cGAS-STING Signaling Pathway and Liver Disease: From Basic Research to Clinical Practice

Roles of cGAS-STING Pathway in Radiotherapy Combined with Immunotherapy for Hepatocellular Carcinoma

Although great strides have been made in the management and treatment of hepatocellular carcinoma (HCC), its prognosis is still poor yielding a high mortality. Immunotherapy is recommended for treating advanced HCC, but its efficiency is hampered because of hepatic immunosuppression. Stimulator of interferon genes (STING) pathway, serving as a critical cytoplasmic DNA-sensing process, is reported to initiate the antitumor immune response, and link the innate immunity to the adaptive immune system. Radiotherapy has been well acknowledged to induce destruction and release of tumor-derived DNA into the cytoplasm, which then activates the cGAS-STING pathway. On this basis, radiotherapy can be used as a sensitizer for immunotherapy, and its combination with immunotherapy may bring in changes to the suboptimal efficacy of immune checkpoint inhibitor monotherapy. In this review, we summarized the roles of cGAS-STING pathway in regulation of radiotherapy combined with immunotherapy for treating HCC.

The combination of Schisandrin C and Luteolin synergistically attenuates hepatitis B virus infection via repressing HBV replication and promoting cGAS-STING pathway activation in macrophages

BACKGROUND

HBV infection can result in severe liver diseases and is one of the primary causes of liver cell carcinoma-related mortality. Liuwei Wuling tablet (LWWL) is a traditional Chinese medicine formula, with a protecting liver and decreasing enzyme activity, usually used to treat chronic hepatitis B with NAs in clinic. However, its main active ingredients and mechanism of action have not been fully investigated. Hence, we aimed to screen the active ingredient and effective ingredient combinations from Liuwei Wuling tablet to explore the anti-herpatitis B virus activity and mechanism.

METHODS

Analysis and screening of effective antiviral components in LWWL by network pharmacology, luteolin (Lut) may be a compound with significant antiviral activity. The mechanism of antiviral action of Lut was also found by real-time PCR detection and western blotting. Meanwhile, we established a co-culture model to investigate the antiviral mechanism of Schisandrin C (SC), one of the main active components of Schisandra chinensis fructus (the sovereign drug of LWWL). Next, HBV-infected mice were established by tail vein injection of pAAV-HBV1.2 plasmid and administered continuously for 20 days. And their antiviral capacity was evaluated by checking serum levels of HBsAg, HBeAg, levels of HBV DNA, and liver levels of HBcAg.

RESULTS

In this study, we conducted network pharmacology analysis on LWWL, and through in vitro experimental validation and data analysis, we found that luteolin (Lut) possessed obviously anti-HBV activity, inhibiting HBV replication by downregulating hepatocyte nuclear factor 4α (HNF4α) via the ERK pathway. Additionally, we established a co-culture system and proved that SC promoted activation of cGAS-STINIG pathway and IFN-β production in THP-1 cells to inhibit HBV replication in HepG2.2.15 cells. Moreover, we found the combination of SC and Lut shows a greater effect in inhibiting HBV compared to SC or Lut alone in HBV-infected mice.

CONCLUSION

Taken together, our study suggests that combination of SC and Lut may be potential candidate drug for the prevention and treatment of chronic hepatitis B.

What are the common downstream molecular events between alcoholic and nonalcoholic fatty liver?

Liver fat storage, also called hepatic steatosis, is increasingly common and represents a very frequent diagnosis in the medical field. Excess fat is not without consequences. In fact, hepatic steatosis contributes to the progression toward liver fibrosis. There are two main types of fatty liver disease, alcoholic fatty liver disease (AFLD) and nonalcoholic fatty liver disease (NAFLD). Although AFLD and NAFLD are similar in their initial morphological features, both conditions involve the same evolutive forms. Moreover, there are various common mechanisms underlying both diseases, including alcoholic liver disease and NAFLD, which are commonalities. In this Review, the authors explore similar downstream signaling events involved in the onset and progression of the two entities but not completely different entities, predominantly focusing on the gut microbiome. Downstream molecular events, such as the roles of sirtuins, cytokeratins, adipokines and others, should be considered. Finally, to complete the feature, some new tendencies in the therapeutic approach are presented.

