ETHANOL INDUCES APOPTOSIS IN CEREBELLAR GRANULE NEURONS BY INHIBITINGINSULIN-LIKE-GROWTH-FACTOR-1 SIGNALING

The ability of ethanol to interfere with insulinlike growth factor 1 ( IGF-1)-mediated cell survival was examined in primary cultured cerebel lar granule neurons. Cells underwent apoptosis when switched from medi um containing 25 mM K+ to one containing 5 mM K+. IGF-1 protected gran ule neurons from apoptosis in medium containing 5 mM K+. Ethanol inhib ited IGF-1-mediated neuronal survival but did not inhibit IGF-1 recept or binding or the neurotrophic action of elevated K+, and failed to po tentiate cell death in the presence of 5 mM K+. Inhibition of neuronal survival by ethanol was not reversed by increasing the concentration of IGF-1. Significant inhibition by ethanol (15-20%) was observed at 1 mM and was half-maximal at 45 mM. The inhibition of IGF-I protection by ethanol corresponded to a marked reduction in the phosphorylation o f insulin receptor substrate 1, the binding of phosphatidylinositol 3- kinase (PI 3-kinase), and a block of IGF-1-stimulated PI 3-kinase acti vity. The neurotrophic response of IGF-1 was also inhibited by the PI 3-kinase inhibitor LY294002, the protein kinase C inhibitor chelerythr ine chloride, and the protein kinase A inhibitor KT5720, but unaffecte d by the mitogen-activated protein kinase kinase inhibitor PD 98059. T hese data demonstrate that ethanol promotes cell death in cerebellar g ranule neurons by inhibiting the antiapoptotic action of IGF-1.