GPAT3 AND GPAT4 DIRECT GLYCEROLIPID DE NOVO SYNTHESIS DURING MACROPHAGE TO FOAM CELL TRANSITION AND THEIR DOWN-REGULATION ALTERS CYTOKINE RELEASE

QUIROGA YOSELY; COLEMAN R; GONZALEZ MARINA CECILIA; PELLÓN MAISON, M.; GONZALEZ BARÓ, MARÍA DEL ROSARIO

Buenos Aires

Congreso; REUNIÓN CONJUNTA DE SOCIEDADES DE BIOCIENCIAS; 2017

Diez Organizaciones Argentinas de Biociencias

Glycerol-3-phosphate acyltransferase (GPAT) initiates de novo glycerolipid synthesis. To study the role of GPAT isoforms during the macrophage to foam cell transition, a model of lipid accumulation during atherosclerosis, we analyzed the expression of the four mammalian GPAT isoforms by qRT-PCR in murine RAW264.7 macrophages and primary bone marrow derived macrophages (BMDM) after oxidized LDL (oxLDL) exposure. The endoplasmic reticulum isoform GPAT3 expression increased 32 and 8-fold after 8 and 24h of treatment, respectively. These data were consistent with an increment in GPAT3/4 activity in both models. The lipid droplet area, as well as triacylglycerol (TAG) and phospholipid (PL) contents also increased after oxLDL treatment. To establish the role of GPAT3 and 4 during macrophage to foam cell transition, we silenced GPAT3 in RAW 264.7 cells (shGpat3 cell line) and obtained BMDM form Gpat3-/- and Gpat4-/- mice. GPAT3 and GPAT4 deficient foam cells accumulate ~30-40 % less LDs, ~25-40% less TAG and ~20% less PL compared to wt or SCR control foam cells. We also analyzed the incorporation of [14C]-acetate and [14C]-oleic acid into lipids during shGpat3 cells, Gpat3-/- and Gpat4-/- BMDM transition to foam cells. We detected fewer counts in total lipids, mainly in the TAG fraction when GPAT3 and 4 were absent or silenced. To investigate the effect of an impaired lipid synthesis due to GPAT3 or GPAT4 deficiency on the inflammatory response, we analyzed the cytokine release in Gpat3-/- and Gpat4-/- BMDM. Cytokine secretion after foam cell transition increased when GPAT4 was absent; while no clear effect was observed in GPAT3 deficient cells. Taken together, these results prove that GPAT3 and 4 contribute to the increase in total glycerolipid content due to an increase in de novo synthesis during macrophage to foam cell transition and that GPAT4 is required to regulate cytokine release during this process.