Retroviral diseases of the nervous system: pathogenic host response or viral gene-mediated neurovirulence?

Lentiviral Infections Persist in Brain despite Effective Antiretroviral Therapy and Neuroimmune Activation

HIV infection persists in different tissue reservoirs among people with HIV (PWH) despite effective antiretroviral therapy (ART). In the brain, lentiviruses replicate principally in microglia and trafficking macrophages. The impact of ART on this viral reservoir is unknown. We investigated the activity of contemporary ART in various models of lentivirus brain infection. HIV-1 RNA and total and integrated DNA were detected in cerebral cortex from all PWH (n = 15), regardless of ART duration or concurrent plasma viral quantity and, interestingly, integrated proviral DNA levels in brain were significantly higher in the aviremic ART-treated group (P < 0.005). Most ART drugs tested (dolutegravir, ritonavir, raltegravir, and emtricitabine) displayed significantly lower 50% effective concentration (EC₅₀) values in lymphocytes than in microglia, except tenofovir, which showed 1.5-fold greater activity in microglia (P < 0.05). In SIV-infected Chinese rhesus macaques, despite receiving suppressive (n = 7) or interrupted (n = 8) ART, brain tissues had similar SIV-encoded RNA and total and integrated DNA levels compared to brains from infected animals without ART (n = 3). SIV and HIV-1 capsid antigens were immunodetected in brain, principally in microglia/macrophages, regardless of ART duration and outcome. Antiviral immune responses were comparable in the brains of ART-treated and untreated HIV- and SIV-infected hosts. Both HIV-1 and SIV persist in brain tissues despite contemporary ART, with undetectable virus in blood. ART interruption exerted minimal effect on the SIV brain reservoir and did not alter the neuroimmune response profile. These studies underscore the importance of augmenting ART potency in different tissue compartments. IMPORTANCE Antiretroviral therapy (ART) suppresses HIV-1 in plasma and CSF to undetectable levels. However, the impact of contemporary ART on HIV-1 brain reservoirs remains uncertain. An active viral reservoir in the brain during ART could lead to rebound systemic infection after cessation of therapy, development of drug resistance mutations, and neurological disease. ART's impact, including its interruption, on brain proviral DNA remains unclear. The present studies show that in different experimental platforms, contemporary ART did not suppress viral burden in the brain, regardless of ART component regimen, the duration of therapy, and its interruption. Thus, new strategies for effective HIV-1 suppression in the brain are imperative to achieve sustained HIV suppression.

A novel Betaretrovirus discovered in cattle with neurological disease and encephalitis

Background

The majority of emerging infectious diseases in humans are of animal origin, and many of them are caused by neuropathogenic viruses. Many cases of neurological disease and encephalitis in livestock remain etiologically unresolved, posing a constant threat to animal and human health. Thus, continuous extension of our knowledge of the repertoire of viruses prone to infect the central nervous system (CNS) is vital for pathogen monitoring and the early detection of emerging viruses. Using high-throughput sequencing (HTS) and bioinformatics, we discovered a new retrovirus, bovine retrovirus CH15 (BoRV CH15), in the CNS of a cow with non-suppurative encephalitis. Phylogenetic analysis revealed the affiliation of BoRV CH15 to the genus Betaretrovirus.

Results

BoRV CH15 genomes were identified prospectively and retrospectively by PCR, RT-PCR, and HTS, with targeting of viral RNA and proviral DNA, in six additional diseased cows investigated over a period of > 20 years and of different geographical origins. The virus was not found in brain samples from healthy slaughtered control animals (n = 130). We determined the full-length proviral genomes from six of the seven investigated animals and, using in situ hybridization, identified viral RNA in the cytoplasm of cells morphologically compatible with neurons in diseased brains.

Conclusions

Further screening of brain samples, virus isolation, and infection studies are needed to estimate the significance of these findings and the causative association of BoRV CH15 with neurological disease and encephalitis in cattle. However, with the full-length proviral sequences of BoRV CH15 genomes, we provide the basis for a molecular clone and further in vitro investigation.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12977-021-00585-x.

Microorganisms' Footprint in Neurodegenerative Diseases

Advancement of science has gifted the human a longer life; however, as neuron cells do not regenerate, the number of people with neurodegeneration disorders rises with population aging. Neurodegeneration diseases occur as a result of neuronal cells loss caused by environmental factors, genetic mutations, proteopathies and other cellular dysfunctions. The negative direct or indirect contributions of various microorganisms in onset or severity of some neurodegeneration disorders and interaction between human immune system and pathogenic microorganisms has been portrayed in this review article. This association may explain the early onset of neurodegeneration disorders in some individuals, which can be traced through detailed study of health background of these individuals for infection with any microbial disease with neuropathogenic microorganisms (bacteria, fungi, viruses). A better understanding and recognition of the relation between microorganisms and neurodegeneration disorders may help researchers in development of novel remedies to avoid, postpone, or make neurodegeneration disorders less severe.

