125 HSP27 a key element of skin regulation subjected to climate variations

Abstract

Humidity, along with other climatic factors such as temperature, can impact the skin health. Indeed, our skin is daily exposed to humidity and temperature variations. All around the world, the daily humidity varies from low to high relative humidity (45% to 90%). In addition, the skin temperature can reach 44°C under sun exposure. The rare studies available show that low humidity causes several changes in the skin (dryness, itchiness, impairment of the desquamation process, skin roughness, and loss skin elasticity). Unfortunately, as most of the studies were performed on murine models, they remain inconclusive about the real effects of humidity and temperature variations on the human skin health. Thus, we developed human skin explant models (heat stress, humidity stress and a combined heat and humidity stresses model) in order to understand the effect of climate on skin physiology. We analyzed epidermis thickness and the expression profiles of loricrin (LOR), filaggrin (FLG), keratin 10 (K10), and HSP27. These markers were chosen upon their relevance in skin homeostasis. In all conditions studied an epidermis thickening was observed suggesting keratinocyte proliferation. In skins exposed to a heat stress, the differentiation process is delayed and decreased. In skins exposed to low humidity an early expression of K10 expression occurs suggesting a disorganized start of the differentiation process. In skins exposed to heat and low humidity the differentiation process of keratinocytes seems to be sustained and overstimulated suggesting an uncontrolled differentiation process. We found that the different environmental conditions studied modulate the expression of HSP27, a central protein regulating LOR and K10 (differentiation process), and the synthesis and processing of proFLG and FLG (epidermis physiology). Our results showed that climatic factors (humidity and/ or temperature) through the modulation of HSP27 expression are responsible in the weakening of skin barrier function due to impairment of skin differentiation process.