Mechano Growth Factor (MGF)

What Is Mechano Growth Factor (MGF)?

Mechano growth factor (MGF) is a form of insulin-like growth factor 1 (IGF-1) that skeletal muscle makes by alternative splicing when it is exercised or damaged. A 2004 review described two muscle IGF-1 forms: one similar to the liver type (IGF-IEa) and one expressed in response to physical activity, named MGF, whose different peptide sequence was linked to replenishing muscle satellite (stem) cells.^[1]

In humans, MGF corresponds to the IGF-1Ec isoform, which arises from alternative splicing of exons 4, 5 and 6 of the IGF-1 gene.^[2] Much of the research focuses on the unique E-domain region at its C-terminus, using a synthetic analog of the last 24 amino acids of that domain.^[2]

Published work now extends well beyond muscle, covering cartilage, bone marrow stem cells, heart, intestinal smooth muscle and the nervous system.^[3][4][5] In the brain, earlier studies reported neuroprotection against 6-hydroxydopamine toxicity and ischemic injury.^[6] Nearly all of this work is preclinical.

Chemical Structure and Molecular Identity

MGF is defined by its E domain, the C-terminal extension that differs between IGF-1 splice variants, rather than by the mature IGF-1 sequence it shares with other isoforms. In the heart, splicing produces IGF-IEa and IGF-IEc (MGF), and the divergence between their E-domain sequences suggests they have different functions.^[4]

PubChem has no compound record for MGF, so this page does not state a formula or molecular weight. The research peptide is described as a synthetic analog of the last 24 amino acids of the IGF-1Ec E domain.^[2]

Published peptide variants

• Phospho-mimetic (S/E18) and phospho-null (S/A18) peptides: made to test a predicted phosphorylation site at serine 18 within a putative 14-3-3 binding motif.^[4]
• CMGF: MGF with a cysteine added to the N-terminus, tested alongside unmodified MGF in neuron culture.^[6]
• MGF E peptide: the E-domain peptide applied to human bone marrow stem cells.^[7]

Because these variants differ at single residues or termini, the exact peptide used in any study should be checked in its methods. A pegylated form, PEG-MGF, is covered on its own page.

Research History and Development

MGF was first described in skeletal muscle as the IGF-1 variant that responds to mechanical load, and later studies traced it to cartilage, heart, gut and brain. Its name reflects that origin as a mechanically sensitive growth factor.^[5][3]

Early interest centered on muscle aging. Reviews reported that the ability to produce MGF declines with age, in parallel with falling growth hormone, and that short-term high-resistance exercise raised MGF mRNA in young but not elderly subjects.^[1][8] One review proposed that growth hormone combined with resistance exercise shifts more IGF-1 splicing toward MGF.^[1]

From the late 2000s, researchers tested MGF in neurodegeneration, cardiac function and stem-cell differentiation. A 2014 review noted that IGF-1Ec is preferentially increased after skeletal muscle injury, during post-infarction heart remodeling and in cancer tissues and cell lines.^[2] A 2023 review concluded that MGF’s role in cartilage remains controversial and its mechanism elusive.^[3]

Mechanisms Studied in Research

Studies suggest the MGF E domain acts through pathways distinct from mature IGF-1, including Erk5-MEF2C signaling in smooth muscle, nucleolin binding in neurons and 14-3-3 interactions in the heart. These mechanisms come from cell and animal experiments.^[9][6][4]

Smooth muscle hypertrophy

In muscle cells from patients with fibrostenotic Crohn’s disease, IGF-IEc transcripts and MGF protein were elevated under the control of endogenous TGF-beta1. Synthetic MGF caused Erk5 and MEF2C phosphorylation and nuclear colocalization, and blocking Erk5 or silencing MEF2C prevented MGF-induced hypertrophy.^[9]

Nucleolin binding in neurons

Mass spectrometry of proteins bound to MGF identified nucleolin as a key partner. Antibodies against nucleolin abolished the protective effect of MGF and CMGF in dorsal root ganglion neurons, and both proteins localized to the nucleolus.^[6]

Cardiac 14-3-3 interactions and cell cycle

In silico analysis of the E domain found a serine 18 phosphorylation site in a putative 14-3-3 binding motif, and 14-3-3 gamma localized to cardiac myofilaments.^[4] In human bone marrow stem cells, MGF lengthened the G1 phase of the cell cycle and slowed proliferation while enhancing differentiation.^[7]

Key Findings From Published Studies

Published studies report that MGF affects neuron survival, neurogenesis, stem-cell differentiation, smooth muscle growth and cardiac function in cell and rodent models, but no controlled human trials have tested it. Results are grouped by model.

Nervous system

• SOD1(G93A) ALS mice: muscle gene delivery of MGF or IGF-1 at symptom onset improved hindlimb strength and motor unit and motoneuron survival; significantly more motoneurons survived with MGF.^[10]
• Aging mouse brain: transgenic MGF overexpression increased proliferating cells in the hippocampal dentate gyrus and subventricular zone. Conditional overexpression started at 1 or 3 months, but not 12 months, increased new olfactory bulb neurons at 24 months and preserved olfactory function.^[5]
• Cisplatin neurotoxicity: endogenous MGF expression in adult dorsal root ganglion neurons reduced cisplatin-induced thermal hyperalgesia in vivo, and MGF and CMGF protected embryonic neurons from cell death in vitro.^[6]

Stem cells, cartilage and heart

• Human bone marrow stem cells: MGF E peptide significantly increased osteogenic, adipogenic and chondrogenic differentiation, and plasmid overexpression confirmed the effect.^[7]
• Cartilage: MGF is highly expressed in chondrocytes of damaged cartilage, including in osteoarthritis, and influences chondrocyte proliferation, migration, differentiation, inflammation and apoptosis.^[3]
• Mouse heart: over 2 weeks, the phospho-mimetic and phospho-null peptides depressed systolic and diastolic function at the lowest and highest dose levels tested, but had opposing effects at the intermediate level, linked to 21 genes including Nr4a2.^[4]
• Crohn’s disease smooth muscle: conditioned media from fibrostenotic muscle cultures induced hypertrophy that was blocked by neutralizing endogenous MGF or pro-IGF-IEc, and smooth muscle actins and smoothelin were increased in affected intestine.^[9]

Human tissue observations

In 99 archived endometrial carcinomas, IGF-1Ec staining was higher in non-endometrioid than endometrioid tumors and correlated negatively with PTEN expression.^[11] These are expression findings, not effects of administered peptide.

MGF peptides differ by length, phosphorylation-site variants and terminal modifications, so HPLC and mass spectrometry data on a certificate of analysis confirm identity.

Regulatory and Research Status

MGF is not approved by the US Food and Drug Administration or any other regulator for human use, and no controlled human trials of the peptide appear in the studies reviewed here. It is used as a research tool in cell culture and animal models.^[2]

Mechano growth factors are named among prohibited growth factors on the World Anti-Doping Agency’s Prohibited List. Reviewers have discussed potential relevance to muscle aging, but those discussions remain hypotheses rather than tested clinical findings.^[1][8]

Open questions

The authors of the ALS mouse study noted that clinical trials of IGF-1 itself in ALS gave conflicting results, which is part of why they examined MGF as an alternative in animals.^[10] For cartilage, a 2023 review described MGF’s role in development, homeostasis and disease as still controversial, with its internal biological mechanism unresolved.^[3] In the mouse heart study, the direction of the effect on contractile function changed across the dose levels tested.^[4]