Molecular dynamic modeling reveals potential sites of N-Aβ
terminal interactions at α7*-nAChR
Informed by our set of findings using single-channel recordings, we
carried out independent molecular dynamic simulations starting from
different docking conformations of the natural N-Aβ fragment placed at
α7+/α7- and α7+/β2- binding interfaces (Figure 6). We calculated that
N-Aβ fragments with different poses appeared to remain bound in the
binding site during the simulation up to 400 ns. The residues of
N-Aβcore hexapeptide, including Y10, H13, H14 (equivalent to Y625, H628,
H629 in APP sequence) and negatively charged Q15 (corresponding to
Aβ10-15) in the Aβ sequence, can form π-stacking
interactions and salt bridges with the aromatic residues (e.g., Y92,
W148, Y187, Y194) and charged residues (e.g., K142, K144, R185 and K191)
of α7- subunit in both α7+/α7- and α7+/β2- interfaces (Figures 6B-B”
and D-D”). This is consistent with the previously published data as
R185 and Y187 in our work are equivalent to R208 and Y210 in Roberts et
al.’s work, and Y187 is also equivalent to Y188 in Forest et al.’s work.
The aforementioned N-Aβcore residues also have interactions with the
residues (e.g., W54, K75 and H114) of α7+ subunit in α7+/α7- interface
and the residues (e.g., W57, F119 and K163) of β2+ subunit in α7+/β2-
interface. The simulation results suggest that several residues of
N-Aβcore (Y10, H13, H14 in full-length Aβ) are critical for the
agonist-like interactions with α7*-nAChR canonical binding sites that
are rich in charged and aromatic residues, although the interacting
residue pairs are not specific. This is consistent with the experiment
data showing that the mutant N-InAβcore 10-SEVAAQ-15 is inactive on
α7*-nAChR single-channel kinetics.
DISCUSSION
In this study, we identified for the first time the activation of human
homomeric α7- and heteromeric α7β2-nAChR single-channel openings by the
human N-Aβ fragment (N-terminal 15 amino acid Aβ peptide fragment) and
by the N-Aβcore (essential core sequence hexapeptide within the N-Aβ
fragment), as we have done for oligomeric Aβ1-42(oAβ42) (George et al., 2021). Specifically, we
demonstrated that N-Aβ fragment and N-Aβcore differentially alter the
biophysical properties of α7*-nAChR subtypes in comparison to activation
by ACh and oAβ42 (summarized in Figure 7).
Here, we provide evidence that N-Aβ fragment exposure alone increases
α7-nAChR component 2 (C2) open-dwell time within bursts and burst
duration relative to effects of ACh alone. Co-administration the N-Aβ
fragment plus ACh increased α7-nAChR C2, burst duration and
Popen relative to effects of ACh alone, while the
α7-nAChR burst duration was higher in the presence of N-Aβ fragment
alone or co-administered with oAβ42 than upon exposure
to oAβ42 alone. However, N-Aβ fragment plus
oAβ42 exposure reduces α7β2-nAChR open-dwell times
within bursts (component 1; C1) relative to effects of
oAβ42 alone. Importantly, at α7β2-nAChR, N-Aβcore
exposure when co-applied with oAβ42 reduces C1, C2,
burst duration, and Popen from elevated levels seen for
oAβ42 treatment alone to those seen upon exposure to
ACh, Aβ core or N-Aβ alone. The current observations, therefore,
substantially expand our understanding of the functional interactions of
α7*-nAChR with Aβ (Grassi et al., 2003; Liu et al., 2009; Wang, Lee,
D’Andrea, et al., 2000; Wang, Lee, Davis, & Shank, 2000) and the
N-terminal domain Aβ peptides at the single-channel level.
Several studies have investigated agonist-like actions of
Aβ1–42 at α7*-nAChR with varying effects (Dineley,
Bell, Bui, & Sweatt, 2002; Fu & Jhamandas, 2003; Lasala, Fabiani,
Corradi, Antollini, & Bouzat, 2019). Mutational and base docking
analyses suggest that a site of interaction between
Aβ1-42 and α7*-nAChR is dependent upon key aromatic
residues in loops A, B, and C in the extracellular, ACh-binding domain
(Espinoza-Fonseca, 2004a, 2004b; Tong, Arora, White, & Nichols, 2011).
This is in accordance with other molecular modeling simulations
suggesting similar docking conformations on the α7-nAChR-AChBP
(acetylcholine binding protein) for N-Aβ fragment and N-Aβcore (Forest
et al., 2018; Tong et al., 2011) at the α7*-nAChR ACh-binding pocket.
More specifically, computational modeling has suggested binding of the
N-Aβ fragment at the C-loop of α7+/α7- interfaces (Roberts, Stokoe,
Sathler, Nichols, & Kim, 2021). Roberts and colleagues identified three
key C-loop residues (R208, Y210 and E211) critical for
Aβ1-42 binding at α7-nAChR. Forest et al. modeled the
N-Aβcore into the known ligand-activation binding pocket in the
α7-nAChR-AChBP chimera and identified that tyrosine (Y188), which is
equivalent to Y210 in Roberts et al.’s work, is critical for Aβ-mediated
activation of the rodent α7*-nAChR (Forest et al., 2018).
