Assessment of CircRNA Expression Profiles and Potential Functions in Brown Adipogenesis

Bibliometric Analysis of Global Research on Circular RNA: Current Status and Future Directions

Circular RNAs (circRNAs) have gained significant attention in recent years. This bibliometric analysis aimed to provide insights into the current state and future trends of global circRNA research. The scientific output on circRNAs from 2010 to 2022 was retrieved from the Web of Science Core Collection with circRNA-related terms as the subjects. Key bibliometric indicators were calculated and evaluated using CiteSpace. A total of 7385 studies on circRNAs were identified. The output and citation number have increased rapidly after 2015. China, the USA, and Germany were top three publishing countries. Currently, circCDR1as, circHIPK3, circPVT1, circSHPRH, and circZNF609 are the most studied circRNAs; and all are related to cancer. The theme of research have shifted from transcript, exon circularization and miRNA sponge topics to the transcriptome, tumor suppressor, and biomarkers, indicating that research interests have evolved from basic to applied research. CircRNAs will continue to be a highly active research area in the near future. From the current understanding of circRNA characterization and regulatory mechanisms as miRNA sponges in cancer, future directions may examine potential diagnostic and therapeutic roles of circRNAs in cancers or the function and mechanism of circRNAs in other diseases.

Epigenetic modifications in obesity-associated diseases

The global prevalence of obesity has reached epidemic levels, significantly elevating the susceptibility to various cardiometabolic conditions and certain types of cancer. In addition to causing metabolic abnormalities such as insulin resistance (IR), elevated blood glucose and lipids, and ectopic fat deposition, obesity can also damage pancreatic islet cells, endothelial cells, and cardiomyocytes through chronic inflammation, and even promote the development of a microenvironment conducive to cancer initiation. Improper dietary habits and lack of physical exercise are important behavioral factors that increase the risk of obesity, which can affect gene expression through epigenetic modifications. Epigenetic alterations can occur in early stage of obesity, some of which are reversible, while others persist over time and lead to obesity-related complications. Therefore, the dynamic adjustability of epigenetic modifications can be leveraged to reverse the development of obesity-associated diseases through behavioral interventions, drugs, and bariatric surgery. This review provides a comprehensive summary of the impact of epigenetic regulation on the initiation and development of obesity-associated cancers, type 2 diabetes, and cardiovascular diseases, establishing a theoretical basis for prevention, diagnosis, and treatment of these conditions.

Expression Analysis of circRNAs in Human Adipogenesis

Purpose

Adipogenesis is one of the major pathways for generating obesity or overweight that can cause a range of metabolic disorders. Circular RNAs (circRNAs), a specific type of RNAs, have a significant influence on metabolic disorders. This study aims to find differentially expressed circRNAs (DECs) during human subcutaneous adipose tissue (SATs) adipogenesis.

Patients and Methods

The human adipose tissue-derived stromal cells (hADSCs) were isolated from human SATs (n = 3), and then induced into adipocytes. Total RNAs were extracted from hADSCs and adipocytes, and he DECs were detected using circRNA microarray. The GO and KEGG pathways of DECs were analyzed by bioinformatic methods, and partial DECs were further validated by quantitative polymerase chain reaction (qPCR).

Results

Our study detected a total of 1987 DECs, among which, 1134 were found upregulated and 853 were downregulated. GO analysis showed that the upregulated DECs have catalytic activity in intracellular organelle and cytoplasms, whereas downregulated DECs are enriched in organelle lumen, and are involved in positive regulation of developmental process. In addition, pathway results demonstrated that upregulated DECs are involved in platinum drug resistance and cellular senescence, and downregulated DECs are enriched in proteoglycans in cancer and focal adhesion pathway. Two circRNAs, namely has_circ_0001600 and has_circ_0001947 were validated to be significantly upregulated in adipocytes compared to hADSCs.

Conclusion

Our study explored DECs between hADSCs derived from SATs and adipocytes, and report that two circRNAs named has_circ_0001600 and has_circ_0001947 might be important factors involved in human adipogenesis, however, the molecular mechanism should be further explored.

CircMAPK9 promotes adipogenesis through modulating hsa-miR-1322/FTO axis in obesity

Circular RNA (circRNA) is a special category of non-coding RNA that has garnered increasing attention in the exploration of lipid metabolism. However, the functional regulation mechanisms of circRNAs in obesity diseases remain unclear. By whole transcriptome sequencing, a total of 164 circular RNAs were found to exhibit differential expression between lean and obese individuals. RT-qPCR was used to detect significant expression of circMAPK9 in obese individuals, and it was closely related to BMI. Western blot, triglyceride detection, and Oil Red O staining were employed to investigate the role of circMAPK9/hsa-miR-1322/FTO in adipogenesis. In adipocytes, the connection between hsa-miR-1322 and circMAPK9 was verified using fluorescence in situ hybridization, luciferase reporter assay, and RNA immunoprecipitation. It was found that circMAPK9 competed for binding hsa-miR-1322 in the cytoplasm, weakening the inhibitory effect on FTO and promoting adipogenesis. Our study revealed the regulatory mechanism and important role of circMAPK9 in the process of adipogenesis.

