Influenza A virus infection of vascular endothelial cells induces GSK-3β-mediated β-catenin degradation in adherens junctions, with a resultant increase in membrane permeability

Endothelial activation and dysfunction caused by influenza A virus (Alphainfluenzavirus influenzae)

Annual epidemics of influenza result in 3-5 million cases of severe illness and more than 600 000 deaths. Severe forms of influenza are usually characterized by vascular endothelial cells damage. Thus, influenza A viruses, including subtypes A(H1N1)pdm09, A(H3N2), as well as highly pathogenic avian influenza viruses, can infect the vascular endothelium, leading to activation and subsequent dysfunction of these cells. In turn, endothelial dysfunction resulting in systemic morphofunctional changes of endothelial cells, which leads to impaired vascular tone, thrombosis and other complications, and is also a risk factor and profoundly implicated in the pathogenesis of many cardiovascular diseases. Thus, endothelial dysfunction is an important aspect of the pathogenesis of severe influenza, which must be considered in the pathogenetic therapy of this infectious disease. The aim of the review is to analyze the causes and specify mechanisms of development of endothelial activation and dysfunction caused by influenza A virus.

SCUBE2 regulates adherens junction dynamics and vascular barrier function during inflammation

AIMS

SCUBE2 (signal peptide-CUB-epidermal growth factor-like domain-containing protein 2) is a secreted or membrane-bound protein originally identified from endothelial cells (ECs). Our previous work showed that SCUBE2 forms a complex with E-cadherin and stabilizes epithelial adherens junctions (AJs) to promote epithelial phenotypes. However, it remains unclear whether SCUBE2 also interacts with vascular endothelial (VE)-cadherin and modulates EC barrier function. In this study, we investigated whether and how SCUBE2 in ECs regulates vascular barrier maintenance.

METHODS AND RESULTS

We showed that SCUBE2 colocalized and interacted with VE-cadherin and VE-protein tyrosine phosphatase (VE-PTP) within EC AJs. Furthermore, SCUBE2 knockdown disrupted EC AJs and increased EC permeability. Expression of EC SCUBE2 was suppressed at both mRNA and protein levels via the nuclear factor-κB signalling pathway in response to pro-inflammatory cytokines or permeability-inducing agents. In line with these findings, EC-specific deletion of Scube2 (EC-KO) in mice impaired baseline barrier function and worsened vascular leakiness of peripheral capillaries after local injection of histamine or vascular endothelial growth factor. EC-KO mice were also sensitive to pulmonary vascular hyperpermeability and leucocyte infiltration in response to acute endotoxin- or influenza virus-induced systemic inflammation. Meanwhile, EC-specific SCUBE2-overexpressing mice were protected from these effects. Molecular studies suggested that SCUBE2 acts as a scaffold molecule enabling VE-PTP to dephosphorylate VE-cadherin, which prevents VE-cadherin internalization and stabilizes EC AJs. As such, loss of SCUBE2 resulted in hyperphosphorylation of VE-cadherin at tyrosine 685, which led to its endocytosis, thus destabilizing EC AJs and reducing barrier function. All of these effects were exacerbated by inflammatory insults.

CONCLUSION

We found that SCUBE2 contributes to vascular integrity by recruiting VE-PTP to dephosphorylate VE-cadherin and stabilize AJs, thereby promoting EC barrier function. Moreover, our data suggest that genetic overexpression or pharmacological up-regulation of SCUBE2 may help to prevent vascular leakage and oedema in inflammatory diseases.

Identification of Causal Relationships between Gut Microbiota and Influenza a Virus Infection in Chinese by Mendelian Randomization

