The EGR1–Artemin Axis in Keratinocytes Enhances the Innervation of Epidermal Sensory Neurons during Skin Inflammation Induced by House Dust Mite Extract from Dermatophagoides farinae

Epidermal hyperinnervation is a critical feature of pruritus during skin inflammation. However, the mechanisms underlying epidermal hyperinnervation are unclear. This study investigates the role of the transcription factor EGR1 in epidermal innervation by utilizing wild-type (Egr1^+/+) and Egr1-null (Egr1^‒/‒) mice topically applied Dermatophagoides farinae extract from dust mite. Our findings revealed that Egr1^‒/‒ mice exhibited reduced scratching behaviors and decreased density of epidermal innervation compared with Egr1^+/+ mice. Furthermore, we identified artemin, a neurotrophic factor, as an EGR1 target responsible for Dermatophagoides farinae extract–induced hyperinnervation. It has been demonstrated that Dermatophagoides farinae extract stimulates toll-like receptors in keratinocytes. To elucidate the cellular mechanism, we stimulated keratinocytes with Pam3CSK4, a toll-like receptor 1/2 ligand. Pam3CSK4 triggered a toll-like receptor 1/2–mediated signaling cascade involving IRAK4, IκB kinase, MAPKs, ELK1, EGR1, and artemin, leading to increased neurite outgrowth and neuronal migration. In addition, increased expression of EGR1 and artemin was observed in the skin tissues of patients with atopic dermatitis. These findings highlight the significance of the EGR1–artemin axis in keratinocytes, promoting the process of epidermal innervation and suggesting it as a potential therapeutic target for alleviating itch and pain associated with house dust mite–induced skin inflammation.