IGF-1 LR3

What Is IGF-1 LR3?

IGF-1 LR3 is a recombinant analogue of endogenous IGF-1 with two modifications: N-terminal methionine extension and glutamic acid→arginine (R3) substitution. The R3 change reduces IGFBP binding affinity >1000×, extending half-life from ~12 minutes to 20–30 hours.

Key Mechanisms

• PI3K→Akt→mTORC1 — phosphorylates S6K1 and 4E-BP1, driving ribosomal biogenesis and protein translation
• Ras→MEK→ERK — cell cycle progression (G1→S via cyclin D1), DNA replication, differentiation
• FOXO suppression — phosphorylates FOXO1/3a, blocking MuRF1 and Atrogin-1 transcription — prevents muscle proteolysis
• Satellite cell activation — drives skeletal muscle stem cell proliferation and myofibre formation

Key References

1. Coleman ME et al. “IGF-I stimulates muscle cell differentiation and myofiber hypertrophy.” J Biol Chem, 1995;270:12109–12116.
2. Foulstone EJ et al. “Role of IGFBP-3 in the IGF axis of human skeletal muscle.” J Cell Physiol, 2003;196:229–240.