Role of circular RNAs in visceral organ fibrosis

The role of non-protein-coding RNAs in ischemic acute kidney injury

Acute kidney injury (AKI) is a condition characterized by a rapid decline in kidney function within a span of 48 hours. It is influenced by various factors including inflammation, oxidative stress, excessive calcium levels within cells, activation of the renin-angiotensin system, and dysfunction in microcirculation. Ischemia-reperfusion injury (IRI) is recognized as a major cause of AKI; however, the precise mechanisms behind this process are not yet fully understood and effective treatments are still needed. To enhance the accuracy of diagnosing AKI during its early stages, the utilization of innovative markers is crucial. Numerous studies suggest that certain noncoding RNAs (ncRNAs), such as long noncoding RNAs (lncRNAs), microRNAs (miRNAs), and circular RNAs (circRNAs), play a central role in regulating gene expression and protein synthesis. These ncRNAs are closely associated with the development and recovery of AKI and have been detected in both kidney tissue and bodily fluids. Furthermore, specific ncRNAs may serve as diagnostic markers and potential targets for therapeutic interventions in AKI. This review aims to summarize the functional roles and changes observed in noncoding RNAs during ischemic AKI, as well as explore their therapeutic potential.

Expression profiles of circular RNAs and interaction networks of competing endogenous RNAs in neurogenic bladder of rats following suprasacral spinal cord injury

Background

Neurogenic bladder (NB) following suprasacral spinal cord injury (SSCI) is an interstitial disease with the structural remodeling of bladder tissue and matrix over-deposition. Circular RNAs (circRNAs) are involved in fibrotic disease development through their post-transcriptional regulatory functions. This study aimed to use transcriptome high-throughput sequencing to investigate the process of NB and bladder fibrosis after SSCI.

Methods

Spinal cord transection at the T10-T11 level was used to construct the SSCI model in rats (10-week-old female Wistar rats, weighing 200 ± 20 g). The bladders were collected without (sham group) and with (SSCI 1-3 groups) NB status. Morphological examination was conducted to assess the extent of bladder fibrosis. Additionally, RNA sequencing was utilized to determine mRNAs and circRNAs expression patterns. The dynamic changes of differentially expressed mRNAs (DEMs) and circRNAs (DECs) in different periods of SSCI were further analyzed.

Results

Bladder weight, smooth muscle cell hypertrophy, and extracellular matrix gradually increased after SSCI. Compared with the sham group, 3,255 DEMs and 1,339 DECs, 3,449 DEMs and 1,324 DECs, 884 DEMs, and 1,151 DECs were detected in the SSCI 1-3 groups, respectively. Specifically, circRNA3621, circRNA0617, circRNA0586, and circRNA4426 were significant DECs common to SSCI 1-3 groups compared with the sham group. Moreover, Gene Ontology (GO) enrichment suggested that inflammatory and chronic inflammatory responses were the key events in NB progression following SSCI. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways enrichment associated with the "Chemokine signaling pathway", the "IL-17 signaling pathway", and the "TGF-beta signaling pathway" suggests their potential involvement in regulating biological processes. The circRNA-miRNA-mRNA interaction networks of DECs revealed rno-circ-2239 (micu2) as the largest node, indicating that the rno-circ-2239-miRNA-mRNA-mediated network may play a critical role in the pathogenesis of SSCI-induced NB.

Conclusions

This study offers a comprehensive outlook on the possible roles of DEMs and DECs in bladder fibrosis and NB progression following SSCI. These findings have the potential to serve as novel biomarkers and therapeutic targets.

CircRNAs: versatile players and new targets in organ fibrosis

Organ fibrosis can occur in virtually all major organs with relentlessly progressive and irreversible progress, ultimately resulting in organ dysfunction and potentially death. Unfortunately, current clinical treatments cannot halt or reverse the progression of fibrosis to end-stage organ failure, and thus, advanced antifibrotic therapeutics are urgently needed. In recent years, a growing body of research has revealed that circular RNAs (circRNAs) play pivotal roles in the development and progression of organ fibrosis through highly diverse mechanisms of action. Thus, manipulating circRNAs has emerged as a promising strategy to mitigate fibrosis across different organ types. In this review, we systemically summarize the current state of knowledge about circRNA biological properties and the regulatory mechanisms of circRNAs. A comprehensive overview of major fibrotic signaling pathways and representative circRNAs that are known to modulate fibrotic signals are outlined. Then, we focus on the research progress of the versatile functional roles and underlying molecular mechanisms of circRNAs in various fibrotic diseases in different organs, including the heart, liver, lung, kidney and skin. Finally, we offer a glimpse into the prospects of circRNA-based interference and therapy, as well as their utilization as biomarkers in the diagnosis and prognosis of fibrotic diseases. Video abstract.

