fibroblast growth factor

fibroblast growth factor is a family of heparin-binding polypeptide growth factors involved in a vast array of biological processes. First identified by Armando R. Cournil and colleagues in the 1970s for their mitogenic activity on fibroblasts, these proteins are now known to be critical for embryogenesis, tissue repair, and metabolism. The family comprises numerous members that exert their effects by binding to specific cell surface receptors, initiating complex intracellular signaling cascades.

Overview

The discovery of fibroblast growth factor activity is credited to research conducted at the Vanderbilt University School of Medicine and the National Institutes of Health. Early work by Denis Gospodarowicz was instrumental in purifying the first members, basic fibroblast growth factor and acidic fibroblast growth factor, from bovine pituitary gland extracts. These factors were initially characterized by their ability to stimulate the proliferation of cells derived from the mesenchyme, such as fibroblasts and endothelial cells. The field expanded significantly with the cloning of the first FGF genes, leading to the identification of a large, evolutionarily conserved family.

Structure and classification

Members of the fibroblast growth factor family share a conserved core region of approximately 120 amino acids that forms a beta-trefoil fold, a structural motif critical for receptor binding. They are classified into several subfamilies based on phylogenetic analysis and mechanism of action. The canonical, paracrine FGFs, such as FGF1 and FGF2, require heparan sulfate proteoglycans as co-receptors for signaling. In contrast, the endocrine-acting FGFs, including FGF19, FGF21, and FGF23, have reduced heparin-binding affinity and function as hormones. The family also includes intracellular FGFs and those with unique roles in organogenesis.

Biological functions

The biological roles of fibroblast growth factors are exceptionally diverse and context-dependent. During embryonic development, specific FGFs are crucial for gastrulation, limb bud formation, and neural tube patterning. For instance, signaling from FGF8 is vital for establishing the midbrain-hindbrain boundary and directing development of the branchial arches. In adult organisms, these factors are key regulators of angiogenesis, wound healing, and tissue homeostasis. They influence processes in the bone marrow, skin, and nervous system, where they can promote neurite outgrowth and support neural stem cell survival.

Signaling pathways

Fibroblast growth factors signal primarily through a subset of tyrosine kinase receptors known as fibroblast growth factor receptors. Ligand binding induces receptor dimerization and autophosphorylation, activating downstream pathways such as the RAS-MAPK cascade, the PI3K-AKT pathway, and the PLCγ pathway. The involvement of heparan sulfate is a hallmark of the system, as it stabilizes the FGF-FGFR complex. The precise signaling outcome is modulated by factors including receptor isoform expression, the cellular context, and the presence of Klotho proteins, which act as co-receptors for the endocrine FGFs.

Clinical significance

Dysregulation of fibroblast growth factor signaling is implicated in numerous human diseases. Gain-of-function mutations in FGFR1, FGFR2, and FGFR3 are causative for several craniosynostosis syndromes, such as Apert syndrome and Crouzon syndrome. Similarly, aberrant signaling is a driver in various cancers, including bladder carcinoma, multiple myeloma, and glioblastoma. Conversely, insufficient FGF activity is associated with conditions like chronic kidney disease-mineral and bone disorder, linked to FGF23 resistance, and impaired wound healing in diabetes mellitus.

Research and therapeutic applications

Research into fibroblast growth factors has spurred significant therapeutic development. Recombinant FGF2 has been investigated for treating corneal ulceration and pressure sores. The endocrine FGFs, particularly FGF21, are major targets for metabolic syndrome and non-alcoholic steatohepatitis, with analogs like efruxifermin in clinical trials. Conversely, FGFR inhibitors, such as erdafitinib approved by the U.S. Food and Drug Administration for urothelial carcinoma, represent a class of targeted oncology drugs. Ongoing research at institutions like the Max Planck Society continues to explore novel FGF-based therapies for tissue engineering and regenerative medicine. Category:Protein families Category:Growth factors