Gene expression in astrocytes is affected by subculture

Astrocytes Control Sensory Acuity via Tonic Inhibition in the Thalamus

Sensory discrimination is essential for survival. However, how sensory information is finely controlled in the brain is not well defined. Here, we show that astrocytes control tactile acuity via tonic inhibition in the thalamus. Mechanistically, diamine oxidase (DAO) and the subsequent aldehyde dehydrogenase 1a1 (Aldh1a1) convert putrescine into GABA, which is released via Best1. The GABA from astrocytes inhibits synaptically evoked firing at the lemniscal synapses to fine-tune the dynamic range of the stimulation-response relationship, the precision of spike timing, and tactile discrimination. Our findings reveal a novel role of astrocytes in the control of sensory acuity through tonic GABA release.

Astrocyte culture models: Molecular and function characterization of primary culture, immortalized astrocytes and C6 glioma cells

The understanding of the physiology of astrocytes and their role in brain function progresses continuously. Primary astrocyte culture is an alternative method to study these cells in an isolated system: in their physiologic and pathologic states. Cell lines are often used as an astrocyte model, since they are easier and faster to manipulate and cost less. However, there are a few studies evaluating the different features of these cells which may put into question the validity of using them as astrocyte models. The aim of this study was to compare primary cultures (PC) with two cell lines - immortalized astrocytes and C6 cells, in terms of protein characterization, morphology and metabolic functional activity. Our results showed, under the same culture condition, that immortalized astrocytes and C6 are positive for differentiated astrocytic markers (eg. GFAP, S100B, AQP4 and ALDH1L1), although expressing them in less quantities then primary astrocyte cultures. Glutamate metabolism and cell communication are reduced in proliferative cells. However, glucose uptake is elevated in C6 lineage cells in comparison with primary astrocytes, probably due to their tumorigenic origin and high proliferation rate. Immortalized astrocytes presented a lower growth rate than C6 cells, and a similar basal morphology as primary astrocytes. However, they did not prove to be as good reproductive models of some of the classic astrocytic functions, such as S100B secretion and GFAP content, especially while under stimulation. In contrast, C6 cells presented similar results in comparison to primary astrocytes in response to stimuli. Here we provide a functional comparison of three astrocytic models, in an attempt to select the most suitable model for the study of astrocytes, optimizing the research in this area of knowledge.

Development of a high throughput drug screening assay to identify compounds that protect oligodendrocyte viability and differentiation under inflammatory conditions

Background

Newly proliferated oligodendrocyte precursor cells (OPCs) migrate and surround lesions of patients with multiple sclerosis (MS) and other demyelinating diseases, but fail to differentiate into oligodendrocytes (OLs) and remyelinate remaining viable axons. The abundance of secreted inflammatory factors within and surrounding these lesions likely plays a major inhibitory role, promoting cell death and preventing OL differentiation and axon remyelination. To identify clinical candidate compounds that may protect existing and differentiating OLs in patients, we have developed a high throughput screening (HTS) assay that utilizes purified rat OPCs.

Results

Using a fluorescent indicator of cell viability coupled with image quantification, we developed an assay to allow the identification of compounds that promote OL viability and differentiation in the presence of the synergistic inflammatory cytokines, tumor necrosis factor α and interferon-γ. We have utilized this assay to screen the NIH clinical collection library and identify compounds that protect OLs and promote OL differentiation in the presence of these inflammatory cytokines.

Conclusion

This primary OL-based cytokine protection assay is adaptable for HTS and may be easily modified for profiling of compounds in the presence of other potentially inhibitory molecules found in MS lesions. This assay should be of use to those interested in identifying drugs for the treatment of MS and other demyelinating diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-016-2219-8) contains supplementary material, which is available to authorized users.

A high throughput drug screening assay to identify compounds that promote oligodendrocyte differentiation using acutely dissociated and purified oligodendrocyte precursor cells

Background

Multiple sclerosis is caused by an autoimmune response resulting in demyelination and neural degeneration. The adult central nervous system has the capacity to remyelinate axons in part through the generation of new oligodendrocytes (OLs). To identify clinical candidate compounds that may promote remyelination, we have developed a high throughput screening (HTS) assay to identify compounds that promote the differentiation of oligodendrocyte precursor cells (OPCs) into OLs.

