Abstract
Macrophage polarization is a process that macrophages exert different functions according to surrounding micro-environment. Macrophages commonly exist in two distinct subsets: classically activated M1 macrophages and alternatively activated M2 macrophages. Circular RNAs (circRNAs) are a novel class of non-coding RNAs generated by back-splicing. Thousands of circRNAs were identified in different cells and tissues. Recent studies have revealed that circRNAs play a crucial role in regulating transcriptional and post-transcriptional gene expression. However, the effects and roles of circRNAs in macrophage polarization have not been well elucidated. Here, circRNAs expression profiles were determined in human THP-1 macrophages incubated in conditions causing activation toward M1 (interferon-γ + LPS) or M2 (interleukin-4) phenotypes. Overall, 9,720 circular RNA were detected from RNA sequencing data. Compared with M2 macrophages, a total of 140 circRNAs were aberrantly expressed in M1 macrophages, including 71 up-regulated circRNAs and 69 down-regulated circRNAs. Quantitative real-time PCR (qRT-PCR) results were generally consistent with the selected differentially expressed circRNAs. Gene Ontology (GO) and KEGG pathway analyses were used to predict biological functions and potential mechanisms of the host linear transcripts of these up-regulated and down-regulated circRNAs. Furthermore, we found that the expression level of circRNA-RNF19B (circRNF19B) in M1 macrophages was significantly higher than that in THP-1 macrophages and M2 macrophages. circRNF19B expression was increased when M2 converted to M1 whereas decreased when M1 converted to M2. Knockdown of circRNF19B following the activation of THP-1 cells using interferon-γ + LPS diminished the expression of M1 macrophages markers and elevated the expression of M2 macrophages markers. In conclusion, these data suggest the involvement of altered circRNAs expression patterns in macrophages exposure to different activating conditions. Circular RNAs may play important roles in regulating macrophage polarization.
Highlights
Macrophages are the essential components of innate immunity with remarkable plasticity and functional heterogeneity (Sica and Mantovani 2012)
In order to investigate alterations in the circRNAs expression profile during macrophage polarization, THP-1 macrophages were further differentiated into M1 macrophages by treating with IFN-γ and LPS and were differentiated into M2 polarization by treating with IL-4. Quantitative realtime PCR (qRT-PCR) and Enzyme-Linked Immunosorbent Assay (ELISA) analysis were performed to identify phenotypic and functional markers of M1 and M2 macrophages
The results showed that circRNF19B expression was significantly up-regulated in M1 macrophages compared with THP-1 macrophages (M0) and M2 macrophages (Figure 7A)
Summary
Macrophages are the essential components of innate immunity with remarkable plasticity and functional heterogeneity (Sica and Mantovani 2012). M2 macrophages are more heterogeneous and assumed to be induced by a variety of stimuli including the Th2 cytokines IL-4 and IL-13, the anti-inflammatory IL-10, M-CSF, glucocorticoids, immune complexes, and apoptotic cells. They are generally identified by high production of IL-10, TGF-β and low production of IL-12 and IL-23 and up-regulation of arginase-1 (Arg-1), mannose receptors (CD206), and scavenger receptors (CD163). M2 macrophages have efficient phagocytic activity, scavenge debris and apoptotic cells, eliminate parasites, dampen inflammation, promote angiogenesis and take part in tissue repair and wound healing (Sica and Mantovani 2012; Orecchioni et al, 2019; Locati et al, 2020)
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