STING and liver disease

A heterogeneous subtype of biliary epithelial senescence may be involved in the pathogenesis of primary biliary cholangitis

BACKGROUND & AIMS

Biliary epithelial senescence is involved in the pathogenesis of primary biliary cholangitis (PBC). We hypothesized that a unique subtype of programmed death-ligand 1 (PD-L1)-positive senescent biliary epithelial cells (BECs) may be related to the pathogenesis of PBC in association with cyclic GMP-AMP synthase (cGAS)- stimulator of interferon genes (STING) pathway.

APPROACH & RESULTS

The expression of PD-L1, STING and their association with senescent markers p16INK4a and p21WAF1/Cip1 were immunohistochemically determined in livers taken from the patients with PBC (n = 87) and 97 diseased and normal control livers. The expression of PD-L1 was significantly increased in a part of senescent BECs with p21WAF1/Cip1 expression in BECs in the damaged small bile ducts in PBC, compared to control livers (p < 0.01). In contrast, PD-L1 was not expressed in BECs in ductular reactions. The expression of STING was significantly increased in BECs in small bile ducts and ductular reactions in PBC, compared to control livers (p < 0.01). The expression of PD-L1, STING and senescence associated secretory phenotypes (SASPs) including interferon (IFN)-beta was significantly increased in senescent BECs induced by a treatment with serum depletion or glycochenodeoxycholic acid (GCDC) for 4-7 days (p < 0.01) and the increase was significantly suppressed by a knockdown of STING using siRNA (p < 0.01). Induction of cellular senescence induced by a treatment with serum depletion or GCDC was significantly suppressed by a knockdown of STING in BECs. (p < 0.01).

CONCLUSION

A unique subtype of senescent BECs with PD-L1 expression associated with cGAS-STING pathway may be involved in the pathogenesis of PBC.

The role of cGAS-STING signaling pathway in ferroptosis

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway has been identified as a crucial mechanism in antiviral defense and innate immunity pathway. Ferroptosis, characterized by iron dependence and lipid peroxidation, represents a specialized form of cell death. A burgeoning collection of studies has demonstrated that the cGAS-STING signaling pathway participates in the homeostatic regulation of the organism by modulating ferroptosis-associated enzyme activity or gene expression. Consequently, elucidating the specific roles of the STING signaling pathway and ferroptosis in vivo is vital for targeted disease intervention. This review systematically examines the interactions between the cGAS-STING signaling pathway and ferroptosis, highlighting their influence on disease progression in the contexts of inflammation, injury, and cancerous cell dynamics. Understanding these interactions may provide novel therapeutic strategies. The STING pathway has been implicated in the regulation of various cell death mechanisms, including apoptosis, pyroptosis, necroptosis, autophagy, and ferroptosis. Our focus primarily addresses the role and mechanism of the cGAS-STING signaling pathway and ferroptosis in diseases, limiting discussion of other cell death modalities and precluding a comprehensive overview of the pathway's additional functions.

Mesenchymal stem cells alleviate autoimmune thyroiditis by modulating macrophage phenotypes and through influencing the STING pathway

BACKGROUND

Hashimoto's thyroiditis is a chronic autoimmune inflammatory disease with a high prevalence and currently lacks effective treatment options. Previous preclinical and clinical trials have established mesenchymal stem cells (MSCs) as a promising therapeutic approach; however, there is limited research on MSC treatment for Hashimoto's thyroiditis, and the underlying molecular mechanisms remain unclear.

METHODS

MSCs isolated from 4 to 6-week-old Lewis rats were employed for thyroiditis treatment. The efficacy of MSCs was assessed through histological and serological parameters. Molecular mechanisms of MSC therapy for Hashimoto's thyroiditis were explored by examining macrophage presence within thyroid tissue and relevant pathways.

RESULTS

In this study, we observed elevated oxidative stress and endoplasmic reticulum stress within the thyroid tissue of Hashimoto's thyroiditis patients, and MSC therapy effectively mitigated this process. Furthermore, we found that the therapeutic potential of MSCs in the EAT model depended on the STING pathway. MSCs reduced endoplasmic reticulum stress and inflammasome levels within the thyroid tissue by modulating the STING pathway. Additionally, MSCs inhibited the expression of IRE1α in thyroid tissue macrophages, thereby reducing the polarization of M1-type macrophages CONCLUSIONS: The STING pathway appears to be a crucial mechanism by which MSCs modulate macrophage polarization in thyroid tissue, offering a potential treatment for thyroiditis.

Activation of α7 Nicotinic Acetylcholine Receptors Inhibits Hepatic Necroptosis and Ameliorates Acute Liver Injury in Mice

BACKGROUND

Acute liver injury is a disease characterized by severe liver dysfunction, caused by significant infiltration of immune cells and extensive cell death with a high mortality. Previous studies demonstrated that the α7 nicotinic acetylcholine receptor (α7nAChR) played a crucial role in various liver diseases. The hypothesis of this study was that activating α7nAChR could alleviate acute liver injury and investigate its possible mechanisms.

METHODS

Acute liver injury was induced by intraperitoneal injection of lipopolysaccharide (LPS)/D-galactosamine (D-Gal) in wild type, α7nAChR knockout (α7nAChR-/-) and stimulator of interferon gene (STING) mutation (Stinggt/gt) mice in the presence or absence of a pharmacologic selective α7nAChR agonist (PNU-282987). The effects of α7nAChR on hepatic injury, inflammatory response, mitochondrial damage, necroptosis, and infiltration of immune cells during acute liver injury were assessed.

