Upregulation of Superoxide Dismutase 2 by Astrocytes in the SIV/Macaque Model of HIV-Associated Neurologic Disease.

HIV-associated neurocognitive disorders (HAND) remain prevalent despite implementation of antiretroviral therapy (ART). Development of HAND is linked to mitochondrial dysfunction and oxidative stress in the brain; therefore, upregulation of antioxidant defenses is critical to curtail neuronal damage. Superoxide dismutase 2 (SOD2) is a mitochondrial antioxidant enzyme essential for maintaining cellular viability. We hypothesized that SOD2 was upregulated during retroviral infection. Using a simian immunodeficiency virus (SIV)-infected macaque model of HIV, quantitative PCR showed elevated SOD2 mRNA in cortical gray ([GM], 7.6-fold for SIV vs uninfected) and white matter ([WM], 77-fold for SIV vs uninfected) during SIV infection. Further, SOD2 immunostaining was enhanced in GM and WM from SIV-infected animals. Double immunofluorescence labeling illustrated that SOD2 primarily colocalized with astrocyte marker glial fibrillary acidic protein (GFAP) in SIV-infected animals. Interestingly, in ART-treated SIV-infected animals, brain SOD2 RNA levels were similar to uninfected animals. Additionally, using principal component analysis in a transcriptomic approach, SOD2 and GFAP expression separated SIV-infected from uninfected brain tissue. Projection of these data into a HIV dataset revealed similar expression changes, thereby validating the clinical relevance. Together, our findings suggest that novel SOD2-enhancing therapies may reduce neuroinflammation in ART-treated HIV-infected patients.

Epigenomic mechanisms of alcohol-induced impaired differentiation of skeletal muscle stem cells; role of Class IIA histone deacetylases.

Loss of functional metabolic muscle mass remains a strong and consistent predictor of mortality among people living with human immunodeficiency virus (PLWH). PLWH have a higher incidence of alcohol use disorder (AUD), and myopathy is a significant clinical comorbidity due to AUD. One mechanism of skeletal muscle (SKM) mass maintenance and repair is by differentiation and fusion of satellite cells (SCs) to existing myofibers. Previous studies demonstrated that chronic binge alcohol (CBA) administration decreases SC differentiation potential, myogenic gene expression, and miR-206 expression in simian immunodeficiency virus (SIV)-infected male rhesus macaques and that miR-206 targets the Class IIA histone deacetylase, HDAC4. The aim of this study was to determine whether alcohol-induced increases in Class IIA HDACs mediate the observed decrease in differentiation potential of SCs. Data show that CBA dysregulated HDAC gene expression in SKM and myoblasts of SIV-infected macaques. CBA and antiretroviral therapy increased HDAC activity in SKM and this was positively correlated with HDAC4 gene expression. In vitro ethanol (ETOH) treatment increased HDAC expression during differentiation and decreased differentiation potential of myoblasts. HDAC expression was negatively correlated with fusion index and myotube formation, indicators of differentiation potential. Treatment with a Class II HDAC inhibitor, TMP195, restored differentiation in ETOH-treated myoblasts. MEF2C expression at day 3 of differentiation was positively correlated with fusion index and myotube formation. These findings suggest that an alcohol-mediated increase in Class IIA HDAC expression contributes to decreased myoblast differentiation by downregulating MEF2C, a transcription factor critical for myogenesis.

The anti-caspase inhibitor Q-VD-OPH prevents AIDS disease progression in SIV-infected rhesus macaques.

Apoptosis has been proposed as a key mechanism responsible for CD4+ T cell depletion and immune dysfunction during HIV infection. We demonstrated that Q-VD-OPH, a caspase inhibitor, inhibits spontaneous and activation-induced death of T cells from SIV-infected rhesus macaques (RMs). When administered during the acute phase of infection, Q-VD-OPH was associated with (a) reduced levels of T cell death, (b) preservation of CD4+/CD8+ T cell ratio in lymphoid organs and in the gut, (c) maintenance of memory CD4+ T cells, and (d) increased specific CD4+ T cell response associated with the expression of cytotoxic molecules. Although therapy was limited to the acute phase of infection, Q-VD-OPH-treated RMs showed lower levels of both viral load and cell-associated SIV DNA as compared with control SIV-infected RMs throughout the chronic phase of infection, and prevented the development of AIDS. Overall, our data demonstrate that Q-VD-OPH injection in SIV-infected RMs may represent an adjunctive therapeutic agent to control HIV infection and delaying disease progression to AIDS.

