DNA methyltransferases control telomere length and telomere recombination in mammalian cells

Telomeres as hallmarks of iPSC aging: a review on telomere dynamics during stemness and cellular reprogramming

Telomeres, the protective ends of chromosome, are key to tissue repair and regeneration. Telomere shortening is linked to aging and age-related disorders, while excessive telomerase activity may support tissue regeneration or transformation. Some of the functions of telomeres and telomerase may be mediated by its important role in the process of stemness. Active telomerase, and subsequent telomerase-dependent telomere extension, supports stem-cells self-renewal and pluripotency - essential for tissue healing. During cellular reprogramming, differentiated cells are converted into induced pluripotent stem cells (iPSCs), which resemble embryonic stem cells. During iPSC derivation, telomere length is reset, enhancing iPSCs' regenerative potential. During this process, incomplete telomerase activation and telomere extension can lead to genomic instability and/or haltered cell functionality. Understanding the intricate relation of telomeres, telomerase and stemness may be critical when designing novel cell-based therapies targeting degenerative diseases or to unlock strategies to delay aging. Here, we explore the recent bibliography linking these areas, raising awareness of their important when designing novel breakthroughs in health and longevity.

Telomeres in skin aging

Skin aging is influenced by both intrinsic and extrinsic factors. The gradual manifestation of changes in telomere length and telomerase activity, as crucial indicators of aging, elucidates the underlying mechanism of skin aging. This review aims to comprehensively analyze the association between telomeres and aging, along with their impact on skin biological function. Firstly, we summarize the structure and function of telomeres and their role in cell division. Subsequently, we discuss the mechanisms through which telomere regulation contributes to aging processes while analyzing its involvement in skin aging by elaborating on biological markers. Furthermore, this paper presents a summary of recent research progress that reveals the correlation between telomere length and skin aging as well as model building methods; it also proposes telomere length as a potential indicator for predicting skin aging. Finally, anti-aging strategies based on telomere protection are discussed including drug therapy and lifestyle adjustments. This paper provides a systematic overview of the role played by telomeres in the field of skin aging for the first time, offering new perspectives and ideas for future prevention and treatment.

i-Motifs as regulatory switches: Mechanisms and implications for gene expression

i-Motifs, cytosine-tetrads, or C-quadruplexes are intercalated structures formed by base pairing between cytosine and protonated cytosine. These structures demonstrate increased stability in acidic environments due to the presence of the latter cytosinium group (i.e., the protonated cytosine). Research has shown that i-motifs are typically disrupted or destabilized at physiological pH levels (7.0-7.4), which makes their potential formation in the nucleus and their biological relevance uncertain. However, in 2018, it was demonstrated that i-motifs exist within the nucleus under physiological conditions, with various intracellular factors contributing to their stability. Identification of i-motifs in the nucleus and their association with gene promoters-particularly with those of proto-oncogenes-has generated significant interest in their potential regulatory functions. Additionally, recent studies suggest that i-motifs may function as switches for gene expression, influencing gene regulation through their folding and stabilization or unfolding and destabilization. This review aims to delve into these mechanisms to improve our understanding of the physiological significance of i-motifs.

Epigenetic biomarkers in aging and longevity: Current and future application

The aging process has been one of the most necessary research fields in the current century, and knowing different theories of aging and the role of different genetic, epigenetic, molecular, and environmental modulating factors in increasing the knowledge of aging mechanisms and developing appropriate diagnostic, therapeutic, and preventive ways would be helpful. One of the most conserved signs of aging is epigenetic changes, including DNA methylation, histone modifications, chromatin remodeling, noncoding RNAs, and extracellular RNAs. Numerous biological processes and hallmarks are vital in aging development, but epigenomic alterations are especially notable because of their importance in gene regulation and cellular identity. The mounting evidence points to a possible interaction between age-related epigenomic alterations and other aging hallmarks, like genome instability. To extend a healthy lifespan and possibly reverse some facets of aging and aging-related diseases, it will be crucial to comprehend global and locus-specific epigenomic modifications and recognize corresponding regulators of health and longevity. In the current study, we will aim to discuss the role of epigenomic mechanisms in aging and the most recent developments in epigenetic diagnostic biomarkers, which have the potential to focus efforts on reversing the destructive signs of aging and extending the lifespan.

The TERT Promoter is Polycomb-Repressed in Neuroblastoma Cells with Long Telomeres

Acquiring a telomere maintenance mechanism is a hallmark of high-risk neuroblastoma and commonly occurs by expressing telomerase (TERT). Telomerase-negative neuroblastoma has long telomeres and utilizes the telomerase-independent alternative lengthening of telomeres (ALT) mechanism. Conversely, no discernable telomere maintenance mechanism is detected in a fraction of neuroblastoma with long telomeres. Here, we show, unlike most cancers, DNA of the TERT promoter is broadly hypomethylated in neuroblastoma. In telomerase-positive neuroblastoma cells, the hypomethylated DNA promoter is approximately 1.5 kb. The TERT locus shows active chromatin marks with low enrichment for the repressive mark, H3K27me3. MYCN, a commonly amplified oncogene in neuroblstoma, binds to the promoter and induces TERT expression. Strikingly, in neuroblastoma with long telomeres, the hypomethylated region spans the entire TERT locus, including multiple nearby genes with enrichment for the repressive H3K27me3 chromatin mark. Furthermore, subtelomeric regions showed enrichment of repressive chromatin marks in neuroblastomas with long telomeres relative to those with short telomeres. These repressive marks were even more evident at the genic loci, suggesting a telomere position effect (TPE). Inhibiting H3K27 methylation by three different EZH2 inhibitors induced the expression of TERT in cell lines with long telomeres and H3K27me3 marks in the promoter region. EZH2 inhibition facilitated MYCN binding to the TERT promoter in neuroblastoma cells with long telomeres. Taken together, these data suggest that epigenetic regulation of TERT expression differs in neuroblastoma depending on the telomere maintenance status, and H3K27 methylation is important in repressing TERT expression in neuroblastoma with long telomeres.

SIGNIFICANCE

The epigenetic landscape of the TERT locus is unique in neuroblastoma. The DNA at the TERT locus, unlike other cancer cells and similar to normal cells, are hypomethylated in telomerase-positive neuroblastoma cells. The TERT locus is repressed by polycomb repressive complex-2 complex in neuroblastoma cells that have long telomeres and do not express TERT. Long telomeres in neuroblastoma cells are also associated with repressive chromatin states at the chromosomal termini, suggesting TPE.

Human telomere length is chromosome end-specific and conserved across individuals

Short telomeres cause age-related disease, and long telomeres contribute to cancer; however, the mechanisms regulating telomere length are unclear. We developed a nanopore-based method, which we call Telomere Profiling, to determine telomere length at nearly single-nucleotide resolution. Mapping telomere reads to chromosome ends showed chromosome end-specific length distributions that could differ by more than six kilobases. Examination of telomere lengths in 147 individuals revealed that certain chromosome ends were consistently longer or shorter. The same rank order was found in newborn cord blood, suggesting that telomere length is determined at birth and that chromosome end-specific telomere length differences are maintained as telomeres shorten with age. Telomere Profiling makes precision investigation of telomere length widely accessible for laboratory, clinical, and drug discovery efforts and will allow deeper insights into telomere biology.

