Imaging decreased brain docosahexaenoic acid metabolism and signaling in iPLA2β (VIA)-deficient mice

Mireille Basselin,Angelo O Rosa,Epolia Ramadan,Yewon Cheon,Lisa Chang,Mei Chen,Deanna Greenstein,Mary Wohltmann,John Turk,Stanley I Rapoport

doi:10.1194/jlr.m008334

Abstract

Ca(2+)-independent phospholipase A(2)β (iPLA(2)β) selectively hydrolyzes docosahexaenoic acid (DHA, 22:6n-3) in vitro from phospholipid. Mutations in the PLA2G6 gene encoding this enzyme occur in patients with idiopathic neurodegeneration plus brain iron accumulation and dystonia-parkinsonism without iron accumulation, whereas mice lacking PLA2G6 show neurological dysfunction and neuropathology after 13 months. We hypothesized that brain DHA metabolism and signaling would be reduced in 4-month-old iPLA(2)β-deficient mice without overt neuropathology. Saline or the cholinergic muscarinic M(1,3,5) receptor agonist arecoline (30 mg/kg) was administered to unanesthetized iPLA(2)β(-/-), iPLA(2)β(+/-), and iPLA(2)β(+/+) mice, and [1-(14)C]DHA was infused intravenously. DHA incorporation coefficients k* and rates J(in), representing DHA metabolism, were determined using quantitative autoradiography in 81 brain regions. iPLA(2)β(-/-) or iPLA(2)β(+/-) compared with iPLA(2)β(+/+) mice showed widespread and significant baseline reductions in k* and J(in) for DHA. Arecoline increased both parameters in brain regions of iPLA(2)β(+/+) mice but quantitatively less so in iPLA(2)β(-/-) and iPLA(2)β(+/-) mice. Consistent with iPLA(2)β's reported ability to selectively hydrolyze DHA from phospholipid in vitro, iPLA(2)β deficiency reduces brain DHA metabolism and signaling in vivo at baseline and following M(1,3,5) receptor activation. Positron emission tomography might be used to image disturbed brain DHA metabolism in patients with PLA2G6 mutations.

Highlights

docosahexaenoic cytosolic PLA2 (DHA) incorporation coefficients k* and rates Jin, representing DHA metabolism, were determined using quantitative autoradiography in 81 brain regions. iPLA2␤؊/؊ or iPLA2␤+/؊ compared with iPLA2␤+/+ mice showed widespread and significant baseline reductions in in in ikbP*rLaaiAnn2d␤re؊Jgi/ni؊ofonarns dDofHiPiAPL.LAAA2␤r2e␤+/c+؊o/+lmimnieciceien. cCbruoetnaqssieusdtaenbntotittwahtiitpvhaerilPyamLleAes2st␤esr’oss reported ability to selectively hydrolyze DHA from phospholipid in vitro, iPLA2␤ deficiency reduces brain DHA metabolism and signaling in vivo at baseline and following
To minimize the effects of neuropathology that appear in older independent phospholipase A2␤ (iPLA2␤)Ϫ/Ϫ mice, we studied 4-month-old mice free of significant histopathology or neurological abnormalities [35]
An arecoline effect on plasma DHA was not determined, because the effect was statistically insignificant in a comparable prior study [34]

Summary

MATERIALS AND METHODS

Procedures were performed under a protocol approved by the Animal Care and Use Committee of the Eunice Kennedy Shriver National Institute of Child Health and Human Development in accordance with National Institutes of Health guidelines Four-month-old male iPLA2␤Ϫ/Ϫ, iPLA2␤+/Ϫ, and littermate iPLA2␤+/+ mice, derived from a C57BL/6 genetic background [24], were maintained in an animal facility with free access to water and food. The diet (PicoLab® Rodent Diet 20, 5053, LabDiet) contained soybean and fishmeal and 4.5% crude fat by weight. Gas-liquid chromatography showed that fatty acid concentrations (as percent of total fatty acid) were: 20.0% saturated, 22.2% monounsaturated, 47.8% linoleic, 5.1% ␣-LNA, 0.13% AA, 1.00% eicosapentaenoic, and 0.87% DHA (1.3 ± 0.0 ␮mol/g diet)

Surgical procedures and tracer infusion

RESULTS

DISCUSSION