Results

Using acutely dissociated and purified rat OPCs coupled with immunofluorescent image quantification, we have developed an OL differentiation assay. We have validated this assay with a known promoter of differentiation, thyroid hormone, and subsequently used the assay to screen the NIH clinical collection library. We have identified twenty-seven hit compounds which were validated by dose response analysis and the generation of half maximal effective concentration (EC₅₀) values allowed for the ranking of efficacy. The assay identified novel promoters of OL differentiation which we attribute to (1) the incorporation of an OL toxicity pre-screen to allow lowering the concentrations of toxic compounds and (2) the utilization of freshly purified, non-passaged OPCs. These features set our assay apart from other OL differentiation assays used for drug discovery efforts.

Conclusions

This acute primary OL-based differentiation assay should be of use to those interested in screening large compound libraries for the identification of drugs for the treatment of MS and other demyelinating diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-016-2220-2) contains supplementary material, which is available to authorized users.

Graphene for improved femtosecond laser based pluripotent stem cell transfection

Pluripotent stem cells are hugely attractive in the tissue engineering research field as they can self-renew and be selectively differentiated into various cell types. For stem cell and tissue engineering research it is important to develop new, biocompatible scaffold materials and graphene has emerged as a promising material in this area as it does not compromise cell proliferation and accelerates specific cell differentiation. Previous studies have shown a non-invasive optical technique for mouse embryonic stem (mES) cell differentiation and transfection using femtosecond (fs) laser pulses. To investigate cellular responses to the influence of graphene and laser irradiation, here we present for the first time a study of mES cell fs laser transfection on graphene coated substrates. First we studied the impact of graphene on Chinese Hamster Ovary (CHO-K1) cell viability and cell cytotoxicity in the absence of laser exposure. These were tested via evaluating the mitochondrial activity through adenosine triphosphates (ATP) luminescence and breakages on the cell plasma membrane assessed using cytosolic lactate dehydrogenase (LDH) screening. Secondly, the effects of fs laser irradiation on cell viability and cytotoxicity at 1064 and 532 nm for cells plated and grown on graphene and pure glass were assessed. Finally, optical transfection of CHO-K1 and mES cells was performed on graphene coated versus plain glass substrates. Our results show graphene stimulated cell viability whilst triggering a mild release of intracellular LDH. We also observed that compared to pure glass substrates; laser irradiation at 1064 nm on graphene plates was less cytotoxic. Finally, in mES cells efficient optical transfection at 1064 (82%) and 532 (25%) nm was obtained due to the presence of a graphene support as compared to pristine glass. Here we hypothesize an up-regulation of cell adhesion promoting peptides or laminin-related receptors of the extracellular matrix (ECM) in cell samples grown and irradiated on graphene substrates. By bringing together advances in optics and nanomaterial sciences we demonstrate pathways for enhancement of pluripotent stem cell biology.

Comparison of primary and secondary rat astrocyte cultures regarding glucose and glutathione metabolism and the accumulation of iron oxide nanoparticles

Astrocyte-rich primary cultures (APCs) are frequently used as a model system for the investigation of properties of brain astrocytes. However, as APCs contain a substantial number of microglial and oligodendroglial cells, biochemical parameters determined for such cultures may at least in part reflect also the presence of the contaminating cell types. To lower the potential contributions of microglial and oligodendroglial cells on properties of the astrocytes in APCs we prepared rat astrocyte-rich secondary cultures (ASCs) by subculturing of APCs and compared these ASCs with APCs regarding basal metabolic parameters, specific enzyme activities and the accumulation of iron oxide nanoparticles. Immunocytochemical characterization revealed that ASCs contained only minute amounts of microglial and oligodendroglial cells. ASCs and APCs did not significantly differ in their specific glucose consumption and lactate production rates, in their specific iron and glutathione contents, in their specific activities of various enzymes involved in glucose and glutathione metabolism nor in their accumulation of iron oxide nanoparticles. Thus, the absence or presence of some contaminating microglial and oligodendroglial cells appears not to substantially modulate the investigated metabolic parameters of astrocyte cultures.

