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

Comprehensive analyses identify potential biomarkers for encephalitis in HIV infection

Human immunodeficiency virus encephalitis (HIVE) is a severe neurological complication after HIV infection. Evidence shows that genetic factors play an important role in HIVE. The aim of the present study was to identify new potential therapeutic targets for HIVE. Differentially expressed gene (DEG), functional annotation and pathway, and protein-protein interaction analyses were performed to identify the hub genes associated with HIVE. Gene co-expression analysis was carried out to confirm the association between the hub genes and HIVE. Finally, the role of the hub genes in HIVE therapy was evaluated by conducting drug-gene interaction analysis. A total of 20 overlapping DEGs closely related to HIVE were identified. Functional annotation and pathway enrichment analysis indicated that the markedly enriched DEG terms included ion transport, type II interferon signaling, and synaptic signaling. Moreover, protein-protein interaction analysis revealed that 10 key HIVE-related genes were hub genes, including SCN8A, CDK5R2, GRM5, SCN2B, IFI44L, STAT1, SLC17A7, ISG15, FGF12, and FGF13. Furthermore, six hub genes were co-expressed with HIVE-associated host genes in human brain tissue. Finally, three hub genes (STAT1, ISG15, and SCN2B) interacted with several inflammation-associated drugs. These findings suggested that SCN8A, CDK5R2, GRM5, SCN2B, IFI44L, STAT1, SLC17A7, ISG15, FGF12, and FGF13 may be new targets for diagnosis and therapy of HIVE.

Clinical neuropathology practice guide 5-2013: markers of neuronal maturation

This review surveys immunocytochemical and histochemical markers of neuronal lineage for application to tissue sections of fetal and neonatal brain. They determine maturation of individual nerve cells as the tissue progresses to mature architecture. From a developmental perspective, neuronal markers are all about timing. These diverse cellular labels may be classified in two ways: 1) time of onset of expression (early; intermediate; late); 2) labeling of subcellular structures or metabolic functions (nucleoproteins; synaptic vesicle proteins; enolases; cytoskeletal elements; calcium-binding; nucleic acids; mitochondria). Apart from these positive markers of maturation, other negative markers are expressed in primitive neuroepithelial cells and early stages of neuroblast maturation, but no longer are demonstrated after initial stages of maturation. These examinations are relevant for studies of normal neuroembryology at the cellular level. In fetal and perinatal neuropathology they provide control criteria for application to malformations of the brain, inborn metabolic disorders and acquired fetal insults in which neuroblastic maturation may be altered. Disorders, in which cells differentiate abnormally, as in tuberous sclerosis and hemimegalencephaly, pose another yet aspect of mixed cellular lineage. The measurement in living patients, especially neonates, of serum and CSF levels of enolases, chromogranins and S-100 proteins as biomarkers of brain damage may potentially be correlated with their corresponding tissue markers at autopsy in infants who do not survive. The neuropathological markers here described can be performed in ordinary hospital laboratories, not just research facilities, and offer another dimension of diagnostic precision in interpreting abnormally developed fetal and postnatal brains.

Systems analysis of human brain gene expression: mechanisms for HIV-associated neurocognitive impairment and common pathways with Alzheimer's disease

Background

Human Immunodeficiency Virus-1 (HIV) infection frequently results in neurocognitive impairment. While the cause remains unclear, recent gene expression studies have identified genes whose transcription is dysregulated in individuals with HIV-association neurocognitive disorder (HAND). However, the methods for interpretation of such data have lagged behind the technical advances allowing the decoding genetic material. Here, we employ systems biology methods novel to the field of NeuroAIDS to further interrogate extant transcriptome data derived from brains of HIV + patients in order to further elucidate the neuropathogenesis of HAND. Additionally, we compare these data to those derived from brains of individuals with Alzheimer’s disease (AD) in order to identify common pathways of neuropathogenesis.

Methods

In Study 1, using data from three brain regions in 6 HIV-seronegative and 15 HIV + cases, we first employed weighted gene co-expression network analysis (WGCNA) to further explore transcriptome networks specific to HAND with HIV-encephalitis (HIVE) and HAND without HIVE. We then used a symptomatic approach, employing standard expression analysis and WGCNA to identify networks associated with neurocognitive impairment (NCI), regardless of HIVE or HAND diagnosis. Finally, we examined the association between the CNS penetration effectiveness (CPE) of antiretroviral regimens and brain transcriptome. In Study 2, we identified common gene networks associated with NCI in both HIV and AD by correlating gene expression with pre-mortem neurocognitive functioning.

