Constitutive knockout of interleukin-6 ameliorates memory deficits and entorhinal astrocytosis in the MRL/lpr mouse model of neuropsychiatric lupus

BACKGROUND

Neuropsychiatric lupus (NPSLE) describes the cognitive, memory, and affective emotional burdens faced by many lupus patients. While NPSLE's pathogenesis has not been fully elucidated, clinical imaging studies and cerebrospinal fluid (CSF) findings, namely elevated interleukin-6 (IL-6) levels, point to ongoing neuroinflammation in affected patients. Not only linked to systemic autoimmunity, IL-6 can also activate neurotoxic glial cells the brain. A prior pre-clinical study demonstrated that IL-6 can acutely induce a loss of sucrose preference; the present study sought to assess the necessity of chronic IL-6 exposure in the NPSLE-like disease of MRL/lpr lupus mice.

METHODS

We quantified 1308 proteins in individual serum or pooled CSF samples from MRL/lpr and control MRL/mpj mice using protein microarrays. Serum IL-6 levels were plotted against characteristic NPSLE neurobehavioral deficits. Next, IL-6 knockout MRL/lpr (IL-6 KO; n = 15) and IL-6 wildtype MRL/lpr mice (IL-6 WT; n = 15) underwent behavioral testing, focusing on murine correlates of learning and memory deficits, depression, and anxiety. Using qPCR, we quantified the expression of inflammatory genes in the cortex and hippocampus of MRL/lpr IL-6 KO and WT mice. Immunofluorescent staining was performed to quantify numbers of microglia (Iba1 +) and astrocytes (GFAP +) in multiple cortical regions, the hippocampus, and the amygdala.

RESULTS

MRL/lpr CSF analyses revealed increases in IL-17, MCP-1, TNF-α, and IL-6 (a priori p-value < 0.1). Serum levels of IL-6 correlated with learning and memory performance (R2 = 0.58; p = 0.03), but not motivated behavior, in MRL/lpr mice. Compared to MRL/lpr IL-6 WT, IL-6 KO mice exhibited improved novelty preference on object placement (45.4% vs 60.2%, p < 0.0001) and object recognition (48.9% vs 67.9%, p = 0.002) but equivalent performance in tests for anxiety-like disease and depression-like behavior. IL-6 KO mice displayed decreased cortical expression of aif1 (microglia; p = 0.049) and gfap (astrocytes; p = 0.044). Correspondingly, IL-6 KO mice exhibited decreased density of GFAP + cells compared to IL-6 WT in the entorhinal cortex (89 vs 148 cells/mm2, p = 0.037), an area vital to memory.

CONCLUSIONS

The inflammatory composition of MRL/lpr CSF resembles that of human NPSLE patients. Increased in the CNS, IL-6 is necessary to the development of learning and memory deficits in the MRL/lpr model of NPSLE. Furthermore, the stimulation of entorhinal astrocytosis appears to be a key mechanism by which IL-6 promotes these behavioral deficits.

Glucocorticoid receptor antagonist CORT113176 attenuates motor and neuropathological symptoms of Huntington's disease in R6/2 mice

Huntington's Disease (HD) is a progressive neurodegenerative disease caused by a mutation in the huntingtin gene. The mutation leads to a toxic gain of function of the mutant huntingtin (mHtt) protein resulting in cellular malfunction, aberrant huntingtin aggregation and eventually neuronal cell death. Patients with HD show impaired motor functions and cognitive decline. Elevated levels of glucocorticoids have been found in HD patients and in HD mouse models, and there is a positive correlation between increased glucocorticoid levels and the progression of HD. Therefore, antagonism of the glucocorticoid receptor (GR) may be an interesting strategy for the treatment of HD. In this study, we evaluated the efficacy of the selective GR antagonist CORT113176 in the commonly used R6/2 mouse model. In male mice, CORT113176 treatment significantly delayed the loss of grip strength, the development of hindlimb clasping, gait abnormalities, and the occurrence of epileptic seizures. CORT113176 treatment delayed loss of DARPP-32 immunoreactivity in the dorsolateral striatum. It also restored HD-related parameters including astrocyte markers in both the dorsolateral striatum and the hippocampus, and microglia markers in the hippocampus. This suggests that CORT113176 has both cell-type and brain region-specific effects. CORT113176 delayed the formation of mHtt aggregates in the striatum and the hippocampus. In female mice, we did not observe major effects of CORT113176 treatment on HD-related symptoms, with the exception of the anti-epileptic effects. We conclude that CORT113176 effectively delays several key symptoms related to the HD phenotype in male R6/2 mice and believe that GR antagonism may be a possible treatment option.

Imaging Neuroinflammation: Quantification of Astrocytosis in a Multitracer PET Approach

