HMGB1-induced autophagy: a new pathway to maintain Treg function during chronic hepatitis B virus infection

HMGB1: A New Target for Ischemic Stroke and Hemorrhagic Transformation

Stroke in China is distinguished by its high rates of morbidity, recurrence, disability, and mortality. The ultra-early administration of rtPA is essential for restoring perfusion in acute ischemic stroke, though it concurrently elevates the risk of hemorrhagic transformation. High-mobility group box 1 (HMGB1) emerges as a pivotal player in neuroinflammation after brain ischemia and ischemia-reperfusion. Released passively by necrotic cells and actively secreted, including direct secretion of HMGB1 into the extracellular space and packaging of HMGB1 into intracellular vesicles by immune cells, glial cells, platelets, and endothelial cells, HMGB1 represents a prototypical damage-associated molecular pattern (DAMP). It is intricately involved in the pathogenesis of atherosclerosis, thromboembolism, and detrimental inflammation during the early phases of ischemic stroke. Moreover, HMGB1 significantly contributes to neurovascular remodeling and functional recovery in later stages. Significantly, HMGB1 mediates hemorrhagic transformation by facilitating neuroinflammation, directly compromising the integrity of the blood-brain barrier, and enhancing MMP9 secretion through its interaction with rtPA. As a systemic inflammatory factor, HMGB1 is also implicated in post-stroke depression and an elevated risk of stroke-associated pneumonia. The role of HMGB1 extends to influencing the pathogenesis of ischemia by polarizing various subtypes of immune and glial cells. This includes mediating excitotoxicity due to excitatory amino acids, autophagy, MMP9 release, NET formation, and autocrine trophic pathways. Given its multifaceted role, HMGB1 is recognized as a crucial therapeutic target and prognostic marker for ischemic stroke and hemorrhagic transformation. In this review, we summarize the structure and redox properties, secretion and pathways, regulation of immune cell activity, the role of pathophysiological mechanisms in stroke, and hemorrhage transformation for HMGB1, which will pave the way for developing new neuroprotective drugs, reduction of post-stroke neuroinflammation, and expansion of thrombolysis time window.

The dual role of regulatory T cells in hepatitis B virus infection and related hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a major contributor to cancer-related deaths worldwide. Hepatitis B virus (HBV) infection is a major etiologic factor leading to HCC. While there have been significant advancements in controlling HBV replication, achieving a complete cure for HBV-related HCC (HBV-HCC) remains an intricate challenge. HBV persistence is attributed to a myriad of mechanisms, encompassing both innate and adaptive immune responses. Regulatory T cells (Tregs) are pivotal in upholding immune tolerance and modulating excessive immune activation. During HBV infection, Tregs mediate specific T cell suppression, thereby contributing to both persistent infection and the mitigation of liver inflammatory responses. Studies have demonstrated an augmented expression of circulating and intrahepatic Tregs in HBV-HCC, which correlates with impaired CD8+ T cell function. Consequently, Tregs play a dual role in the context of HBV infection and the progression of HBV-HCC. In this comprehensive review, we discuss pertinent studies concerning Tregs in HBV infection, HBV-related cirrhosis and HCC. Furthermore, we summarize Treg responses to antiviral therapy and provide Treg-targeted therapies specific to HBV and HCC.

The dynamic shifts of IL-10-producing Th17 and IL-17-producing Treg in health and disease: a crosstalk between ancient "Yin-Yang" theory and modern immunology

The changes in T regulatory cell (Treg) and T helper cell (Th) 17 ratios holds paramount importance in ensuring internal homeostasis and disease progression. Recently, novel subsets of Treg and Th17, namely IL-17-producing Treg and IL-10-producing Th17 have been identified. IL-17-producing Treg and IL-10-producing Th17 are widely considered as the intermediates during Treg/Th17 transformation. These "bi-functional" cells exhibit plasticity and have been demonstrated with important roles in multiple physiological functions and disease processes. Yin and Yang represent opposing aspects of phenomena according to the ancient Chinese philosophy "Yin-Yang" theory. Furthermore, Yin can transform into Yang, and vice versa, under specific conditions. This theory has been widely used to describe the contrasting functions of immune cells and molecules. Therefore, immune-activating populations (Th17, M1 macrophage, etc.) and immune overreaction (inflammation, autoimmunity) can be considered Yang, while immunosuppressive populations (Treg, M2 macrophage, etc.) and immunosuppression (tumor, immunodeficiency) can be considered Yin. However, another important connotation of "Yin-Yang" theory, the conversion between Yin and Yang, has been rarely documented in immune studies. The discovery of IL-17-producing Treg and IL-10-producing Th17 enriches the meaning of "Yin-Yang" theory and further promotes the relationship between ancient "Yin-Yang" theory and modern immunology. Besides, illustrating the functions of IL-17-producing Treg and IL-10-producing Th17 and mechanisms governing their differentiation provides valuable insights into the mechanisms underlying the dynamically changing statement of immune statement in health and diseases.

