS). In this study, a bioinformatic-based approach is proposed to evaluate the effect of missense single-nucleotide polymorphisms (SNPs) in the pig TERT gene on enzyme function and structure, with the prospect of developing genetic markers.

RESULTS

A comparative analysis of the coding and amino acid sequences of the pig TERT was performed with corresponding sequences of other species. The distribution of polymorphisms in the pig TERT gene, with respect to the enzyme's structural-functional domains, was established. A three-dimensional model of the pig TERT structure was obtained through homological modeling. The potential impact of each of the 23 missense SNPs in the pig TERT gene on telomerase function and stability was assessed using predictive bioinformatic tools utilizing data on the amino acid sequence and structure of pig TERT.

CONCLUSIONS

According to bioinformatic analysis of 23 missense SNPs of the pig TERT gene, a predictive effect of rs789641834 (TEN domain), rs706045634 (TEN domain), rs325294961 (TRBD domain) and rs705602819 (RTD domain) on the structural and functional parameters of the enzyme was established. These SNPs hold the potential to serve as genetic markers of productivity traits. Therefore, the possibility of their application in MAS should be further evaluated in associative analysis studies.

First Successful Liver-Alone Transplantation for TERT (Telomerase Reverse Transcriptase)-Telomeropathy-Related Hepatoportal Sclerosis Cirrhosis

Hepatoportal sclerosis is a rare but well-described condition leading to end-stage liver disease. Telomeropathy is a rare genetic disorder which manifests as premature senescence of cells leading to multisystem disease involving bone marrow, lungs and skin. To the best of our knowledge, there is no report of telomeropathy precipitating end-stage liver disease. Our case presented hepatopulmonary syndrome. Herein, we report a successful liver transplantation in a patient who suffered hepatoportal cirrhosis from telomerase reverse transcriptase (TERT)-telomeropathy.

Interaction hub critical for telomerase recruitment and primer-template handling for catalysis

Telomerase processively adds telomeric DNA repeats to chromosome ends using catalytic protein subunit TERT and a template on its RNA subunit TR. Mammalian telomerase is recruited to telomeres by the TEL patch and NOB regions of shelterin component TPP1. Recent cryo-EM structures of human telomerase reveal that a composite TERT TEN-(IFD-TRAP) domain interacts with TPP1. Here, we generate TERT mutants to demonstrate that a three-way TEN-(IFD-TRAP)-TPP1 interaction is critical for telomerase recruitment to telomeres and processive telomere repeat addition. Single mutations of IFD-TRAP at its interface with TR or the DNA primer impair telomerase catalysis. We further reveal the importance of TERT motif 3N and TEN domain loop 99FGF101 in telomerase action. Finally, we demonstrate that TPP1 TEL patch loop residue F172, which undergoes a structural rearrangement to bind telomerase, contributes to the human-mouse species specificity of the telomerase-TPP1 interaction. Our study provides insights into the multiple functions of TERT IFD-TRAP, reveals novel TERT and TPP1 elements critical for function, and helps explain how TPP1 binding licenses robust telomerase action at natural chromosome ends.

Deletion of 184-188 Nucleotides of Human Telomerase RNA Does Not Affect the Telomerase Functioning

Telomerase is a ribonucleoprotein complex, the main components of which are telomerase RNA and reverse transcriptase. Previously, it was shown in our laboratory that human telomerase RNA contains an open reading frame starting at adenine in position 176. The open reading frame encodes the hTERP protein, and the deletion of nucleotides 184-188 of human telomerase RNA disrupts the open reading frame and leads to the absence of hTERP. Human telomerase RNA has a conserved structure, changes in which affect telomerase activity. In this work, we have shown that the deletion of nucleotides 184-188 of telomerase RNA does not affect the functioning of telomerase.

Telomere biology: from disorders to hematological diseases

Variations in the length of telomeres and pathogenic variants involved in telomere length maintenance have been correlated with several human diseases. Recent breakthroughs in telomere biology knowledge have contributed to the identification of illnesses named "telomeropathies" and revealed an association between telomere length and disease outcome. This review emphasizes the biology and physiology aspects of telomeres and describes prototype diseases in which telomeres are implicated in their pathophysiology. We also provide information on the role of telomeres in hematological diseases ranging from bone marrow failure syndromes to acute and chronic leukemias.

