HIV-gp120 affects the functional activity of oligodendrocytes and their susceptibility to complement

HIV-induced neuroinflammation inhibits oligodendrocyte maturation via glutamate-dependent activation of the PERK arm of the integrated stress response

Despite combined antiretroviral therapy (cART), HIV-associated neurocognitive disorder (HAND) affects 30-50% of HIV-positive patients. Importantly, persistent white matter pathologies, specifically corpus callosum thinning and disruption of white matter microstructures observed in patients with HAND despite viral control through cART, raise the possibility that HIV infection in the setting of suboptimal cART may perturb oligodendrocyte (OL) maturation, function and/or survival, influencing HAND persistence in the cART era. To examine the effect of HIV infection on OL maturation, we used supernatants of primary human monocyte-derived macrophages infected with HIV (HIV/MDMs) to treat primary cultures of rat oligodendrocyte precursor cells (OPCs) during their differentiation to mature OLs. Using immunostaining for lineage-specific markers, we found that HIV/MDMs significantly inhibited OPC maturation. Based on our previous studies, we examined the potential role of several signaling pathways, including ionotropic glutamate receptors and the integrated stress response (ISR), and found that AMPA receptors (AMPAR)/kainic acid (KA) receptors (KARs) mediated the HIV/MDMs-induced defect in OL maturation. We also found that the treatment of OPC cultures with glutamate or AMPAR/KAR agonists phenocopied this effect. Blocking ISR activation, specifically the PERK arm of the ISR, protected OPCs from HIV/MDMs-mediated inhibition of OL maturation. Further, while glutamate, AMPA, and KA activated the ISR, inhibition of AMPAR/KAR activation prevented ISR induction in OPCs and rescued OL maturation. Collectively, these data identify glutamate signaling via ISR activation as a potential therapeutic pathway to ameliorate white matter pathologies in HAND and highlight the need for further investigation of their contribution to cognitive impairment.

Opioid and neuroHIV Comorbidity - Current and Future Perspectives

With the current national opioid crisis, it is critical to examine the mechanisms underlying pathophysiologic interactions between human immunodeficiency virus (HIV) and opioids in the central nervous system (CNS). Recent advances in experimental models, methodology, and our understanding of disease processes at the molecular and cellular levels reveal opioid-HIV interactions with increasing clarity. However, despite the substantial new insight, the unique impact of opioids on the severity, progression, and prognosis of neuroHIV and HIV-associated neurocognitive disorders (HAND) are not fully understood. In this review, we explore, in detail, what is currently known about mechanisms underlying opioid interactions with HIV, with emphasis on individual HIV-1-expressed gene products at the molecular, cellular and systems levels. Furthermore, we review preclinical and clinical studies with a focus on key considerations when addressing questions of whether opioid-HIV interactive pathogenesis results in unique structural or functional deficits not seen with either disease alone. These considerations include, understanding the combined consequences of HIV-1 genetic variants, host variants, and μ-opioid receptor (MOR) and HIV chemokine co-receptor interactions on the comorbidity. Lastly, we present topics that need to be considered in the future to better understand the unique contributions of opioids to the pathophysiology of neuroHIV. Graphical Abstract Blood-brain barrier and the neurovascular unit. With HIV and opiate co-exposure (represented below the dotted line), there is breakdown of tight junction proteins and increased leakage of paracellular compounds into the brain. Despite this, opiate exposure selectively increases the expression of some efflux transporters, thereby restricting brain penetration of specific drugs.

New Challenges of HIV-1 Infection: How HIV-1 Attacks and Resides in the Central Nervous System

Acquired immunodeficiency syndrome (AIDS) has become one of the most devastating pandemics in recorded history. The main causal agent of AIDS is the human immunodeficiency virus (HIV), which infects various cell types of the immune system that express the CD4 receptor on their surfaces. Today, combined antiretroviral therapy (cART) is the standard treatment for all people with HIV; although it has improved the quality of life of people living with HIV (PLWH), it cannot eliminate the latent reservoir of the virus. Therefore HIV/AIDS has turned from a fatal disease to a chronic disease requiring lifelong treatment. Despite significant viral load suppression, it has been observed that at least half of patients under cART present HIV-associated neurocognitive disorders (HAND), which have been related to HIV-1 infection and replication in the central nervous system (CNS). Several studies have focused on elucidating the mechanism by which HIV-1 can invade the CNS and how it can generate the effects seen in HAND. This review summarizes the research on HIV-1 and its interaction with the CNS with an emphasis on the generation of HAND, how the virus enters the CNS, the relationship between HIV-1 and cells of the CNS, and the effect of cART on these cells.

