Cigarette smoke induces mitochondrial DNA damage and activates cGAS-STING pathway: application to a biomarker for atherosclerosis

Research progress of cGAS-STING signaling pathway in intestinal diseases

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signal has drawn much consideration due to its sensitivity to DNA in innate immune mechanisms. Activation of the cGAS-STIN signaling pathway induces the production of interferon and inflammatory cytokines, resulting in immune responses, or inflammatory diseases. The intestinal tract is a vital organ for the body's nutrition absorption, recent studies have had various points of view on the job of cGAS-STING pathway in various intestinal sicknesses. Therefore, understanding its role and mechanism in the intestinal environment can help to develop new strategies for the treatment of intestinal diseases. This article examines the mechanism of the cGAS-STING pathway and its function in inflammatory bowel disease, intestinal cancer, and long-injury ischemia-reperfusion, lists the current medications that target it for the treatment of intestinal diseases, and discusses the impact of intestinal flora on this signaling pathway, to offer a theoretical and scientific foundation for upcoming targeted therapies for intestinal disorders via the cGAS-STING pathway.

The cytoplasmic sensor, the AIM2 inflammasome: A precise therapeutic target in vascular and metabolic diseases

Cardio-cerebrovascular diseases encompass pathological changes in the heart, brain and vascular system, which pose a great threat to health and well-being worldwide. Moreover, metabolic diseases contribute to and exacerbate the impact of vascular diseases. Inflammation is a complex process that protects against noxious stimuli but is also dysregulated in numerous so-called inflammatory diseases, one of which is atherosclerosis. Inflammation involves multiple organ systems and a complex cascade of molecular and cellular events. Numerous studies have shown that inflammation plays a vital role in cardio-cerebrovascular diseases and metabolic diseases. The absent in melanoma 2 (AIM2) inflammasome detects and is subsequently activated by double-stranded DNA in damaged cells and pathogens. With the assistance of the mature effector molecule caspase-1, the AIM2 inflammasome performs crucial biological functions that underpin its involvement in cardio-cerebrovascular diseases and related metabolic diseases: The production of interleukin-1 beta (IL-1β), interleukin-18 (IL-18) and N-terminal pore-forming Gasdermin D fragment (GSDMD-N) mediates a series of inflammatory responses and programmed cell death (pyroptosis and PANoptosis). Currently, several agents have been reported to inhibit the activity of the AIM2 inflammasome and have the potential to be evaluated for use in clinical settings. In this review, we systemically elucidate the assembly, biological functions, regulation and mechanisms of the AIM2 inflammasome in cardio-cerebrovascular diseases and related metabolic diseases and outline the inhibitory agents of the AIM2 inflammasome as potential therapeutic drugs.

Release of damaged mitochondrial DNA: A novel factor in stimulating inflammatory response

Mitochondrial DNA (mtDNA) is a circular double-stranded genome that exists independently of the nucleus. In recent years, research on mtDNA has significantly increased, leading to a gradual increase in understanding of its physiological and pathological characteristics. Reactive oxygen species (ROS) and other factors can damage mtDNA. This damaged mtDNA can escape from the mitochondria to the cytoplasm or extracellular space, subsequently activating immune signaling pathways, such as NLR family pyrin domain protein 3 (NLRP3), and triggering inflammatory responses. Numerous studies have demonstrated the involvement of mtDNA damage and leakage in the pathological mechanisms underlying various diseases including infectious diseases, metabolic inflammation, and immune disorders. Consequently, comprehensive investigation of mtDNA can elucidate the pathological mechanisms underlying numerous diseases. The prevention of mtDNA damage and leakage has emerged as a novel approach to disease treatment, and mtDNA has emerged as a promising target for drug development. This article provides a comprehensive review of the mechanisms underlying mtDNA-induced inflammation, its association with various diseases, and the methods used for its detection.

