Membrane-type matrix metalloproteinases (MT-MMPs) are a sub-family of zinc-dependent endopeptidases involved in the degradation of the extracellular matrix. Although MT-MMPs have been mainly characterized in tumor biology, they also play a relevant role during pregnancy. Placental MT-MMPs are required for cytotrophoblast migration and invasion of the uterine wall and in the remodeling of the spiral arteries. They are involved in the fusion of cytotrophoblasts to form the syncytiotrophoblast as well as in angiogenesis. All these processes are crucial for establishing and maintaining a successful pregnancy and, thus, MT-MMP activity has to be tightly regulated in time and space. Indeed, a de-regulation of MT-MMP expression has been linked with pregnancy complications such as preeclampsia (PE), fetal growth restriction (FGR), gestational diabetes mellitus (GDM) and was also found in maternal obesity. Here we review what is currently known about MT-MMPs in the placenta, with a focus on their general features, their localization and their involvement in pregnancy disorders.

The rapidly expanding feto-placental vasculature needs tight control by paracrine and endocrine mechanisms. Here, we focused on paracrine influence by trophoblast, the placental epithelium. We aimed to identify differences in regulation of feto-placental angiogenesis in early versus late pregnancy. To this end, the effect of conditioned media (CM) from early and late pregnancy human trophoblast was tested on network formation, migration and proliferation of human feto-placental endothelial cells. Only CM of late pregnancy trophoblast reduced network formation and migration. Screening of trophoblast transcriptome for anti-angiogenic candidates identified pigment epithelium-derived factor (PEDF) with higher expression and protein secretion in late pregnancy trophoblast. Addition of a PEDF-neutralizing antibody restored the anti-angiogenic effect of CM from late pregnancy trophoblast. Notably, human recombinant PEDF reduced network formation only in combination with VEGF. Also in the CAM assay, the combination of PEDF with VEGF reduced branching of vessels below control levels. Analysis of phosphorylation of ERK1/2 and FAK, two key players in VEGF-induced proliferation and migration, revealed that PEDF altered VEGF signaling, while PEDF alone did not affect phosphorylation of ERK1/2 and FAK. These data suggest that the trophoblast-derived anti-angiogenic molecule PEDF is involved in restricting growth and expansion of the feto-placental endothelium predominantly in late pregnancy and targets to modulate the intracellular effect of VEGF.

During first trimester pregnancy, trophoblast cells invade from the placenta into the maternal decidua where they anchor the placenta and remodel luminal structures like spiral arteries. This process depends on proteases secreted by invading trophoblasts, which degrade extracellular matrix (ECM). We here aimed to identify proteases particularly important for trophoblast invasion. We generated a list of proteases capable of degrading decidual ECM and trophoblast integrins using MEROPS database and compared expression of these proteases between primary trophoblasts isolated from first trimester placenta (FT, n = 3), representing an invasive phenotype, vs trophoblasts isolated from term pregnancy (TT, n = 3), representing a non-invasive trophoblast phenotype. Matrix metalloproteinase 12 (MMP12) revealed highest expression levels in FT, with absent expression in TT. In situ hybridisation and immunofluorescence localised MMP12 specifically to extravillous trophoblasts (evCT) whilst Ki67 co-staining revealed that proliferating trophoblasts of the cell columns were almost negative for MMP12. Quantification revealed a decline in MMP12 positive evCT at the end of first trimester, when oxygen levels start rising. MMP12 promoter analysis identified potential binding sites for hypoxia-inducible factor (HIF-1) and other oxygen-sensitive transcription factors. Moreover, MMP12 protein was increased by low oxygen in FT in vitro and by addition of a HIF-1α activator. Collectively, MMP12 is a highly expressed protease specific for invasive evCT during the first trimester. MMP12 down regulation by increasing oxygen concentration enables temporal expression control of MMP12 and involves several mechanisms including HIF-1α. These findings suggest MMP12 involved in trophoblast invasion during the first trimester.

Type 1 diabetes mellitus (T1DM) is associated with reduced fetal growth in early pregnancy, but a contributing role of the placenta has remained elusive. Thus, we investigated whether T1DM alters placental development in the first trimester. Using a protein array, the level of 60 cell-cycle-related proteins was determined in human first trimester placental tissue (gestational week 5–11) from control (n = 11) and T1DM pregnancies (n = 12). Primary trophoblasts (gestational week 7–12, n = 32) were incubated in the absence (control) or presence of hyperglycemia (25 mM D-glucose) and hyperosmolarity (5.5 mM D-glucose + 19.5 mM D-mannitol). We quantified the number of viable and dead trophoblasts (CASY Counter) and assessed cell cycle distribution (FACS) and trophoblast invasion using a transwell assay. T1DM was associated with a significant (p < 0.05) downregulation of Ki67 (−26%), chk1 (−25%), and p73 (−26%). The number of viable trophoblasts was reduced under hyperglycemia (−23%) and hyperosmolarity (−18%), whereas trophoblast invasion was increased only under hyperglycemia (+6%). Trophoblast cell death and cell cycle distribution remained unaffected. Collectively, our data demonstrate that hyperglycemia decreases trophoblast proliferation as a potential contributing factor to the reduced placental growth in T1DM in vivo.

Fetal sex influences placental function as well as maternal and fetal health, being an important factor to consider in pregnancy studies. However, fetal sex determination in the first trimester of pregnancy still faces some technical limitations. Here we describe an RT-qPCR technique to determine fetal sex based on X-inactive specific transcript (XIST) and DEAD-Box helicase 3 Y-linked (DDX3Y) gene expression. This method is straightforward, reliable, fast and applicable on both, placental tissue and primary cells.