In vitro effects of the small-molecule protein kinase C agonists on HIV latency reactivation.

The persistence of latently HIV-infected cellular reservoirs represents the major obstacle to virus eradication in patients under antiretroviral therapy (ART). Cure strategies to eliminate these reservoirs are thus needed to reactivate proviral gene expression in latently infected cells. In this study, we tested optimal concentrations of PKC agonist candidates (PEP005/Ingenol-3-angelate, prostratin, bryostatin-1, and JQ1) to reactivate HIV latency in vitro, and examined their effects on cell survival, activation and epigenetic histone methylation after treatment alone or in combination in cell line and isolated CD4 T cells from SIV-infected macaques. The results showed that PKC agonists increased cell activation with different degrees of latency reactivation, concomitant with reduced levels of histone methylation. With increasing concentrations, prostratin and byrostain-1 treatment rapidly reduced cell survival and cell activation. The PKC agonist combinations, or in combination with JQ1, led to modest levels of synergistic reactivation of HIV. Remarkably, PEP005 treatment alone caused marked reactivation of HIV latency, similar to PMA stimulation. These findings suggested that PEP005 alone, as indicated its lower cytotoxicity and lower effective dose inducing maximal reactivation, might be a candidate for effectively reactivating HIV latency as part of a therapeutic strategy for HIV infection.

Elevated brain monoamine oxidase activity in SIV- and HIV-associated neurological disease.

We recently demonstrated direct evidence of increased monoamine oxidase (MAO) activity in the brain of a simian immunodeficiency virus (SIV) model of human immunodeficiency virus (HIV)-associated central nervous system (CNS) disease, consistent with previously reported dopamine deficits in both SIV and HIV infection. In this study, we explored potential mechanisms behind this elevated activity. MAO B messenger RNA was highest in macaques with the most severe SIV-associated CNS lesions and was positively correlated with levels of CD68 and GFAP transcripts in the striatum. MAO B messenger RNA also correlated with viral loads in the CNS of SIV-infected macaques and with oxidative stress. Furthermore, in humans, striatal MAO activity was elevated in individuals with HIV encephalitis, compared with activity in HIV-seronegative controls. These data suggest that the neuroinflammation and oxidative stress caused by SIV infection in the CNS may provide the impetus for increased transcription of MAO B and that MAO, and more broadly, oxidative stress, have significant potential as therapeutic targets in CNS disease due to HIV.

Variation of human immunodeficiency virus type-1 reverse transcriptase within the simian immunodeficiency virus genome of RT-SHIV.

RT-SHIV is a chimera of simian immunodeficiency virus (SIV) containing the reverse transcriptase (RT)-encoding region of human immunodeficiency virus type 1 (HIV-1) within the backbone of SIVmac239. It has been used in a non-human primate model for studies of non-nucleoside RT inhibitors (NNRTI) and highly active antiretroviral therapy (HAART). We and others have identified several mutations that arise in the "foreign" HIV-1 RT of RT-SHIV during in vivo replication. In this study we catalogued amino acid substitutions in the HIV-1 RT and in regions of the SIV backbone with which RT interacts that emerged 30 weeks post-infection from seven RT-SHIV-infected rhesus macaques. The virus set points varied from relatively high virus load, moderate virus load, to undetectable virus load. The G196R substitution in RT was detected from 6 of 7 animals at week 4 post-infection and remained in virus from 4 of 6 animals at week 30. Virus from four high virus load animals showed several common mutations within RT, including L74V or V75L, G196R, L214F, and K275R. The foreign RT from high virus load isolates exhibited as much variation as that of the highly variable envelope surface glycoprotein, and 10-fold higher than that of the native RT of SIVmac239. Isolates from moderate virus load animals showed much less variation in the foreign RT than the high virus load isolates. No variation was found in SIVmac239 genes known to interact with RT. Our results demonstrate substantial adaptation of the foreign HIV-1 RT in RT-SHIV-infected macaques, which most likely reflects selective pressure upon the foreign RT to attain optimal activity within the context of the chimeric RT-SHIV and the rhesus macaque host.

