The role of progesterone receptor in hypothalamic kisspeptin neurons

Gal, Arnon

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https://hdl.handle.net/2142/49826 Copy

Description

Title

The role of progesterone receptor in hypothalamic kisspeptin neurons

Author(s)

Gal, Arnon

Issue Date

2014-05-30T17:19:47Z

Director of Research (if dissertation) or Advisor (if thesis)

Ko, CheMyong

Doctoral Committee Chair(s)

Ko, CheMyong

Committee Member(s)

• Bahr, Janice M.
• Wallig, Matthew A.
• Federico, Federico A.
• MacNeill, Amy L.

Department of Study

Pathobiology

Discipline

VMS - Veterinary Pathobiology

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Progesterone receptor
• Kisspeptin neuron
• Gonadotropin releasing hormone (GnRH)
• Regulation
• Hypothalamic-Pituitary-Ovarian axis

Abstract

In recent years, the neuropeptide kisspeptin, secreted by kisspeptin neurons, has been identified as the prime regulator of gonadotropin releasing hormone (GnRH). Kisspeptin neurons express steroid hormone receptors through which gonadal steroids exert both positive and negative feedback to the hypothalamus; estrogen and its receptor, estrogen receptor α (ERα), have been shown to regulate kisspeptin-mediated GnRH release through regulation of kisspeptin expression. However, the roles that the progesterone receptor (Pgr) and the androgen receptor have in progesteronic and androgenic regulation of kisspeptin-mediated GnRH release have not been investigated. Previous studies indicated that Pgr has a critical role in the induction of the GnRH-mediated preovulatory luteinizing hormone (LH) surge. Therefore, kisspeptin neurons may be the cells in which Pgr mediates this action. Hypersecretion of GnRH is associated with the development of polycystic ovaries and hyperandrogenemia. The polycystic ovaries are the source of androgens and high level of androgens induces the development of polycystic ovaries. In addition, hyperandrogenemia may increase GnRH release, potentially through the action on androgen receptor in kisspeptin neurons. Increased LH level secondary to hypersecretion of GnRH increases androgen production in the ovary and therefore may lead to a vicious cycle. There is no literature regarding whether the development of polycystic ovaries is structurally reversible, a question that may have great impact on the understanding of the pathogenesis of this condition. GnRH activates the reproductive axis through induction of gonadotropins release from the pituitary gland; however, quantification of GnRH is challenging because GnRH is secreted into the pituitary portal circulation rather than into the general venous circulation. Serum LH level is a good indicator of GnRH secretion and measurements of serum LH are commonly used for that purpose. Similarly, vaginal exfoliative cytology has been shown to be a good indicator of the cyclic changes in estrogen level throughout the rat estrous cycle. Vaginal exfoliative cytology is commonly used in biomedical and toxicologic studies in mice for the same purpose. Yet, where the rat estrous cycle remains consistently regular from one cycle to the other, the mouse estrous cycle is often irregular. Hence, vaginal exfoliative cytology may not be as good a predictor of the mouse estrous cycle stage as it is in the rat. The hypotheses in this doctoral research are: 1) progesterone and progesterone receptor (Pgr) regulation on kisspeptin expression, or androgenic regulation of Pgr and/or kisspeptin expression increase kisspeptin-mediated GnRH secretion. 2) follicular cysts developed by hyperandrogenism disappear when normal hormonal milieu restored. Thus through their steroid hormone receptors, progesterone and androgens may participate in the pathogenesis of female infertility. To test these hypotheses, the following specific aims were developed: 1) compare the vaginal exfoliative cytology of the mouse estrous cycle with other indicators of the estrous cycle stage in order assess better the function of the hypothalamic pituitary ovarian axis (chapter 1), 2) determine the effect of a high level of testosterone on the expression of Pgr and kisspeptin in kisspeptin neurons and on GnRH release (chapter 2), 3) determine the significance of Pgr expression in kisspeptin neurons in releasing GnRH (chapter 3), and 4) determine the effect that a male level of androgens has on ovarian folliculogenesis (chapter 4). To answer these important questions three main approaches were developed: First, wild type (WT) and kisspeptin-specific Pgr knockout mice were used to determine the role that Pgr has on kisspeptin-mediated GnRH release. The onset of puberty, fertility, and ability to ovulate were used as proxies for GnRH release in this approach. Second, WT mice were used to determine the effects of exogenously administered androgens on Pgr and kisspeptin expression. Similarly, genetically modified mice that spontaneously develop hyperandrogenemia from early age were used and determined the effects that androgens have on Pgr and kisspeptin expression, using serum gonadotropin as an indicator of kisspeptin-mediated GnRH release. Third, ovaries were transplanted to males and re-transplanted back to females to determine the role that androgens have on the development of polycystic ovaries and the reversibility of this development. The results of this research indicate that vaginal fold histology is a more accurate method for classifying the estrous-cycle stages in mice than vaginal exfoliative cytology. In addition, The results of this research indicates that Pgr is critical for kisspeptin-mediated GnRH release; kisspeptin-specific Pgr knockout mice have an earlier onset of puberty, have a progressive loss of fertility and do not ovulate. These abnormalities are of hypothalamic origin because the pituitary gland and ovaries from these mice maintain the ability to respond to stimulation by GnRH and gonadotropins, respectively. In addition this research indicates that high level of androgens do not affect Pgr or kisspeptin expression in kisspeptin neurons and do not lead to an increase in serum LH levels in mice that spontaneously develop hyperandrogenemia. The data from this research also indicate that high level of androgens induce the development of polycystic ovaries, which is a temporal and androgen-dependent process, because after re-establishment of normoandregonemia the development of polycystic ovaries is reversed. In conclusion, vaginal fold histology is recommended for use when determining and confirming the desired estrous-cycle stage in quantitative experiments if the outcome variables are estrous-cycle stage-dependent. A second conclusion in this research is that Pgr plays a critical role in the kisspeptin-mediated regulation of GnRH release. Also, hyperandrogenemia-triggered polycystic ovarian development is reversible. The significance of these findings is: 1) the routine assessment of estrous cycle recommended to include vaginal histology for better accuracy in classification of the estrous cycle stages, 2) Pgr in kisspeptin neuron can be a target for modulation of GnRH secretion, for example as a safer form of contraceptive, and 3) polycystic ovaries have the ability to restore normal structure once the inciting cause that lead to their development removed.

Graduation Semester

2014-05

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Copyright 2014 Arnon Gal

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