GPAT3 is up-regulated during macrophage differentiation

QUIROGA IY; GONZALEZ, MC; COLEMAN, RA; PELLON MAISON, M; GONZALEZ-BARO, MR

Vermont

Congreso; FASEB Summer Research Conferences; 2014

Type-2 diabetes and obesity are characterized by an excessive accumulation of triacylglycerols (TAG) partially caused by a deregulation of glycerol-3-phosphate acyltransferases (GPATs) which catalyze the first step in de novo glycerolipid synthesis, and carnitine palmitoyl transferase 1 (CPT1) which regulates fatty acid oxidization.  In order to study the roles of these enzymes in monocyte-macrophage-foam-cell transition (a model of lipid accumulation during atherogenesis) we tested their expression by qRT-PCR in the murine macrophage RAW264.7 and the human THP-1 monocyte cell line differentiated into foam cells by oxidized LDL (oxLDL) and into macrophage by phorbol esters, respectively.  The treatment of macrophages with oxLDL increases lipid droplet size and number.  Although cholesterol esters are the major neutral lipids in this kind of lipid droplet, we also observed an increase in cellular TAG.  We then analyzed the expression and activity of the four mammalian GPAT isoforms.  Of the mitochondrial isoforms, GPAT1 expression did not change, and GPAT2 expression was negligible in both models.  We then analyzed the endoplasmic reticulum isoforms GPAT3 and 4.  Interestingly, GPAT3 expression increased 35-fold after 8 h of oxLDL exposure of macrophages and 6-fold after 12 h of PMA activation of monocytes.  In contrast, GPAT4 expression significantly increased only after 12 h in the monocyte to macrophage transition.  These results 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-regulated during RAW264.7 cell differentiation to foam cells and that a significant decrease was observed in the human macrophages derived from THP1 monocytes, suggesting that â-oxidation may not be highly active in macrophages, consistent with the anaerobic metabolism hallmark of M1 pro-inflammatory macrophages.