Follicle-stimulating hormone does not impact male bone mass in vivo or human male osteoclasts in vitro

Pituitary crosstalk with bone, adipose tissue and brain

Traditional textbook physiology has ascribed unitary functions to hormones from the anterior and posterior pituitary gland, mainly in the regulation of effector hormone secretion from endocrine organs. However, the evolutionary biology of pituitary hormones and their receptors provides evidence for a broad range of functions in vertebrate physiology. Over the past decade, we and others have discovered that thyroid-stimulating hormone, follicle-stimulating hormone, adrenocorticotropic hormone, prolactin, oxytocin and arginine vasopressin act directly on somatic organs, including bone, adipose tissue and liver. New evidence also indicates that pituitary hormone receptors are expressed in brain regions, nuclei and subnuclei. These studies have prompted us to attribute the pathophysiology of certain human diseases, including osteoporosis, obesity and neurodegeneration, at least in part, to changes in pituitary hormone levels. This new information has identified actionable therapeutic targets for drug discovery.

Extra-Gonadal and Non-Canonical Effects of FSH in Males

Recombinant follicle-stimulating hormone (FSH) is commonly used for the treatment of female infertility and is increasingly being used in males as well, as recommended by notable guidelines. FSH is composed of an α subunit, shared with other hormones, and a β subunit, which confers specificity of biological action by interacting with its surface receptor (FSHR), predominantly located in granulosa and Sertoli cells. However, FSHRs also exist in extra-gonadal tissues, indicating potential effects beyond male fertility. Emerging evidence suggests that FSH may have extra-gonadal effects, including on bone metabolism, where it appears to stimulate bone resorption by binding to specific receptors on osteoclasts. Additionally, higher FSH levels have been associated with worse metabolic and cardiovascular outcomes, suggesting a possible impact on the cardiovascular system. FSH has also been implicated in immune response modulation, as FSHRs are expressed on immune cells and may influence inflammatory response. Furthermore, there is growing interest in the role of FSH in prostate cancer progression. This paper aims to provide a comprehensive analysis of the literature on the extra-gonadal effects of FSH in men, with a focus on the often-conflicting results reported in this field. Despite the contradictory findings, the potential for future development in this area is substantial, and further research is needed to elucidate the mechanisms underlying these effects and their clinical implications.

Follicle-stimulating hormone is associated with low bone mass in postmenopausal women

We evaluated the influence of two endogenous hormones on bone health in older women. Higher FSH was associated with bone disease, especially in lower estradiol environments. FSH attenuated the relationship between estradiol and bone. This may provide a mechanism through which future clinical research intervenes on bone loss.

INTRODUCTION/PURPOSE

Despite preclinical evidence for an inverse association of follicle-stimulating hormone (FSH) and bone mineral density (BMD), no large epidemiologic studies have evaluated the separate and joint influences of FSH and estradiol on bone in postmenopausal women.

METHODS

In a cross-sectional study of 675 postmenopausal women, we evaluated associations of serum FSH and dual X-ray absorptiometry (DXA)-classified areal BMD as well as low bone mass or osteoporosis (T-score <  - 1.0) of the femoral neck and total hip. We stratified this analysis by serum estradiol (cut at the median). We tested whether FSH mediates the association of estradiol and BMD using the Sobel test.

RESULTS

In linear regression models, there was a significant inverse association of serum FSH with both femoral neck and total hip BMD (both p < 0.01) when adjusted for age, hormone therapy (HT) use, and diabetes. In fully adjusted logistic regression models, women in the highest FSH tertile had higher odds of low bone mass/osteoporosis at the femoral neck (OR = 2.98; 95% CI = 1.86-4.77) and at the total hip (OR = 1.74; 95% CI = 1.06-2.84) compared to those in the lowest FSH tertile. We report evidence of effect modification by estradiol in stratified models and an interaction term. FSH met all criteria of a mediator, including an estimated 70% attenuation of the estradiol-BMD relationship (Sobel p value < 0.001).

CONCLUSIONS

FSH is associated with higher odds of having low bone mass/osteoporosis even after accounting for HT use. FSH is a mediator of the relationship between estradiol and BMD in healthy postmenopausal women. Larger, prospective studies of FSH concentrations and bone health are needed.