The recent progress in the development of in vivo biomarkers is rapidly changing how neurodegenerative diseases are conceptualized and diagnosed and how clinical trials are designed today. Alzheimer's disease (AD) - the most common neurodegenerative disorder - is characterized by a complex neuropathology involving the deposition of extracellular amyloid-β (Aβ) plaques and intracellular neurofibrillary tangles (NFTs) of hyperphosphorylated tau proteins, accompanied by the activation of glial cells, i.e., astrocytes and microglia, and neuroinflammatory response, leading to neurodegeneration and cognitive dysfunction. An increasing diversity of positron emission tomography (PET) imaging radiotracers is available to selectively target the different pathophysiological processes of AD. Along with the success of Aβ PET and the more recent tau PET imaging, there is a great interest to develop PET tracers to image glial reactivity and neuroinflammation. While most research to date has focused on imaging microgliosis, there is an upsurge of interest in imaging reactive astrocytes in the AD continuum. There is increasing evidence that reactive astrocytes are morphologically and functionally heterogeneous, with different subtypes that express different markers and display various homeostatic or detrimental roles across disease stages. Therefore, multiple biomarkers are desirable to unravel the complex phenomenon of reactive astrocytosis. In the field of in vivo PET imaging in AD, the research concerning reactive astrocytes has predominantly focused on targeting monoamine oxidase B (MAO-B), most often using either 11C-deuterium-L-deprenyl (11C-DED) or 18F-SMBT-1 PET tracers. Additionally, imidazoline2 binding (I2BS) sites have been imaged using 11C-BU99008 PET. Recent studies in our group using 11C-DED PET imaging suggest that astrocytosis may be present from the early stages of disease development in AD. This chapter provides a detailed description of the practical approach used for the analysis of 11C-DED PET imaging data in a multitracer PET paradigm including 11C-Pittsburgh compound B (11C-PiB) and 18F-fluorodeoxyglucose (18F-FDG). The multitracer PET approach allows investigating the comparative regional and temporal patterns of in vivo brain astrocytosis, fibrillar Aβ deposition, glucose metabolism, and brain structural changes. It may also contribute to understanding the potential role of novel plasma biomarkers of reactive astrocytes, in particular the glial fibrillary acidic protein (GFAP), at different stages of disease progression. This chapter attempts to stimulate further research in the field, including the development of novel PET tracers that may allow visualizing different aspects of the complex astrocytic and microglial response in neurodegenerative diseases. Progress in the field will contribute to the incorporation of PET imaging of glial reactivity and neuroinflammation as biomarkers with clinical application and motivate further investigation on glial cells as therapeutic targets in AD and other neurodegenerative diseases.

Autoimmune glial fibrillary acidic protein astrocytosis mimicking tuberculous meningitis: a retrospective study

BACKGROUND

This study aimed to summarize the clinical features of Autoimmune Glial Fibrillary Acidic Protein Astrocytosis mimicking tuberculosis meningitis to improve clinicians' understanding of this disease.

METHODS

We retrospectively analyzed the clinical manifestations, cerebrospinal fluid results, and imaging data of five patients with Autoimmune Glial Fibrillary Acidic Protein Astrocytosis mimicking tuberculous meningitis who were admitted to Xiangya Hospital Central South University between October 2021 and July 2022.

RESULTS

Five patients were aged 31-59 years, with a male-to-female ratio of 4:1. Among the cases reviewed, four had a history of prodromal infections manifesting as fever and headache. One patient developed limb weakness and numbness with clinical manifestations of meningitis, meningoencephalitis, encephalomyelitis, or meningomyelitis. Cerebrospinal fluid analysis revealed an increased cell count in five cases, with a lymphocyte majority. All five cases had a CSF protein level > 1.0 g/L, CSF/blood glucose ratio < 0.5, and two patients had CSF glucose < 2.2 mmol/L. Decreased CSF chloride was observed in three cases, while increased ADA was observed in one case. Both serum and cerebrospinal fluid were positive for anti-GFAP antibodies in three cases, while in two cases, only CSF was positive for anti-GFAP antibodies. Additionally, hyponatremia and hypochloremia were observed in three cases. No tumors were detected in any of the five patients during tumor screening, and all five cases had a good prognosis following immunotherapy.

CONCLUSION

Anti-GFAP antibody testing should be routinely performed in patients with suspected tuberculosis meningitis to avoid misdiagnosis.

Exploring the role of astrocytic dysfunction and AQP4 in depression

Aquaporin-4 (AQP4) is the water regulating channel found in the terminal processes of astrocytes in the brain and is implicated in regulating the astrocyte functions, whereas in neuropathologies, AQP4 performs an important role in astrocytosis and release of proinflammatory cytokines. However, several findings have revealed the modulation of the AQP4 water channel in the etiopathogenesis of various neuropsychiatric diseases. In the current article, we have summarized the recent studies and highlighted the implication of astrocytic dysfunction and AQP4 in the etiopathogenesis of depressive disorder. Most of the studies have measured the AQP4 gene or protein expression in the brain regions, particularly the locus coeruleus, choroid plexus, prefrontal cortex, and hippocampus, and found that in these brain regions, AQP4 gene expression decreased on exposure to chronic mild stress. Few studies also measured the peripheral AQP4 mRNA expression in the blood and AQP4 autoantibodies in the blood serum and revealed no change in the depressed patients in comparison with normal individuals.

Aquaporin-4 prevents exaggerated astrocytosis and structural damage in retinal inflammation

Abstract

Aquaporin-4 (AQP4) is the molecular target of the immune response in neuromyelitis optica (NMO) that leads to severe structural damage in the central nervous system (CNS) and in the retina. Conversely, AQP4 might be upregulated in astrocytes as a compensatory event in multiple sclerosis. Thus, the functional relevance of AQP4 in neuroinflammation needs to be defined. Here, we tested the role of AQP4 in the retina in MOG(35–55)-induced experimental autoimmune encephalomyelitis (EAE) using optical coherence tomography (OCT), OCT angiography, immunohistology, flow cytometry, and gene expression analysis in wild-type and Aqp4^–/– mice. No direct infiltrates of inflammatory cells were detected in the retina. Yet, early retinal expression of TNF and Iba1 suggested that the retina participated in the inflammatory response during EAE in a similar way in wild-type and Aqp4^–/– mice. While wild-type mice rapidly cleared retinal swelling, Aqp4^–/– animals exhibited a sustainedly increased retinal thickness associated with retinal hyperperfusion, albumin extravasation, and upregulation of GFAP as a hallmark of retinal scarring at later stages of EAE. Eventually, the loss of retinal ganglion cells was higher in Aqp4^–/– mice than in wild-type mice. Therefore, AQP4 expression might be critical for retinal Müller cells to clear the interstitial space from excess vasogenic edema and prevent maladaptive scarring in the retina during remote inflammatory processes of the CNS.

