Peroxisome proliferator-activated receptor gamma agonists inhibit HIV-1 replication in macrophages by transcriptional and post-transcriptional effects

U1 and OM10.1. Myeloid Cell Lines as Surrogate Models of Reversible Proviral Latency

As already discussed for T cell lines, also myeloid cell lines as served as the earliest models of chronic HIV infection. They were particularly relevant in the late 1980s and early 1990s when most experimental in vitro infections were based on laboratory-adapted "T-cell tropic" strains of HIV-1, such as LAI/IIIB or others, that later were found to rely upon CXCR4 as coreceptor for viral entry in addition to CD4 as primary receptor. Although primary macrophages do express CXCR4 together with CD4, virus replication is much less efficient than that observed with CCR5-using "macrophage-tropic" strains, as discussed separately in this book. Although different myeloid cell lines have been used to generate models of chronic HIV-1 infection that could be used to investigate features of proviral reactivation, as reviewed in (Cassol et al. J Leukoc Biol 80:1018-1030, 2006), two cell lines in particular have been broadly used and will be here discussed: the U937-derived U1 and HL-60-derived OM-10.1.

Pharmacological Inhibition of PPARy Boosts HIV Reactivation and Th17 Effector Functions, While Preventing Progeny Virion Release and de novo Infection

The frequency and functions of Th17-polarized CCR6⁺RORyt⁺CD4⁺ T cells are rapidly compromised upon HIV infection and are not restored with long-term viral suppressive antiretroviral therapy (ART). In line with this, Th17 cells represent selective HIV-1 infection targets mainly at mucosal sites, with long-lived Th17 subsets carrying replication-competent HIV-DNA during ART. Therefore, novel Th17-specific therapeutic interventions are needed as a supplement of ART to reach the goal of HIV remission/cure. Th17 cells express high levels of peroxisome proliferator-activated receptor gamma (PPARy), which acts as a transcriptional repressor of the HIV provirus and the rorc gene, which encodes for the Th17-specific master regulator RORyt. Thus, we hypothesized that the pharmacological inhibition of PPARy will facilitate HIV reservoir reactivation while enhancing Th17 effector functions. Consistent with this prediction, the PPARy antagonist T0070907 significantly increased HIV transcription (cell-associated HIV-RNA) and RORyt-mediated Th17 effector functions (IL-17A). Unexpectedly, the PPARy antagonism limited HIV outgrowth from cells of ART-treated people living with HIV (PLWH), as well as HIV replication in vitro. Mechanistically, PPARy inhibition in CCR6⁺CD4⁺ T cells induced the upregulation of transcripts linked to Th17-polarisation (RORyt, STAT3, BCL6 IL-17A/F, IL-21) and HIV transcription (NCOA1-3, CDK9, HTATIP2). Interestingly, several transcripts involved in HIV-restriction were upregulated (Caveolin-1, TRIM22, TRIM5α, BST2, miR-29), whereas HIV permissiveness transcripts were downregulated (CCR5, furin), consistent with the decrease in HIV outgrowth/replication. Finally, PPARy inhibition increased intracellular HIV-p24 expression and prevented BST-2 downregulation on infected T cells, suggesting that progeny virion release is restricted by BST-2-dependent mechanisms. These results provide a strong rationale for considering PPARy antagonism as a novel strategy for HIV-reservoir purging and restoring Th17-mediated mucosal immunity in ART-treated PLWH.

Apolipoprotein E is an HIV-1-inducible inhibitor of viral production and infectivity in macrophages

Apolipoprotein E (ApoE) belongs to a class of cellular proteins involved in lipid metabolism. ApoE is a polymorphic protein produced primarily in macrophages and astrocytes. Different isoforms of ApoE have been associated with susceptibility to various diseases including Alzheimer's and cardiovascular diseases. ApoE expression has also been found to affect susceptibility to several viral diseases, including Hepatitis C and E, but its effect on the life cycle of HIV-1 remains obscure. In this study, we initially found that HIV-1 infection selectively up-regulated ApoE in human monocyte-derived macrophages (MDMs). Interestingly, ApoE knockdown in MDMs enhanced the production and infectivity of HIV-1, and was associated with increased localization of viral envelope (Env) proteins to the cell surface. Consistent with this, ApoE over-expression in 293T cells suppressed Env expression and viral infectivity, which was also observed with HIV-2 Env, but not with VSV-G Env. Mechanistic studies revealed that the C-terminal region of ApoE was required for its inhibitory effect on HIV-1 Env expression. Moreover, we found that ApoE and Env co-localized in the cells, and ApoE associated with gp160, the precursor form of Env, and that the suppression of Env expression by ApoE was cancelled by the treatment with lysosomal inhibitors. Overall, our study revealed that ApoE is an HIV-1-inducible inhibitor of viral production and infectivity in macrophages that exerts its anti-HIV-1 activity through association with gp160 Env via the C-terminal region, which results in subsequent degradation of gp160 Env in the lysosomes.

The effects of PPARγ on the regulation of the TOMM40-APOE-C1 genes cluster

Chromosome 19q13.32 is a gene rich region, and has been implicated in multiple human phenotypes in adulthood including lipids traits, Alzheimer's disease, and longevity. Peroxisome Proliferator Activated Receptor Gamma (PPARγ) is a ligand-activated nuclear transcription factor that plays a role in human complex traits that are also genetically associated with the chromosome 19q13.32 region. Here, we study the effects of PPARγ on the regional expression regulation of the genes clustered within chromosome 19q13.32, specifically TOMM40, APOE, and APOC1, applying two complementary approaches. Using the short hairpin RNA (shRNA) method in the HepG2 cell-line we knocked down PPARγ expression and measured the effect on mRNA expression. We discovered PPARγ knock down increased the levels of TOMM40-, APOE-, and APOC1-mRNAs, with the highest increase in expression observed for APOE-mRNA. To complement the PPARγ knockdown findings we also examined the effects of low doses of PPARγ agonists (nM range) on mRNA expression of these genes. Low (nM) concentrations of pioglitazone (Pio) decreased transcription of TOMM40, APOE, and APOC1 genes, with the lowest mRNA levels for each gene observed at 1.5nM. Similar to the effect of PPARγ knockdown, the strongest response to pioglitazone was also observed for APOE-mRNA, and rosiglitazone (Rosi), another PPARγ agonist, produced results that were consistent with these. In conclusion, our results further established a role for PPARγ in regional transcriptional regulation of chr19q13.32, underpinning the association between PPARγ, the chr19q13.32 genes cluster, and human complex traits and disease.

