cGAS is essential for cellular senescence. Proc Natl Acad Sci U S A. 2017;114:E4612-E4620. [PMID: 28533362 DOI: 10.1073/pnas.1705499114]

Inter-Organelle Membrane Contact Sites and Mitochondrial Quality Control during Aging: A Geroscience View

Mitochondrial dysfunction and failing mitochondrial quality control (MQC) are major determinants of aging. Far from being standalone organelles, mitochondria are intricately related with cellular other compartments, including lysosomes. The intimate relationship between mitochondria and lysosomes is reflected by the fact that lysosomal degradation of dysfunctional mitochondria is the final step of mitophagy. Inter-organelle membrane contact sites also allow bidirectional communication between mitochondria and lysosomes as part of nondegradative pathways. This interaction establishes a functional unit that regulates metabolic signaling, mitochondrial dynamics, and, hence, MQC. Contacts of mitochondria with the endoplasmic reticulum (ER) have also been described. ER-mitochondrial interactions are relevant to Ca²⁺ homeostasis, transfer of phospholipid precursors to mitochondria, and integration of apoptotic signaling. Many proteins involved in mitochondrial contact sites with other organelles also participate to degradative MQC pathways. Hence, a comprehensive assessment of mitochondrial dysfunction during aging requires a thorough evaluation of degradative and nondegradative inter-organelle pathways. Here, we present a geroscience overview on (1) degradative MQC pathways, (2) nondegradative processes involving inter-organelle tethering, (3) age-related changes in inter-organelle degradative and nondegradative pathways, and (4) relevance of MQC failure to inflammaging and age-related conditions, with a focus on Parkinson’s disease as a prototypical geroscience condition.

Ribosomal DNA instability: An evolutionary conserved fuel for inflammaging

Across eukaryotes, ribosomal DNA (rDNA) loci are characterized by intrinsic genomic instability due to their repetitive nature and their base composition that facilitate DNA double strand breaks and RNA:DNA hybrids formation. In the yeast, ribosomal DNA instability affects lifespan via the formation of extrachromosomal rDNA circles (ERC) that accrue into aged cells. In humans, rDNA instability has long been reported in a variety of progeric syndromes caused by the dysfunction of DNA helicases, but its role in physiological aging and longevity still needs to be clarified. Here we propose that rDNA instability leads to the activation of innate immunity and inflammation via the interaction with the cytoplasmic DNA sensing machinery. Owing to the recent clarified role of cytoplasmic DNA in the pro-inflammatory phenotype of senescent cells, we hypothesize that the accrual of rDNA derived molecules (i.e. ERC and RNA:DNA hybrids) may have a role in aging by contributing to inflammaging i.e. the systemic pro-inflammatory drift that associates with the onset of geriatric syndromes and age related dysfunctions in humans.

Senescence in the pathogenesis of age-related macular degeneration

Age-related macular degeneration (AMD) is a complex eye disease underlined by the death of photoreceptors and degeneration of retinal pigment epithelium (RPE) and choriocapillaris (CC). The mechanism(s) responsible for massive and progressive retinal degeneration is not completely known. Senescence, a state of permanent inhibition of cell growth, may be induced by many factors important for AMD pathogenesis and results in senescence-associated secretory phenotype (SASP) that releases growth factors, cytokines, chemokines, proteases and other molecules inducing inflammation and other AMD-related effects. These effects can be induced in the affected cell and neighboring cells, leading to progression of AMD phenotype. Senescent cells also release reactive oxygen species that increase SASP propagation. Many other pathways of senescence-related AMD pathogenesis, including autophagy, the cGAS-STING signaling, degeneration of CC by membrane attack complex, can be considered. A2E, a fluorophore present in lipofuscin, amyloid-beta peptide and humanin, a mitochondria-derived peptide, may link AMD with senescence. Further studies on senescence in AMD pathogenesis to check the possibility of opening a perspective of the use of drugs killing senescent cells (senolytics) and terminating SASP bystander effects (senostatics) might be beneficial for AMD that at present is an incurable disease.

Regulation of cGAS-Mediated Immune Responses and Immunotherapy

Early detection of infectious nucleic acids released from invading pathogens by the innate immune system is critical for immune defense. Detection of these nucleic acids by host immune sensors and regulation of DNA sensing pathways have been significant interests in the past years. Here, current understandings of evolutionarily conserved DNA sensing cyclic GMP-AMP (cGAMP) synthase (cGAS) are highlighted. Precise activation and tight regulation of cGAS are vital in appropriate innate immune responses, senescence, tumorigenesis and immunotherapy, and autoimmunity. Hence, substantial insights into cytosolic DNA sensing and immunotherapy of indispensable cytosolic sensors have been detailed to extend limited knowledge available thus far. This Review offers a critical, in-depth understanding of cGAS regulation, cytosolic DNA sensing, and currently established therapeutic approaches of essential cytosolic immune agents for improved human health.

Selective Loss of Responsiveness to Exogenous but Not Endogenous Cyclic-Dinucleotides in Mice Expressing STING-R231H

Stimulator of interferon genes (STING) plays a central role in innate immune responses to viral and intracellular bacterial infections, and cellular damage. STING is a cytosolic sensor of cyclic dinucleotides (CDNs) including those produced by pathogenic bacteria and those arising endogenously as products of the DNA sensor cGAS (e.g., 2′3′ cGAMP). The two most common alternative allelic variants of STING in humans are STING-R71H-G230A-R293Q (STING-HAQ) and STING-R232H that are found in 20.4% and 13.7–17.6% of the population, respectively. To determine the biologic consequences of these genotypic variations, we generated knock-in mice containing the murine equivalents of each variant and studied their responsiveness to CDNs. Homozygous STING-HAQ (R71H-I229A-R292Q) and STING-R231H mice were found to be unresponsive to all exogenous CDNs tested (ci-di-GMP, ci-di-AMP, 3′3′ cGAMP and Rp,Rp-CDA). Responses of homozygous STING-HAQ mice to endogenous 2′3′ cGAMP was also greatly impaired. However, homozygous STING-R231H mice are fully responsive to 2′3′ cGAMP. Analysis of heterozygous mice revealed reduced responsiveness to exogenous and endogenous CDNs in mice carrying a single copy of STING-HAQ, while STING-R231H heterozygous mice exhibit reduced responsiveness to exogenous but not endogenous CDNs. These findings confirm and extend previous reports by demonstrating differing impact of allelic variation of STING on the ability to sense and respond to exogenous vs. endogenous CDNs. Finally, the STING-R231H variant mouse represents a useful tool with which to examine the relative contributions of STING sensing of exogenous and endogenous CDNs in the context of bacterial infections and CDN-based cancer immunotherapeutics.