Key messages

Genetic ablation of AQP4 leads to a functional derangement of the retinal gliovascular unit with retinal hyperperfusion during autoimmune CNS inflammation.

Genetic ablation of AQP4 results in a structural impairment of the blood retina barrier with extravasation of albumin during autoimmune CNS inflammation.

Eventually, the lack of AQP4 in the retina during an inflammatory event prompts the exaggerated upregulation of GFAP as a hallmark of scarring as well as loss of retinal ganglion cells.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00109-022-02202-6.

Diffusion Tensor Orientation as a Microstructural MRI Marker of Mossy Fiber Sprouting After TBI in Rats

Diffusion tensor imaging (DTI) metrics are highly sensitive to microstructural brain alterations and are potentially useful imaging biomarkers for underlying neuropathologic changes after experimental and human traumatic brain injury (TBI). As potential imaging biomarkers require direct correlation with neuropathologic alterations for validation and interpretation, this study systematically examined neuropathologic abnormalities underlying alterations in DTI metrics in the hippocampus and cortex following controlled cortical impact (CCI) in rats. Ex vivo DTI metrics were directly compared with a comprehensive histologic battery for neurodegeneration, microgliosis, astrocytosis, and mossy fiber sprouting by Timm histochemistry at carefully matched locations immediately, 48 hours, and 4 weeks after injury. DTI abnormalities corresponded to spatially overlapping but temporally distinct neuropathologic alterations representing an aggregate measure of dynamic tissue damage and reorganization. Prominent DTI alterations of were observed for both the immediate and acute intervals after injury and associated with neurodegeneration and inflammation. In the chronic period, diffusion tensor orientation in the hilus of the dentate gyrus became prominently abnormal and was identified as a reliable structural biomarker for mossy fiber sprouting after CCI in rats, suggesting potential application as a biomarker to follow secondary progression in experimental and human TBI.

TDP-43 mediated blood-brain barrier permeability and leukocyte infiltration promote neurodegeneration in a low-grade systemic inflammation mouse model

BACKGROUND

Neuronal cytoplasmic inclusions containing TAR DNA-binding protein 43 (TDP-43) are a neuropathological feature of several neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), and Alzheimer's Disease (AD). Emerging evidence also indicates that systemic inflammation may be a contributor to the pathology progression of these neurodegenerative diseases.

METHODS

To investigate the role of systemic inflammation in the progression of neuronal TDP-43 pathology, AAV9 particles driven by the UCHL1 promoter were delivered to the frontal cortex of wild-type aged mice via intracranial injections to overexpress TDP-43 or green fluorescent protein (GFP) in corticospinal motor neurons. Animals were then subjected to a low-dose (500 μg/kg) intraperitoneal E. coli lipopolysaccharide (LPS) administration challenge for 2 weeks to mimic a chronically altered low-grade systemic inflammatory state. Mice were then subjected to neurobehavioral studies, followed by biochemical and immunohistochemical analyses of the brain tissue.

RESULTS

In the present study, we report that elevated neuronal TDP-43 levels induced microglial and astrocytic activation in the cortex of injected mice followed by increased RANTES signaling. Moreover, overexpression of TDP-43 exerted abundant mouse immunoglobulin G (IgG), CD3, and CD4+ T cell infiltration as well as endothelial and pericyte activation suggesting increased blood-brain barrier permeability. The BBB permeability in TDP-43 overexpressing brains yielded the frontal cortex vulnerable to the systemic inflammatory response following LPS treatment, leading to marked neutrophil infiltration, neuronal loss, reduced synaptosome-associated protein 25 (SNAP-25) levels, and behavioral impairments in the radial arm water maze (RAWM) task.

CONCLUSIONS

These results reveal a novel role for TDP-43 in BBB permeability and leukocyte recruitment, indicating complex intermolecular interactions between an altered systemic inflammatory state and pathologically prone TDP-43 protein to promote disease progression.

Bisphenol A induces DNA damage in cells exerting immune surveillance functions at peripheral and central level

Bisphenol A (BPA) is a synthetic xenoestrogen diffused worldwide. Humans are chronically exposed to low doses of BPA from food and drinks, thus BPA accumulates in tissues posing human health risk. In this study, we investigated the effects of BPA on peripheral blood mononuclear cells (PBMC) from human healthy donors, and in glia and microglia of rat offspring at postnatal day 17 (17PND) from pregnant females who received BPA soon after coupling and during lactation and weaning. Results indicated that BPA affected Phytoemagglutinin (PHA) stimulated PBMC proliferation causing an S-phase cell cycle accumulation at nanomolar concentrations while BPA was almost ineffective in resting PBMC. Furthermore, BPA induced chromosome aberrations and the appearance of shattered cells characterized by high number of fragmented and pulverized chromosomes, suggesting that the compound could cause a massive genomic rearrangement by inducing catastrophic events. The BPA-induced DNA damage was observed mainly in TCD4+ and TCD8+ subsets of T lymphocytes and was mediated by the increase of ERK1/2 phosphorylation, p21/Waf1 and PARP1 protein expression. Intriguingly, we observed for the first time that BPA-induced effects were associated to a sex specific modulation of ERα and ERβ in human PBMC. Immunofluorescence analysis of rat hippocampus corroborated in vitro findings showing that BPA induced ɣH2AX phosphorylation in microglia and astrocytosis by decreasing ERα expression within the dentate gyrus. Overall these results suggest that BPA can alter immune surveillance functions at both peripheral and central level with a potential risk for cancer, neuroinflammation and neurodegeneration.