Chromosome ends and the theory of marginotomy: implications for reproduction

Telomeres are the protective structures located at the ends of linear chromosomes. They were first described in the 1930s, but their biology remained unexplored until the early 70s, when Alexey M. Olovnikov, a theoretical biologist, suggested that telomeres cannot be fully copied during DNA replication. He proposed a theory that linked this phenomenon with the limit of cell proliferation capacity and the "duration of life" (theory of marginotomy), and suggested a potential of telomere lenghthening for the prevention of aging (anti-marginotomy). The impact of proliferative telomere shortening on life expectancy was later confirmed. In humans, telomere shortening is counteracted by telomerase, an enzyme that is undetectable in most adult somatic cells, but present in cancer cells and adult and embryonic stem and germ cells. Although telomere length dynamics are different in male and female gametes during gametogenesis, telomere lengths are reset at the blastocyst stage, setting the initial length of the species. The role of the telomere pathway in reproduction has been explored for years, mainly because of increased infertility resulting from delayed childbearing. Short telomere length in ovarian somatic cells is associated to decreased fertility and higher aneuploidy rates in embryos. Consequently, there is a growing interest in telomere lengthening strategies, aimed at improving fertility. It has also been observed that lifestyle factors can affect telomere length and improve fertility outcomes. In this review, we discuss the implications of telomere theory in fertility, especially in oocytes, spermatozoa, and embryos, as well as therapies to enhance reproductive success.

An Overview of the Epigenetic Modifications in the Brain under Normal and Pathological Conditions

Epigenetic changes are changes in gene expression that do not involve alterations to the DNA sequence. These changes lead to establishing a so-called epigenetic code that dictates which and when genes are activated, thus orchestrating gene regulation and playing a central role in development, health, and disease. The brain, being mostly formed by cells that do not undergo a renewal process throughout life, is highly prone to the risk of alterations leading to neuronal death and neurodegenerative disorders, mainly at a late age. Here, we review the main epigenetic modifications that have been described in the brain, with particular attention on those related to the onset of developmental anomalies or neurodegenerative conditions and/or occurring in old age. DNA methylation and several types of histone modifications (acetylation, methylation, phosphorylation, ubiquitination, sumoylation, lactylation, and crotonylation) are major players in these processes. They are directly or indirectly involved in the onset of neurodegeneration in Alzheimer's or Parkinson's disease. Therefore, this review briefly describes the roles of these epigenetic changes in the mechanisms of brain development, maturation, and aging and some of the most important factors dynamically regulating or contributing to these changes, such as oxidative stress, inflammation, and mitochondrial dysfunction.

Investigating the association between blood metabolites and telomere length: A mendelian randomization study

BACKGROUND

Telomere length refers to the protective cap at the end of chromosomes, and it plays a crucial role in many diseases. The objective of this study is to explore the relationship between blood metabolites and telomere length, aiming to identify novel biological factors that influence telomere length.

METHODS

In this study, we extracted genome-wide association study (GWAS) data for blood metabolites from a sample of 7824 Europeans. Additionally, GWAS data for telomere length were obtained from the Open GWAS database (GWAS ID: ieu-b-4879). The primary analysis of this study utilized the random inverse variance weighted (IVW) method. Complementary analyses were also conducted using the MR-Egger and weighted median approaches. Sensitivity analyses were performed to assess the robustness of the findings. These included the Cochran Q test, MR-Egger intercept test, MR-PRESSO, and leave-one-out analysis. To investigate the possibility of reverse causation, reverse MR analysis was conducted. Additionally, multivariable MR was utilized to evaluate the direct effect of metabolites on telomere length.

RESULTS

The results suggested a potential association between 15-methylpalmitate, taurocholate, levulinate, and X-12712 and telomere length. MVMR analysis further showed that 15-methylpalmitate, taurocholate, and levulinate can directly influence telomere length, regardless of other metabolites.

CONCLUSIONS

This study suggests that 15-methylpalmitate, taurocholate, and levulinate are likely factors correlated with telomere length. These findings will contribute to the development of strategies for protecting telomeres, preventing related diseases, and establishing a new biological foundation for achieving healthy aging.

Targeting 'histone mark': Advanced approaches in epigenetic regulation of telomere dynamics in cancer

Telomere integrity is required for the maintenance of genome stability and prevention of oncogenic transformation of cells. Recent evidence suggests the presence of epigenetic modifications as an important regulator of mammalian telomeres. Telomeric and subtelomeric regions are rich in epigenetic marks that regulate telomere length majorly through DNA methylation and post-translational histone modifications. Specific histone modifying enzymes play an integral role in establishing telomeric histone codes necessary for the maintenance of structural integrity. Alterations of crucial histone moieties and histone modifiers cause deregulations in the telomeric chromatin leading to carcinogenic manifestations. This review delves into the significance of histone modifications and their influence on telomere dynamics concerning cancer. Additionally, it highlights the existing research gaps that hold the potential to drive the development of therapeutic interventions targeting the telomere epigenome.

Incomplete reprogramming of DNA replication timing in induced pluripotent stem cells

Induced pluripotent stem cells (iPSCs) are the foundation of cell therapy. Differences in gene expression, DNA methylation, and chromatin conformation, which could affect differentiation capacity, have been identified between iPSCs and embryonic stem cells (ESCs). Less is known about whether DNA replication timing, a process linked to both genome regulation and genome stability, is efficiently reprogrammed to the embryonic state. To answer this, we compare genome-wide replication timing between ESCs, iPSCs, and cells reprogrammed by somatic cell nuclear transfer (NT-ESCs). While NT-ESCs replicate their DNA in a manner indistinguishable from ESCs, a subset of iPSCs exhibits delayed replication at heterochromatic regions containing genes downregulated in iPSCs with incompletely reprogrammed DNA methylation. DNA replication delays are not the result of gene expression or DNA methylation aberrations and persist after cells differentiate to neuronal precursors. Thus, DNA replication timing can be resistant to reprogramming and influence the quality of iPSCs.

Human telomere length is chromosome specific and conserved across individuals

Short telomeres cause age-related disease and long telomeres predispose to cancer; however, the mechanisms regulating telomere length are unclear. To probe these mechanisms, we developed a nanopore sequencing method, Telomere Profiling, that is easy to implement, precise, and cost effective with broad applications in research and the clinic. We sequenced telomeres from individuals with short telomere syndromes and found similar telomere lengths to the clinical FlowFISH assay. We mapped telomere reads to specific chromosome end and identified both chromosome end-specific and haplotype-specific telomere length distributions. In the T2T HG002 genome, where the average telomere length is 5kb, we found a remarkable 6kb difference in lengths between some telomeres. Further, we found that specific chromosome ends were consistently shorter or longer than the average length across 147 individuals. The presence of conserved chromosome end-specific telomere lengths suggests there are new paradigms in telomere biology that are yet to be explored. Understanding the mechanisms regulating length will allow deeper insights into telomere biology that can lead to new approaches to disease.

Telomerase and mitochondria inhibition promote apoptosis and TET2 and ANMT3a expression in triple negative breast cancer cell lines

Introduction

High metastasis, resistance to common treatments, and high mortality rate, has made triple-negative breast cancer (TNBC) to be the most invasive type of breast cancer. High telomerase activity and mitochondrial biogenesis are involved in breast cancer tumorigenesis. The catalytic subunit of telomerase, telomerase reverse transcriptase (hTERT), plays a role in telomere lengthening and extra-biological functions such as gene expression, mitochondria function, and apoptosis. In this study, it has been aimed to evaluate intrinsic-, extrinsic-apoptosis and DNMT3a and TET2 expression following the inhibition of telomerase and mitochondria respiration in TNBC cell lines.

