Absent In Melanoma 2 Expression Research Articles

Cytosolic DNA sensor AIM2 promotes KRAS-driven lung cancer independent of inflammasomes.

Constitutively active KRAS mutations are among the major drivers of lung cancer, yet the identity of molecular co-operators of oncogenic KRAS in the lung remains ill-defined. The innate immune cytosolic DNA sensor and pattern recognition receptor (PRR) Absent-in-melanoma 2 (AIM2) is best known for its assembly of multiprotein inflammasome complexes and promoting an inflammatory response. Here, we define a role for AIM2, independent of inflammasomes, in KRAS-addicted lung adenocarcinoma (LAC). In genetically defined and experimentally induced (nicotine-derived nitrosamine ketone; NNK) LAC mouse models harboring the KrasG12D driver mutation, AIM2 was highly upregulated compared with other cytosolic DNA sensors and inflammasome-associated PRRs. Genetic ablation of AIM2 in KrasG12D and NNK-induced LAC mouse models significantly reduced tumor growth, coincident with reduced cellular proliferation in the lung. Bone marrow chimeras suggest a requirement for AIM2 in KrasG12D-driven LAC in both hematopoietic (immune) and non-hematopoietic (epithelial) cellular compartments, which is supported by upregulated AIM2 expression in immune and epithelial cells of mutant KRAS lung tissues. Notably, protection against LAC in AIM2-deficient mice is associated with unaltered protein levels of mature Caspase-1 and IL-1β inflammasome effectors. Moreover, genetic ablation of the key inflammasome adapter, ASC, did not suppress KrasG12D-driven LAC. In support of these invivo findings, AIM2, but not mature Caspase-1, was upregulated in human LAC patient tumor biopsies. Collectively, our findings reveal that endogenous AIM2 plays a tumor-promoting role, independent of inflammasomes, in mutant KRAS-addicted LAC, and suggest innate immune DNA sensing may provide an avenue to explore new therapeutic strategies in lung cancer.

Cutting Edge: Cytosolic Receptor AIM2 Is Induced by Peroxisome Proliferator-activated Receptor γ following Mycobacterium tuberculosis Infection of Human Macrophages but Does Not Contribute to IL-1β Release.

AIM2 (absent in melanoma 2), an inflammasome component, mediates IL-1β release in murine macrophages and cell lines. AIM2 and IL-1β contribute to murine control of Mycobacterium tuberculosis (M.tb) infection, but AIM2's impact in human macrophages, the primary niche for M.tb, remains unclear. We show that M.tb, Mycobacterium bovis bacillus Calmette-Guérin (BCG), and M. smegmatis induce AIM2 expression in primary human macrophages. M.tb-induced AIM2 expression is peroxisome proliferator-activated receptor γ (PPARγ)-dependent and M.tb ESX-1-independent, whereas BCG- and M. smegmatis-induced AIM2 expression is PPARγ-independent. PPARγ and NLRP3, but not AIM2, are important for IL-1β release in response to M.tb, and NLRP3 colocalizes with M.tb. This is in contrast to the role for AIM2 in inflammasome activation in mice and peritoneal macrophages. Altogether, we show that mycobacteria induce AIM2 expression in primary human macrophages, but AIM2 does not contribute to IL-1β release during M.tb infection, providing further evidence that AIM2 expression and function are regulated in a cell- and/or species-specific manner.

Absent in melanoma 2 attenuates proliferation and migration and promotes apoptosis of human colorectal cancer cells by activating P38MAPK signaling pathway.

Colorectal cancer (CRC) stands among the top prevalent cancers worldwide and holds a prominent position as a major contributor to cancer-related mortality globally. Absent in melanoma 2 (AIM2), a constituent of the interferon-inducible hematopoietic interferon-inducible nuclear antigens with 200 amino acid repeats protein family, contributes to both cancer progression and inflammasome activation. Despite this understanding, the precise biological functions and molecular mechanisms governed by AIM2 in CRC remain elusive. Consequently, this study endeavors to assess AIM2's expression levels, explore its potential antitumor effects, elucidate associated cancer-related processes, and decipher the underlying signaling pathways in CRC. Our findings showed a reduced AIM2 expression in most CRC cell lines. Elevation of AIM2 levels suppressed CRC cell proliferation and migration, altered cell cycle by inhibiting G1/S transition, and induced cell apoptosis. Further research uncovered the participation of P38 mitogen-activated protein kinase (P38MAPK) in AIM2-mediated modulation of CRC cell apoptosis and proliferation. Altogether, our achievements distinctly underscored AIM2's antitumor role in CRC. AIM2 overexpression inhibited proliferation and migration and induced apoptosis of CRC cells via activating P38MAPK signaling pathway, indicating AIM2 as a prospective and novel therapeutic target for CRC.