Analysis of the N-terminal positively charged residues of the simian immunodeficiency virus Vif reveals a critical amino acid required for the antagonism of rhesus APOBEC3D, G, and H.

Previous studies have shown that apolipoprotein B mRNA editing, enzyme catalytic, polypeptide G (APOBEC3G; hA3G) and F (APOBEC3F; hA3F) proteins interact with a nonlinear binding site located at the N-terminal region of the HIV-1 Vif protein. We have analyzed the role of 12 positively charged amino acids of the N-terminal region of the SIV Vif. Simian-human immunodeficiency viruses (SHIV) were constructed that expressed each of these amino acid substitutions. These viruses were examined for replication in the presence of rhesus macaque APOBEC3 proteins (rhA3A-rhA3H), incorporation of the different A3 proteins into virions, and replication in rhesus macaque PBMC. Similar to other studies, we found that K27 was essential for rhA3G activity and rhA3F but was not important for restriction of SHIVΔvif by rhA3A, rhA3D or rhA3H. Our results identified the arginine at position 14 of the SIV Vif as a critical residue for virus restriction by rhA3D, rhA3G and rhA3H.

APOBEC3G polymorphism as a selective barrier to cross-species transmission and emergence of pathogenic SIV and AIDS in a primate host.

Cellular restriction factors, which render cells intrinsically resistant to viruses, potentially impose genetic barriers to cross-species transmission and emergence of viral pathogens in nature. One such factor is APOBEC3G. To overcome APOBEC3G-mediated restriction, many lentiviruses encode Vif, a protein that targets APOBEC3G for degradation. As with many restriction factor genes, primate APOBEC3G displays strong signatures of positive selection. This is interpreted as evidence that the primate APOBEC3G locus reflects a long-term evolutionary "arms-race" between retroviruses and their primate hosts. Here, we provide direct evidence that APOBEC3G has functioned as a barrier to cross-species transmission, selecting for viral resistance during emergence of the AIDS-causing pathogen SIVmac in captive colonies of Asian macaques in the 1970s. Specifically, we found that rhesus macaques have multiple, functionally distinct APOBEC3G alleles, and that emergence of SIVmac and simian AIDS required adaptation of the virus to evade APOBEC3G-mediated restriction. Our evidence includes the first comparative analysis of APOBEC3G polymorphism and function in both a reservoir and recipient host species (sooty mangabeys and rhesus macaques, respectively), and identification of adaptations unique to Vif proteins of the SIVmac lineage that specifically antagonize rhesus APOBEC3G alleles. By demonstrating that interspecies variation in a known restriction factor selected for viral counter-adaptations in the context of a documented case of cross-species transmission, our results lend strong support to the evolutionary "arms-race" hypothesis. Importantly, our study confirms that APOBEC3G divergence can be a critical determinant of interspecies transmission and emergence of primate lentiviruses, including viruses with the potential to infect and spread in human populations.

In vivo administration of a JAK3 inhibitor to chronically siv infected rhesus macaques leads to NK cell depletion associated with transient modest increase in viral loads.