European Respiratory Society statement on familial pulmonary fibrosis

Genetic predisposition to pulmonary fibrosis has been confirmed by the discovery of several gene mutations that cause pulmonary fibrosis. Although genetic sequencing of familial pulmonary fibrosis (FPF) cases is embedded in routine clinical practice in several countries, many centres have yet to incorporate genetic sequencing within interstitial lung disease (ILD) services and proper international consensus has not yet been established. An international and multidisciplinary expert Task Force (pulmonologists, geneticists, paediatrician, pathologist, genetic counsellor, patient representative and librarian) reviewed the literature between 1945 and 2022, and reached consensus for all of the following questions: 1) Which patients may benefit from genetic sequencing and clinical counselling? 2) What is known of the natural history of FPF? 3) Which genes are usually tested? 4) What is the evidence for telomere length measurement? 5) What is the role of common genetic variants (polymorphisms) in the diagnostic workup? 6) What are the optimal treatment options for FPF? 7) Which family members are eligible for genetic sequencing? 8) Which clinical screening and follow-up parameters may be considered in family members? Through a robust review of the literature, the Task Force offers a statement on genetic sequencing, clinical management and screening of patients with FPF and their relatives. This proposal may serve as a basis for a prospective evaluation and future international recommendations.

Functional genomics for curation of variants in telomere biology disorder associated genes: A systematic review

PURPOSE

Patients with an underlying telomere biology disorder (TBD) have variable clinical presentations, and they can be challenging to diagnose clinically. A genomic diagnosis for patients presenting with TBD is vital for optimal treatment. Unfortunately, many variants identified during diagnostic testing are variants of uncertain significance. This complicates management decisions, delays treatment, and risks nonuptake of potentially curative therapies. Improved application of functional genomic evidence may reduce variants of uncertain significance classifications.

METHODS

We systematically searched the literature for published functional assays interrogating TBD gene variants. When possible, established likely benign/benign and likely pathogenic/pathogenic variants were used to estimate the assay sensitivity, specificity, positive predictive value, negative predictive value, and odds of pathogenicity.

RESULTS

In total, 3131 articles were screened and 151 met inclusion criteria. Sufficient data to enable a PS3/BS3 recommendation were available for TERT variants only. We recommend that PS3 and BS3 can be applied at a moderate and supportive level, respectively. PS3/BS3 application was limited by a lack of assay standardization and limited inclusion of benign variants.

CONCLUSION

Further assay standardization and assessment of benign variants are required for optimal use of the PS3/BS3 criterion for TBD gene variant classification.

Inherited bone marrow failure syndromes: a review of current practices and potential future research directions

PURPOSE OF REVIEW

Recent advances in diagnosis and treatment of inherited bone marrow failure syndromes (IBMFS) have significantly improved disease understanding and patient outcomes. Still, IBMFS present clinical challenges that require further progress. This review aims to provide an overview of the current state of diagnosis and treatment modalities of the major IBMFS seen in paediatrics and present areas of prioritization for future research.

RECENT FINDINGS

Haematopoietic cell transplantation (HCT) for IBMFS has greatly improved in recent years, shifting the research and clinical focus towards cancer predispositions and adverse effects of treatment. Each year, additional novel genes and pathogenic variants are described, and genotype-phenotype mapping becomes more sophisticated. Moreover, novel therapeutics exploring disease-specific mechanisms show promise to complement HCT and treat patients who cannot undergo current treatment options.

SUMMARY

Research on IBMFS should have short-term and long-term goals. Immediate challenges include solidifying diagnostic and treatment guidelines, cancer detection and treatment, and continued optimization of HCT. Long-term goals should emphasize genotype-phenotype mapping, genetic screening tools and gene-targeted therapy.