Neurologic disease in feline immunodeficiency virus infection: disease mechanisms and therapeutic interventions for NeuroAIDS

Feline immunodeficiency virus (FIV) is a lentivirus that causes immunosuppression through virus-mediated CD4+ T cell depletion in feline species. FIV infection is complicated by virus-induced disease in the nervous system. FIV enters the brain soon after primary infection and is detected as FIV-encoded RNA, DNA, and proteins in microglia, macrophages, and astrocytes. FIV infection activates neuroinflammatory pathways including cytokines, chemokines, proteases, and ROS with accompanying neuronal injury and loss. Neurobehavioral deficits during FIV infection are manifested as impaired motor and cognitive functions. Several treatment strategies have emerged from studies of FIV neuropathogenesis including the therapeutic benefits of antiretroviral therapies, other protease inhibitors, anti-inflammatory, and neurotrophic compounds. Recently, insulin's antiviral, anti-inflammatory, and neuroprotective effects were investigated in models of lentivirus brain infection. Insulin suppressed HIV-1 replication in human microglia as well as FIV replication of lymphocytes. Insulin treatment diminished cytokine and chemokine activation in HIV-infected microglia while also protecting neurons from HIV-1 Vpr protein-mediated neurotoxicity. Intranasal (IN) insulin delivery for 6 weeks suppressed FIV expression in the brains of treated cats. IN insulin also reduced neuroinflammation and protected neurons in the hippocampus, striatum, and neocortex of FIV-infected animals. These morphological and molecular effects of IN insulin were confirmed by neurobehavioral studies that showed IN insulin-treated FIV-infected animals displayed improved motor and cognitive performance compared to sham-treated FIV-infected animals. Thus, FIV infection of the nervous system provides a valuable comparative in vivo model for discovering and evaluating disease mechanisms as well as developing therapeutic strategies for NeuroAIDS in humans.

IFN-β and multiple sclerosis: from etiology to therapy and back

Several immunomodulatory treatments are currently available for relapsing-remitting forms of multiple sclerosis (RRMS). Interferon beta (IFN) was the first therapeutic intervention able to modify the course of the disease and it is still the most used first-line treatment in RRMS. Though two decades have passed since IFN-β was introduced in the management of MS, it remains a valid approach because of its good benefit/risk profile. This is witnessed by new efforts of pharmaceutical industry to improve this line: a PEGylated form of subcutaneous IFN-β 1a, (Plegridy(®)) with a longer half-life, has been recently approved in RRMS. This review will survey the various stages of the use of type I IFN in MS, with special attention to the effect of the treatment on the supposed viral etiologic factors associated to the disease. The antiviral activities of IFN (that initially prompted its use as immunomodulatory agent in MS), and the mounting evidences in favor of a viral etiology in MS, allowed us to outline a re-appraisal from etiology to therapy and back.

Involvement of IRS-1 interaction with ADAM10 in the regulation of neurite extension

The insulin-like growth factor-1 (IGF-1) signaling pathway plays an important role in neuronal cell differentiation. Recent studies have shown that IGF-1 has the capacity to counteract the retraction of neuronal processes in response to inflammatory cytokines such as TNF-α, which is a known factor for neuronal injury in the central nervous system. This event is thought to be mediated via interference of TNF-α-induced interaction of β1-integrin with insulin receptor substrate-1 (IRS-1). Here, we demonstrate the interaction of IRS-1 with disintegrin and metalloproteinase ADAM10 through the N-terminal domain of IRS-1 and that this is involved in the regulation of neurite extension and retraction by IGF-1 and TNF-α, respectively. PC12 cells expressing the N-terminal domain show enhanced neurite extension after IGF-1 treatment and reduced neurite depletion relative to control cells after TNF-α treatment. The level of ADAM10 was found to be increased in immunohistochemical studies of HIV encephalitis clinical samples and is present with TNF-α and TNFR1 in both astrocytes and neurons. Altogether, these observations suggest a role for ADAM10 in the mechanism for IGF1/IRS-1 signaling pathway in sustaining the stability of neuronal processes.

ROS upregulation during the early phase of retroviral infection plays an important role in viral establishment in the host cell

Recent studies suggest that low levels of reactive oxygen species (ROS) often modulate normal intracellular signalling pathways, determine cell fates and control cell proliferation. We found that infection of astrocytes with the neuropathogenic retrovirus ts1, a mutant of Moloney murine leukemia retrovirus, upregulated ROS at low levels during the early phase of infection. This upregulation of intracellular ROS with downregulation of NADPH levels during the early phase of ts1 infection was a separate event from the upregulation of ROS during the late phase while ts1-mediated cell death occurred. The treatment of apocynin, a potential inhibitor of NADPH oxidase (NOX), inhibited establishment of the ts1 virus in the host cell. These results suggested that ROS generated as a consequence of the activation of NOX may play an important role in the early events of the virus life cycle leading to the establishment of the virus in the host cell. The in vitro results were further supported by an in vivo experiment which showed that the treatment of apocynin decreased viral titre in the ts1-infected mouse brain and increased the lifespan of infected mice. This study provides the first in vitro and in vivo evidence on a mechanism for how ROS are involved in ts1 retrovirus infection and ts1-mediated neurodegenerative disease. Our findings focusing on the early phase of the ts1 retrovirus life cycle could provide a better understanding of retroviral life cycle, which may offer specific therapeutic targets for suppressing viral replication and alleviating neurodegenerative symptoms in a mouse model.

Differential type 1 interferon-regulated gene expression in the brain during AIDS: interactions with viral diversity and neurovirulence

The lentiviruses, human and feline immunodeficiency viruses (HIV-1 and FIV, respectively), infect the brain and cause neurovirulence, evident as neuronal injury, inflammation, and neurobehavioral abnormalities with diminished survival. Herein, different lentivirus infections in conjunction with neural cell viability were investigated, concentrating on type 1 interferon-regulated pathways. Transcriptomic network analyses showed a preponderance of genes involved in type 1 interferon signaling, which was verified by increased expression of the type 1 interferon-associated genes, Mx1 and CD317, in brains from HIV-infected persons (P<0.05). Leukocytes infected with different strains of FIV or HIV-1 showed differential Mx1 and CD317 expression (P<0.05). In vivo studies of animals infected with the FIV strains, FIV(ch) or FIV(ncsu), revealed that FIV(ch)-infected animals displayed deficits in memory and motor speed compared with the FIV(ncsu)- and mock-infected groups (P<0.05). TNF-α, IL-1β, and CD40 expression was increased in the brains of FIV(ch)-infected animals; conversely, Mx1 and CD317 transcript levels were increased in the brains of FIV(ncsu)-infected animals, principally in microglia (P<0.05). Gliosis and neuronal loss were evident among FIV(ch)-infected animals compared with mock- and FIV(ncsu)-infected animals (P<0.05). Lentiviral infections induce type 1 interferon-regulated gene expression in microglia in a viral diversity-dependent manner, representing a mechanism by which immune responses might be exploited to limit neurovirulence.

