Lipopolysaccharide-induced HIV-1 expression in transgenic mice is mediated by tumor necrosis factor-alpha and interleukin-1, but not by interferon-gamma nor interleukin-6

Identification of Modulators of HIV-1 Proviral Transcription from a Library of FDA-Approved Pharmaceuticals

Human immunodeficiency virus 1 (HIV-1) is the most prevalent human retrovirus. Recent data show that 34 million people are living with HIV-1 worldwide. HIV-1 infections can lead to AIDS which still causes nearly 20,000 deaths annually in the USA alone. As this retrovirus leads to high morbidity and mortality conditions, more effective therapeutic regimens must be developed to treat these viral infections. A key target for intervention for which there are no current FDA-approved modulators is at the point of proviral transcription. One successful method for identifying novel therapeutics for treating infectious diseases is the repurposing of pharmaceuticals that are approved by the FDA for alternate indications. Major benefits of using FDA-approved drugs include the fact that the compounds have well established toxicity profiles, approved manufacturing processes, and immediate commercial availability to the patients. Here, we demonstrate that pharmaceuticals previously approved for other indications can be utilized to either activate or inhibit HIV-1 proviral transcription. Specifically, we found febuxostat, eltrombopag, and resveratrol to be activators of HIV-1 transcription, while mycophenolate was our lead inhibitor of HIV-1 transcription. Additionally, we observed that the infected cells of lymphoid and myeloid lineage responded differently to our lead transcriptional modulators. Finally, we demonstrated that the use of a multi-dose regimen allowed for enhanced activation with our transcriptional activators.

Clash of the Cytokine Titans: counter-regulation of interleukin-1 and type I interferon-mediated inflammatory responses

Over the past decades the notion of 'inflammation' has been extended beyond the original hallmarks of rubor (redness), calor (heat), tumor (swelling) and dolor (pain) described by Celsus. We have gained a more detailed understanding of the cellular players and molecular mediators of inflammation which is now being applied and extended to areas of biomedical research such as cancer, obesity, heart disease, metabolism, auto-inflammatory disorders, autoimmunity and infectious diseases. Innate cytokines are often central components of inflammatory responses. Here, we discuss how the type I interferon and interleukin-1 cytokine pathways represent distinct and specialized categories of inflammatory responses and how these key mediators of inflammation counter-regulate each other.

Lipopolysaccharide induces immune activation and SIV replication in rhesus macaques of Chinese origin

Background

Chronic immune activation is a hallmark of progressive HIV infection and a key determinant of immunodeficiency in HIV-infected individuals. Bacterial lipopolysaccharide (LPS) in the circulation has been implicated as a key factor in HIV infection-related systemic immune activation. We thus investigate the impact of LPS on systemic immune activation in simian immunodeficiency virus (SIV)-infected rhesus macaques of Chinese origin.

Methods

The animals were inoculated intravenously with SIVmac239. The levels of plasma viral load and host inflammatory cytokines in PBMC were measured by real-time RT-PCR. CD4/CD8 ratio and systemic immune activation markers were examined by flow cytometric analysis of PBMCs. White blood cell and neutrophil counts and C Reactive Protein levels were determined using biochemistry analyzer. The plasma levels of LPS were determined by Tachypleus Amebocyte Lysate (TAL) test.

Results

The animals inoculated with SIVmac239 became infected as evidenced by the increased plasma levels of SIV RNA and decreased CD4/CD8 ratio. LPS administration of SIV-infected animals induced a transient increase of plasma SIV RNA and immune activation, which was indicated by the elevated expression of the inflammatory cytokines and CD4+HLA-DR+ T cells in PBMCs.

Conclusions

These data support the concept that LPS is a driving factor in systemic immune activation of HIV disease.

