Expression Of MiRNA-21 In Traumatic Brain Injury And Study Of Its Intervention

Objective:Extensive data indicate that miRNA-21 plays a critical role in biological processes, however, knowledge is limited on the development, cellular differentiation, and tumor generation. Dynamic changes in miRNA-21 expression have been extensively studied in patients with tumor, but how miRNA-21 expression change in response to acute traumatic brain injury remains largely unknown. The primary goal of our study was to evaluate the effects of TBI on miRNA-21 expression in injured brain tissue, and to correlate such changes to the injury-induced neuronal apoptosis. Our study not only have focused on how miRNA-21 affect acute traumatic brain injury, we also explore the pathways of the miRNA-21 participate in wound repair. As previously described that miRNA-21 inhibition of apoptotic cell though down-regulates the expression of it's directly targets. PDCD4 is directly target of miRNA-21, and down-regulated in prostrate cancer, breast cancer, hepatocellular carcinoma, and non-small-cell lung cancer. Although independently, it was shown that these forms of cancer are also associated with up-regulation of miRNA-21.Furthermore,we will study whether through silencing PDCD4 expression with the miRNA-21 led to a reduction of apoptotic neurons in TBI?Methods:We choose several time points post brain injury:12h,24h,48h,72h,1week and 2 weeks, respectively, to tested the miRNA-21 expression level by using qRT-PCR methods in rat cerebral cortex after rats subjected to fluid percussion injury (FPI) and applied stereotactic injection techniques combined with liposomes for miRNA-21. Neurological function was evaluated using Modified Neurological Severity Score (mNSS). This score was used to ensure the relative uniformity of injury severity among rats receiving different treatments. The test was administrated 24 h after FPI by observers who were blinded to the experimental conditions and treatments. Then animals were sacrificed after evaluated, we examined neuronal apoptosis in rat cerebral cortex. Immunohistochemistry and western blot detected the level of PDCD4 protein in the injured and surrounding tissue.Results:We observed strong miRNA-21 expression in injured brain tissue at 48h after TBI in cerebral cortex. We conclude that neuronal apoptosis in injured tissue correlates with miRNA-21 expression deficiency found in injured rats for that the severity of apoptosis is consistent with the extent of miRNA-21 expression. More importantly, both neural apoptosis and miRNA-21 expression injured tissue are significantly change in injured rats receiving miRNA-21 transfection. Our results indicate that miRNA-21 expression increased in response to acute traumatic brain injury. From our data, We can infer that exogenous intervention enhancing the expression of miRNA-21 lead the apoptotic cells decreased, in addition,the number of apoptotic cells and the expression of miRNA-21 have the same trend after TBI. So In this context, the augmentation of miRNA-21 expression induced by exogenous injection is also surprising given that miRNA-21 overexpression inhibit apoptosis. Form PDCD4 immunostaining, the number of PDCD4-positive cells decreased rapidly thereafter and reached a stationary phase at approximately lweek after TBI before declining to baseline. In comparison, PDCD4-positive cells remained constantly lower in brain tissue from the rats with the intervention of miRNA-21 during the same period. On the other hand, the western blot showed the same result with the Immunohistological dection of PDCD4. These show that the apoptotic cells and the level of PDCD4 have the same trend in reduction. It's suggest that the protein level of PDCD4 correlates with the apoptotic neurons levels in injured brain tissue.Conclusion:Recent findings indicate that miRNA-21 promote angiogenesis, cell proliferation inhibition of apoptotic cell though down-regulates or up-regulates the expression of it's directly targets. For a better understanding of miRNA-21's role in brain trauma, and explore the therapeutic potential of miRNA-21. In the next stage,we will select several valuable target genes such as PDCD4,PDCD4 to investigate their regulation and role in central nervous system (CNS) after TBI.