Methods

TNBC cells were treated with IC50 levels of BIBR1532, tigecycline, and also their combination. Then, telomere length, and DNMT3a, TET2, and hTERT expression were evaluated. Finally, apoptosis rate, apoptosis-related proteins, and genes were analyzed.

Results

The present results showed that IC50 level of telomerase and inhibition of mitochondria respiration induced apoptosis but did not leave any significant effect on telomere length. The results also indicated that telomerase inhibition induced extrinsic-apoptosis in MDA-MB-231 and caused intrinsic- apoptosis in MDA-MB-468 cells. Furthermore, it was found that the expression of p53 decreased and was ineffective in cell apoptosis. The expressions of DNMT3a and TET2 increased in cells. In addition, combination treatment was better than BIBR1532 and tigecycline alone.

Conclusion

The inhibition of telomerase and mitochondria respiration caused intrinsic- and extrinsic- apoptosis and increased DNMT3a and TET2 expression and it could be utilized in breast cancer treatment.

Telomere dynamics in human pluripotent stem cells

Pluripotent stem cells (PSCs) are a promising source of stem cells for regenerative therapies. Stem cell function depends on telomere maintenance mechanisms that provide them with the proliferative capacity and genome stability necessary to multiply and regenerate tissues. We show here that established human embryonic stem cells (hESCs) have stable telomere length that is dependent on telomerase but not on alternative mechanisms based on homologous recombination pathways. Here, we show that human-induced pluripotent stem cells (hiPSCs) reprogrammed from somatic cells show progressive telomere lengthening until reaching a length similar to ESCs. hiPSCs also acquire telomeric chromatin marks of ESCs including decreased abundance of tri-methylated histone H3K9 and H4K20 and HP1 heterochromatic marks, as well as of the shelterin component TRF2. These chromatin features are accompanied with increased abundance of telomere transcripts or TERRAs. We also found that telomeres of both hESCs and hiPSCs are well protected from DNA damage during telomere elongation and once full telomere length is achieved, and exhibit stable genomes. Collectively, this study highlights that hiPSCs acquire ESC features during reprogramming and reveals the telomere biology in human pluripotent stem cells (hPSCs).

Novel, clinically relevant genomic patterns identified by comprehensive genomic profiling in ATRX-deficient IDH-wildtype adult high-grade gliomas

Glioblastomas are the most common IDH-wildtype adult high-grade gliomas, frequently harboring mutations in the TERT gene promoter (pTERT) and utilizing the subsequent telomerase overexpression for telomere length maintenance. However, some rare cases show loss of ATRX and use alternative mechanisms of telomere lengthening. In this study, we performed the first complex genomic analysis specifically concentrating on the latter subgroup. Comprehensive genomic profiling of 12 ATRX-deficient and 13 ATRX-intact IDH-wildtype adult high-grade gliomas revealed that ATRX and pTERT mutations are mutually exclusive. DNMT3A alterations were confined to ATRX-deficient, while PTEN mutations to ATRX-intact cases. RAS-MAPK pathway alterations, including NF1 mutations, were more characteristic in the ATRX-deficient group. Variants of genes related to homologous recombination repair showed different patterns of affected genes. Two ATRX-deficient tumors with high tumor mutational burden and mismatch repair deficiency were found. One of these contained a novel fusion involving the NTRK2 and LRRFIP2 genes, while the other showed loss of MSH2 and MSH6 without genetic alterations in the encoding genes suggesting an epigenetic background. Genetic characteristics of ATRX-deficient IDH-wildtype adult high-grade gliomas suggest that these tumors are particularly intriguing targets of potential future therapeutic interventions including immunotherapies combined with MAPK pathway inhibition and DNA repair inhibitors.

Single-cell multi-omics sequencing of human spermatogenesis reveals a DNA demethylation event associated with male meiotic recombination

Human spermatogenesis is a highly ordered process; however, the roles of DNA methylation and chromatin accessibility in this process remain largely unknown. Here by simultaneously investigating the chromatin accessibility, DNA methylome and transcriptome landscapes using the modified single-cell chromatin overall omic-scale landscape sequencing approach, we revealed that the transcriptional changes throughout human spermatogenesis were correlated with chromatin accessibility changes. In particular, we identified a set of transcription factors and cis elements with potential functions. A round of DNA demethylation was uncovered upon meiosis initiation in human spermatogenesis, which was associated with male meiotic recombination and conserved between human and mouse. Aberrant DNA hypermethylation could be detected in leptotene spermatocytes of certain nonobstructive azoospermia patients. Functionally, the intervention of DNA demethylation affected male meiotic recombination and fertility. Our work provides multi-omics landscapes of human spermatogenesis at single-cell resolution and offers insights into the association between DNA demethylation and male meiotic recombination.

Genomic Instability and Epigenetic Changes during Aging

Aging is considered the deterioration of physiological functions along with an increased mortality rate. This scientific review focuses on the central importance of genomic instability during the aging process, encompassing a range of cellular and molecular changes that occur with advancing age. In particular, this revision addresses the genetic and epigenetic alterations that contribute to genomic instability, such as telomere shortening, DNA damage accumulation, and decreased DNA repair capacity. Furthermore, the review explores the epigenetic changes that occur with aging, including modifications to histones, DNA methylation patterns, and the role of non-coding RNAs. Finally, the review discusses the organization of chromatin and its contribution to genomic instability, including heterochromatin loss, chromatin remodeling, and changes in nucleosome and histone abundance. In conclusion, this review highlights the fundamental role that genomic instability plays in the aging process and underscores the need for continued research into these complex biological mechanisms.

Incomplete Reprogramming of DNA Replication Timing in Induced Pluripotent Stem Cells

Induced pluripotent stem cells (iPSC) are a widely used cell system and a foundation for cell therapy. Differences in gene expression, DNA methylation, and chromatin conformation, which have the potential to affect differentiation capacity, have been identified between iPSCs and embryonic stem cells (ESCs). Less is known about whether DNA replication timing - a process linked to both genome regulation and genome stability - is efficiently reprogrammed to the embryonic state. To answer this, we profiled and compared genome-wide replication timing between ESCs, iPSCs, and cells reprogrammed by somatic cell nuclear transfer (NT-ESCs). While NT-ESCs replicated their DNA in a manner indistinguishable from ESCs, a subset of iPSCs exhibit delayed replication at heterochromatic regions containing genes downregulated in iPSC with incompletely reprogrammed DNA methylation. DNA replication delays were not the result of gene expression and DNA methylation aberrations and persisted after differentiating cells to neuronal precursors. Thus, DNA replication timing can be resistant to reprogramming and lead to undesirable phenotypes in iPSCs, establishing it as an important genomic feature to consider when evaluating iPSC lines.