Functional roles of transferrin in the brain

BACKGROUND

Transferrin is synthesized in the brain by choroid plexus and oligodendrocytes, but only that in the choroid plexus is secreted. Transferrin is a major iron delivery protein to the brain, but the amount transcytosed across the brain microvasculature is minimal. Transferrin is the major source of iron delivery to neurons. It may deliver iron to immature oligodendrocytes but this trophic effect declines over time while iron requirements for maintaining myelination continue. Finally, transferrin may play an important role in neurodegenerative diseases through its ability to mobilize iron.

SCOPE OF REVIEW

The role of transferrin in maintaining brain iron homeostasis and the mechanism by which it enters the brain and delivers iron will be discussed. Its relevance to neurological disorders will also be addressed.

MAJOR CONCLUSIONS

Transferrin is the major iron delivery protein for neurons and the microvasculature, but has a limited role for glial cells. The main source of transferrin in the brain is likely from the choroid plexus although the concentration of transferrin at any given time in the brain includes that synthesized in oligodendrocytes. Little is known about brain iron egress or the role of transferrin in this process.

GENERAL SIGNIFICANCE

Neuron survival requires iron, which is predominantly delivered by transferrin. The concentration of transferrin in the cerebrospinal fluid is reflective of brain iron availability and can function as a biomarker in disease. Accumulation of iron in the brain contributes to neurodegenerative processes, thus an understanding of the role that transferrin plays in regulating brain iron homeostasis is essential. This article is part of a Special Issue entitled Transferrins: Molecular mechanisms of iron transport and disorders.

Vascular smooth muscle cell proliferation is influenced by let-7d microRNA and its interaction with KRAS

BACKGROUND

Several microRNAs (miRNAs) have been reported to regulate cardiovascular biological and pathological processes through inhibiting the translation of certain RNA transcripts. However, little is known about the association between miRNAs and vascular smooth muscle cell (VSMC) proliferation. The aim was to investigate the role of miRNAs in VSMC growth and the potential mechanism.

METHODS AND RESULTS

Primary VSMCs were isolated from the medial layer of the thoracic aorta obtained from spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY). miRNA microarrays were used to analyze the difference in miRNA expression between VSMCs of SHR and WKY rats and were validated using TaqMan real-time PCR. Of the potentially related genes under the influence of let-7d identified through literature search, KRAS was verified by western blot and functionally analyzed using miRNA mimics transfection and analysis of transfectants by cell enumeration was made using CCK-8 and flow cytometric analysis of cell cycle progression. let-7d-transfected VSMCs from SHR, WKY and human coronary arteries expressed significantly lower amounts of KRAS protein, displayed reduced cell growth and led to a greater number of cells in the G1 phase than the G2/M phases of the cell cycle.

CONCLUSIONS

let-7d was significantly downregulated in VSMCs as an important regulator of cell proliferation. RAS might be involved in the proliferation regulation by let-7d.

In vitro neural injury model for optimization of tissue-engineered constructs

Stem cell transplantation is a promising approach for the treatment of traumatic brain injury, although the therapeutic benefits are limited by a high degree of donor cell death. Tissue engineering is a strategy to improve donor cell survival by providing structural and adhesive support. However, optimization prior to clinical implementation requires expensive and time-consuming in vivo studies. Accordingly, we have developed a three-dimensional (3-D) in vitro model of the injured host-transplant interface that can be used as a test bed for high-throughput evaluation of tissue-engineered strategies. The neuronal-astrocytic cocultures in 3-D were subjected to mechanical loading (inducing cell death and specific astrogliotic alterations) or to treatment with transforming growth factor-beta1 (TGF-beta1), inducing astrogliosis without affecting viability. Neural stem cells (NSCs) were then delivered to the cocultures. A sharp increase in the number of TUNEL(+) donor cells was observed in the injured cocultures compared to that in the TGF-beta1-treated and control cocultures, suggesting that factors related to mechanical injury, but not strictly astrogliosis, were detrimental to donor cell survival. We then utilized the mechanically injured cocultures to evaluate a methylcellulose-laminin (MC-LN) scaffold designed to reduce apoptosis. When NSCs were co-delivered with MC alone or MC-LN to the injured cocultures, the number of caspase(+) donor cells significantly decreased compared to that with vehicle delivery (medium). Collectively, these results demonstrate the utility of an in vitro model as a pre-animal test bed and support further investigation of a tissue-engineering approach for chaperoned NSC delivery targeted to improve donor cell survival in neural transplantation.

