An Activated Human Follicle-Stimulating Hormone (FSH) Receptor Stimulates FSH-Like Activity in Gonadotropin-Deficient Transgenic Mice

Abstract

FSH mediates its testicular actions via a specific Sertoli cell G protein-coupled receptor. We created a novel transgenic model to investigate a mutant human FSH receptor (FSHR(+)) containing a single amino acid substitution (Asp567Gly) equivalent to activating mutations in related glycoprotein hormone receptors. To examine the ligand-independent gonadal actions of FSHR(+), the rat androgen-binding protein gene promoter was used to direct FSHR(+) transgene expression to Sertoli cells of gonadotropin-deficient hypogonadal (hpg) mice. Both normal and hpg mouse testes expressed FSHR(+) mRNA. Testis weights of transgenic FSHR(+) hpg mice were increased approximately 2-fold relative to hpg controls (P < 0.02) and contained mature Sertoli cells and postmeiotic germ cells absent in controls, revealing FSHR(+)-initiated autonomous FSH-like testicular activity. Isolated transgenic Sertoli cells had significantly higher basal ( approximately 2-fold) and FSH-stimulated ( approximately 50%) cAMP levels compared with controls, demonstrating constitutive signaling and cell-surface expression of FSHR(+), respectively. Transgenic FSHR(+) also elevated testosterone production in hpg testes, in the absence of circulating LH (or FSH), and it was not expressed functionally on steroidogenic cells, suggesting a paracrine effect mediated by Sertoli cells. The FSHR(+) response was additive with a maximal testosterone dose on hpg testicular development, demonstrating FSHR(+) activity independent of androgen-specific actions. The FSHR(+) response was male specific as ovarian expression of FSHR(+) had no effect on hpg ovary size. These findings reveal transgenic FSHR(+) stimulated a constitutive FSH-like Sertoli cell response in gonadotropin-deficient testes, and pathways that induced LH-independent testicular steroidogenesis. This novel transgenic paradigm provides a unique approach to investigate the in vivo actions of mutated activating gonadotropin receptors.

Gonadal defects and hormonal alterations in transgenic mice expressing a single chain human chorionic gonadotropin–lutropin receptor complex

“…The importance of FSH in testicular development has been established in knockout mouse models of FSH and FSH receptor (Kumar et al 1997, Dierich et al 1998. Additionally, expression of FSH or a constitutively active FSH receptor on the gonadotropindeficient hypogonadal (hpg) mouse background, which exhibits reduced testis size, results in an increase in testicular weight (Allan et al 2001, Haywood et al 2002, demonstrating a direct role for FSH in testicular development.…”

Gene expression profiling of mouse Sertoli cell lines

“…Therefore, the WT line should have characteristics close to basal unstimulated conditions, as suggested by the similarity of expression profiling of the parental SK-11 line and the WT line compared with the MUT line. On the other hand, the MUT line not only has a much higher receptor concentration, but also expresses a mutated receptor with some constitutive activity, as shown by the higher cAMP concentrations, which might mimic the effects of moderate chronic stimulation (Haywood et al 2002). Recently, some constitutive activity has also been reported for the overexpressed WT FSHR by using a different Leydig-cell-derived cell line (Baker et al 2003).…”

“…We had previously identified this FSHR mutation in a hypophysectomised man with no detectable serum gonadotropin levels but normal spermatogenesis (Gromoll et al 1996). The MUT FSHR form has been shown to be constitutively active in SK-11 cells in vitro (Simoni et al 1997) and in vivo in transgenic mice (Haywood et al 2002).…”

Mouse models of altered gonadotrophin action: insight into male reproductive disorders

“…The hpg mouse, resulting from a naturally occurring deletion mutation in Gnrh1 (Cattanach et al 1977), with a phenotype of hypogonadotrophic hypogonadism, provides the advantage of testing the effects and direct contribution of FSH/ FSHR-dependent testicular function, in the absence of circulating LH and activation of LHR. Using the rat androgen-binding protein promoter for specific integration into Sertoli cells, Haywood et al (2002) created a transgenic line expressing the human Asp567Gly FSHR CAM (TG-FSHRC). Testicular expression was confirmed, and enhanced ligand-independent cAMP production was detected in cultured TG-FSHC Sertoli cells.…”