Epimutations: Targets or Bystanders for Rejuvenation Biotechnology? (Albert Einstein College of Medicine)
Just as our genes can suffer mutations that damage the instructions cells use to make their encoded proteins, so too our epigenetic structures can suffer epimutations that cause cells to aberrantly turn the expression of particular genes on or off. Some epimutations that occur with age cause harm to us by leading to forms of aging damage (cancer, senescence, or apoptosis) for which rejuvenation biotechnologies are already under development. If those are the only ways that epimutations can harm us, then those rejuvenation biotechnologies will be enough to eliminate their impact on our health. The Albert Einstein College of Medicine (AECOM) epimutations team investigated the possibility that separately from these harms, epimutations could also be contributing to age-related disease. Numerous cells in a tissue could, in this scenario, be engaging in aberrant gene expression, leading over time to cell dysfunction and eventual pathology.
A major focus of the AECOM epimutations group was the development, application, and optimization of single-cell epimutation quantification assays. Unlike adaptive changes in epigenetic states, which often happen systematically across a tissue, each true epimutation occurs at a different, random location in each individual cell that suffers one. This means that each particular epimutation will be individually rare, even if large numbers of cells within a tissue suffer some epimutations. In short, only by looking at each cell’s individual epimutation burden can we get a clear picture of the real load of cells damaged by epimutations in a tissue with age.
With SENS Research Foundation funding, the epimutations team at AECOM adapted an established method for evaluating one epigenetic control structure (DNA methylation) at the level of the base pair for use in single-cell analysis. In 2014, they validated their new assay in mouse tissues, confirming its ability to detect methylation patterns in single fibroblasts (a kind of skin cell), liver cells, and neurons. They were also able to show that the assay can detect epimutations induced in fibroblasts using azacitidine, a drug that strips methyl groups off of DNA in isolated cells. They demonstrated that it could also detect and assay the frequency of epimutations as deviations from the reference pattern across an intact tissue (the liver). These results were recently published in the journal Nucleic Acids Research.
With the new, validated tool in hand, the AECOM epimutations team were able to get the first reliable answers to the key question of the rate of epimutation (other than those causing cancer, senescence, or apoptosis) in the cells of aging tissues, starting with a comparison of the epimutation loads in the livers and brains of normally-aging mice. As an indirect measure of the possible harmful effects of non-cancer epimutations, they also looked at ways to make cautious use of animal models with an increased rate of epimutation.