July 11, 2003

VUMC Study: Endometriosis patients lack critical molecules in uterus

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Jack Wells

VUMC Study: Endometriosis patients lack critical molecules in uterus

Some women who have infertility due to endometriosis lack molecules in the uterus that allow the embryo to attach to the uterine wall, according to a study published in the July 2003 issue of Endocrinology.

Kevin Osteen, Ph.D., professor of Obstetrics and Gynecology at Vanderbilt University Medical Center, is one of the authors of the study that provides a better understanding of the disease, a painful condition in women of reproductive age.

By continuing the studies with larger numbers of women, the research may eventually lead to a non-invasive way to diagnose endometriosis and the ability to develop drugs that correct the dysregulation of genes associated with this disease.

The study is a collaboration of several members of the Specialized Cooperative Center Program in Reproduction Research (SCCPRR). The SCCPRR, part of the National Institute of Child Health and Human Development, supports 14 centers, including one at Vanderbilt. It is a research-based centers program designed to bring together investigators from multiple institutions to focus on reproductive disorders such as endometriosis.

About 10 to 15 percent of all women have endometriosis. Among women with endometriosis, more than half are infertile.

Endometriosis occurs when bits of the endometrium — the tissue that lines the uterus — are expelled from the uterus during menstruation and travel back up into the fallopian tubes and then into the pelvic cavity, and then become implanted on other pelvic organs. Most often the implants develop on the outside of the ovaries, the fallopian tubes, or the uterus. The mislocated cells imitate the menstrual cycle, first thickening and then bleeding as menstruation begins. Because the implants are imbedded within other tissue, there is nowhere for the blood to go. They form blood blisters that irritate the surrounding tissues, and often a cyst forms to encapsulate the blister. The cyst may become a scar or an adhesion. The end result may be infertility.

The study builds on an earlier NICHD-funded study that reported that a molecule called L-selectin needs to be present on the uterine wall before an embryo can attach to the uterus and a pregnancy can begin.

In the current study, the researchers found that at the time the uterus is most receptive to the embryo, women with infertility due to endometriosis have very low levels of an enzyme that is involved in synthesizing the ligand for L-selectin. The ligand is a rubber band-like molecule that helps L-selectin attach to the uterine wall. Because these women lack the enzyme that makes the L-selectin ligand, the embryo may not be able to attach, which would inhibit pregnancy.

The researchers from Stanford, the University of California in San Francisco, Vanderbilt and the University of North Carolina at Chapel Hill collected endometrium samples from 15 volunteers, eight with endometriosis, during the “window of implantation,” which are the days of a woman’s menstrual cycle when the uterus is receptive to an embryo. With the help of a new technology called microarray analysis, where thousands of genes can be screened at once instead of one at a time, the group analyzed more than 12,000 genes and identified large numbers that are not regulated.

Recent Vanderbilt studies have shown that women with endometriosis fail to respond to progesterone during preparation for pregnancy in terms of down-regulating key enzymes that are associated with menstruation. Past studies have shown that the endometrium makes enzymes called matrix metalloproteinases (MMPs) that are linked not only to endometrial breakdown and regulation, but also to invasive processes, such as cancer or endometriosis. In the normal endometrium MMPs are highly regulated and are suppressed during the time that pregnancy is established. This allows the endometrium to avoid menstruation-like breakdown during early pregnancy.

The Endocrinology study found that 91 genes had more than a two-fold increase in gene expression in women with endometriosis, compared to those without the disease, and 115 genes had more than a two-fold decrease in women with endometriosis compared to those without. These genes are believed to be crucial in the development of endometriosis and in loss of fertility associated with the disease. Osteen said the research shows that genes present in the incorrect amount may contribute to the ectopic development of endometriosis and that it may also create an environment where it is difficult for the embryo to attach to the uterus. It also shows that the endometrium of a woman with endometriosis is abnormal.

Vanderbilt will continue its studies as to why the endometrium of women with endometriosis is different.

“There could be environmental influences that account for endometriosis showing up in more women, and in younger women,” Osteen said. “The epidemiology suggests that this disease is showing up in a younger population, in women in their teens. This could be explained by more awareness, mothers being more attuned to their daughter’s health than in the past, but there’s probably more to it than that.”

Osteen said Vanderbilt researchers are exploring the theory that there is a fetal origin with endometriosis, and that environmental endocrine disruptors, such as dioxin, may be involved. Dioxin is a by-product of combustion and a known human carcinogen, perhaps best known for being in Agent Orange during the Vietnam War. Vanderbilt has received funding from the Environmental Protection Agency (EPA) to study the effect of dioxin on endometriosis. Osteen’s group has also received more recent funding from the National Institute of Environmental Health Services to develop a fetal utero exposure model in mice to investigate whether the failure of steroids to regulate the MMPs could have originated from an environmental exposure.

“We’re all exposed to dioxin,” Osteen said. “We can’t avoid it. It’s in our food and our water. What we want to know is, ‘is it a risk factor?’ What we’re finding is that dioxin has been traditionally viewed as a compound that interferes with estrogen action. But we’re finding it interferes with progesterone-mediated endometrial preparation for pregnancy. This is intriguing because we now know that many genes that are important for normal fertility aren’t regulated normally in women with endometriosis. We can induce a similar effect in the lab by exposing the endometrium to dioxin.”

Funding from the Endometriosis Association helped bring Grant Yeaman, Ph.D., a reproductive immunologist, to Vanderbilt from Dartmouth Medical School. Working with Yeaman the Vanderbilt group is also looking into the possibility that a systemic inflammation and an autoimmune response may be components of the disease process. Osteen said that Vanderbilt is also working with a new biotechnology company to explore the development of a non-invasive, diagnostic test for endometriosis.

“This is both an endocrine disease and a steroid-induced immune disease, involving some disruption of the immune system,” he said. “We have shown that women with endometriosis have a hypersensitivity to pro-inflammatory agents that are normally produced in the endometrium.”