Neural Cell Cycle Dysregulation In Ischemic Stroke Model

Cell cycle is a highly regulated process. Timing progression of cell cycle through different phases, G0, G1 S, G2, and M requires an orchestrated functions of several elements, including cyclins, cyclin-dependent kinases (CDKs), retinoblastoma protein (Rb; pocket proteins) and E2F complex proteins. Cyclin-dependent kinase 5 (Cdk5) is a member of the cyclin-dependent kinase family that is widely expressed in many tissues, especially in neurons. Although no relationship with the cell cycle, it plays an important role in the normal neuronal function in maintenance and neural cell death. The use of Cdk5 inhibitors or Cdk5 deletion can reduce cerebral infarction in mice, but the specific mechanism of Cdk5 involved in neuronal cell cycle after ischemic stroke is not clear. Based on the cerebral ischemic model-Middle Cerebral Artery Occlusion (MCAO) model, we applied experimental techniques such as Immunofluorescence assay, immunohistochemistry, and quantitative real-time polymerase chain reaction (qRT-PCR) to investigate:(1) the neural function defect of MCAO model mouse, brain edema, cerebral infarction; (2) the expression of p35, p25 and Cdk5 and GFAP in infarct region following MCAO; (3) the expression of CDKs family members, Cdh1, CyclinA, cyclinB1, CyclinC, p-Histone H3 in the infarct region following MCAO of focal ischemic. The results are as follows:(1) The changes in neurological behaviors after MCAO:circling to the left; falling to the left; longitudinal spinning or seizure activity; 26% brain tissues were dead;(2) After ischemic injury, p35 was cleaved to p25. The protein level of GFAP was obviously increased. The Cdk5 protein expression was significantly decreased; Interestingly, total Cdk5 mRNA level was not affected.(3) Compared with Cdk5 level, Cdhl protein level was significantly increased in the infarct side; The level of cell cycle dependent protein kinases (CDKs) family members in addition to Cdk5 had no significant change; The protein levels of cyclins (cyclinA, cyclinB1 and CyclinC) were also significantly increased.The present study indicates that p35 is cleaved to p25 and the Cdk5 protein expression is significantly lowered in mice after cerebral ischemia. The Cdh1 protein level is significant increased in the infarct side. The abnormal over-expression of cell cycle proteins (CyclinA CyclinB1 CyclinC), and p-Histone H3 are also induced by cerebral ischemia. Thus, Cdhl, which is an ubiquitin ligase mediating the degradation of Cdk5, may act in the upstream of Cdk5 to may lead neurons re-entering into the cell cycle. These data reveal that cerebral ischemia causes cell cycle abnormalities-mediated by Cdk5 dysfunction, which suggesting that Cdk5 and the other cell cycle proteins play a critical role in cerebral ischemia. The studies pave a novel avenue for the future drug development and clinical intervention.