Cathelicidin peptide LL-37 increases UVB-triggered inflammasome activation: Possible implications for rosacea

Background: In patients with rosacea, environmental stressors, especially UVB radiation, trigger disease flares that are characterized by inflammation and vascular hyperactivity. An altered innate immune detection and response system, modulated to a large extent by the aberrant production and processing of human cathelicidin LL-37, is thought to play a central role in disease pathogenesis. Objective: To investigate whether the proinflammatory and proangiogenic effects of UV radiation are enhanced in the presence of cathelicidin LL-37. Methods: Human skin ex vivo and epidermal keratinocytes in vitro were exposed to UVB irradiation. The proinflammatory effects of UVB exposure in the presence and absence of LL-37 were characterized using immunoblot, transfection, qPCR, and a cell-based second messenger assay. ELISA was used to assess cytokine release and the angiogenic potential of endothelial cells was evaluated using an in vitro angiogenesis assay. Results: UVB irradiation triggered the inflammasome-mediated processing and release of IL-1 beta. LL-37 augmented this UV-induced IL-1 beta secretion by acting on the P2X(7) receptor on keratinocytes. P2X(7) receptor activation by UVB and LL-37 resulted in an increase in intracellular calcium concentrations, which enhances inflammasome activation and subsequent IL-1 beta release. Furthermore, IL-1 beta and LL-37 worked synergistically to increase the angiogenic potential of endothelial cells. Conclusion: Cathelicidin LL-37 modulates the proinflammatory and proangiogenic effects of UV radiation and thereby contributes to enhanced sensitivity to sun exposure in rosacea. (C) 2014 Japanese Society for Investigative Dermatology. Published by Elsevier Ireland Ltd. All rights reserved.