Colonization of the cervicovaginal space with Gardnerella vaginalis leads to local inflammation and cervical remodeling in pregnant mice

Abstract

The role of the cervicovaginal (CV) microbiome in regulating cervical function during pregnancy is poorly understood. Gardnerella vaginalis (G. vaginalis) is the most common bacteria associated with the diagnosis of bacterial vaginosis (BV). While BV has been associated with preterm birth (PTB), clinical trials targeting BV do not decrease PTB rates. It remains unknown if G. vaginalis is capable of triggering molecular, biomechanical and cellular events that could lead to PTB. The objective of this study was to determine if cervicovaginal colonization with G. vaginalis, in pregnant mice, induced cervical remodeling and modified cervical function. CD-1 timed-pregnant mice received a 5X108 CFU/mL intravaginal inoculation of G. vaginalis or control on embryonic day 12 (E12) and E13. On E15, the mice were sacrificed and cervicovaginal fluid (CVF), amniotic fluid (AF), cervix, uterus, placentas and fetal membranes (FM) were collected. Genomic DNA was isolated from the CVF, placenta, uterus and FM and QPCR was performed to confirm colonization. IL-6 was measured in the CVF and AF and soluble e-cadherin (seCAD) was assessed in the CVF by ELISA. RNA was extracted from the cervices to evaluate IL-10, IL-8, IL-1β, TNF-α, Tff-1, SPINK-5, HAS-1 and LOX expression via QPCR. Mucicarmine and trichrome staining was used to assess cervical mucin and collagen. Biomechanical properties of the cervix were studied using quasi-static tensile load-to-failure biomechanical tests. G. vaginalis successfully colonized the CV space. This colonization induced immune responses (increased IL-6 levels in CVF and AF, increased mRNA expression of cervical cytokines), altered the epithelial barrier (increased seCAD in the CVF), induced cervical remodeling (increased mucin production, altered collagen) and altered cervical biomechanical properties (a decrease in biomechanical modulus and an increase in maximum strain). The ability of G. vaginalis to induce these molecular, immune, cellular and biomechanical changes suggests that this bacterium may play a pathogenic role in premature cervical remodeling leading to PTB.

Cooperative Interactions between Trichomonas vaginalis and Associated Bacteria Enhance Paracellular Permeability of the Cervicovaginal Epithelium by Dysregulating Tight Junctions

“…Decreased barrier function facilitates the passage of HIV (44) and promotes cervical remodeling, which is an initiating step toward preterm birth (10,17,30). Trichomoniasis and bacterial vaginosis are both associated with increased risk of HIV transmission, premature rupture of membranes, and preterm birth (5)(6)(7)(8)(9)(10)(11)(12)(13)(14). The T. vaginalis parasite is accompanied by species of CST-IV bacteria that are coincidently found in bacterial vaginosis (3,4).…”

“…These infections cause similar vaginitis-related symptoms (e.g., itching and a frothy malodorous discharge) and are associated with pathological complications such as preterm birth (5)(6)(7)(8)(9)(10) and high transmissibility of human immunodeficiency virus (HIV) (11)(12)(13)(14). CST-IV bacteria are known to induce physical, immunological, and biochemical changes in the cervicovaginal mucosa.…”

“…For example, bacterial species of CST-IV promote a greater proinflammatory response in the vagina than lactobacillus-dominant communities (9,(15)(16)(17)(18). In addition, these bacteria (particularly G. vaginalis) affect the integrity of cervicovaginal epithelial barrier (10,17). Although these alterations are likely to contribute to the pathological complications that are similarly associated with both trichomoniasis and BV, such as poor pregnancy outcomes and HIV acquisition, it is unclear if BV-associated bacteria and T. vaginalis act cooperatively in promoting disease.…”

“…With regard to the cervicovaginal mucosa, a compromised epithelial barrier promotes cervical remodeling, which is an initiating step toward preterm birth (30). A link between these events and the composition of the vaginal microbiota has been claimed, and the CST-IV bacterium G. vaginalis, in particular, has been associated with this process (10,15,17,31). Protective lactobacilli, on the other hand, are known to promote cervical health by mitigating effects of proinflammatory molecules and counteracting G. vaginalisinduced disruption of the cervicovaginal barrier (32).…”

Interaction of Gardnerella vaginalis and Vaginolysin with the Apical versus Basolateral Face of a Three-Dimensional Model of Vaginal Epithelium

“…Monospecies cocultures of G. vaginalis on ectocervical, endocervical, and vaginal epithelial cell monolayers induced the secretion of some proinflammatory cytokines, including platelet-derived growth factor bb (PDGF-bb), IL-6, IL-7, granulocyte colony-stimulating factor (G-CSF), and interferon gamma inducible protein 10 kDa (IP-10) (58). Moreover, cervicovaginal colonization by G. vaginalis in pregnant mice resulted in increased levels of IL-6 in cervicovaginal fluid as well as increased IL-1␤, IL-8, and IL-10 gene expression in cervical tissue (59). In a human three-dimensional endometrial epithelial cell model, however, G. vaginalis did not elicit any significant changes in the secretion of IL-6, IL-8, or tumor necrosis factor alpha (TNF-␣) compared to a mock-infected control (60).…”