Cigarette smoking during pregnancy regulates the expression of specific nicotinic acetylcholine receptor (nAChR) subunits in the human placenta.

Smoking during pregnancy is associated with low birth weight, premature delivery, and neonatal morbidity and mortality. Nicotine, a major pathogenic compound of cigarette smoke, binds to the nicotinic acetylcholine receptors (nAChRs). A total of 16 nAChR subunits have been identified in mammals (9 α, 4 ß, and 1 δ, γ and ε subunits). The effect of cigarette smoking on the expression of these subunits in the placenta has not yet been determined, thus constituting the aim of this study. Using RT-qPCR and western blotting, this study investigated all 16 mammalian nAChR subunits in the normal healthy human placenta, and compared mRNA and protein expressions in the placentas from smokers (n = 8) to controls (n = 8). Our data show that all 16 subunit mRNAs are expressed in the normal, non-diseased human placenta and that the expression of α2, α3, α4, α9, ß2 and ß4 subunits is greater than the other subunits. For mRNA, cigarette smoke exposure was associated with increased expression of the α9 subunit, and decreased expression of the δ subunit. At the protein level, expression of both α9 and δ was increased. Thus, cigarette smoking in pregnancy is sufficient to regulate nAChR subunits in the placenta, specifically α9 and δ subunits, and could contribute to the adverse effects of vasoconstriction and decreased re-epithelialisation (α9), and increased calcification and apoptosis (δ), seen in the placentas of smoking women.

Immunohistochemical expression of the nicotinic acetylcholine receptor (nAChR) subunits in the human placenta, and effects of cigarette smoking and preeclampsia.

INTRODUCTION: Cigarette smoking (CS) and preeclampsia (PE), regulate the expression of nicotinic acetylcholine receptor (nAChR) subunits in the placenta, yet no data exist at the histological level. METHODS: Using immunohistochemistry of formalin fixed and paraffin embedded placental tissue, this study quantified the expression of nine nAChR subunits (α2, α3, α4, α5, α7, α9, ß1, ß2, δ) and compared the expression amongst four groups of non-smoker non-PE (controls, n = 8), smokers (n = 8), PE (n = 8), and those who were smokers with PE (smoke + PE, n = 4). Quantification was of the percentage of villi with positive cells stained (% villi with +ve), percentage of positive stained cells per villous (% +ve cells/villous), percentage of positive cells in the decidua (%+ve Decidua), and intensity of staining in the outer villous trophoblast layer. RESULTS: Changes were restricted to the villi (as opposed to the decidua), and were specific to the α9 (smoke + PE), ß1 (smokers), and ß2 (PE) subunits when compared to controls. CS seemed to have a protective effect for the ß2 subunit and an additive effect for the α9 and ß1 subunits within the villous core/stroma cells and not the trophoblast layer. DISCUSSION: These findings support that both CS and PE affect nAChRs in the placenta, but that this is restricted to the villi.