The DNA Sensor AIM2 Determines B Cell Fate after BCR Activation in Chronic Graft-Vs-Host Disease

Prevention and treatment of chronic graft-vs-host disease (cGVHD), a debilitating late immune toxicity in patients after allogeneic hematopoietic stem cell transplantation (allo-HCT), who are otherwise cured of hematological malignancies, remains a major challenge. T cells incite and promote cGVHD through coordinated T-B cell responses. Alloantibody production ( Srinivasan et al, Blood 2012, Jin et al, Blood 2016) and aberrant B Cell Receptor (BCR) signaling ( Allen et al, Blood 2014, Flynn et al, Blood 2015) play fundamental roles in the pathology of cGVHD. B cell-intrinsic pathways in cGVHD remain incompletely understood, limiting our therapeutic capacity for patients. In a single cell RNA sequencing study, we found that transcript levels of the DNA sensor Absent in Melanoma 2 (AIM2) were significantly increased in CD27+ BCR-activated B cell clusters in circulating as well as in tissue-resident cGVHD B cells ( Poe et al, JCI Insight 2023). After confirming AIM2 expression is restricted to the nucleus, we also previously showed that AIM2-expressing B cells were augmented after BCR and interferon-gamma (IFNγ) and/or Toll-like receptor (TLR)-7 or 9 stimulation ( Visentin J, Blood 2022;140 Supp 1), suggesting a context-dependent role for AIM2 after allo-HCT. Our new findings now afford the hypothesis that an AIM2-BCR signaling axis determines B cell fate after allo-HCT. To address this hypothesis, we first examined whether AIM2 modulates the promotion of antibody-secreting cells (ASCs) after BCR activation using a hapten-carrier immunization model. We compared numbers of hapten-specific ASCs from immunized WT and AIM2-KO mouse splenocytes using enzyme-linked immunosorbent spot (ELISPOT). We compared numbers of ASCs on day 3 post-immunization, when early germinal center (GC) formation is known to occur. We found that hapten-specific IgM ASCs were significantly increased in WT splenocytes compared to AIM2-KO (p=0.002). By contrast, when we looked at day 8, when mature GC formation and rapid ASC proliferation is known to occur, we found that AIM2-KO immunized mice had significantly lower numbers of hapten-specific IgM (p=0.005) and IgG (p=0.004) ASCs in AIM2-expressing mice (Figure 1a). Our results suggest a role for AIM2 in regulating the survival of short-lived plasmablast-like ASCs after high affinity antigen encounter and maturation of germinal centers. To further investigate whether AIM2 affects expansion of GC-derived (GL7+CD95+) ASCs, we stimulated B cells purified from wildtype (WT) or global AIM2-deficient (AIM2-KO) mice in vitro with lipopolysaccharide (LPS) and IL-4 +/- BCR stimulation. We found that AIM2-deficient B cells, especially GC-like cell populations, expanded significantly in an anti-IgM concentration-dependent manner up to 12-fold (p=0.03) after 72 hr (Figure 1b). By contrast, B cell expansion was constrained in AIM2-sufficient B cells. This expansion was unlikely to be due to differences in proliferation alone, as we did not detect differential Ki67 expression in stimulated B cells with or without AIM2. Together, these data suggest a role for AIM2 in modulating BCR signaling. Finally, we examined the role of AIM2 in BCR-mediated cell death after chronic antigen exposure using our previously described bone marrow transplant (BMT) model, where recipients of bone marrow and splenocytes (BM+Spl) exhibit cGVHD manifestations ( Poe et al, JCI Insight 2018, Jia et al, Blood 2021). We have previously generated C57BL/6J mice with conditional deficiency of AIM2 only in B cells (AIM2 fl/flMb1 Cre/+, CKO), and used these in our BMT model as donors. At day 58 post BMT, we performed ex vivo stimulation of splenic B cells from BMT recipients. While B cells from CKO BM+Spl recipients expanded ex vivo in an anti-IgM concentration-dependent manner, B cells from AIM2-sufficient BM+Spl recipients demonstrated limited responsiveness ex vivo to BCR stimulation. This extends our in vitro observations by suggesting a role for AIM2 in B cell tolerance after chronic antigen exposure. Ongoing experiments will determine if B cell-intrinsic AIM2 contributes to cGVHD pathogenesis. Thus far, our data reveal a novel role for AIM2 as a B cell survival checkpoint after BCR activation. Further delineation of context-dependent and synergistic AIM2-BCR signaling after allo-HCT will lead to strategies that block the development of cGVHD without adversely affecting anti-tumor activity.

