Expression of microtubule-associated protein 2 by reactive astrocytes

Neurovascular unit, neuroinflammation and neurodegeneration markers in brain disorders

Neurovascular unit (NVU) inflammation via activation of glial cells and neuronal damage plays a critical role in neurodegenerative diseases. Though the exact mechanism of disease pathogenesis is not understood, certain biomarkers provide valuable insight into the disease pathogenesis, severity, progression and therapeutic efficacy. These markers can be used to assess pathophysiological status of brain cells including neurons, astrocytes, microglia, oligodendrocytes, specialized microvascular endothelial cells, pericytes, NVU, and blood-brain barrier (BBB) disruption. Damage or derangements in tight junction (TJ), adherens junction (AdJ), and gap junction (GJ) components of the BBB lead to increased permeability and neuroinflammation in various brain disorders including neurodegenerative disorders. Thus, neuroinflammatory markers can be evaluated in blood, cerebrospinal fluid (CSF), or brain tissues to determine neurological disease severity, progression, and therapeutic responsiveness. Chronic inflammation is common in age-related neurodegenerative disorders including Alzheimer's disease (AD), Parkinson's disease (PD), and dementia. Neurotrauma/traumatic brain injury (TBI) also leads to acute and chronic neuroinflammatory responses. The expression of some markers may also be altered many years or even decades before the onset of neurodegenerative disorders. In this review, we discuss markers of neuroinflammation, and neurodegeneration associated with acute and chronic brain disorders, especially those associated with neurovascular pathologies. These biomarkers can be evaluated in CSF, or brain tissues. Neurofilament light (NfL), ubiquitin C-terminal hydrolase-L1 (UCHL1), glial fibrillary acidic protein (GFAP), Ionized calcium-binding adaptor molecule 1 (Iba-1), transmembrane protein 119 (TMEM119), aquaporin, endothelin-1, and platelet-derived growth factor receptor beta (PDGFRβ) are some important neuroinflammatory markers. Recent BBB-on-a-chip modeling offers promising potential for providing an in-depth understanding of brain disorders and neurotherapeutics. Integration of these markers in clinical practice could potentially enhance early diagnosis, monitor disease progression, and improve therapeutic outcomes.

Longitudinal Neuropathological Consequences of Extracranial Radiation Therapy in Mice

Cancer-related cognitive impairment (CRCI) is a consequence of chemotherapy and extracranial radiation therapy (ECRT). Our prior work demonstrated gliosis in the brain following ECRT in SKH1 mice. The signals that induce gliosis were unclear. Right hindlimb skin from SKH1 mice was treated with 20 Gy or 30 Gy to induce subclinical or clinical dermatitis, respectively. Mice were euthanized at 6 h, 24 h, 5 days, 12 days, and 25 days post irradiation, and the brain, thoracic spinal cord, and skin were collected. The brains were harvested for spatial proteomics, immunohistochemistry, Nanostring nCounter® glial profiling, and neuroinflammation gene panels. The thoracic spinal cords were evaluated by immunohistochemistry. Radiation injury to the skin was evaluated by histology. The genes associated with neurotransmission, glial cell activation, innate immune signaling, cell signal transduction, and cancer were differentially expressed in the brains from mice treated with ECRT compared to the controls. Dose-dependent increases in neuroinflammatory-associated and neurodegenerative-disease-associated proteins were measured in the brains from ECRT-treated mice. Histologic changes in the ECRT-treated mice included acute dermatitis within the irradiated skin of the hindlimb and astrocyte activation within the thoracic spinal cord. Collectively, these findings highlight indirect neuronal transmission and glial cell activation in the pathogenesis of ECRT-related CRCI, providing possible signaling pathways for mitigation strategies.

Comparison of two protocols for the generation of iPSC-derived human astrocytes

BACKGROUND

Astrocytes have recently gained attention as key contributors to the pathogenesis of neurodegenerative disorders including Parkinson's disease. To investigate human astrocytes in vitro, numerous differentiation protocols have been developed. However, the properties of the resulting glia are inconsistent, which complicates the selection of an appropriate method for a given research question. Thus, we compared two approaches for the generation of iPSC-derived astrocytes. We phenotyped glia that were obtained employing a widely used long, serum-free ("LSF") method against an in-house established short, serum-containing ("SSC") protocol which allows for the generation of astrocytes and midbrain neurons from the same precursor cells.

RESULTS

We employed high-content confocal imaging and RNA sequencing to characterize the cultures. The astrocytes generated with the LSF or SSC protocols differed considerably in their properties: while the former cells were more labor-intense in their generation (5 vs 2 months), they were also more mature. This notion was strengthened by data resulting from cell type deconvolution analysis that was applied to bulk transcriptomes from the cultures to assess their similarity with human postmortem astrocytes.

CONCLUSIONS

Overall, our analyses highlight the need to consider the advantages and disadvantages of a given differentiation protocol, when designing functional or drug discovery studies involving iPSC-derived astrocytes.

Single Cerebral Organoid Mass Spectrometry of Cell-Specific Protein and Glycosphingolipid Traits

Cerebral organoids are a prolific research topic and an emerging model system for neurological diseases in human neurobiology. However, the batch-to-batch reproducibility of current cultivation protocols is challenging and thus requires a high-throughput methodology to comprehensively characterize cerebral organoid cytoarchitecture and neural development. We report a mass spectrometry-based protocol to quantify neural tissue cell markers, cell surface lipids, and housekeeping proteins in a single organoid. Profiled traits probe the development of neural stem cells, radial glial cells, neurons, and astrocytes. We assessed the cell population heterogeneity in individually profiled organoids in the early and late neurogenesis stages. Here, we present a unifying view of cell-type specificity of profiled protein and lipid traits in neural tissue. Our workflow characterizes the cytoarchitecture, differentiation stage, and batch cultivation variation on an individual cerebral organoid level.

Isolation and culture of functional adult human neurons from neurosurgical brain specimens

The ability to characterize and study primary neurons isolated directly from the adult human brain would greatly advance neuroscience research. However, significant challenges such as accessibility of human brain tissue and the lack of a robust neuronal cell culture protocol have hampered its progress. Here, we describe a simple and reproducible method for the isolation and culture of functional adult human neurons from neurosurgical brain specimens. In vitro, adult human neurons form a dense network and express a plethora of mature neuronal and synaptic markers. Most importantly, for the first time, we demonstrate the re-establishment of mature neurophysiological properties in vitro, such as repetitive fast-spiking action potentials, and spontaneous and evoked synaptic activity. Together, our dissociated and slice culture systems enable studies of adult human neurophysiology and gene expression under normal and pathological conditions and provide a high-throughput platform for drug testing on brain cells directly isolated from the adult human brain.

Paclitaxel Reduces Brain Injury from Repeated Head Trauma in Mice

Repetitive mild traumatic brain injury (rmTBI) is known to disturb axonal integrity and may play an important role in the pathogenic cascades leading to neurodegeneration. One critical approach to reduce the future onset of neurodegeneration is to intervene in this process at an early stage following a brain injury. Previously we showed that direct application of the microtubule-stabilizing drug, paclitaxel, on the brain following controlled cortical impact improved motor function and reduced lesion size. Herein, we extended these findings to a model of mild brain injury induced by repeated closed-skull impacts. Paclitaxel was administered intranasally to circumvent its poor transport across the blood-brain barrier. Mice received five mild closed-skull impacts (one per day for five days). Intranasal paclitaxel was administered once only, immediately after the first impact. We found that paclitaxel prevented injury-induced deficits in a spatial memory task in a water tread maze. In vivo magnetic resonance imaging (MRI) and positron emission tomography with 18F-flurodeoxyglucose (FDG-PET) revealed that paclitaxel prevented structural injury and hypometabolism. On MRI, apparent, injury-induced microbleeds were observed in 100% of vehicle-treated rmTBI mice, but not in paclitaxel-treated subjects. FDG-PET revealed a 42% increase in whole brain glucose metabolism in paclitaxel-treated mice as compared to vehicle-treated rmTBI. Immunohistochemistry found reduced evidence of axonal injury and synaptic loss. Our results indicate that intranasal paclitaxel administration imparts neuroprotection against brain injury and cognitive impairment in mice. The results from this study support the idea that microtubule-stabilization strategies hold therapeutic promise in mitigating traumatic brain injury.

