-
Aging Cell Jun 2023Telomere length (TL) limits somatic cell replication. However, the shortest among the telomeres in each nucleus, not mean TL, is thought to induce replicative...
Telomere length (TL) limits somatic cell replication. However, the shortest among the telomeres in each nucleus, not mean TL, is thought to induce replicative senescence. Researchers have relied on Southern blotting (SB), and techniques calibrated by SB, for precise measurements of TL in epidemiological studies. However, SB provides little information on the shortest telomeres among the 92 telomeres in the nucleus of human somatic cells. Therefore, little is known about the accumulation of short telomeres with age, or whether it limits the human lifespan. To fill this knowledge void, we used the Telomere-Shortest-Length-Assay (TeSLA), a method that tallies and measures single telomeres of all chromosomes. We charted the age-dependent buildup of short telomeres (<3 kb) in human hematopoietic cells from 334 individuals (birth-89 years) from the general population, and 18 patients with dyskeratosis congenita-telomere biology disorders (DC/TBDs), whose hematopoietic cells have presumably reached or are close to their replicative limit. For comparison, we also measured TL with SB. We found that in hematopoietic cells, the buildup of short telomeres occurs in parallel with the shortening with age of mean TL. However, the proportion of short telomeres was lower in octogenarians from the general population than in patients with DC/TBDs. At any age, mean TL was longer and the proportion of short telomeres lower in females than in males. We conclude that though converging to the TL-mediated replicative limit, hematopoietic cell telomeres are unlikely to reach this limit during the lifespan of most contemporary humans.
Topics: Male; Aged, 80 and over; Female; Humans; Telomere Shortening; Longevity; Cell Division; Telomere
PubMed: 37118904
DOI: 10.1111/acel.13844 -
BMJ Case Reports May 2021Dyskeratosis congenita is a rare disease caused by telomerase dysfunction classically characterised by the triad: skin pigmentation, nail dystrophy and mucosal... (Review)
Review
Dyskeratosis congenita is a rare disease caused by telomerase dysfunction classically characterised by the triad: skin pigmentation, nail dystrophy and mucosal leukoplakia. Few cases are described in literature regarding patients with head and neck squamous cell carcinoma affected by dyskeratosis congenita, and the therapeutic decisions are not yet well defined. A review of the literature of the last 20 years (2001-2021) was performed, and it was analysed the case of a 38-year-old male patient affected by dyskeratosis congenita diagnosed with a squamous cell carcinoma of the inferior alveolar ridge, treated with surgery. The absence of complications and the good postoperative recovery of the patient comfort in saying that resection and reconstructive surgery can be safely performed. The occurrence of disseminated disease 6 months after the treatment warns about the extreme aggressiveness of the pathology, its often systemic nature and the necessity of a multidisciplinary approach as well as further studies.
Topics: Adult; Alveolar Process; Carcinoma, Squamous Cell; Dyskeratosis Congenita; Head and Neck Neoplasms; Humans; Leukoplakia; Male
PubMed: 33975847
DOI: 10.1136/bcr-2021-242459 -
The Journals of Gerontology. Series A,... May 2023The underlying mechanisms of plasma metabolite signatures of human aging and age-related diseases are not clear but telomere attrition and dysfunction are central to...
The underlying mechanisms of plasma metabolite signatures of human aging and age-related diseases are not clear but telomere attrition and dysfunction are central to both. Dyskeratosis congenita (DC) is associated with mutations in the telomerase enzyme complex (TERT, TERC, and DKC1) and progressive telomere attrition. We analyzed the effect of telomere attrition on senescence-associated metabolites in fibroblast-conditioned media and DC patient plasma. Samples were analyzed by gas chromatography/mass spectrometry and liquid chromatography/mass spectrometry. We showed extracellular citrate was repressed by canonical telomerase function in vitro and associated with DC leukocyte telomere attrition in vivo, leading to the hypothesis that altered citrate metabolism detects telomere dysfunction. However, elevated citrate and senescence factors only weakly distinguished DC patients from controls, whereas elevated levels of other tricarboxylic acid cycle (TCA) metabolites, lactate, and especially pyruvate distinguished them with high significance. The DC plasma signature most resembled that of patients with loss of function pyruvate dehydrogenase complex mutations and that of older subjects but significantly not those of type 2 diabetes, lactic acidosis, or elevated mitochondrial reactive oxygen species. Additionally, our data are consistent with further metabolism of citrate and lactate in the liver and kidneys. Citrate uptake in certain organs modulates age-related disease in mice and our data have similarities with age-related disease signatures in humans. Our results have implications for the role of telomere dysfunction in human aging in addition to its early diagnosis and the monitoring of anti-senescence therapeutics, especially those designed to improve telomere function.