Overexpressed CD44 is associated with B-cell activation via the HA-CD44-AIM2 pathway in lupus B cells

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by aberrant development of B cells and excess production of autoantibodies. Our team previously reported that absent in melanoma 2 (AIM2) regulates B-cell differentiation via the Bcl-6-Blimp-1 axis. Notably, in keyhole limpet hemocyanin (KLH)-immunized CD19creAim2f/f mice, the frequency of CD19+CD44+ B cells was decreased, accompanied by a weakened KLH response, indicating that AIM2 deficiency suppressed the antigen-induced B-cell immune response by downregulating the expression of CD44. CD44, a surface marker of T-cell activation and memory, was overexpressed in T cells of SLE patients, but its roles and mechanism in B cells have not been elucidated. In the current work, we revealed that CD44 expression was upregulated in the B cells of SLE patients and MRL/lpr mice, accompanied by elevated AIM2 expression in CD19+CD44+ B-cell subsets, and that its ligand hyaluronan (HA) was also abnormally increased in the serum of SLE patients. Notably, the extrafollicular (EF) region serves as an important site of B-cell activation and differentiation separate from the germinal center, while CD44 expression is concentrated in EF B cells. In addition, in vitro experiments demonstrated that the HA-CD44 interaction stimulated B-cell activation and upregulated the expression of AIM2 and the transcription factor STAT3. Either blocking CD44, knocking down AIM2 expression or suppressing the activity of STAT3 in B cells suppressed B-cell activation and proliferation. Moreover, blocking CD44 downregulated the expression of STAT3 and AIM2, while suppressing the activity of STAT3 decreased the expression of CD44 and AIM2. In summary, overexpressed CD44 in B cells might participate in B-cell activation and proliferation in the EF region via the HA-CD44-AIM2 pathway, providing potential targets for SLE therapy.

Absent in melanoma 2 mediates aging-related cognitive dysfunction by acting on complement-dependent microglial phagocytosis.

Pattern separation (PS) dysfunction is a type of cognitive impairment that presents early during the aging process, and this deficit has been attributed to structural and functional alterations in the dentate gyrus (DG) of the hippocampus. Absent in melanoma 2 (AIM2) is an essential component of the inflammasome. However, whether AIM2 plays a role in aging-associated cognitive dysfunction remains unclear. Here, we found that PS function was impaired in aging mice and was accompanied by marked synaptic loss and increased expression of AIM2 in the DG. Subsequently, we used an AIM2 overexpression virus and mice with AIM2 deletion to investigate the role of AIM2 in regulating PS function and synaptic plasticity and the mechanisms involved. Our study revealed that AIM2 regulates microglial activation during synaptic pruning in the DG region via the complement pathway, leading to impaired synaptic plasticity and PS function in aging mice. These results suggest a critical role for AIM2 in regulating synaptic plasticity and PS function and provide a new direction for ameliorating aging-associated cognitive dysfunction.

The role of AIM2 in human hepatocellular carcinoma and its clinical significance.

AIM2 (absent in melanoma 2) was first discovered as the gene which was not expressed in melanoma cells. It is established that the AIM2 inflammasome function as the double-stranded DNA (dsDNA) sensor, and it plays a crucial role in infectious disorders and cancer. Little is known about the AIM2 expression pattern and its clinical significance in human hepatocellular carcinoma (HCC), understating how AIM2 altered the HCC cells is of high clinical interest. Immunohistochemistry was performed to investigate the AIM2 expression in HCC tissues. Then we constructed the ectopic AIM2-expressed HCC cell line by lentiviral transduction. Biological functional assays were used to analyze the clinical significance of AIM2. AIM2 expression was significantly decreased in human HCC tissues compared with adjacent normal tissues, and the overall survival of HCC patients with higher AIM2 expression was significantly better. Ectopic expression of AIM2 in HCC cells significantly inhibited migration and promoted apoptosis. Furthermore, our study revealed that the notch signaling pathway could be involved in the regulation of AIM2 in the cellular network in HCC cells. AIM2 delayed the tumor progression and correlated with immune cell infiltration. In this study, we suggested AIM2 played an inhibitory role in regulating the growth and metastasis of HCC, which supported the notion that AIM2 could serve as a potential therapeutic target for HCC.

Aim2 Deficiency Ameliorates Lacrimal Gland Destruction and Corneal Epithelium Defects in an Experimental Dry Eye Model.

