Project: Proteolytic remodeling of the extracellular matrix in aberrant synaptic plasticity underlying epilepsy evoked by traumatic brain injury
Traumatic brain injury (TBI) is a serious, underinvestigated health problem. In addition to motor and cognitive disabilities, post-traumatic epilepsy (PTE) represents a frequent major long-term life-compromising outcome after TBI. There is convincing recent evidence that mechanisms for both favorable and unfavorable recovery after TBI relate to axonal and synaptic plasticity, which are strictly controlled by extracellular proteolysis, including focal extrasynaptic matrix degradation. Metalloproteinases (especially MMP-9) as well as serine proteases, such as urokinase type plasminogen activator (uPA) and its receptor uPAR, contribute to extracellular proteolysis, and have recently been identified as emerging novel molecular systems involved in the epileptogenesis, in addition to previously known changes in ion channels and signal transduction pathways. In particular, recent evidence has pointed out the principal role of MMP-9 in remodeling of dendritic spines-which harbor the excitatory synapses-that represents a hallmark of morphological plasticity during epileptogenesis. However, contribution of extracellular proteolysis to this phenomenon is poorly understood. Similarly, signaling mechanisms involved in orchestrating the cellular responses contributing to proteolysisdriven changes in the extracellular milieu are poorly known. The extracellular location of MMP-9 and uPA enzymes makes them particularly attractive as potential targets for future pharmacological therapeutic interventions. In the present proposal we aim at testing a hypothesis that MMP-9 and uPA/uPAR contribute to circuitry remodeling during post-traumatic epileptogenesis. We focus on those two molecular systems, because there is a strong support for their involvement in other models of epileptogenesis, as well as the partners of this consortium have excellent tools and expertise to investigate these molecules. To test our idea we will, first, assess the contribution of MMP-9 and uPA/uPAR to epileptogenesis in an animal model of human PTE. This study involves an extensive use of transgenic mice and locally induced gene and/or protein modifications. Second, we will analyze the cellular and subcellular expression of MMP-9 and uPA/uPAR as well as the possible molecular mechanisms mediating the post-TBI effects of these molecules and their interactome. We will also investigate the dendritic spine dynamics and morphology, to elucidate the contribution of those phenomena to TBI-evoked epileptogenesis, as well as their dependence on specific proteolytic systems. In parallel, we assess the blood plasma levels of the enzymes, as well as effects of functional gene polymorphisms in MMP- 9, uPA, and uPAR on susceptibility to post-traumatic epilepsy (PTE) in humans with TBI. Finally, we will elaborate novel in vivo PET imaging methods during epileptogenesis in animals and humans, including brain visualization of MMP and plasminogen/plasmin enzymatic activities.
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