FGF 19 Human, His
Description
Table 1: Production Systems for FGF19 Human, His
| Expression Host | Molecular Weight | Glycosylation | Purity | Source |
|---|---|---|---|---|
| HEK293 cells | 23.0 kDa | Yes | >95% (SDS-PAGE) | Prospec Bio |
| E. coli | 23.4 kDa | No | >95% (SDS-PAGE) | ACROBiosystems |
Biochemical Assays
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Binding Affinity: FGF19 Human, His binds FGFR4 with an affinity constant (K<sub>D</sub>) of 16.6–63.5 nM, validated via BLI assays .
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Stability: Lyophilized formulations maintain activity at -20°C for long-term storage but require reconstitution in buffers containing arginine or trehalose .
Clinical Correlations
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Liver Disease: Elevated hepatic FGF19 levels correlate with cholestatic liver injury severity (e.g., primary biliary cholangitis) .
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Atherosclerosis: Higher serum FGF19 predicts subclinical atherosclerosis in men with type 2 diabetes (OR = 4.798 per SD increase) .
Table 2: Clinical Associations of FGF19 Levels
Therapeutic Potential
Product Specs
Q&A
What is FGF-19 and what distinguishes it from other FGF family members?
FGF-19 (Fibroblast Growth Factor 19) belongs to the endocrine subfamily of FGFs, which sets it apart from the paracrine-acting FGF subfamilies. The endocrine FGF19 subfamily (comprising FGF19, FGF21, and FGF23) is characterized by poor affinity for heparan sulfate (HS), allowing these proteins to diffuse freely in the HS-rich extracellular matrix and enter the bloodstream. This distinguishes them from paracrine FGFs that remain localized to their site of production. Additionally, FGF-19 has unusually poor affinity for its cognate FGF receptors (FGFRs) and requires βklotho coreceptor proteins to bind, dimerize, and activate these receptors .
Unlike other FGF subfamily members that show high sequence identity (54-88% between members), the FGF19 subfamily exhibits relatively low sequence identity, ranging from 33% between FGF21 and FGF23 to 38% between FGF19 and FGF21. Much of this divergence stems from the heparan sulfate binding site (HBS) regions, with identity in these regions as low as 13% .
What are the structural characteristics of human FGF-19 protein?
The recombinant human FGF-19 protein typically has a molecular mass of approximately 23 kDa in reduced conditions and 22 kDa in non-reduced conditions. It exists as a non-glycosylated monomer . The protein sequence spans from Phe27 to Lys216 of the full-length protein (Accession # O95750) .
How does the FGF-19 signaling pathway function?
FGF-19 primarily binds and activates signaling pathways downstream of FGFR4 in the liver. Unlike paracrine FGFs that can activate their receptors solely through HS-dependent mechanisms, FGF-19 requires βklotho as a coreceptor to bind, dimerize, and activate its cognate FGFRs. This requirement for βklotho restricts FGF-19 signaling to tissues where βklotho is expressed .
The signaling cascade begins when FGF-19 binds to the FGFR4-βklotho complex, causing dimerization of the receptor's extracellular domains. This juxtaposes the intracellular kinase domains, allowing them to trans-phosphorylate each other on the A-loop tyrosines. This phosphorylation increases the intrinsic kinase activity by stabilizing the active conformation of the kinase, initiating downstream signaling cascades .
What is the endocrine axis mediated by FGF-19 and how does it regulate bile acid metabolism?
FGF-19 is a crucial component of an intestine-liver axis that forms a postprandial negative feedback loop regulating bile acid synthesis and release. Traditionally, it was understood that FGF-19 is secreted from intestinal epithelium in response to bile acid release into the intestinal lumen upon food intake .
Through binding to FGFR4 (its main cognate receptor) in the liver, FGF-19 downregulates the CYP7A1 enzyme, preventing overproduction of bile salts and contributing to their homeostasis .
What are the optimal methods for detecting FGF-19 expression in tissue samples?
For detecting FGF-19 in tissue samples, several methodologies can be employed depending on your research question:
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Western Blot: Antibodies specific to human FGF-19, such as goat anti-human FGF-19 antigen affinity-purified polyclonal antibody, can detect FGF-19 at approximately 22 kDa under reducing conditions. This method is effective for analyzing cell lysates and conditioned media from cell lines like COLO 205 and HT-29 .
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Simple Western™: This automated capillary-based immunoassay can detect FGF-19 at approximately 26 kDa in conditioned media from colorectal adenocarcinoma cell lines .
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Direct ELISA: Anti-FGF-19 antibodies can detect human FGF-19 with minimal cross-reactivity (<5%) with other FGF family members such as FGF-7 and FGF-21 .
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qRT-PCR: For measuring FGF-19 mRNA expression in tissues such as gallbladder, common bile duct, and ileum. This technique revealed that FGF-19 is abundantly expressed in the human gallbladder and common bile duct .
How can I establish an in vitro model to study FGF-19 signaling?
To establish an effective in vitro model for studying FGF-19 signaling:
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Cell Selection: Choose cell lines that express FGFR4 and βklotho, the essential components for FGF-19 signaling. Hepatocytes, cholangiocytes, and certain enteroendocrine and enterocytic cell lines are suitable .
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Recombinant Protein: Use high-quality recombinant human FGF-19 protein with verified activity (50-300 ng/mL is typically effective). HEK293-expressed, endotoxin-free preparations ensure physiological post-translational modifications and minimize experimental artifacts .
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Reconstitution Protocol: Carefully follow reconstitution protocols for lyophilized protein. Briefly centrifuge the vial before opening and reconstitute to 0.2 mg/mL in sterile 1x PBS (pH 7.4) containing 0.1% endotoxin-free recombinant human serum albumin (HSA). Gently mix to ensure complete dissolution .
