Cortical neurons are a prominent source of the proinflammatory cytokine osteopontin in HIV-associated neurocognitive disorders

Advanced Biomarkers of Hepatotoxicity in Psychiatry: A Narrative Review and Recommendations for New Psychoactive Substances

One of the factors that increase the effectiveness of the pharmacotherapy used in patients abusing various types of new psychoactive substances (NPSs) is the proper functioning of the liver. However, the articles published to date on NPS hepatotoxicity only address non-specific hepatic parameters. The aim of this manuscript was to review three advanced markers of hepatotoxicity in psychiatry, namely, osteopontin (OPN), high-mobility group box 1 protein (HMGB1) and glutathione dehydrogenase (GDH, GLDH), and, on this basis, to identify recommendations that should be included in future studies in patients abusing NPSs. This will make it possible to determine whether NPSs do indeed have a hepatotoxic effect or whether other factors, such as additional substances taken or hepatitis C virus (HCV) infection, are responsible. NPS abusers are at particular risk of HCV infection, and for this reason, it is all the more important to determine what factors actually show a hepatotoxic effect in them.

Localized microglia dysregulation impairs central nervous system myelination in development

Myelination of neuronal axons is a critical aspect of central nervous system development and function. However, the fundamental cellular and molecular mechanisms influencing human developmental myelination and its failure are not fully understood. Here, we used digital spatial transcriptomics of a rare bank of human developing white matter to uncover that a localized dysregulated innate immune response is associated with impeded myelination. We identified that poorly myelinating areas have a distinct signature of Type II interferon signalling in microglia/macrophages, relative to adjacent myelinating areas. This is associated with a surprising increase in mature oligodendrocytes, which fail to form myelin processes appropriately. We functionally link these findings by showing that conditioned media from interferon-stimulated microglia is sufficient to dysregulate myelin process formation by oligodendrocytes in culture. We identify the Type II interferon inducer, Osteopontin (SPP1), as being upregulated in poorly myelinating brains, indicating a potential biomarker. Our results reveal the importance of microglia-mature oligodendrocyte interaction and interferon signaling in regulating myelination of the developing human brain.

Morphine suppresses peripheral responses and transforms brain myeloid gene expression to favor neuropathogenesis in SIV infection

The twin pandemics of opioid abuse and HIV infection can have devastating effects on physiological systems, including on the brain. Our previous work found that morphine increased the viral reservoir in the brains of treated SIV-infected macaques. In this study, we investigated the interaction of morphine and SIV to identify novel host-specific targets using a multimodal approach. We probed systemic parameters and performed single-cell examination of the targets for infection in the brain, microglia and macrophages. Morphine treatment created an immunosuppressive environment, blunting initial responses to infection, which persisted during antiretroviral treatment. Antiretroviral drug concentrations and penetration into the cerebrospinal fluid and brain were unchanged by morphine treatment. Interestingly, the transcriptional signature of both microglia and brain macrophages was transformed to one of a neurodegenerative phenotype. Notably, the expression of osteopontin, a pleiotropic cytokine, was significantly elevated in microglia. This was especially notable in the white matter, which is also dually affected by HIV and opioids. Increased osteopontin expression was linked to numerous HIV neuropathogenic mechanisms, including those that can maintain a viral reservoir. The opioid morphine is detrimental to SIV/HIV infection, especially in the brain.

Osteopontin/secreted phosphoprotein-1 harnesses glial-, immune-, and neuronal cell ligand-receptor interactions to sense and regulate acute and chronic neuroinflammation

Osteopontin (OPN) also known by its official gene designation secreted phosphoprotein-1 (SPP1) is a fascinating, multifunctional protein expressed in a number of cell types that functions not only in intercellular communication, but also in the extracellular matrix (ECM). OPN/SPP1 possesses cytokine, chemokine, and signal transduction functions by virtue of modular structural motifs that provide interaction surfaces for integrins and CD44-variant receptors. In humans, there are three experimentally verified splice variants of OPN/SPP1 and CD44's ten exons are also alternatively spiced in a cell/tissue-specific manner, although very little is known about how this is regulated in the central nervous system (CNS). Post-translational modifications of phosphorylation, glycosylation, and localized cleavage by specific proteases in the cells and tissues where OPN/SPP1 functions, provides additional layers of specificity. However, the former make elucidating the exact molecular mechanisms of OPN/SPP1 function more complex. Flexibility in OPN/SPP1 structure and its engagement with integrins having the ability to transmit signals in inside-out and outside-in direction, is likely why OPN/SPP1 can serve as an early detector of inflammation and ongoing tissue damage in response to cancer, stroke, traumatic brain injury, pathogenic infection, and neurodegeneration, processes that impair tissue homeostasis. This review will focus on what is currently known about OPN/SPP1 function in the brain.