A mechanistic interpretation, for the common action of the N-Aβ fragment
and the N-Aβcore to elicit α7*-nAChR single-channel openings is that
they act at both receptor subtypes at orthosteric sites between subunit
interfaces. An implication is that the N-Aβcore could represent a
minimal template for α7*-nAChR activation via the N-terminal domain of
oAβ42 and hence the N-Aβ fragment. Uniquely, N-Aβ
fragment exposure alone selectively prolonged homomeric α7-nAChR
open-dwell times (component 2; c2) within bursts and increases total
burst duration, relative to effects of ACh alone. More strikingly,
α7-nAChR burst duration, open-dwell time within bursts, and
Popen were elevated relative to effects of ACh alone
when the N-Aβ fragment was applied in the presence of ACh. The
identification of residues within α7*-nAChR canonical agonist binding
site (i.e., α7+/α7- and/or α7+/β2- interfaces) for
oAβ42, N-Aβ fragment or N-Aβcore does not discount the
possibility that these ligands interact with α7*-nAChR at other sites.
Consistent with previous studies
(George et al., 2021), full-length oAβ42 exposure
enhanced α7β2-nAChR Popen, single-channel open-dwell
time within bursts and total burst duration compared to effects of ACh
alone, or to the effects of N-Aβ fragment or N-Aβcore alone. On the
other hand, oAβ42 was not significantly different in
effect on these parameters for homomeric α7-nAChR from that of ACh,
while the N-Aβ fragment but not the N-Aβcore enhanced open-dwell time
and bursts of the α7-nAChR. That neither N-Aβ fragment nor N-Aβcore
mimic the effects of oAβ42 on α7β2-nAChR of
oAβ42 is noteworthy, especially as both N-Aβ fragment
and N-Aβcore alone activate α7β2-nAChR and α7-nAChR channel openings, to
a similar extent as that of ACh, the natural ligand. This difference may
explain, in part, why the N-Aβ fragment and the N-Aβcore are non-toxic
while being neuroprotective (Forest et al., 2018).
From another perspective, the absence of N-Aβ fragment effects alone or
in combination with ACh on open-dwell time, burst duration or
Popen at α7β2-nAChR is potentially informative. ACh
occupancy at only one of five orthosteric sites in homomeric α7-nAChR
produces maximal current responses (Andersen et al., 2016). ACh
occupancy at a single orthosteric site coupled with N-Aβ fragment
agonisms and positive allosteric modulation (agoPAM) activity at one or
more remaining orthosteric or perhaps peri-orthosteric sites on α7-nAChR
may explain the potentiation of Popen in the presence of
both ACh and N-Aβ fragment. Such action would not occur if the single
α7+/α7- orthosteric site in α7β2-nAChR is occupied by ACh, leaving no
possibility for N-Aβ fragment to also do so, or just allowing for one or
the other ligand to occupy that functional interface. This
interpretation is consistent with prior and current modeling implicating
extended domains for Aβ interactions with α7*-nAChR and would explain
agonist-like action of N-Aβ fragment at both α7- and α7β2-nAChR in
addition to observed N-Aβ fragment agoPAM activity in α7-nAChR in the
presence of ACh.
In view of the findings that
co-exposure to N-Aβcore also neutralizes the ability of
oAβ42 to enhance α7β2-nAChR but not α7-nAChR
Popen, single-channel open-dwell time within bursts, and
total burst duration, another reasonable hypothesis is that the N-Aβcore
sterically hinders oAβ42 interactions at a
non-orthosteric sites involved in the modulatory enhancement of
α7β2-nAChR single-channel kinetics that is not accessed by ACh. This
could imply that oAβ42 residues beyond those present in
N-Aβ fragment or N-Aβcore are involved in potentiation of α7β2-nAChR
channel opening. Indeed, the ability of N-Aβ fragment alone and/or in
combination with ACh to enhance features of α7-nAChR, but not
α7β2-nAChR, channel opening resembles that of a PAM (Andersen et al.,
2016; Williams, Wang, & Papke, 2011). This agoPAM mechanism is
consistent with studies suggesting that oAβ42 enhance
α7-nAChR channel opening by acting both orthosterically and
allosterically (Lasala et al., 2019). The possibility of allosteric
modulation of α7β2-nAChR by the N-Aβ fragment and the N-Aβcore raises
the question as to what extent this non-orthosteric regulation
contributes to the reversal of Aβ-linked deficits in synaptic plasticity
by these Aβ-derived, neuroprotective peptides.
Lastly, it is important to consider the biologically and/or
pathologically relevant concentrations of these reagents and their forms
(e.g., aggregation state). Whereas definitive knowledge of these factorsin situ , particularly at vicinal critical sites (e.g., synapses)
remains to be determined, oAβ42 concentrations from the
low pM range as physiological to high nM-low µM range as neurotoxic have
been reported (Forest et al., 2018). Our previous studies used
oAβ42 at 100 nM, where it enhances basal forebrain
cholinergic neuronal excitability in organotypic cultures (George et
al., 2021), which coincides with a previous study demonstrating that
nAChR-sensitive neurons to cellular toxicity at this concentration
(Arora, Alfulaij, Higa, Panee, & Nichols, 2013). In regard to
single-channel activity of the α7*-nAChR, studies show that
oAβ42 at high nM elicits α7*-nAChR channel activity,
preferentially modulating α7β2-nAChR single-channel kinetics by
enhancing α7β2-nAChR open-dwell times within single-channel bursts.
