Konjac Ceramide Induces Semaphorin 3A Expression via the MAPK/AP-1 Signaling Axis and RORα in Normal Human Epidermal Keratinocytes

Epidermal hyperinnervation is a major cause of intractable itch in barrier dysfunction conditions such as atopic dermatitis. Keratinocyte-derived semaphorin 3A (Sema3A) suppresses epidermal hyperinnervation, but its expression is markedly reduced in barrier-disrupted skin. Although konjac ceramide (kCer) has been reported to act as a Sema3A-like ligand, the mechanisms by which it regulates Sema3A expression in keratinocytes remain unclear. Normal human epidermal keratinocytes (NHEKs) were treated with kCer, konjac glucosylceramide (kGlcCer), or C24 ceramide. Sema3A mRNA and protein levels were assessed by quantitative real-time PCR and enzyme-linked immunosorbent assay, respectively. The involvement of intracellular signaling was examined using mitogen-activated protein kinase (MAPK) inhibitors, activator protein-1 (AP-1) inhibitors, retinoic acid-related orphan receptor alpha (RORα) inverse agonists, and siRNAs targeting c-Jun, c-Fos, and RORα. kCer induced Sema3A expression in NHEKs more potently than kGlcCer or C24 ceramide and promoted Sema3A protein secretion. Pharmacological inhibition or genetic knockdown of MEK1/2, JNK, AP-1 components, or RORα significantly attenuated kCer-induced Sema3A expression, indicating involvement of the MAPK/AP-1 signaling axis and RORα. kCer upregulates Sema3A expression in human keratinocytes through MAPK/AP-1 signaling and RORα, suggesting it may represent a promising antipruritic agent for epidermal hyperinnervation associated with skin barrier dysfunction.