Prostaglandin E(2) inhibits replication of HIV-1 in macrophages through activation of protein kinase A

Metabolomics combined with network pharmacology reveals a role for astragaloside IV in inhibiting enterovirus 71 replication via PI3K-AKT signaling

BACKGROUND

Astragaloside IV (AST-IV), as an effective active ingredient of Astragalus membranaceus (Fisch.) Bunge. It has been found that AST-IV inhibits the replication of dengue virus, hepatitis B virus, adenovirus, and coxsackievirus B3. Enterovirus 71 (EV71) serves as the main pathogen in severe hand-foot-mouth disease (HFMD), but there are no specific drugs available. In this study, we focus on investigating whether AST-IV can inhibit EV71 replication and explore the potential underlying mechanisms.

METHODS

The GES-1 or RD cells were infected with EV71, treated with AST-IV, or co-treated with both EV71 and AST-IV. The EV71 structural protein VP1 levels, the viral titers in the supernatant were measured using western blot and 50% tissue culture infective dose (TCID50), respectively. Network pharmacology was used to predict possible pathways and targets for AST-IV to inhibit EV71 replication. Additionally, ultra-high performance liquid chromatography-high resolution mass spectrometry (UHPLC-HRMS) was used to investigate the potential targeted metabolites of AST-IV. Associations between metabolites and apparent indicators were performed via Spearman's algorithm.

RESULTS

This study illustrated that AST-IV effectively inhibited EV71 replication. Network pharmacology suggested that AST-IV inhibits EV71 replication by targeting PI3K-AKT. Metabolomics results showed that AST-IV achieved these effects by elevating the levels of hypoxanthine, 2-ketobutyric acid, adenine, nicotinic acid mononucleotide, prostaglandin H2, 6-hydroxy-1 H-indole-3- acetamide, oxypurinol, while reducing the levels of PC (14:0/15:0). Furthermore, AST-IV also mitigated EV71-induced oxidative stress by reducing the levels of MDA, ROS, while increasing the activity of T-AOC, CAT, GSH-Px. The inhibition of EV71 replication was also observed when using the ROS inhibitor N-Acetylcysteine (NAC). Additionally, AST-IV exhibited the ability to activate the PI3K-AKT signaling pathway and suppress EV71-induced apoptosis.

CONCLUSION

This study suggests that AST-IV may activate the cAMP and the antioxidant stress response by targeting eight key metabolites, including hypoxanthine, 2-ketobutyric acid, adenine, nicotinic acid mononucleotide, prostaglandin H2, 6-Hydroxy-1 H-indole-3-acetamide, oxypurinol and PC (14:0/15:0). This activation can further stimulate the PI3K-AKT signaling to inhibit EV71-induced apoptosis and EV71 replication.

Lipid droplets in pathogen infection and host immunity

As the hub of cellular lipid metabolism, lipid droplets (LDs) have been linked to a variety of biological processes. During pathogen infection, the biogenesis, composition, and functions of LDs are tightly regulated. The accumulation of LDs has been described as a hallmark of pathogen infection and is thought to be driven by pathogens for their own benefit. Recent studies have revealed that LDs and their subsequent lipid mediators contribute to effective immunological responses to pathogen infection by promoting host stress tolerance and reducing toxicity. In this comprehensive review, we delve into the intricate roles of LDs in governing the replication and assembly of a wide spectrum of pathogens within host cells. We also discuss the regulatory function of LDs in host immunity and highlight the potential for targeting LDs for the diagnosis and treatment of infectious diseases.

Replication of infectious bronchitis virus (IBV) Delmarva (DMV)/1639 variant in primary and secondary lymphoid organs leads to immunosuppression in chickens

Infectious bronchitis virus (IBV) that primarily causes respiratory infection in chickens, disseminate to multiple body systems leading to pathology, results in economic losses to poultry industry. IBV replicates in the bursa of Fabricius (BF), Harderian gland (HG), cecal tonsils (CT), and spleen. The objective of this study was to investigate the immunosuppressive effect of IBV Delmarva (DMV/1639) variant in chickens. Specific pathogen free chickens were infected with the IBV DMV/1639 variant while maintaining an age-matched uninfected control group. At predetermined time points, subsets of the infected and control chickens were observed for changes in body weights and pathological changes. The histopathological lesions were observed in the CT and BF, with minimal lesions in the thymus and spleen. The mRNA expression of pro-inflammatory mediators suggested immunomodulation by IBV, favoring viral replication. Further studies are warranted to observe the functional impact of the IBV DMV/1639 variant's replication in immune organs.

Differential Expression of CREM/ICER Isoforms Is Associated with the Spontaneous Control of HIV Infection

A rare subset of HIV-infected individuals, termed elite controllers (ECs), can maintain long-term control over HIV replication in the absence of antiretroviral therapy (ART). To elucidate the biological mechanism of resistance to HIV replication at the molecular and cellular levels, we performed RNA sequencing and identified alternative splicing variants from ECs, HIV-infected individuals undergoing ART, ART-naive HIV-infected individuals, and healthy controls. We identified differential gene expression patterns that are specific to ECs and may influence HIV resistance, including alternative RNA splicing and exon usage variants of the CREM/ICER gene (cyclic AMP [cAMP]-responsive element modulator/inducible cAMP early repressors). The knockout and knockdown of specific ICER exons that were found to be upregulated in ECs resulted in significantly increased HIV infection in a CD4⁺ T cell line and primary CD4⁺ T cells. Overexpression of ICER isoforms decreased HIV infection in primary CD4⁺ T cells. Furthermore, ICER regulated HIV long terminal repeat (LTR) promoter activity in a Tat-dependent manner. Together, these results suggest that ICER is an HIV host factor that may contribute to the HIV resistance of ECs. These findings will help elucidate the mechanisms of HIV control by ECs and may yield a new approach for treatment of HIV. IMPORTANCE A small group of HIV-infected individuals, termed elite controllers (ECs), display control of HIV replication in the absence of antiretroviral therapy (ART). However, the mechanism of ECs' resistance to HIV replication is not clear. In our work, we found an increased expression of specific, small isoforms of ICER in ECs. Further experiments proved that ICER is a robust host factor to regulate viral replication. Furthermore, we found that ICER regulates HIV LTR promoter activity in a Tat-dependent manner. These findings suggest that ICER is related to spontaneous control of HIV infection in ECs. This study may help elucidate a novel target for treatment of HIV.