Rosiglitazone suppresses HIV-1 Tat-induced vascular inflammation via Akt signaling

Peroxisome proliferator-activated receptor gamma (PPARƔ) contributes to human immunodeficiency virus (HIV)-1-induced dysfunction of brain endothelial cells. The aim of the present study was to evaluate the protection mechanism of PPARƔ against Tat-induced responses of adhesion molecules. We measured the protein expressions of intercellular adhesion molecule (ICAM)-1 and vascular cell adhesion molecule (VCAM)-1 in human brain microvascular endothelial cells (hCMEC/D3) and C57BL/6J mouse brain microvessels with Western blotting and immunofluorescent labeling. The mRNA levels of ICAM-1 and VCAM-1 were determined by real-time reverse-transcriptase polymerase chain reaction. HIV-1 Tat induced overexpression of ICAM-1 but not VCAM-1 in both hCMEC/D3 and brain microvessels, this response was attenuated by treatment with the PPARƔ agonist rosiglitazone. Tat-mediated upregulation of ICAM-1 and VCAM-1 levels were abolished by the addition of PPARƔ antagonist GW9662 and the Akt inhibitor KP3721, indicating that Akt signaling is involved in the PPARƔ-mediated protection of Tat-induced adhesion molecule upregulation. These results show that Akt signaling plays a key role in PPARƔ's vascular inflammatory effects that contribute to blood-brain barrier damage.

A new role for PGA1 in inhibiting hepatitis C virus-IRES-mediated translation by targeting viral translation factors

Previous studies have demonstrated that cyclopentenone prostaglandins (cyPGs) inhibit the replication of a wide variety of DNA and RNA viruses in different mammalian cell types. We investigated a new role for prostaglandin A1 (PGA1) in the inhibition of hepatitis C virus (HCV)-IRES-mediated translation. PGA1 exhibited dose-dependent inhibitory effects on HCV translation in HCV replicon cells. Furthermore, repetitive PGA1 treatment demonstrated the potential to safely induce the suppression of HCV translation. We also validated a new role for PGA1 in the inhibition of HCV-IRES-mediated translation by targeting cellular translation factors, including the small ribosomal subunit (40S) and eukaryotic initiation factors (eIFs). In pull-down assays, biotinylated PGA1 co-precipitated with the entire HCV IRES RNA/eIF3-40S subunit complex. Moreover, the interactions between PGA1 and the elongation factors and ribosomal subunit were dependent upon HCV IRES RNA binding, and the PGA1/HCV IRES RNA/eIF3-40S subunit complex inhibited HCV-IRES-mediated translation. The novel mechanism revealed in this study may aid in the search for more effective anti-HCV drugs.

Multiple APOBEC3 restriction factors for HIV-1 and one Vif to rule them all

Several members of the APOBEC3 family of cellular restriction factors provide intrinsic immunity to the host against viral infection. Specifically, APOBEC3DE, APOBEC3F, APOBEC3G, and APOBEC3H haplotypes II, V, and VII provide protection against HIV-1Δvif through hypermutation of the viral genome, inhibition of reverse transcription, and inhibition of viral DNA integration into the host genome. HIV-1 counteracts APOBEC3 proteins by encoding the viral protein Vif, which contains distinct domains that specifically interact with these APOBEC3 proteins to ensure their proteasomal degradation, allowing virus replication to proceed. Here, we review our current understanding of APOBEC3 structure, editing and non-editing mechanisms of APOBEC3-mediated restriction, Vif-APOBEC3 interactions that trigger APOBEC3 degradation, and the contribution of APOBEC3 proteins to restriction and control of HIV-1 replication in infected patients.

Induction of heat-shock protein 70 by prostaglandin A₁ inhibits HIV-1 Vif-mediated degradation of APOBEC3G

Previous studies have demonstrated that cyclopentenone prostaglandins (cyPGs) inhibit human immunodeficiency virus type 1 (HIV-1) replication in various cell types. This antiviral activity has been associated with the induction of heat-shock protein 70 (HSP70) in infected cells. We investigated a new role of prostaglandin A₁ (PGA₁) in the replication of HIV-1 in non-permissive cells. Because overexpression of HSP70 blocks the viral infectivity factor (Vif)-mediated degradation of APOBEC3G (A3G) via the ubiquitin-proteasome pathway, we examined the effects of PGA₁ on A3G and HIV-1 replication. The induction of HSP70 synthesis by PGA₁ blocked Vif-mediated A3G degradation and enhanced the incorporation of A3G into both wild-type and Vif-deficient viruses. Furthermore, we determined the viral titer of HIV-1 particles produced from PGA₁-treated 293T cells. The induction of HSP70 synthesis by PGA₁ significantly reduced the viral titer in the presence of A3G. Additionally, the p24 Gag antigen levels were dramatically reduced in non-permissive cells treated once or repeatedly with PGA₁. Thus, we showed that PGA₁ inhibits HIV-1 replication, at least in part, by blocking Vif-mediated A3G degradation.

PPARγ and NF-κB regulate the gene promoter activity of their shared repressor, TNIP1

Human TNFAIP3 interacting protein 1 (TNIP1) has diverse functions including support of HIV replication through its interaction with viral Nef and matrix proteins, reduction of TNFα-induced signaling through its interaction with NF-κB pathway proteins, and corepression of agonist-bound retinoic acid receptors and peroxisome proliferator-activated receptors (PPAR). The wide tissue distribution of TNIP1 provides the opportunity to influence numerous cellular responses in these roles and defining control of TNIP1 expression would be central to improved understanding of its impact on cell function. We cloned 6kb of the human TNIP1 promoter and performed predictive and functional analyses to identify regulatory elements. The promoter region proximal to the transcription start site is GC-rich without a recognizable TATA box. In contrast to this proximal ~500bp region, 6kb of the promoter increased reporter construct constitutive activity over five-fold. Throughout the 6kb length, in silico analysis identified several potential binding sites for both constitutive and inducible transcription factors; among the latter were candidate NF-κB binding sequences and peroxisome proliferator response elements (PPREs). We tested NF-κB and PPAR regulation of the endogenous TNIP1 gene and cloned promoter by expression studies, electrophoretic mobility shift assays, and chromatin immunoprecipitations. We validated NF-κB sites in the TNIP1 promoter proximal and distal regions as well as one PPRE in the distal region. The ultimate control of the TNIP1 promoter is likely to be a combination of constitutive transcription factors and those subject to activation such as NF-κB and PPAR.

