IGF-1 splice-variant peptide · muscle
A peptide based on the tail end of one IGF-1 splice variant (IGF-1Ec in humans), a form of IGF-1 that muscle makes after loading or injury. The name usually refers to a short synthetic peptide copying that unique tail, called the E-domain. It is a research compound and has not been studied as a treatment in people.
The IGF-1 gene can be spliced in more than one way. One version, named mechano growth factor, carries a distinct E-domain at its tail, and its message rises in muscle after exercise or injury. The proposed idea is that this E-domain peptide acts separately from mature IGF-1. Early cell-culture work reported that it made myoblasts (muscle precursor cells) multiply while holding back their fusion into fibers, and that blocking the classic IGF-1 receptor did not stop this, suggesting a different receptor. If so, it would act as an early signal that expands the pool of repair cells before mature IGF-1 drives growth. That model rests on a small number of lab studies, and later independent work could not reproduce these effects of the synthetic peptide.
Everything known comes from cell and animal work, plus measurements of the natural gene message in human muscle. In a mouse myoblast cell line, the MGF E-domain peptide increased proliferation and delayed differentiation, and an antibody blocking the IGF-1 receptor did not stop this1.
In human volunteers, a single bout of heavy leg exercise raised MGF mRNA in muscle biopsies of young but not older adults; no peptide was given2. In primary human muscle cells, a 24-amino-acid MGF E peptide extended the proliferative lifespan of cells from newborn and young adult donors, though not older adults, and increased fusion into larger fibers in cultures from all ages3. However, scientists at two drug companies could not reproduce any effect of the peptide on mouse or human myoblasts, mouse muscle stem cells or heart muscle cells, while mature IGF-1 worked in the same assays4. We found no human trials of MGF peptide registered on ClinicalTrials.gov.
Not approved as a medicine by the FDA, and we found no approval by any other regulator. It exists only as a research compound.
We found no published human studies of injected MGF peptide, so its side effects in people are unknown. Its effects on blood sugar, on cell growth or on anything else in humans have not been studied.
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