RESULTS

The expression of α7nAChR in liver tissue was increased in LPS/D-Gal-induced acute liver injury mice. Compared to the age-matched wild-type mice, α7nAChR deficiency decreased the survival rate, exacerbated the hepatic injury accompanied with enhanced inflammatory response and oxidative stress, and aggravated hepatic mitochondrial damage and necroptosis. Conversely, pharmacologic activation of α7nAChR by PNU-282987 displayed the opposite trends. Furthermore, PNU-282987 significantly reduced the proportion of infiltrating monocyte-derived macrophages (CD45+CD11bhiF4/80int), M1 macrophages (CD45+CD11b+F4/80+CD86hiCD163low), and Ly6Chi monocytes (CD45+CD11b+MHC [major histocompatibility complex] ⅡlowLy6Chi), but increased the resident Kupffer cells (CD45+CD11bintF4/80hiTIM4hi) in the damaged hepatic tissues caused by LPS/D-Gal. Interestingly, α7nAChR deficiency promoted the STING signaling pathway under LPS/D-Gal stimulation, while PNU-282987 treatment significantly prevented its activation. Finally, it was found that Sting mutation abolished the protective effects against hepatic injury by activating α7nAChR.

CONCLUSIONS

The authors' study revealed that activating α7nAChR could protect against LPS/D-Gal-induced acute liver injury by inhibiting hepatic inflammation and necroptosis possibly via regulating immune cells infiltration and inhibiting STING signaling pathway.

EDITOR’S PERSPECTIVE

Characterizing the Distribution of a Stimulator of Interferon Genes Agonist and Its Metabolites in Mouse Liver by Matrix-Assisted Laser Desorption/Ionization Imaging Mass Spectrometry

A STING (stimulator of interferon genes) agonist GSK3996915 under investigation in early discovery for hepatitis B was orally dosed to a mouse model for understanding the parent drug distribution in liver, the target organ. Matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS) was used to quantify the distribution of GSK3996915 in liver collected from mice administered a single oral dose at 90 mg/kg. GSK3996915 was detected with a zonal distribution localized in the portal triad and highly concentrated in the main bile ducts, indicating clearance through biliary excretion. High spatial resolution imaging showed the distribution of the parent drug localized to the cellular populations in the sinusoids, including the Kupffer cells. Additionally, a series of drug-related metabolites were observed to be localized in the central zones of the liver. These results exemplify the potential of utilizing MALDI IMS for measuring not only quantitative drug distribution and target exposure but also drug metabolism and elimination in a single suite of experiments. SIGNIFICANCE STATEMENT: An integrated imaging approach utilizing matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI IMS) complemented with immunohistochemistry (IHC) and histology was used to address the question of target exposure at the cellular level. Localized quantification of the parent drug in the target organ and identification of potential metabolites in the context of tissue histology were also achieved in one experimental suite to support characterization of pharmacokinetic properties of the drug in the early discovery stage.

Evaluating the therapeutic potential of genetically engineered probiotic Zbiotics (ZB183) for non-alcoholic steatohepatitis (NASH) management via modulation of the cGAS-STING pathway

NAFLD/NASH has emerged as a global health concern with no FDA-approved treatment, necessitating the exploration of novel therapeutic elements for NASH. Probiotics are known as an important adjunct therapy in NASH. Zbiotics (ZB183) is the first commercially available genetically engineered probiotic. Herein, we aimed to evaluate the potential therapeutic effects of Zbiotics administration on NASH management by modulating the cGAS-STING-signaling pathway-related RNA network. In silico data analysis was performed and three DEGs (MAPK3/EDN1/TNF) were selected with their epigenetic modulators (miR-6888-5p miRNA, and lncRNA RABGAP1L-DT-206). The experimental design included NASH induction with an HSHF diet in Wistar rats and Zbiotics administration in NASH rats in comparison to statin treatment. Liver functions and lipid profile were assessed. Additionally, the expression levels of the constructed molecular network were assessed using RT-PCR. Moreover, the Zbiotics effects in NASH were further validated with histopathological examination of liver and colon samples. Also, immunohistochemistry staining of hepatic TNF-α and colonic occludin was assessed. Oral administration of Zbiotics for four weeks downregulated the expression of the cGAS-STING-related network (MAPK3/EDN1/TNF/miR-6888-5p miRNA/lncRNA RABGAP1L-DT-206) in NASH models. Zbiotics also ameliorated hepatic inflammation and steatosis, as evidenced by a notable improvement in NAS score and decreased hepatic TNF-α levels. Furthermore, Zbiotics exhibited favorable effects on colon health, including increased crypt length, reduced inflammatory cell infiltration, and restoration of colonic mucosa occludin expression. In conclusion, our findings suggest that Zbiotics has potential therapeutic effects on NASH via modulating the gut-liver axis and the cGAS-STING signaling pathway.

