Consequences of genetic manipulations of gonadotrophins and gonadotrophin receptors in mice

Loss of Fshr Prevents Testicular Maturation in Atlantic Salmon (Salmo salar L.)

Early puberty poses a significant challenge for male Atlantic salmon in aquaculture due to its negative impact on growth and welfare. The regulation of puberty in vertebrates involves 2 key reproductive hormones: follicle-stimulating hormone (FSH) and luteinizing hormone (LH) and their gonadal receptors. In male mice lacking FSH receptor, testes size is reduced, but fertility is maintained, while medaka and zebrafish with a disrupted fshr gene exhibit near normal testis size and fertility. In these fishes both Fsh and Lh are present during puberty and Lh may rescue fertility, while in salmonid fish only Fsh is present in the circulation during puberty. Using CRISPR-Cas9, we produced crispants with a high prevalence of fshr mutations at the target site, which remained fertile, although more than half showed a testis development deviating from wild-type (wt) males. Crossing out these F0 crispants to each other produced a viable F1 generation showing frameshift (fshr-/-) or in-frame mutations (fshrif/if). Nearly all wt males matured while all fshr-/- males remained immature with small testes containing A spermatogonia as the furthest developed germ cell type and prepubertal plasma androgen levels. Also, the pituitary transcript levels of gnrhr2bba and lhb, but not for fshb, were reduced in the fshr-/- males compared with maturing males. More than half of the fshrif/if mutant males showed no or a delayed maturation. In conclusion, Atlantic salmon show the unique characteristic that loss of Fshr function alone results in male infertility, offering new opportunities to control precocious puberty or fertility in salmon.

Age-Related Changes in the Testicular Morphophysiology of the Cane Rat (Thryonomys swinderianus)

This study evaluated age-related changes in the testicular morphophysiology of the cane rat (Thryonomys swinderianus) using histological, histochemical, and sex hormonal profile approaches. Twenty (20) pathogen-free male cane rats were used for the investigation. Cane rats were divided into four groups: prepubertal (≤4 months), pubertal (>4 ≤12 months), adult (>12 ≤30 months), and aged (>30 months) of 5 rats each. Blood was collected from the different cane rat groups and processed for sex serum hormonal levels. Testes were also excised and processed routinely for variations in histology, histochemistry (using Masson's trichrome [MT] and Periodic acid-Schiff [PAS]), and histomorphometric evaluations using GIMP2 software. Testosterone concentrations were significantly elevated (P < 0.05) in the prepubertal to adult, while there were no significant differences (P > 0.05) in this hormone between adult and aged. The concentrations of follicle-stimulating hormone (FSH) decreased significantly (P < 0.05) for prepubertal, pubertal, and adult, respectively. There were no significant differences (P > 0.05) between adult and aged for FSH and luteinizing hormone. Histologically, there were scanty interstitial cells, lack of patent lumen, and incomplete spermatogenetic cell series in prepubertal compared to other age groups. Testicular capsular (MT and PAS) staining intensity increased with age advancement, while in the parenchyma, remarkably high intensity was displayed by the pubertal compared to others. Seminiferous tubular and luminal diameters (LD) significantly (P < 0.05) increased with advancing age whereas epithelial height (EH) was markedly increased in pubertal relative to other groups. In conclusion, these sets of data have shown that reproductive activity is directly related to age and is at maximum in adult cane rat.

Possible link between FSH and RANKL release from adipocytes in men with impaired gonadal function including Klinefelter syndrome

INTRODUCTION

The FSH receptor (FSHR) has been found to be expressed in human bone cells and bone marrow-adipocytes, and highly-debated mouse studies have suggested extra-gonadal effects of gonadotropins on glucose, adipocyte and bone homeostasis. These putative effects could be direct or indirectly mediated by endocrine factors released from bone-cells or adipocytes. Here, we investigated whether gonadotropins are linked with glucose- and lipid-metabolism in hypergonadotropic men.

METHODS

Single centre, cross-sectional study of 307 men with idiopathic infertility and 28 men with Klinefelter syndrome (KS).

OUTCOME

associations between serum LH and FSH with soluble-RANKL (sRANKL), osteoprotegerin (OPG), osteocalcin, fasting glucose and insulin, sex steroids, and body composition. Expression of FSHR was studied in human-derived adipocyte-cell-models (hMADS, TERT-hWA) and FSH stimulation of RANKL expression and secretion in hMADS in vitro.

RESULTS

Serum FSH was not directly linked with glucose- and lipid-metabolism. However, FSH was inversely associated with sRANKL in both infertile men and KS men (p = .023 and p = .012). Infertile men with elevated FSH (>11 U/L) had significantly lower sRANKL (p = .015). sRANKL was positively associated with fat percentage, fasting insulin, and glucose (all p < .05). Men with prediabetes had higher sRANKL (p = .021), but lower testosterone (p < .0001) and Inhibin B (p = .005). The FSHR was expressed in the investigated human derived adipocytes, and 3-6 h treatment with FSH markedly increased RANKL release (p < .05).