Exploiting autophagy balance in T and NK cells as a new strategy to implement adoptive cell therapies

Autophagy is an essential cellular homeostasis pathway initiated by multiple stimuli ranging from nutrient deprivation to viral infection, playing a key role in human health and disease. At present, a growing number of evidence suggests a role of autophagy as a primitive innate immune form of defense for eukaryotic cells, interacting with components of innate immune signaling pathways and regulating thymic selection, antigen presentation, cytokine production and T/NK cell homeostasis. In cancer, autophagy is intimately involved in the immunological control of tumor progression and response to therapy. However, very little is known about the role and impact of autophagy in T and NK cells, the main players in the active fight against infections and tumors. Important questions are emerging: what role does autophagy play on T/NK cells? Could its modulation lead to any advantages? Could specific targeting of autophagy on tumor cells (blocking) and T/NK cells (activation) be a new intervention strategy? In this review, we debate preclinical studies that have identified autophagy as a key regulator of immune responses by modulating the functions of different immune cells and discuss the redundancy or diversity among the subpopulations of both T and NK cells in physiologic context and in cancer.

miR-505 inhibits replication of Borna disease virus 1 via inhibition of HMGB1-mediated autophagy

Borna disease virus 1 (BoDV-1) is a highly neurotropic RNA virus which was recently demonstrated to cause deadly human encephalitis. Viruses can modulate microRNA expression, in turn modulating cellular immune responses and regulating viral replication. A previous study indicated that BoDV-1 infection down-regulated the expression of miR-505 in rats. However, the underlying mechanism of miR-505 during BoDV-1 infection remains unknown. In this study, we found that miR-505 can inhibit autophagy activation by down-regulating the expression of its target gene HMGB1, and ultimately inhibit the replication of BoDV-1. Specifically, we found that the expression of miR-505 was significantly down-regulated in rat primary neurons stably infected with BoDV-1. Overexpression of miR-505 can inhibit the replication of BoDV-1 in cells. Bioinformatics analysis and dual luciferase reporter gene detection confirmed that during BoDV-1 infection, the high-mobility group protein B1 (HMGB1) that mediates autophagy is the direct target gene of miR-505. The expression of HMGB1 was up-regulated after BoDV-1 infection, and overexpression of miR-505 could inhibit the expression of HMGB1. Autophagy-related detection found that after infection with BoDV-1, the expression of autophagy-related proteins and autophagy-related marker LC3 in neuronal cells was significantly up-regulated. Autophagy flow experiments and transmission electron microscopy also further confirmed that BoDV-1 infection activated HMGB1-mediated autophagy. Further regulating the expression of miR-505 found that overexpression of miR-505 significantly inhibited HMGB1-mediated autophagy. The discovery of this mechanism may provide new ideas and directions for the prevention and treatment of BoDV-1 infection in the future.

IL-33/ST2 Axis Deficiency Exacerbates Hepatic Pathology by Regulating Treg and Th17 Cells in Murine Schistosomiasis Japonica

Purpose

Schistosoma japonicum-infected IL-33 and ST2 gene deficiency (IL-33^−/− and ST2^−/−, respectively) mice were used to explore the role of the IL-33/ST2 axis in liver pathology targeting regulatory T cells (Treg)/T helper 17 cells (Th17).

Materials and Methods

Each mouse was infected percutaneously with 20 S. japonicum cercariae. Hepatic mass index (HMI), liver egg granulomas, hepatic fibrosis biomarkers and serum levels of alanine aminotransferase (ALT) were investigated. Treg and Th17 frequency was determined by flow cytometry. Expressions of Foxp3, ST2, TGF-β1, IL-10, RORγt, and IL-17A were measured via quantitative real-time polymerase chain reaction (qRT-PCR). Concentrations of TGF-β1, IL-10 and IL-17A were tested with ELISA. In vitro experiments, mRNA expressions of Foxp3, TGF-β1, IL-10, Atg5, Beclin-1 and p62 associated with polarization of Treg by recombinant mouse IL-33 (rmIL-33) were detected by qRT-PCR.

Results

An increased expression of IL-33/ST2 was shown in S. japonicum-infected mice. Deficiency of IL-33 or ST2 gene led to an aggravated liver pathology, which was evidenced by elevated hepatic granuloma volume, HMI and ALT levels and fibrosis, which was demonstrated by increased hepatic collagen deposition in the infected mice. Injection of rmIL-33 into the infected IL-33^−/− mice strongly abrogated the liver pathology and fibrosis, whereas no detectable effect with injecting rmIL-33 into the infected ST2^−/− mice. Furthermore, depletion of the IL-33/ST2 axis inhibited Treg, accompanied by increased Th17. rmIL-33 treatment upregulated Treg and downregulated Th17 in the infected IL-33^−/− mice, while no effect in the infected ST2^−/− mice. rmIL-33 led to elevated expressions of Atg5, Beclin-1 and inhibited expression of p62 in expansion of Treg.

Conclusion

The IL-33/ST2 axis plays a protective role in S. japonicum infected mice, which is closely related to increasing Treg responses as well as suppressing Th17 responses. Expansion of Treg by IL-33 may be associated with its regulation of autophagy.

