FGF21
Encyclopedia
Fibroblast growth factor 21 is a protein
that in humans is encoded by the FGF21 gene
. The protein
encoded by this gene is a member of the fibroblast growth factor
(FGF) family. FGF family members possess broad mitogenic and cell survival activities and are involved in a variety of biological processes including embryonic development
, cell growth, morphogenesis
, tissue repair, tumor growth and invasion.
In mice, brown adipose tissue becomes a source of systemic FGF21 after cold exposure. Norepinephrine, acting via β-adrenergic, cAMP-mediated, mechanisms and subsequent activation of protein kinase A and p38 MAPK, induces FGF21 gene transcription and also FGF21 release in brown adipocytes. ATF2 binding to the FGF21 gene promoter mediates cAMP-dependent induction of FGF21 gene transcription. Release of FGF21 by brown fat in vivo was accompanied by a reduction in systemic FGF21 half-life.
LXR represses FGF21 in humans via an LXR response element located from -37 to -22 bp on the human FGF21 promoter.
uptake in adipocyte
s but not in other cell types. This effect is additive to the activity of insulin
. FGF21 treatment of adipocytes is associated with phosphorylation
of FRS2
, a protein linking FGF receptors to the Ras/MAP kinase pathway
. FGF21 injection in ob/ob mice
results in an increase in Glut1
in adipose tissue. FGF21 also protects animals from diet-induced obesity
when overexpressed in transgenic mice and lowers blood glucose and triglyceride
levels when administered to diabetic
rodents. Treatment of animals with FGF21 results in increased energy expenditure, fat utilization and lipid excretion.
Beta Klotho functions as a cofactor essential for FGF21 activity.
In cows plasma FGF21 was nearly undetectable in late pregnancy, peaked at parturition, and then stabilized at lower, chronically elevated concentrations during early lactation. Plasma FGF21 was similarly increased in the absence of parturition when an energy-deficit state was induced by feed restricting late-lactating dairy cows, implicating energy insufficiency as a cause of chronically elevated FGF21 in EL. The liver was the major source of plasma FGF21 in early lactation with little or no contribution by WAT, skeletal muscle, and mammary gland. Meaningful expression of the FGF21 coreceptor β-Klotho was restricted to liver and WAT in a survey of 15 tissues that included the mammary gland. Expression of β-Klotho and its subset of interacting FGF receptors was modestly affected by the transition from LP to EL in liver but not in WAT.
Mice lacking FGF21 fail to fully induce PGC-1alpha expression in response to a prolonged fast and have impaired gluconeogenesis and ketogenesis.
FGF21 stimulates phosphorylation of fibroblast growth factor receptor substrate 2 and ERK1/2 in the liver. Acute FGF21 treatment induced hepatic expression of key regulators of gluconeogenesis, lipid metabolism, and ketogenesis including glucose-6-phosphatase, phosphoenol pyruvate carboxykinase, 3-hydroxybutyrate dehydrogenase type 1, and carnitine palmitoyltransferase 1α. In addition, injection of FGF21 was associated with decreased circulating insulin
and free fatty acid levels. FGF21 treatment induced mRNA and protein expression of PGC-1α, but in mice PGC-1α expression was not necessary for the effect of FGF21 on glucose metabolism.
In mice FGF21 is strongly induced in liver by prolonged fasting via PPARalpha and in turn induces the transcriptional coactivator PGC-1α and stimulates hepatic gluconeogenesis, fatty acid oxidation, and ketogenesis. FGF21 also blocks somatic growth and sensitizes mice to a hibernation-like state of torpor, playing a key role in eliciting and coordinating the adaptive starvation response. FGF21 expression is also induced in white adipose tissue by PPARgamma, which may indicate it also regulates metabolism in the fed state.
