Mechanisms and Treatment Implications of Differential Vulnerability in the Central Nervous System

About This Grant

Why do clinical trials fail? In our lab, we seek to understand some of the reasons for previous failures in translating preclinical assessments to clinical trial success. In 2 recent publications we elucidated a fundamental biological property of the neurovascular unit—we call this property differential vulnerability, and it means that although neurons are exquisitely sensitive to substrate deprivation and die rapidly, glia (astrocytes and microglia) are much more tolerant; endothelial cells and pericytes are intermediate. Neurons and glia tolerate ischemia on different time scales, suggesting to us that perhaps they need cytoprotection at different times. The molecular and cellular mechanisms underlying differential vulnerability are not clear. We believe that several mechanisms contribute to differential vulnerability, but the relative importance of each remains to be studied. Cerebral ischemia sets in motion a cascade of mechanisms resulting in cell death by one or more mechanisms including ferroptosis, necrosis, apoptosis, necroptosis, and parthanatos, among others. To explore mechanisms of astrocyte response during ischemia, we used regional transcriptomics after MCAo in rats. Agnostic Ingenuity Pathway Analysis of the astrocyte responses led to several candidate pathways and the greatest log-fold change was in the nuclear factor erythroid 2-related factor (Nrf2) mediated oxidative stress response. Other interesting pathways included the unfolded protein reasons and the NGF stimulated transcription response. We now propose a series of studies to test the role of Nrf2 mediated response underlying differential vulnerability. Oxidative injury results when free radicals oxidize and degrade proteins and nucleic acids and react with polyunsaturated fatty acids causing lipid peroxidation. Redox stress subsequently activates necrosis, apoptosis, and ferroptosis, which is also triggered by toxic lipid moieties. Neurons activate several defenses against oxidative stress and ferroptosis, but they depend heavily on astrocytes for both energy and resorption of toxic lipid moieties. These data lead to the central hypothesis to be tested in this project: neurons and astrocytes tolerate ischemia differently as a result of their different capacities to handle redox stress. We will test this hypothesis using state of the art genomic, pharmacological, and physiological manipulations. Specifically, the aims will test the relationship between glycogen metabolism, lipid peroxidation and stress response; test whether cell death mechanisms dependent on free radical stress differ between astrocytes and neurons; test the role of NRF2 in differential vulnerability; and finally look at whole animal stroke after optimized interventions timed and dosed to targeting free radical stress differently in neurons and astrocytes. CONFIDENTIAL