Alkawafi, Isma A. (2015) Role of mammalian target of rapamycin (mTOR) signalling in BeWo trophoblast differentiation and fusion. PhD thesis, University of Warwick.

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Abstract

Foetal growth and development is closely related to the placental transport function, since any defect in this function is associated with pathological foetal growth. Trophoblast differentiation into a multinucleate syncytium is a key biological mechanism. Transcriptional regulation of fusogenic genes to promote fusion and capacity for placental hormonogenesis is achieved by a coordinated action of signals such as cAMP and MAPKs. The mammalian target of rapamycin (mTOR) acts as a placental growth signalling sensor, and this has been implicated in the pathophysiology of diseases such as intrauterine growth restriction (IUGR). This is also implicated in the pathological mechanism of diabetes mellitus, a disease which is associated with excess nutrient availability and insulin resistance. Many researchers have reported a relationship between changes in placental amino acid transporter activity and altered foetal growth. The signalling pathway of the protein kinase mTOR has been proposed to regulate cellular growth in response to growth factors, nutrient and amino acids by inducing transcription and translation. The role of mTOR signalling pathway in early development is confirmed by post implantation lethality in mouse following a complete deletion of mTOR gene. mTOR is an evolutionarily conserved member of the phosphatidylinositol-3-OH (PI-3)-kinase-related kinase (PIKKs), and its upstream activators PI3K and Akt appear to be involved in the control of trophoblast fusion. The precise role of mTOR in the trophoblast differentiation mechanisms is not well understood.

Previous studies have shown that, fusion processes in BeWo cells is stimulated by inhibition of intracellular calcium and down regulation of phosphatidylinositol 3 kinase (PI3K)/Akt pathway. Since PI3K/Akt pathway is the upstream signalling of mTOR pathway, we conducted this study to investigate the role of mTOR signalling pathway in BeWo cells differentiation. Our in-vitro studies showed that inhibition of mTOR by rapamycin, reduced forskolin-induced hCG release, whereas syncytin-1 and -2 mRNA expression was substantially augmented. These findings led us to investigate the effect of forskolin-driven adenylyl cyclase activation on mTOR expression and activity. Forskolin treatment for 24h significantly reduced mTOR protein expression. Moreover, within 10min of forskolin treatment, there was a substantial reduction in basal mTOR phosphorylation at Ser2481 and Ser2448, which is required for mTOR activity. This was associated with increased phosphorylation of p70S6K, at Ser371.Immunohistochemistry showed increased mTOR expression and phospho-mTOR (Ser2448/2481) staining in GDM placenta compared to controls.

Our results identify distinct actions of mTOR on the biochemical and morphological differentiation of BeWo trophoblasts. In addition, it showed increased expression and activity of mTOR in gestational diabetes mellitus (GDM).

Item Type:	Thesis (PhD)
Subjects:	R Medicine > RC Internal medicine
Library of Congress Subject Headings (LCSH):	Rapamycin, Trophoblast
Official Date:	2015
Dates:	Date Event 2015 Submitted
Institution:	University of Warwick
Theses Department:	Warwick Medical School
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Gammatopoulos
Extent:	xvii, 139 leaves : illustrations (colour), charts (colour)
Language:	eng

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