宿主防御肽抗病毒感染机制研究进展

宿主防御肽是一类广泛存在于脊椎动物的小分子多肽,具有广谱的抗菌活性以及抗炎、细胞趋化、促进血管生成和修复损伤等免疫调节功能。以往的研究多集中在宿主防御肽抗细菌和真菌感染的研究上。近年来大量研究发现,宿主防御肽也具有广泛的抗病毒活性,在临床各类病毒病的预防和治疗上具有潜在的应用前景。本文围绕宿主防御肽直接杀伤病毒、调节病毒感染过程和参与宿主抗病毒天然免疫调节这3个方面的作用机制进行综述,为宿主防御肽抗病毒相关研究和相关抗病毒生物药物的研发提供参考和借鉴。     

Expression of iron-related proteins during infection by bovine herpes virus type-1

Bovine herpesvirus 1 (BHV-1), a dsDNA animal virus, is an economically important pathogen of cattle and the aetiological agent of many types of disease. The efficient replication of a DNA virus is strictly dependent on iron since this metal plays a crucial role in the catalytic center of viral ribonucleotide reductase. Consequently, iron metabolism is an important area for virus/host interaction and a large body of evidence suggests that viral infection is potentially influenced by the iron status of the host. The aim of the present study was to address the effects of BHV-1 on iron metabolism in Madin-Darby bovine kidney (MDBK) cells at different times of post-infection. For this purpose, cell viability, iron regulatory proteins (IRPs) activity and levels, transferrin receptor 1 (TfR-1), ferritin expression and LIP were evaluated. Our data demonstrate that a productive BHV-1 infection in MDBK cells determines an overall decrease of IRPs RNA-binding activity without affecting their expression. As consequence of this modulation, an increased ferritin mRNA translation and a decreased TfR-1 mRNA translation were also observed. Moreover, the LIP level was decreased following viral infection. These results are consistent with the hypothesis that by reducing the iron up-take and by enhancing the sequestration of free iron, animal cells will limit the iron availability for virus proliferation. Therefore, the results presented herein support the view that iron metabolism could be critical for the interaction between DNA viruses, such as BHV-1, and mammalian cells. Delineation of the interplay among pathogen and host may provide new antimicrobial agents.     

The Role of Iron In Protozoan and Fungal Infectious Diseases

To survive and replicate in vertebrate hosts, protozoan and fungal invaders must be capable of securing host iron. Successful pathogens obtain the metal from either extraction of heme, binding of siderophilins, binding of siderophores, and/or iron pools within host cells. The actual strategy can vary with the availability of iron in the particular host milieu. As a corollary, hosts have developed an elaborate iron withholding defense system. Conditions that can compromise the system as well as procedures that can strengthen it are reviewed.     

Competing pathways control host resistance to virus via tRNA modification and programmed ribosomal frameshifting

Viral infection depends on a complex interplay between host and viral factors. Here, we link host susceptibility to viral infection to a network encompassing sulfur metabolism, tRNA modification, competitive binding, and programmed ribosomal frameshifting (PRF). We first demonstrate that the iron‐sulfur cluster biosynthesis pathway in Escherichia coli exerts a protective effect during lambda phage infection, while a tRNA thiolation pathway enhances viral infection. We show that tRNA^Lys uridine 34 modification inhibits PRF to influence the ratio of lambda phage proteins gpG and gpGT. Computational modeling and experiments suggest that the role of the iron‐sulfur cluster biosynthesis pathway in infection is indirect, via competitive binding of the shared sulfur donor IscS. Based on the universality of many key components of this network, in both the host and the virus, we anticipate that these findings may have broad relevance to understanding other infections, including viral infection of humans.     

