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Nitric oxide induces macrophage apoptosis following traumatic brain injury in rats
Jia Lu1, Shabbir Moochhala, Md Shirhan
1Defence Medical Research Institute, Defence Science & Technology Agency, 18 Medical Drive, #01-06, MD2, Singapore 117597, Singapore. nmiv6@nus.edu.sg
Abstract:
This study examined the apoptotic mechanisms of macrophages following a lateral fluid percussive brain injury. A marked induction of inducible NO synthase (iNOS) immunoexpression was observed in brain macrophages in the subarachnoid space and lateral ventricles ipsilateral to the injury. Numerous apoptotic macrophages occurred in the same region 7 days after the injury as shown by in situ terminal transferase d-UTP nick-end labeling (TUNEL) and caspase-3 immunohistochemistry. Double immunofluorescence staining showed that only a small number of TUNEL positive cells were iNOS positive; many TUNEL positive cells, however, were observed in the vicinity of iNOS positive cells. Administration of aminoguanidine resulted in a marked reduction of apoptotic cells in the lesioned area suggesting that overproduction of NO is linked to diminution of brain macrophages by apoptosis.
Insights
Brain macrophages undergo apoptosis after injury, partly due to nitric oxide (NO) overproduction. Aminoguanidine treatment reduced this cell death, indicating NO
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Traumatic brain injury (TBI) can trigger inflammatory responses involving macrophages.
- The precise mechanisms of macrophage death following TBI are not fully understood.
Purpose of the Study:
- To investigate the role of inducible nitric oxide synthase (iNOS) in macrophage apoptosis after TBI.
- To determine if nitric oxide (NO) production contributes to macrophage loss in the injured brain.
Main Methods:
- Inducible NO synthase (iNOS) immunoexpression was assessed in brain macrophages.
- Macrophage apoptosis was identified using in situ terminal transferase d-UTP nick-end labeling (TUNEL) and caspase-3 immunohistochemistry.
- The effect of aminoguanidine, an iNOS inhibitor, on apoptotic cells was evaluated.
Main Results:
- Increased iNOS expression was observed in macrophages near the injury site.
- Numerous apoptotic macrophages were detected 7 days post-injury.
- Aminoguanidine treatment significantly reduced the number of apoptotic cells in the injured area.
Conclusions:
- Nitric oxide overproduction by iNOS-expressing macrophages is implicated in macrophage apoptosis following TBI.
- Targeting NO production may be a therapeutic strategy to preserve brain macrophages after injury.