Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) play complementary roles in follicle development and ovulation via a complex interaction in the hypothalamus, anterior pituitary gland, ...reproductive organs, and oocytes. Impairment of the production or action of gonadotropins causes relative or absolute LH and FSH deficiency that compromises gametogenesis and gonadal steroid production, thereby reducing fertility. In women, LH and FSH deficiency is a spectrum of conditions with different functional or organic causes that are characterized by low or normal gonadotropin levels and low oestradiol levels. While the causes and effects of reduced LH and FSH production are very well known, the notion of reduced action has received less attention by researchers. Recent evidence shows that molecular characteristics, signalling as well as ageing, and some polymorphisms negatively affect gonadotropin action. These findings have important clinical implications, in particular for medically assisted reproduction in which diminished action determined by the afore-mentioned factors, combined with reduced endogenous gonadotropin production caused by GnRH analogue protocols, may lead to resistance to gonadotropins and, thus, to an unexpected hypo-response to ovarian stimulation. Indeed, the importance of LH and FSH action has been highlighted by the International Committee for Monitoring Assisted Reproduction Technologies (ICMART) in their definition of hypogonadotropic hypogonadism as gonadal failure associated with reduced gametogenesis and gonadal steroid production due to reduced gonadotropin production or action. The aim of this review is to provide an overview of determinants of reduced FSH and LH action that are associated with a reduced response to ovarian stimulation.
Intracellular variable fragments of heavy‐chain antibody from camelids (intra‐VHH) have been successfully used as chaperones to solve the 3D structure of active G protein‐coupled receptors bound to ...their transducers. However, their effect on signalling has been poorly explored, although they may provide a better understanding of the relationships between receptor conformation and activity. Here, we isolated and characterized iPRC1, the first intra‐VHH recognizing a member of the large glycoprotein hormone receptor family, the follicle‐stimulating hormone receptor (FSHR). This intra‐VHH recognizes the FSHR third intracellular loop and decreases cAMP production in response to FSH, without altering Gαs recruitment. Hence, iPRC1 behaves as an allosteric modulator and provides a new tool to complete structure/activity studies performed thus far on this receptor.
This article reports the characterization of a new intracellular single‐domain antibody (VHH) specific of the third intracellular loop of the follicle‐stimulating hormone receptor. Since it hinders Gαs full activity, it is one of a few negative allosteric intrabodies acting at a G protein‐coupled receptor.
Menopause is associated with bone loss and enhanced visceral adiposity. A polyclonal antibody that targets the β-subunit of the pituitary hormone follicle-stimulating hormone (Fsh) increases bone ...mass in mice. Here, we report that this antibody sharply reduces adipose tissue in wild-type mice, phenocopying genetic haploinsufficiency for the Fsh receptor gene Fshr. The antibody also causes profound beiging, increases cellular mitochondrial density, activates brown adipose tissue and enhances thermogenesis. These actions result from the specific binding of the antibody to the β-subunit of Fsh to block its action. Our studies uncover opportunities for simultaneously treating obesity and osteoporosis.
Follicle-stimulating hormone receptor (FSHR), a G-protein coupled receptor, is an important drug target in the development of novel therapeutics for reproductive indications. The FSHR extracellular ...domains were observed in the crystal structure as a trimer, which enabled us to propose a novel model for the receptor activation mechanism. The model predicts that FSHR binds Asnα52-deglycosylated FSH at a 3-fold higher capacity than fully glycosylated FSH. It also predicts that, upon dissociation of the FSHR trimer into monomers, the binding of glycosylated FSH, but not deglycosylated FSH, would increase 3-fold, and that the dissociated monomers would in turn enhance FSHR binding and signaling activities by 3-fold. This study presents evidence confirming these predictions and provides crystallographic and mutagenesis data supporting the proposed model. The model also provides a mechanistic explanation to the agonist and antagonist activities of thyroid-stimulating hormone receptor autoantibodies. We conclude that FSHR exists as a functional trimer.
A carbohydrate of follicle-stimulating hormone (FSH) has been proposed to sterically block other FSH molecules from binding to the putative receptor (FSHR) trimer.
FSH increases its receptor binding by 3-fold when the steric hindrance is removed.
FSHR forms a functional trimer.
This knowledge may improve designs of therapeutic drugs targeting FSHR.
AbstractObjectiveCongenital FSH deficiency is an exceptional cause of male infertility most often attributed to FSH β gene mutations. The few published cases report azoospermia, severe testicular ...hypotrophy and normal testosterone levels associated with normal virilization. We report the exploration of two young men aged 26 and 27 years with severe sperm abnormalities, moderate testicular hypotrophy and isolated FSH deficiency. MethodsSeveral FSH, LH, total testosterone and inhibin B assays and FSH β gene sequencing were performed. ResultsFSH was almost undetectable at baseline and poorly responsive to GnRH test, whereas LH was normal at baseline and increased after GnRH test. Testosterone levels were within the adult range, while inhibin B levels were upper-normal to high. No FSH β gene mutations were found. Exogenous FSH treatment was followed by spontaneous pregnancy in one case and required intra-cytoplasmic sperm injection (ICSI) in the other. ConclusionsThe paradoxical high levels of inhibin B reflect the presence of functional Sertoli cells and may explain the isolated FSH deficiency. An intra-gonadal factor stimulating inhibin B secretion is discussed.
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.
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