Comparative effects of 3,5-diiodo-L-thyronine and 3,5,3'-triiodo-L-thyronine on mitochondrial damage and cGAS/STING-driven inflammation in liver of hypothyroid rats

Maintaining a well-functioning mitochondrial network through the mitochondria quality control (MQC) mechanisms, including biogenesis, dynamics and mitophagy, is crucial for overall health. Mitochondrial dysfunction caused by oxidative stress and further exacerbated by impaired quality control can trigger inflammation through the release of the damage-associated molecular patterns (mtDAMPs). mtDAMPs act by stimulating the cyclic GMP-AMP synthase (cGAS) stimulator of interferon genes (STING) pathway. Recently, aberrant signalling of the cGAS-STING axis has been recognised to be closely associated with several sterile inflammatory diseases (e.g. non-alcoholic fatty liver disease, obesity). This may fit the pathophysiology of hypothyroidism, an endocrine disorder characterised by the reduction of thyroid hormone production associated with impaired metabolic fluxes, oxidative balance and inflammatory status. Both 3,5,3'-triiodo-L-tyronine (T3) and its derivative 3,5-diiodo-L-thyronine (3,5-T2), are known to mitigate processes targeting mitochondria, albeit the underlying mechanisms are not yet fully understood. Therefore, we used a chemically induced hypothyroidism rat model to investigate the effect of 3,5-T2 or T3 administration on inflammation-related factors (inflammatory cytokines, hepatic cGAS-STING pathway), oxidative stress, antioxidant defence enzymes, mitochondrial DNA (mtDNA) damage, release and repair, and the MQC system in the liver. Hypothyroid rats showed: i) increased oxidative stress, ii) accumulation of mtDNA damage, iii) high levels of circulating cytokines, iv) hepatic activation of cGAS-STING pathways and v) impairment of MQC mechanisms and autophagy. Both iodothyronines restored oxidative balance by enhancing antioxidant defence, preventing mtDNA damage through the activation of mtDNA repair mechanisms (OGG1, APE1, and POLγ) and promoting autophagy progression. Concerning MQC, both iodothyronines stimulated mitophagy and dynamics, with 3,5-T2 activating fusion and T3 modulating both fusion and fission processes. Moreover, only T3 enhanced mitochondrial biogenesis. Notably, 3,5-T2, but not T3, reversed the hypothyroidism-induced activation of the cGAS-STING inflammatory cascade. In addition, it is noteworthy that 3,5-T2 seems more effective than T3 in reducing circulating pro-inflammatory cytokines IL-6 and IL-1B and in stimulating the release of IL-10, a known anti-inflammatory cytokine. These findings reveal novel molecular mechanisms of hepatic signalling pathways involved in hypothyroidism, which could be targeted by natural iodothyronines, particularly 3,5-T2, paving the way for the development of new treatment strategies for inflammatory diseases.

Cocaine-derived hippuric acid activates mtDNA-STING signaling in alcoholic liver disease: Implications for alcohol and cocaine co-abuse

The simultaneous abuse of alcohol-cocaine is known to cause stronger and more unpredictable cellular damage in the liver, heart, and brain. However, the mechanistic crosstalk between cocaine and alcohol in liver injury remains unclear. The findings revealed cocaine-induced liver injury and inflammation in both marmosets and mice. Of note, co-administration of cocaine and ethanol in mice causes more severe liver damage than individual treatment. The metabolomic analysis confirmed that hippuric acid (HA) is the most abundant metabolite in marmoset serum after cocaine consumption and that is formed in primary marmoset hepatocytes. HA, a metabolite of cocaine, increases mitochondrial DNA leakage and subsequently increases the production of proinflammatory factors via STING signaling in Kupffer cells (KCs). In addition, conditioned media of cocaine-treated KC induced hepatocellular necrosis via alcohol-induced TNFR1. Finally, disruption of STING signaling in vivo ameliorated co-administration of alcohol- and cocaine-induced liver damage and inflammation. These findings postulate intervention of HA-STING-TNFR1 axis as a novel strategy for treatment of alcohol- and cocaine-induced excessive liver damage.

cGAS-STING, an important signaling pathway in diseases and their therapy

Since cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway was discovered in 2013, great progress has been made to elucidate the origin, function, and regulating mechanism of cGAS-STING signaling pathway in the past decade. Meanwhile, the triggering and transduction mechanisms have been continuously illuminated. cGAS-STING plays a key role in human diseases, particularly DNA-triggered inflammatory diseases, making it a potentially effective therapeutic target for inflammation-related diseases. Here, we aim to summarize the ancient origin of the cGAS-STING defense mechanism, as well as the triggers, transduction, and regulating mechanisms of the cGAS-STING. We will also focus on the important roles of cGAS-STING signal under pathological conditions, such as infections, cancers, autoimmune diseases, neurological diseases, and visceral inflammations, and review the progress in drug development targeting cGAS-STING signaling pathway. The main directions and potential obstacles in the regulating mechanism research and therapeutic drug development of the cGAS-STING signaling pathway for inflammatory diseases and cancers will be discussed. These research advancements expand our understanding of cGAS-STING, provide a theoretical basis for further exploration of the roles of cGAS-STING in diseases, and open up new strategies for targeting cGAS-STING as a promising therapeutic intervention in multiple diseases.