Short telomeres in alveolar type II cells associate with lung fibrosis in post COVID-19 patients with cancer

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for the coronavirus disease 2019 (COVID-19) pandemic. The severity of COVID-19 increases with each decade of life, a phenomenon that suggest that organismal aging contributes to the fatality of the disease. In this regard, we and others have previously shown that COVID-19 severity correlates with shorter telomeres, a molecular determinant of aging, in patient's leukocytes. Lung injury is a predominant feature of acute SARS-CoV-2 infection that can further progress to lung fibrosis in post-COVID-19 patients. Short or dysfunctional telomeres in Alveolar type II (ATII) cells are sufficient to induce pulmonary fibrosis in mouse and humans. Here, we analyze telomere length and the histopathology of lung biopsies from a cohort of alive post-COVID-19 patients and a cohort of age-matched controls with lung cancer. We found loss of ATII cellularity and shorter telomeres in ATII cells concomitant with a marked increase in fibrotic lung parenchyma remodeling in post- COVID-19 patients compared to controls. These findings reveal a link between presence of short telomeres in ATII cells and long-term lung fibrosis sequel in Post-COVID-19 patients.

The genome-wide mutational consequences of DNA hypomethylation

DNA methylation is important for establishing and maintaining cell identity and for genomic stability. This is achieved by regulating the accessibility of regulatory and transcriptional elements and the compaction of subtelomeric, centromeric, and other inactive genomic regions. Carcinogenesis is accompanied by a global loss in DNA methylation, which facilitates the transformation of cells. Cancer hypomethylation may also cause genomic instability, for example through interference with the protective function of telomeres and centromeres. However, understanding the role(s) of hypomethylation in tumor evolution is incomplete because the precise mutational consequences of global hypomethylation have thus far not been systematically assessed. Here we made genome-wide inventories of all possible genetic variation that accumulates in single cells upon the long-term global hypomethylation by CRISPR interference-mediated conditional knockdown of DNMT1. Depletion of DNMT1 resulted in a genomewide reduction in DNA methylation. The degree of DNA methylation loss was similar to that observed in many cancer types. Hypomethylated cells showed reduced proliferation rates, increased transcription of genes, reactivation of the inactive X-chromosome and abnormal nuclear morphologies. Prolonged hypomethylation was accompanied by increased chromosomal instability. However, there was no increase in mutational burden, enrichment for certain mutational signatures or accumulation of structural variation to the genome. In conclusion, the primary consequence of hypomethylation is genomic instability, which in cancer leads to increased tumor heterogeneity and thereby fuels cancer evolution.

Incomplete erasure of histone marks during epigenetic reprogramming in medaka early development

Epigenetic modifications undergo drastic erasure and reestablishment after fertilization. This reprogramming is required for proper embryonic development and cell differentiation. In mammals, some histone modifications are not completely reprogrammed and play critical roles in later development. In contrast, in nonmammalian vertebrates, most histone modifications are thought to be more intensively erased and reestablished by the stage of zygotic genome activation (ZGA). However, histone modifications that escape reprogramming in nonmammalian vertebrates and their potential functional roles remain unknown. Here, we quantitatively and comprehensively analyzed histone modification dynamics during epigenetic reprogramming in Japanese killifish, medaka (Oryzias latipes) embryos. Our data revealed that H3K27ac, H3K27me3, and H3K9me3 escape complete reprogramming, whereas H3K4 methylation is completely erased during cleavage stage. Furthermore, we experimentally showed the functional roles of such retained modifications at early stages: (i) H3K27ac premarks promoters during the cleavage stage, and inhibition of histone acetyltransferases disrupts proper patterning of H3K4 and H3K27 methylation at CpG-dense promoters, but does not affect chromatin accessibility after ZGA; (ii) H3K9me3 is globally erased but specifically retained at telomeric regions, which is required for maintenance of genomic stability during the cleavage stage. These results expand the understanding of diversity and conservation of reprogramming in vertebrates, and unveil previously uncharacterized functions of histone modifications retained during epigenetic reprogramming.

Links between telomere dysfunction and hallmarks of aging

Aging is characterized by the gradual loss of physiological integrity, leading to impaired function and increased risk of death. This deterioration is the main risk factor for the great majority of chronic diseases, which account for most of the morbidity, death and medical expenses. The hallmarks of aging comprise diverse molecular mechanisms and cell systems, which are interrelated and coordinated to drive the aging process. This review focuses on telomere to analyze the interrelationships between telomere dysfunction and other aging hallmarks and their relative contributions to the initiation and progression of age-related diseases (such as neurodegeneration, cardiovascular disease, and cancer), which will contribute to determine drug targets, improve human health in the aging process with minimal side effects and provide information for the prevention and treatment of age-related diseases.

Reprogramming of fibroblast cells to totipotent state by DNA demethylation

Many attempts have been made to induce high-quality embryonic stem cells such as pluripotent stem cells and totipotent stem cells, but challenges remain to be overcome such as appropriate methods and sources. Demethylation of the genome after fertilization is an important step to initiate zygote gene activation, which can lead to the development of new embryos. Here, we tried to induce totipotent stem cells by mimicking DNA demethylation patterns of the embryo. Our data showed, after induction of DNA demethylation via chemicals or knockdown of Dnmts, cells positive for Nanog, and Cdx2 emerged. These cells could differentiate into the pluripotent and trophoblast lineage cells in-vitro. After transferring these cells to the uterus, they can implant and form embryo-like structures. Our study showed the importance of DNA demethylation roles in totipotent stem cell induction and a new and easy way to induce this cell type.

Telomeres susceptibility to environmental arsenic exposure: Shortening or lengthening?

Maintaining telomere length plays a crucial role in regulating cellular life span. Telomere lengthening or shortening is one of the important biomarkers which could predict the preceding or present diseases. Meanwhile, the impact of environmental arsenic exposure on telomere length has increasingly concerned. Although previous studies demonstrated the effects of arsenic on telomere length, the findings were unclear on whether telomere shortens or lengthens by arsenic exposure. Thus, this manuscript summarized and discussed the telomere length alteration following arsenic exposure and the possible does-response effect of arsenic on telomere length. The present review suggested that different age groups may respond differently to arsenic exposure, and the dose-response effect of arsenic could be a critical factor in its effect on telomere length. Moreover, speciation analysis of arsenic could be more informative in identifying the effect of arsenic on telomere length.

Associations between DNA methylation and telomere length during early life: Insight from wild zebra finches (Taeniopygia guttata)

Telomere length and DNA methylation (DNAm) are two promising biomarkers of biological age. Environmental factors and life history traits are known to affect variation in both these biomarkers, especially during early life, yet surprisingly little is known about their reciprocal association, especially in natural populations. Here, we explore how variation in DNAm, growth rate, and early-life conditions are associated with telomere length changes during development. We tested these associations by collecting data from wild, nestling zebra finches in the Australian desert. We found that increases in the level of DNAm were negatively correlated with telomere length changes across early life. We also confirm previously documented effects of post hatch growth rate and clutch size on telomere length in a natural ecological context for a species that has been extensively studied in the laboratory. However, we did not detect any effect of ambient temperature during developmental on telomere length dynamics. We also found that the absolute telomere length of wild zebra finches, measured using the in-gel TRF method, was similar to that of captive birds. Our findings highlight exciting new opportunities to link and disentangle potential relationships between DNA based biomarkers of ageing, and of physiological reactions to environmental change.

Minimally invasive biomarkers in human and non-human primate evolutionary biology: Tools for understanding variation and adaptation

BACKGROUND

The use of minimally invasive biomarkers (MIBs - physiological biomarkers obtained from minimally invasive sample types) has expanded rapidly in science and medicine over the past several decades. The MIB approach is a methodological strength in the field of human and non-human primate evolutionary biology (HEB). Among humans and our closest relatives, MIBs provide unique opportunities to document phenotypic variation and to operationalize evolutionary hypotheses.

