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P1‐176: FACILITATION EFFECTS OF SUB‐NANOMOLAR CONCENTRATIONS OF Aβ(1‐42) ON α7 NACHRS IN XENOPUS OOCYTES
Author(s) -
Anderson Jonathan Blake,
DeBoeuf Kristi,
Panchal Jay,
Farley Joseph
Publication year - 2018
Publication title -
alzheimer's and dementia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.713
H-Index - 118
eISSN - 1552-5279
pISSN - 1552-5260
DOI - 10.1016/j.jalz.2018.06.180
Subject(s) - xenopus , nicotinic agonist , acetylcholine receptor , chemistry , voltage clamp , nicotinic acetylcholine receptor , microbiology and biotechnology , biophysics , electrophysiology , wild type , allosteric modulator , allosteric regulation , acetylcholine , protein subunit , nicotinic antagonist , receptor , biology , biochemistry , mutant , pharmacology , membrane potential , neuroscience , gene
Background: Several studies (including our own) have found that high nM mM concentrations of amyloid beta (Ab) peptides inhibit alpha 7 (a7) nicotinic acetylcholine receptor (nAChR) activity. In contrast, recent studies suggest that picomolar concentrations interact with a7Rs in a facilitatory way, suggesting potentially positive roles for Ab in certain learningand memory-related processes (Puzzo et al., 2008). The present study aims to characterize the nature of this facilitory interaction. Methods: Mouse a7 nAChR subunit cRNA (WT and M276L) was synthesized from ma7 nAChR/ pGEM-HE plasmid DNA and microinjected into Xenopus laevis oocytes. Functional expression of mouse a7 nAChRs was evaluated fourth day post injection via two electrode voltage clamp (TEVC) of microinjected oocytes clamped at -60mVand exposed to a saturating concentration (500uM) of acetylcholine. Results: 2-4hr exposure to 100pM Ab(42) increased peak amplitudes and slowed desensitization of ACh-evoked a7R currents expressed in Xenopus oocytes, similar to but less strongly than the type II positive allosteric modulator (PAM) PNU 120596. PNU 120596 (but not a type I PAM, genistein) also occluded the effects of 100pM Ab(42). These results suggested that 100pM Ab(42) acts as a weak type II PAM at wild-type (wt) a7Rs. To further test this idea, we mutated murine a7R cDNA at the M2 residue (M276L) previously shown to be critical for type II PAM effects on human a7Rs (Young et al., 2008). Analysis of the ACh-evoked currents of the mutant a7Rs in the presence of: 1) 100pM Ab(42), 2) 15uM PNU 120596, or 3) the combination of 100pM Ab(42) and 15uM PNU120596, indicated the expected reduction in PNU-facilitation and complete elimination of the 100pM Ab(42)-facilitation. Conclusions: Our results for M276L a7Rs suggest that 100 pM Ab(42) does in fact modulate a7R activity through conventional type II PAM action. Furthermore, the apparent occlusion effect suggests that attempts to remedy cognitive deficits in various Alzheimer’s Disease cohorts using PAMs targeting the a7 nAChR may be doomed to failure because Ab peptides attenuate the substantially greater PAM effects that Type 2 PAMs exhibit in the absence of Ab.