Update on the STING Signaling Pathway in Developing Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a prevalent chronic liver condition with limited treatment options. Inflammation caused by metabolic disturbances plays a significant role in NAFLD development. Stimulator of interferon gene (STING), a critical regulator of innate immunity, induces the production of interferons and other pro-inflammatory factors by recognizing cytoplasmic DNA to defend against pathogen infection. The STING-mediated signaling pathway appears to play a vital role in hepatic inflammation, metabolic disorders, and even carcinogenesis. Promisingly, pharmacological interventions targeting STING have shown improvements in the pathological state of NAFLD. Macrophages, dendritic cells, natural killer cells, and T cell pathways regulated by STING present potential novel druggable targets for NAFLD treatment. Further research and development in this area may offer new therapeutic options for managing NAFLD effectively.

STING modulates iron metabolism to promote liver injury and inflammation in acute immune hepatitis

The pathogenesis of Autoimmune Hepatitis (AIH) is closely associated with perturbations in iron ion metabolism, during which Stimulator of Interferon Genes (STING) plays an important role. However, the precise regulatory mechanism remains elusive. In this study, we investigated the relationship between iron dysregulation and STING activation in Concanavalin A (ConA)-induced AIH liver injury. STING knockout (STING-/-) mice and AAV (Adeno-Associated virus)-Sting1-RNAi-treated mice were involved and subjected in AIH. We observed that increased iron dysregulation was linked with STING activation, but this effect was effectively reversed by the administration of iron chelating agent Desferoxamine (DFO) and the antioxidant Ferrostatin-1 (Fer-1). Notably, the iron transport protein Transferrin (TF) and Transferrin Receptor (TfR) exhibited significant accumulation in AIH along with upregulated expression of ferritin protein. Additionally, the deficiency of STING reduced hepatic iron accumulation, mitigated oxidative stress, and attenuated macrophage activation during ConA treatment. Furthermore, liver-specific knockdown of STING using AAV-Sting1-RNAi significantly ameliorated liver iron dysregulation and oxidative stress response induced by Kupffer cells (KCs). KC-derived STING exacerbates liver damage severity in AIH through promoting disturbances in hepatic iron ion metabolism as well as oxidative stress response. These findings provide valuable insights into the pathogenesis of AIH and may pave the way for potential therapeutic strategies targeting STING and iron metabolism in the future.

Chemical Biology Perspectives on STING Agonists as Tumor Immunotherapy

Stimulator of interferon genes (STING) is a crucial adaptor protein in the innate immune response. STING activation triggers cytokine secretion, including type I interferon and initiates T cell-mediated adaptive immunity. The activated immune system converts "cold tumors" into "hot tumors" that are highly responsive to T cells by recruiting them to the tumor microenvironment, ultimately leading to potent and long-lasting antitumor effects. Unlike most immune checkpoint inhibitors, STING agonists represent a groundbreaking class of innate immune agonists that hold great potential for effectively targeting various cancer populations and are poised to become a blockbuster in tumor immunotherapy. This review will focus on the correlation between the STING signaling pathway and tumor immunity, as well as explore the impact of STING activation on other biological processes. Ultimately, we will summarize the development and optimization of STING agonists from a medicinal chemistry perspective, evaluate their potential in cancer therapy, and identify possible challenges for future advancement.

Competition for calnexin binding regulates secretion and turnover of misfolded GPI-anchored proteins

In mammalian cells, misfolded glycosylphosphatidylinositol (GPI)-anchored proteins (GPI-APs) are cleared out of the ER to the Golgi via a constitutive and a stress-inducible pathway called RESET. From the Golgi, misfolded GPI-APs transiently access the cell surface prior to rapid internalization for lysosomal degradation. What regulates the release of misfolded GPI-APs for RESET during steady-state conditions and how this release is accelerated during ER stress is unknown. Using mutants of prion protein or CD59 as model misfolded GPI-APs, we demonstrate that inducing calnexin degradation or upregulating calnexin-binding glycoprotein expression triggers the release of misfolded GPI-APs for RESET. Conversely, blocking protein synthesis dramatically inhibits the dissociation of misfolded GPI-APs from calnexin and subsequent turnover. We demonstrate an inverse correlation between newly synthesized calnexin substrates and RESET substrates that coimmunoprecipitate with calnexin. These findings implicate competition by newly synthesized substrates for association with calnexin as a key factor in regulating the release of misfolded GPI-APs from calnexin for turnover via the RESET pathway.

Stimulator of Interferon Genes (STING) Triggers Adipocyte Autophagy

Innate immune signaling in adipocytes affects systemic metabolism. Cytosolic nucleic acid sensing has been recently shown to stimulate thermogenic adipocyte differentiation and protect from obesity; however, DNA efflux from adipocyte mitochondria is a potential proinflammatory signal that causes adipose tissue dysfunction and insulin resistance. Cytosolic DNA activates the stimulator of interferon response genes (STING), a key signal transducer which triggers type I interferon (IFN-I) expression; hence, STING activation is expected to induce IFN-I response and adipocyte dysfunction. However, we show herein that mouse adipocytes had a diminished IFN-I response to STING stimulation by 2'3'-cyclic-GMP-AMP (cGAMP). We also show that cGAMP triggered autophagy in murine and human adipocytes. In turn, STING inhibition reduced autophagosome number, compromised the mitochondrial network and caused inflammation and fat accumulation in adipocytes. STING hence stimulates a process that removes damaged mitochondria, thereby protecting adipocytes from an excessive IFN-I response to mitochondrial DNA efflux. In summary, STING appears to limit inflammation in adipocytes by promoting mitophagy under non-obesogenic conditions.