HIV-1 infection alters energy metabolism in the brain: Contributions to HIV-associated neurocognitive disorders

The brain is particularly sensitive to changes in energy supply. Defects in glucose utilization and mitochondrial dysfunction are hallmarks of nearly all neurodegenerative diseases and are also associated with the cognitive decline that occurs as the brain ages. Chronic neuroinflammation driven by glial activation is commonly implicated as a contributing factor to neurodegeneration and cognitive impairment. Human immunodeficiency virus-1 (HIV-1) disrupts normal brain homeostasis and leads to a spectrum of HIV-associated neurocognitive disorders (HAND). HIV-1 activates stress responses in the brain and triggers a state of chronic neuroinflammation. Growing evidence suggests that inflammatory processes and bioenergetics are interconnected in the propagation of neuronal dysfunction. Clinical studies of people living with HIV and basic research support the notion that HIV-1 creates an environment in the CNS that interrupts normal metabolic processes at the cellular level to collectively alter whole brain metabolism. In this review, we highlight reports of abnormal brain metabolism from clinical studies and animal models of HIV-1. We also describe diverse CNS cell-specific changes in bioenergetics associated with HIV-1. Moreover, we propose that attention should be given to adjunctive therapies that combat sources of metabolic dysfunction as a mean to improve and/or prevent neurocognitive impairments.

Human immunodeficiency virus protein Tat induces oligodendrocyte injury by enhancing outward K+ current conducted by KV1.3

Brain white matter damage is frequently detected in patients infected with human immunodeficiency virus type 1 (HIV-1). White matter is composed of neuronal axons sheathed by oligodendrocytes (Ols), the myelin-forming cells in central nervous system. Ols are susceptible to HIV-1 viral trans-activator of transcription (Tat) and injury of Ols results in myelin sheath damage. It has been demonstrated that activation of voltage-gated K⁺ (K_V) channels induces cell apoptosis and Ols predominantly express K⁺ channel K_V1.3. It is our hypothesis that Tat injures Ols via activation of K_V1.3. To test this hypothesis, we studied the involvement of K_V1.3 in Tat-induced Ol/myelin injury both in vitro and ex vivo. Application of Tat to primary rat Ol cultures enhanced whole-cell K_V1.3 current recorded under voltage clamp configuration and confirmed by specific K_V1.3 antagonists Margatoxin (MgTx) and 5-(4-phenoxybutoxy) psoralen (PAP). The Tat enhancement of K_V1.3 current was associated with Tat-induced Ol apoptosis, which was blocked by MgTx and PAP or by siRNA knockdown of K_V1.3 gene. The Tat-induced Ol injury was validated in cultured rat brain slices, particularly in corpus callosum and striatum, that incubation of the slices with Tat resulted in myelin damage and reduction of myelin basic protein which were also blocked by aforementioned K_V1.3 antagonists. Further studies revealed that Tat interacts with K_V1.3 as determined by protein pull-down of recombinant GST-Tat with K_V1.3 expressed in rat brains and HEK293 cells. Such protein-protein interaction may alter channel protein phosphorylation, resultant channel activity and consequent Ol/myelin injury. Taken together, these results demonstrate an involvement of K_V1.3 in Tat- induced Ol/myelin injury, a potential mechanism for the pathogenesis of HIV-1-associated white matter damage.

Oligodendrocyte Injury and Pathogenesis of HIV-1-Associated Neurocognitive Disorders

Oligodendrocytes wrap neuronal axons to form myelin, an insulating sheath which is essential for nervous impulse conduction along axons. Axonal myelination is highly regulated by neuronal and astrocytic signals and the maintenance of myelin sheaths is a very complex process. Oligodendrocyte damage can cause axonal demyelination and neuronal injury, leading to neurological disorders. Demyelination in the cerebrum may produce cognitive impairment in a variety of neurological disorders, including human immunodeficiency virus type one (HIV-1)-associated neurocognitive disorders (HAND). Although the combined antiretroviral therapy has markedly reduced the incidence of HIV-1-associated dementia, a severe form of HAND, milder forms of HAND remain prevalent even when the peripheral viral load is well controlled. HAND manifests as a subcortical dementia with damage in the brain white matter (e.g., corpus callosum), which consists of myelinated axonal fibers. How HIV-1 brain infection causes myelin injury and resultant white matter damage is an interesting area of current HIV research. In this review, we tentatively address recent progress on oligodendrocyte dysregulation and HAND pathogenesis.

