Development of neurological disease is associated with increased immune activation in simian immunodeficiency virus-infected macaques

Machine Learning Prediction and Phyloanatomic Modeling of Viral Neuroadaptive Signatures in the Macaque Model of HIV-Mediated Neuropathology

In human immunodeficiency virus (HIV) infection, virus replication in and adaptation to the central nervous system (CNS) can result in neurocognitive deficits in approximately 25% of patients with unsuppressed viremia. While no single viral mutation can be agreed upon as distinguishing the neuroadapted population, earlier studies have demonstrated that a machine learning (ML) approach could be applied to identify a collection of mutational signatures within the virus envelope glycoprotein (Gp120) predictive of disease. The S[imian]IV-infected macaque is a widely used animal model of HIV neuropathology, allowing in-depth tissue sampling infeasible for human patients. Yet, translational impact of the ML approach within the context of the macaque model has not been tested, much less the capacity for early prediction in other, noninvasive tissues. We applied the previously described ML approach to prediction of SIV-mediated encephalitis (SIVE) using gp120 sequences obtained from the CNS of animals with and without SIVE with 97% accuracy. The presence of SIVE signatures at earlier time points of infection in non-CNS tissues indicated these signatures cannot be used in a clinical setting; however, combined with protein structural mapping and statistical phylogenetic inference, results revealed common denominators associated with these signatures, including 2-acetamido-2-deoxy-beta-d-glucopyranose structural interactions and high rate of alveolar macrophage (AM) infection. AMs were also determined to be the phyloanatomic source of cranial virus in SIVE animals, but not in animals that did not develop SIVE, implicating a role for these cells in the evolution of the signatures identified as predictive of both HIV and SIV neuropathology. IMPORTANCE HIV-associated neurocognitive disorders remain prevalent among persons living with HIV (PLWH) owing to our limited understanding of the contributing viral mechanisms and ability to predict disease onset. We have expanded on a machine learning method previously used on HIV genetic sequence data to predict neurocognitive impairment in PLWH to the more extensively sampled SIV-infected macaque model in order to (i) determine the translatability of the animal model and (ii) more accurately characterize the predictive capacity of the method. We identified eight amino acid and/or biochemical signatures in the SIV envelope glycoprotein, the most predominant of which demonstrated the potential for aminoglycan interaction characteristic of previously identified HIV signatures. These signatures were not isolated to specific points in time or to the central nervous system, limiting their use as an accurate clinical predictor of neuropathogenesis; however, statistical phylogenetic and signature pattern analyses implicate the lungs as a key player in the emergence of neuroadapted viruses.

Simian Immunodeficiency Virus-Infected Memory CD4+ T Cells Infiltrate to the Site of Infected Macrophages in the Neuroparenchyma of a Chronic Macaque Model of Neurological Complications of AIDS