Microtubule organization and dynamics in oligodendrocytes, astrocytes, and microglia

Though much is known about microtubule organization and microtubule-based transport in neurons, the development and function of microtubules in glia are more enigmatic. In this review, we provide an overview of the literature on microtubules in ramified brain cells, including oligodendrocytes, astrocytes, and microglia. We focus on normal cell biology-how structure relates to function in these cells. In oligodendrocytes, microtubules are important for extension of processes that contact axons and for elongating the myelin sheath. Recent studies demonstrate that new microtubules can form outside of the oligodendrocyte cell body off of Golgi outpost organelles. In astrocytes and microglia, changes in cell shape and ramification can be influenced by neighboring cells and the extracellular milieu. Finally, we highlight key papers implicating glial microtubule defects in neurological injury and disease and discuss how microtubules may contribute to invasiveness in gliomas. Thus, future research on the mechanisms underlying microtubule organization in normal glial cell function may yield valuable insights on neurological disease pathology.

Multipotent mesenchymal stromal cell-derived exosomes improve functional recovery after experimental intracerebral hemorrhage in the rat

OBJECTIVE

Previous studies have demonstrated that transplanted multipotent mesenchymal stromal cells (MSCs) improve functional recovery in rats after experimental intracerebral hemorrhage (ICH). In this study the authors tested the hypothesis that administration of multipotent MSC-derived exosomes promotes functional recovery, neurovascular remodeling, and neurogenesis in a rat model of ICH.

METHODS

Sixteen adult male Wistar rats were subjected to ICH via blood injection into the striatum, followed 24 hours later by tail vein injection of 100 μg protein of MSC-derived exosomes (treatment group, 8 rats) or an equal volume of vehicle (control group, 8 rats); an additional 8 rats that had identical surgery without blood infusion were used as a sham group. The modified Morris water maze (mMWM), modified Neurological Severity Score (mNSS), and social odor-based novelty recognition tests were performed to evaluate cognitive and sensorimotor functional recovery after ICH. All 24 animals were killed 28 days after ICH or sham procedure. Histopathological and immunohistochemical analyses were performed for measurements of lesion volume and neurovascular and white matter remodeling.

RESULTS

Compared with the saline-treated controls, exosome-treated ICH rats showed significant improvement in the neurological function of spatial learning and motor recovery measured at 26-28 days by mMWM and starting at day 14 by mNSS (p < 0.05). Senorimotor functional improvement was measured by a social odor-based novelty recognition test (p < 0.05). Exosome treatment significantly increased newly generated endothelial cells in the hemorrhagic boundary zone, neuroblasts and mature neurons in the subventricular zone, and myelin in the striatum without altering the lesion volume.

CONCLUSIONS

MSC-derived exosomes effectively improve functional recovery after ICH, possibly by promoting endogenous angiogenesis and neurogenesis in rats after ICH. Thus, cell-free, MSC-derived exosomes may be a novel therapy for ICH.

Altered expression of itch‑related mediators in the lower cervical spinal cord in mouse models of two types of chronic itch

In this study, we focused on several itch-related molecules and receptors in the spinal cord with the goal of clarifying the specific mediators that regulate itch sensation. We investigated the involvement of serotonin receptors, opioid receptors, glia cell markers and chemokines (ligands and receptors) in models of acetone/ether/water (AEW)- and diphenylcyclopropenone (DCP)-induced chronic itch. Using reverse transcription-quantitative polymerase chain reaction, we examined the expression profiles of these mediators in the lower cervical spinal cord (C5-8) of two models of chronic itch. We found that the gene expression levels of opioid receptor mu 1 (Oprm1), 5-hydroxytryptamine receptor 1A (Htr1a) and 5-hydroxytryptamine receptor 6 (Htr6) were upregulated. Among the chemokines, the expression levels of C-C motif chemokine ligand (Ccl)21, Cxcl3 and Cxcl16 and their receptors, Ccr7, Cxcr2 and Cxcr6, were simultaneously upregulated in the spinal cords of the mice in both models of chronic itch. By contrast, the expression levels of Ccl2, Ccl3, Ccl4 and Ccl22 were downregulated. These findings indicate that multiple mediators, such as chemokines in the spinal cord, are altered and may be central candidates in further research into the mechanisms involved in the development of chronic itch.

A single factor induces neuronal differentiation to suppress glioma cell growth

AIM

Glioma, with fast growth and progression features, is the most common and aggressive tumor in the central nervous system and is essentially incurable. This study is aimed at inducing neuronal differentiation to suppress glioma cell growth with a single transcription factor.

METHODS

Overexpression of transcription factor SRY (sex determining region Y)-box 11 (SOX11) and Zic family member 1 (ZIC1) was, respectively, performed in glioma cells with lentivirus infection. CRISPR/Cas9 technology was used to knock out ZIC1 in U87 cells, and knockout efficiency was identified by Western blotting and Sanger sequencing. Cell cycle and apoptosis were detected by flow cytometry. The downstream targets of SOX11 were analyzed by Affymetrix GeneChip microarrays. qRT-PCR and immunofluorescence technique were used to verify gene targets of genetically modified U87 cells. All the cells were imaged by a fluorescence microscope. Gene expression correlation analysis and overall survival analysis based on TCGA dataset are performed by GEPIA.

RESULTS

We induced glioma cells into neuron-like cells to suppress cell growth using a single transcription factor, SOX11 or ZIC1. Besides, we proved that there is a strong correlation between SOX11 and ZIC1. Our study revealed that SOX11 upregulates ZIC1 expression by binding with ZIC1 promoter, and ZIC1 partially mediates SOX11-induced neuronal differentiation in U87 cells. However, SOX11 expression is not regulated by ZIC1. Moreover, high MAP2 expression means better overall survival in TCGA lower grade glioma.

CONCLUSION

This study revealed that glioma cells can be reprogrammed into neuron-like cells using a single factor ZIC1, which may be a potential tumor suppressor gene for gliomas treatment.

Effect of Brain-Derived Neurotrophic Factor on the Neurogenesis and Osteogenesis in Bone Engineering

During bone growth, the lack of a neuralized vascular network in the regenerating area can affect subsequent bone quality. This study aimed to investigate if brain-derived neurotrophic factor (BDNF) could promote neurogenesis and osteogenesis in human bone mesenchymal stem cells (hBMSCs) to improve bone formation during tissue engineering. Initially, a safe and effective BDNF concentration that facilitated hBMSC proliferation in vitro was determined. Subsequently, examination of mineralized nodule formation and evaluation of alkaline phosphatase (ALP) activity and ALP gene expression revealed that the most effective concentration of BDNF to elicit a response in hBMSCs was 100 ng/mL. In addition, we found out that by binding with TrkB receptor, the downstream Erk1/2 was phosphorylated, which promoted the expression of transcription factors, such as Runx2 and Osterix that are associated with osteoblast differentiation. We also found that by day 7 post-treatment, the neurogenic biomarkers, p75 and s100, were highly expressed in 100 ng/mL BDNF-treated hBMSCs. Finally, the effects of BDNF on osteogenesis and neurogenesis in newly formed tissues were assessed using animal models with a β-tricalcium phosphate scaffold. This revealed that treatment with 100 ng/mL BDNF promoted the osteogenesis and neurogenesis of hBMSCs in vivo by increasing expression of the osteogenic marker osteocalcin and various neurogenic biomarkers, including microtubule-associated protein 2, glial fibrillary acidic protein, neural/glial antigen 2, and β-tubulin III. This study has demonstrated that BDNF promotes hBMSC osteogenesis and neurogenesis in vitro and in vivo, and that BDNF may indirectly promote osteogenesis through increased neurogenesis. This further suggests that encouraging neutralization during bone engineering will lead to effective repairing of bone defects. The study may also provide insight into related fields, such as osseoperception and stress feedback regulation after dental implantation.

