LncRNA AFAP1-AS1 Conveyed by Serum Exosomes from Patients with Septic Shock Promotes M1 Macrophage Polarization by Activating MAPK Signaling

Abstract

Background: Septic shock, the most severe form of sepsis syndrome, is life-threatening and requires immediate medical attention. However, due to its poorly understood mechanism, there is no effective treatment for septic shock. Serum exosomes are important mediators of systemic inflammation due to septic shock, and we sought to uncover key signaling molecules in mediation. Methods: Serum exosomes from patients with septic shock (SS-exo) and healthy controls (Normal-exo) were isolated and characterized by western blot, nanoparticle tracking assay (NTA) and transmission electron microscopy (TEM). The long noncoding RNA (lncRNA) actin filament associated protein 1-antisense RNA 1 (AFAP1-AS1) expression levels in exosomes and THP-1 (the human leukemic cell line) cells co-incubated with the exosomes were measured by real-time quantitative reverse transcription PCR (polymerase chain reaction) (qRT-PCR). THP-1 cells were divided into lipopolysaccharide (LPS, 100 ng/mL) group, SS-exo group, SS-exo-shRNA group, and SS-exo-shRNA-AFAP1-AS1 group. The enzyme-linked immunosorbent assay (ELISA) was employed to examine the inflammatory cytokine interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) expression in each group. Flow cytometry was applied to examine cell surface antigens CD86 (cluster of differentiation 86) and CD206 expression in each group. In addition, qRT-PCR was conducted to determine IL-6, inducible nitric oxide synthase (iNOS), Arginase I (Arg1), and interleukin-10 (IL-10) expression levels in each group, and western blotting was employed to examine p-ERK1 (p-extracellular regulated protein kinases 1), ERK1/2, p38 MAPK (mitogen-activated protein kinase), and p-p38 MAPK protein expression levels in each group. Results: We successfully isolated and characterized SS-exo. The AFAP1-AS1 content was significantly increased in SS-exo. AFAP1-AS1 could be transmitted to THP-1 cells and stimulate THP-1 cell polarization to pro-inflammatory macrophages (M1 macrophages), thereby promoting the production of inflammatory factors IL-6 and TNF-α. Western blot revealed that AFAP1-AS1 significantly activated the MAPK signaling pathway. Conclusions: AFAP1-AS1, carried by SS-exo, excites THP-1 cell polarization in M1 macrophages and promotes an inflammatory response by activating the MAPK signaling pathway.