Results

Study 1: WGCNA largely corroborated findings from standard differential gene expression analyses, but also identified possible meta-networks composed of multiple gene ontology categories and oligodendrocyte dysfunction. Differential expression analysis identified hub genes highly correlated with NCI, including genes implicated in gliosis, inflammation, and dopaminergic tone. Enrichment analysis identified gene ontology categories that varied across the three brain regions, the most notable being downregulation of genes involved in mitochondrial functioning. Finally, WGCNA identified dysregulated networks associated with NCI, including oligodendrocyte and mitochondrial functioning. Study 2: Common gene networks dysregulated in relation to NCI in AD and HIV included mitochondrial genes, whereas upregulation of various cancer-related genes was found.

Conclusions

While under-powered, this study identified possible biologically-relevant networks correlated with NCI in HIV, and common networks shared with AD, opening new avenues for inquiry in the investigation of HAND neuropathogenesis. These results suggest that further interrogation of existing transcriptome data using systems biology methods can yield important information.

Cannabinoid receptor expression in HIV encephalitis and HIV-associated neuropathologic comorbidities

AIMS

Cannabinoids have been proposed for treating various neurodegenerative disorders and as adjunct therapy for HIV+ patients with neurologic sequelae. The expression of cannabinoid receptors (CB1 and CB2) has been reported in neurodegenerative diseases and in simian immunodeficiency virus encephalitis, yet the receptor expression in the central nervous system of HIV+ individuals is not known.

METHODS

An anti-CB1 antibody and two anti-CB2 antibodies were employed for immunohistochemistry in the cerebral cortex and white matter of HIV encephalitis (HIVE) and HIV-associated comorbidities, as well as control brains (HIV- and HIV+).

RESULTS

By quantitative image analysis, we observed that CB1 was increased in HIVE brains and those with comorbidities, while CB2 was significantly increased in the white matter of HIVE. Morphologically, CB1 was present in neurones, and both CB1 and CB2 were present in meningeal macrophages and subpial glia in all brains. In HIVE, CB1 was found in white matter microglia and perivascular cells, while CB2 was increased in microglia, astrocytes and perivascular macrophages. Double immunofluorescence with cell-specific markers and immunoblots on primary cultured microglia and astrocytes substantiated the glial localization of the cannabinoid receptors and specificity of the antibodies.

CONCLUSIONS

Our study indicates that cannabinoid receptor expression occurs in glia in HIVE brains, and this may have ramifications for the potential use of cannabinoid ligands in HIV-infected patients.

Aspartoacylase deficiency in the white matter of human immunodeficiency virus encephalitis: novel mechanism in axonal damage

Aspartoacylase/aminoacylase II (ASPA/ACY II) is mainly synthesized in oligodendrocytes to contribute in myelin synthesis. Although axonal damage is seen in the brain with human immunodeficiency virus encephalitis (HIVE), ASPA contribution in the pathology is not known. Immunostaining study showed that ASPA protein is reduced in the white matter of patients with HIVE compared to the control. Western blot study further confirmed ASPA deficiency in the HIVE brain compared to the control. This paper suggests that HIVE condition affects ASPA to contribute in myelin loss/axonal damage seen in the disease.

Induction of the apoptosis inhibitor ARC by Ras in human cancers

Inhibition of apoptosis is critical for carcinogenesis. ARC (apoptosis repressor with caspase recruitment domain) is an endogenous inhibitor of apoptosis that antagonizes both intrinsic and extrinsic apoptosis pathways. Although normally expressed in striated myocytes and neurons, ARC is markedly induced in a variety of primary human epithelial cancers and renders cancer cells resistant to killing. The mechanisms that mediate the induction of ARC in cancer are unknown. Herein we demonstrate that increases in ARC abundance are stimulated by Ras through effects on transcription and protein stability. Overexpression of activated N-Ras or H-Ras in normal cells is sufficient to increase ARC mRNA and protein levels. Similarly, transgenic expression of activated H-Ras induces ARC in both the normal mammary epithelium and resulting tumors of intact mice. Conversely, knockdown of endogenous N-Ras in breast and colon cancer cells significantly reduces ARC mRNA and protein levels. The promoter of the Nol3 locus, encoding ARC, is activated by N-Ras and H-Ras in a MEK/ERK-dependent manner. Ras also stabilizes ARC protein by suppressing its polyubiquitination and subsequent proteasomal degradation. In addition to the effects of Ras on ARC abundance, ARC mediates Ras-induced cell survival and cell cycle progression. Thus, Ras induces ARC in epithelial cancers, and ARC plays a role in the oncogenic actions of Ras.

Expression of the translocator protein of 18 kDa by microglia, macrophages and astrocytes based on immunohistochemical localization in abnormal human brain

AIMS

Microglia are involved in neurodegeneration, are prime targets for anti-inflammatory therapy and are potential biomarkers of disease progression. For example, positron emission tomography imaging employing radioligands for the mitochondrial translocator protein of 18 kDa (TSPO, formerly known as the peripheral benzodiazepine receptor) is being scrutinized to detect neuroinflammation in various diseases. TSPO is presumably present in activated microglia, but may be present in other neural cells.

