Effects of Chronic Ethanol Consumption on Sterol Transfer Proteins in Mouse Brain

Abstract

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.

Sterol Carrier Protein-2 Alters High Density Lipoprotein-mediated Cholesterol Efflux

“…At nonsaturating conditions of HDL, the predominant effect was that of inhibition by SCP-2 expression, whereas at higher HDL level maximal efflux (but not above controls) occurred and overcame inhibition by SCP-2 expression. Substantial evidence in vivo and in vitro is consistent with the interpretation that SCP-2 promotes retention of cholesterol in cells (7,22,30,(41)(42)(43)(44)(45)(46)(47)(48)(49)(50) for utilization in steroidogenesis (27,51), secretion in bile (reviewed in Refs. 23-25, 52, and 53), or secretion as lipoproteins (22).…”

Sterol Carrier Protein-2 Expression Modulates Protein and Lipid Composition of Lipid Droplets

“…untransfected and mock-transfected) (39). Thus, the levels of SCP-2 expression in both SCP-2 overexpressing and in control cells were in the range of those reported for murine tissues (0.01-0.08% of cytosolic proteins) (49). For immunocytochemistry experiments, cells were seeded at a density of 50,000 cells/chamber onto Lab-Tek chamber coverglass slides.…”

FABP1: A Novel Hepatic Endocannabinoid and Cannabinoid Binding Protein

“…Importantly, pharmacological inhibition or ablation of these FABPs found in brain inhibits EC degradation, thereby enhancing EC accumulation and physiological action in brain (7–10). Surprisingly, although the liver form of fatty acid binding protein (FABP1) is not detectable in brain (11–13), nevertheless ablation of FABP1 markedly increases brain EC levels—especially AEA and 2-AG (13). The proposed mechanism whereby FABP1 gene ablation increases brain AEA and 2-AG levels is by its ability to bind ARA such that loss of FABP1 decreases hepatic ARA clearance, increases serum ARA availability for brain uptake, and increases brain ARA substrate for brain synthesis of AEA and 2-AG (13).…”