Innate immune response in neuronopathic forms of Gaucher disease confers resistance against viral-induced encephalitis

Both monogenic diseases and viral infections can manifest in a broad spectrum of clinical phenotypes that range from asymptomatic to lethal, suggesting that other factors modulate disease severity. Here, we examine the interplay between the genetic neuronopathic Gaucher’s disease (nGD), and neuroinvasive Sindbis virus (SVNI) infection. Infection of nGD mice with SVNI had no influence on nGD severity. However, nGD mice were more resistant to SVNI infection. Significantly different inflammatory responses were seen in nGD brains when compared with SVNI brains: the inflammatory response in the nGD brains consisted of reactive astrocytes and microglia with no infiltrating macrophages, but the inflammatory response in the brains of SVNI-infected mice was characterized by infiltration of macrophages and altered activation of microglia and astrocytes. We suggest that the innate immune response activated in nGD confers resistance against viral infection of the CNS.

Myelopathy and Reactive Microgliosis and Astrogliosis in Equine Back Pain

Equine chronic back pain (CBP) has been linked to different pathologic processes, which directly or indirectly involve spinal structures. Thus, making diagnosis and management very challenging with most horses with the condition recommended for early retirement from athletic activity. This study described the spinal cord lesions and the development of reactive microgliosis and astrocytosis in the spinal cords of horse with CBP. Thoracolumbar spinal cord segments from three horses euthanized because of unresolved CBP were dissected and grossly and histopathologically examined. The expression of activated microglia and astrocytes were demonstrated immunohistochemically using polyclonal rabbit anti-Iba-1 and anti-glial fibrillary acidic protein antibodies, respectively. All horses had radiological evidence of varying degrees of kissing spine involving six to nine vertebrae with the majority of the lesions graded between 2 and 5. Grossly, there was myelomalacia with intramedullary hemorrhages. The gray matters of the spinal cords were characterized by hemorrhagic malacic lesions with medullary disintegration. Reactive microgliosis and astrocytosis were evident in the spinal dorsal horns. White matter lesions include axonal swollen and/or loss, satellitosis, and varying degrees of dilation of myelin sheaths with some containing macrophages. In conclusion, the presence of reactive microgliosis and astrogliosis in the spinal dorsal horn indicates that they are possible precipitating factors in the development of equine CBP.

Friends Turn Foe-Astrocytes Contribute to Neuronal Damage in NeuroAIDS

Astrocytes play a wide variety of roles in the central nervous system (CNS). Various facets of astrocyte-neuron interplay, investigated for the past few decades, have placed these most abundant and important glial cell types to be of supreme importance for the maintenance of the healthy CNS. Interestingly, glial dysfunctions have proven to be the major contributor to neuronal loss in several CNS disorders and pathologies. Specifically, in the field of neuroAIDS, glial dysfunction-mediated neuronal stress is a major factor contributing to the HIV-1 neuropathogenesis. As there is increasing evidence that astrocytes harbor HIV-1 and serve as "safe haven" for the dormant virus in the brain, the indirect pathway of neuronal damage has taken over the direct neuronal damage in its contribution to HIV-1 neuropathogenesis. In this review, we provide a brief insight into the astrocyte functions and dysfunctions in different CNS conditions with an elaborated insight into neuroAIDS. Detailed understanding of the role of astrocytes in neuroAIDS will help in the better therapeutic management of the neurological problems associated with HIV-1 patients.

Method for Stimulation of Hippocampal Neurogenesis by Transient Microneedle Insertion

Brief stereotaxic insertion and removal of a microneedle into the hippocampus of mice result in stimulation of hippocampal neurogenesis. This approach has been previously applied to a mouse model of Alzheimer's disease (Song et al., Cell Transplant 25:1853-1861, 2016). Further studies of fundamental cellular mechanisms of the brain's response to micro-injury will be useful for investigation of potential neuroprotective and deleterious effects of targeted microlesions and deep brain stimulation in neurodegenerative diseases.

Permeability changes and effect of chemotherapy in brain adjacent to tumor in an experimental model of metastatic brain tumor from breast cancer

Background

Brain tumor vasculature can be significantly compromised and leakier than that of normal brain blood vessels. Little is known if there are vascular permeability alterations in the brain adjacent to tumor (BAT). Changes in BAT permeability may also lead to increased drug permeation in the BAT, which may exert toxicity on cells of the central nervous system. Herein, we studied permeation changes in BAT using quantitative fluorescent microscopy and autoradiography, while the effect of chemotherapy within the BAT region was determined by staining for activated astrocytes.

Methods

Human metastatic breast cancer cells (MDA-MB-231Br) were injected into left ventricle of female NuNu mice. Metastases were allowed to grow for 28 days, after which animals were injected fluorescent tracers Texas Red (625 Da) or Texas Red dextran (3 kDa) or a chemotherapeutic agent ¹⁴C-paclitaxel. The accumulation of tracers and ¹⁴C-paclitaxel in BAT were determined by using quantitative fluorescent microscopy and autoradiography respectively. The effect of chemotherapy in BAT was determined by staining for activated astrocytes.