Follicle stimulating hormone and estradiol alter immune response in osteoarthritic mice in an opposite manner

Although a number of studies have shown that the occurrence and progression of osteoarthritis (OA) is related to endocrine system dysfunction, there is limited evidence about what roles sex hormones play. The aim of the present study was to examine the capacity of 17β-estradiol (ED) and follicle stimulating hormone (FSH) to alter the differentiation of bone marrow (BM) cells in arthritic mice. The experiments were conducted in collagenase-induced osteoarthritis in mice. Cartilage degradation was observed by safranin and toluidine blue staining. Flow cytometry was used to define different BM and synovial cell populations. The influence of FSH and ED on osteoclastogenesis was studied in BM cultures and on the osteoblastogenesis in primary calvarial cultures. The levels of IL-8, TNF-α, FSH, and osteocalcin were estimated by ELISA. FSH increased cartilage degradation and serum osteocalcin levels, while ED abolished it and lowered serum osteocalcin. FSH elevated the percentage of monocytoid CD14+/RANK+ and B cell CD19+/RANK+ cells in contrast to ED which inhibited the accumulation of these osteogenic populations. Also, ED changed the percentage of CD105+/F4/80+ and CD11c+ cells in the synovium. FSH augmented and ED suppressed macrophage colony-stimulating factor (M-CSF) + receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast (OC) formation, and this correlated with a respective increase and decrease of IL-8 secretion. FSH did not influence osteoblast (OB) formation while ED enhanced this process in association with changes of TNF-α, IL-8, and osteocalcin production. ED reduced osteoclast generation in bone. The key outcome of the current study is that both hormones influenced BM cell differentiation, with FSH favoring osteoclast formation and ED favoring osteoblast accumulation.

A Novel Hypothesis: A Role for Follicle Stimulating Hormone in Abdominal Aortic Aneurysm Development in Postmenopausal Women

An abdominal aortic aneurysm (AAA) is a dilatation of the abdominal aorta, which can potentially be fatal due to exsanguination following rupture. Although AAA is less prevalent in women, women with AAA have a more severe AAA progression compared to men as reflected by enhanced aneurysm growth rates and a higher rupture risk. Women are diagnosed with AAA at an older age than men, and in line with increased osteoporosis and cardiovascular events, the delayed AAA onset has been attributed to the reduction of the protective effect of oestrogens during the menopausal transition. However, new insights have shown that a high follicle stimulating hormone (FSH) level during menopause may also play a key role in those diseases. In this report we hypothesize that FSH may aggravate AAA development and progression in postmenopausal women via a direct and/or indirect role, promoting aorta pathology. Since FSH receptors (FSHR) are reported on many other cell types than granulosa cells in the ovaries, it is feasible that FSH stimulation of FSHR-bearing cells such as aortic endothelial cells or inflammatory cells, could promote AAA formation directly. Indirectly, AAA progression may be influenced by an FSH-mediated increase in osteoporosis, which is associated with aortic calcification. Also, an FSH-mediated decrease in cholesterol uptake by the liver and an increase in cholesterol biosynthesis will increase the cholesterol level in the circulation, and subsequently promote aortic atherosclerosis and inflammation. Lastly, FSH-induced adipogenesis may lead to obesity-mediated dysfunction of the microvasculature of the aorta and/or modulation of the periaortic adipose tissue. Thus the long term increased plasma FSH levels during the menopausal transition may contribute to enhanced AAA disease in menopausal women and could be a potential novel target for treatment to lower AAA-related events in women.

High serum FSH is not a risk factor for low bone mineral density in infertile men

BACKGROUND

Male infertility is associated with a higher long-term morbidity and mortality risk. However, it is not clear which diseases are contributing to this risk. Osteoporosis is a possible factor, as it is a frequent disease and sex steroids regulate both fertility and bone health. Furthermore, there are data indicating that high FSH levels in women are related to low bone mineral density (BMD), independent of estradiol levels. As infertile men often have increased FSH, already from a young age, this could be a risk factor for impaired bone health in later life.

METHODS

One hundred and thirty-seven men with a history of male factor infertility due to spermatogenic failure (SgF men) as well as a control group of 70 men from couples treated with IVF for female factor infertility (non-SgF men) were included in a long-term follow-up study. Men with explained infertility, including testosterone deficiency, were not included. Data from baseline fertility investigations were retrieved from the patient files of the SgF men. At follow-up hormonal and semen analysis were performed and axial, femoral and total body BMD was measured by dual X-ray absorptiometry in all men. Multiple linear regression was used to assess differences between SgF and non-SgF men and to study associations between FSH levels and BMD.

RESULTS

Median follow-up time was 14.8 years (5th-95th percentile 11.3-18.2) after fertility assessment for SgF men and 15.6 years (12.1-18.5) for non-SgF men (p = 0.033). When comparing the two groups, no significant differences in total T, free T or E2 levels were apparent at follow-up. As expected, LH and FSH were higher in SgF men ((median (5th-95th percentile)) for LH (IU/L): 4.3 (2.2-13.6) for SgF men and 3.0 (1.4-5.8) for non-SgF men (p < 0.001); FSH (IU/L): 9.8 (2.8-35.5) versus 3.7 (1.6-8.7); p < 0.001), and inhibin B and semen parameters were lower in SgF men. There were no differences in BMD between the two groups at follow-up. Furthermore, both groups had median Z-scores close to zero at all sites, indicating that BMD is not different when compared to age-matched healthy men. In SgF men, neither baseline FSH, nor FSH at follow-up, was associated with BMD at the different sites at follow-up.

