Transgenic mutant D567G but not wild-type human FSH receptor overexpression provides FSH-independent and promiscuous glycoprotein hormone Sertoli cell signaling

Abstract

We have characterized the in vivo actions of human wild-type FSH receptor (FSHR) overexpressed in Sertoli cells of transgenic (Tg) mice (TgFSHRwt) compared with transgenic overexpression of the human activated mutant FSHR*D567G (TgFSHR*D567G). Testicular TgFSHRwt expression significantly elevated specific FSH binding (>2-fold, P < 0.01) relative to nontransgenic testes, similar to increased FSH binding in TgFSHR*D567G testes. Isolated TgFSHRwt Sertoli cells exhibited higher FSH-stimulated cAMP levels compared with non-Tg or TgFSHR*D567G cells but did not display the elevated FSH-independent basal cAMP levels found in TgFSHR*D567G Sertoli cells. Furthermore, Sertoli cell overexpression of TgFSHR*D567G but not TgFSHRwt allowed promiscuous cAMP responses to human chorionic gonadotropin (300 IU/ml) and TSH (30 mIU/ml), demonstrating increased constitutive signaling and altered glycoprotein hormone specificity via the intracellular D567G substitution rather than FSHR overexpression. Despite elevating Sertoli cell FSH sensitivity, overexpression of TgFSHRwt had no detectable effect upon normal testis function and did not stimulate Sertoli and germ cell development in testes of gonadotropin-deficient hypogonadal (hpg) mice, in contrast to the increased meiotic and postmeiotic germ cell development in TgFSHR*D567G hpg testes. Increased steroidogenic potential of TgFSHR*D567G hpg testes was demonstrated by elevated Cyp11a1 and Star expression, which was not detected in TgFSHRwt hpg testes. Androgen-regulated and Sertoli cell-specific Rhox5 gene expression was increased in TgFSHR*D567G but not TgFSHRwt hpg testes, providing evidence of elevated LH-independent androgen activity due to mutant FSHR*D567G. Hence, transgenic FSHR overexpression in Sertoli cells revealed that the D567G mutation confers autonomous signaling and steroidogenic activity in vivo as well as promiscuous glycoprotein hormone receptor activation, independently of FSHR overexpression alone.

Estradiol Induction of Spermatogenesis Is Mediated via an Estrogen Receptor-α Mechanism Involving Neuroendocrine Activation of Follicle-Stimulating Hormone Secretion

“…This may reflect direct effects of E2 on Leydig cells because circulating levels of LH, the major Leydig cell trophic hormone, are fully suppressed in hpg mice, supported by failure of E2 to increase Leydig cell number (36). Alternatively, E2-mediated stimulation of Leydig cell transcripts may be due to FSH-mediated paracrine signaling between Sertoli and Leydig cells (34). By contrast to E2 stimulatory actions, DHT did not stimulate testicular Cyp11a1 expression in hpg/WT testes, revealing distinct E2 and androgenic regulation of expression of this steroidogenic enzyme.…”

Impact of follicle stimulating hormone receptor variants in fertility

“…Only one of these activating point mutations was found in a male patient, and was shown to have constitutive activity [17,18 ]. All other cases were found in women.…”

Decreased Degradation of Internalized Follicle-Stimulating Hormone Caused by Mutation of Aspartic Acid 6.30550 in a Protein Kinase-CK2 Consensus Sequence in the Third Intracellular Loop of Human Follicle-Stimulating Hormone Receptor1

“…2a). The naturally occurring mutation (hFSHR-D550G) that has been described in a hypophysectomized male with normal gonadal function was reported to result in constitutive activation of the FSHR [46]. In that study, basal but not FSHstimulated cAMP levels were elevated in hFSHR-D550G compared with WT-FSHR.…”

“…Transgenic mice generated harboring the D567G mutation (TgFSHR-D567G) or hFSHR (TgFSHR-WT) on a gonadotropin-deficient background have been evaluated [46]. In that study, cultured TgFSHR-D567G Sertoli cells showed higher levels of FSH-independent cAMP levels, but not FSH-dependent cAMP levels, compared with Sertoli cells from animals harboring the TgFSHR-WT transgene, reaffirming the constitutive active receptor phenotype.…”