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The insulin-like growth factors (IGFs) are proteins with high sequence similarity to insulin. IGFs are part of a complex system that cells use to communicate with their physiologic environment. This complex system (often referred to as the IGF "axis") consists of two cell-surface receptors (IGF1R and IGF2R), two ligands (Insulin-like growth factor 1 (IGF-1) and Insulin-like growth factor 2 (IGF-2)), a family of six high-affinity IGF-binding proteins (IGFBP-1 to IGFBP-6), as well as associatedIGFBP degrading enzymes, referred to collectively as proteases.

Contents [hide] 1 IGF1/GH Axis 2 IGF receptors 3 Organs and tissues affected by IGF-1 4 IGF-Binding Proteins 5 Diseases affected by IGF 6 See also 7 References 8 External links

[edit]IGF1/GH Axis

The IGF "axis" is also commonly referred to as the Growth Hormone/IGF1 Axis. Insulin-like growth factor 1 (IGF-1) is mainly secreted by the liver as a result of stimulation by growth hormone (GH). IGF-1 is important for both the regulation of normal physiology, as well as a number of pathological states, including cancer. The IGF axis has been shown to play roles in the promotion of cell proliferation and the inhibition of cell death (apoptosis). Insulin-like growth factor 2 (IGF-2) is thought to be a primary growth factor required for early development while IGF-1 expression is required for achieving maximal growth. Gene knockout studies in mice have confirmed this, though other animals are likely to regulate the expression of these genes in distinct ways. 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.

Factors that are known to cause variation in the levels of GH and IGF-1 in the circulation include an individuals genetic make-up, the time of day, their age, sex, exercise status, stress levels, genetics, nutrition level and body mass index (BMI), disease state, race, estrogen status andxenobiotic intake.

IGF-I has an involvement in regulating neural development including neurogenesis, myelination, synaptogenesis, and dendritic branching and neuroprotection after neuronal damage. Increased serum levels of IGF-I in children link to higher IQ.^[1]

IGF-1 shape the development of the cochlea through controlling apoptosis. Its deficit can cause hearing loss. Serum level of it also underlies a correlation between short height and reduced hearing abilities particularly around 3–5 years of age, and at age 18 (late puberty).^[2]

[edit]IGF receptors