Galectin-9 restricts hepatitis B virus replication via p62/SQSTM1-mediated selective autophagy of viral core proteins

CBL/Cbl-b mediates Fas degradation to reduce neuronal damage in experimental autoimmune encephalomyelitis

Fas has been shown to positively regulate the differentiation of T helper 17 (Th17) cells in mouse models of experimental autoimmune encephalomyelitis (EAE). Fas protein expression is regulated by ubiquitination but has not been further studied. In this study, we investigated the role of the Fas ubiquitin ligase in Th17 cell differentiation and highlighted its potential as a therapeutic target for EAE. The E3 ubiquitin ligase CBL of Fas was predicted using the online prediction software ubibrowser. Overexpression of CBL significantly reduced Fas protein levels but did not affect mRNA levels. The decrease in Fas protein mediated by CBL overexpression was rescued by the proteasome inhibitor MG132. Co-IP analysis revealed that CBL interacted with Fas. Further results suggested that CBL regulated Fas expression through ubiquitination, thereby affecting Th17 cell differentiation. Cbl-b, a homologue of CBL, significantly promoted the degradation of Fas protein and increased its ubiquitination modification. Furthermore, CBL and Cbl-b could synergistically regulate Fas to influence Th17 cell differentiation. The same conclusion was also reached in animal models. Luxol Fast Blue staining showed that myelinated fibres in the spinal cord were significantly increased after CBL/Cbl-b overexpression in EAE. Finally, flow cytometry and immunofluorescence staining showed that overexpression of CBL or Cbl-b decreased the proportion of Th17 cells in the spinal cord of EAE mice, ultimately reducing neuronal damage. Taken together, these data demonstrate that CBL and Cbl-b can synergistically regulate Fas to inhibit Th17 cell differentiation, thereby alleviating spinal cord nerve injury in the EAE model.

Galectins and Host-Pathogen Interactions: The roles in viral infections

Galectins, a family of carbohydrate-binding proteins, play crucial roles in the host-virus interaction landscape. This review explores the multifaceted contributions of endogenous galectins to various stages of the viral lifecycle, including attachment, replication, assembly, and release of progeny virions. Recent studies have indicated that viral infections can induce the expression and secretion of specific galectins, with elucidated signaling pathways in some cases, enhancing our understanding of their regulatory mechanisms. While many studies have focused on the effects of exogenous recombinant galectins, there is growing interest in the intrinsic functions of endogenous galectins, particularly through genetic alterations in cellular models. This review highlights the need for further research to uncover the complex roles of galectins in modulating viral infections and emphasizes their potential as therapeutic targets in the fight against viral diseases. Understanding these interactions could pave the way for novel strategies to enhance host defense mechanisms and mitigate viral pathogenesis.

Ubiquitin: A double-edged sword in hepatitis B virus-induced hepatocellular carcinoma

Hepatitis B virus is one of the leading causes behind the neoplastic transformation of liver tissue and associated mortality. Despite the availability of many therapies and vaccines, the pathogenic landscape of the virus remains elusive; urging the development of novel strategies based on the fundamental infectious and transformative modalities of the virus-host interactome. Ubiquitination is a widely observed post-translational modification of several proteins, which either regulates the proteins' turnover or impacts their functionalities. In recent years, ample amount of literature has accumulated regarding the ubiquitination dynamics of the HBV proteins as well as the host proteins during HBV infection and carcinogenesis; with direct and detailed characterization of the involvement of HBV in these processes. Interestingly, while many of these ubiquitination events restrict HBV life cycle and carcinogenesis, several others promote the emergence of hepatocarcinoma by putting the virus in an advantageous position. This review sums up the snowballing literature on ubiquitination-mediated regulation of the host-HBV crosstalk, with special emphasis on its influence on the establishment and progression of hepatocellular carcinoma on a molecular level. With the advent of cutting-edge ubiquitination-targeted therapeutic approaches, the findings emanating from this review may potentiate the identification of novel anti-HBV targets for the formulation of novel anticancer strategies to control the HBV-induced hepato-carcinogenic process on a global scale.

Optineurin inhibits IBDV replication via interacting with VP1

Avibirnavirus, specifically Infectious Bursal Disease Virus (IBDV), is a highly contagious pathogen that causes significant economic losses in the poultry industry. The polymerase protein VP1 of IBDV is critical to the viral life cycle, facilitating the synthesis of viral mRNA and the genome. Previous studies have suggested that various host factors influence the regulation of IBDV polymerase activity. In this study, we identified that IBDV infection induces the expression of optineurin (OPTN), a mitophagy receptor and a protein associated with amyotrophic lateral sclerosis (ALS), as well as a negative regulator of interferon I production. The induced expression of OPTN acts as a suppressor of IBDV replication, a function dependent on its ubiquitin-binding domain (UBAN). Furthermore, we demonstrated that OPTN exerts its antiviral effects through direct interactions with VP1 and VP3, which inhibit the polymerase activity of VP1 by preventing K63-linked ubiquitination of VP1. To our knowledge, this study is the first to report that OPTN, upregulated during IBDV infection, functions as a novel antiviral host factor that limits the virus's replicative capacity, offering a potential target for anti-IBDV therapeutic strategies.

The multifaceted roles of selective autophagy receptors in viral infections

Selective autophagy is a protein clearance mechanism mediated by evolutionarily conserved selective autophagy receptors (SARs), which specifically degrades misfolded, misassembled, or metabolically regulated proteins. SARs help the host to suppress viral infections by degrading viral proteins. However, viruses have evolved sophisticated mechanisms to counteract, evade, or co-opt autophagic processes, thereby facilitating viral replication. Therefore, this review aims to summarize the complex mechanisms of SARs involved in viral infections, specifically focusing on how viruses exploit strategies to regulate selective autophagy. We present an updated understanding of the various critical roles of SARs in viral pathogenesis. Furthermore, newly discovered evasion strategies employed by viruses are discussed and the ubiquitination-autophagy-innate immune regulatory axis is proposed to be a crucial pathway to control viral infections. This review highlights the remarkable flexibility and plasticity of SARs in viral infections.

