Regulated expression of Wnts and Frizzleds at specific stages of follicular development in the rodent ovary

Misregulated Wnt/beta-catenin signaling leads to ovarian granulosa cell tumor development

Misregulation of the Wnt/beta-catenin signaling pathway is a hallmark of several forms of cancer. Components of the Wnt/beta-catenin pathway are expressed in ovarian granulosa cells; nevertheless, its potential involvement in granulosa cell tumorigenesis has not been examined. To this end, human (n = 6) and equine (n = 18) granulosa cell tumors (GCT) were analyzed for beta-catenin expression by immunohistochemistry. Unlike granulosa cells of normal ovaries, most (15 of 24) GCT samples showed nuclear localization of beta-catenin, suggesting that activation of the Wnt/beta-catenin pathway plays a role in the etiology of GCT. To confirm this hypothesis, Catnb(flox(ex3)/+); Amhr2(cre/+) mice that express a dominant stable beta-catenin mutant in their granulosa cells were generated. These mice developed follicle-like structures containing disorganized, pleiomorphic granulosa by 6 weeks of age. Even in older mice, these follicle-like lesions grew no larger than the size of antral follicles and contained very few proliferating cells. Similar to corpora lutea, the lesions were highly vascularized, although they did not express the luteinization marker Cyp11a1. Catnb(flox(ex3)/+); Amhr2(cre/+) females were also found to be severely subfertile, and fewer corpora lutea were found to form in response to exogenous gonadotropin compared with control mice. In older mice, the ovarian lesions often evolved into GCT, indicating that they represent a pretumoral intermediate stage. The GCT in Catnb(flox(ex3)/+); Amhr2(cre/+) mice featured many histopathologic similarities to the human disease, and prevalence of tumor development attained 57% at 7.5 months of age. Together, these studies show a causal link between misregulated Wnt/beta-catenin signaling and GCT development and provide a novel model system for the study of GCT biology.

Mice Null for Frizzled4 (Fzd4−/−) Are Infertile and Exhibit Impaired Corpora Lutea Formation and Function1

Previous studies showed that transcripts encoding specific Wnt ligands and Frizzled receptors including Wnt4, Frizzled1 (Fzd1), and Frizzled4 (Fzd4) were expressed in a cell-specific manner in the adult mouse ovary. Overlapping expression of Wnt4 and Fzd4 mRNA in small follicles and corpora lutea led us to hypothesize that the infertility of mice null for Fzd4 (Fzd4-/-) might involve impaired follicular growth or corpus luteum formation. Analyses at defined stages of reproductive function indicate that immature Fzd4-/- mouse ovaries contain follicles at many stages of development and respond to exogenous hormone treatments in a manner similar to their wild-type littermates, indicating that the processes controlling follicular development and follicular cell responses to gonadotropins are intact. Adult Fzd4-/- mice also exhibit normal mating behavior and ovulate, indicating that endocrine events controlling these processes occur. However, Fzd4-/- mice fail to become pregnant and do not produce offspring. Histological and functional analyses of ovaries from timed mating pairs at Days 1.5-7.5 postcoitus (p.c.) indicate that the corpora lutea of the Fzd4-/- mice do not develop normally. Expression of luteal cell-specific mRNAs (Lhcgr, Prlr, Cyp11a1 and Sfrp4) is reduced, luteal cell morphology is altered, and markers of angiogenesis and vascular formation (Efnb1, Efnb2, Ephb4, Vegfa, Vegfc) are low in the Fzd4-/- mice. Although a recently identified, high-affinity FZD4 ligand Norrin (Norrie disease pseudoglioma homolog) is expressed in the ovary, adult Ndph-/- mice contain functional corpora lutea and do not phenocopy Fzd4-/- mice. Thus, Fzd4 appears to impact the formation of the corpus luteum by mechanisms that more closely phenocopy Prlr null mice.

