Xiaoyaosan Promotes Myelin Regeneration and Alleviates Depressive Symptoms in Vascular Dementia Mice with Depression via Promoting Microglia Polarization / 中国实验方剂学杂志

ABSTRACT

Objective:To investigate the effect of Xiaoyaosan on depressive behavioral phenotype in mice with vascular dementia （VaD） mice and its possible mechanism. Method:Sixty three-month-old male C57/BL6 mice were divided into the normal control group， model group， positive control group， as well as low-， medium-， and high-dose Xiaoyaosan groups. Mice in all groups except for the normal control group underwent bilateral carotid artery stenosis. Two weeks later， they were subjected to chronic restraint stress， 6 h per day， for inducing VaD complicated with depression. Mice in the low-， medium-， and high-dose Xiaoyaosan groups were treatment with intragastric administration of Xiaoyaosan decoction （5， 10， 20 g·kg^-1）， the ones in the positive control group with fluoxetine （10 mg·kg^-1）， and those in the normal control group and model group with an equal volume of normal saline for four weeks， during which the restraint stress was maintained. The depressive behavioral phenotype of mice was observed in sugar water preference test and tail suspension test. The fluorescence expression of myelin basic protein （MBP） in ventral hippocampus （vHIP） was detected by fluorescence immunoassay. The ultrastructure of myelin sheath in vHIP was observed by transmission electron microscopy. The protein expression levels of MBP， myelin oligodendrocyte glycoprotein （MOG）， myelin-associated glycoprotein （MAG）， triggering receptor expressed on myeloid cells-2 （TREM2）， inducible nitric oxide synthase （iNOS）， arginase 1 （Arg1）， interleukin-I<italic>β</italic> （IL-1<italic>β</italic>）， tumor necrosis factor-<italic>α</italic> （TNF-<italic>α</italic>）， interleukin-4 （IL-4）， and interleukin-10 （IL-10） were assayed by Western blot. Result:As revealed by behavioral test， compared with the normal control group， the model group exhibited prolonged immobility time and decreased percentage of sugar water preference （<italic>P</italic><0.01）. Compared with the model group， Xiaoyaosan significantly shortened the immobility time of mice （<italic>P</italic><0.05） and increased the percentage of sugar water preference （<italic>P</italic><0.01）. Western blot results showed that the protein expression levels of MBP， MOG， and MAG in vHIP of the model group were remarkably decreased as compared with those of the normal control group （<italic>P</italic><0.01）. The protein expression levels of MBP， MOG， and MAG in vHIP of the low-dose Xiaoyaosan group were increased in contrast to those in the model group （<italic>P</italic><0.05， <italic>P</italic><0.01）， while the protein expression of iNOS was decreased （<italic>P</italic><0.01）. The protein expression levels of MBP， MOG， MAG， TREM2， Arg1， IL-4， and IL-10 in the medium- and high-dose Xiaoyaosan groups were up-regulated （<italic>P</italic><0.05， <italic>P</italic><0.01）， whereas those of iNOS， IL-1<italic>β</italic>， and TNF-<italic>α</italic> were down-regulated （<italic>P</italic><0.01）. The immunofluorescence findings demonstrated that the mean fluorescence intensity of MBP in the model group declined in comparison with that in the normal control group （<italic>P</italic><0.01）， while the mean fluorescence intensities of MBP in the low-， medium-， and high-dose Xiaoyaosan groups were enhanced to different degrees （<italic>P</italic><0.01）. It was observed under the transmission electron microscope that the myelin structure of the model group was loosened and the dense layer was separated and irregularly arranged. Xiaoyaosan improved the structural integrity of myelin sheath and the looseness of lamellar structure. Conclusion:Xiaoyaosan ameliorates the depressive behavioral phenotype of VaD mice， which may be related to the up-regulation of TREM2， the induction of M2 polarization of microglia cells， the enhancement of their anti-inflammatory and phagocytic abilities， and the promotion of damaged myelin sheath regeneration.