Phospholipase d2 ablation ameliorates Alzheimer's disease-linked synaptic dysfunction and cognitive deficits

Growing evidence implicates aberrant lipid signaling in Alzheimer's disease (AD). While phospholipases A2 and C have been recently shown to mediate key actions of amyloid ß-peptide (Aß) through a dysregulation of arachidonic acid and phosphatidylinositol-4,5-bisphosphate metabolism, respectively, the role of phospholipase D (PLD) has so far remained elusive. PLD produces phosphatidic acid (PA), a bioactive lipid involved in multiple aspects of cell physiology, including signaling and membrane trafficking processes. Here we show that oligomeric Aß enhances PLD activity in cultured neurons and that this stimulatory effect does not occur upon ablation of PLD2 via gene targeting. Aß fails to suppress long-term potentiation in PLD2-deficient hippocampal slices, suggesting that PLD2 is required for the synaptotoxic action of this peptide. In vivo PLD activity, as assessed by detection of phosphatidylethanol levels using mass spectrometry (MS) following ethanol injection, is also increased in the brain of a transgenic mouse model of AD (SwAPP). Furthermore, Pld2 ablation rescues memory deficits and confers synaptic protection in SwAPP mice despite a significant Aß load. MS-based lipid analysis of Pld2 mutant brains in the presence or absence of the SwAPP transgene unmasks striking crosstalks between different PA species. This lipid analysis shows an exquisite acyl chain specificity and plasticity in the perturbation of PA metabolism. Collectively, our results point to specific molecular species of PA as key modulators of AD pathogenesis and identify PLD2 as a novel potential target for therapeutics.This work was supported by National Institutes of Health Grants R01 NS056049 and P50 AG008702 (G.D.P.), and R01 NS049442 (O.A.), by the Singapore National Research Foundation under Competitive Research Programme Award No. 2007-04, the Biomedical Research Council of Singapore (R-183-000-211-305), and the National Medical Research Council (R-183-000-224-213) (M. R. W.); as well as from the Portuguese Foundation for Science and Technology SFRH/BD/33237/2007 and the Luso-American Development Foundation (T.G.O.). We thank Sung Ho Ryu and Pietro De Camilli for providing the PLD and synaptophysin antibodies, respectively; Min Suk Kang and Nuno Sousa for critical input; Elizabeta Micevska for technical help with the animals; Sergey Voronov for help with the pilot PLD assays; and Claudia Dall'Armi for the help with confocal microscopy and image analysis. We thank Diego Berman, Kimberly Robinson, Zachary Freyberg, and Scott Small for critical reading of this manuscript. We also thank Michael Frohman for the kind gift of the GFP-hPLD1 and GFP-mPLD2 constructs. Anti-A beta antibodies were a kind gift from Dr. Sonia Jung (Centocor)