Adaptations to aging and stress in the activity of metabolic key enzymes in the epidermis at single cell level

Changes in carbohydrate metabolism are a key feature of aging that are also observed in the epidermis. Additionally, rapid changes in the activity of the pentose phosphate pathway have been recently described as an immediate response to ultraviolet oxidative and genotoxic damage in order to provide nucleotide building blocks and reducing equivalents for antioxidant defenses. Using anin situzymographic image analysis approach, we investigated the maximum enzymatic activities of lactate dehydrogenase (LDH) and glucose 6 phosphate dehydrogenase (G6PD) together with stress and senescence markers in epidermal samples of young versus aged donors and in skin equivalent models containing labeled replicative senescent keratinocytes (KC). G6PD showed a differentiation dependent increase in activity, that decreased with age but also in the presence of senescent KC. LDH activity on the other hand was elevated in aged skin, and did not show a differentiation dependent gradient. Presence of senescent cells in modeled epidermal equivalents led to an induction of LDH activity. Analysis at the single cell level allows to assign the observed changes to cells residing in specific strata and to cells showing specific age related damage. Our initial data suggests an age related decrease of G6PD products and increase in glycolysis that co-localizes with the presence of cells bearing markers of cellular senescence.