Normal Human Epidermal Keratinocytes neonatal

Human Epidermal Keratinocyte Differentiation is Associated with Increased S1P and Downregulated S1P Lyase

Sphingosine 1-phosphate (S1P) lyase is an enzyme that degrades S1P and has been suggested as a drug target for psoriasis treatment. As S1P promotes keratinocyte differentiation, Jeon et al. asked if manipulating S1P lyase would alter human neonatal epidermal keratinocyte (HEKn) cells proliferation and differentiation.

They inhibited S1P lyase in HEKn cells using an S1P lyase-specific inhibitor (SLI) and siRNA targeting S1P lyase 1 (SGPL1). HEKn cells were maintained in low Ca²⁺ (60 μM) or differentiated in high Ca²⁺ (2 mM) medium for 5 days. Western blot analysis revealed that expression of Acer1 and Sphk1, enzymes that produce S1P, were increased under low Ca²⁺ conditions. S1P lyase protein expression was increased over time under both low and high Ca²⁺ conditions (Fig. 1A). High Ca²⁺ downregulated Acer1 but upregulated Sphk1, with no change in S1P lyase expression (Fig. 1B). By using LC/MS/MS analysis they observed that the amount of S1P was increased over time under high Ca²⁺ conditions (Fig. 1C). Treatment with extracellular S1P enhanced protein levels of keratin 1 and involucrin, which are early and late markers of differentiation, respectively (Fig. 1D). Taken together, these data indicate that S1P metabolism is directly coupled to keratinocyte differentiation.

Effect of PM on Proinflammatory Cytokine Expression in C. acnes or PGN Treated HEKn Cells

Recent studies show that particulate matter (PM) can cause oxidative stress and inflammation linked to several skin conditions, but its effect on acne is unknown. Noh et al. investigated whether PM exposure worsens acne-like inflammation in HEKn cells induced by Cutibacterium acnes (C. acnes) and Staphylococcus aureus peptidoglycan (PGN).

Cytotoxicity tests showed no significant effect of C. acnes on HEKn cell viability (Fig. 2A), but PM caused significant cytotoxicity in a dose- and time-dependent manner (Fig. 2B). For further experiments, a PM concentration of 10 μg/cm² was used. HEKn cells were treated with PM and either heat-killed C. acnes or PGN. After 3 hours (mRNA) and 24 hours (protein), the expression of proinflammatory cytokines (IL-1α, IL-1β, IL-6, IL-8, and TNF-α) was measured using qRT-PCR and ELISA. Results showed that PM significantly increased the expression of these cytokines in C. acnes- or PGN-treated cells (Fig. 3), indicating that PM can amplify acne-like inflammation.