Small-molecule chemical probes for the potential therapeutic targets in alcoholic liver diseases

Alcoholic liver disease (ALD) encompasses a range of conditions resulting from prolonged and excessive alcohol consumption, causing liver damage such as alcoholic fatty liver, inflammation, fibrosis, and cirrhosis. Alcohol consumption contributes to millions of deaths each year. So far, the effective treatments for ALD are limited. To date, the most effective treatment for ALD is still prevention by avoiding excessive alcohol consumption, and only few specialized medicines are in the market for the treatment of patients suffering from ALD. Small molecules targeting various pathways implicated in ALD pathogenesis can potentially be used for effective therapeutics development. In this review, we provide a concise overview of the latest research findings on potential therapeutic targets, specifically emphasizing small-molecule interventions for the treatment and prevention of ALD.

Unleashing the efficacy of immune checkpoint inhibitors for advanced hepatocellular carcinoma: factors, strategies, and ongoing trials

Hepatocellular carcinoma (HCC) is a prevalent primary liver cancer, representing approximately 85% of cases. The diagnosis is often made in the middle and late stages, necessitating systemic treatment as the primary therapeutic option. Despite sorafenib being the established standard of care for advanced HCC in the past decade, the efficacy of systemic therapy remains unsatisfactory, highlighting the need for novel treatment modalities. Recent breakthroughs in immunotherapy have shown promise in HCC treatment, particularly with immune checkpoint inhibitors (ICIs). However, the response rate to ICIs is currently limited to approximately 15%-20% of HCC patients. Recently, ICIs demonstrated greater efficacy in "hot" tumors, highlighting the urgency to devise more effective approaches to transform "cold" tumors into "hot" tumors, thereby enhancing the therapeutic potential of ICIs. This review presented an updated summary of the factors influencing the effectiveness of immunotherapy in HCC treatment, identified potential combination therapies that may improve patient response rates to ICIs, and offered an overview of ongoing clinical trials focusing on ICI-based combination therapy.

Activation of cDCs and iNKT cells contributes to triptolide-induced hepatotoxicity via STING signaling pathway and endoplasmic reticulum stress

Triptolide (TP) exhibits therapeutic potential against multiple diseases. However, its application in clinics is limited by TP-induced hepatoxicity. TP can activate invariant natural killer T (iNKT) cells in the liver, shifting Th1 cytokine bias to Th2 cytokine bias. The damaging role of iNKT cells in TP-induced hepatoxicity has been established, and iNKT cell deficiency can mitigate hepatotoxicity. However, the activation of iNKT cells in vitro by TP requires the presence of antigen-presenting cells. Therefore, we hypothesized that TP could induce dendritic cells (DCs) to activate iNKT cells, thereby leading to hepatotoxicity. The hepatic conventional DCs (cDCs) exhibited immunogenic activities after TP administration, upregulating the expression of CD1d, co-stimulatory molecules, and IL-12. Neutralization with IL-12p40 antibody extenuated TP-induced hepatotoxicity and reduced iNKT cell activation, suggesting that IL-12 could cause liver injury by activating iNKT cells. TP triggered the activation and upregulation of STING signaling pathway and increased endoplasmic reticulum (ER) stress. Downregulation of STING reduced cDC immunogenicity, inhibiting the activation of iNKT cells and hepatic damage. These indicated the regulatory effects of STING pathway on cDCs and iNKT cells, and the important roles it plays in hepatoxicity. ER stress inhibitor, 4-phenylbutyrate (4-PBA), also suppressed iNKT cell activation and liver injury, which might be regulated by the STING signaling pathway. Our results demonstrated the possible mechanisms underlying TP-induced hepatoxicity, where the activation of cDCs and iNKT cells was stimulated by upregulated STING signaling and increased ER stress as a result of TP administration.

Activation of Kupffer cells in NAFLD and NASH: mechanisms and therapeutic interventions

Non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH) are emerging as the leading causes of liver disease worldwide. These conditions can lead to cirrhosis, liver cancer, liver failure, and other related ailments. At present, liver transplantation remains the sole treatment option for end-stage NASH, leading to a rapidly growing socioeconomic burden. Kupffer cells (KCs) are a dominant population of macrophages that reside in the liver, playing a crucial role in innate immunity. Their primary function includes phagocytosing exogenous substances, presenting antigens, and triggering immune responses. Moreover, they interact with other liver cells during the pathogenesis of NAFLD, and this crosstalk may either delay or exacerbate disease progression. Stimulation by endogenous signals triggers the activation of KCs, resulting in the expression of various inflammatory factors and chemokines, such as NLRP3, TNF-α, IL-1B, and IL-6, and contributing to the inflammatory cascade. In the past 5 years, significant advances have been made in understanding the biological properties and immune functions of KCs in NAFLD, including their interactions with tissue molecules, underlying molecular mechanisms, signaling pathways, and relevant therapeutic interventions. Having a comprehensive understanding of these mechanisms and characteristics can have enormous potential in guiding future strategies for the prevention and treatment of NAFLD.

