A team of researchers have developed a tissue-specific clock that can measure the biological age of skin.
There is plenty of new evidence that different organs and tissues in our body age at different rates. In particular, the epigenetic state, the pattern of gene expression, of the cells that comprise these different organs and tissues can vary considerably. Changes to the methylation state are one of the ways that gene expression changes during aging, and they are part of the epigenetic alterations hallmark of aging.
Epigenetic alterations in aging include changes to methylation patterns, which generally correlate with a decrease in the amount of heterochromatin and an increase in chromosome fragility and transcriptional alterations (variance in gene expression), remodeling of chromatin (a DNA support structure that assists or impedes its transcription), and transcriptional noise.
By measuring the methylation state, it is possible to get a reasonably accurate view of how biologically old a particular tissue or organ is, based on its gene expression profile.
Today, we want to note a recent study in which researchers have developed a DNA methylation clock specifically for the aging of skin . This is an important step forward, given that tissues and organs tend to age differently and at different rates, so specialized clocks that incorporate these differences are really a must for accurate measurement of aging and validation of interventions that seek to reverse aging.
DNA methylation (DNAm) age constitutes a powerful tool to assess the molecular age and overall health status of biological samples. Recently, it has been shown that tissue-specific DNAm age predictors may present superior performance compared to the pan- or multi-tissue counterparts. The skin is the largest organ in the body and bears important roles, such as body temperature control, barrier function, and protection from external insults. As a consequence of the constant and intimate interaction between the skin and the environment, current DNAm estimators, routinely trained using internal tissues which are influenced by other stimuli, are mostly inadequate to accurately predict skin DNAm age.
It makes sense that a skin-specific methylation clock would arrive first, given the ease of access to the largest organ in the body; if we had such a clock, testing interventions and changes to the age of the skin would be very simple.
The development of methylation and other kinds of epigenetic clocks has recently been an area of great interest to researchers, and, for many people, these types of aging biomarkers are really the gold standard for measuring changes to biological age.
However, it is still the early days of epigenetic clocks, and there is considerable work that needs to be done before highly accurate clocks can be developed. Currently, they can be somewhat hit and miss, depending on the tissue type being examined, and, in some cases, it is not entirely clear what exactly these clocks are measuring and what their results mean in the context of aging.
The need for highly accurate aging biomarkers has never been more urgent, especially as there are now therapies targeting the aging processes in human trials and others are poised to join them. The need to accurately quantify changes to biological age has never been more pressing than it is right now.
 Boroni, M., Zonari, A., de Oliveira, C. R., Alkatib, K., Cruz, E. A. O., Brace, L. E., & de Carvalho, J. L. (2020). Highly accurate skin-specific methylome analysis algorithm as a platform to screen and validate therapeutics for healthy aging. Clinical Epigenetics, 12(1), 1-16.