Rat Sciatic Nerve Axoplasm Proteome Is Enriched with Ribosomal Proteins during Regeneration Processes

Axons
are complex subcellular compartments that are extremely long
in relation to cell bodies, especially in peripheral nerves. Many
processes are required and regulated during axon injury, including
anterograde and retrograde transport, glia-to-axon macromolecular
transfer, and local axonal protein synthesis. Many in vitro omics approaches have been used to gain insight into these processes,
but few have been applied in vivo. Here we adapted
the osmotic ex vivo axoplasm isolation method and
analyzed the adult rat sciatic-nerve-extruded axoplasm by label-free
quantitative proteomics before and after injury. 2087 proteins groups
were detected in the axoplasm, revealing translation machinery and
microtubule-associated proteins as the most overrepresented biological
processes. Ribosomal proteins (73) were detected in the uninjured
axoplasm and increased their levels after injury but not within whole
sciatic nerves. Meta-analysis showed that detected ribosomal proteins
were present in in vitro axonal proteomes. Because
local protein synthesis is important for protein localization, we
were interested in detecting the most abundant newly synthesized axonal
proteins in vivo. With an MS/MS-BONCAT approach,
we detected 42 newly synthesized protein groups. Overall, our work
indicates that proteomics profiling is useful for local axonal interrogation
and suggests that ribosomal proteins may play an important role, especially
during injury.