Acute lung injury is a serious complication of sepsis with high morbidity and mortality. Pyroptosis is a proinflammatory form of programmed cell death that leads to immune dysregulation and organ dysfunction during sepsis. We previously found that adenosine deaminase acting on double-stranded RNA 1 (ADAR1) plays regulatory roles in the pathology of sepsis, but the mechanism of ADAR1 in sepsis-induced pyroptosis and lung injury remains unclear. Here, we mainly investigated the regulatory effects and underlying mechanism of ADAR1 in sepsis-induced lung injury and pyroptosis of pulmonary macrophages through RNA sequencing of clinical samples, caecal ligation and puncture (CLP)-induced septic mouse models, and in vitro cellular experiments using RAW264.7 cells with lipopolysaccharide (LPS) stimulation. The results showed that pyroptosis was activated in peripheral blood mononuclear cells (PBMCs) from patients with sepsis. In the CLP-induced septic mouse model, pyroptosis was mainly activated in pulmonary macrophages. LPS-stimulated RAW264.7 cells showed significantly increased activation of the NLRP3 inflammasome. ADAR1 was downregulated in PMBCs of patients with sepsis, and overexpression of ADAR1 alleviated CLP-induced lung injury and NLRP3 inflammasome activation. Mechanistically, the regulatory effects of ADAR1 on macrophage pyroptosis were mediated by the miR-21/A20/NLRP3 signalling cascade. ADAR1 attenuated sepsis-induced lung injury and hindered the activation of pyroptosis in pulmonary macrophages in sepsis through the miR-21/A20/NLRP3 axis. Our study highlights the role of ADAR1 in protecting pulmonary macrophages against pyroptosis and suggests targeting ADAR1/miR-21 signalling as a therapeutic opportunity in sepsis-related lung injury.

Dermal white adipose tissue (dWAT) is a newly recognized layer of adipocytes within the reticular dermis of the skin. In many mammals, this layer is clearly separated by panniculus carnosus from subcutaneous adipose tissue (sWAT). While, they concentrated around the hair shaft and follicle, sebaceous gland, and arrector pili muscle, and forms a very specific cone geometry in human. Both the anatomy and the histology indicate that dWAT has distinct development and functions. Different from sWAT, the developmental origin of dWAT shares a common precursor with dermal fibroblasts during embryogenesis. Therefore, when skin injury happens and mature adipocytes in dWAT are exposed, they may undergo lipolysis and dedifferentiate into fibroblasts to participate in wound healing as embryogenetic stage. Studies using genetic strategies to selectively ablate dermal adipocytes observed delayed revascularization and re-epithelialization in wound healing. This review specifically summarizes the hypotheses of the functions of dWAT in wound healing. First, lipolysis of dermal adipocytes could contribute to wound healing by regulating inflammatory macrophage infiltration. Second, loss of dermal adipocytes occurs at the wound edge, and adipocyte-derived cells then become ECM-producing wound bed myofibroblasts during the proliferative phase of repair. Third, mature dermal adipocytes are rich resources for adipokines and cytokines and could release them in response to injury. In addition, the dedifferentiated dermal adipocytes are more sensitive to redifferentiation protocol and could undergo expansion in infected wound. We then briefly introduce the roles of dWAT in protecting the skin from environmental challenges: production of an antimicrobial peptide against infection. In the future, we believe there may be great potential for research in these areas: (1) taking advantage of the plasticity of dermal adipocytes and manipulating them in wound healing; (2) investigating the precise mechanism of dWAT expansion in infected wound healing.

