Telomere Research Articles

Possible relationship between the somatic mutations and the formation of cancers

Cancer is one of the most life-threatening diseases and has been studied for more than 3 thousand years (earliest records of cancer research is 1500BC). But there are still insufficient number of efficient treatments for cancer. This is a review started with introducing the cancer and somatic mutations by explaining the hallmarks of cancer, followed by, the discussion of few types of mutations, which may be potential targets regarding to the therapeutic treatments. Also, some potential targets related to those mutations are listed, such as, pRb proteins with its two subunits (p130 and p107), reverse transcriptase telomerase (TERT), shelterin complex and so on. The statement “cancer is caused by accumulation of somatic mutations” can be supported by the positive correlation between cancer and age. In addition, some mutations, which have contribution on increasing mutation frequencies, has been proved to be the factors of cancer. For example, xeroderma pigmentosum, mutations on DNA MMR rep air and BRCA1 and BRCA2 mutations. This overview of the relationship between cancer and those somatic mutations, which may provide potentials for further cancer treatments.

Telomeres and Cancer.

Telomeres cap the ends of eukaryotic chromosomes and are indispensable chromatin structures for genome protection and replication. Telomere length maintenance has been attributed to several functional modulators, including telomerase, the shelterin complex, and the CST complex, synergizing with DNA replication, repair, and the RNA metabolism pathway components. As dysfunctional telomere maintenance and telomerase activation are associated with several human diseases, including cancer, the molecular mechanisms behind telomere length regulation and protection need particular emphasis. Cancer cells exhibit telomerase activation, enabling replicative immortality. Telomerase reverse transcriptase (TERT) activation is involved in cancer development through diverse activities other than mediating telomere elongation. This review describes the telomere functions, the role of functional modulators, the implications in cancer development, and the future therapeutic opportunities.

TIN2 is an architectural protein that facilitates TRF2-mediated trans- and cis-interactions on telomeric DNA.

The telomere specific shelterin complex, which includes TRF1, TRF2, RAP1, TIN2, TPP1 and POT1, prevents spurious recognition of telomeres as double-strand DNA breaks and regulates telomerase and DNA repair activities at telomeres. TIN2 is a key component of the shelterin complex that directly interacts with TRF1, TRF2 and TPP1. In vivo, the large majority of TRF1 and TRF2 are in complex with TIN2 but without TPP1 and POT1. Since knockdown of TIN2 also removes TRF1 and TRF2 from telomeres, previous cell-based assays only provide information on downstream effects after the loss of TRF1/TRF2 and TIN2. Here, we investigated DNA structures promoted by TRF2–TIN2 using single-molecule imaging platforms, including tracking of compaction of long mouse telomeric DNA using fluorescence imaging, atomic force microscopy (AFM) imaging of protein–DNA structures, and monitoring of DNA–DNA and DNA–RNA bridging using the DNA tightrope assay. These techniques enabled us to uncover previously unknown unique activities of TIN2. TIN2S and TIN2L isoforms facilitate TRF2-mediated telomeric DNA compaction (cis-interactions), dsDNA–dsDNA, dsDNA–ssDNA and dsDNA–ssRNA bridging (trans-interactions). Furthermore, TIN2 facilitates TRF2-mediated T-loop formation. We propose a molecular model in which TIN2 functions as an architectural protein to promote TRF2-mediated trans and cis higher-order nucleic acid structures at telomeres.

Telomere Length and Arterial Stiffness Reflected by Brachial-Ankle Pulse Wave Velocity: A Population-Based Cross-Sectional Study.

