Promoted Neuronal Differentiation after Activation of Alpha4/Beta2 Nicotinic Acetylcholine Receptors in Undifferentiated Neural Progenitors

Abstract

BackgroundNeural progenitor is a generic term used for undifferentiated cell populations of neural stem, neuronal progenitor and glial progenitor cells with abilities for proliferation and differentiation. We have shown functional expression of ionotropic N-methyl-D-aspartate (NMDA) and gamma-aminobutyrate type-A receptors endowed to positively and negatively regulate subsequent neuronal differentiation in undifferentiated neural progenitors, respectively. In this study, we attempted to evaluate the possible functional expression of nicotinic acetylcholine receptor (nAChR) by undifferentiated neural progenitors prepared from neocortex of embryonic rodent brains.Methodology/Principal FindingsReverse transcription polymerase chain reaction analysis revealed mRNA expression of particular nAChR subunits in undifferentiated rat and mouse progenitors prepared before and after the culture with epidermal growth factor under floating conditions. Sustained exposure to nicotine significantly inhibited the formation of neurospheres composed of clustered proliferating cells and 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide reduction activity at a concentration range of 1 µM to 1 mM without affecting cell survival. In these rodent progenitors previously exposed to nicotine, marked promotion was invariably seen for subsequent differentiation into cells immunoreactive for a neuronal marker protein following the culture of dispersed cells under adherent conditions. Both effects of nicotine were significantly prevented by the heteromeric α4β2 nAChR subtype antagonists dihydro-β-erythroidine and 4-(5-ethoxy-3-pyridinyl)-N-methyl-(3E)-3-buten-1-amine, but not by the homomeric α7 nAChR subtype antagonist methyllycaconitine, in murine progenitors. Sustained exposure to nicotine preferentially increased the expression of Math1 among different basic helix-loop-helix proneural genes examined. In undifferentiated progenitors from embryonic mice defective of NMDA receptor subunit-1, nicotine was still effective in significantly inhibiting the proliferation.Conclusions/SignificanceFunctional α4β2 nAChR subtype would be constitutively expressed to play a role in the mechanism underlying the determination of proliferation and subsequent differentiation fate into a neuronal lineage in association with preferential promotion of Math1 expression in undifferentiated neural progenitors of developing rodent neocortex independently of NMDA receptor activation.

Glycine transporter-1 regulates the proliferation of neural stem/progenitor cells derived from the embryonic mouse hippocampus

“…Thus, it has been proposed that neurotransmitters may act directly as paracrine or autocrine factors to NPCs under physiological conditions. Indeed, systemic administration of NMDA decreases proliferation of NPCs in the adult murine hippocampal dentate gyrus [29], whereas administration of a dopamine D3 agonist increased proliferation of NPCs in the adult murine subventricular zone [28]. In the present study, we demonstrated the possibility that glycine enhances proliferation of NPCs.…”

“…extracellular glycine is effectively increased by blocking GLYT1 and that this mediates synaptic integration by dual activation of both the glycine receptor and the NMDA receptor [20,21]. Numerous previous studies have shown that proliferation of NPCs is regulated by activation of various receptors and these neurotransmitters; i.e., activation of the GABAA receptor, group I metabotropic glutamate (mGlu) receptor or dopamine D 3 receptor enhances proliferation of NPCs [22][23][24], whereas activation of the NMDA receptor, group III mGlu receptor, or α4β2 nicotinic acetylcholine receptor suppresses proliferative activity [25][26][27][28].…”

Prenatal Nicotine Exposure Impairs the Proliferation of Neuronal Progenitors, Leading to Fewer Glutamatergic Neurons in the Medial Prefrontal Cortex

“…Abbreviations: CS, conditioned stimulus; No-Ext, Noextinction; NPE, non-pre-exposed; N.S., not significant; PE, pre-exposed; US, unconditioned stimulus. Takarada et al (2012) demonstrated that in undifferentiated neural progenitors, continuous exposure to nicotine led to a significant decrease in the capability to form neurospheres and subsequently accelerated neuronal differentiation. Another study showed that chronic administration of nicotine inhibited hippocampal neurogenesis in vivo, but had little effect on the differentiation of neuronal progenitors (Shingo and Kito, 2005).…”

“…For example, the apoptotic effects of nicotine have been observed both in vivo and in vitro in the developing brain (Abreu-Villaca et al, 2004;Qiao et al, 2003). Continuous exposure to nicotine has been reported to have little effect on cell survival in neural progenitors in vitro (Takarada et al, 2012). Recent studies using DNA microarrays have shown that gestational nicotine exposure affects gene expression associated with cell adhesion and cell death/survival in the brains of adolescent rats (Cao et al, , 2013Wei et al, 2011).…”

“…There are contradictory reports regarding the effect of nicotine on the cell cycle. Although some groups have reported that nicotine stimulates the cell cycle progression of vascular smooth muscle cells, lung epithelial cells, pre-osteoblastic cells (Chu et al, 2005;Sato et al, 2008), others have demonstrated that nicotine has an inhibitory effect in lymphocytes and neurospheres (Takarada et al, 2012). It is plausible that nicotine may impinge on cell cycle progression in distinct cell types through different mechanisms.…”