AIMS

This paper overviews the use of MIBs in HEB. Our objectives are to (1) highlight key research topics which successfully implement MIBs, (2) identify promising yet under-investigated areas of MIB application, and (3) discuss current challenges in MIB research, with suggestions for advancing the field.

DISCUSSION AND CONCLUSIONS

A range of MIBs are used to investigate focal topics in HEB, including energetics and life history variation/evolution, developmental plasticity, and social status and dominance relationships. Nonetheless, we identify gaps in existing MIB research on traits such as physical growth and gut function that are central to the field. Several challenges remain for HEB research using MIBs, including the need for additional biomarkers and methods of assessment, robust validations, and approaches that are standardized across labs and research groups. Importantly, researchers must provide better support for adaptation and fitness effects in hypothesis testing (e.g., by obtaining complementary measures of energy expenditure, demonstrating redundancy of function, and performing lifetime/longitudinal analyses). We point to continued progress in the use of MIBs in HEB to better understand the past, present, and future of humans and our closest primate relatives.

Individual Differences in Relative Telomere Length in Mentally Healthy Subjects: The Effect of TERT Gene Polymorphism and Urban Residency

The changes in the telomere length caused by the terminal underreplication in the existing literature are related to depressive disorders. However, the use of the telomere length as a biomarker of depressive states is ambiguous, which is due to the effect of various environmental factors on both the psychoemotional state and cellular aging of an organism. In order to identify the possible use of the relative telomere length (RTL) measured in peripheral blood leukocytes as a biomarker of enhanced liability to depression prior to the clinical symptoms, as well as to determine the link between telomere length, sociodemographic factors, allelic variants of the genes involved in the regulation of telomere elongation, and depression level, the association analysis of reverse transcriptase (TERT rs7726159), telomerase RNA component (TERC rs1317082), and the CST complex encoding protein (OBFC1 rs2487999) gene polymorphisms was performed with RTL and depression level in mentally healthy individuals (N = 1065) aged 18-25 years. Together with genetic variants, the examined regression models included various sociodemographic parameters as predictors. As a result of statistical analysis, we failed to observe the association between RTL and individual differences in depression level in the studied sample. Nevertheless, multiple regression analysis allowed us to construct a statistically significant model of individual variance in RTL (P = 4.3е-4; r ² = 0.018), which included rs7726159 in the TERT gene (P = 0.020; β = 0.078) and such environmental predictors as age (P = 0.001; β = -0.027) and place of residence in childhood (urban/rural area) (P = 0.048; β = 0.063). The data obtained confirm the involvement of TERT gene variants and age in telomere length in mentally healthy individuals aged 18-25 years and indicate a negative effect of urban residency on telomere length shortening, which reflects the cellular aging of an organism.

Site-specific decreases in DNA methylation in replicating cells following exposure to oxidative stress

Oxidative stress is a common feature of inflammation-driven cancers, and it promotes genomic instability and aggressive tumour phenotypes. It is known that oxidative stress transiently modulates gene expression through the oxidation of transcription factors and associated regulatory proteins. Neutrophils are our most abundant white blood cells and accumulate at sites of infection and inflammation. Activated neutrophils produce hypochlorous acid and chloramines, which can disrupt DNA methylation by oxidizing methionine. The goal of the current study was to determine whether chloramine exposure results in sequence-specific modifications in DNA methylation that enable long-term alterations in transcriptional output. Proliferating Jurkat T-lymphoma cells were exposed to sublethal doses of glycine chloramine and differential methylation patterns were compared using Illumina EPIC 850 K bead chip arrays. There was a substantial genome-wide decrease in methylation 4 h after exposure that correlated with altered RNA expression for 24 and 48 h, indicating sustained impacts on exposed cells. A large proportion of the most significant differentially methylated CpG sites were situated towards chromosomal ends, suggesting that these regions are most susceptible to inhibition of maintenance DNA methylation. This may contribute to epigenetic instability of chromosomal ends in rapidly dividing cells, with potential implications for the regulation of telomere length and cellular longevity.

Gestational exposure to NO2 aggravates placental senescence

Placental senescence is a normal physiological process of placenta, while premature placental senescence has been confirmed to be associated with some adverse pregnancy complications. Epidemiological studies indicate that NO₂ exposure can aggravate placental senescence which is represented by fibrosis and abnormal telomere homeostasis, etc. In this study, pregnant C57BL/6 mice were exposed to NO₂ (2.5 ppm, 5 h/day) daily in a dynamic exposure chamber throughout the gestation period, and were sacrificed at embryonic day 13.5 (E13.5), E15.5 and E18.5. Placenta were harvested and conducted for histopathological examination and telomere evaluation. Our results showed that gestational NO₂ exposure significantly aggravated placental fibrosis and calcification, and up-regulated the related bio-markers (connective tissue growth factor (Ctgf) and transforming growth factor-β1 (Tgf-β1)) at E18.5. In addition, gestational exposure to NO₂ also activated senescence related pathway (p53/p21) at E18.5. Furthermore, gestational NO₂ exposure significantly shortened telomere length at E18.5, and the expression of telomere homeostasis regulation genes telomeric repeat binding factor 1 (Trf1), protection of telomeres 1a (Pot1a) and Pot1b were significantly increased while telomerase reverse transcriptase (Tert) was suppressed after NO₂ exposure at E13.5 or E18.5, respectively. Importantly, DNA methylation status of the 22^nd at E13.5 and 32^nd at E18.5 site in sub-telomeric region of chromosome 1 was significantly altered. Based on the above results, our present study indicated that gestational NO₂ exposure could lead to premature placental senescence during the late trimester of pregnancy via aggravation of fibrosis and telomere length shortening regulated by telomere regulatory enzyme and DNA methylation.

Nutrient intakes and telomere length of cell-free circulating DNA from amniotic fluid: findings from the Mamma & Bambino cohort

Pregnancy represents a crucial period in which several exposures—and especially maternal diet—might shape children’s health. Thus, identifying how maternal dietary intakes early affect biological aging in children represents a public health mission. We aimed to assess the relationship between maternal intake of nutrients in early pregnancy and telomere length of cell-free circulating DNA (cfDNA) from amniotic fluid. We used data and samples from the ongoing prospective “Mamma & Bambino” study, which recruits mother–child pairs from Catania at the first prenatal visit. Maternal nutrient intakes were assessed using a Food Frequency Questionnaire, while relative telomere length of cfDNA was assessed by real-time polymerase chain reaction. Our analysis included 174 mother–child pairs. The intakes of iron, vitamin B1, and magnesium were positively correlated with relative telomere length (p-values < 0.05). However, only the intake of magnesium was positively associated with relative telomere length, after applying a linear regression model (β = 0.002; SE = 0.001; p = 0.024). Magnesium deficiency was negatively associated with relative telomere length after adjusting for the same covariates (β = −0.467; SE = 0.176; p = 0.009). To our knowledge, this is the first evidence of a positive relationship between maternal nutrient intake and telomere length of cfDNA. Further efforts are needed for deeply investigating the effect of maternal dietary intakes on telomere length, in order to develop effective public health strategies.