Human endogenous retroviruses in multiple sclerosis: potential for novel neuro-pharmacological research

There is growing evidence that the env genes of two or more human endogenous retroviruses (HERVs) of the W family are contributing to the inflammatory processes, and thus to the pathogenesis, of multiple sclerosis (MS). Increasing understanding of the human endogenous retroviral locus, ERVWE1, and the putative multiple sclerosis associated retrovirus, or MSRV, and in particular of the HERV-W env sequences associated with these, offers the potential of new lines of pharmacological research that might assist diagnosis, prognosis and therapy of multiple sclerosis.

Moloney murine leukemia virus glyco-gag facilitates xenotropic murine leukemia virus-related virus replication through human APOBEC3-independent mechanisms

BACKGROUND

One of the unique features of gammaretroviruses is that they contain an additional extended form of Gag, glyco-gag, which initiates in the leader sequence. MuLV glyco-gag, gPr80Gag, promotes retrovirus replication and disease progression. Although virtually all infectious MuLVs encode glyco-gag, XMRV (xenotropic murine leukemia virus-related virus) lacks the classical gPr80Gag sequence. We examined XMRV to determine if its leader sequence contains glyco-gag activity, whether the presence of conventional gPr80Gag affects replication of XMRV, and we describe the evolution of glyco-gag-deficient MuLVs in Mus.

RESULTS

We introduced several mutations disrupting two putative but noncanonical glyco-gag proteins in the leader sequence region in XMRV and found that those mutations did not affect virus release nor susceptibility to the antiviral activity of hA3G (human APOBEC3G). A chimeric XMRV encoding the Moloney MuLV (M-MuLV) leader sequence (MXMRV) demonstrated that M-MuLV glyco-gag facilitated MXMRV release and increased infectivity. Infectivity assays with several cell lines showed that glyco-gag increases XMRV infectivity in all cell lines tested, but the level of this increase varies in different cell lines. Because MuLV glyco-gag counteracts mouse APOBEC3, we investigated whether M-MuLV glyco-gag enhances XMRV infection by counteracting human APOBEC3. Comparison of hAPOBEC3 isoforms expressed in different cell lines indicated that hA3B was the most likely candidate for a restrictive hA3. However over-expression of hA3B showed no enhanced restriction of infection by XMRV compared to MXMRV. Endogenous MuLVs in the sequenced mouse genome were screened for canonical glyco-gag, which was identified in two clades of xenotropic MuLVs (X-MuLVs) and ecotropic MuLVs, but not in other X-MuLVs or in any polytropic MuLVs.

CONCLUSIONS

M-MuLV glyco-gag facilitates XMRV replication, and the leader sequence region in XMRV does not encode proteins equivalent to M-MuLV glyco-gag. The fact that the ability of glyco-gag to enhance XMRV infection varies in different cell lines suggests a glyco-gag sensitive restrictive factor that further reduces XMRV infectivity. The M-MuLV glyco-gag enhancement for XMRV replication is through a hAPOBEC3 independent mechanism. The absence of glyco-gag in MuLVs carried by western European mice suggests that loss of this sequence is a relatively recent event with limited subspecies distribution.

Phenylbutyric acid suppresses protein accumulation-mediated ER stress in retrovirus-infected astrocytes and delays onset of paralysis in infected mice

Many neurodegenerative diseases are associated with accumulation of misfolded proteins in cells of the central nervous system (CNS). We have previously reported that accumulation of the precursor envelope protein gPr80(env) of ts1, a mutant of Moloney murine leukemia virus (MoMuLV), in the endoplasmic reticulum (ER) of infected astrocytes, results in ER stress, oxidative stress and cell death, subsequently leading to ts1-mediated neurodegeneration in infected mice. In the present study, we assessed whether treatments that reduce the accumulation of gPr80(env) in the ER of ts1-infected astrocytes provided a protective effect against ER stress and cell death. We show that treatment with phenylbutyric acid (PBA) can prevent the unfolded protein response (UPR), ER stress and cell death in cultured ts1-infected astrocytes. The protective effect of PBA is associated with its ability to reduce gPr80(env) accumulation and to increase the expression of proteins involved in protein folding in the ER, such as protein disulfide isomerase (PDI) and ERp44, rather than by decrease mRNA levels of gPr80(env) or alter the proteasomal degradation process for gPr80(env). In infected mice treated with PBA we also noted a reduction in the severity of the neuropathology in brainstem tissues and a delayed onset of paralysis. These results show that PBA is a potentially effective drug for the treatment of neurodegeneration caused by protein accumulation in cells of the CNS.

Host proteome research in HIV infection

Proteomics has been widely used in the last few years to look for new biomarkers and decipher the mechanism of HIV–host interaction. Herein, we review the recent developments of HIV/AIDS proteomic research, including the samples used in HIV/AIDS related research, the technologies used for proteomic study, the diagnosis biomarkers of HIV-associated disease especially HIV-associated neurocognitive impairment, the mechanisms of HIV–host interaction, HIV-associated dementia, substance abuse, and so on. In the end of this review, we also give some prospects about the limitation and future improvement of HIV/AIDS proteomic research.

Human endogenous retroviruses and multiple sclerosis: innocent bystanders or disease determinants?