Methazolamide improves neurological behavior by inhibition of neuron apoptosis in subarachnoid hemorrhage mice

Subarachnoid hemorrhage (SAH) results in significant nerve dysfunction, such as hemiplegia, mood disorders, cognitive and memory impairment. Currently, no clear measures can reduce brain nerve damage. The study of brain nerve protection after SAH is of great significance. We aim to evaluate the protective effects and the possible mechanism of methazolamide in C57BL/6J SAH animal model in vivo and in blood-induced primary cortical neuron (PCNs) cellular model of SAH in vitro. We demonstrate that methazolamide accelerates the recovery of neurological damage, effectively relieves cerebral edema, and improves cognitive function in SAH mice as well as offers neuroprotection in blood- or hemoglobin-treated PCNs and partially restores normal neuronal morphology. In addition, western blot analyses show obviously decreased expression of active caspase-3 in methazolamide-treated SAH mice comparing with vehicle-treated SAH animals. Furthermore, methazolamide effectively inhibits ROS production in PCNs induced by blood exposure or hemoglobin insult. However, methazolamide has no protective effects in morality, fluctuation of cerebral blood flow, SAH grade, and cerebral vasospasm of SAH mice. Given methazolamide, a potent carbonic anhydrase inhibitor, can penetrate the blood–brain barrier and has been used in clinic in the treatment of ocular conditions, it provides potential as a novel therapy for SAH.

Directing lineage specification of human mesenchymal stem cells by decoupling electrical stimulation and physical patterning on unmodified graphene

The organization and composition of the extracellular matrix (ECM) have been shown to impact the propagation of electrical signals in multiple tissue types. To date, many studies with electroactive biomaterial substrates have relied upon passive electrical stimulation of the ionic media to affect cell behavior. However, development of cell culture systems in which stimulation can be directly applied to the material - thereby isolating the signal to the cell-material interface and cell-cell contracts - would provide a more physiologically-relevant paradigm for investigating how electrical cues modulate lineage-specific stem cell differentiation. In the present study, we have employed unmodified, directly-stimulated, (un)patterned graphene as a cell culture substrate to investigate how extrinsic electrical cycling influences the differentiation of naïve human mesenchymal stem cells (hMSCs) without the bias of exogenous biochemicals. We first demonstrated that cyclic stimulation does not deteriorate the cell culture media or result in cytotoxic pH, which are critical experiments for correct interpretation of changes in cell behavior. We then measured how the expression of osteogenic and neurogenic lineage-specific markers were altered simply by exposure to electrical stimulation and/or physical patterns. Expression of the early osteogenic transcription factor RUNX2 was increased by electrical stimulation on all graphene substrates, but the mature marker osteopontin was only modulated when stimulation was combined with physical patterns. In contrast, the expression of the neurogenic markers MAP2 and β3-tubulin were enhanced in all electrical stimulation conditions, and were less responsive to the presence of patterns. These data indicate that specific combinations of non-biological inputs - material type, electrical stimulation, physical patterns - can regulate hMSC lineage specification. This study represents a substantial step in understanding how the interplay of electrophysical stimuli regulate stem cell behavior and helps to clarify the potential for graphene substrates in tissue engineering applications.

L-type voltage-operated calcium channels contribute to astrocyte activation In vitro

We have found a significant upregulation of L-type voltage-operated Ca(++) channels (VOCCs) in reactive astrocytes. To test if VOCCs are centrally involved in triggering astrocyte reactivity, we used in vitro models of astrocyte activation in combination with pharmacological inhibitors, siRNAs and the Cre/lox system to reduce the activity of L-type VOCCs in primary cortical astrocytes. The endotoxin lipopolysaccharide (LPS) as well as high extracellular K(+) , glutamate, and ATP promote astrogliosis in vitro. L-type VOCC inhibitors drastically reduce the number of reactive cells, astrocyte hypertrophy, and cell proliferation after these treatments. Astrocytes transfected with siRNAs for the Cav1.2 subunit that conducts L-type Ca(++) currents as well as Cav1.2 knockout astrocytes showed reduce Ca(++) influx by ∼80% after plasma membrane depolarization. Importantly, Cav1.2 knock-down/out prevents astrocyte activation and proliferation induced by LPS. Similar results were found using the scratch wound assay. After injuring the astrocyte monolayer, cells extend processes toward the cell-free scratch region and subsequently migrate and populate the scratch. We found a significant increase in the activity of L-type VOCCs in reactive astrocytes located in the growing line in comparison to quiescent astrocytes situated away from the scratch. Moreover, the migration of astrocytes from the scratching line as well as the number of proliferating astrocytes was reduced in Cav1.2 knock-down/out cultures. In summary, our results suggest that Cav1.2 L-type VOCCs play a fundamental role in the induction and/or proliferation of reactive astrocytes, and indicate that the inhibition of these Ca(++) channels may be an effective way to prevent astrocyte activation. GLIA 2016. GLIA 2016;64:1396-1415.

Scutellarin promotes microglia-mediated astrogliosis coupled with improved behavioral function in cerebral ischemia

Scutellarin, an anti-inflammatory agent, has been reported to suppress microglia activation. It promotes astrocytic reaction but through activated microglia. Here we sought to determine more specifically the outcomes of scutellarin treatment in reactive astrocytes in rats subjected to middle cerebral artery occlusion (MCAO). GFAP, MAP-2 and PSD-95 expression was assessed in reactive astrocytes in scutellarin injected MCAO rats. Expression of BDNF, NT-3 and IGF-1, and cell cycle markers cyclin-D1/B1 was also evaluated. In vitro, the above-mentioned proteins were also investigated in TNC 1 and primary astrocytes, treated respectively with conditioned medium from BV-2 microglia with or without pretreatment of scutellarin and lipopolysaccharide. Behavioral study was conducted to ascertain if scutellarin would improve the neurological functions of MCAO rats. In MCAO, reactive astrocytes in the penumbral areas were hypertrophic bearing long extending processes; expression of all the above-mentioned markers was markedly augmented. When compared to the controls, TNC1/primary astrocytes responded vigorously to conditioned medium derived from BV-2 microglia treated with scutellarin + lipopolysaccharide as shown by enhanced expression of all the above markers by Western and immunofluorescence analysis. By electron microscopy, hypertrophic TNC1 astrocytes in this group showed abundant microfilaments admixed with microtubules. In MCAO rats given scutellarin treatment, neurological scores were significantly improved coupled with a marked decrease in infarct size when compared with the matching controls. It is concluded that scutellarin is neuroprotective and that it can amplify astrogliosis but through activated microglia. Scutellarin facilitates tissue remodeling in MCAO that maybe linked to improvement of neurological functions.

Altered Loyalties of Neuronal Markers in Cultured Slices of Resected Human Brain Tissue

Organotypic cultures from normal neocortical tissue obtained at epilepsy surgery show a severe injury response. This response involves both neuronal degeneration and the proliferation of reactive cells. A salient feature of the reactive cells is the co-expression of microglial and astrocytic markers. Surprisingly, the reactive cells also began to express neuronal markers Tubulin βIII and MAP2 adding to the confusion about their origin. Concomitant with their appearance in reactive cells MAP2 and Tubulin βIII expression disappeared from neurons. While NeuN expression decreased significantly, it did not entirely disappear from many neurons. Moreover, it was not observed in reactive cells, showing that NeuN is a reliable marker of neurons.

Microtissue engineered constructs with living axons for targeted nervous system reconstruction

As a common feature of many neurological diseases and injury, the loss of axon pathways can have devastating effects on function. Here, we demonstrate a new strategy to restore damaged axon pathways using transplantable miniature constructs consisting of living neurons and axonal tracts internalized within hydrogel tubes. These hydrogel microconduits were developed through an iterative process to support neuronal survival and directed axon growth. The design included hollow agarose tubes providing a relatively stiff outer casing to direct constrained unidirectional outgrowth of axons through a central soft collagen matrix, with overall dimensions of 250 μm inner diameter ×500 μm outer diameter and extending up to several centimeters. The outer casing was also designed to provide structural support of neuronal/axonal cultures during transplantation of the construct. Using neuron culture conditions optimized for the microconduits, dissociated dorsal root ganglia neurons were seeded in the collagen at one end of the conduits. Over the following week, high-resolution confocal microscopy demonstrated that the neurons survived and the somata remained in a tight cluster at the original seeding site. In addition, robust outgrowth of axons from the neurons was found, with axon fascicles constrained in a longitudinal projection along the internal collagen canal and extending over 5 mm in length. Notably, this general geometry recapitulates the anatomy of axon tracts. As such, these constructs may be useful to repair damaged axon projections by providing a transplantable bridge of living axons. Moreover, the small size of the construct permits follow-on studies of minimally invasive transplantation into potentially sensitive regions of the nervous system.