The cGAS-STING pathway in cardiovascular diseases: from basic research to clinical perspectives

The cyclic guanosine monophosphate (GMP)-adenosine monophosphate (AMP) synthase-stimulator of interferon genes (cGAS-STING) signaling pathway, an important component of the innate immune system, is involved in the development of several diseases. Ectopic DNA-induced inflammatory responses are involved in several pathological processes. Repeated damage to tissues and metabolic organelles releases a large number of damage-associated molecular patterns (mitochondrial DNA, nuclear DNA, and exogenous DNA). The DNA fragments released into the cytoplasm are sensed by the sensor cGAS to initiate immune responses through the bridging protein STING. Many recent studies have revealed a regulatory role of the cGAS-STING signaling pathway in cardiovascular diseases (CVDs) such as myocardial infarction, heart failure, atherosclerosis, and aortic dissection/aneurysm. Furthermore, increasing evidence suggests that inhibiting the cGAS-STING signaling pathway can significantly inhibit myocardial hypertrophy and inflammatory cell infiltration. Therefore, this review is intended to identify risk factors for activating the cGAS-STING pathway to reduce risks and to simultaneously further elucidate the biological function of this pathway in the cardiovascular field, as well as its potential as a therapeutic target.

Cytosolic DNA initiates a vicious circle of aging-related endothelial inflammation and mitochondrial dysfunction via STING: the inhibitory effect of Cilostazol

Endothelial senescence, aging-related inflammation, and mitochondrial dysfunction are prominent features of vascular aging and contribute to the development of aging-associated vascular disease. Accumulating evidence indicates that DNA damage occurs in aging vascular cells, especially in endothelial cells (ECs). However, the mechanism of EC senescence has not been completely elucidated, and so far, there is no specific drug in the clinic to treat EC senescence and vascular aging. Here we show that various aging stimuli induce nuclear DNA and mitochondrial damage in ECs, thus facilitating the release of cytoplasmic free DNA (cfDNA), which activates the DNA-sensing adapter protein STING. STING activation led to a senescence-associated secretory phenotype (SASP), thereby releasing pro-aging cytokines and cfDNA to further exacerbate mitochondrial damage and EC senescence, thus forming a vicious circle, all of which can be suppressed by STING knockdown or inhibition. Using next-generation RNA sequencing, we demonstrate that STING activation stimulates, whereas STING inhibition disrupts pathways associated with cell senescence and SASP. In vivo studies unravel that endothelial-specific Sting deficiency alleviates aging-related endothelial inflammation and mitochondrial dysfunction and prevents the development of atherosclerosis in mice. By screening FDA-approved vasoprotective drugs, we identified Cilostazol as a new STING inhibitor that attenuates aging-related endothelial inflammation both in vitro and in vivo. We demonstrated that Cilostazol significantly inhibited STING translocation from the ER to the Golgi apparatus during STING activation by targeting S162 and S243 residues of STING. These results disclose the deleterious effects of a cfDNA-STING-SASP-cfDNA vicious circle on EC senescence and atherogenesis and suggest that the STING pathway is a promising therapeutic target for vascular aging-related diseases. A proposed model illustrates the central role of STING in mediating a vicious circle of cfDNA-STING-SASP-cfDNA to aggravate age-related endothelial inflammation and mitochondrial damage.

mtDNA regulates cGAS-STING signaling pathway in adenomyosis

In various hyperproliferative disorders, damaged mitochondria can release mitochondrial DNA (mtDNA) into the cytoplasm, activating the cGAS-STING signaling pathway and subsequent immune imbalances. Our previous research has demonstrated that hypoxia plays a role in the development of adenomyosis (AM) by inducing mitochondrial dysfunction. However, the precise involvement of the cGAS-STING signaling pathway and mtDNA in AM remains unclear. Therefore, this study aims to investigate the relationship between mtDNA secretion, changes in the cGAS-STING signaling pathway, and the abnormal cellular proliferation observed in AM. We found the cGAS, STING, TBK1, p-TBK1, IRF3, and p-IRF3 proteins levels were significantly elevated in the tissues of patients with AM compared to the control group. Additionally, there was an increase in the expression of the pro-inflammatory cytokines IL-6 and IFN-α in the AM tissues. Hypoxia-induced an increase in the proliferation and migration abilities of endometrial stromal cells (ESCs), accompanied by the activation of the cGAS-STING signaling pathway and elevated levels of IFN-α. Furthermore, hypoxia promoted the leakage of mtDNA into the cytoplasm in AM ESCs, and the deletion of mtDNA reduced the activation of the cGAS-STING pathway. Moreover, knockdown of the STING gene inhibited the expression of TBK1, p-TBK1, IRF3, and p-IRF3 and suppressed the secretion of the inflammatory cytokines IL-6 and IFN-α. Furthermore, the migration and invasion abilities of AM ESCs were significantly diminished after STING knockdown. These findings provide valuable insights into the role of mtDNA release and the cGAS-STING signaling pathway in the pathogenesis of AM.

