Analysis of Gene Expression Patterns and Chromosomal Changes Associated with Aging

Abstract

Age is the largest single risk factor for the development of cancer in mammals. Age-associated chromosomal changes, such as aneuploidy and telomere erosion, may be vitally involved in the initial steps of tumorigenesis. However, changes in gene expression specific for increased aneuploidy with age have not yet been characterized. Here, we address these questions by using a panel of fibroblast cell lines and lymphocyte cultures from young and old age groups. Oligonucleotide microarrays were used to characterize the expression of 14,500 genes. We measured telomere length and analyzed chromosome copy number changes and structural rearrangements by multicolor interphase fluorescence in situ hybridization and 7-fluorochrome multiplex fluorescence in situ hybridization, and we tried to show a relationship between gene expression patterns and chromosomal changes. These analyses revealed a number of genes involved in both the cell cycle and proliferation that are differently expressed in aged cells. More importantly, our data show an association between age-related aneuploidy and the gene expression level of genes involved in centromere and kinetochore function and in the microtubule and spindle assembly apparatus. To verify that some of these genes may also be involved in tumorigenesis, we compared the expression of these genes in chromosomally stable microsatellite instability and chromosomally unstable chromosomal instability colorectal tumor cell lines. Three genes (Notch2, H2AFY2, and CDC5L) showed similar expression differences between microsatellite instability and chromosomal instability cell lines as observed between the young and old cell cultures suggesting that they may play a role in tumorigenesis.

Low-grade chromosomal mosaicism in human somatic and embryonic stem cell populations

“…This is in line with previously reported aneuploidy rates in amniocytes studied by banding methods 2 and hESC studied by metaphase CGH 24 . On the other hand, they are in contrast with the high percentages of non-clonal aneuploidy reported by studies using FISH on cultured somatic cells 3,4 and hESC 25,26 . It is likely that the use of different techniques is the cause of these discrepancies.…”

“…Furthermore, hESC seem to undergo subtelomeric instability at a higher frequency than somatic cells. This is distinctive from the majority of previous studies that focused on analysing single cells, which lacked the resolution to detect the majority of the CNVs described here 3,4,25,26 . As these CNVs are present at very low frequencies in the culture, they also could not be detected using the straight-forward analysis of pooled DNA, as used by most studies for high-resolution screening of cell lines.…”

“…To address the differences in nature and frequency of the CNVs between our data and the high frequencies of whole-chromosome aneuploidies found by studies using FISH 3,4,25,26 , we analysed the amniocyte, fibroblast and hESC lines by FISH on interphase nuclei for two randomly selected chromosomes. We used probes for the centromere and both subtelomeric regions of chromosomes 1 and 18, allowing us to distinguish between full chromosome aneuploidy and segmental gains or losses of chromosome arms or subtelomeric regions.…”

“…For somatic tissues, an important part of the knowledge on mosaicism has been obtained from studies using cytogenetic banding techniques, which provide information on whole chromosome copy number or large aberrations, and fluorescent in situ hybridization (FISH), studying a single locus. These studies have shown that the grade of mosaicism varies from tissue to tissue and the percentage of aneuploid cells increases with age, but provide limited insight on the occurrence of small genetic imbalances [2][3][4][5] . More recently, the group of Abyzov et al 6 made use of the clonal nature of humaninduced pluripotent stem cells (hiPSCs) to show that human skin fibroblasts are highly mosaic, with up to 30% of cells carrying copy number variants (CNVs).…”

Culture of human mesenchymal stem cells at low oxygen tension improves growth and genetic stability by activating glycolysis

“…Human fibroblasts and bone marrow hMSC grown at 20% O 2 (passage 10) presented levels of aneuploidy ranging from 12 to 18%, in line with our previous results. 23,25 Analysis of aneuploidy in cultures of these cells grown for an additional 4-10 passages at 3% O 2 and 20% O 2 confirmed that growth at 3% O 2 reduces the levels of aneuploidy in other cell types of mesenchymal origin (Figure 3d). These results strongly suggest that growth of mesenchymal cells at 20% O 2 for 5-10 passages promotes aneuploidy, and we therefore propose that ROS are a principal cause of aneuploidy in hMSC.…”