Gasdermin E benefits CD8+T cell mediated anti-immunity through mitochondrial damage to activate cGAS-STING-interferonß axis in colorectal cancer.

BACKGROUND: Pyroptosis belongs to a unique type of programmed cell death among which GSDME is reported to exert anti-tumor immunity. However, the underlying mechanisms of how to boost tumor-infiltrating lymphocytes and whether it could benefit the efficacy of ICIs are still unknown. METHODS: CRC samples were used to analyze its relationship with CD8+T cells. GSDME in mouse CRC cell lines CT26/MC38 was overexpressed. The infiltration of CD8+T cells in grafted tumors was determined by multiplex flow cytometric analysis and immunohistochemistry. Transcriptomic analysis was performed in cell lines to define key signatures related to its overexpression. The mechanism of how mtDNA was released by GSDME-induced mitochondrial damage and activated cGAS-STING pathway was observed. Whether GSDME benefited ICIs and the relationships with the genotypes of CRC patients were investigated. RESULTS: It had favorable prognostic value in CRC and was positively associated with increased number and functionality of CD8+T cells both in human samples and animal models. This was due to mitochondrial damage and activation of cGAS-STING-IFNß pathway for the recruitment of CD8+T cells. Mechanically, GSDME overexpression enhanced N-GSDME level, leading to the mitochondrial damage and mtDNA was released into cytosol. Finally, GSDME benefited with ICIs and exhibited positive relationships with MSI in CRC patients. CONCLUSION: We presented the mechanism of GSDME in anti-tumor immunity through activating cGAS-STING-IFNß axis mediated by mitochondrial damage, leading to more infiltration of CD8+T cells with synergistic efficacy with ICIs.

Chronic circadian rhythm disorder induces heart failure with preserved ejection fraction-like phenotype through the Clock-sGC-cGMP-PKG1 signaling pathway.

Emerging evidence has documented that circadian rhythm disorders could be related to cardiovascular diseases. However, there is limited knowledge on the direct adverse effects of circadian misalignment on the heart. This study aimed to investigate the effect of chronic circadian rhythm disorder on heart homeostasis in a mouse model of consistent jetlag. The jetlag model was induced in mice by a serial 8-h phase advance of the light cycle using a light-controlled isolation box every 4 days for up to 3 months. Herein, we demonstrated for the first time that chronic circadian rhythm disorder established in the mouse jetlag model could lead to HFpEF-like phenotype such as cardiac hypertrophy, cardiac fibrosis, and cardiac diastolic dysfunction, following the attenuation of the Clock-sGC-cGMP-PKG1 signaling. In addition, clock gene knock down in cardiomyocytes induced hypertrophy via decreased sGC-cGMP-PKG signaling pathway. Furthermore, treatment with an sGC-activator riociguat directly attenuated the adverse effects of jetlag model-induced cardiac hypertrophy, cardiac fibrosis, and cardiac diastolic dysfunction. Our data suggest that circadian rhythm disruption could induce HFpEF-like phenotype through downregulation of the clock-sGC-cGMP-PKG1 signaling pathway. sGC could be one of the molecular targets against circadian rhythm disorder-related heart disease.

cGAS: action in the nucleus.

As a canonical cytoplasmic DNA sensor, cyclic GMP-AMP synthase (cGAS) plays a key role in innate immunity. In recent years, a growing number of studies have shown that cGAS can also be located in the nucleus and plays new functions such as regulating DNA damage repair, nuclear membrane repair, chromosome fusion, DNA replication, angiogenesis and other non-canonical functions. Meanwhile, the mechanisms underlying the nucleo-cytoplasmic transport and the regulation of cGAS activation have been revealed in recent years. Based on the current understanding of the structure, subcellular localization and canonical functions of cGAS, this review focuses on summarizing the mechanisms underlying nucleo-cytoplasmic transport, activity regulation and non-canonical functions of cGAS in the nucleus. We aim to provide insights into exploring the new functions of cGAS in the nucleus and advance its clinical translation.

