Motor neurone targeting of IGF-1 prevents specific force decline in ageing mouse muscle


  • A. M. Payne and Z. Zheng contributed equally to this work.

Corresponding author O. Delbono: Department of Physiology and Pharmacology, Wake Forest University School of Medicine, 1 Medical Center Boulevard, Winston-Salem, NC 27157, USA. Email:


IGF-1 is a potent growth factor for both motor neurones and skeletal muscle. Muscle IGF-1 is known to provide target-derived trophic effects on motor neurones. Therefore, IGF-1 overexpression in muscle is effective in delaying or preventing deleterious effects of ageing in both tissues. Since age-related decline in muscle function stems partly from motor neurone loss, a tetanus toxin fragment-C (TTC) fusion protein was created to target IGF-1 to motor neurones. IGF-1–TTC retains IGF-1 activity as indicated by [3H]thymidine incorporation into L6 myoblasts. Spinal cord motor neurones effectively bound and internalized the IGF-1–TTC in vitro. Similarly, IGF-1–TTC injected into skeletal muscles was taken up and retrogradely transported to the spinal cord in vivo, a process prevented by denervation of injected muscles. Three monthly IGF-1–TTC injections into muscles of ageing mice did not increase muscle weight or muscle fibre size, but significantly increased single fibre specific force over aged controls injected with saline, IGF-1, or TTC. None of the injections changed muscle fibre type composition, but neuromuscular junction post-terminals were larger and more complex in muscle fibres injected with IGF-1–TTC, compared to the other groups, suggesting preservation of muscle fibre innervation. This work demonstrates that induced overexpression of IGF-1 in spinal cord motor neurones of ageing mice prevents muscle fibre specific force decline, a hallmark of ageing skeletal muscle.