Topoisomerase 1 cleavage complex enables pattern recognition and inflammation during senescence

Cyclic cGMP-AMP synthase (cGAS) is a pattern recognition cytosolic DNA sensor that is essential for cellular senescence. cGAS promotes inflammatory senescence-associated secretory phenotype (SASP) through recognizing cytoplasmic chromatin during senescence. cGAS-mediated inflammation is essential for the antitumor effects of immune checkpoint blockade. However, the mechanism by which cGAS recognizes cytoplasmic chromatin is unknown. Here we show that topoisomerase 1-DNA covalent cleavage complex (TOP1cc) is both necessary and sufficient for cGAS-mediated cytoplasmic chromatin recognition and SASP during senescence. TOP1cc localizes to cytoplasmic chromatin and TOP1 interacts with cGAS to enhance the binding of cGAS to DNA. Retention of TOP1cc to cytoplasmic chromatin depends on its stabilization by the chromatin architecture protein HMGB2. Functionally, the HMGB2-TOP1cc-cGAS axis determines the response of orthotopically transplanted ex vivo therapy-induced senescent cells to immune checkpoint blockade in vivo. Together, these findings establish a HMGB2-TOP1cc-cGAS axis that enables cytoplasmic chromatin recognition and response to immune checkpoint blockade.

Here, the authors show that the topoisomerase 1-DNA covalent cleavage complex plays a critical role in mediating cytoplasmic chromatin fragments recognition by cyclic GMP-AMP synthase during senescence. The proposed axis is crucial to promote the inflammatory senescence-associated secretory phenotype and to enable the response to immune checkpoint blockade.

Autolysosomal degradation of cytosolic chromatin fragments antagonizes oxidative stress-induced senescence

Oxidative stress-induced DNA damage, the senescence-associated secretory phenotype (SASP), and impaired autophagy all are general features of senescent cells. However, the cross-talk among these events and processes is not fully understood. Here, using NIH3T3 cells exposed to hydrogen peroxide stress, we show that stress-induced DNA damage provokes the SASP largely via cytosolic chromatin fragment (CCF) formation, which activates a cascade comprising cGMP-AMP synthase (cGAS), stimulator of interferon genes protein (STING), NF-κB, and SASP, and that autolysosomal function inhibits this cascade. We found that CCFs accumulate in senescent cells with activated cGAS-STING-NF-κB signaling, promoting SASP and cellular senescence. We also present evidence that the persistent accumulation of CCFs in prematurely senescent cells is partially associated with a defect in DNA-degrading activity in autolysosomes and reduced abundance of activated DNase 2α. Intriguingly, we found that metformin- or rapamycin-induced activation of autophagy significantly lessened the size and levels of CCFs and repressed the activation of the cGAS-STING-NF-κB-SASP cascade and cellular senescence. These effects of autophagy activators indicated that autolysosomal function contributes to CCF clearance and SASP suppression, further supported by the fact that the lysosome inhibitor bafilomycin A1 blocked the role of autophagy-mediated CCF clearance and senescence repression.

Blockade of the Phagocytic Receptor MerTK on Tumor-Associated Macrophages Enhances P2X7R-Dependent STING Activation by Tumor-Derived cGAMP

Clearance of apoptotic cells by macrophages prevents excessive inflammation and supports immune tolerance. Here, we examined the effect of blocking apoptotic cell clearance on anti-tumor immune response. We generated an antibody that selectively inhibited efferocytosis by phagocytic receptor MerTK. Blockade of MerTK resulted in accumulation of apoptotic cells within tumors and triggered a type I interferon response. Treatment of tumor-bearing mice with anti-MerTK antibody stimulated T cell activation and synergized with anti-PD-1 or anti-PD-L1 therapy. The anti-tumor effect induced by anti-MerTK treatment was lost in Sting^gt/gt mice, but not in Cgas^-/- mice. Abolishing cGAMP production in Cgas^-/- tumor cells, depletion of extracellular ATP, or inactivation of the ATP-gated P2X7R channel also compromised the effects of MerTK blockade. Mechanistically, extracellular ATP acted via P2X7R to enhance the transport of extracellular cGAMP into macrophages and subsequent STING activation. Thus, MerTK blockade increases tumor immunogenicity and potentiates anti-tumor immunity, which has implications for cancer immunotherapy.

Extracellular cGAMP is a cancer cell-produced immunotransmitter involved in radiation-induced anti-cancer immunity

2'3'-cyclic GMP-AMP (cGAMP) is an intracellular second messenger that is synthesized in response to cytosolic double-stranded DNA and activates the innate immune STING pathway. Our previous discovery of its extracellular hydrolase ENPP1 hinted at the existence of extracellular cGAMP. Here, we detected that cGAMP is continuously exported but then efficiently cleared by ENPP1, explaining why it has previously escaped detection. By developing potent, specific, and cell impermeable ENPP1 inhibitors, we found that cancer cells continuously export cGAMP in culture at steady state and at higher levels when treated with ionizing radiation (IR). In mouse tumors, depletion of extracellular cGAMP decreased tumor-associated immune cell infiltration and abolished the curative effect of IR. Boosting extracellular cGAMP with ENPP1 inhibitors synergized with IR to delay tumor growth. In conclusion, extracellular cGAMP is an anti-cancer immunotransmitter that could be harnessed to treat cancers with low immunogenicity.

Mitochondria-to-nucleus retrograde signaling drives formation of cytoplasmic chromatin and inflammation in senescence

In this study, Vizioli et al. investigated the upstream signaling events that promote cytoplasmic formation of chromatin fragments (CCFs), which are extruded from the nucleus of senescent cells and trigger the senescence-associated secretory phenotype (SASP). They show that dysfunctional mitochondria, linked to down-regulation of nuclear-encoded mitochondrial oxidative phosphorylation genes, trigger a ROS–JNK retrograde signaling pathway that drives CCF formation and hence the SASP.

