Endometrial Epithelial Regeneration

The adult uterus is remarkably plastic, undergoing regular cycles of growth, differentiation, breakdown, and regeneration during the normal menstrual cycle in women, and to a lesser extent in estrous cycling animals that do not menstruate. Also, during pregnancy, the uterus is extensively remodeled to accommodate the embryo/fetus. During menstruation and after pregnancy, much of the endometrium, the inner lining of the uterus, is shed and regenerated. The primary cell types in the endometrium are stromal (mesenchymal) cells and glandular and luminal epithelial cells. The first layer of the endometrium to be repaired/regenerated is the luminal epithelium, that is, the layer of epithelial cells that creates the protective barrier of the uterus. This event is critical to prevent infection as the denuded endometrium is essentially an open wound exposed to the environment. Therefore, proper endometrial regeneration is essential for uterine health and function and disruptions in this process likely contribute to uterine diseases such as endometrial cancer, thin endometrium, and infertility, among others. Our lab investigates mechanisms involved in epithelial regeneration, including epithelial stem/progenitor cells and a process termed mesenchymal-epithelial transition (MET), and our models include mice, cows, and humans. MET is a type of cellular transdifferentiation, whereby a mesenchymal cell transitions into an epithelial cell. Using mouse models to track the fate of stromal (i.e. mesenchymal) cells, my team has determined that endometrial stromal cells undergo MET to help replace the luminal epithelium in postpartum and menstruation mouse models. Current research is geared towards characterizing MET in human cell culture models and understanding the consequences of disrupting this process. These studies provide novel insight into normal endometrial epithelial development and regeneration and offer an avenue for exploring the role of MET in endometrial disease, such as cancer, when dysregulated.

In a related project, we are investigating putative epithelial stem/progenitor cells in the bovine endometrium during postpartum epithelial regeneration and the impacts of uterine infection on this process. 10-25% of dairy cows develop postpartum uterine disease (metritis) caused by pathogenic bacterial infection. Interestingly resolution of the infection early postpartum does not restore normal fertility later postpartum. Subsequently, the typical fate for a cow with postpartum metritis is culling for infertility. In this project, we are focusing our attention on the epithelial glands, which are essential for pregnancy establishment and must also be regenerated postpartum. The overarching hypothesis is that postpartum uterine infection reprograms epithelial stem/progenitor cells during critical stages of regeneration, leading to dysfunctional epithelial glands and long-term infertility. My group is using next generation sequencing technologies, sophisticated cell culture techniques, and xenotransplantation studies to, 1) identify and characterize endometrial epithelial stem/progenitor cells, 2) assess the effects of postpartum infection on epithelial stem/progenitor cell function and ability to repair the epithelium, and 3) determine if postpartum uterine infection reprograms epithelial stem/progenitor cells resulting in long-term impacts on fertility.

Pathogenesis of uterine diseases

Adenomyosis is a benign uterine disease defined by the pathological ectopic location of endometrial epithelial glands and stroma in the myometrium. Symptoms include heavy, prolonged, and painful menstruation, pelvic pain, and infertility, and pose a substantial burden on the quality of life of the affected woman. The true prevalence of the disease among women in the US is unknown but is estimated to range from 8.8% to 61.5%. The pathogenesis of adenomyosis remains unclear, but it is widely accepted that it begins with invasion of endometrial tissue into the compacted smooth muscle layer of the myometrium immediately adjacent to the endometrium through a dysregulated tissue injury repair process. Models of spontaneous adenomyosis are limited but include cattle, which afford the opportunity to

investigate the unmanipulated, natural pathogenesis of the disease and gain valuable insight into disease progression in women. This is a new area of research my group has undertaken. We have begun by characterizing adenomyosis in dairy cattle and found that it occurs in similar rates to women, up to ~50%. So far similarities include a visible breech of the endometrial-myometrial border by stroma and glands, an association with high estrogen levels and progesterone resistance, and fibrosis. Interestingly, these features are exacerbated with postpartum uterine infection (metritis), which may facilitate the breakdown of the endometrial-myometrial border, allowing invasion. We have recently conducted Visium spatial transcriptomics on cow and human uteri with and without adenomyosis to identify common genes and pathways that facilitate disease development. Our overarching goals are twofold: 1) to determine the impacts of adenomyosis on dairy cattle fertility, and 2) to determine the utility of the dairy cow to model disease pathogenesis in women.

Uterine fibroids, benign tumors of the myometrium, are the most common tumor observed in reproductive age women, occurring in 25-89% of women in the United States, and are the leading indication for hysterectomies due to associated morbidities. Knowledge of the pathogenesis of uterine fibroids is limited. It is hypothesized that fibroid tumors develop from fibroid stem/progenitor cells that themselves originate from mutated myometrial stem/progenitor cells. In support of this hypothesis, we identified a population of stem/progenitor cells in the myometrium and fibroids and showed that fibroid stem/progenitor cells had the capacity to form tumors when transplanted under the renal capsule of immunocompromised mice. Short-term hormonal therapies are available to treat uterine fibroids and can provide some relief, but their long-term use is proscribed because of associated side effects; the only definitive treatment for the disease is hysterectomy, resulting in sterility. There is a clear need for better non-surgical, non-hormonal therapeutic options. Towards this end, we conducted integrated epigenome, exome, and transcriptome analyses of uterine fibroids to delineate the molecular landscape of these tumors, and POSTN was shown to be overexpressed in the majority of fibroids analyzed. Subsequently, POSTN overexpression in a myometrial cell line resulted in an upregulation of common fibroid-associated genes and caused a myofibroblast transition of myometrial cells, which are thought to be the main cause of fibroid tumor growth. POSTN is implicated in various cancers and other fibrotic conditions and is being investigated as a druggable target. Based on our work and others, we propose the investigation of POSTN in fibroid growth and as a novel, fertility-sparing, therapeutic target.