MGF

MGF (mechano growth factor) is the name a London research group gave to a splice variant of the IGF-1 gene (IGF-1Ec in humans, IGF-1Eb in rodents) whose messenger RNA rose in rabbit muscle after stretch and overload (McKoy et al., J Physiol 1999). The peptide sold as MGF is a synthetic 24-amino-acid peptide matching the end section (the E domain) of that variant; it is not mature IGF-1. A 2010 review noted that no such peptide had been found in cells, tissues or body fluids, so whether it exists naturally is unproven (Matheny et al., Endocrinology 2010). Cell studies, many involving the original group, reported that the E peptide increased the proliferation of muscle precursor cells. However, when two pharmaceutical companies tried to reproduce these results, the peptide had no measurable effect on mouse or human muscle cells or on primary mouse muscle stem cells, while IGF-1 did (Fornaro et al., Am J Physiol 2014). Human studies have measured MGF messenger RNA in muscle after exercise, but the peptide itself has not been tested in people. A PEGylated form, PEG-MGF, is also made, with the aim of making it more stable. Supplied for laboratory research use only.