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Introduction:  Murine placentation is associated with trophoblast cells invasion of the maternal endometrium and extensive maternal and foetal angiogenesis. Both processes involve proteases-dependent extracellular matrix remodelling. Among the protease inhibitors, plasminogen activator inhibitor-1 (PAI-1) is transiently produced by spongiotrophoblasts and trophoblast giant cells at days 10.5-11.5 day post-coitum (dpc). Although accumulating evidence demonstrates the key role of PA-1 in pathological angiogenesis, its function during placental vascularisation remains to be elucidated. PAI-1 knockout mice are fertile and the litter sizes are normal. We have therefore analysed the consequence of PAI-1 deficiency on murine placentation.

Material and Methods:  We have studied the possible role of PAI-1 by quantitating the placental vessel density, the relative thickness of the labyrinth, decidua and spongiotrophoblast at day 10.5, 12.5 and 14.5 dpc in mice deficient for PAI-1 or in control mice. An original method of computer-assisted image analysis allowed us to quantify alterations of several placental compartments identified with specific monoclonal antibodies (keratin, desmin, fibrinogen and MECA-32). To investigate the differentially expressed genes, we performed laser capture microdissection (LCM), followed by genome-wide expression profiling using high-density oligonucleotides microarray analysis (GeneChip Mouse Genome 430 2.0 Array, Affymetrix). Data were analysed using Ingenuity Pathways Analysis (Ingenuity Systems®, http://www.ingenuity.com).

Results:  At 10.5 and 12.5 dpc, an abnormal placental morphology was observed in both labyrinth and spongiotrophoblast layers in PAI-1-/- mice. Lack of PAI-1 resulted in a transient decreased maternal and fetal vascularisation of the placenta that caused (1) an enhancement in the decidua/labyrinth and labyrinth/spongiotrophoblast thickness ratios, (2) a significant increase of trophoblast density. Normalization of placental morphology occurred by day 14.5 dpc in PAI-1 deficient mice. Statistical analysis of microarrays revealed 706 genes differentially expressed between PAI-1 deficient and normal mice in the labyrinth zone at 10.5 dpc. At 14.5 dpc, only 205 genes are differentially expressed. Using Ingenuity Pathways Analysis, most of those genes were found to be associated to lipid metabolism, cellular growth and proliferation.

Conclusion:  Despite a transient PAI-1 requirement for optimal placental angiogenesis, this gene does not appear to be essential for trophoblast invasion and placentation.