Project description:Cellular senescence is triggered by various distinct stresses and characterized by a permanent cell cycle arrest. Senescent cells secrete a variety of inflammatory factors, collectively referred to as the senescence-associated secretory phenotype (SASP). The mechanism(s) underlying the regulation of the SASP remains incompletely understood. Here we define a role for innate DNA sensing in the regulation of senescence and the SASP. We find that cyclic GMP-AMP synthase (cGAS) recognizes cytosolic chromatin fragments (CCFs) in senescent cells. The activation of cGAS, in turn triggers the production of SASP factors via Stimulator of interferon genes (STING), thereby promoting paracrine senescence. We demonstrate that diverse stimuli of cellular senescence engage the cGAS-STING pathway in vitro and we show cGAS-dependent regulation of senescence upon irradiation and oncogene activation in vivo. Our findings provide insights into the mechanisms underlying cellular senescence by establishing the cGAS-STING pathway as a crucial regulator of senescence and the SASP.
Project description:Senescent endothelial cells accumulate in blood vessels during aging and produce the senescence-associated secretory phenotype (SASP). Age-related cardiovascular disease is promoted by SASP chronic inflammation. SASP establishment has been attributed to DNA damage and cGAS activation through cytoplasmic chromatin fragments. Therefore, DNA sensing has been extensively studied in cellular senescence; RNA sensing, on the other hand, remains unexplored. Here, we uncover a pivotal role for RNA accumulation and sensing in endothelial senescence. Our study suggests that intracellular RNA accumulation is a hallmark of senescent endothelial cells. This is associated with activation of RIG-I RNA sensing, and IRF7-driven IFN innate immune response. Moreover, our results revealed that inhibition of IRF7 or RIG-I were sufficient to extend the lifespan and functionality of endothelial cells. These data link the IFN gene signature with RNA accumulation/sensing in senescent endothelium and suggest IRF7 and RIG-I as potential therapeutic targets to delay vascular aging.
Project description:Sterile inflammation, also known as inflammaging, is a hallmark of tissue ageing. Cellular senescence contributes to tissue aging in part through secretion of proinflammatory factors known as senescence-associated secretory phenotype (SASP). Thioredoxin reductase 1 (TXNRD1) genetic variability is associated with aging and age-associated phenotypes such as late-life survival, activity of daily living, and physical performance at old age. TXNRD1 role in regulating tissue ageing has been attributed to its enzymatic role in regulating cellular redox. Here we show that TXNRD1 drives SASP and inflammaging through the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) innate immune response pathway independently of its enzymatic activity. TXNRD1 localizes to cytoplasmic chromatin fragment and interacts with cGAS in a senescence status dependent manner. TXNRD1 enhances the enzymatic activity of cGAS. TXNRD1 and its interaction with cGAS is necessary for the SASP. TXNRD1 is required for both the tumor-promoting and immune-surveillance functions of senescent cells, which are mediated by SASP in vivo in mouse models. Treatment of aged mice with an TXNRD1 inhibitor that disrupts its interaction with cGAS, but not an inhibitor of its enzymatic activity, downregulated inflammaging in several tissues. In summary, our results report TXNRD1 promotes inflammaging via the innate immune response. They indicate that TXNRD1 and cGAS interaction is a relevant target for selectively suppressing inflammaging.
Project description:Cytosolic DNA activates cyclic GMP-AMP (cGAMP) synthase (cGAS), an innate immune sensor pivotal in anti-microbial defense, senescence, auto-immunity and cancer. cGAS is considered a sequence-independent DNA sensor with limited access to nuclear DNA because of compartmentalization. However, the nuclear envelope is a dynamic barrier and cGAS is present in the nucleus. Here, we identify determinants of nuclear cGAS localization and activation. We show that nuclear-localized cGAS synthesizes cGAMP and induces innate immune activation of dendritic cells, but cGAMP levels are 200-fold lower than following transfection with exogenous DNA. Using cGAS ChIP-seq and a GFP-cGAS knock-in mouse, we find nuclear cGAS enrichment on centromeric satellite DNA, confirmed by imaging, and to a lesser extent with LINE elements. The non-enzymatic N-terminal domain of cGAS determines nucleo-cytoplasmic localization, enrichment on centromeres and activation of nuclear-localized cGAS. These results reveal a preferential functional association of nuclear cGAS with centromeres.
