Ethanol Inhibits L1-mediated Neurite Outgrowth in Postnatal Rat Cerebellar Granule Cells

Abstract

The neuropathology of the effects of ethanol on the developing central nervous system are similar to those of patients with mutations in L1, a neural cell adhesion molecule. This observation suggests that inhibition of L1 plays a role in the pathogenesis of alcohol-related neurodevelopmental disorders. Here we examine the effects of ethanol on L1 homophilic binding and on L1-mediated neurite outgrowth. Ethanol had no effect on cell adhesion or aggregation in a myeloma cell line expressing full-length human L1. In contrast, the rate of L1-mediated neurite outgrowth of rat postnatal day 6 cerebellar granule cells grown on a substratum of Ng-CAM, the chick homologue of L1, was inhibited by 48.6% in the presence of ethanol with a half-maximal concentration of 4.7 mM. The same effect was found with soluble L1-Fc, thus showing that the inhibitory effect is not dependent on cell adhesion. In contrast, neither laminin nor N-cadherin-mediated neurite outgrowth was inhibited by physiologic concentrations of ethanol. We conclude that one mechanism of ethanol's toxicity to the developing central nervous system may be the inhibition of L1-mediated neurite outgrowth.Ethanol is a known human teratogen of immense public health concern. The characteristic pattern of malformations now called fetal alcohol syndrome (FAS) 1 was first described in 1968 (1). The criteria for diagnosis, established by the Fetal Alcohol Syndrome Study Group, are as follows: 1) pre-or postnatal growth retardation, 2) craniofacial dysmorphology including microphthalmia, and 3) neurologic abnormalities including mental retardation (2). Conservative estimates place the overall rate of FAS at 0.33/1000, with 1200 children/year born with FAS (3). Alcohol-related birth and neurodevelopmental defects are thought to be anywhere from 3-4 times as common as FAS (4). The Institute of Medicine has recently divided FAS and other effects into five separate categories, including a category for patients with only neurodevelopmental pathology, alcohol-related neurodevelopmental disorder (5). Although multiple organ systems are affected in FAS, the central nervous system appears to be particularly sensitive. The list of neuropathological anomalies found in FAS infants and children include neuronal-glial heterotopias, cerebellar dysplasia, agenesis of the corpus callosum, hydrocephalus, enlarged lateral ventricles, and microcephaly (2,4,6). Magnetic resonance imaging in 10 patients with FAS revealed central nervous system anomalies in all 10 (7). Six of these patients had midline defects including partial to complete agenesis of the corpus callosum, hypoplastic corpus callosum, cavum septum pellucidi, and cavum vergae. The other four had microcephaly.Overlap of the neuropathological abnormalities observed in FAS with those of patients with L1 mutations has led to the hypothesis that ethanol acts via disruption of L1-mediated events (8). L1 is a member of the Ig superfamily of cell adhesion molecules (9). L1 was initially identified when antibodies to L1 disrupted migratio...

Antagonists of alcohol inhibition of cell adhesion

“…Myeloma cells and insect S2 cells transfected with L1 were also insensitive to ethanol (14,21). In effect, 1-octanol converts L1-expressing NIH 3T3 cells from an ethanolsensitive to an ethanol-insensitive phenotype.…”

“…Because of the similarity in brain lesions in children with fetal alcohol syndrome and those with mutations in the gene for L1, we have speculated that ethanol effects on L1 could play a role in the pathophysiology of fetal alcohol syndrome (11). Interestingly, ethanol potently inhibits L1-mediated neurite extension in cerebellar granule cells (14).…”

An alcohol binding site on the neural cell adhesion molecule L1

“…Ethanol inhibits L1-mediated cell-cell adhesion (L1 adhesion) in NG108-15 neuroblastoma ϫ glioma hybrid cells, cerebellar granule cells, and selected human L1-transfected murine fibroblasts (3,4,7). Low concentrations of ethanol also inhibit L1-mediated neurite outgrowth (8). Third, drugs that block ethanol inhibition of L1 adhesion also prevent ethanol teratogenesis in mouse embryos (9-12).…”

L1 cell adhesion molecule found in human CSF varies as a function of age

“…This soluble form of L1 has been implicated in cell migration (Gutwein et al, 2000Mechtersheimer et al, 2001). The extracellular domain of L1 has been shown to be sufficient for mediating neurite outgrowth (Bearer et al, 1999;Fransen et al, 1998) suggesting that the 170-kDa soluble form may also enhance axon elongation. Thus, the soluble form of L1 may be important in CST development and regeneration.…”