METHODS

We sought to elucidate the protein expression in normal human central nervous system, several neurological diseases (HIV encephalitis, Alzheimer's disease, multiple sclerosis and stroke) and simian immunodeficiency virus encephalitis by performing immunohistochemistry with two anti-TSPO antibodies.

RESULTS

Although the overall parenchymal staining was minimal in normal brain, endothelial and smooth muscle cells, subpial glia, intravascular monocytes and ependymal cells were TSPO-positive. In disease states, elevated TSPO was present in parenchymal microglia, macrophages and some hypertrophic astrocytes, but the distribution of TSPO varied depending on the disease, disease stage and proximity to the lesion or relation to infection. Staining with the two antibodies correlated well in white matter, but one antibody also stained cortical neurones. Quantitative analysis demonstrated a significant increase in TSPO in the white matter of HIV encephalitis compared with brains without encephalitis. TSPO expression was also increased in simian immunodeficiency virus encephalitis.

CONCLUSIONS

This report provides the first comprehensive immunohistochemical analysis of the expression of TSPO. The results are useful for informing the usage of positron emission tomography as an imaging modality and have an impact on the potential use of TSPO as an anti-inflammatory pharmacological target.

Human immunodeficiency virus infection inhibits granulocyte-macrophage colony-stimulating factor-induced microglial proliferation

It is well known that infection by the human immunodeficiency virus (HIV) dysregulates cell physiology, but little information is available on the consequences of HIV infection in primary macrophages and microglia. The authors examined the relationship between cell proliferation and HIV infection in primary cultures of microglia and in human central nervous system (CNS). In cultures infected with HIV (ADA and BaL), granulocyte-macrophage colony-stimulating factor (GM-CSF)-mediated cell proliferation was reduced in productively infected (p24+) cells as compared to p24- cells. The reduction was observed with both Ki67 and BrdU labeling, suggesting a G1/S block. The reduction was insignificant when microglia were infected with a Vpr- mutant virus. In human CNS, proliferating (Ki67+) cells were rare but were increased in the HIV+ and HIV encephalitis (HIVE) groups compared to the HIV- group. A positive correlation between GM-CSF immunoreactivity and Ki67 counts, implicating GM-CSF as a growth factor in human CNS was found. The relationship between total macrophage (CD68+) proliferation and infected macrophage (p24+) proliferation was assessed in HIVE by double labeling. Whereas 1.2% of total CD68+ cells were Ki67+, only 0.5% of HIV p24+ cells were Ki67+ (P < .05). Furthermore, staining for CD45RB (as opposed to CD68) facilitated the identification of Ki67+ microglia, indicating that CD68 could underestimate proliferating microglia. The authors conclude that although there is increased expression of GM-CSF and increased cell proliferation in the CNS of HIV-seropositive individuals, cell proliferation in the productively infected population is actually suppressed. These data suggest that there might be a viral gain in the suppressed host cell proliferation.

Systemic and brain macrophage infections in relation to the development of simian immunodeficiency virus encephalitis

The brains of individuals with lentiviral-associated encephalitis contain an abundance of infected and activated macrophages. It has been hypothesized that encephalitis develops when increased numbers of infected monocytes traffic into the central nervous system (CNS) during the end stages of immunosuppression. The relationships between the infection of brain and systemic macrophages and circulating monocytes and the development of lentiviral encephalitis are unknown. We longitudinally examined the extent of monocyte/macrophage infection in blood and lymph nodes of pigtailed macaques that did or did not develop simian immunodeficiency virus encephalitis (SIVE). Compared to levels in macaques that did not develop SIVE, more ex vivo virus production was detected from monocyte-derived macrophages and nonadherent peripheral blood mononuclear cells (PBMCs) from macaques that did develop SIVE. Prior to death, there was an increase in the number of circulating PBMCs following a rise in cerebrospinal fluid viral load in macaques that did develop SIVE but not in nonencephalitic macaques. At necropsy, macaques with SIVE had more infected macrophages in peripheral organs, with the exception of lymph nodes. T cells and NK cells with cytotoxic potential were more abundant in brains with encephalitis; however, T-cell and NK-cell infiltration in SIVE and human immunodeficiency virus encephalitis was more modest than that observed in classical acute herpes simplex virus encephalitis. These findings support the hypothesis that inherent differences in host systemic and CNS monocyte/macrophage viral production are associated with the development of encephalitis.

