Apolipoprotein D modulates arachidonic acid signaling in cultured cells: implications for psychiatric disorders.

Deficiencies in arachidonic acid (AA) parameters have been reported in schizophrenic patients. AA is a primary binding ligand for apolipoprotein D (apoD), which is increased in response to antipsychotic drug treatment and elevated in subjects with schizophrenia and bipolar disorder. In this study, we investigated whether apoD might modulate AA signaling/mobilization in cultured embryonic kidney (HEK) 293T cells. Immunofluorescent labeling revealed both cytosolic and membrane-bound expression of apoD protein in apoD-transfected cells. In cells expressing apoD, phorbal 12-myristate 13-acetate-induced AA release was inhibited compared to controls and membrane levels of AA were elevated, as indicated by the amount of AA maximally incorporated into membrane phospholipids. In addition, exogenous apoD added directly to the incubation media prevented cellular uptake of free [3H]AA. These results suggest that apoD acts to stabilize membrane-associated AA by preventing release and sequestering free AA in the cell. These actions of apoD may be beneficial to psychiatric patients.