Blocking FSH induces thermogenic adipose tissue and reduces body fat

Screening Gene Knockout Mice for Variation in Bone Mass: Analysis by μCT and Histomorphometry

PURPOSE OF REVIEW

The international mouse phenotyping consortium (IMPC) is producing defined gene knockout mouse lines. Here, a phenotyping program is presented that is based on micro-computed tomography (μCT) assessment of distal femur and vertebra. Lines with significant variation undergo a computer-based bone histomorphometric analysis.

RECENT FINDINGS

Of the 220 lines examined to date, approximately 15% have a significant variation (high or low) by μCT, most of which are not identified by the IMPC screen. Significant dimorphism between the sexes and bone compartments adds to the complexity of the skeletal findings. The μCT information that is posted at www.bonebase.org can group KOMP lines with similar morphological features. The histological data is presented in a graphic form that associates the cellular features with a specific anatomic group. The web portal presents a bone-centric view appropriate for the skeletal biologist/clinician to organize and understand the large number of genes that can influence skeletal health. Cataloging the relative severity of each variant is the first step towards compiling the dataset necessary to appreciate the full polygenic basis of degenerative bone disease.

Sexual Dimorphism and the Origins of Human Spinal Health

Recent observations indicate that the cross-sectional area (CSA) of vertebral bodies is on average 10% smaller in healthy newborn girls than in newborn boys, a striking difference that increases during infancy and puberty and is greatest by the time of sexual and skeletal maturity. The smaller CSA of female vertebrae is associated with greater spinal flexibility and could represent the human adaptation to fetal load in bipedal posture. Unfortunately, it also imparts a mechanical disadvantage that increases stress within the vertebrae for all physical activities. This review summarizes the potential endocrine, genetic, and environmental determinants of vertebral cross-sectional growth and current knowledge of the association between the small female vertebrae and greater risk for a broad array of spinal conditions across the lifespan.

Molecular regulation of follicle-stimulating hormone synthesis, secretion and action

Follicle-stimulating hormone (FSH) plays fundamental roles in male and female fertility. FSH is a heterodimeric glycoprotein expressed by gonadotrophs in the anterior pituitary. The hormone-specific FSHβ-subunit is non-covalently associated with the common α-subunit that is also present in the luteinizing hormone (LH), another gonadotrophic hormone secreted by gonadotrophs and thyroid-stimulating hormone (TSH) secreted by thyrotrophs. Several decades of research led to the purification, structural characterization and physiological regulation of FSH in a variety of species including humans. With the advent of molecular tools, availability of immortalized gonadotroph cell lines and genetically modified mouse models, our knowledge on molecular mechanisms of FSH regulation has tremendously expanded. Several key players that regulate FSH synthesis, sorting, secretion and action in gonads and extragonadal tissues have been identified in a physiological setting. Novel post-transcriptional and post-translational regulatory mechanisms have also been identified that provide additional layers of regulation mediating FSH homeostasis. Recombinant human FSH analogs hold promise for a variety of clinical applications, whereas blocking antibodies against FSH may prove efficacious for preventing age-dependent bone loss and adiposity. It is anticipated that several exciting new discoveries uncovering all aspects of FSH biology will soon be forthcoming.

Bone: best papers of the year 2017

An overview of selected papers related to bone published in 2017 is provided.

PURPOSE

This paper accompanies a lecture at the 2018 Belgian Bone Club annual Clinical Update Symposium held in Brussels on January 20th, discussing the best papers (in the opinion of the author) published in the previous year.

METHODS

A PubMed search using the keyword "bone" and articles published in 2017.

RESULTS

Hot topics include screening for osteoporosis, novel anabolic drugs such as romosozumab and abaloparatide for osteoporosis and rare metabolic bone diseases, as well as long-term efficacy of denosumab and possible risk of multiple vertebral fractures following its discontinuation. Other selected articles cover effectiveness of bisphosphonates and changes in mineralization after long-term use, new guidelines for glucocorticoid- and aromatase inhibitor-induced osteoporosis, increasing use of high-dose vitamin D supplements despite lack of evidence for their widespread high-dose use, and cardiovascular safety concerns surrounding the use of calcium supplements. Other topics discussed are effects of diabetes on bone health, reciprocal crosstalk between bone cells and adipose tissue, and resistance exercise training to prevent bone loss and sarcopenia.

CONCLUSIONS

These papers offer a hopeful outlook for a better treatment and management of patients with osteoporosis and other metabolic bone diseases anno 2018.