The Modulation of Regulatory T Cells via High Mobility Group Box-1/Receptor for Advanced Glycation End-Products/Adenosine Monophosphate-Activated Protein Kinase Axis in Chronic Kidney Diseases with Complication of Sepsis

Chronic kidney diseases (CKD) with complication of sepsis brings great clinical burden worldwide. Regulatory T cells (Tregs) can regulate key immune response during the progression of the diseases. The present study aims to investigate the role of HMGB1 in the regulation of Tregs and find out the potential mechanism. Jurkat cells were stimulated with 0.5 ng/ml TGF-β1 for 24 h to induce phenotypic alternation into Tregs, followed by stimulation with indoxyl sulfate (IS) and lipopolysac-charide (LPS) for 24 h. Then, Tregs were treated with recombinant human HMBG1 (rHMGB1) at different concentrations (10, 100 and 1000 ng/ml). Cell viability of Tregs was assayed by CCK-8. The gene expressions related to proliferation and autophagy were determined using RT-qPCR and western blotting. RAGE was inhibited by transfection with shRNA-RAGE in Tregs. The results showed that HMGB1 and RAGE were upregulated upon IS and LPS induction in Tregs. rHMGB1 significantly promoted the viability, proliferation and function of Tregs at a concentration-dependent way, which was partly reversed by RAGE knockdown. Besides, HMGB1-RAGE could regulate autophagy activity and AMPK-mTOR signaling pathway. In summary, our study concluded that the active autophagy mediated by enhanced HMGB1-RAGE axis through AMPK-mTOR signaling pathway was a potential mechanism to enhance Tregs viability and function in chronic kidney diseases with complication of sepsis.

The lncRNA PVT1 regulates autophagy in regulatory T cells to suppress heart transplant rejection in mice by targeting miR-146a

Regulatory T cells (Tregs) are indispensable for the maintenance of immune tolerance. The purpose of this study was to investigate the effect of the interaction of the lncRNA PVT1 and miR-146a on Treg autophagy and reveal the mechanism to alleviate transplant rejection. PVT1 and miR-146a expression levels were analyzed by qRT-PCR. Bioinformatic analysis and methylation profiling were used to determine the relationship between PVT1 and miR-146a. Altered autophagic status in Tregs was detected by western blotting. The effect of autophagy on Treg function was assessed in cell coculture in vitro and in animal models. Our results showed that PVT1 expression was reduced in Tregs during rejection and negatively correlated with miR-146a expression. Higher PVT1 expression was associated with higher autophagy in Tregs. Further, highly autophagic Tregs had stronger inhibitory effects on CD4⁺ T cells in vitro, prolonged allograft survival and alleviated rejection in vivo. Mechanistic studies showed that overexpression of PVT1 enhanced TNF receptor-associated factor (TRAF) 6 expression by directly targeting miR-146a. MiR-146a overexpression reversed PVT1-induced Treg autophagy and inhibited PVT1-induced TRAF6 expression. The present study shows a novel regulatory pathway of the autophagy program that comprises PVT1, miR-146a, and TRAF6. Our findings may provide potential targets and new therapeutic strategies for transplant rejection.

The Effect and Regulatory Mechanism of High Mobility Group Box-1 Protein on Immune Cells in Inflammatory Diseases

High mobility group box-1 protein (HMGB1), a member of the high mobility group protein superfamily, is an abundant and ubiquitously expressed nuclear protein. Intracellular HMGB1 is released by immune and necrotic cells and secreted HMGB1 activates a range of immune cells, contributing to the excessive release of inflammatory cytokines and promoting processes such as cell migration and adhesion. Moreover, HMGB1 is a typical damage-associated molecular pattern molecule that participates in various inflammatory and immune responses. In these ways, it plays a critical role in the pathophysiology of inflammatory diseases. Herein, we review the effects of HMGB1 on various immune cell types and describe the molecular mechanisms by which it contributes to the development of inflammatory disorders. Finally, we address the therapeutic potential of targeting HMGB1.

HMGB1: An overview of its roles in the pathogenesis of liver disease

High-mobility group box 1 (HMGB1) is an abundant architectural chromosomal protein that has multiple biologic functions: gene transcription, DNA replication, DNA-damage repair, and cell signaling for inflammation. HMGB1 can be released passively by necrotic cells or secreted actively by activated immune cells into the extracellular milieu after injury. Extracellular HMGB1 acts as a damage-associated molecular pattern to initiate the innate inflammatory response to infection and injury by communicating with neighboring cells through binding to specific cell-surface receptors, including Toll-like receptors (TLRs) and the receptor for advanced glycation end products (RAGE). Numerous studies have suggested HMGB1 to act as a key protein mediating the pathogenesis of chronic and acute liver diseases, including nonalcoholic fatty liver disease, hepatocellular carcinoma, and hepatic ischemia/reperfusion injury. Here, we provide a detailed review that focuses on the role of HMGB1 and HMGB1-mediated inflammatory signaling pathways in the pathogenesis of liver diseases.

Knockdown of miR-146a in regulatory T cells suppresses heart transplantation rejection in mice by increasing autophagy

Clinical trials of regulatory T cells (Tregs) have shown that adoptive transfer of Tregs has great promise for the treatment of rejection. However, strategies to improve Treg function are needed in order to enhance their efficacy and reduce the number of Tregs required for adoptive transfer. Autophagy is a process for degrading intracellular components, and it mediates cell death, lymphocyte homeostasis, and Treg function. Studies have shown that the survival and function of Tregs with disrupted autophagy are defective. We found that the autophagic status of Tregs was compromised during acute rejection, allowing us to enhance Treg autophagy by regulating microRNA-146a (miR-146a), which is highly expressed in Tregs and is implicated in their function and metabolism. MiR-146a antagomir-mediated miR-146a knockdown promoted Treg autophagy, as evaluated by Western blot analysis. Further, we evaluated whether altering autophagy affects Treg function in both an in vitro cell coculture model and a heart transplantation model in mice. An increase in autophagy enhanced the inhibitory effects of Tregs on CD4⁺ T cells and dendritic cells (DCs) in vivo and in vitro. In addition, adoptive transfer of highly autophagic Tregs treated with miR-146a antagomir significantly alleviated rejection. Collectively, these data provide a new method that uses miR-146a knockdown to increase Treg efficacy by increasing autophagy.