Marek's Disease Virus Modulates T Cell Proliferation via Activation of Cyclooxygenase 2-Dependent Prostaglandin E2

Marek’s disease virus (MDV), an avian alphaherpesvirus, infects chickens, transforms CD4+ T cells, and induces immunosuppression early during infection. However, the exact mechanisms involved in MDV-induced immunosuppression are yet to be identified. Here, our results demonstrate that MDV infection in vitro and in vivo induces activation of cyclooxygenase-2 (COX-2) and production of prostaglandin E2 (PGE2). This exerts its inhibitory effects on T cell proliferation at day 21 post infection via PGE2 receptor 2 (EP2) and receptor 4 (EP4). Impairment of the MDV-induced T cell proliferation was associated with downregulation of IL-2 and transferrin uptake in a COX-2/PGE2 dependent manner in vitro. Interestingly, oral administration of a COX-2 inhibitor, meloxicam, during MDV infection inhibited COX-2 activation and rescued T cell proliferation at day 21 post infection. Taken together, our results reveal a novel mechanism that contributes to immunosuppression in the MDV-infected chickens.

Lipid droplets and lipid mediators in viral infection and immunity

Lipid droplets (LDs) contribute to key pathways important for the physiology and pathophysiology of cells. In a homeostatic view, LDs regulate the storage of neutral lipids, protein sequestration, removal of toxic lipids and cellular communication; however, recent advancements in the field show these organelles as essential for various cellular stress response mechanisms, including inflammation and immunity, with LDs acting as hubs that integrate metabolic and inflammatory processes. The accumulation of LDs has become a hallmark of infection, and is often thought to be virally driven; however, recent evidence is pointing to a role for the upregulation of LDs in the production of a successful immune response to viral infection. The fatty acids housed in LDs are also gaining interest due to the role that these lipid species play during viral infection, and their link to the synthesis of bioactive lipid mediators that have been found to have a very complex role in viral infection. This review explores the role of LDs and their subsequent lipid mediators during viral infections and poses a paradigm shift in thinking in the field, whereby LDs may play pivotal roles in protecting the host against viral infection.

Nitric Oxide and Immune Responses in Cancer: Searching for New Therapeutic Strategies

In recent years, there has been an increasing interest in understanding the mysterious functions of nitric oxide (NO) and how this pleiotropic signaling molecule contributes to tumorigenesis. This review attempts to expose and discuss the information available on the immunomodulatory role of NO in cancer and recent approaches to the role of NO donors in the area of immunotherapy. To address the goal, the following databases were searched to identify relevant literature concerning empirical evidence: The Cochrane Library, Pubmed, Medline, EMBASE from 1980 through March 2020. Valuable attempts have been made to develop distinctive NO-based cancer therapy. Although the data do not allow generalization, the evidence seems to indicate that low / moderate levels may favor tumorigenesis while higher levels would exert anti-tumor effects. In this sense, the use of NO donors could have an important therapeutic potential within immunotherapy, although there are still no clinical trials. The emerging understanding of NO-regulated immune responses in cancer may help unravel the recent features of this "double-edged sword" in cancer physiological and pathologic processes and its potential use as a therapeutic agent for cancer treatment. In short, in this review, we discuss the complex cellular mechanism in which NO, as a pleiotropic signaling molecule, participates in cancer pathophysiology. We also debate the dual role of NO in cancer and tumor progression, and clinical approaches for inducible nitric oxide synthase (iNOS) based therapy against cancer.

cAMP-Dependent Signaling Pathways as Potential Targets for Inhibition of Plasmodium falciparum Blood Stages

We review the role of signaling pathways in regulation of the key processes of merozoite egress and red blood cell invasion by Plasmodium falciparum and, in particular, the importance of the second messengers, cAMP and Ca²⁺, and cyclic nucleotide dependent kinases. cAMP-dependent protein kinase (PKA) is comprised of cAMP-binding regulatory, and catalytic subunits. The less well conserved cAMP-binding pockets should make cAMP analogs attractive drug leads, but this approach is compromised by the poor membrane permeability of cyclic nucleotides. We discuss how the conserved nature of ATP-binding pockets makes ATP analogs inherently prone to off-target effects and how ATP analogs and genetic manipulation can be useful research tools to examine this. We suggest that targeting PKA interaction partners as well as substrates, or developing inhibitors based on PKA interaction sites or phosphorylation sites in PKA substrates, may provide viable alternative approaches for the development of anti-malarial drugs. Proximity of PKA to a substrate is necessary for substrate phosphorylation, but the P. falciparum genome encodes few recognizable A-kinase anchor proteins (AKAPs), suggesting the importance of PKA-regulatory subunit myristylation and membrane association in determining substrate preference. We also discuss how Pf14-3-3 assembles a phosphorylation-dependent signaling complex that includes PKA and calcium dependent protein kinase 1 (CDPK1) and how this complex may be critical for merozoite invasion, and a target to block parasite growth. We compare altered phosphorylation levels in intracellular and egressed merozoites to identify potential PKA substrates. Finally, as host PKA may have a critical role in supporting intracellular parasite development, we discuss its role at other stages of the life cycle, as well as in other apicomplexan infections. Throughout our review we propose possible new directions for the therapeutic exploitation of cAMP-PKA-signaling in malaria and other diseases caused by apicomplexan parasites.

