Mechano Growth Factor (MGF) is a splice variant of the IGF-1 gene, generated in response to mechanical loading and tissue damage in skeletal muscle. Unlike the systemic IGF-1Ea isoform that circulates in plasma, MGF (IGF-1Ec in humans) acts locally and transiently — with the unique 24-amino-acid C-terminal "E-domain peptide" being the bioactive fragment most studied in research. PEG-MGF is a synthetic version of this E-domain peptide conjugated to polyethylene glycol, extending its plasma half-life from minutes to hours and making it tractable as a research tool for studying satellite-cell activation and skeletal muscle repair pathways.
MGF is the product of alternative splicing of the IGF-1 gene in response to mechanical loading or tissue damage. The full MGF protein contains the standard IGF-1 mature peptide plus a unique 24-amino-acid C-terminal "E-domain" extension. Research has established that the E-domain peptide itself — independent of the IGF-1 portion — is the functionally distinctive component, signalling through a yet-uncharacterised receptor pathway separate from the IGF-1 receptor.
The principal documented biological activity is activation and proliferation of muscle satellite cells (skeletal-muscle progenitor cells responsible for repair after damage). MGF's natural role appears to be the rapid mobilisation of the satellite pool in the early phase of muscle repair, followed by the slower-acting systemic IGF-1Ea isoform that drives the subsequent hypertrophy and remodelling.
PEGylation conjugates the E-domain peptide to polyethylene glycol, extending half-life from minutes (native MGF) to days (PEG-MGF). This extension is what makes PEG-MGF tractable as a research probe; native MGF's very brief plasma life makes systematic dose-response work difficult outside local-injection protocols.
Foundational research from Geoffrey Goldspink and colleagues at University College London characterised MGF as a mechanically-responsive IGF-1 splice variant in the late 1990s. Subsequent work documented that the E-domain peptide alone — without the IGF-1 mature sequence — retains the satellite-cell activation activity, leading to research focus on the isolated E-domain.
The signalling pathway remains incompletely characterised — published work suggests a receptor distinct from the IGF-1 receptor, but the canonical receptor has not been identified. This is the principal open question in MGF molecular pharmacology.
Preclinical muscle-injury research has documented enhanced satellite-cell proliferation and accelerated repair markers with E-domain peptide dosing. Models of muscular dystrophy, age-related sarcopenia and acute muscle injury have all been explored.
Research has also examined MGF in cardiac repair contexts (the heart has its own satellite-cell-equivalent population responsive to mechanical loading) and in cartilage repair models. The compound's research profile is broader than the skeletal-muscle research focus implies.