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Molecular characterization and regulation of gonadotropin-releasing hormone (GnRH) and its receptor mRNA in the human ovary Nathwani, Parimal Suresh
Abstract
With the recent detection of GnRH and its receptor (GnRH-R) in numerous extrapituitary tissues, it is hypothesized that GnRH acts as an autocrine/paracrine regulator of ovarian function. The direct involvement of GnRH in follicular atresia and modulation of ovarian steroidogenesis, further substantiate the extrapituitary actions of this decapeptide. In contrast to the hypothalamus and pituitary, the factors that regulate ovarian GnRH and its receptor remain poorly characterized. As gonadal steroids are key regulators of ovarian functions, the present study investigated the role of 17β-estradiol (E2) and progesterone (P4) in regulating the intrinsic ovarian GnRH axis. Using reverse transcription polymerase chain reaction (RT-PCR), we have isolated the full-length GnRH-R coding region from human granulosa-luteal cells (hGLCs). Sequence analysis revealed that the ovarian GnRH-R cDNA is identical to its pituitary counterpart. Basal expression studies demonstrated that GnRH and GnRH-R mRNA levels significantly increased with time in culture, reaching levels of 160% and 170% on day 8 and 10 of culture compared to day 1 (p<0.05), respectively. On day 5 in culture, hGLCs were treated with E2 and RU486 (a progesterone receptor antagonist) in a dose- and time-dependent fashion. A dose-dependent decrease was observed in GnRH and GnRH-R rnRNA levels after a 24h treatment with E2 (1-100 nM). Time course studies demonstrated that E2 (1 nM) decreased GnRH mRNA levels in a time dependent manner, with a maximal inhibition of 40% at 48h (p<0.05). In contrast, GnRH-R expression exhibited a biphasic pattern with time. A 6h treatment with E2 (1 nM) resulted in a 20% increase in GnRH-R message (p<0.05), whereas a long-term treatment (48h) resulted in a 60% decrease in GnRH-R expression (p<0.05) in hGLCs. Tamoxifen treatment reversed the E2-induced inhibition of GnRH and GnRH-R mRNA expression, indicating that the E2 effect was mediated through its receptor. The progesterone receptor antagonist had no signficant effect on GnRH mRNA levels in hGLCs. However, RU486 induced a timeand dose-dependent decrease in GnRH-R mRNA expression, with a maximal inhibition of 50% at a dose of 10μM for 24h (p<0.05). Since GnRH actions have been associated with atresia and luteolysis, the dynamic balance between E2 and P4 may contribute to the maintenance of the corpus luteum. With the recent identification of a second form of GnRH in the human brain (GnRH-II), the present study examined the expression and function of GnRH-II in human ovarian cells. Using RT-PCR we demonstrated the expression of GnRH-II in hGLCs, an ovarian cancer cell line (OVCAR-3), primary ovarian cancer cells, and human ovarian surface epithelial cells. Functionally like GnRH-I, GnRH-II significantly decreased progesterone secretion in hGLCs (p<0.001). Furthermore, GnRH-II decreased progesterone secretion more than GnRH-I (50% versus 30% compared to control; p<0.05). The GnRH-induced inhibition of progesterone secretion was reversed by antide, a GnRH antagonist. In summary, our studies demonstrate that the ovary possesses an intrinsic GnRH axis that is dynamically regulated during spontaneous luteinization in vitro, and that gonadal steroids are capable of regulating GnRH and its receptor in the human ovary. Coupled with the expression and functional analysis of a second form of GnRH (GnRH-II) in the ovary, our studies strengthen the notion that GnRH acts as an autocrine/paracrine modulator of ovarian functions.
Item Metadata
Title |
Molecular characterization and regulation of gonadotropin-releasing hormone (GnRH) and its receptor mRNA in the human ovary
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
2000
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Description |
With the recent detection of GnRH and its receptor (GnRH-R) in numerous
extrapituitary tissues, it is hypothesized that GnRH acts as an autocrine/paracrine
regulator of ovarian function. The direct involvement of GnRH in follicular atresia and
modulation of ovarian steroidogenesis, further substantiate the extrapituitary actions of
this decapeptide. In contrast to the hypothalamus and pituitary, the factors that regulate
ovarian GnRH and its receptor remain poorly characterized. As gonadal steroids are key
regulators of ovarian functions, the present study investigated the role of 17β-estradiol
(E2) and progesterone (P4) in regulating the intrinsic ovarian GnRH axis. Using reverse
transcription polymerase chain reaction (RT-PCR), we have isolated the full-length
GnRH-R coding region from human granulosa-luteal cells (hGLCs). Sequence analysis
revealed that the ovarian GnRH-R cDNA is identical to its pituitary counterpart. Basal
expression studies demonstrated that GnRH and GnRH-R mRNA levels significantly
increased with time in culture, reaching levels of 160% and 170% on day 8 and 10 of
culture compared to day 1 (p<0.05), respectively. On day 5 in culture, hGLCs were
treated with E2 and RU486 (a progesterone receptor antagonist) in a dose- and time-dependent
fashion. A dose-dependent decrease was observed in GnRH and GnRH-R
rnRNA levels after a 24h treatment with E2 (1-100 nM). Time course studies
demonstrated that E2 (1 nM) decreased GnRH mRNA levels in a time dependent manner,
with a maximal inhibition of 40% at 48h (p<0.05). In contrast, GnRH-R expression
exhibited a biphasic pattern with time. A 6h treatment with E2 (1 nM) resulted in a 20%
increase in GnRH-R message (p<0.05), whereas a long-term treatment (48h) resulted in a
60% decrease in GnRH-R expression (p<0.05) in hGLCs. Tamoxifen treatment reversed
the E2-induced inhibition of GnRH and GnRH-R mRNA expression, indicating that the
E2 effect was mediated through its receptor. The progesterone receptor antagonist had no
signficant effect on GnRH mRNA levels in hGLCs. However, RU486 induced a timeand
dose-dependent decrease in GnRH-R mRNA expression, with a maximal inhibition
of 50% at a dose of 10μM for 24h (p<0.05). Since GnRH actions have been associated
with atresia and luteolysis, the dynamic balance between E2 and P4 may contribute to the
maintenance of the corpus luteum.
With the recent identification of a second form of GnRH in the human brain
(GnRH-II), the present study examined the expression and function of GnRH-II in human
ovarian cells. Using RT-PCR we demonstrated the expression of GnRH-II in hGLCs, an
ovarian cancer cell line (OVCAR-3), primary ovarian cancer cells, and human ovarian
surface epithelial cells. Functionally like GnRH-I, GnRH-II significantly decreased
progesterone secretion in hGLCs (p<0.001). Furthermore, GnRH-II decreased
progesterone secretion more than GnRH-I (50% versus 30% compared to control;
p<0.05). The GnRH-induced inhibition of progesterone secretion was reversed by antide,
a GnRH antagonist.
In summary, our studies demonstrate that the ovary possesses an intrinsic GnRH
axis that is dynamically regulated during spontaneous luteinization in vitro, and that
gonadal steroids are capable of regulating GnRH and its receptor in the human ovary.
Coupled with the expression and functional analysis of a second form of GnRH (GnRH-II)
in the ovary, our studies strengthen the notion that GnRH acts as an
autocrine/paracrine modulator of ovarian functions.
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Extent |
4796093 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-07-07
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0089410
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
2000-05
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.