Analysis of gene expression patterns and chromosomal changes associated with aging

Analysis of premature centromere division (PCD) of the chromosome 18 in peripheral blood lymphocytes in Alzheimer disease patients

Premature centromere division (PCD) of the chromosome 18 was analyzed by using fluorescent in situ hybridization (FISH) on interphase peripheral blood lymphocytes isolated from six sporadic Alzheimer disease (AD) patients and six healthy elderly controls. Results of FISH analysis revealed that chromosome 18 expressed PCD in 5.18% interphase nuclei of AD patients, and in 2.59% interphase nuclei of age-matched controls (p<0.05). Our study also showed that hypoploidy and hyperploidy frequency for chromosome 18 exhibited a statistically significant increase in the AD group compared to the control one. The increase in spontaneous aneuploidy of chromosome 18 in AD patients which is correlated with PCD shows that deregulation of the time of centromere separation can be considered as a manifestation of chromosome instability leading to aneuploidy.

Age-specific hormonal decline is accompanied by transcriptional changes in human sebocytes in vitro

The importance of hormones in endogenous aging has been displayed by recent studies performed on animal models and humans. To decipher the molecular mechanisms involved in aging we maintained human sebocytes at defined hormone-substituted conditions that corresponded to average serum levels of females from 20 (f20) to 60 (f60) years of age. The corresponding hormone receptor expression was demonstrated by reverse transcription-polymerase chain reaction (RT-PCR), Western blotting and immunocytochemistry. Cells at f60 produced significantly lower lipids than at f20. Increased mRNA and protein levels of c-Myc and increased protein levels of FN1, which have been associated with aging, were detected in SZ95 sebocytes at f60 compared to those detected at f20 after 5 days of treatment. Expression profiling employing a cDNA microarray composed of 15 529 cDNAs identified 899 genes with altered expression levels at f20 vs. f60. Confirmation of gene regulation was performed by real-time RT-PCR. The functional annotation of these genes according to the Gene Ontology identified pathways related to mitochondrial function, oxidative stress, ubiquitin-mediated proteolysis, cell cycle, immune responses, steroid biosynthesis and phospholipid degradation - all hallmarks of aging. Twenty-five genes in common with those identified in aging kidneys and several genes involved in neurodegenerative diseases were also detected. This is the first report describing the transcriptome of human sebocytes and its modification by a cocktail of hormones administered in age-specific levels and provides an in vitro model system, which approximates some of the hormone-dependent changes in gene transcription that occur during aging in humans.

Age- and cell cycle-dependent changes in EPC-1/PEDF promoter activity in human diploid fibroblast-like (HDF) cells

The changes in gene expression during senescence are very interesting. Early population doubling cDNA-1 (EPC-1, also known as pigment epithelial derived factor, PEDF) is one of the genes whose expression decreases dramatically during cellular aging. We examined whether or not EPC-1/PEDF promoter activity was affected by the cellular ageing using human diploid lung fibroblast cells in culture. Here we showed the promoter/enhancer region of EPC-1/PEDF existed at more than 1760 bp upstream from the transcriptional initiation site of the gene, and was regulated by both aging and cell cycle. These findings suggest that the expression of the EPC-1/PEDF gene is, at least in part, regulated transcriptionally in the cells. The analysis of the promoter region of the EPC-1/PEDF gene in this paper suggests the age- and cell cycle-dependent expression of specific transcriptional factor(s).

Techniques Used in Studies of Age-Related DNA Methylation Changes

Epigenetic modification of CpG islands (CGIs) in promoter regions is an important regulatory mechanism of gene expression in eukaryotic cells. Hypermethylation of CGIs may silence a gene, whereas hypomethylation of previously methylated CGIs allows gene expression. The pattern of methylation is cell-type-specific and established during development of the organisms. Changes in the methylation pattern have been found in all cancer forms and in aging cells. The epigenetic-related alternations of gene expression status may significantly contribute to the initiation and maintenance of malignant growth. Cancer incidence increases dramatically with age and correlates strongly with age-related methylation changes. Many techniques have been developed to analyze the genome-wide methylation content and the methylation status of specific loci. The majority of methylation screening protocols utilizes methylation-sensitive endonuclease digestion or bisulfite treatment of the template followed by subsequent PCR amplification of a specific sequence. All methods either examine only one specific DNA sequence at a time, or provide limited genomic information on the screened sequences. The principle of our new approach is to combine methylation-sensitive enzyme digestion with the comparative genomic hybridization (CGH) technique to develop an array-based method to screen the entire genome for changes of methylation pattern. The new technique will serve as an efficient tool in understanding the nature of epigenetic changes and their significance to the aging process and cancer development.

Microsatellite instability (MSI) increases with age in normal somatic cells

Small pool PCR (SP-PCR) is a sensitive method for the detection and quantification of microsatellite instability (MSI) in somatic cells. Here we propose that mutant microsatellite fragments accumulate with age in normal somatic cells and that this increase in MSI can be quantified by SP-PCR. MSI at 6 microsatellite loci was determined by SP-PCR in PBL DNA from 17 "normal" blood bank donors. These individuals varied in age from 20 to 67 y/o. MSI phenotypes were plotted against age in a regression analyses. A positive slope indicated a correlation between age and MSI phenotype (p=0.0006). The mean weighted average mutant frequencies across all loci for all individuals in the age groups (0.009 for 20-30 y/o; 0.019 for 35-50 y/o; 0.034 for 60-70 y/o) were also significantly different from each other (p<0.01). A baseline for increases of MSI with age in human somatic cells was therefore begun and the effectiveness of SP-PCR to evaluate low, but significant, levels of MSI, established.

Differential gene expression in normal human mammary epithelial cells treated with malathion monitored by DNA microarrays

Organophosphate pesticides are a major source of occupational exposure in the United States. Moreover, malathion has been sprayed over major urban populations in an effort to control mosquitoes carrying West Nile virus. Previous research, reviewed by the U.S. Environmental Protection Agency, on the genotoxicity and carcinogenicity of malathion has been inconclusive, although malathion is a known endocrine disruptor. Here, interindividual variations and commonality of gene expression signatures have been studied in normal human mammary epithelial cells from four women undergoing reduction mammoplasty. The cell strains were obtained from the discarded tissues through the Cooperative Human Tissue Network (sponsors: National Cancer Institute and National Disease Research Interchange). Interindividual variation of gene expression patterns in response to malathion was observed in various clustering patterns for the four cell strains. Further clustering identified three genes with increased expression after treatment in all four cell strains. These genes were two aldo-keto reductases (AKR1C1 and AKR1C2) and an estrogen-responsive gene (EBBP). Decreased expression of six RNA species was seen at various time points in all cell strains analyzed: plasminogen activator (PLAT), centromere protein F (CPF), replication factor C (RFC3), thymidylate synthetase (TYMS), a putative mitotic checkpoint kinase (BUB1), and a gene of unknown function (GenBank accession no. AI859865). Expression changes in all these genes, detected by DNA microarrays, have been verified by real-time polymerase chain reaction. Differential changes in expression of these genes may yield biomarkers that provide insight into interindividual variation in malathion toxicity.