Telomere elongation facilitated by trichostatin a in cloned embryos and pigs by somatic cell nuclear transfer

Impact of telomere length and mitochondrial DNA copy number variants on survival of newborn cloned calves

An established technology to create cloned animals is through the use of somatic cell nuclear transfer (SCNT), in which reprogramming the somatic cell nucleus to a totipotent state by enucleated oocyte cytoplasm is a necessary process, including telomere length reprogramming. The limitation of this technology; however, is that the live birth rate of offspring produced through SCNT is significantly lower than that of IVF. Whether and how telomere length play a role in the development of cloned animals is not well understood. Only a few studies have evaluated this association in cloned mice, and fewer still in cloned cows. In this study, we investigated the difference in telomere length as well as the abundance of some selected molecules between newborn deceased cloned calves and normal cows of different ages either produced by SCNT or via natural conception, in order to evaluate the association between telomere length and abnormal development of cloned cows. The absolute telomere length and relative mitochondrial DNA (mtDNA) copy number were determined by real-time quantitative PCR (qPCR), telomere related gene abundance by reverse-transcription quantitative PCR (RT-qPCR), and senescence-associated β-galactosidase (SA-β-gal) expression by SA-β-gal staining. The results demonstrate that the newborn deceased SCNT calves had significantly shortened telomere lengths compared to newborn naturally conceived calves and newborn normal SCNT calves. Significantly lower mtDNA copy number, and significantly lower relative abundance of LMNB1 and TERT, higher relative abundance of CDKN1A, and aberrant SA-β-gal expression were observed in the newborn deceased SCNT calves, consistent with the change in telomere length. These results demonstrate that abnormal telomere shortening, lower mtDNA copy number and abnormal abundance of related genes were specific to newborn deceased SCNT calves, suggesting that abnormally short telomere length may be associated with abnormal development in the cloned calves.

Telomere Dynamics in Livestock

Telomeres are repeated sequences of nucleotides at the end of chromosomes. They deteriorate across mitotic divisions of a cell. In Homo sapiens this process of lifetime reduction has been shown to correspond with aspects of organismal aging and exposure to stress or other insults. The early impetus to characterize telomere dynamics in livestock related to the concern that aged donor DNA would result in earlier cell senescence and overall aging in cloned animals. Telomere length investigations in dairy cows included breed effects, estimates of additive genetic control (heritability 0.12 to 0.46), and effects of external stressors on telomere degradation across animal life. Evaluation of telomeres with respect to aging has also been conducted in pigs and horses, and there are fewer reports of telomere biology in beef cattle, sheep, and goats. There were minimal associations of telomere length with animal productivity measures. Most, but not all, work in livestock has documented an inverse relationship between peripheral blood cell telomere length and age; that is, a longer telomere length was associated with younger age. Because livestock longevity affects productivity and profitability, the role of tissue-specific telomere attrition in aging may present alternative improvement strategies for genetic improvement while also providing translational biomedical knowledge.

Telomere length in dromedary camels (Camelus dromedarius) produced by somatic cell nuclear transfer (SCNT) and their age-matched naturally produced counterparts

There are controversial reports on the restoration of eroded telomere length in offspring produced by somatic cell nuclear transfer (SCNT) in different animal species. To the best of our knowledge, no earlier studies report the telomere length in naturally produced or cloned animals in any of the camelid species. Therefore, the present study was conducted to estimate the telomere length in dromedary camels produced by SCNT, the donor cells, and their age-matched naturally produced counterparts by Terminal Restriction Fragment (TRF) length analysis and real-time Q PCR T/S ratio methods. Genomic DNA was extracted from venous blood collected from 6 cloned animals and their age-matched counterparts. Using the southern blot technique, digested DNA was blotted onto a positively charged nylon membrane, and its hybridization was carried out using telomere (TTAGGG)n specific, DIG-labeled hybridization probe (Roche Diagnostics, Germany) at 42 °C for 4 h. Stringent washes were carried out at the same temperature, followed by a chemiluminescence reaction. The signals were captured using the Azure Biosystems C600 gel documentation system. A TeloTool program from MATLAB software with a built-in probe intensity correction algorithm was used for TRF analysis. The experiment was replicated three times, and the data, presented as mean ± SEM, were analyzed using a two-sample t-test (MINITAB statistical software, Minitab ltd, CV3 2 TE, UK). No difference was found in the mean telomere length of cloned camels when compared to their naturally produced age-matched counterparts. However, the telomere length was more (P < 0.05) than that of the somatic cells used for producing the SCNT embryos. A moderate positive Pearson correlation coefficient (r = 0.6446) was observed between the telomere lengths estimated by TRF and Q PCR T/S ratio method. In conclusion, this is the first study wherein we are reporting telomere length in naturally produced and cloned dromedary camels produced by somatic cell nuclear transfer. We found that telomere lengths in cloned camels were similar to their age-matched naturally produced counterparts, suggesting that the camel cytoplast reprograms the somatic cell nucleus and restores the telomere length to its totipotency stage.