These findings contrast with evidence suggesting that high
concentrations of oAβ42 may lead to functional blockade
of α7*-nAChR (Lasala et al., 2019). However, long-term exposure may
convert from agonism to downregulation of α7*-nAChR, contributing to
deficits in cholinergic neurotransmission and to cognitive deficits
observed in AD. The impact of chronic elevated oAβ42 as
well as the N-terminal Aβ peptides on α7*-nAChR channel function remains
to be studied.
In conclusion, our research has expanded our understanding of the range
of Aβ peptides impacting human α7*-nAChR, which could play a role in
both neuronormal biological processes and neurodegenerative conditions.
We speculate that oAβ42/α7β2-nAChR interactions manifest
early in AD development, suggesting that targeting or reducing them
could hold therapeutic value, particularly if the natural responses of
α7*-nAChR to ACh remain unaffected. Together, these findings offer novel
insights into potentially effective strategies for selectively
safeguarding against Aβ-induced neurodegeneration, particularly in the
pre-clinical stages of AD.
FIGURE LEGENDS
Figure 1. Design and functional expression of human α7*nAChR. (A)
Schematic representation of human α7- and α7β2-nAChR DNA constructs. Top
row: Concatenated α7-nAChR homopentamer (containing only α7 subunits)
harboring the sequence for the mCherry fluorophore and fused to the α7
nAChR subunit gene in position 5 (P5); Middle row: Concatenated
α7β2-nAChR (containing two β2 subunits in position 2 and 4) harboring
the sequence for the mCherry fluorophore and fused to the α7 nAChR
subunit gene in position 5 (P5). Bottom row: Construct for the human
nAChR chaperone protein NACHO containing the sequence for the ZsGreen1
fluorophore. (B) Illustration of assembly and stoichiometry of
concatenated human α7-nAChR homopentamer and concatenated human
α7β2-nAChR co-expressed with the nAChR chaperone NACHO + ZsGreen1. (C)
Fluorescent imaging of the α7-nAChR homopentamer transiently expressed
in SH-EP1 cell lines. Left panel represents NACHO expression (as
indicated by ZsGreen1 expression), middle panel represents α7-nAChR
expression (as indicated by mCherry expression), and bottom panel
represents cells co-expressing NACHO and α7-nAChR (merged; yellow). (C’)
Fluorescent imaging of the α7β2-nAChR heteropentamer transiently
expressed in SH-EP1 cell lines. Left panel represents NACHO expression
(as indicated by ZsGreen1 expression), middle panel represents
α7β2-nAChR expression (as indicated by mCherry expression), and bottom
panel represents cells co-expressing NACHO and α7β2-nAChR (merged;
yellow). Arrows indicated cells targeted for cell-attached,
single-channel recordings. Scale bar represents 50 µm.
Figure 2. α7*-nAChR single-channel burst amplitude and burst rates. α7-
and α7β2-single-channel burst amplitudes (Panels A and B; pA) and burst
rates (Panels C and D; bursts/sec) were analyzed for each treatment. No
significant differences in single-channel burst amplitudes or burst
rates were observed across α7*-nAChR subtypes. Differences in
single-channel amplitude and burst rate were determined using two-way
ANOVA with Tukey’s posthoc test for multiple comparisons. Data
represented as mean ± SEM.
Figure 3. Selective enhancement of α7*-nAChR single-channel open
probability (Popen) by oAβ42, N-Aβcore,
and the N-Aβ fragment. (A) Co-application of ACh + N-Aβ fragment
enhanced single-channel Popen of homomeric α7-nAChR
compared to α7-nAChR exposed to ACh alone, N-Aβ fragment alone, ACh +
N-Aβcore, or oAβ42 + N-Aβ fragment. (B) Heteromeric
α7β2-nAChR Popen was enhanced in the presence of
oAβ42 alone compared to α7β2-nAChR exposed to ACh alone,
N-Aβcore alone, N-Aβ fragment alone, or oAβ42 +
N-Aβcore. Further, co-application of oAβ42 + N-Aβ
fragment enhanced α7β2-nAChR Popen compared to groups
treated with oAβ42 + N-Aβcore, ACh + N-Aβ fragment, or
N-Aβ fragment alone. No differences in Popen were
observed between α7β2-nAChR exposed to oAβ42 alone or
oAβ42 + N-Aβ fragment. Differences in α7*-nAChR
single-channel Popen were determined using two-way ANOVA
with Tukey’s post-hoc test for multiple comparisons. Data represented as
mean ± SEM. *p<0.05, ***p<0.001,
****p<0.0001.
Figure 4. Homomeric α7-nAChR single-channel open-dwell times within
bursts and total burst duration. (A) α7-nAChR open-dwell times within
bursts (ms) are best fit with two open-dwell time components indicating
two distinct open-dwell time distributions within bursts (red lines
indicate individual components and black line represents overall fit).
Representative traces demonstrate a binary closed or open state at
uniform amplitudes and various burst durations and accompany each
single-channel open-dwell time histogram. Closed (c) and open (o; dashed
line) states are indicated for each trace. (B) No significant difference
was observed between treatment groups was observed in single-channel
open-dwell time component 1 (C1). (C) Significant differences in
single-channel open-dwell time component 2 (C2) were observed between
treatment groups. α7-nAChR subtypes exposed to ACh + N-Aβ fragment
exhibited the greatest increase in C2 single-channel open-dwell time
compared to ACh alone, N-Aβ fragment alone, ACh + N-Aβcore, or
oAβ42 + N-Aβ fragment. (D) α7-nAChR single-channel burst
duration. Significant differences in α7-nAChR bust duration were
observed for α7-nAChR exposed to N-Aβ fragment alone compared to
α7-nAChR exposed to ACh or oAβ42 alone, N-Aβcore alone,
ACh + N-Aβ fragment, or oAβ42 +N-Aβ fragment. Further,
α7-nAChR single-channel burst duration (ms) was enhanced when the N-Aβ
fragment was co-applied with ACh or oAβ42 when compared
to α7-nAChR exposed to ACh or oAβ42 alone, indicating
the ability of N-Aβ fragment to enhance α7-nAChR burst duration.
