MGF (Mechano Growth Factor)

The C-terminal E-domain peptide of the IGF-1Ec splice variant, sold on the research market as a synthetic 24-residue peptide, with rodent and cell data on muscle progenitor cells, a failed industry replication, and no human trials.

Also referenced as: Mechano growth factor, MGF peptide, PEG-MGF, MGF-24aa-E, MGF E peptide, MGF C-terminal E peptide, Goldspink-MGF

Also appears in: Tissue repair

What is MGF (Mechano Growth Factor)?

“Mechano growth factor” was the name given to a splice variant of the IGF-1 gene whose messenger RNA rises in skeletal muscle after stretch or mechanical loading. It was first cloned from rabbit muscle driven into rapid hypertrophy by stretch: the stretch-induced transcript carried a 52-base-pair insert that shifted the reading frame of the C-terminal E domain, producing a precursor with a different tail from the liver-type IGF-1Ea isoform (Yang et al., Journal of Muscle Research and Cell Motility, 1996, 17(4):487–495). The human counterpart is IGF-1Ec, in which a 49-base-pair exon 5 insert produces the same kind of frameshift and an alternative C-terminal extension, the Ec E-domain (Kandalla et al., Mechanisms of Ageing and Development, 2011, 132(4):154–162; Hameed et al., The Journal of Physiology, 2003, 547(Pt 1):247–254).

What research vendors sell under the name MGF is not that splice variant. It is a synthetic peptide corresponding to the last 24 amino acids of the human Ec E-domain, detached from the mature IGF-1 portion of the molecule, usually written as MGF-24aa-E. Even that short sequence comes in two versions. The native human Ec isoform ends in YQPPSTNKNTKSQRRKGSTFEERK (UniProt P05019-4), while the synthetic peptide used in much of the Goldspink-group literature, and reproduced in their reviews, swaps the penultimate arginine for histidine (…GSTFEEHK), a “stabilized” analogue sold by reagent suppliers as Goldspink-MGF (Zabłocka et al., Frontiers in Endocrinology, 2012, 3:131; Janssen et al., PLoS One, 2016, 11(3):e0150453). Research-market labels rarely say which one is in the vial. A “PEG-MGF” listing is marketed as the 24-residue peptide with a polyethylene glycol group attached to slow clearance. Reading about the splice variant, the synthetic E peptide, and the PEGylated version as one subject is the single largest source of confusion around this compound.

How it works

The proposed mechanism treats the E peptide as a signal distinct from mature IGF-1, acting on muscle progenitor cells rather than driving fiber differentiation. The supporting work is in cells and animals, and parts of it are contested:

• Proliferation without differentiation — in myoblast culture, the MGF E domain increased proliferation while inhibiting terminal differentiation, the opposite of mature IGF-1’s effect. Blocking the IGF-1 receptor with an antibody did not abolish the E-domain effect, which the authors read as action through a different receptor (Yang and Goldspink, FEBS Letters, 2002, 522(1-3):156–160; the paper carries a published erratum in FEBS Letters, 2006, 580(10):2530)
• Mechanical loading changes the transcript, not the peptide — in human quadriceps biopsies taken 2.5 hours after knee-extensor exercise at 80% of one-repetition maximum, MGF mRNA rose significantly in subjects aged 25 to 36 but not in subjects aged 70 to 82, while IGF-1Ea mRNA did not change in either group. Resting MGF levels were roughly 100-fold below IGF-1Ea (Hameed et al., The Journal of Physiology, 2003, 547(Pt 1):247–254). A later study in elderly men found that five weeks of resistance training raised MGF mRNA by 163%, and training combined with growth hormone by 456% (Hameed et al., The Journal of Physiology, 2004, 555(Pt 1):231–240)
• Progenitor-cell activation in primary human cells — the synthetic MGF-24aa-E peptide extended the proliferative life span of satellite cells from neonatal and young adult donors, though not from old adult donors, and increased their fusion potential (Kandalla et al., Mechanisms of Ageing and Development, 2011, 132(4):154–162). An earlier study reported increased desmin-positive progenitor numbers in cultures from healthy, dystrophic, and ALS muscle (Ates et al., FEBS Letters, 2007, 581(14):2727–2732)
• Receptor identity is unresolved and disputed — the E peptide does not itself phosphorylate the IGF-1 receptor, and no dedicated MGF receptor has been identified. One group reported that E-peptide effects on proliferation and migration were abolished by IGF-1 receptor blockade, concluding that the peptides modulate IGF-1 signaling rather than acting independently (Brisson and Barton, PLoS One, 2012, 7(9):e45588). In a receptor-activation assay, neither the human Ec peptide nor the stabilized Goldspink-MGF peptide stimulated the IGF-1 receptor at any concentration tested (Janssen et al., PLoS One, 2016, 11(3):e0150453)

Research status

There are no human trials of exogenous MGF. A search of ClinicalTrials.gov for mechano growth factor, IGF-1Ec, and PEG-MGF as interventions returns no registered study of the peptide in any phase; the only record that names IGF-1Ec is an observational study measuring it in serum as a cancer marker (NCT07151807), not a treatment study. No regulator has reviewed MGF as a drug. The evidence base is cell culture and animal work, roughly two decades old at its core, with a prominent failed replication.

