MGF

01 · What it is

MGF’s evidence base is large, twenty years deep, and organised around a single claimed effect that the most rigorous attempt to reproduce it could not find.

MGF stands for mechano growth factor, a name given by the group that described it to a splice variant of the insulin-like growth factor 1 gene that is upregulated in skeletal muscle after mechanical overload or injury. In humans the variant is IGF-1Ec; in rodents, IGF-1Eb. A 49-base-pair insert in humans, 52 in rodents, shifts the reading frame during splicing and produces a distinct C-terminal E domain ⁴.

The compound sold as MGF is not that protein. It is the 24-residue peptide cleaved from the E domain — written in the literature as MGF-24aa-E, MGF-Ct24E or MGF-C25E — separated from the 70-residue mature IGF-1 sequence that would otherwise accompany it. Everything that follows concerns that peptide, and the distinction matters because the mature IGF-1 portion and the full-length splice variant behave one way in experiments and the isolated E peptide sometimes behaves another.

The claims attached to the E peptide are specific: that it enhances satellite cell proliferation and delays myoblast fusion, and that it therefore represents a strategy for improving muscle regeneration ⁷. Those claims have been tested directly.

In 2014, investigators at two pharmaceutical companies set out to reproduce them. They applied MGF peptide at concentrations up to 500 ng/mL to C2C12 myoblasts, to primary human skeletal muscle myoblasts, and to primary mouse skeletal muscle stem cells. The peptide failed to increase proliferation in any of them. It failed to inhibit differentiation into myotubes. Tested against a separate documented effect — activation of p-ERK but not p-Akt in cardiac myocytes — it produced no activating response, from either the native or a stabilised peptide. In the same experiments, mature IGF-1 and full-length IGF-1Eb produced robust responses. The paper closes: “These results call in to question whether there is a physiological role for MGF” ⁷.

That result is not the whole file, and this guide does not treat it as though it were. Three years earlier, a group working on primary human muscle cultures from donors of different ages found that the MGF-24aa-E peptide significantly increased proliferative life span and delayed senescence in satellite cells — from neonatal and young adult muscle, but not from old adult muscle ⁴. That qualification is important on its own terms, because age-related muscle loss is the context in which the compound is most often discussed.

No human study of MGF exists. Not a pharmacokinetic study, not a tolerability study, not a trial. A 2026 review of compounds acting on the growth hormone–IGF-1 axis places the pegylated form of MGF in its lowest evidence tier, defined by the complete absence of human studies ²²; the unpegylated peptide has no more.

No receptor for the E peptide has been identified anywhere in this literature. That absence is the subject of Section 3 and it is the reason the replication failure lands as hard as it does.

02 · Evidence at a glance

Evidence grade

Preclinical — no human study of any kind is indexed

What it is

The 24-residue C-terminal E-domain peptide of the IGF-1Ec splice variant ⁴

What it is not

The splice variant itself, or IGF-1

Origin of the variant

Alternative splicing of the IGF-1 gene; a 49 bp insert in humans shifts the reading frame ⁴

Replication status of the core claim

Failed. No effect on proliferation or differentiation in three cell types at up to 500 ng/mL ⁷

Countervailing result

Increased proliferative life span in primary human satellite cells from neonatal and young adult, but not old adult, donors ⁴

Receptor

None identified in the indexed literature

Only named binding partner

Nucleolin ¹⁶

Indexed records

206

Human trials

None

Human subjects to date

0

Contradiction within the bone literature

Promotes bone-defect healing in rabbits ⁵; inhibits osteoblast differentiation and mineralisation ⁶

Oncology signals

Expression studied in osteosarcoma ¹⁰ and colorectal cancer ¹⁴

Product identity finding

MGF detected as a contaminant in vials sold as follistatin ¹⁵

Approval status

None, any jurisdiction

03 · Mechanism of action

The splice variant, and why the peptide is not it

Mechanical overload shifts IGF-1 gene splicing toward the Ec isoform. The resulting protein carries the same mature IGF-1 region as the common Ea isoform and a different E domain; the sequence divergence between those E domains is what suggested the isoforms have distinct functions in the first place ¹⁹. In heart, the two isoforms produced by this splicing are IGF-IEa and IGF-IEc, and their E-domain regions differ enough to imply differential function ¹⁹. Thyroid hormone-induced cardiac MGF expression in cultured cells depended on the cells continuing to beat — mechanical activity was required for the transcriptional response ³.