Circ_0047339 promotes the activation of fibroblasts and affects the development of urethral stricture by targeting the miR-4691-5p/TSP-1 axis

Urethral stricture is related to scar tissue fibrosis, but its pathogenesis is still unclear. This study aims to explore the regulatory mechanism of circular RNA (circRNA) in the occurrence and development of urethral stricture. CircRNA microarray was employed to analyze circRNA expression profiles between human urethral scar tissue and normal urethral tissue. The results of circRNA microarray showed that there were 296 differentially expressed genes between urethral scar tissue and normal urethral tissue. The enrichment analysis of Kyoto encyclopedia of genes and genomes showed that these circRNAs were significantly correlated with ECM–receptor interaction. The first nine differentially expressed circRNA were selected to predict the circRNA–miRNA network. RT-qPCR results showed that circ_0047339 was upregulated considerably in urethral scar tissue. Urethral scar fibroblasts were isolated from human urethral scar tissue and cultured in vitro. After silencing circ_0047339, the proliferation of urethral scar cells decreased significantly, and the expressions of Collagen I (COL-1) and α-smooth muscle actin (α-SMA) also reduced. As a competing endogenous RNA, circ_0047339 could increase the expression of TSP-1 by competitively binding miR-4691-5p. In addition, miR-4691-5p mimic transfection could inhibit the proliferation of urethral scar fibroblasts and the presentation of thrombospondin-1 (TSP-1), α-SMA and COL-1, while circ_0047339 overexpression eliminated this inhibition. Our results showed that circ_0047339 might promote the growth and fibrosis of urethral scar fibroblasts through miR-4691-5p/TSP-1 axis, thus promoting the development of urethral stricture.

Epigenetic regulation in radiation-induced pulmonary fibrosis

PURPOSE

Radiation-induced pulmonary fibrosis (RIPF) is a common and serious adverse effect of radiotherapy for thoracic tumors, which occurs in the irreversible stage of radiation-induced lung injury (RILI) >6 months after irradiation. It is characterized by progressive and irreversible destruction of lung tissue and deterioration of lung function, which may impair quality of life and lead to respiratory failure and death. We hope this will draw attention to the involvement of epigenetics in the regulation of RIPF.

CONCLUSIONS

This review summarizes research progress on the role and mechanism of DNA methylation, noncoding RNA and RNA methylation in RIPF or RILI, and the possible role and mechanism of histone modification in RIPF. We have noticed that in tissue fibrosis, the epigenetic regulation mechanisms inside and outside the nucleus can influence each other. We speculate that RIPF may be regulated by an epigenetic regulatory network during its development, and believe that TGF-β, SNAIL, PTEN and EZH2 are four targets worthy of in-depth study.

The Combined Effects of circRNA Methylation Promote Pulmonary Fibrosis

N6-methyladenosine (m6A) is the most common type of RNA methylation modification, mainly occurring on mRNA. Whether m6A-modified circRNAs are involved in pulmonary fibrosis in different settings remains unclear. Using an m6A-circRNA epitranscriptomic chip, candidate circRNAs were selected, among which hsa_circ_0000672 and hsa_circ_0005654 were specifically involved in SiO2-induced pulmonary fibrosis by targeting the same protein, eIF4A3, indicating that the m6A modification of these two circRNAs has a synergistic effect on fibroblast dysfunction induced by SiO2. A mechanistic study revealed that the m6A modification of circRNAs was mainly mediated by the methyltransferase METTL3. Furthermore, METTL3 promoted the activation, migration and activity of pulmonary fibroblasts and participated in SiO2-induced pulmonary fibrosis via the circRNA m6A modification. m6A methylation of circRNAs mediates silica-induced fibrosis, enriching the understanding of circRNAs and uncovering a potential new target for treating fibrosis-related diseases.