MGF

MGF stands for Mechano Growth Factor, and the name says where it comes from: mechanically loaded skeletal muscle temporarily reads the IGF-1 gene differently. The product of this alternative splicing, called IGF-1Ec in humans, carries an E domain that mature IGF-1 lacks. The peptide sold as MGF reproduces that E domain.

The evidence in brief:

• After local muscle injury in rats, MGF mRNA appeared quickly but only for a few days, in step with markers of activated satellite cells; the IGF-IEa variant followed later (2003).
• After heavy strength training, young subjects showed more MGF mRNA in their muscle while older ones did not; IGF-IEa stayed flat in both groups (2003).
• In cell culture the E domain boosted myoblast proliferation and held back their final differentiation, unlike mature IGF-I and apparently through a different receptor (2002).
• A critical minireview (2010) separates the splice variant from the synthetic peptide of 24 amino acids and notes that no natural counterpart has ever been detected in cells or tissues.
• Two pharmaceutical laboratories could not reproduce any effect of the peptide on myoblasts or muscle stem cells in 2014.

Mechanistically, MGF is tied to the early repair cascade and the acute activation of satellite cells, whereas mature IGF-1 addresses long-term hypertrophy. The E domain is supposed to act independently of the IGF-1 receptor; its targets remain unresolved. The half-life is a matter of minutes, so research relies on local applications; for longer duration there is the PEGylated form PEG-MGF.

Thanks to the very short half-life, systemic exposure stays low and the profile is regarded as mild in studies.

• Injection site with local dosing: redness, pressure, brief irritation.
• Because repair cascades are proliferative, there is a theoretical debate about whether existing abnormal tissue might be stimulated along; no evidence exists.
• Occasional short tiredness or a mild feeling of warmth after dosing.
• Rapid clearance limits effect and observations alike.
• Long-term human data are missing, the targets of the E domain remain unclear, and the physiological role of the peptide itself is in question.

This summary is no substitute for medical advice.

• Expression of IGF-I splice variants in young and old human skeletal muscle after high resistance exercise - MGF mRNA after resistance exercise in young and old.
• Minireview: Mechano-growth factor: a putative product of IGF-I gene expression involved in tissue repair and regeneration - critical review of the splice variant and the synthetic peptide.