Insulin action on polyunsaturated phosphatidic acid formation in rat brain: An "in vitro" model with synaptic endings from cerebral cortex na hippocampus

ZULIAN, S.E.; IINCHETA DE BOSCHERO, ´M.G.; GIUSTO, N.M.

NEUROCHEMICAL RESEARCH

SPRINGER/PLENUM PUBLISHERS

Año: 2009 vol. 34 p. 1236 - 1248

0364-3190

Abstract The highly efficient formation of phosphatidicacid from exogenous 1-stearoyl-2-arachidonoyl-sn-glycerol(SAG) in rat brain synaptic nerve endings (synaptosomes)from cerebral cortex and hippocampus is reported. Phos-phatidic acid synthesized from SAG or 1,2-dipalmitoyl-sn-glycerol (DPG)was 17.5 or 2.5 times higher, respectively,than from endogenous synaptosomal diacylglycerides.Insulin increased diacylglycerol kinase (DAGK) action onendogenous substrate in synaptic terminals from hippo-campus and cerebral cortex by 199 and 97%, respectively.Insulin preferentially increased SAG phosphorylation fromhippocampal membranes. In CC synaptosomes insulinincreased phosphatidic acid (PA) synthesis from SAG by100% with respect to controls. Genistein (a tyrosine kinaseinhibitor) inhibited this stimulatory insulin effect. Okadaicacid or cyclosporine, used as Ser/Threo protein phosphataseinhibitors, failed to increase insulin effect on PA formation.GTPcS and particularly NaF were potent stimulators of PAformation from polyunsaturated diacylglycerol but failed toincrease this phosphorylation when added after 5 min ofinsulin exposure. GTPcS and NaF increased phosphatidyl-inositol 4,5 bisphosphate (PIP2) labeling with respect tocontrols when SAG was present. On the contrary, theydecreased polyphosphoinositide labeling with respect tocontrols in the presence of DPG. Our results indicate that aDAGK type 3 (DAGKe) which preferentially, but notselectively, utilizes 1-acyl-2-arachidonoyl-sn-glycerol andwhich could be associated with polyphosphoinositideresynthesis, participates in synaptic insulin signaling.GTPcS and NaF appear to be G protein activators related toinsulin and the insulin receptor, both affecting the signalingmechanism that augments phosphatidic acid formation.