FGF17 Human, His

What is human FGF17 and what signaling pathways does it activate?

Human FGF17 is a member of the fibroblast growth factor family, playing multiple roles in biological functions including angiogenesis, mitogenesis, cell differentiation, and wound repair. FGF17 signals through multiple FGF receptors including FGFR1c, FGFR2c, FGFR3c, and FGFR4 .

Research has demonstrated that FGF17 activates the FGF receptor 3/PI3K/AKT signaling pathway, which is particularly important in protecting against ischemia/reperfusion-induced blood-brain barrier disruption and endothelial cell apoptosis . Treatment with recombinant human FGF17 (rhFGF17) leads to nuclear factor erythroid 2-related factor 2 (Nrf2) nuclear accumulation and upregulation of heme oxygenase-1 (HO-1) expression, suggesting involvement in antioxidant response pathways .

How does FGF17 differ structurally and functionally from other FGF family members?

FGF17 belongs to the FGF8 subfamily and shares high sequence homology with FGF8 and FGF18. Human and mouse FGF17 share 93% identity, indicating high evolutionary conservation . The protein consists of 195 amino acid residues with a molecular weight of approximately 22.7 kDa .

Unlike some other FGF family members with multiple isoforms, human FGF17 has just two isoforms: FGF17a and FGF17b, with FGF17b considered the canonical sequence . This contrasts with mouse FGF17, which has three isoforms .

A distinguishing functional characteristic of FGF17 is its potency as a mitogen in certain contexts. Studies have shown that low-dose recombinant FGF17 (1 ng/ml) is a more potent mitogen than rFGF1 and rFGF8 in prostate cancer cell lines (LNCaP, DU145, and PC3M) .

What are the optimal conditions for using recombinant human FGF17 in cell-based assays?

For optimal FGF17 activity in cell-based assays, researchers should consider the following parameters based on published studies:

When reconstituting lyophilized recombinant FGF17, it's recommended to:

• For carrier-containing protein: Reconstitute at 25 μg/mL in sterile PBS containing at least 0.1% human or bovine serum albumin .

• For carrier-free protein: Reconstitute at 100 μg/mL in sterile PBS .

How can I validate the biological activity of recombinant FGF17 in my experimental system?

Validating FGF17 activity requires multiple complementary approaches:

• Proliferation assays: Measure cell proliferation using:

  • Fluorometric assays with redox-sensitive dyes like Resazurin

  • 3H-thymidine incorporation to measure DNA synthesis

  • The ED50 for proliferation should be in the range of 15-500 ng/mL depending on the assay method

• Signaling pathway activation: Western blotting for:

  • Phosphorylated FGFR1c, 2c, 3c, or 4

  • Phosphorylated AKT (as FGF17 activates the PI3K/AKT pathway)

  • Nuclear translocation of Nrf2

  • Increased expression of HO-1

• Functional assays for specific contexts:

  • For BBB studies: measure trans-endothelial electrical resistance, reduced sodium fluorescein leakage, and decreased ROS generation in brain endothelial cells

  • For prostate cancer studies: compare potency to other FGFs in proliferation assays

What technical challenges might I encounter when expressing recombinant human FGF17?

When expressing recombinant human FGF17, researchers may encounter several technical challenges:

• Protein solubility issues: The yield of soluble rhFGF17 in E. coli expression systems may be limited by inclusion body formation .

• Maintaining biological activity: Ensuring proper folding of the protein, especially after purification from inclusion bodies, is critical for maintaining biological activity .

• Purity considerations: His-tagged FGF17 purification requires optimization to achieve sufficient purity while maintaining activity.

• Storage stability: FGF17 requires careful handling to avoid freeze-thaw cycles. It's recommended to use a manual defrost freezer and avoid repeated freeze-thaw cycles .

• Heparin dependency: Like other FGFs, FGF17 activity is modulated by heparin, which should be included in activity assays at concentrations between 1-10 μg/mL depending on the experimental system .

How is FGF17 implicated in cancer progression and what are the methodological approaches to study this relationship?

