Objective: To investigate the effects of olomoucine, a cyclin dependent protein kinase (CDK) inhibitor, on the microenvironment of axonal regeneration after spinal cord injury (SCI).
Methods: Forty-five SD rats were randomly divided into 3 equal groups: SCI group undergoing SCI by hemisection technique and peritoneal injection of dimethyl sulfoxide (DMSO) solution 30 min after the SCI, SCI + olomoucine (SCI + Olo) group undergoing SCI by hemisection technique and peritoneal injection of olomoucine solution 30 min after the SCI, and sham operation group undergoing sham operation and peritoneal injection of DMSO solution 30 min after the operation. Three days after the operation the injured spinal cord segments of 5 rats from each group were taken out. Western blotting was used to detect the expression of the cell cycle related proteins, cyclin A, cyclin B, cyclin E, and proliferating cell nuclear antigen (PCNA). Immunofluorescence (IF) staining was used to detect the expression of glial fibrillary acidic protein (GFAP), growth associated protein-43 (GAP-43) and chondroitin sulphate proteoglycan (CSPG). Four weeks after the operation specimens of the injured spinal cord segment 15 mm in length were taken out from 5 rats in each group to undergo histological examination. The locomotion function of the hindlimbs was determined by modified Gale combined behavioral scoring (SBS) 1 day and 1, 2, 4, 6, and 8 weeks after the operation.
Results: Western blotting 3 days after the operation showed that the expressions of cyclin A, cyclin B, cyclin E, and PCNA were very weak in the sham operation group, were significantly increased in the SCI group, and were significantly down-regulated in the SCI + Olo group compared with those of the SCI group. IF staining showed that the number of astrocytes was small and the expressions of GFAP, CSPG, and GAP-43 were weak in the sham operation group; in the SCI group the astrocytic proliferation and glial scar was obvious, and the expressions of GFAP, CSPG, and GAP-43 were significantly increased compared with those of the sham operation group (all P < 0.05); and the astrocytic proliferation was significantly weaker and no obvious glial scar could be seen, and the expressions of GFAP and CSPG were weaker in the SCI + Olo group in comparison with the SCI group, however, the GAP-43 expression of the sham operation group was significantly increased compared with that of the sham operation group (P < 0.05). The hindlimbs of the SCI + Olo group and sham operation group were paralyzed without significant difference in the CBS values between these 2 groups, however, two weeks after the operation, the locomotion function scores at different time points of the SCI + Olo group were all significantly improved in comparison with that of the SCI group (all P < 0.05).
Conclusion: Olomoucine promotes the recovery of the locomotion function of the paralyzed hindlimbs, probably through microenvironmental improvement of axonal regeneration by inhibiting the glial scar formation and CSPG secretion as well as upregulating the GAP-43 expression.