This competitive renewal seeks to continue its exploration of that neuronal somatic damage and death triggered by a diffuse traumatic brain injury (TBI) uncomplicated by contusion or mass lesion formation. Although previous studies considering apoptotic and necrotic cell death following TBI have focused on receptor-mediated, oxygen radical-induced and/or ischemic-initiated cell change, work conducted in the previous funding period did not support these assumptions. Rather, our recently published studies have demonstrated that TBI causes immediate posttraumatic membrane perturbation that then sets the stage for subsequent cell damage or necrotic cell death based upon the neuron's ability to reseal the initial membrane damage. These phenomena were observed in diffusely injured neuronal somata throughout the neocortex, interspersed with other intact and unaltered neuronal cell bodies. In concert with this diffuse neuronal somatic membrane perturbation, scattered perisomatic axotomy was also observed, with the caveat that such injury did not result in neuronal cell death. In this competitive renewal, we expand upon these findings utilizing technologies developed in the last funding period to detect traumatically induced neuronal membrane poration, its persistence over time, and its overall implications for necrotic cell death. In these death pathways, specific neurons, showing evidence of initial and continued somatic membrane change via the uptake of intrathecally administered fluorescent dextrans, will be followed over a 24h period. Concomitant immunocytochemical detection of calpain-mediated spectrin proteolysis, 5-calpain activation, lysosomal associated membrane protein release, and/or cathepsin B activation will be evaluated in the same neuron by confocal microscopy and electron microscopy. In concert with these descriptive and mechanistic studies, the modulatory effect of elevated intracranial pressure will be assessed as it is an important confound of human TBI. Lastly, in that membrane poration is most likely non amenable to traditional therapies used to attenuate the damaging consequences of TBI, we will use a novel poloxamer to seal damaged membranes and provide protection. The proposed studies will also focus on diffuse perisomatic axotomy, to better understand its relation, or lack thereof, to the above described phenomena. We believe that the proposed studies are novel and innovative and if successful, they will mandate a rethinking on how neurons are injured and die following diffuse TBI.
We believe that the project proposed is translational and of direct relevance to our better understanding of the pathobiology of traumatic brain injury and its therapeutic management. The themes explored are extremely novel and integrate contemporary cell biological approaches with clinically relevant parameters to address previously underappreciated areas of traumatically-induced brain pathology and its potential modulation by changes in intracranial pressure and systemic physiology.