Activation of canonical Wnt pathway promotes proliferation of retinal stem cells derived from adult mouse ciliary margin

Adult retinal stem cells represent a possible cell source for the treatment of retinal degeneration. However, only a small number of stem cells reside in the ciliary margin. The present study aimed to promote the proliferation of adult retinal stem cells via the Wnt signaling pathway. Ciliary margin cells from 8-week-old mice were dissociated and cultured to allow sphere colony formation. Wnt3a, a glycogen synthase kinase (GSK) 3 inhibitor, fibroblast growth factor (FGF) 2, and a FGF receptor inhibitor were then applied in the culture media. The primary spheres were dissociated to prepare either monolayer or secondary sphere cultures. Wnt3a increased the size of the primary spheres and the number of Ki-67-positive proliferating cells in monolayer culture. The Wnt3a-treated primary sphere cells were capable of self-renewal and gave rise to fourfold the number of secondary spheres compared with nontreated sphere cells. These cells also retained their multilineage potential to express several retinal markers under differentiating culture conditions. The Wnt3a-treated cells showed nuclear accumulation of beta-catenin, and a GSK3 inhibitor, SB216763, mimicked the mitogenic activity of Wnt3a. The proliferative effect of SB216763 was attenuated by an FGF receptor inhibitor but was enhanced by FGF2, with Ki-67-positive cells reaching over 70% of the total cells. Wnt3a and SB216763 promoted the proliferation of retinal stem cells, and this was partly dependent on FGF2 signaling. A combination of Wnt and FGF signaling may provide a therapeutic strategy for in vitro expansion or in vivo activation of adult retinal stem cells.

The partial female to male sex reversal in Wnt-4-deficient females involves induced expression of testosterone biosynthetic genes and testosterone production, and depends on androgen action

Wnt-4 signaling has been implicated in female development, because its absence leads to partial female to male sex reversal in the mouse. Instead of Mullerian ducts, Wnt-4-deficient females have Wolffian ducts, suggesting a role for androgens in maintaining this single-sex duct type in females. We demonstrate here that testosterone is produced by the ovary of Wnt-4-deficient female embryos and is also detected in the embryonic plasma. Consistent with this, the expression of several genes encoding enzymes in the pathway leading to the synthesis of testosterone in the mouse is induced in the Wnt-4-deficient ovary, including Cyp11a, Cyp17, Hsd3b1, Hsd17b1, and Hsd17b3. Inhibition of androgen action with an antiandrogen, flutamide, during gestation leads to complete degeneration of the Wolffian ducts in 80% of the mutant females and degeneration of the cortical layer that resembles the tunica albuginea in the masculinized ovary. However, androgen action is not involved in the sexually dimorphic organization of endothelial cells in the Wnt-4 deficient ovary, because flutamide did not change the organization of the coelomic vessel. These data imply that Wnt-4 signaling normally acts to suppress testosterone biosynthesis in the female, and that testosterone is the putative mediator of the masculinization phenotype in Wnt-4-deficient females.

Abnormal gene expression profiles in human ovaries from polycystic ovary syndrome patients

Polycystic ovary syndrome (PCOS) represents the most common cause of anovulatory infertility and affects 5-10% of women of reproductive age. The etiology of PCOS is still unknown. The current study is the first to describe consistent differences in gene expression profiles in human ovaries comparing PCOS patients vs. healthy normoovulatory individuals. The microarray analysis of PCOS vs. normal ovaries identifies dysregulated expression of genes encoding components of several biological pathways or systems such as Wnt signaling, extracellular matrix components, and immunological factors. Resulting data may provide novel clues for ovarian dysfunction in PCOS. Intriguingly, the gene expression profiles of ovaries from (long-term) androgen-treated female-to-male transsexuals (TSX) show considerable overlap with PCOS. This observation provides supportive evidence that androgens play a key role in the pathogenesis of PCOS. Presented data may contribute to a better understanding of dysregulated pathways in PCOS, which might ultimately reveal novel leads for therapeutic intervention.

Processing and localization of ADAMTS-1 and proteolytic cleavage of versican during cumulus matrix expansion and ovulation

ADAMTS-1 (a disintegrin and metalloprotease with thrombospondin motifs-1) is a member of the ADAMTS family of metalloproteases which, together with ADAMTS-4 and ADAMTS-5, has been shown to degrade members of the lectican family of proteoglycans. ADAMTS-1 mRNA is induced in granulosa cells of periovulatory follicles by the luteinizing hormone surge through a progesterone receptor-dependent mechanism. Female progesterone receptor knockout (PRKO) mice are infertile primarily due to ovulatory failure and lack the normal periovulatory induction of ADAMTS-1 mRNA. We therefore investigated the protein localization and function of ADAMTS-1 in ovulating ovaries. Antibodies against two specific peptide regions, the pro-domain and the metalloprotease domain of ADAMTS-1, were generated. Pro-ADAMTS-1 of 110 kDa was identified in mural granulosa cells and appears localized to cytoplasmic secretory vesicles. The mature (85-kDa pro-domain truncated) form accumulated in the extracellular matrix of the cumulus oocyte complex (COC) during the process of matrix expansion. Each form of ADAMTS-1 protein increased >10-fold after the ovulatory luteinizing hormone surge in wild-type but not PRKO mice. Versican is also localized selectively to the ovulating COC matrix and was found to be cleaved yielding a 70-kDa N-terminal fragment immunopositive for the neoepitope DPEAAE generated by ADAMTS-1 and ADAMTS-4 protease activity. This extracellular processing of versican was reduced in ADAMTS-1-deficient PRKO mouse ovaries. These observations suggest that one function of ADAMTS-1 in ovulation is to cleave versican in the expanded COC matrix and that the anovulatory phenotype of PRKO mice is at least partially due to loss of this function.