Genomic Fingerprint Associated with Familial Idiopathic Pulmonary Fibrosis: A Review

Idiopathic pulmonary fibrosis (IPF) is a severe interstitial lung disease; although the recent introduction of two anti-fibrosis drugs, pirfenidone and Nidanib, have resulted in a significant reduction in lung function decline, IPF is still not curable. Approximately 2-20% of patients with IPF have a family history of the disease, which is considered the strongest risk factor for idiopathic interstitial pneumonia. However, the genetic predispositions of familial IPF (f-IPF), a particular type of IPF, remain largely unknown. Genetics affect the susceptibility and progression of f-IPF. Genomic markers are increasingly being recognized for their contribution to disease prognosis and drug therapy outcomes. Existing data suggest that genomics may help identify individuals at risk for f-IPF, accurately classify patients, elucidate key pathways involved in disease pathogenesis, and ultimately develop more effective targeted therapies. Since several genetic variants associated with the disease have been found in f-IPF, this review systematically summarizes the latest progress in the gene spectrum of the f-IPF population and the underlying mechanisms of f-IPF. The genetic susceptibility variation related to the disease phenotype is also illustrated. This review aims to improve the understanding of the IPF pathogenesis and facilitate his early detection.

Case Report: CTC1 mutations in a patient with diffuse hepatic and splenic hemangiomatosis complicated by Kasabach-Merritt syndrome

Diffuse hemangiomatosis of the liver and spleen is rare. Currently, few studies are available on diffuse hepatic and splenic hemangiomatosis accompanied by Kasabach-Merritt syndrome (KMS). The conserved telomere maintenance component 1 (CTC1) gene contributes to telomere maintenance and replication by forming the telomeric capping complex. Herein, we report a case of diffuse hemangiomatosis in the liver and spleen accompanied by KMS in a 59-year-old woman who carried two novel heterozygous CTC1 variants: c.435+9A>C and c.3074C>T (p.Ala1025Val). Using next-generation sequencing, we detected mutations in the CTC1 gene in our patient, who had chief complaints of fatigue and abdominal distension complicated by severe thrombocytopenia and consumptive coagulopathy. Clinical symptoms, laboratory tests, and imaging findings led to the diagnosis of diffuse hepatic and splenic hemangiomatosis accompanied by KMS. The patient was treated with prednisone, thalidomide, and sirolimus, and her general condition was ameliorated at the 4-month follow-up with improved platelet count and coagulation function. A CTC1 gene mutation may be involved in the pathological process of vascular diseases. A combination treatment regimen of prednisone, thalidomide, and sirolimus may be effective for KMS.

Altered Nucleotide Insertion Mechanisms of Disease-Associated TERT Variants

Telomere biology disorders (TBDs) are a spectrum of diseases that arise from mutations in genes responsible for maintaining telomere integrity. Human telomerase reverse transcriptase (hTERT) adds nucleotides to chromosome ends and is frequently mutated in individuals with TBDs. Previous studies have provided insight into how relative changes in hTERT activity can lead to pathological outcomes. However, the underlying mechanisms describing how disease-associated variants alter the physicochemical steps of nucleotide insertion remain poorly understood. To address this, we applied single-turnover kinetics and computer simulations to the Tribolium castaneum TERT (tcTERT) model system and characterized the nucleotide insertion mechanisms of six disease-associated variants. Each variant had distinct consequences on tcTERT's nucleotide insertion mechanism, including changes in nucleotide binding affinity, rates of catalysis, or ribonucleotide selectivity. Our computer simulations provide insight into how each variant disrupts active site organization, such as suboptimal positioning of active site residues, destabilization of the DNA 3' terminus, or changes in nucleotide sugar pucker. Collectively, this work provides a holistic characterization of the nucleotide insertion mechanisms for multiple disease-associated TERT variants and identifies additional functions of key active site residues during nucleotide insertion.

The Genetic and Epigenetic Footprint in Idiopathic Pulmonary Fibrosis and Familial Pulmonary Fibrosis: A State-of-the-Art Review

