Patients with dysfunctional ovaries, such as those with premature ovarian insufficiency and granulosa cell tumours, do not have normal follicle development and may not respond to traditional assisted reproductive techniques. Using the reaggregated ovary (RO) technique, these patients' oocytes may be reaggregated with functional supporting cells and cultured in vitro to develop fertilisable eggs. However, current research using ROs have only used murine ovaries as a somatic cell source. In this thesis, with the aim of moving towards a clinical treatment, we assessed follicle development in ROs in vitro and progressed to using the technique with human tissues. To assess whether an older murine somatic cell source resulted in advanced follicle development, and how follicle development differed between transplanted and cultured ROs, ROs were generated using postnatal day 2 (P2) and P6 mouse ovaries. To investigate theca cell development in follicles from cultured tissue, mouse ovaries were cultured with mouse serum or encapsulated in hyaluronan hydrogels. Prior to generating and culturing chimeric human-mouse ROs (HuMoROs), competent handling and digestion of bovine cortical tissue was required. Broadly, ROs generated from both P2 and P6 exhibited similar follicle development in vitro after 14 d of culture, and follicles from cultured ROs were more developed than those from transplanted ROs. Theca cell development observed in follicles from cultured ovaries was still poorer than those from in vivo ovaries, even when ovaries were cultured in mouse serum or encapsulated in a hyaluronan hydrogel. Finally, some follicles containing potential human oocytes developed within the generated HuMoROs after 7 d of culture. These results have highlighted the potential of the RO technique as a method to generate fertilisable eggs and identified further aspects which need to be targeted in order to improve the success of the technique.

The layer of cells lining the outer surface of the mammalian ovary, the ovarian surface epithelium (OSE), is a constant feature throughout the dynamic tissue remodeling that occurs throughout the reproductive cycle (follicle growth, ovulation, corpora lutea formation and pregnancy). Abnormal development of these cells is responsible for 90% of all epithelial ovarian cancers in women and epidemiological studies have shown that susceptibility to ovarian cancer is negatively correlated with increasing pregnancy. Little is known about how OSE cells are affected at each stage of the cycle, so the main aim of this study was to determine how the reproductive cycle affected proliferation and degeneration of OSE cells. This study utilised three animal models each with a different type of reproductive cycle: a mono-ovular seasonal breeder (Sheep), a mono-ovular polyoestrous breeder (Cow) and a poly-ovular non human primate (marmoset) to allow comparisons to be made. Comparison of OSE proliferative activity was made in sheep and marmoset at each stage of the cycle including pregnancy and anoestrous. The bovine model was used to investigate apoptotic cell death. Proliferative activity of somatic cells within the sheep ovary was monitored throughout the reproductive cycle by detection of cell cycle markers PCNA and Ki67 using immunohistochemistry. The pattern of OSE proliferation was correlated with the pattern of follicle development at each stage (sheep and marmoset). During pregnancy cell proliferation was significantly lower in OSE and in granulosa cells, reflecting a suppression of mature follicle development during these stages whereas in cycling animals proliferation was increased. Differences in OSE proliferation were observed in relation to the local underlying tissue environment in both sheep and marmoset. Epithelial cell rupture and regeneration enhanced the hormonal mitogenic action on epithelial cells, which showed highest proliferation over corpora lutea in each animal model. To test the hypothesis that these changes are mediated by hormones or growth factors ovine OSE cells were cultured and proliferative activity monitored after treatment with several factors: fetal calf serum (FCS), follicular fluid from follicles of varying sizes, corpora lutea extracts, recombinant human IGF-1, oestradiol and progesterone. IGF alone was demonstrated to have an affect on increasing proliferation of cultured OSE cells. Levels of FSHr and LHr were monitored by quantitative real- time PCR and it was demonstrated that the concentration of gonadotrophin receptors in OSE, increased prior to and after ovulation, at which time the in vivo OSE proliferation also peaked. The in situ apoptosis index was determined in bovine tissue using TUNEL throughout the regular cycle, and at mid and late-pregnancy stages. The results showed that pregnancy induced apoptotic activity in OSE cells and up regulated the tumour suppressor gene p53. Cultured bovine OSE cells also exhibited an increased level of apoptosis following progesterone treatment. Since p53/p53 gene expression in OSE over the corpora lutea producing progesterone also increased, this progesterone-mediated apoptosis may be mediated through an up-regulation of p53 synthesis. The effect of pregnancy and low production of gonadotrophins in the regulation of OSE cell morphology and activity was further investigated in the marmoset monkey (a non-human primate) treated with GnRH antagonist and infused with BrdU to monitor proliferative activity. OSE proliferation was correlated to ovarian events (follicular growth, ovulation and luteinization) and this was suppressed during pregnancy. Inhibition of gonadotrophin secretion by treatment with a GnRH antagonist also markedly inhibited OSE proliferation. Taken together these studies support the hypothesis that pregnancy and periods of anovulation reduce proliferation of OSE cells and alter the pattern of apoptotic cell death and that this effect is independent of species and reproductive pattern. Suppression of gonadotrophins and other growth factors during pregnancy could enhance p53-mediated apoptosis of damaged and mitogenic cells arising from repeated ovulations. This effect may partly explain why increasing number of pregnancies in woman reduces the chance of epithelial ovarian cancers.

