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Induction of cystine transport activity in mouse peritoneal macrophages by bacterial lipopolysaccharide
1Department of Biochemistry, University of Tsukuba, Ibaraki, Japan.
Abstract:
The transport of cystine has been investigated in mouse peritoneal macrophages cultured in vitro. The transport activity for cystine was very low in freshly isolated macrophages but was potently induced during culture in the presence of bacterial lipopolysaccharide (LPS) at concentrations as low as 0.1 ng/ml. The transport activity for cystine was enhanced when the cells were incubated with tumour necrosis factor-alpha (TNF-alpha), but not with interferon-gamma (IFN-gamma) or interleukin-1. IFN-gamma was rather repressive in the induction of the activity by LPS or TNF-alpha. The transport activity for cystine induced by LPS has been characterized. Cystine was transported mainly by Na(+)-independent system and the uptake of cystine was inhibited by extracellular glutamate and homocysteate, but not by aspartate, indicating that the transport of cystine in macrophages treated with LPS is mediated by System xc-. Glutathione content of the macrophages increased when they were exposed to LPS, and this increase was, at least in part, attributable to the induced activity of the cystine transport.
Insights
Bacterial lipopolysaccharide (LPS) potently induces cystine transport in macrophages, enhancing glutathione levels. Tumor necrosis factor-alpha also boosts this transport, while interferon-gamma shows repressive effects.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Macrophage function is critical in immune responses.
- Cystine transport plays a role in cellular metabolism and redox balance.
- Regulation of nutrient transport in macrophages is not fully understood.
Purpose of the Study:
- To investigate the regulation of cystine transport in mouse peritoneal macrophages.
- To identify factors that induce or modulate cystine transport activity.
- To characterize the mechanism of LPS-induced cystine transport.
Main Methods:
- Primary mouse peritoneal macrophages were cultured in vitro.
- Cells were treated with bacterial lipopolysaccharide (LPS), tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), and interleukin-1.
- Cystine uptake was measured, and the transport system was characterized by substrate inhibition and ion dependency.
Main Results:
- Cystine transport was low in naive macrophages but significantly induced by LPS (≥0.1 ng/ml).
- TNF-alpha enhanced cystine transport, while IFN-gamma showed repressive effects on LPS- or TNF-alpha-induced transport.
- LPS-induced cystine transport was Na(+)-independent and inhibited by glutamate and homocysteate, consistent with System xc- mediation.
- LPS treatment led to increased macrophage glutathione content, partly due to induced cystine transport.
Conclusions:
- Bacterial LPS is a potent inducer of cystine transport in macrophages via System xc-.
- TNF-alpha enhances, while IFN-gamma represses, this induced transport.
- Upregulation of cystine transport contributes to increased glutathione synthesis in LPS-stimulated macrophages.