Differences in α7-nAChR single-channel open-dwell times and/or burst
duration were analyzed using a two-way ANOVA with Tukey’s posthoc test
for multiple comparisons. Data represented as mean ± SEM.
*p<0.05, ****p<0.0001.
Figure 5. Heteromeric α7β2-nAChR single-channel open-dwell times within
bursts and total burst duration. (A) α7β2-nAChR open-dwell times within
bursts (ms) are best fit with two open-dwell time components indicating
two distinct open-dwell time distributions within bursts (red lines
indicate individual components and black line represents overall fit).
Representative traces demonstrate a binary closed or open state at
uniform amplitudes and various burst durations and accompany each
single-channel open-dwell time histogram. Closed (c) and open (o; dashed
line) states are indicated for each trace. (B) Significant differences
in single-channel open-dwell time component 1 (C1) were observed for
α7β2-nAChR events elicited with oAβ42 compared to
α7β2-nAChR exposed to ACh alone, N-Aβcore alone, N-Aβ fragment alone,
oAβ42 + N-Aβcore, or oAβ42 + N-Aβ
fragment. (C) Comparison of α7β2-nAChR single-channel open-dwell time
component 2 (C2). C2 open-dwell times were enhanced for α7β2-nAChR in
the presence of oAβ42 alone and were greater than
α7β2-nAChR C2 open-dwell times induced by ACh alone, N-Aβcore alone,
N-Aβ fragment alone, or oAβ42 + N-Aβcore. Further, C2
α7β2-nAChR open-dwell times were similar between α7β2-nAChR exposed to
oAβ42 alone and co-application of oAβ42+ N-Aβ fragment. Application of oAβ42 + N-Aβcore
normalized C2 open-dwell times compared to α7β2-nAChR events elicited
with oAβ42 + N-Aβ fragment. (D) α7β2-nAChR burst
duration. Single-channel burst durations were significantly greater for
α7β2-nAChR events elicited with oAβ42 alone or those
elicited with oAβ42 + N-Aβ fragment. Differences in
oAβ42-induced α7β2-nAChR burst duration were
significantly greater than those elicited with ACh alone, N-Aβcore
alone, N-Aβ fragment alone, or
oAβ42 + N-Aβcore.
Data represented as mean ± SEM. Significance was determined using 2-way
ANOVA as follows: *p<0.05, ***p<0.001,
****p<0.0001.
Figure 6. Aβ/α7*-nAChR molecular dynamic simulations. (A) Simulated
binding pose of a single N-Aβ fragment (highlighted in red) placed
within the homomeric α7-nAChR (α7 subunits represented in yellow). (A’)
Close up of the conical binding site formed between two subunits at the
α7-/α7+ subunit interface. Structural elements with the orthosteric
binding site are labeled and N-Aβ fragment binding restricted within the
square: Loop C (cyan) of α7+ subunit, loop E (purple) and loop D
(magenta) of α7- subunit. (B-B”) Side view of representative snapshots
extracted from three (out of ten; see methods) simulation runs where
N-Aβ fragment remained bound in the binding site after the systems were
simulated for 400 ns. The residues of N-Aβ fragment (colored cyan and
magenta; magenta representing the N-Aβcore) are indicated in red, the
residues of α7+ subunit are indicated in blue, and the residues of α7-
subunit are indicated in purple. (C) Simulated binding pose of a single
N-Aβ fragment (highlighted in red) placed within the heteromeric
α7β2-nAChR (α7 and β2 subunits represented in yellow and green,
respectively). (C’) Close up of the conical binding site formed at the
α7-/β2+ subunit interface. Structural elements within the orthosteric
binding site are labeled: Loop C (cyan) of α7+ subunit, loop E (purple)
and loop D (magenta) of β2- subunit. (D-D”) Side view of representative
snapshots extracted from three (out of ten) simulation runs where N-Aβ
fragment remained bound in the binding site after the systems were
simulated for 400 ns. The residues of N-Aβ fragment are indicated in
red, the residues of α7+ subunit are indicated in blue, and the residues
of β2+ subunit are indicated in purple.
Figure 7. Summary of Aβ-induced alterations in α7*-nAChR single-channel
kinetics.
Supplemental Figure 1 (S1). α7*-nAChRs single-channel closed-dwell time
distributions. α7- and α7β2-nAChR closed-dwell times were best fit to
with 4 closed-dwell time components for all treatments. (A) α7- nAChR
and (B) α7β2-nAChR closed-dwell times. Representative traces (below each
histogram) are included for all experimental groups. Dashed lines
represent closed (c) states. Bursts of single-channel activity
(identified using Qub single-channel software; see methods) are
highlighted within each trace for α7-nAChR (red) and α7β2-nAChR (blue).
