SPHK1 and chronic obstructive pulmonary disease: Taken together with our findings of significant associations between the increased expression of SPHK, S1PR2 and S1PR5, and alveolar macrophage phagocytic ability in COPD, these data support a functional effect of the increased gene expression of S1PR5. S1PR5 has been reported to interact with Rho-G12/13 protein coupled Rho/ROCK signalling pathway in oligodendrocyte precursor cells (OPCs) and appears to mediate their migration [63].