Preconditioning brain white matter against ischemia

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PROJECT SUMMARY A growth in the aging population together with improved stroke care has resulted in an increase in survivors and a rise in recurrent ischemic events, presenting major challenges for overburdened healthcare economics for these patients. Consequently, approaches to induce tolerance in the brain against ischemia have gained new momentum in clinical and experimental studies. However, mechanisms of ischemic preconditioning (IPC) have been primarily studied in gray matter (GM), despite white matter (WM) injury and axon dysfunction being critical components of clinical deficits observed in stroke patients. Moreover, most in vivo models of IPC performed in rodents consist of short episodes of hypoxia/ischemia and are not applicable to translate into clinical settings as therapeutics. Therefore, there is an unmet need to establish clinically applicable pharmacological approaches to preconditioning the brain against ischemia. Our preliminary results show that CX-4945 (Silmitasertib), an FDA- approved Casein Kinase 2 (CK2) inhibitor, preconditions WM, promotes axon function recovery and improves behavioral outcomes after an in vitro or in vivo ischemic injury. Although aging reduces neuronal IPC, CX-4945 comparably preconditions young and aging WM by preserving mitochondrial motility. Because the threshold to precondition is reported to be higher in females, the main goal of this current proposal is to understand the mechanisms of preconditioning conferred by CK2 inhibition in young and aging male and female WM. We have reported that CK2 signals via the CDK5 and AKT pathways to mediate ischemic WM injury. Thus, CK2 inhibition correlates with the preservation of oligodendrocytes, axon structure and function, and conservation of mitochondrial dynamics in young and aging WM. Our preliminary data show that a brief period of CK2 inhibition with CX-4945 effectively preconditions axon function by maintaining mitochondrial motility. Furthermore, preconditioning with CX-4945 considerably attenuates behavioral deficits observed after an in vivo focal subcortical WM injury. We identified miR-501 as an ischemia-upregulated miRNA that is suppressed by CK2 inhibition, and reciprocal interaction between levels of miR-501 and Miro-2 regulates axonal mitochondrial motility. A similar upregulation of miR-501 levels in stroke patient plasma samples compared to age- and sex- matched controls propose CK2 as a clinically relevant therapeutic target. Therefore, we propose to extend these studies by testing our novel hypothesis that CK2 inhibition preconditions WM by differentially regulating the CDK5 and AKT signaling pathways to maintain mitochondrial dynamics by reciprocally regulating miR-501 and Miro-2 levels. We will combine electrophysiology, advanced imaging, functional analysis of mitochondria, mouse miRNA expression and regulation studies, human miRNA expression in plasma and human brain studies, and validation of regulated signaling molecules to determine whether CK2 inhibition acts via CDK5 or AKT to regulate mitochondrial proteins through alteration of miRNA profiles to precondition WM against ischemia.