The Global Epidemic of the Metabolic Syndrome

Metabolic syndrome, variously known also as syndrome X, insulin resistance, etc., is defined by WHO as a pathologic condition characterized by abdominal obesity, insulin resistance, hypertension, and hyperlipidemia. Though there is some variation in the definition by other health care organization, the differences are minor. With the successful conquest of communicable infectious diseases in most of the world, this new non-communicable disease (NCD) has become the major health hazard of modern world. Though it started in the Western world, with the spread of the Western lifestyle across the globe, it has become now a truly global problem. The prevalence of the metabolic syndrome is often more in the urban population of some developing countries than in its Western counterparts. The two basic forces spreading this malady are the increase in consumption of high calorie-low fiber fast food and the decrease in physical activity due to mechanized transportations and sedentary form of leisure time activities. The syndrome feeds into the spread of the diseases like type 2 diabetes, coronary diseases, stroke, and other disabilities. The total cost of the malady including the cost of health care and loss of potential economic activity is in trillions. The present trend is not sustainable unless a magic cure is found (unlikely) or concerted global/governmental/societal efforts are made to change the lifestyle that is promoting it. There are certainly some elements in the causation of the metabolic syndrome that cannot be changed but many are amenable for corrections and curtailments. For example, better urban planning to encourage active lifestyle, subsidizing consumption of whole grains and possible taxing high calorie snacks, restricting media advertisement of unhealthy food, etc. Revitalizing old fashion healthier lifestyle, promoting old-fashioned foods using healthy herbs rather than oil and sugar, and educating people about choosing healthy/wholesome food over junks are among the steps that can be considered.

Circulating molecules that control brown/beige adipocyte differentiation and thermogenic capacity

Obesity may be counteracted by increased energy expenditure. Circulating molecules act in the adipose tissue to influence brown and beige adipocyte function, differentiation, and thermogenic capacity, which in turn affects substrate utilization and impacts energy balance at the organismal level. These molecules have been envisioned as biomarkers and potential candidates for pharmacological interventions to treat obesity. Here we summarize studies that demonstrate the roles of endogenous circulating molecules of a wide variety in regulating the thermogenic potential of brown and beige fat cells. This review describes the state-of-the-art in the field and helps researchers to prioritize their targets in future studies.

Epitope-specific monoclonal antibodies to FSHβ increase bone mass

Pituitary hormones have long been thought solely to regulate single targets. Challenging this paradigm, we discovered that both anterior and posterior pituitary hormones, including FSH, had other functions in physiology. We have shown that FSH regulates skeletal integrity, and, more recently, find that FSH inhibition reduces body fat and induces thermogenic adipose tissue. A polyclonal antibody raised against a short, receptor-binding epitope of FSHβ was found not only to rescue bone loss postovariectomy, but also to display marked antiobesity and probeiging actions. Questioning whether a single agent could be used to treat two medical conditions of public health importance--osteoporosis and obesity--we developed two further monoclonal antibodies, Hf2 and Mf4, against computationally defined receptor-binding epitopes of FSHβ. Hf2 has already been shown to reduce body weight and fat mass and cause beiging in mice on a high-fat diet. Here, we show that Hf2, which binds mouse Fsh in immunoprecipitation assays, also increases cortical thickness and trabecular bone volume, and microstructural parameters, in sham-operated and ovariectomized mice, noted on microcomputed tomography. This effect was largely recapitulated with Mf4, which inhibited bone resorption by osteoclasts and stimulated new bone formation by osteoblasts. These effects were exerted in the absence of alterations in serum estrogen in wild-type mice. We also reconfirm the existence of Fshrs in bone by documenting the specific binding of fluorescently labeled FSH, FSH-CH, in vivo. Our study provides the framework for the future development of an FSH-based therapeutic that could potentially target both bone and fat.

Clinical implications of bone marrow adiposity

Marrow adipocytes, collectively termed marrow adipose tissue (MAT), reside in the bone marrow in close contact to bone cells and haematopoietic cells. Marrow adipocytes arise from the mesenchymal stem cell and share their origin with the osteoblast. Shifts in the lineage allocation of the mesenchymal stromal cell could potentially explain the association between increased MAT and increased fracture risk in diseases such as postmenopausal osteoporosis, anorexia nervosa and diabetes. Functionally, marrow adipocytes secrete adipokines, such as adiponectin, and cytokines, such as RANK ligand and stem cell factor. These mediators can influence both bone remodelling and haematopoiesis by promoting bone resorption and haematopoietic recovery following chemotherapy. In addition, marrow adipocytes can secrete free fatty acids, acting as a energy supply for bone and haematopoietic cells. However, this induced lipolysis is also used by neoplastic cells to promote survival and proliferation. Therefore, MAT could represent a new therapeutic target for multiple diseases from osteoporosis to leukaemia, although the exact characteristics and role of the marrow adipocyte in health and diseases remain to be determined.