Telomere (TL) is a biomarker of biological aging, and its shortening is associated with major risk factors for cardiovascular diseases (CVD). This study aimed to identify whether TL is associated with arterial stiffness as reflected by brachial–ankle pulse wave velocity (baPWV). This population-based cross-sectional study involved 1065 individuals in the Iwaki area, Japan. Total TL length and TL G-tail length were measured by hybridization protection assay. The baPWV was measured on the right and left sides using a non-invasive vascular screening device. The associations between TL and baPWV were assessed by multivariate linear regression. Compared with the shortest total TL tertile, the longest total TL group showed a significant decrease in baPWV (lowest vs. highest tertile: adjusted beta: −41.24, 95% confidence interval (CI): −76.81, −5.68). The mean baPWV decreased with a longer TL (TL G-tail length: p trend < 0.001, total TL: p trend < 0.001). TL G-tail and total TL lengths were inversely associated with baPWV, implicating TL shortening in the development of CVD. This study provides evidence of the factors influencing CVD risks at a very early stage when individuals can still take necessary precautions before CVD gives rise to a symptomatic health outcome.

MRE11 and UBR5 Co-Operate to Suppress RNF168-Mediated Fusion of Dysfunctional Telomeres.

TRF2 is part of the shelterin complex that hides telomeric DNA ends and prevents the activation of the cNHEJ pathway that can lead to chromosomal fusion. TRF2, however, also actively suppresses the cNHEJ pathway by recruiting two proteins, MRE11 and UBR5. MRE11 binds BRCC3, which in turn deubiquitinates γH2AX deposited at exposed telomeric DNA ends and limits RNF168 recruitment to the telomere. UBR5, in contrast directly ubiquitinates and destroys RNF168. The loss of telomeric RNF168 in turn blocks the subsequent recruitment of 53BP1 and prevents the cNHEJ-mediated fusion of chromosomes with exposed telomeric DNA ends. Although MRE11 and UBR5 are both involved in the control of telomeric RNF168 levels and the chromosome fusion process, their relative contributions have not been directly addressed. To do so we genetically suppressed MRE11 and UBR5 alone or in combination in glioma cell lines which we previously showed contained dysfunctional telomeres that were dependent on TRF2 for suppression of telomeric fusion and monitored the effects on events associated with telomere fusion. We here show that while suppression of either MRE11 or UBR5 alone had minimal effects on RNF168 telomeric accumulation, 53BP1 recruitment, and telomeric fusion, their combined suppression led to significant increases in RNF168 and 53BP1 telomeric recruitment and telomeric fusion and eventually cell death, all of which were reversible by suppression of RNF168 itself. These results show that MRE11 and UBR5 co-operate to suppress fusion at dysfunctional telomeres.

Abstract 12533: Progerin Causes a Disproportionate Senescence in Endothelial Cells

Hutchinson-Gilford progeria syndrome (HGPS) is a premature aging disorder caused by the mutation of LMNA gene leading to irreversibly farnesylated lamin A protein, i.e. progerin. The major causes of death in HGPS are coronary and arterial occlusive disease. In the murine model of HGPS, vascular smooth muscle cells (VSMCs) loss is the primary vascular manifestation, which is quite different from the human arterial occlusive disease. To identify the mechanisms of HGPS vascular disease in humans, we differentiated isogenomic endothelial cells (ECs) and VSMCs from the same lines of HGPS-iPSCs and control-iPSCs. Both HGPS-ECs and HGPS-VSMCs manifested cellular hallmarks of aging, including dysmorphic nuclei, impaired proliferation, increased β-galactosidase staining, shortened telomeres, upregulated secretion of inflammatory cytokines, increased DNA damage, loss of heterochromatin and altered shelterin complex expression. However, at similar passage number, HGPS-ECs are more severely affected compared to VSMCs, as indicated by a higher percentage of β-galactosidase positive cells, significantly shortened telomere length, and greater frequency of DNA damage signals. With increasing passage number, there is progressive senescence in HGPS-ECs that is greater than that observed in HGPS-VSMCs. Using immunoprecipitation and mass spectrometry, we compared the integrity of the Shelterin Protein Complex (SPC), which is composed of six different proteins and whose function is to protect the telomeres, on the ECs and VSMCs of HGPS and control cells. We observed increased γH2A.X binding to RAP1 (member of SPC) and to Lamin A (nuclear envelope) in HGPS cells. The expression of γH2A.X was greater in HGPS ECs than VSMCs, and is associated with loss of SPC integrity, telomere shortening and loss of heterochromatin formation. Whereas progerin expression has deleterious effect in both vascular ECs and VSMCs, the severity of dysfunction is more extensive in HGPS-ECs in comparison to HGPS-VSMCs. These studies indicate that an endothelial-targeted therapy may be useful in HGPS.