At a constant transmembrane voltage, both α7- and α7β2-nAChR
closed-dwell times could be best fit with four (4) distinct closed-dwell
time components. For each recording, single-channel bursts were defined
as a series of openings separated by closures shorter than the minimum
inter-burst closed duration (or Tcrit ). Each
closed-dwell time component and minimum inter-burst closed time was
calculated for each of the following ligand exposure conditions and
summarized in Table 1: ACh or oAβ42 alone, N-Aβ fragment
or N-Aβcore alone, ACh + N-Aβcore, oAβ42 + N-Aβcore, ACh
+ N-Aβ fragment, or oAβ42 + N-Aβ fragment. An analysis
of closed-dwell time components revealed a significant interaction
between α7*-nAChR subtype and treatment (F(49,192) =
2.4; P<0.0001). Compared to responses to ACh alone, no
differences in α7-nAChR closed-dwell time components C1-C3 were
observed. However, closed-dwell time component 4 (C4) was reduced for
α7-nAChR exposed to N-Aβcore alone (P < 0.001) or to
oAβ42 + N-Aβ fragment (P< 0.0001) when
compared to α7-nAChR exposed to ACh alone. Conversely, α7-nAChR exposed
to ACh + N-Aβcore showed a significant increase in C4 closed dwell-times
compared to responses to ACh alone (P < 0.05). No differences
in any closed-dwell time components were observed for α7β2-nAChR across
ligand exposure conditions (F(21,96) = 1.072; P =
0.39).All single-channel closed-dwell times were analyzed using a
one-way ANOVA for within-group comparisons and Dunnett’s post-hoc test
for multiple comparisons (ACh as control) and summarized in Table 1.
Supplemental Figure 2 (S2). α7- and α7β2-nAChR closed dwell-times within
bursts. (A) Closed-dwell time distributions within bursts for α7-nAChR.
(B) Closed-dwell time distributions within bursts for α7β2-nAChR. (C
&D) An analysis of α7*-nAChR closed-dwell times revealed a significant
interaction between receptor subtype and treatment
(F(7,140) = 2.1; P < 0.05). Post hocanalysis revealed a significant enhancement in the α7β2-nAChR mean
closed-dwell time within bursts in the presence of N-Aβcore alone, but
only relative to oAβ42 + N-Aβ fragment condition (P
< 0.01). Otherwise, no differences in closed-dwell times
within bursts were evident between α7- and α7β2-nAChR across all
treatment groups (F(1,140) = 0.97; P = 0.05).
Differences in single-channel closed-dwell times within bursts were
determined using two-way ANOVA with Tukey’s posthoc test for multiple
comparisons. Data represented as mean ± SEM. **p<0.01
Supplemental Figure 3 (S3). Cross-group comparisons between α7- and
α7β2-nAChR amplitude, burst rate, open-dwell times within bursts, open
probability (Popen), and burst duration. Data
represented as mean ± SEM. Significance was determined using 2-way ANOVA
as follows: *p<0.05, **p<0.01, ***p<0.001,
****p<0.0001.
Supplemental Figure 4 (S4). The effect of the control Inactive N-Aβcore
hexapeptide (In-Aβcore) on α7*-nAChR single-channel kinetics.
Table 1. α7*-nAChR single-channel closed-dwell time distributions.
Differences in single-channel closed-dwell times were determined using
one-way ANOVA followed by Dunnet’s post hoc comparison (against
ACh as control): *p<0.05, ***p<0.001,
****p<0.0001.
Table 2. α7*-nAChR single-channel amplitudes and burst rates.
Differences in single-channel amplitudes and burst rates were determined
using one-way ANOVA followed by Dunnet’s post hoc comparison
(against ACh as control).
REFERNECES
Andersen, N. D., Nielsen, B. E., Corradi, J., Tolosa, M. F., Feuerbach,
D., Arias, H. R., & Bouzat, C. (2016). Exploring the positive
allosteric modulation of human alpha7 nicotinic receptors from a
single-channel perspective. Neuropharmacology, 107 , 189-200.
doi:10.1016/j.neuropharm.2016.02.032
Arora, K., Alfulaij, N., Higa, J. K., Panee, J., & Nichols, R. A.
(2013). Impact of sustained exposure to beta-amyloid on calcium
homeostasis and neuronal integrity in model nerve cell system expressing
alpha4beta2 nicotinic acetylcholine receptors. J Biol Chem,
288 (16), 11175-11190. doi:10.1074/jbc.M113.453746
Azam, L., Winzer-Serhan, U., & Leslie, F. M. (2003). Co-expression of
alpha7 and beta2 nicotinic acetylcholine receptor subunit mRNAs within
rat brain cholinergic neurons. Neuroscience, 119 (4), 965-977.
doi:10.1016/s0306-4522(03)00220-3
Castellani, R. J., Zhu, X., Lee, H. G., Moreira, P. I., Perry, G., &
Smith, M. A. (2007). Neuropathology and treatment of Alzheimer disease:
did we lose the forest for the trees? Expert Rev Neurother, 7 (5),
473-485. doi:10.1586/14737175.7.5.473
Chakrapani, S., Bailey, T. D., & Auerbach, A. (2004). Gating dynamics
of the acetylcholine receptor extracellular domain. J Gen Physiol,
123 (4), 341-356. doi:10.1085/jgp.200309004
Cirrito, J. R., Yamada, K. A., Finn, M. B., Sloviter, R. S., Bales, K.