Human endogenous retroviruses (HERVs) constitute 5–8% of human genomic DNA and are replication incompetent despite expression of individual HERV genes from different chromosomal loci depending on the specific tissue. Several HERV genes have been detected as transcripts and proteins in the central nervous system, frequently in the context of neuroinflammation. The HERV-W family has received substantial attention in large part because of associations with diverse syndromes including multiple sclerosis (MS) and several psychiatric disorders. A HERV-W-related retroelement, multiple sclerosis retrovirus (MSRV), has been reported in MS patients to be both a biomarker as well as an effector of aberrant immune responses. HERV-H and HERV-K have also been implicated in MS and other neurological diseases but await delineation of their contributions to disease. The HERV-W envelope-encoded glycosylated protein, syncytin-1, is encoded by chromosome 7q21 and exhibits increased glial expression within MS lesions. Overexpression of syncytin-1 in glia induces endoplasmic reticulum stress leading to neuroinflammation and the induction of free radicals, which damage proximate cells. Syncytin-1's receptor, ASCT1 is a neutral amino acid transporter expressed on glia and is suppressed in white matter of MS patients. Of interest, antioxidants ameliorate syncytin-1's neuropathogenic effects raising the possibility of using these agents as therapeutics for neuroinflammatory diseases. Given the multiple insertion sites of HERV genes as complete and incomplete open reading frames, together with their differing capacity to be expressed and the complexities of individual HERVs as both disease markers and bioactive effectors, HERV biology is a compelling area for understanding neuropathogenic mechanisms and developing new therapeutic strategies.

Detection of an infectious retrovirus, XMRV, in blood cells of patients with chronic fatigue syndrome

Chronic fatigue syndrome (CFS) is a debilitating disease of unknown etiology that is estimated to affect 17 million people worldwide. Studying peripheral blood mononuclear cells (PBMCs) from CFS patients, we identified DNA from a human gammaretrovirus, xenotropic murine leukemia virus-related virus (XMRV), in 68 of 101 patients (67%) as compared to 8 of 218 (3.7%) healthy controls. Cell culture experiments revealed that patient-derived XMRV is infectious and that both cell-associated and cell-free transmission of the virus are possible. Secondary viral infections were established in uninfected primary lymphocytes and indicator cell lines after their exposure to activated PBMCs, B cells, T cells, or plasma derived from CFS patients. These findings raise the possibility that XMRV may be a contributing factor in the pathogenesis of CFS.

Effects of interferon-beta therapy on innate and adaptive immune responses to the human endogenous retroviruses HERV-H and HERV-W, cytokine production, and the lectin complement activation pathway in multiple sclerosis

The effects of treatment of multiple sclerosis patients with IFN-beta on elements in the innate and adaptive immune response were analysed in a longitudinal study. We demonstrate significant decreases in anti-Envelope antibody reactivity for the two closely related Gammaretroviral human endogenous retroviruses (HERVs), HERV-H and HERV-W, as a consequence of IFN-beta therapy, closely linked to efficacy of therapy/low disease activity. We also show strong indications of a protective effect of high levels of two components in the innate pathogen-associated molecular pattern recognition: mannan-binding lectin (MBL), and MBL-associated serine protease 3 (MASP-3). Serum levels of typical Th1- and Th2-related, MS-relevant cytokines were also monitored. Overall both Th1- and Th2-associated cytokines were modestly, albeit significantly up-regulated, notably IL-2 and TNF-alpha (MS patients with inactive disease), as well as IL-4 and, to some extent IL-10 (no increase in IL-10 for MS patients with active disease (non-responders)). We found no overall changes in Th1/Th2 ratios. Our results support that HERV-H/HERV-W and the antiviral immune response may play a role in MS development, and that these HERVs have potential as biomarkers for disease activity.

Neurobehavioral performance in feline immunodeficiency virus infection: integrated analysis of viral burden, neuroinflammation, and neuronal injury in cortex

Human immunodeficiency virus (HIV) infection causes motor and neurocognitive abnormalities affecting >50% of children and 20% of adults with HIV/AIDS (acquired immunodeficiency syndrome). The closely related lentivirus, feline immunodeficiency virus (FIV), also causes neurobehavioral deficits. Herein, we investigated the extent to which FIV infection affected specific motor and cognitive tasks in conjunction with viral burden and immune responses within the brain. Neonatal animals were infected with a neurovirulent FIV strain (FIV-Ch) and assessed in terms of systemic immune parameters, viral burden, neurobehavioral performance, and neuropathological features. FIV-infected animals displayed less weight gain and lower blood CD4(+) T-cell levels than mock-infected animals (p < 0.05). Gait analyses disclosed greater gait width with increased variation in FIV-infected animals (p < 0.05). Maze performance showed that FIV-infected animals were slower and made more navigational errors than mock-infected animals (p < 0.05). In the object memory test, the FIV-infected group exhibited fewer successful steps with more trajectory errors compared with the mock-infected group (p < 0.05). Performance on the gait, maze, and object memory tests was inversely correlated with F4/80 and CD3 epsilon expression (p < 0.05) and with viral burden in parietal cortex (p < 0.05). Amino acid analysis in cortex showed that D-serine levels were reduced in FIV-infected animals, which was accompanied by diminished kainate and AMPA receptor subunit expression (p < 0.05). The neurobehavioral findings in FIV-infected animals were associated with increased gliosis and reduced cortical neuronal counts (p < 0.05). The present studies indicated that specific motor and neurocognitive abilities were impaired in FIV infection and that these effects were closely coupled with viral burden, neuroinflammation, and neuronal loss.

