MGF Research: What the IGF-1Ec Splice Variant Is and Why Its Identity Is Disputed

What is MGF?

What is MGF? The abbreviation stands for mechano growth factor, and it is used in the literature for at least two distinct objects. The first is a splice variant of the human IGF1 gene — the transcript variously written IGF-1Ec (human) or IGF-1Eb (rodent) — whose expression in skeletal muscle rises after mechanical loading or damage. The second is a short synthetic peptide corresponding to the C-terminal 24 residues of that variant’s E domain, and it is this 24-mer that is catalogued, sold and analysed under the name MGF.

Keeping those apart is not pedantry; it is the only way the literature reads coherently. UniProt lists “Mechano growth factor” as an alternative name for the IGF1 gene product as a whole (entry P05019), which is accurate at the gene level and unhelpfully ambiguous at the molecule level. Everything below states which of the two is being described. None of it is a statement about an effect in a reader.

Discovery and origin in the literature

The starting point is Yang, Alnaqeeb, Simpson and Goldspink (1996, J Muscle Res Cell Motil, PMID 8884603), who cloned and characterised an IGF-1 isoform expressed in skeletal muscle subjected to stretch. The finding that the IGF1 gene is alternatively spliced in a load-dependent way is solid and has been repeatedly built on: Hill and Goldspink (2003, J Physiol, PMID 12692175) reported that expression and splicing of the gene in rodent muscle tracked with satellite (stem) cell activation after local tissue damage.

The step that generated the commercial molecule came later. Yang and Goldspink (2002, FEBS Lett, PMID 12095637) synthesised the E-domain peptide itself and reported that it behaved differently from mature IGF-1 in myoblast culture — the paper’s framing was that the Ec peptide and mature IGF-1 have different roles in proliferation and differentiation. From that point the 24-mer had an identity of its own, and the trade name followed it.

Two features of that history matter when reading the field. Most of the foundational work came from a single research group, and the name “mechano growth factor” was coined by that group rather than assigned through the standard gene-nomenclature process. Barton (2006, Appl Physiol Nutr Metab, PMID 17213901) and Philippou et al. (2014, Mol Med, PMID 24637928) both survey the IGF-1 isoform landscape and its terminology, and both treat the splicing biology as established while treating the independent bioactivity of the E peptide as an open question.

Reference data

Fields below are drawn from the UniProt record for human IGF-1 (P05019) and from the analytical-chemistry literature. Fields that could not be sourced — including CAS number and a catalogue solubility figure for the peptide — are omitted rather than estimated.

Molecule and analytical facts only. No reconstitution volume, concentration, route or handling instruction is given or implied anywhere on this page.

Mechanisms researchers have examined

The MGF mechanism literature has an unusual shape: the proposed mechanism is defined mainly by what it is not.

• Load-dependent alternative splicing — the best-supported element. Yang et al. (1996) and Hill & Goldspink (2003) reported that mechanical stretch and local damage shift IGF1 splicing toward the Ec/Eb variant in muscle, alongside satellite-cell activation. This is transcript biology, and it is not disputed.
• A proposed receptor-independent action of the E peptide — Yang & Goldspink (2002) reported that the Ec peptide affected myoblast proliferation without the differentiation profile of mature IGF-1, which was interpreted as action outside the IGF-1 receptor. Critically, no receptor for the E peptide has been identified, a gap Matheny et al. (2010, Endocrinology, PMID 20130113) treat as central to the field’s uncertainty.
• Neuroprotective work in non-muscle models — Dluzniewska et al. (2005, FASEB J, PMID 16144956) reported an effect of the autonomous C-terminal IGF-1 Ec peptide in a brain-ischemia model, and Quesada et al. (2009, Exp Neurol, PMID 19735655) reported that C-terminal MGF induced heme oxygenase-1 in a dopamine-neuron model. Both are animal/cell studies in tissues far from the muscle story the name evokes.
• Processing context — in normal IGF-1 biosynthesis the E domain is cleaved off and, on the conventional account, discarded. The MGF hypothesis is that this discarded fragment is itself a signalling molecule. That is a substantial claim, and it is the one under dispute.