HMGB1 suppress the expression of IL-35 by regulating Naïve CD4+ T cell differentiation and aggravating Caspase-11-dependent pyroptosis in acute lung injury

OBJECTIVES

Acute lung injury/acute respiratory distress syndrome (ALI/ARDS) is a severe form of inflammatory lung disease. Its development and progression are regulated by cytokines. The purpose of this study was to determine the effects of HMGB1 involved in the regulation of Treg cells and IL-35.

METHODS

A cecal ligation and puncture (CLP)-induced ALI model was used to investigate the changes in IL-35, Tregs, and the expression of RAGE and caspase-11 after HMGB1 inhibition (glycyrrhizin was used as an inhibitor of HMGB1). CD4+ naïve T cells sorted from C57BL/6 mice spleens were cultured to explore the role of HMGB1 in the differentiation from CD4+ naïve T cells to Tregs.

RESULTS

HMGB1 promoted lung injury and uncontrolled inflammation in the CLP mouse model. HMGB1, NF-κB p65, RAGE, and caspase-11 expression in the lungs of CLP mice decreased significantly after pretreatment with glycyrrhizin. We found that the Treg proportion and IL-35 expression were upregulated in the serum and lung of CLP mice after inhibiting HMGB1. In our in vitro experiments, we found that recombinant HMGB1 significantly suppressed the proportion of CD4+CD25+FOXP3+Tregs differentiated from CD4+ naïve T cells.

CONCLUSIONS

The inhibition of HMGB1 increased the proportion of Treg and expression of IL-35 and alleviated lung injury in the CLP-induced ALI model. Furthermore, inhibition of HMGB1 reduced caspase-11-dependent pyroptosis in the lungs of the CLP-induced ALI model.

Autophagy in liver diseases

Autophagy is the liver cell energy recycling system regulating a variety of homeostatic mechanisms. Damaged organelles, lipids and proteins are degraded in the lysosomes and their elements are re-used by the cell. Investigations on autophagy have led to the award of two Nobel Prizes and a health of important reports. In this review we describe the fundamental functions of autophagy in the liver including new data on the regulation of autophagy. Moreover we emphasize the fact that autophagy acts like a two edge sword in many occasions with the most prominent paradigm being its involvement in the initiation and progress of hepatocellular carcinoma. We also focused to the implication of autophagy and its specialized forms of lipophagy and mitophagy in the pathogenesis of various liver diseases. We analyzed autophagy not only in well studied diseases, like alcoholic and nonalcoholic fatty liver and liver fibrosis but also in viral hepatitis, biliary diseases, autoimmune hepatitis and rare diseases including inherited metabolic diseases and also acetaminophene hepatotoxicity. We also stressed the different consequences that activation or impairment of autophagy may have in hepatocytes as opposed to Kupffer cells, sinusoidal endothelial cells or hepatic stellate cells. Finally, we analyzed the limited clinical data compared to the extensive experimental evidence and the possible future therapeutic interventions based on autophagy manipulation.

Role of HMGB1 in Chemotherapy-Induced Peripheral Neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN), one of major dose-limiting side effects of first-line chemotherapeutic agents such as paclitaxel, oxaliplatin, vincristine, and bortezomib is resistant to most of existing medicines. The molecular mechanisms of CIPN have not been fully understood. High mobility group box 1 (HMGB1), a nuclear protein, is a damage-associated molecular pattern protein now considered to function as a pro-nociceptive mediator once released to the extracellular space. Most interestingly, HMGB1 plays a key role in the development of CIPN. Soluble thrombomodulin (TMα), known to degrade HMGB1 in a thrombin-dependent manner, prevents CIPN in rodents treated with paclitaxel, oxaliplatin, or vincristine and in patients with colorectal cancer undergoing oxaliplatin-based chemotherapy. In this review, we describe the role of HMGB1 and its upstream/downstream mechanisms in the development of CIPN and show drug candidates that inhibit the HMGB1 pathway, possibly useful for prevention of CIPN.

Significance of MR/OPN/HMGB1 axis in NAFLD-associated hepatic fibrogenesis

AIMS

The activation of hepatic stellate cells (HSCs) plays a central role in liver fibrosis, however non-alcoholic fatty liver disease (NAFLD) associated liver fibrogenesis have been poorly understood. We aimed to determine the significance of mineralocorticoid receptor (MR)/osteopontin (OPN)/high-mobility group box-1 (HMGB1) axis in this setting.

MAIN METHODS

Liver specimens were collected from NAFLD patients and murine NAFLD models established with 12-week high fat diet (HFD) for analysis of both upstream signals of MR and intrahepatic MR/OPN/HMGB1 axis. The in vitro cell model of NAFLD-associated liver fibrogenesis was established by treating LX-2 (a cell line of human HSCs) with free fatty acids (FFA). The effects of MR signaling were evaluated using with ALD (MR activator) or eplerenone (Ep, MR antagonist). Moreover, the in vitro loss- and gain- of function approaches were applied to confirm the upstream and downstream relationships of mediators contained in the intracellular MR/OPN/HMGB1 axis of LX-2.