Phenotypic and functional heterogeneity of GFAP-expressing cells in vitro: differential expression of LeX/CD15 by GFAP-expressing multipotent neural stem cells and non-neurogenic astrocytes

Recent findings show that the predominant multipotent neural stem cells (NSCs) isolated from postnatal and adult mouse brain express glial fibrillary acid protein (GFAP), a protein commonly associated with astrocytes, and that primary astrocyte cultures can contain GFAP-expressing cells that act as multipotent NSCs when transferred to neurogenic conditions. The relationship of GFAP-expressing NSCs to GFAP-expressing astrocytes is unclear, but has important implications. We compared the phenotype and neurogenic potential of GFAP-expressing cells derived from different CNS regions and maintained in vitro under different conditions. Multiple labeling immunohistochemistry revealed that both primary astrocyte cultures and adherent neurogenic cultures derived from postnatal or adult periventricular tissue contained subpopulations of GFAP-expressing cells that co-expressed nestin and LeX/CD15, two molecules associated with NSCs. In contrast, GFAP-expressing cells in similar cultures prepared from adult cerebral cortex did not express detectable levels of LeX/CD15, and exhibited no neurogenic potential. Fluorescence-activated cell sorting (FACS) of both primary astrocyte cultures and adherent neurogenic cultures for LeX/CD15 showed that GFAP-expressing cells competent to act as multipotent NSCs were concentrated in the LeX-positive fraction. Using neurosphere assays and a transgenic ablation strategy, we confirmed that the predominant NSCs in primary astrocyte and adherent neurogenic cultures were GFAP-expressing cells. These findings demonstrate that GFAP-expressing cells derived from postnatal and adult forebrain are heterogeneous in both molecular phenotype and neurogenic potential in vitro, and that this heterogeneity exists before exposure to neurogenic conditions. The findings provide evidence that GFAP-expressing NSCs are phenotypically and functionally distinct from non-neurogenic astrocytes.

Comparison of gene expression profiles between frozen original meningiomas and primary cultures of the meningiomas by GeneChip

OBJECTIVE

In vitro experiments are performed on a daily basis to study the molecular biology of tumors. For some benign tumors, however, established cell lines are not always available, or it may not be feasible to establish new ones. In such cases, primary cultures are used to perform in vitro experiments. Gene expression profiles in vitro differ from those in vivo, but information as to which genes have significantly altered levels is limited. In this study, gene expression profiles of meningiomas in primary cultures and frozen tumors were compared.

METHODS

Affymetrix U95A chips were applied to three sets of meningiomas. For each tumor, the gene expression profiles in frozen specimens (Fr) and primary cultures from the same tumor at Pass 5 (P5) and Pass 10 (P10) were compared. A paired t test (P < 0.025) was applied between Fr and P5, and then between Fr and P10. Genes that demonstrated significantly different expression levels in both comparisons were then identified. The expression levels for a subset of these genes were confirmed by quantitative real-time reverse transcription-polymerase chain reaction.

RESULTS

Among 12,000 genes examined, up-regulation of 51 genes by fivefold or more and down-regulation of 19 genes by twofold or more was found in primary cultures (P5 and P10) compared with the corresponding Fr. Up-regulation of genes encoding for extracellular matrix, cytoskeleton, and cell surface receptors was particularly notable.

CONCLUSION

Gene expression of tissue-cultured meningiomas and in situ meningiomas is significantly different for a large number of genes. Therefore, gene expression and therapeutic studies on cultured meningiomas need to be interpreted with caution.

