Abstract TP231: Low Hemoglobin Causes Cerebral Hypoxia Resulting In Changes In Blood-brain Barrier Function In Mice

Abstract

Introduction: Low hemoglobin is associated with stroke and poor cerebrovascular outcomes. It is unclear whether hemoglobin concentrations directly impact cerebrovascular health. Thus, we sought to investigate the role of hemoglobin concentration on cerebral hypoxia and blood brain barrier (BBB) function in murine models of anemia. Hypothesis: Low hemoglobin will cause relevant cerebral hypoxic changes and impair BBB function. Methods: Two different models of anemia and their respective controls were generated from 30 8-week-old, female C57/BL6 mice. The separate cohorts generated included: 1) an acute anemia model cohort via anti-TER119 injection (red blood cell hemolysis) compared to IgG control injected mice; 2) chronic anemia model cohort via iron-deficient chow compared to iron replete diet control. Hemoglobin concentrations were assessed using modified Drabkin assays. Mice were euthanized by intracardiac perfusion with saline and fixative and the brain was dissected and processed for histological analysis of vascular permeability (IgG), microglia number and activation (Iba1 and CD68), response to hypoxia (HIF1α) and endothelial markers of BBB function (GLUT1). Statistical analyses were performed using two-tailed Student's t-tests. Results: Hemoglobin concentrations were lower in our separate anemia model mice compared to their respective controls (acute anemia: 5.5 ± 4.02 vs 13.1 ± 1.69, p=0.007; chronic anemia: 7.9 ± 1.05 vs 11.9 ± 2.31, p=0.0006). Postmortem histological analyses revealed stronger microglial activation (p<0.005) and higher microglial expression of hypoxia-response protein HIF1α (p<0.05) in both acute and chronic anemia models compared to their respective controls. Additionally, anemic mice had increased vascular permeability to serum IgG and decreased expression of the endothelial-specific glucose transporter GLUT1 (p<0.05). Conclusions: Anemic mice appear to display stronger microglial activation, greater HIF1α expression, and BBB dysfunction compared to non-anemic mice. Future studies will be needed to further clarify cellular and molecular mechanisms driving relationships between anemia, hypoxia, BBB dysfunction and clinical outcomes in cerebrovascular disease.