Placental inflammation in high risk pregnancies: a novel therapeutic target to prevent stillbirth

Placental inflammation is apparent with many pregnancy complications associated with placental dysfunction, including fetal growth restriction (FGR), reduced fetal movements (RFM) and stillbirth. Key features of placental inflammation are higher expression of pro-inflammatory cytokines (including interleukin-1; IL1), reduced expression of anti-inflammatory cytokines (e.g. IL-10) and increased numbers of placental macrophages, known as Hofbauer cells. These immune cells are believed to have roles in promoting placental development, especially via production of angiogenic factors, and in fetal immune protection from pathogens. The consequence of the increased numbers in pregnancy pathologies is unknown, but inflammatory cytokines can have detrimental effects on trophoblast cell turnover and function. Hofbauer cells have a predominantly M2 phenotype, with high expression of CD163, but their phenotype has not being fully characterised. Furthermore, it is not known whether there are phenotypic changes in pregnancy pathologies. The regulatory effects of the placental microenvironment (trophoblast and extracellular matrix) on Hofbauer cell phenotype in health and disease is unknown. The hypothesis for this project is that Hofbauer cell phenotype is shaped by the localised placental environment and altered Hofbauer number and / or phenotype contribute to placental dysfunction.
Aims

1. To characterise Hofbauer cell number and phenotype in normal and complicated pregnancies

Approaches: Hofbauer cell number will be quantified by immunohistochemistry and image analysis in placentas from normal and pathological pregnancies (RFM, FGR, stillbirth). Hofbauer cells will be isolated from placentas (normal term and RFM) and multi-colour FACS / CyTOF analysis performed to profile their expression of phenotypic and functional markers. Immunohistochemistry or dual immunofluorescence will be performed for key selected phenotypic markers on placentas from stillbirth and FGR pregnancies.

Outcomes: These studies will provide a comprehensive understanding of Hofbauer cell involvement and phenotypic changes in pregnancy pathologies associated with placental dysfunction.

2. To determine how the placental environment shapes Hofbauer cells behaviour in normal and pathological pregnancies

Approaches: Proteomic and immunohistochemical studies will be performed to determine whether regulatory interactions between trophoblasts and Hofbauer cells resemble those in other mucosal tissues (e.g. the lung). Interactions with key epithelial-derived signalling molecules (e.g. CD200, TGFbeta, IL-10) will be manipulated in vitro in isolated Hofbauer cells and trophoblast and the effect on Hofbauer cell activation status examined. Whether these regulatory interactions are disrupted in pregnancy complications will be determined. The composition of the extracellular matrix in healthy and pathological placentas will be examined by electron microscopy and proteomics. The effect of any alterations in ECM composition on Hofbauer cells activation status and function will be assessed in vitro. The consequences of altered Hofbauer cell activation state on trophoblast function will be examined (including endocrine and transport functions).

Outcomes: These studies will elucidate regulatory effects of the placental microenvironment on Hofbauer cell phenotype and the consequences for placental function.


3. To determine whether therapeutic intervention can restore Hofbauer cell phenotype and placental function
If defective trophoblast/matrix-Hofbauer cell interactions are evident in pathological pregnancies, in vitro analyses (in isolated cells or placental explants) will be performed to determine whether treatment with immunomodulatory agents can restore Hofbauer cell and placental function.

Outcomes: Alteration of Hofbauer cell phenotype may provide a novel therapeutic target for placental dysfunction in pathological pregnancies.