Effects of chronic ethanol consumption on sterol transfer proteins in mouse brain

Although lipids are essential to brain function, almost nothing is known of lipid transfer proteins in the brain. Early reports indicates cross-reactivity of brain proteins with antisera against two native liver sterol transfer proteins, sterol carrier protein-2 (SCP-2) and the liver form of fatty acid-binding protein (L-FABP). Herein, polyclonal antibodies raised against the recombinant liver sterol transfer proteins SCP-2 and L-FABP were used to identify the lipid transfer proteins in the brains of alcohol-treated and control mice. L-FABP was not detectable in brain of either control or chronic ethanol-treated mice. In contrast, SCP-2 not only was present, but its level was significantly (p < 0.05) increased 23 and 50%, respectively, in brain homogenates and synaptosomes of mice exposed to alcohol. To determine whether antibodies against the recombinant liver SCP-2 reflected true levels of SCP-2 in brain, the cDNA sequence for brain SCP-2 was isolated from a brain cDNA library. The mouse brain SCP-2 sequence was 99.99% identical to the mouse liver SCP-2 sequence. The translated sequence differed by only one amino acid, and the replacement was conservative. Thus, unlike the fatty acid binding proteins, the SCP-2 moieties of brain and liver are essentially identical. Polyclonal antibodies against acyl-CoA binding protein, a lipid-binding protein that does not bind or transfer sterol, showed that increased levels of brain SCP-2 with chronic ethanol consumption did not represent a general increase in content of all lipid transfer proteins. Changes in the amount of SCP-2 may contribute to membrane tolerance to ethanol.