Numerous studies have reported a correlation between gut microbiota and influenza A virus (IAV) infection and disease severity. However, the causal relationship between these factors remains inadequately explored. This investigation aimed to assess the influence of gut microbiota on susceptibility to human infection with H7N9 avian IAV and the severity of influenza A (H1N1)pdm09 infection. A two-sample Mendelian randomization analysis was conducted, integrating our in-house genome-wide association study (GWAS) on H7N9 susceptibility and H1N1pdm09 severity with a metagenomics GWAS dataset from a Chinese population. Twelve and fifteen gut microbiotas were causally associated with H7N9 susceptibility or H1N1pdm09 severity, separately. Notably, Clostridium hylemonae and Faecalibacterium prausnitzii were negative associated with H7N9 susceptibility and H1N1pdm09 severity, respectively. Moreover, Streptococcus peroris and Streptococcus sanguinis were associated with H7N9 susceptibility, while Streptococcus parasanguini and Streptococcus suis were correlated with H1N1pdm09 severity. These results provide novel insights into the interplay between gut microbiota and IAV pathogenesis as well as new clues for mechanism research regarding therapeutic interventions or IAV infections. Future studies should concentrate on clarifying the regulatory mechanisms of gut microbiota and developing efficacious approaches to reduce the incidence of IAV infections, which could improve strategy for preventing and treating IAV infection worldwide.

Viral entry and translation in brain endothelia provoke influenza-associated encephalopathy

Influenza-associated encephalopathy (IAE) is extremely acute in onset, with high lethality and morbidity within a few days, while the direct pathogenesis by influenza virus in this acute phase in the brain is largely unknown. Here we show that influenza virus enters into the cerebral endothelium and thereby induces IAE. Three-weeks-old young mice were inoculated with influenza A virus (IAV). Physical and neurological scores were recorded and temporal-spatial analyses of histopathology and viral studies were performed up to 72 h post inoculation. Histopathological examinations were also performed using IAE human autopsy brains. Viral infection, proliferation and pathogenesis were analyzed in cell lines of endothelium and astrocyte. The effects of anti-influenza viral drugs were tested in the cell lines and animal models. Upon intravenous inoculation of IAV in mice, the mice developed encephalopathy with brain edema and pathological lesions represented by micro bleeding and injured astrocytic process (clasmatodendrosis) within 72 h. Histologically, massive deposits of viral nucleoprotein were observed as early as 24 h post infection in the brain endothelial cells of mouse models and the IAE patients. IAV inoculated endothelial cell lines showed deposition of viral proteins and provoked cell death, while IAV scarcely amplified. Inhibition of viral transcription and translation suppressed the endothelial cell death and the lethality of mouse models. These data suggest that the onset of encephalopathy should be induced by cerebral endothelial infection with IAV. Thus, IAV entry into the endothelium, and transcription and/or translation of viral RNA, but not viral proliferation, should be the key pathogenesis of IAE.

Subcapsular sinus macrophages maximize germinal center development in non-draining lymph nodes during blood-borne viral infection

Lymph node (LN) germinal centers (GCs) are critical sites for B cell activation and differentiation. GCs develop after specialized CD169+ macrophages residing in LN sinuses filter antigens (Ags) from the lymph and relay these Ags into proximal B cell follicles. Many viruses, however, first reach LNs through the blood during viremia (virus in the blood), rather than through lymph drainage from infected tissue. How LNs capture viral Ag from the blood to allow GC development is not known. Here, we followed Zika virus (ZIKV) dissemination in mice and subsequent GC formation in both infected tissue-draining and non-draining LNs. From the footpad, ZIKV initially disseminated through two LN chains, infecting LN macrophages and leading to GC formation. Despite rapid ZIKV viremia, non-draining LNs were not infected for several days. Non-draining LN infection correlated with virus-induced vascular leakage and neutralization of permeability reduced LN macrophage attrition. Depletion of non-draining LN macrophages significantly decreased GC B cells in these nodes. Thus, although LNs inefficiently captured viral Ag directly from the blood, GC formation in non-draining LNs proceeded similarly to draining LNs through LN sinus CD169+ macrophages. Together, our findings reveal a conserved pathway allowing LN macrophages to activate antiviral B cells in LNs distal from infected tissue after blood-borne viral infection.