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Signaling Readouts: Establish appropriate readouts for FGF-19 signaling, such as phosphorylation of downstream targets, changes in CYP7A1 expression, or alterations in glucose and lipid metabolism parameters.
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Controls: Include controls such as FGF-19 stimulation in the presence of FGFR4 or βklotho inhibitors/blockers to confirm signaling specificity.
What role does FGF-19 play in metabolic regulation beyond bile acid metabolism?
Beyond its well-established role in bile acid metabolism, FGF-19 functions as a key regulator of glucose and lipid metabolism, often working alongside FGF-21. Research has shown that FGF-19 can:
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Regulate Glucose Metabolism: FGF-19 improves glucose tolerance and insulin sensitivity in metabolic disorders .
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Influence Lipid Metabolism: It modulates lipid profiles and can reduce triglyceride levels, potentially offering therapeutic potential for dyslipidemia .
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Energy Expenditure: FGF-19 increases energy expenditure and can reduce body weight in experimental models of obesity .
How does FGF-19 contribute to hepatocellular carcinoma progression?
FGF-19 can stimulate hepatocyte proliferation, and elevated signaling levels have been correlated with the progression of hepatocellular carcinoma (HCC) . The mechanisms underlying this oncogenic potential include:
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Activation of Mitogenic Pathways: FGF-19, through binding to FGFR4 and βklotho, can activate downstream mitogenic signaling cascades that promote cell proliferation.
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Crosstalk with Tumor-Promoting Pathways: FGF-19 signaling may interact with other pathways involved in hepatocarcinogenesis.
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Alterations in Metabolic Programming: The metabolic effects of FGF-19 may create a microenvironment favorable for tumor growth.
Research has identified that the FGF19-FGFR4 axis represents a potential therapeutic target in HCC, with several approaches being explored to interrupt this signaling pathway in cancer treatment strategies .
How do the three members of the FGF19 subfamily (FGF19, FGF21, FGF23) differ in their physiological roles?
Despite belonging to the same subfamily, FGF19, FGF21, and FGF23 have distinct physiological roles:
| FGF Subfamily Member | Primary Tissue Source | Main Target Tissue | Co-receptor | Principal Physiological Role |
|---|---|---|---|---|
| FGF19 | Gallbladder, bile duct, ileum | Liver | βklotho | Regulates bile acid synthesis and glucose/lipid metabolism |
| FGF21 | Liver, pancreas, adipose tissue | Multiple tissues including liver, adipose tissue | βklotho | Regulates glucose homeostasis, ketogenesis, and energy expenditure |
| FGF23 | Bone | Kidney | αklotho | Regulates serum phosphate and vitamin D homeostasis |
FGF23 participates in a bone-kidney axis crucial for serum phosphate regulation. When serum phosphate rises, FGF23 is secreted from bone and activates FGFR1c in the kidney in an αklotho-dependent manner, promoting phosphate excretion and suppressing vitamin D biosynthesis .
While FGF19 and FGF21 both require βklotho as a coreceptor, they regulate different aspects of metabolism, with some overlapping functions in glucose and lipid homeostasis .
What are the challenges in developing FGF-19-based therapeutics for metabolic diseases?
Developing FGF-19-based therapeutics for metabolic diseases presents several challenges:
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Oncogenic Potential: FGF-19's ability to stimulate hepatocyte proliferation and its association with hepatocellular carcinoma progression raises safety concerns for long-term therapeutic use .
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Receptor Specificity: Ensuring targeted activation of metabolic pathways without triggering proliferative responses requires sophisticated drug design approaches.
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Delivery and Stability: As a protein therapeutic, FGF-19 faces challenges related to delivery, stability, and immunogenicity.
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Complex Signaling Network: FGF-19 participates in complex signaling networks with multiple feedback mechanisms, making it challenging to predict the full spectrum of effects from therapeutic intervention.
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Individual Variability: Differences in baseline FGF-19 levels, receptor expression, and pathway activity may lead to variable responses among patients.
Research approaches to address these challenges include developing FGF-19 analogs with modified receptor binding properties to retain metabolic benefits while eliminating proliferative effects, and exploring combination therapies that target multiple aspects of metabolic dysfunction .
Product Science Overview
The human recombinant FGF19 protein, often tagged with a His-tag for purification purposes, is typically expressed in systems such as E. coli or HEK293 cells . The His-tag, a sequence of histidine residues, facilitates the purification of the protein through affinity chromatography. The recombinant FGF19 protein encompasses amino acids 25-216, with a molecular weight of approximately 23.4 kDa .
FGF19 functions as a hormone-like protein, regulating several metabolic pathways:
- Bile Acid Metabolism: FGF19 is a key regulator of bile acid synthesis in the liver. It inhibits the enzyme cholesterol 7α-hydroxylase (CYP7A1), which is the rate-limiting step in bile acid synthesis .
- Glucose and Lipid Metabolism: FGF19 influences glucose and lipid metabolism, contributing to the maintenance of metabolic homeostasis .
- Cell Proliferation: At supra-physiological doses, FGF19 can increase hepatocyte proliferation and has been implicated in hepatocellular carcinogenesis in experimental models .
Alterations in FGF19 levels have been associated with various diseases:
- Primary Bile Acid Diarrhea: Defective levels of FGF19 can lead to primary bile acid diarrhea, a condition characterized by excessive bile acid synthesis .
- Cancer: Overexpression of FGF19 has been observed in several cancers, including prostate, bladder, and lung cancers. It is notably present in nearly half of hepatocellular carcinomas .