Expression and localization of secreted frizzled-related protein-4 in the rodent ovary: evidence for selective up-regulation in luteinized granulosa cells

Secreted frizzled-related protein-4 (sFRP-4) belongs to a family of soluble proteins that have a Frizzled-like cysteine-rich domain and function as modulators of Wnt-Frizzled (Fz) signals. As several Wnts and Fz are expressed at defined stages of follicular development in rodent ovaries, these studies were undertaken to evaluate the hormone-regulated expression and localization of sFRP-4. In the mouse ovary, the expression of sFRP-4 mRNA was up-regulated in granulosa cells of large antral follicles after human chorionic gonadotropin administration and was also elevated in corpora lutea, as determined by RT-PCR and in situ hybridization analyses. In hypophysectomized rat ovaries, sFRP-4 expression was similarly induced by human chorionic gonadotropin and further up-regulated by PRL. PRL also stimulated the secretion of sFRP-4 protein from luteinized rat granulosa cells in culture. Therefore, regulation of sFRP-4 by LH and PRL may be important for modulating Fz-1, which is known to be expressed in periovulatory follicles, and Wnt-4/Fz-4, which are expressed in corpora lutea.

The molecular phenotype of polycystic ovary syndrome (PCOS) theca cells and new candidate PCOS genes defined by microarray analysis

Polycystic ovary syndrome (PCOS) affects 5% of reproductive aged women and is the leading cause of anovulatory infertility. A hallmark of PCOS is excessive theca cell androgen secretion, which is directly linked to the symptoms of PCOS. Our previous studies demonstrated that theca cells from PCOS ovaries maintained in long term culture persistently secrete significantly greater amounts of androgens than normal theca cells, suggesting an intrinsic abnormality. Furthermore, previous studies suggested that ovarian hyperandrogenemia is inherited as an autosomal dominant trait. However, the genes responsible for ovarian hyperandrogenemia of PCOS have not been identified. In this present study, we carried out microarray analysis to define the gene networks involved in excess androgen synthesis by the PCOS theca cells in order to identify candidate PCOS genes. Our analysis revealed that PCOS theca cells have a gene expression profile that is distinct from normal theca cells. Included in the cohort of genes with increased mRNA abundance in PCOS theca cells were aldehyde dehydrogenase 6 and retinol dehydrogenase 2, which play a role in all-trans-retinoic acid biosynthesis and the transcription factor GATA6. We demonstrated that retinoic acid and GATA6 increased the expression of 17alpha-hydroxylase, providing a functional link between altered gene expression and intrinsic abnormalities in PCOS theca cells. Thus, our analyses have 1) defined a stable molecular phenotype of PCOS theca cells, 2) suggested new mechanisms for excess androgen synthesis by PCOS theca cells, and 3) identified new candidate genes that may be involved in the genetic etiology of PCOS.

CNP gene expression is activated by Wnt signaling and correlates with Wnt4 expression during renal injury

C-type natriuretic peptide (CNP) regulates salt excretion, vascular tone, and fibroblast proliferation and activation. CNP inhibits fibroblast activation in vitro and fibrosis in vivo, but endogenous CNP gene (Nppc) expression during tissue fibrosis has not been reported. We determined that Nppc is induced in renal tubular epithelia and then in interstitial myofibroblasts after unilateral ureteral obstruction (UUO). Induction of Nppc occurred in identical cell populations to those in which Wnt4 is induced after renal injury. In addition, Nppc was activated in Wnt4-expressing cells during nephrogenesis. Wnt signaling components beta-catenin and T cell factor/lymphoid enhancer binding factor (TCF/LEF) specifically bound to cognate elements in the Nppc proximal promoter. Wnt-4, beta-catenin, and LEF-1 activated an Nppc transgene in cultured cells, and transgene activation by Wnt-4 and LEF-1 was dependent on the presence of intact cognate elements. These findings suggest that Wnt-4 stimulates Nppc in a TCF/LEF-dependent manner after renal injury and thus may contribute to limiting renal fibrosis.