Coactivation of TLR4 and TLR2/6 coordinates an additive augmentation on IL-6 gene transcription via p38MAPK pathway in U937 mononuclear cells

Studies have demonstrated that TLR4 and TLR2 expression by monocytes and the blood levels of TLR4 and TLR2 ligand in diabetic patients are significantly incased compared to nondiabetic patients, indicating that more monocytes in diabetic patients may have coactivation of TLR4 and TLR2. Although it has been shown that either TLR4 or TLR2 activation leads to increased expression of proinflammatory cytokines, the effect of coactivation of TLR2 and TLR4 in mononuclear cells on proinflammatory cytokine expression and the underlying molecular mechanisms remain largely unknown. In this study, we found that while TLR1, TLR2, TLR4 and TLR6 were expressed by U937 mononuclear cells, TLR4 was expressed at the highest level. Interestingly, results showed that while activation of either TLR4 or TLR2/6 (TLR2dimerized with TLR6), but not TLR2/1 (TLR2dimerized with TLR1), significantly increased IL-6 expression by U937 mononuclear cells, coactivation of TLR4 and TLR2/6, but not TLR4 and TLR2/1, led to a further augmentation on IL-6 expression by increasing IL-6 transcriptional activity, but not mRNA stability. To explore the signaling mechanisms involved in the augmentation, we found that p38MAPK and NFκB pathways, but not ERK and JNK pathways, were required for the augmentation of IL-6 expression by coactivation of TLR4 and TLR2/6. Furthermore, we found that coactivation of TLR4 and TLR2/6 increased p38 phosphorylation, but not NFkB activity, as compared to activation of TLR4or TLR2/6 alone. Taken together, this study showed that coactivation of TLR4 and TLR2/6 coordinates an additive augmentation of IL-6 gene transcription via p38MAPK pathway in U937 mononuclear cells.

Nuclear receptor signaling inhibits HIV-1 replication in macrophages through multiple trans-repression mechanisms

Sexually transmitted pathogens activate HIV-1 replication and inflammatory gene expression in macrophages through engagement of Toll-like receptors (TLRs). Ligand-activated nuclear receptor (NR) transcription factors, including glucocorticoid receptor (GR), peroxisome proliferator-activated receptor gamma (PPARγ), and liver X receptor (LXR), are potent inhibitors of TLR-induced inflammatory gene expression. We therefore hypothesized that ligand-activated NRs repress both basal and pathogen-enhanced HIV-1 replication in macrophages by directly repressing HIV-1 transcription and by ameliorating the local proinflammatory response to pathogens. We show that the TLR2 ligand PAM3CSK4 activated virus transcription in macrophages and that NR signaling repressed both basal and TLR-induced HIV-1 transcription. NR ligand treatment repressed HIV-1 expression when added concurrently with TLR ligands and in the presence of cycloheximide, demonstrating that they act independently of new cellular gene expression. We found that treatment with NR ligands inhibited the association of AP-1 and NF-κB subunits, as well as the coactivator CBP, with the long terminal repeat (LTR). We show for the first time that the nuclear corepressor NCoR is bound to HIV-1 LTR in unstimulated macrophages and is released from the LTR after TLR engagement. Treatment with PPARγ and LXR ligands, but not GR ligands, prevented this TLR-induced clearance of NCoR from the LTR. Our data demonstrate that both classical and nonclassical trans-repression mechanisms account for NR-mediated HIV-1 repression. Finally, NR ligand treatment inhibited the potent proinflammatory response induced by PAM3CSK4 that would otherwise activate HIV-1 expression in infected cells. Our findings provide a rationale for studying ligand-activated NRs as modulators of basal and inflammation-induced HIV-1 replication.

A novel role for c-Jun N-terminal kinase and phosphoinositide 3-kinase in the liver X receptor-mediated induction of macrophage gene expression

Liver X receptors (LXRs) are ligand-dependent transcription factors that are activated by metabolites of cholesterol, oxysterols, and a number of synthetic agonists. LXRs play potent anti-atherogenic roles in part by stimulating the efflux of cholesterol from macrophage foam cells. The LXR-induced expression of ATP-binding cassette transporter (ABC)-A1 and Apolipoprotein E (ApoE) in macrophages is essential for the stimulation of cholesterol efflux and the prevention of atherosclerotic development. Unfortunately, the signaling pathways underlying such regulation are poorly understood and were therefore investigated in human macrophages. The expression of ApoE and ABCA1 induced by synthetic or natural LXR ligands [TO901317, GW3965, and 22-(R)-hydroxycholesterol (22-(R)-HC), respectively] was attenuated by inhibitors of c-Jun N-terminal kinase (JNK) (curcumin and SP600125) and phosphoinositide 3-kinase (PI3K) (LY294002). Similar results were obtained with ABCG1 and LXR-α, two other LXR target genes. LXR agonists activated several components of the JNK pathway (SEK1, JNK and c-Jun) along with AKT, a downstream target for PI3K. In addition, dominant negative mutants of JNK and PI3K pathways inhibited the LXR-agonists-induced activity of the ABCA1 and LXR-α gene promoters in transfected cells. LXR agonists also induced the binding of activator protein-1 (AP-1), a key transcription factor family regulated by JNK, to recognition sequences present in the regulatory regions of the ApoE and ABCA1 genes. These studies reveal a novel role for JNK and PI3K/AKT signaling in the LXR-regulated expression in macrophages of several key genes implicated in atherosclerosis.

