Effects of retinoic acid on NB 69 human neuroblastoma cells and fetal rat mid brain neurons

Altered excitability and exocytosis in chromaffin cells from the R6/1 mouse model of Huntington's disease is linked to over-expression of mutated huntingtin

As the peripheral sympathoadrenal axis is tightly controlled by the cortex via hypothalamus and brain stem, the central pathological features of Hunting's disease, (HD) that is, deposition of mutated huntingtin and synaptic dysfunctions, could also be expressed in adrenal chromaffin cells. To test this hypothesis we here present a thorough investigation on the pathological and functional changes undergone by chromaffin cells (CCs) from 2-month (2 m) to 7-month (7 m) aged wild-type (WT) and R6/1 mouse model of Huntington's disease (HD), stimulated with acetylcholine (ACh) or high [K⁺ ] (K⁺ ). In order to do this, we used different techniques such as inmunohistochemistry, patch-clamp, and amperometric recording. With respect to WT cells, some of the changes next summarized were already observed in HD mice at a pre-disease stage (2 m); however, they were more pronounced at 7 m when motor deficits were clearly established, as follows: (i) huntingtin over-expression as nuclear aggregates in CCs; (ii) smaller CC size with decreased dopamine β-hydroxylase expression, indicating lesser number of chromaffin secretory vesicles; (iii) reduced adrenal tissue catecholamine content; (iv) reduced Na⁺ currents with (v) membrane hyperpolarization and reduced ACh-evoked action potentials; (v) reduced [Ca²⁺ ]_c transients with faster Ca²⁺ clearance; (vi) diminished quantal secretion with smaller vesicle quantal size; (vii) faster kinetics of the exocytotic fusion pore, pore expansion, and closure. On the basis of these data, the hypothesis is here raised in the sense that nuclear deposition of mutated huntingtin in adrenal CCs of R6/1 mice could be primarily responsible for poorer Na⁺ channel expression and function, giving rise to profound depression of cell excitability, altered Ca²⁺ handling and exocytosis. OPEN PRACTICES: This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/. Cover Image for this issue: doi: 10.1111/jnc.14201.

Protection by glia-conditioned medium in a cell model of Huntington disease

The physiological role of huntingtin and the pathogenic mechanisms that produce the disease are unknown. Mutant huntingtin changes its normal localization and produces cytoplasmic and intranuclear inclusions, changes gene transcription, alters synaptic transmission, impairs mitochondrial activity and activates caspases and other pro-apoptotic molecules, promotes excitotoxicity, energy deficits, synthesis and release reduction of neurotrophic factors and oxidative stress. Previous studies confirm that the mutant huntingtin difficult neurotrophic function of astrocytes leading to neuronal dysfunction in Huntington’s disease. Our objective was to study the neuroprotective potential role of glia-conditioned medium (GCM) in an in vitro model of Huntington’s disease. We used conditionally-immortalized striatal neuronal progenitor cell lines (STHdhQ7/Q7 and STHdhQ111/Q111) expressing endogenous levels of normal and mutant huntingtin with 7 and 111 glutamines, respectively. We studied the protection of fetal and postnatal glia conditioned medium (GCM) on H2O2 (2 µM), glutamate (5 mM) and 3-nitropropionic acid (2.5 mM) related toxicity. We also compared the neuroprotective effects of GCM versus that of the growth factors bFGF, BDNF and GDNF. Fetal GCM protects from every toxin, reducing the cell death and increasing the cell survival. Fetal GCM reduces the caspases fragmentation of the protein PARP, the expression of chaperone Hsp70 and the accumulation of ROS and polyubiquitinated proteins. In addition, in Q111 striatal cells treated with H2O2 (2 µM) for 24 hours, the intracellular GSH levels are higher in the presence of GCM. Notably, the 13-day and 2-month postnatal GCM, totally protects from H2O2 induced cell death in mutant striatal cells. GCM neuroprotective effects are more potent than those of the already identified neurotrophic factors. We conclude that GCM protects Q111 cells from neuronal neurotoxins and the effects of GCM are more potent than those of any known neurotrophic factor. GCM may contain new and more potent, as yet unidentified, neurotrophic molecules, potentially useful in patients with Huntington’s disease.

