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RNA editing enzyme APOBEC3A promotes pro-inflammatory (M1) macrophage polarization

ABSTRACT: Macrophages acquire a pro-inflammatory M1 phenotype in response to microbial products or pro-inflammatory cytokines through incompletely understood molecular mechanisms. We recently described the induction of APOBEC3A-mediated cellular site-specific cytosine-to-uracil (C>U) RNA editing during M1 macrophage polarization. However, the functional significance of this RNA editing is unknown. Here, we find that cellular RNA editing by APOBEC3A can also be induced by influenza or Maraba virus infections in normal macrophages, and by interferons in tumor-associated macrophages. Gene knockdown and RNA Seq analyses show that APOBEC3A induces C>U RNA editing (range 7%-88%) of 209 exonic or UTR sites in 203 genes during M1 polarization of monocyte-derived macrophages. The highest level of deleterious protein-recoding C>U RNA editing is observed in THOC5, which encodes a key nuclear protein implicated in the export of mRNAs during M-CSF driven macrophage differentiation. Knockdown of APOBEC3A in M1 macrophages reduces pro-inflammatory IL6, IL23A, and IL12B gene expression, CD80 and CD86 surface protein expression, and TNF-α, IL-1β and IL-6 cytokine secretion, and increases glycolysis and glycolytic capacity. These results demonstrate that APOBEC3A cytidine deaminase plays an important role in transcriptomic and functional polarization of pro-inflammatory M1 macrophages.

ORGANISM(S): Homo sapiens

PROVIDER: GSE146867 | GEO | 2020/03/13

REPOSITORIES: GEO

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Project description:Macrophages are essential cells of the immune system that alter their inflammatory profile depending on their microenvironment. Alternative polyadenylation in the 3'UTR (3'UTR-APA) and intronic polyadenylation (IPA) are mechanisms that modulate gene expression, in particular in cancer and activated immune cells. Yet, how polarization and colorectal cancer (CRC) cells microenvironment affect 3'UTR-APA and IPA in primary human macrophages remains unknown. Here, primary human monocytes were isolated from healthy donors, differentiated and polarized into a pro-inflammatory state and ChrRNA-Seq and 3'RNA-Seq were performed to quantify gene expression and characterize new 3’UTR-APA and IPA mRNA isoforms. Our results show that polarization of human macrophages from naïve to a pro-inflammatory state causes a marked increase both in proximal polyA site selection in the 3'UTR and in IPA events, in genes relevant for macrophage functions. Additionally, we found a negative correlation between differential gene expression and IPA during pro-inflammatory polarization of primary human macrophages. As macrophages are abundant immune cells in the CRC microenvironment that either promote or abrogate cancer progression, we investigated how indirect exposure to CRC cells affects macrophage gene expression and 3'UTR-APA and IPA mRNA events. Co-culture with CRC cells alters the inflammatory phenotype of macrophages, increases the expression of pro-tumoral genes and induce 3’UTR-APA alterations. Notably, some of these gene expression differences were also found in tumour-associated macrophages of CRC patients, indicating that they are physiological relevant. Upon macrophage pro-inflammatory polarization SRSF12 is the pre-mRNA processing gene that is most upregulated. After SRSF12 knockdown in M1 macrophages there is a global downregulation of gene expression, in particular in genes involved in gene expression regulation and in immune responses. Our results reveal new 3’UTR-APA and IPA mRNA isoforms produced during pro-inflammatory polarization of primary human macrophages and CRC co-culture that may be used in the future as diagnostic or therapeutic tools.

Project description:Inflammation is the natural defensive response of the immune system to an injury or infection and is regulated by small molecule mediators triggering different phases of the inflammatory process. In particular, lipid mediators (LM) and cytokines exhibit crucial regulatory functions in the progression and resolution of inflammation. Macrophages play a central role in this process and can adopt distinct phenotypes with specialized functions depending on their microenvironment: inflammatory M1 macrophages drive inflammation by the release of pro-inflammatory cytokines and LMs, like prostaglandins (PG) and leukotrienes (LT), while resolving M2 macrophages promote inflammation resolution and tissue regeneration by production of anti-inflammatory cytokines and specialized pro resolving mediators (SPM). Aging is associated with chronic and unresolved, low-grade inflammation (“inflammaging”) and aging-related dysfunction of macrophages in the resolution of inflammation and tissue maintenance has been reported. Yet, the underlying molecular mechanisms and functional consequences of latter processes remain poorly understood. Here, we show that polarization of peritoneal macrophages (PM) from geriatric mice towards an M2-like phenotype is impaired versus adult mice, resulting in aberrant LM formation and cytokine release. In PMs isolated from adult mice (PM-A) we observed a shift in LM formation from PGs and LTs to SPMs already after 4 h of polarization towards M2 with interleukin (IL) 4. In contrast, PMs from geriatric mice (PM-G) produced mainly LTs and PGs upon polarization. This pattern persists over the course of 48 h of polarization. Proteomic profiling revealed that polarization of PM A towards M2 yields a more distinct phenotype, clearly separated from M1, when compared to PM-G. We observed similar aging-related changes in the lipidome and cytokine profile of spleen, lung and liver tissue from mice. Hence, we hypothesize that during aging macrophage polarization towards M2 is impaired, which in turn drives chronic inflammation and disturbs tissue maintenance. By combining state-of-the art lipidomic and proteomic profiling we aim to uncover new molecular targets for pharmaceutical interventions to improve therapeutic strategies for elderly patients with chronic inflammatory diseases.

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RNA editing enzyme APOBEC3A promotes pro-inflammatory (M1) macrophage polarization

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