Dual lentivirus infection potentiates neuroinflammation and neurodegeneration: viral copassage enhances neurovirulence

Infection by multiple lentiviral strains is recognized as a major driving force in the human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) epidemic, but the neuropathogenic consequences of multivirus infections remain uncertain. Herein, we investigated the neurovirulence and underlying mechanisms of dual lentivirus infections with distinct viral strains. Experimental feline immunodeficiency virus (FIV) infections were performed using cultured cells and an in vivo model of AIDS neuropathogenesis. Dual infections were comprised of two FIV strains (FIV-Ch and FIV-PPR) as copassaged or superinfected viruses, with subsequent outcome analyses of host immune responses, viral load, neuropathological features, and neurobehavioral performance. Dual infections of feline macrophages resulted in greater IL-1beta (interleukin-1beta), TNF-alpha (tumor necrosis factor alpha), and IDO (indoleamine 2,3-dioxygenase) expression and associated neurotoxic properties. FIV coinfection and sequential superinfection in vivo also induced greater IL-1beta, TNF-alpha, and IDO expression in the basal ganglia (BG) and cortex (CTX), compared to the monovirus- and mock-infected groups, although viral loads were similar in single virus- and dual virus-infected animals. Immunoblot analyses disclosed lower synaptophysin immunoreactivity in the CTX resulting from FIV super- and coinfections. Cholinergic and GABAergic neuronal injury was evident in the CTX of animals with dual FIV infections. With increased glial activation and neuronal loss in dual FIV-infected brains, immunohistochemical analysis also revealed elevated detection of cleaved caspase-3 in dysmorphic neurons, which was associated with worsened neurobehavioral abnormalities among animals infected with the copassaged viruses. Dual lentivirus infections caused an escalation in neuroinflammation and ensuing neurodegeneration, underscoring the contribution of infection by multiple viruses to neuropathogenesis.

HIV infection of the central nervous system: clinical features and neuropathogenesis

Almost 65 million people worldwide have been infected with HIV since it was first identified in the early 1980s. Neurologic disorders associated with HIV type 1 affect between 40% and 70% of infected individuals. The most significant of these disorders include HIV-associated neurocognitive disorder, which comprises HIV-associated dementia, mild neurocognitive disorder, and asymptomatic neurocognitive impairment. Despite the availability of combination antiretroviral therapy, HIV-related central nervous system disorders continue to represent a substantial personal, economic, and societal burden. This review summarizes the clinical manifestations, diagnosis, treatment, and pathogenesis of the primary HIV-associated central nervous system disorders.

Comparative expression of human endogenous retrovirus-W genes in multiple sclerosis

Human endogenous retroviruses (HERVs) have been associated with multiple sclerosis (MS) pathogenesis. Several related HERV-W sequences have been implicated in disease occurrence and progression; the MS retrovirus (MSRV) is one such element whose envelope protein has been recently demonstrated to be involved in innate immune pathogenesis. To distinguish MSRV from other HERV-W sequences we analyzed the relative abundance of individual HERV-W env sequences by employing a real-time PCR approach using specific oligonucleotide primers and tissue samples from MS and non-MS patients. Our analyses reveal that ERVWE1 env-encoding DNA and RNA exhibited increased detection (p < 0.05) and expression (p < 0.01) in the brains of MS patients. Similarly, ERVWE1 env transcripts were inducible in glial cells (p < 0.05), while comparable changes in MSRV abundance were not observed. These results indicate that individual HERVs might have distinct roles in MS pathogenesis.

Neurological evaluation of untreated human immunodeficiency virus infected adults in Ethiopia

Human immunodeficiency virus (HIV) has been implicated in neurological complications in developed countries. Developing countries have different viral clades and potentially different genetic and social risks for these complications. Baseline neurological performance measures associated with HIV infection have rarely been available from developing countries. The authors carried our a cross-sectional neurological evaluation of a cohort of community-dwelling treatment-naïve HIV-infected patients and similar control subjects from the same communities in Ethiopia. Blinded evaluation using standardized structured questionnaires and a neurological examination was performed by neurologists and treating physicians trained by an HIV neurology specialist. Quantitative performance measures for cognitive and motor function were employed. Data were analyzed with descriptive statistical methods, standard contingency table methods, and nonparametric methods. HIV-positive and control groups were similar by age, gender, and job site. Participants included 73 HIV-positive and 87 HIV-negative controls. Fingertapping speed in the dominant hand was more poorly performed in HIV positives than negatives (P = .01) and was significantly associated with HIV viral load levels (P = .03). Other quantitative neuropsychiatric tests including timed gait, grooved pegboard, task learning, and animal naming did not show significant differences between the two groups. The overall prevalence of central nervous system (CNS) and/or peripheral nervous system (PNS) disease did not significantly differ in the two populations. HIV patients had slowed fingertapping speed correlating with viral load. Other measures of CNS and/or peripheral nervous performance did not differ from controls. The unanticipated minor evidence of HIV-associated neurocognitive and peripheral nerve deficits in this untreated HIV-positive population invite further investigation.

