Impact of Fabp1 Gene Ablation on Uptake and Degradation of Endocannabinoids in Mouse Hepatocytes |
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| Authors: | Avery L McIntosh Huan Huang Danilo Landrock Gregory G Martin Shengrong Li Ann B Kier Friedhelm Schroeder |
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| Affiliation: | 1. Departments of Physiology and Pharmacology, Texas A&M University, 664 Raymond Stotzer Pkwy, 4466 TAMU, College Station, TX 77843‐4466, USA;2. Departments of Pathobiology, Texas A&M University, 664 Raymond Stotzer Pkwy, 4467 TAMU, College Station, TX 77843‐4467, USA;3. Avanti Polar Lipids, 700 Industrial Park Drive, Alabaster, AL 35007‐9105, USA |
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| Abstract: | Liver fatty‐acid‐binding protein (FABP1, L‐FABP) is the major cytosolic binding/chaperone protein for both precursor arachidonic acid (ARA) and the endocannabinoid (EC) products N‐arachidonoylethanolamine (AEA) and 2‐arachidonoylglycerol (2‐AG). Although FABP1 regulates hepatic uptake and metabolism of ARA, almost nothing is known regarding FABP1’s impact on AEA and 2‐AG uptake, intracellular distribution, and targeting of AEA and 2‐AG to degradative hepatic enzymes. In vitro assays revealed that FABP1 considerably enhanced monoacylglycerol lipase hydrolysis of 2‐AG but only modestly enhanced AEA hydrolysis by fatty‐acid amide hydrolase. Conversely, liquid chromatography–mass spectrometry of lipids from Fabp1 gene‐ablated (LKO) hepatocytes confirmed that loss of FABP1 markedly diminished hydrolysis of 2‐AG. Furthermore, the real‐time imaging of novel fluorescent NBD‐labeled probes (NBD‐AEA, NBD‐2‐AG, and NBD‐ARA) resolved FABP1’s impact on uptake vs intracellular targeting/hydrolysis. FABP1 bound NBD‐ARA with 2:1 stoichiometry analogous to ARA, but bound NBD‐2‐AG and NBD‐AEA with 1:1 stoichiometry—apparently at different sites in FABP1’s binding cavity. All three probes were taken up, but NBD‐2‐AG and NBD‐AEA were targeted to lipid droplets. LKO reduced the uptake of NBD‐ARA as expected, significantly enhanced that of NBD‐AEA, but had little effect on NBD‐2‐AG. These data indicated that FABP1 impacts hepatocyte EC levels by binding EC and differentially impacts their intracellular hydrolysis (2‐AG) and uptake (AEA). |
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| Keywords: | AEA 2‐AG Endocannabinoid FAAH FABP1 Hepatocyte MAGL Mouse |
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