Pharmacological Chaperoning of Nicotinic Acetylcholine Receptors Reduces the Endoplasmic Reticulum Stress Response

Abstract

We report the first observation that endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) can decrease when a central nervous system drug acts as an intracellular pharmacological chaperone for its classic receptor. Transient expression of ␣4␤2 nicotinic receptors (nAChRs) in Neuro-2a cells induced the nuclear translocation of activating transcription factor 6 (ATF6), which is part of the UPR. Cells were exposed for 48 h to the full agonist nicotine, the partial agonist cytisine, or the competitive antagonist dihydro-␤-erythroidine; we also tested mutant nAChRs that readily exit the ER. Each of these four manipulations increased Sec24D-enhanced green fluorescent protein fluorescence of condensed ER exit sites and attenuated translocation of ATF6-enhanced green fluorescent protein to the nucleus. However, we found no correlation among the manipulations regarding other tested parameters [i.e., changes in nAChR stoichiometry (␣4 2 ␤2 3 versus ␣4 3 ␤2 2 ), changes in ER and trans-Golgi structures, or the degree of nAChR up-regulation at the plasma membrane]. The four manipulations activated 0 to 0.4% of nAChRs, which shows that activation of the nAChR channel did not underlie the reduced ER stress. Nicotine also attenuated endogenously expressed ATF6 translocation and phosphorylation of eukaryotic initiation factor 2␣ in mouse cortical neurons transfected with ␣4␤2 nAChRs. We conclude that, when nicotine accelerates ER export of ␣4␤2 nAChRs, this suppresses ER stress and the UPR. Suppression of a sustained UPR may explain the apparent neuroprotective effect that causes the inverse correlation between a person's history of tobacco use and susceptibility to developing Parkinson's disease. This suggests a novel mechanism for neuroprotection by nicotine.

Identification and Characterization of Poly(I:C)-induced Molecular Responses Attenuated by Nicotine in Mouse Macrophages

“…Thus it is entirely plausible that nicotine trapped in the ER and other organelles could be involved in downregulating the release of Ca 21 from intracellular stores from poly(I:C)-stimulated macrophages. An emerging hypothesis (SePhaChARNS: selective pharmacological chaperone of acetylcholine receptor number and stoichiometry) that is gaining ground (and mostly shown to be valid so far for neuronal a4b2-nAChR), substantiates that physiologically relevant manipulations of nAChRs take place in the ER, not at the cell surface membrane (Kuryatov et al, 2005;Srinivasan et al, 2011Srinivasan et al, , 2012, and a sustained interaction between nicotine and nascent nAChRs exerts were treated with 5 mM nicotine for 10 minutes followed by stimulation with poly(I:C) at 20 mg/ml for 30 minutes. (C) mouse peritoneal macrophages were incubated with 5 mM nicotine or PBS (control) for 30 minutes.…”

Biosynthesis of ionotropic acetylcholine receptors requires the evolutionarily conserved ER membrane complex

“…For example, a rare mutation in the human β4 AChR subunit has been linked to amyotrophic lateral sclerosis (6), and this mutation was shown to impair the export of α4β4 AChRs from the endoplasmic reticulum (ER) (7). ER retention of AChRs was also proposed to influence ER stress and the unfolded protein response (UPR) in dopaminergic neurons (8). In the smoker's brain, an enhancement of AChR expression likely contributes to tobacco addiction.…”

Weight of evidence evaluation of a network of adverse outcome pathways linking activation of the nicotinic acetylcholine receptor in honey bees to colony death

“…Desensitization is characterized by an initial opening of the ion channel and ion exchange across the cell membrane followed by rapid channel closure and inactivity, effectively inhibiting neurotransmission (Quick and Lester, 2002). Further, inhibition of nAChR activity from desensitization can lead to an up-regulation in nAChR expression, termed pharmacological chaperoning (Srinivasan et al, 2012;Flores et al, 1992;Marszalec et al, 2005). Exposure to imidacloprid and thiamethoxam for 72 or 48 h, respectively was shown to significantly increase transcriptional abundance of nAChRα1 subunit in the honey bee brain (Christen et al, 2016).…”