Cellular senescence is a potent tumor suppressor mechanism but also contributes to aging and aging-related diseases. Senescence is characterized by a stable cell cycle arrest and a complex proinflammatory secretome, termed the senescence-associated secretory phenotype (SASP). We recently discovered that cytoplasmic chromatin fragments (CCFs), extruded from the nucleus of senescent cells, trigger the SASP through activation of the innate immunity cytosolic DNA sensing cGAS–STING pathway. However, the upstream signaling events that instigate CCF formation remain unknown. Here, we show that dysfunctional mitochondria, linked to down-regulation of nuclear-encoded mitochondrial oxidative phosphorylation genes, trigger a ROS–JNK retrograde signaling pathway that drives CCF formation and hence the SASP. JNK links to 53BP1, a nuclear protein that negatively regulates DNA double-strand break (DSB) end resection and CCF formation. Importantly, we show that low-dose HDAC inhibitors restore expression of most nuclear-encoded mitochondrial oxidative phosphorylation genes, improve mitochondrial function, and suppress CCFs and the SASP in senescent cells. In mouse models, HDAC inhibitors also suppress oxidative stress, CCF, inflammation, and tissue damage caused by senescence-inducing irradiation and/or acetaminophen-induced mitochondria dysfunction. Overall, our findings outline an extended mitochondria-to-nucleus retrograde signaling pathway that initiates formation of CCF during senescence and is a potential target for drug-based interventions to inhibit the proaging SASP.

Transposable Elements Cross Kingdom Boundaries and Contribute to Inflammation and Ageing: Somatic Acquisition of Foreign Transposable Elements as a Catalyst of Genome Instability, Epigenetic Dysregulation, Inflammation, Senescence, and Ageing

The de-repression of transposable elements (TEs) in mammalian genomes is thought to contribute to genome instability, inflammation, and ageing, yet is viewed as a cell-autonomous event. In contrast to mammalian cells, prokaryotes constantly exchange genetic material through TEs, crossing both cell and species barriers, contributing to rapid microbial evolution and diversity in complex communities such as the mammalian gut. Here, it is proposed that TEs released from prokaryotes in the microbiome or from pathogenic infections regularly cross the kingdom barrier to the somatic cells of their eukaryotic hosts. It is proposed this horizontal transfer of TEs from microbe to host is a stochastic, ongoing catalyst of genome destabilization, resulting in structural and epigenetic variations, and activation of well-evolved host defense mechanisms contributing to inflammation, senescence, and biological ageing. It is proposed that innate immunity pathways defend against the horizontal acquisition of microbial TEs, and that activation of this pathway during horizontal transposon transfer promotes chronic inflammation during ageing. Finally, it is suggested that horizontal acquisition of prokaryotic TEs into mammalian genomes has been masked and subsequently under-reported due to flaws in current sequencing pipelines, and new strategies to uncover these events are proposed.

Blockade of Stat3 oncogene addiction induces cellular senescence and reveals a cell-nonautonomous activity suitable for cancer immunotherapy

Stat3 is constitutively activated in several tumor types and plays an essential role in maintaining their malignant phenotype and immunosupression. To take advantage of the promising antitumor activity of Stat3 targeting, it is vital to understand the mechanism by which Stat3 regulates both cell autonomous and non-autonomous processes. Here, we demonstrated that turning off Stat3 constitutive activation in different cancer cell types induces senescence, thus revealing their Stat3 addiction. Taking advantage of the senescence-associated secretory phenotype (SASP) induced by Stat3 silencing (SASP-siStat3), we designed an immunotherapy. The administration of SASP-siStat3 immunotherapy induced a strong inhibition of triple-negative breast cancer and melanoma growth associated with activation of CD4 + T and NK cells. Combining this immunotherapy with anti-PD-1 antibody resulted in survival improvement in mice bearing melanoma. The characterization of the SASP components revealed that type I IFN-related mediators, triggered by the activation of the cyclic GMP-AMP synthase DNA sensing pathway, are important for its immunosurveillance activity. Overall, our findings provided evidence that administration of SASP-siStat3 or low dose of Stat3-blocking agents would benefit patients with Stat3-addicted tumors to unleash an antitumor immune response and to improve the effectiveness of immune checkpoint inhibitors.

Elucidating Proteoform Dynamics Underlying the Senescence Associated Secretory Phenotype

Primary diploid cells exit the cell cycle in response to exogenous stress or oncogene activation through a process known as cellular senescence. This cell-autonomous tumor-suppressive mechanism is also a major mechanism operative in organismal aging. To date, temporal aspects of senescence remain understudied. Therefore, we use quantitative proteomics to investigate changes following forced HRAS^G12V expression and induction of senescence across 1 week in normal diploid fibroblasts. We demonstrate that global intracellular proteomic changes correlate with the emergence of the senescence-associated secretory phenotype and the switch to robust cell cycle exit. The senescence secretome reinforces cell cycle exit, yet is largely detrimental to tissue homeostasis. Previous studies of secretomes rely on ELISA, bottom-up proteomics or RNA-seq. To date, no study to date has examined the proteoform complexity of secretomes to elucidate isoform-specific, post-translational modifications or regulated cleavage of signal peptides. Therefore, we use a quantitative top-down proteomics approach to define the molecular complexity of secreted proteins <30 kDa. We identify multiple forms of immune regulators with known activities and affinities such as distinct forms of interleukin-8, as well as GROα and HMGA1, and temporally resolve secreted proteoform dynamics. Together, our work demonstrates the complexity of the secretome past individual protein accessions and provides motivation for further proteoform-resolved measurements of the secretome.

Nucleic Acid Sensors and Programmed Cell Death

Nucleic acids derived from microorganisms are powerful triggers for innate immune responses. Proteins called RNA and DNA sensors detect foreign nucleic acids and, in mammalian cells, include RIG-I, cGAS, and AIM2. On binding to nucleic acids, these proteins initiate signaling cascades that activate host defense responses. An important aspect of this defense program is the production of cytokines such as type I interferons and IL-1β. Studies conducted over recent years have revealed that nucleic acid sensors also activate programmed cell death pathways as an innate immune response to infection. Indeed, RNA and DNA sensors induce apoptosis, pyroptosis, and necroptosis. Cell death via these pathways prevents replication of pathogens by eliminating the infected cell and additionally contributes to the release of cytokines and inflammatory mediators. Interestingly, recent evidence suggests that programmed cell death triggered by nucleic acid sensors plays an important role in a number of noninfectious pathologies. In addition to nonself DNA and RNA from microorganisms, nucleic acid sensors also recognize endogenous nucleic acids, for example when cells are damaged by genotoxic agents and in certain autoinflammatory diseases. This review article summarizes current knowledge on the links between nucleic acid sensing and cell death and explores important open questions for future studies in this area.