Cigarette Smoking and Atherosclerotic Cardiovascular Disease

The detrimental effects of cigarette smoking on cardiovascular health, particularly atherosclerosis and thrombosis, are well established, and more detailed mechanisms continue to emerge. As the fundamental pathophysiology of the adverse effects of smoking, endothelial dysfunction, inflammation, and thrombosis are considered to be particularly important. Cigarette smoke induces endothelial dysfunction, leading to impaired vascular dilation and hemostasis regulation. Factors contributing to endothelial dysfunction include reduced bioavailability of nitric oxide, increased levels of superoxide anion, and endothelin release. Chronic inflammation of the vascular wall is a central pathogenesis of smoking-induced atherosclerosis. Smoking systemically elevates inflammatory markers and induces the expression of adhesion molecules and cytokines in various tissues. Pattern recognition receptors and damage-associated molecular patterns play crucial roles in the mechanism underlying smoking-induced inflammation. Smoking-induced DNA damage and activation of innate immunity, such as the NLRP3 inflammasome, cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway, and Toll-like receptor 9, are shown to amplify inflammatory cytokine expression. Cigarette smoke-induced oxidative stress and inflammation influence platelet adhesion, aggregation, and coagulation via adhesion molecule upregulation. Furthermore, it affects the coagulation cascade and fibrinolysis balance, causing thrombus formation. Matrix metalloproteinases contribute to plaque vulnerability and atherothrombotic events. The impact of smoking on inflammatory cells and adhesion molecules further intensifies the risk of atherothrombosis. Collectively, exposure to cigarette smoke exerts profound effects on endothelial function, inflammation, and thrombosis, contributing to the development and progression of atherosclerosis and atherothrombotic cardiovascular diseases. Understanding these intricate mechanisms highlights the urgent need for smoking cessation to protect cardiovascular health. This comprehensive review investigates the multifaceted mechanisms through which smoking contributes to these life-threatening conditions.

Mitochondrial DNA leakage triggers inflammation in age-related cardiovascular diseases

Mitochondrial dysfunction is one of the hallmarks of cardiovascular aging. The leakage of mitochondrial DNA (mtDNA) is increased in senescent cells, which are resistant to programmed cell death such as apoptosis. Due to its similarity to prokaryotic DNA, mtDNA could be recognized by cellular DNA sensors and trigger innate immune responses, resulting in chronic inflammatory conditions during aging. The mechanisms include cGAS-STING signaling, TLR-9 and inflammasomes activation. Mitochondrial quality controls such as mitophagy could prevent mitochondria from triggering harmful inflammatory responses, but when this homeostasis is out of balance, mtDNA-induced inflammation could become pathogenic and contribute to age-related cardiovascular diseases. Here, we summarize recent studies on mechanisms by which mtDNA promotes inflammation and aging-related cardiovascular diseases, and discuss the potential value of mtDNA in early screening and as therapeutic targets.

Circulating cell-free DNA and its association with cardiovascular disease: what we know and future perspectives

PURPOSE OF REVIEW

The aim of this review is to explore a possible link between cell-free DNA (cfDNA) and cardiovascular disease (CVD), which may hold valuable potential for future diagnostics.

RECENT FINDINGS

cfDNA has become topic of high interest across several medical fields. cfDNA is used as a diagnostic biomarker in cancer, prenatal care, and transplantation. In addition, cfDNA may play an unrecognized role in biological processes that are involved in or underlying various disease states, for example, inflammation. Elevated levels of cfDNA are associated with various elements of CVD, cardio-metabolic risk factors, and autoimmune diseases. Mitochondrial cfDNA and neutrophil extracellular traps may play distinct roles. Total circulating cfDNA may reflect the unspecific accumulation of stressors and the organism's susceptibility and resilience to such stressors. As such, cfDNA, in a stressful situation, may provide predictive value for future development of CVD. We suggest exploring such possibility through a large-scale prospective cohort study of pregnant women.