Epigenetic Reprogramming in Early Animal Development

Dramatic nuclear reorganization occurs during early development to convert terminally differentiated gametes to a totipotent zygote, which then gives rise to an embryo. Aberrant epigenome resetting severely impairs embryo development and even leads to lethality. How the epigenomes are inherited, reprogrammed, and reestablished in this critical developmental period has gradually been unveiled through the rapid development of technologies including ultrasensitive chromatin analysis methods. In this review, we summarize the latest findings on epigenetic reprogramming in gametogenesis and embryogenesis, and how it contributes to gamete maturation and parental-to-zygotic transition. Finally, we highlight the key questions that remain to be answered to fully understand chromatin regulation and nuclear reprogramming in early development.

Clonal hematopoiesis: Mutation-specific adaptation to environmental change

Clonal hematopoiesis of indeterminate potential (CHIP) describes a widespread expansion of genetically variant hematopoietic cells that increases exponentially with age and is associated with increased risks of cancers, cardiovascular disease, and other maladies. Here, we discuss how environmental contexts associated with CHIP, such as old age, infections, chemotherapy, or cigarette smoking, alter tissue microenvironments to facilitate the selection and expansion of specific CHIP mutant clones. Further, we consider major remaining gaps in knowledge, including intrinsic effects, clone size thresholds, and factors affecting clonal competition, that will determine future application of this field in transplant and preventive medicine.

Telomere length and vitamin B12

Telomeres are non-coding nucleoprotein structures consisting of a highly conserved tandem repeat DNA sequence that caps the ends of chromosomes in eukaryotes. Telomeres confer chromosomal stability, protect the genome from nucleolytic degradation, avoid aberrant recombination and improper repair, and prevent random fusion of chromosomes. The end-replication problem results in telomere shortening with every cell division, eventually leading to cellular senescence and aging. Telomere length (TL) is thereby an ideal candidate for "biological aging." Telomeres possess guanine-rich repeats, which are highly susceptible to oxidative stress. Epidemiological studies have indicated the association of telomere attrition with mortality and various age-related diseases. Micronutrients comprising vitamins and minerals act as potential modulators of stress and can influence TL. Research has indicated that vitamin B12 (B12) regulates oxidative stress and maintains genomic stability, thereby influencing telomere integrity and cellular aging. The deficiency of B12 leads to elevated levels of homocysteine, which reduces the methylation potential and increases oxidative stress, thereby compromising the TL. Telomere shortening and mitochondrial dysfunction are independently linked to aging. However, they are connected through telomerase reverse transcriptase activity, which regulates mitochondrial biogenesis. Further, experimental evidence indicated the positive association of B12 with relative TL and mitochondrial DNA copy number, an indirect index of mitochondrial biogenesis. The present chapter provides some insights into the role of B12 in influencing TL. Exploring their association might open new avenues to understand the pathophysiology of aging and age-related diseases.

DNMT1: catalytic and non-catalytic roles in different biological processes

DNMT1 is the main enzyme that uses the information on DNA methylation patterns in the parent strand and methylates the daughter strand in freshly replicated hemimethylated DNA. It is widely known that DNMT1 is a component of the epigenetic machinery mediating gene repression via increased promoter methylation. However, recent data suggest that DNMT1 can also modulate gene expression independent of its catalytic activity and participates in multiple processes including the cell cycle, DNA damage repair and stem cell function. This review summarizes the noncanonical functions of DNMT1, some of which are clearly independent of maintenance methylation. Finally, phenotypic data on altered DNMT1 levels suggesting that maintenance of optimal levels of DNMT1 is vital for normal development and health is presented.

Mendelian randomization supports bidirectional causality between telomere length and clonal hematopoiesis of indeterminate potential

Human genetic studies support an inverse causal relationship between leukocyte telomere length (LTL) and coronary artery disease (CAD), but directionally mixed effects for LTL and diverse malignancies. Clonal hematopoiesis of indeterminate potential (CHIP), characterized by expansion of hematopoietic cells bearing leukemogenic mutations, predisposes both hematologic malignancy and CAD. TERT (which encodes telomerase reverse transcriptase) is the most significantly associated germline locus for CHIP in genome-wide association studies. Here, we investigated the relationship between CHIP, LTL, and CAD in the Trans-Omics for Precision Medicine (TOPMed) program (n = 63,302) and UK Biobank (n = 47,080). Bidirectional Mendelian randomization studies were consistent with longer genetically imputed LTL increasing propensity to develop CHIP, but CHIP then, in turn, hastens to shorten measured LTL (mLTL). We also demonstrated evidence of modest mediation between CHIP and CAD by mLTL. Our data promote an understanding of potential causal relationships across CHIP and LTL toward prevention of CAD.

TIN2 deficiency leads to ALT-associated phenotypes and differentiation defects in embryonic stem cells

Telomere integrity is critical for embryonic development, and core telomere-binding proteins, such as TIN2, are key to maintaining telomere stability. Here, we report that homozygous Tin2^S341X resulted in embryonic lethality in mice and reduced expression of Tin2 in the derived mouse embryonic stem cells (mESCs). Homozygous mutant mESCs were able to self-renew and remain undifferentiated but displayed many phenotypes associated with alternative lengthening of telomeres (ALT), including excessively long and heterogeneous telomeres, increased ALT-associated promyelocytic leukemia (PML) bodies, and unstable chromosomal ends. These cells also showed upregulation of Zscan4 expression and elevated targeting of DAXX/ATRX and H3K9me3 marks on telomeres. Furthermore, the mutant mESCs were impeded in their differentiation capacity. Upon differentiation, DAXX/ATRX and PML bodies disassociated from telomeres in these cells, where elevated DNA damage was also apparent. Our results reveal differential responses to telomere dysfunction in mESCs versus differentiated cells and highlight the critical role of TIN2 in embryonic development.

LINE-1 and SINE-B1 mapping and genome diversification in Proechimys species (Rodentia: Echimyidae)

This study aimed to understand the impact of LINE-1 and SINE-B1 retroelements on the architecture and karyotypic diversification of five rodent species of the genus Proechimys from different regions of the Amazon. Karyotype comparisons were performed using fluorescent interspecific in situ hybridization. The L1 and B1 retroelements showed a non-random arrangement and a conserved pattern when the genomes of the five species of Proechimys were compared, including the two cytotypes of Proechimys guyannensis The signal homeology among the chromosomes and the degree of similarity among the formed clusters indicate rearrangements such as fusion/fission, and demonstrates that these retroelements can behave as derived characters shared in Proechimys The differentiated distribution and organization of these retroelements in the karyotypes and in the chromosomal fiber, respectively, may represent a strong indication of their role as generating sources of karyotypic diversity in the genus Proechimys and provide insights into the evolutionary relationships between taxa.

A complex network of interactions governs DNA methylation at telomeric regions

DNA methylation modulates telomere function. In Arabidopsis thaliana, telomeric regions have a bimodal chromatin organization with unmethylated telomeres and methylated subtelomeres. To gain insight into this organization we have generated TAIR10-Tel, a modified version of the Arabidopsis reference genome with additional sequences at most chromosome ends. TAIR10-Tel has allowed us to analyse DNA methylation at nucleotide resolution level in telomeric regions. We have analysed the wild-type strain and mutants that encode inactive versions of all currently known relevant methyltransferases involved in cytosine methylation. These analyses have revealed that subtelomeric DNA methylation extends 1 to 2 kbp from Interstitial Telomeric Sequences (ITSs) that abut or are very near to telomeres. However, DNA methylation drops at the telomeric side of the telomere-subtelomere boundaries and disappears at the inner part of telomeres. We present a comprehensive and integrative model for subtelomeric DNA methylation that should help to decipher the mechanisms that govern the epigenetic regulation of telomeres. This model involves a complex network of interactions between methyltransferases and subtelomeric DNA sequences.