Project description:Cytosolic DNA activates cyclic GMP-AMP (cGAMP) synthase (cGAS), an innate immune sensor pivotal in anti-microbial defense, senescence, auto-immunity and cancer. cGAS is considered a sequence-independent DNA sensor with limited access to nuclear DNA because of compartmentalization. However, the nuclear envelope is a dynamic barrier and cGAS is present in the nucleus. Here, we identify determinants of nuclear cGAS localization and activation. We show that nuclear-localized cGAS synthesizes cGAMP and induces innate immune activation of dendritic cells, but cGAMP levels are 200-fold lower than following transfection with exogenous DNA. Using cGAS ChIP-seq and a GFP-cGAS knock-in mouse, we find nuclear cGAS enrichment on centromeric satellite DNA, confirmed by imaging, and to a lesser extent with LINE elements. The non-enzymatic N-terminal domain of cGAS determines nucleo-cytoplasmic localization, enrichment on centromeres and activation of nuclear-localized cGAS. These results reveal a preferential functional association of nuclear cGAS with centromeres.
Project description:Spontaneous control of HIV-1 replication in the absence of anti-retroviral therapy (ART) naturally occurs in a small proportion of HIV-1-infected individuals known as elite controllers (EC), likely as a result of improved innate and adaptive immune mechanisms. Previous studies suggest that enhanced cytosolic immune recognition of HIV-1 reverse transcripts in conventional dendritic cells (mDC) from EC enables effective induction of antiviral effector T cell responses. However, the specific molecular circuits responsible for such improved innate recognition of HIV-1 in mDC from these individuals remain unknown. Here, we identified a subpopulation of EC whose mDC displayed higher baseline abilities to respond to intracellular HIV-1 dsDNA stimulation. A computational analysis of transcriptional signatures from such high responder EC, combined with functional studies, suggested cytosolic recognition of HIV-1 dsDNA by cGAS, combined with sensing of viral mRNA by RIG-I after polymerase III-mediated HIV-1 DNA transcription. Together, our work identifies collaborative networks of innate sensing pathways that enhance cell-intrinsic abilities of mDC to induce antiviral innate responses against HIV-1; these observations might be useful for the therapeutic induction of effective antiviral immune responses.
Project description:Cellular innate immune sensors of DNA are essential for host defense against invading pathogens. However, the presence of self-derived DNA inside cells poses a biological risk of triggering an inappropriate immune response. The mechanisms limiting induction of inflammation by self nucleic acids are poorly understood. BLM RecQ like helicase is essential for the maintenance of genome integrity and deficient in Bloom syndrome, a rare genetic disease characterized by genome instability, susceptibility to cancer and immunodeficiency. Here, we show that BLM-deficient cells exhibit a constitutively upregulated inflammatory interferon-stimulated gene (ISG) signature. Restoring BLM expression reverts ISG expression to baseline. ISG expression in BLM-deficient fibroblasts is mediated by the cGAS-STING-IRF3 cytosolic DNA sensing pathway. Increased DNA damage or downregulation of the cytoplasmic exonuclease TREX1 enhances ISG expression in BS fibroblasts, and cytoplasmic micronuclei positive for cGAS are increased in BLM-deficient fibroblasts. Finally, BS patients demonstrate elevated ISG expression in peripheral blood. We conclude that BLM is essential to limit the expression of pro-inflammatory genes resulting from the sensing of DNA damage products by the cGAS-STING-IRF3 pathway. These results reveal an unexpected role for BLM in limiting ISG induction, thus connecting DNA damage to innate immunity, which may contribute to human pathogenesis.
Project description:Here we report that exogenous IL-1β induces TBK1-mediated interferon regulatory factor 3 (IRF3) activation and autophagic flux in human myeloid and epithelial cells. IL-1β-induced innate immune activation is dependent upon the DNA sensing pathway adaptor, stimulator of interferon genes (STING), through the recognition of mitochondrial DNA by cyclic GMP-AMP synthase (cGAS). Thus, IL-1β potentiates pathogen-induced interferon production and signal transducer and activator of transcription (STAT) signaling to amplify innate immune responses.
Project description:DNA derived from the genetic material of pathogens or from cellular DNA damage provides a molecular pattern that can be sensed by pattern-recognition receptors of the mammalian innate immune system. In recent years, the cyclic GMP-AMP synthase (cGAS) protein has been characterized as a primary cytosolic DNA sensor during infection with bacteria, DNA viruses, or retroviruses. While the role of cGAS in downstream immune signaling through STING-TBK1-IRF3 proteins is well-defined, regulatory mechanisms of cGAS activity, such as through post-translational modifications (PTMs), are still an active area of research. Here, we report a comprehensive characterization of cGAS phosphorylations and acetylations in three different cell types. Data-dependent proteomic analyses of immunoaffinity purified cGAS was performed in HEK293T cells under control and DNA-challenged conditions (N = 3 each) and human fibroblasts (HFF) cells under control and HSV-1 infected conditions (N = 4 each) to generate candidate cGAS PTM sites. Using parallel reaction monitoring, a total of 11 PTMs (4 phosphorylations and 7 acetylations) were validated in HEK293T, HFF, and THP-1 cells. Of these, 3 phosphorylations and 5 acetylations have not been previously identified. The functions of these modifications were by generating a series of mutants and measuring cGAS-dependent apoptotic and immune signaling activities.