The failed replication. Investigators at two pharmaceutical companies attempted to reproduce the central myoblast claims. Concentrations of MGF peptide up to 500 ng/mL failed to increase proliferation of C2C12 cells or primary human skeletal muscle myoblasts, failed to inhibit differentiation into myotubes, and failed to activate p-ERK in cardiac myocytes, while mature IGF-1 and full-length IGF-1Eb produced robust responses in the same systems. Primary mouse muscle stem cells showed no significant effect either, and the cardiac assay was negative for both the native and a stabilized MGF peptide. The authors concluded that the results call into question whether the peptide has a physiological role at all (Fornaro et al., American Journal of Physiology: Endocrinology and Metabolism, 2014, 306(2):E150–E156).

The conceptual critique. A minireview had already argued that the MGF literature rests on unstable foundations: rodent and human isoform names had been applied loosely despite the isoforms having different C-termini, and no naturally occurring free E peptide had been isolated from cells, conditioned medium, tissue, or biological fluids, so the activities of a synthetic 24-residue peptide could not be assumed to belong to any real product of IGF-1 gene expression (Matheny et al., Endocrinology, 2010, 151(3):865–875). Immunoblotting work later reported detecting the human Ec and rodent Eb peptides alongside their precursor in muscle, liver, and heart, and showed that furin digestion of tissue lysates could release the free Ec peptide (Vassilakos et al., Growth Hormone and IGF Research, 2017, 32:22–28), which addresses the existence question without establishing a physiological function for the free peptide.

Animal data outside muscle. The strongest in vivo results are cardiac and neurological, not hypertrophic. In a gerbil model of transient brain ischemia, the synthetic MGF C-terminal peptide protected vulnerable hippocampal neurons, with the effect reported as independent of the IGF-1 receptor (Dluzniewska et al., FASEB Journal, 2005, 19(13):1896–1898). In sheep with microsphere-induced infarcts, the MGF E domain preserved cardiac function and left about 35% less compromised myocardium than control (Carpenter et al., Heart, Lung and Circulation, 2008, 17(1):33–39). In cultured H9c2 cardiac cells the peptide was taken up rapidly and localized to the nucleus without activating the IGF-1 receptor, and in mice given the peptide at the time of myocardial infarction, the decline in systolic and diastolic function was attenuated at two weeks (Mavrommatis et al., Molecular and Cellular Biochemistry, 2013, 381(1-2):69–83).

A cautionary in vivo muscle result. When rodent E-peptides were expressed in mouse skeletal muscle by viral vector, with mature IGF-1 inactivated by mutation, the EB peptide produced significant hypertrophy that was IGF-1 receptor dependent — but the added mass came with a loss of muscle strength (Brisson et al., American Journal of Physiology: Endocrinology and Metabolism, 2014, 306(8):E965–E974). Larger mass and better function are not the same endpoint in this literature.

What analytical chemistry found in circulating products. Doping-control laboratories have characterized material sold through illicit channels. Two preparations were shown to contain a C-terminally amidated analogue of human MGF rather than the unmodified peptide, with a diagnostic transition identified to tell the modified form from the endogenous one (Esposito et al., Rapid Communications in Mass Spectrometry, 2012, 26(6):686–692). A product marketed as “full-length MGF” proved to be a recombinant protein of monoisotopic mass 12,264.9 Da, closely related to IGF-1Ec but with the terminal lysine eliminated and an R109H substitution, and was brought within routine testing at 0.25 ng/mL (Thevis et al., Growth Hormone and IGF Research, 2014, 24(6):276–280). That full-length material reached maximal IGF-1 receptor activation comparable to recombinant human IGF-1 at high equimolar concentrations but with far lower potency (EC50 7.83 versus 0.86 nmol/L), while the short E peptides did not activate the receptor at all (Janssen et al., PLoS One, 2016, 11(3):e0150453).

