Related Experiment Videos
Caspase-8 expression and proteolysis in human brain after severe head injury
Xiaopeng Zhang1, Steven H Graham, Patrick M Kochanek
1Department of Critical Care Medicine, The Safar Center for Resuscitation Research and the Brain Trauma Research Center, University of Pittsburgh, PA 15260, USA.
Abstract:
Programmed cell death involves a complex and interrelated cascade of cysteine proteases termed caspases that are synthesized as inactive zymogens, which are proteolytically processed to active enzymes. Caspase-8 is an initiator caspase that becomes activated when Fas death receptor-Fas ligand (FasL) coupling on the cell surface leads to coalescence of a "death complex" perpetuating the programmed cell death cascade. In this study, brain tissue samples removed from adult patients during the surgical management of severe intracranial hypertension after traumatic brain injury (TBI; n=17) were compared with postmortem control brain tissue samples (n=6). Caspase-8 mRNA was measured by semiquantitative reverse transcription and polymerase chain reaction, and caspase-8 protein was examined by Western blot and immunocytochemistry. Fas and FasL were also examined using Western blot. Caspase-8 mRNA and protein were increased in TBI patients vs. controls, and caspase-8 protein was predominately expressed in neurons. Proteolysis of caspase-8 to 20-kDa fragments was seen only in TBI patients. Fas was also increased after TBI vs. control and was associated with relative levels of caspase-8, supporting formation of a death complex. These data identify additional steps in the programmed cell death cascade involving Fas death receptors and caspase-8 after TBI in humans.
Insights
Traumatic brain injury (TBI) increases programmed cell death markers, including caspase-8 (an initiator protease) and Fas death receptors, in human brain tissue. These findings reveal key steps in TBI-induced neuronal death pathways.
Area of Science:
- Neuroscience
- Cell Biology
- Pathology
Background:
- Programmed cell death is regulated by caspases, synthesized as inactive zymogens.
- Caspase-8 activation initiates cell death cascades upon Fas death receptor signaling.
- Traumatic brain injury (TBI) can trigger complex cellular responses, including apoptosis.
Purpose of the Study:
- To investigate the role of caspase-8 and Fas death receptors in human traumatic brain injury.
- To determine if caspase-8 is activated and expressed in neurons following TBI.
Main Methods:
- Analysis of human brain tissue from TBI patients (n=17) and postmortem controls (n=6).
- Measurement of caspase-8 mRNA via reverse transcription and polymerase chain reaction.
- Assessment of caspase-8, Fas, and Fas ligand (FasL) protein levels using Western blot and immunocytochemistry.
Main Results:
- Caspase-8 mRNA and protein levels were elevated in TBI brain tissue compared to controls.
- Increased caspase-8 protein was primarily observed in neurons.
- Proteolytic processing of caspase-8 and increased Fas protein were evident in TBI samples.
- Elevated Fas levels correlated with caspase-8 levels, suggesting death complex formation.
Conclusions:
- Traumatic brain injury upregulates caspase-8 and Fas death receptor pathways in the human brain.
- These findings elucidate critical molecular events in TBI-induced programmed cell death.
- Caspase-8 activation and Fas receptor signaling are key components of the cell death cascade following human TBI.