Dry eye disease (DED) is a multifactorial disease that is associated with inflammation. Excessive DNA is present in the tear fluid of patients with DED. Absent in melanoma 2 (AIM2) is a key DNA sensor. This study aimed to investigate the role of AIM2 in the pathogenesis of DED. DED was induced by injection of scopolamine (SCOP). Aberrant DNA was detected by cell-free DNA (cfDNA) ELISA and immunostaining. Corneal epithelial defects were assessed by corneal fluorescein staining, zonula occludens-1 immunostaining and TUNEL. Tear production was analyzed by phenol red thread test. Lacrimal gland (LG) histology was evaluated by hematoxylin and eosin staining, and transmission electron microscopy examination. Macrophage infiltration in LG was detected by immunohistochemistry for the macrophage marker F4/80. Gene expression was analyzed by RT-qPCR. Protein production was examined by immunoblot analysis or ELISA. Aim2-/- mice displayed a normal structure and function of LG and cornea under normal conditions. In SCOP-induced DED, wild type (WT) mice showed increased cfDNA in tear fluid, and aberrant accumulations of dsDNA accompanied by increased AIM2 expression in the LG. In SCOP-induced DED, WT mice displayed damaged structures of LG, reduced tear production, and severe corneal epithelium defects, whereas Aim2-/- mice had a better preserved LG structure, less decreased tear production, and improved clinical signs of dry eye. Furthermore, genetic deletion of Aim2 suppressed the increased infiltration of macrophages and inhibited N-GSDMD and IL18 production in the LG of SCOP-induced DED. Aim2 deficiency alleviates ocular surface damage and LG inflammation in SCOP-induced DED.

Neutrophil extracellular traps promote keratinocyte inflammation via AIM2 inflammasome and AIM2-XIAP in psoriasis.

The infiltration of neutrophils in the epidermis and the release of neutrophil extracellular traps (NETs) are important events in the pathogenesis of psoriasis, but the regulatory roles and internal mechanism of NETs in psoriasis are largely unknown. Here, we demonstrate that NETs can activate the absent-in-melanoma-2 (AIM2) inflammasome in keratinocytes through the p38-MAPK signalling pathway, and targeting NETs with CI-amidine in vivo reduces AIM2 expression and ameliorates imiquimod-induced psoriasis-like phenotype in mice. Notably, NETs-activated AIM2 in keratinocytes not only promotes IL-1β production through the classical inflammasome pathway but also promotes IFN-γ production via X-linked inhibitor of apoptosis protein (XIAP), thereby mediating the immune responses of keratinocytes. In conclusion, our study demonstrates that the NETs-AIM2 axis exerts multiple pro-inflammatory effects on keratinocytes and may serve as a potential target for psoriasis therapy.

Pan-cancer analysis of AIM2 inflammasomes with potential implications for immunotherapy in human cancer: A bulk omics research and singlecell sequencing validation.

BackgroundThe absent in melanoma 2 (AIM2) inflammasome is a multi-protein platform that recognizes aberrant cytoplasmic double-stranded DNA(dsDNA) and induces cytokine maturation, release, and pyroptosis. Some studies found that the AIM2 inflammasome was a double-edged sword in many cancers. However, there have been fewer studies on AIM2 inflammasomes in pan-cancer.MethodsGene expression was analyzed using The Cancer Genome Atlas (TCGA) database and The Genotype-Tissue Expression (GTEx) database. Immunohistochemistry (IHC) was used to validate the expression of the AIM2. We used the survival curve to explore the prognostic significance of the AIM2 inflammasomes in pan-cancer. Mutations and methylation of AIM2 inflammasome-related genes (AIM2i-RGs) were also comprehensively analyzed. Single sample gene set enrichment analysis was used to calculate the AIM2 inflammasomes score and explore the correlation of the AIM2 inflammasomes score with immune-related genes and immune infiltrations. The function of AIM2 inflammasomes in pan-cancer was analyzed at the single-cell level. Single-cell transcriptome sequencing (scRNA-seq) data was used to assess the activation state of the AIM2 inflammasomes in the tumor microenvironment.ResultsWe found that AIM2i-RGs were aberrantly expressed in tumors and were strongly associated with prognosis. In pan-cancer, the expression of AIM2i-RGs was positively associated with copy number variation and negatively associated with methylation. In AIM2i-RGs, missense mutations were the predominant type of single nucleotide polymorphism. Moreover, we found that the drugs dimethyloxallyl glycine (DMOG) and Z-LNle-CHO may be sensitive to the AIM2 inflammasomes. The AIM2 inflammasomes score was significantly and positively correlated with the tumor immunity score and the stroma score. In most tumors, the AIM2 inflammasomes score was significantly and positively correlated with CD8+ T cell abundance in the tumor microenvironment. Additionally, the AIM2 inflammasomes score was significantly correlated with immune checkpoint genes in pan-cancer as well as immune checkpoint therapy-related markers including tumor mutational burden (TMB), microsatellite instability(MSI), and tumor immune dysfunction and exclusion(TIDE). scRNA-seq analysis suggested that AIM2 inflammasomes differ significantly among different cells in the tumor microenvironment. IHC confirmed low expression of AIM2 in colorectal cancer.DiscussionAIM2 inflammasomes may be a new target for future tumor therapy It is likely involved in tumor development, and its high expression may serve as a predictor of tumor immunotherapy efficacy.