Vascular Endothelial Growth Factor (VEGF) has been shown to be an absolute requirement for ovarian follicle development. Although VEGF is commonly regarded primarily as an angiogenic factor, granulosa cells are a major site of VEGF synthesis in the follicle and they express VEGF receptors (VEGFR1 and VEGFR2). Further, the development of the dominant follicle is characterised by a substantial increase in granulosa cell expression of VEGF and its receptors. In spite of this, potential non-angiogenic effects of VEGF in these follicles have not been elucidated. The objective of the three studies described in this thesis was to use an in vitro bovine granulosa cell model to investigate the roles of VEGF during development of the dominant follicle. In addition, in light of evidence in other cell types, potential interactions between VEGF signalling and heterotrimeric protein signalling in these follicles were also investigated. In the first study, granulosa cells were obtained from healthy follicles with diameters of 4 to 8 mm (corresponding to just before the selection of a dominant follicle during a follicular wave) or 9 to 14 mm (encompassing all developmental stages of a dominant follicle) and exposed to a range of VEGF concentrations (1 to 100 ng/ml) encompassing concentrations found naturally in bovine dominant follicles. VEGF at 1 ng/ml, but not at higher concentrations (P > 0.1), induced significant proliferation of bovine granulosa cells from 4 to 8 mm follicles (P = 0.024) and increased the proliferative response of these cells to FSH (P = 0.045). VEGF also induced a dose-dependent increase in ERK1/2 activation by granulosa cells from 4 to 8 mm follicles (P < 0.03) but did not have any effect on expression of the steroidogenic enzyme, CYP11A1, by these cells (P > 0.1). VEGF, at a dose of 1 ng/ml (P = 0.003), but not at higher doses (P > 0.1), induced an increase in COX-2 expression by granulosa cells from 9 to 14 mm follicles. In addition, LH stimulation of both ERK phosphorylation (P < 0.05) and COX-2 expression (P < 0.05) in granulosa cells from 9 to 14 mm follicles were prevented (P > 0.1) by specific inhibition of VEGFR2, indicating that VEGF may mediate COX-2 responses to LH in these cells. The second study sought to examine the expression of heterotrimeric G-protein á subunits and PLCâ isoforms by real-time PCR and westen blotting in bovine granulosa cells throughout follicle development to identify specific molecular components of heterotrimeric G-protein pathways that may functionally interact with intracellular VEGF signals. Results showed that GNAS, GNA11 and GNAI2 were all expressed at significantly (P < 0.05) higher levels in granulosa cells of pre-ovulatorysize follicles (10.0 to 13.9 mm) than in cells from smaller follicles (2.0 to 5.9 mm and 6.0 to 9.9 mm). In addition, all PLCB isoforms except PLCB2 were expressed in bovine granulosa cells with PLCB3 being more abundant than PLCB1 and -4. Levels of PLCB3 in granulosa cells from pre-ovulatory-size follicles were much higher (>16-fold; P < 0.005) than in smaller follicles. Immunocytochemical analysis revealed that PLCB3 was located primarily in the cytoplasm, whereas PLCB1 was distributed primarily in the nucleus. These results identified Gs, Gq/11, Gi2 and PLCâ3 as candidates for cross-talk between VEGF and heterotrimeric G-protein signalling during the development of the dominant follicle. The potential involvement of these molecules on VEGF-induced responses in granulosa cells from 9-14 mm follicles was investigated in the third study by determining the effects of specific inhibitors of Gi (pertussis toxin, PTX) or Gq/11 (YM-25489) or PLCB3 siRNAs on VEGF-induced p-ERK. Results showed a 2.3 fold mean increase in p-ERK in response to VEGF in the absence of G protein inhibitors (P < 0.0001) but a VEGF response that was completely or partially abolished, respectively, in the presence of PTX (P > 0.8) or YM-25489 (1.6-fold mean increase relative to untreated controls; P = 0.039). LH induced a 1.6 fold increase in p-ERK1/2 (P < 0.02) and this response was prevented by pre-incubation with PTX (P > 0.4) or YM-25489 (P > 0.5). In contrast, similar EGF-induced phosphorylation of ERK (about 5-fold relative to controls) occurred in the absence (P < 0.003) or presence of PTX (P < 0.003) or YM-25489 (P < 0.003). Transfection of granulosa cells with 3 siRNAs targeting PLCB3 that had been previously validated by western blotting and immunocytochemistry had no effect (P = > 0.7) on phosphorylation of ERK in response to VEGF, LH or EGF in granulosa cells. In conclusion, taken together, these results suggest novel roles of VEGF in stimulating granulosa cell proliferation and expression of COX-2 in bovine dominant follicles and implicate VEGF in synergising and/or mediating the effects of gonadotrophins in these cells. In addition, these results indicate a requirement for Gi2 and Gq/11 in VEGF activation of ERK1/2 and induction of the above responses in granulosa cells.

No description available.