Correlates of Plasma NT-proBNP/Cyclic GMP Ratio in Heart Failure With Preserved Ejection Fraction: An Analysis of the RELAX Trial.

BACKGROUND: Phosphodiesterases degrade cyclic GMP (cGMP), the second messenger that mediates the cardioprotective effects of natriuretic peptides. High natriuretic peptide/cGMP ratio may reflect, in part, phosphodiesterase activity. Correlates of natriuretic peptide/cGMP in patients with heart failure with preserved ejection fraction are not well understood. Among patients with heart failure with preserved ejection fraction in the RELAX (Phosphodiesterase-5 Inhibition to Improve Clinical Status and Exercise Capacity in Heart Failure With Preserved Ejection Fraction) trial, we examined (1) cross-sectional correlates of circulating NT-proBNP (N-terminal pro-B-type natriuretic peptide)/cGMP ratio, (2) whether selective phosphodiesterase-5 inhibition by sildenafil changed the ratio, and (3) whether the effect of sildenafil on 24-week outcomes varied by baseline ratio. METHODS AND RESULTS: In 212 subjects, NT-proBNP/cGMP ratio was calculated at randomization and 24 weeks. Correlates of the ratio and its change were examined in multivariable proportional odds models. Whether baseline ratio modified the sildenafil effect on outcomes was examined by interaction terms. Higher NT-proBNP/cGMP ratio was associated with greater left ventricular mass and troponin, the presence of atrial fibrillation, and lower estimated glomerular filtration rate and peak oxygen consumption. Compared with placebo, sildenafil did not alter the ratio from baseline to 24 weeks (P=0.17). The effect of sildenafil on 24-week change in peak oxygen consumption, left ventricular mass, or clinical composite outcome was not modified by baseline NT-proBNP/cGMP ratio (P-interaction >0.30 for all). CONCLUSIONS: Among patients with heart failure with preserved ejection fraction, higher NT-proBNP/cGMP ratio associated with an adverse cardiorenal phenotype, which was not improved by selective phosphodiesterase-5 inhibition. Other phosphodiesterases may be greater contributors than phosphodiesterase-5 to the adverse phenotype associated with a high natriuretic peptide/cGMP ratio in HFpEF. REGISTRATION INFORMATION: clinicaltrials.gov. Identifier: NCT00763867.

Octadecyl Gallate and Lipid-Modified MnSe2 Nanoparticles Enhance Radiosensitivity in Esophageal Squamous Cell Carcinoma and Promote Radioprotection in Normal Tissues.

Radiotherapy, a widely used therapeutic strategy for esophageal squamous cell carcinoma (ESCC), is always limited by radioresistance of tumor tissues and side-effects on normal tissues. Herein, a signature based on four core genes of cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway, is developed to predict prognosis and assess immune cell infiltration, indicating that the cGAS-STING pathway and radiotherapy efficacy are closely intertwined in ESCC. A novel lipid-modified manganese diselenide nanoparticle (MnSe2-lipid) with extraordinarily uniform sphere morphology and tumor microenvironment (TME) responsiveness is developed to simultaneously overcome radioresistance and reduce side-effects of radiation. The uniform MnSe2 encapsulated lipid effectively achieves tumor accumulation. Octadecyl gallate on surface of MnSe2 forming pH-responsive metal-phenolic covalent realizes rapid degradation in TME. The released Mn2+ promotes radiosensitivity by generating reactive oxygen species induced by Fenton-like reaction and activating cGAS-STING pathway. Spontaneously, selenium strengthens immune response by promoting secretion of cytokines and increasing white blood cells, and performs antioxidant activity to reduce side-effects of radiotherapy. Overall, this multifunctional remedy which is responsive to TME is capable of providing radiosensitivity by cGAS-STING pathway-mediated immunostimulation and chemodynamic therapy, and radioprotection of normal tissues, is highlighted here to optimize ESCC treatment.

Interaction between the SFTSV envelope glycoprotein Gn and STING inhibits the formation of the STING-TBK1 complex and suppresses the NF-κB signaling pathway.

Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging tick-borne bunyavirus with high pathogenicity. There has been a gradual increase in the number of reported cases in recent years, with high morbidity and mortality rates. The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway plays an important role in the innate immune defense activated by viral infection; however, the role of the cGAS-STING signaling pathway during SFTSV infection is still unclear. In this study, we investigated the relationship between SFTSV infection and cGAS-STING signaling. We found that SFTSV infection caused the release of mitochondrial DNA into the cytoplasm and inhibits downstream innate immune signaling pathways by activating the cytoplasmic DNA receptor cGAS. We found that the SFTSV envelope glycoprotein Gn was a potent inhibitor of the cGAS-STING pathway and blocked the nuclear accumulation of interferon regulatory factor 3 and p65 to inhibit downstream innate immune signaling. Gn of SFTSV interacted with STING to inhibit STING dimerization and inhibited K27-ubiquitin modification of STING to disrupt the assembly of the STING-TANK-binding kinase 1 complex and downstream signaling. In addition, Gn was found to be involved in inducing STING degradation, further inhibiting the downstream immune response. In conclusion, this study identified the important role of the glycoprotein Gn in the antiviral innate immune response and revealed a novel mechanism of immune escape for SFTSV. Moreover, this study increases the understanding of the pathogenic mechanism of SFTSV and provides new insights for further treatment of SFTS. IMPORTANCE: Severe fever with thrombocytopenia syndrome virus (SFTSV) is a newly discovered virus associated with severe hemorrhagic fever in humans. However, the role of the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway during SFTSV infection is still unclear. We found that SFTSV infection inhibits downstream innate immune signaling pathways by activating the cytoplasmic DNA receptor cGAS. In addition, SFTSV Gn blocked the nuclear accumulation of interferon regulatory factor 3 and p65 to inhibit downstream innate immune signaling. Moreover, we determined that Gn of SFTSV inhibited K27-ubiquitin modification of STING to disrupt the assembly of the STING-TANK-binding kinase 1 complex and downstream signaling. We found that the SFTSV envelope glycoprotein Gn is a potent inhibitor of the cGAS-STING pathway. In conclusion, this study highlights the crucial function of the glycoprotein Gn in the antiviral innate immune response and reveals a new method of immune escape of SFTSV.

Paracrine and endocrine pathways of natriuretic peptides assessed by ligand-receptor mapping in the Japanese eel brain.

The natriuretic peptide (NP) family consists of cardiac NPs (ANP, BNP, and VNP) and brain NPs (CNPs) in teleosts. In addition to CNP1-4, a paralogue of CNP4 (named CNP4b) was recently discovered in basal teleosts including Japanese eel. Mammals have lost most Cnps during the evolution, but teleost cnps were conserved and diversified, suggesting that CNPs are important hormones for maintaining brain functions in teleost. The present study evaluated the potency of each Japanese eel CNP to their NP receptors (NPR-A, NPR-B, NPR-C, and NPR-D) overexpressed in CHO cells. A comprehensive brain map of cnps- and nprs-expressing neurons in Japanese eel was constructed by integrating the localization results obtained by in situ hybridization. The result showed that CHO cells expressing NPR-A and NPR-B induced strong cGMP productions after stimulation by cardiac and brain NPs, respectively. Regarding brain distribution of cnps, cnp1 is engaged in the ventral telencephalic area and periventricular area including the parvocellular preoptic nucleus (Pp), anterior/posterior tuberal nuclei, and periventricular gray zone of the optic tectum. cnp3 is found in the habenular nucleus and prolactin cells in the pituitary. cnp4 is expressed in the ventral telencephalic area, while cnp4b is expressed in the motoneurons in the medullary area. Such CNP isoform-specific localizations suggest that function of each CNP has diverged in the eel brain. Furthermore, the Pp lacking the blood-brain barrier expressed both npra and nprb, suggesting that endocrine and paracrine NPs interplay for regulating the Pp functions in Japanese eels.

Decomposable Nanoagonists Enable NIR-Elicited cGAS-STING Activation for Tandem-Amplified Photodynamic-Metalloimmunotherapy.

