Ethanol Induces Apoptosis in Cerebellar Granule Neurons by Inhibiting Insulin‐Like Growth Factor 1 Signaling

Abstract

The ability of ethanol to interfere with insulinlike growth factor 1 (IGF-1 )-mediated cell survival was examined in primary cultured cerebellar granule neurons. Cells underwent apoptosis when switched from medium containing 25 mM Kto one containing 5 mM K~. IGF-1 protected granule neurons from apoptosis in medium containing 5 mM K~.Ethanol inhibited IGF-1-mediated neuronal survival but did not inhibit IGF-1 receptor binding or the neurotrophic action of elevated K~,and failed to potentiate 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-1 protection by ethanol corresponded to a marked reduction in the phosphorylation of insulin receptor substrate 1, the binding of phosphatidylinositol 3-kinase (P1 3-kinase), and a block of IGF-1 -stimulated P1 3-kinase activity. The neurotrophic response of IGF-1 was also inhibited by the P1 3-kinase inhibitor LY294002, the protein kinase C inhibitor chelerythrine chloride, and the protein kinase A inhibitor KT5720, but unaffected by the mitogen-activated protein kinase kinase inhibitor PD 98059. These data demonstrate that ethanol promotes cell death in cerebellar granule neurons by inhibiting the antiapoptotic action of IGF-1. Key Words: Ethanol-Insulin-like growth factor 1 -Apoptosis-Cerebellar granule neurons.

Ethanol Impairs Insulin-stimulated Neuronal Survival in the Developing Brain

“…Ethanol impairs neuronal growth and viability in the developing CNS by inhibiting growth factor-stimulated signaling mechanisms (9,11,13,18,51). Previous in vitro studies showed that ethanol inhibition of insulin-stimulated cell growth and viability were mediated by reduced activation of mitogen-activated protein kinase (42,43) and PI3 kinase (11,47).…”

“…Previous experiments demonstrated that neuronal loss following ethanol exposure was mediated by apoptosis (8 -10) or mitochondrial dysfunction (10 -12), and recent studies correlated these adverse effects of ethanol to inhibition of growth factor-stimulated survival signaling (9,(11)(12)(13). In the developing CNS, insulin and insulin-like growth factor type 1 (IGF-1) 1 receptors are abundantly expressed (14 -16), and the corresponding growth factor-stimulated responses are critical mediators of neuronal growth, viability, energy metabolism, and synapse formation.…”

“…In the developing CNS, insulin and insulin-like growth factor type 1 (IGF-1) 1 receptors are abundantly expressed (14 -16), and the corresponding growth factor-stimulated responses are critical mediators of neuronal growth, viability, energy metabolism, and synapse formation. Because insulin and IGF-1 signaling pathways are among the important targets of ethanol neurotoxicity in immature nervous system (9,13,17,18), neuronal loss associated with microencephaly in ethanol-exposed fetuses may be caused, in part, by ethanol inhibition of insulin/IGF-1-stimulated survival mechanisms.…”

In Utero Ethanol Suppresses Cerebellar Activator Protein-1 and Nuclear Factor-κB Transcriptional Activation in a Rat Fetal Alcohol Syndrome Model

“…Neurotrophic factors can protect cells from programmed death (Cui et al, 1997;Luo et al, 1997;Zhang et al, 1998;Ikonomidou et al, 1999). There is evidence that some neurotrophic factors activate AP-1 and/or NF-B.…”

Association of Heterotrimeric Gi with the Insulin-like Growth Factor-I Receptor

“…Rat cerebellar granule neurons were prepared from 7-day-old rat pups as reported previously (42,43). Briefly, cerebella were obtained from postnatal day 7 Harlan Sprague-Dawley rat pups, cross-chopped (400 ϫ 400 M), and then treated with 0.025% trypsin-EDTA (including 0.01% DNase I) for 15 min, 37°C.…”