Aptamer functionalized and reduced graphene oxide hybridized porous polymers SPE coupled with LC-MS for adsorption and detection of human α-thrombin.

In this study, reduced graphene oxide (rGO) hybridized high internal phase emulsions were developed and polymerized as porous carriers for aptamer (5'/5AmMC6/-AGT CCG TGG TAG GGC AGG TTG GGG TGA CT-3') modification to enrich human α-thrombin from serum. The structure and properties of the materials were confirmed by scanning electron microscope (SEM), Fourier transform infrared spectroscope (FT-IR), and X-ray photoelectron spectra (XPS). The adsorption ability and selectivity were studied and the thrombin was detected with liquid chromatography-mass spectrometry (LC-MS). The adsorption of thrombin onto the sorbent was achieved within 30min and the desorption was realized using 5.0mL of acetonitrile/water (80/20, v/v). The thrombin was quantified by LC-MS according to its characteristic peptide sequence of ELLESYIDGR.

The evolution of metazoan shelterin.

The mammalian telomeric shelterin complex-comprised of TRF1, TRF2, Rap1, TIN2, TPP1, and POT1-blocks the DNA damage response at chromosome ends and interacts with telomerase and the CST complex to regulate telomere length. The evolutionary origins of shelterin are unclear, partly because unicellular organisms have distinct telomeric proteins. Here, we describe the evolution of metazoan shelterin, showing that TRF1 emerged in vertebrates upon duplication of a TRF2-like ancestor. TRF1 and TRF2 diverged rapidly during vertebrate evolution through the acquisition of new domains and interacting factors. Vertebrate shelterin is also distinguished by the presence of an HJRL domain in the split C-terminal OB fold of POT1, whereas invertebrate POT1s carry inserts of variable nature. Importantly, the data reveal that, apart from the primate and rodent POT1 orthologs, all metazoan POT1s are predicted to have a fourth OB fold at their N termini. Therefore, we propose that POT1 arose from a four-OB-fold ancestor, most likely an RPA70-like protein. This analysis provides insights into the biology of shelterin and its evolution from ancestral telomeric DNA-binding proteins.