Binding of HIV-1 gp120 to DC-SIGN promotes ASK-1-dependent activation-induced apoptosis of human dendritic cells

During disease progression to AIDS, HIV-1 infected individuals become increasingly immunosuppressed and susceptible to opportunistic infections. It has also been demonstrated that multiple subsets of dendritic cells (DC), including DC-SIGN(+) cells, become significantly depleted in the blood and lymphoid tissues of AIDS patients, which may contribute to the failure in initiating effective host immune responses. The mechanism for DC depletion, however, is unclear. It is also known that vast quantities of viral envelope protein gp120 are shed from maturing HIV-1 virions and form circulating immune complexes in the serum of HIV-1-infected individuals, but the pathological role of gp120 in HIV-1 pathogenesis remains elusive. Here we describe a previously unrecognized mechanism of DC death in chronic HIV-1 infection, in which ligation of DC-SIGN by gp120 sensitizes DC to undergo accelerated apoptosis in response to a variety of activation stimuli. The cultured monocyte-derived DC and also freshly-isolated DC-SIGN(+) blood DC that were exposed to either cross-linked recombinant gp120 or immune-complex gp120 in HIV(+) serum underwent considerable apoptosis after CD40 ligation or exposure to bacterial lipopolysaccharide (LPS) or pro-inflammatory cytokines such as TNFα and IL-1β. Furthermore, circulating DC-SIGN(+) DC that were isolated directly from HIV-1(+) individuals had actually been pre-sensitized by serum gp120 for activation-induced exorbitant apoptosis. In all cases the DC apoptosis was substantially inhibited by DC-SIGN blockade. Finally, we showed that accelerated DC apoptosis was a direct consequence of excessive activation of the pro-apoptotic molecule ASK-1 and transfection of siRNA against ASK-1 significantly prevented the activation-induced excessive DC death. Our study discloses a previously unknown mechanism of immune modulation by envelope protein gp120, provides new insights into HIV immunopathogenesis, and suggests potential therapeutic approaches to prevent DC depletion in chronic HIV infection.

HIV-1 infected individuals become increasingly immunocompromised and susceptible to opportunistic infection during disease progression, which is associated with significant reduction of the dendritic cell number in the peripheral blood or secondary lymphoid tissues. Because dendritic cells are the most powerful antigen-presenting cells, their survival is critical for host defence and inadequate dendritic cell number will fail to induce effective host immune responses. Here we describe a mechanism that may at least partly explain why dendritic cells become significantly depleted in chronic HIV-1 infection. We found that after binding of the HIV-1 envelope protein gp120 to the dendritic cell surface protein DC-SIGN, the subsequent activation by CD40 ligation, or by exposure to bacterial product lipopolysaccharide or pro-inflammatory cytokines such as TNF-α and IL-1β, will lead to overexpression of pro-apoptotic molecule ASK-1, resulting in excessive dendritic cell death. We also confirmed that DC-SIGN(+) dendritic cells in the blood of HIV-1 infected individuals have actually been pre-sensitized by viral gp120, which exists in vast amount in the blood, for activation-induced exorbitant death. Our study thus reveals a previously unknown pathway for dendritic cell depletion and provides clues for potential therapeutic approaches to prevent DC depletion in chronic HIV infection.

Renal HIV expression is unaffected by serum LPS levels in an HIV transgenic mouse model of LPS induced kidney injury

Acute kidney injury (AKI) is associated with increased rates of mortality. For unknown reasons, HIV infected individuals have a higher risk of AKI than uninfected persons. We tested our hypothesis that increased circulating LPS increases renal expression of HIV and that HIV transgenic (Tg26) mice have increased susceptibility to AKI. Tg26 mice harbor an HIV transgene encoding all HIV genes except gag and pol, and develop a phenotype analogous to HIVAN. Mice were used at 4-6 weeks of age before the onset of gross renal disease. Mice were injected i.p. with LPS or sterile saline. Renal function, tubular injury, cytokine expression, and HIV transcription were evaluated in Tg26 and wild type (WT) mice. LPS injection induced a median 60.1-fold increase in HIV expression in spleen but no change in kidney. There was no significant difference in renal function, cytokine expression, or tubular injury scores at baseline or 24 hours after LPS injection. HIV transcription was also analyzed in vitro using a human renal tubular epithelial cell (RTEC) line. HIV transcription increased minimally in human RTEC, by 1.47 fold, 48 hours after LPS exposure. We conclude that Tg26 mice do not increase HIV expression or have increased susceptibility to LPS induced AKI. The increased risk of AKI in HIV infected patients is not mediated via increased renal expression of HIV in the setting of sepsis. Moreover, renal regulation of HIV transcription is different to that in the spleen.