Proteolytic processing of SDF-1alpha reveals a change in receptor specificity mediating HIV-associated neurodegeneration

Proteolytic cleavage of constitutively expressed proteins can generate peptides with novel bioactive properties. Matrix metalloproteinase (MMP)-2 cleaves the 4 amino-terminal residues of the chemokine, stromal cell-derived factor (SDF)-1alpha, yielding a highly neurotoxic molecule, SDF(5-67), which fails to bind to its cognate receptor, CXCR4. Herein, we detected SDF(5-67) in brain monocytoid cells of HIV-infected persons, particularly in those with HIV-associated dementia. SDF(5-67) activated cell type-specific expression of proinflammatory genes including IL-1beta, TNFalpha, indoleamine 2',3'-dioxygenase (IDO), and IL-10 in both astrocytic and monocytoid cells (P < 0.05). Unlike SDF-1alpha, SDF(5-67) caused neuronal membrane perturbations with ensuing neurotoxicity and apoptosis (P < 0.05) through engagement of an inducible receptor. CXCR3 antagonists and siRNA-mediated knockdown of CXCR3 inhibited SDF(5-67)-stimulated neurophysiological changes, neuronal death, and neuroimmune activation (P < 0.05). Moreover SDF(5-67) bound directly to CXCR3 in a competitive manner, mediated by its amino terminus. In vivo neuroinflammation, neuronal loss, and neurobehavioral abnormalities caused by SDF(5-67) (P < 0.05) were prevented by a CXCR3 antagonist. These studies reveal additive neuropathogenic properties exerted by a proteolytically cleaved chemokine as consequences of a change in receptor specificity, culminating in neurodegeneration.

Quantitative analysis of human endogenous retrovirus-W env in neuroinflammatory diseases

Although human endogenous retroviruses (HERVs) constitute 8% of the human genome, their role(s) in health and disease remain uncertain. Nonetheless, increased HERV gene activity has been reported in neuroinflammatory diseases such as multiple sclerosis (MS). The human endogenous retrovirus (HERV)-W7q envelope gene encodes a glycosylated envelope protein, syncytin-1, which is expressed in many tissues. Analysis of HERV envelopes (env) revealed a selectively increased abundance of syncytin-1 encoding RNA in brains from patients with MS (p<0.01) relative to non-MS patients. However, HERV env expression from blood-derived leukocytes did not differ between groups. A quantitative PCR-based assay for syncytin-1 RNA showed that median viral RNA levels were higher in brains of MS patients (5.0 log10 copies/microg RNA) relative to non-MS patients (4.6 log10 copies/microg RNA) (p<0.05). Median syncytin-1 DNA levels in MS brains (9.8 log10/microg DNA) were higher than non-MS brain tissue (7.9 log10/microg DNA) (p<0.001) without evidence of new integration events. In contrast, there were no differences in syncytin-1 RNA copy numbers between groups in both CSF (non-MS: 5.0 log10/ml versus MS: 3.8 log10/ml) and plasma (non-MS: 5.033 log10/ml versus MS: 2.9 log10/ml). These observations emphasize the selective induction of syncytin-1 in brain tissue of MS patients but also illustrate the complex dynamics of this retroelement in neuroinflammatory processes.

Gene-environment interactions in multiple sclerosis: innate and adaptive immune responses to human endogenous retrovirus and herpesvirus antigens and the lectin complement activation pathway

Aspects of gene-environment interactions in multiple sclerosis (MS) were analysed in serum samples from 46 MS families (25 sporadic MS cases and 42 familial MS cases): antibodies to the MS-associated human endogenous retrovirus HERV-H, and levels of three components in the innate pathogen-associated molecular pattern recognition: mannan-binding lectin (MBL), and MASP-2 and MASP-3. For representative MS families, we also determined herpesvirus serology for HSV-1, VZV, and EBV; and tissue typed for HLA-B, and HLA DR and DQ. In MS, a significant correlation between elevated immune reactivity to HERV-H Env and disease activity was demonstrated, as were indications of a protective effect of high MBL and MASP-3 levels. The HLA alleles B*07, DRB*02, and DQB1*06 were commonly present together in the MS families, both in MS patients, and in unaffected family members. Our results support that HERV-H and the antiviral immune response may play a role in MS development, and also underline the tenuous nature of specific genetic contributions to this complex disease.

Proteinase-activated receptor-2 induction by neuroinflammation prevents neuronal death during HIV infection

Proteinase-activated receptors (PARs), a newly discovered subgroup of G-protein coupled receptors, are widely expressed by neural cells, but their roles in the nervous system remain uncertain. In this study, we report that PAR-2 was up-regulated on neurons in conjunction with neuroinflammation in brain tissue from patients with HIV-1-associated dementia. The inflammatory cytokines TNF-alpha and IL-1beta were also increased in HIV-1-associated dementia brains compared with patients without dementia (p < 0.05), but these same cytokines induced PAR-2 expression on neurons. Enhanced PAR-2 expression and subsequent activation prevented neuronal cell death and induction of the tumor suppressor, p53, caused by the HIV-encoded protein, Tat (p < 0.01). Intrastriatal implantation of a PAR-2 peptide agonist also inhibited Tat-induced neurotoxicity in a mouse model of HIV neuropathogenesis (p < 0.05). Moreover, PAR-2 null animals showed more severe neuroinflammation and neuronal loss caused by Tat neurotoxicity (p < 0.05). TNF-alpha protected wild-type neurons from Tat-related neurotoxicity, but in PAR-2-deficient neurons, the same concentrations of TNF-alpha were cytotoxic (p < 0.001). Thus, neuroinflammation can exert protective effects by which it induces PAR-2 expression with the ensuing abrogation of neuronal death.

Association of human endogenous retroviruses with multiple sclerosis and possible interactions with herpes viruses

The hypothesis that human endogenous retroviruses (HERVs) play a role in autoimmune diseases is subject to increasing attention. HERVs represent both putative susceptibility genes and putative pathogenic viruses in the immune-mediated neurological disease multiple sclerosis (MS). Gammaretroviral HERV sequences are found in reverse transcriptase-positive virions produced by cultured mononuclear cells from MS patients, and they have been isolated from MS samples of plasma, serum and CSF, and characterised to some extent at the nucleotide, protein/enzyme, virion and immunogenic level. Two types of sequences, HERV-H and HERV-W, have been reported. No known HERV-H or HERV-W copy contains complete ORFs in all prerequisite genes, although several copies have coding potential, and several such sequences are specifically activated in MS, apparently resulting in the production of complete, competent virions. Increased antibody reactivity to specific Gammaretroviral HERV epitopes is found in MS serum and CSF, and cell-mediated immune responses have also been reported. Further, HERV-encoded proteins can have neuropathogenic effects. The activating factor(s) in the process resulting in protein or virion production may be members of the Herpesviridae. Several herpes viruses, such as HSV-1, VZV, EBV and HHV-6, have been associated with MS pathogenesis, and retroviruses and herpes viruses have complex interactions. The current understanding of HERVs, and specifically the investigations of HERV activation and expression in MS are the major subjects of this review, which also proposes to synergise the herpes and HERV findings, and presents several possible pathogenic mechanisms for HERVs in MS.