Novel Germline POT1 Variant Predisposes to Childhood Acute Myeloid Leukemia

Introduction: Current studies indicate a contribution of germline predisposition in the development of approximately 8.5% of childhood cancers (Zhang J. et al., N Engl J Med, 2015), although their apparent rate is estimated to be much higher. Understanding tumor evolution based on a predisposed cell can open unknown doors for prevention and therapy of childhood cancer e.g., leukemia. Here we present a novel rare (MAF<0.1%) germline POT1 variant (Q199*) predisposing to acute myeloid leukemia (AML). POT1 as part of the telomeric shelterin complex is known to play an important role in DNA damage protection, telomere length maintenance and chromosomal stability (Calvete O. et al., Nat. Commun., 2015). POT1 variants are associated with a broad range of cancer, including myeloid and lymphoid neoplasms in adults (Lim T.L. et al., Leukemia, 2021), but not yet described for myeloid malignancies in childhood.Methods: Whole exome sequencing (WES) was implemented to identify germline variants. To assess the effect of POT1 p.Q199*, patient's fibroblast and stably transfected HEK293T cells were used as cell models. The variant's functional impact was experimentally tested performing yH2AX and 53BP1 immunofluorescence assays for DNA damage detection, qRT-PCR for telomere length measurement and telomere FISH to assess chromosomal instability.Results: Utilizing WES to detect variants within shelterin complex genes we analyzed genomic data of an unselected German parent-child cohort of children with cancer (n=60, TRIO-DD), as well as a recently published parent-child pediatric cancer cohort (n=158, TRIO-D) (Wagener R. et al., Eur. J. Hum. Genet, 2021). Here, we identified a novel germline POT1 variant in a boy affected with Myelodysplastic syndrome (MDS) and secondary AML (7q-). This novel germline variant constitutes a stop-gain mutation causing a substitution of the amino acid Glutamine by a stop codon (p.Q199*).QRT-PCR analysis within the patient's fibroblasts showed a significant (student's t-test p=0.0037) reduction of POT1 mRNA expression to ≈0.5 compared to POT1 wildtype. Western Blot analysis revealed reduced POT1 levels, confirming the loss of one POT1 allele mediated by p.Q199*. Thereupon, POT1 p.Q199* cloning and stable transfection into Hek293T cells was performed to test the variant's cooperative functionality in a controlled environment. Subsequently, POT1 p.Q199* lead to a drastically significant (student's t-test p=<0.001) increase of DNA double strand breaks in transfected Hek293T cells determined by yH2AX and 53BP1 immunofluorescence assays, which is in line with a deregulated DNA damage response and inappropriate repair by non-homologous end joining.In addition, we detected dysregulation of telomere length maintenance. Here, relative telomere length measurement by means of qRT-PCR indicated significant (student's t-test p=0.019) telomere elongation in POT1 p.Q199* fibroblast cells. Furthermore telomere FISH on metaphase chromosomes was performed to analyse chromosomal stability. In POT1 p.Q199* Hek293T cells we identified a significant (student's t-test p=0.002) increase in telomere fragility compared to POT1 WT cells.Conclusion: Taken together, we present the functional effects of POT1 p.Q199* leading to a significant increase of DNA damage, telomere length and chromosomal instability. Our results on functional dysregulation strengthen a potential genetic predisposition to childhood AML mediated by germline POT1 variants. DisclosuresNo relevant conflicts of interest to declare.

Relationships of Telomere Homeostasis with Oxidative Stress and Cardiac Dysfunction in Human Ischaemic Hearts

Although the roles of telomeres and oxidative stress in ischaemic cardiomyopathy (ICM) are known, mechanisms of telomere homeostasis and their relationship with oxidative stress are incompletely understood. We performed two RNA-seq analyses (mRNA n = 23; ncRNA n = 30) and protein validation on left ventricles of explanted hearts from ICM and control subjects. We observed dysregulation of the shelterin and cohesin complexes, which was related to an increase in the response to cellular oxidative stress. Moreover, we found alterations at mRNA level in the mechanisms of telomeric DNA repair. Specifically, increased RAD51D mRNA levels were correlated with left ventricular diameters. RAD51D protein levels were unaltered, however, and were inversely corelated with the miR-103a-3p upregulation. We also observed the overexpression of lncRNAs (TERRA and GUARDIN) involved in telomere protection in response to stress and alterations in their regulatory molecules. Expression of the TERRA transcription factor ATF7 was correlated with superoxide dismutase 1 expression and left ventricular diameters. The levels of GUARDIN and its transcription factor FOSL2 were correlated with those of catalase. Therefore, we showed specific alterations in the mechanisms of telomeric DNA repair and protection, and these alterations are related to an increase in the response mechanisms to oxidative stress and cardiac dysfunction in ICM.

The histone chaperone FACT facilitates heterochromatin spreading by regulating histone turnover and H3K9 methylation states.

SUMMARYHeterochromatin formation requires three distinct steps: nucleation, self-propagation (spreading) along the chromosome, and faithful maintenance after each replication cycle. Impeding any of those steps induces heterochromatin defects and improper gene expression. The essential histone chaperone FACT (facilitates chromatin transcription) has been implicated in heterochromatin silencing, but the mechanisms by which FACT engages in this process remain opaque. Here, we pinpoint its function to the heterochromatin spreading process in fission yeast. FACT impairment reduces nucleation-distal H3K9me3 and HP1/Swi6 accumulation at subtelomeres and derepresses genes in the vicinity of heterochromatin boundaries. FACT promotes spreading by repressing heterochromatic histone turnover, which is crucial for the H3K9me2 to me3 transition that enables spreading. FACT mutant spreading defects are suppressed by removal of the H3K9 methylation antagonist Epe1. Together, our study identifies FACT as a histone chaperone that promotes heterochromatin spreading and lends support to the model that regulated histone turnover controls the propagation of repressive methylation marks.