TAK1 deficiency promotes liver injury and tumorigenesis via ferroptosis and macrophage cGAS-STING signalling

BACKGROUND & AIMS

Oxidative stress-mediated ferroptosis and macrophage-related inflammation play an important role in various liver diseases. Here, we explored if and how hepatocyte ferroptosis regulates macrophage stimulator of interferon genes (STING) activation in the development of spontaneous liver damage, fibrosis, and tumorigenesis.

METHODS

We used a transforming growth factor-beta-activated kinase 1 (TAK1) deficiency-induced model of spontaneous liver damage, fibrosis, and tumorigenesis to investigate hepatocyte ferroptosis and its impact on macrophage STING signalling. Primary hepatocytes and macrophages were used for in vitro experiments.

RESULTS

Significant liver injury and increased numbers of intrahepatic M1 macrophages were found in hepatocyte-specific TAK1-deficient (TAK1ΔHEP) mice, peaking at 4 weeks and gradually decreasing at 8 and 12 weeks. Meanwhile, activation of STING signalling was observed in livers from TAK1ΔHEP mice at 4 weeks and had decreased at 8 and 12 weeks. Treatment with a STING inhibitor promoted macrophage M2 polarisation and alleviated liver injury, fibrosis, and tumour burden. TAK1 deficiency exacerbated liver iron metabolism in mice with a high-iron diet. Moreover, consistent with the results from single-cell RNA-Seq dataset, TAK1ΔHEP mice demonstrated an increased oxidative response and hepatocellular ferroptosis, which could be inhibited by reactive oxygen species scavenging. Suppression of ferroptosis by ferrostatin-1 inhibited the activation of macrophage STING signalling, leading to attenuated liver injury and fibrosis and a reduced tumour burden. Mechanistically, increased intrahepatic and serum levels of 8-hydroxydeoxyguanosine were detected in TAK1ΔHEP mice, which was suppressed by ferroptosis inhibition. Treatment with 8-hydroxydeoxyguanosine antibody inhibited macrophage STING activation in TAK1ΔHEP mice.

CONCLUSIONS

Hepatocellular ferroptosis-derived oxidative DNA damage promotes macrophage STING activation to facilitate the development of liver injury, fibrosis, and tumorigenesis. Inhibition of macrophage STING may represent a novel therapeutic approach for the prevention of chronic liver disease.

IMPACT AND IMPLICATIONS

The precise mechanism by which hepatocyte ferroptosis regulates macrophage STING activation in the progression of liver damage, fibrosis, and tumorigenesis remains unclear. Herein, we show that deletion of TAK1 in hepatocytes caused oxidative stress-mediated ferroptosis and macrophage-related inflammation in the development of spontaneous liver injury, fibrosis, and hepatocellular carcinoma.

Licorice extract inhibits the cGAS-STING pathway and protects against non-alcoholic steatohepatitis

Background: Inflammation and fibrosis are typical symptoms of non-alcoholic steatohepatitis (NASH), which is one of the most common chronic liver diseases. The cGAS-STING signaling pathway has been implicated in the progression of NASH, and targeting this pathway may represent a new therapeutic strategy. Licorice is a widely used herb with anti-inflammatory and liver-protective properties. In this study, we assessed the effect of licorice extract on the cGAS-STING pathway.

Methods: Bone marrow-derived macrophages (BMDMs) were treated with licorice extract and then stimulated with HT-DNA, 2'3'-cGAMP, or other agonists to activate the cGAS-STING pathway. Quantitative real-time PCR and western blot were conducted to analyze whether licorice extract could affect the cGAS-STING pathway. Methionine and choline-deficient diet (MCD) was used to induce NASH in mice, which were treated with licorice extract (500 mg/kg) by gavage and/or c-176 (15 mg/kg) by intraperitoneal injection every 2 days. After 6 weeks of treatment, histological analysis of liver tissue was performed, along with measurements of plasma biochemical parameters.

Results: Licorice extract inhibits cGAS-STING pathway activation. Mechanistically, it might function by inhibiting the oligomerization of STING. Treatment with licorice extract reduced inflammation and fibrosis in MCD diet-induced NASH mice models. Furthermore, we found that the therapeutic effect of combination treatment with licorice extract and C-176 (STING inhibitor) on the pathology and fibrosis of MCD diet-induced NASH models was similar to that of licorice extract or C-176 administered alone.

Conclusion: Licorice extract can inhibit the cGAS-STING pathway and improve hepatic inflammation and fibrosis in NASH mice models. It strongly suggests that licorice extract may be a candidate therapeutic for NASH.

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.

Engineering antiviral immune-like systems for autonomous virus detection and inhibition in mice

The ongoing COVID-19 pandemic has demonstrated that viral diseases represent an enormous public health and economic threat to mankind and that individuals with compromised immune systems are at greater risk of complications and death from viral diseases. The development of broad-spectrum antivirals is an important part of pandemic preparedness. Here, we have engineer a series of designer cells which we term autonomous, intelligent, virus-inducible immune-like (ALICE) cells as sense-and-destroy antiviral system. After developing a destabilized STING-based sensor to detect viruses from seven different genera, we have used a synthetic signal transduction system to link viral detection to the expression of multiple antiviral effector molecules, including antiviral cytokines, a CRISPR-Cas9 module for viral degradation and the secretion of a neutralizing antibody. We perform a proof-of-concept study using multiple iterations of our ALICE system in vitro, followed by in vivo functionality testing in mice. We show that dual output ALICE_SaCas9+Ab system delivered by an AAV-vector inhibited viral infection in herpetic simplex keratitis (HSK) mouse model. Our work demonstrates that viral detection and antiviral countermeasures can be paired for intelligent sense-and-destroy applications as a flexible and innovative method against virus infection.

