In the absence of readily available physiological models of human growth, the effects of oestradiol on the human C28/I2 chondrocyte cell line were studied. The classical oestrogen receptors, ERα and ERβ, were shown to be expressed in both murine and human chondrocyte cell lines. Oestradiol and related chemicals, which alter the function of the oestrogen receptors (ER), were exploited to tease out the different functions of each ER in the growth plate. In the absence of foetal bovine serum, oestradiol had no effect on proliferation, differentiation or apoptosis of chondrocyte cells in monolayer culture or on the growth of the foetal metatarsal culture system. In addition, oestradiol did not convey a protective effect on chondrocytes exposed to the pro-inflammatory cytokines, tumour necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) in monolayer culture. However, endogenous oestrogen appears to play an important role in maintaining chondrocyte proliferation in monolayer culture and mineralisation in metatarsal culture as reflected by the inhibitory effects of Faslodex, the non-specific ER antagonist, on chondrocytes and metatarsals in culture. In the presence of methyl-piperidino-pyrazole (MPP), a selective ERα antagonist, and raloxifene, a selective oestrogen receptor modulator with higher ERβ binding affinity, a reduction in chondrocyte proliferation and increase in apoptosis was observed in murine and human chondrocytes. Similarly, a marked reduction in linear growth occurred when foetal murine metatarsals were exposed to MPP and raloxifene in combination. A less marked reduction in growth was observed in MPP-treated metatarsals. These findings suggest that the oestrogen receptors may have opposing actions in the growth plate with ERβ acting like a brake on chondrocyte growth and ERα promoting growth. ERβ may regulate cell proliferation through control of cell cycle modulators affecting G1/S phase transition as MPP and raloxifene in combination reduced cyclin E and p53 levels on Western blot analysis. The aim of the second part of my thesis was to investigate the effect of oral oestrogen on linear growth in girls with primary ovarian insufficiency (POI). A retrospective review of girls with POI treated at a tertiary endocrinology clinic over an 11 year period was performed. As expected the majority of girls with POI had Turner syndrome (TS; 83.7%). Non-TS associated POI was rare and the leading cause was iatrogenic secondary to the effects of total body irradiation for bone marrow transplantation (12.8%). A significant proportion of these girls developed POI after full pubertal development so few cases were available to investigate the effect of oestrogen on growth. The oral oestrogen regime followed in individual patients with TS was highly variable so it was not possible to assess the effects of dose on height velocity or bone maturation in this retrospective audit. However, the second clinical study examined in detail the effect of oestrogen on growth in TS girls who received a standardised course of oral ethinylestradiol for pubertal induction and a standard dose of growth hormone (10 mg/m2/week). These girls participated in a prospective randomised double-blind placebo-controlled multi-centre study of growth promoting treatment in TS. The girls were initially randomised to oxandrolone or placebo at 9 years of age and further randomised to oral ethinylestradiol at 12 or 14 years of age. The results of this study are embargoed until published. The laboratory effects of oestradiol found in this thesis suggest that ERα may stimulate or maintain growth, and ERβ may inhibit growth. The obvious question is how these observations might be involved in the complex relationship between puberty, oestrogen and height velocity in humans. As affinity studies show that the half maximal effective concentration (EC50) of ERα is achieved at slightly lower concentrations of oestradiol than ERβ it is conceivable that the ERα effect could predominate at lower systemic oestradiol concentrations and that ERβ could become more important at higher concentrations for example in later puberty. Alternatively, it is possible that the expression of ERα reduces or ERβ increases in the growth plate after reaching peak height velocity.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:516380 |
| Date | January 2010 |
| Creators | Perry, Rebecca Jane |
| Publisher | University of Glasgow |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://theses.gla.ac.uk/1881/ |
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