PANoptosis in Viral Infection: The Missing Puzzle Piece in the Cell Death Field

In the past decade, emerging viral outbreaks like SARS-CoV-2, Zika and Ebola have presented major challenges to the global health system. Viruses are unique pathogens in that they fully rely on the host cell to complete their lifecycle and potentiate disease. Therefore, programmed cell death (PCD), a key component of the host innate immune response, is an effective strategy for the host cell to curb viral spread. The most well-established PCD pathways, pyroptosis, apoptosis and necroptosis, can be activated in response to viruses. Recently, extensive crosstalk between PCD pathways has been identified, and there is evidence that molecules from all three PCD pathways can be activated during virus infection. These findings have led to the emergence of the concept of PANoptosis, defined as an inflammatory PCD pathway regulated by the PANoptosome complex with key features of pyroptosis, apoptosis, and/or necroptosis that cannot be accounted for by any of these three PCD pathways alone. While PCD is important to eliminate infected cells, many viruses are equipped to hijack host PCD pathways to benefit their own propagation and subvert host defense, and PCD can also lead to the production of inflammatory cytokines and inflammation. Therefore, PANoptosis induced by viral infection contributes to either host defense or viral pathogenesis in context-specific ways. In this review, we will discuss the multi-faceted roles of PCD pathways in controlling viral infections.     

Ferritinophagy drives uropathogenic Escherichia coli persistence in bladder epithelial cells

Autophagy is a cellular recycling pathway, which in many cases, protects host cells from infections by degrading pathogens. However, uropathogenic Escherichia coli (UPEC), the predominant cause of urinary tract infections (UTIs), persist within the urinary tract epithelium (urothelium) by forming reservoirs within autophagosomes. Iron is a critical nutrient for both host and pathogen, and regulation of iron availability is a key host defense against pathogens. Iron homeostasis depends on the shuttling of iron-bound ferritin to the lysosome for recycling, a process termed ferritinophagy (a form of selective autophagy). Here, we demonstrate for the first time that UPEC shuttles with ferritin-bound iron into the autophagosomal and lysosomal compartments within the urothelium. Iron overload in urothelial cells induces ferritinophagy in an NCOA4-dependent manner causing increased iron availability for UPEC, triggering bacterial overproliferation and host cell death. Addition of even moderate levels of iron is sufficient to increase and prolong bacterial burden. Furthermore, we show that lysosomal damage due to iron overload is the specific mechanism causing host cell death. Significantly, we demonstrate that host cell death and bacterial burden can be reversed by inhibition of autophagy or inhibition of iron-regulatory proteins, or chelation of iron. Together, our findings suggest that UPEC persist in host cells by taking advantage of ferritinophagy. Thus, modulation of iron levels in the bladder may provide a therapeutic avenue to controlling UPEC persistence, epithelial cell death, and recurrent UTIs.     

Iron metabolism: microbes,mouse, and man

Recent advances in research on iron metabolism have revealed the identity of a number of genes, signal transduction pathways, and proteins involved in iron regulation in mammals. The emerging paradigm is a coordination of homeostasis within a network of classical iron metabolic pathways and other cellular processes such as cell differentiation, growth, inflammation, immunity, and a host of physiologic and pathologic conditions. Iron, immunity, and infection are intricately linked and their regulation is fundamental to the survival of mammals. The mutual dependence on iron by the host and invading pathogenic organisms elicits competition for the element during infection. While the host maintains mechanisms to utilize iron for its own metabolism exclusively, pathogenic organisms are armed with a myriad of strategies to circumvent these measures. This review explores iron metabolism in mammalian host, defense mechanisms against pathogenic microbes and the competitive devices of microbes for access to iron.     

Iron and neoplasia

Normal and neoplastic cells (like nonpathogenic and pathogenic microorganisms) apparently have similar needs and tolerances for iron, but neoplastic cells (like pathogenic microorganisms) may exhibit altered mechanisms of iron acquisition that permit continued growth in host iron-restricted tissues. Excess iron tends to interfere with host defense against malignant cells (as well as against microbial invaders); severe iron deficiency may likewise be detrimental. Elevated temperature is more toxic towards neoplastic than to normal host cells; it is not yet known whether the site of action of heat might be associated with iron acquisition (as has been demonstrated for gram negative bacteria). Persons or animals with iron overload tend to be at greater risk than normal hosts in the development of neoplasms. Construction of animal models of iron overload, although difficult, is strongly indicated at this time. Based on such models, decisions then can be made about the extent to which (a) nutritional immunity against neoplastic cells is practiced by vertebrate hosts and (b) clinical procedures could be employed to strengthen such immunity as an adjunct to radiotherapy, chemotherapy, and surgery.     