Topics: Humans; Animals; Mice; Dyskeratosis Congenita; Telomerase; Diabetes Mellitus, Type 2; Telomere; Mutation; Citrates; Lactates; Nuclear Proteins; Cell Cycle Proteins
PubMed: 36651908
DOI: 10.1093/gerona/glad018 -
Life Science Alliance Jan 2022Telomerase extends chromosome ends in somatic and germline stem cells to ensure continued proliferation. Mutations in genes critical for telomerase function result in...
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.
Topics: Amino Acid Sequence; Animals; CRISPR-Cas Systems; Dyskeratosis Congenita; Fertility; Gene Editing; Germ Cells; Hematopoiesis; Homozygote; Humans; Lymphopoiesis; Male; Mice; Mice, Knockout; Models, Molecular; Mutation; Organ Specificity; Sperm Count; Structure-Activity Relationship; Telomere-Binding Proteins
PubMed: 34645668
DOI: 10.26508/lsa.202101208 -
Cellular and Molecular Gastroenterology... 2023Dyskeratosis congenita (DC) is a telomere biology disorder caused primarily by mutations in the DKC1 gene. Patients with DC and related telomeropathies resulting from...
BACKGROUND & AIMS
Dyskeratosis congenita (DC) is a telomere biology disorder caused primarily by mutations in the DKC1 gene. Patients with DC and related telomeropathies resulting from premature telomere dysfunction experience multiorgan failure. In the liver, DC patients present with nodular hyperplasia, steatosis, inflammation, and cirrhosis. However, the mechanism responsible for telomere dysfunction-induced liver disease remains unclear.
METHODS
We used isogenic human induced pluripotent stem cells (iPSCs) harboring a causal DC mutation in DKC1 or a CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/Cas9)-corrected control allele to model DC liver pathologies. We differentiated these iPSCs into hepatocytes (HEPs) or hepatic stellate cells (HSCs) followed by generation of genotype-admixed hepatostellate organoids. Single-cell transcriptomics were applied to hepatostellate organoids to understand cell type-specific genotype-phenotype relationships.
RESULTS
Directed differentiation of iPSCs into HEPs and stellate cells and subsequent hepatostellate organoid formation revealed a dominant phenotype in the parenchyma, with DC HEPs becoming hyperplastic and also eliciting a pathogenic hyperplastic, proinflammatory response in stellate cells independent of stellate cell genotype. Pathogenic phenotypes in DKC1-mutant HEPs and hepatostellate organoids could be rescued via suppression of serine/threonine kinase AKT (protein kinase B) activity, a central regulator of MYC-driven hyperplasia downstream of DKC1 mutation.
CONCLUSIONS
Isogenic iPSC-derived admixed hepatostellate organoids offer insight into the liver pathologies in telomeropathies and provide a framework for evaluating emerging therapies.
