In this proposal, we will use a mouse model of controlled cortical impact to test the idea that secondary cell death after traumatic brain injury is mediated by matrix metalloproteinases (MMP) which disrupt cell-matrix and cell-cell interactions, thus triggering apoptosis in brain regions beyond the site of original impact. Our working hypothesis states that: 1) mechanical stress induced by trauma activate MAP kinase signal transduction pathways, 2) MAP kinease pathways upregulate MMP expression, 3) MMP disrupts the extracellular matrix, and 4) disruption of cell-matrix and cell-cell interactions lead to apoptotic cell death. Preliminary data show that (a) the mouse model of controlled cortical impact is stable and reproducible in our lab; (b) western blots from traumatized brain show activation of the MAP kinase pathways ERK and SAPK2/p38; (c) the ERK/MAP kinase pathway upregulates MMP in vitro; (d) MMP activation occurs after trauma in vivo; (e) knockout mice deficient in MMP-9 show reduced injury after stroke and trauma, (f) direct injection of MMP-7 into mouse brain induces apoptosis; and (g) inhibition of the ERK/MAP kinase pathway reduces injury after stroke. We will extend our preliminary findings by pursuing the following specific aims. 1. Define the signaling pathways that lead to MMP upregulation and apoptosis after trauma. MMP gene promoter regions contain AP1 sites. Therefore, we propose that upstream activators of MMP involve MAP kinase signal transduction pathways. We will map the regional and temporal profiles of three major MAP kinsaes after trauma: ERK, SAPK1/JNK, and SAPK2/p38. Correlations between MAP kinase pathways, MMP expression , matrix disruption and apoptotic cell death will be assessed. 2. Characterize the role of specific MMP after trauma. We will examine morphological, biochemical and behavioral responses to trauma in MMP-2, MMP-7 and MMP-9 knockout mice, and transgenic mice overexpressing tissue inhibitor of MMP (TIMP-1). 3. Test the Neuroprotective effects of inhibitors of the ERK pathway (PD98059, U0216), p38 pathway (SB203580) and MMP (BB-94) for traumatic brain injury. Both morphological and behavioral outcomes will be measured. To date, there are not effective treatments for traumatic brain injury. Results from these proposed experiments will help identify MMP and upstream MAP kinase pathways as viable therapeutic targets for this devastating condition.
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