Axonal protein synthesis and degradation are necessary for efficient growth cone regeneration.
Axonal regeneration can occur within hours of injury, the first step being the formation of a new growth cone. For sensory and retinal axons, regenerative ability in vivo correlates with the potential to form a new growth cone after axotomy in vitro. We show that this ability to regenerate a new growth cone depends on local protein synthesis and degradation within the axon. Axotomy in vitro leads to a fourfold to sixfold increase in 3H-leucine incorporation in both neurones and axons, starting within 10 min and peaking 1 h after axotomy. Application of protein synthesis inhibitors (cycloheximide and anisomycin) to cut axons, including axons whose cell bodies were removed, or proteasome inhibitors (lactacystin and N-acetyl-Nor-Leu-Leu-Al) all result in a reduction in the proportion of transected axons able to reform growth cones. Similar inhibition of growth cone formation was observed on addition of target of rapamycin (TOR), p38 MAPK (mitogen-activated protein kinase), and caspase-3 inhibitors. Comparing retinal and sensory axons of different developmental stages, levels of ribosomal protein P0 and phosphorylated translation initiation factor are high in sensory axons, lower in embryonic axons, and absent in adult retinal axons. Conditioning lesions, which increase the regenerative ability of sensory axons, lead to increases in intra-axonal protein synthetic and degradative machinery both in vitro and in vivo. Collectively, these findings suggest that local protein synthesis and degradation, controlled by various TOR-, p38 MAPK-, and caspase-dependent pathways, underlie growth cone initiation after axotomy.
Verma
Poonam
P
Cambridge University Centre for Brain Repair, Cambridge CB2 2PY, United Kingdom.
Chierzi
Sabrina
S
Codd
Amanda M
AM
Campbell
Douglas S
DS
Meyer
Ronald L
RL
Holt
Christine E
CE
Fawcett
James W
JW
D000375:Aging / Q000502:physiology; D000818:Animals; D001369:Axons / Q000378:metabolism / Q000502:physiology*; D019771:Axotomy; D053148:Caspase 3; D061945:Caspase Inhibitors; D020169:Caspases / Q000502:physiology; D002478:Cells, Cultured; D005260:Female; D005727:Ganglia, Spinal / Q000166:cytology; D020439:Growth Cones / Q000502:physiology*; D009416:Nerve Regeneration / Q000502:physiology*; D009419:Nerve Tissue Proteins / Q000096:biosynthesis / Q000378:metabolism*; D009475:Neurons, Afferent / Q000502:physiology* / Q000648:ultrastructure; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011494:Protein Kinases / Q000502:physiology; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012160:Retina / Q000196:embryology / Q000502:physiology / Q000648:ultrastructure*; D012584:Sciatic Nerve / Q000293:injuries; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D058570:TOR Serine-Threonine Kinases; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000502:physiology
D061945:Caspase Inhibitors; D009419:Nerve Tissue Proteins; D061988:Proteasome Inhibitors; D047428:Protein Kinase Inhibitors; D011500:Protein Synthesis Inhibitors; D011494:Protein Kinases; C546845:mTOR protein, rat; D058570:TOR Serine-Threonine Kinases; D048051:p38 Mitogen-Activated Protein Kinases; C505410:Casp3 protein, rat; D053148:Caspase 3; D020169:Caspases; D046988:Proteasome Endopeptidase Complex