Retinoid supplementation of differentiating human neural progenitors and embryonic stem cells leads to enhanced neurogenesis in vitro

Retinoids are important molecules involved in the development and homeostasis of the nervous system. As such, various retinoid derivatives are often found in culture media and supplement formulations to support the growth and maintenance of neural cells. However, all-trans-retinoic acid (ATRA) and its associated derivatives are light sensitive and are highly susceptible to isomerisation. This can lead to variability in retinoid concentrations and the nature of the retinoid species present in culture solutions which in turn can influence biological activity and introduce inconsistency. We have previously described the development of the synthetic retinoid derivative, EC23, as a chemically and light stable alternative that does not degrade and has biological activity similar to ATRA. In this study we demonstrate that the addition of exogenous retinoid can significantly enhance neuronal differentiation of both human neuroprogenitor and human embryonic stem cells. In the former, both ATRA and EC23 induced increased maturation and stabilisation of the axonal cytoskeleton. However, EC23 was particularly potent at lower nanomolar concentrations resulting in significantly greater neurogenesis than ATRA. In ES cells enhanced motor neuron marker expression was also detected in response to both retinoids when incorporated into an established protocol for neuronal differentiation. We propose that synthetic retinoid EC23 represents a valuable addition to the formulation of new and existing culture supplements to enhance neuronal differentiation whilst enabling improved consistency.

Differentiation of mouse Neuro 2A cells into dopamine neurons

Neuro 2A (N2a) is a mouse neural crest-derived cell line that has been extensively used to study neuronal differentiation, axonal growth and signaling pathways. A convenient characteristic of these cells is their ability to differentiate into neurons within a few days. However, most differentiation methods reported for N2a cells do not provide information about the neuronal types obtained after each treatment. In this study, we evaluated the generation of N2a dopamine neurons following treatment with a number of factors known to induce neuronal differentiation. Our results showed that N2a cells express Nurr-related factor 1 (Nurr1) and produce low levels of tyrosine hydroxylase (TH) and dopamine. Both TH and dopamine levels were significantly enhanced in the presence of dibutyryl cyclic adenosine monophosphate (dbcAMP), as evidenced by Western blot, immunocytochemistry and high performance liquid chromatography (HPLC). In contrast to dbcAMP, other factors such as transforming growth factor beta1 (TGF beta 1), bone morphogenetic protein 4 (BMP4), glial cell-derived neurotrophic factor (GDNF) and retinoic acid (RA) did not increase TH expression. Further investigation confirmed that the effect of dbcAMP on production of TH-positive neurons was mediated through cyclic AMP (cAMP) responsive element binding protein (CREB) and it was antagonized by RA. Thus, although various treatments can be used to generate N2a neurons, only dbcAMP significantly enhanced the formation of dopamine neurons. Taken together, this study provided a simple and reliable method to generate dopamine neurons for rapid and efficient physiological and pharmacological assays.

Influence of retinoic acid and lithium on proliferation and dopaminergic potential of human NT2 cells

