Researchers here find a disconnect between DNA methylation patterns shown to correlate well with age and processes associated with longer telomere length. Telomeres are caps of repeated DNA at the ends of chromosomes that shorten with each cell division, a part of the mechanism limiting the life span of somatic cells. Their average length tends to shorten with age when considered across large populations in a statistical analysis, but this is a tenuous relationship that has also failed to appear in some smaller studies. Here, it seems that older ages as assessed by DNA methylation can correlate with differences in telomerase, the enzyme responsible for lengthening telomeres, that are associated with longer telomeres.

In any given individual, average telomere length as currently measured in leukocytes from a blood sample is dynamic in response to circumstances; it reflects pace of cell division and the rate at which new cells with long telomeres are generated by stem cells. Unfortunately the large degree of individual and circumstantial variation means that there is little to be meaningfully said about the present value - the information is not actionable in all but rare cases of exceptionally short average length due to disease. The epigenetic clocks derived from DNA methylation measurements are much more solid, repeatable, useful metrics, judging from the evidence to date.

In that broader context, it is interesting to find signs that these two approaches to measuring an aspect of aging are not on the same page, though I think the researchers here overstate the significance of their work and/or engage with a strawman to some degree in their comments. What they have found does fit in with the evidence to date supporting the idea that telomere length is only very loosely associated with aging, with considerable variation between individuals. That is somewhat distinct from the question of whether or not telomerase gene therapies are a useful approach to the treatment of aging or other conditions.

Researchers analyzed blood samples from nearly 10,000 people to find that genetic markers in the gene responsible for keeping telomeres (tips of chromosomes) youthfully longer, did not translate into a younger biologic age as measured by changes in proteins coating the DNA. DNA methylation age is a biomarker of chronological age and predicts lifespan, but its underlying molecular mechanisms are unknown. In this genome-wide association study, researchers found gene variants mapping to five loci associated with intrinsic epigenetic age acceleration (IEAA) and gene variants in three loci associated with extrinsic epigenetic age acceleration. Variants in the gene called Telomerase Reverse Transcriptase (TERT) on chromosome 5 that were associated with older IEAA were also associated with longer telomeres indicating a critical role for TERT in regulating the epigenetic clock, in addition to its established role of compensating for cell replication-dependent telomere shortening. "We calculated the epigenetic aging rate for each person using a previously described epigenetic clock method. Next, we related the epigenetic aging rate to millions of genetic locations (SNPs) across all of the chromosomes. Then we studied the SNPs that had very significant associations with epigenetic aging rates. To our surprise, one of these locations was the TERT locus. The finding is surprising because this was not a study of telomere length. TERT is a subunit of the enzyme telomerase, which is widely known because it has been touted as an anti-aging enzyme. Our study highlights the error in the notion that activation of telomerase (as advocated by some) will cure aging. Instead, our study shows that an anti-aging therapy based on telomerase expression would be accompanied by continued aging."

Link: https://www.eurekalert.org/pub_releases/2018-02/hsif-gwa020218.php