Characterization of a nucleus located mollusc mitoferrin and its response to OsHV-1 infection

Mitoferrin genes as members of SLC25 family are conservatively existed across species, mainly locate on mitochondria and serve an important role in the regulation of whole cellular iron metabolism. Available iron withholding from pathogens presents an important host defense strategy, while the regulation role of mitoferrin against invading pathogens is largely unknown. In this study, a unique mollusc mitoferrin gene was identified in ark clams, named SbmiFn, that showed conserved three-dimensional structure with other mitoferrins, and its iron binding activity was verified by iron chelating assay. Besides cytoplasmic distribution, colocalization between SbmiFn and nuclei was observed by immunohistochemistry assay. Moreover, the response of SbmiFn to viral pathogen OsHV-1 was investigated. The results showed that nucleus located signal of SbmiFn was enhanced, the expressions of SbmiFn and ferritin were coordinately decreased, which might assist host against OsHV-1 replication as the increase of OsHV-1 copies were hardly detected after that. These results refreshed our knowledge on the sequence, structure and functional characteristics of mitoferrin subfamily, and would contribute to further comparative studies on iron metabolism.     

病毒感染引起的炎症反应：宿主对抗病毒的“双刃剑”

先天性免疫系统作为宿主抵抗外来病原入侵的第一道防线,也是最迅速的防御系统。宿主先天性免疫系统中的模式识别受体识别入侵信号并激活炎症信号通路,诱导产生大量促炎性细胞因子,引起炎症反应。病毒感染是激活炎症反应的条件之一,诱导机体产生强烈的免疫应答,强大的炎症反应调控网络在宿主抗病毒过程中发挥关键作用,以维持机体的平衡。本文综述了病毒感染引起的炎症反应,重点介绍了宿主对炎症反应的调控网络,以及DNA和RNA病毒对炎症反应的调节机制,为病毒感染引起的免疫性疾病的治疗提供参考。     

Essential role of Rnd1 in innate immunity during viral and bacterial infections

Intracellular and cell surface pattern-recognition receptors (PRRs) are an essential part of innate immune recognition and host defense. Here, we have compared the innate immune responses between humans and bats to identify a novel membrane-associated protein, Rnd1, which defends against viral and bacterial infection in an interferon-independent manner. Rnd1 belongs to the Rho GTPase family, but unlike other small GTPase members, it is constitutively active. We show that Rnd1 is induced by pro-inflammatory cytokines during viral and bacterial infections and provides protection against these pathogens through two distinct mechanisms. Rnd1 counteracts intracellular calcium fluctuations by inhibiting RhoA activation, thereby inhibiting virus internalisation. On the other hand, Rnd1 also facilitates pro-inflammatory cytokines IL-6 and TNF-α through Plxnb1, which are highly effective against intracellular bacterial infections. These data provide a novel Rnd1-mediated innate defense against viral and bacterial infections.Subject terms: Viral infection, Pattern recognition receptors     

Hepcidin and Host Defense against Infectious Diseases

Hepcidin is the master regulator of iron homeostasis in vertebrates. The synthesis of hepcidin is induced by systemic iron levels and by inflammatory stimuli. While the role of hepcidin in iron regulation is well established, its contribution to host defense is emerging as complex and multifaceted. In this review, we summarize the literature on the role of hepcidin as a mediator of antimicrobial immunity. Hepcidin induction during infection causes depletion of extracellular iron, which is thought to be a general defense mechanism against many infections by withholding iron from invading pathogens. Conversely, by promoting iron sequestration in macrophages, hepcidin may be detrimental to cellular defense against certain intracellular infections, although critical in vivo studies are needed to confirm this concept. It is not yet clear whether hepcidin exerts any iron-independent effects on host defenses.     