Cyclooxygenase-2 Facilitates Newcastle Disease Virus Proliferation and Is as a Target for Canthin-6-One Antiviral Activity

Cyclooxygenase-2 (COX-2), one of the mediators of inflammation in response to viral infection, plays an important role in host antiviral defense system. But its role in Newcastle disease virus (NDV) proliferation process remains unclear. This study revealed that inhibition of COX-2 could benefit NDV proliferation and overexpression of COX-2 dose-dependently suppressed NDV proliferation. Overexpression of COX-2 also showed inhibitory effect on NDV-induced endoplasmic reticulum (ER)-stress and autophagy, also promoted the expression of antiviral genes. However, prostaglandin E₂ (PGE₂), the major product of COX-2, had indistinctive effects on NDV proliferation. At variant time point post viral infection, a tight regulation pattern of COX-2 by NDV was observed. Using inhibitors and siRNA against signaling molecules, the nuclear factor-κB (NF-κB) and melanoma differentiation-associated gene 5 (MDA5) were identified as critical factors for NDV induced COX-2 expression. Nonetheless, at late stage of NDV proliferation, substantial suppression of COX-2 protein synthesis could be detected, accompanied by a decrease in mRNA half-life. Furthermore, three C ring-truncated canthin-6-one analogs were used to activate COX-2 expression and showed inhibitory effect on NDV proliferation with the effective concentrations on μM level. Taken together, these results illustrated a novel NDV-regulated cellular mechanism and indicated that COX-2 is an important regulator of NDV proliferation which can serve as a potential target for anti-NDV agents.

Imiquimod suppresses respiratory syncytial virus (RSV) replication via PKA pathway and reduces RSV induced-inflammation and viral load in mice lungs

Respiratory syncytial virus (RSV) is a leading cause of lower respiratory tract disease and bronchiolitis in children, as well as an important cause of morbidity and mortality in elderly and immunocompromised individuals. However, there is no safe and efficacious RSV vaccine or antiviral treatment. Toll Like Receptors (TLR) are important molecular mediators linking innate and adaptive immunity, and their stimulation by cognate agonists has been explored as antiviral agents. Imiquimod is known as a TLR7 agonist, but additionally acts as an antagonist for adenosine receptors. In this study, we demonstrate that imiquimod, but not resiquimod, has direct anti-RSV activity via PKA pathway in HEp-2 and A549 cells, independently of an innate response. Imiquimod restricts RSV infection after viral entry into the host cell, interfering with viral RNA and protein synthesis. Probably as a consequence of these anti-RSV properties, imiquimod displays cytokine modulating activity in RSV infected epithelial cells. Moreover, in a murine model of RSV infection, imiquimod treatment improves the course of acute disease, evidenced by decreased weight loss, reduced RSV lung titers, and attenuated airway inflammation. Consequently, imiquimod represents a promising therapeutic alternative against RSV infection and may inform the development of novel therapeutic targets to control RSV pathogenesis.

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Imiquimod has direct anti-RSV activity via PKA pathway, independently of an innate response.

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Imiquimod restricts RSV infection after viral entry into the host cell, interfering with viral RNA and protein synthesis.

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Imiquimod reduces cytokine production in RSV infected epithelial cells, probably as a result of its anti-RSV properties.

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Imiquimod reduces RSV lung titers and decreases weight loss and airway inflammation in a murine model of RSV infection.

Feline calicivirus- and murine norovirus-induced COX-2/PGE2 signaling pathway has proviral effects

Cyclooxygenases (COXs)/prostaglandin E₂ (PGE₂) signaling pathways are known to modulate a variety of homeostatic processes and are involved in various pathophysiological conditions. COXs/PGE₂ signaling pathways have also been demonstrated to have proviral or antiviral effects, which appeared different even in the same virus family. A porcine sapovirus Cowden strain, a member of genus Sapovirus within the Caliciviridae family, induces strong COX-2/PGE₂ but transient COX-1/PGE₂ signaling to enhance virus replication. However, whether infections of other viruses in the different genera activate COXs/PGE₂ signaling, and thus affect the replication of viruses, remains unknown. In the present study, infections of cells with the feline calicivirus (FCV) F9 strain in the genus Vesivirus and murine norovirus (MNV) CW-1 strain in the genus Norovirus only activated the COX-2/PGE₂ signaling in a time-dependent manner. Treatment with pharmacological inhibitors or transfection of small interfering RNAs (siRNAs) against COX-2 enzyme significantly reduced the production of PGE₂ as well as FCV and MNV replications. The inhibitory effects of these pharmacological inhibitors against COX-2 enzyme on the replication of both viruses were restored by the addition of PGE₂. Silencing of COX-1 via siRNAs and inhibition of COX-1 via an inhibitor also decrease the production of PGE₂ and replication of both viruses, which can be attributed to the inhibition COX-1/PGE₂ signaling pathway. These data indicate that the COX-2/PGE₂ signaling pathway has proviral effects for the replication of FCV and MNV, and pharmacological inhibitors against these enzymes serve as potential therapeutic candidates for treating FCV and MNV infections.

Prostaglandin E2 Increases Lentiviral Vector Transduction Efficiency of Adult Human Hematopoietic Stem and Progenitor Cells

Gene therapy currently in development for hemoglobinopathies utilizes ex vivo lentiviral transduction of CD34⁺ hematopoietic stem and progenitor cells (HSPCs). A small-molecule screen identified prostaglandin E₂ (PGE₂) as a positive mediator of lentiviral transduction of CD34⁺ cells. Supplementation with PGE₂ increased lentiviral vector (LVV) transduction of CD34⁺ cells approximately 2-fold compared to control transduction methods with no effect on cell viability. Transduction efficiency was consistently increased in primary CD34⁺ cells from multiple normal human donors and from patients with β-thalassemia or sickle cell disease. Notably, PGE₂ increased transduction of repopulating human HSPCs in an immune-deficient (nonobese diabetic/severe combined immunodeficiency/interleukin-2 gamma receptor null [NSG]) xenotransplantation mouse model without evidence of in vivo toxicity, lineage bias, or a de novo bias of lentiviral integration sites. These data suggest that PGE₂ improves lentiviral transduction and increases vector copy number, therefore resulting in increased transgene expression. As a result, PGE₂ may be useful in clinical gene therapy applications using lentivirally modified HSPCs.

cAMP-dependent activation of protein kinase A attenuates respiratory syncytial virus-induced human airway epithelial barrier disruption