Results

The mean permeability of texas Red (625 Da) within BAT region increased 1.0 to 2.5-fold when compared to normal brain, whereas, Texas Red dextran (3 kDa) demonstrated mean permeability increase ranging from 1.0 to 1.8-fold compared to normal brain. The K_in values in the BAT for both Texas Red (625 Da) and Texas Red dextran (3 kDa) were found to be 4.32 ± 0.2 × 10⁵ mL/s/g and 1.6 ± 1.4 × 10⁵ mL/s/g respectively and found to be significantly higher than the normal brain. We also found that there is significant increase in accumulation of ¹⁴C-Paclitaxel in BAT compared to the normal brain. We also observed animals treated with chemotherapy (paclitaxel (10 mg/kg), erubilin (1.5 mg/kg) and docetaxel (10 mg/kg)) showed activated astrocytes in BAT.

Conclusions

Our data showed increased permeation of fluorescent tracers and ¹⁴C-paclitaxel in the BAT. This increased permeation lead to elevated levels of activated astrocytes in BAT region in the animals treated with chemotherapy.

Longitudinal association between astrocyte function and glucose metabolism in autosomal dominant Alzheimer's disease

PURPOSE

The spatial resolution of ¹⁸F-fluorodeoxyglucose PET does not allow the specific cellular origin of its signal to be determined, but it is commonly accepted that transport and trapping of ¹⁸F-fluorodeoxyglucose reflects neuronal glucose metabolism. The main frameworks for the diagnosis of Alzheimer's disease suggest that hypometabolism measured with ¹⁸F-fluorodeoxyglucose PET is a biomarker of neuronal injury and neurodegeneration. There is preclinical evidence to suggest that astrocytes contribute, at least partially, to the in vivo ¹⁸F-fluorodeoxyglucose PET signal. However, due to a paucity of PET tracers for imaging astrocytic processes, the relationship between astrocyte function and glucose metabolism in human brain is not fully understood. The aim of this study was to investigate the longitudinal association between astrocyte function and glucose metabolism in Alzheimer's disease.

METHODS

The current investigation combined longitudinal PET data from patients with autosomal dominant Alzheimer's disease, including data on astrocyte function (¹¹C-deuterium-L-deprenyl binding) and glucose metabolism (¹⁸F-fluorodeoxyglucose uptake). Research participants included 7 presymptomatic and 4 symptomatic mutation carriers (age 44.9 ± 9.8 years and 58.0 ± 3.7 years, respectively) and 16 noncarriers (age 51.1 ± 14.2 years). Eight carriers and eight noncarriers underwent longitudinal follow-up PET imaging at an average of 2.8 ± 0.2 and 3.0 ± 0.5 years from baseline, respectively.

RESULTS

Longitudinal decline in astrocyte function as measured using ¹¹C-deuterium-L-deprenyl PET was significantly associated with progressive hypometabolism (¹⁸F-fluorodeoxyglucose uptake) in mutation carriers; no significant association was observed in noncarriers.

CONCLUSION

The emerging data shift the accepted wisdom that decreases in cerebral metabolism measured with ¹⁸F-fluorodeoxyglucose solely reflect neuronal injury, and places astrocytes more centrally in the development of Alzheimer's disease.

Calcineurin A beta deficiency ameliorates HFD-induced hypothalamic astrocytosis in mice

Astrocytosis is a reactive process involving cellular, molecular, and functional changes to facilitate neuronal survival, myelin preservation, blood brain barrier function and protective glial scar formation upon brain insult. The overall pro- or anti-inflammatory impact of reactive astrocytes appears to be driven in a context- and disease-driven manner by modulation of astrocytic Ca²⁺ homeostasis and activation of Ca²⁺/calmodulin-activated serine/threonine phosphatase calcineurin. Here, we aimed to assess whether calcineurin is dispensable for astrocytosis in the hypothalamus driven by prolonged high fat diet (HFD) feeding.

Global deletion of calcineurin A beta (gene name: Ppp3cb) led to a decrease of glial fibrillary acidic protein (GFAP)-positive cells in the ventromedial hypothalamus (VMH), dorsomedial hypothalamus (DMH), and arcuate nucleus (ARC) of mice exposed chronically to HFD. The concomitant decrease in Iba1-positive microglia in the VMH further suggests a modest impact of Ppp3cb deletion on microgliosis. Pharmacological inhibition of calcineurin activity by Fk506 had no impact on IBA1-positive microglia in hypothalami of mice acutely exposed to HFD for 1 week. However, Fk506-treated mice displayed a decrease in GFAP levels in the ARC. In vivo effects could not be replicated in cell culture, where calcineurin inhibition by Fk506 had no effect on astrocytic morphology, astrocytic cell death, GFAP, and vimentin protein levels or microglia numbers in primary hypothalamic astrocytes and microglia co-cultures. Further, adenoviral overexpression of calcineurin subunit Ppp3r1 in primary glia culture did not lead to an increase in GFAP fluorescence intensity.

Overall, our results point to a prominent role of calcineurin in mediating hypothalamic astrocytosis as response to acute and chronic HFD exposure. Moreover, discrepant findings in vivo and in cell culture indicate the necessity of studying astrocytes in their “natural” environment, i.e., preserving an intact hypothalamic microenvironment with neurons and non-neuronal cells in close proximity.

Morphine-Mediated Brain Region-Specific Astrocytosis Involves the ER Stress-Autophagy Axis

A recent study from our lab has revealed a link between morphine-mediated autophagy and synaptic impairment. The current study was aimed at investigating whether morphine-mediated activation of astrocytes involved the ER stress/autophagy axis. Our in vitro findings demonstrated upregulation of GFAP indicating astrocyte activation with a concomitant increase in the production of proinflammatory cytokines in morphine-exposed human astrocytes. Using both pharmacological and gene-silencing approaches, it was demonstrated that morphine-mediated defective autophagy involved upstream activation of ER stress with subsequent downstream astrocyte activation via the μ-opioid receptor (MOR). In vivo validation demonstrated preferential activation of ER stress/autophagy axis in the areas of the brain not associated with pain such as the basal ganglia, frontal cortex, occipital cortex, and the cerebellum of morphine-dependent rhesus macaques, and this correlated with increased astrocyte activation and neuroinflammation. Interventions aimed at blocking either the MOR or ER stress could thus likely be developed as promising therapeutic targets for abrogating morphine-mediated astrocytosis.

