Human Cortical Neuronal Cell Line (Hcn-1): Further in Vitro Characterization and Suitability for Brain Transplantation

Neural Transplantation: Prospects for Clinical use

Neural transplantation has been extensively applied in Parkinson's disease, including numerous clinical studies, studies in animal models, and related basic research on cell biology. There is evidence that the clinical trials of both adrenal medulla transplantation and fetal substantia nigra transplantation have produced a detectable clinical effect, although it is not yet clear whether the clinical benefit is sufficient to justify a more widespread application of these procedures. Studies of long-term outcome and quantitative tests are important in assaying the degree of benefit produced by transplantation procedures in Parkinson's disease and for developing improved and refined procedures. Other disease-related applications of neural transplantation are beginning to be developed. These include Huntington's disease, chronic pain, epilepsy, spinal cord injury, and perhaps even demyelinating diseases and cortical ischemic injury. Although most of these applications lie in the future, it is not too soon to begin to consider the scientific justification that should be required for initiation of human clinical trials.

Factors involved in the determination of the neurotransmitter phenotype of developing neurons of the CNS: Applications in cell replacement treatment for Parkinson's disease

The developmental stages involved in the conversion of stem cells to fully functional neurons of specific neurotransmitter phenotype are complex and not fully understood. Over the past decade many studies have been published that demonstrate that in vitro manipulation of the epigenetic environment of the stem cells allows experimental control of final neuronal phenotypic choice. This review presents the evidence for the involvement of a number of endogenous neurobiochemicals, which have been reported to potently influence DAergic (and other neurotransmitter) phenotype expression in vitro. They act at different stages on the pathway to neurotransmitter phenotype determination, and in different ways. Many are better known for their involvement in other aspects of development, and in other biochemical roles. Their proper place, and precise roles, in neurotransmitter phenotype determination in vivo will no doubt be determined in the future. Meanwhile, considerable medical benefits are offered from producing large, long-term, viable cryostores of self-regenerating multipotential neural precursor cells (i.e., brain stem cells), which can be used for cell replacement therapies in the treatment of degenerative brain diseases, such as Parkinson's disease.

Human secreted attractin disrupts neurite formation in differentiating cortical neural cells in vitro

Mutations at the Atrn locus that encodes a transmembrane protein with a large ectodomain are responsible for a juvenile-onset neurodegeneration manifest as hypomyelination and cerebral vacuole development in several rodent species. In addition to a membrane isoform, the human Atm locus generates by alternative splicing a secreted form corresponding to the entire ectodomain that then circulates at high concentration in the periphery, released in part by activated T lymphocytes. We report here that the secreted form mRNA is downregulated throughout representative discrete regions of the human brain while membrane attractin mRNA is well represented, resulting in the apparent absence of secreted attractin protein in cerebrospinal fluid (CSF). Transcription of attractin secreted form mRNA is strongly downregulated upon differentiation of a human cortical neuron-derived cell line (HCN-1A) to a mature neuron phenotype in response to nerve growth factor. Recombinant secreted attractin disrupts neurite formation by differentiated HCN-1A cells, resulting in higher levels of branching with shorter processes. This effect is duplicated by anti-attractin and by human serum but not by human serum depleted of attractin or by CSF We propose that inappropriate expression of secreted attractin in the CNS blocks membrane attractin function and that its presence, either by leakage from the periphery, aberrant transcription, or release from inflammatory foci may affect neuron extracellular interactions leading to neurodegeneration in the human.

A murine dopamine neuron-specific cDNA library and microarray: increased COX1 expression during methamphetamine neurotoxicity

Due to brain tissue heterogeneity, the molecular genetic profile of any neurotransmitter-specific neuronal subtype is unknown. The purpose of this study was to purify a population of dopamine neurons, construct a cDNA library, and generate an initial gene expression profile and a microarray representative of dopamine neuron transcripts. Ventral mesencephalic dopamine neurons were purified by fluorescent-activated cell sorting from embryonic day 13.5 transgenic mice harboring a 4.5-kb rat tyrosine hydroxylase promoter-lacZ fusion. Nine-hundred sixty dopamine neuron cDNA clones were sequenced and arrayed for use in studies of gene expression changes during methamphetamine neurotoxicity. A neurotoxic dose of methamphetamine produced a greater than twofold up-regulation of the mitochondrial cytochrome c oxidase polypeptide I transcript from adult mouse substantia nigra at 12 h posttreatment. This is the first work to describe a gene expression profile for a neuronal subtype and to identify gene expression changes during methamphetamine neurotoxicity.