Airway epithelium forms a barrier to the outside world and has a crucial role in susceptibility to viral infections. Cyclic adenosine monophosphate (cAMP) is an important second messenger acting via two intracellular signaling molecules: protein kinase A (PKA) and the guanidine nucleotide exchange factor, Epac. We sought to investigate effects of increased cAMP level on the disruption of model airway epithelial barrier caused by RSV infection and the molecular mechanisms underlying cAMP actions. Human bronchial epithelial cells were infected with RSV-A2 and treated with either cAMP releasing agent, forskolin, or cAMP analogs. Structure and functions of the Apical Junctional Complex (AJC) were evaluated by measuring transepithelial electrical resistance and permeability to FITC-dextran, and determining localization of AJC proteins by confocal microscopy. Increased intracellular cAMP level significantly attenuated RSV-induced disassembly of AJC. These barrier-protective effects of cAMP were due to the activation of PKA signaling and did not involve Epac activity. Increased cAMP level reduced RSV-induced reorganization of the actin cytoskeleton, including apical accumulation of an essential actin-binding protein, cortactin, and inhibited expression of the RSV F protein. These barrier-protective and antiviral-function of cAMP signaling were evident even when cAMP level was increased after the onset of RSV infection. Taken together, our study demonstrates that cAMP/PKA signaling attenuated RSV-induced disruption of structure and functions of the model airway epithelial barrier by mechanisms involving the stabilization of epithelial junctions and inhibition of viral biogenesis. Improving our understanding of the mechanisms involved in RSV-induced epithelial dysfunction and viral pathogenesis will help to develop novel anti-viral therapeutic approaches.

Prostaglandin E2 As a Modulator of Viral Infections

Viral infections are a major cause of infectious diseases worldwide. Inflammation and the immune system are the major host defenses against these viral infection. Prostaglandin E2 (PGE2), an eicosanoid generated by cyclooxygenases, has been shown to modulate inflammation and the immune system by regulating the expression/concentration of cytokines. The effect of PGE2 on viral infection and replication is cell type- and virus-family-dependent. The host immune system can be modulated by PGE2, with regards to immunosuppression, inhibition of nitrogen oxide (NO) production, inhibition of interferon (IFN) and apoptotic pathways, and inhibition of viral receptor expression. Furthermore, PGE2 can play a role in viral infection directly by increasing the production and release of virions, inhibiting viral binding and replication, and/or stimulating viral gene expression. PGE2 may also have a regulatory role in the induction of autoimmunity and in signaling via Toll-like receptors. In this review the known effects of PGE2 on the pathogenesis of various infections caused by herpes simplex virus, rotavirus, influenza A virus and human immunodeficiency virus as well the therapeutic potential of PGE2 are discussed.

Synergistic reactivation of latent HIV-1 provirus by PKA activator dibutyryl-cAMP in combination with an HDAC inhibitor

HIV-1 reservoirs remain a major barrier to HIV-1 eradication. Although combination antiretroviral therapy (cART) can successfully reduce viral replication, it cannot reactivate HIV-1 provirus in this reservoir. Therefore, HIV-1 provirus reactivation strategies by cell activation or epigenetic modification are proposed for the eradication of HIV-1 reservoirs. Although treatment with the protein kinase A (PKA) activator cyclic AMP (cAMP) or epigenetic modifying agents such as histone deacetylase inhibitors (HDACi) alone can induce HIV-1 reactivation in latently infected cells, the synergism of these agents has not been fully evaluated. In the present study, we observed that treatment with 500μM of dibutyryl-cAMP, 1μM of vorinostat, or 1μM of trichostatin A alone effectively reactivated HIV-1 in both ACH2 and NCHA1 cells latently infected with HIV-1 without cytotoxicity. In addition, treatment with the PKA inhibitor KT5720 reduced the increased HIV-1 p24 level in the supernatant of these cells. After dibutyryl-cAMP treatment, we found an increased level of the PKA substrate phosphorylated cyclic AMP response element-binding protein. When we treated cells with a combination of dibutyryl-cAMP and vorinostat or trichostatin A, the levels of HIV-1 p24 in the supernatant and levels of intracellular HIV-1 p24 were dramatically increased in both ACH2 and NCHA1 cells compared with those treated with a single agent. These results suggest that combined treatment with a PKA activator and an HDACi is effective for reactivating HIV-1 in latently infected cells, and may be an important approach to eradicate HIV-1 reservoirs.

Antibiotic and Antiinflammatory Therapy Transiently Reduces Inflammation and Hypercoagulation in Acutely SIV-Infected Pigtailed Macaques

Increased chronic immune activation and inflammation are hallmarks of HIV/SIV infection and are highly correlated with progression to AIDS and development of non-AIDS comorbidities, such as hypercoagulability and cardiovascular disease. Intestinal dysfunction resulting in microbial translocation has been proposed as a lead cause of systemic immune activation and hypercoagulability in HIV/SIV infection. Our goal was to assess the biological and clinical impact of a therapeutic strategy designed to reduce microbial translocation through reduction of the microbial content of the intestine (Rifaximin-RFX) and of gut inflammation (Sulfasalazine-SFZ). RFX is an intraluminal antibiotic that was successfully used in patients with hepatic encephalopathy. SFZ is an antiinflammatory drug successfully used in patients with mild to moderate inflammatory bowel disease. Both these clinical conditions are associated with increased microbial translocation, similar to HIV-infected patients. Treatment was administered for 90 days to five acutely SIV-infected pigtailed macaques (PTMs) starting at the time of infection; seven untreated SIVsab-infected PTMs were used as controls. RFX+SFZ were also administered for 90 days to three chronically SIVsab-infected PTMs. RFX+SFZ administration during acute SIVsab infection of PTMs resulted in: significantly lower microbial translocation, lower systemic immune activation, lower viral replication, better preservation of mucosal CD4⁺ T cells and significantly lower levels of hypercoagulation biomarkers. This effect was clear during the first 40 days of treatment and was lost during the last stages of treatment. Administration of RFX+SFZ to chronically SIVsab–infected PTMs had no discernible effect on infection. Our data thus indicate that early RFX+SFZ administration transiently improves the natural history of acute and postacute SIV infection, but has no effect during chronic infection.

We report that administration of the intraluminal antibiotic Rifaximin and the gut-focused anti-inflammatory drug Sulfasalazine to acutely SIV-infected pigtailed macaques is associated with a transient disruption of the vicious circle of inflammation-microbial translocation-immune activation which is pathognomonic to pathogenic HIV/SIV infection and drives HIV disease progression and non-AIDS comorbidities in HIV-infected patients. This therapeutic approach resulted in transient lower microbial translocation, lower systemic immune activation, lower viral replication, better preservation of mucosal CD4⁺ T cells and lower levels of hypercoagulation biomarkers throughout acute SIV infection. Our results thus support the use of therapeutic approaches to reduce microbial translocation, improve the clinical outcome of HIV-infected patients receiving antiretroviral therapy and prevent non-AIDS comorbidities. Our results also reinforce the importance of early therapeutic management of HIV infection.