Imaging Neuroinflammation: Quantification of Astrocytosis in a Multitracer PET Approach

The recent progress in the development of in vivo biomarkers is rapidly changing how neurodegenerative diseases are conceptualized and diagnosed, and how clinical trials are designed today. Alzheimer's disease (AD)-the most common neurodegenerative disorder-is characterized by a complex neuropathology involving the deposition of extracellular amyloid-β (Aβ) plaques and intracellular neurofibrillary tangles (NFT) of hyperphosphorylated tau proteins, accompanied by the activation of glial cells-astrocytes and microglia-and neuroinflammatory responses, leading to neurodegeneration and cognitive dysfunction. An increasing diversity of positron emission tomography (PET) imaging radiotracers are available to selectively target the different pathophysiological processes of AD. Along with the success of Aβ PET and the more recent tau PET imaging, there is also a great interest to develop PET tracers to image glial activation and neuroinflammation. While most research to date has focused on imaging microgliosis, recent studies using ¹¹C-deuterium-L-deprenyl (¹¹C-DED) PET imaging suggest that astrocytosis may be present from very early stages of disease development in AD. This chapter provides a detailed description of the practical approach used for the analysis of ¹¹C-DED PET imaging data in a multitracer PET paradigm including ¹¹C-Pittsburgh compound B (¹¹C-PiB) and ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG). The multitracer PET approach allows investigating the comparative regional and temporal patterns of in vivo brain astrocytosis, fibrillar Aβ deposition, and glucose metabolism in patients at different stages of disease progression. This chapter attempts to stimulate further research in the field, including the development of novel PET tracers that may allow visualizing different aspects of the complex astrocytic and microglial responses in neurodegenerative diseases. Progress in the field will contribute to the incorporation of PET imaging of glial activation and neuroinflammation as biomarkers with clinical application, and motivate further investigation on glial cells as therapeutic targets in AD and other neurodegenerative diseases.

Frequent mild head injury promotes trigeminal sensitivity concomitant with microglial proliferation, astrocytosis, and increased neuropeptide levels in the trigeminal pain system

BACKGROUND

Frequent mild head injuries or concussion along with the presence of headache may contribute to the persistence of concussion symptoms.

METHODS

In this study, the acute effects of recovery between mild head injuries and the frequency of injuries on a headache behavior, trigeminal allodynia, was assessed using von Frey testing up to one week after injury, while histopathological changes in the trigeminal pain pathway were evaluated using western blot, ELISA and immunohistochemistry.  RESULTS: A decreased recovery time combined with an increased mild closed head injury (CHI) frequency results in reduced trigeminal allodynia thresholds compared to controls. The repetitive CHI group with the highest injury frequency showed the greatest reduction in trigeminal thresholds along with greatest increased levels of calcitonin gene-related peptide (CGRP) in the trigeminal nucleus caudalis. Repetitive CHI resulted in astrogliosis in the central trigeminal system, increased GFAP protein levels in the sensory barrel cortex, and an increased number of microglia cells in the trigeminal nucleus caudalis.

CONCLUSIONS

Headache behavior in rats is dependent on the injury frequency and recovery interval between mild head injuries. A worsening of headache behavior after repetitive mild head injuries was concomitant with increases in CGRP levels, the presence of astrocytosis, and microglia proliferation in the central trigeminal pathway. Signaling between neurons and proliferating microglia in the trigeminal pain system may contribute to the initiation of acute headache after concussion or other traumatic brain injuries.

Blunted Respiratory Responses in the Streptozotocin-Induced Alzheimer's Disease Rat Model

Alzheimer's disease (AD) is known for the progressive decline of cognition and memory. In addition to these disease-defining symptoms, impairment of respiratory function is frequently observed and often expressed by sleep-disordered breathing or reduced ability to adjust respiration when oxygen demand is elevated. The mechanisms for this are widely unknown. Postmortem analysis from the brainstem of AD patients reveals pathological alterations, including in nuclei responsible for respiratory control. In this study, we analyzed respiratory responses and morphological changes in brainstem nuclei following intracerebroventricular (ICV) injections of streptozotocin (STZ), a rat model commonly used to mimic sporadic AD. ICV-STZ induced significant astrogliosis in the commissural part of the nucleus tractus solitarii, an area highly involved in respiration control. The astrogliosis was identified by a significant increase in S100B-immunofluorescence that is similar to the astrogliosis found in the CA1 region of the hippocampus. Using plethysmography, the control group displayed a typical age-dependent decrease of ventilation that was absent in the STZ rat group. This is indicative of elevated minute ventilation at rest after STZ treatment. Peripheral chemoreflex responses were significantly blunted in STZ rats as seen by a reduced respiratory rate and minute ventilation to hypoxia. Central chemoreflex responses to hypercapnia, on the other hand, only decreased in respiratory rate following STZ treatment. Overall, our results show that ICV-STZ induces respiratory dysfunction at rest and in response to hypoxia. This provides a new tool to study the underlying mechanisms of breathing disorders in clinical AD.

