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Published on: March 16, 2017
Molecular and metabolic evidence for the restricted expression of inducible nitric oxide synthase in healing wounds
J S Reichner1, A J Meszaros, C A Louis
1Department of Surgery, Division of Surgical Research, Brown University and Rhode Island Hospital, Providence, Rhode Island 02903, USA. Jonathan_Reichner@brown.edu
Abstract:
Tissue injury initiates a temporally ordered sequence of local cellular and metabolic responses presumably necessary for successful repair. Previous investigations demonstrated that metabolic evidence for nitric oxide synthase (NOS) activity is detectable in wounds only during the initial 48 to 72 hours of the repair process. Present results identify the cell types contributing inducible NOS (iNOS) to experimental wounds in rats. iNOS antigen was expressed in most macrophages present in wounds 6 to 24 hours after injury, and these cells exhibited NAPDH diaphorase and NOS activity. Polymorphonuclear leukocytes contained little iNOS antigen and no NADPH diaphorase activity and were minimally able to convert L-arginine to L-citrulline. The frequency of iNOS-positive macrophages declined on days 3 and 5 after wounding. By day 10, most macrophages in the wound were negative for iNOS. These cells, however, acquired iNOS antigen and activity in culture. Wound fluids, but not normal rat serum, suppressed the induction of iNOS during culture. Findings indicate that the expression of iNOS in healing wounds is restricted to macrophages present during the early phases of repair and that components of wound fluid suppress the induction of iNOS in macrophages in late wounds. Polymorphonuclear leukocytes contribute little iNOS activity to the healing wound.
Insights
In healing wounds, macrophages express inducible nitric oxide synthase (iNOS) early after injury. Wound fluid components later suppress iNOS induction in macrophages, limiting their role in later repair stages.
Area of Science:
- Wound healing research
- Immunology
- Cellular biology
Background:
- Tissue injury triggers a sequence of cellular and metabolic responses essential for repair.
- Metabolic evidence for nitric oxide synthase (NOS) activity in wounds is limited to the initial 48-72 hours.
- The specific cell types contributing inducible NOS (iNOS) to early wound repair were not fully identified.
Purpose of the Study:
- To identify the cell types responsible for inducible NOS (iNOS) expression in experimental rat wounds.
- To investigate the temporal dynamics of iNOS expression in different immune cells during wound healing.
- To explore the influence of wound fluid on iNOS induction in macrophages.
Main Methods:
- Immunohistochemical detection of iNOS antigen in rat wound tissues at various time points post-injury.
- Assessment of NADPH diaphorase and NOS activity in wound cells.
- In vitro culture of macrophages with wound fluid and normal rat serum to evaluate iNOS induction.
Main Results:
- iNOS antigen and activity were primarily found in macrophages within the first 6-24 hours after injury.
- Polymorphonuclear leukocytes showed minimal iNOS antigen and activity.
- iNOS-positive macrophage frequency decreased by days 3 and 5, with most macrophages negative by day 10.
- Macrophages cultured from late wounds acquired iNOS antigen and activity, but this induction was suppressed by wound fluid.
Conclusions:
- Macrophage-derived iNOS is crucial during the early phases of wound repair.
- Components present in wound fluid actively suppress iNOS induction in macrophages during later stages of healing.
- Polymorphonuclear leukocytes contribute negligibly to iNOS activity in healing wounds.
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