Demyelinating and nondemyelinating strains of mouse hepatitis virus differ in their neural cell tropism

Some strains of mouse hepatitis virus (MHV) can induce chronic inflammatory demyelination in mice that mimics certain pathological features of multiple sclerosis. We have examined neural cell tropism of demyelinating and nondemyelinating strains of MHV in order to determine whether central nervous system (CNS) cell tropism plays a role in demyelination. Previous studies demonstrated that recombinant MHV strains, isogenic other than for the spike gene, differ in the extent of neurovirulence and the ability to induce demyelination. Here we demonstrate that these strains also differ in their abilities to infect a particular cell type(s) in the brain. Furthermore, there is a correlation between the differential localization of viral antigen in spinal cord gray matter and that in white matter during acute infection and the ability to induce demyelination later on. Viral antigen from demyelinating strains is detected initially in both gray and white matter, with subsequent localization to white matter of the spinal cord, whereas viral antigen localization of nondemyelinating strains is restricted mainly to gray matter. This observation suggests that the localization of viral antigen to white matter during the acute stage of infection is essential for the induction of chronic demyelination. Overall, these observations suggest that isogenic demyelinating and nondemyelinating strains of MHV, differing in the spike protein expressed, infect neurons and glial cells in different proportions and that differential tropism to a particular CNS cell type may play a significant role in mediating the onset and mechanisms of demyelination.

Disturbance of nuclear and cytoplasmic TAR DNA-binding protein (TDP-43) induces disease-like redistribution, sequestration, and aggregate formation

TAR DNA-binding protein 43 (TDP-43) is the disease protein in frontotemporal lobar degeneration with ubiquitin-positive inclusions (FTLD-U) and amyotrophic lateral sclerosis (ALS). Although normal TDP-43 is a nuclear protein, pathological TDP-43 is redistributed and sequestered as insoluble aggregates in neuronal nuclei, perikarya, and neurites. Here we recapitulate these pathological phenotypes in cultured cells by altering endogenous TDP-43 nuclear trafficking and by expressing mutants with defective nuclear localization (TDP-43-DeltaNLS) or nuclear export signals (TDP-43-DeltaNES). Restricting endogenous cytoplasmic TDP-43 from entering the nucleus or preventing its exit out of the nucleus resulted in TDP-43 aggregate formation. TDP-43-DeltaNLS accumulates as insoluble cytoplasmic aggregates and sequesters endogenous TDP-43, thereby depleting normal nuclear TDP-43, whereas TDP-43-DeltaNES forms insoluble nuclear aggregates with endogenous TDP-43. Mutant forms of TDP-43 also replicate the biochemical profile of pathological TDP-43 in FTLD-U/ALS. Thus, FTLD-U/ALS pathogenesis may be linked mechanistically to deleterious perturbations of nuclear trafficking and solubility of TDP-43.

Cytoskeleton and Vesicle Mobility in Astrocytes

Exocytotic vesicles in astrocytes are increasingly viewed as essential in astrocyte-to-neuron communication in the brain. In neurons and excitable secretory cells, delivery of vesicles to the plasma membrane for exocytosis involves an interaction with the cytoskeleton, in particular microtubules and actin filaments. Whether cytoskeletal elements affect vesicle mobility in astrocytes is unknown. We labeled single vesicles with fluorescent atrial natriuretic peptide and monitored their mobility in rat astrocytes with depolymerized microtubules, actin, and intermediate filaments and in mouse astrocytes deficient in the intermediate filament proteins glial fibrillary acidic protein and vimentin. In astrocytes, as in neurons, microtubules participated in directional vesicle mobility, and actin filaments played an important role in this process. Depolymerization of intermediate filaments strongly affected vesicle trafficking and in their absence the fraction of vesicles with directional mobility was reduced.

The BTB domain of the nuclear matrix protein NRP/B is required for neurite outgrowth

The neuronal nuclear matrix protein, NRP/B, contains a BTB domain and kelch repeats and is expressed in primary neurons but not in primary glial cells. To examine the function of NRP/B in neurons, we analyzed the structure/function of the NRP/B-BTB domain and its role in neurite outgrowth. Based on three-dimensional modeling of NRP/B, we generated an NRP/B-BTB mutant containing three mutations in the conserved amino acids D47A, H60A and R61D that was termed BTB mutant A. BTB mutant A significantly reduced the dimerization of NRP/B compared to wild-type NRP/B. The NRP/B-BTB domain was required for nuclear localization and mediated the association of NRP/B with p110RB through the TR subdomain within the B pocket of p110RB. Overexpression of wild-type NRP/B and NRP/B-BTB domain significantly induced neurite outgrowth in PC12 cells and enhanced the G0-G1 cell population by ∼23% compared to the control cells, whereas NRP/B-BTB mutant A reduced neurite outgrowth by 70-80%, and inhibited NRP/B-p110RB association. Single cell microinjection of NRP/B-specific antibodies also blocked the neurite outgrowth of PC12 cells upon NGF stimulation. Interference of NRP/B expression by small interfering RNA (NRP/B-siRNA) inhibited neurite outgrowth and suppressed the NGF-induced outgrowth of neurites in PC12 cells. Additionally, p110RB phosphorylation at serine residue 795 was significantly reduced in PC12 cells treated with NRP/B siRNA compared to those treated with control GFP-siRNA, indicating that p110RB is a downstream target of NRP/B. Thus, the BTB domain of NRP/B regulates neurite outgrowth through its interaction with the TR subdomain within the B pocket of p110RB, and the conserved amino acids D47A, H60A and R61D within this domain of NRP/B are crucial residues for neurite extension in neuronal cells. These findings support a role for the BTB-domain of NRP/B as an important regulator of neuronal differentiation.

Tumorigenicity issues of embryonic carcinoma-derived stem cells: relevance to surgical trials using NT2 and hNT neural cells

Cell therapy is a rapidly moving field with new cells, cell lines, and tissue-engineered constructs being developed globally. As these novel cells are further developed for transplantation studies, it is important to understand their safety profiles both prior to and posttransplantation in animals and humans. Embryonic carcinoma-derived cells are considered an important alternative to stem cells. The NTera2/D1 teratocarcinoma cell-line (or NT2-N cells) gives rise to neuron-like cells called hNT neurons after exposure to retinoic acid. NT2 cells form tumors upon transplantation into the rodent. However, when the NT2 cells are treated with retinoic acid to produce hNT cells, they terminally differentiate into post-mitotic neurons with no sign of tumorigenicity. Preliminary human transplantation studies in the brain of stroke patients also demonstrated a lack of tumorigenicity of these cells. This review focuses on the use of hNT neurons in cell transplantation for the treatment in central nervous system (CNS) diseases, disorders, or injuries and on the mechanism involved in retinoic acid exposure, final differentiation state, and subsequent tumorigenicity issues that must be considered prior to widespread clinical use.

High molecular weight microtubule-associated protein 2 over-expression in neuronal migration disorders caused by N-methyl-D-aspartate receptor activation in hamsters

To evaluate the neuronal cytoarchitectural changes in neuronal migration disorders, the immunohistochemical expression of microtubule-associated proteins (MAPs) was analyzed using the experimental model induced by ibotenate in newborn hamsters. The cortical lesions observed after intracerebral ibotenate injections strongly resembled the following neuronal migration disorders: (1) microgyria; (2) focal subcortical heterotopia; (3) focal subependymal heterotopia; and (4) leptomeningeal glioneuronal heterotopia. Microgyria and leptomeningeal glioneuronal heterotopia had MAP2 (HM-2: high and low-molecular-weight forms of MAP2) immunoreactive dendritic processes or neuronal elements. The high molecular weight isoform of MAP2 (AP-20), which is more characteristic of mature neurons, showed enhanced expression in neurons of focal subcortical or subependymal heterotopia, although MAP1B (AA6: early form of MAP) immunoreactive elements were not detected in these heterotopic areas. We conclude that high molecular weight isoform of MAP2 is closely associated with cytoarchitectural repair and remodeling of neuronal processes, resulting in neuronal heterotopia after NMDA receptor activation.