AP-1 contributes to endosomal targeting of the ubiquitin ligase RNF13 via a secondary and novel non-canonical binding motif

Cellular trafficking between organelles is typically assured by short motifs that contact carrier proteins to transport them to their destination. The ubiquitin E3 ligase RING finger protein 13 (RNF13), a regulator of proliferation, apoptosis and protein trafficking, localizes to endolysosomal compartments through the binding of a dileucine motif to clathrin adaptor protein complex AP-3. Mutations within this motif reduce the ability of RNF13 to interact with AP-3. Here, our study shows the discovery of a glutamine-based motif that resembles a tyrosine-based motif within the C-terminal region of RNF13 that binds to the clathrin adaptor protein complex AP-1, notably without a functional interaction with AP-3. Using biochemical, molecular and cellular approaches in HeLa cells, our study demonstrates that a RNF13 dileucine variant uses an AP-1-dependent pathway to be exported from the Golgi towards the endosomal compartment. Overall, this study provides mechanistic insights into the alternate route used by this variant of the dileucine sorting motif of RNF13.

Colchicine-mediated selective autophagic degradation of HBV core proteins inhibits HBV replication and HBV-related hepatocellular carcinoma progression

The HBV core protein (HBc) is an important viral protein of HBV that plays an indispensable role in the lifecycle of HBV, including capsid assembly and transport, reverse transcription and virus release. In recent years, evidence has shown that HBc may be involved in the malignant progression of HCC. Thus, HBc is an attractive target for antiviral agents and provides a new strategy for the treatment of HBV-related HCC. Here, we identified a novel anti-HBc compound-colchicine, an alkaloid compound-that promoted selective autophagic degradation of HBc through the AMPK/mTOR/ULK1 signalling pathway. We further confirmed that colchicine promoted the selective autophagy of HBc by enhancing the binding of HBc to the autophagy receptor p62. Finally, we evaluated the effects of colchicine on HBV replication and HBc-mediated HCC metastasis in vitro and in vivo. Our research indicated that the inhibitory effects of colchicine on HBV and HBV-related HCC depend on the selective autophagic degradation of HBc. Thus, colchicine is not only a promising therapeutic strategy for chronic hepatitis B but also a new treatment for HBV-related HCC.

Damage-associated molecular patterns in viral infection: potential therapeutic targets

Frequent viral infections leading to infectious disease outbreaks have become a significant global health concern. Fully elucidating the molecular mechanisms of the immune response against viral infections is crucial for epidemic prevention and control. The innate immune response, the host's primary defense against viral infection, plays a pivotal role and has become a breakthrough in research mechanisms. A component of the innate immune system, damage-associated molecular patterns (DAMPs) are involved in inducing inflammatory responses to viral infections. Numerous DAMPs are released from virally infected cells, activating downstream signaling pathways via internal and external receptors on immune cells. This activation triggers immune responses and helps regulate viral host invasion. This review examines the immune regulatory mechanisms of various DAMPs, such as the S100 protein family, high mobility group box 1 (HMGB1), and heat shock proteins, in various viral infections to provide a theoretical basis for designing novel antiviral drugs.

The role of galectins in the regulation of autophagy and inflammasome in host immunity

Galectins, a family of glycan-binding proteins have been shown to bind a wide range of glycans. In the cytoplasm, these glycans can be endogenous (or "self"), originating from damaged endocytic vesicles, or exogenous (or "non-self"), found on the surface of invading microbial pathogens. Galectins can detect these unusual cytosolic exposures to glycans and serve as critical regulators in orchestrating immune responses in innate and adaptive immunity. This review provides an overview of how galectins modulate host cellular responses, such as autophagy, xenophagy, and inflammasome-dependent cell death program, to infection.

DDX58 variant triggers IFN-β-induced autophagy in trabecular meshwork and influences intraocular pressure

Singleton-Merten syndrome (SMS) is a rare immunogenetic disorder affecting multiple systems, characterized by dental dysplasia, aortic calcification, glaucoma, skeletal abnormalities, and psoriasis. Glaucoma, a key feature of both classical and atypical SMS, remains poorly understood in terms of its molecular mechanism caused by DDX58 mutation. This study presented a novel DDX58 variant (c.1649A>C [p.Asp550Ala]) in a family with childhood glaucoma. Functional analysis showed that DDX58 variant caused an increase in IFN-stimulated gene expression and high IFN-β-based type-I IFN. As the trabecular meshwork (TM) is responsible for controlling intraocular pressure (IOP), we examine the effect of IFN-β on TM cells. Our study is the first to demonstrate that IFN-β significantly reduced TM cell viability and function by activating autophagy. In addition, anterior chamber injection of IFN-β remarkably increased IOP level in mice, which can be attenuated by treatments with autophagy inhibitor chloroquine. To uncover the specific mechanism underlying IFN-β-induced autophagy in TM cells, we performed microarray analysis in IFN-β-treated and DDX58 p.Asp550Ala TM cells. It showed that RSAD2 is necessary for IFN-β-induced autophagy. Knockdown of RSAD2 by siRNA significantly decreased autophagy flux induced by IFN-β. Our findings suggest that DDX58 mutation leads to the overproduction of IFN-β, which elevates IOP by modulating autophagy through RSAD2 in TM cells.

OASL suppresses infectious bursal disease virus replication by targeting VP2 for degrading through the autophagy pathway

Infectious bursal disease (IBD) is an acute and fatal immunosuppressive disease caused by infectious bursal disease virus (IBDV). As an obligate intracellular parasite, IBDV infection is strictly regulated by host factors. Knowledge on the antiviral activity and possible mechanism of host factors might provide the theoretical basis for the prevention and control of IBD. In this study, RNA-sequencing results indicated that many host factors were induced by IBDV infection, among which the expression levels of OASL (2´,5´-oligadenylate synthetase-like protein) was significantly upregulated. OASL overexpression significantly inhibited IBDV replication, whereas OASL knockdown promoted IBDV replication. Interestingly, the antiviral ability of OASL was independent of its canonical enzymatic activity, i.e., OASL targeted viral protein VP2 for degradation, depending on the autophagy receptor p62/SQSTM1 in the autophagy pathway. Additionally, the 316 lysine (K) of VP2 was the key site for autophagy degradation, and its replacement with arginine disrupted VP2 degradation induced by OASL and enhanced IBDV replication. Importantly, our results for the first time indicate a unique and potent defense mechanism of OASL against double-stranded RNA virus by interaction with viral proteins, which leads to their degradation.

