Increase In Number Of Glial Cells Research Articles

Elucidating cellular contributions to tau-mediated neurodegeneration using drosophila and single-cell transcriptomics.

Alzheimer's Dementia (AD) is neuropathologically defined by aggregations of amyloid-beta plaques and tau neurofibrillary tangles in the brain, with tau pathology being most strongly correlated with cognitive decline. Systems biology approaches profiling post-mortem human AD brain tissue have highlighted involvement of key processes such as innate immunity and translational regulation. However, interpretation of cross-sectional post-mortem gene expression data is confounded by co-morbidities and mixed brain pathologies at autopsy. Moreover, characterizing longitudinal, age-related changes in Alzheimer's dementia (AD) is of particular importance because clinical manifestation of AD is a decades-long process, and age is the strongest known risk factor. We previously completed RNA-sequencing and proteomics of several highly tractable, longitudinal, Drosophila models of tauopathy to characterize tau- and age-specific perturbations. However, cellular heterogeneity confounds interpretation of bulk tissue data. We thus leverage single cell RNA sequencing (scRNA-seq) to explore cell-specific contributions to tau- and age-mediated gene expression. Whole brains of adult Drosophila pan-neuronally expressing a mutant variant of human Tau (R406W) and controls were dissociated for scRNA-seq (10x Genomics Chromium) at 1-, 10-, and 20- days of age. Perturbations in cellular composition and gene expression were quantified. To address cross-species conservation of tau-mediated scRNAseq signatures, we leverage existing human AD brain scRNA-seq data. As expected, we highlight evidence for tau-mediated degeneration of Kenyon cells, a neuronal population in the Drosophila "mushroom body" that is required for learning and memory, along with a concomitant increase in glial cell numbers (e.g. gliosis). Gene set enrichment analysis reveal overrepresentation of acetylcholine receptor regulation pathways in vulnerable mushroom body neurons. Interestingly, regularized regression analyses highlight innate immune activity as predictive of tau-related neuronal reduction. Cluster-specific transcriptional signatures between flies and humans demonstrate strong correlations among inferred cell identities. Our results comprise a powerful single cell transcriptomic resource for studying tau-mediated disruption of gene expression and dynamic age-dependent changes at cellular resolution in a tractable model system that is amenable for high throughput functional validation.

PP75. DROSOPHILA MELANOGASTER AS A MODEL ORGANISM TO STUDY GLIOMA: LOCATION AND IDENTIFICATION OF FOLLISTATIN

Gliomas are the most common, malignant brain tumour found in the central nervous system. The main characteristics of gliomas is their rapid proliferation, resistance to current chemotherapies and their ability to infiltrate the brain. Brain tumours have a low survival rate due to the lack of available treatments. In the UK between 2010 and 2011, the survival rate was 14% for 10 or more year. The mortality rates for malignant brain and CNS tumours have increased by up to 24% in the UK between 1970 and 2012. As there is difficulty obtaining glioma samples, it is important to identify a suitable model organism. The main signalling pathways seen to be activated in human glioma development are the epithelial growth factor receptor (EGFR) and phosphatidylinositol-3 kinase (PI3K) pathways. The homologous EFGR and PI3K pathways have been studied greatly in drosophila, and show that there must be co-activation of the EGFR and PI3K pathways for cancer development to occur; leading to an increase in glial cell numbers by 50-100x fold. Follistatin is a protein which has been identified as a biomarker in malignant gliomas; by comparing normal serum to glioma serum it has shown that there is an overexpression of follistatin. Gliomas can be replicated in drosophila as there has been a high level of homology identified in human diseased states and in neural development. Follistatin studies have shown it has important roles in development and differentiation of tissues and organs. It acts as an inhibitor, binding to activin, bone morphogenetic proteins and other proteins which can be found in vertebrates. Follistatin has been identified within a number of different cancer types (such as prostate and ovarian), and plays an important role in cancer metastasis and angiogenesis. Serum studies have revealed follistatin is present in the early stages of cancer development; however the location and role of follistatin in cancer development has not been identified. Drosophila contain a homolog of follistatin, which will allow studies of follistatin in cancer within drosophila. By using drosophila as a model organism it will allow the location of follistatin and its involvement in glioma development to be identified. Immunohistochemistry is used to identify the location and distribution of a protein within a tissue or an organ. It is commonly used to identify which proteins are present in specific types of cancer. Follistatin has been identified to play a role in the early stages of glioma development. Therefore by using immunohistochemistry follistatin can be identified throughout the different stages of glioma development and possibly identify its role in this development. The aim of the research is to identify and locate the protein follistatin in drosophila by using immunohistochemistry. Using different larval instar stages, this will identify the distribution of follistatin in different stages of neural development. The hypothesis would be that follistatin is involved in the early stages of glial development and the distribution is important in glioma development compared to normal neural development.