CONCLUSION

Men with spermatogenic failure are not at increased risk for impaired bone health when middle aged. Furthermore, infertile men with high FSH levels do not have lower BMD.

FSH Beyond Fertility

The traditional view of follicle-stimulating hormone (FSH) as a reproductive hormone is changing. It has been shown that FSH receptors (FSHRs) are expressed in various extra-gonadal tissues and mediate the biological effects of FSH at those sites. Molecular, animal, epidemiologic, and clinical data suggest that elevated serum FSH may play a significant role in the evolution of bone loss and obesity, as well as contributing to cardiovascular and cancer risk. This review summarizes recent data on FSH action beyond reproduction.

Extragonadal FSHR Expression and Function-Is It Real?

Expression of the follicle-stimulating hormone receptor (FSHR), besides gonadal tissues, has recently been detected in several extragonadal normal and tumorous tissues, including different types of primary and metastatic cancer and tumor vessel endothelial cells (TVEC). The suggested FSH actions in extragonadal tissues include promotion of angiogenesis, myometrial contractility, skeletal integrity, and adipose tissue accumulation. Non-malignant cells within cancer tissue have been shown to be devoid of FSHR expression, which implies a potential role of FSHR as a diagnostic, prognostic, or even a therapeutic tool. There are shared issues between several of the published reports questioning the validity of some of the conclusion. Firstly, protein expression of FSHR was performed solely with immunohistochemistry (IHC) using either an unavailable "in house" FSHR323 monoclonal antibody or poorly validated polyclonal antibodies, usually without additional methodological quality control and confirmations. Secondly, there is discrepancy between the hardly traceable or absent FSHR gene amplification/transcript data and non-reciprocal strong FSHR protein immunoreactivity. Thirdly, the pharmacological high doses of recombinant FSH used in in vitro studies also jeopardizes the physiological or pathophysiological meaning of the findings. We performed in this review a critical analysis of the results presenting extragonadal expression of FSHR and FSH action, and provide a rationale for the validation of the reported results using additional more accurate and sensitive supplemental methods, including in vivo models and proper positive and negative controls.

FSH, Bone Mass, Body Fat, and Biological Aging

The Study of Women's Health Across the Nation has taught us that impending ovarian failure during late perimenopause is associated with a sharp rise in serum FSH, which coincides with the most rapid rate of bone loss and the onset of visceral adiposity. At this time in a woman's life, serum estrogen levels are largely unaltered, so the hypothesis that hypoestrogenemia is the sole cause of bone loss and visceral obesity does not offer a full explanation. An alternative explanation, arising from animal models and human data, is that both physiologic aberrations, obesity and osteoporosis, arise at least in part from rising FSH levels. Here, we discuss recent findings on the mechanism through which FSH exerts biological actions on bone and fat and review clinical data that support a role for FSH in causing osteoporosis and obesity. We will also provide a conceptual framework for using a single anti-FSH agent to prevent and treat both osteoporosis and obesity in women across the menopausal transition.

Actions of pituitary hormones beyond traditional targets

Studies over the past decade have challenged the long-held belief that pituitary hormones have singular functions in regulating specific target tissues, including master hormone secretion. Our discovery of the action of thyroid-stimulating hormone (TSH) on bone provided the first glimpse into the non-traditional functions of pituitary hormones. Here we discuss evolving experimental and clinical evidence that growth hormone (GH), follicle-stimulating hormone (FSH), adrenocorticotrophic hormone (ACTH), prolactin, oxytocin and arginine vasopressin (AVP) regulate bone and other target tissues, such as fat. Notably, genetic and pharmacologic FSH suppression increases bone mass and reduces body fat, laying the framework for targeting the FSH axis for treating obesity and osteoporosis simultaneously with a single agent. Certain 'pituitary' hormones, such as TSH and oxytocin, are also expressed in bone cells, providing local paracrine and autocrine networks for the regulation of bone mass. Overall, the continuing identification of new roles for pituitary hormones in biology provides an entirely new layer of physiologic circuitry, while unmasking new therapeutic targets.

