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Cytokine Release by Microglia Exposed to Neurologic Injury Is Amplified by Lipopolysaccharide
Michael C Scott1, Olivia LeBlanc1, Harper Day1
1Department of Pediatric Surgery, University of Texas Health Science Center at Houston, Houston, Texas.
Introduction:
Traumatic brain injury (TBI) is a leading cause of death and morbidity in the trauma population. Microglia drive the secondary neuroinflammatory response after TBI. We sought to determine if the microglial response to neurologic injury was exacerbated by a second stimulus after exposure to neurologic injury.
Methods:
Sprague-Dawley rats (age 2-3 wk) were divided into injured and noninjured groups. Injured rats underwent a controlled cortical impact injury; noninjured rats remained naïve to any injury and served as the control group. Primary rat microglia were isolated and applied to in vitro cultures. After incubation for 24 h, the microglia were stimulated with lipopolysaccharide (LPS) or norepinephrine. Twenty-four hours after stimulation, cell culture supernatant was collected. Tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6) production were measured by standard enzyme-linked immunosorbent assays. GraphPad Prism was used for statistical analysis.
Results:
When compared to noninjured microglia, LPS induced a significantly greater production of TNF-α in microglia isolated from the injured ipsilateral (versus noninjured = 938.8 ± 155.1, P < 0.0001) and injured contralateral hemispheres (versus noninjured = 426.6 ± 155.1, P < 0.0001). When compared to microglia from noninjured cerebral tissue, IL-6 production was significantly greater after LPS stimulation in the injured ipsilateral hemisphere (mean difference versus noninjured = 9540 ± 3016, P = 0.0101) and the contralateral hemisphere (16,700 ± 3016, P < 0.0001). Norepinephrine did not have a significant effect on IL-6 or TNF-α production.
Conclusions:
LPS stimulation may amplify the release of proinflammatory cytokines from postinjury microglia. These data suggest that post-TBI complications, like sepsis, may propagate neuroinflammation by augmenting the proinflammatory response of microglia.
Insights
Traumatic brain injury (TBI) can worsen neuroinflammation. Lipopolysaccharide (LPS) stimulation amplified proinflammatory cytokine release from microglia after injury, suggesting secondary insults like sepsis may exacerbate TBI outcomes.
Area of Science:
- Neuroscience
- Immunology
- Trauma Research
Background:
- Traumatic brain injury (TBI) is a major cause of death and disability.
- Microglia play a key role in the secondary neuroinflammatory response following TBI.
- This study investigates if a secondary stimulus exacerbates the microglial response to a prior neurologic injury.
Purpose of the Study:
- To determine if microglial response to neurologic injury is amplified by a secondary stimulus.
- To investigate the effect of lipopolysaccharide (LPS) and norepinephrine on cytokine production in microglia from injured and non-injured rats.
Main Methods:
- Controlled cortical impact injury was induced in Sprague-Dawley rats.
- Primary microglia were isolated from injured and non-injured rat brains.
- Microglia were stimulated with LPS or norepinephrine in vitro.
- Tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6) levels in cell culture supernatant were measured using ELISA.
Main Results:
- LPS significantly increased TNF-α production in microglia from both ipsilateral and contralateral hemispheres compared to non-injured controls.
- LPS stimulation led to significantly greater IL-6 production in microglia from both injured hemispheres compared to controls.
- Norepinephrine did not significantly affect IL-6 or TNF-α production.
Conclusions:
- Lipopolysaccharide (LPS) stimulation can amplify the release of proinflammatory cytokines from microglia in the context of post-TBI.
- These findings suggest that secondary insults, such as sepsis, may propagate neuroinflammation by enhancing the microglial proinflammatory response after TBI.
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