Innate immune responses are reasoned to play an important role during both acute and chronic SIV infection and play a deterministic role during the acute stages on the rate of infection and disease progression. NK cells are an integral part of the innate immune system but their role in influencing the course of SIV infection has been a subject of debate. As a means to delineate the effect of NK cells on SIV infection, use was made of a Janus kinase 3 (JAK3) inhibitor that has previously been shown to be effective in the depletion of NK cells in vivo in nonhuman primates (NHP). Extensive safety and in vitro/in vivo PK studies were conducted and an optimal dose that depletes NK cells and NK cell function in vivo identified. Six chronically SIV infected rhesus macaques, 3 with undetectable/low plasma viral loads and 3 with high plasma viral loads were administered a daily oral dose of 10 mg/kg for 35 days. Data obtained showed that, at the dose tested, the major cell lineage affected both in the blood and the GI tissues were the NK cells. Such depletion appeared to be associated with a transient increase in plasma and GI tissue viral loads. Whereas the number of NK cells returned to baseline values in the blood, the GI tissues remained depleted of NK cells for a prolonged period of time. Recent findings show that the JAK3 inhibitor utilized in the studies reported herein has a broader activity than previously reported with dose dependent effects on both JAK2 and JAK1 suggests that it is likely that multiple pathways are affected with the administration of this drug that needs to be taken into account. The findings reported herein are the first studies on the use of a JAK3 inhibitor in lentivirus infected NHP.

T cells target APOBEC3 proteins in human immunodeficiency virus type 1-infected humans and simian immunodeficiency virus-infected Indian rhesus macaques.

APOBEC3 proteins mediate potent antiretroviral activity by hypermutating the retroviral genome during reverse transcription. To counteract APOBEC3 and gain a replicative advantage, lentiviruses such as human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV) have evolved the Vif protein, which targets APOBEC3 proteins for proteasomal degradation. However, the proteasome plays a critical role in the generation of T cell peptide epitopes. Whether Vif-mediated destruction of APOBEC3 proteins leads to the generation and presentation of APOBEC3-derived T cell epitopes on the surfaces of lentivirus-infected cells remains unknown. Here, using peptides derived from multiple Vif-sensitive APOBEC3 proteins, we identified APOBEC3-specific T cell responses in both HIV-1-infected patients and SIV-infected rhesus macaques. These results raise the possibility that these T cell responses may be part of the larger antiretroviral immune response.

Vif proteins of human and simian immunodeficiency viruses require cellular CBFß to degrade APOBEC3 restriction factors.

HIV-1 requires the cellular transcription factor CBFß to stabilize its accessory protein Vif and promote APOBEC3G degradation. Here, we demonstrate that both isoforms of CBFß allow for increased steady-state levels of Vif, enhanced APOBEC3G degradation, and increased viral infectivity. This conserved functional interaction enhances the steady-state levels of Vif proteins from multiple HIV-1 subtypes and is required for the degradation of all human and rhesus Vif-sensitive APOBEC3 proteins by their respective lentiviral Vif proteins.

Increased APOBEC3G and APOBEC3F expression is associated with low viral load and prolonged survival in simian immunodeficiency virus infected rhesus monkeys.

BACKGROUND: The cytidine deaminases APOBEC3G (A3G) and APOBEC3F (A3F) are innate cellular factors that inhibit replication of a number of viruses, including HIV-1. Since antiviral activity of APOBEC3 has been mainly confirmed by in vitro data, we examined their role for disease progression in the SIV/macaque model for AIDS. RESULTS: We quantified A3G and A3F mRNA in PBMC and leukocyte subsets of uninfected and SIVmac-infected rhesus macaques. Compared with uninfected animals, we found increased A3G and A3F mRNA levels in PBMC, purified CD4+ T-cells and CD14+ monocytes as well as lymph node cells from asymptomatic SIV-infected macaques. APOBEC3 mRNA levels correlated negatively with plasma viral load, and highest amounts of APOBEC3 mRNA were detected in long term non-progressors (LTNPs). During acute viremia, A3G mRNA increased in parallel with MxA, a prototype interferon-stimulated gene indicating a common regulation by the initial interferon response. This association disappeared during the asymptomatic stage. CONCLUSION: Our findings suggest a protective effect of APOBEC3 for HIV and SIV in vivo and indicate regulation of APOBEC3 by interferon during early infection and by contribution of other, hitherto undefined factors at later disease stages. Elucidating the regulatory mechanisms leading to increased APOBEC3 mRNA levels in LTNPs could help to develop new therapies against HIV.