Activation of the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway has emerged as an efficient strategy to improve the therapeutic outcomes of immunotherapy. However, the "constantly active" mode of current STING agonist delivery strategies typically leads to off-target toxicity and hyperimmunity. To address this critical issue, herein a metal-organic frameworks-based nanoagonist (DZ@A7) featuring tumor-specific and near-infrared (NIR) light-enhanced decomposition is constructed for precisely localized STING activation and photodynamic-metalloimmunotherapy. The engineered nanoagonist enabled the generation of mitochondria-targeted reactive oxygen species under NIR irradiation to specifically release mitochondrial DNA (mtDNA) and inhibit the repair of nuclear DNA via hypoxia-responsive drugs. Oxidized tumor mtDNA serves as an endogenous danger-associated molecular pattern that activates the cGAS-STING pathway. Concurrently, NIR-accelerated zinc ions overloading in cancer cells further enhance the cGAS enzymatic activity through metalloimmune effects. By combining the synergistically enhanced activation of the cGAS-STING pathway triggered by NIR irradiation, the engineered nanoagonist facilitated the maturation of dendritic cells and infiltration of cytotoxic T lymphocytes for primary tumor eradication, which also established a long-term anti-tumor immunity to suppress tumor metastasis. Therefore, the developed nanoagonist enabled NIR-triggered, agonist-free, and tandem-amplified activation of the cGAS-STING pathway, thereby offering a distinct paradigm for photodynamic-metalloimmunotherapy.

The cGAS-STING pathway: a therapeutic target in diabetes and its complications.

Diabetic wound healing (DWH) represents a major complication of diabetes where inflammation is a key impediment to proper healing. The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway has emerged as a central mediator of inflammatory responses to cell stress and damage. However, the contribution of cGAS-STING activation to impaired healing in DWH remains understudied. In this review, we examine the evidence that cGAS-STING-driven inflammation is a critical factor underlying defective DWH. We summarize studies revealing upregulation of the cGAS-STING pathway in diabetic wounds and discuss how this exacerbates inflammation and senescence and disrupts cellular metabolism to block healing. Partial pharmaceutical inhibition of cGAS-STING has shown promise in damping inflammation and improving DWH in preclinical models. We highlight key knowledge gaps regarding cGAS-STING in DWH, including its relationships with endoplasmic reticulum stress and metal-ion signaling. Elucidating these mechanisms may unveil new therapeutic targets within the cGAS-STING pathway to improve healing outcomes in DWH. This review synthesizes current understanding of how cGAS-STING activation contributes to DWH pathology and proposes future research directions to exploit modulation of this pathway for therapeutic benefit.

3-N-butylphthalide attenuates neuroinflammation in rotenone-induced Parkinson's disease models via the cGAS-STING pathway.

Neuroinflammation is crucial in the onset and progression of dopaminergic neuron loss in Parkinson's disease (PD). We aimed to determine whether 3-N-Butylphthalide (NBP) can protect against PD by inhibiting the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway and the inflammatory response of microglia. MitoSOX/MitoTracker/Hoechst staining was used to detect the levels of mitochondrial reactive oxygen species (ROS) in BV2 cells. Quantitative Real-Time Polymerase Chain Reaction was used to measure the levels of free cytoplasmic mitochondrial DNA (mtDNA) in BV2 cells and mouse brain tissues. Behavioral impairments were assessed using rotarod, T-maze, and balance beam tests. Dopaminergic neurons and microglia were observed using immunohistochemical staining. Expression levels of cGAS, STING, nuclear factor kappa-B (NfκB), phospho- NfκB (p-NfκB), inhibitor of NfκBα (IκBα), and phospho-IκBα (p-IκBα) proteins in the substantia nigra and striatum were detected using Western Blot. NBP decreased mitochondrial ROS levels in rotenone-treated BV2 cells. NBP alleviated behavioral impairments and protected against rotenone-induced microgliosis and damage to dopaminergic neurons in the substantia nigra and striatum of rotenone-induced PD mice. NBP decreased rotenone-induced mtDNA leakage and mitigated neuroinflammation by inhibiting cGAS-STING pathway activation. NBP exhibited a protective effect in rotenone-induced PD models by significantly inhibiting the cGAS-STING pathway. Moreover, NBP can alleviate neuroinflammation, and is a potential therapeutic drug for alleviating clinical symptoms and delaying the progression of PD. This study provided insights for the potential role of NBP in PD therapy, potentially mitigating neurodegeneration, and consequently improving the quality of life and lifespan of patients with PD. The limitations are that we have not confirmed the exact mechanism by which NBP decreases mtDNA leakage, and this study was unable to observe the actual clinical therapeutic effect, so further cohort studies are required for validation.