That biology is well established. It concerns a splice variant expressed inside a muscle fibre in response to load. It is not evidence about a 24-residue fragment injected from outside.

The receptor problem

There is no identified receptor for the E peptide. The mature IGF-1 region binds the type 1 IGF receptor; the E peptide does not, and the literature has never established what it binds instead.

That absence is why the field’s mechanistic papers read as a list of downstream pathways with nothing at the top. In periodontal ligament stem cells, MGF acted through Fyn-RhoA-YAP signalling ²¹. In mechanically injured human anterior cruciate ligament fibroblasts, it targeted Rac1-PAK1/2 and RhoA-ROCK1 ¹⁸. In cardiac muscle, the E domain modulated contractile function through 14-3-3 protein interactomes ¹⁹. Each of these is a plausible intracellular cascade. None of them explains how a peptide outside a cell initiates it.

The single named binding partner in the entire indexed literature is nucleolin — a nucleolar phosphoprotein that also traffics to the cell surface. MGF was shown to interact with nucleolin in work on cisplatin-induced neurotoxicity ¹⁶. One interaction, in one context, is not a receptor account.

The 2014 replication attempt tested the mechanistic claim as directly as the functional one: MGF did not activate p-ERK in cardiac myocytes, native or stabilised, while IGF-1 did ⁷.

Delivery, and what it implies

A 24-residue peptide has a short half-life. Microencapsulation of the E peptide was developed specifically for sustained delivery and bioactivity maintenance ⁹, and a stabilised variant was among the forms tested in the replication attempt ⁷. Work of this kind exists because the unmodified peptide does not persist. Its existence is a fact about the molecule’s pharmacokinetics, and the positive in vitro results obtained under continuous exposure in a dish do not transfer to a bolus injection.

04 · Key research findings

Muscle — the claim, and the failure to reproduce it. The foundational functional claim is that the E peptide activates satellite cells. In primary human muscle cell cultures, MGF-24aa-E significantly increased proliferative life span and delayed senescence in cells from neonatal and young adult donors, with hypertrophy and a significant decrease in the percentage of reserve cells across all cultures — but the proliferative effect was absent in cells from old adult muscle ⁴. In mice, a synthetic E peptide improved the success of myogenic precursor cell transplantation ¹.

Against this, the 2014 industry replication found nothing. Up to 500 ng/mL, on C2C12 cells, primary human skeletal muscle myoblasts and primary mouse skeletal muscle stem cells: no proliferative response, no inhibition of myotube differentiation, no p-ERK activation in cardiac myocytes. IGF-1 and full-length IGF-1Eb worked in the same hands, in the same experiments ⁷.

Two laboratories, overlapping cell types, opposite results — and the one that found nothing was designed to find something, ran the positive controls, and published the null.

Bone — a literature that contradicts itself. MGF and its 24-residue E peptide were reported to promote osteoblast proliferation and bone-defect healing in rabbits ⁵. The following year, a separate group reported that the same E peptide inhibits the differentiation and mineralisation of osteoblasts ⁶. Both results are in the indexed record. Later work found MGF enhanced differentiation of human bone marrow-derived mesenchymal stem cells in vitro ¹¹ and regulated their migration and differentiation ⁸.

Proliferation and differentiation are opposing programmes in bone. A factor that increases cell number while blocking mineralisation has not obviously helped the tissue, and no study has reconciled the two findings.

Connective tissue. A synthetic E peptide (MGF-C25E) produced a significantly increased Achilles functional index in rats with injured tendon ¹². In human ACL fibroblasts subjected to sublethal mechanical injury, MGF improved cell mobility through Rac1-PAK1/2 and RhoA-ROCK1 pathways ¹⁸. In chondrocytes under severe hypoxia, pretreatment with the E peptide improved proliferation and extracellular matrix synthesis in an osteoarthritis model ¹⁷, and a 2023 review surveyed the chondrocyte and cartilage-defect literature ²⁰.