Ms Phillips and Dr Blier Reply

Article AbstractBecause this piece does not have an abstract, we have provided for your benefit the first 3 sentences of the full text.To the Editor: We thank Dr Maany for his comments regarding our article, which documented an increased brain volume with sustained remission in patients with treatment-resistant depression. In his letter, Dr Maany asks us to speculate about the cellular basis that underlies the volume increases we observed in remitted patients. Proposed mechanisms that could contribute to increased brain volume among antidepressant-treated patients may include regeneration of neurons, increase in glial cell numbers, larger neuropil volume, more blood vessels, or less apoptosis.

Amyloid-β oligomers link depressive-like behavior and cognitive deficits in mice

Depression is one of the most common psychiatric symptoms in Alzheimer's disease (AD), and considerable evidence indicates that major depressive disorder increases the risk of AD.1, 2, 3 To date, however, the molecular mechanisms underlying the clinical association between depression and AD have remained elusive. Soluble oligomers of the amyloid-β peptide (AβOs) accumulate in the brains of AD patients and are increasingly recognized as the proximal neurotoxins responsible for synapse failure and memory deficits in AD.4, 5 We have hypothesized that AβOs might be mechanistically linked to behavioral changes in AD. In order to test this hypothesis, mice were given a single intracerebroventricular (i.c.v.) injection of 10 pmol AβOs and were subsequently evaluated in the Porsolt forced swim test (FST) for assessment of depressive-like behavior. Compared with vehicle-injected control mice, AβO-injected mice exhibited a significant increase in immobility in the FST, both 24 h and 8 days after AβO injections (Figure 1a). Similar results were obtained when animals were assessed in the tail suspension test, another classical task to evaluate depressive-like behavior in rodents (Supplementary Figure S1a). AβO-induced immobility in the FST was blocked by anti-depressant (fluoxetine) treatment (Figure 1a). An important feature of depressive disorder is anhedonic behavior, including decreased interest for pleasurable sensorial experiences. Whereas vehicle-injected mice exhibited an expected preference for sucrose solution over plain water, AβO-injected mice did not exhibit such preference, indicating that AβOs instigate anhedonic behavior (Figure 1b). Figure 1 Amyloid-β oligomers (AβOs) induce depressive-like behavior, memory deficits and hippocampal recruitment of microglia and astrocytes in mice. Three-month-old Swiss mice received a single intracerebroventricular (i.c.v.) injection of AβOs ... As memory deficit is the main clinical symptom of AD, we investigated the impact of AβOs on mice memory using the novel object recognition (OR) task. Results showed that 24 h after i.c.v. injection, AβO-treated mice spent equal amounts of time exploring both old (familiar) and new (novel) objects, indicating a deficit in declarative recognition memory, whereas vehicle-injected animals exhibited a significant preference for