Effect of truncated apolipoprotein E4 on the neurofilament phosphorylation in cultured neurons

Jie ZHOU; Juan CHEN; Zhihong XIAO; Guangyao JIN; Youmei FENG

ABSTRACT

BACKGROUND:

The degree of neurofilament (NF) phosphorylation is closely correlated with the occurrence of Alzheimer disease (AD), and apolipoprotein E4 (apoE4) is a generally acknowledged liability factor for AD, but the effect and mechanism of apoE4 on the NF phosphorylation in neurons are not very clear. It has been reported that in the neurons cultured in vitro and in brain tissue of AD patients, the amino acid residues of apoE4 protein C terminal (272-299) could be truncated by hydrolysis,and produce truncated-apoE4 fragment. The latter interacts with the NF phosphorylation in neurofibrillary tangles (NFTs), which are the characteristic pathological changes of AD.

OBJECTIVE:

To observe the effect of truncated-apoE4 overexpression on the NF phosphorylation in the cultured neurons.

DESIGN:

A non-randomized controlled observation.

SETTING:

Department of Biochemistry and Molecular Biology, School of Basic Medical Sciences, Tongji Medical College, Huazhong University of Science and Technology.MATERIALS The experiment was carried out in the Laboratory of Biochemistry and Molecular Biology, Tongji Medical College, Huazhong University of Science and Technology in December 2005. The mice neuroma cell strain N2a was provided by Dr. Xu.

METHODS:

The truncated-apoE4(△272-299) cDNA was subcloned into pEGFP-c3 to form pEGFP-T-apoE4 recombinant. Then pEGFP-c3, pEGFP-apoE4 and pEGFP-T-apoE4 were transfected into N2a cells by lipofectamine2000 respectively. NF phosphorylation was detected by Western blot assay. The activities of glycogen synthase kinase-3 (GSK-3) and cyclin-dependent kinase 5(CDK-5) were measured.MAIN OUTCOME

MEASURES:

The degree of NF phosphorylation and the activities of GSK-3 and CDK-5 were mainly observed.

RESULTS:

In the transfected groups, the contents of phosphorylated NF were significantly increased, the GSK-3 activities were significantly increased, which were the most significant in the pEGFP-T-apoE4 transfected group (P＜0.05), but the CDK-5 activities were not significantly different from that in th e control group (P＞0.05).

CONCLUSION:

These results indicate that in vitro overexpression of truncated-apoE4(△272-299) can lead to NF hyperphosphorylation by activating of GSK-3 but not CDK-5, which may be the underline mechanism of AD induced by truncated-apoE4(△272-299).