Putative roles of purinergic signaling in human immunodeficiency virus-1 infection

Reviewers

This article was reviewed by Neil S. Greenspan and Rachel Gerstein.

Nucleotides and nucleosides act as potent extracellular messengers via the activation of the family of cell-surface receptors termed purinergic receptors. These receptors are categorized into P1 and P2 receptors (P2Rs). P2Rs are further classified into two distinct families, P2X receptors (P2XRs) and P2Y receptors (P2YRs). These receptors display broad tissue distribution throughout the body and are involved in several biological events. Immune cells express various P2Rs, and purinergic signaling mechanisms have been shown to play key roles in the regulation of many aspects of immune responses. Researchers have elucidated the involvement of these receptors in the host response to infections. The evidences indicate a dual function of these receptors, depending on the microorganism and the cellular model involved. Three recent reports have examined the relationship between the level of extracellular ATP, the mechanisms underlying purinergic receptors participating in the infection mechanism of HIV-1 in the cell. Although preliminary, these results indicate that purinergic receptors are putative pharmacological targets that should be further explored in future studies.

Phosphodiesterase 8a supports HIV-1 replication in macrophages at the level of reverse transcription

BACKGROUND

HIV-1 infected macrophages play a key role in HIV-1 infection. Even during anti-retroviral treatment, macrophages keep producing virus due to suboptimal tissue penetration and reduced efficacy of antiretrovirals. It is therefore of major importance to understand which host factors are involved in HIV-1 replication in macrophages. Previously, we have shown that genetic polymorphisms in phosphodiesterase 8a (PDE8A) are strongly associated with HIV-1 replication in these cells. Here we analyzed the mechanism and regulation of PDE8A in HIV-1 replication in macrophages.

RESULTS

PDE8A mRNA expression strongly increases upon differentiation of monocytes into macrophages, which corresponds to the increased susceptibility of mature macrophages to HIV-1. In parallel, expression of microRNA miR-145-5p, predicted to target PDE8A mRNA, strongly decreased. The interaction of miR-145-5p with the 3' UTR of PDE8A mRNA could be experimentally validated, suggesting that indeed miR-145-5p can regulate PDE8A expression levels. Knockdown of PDE8A in macrophages resulted in a decrease in total HIV-1 replication and proviral DNA levels. These observations confirm that PDE8A regulates HIV-1 replication in macrophages and that this effect is mediated through early steps in the viral replication cycle.

CONCLUSIONS

PDE8A is highly expressed in macrophages, and its expression is regulated by miR-145-5p. Our findings strongly suggest that PDE8A supports HIV-1 replication in macrophages and that this effect is mediated at the level of reverse transcription.

Prostaglandin E2 reduces the release and infectivity of new cell-free virions and cell-to-cell HIV-1 transfer

Background

The course of human immunodeficiency virus type-1 (HIV-1) infection is influenced by a complex interplay between viral and host factors. HIV infection stimulates several proinflammatory genes, such as cyclooxigense-2 (COX-2), which leads to an increase in prostaglandin (PG) levels in the plasma of HIV-1-infected patients. These genes play an indeterminate role in HIV replication and pathogenesis. The effect of prostaglandin E₂ (PGE₂) on HIV infection is quite controversial and even contradictory, so we sought to determine the role of PGE₂ and the signal transduction pathways involved in HIV infection to elucidate possible new targets for antiretrovirals.

Results

Our results suggest that PGE₂ post-infection treatment acts in the late stages of the viral cycle to reduce HIV replication. Interestingly, viral protein synthesis was not affected, but a loss of progeny virus production was observed. No modulation of CD4 CXCR4 and CCR5 receptor expression, cell proliferation, or activation after PGE₂ treatment was detected. Moreover, PGE₂ induced an increase in intracellular cAMP (cyclic AMP) levels through the EP2/EP4 receptors. PGE₂ effects were mimicked by dbcAMP and by a specific Epac (exchange protein directly activated by cyclic AMP) agonist, 8-Cpt-cAMP. Treatment with PGE₂ increased Rap1 activity, decreased RhoA activity and subsequently reduced the polymerization of actin by approximately 30% compared with untreated cells. In connection with this finding, polarized viral assembly platforms enriched in Gag were disrupted, altering HIV cell-to-cell transfer and the infectivity of new virions.

Conclusions

Our results demonstrate that PGE₂, through Epac and Rap activation, alters the transport of newly synthesized HIV-1 components to the assembly site, reducing the release and infectivity of new cell-free virions and cell-to-cell HIV-1 transfer.

Modulation of murine macrophage TLR7/8-mediated cytokine expression by mesenchymal stem cell-conditioned medium

Increasing evidence suggests that mesenchymal stem cells (MSCs) play anti-inflammatory roles during innate immune responses. However, little is known about the effect of MSCs or their secretions on the ligand response of Toll-like receptor (TLR) 7 and TLR8, receptors that recognize viral single-stranded RNA (ssRNA). Macrophages play a critical role in the innate immune response to ssRNA virus infection; therefore, we investigated the effect of MSC-conditioned medium on cytokine expression in macrophages following stimulation with TLR7/8 ligands. After stimulation with TLR7/8 ligand, bone marrow-derived macrophages cultured with MSCs or in MSC-conditioned medium expressed lower levels of tumor necrosis factor (TNF) α and interleukin (IL) 6 and higher levels of IL-10 compared to macrophages cultured without MSCs or in control medium, respectively. The modulations of cytokine expression were associated with prostaglandin E₂ (PGE₂) secreted by the MSCs. PGE₂ enhanced extracellular signal-related kinase (ERK) signaling and suppressed nuclear factor-κB (NF-κB) signaling. Enhanced ERK signaling contributed to enhanced IL-10 production, and suppression of NF-κB signaling contributed to the low production of TNF-α. Collectively, these results indicate that MSCs and MSC-conditioned medium modulate the cytokine expression profile in macrophages following TLR7/8-mediated stimulation, which suggests that MSCs play an immunomodulatory role during ssRNA virus infection.