PhotoPyro-Induced cGAS-STING Pathway Activation Enhanced Anti-Melanoma Immunotherapy via a Manganese-Coordinated Nanomedicine.

Malignant melanoma is an aggressive skin cancer with a high metastatic and mortality rate. Owing to genetic alterations, melanoma cells are resistant to apoptosis induction, which reduces the efficacy of most adjuvant systemic anticancer treatments in clinical. Here, a noninvasive strategy for anti-melanoma immunotherapy based on a manganese-coordinated nanomedicine is provided. Supplemented with photoirradiation, photon-mediated reactive oxygen species generation by photosensitizer chlorin e6 initiates photon-controlled pyroptosis activation (PhotoPyro) and promotes antitumor immunity. Simultaneously, photoirradiation-triggered double-stranded DNA generation in the cytosol would activate the Mn2+ -sensitized cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway, which further augment the PhotoPyro-induced immune response. The syngeneic effect of these immunostimulatory pathways significantly benefits dendritic cell maturation by damage-associated molecular patterns and proinflammatory cytokines secretion, thereby activating T cells and remarkably eliciting a systemic antitumor immune response to inhibiting both primary and distant tumor growth. Collaboratively, the photoirradiation-triggered PhotoPyro and cGAS-STING pathway activation by nanomedicine administration could enhance the antitumor capacity of immunotherapy and serve as a promising strategy for melanoma treatment.

Role of micronucleus-activated cGAS-STING signaling in antitumor immunity / 浙江大学学报·医学版

cGAS-STING signaling is a significant component of the innate immune system and functions as a vital sentinel mechanism to monitor cellular and tissue aberrations in microbial invasion and organ injury. cGAS, a cytosolic DNA sensor, is specialized in recognizing abnormally localized cytoplasmic double-stranded DNA (dsDNA) and catalytically synthesizes the second messenger cyclic-GMP-AMP (cGAMP), which initiates a cascade of type I interferon and inflammatory responses mediated by STING. Micronucleus, a byproduct of chromosomal missegregation during anaphase, are also significant contributors to cytoplasmic dsDNA. These unstable subcellular structures are susceptible to irreversible nuclear envelope rupture, exposing genomic dsDNA to the cytoplasm, which potently recruits cGAS and activates STING-mediated innate immune signaling and its downstream activities, including type I interferon and classical nuclear factor-κB (NF-κB) signaling pathways lead to senescence, apoptosis, autophagy activating anti-cancer immunity or directly killing tumor cells. However, sustained STING activation-induced endoplasmic reticulum stress, activated chronic type I interferon and nonclassical NF-κB signaling pathways remodel immunosuppressive tumor microenvironment, leading to immune evasion and facilitating tumor metastasis. Therefore, activated cGAS-STING signaling plays a dual role of suppressing or facilitating tumor growth in tumorigenesis and therapy. This review elaborates on research advances in mechanisms of micronucleus inducing activation of cGAS-STING signaling and its implications in tumorigenesis and therapeutic strategies of malignant tumors.

Dosing Challenges and Benefits of Vericiguat in a Patient With Decompensated Heart Failure: A Case Report.