Our laboratory is working with the human NTera2/D1 (NT2) cell line, which has properties similar to those of progenitor cells in the central nervous system (CNS). These neural-like precursor cells can differentiate into all three major lineages, neurons, astrocytes, and oligodendrocytes. The pure neuronal population, hNT neurons, possess characteristics of dopamine (DA) cells. First, we analyzed whether the retinoic acid (RA)-treated hNT neurons and the NT2 precursor cells expressed two transcription factors required for development of the midbrain DA neurons. We report that NT2 cells endogenously expressed Engrailed-1 and Ptx3, whereas RA-treated hNT neurons did not express Engrailed-1 or Ptx3. Next we examined the influence of lithium treatment on Engrailed-1 and Ptx3 as well as another critical transcription factor, Nurr1. Previous research has shown that lithium can mimic the Wnt pathway, which is important for the induction of these transcription factors. Finally, we investigated the effect of lithium treatment on the viability and proliferation of NT2 cells, because lithium has been shown to stimulate neurogenesis in adult neural precursors. Lithium treatment increased the viability and proliferation of NT2 cells. The expression of transcription factors essential for the induction and maintenance of the DA phenotype was not increased in NT2 after lithium treatment. We conclude that the NT2 cell line is an excellent in vitro model system for studying the influence of pharmalogical agents on proliferation, differentiation, and apoptosis of a human neural progenitor cell line.

Nutrients as trophic factors in neurons and the central nervous system: role of retinoic acid

In multicellular organisms, death, survival, proliferation, and differentiation of a given cell depend on signals produced by neighboring and/or distant cells, resulting in the coordinated development and function of the various tissues. In the nervous system, control of cell survival and differentiation is achieved through the action of a distinct group of polypeptides collectively known as neurotrophic factors. Recent findings support the view that trophic factors also are involved in the response of the nervous system to acute injury. By contrast, nutrients are not traditionally viewed as potential trophic factors; however, there is increasing evidence that at least some influence neuronal differentiation. During development the brain is responsive to variations in nutrient supply, and this increased sensitivity or vulnerability of the brain to nutrient supply may reappear during neuronal repair, a period during which a rapid membrane resynthesis and reestablishment of synthetic pathways occur. To further evaluate the potential of specific nutrients to act as pharmacologic agents in the repair of injured neurons, the effects of retinoic acid, an active metabolite of vitamin A, and its role as a trophic factor are discussed. This literature review is intended to provide background information regarding the effect of retinoic acid on the cholinergic phenotype and the differentiation of these neurons and to explain how it may promote neuronal repair and survival following injury.

Nucleoside Diphosphate Kinase A/nm23-H1 Promotes Metastasis of NB69-Derived Human Neuroblastoma

Nucleoside diphosphate kinase A (NDPK-A), encoded by the nm23-H1 gene, acts as a metastasis suppressor in certain human tumors such as breast carcinoma. However, evidence also points to NDPK-A functioning as a metastasis promoter in other human tumors including neuroblastoma. In fact, amplification and overexpression of nm23-H1 as well as S120G mutation of NDPK-A (NDPK-AS120G) have been detected in 14% to 30% of patients with advanced stages of neuroblastoma. To test whether NDPK-A promotes neuroblastoma metastasis, we established stable transfectants and an orthotopic xenograft animal model from the human neuroblastoma NB69 cell line. We demonstrate that overexpressed NDPK-A or NDPK-AS120G increased both incidence and colonization of neuroblastoma metastasis in animal lungs without significantly affecting primary tumor development. In vitro, these metastasis-associated NDPK-A aberrations abrogated retinoic acid-induced neuronal differentiation while increasing cloning efficiency, cell survival, and colony formation of NB69 derivatives. Furthermore, NDPK-AS120G reduced cell adhesion and increased cell migration. Compared with its wild-type, NDPK-AS120G appears more effective in promoting neuroblastoma metastasis. Our results provide the first evidence that NDPK-A behaves as a metastasis promoter at least in human neuroblastoma derived from NB69 cells. The findings not only suggest a prognostic value of NDPK-A in neuroblastoma patients but also caution NDPK-A-targeted treatment for patients with different tumor types.

