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Wingless-type mouse mammary tumor virus integration site regulation of bovine theca cells
1Department of Animal and Food Sciences, Oklahoma State University, Stillwater, OK 74078, USA.
Abstract:
Ovarian paracrine mediation by components of the wingless-type mouse mammary tumor virus integration site ligands (WNT1 to 11) and their receptors, frizzled family members (FZD1 to 10), has been proposed. Secreted truncated forms of FZD proteins (e.g., secreted frizzled-related protein 4 [SFRP4]) block the action of WNT ligands. Dickkopf-1 (DKK1) is another WNT antagonist, and R-spondin-1 (RSPO1) is one of a group of four secreted proteins that enhance WNT/β-catenin signaling. Our hypothesis was that granulosa cells signal theca cells (TCs) via SFRP4, DKK1, RSPO1, and WNT secretion to regulate TC differentiation and proliferation. Therefore, in vitro experiments were conducted to study the effects of WNT family member 3A (WNT3A), WNT5A, RSPO1, DKK1, insulin-like growth factor 1 (IGF1), bone morphogenetic protein 7 (BMP7), Indian hedgehog (IHH), and fibroblast growth factor 9 (FGF9) on bovine TC proliferation and steroidogenesis. TCs of large (8 to 20 mm) and small (3 to 6 mm) follicles were collected from bovine ovaries; TC monolayers were established in vitro and treated with various doses of recombinant human WNT3A, WNT5A, RSPO1, DKK1, IGF1, FGF9, BMP7, IHH, and/or ovine luteinizing hormone (LH) in serum-free medium for 48 h. In experiment 1, using LH-treated TC, IGF1, IHH, and WNT3A increased (P < 0.05) cell numbers and androstenedione production, whereas WNT3A and BMP7 inhibited (P < 0.05) progesterone production. In experiment 2, FGF9 blocked (P < 0.05) the WNT3A-induced increase in androstenedione production in LH plus IGF1-treated TC. In experiment 3, RSPO1 further increased (P < 0.05) LH plus IGF1-induced progesterone and androstenedione production. In experiment 4, SFRP4 and DKK1 alone had no significant effect on TC proliferation or progesterone production of large-follicle TC but both blocked the inhibitory effect of WNT5A on androstenedione production. In contrast, DKK1 alone inhibited (P < 0.05) small-follicle TC androstenedione production whereas SFRP4 was without effect. We conclude that the ovarian TC WNT system is functional in cattle, with WNT3A increasing proliferation and androstenedione production of TC.
Insights
The ovarian WNT signaling pathway regulates bovine theca cell (TC) proliferation and steroidogenesis. WNT3A enhances TC proliferation and androstenedione production, while antagonists like Dickkopf-1 (DKK1) and secreted frizzled-related protein 4 (SFRP4) modulate these effects.
Area of Science:
- Reproductive Biology
- Endocrinology
- Cell Signaling
Background:
- Ovarian paracrine signaling involves wingless-type mouse mammary tumor virus integration site ligands (WNT) and their receptors.
- Secreted frizzled-related proteins (SFRPs) and Dickkopf-1 (DKK1) antagonize WNT signaling, while R-spondin-1 (RSPO1) enhances it.
- The hypothesis is that granulosa cells signal theca cells (TCs) via these factors to regulate TC differentiation and proliferation.
Purpose of the Study:
- To investigate the effects of WNT pathway components and other growth factors on bovine TC proliferation and steroidogenesis.
- To elucidate the role of WNT3A, WNT5A, RSPO1, DKK1, SFRP4, IGF1, BMP7, IHH, and FGF9 in regulating TC function.
Main Methods:
- Bovine TCs from large and small follicles were cultured in vitro.
- TC monolayers were treated with recombinant human WNT3A, WNT5A, RSPO1, DKK1, IGF1, FGF9, BMP7, IHH, and/or ovine luteinizing hormone (LH).
- Cell proliferation and steroidogenesis (androstenedione and progesterone production) were measured after 48 hours.
Main Results:
- WNT3A, IGF1, and IHH increased TC proliferation and androstenedione production; WNT3A and BMP7 inhibited progesterone production.
- FGF9 counteracted WNT3A-induced androstenedione production.
- RSPO1 augmented LH plus IGF1-induced progesterone and androstenedione production.
- DKK1 and SFRP4 blocked WNT5A's inhibitory effect on androstenedione production; DKK1 inhibited small-follicle TC androstenedione production.
Conclusions:
- The ovarian TC WNT system is functional in cattle.
- WNT3A is a key regulator, promoting TC proliferation and androstenedione production.
- WNT antagonists and agonists differentially modulate TC steroidogenesis and proliferation, indicating complex paracrine regulation.