Simian immunodeficiency virus (SIV)-infected nonhuman primates can serve as a relevant model for AIDS neuropathogenesis. Current SIV-induced encephalitis (SIVE)/neurological complications of AIDS (neuroAIDS) models are generally associated with rapid progression to neuroAIDS, which does not reflect the tempo of neuroAIDS progression in humans. Recently, we isolated a neuropathogenic clone, SIVsm804E-CL757 (CL757), obtained from an SIV-infected rhesus macaque (RM). CL757 causes a more protracted progression to disease, inducing SIVE in 50% of inoculated animals, with high cerebral spinal fluid viral loads, multinucleated giant cells (MNGCs), and perivascular lymphocytic cuffing in the central nervous system (CNS). This latter finding is reminiscent of human immunodeficiency virus (HIV) encephalitis in humans but not generally observed in rapid progressor animals with neuroAIDS. Here, we studied which subsets of cells within the CNS were targeted by CL757 in animals with neurological symptoms of SIVE. Immunohistochemistry of brain sections demonstrated infiltration of CD4+ T cells (CD4) and macrophages (MΦs) to the site of MNGCs. Moreover, an increase in mononuclear cells isolated from the brain tissues of RMs with SIVE correlated with increased cerebrospinal fluid (CSF) viral load. Subset analysis showed a specific increase in brain CD4+ memory T cells (Br-mCD4), brain-MΦs (Br-MΦs), and brain B cells (Br-B cells). Both Br-mCD4s and Br-MΦs harbored replication-competent viral DNA, as demonstrated by virus isolation by coculture. However, only in animals exhibiting SIVE/neuroAIDS was virus isolated from Br-MΦs. These findings support the use of CL757 to study the pathogenesis of AIDS viruses in the central nervous system and indicate a previously unanticipated role of CD4s cells as a potential reservoir in the brain.IMPORTANCE While the use of combination antiretroviral therapy effectively suppresses systemic viral replication in the body, neurocognitive disorders as a result of HIV infection of the central nervous system (CNS) remain a clinical problem. Therefore, the use of nonhuman primate models is necessary to study mechanisms of neuropathogenesis. The neurotropic, molecular clone SIVsm804E-CL757 (CL757) results in neuroAIDS in 50% of infected rhesus macaques approximately 1 year postinfection. Using CL757-infected macaques, we investigate disease progression by examining subsets of cells within the CNS that were targeted by CL757 and could potentially serve as viral reservoirs. By isolating mononuclear cells from the brains of SIV-infected rhesus macaques with and without encephalitis, we show that immune cells invade the neuroparenchyma and increase in number in the CNS in animals with SIV-induced encephalitis (SIVE). Of these cells, both brain macrophages and brain memory CD4+ T cells harbor replication-competent SIV DNA; however, only brain CD4+ T cells harbored SIV DNA in animals without SIVE. These findings support use of CL757 as an important model to investigate disease progression in the CNS and as a model to study virus reservoirs in the CNS.

Brain PET Imaging: Value for Understanding the Pathophysiology of HIV-associated Neurocognitive Disorder (HAND)

PURPOSE OF REVIEW

The purpose of this review is to summarize recent developments in PET imaging of neuropathologies underlying HIV-associated neurocognitive dysfunction (HAND). We concentrate on the recent post antiretroviral era (ART), highlighting clinical and preclinical brain PET imaging studies.

RECENT FINDINGS

In the post ART era, PET imaging has been used to better understand perturbations of glucose metabolism, neuroinflammation, the function of neurotransmitter systems, and amyloid/tau protein deposition in the brains of HIV-infected patients and HIV animal models. Preclinical and translational findings from those studies shed a new light on the complex pathophysiology underlying HAND. The molecular imaging capabilities of PET in neuro-HIV are great complements for structural imaging modalities. Recent and future PET imaging studies can improve our understanding of neuro-HIV and provide biomarkers of disease progress that could be used as surrogate endpoints in the evaluation of the effectiveness of potential neuroprotective therapies.

Poly (rC) binding protein 2 interacts with VP0 and increases the replication of the foot-and-mouth disease virus

Foot-and-mouth disease virus (FMDV) causes a highly contagious and debilitating disease in cloven-hoofed animals, which leads to devastating economic consequences. Previous studies have reported that some FMDV proteins can interact with host proteins to affect FMDV replication. However, the influence of the interactions between FMDV VP0 protein and its partners on FMDV replication remains unknown. In this study, we found that the overexpression of poly (rC) binding protein 2 (PCBP2) promoted FMDV replication, whereas the knockdown of PCBP2 suppressed FMDV replication. Furthermore, PCBP2 can interact with FMDV VP0 protein to promote the degradation of VISA via the apoptotic pathway. Further studies demonstrated that FMDV VP0 protein enhanced the formation of the PCBP2-VISA complex. Ultimately, we found that the degradation of VISA was weaker in PCBP2-knockdown and FMDV VP0-overexpressing cells, or FMDV VP0-knockdown cells than in the control cells. Summarily, our data revealed that the interaction between PCBP2 and VP0 could promote FMDV replication via the apoptotic pathway.