Emerging concepts in the epidemiology, pathophysiology, and clinical care of osteoporosis across the menopausal transition

Bone loss in women accelerates during perimenopause, and continues into old age. To-date, there has been little progress made in stratifying for fracture risk in premenopausal and early postmenopausal women. Epidemiologic data suggests that changes in serum FSH could predict decrements in bone mass during peri- and postmenopause. In bone, FSH stimulates osteoclast formation by releasing osteoclastogenic cytokines. Here, we address the evidence for bone loss across the menopausal transition, discuss strategies for detection and treatment of early postmenopausal osteoporosis, and describe the role FSH plays in physiology and likely in pathophysiology of early postmenopausal bone loss.

Extragonadal Actions of FSH: A Critical Need for Novel Genetic Models

Follicle-stimulating hormone (FSH) is critical for ovarian folliculogenesis and essential for female fertility. FSH binds to FSH receptors (FSHRs) and regulates estrogen production in ovarian granulosa cells to orchestrate female reproductive physiology. Ovarian senescence that occurs as a function of aging results in loss of estrogen production, and this is believed to be the major reason for bone loss in postmenopausal women. Although conflicting, studies in rodents and humans during the last decade have provided genetic, pharmacological, and physiological evidence that elevated FSH levels that occur in the face of normal or declining estrogen levels directly regulate bone mass and adiposity. Recently, an efficacious blocking polyclonal FSHβ antibody was developed that inhibited ovariectomy-induced bone loss and triggered white-to-brown fat conversion accompanied by mitochondrial biogenesis in mice. Moreover, additional nongonadal targets of FSH action have been identified, and these include the female reproductive tract (endometrium and myometrium), the placenta, hepatocytes, and blood vessels. In this mini-review, I summarize these studies in mice and humans and discuss critical gaps in our knowledge, yet unanswered questions, and the rationale for developing novel genetic models to unambiguously address the extragonadal actions of FSH.

In Vivo and In Vitro Impact of Carbohydrate Variation on Human Follicle-Stimulating Hormone Function

Human follicle-stimulating hormone (FSH) exhibits both macro- and microheterogeneity in its carbohydrate moieties. Macroheterogeneity results in three physiologically relevant FSHβ subunit variants, two that possess a single N-linked glycan at either one of the two βL1 loop glycosylation sites or one with both glycans. Microheterogeneity is characterized by 80 to over 100 unique oligosaccharide structures attached to each of the 3 to 4 occupied N-glycosylation sites. With respect to its receptor, partially glycosylated (hypo-glycosylated) FSH variants exhibit higher association rates, greater apparent affinity, and greater occupancy than fully glycosylated FSH. Higher receptor binding-activity is reflected by greater in vitro bioactivity and, in some cases, greater in vivo bioactivity. Partially glycosylated pituitary FSH shows an age-related decline in abundance that may be associated with decreased fertility. In this review, we describe an integrated approach involving genetic models, in vitro signaling studies, FSH biochemistry, relevance of physiological changes in FSH glycoform abundance, and characterize the impact of FSH macroheterogeneity on fertility and reproductive aging. We will also address the controversy with regard to claims of a direct action of FSH in mediating bone loss especially at the peri- and postmenopausal stages.

The Relationship between Follicle-stimulating Hormone and Bone Health: Alternative Explanation for Bone Loss beyond Oestrogen?

Bone loss in women commences before the onset of menopause and oestrogen deficiency. The increase of follicle-stimulating hormone (FSH) precedes oestrogen decline and may be a cause for bone loss before menopause. This review summarizes the current evidence on the relationship between FSH and bone derived from cellular, animal and human studies. Cellular studies found that FSH receptor (FSHR) was present on osteoclasts, osteoclast precursors and mesenchymal stem cells but not osteoblasts. FSH promoted osteoclast differentiation, activity and survival but exerted negligible effects on osteoblasts. Transgenic FSHR or FSH knockout rodents showed heterogenous skeletal phenotypes. Supplementation of FSH enhanced bone deterioration and blocking of FSH action protected bone of rodents. Human epidemiological studies revealed a negative relationship between FSH and bone health in perimenopausal women and elderly men but the association was attenuated in postmenopausal women. In conclusion, FSH may have a direct action on bone health independent of oestrogen by enhancing bone resorption. Its effects may be attenuated in the presence of overt sex hormone deficiency. More longitudinal studies pertaining to the effects of FSH on bone health, especially on fracture risk, should be conducted to validate this speculation.