R., May, P. C., … Holtzman, D. M. (2005). Synaptic activity
regulates interstitial fluid amyloid-beta levels in vivo. Neuron,
48 (6), 913-922. doi:10.1016/j.neuron.2005.10.028
Ciuraszkiewicz, A., Schreibmayer, W., Platzer, D., Orr-Urtreger, A.,
Scholze, P., & Huck, S. (2013). Single-channel properties of
alpha3beta4, alpha3beta4alpha5 and alpha3beta4beta2 nicotinic
acetylcholine receptors in mice lacking specific nicotinic acetylcholine
receptor subunits. J Physiol, 591 (13), 3271-3288.
doi:10.1113/jphysiol.2012.246595
Cline, E. N., Bicca, M. A., Viola, K. L., & Klein, W. L. (2018). The
Amyloid-beta Oligomer Hypothesis: Beginning of the Third Decade. J
Alzheimers Dis, 64 (s1), S567-S610. doi:10.3233/JAD-179941
Dineley, K. T., Bell, K. A., Bui, D., & Sweatt, J. D. (2002). beta
-Amyloid peptide activates alpha 7 nicotinic acetylcholine receptors
expressed in Xenopus oocytes. J Biol Chem, 277 (28), 25056-25061.
doi:10.1074/jbc.M200066200
Eberhardt, J., Santos-Martins, D., Tillack, A. F., & Forli, S. (2021).
AutoDock Vina 1.2.0: New Docking Methods, Expanded Force Field, and
Python Bindings. J Chem Inf Model, 61 (8), 3891-3898.
doi:10.1021/acs.jcim.1c00203
Espinoza-Fonseca, L. M. (2004a). Base docking model of the homomeric
alpha7 nicotinic receptor-beta-amyloid(1-42) complex. Biochem
Biophys Res Commun, 320 (2), 587-591. doi:10.1016/j.bbrc.2004.05.207
Espinoza-Fonseca, L. M. (2004b). Molecular docking of four
beta-amyloid1-42 fragments on the alpha7 nicotinic receptor: delineating
the binding site of the Abeta peptides. Biochem Biophys Res
Commun, 323 (4), 1191-1196. doi:10.1016/j.bbrc.2004.08.218
Forest, K. H., Alfulaij, N., Arora, K., Taketa, R., Sherrin, T.,
Todorovic, C., … Nichols, R. A. (2018). Protection against
beta-amyloid neurotoxicity by a non-toxic endogenous N-terminal
beta-amyloid fragment and its active hexapeptide core sequence. J
Neurochem, 144 (2), 201-217. doi:10.1111/jnc.14257
Forest, K. H., Taketa, R., Arora, K., Todorovic, C., & Nichols, R. A.
(2021). The Neuroprotective Beta Amyloid Hexapeptide Core Reverses
Deficits in Synaptic Plasticity in the 5xFAD APP/PS1 Mouse Model.Front Mol Neurosci, 14 , 576038. doi:10.3389/fnmol.2021.576038
Fu, W., & Jhamandas, J. H. (2003). Beta-amyloid peptide activates
non-alpha7 nicotinic acetylcholine receptors in rat basal forebrain
neurons. J Neurophysiol, 90 (5), 3130-3136.
doi:10.1152/jn.00616.2003
George, A. A., Vieira, J. M., Xavier-Jackson, C., Gee, M. T., Cirrito,
J. R., Bimonte-Nelson, H. A., … Whiteaker, P. (2021).
Implications of Oligomeric Amyloid-Beta (oAbeta(42)) Signaling through
alpha7beta2-Nicotinic Acetylcholine Receptors (nAChRs) on Basal
Forebrain Cholinergic Neuronal Intrinsic Excitability and Cognitive
Decline. J Neurosci, 41 (3), 555-575.
doi:10.1523/JNEUROSCI.0876-20.2020
Grassi, F., Palma, E., Tonini, R., Amici, M., Ballivet, M., & Eusebi,
F. (2003). Amyloid beta(1-42) peptide alters the gating of human and
mouse alpha-bungarotoxin-sensitive nicotinic receptors. J Physiol,
547 (Pt 1), 147-157. doi:10.1113/jphysiol.2002.035436
Grosman, C., & Auerbach, A. (2000). Kinetic, mechanistic, and
structural aspects of unliganded gating of acetylcholine receptor
channels: a single-channel study of second transmembrane segment 12’
mutants. J Gen Physiol, 115 (5), 621-635.
doi:10.1085/jgp.115.5.621
Grosman, C., & Auerbach, A. (2001). The dissociation of acetylcholine
from open nicotinic receptor channels. Proc Natl Acad Sci U S A,
98 (24), 14102-14107. doi:10.1073/pnas.251402498
Gu, S., Matta, J. A., Lord, B., Harrington, A. W., Sutton, S. W.,
Davini, W. B., & Bredt, D. S. (2016). Brain alpha7 Nicotinic
Acetylcholine Receptor Assembly Requires NACHO. Neuron, 89 (5),
948-955. doi:10.1016/j.neuron.2016.01.018
Humphrey, W., Dalke, A., & Schulten, K. (1996). VMD: visual molecular
dynamics. J Mol Graph, 14 (1), 33-38, 27-38.
doi:10.1016/0263-7855(96)00018-5
Inayathullah, M., & Teplow, D. B. (2011). Structural dynamics of the
DeltaE22 (Osaka) familial Alzheimer’s disease-linked amyloid
beta-protein. Amyloid, 18 (3), 98-107.
doi:10.3109/13506129.2011.580399
Jack, C. R., Jr., Bennett, D. A., Blennow, K., Carrillo, M. C., Dunn,
B., Haeberlein, S. B., … Contributors. (2018). NIA-AA Research
Framework: Toward a biological definition of Alzheimer’s disease.Alzheimers Dement, 14 (4), 535-562. doi:10.1016/j.jalz.2018.02.018
Jorgensen, W. L., Chandrasekhar, J., Buckner, J. K., & Madura, J. D.