Muscarinic receptor subtypes as potential targets to modulate oligodendrocyte progenitor survival, proliferation, and differentiation

Acetylcholine (ACh) is a major neurotransmitter but also an important signaling molecule in neuron-glia interactions. Expression of ACh receptors has been reported in several glial cell populations, including oligodendrocytes (OLs). Nonetheless, the characterization of muscarinic receptors in these cells, as well as the description of the cholinergic effects at different stages of OL development, is still incomplete. In this study, we characterized the pattern of expression of muscarinic receptor subtypes in primary cultures of rat oligodendrocyte progenitor cells (OPC) and mature OLs, at both mRNA and protein levels. We found that muscarinic receptor expression is developmentally regulated. M1, M3, and M4 receptors were the main subtypes expressed in OPC, whereas all receptor subtypes were expressed at low levels in mature OLs. Exposure of OPC to muscarine enhanced cell proliferation, an effect mainly due to M1, M3, and M4 receptor subtypes as demonstrated by pharmacological competition with selective antagonists. Conversely, M2 receptor activation impaired OPC survival. In line with the mitogenic activity, muscarinic receptor activation increased the expression of platelet derived growth factor receptor α. Muscarine stimulation increased CX32 and myelin basic protein expression, left unaffected that of myelin proteolipid protein (PLP), and decreased member of the family of epidermal growth factor receptor (EGFR) ErbB3/ErbB4 receptor expression indicating a predominant role of muscarinic receptors in OPC. These findings suggest that ACh may contribute to the maintenance of an immature proliferating progenitor pool and impair the progression toward mature stage. This hypothesis is further supported by increased expression of Notch-1 in OL on muscarinic activation.

HIV-1 gp120-induced axonal injury detected by accumulation of β-amyloid precursor protein in adult rat corpus callosum

HIV-1 brain infection induces neurodegeneration. While most studies focus on HIV-1-mediated neuronal injury, relatively few have investigated HIV-1-associated white matter damage. Corpus callosum (CC) is one of frequently involved white matter structures in HIV-1-associated white matter damage. Utilizing a model of ex vivo treatment of brain slice containing CC with HIV-1 glycoprotein 120 (gp120), we examined axonal injury by analyzing β-amyloid precursor protein (β-APP) accumulation in the axon. Incubation of CC slice with gp120 produced a significant higher density of β-APP in the CC tissue compared with non-gp120-treated controls, suggesting the presence of axonal damage in the CC. The gp120-induced CC axonal damage was blocked by a chemokine CXCR4 receptor antagonist T140 but not by an NMDA receptor blocker MK801 as demonstrated by Western blot analysis of β-APP, indicating that gp120 evokes the CC axonal injury through CXCR4 receptor. Immunocytochemical studies revealed a surprisingly high density of CXCR4-positive immunoreactivity in the CC. The CXCR4-positive labeling was distributed along the nerve fibers. Moreover, double labeling of anti-CXCR4 with either anti-neuronal nuclei or anti-myelin/oligodendrocyte-specific protein antibody revealed co-localization of CXCR4 and myelin/oligodendrocytes in some fiber-like structures, inferring that some neurons and oligodendrocytes in the CC express CXCR4. Taken together, these results indicate that gp120 induced axonal damage via CXCR4 in the CC.

White matter changes in HIV-1 infected brains: a combined gross anatomical and ultrastructural morphometric investigation of the corpus callosum

OBJECTIVE

The HIV-1 associated cognitive/motor complex is characterized by cognitive, motor and behavioral disturbances. Besides a significant loss of neurons in the cerebral cortex and subcortical nuclei, a possible morphological substrate of this complex is also given by changes of the white matter as seen in HIV-1 leucoencephalopathy (HIVL), which is characterized by widespread diffuse pallor of myelin and the presence of gliomesenchymal nodules with multinucleated giant cells.

METHODS

The corpus callosum as a sensitive marker for damage of the cerebral white matter was investigated by morphometry both at the macroscopic and electronmicroscopic level.

RESULTS

In HIV-1 infected brains, a significant decrease of the profile area of the whole corpus callosum as well as of its different parts was noted. The absolute number of nerve fibers was significantly decreased, in particular in the frontal and occipital parts of the corpus callosum. Moreover, several morphometric parameters for nerve fibers, axons and myelin sheaths indicate in some areas a reduction of nerve fibers and axons, as well as a diminished myelin sheath thickness, whereas, in other regions, swelling of axons and myelin sheaths was observed.