PPARgamma and LXR signaling inhibit dendritic cell-mediated HIV-1 capture and trans-infection

Dendritic cells (DCs) contribute to human immunodeficiency virus type 1 (HIV-1) transmission and dissemination by capturing and transporting infectious virus from the mucosa to draining lymph nodes, and transferring these virus particles to CD4+ T cells with high efficiency. Toll-like receptor (TLR)-induced maturation of DCs enhances their ability to mediate trans-infection of T cells and their ability to migrate from the site of infection. Because TLR-induced maturation can be inhibited by nuclear receptor (NR) signaling, we hypothesized that ligand-activated NRs could repress DC-mediated HIV-1 transmission and dissemination. Here, we show that ligands for peroxisome proliferator-activated receptor gamma (PPARgamma) and liver X receptor (LXR) prevented proinflammatory cytokine production by DCs and inhibited DC migration in response to the chemokine CCL21 by preventing the TLR-induced upregulation of CCR7. Importantly, PPARgamma and LXR signaling inhibited both immature and mature DC-mediated trans-infection by preventing the capture of HIV-1 by DCs independent of the viral envelope glycoprotein. PPARgamma and LXR signaling induced cholesterol efflux from DCs and led to a decrease in DC-associated cholesterol, which has previously been shown to be required for DC capture of HIV-1. Finally, both cholesterol repletion and the targeted knockdown of the cholesterol transport protein ATP-binding cassette A1 (ABCA1) restored the ability of NR ligand treated cells to capture HIV-1 and transfer it to T cells. Our results suggest that PPARgamma and LXR signaling up-regulate ABCA1-mediated cholesterol efflux from DCs and that this accounts for the decreased ability of DCs to capture HIV-1. The ability of NR ligands to repress DC mediated trans-infection, inflammation, and DC migration underscores their potential therapeutic value in inhibiting HIV-1 mucosal transmission.

Troglitazone, a ligand of peroxisome proliferator-activated receptor-{gamma}, stabilizes NUCB2 (Nesfatin) mRNA by activating the ERK1/2 pathway: isolation and characterization of the human NUCB2 gene

We recently identified a novel satiety peptide, nesfatin-1, containing 82 amino acids derived from the precursor peptide, nucleobindin 2 (NUCB2), from a troglitazone (TZ)-induced cDNA library. We examined the molecular mechanism underlying TZ-induced NUCB2 mRNA expression. Although TZ induced the mRNA expression in HTB185 cells, a nuclear run-on assay revealed no significant change in the transcription of the gene. Surprisingly, HTB185 cells possessed no functional peroxisome proliferator-activated receptor-gamma. We therefore examined the effect of TZ on the mRNA's stability. The half-life of NUCB2 mRNA was approximately 6 h, and incubation with TZ increased this to 27 h. Furthermore, this increase was completely inhibited by an ERK inhibitor, PD98059, and phosphorylated ERK1/2 was significantly increased after 30 min incubation with TZ. In addition, we cloned the entire NUCB2 gene and identified four adenylate/uridylate-rich elements (AREs) in the 3' untranslated region (UTR), to which several proteins of HTB185 extracts treated with TZ bound. The reporter assay fused with 3'UTR showed that the second and third AREs were crucial. Furthermore, the human NUCB2 gene spanned 55 kb and contained 14 exons and 13 introns. The transcriptional start site formed clusters around 246 bp upstream from the translational start site. We confirmed that a construct containing 5889 bp of the promoter region was very active in neuron-derived cell lines but not stimulated by TZ. These findings demonstrated a novel action of derivatives of thiazolidinediones, oral insulin-sensitizing antidiabetic agents, to stabilize the mRNA of NUCB2 through AREs in the 3'UTR by activating the ERK1/2 pathway independently of peroxisome proliferator-activated receptor-gamma.

Host hindrance to HIV-1 replication in monocytes and macrophages

Monocytes and macrophages are targets of HIV-1 infection and play critical roles in multiple aspects of viral pathogenesis. HIV-1 can replicate in blood monocytes, although only a minor proportion of circulating monocytes harbor viral DNA. Resident macrophages in tissues can be infected and function as viral reservoirs. However, their susceptibility to infection, and their capacity to actively replicate the virus, varies greatly depending on the tissue localization and cytokine environment. The susceptibility of monocytes to HIV-1 infection in vitro depends on their differentiation status. Monocytes are refractory to infection and become permissive upon differentiation into macrophages. In addition, the capacity of monocyte-derived macrophages to sustain viral replication varies between individuals. Host determinants regulate HIV-1 replication in monocytes and macrophages, limiting several steps of the viral life-cycle, from viral entry to virus release. Some host factors responsible for HIV-1 restriction are shared with T lymphocytes, but several anti-viral mechanisms are specific to either monocytes or macrophages. Whilst a number of these mechanisms have been identified in monocytes or in monocyte-derived macrophages in vitro, some of them have also been implicated in the regulation of HIV-1 infection in vivo, in particular in the brain and the lung where macrophages are the main cell type infected by HIV-1. This review focuses on cellular factors that have been reported to interfere with HIV-1 infection in monocytes and macrophages, and examines the evidences supporting their role in vivo, highlighting unique aspects of HIV-1 restriction in these two cell types.

PPAR and liver injury in HIV-infected patients

Due to the introduction of active HIV antiretroviral treatment, AIDS-related morbidity and mortality have markedly decreased and liver diseases are now a major cause of morbidity and mortality in HIV-infected patients. Chronic liver injury encompasses a wide spectrum of diseases due to HCV and HBV coinfection, drug-related toxicity, and NASH. HIV-infected patients who are receiving treatment present with a high prevalence of metabolic complications and lipodystrophy. Those patients are at high risk of nonalcoholic fatty liver disease, the liver feature of the metabolic syndrome. This review will focus on (1) the liver injuries in HIV-infected patients; (2) both the current experimental and human data regarding PPAR and liver diseases; (3) the interactions between HIV and PPAR; (4) the potential use of PPAR agonists for the management of HIV-related liver diseases.

