Roles of Werner Syndrome Protein in Protection of Genome Integrity

Objective: Clinical trials of cardiac cell therapy have indicated limited benefits in aging patients, even though preclinical studies using young animals consistently reported significant improvements. Animal studies have demonstrated reduced efficacy of donor cells isolated from older individuals. Here, we evaluated the effects of donor age on the function of human mesenchymal stem cells (hMSCs) in the context of cell therapy for ischemic cardiomyopathy. Methods: In vitro, we compared the growth and clonogenic potential of hMSCs isolated from young or old patients (1–5 vs. 50–70 years old). In vivo, we injected young or old hMSCs (2.0 × 106) (or medium) into the infarcted myocardia of immunosuppressed rats immediately after coronary artery ligation (myocardial infarction [MI]). We assessed cardiac function (echocardiography) at 1, 2, and 4 weeks after MI, and myocardial matrix metalloproteinase-2 (MMP-2), MMP-9, and tissue inhibitor of matrix metalloproteinase-3 (TIMP-3) levels at 1 week. Result...

The Effect of Age on the Efficacy of Human Mesenchymal Stem Cell Transplantation after a Myocardial Infarction

Organisms are constantly exposed to various environmental insults which could adversely affect the stability of their genome. To protect their genomes against the harmful effect of these environmental insults, organisms have evolved highly diverse and efficient repair mechanisms. Defective DNA repair processes can lead to various kinds of chromosomal and developmental abnormalities. RecQ helicases are a family of evolutionarily conserved, DNA unwinding proteins which are actively engaged in various DNA metabolic processes, telomere maintenance and genome stability. Bacteria and lower eukaryotes, like yeast, have only one RecQ homolog, whereas higher eukaryotes including humans possess multiple RecQ helicases. These multiple RecQ helicases have redundant and/or non-redundant functions depending on the types of DNA damage and DNA repair pathways. Humans have five different RecQ helicases and defects in three of them cause autosomal recessive diseases leading to various kinds of cancer predisposition and/or aging phenotypes. Emerging evidence also suggests that the RecQ helicases have important roles in telomere maintenance. This review mainly focuses on recent knowledge about the roles of RecQ helicases in DNA double strand break repair and telomere maintenance which are important in preserving genome integrity.

RecQ helicases in DNA double strand break repair and telomere maintenance

Telomeres are specialised nucleoproteic complexes localised at the physical ends of linear eukaryotic chromosomes that maintain their stability and integrity. In vertebrate chromosomes, the DNA component of telomeres is constituted by (TTAGGG)n repeats, which can be localised at the terminal regions of chromosomes (true telomeres) or at intrachromosomal sites (interstitial telomeric sequences or ITSs, located at the centromeric region or between the centromere and the telomere). In the past two decades, the use of molecular cytogenetic techniques has led to a new spectrum of spontaneous and clastogen-induced chromosomal aberrations being identified, involving telomeres and ITSs. Some aberrations involve the chromosome ends and, indirectly, the telomeric repeats located at the terminal regions of chromosomes (true telomeres). A second type of aberrations directly involves the telomeric sequences located at the chromosome ends. Finally, there is a third class of aberrations that specifically involves the ITSs. The aims of this review are to provide a detailed description of these aberrations and to summarise the available data regarding their induction by physical and chemical mutagens.

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Chromosomal aberrations involving telomeres and interstitial telomeric sequences.

Chromosomal instability (CIN) is an important hallmark to oncogenesis and can be diagnosed morphologically by the presence of nuclear anomalies such as micronuclei (MN), nucleoplasmic bridges (NPBs), and nuclear buds (NBuds). We have identified additional nuclear anomalies formed under folate-deficient conditions, defined as "fused" nuclei (FUS), "circular" nuclei (CIR), and "horse-shoe" nuclei (HS) and investigated their suitability for inclusion as additional CIN biomarkers in the lymphocyte cytokinesis-block micronucleus cytome (CBMN-Cyt) assay. Although the morphological appearance of FUS, CIR, and HS suggested an origin from multiple NPB in the fusion region between the two nuclei, the very low frequency of dicentric chromosomes in metaphase spreads from these cultures did not support this model. Fluorescence in situ hybridization (FISH) analysis of cytokinesis-blocked binucleated (BN) cells with peptide nucleic acid probes for telomeres and centromeres (PNA-FISH) revealed a high proportion of fusion regions contained both centromeric and telomeric DNA. This suggests that folate deficiency may disrupt the process of sister chromatid separation and chromosome segregation during mitosis. It was concluded that the FUS, CIR, and HS morphologies represent promising biomarkers of CIN that are sensitive to folate deficiency, and further validation and investigation of the mechanisms responsible for their formation is warranted.

Folate deficiency is associated with the formation of complex nuclear anomalies in the cytokinesis-block micronucleus cytome assay

Telomeres and telomerase appear to participate in the repair of broken DNA ends produced by oxidative damage Arsenite is an environmental contaminant and a potent human carcinogen, which induces oxidative stress on cells via the generation of reactive oxygen species affecting cell viability and chromosome stability It promotes telomere attrition and reduces cell survival by apoptosis In this study, we used mouse embryonic fibroblasts (MEFs) from mice lacking telomerase RNA component (mTERC(-/-) mice) with long (early passage or EP) and short (late passage or LP) telomeres to investigate the extent of oxidative damage by comparing the differences in DNA damage, chromosome instability, and cell survival at 24 and 48 h of exposure to sodium arsenite (As3+; NaAsO2) There was significantly high level of DNA damage in mTERC(-/-) cells with short telomeres as determined by alkaline comet assay Consistent with elevated DNA damage, increased micronuclei (MN) induction reflecting gross genomic instability was also observed Fluorescence in situ hybridization (FISH) analysis revealed that increasing doses of arsenite augmented the chromosome aberrations, which contributes to genomic instability leading to possibly apoptotic cell death and cell cycle arrest Microarray analysis has revealed that As3+ treatment altered the expression of 456 genes of which 20% of them have known functions in cell cycle and DNA damage signaling and response, cell growth, and/or maintenance Results from our studies imply that short dysfunctional telomeres impair the repair of oxidative damage caused by arsenite The results will have implications in risk estimation as well as cancer chemotherapy

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/jcp.23064

Wanru Fang

Papers

Short dysfunctional telomeres impair the repair of arsenite-induced oxidative damage in mouse cells.