Taohong siwu decoction attenuates AIM2 and NLRC4 inflammasomes by ameliorates deoxyribonucleic acid damage after ischemic stroke.

Taohong siwu decoction (THSWD) has been shown to have a therapeutic effect on ischemic strokes (IS). However, it is not clear to us whether THSWD reduces deoxyribonucleic acid (DNA) damage after stroke and reduces the inflammatory response caused by the damage. Therefore, we constructed an IS model (I/R) in rats and performed oxygen-glucose deprivation/reoxygenation (OGD/R) on BV2 cells. Then ELISA, immunofluorescence staining, immunohistochemistry staining, and RT-qPCR were performed to detect the expressions of absent in melanoma 2 (AIM2), NLRC4, and Caspase-1 inflammasomes and other inflammatory factors. Experimental stroke causes DNA damage, and we found that the aforementioned inflammasomes as well as inflammatory factors were significantly inhibited after treatment with THSWD by comparing the model group with the model administration group. In addition, we examined the expression of AIM2, NLRC4, and Caspase-1 in BV2 cells of OGD/R and found that the expression of the aforementioned inflammasomes was significantly decreased in OGD/R by administration of THSWD-containing serum. Our data suggest that THSWD can reduced DNA damage after stroke as well as the inflammatory response caused by the damage.

Abstract 302: Upregulation Of The Absent-in-melanoma 2 Inflammasome Correlates With Markers Of DNA Damage And Cell Cycle Dysregulation In Peripheral Arterial Disease

Introduction: We showed that myoblasts (Mb) in peripheral arterial disease (PAD) differentiate poorly and have evidence of inflammasome activation. Absent-in-melanoma 2 (AIM2), an inflammasome and mediator of pyroptosis, binds damaged DNA which also triggers the G2/M DNA damage checkpoint including CDC2 and its regulator, polo-like kinase 1 (PLK1). Dysregulated checkpoints can cause faulty replication, but a link between checkpoint function and AIM2 is not known. We hypothesize that AIM2 expression in PAD Mb correlates with increased DNA damage and a dysregulated G2/M DNA damage checkpoint. Methods: Cells were harvested from ischemic and perfused muscle obtained during amputations for PAD. Mb (Pax7-/MyoD+) were isolated using sequential plating and cell sorting. Mb from healthy donors (PAD -) were purchased (Cook MyoSite®). AIM2, γH2AX (DNA damage marker), PLK1 and CDC2 were measured with immunofluorescence (5 images/dish). Mb were treated with the PLK1-inhibitor BI2536 (10nM; 1h) to assess checkpoint responsiveness. ANOVA with post-hoc analysis confirmed statistical significance (α=0.05). Results: γH2AX expression was elevated in all PAD groups compared to PAD (-) Mb (N=3-4/PAD group). While PLK1 expression was similar across groups, CDC2 was lower in all ischemic PAD groups relative to perfused PAD Mb. BI2536 attenuated CDC2 expression in perfused PAD Mb (p = 0.006) while Mb in ischemic PAD remained unresponsive. AIM2 expression was significantly higher in ischemic Mb compared to perfused and PAD (-) Mb, correlating with high γH2AX and low CDC2. Results are summarized in Figure 1. Conclusion: Here, we show that in PAD Mb, AIM2 correlates with DNA damage, attenuated DNA damage checkpoint protein expression and diminished CDC2 responsiveness to BI2536. Thus, AIM2 may promote pyroptosis in the setting of defective DNA damage mechanisms that would otherwise prompt apoptosis. Whether these pathways are reversed by revascularization is a topic of further study.

AIM2 Inflammasome Activation Contributes to Aortic Dissection in a Sporadic Aortic Disease Mouse Model.

