Mitochondrial and glycolytic activity of UV-irradiated human keratinocytes and its stimulation by a Saccharomyces cerevisiae autolysate

• Bioenergetics of UV-irradiated keratinocytes is analyzed via extracellular flux.
• UV-stress results in mitochondrial dysfunction and downregulation of related genes.
• A Saccharomyces lysate stimulates metabolism and expression of mitochondrial genes.
• SCA can compensate for UV-induced decreased respiratory capacity in skin.

Cutaneous aging is correlated with mitochondrial dysfunction and a concomitant decline in energy metabolism that can be accelerated by extrinsic factors such as UV radiation (UVR). In this study we compared cellular bioenergetics of normal and UV-irradiated primary human epidermal keratinocytes. Moreover, we investigated the influence of a Saccharomyces cerevisiae autolysate (SCA) on stressed keratinocytes to regain cellular homeostasis. Cellular metabolism was assessed by extracellular flux analysis which measures oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) as well as by ATP quantification. The expression level of ten mitochondria related genes in normal and UVR-stimulated (60 mJ/cm2 UVB) keratinocytes was quantified by real-time PCR and the impact of SCA addition was determined. Sublethal UV stress increased mitochondrial dysfunction in keratinocytes which resulted in reduced viability, uncoupled oxidative phosphorylation, and down-regulated mitochondrial gene expression. Particularly, gene expression of SHDA, UPC2, BID, and ATP5A1 was reduced about twofold within 4 h. Treatment of keratinocytes with SCA shifted cellular metabolism towards a more energetic status by increasing the respiratory rate and glycolysis. SCA also stimulated cellular ATP production after short (4 h) and prolonged (22 h) incubations and induced the expression of genes related to mitochondrial function towards normal expression levels upon UV irradiation. The decreased respiratory capacity of UV-irradiated keratinocytes was partially compensated by the addition of SCA which enhanced glycolytic activity and thereby increased cellular resistance to environmental stress.