Current and Future States of Natural Killer Cell-Based Immunotherapy in Hepatocellular Carcinoma

Natural killer (NK) cells are innate lymphoid cells that exhibit high levels of cytotoxicity against NK-specific targets. NK cells also produce various cytokines, and interact with T cells, B cells, and dendritic cells to effectively serve as frontliners of the innate immune system. Produce various cytokines, and interact with T cells, B cells, and dendritic cells to effectively serve as frontliners of the innate immune system. Moreover, NK cells constitute the second most common immune cell in the liver. These properties have drawn significant attention towards leveraging NK cells in treating liver cancer, especially hepatocellular carcinoma (HCC), which accounts for 75% of all primary liver cancer and is the fourth leading cause of cancer-related death worldwide. Notable anti-cancer functions of NK cells against HCC include activating antibody-dependent cell cytotoxicity (ADCC), facilitating Gasdermin E-mediated pyroptosis of HCC cells, and initiating an antitumor response via the cGAS-STING signaling pathway. In this review, we describe how these mechanisms work in the context of HCC. We will then discuss the existing preclinical and clinical studies that leverage NK cell activity to create single and combined immunotherapies.

STING1 deficiency ameliorates immune-mediated crescentic glomerulonephritis in mice

Rapidly progressive/crescentic glomerulonephritis (RPGN/CGN) involves the formation of glomerular crescents by maladaptive differentiation of parietal epithelial cells that leads to rapid loss of renal function. The molecular mechanisms of crescent formation are poorly understood. Therefore, new insights into molecular mechanisms could identify alternative therapeutic targets for RPGN/CGN. Analysis of kidney biopsies from patients with RPGN revealed increased interstitial, glomerular, and tubular expression of STING1, an accessory protein of the c-GAS-dependent DNA-sensing pathway, which was also observed in murine nephrotoxic nephritis induced by an anti-GBM antibody. STING1 was expressed by key cell types involved in RPGN and crescent formation such as glomerular parietal epithelial cells, and tubular cells as well as by inflammation accessory cells. In functional in vivo studies, Sting1-/- mice with nephrotoxic nephritis had lower kidney cytokine expression, milder kidney infiltration by innate and adaptive immune cells, and decreased disease severity. Pharmacological STING1 inhibition mirrored these findings. Direct STING1 agonism in parietal and tubular cells activated the NF-κB-dependent cytokine response and the interferon-induced genes (ISGs) program. These responses were also triggered in a STING1-dependent manner by the pro-inflammatory cytokine TWEAK. These results identify STING1 activation as a pathological mechanism in RPGN/CGN and TWEAK as an activator of STING1. Pharmacological strategies targeting STING1, or upstream regulators may therefore be potential alternatives to treat RPGN. © 2023 The Pathological Society of Great Britain and Ireland.

Therapeutic Potential of Biochanin A in Herpes Simplex Keratitis

Herpes simplex keratitis (HSK) is a blinding eye disease that is initiated by the herpes simplex virus type 1 (HSV-1). Resistance to acyclovir (ACV) and the side effects of corticosteroid drugs have become concerning issues, so it is crucial to develop new antivirals for treating HSK. In this study, we report that biochanin A (BCA), a naturally occurring flavonoid compound, provides multifaceted protective effects with anti-viral, anti-inflammatory, anti-oxidative stress and anti-apoptotic activities to alleviate HSK. The results show that BCA significantly inhibited HSV-1 replication in vitro and further proved that BCA principally influenced the early stage of virus infection. We reveal that BCA downregulated the expression of pro-inflammatory factors triggered by HSV-1, including TNF-α, RANTES, IL-1β and IL-6. Furthermore, BCA treatment alleviated oxidative stress and apoptotic arising from HSV-1 infection. Lastly, we induced HSK in male C57BL/6 mice and treated them with either BCA or phosphate buffer solution (PBS) eye drops. We observed the ocular surface lesions; determined the virus load in the tear fluid, corneas as well as trigeminal ganglions (TGs); and detected the levels of inflammation and apoptosis in the corneas simultaneously. These results show that BCA inhibits HSV-1 and alleviates the corneal lesion degree. Our study illustrates that BCA is a promising therapeutic approach for application in treating HSK.