Expression of STING Is Increased in Monocyte-Derived Macrophages and Contributes to Liver Inflammation in Hepatic Ischemia-Reperfusion Injury

Ischemia/reperfusion (I/R) injury, aggravated by innate immune cell-mediated inflammatory response, is a major problem in liver transplantation. Stimulator of interferon gene (STING) is a crucial regulatory signaling molecule in the DNA-sensing pathway, and its activation can produce strong innate immunity. However, the STING-mediated innate immune pathway in hepatic I/R injury has not been fully elucidated. In this study, we first examined the STING expression changes in the liver tissues of mice after hepatic I/R injury by using quantitative polymerase chain reaction and Western blot assays. We then investigated the role of STING in I/R injury by using a murine hepatic I/R model. STING up-regulation in mouse liver tissues in response to I/R injury and STING deficiency in myeloid cells was found to significantly ameliorate I/R-induced liver injury and inflammatory responses. STING inhibitors were also able to ameliorate hepatic I/R injury. Mechanically, STING may have a protective effect on hepatic I/R injury by the inhibition of hypoxia-inducible factor-1 alpha and enhancement of phosphorylated AMP-activated protein kinase to reduce macrophage activation. These findings show the potential regulatory effects of STING in hepatic I/R and suggest a new method for clinical protection of hepatic I/R injury.

An optimized herbal combination for the treatment of liver fibrosis: Hub genes, bioactive ingredients, and molecular mechanisms

ETHNOPHARMACOLOGICAL RELEVANCE

Liver fibrosis is a chronic liver disease that can lead to cirrhosis, liver failure, and hepatocellular carcinoma, and it is associated with long-term adverse outcomes and mortality. As a primary resource for complementary and alternative medicine, traditional Chinese medicine (TCM) has accumulated a large number of effective formulas for the treatment of liver fibrosis in clinical practice. However, studies on how to systematically optimize TCM formulas are still lacking.

AIM OF THE REVIEW

To provide a methodological reference for the systematic optimization of TCM formulae against liver fibrosis and explored the underlying molecular mechanisms; To provide an efficient method for searching for lead compounds from natural sources and developing from herbal medicines; To enable clinicians and patients to make more reasonable choices and promote the effective treatment toward those patients with liver fibrosis.

MATERIALS AND METHODS

TCM formulas related to treating liver fibrosis were collected from the Web of Science, PubMed, the China National Knowledge Infrastructure (CNKI), Wan Fang, and the Chinese Scientific Journals Database (VIP). Furthermore, the TCM compatibility patterns were mined using association analysis. The core TCM combinations were found by designing an optimized formulas algorithm. Finally, the hub target proteins, potential molecular mechanisms, and active compounds were explored through integrative pharmacology and docking-based inverse virtual screening (IVS) approaches.

RESULTS

We found that the herbs for reinforcing deficiency, activating blood, removing blood stasis, and clearing heat were the basis of TCM formulae patterns. Furthermore, the combination of Salviae Miltiorrhizae (Salvia miltiorrhiza Bunge; Chinese salvia/Danshen), Astragali Radix (Astragalus membranaceus (Fisch.) Bunge; Astragalus/Huangqi), and Radix Bupleuri (Bupleurum chinense DC.; Bupleurum/Chaihu) was identified as core groups. A total of six targets (TNF, STAT3, EGFR, IL2, ICAM1, PTGS2) play a pivotal role in TCM-mediated liver fibrosis inhibition. (-)-Cryptotanshinone, Tanshinaldehyde, Ononin, Thymol, Daidzein, and Formononetin were identified as active compounds in TCM. And mechanistically, TCM could affect the development of liver fibrosis by regulating inflammation, immunity, angiogenesis, antioxidants, and involvement in TNF, MicroRNAs, Jak-STAT, NF-kappa B, and C-type lectin receptors (CLRs) signaling pathways. Molecular docking results showed that key components had good potential to bind to the target genes.

CONCLUSION

In summary, this study provides a methodological reference for the systematic optimization of TCM formulae and exploration of underlying molecular mechanisms.

Multiplexed Digital Spatial Protein Profiling Reveals Distinct Phenotypes of Mononuclear Phagocytes in Livers with Advanced Fibrosis

Background and Aims: Intrahepatic mononuclear phagocytes (MPs) are critical for the initiation and progression of liver fibrosis. In this study, using multiplexed digital spatial protein profiling, we aimed to derive a unique protein signature predicting advanced liver fibrosis. Methods: Snap-frozen liver tissues from various chronic liver diseases were subjected to spatially defined protein-based multiplexed profiling (Nanostring GeoMX^TM). A single-cell RNA sequencing analysis was performed using Gene Expression Omnibus (GEO) datasets from normal and cirrhotic livers. Results: Sixty-four portal regions of interest (ROIs) were selected for the spatial profiling. Using the results from the CD68⁺ area, a highly sensitive and specific immune-related protein signature (CD68, HLA-DR, OX40L, phospho-c-RAF, STING, and TIM3) was developed to predict advanced (F3 and F4) fibrosis. A combined analysis of single-cell RNA sequencing data from GEO datasets (GSE136103) and spatially-defined, protein-based multiplexed profiling revealed that most proteins upregulated in F0-F2 livers in portal CD68⁺ cells were specifically marked in tissue monocytes, whereas proteins upregulated in F3 and F4 livers were marked in scar-associated macrophages (SAMacs) and tissue monocytes. Internal validation using mRNA expression data with the same cohort tissues demonstrated that mRNA levels for TREM2, CD9, and CD68 are significantly higher in livers with advanced fibrosis. Conclusions: In patients with advanced liver fibrosis, portal MPs comprise of heterogeneous populations composed of SAMacs, Kupffer cells, and tissue monocytes. This is the first study that used spatially defined protein-based multiplexed profiling, and we have demonstrated the critical difference in the phenotypes of portal MPs between livers with early- or late-stage fibrosis.

