Subcellular distribution of choline acetyltransferase by immunogold electron microscopy in non-neuronal cells: placenta, airways and murine embryonic stem cells

Impact of Prenatal Nicotine Exposure on Placental Function and Respiratory Neural Network Development

Smoking during pregnancy is associated with multiple undesirable outcomes in infants, such as low birth weight, increased neonatal morbidity and mortality, and catastrophic conditions like sudden infant death syndrome (SIDS). Nicotine, the most addictive and teratogenic substance in tobacco smoke, reaches and crosses the placenta and can be accumulated in the amniotic fluid and distributed by fetal circulation, altering the cholinergic transmission by acting on the nicotinic acetylcholine receptors (nAChRs) expressed from very early gestational stages in the placenta and fetal tissue. Because nAChRs influence the establishment of feto-maternal circulation and the emergence of neuronal networks, prenatal nicotine exposure can lead to multiple alterations in newborns. In this mini-review, we discuss the undeniable effects of nicotine in the placenta and the respiratory neural network as examples of how prenatal nicotine and smoking exposition can affect brain development because dysfunction in this network is involved in SIDS etiology.

Methylation-reprogrammed CHRM3 results in vascular dysfunction in the human umbilical vein following IVF-ET

Assisted reproductive technology (ART) has been used globally among infertile couples. However, many epidemiological investigations have indicated that ART is associated with a range of long-term adverse health outcomes in offspring, including cardiovascular disease, obesity and increased plasma lipid levels. Until now, direct evidence has been limited regarding the pathological changes in vascular function in fetuses with ART. In this study, human umbilical cords were collected from healthy normal pregnancies and IVF-ET pregnancies. Vascular functional studies involving acetylcholine (ACh), antagonists of its specific receptors, and L-type calcium channel/PKC-MLC20 phosphorylation pathway specific inhibitors were conducted. Quantitative real-time PCR, Western blotting and methylation analyses were performed on umbilical vein samples. We found that the umbilical vein constriction induced by ACh in the IVF-ET group was significantly attenuated compared with that in the healthy normal pregnancy group, which was not only associated with the hypermethylation of ACh muscarinic receptor subtype 3 (CHRM3) and decreased expression of CHRM3, PKCβ and CaV1.2, but was also related to the reduced phosphorylation of MLC20. The present study revealed that the hypermethylation of CHRM3, leading to a reduction in CHRM3 expression and downregulation of the CaV1.2/PKC-MLC20 phosphorylation pathway, was responsible for the decreased sensitivity to ACh observed in the umbilical vein under IVF-ET conditions. The hypermethylation of CHRM3 caused by IVF-ET might play an important role in altered vasoconstriction and impact cardiovascular systems in the long run.

Roles of ion channels in regulation of acetylcholine-mediated vasoconstrictions in umbilical cords of rabbit/rats

We recently demonstrated that acetylcholine (ACh) produced reliable vasoconstrictions in the umbilical cords. This study investigated the possible mechanisms with different antagonists. ACh-mediated vasoconstrictions were decreased by voltage-operated calcium (Ca²⁺) channels antagonist nifedipine or inositol-1,4,5-trisphosphate-mediated Ca²⁺ release antagonist 2-aminoethyl diphenylborinate, indicating that both extracellular and intracellular calcium modulated the ACh-stimulated umbilical contraction. Intracellular Ca²⁺ concentrations were increased simultaneously with vasoconstrictions by ACh in the umbilical vessels. Inhibiting large-conductance calcium-dependent potassium (BK) channels enhanced ACh-mediated contraction, whereas inhibiting voltage dependent potassium (K⁺), inward rectifier K⁺ and ATP-sensitive K⁺ channels had no effects. Incubation with specific K⁺ channel inhibitors showed that ACh suppressed BK currents rather than 4-aminopyridine-sensitive K⁺ channels currents. The results suggested that blood vessels in umbilical cords had special characteristics in response to cholinergic signals. ACh-stimulated umbilical vasoconstrictions were mediated via muscarinic receptor subtype 1/3-protein kinase C/cyclooxygenase-BK channel pathways.

