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Plain Z, Voliotis M, McArdle CA, Tsaneva-Atanasova K. Modelling KNDy neurons and gonadotropin-releasing hormone pulse generation. CURRENT OPINION IN ENDOCRINE AND METABOLIC RESEARCH 2022; 27:100407. [PMID: 36632147 PMCID: PMC9823092 DOI: 10.1016/j.coemr.2022.100407] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
The pulsatile release of gonadotropin-releasing hormone (GnRH) and its frequency are crucial for healthy reproductive function. To understand what drives GnRH pulses, a combination of experimental and mathematical modelling approaches has been used. Early work focussed on the possibility that GnRH pulse generation is an intrinsic feature of GnRH neurons, with autocrine feedback generating pulsatility. However, there is now ample evidence suggesting that a network of upstream neurons secreting kisspeptin, neurokinin-B and dynorphin are the source of this GnRH pulse generator. The interplay of slow positive and negative feedback via neurokinin-B and dynorphin, respectively, allows the network to act as a relaxation oscillator, driving pulsatile secretion of kisspeptin, and consequently, of GnRH and LH. Here, we review the mathematical modelling approaches exploring both scenarios and suggest that with pulsatile GnRH secretion driven by the KNDy pulse generator, autocrine feedback still has the potential to modulate GnRH output.
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Affiliation(s)
- Zoe Plain
- Department of Mathematics and Living Systems Institute, College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, UK
| | - Margaritis Voliotis
- Department of Mathematics and Living Systems Institute, College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, UK,Corresponding author: Voliotis, Margaritis
| | | | - Krasimira Tsaneva-Atanasova
- Department of Mathematics and Living Systems Institute, College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, UK
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Li L, Li L, Li P. Effects of controlled ovarian stimulation on thyroid function during pregnancy. Biol Reprod 2022; 107:1376-1385. [PMID: 35960990 DOI: 10.1093/biolre/ioac159] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Controlled ovarian stimulation (COS) is a major component of assisted reproductive technologies. Clinically, it has been observed that, some women experience changes in thyrotropin levels following COS, which then bring about subclinical hypothyroidism and may adversely affect conception. Studies have also shown that the specific degree as well as the tendency of changes in thyroid function vary with differences in thyroid function before pregnancy, thyroid autoimmunity, the COS regimen, and the observation time point. However, the associated pathophysiological mechanism of the effects of COS on pregnancy has not yet been fully elucidated. This may be because increased estradiol levels, caused by COS, induce increased levels of thyroxine-binding globulin, resulting in a decrease in free thyroxine (FT4) level and an increase in TSH level. Conversely, it has also been observed that human chorionic gonadotropin (hCG) can act directly on thyroid cells, exerting opposite effects on FT4 and TSH levels. Additionally, the effects of COS on thyroid function may be more pronounced, especially in women with autoimmune thyroid disease or thyroid dysfunction before pregnancy, ultimately leading to subclinical hypothyroidism. Here, we review recent research progress regarding the effects of COS on thyroid function during pregnancy.
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Affiliation(s)
- Lingfei Li
- Department of Endocrinology, Shengjing Hospital of China Medical University, Shenyang, Liaoning Province, People's Republic of China
| | - Ling Li
- Department of Endocrinology, Shengjing Hospital of China Medical University, Shenyang, Liaoning Province, People's Republic of China
| | - Ping Li
- Department of Endocrinology, Shengjing Hospital of China Medical University, Shenyang, Liaoning Province, People's Republic of China
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Okitsu-Sakurayama S, Higa-Nakamine S, Torihara H, Higashiyama S, Yamamoto H. Roles of Pyk2 in signal transduction after gonadotropin-releasing hormone receptor stimulation. J Cell Physiol 2020; 236:3033-3043. [PMID: 32984962 DOI: 10.1002/jcp.30077] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2020] [Revised: 09/03/2020] [Accepted: 09/08/2020] [Indexed: 12/13/2022]
Abstract
The receptor for gonadotropin-releasing hormone (GnRH) is highly expressed in hypothalamic neurons. It has been reported that GnRH treatment of cultured GnRH neurons (GT1-7 cells) activated proline-rich tyrosine kinase 2 (Pyk2), and Pyk2 was involved in the activation of extracellular signal-regulated protein kinase 1 (ERK1) and ERK2 (ERK1/2). In the present study, we first examined the possibility that GnRH treatment might activate epidermal growth factor receptor (EGFR). We found that activation of EGFR after GnRH treatment for 5 min was much less than after EGF or heparin-binding EGF treatment. Next, we examined whether or not Pyk2 bound to growth factor receptor-binding protein 2 (Grb2). We overexpressed FLAG-fused Pyk2 in GT1-7 cells, and immunoprecipitated Pyk2 using an anti-FLAG antibody. The binding of Pyk2 to Grb2 was detected only after GnRH treatment. In contrast, a site-directed mutant of Pyk2 wherein tyrosine 881 was mutated to phenylalanine did not bind to Grb2. Studies with small interfering RNA and inhibitors indicated that the activation of Grb2/Ras/Raf/MEK was a major pathway to ERK1/2 activation after the short-term treatment of GT1-7 cells with GnRH.
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Affiliation(s)
- Shiho Okitsu-Sakurayama
- Department of Biochemistry, Graduate School of Medicine, University of the Ryukyus, Okinawa, Japan
| | | | - Hidetsugu Torihara
- Department of Biochemistry, Graduate School of Medicine, University of the Ryukyus, Okinawa, Japan
| | - Shigeki Higashiyama
- Division of Cell Growth and Tumor Regulation, Department of Biochemistry and Molecular Genetics, Proteo-Science Center, Ehime University Graduate School of Medicine, Ehime University, Toon, Ehime, Japan
| | - Hideyuki Yamamoto
- Department of Biochemistry, Graduate School of Medicine, University of the Ryukyus, Okinawa, Japan
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Higa‐Nakamine S, Okitsu‐Sakurayama S, Kina S, Yamamoto H. Fyn‐mediated phosphorylation of Pyk2 promotes its activation and dissociation downstream of gonadotropin‐releasing hormone receptor. FEBS J 2020; 287:3551-3564. [DOI: 10.1111/febs.15231] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2019] [Revised: 12/13/2019] [Accepted: 01/27/2020] [Indexed: 11/27/2022]
Affiliation(s)
- Sayomi Higa‐Nakamine
- Department of Biochemistry Graduate School of Medicine University of the Ryukyus Okinawa Japan
| | - Shiho Okitsu‐Sakurayama
- Department of Biochemistry Graduate School of Medicine University of the Ryukyus Okinawa Japan
| | - Shinichiro Kina
- Department of Oral and Maxillofacial Functional Rehabilitation Graduate School of Medicine University of the Ryukyus Okinawa Japan
| | - Hideyuki Yamamoto
- Department of Biochemistry Graduate School of Medicine University of the Ryukyus Okinawa Japan
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Lehnert J, Khadra A. How Pulsatile Kisspeptin Stimulation and GnRH Autocrine Feedback Can Drive GnRH Secretion: A Modeling Investigation. Endocrinology 2019; 160:1289-1306. [PMID: 30874725 DOI: 10.1210/en.2018-00947] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/07/2018] [Accepted: 03/09/2019] [Indexed: 02/03/2023]
Abstract
Pulsatile secretion of GnRH from hypothalamic GnRH neurons tightly regulates the release of mammalian reproductive hormones. Although key factors such as electrical activity and stimulation by kisspeptin have been extensively studied, the underlying mechanisms that regulate GnRH release are still not fully understood. Previously developed mathematical models studied hormonal release and electrical properties of GnRH neurons separately, but they never integrated both components. Herein, we present a more complete biophysical model to investigate how electrical activity and hormonal release interact. The model consists of two components: an electrical submodel comprised of a modified Izhikevich formalism incorporating several key ionic currents to reproduce GnRH neuronal bursting behavior, and a hormonal submodel that incorporates pulsatile kisspeptin stimulation and a GnRH autocrine feedback mechanism. Using the model, we examine the electrical activity of GnRH neurons and how kisspeptin affects GnRH pulsatility. The model reproduces the noise-driven bursting behavior of GnRH neurons as well as the experimentally observed electrophysiological effects induced by GnRH and kisspeptin. Specifically, the model reveals that external application of GnRH causes a transient hyperpolarization followed by an increase in firing frequency, whereas administration of kisspeptin leads to long-lasting depolarization of the neuron. The model also shows that GnRH release follows a pulsatile profile similar to that observed experimentally and that kisspeptin and GnRH exhibit ∼7-1 locking in their pulsatility. These results suggest that external kisspeptin stimulation with a period of ∼8 minutes drives the autocrine mechanism beyond a threshold to generate pronounced GnRH pulses every hour.
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Affiliation(s)
- Jonas Lehnert
- Department of Quantitative Life Sciences, McGill University, Montreal, Quebec, Canada
| | - Anmar Khadra
- Department of Quantitative Life Sciences, McGill University, Montreal, Quebec, Canada
- Department of Physiology, McGill University, Montreal, Quebec, Canada
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Weinman MA, Fischer JA, Jacobs DC, Goodall CP, Bracha S, Chappell PE. Autocrine production of reproductive axis neuropeptides affects proliferation of canine osteosarcoma in vitro. BMC Cancer 2019; 19:158. [PMID: 30777054 PMCID: PMC6379937 DOI: 10.1186/s12885-019-5363-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2018] [Accepted: 02/11/2019] [Indexed: 01/19/2023] Open
Abstract
Background Osteosarcoma strikes hundreds of people each year, of both advanced and younger ages, and is often terminal. Like many tumor types, these bone tumors will frequently undergo a neuroendocrine transition, utilizing autocrine and/or paracrine hormones as growth factors and/or promoters of angiogenesis to facilitate progression and metastasis. While many of these factors and their actions on tumor growth are characterized, some tumor-derived neuropeptides remain unexplored. Methods Using validated canine osteosarcoma cell lines in vitro, as well as cells derived from spontaneous tumors in dogs, we explored the autocrine production of two neuropeptides typically found in the hypothalamus, and most closely associated with reproduction: gonadotropin-releasing hormone (GnRH) and kisspeptin (Kiss-1). We evaluated gene expression and protein secretion of these hormones using quantitative RT-PCR and a sensitive radioimmunoassay, and explored changes in cell proliferation determined by MTS cell viability assays. Results Our current studies reveal that several canine osteosarcoma cell lines (COS, POS, HMPOS, D17, C4) synthesize and secrete GnRH and express the GnRH receptor, while COS and POS also express kiss1 and its cognate receptor. We have further found that GnRH and kisspeptin, exogenously applied to these tumor cells, exert significant effects on both gene expression and proliferation. Of particular interest, kisspeptin exposure stimulated GnRH secretion from COS, similarly to the functional relationship observed within the neuroendocrine reproductive axis. Additionally, GnRH and kisspeptin treatment both increased COS proliferation, which additionally manifested in increased expression of the bone remodeling ligand rankl within these cells. These effects were blocked by treatment with a specific GnRH receptor inhibitor. Both neuropeptides were found to increase expression of the specific serotonin (5HT) receptor htr2a, the activation of which has previously been associated with cellular proliferation, suggesting that production of these factors by osteosarcoma cells may act to sensitize tumors to circulating 5HT of local and/or enteric origin. Conclusions Here we report that kisspeptin and GnRH act as autocrine growth factors in canine osteosarcoma cells in vitro, modulating RANKL and serotonin receptor expression in a manner consistent with pro-proliferative effects. Pharmacological targeting of these hormones may represent new avenues of osteosarcoma treatment. Electronic supplementary material The online version of this article (10.1186/s12885-019-5363-4) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Marcus A Weinman
- Department of Clinical Sciences, Carlson College of Veterinary Medicine, Oregon State University, Corvallis, OR, 97331, USA
| | - Jacob A Fischer
- Department of Biomedical Sciences, Carlson College of Veterinary Medicine, Oregon State University, Corvallis, OR, 97331, USA
| | - Dakota C Jacobs
- Department of Biomedical Sciences, Carlson College of Veterinary Medicine, Oregon State University, Corvallis, OR, 97331, USA
| | - Cheri P Goodall
- Department of Biomedical Sciences, Carlson College of Veterinary Medicine, Oregon State University, Corvallis, OR, 97331, USA
| | - Shay Bracha
- Department of Clinical Sciences, Carlson College of Veterinary Medicine, Oregon State University, Corvallis, OR, 97331, USA
| | - Patrick E Chappell
- Department of Biomedical Sciences, Carlson College of Veterinary Medicine, Oregon State University, Corvallis, OR, 97331, USA.