(1986). Computer simulations of organic reactions in solution. Ann
N Y Acad Sci, 482 , 198-209. doi:10.1111/j.1749-6632.1986.tb20951.x
Khiroug, S. S., Harkness, P. C., Lamb, P. W., Sudweeks, S. N., Khiroug,
L., Millar, N. S., & Yakel, J. L. (2002). Rat nicotinic ACh receptor
alpha7 and beta2 subunits co-assemble to form functional heteromeric
nicotinic receptor channels. J Physiol, 540 (Pt 2), 425-434.
doi:10.1113/jphysiol.2001.013847
Lasala, M., Fabiani, C., Corradi, J., Antollini, S., & Bouzat, C.
(2019). Molecular Modulation of Human alpha7 Nicotinic Receptor by
Amyloid-beta Peptides. Front Cell Neurosci, 13 , 37.
doi:10.3389/fncel.2019.00037
Lawrence, J. L., Tong, M., Alfulaij, N., Sherrin, T., Contarino, M.,
White, M. M., … Nichols, R. A. (2014). Regulation of presynaptic
Ca2+, synaptic plasticity and contextual fear conditioning by a
N-terminal beta-amyloid fragment. J Neurosci, 34 (43),
14210-14218. doi:10.1523/JNEUROSCI.0326-14.2014
Liu, Q., Huang, Y., Shen, J., Steffensen, S., & Wu, J. (2012).
Functional alpha7beta2 nicotinic acetylcholine receptors expressed in
hippocampal interneurons exhibit high sensitivity to pathological level
of amyloid beta peptides. BMC Neurosci, 13 , 155.
doi:10.1186/1471-2202-13-155
Liu, Q., Huang, Y., Xue, F., Simard, A., DeChon, J., Li, G., …
Wu, J. (2009). A novel nicotinic acetylcholine receptor subtype in basal
forebrain cholinergic neurons with high sensitivity to amyloid peptides.J Neurosci, 29 (4), 918-929. doi:10.1523/JNEUROSCI.3952-08.2009
Lukas, R. J., Changeux, J. P., Le Novere, N., Albuquerque, E. X.,
Balfour, D. J., Berg, D. K., … Wonnacott, S. (1999).
International Union of Pharmacology. XX. Current status of the
nomenclature for nicotinic acetylcholine receptors and their subunits.Pharmacol Rev, 51 (2), 397-401. Retrieved from
https://www.ncbi.nlm.nih.gov/pubmed/10353988
Marchesi, V. T. (2012). Alzheimer’s disease 2012: the great amyloid
gamble. Am J Pathol, 180 (5), 1762-1767.
doi:10.1016/j.ajpath.2012.03.004
Mehta, T. K., Dougherty, J. J., Wu, J., Choi, C. H., Khan, G. M., &
Nichols, R. A. (2009). Defining pre-synaptic nicotinic receptors
regulated by beta amyloid in mouse cortex and hippocampus with receptor
null mutants. J Neurochem, 109 (5), 1452-1458.
doi:10.1111/j.1471-4159.2009.06070.x
Minkeviciene, R., Rheims, S., Dobszay, M. B., Zilberter, M.,
Hartikainen, J., Fulop, L., … Tanila, H. (2009). Amyloid
beta-induced neuronal hyperexcitability triggers progressive epilepsy.J Neurosci, 29 (11), 3453-3462. doi:10.1523/JNEUROSCI.5215-08.2009
Moretti, M., Zoli, M., George, A. A., Lukas, R. J., Pistillo, F.,
Maskos, U., … Gotti, C. (2014). The novel alpha7beta2-nicotinic
acetylcholine receptor subtype is expressed in mouse and human basal
forebrain: biochemical and pharmacological characterization. Mol
Pharmacol, 86 (3), 306-317. doi:10.1124/mol.114.093377
Murray, T. A., Bertrand, D., Papke, R. L., George, A. A., Pantoja, R.,
Srinivasan, R., … Lukas, R. J. (2012). alpha7beta2 nicotinic
acetylcholine receptors assemble, function, and are activated primarily
via their alpha7-alpha7 interfaces. Mol Pharmacol, 81 (2),
175-188. doi:10.1124/mol.111.074088
Palop, J. J., Chin, J., Roberson, E. D., Wang, J., Thwin, M. T.,
Bien-Ly, N., … Mucke, L. (2007). Aberrant excitatory neuronal
activity and compensatory remodeling of inhibitory hippocampal circuits
in mouse models of Alzheimer’s disease. Neuron, 55 (5), 697-711.
doi:10.1016/j.neuron.2007.07.025
Palop, J. J., & Mucke, L. (2009). Epilepsy and cognitive impairments in
Alzheimer disease. Arch Neurol, 66 (4), 435-440.