Extranuclear Inheritance of Mitochondrial Genome and Epigenetic Reprogrammability of Chromosomal Telomeres in Somatic Cell Cloning of Mammals

The effectiveness of somatic cell nuclear transfer (SCNT) in mammals seems to be still characterized by the disappointingly low rates of cloned embryos, fetuses, and progeny generated. These rates are measured in relation to the numbers of nuclear-transferred oocytes and can vary depending on the technique applied to the reconstruction of enucleated oocytes. The SCNT efficiency is also largely affected by the capability of donor nuclei to be epigenetically reprogrammed in a cytoplasm of reconstructed oocytes. The epigenetic reprogrammability of donor nuclei in SCNT-derived embryos appears to be biased, to a great extent, by the extranuclear (cytoplasmic) inheritance of mitochondrial DNA (mtDNA) fractions originating from donor cells. A high frequency of mtDNA heteroplasmy occurrence can lead to disturbances in the intergenomic crosstalk between mitochondrial and nuclear compartments during the early embryogenesis of SCNT-derived embryos. These disturbances can give rise to incorrect and incomplete epigenetic reprogramming of donor nuclei in mammalian cloned embryos. The dwindling reprogrammability of donor nuclei in the blastomeres of SCNT-derived embryos can also be impacted by impaired epigenetic rearrangements within terminal ends of donor cell-descended chromosomes (i.e., telomeres). Therefore, dysfunctions in epigenetic reprogramming of donor nuclei can contribute to the enhanced attrition of telomeres. This accelerates the processes of epigenomic aging and replicative senescence in the cells forming various tissues and organs of cloned fetuses and progeny. For all the above-mentioned reasons, the current paper aims to overview the state of the art in not only molecular mechanisms underlying intergenomic communication between nuclear and mtDNA molecules in cloned embryos but also intrinsic determinants affecting unfaithful epigenetic reprogrammability of telomeres. The latter is related to their abrasion within somatic cell-inherited chromosomes.

From molecular promise to preclinical results: HDAC inhibitors in the race for healthy aging drugs

Reversing or slowing the aging process brings great promise to treat or prevent age‐related disease, and targeting the hallmarks of aging is a strategy to achieve this. Epigenetics affects several if not all of the hallmarks of aging and has therefore emerged as a central target for intervention. One component of epigenetic regulation involves histone deacetylases (HDAC), which include the “classical” histone deacetylases (of class I, II, and IV) and sirtuin deacetylases (of class III). While targeting sirtuins for healthy aging has been extensively reviewed elsewhere, this review focuses on pharmacologically inhibiting the classical HDACs to promote health and longevity. We describe the theories of how classical HDAC inhibitors may operate to increase lifespan, supported by studies in model organisms. Furthermore, we explore potential mechanisms of how HDAC inhibitors may have such a strong grasp on health and longevity, summarizing their links to other hallmarks of aging. Finally, we show the wide range of age‐related preclinical disease models, ranging from neurodegeneration to heart disease, diabetes to sarcopenia, which show improvement upon HDAC inhibition.

