MGF: muscle-repair signal released by exercise (Mechano Growth Factor)
A natural protein fragment the body makes after exercise to activate muscle repair cells; studied only in animals and lab dishes, not yet an approved drug.
A researcher, an agent, or an algorithm wrote down the sequence and picked a target to hit.
An AI model like OpenFold3 or AlphaFold built a 3D structure and scored how well it fits the binding site.
A second contributor repeated the computation on their own hardware and the scores matched.
A chemistry service or a researcher ordered the sequence, it was manufactured, and mass spectrometry confirmed the right molecule was produced.
A binding or activity measurement confirmed that it actually does what the computer predicted — or didn't.
Snapshot
Class: IGF-1 splice variant / growth factor peptide
Evidence tier: Animal-only evidence
Status: Not approved for any therapeutic use; distributed through research-chemical channels labeled "not for human use"
Best-supported effect: Satellite cell activation and muscle repair signaling in rodent models and human cell culture; mechanistic framework for load-gated IGF-1 splicing is reasonably characterized in preclinical systems
Main caveat: No human clinical trials of synthetic MGF for any indication; no pharmacokinetic or dose-ranging data in humans; receptor identity incompletely characterized; independent replication of foundational work described in source as thinner than ideal
What this is
MGF (Mechano Growth Factor), also designated IGF-1Ec, is an alternatively spliced isoform of IGF-1 produced locally in skeletal muscle in response to mechanical loading and tissue damage. It is distinct from the systemic liver-derived isoform (IGF-1Ea): the Ec splice variant carries a unique C-terminal E-domain peptide that is absent from systemic IGF-1. The endogenous splice variant was characterized principally by Geoffrey Goldspink and colleagues at the Royal Free and University College London Medical School through the 1990s and 2000s, who proposed that the E-domain activates muscle satellite (stem) cells and expands the progenitor pool before the cleaved IGF-1 portion drives differentiation. Synthetic MGF — typically the isolated E-domain peptide or an intact IGF-1Ec analogue — has no approved therapeutic use. It carries extreme intrinsic instability in solution, with activity reported lost within hours to a day at ambient temperature. A PEGylated variant (PEG-MGF) was developed to address this instability, though PEGylation changes the pharmacological regime from a localized pulsatile response to a more sustained systemic exposure pattern. The specific receptor mediating E-domain effects has not been definitively identified, and independent replication of the foundational mechanistic work is described in available literature as thinner than ideal.
Evidence map
| Evidence layer | Grade | What it supports |
|---|---|---|
| Human | Not present (synthetic MGF) | No human trials of synthetic MGF for any indication are present in available literature. Human studies in available literature measure endogenous MGF expression during exercise, resistance training, or in response to rhGH — they are endogenous biology studies, not synthetic-MGF administration trials, and do not constitute evidence for exogenous peptide efficacy. |
| Animal | Moderate | Satellite cell activation and muscle repair signaling demonstrated in rodent models. A cardiac protection signal in an acute myocardial infarction rodent model is also reported in available literature. |
| In vitro | Moderate | E-domain peptide activates human muscle progenitor cells and increases their fusion potential in cell culture across age groups. Biological activity of the IGF-1Ec E-domain addressed in assay systems. |
| Computational | Not present | No computational or structural prediction data present in source. |
| Mechanism | Plausible — partially characterized | Alternative splicing of the IGF-1 gene gated by mechanotransduction is established in available literature. The E-domain is proposed to act through a receptor distinct from the canonical IGF-1R; however, the identity of that receptor has not been definitively established and remains an active research gap. |
A large share of the mechanistic framework originates from one research program (Goldspink group). Independent replication across other labs, species, and study designs is described in available literature as thinner than ideal, which limits confidence in the robustness of the evidence base.
Claim check
| Claim | Verdict | Evidence layer | Confidence |
|---|---|---|---|
| Satellite cell activation and muscle repair signaling in preclinical systems | Supported (animal / in vitro) | Animal + in vitro | Medium — mechanistic framework preclinically established; receptor identity and synthetic-MGF dose-response in animal models not fully characterized; independent replication thinner than ideal |
| Enhanced muscle repair or hypertrophy from synthetic MGF in humans | Not established | Human | High — no human efficacy trials; no pharmacokinetic data in humans; translation from preclinical satellite cell biology to injectable-peptide benefit has not been demonstrated |
| MGF is the key signal that unlocks muscle growth beyond training alone | Weak / not established | Animal + in vitro | High — source characterizes MGF as one component of the load-response cascade, not a master switch; human synthetic-MGF hypertrophy trials are absent |
| PEG-MGF is pharmacologically equivalent to native MGF with longer duration | Contradicted / not established | Animal + in vitro (mechanistic) | Medium — PEGylation extends half-life but shifts the pharmacologic regime from a mechanically localized pulsatile response to sustained systemic exposure; source describes equivalence as debatable, not demonstrated |
| Synthetic MGF is safer because it is "natural" and acts locally | Not established | None | High — endogenous IGF-1Ec occurs at specific local concentrations during mechanically gated repair; injecting synthetic peptide at pharmacologic doses is not physiologically equivalent; human safety profile is uncharacterized |
| Neuroprotective effects via stem cell activation in neural tissue | Weak (preclinical) | Animal + in vitro | Low — source describes this as a proposed property by analogy to muscle satellite cell activation; no dedicated human or animal neuroprotection study of synthetic MGF individually extracted in this card |
Experimental exposure
This section reports exposure used in animal experiments and in vitro assays. It does not establish human dosing.