B-esterase determination and organophosphate insecticide inhibitory effects in JEG-3 trophoblasts

The placenta and trophoblasts express several B-esterases. This family includes acethylcholinesterase (AChE), carboxylesterase (CES) and butyrylcholinesterase (BChE), which are important targets of organophosphate insecticide (OP) toxicity. To better understand OP effects on trophoblasts, B-esterase basal activity and kinetic behavior were studied in JEG-3 choriocarcinoma cell cultures. Effects of the OP azinphos-methyl (Am) and chlorpyrifos (Cp) on cellular enzyme activity were also evaluated. JEG-3 cells showed measurable activity levels of AChE and CES, while BChE was undetected. Recorded Km for AChE and CES were 0.33 and 0.26 mM respectively. Native gel electrophoresis and RT-PCR analysis demonstrated CES1 and CES2 isoform expression. Cells exposed for 4 and 24 h to the OP Am or Cp, showed a differential CES and AChE inhibition profiles. Am inhibited CES and AChE at 4 h treatment while Cp showed the highest inhibition profile at 24 h. Interestingly, both insecticides differentially affected CES1 and CES2 activities. Results demonstrated that JEG-3 trophoblasts express AChE, CES1 and CES2. B-esterase enzymes were inhibited by in vitro OP exposure, indicating that JEG-3 cells metabolization capabilities include phase I enzymes, able to bioactivate OP. In addition, since CES enzymes are important for medicinal drug activation/deactivation, OP exposure may interfere with trophoblast CES metabolization, probably being relevant in a co-exposure scenario during pregnancy.

Acetylcholine contributes to control the physiological inflammatory response during the peri-implantation period

BACKGROUND

Maternal antigen-presenting cells attracted to the pregnant uterus interact with trophoblast cells and modulate their functional profile to favour immunosuppressant responses. Non-neuronal cholinergic system is expressed in human cytotrophoblast cells and in immune cells with homeostatic regulatory functions.

AIM

The aim of this work was to evaluate whether non-neuronal acetylcholine conditions maternal monocyte and DC migration and activation profiles.

METHODS

We used an in vitro model resembling maternal-placental interface represented by the co-culture of human trophoblast cells (Swan-71 cell line) and monocytes or DC.

RESULTS

When cytotrophoblast cells were treated with neostigmine (Neo) to concentrate endogenous acetylcholine levels, monocyte migration was increased. In parallel, high levels of IL-10 and decreased levels of TNF-α were observed upon interaction of maternal monocytes with trophoblast cells. This effect was synergized by Neo and was prevented by atropine, a muscarinic acetylcholine receptor antagonist. Similarly, trophoblast cells increased the migration of DC independently of Neo treatment; however, enhanced IL-10 and MCP-1 synthesis in trophoblast-DC co-cultures with no changes in TNF-α and IL-6 was observed. In fact, there were no changes in HLA-DR, CD86 or CD83 expression. Finally, trophoblast cells treated with Neo increased the expression of two antigen-presenting cells attracting chemokines, MCP-1, MIP-1α and RANTES through muscarinic receptors, and it was prevented by atropine.

CONCLUSIONS

Our present results support a novel role of acetylcholine synthesized by trophoblast cells to modulate antigen-presenting cell migration and activation favouring an immunosuppressant profile that contributes to immune homeostasis maintenance at the maternal-foetal interface.

Non-neuronal cholinergic system in airways and lung cancer susceptibility

In the airway tract acetylcholine (ACh) is known to be the mediator of the parasympathetic nervous system. However ACh is also synthesized by a large variety of non-neuronal cells. Strongest expression is documented in neuroendocrine and in epithelial cells (ciliated, basal and secretory elements). Growing evidence suggests that a cell-type specific Ach expression and release do exist and act with local autoparacrine loop in the non-neuronal airway compartment. Here we review the molecular mechanism by which Ach is involved in regulating various aspects of innate mucosal defense, including mucociliary clearance, regulation of macrophage activation as well as in promoting epithelial cells proliferation and conferring susceptibility to lung carcinoma onset. Importantly this non-neuronal cholinergic machinery is differently regulated than the neuronal one and could be specifically therapeutically targeted.

