Expression of Nogo-A in dorsal root ganglion in rats with cauda equina injury.

Objective: To investigate the expression of Nogo-A in dorsal root ganglion (DRG) in rats with cauda equina injury and the therapeutic effects of blocking Nogo-A and its receptor.

Methods And Materials: Fifty-eight male Sprague-Dawley rats were divided randomly into either the sham operation group (n = 24) or the cauda equina compression (CEC) control group (n = 34). Behavioral, histological, and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) analyses were conducted to assess the establishment of the model. The dynamic expression change of Nogo-A was evaluated using real time-qPCR. Immunofluorescence was used to evaluate the expression of Nogo-A in the DRG and cauda equina. Furthermore, 20 male Sprague-Dawley rats were equally divided into 4 groups, including the sham group, the CEC group, the NEP1-40 (the NgR antagonist peptide) treatment group, and the JTE-013 (the S1PR2 antagonist) treatment group. Behavioral assessments and western blotting were used to evaluate the therapeutic effect of cauda equina injury via blocking Nogo-A and its receptor.

Results: Tactile allodynia and heat hyperalgesia in the CEC model developed as soon as 1 day after surgery and recovered to normal at 7 days, which was followed by the downregulation of Nogo-A in DRG neurons. However, the locomotor function impairment in the CEC model showed a different prognosis from the sensory function, which was consistent with the expression change of Nogo-A in the spinal cord. Immunofluorescence results also demonstrated that Nogo A-positive/NF200-negative neurons and axons increased in the DRG and cauda equina 7 days after surgery. Surprisingly, Schwann cells, which myelinate axons in the PNS, also expressed considerable amounts of Nogo-A. Then, after blocking the Nogo-A/NgR signaling pathway by NEP1-40, significant improvement of mechanical allodynia was identified in the first 2 days after the surgery. Western blotting suggested the NEP1-40 treatment group had lower expression of cleaved caspase-3 than the CEC and JTE-013 treatment group.

Conclusion: Neuronal Nogo-A in the DRG may be involved in regeneration and play a protective role in the CEC model. Whereas Nogo-A, released from the injured axons or expressed by Schwann cells, may act as an inhibiting factor in the process of CEC repairment. Thus, blocking the Nogo-A/NgR signaling pathway can alleviate mechanical allodynia by apoptosis inhibition.