Immortalization and characterization of rat microglial cells

Glioma-associated microglia/macrophages (GAMs) in glioblastoma: Immune function in the tumor microenvironment and implications for immunotherapy

Glioma is a mixed solid tumor composed of neoplastic and non-neoplastic components. Glioma-associated macrophages and microglia (GAMs) are crucial elements of the glioma tumor microenvironment (TME), regulating tumor growth, invasion, and recurrence. GAMs are also profoundly influenced by glioma cells. Recent studies have revealed the intricate relationship between TME and GAMs. In this updated review, we provide an overview of the interaction between glioma TME and GAMs based on previous studies. We also summarize a series of immunotherapies targeting GAMs, including clinical trials and preclinical studies. Specifically, we discuss the origin of microglia in the central nervous system and the recruitment of GAMs in the glioma background. We also cover the mechanisms through which GAMs regulate various processes associated with glioma development, such as invasiveness, angiogenesis, immunosuppression, recurrence, etc. Overall, GAMs play a significant role in the tumor biology of glioma, and a better understanding of the interaction between GAMs and glioma could catalyze the development of new and effective immunotherapies for this deadly malignancy.

Increased Amyloid Precursor Protein and Tau Expression Manifests as Key Secondary Cell Death in Chronic Traumatic Brain Injury

In testing the hypothesis of Alzheimer's disease (AD)‐like pathology in late stage traumatic brain injury (TBI), we evaluated AD pathological markers in late stage TBI model. Sprague–Dawley male rats were subjected to moderate controlled cortical impact (CCI) injury, and 6 months later euthanized and brain tissues harvested. Results from H&E staining revealed significant 33% and 10% reduction in the ipsilateral and contralateral hippocampal CA3 interneurons, increased MHCII‐activated inflammatory cells in many gray matter (8–20‐fold increase) and white matter (6–30‐fold increased) regions of both the ipsilateral and contralateral hemispheres, decreased cell cycle regulating protein marker by 1.6‐ and 1‐fold in the SVZ and a 2.3‐ and 1.5‐fold reductions in the ipsilateral and contralateral dentate gyrus, diminution of immature neuronal marker by two‐ and onefold in both the ipsilateral and contralateral SVZ and dentate gyrus, and amplified amyloid precursor protein (APP) distribution volumes in white matter including corpus callosum, fornix, and internal capsule (4–38‐fold increase), as well as in the cortical gray matter, such as the striatum hilus, SVZ, and dentate gyrus (6–40‐fold increase) in TBI animals compared to controls (P's < 0.001). Surrogate AD‐like phenotypic markers revealed a significant accumulation of phosphorylated tau (AT8) and oligomeric tau (T22) within the neuronal cell bodies in ipsilateral and contralateral cortex, and dentate gyrus relative to sham control, further supporting the rampant neurodegenerative pathology in TBI secondary cell death. These findings indicate that AD‐like pathological features may prove to be valuable markers and therapeutic targets for late stage TBI. J. Cell. Physiol. 232: 665–677, 2017. © 2016 The Authors. Journal of Cellular Physiology Published by Wiley Periodicals, Inc.

Immortalized neurons for the study of hypothalamic function

The hypothalamus is a vital part of the central nervous system: it harbors control systems implicated in regulation of a wide range of homeostatic processes, including energy balance and reproduction. Structurally, the hypothalamus is a complex neuroendocrine tissue composed of a multitude of unique neuronal cell types that express a number of neuromodulators, including hormones, classical neurotransmitters, and specific neuropeptides that play a critical role in mediating hypothalamic function. However, neuropeptide and receptor gene expression, second messenger activation, and electrophysiological and secretory properties of these hypothalamic neurons are not yet fully defined, primarily because the heterogeneity and complex neuronal architecture of the neuroendocrine hypothalamus make such studies challenging to perform in vivo. To circumvent this problem, our research group recently generated embryonic- and adult-derived hypothalamic neuronal cell models by utilizing the novel molecular techniques of ciliary neurotrophic factor-induced neurogenesis and SV40 T antigen transfer to primary hypothalamic neuronal cell cultures. Significant research with these cell lines has demonstrated their value as a potential tool for use in molecular genetic analysis of hypothalamic neuronal function. Insights gained from hypothalamic immortalized cells used in conjunction with in vivo models will enhance our understanding of hypothalamic functions such as neurogenesis, neuronal plasticity, glucose sensing, energy homeostasis, circadian rhythms, and reproduction. This review discusses the generation and use of hypothalamic cell models to study mechanisms underlying the function of individual hypothalamic neurons and to gain a more complete understanding of the overall physiology of the hypothalamus.

Immortalized human microglial cell line: phenotypic expression

Microglia are a major neuroglial component of the CNS, playing an important role as resident immunocompetent and phagocytic cells in the CNS in the event of injury and disease. To understand the role of microglia in the CNS in health and diseases, we have recently established an immortalized clonal cell line of human microglia, HMO6, from human embryonic telencephalon tissue by using a retroviral vector encoding v-myc. This immortalized microglia HMO6 cell line exhibits cell-type-specific antigens for microglia, including CD11b (Mac-1), CD68, CD86 (B7-2), HLA-ABC, HLA-DR, and RCA-1 lectin, and actively phagocytoses latex beads.