ADAR1 (adenosine deaminase acting on double‐stranded RNA 1) is an RNA‐editing enzyme that me‐diates adenosine‐to‐inosine RNA editing events, an important post‐transcriptional modification mechanism that can alter the coding properties of mRNA or regulate microRNA biogenesis. ADAR1 also regulates the innate immune response. Here, we have demonstrated that ADAR1 expression increased in LPS‐stimulated macrophages. Silencing ADAR1 by using small interfering RNA in macrophages resulted in the pronounced polarization of macrophages to M1, whereas ADAR1 overexpression promoted M2 polarization, which indicated that ADAR1 can inhibit macrophage hyperpolarization and prevent immune hyperactivity. The RNA‐RNP immunoprecipitation binding assay demonstrated a direct interaction between ADAR1 and miR‐21 precursor. Significant up‐regulation in IL‐10 and down‐regulation in miR‐21 were observed in ADAR1‐overexpressing macrophages. We evaluated miR‐21 target mRNAs and macrophage polarization signaling pathways and found that forkhead box protein O1 (Foxo1) was up‐regulated in cells that overexpressed ADAR1. In a mouse allogeneic skin transplantation model, grafts in the ADAR1‐overexpressed group survived longer and suffered less immune cell infiltration. In ADAR1‐overexpressed recipients, splenic macrophages were significantly polarized to M2, and levels of sera IL‐10 were markedly higher than those in the control group. In summary, ADAR1 modulates macrophage M2 polarization via the ADAR1‐miR‐21‐Foxo1‐IL‐10 axis, thereby suppressing allogeneic graft rejection.—Li, J., Xie, J., Liu, S., Li, X., Zhang, D., Wang, X., Jiang, J., Hu, W., Zhang, Y., Jin, B., Zhuang, R., Yin, W. ADAR1 attenuates allogeneic graft rejection by suppressing miR‐21 biogenesis in macrophages and promoting M2 polarization. FASEB J. 32, 5162–5173 (2018). www.fasebj.org

Adenosine deaminase acting on double-stranded RNA 1 (ADAR1) mediates adenosine-to-inosine (A-to-I) RNA editing events. ADAR1 is highly expressed in “septic” macrophages and in small intestinal tissues of mice with sepsis. Overexpression of ADAR1 suppresses inflammation and intestinal damage. However, the specific underlying mechanism is unclear. This study was conducted to explore how microRNA (miRNA) regulates the anti-inflammatory mechanism of macrophages following ADAR1 upregulation. A murine sepsis model was established by cecal ligation and puncture (CLP). Mice were randomly assigned to sham, CLP, and CLP+ADAR1 groups. Hematoxylin and eosin (HE) staining and fluorescence isothiocyanate-dextran were used to evaluate intestinal injury and permeability. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR), western blotting, and Luminex assays were performed to detect changes in the expression of inflammatory cytokines. Adenoviruses were used to express ADAR1 in RAW 264.7 cells. Ribonucleoprotein immunoprecipitation analysis was conducted to detect the binding of ADAR1 and miRNAs. A dual-luciferase reporter assay was used to detect the binding of miRNAs and regulatory factors. We observed that ADAR1 significantly increased the expression of suppressor of cytokine signaling 3 (SOCS3) in macrophages and reduced the expression of interleukin-6 in macrophages and the serum, thereby reducing intestinal permeability and mucosal injury in mice with sepsis. The RNA-ribonucleoprotein immunoprecipitation binding assay and qRT-PCR demonstrated a direct interaction between ADAR1 and pri-miR-30a. The luciferase assay demonstrated that SOCS3 was significantly inhibited by miR-30a-5p, the mature product of miR-30a. Thus, ADAR1 exerts a protective effect against sepsis by reducing inflammation and organ damage via the ADAR1-miR-30a-SOCS3 axis.

Despite significant advances in anti-infective treatment and organ function support technology in recent years, the mortality rate of sepsis remains high. In addition to the high costs of sepsis treatment, the increasing consumption of medical resources also aggravates economic pressure and social burden. Extracellular vesicles (EVs) are membrane vesicles released from different types of activated or apoptotic cells to mediate intercellular communication, which can be detected in both human and animal body fluids. A growing body of researches suggest that EVs play an important role in the pathogenesis of sepsis. In this review, we summarize the predominant roles of EVs in various pathological processes during sepsis and its related organ dysfunction.