the novel object (Figure 1c). Treatment with fluoxetine prevented the memory deficit induced by AβOs (Figure 1c). Control measurements showed no changes in spontaneous exploratory or locomotor activities of fluoxetine-, saline-, vehicle- or AβO-injected animals during the training phase of the OR test (Supplementary Figure S1c–e). As the hippocampus is a key anatomical structure for OR memory, we sought to determine whether AβOs injected i.c.v. reached the hippocampus. Indeed, robust AβO immunoreactivity was verified using an anti-oligomer monoclonal antibody (NU4)6 in hippocampi from AβO-injected mice, but not in hippocampi from control vehicle-injected animals (Supplementary Figure S1b). Together, these results indicate that AβOs have an acute impact on memory, learning and mood in mice, and that fluoxetine treatment prevented both cognitive impairment and depressive-like behavior induced by AβOs. The beneficial actions of fluoxetine have been partly ascribed to its anti-inflammatory effect. This led us to ask whether AβOs triggered an inflammatory response in the mouse brain. The brains of mice used in the tests described above were analyzed for levels of pro-inflammatory cytokines after i.c.v. injection of AβOs or vehicle. AβO-injected animals showed significantly elevated brain levels of interleukin-1β and tumor necrosis factor-α compared with vehicle-injected animals (Figure 1d, e). Sections from the hippocampus and cortex of AβO- or vehicle-injected mice were further immunostained for the presence of microglia (anti-Iba-1 antibody) and astrocytes (anti-GFAP antibody). Compared with vehicle-injected animals, AβO-injected mice showed markedly increased immunoreactivities for both Iba-1 and GFAP in the hippocampus and cortex 24 h after injection (Figure 1f–o, and Supplementary Figure 1f–o). The increase in glial cell numbers instigated by AβOs was blocked by fluoxetine treatment of the animals before AβO injection (Figure 1f–o, and Supplementary Figure 1f–o). The current findings establish that AβOs link memory impairment and depressive-like behavior in mice, providing molecular mechanistic support to clinical evidence connecting AD and depressive disorder. The impact of AβOs on mood, learning and memory, and its prevention by fluoxetine, can likely be attributed to the activation of inflammatory pathways (as shown here) and, possibly, to the deregulation of the serotonergic axis. The latter possibility is in line with the observation that pro-inflammatory cytokines impact serotonin metabolism7, 8 and that increased serotonin levels are associated with lower brain Aβ levels in transgenic mouse models of AD and in humans.9 Moreover, 5-HT1A and 5-HT2A receptors have been reported to be reduced in post-mortem AD brain,10 and 5-HT1A receptors have been found to be reduced in vivo in AD.11 Brain disturbances that place a person at risk for developing depression and AD are still largely unknown. By revealing that AβOs underlie both cognitive and depressive-like symptoms in mice, our results suggest a mechanism by which elevated brain levels of AβOs may be linked to changes in cognition and mood in AD.