The mechanism of LPS-induced HIV type I activation in transgenic mouse macrophages

In the course of the development of acquired immunodeficiency syndrome (AIDS), bacterial infection causes deleterious effects on the progression of the disease; bacterial LPS in the circulation activate immune cells, resulting in the acceleration of HIV replication. However, the precise HIV activation mechanisms in infected hosts remain largely unknown. Previously, we generated transgenic (Tg) mice carrying the HIV type I (HIV-1) genome and showed that LPS induces the activation of HIV-1 in splenocytes through the induction of tumor necrosis factor (TNF) and IL-1, although similarly induced IFN-gamma and IL-6 are not involved. In this study, we analyzed the mechanisms of HIV-1 activation in macrophages using these HIV-1 Tg mice, because macrophages are one of the major reservoirs of HIV-1. In contrast to splenocytes, direct Toll-like receptor (TLR) 4 signaling rather than TLR-induced pro-inflammatory cytokines was responsible for the LPS-induced activation of HIV-1 in macrophages, because the time course of HIV-1 activation was earlier than that observed in splenocytes and TNF neutralization did not inhibit the activation. p38 mitogen-activated protein kinase (MAPK) and nuclear factor kappa B (NF-kappaB) activation, but neither extracellular signal-regulated kinase nor c-Jun N-terminal kinase activation, were required for the activation, because only inhibitors for p38 MAPK and NF-kappaB suppressed activation of HIV-1. Furthermore, we showed that myeloid differentiation primary response gene (MyD) 88, rather than Toll/IL-1R domain-containing adaptor inducing IFN-beta (TRIF), was required as an adaptor molecule for this activation using Myd88(-/-) mice and Dynasore, a specific inhibitor for TRIF, and small interfering RNAs specific for Myd88 and Trif. These observations suggest that suppression of these molecules, which are involved in the TLR4-MyD88 pathway and the downstream p38 MAPK and NF-kappaB pathways, should be beneficial to prevent development of AIDS in HIV-1-infected people.

Reduction of ventricular sodium current in a mouse model of HIV

INTRODUCTION

Cardiac arrhythmias have been reported in AIDS patients. Arrhythmias can arise from alterations in ventricular Na(+) channel function. However, it is unknown whether HIV affects cardiac Na(+) channel function. Therefore, the purpose of this study was to characterize the effect of HIV on ventricular Na(+) current (I(Na)) in a transgenic model of HIV (CD4C/HIV mice), which exhibit a severe AIDS-like disease.

METHODS AND RESULTS

Patch-clamp techniques were used to examine I(Na) and action potentials (AP) in ventricular myocytes isolated from HIV and wild-type (WT) mice. In HIV myocytes peak I(Na) was reduced (at -50 mV: HIV, -55.3 +/- 4.3 pA/pF, n = 15; WT, -79.4 +/- 5.2 pA/pF, n = 16, P < 0.05), whereas late I(Na) was similar in both groups (HIV, -4.3 +/- 0.4 pA/pF; WT, -4.4 +/- 0.4 pA/pF, n = 22/group). AP amplitude (HIV 91.5 +/- 4.7 mV, n = 12; WT 104.4 +/- 3.1 mV, n = 15, P < 0.05) and the maximal velocity of the AP upstroke (V(max); HIV, 57.2 +/- 9.3 mV/ms, n = 12; WT, 113.5 +/- 8 mV/ms, n = 15, P < 0.05) were decreased in HIV myocytes. ECG recordings revealed that the QRS complex was prolonged in HIV mice (HIV, 15.7 +/- 0.2 ms, n = 22; WT, 14.1 +/- 0.5 ms, n = 10, P < 0.05). The serum levels of interleukin-1beta were elevated in HIV mice (HIV, 18.1 +/- 3.1 pg/mL, n = 3; WT, 5.1 +/- 1.1 pg/mL, n = 4, P < 0.05) in line with previous evidence that suggests that elevated levels of cytokines can affect cardiac ion currents.