Made available in DSpace on 2017-07-10T14:17:11Z (GMT). No. of bitstreams: 1 FINALIZADA _ABRIL2015.pdf: 3170133 bytes, checksum: 1d4668fdaca4f714ff23eb80e3ac0b68 (MD5) Previous issue date: 2015-06-30 / The prevalence of obesity has increased in recent decades in many countries, and harmful effects to the body can begin in childhood and persist into adulthood. Obesity is associated with disturbances of reproductive function in women and in female rodents, such as early onset of puberty, change in menstrual / estrous cycle and infertility, with impaired ovulation or anovulation (lack of ovulation). Angiotensin II (Ang II) appears to exert effects on reproduction and obesity, contributing to the development of the deleterious effects of obesity and affecting pre-ovulatory surge of luteinizing hormone (LH), estradiol and progesterone, thus reducing ovulation in adult rats. The objective of this study was to evaluate losartan effect, an antagonist of Ang II AT1 receptor, administrated in adulthood, in follicular development of adult Wistar rats with obesity induced by cafeteria diet. After weaning at 21 days of life, female Wistar rats were divided into 02 groups: control (CTL) that received standard chow diet; Cafeteria (CAF) received the cafeteria diet. From 70 days of life began losartan administration by gavage. The CTL group received water in gavage (CTL) and CAF group was separated into 02 groups, CAF (which received water in gavage) and CAF + LOS (who received losartan in gavage), in total 03 groups were performed. 05 animals were used per group. Euthanasia was performed on the first proestrous after 30 days of administration of losartan or water. The retroperitoneal, perigonadal and subcutaneous fat were removed and weighed. Morphological analysis of ovaries was performed, proceeding to count the number of primary follicles, secondary, antral and mature follicles per ovary. Was also collected blood sample for determination of FSH, LH, prolactin and progesterone. Body weight and the weight of the 03 fats were measured, and the number of antral follicles were higher in group CAF in relation to the group CTL (p <0.001). However, FSH and LH levels were lower in the CAF animals compared to the animals of the group CTL (p <0.001). The administration of losartan normalized the body weight and accumulation of retroperitoneal and subcutaneous fat as well as the number of antral follicles. Thus, we suggest that the use of the antagonist of Ang II AT1 receptor, losartan, in adulthood, can improve follicular development in females with cafeteria diet-induced obesity and, can be, in the future, an coadjuvant drug in the treatment of infertility associated to obesity. / A prevalência da obesidade aumentou nas últimas décadas em vários países, tendo efeitos prejudiciais ao organismo que podem iniciar na infância e persistir até a vida adulta. A obesidade está associada a distúrbios da função reprodutiva, em mulheres e em fêmeas de roedores, como início precoce da puberdade, alteração do ciclo menstrual/estral e infertilidade, com alterações da ovulação (disovulias) ou anovulação (ausência da ovulação). A Angiotensina II (Ang II) parece exercer efeitos sobre a reprodução e a obesidade, contribuindo para o desenvolvimento dos efeitos deletérios da obesidade e afetando o pico pré-ovulatório do hormônio luteinizante (LH), progesterona e estradiol, reduzindo, consequentemente, a ovulação em ratas adultas. O objetivo deste estudo foi avaliar o efeito do losartan, um antagonista do receptor AT1 da Ang II, sobre o desenvolvimento folicular de ratas Wistar adultas, com obesidade induzida pela dieta de cafeteria. Após o desmame, aos 21 dias de vida, ratas Wistar foram separadas em 02 grupos: controle (CTL) que recebeu ração padrão e Cafeteria (CAF) que recebeu a dieta de cafeteria. A partir dos 70 dias de vida iniciou-se a administração de losartan por gavagem. O grupo CTL recebeu água na gavagem (CTL) e o grupo CAF foi separado em 02 grupos, CAF (que recebeu água na gavagem) e CAF+LOS (que recebeu losartan na gavagem), totalizando 03 grupos. Foram utilizados 05 animais por grupo. A eutanásia foi realizada no primeiro proestro após 30 dias da administração de losartan ou de água. As gorduras retroperitoneal, perigonadal e subcutânea foram retiradas e pesadas. Foi realizada a análise morfológica dos ovários, procedendo-se a contagem do número dos folículos primários, secundários, antrais e maduros por ovário. Também foi coletado o sangue total para dosagens de FSH, LH, Prolactina e Progesterona. O peso corporal, bem como, o peso das 03 gorduras foram avaliados, e, o número de folículos antrais foi estatisticamente maior no grupo CAF em relação ao CTL (p<0,001). Todavia, as concentrações de FSH e LH foram menores nos animais CAF em relação ao CTL (p<0,001). A administração do losartan normalizou o peso corporal e o acúmulo das gorduras retroperitoneal e subcutânea, bem como, o número de folículos antrais. Dessa forma, sugerimos que o uso do antagonista do receptor AT1 da Ang II, o losartan, na vida adulta, possa contribuir para melhorar o desenvolvimento folicular em fêmeas com obesidade induzida pela dieta de cafeteria e, futuramente, ser uma droga coadjuvante no tratamento da infertilidade associada à obesidade.