IMPORTANCE

OASL (2´,5´-oligadenylate synthetase-like protein) exhibits broad-spectrum antiviral effects against single-stranded RNA viruses in mammals, potentially serving as a promising target for novel antiviral strategies. However, its role in inhibiting the replication of double-stranded RNA viruses (dsRNA viruses), such as infectious bursal disease virus (IBDV), in avian species remains unclear. Our findings indicated a unique and potent defense mechanism of OASL against dsRNA viruses. It has been previously shown in mammals that OASL inhibits virus replication through increasing interferon production. The groundbreaking aspect of our study is the finding that OASL has the ability to interact with IBDV viral protein VP2 and target it for degradation and thus exerts its antiviral effect. Our results reveal the interaction between avian natural antiviral immune response and IBDV infection. Our study not only enhances our understanding of bird defenses against viral infections but can also inform strategies for poultry disease management.

Intracellular Host Restriction of Hepatitis B Virus Replication

The hepatitis B virus (HBV) infects hepatocytes and hijacks host cellular mechanisms for its replication. Host proteins can be frontline effectors of the cell's defense and restrict viral replication by impeding multiple steps during its intracellular lifecycle. This review summarizes many of the well-described restriction factors, their mechanisms of restriction, and counteractive measures of HBV, with a special focus on viral transcription. We discuss some of the limitations and knowledge gaps about the restriction factors, highlighting how these factors may be harnessed to facilitate therapeutic strategies against HBV.

Perilipin 2 inhibits replication of hepatitis B virus deoxyribonucleic acid by regulating autophagy under high-fat conditions

Hepatitis B virus (HBV) infection poses a global health concern without a definitive cure; however, antiviral medications can effectively suppress viral replication. This study delves into the intricate interplay between lipid metabolism and HBV replication, implicating molecular mechanisms such as the stearoyl coenzyme A desaturase 1 autophagy pathway, SAC1-like phosphatidylinositol phosphatase, and galectin-9 mediated selective autophagy of viral core proteins in regulating HBV replication. Within lipid droplets, perilipin 2 (PLIN2) emerges as a pivotal guardian, with its overexpression protecting against autophagy and downregulation stimulating triglyceride catabolism through the autophagy pathway. This editorial discusses the correlation between hepatic steatosis and HBV replication, emphasizing the role of PLIN2 in this process. The study underscores the multifaceted roles of lipid metabolism, autophagy, and perilipins in HBV replication, shedding light on potential therapeutic avenues.

An Overview of the Unfolded Protein Response (UPR) and Autophagy Pathways in Human Viral Oncogenesis

Autophagy and Unfolded Protein Response (UPR) can be regarded as the safe keepers of cells exposed to intense stress. Autophagy maintains cellular homeostasis, ensuring the removal of foreign particles and misfolded macromolecules from the cytoplasm and facilitating the return of the building blocks into the system. On the other hand, UPR serves as a shock response to prolonged stress, especially Endoplasmic Reticulum Stress (ERS), which also includes the accumulation of misfolded proteins in the ER. Since one of the many effects of viral infection on the host cell machinery is the hijacking of the host translational system, which leaves in its wake a plethora of misfolded proteins in the ER, it is perhaps not surprising that UPR and autophagy are common occurrences in infected cells, tissues, and patient samples. In this book chapter, we try to emphasize how UPR, and autophagy are significant in infections caused by six major oncolytic viruses-Epstein-Barr (EBV), Human Papilloma Virus (HPV), Human Immunodeficiency Virus (HIV), Human Herpesvirus-8 (HHV-8), Human T-cell Lymphotropic Virus (HTLV-1), and Hepatitis B Virus (HBV). Here, we document how whole-virus infection or overexpression of individual viral proteins in vitro and in vivo models can regulate the different branches of UPR and the various stages of macro autophagy. As is true with other viral infections, the relationship is complicated because the same virus (or the viral protein) exerts different effects on UPR and Autophagy. The nature of this response is determined by the cell types, or in some cases, the presence of diverse extracellular stimuli. The vice versa is equally valid, i.e., UPR and autophagy exhibit both anti-tumor and pro-tumor properties based on the cell type and other factors like concentrations of different metabolites. Thus, we have tried to coherently summarize the existing knowledge, the crux of which can hopefully be harnessed to design vaccines and therapies targeted at viral carcinogenesis.

The cGAS-STING pathway in viral infections: a promising link between inflammation, oxidative stress and autophagy

The host defence responses play vital roles in viral infection and are regulated by complex interactive networks. The host immune system recognizes viral pathogens through the interaction of pattern-recognition receptors (PRRs) with pathogen-associated molecular patterns (PAMPs). As a PRR mainly in the cytoplasm, cyclic GMP-AMP synthase (cGAS) senses and binds virus DNA and subsequently activates stimulator of interferon genes (STING) to trigger a series of intracellular signalling cascades to defend against invading pathogenic microorganisms. Integrated omic and functional analyses identify the cGAS-STING pathway regulating various host cellular responses and controlling viral infections. Aside from its most common function in regulating inflammation and type I interferon, a growing body of evidence suggests that the cGAS-STING signalling axis is closely associated with a series of cellular responses, such as oxidative stress, autophagy, and endoplasmic reticulum stress, which have major impacts on physiological homeostasis. Interestingly, these host cellular responses play dual roles in the regulation of the cGAS-STING signalling axis and the clearance of viruses. Here, we outline recent insights into cGAS-STING in regulating type I interferon, inflammation, oxidative stress, autophagy and endoplasmic reticulum stress and discuss their interactions with viral infections. A detailed understanding of the cGAS-STING-mediated potential antiviral effects contributes to revealing the pathogenesis of certain viruses and sheds light on effective solutions for antiviral therapy.

Association of ATG16L1 and ATG5 gene polymorphisms with susceptibility to hepatitis B virus infection and progression to HCC in central China

Hepatitis B virus (HBV) infection is a severe public health problem worldwide. The relationship between polymorphisms of autophagy-related 16-like 1 gene (ATG16L1) and autophagy-related gene 5 (ATG5) with susceptibility to the stage of HBV infection has been reported in different populations. Nevertheless, this association is not seen in the population of central China. This study recruited 452 participants, including 246 HBV-infected patients (139 chronically infected HBV without hepatocellular carcinoma [HCC] and 107 HBV-related HCC patients) and 206 healthy controls. Genotyping of ATG16L1 rs2241880 and ATG5 rs688810 were performed using Sanger sequencing and polymerase chain reaction-restriction fragment length polymorphism, respectively. Our results indicated that the G allele of ATG16L1 rs2241880 was more frequent in healthy controls than in patients with chronicHBV infection. After adjusting for age and sex, an association between the ATG16L1 rs2241880 polymorphism and HBV infection was significant under the dominant and allele models (p = 0.009 and 0.003, respectively). However, no association between the ATG5 polymorphisms and HBV infection was observed. We also did not find a significant association between ATG16L1 and ATG5 polymorphisms and the progression of HBV-related HCC. Therefore, the genetic polymorphism of ATG16L1 rs2241880 may be associated with susceptibility to HBV infection in the population of central China.