Topics: Humans; Induced Pluripotent Stem Cells; Hyperplasia; Liver; Cell Differentiation; Organoids; Nuclear Proteins; Cell Cycle Proteins
PubMed: 37302654
DOI: 10.1016/j.jcmgh.2023.06.003 -
Blood Oct 2020Inherited bone marrow failure syndromes (IBMFSs) are characterized by ineffective hematopoiesis and increased risk for developing myeloid malignancy. The... (Review)
Review
Inherited bone marrow failure syndromes (IBMFSs) are characterized by ineffective hematopoiesis and increased risk for developing myeloid malignancy. The pathophysiologies of different IBMFSs are variable and can relate to defects in diverse biological processes, including DNA damage repair (Fanconi anemia), telomere maintenance (dyskeratosis congenita), and ribosome biogenesis (Diamond-Blackfan anemia, Shwachman-Diamond syndrome). Somatic mutations leading to clonal hematopoiesis have been described in IBMFSs, but the distinct mechanisms by which mutations drive clonal advantage in each disease and their associations with leukemia risk are not well understood. Clinical observations and laboratory models of IBMFSs suggest that the germline deficiencies establish a qualitatively impaired functional state at baseline. In this context, somatic alterations can promote clonal hematopoiesis by improving the competitive fitness of specific hematopoietic stem cell clones. Some somatic alterations relieve baseline fitness constraints by normalizing the underlying germline deficit through direct reversion or indirect compensation, whereas others do so by subverting senescence or tumor-suppressor pathways. Clones with normalizing somatic mutations may have limited transformation potential that is due to retention of functionally intact fitness-sensing and tumor-suppressor pathways, whereas those with mutations that impair cellular elimination may have increased risk for malignant transformation that is due to subversion of tumor-suppressor pathways. Because clonal hematopoiesis is not deterministic of malignant transformation, rational surveillance strategies will depend on the ability to prospectively identify specific clones with increased leukemic potential. We describe a framework by which an understanding of the processes that promote clonal hematopoiesis in IBMFSs may inform clinical surveillance strategies.
Topics: Animals; Biomarkers; Clonal Evolution; Clonal Hematopoiesis; Congenital Bone Marrow Failure Syndromes; DNA Damage; Diagnosis, Differential; Disease Susceptibility; Genetic Predisposition to Disease; Hematopoiesis; Hematopoietic Stem Cells; Humans; Mutation; Phenotype
PubMed: 32736377
DOI: 10.1182/blood.2019000990 -
Disease Models & Mechanisms Oct 2023p53 (encoded by Trp53) is a tumor suppressor, but mouse models have revealed that increased p53 activity may cause bone marrow failure, likely through dimerization...
p53 (encoded by Trp53) is a tumor suppressor, but mouse models have revealed that increased p53 activity may cause bone marrow failure, likely through dimerization partner, RB-like, E2F4/E2F5 and MuvB (DREAM) complex-mediated gene repression. Here, we designed a systematic approach to identify p53-DREAM pathway targets, the repression of which might contribute to abnormal hematopoiesis. We used Gene Ontology analysis to study transcriptomic changes associated with bone marrow cell differentiation, then chromatin immunoprecipitation-sequencing (ChIP-seq) data to identify DREAM-bound promoters. We next created positional frequency matrices to identify evolutionary conserved sequence elements potentially bound by DREAM. The same approach was developed to find p53-DREAM targets associated with brain abnormalities, also observed in mice with increased p53 activity. Putative DREAM-binding sites were found for 151 candidate target genes, of which 106 are mutated in a blood or brain genetic disorder. Twenty-one DREAM-binding sites were tested and found to impact gene expression in luciferase assays, to notably regulate genes mutated in dyskeratosis congenita (Rtel1), Fanconi anemia (Fanca), Diamond-Blackfan anemia (Tsr2), primary microcephaly [Casc5 (or Knl1), Ncaph and Wdr62] and pontocerebellar hypoplasia (Toe1). These results provide clues on the role of the p53-DREAM pathway in regulating hematopoiesis and brain development, with implications for tumorigenesis.
Topics: Animals; Mice; Brain; Cell Cycle Proteins; Cyclin-Dependent Kinase Inhibitor p21; Promoter Regions, Genetic; Tumor Suppressor Protein p53
PubMed: 37661832
DOI: 10.1242/dmm.050376 -
Biochemical Society Transactions Nov 2021Telomerase ribonucleoprotein was discovered over three decades ago as a specialized reverse transcriptase that adds telomeric repeats to the ends of linear eukaryotic... (Review)
Review
Telomerase ribonucleoprotein was discovered over three decades ago as a specialized reverse transcriptase that adds telomeric repeats to the ends of linear eukaryotic chromosomes. Telomerase plays key roles in maintaining genome stability; and its dysfunction and misregulation have been linked to different types of cancers and a spectrum of human genetic disorders. Over the years, a wealth of genetic and biochemical studies of human telomerase have illuminated its numerous fascinating features. Yet, structural studies of human telomerase have lagged behind due to various challenges. Recent technical developments in cryo-electron microscopy have allowed for the first detailed visualization of the human telomerase holoenzyme, revealing unprecedented insights into its active site and assembly. This review summarizes the cumulative work leading to the recent structural advances, as well as highlights how the future structural work will further advance our understanding of this enzyme.