Transrectal ovarian ultrasonography and hormone measurements were used to study ovarian antral follicular dynamics and development of luteal structures during the middle portion of the breeding season in non-prolific cross-bred Western white-faced ewes and prolific Finn sheep. Studies were also done on ovarian activity in Western white-faced ewes during the transition to seasonal anoestrus and at the onset of the breeding season. Lastly, two experiments were carried out to examine ovulatory responses and subsequent luteal function in Western white-faced ewes treated with luteolysin (PgF 2á) and progestogen (medroxyprogesterone acetate-MAP) during the luteal phase of the oestrous cycle and after ovulation induction with gonadotrophin-releasing hormone (GnRH) in mid-anoestrus. The results of the present experiments showed that the growth of ovine antral follicles reaching ovulatory sizes of >=5 mm in diameter occurred in a wave-like pattern throughout the oestrous cycle in both breeds of sheep under study. There were typically 3 or 4 waves of follicle production throughout the 17-day interovulatory period. Ovarian follicular emergence, or beginning of growth from the pool of 3-mm follicles, appeared to be primarily controlled by changes in circulating concentrations of follicle-stimulating hormone (FSH). In cyclic ewes, the largest ovarian follicles acquired the ability to secrete oestradiol from the day of emergence and a peak of oestradiol secretion occurred about the time they reached their maximum diameter. The high ovulation rate in prolific Finn sheep appeared to be achieved mainly by the ovulation of follicles emerging in the last two waves of the interovulatory interval. Interestingly, prolific Finn ewes produced more but smaller corpora lutea (CL) and had lower serum concentrations of progesterone during the luteal phase of the oestrous cycle as compared to non-prolific Western white-faced ewes. During the transition into seasonal anoestrus in Western white-faced ewes, FSH secretion resembled that during the breeding season but the pattern of emergence of sequential follicular waves was dissociated from FSH and oestradiol secretion. Prior to the first ovulation of the breeding season, there was a distinct elevation in circulating concentrations of progesterone produced by luteinized unovulated follicles and/or interstitial tissue of unknown origin. This increase in serum levels of progesterone, heralding the resumption of ovulatory cycles, did not alter the rhythmic pattern FSH secretion or follicular wave emergence. Treatment of non-prolific Western white-faced ewes with PgF2á and MAP applied late in the oestrous cycle changed follicular dynamics and increased ovulation rate to resemble that in prolific Finn sheep. Effects of MAP on the recruitment and growth of ovulatory follicles in Western white-faced ewes did not have a clear gonadotrophic dependancy, suggesting a possible local regulation of ovarian activity by progestins in ewes. Following the induction of ovulation with GnRH in anoestrous Western white-faced ewes, an array of ovarian responses were detected with ultrasonography, including failure of ovulation of large antral follicles, normal (fall-lifespan) and short-lived CL post-ovulation, and luteinized cystic-like follicles. The normal luteinization of ovulated follicles appeared to be related to the amplitude of episodic elevations in daily serum FSH concentrations before induction of ovulation and characteristics of the preovulatory LH surge.