GPAT EXPRESSION IN MACROPHAGE DIFFERENTIATION MODELS

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

New Yersey

Congreso; Lipids and Methabolic Diseases Symposium; 2015

Type-2 diabetes and obesity arecharacterized by an excessive accumulation of triacylglycerols (TAG) partiallycaused by a deregulation of glycerol-3-phosphate acyltransferases (GPATs) whichcatalyze the first step in de novo glycerolipid synthesis. In order to studythe role of these enzymes in monocyte-macrophage-foam-cell transition (a modelof lipid accumulation during atherogenesis) and in macrophage activation (amodel of inflammation) we tested Gpat expression by qRT-PCR in the murinemacrophage RAW264.7 either differentiated into foam cells by oxidized LDL(oxLDL) or activated by Kdo2-Lipid A (KLA), and in the human THP-1monocyte cell line differentiated into macrophage by phorbol esters (PMA).  The treatment of macrophages with oxLDL and KLAincreased lipid droplet size and number, as well as cellular TAG content.  We then analyzed the expression and activityof the four mammalian GPAT isoforms.  Ofthe mitochondrial isoforms, GPAT1 expression decreased in RAW cells after oxLDLand KLA treatment and did not change in THP-1 cells, and GPAT2 expression wasnegligible in the three models.  We thenanalyzed the endoplasmic reticulum isoforms GPAT3 and 4.  Interestingly, GPAT3 expression increased35-fold after 8 h of oxLDL treatment, 6-fold after 8 h exposureof macrophages, and 6-fold after 12 h of PMA activation of monocytes.  GPAT4 expression significantly increasedafter 8 h in macrophage activation and after 12 h in the monocyte to macrophagetransition.  These data were consistentwith GPAT activity assays, since N-ethylmaleimide (NEM) sensitive activity(GPAT2, 3 and 4) increased after oxLDL and KLA treatment, correlating withGPAT3 and 4 expressions. These results suggest that GPAT3 could be responsiblefor the increase in the total glycerolipid content during all the macrophagedifferentiation processes studied, and GPAT4 could contribute to thisaccumulation during macrophage activation.