The absent in melanoma 2 (AIM2) inflammasome induces pyroptosis, tissue inflammation, and extracellular matrix destruction. We tested the hypothesis that the AIM2 inflammasome contributes to aortic aneurysm and dissection (AAD) development by promoting pyroptosis in smooth muscle cells (SMCs). We examined AIM2 expression in aortic tissues from patients with ascending thoracic aortic aneurysm (ATAA) and aortic dissection (ATAD) and from organ donor controls. AIM2's role in AAD development was evaluated in AIM2-deficient mice in a sporadic AAD model induced by challenging mice with a high-fat diet and angiotensin II infusion. The direct effects of dsDNA on SMC death in vitro were studied. Western blot analyses showed that AIM2 was increased in ATAD compared to ATAA and control tissue. Immunofluorescence demonstrated increased AIM2 in SMCs and macrophages in the aortic media and adventitia of dissected tissue. Increased AIM2 abundance was associated with increased cleavage of caspase-1 and cleavage of gasdermin-D, indicating activation of pyroptosis. In a mouse model of sporadic AAD induced by high-fat diet and angiotensin II infusion, AIM2-deficient mice showed significant reduction in aortic dissection, but not aneurysm formation in all aortic segments, versus wild-type mice. Finally, treating cultured human aortic SMCs with double-stranded DNA induced AIM2 expression, caspase-1 cleavage, and gasdermin-D cleavage; these effects were reduced by silencing AIM2 and caspase-1 genes, suggesting involvement of the AIM2 inflammasome in cytosolic DNA-induced activation of SMC pyroptosis. Activation of the AIM2 inflammasome cascade contributes to aortic degeneration and dissection, in part, by activating pyroptosis.

Skin CD4+ Trm cells distinguish acute cutaneous lupus erythematosus from localized discoid lupus erythematosus/subacute cutaneous lupus erythematosus and other skin diseases

BackgroundAlthough the contribution of aberrant CD4+ T cell signaling to systemic lupus erythematosus (SLE) is well established, its role in cutaneous lupus erythematosus (CLE) skin is largely unknown. Because the rate of systemic manifestations varies in each subtype, resident memory CD4+ T cells in lesions that are responsible for only skin-associated tissue responses may vary in each subtype. However, the role of CD4+ tissue-resident memory T (CD4+ Trm) cells in each CLE subtype remains unclear. ObjectivesTo analyze and compare CD4+ Trm cells and absent in melanoma 2 (AIM2) identified by smart RNA sequencing (Smart-seq) in CD4+ Trm cells from patients with acute CLE (ACLE), subacute CLE (SCLE), and localized discoid lupus erythematosus (localized DLE) lesions. MethodsWe performed Smart-seq to investigate differences in dermal CD4+ Trm cells between patients with ACLE and normal controls (NCs). Multicolor immunohistochemistry was utilized to measure the levels of AIM2 in CD4+ Trm cells present in the skin of 134 clinical patients, which included patients with localized DLE (n = 19), ACLE (n = 19), SCLE (n = 16), psoriasis (n = 12), rosacea (n = 17), lichen planus (n = 18), and annular granuloma (n = 15), as well as NCs (n = 18). ResultsThe Smart-seq data showed higher AIM2 expression in skin CD4+ Trm cells from ACLE lesions than NCs (fold change >10, adjusted P < 0.05). AIM2 expression in CD4+ Trm cells did not vary according to age or sex. AIM2 expression in CD4+ Trm cells was significantly lower in patients with ACLE (6.38 ± 5.22) than localized DLE (179.41 ± 160.98, P < 0.0001) and SCLE (63.43 ± 62.27, P < 0.05). In an overall comparison of ACLE with localized DLE and SCLE, the receiver operating characteristic curve for AIM2 expression in CD4+ Trm cells had a sensitivity of 100.00% and a specificity of 82.86% at a cutoff value of 18.26. In a comparison of ACLE with localized DLE, the sensitivity was 89.47%, and the specificity was 100.00% at a cutoff value of 12.26. In a comparison of ACLE with SCLE, the sensitivity was 100.00%, and the specificity was 75.00% at a cutoff value of 18.26. ConclusionsThe number of CD4+ Trm cells is increased in lesions of SCLE and localized DLE compared to ACLE, suggesting that CD4+ Trm cells may have a more crucial role in persistent lesions of SCLE and localized DLE. In addition, AIM2 expression in CD4+ Trm cells discriminates patients with ACLE from those with localized DLE and SCLE.

AIM2 inhibits the proliferation, invasion and migration, and promotes the apoptosis of osteosarcoma cells by inactivating the PI3K/AKT/mTOR signaling pathway.