Effects of trichostatin A on pig SCNT blastocyst formation rate and cell number: A meta-analysis

Although somatic cell nuclear transfer (SCNT) can be used to create transgenic pigs for human xenotransplantation, low efficiency limits its use. Trichostatin A (TSA) promotes SCNT embryo development, but whether TSA modifies SCNT blastocyst numbers is unclear. Thus, there is an urgent need to understand whether TSA modifies the rate and number of embryos that grow from oocytes to blastocysts in culture and what types of cell signaling pathways may be involved. Thus, we identified 63 reports, of which 13 are included in this meta-analysis. Data show that TSA significantly increased the SCNT blastocyst formation rate, but did not change blastocyst cell number. Due to study heterogeneity (I²>50%), we hypothesized that donor cells were of different backgrounds so we analyzed two donor cell subgroups: fetal and adult fibroblasts. Analysis of the fetal fibroblast subgroups showed no heterogeneity, but the adult fibroblast subgroups were heterogeneous, suggesting epigenetic reprogramming of fetal fibroblasts by TSA. Adult fibroblast heterogeneity may be complex and reprogramming by TSA is more difficult. Thus, TSA fibroblasts reprogramming is the source of heterogeneity in this meta-analysis. More work is needed to better understand how TSA influences SCNT pig embryonic development, and histone deacetylase inhibitors can be assessed with respect to SCNT pig embryos. Finally, efforts in epigenetic research may improve SCNT pig embryo outcomes.

Linking Telomere Regulation to Stem Cell Pluripotency

Embryonic stem cells (ESCs), somatic cell nuclear transfer ESCs, and induced pluripotent stem cells (iPSCs) represent the most studied group of PSCs. Unlimited self-renewal without incurring chromosomal instability and pluripotency are essential for the potential use of PSCs in regenerative therapy. Telomere length maintenance is critical for the unlimited self-renewal, pluripotency, and chromosomal stability of PSCs. While telomerase has a primary role in telomere maintenance, alternative lengthening of telomere pathways involving recombination and epigenetic modifications are also required for telomere length regulation, notably in mouse PSCs. Telomere rejuvenation is part of epigenetic reprogramming to pluripotency. Insights into telomere reprogramming and maintenance in PSCs may have implications for understanding of aging and tumorigenesis. Here, I discuss the link between telomere elongation and homeostasis to the acquisition and maintenance of stem cell pluripotency, and their regulatory mechanisms by epigenetic modifications.

Effects of donor cells' sex on nuclear transfer efficiency and telomere lengths of cloned goats

The aim of this study was to investigate the effects of donor cells' sex on nuclear transfer efficiency and telomere length of cloned goats from adult skin fibroblast cells. The telomere length of somatic cell cloned goats and their offspring was determined by measuring their mean terminal restriction fragment (TRF) length. The result showed that (i) reconstructed embryos with fibroblast cells from males Boer goats obtained significantly higher kids rate and rate of live kids than those of female embryos and (ii) the telomere lengths of four female cloned goats were shorter compared to their donor cells, but five male cloned goats had the same telomere length with their donor cells, mainly due to great variation existed among them. The offspring from female cloned goats had the same telomere length with their age-matched counterparts. In conclusion, the donor cells' sex had significant effects on nuclear transfer efficiency and telomere lengths of cloned goats.

Roles for Histone Acetylation in Regulation of Telomere Elongation and Two-cell State in Mouse ES Cells

Mammalian telomeres and subtelomeres are marked by heterochromatic epigenetic modifications, including repressive DNA methylation and histone methylation (e.g., H3K9me3 and H4K20me3). Loss of these epigenetic marks results in increased rates of telomere recombination and elongation. Other than these repressive epigenetic marks, telomeric and subtelomeric H3 and H4 are underacetylated. Yet, whether histone acetylation also regulates telomere length has not been directly addressed. We thought to test the effects of histone acetylation levels on telomere length using histone deacetylase (HDAC) inhibitor (sodium butyrate, NaB) that mediates histone hyperacetylation and histone acetyltransferase (HAT) inhibitor (C646) that mediates histone hypoacetylation. We show that histone hyperacetylation dramatically elongates telomeres in wild-type ES cells, and only slightly elongates telomeres in Terc(-/-) ES cells, suggesting that Terc is involved in histone acetylation-induced telomere elongation. In contrast, histone hypoacetylation shortens telomeres in both wild-type and Terc(-/-) ES cells. Additionally, histone hyperacetylation activates 2-cell (2C) specific genes including Zscan4, which is involved in telomere recombination and elongation, whereas histone hypoacetylation represses Zscan4 and 2C genes. These data suggest that histone acetylation levels affect the heterochromatic state at telomeres and subtelomeres, and regulate gene expression at subtelomeres, linking histone acetylation to telomere length maintenance.