Radiosurgery and Immunotherapy in the Treatment of Brain Metastases

Radiation therapy represents a mainstay of treatment for patients with brain metastases. Recently, the widespread adoption of immune checkpoint blockade has led to keen interest in treating cancers with checkpoint inhibitors in place of, or as an adjunct to, traditional chemotherapy. However, with the exception of melanoma, immune checkpoint blockade in solid tumors has failed to achieve significant brain control in patients with brain metastases. The possibility of combining immune checkpoint blockade with radiation for the treatment of brain and other metastases represents an exciting new strategy that is in its early stages of investigation. Success with this combinatorial strategy has the potential to result in enhanced rates of brain control, less brain exposure to radiation, and improved cognitive outcomes. In this review, we discuss the mechanisms behind this synergy, describe its limitations, and suggest ways to move the field forward.

Cyclic GMP-AMP synthase is essential for cytosolic double-stranded DNA and fowl adenovirus serotype 4 triggered innate immune responses in chickens

Cyclic GMP-AMP (cGAMP) synthase (cGAS) is a predominant DNA sensor inducing the activation of the innate immune responses that produce proinflammatory cytokines and type I interferons, which has been well-investigated in mammals. However, chicken cGAS (chcGAS), which participates in avian innate immunity, has not been well-investigated. Here, we cloned the complete open reading frame sequence of chcGAS. Multiple sequence alignment and phylogenetic analysis revealed that chcGAS was homologous to mammalian cGAS. The chcGAS mRNA was highly expressed in the bone marrow and ileum. The subcellular localization of chcGAS was mainly in the cytoplasm, and partial co-localization was observed in the endoplasmic reticulum. Through overexpression and RNA interference, we demonstrated that chcGAS responded to exogenous dsDNA, HS-DNA, and poly(dA:dT), and to self dsDNA from the DNA damage response, thereby triggering the activation of STING/TBK1/IRF7-mediated innate immunity in both chicken embryonic fibroblasts and chicken liver cancer cells. Furthermore, downregulation of chcGAS enhanced the infection of fowl adenovirus serotype 4 in LMH cells. Our results demonstrated that chcGAS was an important cytosolic DNA sensor activating innate immune responses and may shed light on a strategy for preventing infectious diseases in the poultry industry.

Regulation of cGAS- and RLR-mediated immunity to nucleic acids

Pathogen-derived nucleic acids are crucial signals for innate immunity. Despite the structural similarity between those and host nucleic acids, mammalian cells have been able to evolve powerful innate immune signaling pathways that originate from the detection of cytosolic nucleic acid species, one of the most prominent being the cGAS-STING pathway for DNA and the RLR-MAVS pathway for RNA, respectively. Recent advances have revealed a plethora of regulatory mechanisms that are crucial for balancing the activity of nucleic acid sensors for the maintenance of overall cellular homeostasis. Elucidation of the various mechanisms that enable cells to maintain control over the activity of cytosolic nucleic acid sensors has provided new insight into the pathology of human diseases and, at the same time, offers a rich and largely unexplored source for new therapeutic targets. This Review addresses the emerging literature on regulation of the sensing of cytosolic DNA and RNA via cGAS and RLRs.

The Role of Senescence in the Development of Nonalcoholic Fatty Liver Disease and Progression to Nonalcoholic Steatohepatitis

In recent years, cellular senescence has generated a lot of interest among researchers because of its involvement in both the normal aging process and common human diseases. During senescence, cells undergo alterations that include telomere shortening, nuclear area enlargement, and genomic and mitochondrial DNA damage, leading to irreversible cell cycle arrest, and secretion of proinflammatory cytokines. Evidence suggests that the complex process of senescence is involved in the development of a plethora of chronic diseases including metabolic and inflammatory disorders and tumorigenesis. Recently, several human and animal studies have emphasized the involvement of senescence in the pathogenesis and development of liver steatosis including the progression to nonalcoholic steatohepatitis (NASH) as characterized by the additional emergence of inflammation, hepatocyte ballooning, and liver fibrosis. The development of nonalcoholic fatty liver disease (NAFLD) and its progression to NASH are commonly accompanied by several pathophysiological events including metabolic dysregulation and inflammatory phenomena occurring within the liver that may contribute to or derive from cellular senescence, implying that the latter may be both a stimulus and a consequence of the disease. Conclusion: In this review, we summarize the current literature on the impact of cellular senescence in NAFLD/NASH and discuss the effectiveness and safety of novel senolytic drugs and therapeutic options available to delay or treat the disease. Finally, we identify the open questions and issues to be addressed in the near future.

Senolytics and Senostatics: A Two-Pronged Approach to Target Cellular Senescence for Delaying Aging and Age-Related Diseases

Aging is the most important single risk factor for many chronic diseases such as cancer, metabolic syndrome, and neurodegenerative disorders. Targeting aging itself might, therefore, be a better strategy than targeting each chronic disease individually for enhancing human health. Although much should be achieved for completely understanding the biological basis of aging, cellular senescence is now believed to mainly contribute to organismal aging via two independent, yet not mutually exclusive mechanisms: on the one hand, senescence of stem cells leads to exhaustion of stem cells and thus decreases tissue regeneration. On the other hand, senescent cells secrete many proinflammatory cytokines, chemokines, growth factors, and proteases, collectively termed as the senescence-associated secretory phenotype (SASP), which causes chronic inflammation and tissue dysfunction. Much effort has been recently made to therapeutically target detrimental effects of cellular senescence including selectively eliminating senescent cells (senolytics) and modulating a proinflammatory senescent secretome (senostatics). Here, we discuss current progress and limitations in understanding molecular mechanisms of senolytics and senostatics and therapeutic strategies for applying them. Furthermore, we propose how these novel interventions for aging treatment could be improved, based on lessons learned from cancer treatment.

Autophagy, Cellular Aging and Age-related Human Diseases

Macroautophagy/autophagy is a conserved degradation system that engulfs intracytoplasmic contents, including aggregated proteins and organelles, which is crucial for cellular homeostasis. During aging, cellular factors suggested as the cause of aging have been reported to be associated with progressively compromised autophagy. Dysfunctional autophagy may contribute to age-related diseases, such as neurodegenerative disease, cancer, and metabolic syndrome, in the elderly. Therefore, restoration of impaired autophagy to normal may help to prevent age-related disease and extend lifespan and longevity. Therefore, this review aims to provide an overview of the mechanisms of autophagy underlying cellular aging and the consequent disease. Understanding the mechanisms of autophagy may provide potential information to aid therapeutic interventions in age-related diseases.