The deubiquitinase USP40 preserves endothelial integrity by targeting the heat shock protein HSP90β

Endothelial cell (EC) barrier disruption and inflammation are the pathological hallmarks of vascular disorders and acute infectious diseases and related conditions, including the coronavirus disease 2019 (COVID-19) and sepsis. Ubiquitination plays a critical role in regulating the stability, intracellular trafficking, and enzymatic activity of proteins and is reversed by deubiquitinating enzymes (DUBs). The role of DUBs in endothelial biology is largely unknown. In this study, we report that USP40, a poorly characterized DUB, prevents EC barrier disruption through reductions in the activation of RhoA and phosphorylation of myosin light chain (MLC) and cofilin. Furthermore, USP40 reduces EC inflammation through the attenuation of NF-ĸB activation, ICAM1 expression, and leukocyte-EC adhesion. We further show that USP40 activity and expression are reduced in response to endotoxin challenge. Global depletion of USP40 and EC-targeted USP40 depletion in mice exacerbated experimental lung injury, whereas lentiviral gene transfer of USP40 protected against endotoxin-induced lung injury. Using an unbiased approach, we discovered that the protective effect of USP40 occurs through the targeting of heat shock protein 90β (HSP90β) for its deubiquitination and inactivation. Together, these data reveal a critical protective role of USP40 in vascular injury, identifying a unique mechanistic pathway that profoundly impacts endothelial function via DUBs.

miR-342-5p targets CTNNBIP1 to promote enterovirus 71 replication

OBJECTIVE

The aim of this research was to explore the role of miR-342-5p in EV71 replication.

METHODS

Peritoneal injection of EV71 (107 TCID50/mL) at 50, 100, and 150 μL was conducted to infect 12-day-old suckling mice (n = 10 per group), and clinical scores and survival rates were recorded during a 6-day trial duration and followed by transcriptome sequencing of collected spinal cord tissues. The differential miRNAs and target genes of the infected and uninfected EV71 mice were analyzed. The miR-342 and CTNNBIP1 binding sites were detected using a dual luciferase reporter assay. Cell viability was detected by CCK-8. RT-qPCR, Western blot, immunofluorescence, and immunohistochemistry assays were conducted to detect VP1 protein levels.

RESULTS

Transcriptome sequencing analyses know that the Wnt pathway played a role in EV71 infection, and the CTNNBIP1 gene in this pathway was the target gene of miR-342-5p. Whether in HMC3 cells or in the spinal cord tissue from the suckling mice, high levels of miR-342-5p markedly promoted EV71 VP1 mRNA and protein expression, elevated TNF-α, IL-6, and IL-10 levels, and inhibited IFN-β levels. In addition, highly expressed miR-342-5p destroyed neuronal structure in spinal cord tissues and reduced the number of glial cells. Highly expressed CTNNBIP1 blocked the promotion of miR-342-5p in EV71 replication, and inhibited TNF-α, IL-6, and IL-10 levels, whereas elevated IFN-β levels. This mechanism is that miR-342-5p can target the CTNNBIP1 3' UTR region, inhibit its expression and reduce its binding to CTNNB1, thus enhancing the interaction between CTNNB1 and TCF4 and activating the Wnt pathway-mediated type I interferon response.

CONCLUSION

In nerve cells and tissues, the overexpression of miR-342-5p promoted the replication of EV71 and attenuated the innate immune response to antiviral disease via Wnt/CTNNB1 signaling pathway.