KEY FINDINGS

In NAFLD condition, both human and mouse liver tissue samples demonstrated a significant up-regulation of MR/OPN/HMGB1 axis simultaneously with enhanced expression of pro-fibrogenic markers, including ACTA2, TIMP1, TGFB1 and COL1A1. Besides, enhanced production of serum aldosterone (ALD) was also observed in mouse NAFLD models. Moreover, the in vitro data demonstrated MR play an essential role in FFA-induced HSCs fibrogenesis. Meanwhile, MR acts as the upstream effector mediator of OPN and shares downstream HMGB1 with OPN.

SIGNIFICANCE

The MR/OPN/HMGB1 axis could be therapeutically targeted to treat NAFLD associated hepatic fibrogenesis.

Regulatory T Cell Plasticity and Stability and Autoimmune Diseases

CD4⁺CD25⁺ regulatory T cells (Tregs) are a class of CD4⁺ T cells with immunosuppressive functions that play a critical role in maintaining immune homeostasis. However, in certain disease settings, Tregs demonstrate plastic differentiation, and the stability of these Tregs, which is characterized by the stable expression or protective epigenetic modifications of the transcription factor Foxp3, becomes abnormal. Plastic Tregs have some features of helper T (Th) cells, such as the secretion of Th-related cytokines and the expression of specific transcription factors in Th cells, but also still retain the expression of Foxp3, a feature of Tregs. Although such Th-like Tregs can secrete pro-inflammatory cytokines, they still possess a strong ability to inhibit specific Th cell responses. Therefore, the plastic differentiation of Tregs not only increases the complexity of the immune circumstances under pathological conditions, especially autoimmune diseases, but also shows an association with changes in the stability of Tregs. The plastic differentiation and stability change of Tregs play vital roles in the progression of diseases. This review focuses on the phenotypic characteristics, functions, and formation conditions of several plastic Tregs and also summarizes the changes of Treg stability and their effects on inhibitory function. Additionally, the effects of Treg plasticity and stability on disease prognosis for several autoimmune diseases were also investigated in order to better understand the relationship between Tregs and autoimmune diseases.

Interplay between Cellular Autophagy and Hepatitis B Virus Replication: A Systematic Review

Autophagy, a conserved process in which cells break down and destroy old, damaged, or abnormal proteins and other substances in the cytoplasm through lysosomal degradation, occurs via autophagosome formation and aids in the maintenance of intracellular homeostasis. Autophagy is closely associated with hepatitis B virus (HBV) replication and assembly. Currently, HBV infection is still one of the most serious public health issues worldwide. The unavailability of satisfactory therapeutic strategies for chronic HBV infection indicates an urgent need to elucidate the mechanisms underlying the pathogenesis of HBV infection. Increasing evidence has shown that HBV not only possesses the ability to induce incomplete autophagy but also evades autophagic degradation, indicating that HBV utilizes or hijacks the autophagy machinery for its own replication. Therefore, autophagy might be a crucial target pathway for controlling HBV infection. The definite molecular mechanisms underlying the association between cellular autophagy and HBV replication require further clarification. In this review, we have summarized and discussed the latest findings on the interplay between autophagy and HBV replication.

Autophagy Promotes Porcine Parvovirus Replication and Induces Non-Apoptotic Cell Death in Porcine Placental Trophoblasts

Autophagy plays important roles in the infection and pathogenesis of many viruses, yet the regulatory roles of autophagy in the process of porcine parvovirus (PPV) infection remain unclear. Herein, we show that PPV infection induces autophagy in porcine placental trophoblasts (PTCs). Induction of autophagy by rapamycin (RAPA) inhibited the occurrence of apoptotic cell death, yet promoted viral replication in PPV-infected cells; inhibition of autophagy by 3-MA or ATG5 knockdown increased cellular apoptosis and reduced PPV replication. Interestingly, we found that in the presence of caspase-inhibitor zVAD-fmk, PPV induces non-apoptotic cell death that was characterized by lysosomal damage and associated with autophagy. Induction of complete autophagy flux by RAPA markedly promoted PPV replication compared with incomplete autophagy induced by RAPA plus bafilomycin (RAPA/BAF) in the early phase of PPV infection (24 h.p.i.). Meanwhile, induction of complete autophagy with RAPA increased lysosomal damage and non-apoptotic cell death in the later phase of PPV infection. Therefore, our data suggest that autophagy can enhance PPV replication and promote the occurrence of lysosomal-damage-associated non-apoptotic cell death in PPV-infected porcine placental trophoblasts.

Johnny on the Spot-Chronic Inflammation Is Driven by HMGB1

Although much has been made of the role of HMGB1 acting as an acute damage associated molecular pattern (DAMP) molecule, prompting the response to tissue damage or injury, it is also released at sites of chronic inflammation including sites of infection, autoimmunity, and cancer. As such, the biology is distinguished from homeostasis and acute inflammation by the recruitment and persistence of myeloid derived suppressor cells, T regulatory cells, fibrosis and/or exuberant angiogenesis depending on the antecedents and the other individual inflammatory partners that HMGB1 binds and focuses, including IL-1β, CXCL12/SDF1, LPS, DNA, RNA, and sRAGE. High levels of HMGB1 released into the extracellular milieu and its persistence in the microenvironment can contribute to the pathogenesis of many if not all autoimmune disorders and is a key factor that drives inflammation further and worsens symptoms. HMGB1 is also pivotal in the maintenance of chronic inflammation and a “wound healing” type of immune response that ultimately contributes to the onset of carcinogenesis and tumor progression. Exosomes carrying HMGB1 and other instructive molecules are released and shape the response of various cells in the chronic inflammatory environment. Understanding the defining roles of REDOX, DAMPs and PAMPs, and the host response in chronic inflammation requires an alternative means for positing HMGB1's central role in limiting and focusing inflammation, distinguishing chronic from acute inflammation.