The cGAS-STING pathway in diabetic retinopathy and age-related macular degeneration

Diabetic retinopathy and age-related macular degeneration are common retinal diseases with shared pathophysiology, including oxidative stress-induced inflammation. Cellular mechanisms responsible for converting oxidative stress into retinal damage are ill-defined but have begun to clarify. One common outcome of retinal oxidative stress is mitochondrial damage and subsequent release of mitochondrial DNA into the cytosol. This leads to activation of the cGAS-STING pathway, resulting in interferon release and disease-amplifying inflammation. This review summarizes the evolving link between aberrant cGAS-STING signaling and inflammation in common retinal diseases and provides prospective for targeting this system in diabetic retinopathy and age-related macular degeneration. Further defining the roles of this system in the retina is expected to reveal new disease pathology and novel therapeutic approaches.

Expression of STING in Women with Morbid Obesity and Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is the most prevalent chronic hepatic disease. Although mostly benign, this disease can evolve into nonalcoholic steatohepatitis (NASH). The stimulator of interferon genes (STING) plays an important role in the immune response against stressed cells, but this protein may also be involved in liver lipogenesis and microbiota composition. In this study, the role of STING in NAFLD was evaluated by RT–qPCR to analyze STING mRNA abundance and by immunohistochemical analysis to evaluate protein expression in liver biopsies from a cohort composed of 69 women with morbid obesity classified according to their liver involvement (normal liver, n = 27; simple steatosis (SS), n = 26; NASH, n = 16). The results showed that STING mRNA expression in the liver increases with the occurrence of NAFLD, specifically in the SS stage in which the degree of steatosis is mild or moderate. Protein analysis corroborated these results. Positive correlations were observed among hepatic STING mRNA abundance and gamma-glutamyl transferase and alkaline phosphatase levels, hepatic Toll-like receptor 9 expression and some circulating microbiota-derived bile acids. In conclusion, STING may be involved in the outcome and progression of NAFLD and may be related to hepatic lipid metabolism. However, further studies are needed to confirm these findings.

Role of the cGAS-STING Pathway in Aging-related Endothelial Dysfunction

Endothelial dysfunction develops gradually with age, and is the foundation of many age-related diseases in the elderly. The purpose of this study was to investigate the role of the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway in aging-related endothelial dysfunction. Endothelial functional parameters and biochemical indices of vascular function were examined in 2-, 6-, 12- and 24-month-old mice. Then, 6-month-old mice were administered RU.521, a specific inhibitor of cGAS, for 6 months, and endothelial functional parameters and biochemical indices of vascular function were re-examined. An in vitro model of cell senescence was established by treating human aortic endothelial cells (HAECs) with D-Galactose (D-GAL). Using inhibitors or siRNA interference, cGAS and STING were suppressed or silenced in senescent HAECs, and changes in the expression of eNOS, the senescence markers, p53, p21 and p16, components of the cGAS-STING pathway and Senescence-Associated β-galactosidase (SA-β-gal) staining were examined. Finally, cGAS, STING and p-IRF3 levels were measured in aorta tissue sections from eight patients. A decline in endothelial function, up-regulation of p53, p21 and p16 expression, and activation of the cGAS-STING pathway were observed in aging mice. Inhibition of cGAS was found to improve endothelial function and reverse the increased expression of aging markers. Our in vitro data demonstrated that D-GAL induced a decrease in eNOS expression and cell senescence, which could be partly reversed by cGAS inhibitor, STING inhibitor, siRNA-cGAS and siRNA-STING treatment. Higher expression levels of cGAS, STING and p-IRF3 were observed in aged human aortic intima tissue compared to young aortic intima tissue. Our study demonstrated that activation of the cGAS-STING pathway played a vital role in aging-related endothelial dysfunction. Thus, the cGAS-STING pathway may be a potential target for the prevention of cardiovascular diseases in the elderly.