Spotlight on liver macrophages for halting liver disease progression and injury

INTRODUCTION

Over the past two decades, understanding of hepatic macrophage biology has provided astounding details of their role in the progression and regression of liver diseases. The hepatic macrophages constitute resident macrophages, Kupffer cells, and circulating bone marrow monocyte-derived macrophages, which play a diverse role in liver injury and repair. Imbalance in the macrophage population leads to pathological consequences and is responsible for the initiation and progression of acute and chronic liver injuries. Further, distinct populations of hepatic macrophages and their high heterogeneity make their complex role enigmatic. The unique features of distinct phenotypes of macrophages have provided novel biomarkers for defining the stages of liver diseases. The distinct mechanisms of hepatic macrophages polarization and recruitment have been at the fore front of research. In addition, the secretome of hepatic macrophages and their immune regulation has provided clinically relevant therapeutic targets.

AREAS COVERED

Herein we have highlighted the current understanding in the area of hepatic macrophages, and their role in the progression of liver injury.

EXPERT OPINION

It is essential to ascertain the physiological and pathological role of evolutionarily conserved distinct macrophage phenotypes in different liver diseases before viable approaches may see a clinical translation.

Schisandrin B targets cannabinoid 2 receptor in Kupffer cell to ameliorate CCl4-induced liver fibrosis by suppressing NF-κB and p38 MAPK pathway

BACKGROUND

Lignans, the major bioactive components of Schisandra chinensis, displays an anti-liver fibrosis effect. However, which one is the most effective lignan and what is its molecular mechanisms are still unclear.

PURPOSE

This research aimed to screen the most effective components of lignans, identify and verify its pharmacological target, and investigate its molecular mechanism against liver fibrosis.

METHODS

First, the most effective lignans were screened by a comprehensive RAW264.7/CMC system and LPS-induced RAW264.7. Second, the potential targets were predicted by a liver fibrosis domain-specific chemo-genomics knowledgebase and further verified by competition binding assay. Third, the effect of anti-liver fibrosis was evaluated by employing RAW264.7, co-cultured hepatic stellate cells (HSC) and CCl4-induced liver fibrosis CB2-/- mice. The qPCR, ELISAs, western blot analyses, and immunofluorescence were used to evaluate the expression of main inflammatory factors and key proteins in NF-κB and p38 MAPK pathway.

RESULTS

Schisandrin B was identified as the most effective component for attenuating liver fibrosis, and CB2 was proven to be a potential target for anti-liver fibrosis. The in vitro and in vivo assays indicated that schisandrin B ameliorated CCl4-induced liver fibrosis through suppressing NF-κB and p38 MAPK pathway in Kupffer cells by targeting CB2 receptor CONCLUSION: Schisandrin B targets CB2 receptor to inhibit Kupffer cell polarization by downregulating the NF-κB and p38 MAPK signaling pathways for ameliorating liver fibrosis.

Impact of intracellular innate immune receptors on immunometabolism

Immunometabolism, which is the metabolic reprogramming of anaerobic glycolysis, oxidative phosphorylation, and metabolite synthesis upon immune cell activation, has gained importance as a regulator of the homeostasis, activation, proliferation, and differentiation of innate and adaptive immune cell subsets that function as key factors in immunity. Metabolic changes in epithelial and other stromal cells in response to different stimulatory signals are also crucial in infection, inflammation, cancer, autoimmune diseases, and metabolic disorders. The crosstalk between the PI3K-AKT-mTOR and LKB1-AMPK signaling pathways is critical for modulating both immune and nonimmune cell metabolism. The bidirectional interaction between immune cells and metabolism is a topic of intense study. Toll-like receptors (TLRs), cytokine receptors, and T and B cell receptors have been shown to activate multiple downstream metabolic pathways. However, how intracellular innate immune sensors/receptors intersect with metabolic pathways is less well understood. The goal of this review is to examine the link between immunometabolism and the functions of several intracellular innate immune sensors or receptors, such as nucleotide-binding and leucine-rich repeat-containing receptors (NLRs, or NOD-like receptors), absent in melanoma 2 (AIM2)-like receptors (ALRs), and the cyclic dinucleotide receptor stimulator of interferon genes (STING). We will focus on recent advances and describe the impact of these intracellular innate immune receptors on multiple metabolic pathways. Whenever appropriate, this review will provide a brief contextual connection to pathogenic infections, autoimmune diseases, cancers, metabolic disorders, and/or inflammatory bowel diseases.

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.