COX1 and COX2 expression in non-neuronal cellular compartments of the rhesus macaque brain during lentiviral infection.

Recent evidence suggests that cyclooxygenases COX1 and COX2 differentially affect brain immunity. Limited data exist about their expressional changes in neurodegenerative diseases such as neuro-AIDS. Here, we analyzed the regulation of non-neuronal COX1/2 expression in rhesus macaque brain during infection with SIV(δ670) and antiretroviral treatment. COX1 was constitutively expressed in microglia and endothelial cells and was not changed in early SIV infection. Late stage of disease was characterized by increased COX1 expression in globally activated microglia, macrophage nodules, infiltrates, and multinucleated giant cells. Endothelial COX1 expression was unaltered. In contrast, COX2 was not expressed in non-neuronal cells in the brain of uninfected and asymptomatically SIV-infected monkeys but was induced in nodule- and syncytium-forming macrophages and in endothelial cells in areas with infiltrates and SIV in monkeys with AIDS. Antiretroviral treatment of AIDS-diseased monkeys with 6-chloro-2',3'-dideoxyguanosine markedly reduced SIV burden, appearance of COX1-positive macrophage nodules, giant cells, and infiltrates, and COX2 induction in the brain. However, the number of COX1-positive diffuse microglia was still increased in antiretrovirally treated animals as compared to uninfected or asymptomatic SIV-infected monkeys. Our data imply that both COX isoforms are differentially regulated and may distinctly modulate local immune responses in the brain during lentiviral disease.

Mechanisms of minocycline-induced suppression of simian immunodeficiency virus encephalitis: inhibition of apoptosis signal-regulating kinase 1.

Human immunodeficiency virus (HIV) infection of the central nervous system (CNS) can lead to cognitive dysfunction, even in individuals treated with highly active antiretroviral therapy. Using an established simian immunodeficiency virus (SIV)/macaque model of HIV CNS disease, we previously reported that infection shifts the balance of activation of mitogen-activated protein kinase (MAPK) signaling pathways in the brain, resulting in increased activation of the neurodegenerative MAPKs p38 and JNK. Minocycline treatment of SIV-infected macaques reduced the incidence and severity of SIV encephalitis in this model, and suppressed the activation of p38 in the brain. The purpose of this study was to further examine the effects of minocycline on neurodegenerative MAPK signaling. We first demonstrated that minocycline also decreases JNK activation in the brain and levels of the inflammatory mediator nitric oxide (NO). We next used NO to activate these MAPK pathways in vitro, and demonstrated that minocycline suppresses p38 and c-Jun N-terminal kinase (JNK) activation by reducing intracellular levels, and hence, activation of apoptosis signal-regulating kinase 1 (ASK1), a MAPK kinase capable of selectively activating both pathways. We then demonstrated that ASK1 activation in the brain during SIV infection is suppressed by minocycline. By suppressing p38 and JNK activation pathways, which are important for the production of and responses to inflammatory mediators, minocycline may interrupt the vicious cycle of inflammation that both results from, and promotes, virus replication in SIV and HIV CNS disease.

Regulatory T-cell markers, indoleamine 2,3-dioxygenase, and virus levels in spleen and gut during progressive simian immunodeficiency virus infection.