Loss of Sam50 in hepatocytes induces cardiolipin-dependent mitochondrial membrane remodeling to trigger mtDNA release and liver injury

BACKGROUND AND AIMS

Sam50, a key component of the sorting and assembly machinery (SAM) complex, is also involved in bridging mitochondrial outer-membrane and inner-membrane contacts. However, the physiological and pathological functions of Sam50 remain largely unknown.

APPROACH AND RESULTS

Here we show that Sam50 interacts with MICOS (mitochondrial contact site and cristae organizing system) and ATAD3 (ATPase family AAA domain-containing protein 3) to form the Sam50-MICOS-ATAD3-mtDNA axis, which maintains mtDNA stability. Loss of Sam50 causes mitochondrial DNA (mtDNA) aggregation. Furthermore, Sam50 cooperates with Mic60 to bind to cardiolipin, maintaining the integrity of mitochondrial membranes. Sam50 depletion leads to cardiolipin externalization, which causes mitochondrial outer-membrane and inner-membrane (including crista membrane) remodeling, triggering Bax mitochondrial recruitment, mtDNA aggregation, and release. Physiologically, acetaminophen (an effective antipyretic and analgesic)-caused Sam50 reduction or Sam50 liver-specific knockout induces mtDNA release, leading to activation of the cGAS-STING pathway and liver inflammation in mice. Moreover, exogenous expression of Sam50 remarkably attenuates APAP-induced liver hepatoxicity.

CONCLUSIONS

Our findings uncover the critical role of Sam50 in maintaining mitochondrial membrane integrity and mtDNA stability in hepatocytes and reveal that Sam50 depletion-induced cardiolipin externalization is a signal of mtDNA release and controls mtDNA-dependent innate immunity.

PCBP2 Reduced Oxidative Stress-Induced Apoptosis in Glioma through cGAS/STING Pathway by METTL3-Mediated m6A Modification

Purpose

The most prevalent primary malignant tumor of CNS is glioma, which has a dismal prognosis. The theory of oxidative stress is one of the important theories in the study of its occurrence and development mechanism. In this study, the impacts of PCBP2 on glioma sufferers and the possible mechanisms were examined.

Methods

Patients with glioma were obtained from May 2017 to July 2018. Quantitative PCR, microarray analysis, western blot analysis, and immunofluorescence were used in this experiment.

Results

PCBP2 mRNA expression level and protein expression in patients with glioma were upregulated compared with paracancerous tissue. OS and DFS of PCBP2 low expression in patients with glioma were higher than those of PCBP2 high expression. PCBP2 promoted the progression and metastasis of glioma. PCBP2 reduced oxidative stress-induced apoptosis of glioma. PCBP2 suppressed the cGAS/STING pathway of glioma. PCBP2 protein interlinked with cGAS and cGAS was one target for PCBP2. METTL3-mediated m6A modification increases PCBP2 stability.

Conclusion

Along the cGAS-STING signal pathway, PCBP2 decreased the apoptosis that oxidative stress-induced glioma caused, which might be a potential target to suppress oxidative stress-induced apoptosis of glioma.

Regulation of cGAS Activity and Downstream Signaling

Cyclic GMP-AMP synthase (cGAS) is a predominant and ubiquitously expressed cytosolic onfirmedDNA sensor that activates innate immune responses by producing a second messenger, cyclic GMP-AMP (cGAMP), and the stimulator of interferon genes (STING). cGAS contains a highly disordered N-terminus, which can sense genomic/chromatin DNA, while the C terminal of cGAS binds dsDNA liberated from various sources, including mitochondria, pathogens, and dead cells. Furthermore, cGAS cellular localization dictates its response to foreign versus self-DNA. Recent evidence has also highlighted the importance of dsDNA-induced post-translational modifications of cGAS in modulating inflammatory responses. This review summarizes and analyzes cGAS activity regulation based on structure, sub-cellular localization, post-translational mechanisms, and Ca²⁺ signaling. We also discussed the role of cGAS activation in different diseases and clinical outcomes.

