Elucidation of nitric oxide resistance mechanisms in motor neurons

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DESCRIPTION (provided by applicant): Nitric oxide (NO) is a free radical that is utilized by the CNS for normal physiological functions. However, when it is released in inappropriate locations or in excess, NO results in the formation of nitrotyrosine, a marker for NO-mediated damage, and massive cell death. Cell death and nitrotyrosine formation are seen in spinal cord injury and in neurodegenerative diseases such as Alzheimer's, multiple sclerosis (MS) and amyotrophic lateral sclerosis (ALS). Interestingly, motor neuron cells pretreated with sub-toxic doses of NO gain significant resistance to normally toxic doses of NO, a phenomenon we termed induced adaptive resistance (IAR). Furthermore, when exposed to toxic doses of NO, adapted cells have little to no nitrotyrosine formation. IAR is dependent on the heme metabolizing enzyme, heme oxygenase 1 (HO-1). The overall aim of this grant is elucidate and dissect the IAR phenomenon and by so doing, begin to understand native resistance mechanisms in the CNS that can be utilized to protect neurons against NO-mediated damage seen in CNS injury and neurodegenerative disease. The aims are: 1. To determine whether NO-induced cell death is due to the associated nitration of cellular proteins. If so then a) blocking 3NY formation should also block killing by NO and b) the nitration of cellular proteins, in the absence of NO treatment, should be sufficient to kill cells. 2. To determine how HO1 induces adaptive resistance to NO. Potentially, HO1 may induce adaptive resistance to NO by a.) lowering intracellular concentration of heme, b.) by the generation of heme metabolites such as bilirubin and carbon monoxide, c) by the combination of these actions, d) or by some other unknown activity associated with HO1. 3. To determine whether continuous exposure to low levels of NO will give continuous resistance to toxic NO challenge. An investigation of whether the window of IAR can be expanded has obvious therapeutic implications. PUBLIC HEALTH RELEVANCE: Cell damage and death from the free radical, nitric oxide (NO), is seen in neurodegenerative diseases such as multiple sclerosis (MS) and amyotrophic lateral sclerosis (ALS), as well as in acute injuries, such as stroke, brain trauma and spinal cord injury. Low dose NO induces production of a gene product, heme oxygenase 1 (HO1), which protects neurons against NO-mediated cell damage from high doses of NO and the aims of this grant are to find out how. The dissection and manipulation of the HO1- mediated pathway by which low dose NO lends protection against out of context or high dose NO will help us identify therapeutic targets for the treatment or prevention of NO mediated damage and thus mitigate the effects of MS, ALS and CNS injury.