Ischemic preconditioning, induced by a sub-lethal duration of ischemia, triggers endogenous responses that protect the brain against a subsequent, severe ischemic insult, a phenomenon known as "tolerance". Ischemic tolerance requires new protein synthesis, involves genomic reorganization, and is transient. Our long-term objective is to elucidate the molecular mechanisms by which the preconditioning stimulus induces tolerance. Our studies support the conceptual framework that preconditioning regulates the interaction between mRNAs and RISCs leading to increased translation of the mRNAs, particularly those that function as transcriptional regulators that can reprogram the genome and attenuate responses to ischemic injury, resulting in tolerance. We will the following aims to test specific mechanisms of ischemic preconditioning-induced tolerance, including (1) the molecular mechanisms of ischemic preconditioning-induced regulation of RISCs, (2) the regulation of RISC-bound RNAs by ischemic preconditioning, (3) the regulation of the nuclear proteome and transcription rates by ischemic preconditioning, and (4) to overall test of the conceptual framework: tolerance by regulation of miRNAs and mRNAs. These studies are directly related to the mission of NIH and NINDS in that ischemic brain injuries are among the most common and important causes of disability and death worldwide. Clinical evidence suggests that endogenous preconditioning triggered by a transient ischemic attack is present in the human brain. While not without challenges, promising strategies to elicit endogenous brain protection are under clinical development. Thus, we will use a combination of biochemical, molecular, and proteomic studies to examine these distinct and novel mechanisms of in vivo ischemic preconditioning on the induction of tolerance. Our goal is to provide evidence for miRNAs as effectors of endogenous neuroprotection that will translate into novel strategies for the treatment or prevention of ischemic brain injury. PUBLIC HEALTH RELEVANCE: Ischemic brain injuries due to stroke or cardiac arrest are common and prominent causes of disability and death worldwide. Yet, there is evidence to suggest that a transient ischemic attack can actually protect the human brain from a subsequent, more severe ischemic attack. As we can model this protection in laboratory studies, this research will improve public health through the identification of novel mechanisms that contribute to this protection, and their translation into clinical strategies for the treatment or prevention of ischemic brain injury.