15-Deoxy-Delta12,14-prostaglandin J2 inhibits HIV-1 transactivating protein, Tat, through covalent modification

Controlling the HIV/AIDS epidemic remains a major challenge, with approximately 5 million new HIV infections annually. Cyclopentenone prostaglandins (CyPG), such as 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)), are arachidonic acid-derived endogenous electrophiles that possess anti-HIV activity by an unknown mechanism. Given that the reactive alpha,beta-unsaturated ketone in the cyclopentenone ring of 15d-PGJ(2) covalently modifies key Cys thiols in select proteins, we hypothesized that 15d-PGJ(2) inhibits HIV transcription and replication by targeting Cys thiols in HIV-1 Tat. Tat is a potent transactivator of viral gene expression required for HIV transcriptional elongation and replication. Our studies indicate that 15d-PGJ(2) treatment of cells inhibits Tat-dependent transcription and replication of HIV-1, while 9,10-dihydro-15d-PGJ(2), PGE(2), PGF(2alpha), or PGD(2) that lack the reactive alpha,beta-unsaturated ketone were ineffective. The inhibition of Tat activity by 15d-PGJ(2) was dose-dependent, with an IC(50) of 1.2 microM and independent of NF-kappaB pathway. Furthermore, using a biotinylated derivative of 15d-PGJ(2), we demonstrate that 15d-PGJ(2) modifies free Cys-thiols in Tat to form covalent Michael adducts and that the interaction was further increased on reduction of Tat. 15d-PGJ(2)-modified Tat was unable to transactivate the HIV long terminal repeat in U937 human macrophages. These data demonstrate that Tat acts as a molecular target of CyPG leading to the inhibition of transcription and also suggest a novel therapeutic approach to complement current antiretroviral strategies for HIV/AIDS.

PPARalpha and PPARgamma attenuate HIV-induced dysregulation of tight junction proteins by modulations of matrix metalloproteinase and proteasome activities

The blood-brain barrier (BBB) plays an important role in HIV trafficking into the brain and the development of the central nervous system complications in HIV infection. Tight junctions are the main structural and functional elements that regulate the BBB integrity. Exposure of human brain microvascular endothelial cells (hCMEC/D3 cell line) to HIV-infected monocytes resulted in decreased expression of tight junction proteins, such as junctional adhesion molecule-A (JAM)-A, occludin, and zonula occludens (ZO)-1. Control experiments involved exposure to uninfected monocytes. Alterations of tight junction protein expression were associated with increased endothelial permeability and elevated transendothelial migration of HIV-infected monocytes across an in vitro model of the BBB. Notably, overexpression of the peroxisome proliferator-activated receptor (PPAR)alpha or PPARgamma attenuated HIV-mediated dysregulation of tight junction proteins. With the use of exogenous PPARgamma agonists and silencing of PPARalpha or PPARgamma, these protective effects were connected to down-regulation of matrix metalloproteinase (MMP) and proteasome activities. Indeed, the HIV-induced decrease in the expression of JAM-A and occludin was restored by inhibition of MMP activity. Moreover, both MMP and proteasome inhibitors attenuated HIV-mediated altered expression of ZO-1. The present data indicate that down-regulation of MMP and proteasome activities constitutes a novel mechanism of PPAR-induced protections against HIV-induced disruption of brain endothelial cells.

The effects of Thiazolidinediones on metabolic complications and Lipodystrophy in HIV-infected patients

Highly active antiretroviral therapy (HAART)-associated metabolic complications include lipoatrophy (loss of subcutaneous adipose tissue (SAT)) and insulin resistance. Thiazolidinediones are insulin-sensitizing antidiabetic agents which-as an untoward side effect in obese diabetic patients-increase SAT. Furthermore, troglitazone has improved lipoatrophy and glycemic control in non-HIV patients with various forms of lipodystrophy. These data have led to 14 clinical trials to examine whether thiazolidinediones could be useful in the treatment of HAART-associated metabolic complications. The results of these studies indicate very modest, if any, effect on lipoatrophic SAT, probably due to ongoing HAART negating the beneficial effect. The benefit might be more prominent in patients not taking thymidine analoges. Despite the poor effect on lipoatrophy, thiazolidin-ediones improved insulin sensitivity. However, especially rosiglitazone induced harmful effects on blood lipids. Current data do not provide evidence for the use of thiazolidinediones in the treatment of HAART-associated lipoatrophy, but treatment of lipoatrophy-associated diabetes may be warranted. The role of thiazolidinediones for novel indications, such as hepatosteatosis, should be studied in these patients.

HIV-1 infection and the PPARγ-dependent control of adipose tissue physiology

PPARγ is a ligand-dependent master transcription factor controlling adipocyte differentiation as well as multiple biological processes taking place in other cells present in adipose tissue depots such as macrophages. Recent research indicates that HIV-1 infection-related events may alter adipose tissue biology through several mechanisms involving PPARγ, ranging from direct effects of HIV-1-encoded proteins on adipocytes to the promotion of a proinflammatory environment that interferes with PPARγ actions. This effect of HIV-1 on adipose tissue cells can occur even in the absence of direct infection of adipocytes, as soluble HIV-1-encoded proteins such as Vpr may enter cells and inhibit PPARγ action. Moreover, repression of PPARγ actions may relieve inhibitory pathways of HIV-1 gene transcription, thus enhancing HIV-1 effects in infected cells. HIV-1 infection-mediated interference of PPARγ-dependent pathways in adipocytes and other cells inside adipose depots such as macrophages is likely to create an altered local environment that, after antiretroviral treatment, leads to lipodystrophy in HIV-1-infected and HAART-treated patients.

PGJ2 antagonizes NF-kappaB-induced HIV-1 LTR activation in colonic epithelial cells

Intestinal epithelial cells play an important role in early stages of HIV-1 infection and long-term persistence of the virus. Here we determined the mechanism that regulates HIV-1 activation via prostaglandin J(2) (PGJ(2)) in Caco-2 cells. We showed that treatment of Caco-2 cells with PGJ(2) decreased the infectivity of a luciferase reporter virus, pHXB-luc, as well as HIV production following infection of cells with a X4-tropic virus by antagonizing sodium butyrate, a cellular activator known to induce HIV-1 transcription. Transfection of intestinal epithelial cells such as Caco-2, HT-29 and SW620 cells with full-length HIV-1 LTR (pLTR-luc) revealed that PGJ(2) reduced HIV-1 LTR-mediated reporter gene activity. The involvement of NF-kappaB in the PGJ(2)-dependent down-regulation of HIV-1 transcription was further assessed using the kappaB-regulated luciferase-encoding vectors. In Caco-2 cells, PGJ(2) decreased IKK activity, resulting in reduced NF-kappaB translocation to the nucleus. Since sodium butyrate has been associated with a chronic stress response in AIDS patients, our results suggest that addition of PGJ(2) in the environment of infected intestinal epithelial cells could reduce HIV-1 transcription.