Telomere length maintenance, shortening, and lengthening

Telomeres maintain chromosome stability and cell replicative capacity. Telomere shortening occurs concomitant with aging. Short telomeres are associated with some diseases, such as dyskeratosis congenita, idiopathic pulmonary fibrosis, and aplastic anemia. Telomeres are longer in pluripotent stem cells than in somatic cells and lengthen significantly during preimplantation development. Furthermore, telomere elongation during somatic cell reprogramming is of great importance in the acquisition of authentic pluripotency. This review focuses primarily on regulatory mechanisms of telomere length maintenance in pluripotent cells, telomere length extension in early embryo development, and also telomere rejuvenation in somatic cell reprogramming. Telomere related diseases are also discussed in this review.

Histone deacetylase inhibitor induces the expression of select epithelial genes in mouse utricle sensory epithelia-derived progenitor cells

Mouse utricle sensory epithelial cell-derived progenitor cells (MUCs), which have hair cell progenitor and mesenchymal features via epithelial-to-mesenchymal transition (EMT) as previously described, provide a potential approach for hair cell regeneration via cell transplantation. In this study, we treated MUCs with trichostatin A (TSA) to determine whether histone deacetylase inhibitor is able to stimulate the expression of epithelial genes in MUCs, an essential step for guiding mesenchymal-like MUCs to become sensory epithelial cells. After 72 h of TSA treatment, MUCs acquired epithelial-like features, which were indicated by increased expression of epithelial markers such as Cdh1, Krt18, and Dsp. Additionally, TSA decreased the expression of mesenchymal markers, including Zeb1, Zeb2, Snai1, and Snai2, and prosensory genes Lfng, Six1, and Dlx5. Moreover, the expression of the hair cell genes Atoh1 and Myo6 was increased in TSA-treated MUCs. We also observed significantly decreased expression of Hdac2 and Hdac3 in TSA-treated MUCs. However, no remarkable change was detected in protein expression using immunofluorescence, indicating that TSA-induced HDAC inhibition may contribute to the initial stage of the mesenchymal-to-epithelial phenotypic change. In the future, more work is needed to induce hair cell regeneration using inner ear tissue-derived progenitors to achieve an entire mesenchymal-to-epithelial transition.

The effect of chemotherapeutic agents on telomere length maintenance in breast cancer cell lines

Mammalian telomeric DNA consists of tandem repeats of the sequence TTAGGG associated with a specialized set of proteins, known collectively as Shelterin. These telosomal proteins protect the ends of chromosomes against end-to-end fusion and degradation. Short telomeres in breast cancer cells confer telomere dysfunction and this can be related to Shelterin proteins and their level of expression in breast cancer cell lines. This study investigates whether expression of Shelterin and Shelterin-associated proteins are altered, and influence the protection and maintenance of telomeres, in breast cancer cells. 5-aza-2′-deoxycytidine (5-aza-CdR) and trichostatin A (TSA) were used in an attempt to reactivate the expression of silenced genes. Our studies have shown that Shelterin and Shelterin-associated genes were down-regulated in breast cancer cell lines; this may be due to epigenetic modification of DNA as the promoter region of POT1 was found to be partially methylated. Shelterin genes expression was up-regulated upon treatment of 21NT breast cancer cells with 5-aza-CdR and TSA. The telomere length of treated 21NT cells was measured by q-PCR showed an increase in telomere length at different time points. Our studies have shown that down-regulation of Shelterin genes is partially due to methylation in some epithelial breast cancer cell lines. Removal of epigenetic silencing results in up-regulation of Shelterin and Shelterin-associated genes which can then lead to telomere length elongation and stability.