Role of Foxp3/Treg and RORγt/Th17 imbalance in chronic hepatitis B virus infection

A wide range of immune-mediated liver damage can be seen during infection with hepatitis B virus (HBV). Failure of HBV immune clearance leads to chronic hepatitis and greatly increases the risk of liver cirrhosis and hepatocellular carcinoma. Recently, there have been many studies on the relationship between the outcome of HBV infection and the immune status of patients. The immune response of T lymphocytes in HBV infection plays an important role, especially the imbalance of regulatory T cells (Treg)/Helper T cell 17 (Th17). The imbalance between the Treg and Th17 is an important mechanism of persistent HBV infection and inflammatory injury of the liver. To better reveal the underlying mechanisms, we systematically review the roles of Treg and Th17 and discuss the relationship between Treg and Th17 during HBV infection as well as the changes in the two related specific transcription factors, retinoid-related orphan nuclear receptor γt (RORγt) and forkhead/winged helix family transcription factor 3 (Foxp3). The research on HBV immunotargeting therapy in recent years has suggested the role of Foxp3/Treg and RORγt/Th17 imbalance in HBV infection. Such findings provide new ideas for the treatment of chronic hepatitis B.

Autophagy in regulatory T cells: A double-edged sword in disease settings

Autophagy is an evolutionarily conserved catabolic process that directs cytoplasmic proteins, organelles and microbes to lysosomes for degradation. It not only represents an essential cell-intrinsic mechanism to protect against internal and external stresses but also shapes both innate and adaptive immunity. Regulatory T cells (Tregs) are a developmentally and functionally distinct T cell subpopulation engaged in sustaining immunological self-tolerance and homeostasis. There is compelling evidence that autophagy is actively regulated in Tregs and serves as a central signal-dependent controller for Tregs by restraining excessive apoptotic and metabolic activities. In this review, we discuss how autophagy modulates the stability and functionality of Tregs in different disease settings, and provide a perspective on how manipulation of autophagy enables better control of immune response by targeting the generation of Tregs and the maintenance of their stability.

Type 3 innate lymphoid cell: a new player in liver fibrosis progression

Type 3 innate lymphoid cell (ILC3) has recently emerged as a crucial effector in inflammatory and fibrotic diseases. The present study was designed to determine the roles of ILC3 in liver fibrosis. By flow cytometry, we documented increased frequencies of peripheral ILC3 (Lin-CD127+CD117+CD294- lymphocytes) in patients, especially at the advanced stage of hepatitis B virus (HBV)-related chronic liver diseases, and demonstrated their correlations with disease progression. The in vitro fibrogenic effects by ILC3 were determined by co-culture experiments with LX-2 (a human hepatic stellate cell (HSC) line). The data indicate that pathogenic ILC3 can directly promote LX-2 fibrogenesis in non-contact manners by producing interleukin (IL)-17A and IL-22. Additionally, they had indirect fibrogenic effects by producing IL-22 to suppress interferon (IFN)-γ (a well-known anti-fibrotic cytokine) production by other immune cells. In carbon tetrachloride (CCl4)-induced wild-type mouse liver fibrosis models, we also documented significantly increased frequencies of both non-natural killer (NK) ILC (Lin-CD127+ lymphocytes) and ILC3 (Lin-CD127+RORγt+ lymphocytes) in liver and spleen specimens. Furthermore, the ILC3 from fibrotic mice contained more IL-17A+ILC3 and IL-22+ILC3 subsets than those from normal and less-fibrotic mice. The in vivo effects of ILC3 in liver fibrogenesis were further determined using RAG-1-/- mice with ILC depletion and further adoptive transfer of ILC3 from wild-type mice. The immunohistochemical staining of liver specimens showed the beneficial effects by ILC depletion and the detrimental effects by ILC3 transfer in CCl4-induced mouse liver fibrosis models. Collectively, ILC3 plays a pro-fibrotic role in liver fibrosis progression.

Autophagy, EVs, and Infections: A Perfect Question for a Perfect Time

Autophagy, a highly conserved process, serves to maintain cellular homeostasis in response to an extensive variety of internal and external stimuli. The classic, or canonical, pathway of autophagy involves the coordinated degradation and recycling of intracellular components and pathogenic material. Proper regulation of autophagy is critical to maintain cellular health, as alterations in the autophagy pathway have been linked to the progression of a variety of physiological and pathological conditions in humans, namely in aging and in viral infection. In addition to its canonical role as a degradative pathway, a more unconventional and non-degradative role for autophagy has emerged as an area of increasing interest. This process, known as secretory autophagy, is gaining widespread attention as many viruses are believed to use this pathway as a means to release and spread viral particles. Moreover, secretory autophagy has been found to intersect with other intracellular pathways, such as the biogenesis and secretion of extracellular vesicles (EVs). Here, we provide a review of the current landscape surrounding both degradative autophagy and secretory autophagy in relation to both aging and viral infection. We discuss their key features, while describing their interplay with numerous different viruses (i.e. hepatitis B and C viruses, Epstein-Barr virus, SV40, herpesviruses, HIV, chikungunya virus, dengue virus, Zika virus, Ebola virus, HTLV, Rift Valley fever virus, poliovirus, and influenza A virus), and compare secretory autophagy to other pathways of extracellular vesicle release. Lastly, we highlight the need for, and emphasize the importance of, more thorough methods to study the underlying mechanisms of these pathways to better advance our understanding of disease progression.