Murine coronavirus spike glycoprotein mediates degree of viral spread, inflammation, and virus-induced immunopathology in the central nervous system

The mouse hepatitis virus (MHV) spike glycoprotein is a major determinant of neurovirulence. We investigated how alterations in spike affect neurovirulence using two isogenic recombinant viruses differing exclusively in spike. S(4)R, containing the MHV-4 spike gene, is dramatically more neurovirulent than S(A59)R, containing the MHV-A59 spike gene (J. J. Phillips, M. M. Chua, E. Lavi, and S. R. Weiss, 1999, J. Virol. 73, 7752-7760). We examined the contribution of differences in cellular tropism, viral spread, and the immune response to infection to the differential neurovirulence of S(4)R and S(A59)R. MHV-4 spike-mediated neurovirulence was associated with extensive viral spread in the brain in both neurons and astrocytes. Infection of primary hippocampal neuron cultures demonstrated that S(4)R spread more rapidly than S(A59)R and suggested that spread may occur between cells in close physical contact. In addition, S(4)R infection induced a massive influx of lymphocytes into the brain, a higher percentage of CD8(+) T cells, and a higher frequency of MHV-specific CD8(+) T cells relative S(A59)R infection. Despite this robust and viral-specific immune response to S(4)R infection, infection of RAG1-/- mice suggested that immune-mediated pathology also contributes to the high neurovirulence of S(4)R.

MAP2 Isoforms in Developing Cat Cerebral Cortex and Corpus Callosum

The microtubule-associated protein MAP2 was studied in the developing cat visual cortex and corpus callosum. Biochemically, no MAP2a was detectable in either structure during the first postnatal month; adult cortex revealed small amounts of MAP2a. MAP2b was abundant in cortical tissue during the first postnatal month and decreased in concentration towards adulthood; it was barely detectable in corpus callosum at all ages. MAP2c was present in cortex and corpus callosum at birth; in cortex it consisted of three proteins of similar molecular weights between 65 and 70 kD. The two larger, phosphorylated forms disappeared after postnatal day 28, the smaller form after day 39. In corpus callosum, MAP2c changed from a phosphorylated to an unphosphorylated variant during the first postnatal month and then disappeared. Immunocytochemical experiments revealed MAP2 in cell bodies and dendrites of neurons in all cortical layers, from birth onwards. In corpus callosum, in the first month after birth, a little MAP2, possibly MAP2c, was detectable in axons. The present data indicate that MAP2 isoforms differ in their cellular distribution, temporal appearance and structural association, and that their composition undergoes profound changes during the period of axonal stabilization and dendritic maturation.

Microtubule-associated protein 2 (MAP-2) is expressed in low and high grade diffuse astrocytomas

The expression of neuronal antigens in diffuse astrocytomas has not been thoroughly evaluated. We have investigated the expression of microtubule associated protein 2 (MAP-2), synaptophysin and non-phosphorylated epitopes of neurofilament protein (NFP) by immunohistochemistry in 15 low grade diffuse astrocytomas and 15 glioblastomas. MAP-2 was strongly expressed in 97% of cases, using an antibody to both low and high molecular weight isoforms. An antibody specific to high molecular weight isoforms of MAP-2 (hmw-MAP-2) revealed weaker, focal staining in 60% of cases with greater expression in the glioblastomas (P=0.027). NFP was expressed in 50% of cases, but was generally weak and focal. There was little evidence of synaptophysin expression. We conclude that MAP-2 expression in astrocytomas is due predominantly to low molecular weight isoforms, which may be expressed in astrocytes as well as neurons. Focal expression of hmw-MAP-2 and NFP, however, suggest that neuronal antigens may be expressed, particularly in high grade astrocytomas. Immunopositivity for these antigens should not preclude the diagnosis of diffuse astrocytoma.

Neurite outgrowth inhibitors in gliotic tissue

Gliotic tissue is the major obstacle to axon regeneration after CNS injury. We designed tissue culture assays to search for molecules responsible for neurite outgrowth inhibition in gliotic tissue. All the inhibitory activity in injured brain tissue was located in a plasma membrane heparan-sulphate and condroitin-sulphate type-proteoglycan of apparent molecular weight 200 kDalton. The proteoglycan core protein (apparent MW 48,000 kD) was biologically inactive, whereas the glycosamine-glycan (GAG) chains accounted for the inhibitory activity. Because of its cell location and mode of induction, the inhibitor was called injured membrane proteoglycan, IMP. IMP prevented neurite outgrowth initiation when attached to the culture substrate and caused growth cone collapse when added in solution to neurons with already growing neurites. We concluded that IMP was responsible for preventing injured CNS fibre regeneration. Double-staining immunohistochemistry of normal and gliotic tissue with anti-IMP monoclonal antibodies together with glial and neuronal markers, permitted the unequivocal definition of inhibitor presenting cells by confocal microscopy. IMP-immunostaining in normal CNS was observed exclusively on neurons. However, after a lesion, immunostaining occurred primarily on intensely GFAP-positive reactive astrocytes, but not on OX-42 positive microglia. The availability of antibodies permitted rapid affinity-purification of the neurite inhibitor and comparison with similar molecules possibly expressed during development. IMP itself or a highly related form, was expressed in embryonic brain, reaching maximal expression around postnatal day 3 and decreasing strongly in normal adult tissue. Perinatal rat brain proteoglycans inhibited neurite outgrowth similarly, though not identically, to IMP. Our data suggest that perinatal membrane and injured membrane proteoglycans may differ in GAG composition. IMP-like immunoreactivity was also found in developing brain, predominantly in neurons in normal brain, associating after a lesion with reactive astrocytes. Thes results suggest that injury evokes re-expression of IMP previously expressed during CNS development. One of the monoclonal antibodies to IMP blocked inhibitory activity, restoring neurite outgrowth in vitro. We are currently preparing Fab fragments to test the possibility that the antibody may block inhibition of central sprout growth in vivo. The combined use of blocking antibody fragments to neurite outgrowth inhibitors and transplants of growth-promoting glia, may help in the repair brain and spinal cord lesions.

N-cadherin at the glial scar in the rat

Following injury to the central nervous system (CNS), astrocytes become reactive and in many cases form a glial scar. Very little is known about the adhesive interactions between astrocytes at the glial scar, even though reactive gliosis and scar formation are a central issue in CNS wound healing. In the present study, we examine the role of cadherin in the process of scar formation using immunohistochemistry and immunoblot methods. When a stab wound was made in the cerebral cortex of the rat, cadherins were consistently upregulated by the reactive astrocytes at the glial scar. Our immunoblot analysis demonstrates that the increase in cadherin immunoreactivity was due to a threefold upregulation of a single protein with a molecular weight of 135 kDa. The size (135 kDa) and location of the immunoreactive protein at regions of cell-cell contact in cultured astrocytes indicates that the immunoreactive protein is N-cadherin. These data are the first to demonstrate that N-cadherin plays a prominent role in the response of astrocytes to injury, including the formation and maintenance of the glial scar.

NRP/B, a novel nuclear matrix protein, associates with p110(RB) and is involved in neuronal differentiation

The nuclear matrix is defined as the insoluble framework of the nucleus and has been implicated in the regulation of gene expression, the cell cycle, and nuclear structural integrity via linkage to intermediate filaments of the cytoskeleton. We have discovered a novel nuclear matrix protein, NRP/B (nuclear restricted protein/brain), which contains two major structural elements: a BTB domain-like structure in the predicted NH2 terminus, and a "kelch motif" in the predicted COOH-terminal domain. NRP/B mRNA (5.5 kb) is predominantly expressed in human fetal and adult brain with minor expression in kidney and pancreas. During mouse embryogenesis, NRP/B mRNA expression is upregulated in the nervous system. The NRP/B protein is expressed in rat primary hippocampal neurons, but not in primary astrocytes. NRP/B expression was upregulated during the differentiation of murine Neuro 2A and human SH-SY5Y neuroblastoma cells. Overexpression of NRP/B in these cells augmented neuronal process formation. Treatment with antisense NRP/B oligodeoxynucleotides inhibited the neurite development of rat primary hippocampal neurons as well as the neuronal process formation during neuronal differentiation of PC-12 cells. Since the hypophosphorylated form of retinoblastoma protein (p110(RB)) is found to be associated with the nuclear matrix and overexpression of p110(RB) induces neuronal differentiation, we investigated whether NRP/B is associated with p110(RB). Both in vivo and in vitro experiments demonstrate that NRP/B can be phosphorylated and can bind to the functionally active hypophosphorylated form of the p110(RB) during neuronal differentiation of SH-SY5Y neuroblastoma cells induced by retinoic acid. Our studies indicate that NRP/B is a novel nuclear matrix protein, specifically expressed in primary neurons, that interacts with p110(RB) and participates in the regulation of neuronal process formation.

