Reduced neuronal cell death after experimental brain injury in mice lacking a functional alternative pathway of complement activation.
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.


CONCLUSIONS
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.
Leinhase
Iris
I
Department of Trauma and Reconstructive Surgery, Charité University Medical School, Campus Benjamin Franklin, 12200 Berlin, Germany. iris.leinhase@charite.de
Holers
V Michael
VM
Thurman
Joshua M
JM
Harhausen
Denise
D
Schmidt
Oliver I
OI
Pietzcker
Malte
M
Taha
Mohy E
ME
Rittirsch
Daniel
D
Huber-Lang
Markus
M
Smith
Wade R
WR
Ward
Peter A
PA
Stahel
Philip F
PF
D000818:Animals; D001921:Brain / Q000378:metabolism / Q000503:physiopathology*; D001930:Brain Injuries / Q000378:metabolism / Q000503:physiopathology*; D016923:Cell Death; D003167:Complement Activation; D011415:Complement Factor B / Q000172:deficiency / Q000378:metabolism*; D015536:Down-Regulation; D016489:Head Injuries, Closed / Q000378:metabolism / Q000503:physiopathology; D051379:Mice; D018345:Mice, Knockout; D009474:Neurons; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D015854:Up-Regulation; D019014:fas Receptor / Q000378:metabolism
D019253:Proto-Oncogene Proteins c-bcl-2; D019014:fas Receptor; D011415:Complement Factor B