Cellular senescence and senescence-associated secretory phenotype via the cGAS-STING signaling pathway in cancer

Cellular senescence is historically regarded as a tumor suppression mechanism to prevent damaged cells from aberrant proliferation in benign and premalignant tumors. However, recent findings have suggested that senescent cells contribute to tumorigenesis and age‐associated pathologies through the senescence‐associated secretory phenotype (SASP). Therefore, to control age‐associated cancer, it is important to understand the molecular mechanisms of the SASP in the cancer microenvironment. New findings have suggested that the cyclic GMP‐AMP synthase (cGAS)‐stimulator of interferon genes (STING) signaling pathway, a critical indicator of innate immune response, triggers the SASP in response to accumulation of cytoplasmic DNA (cytoplasmic chromatin fragments, mtDNA and cDNA) in senescent cells. Notably, the cGAS‐STING signaling pathway promotes or inhibits tumorigenesis depending on the biological context in vivo, indicating that it may be a potential therapeutic target for cancer. Herein, we review the regulatory machinery and biological function of the SASP via the cGAS‐STING signaling pathway in cancer.

Epistatic effect of TLR3 and cGAS-STING-IKKε-TBK1-IFN signaling variants on colorectal cancer risk

Objective

The TLR3/cGAS‐STING‐IFN signaling has recently been reported to be disturbed in colorectal cancer due to deregulated expression of the genes involved. Our study aimed to investigate the influence of potential regulatory variants in these genes on the risk of sporadic colorectal cancer (CRC) in a Czech cohort of 1424 CRC patients and 1114 healthy controls.

Methods

The variants in the TLR3, CGAS, TMEM173, IKBKE, and TBK1 genes were selected using various online bioinformatic tools, such as UCSC browser, HaploReg, Regulome DB, Gtex Portal, SIFT, PolyPhen2, and miRNA prediction tools.

Results

Logistic regression analysis adjusted for age and sex detected a nominal association between CRC risk and three variants, CGAS rs72960018 (OR: 1.68, 95% CI: 1.11‐2.53, P‐value = .01), CGAS rs9352000 (OR: 2.02, 95% CI: 1.07‐3.84, P‐value = .03) and TMEM173 rs13153461 (OR: 1.53, 95% CI: 1.03‐2.27, P‐value = .03). Their cumulative effect revealed a threefold increased CRC risk in carriers of 5‐6 risk alleles compared to those with 0‐2 risk alleles. Epistatic interactions between these genes and the previously genotyped IFNAR1, IFNAR2, IFNA, IFNB, IFNK, IFNW, IRF3, and IRF7 genes, were computed to test their effect on CRC risk. Overall, we obtained nine pair‐wise interactions within and between the CGAS, TMEM173, IKBKE, and TBK1 genes. Two of them remained statistically significant after Bonferroni correction. Additional 52 interactions were observed when IFN variants were added to the analysis.

Conclusions

Our data suggest that epistatic interactions and a high number of risk alleles may play an important role in CRC carcinogenesis, offering novel biological understanding for the CRC management.

The Cytosolic DNA-Sensing cGAS-STING Pathway in Cancer

The recognition of DNA as an immune-stimulatory molecule is an evolutionarily conserved mechanism to initiate rapid innate immune responses against microbial pathogens. The cGAS-STING pathway was discovered as an important DNA-sensing machinery in innate immunity and viral defense. Recent advances have now expanded the roles of cGAS-STING to cancer. Highly aggressive, unstable tumors have evolved to co-opt this program to drive tumorigenic behaviors. In this review, we discuss the link between the cGAS-STING DNA-sensing pathway and antitumor immunity as well as cancer progression, genomic instability, the tumor microenvironment, and pharmacologic strategies for cancer therapy. SIGNIFICANCE: The cGAS-STING pathway is an evolutionarily conserved defense mechanism against viral infections. Given its role in activating immune surveillance, it has been assumed that this pathway primarily functions as a tumor suppressor. Yet, mounting evidence now suggests that depending on the context, cGAS-STING signaling can also have tumor and metastasis-promoting functions, and its chronic activation can paradoxically induce an immune-suppressive tumor microenvironment.

Ribosome biogenesis restricts innate immune responses to virus infection and DNA

Ribosomes are universally important in biology and their production is dysregulated by developmental disorders, cancer, and virus infection. Although presumed required for protein synthesis, how ribosome biogenesis impacts virus reproduction and cell-intrinsic immune responses remains untested. Surprisingly, we find that restricting ribosome biogenesis stimulated human cytomegalovirus (HCMV) replication without suppressing translation. Interfering with ribosomal RNA (rRNA) accumulation triggered nucleolar stress and repressed expression of 1392 genes, including High Mobility Group Box 2 (HMGB2), a chromatin-associated protein that facilitates cytoplasmic double-stranded (ds) DNA-sensing by cGAS. Furthermore, it reduced cytoplasmic HMGB2 abundance and impaired induction of interferon beta (IFNB1) mRNA, which encodes a critical anti-proliferative, proinflammatory cytokine, in response to HCMV or dsDNA in uninfected cells. This establishes that rRNA accumulation regulates innate immune responses to dsDNA by controlling HMGB2 abundance. Moreover, it reveals that rRNA accumulation and/or nucleolar activity unexpectedly regulate dsDNA-sensing to restrict virus reproduction and regulate inflammation. (145 words)

Tight nuclear tethering of cGAS is essential for preventing autoreactivity

cGAS is an intracellular innate immune sensor that detects double-stranded DNA. The presence of billions of base pairs of genomic DNA in all nucleated cells raises the question of how cGAS is not constitutively activated. A widely accepted explanation for this is the sequestration of cGAS in the cytosol, which is thought to prevent cGAS from accessing nuclear DNA. Here, we demonstrate that endogenous cGAS is predominantly a nuclear protein, regardless of cell cycle phase or cGAS activation status. We show that nuclear cGAS is tethered tightly by a salt-resistant interaction. This tight tethering is independent of the domains required for cGAS activation, and it requires intact nuclear chromatin. We identify the evolutionarily conserved tethering surface on cGAS and we show that mutation of single amino acids within this surface renders cGAS massively and constitutively active against self-DNA. Thus, tight nuclear tethering maintains the resting state of cGAS and prevents autoreactivity.

