Particulate matters induce apoptosis in human hair follicular keratinocytes

Background: Particulate matters (PM) comprise a heterogeneous mixture of particles suspended in air. A recent study found that urban PMs may penetrate into hair follicles via transfollicular and transdermal routes in dorsal skin. Objective: To investigate the effects of PM on ex vivo cultured human scalp hair follicles and hair follicular keratinocytes in vitro. Methods: TUNEL staining was employed to check cells undergoing apoptosis in cultured hair follicles after PM treatment. MTT assay was employed to check cell viability after PM treatment. Quantitative real-time PCR analysis was employed to quantitate the expression of inflammatory genes, matrix metalloproteinases (MMPs), and Duox1. Inflammatory cytokine levels were measured by ELISA after PM treatment. The level of reactive oxygen species (ROS) production was measured using a chemical fluorescent probe by a fluorescence plate reader. Results: Abundant TUNEL-positive cells were observed in the keratinocyte region of hair including the epidermis, sebaceous gland, outer root sheath (ORS), inner root sheath (IRS), and bulb region. The viability of follicular cells, including the ORS, was found to be decreased upon PM exposure. mRNA expression and protein levels of inflammatory response genes and MMPs were upregulated in a dose-dependent manner by PM treatment. ROS levels were also increased by PM. Conclusion: These data strongly suggest that penetrated PMs from air pollution may cause apoptotic cell death to follicular keratinocytes by increased production of ROS and inflammatory cytokines, which could impair hair growth.