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Activation of Pyk2 by CaM kinase II in cultured hypothalamic neurons and gonadotroph cells. J Cell Physiol 2018; 234:6865-6875. [DOI: 10.1002/jcp.27443] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2018] [Accepted: 08/27/2018] [Indexed: 11/07/2022]
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Recanati MA, Du H, Kramer KJ, Hüttemann M, Welch RA. Antisense techniques provide robust decrease in GnRH receptor expression with minimal cytotoxicity in GT1-7 cells. Syst Biol Reprod Med 2018; 64:389-398. [PMID: 30136857 DOI: 10.1080/19396368.2018.1499153] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
The episodic pattern of gonadotropin-releasing hormone (GnRH) secretion from the hypothalamus is driven by an integrated network of cells termed the GnRH pulse generator. Cultured and immortalized GnRH neurons also produce a pulsatile pattern of GnRH secretions when grown in the absence of other cell types, suggesting the presence of an intrinsic oscillator mediating GnRH secretion. The mechanisms underlying such pulsatility comprise one of the most tantalizing problems in contemporary neuroendocrinology. In order to study the mechanism by which GnRH is produced in a pulsatile fashion, the autocrine effect of GnRH on GnRH-producing neurons must be eliminated. This may be performed by downregulating the expression of the GnRH receptor. Treatment with three 21-mer exogenous phosphorothioates and transient transfections with an inducible plasmid containing an antisense construct to the GnRH receptor gene decreased GnRH receptor expression further. This resulted in less cytotoxicity compared to inhibition of RNA or protein synthesis with actinomycin D, α-amanitin, puromycin, and cycloheximide. This study shows methods and optimized conditions established for the generation of a stable GT1-7 cell line containing an inducible construct allowing the downregulation of GnRH receptor expression. ABBREVIATIONS ANOVA: analysis of the variance; DMEM: Dulbecco's modified Eagle's medium; GnRH: gonadotropin-releasing hormone; RXR: retinoid X receptor.
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Affiliation(s)
| | - Hongling Du
- a Department of Obstetrics and Gynecology , Wayne State University , Detroit , MI , USA
| | | | - Maik Hüttemann
- c Center for Molecular Medicine and Genetics , Wayne State University , Detroit , MI , USA
| | - Robert A Welch
- a Department of Obstetrics and Gynecology , Wayne State University , Detroit , MI , USA
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Kanasaki H, Oride A, Mijiddorj T, Sukhbaatar U, Kyo S. How is GnRH regulated in GnRH-producing neurons? Studies using GT1-7 cells as a GnRH-producing cell model. Gen Comp Endocrinol 2017; 247:138-142. [PMID: 28131616 DOI: 10.1016/j.ygcen.2017.01.025] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/13/2016] [Revised: 01/05/2017] [Accepted: 01/23/2017] [Indexed: 12/24/2022]
Abstract
Hypothalamic secretion of gonadotropin-releasing hormone (GnRH) has been established as a principle pathway for initiating and integrating female reproductive function. GnRH stimulates the release of two gonadotropins-luteinizing hormone and follicle-stimulating hormone-from the anterior pituitary, which eventually stimulate the synthesis of sex steroids in association with follicular growth and ovulation. This reproductive control of the hypothalamic-pituitary-gonadal (HPG) axis also mediates gonadal feedback mechanisms. Although GnRH neurons certainly play a pivotal role in the HPG axis, the detailed mechanisms of their functional network, including regulatory systems, remain unknown. After the discovery of the indispensable role of kisspeptin in the development of human reproductive functions, our understanding of the neuroendocrine regulation of the HPG axis was revolutionized, and it is now recognized that kisspeptin acts upstream of GnRH and is responsible for sex steroid feedback mechanisms. Kisspeptin can stimulate gonadotropin release from the pituitary gland by stimulating GnRH release and GnRH antagonists prevent kisspeptin-induced gonadotropin release. Furthermore, it has been shown that GnRH neurons express kisspeptin receptors. Nevertheless, the detailed mechanisms underlying the regulation of homogeneous populations of GnRH neurons are still largely unknown because of the limitations of experimental models used for investigation. The hypothalamus consists of a complex network of distinct neuronal cells, and it is difficult to isolate single-cell populations of GnRH neurons. The establishment of GnRH-expressing cell lines has allowed us to examine the events happening at the single-cell level. In this review, we describe in vitro studies using a GnRH-producing cell model, GT1-7 cells, which have been used to examine how GnRH-producing cells respond to hypothalamic factors and how they are involved in GnRH synthesis.
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Affiliation(s)
- Haruhiko Kanasaki
- Department of Obstetrics and Gynecology, Shimane University Faculty of Medicine, Izumo 693-8501, Japan.
| | - Aki Oride
- Department of Obstetrics and Gynecology, Shimane University Faculty of Medicine, Izumo 693-8501, Japan
| | - Tselmeg Mijiddorj
- Department of Obstetrics and Gynecology, Shimane University Faculty of Medicine, Izumo 693-8501, Japan
| | - Unurjargal Sukhbaatar
- Department of Obstetrics and Gynecology, Shimane University Faculty of Medicine, Izumo 693-8501, Japan
| | - Satoru Kyo
- Department of Obstetrics and Gynecology, Shimane University Faculty of Medicine, Izumo 693-8501, Japan
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Omoto Y, Higa-Nakamine S, Higa A, Yamamoto H. ErbB4 cleavage by gonadotropin-releasing hormone receptor stimulation in cultured gonadotroph cells. Eur J Pharmacol 2017; 799:171-179. [DOI: 10.1016/j.ejphar.2017.02.006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2016] [Revised: 02/01/2017] [Accepted: 02/03/2017] [Indexed: 11/29/2022]
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Woller MJ, Meyer S, Ada-Nguema A, Waechter-Brulla D. Dissecting Autocrine Effects on Pulsatile Release of Gonadotropin-Releasing Hormone in Cultured Rat Hypothalamic Tissue. Exp Biol Med (Maywood) 2016; 229:56-64. [PMID: 14709777 DOI: 10.1177/153537020422900107] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
The control of reproductive function is manifested centrally through the control of hypothalamic release of gonadotropin-releasing hormone (GnRH) in episodic events or pulses. For GnRH release to occur in pulses, GnRH neurons must coordinate release events periodically to elicit a bolus of GnRH. We used a perifusion culture system to examine the release of GnRH from both intact hypothalami and enzymatically dispersed hypothalamic cells after challenge with GnRH analogs to evaluate the role of anatomical neuronal connections on autocrine/paracrine signals by GnRH on GnRH neurons. The potent GnRH agonist des-Gly10-D-Ala6-GnRH N-ethylamide, potent GnRH antagonists D-Phe2-D-Ala6-GnRH and D-Phe2,6-Pro3-GnRH or vehicle were infused, whereas GnRH release from hypothalamic tissue and cells were measured. PULSAR analysis of GnRH release profiles was conducted to evaluate parameters of pulsatile GnRH release. Infusion of the GnRH agonist resulted in a decrease in mean GnRH (P < 0.001), pulse nadir (P < 0.01), and pulse frequency (P < 0.05) but no effect on pulse amplitude. Infusion of GnRH antagonists resulted in an increase in mean GnRH (P < 0.001), pulse nadir (P < 0.05), and pulse frequency (P < 0.05) and in GnRH pulse amplitude only in dispersed cells (P < 0.05). These results are consistent with the hypothesis that GnRH inhibits endogenous GnRH release by an ultrashort-loop feedback mechanism and that treatment of hypothalamic tissue or cells with GnRH agonist inhibits ultrashort-loop feedback, whereas treatment with antagonists disrupts normal feedback to GnRH neurons and elicits an increased GnRH signal.
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Affiliation(s)
- Michael J Woller
- Biological Sciences, University of Wisconsin-Whitewater, Whitewater, Wisconsin 53190, USA.
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Sukhbaatar U, Kanasaki H, Mijiddorj T, Oride A, Hara T, Yamada T, Kyo S. Expression of GnRH and Kisspeptin in Primary Cultures of Fetal Rat Brain. Reprod Sci 2016; 24:227-233. [PMID: 27313117 DOI: 10.1177/1933719116653679] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Genetic studies in humans or in vivo studies using animals have shown that kisspeptin released from the hypothalamus controls secretion of gonadotropin-releasing hormone (GnRH) from GnRH neurons, and subsequently GnRH induces gonadotropin secretion from the anterior pituitary. Kisspeptin did not stimulate GnRH expression in the GnRH-producing cell line GT1-7. Thus, we cultured GnRH and kisspeptin neurons from whole fetal rat brain and examined the regulation of GnRH and kisspeptin. Expression of GnRH messenger RNA (mRNA) was unchanged by estradiol (E2) treatment in these primary cultures. In contrast, kisspeptin mRNA expression was increased 2.00 ± 0.23-fold by E2 treatment. When these cultures were stimulated by kisspeptin-10, GnRH mRNA was significantly increased up to 1.51 ± 0.35-fold. Expression of GnRH mRNA was also stimulated 1.84 ± 0.33-fold by GnRH itself. Interestingly, kisspeptin mRNA was significantly increased up to 2.43 ± 0.40-fold by kisspeptin alone. In addition, kisspeptin mRNA expression was significantly increased by stimulation with GnRH (1.46 ± 0.21-fold). Our observations demonstrated that kisspeptin, but not GnRH, was upregulated by E2 and that kisspeptin stimulates GnRH mRNA expression in primary cultures of whole fetal rat brain. Furthermore, GnRH and kisspeptin stimulate their own neurons to produce GnRH or kisspeptin, respectively.