Mechanisms of immune aging in HIV

Massive CD4+ T-cell depletion as well as sustained immune activation and inflammation are hallmarks of Human Immunodeficiency Virus (HIV)-1 infection. In recent years, an emerging concept draws an intriguing parallel between HIV-1 infection and aging. Indeed, many of the alterations that affect innate and adaptive immune subsets in HIV-infected individuals are reminiscent of the process of immune aging, characteristic of old age. These changes, of which the presumed cause is the systemic immune activation established in patients, likely participate in the immuno-incompetence described with HIV progression. With the success of antiretroviral therapy (ART), HIV-seropositive patients can now live for many years despite chronic viral infection. However, acquired immunodeficiency syndrome (AIDS)-related opportunistic infections have given way to chronic diseases as the leading cause of death since HIV infection. Therefore, the comparison between HIV-1 infected patients and uninfected elderly individuals goes beyond the sole onset of immunosenescence and extends to the deterioration of several physiological functions related to inflammation and systemic aging. In light of this observation, it is interesting to understand the precise link between immune activation and aging in HIV-1 infection to figure out how to best care for people living with HIV (PLWH).

Epigenetic features in regulation of telomeres and telomerase in stem cells

The epigenetic nature of telomeres is still controversial and different human cell lines might show diverse histone marks at telomeres. Epigenetic modifications regulate telomere length and telomerase activity that influence telomere structure and maintenance. Telomerase is responsible for telomere elongation and maintenance and is minimally composed of the catalytic protein component, telomerase reverse transcriptase (TERT) and template forming RNA component, telomerase RNA (TERC). TERT promoter mutations may underpin some telomerase activation but regulation of the gene is not completely understood due to the complex interplay of epigenetic, transcriptional, and posttranscriptional modifications. Pluripotent stem cells (PSCs) can maintain an indefinite, immortal, proliferation potential through their endogenous telomerase activity, maintenance of telomere length, and a bypass of replicative senescence in vitro. Differentiation of PSCs results in silencing of the TERT gene and an overall reversion to a mortal, somatic cell phenotype. The precise mechanisms for this controlled transcriptional silencing are complex. Promoter methylation has been suggested to be associated with epigenetic control of telomerase regulation which presents an important prospect for understanding cancer and stem cell biology. Control of down-regulation of telomerase during differentiation of PSCs provides a convenient model for the study of its endogenous regulation. Telomerase reactivation has the potential to reverse tissue degeneration, drive repair, and form a component of future tissue engineering strategies. Taken together it becomes clear that PSCs provide a unique system to understand telomerase regulation fully and drive this knowledge forward into aging and therapeutic application.

Health repercussions of environmental exposure to lead: Methylation perspective

Lead (Pb) exposure has been a major public health concern for a long time now due to its permanent adverse effects on the human body. The process of lead toxicity has still not been fully understood, but recent advances in Omics technology have enabled researchers to evaluate lead-mediated alterations at the epigenome-wide level. DNA methylation is one of the widely studied and well-understood epigenetic modifications. Pb has demonstrated its ability to induce not just acute deleterious health consequences but also alters the epi-genome such that the disease manifestation happens much later in life as supported by Barkers Hypothesis of the developmental origin of health and diseases. Furthermore, these alterations are passed on to the next generation. Based on previous in-vivo, in-vitro, and human studies, this review provides an insight into the role of Pb in the development of several human disorders.

Exposure to hypomethylating 5-aza-2'-deoxycytidine (decitabine) causes rapid, severe DNA damage, telomere elongation and mitotic dysfunction in human WIL2-NS cells

BACKGROUND

5-aza-2'-deoxycytidine (5azadC, decitabine) is a DNA hypomethylating agent used in the treatment of myelodysplastic syndromes. Due to cytotoxic side effects dose optimization is essential. The aim of this study was to define and quantify the effects of 5azadC on biomarkers of chromosomal stability, and telomere length, in human lymphoblastoid cell line, WIL2-NS, at clinically relevant dosages.

METHODS

Human WIL2-NS cells were maintained in complete medium containing 0, 0.2 or 1.0 μM 5azadC for four days, and analysed daily for telomere length (flow cytometry), chromosomal stability (cytokinesis-block micronucleus cytome (CBMN-cyt) assay), and global methylation (%5me-C).

RESULTS

DNA methylation decreased significantly in 1.0 μM 5azadC, relative to control (p < 0.0001). Exposure to 1.0 μM 5azadC resulted in 1.7-fold increase in telomere length (p < 0.0001), in parallel with rapid increase in biomarkers of DNA damage; (micronuclei (MN, 6-fold increase), nucleoplasmic bridges (NPB, a 12-fold increase), and nuclear buds (NBud, a 13-fold increase) (all p < 0.0001). Fused nuclei (FUS), indicative of mitotic dysfunction, showed a 5- and 13-fold increase in the 0.2 μM and 1.0 μM conditions, respectively (p = 0.001) after 4 days.

CONCLUSIONS

These data show that (i) clinically relevant concentrations of 5azadC are highly genotoxic; (ii) hypomethylation was associated with increased TL and DNA damage; and (iii) longer TL was associated with chromosomal instability. These findings suggest that lower doses of 5azdC may be effective as a hypomethylating agent, while potentially reducing DNA damage and risk for secondary disease.

Aging under Pressure: The Roles of Reactive Oxygen and Nitrogen Species (RONS) Production and Aging Skeletal Muscle in Endothelial Function and Hypertension-From Biological Processes to Potential Interventions

The proportion of adults living with hypertension increases significantly with advancing age. It is therefore important to consider how health and vitality can be maintained by the aging population until end of life. A primary risk factor for the progression of cardiovascular diseases (CVD) is hypertension, so exploring the factors and processes central to this burden of disease is essential for healthy aging. A loss of skeletal muscle quantity and quality is characteristic in normal aging, with a reduction of vasodilatory capacity caused by endothelial dysfunction, and subsequent increase in peripheral resistance and risk for hypertension. Reactive Oxygen and Nitrogen Species (RONS) encompass the reactive derivatives of NO and superoxide, which are continuously generated in contracting skeletal muscle and are essential mediators for cellular metabolism. They act together as intra and intercellular messengers, gene expression regulators, and induce programmed cell death. In excessive amounts RONS can inflict damage to endothelial and skeletal muscle cells, alter signaling pathways or prematurely promote stress responses and potentially speed up the aging process. The age-related increase in RONS by skeletal muscle and endothelial mitochondria leads to impaired production of NO, resulting in vascular changes and endothelial dysfunction. Changes in vascular morphology is an early occurrence in the etiology of CVDs and, while this is also a normal characteristic of aging, whether it is a cause or a consequence of aging in hypertension remains unclear. This review serves to focus on the roles and mechanisms of biological processes central to hypertension and CVD, with a specific focus on the effects of aging muscle and RONS production, as well as the influence of established and more novel interventions to mediate the increasing risk for hypertension and CVD and improve health outcomes as we age.