FGF17 shows significant upregulation in prostate cancer with strong correlation to disease aggressiveness. Research has revealed:

• Expression correlation with disease severity:

  • A significant linear correlation exists between increasing Gleason sum scores and FGF17 expression using both immunohistochemistry (p < 0.0001, rho = 0.99) and RT-PCR (p = 0.008, rho = 0.99)

  • High-grade prostate cancer (Gleason sum score 7-10) shows approximately fourfold upregulation of FGF17 mRNA expression compared to benign prostatic hyperplasia (p < 0.0001)

  • Patients with tumors displaying high FGF17 expression have worse survival outcomes (p = 0.044) and higher risk of metastatic progression (p < 0.0001)

• Methodological approaches for studying FGF17 in cancer:

  • Semi-quantitative RT-PCR to assess mRNA expression levels in tumor vs. normal tissue

  • Immunohistochemistry for protein-level analysis with correlation to clinicopathological parameters

  • In vitro proliferation assays comparing FGF17 potency to other FGFs

  • Analysis of cross-talk between FGF17 and FGF8, as FGF8 induces expression of FGF17 in prostate cancer cell lines

• Experimental models:

  • Prostate cancer cell lines (LNCaP, DU145, and PC3M) have been validated for FGF17 studies

  • Patient tissue samples can be analyzed by comparing cancer specimens with different Gleason scores to benign prostatic hyperplasia samples

What is the role of FGF17 in neuroprotection and how can researchers study its therapeutic potential?

Recent research has uncovered FGF17's neuroprotective role in cerebral ischemia, providing several methodological approaches to study its therapeutic potential:

• Observed pathophysiological changes:

  • Reduced FGF17 levels in serum of ischemic stroke patients

  • Decreased FGF17 expression in mouse brains after middle cerebral artery occlusion (MCAO)

  • Reduced FGF17 in oxygen-glucose deprivation/reoxygenation (OGD/R)-treated brain microvascular endothelial cells

• Therapeutic effects of rhFGF17 administration:

  • Decreased infarct volume

  • Improved neurological deficits

  • Reduced Evans Blue leakage (indicating preserved BBB integrity)

  • Upregulated tight junction protein expression

• In vitro experimental approaches:

  • Brain microvascular endothelial cell (bEnd.3) model with OGD/R

  • Trans-endothelial electrical resistance measurement

  • Sodium fluorescein leakage assays

  • ROS detection assays

  • Cell viability assessment

• Molecular mechanism studies:

  • FGF receptor 3/PI3K/AKT signaling pathway activation analysis

  • Nrf2 nuclear translocation assessment

  • HO-1 expression quantification

  • Apoptosis marker analysis

How can I reconcile contradictory findings about FGF17 function in different experimental systems?

When facing contradictory results regarding FGF17 function, consider these methodological approaches to reconciliation:

• Context-dependent effects analysis:

  • Systematically compare cell types, as FGF17 effects may vary due to differential receptor expression

  • Evaluate developmental timing influences, as FGF17 functions are stage-specific

  • Assess disease state context (normal vs. pathological conditions)

• Concentration-dependent response profiling:

  • Perform comprehensive dose-response studies (1-750 ng/mL) based on published effective concentrations

  • Consider that low concentrations (1 ng/mL) may be more potent for cancer cell proliferation

  • Higher concentrations (100-500 ng/mL) may be required for other cell types

• Experimental design harmonization:

  • Standardize heparin concentrations (1-10 μg/mL) across experiments

  • Compare in vitro findings with in vivo models

  • Distinguish between acute and chronic FGF17 exposure effects

• Isoform specification:

  • Clearly identify which FGF17 isoform (FGF17a or FGF17b) is being studied

  • Consider potential differential functions between isoforms

• Interaction analysis with related FGFs:

  • Measure both FGF8 and FGF17 levels simultaneously

  • Design experiments that account for FGF8's ability to induce FGF17 expression

  • Consider redundancy with FGF18 due to high sequence homology

How do FGF17 and FGF8 interact in signaling cascades, and what experimental designs best capture their cross-talk?

