Assessment of CircRNA Expression Profiles and Potential Functions in Brown Adipogenesis

Abstract

Brown adipose tissue (BAT) is specialized for energy expenditure, thus a better understanding of the regulators influencing BAT development could provide novel strategies to defense obesity. Many protein-coding genes, miRNAs, and lncRNAs have been investigated in BAT development, however, the expression patterns and functions of circRNA in brown adipogenesis have not been reported yet. This study determined the circRNA expression profiles across brown adipogenesis (proliferation, early differentiated, and fully differentiated stages) by RNA-seq. We identified 3,869 circRNAs and 36.9% of them were novel. We found the biogenesis of circRNA was significantly related to linear mRNA transcription, meanwhile, almost 70% of circRNAs were generated by alternative back-splicing. Next, we examined the cell-specific and differentiation stage-specific expression of circRNAs. Compared to white adipocytes, nearly 30% of them were specifically expressed in brown adipocytes. Further, time-series expression analysis showed circRNAs were dynamically expressed, and 117 differential expression circRNAs (DECs) in brown adipogenesis were identified, with 77 upregulated and 40 downregulated. Experimental validation showed the identified circRNAs could be successfully amplified and the expression levels detected by RNA-seq were reliable. For the potential functions of the circRNAs, GO analysis suggested that the decreased circRNAs were enriched in cell proliferation terms, while the increased circRNAs were enriched in development and thermogenic terms. Bioinformatics predictions showed that DECs contained numerous binding sites of functional miRNAs. More interestingly, most of the circRNAs contained multiple binding sites for the same miRNA, indicating that they may facilitate functions by acting as microRNA sponges. Collectively, we characterized the circRNA expression profiles during brown adipogenesis and provide numerous novel circRNAs candidates for future brown adipogenesis regulating studies.

Comprehensive Analysis of circRNA Expression Profiles in Human Brown Adipose Tissue

“… 28 Li et al reported that circScd1 overexpression promotes steatosis in non-alcoholic fatty liver. 29 Previous reports also showed that circRNAs are abundantly expressed in BAT and WAT of mice, 22 , 23 however, there is no clear report on circRNA expression profiles in human BAT and WAT. So, here we aimed to explore the DECs between BAT and WAT, and attempted to identify some novel biomarkers for metabolic diseases.…”

“… 14–16 Numerous studies indicated that circRNAs play a critical role in the development of various diseases. 17–21 Recent reports indicate that circRNAs are differentially expressed in mice BAT and WAT, 22 , 23 but the pattern of differentially expressed circRNAs in human BAT and WAT remains unclear.…”

Epigenetic modifications in obesity‐associated diseases

“…A recent study identified circRNAs profiles in white and brown AT, which provided circRNA candidates for regulating adipose formation. 186,187 Studies suggested that circ-SAMD4A increased preadipocyte differentiation, 188 and circArhgap5-2 played an essential role in adipogenesis and lipid metabolism. 189 Evidence suggests that downregulated hsa_circ_000839 in patients with BC exhibits a negative correlation with BMI, but the underlying mechanism is still unclear.…”

“…On the contrary, circARF3 (ADP‐ribosylation factor 3) could also strengthen mitophagy to subdue adipose inflammation by combining miRNA‐103., 185 but whether changes in this inflammatory state affect tumor development have not been confirmed. A recent study identified circRNAs profiles in white and brown AT, which provided circRNA candidates for regulating adipose formation 186,187 . Studies suggested that circSAMD4A increased preadipocyte differentiation, 188 and circArhgap5‐2 played an essential role in adipogenesis and lipid metabolism 189 …”

Expression Analysis of circRNAs in Human Adipogenesis

“… 10 In addition, two other studies explored the mouse white and brown adipogenesis, respectively. 11 , 12 Furthermore, some studies assessed the differentially expressed circRNAs (DECs) of VATs in human obese compare to lean individuals and VATs compare to subcutaneous adipose tissue (SATs). 8 , 13 In other animals, for instance, the circRNAs expression of Yak and Pig of SATs adipogenesis were also evaluated.…”