| Context | System | Experimental exposure | Duration | Endpoint | Limitation |
|---|---|---|---|---|---|
| Rodent mechanical-loading / stretch models | Rat skeletal muscle | Endogenous MGF expression studied following exercise or mechanical overload; synthetic MGF dose not individually extracted from source | Varied by study | Satellite cell proliferation markers, muscle fiber area, MGF gene expression | Endogenous-expression data; synthetic-MGF dose-response in rodents not individually extracted |
| In vitro cell assay | Human muscle progenitor cell culture | E-domain peptide; exact concentration range not individually extracted in source | Not individually extracted | Progenitor cell activation, fusion potential across age groups | Cell-assay only; not an in vivo or in-human exposure model |
| Rodent cardiac model | Rat acute myocardial infarction model | Synthetic MGF; exact dose not individually extracted in source | Not individually extracted | Cardiac function preservation | Preclinical only; cardiac indication; no human translation established |
Community-described protocols (100–200 mcg intramuscular injection per site, post-workout timing, 4–6 week cycles) are sourced exclusively from community convention with no clinical dose-ranging study underpinning them. These are not represented in the studied experimental evidence base and do not appear in this section.
Preclinical safety signals
| Signal | System | Notes |
|---|---|---|
| Injection-site soreness and localized swelling | per available sources | Listed in source; no formal preclinical toxicology table extracted in this card |
| Theoretical uncontrolled satellite cell activation | Theoretical / mechanistic | Source identifies this as a theoretical concern; not characterized in animal or human data |
| Theoretical tumor-promotion risk | Theoretical | Source notes satellite-cell activation and IGF-1 axis engagement raise theoretical tumor-promotion concerns; magnitude not quantified in any study present in available literature |
| Long-term local tissue effects from repeated injection | Not established | No systematic study of repeated synthetic-MGF injection on fiber-type composition, fibroblast activity, or fibrotic change in source |
| PEG hypersensitivity (PEG-MGF variant only) | Class-level context | Source notes PEG hypersensitivity is a documented class effect; relevant to the PEGylated variant only |
| Human safety profile | Essentially uncharacterized | Source states the human safety profile is "essentially unknown" |
Regulatory status
| Region / body | Status | Notes |
|---|---|---|
| US (FDA) | Not approved | No approved medical indication; distributed through research-chemical channels labeled "not for human use"; distribution for human consumption is unauthorized under the FD&C Act; not a scheduled controlled substance |
| EU | Not authorized (per available sources) | Per available sources, no EU authorization as a medicine; status not independently verified in this card |
| UK | Not authorized (per available sources) | Per available sources, no UK authorization; status not independently verified in this card |
| Canada | Not authorized (per available sources) | Per available sources, no authorization in Canada; status not independently verified in this card |
| Australia (TGA) | Schedule 4 — prescription-only (per available sources) | Per available sources, Australian TGA treats synthetic MGF as a Schedule 4 prescription-only substance; status not independently verified in this card |
| WADA | Prohibited at all times (per available sources) | Per available sources, MGF is prohibited at all times under WADA as a growth factor; Per available sources, mass-spectrometric detection methods for MGF have been described in doping-control literature; PEG-MGF is treated as equally prohibited per source; current WADA Prohibited List status not independently verified in this card |
Mechanism
MGF is generated by alternative splicing of the IGF-1 gene. In skeletal muscle, mechanical loading and tissue damage trigger a mechanotransduction cascade that favors the Ec splice isoform (IGF-1Ec in humans; IGF-1Eb in rodents). This produces a transcript encoding a unique C-terminal E-domain peptide not present in the systemic hepatic IGF-1Ea isoform. The proposed mechanism holds that the E-domain peptide acts through a receptor distinct from the canonical IGF-1 receptor to activate muscle satellite cells, promoting their proliferation without premature differentiation — expanding the progenitor pool in the period immediately following mechanical load and damage. Subsequently, once the E-domain is cleaved, the IGF-1 portion of the molecule is proposed to drive satellite cell differentiation and hypertrophy through the standard IGF-1R / PI3K / Akt axis.
The specific receptor mediating E-domain satellite cell activation has not been definitively identified. This is an active research gap and a key limitation of the mechanistic framework. Whether injected synthetic MGF recapitulates the localized, acutely timed endogenous signaling event has not been established in humans. Published research also describes a proposed neuroprotective role for MGF via analogous stem cell activation in neural tissue, though no dedicated study of synthetic MGF for neural endpoints was individually extracted.