CONCLUSIONS

The observed changes are considered to represent subtle changes affecting nerve fibers before histological evidence of HIVL, and might represent one aspect of the morphological substrates preceeding the development of the HIV-1 related cognitive/motor complex.

Cellular localization of TRPC3 channel in rat brain: preferential distribution to oligodendrocytes

In the present work we describe the cellular localization of TRPC3 in non-excitable cells as compared to the neurons in normal rat brain. We performed a double labeling study for TRPC3 and one of the following cell-specific markers: mouse anti-glial fibrillary acidic protein (GFAP) for astrocytes; mouse anti-RIP for oligodendrocytes, or mouse anti-OX42 for microglia, or mouse anti-NeUN for neuronal nuclei or mouse anti-tyrosine hydroxylase (TH) for detection of dopaminergic neurons of the substantia nigra. Our double label immunofluorescence study showed that that TRPC3 is mainly localized in oligodendrocytes. These result were confirmed by the electron microscopy study, which showed TRPC3 immunoreactivity in oligodendrocytes. Consistent with the evidence that calcium homeostasis is important to oligodendrocytes for development, myelination, and demyelination [Microsc. Res. Tech. 52 (2001) 672], we can speculate that the distribution of TRPC3 in oligodendrocytes plays a role in myelination and or demyelination processes.

Human immunodeficiency virus infection of the brain: pitfalls in evaluating infected/affected cell populations

Monocyte/macrophages and CD4 T-cells are the primary hematopoietic targets of productive HIV infection. In the brain, potential cellular targets for HIV infection include perivascular and parenchymal macrophages/microglia, oligodendrocytes, endothelia, neurons, and astrocytes. We examine evidence of productive and non-productive infection for each cell type in the brains of HIV-infected patients with and without HIV encephalitis. Despite the voluminous literature and substantial experimental effort over the past two decades, evidence for productive infection of any brain cell other than macrophages is left wanting.

Up-regulation of MAP2e-expressing oligodendrocytes in the white matter of patients with HIV-1 encephalitis

HIV-1 encephalitis (HIVE) is characterized by infection of macrophages and microglial cells, diffuse gliosis, and damage to neuronal populations. The nature of the white matter damage in HIVE remains elusive, and little is known about the status of the oligodendrocyte in HIVE. We have recently described a novel isoform of microtubule-associated protein-2 (MAP2e), which is expressed transiently in developing oligodendrocytes during myelination, and in remyelinating oligodendrocytes in multiple sclerosis lesions. In this study, we tested the hypothesis that MAP2e expression would be increased in the white matter of HIVE. We analysed brain sections from patients with HIVE and controls (HIV+ and HIV-) by immunocytochemistry and found that MAP2e+ cells are significantly increased in HIVE (range, 5-167 cells per cm2) compared to controls (range, 1-25 cells per cm2). MAP2e+ cells were negative for GFAP, CD68, LN3, RCA-1, von Willebrand factor and HIV-1 p24, but positive for MBP or Luxol-Fast Blue, supporting their oligodendroglial lineage. A topographical association between MAP2e and HIV-1 p24 expression was noted, but not between MAP2e and beta-APP, a marker of damaged axons. Our results demonstrate that MAP2e can serve as a marker of white matter damage in HIVE and support the notion that oligodendrocyte damage/repair occurs during HIV-1 infection.

HIV-1 and the brain: connections between HIV-1-associated dementia, neuropathology and neuroimmunology

AIDS patients frequently exhibit neurological disorders due to the neurotoxic events that result from HIV-1 and/or opportunistic infections in the brain. This review examines recent clinical findings related to HIV-1-associated dementia, and outlines current areas of basic research that may clarify how HIV-1-associated encephalopathy produces clinical symptoms of brain dysfunction.

Calcium signalling in cells of oligodendroglial lineage

Intracellular Ca2+ is the key signal that regulates the efficacy of neurotransmitter release and synaptic plasticity in neurons but is also an important second messenger involved in the signal transduction and modulation of gene expression in both excitable and non-excitable cells. Glial cells, including cells of oligodendroglial (OLG) lineage, are capable of responding to extracellular stimuli via changes in the intracellular Ca2+. This review article focuses on the mechanisms of Ca2+ signalling in cells of OLG lineage with the goal of providing the basis for understanding the relevance of receptor- and non-receptor-mediated signalling to oligodendroglial development, myelination, and demyelination. Conclusions to date indicate that cells of OLG lineage exhibit remarkable plasticity with regard to the expression of ion channels and receptors linked to Ca2+ signalling and that perturbation of [Ca2](i) homeostasis contributes to the pathogenesis of demyelinating diseases.