Microglia in health and disease

Microglia, one of three glial cell types in the central nervous system (CNS), play an important role as resident immunocompetent and phagocytic cells in the CNS in the event of injury and disease. It was del Rio Hortega in 1927 who determined that microglia belong a distinct glial cell type apart from astrocytes and oligodendrocytes, and since 1970s there has been wide recognition that microglia are immune effectors in the CNS that respond to pathological conditions and participate in initiation and progression of neurological disorders including Alzheimer's disease, Parkinson's disease, multiple sclerosis, and acquired immune deficiency syndrome dementia complex by releasing potentially cytotoxic molecules such as proinflammatory cytokines, reactive oxygen intermediates, proteinases and complement proteins. There is also evidence to suggest that microglia are capable of secreting neurotrophic or neuron survival factors upon activation via inflammation or injury. It is thus timely to review current status of knowledge on biology and immunology of microglia, and consider new directions of investigation on microglia in health and disease.

An acidic fibroblast growth factor-like factor secreted into the brain cell culture medium upregulates apoE synthesis, HDL secretion and cholesterol metabolism in rat astrocytes

Production and release of apolipoprotein (apo) E and cholesterol were highly upregulated in the astrocytes prepared by 1-week secondary culture after 1-month primary culture of rat fetal brain cells (M/W cells) in comparison to the cells prepared by a conventional method of 1-week primary and 1-week secondary culture (W/W cells). Both cell preparations were mostly composed of astrocytes with small population of other glial cells, except that type-2 astrocyte-like cells accounted for 5-15% of M/W cells indicating more activated and/or matured status. The conditioned medium of the 1-month primary culture stimulated W/W cells to increase the release of apoE and cholesterol into the medium. The treatment of W/W cells by acidic fibroblast growth factor (aFGF) similarly upregulated biosyntheses and release of apoE and cholesterol. The effect of the conditioned medium was completely inhibited by pretreatment with an anti-aFGF antibody. The increase of the aFGF message was demonstrated in the brain cells after 1-month primary culture. The findings suggested that an aFGF-like trophic factor upregulates biosynthesis and secretion of apoE-high density lipoprotein (HDL) in astrocytes probably by autocrine stimulation in this culture system. Since this cytokine is highly expressed in the development or post-injury period of the brain, it putatively activates intercellular cholesterol transport to support construction or recovery of the brain.

Phenotypic and functional changes in glial cells as a function of age

Both in vivo and in vitro investigations point to an important role for the immune system in the development of age-related neurodegeneration. Microglia isolated from aged female F344 rats, 18-20 months, show a higher percentage of cells with an ameboid morphology indicative of activation, whereas, astrocytes had a quiescent morphology. The ability of astrocytes and microglia to attenuate toxin-induced neuronal injury was examined. Post-natal day 1-3 pup cells optimally rescued neurons from Abeta-induced toxicity, whereas mixed glial cells from 18-20 month old rats were unable to rescue neurons from Abeta-induced toxicity. Our results suggested the appearance of a neurotoxic co-factor, therefore we investigated the basal level of nitric oxide and pro-inflammatory cytokines to determine if altered levels of immune mediators play a role in the toxicity. Mitogen-stimulated nitric oxide production increased 10 fold with age of donor, whereas, only the pup cells expressed an increase in TNF-alpha production. Basal levels of pro-inflammatory cytokines, as measured by RNA protection assays, increased with age. In particular, IL-1beta was increased 2 fold between adult and aged glial cells. The elevated cytokine expression may contribute to enhanced susceptibility to neurodegenerative diseases.

Immobilized amyloid precursor protein constructs: a tool for the in vitro screening of glial cell reactivity

Astrocytes and microglia are closely associated with amyloid plaques in Alzheimer's disease (AD). Microglia constitute the first barrier surrounding plaques, although they seem to be unable to remove them efficiently. We evaluated the reaction of microglial cells from neonatal rats and mice to plaque mimetics. The C-terminal part of the amyloid precursor protein (APP) or amyloid peptide (A beta) was immobilized to either 60-microm or 2.8-microm beads and incubated with microglial cells. Beads of 60 microm, having approximately the size of senile plaques, were not phagocytosed, in contrast to 2.8-microm beads, which were phagocytosed by microglia but not by astrocytes. Once taken up by the cells, proteins immobilized to the beads were degraded rapidly, as confirmed by mass spectrometry and immunofluorescence with an antibody against beta-amyloid. On the other hand, no protein degradation was observed with 60-microm beads. Also, probably as a reaction to its incapability to phagocytose the beads, glia organized around the beads and started to proliferate. Cell proliferation was more pronounced when the beads contained the A beta epitope compared with the beads with an inert surface. This in vitro effect could be exploited to set up a screening assay for compounds that ameliorate the adverse reaction of microglia supposed to contribute to the pathogenesis of AD.