The Role of Osteopontin in Microglia Biology: Current Concepts and Future Perspectives

The innate immune landscape of the central nervous system (CNS), including the brain and the retina, consists of different myeloid cell populations with distinct tasks to fulfill. Whereas the CNS borders harbor extraparenchymal CNS-associated macrophages whose main duty is to build up a defense against invading pathogens and other damaging factors from the periphery, the resident immune cells of the CNS parenchyma and the retina, microglia, are highly dynamic cells with a plethora of functions during homeostasis and disease. Therefore, microglia are constantly sensing their environment and closely interacting with surrounding cells, which is in part mediated by soluble factors. One of these factors is Osteopontin (OPN), a multifunctional protein that is produced by different cell types in the CNS, including microglia, and is upregulated in neurodegenerative and neuroinflammatory conditions. In this review, we discuss the current literature about the interaction between microglia and OPN in homeostasis and several disease entities, including multiple sclerosis (MS), Alzheimer’s and cerebrovascular diseases (AD, CVD), amyotrophic lateral sclerosis (ALS), age-related macular degeneration (AMD) and diabetic retinopathy (DR), in the context of the molecular pathways involved in OPN signaling shaping the function of microglia. As nearly all CNS diseases are characterized by pathological alterations in microglial cells, accompanied by the disturbance of the homeostatic microglia phenotype, the emergence of disease-associated microglia (DAM) states and their interplay with factors shaping the DAM-signature, such as OPN, is of great interest for therapeutical interventions in the future.

The Yin-Yang of osteopontin in nervous system diseases: damage versus repair

Osteopontin is a broadly expressed pleiotropic protein, and is attracting increased attention because of its role in the pathophysiology of several inflammatory, degenerative, autoimmune, and oncologic diseases. In fact, in the last decade, several studies have shown that osteopontin contributes to tissue damage not only by recruiting harmful inflammatory cells to the site of lesion, but also increasing their survival. The detrimental role of osteopontin has been indeed well documented in the context of different neurological conditions (i.e., multiple sclerosis, Parkinson's, and Alzheimer's diseases). Intriguingly, recent findings show that osteopontin is involved not only in promoting tissue damage (the Yin), but also in repair/regenerative mechanisms (the Yang), mostly triggered by the inflammatory response. These two apparently discordant roles are partly related to the presence of different functional domains in the osteopontin molecule, which are exposed after thrombin or metalloproteases cleavages. Such functional domains may in turn activate intracellular signaling pathways and mediate cell-cell and cell-matrix interactions. This review describes the current knowledge on the Yin and Yang features of osteopontin in nervous system diseases. Understanding the mechanisms behind the Yin/Yang would be relevant to develop highly specific tools targeting this multifunctional protein.

Osteopontin/secreted phosphoprotein-1 behaves as a molecular brake regulating the neuroinflammatory response to chronic viral infection

BACKGROUND

Osteopontin (OPN) as a secreted signaling protein is dramatically induced in response to cellular injury and neurodegeneration. Microglial inflammatory responses in the brain are tightly associated with the neuropathologic hallmarks of neurodegenerative disease, but understanding of the molecular mechanisms remains in several contexts poorly understood.

METHODS

Micro-positron emission tomography (PET) neuroimaging using radioligands to detect increased expression of the translocator protein (TSPO) receptor in the brain is a non-invasive tool used to track neuroinflammation in living mammals.

RESULTS

In humanized, chronically HIV-infected female mice in which OPN expression was knocked down with functional aptamers, uptake of TSPO radioligand DPA-713 was markedly upregulated in the cortex, olfactory bulb, basal forebrain, hypothalamus, and central grey matter compared to controls. Microglia immunoreactive for Iba-1 were more abundant in some HIV-infected mice, but overall, the differences were not significant between groups. TSPO+ microglia were readily detected by immunolabeling of post-mortem brain tissue and unexpectedly, two types of neurons also selectively stained positive for TSPO. The reactive cells were the specialized neurons of the cerebellum, Purkinje cells, and a subset of tyrosine hydroxylase-positive neurons of the substantia nigra.

