Faculty Bibliography

The widely used mouse air pouch model of acute inflammation is inducible in a variety of inbred strains, but the potential influence of genetic background and gender on inflammation severity has never been examined. We directly compared the degree of inflammation induced in the air pouch model across four commonly utilized inbred strains in both male and female mice. We then applied an in silico mapping method to identify loci potentially associated with determining inflammation severity for each gender. Air pouches were induced by subcutaneous injection 3 (3 cc) and 5 (1.5 cc) days prior to the experiment. 4h after carrageenan injection, exudates were retrieved and leukocyte concentration quantified using a hemocytometer. The in silico mapping method was applied as described below. The strain order for mean leukocyte count/mL in inflamed exudates differed between genders. In males, the order was C57BL/6J > BALB/cByJ > DBA/2J > DBA/1J, while in females the order was BALB/cByJ > DBA/2J > C57BL/6J > DBA/1J. The difference in inflammation severity between genders reached significance only in C57BL/6J mice. Independent in silico analysis based on phenotypic data from male versus female mice identified distinct sets of loci as potentially associated with the exudate count reached. We conclude that the degree of inflammation induced in the mouse air pouch model of inflammation is strain-specific and, therefore, genetically based, and the pattern of interstrain differences is altered in male relative to female mice. The loci identified by in silico mapping likely contain genes with differential roles in determining this phenotype between genders

BACKGROUND: Cholesterol 27-hydroxylase, an enzyme expressed at high levels by human monocytes/macrophages, provides a first line of defense against the development of atherosclerosis. Prior studies have suggested that the cytokine interferon-gamma (IFN-gamma) promotes atherosclerosis. We therefore examined the effect of IFN-g on macrophage foam cell formation and on expression of the anti-atherogenic 27-hydroxylase in THP-1 human monocytes/macrophages. MATERIAL/METHODS: THP-1 monocytes and acetylated LDL-treated THP-1 macrophages were incubated in the presence or absence of IFN-gamma (500 U/ml) with or without the addition of IFN- gamma receptor blocking or neutralizing antibody. Foam cell formation was quantified based on percentage of macrophages harboring oil red O-stained globules. Cellular mRNA and protein were isolated. 27-Hydroxylase message was measured by RT-PCR and 27-hydroxylase protein by immunoblot. RESULTS: IFN-gamma -treated THP-1 macrophages exhibit increased foam cell transformation compared to untreated cells under cholesterol loading conditions. IFN-gamma-promoted foam cell formation is abolished by pre-treatment with either IFN-gamma neutralizing or IFN-gamma receptor blocking antibody. IFN-gamma diminishes cholesterol 27-hydroxylase expression in THP-1, and this IFN-gamma -induced downregulation is prevented by pre-treating the cultured cells with either IFN-gamma neutralizing or IFN-gamma receptor blocking antibody. CONCLUSIONS: Imbalances in cellular cholesterol flux within macrophages lead to formation of lipid-laden foam cells, a critical step in the pathogenesis of atherosclerosis. We have demonstrated that IFN-gamma, acting through the IFN-gamma receptor, decreases expression of 27-hydroxylase and increases propensity to foam cell formation in the cell line THP-1. These observations suggest that one mechanism by which IFN-g promotes atherosclerosis may involve affecting expression of cholesterol 27-hydroxylase, a cholesterol homeostatic protein