Bacterial vaginosis (BV), caused by an imbalance in the vaginal microbiome, affects over 50 percent of women 18 to 49 years of age (1). BV, which is triggered by an overgrowth of harmful bacteria, causes discomfort, increases susceptibility to sexually transmitted infections, and may cause pregnancy complications such as preterm birth.
Researchers from the Wyss Institute led by biomedical engineer Donald Ingber investigated a new way to study the female reproductive system. They engineered an organ-on-a-chip that mimics the human cervix. These cervix chips provide a new model for scientists to investigate the complex microenvironment of the cervix and advance women’s health therapies (2).
“Bacterial vaginosis … is a major cause of preterm labor, loss of pregnancy, as well as increased incidence of HIV,” said Ingber. “There is no human model of [BV], and the animal models are not really that relevant.”
As BV progresses, aggressive pathogenic bacteria migrate from the vagina into the cervix, where mucus production and immune cells act as gatekeepers against infection. When pathogenic bacteria take over the local microenvironment, the microbiome changes. The pathological outcomes of this invasion are associated with alterations in the protective mucus layer, leading to infection.
Currently, antibiotics are the gold-standard treatment for BV, but they often fail to eliminate the invading bacteria due to drug resistance. Antibiotic therapies also do not prevent the recurrence of this condition in more than 60 percent of women (3). Although BV was first described more than a century ago, the pathogenic events following the initial infection remain unclear, and researchers need competent models to study this condition.
Ingber and his team’s new cervix chip contains two parallel microchannels separated by a porous membrane, resembling the layers within the human cervix. The researchers plated human cervical epithelial cells in one channel and fibroblasts in the other. The porous membrane contained extracellular matrix components and vital structural proteins, such as fibronectin, which provided a scaffold between the two microchannels and allowed for communication between the layers.
“I'm always amazed a little bit in how well these models are able to recapitulate the host physiology when we recreate the host environment,” said Ingber.
I'm always amazed a little bit in how well these models are able to recapitulate the host physiology when we recreate the host environment.
- Donald Ingber, Wyss Institute
Proper mucus production is a defining characteristic of a healthy cervix. After five days of cell culture, the researchers observed mucus accumulation on the chip's epithelial surface, confirming its functionality. To validate mucus production, the researcher used fluorescent staining with wheat germ agglutinin lectin, a marker for glycoproteins found in mucus. Immunofluorescence microscopy revealed the presence of mucin 5B, an essential mucus protein abundantly secreted by goblet cells within the epithelium.
To mimic healthy and pathological microbial conditions in the cervix chip, the researchers first populated it with Lactobacillus crispatus from healthy women. These bacteria dominate healthy cervical microbiomes. The L. crispatus bacteria caused the mucus layer to thicken and improved its quality while leaving the underlying epithelium fully intact during three days of co-culture. The mucus induced the expression of proteins in cervical epithelial cells that are involved in differentiation and protection against pathogens.
When the team populated the cervix chip with Gardnerella vaginalis from women with BV, the epithelium’s barrier functions became severely compromised. In addition, pro-inflammatory markers such as interleukin-6 and tumor necrosis factor alpha, which are associated with pathogenic processes, were significantly elevated.
“What I'm most excited about is the mucus,” said Caroline Mitchell, a gynecologist at Harvard University who was not part of the study. “The cervix chip makes mucus and mucins, and then if you add microbes, you can tell what's the effect. How do some components of the mucin make them grow differently or behave differently? So, it allows really mechanistic experiments that have not, to this date, been possible anywhere else.”
Numerous conditions lack adequate human models to study disease pathology accurately. Ingber’s group believes the cervical chip technology can be modified for other organs. They are currently conducting studies using the cervix chip to test non-hormonal contraceptives and how they can influence the sperm-cervix microenvironment.
References
- Wu, S., Hugerth, L.W., Schuppe-Koistinen, I. & Du, J. The right bug in the right place: opportunities for bacterial vaginosis treatment. npj Biofilms Microbiomes 8, 1–11 (2022).
- Izadifar, Z. et al. Mucus production, host-microbiome interactions, hormone sensitivity, and innate immune responses modeled in human cervix chips. Nat Commun 15, 4578 (2024).
- Carter, K.A., Tuddenham, S. & Brotman, R.M. Dequalinium Chloride—An Emerging Option in the Sparse Landscape of Bacterial Vaginosis Therapies. JAMA Netw Open 7, (2024).