CONCLUSIONS

In female mice with wild-type levels of osteopontin, increased levels of TSPO ligand uptake in the brain was seen in animals with the highest levels of persistent HIV replication. In contrast, in mice with lower levels of osteopontin, the highest levels of TSPO uptake was seen, in mice with relatively low levels of persistent infection. These findings suggest that osteopontin may act as a molecular brake regulating in the brain, the inflammatory response to HIV infection.

Osteopontin and Integrin Mediated Modulation of Post-Synapses in HIV Envelope Glycoprotein Exposed Hippocampal Neurons

The advent of Human Immunodeficiency Virus (HIV) antiretrovirals have reduced the severity of HIV related neurological comorbidities but they nevertheless remain prevalent. Synaptic degeneration due to the action of several viral factors released from infected brain myeloid and glia cells and inflammatory cytokines has been attributed to the manifestation of a range of cognitive and behavioral deficits. The contributions of specific pro-inflammatory factors and their interplay with viral factors in the setting of treatment and persistence are incompletely understood. Exposure of neurons to chemokine receptor-4(CXCR4)-tropic HIV-1 envelope glycoprotein (Env) can lead to post-synaptic degradation of dendritic spines. The contribution of members of the extracellular matrix (ECM) and specifically, of perineuronal nets (PNN) toward synaptic degeneration, is not fully known, even though these structures are found to be disrupted in post-mortem HIV-infected brains. Osteopontin (Opn, gene name SPP1), a cytokine-like protein, is found in abundance in the HIV-infected brain. In this study, we investigated the role of Opn and its ECM integrin receptors, β1- and β3 integrin in modifying neuronal synaptic sculpting. We found that in hippocampal neurons incubated with HIV-1 Env protein and recombinant Opn, post-synaptic-95 (PSD-95) puncta were significantly increased and distributed to dendritic spines when compared to Env-only treated neurons. This effect was mediated through β3 integrin, as silencing of this receptor abrogated the increase in post-synaptic spines. Silencing of β1 integrin, however, did not block the increase of post-synaptic spines in hippocampal cultures treated with Opn. However, a decrease in the PNN to βIII-tubulin ratio was found, indicating an increased capacity to support spine growth. From these results, we conclude that one of the mechanisms by which Opn counters the damaging impact of the HIV Env protein on hippocampal post-synaptic plasticity is through complex interactions between Opn and components of the ECM which activate downstream protective signaling pathways that help maintain the potential for effective post-synaptic plasticity.

The Role of Osteopontin in Amyotrophic Lateral Sclerosis: A Systematic Review

Context: Osteopontin (OPN) is a matrix phosphoprotein expressed by a variety of tissues and cells, including the immune system and the nervous system. Previous studies have shown that OPN may have a role in neurodegenerative diseases, including multiple sclerosis, Parkinson’s disease, and Alzheimer’s disease. Objectives: The present study aimed to systematically review studies investigating the role of OPN in amyotrophic lateral sclerosis (ALS) patients or the disease animal model. Evidence Acquisition: We searched the Cochrane Library, PubMed, Web of Science, and Scopus to find relevant articles published up to January 20, 2019. Both human and animal model studies of ALS were considered. Results: A total of nine articles (four human studies and five animal model studies) were included. Two of the human studies reported that the CSF levels of OPN were higher among ALS patients compared to controls. The other two human studies found that OPN levels in cortical neurons did not differ significantly between ALS cases and the non-neurological control group. One of the studies found that the expression level of OPN in astrocytes was similar between ALS patients and the control group, but the level of microglial OPN significantly increased in ALS cases. Four of the animal model studies reported that the expression of OPN mRNA in spinal cord microglia significantly increased during the disease progression. The remaining animal model study found that OPN was selectively expressed by fast fatigue-resistant and slow motor neurons (MNs), which are resistant to ALS, and that the OPN expression was low among fast-fatigable MNs. Conclusions: Prompt microglial activation is a hallmark pathology of ALS, and OPN is among the most widely expressed proteins by these activated glial cells. Therefore, OPN might have a role in ALS pathogenesis. The existing evidence is not sufficient to justify whether OPN has a neurotoxic or neuroprotective role in ALS. We encourage researchers to investigate the role of OPN in ALS pathogenesis more extensively.