Research findings by area

The replication problem

The single most important paper for anyone reading about this compound is Fornaro et al. (2014, Am J Physiol Endocrinol Metab, PMID 24253050). Its title states the result plainly: the 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. The authors examined the peptide across cell systems relevant to the original claim and did not reproduce the reported myoblast activity.

That does not erase the earlier work, and this page does not present it as a refutation by fiat. What it establishes is that the central bioactivity claim attached to the marketed molecule has been directly tested by an independent group and not confirmed. Read alongside Matheny et al. (2010), who reviewed the field four years earlier and chose the word putative in their own title, the honest position is that the E peptide’s status as an independent growth factor remains unresolved in the published record.

What analytical chemistry found in the products

Separately from the biology, two analytical papers examined what unregulated MGF material actually contains. Esposito, Deventer and Van Eenoo (2012, Rapid Commun Mass Spectrom, PMID 22328223) characterised two black-market preparations and reported that both were C-terminally amidated analogues of human MGF rather than the native sequence — a one-dalton difference per y-series ion, invisible to any purity percentage and detectable only by mass spectrometry. Thevis et al. (2014, Growth Horm IGF Res, PMID 25466910) characterised a “full-length MGF” product offered through illicit channels and found a protein of monoisotopic mass 12,264.9 Da whose sequence resembled IGF-1Ec but carried an eliminated terminal lysine and an R109H substitution.

Stated neutrally: in both published analyses, the material circulating under this name was not the molecule the name implies. That is a documented identity problem, and it is the reason the verification section below is the most practically useful part of this page.

Non-muscle models

The neuroprotection literature (Dluzniewska 2005; Quesada 2009) is the part of the MGF record least connected to the reason the compound is sought. Both are preclinical, both use the E peptide, and neither has a human counterpart. They are reported here for completeness and because they are genuinely the more mechanistically curious end of the field — not as evidence of anything in people.

Research models and evidence status

The models are cell culture and rodent throughout, plus analytical chemistry on seized or purchased product. There is no human interventional literature on the MGF peptide of any kind.

What is not established

No receptor for the E-domain peptide has been identified. The independent bioactivity of the peptide on muscle cells was directly tested by Fornaro et al. (2014) and not reproduced. No approved product contains MGF and it holds no registered indication anywhere. No human pharmacokinetic data exist — there is no published half-life, clearance route or bioavailability figure for the 24-mer, which is worth noting because half-life claims are the usual justification given for the pegylated version. Nothing on this page should be read as an outcome, a benefit, or a use.

On regulatory and anti-doping status, reported as fact rather than as a use case: Thevis et al. (2014) record that MGF has been prohibited under World Anti-Doping Agency regulations since 2005, within the growth-factor class of section S2 of the Prohibited List.

MGF among the IGF-axis compounds

This cluster confuses easily, so the distinctions are worth stating flatly. MGF is an IGF-1 gene product fragment whose independent activity is disputed. IGF-1 LR3 is a full-length engineered IGF-1 analogue that acts at the IGF-1 receptor and is well characterised as a cell-culture reagent. IGF-1 DES is the des(1–3) truncation of native IGF-1, defined by its reduced binding-protein affinity. All three are ligands or ligand fragments.

The other half of this cluster works in the opposite direction. GDF-8 is myostatin itself — a negative regulator, a target rather than an agonist. Follistatin-344 is an endogenous antagonist of myostatin and activin. ACE-031 is a soluble receptor decoy whose clinical programme was stopped on safety grounds. Receptor-family and mechanism context only; nothing here is a protocol, a stack or a recommendation.

How to verify this compound yourself

MGF is the compound in this cluster where identity testing does the most work, because the published analyses of unregulated product both found the wrong molecule at high chemical purity:

• Mass-spec identity — the decisive check. A C-terminal amidation shifts the mass by roughly one dalton per relevant fragment ion (Esposito et al. 2012); a substituted or truncated full-length variant shifts it more (Thevis et al. 2014). Neither shows up as an impurity peak. Only a mass spectrum compared against the expected sequence distinguishes them.
• HPLC purity — reversed-phase chromatography reports purity as a percentage of the chromatogram and resolves synthesis-related impurities such as deletion sequences and oxidation products. It says nothing about whether the main peak is the intended molecule.
• Endotoxin and sterility — where tested, separate quality attributes reported in EU/mg or as a sterility result, independent of chemical purity and independent of identity.