Follicular Stimulating Hormone Accelerates Atherogenesis by Increasing Endothelial VCAM-1 Expression

Rationale: Postmenopausal atherosclerosis (AS) has for decades been attributed to estrogen deficiency. Although the follicular stimulating hormone (FSH) levels rise sharply in parallel, the direct effect of FSH on AS has never been investigated. In this study, we explored the possible role of FSH in the development of AS. Methods: This was a prospective cohort study of 48 healthy premenopausal and 15 postmenopausal women. ApoE knockout mice were used as atherosclerosis model and human umbilical vascular endothelial cells (HUVECs) were cultured as cell model. Serum hormones and vascular cell adhesion molecule-1 (VCAM-1) levels were measured. Real-time PCR, histology for atherosclerotic lesions, immunofluorescence, luciferase assay, transfection experiments, flow chamber adhesion assay and western blot were performed. Results: In ApoE knockout mice, administration of FSH increased the atherosclerotic lesions and serum VCAM-1 concentration. Importantly, in blood samples of postmenopausal women, we detected significantly higher levels of FSH and VCAM-1 compared with those from premenopausal women, and there was a positive correlation between these two molecules. In cultured HUVECs, FSH receptor (FSHR) mRNA and protein expression were detected and FSH enhanced VCAM-1 expression. This effect was mediated by the activation of nuclear factor κB (NF-κB), which was sequentially enhanced by the activation of PI3K/Akt/mTOR cascade. FSH first enhanced Gα_S activity resulting in elevated cAMP level and PKA activity, which relayed the signals from FSHR to the PI3K/Akt/mTOR cascade. Furthermore, FSHR was detected in endothelial caveolae fraction and interacted with caveolin-1 and Gα_S. The disruption of caveolae or the silencing of caveolin-1 blocked FSH effects on signaling activation and VCAM-1 expression, suggesting the existence of a functional signaling module in membrane caveolae. Finally, FSH increased human monocyte adhesion to HUVECs which was reversed by the VCAM-1 neutralizing antibody. Conclusion: FSHR was located in the membrane caveolae of HUVECs and FSH promoted VCAM-1 expression via FSHR/Gα_S /cAMP/PKA and PI3K/Akt/mTOR/NF-κB pathway. This may contribute to the deleterious role of FSH in the development of AS in postmenopausal women.

Pituitary-bone connection in skeletal regulation

Pituitary hormones have traditionally been thought to exert specific, but limited function on target tissues. More recently, the discovery of these hormones and their receptors in organs such as the skeleton suggests that pituitary hormones have more ubiquitous functions. Here, we discuss the interaction of growth hormone (GH), follicle stimulating hormone (FSH), thyroid stimulating hormone (TSH), adrenocorticotrophic hormone (ACTH), prolactin, oxytocin and arginine vasopressin (AVP) with bone. The direct skeletal action of pituitary hormones therefore provides new insights and therapeutic opportunities for metabolic bone diseases, prominently osteoporosis.

Beyond Reproduction: Pituitary Hormone Actions on Bone

The long-held belief that pituitary hormones act solely on master targets was first questioned when we documented G protein-coupled receptors for thyroid-stimulating hormone, follicle-stimulating hormone, adrenocorticotrophic hormone, oxytocin, and vasopressin on bone cells. These evolutionarily conserved hormones and their receptors are known to have primitive roles, and exist in invertebrate species as far down as coelenterates. It is not surprising therefore that each such hormone has multiple hitherto unrecognized functions in mammalian integrative physiology, and hence, becomes a potential target for therapeutic intervention. Here we discuss the skeletal actions of pituitary hormones.

Bone Mineral Density in Adolescent Girls with Hypogonadotropic and Hypergonadotropic Hypogonadism

OBJECTIVE

Deficiency of sex steroids has a negative impact on bone mineral content. In studies conducted on postmenopausal women and animal studies, elevated follicle-stimulating hormone (FSH) levels were found to be correlated with a decrease in bone mineralization and osteoporosis. The aim of the present study was to evaluate bone mineral density (BMD) in adolescent girls with hypogonadotropic and hypergonadotropic hypogonadism and also to investigate the correlation between FSH level and BMD.

METHODS

The study group included 33 adolescent girls with hypogonadism (14 with hypogonadotropic hypogonadism and 19 with hypergonadotropic hypogonadism). FSH, luteinizing hormone, estradiol levels, and BMD (using dual energy x-ray absorptiometry) were measured.

RESULTS

There were no statistically significant differences between the chronological age and bone age of the two patient groups, namely, with hypogonadotropic and hypergonadotropic hypogonadism. There was also no significant difference between BMD z-score values obtained from measurements from the spine and the femur neck of patients in the two groups (p-values were 0.841 and 0.281, respectively). In the hypergonadotropic group, a moderately negative correlation was detected between FSH level and BMD z-score measured from the femur neck (ρ=-0.69, p=0.001), whilst no correlation was observed between FSH levels and height adjusted BMD-z scores measured from the spine (ρ=0.17, p=0.493). FSH level was not found to be an independent variable affecting BMD z-score.