Neurospheres modified to produce glial cell line-derived neurotrophic factor increase the survival of transplanted dopamine neurons

Glial cell line-derived neurotrophic factor (GDNF) has been shown to increase the survival of dopamine neurons in a variety of in vitro and in vivo model systems. Therefore, it constitutes an important therapeutic protein with the potential to ameliorate dopamine neuronal degeneration in Parkinson's disease or to support dopamine neuronal replacement strategies. However, biophysical and practical considerations present obstacles for the direct delivery of the GDNF protein to CNS neurons. Here we show that rodent neural precursor cells isolated and expanded in culture as neurospheres (NS) can be genetically modified to express green fluorescent protein (GFP) or to release GDNF using lentiviral constructs. GDNF-NS increased the fibre outgrowth of primary embryonic dopamine neurons in cocultures, showing that the protein was released in biologically significant quantities. Furthermore, after transplantation into the 6-hydroxydopamine-lesioned rat striatum, GDNF-NS significantly increased the survival of cografted primary dopamine neurons. However, this was not reflected in behavioural recovery in these animals. We found that, by 6 weeks, few cells expressed GDNF or GFP, suggesting either that transgene expression was down-regulated over time or that the cells died. This may explain the initial effects on dopamine neuronal survival within the graft but the lack of long-term effect on subsequent fibre outgrowth and behaviour. Providing sustained levels of neural precursor-mediated transgene expression can be achieved following transplantation in the future; this approach may prove beneficial as an alternative therapeutic strategy in the cell-based management of Parkinson's disease.

Human and rabbit cavernosal smooth muscle cells express Rho-kinase

Rho-kinase is an enzyme involved in the Ca2+-sensitizing pathway in smooth muscle cells. Inhibition of this enzyme has been recently demonstrated to elicit penile erection by relaxing cavernosal smooth muscle. We aimed to investigate the presence and activity of Rho-kinase in human cavernosal smooth muscle. Primary culture of smooth muscle cells from human and rabbit penile corpus cavernosum was developed, and cells showed characteristic myocyte morphology and alpha-actin immunoreactivity. The presence of Rho-kinase was demonstrated by indirect immunofluorescence and Western blotting. A specific inhibitor of Rho-kinase, Y-27632, inhibited in a concentration-dependent manner the kinase activity of the protein immunoprecipitated with anti-Rho-kinase antibody. These results demonstrate for the first time expression and activity of Rho-kinase in human penile cavernosal smooth muscle cells and suggest that these cells can provide a cellular model for the study of enzymes involved in Ca2+-sensitizing pathways.

Alternative splicing prevents transferrin secretion during differentiation of a human oligodendrocyte cell line

Transferrin, the iron-transport protein of vertebrate serum, is synthesized mainly in the liver, from which it is secreted into the blood. Transferrin is also synthesized in oligodendrocytes and is an early marker of their differentiation. We have analyzed the regulation of transferrin expression in HOG cells, a human oligodendrocyte cell line. Transferrin expression was correlated with the appearance of oligodendrocyte differentiation markers when cells were exposed to differentiation medium. In contrast to the protein expressed in hepatocytes or in Sertoli cells, transferrin was secreted by neither HOG cells nor immature rat primary oligodendrocytes in vitro. Moreover, transferrin appears to be localized in the cytosol and not in the secretory compartment, as is expected for secreted proteins. This transferrin localization was correlated with the synthesis of a specific transcript, resulting from an alternative splicing, which leads to the elimination of the signal peptide sequence. These results suggest the existence of a functional difference between transferrin synthesized in the brain and in other organs such as liver and testis. They are in accordance with the hypothesis that transferrin plays a specific role, other than iron transport, in oligodendrocyte maturation and in the myelination process.

Intermediate filament protein synemin is transiently expressed in a subset of astrocytes during development

Synemin, a developmentally regulated protein first described in muscle cells, has recently been recognized as an intermediate filament (IF) protein. Because IF proteins are invaluable markers of cell origin within the nervous system, we were interested in determining the expression pattern of synemin in the brain. Our results show that, during development of the rat cortex, synemin is expressed only in a subpopulation of astrocytic cells expressing GFAP as well as vimentin and nestin. Unlike GFAP, however, synemin is not expressed in mature astrocytes and, unlike vimentin and nestin, synemin is not present in astrocytic precursors before GFAP expression. Taken together with morphological evidence, the time course of synemin expression, as determined by Western blotting, suggests that synemin is expressed in radial glial cells undergoing morphological transformation into astrocytes. Studies of synemin expression in vitro demonstrate that, early in primary culture, the majority of polygonal astrocytes are derived from synemin(+) radial glial cells. With time in culture, however, polygonal astrocytes either stop expressing synemin or are overgrown by cells not expressing synemin. The unique pattern of synemin expression, both in vivo and in vitro, suggests that the use of synemin as a marker will add a new dimension to studies of astrocytic differentiation.

