IGF1

IGF-1, or insulin-like growth factor 1, is a peptide hormone with structural similarity to insulin. It is produced primarily by the liver in response to growth hormone (GH) stimulation and acts as a principal mediator of GH actions on growth and metabolism. In blood, IGF-1 is largely bound to IGF-binding proteins, and a substantial portion circulates in a ternary complex with the acid-labile subunit to prolong its half-life.

IGF-1 is also synthesized locally in various tissues, including cartilage, muscle, and brain, where it can act in an autocrine or paracrine manner. Its production is regulated by nutritional status, age, sex steroids, and insulin, in addition to GH signaling through pathways such as JAK-STAT.

IGF-1 exerts most of its biological effects by binding to the IGF-1 receptor (IGF1R), a receptor tyrosine kinase. Receptor activation triggers signaling cascades, notably the PI3K-AKT and MAPK pathways, promoting cell proliferation, protein synthesis, and survival. In growing long bones, IGF-1 stimulates chondrocyte proliferation and bone elongation; it also influences muscle mass, bone density, and metabolic processes.

Clinically, serum IGF-1 levels are used to assess the GH axis, helping diagnose GH deficiency and acromegaly. Low IGF-1 suggests GH deficiency or GH resistance, while high IGF-1 indicates GH excess. Therapeutically, recombinant human IGF-1 (mecasermin) is approved for severe IGF-1 deficiency, including GH insensitivity syndromes.