Expression of autophagic and ubiquitin-proteasome proteins in the peripheral nervous system after nerve injury

Background: Autophagy and ubiquitin-proteasome (UPS) are two main degradation systems for intracellular proteins. They are essential for homeostasis of neurons during normal and pathological conditions, but their changes after nerve injury remain unclear. Objective: To examine the protein expression of autophagy and UPS in the dorsal root ganglia (DRG), including intact and injured sciatic nerves after crush injury in rats. Methods: Left sciatic nerve crush was done in all Wistar rats and the specimens were removed at 1, 3, 7, and 14 days after injury. Expression of the autophagic (Beclin-1 and p62) and UPS proteins [muscle ring finger-1 (MuRF1) and ubiquitinated proteins] was measured using Western blot analysis. Results: Expression of p62 was significantly increased in the injured versus intact sciatic nerves on day 1 and day 7 (P < 0.05 and P < 0.01, respectively). There was a trend toward higher expression of Beclin-1 on the crushed nerve. In the DRG, expression of p62 and Beclin-1 was not significantly different between the two sides. Expression of MuRF1 and ubiquitinated proteins was not significantly different between the left and right DRG. The low quantity of MuRF1 and high variations in the ubiquitinated protein levels in the nerve prevented further analysis. Conclusions: These results indicated the induction of autophagy with accumulation of autophagosomes in the nerve, but not DRG, after nerve injury. Future studies on the effects of the autophagic changes and the precise activity of UPS in nerve trauma are crucial.