Peroxisome proliferator-activated receptor-gamma activation suppresses HIV-1 replication in an animal model of encephalitis

OBJECTIVE

Poor penetration of antiretroviral therapy across the blood-brain barrier poses an impediment on control of HIV-1 infection in brain macrophages. Peroxisome proliferator-activated receptor (PPAR)-gamma, a member of the nuclear receptors family, regulates important physiological functions (including anti-inflammatory effects) in response to ligand-mediated activation. As PPARgamma agonists are rapidly absorbed by oral administration and efficiently permeate the blood-brain barrier, we hypothesized that PPARgamma stimulation may suppress HIV-1 replication.

DESIGN AND METHODS

We investigated the effect of PPARgamma ligand (rosiglitazone) on HIV-1 replication in human monocyte-derived macrophages and in vivo using a murine model (immunodeficient mice reconstituted with human lymphocytes and intracerebrally inoculated with HIV-1 infected macrophages) of HIV-1 encephalitis.

RESULTS

Treatment with rosiglitazone caused a significant decrease of virus infection in macrophages. PPARgamma stimulation inhibited virus replication by modulating NF-kappaB activation in a receptor-dependent manner, leading to downregulation of HIV-1 long terminal repeat (LTR) promoter activity and suppression of HIV-1 replication. These effects were PPARgamma specific as PPARgamma silencing or addition of PPARgamma antagonist abolished effects of PPARgamma stimulation on HIV-1 LTR and virus replication. Using a murine model for HIV-1 encephalitis, we demonstrated that PPARgamma ligand suppressed HIV-1 replication in macrophages in brain tissue and reduced viremia by 50%.

CONCLUSION

In vitro data delineated the novel mechanism by which PPARgamma activation suppresses HIV-1 replication, and in vivo findings underscored the ability of PPARgamma agonists to reduce HIV-1 replication in lymphocytes and brain macrophages, thus offering a new therapeutic intervention in brain and systemic infection.

PPARalpha and PPARgamma effectively protect against HIV-induced inflammatory responses in brain endothelial cells

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors which down-regulate inflammatory signaling pathways. Therefore, we hypothesized that alterations of PPAR functions can contribute to human immunodeficiency virus-1 (HIV-1)-induced dysfunction of brain endothelial cells. Indeed, treatment with HIV-1 transactivator of transcription (Tat) protein decreased PPAR transactivation in brain endothelial cells. We next stably over-expressed PPARalpha and PPARgamma in a newly developed cell line of human brain endothelial cells (hCMEC/D3 cells). Tat-induced up-regulation of inflammatory mediators, such as interleukin (IL)-1beta, tumor necrosis factor-alpha, CCL2, and E-selectin were markedly attenuated in hCMEC/D3 over-expressing PPARalpha or PPARgamma. These results were confirmed in CCL2 and E-selectin promoter activity studies. Similar protective effects were observed in hCMEC/D3 after activation of PPARgamma by exogenous PPAR agonists (dPGJ(2) and rosiglitazone). PPAR over-expression also prevented Tat-induced binding activity and transactivation of nuclear factor-kappaB. Importantly, increased PPAR activity attenuated induction of IL-1beta, tumor necrosis factor-alpha, CCL2, and E-selectin in hCMEC/D3 cells co-cultured with HIV-1-infected Jurkat cells. The protective effects of PPAR over-expression were reversed by the antagonists of PPARalpha (MK886) or PPARgamma (GW9662). The present data suggest that targeting PPAR signaling may provide a novel therapeutic approach to attenuate HIV-1-induced local inflammatory responses in brain endothelial cells.

OTK18, a zinc-finger protein, regulates human immunodeficiency virus type 1 long terminal repeat through two distinct regulatory regions

It has previously been shown by our laboratory that OTK18, a human immunodeficiency virus (HIV)-inducible zinc-finger protein, reduces progeny-virion production in infected human macrophages. OTK18 antiviral activity is mediated through suppression of Tat-induced HIV-1 long terminal repeat (LTR) promoter activity. Through the use of LTR-scanning mutant vectors, the specific regions responsible for OTK18-mediated LTR suppression have been defined. Two different LTR regions were identified as potential OTK18-binding sites by an enhanced DNA-transcription factor ELISA system; the negative-regulatory element (NRE) at -255/-238 and the Ets-binding site (EBS) at -150/-139 in the LTR. In addition, deletion of the EBS in the LTR blocked OTK18-mediated LTR suppression. These data indicate that OTK18 suppresses LTR activity through two distinct regulatory elements. Spontaneous mutations in these regions might enable HIV-1 to escape from OTK18 antiretroviral activity in human macrophages.

Stimulated trans-acting factor of 50 kDa (Staf50) inhibits HIV-1 replication in human monocyte-derived macrophages

In order to identify cellular genes which interfere with HIV-1 replication in monocyte-derived macrophages (MAC), cells were stimulated with interferon (IFN) or lipopolysaccharide (LPS) leading to a pronounced inhibition of HIV-1 infection in these cells, and the resulting gene expression was analyzed. Using the microarray technology we identified a gene named Stimulated Trans-Acting Factor of 50 kDa (Staf50), which is known to repress the activity of the HIV-1 LTR. Analysis of the Staf50 expression by real-time PCR showed an overexpression in IFNalpha (up to 20-fold) and LPS (up to 10-fold)-stimulated MAC as well as in infected cells (up to 3-fold). For stable overexpression, 293 T cells and primary macrophages were transduced with Staf50-IRES-GFP bicistronic pseudotype viruses. After transduction, 293 T CD4/CCR5 and MAC were infected with HIV-1, and virus replication was monitored by p24 ELISA. Overexpression of Staf50 inhibited the HIV-1 infection between 50% and 90% in 293 T CD4/CCR5 as well as in MAC. Our findings suggest that host genetic effects in combination with viral properties determine the susceptibility of an appropriate target cell for HIV-1 infection as well as the replication potential of the virus in the cell resulting in an overall productive infection.

Peroxisome proliferator-activated receptor-γ agonists inhibit the replication of respiratory syncytial virus (RSV) in human lung epithelial cells

We have previously shown that peroxisome proliferator-activated receptor-gamma (PPARgamma) agonists inhibited the inflammatory response of RSV-infected human lung epithelial cells. In this study, we supply evidence that specific PPARgamma agonists (15d-PGJ2, ciglitazone, troglitazone, Fmoc-Leu) efficiently blocked the RSV-induced cytotoxicity and development of syncytia in tissue culture (A549, HEp-2). All PPARgamma agonists under study markedly inhibited the cell surface expression of the viral G and F protein on RSV-infected A549 cells. This was paralleled by a reduced cellular amount of N protein-encoding mRNA determined by real-time RT-PCR. Concomitantly, a reduced release of infectious progeny virus into the cell supernatants of human lung epithelial cells (A549, normal human bronchial epithelial cells (NHBE)) was observed. Similar results were obtained regardless whether PPARgamma agonists were added prior to RSV infection or thereafter, suggesting that the agonists inhibited viral gene expression and not the primary adhesion or fusion process.