Activation of AMPK and SIRT1 by FGF21 in adipocytes enhanced mitochondrial oxidative capacity as demonstrated by increases in oxygen consumption, citrate synthase activity, and induction of key metabolic genes. The effects of FGF21 on mitochondrial function require serine/threonine kinase 11 (STK11/LKB1), which activates AMPK. Inhibition of AMPK, SIRT1, and PGC-1alpha activities attenuated the effects of FGF21 on oxygen consumption and gene expression, indicating that FGF21 regulates mitochondrial activity and enhances oxidative capacity through an LKB1-AMPK-SIRT1-PGC1alpha-dependent mechanism in adipocytes, resulting in increased phosphorylation of AMPK, increased cellular NAD+ levels and activation of SIRT1 and deacetylation of SIRT1 targets PGC-1alpha and histone 3.
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
that in humans is encoded by the FGF21 gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
. The protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
encoded by this gene is a member of the fibroblast growth factor
Fibroblast growth factor
Fibroblast growth factors, or FGFs, are a family of growth factors involved in angiogenesis, wound healing, and embryonic development. The FGFs are heparin-binding proteins and interactions with cell-surface associated heparan sulfate proteoglycans have been shown to be essential for FGF signal...
(FGF) family. FGF family members possess broad mitogenic and cell survival activities and are involved in a variety of biological processes including embryonic development
Embryogenesis
Embryogenesis is the process by which the embryo is formed and develops, until it develops into a fetus.Embryogenesis starts with the fertilization of the ovum by sperm. The fertilized ovum is referred to as a zygote...
, cell growth, morphogenesis
Morphogenesis
Morphogenesis , is the biological process that causes an organism to develop its shape...
, tissue repair, tumor growth and invasion.
Regulation
FGF21 is specifically induced by HMGCS2 activity. The oxidized form of ketone bodies (acetoacetate) in a cultured medium also induced FGF21, possibly via a SIRT1-dependent mechanism. HMGCS2 activity has also been shown to be increased by deacetylation of lysines 310, 447, and 473 via SIRT3 in the mitochondria.In mice, brown adipose tissue becomes a source of systemic FGF21 after cold exposure. Norepinephrine, acting via β-adrenergic, cAMP-mediated, mechanisms and subsequent activation of protein kinase A and p38 MAPK, induces FGF21 gene transcription and also FGF21 release in brown adipocytes. ATF2 binding to the FGF21 gene promoter mediates cAMP-dependent induction of FGF21 gene transcription. Release of FGF21 by brown fat in vivo was accompanied by a reduction in systemic FGF21 half-life.
LXR represses FGF21 in humans via an LXR response element located from -37 to -22 bp on the human FGF21 promoter.
Function
FGF21 stimulates glucoseGlucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
uptake in adipocyte
Adipocyte
However, in some reports and textbooks, the number of fat cell increased in childhood and adolescence. The total number is constant in both obese and lean adult...
s but not in other cell types. This effect is additive to the activity of insulin
Insulin
Insulin is a hormone central to regulating carbohydrate and fat metabolism in the body. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle....
. FGF21 treatment of adipocytes is associated with phosphorylation
Phosphorylation
Phosphorylation is the addition of a phosphate group to a protein or other organic molecule. Phosphorylation activates or deactivates many protein enzymes....
of FRS2
FRS2
Fibroblast growth factor receptor substrate 2 is a protein that in humans is encoded by the FRS2 gene.-Interactions:FRS2 has been shown to interact with PRKCI, Grb2, PTPN11, Fibroblast growth factor receptor 1, TrkA, Cbl gene and SOS1....
, a protein linking FGF receptors to the Ras/MAP kinase pathway
MAPK/ERK pathway
The MAPK/ERK pathway is a chain of proteins in the cell that communicates a signal from a receptor on the surface of the cell to the DNA in the nucleus of the cell. The signal starts when a growth factor binds to the receptor on the cell surface and ends when the DNA in the nucleus expresses a...