Noncytotoxic functions of killer cell granzymes in viral infections

Cytotoxic lymphocytes produce granules armed with a set of 5 serine proteases (granzymes (Gzms)), which, together with the pore-forming protein (perforin), serve as a major defense against viral infections in humans. This granule-exocytosis pathway subsumes a well-established mechanism in which target cell death is induced upon perforin-mediated entry of Gzms and subsequent activation of various (apoptosis) pathways. In the past decade, however, a growing body of evidence demonstrated that Gzms also inhibit viral replication and potential reactivation in cell death–independent manners. For example, Gzms can induce proteolysis of viral or host cell proteins necessary for the viral entry, release, or intracellular trafficking, as well as augment pro-inflammatory antiviral cytokine response. In this review, we summarize current evidence for the noncytotoxic mechanisms and roles by which killer cells can use Gzms to combat viral infections, and we discuss the potential thereof for the development of novel therapies.     

Mechanisms of inhibition of the host interferon alpha/beta-mediated antiviral responses by viruses

Complex multicellular organisms have evolved sophisticated mechanisms to prevent and control infection by pathogens. Among these mechanisms, the type I interferon or interferon alpha/beta system represents one of the first lines of defense against viral infections. Typically, viral infection induces the synthesis and secretion of interferon alpha/beta by the infected cell, which in turn activates signaling pathways leading to an antiviral state. As a counter measure, many viruses have developed intriguing mechanisms to evade the interferon alpha/beta system of the host. In this review, we will summarize recent research developments in this interesting field of virus-host cell interactions.     

Reactive oxygen species and nitric oxide in viral diseases

Metabolites derived from superoxide (o₂ ^??) and nitric oxide (NO?) play an important role in antimicrobial and antitumoral defense, but may also harm the host. Low levels of such metabolites can also facilitate viral replication because of their mitogenic effects on cells. Most viruses grow better in proliferating cells, and indeed, many viruses induced in their host cell changes similar to those seen early after treatment with mitogenic lectins. Influenza and paramyxoviruses activate in phagocytes the generation of superoxide by a mechanism involving the interaction between the viral surface glycoproteins and the phagocyte’s plasma membrane. Interestingly, viruses that activate this host defense mechanism are toxic when injected in the bloodstream of animals. Mice infected with influenza virus undergo oxidative stress. In addition, a wide array of cytokines are formed in the lung, contributing to the systemic effects of influenza. Oxidative stress is seen also in chronic viral infections, such as AIDS and viral hepatitis. Oxidant production in viral hepatitis may contribute to the emergence of hepatocellular carcinoma, a tumor seen in patients after years of chronic inflammation of the liver. Antioxidants and agents that downregulate proinflammatory cytokines and lipid mediators may be a useful complement to specific antiviral drugs in the therapy of viral diseases.     

RNAseq expression analysis of resistant and susceptible mice after influenza A virus infection identifies novel genes associated with virus replication and important for host resistance to infection

Background

The host response to influenza A infections is strongly influenced by host genetic factors. Animal models of genetically diverse mouse strains are well suited to identify host genes involved in severe pathology, viral replication and immune responses. Here, we have utilized a dual RNAseq approach that allowed us to investigate both viral and host gene expression in the same individual mouse after H1N1 infection.

Results

We performed a detailed expression analysis to identify (i) correlations between changes in expression of host and virus genes, (ii) host genes involved in viral replication, and (iii) genes showing differential expression between two mouse strains that strongly differ in resistance to influenza infections. These genes may be key players involved in regulating the differences in pathogenesis and host defense mechanisms after influenza A infections. Expression levels of influenza segments correlated well with the viral load and may thus be used as surrogates for conventional viral load measurements. Furthermore, we investigated the functional role of two genes, Reg3g and Irf7, in knock-out mice and found that deletion of the Irf7 gene renders the host highly susceptible to H1N1 infection.

Conclusions

Using RNAseq analysis we identified novel genes important for viral replication or the host defense. This study adds further important knowledge to host-pathogen-interactions and suggests additional candidates that are crucial for host susceptibility or survival during influenza A infections.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1867-8) contains supplementary material, which is available to authorized users.     