In vitro properties of a newly established medulloblastoma cell line, MCD-1

Medulloblastomas are poorly differentiated brain tumors believed to arise from primitive pleuripotential stem cells, and tend to express mixed neuronal and glial properties. In the present study, we examined immunohistochemical and neurotransmitter phenotypic properties in a newly established medulloblastoma cell line, MCD-1. MCD-1 cells were immortal, not contact-inhibited, but did not grow in soft agar. Immunohistochemical studies showed positive staining for neurofilament protein (NF), neuron-specific enolase (NSE), synaptophysin, MAP 2, tau, NCAM 180, vimentin, and S-100 protein. The cells expressed specific uptake of glutamate, serotonin, and choline, but not GABA or dopamine. A significant increase in process extension was seen in response to agents that enhance intracellular cyclic AMP, especially 3-isobutyl-1-methylxanthine (IBMX). Process formation induced by IBMX was associated with a decrease in cell proliferation as evidenced by a reduction in numbers of cells incorporating 5-bromo-2-deoxyuridine (BrdU). No increase in process extension was observed following exposure to NGF or retinoic acid. MCD-1 cells were shown to produce transforming growth factor beta (TGF beta), and were immunopositive for mutant p53. Transfection assays with the PG13-Luc reporter plasmid, which contains a p53-responsive enhancer element and a luciferase reporter gene, suggested MCD-1 cells are deficient in wild-type p53 and do not activate p53 on treatment with the anticancer agent adriamycin. The MCD-1 cell line is suggested to represent an abnormally differentiated cell type, which has some properties consistent with a multipotent neuronal phenotype while retaining some properties of immature cells of a glial lineage. The MCD-1 cell line can be used to provide a model of a medulloblastoma cell line that is resistant to growth-controlling and anticancer agents.

Physiological relevance and functional potential of central nervous system-derived cell lines

Central nervous system (CNS)-derived neural cell lines have proven to be extremely useful for delineating mechanisms controlling such diverse phenomena as cell lineage choice and differentiation, synaptic maturation, neurotransmitter synthesis and release, and growth factor signalling. In addition, there has been hope that such lines might play pivotal roles in CNS gene therapy and repair. The ability of some neural cell lines to integrate normally into the CNS following transplantation and to express foreign, often corrective gene products in situ might offer potential therapeutic approaches to certain neurodegenerative diseases. Five general strategies have evolved to develop neural cell lines: isolation and cloning of spontaneous or mutagenically induced malignancies, targeted oncogenesis in transgenic mice, somatic cell fusion, growth factor mediated expansion of CNS progenitor or stem cells, and retroviral transduction of neuroepithelial precursors. in this article, we detail recent progress in these areas, focusing on those cell lines that have enabled novel insight into the mechanisms controlling neuronal cell lineage choice and differentiation, both in vitro and in vivo.

Rapid neurite formation in a human cortical neuronal cell line

The subclone HCN-1 was derived from parental cell lines from cortical tissue of a patient with unilateral megalencephaly growth and immunochemistry staining characteristics [G. V. Ronnett et al. (1990) Human cortical neuronal cell line: establishment from a patient with unilateral megalencephaly. Science 248, 603-605]. As we and others have shown, HCN-1A cells can be induced to differentiate to a neuronal-like morphology. HCN-1A cells stain positively for neurofilament, neuron-specific enolase and the low-affinity neurotrophin receptors, p75NGFR, but not for myelin basic protein, S-100, or glial fibrillary acidic protein (GFAP). HCN-1A cells also stain positively for gamma-aminobutyric acid and glutamate. In the present study, we examine the effects of cell density on the requirements for efficient induction of differentiation of HCN-1A cells and analyze the time course of this induction and its reversion. We also characterize the changes in cytoskeletal proteins of HCN-1A cells in response to their differentiation neuronal phenotype.

Transplanted human neurons derived from a teratocarcinoma cell line (NTera-2) mature, integrate, and survive for over 1 year in the nude mouse brain

Retinoic acid (RA) induces a human teratocarcinoma cell line (NTera-2 or NT2) to give rise exclusively to post-mitotic neuron-like (NT2N) cells, but NT2N cells never acquire a fully mature neuronal phenotype in vitro. To determine whether NT2N cells can mature into adult neuron-like cells in vivo, purified NT2N cells were grafted into different regions of the central nervous system (CNS) of adult and neonatal athymic mice, and the grafts were examined immunohistochemically by light, confocal, and electron microscopy using antibodies to a panel of developmentally regulated neuronal polypeptides. NT2N grafts were distinguished from endogenous mouse neurons with antibodies that recognize human or murine specific epitopes in selected neuronal polypeptides. Viable NT2N cells were identified in > 89% of graft recipients (N = 90), and some grafts survived 14 months. Within 3 weeks of implantation, grafted NT2N cells re-extended their processes, and the location of the grafts (e.g., septum versus neocortex) appeared to determine the extent to which processes were elaborated. Within the early post-transplantation period, grafted NT2N cells expressed the same neuronal polypeptides as their in vitro counterparts. However, between 6 weeks and 4-6 months post-implantation, the grafted NT2N cells progressively acquired the molecular phenotype of fully mature in vivo neurons as evidenced by dramatically increased expression of the most highly phosphorylated isoforms of the heavy neurofilament subunit, and the de novo expression of adult CNS tau. Notably, the time course for the extension of processes and the expression of neuronal polypeptides by NT2N grafts was similar in neonatal and adult mice. Although grafted NT2N cells formed synapse-like structures and elaborated dendrites and axons, these axons remained unmyelinated. Finally, none of the transplanted NT2N cells reverted to a neoplastic state. These studies demonstrate that pure populations of grafted human NT2N cells acquire a fully mature neuronal phenotype in vivo, and that these cells integrate and survive for > 1 year post-implantation in the mouse CNS. These human neuron-like cells are an attractive model system for studies of neuronal development, polarity and transplantation.

