Endometriosis may be caused by bacterial infections

Infections with a bacteria that contributes to gum disease may cause endometriosis, a condition in which tissues lining the uterus grow outside of it and form painful lesions. The finding suggests antibiotics could prevent or treat the condition.

Yutaka Kondo at Nagoya University in Japan and his colleagues examined endometrial tissue samples from 28 women, half of whom were diagnosed with endometriosis.

Genetic analysis of the samples revealed abnormalities in cells called fibroblasts, which form connective tissues. These fibroblasts had increased activity in 13 genes compared with those from people without the condition. One gene, TAGLN, drives production of a protein to help cells proliferate and migrate, potentially explaining why endometrial cells grow outside the uterus in endometriosis.

TAGLN activity is also boosted by inflammation, which can occur due to bacterial infection. Using a fluorescent dye, the researchers searched for bacterial pathogens inside endometrial tissues collected from a separate group of 84 women, half of whom had endometriosis. They detected Fusobacterium nucleatum in 64 per cent of those with the condition versus 7 per cent of those without it.

Next, the researchers used a mouse model to understand the role F. nucleatum may play in the condition. Mice don’t menstruate, so they cannot develop endometriosis. To mimic the condition, the researchers first infected mice with F. nucleatum. Then, they collected uterine samples and injected them into the abdomens of 12 other mice. The mice received weekly hormone injections to promote the growth of lesions.

After four weeks, the average number of endometrial lesions in mice that received infected uterine samples was more than double that seen in nine other mice given uninfected samples. The lesions were also about five times as large as those in the control animals, suggesting F. nucleatum encourages endometrial lesions to grow and spread.

In a later test in mice, antibiotics prevented the endometrial tissue from proliferating outside the uterus and reduced lesion size. The researchers did not test antibiotic treatment for endometriosis in humans. “We don’t know that eradication of this bacteria is truly effective for the treatment of endometriosis,” says Kondo. “Those studies are ongoing.”

F. nucleatum is commonly found in the mouth and contributes to gum disease. Kondo’s team has shown it can travel through blood, which may be how it infects endometrial cells. “This bacterium can also be found in the rectum, which is quite close to the vagina,” he says, indicating another potential transmission route.

“I would find it unusual that it’s a single pathogen that’s causing endometriosis, rather than a cluster of pathogens or many pathogens independently contributing to the disease,” says Christine Metz at the Feinstein Institutes for Medical Research in New York. But she says these results align with previous research that has linked chronic endometritis – a separate condition caused by bacterial infections – with an increased risk of endometriosis.