Vericiguat has emerged as a promising add-on therapy for decompensated heart failure with reduced ejection fraction (HFrEF) patients requiring hospitalization or IV diuretic administration. In the VICTORIA trial (Vericiguat Global Study in Subjects with Heart Failure with Reduced Ejection Fraction), vericiguat was demonstrated to significantly reduce mortality and hospitalization rates. However, the effect of vericiguat on patients receiving SGLT2 inhibitors remains uncertain. In this report, we present a complicated case of dilated heart failure receiving low doses of foundational therapy due to a patient's intolerance but still experiencing recurrent hospital readmissions. Following six months of low-dose vericiguat as an add-on therapy, the patient exhibited important improvements in various clinical parameters, including cardiac and renal function. Nonetheless, further investigation is crucial to substantiate the additional benefits of combination therapy. These findings provide further evidence for the potential benefits of vericiguat when treating HFrEF.

The discovery of hidden guanylate cyclases (GCs) in the Homo sapiens proteome.

Recent discoveries have established functional guanylate cyclase (GC) catalytic centers with low activity within kinase domains in plants. These crypto GCs generate guanosine 3',5'-cyclic monophosphate (cGMP) essential for both intramolecular and downstream signaling. Here, we have set out to search for such crypto GCs moonlighting in kinases in the H. sapiens proteome and identified 18 candidates, including the neurotropic receptor tyrosine kinase 1 (NTRK1). NTRK1 shows a domain architecture much like plant receptor kinases such as the phytosulfokine receptor, where a functional GC essential for downstream signaling is embedded within a kinase domain. In vitro characterization of the NTRK1 shows that the embedded NTRK1 GC is functional with a marked preference for Mn2+ over Mg2+. This therefore points to hitherto unsuspected roles of cGMP in intramolecular and downstream signaling of NTRK1 and the role of cGMP in NTRK1-dependent growth and neoplasia.

GUCY2C signaling limits dopaminergic neuron vulnerability to toxic insults.

Mitochondrial dysfunction and reactive oxygen species (ROS) accumulation within the substantia nigra pars compacta (SNpc) are central drivers of dopaminergic (DA) neuron death in Parkinson's disease (PD). Guanylyl cyclases, and their second messengers cyclic (c)GMP, support mitochondrial function, protecting against ROS and promoting cell survival in a number of tissues. However, the role of the guanylyl cyclase-cGMP axis in defining the vulnerability of DA neurons in the SNpc in PD remains unclear, in part due to the challenge of manipulating cGMP levels selectively in midbrain DA neurons. In that context, guanylyl cyclase C (GUCY2C), a receptor primarily expressed by intestinal epithelial cells, was discovered recently in midbrain DA neurons. Here, we demonstrate that GUCY2C promotes mitochondrial function, reducing oxidative stress and protecting DA neurons from degeneration in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of neurodegeneration. GUCY2C is overexpressed in the SNpc in PD patients and in mice treated with MPTP, possibly reflecting a protective response to oxidative stress. Moreover, cGMP signaling protects against oxidative stress, mitochondrial impairment, and cell death in cultured DA neurons. These observations reveal a previously unexpected role for the GUCY2C-cGMP signaling axis in controlling mitochondrial dysfunction and toxicity in nigral DA neurons, highlighting the therapeutic potential of targeting DA neuron GUCY2C to prevent neurodegeneration in PD.

Phosphodiesterase 2 and Its Isoform a as Therapeutic Targets in the Central Nervous System Disorders.

Cyclic adenosine monophosphates (cAMP) and cyclic guanosine monophosphate (cGMP) are two essential second messengers, which are hydrolyzed by phosphodiesterase's (PDEs), such as PDE-2. Pharmacological inhibition of PDE-2 (PDE2A) in the central nervous system improves cAMP and cGMP signaling, which controls downstream proteins related to neuropsychiatric, neurodegenerative, and neurodevelopmental disorders. Considering that there are no specific treatments for these disorders, PDE-2 inhibitors' development has gained more attention in the recent decade. There is high demand for developing new-generation drugs targeting PDE2 for treating diseases in the central nervous and peripheral systems. This review summarizes the relationship between PDE-2 with neuropsychiatric, neurodegenerative, and neurodevelopmental disorders as well as its possible treatment, mainly involving inhibitors of PDE2.

Discovery of novel cGAS inhibitors based on natural flavonoids.

