The Dynamic Levels And Significance Of The TREM-1Expression In The Rat Model Of Brain Injury Caused By PLY

Background and objectivePneumolysin (PLY) is released after Streptococcus pneumoniae (S.pn) dissolved. as a major virulence factor of S.pn, PLY has multiple functions, it can disrupt the tight junction between cells which constitute the blood-brain barrier, causing cells self-dissolution, stimulate the release of inflammatory factors, and inducing cell apoptosis, then resulted in serous brain damage.,which is closely related to the prognosis of the children patient have pneumococcal meningitis, and Play a key role in the development of pneumococcal meningitis. Therefor,further study on the mechanisms of how PLY cause the brain damage and adopt appropriate measures to block the process of PLY caused brain damage is of a great significance.TREM-1is a recently discovered receptor which expressed on neutrophil and monocyte/macrophage.As a key substance stimulate and amplify the inflammation cascade after an infection disease, TREM-1is mainly through the receptor recognition model (TLRs) to stimulate the release of the pro-inflammatory cytokines (including the TNF-a, IL-6, IL-8etc.), causing tissue damage. Although its natural ligand has not yet been found, but in the bacterial and fungal infection disease can be found in the higher. To date, the study confirmed that in sepsis, pneumonia, acute suppurative cholangitis and other acute bacterial infectious diseases,TREM-1was found expressed on surface of neutrophils, monocytes and macrophages, but report in the central nervous system infectious disease especially in infants and young children with bacterial meningitis is not many.In this experiment,we produced an infectious brain injury rat model through injecting the PLY into the rat’s left internal carotid artery, then detect the TREM-1expression levels at different time points, and the correlation with the brain injury.To explore the mechanism of PLY played in the inflammatory reaction in vivo,and find how does the PLY play a role during the inflammatory process of brain injury.Materials and methodsWe randomly divided64infant rats into two groups,the pneumolysin group(PLY group, n=32):In the left internal carotid artery with a injection of0.1mL (8μg) PLY; control group (group NS, n=32):inject the left internal carotid artery of rat with an equal volume of saline. Both two groups are divided into4h,6h,12h,24h4subgroups according to the different time points after injection into PLY, each subgroup include8infant rats. At each time point we execute the8infant rats, after the execution of each rat,the sample of brain tissue were prepared by tissue homogenate and make the paraffin sections. The expression of the NSE protein and GFAP protein in the cerebral cortex and hippocampus were measured by the immunohistochemistry (SP), And enzyme linked immunosorbent assay (ELISA) were used to detect the expression levels of TREM-1, C1q, TNF-α, IL-6protein in brain tissue. All data were analyzed by SPSS17.0software. Several groups of samples were compared with single factor analysis of variance, correlation between the two samples was analyzed by Pearson correlation analysis,the significance level is a<0.05.Result1. Morphological and behavioral change:In the PLY group the left eye of the infant rat we can see the enophthalmos, necrosis,the eyelid completely closed,and even in the corner of eye we can see a visible bleeding.The weight loss of the infant rat was up to10%-15%. In the anatomical observation,we can see the left brain volume is bigger than the right brain, with the brain swelling, dural tension, cerebral vascular congestion significantly. In PLY group, After the HE staining under light microscope,the formation of new blood vessels,and the cerebral vascular gap widened, neurons, different degrees of glial cell swelling,and vacuolar degeneration can be seen. While in NS group none of the above changes could be seen.2. The level of TREM-1in the PLY group reached a peak in the4h time point, in the6h time point,the level of TREM-1is still high, both groups have the statistical difference with the control group(P<0.05), while decreased levels of TREM-1were found in12h and24h subgroups, and when compared with the control group there is no significant difference.The Clq levels reached the peak at6h time point, in12h time point the level is still high, and have a statistical significance when compared with the control group(P<0.05).While in4h and24h time point,the levels of Clq have no significant difference between the PLY and the control group. At each time point levels of TNF-a and IL-6were all significantly higher than those in the control group, and reached a peak in the24h time point, the difference was statistically significant (P<0.05).The level of TREM-1and Clq were uncorrelated, the correlation coefficient is r=0.052,(P=0.778);the TNF-α level is correlated with TREM-l,and the correlation coefficient is r=0.737,(P<0.05);the level of IL-6is correlated with TREM-1,the correlation is r=0.659,(P<0.05).3. The level of GFAP and TREM-1were correlated, the correlation coefficient is r=0.570,(P<0.05); correlation between NSE level and TREM-llevel was found, the correlation coefficient between them is r=0.641,(P<0.05).Conclusion1. PLY can up-regulate the expression of TREM-1, and thus participate in the inflammatory process, to promote the release of inflammatory cytokines.2. TREM-1is involved in the pathological process of brain damage induced by PLY.3. The effect of TREM-1in the brain damage caused by PLY is not through the classical complement pathway.