Idiopathic pulmonary fibrosis (IPF) is a rare disease of the lung with a largely unknown etiology and a poor prognosis. Intriguingly, forms of familial pulmonary fibrosis (FPF) have long been known and linked to specific genetic mutations. There is little evidence of the possible role of genetics in the etiology of sporadic IPF. We carried out a non-systematic, narrative literature review aimed at describing the main known genetic and epigenetic mechanisms that are involved in the pathogenesis and prognosis of IPF and FPF. In this review, we highlighted the mutations in classical genes associated with FPF, including those encoding for telomerases (TERT, TERC, PARN, RTEL1), which are also found in about 10-20% of cases of sporadic IPF. In addition to the Mendelian forms, mutations in the genes encoding for the surfactant proteins (SFTPC, SFTPA1, SFTPA2, ABCA3) and polymorphisms of genes for the mucin MUC5B and the Toll-interacting protein TOLLIP are other pathways favoring the fibrogenesis that have been thoroughly explored. Moreover, great attention has been paid to the main epigenetic alterations (DNA methylation, histone modification and non-coding RNA gene silencing) that are emerging to play a role in fibrogenesis. Finally, a gaze on the shared mechanisms between cancer and fibrogenesis, and future perspectives on the genetics of pulmonary fibrosis have been analyzed.

Severe immunochemotherapy-induced toxicities in a patient with dyskeratosis congenita and literature review

OBJECTIVES

Dyskeratosis congenita (DC) is a rare inherited disease characterized by the triad of reticulate hyperpigmentation, nail dystrophy and oral leukoplakia. DC patients are considered vulnerable to external pressure, such as immunochemotherapy. There are very few cases reporting severe therapy-induced toxicities in patients with DC.

METHODS

A 27-year-old woman was admitted to our hospital with a 4-month history of pancytopenia and a 7-day history of dyspnea with coughing. She was diagnosed with non-Hodgkin's lymphoma 5 months ago. She received immunochemotherapy due to non-Hodgkin's lymphoma but experienced recurrent fever, oral ulcer, pancytopenia, dyspnea and other symptoms during immunochemotherapy. On admission, she experienced an aggravation of respiratory symptoms, recurrent infections and acute heart failure.

RESULTS

Laboratory examination confirmed pancytopenia, and chest computed tomography showed interstitial lung disease (ILD). Genetic analysis results confirmed the presence of DC and a TINF2 gene mutation. With continuous supportive and anti-infection treatment, her condition finally stabilized. She was discharged from the hospital after nearly 2 months.

DISCUSSION

We reviewed similar cases and found common features that could be useful. However, the reported cases are very limited. More cases and studies are needed.

CONCLUSION

These cases indicate that DC patients seem more vulnerable to therapy toxicities; thus, physicians should be careful when treating these patients with chemotherapy drugs or radiation therapy. Reduced-intensity therapy may be considered.

Updates of cancer hallmarks in patients with inborn errors of immunity

PURPOSE OF REVIEW

The development of cancer in patients with genetically determined inborn errors of immunity (IEI) is much higher than in the general population. The hallmarks of cancer are a conceptualization tool that can refine the complexities of cancer development and pathophysiology. Each genetic defect may impose a different pathological tumor predisposition, which needs to be identified and linked with known hallmarks of cancer.

RECENT FINDINGS

Four new hallmarks of cancer have been suggested, recently, including unlocking phenotypic plasticity, senescent cells, nonmutational epigenetic reprogramming, and polymorphic microbiomes. Moreover, more than 50 new IEI genes have been discovered during the last 2 years from which 15 monogenic defects perturb tumor immune surveillance in patients.

SUMMARY

This review provides a more comprehensive and updated overview of all 14 cancer hallmarks in IEI patients and covers aspects of cancer predisposition in novel genes in the ever-increasing field of IEI.

Telomere biology disorders: time for moving towards the clinic?

Telomere biology disorders (TBDs) are a group of rare diseases caused by mutations that impair telomere maintenance. Mutations that cause reduced levels of TERC/hTR, the telomerase RNA component, are found in most TBD patients and include loss-of-function mutations in hTR itself, in hTR-binding proteins [NOP10, NHP2, NAF1, ZCCHC8, and dyskerin (DKC1)], and in proteins required for hTR processing (PARN). These patients show diverse clinical presentations that most commonly include bone marrow failure (BMF)/aplastic anemia (AA), pulmonary fibrosis, and liver cirrhosis. There are no curative therapies for TBD patients. An understanding of hTR biogenesis, maturation, and degradation has identified pathways and pharmacological agents targeting the poly(A) polymerase PAPD5, which adds 3'-oligoadenosine tails to hTR to promote hTR degradation, and TGS1, which modifies the 5'-cap structure of hTR to enhance degradation, as possible therapeutic approaches. Critical next steps will be clinical trials to establish the effectiveness and potential side effects of these compounds in TBD patients.