Elevated retrotransposon activity and genomic instability in primed pluripotent stem cells

BACKGROUND

Naïve and primed pluripotent stem cells (PSCs) represent two different pluripotent states. Primed PSCs following in vitro culture exhibit lower developmental potency as evidenced by failure in germline chimera assays, unlike mouse naïve PSCs. However, the molecular mechanisms underlying the lower developmental competency of primed PSCs remain elusive.

RESULTS

We examine the regulation of telomere maintenance, retrotransposon activity, and genomic stability of primed PSCs and compare them with naïve PSCs. Surprisingly, primed PSCs only minimally maintain telomeres and show fragile telomeres, associated with declined DNA recombination and repair activity, in contrast to naïve PSCs that robustly elongate telomeres. Also, we identify LINE1 family integrant L1Md_T as naïve-specific retrotransposon and ERVK family integrant IAPEz to define primed PSCs, and their transcription is differentially regulated by heterochromatic histones and Dnmt3b. Notably, genomic instability of primed PSCs is increased, in association with aberrant retrotransposon activity.

CONCLUSIONS

Our data suggest that fragile telomere, retrotransposon-associated genomic instability, and declined DNA recombination repair, together with reduced function of cell cycle and mitochondria, increased apoptosis, and differentiation properties may link to compromised developmental potency of primed PSCs, noticeably distinguishable from naïve PSCs.

A Tale of Two States: Pluripotency Regulation of Telomeres

Inside the nucleus, chromatin is functionally organized and maintained as a complex three-dimensional network of structures with different accessibility such as compartments, lamina associated domains, and membraneless bodies. Chromatin is epigenetically and transcriptionally regulated by an intricate and dynamic interplay of molecular processes to ensure genome stability. Phase separation, a process that involves the spontaneous organization of a solution into separate phases, has been proposed as a mechanism for the timely coordination of several cellular processes, including replication, transcription and DNA repair. Telomeres, the repetitive structures at the end of chromosomes, are epigenetically maintained in a repressed heterochromatic state that prevents their recognition as double-strand breaks (DSB), avoiding DNA damage repair and ensuring cell proliferation. In pluripotent embryonic stem cells, telomeres adopt a non-canonical, relaxed epigenetic state, which is characterized by a low density of histone methylation and expression of telomere non-coding transcripts (TERRA). Intriguingly, this telomere non-canonical conformation is usually associated with chromosome instability and aneuploidy in somatic cells, raising the question of how genome stability is maintained in a pluripotent background. In this review, we will explore how emerging technological and conceptual developments in 3D genome architecture can provide novel mechanistic perspectives for the pluripotent epigenetic paradox at telomeres. In particular, as RNA drives the formation of LLPS, we will consider how pluripotency-associated high levels of TERRA could drive and coordinate phase separation of several nuclear processes to ensure genome stability. These conceptual advances will provide a better understanding of telomere regulation and genome stability within the highly dynamic pluripotent background.

Telomere Length in Chromosomally Normal and Abnormal Miscarriages and Ongoing Pregnancies and Its Association with 5-hydroxymethylcytosine Patterns

The present study investigates telomere length (TL) in dividing chorionic cytotrophoblast cells from karyotypically normal and abnormal first trimester miscarriages and ongoing pregnancies. Using Q-FISH, we measured relative TLs in the metaphase chromosomes of 61 chorionic villous samples. Relative TLs did not differ between karyotypically normal samples from miscarriages and those from ongoing pregnancies (p = 0.3739). However, among the karyotypically abnormal samples, relative TLs were significantly higher in ongoing pregnancies than in miscarriages (p < 0.0001). Relative TLs were also significantly higher in chorion samples from karyotypically abnormal ongoing pregnancies than in those from karyotypically normal ones (p = 0.0018) in contrast to miscarriages, where relative TL values were higher in the karyotypically normal samples (p = 0.002). In the karyotypically abnormal chorionic cytotrophoblast, the TL variance was significantly lower than in any other group (p < 0.05). Assessed by TL ratios between sister chromatids, interchromatid TL asymmetry demonstrated similar patterns across all of the chorion samples (p = 0.22) but significantly exceeded that in PHA-stimulated lymphocytes (p < 0.0001, p = 0.0003). The longer telomere was predominantly present in the hydroxymethylated sister chromatid in chromosomes featuring hemihydroxymethylation (containing 5-hydroxymethylcytosine in only one sister chromatid)-a typical sign of chorionic cytotrophoblast cells. Our results suggest that the phenomena of interchromatid TL asymmetry and its association to 5hmC patterns in chorionic cytotrophoblast, which are potentially linked to telomere lengthening through recombination, are inherent to the development programme. The TL differences in chorionic cytotrophoblast that are associated with karyotype and embryo viability seem to be determined by heredity rather than telomere elongation mechanisms. The inheritance of long telomeres by a karyotypically abnormal embryo promotes his development, whereas TL in karyotypically normal first-trimester embryos does not seem to have a considerable impact on developmental capacity.

Insights Into the Function and Clinical Application of HDAC5 in Cancer Management

Histone deacetylase 5 (HDAC5) is a class II HDAC. Aberrant expression of HDAC5 has been observed in multiple cancer types, and its functions in cell proliferation and invasion, the immune response, and maintenance of stemness have been widely studied. HDAC5 is considered as a reliable therapeutic target for anticancer drugs. In light of recent findings regarding the role of epigenetic reprogramming in tumorigenesis, in this review, we provide an overview of the expression, biological functions, regulatory mechanisms, and clinical significance of HDAC5 in cancer.

Telomere Length in Metaphase Chromosomes of Human Triploid Zygotes

The human lifespan is strongly influenced by telomere length (TL) which is defined in a zygote—when two highly specialised haploid cells form a new diploid organism. Although TL is a variable parameter, it fluctuates in a limited range. We aimed to establish the determining factors of TL in chromosomes of maternal and paternal origin in human triploid zygotes. Using Q-FISH, we examined TL in the metaphase chromosomes of 28 human triploid zygotes obtained from 22 couples. The chromosomes’ parental origin was identified immunocytochemically through weak DNA methylation and strong hydroxymethylation in the sperm-derived (paternal) chromosomes versus strong DNA methylation and weak hydroxymethylation in the oocyte-derived (maternal) ones. In 24 zygotes, one maternal and two paternal chromosome sets were identified, while the four remaining zygotes contained one paternal and two maternal sets. For each zygote, we compared mean relative TLs between parental chromosomes, identifying a significant difference in favour of the paternal chromosomes, which attests to a certain “imprinting” of these regions. Mean relative TLs in paternal or maternal chromosomes did not correlate with the respective parent’s age. Similarly, no correlation was observed between the mean relative TL and sperm quality parameters: concentration, progressive motility and normal morphology. Based on the comparison of TLs in chromosomes inherited from a single individual’s gametes with those in chromosomes inherited from different individuals’ gametes, we compared intraindividual (intercellular) and interindividual variability, obtaining significance in favour of the latter and thus validating the role of heredity in determining TL in zygotes. A comparison of the interchromatid TL differences across the chromosomes from sets of different parental origin with those from PHA-stimulated lymphocytes showed an absence of a significant difference between the maternal and paternal sets but a significant excess over the lymphocytes. Therefore, interchromatid TL differences are more pronounced in zygotes than in lymphocytes. To summarise, TL in human zygotes is determined both by heredity and parental origin; the input of other factors is possible within the individual’s reaction norm.