A novel approach to identify proteins associated with the inhibition of neurite growth

In the present study, a novel combination of techniques was used to identify the genes that may be involved in the lack of axonal regeneration in the mammalian adult central nervous system (CNS). The key features of this approach are: (1) a functional assay that can be affected by antibody perturbation; (2) increased specificity of the polyclonal antiserum by adsorption; (3) the expression cloning of the genes from a lambdagt11 library; (4) amplification of the insert cDNA by PCR; and (5) the direct cycle sequencing of PCR products. In this culture assay system, neurons were plated directly on sections of the rat CNS. This assay system could be used to demonstrate the lack of neuronal attachment to or neurite extension over myelinated regions of the CNS (white matter). This prohibitive nature of the CNS sections could be masked by a rabbit polyclonal antiserum directed against rat CNS white matter. This data indicates that the anti-white matter antiserum recognizes and neutralizes inhibitory molecules on the surface of the sections. Making the assumption that the prohibitive antigen is associated with the cell membrane, the antiserum was adsorbed against a soluble protein fraction of the adult rat brain. This adsorption significantly increased the specificity of the antiserum as demonstrated by immunoblot methods. The adsorbed antiserum was then used to screen the cDNA library of the adult rat brain. The present report describes this novel combination of techniques allowing one to go from a functional tissue culture assay system to defining the molecular basis for the cellular interactions.

Optic disc and optic nerve of the blind cape mole-rat (Georychus capensis): a proposed model for naturally occurring reactive gliosis

Recent studies of the visual system of animal species that live in a subterranean environment show not only regressive but also progressive morphological features. In this regard the aim of the present investigation is to describe the structural organisation of the eye and optic nerve of the adult Cape mole-rat, with special emphasis on both glial cell population and myelination. The main results are: (a) astrocytes show identical features to those occurring in reactive gliosis; (b) optic fibers vary greatly in diameter; (c) very small axons are myelinated and are often surrounded by a thicker sheath than larger optic fibers; (d) a large onion bulb-like structure composed of optic fibers, glia, and ganglion cells is found within the choriocapillary layer. These results suggest that the Cape mole-rat and probably other subterranean rodents may serve as a model to study spontaneous gliosis as well as mechanisms involved in myelination and degenerative processes.

Okadaic acid modulates the cytoskeleton changes induced by amyloid peptide (25-35) in cultured astrocytes

Amyloid beta-protein (25-35) (betaA) induced a marked morphological change in astrocytes, changing their flat polygonal shape into a stellate process-bearing morphology. The changes induced by betaA were concentration and time-dependent, whereas the addition of a scrambled peptide did not alter astrocyte morphology. We discard the possibility of betaA-astrocytes being type II-like astrocytes. We also analysed the influence of the presence of kinase and phosphate inhibitors on this morphological change. Our data indicate that the betaA-induced phenotype was not affected by the inhibition of protein tyrosine kinase or tyrosine phosphatases. Only the addition of okadaic acid to astrocytes prevented the morphological transformation from flat to stellate shape, induced by betaA (25-35). Inhibition of the stellate phenotype by okadaic acid was initiated at a concentration of 10 nM which suggested that either phosphatase 2A or 1 plays an important role in the betaA astrocytic transformation.

Selective destruction of stable microtubules and axons by inhibitors of protein serine/threonine phosphatases in cultured human neurons

Paired helical filaments (PHFs) in the neurofibrillary tangles (NFTs) in Alzheimer's disease (AD) brains are composed of highly phosphorylated isoforms of tau (PHFtau) that fail to bind microtubules (MTs), and the levels of MT-binding competent tau are decreased in AD brains with abundant PHFtau. Because this loss of MT binding could compromise the viability of tangle-bearing AD neurons by destabilizing MTs, we asked whether these events could be initiated by inhibiting protein phosphatase 1 (PP1) and PP2A in cultured human neurons (NT2N cells) using okadaic acid (OK) and calyculin-A (CL-A). The treatment of NT2N cells with OK and CL-A increased tau phosphorylation, decreased the binding of tau to MTs, and selectively depolymerized the more stable detyrosinated MTs but not the more labile tyrosinated MTs. Significantly, this led to the rapid degeneration of axons, which are enriched in the more stable detyrosinated MTs, and PP2A was implicated in the initiation of this cascade of events because PP2A but not PP1 was closely associated with MTs in the NT2N cells. These studies imply that inactivation of PP2A in vulnerable neurons of the AD brain may play a mechanistic role in the conversion of normal tau into PHFtau, in the depolymerization of stable MTs, and in the degeneration of axons emanating from tangle-bearing neurons.

Selective destruction of stable microtubules and axons by inhibitors of protein serine/threonine phosphatases in cultured human neurons

Paired helical filaments (PHFs) in the neurofibrillary tangles (NFTs) in Alzheimer's disease (AD) brains are composed of highly phosphorylated isoforms of tau (PHFtau) that fail to bind microtubules (MTs), and the levels of MT-binding competent tau are decreased in AD brains with abundant PHFtau. Because this loss of MT binding could compromise the viability of tangle-bearing AD neurons by destabilizing MTs, we asked whether these events could be initiated by inhibiting protein phosphatase 1 (PP1) and PP2A in cultured human neurons (NT2N cells) using okadaic acid (OK) and calyculin-A (CL-A). The treatment of NT2N cells with OK and CL-A increased tau phosphorylation, decreased the binding of tau to MTs, and selectively depolymerized the more stable detyrosinated MTs but not the more labile tyrosinated MTs. Significantly, this led to the rapid degeneration of axons, which are enriched in the more stable detyrosinated MTs, and PP2A was implicated in the initiation of this cascade of events because PP2A but not PP1 was closely associated with MTs in the NT2N cells. These studies imply that inactivation of PP2A in vulnerable neurons of the AD brain may play a mechanistic role in the conversion of normal tau into PHFtau, in the depolymerization of stable MTs, and in the degeneration of axons emanating from tangle-bearing neurons.

Age-dependent changes in the immunoreactivity for neurofilaments in rabbit hippocampus

The distribution of the three subunits of neurofilaments was examined in the hippocampus of young adult rabbits (three months of age), employing a panel of six monoclonal antibodies. Thereafter, age-dependent and subunit-selective changes in neurofilament immunoreactivity in the ageing rabbit hippocampus were studied, using animals of one, three, six, 12, 24, 30, 36, 48, and 60 months. Principal cells, interneurons, axons, and various fibre systems were immunoreactive for all three subunits, although the localization and staining intensity of neurofilament immunoreactivity depended on the antibody used. Small cells immunopositive for the low subunit of neurofilament (presumably glial cells) were found abundantly in the hippocampal formation at one month, and (occasionally) at 30-36 months. Young rabbits (one to three months of age) had high numbers of interneurons stained for the high subunit of neurofilament in the stratum oriens/pyramidale. The number declined and plateaued to approximately 78% at six to 30 months, and further declined and plateaued to approximately 56% at 36-60 months. The first decline may reflect a process of maturation, while the latter decline most likely relates to ageing. Ageing pyramidal cells in 48-60 months animals revealed a slight increase for the low subunit of neurofilament, but no changes for the other subunits. Transient changes in neurofilament immunoreactivity were a striking observation in dentate gyrus granule cells during ageing. The staining intensity for the low subunit of neurofilament decreased gradually from one to 24-30 months until it was no longer detectable in these cells. The immunoreactivity then reappeared, most notably in granule cells lining the hilus, at the age of 36-48 months. By 60 months all granule cells were nearly immunonegative for this subunit. Axonal aberrations, immunoreactive for all three subunits, were found throughout the hippocampal formation. These aberrations first appeared in 24-month-old animals and increased in number and maximal size in older rabbits. The alterations in neurofilament immunoreactivity in the ageing hippocampus correlated with age-associated learning disabilities in the acquisition of a hippocampally-dependent learning task. The potential relevance of changes in the cytoskeletal profile of hippocampal neurons to age-associated learning and memory disabilities is discussed.