Synaptotagmin-7 mediates cardiac hypertrophy by targeting autophagy

Sustained cardiac hypertrophy damages the heart and weakens cardiac function, often leading to heart failure and even death. Pathological cardiac hypertrophy has become a central therapeutic target for many heart diseases including heart failure. However, the underlying mechanisms of cardiac hypertrophy, especially the involvement of autophagy program, are still ill-understood. Synaptotagmin-7 (Syt7), a multifunctional and high-affinity calcium sensor, plays a pivotal role in asynchronous neurotransmitter release, synaptic facilitation, and vesicle pool regulation during synaptic transmission. However, little is known about whether Syt7 is expressed in the myocardium and involved in the pathogenesis of heart diseases. Here we showed that Syt7 was significantly upregulated in Ang II-treated hearts and cardiomyocytes. Homozygous syt7 knockout (syt7-/-) mice exhibited significantly attenuated cardiac hypertrophy and fibrosis and improved cardiac function. We further found that Syt7 exerted a pro-hypertrophic effect by suppressing the autophagy process. In exploring the upstream mechanisms, microRNA (miR)-93 was identified to participate in the regulation of Syt7 expression. miR-93 protected hearts against Ang II-induced hypertrophy through targeting Syt7-autophagy pathway. In summary, our data reveal a new cardiac hypertrophy regulator and a novel hypertrophy regulating model composed of miR-93, Syt7 and autophagy program. These molecules may serve as potential therapeutic targets in the treatment of cardiac hypertrophy and heart failure.

Feedback loop regulation between viperin and viral hemorrhagic septicemia virus through competing protein degradation pathways

Viperin is an antiviral protein that exhibits a remarkably broad spectrum of antiviral activity. Viperin-like proteins are found all kingdoms of life, suggesting it is an ancient component of the innate immune system. However, viruses have developed strategies to counteract viperin's effects. Here, we describe a feedback loop between viperin and viral hemorrhagic septicemia virus (VHSV), a common fish pathogen. We show that Lateolabrax japonicus viperin (Ljviperin) is induced by both IFN-independent and IFN-dependent pathways, with the C-terminal domain of Ljviperin being important for its anti-VHSV activity. Ljviperin exerts an antiviral effect by binding both the nucleoprotein (N) and phosphoprotein (P) of VHSV and induces their degradation through the autophagy pathway, which is an evolutionarily conserved antiviral mechanism. However, counteracting viperin's activity, N protein targets and degrades transcription factors that up-regulate Ljviperin expression, interferon regulatory factor (IRF) 1 and IRF9, through ubiquitin-proteasome pathway. Together, our results reveal a previously unknown feedback loop between viperin and virus, providing potential therapeutic targets for VHSV prevention.

Importance

Viral hemorrhagic septicaemia (VHS) is a contagious disease caused by the viral hemorrhagic septicaemia virus (VHSV), which poses a threat to over 80 species of marine and freshwater fish. Currently, there are no effective treatments available for this disease. Understanding the mechanisms of VHSV-host interaction is crucial for preventing viral infections. Here, we found that, as an ancient antiviral protein, viperin degrades the N and P proteins of VHSV through the autophagy pathway. Additionally, the N protein also impacts the biological functions of IRF1 and IRF9 through the ubiquitin-proteasome pathway, leading to the suppression of viperin expression. Therefore, the N protein may serve as a potential virulence factor for the development of VHSV vaccines and screening of antiviral drugs. Our research will serve as a valuable reference for the development of strategies to prevent VHSV infections.

Autophagy as a dual-faced host response to viral infections

Autophagy selectively degrades viral particles or cellular components, either facilitating or inhibiting viral replication. Conversely, most viruses have evolved strategies to escape or exploit autophagy. Moreover, autophagy collaborates with the pattern recognition receptor signaling, influencing the expression of adaptor molecules involved in the innate immune response and regulating the expression of interferons (IFNs). The intricate relationship between autophagy and IFNs plays a critical role in the host cell defense against microbial invasion. Therefore, it is important to summarize the interactions between viral infections, autophagy, and the host defense mechanisms against viruses. This review specifically focuses on the interactions between autophagy and IFN pathways during viral infections, providing a comprehensive summary of the molecular mechanisms utilized or evaded by different viruses.

Galectin 9 restricts viral replication in teleost via autophagy-antiviral pathway and polarizes M2 macrophages for anti-inflammatory response: New insights into functional properties of fish Galectin-9 from Planiliza haematocheilus

Galectin 9 (Gal9) is a tandem repeat type ß-galactoside-binding galectin that mediates various cellular biochemical and immunological functions. Many studies have investigated the functional properties of Gal9 in mammals; however, knowledge of fish Gal9 is limited to antibacterial studies. In this context, our aim was to clone Gal9 from Planiliza haematocheilus (PhGal9) and investigate its structural and functional characteristics. We discovered the PhGal9 open reading frame, which was 969 base pairs long and encoded a 322 amino acid protein. PhGal9 had a projected molecular weight of 35.385 kDa but no signal peptide sequence. PhGal9 mRNA was ubiquitously produced in all investigated tissues but was predominant in the intestine, spleen, and brain. Its mRNA expression was increased in response to stimulation by Poly(I:C), LPS, and L. garvieae. The rPhGal9 exhibited a dose-dependent agglutination potential toward gram-positive and gram-negative bacteria at a minimum concentration of 50 μg/mL. Overexpression of PhGal9 promoted M2-like phenotype changes in mouse macrophages, and RT-qPCR analysis of M1 and M2 marker genes confirmed M2 polarization with upregulation of M2 marker genes. In the antiviral assay, the expression levels of Viral Hemorrhagic Septicemia Virus (VHSV) glycoproteins, phosphoproteins, nucleoproteins, non-virion proteins, matrix proteins, and RNA polymerase were significantly reduced in PhGal9-overexpressed cells. Furthermore, the mRNA expression of autophagic genes (sqstm1, tax1bp1b, rnf13, lc3, and atg5) and antiviral genes (viperin) were upregulated in PhGal9 overexpressed cells. For the first time in teleosts, our study demonstrated that PhGal9 promotes M2 macrophage polarization by upregulating M2-associated genes (egr2 and cmyc) and suppressing M1-associated genes (iNOS and IL-6). Furthermore, our results show that exogenous and endogenous PhGal9 prevented VHSV attachment and replication by neutralizing virion and autophagy, respectively. Gal9 may be a potent modulator of the antimicrobial immune response in teleost fish.