Innate Immune Response to Cytoplasmic DNA: Mechanisms and Diseases

DNA has been known to be a potent immune stimulus for more than half a century. However, the underlying molecular mechanisms of DNA-triggered immune response have remained elusive until recent years. Cyclic GMP-AMP synthase (cGAS) is a major cytoplasmic DNA sensor in various types of cells that detect either invaded foreign DNA or aberrantly located self-DNA. Upon sensing of DNA, cGAS catalyzes the formation of cyclic GMP-AMP (cGAMP), which in turn activates the ER-localized adaptor protein MITA (also named STING) to elicit the innate immune response. The cGAS-MITA axis not only plays a central role in host defense against pathogen-derived DNA but also acts as a cellular stress response pathway by sensing aberrantly located self-DNA, which is linked to the pathogenesis of various human diseases. In this review, we summarize the spatial and temporal mechanisms of host defense to cytoplasmic DNA mediated by the cGAS-MITA axis and discuss the association of malfunctions of this axis with autoimmune and other diseases.

Targeting senescent cells in translational medicine

Organismal ageing is a complex process driving progressive impairment of functionality and regenerative potential of tissues. Cellular senescence is a state of stable cell cycle arrest occurring in response to damage and stress and is considered a hallmark of ageing. Senescent cells accumulate in multiple organs during ageing, contribute to tissue dysfunction and give rise to pathological manifestations. Senescence is therefore a defining feature of a variety of human age-related disorders, including cancer, and targeted elimination of these cells has recently emerged as a promising therapeutic approach to ameliorate tissue damage and promote repair and regeneration. In addition, in vivo identification of senescent cells has significant potential for early diagnosis of multiple pathologies. Here, we review existing senolytics, small molecules and drug delivery tools used in preclinical therapeutic strategies involving cellular senescence, as well as probes to trace senescent cells. We also review the clinical research landscape in senescence and discuss how identifying and targeting cellular senescence might positively affect pathological and ageing processes.

Interrupting cyclic dinucleotide-cGAS-STING axis with small molecules

The cyclic dinucleotide-cGAS-STING axis plays important roles in host immunity. Activation of this signaling pathway, via cytosolic sensing of bacterial-derived c-di-GMP/c-di-AMP or host-derived cGAMP, leads to the production of inflammatory interferons and cytokines that help resolve infection. Small molecule activators of the cGAS-STING axis have the potential to augment immune response against various pathogens or cancer. The aberrant activation of this pathway, due to gain-of-function mutations in any of the proteins that are part of the signaling axis, could lead to various autoimmune diseases. Inhibiting various nodes of the cGAS-STING axis could provide relief to patients with autoimmune diseases. Many excellent reviews on the cGAS-STING axis have been published recently, and these have mainly focused on the molecular details of the cGAS-STING pathway. This review however focuses on small molecules that can be used to modulate various aspects of the cGAS-STING pathway, as well as other parallel inflammatory pathways.

Barley-ß-glucans reduce systemic inflammation, renal injury and aortic calcification through ADAM17 and neutral-sphingomyelinase2 inhibition

In chronic kidney disease (CKD), hyperphosphatemia-induced inflammation aggravates vascular calcification (VC) by increasing vascular smooth muscle cell (VSMC) osteogenic differentiation, ADAM17-induced renal and vascular injury, and TNFα-induction of neutral-sphingomyelinase2 (nSMase2) to release pro-calcifying exosomes. This study examined anti-inflammatory β-glucans efficacy at attenuating systemic inflammation in health, and renal and vascular injury favoring VC in hyperphosphatemic CKD. In healthy adults, dietary barley β-glucans (Bβglucans) reduced leukocyte superoxide production, inflammatory ADAM17, TNFα, nSMase2, and pro-aging/pro-inflammatory STING (Stimulator of interferon genes) gene expression without decreasing circulating inflammatory cytokines, except for γ-interferon. In hyperphosphatemic rat CKD, dietary Bβglucans reduced renal and aortic ADAM17-driven inflammation attenuating CKD-progression (higher GFR and lower serum creatinine, proteinuria, kidney inflammatory infiltration and nSMase2), and TNFα-driven increases in aortic nSMase2 and calcium deposition without improving mineral homeostasis. In VSMC, Bβglucans prevented LPS- or uremic serum-induced rapid increases in ADAM17, TNFα and nSMase2, and reduced the 13-fold higher calcium deposition induced by prolonged calcifying conditions by inhibiting osteogenic differentiation and increases in nSMase2 through Dectin1-independent actions involving Bβglucans internalization. Thus, dietary Bβglucans inhibit leukocyte superoxide production and leukocyte, renal and aortic ADAM17- and nSMase2 gene expression attenuating systemic inflammation in health, and renal injury and aortic calcification despite hyperphosphatemia in CKD.

Bioactive modulators targeting STING adaptor in cGAS-STING pathway

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING)-pathway triggers innate immune responses by recognizing cytosolic DNA. Recent studies revealed that STING adaptor associates with various diseases, and several modulators targeting STING have been identified including three agonists that have entered clinical trials for treating cancer over the past 2 years. In particular, the efficacy of STING agonists and/or antagonists suggests adaptor STING as a potential therapeutic target for diverse diseases. Herein, we summarize the latest advances in understanding STING functioning and provide an overview of recent STING modulator discoveries, including structural details and the potential therapeutic applications of these modulators.

PROPERTIES AND FUNCTIONS OF THE NOVEL TYPE I INTERFERON EPSILON

Interferon epsilon (IFNε) is a type I IFN with unusual patterns of expression and therefore, function. It is constitutively expressed by reproductive tract epithelium and regulated by hormones during estrus cycle, reproduction, and menopause and by exogenous hormones. The IFNe protein is encoded by a gene in the type I IFN locus, binds to IFNAR1 and 2 which are required for signaling via the JAK STAT pathway. Its affinity for binding receptors and transducing signals is less potent than IFNα or β subtypes in vitro. Nevertheless, in vivo experiments indicate its efficacy in regulating mucosal immune responses and protecting from bacterial and viral infections. These studies demonstrate a different mechanism of action to type I IFNs. In this organ system with dynamic fluxes in cellularity, requirement to tolerate an implanted fetus, and be protected from disease, there is co-option of a special IFN from a family of effective immunoregulators, with unique controls and modified potency to make it a safe and effective constitutive reproductive tract cytokine.