Neurogenesis in postnatal rat spinal cord: a study in primary culture

Spinal cord injuries result in paralysis, because when damaged neurons die they are not replaced. Neurogenesis of electrophysiologically functional neurons occurred in spinal cord cultured from postnatal rats. In these cultures, the numbers of immunocytochemically identified neurons increased over time. Additionally, neurons identified immunocytochemically or electrophysiologically incorporated bromodeoxyuridine, confirming they had differentiated from mitotic cells in vitro. These findings suggest that postnatal spinal cord retains the capacity to generate functional neurons. The presence of neuronal precursor cells in postnatal spinal cord may offer new therapeutic approaches for restoration of function to individuals with spinal cord injuries.

Astrocyte growth, reactivity, and the target of the antiproliferative antibody, TAPA

Reactive astrocytes form a scar after injury to the CNS that many investigators believe contributes to the lack of functional regeneration. In the present study, we identify an astrocytic membrane protein that appears to play an important role in reactive gliosis and scar formation. Cultures of rat astrocytes were used as a model system to produce and to screen monoclonal antibodies that would alter cell growth. One antibody, AMP1, was identified that depresses the mitotic activity of cultured glial cells and alters their morphology. Expression cloning reveals that the antigen on the external surface of the cultured glial cells has a high degree of homology with the human lymphocyte protein called Target of the Anti-Proliferative Antibody (TAPA-1; this rat protein will be referred to as rTAPA). rTAPA is a member of the tetramembrane-spanning superfamily of proteins and, as with other members of this family of proteins, rTAPA is associated with the regulation of cellular interactions and mitotic activity. After an injury to the cerebral cortex, there is a dramatic increase in AMP1 immunoreactivity that is spatially restricted to the reactive astrocytes at the glial scar. This change represents an upregulation of a membrane protein, rTAPA, that is approximately equal to the increase observed for glial fibrillary acidic protein. The high levels of rTAPA at the site of CNS injury and the AMP1 antibody perturbation studies indicate that rTAPA may play a prominent role in the response of astrocytes to injury and in glial scar formation.

Astrocyte growth, reactivity, and the target of the antiproliferative antibody, TAPA

Reactive astrocytes form a scar after injury to the CNS that many investigators believe contributes to the lack of functional regeneration. In the present study, we identify an astrocytic membrane protein that appears to play an important role in reactive gliosis and scar formation. Cultures of rat astrocytes were used as a model system to produce and to screen monoclonal antibodies that would alter cell growth. One antibody, AMP1, was identified that depresses the mitotic activity of cultured glial cells and alters their morphology. Expression cloning reveals that the antigen on the external surface of the cultured glial cells has a high degree of homology with the human lymphocyte protein called Target of the Anti-Proliferative Antibody (TAPA-1; this rat protein will be referred to as rTAPA). rTAPA is a member of the tetramembrane-spanning superfamily of proteins and, as with other members of this family of proteins, rTAPA is associated with the regulation of cellular interactions and mitotic activity. After an injury to the cerebral cortex, there is a dramatic increase in AMP1 immunoreactivity that is spatially restricted to the reactive astrocytes at the glial scar. This change represents an upregulation of a membrane protein, rTAPA, that is approximately equal to the increase observed for glial fibrillary acidic protein. The high levels of rTAPA at the site of CNS injury and the AMP1 antibody perturbation studies indicate that rTAPA may play a prominent role in the response of astrocytes to injury and in glial scar formation.

Up-regulation of a keratan sulfate proteoglycan following cortical injury in neonatal rats

The up-regulation of the keratan sulfate proteoglycan (ABAKAN) was examined using indirect immunohistochemical methods. Previous studies indicate that the keratan sulfate proteoglycan is associated with astrocytes in the optic nerve and in the developing rat brain. In model culture systems, this proteoglycan is capable of inhibiting the growth of neurites over laminin. To determine whether the proteoglycan is up-regulated specifically during reactive gliosis, stab wounds were made in the cerebral cortex of early postnatal rats, and the up-regulation of the proteoglycan was related to the developmentally regulated gliotic response to injury. Following a stab wound in the cortex of the late postnatal rat, reactive gliosis was consistently observed along with an up-regulation of ABAKAN. When the cortex was injured on postnatal day 2, there was a variable gliotic response and considerable variation in the regulation of proteoglycan expression. Biochemical analysis revealed that ABAKAN is a large proteoglycan with multiple keratan sulfate side-chains, at least one chondroitin sulfate side-chain and at least one additional carbohydrate chain with a terminal 3-sulfoglucuronic acid. Taken together, these data demonstrate that the boundary proteoglycan ABAKAN is also associated with reactive gliosis during early postnatal development.

Differential cellular response after glutamate analog hippocampal damage

The tissue response after brain damage implicates the cellular "activation" of astrocytes and microglia. This glial response is referred as reactive gliosis. Using immunohistochemical markers, we have analyzed the neuronal and glial response to some neurotoxic-induced lesions. We have compared the effects of two glutamate analogs, AMPA and kainic acid, with those of traumatic injury. Our data showed that the time-course of appearance, the relative contribution of and the behavior of reactive astrocytes and microglial cells were clearly different after AMPA or kainic acid administration. The immunoreactivity associated with microglia response, with respect to the immunoreactivity associated with reactive astrocytes, was higher after AMPA damage than after kainic acid treatment. In both cases, however, glial cells were more abundant than after traumatic lesions. Interestingly, the CA1 pyramidal neurons affected by AMPA and some cortical neurons affected by traumatic injury responded with an overexpression of amyloid precursor protein, whereas no neuronal response was detected after the kainic acid treatment. Our data suggest that the gliotic response is highly specific to the type of insult and heterogeneous depending on the brain area affected.

Microtubule-associated proteins in developing oligodendrocytes: transient expression of a MAP2c isoform in oligodendrocyte precursors

The morphological differentiation of oligodendrocytes is characterized by the formation of multiple, microtubule-rich processes which endow these cells with the ability to myelinate many axons simultaneously. Since microtubule-associated proteins (MAPs) strongly influence the structure and function of microtubules, we have investigated their expression in cultured differentiating oligodendrocytes in order to gain insights into MAP function during process formation and stabilization. MAP1B has been compared with two other structural MAPs: MAP4, which is an ubiquitously expressed protein, and MAP2, which hitherto was thought to be confined to neurons and reactive astrocytes. Immunofluorescence microscopy showed that the colocalization of MAP4 with microtubules in oligodendrocyte processes is not as extensive as found previously for MAP1B (Vouyiouklis and Brophy: J Neurosci Res 35:257-267, 1993). Nevertheless, like MAP1B, the expression of MAP4 increases during oligodendrocyte differentiation. In contrast, the expression of MAP2 is transiently elevated in preoligodendrocytes but declines precipitously at the onset of terminal differentiation. Cells of the oligodendrocyte lineage exclusively express a novel isoform of MAP2c which is primarily localized in the cell bodies of preoligodendrocytes. This suggests that MAP2c assists in the initiation of process extension rather than in the stabilization of microtubules in the cytoplasm-filled membranous extensions of mature cells. MAP-tau was not expressed at any developmental stage by oligodendrocytes. The distinct subcellular localizations and patterns of developmental expression of MAP1B, MAP4, and MAP2c suggest that these MAPs have different roles in the regulation of the microtubule network during the differentiation of myelin-forming oligodendrocytes.

