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Macrophage Uptake of Necrotic Cell DNA Activates the AIM2 Inflammasome to Regulate a Proinflammatory Phenotype in CKD.

ABSTRACT: Nonmicrobial inflammation contributes to CKD progression and fibrosis. Absent in melanoma 2 (AIM2) is an inflammasome-forming receptor for double-stranded DNA. AIM2 is expressed in the kidney and activated mainly by macrophages. We investigated the potential pathogenic role of the AIM2 inflammasome in kidney disease. In kidneys from patients with diabetic or nondiabetic CKD, immunofluorescence showed AIM2 expression in glomeruli, tubules, and infiltrating leukocytes. In a mouse model of unilateral ureteral obstruction (UUO), Aim2 deficiency attenuated the renal injury, fibrosis, and inflammation observed in wild-type (WT) littermates. In bone marrow chimera studies, UUO induced substantially more tubular injury and IL-1β cleavage in Aim2-/- or WT mice that received WT bone marrow than in WT mice that received Aim2-/- bone marrow. Intravital microscopy of the kidney in LysM(gfp/gfp) mice 5-6 days after UUO demonstrated the significant recruitment of GFP+ proinflammatory macrophages that crawled along injured tubules, engulfed DNA from necrotic cells, and expressed active caspase-1. DNA uptake occurred in large vacuolar structures within recruited macrophages but not resident CX3CR1+ renal phagocytes. In vitro, macrophages that engulfed necrotic debris showed AIM2-dependent activation of caspase-1 and IL-1β, as well as the formation of AIM2+ ASC specks. ASC specks are a hallmark of inflammasome activation. Cotreatment with DNaseI attenuated the increase in IL-1β levels, confirming that DNA was the principal damage-associated molecular pattern in this process. Therefore, the activation of the AIM2 inflammasome by DNA from necrotic cells drives a proinflammatory phenotype that contributes to chronic injury in the kidney.

SUBMITTER: Komada T

PROVIDER: S-EPMC5875955 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundAIM2, a cytosolic DNA sensor, plays an important role during infection caused by pathogens with double-stranded DNA; however, its role in human cytomegalovirus (HCMV) infection remains unclear. Previously, we showed an increase in AIM2 protein levels during the early stage of HCMV infection and a decrease 24 h post infection. Because HCMV has developed a variety of strategies to evade host immunity, we speculated that this decline might be attributed to a viral immune escape mechanism. The tegument protein pUL83 is an important immune evasion protein and several studies have reported that pUL83 binds to specific cellular proteins, such as AIM2-like receptor IFI16, to affect their functions. To determine whether pUL83 contributes to the variation in AIM2 levels during HCMV infection, we investigated the pUL83/AIM2 interaction and its impact on the AIM2 inflammasome activation.MethodsWe constructed plasmids expressing recombinant pUL83 and AIM2 proteins for two-hybrid and chemiluminescence assays. Using co-immunoprecipitation and immunofluorescent co-localization, we confirmed the interaction of pUL83/AIM2 in THP-1-derived macrophages infected with HCMV AD169 strain. Furthermore, by investigating the expression and cleavage of inflammasome-associated proteins in recombinant HEK293T cells expressing AIM2, apoptosis-associated speck-like protein (ASC), pro-caspase-1 and pro-IL-1β, we evaluated the effect of pUL83 on the AIM2 inflammasome.ResultsAn interaction between pUL83 and AIM2 was detected in macrophages infected with HCMV as well as in transfected HEK293T cells. Moreover, transfection of the pUL83 expression vector into recombinant HEK293T cells stimulated by poly(dA:dT) resulted in reduced expression and activation of AIM2 inflammasome-associated proteins, compared with the absence of pUL83.ConclusionsOur data indicate that pUL83 interacts with AIM2 in the cytoplasm during the early stages of HCMV infection. The pUL83/AIM2 interaction deregulates the activation of AIM2 inflammasome. These findings reveal a new strategy of immune evasion developed by HCMV, which may facilitate latent infection.

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Macrophage Uptake of Necrotic Cell DNA Activates the AIM2 Inflammasome to Regulate a Proinflammatory Phenotype in CKD.

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