The triggers of the cGAS-STING pathway and the connection with inflammatory and autoimmune diseases

Cyclic GMP-AMP synthase (cGAS) is a cytosolic nucleic acid sensor that can bind to dsDNA. It maintains an autoinhibited state in the absence of cytosolic dsDNA, while when activated, it in turn activates its adaptor protein STING, ultimately triggering a cascade that produces inflammatory cytokines and type I interferons (IFNs). With further research, additional types of nucleic acids have been found to be activators of the cGAS-STING pathway. The cGAS-STING pathway can provide protection or resistance against infections; however, improper or overactivation might cause severe inflammatory pathologies, including autoimmunity. This article systematically reviews the latest research progress on the axis, including categorical pathway triggers, the connection with autoimmune disease and drug therapy progress.

Myeloid immunosuppression and immune checkpoints in the tumor microenvironment

Tumor-promoting inflammation and the avoidance of immune destruction are hallmarks of cancer. While innate immune cells, such as neutrophils, monocytes, and macrophages, are critical mediators for sterile and nonsterile inflammation, persistent inflammation, such as that which occurs in cancer, is known to disturb normal myelopoiesis. This disturbance leads to the generation of immunosuppressive myeloid cells, such as myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs). Due to their potent suppressive activities against effector lymphocytes and their abundance in the tumor microenvironment, immunosuppressive myeloid cells act as a major barrier to cancer immunotherapy. Indeed, various therapeutic approaches directed toward immunosuppressive myeloid cells are actively being tested in preclinical and clinical studies. These include anti-inflammatory agents, therapeutic blockade of the mobilization and survival of myeloid cells, and immunostimulatory adjuvants. More recently, immune checkpoint molecules expressed on tumor-infiltrating myeloid cells have emerged as potential therapeutic targets to redirect these cells to eliminate tumor cells. In this review, we discuss the complex crosstalk between cancer-related inflammation and immunosuppressive myeloid cells and possible therapeutic strategies to harness antitumor immune responses.

Putting the brakes on the cell cycle: mechanisms of cellular growth arrest

Precise regulation of cellular proliferation is critical to tissue homeostasis and development, but misregulation leads to diseases of excess proliferation or cell loss. To achieve precise control, cells utilize distinct mechanisms of growth arrest such as quiescence and senescence. The decision to enter these growth-arrested states or proliferate is mediated by the core cell-cycle machinery that responds to diverse external and internal signals. Recent advances have revealed the molecular underpinnings of these cell-cycle decisions, highlighting the unique nature of cell-cycle entry from quiescence, identifying endogenous DNA damage as a quiescence-inducing signal, and establishing how persistent arrest is achieved in senescence.

Cellular senescence in development, regeneration and disease

Cellular senescence is a state comprising an essentially irreversible proliferative arrest combined with phenotypic changes and pronounced secretory activity. Although senescence has long been linked with aging, recent studies have uncovered functional roles for senescence in embryonic development, regeneration and reprogramming, and have helped to advance our understanding of this process as a highly coordinated and programmed cellular state. In this Primer article, we summarize some of the key findings in the field and attempt to explain them in a simple model that reconciles the normal and pathological roles for senescence. We discuss how a primary role of cellular senescence is to contribute to normal development, cell plasticity and tissue repair, as a dynamic and tightly regulated cellular program. However, when this process is perturbed, the beneficial effects turn detrimental and can contribute to disease and aging.

DAMP-sensing receptors in sterile inflammation and inflammatory diseases

The innate immune system has the capacity to detect 'non-self' molecules derived from pathogens, known as pathogen-associated molecular patterns, via pattern recognition receptors. In addition, an increasing number of endogenous host-derived molecules, termed damage-associated molecular patterns (DAMPs), have been found to be sensed by various innate immune receptors. The recognition of DAMPs, which are produced or released by damaged and dying cells, promotes sterile inflammation, which is important for tissue repair and regeneration, but can also lead to the development of numerous inflammatory diseases, such as metabolic disorders, neurodegenerative diseases, autoimmune diseases and cancer. Here we examine recent discoveries concerning the roles of DAMP-sensing receptors in sterile inflammation and in diseases resulting from dysregulated sterile inflammation, and then discuss insights into the cross-regulation of these receptors and their ligands.

Chromatin-bound cGAS is an inhibitor of DNA repair and hence accelerates genome destabilization and cell death

DNA repair via homologous recombination (HR) is indispensable for genome integrity and cell survival but if unrestrained can result in undesired chromosomal rearrangements. The regulatory mechanisms of HR are not fully understood. Cyclic GMP-AMP synthase (cGAS) is best known as a cytosolic innate immune sensor critical for the outcome of infections, inflammatory diseases, and cancer. Here, we report that cGAS is primarily a chromatin-bound protein that inhibits DNA repair by HR, thereby accelerating genome destabilization, micronucleus generation, and cell death under conditions of genomic stress. This function is independent of the canonical STING-dependent innate immune activation and is physiologically relevant for irradiation-induced depletion of bone marrow cells in mice. Mechanistically, we demonstrate that inhibition of HR repair by cGAS is linked to its ability to self-oligomerize, causing compaction of bound template dsDNA into a higher-ordered state less amenable to strand invasion by RAD51-coated ssDNA filaments. This previously unknown role of cGAS has implications for understanding its involvement in genome instability-associated disorders including cancer.

Causes and consequences of genomic instability in laminopathies: Replication stress and interferon response

Mammalian nuclei are equipped with a framework of intermediate filaments that function as a karyoskeleton. This nuclear scaffold, formed primarily by lamins (A-type and B-type), maintains the spatial and functional organization of the genome and of sub-nuclear compartments. Over the past decade, a body of evidence has highlighted the significance of these structural nuclear proteins in the maintenance of nuclear architecture and mechanical stability, as well as genome function and integrity. The importance of these structures is now unquestioned given the wide range of degenerative diseases that stem from LMNA gene mutations, including muscular dystrophy disorders, peripheral neuropathies, lipodystrophies, and premature aging syndromes. Here, we review our knowledge about how alterations in nuclear lamins, either by mutation or reduced expression, impact cellular mechanisms that maintain genome integrity. Despite the fact that DNA replication is the major source of DNA damage and genomic instability in dividing cells, how alterations in lamins function impact replication remains minimally explored. We summarize recent studies showing that lamins play a role in DNA replication, and that the DNA damage that accumulates upon lamins dysfunction is elicited in part by deprotection of replication forks. We also discuss the emerging model that DNA damage and replication stress are “sensed” at the cytoplasm by proteins that normally survey this space in search of foreign nucleic acids. In turn, these cytosolic sensors activate innate immune responses, which are materializing as important players in aging and cancer, as well as in the response to cancer immunotherapy.