A Rare Heterozygous TINF2 Deletional Frameshift Mutation in a Chinese Pedigree With a Spectrum of TBDs Phenotypes

Telomere biology disorders (TBDs) induced by TINF2 mutations manifest clinically with a spectrum of phenotypes, from silent carriers to a set of overlapping conditions. A rare TINF2 frameshift mutation (c.591delG) encoding a truncated mutant TIN2 protein (p.W198fs) was identified in a 6-years-and-3-month-old Chinese girl with neuroblastoma (NB) by next generation sequencing and confirmed by Sanger sequencing. To explore the possible implications of TINF2 mutations in TBDs development, the TINF2 mutant was transfected into the human embryonic kidney (HEK) 293T cells, and mRNA expression of the shelterin complex components as well as the cellular distribution of mutant TIN2 were examined. The TINF2 mutation was phenotypically associated with short stature in the proband, nail dystrophy and spotted hypopigmentation in her mother, and psoriasis in her older brother. I-TASSER modeling analysis revealed conformational changes of the mutant TIN2 protein and loss of pivotal domains downstream of the 198th amino acid. Additionally, mRNA expression of the shelterin components was downregulated, and TIN2 mutant protein expression was reduced in HEK293T cells transfected with mutant TINF2. Furthermore, instead of being restricted to the nucleus, the mutant TIN2 was identified in both the cytoplasm and the nucleus. The TINF2 gene mutation might impair the function of the shelterin complex and the telomere maintenance mechanisms, both of which are involved in the development of TBDs. TBDs have been associated with increased cancer risk. To the best of our knowledge, this is the first report of NB in patients with TBDs. The relationship between the TINF2 mutation and NB may need to further study.

[Telomeres and lung]

Genetic studies of familial forms of interstitial lung disease (ILD) have led to the discovery of telomere-related gene (TRG) mutations (TERT, TERC, RTEL1, PARN, DKC1, TINF2, NAF1, NOP10, NHP2, ACD, ZCCH8) in approximately 30% of familial ILD forms. ILD patients with TRG mutation are also subject to extra-pulmonary (immune-hematological, hepatic and/or mucosal-cutaneous) manifestations. TRG mutations may be associated not only with idiopathic pulmonary fibrosis (IPF), but also with non-IPF ILDs, including idiopathic and secondary ILDs, such as hypersensitivity pneumonitis (HP). The presence of TRG mutation may also be associated with an accelerated decline of forced vital capacity (FVC) or poorer prognosis after lung transplantation, notwithstanding which, usual ILD treatments may be proposed. Lastly, patients and their relatives are called upon to reduce their exposure to environmental lung toxicity, and are likely to derive benefit from specific genetic counseling and pre-symptomatic genetic testing.

MAPK/ERK-CBP-RFPL-3 Mediates Adipose-Derived Stem Cell-Induced Tumor Growth in Breast Cancer Cells by Activating Telomerase Reverse Transcriptase Expression

Adipose-derived stem cells (ASCs) improve the self-renewal and survival of fat grafts in breast reconstruction after oncology surgery. However, ASCs have also been found to enhance breast cancer growth, and its role in tumor proliferation remains largely elusive. Here, we explored a novel mechanism that mediates hTERT reactivation during ASC-induced tumor growth in breast cancer cells. In this study, we found the proliferative ability of breast cancer cells markedly increased with ASC coculture. To explore the molecular mechanism, we treated cells with anibody/inhibitor and found that the activation of MEK-ERK pathway was triggered in breast cancer cells by SCF secreted from ASCs, leading to the nuclear recruitment of CBP. As a coactivator of hTERT, CBP subsequently coordinated with RFPL-3 upregulated hTERT transcription and telomerase activity. The inhibition of CBP and RFPL-3 abrogated the activation of hTERT transcription and the promotion of proliferation in breast cancer cells with cocultured ASCs in vitro and in vivo. Collectively, our study findings indicated that CBP coordination with RFPL-3 promotes ASC-induced breast cancer cell proliferation by anchoring to the hTERT promoter and upregulating telomerase activity, which is activated by the MAPK/ERK pathway.

