The Roles And Mechanisms Of MicroRNA-152in Regeneration Of Neurites After Spinal Cord Injury

The incidence of spinal cord injury (SCI) worldwide is about11to60cases permillion people annually. Because spinal cord is closely related to the body’s sensory andmotor function, and its self-repair and regeneration capacity is pretty limited, SCI patientssuffer from feel loss and motor dysfunction, which cause tremendous pain and burden forboth the patients and their families. A series of pathophysiological changes happen in afew minutes to a few years after SCI. The body’s motor and sensory dysfunctions arecaused by the combined effects of many complex factors. Due to the complexity of thepathological process and the local environment after injury, there are still no satisfactorytreatment methods till now. Therefore finding an effective treatment for SCI is a greatchallenge for both basic and clinical medical workers.MicroRNAs (miRNAs) are a kind of non-coding RNAs, which has only about22nucleotides. miRNAs primarily combine the3’ untranslational region (3’UTR) of theirtarget genes, thus induce the degradation of mRNAs or inhibition their translation. miRNAis an important post-transcriptional regulation of gene expression and plays an importantregulatory role in many physiological and pathological processes. miRNAs extensively exist in various systems, the central nervous system (CNS) included. They involve inalmost every step of CNS development, including neural model determination, neuralstem cells differentiation, the establishment and maintenance of neuron properties, axonguidance, synaptic plasticity as well as long-term memory and so on. miRNA microarrayin our previous experiment showed that the expression level of microRNA-152(miR-152)increased after SCI. And in situ hybridization indicated that the elevated miR-152mainlylocated in neurons around the lesion site. miR-152as well as miR-148a and miR-148bbelong to miR-148/152family. The majority studies of this miRNA family have focusedon their functions in immune system and cancer. Although we know that the expression ofmiR-152increases in rat injured spinal cord, but its specific distribution in spinal cordtissue and the corresponding regulatory role as well as its mechanisms is still notelucidated. By comparing the miRNA expression profiles of mature neurons,neuroblastoma cells and neural precursors, we found that mature neurons have lowermiR-152expression, which suggest that it may affect axonal growth through regulatingthe expression Nrp1and Robo1, but the exact mechanism is not clear yet.Our research found that miR-152expression level in CNS continued to rise since theearly embryo to birth. qPCR also confirmed the upregulated expression level of miR-152after spinal cord injury. Neurons exist in a very complex environment after SCI. Using twoin vitro injury models, H2O2-induced oxidative stress model as well as neuron scratchmodel, we found that the expression level of miR-152elevated in both models in atime-dependent manner. To determine the role of miR-152on neurons, we cultured neuroncell lines, PC12cells and SH-SY5Y cells. We also isolated cortical neurons form B6mice.Giving them miR-152mimics or inhibitors separately, we observed that the neurites of allthe three cell types in miR-152over-expressed groups were shorter than in theircorresponding control groups. However inhibition of miR-152didn’t bring significantdifference according to neurites outgrowth. We also found that in cultured cortical neurons,over-expression of miR-152decreased the expression of MAP2、Tau and GAP-43. Basedon these findings, using TargetScan、PicTar and other softwares and databases, wepredicted HuD may be the target gene of miR-152. This prediction was confirmed by dual luciferase reporter detection and Western-bolt analysis. What’s more, the expression ofHuD decreased in injured spinal cord, which further suggested it is the target gene ofmiR-152. Over-expression of miR-152significantly promoted PC12cells proliferation ina miR-152concentration-dependent manner. This phenomenon may be caused byinhibition of CDK19by miR-152.Studies on the roles and mechanisms of miR-152on neuronal regeneration after micespinal cord injury could not only theoretically help to reveal neurites regenerationregulatory mechanisms after spinal cord injury, but also lay the foundation and providenew ideas for the clinical treatment of spinal cord injury.