Studies on the androgen receptor and steroid metabolising enzymes in the human endometrium

• Main Author: Burton, Kevin Anthony
• Published: University of Glasgow 2004
• Subjects: QH301 Biology
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.761835

Activation of sex steroid receptors is a key event in the regulation of uterine function. The expression of sex steroid receptors such as Oestrogen and Progesterone have been well characterised in normal human endometrial tissue. Expression of the androgen receptor (AR) has not been well characterised. The characterisation of AR in human endometrium is important to determine the role of androgens in physiological uterine events such as implantation and menstruation. The term "Intracrinology" refers to the ability of a peripheral target tissue to synthesise sex steroids. The expression pattern of metabolising enzymes determines a tissues steroidogenic potential. Key sex steroid metabolising enzymes include the 17β-hydroxysteroid dehydrogenases (17β -HSD), 5α-reductases (5αR), 3β-hydroxysteroid dehydrogenases (3β -HSD) and Aromatase. The objectives of this thesis were thus to determine in human endometrium; 1. The spatial and temporal expression of androgen receptor mRNA and protein in endometrium across the menstrual cycle. 2. The expression of critical androgen metabolising enzymes across the menstrual cycle - 17β -HSD type 2 mRNA and protein; 17β -HSD type 5 mRNA; 3β -HSD type 1 and 2 mRNA; and 5αR types 1 and 2 mRNA. 3. The spatial and temporal localisation, in endometrium exposed to high dose intra-uterine levonorgestrel, of AR mRNA and protein; 17β -HSD2 mRNA and protein; 17β -HSDS mRNA; 3β -HSD1 and 2 mRNA; and 5αRl and 2 mRNA. Endometrial biopsies from both normal endometrium and endometrium exposed to high dose intra-uterine levonorgestrel were subjected to optimised immunohistochemical protocols to determine the spatial and temporal immunolocalisation of the androgen receptor and 17β -HSD2. In-situ hybridisation (ISH) techniques were employed to localise AR mRNA in full thickness endometrial biopsies. Taqman real time RT-PCR examined the temporal variation in mRNA expression for AR; 17β -HSD2 and 5; 3β -HSD1 and 2; and 5aRl and 2 in normal endometrium and endometrium exposed to high dose intra-uterine levonorgestrel. The results determined that AR is expressed in the endometrial stromal compartment with down regulation of AR protein and mRNA in the late secretory phase. This localisation was confirmed with ISH data. Endometrium exposed to high dose intra-uterine levonorgestrel exhibits a significant decrease in stromal AR protein immunoreactivity when compared with proliferative endometrium. Temporal variations in expression of steroid metabolising enzymes were studied. Significantly elevated levels of 17β -HSD2 are expressed in the glandular compartment of mid secretory phase endometrium. Endometrium exposed to high dose levonorgestrel exhibited high levels of endometrial 17β -HSD2 protein in the first month after insertion of a LNG lUS, associated with high levels of 17β -HSD2 mRNA expression in endometrial tissue at the three month time point. Thus, increased levels of 17β-HSD2 would indicate the potential for lowered intracellular oestradiol levels at this time (since this enzyme converts oestradiol to the less potent oestrogen, oestrone). Thereafter, levels of 17β-HSD2 protein and mRNA significantly decline. 17β -HSD5 mRNA is also significantly increased in the mid secretory phase. The peri-menstrual period is associated with significant elevations in mRNA levels for both 3β-HSD enzymes and 5αR 2. 5αR 1 is significantly elevated in the mid-cycle phases. In endometrium exposed to high dose intrauterine levonorgestrel, an increased expression of 3P-HSD and a reduced expression of 5aR 2 are noted. In conclusion, AR had been localised to the endometrial stromal compartment with a significant down regulation noted in the late secretory phase. The expression pattern of metabolising enzymes identified in this study is consistent with the secretory phase human endometrium possessing significantly greater steroidogenic potential than the proliferative phase. Furthermore, the available literature suggests that secretory endometrium is a significant source of androgen production. Data has been published that implicates androgens as having an important role in physiological events such as implantation. However, the precise role and regulation of androgens, the androgen receptor and the metabolising enzymes in human endometrium requires further study Novel data is also described here regarding the effect of high local doses of progestogen on local tissue androgen receptor and sex steroid metabolising enzymes. Such data suggests a potential role for progestogens in influencing the uterine environment that may lead to novel interventions for the problematic breakthrough bleeding suffered by progestogen only contraceptive users.