High levels of viral replication occur in gut-associated lymphoid tissue (GALT) and other lymphoid tissues (LT) since the early phase of human/simian immunodeficiency virus (HIV/SIV) infection. Regulatory T cells (T(reg)), a subset of immunosuppressive T cells expressing CTLA-4 and the FoxP3 transcription factor, accumulate in LT during HIV/SIV infection. Here we show that FoxP3 and CTLA-4 mRNA are increased in leukocytes from the spleens, lymph nodes (LN), and mucosal sites of chronically SIV-infected macaques with high viremia (SIV(HI)) compared to animals with low viremia (SIV(LO)). FoxP3 and CTLA-4 correlated with SIV RNA levels in tissues; SIV virus levels in the spleen, inguinal LN, mesenteric LN, colon, and jejunum directly correlated with the plasma virus level. Importantly, CTLA-4 and FoxP3 mRNA were predominantly increased in the CD25(-) subpopulation of leukocytes from SIV(HI), further challenging the classical definition of T(reg) as CD4(+) CD25(+) T cells. Similar to CTLA-4 and FoxP3, expression of indoleamine 2,3-dioxygenase (IDO), an immunosuppressive enzyme induced by T(reg) in antigen-presenting cells, was increased in the spleens, mesenteric LN, colons, and jejuna from SIV(HI) compared to SIV(LO) and directly correlated to SIV RNA in the same tissues. Accordingly, plasma kynurenine/tryptophan, a marker for IDO enzymatic activity, was significantly higher in SIV(HI) compared to SIV(LO) and correlated with plasma viral levels. Increased T(reg) and IDO in LT of SIV-infected macaques may be the consequence of increased tissue inflammation and/or may favor virus replication during the chronic phase of SIV infection.

Death of CD4+ T cells from lymph nodes during primary SIVmac251 infection predicts the rate of AIDS progression.

Immunological and virological events that occur during the earliest stages of SIV infection are now considered to have a major impact on subsequent disease progression. In the present study, we demonstrate a clear correlation between progression to AIDS and the rate of in vitro CD4+ (but not CD8+) T cell death in lymph nodes. The dying CD4+ T cells were effector memory T cells, which are critical for the immune response to pathogens. However, there was no correlation between the rate of the viral replication within lymph nodes and the extent of Fas ligand-mediated death, despite the increased sensitivity of CD4+ T cells to death in response to recombinant human Fas ligand. CD4+ T cell death was caspase and apoptosis-inducing factor independent but was clearly associated with mitochondrion damage. Interestingly, higher expression levels of the active form of Bak, a proapoptotic molecule involved in mitochondrial membrane permeabilization, were observed in SIV-infected macaques progressing more rapidly to AIDS. Finally, we demonstrated that the strain of SIV we used requires CCR5 and BOB/GRP15 molecules as coreceptors and caused death of unstimulated noncycling primary CD4+ T cells. Altogether, these results demonstrate that CD4+ T cell death occurring early after SIV infection is a crucial determinant of progression to AIDS and that it is mediated by the intrinsic death pathway.

Dysregulation of mitogen-activated protein kinase signaling pathways in simian immunodeficiency virus encephalitis.

Central nervous system (CNS) disease is a frequent complication of human immunodeficiency virus (HIV)-1 infection. Identification of cellular mechanisms that control virus replication and that mediate development of HIV-associated neuropathology will provide novel strategies for therapeutic intervention. The milieu of the CNS during HIV infection is extraordinarily complex because of infiltration of inflammatory cells and production of chemokines, cytokines, and neurotoxic molecules. Cells in the CNS must integrate signaling pathways activated simultaneously by products of virus replication and infiltrating immune cells. In this study, we examined activation of mitogen-activated protein kinases (MAPKs) in the CNS of simian immunodeficiency virus-infected macaques during acute, asymptomatic, and terminal infection. We demonstrate that significantly increased (P < 0.02) activation of ERK MAPK, typically associated with anti-apoptotic and neuroprotective pathways, occurs predominantly in astrocytes and immediately precedes suppression of virus replication and macrophage activation that occur after acute infection. In contrast, significantly increased activation of proapoptotic, neurodegenerative MAPKs JNK (P = 0.03; predominantly in macrophages/microglia), and p38 (P = 0.03; predominantly in neurons and astrocytes) after acute infection correlates with subsequent resurgent virus replication and development of neurological lesions. This shift from classically neuroprotective to neurodegenerative MAPK pathways suggests that agents that inhibit activation of JNK/p38 may be protective against HIV-associated CNS disease.

Caspase-dependent and -independent T-cell death pathways in pathogenic simian immunodeficiency virus infection: relationship to disease progression.

