The Research Of Circular RNA Circ＿0002538 Promoting Myelination In Diabetic Peripheral Neuropathy Through MiR-138-5p/PLLP Axis

Objective:In the twenty-first century,diabetes mellitus has become one of the most important public health challenges,bringing a heavy burden to countries around the world.Diabetic peripheral neuropathy(DPN)is the most prevalent complication of diabetes.Its pathogenic mechanism is still unclear,and the treatment effect is not satisfactory.Noncoding RNAs have been reported to play important roles in a variety of physiological and pathobiological activities.This study intends to explore the pathogenic mechanism and therapeutic target of DPN by noncoding RNA sequencing and protein profiling sequencing.Methods:The skin and sural nerves were obtained from the lower limbs of diabetic and non-diabetic patients,respectively,and the occurrence of DPN was confirmed by intraepidermal nerve fiber density and transmission electron microscopy.Primary Schwann cells(SCs)were extracted and assessed with Edu assay and Transwell assay.Then circular RNA(circRNA),microRNA(miRNA)sequencing and protein profiling were performed on three pairs of diabetic and non-diabetic sural nerve tissues.Gene Ontology(GO),KEGG pathway,and protein-protein interaction(PPI)analysis were used to explore the potential functions of differentially expressed proteins.Competing endogenous RNA(ceRNA)networks were constructed based on real-time polymerase chain reaction(RT-PCR)results and bioinformatics analysis.The function of circ＿0002538 with high expression abundance and significant differential expression was verified in SCs by dual luciferase reporter gene,lentiviral transfection,and Transwell assays,as well as its mechanism.Finally,the effects of circ＿0002538 overexpression on myelination and neurological recovery were evaluated using a mouse model of DPN.Results:The density of subcutaneous nerve fibers from diabetic patients was lower than that of non-diabetic patients,and the sural nerve in diabetic patients showed more pronounced demyelination.Protein profiling predicted 265 differentially expressed proteins,and GO analysis indicated that the differentially expressed proteins were enriched in myelination and mitochondrial oxidative phosphorylation processes.RT-PCR verified 11 differentially expressed circRNAs and 16 differentially expressed miRNAs that were consistent with RNA sequencing data.The ceRNA network based on differentially expressed circRNAs,miRNAs,and differential proteins suggested that the circ＿0002538-miR-138-5p-plasmolipin(PLLP)axis might be critical for DPN.The expression levels of circ＿0002538 and PLLP were down-regulated in diabetic peripheral nerve tissue.Overexpression of circ＿0002538 promoted the migration ability of SCs in vitro.miR-138-5p inhibited SC migration by targeting PLLP,while circ＿0002538 upregulated PLLP protein expression by sponging miR-138-5p.Downregulation of PLLP resulted in demyelination of normal nerves by affecting SC migration.Overexpression of circ＿0002538 in the sciatic nerve of diabetic mice ameliorated the symptoms of DPN.Conclusions:The present research provided novel insights into the pathogenesis of DPN,in which the circ＿0002538/miR-138-5p/PLLP axis was suppressed in SCs and hence caused demyelination.These findings expanded the role of circRNAs in DPN and provided potential therapeutic targets for DPN.