Role of STING signaling pathway in liver diseases

The cGAS-STING signaling pathway is an important part of the innate immune system, which could trigger the expression of a series of inflammatory factors represented by interferon type 1 (IFN-1). This pathway plays an important role in many diseases such as infectious diseases, autoimmune diseases, and tumors. In recent years, it has been found that the cGAS-STING signaling pathway is important in the physiological and pathological processes of the liver, and is closely related to the progression of liver diseases. This paper reviews the role of the cGAS-STING signaling pathway in common liver diseases such as chronic hepatitis B, alcoholic liver disease, nonalcoholic fatty liver disease, and liver cancer, as well as its application in the treatment of liver diseases.

Regulation of Pattern-Recognition Receptor Signaling by HBX During Hepatitis B Virus Infection

As a small DNA virus, hepatitis B virus (HBV) plays a pivotal role in the development of various liver diseases, including hepatitis, cirrhosis, and liver cancer. Among the molecules encoded by this virus, the HBV X protein (HBX) is a viral transactivator that plays a vital role in HBV replication and virus-associated diseases. Accumulating evidence so far indicates that pattern recognition receptors (PRRs) are at the front-line of the host defense responses to restrict the virus by inducing the expression of interferons and various inflammatory factors. However, depending on HBX, the virus can control PRR signaling by modulating the expression and activity of essential molecules involved in the toll-like receptor (TLR), retinoic acid inducible gene I (RIG-I)-like receptor (RLR), and NOD-like receptor (NLR) signaling pathways, to not only facilitate HBV replication, but also promote the development of viral diseases. In this review, we provide an overview of the mechanisms that are linked to the regulation of PRR signaling mediated by HBX to inhibit innate immunity, regulation of viral propagation, virus-induced inflammation, and hepatocarcinogenesis. Given the importance of PRRs in the control of HBV replication, we propose that a comprehensive understanding of the modulation of cellular factors involved in PRR signaling induced by the viral protein may open new avenues for the treatment of HBV infection.

Novel Molecular Therapeutics Targeting Signaling Pathway to Control Hepatitis B Viral Infection

Numerous canonical cellular signaling pathways modulate hepatitis B virus (HBV) replication. HBV genome products are known to play a significant role in regulating these cellular pathways for the liver’s viral-related pathology and physiology and have been identified as the main factor in hepatocarcinogenesis. Signaling changes during viral replication ultimately affect cellular persistence, multiplication, migration, genome instability, and genome damage, leading to proliferation, evasion of apoptosis, block of differentiation, and immortality. Recent studies have documented that numerous signaling pathway agonists or inhibitors play an important role in reducing HBV replication in vitro and in vivo, and some have been used in phase I or phase II clinical trials. These optional agents as molecular therapeutics target cellular pathways that could limit the replication and transcription of HBV or inhibit the secretion of the small surface antigen of HBV in a signaling-independent manner. As principle-based available information, a combined strategy including antiviral therapy and immunomodulation will be needed to control HBV infection effectively. In this review, we summarize recent findings on interventions of molecular regulators in viral replication and the interactions of HBV proteins with the components of the various targeting cellular pathways, which may assist in designing novel agents to modulate signaling pathways to prevent HBV replication or carcinogenesis.

Involvement of STING signaling pathway in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is one of the major chronic liver diseases worldwide, which seriously threatens human health and has become a major public health problem. Immune mechanism plays a key role in the occurrence and development of NAFLD. Interferon gene stimulating factor (STING) is a key connector protein of the immune system, and its related signaling pathway has become a recent hot research topic. This signaling pathway may be involved in the occurrence and development of NAFLD by mediating liver inflammation, lipid metabolism, apoptosis, and other processes that affect liver metabolic homeostasis. Combining relevant reports and the latest literature, this paper reviews NAFLD and immunity, the composition of STING signaling pathway, and the relationship between the STING signaling pathway and NAFLD, in order to provide ideas for further in-depth study of the complex relationship between the STING signaling pathway and NAFLD and the development of relevant targeted drugs.