Submitted on July 24, 2006
Revised on August 16, 2006
Accepted on August 16, 2006
Endogenous versus exogenous fatty acid availability affects lysosomal acidity and MHC class II expression
Susan C. Schweitzer, Ashleigh M. Reding, Holly M. Patton, Thomas P. Sullivan, Christopher E. Stubbs, Elizabeth Villalobos-Menuey, Sally A. Huber, and M. Karen Newell
Biology, University of Colorado, Colorado Springs, Colorado Springs, CO 80918
Corresponding Author: mnewell{at}uccs.edu
ABSTRACT Although the immune system, inflammation, and cellular metabolism are linked to diseases associated with dyslipidemias, the mechanism(s) remain unclear. To determine if there is a mechanistic link between lipid availability and inflammation/immune activation, we evaluated macrophage cell lines incubated under conditions of altered exogenous and endogenous lipid availability. Limiting exogenous lipids results in decreased lysosomal acidity and decreased lysosomal enzymatic activity. Both lysosomal parameters are restored with the addition of oleoyl CoA, suggesting that fatty acids play a role in the regulation of lysosomal function. Cell surface expression of major histocompatibility complex-encoded molecules (MHC) is also decreased in the absence of exogenous lipids. Additionally, we observe decreased gamma interferon stimulation of cell surface MHC class II. Using cerulenin to limit the endogenous synthesis of fatty acids results in decreased cell surface expression of MHC class II, but does not appear to alter lysosomal acidity, suggesting lysosomal acidity is dependent on exogenous, but not endogenous fatty acid availability. Testing these conclusions in an in vivo mouse model, we observe statistically significant, dietary dependent differences in lysosomal acidity and MHC class II cell surface expression. Collectively, these data demonstrate a mechanistic link between lipid availability and early events in the immune response.
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