SUMMARY

There is no doubt that cfDNA is a valuable biomarker. For CVD, its potential is indicated but less explored. New studies may identify cfDNA as a valuable circulating cardiovascular risk marker to help improve risk stratification.

Circulating cell-free mitochondrial DNA levels and glucocorticoid sensitivity in a cohort of male veterans with and without combat-related PTSD

Circulating cell-free mitochondrial DNA (ccf-mtDNA) is a biomarker of cellular injury or cellular stress and is a potential novel biomarker of psychological stress and of various brain, somatic, and psychiatric disorders. No studies have yet analyzed ccf-mtDNA levels in post-traumatic stress disorder (PTSD), despite evidence of mitochondrial dysfunction in this condition. In the current study, we compared plasma ccf-mtDNA levels in combat trauma-exposed male veterans with PTSD (n = 111) with those who did not develop PTSD (n = 121) and also investigated the relationship between ccf mt-DNA levels and glucocorticoid sensitivity. In unadjusted analyses, ccf-mtDNA levels did not differ significantly between the PTSD and non-PTSD groups (t = 1.312, p = 0.191, Cohen's d = 0.172). In a sensitivity analysis excluding participants with diabetes and those using antidepressant medication and controlling for age, the PTSD group had lower ccf-mtDNA levels than did the non-PTSD group (F(1, 179) = 5.971, p = 0.016, partial η2 = 0.033). Across the entire sample, ccf-mtDNA levels were negatively correlated with post-dexamethasone adrenocorticotropic hormone (ACTH) decline (r = -0.171, p = 0.020) and cortisol decline (r = -0.149, p = 0.034) (viz., greater ACTH and cortisol suppression was associated with lower ccf-mtDNA levels) both with and without controlling for age, antidepressant status and diabetes status. Ccf-mtDNA levels were also significantly positively associated with IC50-DEX (the concentration of dexamethasone at which 50% of lysozyme activity is inhibited), a measure of lymphocyte glucocorticoid sensitivity, after controlling for age, antidepressant status, and diabetes status (β = 0.142, p = 0.038), suggesting that increased lymphocyte glucocorticoid sensitivity is associated with lower ccf-mtDNA levels. Although no overall group differences were found in unadjusted analyses, excluding subjects with diabetes and those taking antidepressants, which may affect ccf-mtDNA levels, as well as controlling for age, revealed decreased ccf-mtDNA levels in PTSD. In both adjusted and unadjusted analyses, low ccf-mtDNA levels were associated with relatively increased glucocorticoid sensitivity, often reported in PTSD, suggesting a link between mitochondrial and glucocorticoid-related abnormalities in PTSD.

Mitochondrial DNA is a key driver in cigarette smoke extract-induced IL-6 expression

Smoking is an independent risk factor for atherosclerosis, the primary pathogenesis of which is inflammation. We recently reported that cigarette smoke extract (CSE) causes cytosolic and extracellular accumulation of both nuclear (n) and mitochondrial (mt) DNA, which leads to inflammation in human umbilical vein endothelial cells (HUVECs). In this study, we examined whether inflammation induction depends more on cytosolic nDNA or mtDNA, and which chemical constituents of CSE are involved. Acrolein (ACR), methyl vinyl ketone (MVK), and 2-cyclopenten-1-one (CPO) were used in the experiments, as these are the major cytotoxic factors in CSE in various cell types. Stimulation with ACR, MVK, or CPO alone resulted in the accumulation of DNA double-strand breaks (DSBs), but not oxidative DNA damage, accumulation of cytosolic DNA, or increased expression of inflammatory cytokines. Simultaneous administration of all three constituents (ALL) resulted in oxidative DNA damage in both the nucleus and mitochondria, accumulation of DSBs, reduced mitochondrial membrane potential, induction of minority mitochondrial outer membrane permeabilization, accumulation of cytosolic free DNA, and increased expression of inflammatory cytokines such as IL-6 and IL-1α. Treatment with N-acetyl-L-cysteine, a reactive oxygen species scavenger, suppressed oxidative DNA damage and the increased expression of IL-6 and IL-1α induced by ALL or CSE. The ALL- or CSE-induced increase in IL-6 expression, but not that of IL-1α, was suppressed by mtDNA depletion. In conclusion, ACR, MVK, and CPO may strongly contribute to CSE-induced inflammation. More importantly, cytosolic free mtDNA is thought to play an important role in IL-6 expression, a central mediator of inflammation.