TGF-beta1 increases tyrosine hydroxylase expression by a mechanism blocked by BMP-2 in human neuroblastoma SH-SY5Y cells

Human neuroblastoma SH-SY5Y cells were used to study the effects of transforming growth factor beta1 (TGF-beta1) and bone morphogenetic protein 2 (BMP-2) on neuronal differentiation and acquisition of a catecholaminergic phenotype. SH-SY5Y cells express the intracellular factors activated through the receptors of the TGFbeta superfamily members, Smad1 and Smad4, as in basal conditions or after differentiation with 12-O-tetradecanoyl-phorbol-13-acetate (TPA) or retinoic acid (RA). TGF-beta1 and BMP-2 induce differentiation in SH-SY5Y cells by different pathways: the effect of TGF-beta1 is potentiated by TPA and the effect of BMP-2 is blocked by RA. Cell differentiation due to TGF-beta1 treatment is accompanied by an increase in tyrosine hydroxylase (TH) expression, more pronounced in the presence of TPA or RA and counteracted by BMP-2. BMP-2 and RA both induce noncatecholaminergic cell differentiation, and together they may induce choline acetyltransferase expression in serum-cultured cells. In conclusion, our results suggest that TGF-beta1 and BMP-2 may contribute, in opposite ways, to regulation of the neuronal catecholaminergic phenotype.

Retinoic acid treatment enhances the acetylcholine contents in the human teratocarcinoma cell line NTera-2

Human NTera-2/clone D1 teratocarcinoma cells are induced by retinoic acid (RA) to differentiate into postmitotic cells with morphological and biochemical characteristics of embryonic human neurones. Currently only limited information concerning peptide-contents and neurotransmitter pools of these cells is available. Zeller and Strauss [Int. J. Dev. Neurosci. 1995;13(5):437] described an increase in choline acetyltransferase (ChAT) activity in RA-treated, but not in untreated NTera-2 cells, suggesting the induction of a cholinergic phenotype during treatment with RA. In the present study we investigated the effect of RA-differentiation on the amount of the neurotransmitters acetylcholine (ACh), and dopamine in NTera-2 in order to specify the transmitter phenotype induced by RA-differentiation. We found that a 4-week treatment of NTera-2 cells with 10 microM RA markedly increased the ACh-content of these cells, while dopamine levels were unchanged. Depolarisation with potassium (60 mM) enhanced ACh-outflow in the differentiated cells in a Ca(++) dependent way. Also neuropeptides like substance P and NPY were detectable in the undifferentiated NTera-2 cells, while vasointestinal peptide (VIP) could not be found in either precursor or RA-differentiated cells. Differentiation was accompanied by a marked reduction of neutral endopeptidase enzyme activity and aminopeptidase activity. From these observations it was concluded that RA induces a cholinergic neurochemical differentiation of this human teratocarcinoma cell line, and that these cells might provide a model system to investigate cholinergic properties of human origin.

Functional implications of the noradrenergic-cholinergic switch induced by retinoic acid in NB69 neuroblastoma cells

Some neuroblastoma cell lines change their neurotransmitter phenotype from noradrenergic to cholinergic under retinoic acid treatment. Such "neurotransmitter switch" seems to be a consequence of changes in the expression and activity of the biosynthetic machinery for both neurotransmitters. In this study, we have characterized this "neurotransmitter switch" induced by retinoic acid in a human neuroblastoma cell line (NB69) showing catecholaminergic characteristics. Retinoic acid treatment reduced tyrosine hydroxylase activity and noradrenaline levels in NB69 cells but did not modify the expression of this enzyme. Moreover, the calcium-dependent release of [(3)H]noradrenaline in control cells was highly reduced by retinoic acid treatment. On the other hand, NB69 cells treated with retinoic acid enhanced the expression of choline acetyltransferase and acquired the capability to release [(3)H]acetylcholine in a calcium-dependent way. In addition, we found that the expression of the vesicular monoamine transporter 2 (VMAT2) and the vesicular acetylcholine transporter (VAChT) was increased in those cells treated with retinoic acid. Immunostaining revealed that retinoic acid treatment changed the cellular distribution of both vesicular monoamine transporter 2 and vesicular acetylcholine transporter. In conclusion, retinoic acid induces a noradrenergic to cholinergic switch in NB69 cells by acting at several levels of the neurotransmitter phenotypic expression.