The Effect Of Apolipoprotein E On Blood-brain Barrier Permeability In Experimental Autoimmune Encephalomyelitis

Objective This study was designed to explore the apolipoprotein E (ApoE)effect on metalloproteinase-9(MMP-9) expressed and blood-brain barrierpermeability in experimental autoimmune encephalomyelitis (EAE).Methods To established EAE model, we immunized with myelinoligodendrocyte glycoprotein peptides (MOG35-55) at the wild-type (WT) miceand ApoE-deficient (ApoE-/-) mice on the C57BL/6J back ground, and dividedinto two EAE(E)groups: E-ApoE-/-group and E-WT group. Meanwhilecompared with the two normal control (C) groups: ApoE (C-ApoE/) and WT(C-WT). The BBB permeability was detected by quantitative measurement forEvan’s blue (EB) content in the CNS. The histopathologic changes were observedby hematoxylin-eosin staining and the expressions of metalloproteinase-9(MMP-9) and tissue inhibitor of matrix metalloproteinase1(TIMP-1) werequantified by immunohistochemistry. The mRNA and protein levels of MMP-9,TIMP-1and junction proteins (Occludin and Claudin-5) expression in brain weremeasured by real-time RT-PCR and Western blot, respectively.Result Compared with E-WT group, E-ApoE-/-group showed theenhancement of the maximum and mean clinical score (P<0.05), but displayed asimilar onset day (P>0.05). In the E-ApoE-/-group, the inflammatory cellinfiltrated into the CNS more significantly, while the EB levels in the brain tissue were also significantly higher than the E-WT group (P<0.05). Comparedwith the two normal control groups, the mRNA and protein expression levels ofclaudin-5and occludin were significantly reduced in EAE-affected groups(P<0.05). Compared with the E-WT group the mRNA and protein expression ofclaudin-5and occludin was significantly suppressed in E-ApoE-/-group(P<0.05). The mRNA expression of MMP-9was up-regulated in the two EAEgroups compared with the two control groups (P<0.05). Even more,ApoE-deficiency increased MMP-9mRNA expression significantly EAE groups(P<0.05). Quantitative measurements of activity expression protein expressionof MMP-9by Western blot or Gelatin zymography analysis revealed similarresults, respectively. On the other hand, the mRNA and protein expression levelsof TIMP-1were down-regulated in the two EAE groups comparison withcontrol groups (P<0.05). But there was no significant changed between the twoEAE groups (P>0.05).Conclusions Lack of ApoE could enhance pathological damage andcontributes to the loss of the BBB integrity. ApoE-deficiency upregulated theexpression and activity of MMP-9may associate with BBB breakdown, whichsuggest that ApoE plays an important role in maintaining BBB integrity. Ourresult suggests that the protective role of ApoE in EAE by maintaining BBBintegrity could be another interesting therapeutic target at MS/EAE.