Soluble amyloid precursor protein α reduces neuronal injury and improves functional outcome following diffuse traumatic brain injury in rats

Amyloid precursor protein (APP) has previously been shown to increase following traumatic brain injury (TBI). Whereas a number of investigators assume that increased APP may lead to the production of neurotoxic Aβ and be deleterious to outcome, the soluble α form of APP (sAPPα) is a product of the non-amyloidogenic cleavage of amyloid precursor protein that has previously been shown in vitro to have many neuroprotective and neurotrophic functions. However, no study to date has addressed whether sAPPα may be neuroprotective in vivo. The present study examined the effects of in vivo, posttraumatic sAPPα administration on functional motor outcome, cellular apoptosis, and axonal injury following severe impact–acceleration TBI in rats. Intracerebroventricular administration of sAPPα at 30 min posttrauma significantly improved motor outcome compared to vehicle-treated controls as assessed using the rotarod task. Immunohistochemical analysis using antibodies directed toward caspase-3 showed that posttraumatic treatment with sAPPα significantly reduced the number of apoptotic neuronal perikarya within the hippocampal CA3 region and within the cortex 3 days after injury compared to vehicle-treated animals. Similarly, sAPPα-treated animals demonstrated a reduction in axonal injury within the corpus callosum at all time points, with the reduction being significant at both 3 and 7 days postinjury. Our results demonstrate that in vivo administration of sAPPα improves functional outcome and reduces neuronal cell loss and axonal injury following severe diffuse TBI in rats. Promotion of APP processing toward sAPPα may thus be a novel therapeutic strategy in the treatment of TBI.