Cell-associated and tissue-wide reconfiguration of epidermal metabolism by senescent keratinocytes

Summary: Abstract Body: Adaptive reconfiguration of metabolic pathways is use by epidermal keratinocyte (KC) as a first line of defense against ultraviolet oxidative and genotoxic damage. Rapid activation of the pentose phosphate pathway (PPP) provides metabolites essential for redox responses and DNA-damage repair. Changes in metabolism are however also a hallmark of aging at the cellular level known as cellular senescence. To investigate senescence related changes in aged skin we used a multimodal tissue cytometry approach. Combining tissue cytometry and image-based in situ zymographic assays we measured the peak activities of glucose 6 phosphate dehydrogenase (G6PD, PPP) and lactate dehydrogenase (LDH) in association with stress, aging and senescence markers in human skin samples and Skin equivalents (SE). In human epidermis we found an age-related increase of LDH and a decrease of G6PD activity, the latter forming an inward out positive gradient of activity in young epidermis, which is lost in aging. While LDH activity correlated to loss of LaminB1 staining, the global decrease of G6PD appeared to be unrelated to senescence markers. We then assessed whether introduction of senescent cells into SE would recapitulate these findings. Indeed, incorporating 5% labelled replicatively senescent KC led to cell associated increased LDH and globally decreased G6PD activity. Our findings suggest that presence of senescent cells contributes to the age-related loss of a potentially protective gradient of G6PD-generated reducing equivalents in the epidermis, and that senescent epidermal cells utilize increasingly LDH for energy production. Targeting these metabolic pathways may help to temporarily restore metabolites needed for cell repair. Christopher Kremslehner^{1, 4}, Christina Bauer^{1, 4}, Ionela-Mariana Nagelreiter^{1, 4}, Sandra Forestier², Gaelle Gendronneau², Agnes Tessier², Youcef Ben Khalifa², Elisabeth Ponweiser³, Arvand Haschemi³, Florian Gruber^{1, 4} 1. Department of Dermatology, Medizinische Universitat Wien, Vienna, Vienna, Austria. 2. CHANEL Parfums Beauté, Pantin, France. 3. Clinical Institute for Laboratory Medicine, Medizinische Universitat Wien, Vienna, Vienna, Austria. 4. SKINMAGINE, Christian Doppler Laboratory for Skin Multimodal Analytical Imaging of Aging and Senescence, Vienna, Austria. Epidermal Structure and Barrier Function