Caspase 7: increased expression and activation after traumatic brain injury in rats Stephen F. Larner,* Deborah M. McKinsey,* Ronald L. Hayes* ,  and Kevin K. W. Wang* ,   *Center for Traumatic Brain Injury Studies, Department of Neuroscience and  Center for Neuroproteomics and Biomarkers Research, Department of Psychiatry, McKnight Brain Institute of the University of Florida, Gainesville, Florida, USA Abstract Caspases, a cysteine proteinase family, are required for the initiation and execution phases of apoptosis. It has been suggested that caspase 7, an apoptosis executioner implica- ted in cell death proteolysis, is redundant to the main execu- tioner caspase 3 and it is generally believed that it is not present in the brain or present in only minute amounts with highly restricted activity. Here we report evidence that caspase 7 is up-regulated and activated after traumatic brain injury (TBI) in rats. TBI disrupts homeostasis resulting in pathological apoptotic activation. After controlled cortical impact TBI of adult male rats we observed, by semiquantita- tive real-time PCR, increased mRNA levels within the trau- matized cortex and hippocampus peaking in the former about 5 days post-injury and in the latter within 6–24 h of trauma. The activation of caspase 7 protein after TBI, demonstrated by immunoblot by the increase of the active form of caspase 7 peaking 5 days post-injury in the cortex and hippocampus, was found to be up-regulated in both neurons and astrocytes by immunohistochemistry. These findings, the first to docu- ment the up-regulation of caspase 7 in the brain after acute brain injury in rats, suggest that caspase 7 activation could contribute to neuronal cell death on a scale not previously recognized. Keywords: apoptosis, caspase, caspase 7, cell death, trau- matic brain injury. J. Neurochem. (2005) 94, 97–108. Traumatic brain injury (TBI), a serious health issue in the USA according to the Centers for Disease Control and Prevention, afflicts about 1.5 million new patients annually. TBI is frequently referred to as the silent epidemic because the resulting pathologies tend to be emotional and cognitive (e.g. impaired memory, change in character traits and difficulty in concentrating) rather than physical (Gerberding 2003). Despite about 2% of the US population suffering from some form of TBI-related disability, no known pharmacolo- gical treatment is currently available. TBI causes progressive neuronal degeneration resulting from acute and delayed cell death mediated in part by calpains (Kampfl et al. 1996) and in part by apoptotic-inducing caspases (Rink et al. 1995; Colicos et al. 1996; Yakovlev et al. 1997; Conti et al. 1998; Newcomb et al. 1999; Clark et al. 2000). Apoptosis, programmed cell death (type I), a conserved active molecular process, often requires transcription and translation of proteins for initiation (Rink et al. 1995). Characterized by proteolysis of cellular components, apop- tosis is critical to the pruning of the CNS during development (Oppenheim 1991; Raff et al. 1993; Vaux and Korsmeyer 1999) and for tissue homeostasis requiring the elimination of aged and abnormal cells (Johnson et al. 1999). Although apoptosis is under strict control under normal conditions, alterations in the apoptotic pathways have been implicated in many diseases, such as cancer and neurodegenerative disorders (Thompson 1995; Yuan and Yankner 2000), and play a role in the pathology that occurs after TBI. Apoptosis is often associated with the sequential-activa- ting cascade of a family of cysteine-dependent aspartate- Received December 10, 2004; revised manuscript received February 15, 2005; accepted February 18, 2005. Address correspondence and reprint requests to Stephen F. Larner, PhD, Center for Traumatic Brain Injury Studies, Department of Neuro- science, 100 S. Newell Drive, Box 100244, McKnight Brain Institute of the University of Florida, Gainesville, FL 32610, USA. E-mail: sflarner@ufl.edu Abbreviations used: DAPI, 4¢,6¢-diamino-2-phenylindolehydrocloride; DEPC, Diethyl pyrocarbonate; ER, endoplasmic reticulum; GAPDH, Glyceraldehyde-3-phosphatedehydrogenase; PARP, Poly (ADP-Ribose); SDS, sodium dodecyl sulfate; TAE, Tris Acetate Electrophoresis; TBI, traumatic brain injury. Journal of Neurochemistry , 2005, 94, 97–108 doi:10.1111/j.1471-4159.2005.03172.x Ó 2005 International Society for Neurochemistry, J. Neurochem. (2005) 94, 97–108 97