Changing expression profiles of circular RNA reveal the key regulators and interaction networks of competing endogenous RNA in neurogenic bladder after suprasacral spinal cord injured
Background: Neurogenic bladder (NB) after suprasacral spinal cord injury (SSCI) is an interstitial disease with structural remodeling of bladder tissue and matrix over-deposition. Circular RNAs (circRNAs), which have extensive post-transcriptional regulatory functions, widely participate in the pathogenesis of fibrotic diseases and may be promising new biomarkers and potential therapeutic targets. However, the expression profiles and possible roles of circRNAs in bladder fibrosis and NB after SSCI still remain elusive.  Methods: Spinal cord transection at the T10–T11 level was used to construct the NB after SSCI model in rats. The bladders were collected in rats without (sham) and with (SSCI 1-3 groups) NB status. Morphological observation was performed to detect the severity of bladder fibrosis. The expression profiles of mRNAs and circRNAs were detected by transcriptome high-through-put sequencing. The dynamic changes of differentially expressed mRNAs (DEMs) and circRNAs (DECs) in different time periods of SSCI were further analyzed. Moreover, Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway were performed to investigate the potential functions. In addition, the co-expression network (circRNA–miRNA–mRNA) was constructed to understand the internal regulating relationships of these DEMs and DECs. The top ten common expressed DECs in each NB stage were subjected to Quantitative Real-Time Polymerase Chain Reaction (qRT-PCR) to verify their expression.  Results: Bladder weight, smooth muscle cells hypertrophy, and extracellular matrix gradually increased over time after SSCI. Compared with the normal control (NC) group, 3255 DEMs and 1339 DECs, 3449 DEMs and 1324 DECs, 884 DEMs and 1151 DECs were detected in the SSCI 1-3 groups, respectively. Specifically, circRNA3621, circRNA5775, circRNA3111, and circRNA0586 were significant DECs common to SSCI 1–3 compared with NC group. Moreover, GO enrichment suggested that “inflammatory response”, “inflammatory response” and “chronic inflammatory response” were the key events in NB progression. The KEGG pathway related to “Chemokine signaling pathway”, “IL-17 signaling pathway”, and “TGF-beta signaling pathway” were enriched, implying potential roles in regulatory process.   Conclusion: This study provides a systematic perspective on the potential functions of these DEMs and DECs during bladder fibrosis process and NB after SSCI, and could help pave the way for effective therapeutics for this devastating and complex disease. Overall design: Twenty female Wistar rats were randomly divided into suprasacral spinal cord injured (SCI) 1–3 and normal control (NC) groups. The spinal cord was completely transected at the T9–T10 level to establish the SCI model. Bladder tissues were collected on days 7, 14, and 28 after the operation. The expression profiles of circRNAs were detected by high-through-put sequencing. Differentially expressed circRNAs (DECs) were chosen for qRT-PCR verification to validate the RNA sequencing results. The results revealed the expression profiles and possible roles of circRNAs in neurogenic bladder of SCI.