Human endogenous retrovirus glycoprotein–mediated induction of redox reactants causes oligodendrocyte death and demyelination

Human endogenous retroviruses (HERVs) constitute 8% of the human genome and have been implicated in both health and disease. Increased HERV gene activity occurs in immunologically activated glia, although the consequences of HERV expression in the nervous system remain uncertain. Here, we report that the HERV-W encoded glycoprotein syncytin is upregulated in glial cells within acute demyelinating lesions of multiple sclerosis patients. Syncytin expression in astrocytes induced the release of redox reactants, which were cytotoxic to oligodendrocytes. Syncytin-mediated neuroinflammation and death of oligodendrocytes, with the ensuing neurobehavioral deficits, were prevented by the antioxidant ferulic acid in a mouse model of multiple sclerosis. Thus, syncytin's proinflammatory properties in the nervous system demonstrate a novel role for an endogenous retrovirus protein, which may be a target for therapeutic intervention.

Emergence of vertebrate retroviruses and envelope capture

Retroviruses are members of the superfamily of retroelements, mobile genetic elements that transpose via an RNA intermediate. However, retroviruses are distinct from other retroelements in that their "transposition" is not confined to single cells but extends to neighboring cells and organisms. As such, the "transposition" of these elements is defined as infection. It appears that a key step in the conversion of a retrotransposon into a retrovirus is the modular acquisition or capture of an envelope glycoprotein (Env) which facilitates dissemination from its initial host cell. Here we present several examples of retroviruses for which envelope capture has been identified. Indeed, capture may explain the notable conservation of env sequences among otherwise phylogenetically distant retroviruses. In a recent example, sequence homologies reported between the env of the phylogenetically distant murine leukemia viruses (MLV) and human T cell leukemia viruses (HTLV) argue in favor of an env capture by the latter. Env acquisition can provide new adaptive properties to replication-competent viruses in addition to altering their host range. Also, the captured env can alter the spectrum of physiological affects of infection in new host cells and organisms. The elucidation of such envelope exchanges and properties thereof should contribute significantly to the clarification of retroviral phylogeny, insight into retroviral pathogenesis, and to the discovery of new retroviruses.

Growth hormone prevents human immunodeficiency virus-induced neuronal p53 expression

Growth hormone (GH) is neuroprotective, presumably through its actions on GH receptor-mediated pathways. Here, we examined the effects of GH using in vitro and in vivo assays of human immunodeficiency virus (HIV)-induced neuronal injury. Neuronal cultures were in assays of neurotoxicity induced by supernatants from HIV-1 tat-transfected monocytoid cells (Tat supernatant). GH treatment reduced neuronal death compared with untreated cultures (p < 0.001), which was blocked by a GH receptor antagonist, B2036. Tat supernatant-induced p53 expression in neurons was also reduced by GH treatment. Expression of both p53 and GH receptor were increased in brain tissue from HIV-infected persons compared with controls (p < 0.05). Mice receiving intrastriatal implants of Tat supernatant and treated with GH showed less neurobehavioral abnormalities together with reduced neuroinflammation and neuronal injury compared with untreated animals (p < 0.01). Three acquired immunodeficiency syndrome-defined patients with neurocognitive impairment were serially evaluated during daily GH treatment showing a sustained improvement in neuropsychological performance (p < 0.01). GH prevents neuronal death through its actions on neurons involving a p53-mediated pathway and also improved in vivo neurological function, indicating that GH may have a role in the treatment of HIV-induced neurodegeneration.

HIV-induced metalloproteinase processing of the chemokine stromal cell derived factor-1 causes neurodegeneration

The mechanisms of neurodegeneration that result in human immunodeficiency virus (HIV) type 1 dementia have not yet been identified. Here, we report that HIV-infected macrophages secrete the zymogen matrix metalloproteinase-2 (MMP-2), which is activated by exposure to MT1-MMP on neurons. Stromal cell-derived factor 1 alpha (SDF-1), a chemokine overexpressed by astrocytes during HIV infection, was converted to a highly neurotoxic protein after precise proteolytic processing by active MMP-2, which removed the N-terminal tetrapeptide. Implantation of cleaved SDF-1(5-67) into the basal ganglia of mice resulted in neuronal death and inflammation with ensuing neurobehavioral deficits that were abrogated by neutralizing antibodies to SDF-1 and an MMP inhibitor drug. Hence, this study identifies a new in vivo neurotoxic pathway in which cleavage of a chemokine by an induced metalloproteinase results in neuronal apoptosis that leads to neurodegeneration.