MAGI1 inhibits interferon signaling to promote influenza A infection

We have shown that membrane-associated guanylate kinase with inverted domain structure-1 (MAGI1), a scaffold protein with six PSD95/DiscLarge/ZO-1 (PDZ) domains, is involved in the regulation of endothelial cell (EC) activation and atherogenesis in mice. In addition to causing acute respiratory disease, influenza A virus (IAV) infection plays an important role in atherogenesis and triggers acute coronary syndromes and fatal myocardial infarction. Therefore, the aim of this study is to investigate the function and regulation of MAGI1 in IAV-induced EC activation. Whereas, EC infection by IAV increases MAGI1 expression, MAGI1 depletion suppresses IAV infection, suggesting that the induction of MAGI1 may promote IAV infection. Treatment of ECs with oxidized low-density lipoprotein (OxLDL) increases MAGI1 expression and IAV infection, suggesting that MAGI1 is part of the mechanistic link between serum lipid levels and patient prognosis following IAV infection. Our microarray studies suggest that MAGI1-depleted ECs increase protein expression and signaling networks involve in interferon (IFN) production. Specifically, infection of MAGI1-null ECs with IAV upregulates expression of signal transducer and activator of transcription 1 (STAT1), interferon b1 (IFNb1), myxovirus resistance protein 1 (MX1) and 2'-5'-oligoadenylate synthetase 2 (OAS2), and activate STAT5. By contrast, MAGI1 overexpression inhibits Ifnb1 mRNA and MX1 expression, again supporting the pro-viral response mediated by MAGI1. MAGI1 depletion induces the expression of MX1 and virus suppression. The data suggests that IAV suppression by MAGI1 depletion may, in part, be due to MX1 induction. Lastly, interferon regulatory factor 3 (IRF3) translocates to the nucleus in the absence of IRF3 phosphorylation, and IRF3 SUMOylation is abolished in MAGI1-depleted ECs. The data suggests that MAGI1 inhibits IRF3 activation by maintaining IRF3 SUMOylation. In summary, IAV infection occurs in ECs in a MAGI1 expression-dependent manner by inhibiting anti-viral responses including STATs and IRF3 activation and subsequent MX1 induction, and MAGI1 plays a role in EC activation, and in upregulating a pro-viral response. Therefore, the inhibition of MAGI1 is a potential therapeutic target for IAV-induced cardiovascular disease.

Anti-high mobility group box 1 monoclonal antibody suppressed hyper-permeability and cytokine production in human pulmonary endothelial cells infected with influenza A virus

Objective

High mobility group box-1 (HMGB1) has been reported to be involved in influenza A virus-induced acute respiratory distress syndrome (ARDS). We studied the efficacy of an anti-HMGB1 mAb using an in vitro model of TNF-α stimulation or influenza A virus infection in human pulmonary microvascular endothelial cells (HMVECs).

Methods

Vascular permeability of HMVECs was quantified using the Boyden chamber assay under tumor necrosis factor-α (TNF-α) stimulation or influenza A virus infection in the presence of anti-HMGB1 mAb or control mAb. The intracellular localization of HMGB1 was assessed by immunostaining. Extracellular cytokine concentrations and intracellular viral mRNA expression were quantified by the enzyme-linked immunosorbent assay and quantitative reverse transcription PCR, respectively.

Results

Vascular permeability was increased by TNF-α stimulation or influenza A infection; HMVECs became elongated and the intercellular gaps were extended. Anti-HMGB1 mAb suppressed both the increase in permeability and the cell morphology changes. Translocation of HMGB1 to the cytoplasm was observed in the non-infected cells. Although anti-HMGB1 mAb did not suppress viral replication, it did suppress cytokine production in HMVECs.

Conclusion

Anti-HMGB1 mAb might be an effective therapy for severe influenza ARDS.

Ubiquitin-based modifications in endothelial cell-cell contact and inflammation

Endothelial cell-cell contacts are essential for vascular integrity and physiology, protecting tissues and organs from edema and uncontrolled invasion of inflammatory cells. The vascular endothelial barrier is dynamic, but its integrity is preserved through a tight control at different levels. Inflammatory cytokines and G-protein-coupled receptor agonists, such as histamine, reduce endothelial integrity and increase vascular leakage. This is due to elevated myosin-based contractility, in conjunction with phosphorylation of proteins at cell-cell contacts. Conversely, reducing contractility stabilizes or even increases endothelial junctional integrity. Rho GTPases are key regulators of such cytoskeletal dynamics and endothelial cell-cell contacts. In addition to signaling-induced regulation, the expression of junctional proteins, such as occludin, claudins and vascular endothelial cadherin, also controls endothelial barrier function. There is increasing evidence that, in addition to protein phosphorylation, ubiquitylation (also known as ubiquitination) is an important and dynamic post-translational modification that regulates Rho GTPases, junctional proteins and, consequently, endothelial barrier function. In this Review, we discuss the emerging role of ubiquitylation and deubiquitylation events in endothelial integrity and inflammation. The picture that emerges is one of increasing complexity, which is both fascinating and promising given the clinical relevance of vascular integrity in the control of inflammation, and of tissue and organ damage.

