IGF-1 LR3 and PEG-MGF are both derived from insulin-like growth factor 1 (IGF-1), but they come from different parts of the IGF-1 system and are used to ask different questions. IGF-1 LR3 is an engineered analog of mature IGF-1 that escapes the binding proteins that normally restrict IGF-1 activity. MGF, by contrast, is a synthetic peptide based on the unique E domain of one IGF-1 splice variant, and PEG-MGF is a pegylated form of that peptide. This article compares the two and is clear about where the evidence is strong and where it is thin.
Both compounds are supplied by BioSim for laboratory research only. They are not for human or veterinary use, and nothing here is guidance on administration to people or animals.
Background: IGF-1, Its Binding Proteins and Its Splice Variants
Mature IGF-1 is a 70-amino-acid peptide that signals through the type 1 IGF receptor (IGF-1R). In tissue fluids and plasma, most IGF-1 is held by IGF-binding proteins (IGFBPs), which limit how much free IGF-1 reaches cells. Analogs that bind IGFBPs weakly therefore behave as more potent agonists in many systems.
The IGF-1 gene is also alternatively spliced. Different E-domain exons produce precursor forms with different C-terminal extensions. In muscle, one splice variant, called IGF-IEb in rodents and IGF-IEc in humans, responds to mechanical stress and damage and was named mechano growth factor (MGF) (Kandalla et al., 2011; Matheny et al., 2010).
IGF-1 LR3: An IGFBP-Evading Analog
IGF-1 LR3 (Long R3 IGF-1) is an 83-amino-acid analog of IGF-1. It carries two changes: arginine in place of glutamic acid at position 3, and a 13-residue N-terminal extension derived from the start of porcine growth hormone. The extension was introduced partly to improve folding during recombinant production (Francis et al., 1992).
Key findings:
- Cell potency. In L6 rat myoblasts, the Long IGF-I analogs were more potent than authentic IGF-I at stimulating protein and DNA synthesis and inhibiting protein breakdown. In cell lines that secrete IGFBPs, Long [Arg3]-IGF-I was among the most potent analogs. In chicken embryo fibroblasts, which do not secrete detectable IGFBPs, it was less potent than IGF-I, showing that the gain in potency comes from reduced IGFBP binding (Francis et al., 1992).
- Receptor binding. LR3IGF-I binds the type 1 IGF receptor about 3-fold less well than IGF-I does (Tomas et al., 1992).
- Animal models. In rats given dexamethasone, a catabolic model, IGF-I partially reversed weight and nitrogen loss, and the analogs that bind IGFBPs poorly, including LR3IGF-I, were about 2.5-fold more potent than IGF-I. The authors linked this to the rise in plasma IGFBPs, particularly IGFBP-3, which would restrict IGF-I but not the analogs (Tomas et al., 1992).
IGF-1 LR3 is widely used in cell culture as a stable, IGFBP-resistant IGF-1R agonist, and in studies of muscle protein turnover and growth signaling.
MGF and PEG-MGF: The E-Domain Peptide
The research peptide called MGF is a synthetic peptide corresponding to the 24 most C-terminal residues of the IGF-IEb precursor, from the region unique to that splice variant (Matheny et al., 2010). It is not the same as mature IGF-1, and it is thought to act independently of IGF-1R.
Key findings:
- Expression after damage. After mechanical or chemical damage to rat muscle, MGF mRNA was expressed rapidly and declined within a few days, while IGF-IEa rose more slowly. The timing, alongside satellite cell activation markers, suggested an early MGF pulse linked to satellite cell activation (Hill & Goldspink, 2003).
- Proliferation vs differentiation. In a myoblast cell model, the MGF E domain increased proliferation and inhibited terminal differentiation, unlike mature IGF-1. Blocking IGF-1R with an antibody did not prevent the effect, which indicated a different receptor (Yang & Goldspink, 2002).
- Human muscle progenitor cells. The MGF-24aa-E peptide increased the proliferative life span and delayed senescence of satellite cells from neonatal and young adult muscle, but not from old adult muscle (Kandalla et al., 2011).
Important caveats
A detailed review drew a sharp line between the synthetic peptide and the biology of the IGF-1 gene. Synthetic MGF has been shown to promote cell proliferation and survival, but no analogous peptide product of the Igf1 gene has been identified in or isolated from cells, conditioned medium, animal tissues or biological fluids (Matheny et al., 2010). The receptor for the E peptide has also not been identified. Results with synthetic MGF should be read as effects of a defined synthetic peptide, not necessarily of a natural hormone.
PEG-MGF adds a polyethylene glycol (PEG) chain to the MGF peptide. Pegylation is a general strategy for slowing enzymatic breakdown and clearance of peptides. Most published MGF studies used the unmodified E peptide, and peer-reviewed data on the pegylated form specifically are limited. Researchers using PEG-MGF should not assume that every finding with unmodified MGF transfers directly, and should include their own characterization and controls.