Osteosarcoma is a primary bone tumor that mainly occurs in children and adolescents. Absent in melanoma 2 (AIM2) has been demonstrated to be involved in regulating the occurrence and development of cancer, exerting oncogenic and pro-cancer effects; however, its role in osteosarcoma is poorly understood. The present study aimed to explore the function and molecular mechanism of AIM2 in the progression of osteosarcoma. In the present study, AIM2 expression was predicted using the Cancer Cell Line Encyclopedia database and examined in several osteosarcoma cell lines using reverse transcription-quantitative PCR and western blotting. Following AIM2 overexpression, cell proliferation and apoptosis were examined using Cell Counting Kit-8, colony formation and TUNEL staining assays. The expression levels of proteins related to apoptosis, epithelial-mesenchymal transition (EMT) and the PI3K/AKT/mTOR signaling pathway were determined by western blotting. Additionally, cell invasion and migration were assessed using Transwell and wound healing assays. After addition of the PI3K/AKT/mTOR signaling pathway inhibitor LY294002 or activator 740Y-P, cell function analysis was performed. The results demonstrated that AIM2 was expressed at low levels in osteosarcoma cell lines. AIM2 overexpression inhibited proliferation, invasion, migration and EMT, and promoted apoptosis in osteosarcoma cells. Furthermore, the levels of phosphorylated (p)-PI3K, p-AKT and p-mTOR were markedly downregulated following AIM2 overexpression. Furthermore, LY294002 treatment had the same effects as AIM2 upregulation on osteosarcoma cell proliferation, apoptosis, invasion, migration and EMT. By contrast, 740Y-P reversed the effects of AIM2 overexpression on the behavior of osteosarcoma cells. Overall, the findings of the present study demonstrated that AIM2 may inhibit the progression of osteosarcoma by inactivating the PI3K/AKT/mTOR signaling pathway, and suggested that AIM2 may be a promising marker for the treatment of osteosarcoma.

Downregulating expression of OPTN elevates neuroinflammation via AIM2 inflammasome- and RIPK1-activating mechanisms in APP/PS1 transgenic mice

BackgroundNeuroinflammation is thought to be a cause of Alzheimer’s disease (AD), which is partly caused by inadequate mitophagy. As a receptor of mitophagy, we aimed to reveal the regulatory roles of optineurin (OPTN) on neuroinflammation in the pathogenesis of AD.MethodsBV2 cells and APP/PS1 transgenic (Tg) mice were used as in vitro and in vivo experimental models to determine the regulatory roles of OPTN in neuroinflammation of AD. Sophisticated molecular technologies including quantitative (q) RT-PCR, western blot, enzyme linked immunosorbent assay (ELISA), co-immunoprecipitation (Co-IP) and immunofluorescence (IF) were employed to reveal the inherent mechanisms.ResultsAs a consequence, key roles of OPTN in regulating neuroinflammation were identified by depressing the activity of absent in melanoma 2 (AIM2) inflammasomes and receptor interacting serine/threonine kinase 1 (RIPK1)-mediated NF-κB inflammatory mechanisms. In detail, we found that expression of OPTN was downregulated, which resulted in activation of AIM2 inflammasomes due to a deficiency in mitophagy in APP/PS1 Tg mice. By ectopic expression, OPTN blocks the effects of Aβ oligomer (Aβo) on activating AIM2 inflammasomes by inhibiting mRNA expression of AIM2 and apoptosis-associated speck-like protein containing a C-terminal caspase recruitment domain (ASC), leading to a reduction in the active form of caspase-1 and interleukin (IL)-1β in microglial cells. Moreover, RIPK1 was also found to be negatively regulated by OPTN via ubiquitin protease hydrolysis, resulting in the synthesis of IL-1β by activating the transcriptional activity of NF-κB in BV2 cells. As an E3 ligase, the UBAN domain of OPTN binds to the death domain (DD) of RIPK1 to facilitate its ubiquitination. Based on these observations, ectopically expressed OPTN in APP/PS1 Tg mice deactivated microglial cells and astrocytes via the AIM2 inflammasome and RIPK-dependent NF-κB pathways, leading to reduce neuroinflammation.ConclusionsThese results suggest that OPTN can alleviate neuroinflammation through AIM2 and RIPK1 pathways, suggesting that OPTN deficiency may be a potential factor leading to the occurrence of AD.

AIM2 Suppresses Inflammation and Epithelial Cell Proliferation during Glomerulonephritis.