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Affiliation(s)
- Unurjargal Sukhbaatar
- 1 Department of Obstetrics and Gynecology, Faculty of Medicine, Shimane University School of Medicine, Izumo, Shimane, Japan
| | - Haruhiko Kanasaki
- 1 Department of Obstetrics and Gynecology, Faculty of Medicine, Shimane University School of Medicine, Izumo, Shimane, Japan
| | - Tselmeg Mijiddorj
- 1 Department of Obstetrics and Gynecology, Faculty of Medicine, Shimane University School of Medicine, Izumo, Shimane, Japan
| | - Aki Oride
- 1 Department of Obstetrics and Gynecology, Faculty of Medicine, Shimane University School of Medicine, Izumo, Shimane, Japan
| | - Tomomi Hara
- 1 Department of Obstetrics and Gynecology, Faculty of Medicine, Shimane University School of Medicine, Izumo, Shimane, Japan
| | - Takaya Yamada
- 2 Department of Experimental Animals, Interdisciplinary Center for Science Research, Organization for Research, Shimane University, Izumo, Shimane, Japan
| | - Satoru Kyo
- 1 Department of Obstetrics and Gynecology, Faculty of Medicine, Shimane University School of Medicine, Izumo, Shimane, Japan
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13
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Norwitz ER, Jeong KH, Chin WW. Molecular Mechanisms of Gonadotropin-Releasing Hormone Receptor Gene Regulation. ACTA ACUST UNITED AC 2016. [DOI: 10.1177/107155769900600402] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Affiliation(s)
- Errol R. Norwitz
- Division of Maternal-Fetal Medicine, Department of Obstetries & Gynecology, and Division of Molecular Genetics. Department of Medicine, Brigham & Women's Hospital, Harvard Medical School, Boston, Massachusetts
| | | | - William W. Chin
- Division of Maternal-Fetal Medicine, Department of Obstetries & Gynecology, and Division of Molecular Genetics. Department of Medicine, Brigham & Women's Hospital, Harvard Medical School, Boston, Massachusetts
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14
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Gizzo S, Noventa M, Quaranta M, Vitagliano A, Esposito F, Andrisani A, Venturella R, Alviggi C, Plebani M, Gangemi M, Nardelli GB, D’Antona D. The Potential Role of GnRH Agonists and Antagonists in Inducing Thyroid Physiopathological Changes During IVF. Reprod Sci 2015; 23:515-23. [DOI: 10.1177/1933719115608000] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Affiliation(s)
- Salvatore Gizzo
- Department of Woman and Child Health, University of Padua, Padua, Italy
| | - Marco Noventa
- Department of Woman and Child Health, University of Padua, Padua, Italy
| | - Michela Quaranta
- Department of Obstetrics and Gynecology, University of Verona, Verona, Italy
| | | | - Federica Esposito
- Department of Woman and Child Health, University of Padua, Padua, Italy
| | | | - Roberta Venturella
- Department of Obstetrics and Gynecology, University of Catanzaro, Catanzaro, Italy
| | - Carlo Alviggi
- Department of Neurosciences and Reproductive Science, University Federico II of Naples, Naples, Italy
| | - Mario Plebani
- Department of Laboratory Medicine, University of Padua, Padua, Italy
| | - Michele Gangemi
- Department of Woman and Child Health, University of Padua, Padua, Italy
| | | | - Donato D’Antona
- Department of Woman and Child Health, University of Padua, Padua, Italy
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15
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Higa-Nakamine S, Maeda N, Toku S, Yamamoto H. Involvement of Protein Kinase D1 in Signal Transduction from the Protein Kinase C Pathway to the Tyrosine Kinase Pathway in Response to Gonadotropin-releasing Hormone. J Biol Chem 2015; 290:25974-85. [PMID: 26338704 DOI: 10.1074/jbc.m115.681700] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2015] [Indexed: 11/06/2022] Open
Abstract
The receptor for gonadotropin-releasing hormone (GnRH) belongs to the G protein-coupled receptors (GPCRs), and its stimulation activates extracellular signal-regulated protein kinase (ERK). We found that the transactivation of ErbB4 was involved in GnRH-induced ERK activation in immortalized GnRH neurons (GT1-7 cells). We found also that GnRH induced the cleavage of ErbB4. In the present study, we examined signal transduction for the activation of ERK and the cleavage of ErbB4 after GnRH treatment. Both ERK activation and ErbB4 cleavage were completely inhibited by YM-254890, an inhibitor of Gq/11 proteins. Down-regulation of protein kinase C (PKC) markedly decreased both ERK activation and ErbB4 cleavage. Experiments with two types of PKC inhibitors, Gö 6976 and bisindolylmaleimide I, indicated that novel PKC isoforms but not conventional PKC isoforms were involved in ERK activation and ErbB4 cleavage. Our experiments indicated that the novel PKC isoforms activated protein kinase D (PKD) after GnRH treatment. Knockdown and inhibitor experiments suggested that PKD1 stimulated the phosphorylation of Pyk2 by constitutively activated Src and Fyn for ERK activation. Taken together, it is highly possible that PKD1 plays a critical role in signal transduction from the PKC pathway to the tyrosine kinase pathway. Activation of the tyrosine kinase pathway may be involved in the progression of cancer.
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Affiliation(s)
- Sayomi Higa-Nakamine
- From the Department of Biochemistry, Graduate School of Medicine, University of the Ryukyus, Okinawa 903-0215, Japan
| | - Noriko Maeda
- From the Department of Biochemistry, Graduate School of Medicine, University of the Ryukyus, Okinawa 903-0215, Japan
| | - Seikichi Toku
- From the Department of Biochemistry, Graduate School of Medicine, University of the Ryukyus, Okinawa 903-0215, Japan
| | - Hideyuki Yamamoto
- From the Department of Biochemistry, Graduate School of Medicine, University of the Ryukyus, Okinawa 903-0215, Japan
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16
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Sukhbaatar U, Mijiddorj T, Oride A, Kanasaki H. Stimulation of δ subunit-containing GABAA receptor by DS1 increases GnRH receptor expression but reduces GnRH mRNA expression in GnRH-producing GT1-7 cells. Endocrine 2015; 49:222-30. [PMID: 25355308 DOI: 10.1007/s12020-014-0464-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/10/2014] [Accepted: 10/23/2014] [Indexed: 12/23/2022]
Abstract
Acting via ionotropic GABAA receptors, the neurotransmitter γ-aminobutyric acid (GABA) is an important modulator of gonadotropin-releasing hormone (GnRH) neurons. In the present study, we examined the effect of DS1, a GABAA α4β3δ receptor agonist, on a strain of mouse hypothalamic immortalized GnRH neuronal cells, the GT1-7 cell line. DS1 increased the activities of serum-response element (SRE) and cAMP-response element (CRE) promoters, which reflect the activities of extracellular signal-regulated kinase and cAMP/protein kinase A (PKA) pathways, respectively. In G protein-coupled receptor 54 (GPR54)-overexpressing GT1-7 cells, both DS1 and kisspeptin-10 stimulated SRE promoter activity, and combined treatment with DS1 and kisspeptin further increased SRE promoter activity compared with DS1 or kisspeptin alone. Pituitary adenylate cyclase-activating polypeptide (PACAP) increased CRE promoter activity in PACAP type I receptor-overexpressing GT1-7 cells, with an effect similar to that of DS1 alone, and combined stimulation with PACAP and DS1 potentiated their individual effects. DS1 stimulated the transcriptional activity of GnRH receptor, and DS1 induced GnRH receptor mRNA and protein expression. PACAP-increased GnRH receptor expression was enhanced in the presence of DS1. However, DS1 significantly inhibited the basal expression of GnRH mRNA in GT1-7 cells. Our current observations suggest that DS1 exerts its stimulatory effect on the intracellular signal transduction system via GABAA α4β3δ receptors in GnRH-producing neurons. Stimulation with DS1 increased the expression of GnRH receptor but decreased the basal expression of GnRH mRNA.
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Affiliation(s)
- Unurjargal Sukhbaatar
- Department of Obstetrics and Gynecology, Shimane University School of Medicine, 89-1 Enya, Izumo City, Shimane Prefecture, 693-8501, Japan
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17
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Nunemaker CS, Satin LS. Episodic hormone secretion: a comparison of the basis of pulsatile secretion of insulin and GnRH. Endocrine 2014; 47:49-63. [PMID: 24610206 PMCID: PMC4382805 DOI: 10.1007/s12020-014-0212-3] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/04/2014] [Accepted: 02/13/2014] [Indexed: 01/01/2023]
Abstract
Rhythms govern many endocrine functions. Examples of such rhythmic systems include the insulin-secreting pancreatic beta-cell, which regulates blood glucose, and the gonadotropin-releasing hormone (GnRH) neuron, which governs reproductive function. Although serving very different functions within the body, these cell types share many important features. Both GnRH neurons and beta-cells, for instance, are hypothesized to generate at least two rhythms endogenously: (1) a burst firing electrical rhythm and (2) a slower rhythm involving metabolic or other intracellular processes. This review discusses the importance of hormone rhythms to both physiology and disease and compares and contrasts the rhythms generated by each system.
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Affiliation(s)
- Craig S. Nunemaker
- Division of Endocrinology and Metabolism, Department of, Medicine, University of Virginia, P.O. Box 801413, Charlottesville, VA 22901, USA,
| | - Leslie S. Satin
- Pharmacology Department, University of Michigan Medical School, 5128 Brehm Tower, Ann Arbor, MI 48105, USA
- Brehm Diabetes Research Center, University of Michigan, Medical School, 5128 Brehm Tower, Ann Arbor, MI 48105, USA
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18
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Abstract
Transient receptor potential (TRP) ion channels have been detected in neurons that are part of the neural network controlling reproductive physiology and behavior. In this chapter we will primarily take a look at the classical/canonical TRP (TRPC) channels but will also examine some other members of the TRP channel superfamily in reproductive (neuro)endocrinology. The referenced data suggest that different TRP proteins could play functional roles at different levels of the reproductive pathway. Still, our understanding of TRP channel involvement in (neuro)endocrinology is quite limited. Due to their mechanism of activation and complex regulation, these channels are however ideally suited to be part of the transduction machinery of hormone-secreting cells.
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Affiliation(s)
- Trese Leinders-Zufall
- Department of Physiology, University of Saarland School of Medicine, 66421, Homburg, Germany,
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19
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Sukhbaatar U, Kanasaki H, Mijiddorj T, Oride A, Miyazaki K. Expression of gonadotropin-inhibitory hormone receptors in mouse pituitary gonadotroph LβT2 cells and hypothalamic gonadotropin-releasing hormone-producing GT1-7 cells. Endocr J 2014; 61:25-34. [PMID: 24088662 DOI: 10.1507/endocrj.ej13-0238] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Gonadotropin-inhibitory hormone (GnIH) was first identified in quail as a novel neurohormone that acts directly on the anterior pituitary to inhibit gonadotropin release. GnIH inhibits not only gonadotropin release from the pituitary gland but also inhibits the release of gonadotropin-releasing hormone (GnRH) from the hypothalamus. In this study, we examined how GnIH receptors were regulated in pituitary gonadotroph cells and GnRH-producing neurons in the hypothalamus. In the mouse pituitary gonadotroph cell line LβT2, GnRH increased expression of the GnIH receptor, G-protein coupled receptor 74 (GPR74). GnRH also stimulated the expression of GPR74 and GPR147 in primary cultures of rat anterior pituitary cells. In addition, when GnRH was administered to LβT2 cells in a pulsatile manner, low frequency GnRH pulse stimulation stimulated GPR74 and GPR147 expression more than did high frequency GnRH pulses. In the mouse hypothalamic GnRH-producing cell line GT1-7, hypothalamic kisspeptin did not significantly increase the expression of GnIH receptors. However, the intermittent administration of kisspeptin to GT1-7 cells significantly increased GPR74 and GPR147 mRNA expression. The overexpression of either constitutively active MEK kinase (MEKK) or protein kinase A (PKA) in LβT2 cells increased the expression of GPR74 mRNA. Conversely, in GT1-7 cells, although the overexpression of either MEKK or PKA failed to stimulate GnIH receptor expression, the combined overexpression of both kinases together increased GPR74 and GPR147 mRNA levels. Our current observations suggest that two central controllers of reproductive function, GnRH and kisspeptin, stimulate the expression of GnIH receptors in pituitary gonadotroph cells and hypothalamic GnRH neurons.