Expression of inducible nitric oxide synthase and elevation of tyrosine nitration of a 32-kilodalton cellular protein in brain capillary endothelial cells from rats infected with a neuropathogenic murine leukemia virus

PVC-211 murine leukemia virus (MuLV) is a neuropathogenic variant of Friend MuLV (F-MuLV) which causes a rapidly progressive spongiform neurodegenerative disease in rodents. The primary target of PVC-211 MuLV infection in the brain is the brain capillary endothelial cell (BCEC), which is resistant to F-MuLV infection. Previous studies have shown that changes in the envelope gene of PVC-211 MuLV confer BCEC tropism to the virus. However, little is known about how infection of BCECs by PVC-211 MuLV induces neurological disease. Previous results suggest that nitric oxide (NO), which has been implicated as a potential neurotoxin, is involved in PVC-211 MuLV-induced neurodegeneration. In this study, we show that expression of inducible nitric oxide synthase (iNOS), which produces NO from L-arginine, is induced in BCECs from PVC-211 MuLV-infected rats. Furthermore, elevated levels of a 32-kDa cellular protein modified by 3-nitrotyrosine, which is a hallmark of NO production, were observed in virus-infected BCECs. BCECs from rats infected with BCEC-tropic but nonneuropathogenic PVF-e5 MuLV, which is a chimeric virus between PVC-211 MuLV and F-MuLV, fail to induce either iNOS expression or elevation of tyrosine nitration of a 32-kDa protein. These results suggest that expression of iNOS and nitration of tyrosine residues of a 32-kDa protein in PVC-211 MuLV-infected BCECs may play an important role in neurological disease induction.

Neurovirulence depends on virus input titer in brain in feline immunodeficiency virus infection: evidence for activation of innate immunity and neuronal injury

Lentiruses cause neurological disease depending on the virus strain and its neurotropism, yet it remains uncertain to what the impact of infectious virus quantity in the brain early in infection is on the subsequent development of neurological disease or neurovirulence. We investigated the relationship between infectious virus input titer and the resulting neurovirulence, using ex vivo and in vivo assays of feline immunodeficiency virus (FIV)-induced neurovirulence. FIV infection of cell cultures and neonatal cats was performed using 10(2.5) (low-titer) or 10(4.5) (high-titer) 50% tissue culture infectious doses (TCID(50))/ml of the neurovirulent FIV strain, V1CSF. Ex vivo neurotoxicity assays revealed that conditioned medium (CM) from feline macrophages infected with high-titer (P <.001) or low-titer (P <.01) V1CSF induced greater neuronal death than CM from mock-infected cells. In vivo, animals infected intracranially with high-titer V1CSF showed neurodevelopmental delays compared to mock-infected animals (P <.001) and animals infected with low-titer V1CSF (P <.02), concurrent with reduced weight gains and greater depletion of CD4+ cells over a 12-week period. Neuropathological changes, including astrogliosis, macrophage activation, and neuronal damage, were evident in V1CSF-infected animals and were viral titer dependent. In vivo magnetic resonance (MR) spectroscopy and proton nuclear magnetic resonance ((1)H-NMR) spectroscopy of tissue extracts revealed evidence of neuronal injury, including reduced N-acetyl aspartate/creatine (P <.05) and increased trimethylamine/creatine (P <.05) ratios, in the frontal cortex of high-titer V1CSF-infected animals compared to the other groups. T2-weighted MR imaging detected increased signal intensities in the frontal cortex and white matter of V1CSF-infected animals relative to controls, which was more evident as viral titer increased (P <.01). The present findings indicate that lentivirus infectious titers in the brain during the early stages of infection determine the severity of neurovirulence, reflected by neurobehavioral deficits, together with neuroradiological and neuropathological findings of activation of innate immunity and neuronal injury.

Dendritic spine pathology: cause or consequence of neurological disorders?

Altered dendritic spines are characteristic of traumatized or diseased brain. Two general categories of spine pathology can be distinguished: pathologies of distribution and pathologies of ultrastructure. Pathologies of spine distribution affect many spines along the dendrites of a neuron and include altered spine numbers, distorted spine shapes, and abnormal loci of spine origin on the neuron. Pathologies of spine ultrastructure involve distortion of subcellular organelles within dendritic spines. Spine distributions are altered on mature neurons following traumatic lesions, and in progressive neurodegeneration involving substantial neuronal loss such as in Alzheimer's disease and in Creutzfeldt-Jakob disease. Similarly, spine distributions are altered in the developing brain following malnutrition, alcohol or toxin exposure, infection, and in a large number of genetic disorders that result in mental retardation, such as Down's and fragile-X syndromes. An important question is whether altered dendritic spines are the intrinsic cause of the accompanying neurological disturbances. The data suggest that many categories of spine pathology may result not from intrinsic pathologies of the spiny neurons, but from a compensatory response of these neurons to the loss of excitatory input to dendritic spines. More detailed studies are needed to determine the cause of spine pathology in most disorders and relationship between spine pathology and cognitive deficits.

Progress in clinical neurosciences: The neuropathogenesis of HIV infection: host-virus interaction and the impact of therapy

Despite the availability of highly active antiretroviral therapy (HAART), primary HIV-related neurological diseases remain major problems in HIV clinics. The present review examines the pathogenesis of HIV-related dementia and the less severe minor cognitive and motor deficit, together with distal sensory and drug-induced toxic polyneuropathies. Abnormal host immune responses within the nervous system and the role of viral expression and diversity are emphasized in relation to neurovirulence. Induction of innate immune responses within the central and peripheral nervous systems, largely mediated by cells of macrophage lineage, appear to be common to the development of primary HIV-related neurological disease. Activation of these cell types results in the release of a cascade of inflammatory molecules including cytokines, chemokines, matrix metalloproteinases, and arachidonic acid metabolites that influence neuronal survival. Individual viral proteins encoded by envelope and tat genes and discrete sequences within these genes influence the extent to which these pro-inflammatory molecules are induced. At the same time, systemic immune suppression may influence the occurrence and severity of HIV-related neurological diseases. Implementation of HAART and neuroprotective treatments improves neurological function although the evolution of drug-resistant viral strains limits the sustained benefits of HAART.