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Nitric oxide via macrophage iNOS induces apoptosis following traumatic spinal cord injury
K Satake1, Y Matsuyama, M Kamiya
1Department of Orthopaedic Surgery, Nagoya University School of Medicine, Nagoya 466-8550, Japan.
Abstract:
To investigate the pathophysiological mechanisms involved in post-traumatic impairment of the spinal cord, we analyzed expression patterns of the inducible nitric oxide synthase (iNOS) gene following acute injury of rat spinal cord using a weight drop technique. PCR analysis revealed that iNOS mRNA appeared at 3-12 h after injury and declined thereafter. Immunohistochemical analysis showed that iNOS-positive cells invaded the lesioned area through the perivascular space at 6 h after injury. The population of these cells peaked at 24 h and then declined to disappear 3 days after injury. The iNOS-positive cells were also stained with ED-2 but not with ED-1 or OX-42, indicating that these cells were macrophages and/or perivascular cells. In parallel with the appearance of iNOS-positive cells, other cells emerged that were positively stained by the terminal deoxynucleotidyl-transferase-mediated dUDP-biotin nick end-labeling (TUNEL) assay. TUNEL-positive cells were scattered in the lesioned area 1 day after injury, but some in the surrounding area close to iNOS-positive cells. Administration of L-Ng-nitro-arginine methylester, a competitive inhibitor of NOS, resulted in a reduction of TUNEL-positive cells in the lesioned area. These results suggest that nitric oxide generated by iNOS of macrophages and/or perivascular cells plays a significant role in eliminating damaged cells from the lesioned area by apoptosis.
Insights
Inducible nitric oxide synthase (iNOS) in macrophages and perivascular cells contributes to spinal cord injury repair by promoting apoptosis of damaged cells. This study reveals iNOS
Area of Science:
- Neuroscience
- Immunology
- Pathophysiology
Background:
- Spinal cord injury (SCI) triggers complex pathophysiological responses.
- Understanding the molecular mechanisms of SCI is crucial for developing effective treatments.
Purpose of the Study:
- To investigate the role of inducible nitric oxide synthase (iNOS) in the cellular mechanisms following acute spinal cord injury in rats.
- To identify the cell types expressing iNOS and their contribution to tissue repair.
Main Methods:
- Acute spinal cord injury induced using a weight drop technique in rats.
- Analysis of iNOS gene expression via PCR.
- Immunohistochemical staining to identify iNOS-positive cells (macrophages/perivascular cells) and apoptotic cells (TUNEL assay).
- Pharmacological inhibition of nitric oxide synthase (NOS) using L-Ng-nitro-arginine methylester.
Main Results:
- iNOS mRNA expression detected 3-12 hours post-injury, peaking at 24 hours.
- iNOS-positive cells, identified as macrophages/perivascular cells, infiltrated the lesion site.
- Apoptotic cells (TUNEL-positive) appeared in the lesion area, correlating with iNOS-positive cell presence.
- Inhibition of NOS reduced the number of apoptotic cells, suggesting a role for nitric oxide.
Conclusions:
- Nitric oxide produced by iNOS in macrophages/perivascular cells plays a significant role in clearing damaged cells via apoptosis after spinal cord injury.
- These findings elucidate a key mechanism in the post-traumatic repair process of the spinal cord.