Cyclic GMP-AMP synthase (cGAS) plays an important role in the inflammatory response. It has been reported that aberrant activation of cGAS is associated with a variety of immune-mediated inflammatory disorders. The development of small molecule inhibitors of cGAS has been considered as a promising therapeutic strategy for the diseases. Flavonoids, a typical class of natural products, are known for their anti-inflammatory activities. Although cGAS is closely associated with inflammation, the potential effects of natural flavonoid compounds on cGAS have been rarely studied. Therefore, we screened an in-house natural flavonoid library by pyrophosphatase (PPiase) coupling assay and identified novel cGAS inhibitors baicalein and baicalin. Subsequently, crystal structures of the two natural flavonoids in complex with human cGAS were determined, which provide mechanistic insight into the anti-inflammatory activities of baicalein and baicalin at the molecular level. After that, a virtual screening based on the crystal structures of baicalein and baicalin in complex with human cGAS was performed. As a result, compound C20 was identified to inhibit both human and mouse cGAS with IC50 values of 2.28 and 1.44 µM, respectively, and its detailed interactions with human cGAS were further revealed by the X-ray crystal structure determination. These results demonstrate the potential of natural products used as hits in drug discovery and provide valuable hints for further development of cGAS inhibitors.

Volatile anesthetics inhibit presynaptic cGMP signaling to depress presynaptic excitability in rat hippocampal neurons.

Volatile anesthetics alter presynaptic function through effects on Ca2+ influx and neurotransmitter release. These actions are proposed to play important roles in their pleiotropic neurophysiological effects including immobility, unconsciousness and amnesia. Nitric oxide and cyclic guanosine monophosphate (NO/cGMP) signaling has been implicated in presynaptic mechanisms, and disruption of NO/cGMP signaling has been shown to alter sensitivity to volatile anesthetics in vivo. We investigated volatile anesthetic actions NO/cGMP signaling in relation to presynaptic function in cultured rat hippocampal neurons using pharmacological tools and genetically encoded biosensors and sequestering probes of cGMP levels. Using the fluorescent cGMP biosensor cGull, we found that electrical stimulation-evoked NMDA-type glutamate receptor-independent presynaptic cGMP transients were inhibited 33.2% by isoflurane (0.51 mM) and 26.4% by sevoflurane (0.57 mM) (p < 0.0001) compared to control stimulation without anesthetic. Stimulation-evoked cGMP transients were blocked by the nonselective inhibitor of nitric oxide synthase N-ω-nitro-l-arginine, but not by the selective neuronal nitric oxide synthase inhibitor N5-(1-imino-3-butenyl)-l-ornithine. Isoflurane and sevoflurane inhibition of stimulation-evoked increases in presynaptic Ca2+ concentration, measured with synaptophysin-GCaMP6f, and of synaptic vesicle exocytosis, measured with synaptophysin-pHlourin, was attenuated in neurons expressing the cGMP scavenger protein sponge (inhibition of exocytosis reduced by 54% for isoflurane and by 53% for sevoflurane). The anesthetic-induced reduction in presynaptic excitability was partially occluded by inhibition of HCN channels, a cGMP-modulated excitatory ion channel that can facilitate glutamate release. We propose that volatile anesthetics depress presynaptic cGMP signaling and downstream effectors like HCN channels that are essential to presynaptic function and excitability. These findings identify novel mechanisms by which volatile anesthetics depress synaptic transmission via second messenger signaling involving the NO/cGMP pathway in hippocampal neurons.

Activation of a Vibrio cholerae CBASS anti-phage system by quorum sensing and folate depletion.

IMPORTANCE: To counteract infection with phage, bacteria have evolved a myriad of molecular defense systems. Some of these systems initiate a process called abortive infection, in which the infected cell kills itself to prevent phage propagation. However, such systems must be inhibited in the absence of phage infection to prevent spurious death of the host. Here, we show that the cyclic oligonucleotide based anti-phage signaling system (CBASS) accomplishes this by sensing intracellular folate molecules and only expressing this system in a group. These results enhance our understanding of the evolution of the seventh Vibrio cholerae pandemic and more broadly how bacteria defend themselves against phage infection.