MGF (Mechano Growth Factor)

At a Glance

Classification: Splice variant of the insulin-like growth factor 1 (IGF1) gene and its 24-amino-acid C-terminal E-domain peptide; proposed local (autocrine/paracrine) muscle-repair signal; receptor not identified

MGF (mechano growth factor) is the name a UK research group gave to a version of the IGF-1 gene product that muscle makes after stretch, overload or damage. The IGF-1 gene can be spliced in different ways. One version (IGF-1Ec in humans, called IGF-1Eb in rodents) ends in a distinct C-terminal "E-peptide". "MGF" refers both to that splice-variant mRNA and to a synthetic 24-amino-acid peptide made from its E-domain. Evidence is mixed: • Muscle stretch and resistance exercise increase MGF mRNA in animals and young people • The original lab reported that the synthetic E-peptide boosted myoblast proliferation • Researchers at two pharmaceutical companies could not reproduce any effect of the MGF peptide on myoblasts or muscle stem cells. There are no human trials of MGF peptide. It is not approved, and WADA specifically lists mechano growth factors as prohibited.

What Is MGF (Mechano Growth Factor)?

IGF-1Ea → the main IGF-1 splice form; produces mature IGF-1 plus the Ea peptide IGF-1Ec (human) / IGF-1Eb (rodent) = "MGF" → produces mature IGF-1 plus a distinct E-peptide MGF peptide (research market) → synthetic 24-amino-acid E-domain peptide, often with modifications for stability PEG-MGF → PEGylated version of the synthetic peptide designed to last longer Mature IGF-1 is the same 70-amino-acid hormone regardless of splice form; the debate is about whether the E-peptide has its own activity.

What Are Researchers Studying?

How Does It Work?

Proposed (contested) model: mechanical load or muscle damage ↓ alternative splicing of the IGF1 gene toward IGF-1Ec/Eb ("MGF") ↓ mature IGF-1 (acts on IGF-1 receptor) + a distinct E-peptide ↓ E-peptide proposed to activate satellite-cell / myoblast proliferation through an unidentified receptor ↓ local muscle repair. The splicing response is reasonably established. Independent activity of the synthetic E-peptide is not.

What Does the Research Show?

Notable Studies

What We Still Don't Know

• Whether a free MGF E-peptide actually exists in the body (none has been isolated) • Whether the E-peptide has any biological activity of its own (studies conflict) • What receptor, if any, mediates proposed E-peptide effects • Whether synthetic MGF or PEG-MGF has any effect on human muscle (no human trials) • Stability and half-life of the native peptide in the body • Safety of research-market MGF products

Related Compounds

Sources & References

1. McKoy G et al. Expression of insulin growth factor-1 splice variants and structural genes in rabbit skeletal muscle induced by stretch and stimulation. Journal of Physiology. 1999.
2. Yang SY et al. Different roles of the IGF-I Ec peptide (MGF) and mature IGF-I in myoblast proliferation and differentiation. FEBS Letters. 2002.
3. Hameed M et al. Expression of IGF-I splice variants in young and old human skeletal muscle after high resistance exercise. Journal of Physiology. 2003.
4. Fornaro M et al. Mechano-growth factor peptide, the COOH terminus of unprocessed insulin-like growth factor 1, has no apparent effect on myoblasts or primary muscle stem cells. American Journal of Physiology - Endocrinology and Metabolism. 2014.
5. Matheny RW Jr, et al. Minireview: Mechano-growth factor: a putative product of IGF-I gene expression involved in tissue repair and regeneration. Endocrinology. 2010.