The goal of the proposed work is to determine the mechanisms of the early structural consequences of neural trauma and to develop strategies for acute intervention in traumatic brain injury (TBI) that address the primary mechanisms of axonal injury. The underlying hypothesis for this research is that initial mechanical trauma to the cell membranes leads to cytoskeletal disruptions and alterations of axonal transport and that acute intervention to restore membrane integrity and preserve axonal cytoskeleton and transport processes can dramatically reduce secondary degeneration and cell death. Specific Hypotheses to be tested are 1) Axonal cytoskeletal disruption and impaired axonal transport are causally related to membrane disruption, and acute repair of the axolemma by poloxamer P188 can prevent these effects;2) JNK-3 activation is causally related to membrane damage, and axonal transport is, in part, impaired by the actions of JNK-3;and 3) Mild injury will be manifest in axonal pathology, the time course of which is modulated by injury severity. We have developed and in vitro model of focal axonal injury in primary chick forebrain (CFB) neurons that mimics many features observed in vivo. In particular, focal swelling, or axonal beads, appeared within one hour following the mechanical insult. Co-localized with the beads were focal disruptions of microtubules and the accumulation of membrane bound organelles indicating a disruption of axonal transport. We characterized the membrane damage as a result of the mechanical trauma and showed that treatment with Poloxamer 188 (P188), a water soluble, non-ionic surfactant restored membrane integrity and significantly inhibited axonal beading in CFB neurons. We also have an in vivo model that produces axonal injury in the deep white matter. In this model, we have demonstrated membrane damage, focal accumulation of amyloid precursor protein (APP), and focal activation of JNK-3. Significantly, injured JNK-3 deficient mice do not exhibit the severe cognitive deficits seen in age-matched WT littermates. The following Specific Aims were developed to test these hypotheses:
Aim 1 : To determine the causal relationship between mechanically-induced membrane damage and subsequent alterations of cytoskeletal structure and axonal transport and to test whether acute treatment with an agent that promotes membrane repair can preserve axonal structure and function and thereby prevent secondary degeneration.
Aim 2 : To determine the mechanism of focal activation of the MAP kinase, JNK-3, in injured axons and its role in axonal pathology and to test the effect of acute membrane repair on JNK activation.
Aim 3 : To determine the window of opportunity for therapeutic intervention for both membrane repair and inhibition of JNK-3.
Currently, acute care for trauma victims deals mainly with preserving or restoring basic life support systems, e.g., cardiac and respiratory function, and managing mass lesions in the brain to prevent death and/or further brain damage. This research, if successful, will provide the basis for a new approach to the treatment of traumatic brain injury in which early intervention to preserve the structural integrity of neurons will stave off the secondary degenerative processes that result in persistent neurological deficits. Successful completion of the proposed research will hopefully emphasize the importance of the early treatment of neuronal injury as an important therapeutic consideration in addition to the current focus on delayed treatments aimed at halting secondary degeneration.
|Creed, Jennifer A; DiLeonardi, Ann Mae; Fox, Douglas P et al. (2011) Concussive brain trauma in the mouse results in acute cognitive deficits and sustained impairment of axonal function. J Neurotrauma 28:547-63|