Gestational diabetes mellitus (GDM) impacts up to 1 in 10 pregnancies in the US and significantly increases the risk of complications

Gestational diabetes mellitus (GDM) impacts up to 1 in 10 pregnancies in the US and significantly increases the risk of complications, including infant macrosomia, neonatal hypoglycemia, preeclampsia, premature labor, and Cesarean delivery. It also increases the risk of postpartum complications in both mother and child including late onset diabetes and cardiovascular disease. Causal mechanisms explaining how GDM predisposes to these adverse outcomes are poorly defined, but the placenta is increasingly appreciated to be a target organ of diabetes. This proposal addresses a potential cause of exaggerated placental inflammation in GDM related to increased iron accumulation by macrophages within this vital organ. Placental macrophages (PMs) play an important role in normal placental development and govern maternal-fetal tolerance and tissue inflammatory tone. Notably, PM numbers increase and they take on a more pro-inflammatory phenotype in GDM. We recently found that healthy human PMs accumulate iron through undefined mechanisms. Using a mouse model of GDM, we also found increased tissue iron staining and greater macrophage infiltration in diseased placentae, along with increased fetal resorption (fewer live pups). A potential explanation for increased placental iron in GDM is the previously described higher expression of the hemoglobin-haptoglobin receptor (CD163) by PMs affected by GDM. Thus, our central hypothesis is that PMs exhibit an exaggerated proinflammatory phenotype in GDM, related to an increased accumulation of intracellular iron and enhanced CD163 expression.
This proposal brings together a new multidisciplinary team of investigators to test our hypothesis through three specific aims: In Aim 1 we will characterize the cellular immunophenotype of the mouse placenta in GDM, with a special focus on PMs, CD163 expression, and intracellular iron storage. Immunophenotyping studies in a robust mouse model of GDM will assess leukocyte phenotypes including macrophages (both M1 and M2 subtypes), CD4+ cells, CD8+ cells, NK cells (NK1.1+ or CD335+), and neutrophils (Neu7/4+). Tissue inflammation will be assessed by histology and flow cytometry and macrophage expression of CD163 and accumulation of iron will be assessed. In Aim 2 we will determine the cellular inflammatory phenotype of human placental tissues affected by GDM using archived tissue specimens linked to clinical meta-data from the electronic medical record, with a special focus on PMs, CD163 expression, and intracellular iron storage. Case and control placentae will be analyzed histologically for inflammation. Macrophage abundance, polarization, and iron accumulation will be determined by specific tissue immunostaining (and iron staining). These studies will help validate a mouse model of GDM using human tissues, while advancing our understanding of the impact that GDM has on placental biology. They will also provide critical preliminary data for externally-supported grants that can expand institutional efforts to prevent and treat GDM.