CONCLUSION

BMD z-scores were detected to be similar in adolescent girls with hypogonadotropic and hypergonadotropic hypogonadism, and FSH levels were not found to have a clinically relevant impact on BMD.

Follicle-Stimulating Hormone Increases the Risk of Postmenopausal Osteoporosis by Stimulating Osteoclast Differentiation

Objective

The objectives of this study were to observe the changes in follicle-stimulating hormone (FSH) and bone mineral density (BMD) in postmenopausal women, to research the relationship between FSH and postmenopausal osteoporosis, and to observe the effects of FSH on osteoclast differentiation in RAW264.7 cells.

Methods

We analyzed 248 postmenopausal women with normal bone metabolism. A radioimmunoassay (RIA) was used to detect serum FSH, luteinizing hormone (LH), and estradiol (E₂). Dual-energy X-ray absorptiometry was used to measure forearm BMD. Then, we analyzed the age-related changes in serum FSH, LH and E₂. Additionally, FSH serum concentrations were compared between a group of postmenopausal women with osteoporosis and a control group. Osteoclasts were induced from RAW264.7 cells in vitro by receptor activator of nuclear factor kappa B ligand (RANKL), and these cells were treated with 0, 5, 10, and 20 ng/ml FSH. After the osteoclasts matured, tartrate-resistant acid phosphatase (TRAP) staining was used to identify osteoclasts, and the mRNA expression levels of genes involved in osteoclastic phenotypes and function, such as receptor activator of NF-κB (Rank), Trap, matrix metalloproteinase-9 (Mmp-9) and Cathepsin K, were detected in different groups using real-time PCR (polymerase chain reaction).

Results

1. FSH serum concentrations in postmenopausal women with osteoporosis increased notably compared with the control group. 2. RANKL induced RAW264.7 cell differentiation into mature osteoclasts in vitro. 3. FSH increased mRNA expression of genes involved in osteoclastic phenotypes and function, such as Rank, Trap, Mmp-9 and Cathepsin K, in a dose-dependent manner.

Conclusions

The circulating concentration of FSH may play an important role in the acceleration of bone loss in postmenopausal women. FSH increases osteoclastogenesis in vitro.

Effect of azaline B on follicular development and functions in the hamster

The usefulness of azaline B, a GnRH antagonist, in suppressing gonadotropin secretion in the golden hamster was examined by examining follicular development, steroidogenesis and expression of steroidogenic enzymes. Serum levels of P and E declined significantly, while FSH or LH was undetectable in azaline B-treated hamsters. FSH significantly increased serum E levels, whereas LH upregulated serum P levels. The formation of antral follicles ceased in azaline-treated hamsters, but was reversed by FSH with or without LH supplement. FSH also activated the primordial follicle pool resulting in increased formation of primary and preantral follicles. Further, an increasing trend in the formation of preantral follicles in response to E or E + P, and the formation of antral follicles in response to E + P treatment was evident. The level of Cyp11a1 mRNA increased markedly in LH- or LH + FSH-treated hamsters, whereas FSH with or without LH upregulated Cyp17a1, Cyp19a1 and Fshr mRNA expression. E without or with P also upregulated ovarian Cyp19a1 mRNA expression. The expression of enzyme protein corroborated the mRNA data. In summary, azaline B is an efficient GnRH antagonist in the hamster, and will be useful in studying the selective effect of gonadotropins on ovarian functions without disrupting the physiological functions of other hormones in ovarian cells.

FSH suppression does not affect bone turnover in eugonadal men

CONTEXT

In vitro and animal studies have reported conflicting results regarding an independent role for FSH in the regulation of bone turnover.

OBJECTIVE

Our objective was to test the hypothesis that suppressing serum FSH while holding serum gonadal steroid levels stable in the eugonadal range will affect biochemical markers of bone metabolism in healthy men.

PARTICIPANTS, DESIGN, AND SETTING

Eugonadal men aged 20 to 50 years participated in this randomized controlled trial at a tertiary care academic teaching hospital.

INTERVENTIONS

Participants received monthly GnRH analog injections to suppress FSH secretion plus daily topical testosterone gel in prespecified doses (intervention group). Controls received matching placebos (control group). Subjects in the intervention group were individually matched with subjects in the control group to ensure that the mean testosterone and estradiol levels (measured every 4 weeks during the 16-week study period) in the 2 groups were similar.

MAIN OUTCOME MEASURES

Biochemical markers of bone resorption (serum N-terminal telopeptide and C-terminal telopeptide), bone formation (serum osteocalcin), and FSH were measured at baseline and after 16 weeks of treatment.