Leptin and Adiponectin in the HIV Associated Metabolic Syndrome: Physiologic and Therapeutic Implications

Leptin and adiponectin represent two newly discovered adipose tissue derived hormones with important roles in energy homeostasis and insulin resistance. Their interrelations with the manifestations of the HIV associated metabolic syndrome and specific somatomorphic changes i.e. fat redistribution is reviewed. A synopsis of published studies is presented and the potential role of leptin and adiponectin is discussed. We have described an association of the HIV metabolic syndrome with a state of reduced insulin sensitivity due to adiponectin deficiency. The metabolic syndrome is also accompanied by leptin deficiency in lipoatrophic subjects and possibly by a leptin resistance state in lipohypertrophic patients. Adiponectin and / or leptin therapy in a manner similar to other leptin deficiency states may assist in the future management of such patients.

Peroxisome-proliferator-activated receptor-gamma agonists inhibit the release of proinflammatory cytokines from RSV-infected epithelial cells

The epithelial cells of the airways are the target cells for respiratory syncytial virus (RSV) infection and the site of the majority of the inflammation associated with the disease. Recently, peroxisome-proliferator-activated receptor gamma (PPARgamma), a member of the nuclear hormone receptor superfamily, has been shown to possess anti-inflammatory properties. Therefore, we investigated the role of PPARgamma agonists (15d-PGJ(2), ciglitazone and troglitazone) on the synthesis of RSV-induced cytokine release from RSV-infected human lung epithelial cells (A549). We observed that all PPARgamma ligands inhibited dose-dependently the release of TNF-alpha, GM-CSF, IL-1alpha, IL-6 and the chemokines CXCL8 (IL-8) and CCL5 (RANTES) from RSV-infected A549 cells. Concomitantly, the PPARgamma ligands diminished the cellular amount of mRNA encoding for IL-6, CXCL8 and CCL5 and the RSV-induced binding activity of the transcription factors NF-kappaB (p65/p50) and AP-1 (c-fos), respectively. Our data presented herein suggest a potential application of PPARgamma ligands in the anti-inflammatory treatment of RSV infection.

Rosiglitazone induces interleukin-1 receptor antagonist in interleukin-1beta-stimulated rat synovial fibroblasts via a peroxisome proliferator-activated receptor beta/delta-dependent mechanism

OBJECTIVE

To study the potency of 2 peroxisome proliferator-activated receptor gamma (PPARgamma) agonists, 15-deoxy-Delta(12,14)-prostaglandin J(2) (15-deoxy-PGJ(2)) and rosiglitazone, to modulate the expression of interleukin-1 receptor antagonist (IL-1Ra) in rat synovial fibroblasts.

METHODS

Levels of messenger RNA for IL-1Ra and PPAR isotypes (alpha, beta/delta, gamma) were assessed by real-time polymerase chain reaction in rat synovial fibroblasts exposed to 10 ng/ml of IL-1beta. PPAR levels were assessed by Western blotting and secreted IL-1Ra levels by immunoassay. The potency of PPARgamma agonists and the PPARbeta/delta agonist GW-501516 on IL-1Ra levels was tested in the range of 1-10 microM and at 100 pM, respectively. The contribution of PPARgamma to the effects of rosiglitazone on IL-1Ra secretion was examined either by its overexpression or by inhibition using wild-type or dominant-negative constructs and the antagonist GW-9662 (10 microM), respectively. The dominant-negative strategy was also performed to investigate the possible contribution of PPARbeta/delta and NF-kappaB activation.

RESULTS

IL-1beta-induced IL-1Ra production was increased by 10 microM rosiglitazone but was reduced dose-dependently by 15-deoxy-PGJ(2). Both agonists lowered IL-1beta secretion, but rosiglitazone alone reduced the imbalance of IL-1beta/IL-1Ra toward basal levels. Enhancement of IL-1beta-induced IL-1Ra production by rosiglitazone was not affected by PPARgamma overexpression or by its inhibition with dominant-negative PPARgamma or GW-9662. Inhibition of NF-kappaB was also ineffective against rosiglitazone but abolished the stimulating effect of IL-1beta on IL-1Ra. All PPAR isotypes were expressed constitutively in rat synoviocytes, but PPARgamma decreased dramatically upon IL-1beta exposure, whereas PPARbeta/delta remained stable. Dominant-negative PPARbeta/delta abolished the enhancement of IL-1Ra by rosiglitazone, whereas GW-501516 reproduced the effect of rosiglitazone on IL-1Ra secretion.

CONCLUSION

Rosiglitazone stimulates IL-1Ra production by a PPARbeta/delta mechanism in activated rat synovial fibroblasts, further contributing to its potential antiarthritic properties and opening new perspectives for the modulation of inflammatory genes by specific PPAR agonists in articular cells.

Human immunodeficiency virus type 1-induced macrophage gene expression includes the p21 gene, a target for viral regulation

In contrast to CD4+ T cells, human immunodeficiency virus type 1 (HIV-1)-infected macrophages typically resist cell death, support viral replication, and consequently, may facilitate HIV-1 transmission. To elucidate how the virus commandeers the macrophage's intracellular machinery for its benefit, we analyzed HIV-1-infected human macrophages for virus-induced gene transcription by using multiple parameters, including cDNA expression arrays. HIV-1 infection induced the transcriptional regulation of genes associated with host defense, signal transduction, apoptosis, and the cell cycle, among which the cyclin-dependent kinase inhibitor 1A (CDKN1A/p21) gene was the most prominent. p21 mRNA and protein expression followed a bimodal pattern which was initially evident during the early stages of infection, and maximum levels occurred concomitant with active HIV-1 replication. Mechanistically, viral protein R (Vpr) independently regulates p21 expression, consistent with the reduced viral replication and lack of p21 upregulation by a Vpr-negative virus. Moreover, the treatment of macrophages with p21 antisense oligonucleotides or small interfering RNAs reduced HIV-1 infection. In addition, the synthetic triterpenoid and peroxisome proliferator-activated receptor gamma ligand, 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO), which is known to influence p21 expression, suppressed viral replication. These data implicate p21 as a pivotal macrophage facilitator of the viral life cycle. Moreover, regulators of p21, such as CDDO, may provide an interventional approach to modulate HIV-1 replication.