1333 Transsynaptic cell death does not occur in substantia migra pars reticulata in developing rats

The substantia nigra and globus pallidus (two iron-rich brain areas) receive a substantial innervation from the neostriatum, a considerable amount of which is GABAergic. Because of this anatomic relationship and the finding that prevention of GABA degradation in these two areas decreases their histochemical levels of iron, GABAergic transmission/metabolism may be important in regulating brain iron levels. Therefore, the present study investigated the effects of denervation of striatal/pallidal inputs to globus pallidus/substantia nigra on iron levels and associated pathologic changes in globus pallidus/substantia nigra. Adult male Sprague-Dawley rats received unilateral ibotenic acid infusions resulting in comprehensive lesions of the entire neostriatum/globus pallidus complex, or of either the anterior neostriatum or the posterior neostriatum/globus pallidus. Animals were killed at one week or one month following surgery. Between one week and one month postlesioning, comprehensive neostriatum/globus pallidus lesions induced a progressive decrease in substantia nigra volume, as well as a progressive increase in both substantia nigra zona reticularis iron staining and substantia nigra iron concentration. By one month following neostriatum/globus pallidus lesions, a marked 73% loss of substantia nigra zona reticularis neurons occurred in association with a 65% increase in glial cell numbers within zona reticularis. Compared to comprehensive neostriatum/globus pallidus lesions at the one month postlesion time point, more restricted anterior neostriatum and posterior neostriatum/globus pallidus lesions induced a less severe atrophy of the substantia nigra, a small (anterior neostriatum lesions) to moderate (posterior neostriatum/globus pallidus lesions) increase in substantia nigra zona reticularis iron staining, and either no zona reticularis neuronal loss (anterior neostriatum lesions) or limited zona reticularis neuronal loss selectively within areas of increased iron staining.These results suggests that destruction of striatal/pallidal innervation to the substantia nigra's zona reticularis induces a disruption of zona reticularis iron homeostasis, resulting in a redistribution and/or accumulation of iron in the zona reticularis and consequent zona reticularis of the substantia nigra neurodegeneration. The results further suggest that loss or dysfunction of striatonigral/striatopallidal GABAergic neurons in several neurodegenerative diseases (including Hallervorden-Spatz syndrome, progressive supranuclear palsy, multiple system atrophy, and Parkinson's disease) may result in an increase or redistribution of nigral iron to cause loss of substantia nigra neurons.

1332 Protective effects of adenosine against hypoxic injury in cultured rat cortical neurons

The substantia nigra and globus pallidus (two iron-rich brain areas) receive a substantial innervation from the neostriatum, a considerable amount of which is GABAergic. Because of this anatomic relationship and the finding that prevention of GABA degradation in these two areas decreases their histochemical levels of iron, GABAergic transmission/metabolism may be important in regulating brain iron levels. Therefore, the present study investigated the effects of denervation of striatal/pallidal inputs to globus pallidus/substantia nigra on iron levels and associated pathologic changes in globus pallidus/substantia nigra. Adult male Sprague-Dawley rats received unilateral ibotenic acid infusions resulting in comprehensive lesions of the entire neostriatum/globus pallidus complex, or of either the anterior neostriatum or the posterior neostriatum/globus pallidus. Animals were killed at one week or one month following surgery. Between one week and one month postlesioning, comprehensive neostriatum/globus pallidus lesions induced a progressive decrease in substantia nigra volume, as well as a progressive increase in both substantia nigra zona reticularis iron staining and substantia nigra iron concentration. By one month following neostriatum/globus pallidus lesions, a marked 73% loss of substantia nigra zona reticularis neurons occurred in association with a 65% increase in glial cell numbers within zona reticularis. Compared to comprehensive neostriatum/globus pallidus lesions at the one month postlesion time point, more restricted anterior neostriatum and posterior neostriatum/globus pallidus lesions induced a less severe atrophy of the substantia nigra, a small (anterior neostriatum lesions) to moderate (posterior neostriatum/globus pallidus lesions) increase in substantia nigra zona reticularis iron staining, and either no zona reticularis neuronal loss (anterior neostriatum lesions) or limited zona reticularis neuronal loss selectively within areas of increased iron staining.These results suggests that destruction of striatal/pallidal innervation to the substantia nigra's zona reticularis induces a disruption of zona reticularis iron homeostasis, resulting in a redistribution and/or accumulation of iron in the zona reticularis and consequent zona reticularis of the substantia nigra neurodegeneration. The results further suggest that loss or dysfunction of striatonigral/striatopallidal GABAergic neurons in several neurodegenerative diseases (including Hallervorden-Spatz syndrome, progressive supranuclear palsy, multiple system atrophy, and Parkinson's disease) may result in an increase or redistribution of nigral iron to cause loss of substantia nigra neurons.

Time-dependent changes in iron levels and associated neuronal loss within the substantia nigra following lesions within the neostriatum/globus pallidus complex.