RESULTS

Serum FSH declined by 2% in the control group and by 60% in the intervention group (P < .0001 for the between-group difference). Despite the substantial suppression of serum FSH in the intervention group, serum N-terminal telopeptide, C-terminal telopeptide, and osteocalcin did not change in the intervention group, nor were any between-group differences observed.

CONCLUSION

When gonadal steroid levels are held constant, short-to midterm suppression of FSH does not affect bone turnover in men. FSH does not appear to be a significant regulator of bone metabolism in eugonadal men.

FSH and TSH in the regulation of bone mass: the pituitary/immune/bone axis

Recent evidences have highlighted that the pituitary hormones have profound effects on bone, so that the pituitary-bone axis is now becoming an important issue in the skeletal biology. Here, we discuss the topical evidence about the dysfunction of the pituitary-bone axis that leads to osteoporotic bone loss. We will explore the context of FSH and TSH hormones arguing their direct or indirect role in bone loss. In addition, we will focus on the knowledge that both FSH and TSH have influence on proinflammatory and proosteoclastogenic cytokine expression, such as TNFα and IL-1, underlining the correlation of pituitary-bone axis to the immune system.

Blocking FSH action attenuates osteoclastogenesis

A direct effect of FSH on bone turnover via stimulation of osteoclast formation has been reported. Here we show that monoclonal or polyclonal antibodies to FSH inhibit osteoclast formation induced by FSH to an extent similar to that noted in FSH receptor (FSHR) knockout cells. Furthermore, we document the amplification of FSHR cDNA from well-characterized human CD14+ osteoclast precursors and osteoclasts, and the direct sequencing of the PCR products to definitively establish the expression of FSHRs. At these sites, the FSHR was expressed predominantly as an isoform that omits exon 9, a linker between the FSH-binding region and a long, invariant signaling domain of the receptor. These data provide compelling evidence for expression of a FSH receptor isoform in osteoclasts and their precursors.

Decreased bone mineral density in rats rendered follicle-deplete by an ovotoxic chemical correlates with changes in follicle-stimulating hormone and inhibin A

Bone loss during perimenopause, an estrogen-sufficient period, correlates with elevated serum follicle-stimulating hormone (FSH) and decreased inhibins A and B. Utilizing a recently described ovotoxin-induced animal model of perimenopause characterized by a prolonged estrogen-replete period of elevated FSH, we examined longitudinal changes in bone mineral density (BMD) and their association with FSH. Additionally, serum inhibin levels were assessed to determine whether elevated FSH occurred secondary to decreased ovarian inhibin production and, if so, whether inhibins also correlated with BMD. BMD of the distal femur was assessed using dual-energy X-ray absorptiometry (DXA) over 19 months in Sprague-Dawley rats treated at 1 month with vehicle or 4-vinylcyclohexene diepoxide (VCD, 80 or 160 mg/kg daily). Serum FSH, inhibins A and B, and 17-ß estradiol (E(2)) were assayed and estrus cyclicity was assessed. VCD caused dose-dependent increases in FSH that exceeded values occurring with natural senescence, hastening the onset and prolonging the duration of persistent estrus, an acyclic but E(2)-replete period. VCD decreased serum inhibins A and B, which were inversely correlated with FSH (r(2) = 0.30 and 0.12, respectively). In VCD rats, significant decreases in BMD (5-13%) occurred during periods of increased FSH and decreased inhibins, while BMD was unchanged in controls. In skeletally mature rats, FSH (r(2) = 0.13) and inhibin A (r(2) = 0.15) correlated with BMD, while inhibin B and E(2) did not. Thus, for the first time, both the hormonal milieu of perimenopause and the association of dynamic perimenopausal changes in FSH and inhibin A with decreased BMD have been reproduced in an animal model.

Current concepts of follicle-stimulating hormone receptor gene regulation

Follicle-stimulating hormone (FSH), a pituitary glycoprotein hormone, is an integral component of the endocrine axis that regulates gonadal function and fertility. To transmit its signal, FSH must bind to its receptor (FSHR) located on Sertoli cells of the testis and granulosa cells of the ovary. Thus, both the magnitude and the target of hormone response are controlled by mechanisms that determine FSHR levels and cell-specific expression, which are supported by transcription of its gene. The present review examines the status of FSHR/Fshr gene regulation, emphasizing the importance of distal sequences in FSHR/Fshr transcription, new insights gained from the influx of genomics data and bioinformatics, and emerging trends that offer direction in deciphering the FSHR/Fshr regulatory landscape.

Effects of suppression of follicle-stimulating hormone secretion on bone resorption markers in postmenopausal women

CONTEXT

It has recently been proposed that the increase in bone resorption after the menopause may not be due principally to estrogen deficiency but rather to the concomitant increase in circulating FSH levels.

