Sphingosine Kinase1 Is Pivotal for FcεRI-Mediated Mast Cell Signaling and Functional Responses In Vitro and In Vivo

Mast cell degranulation is pivotal to allergic diseases; investigating novel pathways triggering mast cell degranulation would undoubtedly have important therapeutic potential. Fc epsilon RI-mediated degranulation has contradictorily been shown to require SphK1 or SphK2, depending on the reports. We investigated the in vitro and in vivo specific role(s) of SphK1 and SphK2 in Fc epsilon RI-mediated responses, using specific small interfering RNA-gene silencing. The small interfering RNA-knockdown of SphK1 in mast cells inhibited several signaling mechanisms and effector functions, triggered by Fc epsilon RI stimulation including: Ca2+ signals, NF kappa B activation, degranulation, cytokine/chemokine, and eicosanoid production, whereas silencing SphK2 had no effect at all. Moreover, silencing SPHK1 in vivo, in different strains of mice, strongly inhibited mast cell-mediated anaphylaxis, including inhibition of vascular permeability, tissue mast cell degranulation, changes in temperature, and serum histamine and cytokine levels, whereas silencing SPHK2 had no effect and the mice developed anaphylaxis. Our data differ from a recent report using SPHK1(-/-) and SPHK2(-/-) mice, which showed that SphK2 was required for FC epsilon RI-mediated mast cell responses. We performed experiments in mast cells derived from SPHK1(-/-) and SPHK2(-/-) mice and show that the calcium response and degranulation, triggered by Fc epsilon RI-cross-linking, is not different from that triggered in wild-type cells. Moreover, IgE-mediated anaphylaxis in the knockout mice showed similar levels in temperature changes and serum histamine to that from wild-tvpe mice, indicating that there was no protection from anaphylaxis for either knockout mice. Thus, our data strongly suggest a previously unrecognized compensatory mechanism in the knockout mice, and establishes a role for SphK1 in IgE-mediated mast cell responses. The Journal of Immunology, 2009, 183: 221-227.