Novel insight into cGAS-STING pathway in ischemic stroke: from pre- to post-disease

Ischemic stroke, a primary cause of disability and the second leading cause of mortality, has emerged as an urgent public health issue. Growing evidence suggests that the Cyclic GMP-AMP synthase (cGAS)- Stimulator of interferon genes (STING) pathway, a component of innate immunity, is closely associated with microglia activation, neuroinflammation, and regulated cell death in ischemic stroke. However, the mechanisms underlying this pathway remain inadequately understood. This article comprehensively reviews the existing literature on the cGAS-STING pathway and its multifaceted relationship with ischemic stroke. Initially, it examines how various risk factors and pre-disease mechanisms such as metabolic dysfunction and senescence (e.g., hypertension, hyperglycemia, hyperlipidemia) affect the cGAS-STING pathway in relation to ischemic stroke. Subsequently, we explore in depth the potential pathophysiological relationship between this pathway and oxidative stress, endoplasmic reticulum stress, neuroinflammation as well as regulated cell death including ferroptosis and PANoptosis following cerebral ischemia injury. Finally, it suggests that intervention targeting the cGAS-STING pathway may serve as promising therapeutic strategies for addressing neuroinflammation associated with ischemic stroke. Taken together, this review concludes that targeting the microglia cGAS-STING pathway may shed light on the exploration of new therapeutic strategies against ischemic stroke.

GSDME in Endothelial Cells: Inducing Vascular Inflammation and Atherosclerosis via Mitochondrial Damage and STING Pathway Activation

The initiation of atherosclerotic plaque is characterized by endothelial cell inflammation. In light of gasdermin E's (GSDME) role in pyroptosis and inflammation, this study elucidates its function in atherosclerosis onset. Employing Gsdme- and apolipoprotein E-deficient (Gsdme-/-/ApoE-/-) and ApoE-/- mice, an atherosclerosis model was created on a Western diet (WD). In vitro examinations with human umbilical vein endothelial cells (HUVECs) included oxidized low-density lipoprotein (ox-LDL) exposure. To explore the downstream mechanisms linked to GSDME, we utilized an agonist targeting the stimulator of the interferon genes (STING) pathway. The results showed significant GSDME activation in ApoE-/- mice arterial tissues, corresponding with atherogenesis. Gsdme-/-/ApoE-/- mice displayed fewer plaques and decreased vascular inflammation. Meanwhile, GSDME's presence was confirmed in endothelial cells. GSDME inhibition reduced the endothelial inflammation induced by ox-LDL. GSDME was linked to mitochondrial damage in endothelial cells, leading to an increase in cytoplasmic double-stranded DNA (dsDNA). Notably, STING activation partially offset the effects of GSDME inhibition in both in vivo and in vitro settings. Our findings underscore the pivotal role of GSDME in endothelial cells during atherogenesis and vascular inflammation, highlighting its influence on mitochondrial damage and the STING pathway, suggesting a potential therapeutic target for vascular pathologies.