CONCLUSION

KS and infertile men with prediabetes have low Inhibin B, and testosterone but elevated RANKL compared with non-prediabetic men despite comparable levels of serum gonadotropins. Serum FSH and sRANKL was inversely associated in both infertile and KS men, but the increased release of RANKL from FSH treated adipocytes suggest a direct effect of FSH on RANKL production in some tissues. Further studies are required to clarify whether FSH targets RANKL in the skeleton. ClinicalTrial_ID:NCT01304927.

Gain-of-Function Genetic Models to Study FSH Action

Follicle-stimulating hormone (FSH) is a pituitary-derived gonadotropin that plays key roles in male and female reproduction. The physiology and biochemistry of FSH have been extensively studied for many years. Beginning in the early 1990s, coincident with advances in the then emerging transgenic animal technology, and continuing till today, several gain-of-function (GOF) models have been developed to understand FSH homeostasis in a physiological context. Our group and others have generated a number of FSH ligand and receptor GOF mouse models. An FSH GOF model when combined with Fshb null mice provides a powerful genetic rescue platform. In this chapter, we discuss different GOF models for FSH synthesis, secretion and action and describe additional novel genetic models that could be developed in the future to further refine the existing models.

Impact of G protein-coupled receptor heteromers in endocrine systems

The fine-tuning of endocrine homeostasis is regulated by dynamic receptor mediated processes. The superfamily of G protein-coupled receptors (GPCRs) have diverse roles in the modulation of all endocrine axes, thus understanding the mechanisms underpinning their functionality is paramount for treatment of endocrinopathies. Evidence over the last 20 years has highlighted homo and heteromerization as a key mode of mediating GPCR functional diversity. This review will discuss the concept of GPCR heteromerization and its relevance to endocrine function, detailing in vitro and in vivo evidence, and exploring current and potential pharmacological strategies for specific targeting of GPCR heteromers in endocrine heath and disease.

Human LH and hCG stimulate differently the early signalling pathways but result in equal testosterone synthesis in mouse Leydig cells in vitro

BACKGROUND

Human luteinizing hormone (LH) and chorionic gonadotropin (hCG) are glycoprotein hormones regulating development and reproductive functions by acting on the same receptor (LHCGR). We compared the LH and hCG activity in gonadal cells from male mouse in vitro, i.e. primary Leydig cells, which is a common tool used for gonadotropin bioassay. Murine Leydig cells are naturally expressing the murine LH receptor (mLhr), which binds human LH/hCG.

METHODS

Cultured Leydig cells were treated by increasing doses of recombinant LH and hCG, and cell signaling, gene expression and steroid synthesis were evaluated.

RESULTS

We found that hCG is about 10-fold more potent than LH in cAMP recruitment, and slightly but significantly more potent on cAMP-dependent Erk1/2 phosphorylation. However, no significant differences occur between LH and hCG treatments, measured as activation of downstream signals, such as Creb phosphorylation, Stard1 gene expression and testosterone synthesis.

CONCLUSIONS

These data demonstrate that the responses to human LH/hCG are only quantitatively and not qualitatively different in murine cells, at least in terms of cAMP and Erk1/2 activation, and equal in activating downstream steroidogenic events. This is at odds with what we previously described in human primary granulosa cells, where LHCGR mediates a different pattern of signaling cascades, depending on the natural ligand. This finding is relevant for gonadotropin quantification used in the official pharmacopoeia, which are based on murine, in vivo bioassay and rely on the evaluation of long-term, testosterone-dependent effects mediated by rodent receptor.

Mouse Models for the Study of Synthesis, Secretion, and Action of Pituitary Gonadotropins

Gonadotropins play fundamental roles in reproduction. More than 30years ago, Cga transgenic mice were generated, and more than 20years ago, the phenotypes of Cga null mice were reported. Since then, numerous mouse strains have been generated and characterized to address several questions in reproductive biology involving gonadotropin synthesis, secretion, and action. More recently, extragonadal expression, and in some cases, functions of gonadotropins in nongonadal tissues have been identified. Several genomic and proteomic approaches including novel mouse genome editing tools are available now. It is anticipated that these and other emerging technologies will be useful to build an integrated network of gonadotropin signaling pathways in various tissues. Undoubtedly, research on gonadotropins will continue to provide new knowledge and allow us transcend from benchside to the bedside.