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / Nitric oxide (NO) is an important regulator of ovarian activity, and is produced by a family of nitric oxide synthases (NOS), being inducible (iNOS) and endothelial (eNOS) isoforms present in the ovaries of several species. In cows, even though NO production had been demonstrated in follicular fluid and by granulosa cells (GC) cultured in vitro, it is not known which enzyme is responsible for NO synthesis or how expression is regulated during follicular development. The objectives of the present study were to determine the abundance of iNOS and eNOS mRNAs in dominant and subordinate follicles in vivo, to determine the regulation of iNOS expression by FSH, growth factors and estradiol (E2) in vitro, to stimulate NO production in bovine CG and to determine the action of iNOS on bovine granulosa cell health/apoptosis. The two largest follicles on days 1 to 5 of the first follicular wave of the cycle were collected from each pair of ovaries from six cows. Dominant follicles presented higher levels of mRNA for iNOS compared to subordinate follicles (P<0.01). GC cultures were performed with ovaries collected at abattoir. FSH (P<0.05) and IGF1 (P<0.01) stimulated E2 secretion and upregulated iNOS mRNA abundance in a dose-dependent manner. Moreover, both FGF2 (P<0.05) and EGF (P<0.01) decreased iNOS expression and E2 secretion in FSH and IGF-treated cells, respectively. Graded doses of FSH in the presence of a non-aromatizable androgen (DHT) did not stimulate iNOS mRNA level. In addition, both FSH and IGF1 in the presence of an estrogen receptor antagonist were not able to upregulate iNOS mRNA abundance, whereas E2 alone stimulated NO production in vitro. In terms of cell health/apoptosis, the treatment with an iNOS-selective inhibitor increased the pro-apoptotic factor FasL mRNA levels and the percentage of dead cells (P<0.05). In conclusion, bovine granulosa cells express predominantly iNOS, and increased iNOS mRNA levels are associated with emergence of the dominant follicle. FSH and IGF1 stimulate iNOS mRNA levels through increased E2 secretion, and physiological levels of NOS activity may contribute to growth and survival of bovine granulosa cells. / O óxido nítrico (NO) é um importante regulador da atividade ovariana que é produzido a partir da ação de uma família de enzimas denominadas sintases do óxido nítrico (NOS). As isoformas induzível (iNOS) e endotelial (eNOS) estão presentes nos ovários de diversas espécies. Em vacas, embora a produção de NO já tenha sido detectada no fluído folicular e também no meio de cultivo de células da granulosa (CG), não se sabe qual enzima é responsável pela síntese de NO nem como ocorre a regulação de sua expressão ao longo do desenvolvimento folicular. Os objetivos do presente estudo foram determinar a abundância de RNAm para iNOS e eNOS em CG provenientes de folículos dominantes e subordinados in vivo; determinar a regulação da expressão da iNOS por FSH, fatores de crescimento e estradiol (E2) in vitro; estimular a produção de NO e determinar a ação da iNOS na relação entre saúde e apoptose das CG bovina. Foram coletados os dois maiores folículos presentes em cada par de ovários de seis vacas entre os dias 1 e 5 da primeira onda folicular do ciclo estral. Folículos dominantes apresentaram níveis mais elevados de RNAm para iNOS comparados aos folículos subordinados (P<0.01). Cultivos de CG foram realizados com ovários coletados em abatedouro. Ambos FSH (P<0.05) e IGF1 (P<0.01) estimularam a secreção de E2 e a expressão de iNOS de maneira dose-dependente. Além disso, tanto FGF2 (P<0.05) como EGF (P<0.01) diminuiram a expressão de iNOS e a secreção de E2 em células tratadas com FSH e IGF1, respectivamente. Utilizando diferentes doses de FSH na presença de um andrógeno não-aromatizável (DHT), não foi possível estimular a expressão de iNOS. Ainda, tanto o FSH como o IGF1 não foram capazes de elevar a abundância de RNAm para iNOS na presença de um antagonista não seletivo dos receptores