Blood Brain Barrier Impairment in HIV-Positive Naïve and Effectively Treated Patients: Immune Activation Versus Astrocytosis

Blood brain barrier (BBB) damage is a common feature in central nervous system infections by HIV and it may persist despite effective antiretroviral therapy. Astrocyte involvement has not been studied in this setting. Patients were enrolled in an ongoing prospective study and subjects with central nervous system-affecting disorders were excluded. Patients were divided into two groups: treated subjects with cerebrospinal fluid (CSF) HIV RNA <50 copies/mL (CSF-controllers) and in late-presenters CD4+ T lymphocytes <100/uL. CSF biomarkers of neuronal or astrocyte damage were measured and compared to CSF serum-to-albumin ratio. 134 patients were included; 67 subjects in each group (50 %) with similar demographic characteristics (with the exception of older age in CSF controllers). CD4 (cells/uL), plasma and CSF HIV RNA (Log₁₀ copies/mL) were 43 (20-96), 5.6 (5.2-6) and 3.9 (3.2-4.7) in LPs and 439 (245-615), <1.69 (9 patients <2.6) and <1.69 in CSFc. BBB impairment was observed in 17 late-presenters (25.4 %) and in 9 CSF-controllers (13.4 %). CSF biomarkers were similar but for higher CSF neopterin values in late-presenters (2.3 vs. 0.6 ng/mL, p < 0.001). CSARs were associated with CSF neopterin (rho = 0.31, p = 0.03) and HIV RNA (rho = 0.24, p = 0.05) in late-presenters and with CSF tau (rho = 0.51, p < 0.001), p-tau (rho = 0.47, p < 0.001) and S100beta (rho = 0.33, p = 0.009) in CSF-controllers. In HAART-treated subjects with suppressed CSF HIV RNA, BBB altered permeability was associated with markers of neuronal damage and astrocytosis. Additional treatment targeting astrocytosis and/or viral protein production might be needed in order to reduce HIV effects in the central nervous system.

Demyelination-Induced Inflammation Attracts Newly Born Neurons to the White Matter

There is compelling evidence that microglial activation negatively impacts neurogenesis. However, microglia have also been shown to promote recruitment of newly born neurons to injured areas of the gray matter. In the present study, we explored whether demyelination-triggered inflammation alters the process of neurogenesis in the white matter. A 2-μl solution of 0.04 % ethidium bromide was stereotaxically injected into the corpus callosum of adult male rats. Brain inflammation was dampened by daily injections of progesterone (5 mg/kg, s.c.) for 14 days. Control rats received oil (s.c.). Newly born neurons (DCX and Tbr2), microglia (Iba-1), astrocytes (vimentin or GFAP), oligodendrocyte progenitor cells (OPCs; NG2), and mature oligodendrocytes (CC-1) were monitored in the vicinity of demyelination site using immunofluorescent staining. Western blot was used to explore microglial polarization using M1 (iNOS) and M2 (arginase-1) markers. Focal demyelination elicited strong microglial and astroglial activation and reduced the number of OPCs at the site of demyelination. This inflammatory response was associated with enhanced number of newly born neurons in the white matter and the subventricular zone (SVZ). A proportion of newly born neurons within the white matter showed features of OPCs. Interestingly, blunting brain inflammation led to reduced neurogenesis around the demyelination area and in the SVZ. These data suggest that the white matter inflammation creates a conducive environment for the recruitment of newly born neurons. The fact that a sizable fraction of these newly born neurons adopt OPC features suggests that they could contribute to the remyelination process.

The Cox-2 Inhibitor Meloxicam Ameliorates Neuroinflammation and Depressive Behavior in Adult Mice after Splenectomy

BACKGROUND

Peripheral surgical trauma may incite neuroinflammation that leads to neuronal dysfunction associated with both depression and cognitive deficits. In a previous study, we found that adult mice developed neuroinflammation and short-term working memory dysfunction in a delayed, transient manner after splenectomy that was ameliorated by the cyclooxygenase-2 inhibitor meloxicam. We tested the hypothesis that splenectomy in mice would also cause anhedonia, the diminished response to pleasure or rewarding stimuli that is a hallmark of depression, and that treatment with meloxicam would be ameliorative.

METHODS

After Institutional Animal Care and Use Committee approval, Swiss-Webster mice underwent sucrose preference training before being randomized into groups on day 0, when they had either splenectomy and anesthesia or anesthesia alone. Within each group, half were randomized to receive intraperitoneal saline at 24 hours, while the other half received intraperitoneal meloxicam at 24 hours. Sucrose preference ratios were determined on days 1, 5, 9, and 14. Additional mice were randomized into groups for brain histochemistry. Specimens were stained for glial fibrillary acidic protein (GFAP), a marker of astrocytes, and CD45, a protein tyrosine phosphatase that identifies microglial activation.

RESULTS

On day 5, mice receiving splenectomy and saline demonstrated diminished sucrose preference, which was not seen in mice receiving splenectomy and meloxicam. Semiquantitative analysis of histological slides taken from splenectomized mice treated with meloxicam revealed reduced microglial-based neuroinflammation and reactive astrocytosis compared to mice receiving saline.

CONCLUSION

Splenectomy in mice is associated with neuroinflammation and anhedonia, as evidenced by reactive microgliosis, astrocytosis, and behavioral changes. Postsurgical treatment with meloxicam attenuates both neuroinflammation and anhedonia. These findings suggest that cyclooxygenase-2-dependent mechanisms may play a role in the development of postoperative mood disorders, possibly via modulation of peripheral effects on neuroinflammation.

