Gardnerella vaginalis impairs extravillous trophoblast invasion via extracellular matrix-mediated MMP2 downregulation

Proper placental development is crucial during pregnancy, and extravillous trophoblasts (EVTs) play a key role in this process. Disturbances in EVT invasion are associated with complications, such as infertility and placental dysplasia. Recent studies have suggested that the female genital tract microbiota, particularly Gardnerella vaginalis (G. vaginalis), affects placentation. This study aimed to investigate the mechanisms by which the female genital tract microbiota influence placental development.

The EVT cell line, Swan 71 (Sw. 71), was used to assess bacterial effects on EVT. Bacterial strains Lactobacillus crispatus, Lactobacillus iners, and G. vaginalis were cultured, and their culture supernatants or heat-killed bacteria were added to Sw. 71. Cell migration and invasion assays, real-time RT-PCR, and matrix metalloproteinase (MMP) 2 activity assays were performed.

The culture supernatant of G. vaginalis significantly reduced the invasiveness of Sw. 71, while heat-killed bacteria had no effect. G. vaginalis did not affect MMP2 mRNA expression in Sw. 71 without an extracellular matrix (ECM); however, it significantly suppressed MMP2 mRNA expression and protein activity in Sw. 71 cultured on ECM. Expression of endogenous MMP inhibitors remained unchanged under ECM conditions.

These results indicate that the soluble factors of G. vaginalis, rather than the bacterial cell structure itself, suppress MMP2 and inhibit invasion. This effect was observed only in the presence of the ECM, suggesting the existence of an ECM-mediated mechanism to inhibit invasion. Our findings identify a novel mechanism by which G. vaginalis impairs placentation, with potential implications for infertility and preeclampsia.