Studies of human immunodeficiency virus (HIV) and nonhuman primate models of pathogenic and nonpathogenic simian immunodeficiency virus (SIV) infections have suggested that enhanced ex vivo CD4 T-cell death is a feature of pathogenic infection in vivo. However, the relative contributions of the extrinsic and intrinsic pathways to programmed T-cell death in SIV infection have not been studied. We report here that the spontaneous death rate of CD4+ T cells from pathogenic SIVmac251-infected rhesus macaques ex vivo is correlated with CD4 T-cell depletion and plasma viral load in vivo. CD4+ T cells from SIVmac251-infected macaques showed upregulation of the death ligand (CD95L) and of the proapoptotic proteins Bim and Bak, but not of Bax. Both CD4+ and CD8+ T cells from SIVmac251-infected macaques underwent caspase-dependent death following CD95 ligation. The spontaneous death of CD4+ and CD8+ T cells was not prevented by a decoy CD95 receptor or by a broad-spectrum caspase inhibitor (zVAD-fmk), suggesting that this form of cell death is independent of CD95/CD95L interaction and caspase activation. IL-2 and IL-15 prevented the spontaneous death of CD4+ and CD8+ T cells, whereas IL-10 prevented only CD8 T-cell death and IL-7 had no effect on T-cell death. Our results indicate that caspase-dependent and caspase-independent pathways are involved in the death of T cells in pathogenic SIVmac251-infected primates.

Regulation of indoleamine 2,3-dioxygenase expression in simian immunodeficiency virus-infected monkey brains.

The human immunodeficiency virus type 1-associated cognitive-motor disorder, including the AIDS dementia complex, is characterized by brain functional abnormalities that are associated with injury initiated by viral infection of the brain. Indoleamine 2,3-dioxygenase (IDO), the first and rate-limiting enzyme in tryptophan catabolism in extrahepatic tissues, can lead to neurotoxicity through the generation of quinolinic acid and immunosuppression and can alter brain chemistry via depletion of tryptophan. Using the simian immunodeficiency virus (SIV)-infected rhesus macaque model of AIDS, we demonstrate that cells of the macrophage lineage are the main source for expression of IDO in the SIV-infected monkey brain. Animals with SIV encephalitis have the highest levels of IDO mRNA, and the level of IDO correlates with gamma interferon (IFN-gamma) and viral load levels. In vitro studies on mouse microglia reveal that IFN-gamma is the primary inducer of IDO expression. These findings demonstrate the link between IDO expression, IFN-gamma levels, and brain pathology signs observed in neuro-AIDS.

Identification of protein kinases dysregulated in CD4(+) T cells in pathogenic versus apathogenic simian immunodeficiency virus infection.

Human immunodeficiency virus infection in humans and simian immunodeficiency virus (SIV) infection in rhesus macaques (RM) leads to a generalized loss of immune responses involving perturbations in T-cell receptor (TCR) signaling. In contrast, naturally SIV-infected sooty mangabeys (SM) remain asymptomatic and retain immune responses despite relatively high viral loads. However, SIV infection in both RM and SM led to similar decreases in TCR-induced Lck phosphorylation. In this study, a protein tyrosine kinase (PTK) differential display method was utilized to characterize the effects of in vivo SIV infection on key signaling molecules of the CD4(+) T-cell signaling pathways. The CD4(+) T cells from SIV-infected RM, but not SIV-infected SM, showed chronic downregulation of baseline expression of MLK3, PRK, and GSK3, and symptomatically SIV-infected RM showed similar downregulation of MKK3. In vitro TCR stimulation with or without CD28 costimulation of CD4(+) T cells did not lead to the enhancement of gene transcription of these PTKs. While the CD4(+) T cells from SIV-infected RM showed a significant increase of the baseline and anti-TCR-mediated ROR2 transcription, SIV infection in SM led to substantially decreased anti-TCR-stimulated ROR2 transcription. TCR stimulation of CD4(+) T cells from SIV-infected RM (but not SIV-infected SM) led to the repression of CaMKKbeta and the induction of gene transcription of MLK2. Studies of the function of these molecules in T-cell signaling may lead to the identification of potential targets for specific intervention, leading to the restoration of T-cell responses.