OR04-6 SMAD signaling in gonadotropes is critical for normal FSH synthesis and fertility in mice

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: OR04-GnRH & Gonadotroph Biology & Signaling
Saturday, June 15, 2013: 11:30 AM-1:00 PM
Presentation Start Time: 12:45 PM
Room 135 (Moscone Center)
Jerome Fortin*1, Ulrich Boehm2, Chuxia Deng3 and Daniel J Bernard4
1McGill University, Montreal, QC, Canada, 2Univ of Saarland Med Sch, 66421 Homburg, Germany, 3NIH, Bethesda, MD, 4McGill Univ, Montreal, QC, Canada
In mammals, follicle-stimulating hormone (FSH), a dimeric protein produced by pituitary gonadotrope cells, is required for proper reproductive function. Activins, members of the TGFβ family, are potent and selective regulators of FSH synthesis. Thus far, experiments in cell lines have shown that activins stimulate the transcription of the FSH β (FSHβ/Fshb) subunit via the effector proteins, SMAD2 and SMAD3, downstream of heteromeric type I/type II receptor complexes. Receptor-regulated SMAD2/3 partner with the obligatory co-SMAD, SMAD4, and bind to the Fshb promoter in cooperation with other transcription factors, such as forkhead box L2 (FOXL2), to activate Fshb transcription. We recently made the unexpected observation that mice lacking the full-length forms of both SMAD2 and SMAD3 in gonadotropes have normal FSH levels and fertility. To test whether any SMAD-dependent signaling is required for FSH synthesis, we crossed mice carrying floxed alleles of Smad4 (Smad4fl/fl) with GnRHR-IRES-Cre (GRIC) mice, which express Cre recombinase exclusively in gonadotropes, to generate Smad4-conditional knockout mice (hereafter S4cKO). S4cKO males had reduced testes weights and sperm production, whereas females had smaller ovaries and reduced fertility compared with control littermates. The subfertility in females was secondary to impaired ovarian follicle maturation beyond the pre-antral stage but not due to intrinsic ovarian dysfunction, as S4cKO animals ovulated normally in response to exogenous gonadotropins. Hypogonadism in S4cKO mice was largely explained by FSH deficiency in both males and females. The phenotype was particularly striking in S4cKO males, where serum FSH and pituitary Fshb mRNA levels were reduced by 90%. In addition, S4cKO males had elevated pituitary expression of the GnRH receptor (Gnrhr) and reduced expression of the gonadotropin α subunit (Cga). Pituitary activin receptor (Acvr1b, Acvr2), luteinizing hormone β subunit (Lhb), and Foxl2 mRNA levels were normal. Cultured pituitary cells from S4cKO mice showed dramatically lower basal and activin-stimulated Fshb transcription compared with cells from control mice. A similar, but milder effect was observed upon ex vivo (acute) deletion of Smad4 in pituitary cells from Smad4fl/fl mice. Together, these results demonstrate that SMAD signaling in gonadotropes is necessary for Fshb transcription, FSH synthesis, and fertility in vivo. The receptor-regulated SMAD(s) in this system remain to be identified.

Nothing to Disclose: JF, UB, CD, DJB

*Please take note of The Endocrine Society's News Embargo Policy at http://www.endo-society.org/endo2013/media.cfm

Sources of Research Support: CIHR grant MOP-89991 to DJB; CIHR graduate scholarship to JF
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