Leveraging Sex Differences to Understand the Brain Macrophage Response to Perinatal Hypoxia-Ischemia

University Of Colorado Denver, Aurora CO

Investigators

Abstract

PROJECT SUMMARY Perinatal hypoxic ischemic encephalopathy (HIE) is globally the second most common cause of death and disability in neonates. Although the brain immune response contributes to the pathophysiology of HIE, no current treatment targets the immune response. A major component of this immune response involves macrophages, which have notable sex differences. Microglia are the brain’s resident macrophages, and they are often grouped together with another type of macrophage found in the brain after injury: peripheral blood monocyte-derived macrophages (MDMs). Despite evidence that microglia may be protective after injury while MDMs may be harmful, many tools do not distinguish between these two types of macrophages. My goal in this grant is to leverage sex to gain a mechanistic understanding of the brain macrophage response after hypoxia-ischemia (HI) in the developing brain. I previously showed that pharmacologically depleting microglia worsens HI-induced lesion in females, but has the opposite effect in males. These data suggest that microglia are protective in female brains; in male brains, microglia may not be as protective, and MDMs may play a larger role after injury. First, I will determine if the primary macrophage contributor to lesion severity after HI is microglia or MDMs, and whether this differs by sex. I will do this using genetic approaches to specifically deplete microglia or MDMs. Second, I will use mice engineered to fluorescently label MDMs to characterize the relative contribution of microglia vs. MDMs after HI in male and female mice. These same mice will then be used for spatial transcriptomics to find the gene expression differences in male and female microglia and MDMs around the HI lesion. Third, I will look upstream of these cells to test if the root of the sex difference in HI lesion after microglial depletion is due to sex chromosomes or gonadal hormones. I will use the Four Core Genotype mice that include XX and XY male mice with testes and XX and XY female mice with ovaries. All together, this work will elucidate the macrophage response to HI in the developing brain. Using sex as a critical variable provides contrast, exposes varying paths to an outcome, and can reveal new therapeutic targets for HIE. My long-term goal is to be a child neurologist who leverages my research expertise in macrophages of the developing brain and clinical skills in neonatal brain injury to develop targeted therapies to improve outcomes for children after HIE. Through this K08 proposal, I will gain experience using transgenic mice, interpreting sex as a critical variable, understanding macrophage biology, and analyzing spatial transcriptomic data. Each member of my mentoring team provides specific expertise to address my training goals. The resulting skill set will leave me uniquely poised as a neonatal neurologist with expertise in the brain macrophage response to perinatal HI. These translational preclinical studies will provide the foundation for my independent investigation and future R01 proposals.