Newer work. Activity has shifted to other tissues rather than to clinical development: a 2023 review covers MGF in chondrocytes and cartilage defects and notes that the protease producing endogenous MGF has not been found, that specific antibodies able to recognize the synthetic sequence are lacking, and that the mechanism remains unclear with much of the evidence in vitro (Liu et al., Acta Biochimica et Biophysica Sinica, 2023, 55(5):701–712). Background reviews on the splicing mechanism and on the E domain’s putative bioactivity remain the standard entry points (Goldspink, Physiology, 2005, 20:232–238; Vassilakos et al., Hormones (Athens), 2014, 13(2):182–196).

Where regulators have touched it. No marketing application for MGF or PEG-MGF has ever been filed with the FDA or any other drug regulator. The only regulatory handling is on the compounding side, through the FDA’s lists of bulk drug substances nominated for section 503A compounding. PEG-MGF was among the peptides the FDA placed in Category 2 (“bulk drug substances that raise significant safety risks”) in 2023. On April 15, 2026, the FDA announced it would remove twelve of those peptides from Category 2 and consult its Pharmacy Compounding Advisory Committee on whether to add them to the 503A bulks list; “Mechano Growth Factor, Pegylated (PEG-MGF)” was slated for a committee session before the end of February 2027 rather than the July 2026 meeting. The FDA’s category document as updated May 14, 2026 no longer lists PEG-MGF in Category 2 and carries plain “Mechano growth factor (MGF)” in Category 3, substances nominated without adequate support. Removal from Category 2 does not by itself make a substance eligible for compounding, and no committee recommendation or rule on PEG-MGF has been issued as of October 2026.

Common dosage forms

• Lyophilized powder in vials (research market) — the synthetic 24-residue E peptide, supplied as freeze-dried powder for reconstitution and typically labeled in milligrams. Listings appear both as MGF and as “MGF (IGF-1Ec)”, and almost never state whether the sequence is the native Ec terminus or the arginine-to-histidine stabilized analogue.
• Separate PEG-MGF listings — the same peptide marketed in a PEGylated form, also as lyophilized vial powder, and priced and labeled independently of the unmodified version.
• Multi-compound research blends — MGF appears as one component of premixed vials combined with growth hormone secretagogues or repair peptides, where a single vial carries several labeled quantities.
• No pharmacy or clinical formats — there is no approved drug product containing MGF, so no pen, cartridge, prefilled syringe, oral, or topical pharmaceutical presentation exists. Nothing on the research market has an FDA-reviewed label, strength, or purity specification, and no compounding pharmacy may lawfully prepare it under section 503A unless and until it is added to the bulks list.

Key considerations

• No approval anywhere and no clinical program. MGF has never been approved by the FDA or any other regulator, has no marketing application pending, and has no registered human trial as of October 2026. The one live regulatory thread is a compounding-list review of PEG-MGF scheduled before the end of February 2027, which concerns pharmacy access, not evidence of efficacy. The Research Market status reflects the absence of US approval or any development program aimed at approval.
• The name covers three different things. The IGF-1Ec splice variant is an endogenous full-length precursor protein; the research-market “MGF” is a 24-residue synthetic fragment of that protein’s E domain, often in a modified stabilized sequence; “PEG-MGF” is that fragment with a PEG group attached. Findings about one do not transfer to the others — the receptor-activation data make this explicit, since full-length material engaged the IGF-1 receptor while the short peptides did not. Rodent papers calling IGF-1Eb “MGF” add a fourth layer, because the rodent Eb and human Ec C-termini are not the same sequence.
• A central claim failed independent replication. The myoblast proliferation and delayed-fusion effects that underpin the muscle-growth framing were not reproducible at two pharmaceutical companies across cell lines, primary human myoblasts, and primary mouse muscle stem cells. Any reading of this compound has to account for that result, and for the finding that virally driven E-peptide expression increased mouse muscle mass while reducing strength.
• The PEGylated version has essentially no literature. Published analytical characterizations of illicit MGF products describe an amidated 24-residue analogue and a recombinant full-length protein; no peer-reviewed pharmacokinetic or efficacy study of a PEGylated MGF peptide appears in the indexed literature. The half-life extension claimed for PEG-MGF is an inference from PEGylation chemistry generally, not a measured property of this product, and analytical work has found that what is in the vial differs from what is on the label.
• Prohibited in sport, and the safety record is empty rather than clean. Mechano growth factors (MGFs) are named in the 2026 WADA Prohibited List under S2, growth factors and growth factor modulators, and the class has been prohibited since 2005, with detection methods in routine use. Because no human study has been run, there is no characterized dose-response, no adverse-event profile, and no toxicology; the IGF pathway’s known concerns around tissue proliferation have not been evaluated for this peptide in people at all.