Neuronal and microglial localization of secreted phosphoprotein 1 (osteopontin) in intact and damaged motor cortex of macaques

We previously reported that mRNA encoding secreted phosphoprotein 1 (SPP1), also known as osteopontin, is preferentially expressed in large neurons in layer V of the macaque motor cortex, most of which are presumed to be corticospinal tract neurons. As a first step to elucidating the cellular function of SPP1 in macaque neurons, we examined the localization of SPP1 in the primary motor cortex (M1) of the macaque by using immunohistochemistry. SPP1 immunoreactivity was found to be localized in the cell bodies of neurons, but not outside the cells, indicating that SPP1 was not secreted from these neurons. The results of electron microscope analysis and double-labeling analysis with marker proteins suggested that SPP1 was localized in the mitochondria of neurons. The distributions of SPP1 in the neurons corresponded to those of integrin αV, a putative receptor for SPP1. The distribution of SPP1 was also investigated in macaques whose M1 had been lesioned. We found that SPP1 was secreted by proliferated microglia in the lesioned area. Double-labeling analysis indicated that SPP1 immunoreactivity in the microglia was colocalized with CD44, another putative receptor for SPP1. Success rates in the small-object-retrieval task were positively correlated with SPP1 immunoreactivity in the neurons in the perilesional area. SPP1 has multiple roles in the macaque motor cortex, and it may be a key protein during recovery of hand movement after brain damage.

Immune Activation, Inflammation, and Non-AIDS Co-Morbidities in HIV-Infected Patients under Long-Term ART

Despite effective antiretroviral therapy (ART), people living with HIV (PLWH) still present persistent chronic immune activation and inflammation. This condition is the result of several factors including thymic dysfunction, persistent antigen stimulation due to low residual viremia, microbial translocation and dysbiosis, caused by the disruption of the gut mucosa, co-infections, and cumulative ART toxicity. All of these factors can create a vicious cycle that does not allow the full control of immune activation and inflammation, leading to an increased risk of developing non-AIDS co-morbidities such as metabolic syndrome and cardiovascular diseases. This review aims to provide an overview of the most recent data about HIV-associated inflammation and chronic immune exhaustion in PLWH under effective ART. Furthermore, we discuss new therapy approaches that are currently being tested to reduce the risk of developing inflammation, ART toxicity, and non-AIDS co-morbidities.

Osteopontin counters human immunodeficiency virus type 1-induced impairment of neurite growth through mammalian target of rapamycin and beta-integrin signaling pathways

Despite the fact that human immunodeficiency virus type 1 (HIV-1) does not enter or replicate in neurons, its infection of a subset of resident brain glia cells (microglia and astrocytes) induces via disparate mechanisms, dysregulation of glutamate metabolism, neurotoxicity, and inflammation. Antiretroviral therapies suppress viral load, but cellular activation and release of proinflammatory factors, some of which is likely related to viral reservoirs, continue to promote a microenvironment that is injurious to neurons. However, the molecular mechanisms remain to be identified. Osteopontin (OPN) is a proinflammatory cytokine-like, extracellular matrix protein that is elevated within the brain and CSF in several neurodegenerative disorders, including HIV-associated cognitive disorder. However, the impact of elevated OPN on neuronal integrity and function in HIV-infected individuals who exhibit cognitive dysfunction remains unknown. In this study, using a neuronal cell line and primary cultures of cortical rat neurons, we identify the mammalian target of rapamycin pathway involvement in a signaling interaction between OPN-β1-integrins and the HIV-1 envelope glycoprotein, which stimulates neurite growth. These findings link for the first time HIV X4-envelope receptor engagement and osteopontin-mediated signaling through β1-integrin receptors to the mTOR pathway and alterations in the cytoskeleton of cortical neurons.

HIV-1-associated neurocognitive disorder: epidemiology, pathogenesis, diagnosis, and treatment

The modern antiretroviral treatment of human immunodeficiency virus (HIV-1) infection has considerably lowered the incidence of opportunistic infections. With the exception of the most severe dementia manifestations, the incidence and prevalence of HIV-associated neurocognitive disorders (HAND) have not decreased, and HAND continues to be relevant in daily clinical practice. Now, HAND occurs in earlier stages of HIV infection, and the clinical course differs from that before the widespread use of combination antiretroviral treatment (cART). The predominant clinical feature is a subcortical dementia with deficits in the domains concentration, attention, and memory. Motor signs such as gait disturbance and impaired manual dexterity have become less prominent. Prior to the advent of cART, the cerebral dysfunction could at least partially be explained by the viral load and by virus-associated histopathological findings. In subjects where cART has led to undetectable or at least very low viral load, the pathogenic virus-brain interaction is less direct, and an array of poorly understood immunological and probably toxic phenomena are discussed. This paper gives an overview of the current concepts in the field of HAND and provides suggestions for the diagnostic and therapeutic management.