Hepatic senescence, the good and the bad

Gradual alterations of cell’s physiology and functions due to age or exposure to various stresses lead to the conversion of normal cells to senescent cells. Once becoming senescent, the cell stops dividing permanently but remains metabolically active. Cellular senescence does not have a single marker but is characterized mainly by a combination of multiple markers, such as, morphological changes, expression of cell cycle inhibitors, senescence associated β-galactosidase activity, and changes in nuclear membrane. When cells in an organ become senescent, the entire organism can be affected. This may occur through the senescence-associated secretory phenotype (SASP). SASP may exert beneficial or harmful effects on the microenvironment of tissues. Research on senescence has become a very exciting field in cell biology since the link between age-related diseases, including cancer, and senescence has been established. The loss of regenerative and homeostatic capacity of the liver over the age is somehow connected to cellular senescence. The major contributors of senescence properties in the liver are hepatocytes and cholangiocytes. Senescent cells in the liver have been implicated in the etiology of chronic liver diseases including cirrhosis and hepatocellular carcinoma and in the interference of liver regeneration. This review summarizes recently reported findings in the understanding of the molecular mechanisms of senescence and its relationship with liver diseases.

How Cells Handle DNA Breaks during Mitosis: Detection, Signaling, Repair, and Fate Choice

Mitosis is controlled by a complex series of signaling pathways but mitotic control following DNA damage remains poorly understood. Effective DNA damage sensing and repair is integral to survival but is largely thought to occur primarily in interphase and be repressed during mitosis due to the risk of telomere fusion. There is, however, increasing evidence to suggest tight control of mitotic progression in the incidence of DNA damage, whether induced in mitotic cells or having progressed from failed interphase checkpoints. Here we will discuss what is known to date about signaling pathways controlling mitotic progression and resulting cell fate in the incidence of mitotic DNA damage.

cGAS in action: Expanding roles in immunity and inflammation

DNA is highly immunogenic. It represents a key pathogen-associated molecular pattern (PAMP) during infection. Host DNA can, however, also act as a danger-associated molecular pattern (DAMP) and elicit strong inflammatory responses. The cGAS-STING pathway has emerged as a major pathway that detects intracellular DNA. Here, we highlight recent advances on how cGAS and STING mediate inflammatory responses and how these are regulated, allowing cells to readily respond to infections and noxious agents while avoiding the inappropriate sensing of self-DNA. A particular focus is placed on the role of cGAS in the context of sterile inflammatory conditions. Manipulating cGAS or STING may open the door for new therapeutic strategies for the treatment of acute and chronic inflammation relevant to many human diseases.

Characterization of DNA bound cyclic GMP-AMP synthase using atomic force microscopy imaging

The protocol described herein allows for acquiring topography images of DNA-protein complexes using Atomic Force Microscopy imaging. Since the very beginning of this method, AFM has been an indispensable tool for characterization of biomolecular complexes with exceptional capability of observing single complexes. This method can visualize structural characteristics of DNA-protein assemblies and evaluate differences between individual complexes. Although this protocol is generally applicable to a large number of various proteins complexed with DNA, we use cyclic G/AMP synthase (cGAS) enzyme as a case study for the protocol description.

Unmasking senescence: context-dependent effects of SASP in cancer

Cellular senescence plays a critical role in tumorigenesis. Once thought of as a tissue culture artefact by some researchers, senescence is now a major field of study. Although there are common molecular mechanisms that enforce the growth arrest that characterizes the phenotype, the impact of senescence is varied and can, in some instances, have opposite effects on tumorigenesis. It has become clearer that the cell of origin and the tissue in question dictate the impact of senescence on tumorigenesis. In this Review, we unravel this complexity by focusing on how senescence impacts tumorigenesis when it arises within incipient tumour cells versus stromal cells, and how these roles can change in different stages of disease progression. In addition, we highlight the diversity of the senescent phenotype and its functional output beyond growth arrest: the senescence-associated secretory phenotype (SASP). Fortunately, a number of new genetic and pharmacologic tools have been developed that are now allowing the senescence phenotype to be parsed further.

DNA sensing by the cGAS-STING pathway in health and disease

The detection of pathogens through nucleic acid sensors is a defining principle of innate immunity. RNA-sensing and DNA-sensing receptors sample subcellular compartments for foreign nucleic acids and, upon recognition, trigger immune signalling pathways for host defence. Over the past decade, our understanding of how the recognition of nucleic acids is coupled to immune gene expression has advanced considerably, particularly for the DNA-sensing receptor cyclic GMP-AMP synthase (cGAS) and its downstream signalling effector stimulator of interferon genes (STING), as well as the molecular components and regulation of this pathway. Moreover, the ability of self-DNA to engage cGAS has emerged as an important mechanism fuelling the development of inflammation and implicating the cGAS-STING pathway in human inflammatory diseases and cancer. This detailed mechanistic and biological understanding is paving the way for the development and clinical application of pharmacological agonists and antagonists in the treatment of chronic inflammation and cancer.

The cGAS/STING pathway: a sensor of senescence-associated DNA damage and trigger of inflammation in early age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of irreversible blindness among the elderly. Considering the relatively limited effect of therapy on early AMD, it is important to focus on the pathogenesis of AMD, especially early AMD. Ageing is one of the strongest risk factors for AMD, and analysis of the impact of ageing on AMD development is valuable. Among all the ageing hallmarks, increased DNA damage accumulation is regarded as the beginning of cellular senescence and is related to abnormal expression of inflammatory cytokines, which is called the senescence-associated secretory phenotype (SASP). The exact pathway for DNA damage that triggers senescence-associated hallmarks is poorly understood. Recently, mounting evidence has shown that the cGAS/STING pathway is an important DNA sensor related to proinflammatory factor secretion and is associated with another hallmark of ageing, SASP. Thus, we hypothesized that the cGAS/STING pathway is a vital signalling pathway for early AMD development and that inhibition of STING might be a potential therapeutic strategy for AMD cases.