<Emphasis Type="Italic">Drosophila melanogaster</Emphasis> as a model for studying the function of animal viral proteins

Studies in which Drosophila melanogaster individuals carrying transgenes of animal viruses were used to analyze the action of animal viral proteins on the cell are reviewed. The data presented suggest that host specificity of viruses is determined by their proteins responsible for the penetration of the virus into the cell, while viral proteins responsible for interactions with the host cell are much less host-specific. Due to this, the model of Drosophila with its developed system of searching for genetic interactions can be used to find intracellular targets for the action of viral proteins of the second group.     

MicroRNAs and human retroviruses

MicroRNAs (miRNAs) are small non-coding RNAs that control a multitude of critical processes in mammalian cells. Increasing evidence has emerged that host miRNAs serve in animal cells to restrict viral infections. In turn, many viruses encode RNA silencing suppressors (RSS) which are employed to moderate the potency of the cell's miRNA selection against viral replication. Some viruses also encode viral miRNAs. In this review, we summarize findings from human immunodeficiency virus type 1 (HIV-1) and human T-cell leukemia virus type 1 (HTLV-1) that illustrate examples of host cell miRNAs that target the viruses, of RSS encoded by viruses, and of host cell miRNA profile changes that are seen in infected cells. This article is part of a Special Issue entitled: MicroRNAs in viral gene regulation.     

Type I interferons and autoimmunity: lessons from the clinic and from IRF-2-deficient mice

Type I interferons (IFN-alpha/beta) are produced upon viral and bacterial infections and play essential roles in host defense. However, since IFN-alpha/beta have multiple regulatory functions on innate and adoptive immunity, dysregulation of the IFN-alpha/beta system both in uninfected hosts and during immune responses against infection can result in immunopathologies. In fact, IFN-alpha/beta therapy often accompanies autoimmune-like symptoms. In this regard, we have recently found that mice lacking IFN regulatory factor (IRF)-2, a negative regulator of IFN-alpha/beta signaling, develop spontaneous, CD8(+) T cell-dependent skin inflammation. This unique animal model, together with other animal models, highlights the importance of the mechanism maintaining the homeostasis in the IFN-alpha/beta system even in the absence of infection.     

Human cytomegalovirus gene expression is silenced by Daxx-mediated intrinsic immune defense in model latent infections established in vitro

In addition to productive lytic infections, herpesviruses such as human cytomegalovirus (HCMV) establish a reservoir of latently infected cells that permit lifelong colonization of the host. When latency is established, the viral immediate-early (IE) genes that initiate the lytic replication cycle are not expressed. HCMV IE gene expression at the start of a lytic infection is facilitated by the viral pp71 protein, which is delivered to cells by infectious viral particles. pp71 neutralizes the Daxx-mediated cellular intrinsic immune defense that silences IE gene expression by generating a repressive chromatin structure on the viral major IE promoter (MIEP). In naturally latently infected cells and in cells latently infected in vitro, the MIEP also adopts a similar silenced chromatin structure. Here we analyze the role of Daxx in quiescent HCMV infections in vitro that mimic some, but not all, of the characteristics of natural latency. We show that in these "latent-like" infections, the Daxx-mediated defense that represses viral gene expression is not disabled because pp71 and Daxx localize to different cellular compartments. We demonstrate that Daxx is required to establish quiescent HCMV infections in vitro because in cells that would normally foster the establishment of these latent-like infections, the loss of Daxx causes the lytic replication cycle to be initiated. Importantly, the lytic cycle is inefficiently completed, which results in an abortive infection. Our work demonstrates that, in certain cell types, HCMV must silence its own gene expression to establish quiescence and prevent abortive infection and that the virus usurps a Daxx-mediated cellular intrinsic immune defense mechanism to do so. This identifies Daxx as one of the likely multiple viral and cellular determinants in the pathway of HCMV quiescence in vitro, and perhaps in natural latent infections as well.