The substantia nigra and globus pallidus (two iron-rich brain areas) receive a substantial innervation from the neostriatum, a considerable amount of which is GABAergic. Because of this anatomic relationship and the finding that prevention of GABA degradation in these two areas decreases their histochemical levels of iron, GABAergic transmission/metabolism may be important in regulating brain iron levels. Therefore, the present study investigated the effects of denervation of striatal/pallidal inputs to globus pallidus/substantia nigra on iron levels and associated pathologic changes in globus pallidus/substantia nigra. Adult male Sprague-Dawley rats received unilateral ibotenic acid infusions resulting in comprehensive lesions of the entire neostriatum/globus pallidus complex, or of either the anterior neostriatum or the posterior neostriatum/globus pallidus. Animals were killed at one week or one month following surgery. Between one week and one month postlesioning, comprehensive neostriatum/globus pallidus lesions induced a progressive decrease in substantia nigra volume, as well as a progressive increase in both substantia nigra zona reticularis iron staining and substantia nigra iron concentration. By one month following neostriatum/globus pallidus lesions, a marked 73% loss of substantia nigra zona reticularis neurons occurred in association with a 65% increase in glial cell numbers within zona reticularis. Compared to comprehensive neostriatum/globus pallidus lesions at the one month postlesion time point, more restricted anterior neostriatum and posterior neostriatum/globus pallidus lesions induced a less severe atrophy of the substantia nigra, a small (anterior neostriatum lesions) to moderate (posterior neostriatum/globus pallidus lesions) increase in substantia nigra zona reticularis iron staining, and either no zona reticularis neuronal loss (anterior neostriatum lesions) or limited zona reticularis neuronal loss selectively within areas of increased iron staining. These results suggest that destruction of striatal/pallidal innervation to the substantia nigra's zona reticularis induces a disruption of zona reticularis iron homeostasis, resulting in a redistribution and/or accumulation of iron in the zona reticularis and consequent zona reticularis of the substantia nigra neurodegeneration. The results further suggest that loss or dysfunction of striatonigral/striatopallidal GABAergic neurons in several neurodegenerative diseases (including Hallervorden-Spatz syndrome, progressive supranuclear palsy, multiple system atrophy, and Parkinson's disease) may result in an increase or redistribution of nigral iron to cause loss of substantia nigra neurons.

There is less thalamic degeneration in neonatal-lesioned than in adult-lesioned cats after cerebral hemispherectomy

In order to study age-related processes of degeneration and recovery, the left hemitelencephalon was surgically removed in 5 adult cats and 5 neonatal kittens which were compared to 5 intact controls. After long survival, brains were sectioned in the coronal plane and thionine-stained. Drawings of gross and microscopic thalamic structures were made at 4 planes and computer-digitized to provide 7 measures: total thalamic area at planes A 7.5 and A 8.5; counts of neuroglia, small neurons (31-100 microns2) and large neurons (101-1000 microns2); area of neuroglia, small neurons and large neurons. All cellular measurements were in the ventrobasal complex at planes A 8.0 and A 10.0. Morphological changes were found bilaterally in all lesioned cats. Ipsilateral to the ablation in adult-lesioned cats, thalamic area, large neuron count and glia cells size were markedly and significantly decreased (P less than 0.01), while in neonatal-lesioned cats these changes were present but significantly reduced in magnitude compared to adult-lesioned animals. In addition, adult-lesioned cats showed a marked increase in glial cell numbers (P less than 0.01) and a decrease in small neuron size (P less than 0.01), while kitten-lesioned animals did not show changes in these measures. In the intact side of the brain, the thalamus of adult-lesioned cats was decreased in size (P less than 0.01), and glial cells were decreased in number and size (P less than 0.05), while in kitten-lesioned brains there were few changes. In both lesioned groups large neurons showed a significant increase in size (P less than 0.01). We conclude that neonatal hemispherectomy results in markedly less thalamic atrophy, retrograde neuronal degeneration and gliosis than the equivalent lesion in adults. The changes are discussed in the context of the increased neuroanatomical reorganization and functional recovery which were reported in neonatal- vs adult-lesioned animals.