For reasons yet to be determined, the composition of the skin microbiome changes with age. It is also unclear as to whether these changes contribute to skin aging in any meaningful way, or are instead a consequence of skin aging. Researchers here perform a proof of concept study to identify bacterial activities that differ in the microbiome of old versus young skin. There is little to be learned from these initial results, but in principle a much more comprehensive set of data might point the way towards specific experiments that could be conducted, changing the balance of populations in the skin microbiome in measured ways to see if the function of aged skin improves as a result.
The human skin is inhabited by a large number and variety of microorganisms, including bacteria, fungi, and viruses. Although over- and underrepresented bacterial taxa can be readily associated with younger or older skin, the limiting step and challenge in the analysis of these data is the interpretation of biological relevance in context of the research question or hypothesis. Specifically, little insight is currently available in literature on the interplay between microbial functionalities and human cellular processes (referred to as co-metabolism).
To obtain more insight into the connection between the skin microbiome and the human physiological processes involved in skin aging, we performed a systematic study on interconnected pathways of human and bacterial metabolic processes that are known to play a role in skin aging. The bacterial genes in these pathways were subsequently used to create Hidden Markov Models (HMMs), which were applied to screen for presence of defined functionalities in both genomic and metagenomic datasets of skin-associated bacteria. These models were further applied on 16S rRNA gene sequencing data from skin microbiota samples derived from female volunteers of two different age groups: 25-28 years ('young') and 59-68 years ('old').
The results show that the main bacterial pathways associated with aging skin are those involved in the production of pigmentation intermediates, fatty acids, and ceramides. This study furthermore provides evidence for a relation between skin aging and bacterial enzymes involved in protein glycation. Taken together, the results and insights described in this paper provide new leads for intervening with bacterial processes that are associated with aging of human skin.