Ovulatory surges of human CG prevent hormone-induced granulosa cell tumor formation leading to the identification of tumor-associated changes in the transcriptome

Granulosa cell tumors comprise approximately 10% of ovarian tumors and, although rare, are clinically important due to their potential for malignancy and recurrence. Although their morphological features have been carefully described, the global changes in gene expression associated with their formation remain undetermined. To initiate this characterization, we used a transgenic mouse model in which granulosa cell tumors occur with 100% penetrance in CF-1 mice that harbor a novel transgene encoding a chimeric LHbeta subunit. When this transgene is expressed in other strains of mice, including (C57BL/6 female symbol x CF-1 male symbol,Tg) F1 hybrids, luteomas develop even though levels of LH remain high. This dichotomous response permits a longitudinal comparison of global changes in transcriptomes uniquely associated with either granulosa cell tumors or luteomas. Herein we report numerous changes in the transcriptome, including a decrease in LH receptor mRNA and increases in several mRNAs that encode secreted proteins previously associated with granulosa cell tumors. Furthermore, we identified a constellation of mRNAs that encode proteins that may serve as new markers for this tumor phenotype. Additional experiments indicated that periodic treatment with human CG prevented formation of granulosa cell tumors in mice genetically predisposed to tumor development and, instead, led to the appearance of luteomas. More importantly, ovarian transcriptomes from the luteomas induced by ovulatory doses of human CG permitted refined confirmation of gene expression changes that were uniquely associated with either granulosa cell tumors in the permissive CF-1 genetic background or in luteomas in the F1 hybrids. Together, these dynamic changes in the ovarian transcriptome indict various signaling pathways potentially involved in mediating the actions of LH over time and, depending on genetic background, the formation of either a luteoma or a granulosa cell tumor.

Expression of FKHR, FKHRL1, and AFX genes in the rodent ovary: evidence for regulation by IGF-I, estrogen, and the gonadotropins

Follicular development is dependent on both intraovarian growth regulatory factors, such as IGF-I and estrogen, as well as the pituitary gonadotropins, FSH and LH. Recently, we have shown that FSH impacts the IGF-I pathway via stimulation of the PI3K cascade leading to phosphorylation of protein kinase B (PKB)/Akt and the PKB-related kinase, Sgk. This study was undertaken to determine if during ovarian follicular development FSH regulates putative targets of PKB and Sgk, namely specific Forkhead transcription factor family members. Using in vivo and in vitro mouse and rat models, we show 1) that FKHR [Forkhead homolog of rhabdomysarcoma = Forkhead box binding protein (Foxo1), FKHRL1 (Forkhead-like protein-1 = Foxo3), and AFX (a Forkhead transcription factor = Foxo4); all defined according to the Human and Mouse Gene Nomenclature Committee) are expressed in the rodent ovary and 2) that FSH regulates transcription of the FKHR gene as well as phosphorylation of FKHR protein. Specifically, FSH/PMSG (primarily via E2) enhance expression of the FKHR gene in granulosa cells of developing follicles. Furthermore, E2 enhances expression of other IGF-I pathway components (IGF-1Rbeta and Glut-1), and IGF-I enhances expression of ERbeta, indicating that these two hormones comprise an autocrine regulatory network within growing follicles. In contrast, FSH and LH/human CG (via cAMP, PKA, and PI3K pathways) terminate FKHR expression as granulosa cells differentiate to luteal cells. In naïve granulosa cells, both FSH and IGF-I stimulate rapid phosphorylation of FKHR at multiple sites causing its redistribution from the nucleus to the cytoplasm in a PI3K-dependent manner. However, the effects of FSH and IGF-I differ markedly in differentiated granulosa cells in which FSH (but not IGF-I) induces Sgk and enhances phosphorylation of FKHR, PKB, and Sgk. The elevated expression of FKHR in granulosa cells of growing follicles indicates that FKHR may be linked to the proliferation of granulosa cells and that its phosphorylation by FSH, IGF-I, and other factors may impact its functional activity in this process. Thus, as a target of FSH (cAMP), E2 and IGF-I signaling in granulosa cells, FKHR likely coordinates numerous cell survival mechanisms.