Brain trauma induces inflammation in both the endothelium and the brain parenchyma, collectively termed the neurovascular unit. While neurons die quickly by necrosis following traumatic brain injury (TBI), a vicious cycle of inflammation in endothelial cells exacerbates the injury. In activated endothelial cells, excessive superoxide reacts with nitric oxide (NO) to form peroxynitrite. At high levels following TBI, peroxynitrite is involved in blood brain barrier (BBB) leakage, altered enzymatic functions, and neurobehavior impairment. It activates AMP Kinase (AMPK), which in turn may up regulate the superoxide-producing activity of endothelial nitric oxide synthase (eNOS), and thus maintains a vicious cycle of neuroinflammatory secondary injury. The nitrosylating agent S-nitrosoglutathione (GSNO) is capable of reducing the levels of peroxynitrite and inhibiting the activity of AMPK. It also restores the levels of glutathione and protects the integrity of the neurovascular unit. Therefore, this study will investigate whether GSNO treatment ameliorates TBI-induced neuroinflammatory damage to the neurovascular unit via nitrosylation. We hypothesize that GSNO blocks the vicious AMPK/eNOS/peroxynitrite cycle, thus reducing the neurovascular injury and aiding functional recovery in TBI.
In Specific Aim 1, pharmacological agents (GSNO, a peroxynitrite scavenger, and an AMPK selective inhibitor) will be used as therapeutic tools to dissect the regulation of AMPK and amelioration of TBI in a controlled cortical impact mouse model.
In Specific Aim 2, the elucidated mechanisms will be further examined and validated using AMPK alpha 1/2 knockout mice, AMPK alpha over-expressing transgenic mice, and wild type mice.
In Specific Aim 3, we will determine whether GSNO-mediated nitrosylation of either AMPK or its upstream kinase LKB1 is responsible for the inhibition of aberrant eNOS activity and the reduced formation of peroxynitrite. The complementary pharmacological and genetic approach will determine the role of AMPK in TBI. GSNO, unlike conventional NO donors, is a non-toxic endogenous NO modulator and nitrosylating agent. Understanding S-nitrosylation mechanism and the unique AMPK/eNOS/peroxynitrite pathway may lead to new strategies for the treatment of neuroinflammatory brain trauma that target not only its neuronal consequences but also its vascular causes and exacerbations.
As a consequence of war, accidents and sport injury, an increasing number of young Americans are suffering from brain trauma. Current treatment is limited to supportive care because the neuroinflammatory mechanisms of traumatic brain injury are not well understood. The success of this proposed mechanistic intervention using S-nitrosoglutathione would provide a novel neurovascular approach to treating brain trauma.
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