GPAT3 is up-regulated during macrophage differentiation

QUIROGA, I.Y.; GONZALEZ, M.C.; COLEMAN, R.A.; PELLON-MAISON, M.; GONZALEZ BARO, M.R.

Saxtons River

Congreso; FASEB Science Research Conferences- Lipid droplets and molecular consequences of neutral lipid storage; 2014

FASEB

Type-2 diabetes and obesity are characterized by an excessiveaccumulation of triacylglycerols (TAG) partially caused by a deregulation ofglycerol-3-phosphate acyltransferases (GPATs) which catalyze the first step in denovo glycerolipid synthesis, and carnitine palmitoyl transferase 1 (CPT1) whichregulates fatty acid oxidization.  Inorder to study the roles of these enzymes in monocyte-macrophage-foam-celltransition (a model of lipid accumulation during atherogenesis) we tested theirexpression by qRT-PCR in the murine macrophage RAW264.7 and the human THP-1monocyte cell line differentiated into foam cells by oxidized LDL (oxLDL) andinto macrophage by phorbol esters, respectively.  The treatment of macrophages with oxLDLincreases lipid droplet size and number. Although cholesterol esters are the major neutral lipids in this kind oflipid droplet, we also observed an increase in cellular TAG.  We then analyzed the expression and activityof the four mammalian GPAT isoforms.  Ofthe mitochondrial isoforms, GPAT1 expression did not change, and GPAT2expression was negligible in both models.  We then analyzed the endoplasmic reticulum isoformsGPAT3 and 4.  Interestingly, GPAT3expression increased 35-fold after 8 h of oxLDL exposure of macrophages and 6-foldafter 12 h of PMA activation of monocytes. In contrast, GPAT4 expression significantly increased only after 12 h inthe monocyte to macrophage transition.  Theseresults were consistent with GPAT activity assays, since N-ethylmaleimide(NEM) sensitive activity (GPAT2, 3 and 4) but not NEM resistant activity(GPAT1) increased after oxLDL treatment, correlating with GPAT3 expression.  We also found that CPT1a was up-regulatedduring RAW264.7 cell differentiation to foam cells and that a significantdecrease was observed in the human macrophages derived from THP1 monocytes,suggesting that β-oxidation may not be highly active in macrophages, consistentwith the anaerobic metabolism hallmark of M1 pro-inflammatory macrophages.