doi:10.1001/archneurol.2009.15
Peng, J. H., Lucero, L., Fryer, J., Herl, J., Leonard, S. S., & Lukas,
R. J. (1999). Inducible, heterologous expression of human
alpha7-nicotinic acetylcholine receptors in a native nicotinic
receptor-null human clonal line. Brain Res, 825 (1-2), 172-179.
doi:10.1016/s0006-8993(99)01066-5
Portelius, E., Price, E., Brinkmalm, G., Stiteler, M., Olsson, M.,
Persson, R., … Blennow, K. (2011). A novel pathway for amyloid
precursor protein processing. Neurobiol Aging, 32 (6), 1090-1098.
doi:10.1016/j.neurobiolaging.2009.06.002
Portelius, E., Tran, A. J., Andreasson, U., Persson, R., Brinkmalm, G.,
Zetterberg, H., … Westman-Brinkmalm, A. (2007). Characterization
of amyloid beta peptides in cerebrospinal fluid by an automated
immunoprecipitation procedure followed by mass spectrometry. J
Proteome Res, 6 (11), 4433-4439. doi:10.1021/pr0703627
Puzzo, D., Privitera, L., Leznik, E., Fa, M., Staniszewski, A., Palmeri,
A., & Arancio, O. (2008). Picomolar amyloid-beta positively modulates
synaptic plasticity and memory in hippocampus. J Neurosci,
28 (53), 14537-14545. doi:10.1523/JNEUROSCI.2692-08.2008
Qin, F., Auerbach, A., & Sachs, F. (2000a). A direct optimization
approach to hidden Markov modeling for single channel kinetics.Biophys J, 79 (4), 1915-1927. doi:10.1016/S0006-3495(00)76441-1
Qin, F., Auerbach, A., & Sachs, F. (2000b). Hidden Markov modeling for
single channel kinetics with filtering and correlated noise.Biophys J, 79 (4), 1928-1944. doi:10.1016/S0006-3495(00)76442-3
Roberts, J. P., Stokoe, S. A., Sathler, M. F., Nichols, R. A., & Kim,
S. (2021). Selective coactivation of alpha7- and alpha4beta2-nicotinic
acetylcholine receptors reverses beta-amyloid-induced synaptic
dysfunction. J Biol Chem, 296 , 100402.
doi:10.1016/j.jbc.2021.100402
Stine, W. B., Jungbauer, L., Yu, C., & LaDu, M. J. (2011). Preparing
synthetic Abeta in different aggregation states. Methods Mol Biol,
670 , 13-32. doi:10.1007/978-1-60761-744-0_2
Thinschmidt, J. S., Frazier, C. J., King, M. A., Meyer, E. M., & Papke,
R. L. (2005). Medial septal/diagonal band cells express multiple
functional nicotinic receptor subtypes that are correlated with firing
frequency. Neurosci Lett, 389 (3), 163-168.
doi:10.1016/j.neulet.2005.07.038
Tong, M., Arora, K., White, M. M., & Nichols, R. A. (2011). Role of key
aromatic residues in the ligand-binding domain of alpha7 nicotinic
receptors in the agonist action of beta-amyloid. J Biol Chem,
286 (39), 34373-34381. doi:10.1074/jbc.M111.241299
Vassar, R., Bennett, B. D., Babu-Khan, S., Kahn, S., Mendiaz, E. A.,
Denis, P., … Citron, M. (1999). Beta-secretase cleavage of
Alzheimer’s amyloid precursor protein by the transmembrane aspartic
protease BACE. Science, 286 (5440), 735-741.
doi:10.1126/science.286.5440.735
Vossel, K. A., Beagle, A. J., Rabinovici, G. D., Shu, H., Lee, S. E.,
Naasan, G., … Mucke, L. (2013). Seizures and epileptiform
activity in the early stages of Alzheimer disease. JAMA Neurol,
70 (9), 1158-1166. doi:10.1001/jamaneurol.2013.136
Wang, H. Y., Lee, D. H., D’Andrea, M. R., Peterson, P. A., Shank, R. P.,
& Reitz, A. B. (2000). beta-Amyloid(1-42) binds to alpha7 nicotinic
acetylcholine receptor with high affinity. Implications for Alzheimer’s
disease pathology. J Biol Chem, 275 (8), 5626-5632.
doi:10.1074/jbc.275.8.5626
Wang, H. Y., Lee, D. H., Davis, C. B., & Shank, R. P. (2000). Amyloid
peptide Abeta(1-42) binds selectively and with picomolar affinity to
alpha7 nicotinic acetylcholine receptors. J Neurochem, 75 (3),
1155-1161. doi:10.1046/j.1471-4159.2000.0751155.x
Whiteaker, P., & George, A. A. (2023). Discoveries and future
significance of research into amyloid-beta/alpha7-containing nicotinic
acetylcholine receptor (nAChR) interactions. Pharmacol Res, 191 ,
106743. doi:10.1016/j.phrs.2023.106743
Williams, D. K., Wang, J., & Papke, R. L. (2011). Investigation of the
molecular mechanism of the alpha7 nicotinic acetylcholine receptor
positive allosteric modulator PNU-120596 provides evidence for two
distinct desensitized states. Mol Pharmacol, 80 (6), 1013-1032.
doi:10.1124/mol.111.074302
York, D. M., Wlodawer, A., Pedersen, L. G., & Darden, T. A. (1994).
Atomic-level accuracy in simulations of large protein crystals.Proc Natl Acad Sci U S A, 91 (18), 8715-8718.
doi:10.1073/pnas.91.18.8715