. FGF21 injection in ob/ob mice
Ob/ob mice
The ob/ob or obese mouse is a mutant mouse that eats excessively and becomes profoundly obese. It is an animal model of type II diabetes. Identification of the gene mutated in ob led to the discovery of the hormone leptin, which is important in the control of appetite.The first ob/ob mouse arose by...
results in an increase in Glut1
GLUT1
Glucose transporter 1 , also known as solute carrier family 2, facilitated glucose transporter member 1 is a protein that in humans is encoded by the SLC2A1 gene...
in adipose tissue. FGF21 also protects animals from diet-induced obesity
Obesity
Obesity is a medical condition in which excess body fat has accumulated to the extent that it may have an adverse effect on health, leading to reduced life expectancy and/or increased health problems...
when overexpressed in transgenic mice and lowers blood glucose and triglyceride
Triglyceride
A triglyceride is an ester derived from glycerol and three fatty acids. There are many triglycerides, depending on the oil source, some are highly unsaturated, some less so....
levels when administered to diabetic
Diabetes mellitus
Diabetes mellitus, often simply referred to as diabetes, is a group of metabolic diseases in which a person has high blood sugar, either because the body does not produce enough insulin, or because cells do not respond to the insulin that is produced...
rodents. Treatment of animals with FGF21 results in increased energy expenditure, fat utilization and lipid excretion.
Beta Klotho functions as a cofactor essential for FGF21 activity.
In cows plasma FGF21 was nearly undetectable in late pregnancy, peaked at parturition, and then stabilized at lower, chronically elevated concentrations during early lactation. Plasma FGF21 was similarly increased in the absence of parturition when an energy-deficit state was induced by feed restricting late-lactating dairy cows, implicating energy insufficiency as a cause of chronically elevated FGF21 in EL. The liver was the major source of plasma FGF21 in early lactation with little or no contribution by WAT, skeletal muscle, and mammary gland. Meaningful expression of the FGF21 coreceptor β-Klotho was restricted to liver and WAT in a survey of 15 tissues that included the mammary gland. Expression of β-Klotho and its subset of interacting FGF receptors was modestly affected by the transition from LP to EL in liver but not in WAT.
Clinical Significance
Serum FGF-21 levels were significantly increased in patients with T2DM which may indicate a role in the pathogenesis of T2DM. Elevated levels also correlate with liver fat content in non-alcoholic fatty liver disease and positively correlate with BMI in humans suggesting obesity as a FGF21-resistant state.Mice lacking FGF21 fail to fully induce PGC-1alpha expression in response to a prolonged fast and have impaired gluconeogenesis and ketogenesis.
FGF21 stimulates phosphorylation of fibroblast growth factor receptor substrate 2 and ERK1/2 in the liver. Acute FGF21 treatment induced hepatic expression of key regulators of gluconeogenesis, lipid metabolism, and ketogenesis including glucose-6-phosphatase, phosphoenol pyruvate carboxykinase, 3-hydroxybutyrate dehydrogenase type 1, and carnitine palmitoyltransferase 1α. In addition, injection of FGF21 was associated with decreased circulating insulin
Insulin
Insulin is a hormone central to regulating carbohydrate and fat metabolism in the body. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle....
and free fatty acid levels. FGF21 treatment induced mRNA and protein expression of PGC-1α, but in mice PGC-1α expression was not necessary for the effect of FGF21 on glucose metabolism.
In mice FGF21 is strongly induced in liver by prolonged fasting via PPARalpha and in turn induces the transcriptional coactivator PGC-1α and stimulates hepatic gluconeogenesis, fatty acid oxidation, and ketogenesis. FGF21 also blocks somatic growth and sensitizes mice to a hibernation-like state of torpor, playing a key role in eliciting and coordinating the adaptive starvation response. FGF21 expression is also induced in white adipose tissue by PPARgamma, which may indicate it also regulates metabolism in the fed state.
Activation of AMPK and SIRT1 by FGF21 in adipocytes enhanced mitochondrial oxidative capacity as demonstrated by increases in oxygen consumption, citrate synthase activity, and induction of key metabolic genes. The effects of FGF21 on mitochondrial function require serine/threonine kinase 11 (STK11/LKB1), which activates AMPK. Inhibition of AMPK, SIRT1, and PGC-1alpha activities attenuated the effects of FGF21 on oxygen consumption and gene expression, indicating that FGF21 regulates mitochondrial activity and enhances oxidative capacity through an LKB1-AMPK-SIRT1-PGC1alpha-dependent mechanism in adipocytes, resulting in increased phosphorylation of AMPK, increased cellular NAD+ levels and activation of SIRT1 and deacetylation of SIRT1 targets PGC-1alpha and histone 3.