Recent advances in hematopoietic cell transplantation for inherited bone marrow failure syndromes

Inherited bone marrow failure syndromes (IBMFSs) are a group of rare genetic disorders characterized by bone marrow failure with unique phenotypes and predisposition to cancer. Classical IBMFSs primarily include Fanconi anemia with impaired DNA damage repair, dyskeratosis congenita with telomere maintenance dysfunction, and Diamond-Blackfan anemia with aberrant ribosomal protein biosynthesis. Recently, comprehensive genetic analyses have been implemented for the definitive diagnosis of classic IBMFSs, and advances in molecular genetics have led to the identification of novel disorders such as AMeD and MIRAGE syndromes. Allogeneic hematopoietic cell transplantation (HCT), a promising option to overcome impaired hematopoiesis in patients with IBMFSs, does not correct nonhematological defects and may enhance the risk of secondary malignancies. Disease-specific management is necessary because IBMFSs differ in underlying defects and are associated with varying degrees of risk for clonal evolution and early or late complications after HCT. In addition, long-term follow-up is essential to detect complications related to the IBMFS or HCT. This review provides a summary of current clinical practices along with the latest data on HCT in IBMFSs.

Structure of active human telomerase with telomere shelterin protein TPP1

Human telomerase is a RNA-protein complex that extends the 3' end of linear chromosomes by synthesizing multiple copies of the telomeric repeat TTAGGG¹. Its activity is a determinant of cancer progression, stem cell renewal and cellular aging^2-5. Telomerase is recruited to telomeres and activated for telomere repeat synthesis by the telomere shelterin protein TPP1^6,7. Human telomerase has a bilobal structure with a catalytic core ribonuclear protein and a H and ACA box ribonuclear protein^8,9. Here we report cryo-electron microscopy structures of human telomerase catalytic core of telomerase reverse transcriptase (TERT) and telomerase RNA (TER (also known as hTR)), and of telomerase with the shelterin protein TPP1. TPP1 forms a structured interface with the TERT-unique telomerase essential N-terminal domain (TEN) and the telomerase RAP motif (TRAP) that are unique to TERT, and conformational dynamics of TEN-TRAP are damped upon TPP1 binding, defining the requirements for recruitment and activation. The structures further reveal that the elements of TERT and TER that are involved in template and telomeric DNA handling-including the TEN domain and the TRAP-thumb helix channel-are largely structurally homologous to those in Tetrahymena telomerase¹⁰, and provide unique insights into the mechanism of telomerase activity. The binding site of the telomerase inhibitor BIBR1532^11,12 overlaps a critical interaction between the TER pseudoknot and the TERT thumb domain. Numerous mutations leading to telomeropathies^13,14 are located at the TERT-TER and TEN-TRAP-TPP1 interfaces, highlighting the importance of TER-TERT and TPP1 interactions for telomerase activity, recruitment and as drug targets.

Telomere Dysfunction in Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis is an age-dependent progressive and fatal lung disease of unknown etiology, which is characterized by the excessive accumulation of extracellular matrix inside the interstitial layer of the lung parenchyma that leads to abnormal scar architecture and compromised lung function capacity. Recent genetic studies have attributed the pathological genes or genetic mutations associated with familial idiopathic pulmonary fibrosis (IPF) and sporadic IPF to telomere-related components, suggesting that telomere dysfunction is an important determinant of this disease. In this study, we summarized recent advances in our understanding of how telomere dysfunction drives IPF genesis. We highlighted the key role of alveolar stem cell dysfunction caused by telomere shortening or telomere uncapping, which bridged the gap between telomere abnormalities and fibrotic lung pathology. We emphasized that senescence-associated secretory phenotypes, innate immune cell infiltration, and/or inflammation downstream of lung stem cell dysfunction influenced the native microenvironment and local cell signals, including increased transforming growth factor-beta (TGF-β) signaling in the lung, to induce pro-fibrotic conditions. In addition, the failed regeneration of new alveoli due to alveolar stem cell dysfunction might expose lung cells to elevated mechanical tension, which could activate the TGF-β signaling loop to promote the fibrotic process, especially in a periphery-to-center pattern as seen in IPF patients. Understanding the telomere-related molecular and pathophysiological mechanisms of IPF would provide new insights into IPF etiology and therapeutic strategies for this fatal disease.