A galectin-9 involved in the microbial recognition and haemocyte autophagy in the Pacific oyster Crassostrea gigas

Galectin-9 is a tandem-repeat type member of galectin family participating in various immune responses, such as cell agglutination, phagocytosis, and autophagy. In the present study, a tandem repeat galectin-9 (defined as CgGal-9) was identified from Pacific oyster Crassostrea gigas, which consisted of two conserved carbohydrate recognition domains (CRDs) joined by a linker peptide. CgGal-9 was closely clustered with CaGal-9 from C. angulata, and they were assigned into the branch of invertebrate galectin-9s in the phylogenetic tree. The mRNA transcripts of CgGal-9 were detected in all the tested tissues, with the highest expression level in haemocytes. The mRNA expressions of CgGal-9 in haemocytes increased significantly after lipopolysaccharide (LPS) and Vibrio splendidus stimulation. The recombinant CgGal-9 was able to bind all the examined pathogen-associated molecular patterns (LPS, peptidoglycan, and mannose) and microbes (V. splendidus, Escherichia coli, Micrococcus luteus, Staphylococcus aureus, Bacillus subtilis, and Pichia pastoris), and agglutinated most of them in the presence of Ca2+. In CgGal-9-RNAi oysters, the mRNA expressions of autophagy related genes (CgBeclin1, CgATG5, CgP62 and CgLC3) in haemocytes decreased significantly while that of CgmTOR increased significantly at 3 h after V. splendidus stimulation. The autophagy level and mRNA expressions of autophagy related genes decreased in haemocytes after CgGal-9 was blocked by the corresponding antibody. These results revealed that CgGal-9 was able to bind different microbes and might be involved in haemocyte autophagy in the immune response of oyster.

RNF13 protects against pathological cardiac hypertrophy through p62-NRF2 pathway

Heart failure (HF) severely impairs human health because of its high incidence and mortality. Cardiac hypertrophy is the main cause of HF, while its underlying mechanism is not fully clear. As an E3 ubiquitin ligase, Ring finger protein 13 (RNF13) plays a crucial role in many disorders, such as liver immune, neurological disease and tumorigenesis, whereas the function of RNF13 in cardiac hypertrophy remains largely unknown. In the present study, we found that the protein expression of RNF13 is up-regulated in the transverse aortic constriction (TAC)-induced murine hypertrophic hearts and phenylephrine (PE)-induced cardiomyocyte hypertrophy. Functional investigations indicated that RNF13 global knockout mice accelerates the degree of TAC-induced cardiac hypertrophy, including cardiomyocyte enlargement, cardiac fibrosis and heart dysfunction. On the contrary, adeno-associated virus 9 (AAV9) mediated-RNF13 overexpression mice alleviated cardiac hypertrophy. Furthermore, we demonstrated that adenoviral RNF13 attenuates the PE-induced cardiomyocyte hypertrophy and down-regulates the expression of cardiac hypertrophic markers, while the opposite results were observed in the RNF13 knockdown group. The RNA-sequence of RNF13 knockout and wild type mice showed that RNF13 deficiency activates oxidative stress after TAC surgery. In terms of the mechanism, we found that RNF13 directly interacted with p62 and promoted the activation of downstream NRF2/HO-1 signaling. Finally, we proved that p62 knockdown can reverse the effect of RNF13 in cardiac hypertrophy. In conclusion, RNF13 protects against the cardiac hypertrophy via p62-NRF2 axis.

30 years of nanobodies - an ongoing success story of small binders in biological research

A milestone in the field of recombinant binding molecules was achieved 30 years ago with the discovery of single-domain antibodies from which antigen-binding variable domains, better known as nanobodies (Nbs), can be derived. Being only one tenth the size of conventional antibodies, Nbs feature high affinity and specificity, while being highly stable and soluble. In addition, they display accessibility to cryptic sites, low off-target accumulation and deep tissue penetration. Efficient selection methods, such as (semi-)synthetic/naïve or immunized cDNA libraries and display technologies, have facilitated the isolation of Nbs against diverse targets, and their single-gene format enables easy functionalization and high-yield production. This Review highlights recent advances in Nb applications in various areas of biological research, including structural biology, proteomics and high-resolution and in vivo imaging. In addition, we provide insights into intracellular applications of Nbs, such as live-cell imaging, biosensors and targeted protein degradation.

Streptococcus uberis induced expressions of pro-inflammatory IL-6, TNF-α, and IFN-γ in bovine mammary epithelial cells associated with inhibited autophagy and autophagy flux formation

Autophagy is a highly conserved cellular defensive mechanism that can eliminate bacterial pathogens such as Streptococcus uberis, that causes mastitis in cows. However, S. uberis induced autophagy is still unclear. In this study, we tested if certain inflammatory cytokines such as IL-6, TNF-α, and IFN-γ, critical in mastitis due to S. uberis infection, regulate autophagy activation in bovine mammary epithelial cells (bMECs). Using Western blot and laser scanning confocal microscope in bMECs challenged by S. uberis, showed that the expression of IL-6, TNF-α, IFN-γ oscillated with the expressions of autophagic Atg5, ULK1, PTEN, P62, and LC3ӀӀ/LC3Ӏ. S. uberis infection induced autophagosomes and LC3 puncta in bMECs with upregulation of Atg5, ULK1, PTEN, LC3ӀӀ/LC3Ӏ, and downregulation of P62. The levels of IL-6, TNF-α, and IFN-γ increased during autophagy flux formation to decrease during autophagy induction. Autophagy inhibition increased the expression of IL-6, TNF-α, and IFN-γ and increased S. uberis burden. This study indicates autophagy is induced during S. uberis infection and IL-6, TNF-α, and IFN-γ contribute to autophagy and autophagy flux formation.