15-Deoxy-Δ12,14-Prostaglandin J2 Inhibits IFN-Inducible Protein 10/CXC Chemokine Ligand 10 Expression in Human Microglia: Mechanisms and Implications

Regulation of cytokine and chemokine expression in microglia may have implications for CNS inflammatory disorders. In this study we examined the role of the cyclopentenone PG 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)) in microglial inflammatory activation in primary cultures of human fetal microglia. 15d-PGJ(2) potently inhibited the expression of microglial cytokines (IL-1, TNF-alpha, and IL-6). We found that 15d-PGJ(2) had differential effects on the expression of two alpha-chemokines; whereas the Glu-Lys-Arg (ELR)(-) chemokine IFN-inducible protein-10/CXCL10 was inhibited, the ELR(+) chemokine IL-8/CXCL8 was not inhibited. These findings were shown in primary human microglia and the human monocytic cells line THP-1 cells, using diverse cell stimuli such as bacterial endotoxin, proinflammatory cytokines (IL-1 and TNF-alpha), IFN-beta, and HIV-1. Furthermore, IL-8/CXCL8 expression was induced by 15d-PGJ(2) alone or in combination with TNF-alpha or HIV-1. Combined results from EMSA, Western blot analysis, and immunocytochemistry showed that 15d-PGJ(2) inhibited NF-kappaB, Stat1, and p38 MAPK activation in microglia. Adenoviral transduction of super-repressor IkappaBalpha, dominant negative MKK6, and dominant negative Ras demonstrated that NF-kappaB and p38 MAPK were involved in LPS-induced IFN-inducible protein 10/CXCL10 production. Interestingly, although LPS-induced IL-8/CXCL8 was dependent on NF-kappaB, the baseline or 15d-PGJ(2)-mediated IL-8/CXCL8 production was NF-kappaB independent. Our results demonstrate that 15d-PGJ(2) has opposing effects on the expression of two alpha-chemokines. These data may have implications for CNS inflammatory diseases.

HIV-1 Nef protein in the nucleus influences adipogenesis as well as viral transcription through the peroxisome proliferator-activated receptors

BACKGROUND

Although the HIV-1 Nef protein (27 kDa) localizes primarily in cytoplasm, there is considerable evidence suggesting its occasional localization in the nucleus. Nef is known to play an important role in transcriptional events and viral replication, but the actual target of Nef in the nucleus remains to be identified.

OBJECTIVE

To examine the functional roles of Nef in the nucleus and its possible interactions with other unknown factors in the nucleus.

METHODS

High-density microarray analysis was used to screen directly the unique functions of Nef on host gene transcription. The nuclear localization of Nef and its effects on the expression of peroxisome proliferator-activated receptors (PPAR) was examined using PPAR promoter/reporter assay and immunoblotting. A long terminal repeat/reporter assay was used to investigated the effects of Nef and PPAR on viral transcription.

RESULTS

Nef in the nucleus suppressed PPAR gamma expression and reduced fatty acid levels in human T and macrophage cell lines. Expression of Nef or PPAR suppressed viral replication; the effect of PPAR gamma or retinoid X receptor-alpha on viral replication were reduced by coexpression of Nef in MT(-)4 T cells.

CONCLUSION

Nef may be involved in both viral replication and the wasting syndrome associated with AIDS.

Regulation of HIV-1 gene transcription: from lymphocytes to microglial cells

Transcription is a crucial step for human immunodeficiency virus type 1 (HIV-1) expression in all infected host cells, from T lymphocytes, thymocytes, monocytes, macrophages, and dendritic cells in the immune system up to microglial cells in the central nervous system. To maximize its replication, HIV-1 adapts transcription of its integrated proviral genome by ideally exploiting the specific cellular environment and by forcing cellular stimulatory events and impairing transcriptional inhibition. Multiple cell type-specific interplays between cellular and viral factors perform the challenge for the virus to leave latency and actively replicate in a great diversity of cells, despite the variability of its long terminal repeat region in different HIV strains. Knowledge about the molecular mechanisms underlying transcriptional regulatory events helps in the search for therapeutic agents that target the step of transcription in anti-HIV strategies.

Stimulation of peroxisome proliferator-activated receptors alpha and gamma blocks HIV-1 replication and TNFalpha production in acutely infected primary blood cells, chronically infected U1 cells, and alveolar macrophages from HIV-infected subjects

Metabolic disorders in HIV-infected patients, especially those receiving highly active antiretroviral therapy (HAART) regimens containing protease inhibitors, are associated with insulin resistance. These metabolic disorders include fat redistribution, diabetes, and hypertriglyceridemia. Thiazolidinediones (TZDs) are used to treat patients with diabetes secondary to insulin resistance, and TZDs are being studied in HAART-related metabolic disorders. We studied the effects of TZDs (peroxisome proliferator-activated receptor-gamma [PPARgamma] agonists) and a PPARalpha agonist on HIV replication and TNFalpha production in peripheral blood mononuclear cells (PBMCs) acutely infected with HIV-1, in a chronically infected monoblastoid cell line (U1) and in alveolar macrophages (AMs) from HIV-infected subjects and uninfected controls. Rosiglitazone, ciglitazone, troglitazone, and PgJ (PPARgamma agonists) as well as fenofibrate (PPARalpha agonist) inhibited HIV replication in both PBMCs and U1 cells. These agents also inhibited TNFalpha production, but the magnitude of TNFalpha inhibition was not directly correlated with the quantitative decreases in HIV replication. In AMs, ciglitazone, rosiglitazone, and troglitazone reduced TNFalpha production. We hypothesize that alterations in mitogen-activated protein kinase signaling pathways have contemporaneous and interrelated effects on HIV replication, cytokine production, and lipid metabolism. Modulation of these pathways using PPAR agonists may improve the metabolic alterations during HAART in conjunction with desirable decreases in HIV replication and TNFalpha production.