de E2, enquanto que, E2 sozinho estimulou a produção de NO em CG in vitro. No que diz respeito à relação saúde/apoptose das CG, o tratamento com um inibidor seletivo da iNOS aumentou os níveis de RNAm para o fator pró-apoptótico FasL e o percentual de células mortas (P<0.05). Concluindo, células da granulosa bovina expressam predominantemente iNOS, sendo que o aumento da expressão dessa isoforma está associado com a emergência do folículo dominante. FSH e IGF1 promovem o aumento dos níveis de RNAm para a iNOS através do estímulo da secreção de E2 e, níveis fisiológicos da atividade das NOS podem contribuir para o crescimento e sobrevivência das células da granulosa bovina.

Les Wnts représentent une famille de glycoprotéines de signalisation qui sont connues pour les nombreux rôles qu'ils jouent durant le développement embryonnaire et dans la cancerogénèse. Plusieurs Wnts, leurs récepteurs (Fzd) et d'autres composants des voies de signalisation des Wnt sont exprimés dans l’ovaire postnatal, et il a été démontré que l’expression de certains de ces gènes est régulée pendant le développement et l'ovulation/luteinization folliculaires. Toutefois, leurs rôles physiologiques dans l’ovaire demeurent mal définis. Pour étudier le rôle de WNT4 dans le développement folliculaire, nous avons entrepris d’identifier ses cibles transcriptionnels dans les cellules de la granulosa. Pour ce faire, nous avons employé la souris Catnbflox(ex3)/flox(ex3), chez laquelle une activation constitutive de la voie de Wnt/β-catenin a lieu suite à l’action de la recombinare Cre. Des cellules de la granulosa de ces souris ont été mises en culture et infectées avec un adenovirus pour causer la surexpression de WNT4 ou l’expression de Cre. L’ARN a alors été extrait de ces cellules et analysé par micro-puce. Les résultats ont démontré qu’une forte proportion des gènes induits par WNT4 étaient des gènes impliqués dans la réponse cellulaire au stress. Presque tous gènes induits par WNT4 ont également été induits par Cre, indiquant que WNT4 signale via la voie Wnt/β-catenin dans ces cellules. Nos résultats suggèrent donc que WNT4 favorise la survie des follicules par l’induction de gènes de réponse au stress dans les cellules de la granulosa, augmentant ainsi la résistance cellulaire à l'apoptose. / The Wnts comprise a large family of local-acting, secreted glycoprotein signaling molecules that are known mostly for the numerous roles they play in embryonic development and cancer. Several Wnts, their cognate receptors of the Frizzled (Fzd) family and other components of the Wnt signaling pathways are expressed in the postnatal ovary, and several have been shown to exhibit specific patterns of regulation in response to gonadotropin stimulation. Nonetheless, their role(s) in ovarian physiology remain poorly defined. To study the role of WNT4 in follicle development, we endeavoured to identify its transcriptional targets in granulosa cells. To this end, we used the Catnbflox(ex3)/flox(ex3) mouse model, in which constitutive activation of the Wnt/β-catenin pathway is obtained following Cre-mediated genetic recombination. Cultured granulosa cells from these mice were infected with adenoviruses to either overexpress WNT4 or to express Cre. RNA from these cells was then extracted and subjected to microarray analysis. Results revealed that a large proportion of the genes induced by WNT4 were genes previously shown to mediate cellular stress responses. Nearly all genes that were up-regulated by WNT4 were also induced by the Cre, indicating that WNT4 signals via the Wnt/β-catenin pathway in these cells. Our findings suggest that WNT4 mediates ovarian follicle survival by inducing a stress response in granulosa cells, thereby increasing their resistance to apoptosis.