Galectin-9 interacts with Vamp-3 to regulate cytokine secretion in dendritic cells

Intracellular vesicle transport is essential for cellular homeostasis and is partially mediated by SNARE proteins. Endosomal trafficking to the plasma membrane ensures cytokine secretion in dendritic cells (DCs) and the initiation of immune responses. Despite its critical importance, the specific molecular components that regulate DC cytokine secretion are poorly characterised. Galectin-9, a ß-galactoside-binding protein, has emerged as a novel cellular modulator although its exact intracellular roles in regulating (immune) cell homeostasis and vesicle transport are virtually unknown. We investigated galectin-9 function in primary human DCs and report that galectin-9 is essential for intracellular cytokine trafficking to the cell surface. Galectin-9-depleted DCs accumulate cytokine-containing vesicles in the Golgi complex that eventually undergo lysosomal degradation. We observed galectin-9 to molecularly interact with Vamp-3 using immunoprecipitation-mass-spectrometry and identified galectin-9 was required for rerouting Vamp-3-containing endosomes upon DC activation as the underlying mechanism. Overall, this study identifies galectin-9 as a necessary mechanistic component for intracellular trafficking. This may impact our general understanding of vesicle transport and sheds new light into the multiple roles galectins play in governing cell function.

The interrelation of galectins and autophagy

Autophagy is a vital physiological process that maintains intracellular homeostasis by removing damaged organelles and senescent or misfolded molecules. However, excessive autophagy results in cell death and apoptosis, which will lead to a variety of diseases. Galectins are a type of animal lectin that binds to β-galactosides and can bind to the cell surface or extracellular matrix glycans, affecting a variety of immune processes in vivo and being linked to the development of many diseases. In many cases, galectins and autophagy both play important regulatory roles in the cellular life course, yet our understanding of the relationship between them is still incomplete. Galectins and autophagy may share common etiological cofactors for some diseases. Hence, we summarize the relationship between galectins and autophagy, aiming to draw attention to the existence of multiple associations between galectins and autophagy in a variety of physiological and pathological processes, which provide new ideas for etiological diagnosis, drug development, and therapeutic targets for related diseases.

Human Cytomegalovirus UL23 Antagonizes the Antiviral Effect of Interferon-γ by Restraining the Expression of Specific IFN-Stimulated Genes

Interferon-γ (IFN-γ) is a critical component of innate immune responses in humans to combat infection by many viruses, including human cytomegalovirus (HCMV). IFN-γ exerts its biological effects by inducing hundreds of IFN-stimulated genes (ISGs). In this study, RNA-seq analyses revealed that HCMV tegument protein UL23 could regulate the expression of many ISGs under IFN-γ treatment or HCMV infection. We further confirmed that among these IFN-γ stimulated genes, individual APOL1 (Apolipoprotein-L1), CMPK2 (Cytidine/uridine monophosphate kinase 2), and LGALS9 (Galectin-9) could inhibit HCMV replication. Moreover, these three proteins exhibited a synergistic effect on HCMV replication. UL23-deficient HCMV mutants induced higher expression of APOL1, CMPK2, and LGALS9, and exhibited lower viral titers in IFN-γ treated cells compared with parental viruses expressing full functional UL23. Thus, UL23 appears to resist the antiviral effect of IFN-γ by downregulating the expression of APOL1, CMPK2, and LGALS9. This study highlights the roles of HCMV UL23 in facilitating viral immune escape from IFN-γ responses by specifically downregulating these ISGs.

Nonstructural proteins 2B and 4A of Tembusu virus induce complete autophagy to promote viral multiplication in vitro

Tembusu virus (TMUV) is an emerging flavivirus that has broken out in different regions of China. TMUV infection has been reported to induce autophagy in duck embryo fibroblast cells. However, the molecular mechanisms underlying this autophagy induction remain unclear. Here, we explored the interactions between autophagy and TMUV and the effects of the structural and nonstructural proteins of TMUV on autophagy in vitro. Among our results, TMUV infection enhanced autophagy to facilitate viral replication in HEK293T cells. After pharmacologically inducing autophagy with rapamycin (Rapa), the replication of TMUV increased by a maximum of 14-fold compared with the control group. To determine which TMUV protein primarily induced autophagy, cells were transfected with two structural proteins and seven nonstructural proteins of TMUV. Western blotting showed that nonstructural proteins 2B (NS2B) and 4 A (NS4A) of TMUV significantly induced the conversion of microtubule-associated protein 1 light chain 3 (LC3) from LC3-I to LC3-II in HEK293T cells. In addition, through immunofluorescence assays, we found that NS2B and NS4A significantly increased the punctate fluorescence of GFP-LC3-II. Furthermore, we found that both NS2B and NS4A interacted with polyubiquitin-binding protein sequestosome 1 (SQSTM1/p62) in a coimmunoprecipitation assay. Moreover, the autophagic degradation of p62 and LC3 mediated by NS2B or NS4A was inhibited by treatment with the autophagic flux inhibitor chloroquine (CQ). These results confirmed the vital effects of NS2B and NS4A in TMUV-induced complete autophagy and clarified the importance of complete autophagy for viral replication, providing novel insight into the relationship between TMUV and autophagy.

Hepatocytes: A key role in liver inflammation

Hepatocytes, the major parenchymal cells in the liver, are responsible for a variety of cellular functions including carbohydrate, lipid and protein metabolism, detoxification and immune cell activation to maintain liver homeotasis. Recent studies show hepatocytes play a pivotal role in liver inflammation. After receiving liver insults and inflammatory signals, hepatocytes may undergo organelle damage, and further respond by releasing mediators and expressing molecules that can act in the microenvironment as well as initiate a robust inflammatory response. In this review, we summarize how the hepatic organelle damage link to liver inflammation and introduce numerous hepatocyte-derived pro-inflammatory factors in response to chronic liver injury.