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Affiliation(s)
- Unurjargal Sukhbaatar
- Department of Obstetrics and Gynecology, Shimane University School of Medicine, Izumo 693-8501, Japan
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20
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Abstract
Gonadotrophin-releasing hormone (GnRH)-secreting neurones are the final output of the central nervous system driving fertility in all mammals. Although it has been known for decades that the efficiency of communication between the hypothalamus and the pituitary depends on the pulsatile profile of GnRH secretion, how GnRH neuronal activity is patterned to generate pulses at the median eminence is unknown. To date, the scattered distribution of the GnRH cell bodies remains the main limitation to assessing the cellular events that could lead to pulsatile GnRH secretion. Taking advantage of the unique developmental feature of GnRH neurones, the nasal explant model allows primary GnRH neurones to be maintained within a micro-network where pulsatile secretion is preserved and where individual cellular activity can be monitored simultaneously across the cell population. This review summarises the data obtained from work using this in vitro model, and brings some insights into GnRH cellular physiology.
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Affiliation(s)
- S Constantin
- Department of Physiology, Centre for Neuroendocrinology, University of Otago, Dunedin, New Zealand.
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21
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Frattarelli JL, Krsmanovic LZ, Catt KJ. The relationship between pulsatile GnRH secretion and cAMP production in immortalized GnRH neurons. Am J Physiol Endocrinol Metab 2011; 300:E1022-30. [PMID: 21447787 PMCID: PMC3118589 DOI: 10.1152/ajpendo.00081.2011] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In perifused immortalized GnRH neurons (GT1-7), simultaneous measurements of GnRH and cAMP revealed that the secretory profiles for both GnRH and cAMP are pulsatile. An analysis of GnRH and cAMP pulses in 16 independent experiments revealed that 25% of pulses coincide. Inversion of the peak and nadir levels was found in 33% and random relationship between GnRH and cAMP found in 42% of analyzed pulses. The random relation between GnRH and cAMP pulse resets to synchronous after an inverse relation between pulses occurred during the major GnRH release, indicating that GnRH acts as a switching mechanism to synchronize cAMP and GnRH release in perifused GT1-7 neurons. Activation of GnRH receptors with increasing agonist concentrations caused a biphasic change in cAMP levels. Low nanomolar concentrations increased cAMP production, but at high concentrations the initial increase was followed by a rapid decline to below the basal level. Blockade of the GnRH receptors by peptide and nonpeptide antagonists generated monotonic nonpulsatile increases in both GnRH and cAMP production. These findings indicate that cAMP positively regulates GnRH secretion but does not participate in the mechanism of pulsatile GnRH release.
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Affiliation(s)
- John L Frattarelli
- Section on Hormonal Regulation, Program in Developmental Endocrinology and Genetics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
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22
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Wen S, Götze IN, Mai O, Schauer C, Leinders-Zufall T, Boehm U. Genetic identification of GnRH receptor neurons: a new model for studying neural circuits underlying reproductive physiology in the mouse brain. Endocrinology 2011; 152:1515-26. [PMID: 21303944 DOI: 10.1210/en.2010-1208] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
GnRH signaling regulates reproductive physiology in vertebrates via the hypothalamic-pituitary-gonadal axis. In addition, GnRH signaling has been postulated to act on the brain. However, elucidating its functional role in the central nervous system has been hampered because of the difficulty in identifying direct GnRH signaling targets in live brain tissue. Here we used a binary genetic strategy to visualize GnRH receptor (GnRHR) neurons in the mouse brain and started to characterize these cells. First, we expressed different fluorescent proteins in GnRHR neurons and mapped their precise distribution throughout the brain. Remarkably, neuronal GnRHR expression was only initiated after postnatal day 16, suggesting peri- and postpubertal functions of GnRH signaling in this organ. GnRHR neurons were found in different brain areas. Many GnRHR neurons were identified in areas influencing sexual behaviors. Furthermore, GnRHR neurons were detected in brain areas that process olfactory and pheromonal cues, revealing one efferent pathway by which the neuroendocrine hypothalamus may influence the sensitivity towards chemosensory cues. Using confocal Ca(2+) imaging in brain slices, we show that GnRHR neurons respond reproducibly to extracellular application of GnRH or its analog [D-TRP(6)]-LH-RH, indicating that these neurons express functional GnRHR. Interestingly, the duration and shape of the Ca(2+) responses were similar within and different between brain areas, suggesting that GnRH signaling may differentially influence brain functions to affect reproductive success. Our new mouse model sets the stage to analyze the next level of GnRH signaling in reproductive physiology and behavior.
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Affiliation(s)
- Shuping Wen
- Institute for Neural Signal Transduction, Center for Molecular Neurobiology, Falkenried 94, D-20251 Hamburg, Germany
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23
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Rønnekleiv OK, Bosch MA, Zhang C. Regulation of endogenous conductances in GnRH neurons by estrogens. Brain Res 2010; 1364:25-34. [PMID: 20816765 PMCID: PMC2992606 DOI: 10.1016/j.brainres.2010.08.096] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2010] [Revised: 08/24/2010] [Accepted: 08/27/2010] [Indexed: 11/20/2022]
Abstract
17β-estradiol (E2) regulates the activity of the gonadotropin-releasing hormone (GnRH) neurons through both presynaptic and postsynaptic mechanisms, and this ovarian steroid hormone is essential for cyclical GnRH neuronal activity and secretion. E2 has significant actions to modulate the mRNA expression of numerous ion channels in GnRH neurons and/or to enhance (suppress) endogenous conductances (currents) including potassium (K(ATP), A-type) and calcium low voltage T-type and high voltage L-type currents. Also, it is well documented that E2 can alter the excitability of GnRH neurons via direct action, but the intracellular signaling cascades mediating these actions are not well understood. As an example, K(ATP) channels are critical ion channels needed for maintaining GnRH neurons in a hyperpolarized state for recruiting T-type calcium channels that are important for burst firing in GnRH neurons. E2 modulates the activity of K(ATP) channels via a membrane-initiated signaling pathway in GnRH neurons. Obviously there are other channels, including the small conductance activated K(+) (SK) channels, that maybe modulated by this signaling pathway, but the ensemble of mER-, ERα-, and ERβ-mediated effects both pre- and post-synaptic will ultimately dictate the excitability of GnRH neurons.
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Affiliation(s)
- Oline K Rønnekleiv
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, OR 97239, USA.
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24
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Krsmanovic LZ, Hu L, Leung PK, Feng H, Catt KJ. Pulsatile GnRH secretion: roles of G protein-coupled receptors, second messengers and ion channels. Mol Cell Endocrinol 2010; 314:158-63. [PMID: 19486924 PMCID: PMC2815227 DOI: 10.1016/j.mce.2009.05.015] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/23/2009] [Revised: 05/21/2009] [Accepted: 05/24/2009] [Indexed: 12/31/2022]
Abstract
The pulsatile secretion of GnRH from normal and immortalized hypothalamic GnRH neurons is highly calcium-dependent and is stimulated by cAMP. It is also influenced by agonist activation of the endogenous GnRH receptor (GnRH-R), which couples to multiple G proteins. This autocrine mechanism could serve as a timer to determine the frequency of pulsatile GnRH release by regulating Ca(2+)- and cAMP-dependent signaling and GnRH neuronal firing. The firing of individual and/or bursts of action potentials (APs) in spontaneously active GnRH neurons is followed by afterhyperpolarization (AHP) that lasts from several milliseconds to several seconds. GnRH-induced activation of GnRH neurons causes a significant increase in medium AHP that is partially sensitive to apamin. GnRH-induced modulation of Ca(2+) influx and the consequent changes in AHP current suggest that the GnRH receptors expressed in hypothalamic GnRH neurons are important modulators of their neuronal excitability. The coexistence of multiple regulatory mechanisms could provide a high degree of redundancy in the maintenance of this crucial component of the reproductive process. It is also conceivable that this multifactorial system could reflect the gradation from simple to more complex neuroendocrine control systems for regulating hypothalamo-pituitary function and gonadal activity during the evolution of the GnRH pulse generator.
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Affiliation(s)
- Lazar Z Krsmanovic
- Section on Hormonal Regulation, PDEGEN, NICHD, NIH, Bethesda, MD 20892, USA.
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25
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Bose S, Leclerc GM, Vasquez-Martinez R, Boockfor FR. Administration of connexin43 siRNA abolishes secretory pulse synchronization in GnRH clonal cell populations. Mol Cell Endocrinol 2010; 314:75-83. [PMID: 19716855 PMCID: PMC2783823 DOI: 10.1016/j.mce.2009.08.016] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/19/2009] [Revised: 08/18/2009] [Accepted: 08/21/2009] [Indexed: 12/01/2022]
Abstract
GnRH is released from hypothalamic neurons in coordinated pulses, but the cellular basis for this process is poorly understood. Previously, we found that secretory pulses from GT1-7 cells became synchronized with time in culture. Using this culture model, we investigated whether the gap junction proteins connexin43 (Cx43) and/or connexin26 (Cx26) are involved in this synchronization. Our results reveal that cytoplasmic densities immunoreactive for Cx43, and mRNA or protein for Cx43 increase with time in culture. Also, microinjection of day-3 cultures with siRNA for Cx43 abolished synchronized activity at day 7. Interestingly, cytoplasmic plaques, mRNA, or protein for Cx26 remained stable with culture time and Cx26 siRNA administration did not alter secretory activity. Our findings demonstrate that Cx43, but not Cx26 is necessary for synchronized secretory activity in these GT1-7 cultures and raise the possibility that Cx43-related gap junctions may be important in GnRH neuronal coordination in the hypothalamus.
