Hyperkeratinization and Proinflammatory Cytokine Expression in Meibomian Glands Induced by Staphylococcus aureus

This exploratory study aimed to investigate the morphological and pathological alterations of the meibomian gland (MG) with the Staphylococcus aureus crude extracts (SACEs) treatment.

Mouse MG explants were cultured and differentiated with or without SACEs for 48 hours. Explant's viability and cell death were determined by thiazolyl blue tetrazolium bromide (MTT) assay and TUNEL assay. MG morphology was observed by Hematoxylin and Eosin staining. Lipid droplet production was detected by Nile Red staining and LipidTox immunostaining. The pro-inflammatory cytokines were detected by ELISA. The relative gene and protein expression in MG explants was determined via quantitative RT-PCR, immunostaining, and immunoblotting. The components of the SACEs were analyzed by immunoblotting and silver staining.

Our findings demonstrated that the SACEs treatment induced overexpression of keratin 1 (Krt1) in the ducts and acini of MG explants, accompanied by a decrease in viability and an increase in cell death in explants. Furthermore, the SACEs treatment dose-dependently increased the levels of TNF-α, IL-1β, and IL-6 in MG explants. The SACEs treatment induced activation of the nuclear factor kappa B (NF-κB) and AIM2 (absent in melanoma 2)/ASC (apoptosis-associated speck-like protein containing a caspase recruitment domain) inflammasome signaling pathway in explants. Further investigation showed expression of the key adipogenesis-related molecule peroxisome proliferator-activated receptor γ was decreased after SACEs treatment. However, no change was found in the lipid synthesis of MG explants after treatment with the SACEs. Staphylococcal enterotoxins B (SEB) was detected in the SACEs. SEB induced the overexpression of Krt1 and IL-1β in ducts and acini of MG explants.

Our findings confirm that Staphylococcus aureus induced hyperkeratinization and pro-inflammatory cytokines expression in MG explants ducts and acini. These effects might be mediated by SEB. Activation of the NF-κB and AIM2/ASC signaling pathway is involved in this process.