XBP-1 REGULATION OF ARACHIDONIC ACID AND GLICEROLIPIDS METABOLISM IN RENAL EPITHELIAL CELLS UNDER OSMOTIC STRESS

PARRA, LEANDRO; CASALI, CECILIA I.; ERJAVEC, LUCIANA C.; MOREL GÓMEZ, EMANUEL; SETTON-AVRUJ, PATRICIA C.; FERNÁNDEZ TOME, MARÍA C.

CABA

Congreso; LVII Annual Meeting of the Argentine Society for Biochemistry and Molecular Biology Research (SAIB) - XVI Annual Meeting of the Argentinean Society for General Microbiology (SAMIGE); 2021

SAIB (Sociedad Argentina de Investigación Bioquímica y en Biología Molecular)

Hyperosmolarity is a key controversial signal for renal cells. Under physiological conditions, it induces renal celldifferentiation and maturation of urine concentrating system. However, abrupt changes in environmental osmolaritymay also induce cell stress that can lead to death. To adapt and survive in such adverse conditions, renal cells implementdifferent osmoprotective mechanisms that includes both the upregulation of cyclooxygenase-2 (COX-2) expression andprostaglandins (PGs) synthesis from arachidonic acid (AA), and a coordinated increase in phospholipids (PL) andtriacylglycerides (TAG) biosynthesis. We previously shown that hyperosmolarity induces ER stress and activates theunfolded protein response (UPR) in Madyn Darby Canine Kidney Cells (MDCK) through IRE1α-XBP1s pathway, andthat XBP1s modulates lipid synthesis regulating lipogenic enzymes expression. In the present work we evaluated howXBP1s modulates phospholipase A2 (PLA2)/COX-2/PGs pathway and its relationship with lipid synthesis inductionunder osmotic stress. MDCK cells were subjected to hyperosmolarity (298-512 mOsm/kg H2O) for different periodsof time (0, 12, 24 and 48 h) and treated with different PLA2 (cPLA2, iPLA2 and sPLA2) and IRE1α inhibitors. RT-PCR studies showed that hyperosmolarity increased cPLA2 expression at 24 and 48 h but did not upregulate iPLA2expression. Inhibition of cPLA2 but not iPLA2 nor sPLA2 prevented hyperosmolarity-induced lipid synthesis and lipiddroplets accumulation. Furthermore, IRE1α RNase activity inhibition was accompanied by a decrease in cPLA2 andCOX-2 but not in iPLA2 expression evaluated by RT-PCR. Instead, western blot analysis showed a significant increasein COX-2 protein levels when xbp1 (u) splicing was blocked by IRE1α inhibitor. Our findings suggest that the UPRmodulates glycerolipids metabolism under osmotic stress by regulating cPLA2/COX-2/PGs axis.