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Aliases | FST , FS, follistatin | ||||||||||||||||||||||||||||||||||||||||||||||||||
External IDs | OMIM: 136470; MGI: 95586; HomoloGene: 7324; GeneCards: FST; OMA:FST - orthologs | ||||||||||||||||||||||||||||||||||||||||||||||||||
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Follistatin, also known as activin-bindings protein, is a protein that in humans is encoded by the FST gene. [5] [6] Follistatin is an autocrine glycoprotein that is expressed in nearly all tissues of higher animals. [6]
Its primary function is the binding and bioneutralization of members of the TGF-β superfamily, with a particular focus on activin, a paracrine hormone.
An earlier name for the same protein was FSH-suppressing protein (FSP). At the time of its initial isolation from follicular fluid, it was found to inhibit the anterior pituitary's secretion of follicle-stimulating hormone (FSH).
Follistatin is part of the inhibin-activin-follistatin axis.
Three isoforms, FS-288, FS-300, and FS-315 have been reported. Two, FS-288 and FS-315, are created by alternative splicing of the primary mRNA transcript. FS-300 (porcine follistatin) is thought to be the product of posttranslational modification via truncation of the C-terminal domain from the primary amino-acid chain.
Although FS is ubiquitous, its highest concentration is in the female ovary, followed by the skin.
Follistatin is produced by folliculostellate (FS) cells of the anterior pituitary. FS cells make numerous contacts with the classical endocrine cells of the anterior pituitary including gonadotrophs.
In tissues, activin plays a significant role in cellular proliferation, while follistatin acts as safeguard against uncontrolled cellular proliferation and an instrument of cellular differentiation. These roles are vital for rebuilding and repairing tissue, and may account for the high prevalence of follistatin in the skin.
In the blood, activin and follistatin are involved in the inflammatory response following tissue injury or pathogenic incursion. The source of follistatin in circulating blood plasma has yet to be determined; however, endothelial cells (lining blood vessels), or macrophages and monocytes (circulating within the blood) have been proposed as likely origins, given its autocrine nature.
Follistatin acts as an inhibitor for bone morphogenic proteins (BMPs) involved in embryo development. Since BMPs facilitate the ectoderm becoming the epidermal ectoderm, their inhibition allows the ectoderm to become the neuroectoderm - eventually forming the neural plate. Other inhibitors involved in this process are noggin and chordin.
Follistatin and BMPs also participate in folliculogenesis within the ovary. The main role of follistatin is for progression of the follicle from early antral to antral/dominant in the oestrus/menstrus ovary. Follistatin is also involved in the promotion of cellular differentiation of estrogen - by converting granulosa cells (GC) to progesterone in the dominant follicle - and production of large lutein cells (LLC) in the corpus luteum.
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Follistatin is studied for its role in regulation of muscle growth in mice, as an antagonist to myostatin (also known as GDF-8, a TGF superfamily member) which inhibits excessive muscle growth. Lee and McPherron demonstrated that inhibition of GDF-8, either by genetic elimination (knockout mice) or by increasing the amount of follistatin, resulted in increased muscle mass. [7] [8] In 2009, research with macaque monkeys demonstrated that regulating follistatin via gene therapy also resulted in muscle growth and increases in strength. [9]
Increased levels of follistatin, by leading to increased muscle mass of certain core muscular groups, can increase life expectancy in cases of spinal muscular atrophy (SMA) in animal models. [10]
Elevated circulating follistatin levels are also associated with increased risk of type 2 diabetes, early death, heart failure, stroke and chronic kidney disease. It has been demonstrated that follistatin contributes to insulin resistance in type 2 diabetes development and nonalcoholic fatty liver disease (NAFLD). The genetic regulation of follistatin secretion from the liver is via Glucokinase regulatory protein (GCKR) identified by large GWAS studies. [11] [12]
It is also investigated for its involvement in polycystic ovary syndrome (PCOS), in part to resolve debate as to its direct role in this disease. [13]
Sporadic inclusion body myositis, a variant of inflammatory myopathy, involves muscle weakness. In one clinical trial, rAAV1.CMV.huFS344, 6 × 1011 vg/kg, walk test results significantly improved versus untreated controls, along with decreased fibrosis and improved regeneration.
ACE-083, a follistatin-based fusion protein, was investigated for treatment focal or asymmetric myopathies. Intramuscular ACE-083 increased growth and force production in injected muscle in wild-type mice and mouse models of Charcot-Marie-Tooth disease (CMT) and Duchenne muscular dystrophy, without systemic effects or endocrine disruption. [14]
AAV-mediated FST reduced obesity-induced inflammatory adipokines and cytokines systemically and in synovial fluid. Mice receiving FST therapy were protected from post-traumatic osteoarthritis and bone remodeling from joint injury. [15]
In another mouse study, high dose animals showed significant quadriceps growth.