Characterization of Cellular Immune Responses in Thai Individuals With and Without HIV-Associated Neurocognitive Disorders

HIV-associated neurocognitive disorder (HAND) remains a challenge despite antiretroviral therapy (ART), and has been linked to monocyte/macrophage (M/M) migration to the brain. Due to the potential impact of T cell effector mechanisms in eliminating activated/HIV-infected M/M, T cell activation may play a role in the development of HAND. We sought to investigate the relationship between cognition and both CD8⁺ T cell activation (HLA-DR⁺/CD38⁺) and HIV-specific CD8⁺ T cell responses at the time of HIV diagnosis and 12 months postinitiation of ART. CD8⁺ T cell activation was increased in HAND compared to cognitive normal (NL) individuals and correlated directly with plasma viral load and inversely with the cognitive status. In addition, Gag-specific cytolytic activity (CD107a/b⁺) was decreased in HAND compared with NL individuals and correlated with their neurological testing, suggesting a potential role of cytotoxic CD8⁺ T cells in the mechanism of HAND development.

A SIV molecular clone that targets the CNS and induces neuroAIDS in rhesus macaques

Despite effective control of plasma viremia with the use of combination antiretroviral therapies (cART), minor cognitive and motor disorders (MCMD) persist as a significant clinical problem in HIV-infected patients. Non-human primate models are therefore required to study mechanisms of disease progression in the central nervous system (CNS). We isolated a strain of simian immunodeficiency virus (SIV), SIVsm804E, which induces neuroAIDS in a high proportion of rhesus macaques and identified enhanced antagonism of the host innate factor BST-2 as an important factor in the macrophage tropism and initial neuro-invasion of this isolate. In the present study, we further developed this model by deriving a molecular clone SIVsm804E-CL757 (CL757). This clone induced neurological disorders in high frequencies but without rapid disease progression and thus is more reflective of the tempo of neuroAIDS in HIV-infection. NeuroAIDS was also induced in macaques co-inoculated with CL757 and the parental AIDS-inducing, but non-neurovirulent SIVsmE543-3 (E543-3). Molecular analysis of macaques infected with CL757 revealed compartmentalization of virus populations between the CNS and the periphery. CL757 exclusively targeted the CNS whereas E543-3 was restricted to the periphery consistent with a role for viral determinants in the mechanisms of neuroinvasion. CL757 would be a useful model to investigate disease progression in the CNS and as a model to study virus reservoirs in the CNS.

Despite effective control of plasma viremia with the use of combination antiretroviral therapies, neurologic disease resulting from HIV-infection of the central nervous system (CNS) persists as a significant clinical problem. Non-human primate models are therefore required to study mechanisms of disease progression in the CNS. We generated an infectious molecular clone (CL757) of an SIV isolate from the brain of a macaque with neuroAIDS. This cloned virus induced neurological disorders in 50% of rhesus macaques infected but without rapid disease progression often seen in other commonly used animal models. Molecular analysis of tissues from macaques infected with CL757 revealed that the variants isolated from the CNS and the periphery became genetically distinct from one another. When co-inoculated with an AIDS-inducing, non-neurovirulent clone (E543-3), CL757 targeted the CNS consistent with its neurovirulence. CL757 would be a useful model to investigate disease progression in the CNS and as a model to study virus reservoirs in the CNS.

Macrophages in Progressive Human Immunodeficiency Virus/Simian Immunodeficiency Virus Infections

The cells that are targeted by primate lentiviruses (HIV and simian immunodeficiency virus [SIV]) are of intense interest given the renewed effort to identify potential cures for HIV. These viruses have been reported to infect multiple cell lineages of hematopoietic origin, including all phenotypic and functional CD4 T cell subsets. The two most commonly reported cell types that become infected in vivo are memory CD4 T cells and tissue-resident macrophages. Though viral infection of CD4 T cells is routinely detected in both HIV-infected humans and SIV-infected Asian macaques, significant viral infection of macrophages is only routinely observed in animal models wherein CD4 T cells are almost entirely depleted. Here we review the roles of macrophages in lentiviral disease progression, the evidence that macrophages support viral replication in vivo, the animal models where macrophage-mediated replication of SIV is thought to occur, how the virus can interact with macrophages in vivo, pathologies thought to be attributed to viral replication within macrophages, how viral replication in macrophages might contribute to the asymptomatic phase of HIV/SIV infection, and whether macrophages represent a long-lived reservoir for the virus.