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Affiliation(s)
- Sudeep Bose
- Department of Cell Biology and Anatomy, Medical University of South Carolina, 173 Ashley Avenue, Charleston, South Carolina
| | - Gilles M. Leclerc
- Department of Pediatrics, Hematology and Oncology, University of Miami, Miami, Florida
| | - Rafael Vasquez-Martinez
- Department of Cellular Biology, Physiology and Immunology, University of Cordoba, Cordoba, Spain
| | - Fredric R. Boockfor
- Department of Cell Biology and Anatomy, Medical University of South Carolina, 173 Ashley Avenue, Charleston, South Carolina
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26
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Krsmanovic LZ, Hu L, Leung PK, Feng H, Catt KJ. The hypothalamic GnRH pulse generator: multiple regulatory mechanisms. Trends Endocrinol Metab 2009; 20:402-8. [PMID: 19740674 PMCID: PMC2769988 DOI: 10.1016/j.tem.2009.05.002] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/26/2009] [Revised: 05/04/2009] [Accepted: 05/05/2009] [Indexed: 12/30/2022]
Abstract
Pulsatile secretion of gonadotropin-releasing hormone (GnRH) release is an intrinsic property of hypothalamic GnRH neurons. Pulse generation has been attributed to multiple specific mechanisms, including spontaneous electrical activity of GnRH neurons, calcium and cAMP signaling, a GnRH receptor autocrine regulatory component, a GnRH concentration-dependent switch in GnRH receptor (GnRH-R) coupling to specific G proteins, the expression of G protein-coupled receptors (GPCRs) and steroid receptors, and homologous and heterologous interactions between cell membrane receptors expressed in GnRH neurons. The coexistence of multiple regulatory mechanisms for pulsatile GnRH secretion provides a high degree of redundancy in maintaining this crucial component of the mammalian reproductive process. These studies provide insights into the basic cellular and molecular mechanisms involved in GnRH neuronal function.
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Affiliation(s)
- Lazar Z Krsmanovic
- Section on Hormonal Regulation, Program on Developmental Endocrinology and Genetics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
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27
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An integrated model of electrical spiking, bursting, and calcium oscillations in GnRH neurons. Biophys J 2009; 96:4514-24. [PMID: 19486674 DOI: 10.1016/j.bpj.2009.03.037] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2008] [Revised: 02/28/2009] [Accepted: 03/11/2009] [Indexed: 11/22/2022] Open
Abstract
The plasma membrane electrical activities of neurons that secrete gonadotropin-releasing hormone (GnRH) have been studied extensively. A couple of mathematical models have been developed previously to explain different aspects of these activities. The goal of this article is to develop a single model that accounts for the previously modeled experimental results and some more recent results that have not been accounted for. The latter includes two types of membrane potential bursting mechanisms and their associated cytosolic calcium oscillations. One bursting mechanism has not been reported in experiments and is thus regarded as a model prediction. Although the model is mainly based on data collected in immortalized GnRH cell lines, it is capable of explaining some properties of GnRH neurons observed in several other preparations including mature GnRH neurons in hypothalamic slices. We present a spatial model that incorporates a detailed description of calcium dynamics in a three-dimensional cell body with the ion channels evenly distributed on the cell surface. A phenomenological reduction of the spatial model into a simplified form is also presented. The simplified model will facilitate the study of the roles of plasma membrane electrical activities in the pulsatile release of GnRH.
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28
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Abstract
Gonadotrophin-releasing hormone (GnRH) was first isolated in the mammal and shown to be the primary regulator of the reproductive system through its initiation of pituitary gonadotrophin release. Subsequent to its discovery, this form of GnRH has been shown to be one of many structural variants found in the brain and peripheral tissues. Accordingly, the original form first discovered and cloned in the mammal is commonly referred to as GnRH-I. In addition to the complex regulation of GnRH-I synthesis, release and function, further evidence suggests that the processing of GnRH-I produces yet another layer of complexity in its activity. GnRH-I is processed by a zinc metalloendopeptidase EC 3.4.24.15 (EP24.15), which cleaves the hormone at the covalent bond between the fifth and sixth residue of the decapeptide (Tyr(5)-Gly(6)) to form GnRH-(1-5). It was previously thought that the cleavage of GnRH-I by EP24.15 represents the initiation of its degradation. Here, we review the evidence for the involvement of GnRH-(1-5), the metabolite of GnRH-I, in the regulation of GnRH-I synthesis, secretion and facilitation of reproductive behaviour.
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Affiliation(s)
- T John Wu
- Program in Neuroscience, Uniformed Services University of the Health Sciences, Bethesda, MD 20814, USA.
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29
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Ishii H, Tanaka N, Kobayashi M, Kato M, Sakuma Y. Gene structures, biochemical characterization and distribution of rat melatonin receptors. J Physiol Sci 2009; 59:37-47. [PMID: 19340560 PMCID: PMC10717452 DOI: 10.1007/s12576-008-0003-9] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2008] [Accepted: 10/10/2008] [Indexed: 12/15/2022]
Abstract
G-protein coupled receptors for the pineal hormone melatonin have been partially cloned from rats. However, insufficient information about their cDNA sequences has hindered studies of their distribution and physiological responses to melatonin using rats as an animal model. We have cloned cDNAs of two rat membrane melatonin receptor subtypes, melatonin receptor 1a (MT1) and melatonin receptor 1b (MT2), using a rapid amplification of cDNA end (RACE) method. The rat MT1 and MT2 cDNAs encode proteins of 353 and 364 amino acids, respectively, and show 78-93% identities with the human and mouse counterparts. Stable expression of either rat MT1 or MT2 in NIH3T3 cells resulted in high affinity 2-[(125)I]-iodomelatonin ((125)I-Mel) binding (K (d) = 73.2 +/- 9.0 and 73.7 +/- 2.9 pM, respectively), and exhibited a similar rank order of inhibition of specific (125)I-Mel binding by five ligands (2-iodomelatonin > melatonin > 6-hydroxymelatonin > luzindole > N-acetyl-5-hydroxytryptamine). RT-PCR analysis showed that MT1 is highly expressed in the hypothalamus, lung, kidney, adrenal gland, stomach, and ovary, while MT2 is highly expressed in the hippocampus, kidney, and ovary. We also performed multi-cell RT-PCR to examine the expression of mRNAs encoding MT1 and MT2 in adult GnRH neurons. MT1 was weakly expressed in male GnRH neurons, and was less expressed in the female neurons. MT2 expression was undetectable in GnRH neurons from either sex. This study delineates the gene structures, fundamental properties, and distribution of both rat melatonin receptor subtypes, and may offer opportunities to assess the physiological significance of melatonin in rats.
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MESH Headings
- Amino Acid Sequence
- Animals
- Base Sequence
- Brain/physiology
- Cloning, Molecular
- Endocrine Glands/physiology
- Gonadotropin-Releasing Hormone/metabolism
- Green Fluorescent Proteins/genetics
- Kidney/physiology
- Lung/physiology
- Melatonin/metabolism
- Mice
- Molecular Sequence Data
- NIH 3T3 Cells
- Nucleic Acid Amplification Techniques
- RNA, Messenger/genetics
- Rats
- Rats, Transgenic
- Rats, Wistar
- Receptor, Melatonin, MT1/genetics
- Receptor, Melatonin, MT1/metabolism
- Receptor, Melatonin, MT2/genetics
- Receptor, Melatonin, MT2/metabolism
- Reverse Transcriptase Polymerase Chain Reaction
- Stomach/physiology
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Affiliation(s)
- Hirotaka Ishii
- Department of Physiology, Nippon Medical School, Bunkyo-ku, Tokyo, 113-8602, Japan.
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30
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Robust synchrony and rhythmogenesis in endocrine neurons via autocrine regulations in vitro and in vivo. Bull Math Biol 2008; 70:2103-25. [PMID: 18797973 DOI: 10.1007/s11538-008-9328-z] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2007] [Accepted: 04/29/2008] [Indexed: 10/21/2022]
Abstract
Episodic pulses of gonadotropin-releasing hormone (GnRH) are essential for maintaining reproductive functions in mammals. An explanation for the origin of this rhythm remains an ultimate goal for researchers in this field. Some plausible mechanisms have been proposed among which the autocrine-regulation mechanism has been implicated by numerous experiments. GnRH binding to its receptors in cultured GnRH neurons activates three types of G-proteins that selectively promote or inhibit GnRH secretion (Krsmanovic et al. in Proc. Natl. Acad. Sci. 100:2969-2974, 2003). This mechanism appears to be consistent with most data collected so far from both in vitro and in vivo experiments. Based on this mechanism, a mathematical model has been developed (Khadra and Li in Biophys. J. 91:74-83, 2006) in which GnRH in the extracellular space plays the roles of a feedback regulator and a synchronizing agent. In the present study, we show that synchrony between different neurons through sharing a common pool of GnRH is extremely robust. In a diversely heterogeneous population of neurons, the pulsatile rhythm is often maintained when only a small fraction of the neurons are active oscillators (AOs). These AOs are capable of recruiting nonoscillatory neurons into a group of recruited oscillators while forcing the nonrecruitable neurons to oscillate along. By pointing out the existence of the key elements of this model in vivo, we predict that the same mechanism revealed by experiments in vitro may also operate in vivo. This model provides one plausible explanation for the apparently controversial conclusions based on experiments on the effects of the ultra-short feedback loop of GnRH on its own release in vivo.
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31
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Gill JC, Wadas B, Chen P, Portillo W, Reyna A, Jorgensen E, Mani S, Schwarting GA, Moenter SM, Tobet S, Kaiser UB. The gonadotropin-releasing hormone (GnRH) neuronal population is normal in size and distribution in GnRH-deficient and GnRH receptor-mutant hypogonadal mice. Endocrinology 2008; 149:4596-604. [PMID: 18499748 PMCID: PMC2553368 DOI: 10.1210/en.2008-0403] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Hypothalamic GnRH neurons are essential for initiation and regulation of reproductive function. In addition to pituitary gonadotrope stimulation, activity of GnRH through its receptor (GnRHR) has been suggested to include autocrine regulation of the GnRH neuron. Two hypogonadal mouse strains, the Gnrh1 mutant (hpg) mice and Gnrhr mutant mice were used to investigate the potential role of GnRH signaling in the proper development and maintenance of GnRH neurons. Immunocytochemical analysis of heterozygous hpg mice revealed a GnRH neuron population that was normal in size and distribution, indicating no effect from reduced Gnrh1 gene dosage on the neurons themselves. To visualize GnRH neurons in homozygous GnRH-deficient hpg mice, heterozygous hpg mice were crossed with GnRH-green fluorescent protein (GFP) transgenic mice with targeted expression of the GFP reporter gene in GnRH neurons. Analysis of forebrains of homozygous hpg/GFP-positive mice immunostained for GFP revealed a normal population size and appropriate distribution of GnRH neurons in hpg mice, with immunoreactive neuronal processes present at the median eminence. Similarly, adult mice deficient in functional GnRHR possessed a full complement of GnRH neurons in the basal forebrain that was indistinguishable from the distribution of GnRH neurons in their wild-type counterparts. Moreover, hpg/GFP neurons retained the ability to generate spontaneous bursts of action potential firing activity, suggesting that GnRH peptide is not required for this function. These data establish that autocrine-paracrine GnRH-signaling is not a prerequisite for the developmental migration of GnRH neurons into the brain or for the projection of GnRH neurosecretory axons.