Mouse epidermal growth factor-responsive neural precursor cells increase the survival and functional capacity of embryonic rat dopamine neurons in vitro

We have grown expanded populations of epidermal growth factor (EGF)-responsive mouse striatal precursor cells and subsequently co-cultured these with primary E14 rat ventral mesencephalon. The aim of these experiments was to induce dopaminergic (DA) neuronal phenotypes from the murine precursors. While no precursor cell-derived neurons were induced to express tyrosine hydroxylase (TH), there was a dramatic 30-fold increase in the survival of rat-derived TH-positive neurons in the co-cultures. The effect was not explicable solely in terms of total plating density, and was accompanied by a significantly enhanced capacity for [3H]dopamine uptake in the co-cultures compared to rat alone cultures. The present data show that, although primary rat E14 mesencephalic cells are incapable of inducing the development of DA neurons from EGF-responsive mouse neural precursor cells, such precursors will differentiate into cells capable of enhancing the survival and overall functional efficacy of primary embryonic dopamine neurons.

Dexamethasone regulates basic fibroblast growth factor, nerve growth factor and S100beta expression in cultured hippocampal astrocytes

Glucocorticoids regulate hippocampal neuron survival during fetal development, in the adult, and during aging; however, the mechanisms underlying the effects are unclear. Since astrocytes contain adrenocortical receptors and synthesize and release a wide variety of growth factors, we hypothesized that glucocorticoids may alter neuron-astrocyte interactions by regulating the expression of growth factors in hippocampal astrocytes. In this study, three growth factors, which are important for hippocampal neuron development and survival, were investigated: basic fibroblast growth factor (bFGF), nerve growth factor (NGF), and S100beta. Enriched type I astrocyte cultures were treated with 1 microM dexamethasone (DEX), a synthetic glucocorticoid, for up to 120 h. Cells and culture medium were collected and total RNA and protein were measured at 6, 12, 24, 48, 72, 96 and 120 h after the initiation of hormone treatment. Growth factor mRNA levels were measured and quantified using solution hybridization-RNase protection assays and protein levels were quantified using ELISA methods. We report that DEX stimulates the bFGF mRNA levels over the 120-h treatment. In contrast, DEX suppresses NGF mRNA continuously over the same period of treatment. DEX induces a biphasic response in S100beta mRNA levels. In addition, some of the changes in gene expression are translated into parallel changes in protein levels of these growth factors. Our results demonstrate that dexamethasone can differentially regulate the expression of growth factors in hippocampal astrocytes in vitro. This suggests that one of the mechanisms through which glucocorticoids affect hippocampal functions may be by regulating the expression of astrocyte-derived growth factors.

Effects of ATP analogues and basic fibroblast growth factor on astroglial cell differentiation in primary cultures of rat striatum

We have used primary cultures of rat striatum to study the effects of ATP analogues on the elongation of astrocytic processes, a parameter of astroglial cell differentiation. Parallel studies were performed with basic fibroblast growth factor, a known regulator of astroglial cell function. After three days in culture, both the growth factor and alpha beta-methylene-ATP induced dramatic increases in the mean length of astrocytic processes/cell. For both agents, effects were dose-dependent. The effect of alpha beta-methylene-ATP was antagonized by the trypanoside suramin and mimicked by 2-methyl-thio-ATP, suggesting the involvement of a suramin-sensitive P2-purinoceptor. Neither an additive nor a synergistic effect between alpha beta-methylene-ATP and basic fibroblast growth factor on the elongation of processes was detected in cultures exposed to both agents. Indeed, an inhibition with respect to the effects induced by either agent alone was recorded, suggesting that the growth factor and the purine analogue can modulate astrocytic differentiation by activation of common intracellular pathways. It is concluded that, like basic fibroblast growth factor, ATP can promote the maturation of astrocytes towards a more differentiated phenotype characterized by the presence of longer astrocytic processes. These findings might have interesting implications for astroglial cell differentiation during brain development and for ischemia- and trauma-associated hypergliosis.