4 Placental Hofbauer Cells As a Proxy Cell Type for Fetal Brain Microglia

Abstract

Both placental and brain immune activation have been reported in maternal obesity-exposed (MATOB) offspring, and MATOB offspring have an increased risk for autism spectrum disorder, ADHD, and cognitive deficits. Microglia, the resident brain immune cells, have been implicated in these morbidities. Hofbauer cells (HBCs), resident fetal placental macrophages, and microglia, resident brain macrophages, share a common embryonic origin in the fetal yolk sac in mice and humans. Because direct evaluation of microglial function in a living human fetus or neonate is impossible, we sought to determine whether HBCs could serve as a more accessible biologic surrogate for fetal brain microglia in MATOB and control murine pregnancy. C57BL6/J dams were fed either a 60% high-fat diet or 10% fat control diet for 14 weeks pre-breeding and during pregnancy. At e17.5, fetal brain microglia and corresponding placental macrophages were isolated from fresh tissue. We performed single-cell RNA-sequencing on microglia and matched placental macrophages (10x Genomics, N=16, 4 replicates/group). 77,999 cells were sequenced. Canonical microglial and HBC markers were expressed in both cell types. Unsupervised analyses identified clusters within and across samples that share a significant fraction of “marker genes” (expressed more highly in cells from that cluster than in all other cells). Subsets of HBCs closely resembled subsets of microglia, with overlap analysis of marker genes demonstrating numerous clusters with 80-100% overlap between microglia and HBCs. This was true for both MATOB and CD. ScRNA-Seq elucidated novel shared gene programs and cell states that define HBCs and microglia. Shared gene programs in HBCs and microglia suggest that HBCs may be used as a proxy cell type to assay fetal brain microglial programming, in both MATOB and control mouse pregnancy. This finding may have broader implications for assaying the impact of maternal exposures beyond obesity on fetal brain development.