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Affiliation(s)
- John C Gill
- Division of Endocrinology, Diabetes and Hypertension, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA
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Hu L, Gustofson RL, Feng H, Leung PK, Mores N, Krsmanovic LZ, Catt KJ. Converse regulatory functions of estrogen receptor-alpha and -beta subtypes expressed in hypothalamic gonadotropin-releasing hormone neurons. Mol Endocrinol 2008; 22:2250-9. [PMID: 18701637 DOI: 10.1210/me.2008-0192] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Estradiol (E(2)) acts as a potent feedback molecule between the ovary and hypothalamic GnRH neurons, and exerts both positive and negative regulatory actions on GnRH synthesis and secretion. However, the extent to which these actions are mediated by estrogen receptors (ERs) expressed in GnRH neurons has been controversial. In this study, Single-cell RT-PCR revealed the expression of both ERalpha and ERbeta isoforms in cultured fetal and adult rat hypothalamic GnRH neurons. Both ERalpha and ERbeta or individual ERs were expressed in 94% of cultured fetal GnRH neurons. In adult female rats at diestrus, 68% of GnRH neurons expressed ERs, followed by 54% in estrus and 19% in proestrus. Expression of individual ERs was found in 24% of adult male GnRH neurons. ERalpha exerted marked G(i)-mediated inhibitory effects on spontaneous action potential (AP) firing, cAMP production, and pulsatile GnRH secretion, indicating its capacity for negative regulation of GnRH neuronal function. In contrast, increased E(2) concentration and ERbeta agonists increase the rate of AP firing, GnRH secretion, and cAMP production, consistent with ERbeta-dependent positive regulation of GnRH secretion. Consonant with the coupling of ERalpha to pertussis toxin-sensitive G(i/o) proteins, E(2) also activates G protein-activated inwardly rectifying potassium channels, decreasing membrane excitability and slowing the firing of spontaneous APs in hypothalamic GnRH neurons. These findings demonstrate that the dual actions of E(2) on GnRH neuronal membrane excitability, cAMP production, and GnRH secretion are mediated by the dose-dependent activation of ERalpha and ERbeta expressed in hypothalamic GnRH neurons.
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Affiliation(s)
- Lian Hu
- Endocrinology and Reproduction Research Branch, PDEGEN, National Institue of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-4510, USA
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Xu C, Roepke TA, Zhang C, Rønnekleiv OK, Kelly MJ. Gonadotropin-releasing hormone (GnRH) activates the m-current in GnRH neurons: an autoregulatory negative feedback mechanism? Endocrinology 2008; 149:2459-66. [PMID: 18218690 PMCID: PMC2329261 DOI: 10.1210/en.2007-1178] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/27/2007] [Accepted: 01/15/2008] [Indexed: 11/19/2022]
Abstract
GnRH autoregulates GnRH neurons through an ultrashort feedback loop. One potential mechanism is the regulation of K(+) channel activity through the GnRH receptor. Whereas GnRH inhibits the activity of the M-current in peripheral neurons, there is no direct evidence that the M-current is involved in the autoregulatory pathway of GnRH or if the M-current is expressed in GnRH neurons. The M-current is a noninactivating, subthreshold K(+) current that inhibits cell excitability and is ubiquitously expressed in the central nervous system. We found that GnRH neurons expressed the neuronal M-current subunits, KCNQ2, -3, and -5 in addition to GnRH receptor (GnRH R1). Therefore, using whole-cell patch clamp recording and single-cell RT-PCR, we explored the effects of mammalian GnRH peptide on enhanced green fluorescent protein-tagged GnRH neurons acutely dispersed as well as in slice preparations. GnRH (100nm) inhibited GnRH neuronal excitability by hyperpolarizing the membrane. In the presence of CdCl(2), BaCl(2), and tetrodotoxin, GnRH activated an outward current in a dose-dependent manner (EC(50) 11 nm) in 30% of GnRH neurons. In voltage clamp, the selective M-channel blocker, XE-991, inhibited a K(+) current in GnRH neurons. XE-991 also antagonized the outward K(+) current induced by GnRH. Moreover, the GnRH effects on the M-current were blocked by the GnRH R1 antagonist antide. Therefore, these findings indicate that GnRH activates the M-current in a subpopulation of GnRH neurons via GnRH R1. This ultrashort circuit is one potential mechanism by which GnRH could modulate its own neuronal excitability through an autoreceptor.
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Affiliation(s)
- Chun Xu
- Department of Physiology and Pharmacology, Oregon National Primate Research Center, Oregon Health and Science University, Portland, Oregon 97239, USA
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Yamanaka A, Hiragami Y, Maeda N, Toku S, Kawahara M, Naito Y, Yamamoto H. Involvement of CaM kinase II in gonadotropin-releasing hormone-induced activation of MAP kinase in cultured hypothalamic neurons. Arch Biochem Biophys 2007; 466:234-41. [PMID: 17706588 DOI: 10.1016/j.abb.2007.06.009] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2007] [Accepted: 06/13/2007] [Indexed: 10/23/2022]
Abstract
Gonadotropin-releasing hormone (GnRH) is secreted from hypothalamic GnRH neurons. There is accumulating evidence that GnRH neurons have GnRH receptors and that the autocrine action of GnRH activates MAP kinase. In this study, we found that KN93, an inhibitor of Ca(2+)/calmodulin-dependent protein kinases (CaM kinases), inhibited the GnRH-induced activation of MAP kinase in immortalized GnRH neurons (GT1-7 cells). Immunoblot analysis indicated that the CaM kinase IIdelta2 isoform (CaM kinase IIdelta2) and synapsin I were expressed in GT1-7 cells. GnRH treatment rapidly increased phosphorylation of synapsin I at serine 603, a specific phosphorylation site for CaM kinase II, suggesting that GnRH treatment rapidly activated CaM kinase IIdelta2. In addition, when we stably overexpressed CaM kinase IIdelta2 in GT1-7 cells, the activation of MAP kinase was strongly enhanced. These results suggest that CaM kinase IIdelta2 was involved in the GnRH-induced activation of MAP kinase in GT1-7 cells.
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Affiliation(s)
- Ayana Yamanaka
- Department of Biochemistry, School of Medicine, University of the Ryukyus, 207 Uehara, Nishihara, Okinawa, Japan
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Rasier G, Parent AS, Gérard A, Lebrethon MC, Bourguignon JP. Early maturation of gonadotropin-releasing hormone secretion and sexual precocity after exposure of infant female rats to estradiol or dichlorodiphenyltrichloroethane. Biol Reprod 2007; 77:734-42. [PMID: 17596564 DOI: 10.1095/biolreprod.106.059303] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
An increase in the frequency of pulsatile gonadotropin-releasing hormone (GnRH) secretion in vitro and a reduction in LH response to GnRH in vivo characterize hypothalamic-pituitary maturation before puberty in the female rat. In girls migrating for international adoption, sexual precocity is frequent and could implicate former exposure to the insecticide dichlorodiphenyltrichloroethane (DDT), since a long-lasting DDT derivative has been detected in the serum of such children. We aimed at studying the effects of early transient exposure to estradiol (E(2)) or DDT in vitro and in vivo in the infantile female rat. Using a static incubation system of hypothalamic explants from 15-day-old female rats, a concentration- and time-dependent reduction in GnRH interpulse interval (IPI) was seen during incubation with E(2) and DDT isomers. These effects were prevented by antagonists of alpha-amino-3-hydroxy-5-methylisoxazole-4 propionic acid (AMPA)/kainate receptors and estrogen receptor. Also, o,p'-DDT effects were prevented by an antagonist of the aryl hydrocarbon orphan dioxin receptor (AHR). After subcutaneous injections of E(2) or o,p'-DDT between Postnatal Days (PNDs) 6 and 10, a decreased GnRH IPI was observed on PND 15 as an ex vivo effect. After DDT administration, serum LH levels in response to GnRH were not different from controls on PND 15, whereas they tended to be lower on PND 22. Subsequently, early vaginal opening (VO) and first estrus were observed together with a premature age-related decrease in LH response to GnRH. After prolonged exposure to E(2) between PNDs 6 and 40, VO occurred at an earlier age, but first estrus was delayed. We conclude that a transient exposure to E(2) or o,p'-DDT in early postnatal life is followed by early maturation of pulsatile GnRH secretion and, subsequently, early developmental reduction of LH response to GnRH that are possible mechanisms of the subsequent sexual precocity. The early maturation of pulsatile GnRH secretion could involve effects mediated through estrogen receptor and/or AHR as well as AMPA/kainate subtype of glutamate receptors.
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Affiliation(s)
- Grégory Rasier
- Developmental Neuroendocrinology Unit, Centre for Cellular and Molecular Neurobiology, University of Liège, University Hospital, B-4000 Liège (Sart-Tilman), Belgium
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Leclerc GM, Boockfor FR. Calcium influx and DREAM protein are required for GnRH gene expression pulse activity. Mol Cell Endocrinol 2007; 267:70-9. [PMID: 17241740 PMCID: PMC1852481 DOI: 10.1016/j.mce.2006.12.040] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/14/2006] [Revised: 10/28/2006] [Accepted: 12/19/2006] [Indexed: 12/19/2022]
Abstract
Recent evidence using GT1-7 cells indicates that GnRH pulsatility depends on exocytotic-release and gene transcription events. To determine whether calcium or DREAM may play a role in linking these processes, we used an L-type Ca(2+)-blocker (nimodipine) and found that not only GnRH gene expression (GnRH-GE) pulse activity was abolished but also that binding of proteins to OCT1BS-a (essential site for GnRH-GE pulses) was reduced. We further found that only EF-hand forms of DREAM were expressed in GT1-7 and that DREAM was part of the complex binding to OCT1BS-a. Finally, microinjection of DREAM antibody into cells abolished GnRH-GE pulses demonstrating its importance in pulsatility. These results reveal that calcium and DREAM may bridge cytoplasmic and nuclear events enabling temporal coordination of intermittent activity. Expression of DREAM in various cell types coupled with the universal role of calcium raise the possibility that these factors may play similar role in other secretory cells.
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Affiliation(s)
- Gilles M Leclerc
- Laboratory of Molecular Dynamics, Department of Cell Biology and Anatomy Medical University of South Carolina, 173 Ashley Avenue, Charleston, SC 29425, USA
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Walters K, Chin YP, Wu TJ. A processed metabolite of luteinizing hormone-releasing hormone has proliferative effects in endometrial cells. Am J Obstet Gynecol 2007; 196:33.e1-5. [PMID: 17240223 DOI: 10.1016/j.ajog.2006.07.054] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2006] [Revised: 05/17/2006] [Accepted: 07/05/2006] [Indexed: 01/05/2023]
Abstract
OBJECTIVE The purpose of this study is to determine the possible role of the processed peptide of LHRH, LHRH-(1-5), in regulating growth of endometrial cancer cells. STUDY DESIGN An endometrial cancer cell line, the Ishikawa cell line, was cultured under standard conditions and treated in a dose-dependent manner with 1 of 2 hormones, LHRH and LHRH-(1-5) to determine the ability of these peptides to regulate cellular growth. A tetrazolium-based assay was used to determine the effect these peptides have on cell proliferation. Furthermore, enzyme-linked immunosorbent assay (ELISA)-based assays were used to determine the expression of caspase-3/7 and pERK-1/2. Statistical analyses were conducted using an analysis of variance followed by Fisher LSD as the post-hoc test. RESULTS The results show that LHRH is anti-proliferative whereas LHRH-(1-5) is proliferative on the cells. Furthermore, LHRH-(1-5) decreased caspase-3/7 and pERK1/2 expression. CONCLUSION This is the first time LHRH-(1-5) is shown to have proliferative effects on cells.
