Identification of autotaxin as a neurite retraction‐inducing factor of PC12 cells in cerebrospinal fluid and its possible sources

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Abstract
Cerebrospinal fluid (CSF) induced neurite retraction of differentiated PC12 cells; the action was observed in 15 min (a rapid response) and the activity further increased until 6 h (a long‐acting response) during exposure of CSF to the cells. The CSF action was sensitive to monoglyceride lipase and diminished by homologous desensitization with lysophosphatidic acid (LPA) and by pretreatment with an LPA receptor antagonist Ki16425. Although fresh CSF contains LPA to some extent, the LPA content in the medium was increased during culture of PC12 cells with CSF. The rapid response was mimicked by exogenous LPA, and a long‐acting response was duplicated by a recombinant autotaxin, lysophospholipase D (lyso‐PLD). Although the lyso‐PLD substrate lysophosphatidylcholine (LPC) was not detected in CSF, lyso‐PLD activity and an ∼120‐kDa autotaxin protein were detected in CSF. On the other hand, LPC but not lyso‐PLD activity was detected in the conditioned medium of a PC12 cell culture without CSF. Among neural cells examined, leptomeningeal cells expressed the highest lyso‐PLD activity and autotaxin protein. These results suggest that leptomeningeal cells may work as one of the sources for autotaxin, which may play a critical role in LPA production and thereby regulate axonal and neurite morphological change.