- Title
- Identifying female lower reproductive tract stem/progenitor cells and study their role in epithelial regeneration
- Creator
- Ali, Ayesha
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2019
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The human vagina is an underappreciated organ that is not merely a passageway for vaginal discharge, menses, sperm, and neonates, but can profoundly affect the health of generations. The vaginal epithelium is one of the site where bacterial communities are normally present which is often regarded as the vaginal microbiome (VMB. The VMB is dominated mainly by Lactobacillus spp. and presents the first line of defence against pathogenic invasion in the lower reproductive tract. However this VMB may be altered by exogenous factors that may impact reproductive health outcomes. For example, bacterial vaginosis (BV) affects 10–15% of women of reproductive age and is associated with genital tract infections and pregnancy complications, including pelvic inflammatory disease, premature rupture of membranes, intrauterine growth restriction, intrauterine fetal demise, chorioamnionitis, endometritis, preterm labor and delivery, postpartum infection, ectopic pregnancy and tubal factor infertility. The cost of BV-related pregnancy complications including preterm births is estimated to be $26.2 billion annually. Similar statistics can be found for fungal vaginitis. Approximately three out of four women experience at least one episode of vaginal candidiasis, whereas 20% of healthy women are asymptomatically colonized with Candida. The vaginal epithelium undergoes significant structural changes at various stages in a woman’s life that are directly linked to the levels of oestrogen. When menopause sets in and the reproductive life is over, there is a marked reduction in the circulating levels of oestrogen due to decline in the follicular reserves. These females suffer from vaginal atrophy that is described as the thinning of walls of the vagina and known to occur in post-menopausal women primarily. This leads to lower lactic acid production resulting in high pH environment in the vagina that promotes the growth of pathogens and other opportunistic organisms. This thinning of vaginal epithelium predisposes for other vaginal infections such as sexually transmitted diseases (STIs) among them are genital herpes, human papillomavirus, chlamydia, gonorrhea, syphilis, and human immunodeficiency virus (HIV). The incidence of vaginal infection due to altered VMB or oestrogen levels can be related to abnormalities in vaginal epithelial proliferation and differentiation. To date, not much is known about the vaginal cellular biology and the mechanisms of vaginal tissue maintenance. The vagina is a highly regenerative organ, and the vaginal epithelium undergoes cycles of proliferation and differentiation throughout the reproductive life of a female. The experimental or age-related decline in oestrogen levels in mice and humans leads to regression of the vaginal epithelium, which is reversed upon external supplementation of oestrogen. This exceptional regenerative capacity of vagina suggests the existence of a population of epithelial stem/progenitor cells. However, due to the lack of vaginal stem cell marker, there is no definitive evidence for the existence of vaginal stem cells. In this thesis, we have identified vaginal stem cells within their resident niches and defined their specific markers. By using unbiased thymidine analogue-based lineage tracing techniques, we identified a rare population of highly proliferating stem cells in the basal compartment of the vaginal epithelium. To support this finding, we used a suite of transgenic mouse models to label genetically the vaginal epithelial lineages and then traced the fate of labelled cells to identify adult stem cells. We showed that vaginal epithelium could self-renew, during normal growth and regeneration throughout life. Furthermore, we identified Axin2 as a marker for vaginal stem/progenitor cells. These Axin2 expressing basal cells both self-renew and give rise to differentiated cells over a long period. We also found that these cells are ovariectomy resistant stem/progenitor cells, as following ovariectomy they proliferate and expand in response to hormone supplementation and thereby reconstitute the entire vaginal epithelium. Our analysis of the Wnt pathway, which is predominantly limited to and utilized as a marker of stem cells in other organ systems, was also active in vaginal epithelium. In ovariectomized mice, regeneration of vaginal epithelium upon estrogen supplementation was accompanied by upregulation of Wnt signaling. To understand the functional importance of the Wnt pathway in the vaginal epithelium, we developed a mouse model with conditional knockout of β-catenin (Ctnnb1) which revealed that vaginal stem cells could self-renew but are unable to undergo differentiation in the absence of Wnt/β-catenin signaling, mimicking the epithelium of the atrophic vagina. In conclusion, my work has identified a unique population of vaginal stem cells and defined the role of canonical Wnt signaling in self-renewal and differentiation of these cells.
- Subject
- vaginal epithelium; STIs; stem cell; Wnt; organoids
- Identifier
- http://hdl.handle.net/1959.13/1411019
- Identifier
- uon:36270
- Rights
- Copyright 2019 Ayesha Ali
- Language
- eng
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Thesis | 4 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 440 KB | Adobe Acrobat PDF | View Details Download |