Sexually dimorphic metabolism of branched-chain lipids in C57BL/6J mice

Abstract

Despite the importance of branched chain lipid oxidation in detoxification, almost nothing is known regarding factors regulating peroxisomal uptake, targeting, and metabolism. One peroxisomal protein, sterol carrier protein-x (SCP-x), is thought to catalyze a key thiolytic step in branched chain lipid oxidation. When mice with substantially lower hepatic levels of SCP-x were tested for susceptibility to dietary stress with phytol (a phytanic acid precursor and peroxisome proliferator), livers of phytol-fed female but not male mice i ) accumulated phytol metabolites (phytanic acid, pristanic acid, and ⌬ -2,3-pristanic acid); ii ) exhibited decreased fat tissue mass and increased liver mass/ body mass; iii ) displayed signs of histopathological lesions in the liver; and iv ) demonstrated significant alterations in hepatic lipid distributions. Moreover, both male and female mice exhibited phytol-induced peroxisomal proliferation, as demonstrated by liver morphology and upregulation of the peroxisomal protein catalase. In addition, levels of liver fatty acid binding protein, along with SCP-2 and SCP-x, increased, suggesting upregulation mediated by phytanic acid, a known ligand agonist of the peroxisomal proliferator-activated receptor ␣ . In summary, the present work establishes a role for SCP-x in branched chain lipid catabolism and demonstrates a sexual dimorphic response to phytol, a precursor of phytanic acid, in lipid parameters and hepatotoxicity.

Overexpression of sterol carrier protein-2 differentially alters hepatic cholesterol accumulation in cholesterol-fed mice

“…of the mature 13 kDa SCP-2 (derived from complete posttranslational cleavage of the 15 kDa pro-SCP-2) in the SCP-2-overexpressing mice were well within the range of SCP-2 protein expression in response to normal physiological and pharmacological conditions where levels of SCP-2 can range nearly 3-fold in response to i) dietary branched-chain fatty acids that, acting as peroxisomal proliferator agents, upregulate SCP-2 nearly 2-fold in both male and female mice (22); and ii) drug-induced diabetes and cholesterol lowering drugs that downregulate SCP-2 expression 25-90% (reviewed in Ref. 18).…”

“…Lipid standards were purchased from Nu-Chek Prep (Elysian, MN). Rabbit polyclonal antibodies directed against mouse SCP-2 (recognizing 58 kDa SCP-x, 15 kDa pro-SCP-2, and 13.2 kDa SCP-2) and rat liver fatty acid binding protein (L-FABP) were prepared as described earlier (21,22). Rabbit polyclonal antibodies were purchased from the following sources: anticaveolin-1 from BD Transduction Laboratories (Lexington, KY); anti-3a-hydroxysteroid dehydrogenase from USBiological (Swampscott, MA); anti-ABCA-1 and anti-SR-B1 from Novus Biologicals (Littleton, CO); anti-sterol regulatory element binding protein 1 (SREBP-1), anti-membraneassociated protein 17 kDa (MAP-17), and postsynaptic density protein/Drosophila disc large tumor suppressor (dlg)/tight junction protein (ZO1) (PDZK1) from Santa Cruz Biotechnology (Santa Cruz, CA); anti-HMG-CoA reductase from Upstate Cell Signaling Solutions (Lake Placid, NY); and anti-ACAT2 from Cayman Chemical (Ann Arbor, MI).…”

“…Briefly, since each protein of interest and the housekeeping gene GAPDH was easily resolved by size on the tricine gels, the membranes were cut into two so that each Western blot was probed with antisera against the protein of choice and GAPDH. Proteins were quantified by densitometric analysis after image acquisition using a single-chip CCD video camera and a computer workstation (IS-500 system from Alpha Innotech, San Leandro, CA) (22). Image files were analyzed (mean 8-bit gray-scale density) using ImageJ.…”

“…Levels of SCP-2 in the liver, kidney, heart, brain, and intestine from control-fed male and female WT and SCP-2 overexpression mice were determined by Western blotting as described in (22). In order to determine whether SCP-2 overexpression and/or a cholesterol-rich diet altered levels of key proteins involved in lipid metabolism, protein levels in male and female WT and SCP-2 overexpression mice on control and cholesterol (1.25%) diets were measured by Western blotting as described in (22) in the following groups: i) proteins that bind/transport cholesterol and bile acids, including SCP-2, L-FABP, caveolin-1, and 3a-hydroxysteroid dehydrogenase (3a-HSD); ii) proteins involved in cholesterol uptake, efflux, and storage, such as LDL-receptor, SR-B1, PDZK1, MAP-17, ABCA-1, apolipoprotein A1 (apoA1), and ACAT2; and iii) enzymes and nuclear receptors involved in cholesterol and bile acid synthesis, including HMG-CoA reductase, CYP7A1, CYP27A1, SCP-x, LXR-a, and SHP.…”

“…The anesthetized mice were then euthanized by cervical dislocation, and livers were harvested and weighed. Liver slices were excised for morphological examination of lipid droplets with remaining portions snap-frozen on dry ice and stored at 280°C for lipid and Western analyses as described in (22).…”