Erythropoietin alleviates spinal neuron apoptosis via c-Jun N-terminal kinase-c-Jun pathway

Objective To study the neural protective mechanism of erythropoietin (EPO) following root avulsion (RA). Methods Sixty-three adult Wistar rats were randomly divided into two groups: control group (avulsion + 1 ml normal saline s. c. on alternate days), EPO-treated group (avulsion + 1 000 U/kg EPO s. c. on alternate days). The rats were sacrificed at 0 (after awake), 1, 2, 4, 7 and 14 days after avulsion for harvesting C5-T1 spinal samples. Immunohistochemistry was used to detect cleaved-poly adenosine diphosphate-ribose polymerase (Cleaved-PARP), c-Jun and phosphorylated c-Jun N-terminal kinase (p-JNK) in spinal neurons. Results (1) The expression of Cleaved-PARP was significantly decreased in EPO-treated group at 2, 4, and 7 days post-avulsion (3 173.3±153.1, 8 943.2±351.5 and 7 017.9±424.7) as compared with control group (10 575.1±594.3, 12 737.1±385.3 and 10 256.9±629.4) (F=4 363.938, 1 587.489, 545.925, P<0.01). (2) The expression of c-Jun in EPO-treated group was significantly lower at 1, 2, 4 and 7 day(s) (1 351.2±253.7, 2 386.8±305.8, 1 898.2±138.0 and 1 547.1±163.9) than in control group (2 165.8±205.7, 3 378.1±272.5, 2 835.2±166.8, 2 579.8±264.8) (F=186.613, 175.719, 562.005, 329.896, P<0.01). (3) The expression of p-JNK in EPO-treated group was significantly lower at 1, 2, 4 days after avulsion (1 407.1±121.7, 1 925.6±126.6 and 4 892.3±330.2) than in control group (3 041.5±139.6, 9 243.8±573.9 and 5 486.6±358.4) (F=2 336.447, 4 651.806, 44.617, P<0.01). The peak of p-JNK was postponed to 4th day in EPO-treated group as compared with 2nd day in control group. Conclusion Down-regulation of p-JNK and c-Jun is the anti-apoptosis mechanism of EPO for spinal neurons. Key words: Root avulsion injury; Erythropoietin; Spinal cord neuron; C-poly adenosine diphosphate-ribose polymerase; C-Jun N-terminal kinase; C-Jun