CONCLUSION

Overall, our observations suggest that elevated levels of proinflammatory cytokines in CD4C/HIV mice could alter Na(+) channel function, thus altering cardiac depolarization and contribute to the generation of arrhythmias.

Nuclear import of the preintegration complex is blocked upon infection by human immunodeficiency virus type 1 in mouse cells

Mouse cells do not support human immunodeficiency virus type 1 (HIV-1) replication because of host range barriers at steps including virus entry, transcription, RNA splicing, polyprotein processing, assembly, and release. The exact mechanisms for the suppression, however, are not completely understood. To elucidate further the barriers against HIV-1 replication in mouse cells, we analyzed the replication of the virus in lymphocytes from human CD4/CXCR4 transgenic mice. Although primary splenocytes and thymocytes allowed the entry and reverse transcription of HIV-1, the integration efficiency of the viral DNA was greatly reduced in these cells relative to human peripheral blood mononuclear cells, suggesting an additional block(s) before or at the point of host chromosome integration of the viral DNA. Preintegration processes were further analyzed using HIV-1 pseudotyped viruses. The reverse transcription step of HIV-1 pseudotyped with the envelope of murine leukemia virus or vesicular stomatitis virus glycoprotein was efficiently supported in both human and mouse cells, but nuclear import of the preintegration complex (PIC) of HIV-1 was blocked in mouse cells. We found that green fluorescent protein (GFP)-labeled HIV-1 integrase, which is known to be important in the nuclear localization of the PIC, could not be imported into the nucleus of mouse cells, in contrast to human cells. On the other hand, GFP-Vpr localized exclusively to the nuclei of both mouse and human cells. These observations suggest that, due to the dysfunction of integrase, the nuclear localization of PIC is suppressed in mouse cells.

Distinct contribution of IL-6, TNF-alpha, IL-1, and IL-10 to T cell-mediated spontaneous autoimmune arthritis in mice

Cytokines play key roles in spontaneous CD4(+) T cell-mediated chronic autoimmune arthritis in SKG mice, a new model of rheumatoid arthritis. Genetic deficiency in IL-6 completely suppressed the development of arthritis in SKG mice, irrespective of the persistence of circulating rheumatoid factor. Either IL-1 or TNF-alpha deficiency retarded the onset of arthritis and substantially reduced its incidence and severity. IL-10 deficiency, on the other hand, exacerbated disease, whereas IL-4 or IFN-gamma deficiency did not alter the disease course. Synovial fluid of arthritic SKG mice contained high amounts of IL-6, TNF-alpha, and IL-1, in accord with active transcription of these cytokine genes in the afflicted joints. Notably, immunohistochemistry revealed that distinct subsets of synovial cells produced different cytokines in the inflamed synovium: the superficial synovial lining cells mainly produced IL-1 and TNF-alpha, whereas scattered subsynovial cells produced IL-6. Thus, IL-6, IL-1, TNF-alpha, and IL-10 play distinct roles in the development of SKG arthritis; arthritogenic CD4(+) T cells are not required to skew to either Th1 or Th2; and the appearance of rheumatoid factor is independent of joint inflammation. The results also indicate that targeting not only each cytokine but also each cell population secreting distinct cytokines could be an effective treatment of rheumatoid arthritis.

