- Title
- Understanding the role of the mTOR signalling pathway in the ovary during folliculogenesis, PCOS and hyperandrogenism
- Creator
- Sercombe, Lisa
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2020
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Polycystic ovary syndrome (PCOS) is a complex and heterogeneous reproductive and endocrine disorder. Symptoms of PCOS include hyperandrogenism, polycystic ovaries and infrequent or absent menstruation. PCOS is also the leading cause of anovulation associated infertility in women. Reduced fertility in PCOS patients arises due to follicular dysfunction, which culminates in the continuous arrest of mid antral follicles followed by polycystic remodelling. The cause of PCOS is ill defined because the disease pathophysiology is poorly understood. Previous research has alluded to the dysfunction of the mammalian target of rapamycin (mTOR) signalling pathway in PCOS. However, no study thus far has comprehensively investigated the relationship between the mTOR signalling pathway and PCOS. Hyperandrogenism is thought to be a key pathogenic factor in PCOS, as women with clinical androgen excess and animal models exhibit many of the ovarian features of PCOS. Yet, the precise mechanisms through which hyperandrogenism causes reproductive dysfunction in PCOS is unclear. Animal models of PCOS are limited because they indirectly induce PCOS via systemic hyperandrogenism, which requires several months to produce the desired phenotype. Culturing ovaries in vitro can overcome these limitations of PCOS animal models. In vitro methods have been widely used in research to establish ovarian development and biology, toxicology, and also ovarian disorders. Thus, in vitro models are a promising methodology to characterise the molecular mechanisms related to hyperandrogenism, the mTOR signalling pathway and PCOS. The capacity of ovary culture models to recapitulate in situ counterparts is ill-defined, particularly the molecular mechanisms. Therefore, the first point of investigation of this thesis was a comparative proteomic analysis of in vitro cultured ovaries. A liquid chromatography tandem mass spectrometry (LC-MS/MS) proteomic approach was used to compare the protein profile of ovaries cultured in vitro to those in situ. The results showed that overall, ovaries cultured in vitro are similar to that in situ, as they share the majority of proteins and most of which are comparably expressed. In addition, we demonstrated that mTOR pathways were conserved within ovaries cultured in vitro. Accordingly, in vitro cultured ovaries were able to signal through mTOR pathway(s) similar to if they remained in vivo. Taken together, organ culture models are an appropriate methodology to investigate the ovarian mechanisms of PCOS. Chapter two of this thesis characterised the expression of mTOR pathway markers within PCOS cysts. This analysis revealed that mTOR pathway signalling within the granulosa cells lining PCOS cysts was differentially deregulated. Based upon this differential mTOR pathway activity as well as histological differences, two cyst types were characterised within PCOS ovaries, multilayered and flattened. In the same chapter (chapter 3), the cause of aberrant mTOR signalling in PCOS was investigated using an in vitro culture model of moderate ovarian hyperandrogenism. This revealed that moderate hyperandrogenism induces abnormal mTOR signalling similar to that of multilayered PCOS cysts, suggesting a relationship between androgen excess, cystogenesis and mTOR signalling activity in PCOS ovaries. The final chapter (chapter 4), utilised an in vitro model to examine how androgen excess progressively impairs ovarian function. A label-free quantification (LFQ) LC MS/MS proteomic approach was used to characterise the protein profile of moderate and severe ovarian hyperandrogenism. Ingenuity pathway analysis showed that of moderate and severe hyperandrogenism deregulates mTOR signalling comparable to the multilayered and flattened cysts of PCOS ovaries, respectively. These results again suggest that hyperandrogenism deregulated mTOR signalling in PCOS. This thesis, for the first time, identified that mTOR signalling is deregulated in PCOS ovaries. Furthermore, hyperandrogenism in PCOS progressively promotes cystogenesis in a dual manner, (1) first attenuating pS6K signalling triggering follicular arrest and granulosa apoptosis, (2), later by increasing mTOR signalling to preserve cysts and the functions of their granulosa cell layer. Together, this finding showcases a mechanism through which androgen excess increasingly deregulates the mTOR signalling in PCOS ovaries and thereby promotes cystogenesis. Current treatment methods for PCOS are limited because they only pacify symptoms. The novelty of this thesis is that we identified a novel therapeutic target, which is based upon molecular mechanisms of PCOS rather than symptoms.
- Subject
- polycystic ovary syndrome; granulosa cell; mTOR; ovary
- Identifier
- http://hdl.handle.net/1959.13/1418273
- Identifier
- uon:37321
- Rights
- Copyright 2020 Lisa Sercombe
- Language
- eng
- Full Text
- Hits: 899
- Visitors: 1370
- Downloads: 540
| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Thesis | 17 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 348 KB | Adobe Acrobat PDF | View Details Download |