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Exposure to airborne particulate matter (PM) has significant effects on human health mainly leading to cardio-respiratory diseases. However very few data are available regarding the impact of PM on the skin, so to better understand the impact of fine particle (PM 0.3-2.5 ) on both inflammatory response and epidermal structure, we exposed a reconstructed human epidermis (RHE) to several doses of PM collected in Cotonou (Benin, West Africa). After 24 h of exposure, inflammatory response, histological observations, and gene expression related to oxidative stress, antioxidant defense and structural damages were determined. No PM-linked changes in tissue morphology or membrane integrity were observable. PM was however cytotoxic in a dose dependent manner. An inflammatory response appeared as shown by the increase in IL-1α and IL-8 cytokine productions. PM also induced oxidative stress, leading to an increase in 4-HNE immunostaining and to the up-regulation of HMOX1, MT1G and MT1E. Finally, PM had a negative impact on fundamental skin functions such as tissue anchorage, cell differentiation, cornification / skin desquamation and apoptosis. Our data show that airborne fine particles have an adverse effect on skin integrity, most probably leading to accelerated ageing., (Copyright © 2019 Elsevier B.V. All rights reserved.)

The effects of air pollution on health are gaining increasing research interest with limited data on skin alterations available. It was suggested that air pollution is a trigger factor for sensitive skin (SS). However, this data was based on surveys with a lack of experimental data. SS is related to altered skin nerve endings and cutaneous neurogenic inflammation. TTe present study was to assess the in vitro effect of particulate matter (PM) on epidermis and nerve ending homeostasis. PM samples were collected according to a validated protocol. Reconstructed human epidermis (RHE, Episkin®) was exposed to PM and subsequently the supernatants were transferred to a culture of PC12 cells differentiated into sensory neurons (SN). Cell viability, axonal growth and neuropeptide‐release were measured. The modulation of the expression of different inflammatory, keratinocytes differentiation and neurites growth markers was assessed. PM samples contained a high proportion of particles with a size below 1 μm and a complex chemical composition. Transcriptomic and immunohistochemical analyses revealed that PM altered keratinocytes terminal differentiation and induced an inflammatory response. While viability and functionality of the SN were not modified, their outgrowth was significantly decreased after incubation with PM‐exposed Episkin® supernatants. This was closely related to the modification of nerve growth factor/semaphorin 3A balance. This study showed that air pollutants have negative effects on keratinocytes and sensory nerve endings including inflammatory responses. These effects are probably involved in the SS pathophysiology and might be involved in inflammatory skin disorders. [ABSTRACT FROM AUTHOR]