Although the pathogenesis of atopic dermatitis (AD) is not entirely clear, AD has been associated with filaggrin loss-of-function mutations, Th2 cytokines, and colonization with the gram-positive cocci S. aureus that contribute to the skin barrier defect and disease severity. To mimic skin scratching in AD patients, we performed scalpel cuts on the backs of filaggrindeficient (ft/ft) and wt (Balb/c) mice. Unexpectedly, w21 days after the skin injury, ft/ft mice but not wt mice spontaneously developed an expanding area of inflammation at the site of skin injury with clinical alopecia, erythema, and scale, histologic acanthosis and grampositive cocci colonization in the stratum corneum, an inflammatory infiltrate of monocytes, eosinophils, mast cells and neutrophils, and increased protein levels of (e.g., IL-1b) and the Th2-related cytokines (e.g., IL-33 and IL-31). Interestingly, topical treatment with a potent corticosteroid ointment (clobetasol) resulted in a greater degree of skin inflammation, and histologic sections revealed a marked increase in abundance of gram-positive cocci throughout the stratum corneum and hair follicles. In contrast, topical treatment with an antibiotic ointment (Neosporin) resulted in resolution of clinical and histologic skin inflammation, decreased inflammatory infiltrate, and reduced levels of proinflammatory and Th2 cytokines. Taken together, these findings provide a new in vivo mouse model of spontaneous AD development to investigate the specific roles of filaggrin deficiency, skin injury, and bacterial skin colonization in the pathogenesis of AD.
492Gastrin releasing peptide receptor and PI3K-gamma are partners in the transmission of itch Gastrin-releasing peptide (GRP) and its receptor (GRPR) are important components of the itch pathway. Signaling pathways downstream of GRPR activation are not clear. We used several approaches to further assess GRPR localization and investigate the related downstream signaling pathways. Functional GRPR is likely expressed by naive DRG sensory neurons since GRP induces calcium flux in small capsaicin-sensitive neurons. Expression profiling reveals that PI3K-gamma is downstream of GRP/GRPR, as observed by GRP-induced Akt phosphorylation in GRPR-transfected cells and ex vivo naive mouse spinal cords. Intrathecal GRP administration caused intense scratching behavior, an effect inhibited by pharmacological blockade of GRPR. We assessed whether the GRP/GRPR is involved in chronic itch using the dry skin model and found that a GRPR antagonist reduced itching. The activation of PI3Kgamma was demonstrated in both itching models, an effect prevented by GRPR blockade. These findings suggest that PI3K-gamma is downstream of GRPR activity. A Pi3K-gamma inhibitor reversed both GRP-and dry skin-induced itch in a concentration-dependent manner. Together, these results indicate that GRPR is expressed by DRG sensory neurons and mediate itch via the Pi3K-gamma/Akt pathway.