IGF

IGF, or insulin-like growth factor, refers to a family of peptide hormones with two main members, IGF-1 and IGF-2. They resemble insulin in structure and regulate growth and development. Most circulating IGF-1 is produced in the liver under growth hormone (GH) control, while IGF-2 is expressed in many tissues and plays a prominent role in fetal growth. Local production by cells adds to autocrine and paracrine signaling. In the bloodstream, IGFs are bound by IGF-binding proteins (IGFBPs), especially IGFBP-3 in a complex with the acid-labile subunit, which modulates bioavailability and half-life.

IGFs act primarily through the IGF-1 receptor (IGF1R), a receptor tyrosine kinase, and also interact with IGF2 receptors in a more limited way. Binding initiates signaling cascades such as the PI3K-AKT and MAPK pathways, promoting cell growth, survival, and metabolism. Physiologically, IGFs drive somatic growth, bone and muscle development, and support organ growth during development. IGF-1 mediates many effects of GH, while IGF-2 has a major role in fetal growth. Nutritional status and insulin levels influence IGF production and activity.

Clinical significance includes using serum IGF-1 levels as a biomarker of GH activity and as part of the evaluation of growth disorders. IGF-1 levels vary with age, sex, and nutrition, requiring age- and context-specific interpretation. Therapeutically, recombinant IGF-1 can treat certain GH-insensitive conditions such as Laron syndrome. The IGF axis is also studied in oncology because IGF signaling can promote tumor growth; however, targeting IGF1R has yielded limited clinical success so far.