Dyskerin: an essential pseudouridine synthase with multifaceted roles in ribosome biogenesis, splicing, and telomere maintenance

Dyskerin and its homologs are ancient and conserved enzymes that catalyze the most common post-transcriptional modification found in cells, pseudouridylation. The resulting pseudouridines provide stability to RNA molecules and regulate ribosome biogenesis and splicing events. Dyskerin does not act independently-it is the core component of a protein heterotetramer, which associates with RNAs that contain the H/ACA motif. The variety of H/ACA RNAs that guide the function of this ribonucleoprotein (RNP) complex highlights the diversity of cellular processes in which dyskerin participates. When associated with small nucleolar (sno) RNAs, it regulates ribosomal (r) RNAs and ribosome biogenesis. By interacting with small Cajal body (sca) RNAs, it targets small nuclear (sn) RNAs to regulate pre-mRNA splicing. As a component of the telomerase holoenzyme, dyskerin binds to the telomerase RNA to modulate telomere maintenance. In a disease context, dyskerin malfunction can result in multiple detrimental phenotypes. Mutations in DKC1, the gene that encodes dyskerin, cause the premature aging syndrome X-linked dyskeratosis congenita (X-DC), a still incurable disorder that typically leads to bone marrow failure. In this review, we present the classical and most recent findings on this essential protein, discussing the evolutionary, structural, and functional aspects of dyskerin and the H/ACA RNP. The latest research underscores the role that dyskerin plays in the regulation of gene expression, translation efficiency, and telomere maintenance, along with the impacts that defective dyskerin has on aging, cell proliferation, haematopoietic potential, and cancer.

The S-adenosylmethionine analog sinefungin inhibits the trimethylguanosine synthase TGS1 to promote telomerase activity and telomere lengthening

Mutations in many genes that control the expression, the function, or the stability of telomerase cause telomere biology disorders (TBDs), such as dyskeratosis congenita, pulmonary fibrosis, and aplastic anemia. Mutations in a subset of the genes associated with TBDs cause reductions of the telomerase RNA moiety hTR, thus limiting telomerase activity. We have recently found that loss of the trimethylguanosine synthase TGS1 increases both hTR abundance and telomerase activity and leads to telomere elongation. Here, we show that treatment with the S-adenosylmethionine analog sinefungin inhibits TGS1 activity, increases the hTR levels, and promotes telomere lengthening in different cell types. Our results hold promise for restoring telomere length in stem and progenitor cells from TBD patients with reduced hTR levels.

Differential impact of a dyskeratosis congenita mutation in TPP1 on mouse hematopoiesis and germline

A TPP1 mutation known to cause telomere shortening and bone marrow failure in humans recapitulates telomere loss but results in severe germline defects in mice without impacting murine hematopoiesis.

Telomerase extends chromosome ends in somatic and germline stem cells to ensure continued proliferation. Mutations in genes critical for telomerase function result in telomeropathies such as dyskeratosis congenita, frequently resulting in spontaneous bone marrow failure. A dyskeratosis congenita mutation in TPP1 (K170∆) that specifically compromises telomerase recruitment to telomeres is a valuable tool to evaluate telomerase-dependent telomere length maintenance in mice. We used CRISPR-Cas9 to generate a mouse knocked in for the equivalent of the TPP1 K170∆ mutation (TPP1 K82∆) and investigated both its hematopoietic and germline compartments in unprecedented detail. TPP1 K82∆ caused progressive telomere erosion with increasing generation number but did not induce steady-state hematopoietic defects. Strikingly, K82∆ caused mouse infertility, consistent with gross morphological defects in the testis and sperm, the appearance of dysfunctional seminiferous tubules, and a decrease in germ cells. Intriguingly, both TPP1 K82∆ mice and previously characterized telomerase knockout mice show no spontaneous bone marrow failure but rather succumb to infertility at steady-state. We speculate that telomere length maintenance contributes differently to the evolutionary fitness of humans and mice.