This is the most internally consistent branch of the file, and it is entirely animal and cell work.

Nervous system. MGF promoted neurogenesis in the aging mouse brain ¹³. It protected against cisplatin-induced neurotoxicity through an interaction with nucleolin — the only named molecular partner in this literature ¹⁶.

The neuroprotection work is where the mechanistic account is least vague, and it is also the branch furthest from the use the compound is marketed for.

Heart. MGF reduced loss of cardiac function in a rat model of acute myocardial infarction ². The E domain modulated cardiac contractile function through 14-3-3 protein interactomes ¹⁹. Cardiac expression of the variant is induced by thyroid hormone and depends on the cells continuing to beat ³.

The cardiac work studies the splice variant and its E domain in situ far more than it studies an injected peptide, and the 2014 null result was obtained in cardiac myocytes ⁷.

Oncology. MGF expression was investigated in osteosarcoma cell lines, where the E peptide had a regulatory role ¹⁰, and in colorectal cancer using fluorescent gold nanoparticles ¹⁴.

Both are expression and mechanism studies rather than safety studies, but a growth-associated splice product being differentially expressed in two tumour types is the kind of observation that would normally precede a carcinogenicity question. That question has not been asked.

Product identity. In an analysis of 17 black-market products labelled as follistatin, MGF was among the growth-promoting peptides found in vials that did not contain the substance on the label ¹⁵.

The only appearance of MGF material in an analytical chemistry record is as a contaminant in something else.

05 · Evidence overview

06 · Safety profile

Animal data. No formal toxicology exists in any species. The rabbit bone-defect ⁵, rat tendon ¹², rat myocardial infarction ² and mouse neurogenesis ¹³ studies report efficacy endpoints over days to weeks and do not systematically record adverse events. The one finding with a plausible safety reading is the osteoblast result: inhibition of differentiation and mineralisation ⁶ would be an unwanted effect in any bone-healing context, and it comes from the same peptide credited with promoting bone-defect healing elsewhere ⁵.

Human data. None exists. There is no reported human exposure to MGF peptide in the peer-reviewed literature at any dose, by any route, for any duration.

What is genuinely unknown. Whether the peptide has a physiological role at all — that is not rhetorical framing, it is the closing sentence of the largest replication attempt ⁷. What it binds, since no receptor has been identified and nucleolin ¹⁶ is a single interaction in a single context. Its pharmacokinetics in any species, absent entirely, with the development of encapsulated formulations ⁹ the only indirect evidence that the unmodified peptide clears quickly. Repeat-dose toxicology, genotoxicity, reproductive toxicology and carcinogenicity, none of which has been performed — the last of these notable because differential expression in osteosarcoma ¹⁰ and colorectal cancer ¹⁴ is documented and untested as a risk. Immunogenicity, unassessed, and relevant for a 24-residue fragment presenting a non-native terminus. And whether anything sold under this name contains it, given that the sole analytical record of MGF material describes it as an unlabelled contaminant ¹⁵.

07 · US regulatory status

Current as of 6 September 2026. MGF is not approved as a drug in the United States or any other jurisdiction and is not a controlled substance.

No marketing authorisation has been sought or granted anywhere for the E peptide. No investigational new drug programme appears in the peer-reviewed record. The compound’s development history, as far as the indexed literature shows it, consists of academic characterisation from roughly 2007 onward and one industry attempt at replication that did not proceed further ⁷.

Under the World Anti-Doping Code, growth factors affecting muscle are prohibited at all times. Detection work is limited: the one analytical method in which MGF appears was developed for follistatin and found MGF incidentally ¹⁵. Competitors should consult the current Prohibited List directly rather than rely on secondary summaries, including this one.

