Summary: Ischemic brain damage due to cardiac arrest or stroke is one of the most complex pathophysiologic processes. To successfully treat ischemic brain injury, one need to target several cellular pathways and cell-type within the brain. NAD+ is an essential cofactor involved in multiple bioenergetic reactions and its degradation after ischemia leads to pathologic cellular metabolism and inhibition of energy production. The majority of cellular NAD+ is re-synthetized via the salvage pathway, where nicotinamide mononucleotide (NMN) is converted to NAD+. Our recent studies demonstrated that administration of NMN dramatically ameliorates ischemic brain injury following transient global cerebral ischemia. Furthermore, NMN treatment inhibited post-ischemic NAD+ catabolism, reduced poly-ADP-ribose generation, and reversed the excessive mitochondrial fragmentation. Finally, the ischemia-induced changes in mitochondrial protein acetylation were inhibited in NMN injected animals. Overall goal of this proposed project is to develop the most effective treatment strategy utilizing NMN that will dramatically reduce ischemic brain damage and characterize the mechanism of its neuroprotection. We hypothesize that NMN administration after ischemia will significantly inhibit neurodegeneration due to its multi-targeted effect and ability to improve mitochondrial functions and cellular bioenergetics. Specific Aim 1 is focused on the NMN-induced protein acetylation mechanisms that modulate mitochondrial dynamics and function. The role of Sirt1 and Sirt3 dependent deacetylation in mitochondrial fusion and fission will be determined using our transgenic animal models that concomitantly express mitochondria targeted eYFP and Sirt1 or Sirt3. Additionally, SIRT1, and SIRT3 knockout animals will be used as tools for inhibition of deacetylase activity. In specific Aim 2, we will perform time-dependent studies of NMN administration following global cerebral ischemia in mice. We will use unbiased stereological quantification of neuronal cell death, and multiple cognitive tests will be performed to assess the efficacy of treatment. The recovery periods will vary from 7 days up to 6 months after ischemic insult. In specific Aim 3, we will determine the neuroprotective effect of the NMN treatment by using the most neuroprotective protocol determined in Aim 2 on female and aged animals. The significance of this work is that it proposes to identify NMN as a protective compound that will significantly impact the clinical application of NAD+ precursors as therapeutic compounds for acute brain injury and potentially reveal new targets for neuroprotection.