The multifunctional role of IGF-1 in peripheral nerve regeneration.

The elements of peripheral nerve regeneration comprise a complex combination of nerve growth, muscle satellite cells proliferation and differentiation and vessel growth. There is also increasing evidence that growth factors may act at multiple levels in the regenerative response. One such factor affecting multiple cell processes is insulin-like growth factor (IGF-1). As a neurotrophic factor IGF-1 is known to promote nerve elongation and branching. As a myogenic factor, IGF-1 promotes satellite cell proliferation, differentiation and muscle hypertrophy. As an angiogenic factor, IGF-1 is known to promote angiogenesis in regenerating skeletal muscle by activating VEGF and VEGF receptors. Additionally, recent studies show that IGF-1 may also promote the activation of muscle stem cells during the regenerative process. This review will outline the pathways by which IGF-1 affects multiple layers of the regenerative response and how these pathways converge to promote the regeneration of nerves.