Induction of CRMP‐2 phosphorylation by CDK5 restricts the repair of damaged optic nerve

Abstract

Objective To study the mechanism of collapsin response mediator protein‐2 (CRMP‐2) phosphorylation changes and cyclin‐dependent kinase 5 (CDK5) expression after optic nerve injury. Methods Optic nerve injury rat models were constructed, the messenger RNA (mRNA) level of CRMP‐2 in optic nerve tissues was determined by quantitative reverse transcription polymerase chain reaction (qRT‐PCR) after building models 0, 3, 7, and 14 days. The protein expression of CRMP‐2, phospho‐CRMP‐2 (p‐CRMP‐2), and CDK5 were also determined by western blot analysis. Lentivirus overexpressing CRMP‐2 and CRMP‐2 small interfering RNA (siRNA) plasmid were designed and transfected to retina ganglion cells (RGCs), and then the neurites outgrowth of RGCs were cultured with CDK5 inhibitor or CDK5 activator was determined by tubulin staining. Inhibition on CDK5 promotes injured optic nerve by using carrying CDK5 siRNA inject into vitreous chamber. Results There was no significant change in CRMP‐2 expression in optic nerve injury rat, while p‐CRMP‐2 expression was evidently increased compared with sham operation group. The expression level of CDK5 in optic nerve tissue was upregulated after optic nerve injury in rat, and the upward trend of p‐CRMP‐2 and CDK5 was consistent with the time after the injury was prolonged. Inhibition on CDK5 evidently decreased the expression of p‐CRMP‐2. CDK5 siRNA had an obvious repair effect on the injured optic nerve. Conclusion The increase of CDK5 activity can lead to CRMP‐2 hyperphosphorylation, which results in the difficult repair of damaged optic nerve. Therefore, inhibition on CDK5 could promote the repair of damaged optic nerve.

Discovery and Optimization of Highly Selective Inhibitors of CDK5

“…Reintroduction of a single fluorine (12, CDK5 IC 50 1.1 nM, 44× selective over CDK2) maintained good potency and hinted that this substituent may be necessary for selectivity. We then Further exploration around the 5-position showed that small alkyl groups such as ethyl (20) and trifluoromethyl (21) maintained the potency and selectivity, as did the more polar isopropoxy substituent (22). While we suspected that the selectivity of 4-substituted compounds such as 15 and 16 may arise from optimization of the hydroxymethyl pyrazole present in 1, the R 5 substituent in 18 and 19 could orient toward either the interior of the binding pocket or toward the solvent.…”

“…11, 12,13,15,16,17,18,19,20,21,24,29,31, and 32 were prepared in a manner similar to GFB-12630 using the appropriate aniline as a starting material.…”

“…8 Studies have linked CDK5 with several pathways that mediate cyst growth, including phosphorylation of CRMP2, 5 drebrin, 9 and NDE1. 10,11 CDK5 is implicated in a wide variety of diseases, including neurodegeneration, 12−14 stroke, 15,16 pain, 17−19 glaucoma, 20 and cancer, 21,22 including as a potential target for combined immunotherapy. 23 Since CDK5, unlike other CDKs, does not actually regulate the cell cycle, inhibition has been well explored as a target for drug discovery.…”

“…CDK5 is implicated in a wide variety of diseases, including neurodegeneration, − stroke, , pain, − glaucoma, and cancer, , including as a potential target for combined immunotherapy . Since CDK5, unlike other CDKs, does not actually regulate the cell cycle, inhibition has been well explored as a target for drug discovery. − …”

The role of Cdk5 in neurological disorders

“…Cdk5 is found to induce mitochondrial kinetic defects in optic neuropathy (Rong et al, 2020 ). Cdk5 phosphorylates CRMP-2, which will aggravate optic nerve damage (Chen et al, 2019 ). Cdk5 contributes to oxidative stress (Guo et al, 2018 ) and endoplasmic reticulum stress (Shi et al, 2018 ).…”