OBJECTIVE

The objective of the study was to test whether suppression of FSH secretion in postmenopausal women reduces levels of bone resorption markers.

DESIGN

This was a prospective study.

SETTING

The study was conducted at a clinical research unit.

PARTICIPANTS AND INTERVENTIONS

Postmenopausal women were treated with a GnRH agonist (leuprolide acetate, 7.5 mg im every 28 d; n = 21) or placebo injections (control; n = 20). Both groups received the aromatase inhibitor, letrozole, 2.5 mg/d, to eliminate variations in endogenous estrogen levels as a confounder.

MAIN OUTCOME MEASURES

Serum FSH and bone resorption markers [serum C-terminal telopeptide of type I collagen (CTX) and tartrate-resistant acid phosphatase 5b (TRAP5b)] at d 105 (3.5 months) of treatment as compared with baseline.

RESULTS

Compared with baseline, serum FSH levels did not change significantly in controls (+6%) but were reduced (-86%, into the premenopausal range) in the GnRH group. Due to the aromatase inhibitor-induced reduction in estrogen production, serum CTX and TRAP5b levels increased significantly in controls (+20 and +10%, respectively). In the GnRH group, suppression of FSH secretion did not reduce serum CTX or TRAP5b levels; rather, both markers also increased in these women (+34 and +15%, respectively; P = 0.161 and 0.266 for comparison of percent changes between groups).

CONCLUSIONS

This direct interventional study demonstrates that FSH does not regulate bone resorption in postmenopausal women.

Reproductive hormones and bone

Hypothalamic gonadotropin-releasing hormone (GnRH) stimulates secretion of pituitary luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which directly regulate ovarian function. Pituitary FSH can modulate osteoclast development, and thereby influence bone turnover. Pituitary oxytocin and prolactin effects on the skeleton are not merely limited to pregnancy and lactation; oxytocin stimulates osteoblastogenesis and bone formation, whereas prolactin exerts skeletal effects in an age-dependent manner. Cyclic levels of inhibins and estrogen suppress FSH and LH, respectively, and also suppress bone turnover via their suppressive effects on osteoblast and osteoclast differentiation. However, continuous exposure to inhibins or estrogen/androgens is anabolic for the skeleton in intact animals and protects against gonadectomy-induced bone loss. Alterations of one hormone in the hypothalamic-pituitary-gonadal (HPG) axis influence other bone-active hormones in the entire feedback loop in the axis. Thus, we propose that the action of the HPG axis should be extended to include its combined effects on the skeleton, thus creating the HPG skeletal (HPGS) axis.

Follicle-stimulating hormone increases cholangiocyte proliferation by an autocrine mechanism via cAMP-dependent phosphorylation of ERK1/2 and Elk-1

Sex hormones regulate cholangiocyte hyperplasia in bile duct-ligated (BDL) rats. We studied whether follicle-stimulating hormone (FSH) regulates cholangiocyte proliferation. FSH receptor (FSHR) and FSH expression was evaluated in liver sections, purified cholangiocytes, and cholangiocyte cultures (NRICC). In vivo, normal female and male rats were treated with FSH or immediately after BDL with antide (a gonadotropin-releasing hormone antagonist blocking FSH secretion) or a neutralizing FSH antibody for 1 wk. We evaluated 1) cholangiocyte proliferation in sections and cholangiocytes and 2) changes in secretin-stimulated cAMP (functional index of cholangiocyte growth) levels, and ERK1/2 and Elk-1 phosphorylation. NRICC were stimulated with FSH before evaluation of proliferation, cAMP/IP(3) levels, and ERK1/2 and Elk-1 phosphorylation. To determine whether FSH regulates cholangiocyte proliferation by an autocrine mechanism, we evaluated the effects of 1) cholangiocyte supernatant (containing FSH) on NRICC proliferation and 2) FSH silencing in NRICC before measuring proliferation and ERK1/2 and Elk-1 phosphorylation. Cholangiocytes and NRICC express FSHR and FSH and secrete FSH. In vivo administration of FSH to normal rats increased, whereas administration of antide and anti-FSH antibody to BDL rats decreased 1) ductal mass and 2) secretin-stimulated cAMP levels, proliferation, and ERK1/2 and Elk-1 phosphorylation in cholangiocytes compared with controls. In NRICC, FSH increased cholangiocyte proliferation, cAMP levels, and ERK1/2 and Elk-1 phosphorylation. The supernatant of cholangiocytes increased NRICC proliferation, inhibited by preincubation with anti-FSH antibody. Silencing of FSH gene decreases cholangiocyte proliferation and ERK1/2 and Elk-1 phosphorylation. Modulation of cholangiocyte FSH expression may be important for the management of cholangiopathies.