Enhanced antagonism of BST-2 by a neurovirulent SIV envelope

Current antiretroviral therapy (ART) is not sufficient to completely suppress disease progression in the CNS, as indicated by the rising incidence of HIV-1-associated neurocognitive disorders (HAND) among infected individuals on ART. It is not clear why some HIV-1-infected patients develop HAND, despite effective repression of viral replication in the circulation. SIV-infected nonhuman primate models are widely used to dissect the mechanisms of viral pathogenesis in the CNS. Here, we identified 4 amino acid substitutions in the cytoplasmic tail of viral envelope glycoprotein gp41 of the neurovirulent virus SIVsm804E that enhance replication in macrophages and associate with enhanced antagonism of the host restriction factor BM stromal cell antigen 2 (BST-2). Rhesus macaques were inoculated with a variant of the parental virus SIVsmE543-3 that had been engineered to contain the 4 amino acid substitutions present in gp41 of SIVsm804E. Compared with WT virus-infected controls, animals infected with mutant virus exhibited higher viral load in cerebrospinal fluid. Together, these results are consistent with a potential role for BST-2 in the CNS microenvironment and suggest that BST-2 antagonists may serve as a possible target for countermeasures against HAND.

Modeling HIV-1 Induced Neuroinflammation in Mice: Role of Platelets in Mediating Blood-Brain Barrier Dysfunction

The number of HIV-1 positive individuals developing some form of HIV-associated neurocognitive disorder (HAND) is increasing. In these individuals, the integrity of the blood-brain barrier (BBB) is compromised due to an increase in exposure to pro-inflammatory mediators, viral proteins, and virus released from infected cells. It has been shown that soluble CD40L (sCD40L) is released upon platelet activation and is an important mediator of the pathogenesis of HAND but the underlying mechanisms are unclear, emphasizing the need of an effective animal model. Here, we have utilized a novel animal model in which wild-type (WT) mice were infected with EcoHIV; a derivative of HIV-1 that contains a substitution of envelope protein gp120 with that of gp80 derived from murine leukemia virus-1 (MuLV-1). As early as two-weeks post-infection, EcoHIV led to increased permeability of the BBB associated with decreased expression of tight junction protein claudin-5, in CD40L and platelet activation-dependent manner. Treatment with an antiplatelet drug, eptifibatide, in EcoHIV-infected mice normalized BBB function, sCD40L release and platelet activity, thus implicating platelet activation and platelet-derived CD40L in virally induced BBB dysfunction. Our results also validate and underscore the importance of EcoHIV infection mouse model as a tool to explore therapeutic targets for HAND.

Tissue myeloid cells in SIV-infected primates acquire viral DNA through phagocytosis of infected T cells

The viral accessory protein Vpx, expressed by certain simian and human immunodeficiency viruses (SIVs and HIVs), is thought to improve viral infectivity of myeloid cells. We infected 35 Asian macaques and African green monkeys with viruses that do or do not express Vpx and examined viral targeting of cells in vivo. While lack of Vpx expression affected viral dynamics in vivo, with decreased viral loads and infection of CD4⁺ T cells, Vpx expression had no detectable effect on infectivity of myeloid cells. Moreover, viral DNA was observed only within myeloid cells in tissues not massively depleted of CD4⁺ T cells. Myeloid cells containing viral DNA also showed evidence of T cell phagocytosis in vivo, suggesting that their viral DNA may be attributed to phagocytosis of SIV-infected T cells. These data suggest that myeloid cells are not a major source of SIV in vivo, irrespective of Vpx expression.

Characterization of simian immunodeficiency virus (SIV) that induces SIV encephalitis in rhesus macaques with high frequency: role of TRIM5 and major histocompatibility complex genotypes and early entry to the brain