Pituitary gonadotrophic hormone synthesis, secretion, subunit gene expression and cell structure in normal and follicle-stimulating hormone β knockout, follicle-stimulating hormone receptor knockout, luteinising hormone receptor knockout, hypogonadal and ovariectomised female mice

To investigate the relationship between gonadotroph function and ultrastructure, we have compared, in parallel in female mice, the effects of several different mutations that perturb the hypothalamic-pituitary-gonadal axis. Specifically, serum and pituitary gonadotrophin concentrations, gonadotrophin gene expression, gonadotroph structure and number were measured. Follicle-stimulating hormone β knockout (FSHβKO), follicle-stimulating hormone receptor knockout (FSHRKO), luteinising hormone receptor knockout (LuRKO), hypogonadal (hpg) and ovariectomised mice were compared with control wild-type or heterozygote female mice. Serum levels of LH were elevated in FSHβKO and FSHRKO compared to heterozygote females, reflecting the likely decreased oestrogen production in KO females, as demonstrated by the threadlike uteri and acyclicity. As expected, there was no detectable FSH in the serum or pituitary and an absence of expression of the FSHβ subunit gene in FSHβKO mice. However, there was a significant increase in expression of the FSHβ and LHβ subunit genes in FSHRKO female mice. The morphology of FSHβKO and FSHRKO gonadotrophs was not significantly different from the control, except that secretory granules in FSHRKO gonadotrophs were larger in diameter. In LuRKO and ovariectomised mice, stimulation of LHβ and FSHβ mRNA, as well as serum protein concentrations, were reflected in subcellular changes in gonadotroph morphology, including more dilated rough endoplasmic reticula and fewer, larger secretory granules. In the gonadotophin-releasing hormone deficient hpg mouse, gonadotrophin mRNA and protein levels were significantly lower than in control mice and gonadotrophs were correspondingly smaller with less abundant endoplasmic reticula and reduced numbers of secretory granules. In summary, major differences in pituitary content and serum concentrations of the gonadotrophins LH and FSH were found between control and mutant female mice. These changes were associated with changes in expression of the gonadotrophin subunit genes and were reflected in the cellular structure and secretory granule appearance within the gonadotroph cells.

The permissive role of prolactin as a regulator of luteinizing hormone action in the female mouse ovary and extragonadal tumorigenesis

Transgenic female mice overexpressing the hCGβ subunit (hCGβ(+)) and producing elevated levels of luteinizing hormone (LH)/hCG bioactivity present as young adults with enhanced ovarian steroidogenesis, precocious puberty, and infertility. They subsequently develop pituitary prolactinomas, high circulating prolactin (PRL) levels, and marked mammary gland lobuloalveolar development followed by adenocarcinomas. None of these phenotypes appear in gonadectomized mice, indicating that the hCG-induced aberrations of ovarian function are responsible for the extragonadal phenotypes. PRL receptor-deficient (PRLR(-/-)) female mice are sterile, despite ovulating, due to a failure of embryo implantation, as a consequence of decreased ovarian LH receptor (Lhcgr) expression and inadequate corpus luteum formation and progesterone production. To study further the presumed permissive role of PRL in the maintenance of gonadal responsiveness to LH/hCG stimulation, we crossed the hCGβ(+) and PRLR(-/-) mice. The double-mutant hCGβ(+)/PRLR(-/-) females remained sterile with an ovarian phenotype similar to PRLR(-/-) mice, indicating that LH action, Lhcgr expression, and consequent luteinization are not possible without simultaneous PRL signaling. The high frequency of pituitary prolactinomas in PRLR(-/-) mice was not affected by transgenic hCGβ expression. In contrast, none of the hCGβ(+)/PRLR(-/-) females showed either mammary gland lobuloalveolar development or tumors, and the increased mammary gland Wnt-5b expression, possibly responsible for the tumorigenesis in hCGβ(+) mice, was absent in double-mutant mice. Hence, high LH/hCG stimulation is unable to compensate for missing PRL signaling in the maintenance of luteal function. PRL thus appears to be a major permissive regulator of LH action in the ovary and of its secondary extragonadal effects.

Endocrinology of the aging male

The endocrinology of the aging male is complex, with multiple hormones along the hypothalamic-pituitary-testicular (HPT) axis interacting with one another in feedback. As men age, there is a small and progressive (not precipitous, as in women) decline in several sex hormones, in particular testosterone and dehydroepiandrosterone, and related increases in luteinizing hormone, follicle-stimulating hormone, and sex hormone-binding globulin. The importance of these changes is wide-ranging because of the ubiquitous role of sex hormones in male physiology. This chapter discusses the endocrinology of the aging male. We provide an overview of the regulation of the HPT axis with an emphasis on the changes that occur with aging and the measurement of gonadal steroids, including hormone pulsatility, within-subject and circadian variations. The difficulties of assessing the symptoms of late-onset hypogonadism are highlighted. There is a comprehensive discussion of the epidemiology of sex hormone changes, including their age associations, prevalence of symptomatic hypogonadism, secular changes, risk factors, and the association of sex hormones with outcomes.