Sphingosine kinase 1 activation enhances epidermal innate immunity through sphingosine-1-phosphate stimulation of cathelicidin production

Background: The ceramide metabolite, sphingosine-1-phosphate (SIP), regulates multiple cellular functions in keratinocytes (KC). We recently discovered that production of a key innate immune element, cathelicidin antimicrobial peptide (CAMP), is stimulated via a NF-kappa B-dependent mechanism that is activated by SIP when SE, is generated by sphingosine kinase (SPHK) I. Objective: We investigated whether pharmacological modulation of SPHK1 activity, using a novel synthetic SPHK1 activator, (S)-methyl 2-(hexanamide)-3-(4-hydroxyphenyl) propanoate (MHP), stimulates CAMP expression. Methods: MHP-mediated changes in both SIP and CAMP downstream mediators were analyzed in normal cultured human KC by qRT-PCR. Western immunoblot, ELISA, confocal microscopy for immunohistochemistry, HPLC and ESI-LC/MS/MS, and microbial pathogen invasion/colonization in a human epidermal organotypic model. Results: Treatment with MHP directly activated SPHK1 and increased cellular SIP content in normal cultured human KC. Because MHP did not inhibit SIP lyase activity, which hydrolyses SIP, augumented SE) levels could be attributed to increased synthesis rather than blockade of SIP degradation. Next, we found that exogenous MHP significantly stimulated CAMP mRNA and protein production in KC, increases that were significantly suppressed by siRNA directed against SPHK1, but not by a scrambled control siRNA. NF-kappa B activation, assessed by nuclear translocation of NF-kappa B, occurred in cells following incubation with MHP. Conversely, pretreatment with a specific inhibitor of SPHK1 decreased MHP-induced nuclear translocation of NF-kappa B, and significantly attenuated the MHP-mediated increase in CAMP production. Finally, topical MHP significantly suppressed invasion of the virulent Staphylococcus aureus into murine skin explants. Conclusion: MHP activation of SPHK1, a target enzyme of CAMP production, can stimulate innate immunity. (C) 2015. Japanese Society for Investigative Dermatology. Published by Elsevier Ireland Ltd. All rights reserved.