Germline POT1 Deregulation Can Predispose to Myeloid Malignancies in Childhood.

While the shelterin complex guards and coordinates the mechanism of telomere regulation, deregulation of this process is tightly linked to malignant transformation and cancer. Here, we present the novel finding of a germline stop-gain variant (p.Q199*) in the shelterin complex gene POT1, which was identified in a child with acute myeloid leukemia. We show that the cells overexpressing the mutated POT1 display increased DNA damage and chromosomal instabilities compared to the wildtype counterpart. Protein and mRNA expression analyses in the primary patient cells further confirm that, physiologically, the variant leads to a nonfunctional POT1 allele in the patient. Subsequent telomere length measurements in the primary cells carrying heterozygous POT1 p.Q199* as well as POT1 knockdown AML cells revealed telomeric elongation as the main functional effect. These results show a connection between POT1 p.Q199* and telomeric dysregulation and highlight POT1 germline deficiency as a predisposition to myeloid malignancies in childhood.

Téloméropathies de recrutement hématologique : étude de 15 cas

IntroductionTelomeres are composed of a repeated sequence of double-stranded nucleotides TTAGGG and numerous proteins including the Shelterin complex. Their main role is to maintain the stability of the genome during cell replication through a mechanism of copying the repeted sequence by the telomerase complexe. All the diseases involving a deregulation of this complex are now grouped together under the term telomeropathies. They are difficult to diagnose and manage. Our objective was to describe the clinico-biological characteristics and treatments used, in patients affected by telomeropathies previously seen by an hematologist followed at the Lille University Hospital Center. MethodsThis is a retrospective, single-center study carried out within the department of internal medicine-clinical immunology, Reference center for rare autoimmune and systemic diseases at Lille University Hospital Center between 2005 and 2020 including all patients followed for telomeropathy. ResultsProbands and relatives were included. Fifteen patients were studied from 10 independant families. Sixty percent had an heterozygous TERC gene mutation. Sixty seven percent had haematological diseases including macrocytosis, anemia and/or thrombocytopenia, 20 % had a fibrotic hepatic disease, 27 % had a fibrotic pulmonary disease. Lymphocyte immunophenotyping showed a double negative T lymphocyte population with γδ TCR expression in 5 (33 %) patients. Forty-seven percent of the patients had not received any treatment. Twenty-seven percent were on androgen therapy. Twenty percent had received cyclosporine and 13 % anti-lymphocyte serum in the context of initial misdiagnosis. ConclusionIt is important to be aware of the complexity of telomeropathies, a differential diagnosis of immune aplastic anemia, in order to optimize management and avoid inappropriate treatments. Allografting of hematopoietic stem cells is the only potentially curative treatment. Our analysis found particularities in immunophenotyping lymphocyte not previously described to our knowledge, whose physiopathological imputability remains to be demonstrated.

PSIX-29 Study of the association of mtDNA haplogroups and Ages of 100 days in pigs

Abstract The aim of the work was to determine the mtDNA haplogroups and assess their associations with Days_100 in pigs based on sequencing the D-loop region. The research was carried out on Landrace sows (n = 123). To amplification a fragment of mtDNA D-loop conducted PCR using the following primers: F5 ‘ - TGC AAA CCA AAA CGC CAA GT-3’ and R: 3 ‘ - TTT TTG GGG TTT GGC AAG GC-5. Statistical analyzes were performed using Linear mixed model fit by REML (‘lmerModLmerTest’). The studied group of pigs had the largest number of D haplogroups, which were definitely in 66 sows (53.7%). Haplogroup E was identified in 18 sows (14.6%). Among the haplogroups of Asian origin, which include A, B and C, only genotype C was present. Statistical differences for D100 were established between Hap_C and Hap_E. The presented results indicate the influence of mtDNA haplogroups on Days_100 and pigs of hapogroup E showed the best results compared to analogs of haplogroup E. This may be due to the fact that haplotype E is of European origin, and haplotype C is of Asian origin. Breeding commercial European pigs is focused on increasing the growth rate, and this significantly reduces pig keeping costs and increases production efficiency. It should be noted that changes in growth rate are associated with more intense metabolic processes where mitochondria play a significant role. This may be reflected at the genetic level being determined by the nucleotide sequence of mtDNAs and at the haplotype level in particular. This research was funded by Ministry of Science and Higher Education of the Russian Federation (0445-2021-0008).

