CONICET | Buscador de Institutos y Recursos Humanos

*Both must be considered as first author.Hyperosmolarity is a key controversial signal for renal cells. Under physiological conditions, it induces renal cell differentiation and maturationof urine concentrating system. However, abrupt changes in environmental osmolarity may also induce cell stress that can lead to death. Bothconditions require lipid synthesis either for membrane expansion or for osmoprotection. In Madin-Darby canine kidney (MDCK) cells weshowed that hyperosmolarity upregulates phospholipid (PL) as well as triglycerides (TAG) de novo synthesis. We also showed thathyperosmolarity activates SREBP-mediated transcriptional regulation of lipogenic genes such us lipin and diacylglycerol acyltransferase(DGAT) enzymes. In the present work we evaluated which signaling pathway mediates hyperosmolarity upregulation of lipid. MDCK weresubjected to hyperosmolality (298-512 mOsm/kg H2O) for 48h, treated with different phospholipases (PLA2, PLD, PLC-PI and PLC-PC) orkinases (PI3K, PKC or MAPKs) inhibitors and labeled using [14C]-Glycerol. After treatments, lipids were extracted, separated by TLC andquantified. Neither MAPKs inhibitors nor PKC and PI3K were mediating TAG, but not PL, synthesis. PLC-PI and PLC-PC inhibitors increasedPL and TAG synthesis; PLD activity was also involved in PL and TAG homeostasis. cPLA2 inhibitors prevented hyperosmotic-induced lipidsynthesis. Such decrease seemed to be due to a down regulation of lipin2 and DGAT1 and DGAT2 expression which were evaluated by RTPCR. As PLA2 activity generates arachidonic acid (AA) to form prostaglandins (PGs), we evaluated the effect of PGs synthesis inhibitor in lipidsynthesis; either indomethacin or NS398 significantly increased lipid metabolism. Thus, hyperosmolar induced lipid metabolism is modulated bydifferent signaling systems, specially by the axis PLA2 ? COX2.