Leukotrienes inhibit early stages of HIV-1 infection in monocyte-derived microglia-like cells

BACKGROUND

Microglia are one of the main cell types to be productively infected by HIV-1 in the central nervous system (CNS). Leukotriene B4 (LTB4) and cysteinyl-leukotrienes such as LTC4 are some of the proinflammatory molecules produced in infected individuals that contribute to neuroinflammation. We therefore sought to investigate the role of leukotrienes (LTs) in HIV-1 infection of microglial cells.

METHODS

To evaluate the role of LTs on HIV-1 infection in the CNS, monocyte-derived microglial-like cells (MDMis) were utilized in this study. Leukotriene-treated MDMis were infected with either fully replicative brain-derived HIV-1 isolates (YU2) or R5-tropic luciferase-encoding particles in order to assess viral production and expression. The efficacy of various steps of the replication cycle was evaluated by means of p24 quantification by ELISA, luciferase activity determination and quantitative real-time polymerase chain reaction (RT-PCR).

RESULTS

We report in this study that virus replication is reduced upon treatment of MDMis with LTB4 and LTC4. Additional experiments indicate that these proinflammatory molecules alter the pH-independent entry and early post-fusion events of the viral life cycle. Indeed, LT treatment induced a diminution in integrated proviral DNA while reverse-transcribed viral products remained unaffected. Furthermore, decreased C-C chemokine receptor type 5 (CCR5) surface expression was observed in LT-treated MDMis. Finally, the effect of LTs on HIV-1 infection in MDMis appears to be mediated partly via a signal transduction pathway involving protein kinase C.

CONCLUSIONS

These data show for the first time that LTs influence microglial cell infection by HIV-1, and may be a factor in the control of viral load in the CNS.

Interactions between prostaglandins, leukotrienes and HIV-1: possible implications for the central nervous system

In HIV-1-infected individuals, there is often discordance between viremia in peripheral blood and viral load found in the central nervous system (CNS). Although the viral burden is often lower in the CNS compartment than in the plasma, neuroinflammation is present in most infected individuals, albeit attenuated by the current combined antiretroviral therapy. The HIV-1-associated neurological complications are thought to result not only from direct viral replication, but also from the subsequent neuroinflammatory processes. The eicosanoids - prostanoids and leukotrienes - are known as potent inflammatory lipid mediators. They are often present in neuroinflammatory diseases, notably HIV-1 infection. Their exact modulatory role in HIV-1 infection is, however, still poorly understood, especially in the CNS compartment. Nonetheless, a handful of studies have provided evidence as to how these lipid mediators can modulate HIV-1 infection. This review summarizes findings indicating how eicosanoids may influence the progression of neuroAIDS.

cAMP during HIV infection: friend or foe?

Intracellular levels of cyclic adenosine 3',5'-monophosphate (cAMP) are important regulators of immune cells, partially determining the balance between activation and suppression. In this review, we discuss the mechanisms by which HIV infection increases cAMP levels in T cells, as well as the effect of cAMP on HIV-specific responses and its effect on HIV replication and infection. Results suggest that increased cAMP levels during HIV infection may have a dual and opposite roles. On the one hand, they could have a protective effect by limiting viral replication in infected cells and decreasing viral entry. On the other hand, they could have a detrimental role by reducing HIV-specific antiviral immune responses, thus reducing the clearance of the virus and contributing to T cell dysfunction. Future studies are thus needed to further define the beneficial versus detrimental roles of cAMP, as they could help establish new therapeutic targets to combat HIV replication and/or identify novel ways to boost antiviral immune responses.

Polymorphism in HIV-1 dependency factor PDE8A affects mRNA level and HIV-1 replication in primary macrophages

Four genome-wide RNAi screens have recently identified hundreds of HIV-1 dependency factors (HDFs). Previously, we reported a large variation in the ability of HIV-1 to replicate in monocyte-derived macrophages (MDM) derived from >400 healthy seronegative blood donors. Here we determined whether SNPs in genes encoding newly identified HDFs were associated with this variation in HIV-1 replication. We found a significant association between the minor allele of SNP rs2304418 in phosphodiesterase 8A (PDE8A) and lower HIV-1 replication (p=2.4×10(-6)). The minor allele of SNP rs2304418 was also significantly associated with lower PDE8A mRNA levels in MDM (p=8.3×10(-5)). In accordance with this, overexpression of PDE8A in HEK293T cells resulted in increased HIV-1 replication, while subsequent knock-down of PDE8A decreased replication. This study links host genetic variation in a newly identified HDF to variation in HIV-1 replication in a relevant primary target cell for HIV-1 and may provide new leads for treatment of this infection.

The therapeutic potential of adenosine triphosphate as an immune modulator in the treatment of HIV/AIDS: a combination approach with HAART

Extracellular adenosine triphosphate (eATP) is a potent molecule that has the capacity to modulate various aspects of cell functions including gene expression. This element of modulation is essential to the role of ATP as a therapeutic agent. The hypothesis presented is that ATP can have an important impact on the treatment of HIV infection. This is supported in part by published research, although a much greater role for ATP is suggested than prior authors ever thought possible. ATP has the ability to enhance the immune system and could thus improve the host's own defense mechanisms to eradicate the virus-infected cells and restore normal immune function. This could provide effective therapy when used in conjunction with highly active antiretroviral therapies (HAART) to eliminate the latently infected cells. The key lies in applying ATP through the methodology described. This article presents a strategy for using ATP therapeutically along with background evidence to substantiate the importance of using ATP in the treatment of HIV infection.

Genome-wide association study identifies single nucleotide polymorphism in DYRK1A associated with replication of HIV-1 in monocyte-derived macrophages

BACKGROUND

HIV-1 infected macrophages play an important role in rendering resting T cells permissive for infection, in spreading HIV-1 to T cells, and in the pathogenesis of AIDS dementia. During highly active anti-retroviral treatment (HAART), macrophages keep producing virus because tissue penetration of antiretrovirals is suboptimal and the efficacy of some is reduced. Thus, to cure HIV-1 infection with antiretrovirals we will also need to efficiently inhibit viral replication in macrophages. The majority of the current drugs block the action of viral enzymes, whereas there is an abundance of yet unidentified host factors that could be targeted. We here present results from a genome-wide association study identifying novel genetic polymorphisms that affect in vitro HIV-1 replication in macrophages.