Intracellular Follicle-Stimulating Hormone Receptor Trafficking and Signaling

Models of G protein-coupled receptor (GPCR) signaling have dramatically altered over the past two decades. Indeed, GPCRs such as the follicle-stimulating hormone receptor (FSHR) have contributed to these new emerging models. We now understand that receptor signaling is highly organized at a spatial level, whereby signaling not only occurs from the plasma membrane but distinct intracellular compartments. Recent studies in the role of membrane trafficking and spatial organization of GPCR signaling in regulating gonadotropin hormone receptor activity has identified novel intracellular compartments, which are tightly linked with receptor signaling and reciprocally regulated by the cellular trafficking machinery. Understanding the impact of these cell biological mechanisms to physiology and pathophysiology is emerging for certain GPCRs. However, for FSHR, the potential impact in both health and disease and the therapeutic possibilities of these newly identified systems is currently unknown, but offers the potential to reassess prior strategies, or unveil novel opportunities, in targeting this receptor.

Lessons from Cre-Mice and Indicator Mice

The adult human adipose tissue is predominantly composed of white adipocytes. However, within certain depots, adipose tissue contains thermogenically active brown-like adipocytes, which have been evolutionarily conserved in mammals. This chapter will give a brief overview on the methods used to genetically target and trace both white and brown adipocytes using techniques such as bacterial artificial chromosome (BAC) cloning to create transgenic mouse models and the tools with which genetic recombination is mediated in vivo (e.g., Cre-loxP, CreERT, and Tet-On). The chapter furthermore critically discusses the strength and limitation of the various systems used to target mature white and brown adipocytes (ap2-Cre, Adipoq-Cre, and Ucp1-Cre). Based on these systems, it is evident that our knowledge of mature adipocyte categorization into brown, white, brite, or beige adipocytes is strongly influenced by the use of the various genetic mouse models described in this chapter. Our evaluation of different studies using the aforementioned systems focuses on key genes, which have been reported to maintain adipocyte's function (insulin receptor, Raptor, or Atgl).

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.

Structure-Function Relationships of the Follicle-Stimulating Hormone Receptor

The follicle-stimulating hormone receptor (FSHR) plays a crucial role in reproduction. This structurally complex receptor is a member of the G-protein coupled receptor (GPCR) superfamily of membrane receptors. As with the other structurally similar glycoprotein hormone receptors (the thyroid-stimulating hormone and luteinizing hormone-chorionic gonadotropin hormone receptors), the FSHR is characterized by an extensive extracellular domain, where binding to FSH occurs, linked to the signal specificity subdomain or hinge region. This region is involved in ligand-stimulated receptor activation whereas the seven transmembrane domain is associated with receptor activation and transmission of the activation process to the intracellular loops comprised of amino acid sequences, which predicate coupling to effectors, interaction with adapter proteins, and triggering of downstream intracellular signaling. In this review, we describe the most important structural features of the FSHR intimately involved in regulation of FSHR function, including trafficking, dimerization, and oligomerization, ligand binding, agonist-stimulated activation, and signal transduction.

Small Molecule Follicle-Stimulating Hormone Receptor Agonists and Antagonists

The follicle-stimulating hormone receptor (FSHR) has been targeted therapeutically for decades, due to its pivotal role in reproduction. To date, only purified and recombinant/biosimilar FSH have been used to target FSHR in assisted reproduction, with the exception of corifollitropin alfa; a modified gonadotropin in which the FSH beta subunit is joined to the C-terminal peptide of the human choriogonadotropin beta subunit, to extend serum half-life. Assisted reproduction protocols usually entail the trauma of multiple injections of FSH to initiate and promote folliculogenesis, which has prompted the development of a number of orally-available low molecular weight (LMW) chemical scaffolds targeting the FSHR. Furthermore, the recently documented roles of the FSHR in diverse extragonadal tissues, including cancer, fat metabolism, and bone density regulation, has highlighted the potential utility of LMW modulators of FSHR activity. Despite these chemical scaffolds encompassing a spectrum of in vitro and in vivo activities and pharmacological profiles, none have yet reached the clinic. In this review we discuss the major chemical classes of LMW molecules targeting the FSHR, and document their activity profiles and current status of development, in addition to discussing potential clinical applications.