White matter lesions in an unselected cohort of the elderly: astrocytic, microglial and oligodendrocyte precursor cell responses

White matter lesions in an unselected cohort of the elderly: astrocytic, microglial and oligodendrocyte precursor cell responsesHyperintense lesions are frequently identified in T2-weighted magnetic resonance images (MRI) in the ageing brain. The pathological correlate and pathogenesis of white matter lesions (WML) remain unclear, and it is uncertain whether pathology and pathogenesis differ in periventricular lesions (PVL) compared with deep subcortical lesions (DSCL). Therefore we characterized astrocytic, microglial and oligodendrocyte responses in PVL and DSCL and compared them with control white matter using immunohistochemistry. Both PVL and DSCL were associated with severe myelin loss and increased microglia (P = 0.069 and P < 0.001), compared with nonlesional aged brain. Clasmatodendritic astroglia, immunoreactive for the serum protein fibrinogen, were present in 67% of PVL examined and 42% of DSCL. Compared with control and DSCL cases, more MAP-2 +13 positive remyelinating oligodendrocytes (P = 0.003 and P = 0.035) and platelet-derived growth factor alpha receptor positive reactive astrocytes (P < 0.001) were present in the perilesional white matter of PVL. In addition to a role for hypoperfusion, our data suggest that dysfunction of the blood-brain barrier may also contribute to the pathogenesis of a proportion of cerebral WML associated with ageing, and that attempts at remyelination are only associated with PVL and not DSCL.

CD45 isoform expression in microglia and inflammatory cells in HIV-1 encephalitis

CD45 is a membrane tyrosine phosphatase that modulates the function of the hematopoietic cells. In vitro, agonist antibodies to CD45RO or CD45RB isoforms have been shown to suppress microglial activation, but whether microglia in vivo express these isoforms in HIV encephalitis (HIVE) is unknown. Brain sections from control and HIVE were immunostained for CD45 isoforms using exon‐specific antibodies (RA, RB, RC and RO). RA and RC were limited to rare lymphocytes, while RB expression was robust in microglia and inflammatory cells. RO was low in control microglia, but increased in HIVE. RO was also localized to macrophages and CD8+ T cells. Targeting CD45 in vivo with isoform‐specific antibodies remains a therapeutic option for neuroinflammatory diseases.

HIV-1 expression protects macrophages and microglia from apoptotic death

Macrophages and microglia are the predominant cells infected with HIV-1 in the brain, yet the effects of productive HIV infection on the fate of these cells are poorly understood. In this study, we tested the hypothesis that HIV-1 expression influences cell death in infected macrophages and microglial cells. We detected apoptosis by terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling (TUNEL) in the cerebral white matter of control and HIV encephalitis (HIVE) brains, and quantitatively analysed apoptotic cells with respect to their location (vessel-associated vs. parenchymal), CD68 expression, and HIV-1 p24 expression. There were more vessel-associated, but not more parenchymal, TUNEL+ cells in HIVE cases as compared to controls. Vessel-associated TUNEL+ cells were primarily endothelial cells (von Willebrand factor+) or macrophages (CD68+). TUNEL+/CD68+ cells were present in both control and HIVE cases in similar frequencies (2.1 +/- 0.7% vs. 1.9 +/- 0.7% of total CD68+ populations, respectively). In HIVE, TUNEL+/p24+ cells were 0.4 +/- 0.2% of the total p24+ cell population, which was lower than the frequency of TUNEL+/CD68+ cells (1.9 +/- 0.7%) in the total CD68+ macrophage population. These results suggest that HIV-1-infected macrophages and microglia are resistant to apoptosis, and may contribute to the formation of a central nervous system viral reservoir.

Preferential vulnerability of astroglia and glial precursors to combined opioid and HIV-1 Tat exposure in vitro

Human immunodeficiency virus (HIV)-1 infection can cause characteristic neural defects such as progressive motor dysfunction, striatal pathology and gliosis. Recent evidence suggests that HIV-induced pathogenesis is exacerbated by heroin abuse and that the synergistic neurotoxicity is a direct effect of heroin on the CNS, an alarming observation considering the high incidence of HIV infection with injection drug abuse. Although HIV infection results in neurodegeneration, neurons themselves are not directly infected. Instead, HIV affects microglia and astroglia, which subsequently contributes to the neurodegenerative changes. Opioid receptors are widely expressed by macroglia and macroglial precursors, and the activation of mu-opioid receptors can modulate programmed cell death, as well as the response of neural cells to cytotoxic insults. For this reason, we questioned whether opioid drugs might modify the vulnerability of macroglia and macroglial precursors to HIV-1 Tat protein. To address this problem, the effects of morphine and/or HIV Tat(1-72) on the viability of macroglia and macroglial precursors were assessed in mixed-glial cultures derived from mouse striatum. Our findings indicate that sustained exposure to morphine and Tat(1-72) viral protein induces the preferential death of glial precursors and some astrocytes. Moreover, the increased cell death is mediated by mu-opioid receptors and accompanied by the activation of caspase-3. Our results imply that opiates can enhance the cytotoxicity of HIV-1 Tat through direct actions on glial precursors and/or astroglia, suggesting novel cellular targets for HIV-opiate interactions.