Astrocytes Express Elements of the Class II Endocytic Pathway and Process Central Nervous System Autoantigen for Presentation to Encephalitogenic T Cells

Astrocytes are nonprofessional APCs that may participate in Ag presentation and activation of pathogenic CD4+ T cells involved in central nervous system (CNS) inflammatory diseases. Using immortalized pure astrocytes as a complement to the study of primary astrocytes, we investigated whether these astrocytes express elements involved in the class II endocytic pathway and if they are capable of processing native myelin basic protein (MBP), a step that could be necessary for initiating or perpetuating T cell recognition of this self-Ag in vivo. Upon IFN-γ-stimulation, primary and immortalized astrocytes up-regulate class II transactivator (CIITA), invariant chain (Ii) (p31 and p41), H-2Ma, and H-2Mb. Analysis of CIITA cDNA sequences demonstrated that CIITA transcription in astrocytes is directed by a promoter (type IV) that mediates IFN-γ-inducible CIITA expression and encodes a CIITA protein that differs in its N-terminal sequence from CIITA reported in professional APC. Comparing live and fixed APC for Ag presentation, we show that Ag processing by APC is required for presentation of native MBP to autopathogenic T cells specific for the major MBP epitope, Ac1-11. We have observed that primary astrocytes and some, but not all, astrocyte lines in the absence of contaminating microglia are capable of processing and presenting native MBP, suggesting that there may be heterogeneity. Our study provides definitive evidence that astrocytes are capable of processing CNS autoantigen, indicating that astrocytes have potential for processing and presentation of CNS autoantigen to proinflammatory T cells in CNS autoimmune disease.

Intrastriatal transplantation of rat adrenal chromaffin cells seeded on microcarrier beads promote long-term functional recovery in hemiparkinsonian rats

Possible biologic treatments for Parkinson's disease, a disorder caused by the deterioration of dopaminergic neurons bridging the nigrostriatal system, have recently focused on fetal cell transplantation. Because of ethical and tissue availability issues concerning fetal cell transplantation, alternative cell sources are being developed. The adrenal medulla has been used as a cell transplant source because of the capacity of the cells to provide catecholamines and to transform into a neuronal phenotype. However, adrenal tissue transplants have shown limited success, primarily because of their lack of long-term viability. Recently, seeding adrenal chromaffin cells on microcarrier beads has been shown to enhance the cell viability following neural transplantation. In the present study, we further investigated whether transplantation of rat adrenal chromaffin cells seeded on microcarrier beads into the striatum of 6-hydroxydopamine-induced hemiparkinsonian rats would result in a sustained functional recovery. Behavioral tests using the apomorphine-induced rotational and elevated body swing tests up to 12 months posttransplantation revealed a significant behavioral recovery in animals that received adrenal chromaffin cells seeded on microcarrier beads compared to animals that received adrenal chromaffin cells alone, medium alone, or beads alone. Histological examination of tissue at 14 months posttransplantation revealed evidence of tyrosine hydroxylase-positive cells and an on-going glial response in animals transplanted with adrenal chromaffin cells seeded on microcarrier beads, in contrast to absence of such immunoreactive responses in the other groups. These findings support a facilitator role for microcarrier beads in transplantation of adrenal chromaffin cells or other cells that are easily rejected by the CNS.

Genetic influences on cellular reactions to brain injury: activation of microglia in denervated neuropil in mice carrying a mutation (Wld(S)) that causes delayed Wallerian degeneration

This study examines the relationship between the appearance of degenerative changes in synaptic terminals and axons and the activation of microglia in denervated neuropil regions of normal mice of the C57BL/6 strain and mutant mice (Wld(S)), in which Wallerian degeneration is substantially delayed. The time course of degenerative changes in synaptic terminals and axons was assessed using selective silver staining. Microglial cells were identified by immunostaining for Mac-1, a monoclonal antibody to the CR3 complement receptor, and by histochemical staining for nucleoside diphosphatase (NDPase). Increased argyrophilia, indicative of degenerative changes, was evident as early as 1 day postlesion in normal mice, but was not seen until 6-8 days in mice with the Wld(S) mutation. Microglial activation in normal C57BL/6 mice was evident by 24 hours postlesion, as evidenced by increased immunostaining for Mac-1, increased histochemical staining for NDPase, and morphological changes indicative of an activated phenotype (short, thick processes). Quantitative evaluation of immunostaining for Mac-1 revealed that peak activation occurred between 2 and 6 days postlesion with a return to a quiescent phenotype by 12 days. In contrast, the microglial response was significantly delayed and prolonged in mice bearing the Wld(S) mutation. Activated microglia were not seen within the deafferented area until 6 to 8 days postlesion and peak activation occurred between 12 and 20 days postlesion. These data suggest that the response of microglia in denervated neuropil zones is triggered by the same types of degenerative changes that cause increased argyrophilia as detected by selective silver staining methods.