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Reduced neuronal cell death after experimental brain injury in mice lacking a functional alternative pathway of
Iris Leinhase1, V Michael Holers, Joshua M Thurman
1Department of Trauma and Reconstructive Surgery, Charité University Medical School, Campus Benjamin Franklin, 12200 Berlin, Germany. iris.leinhase@charite.de
Background:
Neuroprotective strategies for prevention of the neuropathological sequelae of traumatic brain injury (TBI) have largely failed in translation to clinical treatment. Thus, there is a substantial need for further understanding the molecular mechanisms and pathways which lead to secondary neuronal cell death in the injured brain. The intracerebral activation of the complement cascade was shown to mediate inflammation and tissue destruction after TBI. However, the exact pathways of complement activation involved in the induction of posttraumatic neurodegeneration have not yet been assessed. In the present study, we investigated the role of the alternative complement activation pathway in contributing to neuronal cell death, based on a standardized TBI model in mice with targeted deletion of the factor B gene (fB-/-), a "key" component required for activation of the alternative complement pathway.
Results:
After experimental TBI in wild-type (fB+/+) mice, there was a massive time-dependent systemic complement activation, as determined by enhanced C5a serum levels for up to 7 days. In contrast, the extent of systemic complement activation was significantly attenuated in fB-/- mice (P < 0.05,fB-/- vs. fB+/+; t = 4 h, 24 h, and 7 days after TBI). TUNEL histochemistry experiments revealed that posttraumatic neuronal cell death was clearly reduced for up to 7 days in the injured brain hemispheres of fB-/- mice, compared to fB+/+ littermates. Furthermore, a strong upregulation of the anti-apoptotic mediator Bcl-2 and downregulation of the pro-apoptotic Fas receptor was detected in brain homogenates of head-injured fB-/- vs. fB+/+ mice by Western blot analysis.
Conclusion:
The alternative pathway of complement activation appears to play a more crucial role in the pathophysiology of TBI than previously appreciated. This notion is based on the findings of (a) the significant attenuation of overall complement activation in head-injured fB-/- mice, as determined by a reduction of serum C5a concentrations to constitutive levels in normal mice, and (b) by a dramatic reduction of TUNEL-positive neurons in conjunction with an upregulation of Bcl-2 and downregulation of the Fas receptor in head-injured fB-/- mice, compared to fB+/+ littermates. Pharmacological targeting of the alternative complement pathway during the "time-window of opportunity" after TBI may represent a promising new strategy to be pursued in future studies.
Insights
Targeting the alternative complement pathway after traumatic brain injury (TBI) reduces neuronal cell death. Blocking factor B (fB) in mice significantly decreased complement activation and protected the brain from secondary injury.
Area of Science:
- Neuroscience
- Immunology
- Pathophysiology
Background:
- Traumatic brain injury (TBI) neuroprotection strategies have largely failed clinical translation.
- Understanding secondary neuronal cell death mechanisms post-TBI is critical.
- The role of specific complement activation pathways in TBI-induced neurodegeneration requires further elucidation.
Purpose of the Study:
- To investigate the contribution of the alternative complement activation pathway to neuronal cell death following TBI.
- To assess the impact of deleting factor B (fB), a key component of the alternative pathway, on TBI outcomes.
Main Methods:
- Utilized a standardized TBI model in mice with targeted deletion of the factor B gene (fB-/-).
- Measured systemic complement activation via serum C5a levels.
- Assessed neuronal cell death using TUNEL histochemistry.
- Analyzed apoptosis-related protein expression (Bcl-2, Fas) via Western blot.
Main Results:
- Experimental TBI induced massive, time-dependent systemic complement activation in wild-type (fB+/+) mice.
- Complement activation was significantly attenuated in fB-/- mice post-TBI.
- Neuronal cell death was markedly reduced in the injured brain hemispheres of fB-/- mice compared to fB+/+ littermates.
- fB-/- mice exhibited upregulation of anti-apoptotic Bcl-2 and downregulation of pro-apoptotic Fas receptor post-TBI.
Conclusions:
- The alternative complement pathway plays a significant role in TBI pathophysiology.
- Targeting the alternative complement pathway, specifically factor B, attenuates complement activation and reduces post-TBI neurodegeneration.
- Pharmacological inhibition of the alternative complement pathway presents a promising therapeutic strategy for TBI.