Luteinizing hormone is a hormone produced by gonadotropic cells in the anterior pituitary gland. The production of LH is regulated by gonadotropin-releasing hormone (GnRH) from the hypothalamus. In females, an acute rise of LH known as an LH surge, triggers ovulation and development of the corpus luteum. In males, where LH had also been called interstitial cell–stimulating hormone (ICSH), it stimulates Leydig cell production of testosterone. It acts synergistically with follicle-stimulating hormone (FSH).
Follicle-stimulating hormone (FSH) is a gonadotropin, a glycoprotein polypeptide hormone. FSH is synthesized and secreted by the gonadotropic cells of the anterior pituitary gland and regulates the development, growth, pubertal maturation, and reproductive processes of the body. FSH and luteinizing hormone (LH) work together in the reproductive system.
Myostatin is a protein that in humans is encoded by the MSTN gene. Myostatin is a myokine that is produced and released by myocytes and acts on muscle cells to inhibit muscle growth. Myostatin is a secreted growth differentiation factor that is a member of the TGF beta protein family.
Anti-Müllerian hormone (AMH), also known as Müllerian-inhibiting hormone (MIH), is a glycoprotein hormone structurally related to inhibin and activin from the transforming growth factor beta superfamily, whose key roles are in growth differentiation and folliculogenesis. In humans, it is encoded by the AMH gene, on chromosome 19p13.3, while its receptor is encoded by the AMHR2 gene on chromosome 12.
The hypothalamic–pituitary–gonadal axis refers to the hypothalamus, pituitary gland, and gonadal glands as if these individual endocrine glands were a single entity. Because these glands often act in concert, physiologists and endocrinologists find it convenient and descriptive to speak of them as a single system.
Bone morphogenetic protein 4 is a protein that in humans is encoded by BMP4 gene. BMP4 is found on chromosome 14q22-q23.
Activin receptor type-2A is a protein that in humans is encoded by the ACVR2A gene. ACVR2A is an activin type 2 receptor.
Activin receptor type-2B is a protein that in humans is encoded by the ACVR2B gene. ACVR2B is an activin type 2 receptor.
Growth differentiation factor 11 (GDF11), also known as bone morphogenetic protein 11 (BMP-11), is a protein that in humans is encoded by the growth differentiation factor 11 gene. GDF11 is a member of the Transforming growth factor beta family.
Inhibin, beta A, also known as INHBA, is a protein which in humans is encoded by the INHBA gene. INHBA is a subunit of both activin and inhibin, two closely related glycoproteins with opposing biological effects.
Inhibin, alpha, also known as INHA, is a protein which in humans is encoded by the INHA gene.
Follistatin-related protein 3 is a protein that in humans is encoded by the FSTL3 gene.
Serine-threonine kinase receptor-associated protein is an enzyme that in humans is encoded by the STRAP gene.
Follistatin-related protein 1 is a protein that in humans is encoded by the FSTL1 gene.
Inhibin, beta B, also known as INHBB, is a protein which in humans is encoded by the INHBB gene. INHBB is a subunit of both activin and inhibin, two closely related glycoproteins with opposing biological effects.
Activin and inhibin are two closely related protein complexes that have almost directly opposite biological effects. Identified in 1986, activin enhances FSH biosynthesis and secretion, and participates in the regulation of the menstrual cycle. Many other functions have been found to be exerted by activin, including roles in cell proliferation, differentiation, apoptosis, metabolism, homeostasis, immune response, wound repair, and endocrine function. Conversely, inhibin downregulates FSH synthesis and inhibits FSH secretion. The existence of inhibin was hypothesized as early as 1916; however, it was not demonstrated to exist until Neena Schwartz and Cornelia Channing's work in the mid-1970s, after which both proteins were molecularly characterized ten years later.
A myokine is one of several hundred cytokines or other small proteins and proteoglycan peptides that are produced and released by skeletal muscle cells in response to muscular contractions. They have autocrine, paracrine and/or endocrine effects; their systemic effects occur at picomolar concentrations.
WAP, follistatin/kazal, immunoglobulin, kunitz and netrin domain containing 2 is a protein that in humans is encoded by the WFIKKN2 gene.
Ovarian follicle activation can be defined as primordial follicles in the ovary moving from a quiescent (inactive) to a growing phase. The primordial follicle in the ovary is what makes up the “pool” of follicles that will be induced to enter growth and developmental changes that change them into pre-ovulatory follicles, ready to be released during ovulation. The process of development from a primordial follicle to a pre-ovulatory follicle is called folliculogenesis.
Myostatin inhibitors are a class of drugs that work by blocking the effect of myostatin, which inhibits muscle growth. In animal models and limited human studies, myostatin inhibitors have increased muscle size. They are being developed to treat obesity, sarcopenia, muscular dystrophy, and other illnesses.