Molecular Characterization of Experimental Traumatic Brain Injury

Traumatic brain injury (TBI) is the most common cause of mortality and disability in the younger (<50 years) Swedish population with an incidence rate of 20,000 cases per year. This thesis aims to increase the understanding of brain injury mechanisms, especially in a molecular and cellular context. Bone morphogenetic protein (BMP) signalling was examined in three genetically modified mice (two “loss-of-function”, one “gain-of-function”) exposed to TBI (controlled cortical impact, CCI) with CaMKII used as promoter for Cre-driven recombination in postnatal forebrain neurons. The mice survived, developed normally and did not show any obvious phenotypes except for an upregulation in Mtap2 mRNA in mice with impaired BMP signalling. Reactive Gfap and Timp1 mRNA expression measured using quantitative RT-PCR (qRT-PCR) was reduced in the mice overexpressing BMP signals. The BMP signalling pathway was further studied in cultured PC12 cells with BMP4 and NGF added. Egr3 expression was substantially increased by these growth factors. Blocking Egr or Junb functions reduced neurite outgrowth. TBI-induced mRNA expression changes in 100 selected genes in C57BL/6J mouse neocortex and hippocampus were measured using qRT-PCR at different time points post-injury. Several distinct gene clusters with similar expression patterns were identified. GeneChip analysis (Affymetrix) of the injured mouse neocortex at three days revealed 146 transcripts significantly upregulated, confirming and extending the qRT-PCR results. The findings demonstrate marked increases after injury among chemokine transcripts and activation of many genes involved in inflammation. In conclusion, the present study has revealed transcriptional changes in specific signalling pathways after brain injury. The results may help to identify novel targets for neuroprotective interventions after traumatic brain injury