Topics: Biocatalysis; Catalytic Domain; Cryoelectron Microscopy; Dyskeratosis Congenita; Holoenzymes; Humans; Models, Molecular; Mutation; Telomerase; Telomere; Telomere Homeostasis
PubMed: 34623385
DOI: 10.1042/BST20200042 -
American Journal of Human Genetics Aug 2022Dyskeratosis congenita (DC) is an inherited bone-marrow-failure disorder characterized by a triad of mucocutaneous features that include abnormal skin pigmentation, nail...
Dyskeratosis congenita (DC) is an inherited bone-marrow-failure disorder characterized by a triad of mucocutaneous features that include abnormal skin pigmentation, nail dystrophy, and oral leucoplakia. Despite the identification of several genetic variants that cause DC, a significant proportion of probands remain without a molecular diagnosis. In a cohort of eight independent DC-affected families, we have identified a remarkable series of heterozygous germline variants in the gene encoding thymidylate synthase (TYMS). Although the inheritance appeared to be autosomal recessive, one parent in each family had a wild-type TYMS coding sequence. Targeted genomic sequencing identified a specific haplotype and rare variants in the naturally occurring TYMS antisense regulator ENOSF1 (enolase super family 1) inherited from the other parent. Lymphoblastoid cells from affected probands have severe TYMS deficiency, altered cellular deoxyribonucleotide triphosphate pools, and hypersensitivity to the TYMS-specific inhibitor 5-fluorouracil. These defects in the nucleotide metabolism pathway resulted in genotoxic stress, defective transcription, and abnormal telomere maintenance. Gene-rescue studies in cells from affected probands revealed that post-transcriptional epistatic silencing of TYMS is occurring via elevated ENOSF1. These cell and molecular abnormalities generated by the combination of germline digenic variants at the TYMS-ENOSF1 locus represent a unique pathogenetic pathway for DC causation in these affected individuals, whereas the parents who are carriers of either of these variants in a singular fashion remain unaffected.
Topics: Dyskeratosis Congenita; Germ Cells; Heterozygote; Humans; Nucleotides; Thymidylate Synthase
PubMed: 35931051
DOI: 10.1016/j.ajhg.2022.06.014 -
Human Pathology (New York) Sep 2021Dyskeratosis congenita is a disease of impaired tissue maintenance downstream of telomere dysfunction. Characteristically, patients present with the clinical triad of...
Dyskeratosis congenita is a disease of impaired tissue maintenance downstream of telomere dysfunction. Characteristically, patients present with the clinical triad of nail dystrophy, oral leukoplakia, and skin pigmentation defects, but the disease involves degenerative changes in multiple organs. Mutations in telomere-binding proteins such as TINF2 (TRF1-interacting nuclear factor 2) or in telomerase, the enzyme that counteracts age related telomere shortening, are causative in dyskeratosis congenita. We present a patient who presented with severe hypoxemia at age 13. The patient had a history of myelodysplastic syndrome treated with bone marrow transplant at the age of 5. At age 18 she was hospitalized for an acute pneumonia progressing to respiratory failure, developed renal failure and ultimately, she and her family opted to withdraw support as she was not a candidate for a lung transplant. Sequencing of the patient's TINF2 locus revealed a heterozygous mutation (c.844C > T, Arg282Cys) which has previously been reported in a subset of dyskeratosis congenita patients. Tissue sections from multiple organs showed degenerative changes including disorganized bone remodeling, diffuse alveolar damage and small vessel proliferation in the lung, and hyperkeratosis with hyperpigmentation of the skin. Autopsy samples revealed a bimodal distribution of telomere length, with telomeres from donor hematopoietic tissues being an age-appropriate length and those from patient tissues showing pathogenic shortening, with the shortest telomeres in lung, liver, and kidney. We report for the first time a survey of degenerative changes and telomere lengths in multiple organs in a patient with dyskeratosis congenita.
PubMed: 34522616
DOI: 10.1016/j.ehpc.2021.200517