Cellular and Molecular Mechanism Underlying the Protective Role of HO-1 in Traumatic Brain Injury

Traumatic brain injuries (TBIs) is a serious brain injured disease in both industrialized and developing countries, and a leading cause of mortality and morbidity among young people. An increase in glutamate production to activate glutamate receptors has been shown in TBI- induced neuronal death, and two Glutamate receptors including AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) and NMDA (N-methyl-D-aspartic acid) receptors have been identified. In cortal neurons, increased responses to AMPA-receptor agonists via stimulating free intracellular Ca+2 and increasing the levels of AMPA receptors and proinflammatory cytokine TNFα by TBI have been reported. In vivo study indicated that elevation of AMPA receptors is critical for TBI-induced neuronal cell death. Therefore, agents with ability to block AMPA receptors activation -induced neuron cell death reserve beneficial effect in treatment of TBI patients. Heme oxygenase-1 (HO-1) is a heat shock protein with the molecular weight 32kDa (HSP32) in response to a variety of stimulus. Several beneficial effects such as cytoprotection, antiinflamation, and antioxidant of HO-1 have been identified. Our studies show that HO-1 may suppress LPS or LTA-induced iNOS/NO production in macrophages, and protect glial C6 cells from ROS and anoxia-induced apoptosis. We further found that HO-1 overexpression inhibits tumor invasion via blocking MAPK activation in human breast carcinoma. However, the protective effect of HO-1 against TBI-induced cell death is still unclear. In the present project, we will investigate the cytoprotective activity of HO-1 in against AMPA receptors activation-induced apoptosis of neuronal cells, and roles of ROS-MAPKs-AP-1/NF-kB signal cascade in HO-1 against AMPA-induced cell death will be investigated. A selective AMPA receptors agonist AMPA will be used in the study to activate AMPA receptors in immortalized neuron-like cells including C6 glia cells、PC12 neural cells, and primary neuronal cells from rat, and the protective effect of HO-1 will be examined. Additionally, primary culture of neuronal cells from rate will be performed to verify the key data from immortalized cells. Specific aims and hypotheisis are described below. Specific Aim I (1st year): To investigate the protective activity of HO-1 against AMPA-induced neuronal apoptosis Hypothesis 1: HO-1 induction protects cells from AMPA-induced apoptosis Specific Aim II (2nd year): To investigate the contributions of HO-1 byproducts including CO, biliverdin, and iron on HO-1 against AMPA-induced neuronal apoptosis Hypothesis II: HO-1 protects cells from AMPA/CYZ-induced apoptosis through stimulating its byproducts production Specific Aim III (3rd year): To investigate the vivo protective effect of HO-1 and its byproducts against TBI-induced neuronal death in mice Hypothesis III: HO-1 and its byproducts protect TBI-induced neuronal death in vivo