Background:
Methylation patterns determine how genes are expressed and distinguish one cell type from another. Epigenetic drift is a stochastic process that occurs when genes lose or gain methylation inappropriately, thus detuning cells for their particular function. The methylation pattern of selected genes can be used as a genetic clock that correlates well with chronological age — Horvath’s clock, for instance. How to reverse the clock is an open question.
Telomeres can be used as a separate clock, and as cells age and divide their telomeres shorten and eventually the cells become senescent. Telomerase is an enzyme that restores telomeres to a more youthful age, thus that clock can be reversed. Supplements are sold that purport to protect and lengthen telomeres. From LEF.
Paradox:
Oddly, gene variants associated with longer telomeres are associated with faster epigenetic aging. It seems that turning back one clock advances the other.
Hypothesis:
Most somatic cells typically have undetectable levels of telomerase and thus their ability to divide is finite. If you took supplements that allowed those cells to live longer and divide more times, the expanded numbers of epigenetically old cells would increase the average epigenetic age of the body and advance Horvath’s clock. Conversely, somatic cells derived from stem cells (with their zero age epigenetics) bring down the average epigenetic age. Thus, by using stem cell activators along with telomerase activators that don’t affect somatic cells, the average epigenetic and telomeric age of the body can be decreased. Old somatic cells with damaged epigenetics die and are replaced with stem-cell-derived daughter cells with zero epigenetic age and full length telomeres. Both clocks are reversed.
Notes:
1. The paradox: Long telomeres and epigenetic aging are inversely correlated—
The paradoxical finding that TERT alleles associated with longer telomeres are associated with higher IEAA [intrinsic epigenetic age acceleration] ... While the paradoxical finding cannot be disputed on scientific grounds, its biological interpretation remains to be elucidated.
https://www.nature.c...467-017-02697-5
2. Where stem cells get their epigenetic patterns for differentiation is not yet understood. But clearly part of the pattern must be created de novo and thus starts off with zero age.
In contrast to maintenance methylation, the mechanism(s) that determine the specificity of de novo methylation are not completely elucidated.
https://www.ncbi.nlm...les/PMC5027477/
3. Transplantation of blood stem cells reduces the epigenetic age, at least temporarily—
Dynamics of epigenetic age following hematopoietic stem cell transplantation
we observed a strong decrease in DNAm age (termed “rejuvenation”) within the first six months of transplantation… We measured a decrease in mean DNAm age to a minimum until day +178 … after transplantation. Afterwards, significant accelerated epigenetic aging was observed.
https://www.ncbi.nlm...les/PMC5541887/