Subtelomeric Chromatin in the Fission Yeast S. pombe.

Telomeres play important roles in safeguarding the genome. The specialized repressive chromatin that assembles at telomeres and subtelomeric domains is key to this protective role. However, in many organisms, the repetitive nature of telomeric and subtelomeric sequences has hindered research efforts. The fission yeast S. pombe has provided an important model system for dissection of chromatin biology due to the relative ease of genetic manipulation and strong conservation of important regulatory proteins with higher eukaryotes. Telomeres and the telomere-binding shelterin complex are highly conserved with mammals, as is the assembly of constitutive heterochromatin at subtelomeres. In this review, we seek to summarize recent work detailing the assembly of distinct chromatin structures within subtelomeric domains in fission yeast. These include the heterochromatic SH subtelomeric domains, the telomere-associated sequences (TAS), and ST chromatin domains that assemble highly condensed chromatin clusters called knobs. Specifically, we review new insights into the sequence of subtelomeric domains, the distinct types of chromatin that assemble on these sequences and how histone H3 K36 modifications influence these chromatin structures. We address the interplay between the subdomains of chromatin structure and how subtelomeric chromatin is influenced by both the telomere-bound shelterin complexes and by euchromatic chromatin regulators internal to the subtelomeric domain. Finally, we demonstrate that telomere clustering, which is mediated via the condensed ST chromatin knob domains, does not depend on knob assembly within these domains but on Set2, which mediates H3K36 methylation.

Ccq1-Raf2 interaction mediates CLRC recruitment to establish heterochromatin at telomeres.

Telomeres, highly ordered DNA-protein complexes at eukaryotic linear chromosome ends, are specialized heterochromatin loci conserved among eukaryotes. In Schizosaccharomyces pombe, the shelterin complex is important for subtelomeric heterochromatin establishment. Despite shelterin has been demonstrated to mediate the recruitment of the Snf2/histone deacetylase-containing repressor complex (SHREC) and the Clr4 methyltransferase complex (CLRC) to telomeres, the mechanism involved in telomeric heterochromatin assembly remains elusive due to the multiple functions of the shelterin complex. Here, we found that CLRC plays a dominant role in heterochromatin establishment at telomeres. In addition, we identified a series of amino acids in the shelterin subunit Ccq1 that are important for the specific interaction between Ccq1 and the CLRC subunit Raf2. Finally, we demonstrated that the Ccq1-Raf2 interaction is essential for the recruitment of CLRC to telomeres, that contributes to histone H3 lysine 9 methylation, nucleosome stability and the shelterin-chromatin association, promoting a positive feedback mechanism for the nucleation and spreading of heterochromatin at subtelomeres. Together, our findings provide a mechanistic understanding of subtelomeric heterochromatin assembly by shelterin-dependent CLRC recruitment to chromosomal ends.

Increase in lamin B1 promotes telomere instability by disrupting the shelterin complex in human cells.