The role of autophagy in viral infections

Autophagy is an evolutionarily conserved catabolic cellular process that exerts antiviral functions during a viral invasion. However, co-evolution and co-adaptation between viruses and autophagy have armed viruses with multiple strategies to subvert the autophagic machinery and counteract cellular antiviral responses. Specifically, the host cell quickly initiates the autophagy to degrade virus particles or virus components upon a viral infection, while cooperating with anti-viral interferon response to inhibit the virus replication. Degraded virus-derived antigens can be presented to T lymphocytes to orchestrate the adaptive immune response. Nevertheless, some viruses have evolved the ability to inhibit autophagy in order to evade degradation and immune responses. Others induce autophagy, but then hijack autophagosomes as a replication site, or hijack the secretion autophagy pathway to promote maturation and egress of virus particles, thereby increasing replication and transmission efficiency. Interestingly, different viruses have unique strategies to counteract different types of selective autophagy, such as exploiting autophagy to regulate organelle degradation, metabolic processes, and immune responses. In short, this review focuses on the interaction between autophagy and viruses, explaining how autophagy serves multiple roles in viral infection, with either proviral or antiviral functions.

Ciliatoside A, isolated from Peristrophe japonica, inhibits HBsAg expression and cccDNA transcription by inducing autophagy

Hepatitis B surface antigen (HBsAg) loss and seroconversion are considered as an end point of a functional cure. Therefore, it is crucial to find new agents which could efficiently decrease HBsAg. Traditional herbal plants have been considered as an important source of new hepatitis B drugs development for their extensive use in antimicrobial and anti-inflammation. In this study, Peristrophe japonica, which could remarkably reduce HBsAg in the supernatant of HepG2.2.15 cells, was screened out for further extraction. Here, an active ethyl acetate fraction of Peristrophe japonica containing 34 sub-fractions was extracted. Subsequently, the monomeric compound Ciliatoside A was isolated and identified as a potential antiviral reagent with low cytotoxicity from Fraction 30. Ciliatoside A exhibited strong inhibition on intracellular and circulating HBsAg and HBV RNAs in HBV-infected cells and an HBV recombinant-cccDNA mouse model. The mechanistic study revealed that Ciliatoside A exhibited a potent anti-HBV effect through inducing autophagy-lysosomal pathway to autophagic degradation of HBc by activating AMPK-ULK1 axis and inhibiting mTOR activation. In summary, we have identified a novel antiviral compound Ciliatoside A isolated from Peristrophe japonica. This study may provide important direction and new ideas for the discovery of hepatitis B cure drugs.

Galectin-9/Tim-3 pathway mediates dopaminergic neurodegeneration in MPTP-induced mouse model of Parkinson's disease

Galectin-9 (Gal-9) is a crucial immunoregulatory mediator in the central nervous system. Microglial activation and neuroinflammation play a key role in the degeneration of dopaminergic neurons in the substantia nigra (SN) in Parkinson's disease (PD). However, it remains unknown whether Gal-9 is involved in the pathogenesis of PD. We found that MPP+ treatment promoted the expression of Gal-9 and pro-inflammatory cytokines (IL-6, IL-1β, TNF-α, and MIP-1α) in a concentration-dependent manner in BV2 cells. Gal-9 enhanced neurodegeneration and oxidative stress induced by MPP+ in SH-SY5Y cells and primary neurons. Importantly, deletion of Gal-9 or blockade of Tim-3 ameliorated microglial activation, reduced dopaminergic neuronal loss, and improved motor performance in an MPTP-induced mouse model of PD. These observations demonstrate a pathogenic role of the Gal-9/Tim-3 pathway in exacerbating microglial activation, neuroinflammation, oxidative stress, and dopaminergic neurodegeneration in the pathogenesis of PD.

Host Combats IBDV Infection at Both Protein and RNA Levels

Infectious bursal disease (IBD) is an acute, highly contagious, and immunosuppressive avian disease caused by infectious bursal disease virus (IBDV). In recent years, with the emergence of IBDV variants and recombinant strains, IBDV still threatens the poultry industry worldwide. It seems that the battle between host and IBDV will never end. Thus, it is urgent to develop a more comprehensive and effective strategy for the control of this disease. A better understanding of the mechanisms underlying virus-host interactions would be of help in the development of novel vaccines. Recently, much progress has been made in the understanding of the host response against IBDV infection. If the battle between host and IBDV at the protein level is considered the front line, at the RNA level, it can be taken as a hidden line. The host combats IBDV infection at both the front and hidden lines. Therefore, this review focuses on our current understanding of the host response to IBDV infection at both the protein and RNA levels.

Galectin-9 protects humanized-ACE2 immunocompetent mice from SARS-CoV-2 infection

SARS-CoV-2 remains a global health crisis even with effective vaccines and the availability of FDA approved therapies. Efforts to understand the complex disease pathology and develop effective strategies to limit mortality and morbidity are needed. Recent studies reveal circulating Galectin-9 (gal-9), a soluble beta-galactoside binding lectin with immunoregulatory properties, are elevated in SARS-CoV-2 infected individuals with moderate to severe disease. Moreover, in silico studies demonstrate gal-9 can potentially competitively bind the ACE2 receptor on susceptible host cells. Here, we determined whether early introduction of exogenous gal-9 following SARS-CoV-2 infection in humanized ACE2 transgenic mice (K18-hACE2) may reduce disease severity. Mice were infected and treated with a single dose of a human recombinant form of gal-9 (rh-gal-9) and monitored for morbidity. Subgroups of mice were humanely euthanized at 2- and 5- days post infection (dpi) for viral levels by plaque assay, immune changes measures by flow cytometry, and soluble mediators by protein analysis from lung tissue and bronchoalveolar Lavage fluid (BALF). Mice treated with rh-gal-9 during acute infection had improved survival compared to PBS treated controls. At 5 dpi, rh-gal-9 treated mice had enhanced viral clearance in the BALF, but not in the lung parenchyma. Increased T and dendritic cells and decreased neutrophil frequencies in the lung at 5 dpi were observed, whereas BALF had elevated levels of type-I interferons and proinflammatory cytokines. These results suggest a role for rh-gal-9 in limiting acute COVID-19. Further studies are required to determine the optimal design of gal-9 treatment to effectively ameliorate COVID-19 disease.