Influence of Coinfecting Pathogens on HIV Expression: Evidence for a Role of Toll-Like Receptors

Immune activation of HIV gene expression as a consequence of the host response to coinfecting pathogens has been implicated as an important factor in AIDS progression. Immune responsiveness to many of the infectious agents associated with HIV has been demonstrated to depend on a family of innate recognition molecules, known as Toll-like receptors (TLR). Therefore, TLR-pathogen interactions could play an indirect role in regulating HIV-associated disease. In this review, we summarize emerging evidence for the influence of TLR recognition on HIV gene activation and AIDS progression.

Latent HIV-1 reactivation in transgenic mice requires cell cycle -dependent demethylation of CREB/ATF sites in the LTR

OBJECTIVE

We previously produced a line of transgenic mice that carried the HIV-1 genome deficient in the gene. Although the HIV-1 genome in the lymphocytes was dormant under normal physiological conditions, it could be reactivated by lipopolysaccharide (LPS) administration via induction of interleukin-1alpha/beta and tumour necrosis factor-alpha. In this report, we analysed further the reactivation mechanism of the latent HIV-1 using this transgenic mouse model.

DESIGN

and methods: Possible involvement of CpG methylation in HIV-1 latency was examined by treating transgenic lymphocytes with a demethylating agent, 5'-azacytidine. CpG methylation in the HIV-1 long terminal repeat (LTR) was analysed using the bisulfite genomic sequencing method. As previous studies suggested that CpG demethylation depended on the cell cycle progression, we analysed the relation between cell cycle progression and LPS-induced reactivation of HIV-1 by labelling lymphocytes with an intracellular fluorescein, carboxyfluorescein diacetate succinimidyl ester.

RESULTS

We found that 5'-azacytidine enhanced HIV-1 expression ninefold compared to treatment with LPS alone. Furthermore, HIV-1 p24 induction by LPS was observed only in cells that had undergone cell division, while induction was prevented in cells in which cell cycle progression was blocked either by mimosine, aphidicolin, or nocodazole. LPS-induced HIV-1 reactivation was associated with demethylation of two CpG sites located in the CREB/ATF binding sites in the HIV-1 LTR in a cell cycle-dependent manner.

CONCLUSIONS

These observations indicate that cell cycle progression-dependent demethylation of the CREB/ATF sites in the LTR is crucial for the reactivation of latent HIV-1 genome in transgenic mice.

Feedback between glial tumor necrosis factor-alpha and gp120 from HIV-infected cells helps maintain infection and destroy neurons

An envelope glycoprotein, gp20, of the human immunodeficiency virus (HIV) interacts with host systems to promote HIV replication. gp120 is also involved in tissue-destructive positive feedback cycles that contribute to HIV-related but non-lymphocytic-, non-immunodeficiency-related tissue-destructive morbidity. Exposure to gp120 results in tumor necrosis factor-alpha (TNF) upregulation, particularly in cells of monocyte lineage. The resultant increased TNF in the microenvironment of the TNF-producing monocyte lineage cells results in increased occupancy of TNF receptors on nearby lymphocytes, monocytes or glia in which HIV does replicate. Such TNF binding increases HIV replication. Increased replication results in increased gp120 available to bind to monocyte lineage cells, further increasing or maintaining those cells' TNF production in the face of other TNF suppressive forces. A trophic environment (TNF) for HIV replication is thereby maintained. gp120 raises cAMP levels. Increased cAMP is inherently TNF-suppressive. This is a moderating negative feedback element embedded within the larger positive feedback cycle. HIV does not effectively replicate in neurons yet many HIV infections show significant neuron loss. gp120 stimulates glia to synthesize TNF. Increased TNF stimulates HIV to replicate in the cells present in which HIV is able to replicate. TNF also damages nearby neurons. The resultant increased gp120 would further stimulate glia, and the stimulated glia's TNF would damage local neurons. Damaged neurons make factors that activate glia to upregulate TNF synthesis. These feedback cycles centering on gp120 and TNF contribute to HIV pathophysiology, neuron loss and maintenance of infection.