The effects of mir-20A and mir-125B expressions on apoptosis and inflammation in experimental spinal cord injury

MicroRNAs (miRNAs) are a class of short (18-25 nucleotide), noncodingRNAs that bind to target messenger RNAs, blocking their translation. MiRNAs are involved in many physiological and pathological processes in the cell and play an important role in post-transcriptional gene regulation. Furthermore, miRNAs play critical roles in the organism, such as post-transcriptional regulation of gene expression, metabolic regulation, memory, synaptic development, embryogenesis, organogenesis, differentiation and growth control. Additionally, in recent studies, it has been reported that miRNAs have significant roles in cancer, metabolic disorders, cardiovascular diseases, viral infections and traumatic neurological injuries. Changes in the expression levels of miRNAs is the major cause of functional disorders that occured in the cells. It is revealed that there is a close relationship between varying expression levels of miRNA and formation, diagnosis and treatment of diseases. Nowadays, miRNAs are used as a new biomarker for the development of disease in moleculer medicine. Spinal cord injury (SCI), is a serious central nervous system disorder leads to complete or partial loss of sensory and motor functions. Although various treatment strategies has been developed until today, there is still no effective treatment protocol for functional recovery after spinal cord injury. In recent years, researches and bioinformatic analyses showed that the variations in miRNA expression levels can cause seconder tissue damage in SCI pathogenesis. It has been reported that in experimental SCI model in rats, approximately 300 miRNAs are expressed and significant expression changes occured in 97 of those miRNAs according to the microarray analyses. It is suggested that miRNAs can be potential targets in SCI treatment. On the other hand It is also suggested that miRNAs may have protective and harmful effects in SCI pathogenesis. However, the underlying mechanisms of spinal cord injury pathogenesis is still unclear today. In this study we aimed to investigate the relationship between miR-20a and miR-125b expressions and apoptosis and inflamation in experimental SCI model in rats with using microscopic, immunohistochemical and molecular biological methods. Fourty two wistar rats were divided into 3 main groups as intact control group; they did not receive any operation, sham operation group; we created laminectomy on T2-T7 levels of spinal cord, and experimental group received spinal cord compression injury. Following injury the experimental group subdivided into 2 groups as: experimental control group, which did not receive any drug administration, methylprednisolone treatment group; they received MP following injury. Tissue samples were obtained from all groups at 1, 3, 7 and 14. days after injury for light and electron microscopic, immunohistochemical and molecular biological examinations. We found an increase in TNF-α and IL-6 levels in experimental control group on 1. and 3. days. We also obtained that there were a significant decrease in both cytokines expressions in experimental control group on 7. and 14. days and MP treatment group. Moreover we observed an increase on kaspaz-3 levels in experimental control group on 1. day. On the other hand, in experimental control group on 3, 7 and 14. days and in the treatment group there were a significant decrease in kaspaz-3 levels. Furthermore we found structural degenerations in neurons, glia cells and axons in the SCI groups of the light and electron microscopic examinations. These degenerations were more prominent in 1 and 3 days injury groups. However, the ultrastructure of the cells were well preserved in MP treatment group when compared with experimental control groups. Also, we obtained that the expression of miR-20a was upregulated in experimental control group on 1 and 3 days and in treatment group on 1 day after injury. In contrast we observed that miR-125b expression was downregulated in experimental control groups on 3 and 7. days. When all results are evaluated together, we understood that after experimental SCI, miR-20a upregulation could induce proinflammatory molecules and thus increase inflammation. On the other hand, we understood that miR-125b may be associated with caspase-3 and after injury miR-125b downregulation may inhibit apoptosis. These results suggest that miR-20a and miR-125b could be considered as biomarkers and treatment agents in SCI.