Nicotine exposure during differentiation causes inhibition of N-myc expression

Background

The ability of chemicals to disrupt neonatal development can be studied using embryonic stem cells (ESC). One such chemical is nicotine. Prenatal nicotine exposure is known to affect postnatal lung function, although the mechanisms by which it has this effect are not clear. Since fibroblasts are a critical component of the developing lung, providing structure and secreting paracrine factors that are essential to epithelialization, this study focuses on the differentiation of ESC into fibroblasts using a directed differentiation protocol.

Methods

Fibroblasts obtained from non-human primate ESC (nhpESC) differentiation were analyzed by immunohistochemistry, immunostaining, Affymetrix gene expression array, qPCR, and immunoblotting.

Results

Results of these analyses demonstrated that although nhpESCs differentiate into fibroblasts in the presence of nicotine and appear normal by some measures, including H&E and SMA staining, they have an altered gene expression profile. Network analysis of expression changes demonstrated an over-representation of cell-cycle related genes with downregulation of N-myc as a central regulator in the pathway. Further investigation demonstrated that cells differentiated in the presence of nicotine had decreased N-myc mRNA and protein expression and longer doubling times, a biological effect consistent with downregulation of N-myc.

Conclusions

This study is the first to use primate ESC to demonstrate that nicotine can affect cellular differentiation from pluripotency into fibroblasts, and in particular, mediate N-myc expression in differentiating ESCs. Given the crucial role of fibroblasts throughout the body, this has important implications for the effect of cigarette smoke exposure on human development not only in the lung, but in organogenesis in general.

Acetylcholine receptors regulate gene expression that is essential for primitive streak formation in murine embryoid bodies

Muscarinic acetylcholine receptors (mAchRs) are critical components of the cholinergic system, which is the key regulator of both the central and peripheral nervous systems in mammals. Interestingly, several components of the cholinergic system, including mAchRs and choline acetyltransferase (ChAT), have recently been found to be expressed in mouse embryonic stem (ES) cells and human placenta. These results raise the intriguing possibility that mAchRs play physiological roles in the regulation of early embryogenesis. Early embryogenesis can be mimicked in vitro using an ES cell-based culture system in which the cells form a primitive streak-like structure and efficiently develop into mesodermal progenitors. Here we report that chemical inhibitors specifically targeting mAchRs suppressed the expression of genes essential for primitive streak formation, including Wnt3, and thereby blocked mesodermal progenitor differentiation. Interestingly, mAchR inhibitors also reduced the expression of Cyp26a1, an enzyme involved in the catabolism of retinoic acid (RA). RA is an important regulator of Wnt3 signaling. Our study presents evidence indicating that mAchRs influence RA signaling necessary for the induction of the primitive streak. To our knowledge, this is the first report showing that mAchRs have important functions not only in adult mammals but also during early mammalian embryogenesis.

Cotinine inhibits the pro-inflammatory response initiated by multiple cell surface Toll-like receptors in monocytic THP cells

Background

The primary, stable metabolite of nicotine [(S)-3-(1-methyl-2-pyrrolidinyl) pyridine] in humans is cotinine [(S)-1-methyl-5-(3-pyridinyl)-2-pyrrolidinone]. We have previously shown that cotinine exposure induces convergence and amplification of the GSK3β-dependent PI3 kinase and cholinergic anti-inflammatory systems. The consequence is reduced pro-inflammatory cytokine secretion by human monocytes responding to bacteria or LPS, a TLR4 agonist.

Findings

Here we show that cotinine-induced inflammatory suppression may not be restricted to individual Toll-like receptors (TLRs). Indeed, in monocytic cells, cotinine suppresses the cytokine production that is normally resultant upon agonist-specific engagement of all of the major surface exposed TLRs (TLR 2/1; 2/6; 4 and 5), although the degree of suppression varies by TLR.

Conclusions

These results provide further mechanistic insight into the increased susceptibility to multiple bacterial infections known to occur in smokers. They also establish THP-1 cells as a potentially suitable model with which to study the influence of tobacco components and metabolites on TLR-initiated inflammatory events.