08 · Limitations of the evidence

1. The central claim failed independent replication, and the replication was better designed than most of the work it tested. Three cell types including primary human myoblasts and primary mouse muscle stem cells, concentrations to 500 ng/mL, native and stabilised peptide, positive controls that worked. Nothing ⁷. This is the single most important fact about MGF and it is rarely presented alongside the compound.
2. No receptor has been identified. Twenty years of mechanistic papers describe downstream cascades — Fyn-RhoA-YAP ²¹, Rac1-PAK1/2 and RhoA-ROCK1 ¹⁸, 14-3-3 interactomes ¹⁹ — without establishing what the peptide binds at the cell surface to start any of them. Nucleolin ¹⁶ is one interaction in one paper. A mechanism with no receptor is a description of correlated events.
3. There is no human evidence of any kind. Not one indexed study reports administration of MGF peptide to a person.
4. The splice-variant biology is repeatedly used to support claims about the peptide. That the IGF-1Ec transcript rises after mechanical loading ³ is well established and says nothing about what an isolated 24-residue fragment does when injected. Much of the field’s framing depends on this elision, and this guide has tried not to reproduce it.
5. The bone literature contradicts itself and has not been reconciled. Promotion of osteoblast proliferation and defect healing ⁵ against inhibition of differentiation and mineralisation ⁶. Neither result has been retracted; neither has been explained by the other.
6. Animal-to-human translation is untested and unusually uncertain here. The rodent variant (IGF-1Eb) and the human variant (IGF-1Ec) differ in the length of the splice insert — 52 base pairs against 49 ⁴ — which means the E-domain sequences studied in rodents are not the human sequence. A field whose animal models express a different peptide from the one sold has a translation problem before any species difference in physiology is considered.
7. Publication bias is a live concern in a file with one published null. The 2014 replication exists because two companies had a commercial reason to test the claim and no reason to suppress a negative result ⁷. Academic groups working on a molecule they believe in do not face the same incentive, and the number of unpublished attempts is unknown.
8. No randomised controlled trial exists, in any species, for any endpoint.
9. The one age group the compound is discussed for is the one where the positive result failed. The satellite cell effect was present in neonatal and young adult donors and absent in old adult donors ⁴. That qualification appears in the original paper’s own results.
10. Material identity is unestablished. The only analytical record of MGF material found it in vials labelled as something else ¹⁵. No published analysis has examined a product sold as MGF.

09 · References

1. Mills P, Dominique JC, Lafrenière JF, Bouchentouf M, Tremblay JP. A synthetic mechano growth factor E peptide enhances myogenic precursor cell transplantation success. Am J Transplant. 2007 Oct;7(10):2247–2259.

   PMID 17845560 ↗

2. Carpenter V, Matthews K, Devlin G, et al. Mechano-growth factor reduces loss of cardiac function in acute myocardial infarction. Heart Lung Circ. 2008 Feb;17(1):33–39.

   PMID 17581790 ↗

3. van Dijk-Ottens M, Vos IH, Cornelissen PW, de Bruin A, Everts ME. Thyroid hormone-induced cardiac mechano growth factor expression depends on beating activity. Endocrinology. 2010 Feb;151(2):830–838.

   PMID 20032059 ↗

4. Kandalla PK, Goldspink G, Butler-Browne G, Mouly V. Mechano Growth Factor E peptide (MGF-E), derived from an isoform of IGF-1, activates human muscle progenitor cells and induces an increase in their fusion potential at different ages. Mech Ageing Dev. 2011 Apr;132(4):154–162.

   PMID 21354439 ↗

5. Deng M, Zhang B, Wang K, et al. Mechano growth factor E peptide promotes osteoblasts proliferation and bone-defect healing in rabbits. Int Orthop. 2011 Jul;35(7):1099–1106.

   PMID 21057789 ↗

6. Xin C, Bingbing Z, Yuanliang W, et al. Mechano-growth factor E peptide inhibits the differentiation and mineralization of osteoblasts. Arch Oral Biol. 2012 Jun;57(6):720–727.

   PMID 22186070 ↗

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 Jan 15;306(2):E150–E156.