METHODOLOGY/PRINCIPAL FINDINGS

Monocyte-derived macrophages from 393 blood donors were infected with HIV-1 and viral replication was determined using Gag p24 antigen levels. Genomic DNA from individuals with macrophages that had relatively low (n = 96) or high (n = 96) p24 production was used for SNP genotyping with the Illumina 610 Quad beadchip. A total of 494,656 SNPs that passed quality control were tested for association with HIV-1 replication in macrophages, using linear regression. We found a strong association between in vitro HIV-1 replication in monocyte-derived macrophages and SNP rs12483205 in DYRK1A (p = 2.16 × 10(-5)). While the association was not genome-wide significant (p<1 × 10(-7)), we could replicate this association using monocyte-derived macrophages from an independent group of 31 individuals (p = 0.0034). Combined analysis of the initial and replication cohort increased the strength of the association (p = 4.84 × 10(-6)). In addition, we found this SNP to be associated with HIV-1 disease progression in vivo in two independent cohort studies (p = 0.035 and p = 0.0048).

CONCLUSIONS/SIGNIFICANCE

These findings suggest that the kinase DYRK1A is involved in the replication of HIV-1, in vitro in macrophages as well as in vivo.

Nitric oxide and redox mechanisms in the immune response

The role of redox molecules, such as NO and ROS, as key mediators of immunity has recently garnered renewed interest and appreciation. To regulate immune responses, these species trigger the eradication of pathogens on the one hand and modulate immunosuppression during tissue-restoration and wound-healing processes on the other. In the acidic environment of the phagosome, a variety of RNS and ROS is produced, thereby providing a cauldron of redox chemistry, which is the first line in fighting infection. Interestingly, fluctuations in the levels of these same reactive intermediates orchestrate other phases of the immune response. NO activates specific signal transduction pathways in tumor cells, endothelial cells, and monocytes in a concentration-dependent manner. As ROS can react directly with NO-forming RNS, NO bioavailability and therefore, NO response(s) are changed. The NO/ROS balance is also important during Th1 to Th2 transition. In this review, we discuss the chemistry of NO and ROS in the context of antipathogen activity and immune regulation and also discuss similarities and differences between murine and human production of these intermediates.

Cyclooxygenase activity is important for efficient replication of mouse hepatitis virus at an early stage of infection

Cyclooxygenases (COXs) play a significant role in many different viral infections with respect to replication and pathogenesis. Here we investigated the role of COXs in the mouse hepatitis coronavirus (MHV) infection cycle. Blocking COX activity by different inhibitors or by RNA interference affected MHV infection in different cells. The COX inhibitors reduced MHV infection at a post-binding step, but early in the replication cycle. Both viral RNA and viral protein synthesis were affected with subsequent loss of progeny virus production. Thus, COX activity appears to be required for efficient MHV replication, providing a potential target for anti-coronaviral therapy.

Interaction of macrophages with apoptotic cells enhances HIV Type 1 replication through PGE2, PAF, and vitronectin receptor

Phagocytosis of apoptotic cells by macrophages increases secretion of soluble mediators and generates an antiinflammatory environment. We previously reported that phagocytosis of apoptotic cells by HIV-1-infected macrophages enhances viral replication, with the participation of the cytokine transforming growth factor- beta1 and an integrin receptor. Now, we describe the role of prostaglandin E2 (PGE2), platelet-activating factor (PAF), and the integrin alphaVbeta3 (vitronectin receptor, VnR) in this phenomenon. Exacerbation of HIV-1 growth induced by phagocytosis of apoptotic cells was inhibited when HIV-1-infected macrophages were treated with a cyclooxygenase 2 inhibitor, or with a PAF receptor antagonist (BN 52021) immediately after macrophage interaction with apoptotic cells. Treatment of HIV-1-infected macrophages with BN 52021 decreased viral replication, whereas addition of PGE2 or PAF to these cells enhanced viral replication. Monoclonal antibodies (MAbs) to VnR reduced the macrophage uptake of apoptotic cells, prevented the enhancement of HIV-1 growth upon the engulfment of apoptotic cells, and potently augmented viral replication in HIV-1-infected macrophages in the absence of apoptotic cells. In conclusion, PGE2 and PAF, and ligation of VnR as well, contribute to amplify viral growth in HIV-1-infected macrophages upon uptake of apoptotic cells.

Impaired complement-mediated phagocytosis by HIV type-1-infected human monocyte-derived macrophages involves a cAMP-dependent mechanism

HIV-1 infection of cells of macrophage lineage impairs a number of effector functions performed by these cells, including phagocytosis of opsonized pathogens. In this study we investigate the effects of HIV-1 on the mechanism of complement (C')-mediated phagocytosis by human monocyte-derived macrophages (MDM). Using C'-opsonized sheep red blood cells (sRBC) as targets, we demonstrate that phagocytosis is inhibited by HIV-1 infection in vitro. Inhibition is not due to downregulation of surface C' receptors (R) or altered binding of C'-opsonized targets to HIV-1-infected MDM, suggesting a postreceptor-mediated mechanism of suppression. Having shown that increased levels of intracellular cAMP in uninfected MDM inhibit phagocytosis, we demonstrate that HIV-1 infection of MDM is associated with increased intracellular cAMP. Using the adenylate cyclase inhibitors 2',5'-dideoxyadenosine and MDL-12,330A, we show that phagocytosis by HIV-1- infected MDM can be restored by inhibition of cAMP production. Defective phagocytosis by HIV-1-infected MDM did not correlate with prostaglandin secretion, and was less in uninfected MDM within the HIV-1-infected cell culture suggesting a minimal bystander effect. Inhibition required viral entry but not active viral replication, as shown by use of the antiretroviral drug lamivudine. Hence, our study suggests that HIV-1 impairs C'R-mediated phagocytosis in MDM by elevating intracellular cAMP levels, independent of prostaglandin secretion, and contributes to our understanding of how HIV-1 impairs cell-mediated immunity.

