Insulin-like Growth Factor (IGF) [Neurosurgery Wiki]

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==== Insulin-like Growth Factor (IGF) ====

**Insulin-like Growth Factors (IGFs)** are peptide hormones structurally similar to insulin, playing a key role in growth, development, and cellular regulation. There are two main types:

=== IGF-1 (Insulin-like Growth Factor 1) ===
  * Primarily produced in the **liver** in response to **growth hormone (GH)** stimulation.
  * Acts as the main mediator of the **anabolic and growth-promoting effects** of GH.
  * Essential for **childhood growth** and contributes to **tissue repair, muscle maintenance,** and **metabolic regulation** in adulthood.
  * Levels decline with **age** and are influenced by **nutrition**, **exercise**, and **health status**.

=== IGF-2 (Insulin-like Growth Factor 2) ===
  * More active during **fetal development**.
  * Functions largely **independent of GH**.
  * Its role in adults remains less clearly understood.

=== Biological Properties ===
  * **Mitogenic**: Stimulates cell proliferation.
  * **Anti-apoptotic**: Promotes cell survival.
  * Binds to **IGF receptors**, especially **IGF-1R**, activating pathways such as **PI3K-AKT** and **MAPK**.
  * Circulates bound to **IGF-binding proteins (IGFBPs)**, especially **IGFBP-3**, which regulate its bioavailability.

=== Clinical Relevance ===
  * ↑ IGF-1: Associated with **acromegaly**, **neoplasms**, and **insulin resistance**.
  * ↓ IGF-1: Linked to **growth disorders**, **frailty**, **osteoporosis**, and **aging**.