Human ß-defensin-3 increases the expression of interleukin-37 through CCR6 in human keratinocytes.

BACKGROUND: Interleukin (IL)-37, a new member of the IL-1 family, is characterized as a fundamental inhibitor of innate immunity: it dampens the production of proinflammatory cytokines, protects against inflammatory and autoimmune diseases, and plays a potent immunosuppressive role in the pathogenesis of psoriasis. IL-37 is highly expressed in psoriatic skin, in which human ß-defensins (hBDs) have been detected. Although hBDs enhance the production of cytokines, including IL-1 cytokines, whether they stimulate the production of IL-37 remains unclear. OBJECTIVES: To assess the ability of hBDs to stimulate IL-37 expression/production by human keratinocytes and to determine the mechanism involved. METHODS: Real-time PCR and Western blotting were used to evaluate IL-37 expression. Caspase activities were assessed using colorimetric assay kits. A CCR6 antibody, siRNA, and caspase, Smad3, MAPK and NF-κB inhibitors were used to investigate the signaling mechanism of hBDs. RESULTS: Among the four hBDs used, only hBD-3 up-regulated the mRNA and protein expression of IL-37. The combination of TNF-α, EGF and poly (I:C) with hBD-3 synergistically enhanced the mRNA but not the protein expression of IL-37. Furthermore, hBD-3 increased the release of IL-37 into the culture supernatants. Evaluation of the signaling mechanism of hBD-3 suggested that caspases 1 and 4, Smad3, CCR6, MAPKs and NF-κB were required for hBD-3-mediated IL-37 expression. CONCLUSIONS: The finding that hBD-3 stimulates IL-37 expression, a novel target for the pathogenesis and therapy of cutaneous inflammatory diseases, provides evidence that hBDs contribute to the suppression of inflammatory and innate immune responses through the regulation of IL-37 expression.

Host defense (Antimicrobial) peptide, human ß-defensin-3, improves the function of the epithelial tight-junction barrier in human keratinocytes.

Human ß-defensins (hBDs) are host defense peptides that not only exhibit microbicidal properties but also stimulate various cellular activities, including keratinocyte proliferation, migration, and wound healing. hBDs are overexpressed in the skin in cases of psoriasis but are downregulated in atopic dermatitis skin, although both diseases are associated with stratum corneum barrier defects. Because the tight-junction (TJ) barrier is also dysfunctional in both atopic dermatitis and psoriasis patients, we hypothesized that hBDs may regulate the TJ barrier function in keratinocytes. We observed that, among the hBDs tested, only hBD-3 increased the expression of several claudins and their localization along the cell-cell borders. In addition, hBD-3 elevated the transepithelial electrical resistance and reduced the paracellular permeability of keratinocyte layers, and this effect was reversed by the claudin inhibitor ochratoxin A, CCR6 antibody, and CCR6 small interfering RNA. Moreover, hBD-3 enhanced the activation of Rac1, atypical protein kinase C, glycogen synthase kinase-3, and phosphatidylinositol 3 kinase, which are required for the hBD-3-mediated regulation of the TJ barrier function, as evidenced by the effects of their respective inhibitors. Collectively, our findings provide evidence regarding the contribution of host defense peptides to the innate immunity of skin by regulating TJ barrier function, in addition to their antimicrobial and other immunomodulatory activities.