Isolation of induced pluripotent stem cell-derived endothelial progenitor cells from sac-like structures

Transplanted endothelial progenitor cells (EPCs) repair blood vessels and exert regenerative effects on disorders such as lower limb ischemia. EPCs serve as a model for pathophysiological and pharmacokinetic studies, which is important for drug discovery. However, primary human EPCs are phenotypically unstable, which limits their clinical utility. Therefore, we employed human induced pluripotent stem (iPS) cells to circumvent this problem. Here we focused on human iPS cell-derived sac-like structures (iPS-sacs), which contain endothelial lineage cells and hematopoietic lineage cells. Previous studies isolated only hematopoietic lineage cells from iPS-sacs. Therefore, here we attempted to isolate EPCs. However, iPS-sacs generated by a published protocol did not contain sufficient EPCs. Therefore, to generate iPS-sacs highly enriched in EPCs, we added the glycogen synthase kinase 3 beta (GSK3β) inhibitor CHIR-99021 to the culture medium early during differentiation. The cells rapidly differentiated into mesoderm to yield abundant EPCs, and CHIR-99021 increased the proportion of EPCs contained in iPS-sacs. EPCs, which were purified using anti-platelet endothelial cell adhesion molecule (PECAM1) antibody-conjugated beads, expressed markers of immature endothelial cells. Purified EPCs formed tube-like structures and incorporated acetylated low density lipoprotein (Ac-LDL), reflecting endothelial phenotypes. The simple method described here will likely improve regenerative medicine and facilitate basic studies on the endothelial lineage.

Differentiation of Human Pluripotent Stem Cells into Functional Endothelial Cells in Scalable Suspension Culture

Endothelial cells (ECs) are involved in a variety of cellular responses. As multifunctional components of vascular structures, endothelial (progenitor) cells have been utilized in cellular therapies and are required as an important cellular component of engineered tissue constructs and in vitro disease models. Although primary ECs from different sources are readily isolated and expanded, cell quantity and quality in terms of functionality and karyotype stability is limited. ECs derived from human induced pluripotent stem cells (hiPSCs) represent an alternative and potentially superior cell source, but traditional culture approaches and 2D differentiation protocols hardly allow for production of large cell numbers. Aiming at the production of ECs, we have developed a robust approach for efficient endothelial differentiation of hiPSCs in scalable suspension culture. The established protocol results in relevant numbers of ECs for regenerative approaches and industrial applications that show in vitro proliferation capacity and a high degree of chromosomal stability.

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Efficient generation of hiPSC-derived ECs in scalable suspension culture

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High degree of chromosomal stability of hiPSC-ECs after in vitro expansion

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Generation of relevant numbers of hiPSC-ECs for regenerative approaches

Clarithromycin suppresses induction of monocyte chemoattractant protein-1 and matrix metalloproteinase-9 and improves pathological changes in the lungs and heart of mice infected with influenza A virus

The influenza A virus (IAV)-cytokine-trypsin/matrix metalloproteinase-9 (MMP-9) cycle is one of the important mechanisms of multiple organ failure in severe influenza. Clarithromycin, a macrolide antibiotic, has immune modulatory and anti-inflammatory effects. We analyzed the effects of clarithromycin on the induction of chemokines, cytokines, MMP-9, trypsin, vascular hyper-permeability and inflammatory aggravation in mice with IAV infection. IAV/Puerto Rico/8/34(H1N1) infection increased the levels of monocyte chemoattractant protein-1 (MCP-1) and cytokines in serum, and MMP-9 and trypsin in serum and/or the lungs and heart. Clarithromycin significantly suppressed the induction of serum MCP-1 and MMP-9 and vascular hyperpermeability in these organs in the early phase of infection, but did not suppress the induction of trypsin, IL-6 or IFN-γ. Histopathological examination showed that clarithromycin tended to reduce inflammatory cell accumulation in the lungs and heart. These results suggest that clarithromycin suppresses infection-related inflammation and reduces vascular hyperpermeability by suppressing the induction of MCP-1 and MMP-9.