CSF YKL-40 and pTau181 are related to different cerebral morphometric patterns in early AD

Cerebrospinal fluid (CSF) concentrations of YKL-40 that serve as biomarker of neuroinflammation are known to be altered along the clinico-biological continuum of Alzheimer's disease (AD). The specific structural cerebral correlates of CSF YKL-40 were evaluated across the early stages of AD from normal to preclinical to mild dementia. Nonlinear gray matter (GM) volume associations with CSF YKL-40 levels were assessed in a total of 116 subjects, including normal controls and those with preclinical AD as defined by CSF Aβ < 500 pg/mL, mild cognitive impairment (MCI) due to AD, or mild AD dementia. Age-corrected YKL-40 levels were increased in MCIs versus the rest of groups and showed an inverse u-shaped association with p-tau values. A similar nonlinear relationship was found between GM volume and YKL-40 in inferior and lateral temporal regions spreading to the supramarginal gyrus, insula, inferior frontal cortex, and cerebellum in MCI and AD. These findings for YKL-40 remained unchanged after adjusting for p-tau, which was found to be associated with GM volumes in distinct anatomic areas. CSF YKL-40, a biomarker of glial inflammation, is associated with a cerebral structural signature distinct from that related to p-tau neurodegeneration at the earliest stages of cognitive decline due to AD.

Hyperexcitability and epileptic seizures in a model of frontotemporal dementia

Epileptic seizures are more common in patients with Alzheimer disease than in the general elderly population. Abnormal forms of hyperphosphorylated tau accumulate in Alzheimer disease and other tauopathies. Aggregates of tau are also found in patients with epilepsy and in experimental models of epilepsy. We report here the analysis of epileptic activity and neuropathological correlates of a transgenic line over-expressing human mutant tau, a model of frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17). The FTDP-17 model displays spontaneous epileptic activity and seizures with spike-wave complexes in the EEG, and a higher sensitivity to the GABAA receptor antagonist pentylenetetrazol (PTZ) when compared to age-matched controls, showing a notably increased seizure length and a shorter latency to develop severe seizures. FTDP-17 human tau mutants also display lower convulsive thresholds and higher lethality after PTZ injections. Astrocytosis and activated microglia are prominent in the hippocampus and other brain regions of young FTDP-17 mice where the human mutant tau transgene is expressed, before the appearance of hyperphosphorylated tau aggregates in these structures. FTDP-17 human mutant tau over-expression produces epilepsy and increased GABAA receptor-mediated hyperexcitability in the absence of Aβ pathology. Although aggregates of hyperphosphorylated tau have been observed in patients with epilepsy and in different chemically and electrically generated models of epilepsy, the FTDP-17 tau mutant analyzed here is the first model of genetically modified tau that presents with epilepsy. This model may represent a valuable tool to assay novel treatments in order to reduce tau pathology, a potential factor which may be involved in the development of epileptic seizures in dementia and other neurodegenerative diseases.

Suppression of cytochrome P450 reductase expression promotes astrocytosis in subventricular zone of adult mice

The aim of this study was to determine the role of NADPH-cytochrome P450 reductase (CPR) and CPR-dependent enzymes in neural stem cell (NSC) genesis in the brain. A mouse model with globally suppressed Cpr gene expression (Cpr-low mouse) was studied for this purpose. Cpr-low and wild-type (WT) mice were compared immunohistochemically for the expression of markers of cell proliferation (Ki67), immature neurons (doublecortin, DCX), oligodendrocytes (oligodendrocyte transcription factor 2, OLIG2), and astrocytes (glial fibrillary acidic protein, GFAP) in the SVZ, and for the in vitro capability of their SVZ cells to form neurospheres and differentiate into astrocytes. We found that the abundance of SVZ cells that are positive for Ki67 or GFAP expression, but not the abundance of SVZ cells that are positive for DCX and OLIG2 expression, was significantly increased in Cpr-low mice, at various ages, compared with WT mice. Furthermore, extents of astrocyte differentiation and growth, but not neurosphere formation, from SVZ cells of the Cpr-low mice were significantly increased, compared with WT mice. These results suggest that CPR and CPR-dependent enzymes play a role in suppressing astrocytosis in the SVZ of adult mice.

Imaging astrocytosis with PET in Creutzfeldt-Jakob disease: case report with histopathological findings

In a previous study, patients with suspect Creutzfeldt-Jakob's disease (CJD) have been examined with Positron Emission Tomography (PET) combining N-[11C-methyl]-L-deuterodeprenyl (DED) and [(18)F] 2- fluorodeoxyglucose (FDG) in an attempt to detect astrocytosis and neuronal dysfunction, two of the hallmarks in CJD. Increased DED uptake with pronounced hypometabolism matching the areas with high DED retention was found in the fronto-parieto-occipital areas and cerebellum of patients with confirmed CJD. However, the temporal lobes did not present such a pattern. In 6 of the 15 examined patients the autopsy was performed, but a strict comparison between the PET results and the histopathology could not be done. Recently, one patient with suspect CJD was examined with PET using DED and FDG. The results of the examinations in this patient showed a pattern similar to that found in the brain of the CJD patients from the first study. The patient died shortly after the examination and an autopsy could be performed. The autopsy showed neuronal death, astrocytosis and spongiform changes in the brain. The diagnosis of definite sporadic CJD was established by the Western blot analysis, confirming the presence of the prion resistant protein (PrPres). The PET data demonstrated high DED uptake and extreme low glucose uptake in the left brain hemisphere whereas the right side was less affected. The autopsy was performed allowing the comparison between high DED uptake and the histopathological findings of reactive astrocytosis revealed by immunostaining with antibodies against glial fibrillary acid protein (GFAP). The results confirmed the presence of a pattern with high ratio DED/FDG, similar to that found in the previous study and revealing for the first time, a good correlation between high DED uptake and high density of reactive astrocytes as demonstrated by immunostaining.