Prototheca bovis induces autophagy in bovine mammary epithelial cells via the HIF-1α and AMPKα/ULK1 pathway

Prototheca bovis, a highly contagious pathogen, causes bovine mastitis, resulting in premature culling of affected cows and severe economic losses. Infection with P. bovis caused oxidative stress and apoptosis in bovine mammary epithelial cells (bMECs); however, mechanisms underlying P. bovis-induced autophagy remain unclear. Therefore, the autophagy flux induced by P. bovis in bMECs was analyzed by Western blot and laser scanning confocal microscopy. Expression levels of proteins in the HIF-1α and AMPKα/ULK1 pathway, including HIF-1α, AMPKα, p-AMPKα, ULK1, p-ULK1, mTOR, and p-mTOR, plus expression of autophagy-related genes including SQSTM1/p62, Atg5, Beclin1, and LC3II/LC3I, were quantified with Western blot. Infection with P. bovis induced autophagosomes and LC3 puncta in bMECs that were detected using transmission electron microscopy and laser scanning confocal microscopy, respectively. In addition, lysosome-associated proteins Rab7 and LAMP2a, and lysosomal activity were measured with Western blot and laser scanning confocal microscopy. Infection with P. bovis induced an unobstructed autophagic flux, increased protein expression of LC3II/LC3I, and decreased SQSTM1/p62 protein expression at 6 hpi. Furthermore, P. bovis upregulated protein expression in the HIF-1α and AMPKα/ULK1 pathway and increased the ratio of LC3II/LC3I, implying autophagy was activated in bMECs. However, deletion of AMPKα or ULK1 decreased LC3II/LC3I expression levels and LC3 puncta numbers, suggesting that autophagy was inhibited in bMECs. Additionally, deficiency of HIF-1α decreased protein expression of AMPKα and ULK1 as well as LC3 puncta numbers, and autophagy induced by P. bovis was also inhibited in bMECs. At 6 hpi, lysosome-associated protein Rab7 was decreased and LAMP2a was increased, indicating normal autophagy. In contrast, at 12 hpi, expression of Rab7 and LAMP2a proteins indicated that autophagy was inhibited in bMECs at that time. Therefore, we confirmed that P. bovis infection induced autophagy in bMECs via the HIF-1α and AMPKα/ULK1 pathway, with involvement of lysosome-associated protein Rab7 and LAMP2a.

Nectin4 antagonises type I interferon production by targeting TRAF3 for autophagic degradation and disrupting TRAF3-TBK1 complex formation

Autophagy, a conserved cellular degradative process, plays a crucial role in innate immunity during viral infections. Nervous necrosis virus (NNV), a leading cause of fish diseases with morbidity and mortality, triggers cell autophagy to promote viral replication; however, the details of how NNV utilises autophagy to facilitate its own replication remain largely unexplored. Here, we investigated the mechanism by which the sea perch Nectin4 (LjNectin4), a receptor of NNV, regulates autophagy and the innate immune system by targeting TNFR-associated factor 3 (TRAF3). Our data demonstrated that LjNectin4 directly binds to the NNV capsid protein and facilitates NNV entry, indicating that LjNectin4 functions as an NNV receptor. Moreover, LjNectin4 promoted NNV replication by inhibiting key elements of the RLR signalling pathway (MDA5, MAVS, TRAF3, TBK1, and IRF3)-induced IFN response. Mechanistically, LjNectin4 directly interacted with TRAF3 and promoted its autophagy-mediated lysosomal degradation. Domain mapping of the interaction between TRAF3 and LjNectin4 or TBK1 showed that both LjNectin4 and TBK1 interacted with the ZF2 and TRAF-C domains of TRAF3, suggesting that LjNectin4 blocked TRAF3-TBK1 complex formation. Collectively, our study revealed that NNV utilises LjNectin4 to suppress IFN production by mediating TRAF3 autophagic degradation and disrupting the TRAF3-TBK1 complex, thereby promoting NNV replication.

A guide to membrane atg8ylation and autophagy with reflections on immunity

The process of membrane atg8ylation, defined herein as the conjugation of the ATG8 family of ubiquitin-like proteins to membrane lipids, is beginning to be appreciated in its broader manifestations, mechanisms, and functions. Classically, membrane atg8ylation with LC3B, one of six mammalian ATG8 family proteins, has been viewed as the hallmark of canonical autophagy, entailing the formation of characteristic double membranes in the cytoplasm. However, ATG8s are now well described as being conjugated to single membranes and, most recently, proteins. Here we propose that the atg8ylation is coopted by multiple downstream processes, one of which is canonical autophagy. We elaborate on these biological outputs, which impact metabolism, quality control, and immunity, emphasizing the context of inflammation and immunological effects. In conclusion, we propose that atg8ylation is a modification akin to ubiquitylation, and that it is utilized by different systems participating in membrane stress responses and membrane remodeling activities encompassing autophagy and beyond.

Targeting Selective Autophagy as a Therapeutic Strategy for Viral Infectious Diseases

Autophagy is an evolutionarily conserved lysosomal degradation system which can recycle multiple cytoplasmic components under both physiological and stressful conditions. Autophagy could be highly selective to deliver different cargoes or substrates, including protein aggregates, pathogenic proteins or superfluous organelles to lysosome using a series of cargo receptor proteins. During viral invasion, cargo receptors selectively target pathogenic components to autolysosome to defense against infection. However, viruses not only evolve different strategies to counteract and escape selective autophagy, but also utilize selective autophagy to restrict antiviral responses to expedite viral replication. Furthermore, several viruses could activate certain forms of selective autophagy, including mitophagy, lipophagy, aggrephagy, and ferritinophagy, for more effective infection and replication. The complicated relationship between selective autophagy and viral infection indicates that selective autophagy may provide potential therapeutic targets for human infectious diseases. In this review, we will summarize the recent progress on the interplay between selective autophagy and host antiviral defense, aiming to arouse the importance of modulating selective autophagy as future therapies toward viral infectious diseases.

Crosstalk between the innate immune system and selective autophagy in hepatitis B virus infection

Although the involvement of macroautophagy/autophagy in hepatitis B virus (HBV) infection has become clearer recently, whether selective autophagy plays an important role in suppressing HBV remains uncertain. We recently found that LGALS9 (galectin 9) is an interferon (IFN)-inducible protein involved in the suppression of HBV replication. Expression of LGALS9 in HBV-infected cells causes the formation of cytoplasmic puncta that degrade the HBV core protein (HBc) in conjunction with RSAD2/viperin, another IFN-inducible protein. LGALS9 binds to HBc via RSAD2 and promotes the autoubiquitination of RNF13 (ring finger protein 13) to recruit SQSTM1/p62, resulting in the formation of LC3-positive autophagosomes that degrade HBc. Both LGALS9 and RSAD2 are encoded by IFN-stimulated genes that act synergistically to induce HBc proteolysis in HBV-infected hepatocytes in an IFN-dependent manner. These results reveal a crosstalk mechanism between the innate immune system and selective autophagy during viral infection.