Roles Of P75^ICD/CDK5 Signaling Pathway Upon Intracerebral Hemorrhage-induced Neuronal Apoptosis

Objective Intracerebral hemorrhage（ICH） is the most acute and severe stroke type, which occupies high mortality and morbidity in department of neurology. Recently, cyclin-dependent kinase 5（CDK5） is found play essential roles in the process of central nervous system（CNS） diseases. However, the specific roles of CDK5 in neuronal activities adjacent to hematoma after ICH have not been clarified. To investigate the role of CDK5 in neuronal apoptosis following ICH will provide a new idea for clinical drug treatment and medicine development in near future. What’s more, our previous studies discovered that neurotrophin receptor p75^NTR could be interacted with p35, neuron-specificity activator of CDK5. And further studies verified that it could promote p35-p25 nuclear translocation. Thus, roles of the interaction between p75^NTR and p35 in neuronal apoptosis after ICH bring us great interesting, and will also provide us a new insight into the exploration of ICH in the further studies.Methods Autologous whole blood（50 μl） collected from caudal vain was quickly introduced into right basal ganglia was use to simulate clinical ICH; establish ICH model in vitro by culturing primary cortical neuron, human embryonic kidney 293 T cells; western blot and immunofluoresence were used to investigate the relationship between p35-p25/CDK5 signaling pathway and neuronal apoptosis adjacent to hematoma after ICH. RNAi specific to CDK5 kinase was employed to clarify the causality between CDK5 and neuronal apoptosis following ICH in vitro. Additionally, we examined the interaction between p75^ICD and p35 as well as its potential action sites by incubating primary cortical neuron and 293 T cells. Eventually, we c larify the interactions and potential roles of p75^ICD and p35-p25/CDK5 following ICH through in rat ICH model.Results CDK5 protein level and kinase activity were both up-regulated adjacent to hematoma after ICH, and peaked at day 2; from immunofluorescent staining, we found that increased level of CDK5 was located to neurons, which also related to neuronal apoptosis after ICH. We verified that CDK5 kinase was the mainly form to regulate neuronal apoptosis after ICH. It showed that silence of CDK5 kinase activity by inhibiting its neuronal specific ity activator, sip35/25, could effective reduce neuronal apoptosis and the phosphorylation of MEF2 D, a pro-survival factor, which inactivated its pro-survival roles; neurotrophin receptor p75^NTR could interact with p35 in primary cortical neurons and brain tissues after ICH, and the interact site was located at its intracellular domain, p75^ICD; the interaction between p75^ICD and p35 would promote the nucleus transposition of p25/CDK5 complex.Conclusions 1. p35-p25/CDK5 signal pathway played an important role in neuronal apoptosis adjacent the hematoma after ICH. 2. Neurotrophin receptor p75^NTR could interact with p35, which promote the nucleus transposition of p25/CDK5.