HMGB1-induced autophagy facilitates hepatic stellate cells activation: a new pathway in liver fibrosis

High-mobility group box-1 (HMGB1) plays a context-dependent role in autophagy, which is required for hepatic stellate cells (HSCs) activation. However, the significance of HMGB1-induced HSCs autophagy in liver fibrosis has not been elucidated. Here, we first documented an enrichment of peripheral and intrahepatic HMGB1 signal in hepatitis B virus (HBV)-related liver fibrosis progression, and presented a direct evidence of anatomic proximity of HMGB1 with a-SMA (a marker for HSCs activation) in cirrhotic liver specimens. Then, we demonstrated the autophagy-inducing effects by serum-sourced HMGB1 in both primary murine HSCs and human HSCs cell line (LX-2), reflected by increased number of autophagic vacuoles (AVs) under the transmission electron microscope (TEM) and up-regulated protein expression of lipidated microtubule-associated light chain 3 (LC3-II) (a marker for autophagosome) in Western blot analysis. Intriguingly, there is a possible translocation of endogenous HMGB1 from the nucleus to cytoplasm to extracellular space, during exogenous HMGB1-induced HSCs autophagy. Meanwhile, the dose- and time-dependent effects by recombinant HMGB1 (rHMGB1) in enhancing LX-2 autophagy and fibrogenesis have been revealed with activated extracellular regulated protein kinase (ERK)/c-Jun N-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) and restrained mammalian target of rapamycin (mTOR)/STAT3 signaling pathways. Additionally, the ERK or JNK inhibitor could not only inhibit rHMGB1-induced autophagy and fibrogenesis in LX-2 cells, but also restore the suppressed mTOR and STAT3 pathways. Furthermore, using LC3-siRNA transfected LX-2, we found HMGB1-induced fibrogenesis is dependent on its autophagy-inducing effects. Finally, we elucidated the involvement of extracellular HMGB1-receptor for advenced glycation end product (RAGE) axis and endogenous HMGB1 in exogenous HMGB1-induced effects. Our findings could open new perspectives in developing an antifibrotic therapy by targetting the HSCs autophagy.

The Therapeutic and Pathogenic Role of Autophagy in Autoimmune Diseases

Autophagy is a complicated cellular mechanism that maintains cellular and tissue homeostasis and integrity via degradation of senescent, defective subcellular organelles, infectious agents, and misfolded proteins. Accumulating evidence has shown that autophagy is involved in numerous immune processes, such as removal of intracellular bacteria, cytokine production, autoantigen presentation, and survival of lymphocytes, indicating an apparent and important role in innate and adaptive immune responses. Indeed, in genome-wide association studies, autophagy-related gene polymorphisms have been suggested to be associated with the pathogenesis of several autoimmune and inflammatory disorders, such as systemic lupus erythematosus, psoriasis, rheumatoid arthritis, inflammatory bowel disease, and multiple sclerosis. In addition, conditional knockdown of autophagy-related genes in mice displayed therapeutic effects on several autoimmune disease models by reducing levels of inflammatory cytokines and autoreactive immune cells. However, the inhibition of autophagy accelerates the progress of some inflammatory and autoimmune diseases via promotion of inflammatory cytokine production. Therefore, this review will summarize the current knowledge of autophagy in immune regulation and discuss the therapeutic and pathogenic role of autophagy in autoimmune diseases to broaden our understanding of the etiopathogenesis of autoimmune diseases and shed light on autophagy-mediated therapies.

Baicalin Inhibits Haemophilus Parasuis-Induced High-Mobility Group Box 1 Release during Inflammation

Haemophilus parasuis (H. parasuis) can cause Glässer’s disease in pigs. However, the molecular mechanism of the inflammation response induced by H. parasuis remains unclear. The high-mobility group box 1 (HMGB1) protein is related to the pathogenesis of various infectious pathogens, but little is known about whether H. parasuis can induce the release of HMGB1 in piglet peripheral blood monocytes. Baicalin displays important anti-inflammatory and anti-microbial activities. In the present study, we investigated whether H. parasuis can trigger the secretion of HMGB1 in piglet peripheral blood monocytes and the anti-inflammatory effect of baicalin on the production of HMGB1 in peripheral blood monocytes induced by H. parasuis during the inflammation response. In addition, host cell responses stimulated by H. parasuis were determined with RNA-Seq. The RNA-Seq results showed that H. parasuis infection provokes the expression of cytokines and the activation of numerous pathways. In addition, baicalin significantly reduced the release of HMGB1 in peripheral blood monocytes induced by H. parasuis. Taken together, our study showed that H. parasuis can induce the release of HMGB1 and baicalin can inhibit HMGB1 secretion in an H. parasuis-induced peripheral blood monocytes model, which may provide a new strategy for preventing the inflammatory disorders induced by H. parasuis.