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Affiliation(s)
- Kathryn Walters
- Laboratory of Neuroendocrinology and Women's Health Research, Department of Obstetrics and Gynecology, Uniformed Services University of the Health Sciences, Bethesda, MD 20814, USA
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Arroyo A, Kim B, Rasmusson RL, Bett G, Yeh J. Hyperpolarization-activated cation channels are expressed in rat hypothalamic gonadotropin-releasing hormone (GnRH) neurons and immortalized GnRH neurons. ACTA ACUST UNITED AC 2006; 13:442-50. [PMID: 16879992 DOI: 10.1016/j.jsgi.2006.05.010] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2005] [Indexed: 10/24/2022]
Abstract
OBJECTIVES The current research was conducted to determine whether hyperpolarization-activated cyclic nucleotide-gated (HCN1-4) channels are expressed in gonadotropin-releasing hormone (GnRH) neurons in the female rat hypothalamus and immortalized GnRH neurons (GT1-7 cells). METHODS Double-label fluorescence immunohistochemistry was used to colocalize HCN1-4 channels and GnRH in GnRH neurons in the female rat hypothalamus. Reverse transcriptase-polymerase chain reaction (RT-PCR), Western blotting, and immunocytochemistry were used to analyze HCN channel gene expression in GT1-7 cells. RESULTS Double-label fluorescence immunohistochemistry showed that 43% of hypothalamic GnRH neurons immunostained for HCN2 and 90% of GnRH neurons immunostained for HCN3. RT-PCR and Western blot showed expression of all four HCN channel subunits in GT1-7 cells. Double-label immunocytochemistry showed cytoplasmic immunostaining of HCN2 and HCN3 in GT1-7 cells. CONCLUSIONS This study demonstrates for the first time that HCN channels are expressed in GnRH neurons in the rat hypothalamus and GT1-7 cells. Our research supports the hypothesis that HCN channels may be involved in electrical bursting activity and pulsatile GnRH secretion in endogenous GnRH neurons and GT1-7 cells.
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Affiliation(s)
- Armando Arroyo
- Department of Gynecology-Obstetrics, University at Buffalo, School of Medicine and Biomedical Sciences, Buffalo, New York 14222, USA.
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Hu L, Wada K, Mores N, Krsmanovic LZ, Catt KJ. Essential role of G protein-gated inwardly rectifying potassium channels in gonadotropin-induced regulation of GnRH neuronal firing and pulsatile neurosecretion. J Biol Chem 2006; 281:25231-40. [PMID: 16825187 DOI: 10.1074/jbc.m603768200] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Activation of the luteinizing hormone/human chorionic gonadotropin (LH/hCG) receptor (LHR) in cultured hypothalamic cells and immortalized GnRH (gonadotropin-releasing hormone) neurons (GT1-7 cells) transiently stimulates and subsequently inhibits cAMP production and pulsatile GnRH release. The marked and delayed impairment of cAMP signaling and episodic GnRH release in GT1-7 cells is prevented by pertussis toxin (PTX). This, and the LH-induced release of membrane-bound Galpha(s) and Galpha(i3) subunits, are indicative of differential G protein coupling to the LHR. Action potential (AP) firing in identified GnRH neurons also initially increased and then progressively decreased during LH treatment. The inhibitory action of LH on AP firing was also prevented by PTX. Reverse transcriptase-PCR analysis of GT1-7 neurons revealed the expression of G protein-gated inwardly rectifying potassium (GIRK) channels in these cells. The LH-induced currents were inhibited by PTX and were identified as GIRK currents. These responses indicate that agonist stimulation of endogenous LHR expressed in GnRH neurons activates GIRK channels, leading to suppression of membrane excitability and inhibition of AP firing. These findings demonstrate that regulation of GIRK channel function is a dominant factor in gonadotropin-induced abolition of pulsatile GnRH release. Furthermore, this mechanism could contribute to the suppression of pituitary function during pregnancy.
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Affiliation(s)
- Lian Hu
- Endocrinology and Reproduction Research Branch, NICHD, National Institutes of Health, Bethesda, Maryland 20892-4510, USA
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Khadra A, Li YX. A model for the pulsatile secretion of gonadotropin-releasing hormone from synchronized hypothalamic neurons. Biophys J 2006; 91:74-83. [PMID: 16603486 PMCID: PMC1479076 DOI: 10.1529/biophysj.105.080630] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Cultured gonadotropin-releasing hormone (GnRH) neurons have been shown to express GnRH receptors. GnRH binding to its receptors activates three types of G-proteins at increasing doses. These G-proteins selectively activate or inhibit GnRH secretion by regulating the intracellular levels of Ca2+ and cAMP. Based on these recent observations, we build a model in which GnRH plays the roles of a feedback regulator and a diffusible synchronizing agent. We show that this GnRH-regulated GnRH-release mechanism is sufficient for generating pulsatile GnRH release. The model reproduces the observed effects of some key drugs that disturb the GnRH pulse generator in specific ways. Simulations of 100 heterogeneous neurons revealed that the synchronization mediated by a common pool of diffusible GnRH is robust. The population can generate synchronized pulsatile signals even when all the individual GnRH neurons oscillate at different amplitudes and peak at different times. These results suggest that the positive and negative effects of the autocrine regulation by GnRH on GnRH neurons are sufficient and robust in generating GnRH pulses.
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Affiliation(s)
- Anmar Khadra
- Department of Mathematics, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z2
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Neithardt A, Farshori MP, Shah FB, Catt KJ, Shah BH. Dependence of GnRH-induced phosphorylation of CREB and BAD on EGF receptor transactivation in GT1-7 neuronal cells. J Cell Physiol 2006; 208:586-93. [PMID: 16741954 DOI: 10.1002/jcp.20697] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The hypothalamic neuropeptide, gonadotropin releasing hormone (GnRH), is a primary regulatory factor in the neuroendocrine control of reproduction. The GnRH decapeptide is released in an episodic manner from hypothalamic GnRH neurons, which are known to express GnRH receptors. Here we examined the signaling pathways by which autocrine GnRH stimulation generates cell survival and proliferative signals in hypothalamic GT1-7 cells. Both GnRH and epidermal growth factor (EGF) caused rapid phosphorylation of cyclic AMP response element binding protein (CREB) and BAD. The selective epidermal growth factor receptor (EGF-R) antagonist, AG1478, attenuates the phosphorylation of these proteins by GnRH and EGF. Inhibition of PKC and Src abolished the stimulatory effects of GnRH, but not that of EGF, consistent with a critical role of these signaling molecules upstream of the EGF-R. All of these effects of GnRH were mimicked by phorbol 12 myristate 13-acetate (PMA). Consistent with the prosurvival and mitogenic effects of phosphoinositide 3-kinase/Akt (P13-K/Akt) downstream of the EGF-R, inhibition of P13-K diminished the activation of these proteins following stimulation with GnRH, EGF, and PMA. Overexpression of dominant negative Akt attenuated agonist-induced phosphorylation of BAD, but not that of ERK1/2 and CREB. Moreover, overexpression of wild-type RSK-1 resulted in enhanced basal as well as agonist-induced phosphorylation of CREB and BAD, indicating a critical role of RSK-1 in activating cytosolic as well as nuclear proteins. These data reveal novel signaling mechanisms of GnRH-induced phosphorylation of CREB and BAD in GT1-7 neurons through transactivation of the EGF-R.
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Affiliation(s)
- Adrienne Neithardt
- Section on Hormonal Regulation, Endocrinology and Reproduction Research Branch, NICHD, National Institutes of Health, Bethesda, Maryland 20892-4510, USA
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Shah BH, Shah FB, Catt KJ. Role of metalloproteinase-dependent EGF receptor activation in α1-adrenoceptor-stimulated MAP kinase phosphorylation in GT1-7 neurons. J Neurochem 2006; 96:520-32. [PMID: 16336626 DOI: 10.1111/j.1471-4159.2005.03585.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Adrenoceptors (ARs) are involved in the regulation of gonadotropin-releasing hormone (GnRH) release from native and immortalized hypothalamic (GT1-7) neurons. However, the AR-mediated signaling mechanisms and their functional significance in these cells are not known. Stimulation of GT1-7 cells with the alpha1-AR agonist, phenylephrine (Phe), causes phosphorylation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) mitogen-activated protein (MAP) kinases that is mediated by protein kinase C (PKC)-dependent transactivation of the epidermal growth factor receptor (EGF-R). Phe stimulation causes shedding of the soluble ligand, heparin-binding EGF (HB-EGF), as a consequence of matrix metalloproteinase (MMP) activation. Phe-induced phosphorylation of the EGF-R, and subsequently of Shc and ERK1/2, was attenuated by inhibition of MMP or HB-EGF with the selective inhibitor, CRM197, or by a neutralizing antibody. In contrast, phosphorylation of the EGF-R, Shc and ERK1/2 by EGF and HB-EGF was independent of PKC and MMP activity. Moreover, inhibition of Src attenuated ERK1/2 responses by Phe, but not by HB-EGF and EGF, indicating that Src acts upstream of the EGF-R. Consistent with a potential role of reactive oxygen species (ROS), Phe-induced phosphorylation of EGF-R was attenuated by the antioxidant, N-acetylcysteine. These data suggest that activation of the alpha1-AR causes phosphorylation of ERK1/2 through activation of PKC, ROS and Src, and shedding of HB-EGF, which binds to and activates the EGF-R.
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Affiliation(s)
- Bukhtiar H Shah
- Endocrinology and Reproduction Research Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-4510, USA.
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Neuromodulatory Functions of Terminal Nerve‐GnRH Neurons. ACTA ACUST UNITED AC 2006. [DOI: 10.1016/s1546-5098(06)25011-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/17/2023]
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Leclerc GM, Boockfor FR. Identification of a novel OCT1 binding site that is necessary for the elaboration of pulses of rat GnRH promoter activity. Mol Cell Endocrinol 2005; 245:86-92. [PMID: 16337733 DOI: 10.1016/j.mce.2005.10.026] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/29/2005] [Revised: 10/19/2005] [Accepted: 10/27/2005] [Indexed: 11/27/2022]
Abstract
Recent evidence from our laboratory demonstrated that the OCT1 protein was necessary for GnRH gene promoter pulse activity through its interaction with a specific OCT1 binding site (OCT1BS-a, -1,774/-1,781). In light of the importance of this POU homeoprotein in pulsatile function, we focused on two other highly conserved OCT1 sites within this region, OCT1BS-b (-1,694/-1,701, previously AT-b), and OCT1BS-c (-1,569/-1,562). Mutagenesis of these sites revealed that alteration of OCT1BS-c, but not OCT1BS-b, virtually abolished gene expression pulses in GT1-7 cells. EMSAs confirmed that OCT1 can bind to both sites. Taken together, our findings demonstrate clearly that more than one Oct1 binding site is necessary for GnRH promoter pulses. Moreover, the lack of an influence observed with OCT1BS-b on pulse activity indicates that OCT1 action is not general to all OCT1 sites, but specific to certain octamer sequences in the NSE region of the GnRH promoter.
