Stem Cells Responsible for Endometrial Regeneration and Cancer Discovered

A recent study has demonstrated that stem cells located in endometrial glands are responsible for the endometrium’s ability to self-renew during growth and regeneration. When these cells were removed, the endometrium was unable to repair itself, and when mutated, endometrial cancer developed.

Technology Networks spoke with Dr Pradeep Tanwar, senior author of the study, and Dr Shafiq Syed, first author, to learn more about the research and the significance of the findings.

Q: What was the rationale behind the study?

A: Endometrial regeneration following menses and parturition is a remarkable example of controlled tissue remodelling unparalleled in other organs. It is to the uterus what a rhythmic heartbeat is to the heart. There lies a perfect analogy that you can draw between the two organs. As with the heartbeat, any aberrations in this process underlies the major uterine disorders including cancer -- the most common gynaecological malignancy, adenomyosis, infertility, recurrent pregnancy loss and endometriosis. The process is so important, obviously one wonders what are the underlying mechanisms? What is the source for this immense regenerative power of the uterus? As with most of the organs, we know adult stem cells are responsible. These cells have also been hypothesized to be responsible for endometrial cancer almost 7 decades ago. However, the identity of such cells has ever since baffled scientists all over the world.

Over time a number of independent studies have suggested numerous different cell types as endometrial stem cells. These reports, apart from being ambiguous, do not account for the complete endometrial regeneration. Most important, the ability to precisely mark and isolate them for further investigations has remained evasive. The lack of adequate knowledge about uterine biology and the ambiguity in the existing literature has either hampered or diluted the focus of scientific efforts to identify the true stem cells of the endometrium.

Almost 7 years ago we embarked on this journey of investigating the contribution of numerous different cell types in endometrial epithelial regeneration and in the process cleared the air and identified the actual stem cell. We used the state-of-the-art technique of lineage tracing and discovered the marker of endometrial stem cells giving us the ability to isolate these cells and study their behaviour both in vivo and in vitro. We go even further and show that these are the cells responsible for endometrial cancer development.

Q: Can you tell us about endometrial regeneration and its importance?

A: Every menstrual cycle and for >400 such cycles in a woman’s reproductive life span, the uterus sheds its inner lining to a thickness of ~4-10 mm and is completely regenerated back within a week. The process has both evolutionary as well as physiological significance. Endometrial regeneration allows the uterus to grow fresh inner lining following menses and keep it ready for the possible subsequent pregnancy. Proper regeneration of endometrial glands is necessary to support the growth of pre-implantation embryos. The fact that most uterine disorders can be associated with aberrant endometrial regeneration further underscores the importance of this process. For example, insufficient regeneration particularly that of glands results in female infertility, Asherman’s syndrome, recurrent pregnancy loss etc., while uncontrolled growth/regeneration leads to cancer development, adenomyosis and endometriosis.

Q: In your research, you used in vivo lineage tracing. Can you tell us about this technique and why it was chosen?

A: If you want to know the fate of any given cell in an organ, which is basically an ensemble of cells indistinguishable from each other, you need to be able to mark the cell such that the cell itself and its subsequent progenies are labelled permanently making them distinguishable from all other cells. Lineage tracing is a state-of-the-art technique that is used to do exactly that. Therefore, it is a technique of marking cells permanently for chasing their fate, such that the contribution of any given cell towards the organ regeneration and homeostasis can be investigated. It is arguably the most reliable technique to identify stem cells.

A cell in its native environment (inside the body) behaves differently than when taken outside of the body and cultured in, for example, plastic plates. Therefore, investigations to identify the stemness of a cell have to be carried out in the native context of that cell. Lineage tracing using genetically modified animals allows permanent labelling of cells and the subsequent fate tracing of their progenies within the native microenvironment. That is why we chose this technique in our study. The ambiguity in the existing literature regarding the true identity of endometrial stem cells is partly because most of these studies are based on in vitro assays rather than the lineage tracing analysis.

Q: Can you give us an overview of your main findings and their significance?

A: There are several main highlights from our study.

First, we ruled out comprehensively the contribution of any non-epithelial cell including mesenchymal cells and bone marrow derived cells towards the endometrial regeneration. This finding is absolutely important and highlights the need to revisit the existing strategies of using these mesenchymal and bone marrow derived cells in treating various uterine disorders.

We further identified the specific marker of endometrial stem cells and show that these cells are responsible for endometrial regeneration throughout life including following parturition. More importantly, we show that these are the cells of origin for endometrial cancer, and therefore are also the endometrial cancer stem cells. We further identified the associated signalling pathways. This enables us to target these cells and the pathways in order to treat various uterine disorders including infertility and cancer.

The ability to mark and isolate endometrial stem cells and cancer stem cells and then grow mini uteri and tumoroids from them in culture plates as we show in this study has immense potential in designing novel treatment strategies tailored to individual patients. You can take a small patient biopsy or cancer sample, isolate the stem/cancer stem cells using this newly discovered marker, grow mini uteri/ tumoroids from these cells in culture plates from individual patients and test various drugs for their efficacy and sensitivity. This will ultimately enable us to design effective treatment strategies specific to individual patients.

Q: What role could these cells play in endometriosis?

A: The pathogenesis of endometriosis has remained a mystery. Over the years, several theories have been proposed, the most popular one being the theory of retrograde menstruation. Endometriosis is basically endometrial tissue growth in ectopic locations. The fact that the stem cells that we have discovered in this study have the ability to regenerate the entire endometrium makes them ideal suspects in endometriosis. We believe that these stem cells when dysregulated before being shed in retrograde menses can seed ectopic locations like the peritoneal cavity or ovarian surface and generate the endometriotic tissues giving rise to endometriosis.

Q: What are the next steps for your research?

A: With the true identity of endometrial stem cells in sight, there is so much that you can do to alleviate the problems of uterine disorders.

We plan to isolate these stem cells using our newly discovered markers from human patient samples of normal endometrium, endometrial cancer, endometriosis etc, grow patient specific organoids for further investigations as to how these stem cells and the associated pathways change in these disease conditions. Now that we only need to focus specifically on these cells rather than the entire uterus, it will definitely accelerate the investigations into the underlying pathogenesis of these diseases and therefore the designing of novel treatment strategies. Since these cells turned out to be the cancer initiating cells, we plan to look into the ways of targeting these cells specifically in treatment strategies aimed at resolving the problem of endometrial cancer recurrence.

Nevertheless, uncovering regulatory networks involved in stem cell maintenance and differentiation and comparing them between the normal and dysfunctional endometrium will provide novel insights into the disease pathogenesis and treatment.

We are particularly interested in investigating how these cells are dysregulated in the pathogenesis of endometriosis. We are hopeful that it will unravel for the first time the underlying causes of this mysterious disease.

Dr Pradeep Tanwar and Dr Shafiq Syed were speaking to Anna MacDonald, Science Writer, Technology Networks. Pradeep Tanwar is Associate Professor at the Hunter Medical Research Institute. Shafiq Syed is an Early Career Researcher at the Hunter Medical Research Institute and Associate Lecturer at the University of Newcastle.