| Summary: | 碩士 === 國立政治大學 === 神經科學研究所 === 102 === Honokiol is a natural compound, extracted from the Magnolia officinalis, and is known as its anti-oxidative, anti-inflammatory and neuroprotective effects. The previous study has been demonstrated that the honokiol can protect striatal dopamine neuron against 6-OHDA induced damage and reverse the apomorphine-induced rotational behavior in Parkinson’s disease model of rats. However, the cellular mechanisms for its neuroprotective effects are not fully investigated. Protein kinase Casine kinase 2 (CK2) is a serine/threonine kinase has a highly abundant expression in the striatum compared with other brain areas. Further, CK2 is shown to regulate many neuronal functions including neuroprotection. The nuclear factor E2-related factor 1 (Nrf1) has been identified as one of the substrate proteins for CK2 and is indicated to involve in the induction of proteasome subunits gene expressions in mouse embryonic fibroblasts. The anti-apoptotic protein myeloid cell leukemia 1 (Mcl-1) is shown to play a critical initiation role during the apoptosis process due to its synthesis blockage and proteasome degradation. The present study is aimed to investigate whether one of protective effects of honokiol is through CK2-mediated Nrf1 signaling pathway to regulate the proteasome activity in the mouse N2a neuroblastoma cell line. In the current results, transfection of the CK2α-EGFP plasmid DNA increased Nrf1 phosphorylation accompanied with the decrease in the proteasome activity but increased the ubiquitinated Mcl-1 protein. Whereas, transfection of CK2α siRNA decreased Nrf1 phosphorylation leading to the increase in proteasome activity and Mcl-1 protein degradation. The 24 hr duration of honokiol post-treatment only slightly reversed the knock-down effect of CK2α siRNA on CK2α and Mcl-1 protein levels. However, 5 hr duration of honokiol post-treatment could partially reverse the Mcl-1 protein level and proteasome activity but no effect on CK2α protein levels. In the H2O2-induced oxidative stress condition, only 3 hr duration of honokiol post-treatment could protect cells against H2O2-induced cell death. In the experiments of in vivo rat animal model, local administration of honokiol was found to increase phospho-TH, naive TH, GAD as well as acetylated Histone H3 protein levels. These above results suggest one of the protective mechanisms of honokiol might be through CK2-mediated Nrf1 signaling to inhibit the proteasome activity. and to promote cell survival under oxidative stress. Beside these functions, honokiol might also involve in the regulation of nurophysiological functions of dopamine and GABA neurons.
|
|---|