Systematic Investigation of the Effect of Lactobacillus acidophilus TW01 on Potential Prevention of Particulate Matter (PM)2.5-Induced Damage Using a Novel In Vitro Platform

Exposure to ambient particulate matter (PM) and cigarette smoking (CS) is a risk factor for respiratory/lung infections and metabolic disorders. Lung-gut axis disruption involving the upregulation of oxidative stress, systemic inflammation, and gut barrier dysfunction by PM is one of the potential mechanisms. Thus, we designed a novel in vitro platform for pre-selecting probiotics with potentially protective effects against PM-induced lung damage through the lung-gut axis to reduce animal usage. The results showed that a high dose of Lactobacillus acidophilus TW01 (1 × 108 CFU/mL) inhibited reactive oxygen species (ROS) production. This strain could also reduce respiratory epithelial cell death induced by cigarette smoke extraction (CSE), as well as promoting Caco-2 cell migration in 1 × 106 CFU/mL. Although further animal experiments are needed to validate the in vitro findings, L. acidophilus TW01 is a promising probiotic strain for the potential prevention of PM2.5-induced damage.

Nucleic acid sensor STING drives remodeling and its inhibition enhances steroid responsiveness in chronic obstructive pulmonary disease

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is progressive and irreversible chronic lung inflammatory disease. Cigarette smoke, the main cause of COPD, is often associated with double-stranded DNA release which potentially activates DNA-sensing pathways, such as STING. This study, therefore, analyzed the role of STING pathway in inducing pulmonary inflammation, steroid resistance, and remodeling in COPD.

METHODS

Primary cultured lung fibroblasts were isolated from healthy non-smoker, healthy smoker, and smoker COPD individuals. The expression of STING pathway, remodeling, and steroid resistance signatures were investigated in these fibroblasts upon LPS stimulation and treatment with dexamethasone and/or STING inhibitor, at both mRNA and protein levels using qRT-PCR, western blot, and ELISA.

RESULTS

At baseline, STING was elevated in healthy smoker fibroblasts and to a higher extent in smoker COPD fibroblasts when compared to healthy non-smoker fibroblasts. Upon using dexamethasone as monotherapy, STING activity was significantly inhibited in healthy non-smoker fibroblasts but showed resistance in COPD fibroblasts. Treating both healthy and COPD fibroblasts with STING inhibitor in combination with dexamethasone additively inhibited STING pathway in both groups. Moreover, STING stimulation triggered a significant increase in remodeling markers and a reduction in HDAC2 expression. Interestingly, treating COPD fibroblasts with the combination of STING inhibitor and dexamethasone alleviated remodeling and reversed steroid hyporesponsiveness through an upregulation of HDAC2.

CONCLUSION

These findings support that STING pathway plays an important role in COPD pathogenesis, via inducing pulmonary inflammation, steroid resistance, and remodeling. This raises the possibility of using STING inhibitor as a potential therapeutic adjuvant in combination with common steroid treatment.

Tetrandrine alleviates atherosclerosis via inhibition of STING-TBK1 pathway and inflammation in macrophages

Atherosclerosis (AS) is a chronic inflammatory disease. Recent studies have showed that stimulator of interferon genes (STING), an important protein in innate immunity, mediates pro-inflammatory activation of macrophages in the development of AS. Tetrandrine (TET) is a natural bisbenzylisoquinoline alkaloid isolated from Stepania tetrandra and possesses anti-inflammatory activities, with unknown effects and mechanisms in AS. In this study, we explored the anti-atherosclerotic effects of TET and investigated the underlying mechanisms. Mouse primary peritoneal macrophages (MPMs) are challenged with cyclic guanosine monophosphate-adenosine monophosphate (cGAMP) or oxidized LDL (oxLDL). We found that pretreatment with TET dose-dependently inhibited cGAMP- or oxLDL-induced STING/ TANK-binding kinase 1 (TBK1) signaling, then suppressing nuclear factor kappa-B (NF-κB) activation and pro-inflammatory factor expression in MPMs. ApoE^-/- mice were fed a high-fat diet (HFD) to develop an atherosclerotic phenotype. Administration of TET at 20 mg/kg/day significantly reduced HFD-induced atherosclerotic plaques, accompanied with decreased macrophage infiltration, inflammatory cytokine production, fibrosis, and STING/TBK1 activation in aortic plaque lesions. In summary, we demonstrate that TET inhibits STING/TBK1/NF-κB signaling pathway to reduce inflammation in oxLDL-challenged macrophages and alleviate atherosclerosis in HFD-fed ApoE^-/- mice. These findings proved that TET could be a potential therapeutic candidate for the treatment of atherosclerosis-related diseases.