Osteopontin facilitates West Nile virus neuroinvasion via neutrophil "Trojan horse" transport

West Nile virus (WNV) can cause severe human neurological diseases including encephalitis and meningitis. The mechanisms by which WNV enters the central nervous system (CNS) and host-factors that are involved in WNV neuroinvasion are not completely understood. The proinflammatory chemokine osteopontin (OPN) is induced in multiple neuroinflammatory diseases and is responsible for leukocyte recruitment to sites of its expression. In this study, we found that WNV infection induced OPN expression in both human and mouse cells. Interestingly, WNV-infected OPN deficient (Opn ^-/-) mice exhibited a higher survival rate (70%) than wild type (WT) control mice (30%), suggesting OPN plays a deleterious role in WNV infection. Despite comparable levels of viral load in circulating blood cells and peripheral organs in the two groups, WNV-infected polymorphonuclear neutrophil (PMN) infiltration and viral burden in brain of Opn ^-/- mice were significantly lower than in WT mice. Importantly, intracerebral administration of recombinant OPN into the brains of Opn ^-/- mice resulted in increased WNV-infected PMN infiltration and viral burden in the brain, which was coupled to increased mortality. The overall results suggest that OPN facilitates WNV neuroinvasion by recruiting WNV-infected PMNs into the brain.

Spatiotemporal expression of osteopontin in the striatum of rats subjected to the mitochondrial toxin 3-nitropropionic acid correlates with microcalcification

Our aim was to elucidate whether osteopontin (OPN) is involved in the onset of mineralisation and progression of extracellular calcification in striatal lesions due to mitochondrial toxin 3-nitropropionic acid exposure. OPN expression had two different patterns when observed using light microscopy. It was either localised to the Golgi complex in brain macrophages or had a small granular pattern scattered in the affected striatum. OPN labelling tended to increase in number and size over a 2-week period following the lesion. Ultrastructural investigations revealed that OPN is initially localised to degenerating mitochondria within distal dendrites, which were then progressively surrounded by profuse OPN on days 7–14. Electron probe microanalysis of OPN-positive and calcium-fixated neurites indicated that OPN accumulates selectively on the surfaces of degenerating calcifying dendrites, possibly via interactions between OPN and calcium. In addition, 3-dimensional reconstruction of OPN-positive neurites revealed that they are in direct contact with larger OPN-negative degenerating dendrites rather than with fragmented cell debris. Our overall results indicate that OPN expression is likely to correlate with the spatiotemporal progression of calcification in the affected striatum, and raise the possibility that OPN may play an important role in the initiation and progression of microcalcification in response to brain insults.

Understanding the MIND phenotype: macrophage/microglia inflammation in neurocognitive disorders related to human immunodeficiency virus infection

Tissue macrophages play important roles in maintaining homeostasis in most organs of the body including the brain where microglia represent the resident phagocytic cells of this compartment. The possibility of one day harnessing macrophage plasticity to treat or ameliorate disorders including obesity, cancer, organ damage, intestinal disorders, neurodegeneration, and cardiovascular disease in which these cells play a role, is a very exciting prospect. Inflammatory signaling is required for regenerative repair, healing, and pathogen clearance functions. However, when the inflammatory response persists in a chronic fashion over an extended period of time, damage to neurons is followed by neuronal injury and dysfunction. Macrophages in the brain are heterogeneous arising from tissues during embryogenesis, and in the adult, from bone marrow derived monocytes that enter through the blood-brain-barrier. While much of our insight regarding macrophage functional subtypes has been garnered through elegant studies in mice, which are amenable to genetic manipulation, far less is known about such cells in human tissues, and particularly in the brain under normal, disease, or injurious conditions. In this regard, non-human primate models for human immunodeficiency virus have been extremely useful for understanding the contribution of bone marrow-derived monocytes in neurological disease and their interaction and impact on the activation state of resident microglia in the brain. This review will focus on what has been learned from the rhesus macaque models about the types of macrophages present in the brains of animals with encephalitis. In vitro studies, which have used human blood monocytes differentiated into macrophages to address the question of macrophage subsets in HIV infection will be highlighted. Recent insights on macrophage phenotype and persistent inflammation in the brain in HIV-associated neurocognitive disorder from immunohistochemical studies on human autopsy tissue will be examined.