Circular RNA- and microRNA-Mediated Post-Transcriptional Regulation of Preadipocyte Differentiation in Adipogenesis: From Expression Profiling to Signaling Pathway

Adipogenesis is an indispensable cellular process that involves preadipocyte differentiation into mature adipocyte. Dysregulated adipogenesis contributes to obesity, diabetes, vascular conditions and cancer-associated cachexia. This review aims to elucidate the mechanistic details on how circular RNA (circRNA) and microRNA (miRNA) modulate post-transcriptional expression of targeted mRNA and the impacted downstream signaling and biochemical pathways in adipogenesis. Twelve adipocyte circRNA profiling and comparative datasets from seven species are analyzed using bioinformatics tools and interrogations of public circRNA databases. Twenty-three circRNAs are identified in the literature that are common to two or more of the adipose tissue datasets in different species; these are novel circRNAs that have not been reported in the literature in relation to adipogenesis. Four complete circRNA-miRNA-mediated modulatory pathways are constructed via integration of experimentally validated circRNA-miRNA-mRNA interactions and the downstream signaling and biochemical pathways involved in preadipocyte differentiation via the PPARγ/C/EBPα gateway. Despite the diverse mode of modulation, bioinformatics analysis shows that the circRNA-miRNA-mRNA interacting seed sequences are conserved across species, supporting mandatory regulatory functions in adipogenesis. Understanding the diverse modes of post-transcriptional regulation of adipogenesis may contribute to the development of novel diagnostic and therapeutic strategies for adipogenesis-associated diseases and in improving meat quality in the livestock industries.

Comprehensive Analysis of circRNA Expression Profiles in Human Brown Adipose Tissue

PURPOSE

Brown adipose tissue (BAT) can rapidly generate heat and improve energy metabolism. Circular RNAs (circRNAs) are cellular endogenous non-coding RNAs, which can regulate the development and progress of different diseases. However, the role of circRNAs in human BAT is not fully understood. Here, we analyzed the differentially expressed circRNAs (DECs) in human BAT, as well as in white adipose tissue (WAT), and identified new biomarkers of BAT.

PATIENTS AND METHODS

Three human BAT and three human subcutaneous WAT samples were selected, and circRNA microarray was performed. Additionally, quantitative real-time polymerase chain reaction (qRT-PCR) was applied to determine the expression of six circRNAs. Finally, the functional analysis was performed by bioinformatics.

RESULTS

Compared to WAT, 152 upregulated circRNAs and 201 downregulated circRNAs were identified in BAT. The DECs were further subjected to GO and KEGG enrichment analysis. Several circRNAs, for example, hsa_circ_0006168, hsa_circ_26337 and hsa_circ_0007507 were found upregulated and hsa_circ_0030162 was found downregulated in human BAT compared to WAT.

CONCLUSION

This study profiles the circRNA expression in human BAT and WAT, and suggests hsa_circ_0006168, hsa_circ_26337, hsa_circ_0007507, and hsa_circ_0030162 as novel biomarkers for human BAT.

RNA-seq profiling of white and brown adipocyte differentiation treated with epigallocatechin gallate

Due to serious adverse effects, many of the approved anti-obesity medicines have been withdrawn, and the selection of safer natural ingredients is of great interest. Epigallocatechin gallate (EGCG) is one of the major green tea catechins, and has been demonstrated to possess an anti-obesity function by regulating both white and brown adipose tissue activity. However, there are currently no publicly available studies describing the effects of EGCG on the two distinct adipose tissue transcriptomes. The stromal vascular fraction (SVF) cell derived from adipose tissue is a classic cell model for studying adipogenesis and fat accumulation. In the current study, primary WAT and BAT SVF cells were isolated and induced to adipogenic differentiation in the presence or absence of EGCG. RNA-seq was used to determine genes regulated by EGCG and identify the key differences between the two functionally distinct adipose tissues. Taken together, we provide detailed stage- and tissue-specific gene expression profiles affected by EGCG. These data will be valuable for obesity-related clinical/basic research.

Measurement(s)	white adipose tissue transcriptome • brown adipose tissue transcriptome
Technology Type(s)	RNA sequencing
Factor Type(s)	epigallocatechin gallate presence

Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.19067663