Telomere maintenance is essential to preserve genomic stability and involves telomere-specific proteins, DNA replication and repair proteins. Lamins are key components of the nuclear envelope and play numerous roles, including maintenance of the nuclear integrity, regulation of transcription, and DNA replication. Elevated levels of lamin B1, one of the major lamins, have been observed in some human pathologies and several cancers. Yet, the effect of lamin B1 dysregulation on telomere maintenance remains unknown. Here, we unveil that lamin B1 overexpression drives telomere instability through the disruption of the shelterin complex. Indeed, lamin B1 dysregulation leads to an increase in telomere dysfunction-induced foci, telomeric fusions and telomere losses in human cells. Telomere aberrations were preceded by mislocalizations of TRF2 and its binding partner RAP1. Interestingly, we identified new interactions between lamin B1 and these shelterin proteins, which are strongly enhanced at the nuclear periphery upon lamin B1 overexpression. Importantly, chromosomal fusions induced by lamin B1 in excess were rescued by TRF2 overexpression. These data indicated that lamin B1 overexpression triggers telomere instability through a mislocalization of TRF2. Altogether our results point to lamin B1 as a new interacting partner of TRF2, that is involved in telomere stability.

YOUNG WOMEN DIAGNOSED WITH DISTAL CANCER SHOW TELOMERE ALTERATIONS IN THE OVARY

Telomeres play an essential role in the protection of chromosomes. Telomere length (TL) decreases progressively with age, limiting the number of cell divisions and inducing cellular senescence or apoptosis. The loss of telomere protection (TP), which depends on the Shelterin complex, leads to a state of genomic instability that can promote cancer. The aim of this study is to determine whether the telomere pathway is altered in the ovary of women with distal cancer at the time of diagnosis, and the possible role of peripheral blood mononuclear cells (PBMC) TL as biomarker of fertility. 15 women with non-ovarian cancer (Cn) and 13 controls (Ct) were recruited at the Hospital La Fe (Valencia). Ovarian biopsies and blood samples were obtained before therapy. Ovarian biopsies were collected during process of fertility preservation in patients, and in controls, during tubal ligation. Ovarian samples were embedded in paraffin. Blood cells were processed with a Ficoll gradient to isolate PBMC. Telomere length was measured by Fluorescence in Situ Hybridization (FISH), and TP was analyzed by immunofluorescence of the TRF1 Shelterin. Participants were divided into two groups, young women (<33 years old, Y) and older women (>33 years old, O). Mean age and anti-mullerian hormone (AMH) of controls and patients were: YCt (30 ± 3.55 years, 3.87 ± 2.09 ng/mL) and OCt (37.6 ± 2.11 years, 3.87 ± 2.44 ng/mL); YCn (25.18 ± 6.24 years, 3.72 ± 1.92 ng/mL) and OCn (36 ± 1.82 years, 1.29 ± 0.55 ng/mL). Regarding younger women, ovarian TL was higher in controls than in patients (42.62 ± 3.91 and 39.61 ± 3.25 a.u., respectively). In PBMC, similar results were obtained (controls 86.54 ± 9.29 and patients 75.21 ± 14.26 a.u.), but TL differences were not statistically significant. Both ovarian and blood TL showed a positive correlation trend. Ovarian TP was higher in controls than in patients (47.14 ± 4.14 and 43.34 ± 4.32 a.u., respectively), but this trend was not observed in PBMC. Regarding older women, no differences were observed between controls and patients in TL or TP in the ovary. However, in PBMC from the control group TL was higher than in patients (79.75 ± 9.86 and 76.87 ± 4.44 a.u., respectively). In addition, a better TP was found in controls compared to patients (354.5 ± 154 and 274.6 ± 25.49 a.u., p = 0.0132). TL shows a tendency to be shorter in non-ovarian cancer patients than in controls, this difference is observed at the ovarian and blood levels in young women. TP tends to be lower in the ovary of young women with cancer than in controls of the same age group. This suggests a systemic effect of cancer both at the ovary and blood levels in young women. In older women, differences in TL between controls and patients were harder to find. Possibly a higher number of older patients would clarify the results.

