Ethanol Impairs Insulin-stimulated Neuronal Survival in the Developing Brain

Abstract

Gestational exposure to ethanol causes fetal alcohol syndrome, which is associated with cerebellar hypoplasia. Previous in vitro studies demonstrated ethanol-impaired neuronal survival with reduced signaling through the insulin receptor (IR␤). We examined insulin signaling in an experimental rat model of chronic gestational exposure to ethanol in which the pups exhibited striking cerebellar hypoplasia with increased apoptosis. Immunoprecipitation and Western blot analyses detected reduced levels of tyrosyl-phosphorylated IR␤, tyrosyl-phosphorylated insulin receptor substrate-1 (IRS-1), and p85-associated IRS-1 but no alterations in IR␤, IRS-1, or p85 protein expression in cerebellar tissue from ethanol-exposed pups. In addition, ethanol exposure significantly reduced the levels of total phosphoinositol 3-kinase, Akt kinase, phospho-BAD (inactive), and glyceraldehyde-3-phosphate dehydrogenase and increased the levels of glycogen synthase kinase-3 activity, activated BAD, phosphatase and tensin homolog deleted in chromosome 10 (PTEN) protein, and PTEN phosphatase activity in cerebellar tissue. Cerebellar neurons isolated from ethanol-exposed pups had reduced levels of insulin-stimulated phosphoinositol 3-kinase and Akt kinase activities and reduced insulin inhibition of PTEN and glycogen synthase kinase-3 activity. The results demonstrate that cerebellar hypoplasia produced by chronic gestational exposure to ethanol is associated with impaired survival signaling through insulin-regulated pathways, including failure to suppress PTEN function.Ethanol exposure during development is one of the leading causes of mental retardation in Europe and North America. Heavy gestational exposure to ethanol can cause fetal alcohol syndrome, which encompasses a broad array of neurologic and systemic lesions including central nervous system (CNS) malformations such as microencephaly, reduced cerebral white matter volume, ventriculomegaly, cerebellar hypoplasia, and disorders of neuronal migration (1). Experimental models of fetal alcohol syndrome have demonstrated that the accompanying CNS abnormalities are associated with impaired neuronal survival, growth, synaptogenesis, maturation, neurotransmitter function, and intracellular adhesion (2-7). Even with shorter durations and lower levels of exposure, ethanol can be neurotoxic during development and substantially reduce the populations of CNS neurons (2).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, 11-13). 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. Because insulin and IGF-1 signaling pathways are among the important tar...

Lithium blocks ethanol-induced modulation of protein kinases in the developing brain

“…1), as reported earlier [23]. Although the upstream events triggered by ethanol, which leads to caspase-3 activation in the brain, have not been fully elucidated, involvement of the PI3K/Akt pathway has been implicated [4,[8][9][10]. We found that ethanol reduced phospho-Akt and phospho-GSK-3β levels without changing the levels of Akt and GSK-3β at 4 h after the first ethanol injection (Fig.…”

“…Previous studies using cultured neurons indicate that ethanol perturbs functions of neurotrophic factors (such as brain-derived neurotrophic factor and insulin-like growth factor-I) probably through blockade of NMDA receptors [7][8][9] leading to the inhibition of PI3K [8,9]. The suppression of Akt [4] and activation of GSK-3 [10], downstream effects of PI3K inhibition, have also been reported in the developing brain exposed to ethanol. Our recent study showed that apoptotic neurodegeneration in P7 mice induced by acute ethanol exposure was accompanied by inactivation of Akt and activation of GSK-3β, which was indicated by decreases in phosphorylation levels of both protein kinases [11].…”

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“…Similar effects of serum withdrawal were also seen in cultured Neuroblastoma-2a cells [45]. Thus it seems that the reduction in PTEN expression to alcohol during gestation [47]. In this model the mice showed marked cerebellar hypoplasia and cell death indicating a correlation of PTEN with neuronal death [47].…”