Ethanol causes the redistribution of L1 cell adhesion molecule in lipid rafts

Abstract

Fetal alcohol spectrum disorder is estimated to affect 1% of live births. The similarities between children with fetal alcohol syndrome and those with mutations in the gene encoding L1 cell adhesion molecule (L1) implicates L1 as a target of ethanol developmental neurotoxicity. Ethanol specifically inhibits the neurite outgrowth promoting function of L1 at pharmacologic concentrations. Emerging evidence shows that localized disruption of the lipid rafts reduces L1-mediated neurite outgrowth. We hypothesize that ethanol impairment of the association of L1 with lipid rafts is a mechanism underlying ethanol's inhibition of L1-mediated neurite outgrowth. In this study, we examine the effects of ethanol on the association of L1 and lipid rafts. We show that, in vitro, L1 but not N-cadherin shifts into lipid rafts following treatment with 25 mM ethanol. The ethanol concentrations causing this effect are similar to those inhibiting L1-mediated neurite outgrowth. Increasing chain length of the alcohol demonstrates the same cutoff as that previously shown for inhibition of L1-L1 binding. In addition, in cerebellar granule neurons (CGN) in which lipid rafts are disrupted with methyl-beta-cyclodextrin (MBCD), the rate of L1-mediated neurite outgrowth on L1-Fc is reduced to background rate and that this background rate is not ethanol sensitive. These data indicate that ethanol may inhibit L1-mediated neurite outgrowth by retarding L1 trafficking through a lipid raft compartment.

Choline Partially Prevents the Impact of Ethanol on the Lipid Raft Dependent Functions of L1 Cell Adhesion Molecule

“…We have shown the ethanol interferes with this trafficking both in vivo and in vitro , and disrupts L1 signaling (Fig. 2 – 8, (Yeaney et al, 2009; Littner et al, 2013; Tang et al, 2006; Tang et al, 2011; Tang et al, 2011)). Recent evidence from several laboratories supports the important role of lipid rafts in ethanol toxicity (Sebastian and Nagy, 2005; Szabo et al, 2007; Blanco et al, 2008).…”

“…We have previously shown that ethanol alters the distribution of L1 in lipid rafts both in vitro (Tang et al, 2011) and in vivo (Littner et al, 2013). As shown in Figure 7, choline addition alone did not alter L1 distribution in lipid rafts.…”

“…L1 functions through signaling cascades and protein trafficking, most notably trafficking through lipid rafts (Tang et al, 2011; Nakai and Kamiguchi, 2002). We have shown the ethanol interferes with this trafficking both in vivo and in vitro , and disrupts L1 signaling (Fig.…”

“…Cells were viewed on a Zeiss Observer Z1 fluorescence inverted microscope (Carl Zeiss, Oberkochen, Germany). Images were captured using Axiovision camera software (Carl Zeiss), and neurite length was measured using Image J software (National Institutes of Health, Bethesda, MD) (Bearer et al, 1999; Tang et al, 2011). …”

“…L1-mediated neurite outgrowth is dependent on L1-lipid raft interactions. Neurite outgrowth on L1 is inhibited in the presence of lipid raft disrupting agents: 1) methyl-β-cyclodextrin, a cholesterol chelator (Tang et al, 2011; Nakai and Kamiguchi, 2002), 2) lovastatin, an inhibitor of cholesterol synthesis (Nakai and Kamiguchi, 2002); and 3) fumonisin B1, an inhibitor of sphingolipid synthesis (Nakai and Kamiguchi, 2002). Ethanol exposure increases the proportion of L1 present in lipid rafts, but not N-cadherin, both i n vitro and in vivo (Littner et al, 2013; Tang et al, 2011) suggesting an impact of ethanol on protein trafficking through lipid rafts.…”