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Matrix protein regulation of PMN oxidative metabolism during ischemia
1Department of Surgery, Brown University School of Medicine/Rhode Island Hospital, Providence 02903.
Abstract:
Matrix proteins upregulate polymorphonuclear neutrophil (PMN) oxidative metabolism in a normoxic environment. We sought to investigate the relationship between matrix proteins and adherent PMN oxidative metabolism during acute ischemia. PMN adherent to buffer, fibronectin, Arg-Gly-Asp-Ser (RGDS), or laminin were placed in either normoxic or ischemic media. PMN adherence, superoxide anion production, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) formazan production, and surface receptor expression (CD64, CD32w, CD16, CD35, and CD11b/CD18) using monoclonal antibodies directed against these receptors were assayed. Ischemia increased PMN adherence unless the PMN were adhered to fibronectin or RGDS. Ischemia reduced PMN superoxide anion, MTT formazan, and H2O2 production unless the PMN were adhered to fibronectin or RGDS. Fibronectin and RGDS prevented ischemic-induced suppression of FcR expression. Immunofluorescent studies demonstrated capping and clustering of PMN Fc and complement receptors during ischemia while adhered on matrix proteins. These results demonstrate that 1) ischemia suppresses matrix protein upregulation of PMN oxidative metabolism, which is restored by fibronectin; 2) fibronectin-mediated restoration of PMN oxidative metabolism involves the binding epitope of fibronectin; and 3) fibronectin maintains PMN oxidative metabolism during ischemia in part by maintaining PMN FcR on the cell surface and by recruiting a new population of PMN capable of undergoing oxidative metabolism.
Insights
Fibronectin restores polymorphonuclear neutrophil (PMN) oxidative metabolism during ischemia, preventing suppression of Fc receptor expression. This highlights fibronectin's role in maintaining PMN function under ischemic conditions.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Matrix proteins, such as fibronectin, normally enhance polymorphonuclear neutrophil (PMN) oxidative metabolism in normoxic conditions.
- Acute ischemia can suppress PMN oxidative metabolism and alter cell surface receptor expression.
Purpose of the Study:
- To investigate how matrix proteins affect adherent PMN oxidative metabolism during acute ischemia.
- To determine if fibronectin or its binding epitope (RGDS) can prevent ischemia-induced suppression of PMN oxidative metabolism and receptor expression.
Main Methods:
- PMN were adhered to various substrates (buffer, fibronectin, RGDS, laminin) and exposed to normoxic or ischemic media.
- Assays included PMN adherence, superoxide anion and H2O2 production, MTT formazan production, and surface receptor expression (FcR, CR, CD11b/CD18) via monoclonal antibodies.
- Immunofluorescence was used to study receptor capping and clustering.
Main Results:
- Ischemia increased PMN adherence to most substrates, but fibronectin and RGDS inhibited this effect.
- Ischemia reduced PMN oxidative metabolism (superoxide, MTT, H2O2 production), except when PMN were on fibronectin or RGDS.
- Fibronectin and RGDS prevented the ischemic suppression of Fc receptor (FcR) expression, and immunofluorescence showed receptor capping during ischemia on matrix proteins.
Conclusions:
- Ischemia suppresses matrix protein-induced PMN oxidative metabolism, but fibronectin restores it.
- Fibronectin's restoration of PMN oxidative metabolism involves its specific binding epitope.
- Fibronectin maintains PMN oxidative metabolism during ischemia by preserving FcR on the cell surface and potentially recruiting new PMN populations.