Abstract
Although the immune system, inflammation, and cellular metabolism are linked to diseases associated with dyslipidemias, the mechanism(s) remain unclear. To determine whether 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 (MHC)-encoded molecules 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 that lysosomal acidity is dependent on exogenous, but not endogenous, fatty acid availability. Testing these conclusions in an in vivo mouse model, we observed statistically significant, diet-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.
Highlights
The immune system, inflammation, and cellular metabolism are linked to diseases associated with dyslipidemias, the mechanism(s) remain unclear
Recent work suggests that the immune system [22, 23], inflammation [24], and oxidative damage [25] are key components of many diseases associated with dyslipidemias
Using in vitro cell cultures and an in vivo mouse model, we demonstrate that limiting the availability of lipid affects lysosomal acidity and major histocompatibility complex (MHC) class II cell surface expression
Summary
Inflammation, and cellular metabolism are linked to diseases associated with dyslipidemias, the mechanism(s) remain unclear. 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 that lysosomal acidity is dependent on exogenous, but not endogenous, fatty acid availability. Testing these conclusions in an in vivo mouse model, we observed statistically significant, diet-dependent differences in lysosomal acidity and MHC class II cell surface expression These data demonstrate a mechanistic link between lipid availability and early events in the immune response.—Schweitzer, S. Results from our in vitro model, in which we limit either exogenous availability or the endogenous synthesis of fatty acids, are consistent with the interpretation that fatty acids are important in both maintaining lysosomal acidity and determining the level of expression of cell surface MHC class II molecules. Our in vivo dietary model suggests that dietary lipids influence lysosomal acidity and supports a diet-dependent effect on the level of cell surface MHC class II expression
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