Chemistry
| Field | Value |
|---|---|
| Common name | MGF; Mechano Growth Factor |
| Also known as | IGF-1Ec (human isoform); IGF-1Eb (rodent isoform) |
| Molecule class | IGF-1 splice variant; C-terminal E-domain peptide (or full IGF-1Ec analogue) |
| Origin | Endogenous splice variant; synthetic research-chemical form |
| Topology | Linear |
| Key structural feature | Unique C-terminal E-domain distinguishes MGF from systemic IGF-1Ea; this domain is the basis of the proposed satellite cell activation mechanism |
| Intrinsic stability | Extreme instability in solution; activity reported lost within hours to one day at ambient temperature; native half-life on the order of minutes |
| Modified form | PEG-MGF — polyethylene glycol conjugate; extends circulating half-life and solution shelf life; alters pharmacological profile away from the localized pulsatile mechanistic premise |
| Sequence | Specific amino acid sequence for the synthetic form not provided in source; sequence confidence: not provided in source |
| Molecular weight | Not provided in source |
| CAS | Not provided in source |
Open questions
- Human translation: No human clinical trials of synthetic MGF for any indication have been conducted. Whether satellite cell activation observed in rodent and in vitro models occurs with injected synthetic MGF in humans at any dose is entirely undemonstrated.
- Receptor identity: The specific receptor through which the E-domain activates satellite cells has not been definitively identified. Without confirmed receptor identity, the pharmacological selectivity and target engagement of synthetic E-domain peptides in vivo cannot be established.
- In vivo bioavailability after injection: MGF's half-life is on the order of minutes. The fraction of an injected dose that reaches and activates target tissue before degradation in humans has not been quantified. This is a fundamental pharmacokinetic gap underlying the entire translational rationale.
- PEG-MGF equivalence and mechanism shift: PEGylation transforms the pharmacological regime from a localized, acutely timed pulsatile response to a sustained systemic exposure. Whether the proposed satellite-cell-activating mechanism operates effectively in that sustained-exposure regime has not been demonstrated; published literature explicitly describes equivalence as debatable.
- Independent replication: The MGF mechanistic framework is strongly associated with the Goldspink research program. independent replication of key findings in other labs, species, and study designs as thinner than ideal — limiting confidence in the robustness and generalizability of the evidence base.
- Long-term local tissue effects: Repeated intramuscular injection of a satellite-cell-activating growth factor peptide into the same muscle site could plausibly affect fiber-type composition, fibroblast activity, or fibrotic change over extended periods. No systematic study of these outcomes exists in available literature.
- Cancer risk characterization: The theoretical tumor-promotion concern from satellite-cell activation and IGF-1-axis engagement is named in available literature as a contraindication basis but has not been quantified in any preclinical or human study present in this card.
Research directions for this peptide, selected from the current sources — hypotheses you can explore and model. None of it is proven yet; tap any one to see the full thinking.
Does the MGF peptide activate a completely different receptor than the one usually blamed for its effects?
If true, it would explain why decades of IGF-1 receptor research has not fully accounted for MGF's unique activity in muscle stem cells, and could point scientists toward a genuinely new drug target for muscle-wasting diseases.
Does MGF work primarily by sticking to the protein scaffold around muscle stem cells rather than by directly docking with a receptor?
If true, it would explain why injected MGF rapidly disappears from the bloodstream and why effects are local, guiding engineers to design versions that stick better to the repair site and last longer.
Does aging selectively silence MGF production in muscles even when the body still makes normal amounts of IGF-1?
If true, it would explain why giving older people more IGF-1 has not reliably reversed muscle loss, and could justify a targeted MGF-based treatment for sarcopenia that acts through a pathway IGF-1 therapies miss.
Does MGF preferentially stimulate repair in fast-twitch muscle fibers, the type that wither fastest with age and inactivity?
If true, it would mean MGF could restore the specific muscle quality lost in aging and chronic illness more precisely than existing therapies, potentially improving strength and fall prevention in older patients.
Could replacing two proline amino acids in MGF produce a version that lasts long enough to be tested as a drug?
If true, it would unlock the ability to run proper dose and safety studies that currently cannot be done because the natural peptide breaks down almost instantly, potentially rescuing a promising muscle-repair molecule from pharmacokinetic obscurity.
▸full evidence table2 metrics
| metric | value | tool |
|---|---|---|
| ipTM | 0.3965228796005249 | openfold3-mlx |
| ranking score | 0.557393491268158 | openfold3-mlx |
▸structural qualityopenfold3
| metric | value | note |
|---|---|---|
| gpde | 0.670 | global PDE — lower = better |
| disorder | 0.174 | fraction disordered |
| chain pair ipTM (A, B) | 0.397 | interface quality |
▸3-letter notation
▸recipeopenfold3-mlx 0.3.1
| parameter | value |
|---|---|
| model | openfold3-mlx 0.3.1 |
| weights | — |
| hardware | — |
| mlx version | — |
| python | — |
| random seed | — |
| msa strategy | — |
| diffusion samples | 1 |
| runtime | 91s |
| predicted by | mlx@peptide |
| predicted at | 2026-05-03 |
▸citationbibtex
@peptide{pep10913,
sequence = {YQPPSTNKNTKSQRRKGSTFEEHK},
target = {igf-1r},
author = {peptidemodel},
year = {2026},
status = {computed}
}