In the United States, one in three women of reproductive age is obese. In epidemiologic studies, maternal obesity is associated with neurodevelopmental morbidity in children, including cognitive deficits, autism spectrum disorder, anxiety and depression, disordered eating, and attention deficit hyperactivity disorder. Many of these disorders have a sex bias, and aberrant brain immune activation (microglial priming, or ?trained immunity?), has been implicated in their pathogenesis. While direct evaluation of microglial function in a living human fetus or neonate is impossible, resident placental macrophages (Hofbauer cells) and microglia have a common origin in the fetal yolk sac. ?Fetal Brain-Placental Immune Activation in Maternal Obesity? is a pre-clinical R01 that tests the hypothesis that maternal obesity-associated inflammatory priming of fetal brain microglia and placental Hofbauer cells is a targetable mechanism underlying offspring cognitive deficits. A key translational aspect of the funded project is the use of single-cell RNA sequencing (scRNA-Seq) to determine whether Hofbauer cells represent a novel biologic surrogate for microglial immunoreactivity in the setting of maternal obesity. In 2019, we were funded to complete the following specific aims:
Aim 1 a: Determine whether maternal obesity primes fetal brain and placental resident macrophages to overrespond to an immune challenge.
Aim 1 b: Evaluate whether Hofbauer cells can serve as a biologic surrogate for brain microglial priming, using scRNA-Seq and flow cytometry.
Aim 2 : Determine if targeted ablation of pro-inflammatory signaling in fetal resident tissue macrophages (including microglia and placental Hofbauer cells) rescues hippocampal learning deficits in offspring, using a novel Cx3cr1-CreBT:MyD88f/f transgenic mouse. Both sexes are evaluated in all experiments, except the scRNA-Seq in Aim 1b. We have completed initial sequencing for 16 male brain and placental macrophage samples from obese and lean dams. We have demonstrated novel gene programs and cell states that define male microglia and Hofbauer cells in the context of maternal obesity. This administrative supplement proposal aims to expand the scRNA-Seq experiments in Aim 1b of the parent grant to include female fetal microglia and placental macrophages. This will allow us to test whether maternal obesity induces sex-specific alterations in fetal microglial and Hofbauer cell programs, and whether Hofbauer cell subsets can serve as a biologic surrogate for fetal brain microglial priming in the setting of maternal obesity. Determination of how fetal sex impacts microglial and placental macrophage gene programs and cell states will generate key insights into how obesity-associated brain and placental immune activation influences sex-specific neurodevelopmental outcomes. If Hofbauer cells can serve as a more accessible cell type that provides information about brain microglial function in maternal obesity, there may be broader implications for assaying the impact of other maternal exposures on fetal brain immune activation. Understanding sex differences in fetal brain and placental immune programming in maternal obesity is critical to designing precision therapies.
Maternal obesity has been linked to cognitive deficits in humans and sex-specific hippocampal learning deficits in mice; microglia, the immune cells of the brain, may play a role. Sex differences in fetal brain and placental inflammation have been noted in obese pregnancy, but the relationship between placental and brain inflammation still needs to be elucidated. We bridge this gap by examining a population of immune cells in the placenta (Hofbauer cells) that have the same embryonic origin as microglia, using single-cell RNA sequencing to determine the impact of maternal obesity and fetal sex on microglial and Hofbauer cell programs. If we identify sex differences in brain and placental immune programming in the setting of maternal obesity, these findings will guide the design of targeted therapies to prevent neurodevelopmental morbidity in offspring of both sexes.