The clinical and functional effects of TERT variants in myelodysplastic syndrome

Germline pathogenic TERT variants are associated with short telomeres and an increased risk of developing myelodysplastic syndrome (MDS) among patients with a telomere biology disorder. We identified TERT rare variants in 41 of 1514 MDS patients (2.7%) without a clinical diagnosis of a telomere biology disorder who underwent allogeneic transplantation. Patients with a TERT rare variant had shorter telomere length (P < .001) and younger age at MDS diagnosis (52 vs 59 years, P = .03) than patients without a TERT rare variant. In multivariable models, TERT rare variants were associated with inferior overall survival (P = .034) driven by an increased incidence of nonrelapse mortality (NRM; P = .015). Death from a noninfectious pulmonary cause was more frequent among patients with a TERT rare variant. Most variants were missense substitutions and classified as variants of unknown significance. Therefore, we cloned all rare missense variants and quantified their impact on telomere elongation in a cell-based assay. We found that 90% of TERT rare variants had severe or intermediate impairment in their capacity to elongate telomeres. Using a homology model of human TERT bound to the shelterin protein TPP1, we inferred that TERT rare variants disrupt domain-specific functions, including catalysis, protein-RNA interactions, and recruitment to telomeres. Our results indicate that the contribution of TERT rare variants to MDS pathogenesis and NRM risk is underrecognized. Routine screening for TERT rare variants in MDS patients regardless of age or clinical suspicion may identify clinically inapparent telomere biology disorders and improve transplant outcomes through risk-adapted approaches.

Occurrence, functionality and abundance of the TERT promoter mutations

Telomere shortening at chromosomal ends due to the constraints of the DNA replication process acts as a tumor suppressor by restricting the replicative potential in primary cells. Cancers evade that limitation primarily through the reactivation of telomerase via different mechanisms. Mutations within the promoter of the telomerase reverse transcriptase (TERT) gene represent a definite mechanism for the ribonucleic enzyme regeneration predominantly in cancers that arise from tissues with low rates of self-renewal. The promoter mutations cause a moderate increase in TERT transcription and consequent telomerase upregulation to the levels sufficient to delay replicative senescence but not prevent bulk telomere shortening and genomic instability. Since the discovery, a staggering number of studies have resolved the discrete aspects, effects and clinical relevance of the TERT promoter mutations. The promoter mutations link transcription of TERT with oncogenic pathways, associate with markers of poor outcome and define patients with reduced survivals in several cancers. In this review, we discuss the occurrence and impact of the promoter mutations and highlight the mechanism of TERT activation. We further deliberate on the foundational question of the abundance of the TERT promoter mutations and a general dearth of functional mutations within noncoding sequences, as evident from pan-cancer analysis of the whole-genomes. We posit that the favorable genomic constellation within the TERT promoter may be less than a common occurrence in other noncoding functional elements. Besides, the evolutionary constraints limit the functional fraction within the human genome, hence the lack of abundant mutations outside the coding sequences.

Structural genomics approach to investigate deleterious impact of nsSNPs in conserved telomere maintenance component 1

Conserved telomere maintenance component 1 (CTC1) is an important component of the CST (CTC1-STN1-TEN1) complex, involved in maintaining the stability of telomeric DNA. Several non-synonymous single-nucleotide polymorphisms (nsSNPs) in CTC1 have been reported to cause Coats plus syndrome and Dyskeratosis congenital diseases. Here, we have performed sequence and structure analyses of nsSNPs of CTC1 using state-of-the-art computational methods. The structure-based study focuses on the C-terminal OB-fold region of CTC1. There are 11 pathogenic mutations identified, and detailed structural analyses were performed. These mutations cause a significant disruption of noncovalent interactions, which may be a possible reason for CTC1 instability and consequent diseases. To see the impact of such mutations on the protein conformation, all-atom molecular dynamics (MD) simulations of CTC1-wild-type (WT) and two of the selected mutations, R806C and R806L for 200 ns, were carried out. A significant conformational change in the structure of the R806C mutant was observed. This study provides a valuable direction to understand the molecular basis of CTC1 dysfunction in disease progression, including Coats plus syndrome.