“…The intermediary pathways that allow SphK2 to regulate the expression and localization of the junctional proteins at the BBB have yet to be clarified, but it would not be unexpected if SphK2-derived S1P signaling proceeded via mediators and pathways already known to regulate BBB tight junctions and/or BBB permeability, such as nitric oxide, vascular endothelial growth factor, proteases, and reactive oxygen species, as well as the actin cytoskeleton, caveolae, and pericytes (Sandoval and Witt, 2008). Indeed, there is evidence from studies in the peripheral vasculature that S1P activates endothelial nitric oxide synthase via PI3K/ Akt, counteracts the deleterious effects of reactive oxygen species on vascular endothelium via ERK1/2 and endothelial nitric oxide synthase (Igarashi and Michel, 2008), and regulates pericyte recruitment via N-cadherin signaling (Paik et al, 2004). Sphingosine-1-phosphate R1 receptor activation also induces intracellular calcium release from the endoplasmic reticulum and Rac-1 activation, promoting adherens junction formation at the endothelial cell periphery that can block vascular endothelial growth factorinduced vascular permeability (Hoang et al, 2011;Mehta et al, 2005).…”