NRSA Fellowship for Kulbe: Multi-mechanistic Protection of Mitochondria Following Traumatic Brian Injury

Over five million people currently live with a disability resulting from a traumatic brain injury (TBI), with an associated economic burden of 60 billion dollars annually. Clinically there are limited treatment options for TBI, and single mechanism agents are unlikely to prevent the devastating neurologic consequences of TBI. Therefore, multi-mechanistic combinational therapies must be developed. Synaptic and non-synaptic mitochondrial dysfunction, as well as lipid peroxidation are key contributors to the pathology associated with TBI. Following injury, increased intra-cellular Ca++ is sequestered by mitochondria in an attempt to maintain Ca++ homeostasis. This uptake stresses the mitochondria, resulting in formation of the mitochondrial permeability transition pore (mPTP), activation of mtNOS, and increased formation of reactive oxygen and nitrogen species (ROS/RNS). These reactive species initiate lipid peroxidation, resulting in formation of lipid peroxyl radicals (LOO•), which break down to form the highly neurotoxic aldehydes, 4-HNE and acrolein. These neurotoxic aldehydes bind cellular and mitochondrial proteins, causing oxidative damage, enhancing mitochondrial dysfunction, and augmenting formation of mPTP, with synaptic mitochondria being particularly susceptible. Following mPTP formation, mitochondria stop producing ATP, lose their calcium buffering capacity, and release Ca++ back into the cytosol, activating calpain, which results in cytoskeletal degradation. Ultimately, synaptic dysregulation, neurodegeneration and neurologic impairment ensue. Protecting mitochondria following TBI can help attenuate downstream pathology and improve outcome. As central Combinational therapies, which protect mitochondria using distinct but complimentary mechanisms, offer a promising therapeutic approach for the treatment of TBI. We investigate two FDA-approved drugs that have been shown in preliminary studies to produce partial protection of mitochondria following experimental TBI. The antidepressant, phenelzine (PZ), scavenges neurotoxic aldehydes, while the immunosuppressant, cyclosporine A (CsA), inhibits formation of mPTP. Our overall hypothesis is that neurotoxic aldehyde scavenging and inhibition of mPTP are complimentary, and that combining these two mechanisms will additively or synergistically attenuate synaptic and non-synaptic mitochondrial dysfunction following severe controlled cortical impact (CCI) in rats, leading to decreased lipid peroxidation-induced oxidative damage, decreased cytoskeletal degradation, decreased neurodegeneration, and improved motor and cognitive function. The ultimate goal of this work is to identify differential responses non-synaptic and synaptic mitochondria have to pharmacotherapy intervention following injury, as well as identify combinational therapies that can effectively translate to neuroprotective success in human TBI.