Abstract MP45: The Roles Of Telomeric Repeat Binding Factor 2-interacting Protein (TERF2IP) K240 Sumoylation In Endothelial Cells On Atherogenesis

Background and Objectives: It is not yet clear how the pro-atherogenic signaling events in endothelial cells (ECs) such as those that lead to EC senescence, apoptosis and activation are interconnected and promote atherosclerotic plaque formation in the area exposed to disturbed blood flow (d-flow). TERF2IP, a member of the shelterin complex of the telomere, regulates all three pathological events. We investigated the role of TERF2IP K240 SUMOylation in the process of d-flow-induced atherosclerotic plaque formation. Methods and Results: We found that d-flow increased TERF2IP K240 SUMOylation in ECs and that it was suppressed by a p90RSK specific inhibitor, FMK-MEA. This SUMOylation was independent of TERF2IP S205 phosphorylation. The d-flow-induced senescence, DNA damage, and apoptosis were inhibited in ECs with TERF2IP depletion or point-mutated phosphorylation (S205A) and SUMOylation (K240R) sites. NF-κB activation induced by d-flow or overexpression of p90RSK was also significantly inhibited in ECs overexpressing the TERF2IP S205A phosphorylation mutant. However, cells overexpressing the TERF2IP K240R SUMOylation mutant showed no effect on the d-flow or p90RSK-medaited NF-κB activation. To determine the biological function of TERF2IP K240 SUMOylation, we generated TERF2IP K240R knock-in (KI) mice and examined d-flow-induced atherosclerotic plaque formation using partial left carotid ligation model mice fed a high-fat diet after AAV8-PCSK9 injection. We found no differences in body weights and cholesterol levels between TERF2IP K240R KI and wild type control (WT) mice, but plaque formation was significantly inhibited in the KI mice compared to WT animals (Oil Red O positive area (%): 19.0 +/- 12.5 (KI mice, n=8) vs 61.2 +/- 24.3 (WT mice, n=7), p = 0.0008). Bone marrow from WT mice were transplanted into KI and WT mice, which were then injected with AAV8-PCSK9 virus and fed a high-fat diet for 16 weeks, but we still found that plaque formation was inhibited in the KI mice. Conclusion: TERF2IP SUMOylation plays a role in in EC senescence but not in activation. The significant inhibition of plaque formation in the TERF2IP K240R KI mice is due to downregulation of TERF2IP SUMOylation in ECs not in myeloid cells.

Structure, dynamics, and regulation of TRF1-TIN2-mediated trans- and cis-interactions on telomeric DNA

TIN2 is a core component of the shelterin complex linking double-stranded telomeric DNA-binding proteins (TRF1 and TRF2) and single-strand overhang-binding proteins (TPP1-POT1). In vivo, the large majority of TRF1 and TRF2 exist in complexes containing TIN2 but lacking TPP1/POT1; however, the role of TRF1-TIN2 interactions in mediating interactions with telomeric DNA is unclear. Here, we investigated DNA molecular structures promoted by TRF1-TIN2 interaction using atomic force microscopy (AFM), total internal reflection fluorescence microscopy (TIRFM), and the DNA tightrope assay. We demonstrate that the short (TIN2S) and long (TIN2L) isoforms of TIN2 facilitate TRF1-mediated DNA compaction (cis-interactions) and DNA-DNA bridging (trans-interactions) in a telomeric sequence- and length-dependent manner. On the short telomeric DNA substrate (six TTAGGG repeats), the majority of TRF1-mediated telomeric DNA-DNA bridging events are transient with a lifetime of ~1.95 s. On longer DNA substrates (270 TTAGGG repeats), TIN2 forms multiprotein complexes with TRF1 and stabilizes TRF1-mediated DNA-DNA bridging events that last on the order of minutes. Preincubation of TRF1 with its regulator protein Tankyrase 1 and the cofactor NAD+ significantly reduced TRF1-TIN2 mediated DNA-DNA bridging, whereas TIN2 protected the disassembly of TRF1-TIN2 mediated DNA-DNA bridging upon Tankyrase 1 addition. Furthermore, we showed that TPP1 inhibits TRF1-TIN2L-mediated DNA-DNA bridging. Our study, together with previous findings, supports a molecular model in which protein assemblies at telomeres are heterogeneous with distinct subcomplexes and full shelterin complexes playing distinct roles in telomere protection and elongation.