See how to read a COA for what each line on a certificate means, how to verify peptide purity for how the two methods fit together, and the self-serve verify tool to check the exact batch on a vial in hand.

Research-grade sourcing and verification

For laboratory research use only. MGF is not held in stock; it is listed as available to order in the sourcing catalogue, with a typical lead time of two to three weeks and a quote on request. Material supplied ships with a per-batch Certificate of Analysis reporting HPLC purity (%) and mass-spec identity confirmation at the lot level — which, on a compound whose published black-market analyses both returned a different molecule than the label claimed, is the whole point. Sourcing and identity-assurance framing only.

Frequently asked questions

Literature cited

1. Yang S, Alnaqeeb M, Simpson H, Goldspink G. “Cloning and characterization of an IGF-1 isoform expressed in skeletal muscle subjected to stretch.” J Muscle Res Cell Motil. 1996;17(4):487–95. PMID 8884603. pubmed.ncbi.nlm.nih.gov/8884603.
2. Yang SY, Goldspink G. “Different roles of the IGF-I Ec peptide (MGF) and mature IGF-I in myoblast proliferation and differentiation.” FEBS Lett. 2002;522(1-3):156–60. PMID 12095637. pubmed.ncbi.nlm.nih.gov/12095637.
3. Hill M, Goldspink G. “Expression and splicing of the insulin-like growth factor gene in rodent muscle is associated with muscle satellite (stem) cell activation following local tissue damage.” J Physiol. 2003;549(Pt 2):409–18. PMID 12692175. pubmed.ncbi.nlm.nih.gov/12692175.
4. Dluzniewska J, Sarnowska A, Beresewicz M, et al. “A strong neuroprotective effect of the autonomous C-terminal peptide of IGF-1 Ec (MGF) in brain ischemia.” FASEB J. 2005;19(13):1896–8. PMID 16144956. pubmed.ncbi.nlm.nih.gov/16144956.
5. Quesada A, Micevych P, Handforth A. “C-terminal mechano growth factor protects dopamine neurons: a novel peptide that induces heme oxygenase-1.” Exp Neurol. 2009;220(2):255–66. PMID 19735655. pubmed.ncbi.nlm.nih.gov/19735655.
6. Matheny RW Jr, Nindl BC, Adamo ML. “Minireview: Mechano-growth factor: a putative product of IGF-I gene expression involved in tissue repair and regeneration.” Endocrinology. 2010;151(3):865–75. PMID 20130113. pubmed.ncbi.nlm.nih.gov/20130113.
7. Fornaro M, Hinken AC, Needle S, 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.” Am J Physiol Endocrinol Metab. 2014;306(2):E150–6. PMID 24253050. pubmed.ncbi.nlm.nih.gov/24253050.
8. Philippou A, Maridaki M, Pneumaticos S, Koutsilieris M. “The complexity of the IGF1 gene splicing, posttranslational modification and bioactivity.” Mol Med. 2014;20(1):202–14. PMID 24637928. pubmed.ncbi.nlm.nih.gov/24637928.
9. Barton ER. “The ABCs of IGF-I isoforms: impact on muscle hypertrophy and implications for repair.” Appl Physiol Nutr Metab. 2006;31(6):791–7. PMID 17213901. pubmed.ncbi.nlm.nih.gov/17213901.
10. Esposito S, Deventer K, Van Eenoo P. “Characterization and identification of a C-terminal amidated mechano growth factor (MGF) analogue in black market products.” Rapid Commun Mass Spectrom. 2012;26(6):686–92. PMID 22328223. pubmed.ncbi.nlm.nih.gov/22328223.
11. Thevis M, Thomas A, Geyer H, Schänzer W. “Mass spectrometric characterization of a biotechnologically produced full-length mechano growth factor (MGF) relevant for doping controls.” Growth Horm IGF Res. 2014;24(6):276–80. PMID 25466910. pubmed.ncbi.nlm.nih.gov/25466910.
12. UniProt Consortium. “IGF1_HUMAN (P05019) — Insulin-like growth factor 1.” uniprot.org/uniprotkb/P05019 (precursor length, chain boundaries, isoform sequences, alternative name “Mechano growth factor”).