Matrix Metalloproteinase 1 in Pre-eclampsia and Fetal Growth Restriction: Reduced Gene Expression in Decidual Tissue and Protein Expression in Extravillous Trophoblasts

Superficial invasion of extravillous trophoblasts (EVTs) and impaired spiral artery remodelling are characterizing phenomena in pregnancies complicated by pre-eclampsia (PE) and fetal growth restriction (FGR). However, the underlying causes remain unclear. In this study, gene expression in decidua basalis tissue from pregnancies complicated with PE and/or FGR (n = 18) and normal pregnancies (n = 17) was assessed by Affymetrix HG Focus microarray to obtain hints of mechanisms involved in the pathogenesis. A total of 200 differentially expressed transcripts were detected at a false discovery rate (FDR) ≤ 0.1. Several genes involved in trophoblast differentiation and invasion were downregulated, including the matrix metalloproteinases (MMPs) MMP1, -7 and -12. MMPs are a family of enzymes involved in degradation of extracellular matrix and have been ascribed a permissive role in trophoblast invasion. MMP1 had the highest fold change among the differentially expressed genes (four-fold downregulated) and was chosen for further investigation. Reduced MMP1 mRNA in decidual tissue was confirmed by RT-qPCR. MMP1 protein expression in EVTs was assessed by double immunofluorescence analysis, using antibodies against pro-MMP1 and cytokeratin 7. The proportion of MMP1 positive EVTs was reduced in all subgroups of cases (PE: n = 18, FGR: n = 11 and PE + FGR: n = 30) compared to controls (n = 23) (all p’s < 0.05). Based on these findings, we hypothesize that reduced levels of MMP1 protein in EVTs could be linked to the impaired trophoblast invasion in PE and/or FGR.