The process of reinnervation in the dentate gyrus of adult rats: gene expression by neurons during the period of lesion-induced growth

Neurons in the hippocampal dentate gyrus are extensively reinnervated following the destruction of their normal inputs from the ipsilateral entorhinal cortex (EC). The present study evaluates gene expression by dentate granule neurons and the neurons giving rise to the sprouting connections during the period of synapse growth. Adult male rats were prepared for in situ hybridization at 2, 4, 6, 8, 10, 12, 14, 20, and 30 days following unilateral EC lesions. Sections were hybridized using 35S-labeled cRNA probes for mRNAs that encode proteins thought to be important for neuronal structure and/or synapse function, including (1) mRNAs that are normally present in dendrites--the mRNAs for the high molecular weight microtubule-associated protein 2 (MAP2) and the alpha-subunit of calcium/calmodulin-dependent protein kinase II (CAMII kinase), (2) mRNAs that are upregulated in neurons that are regenerating their axons (T alpha 1 tubulin and F1/GAP43) and (3) mRNAs for proteins that are the principal constituents of neurofilaments and microtubules (the low molecular weight neurofilament protein NF68 and beta-tubulin). Although there were small changes in the levels of labeling for the mRNAs that are normally present in dendrites, there were no dramatic increases in the levels of any of the mRNAs either in dentate granule cells or in neurons giving rise to the reinnervating fibers at any postlesion interval. These results indicate that neurons in mature animals can substantially remodel their synaptic terminals and their dendrites in the absence of large-scale changes in gene expression (at least as measured by steady-state mRNA levels at various time points).

Regulation of regional differences in the differentiation of cerebral cortical neurons by EGF family-matrix interactions

Both lineage-based and epigenetic regulation have been postulated as mechanisms to control the formation of discrete areas in the cerebral cortex, but specific genes or signaling pathways that may be involved have yet to be defined. In this paper, we examine whether progenitors, isolated from the cerebral wall prior to neurogenesis, can respond to exogenous cues by adopting a region-specific phenotype. The expression of the limbic system-associated membrane protein (LAMP), a neuron-specific marker of limbic cortical areas, was monitored in cultured neurons arising from precursors harvested from presumptive perirhinal (limbic) and sensorimotor (nonlimbic) zones at embryonic day 12 in the rat. Neuronal phenotype in all cultures was identified by expression of microtubule-associated protein-2 (MAP2). On a substrate of poly-lysine, over 80% of the precursors from the limbic area that differentiate into neurons express a LAMP+ phenotype. Approximately 20% of the neurons generated from precursors of the sensorimotor region become LAMP+. However, modification of the microenvironment had a significant effect on the differentiation of the sensorimotor precursors. When the nonlimbic precursors are grown on Matrigel, there is a 2-fold increase in the number of MAP2+/LAMP+ double-labeled neurons. Dissection of the Matrigel components reveals that in combination with growth factor-deficient Matrigel or collagen type IV, epidermal growth factor and transforming growth factor-alpha increase LAMP expression in the sensorimotor population. Delaying the addition of growth factor until after most cell division had ceased failed to increase the number of LAMP+ neurons. Another growth factor in Matrigel, platelet-derived growth factor, does not produce the same effect. Our results indicate that local signals can regulate the differentiation of cortical progenitors, providing a potential mechanism for establishing an early commitment to specific regional phenotypes in the developing cerebral wall that relate to future functional domains in the cortex.

Reexpression of developmentally regulated MAP2c mRNA after ischemia: colocalization with hsp72 mRNA in vulnerable neurons

Levels of mRNAs encoding the microtubule-associated proteins MAP2b and MAP2c as well as the 70-kDa stress protein [72-kDa heat shock protein (hsp72)] were evaluated in postischemic rat brain by in situ hybridization with oligonucleotide probes corresponding to the known rat sequences. Rats were subjected to 10-min cardiac arrest, produced by compression of major thoracic vessels, followed by resuscitation. The normally expressed MAP2b mRNA showed transient twofold elevations in all hippocampal neuron populations at 6-h recirculation, followed by a return to control levels by 24 h. MAP2b hybridization was progressively lost thereafter from the vulnerable CA1 and outer cortical layers, preceding both the fall in immunoreactive MAP2b and the eventual cell loss in these regions. The depletion of MAP2b mRNA coincided with an increase in the alternatively spliced MAP2c in vulnerable regions during 12-48 h of recirculation, precisely overlapping the late component of hsp72 expression that persisted in these cell populations. Previous studies have suggested that the initial induction of hsp72 provides an index of potential postischemic injury in neuron populations that may or may not be injured, while lasting hsp72 mRNA expression is associated with cell damage. In contrast, the present results demonstrate that MAP2c expression under these conditions occurs uniquely in neuron populations subject to injury. Available evidence suggests that MAP2c expression represents a plastic response in subpopulations of neurons that will survive in these regions, although it remains to be explicitly determined whether it may also be transiently expressed in dying cells. In any case, these observations demonstrate that reexpression of developmentally regulated MAP2c mRNA is a relatively late postischemic response in vulnerable cell populations, indicating that pathways regulating MAP2 splicing may be closely associated with mechanisms of neuron injury and/or recovery.

Expression of a keratin sulfate proteoglycan during development of the dorsal lateral geniculate nucleus in the ferret

ABAKAN is a keratin sulfate proteoglycan that was identified in rat brain by monoclonal antibody TED15 (Geisert et al. [1992] Brain Res. 571:165-168). It blocks neuronal attachment and neurite outgrowth in culture, is associated with astrocytes, and marks the boundaries of areas in the developing rat brain (Geisert and Bidanset [1993] Dev. Brain Res., 75:163-173). In the present study TED15 was used to examine the distribution of ABAKAN during laminar development of the dorsal lateral geniculate nucleus in ferrets. This distribution was also compared with that of astrocytes as displayed with antibodies to GFAP. In the adult, TED15 and anti-glial fibrillary acidic protein (GFAP) labeling are similar. Both are fairly uniform in the nucleus although somewhat elevated near the optic tract and in the interlaminar zone between laminae A and A1. During development the pattern is quite different. At postnatal day 1 (P1), before lamination is evident, TED15 and anti-GFAP labeling are light in the nucleus. By P10, when laminae are emerging, both are elevated in the A-A1 interlaminar zone and in the C laminae. At P18, when laminae are distinct, TED15 labels the A-A1 interlaminar zone, and it marks the borders between the ON and OFF leaflets within A and A1 (Stryker and Zahs [1983] J. Neurosci. 3:1943-1951). In comparison, anti-GFAP marks the interlaminar zone but not the ON/OFF leaflets. By 6 weeks the nucleus resembles the adult nucleus. These results show that ABAKAN marks the boundaries of the major functional subdivisions of the lateral geniculate nucleus in the developing ferret and suggest that it plays a role in lamination.

NTera 2 cells: a human cell line which displays characteristics expected of a human committed neuronal progenitor cell

We have identified a human cell line with a phenotype resembling committed CNS neuronal precursor cells. NTera 2/cl.D1 (NT2/D1) cells expressed nestin and vimentin, intermediate filament (IF) proteins expressed in neuroepithelial precursor cells, as well as MAP1b, a microtubule-associated protein (MAP) expressed in human neuroepithelium. NT2/D1 cells also expressed the cell adhesion molecules NCAM and N-cadherin which are thought to be important in cell-cell interactions within the neuroepithelium. These NT2/D1 cells also expressed small amounts of NF-L, alpha-internexin, NF-M, and MAP2c, indicating that they are committed to a neuronal fate. Previous studies have shown that, following RA treatment, a proportion of NT2/D1 cells terminally differentiate into neurons and that this occurs via an asymmetric stem cell mode of differentiation. In light of the identification of the neuroepithelial phenotype of NT2/D1 cells we decided to examine more closely the relationship of in vitro neurogenesis in NT2/D1 cells, during RA treatment to that of neurons in vivo. Three days after RA treatment, islands of NT2/D1 cells showed increased expression of neurofilament proteins and increased phosphorylation of NF-M. By 10-14 days, these cells began to resemble neurons morphologically, i.e., with rounded cell bodies and processes. These neuronal cells were clustered into clumps which rested on top of a layer of progenitor cells. In this upper layer, the neurons began to express MAP2b and tau and extinguished their expression of nestin. Recently, we developed a method for obtaining pure cultures of neurons from RA treated NT2/D1 cells. The phenotype of these postmitotic neurons is clearly dissociated from that of the untreated NT2/D1 cells. Given the data obtained in this study and the characterization of the neurons derived from NT2/D1 cells, we propose that NT2/D1 cells are a committed human neuronal precursor cell line which retains some stem cell characteristics and is capable only of terminal differentiation into neurons.