Although nonhuman primate models of neuro-AIDS have made tremendous contributions to our understanding of disease progression in the central nervous system (CNS) of human immunodeficiency virus type 1 (HIV-1)-infected individuals, each model holds advantages and limitations. In this study, in vivo passage of SIVsmE543 was conducted to obtain a viral isolate that can induce neuropathology in rhesus macaques. After a series of four in vivo passages in rhesus macaques, we have successfully isolated SIVsm804E. SIVsm804E shows efficient replication in peripheral blood mononuclear cells (PBMCs) and monocyte-derived macrophages (MDMs) in vitro and induces neuro-AIDS in high frequencies in vivo. Analysis of the acute phase of infection revealed that SIVsm804E establishes infection in the CNS during the early phase of the infection, which was not observed in the animals infected with the parental SIVsmE543-3. Comprehensive analysis of disease progression in the animals used in the study suggested that host major histocompatibility complex class I (MHC-I) and TRIM5α genotypes influence the disease progression in the CNS. Taken together, our findings show that we have successfully isolated a new strain of simian immunodeficiency virus (SIV) that is capable of establishing infection in the CNS at early stage of infection and causes neuropathology in infected rhesus macaques at a high frequency (83%) using a single inoculum, when animals with restrictive MHC-I or TRIM5α genotypes are excluded. SIVsm804E has the potential to augment some of the limitations of existing nonhuman primate neuro-AIDS models.

IMPORTANCE

Human immunodeficiency virus (HIV) is associated with a high frequency of neurologic complications due to infection of the central nervous system (CNS). Although the use of antiviral treatment has reduced the incidence of severe complications, milder disease of the CNS continues to be a significant problem. Animal models to study development of neurologic disease are needed. This article describes the development of a novel virus isolate that induces neurologic disease in a high proportion of rhesus macaques infected without the need for prior immunomodulation as is required for some other models.

Astrocytic growth through the autocrine/paracrine production of IL-1β in the early infectious phase of fowl glioma-inducing virus

Fowl glioma is characterized morphologically by multiple nodular astrocytic growth with disseminated non-suppurative encephalitis. The disease is caused by fowl glioma-inducing virus (FGV) and its variants, belonging to subgroup A of avian leukosis virus (ALV-A). Fifty-seven FGV variants have so far been isolated from Japanese fowls and these variants have a variable degree of glioma inducibility. However, how these ALVs induce glioma with different degrees and frequencies has not been fully elucidated. In this study, we investigated the relationship between intracerebral viral replication and astrocytic growth in the early infectious phase. Replication abilities of two ALV strains, Sp-53 (a FGV variant) and ALV-based replication-competent vector RCAS(A) without glioma inducibility, were compared in the brains of C/O specific pathogen free chickens at 35 days of age. Sp-53 replicated faster than RCAS(A), and the histological score and the level of interleukin (IL)-1β in brains increased depending on the level of intracerebral viral RNA. Up-regulation of IL-1β was also demonstrated in primary cultured astrocytes. These results suggest that the astrocytic growth in this phase is enhanced through the autocrine/paracrine production of IL-1β in the FGV-infected astrocytes.

Laser capture microdissection assessment of virus compartmentalization in the central nervous systems of macaques infected with neurovirulent simian immunodeficiency virus

Nonhuman primate-simian immunodeficiency virus (SIV) models are powerful tools for studying the pathogenesis of human immunodeficiency virus type 1 (HIV-1) in the brain. Our laboratory recently isolated a neuropathogenic viral swarm, SIVsmH804E, a derivative of SIVsmE543-3, which was the result of sequential intravenous passages of viruses isolated from the brains of rhesus macaques with SIV encephalitis. Animals infected with SIVsmH804E or its precursor (SIVsmH783Br) developed SIV meningitis and/or encephalitis at high frequencies. Since we observed macaques with a combination of meningitis and encephalitis, as well as animals in which meningitis or encephalitis was the dominant component, we hypothesized that distinct mechanisms could be driving the two pathological states. Therefore, we assessed viral populations in the meninges and the brain parenchyma by laser capture microdissection. Viral RNAs were isolated from representative areas of the meninges, brain parenchyma, terminal plasma, and cerebrospinal fluid (CSF) and from the inoculum, and the SIV envelope fragment was amplified by PCR. Phylogenetic analysis of envelope sequences from the conventional progressors revealed compartmentalization of viral populations between the meninges and the parenchyma. In one of these animals, viral populations in meninges were closely related to those from CSF and shared signature truncations in the cytoplasmic domain of gp41, consistent with a common origin. Apart from magnetic resonance imaging (MRI) and positron-emission tomography (PET) imaging, CSF is the most accessible assess to the central nervous system for HIV-1-infected patients. However, our results suggest that the virus in the CSF may not always be representative of viral populations in the brain and that caution should be applied in extrapolating between the properties of viruses in these two compartments.