HMGB1 regulates T helper 2 and T helper17 cell differentiation both directly and indirectly in asthmatic mice

The Th (T helper) 2 response is characteristic of allergic asthma, and Th17 cells are involved in more severe asthma. Recent studies demonstrated that HMGB1 (High mobility group box 1 protein) regulates airway inflammation and the Th2, Th17 inflammatory response in asthma. HMGB1 can interact with Toll-like receptors (TLR) 2 and 4, and the receptor for advanced glycation end products (RAGE), activating the NF-κB (nuclear factor kappa B) signaling pathway and inducing the release of downstream inflammatory mediators. Both Th cells and dendritic cells express TLR2, TLR4, and RAGE receptors. Therefore, we speculate that HMGB1 could regulate the differentiation of Th2, Th17 cells in asthma through direct and indirect mechanisms. An ovalbumin (OVA)-induced mouse asthmatic model was established. Anti-HMGB1 antibody or rHMGB1 was administered to OVA-sensitized mice 30 min prior to each challenge. For in vitro studies, magnetically separated CD4⁺ naive T cells were stimulated with or without rHMGB1 and/or anti-HMGB1 antibody. BMDCs (bone marrow-derived dendritic cells)-stimulated with or without rHMGB1 and/or anti-HMGB1 antibody were cocultured with CD4⁺ naive T cells. Our study showed that administration of rHMGB1 aggravated airway inflammation and mucus production, and induced Th2, Th17 polarization in asthmatic mice, and that anti-HMGB1 antibody weakened characteristic features of asthma and blocked the Th2, Th17 inflammatory responses. HMGB1 could directly act on naive T cells to induce differentiation of Th2, Th17 cells in vitro through activating the TLR2, TLR4, RAGE-NF-κB signal pathway in CD4⁺ naive T cells. HMGB1 could also indirectly promote Th2, Th17 differentiation via activating the TLR2, TLR4, RAGE-NF-κB signal pathway in DCs to mediate their maturation and antigen-presenting ability in vitro.

Targeting autophagy in liver cancer

Autophagy is a catabolic cellular process conserved in animals. It is characterized by the main role of recycling all the non-functional products of the cells. Once, autophagy players detect non-functioning sub-cellular organelles and proteins, they start the so-called nucleation process. The organelles will be surrounded by a double membrane vesicle mainly constituted by endoplasmic reticulum (ER) membrane and autophagy proteins, e.g., MAP1LC3B, Beclin-1, VPS34, Unc-51 like autophagy activating kinase (ULK1) and ubiquitination-related proteins. Then the autophagic membrane will go through an elongation phase involving additional autophagy players. Once the autophagic vesicle is complete, the sub-cellular organelles will be isolated from the rest of the cytosol and driven to the final fusion with lysosomes. Here, the digestion process will end. Alteration and or impairment of autophagy have been shown to be correlated with development of diseases affecting the central nervous system, e.g., Alzheimer and other neurodegenerative diseases. Nonetheless, autophagy defect is responsible for tumorigenesis in blood and solid malignancies, in particular liver cancer. Malignancies of the liver are determined by several genetics and epigenetics mechanisms triggering the up-regulation of survival mechanisms and resistance to cell death. Furthermore, liver cancer could result from pathologic conditions like cirrhosis and fibrosis related to virus infection, aflatoxin, alcohol consumption and high fat diet together with insulin resistance. The role exerted by autophagy in the pathogenesis of the liver and tumor development has been evidenced in recent years. The alteration of autophagy assumes a fundamental role for liver tumorigenesis determining an accumulation of non-functional proteins and organelles that trigger oxidative stress leading to genotoxic stress and gene alterations. Furthermore, the absence of this degradation mechanism could prompt the cells to alter their metabolic status and turn into malignant cells. Interestingly, the heterozygous loss of function of Beclin-1 is able to trigger liver tumorigenesis or even the simple accumulation of proteins caused by the block of the final autolysosome fusion and degradation process is responsible for liver cancer development. This review highlights the importance of targeting the autophagy process in liver cancer in order to restore its function and to promote autophagy-mediated cell demise.

An optimized HMGB1 expressed by recombinant rabies virus enhances immunogenicity through activation of dendritic cells in mice

Rabies remains an important public health threat, killing approximately 59,000 people worldwide annually, most of which are from the developing countries of Africa and Asia where dog rabies are endemic. Therefore, developing an affordable and efficacious vaccine for dog-mediated rabies control is needful in these countries. Our previous studies indicated that over-expression of granulocyte-macrophage colony stimulating factor (GM-CSF) or macrophage inflammatory protein-1 (MIP-1α or CCL3) by recombinant rabies virus (rRABV) could enhance the immunogenicity by activating dendritic cells (DCs). In this study, to further characterize the role of activating DCs in RABV immunogenicity, High mobility group box 1 (HMGB1), a highly conserved and non-histone chromosomal protein that can promote DCs maturation and activation, were investigated. The wild-type HMGB1 (HMGB1wt) and an optimized HMGB1 (HMGB1mut) were individually inserted into the genome of the rRABV strain LBNSE (designated as LBNSE-HMGB1wt and LBNSE-HMGB1mut, respectively), and the effect of over-expression of HMGB1 on the immunogenicity of RABV was investigated. The results demonstrated that LBNSE-HMGB1mut could promote significantly more DCs activation, and the recruitment of follicular helper T, germinal center B and plasma cells in vaccinated mice than those immunized with LBNSE-HMGB1wt or parent virus LBNSE. Further investigations suggested that mice vaccinated with LBNSE-HMGB1mut produced significantly higher level of RABV-neutralizing antibodies and offered a better protection than those vaccinated with LBNSE or LBNSE-HMGB1wt. Taken together, these data provides a better understanding of the mechanism for HMGB1 as a potential adjuvant in enhancing the immunogenicity of RABV, which would contribute to developing more-efficacious rabies vaccines.