Insulin-like growth factor

While IGF-2 may be primarily fetal in action it is also essential for development and function of organs such as the brain, liver, and kidney.

[2][3][4] IGF-1 has an involvement in regulating neural development including neurogenesis, myelination, synaptogenesis, and dendritic branching and neuroprotection after neuronal damage.

There is currently significant data suggesting that IGFBPs play important roles in addition to their ability to regulate IGFs.

IGFBP-1 production from the liver is significantly elevated during insulinopenia while serum levels of bioactive IGF-1 is increased by insulin.

[11] Nematodes, fruit-flies, and other organisms have an increased life span when the gene equivalent to the mammalian insulin is knocked out.

It is somewhat difficult to relate this finding to the mammals, however, because in the smaller organism there are many genes (at least 37 in the nematode Caenorhabditis elegans[12]) that are "insulin-like" or "IGF-1-like", whereas in the mammals insulin-like proteins comprise only seven members (insulin, IGFs, relaxins, EPIL, and relaxin-like factor).

[14] Additionally, C. elegans do not have specialized organs such as the (Islets of Langerhans), which sense insulin in response to glucose homeostasis.

Moreover, IGF1 affects lifespan in nematodes by causing dauer formation, a developmental stage of C. elegans larva.

Therefore, it is an open question as to whether either IGF-1 or insulin in the mammal may perturb aging, although there is the suggestion that dietary restriction phenomena may be related.