Constitutively Expressed IFITM3 Protein in Human Endothelial Cells Poses an Early Infection Block to Human Influenza Viruses

A role for pulmonary endothelial cells in the orchestration of cytokine production and leukocyte recruitment during influenza virus infection, leading to severe lung damage, has been recently identified. As the mechanistic pathway for this ability is not fully known, we extended previous studies on influenza virus tropism in cultured human pulmonary endothelial cells. We found that a subset of avian influenza viruses, including potentially pandemic H5N1, H7N9, and H9N2 viruses, could infect human pulmonary endothelial cells (HULEC) with high efficiency compared to human H1N1 or H3N2 viruses. In HULEC, human influenza viruses were capable of binding to host cellular receptors, becoming internalized and initiating hemifusion but failing to uncoat the viral nucleocapsid and to replicate in host nuclei. Unlike numerous cell types, including epithelial cells, we found that pulmonary endothelial cells constitutively express a high level of the restriction protein IFITM3 in endosomal compartments. IFITM3 knockdown by small interfering RNA (siRNA) could partially rescue H1N1 virus infection in HULEC, suggesting IFITM3 proteins were involved in blocking human influenza virus infection in endothelial cells. In contrast, selected avian influenza viruses were able to escape IFITM3 restriction in endothelial cells, possibly by fusing in early endosomes at higher pH or by other, unknown mechanisms. Collectively, our study demonstrates that the human pulmonary endothelium possesses intrinsic immunity to human influenza viruses, in part due to the constitutive expression of IFITM3 proteins. Notably, certain avian influenza viruses have evolved to escape this restriction, possibly contributing to virus-induced pneumonia and severe lung disease in humans.

IMPORTANCE

Avian influenza viruses, including H5N1 and H7N9, have been associated with severe respiratory disease and fatal outcomes in humans. Although acute respiratory distress syndrome (ARDS) and progressive pulmonary endothelial damage are known to be present during severe human infections, the role of pulmonary endothelial cells in the pathogenesis of avian influenza virus infections is largely unknown. By comparing human seasonal influenza strains to avian influenza viruses, we provide greater insight into the interaction of influenza virus with human pulmonary endothelial cells. We show that human influenza virus infection is blocked during the early stages of virus entry, which is likely due to the relatively high expression of the host antiviral factors IFITMs (interferon-induced transmembrane proteins) located in membrane-bound compartments inside cells. Overall, this study provides a mechanism by which human endothelial cells limit replication of human influenza virus strains, whereas avian influenza viruses overcome these restriction factors in this cell type.

Transcriptional and Bioinformatic Analysis Provide a Relationship between Host Response Changes to Marek's Disease Viruses Infection and an Integrated Long Terminal Repeat

GX0101, Marek's disease virus (MDV) strain with a long terminal repeat (LTR) insert of reticuloendotheliosis virus (REV), was isolated from CVI988/Rispens vaccinated birds showing tumors. We have constructed a LTR deleted strain GX0101ΔLTR in our previous study. To compare the host responses to GX0101 and GX0101ΔLTR, chicken embryo fibroblasts (CEF) cells were infected with two MDV strains and a gene-chip containing chicken genome was employed to examine gene transcription changes in host cells in the present study. Of the 42,368 chicken transcripts on the chip, there were 2199 genes that differentially expressed in CEF infected with GX0101 compared to GX0101ΔLTR significantly. Differentially expressed genes were distributed to 25 possible gene networks according to their intermolecular connections and were annotated to 56 pathways. The insertion of REV LTR showed the greatest influence on cancer formation and metastasis, followed with immune changes, atherosclerosis, and nervous system disorders in MDV-infected CEF cells. Based on these bio functions, GX0101 infection was predicated with a greater growth and survival inhibition but lower oncogenicity in chickens than GX0101ΔLTR, at least in the acute phase of infection. In summary, the insertion of REV LTR altered the expression of host genes in response to MDV infection, possibly resulting in novel phenotypic properties in chickens. Our study has provided the evidence of retroviral insertional changes of host responses to herpesvirus infection for the first time, which will promote to elucidation of the possible relationship between the LTR insertion and the observed phenotypes.

