Mechanism Of Astrocytes In Infectious Brain Edema Of Rats Induced By Lipid Polysaccharide

Objective: To observe apoptosis and activation of astrocytes and its expression of iNOS and AQP4 in rats with infectious brain edema induced by lipid polysaccharide (LPS),and to discuss the role of astrocytes in the formation and development of infectious brain edema.Methods: Eighty-four adult SD male rats were randomly divided into 3 groups: control group (group C, n=12), saline group (group S, n=12), LPS group (group L, n=60). Group L was further divided into 5 subgroups according to different time points after LPS injection: 6h, 12h, 24h, 48h,72h (n=12/each subgroup).Left common carotid artery, external carotid artery and internal carotid artery of rats were only separated in group C, without lipopolysaccharide injection; sterile saline 0.15 ml was injected into left internal carotid artery of rats in group S; LPS150μg( 0.15ml) was injected into left internal carotid artery of rats in group L to establish a rat infectious cerebral edema model. HE staining, dry-wet weight, evan blue,flow cytometry,RT-PCR and immunohistochemistry methods were used respectively to measure the pathological morphology of brain tissue, brain water content, blood-brain barrier (BBB) integrity, astrocytes apoptosis, AQP4 mRNA and protein expression ,GFAP and iNOS protein level.Results:1.Pathological morphology of brain tissue: diffuse edema was observed in rat brain tissue in group L , with mussily arranged vertebral somatic,degenerated and necrosised nerve cells,and infiltrated inflammatory cells . No obvious change was found in group C and group S, in which nerve cells were well arranged.2.Brain water content and EB content: brain water content and EB content were increased 6 h after lipopolysaccharide injection , up to a peak at 12 h, returned to normal at 72 h. Brain water content and EB content were positively related(r=0.767,P <0.01 ).3.Expression of brain AQP4 mRNA and protein: except group L:72h, AQP4 mRNA and protein were significantly increased (p<0.05), up to a peak at 12 h, then declined gradually. No significant difference was found between group C and group S (p<0.05). AQP4 mRNA was positively related respectively with its protein(r=0.991,P<0.01), brain water content(r=0.739, P<0.01 ), and EB content(r=0.930, P<0.01 ).4.Astrocytes apoptosis and iNOS and AQP4 expression: The apoptosis rate of astrocytes in group L was significantly increased at each time point (p<0.05), up to a peak at 24 h. with swollen cell bodies and increased neurites. Except group L:72 h, the expression of iNOS and GFAP were significantly increased (p<0.05), up to a peak at 12 h. The expression of each protein was weak in group C and the group S, and no significant difference was found between them (p>0.05).Conclusions:1. LPS can cause diffuse edema, cell degeneration and increased brain water content and EB content, which indicates LPS could cause infectious cerebral edema through damaging blood brain barrier. .2.LPS can cause the morphological change of astrocytes, the increased expression of GFAP, iNOS and AQP4 which is positively related with the integrity of BBB and the brain water content, suggesting that LPS could cause abnormal activation of astrocytes and promote the formation and development of infectious cerebral edema.3.The apoptosis of astrocytes is increased after LPS injection,whose peak is later than that of its activation and iNOS expression. it is concluded that the activation of astrocytes and the inflammation it mediated may participate in the formation and development of infectious cerebral edema by promoting cell apoptosis.