Effects of the gut microbiota on placental angiogenesis and intrauterine growth in gnotobiotic mice.

Environmental causes of intrauterine growth restriction (IUGR) remain poorly characterized. Here, we compare germ-free (GF) and conventionally raised (CONV-R) mice to assess the effects of the gut microbiota on placental/fetal development at embryonic day (E)11.5 (end of placentation) and E17.5 (near term). Pregnancy- and microbiota-associated changes in gene expression occur along the gut, including those related to angiogenesis, while bacterial composition and fermentation activity remain stable. Placental weights at E11.5 and fetal weights at E17.5 are significantly reduced in GF animals. Compared to CONV-R dams, the GF maternal decidua exhibits similar vascular histomorphometric features at E11.5 and E17.5, and numbers of uterine NK-cells (effectors of vascular remodeling) at E11.5. In contrast, angiogenesis is disturbed in the GF fetal-derived placental compartment (junctional and/or labyrinth zones) at E11.5, as judged by i) increased levels of proangiogenic proteins (angiopoietin-2, FGF-2, follistatin, SDF-1, VEGF-A, VEGF-C); ii) increased levels of phos-VEGFR2 and phos-p38-MAPK yet reduction in phos-ERK1/2; and iii) reduced expression of junctional zone glycoprotein genes associated with angiogenesis and fetal growth, resulting in reduced endothelial cell density at the labyrinth zone at E17.5. Colonization of GF mice before pregnancy with cecal microbiota from CONV-R animals rescues fetal growth and altered transcriptomic, proteomic, and immunohistochemical features in the fetal GF placental compartment. Single-nucleus RNA-sequencing demonstrated increased expression of mitochondrial and ribosomal-associated oxidative stress genes in endothelial cell clusters in the GF fetal placental compartment (E11.5, E17.5), mimicking oxidative stress signatures in human IUGR. These results provide a rationale for seeking microbial targets for treating/preventing IUGR.