FGF17 and FGF8 exhibit significant cross-talk with important experimental design implications:

• Known interactions:

  • FGF8 induces FGF17 expression in prostate cancer cell lines (LNCaP, DU145, and PC3M)

  • FGF17 may serve as a mediator of FGF8 function in prostate carcinogenesis

  • Both share high sequence homology and similar expression patterns during embryogenesis

• Optimal experimental designs for cross-talk studies:

  • Sequential stimulation experiments: Treat cells with FGF8 first, then measure FGF17 expression kinetics

  • Knockdown studies: Use siRNA against FGF17 to determine which FGF8 effects are FGF17-dependent

  • Co-immunoprecipitation: Assess potential protein-protein interactions

  • Receptor competition assays: Determine if pre-treatment with one FGF affects binding or signaling of the other

• Critical controls and considerations:

  • Include dose-response analyses for both factors individually before combination studies

  • Validate antibody specificity due to high sequence homology

  • Consider temporal dynamics, as some effects may be immediate while others require new protein synthesis

  • Measure both mRNA and protein levels to distinguish transcriptional from post-transcriptional effects

What are the analytical challenges in differentiating the unique contributions of FGF17 from other FGFs in developmental processes?

Differentiating FGF17's unique contributions presents several analytical challenges requiring sophisticated methods:

• Spatiotemporal expression mapping challenges:

  • FGF17 is expressed in embryonic brain, hindgut, developing skeleton, tail bud, major arteries, and heart

  • Overlapping expression with FGF8 and FGF18 requires precise microdissection techniques

  • Single-cell RNA sequencing can help resolve cell-specific expression patterns

• Functional redundancy assessment:

  • Conditional and inducible knockout models are needed to bypass developmental lethality

  • Domain-swap experiments between FGF17 and related FGFs can identify unique functional domains

  • Receptor-specific blocking antibodies can help determine which receptor interactions are unique to FGF17

• Technical considerations for specific developmental contexts:

  • For midbrain/hindbrain junction studies, ex vivo explant cultures with localized FGF17 application

  • For vascular development, endothelial-specific conditional expression systems

  • For skeletal development, mesenchymal stem cell differentiation assays with FGF17 supplementation

• Data integration approaches:

  • Multi-omics analysis combining transcriptomics, proteomics, and phosphoproteomics

  • Systems biology modeling of FGF signaling networks

  • Machine learning algorithms to identify FGF17-specific gene expression signatures

What are the key knowledge gaps in FGF17 biology that require methodological innovation?

Despite significant progress, several knowledge gaps remain in FGF17 biology that require innovative approaches:

• Structural biology of FGF17-receptor complexes:

  • Need for crystal structures of FGF17 bound to different FGFRs

  • Comparison with FGF8-receptor complexes to identify specificity determinants

  • Application of cryo-EM for visualizing signaling complexes in native-like environments

• Isoform-specific functions:

  • Differentiation between FGF17a and FGF17b functions remains poorly characterized

  • Development of isoform-specific antibodies and expression constructs

  • CRISPR-based isoform-specific genome editing approaches

• Tissue-specific roles beyond currently known functions:

  • FGF17's role in tissues where expression has been documented but function is unclear

  • Development of tissue-specific inducible expression systems

  • Spatial transcriptomics to map FGF17 effects with high anatomical resolution

• Long-term physiological impacts of FGF17 dysregulation:

  • Longitudinal studies in conditional knockout or overexpression models

  • Integration of metabolomics with transcriptomics for comprehensive phenotyping

  • Development of non-invasive imaging methods to track FGF17-dependent processes in vivo

What are the most promising therapeutic applications of FGF17 modulation based on current research findings?

Current research suggests several promising therapeutic applications for FGF17 modulation:

• Neuroprotection in ischemic stroke:

  • rhFGF17 administration decreases infarct volume, improves neurological deficits, and preserves BBB integrity

  • Development of delivery systems for targeted brain delivery

  • Exploration of optimal therapeutic window post-stroke

  • Combinations with existing stroke therapies

• Cancer therapy approaches:

  • FGF17 inhibition in prostate cancer, given its correlation with aggressive disease

  • Development of FGF17-specific neutralizing antibodies

  • Small molecule inhibitors of FGF17-FGFR interactions

  • Combination with standard-of-care therapies for prostate cancer

• Methodological considerations for therapeutic development:

  • Pharmacokinetic and pharmacodynamic profiling of rhFGF17

  • Biomarker development to identify patients likely to respond to FGF17-targeted therapies

  • Consideration of FGF8-FGF17 relationships when targeting either factor

  • Development of controlled-release formulations to optimize biological effects