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A rat epigenetic clock recapitulates phenotypic aging and co-localizes with heterochromatin-associated histone modifications

ABSTRACT: Aging has been shown to be a strong driver of DNA methylation changes, leading to the development of robust biomarkers in humans and more recently, in mice. This study aimed to generate a novel epigenetic clock in rats—a model with unique physical, physiological, and biochemical advantages for studying mammalian aging. Additionally, we incorporated behavioral data, unsupervised machine learning, and network analysis to identify epigenetic signals that not only track with age, but also relate to phenotypic aging and reflect higher-order molecular aging changes. We used DNAm data from reduced representation bisulfite sequencing (RRBS) to train an epigenetic age (DNAmAge) measure in Fischer 344 CDF (F344) rats. In an independent sample of n=32 F344 rats, we found that this measure correlated with age at (r=0.93), and related to physical functioning (5.9e-3), after adjusting for age and differential cell counts. DNAmAge was also found to correlate with age in C57BL/6 mice (r=0.79), and was decreased in response to caloric restriction (CR), such that the longer the animal was on a CR diet, the greater the decrease in DNAm. We also observed resetting of DNAm when kidney and lung fibroblasts when converted to induced pluripotent stem cells (iPSCs). Using weighted gene correlation network analysis (WGCNA) we identified two modules that appeared to drive our DNAmAge measure. These two modules contained CpGs in intergenic regions that showed substantial overlap with histone marks H3K9me3, H3K27me3, and E2F1 transcriptional factor binding. In moving forward, our ability to unravel the complex signals linking DNA methylation changes to functional aging would require experimental studies in model systems in which longitudinal epigenetic changes can be related to other molecular and physiological hallmarks of aging.

ORGANISM(S): Rattus norvegicus

PROVIDER: GSE161141 | GEO | 2020/11/11

REPOSITORIES: GEO

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Project description:Sustained caloric restriction (CR) extends lifespan in animal models but the mechanism and primary tissue target(s) have not been identified. Gene expression changes with aging and CR were examined in both heart and subcutaneous white adipose tissue (WAT) of F344 male rats using AffymetrixÂ® RAE 230 arrays and validated by qRT-PCR on 18 genes. In heart, age- associated changes but not CR-associated changes in old. In WAT, genes were identified where the aging change is suppressed by CR (candidate markers of healthy aging) and those affected by CR but not normal aging (candidate longevity assurance genes). 10-21% of age-associated genes were regulated in common between tissues. Gene set enrichment analysis (GSEA) revealed coordinate small magnitude changes in ribosomal, proteasomal, and mitochondrial genes with similarities between heart and WAT. Further analysis revealed PPARgamma as a potential upstream regulator of altered gene expression in old CR WAT. These results demonstrate a reduced mRNA response to CR with age in heart relative to WAT. In WAT, we identified candidate CR mimetic targets and candidate markers of healthy aging. These data suggest a role for subcutaneous WAT in the effects of CR and strengthen the role for PPAR signaling in aging and CR while indicating that the effects of CR in heart can occur independent of global changes in mRNA level. Experiment Overall Design: Tissues (n=5-7 animals per group) were obtained from the NIH-NIA aging rodent tissue bank. According to supplier records, animals were housed in a specific pathogen free barrier facility under contract with BioReliance. AL animals were housed 3 per cage and CR animals were housed singly. CR (60% of AL) was initiated at 4 months of age with a switch from the NIH 31 to NIH fortified diet. F344 male rats were sacrificed at 4 months (4AL) or 28 months of age (28AL, 28CR). Animals with gross tumor pathologies were excluded from the study. All animals were euthanized by CO2 asphixiation and tissues were frozen in liquid nitrogen then stored at â80Â°C. Subcutaneous WAT was collected from the abdominal region. Recorded body weights differed dramatically between the 3 groups (4AL = 253Â±8 g, 28AL = 382Â±20 g, 28CR = 288Â±7 g) and heart weight as a fraction of body weight was not significantly different between the groups (data not shown). The apical ~1/3 of the heart was homogenized for the expression studies. Sections from the cut face were stained with haematoxylin and eosin to confirm expected aging-associated pathology changes.

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A rat epigenetic clock recapitulates phenotypic aging and co-localizes with heterochromatin-associated histone modifications

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