Absent in melanoma-2 (AIM2) is an inflammasome-forming innate immune sensor for dsDNA but also exhibits inflammasome-independent functions such as restricting cellular proliferation. AIM2 is expressed in the kidney, but its localization and function are not fully characterized. In normal human glomeruli, AIM2 localized to podocytes. In patients with glomerulonephritis, AIM2 expression increased in CD44+-activated parietal epithelial cells within glomerular crescents. To explore AIM2 effects in glomerular disease, studies in Aim2 -/- mice were performed. Aim2-/- glomeruli showed reduced expression of Wilm tumor gene-1 (WT1), WT1-driven podocyte genes, and increased proliferation in outgrowth assays. In a nephrotoxic serum (NTS)-induced glomerulonephritis model, Aim2-/- (B6) mice exhibited more severe glomerular crescent formation, tubular injury, inflammation, and proteinuria compared with wild-type controls. Inflammasome activation markers were absent in both Aim2 -/- and wild-type kidneys, despite an increased inflammatory transcriptomic signature in Aim2 -/- mice. Aim2 -/- mice also demonstrated dysregulated cellular proliferation and an increase in CD44+ parietal epithelial cells during glomerulonephritis. The augmented inflammation and epithelial cell proliferation in Aim2 -/- (B6) mice was not due to genetic background, as Aim2 -/- (B6.129) mice demonstrated a similar phenotype during NTS glomerulonephritis. The AIM2-like receptor (ALR) locus was necessary for the inflammatory glomerulonephritis phenotype observed in Aim2 -/- mice, as NTS-treated ALR -/- mice displayed equal levels of injury as wild-type controls. Podocyte outgrowth from ALR -/- glomeruli was still increased, however, confirming that the ALR locus is dispensable for AIM2 effects on epithelial cell proliferation. These results identify a noncanonical role for AIM2 in suppressing inflammation and epithelial cell proliferation during glomerulonephritis.

AIM2 deficiency in B cells ameliorates systemic lupus erythematosus by regulating Blimp-1\u2013Bcl-6 axis-mediated B-cell differentiation

Absent in melanoma 2 (AIM2) has been reported to be a component of inflammasomes in innate immune cells. Surprisingly, AIM2 is expressed by B cells, and higher AIM2 expression is observed in the B cells from lupus patients. To date, the inflammasome-independent function of AIM2 in B cells remains unclear. Here, we report increased expression of AIM2 in human tonsil memory and germinal center (GC) B cells and in memory B cells and plasma cells from the circulation and skin lesions of lupus patients. Conditional knockout of AIM2 in B cells reduces the CD19+ B-cell frequency in lymph nodes and spleens, and dampens KLH-induced IgG1-antibody production. In a pristane-induced mouse model of lupus, AIM2 deficiency in B cells attenuates lupus symptoms and reduces the frequency of GC B cells, T follicular helper (Tfh) cells, plasmablast cells, and plasma cells. Furthermore, the loss of AIM2 in human B cells leads to the increased expression of Blimp-1 and reduces the expression of Bcl-6. However, the silencing of Blimp-1 and Bcl-6 has no significant effect on AIM2 expression, indicating that AIM2 might be the upstream regulator for Blimp-1 and Bcl-6. In addition, IL-10 is found to upregulate AIM2 expression via DNA demethylation. Together, our findings reveal that AIM2 is highly expressed in the B cells of lupus patients and promotes B-cell differentiation by modulating the Bcl-6–Blimp-1 axis, providing a novel target for SLE treatment.

STAT3-mediated upregulation of the AIM2 DNA sensor links innate immunity with cell migration to promote epithelial tumourigenesis

ObjectiveThe absent in melanoma 2 (AIM2) cytosolic pattern recognition receptor and DNA sensor promotes the pathogenesis of autoimmune and chronic inflammatory diseases via caspase-1-containing inflammasome complexes. However, the role of...

AIM2 regulates anti-tumor immunity and is a viable therapeutic target for melanoma.

The STING and absent in melanoma 2 (AIM2) pathways are activated by the presence of cytosolic DNA, and STING agonists enhance immunotherapeutic responses. Here, we show that dendritic cell (DC) expression of AIM2 within human melanoma correlates with poor prognosis and, in contrast to STING, AIM2 exerts an immunosuppressive effect within the melanoma microenvironment. Vaccination with AIM2-deficient DCs improves the efficacy of both adoptive T cell therapy and anti-PD-1 immunotherapy for "cold tumors," which exhibit poor therapeutic responses. This effect did not depend on prolonged survival of vaccinated DCs, but on tumor-derived DNA that activates STING-dependent type I IFN secretion and subsequent production of CXCL10 to recruit CD8+ T cells. Additionally, loss of AIM2-dependent IL-1β and IL-18 processing enhanced the treatment response further by limiting the recruitment of regulatory T cells. Finally, AIM2 siRNA-treated mouse DCs in vivo and human DCs in vitro enhanced similar anti-tumor immune responses. Thus, targeting AIM2 in tumor-infiltrating DCs is a promising new treatment strategy for melanoma.