Hepatitis C virus stimulates the expression of cyclooxygenase-2 via oxidative stress: role of prostaglandin E2 in RNA replication

Hepatitis C virus (HCV) infection is a major cause of chronic liver disease, which can lead to the development of liver cirrhosis and hepatocellular carcinoma. Recently, the activation of cyclooxygenase-2 (Cox-2) has been implicated in the HCV-associated hepatocellular carcinoma. In this study, we focus on the signaling pathway leading to Cox-2 activation induced by HCV gene expression. Here, we demonstrate that the HCV-induced reactive oxygen species and subsequent activation of NF-kappaB mediate the activation of Cox-2. The HCV-induced Cox-2 was sensitive to antioxidant (pyrrolidine dithiocarbamate), Ca(2+) chelator (BAPTA-AM), and calpain inhibitor (N-acetyl-Leu-Leu-Met-H). The levels of prostaglandin E(2) (PGE(2)), the product of Cox-2 activity, are increased in HCV-expressing cells. Furthermore, HCV-expressing cells treated with the inhibitors of Cox-2 (celecoxib and NS-398) showed significant reduction in PGE(2) levels. We also observed the enhanced phosphorylation of Akt and its downstream substrates glycogen synthase kinase-3beta and proapoptotic Bad in the HCV replicon-expressing cells. These phosphorylation events were sensitive to inhibitors of Cox-2 (celecoxib and NS-398) and phosphatidylinositol 3-kinase (LY294002). Our results also suggest a potential role of Cox-2 and PGE(2) in HCV RNA replication. These studies provide insight into the mechanisms by which HCV induces intracellular events relevant to liver pathogenesis associated with viral infection.

Macrophage inflammatory protein 1alpha inhibits postentry steps of human immunodeficiency virus type 1 infection via suppression of intracellular cyclic AMP

Primary isolates of human immunodeficiency virus type 1 (HIV-1) predominantly use chemokine receptor CCR5 to enter target cells. The natural ligands of CCR5, the beta-chemokines macrophage inflammatory protein 1alpha (MIP-1alpha), MIP-1beta, and RANTES, interfere with HIV-1 binding to CCR5 receptors and decrease the amount of virions entering cells. Although the inhibition of HIV-1 entry by beta-chemokines is well documented, their effects on postentry steps of the viral life cycle and on host cell components that control the outcome of infection after viral entry are not well defined. Here, we show that all three beta-chemokines, and MIP-1alpha in particular, inhibit postentry steps of the HIV-1 life cycle in primary lymphocytes, presumably via suppression of intracellular levels of cyclic AMP (cAMP). Productive HIV-1 infection of primary lymphocytes requires cellular activation. Cell activation increases intracellular cAMP, which is required for efficient synthesis of proviral DNA during early steps of viral infection. Binding of MIP-1alpha to cognate receptors decreases activation-induced intracellular cAMP levels through the activation of inhibitory G proteins. Furthermore, inhibition of one of the downstream targets of cAMP, cAMP-dependent PKA, significantly inhibits synthesis of HIV-1-specific DNA without affecting virus entry. These data reveal that beta-chemokine-mediated inhibition of virus replication in primary lymphocytes combines inhibitory effects at the entry and postentry levels and imply the involvement of beta-chemokine-induced signaling in postentry inhibition of HIV-1 infection.

Inhibition of cyclooxygenase activity reduces rotavirus infection at a postbinding step

Elevated levels of prostaglandins (PGs), products of cyclooxygenases (COXs), are found in the plasma and stool of rotavirus-infected children. We sought to determine the role of COXs, PGs, and the signal transduction pathways involved in rotavirus infection to elucidate possible new targets for antiviral therapy. Human intestinal Caco-2 cells were infected with human rotavirus Wa or simian rotavirus SA-11. COX-2 mRNA expression and secreted PGE2 levels were determined at different time points postinfection, and the effect of COX inhibitors on rotavirus infection was studied by an immunofluorescence assay (IFA). To reveal the signal transduction pathways involved, the effect of MEK, protein kinase A (PKA), p38 mitogen-activated protein kinase (MAPK), and NF-kappaB inhibitors on rotavirus infection was analyzed. In infected Caco-2 cells, increased COX-2 mRNA expression and secreted PGE2 levels were detected. Indomethacin (inhibiting both COX-1 and COX-2) and specific COX-1 and COX-2 inhibitors reduced rotavirus infection by 85 and 50%, respectively, as measured by an IFA. Indomethacin reduced virus infection at a postbinding step early in the infection cycle, inhibiting virus protein synthesis. Indomethacin did not seem to affect viral RNA synthesis. Inhibitors of MEK, PKA, p38 MAPK, and NF-kappaB decreased rotavirus infection by at least 40%. PGE2 counteracted the effect of the COX and PKA inhibitors but not of the MEK, p38 MAPK, and NF-kappaB inhibitors. Conclusively, COXs and PGE2 are important mediators of rotavirus infection at a postbinding step. The ERK1/2 pathway mediated by PKA is involved in COX induction by rotavirus infection. MAPK and NF-kappaB pathways are involved in rotavirus infection but in a PGE2-independent manner. This report offers new perspectives in the search for therapeutic agents in treatment of severe rotavirus-mediated diarrhea in children.

The role and regulation of COX-2 during viral infection

Prostaglandins are lipid mediators, generated by cyclooxygenase (COX), that have been shown to participate in the regulation of virus replication and the modulation of inflammatory responses following infection. A number of studies support a role for PGE2 in the modulation of virus replication and virulence in a cell type and virus selective manner. Virus infection also stimulates the expression of a number of proinflammatory gene products, including COX-2, inducible nitric oxide synthase (iNOS) as well as proinflammatory cytokines. This review will focus on the mechanisms by which proinflammatory prostaglandin production regulates virus replication and virulence. In addition, the signaling pathways that are activated during a virus infection, and that regulate proinflammatory gene expression in macrophages will be reviewed. Specific attention will be placed on the ability of virus infection to activate multiple signaling cascades (such as PKR, MAPK, iPLA2, NF-kappaB) and how these pathways are integrated in the regulation of individual target gene expression.