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Affiliation(s)
- Gilles M Leclerc
- Laboratory of Molecular Dynamics, Department of Cell Biology and Anatomy, Medical University of South Carolina, 173 Ashley Avenue, Charleston, 29425, USA
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Wu TJ, Mani SK, Glucksman MJ, Roberts JL. Stimulation of luteinizing hormone-releasing hormone (LHRH) gene expression in GT1-7 cells by its metabolite, LHRH-(1-5). Endocrinology 2005; 146:280-6. [PMID: 15486221 DOI: 10.1210/en.2004-0560] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Given the central role of the decapeptide LHRH in reproduction and reproductive behavior, it is important to focus on delineating the possible effects of this gene and its products in the regulation of hormone-dependent reproductive processes. In the female, ovulation is preceded by a marked increase in LHRH release; the increase in LHRH release culminates in a preovulatory LH surge, which coincides with a period of sexual receptivity. In contrast to the belief that the proteolytic metabolism of LHRH serves only as a degradative process that removes excess LHRH and attenuates signal transduction through the LHRH receptor, we hypothesized that a metabolite of the decapeptide, LHRH-(1-5), can directly regulate LHRH neuronal function. This study demonstrates the ability of LHRH-(1-5) peptide to regulate LHRH gene expression in the LHRH neuronal cell line, the GT(1-7) cell. The results show that LHRH-(1-5) stimulated LHRH gene expression at the posttranscriptional level. In contrast to the LHRH suppression of its own gene expression, the coadministration of LHRH with the metalloendopeptidase, EC 3.4.24.15, an endopeptidase known to cleave LHRH to form LHRH(1-5), shows a reversal of effect, a stimulation of LHRH gene expression. Finally, the effect of LHRH-(1-5) on LHRH gene expression appears to be mediated by the calcium/calmodulin-dependent protein kinase. The present study supports the hypothesis that the physiological metabolite of LHRH, LHRH-(1-5), is functionally capable of regulating the reproductive neuroendocrine system.
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Affiliation(s)
- T J Wu
- Department of Obstetrics and Gynecology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814, USA.
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Cariboni A, Pimpinelli F, Colamarino S, Zaninetti R, Piccolella M, Rumio C, Piva F, Rugarli EI, Maggi R. The product of X-linked Kallmann's syndrome gene (KAL1) affects the migratory activity of gonadotropin-releasing hormone (GnRH)-producing neurons. Hum Mol Genet 2004; 13:2781-91. [PMID: 15471890 DOI: 10.1093/hmg/ddh309] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
X-linked Kallmann's syndrome (KS) is a genetic disease characterized by anosmia and hypogonadism due to impairment in the development of olfactory axons and in the migration of gonadotropin-releasing hormone (GnRH)-producing neurons. Deletions or point mutations of a gene located at Xp22.3 (KAL1) are responsible for the disease. This gene encodes for a secreted heparin-binding protein (KAL or anosmin-1) which exhibits similarities with cell-adhesion molecules. In the present study, we show for the first time a direct action of anosmin-1 on the migratory activity of GnRH neurons. Specifically, we exposed immortalized migrating GnRH neurons (GN11 cells) to conditioned media (CM) of COS or CHO cells transiently transfected with human KAL1 gene in microchemotaxis and collagen gel assays. We found that anosmin-1-enriched media produced a cell-specific chemotactic response of GN11 cells. None of the CM enriched on three forms of anosmin-1 carrying different missense mutations (N267K, E514K and F517L) found in patients affected by X-linked KS affected the chemomigration of GN11 cells. Anosmin binds to the GN11 cell surface by interacting with the heparan sulphate proteoglycans, and the chemotactic effect of anosmin-1-enriched CM can be specifically blocked by heparin or by heparitinase pretreatment. These results strongly suggest an involvement of anosmin-1 in the control of the migratory behaviour of GnRH neurons and provide novel information on the pathogenesis of KS.
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Affiliation(s)
- Anna Cariboni
- Department of Endocrinology, University of Milano, Milano, Italy
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Haneda K, Oka Y. Selective modulation of voltage-gated calcium channels in the terminal nerve gonadotropin-releasing hormone neurons of a teleost, the dwarf gourami (Colisa lalia). Endocrinology 2004; 145:4489-99. [PMID: 15231709 DOI: 10.1210/en.2004-0353] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
GnRH neurons in the terminal nerve (TN) have been suggested to function as a neuromodulatory system that regulates long-lasting changes in the animal behavior. Here we examined electrophysiological properties of TN-GnRH neurons in a teleost (dwarf gourami, Colisa lalia), focusing on the voltage-gated Ca2+ channels, which are thought to be coupled to several cellular events such as GnRH release. TN-GnRH neurons showed low-voltage activated (LVA) currents and three types of pharmacologically distinct high-voltage activated (HVA) currents. The L- and N-type currents constituted 30.7 +/- 3.1 and 41.0 +/- 3.9%, respectively, of HVA currents, which was recorded at the holding potential of -60 mV to inactivate the LVA currents. Although P/Q-type current was small and negligible, R-type current accounted for the remaining 23.6 +/- 1.6% of HVA currents. Next we examined the possibility of Ca2+ channel modulation induced by GnRH released in a paracrine/autocrine manner. HVA currents of up to 40% was inhibited by the application of salmon GnRH, which is the same molecular species of GnRH as is synthesized by TN-GnRH neurons themselves. However, salmon GnRH had no measurable effects on LVA currents. The inhibition of HVA currents had a dose dependence (EC50 was 11.5 nm) and type specificity among different HVA currents; N- and R-type currents were preferentially inhibited, but L-type currents had by far lower sensitivity. The physiological significance of different Ca2+ influx pathways, and their paracrine/autocrine regulation mechanisms in TN-GnRH neurons are discussed.
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Affiliation(s)
- Kosuke Haneda
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
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Huirne JAF, van Loenen ACD, Schats R, McDonnell J, Hompes PGA, Schoemaker J, Homburg R, Lambalk CB. Dose-finding study of daily gonadotropin-releasing hormone (GnRH) antagonist for the prevention of premature luteinizing hormone surges in IVF/ICSI patients: antide and hormone levels. Hum Reprod 2004; 19:2206-15. [PMID: 15333605 DOI: 10.1093/humrep/deh357] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
BACKGROUND The aim of this study was to define the minimal effective dose of antide (Iturelix) to prevent premature luteinizing hormone (LH) surges in in vitro fertilization (IVF) patients. METHODS In a prospective, single centre study, 144 IVF/ICSI patients were stimulated with r-hFSH from cycle day 2 and from cycle day 6 onwards, cotreated with daily 2 mg/2 ml (n=30), 1 mg/ml (n=30), 0.5 mg/ml (n=31), 0.5 mg/0.5 ml (n=23) and 0.25 mg/ml (n=30) GnRH antagonist (antide). Serum samples were taken three times daily during antide administration to assess antide and hormone levels. The minimal effective dose was defined as the lowest dose group with <2 LH surges (LH >12.4 IU/l and progesterone >2 ng/ml). RESULTS Serum antide levels, mean LH and E2 levels per day and their area under the curves were dose-related to antide. The bioavailability of antide almost doubled after dilution in larger volumes. Pre-injection LH levels gradually increased during GnRH antagonist treatment. LH surges occurred in the lowest dose groups 0.5 mg/ml (3.2%), 0.5 mg/0.5 ml (6.7%) and 0.25 mg/ml (13.3%). Hence, 0.5 mg/ml is considered to be the minimal effective dose. Antide was overall well tolerated and safe. CONCLUSIONS 0.5 mg/ml antide is the minimal effective dose to prevent an untimely LH surge in IVF patients stimulated with r-hFSH.
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Affiliation(s)
- Judith A F Huirne
- Division of Reproductive Medicine, Department of Obstetrics and Gynaecology, Vrije Universiteit medical centre (VUmc), Amsterdam, The Netherlands
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Martinez-Fuentes AJ, Hu L, Krsmanovic LZ, Catt KJ. Gonadotropin-Releasing Hormone (GnRH) Receptor Expression and Membrane Signaling in Early Embryonic GnRH Neurons: Role in Pulsatile Neurosecretion. Mol Endocrinol 2004; 18:1808-17. [PMID: 15184526 DOI: 10.1210/me.2003-0321] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The characteristic pulsatile secretion of GnRH from hypothalamic neurons is dependent on an autocrine interaction between GnRH and its receptors expressed in GnRH-producing neurons. The ontogeny and function of this autoregulatory process were investigated in studies on the properties of GnRH neurons derived from the olfactory placode of the fetal rat. An analysis of immunocytochemically identified, laser-captured fetal rat hypothalamic GnRH neurons, and olfactory placode-derived GnRH neurons identified by differential interference contrast microscopy, demonstrated coexpression of mRNAs encoding GnRH and its type I receptor. Both placode-derived and immortalized GnRH neurons (GT1-7 cells) exhibited spontaneous electrical activity that was stimulated by GnRH agonist treatment. This evoked response, as well as basal neuronal firing, was abolished by treatment with a GnRH antagonist. GnRH stimulation elicited biphasic intracellular calcium ([Ca2+]i) responses, and both basal and GnRH-stimulated [Ca2+]i levels were reduced by antagonist treatment. Perifused cultures released GnRH in a pulsatile manner that was highly dependent on extracellular Ca2+. The amplitude of GnRH pulses was increased by GnRH agonist stimulation and was diminished during GnRH antagonist treatment. These findings demonstrate that expression of GnRH receptor, GnRH-dependent activation of Ca2+ signaling, and autocrine regulation of GnRH release are characteristics of early fetal GnRH neurons and could provide a mechanism for gene expression and regulated GnRH secretion during embryonic migration.
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Affiliation(s)
- Antonio J Martinez-Fuentes
- Endocrinology and Reproduction Research Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-4510, USA
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Xu C, Xu XZ, Nunemaker CS, Moenter SM. Dose-dependent switch in response of gonadotropin-releasing hormone (GnRH) neurons to GnRH mediated through the type I GnRH receptor. Endocrinology 2004; 145:728-35. [PMID: 14576189 DOI: 10.1210/en.2003-0562] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Pulsatile release of GnRH provides central control of reproduction. GnRH neuron activity is likely synchronized to produce hormone pulses, but the mechanisms are largely unknown. One candidate for communication among these neurons is GnRH itself. Cultured embryonic and immortalized GnRH neurons express GnRH receptor type I (GnRHR-1), but expression has not been shown in adult GnRH neurons. Using mice that express green fluorescent protein (GFP) in GnRH neurons, we tested whether adult GnRH neurons express GnRHR-1. GFP-positive (n = 42) and -negative neurons (n = 22) were harvested from brain slices, and single-cell RT-PCR was performed with cell contents. Fifty-two percent of the GnRH neurons tested expressed GnRHR-1, but only 9% of non-GnRH hypothalamic neurons expressed GnRHR-1; no false harvest controls (n = 13) were positive. GnRHR-1 expression within GnRH neurons suggested a physiological ultrashort loop feedback role for GnRH. Thus, we examined the effect of GnRH on the firing rate of GnRH neurons. Low-dose GnRH (20 nm) significantly decreased firing rate in 12 of 22 neurons (by 42 +/- 4%, P < 0.05), whereas higher doses increased firing rate (200 nm, five of 10 neurons, 72 +/- 26%; 2000 nm, nine of 13 neurons, 53 +/- 8%). Interestingly, the fraction of GnRH neurons responding was similar to the fraction in which GnRHR-1 was detected. Together, these data demonstrate that a subpopulation of GnRH neurons express GnRHR-1 and respond to GnRH with altered firing. The dose dependence suggests that this autocrine control of GnRH neurons may be not only a mechanism for generating and modulating pulsatile release, but it may also be involved in the switch between pulse and surge modes of release.
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Affiliation(s)
- Chun Xu
- Department of Internal Medicine, P.O. Box 800578, University of Virginia, Charlottesville, VA 22908, USA
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