AMPK controls the regenerative programme of DRG sensory neurons after injury

Abstract

Regeneration after injury occurs in axons that lie in the peripheral nervous system but it fails in the central nervous system limiting functional recovery. Despite recent progress, to date we ignore the molecular identity of peripheral versus central projecting axons that might underpin this differential regenerative ability. To fill this knowledge gap, here we combined axoplasmic proteomics from sciatic or centrally projecting branches of L4-6 DRG with RNAseq to compare axonal and cell body responses between a regeneration-incompetent central spinal versus regeneration-competent peripheral sciatic nerve injury. This allowed identifying for the first time signalling pathways uniquely represented in peripheral versus central projecting L4- 6 DRG axons, including prior and subsequent to an injury. Next, RNAseq and proteomics network and pathway analysis suggested AMPK as master regulator controlling axonal regenerative signalling pathways. AMPK immunoprecipitation followed by mass spectrometry from DRG suggested that the 26S proteasome and the 26S regulatory subunit PSMC5 are preferentially bound to AMPKα for proteosomal degradation following sciatic axotomy. Mechanistically, we found that phosphorylation of proteosomal subunit PSMC5 and injury activated CaMKIIα are required for AMPKα1 degradation after sciatic injury. Moreover, ubiquitin E3 ligase Trim28 regulates AMPKα1 expression. Finally, conditional deletion of AMPKα1 promotes multiple regenerative signals, axonal regeneration and functional recovery of sensory axons across the injured spinal cord, suggesting inhibition of AMPK as novel regenerative target following spinal injury.