Human cortical neuronal (HCN) cell lines: a model for amyloid beta neurotoxicity

Human cortical neuronal cell lines HCN-1A and HCN-2 are killed for following exposure of the differentiated cells to amyloid beta-peptide(1-40), a component of senile plaques and other amyloid deposits in brains from Alzheimer's patients. We present a model of A beta toxicity uncomplicated by the presence of other cell types that can be used to address the mechanism of A beta neurotoxicity. This model will be useful in the evaluation of neuroprotective compounds which may attenuate cortical neuronal loss in Alzheimer's disease.

Differentiation of an immortalized CNS neuronal cell line decreases their susceptibility to cytotoxic T cell lysis in vitro

RN33B cells are a temperature-sensitive neuronal cell line derived from rat E12 medullary raphe nucleus (Whittemore and White (1993) Brain Research 615, 27-40). Undifferentiated RN33B cells express class I but not class II antigens of the major histocompatibility complex (MHC), and intercellular adhesion molecule-1 (ICAM-1), a ligand for lymphocyte function associated antigen-1 (LFA-1), expressed on cytotoxic T lymphocytes (CTLs). Treatment of undifferentiated RN33B cells with interferon-gamma (IFN-gamma) upregulated both class I MHC and ICAM-1. After neuronal differentiation, expression of class I MHC antigens or ICAM-1 was undetected, even after IFN-gamma treatment. The neuronally differentiated RN33B cells were also markedly less susceptible to lysis by alloantigen-specific CTLs. These data suggest that intrinsic to the differentiation of CNS neurons is a mechanism to escape CTL-mediated cell lysis.

Human cortical neuronal cell line: a model for HIV-1 infection in an immature neuronal system

HCN-1A is a human cerebral cortical neuronal cell line having properties consistent with cells of immature neuronal origin. This article details evidence for productive low-level infection of HCN-1A cells with human immunodeficiency virus type 1 (HIV-1). In vitro exposure to HCN-1A monolayers to a high titer of either LAV/HTLV-IIIB or HTLV-IIIMN resulted in HIV-1 p24 antigen production and a moderate increase in reverse transcriptase activity in cell-free supernatants. The cells in both LAV/HTLV-IIIB- and HTLV-IIIMN-infected cultures were passaged and proliferated as long as 5 weeks while continuing to express low levels of viral antigen. Virus-positive cells were detected by indirect immunofluorescence, using serum from an individual with acquired immune deficiency syndrome (AIDS) as well as with a gp120 monoclonal antibody. Confirmation of HCN-1A infection was provided by polymerase chain reaction analyses of both nuclear and cytoplasmic DNA and by de novo synthesis of viral proteins as shown by metabolic labeling and immunoprecipitation. Virus in cell-free supernatants from infected HCN-1A cultures was passaged to a permissive human T cell line (A3.01). HCN-1A cells had no detectable surface CD4 protein or CD4 message. However, the cells expressed the membrane glycolipids, galactocerebroside and sulfatide, possible receptors for gp120 on cells of neuronal origin. Undifferentiated HCN-1A cells provide an in vitro model for investigating potential interactions of HIV-1 with a homogeneous population of immature cortical neurons.

Ionic channel currents in cultured neurons from human cortex

Ionic channels in human cortical neurons have not been studied extensively. HCN-1 and HCN-1A cells, which recently were established as continuous cultures from human cortical tissue, have been shown by histochemical and immunochemical methods to exhibit a neuronal phenotype, but expression of functional ionic channels was not demonstrated. For the present study, HCN-1 and HCN-1A cells were cultured in Dulbecco's modified Eagle's medium with 15% fetal calf serum, in some cases supplemented with 10 ng/ml nerve growth factor, 10 microM forskolin, and 1 mM dibutyryl cyclic adenosine monophosphate to promote differentiation. Cells or membrane patches were voltage clamped using conventional patch clamp techniques. In HCN-1A cells, we identified a tetrodotoxin-sensitive Na+ current, two types of Ca2+ channel current, including L-type current and a second type that in some respects resembled N-type current, and four types of K+ current, including a delayed outward rectifier that showed voltage-dependent inactivation, two types of noninactivating Ca(2+)-activated K+ channels with slope conductances of 146 and 23 pS (K+i/K+o 145 mM/5 mM), and less frequently, a noninactivating, intermediate conductance channel that was not sensitive to internal Ca2+. When HCN-1A cells were examined after 3 days of exposure to differentiating agents, pronounced morphological changes were evident but no differences in ionic currents were apparent. HCN-1 cells also exhibited K+ and Ca2+ channel currents, but Na+ currents were not detected in these cells.(ABSTRACT TRUNCATED AT 250 WORDS)