Les Wnts représentent une famille de glycoprotéines de signalisation qui sont connues pour les nombreux rôles qu'ils jouent durant le développement embryonnaire et dans la cancerogénèse. Plusieurs Wnts, leurs récepteurs (Fzd) et d'autres composants des voies de signalisation des Wnt sont exprimés dans l’ovaire postnatal, et il a été démontré que l’expression de certains de ces gènes est régulée pendant le développement et l'ovulation/luteinization folliculaires. Toutefois, leurs rôles physiologiques dans l’ovaire demeurent mal définis. Pour étudier le rôle de WNT4 dans le développement folliculaire, nous avons entrepris d’identifier ses cibles transcriptionnels dans les cellules de la granulosa. Pour ce faire, nous avons employé la souris Catnbflox(ex3)/flox(ex3), chez laquelle une activation constitutive de la voie de Wnt/β-catenin a lieu suite à l’action de la recombinare Cre. Des cellules de la granulosa de ces souris ont été mises en culture et infectées avec un adenovirus pour causer la surexpression de WNT4 ou l’expression de Cre. L’ARN a alors été extrait de ces cellules et analysé par micro-puce. Les résultats ont démontré qu’une forte proportion des gènes induits par WNT4 étaient des gènes impliqués dans la réponse cellulaire au stress. Presque tous gènes induits par WNT4 ont également été induits par Cre, indiquant que WNT4 signale via la voie Wnt/β-catenin dans ces cellules. Nos résultats suggèrent donc que WNT4 favorise la survie des follicules par l’induction de gènes de réponse au stress dans les cellules de la granulosa, augmentant ainsi la résistance cellulaire à l'apoptose. / The Wnts comprise a large family of local-acting, secreted glycoprotein signaling molecules that are known mostly for the numerous roles they play in embryonic development and cancer. Several Wnts, their cognate receptors of the Frizzled (Fzd) family and other components of the Wnt signaling pathways are expressed in the postnatal ovary, and several have been shown to exhibit specific patterns of regulation in response to gonadotropin stimulation. Nonetheless, their role(s) in ovarian physiology remain poorly defined. To study the role of WNT4 in follicle development, we endeavoured to identify its transcriptional targets in granulosa cells. To this end, we used the Catnbflox(ex3)/flox(ex3) mouse model, in which constitutive activation of the Wnt/β-catenin pathway is obtained following Cre-mediated genetic recombination. Cultured granulosa cells from these mice were infected with adenoviruses to either overexpress WNT4 or to express Cre. RNA from these cells was then extracted and subjected to microarray analysis. Results revealed that a large proportion of the genes induced by WNT4 were genes previously shown to mediate cellular stress responses. Nearly all genes that were up-regulated by WNT4 were also induced by the Cre, indicating that WNT4 signals via the Wnt/β-catenin pathway in these cells. Our findings suggest that WNT4 mediates ovarian follicle survival by inducing a stress response in granulosa cells, thereby increasing their resistance to apoptosis.

No description available.