Growth Factor

A growth factor is a signaling protein or peptide that regulates cell proliferation, differentiation, migration, or survival by binding to specific surface receptors. They are generally active at nanomolar to picomolar concentrations and act in an autocrine (on the producing cell), paracrine (on neighboring cells), or endocrine (at distance via the circulation) manner.

Main families include insulin-like growth factors (IGF-1, IGF-2, complexed with circulating IGFBPs), epidermal growth factors (EGF, TGF-α, HB-EGF, amphiregulin), fibroblast growth factors (FGF1 to FGF23, including FGF19 and FGF21 used in metabolic research), vascular endothelial growth factors (VEGF-A, B, C, D, crucial for angiogenesis), platelet-derived growth factors (PDGF-A to D), hepatocyte growth factors (HGF), neurotrophins (NGF, BDNF, NT-3, NT-4), and the TGF-β family (including BMPs and activins).

The majority signal through receptor tyrosine kinases (RTKs): ligand-induced dimerization, autophosphorylation of tyrosine residues, recruitment of SH2/PTB-domain proteins (GRB2, Shc, PLCγ), activation of Ras-MAPK and PI3K-Akt-mTOR cascades. The TGF-β family signals differently through serine/threonine kinase receptors and Smads.

Negative regulation is achieved by receptor internalization after binding, dephosphorylation by tyrosine phosphatases (PTPs), ubiquitination (c-Cbl), and recycling or lysosomal degradation. Imbalance in these circuits is common in oncology (EGFR amplification, activating FGFR mutations) and represents a major therapeutic target.

In research, growth factor mimetic peptides (BPC-157, TB-500, thymosin-β4, VEGF-derived peptides) are studied for their effects on wound healing, angiogenesis, musculoskeletal regeneration, and neuroplasticity, in vitro and in animal models.