Can FSH influence longevity?

It was recently reported that the extragonadal actions of follicle‐stimulating hormone (FSH) include regulation of brown and white adipose tissue function and thermogenesis. Based on these findings and on our evidence for reduced FSH levels and enhanced thermogenesis in long‐lived growth hormone (GH)‐deficient mice and GH‐resistant mice, we suggest that FSH may have a role in the control of aging and longevity. We speculate that alterations in FSH secretion may represent one of the mechanisms of trade‐offs between reproduction and aging.

Chenodeoxycholic acid attenuates high-fat diet-induced obesity and hyperglycemia via the G protein-coupled bile acid receptor 1 and proliferator-activated receptor γ pathway

G protein-coupled bile acid receptor 1 (TGR5) serves a key function in regulating glycometabolism. TGR5 is highly expressed in the mitochondria of brown adipose tissue (BAT) and downregulates adenosine triphosphate synthesis via the bile acid-TGR5-cyclic adenosine monophosphate-2-iodothyronine deiodinase (D2)-triiodothyronine-uncoupling protein pathway, thus regulating energy homeostasis and reducing body weight. Chenodeoxycholic acid (CDCA), the primary bile acid, is a natural ligand of TGR5. The present study aimed to characterize the ability of CDCA to reduce high-fat diet-induced obesity and improve glucose tolerance. A mouse model of diet-induced obesity was constructed. The results demonstrated that a high-fat diet significantly increased the weight of mice after 10 weeks (P<0.05), but following the addition of CDCA and continued feeding for another 10 weeks, a decrease in weight was detected and no significant difference in final weight was observed between the high fat diet group treated with CDCA and the group fed a normal diet. Furthermore, CDCA treatment significantly increased glucose tolerance (P<0.001, P<0.01 and P<0.01 at 15, 40 and 60 min after glucose injection, respectively) and significantly decreased serum insulin levels compared with mice fed a high-fat diet alone. Staining of the liver with hematoxylin and eosin and oil red O revealed that the CDCA-treated group exhibited significantly lower fat accumulation in BAT and WAT compared with mice fed a high-fat diet alone (P<0.001). Reverse transcription-quantitative polymerase chain reaction analysis demonstrated that the expression of D2 activation system-related factors was significantly increased in BAT from mice treated with CDCA (P<0.001), confirming the role of TGR5 in modulating high-fat diet-induced obesity. In addition, CDCA inhibited adipocyte differentiation in 3T3-L1 cells and inhibited ligand-stimulated peroxisome proliferator-activated receptor γ (PPARγ) transcriptional activity. These results suggest that CDCA may prevent high-fat diet-induced obesity and hyperglycemia, and that these beneficial effects are mediated via the activation of TGR5 and inhibition of PPARγ transcriptional activity.

Inflammation and bone mineral density: A Mendelian randomization study

Osteoporosis is a common age-related disorder leading to an increase in osteoporotic fractures and resulting in significant suffering and disability. Inflammation may contribute to osteoporosis, as it does to many other chronic diseases. We examined whether inflammation is etiologically relevant to osteoporosis, assessed from bone mineral density (BMD), as a new potential target of intervention, or whether it is a symptom/biomarker of osteoporosis. We obtained genetic predictors of inflammatory markers from genome-wide association studies and applied them to a large genome wide association study of BMD. Using two-sample Mendelian randomization, we obtained unconfounded estimates of the effect of high-sensitivity C-reactive protein (hsCRP) on BMD at the forearm, femoral neck, and lumbar spine. After removing potentially pleiotropic single nucleotide polymorphisms (SNPs) possibly acting via obesity-related traits, hsCRP, based on 16 SNPs from genes including CRP, was not associated with BMD. A causal relation of hsCRP with lower BMD was not evident in this study.

Burning Fat and Building Bone by FSH Blockade

The rise of follicle-stimulating hormone (FSH) is a hallmark of menopause associated with osteoporosis and visceral adiposity. In Nature, Zaidi and colleagues (Liu et al., 2017) report that blocking FSH action reduces body fat by promoting brown/beige fat thermogenesis, potentially providing a new intervention for the treatment of menopause-related metabolic diseases.

Papers of note in Nature (7656)

This week’s articles highlight the role of follicle-stimulating hormone in postmenopausal adipose tissue accumulation, the importance of a sphingolipid for T cell survival, and the cryo-EM structure of a G protein–coupled receptor complex.