   PMID 24253050 ↗

8. Cui H, Yi Q, Feng J, Yang L, Tang L. Mechano growth factor E peptide regulates migration and differentiation of bone marrow mesenchymal stem cells. J Mol Endocrinol. 2014 Jan 30;52(2):111–120.

   PMID 24323763 ↗

9. Niu X, Chen P, Jia X, et al. Microencapsulation of mechano growth factor E peptide for sustained delivery and bioactivity maintenance. Int J Pharm. 2014 Jul 20;469(1):214–221.

   PMID 24768406 ↗

10. Shang J, Fan X, Liu H. The role of mechano-growth factor E peptide in the regulation of osteosarcoma. Oncol Lett. 2015 Aug;10(2):697–704.

    PMID 26622556 ↗

11. Li H, Lei M, Luo Z, et al. Mechano-growth factor enhances differentiation of bone marrow-derived mesenchymal stem cells. Biotechnol Lett. 2015 Nov;37(11):2341–2348.

    PMID 26330369 ↗

12. Zhang B, Luo Q, Kuang D, Ju Y, Song G. Mechano-growth factor E peptide promotes healing of rat injured tendon. Biotechnol Lett. 2016 Oct;38(10):1817–1825.

    PMID 27334712 ↗

13. Tang JJ, Podratz JL, Lange M, Scrable HJ, Jang MH, Windebank AJ. Mechano growth factor, a splice variant of IGF-1, promotes neurogenesis in the aging mouse brain. Mol Brain. 2017 Jul 7;10(1):23.

    PMID 28683812 ↗

14. Alagaratnam S, Yang SY, Loizidou M, Fuller B, Ramesh B. Mechano-growth factor expression in colorectal cancer investigated with fluorescent gold nanoparticles. Anticancer Res. 2019 Apr;39(4):1705–1710.

    PMID 30952709 ↗

15. Reichel C, Gmeiner G, Thevis M. Detection of black market follistatin 344. Drug Test Anal. 2020.

    PMID 31758732 ↗

16. Podratz JL, Tang JJ, Polzin MJ, et al. Mechano growth factor interacts with nucleolin to protect against cisplatin-induced neurotoxicity. Exp Neurol. 2020 Sep;331:113376.

    PMID 32511954 ↗

17. Sha Y, Cai W, Mohanad Khalid A, et al. Pretreatment with mechano growth factor E peptide attenuates osteoarthritis through improving cell proliferation and extracellular matrix synthesis in chondrocytes under severe hypoxia. Int Immunopharmacol. 2021 Aug;97:107628.

    PMID 34015701 ↗

18. Sha Y, Zhang B, Chen L, Hong H, Chi Q. Mechano growth factor accelerates ACL repair and improves cell mobility of mechanically injured human ACL fibroblasts by targeting Rac1-PAK1/2 and RhoA-ROCK1 pathways. Int J Mol Sci. 2022 Apr 14;23(8):4331.

    PMID 35457148 ↗

19. Solís C, Thompson WC, Peña JR, et al. Mechano-growth factor E-domain modulates cardiac contractile function through 14-3-3 protein interactomes. Front Physiol. 2022 Nov 16;13:1028345.

    PMID 36467694 ↗

20. Liu Y, Duan M, Zhang D, Xie J. The role of mechano growth factor in chondrocytes and cartilage defects: a concise review. Acta Biochim Biophys Sin (Shanghai). 2023 May 12;55(5):701–712.

    PMID 37171185 ↗

21. Feng F, Tu T, Wang H, et al. Mechano-growth factor regulates periodontal ligament stem cell proliferation and differentiation through Fyn-RhoA-YAP signaling. Biochem Biophys Res Commun. 2024 Nov 12;733:150450.

    PMID 39067248 ↗

22. Dominikowski A, Rękoś K, Olejarz M, Szczepanek-Parulska E, Domin R, Ruchała M. The emerging landscape of performance-enhancing peptides modulating GH-IGF1 axis: bridging the gap between clinical evidence and patient self-administration. Front Endocrinol (Lausanne). 2026.

    PMID 42395176 ↗