Energy metabolic disorder is a major risk factor in severe influenza virus infection: Proposals for new therapeutic options based on animal model experiments

Severe influenza is characterized by cytokine storm and multiorgan failure. Influenza patients with underlying diseases show a rapid progression in disease severity. The major mechanism that underlies multiorgan failure during the progressive stage of infection, particularly in patients with underlying risk factors, is mitochondrial energy crisis. The relationship between the factors that determine infection severity, such as influenza virus, cytokines, cellular trypsin as a hemagglutinin processing protease for viral multiplication, accumulation of metabolic intermediates and ATP crisis in mitochondria, is termed the "influenza virus-cytokine-trypsin" cycle. This occurs during the initial stages of infection, and is interconnected with the "metabolic disorders-cytokine" cycle in the middle to late phase of infection. Experiments using animal models have highlighted the complex relationship between these two cycles. New treatment options have been proposed that target the ATP crisis and multiorgan failure during the late phase of infection, rather than antiviral treatments with neuraminidase inhibitors that work during the initial phase. These options are (i) restoration of glucose oxidation in mitochondria by diisopropylamine dichloroacetate, which inhibits infection-induced pyruvate dehydrogenase kinase 4 activity, and (ii) restoration of long-chain fatty acid oxidation in mitochondria by l-carnitine and bezafibrate, an agonist of peroxisome proliferation-activated receptors-β/δ, which transcriptionally upregulates carnitine palmitoyltransferase II. The latter is particularly effective in patients with influenza-associated encephalopathy who have thermolabile and short half-life compound variants of carnitine palmitoyltransferase II.

Exploring the associations of host genes for viral infection revealed by genome-wide RNAi and virus-host protein interactions

Genome-wide RNA interference screens have greatly facilitated the identification of essential host factors (EHFs) for viral infections, whose knockdown effects significantly influence virus replication but not host cell viability. However, little has been done to link EHFs with another important host factor type, i.e., virus targeting proteins (VTPs) that viruses directly interact with for intracellular survival, hampering the integrative understanding of virus-host interactions. Using EHFs and VTPs for human immunodeficiency virus type 1 (HIV-1) and influenza A virus (IAV) infections, we found in general that despite limited overlap, EHFs and VTPs are both among the most differentially dysregulated genes in host transcriptional response to HIV and IAV infections, and notably they show consistency in regulation orientation. In the human protein-protein interaction network, both EHFs and VTPs hold topologically important positions at the global center, and importantly their direct interactions are statistically significant. We also identified BRCA1 and TP53 (or SMAD3 and PIK3R1) being the most extensive VTP-interacting EHFs (or EHF-interacting VTPs) for HIV-1 and IAV, which hold great potential in deciphering specific infection features and discovery of host directed antivirals. Further, most EHFs are the upstream regulators of VTPs when mapped in the same signaling pathways, some of which present intensive cross links. Collectively, these results provide insights into functional associations of the identified host gene factors for viral infections and highlight the regulatory significance of EHFs, and the necessity of their selective exploitation in confrontation to viral infections.

Influenza virus pathogenicity regulated by host cellular proteases, cytokines and metabolites, and its therapeutic options

Influenza A virus (IAV) causes significant morbidity and mortality. The knowledge gained within the last decade on the pandemic IAV(H1N1)2009 improved our understanding not only of the viral pathogenicity but also the host cellular factors involved in the pathogenicity of multiorgan failure (MOF), such as cellular trypsin-type hemagglutinin (HA0) processing proteases for viral multiplication, cytokine storm, metabolic disorders and energy crisis. The HA processing proteases in the airway and organs for all IAV known to date have been identified. Recently, a new concept on the pathogenicity of MOF, the "influenza virus-cytokine-trypsin" cycle, has been proposed involving up-regulation of trypsin through pro-inflammatory cytokines, and potentiation of viral multiplication in various organs. Furthermore, the relationship between causative factors has been summarized as the "influenza virus-cytokine-trypsin" cycle interconnected with the "metabolic disorders-cytokine" cycle. These cycles provide new treatment concepts for ATP crisis and MOF. This review discusses IAV pathogenicity on cellular proteases, cytokines, metabolites and therapeutic options.