Changes of collapsin response mediator protein-2 and its phosphorylated protein levels following optic nerve injury

Background

Collapsin response mediator protein-2 (CRMP-2) can promote the growth of axons, but CRMP-2 occurs hyperphosphorylation under the induction of cyclin-dependent kinase-5 (CDK5) after central nervous system injury, which leads to the collapse of the growth cone and hinders the repair of nervous system.Being a central nervous system tissue, whether the expressions of CRMP-2 and its phosphorylated protein (p-CRMP-2) change after optic nerve injury are rarely studied.

Objective

This study was to investigate the dynamic changes of CRMP-2 and p-CRMP-2 expressions in injured optic nerve tissue.

Methods

Forty-eight 8-or 9-week-old BALB/c mice were randomly divided into the sham operation group and postoperative 3-, 7-and 14-day group.Optic nerves were exposed and clamped at retrobulbar 2 mm for 10 seconds in the right eyes during the surgery in the postoperative 3-, 7-and 14-day groups, and the same operation was performed except the clamp of optic nerve in the sham operation group.The optic nerve tissue was obtained from the eyes 3, 7 and 14 days after surgery.The relative expression levels of CRMP-2 mRNA and CRMP-2, p-CRMP-2 and CDK5 proteins in the tissue were detected by real-time fluorescence quantitative PCR and Western blot, respectively.The use and care of the experimental animals complied with the Regulation for the Administration of Affair Concerning Experimental Animals of Third Military Medical University.

Results

No significant differences were found in the expression levels of CRMP-2 mRNA and CRMP-2 protein among the sham operation group and postoperative 3-, 7-and 14-day groups (CRMP-2 mRNA: F=2.971, P=0.097; CRMP-2 protein: F=1.202, P=0.370). The relative expression levels of p-CRMP-2 protein in the optical nerve were 0.001±0.000, 0.064±0.003, 0.136±0.005 and 0.346±0.012, and those of CDK5 protein were 0.440±0.009, 0.723±0.011, 0.874±0.015 and 0.952±0.019 in the sham operation group and postoperative 3-, 7-and 14-day groups respectively, showing statistically significant differences among them (p-CRMP-2: F=445.600, P<0.001; CDK5: F=186.600, P<0.001), and the relative expression levels of p-CRMP-2 and CDK5 protein were evidently higher in the optical nerve tissue in the postoperative 3-, 7-and 14-day groups than those in the sham operation group (all at P<0.01).

Conclusions

There are not significant changes in the expression level of CRMP-2 in the BALB/c mice after optic nerve injury.However, the expression levels of p-CRMP-2 and CDK5 proteins are gradually upregulated as the extending of injured time.

Collapsin response mediator protein-2; Cyclin-dependent kinase-5; Central nervous system; Injury, optic nerve; Growth cones; Protein phosphorylation; Mice, BALB/c