Side-by-Side Comparison
| Property | IGF-1 LR3 | PEG-MGF |
|---|---|---|
| Origin | Engineered analog of mature IGF-1 | Pegylated synthetic E-domain peptide of the IGF-IEb/Ec splice variant |
| Length | 83 amino acids | 24-residue peptide plus PEG chain |
| Receptor | Type 1 IGF receptor | Not identified; appears independent of IGF-1R |
| Key property | Weak IGFBP binding, so higher potency where IGFBPs are present | Promotes proliferation and delays differentiation of muscle precursor cells (unmodified MGF data) |
| Evidence base | Well characterized in cell and animal studies | Moderate for unmodified MGF; limited for the pegylated form |
| Key references | Francis et al., 1992; Tomas et al., 1992 | Yang & Goldspink, 2002; Matheny et al., 2010 |
Experimental Design Notes
- Match the compound to the question. Use IGF-1 LR3 when the study needs sustained IGF-1R activation in the presence of IGFBPs. Use MGF or PEG-MGF when the question concerns satellite cell activation or the proliferation-to-differentiation switch.
- Include receptor controls. An IGF-1R blocking antibody or inhibitor can show whether an effect depends on IGF-1R, as in Yang & Goldspink (2002).
- Consider IGFBPs in the medium. Serum and many cell types contain IGFBPs, which change the apparent potency of IGF-1 and its analogs (Francis et al., 1992).
- Account for donor age. Responses of muscle precursor cells to MGF varied with donor age (Kandalla et al., 2011).
For related reading, see our tissue repair research overview, the HGH research guide and our Growth and Performance category.
Handling in the Lab
Both compounds are supplied lyophilized. Reconstitute with a suitable sterile diluent, swirl gently rather than shaking, aliquot the stock and avoid repeated freeze-thaw cycles. Larger peptides such as IGF-1 LR3 can adsorb to plastic at low concentrations, so many labs add a carrier protein to dilute working solutions. See our storage and stability guide for more detail.
Frequently Asked Questions
Is MGF a form of IGF-1?
It is derived from the IGF-1 gene, but the research peptide corresponds to the unique E-domain region of one splice variant, not to mature IGF-1, and it appears to act through a different receptor (Yang & Goldspink, 2002).
Why is IGF-1 LR3 more potent than IGF-1 in many systems?
It binds IGF-binding proteins poorly, so more of it stays free to activate IGF-1R, even though it binds the receptor itself somewhat less well (Tomas et al., 1992).
How do I confirm the identity of my lot?
Every BioSim lot is third-party tested, with identity confirmed by mass spectrometry. Available certificates are published on our COA page.
References
- Francis GL, Ross M, Ballard FJ, et al. (1992). Novel recombinant fusion protein analogues of insulin-like growth factor (IGF)-I indicate the relative importance of IGF-binding protein and receptor binding for enhanced biological potency. Journal of molecular endocrinology, 8(3), 213-23. PMID: 1378742 · DOI: 10.1677/jme.0.0080213
- Hill M, Goldspink G (2003). 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. The Journal of physiology, 549(Pt 2), 409-18. PMID: 12692175 · DOI: 10.1113/jphysiol.2002.035832
- Kandalla PK, Goldspink G, Butler-Browne G, et al. (2011). 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. Mechanisms of ageing and development, 132(4), 154-62. PMID: 21354439 · DOI: 10.1016/j.mad.2011.02.007
- Matheny RW Jr, Nindl BC, Adamo ML (2010). Minireview: Mechano-growth factor: a putative product of IGF-I gene expression involved in tissue repair and regeneration. Endocrinology, 151(3), 865-75. PMID: 20130113 · DOI: 10.1210/en.2009-1217
- Tomas FM, Knowles SE, Owens PC, et al. (1992). Insulin-like growth factor-I (IGF-I) and especially IGF-I variants are anabolic in dexamethasone-treated rats. The Biochemical journal, 282 ( Pt 1)(Pt 1), 91-7. PMID: 1371669 · DOI: 10.1042/bj2820091
- Yang SY, Goldspink G (2002). Different roles of the IGF-I Ec peptide (MGF) and mature IGF-I in myoblast proliferation and differentiation. FEBS letters, 522(1-3), 156-60. PMID: 12095637 · DOI: 10.1016/s0014-5793(02)02918-6
Research These Compounds: IGF-1 LR3 1mg and PEG-MGF 2mg from BioSim Peptides: 99%+ purity, every lot third-party tested with identity confirmed by mass spectrometry, and available certificates published on our COA page. For laboratory research use only. Not for human consumption.
