PubMed 19126755

It is noteworthy that the alpha7 nAChR activity increases intracellular accumulation of Abeta in neurons (336), and Abeta peptides, in addition to modulating nAChR activity, downregulate the expression of nAChRs (197).

BEL
act(p(HGNC:CHRNA7)) increases a(CHEBI:"amyloid-beta", loc(GO:intracellular))
Hash
f55b196958
MeSHAnatomy
Neurons
TextLocation
Review
Networks

PubMed 19293145

In addition, not only have alpha7 nAChRs been found colocalized with plaques (Wang et al., 2000b) but alpha7 and alpha4 subunits are also positively correlated with neurons that accumulate Abeta (Wevers et al., 1999).

BEL
p(HGNC:CHRNA7) positiveCorrelation a(CHEBI:"amyloid-beta")
Hash
01d7ae89c7
MeSHAnatomy
Neurons
Networks
BEL
a(CHEBI:"amyloid-beta") positiveCorrelation p(HGNC:CHRNA7)
Hash
b5895df4d7
MeSHAnatomy
Neurons
Networks

PubMed 19293145

In SHSY5Y cells, RNA interference (RNAi) knockdown of alpha7 enhanced Abeta toxicity (Qi et al., 2007), and alpha7 antagonists, but not alpha4beta2 antagonists, block galantamine protection of cultured rat neurons (Kihara et al., 2004). Donepezil protects cultured rat cortical neurons against Abeta toxicity through both alpha7 and non-alpha7 nAChRs (Takada et al., 2003). It is therefore likely that alpha7 nAChRs are the primary mediators of nicotine neuroprotection, but in some cells, non-alpha7 subtypes are also likely to contribute.

PubMed 19293145

An indication that nAChRs may play a role in Abeta internalization comes from a close inspection of cholinergic neurons in brains from patients with AD, which revealed that neurons with high expression levels of alpha7 also contained large amounts of intracellular Abeta (Nagele et al., 2002). Addition of Abeta to the culture medium of neuroblastoma cells overexpressing alpha7 results in more Abeta internalization than in control cells with lower levels of alpha7 expression (Nagele et al., 2002).

BEL
p(HGNC:CHRNA7) increases a(CHEBI:"amyloid-beta")
Hash
0c34e691d2
MeSHAnatomy
Brain, Neurons
MeSHDisease
Alzheimer Disease
Networks

PubMed 19293145

In contrast, Small et al. (2007) found no displacement of alpha-BTX from SH-SY5Y cells (a cell line very closely related to that used by Wang et al.) by either amyloid or methyllycaconitine. Wang et al. (2000b) also showed similar staining of human AD cortical neurons by alpha7 and Abeta antibodies in double immunofluorescence, suggesting that in human cortical neurons, alpha7 and Abeta are closely associated, although such an approach does not prove direct binding. However another study (Small et al., 2007) showed no displacement of labeled alpha-bungarotoxin from cell lines expressing rat alpha7 nAChRs.

BEL
p(HGNC:CHRNA7) association a(CHEBI:"amyloid-beta")
Hash
2ec872c128
CellLine
SH-SY5Y
Networks
BEL
a(CHEBI:"amyloid-beta") association p(HGNC:CHRNA7)
Hash
8e292da78a
CellLine
SH-SY5Y
Networks

PubMed 17009926

This prospect was supported by the finding that α7 nAChRs were found in plaques (159), and α7 and α4 subunits positively correlated with neurons that accumulated Aβ and hyperphosphorylated tau in AD brain tissue (161).

BEL
p(HGNC:CHRNA7) positiveCorrelation a(CHEBI:"amyloid-beta")
Hash
36cd7e385a
Cell
neuron
MeSHAnatomy
Brain
MeSHDisease
Alzheimer Disease
Networks
BEL
a(CHEBI:"amyloid-beta") positiveCorrelation p(HGNC:CHRNA7)
Hash
731f46f17c
Cell
neuron
MeSHAnatomy
Brain
MeSHDisease
Alzheimer Disease
Networks

PubMed 29191965

AD brains show an upregulation of CHRNA7 (acr-14 homolog in humans) (84), where it may mediate the Ab-induced tau pathology (85).

BEL
p(HGNC:CHRNA7) regulates act(a(CHEBI:"amyloid-beta"))
Hash
5812e33407
MeSHAnatomy
Brain
Species
6239
Networks

PubMed 19293145

Curiously, although most studies are in agreement that nAChRs need to be activated to mediate their protective effects, mouse cortical neurons are protected by the alpha7 antagonist methyllycaconitine (Martin et al., 2004), raising the possibility that neuroprotection by alpha7 agonists may be through desensitization rather than activation of this rapidly desensitizing receptor. This would be consistent with the alpha7- dependent activation of intracellular signaling pathways by Abeta (Bell et al., 2004), but the opposite effects on cell survival exerted by Abeta and nicotine means that other mechanisms must be sought, such as ligand-specific coupling to downstream signaling pathways.

PubMed 19293145

Abeta action on nAChRs depends on subunit composition; it has been reported to block alpha7, transiently potentiate alpha4beta2 before blocking, and to have no action on alpha3beta4 (Pym et al., 2005). However, in contrast to its reported transient enhancement when expressed in oocytes, an inhibition of alpha4beta2 has been reported when expressed in human SH-EP1 cells (Wu et al., 2004).

PubMed 19293145

Again, despite numerous reports of a block of alpha7, one study indicated that Abeta failed to block alpha7, even though it blocked alpha4beta2, alpha2beta2 and alpha4alpha5beta2 receptors (Lamb et al., 2005).

PubMed 19293145

It has also been observed that although Abeta inhibits recombinant human and mouse alpha7 nAChRs, transgenic mice overexpressing human Abeta express functional alpha7 nAChRs, and the amplitude of alpha7- mediated currents is no different from that of wild-type mice (Spencer et al., 2006).

BEL
a(CHEBI:"amyloid-beta") causesNoChange act(p(HGNC:CHRNA7))
Hash
aa9d820721
Species
10090
Networks

PubMed 19293145

Similar effects of Abeta on nAChR expression have been confirmed in studies using cultured cells; Abeta causes a reduced expression of nAChRs in PC12 cells (Guan et al., 2001), and alpha4, alpha3, and alpha7 expression are all increased in cultured rat astrocytes (Xiu et al., 2005).

BEL
a(CHEBI:"amyloid-beta") increases p(HGNC:CHRNA7)
Hash
c2cba8c9ef
MeSHAnatomy
Astrocytes
Species
10116
Networks

About

BEL Commons is developed and maintained in an academic capacity by Charles Tapley Hoyt and Daniel Domingo-Fernández at the Fraunhofer SCAI Department of Bioinformatics with support from the IMI project, AETIONOMY. It is built on top of PyBEL, an open source project. Please feel free to contact us here to give us feedback or report any issues. Also, see our Publishing Notes and Data Protection information.

If you find BEL Commons useful in your work, please consider citing: Hoyt, C. T., Domingo-Fernández, D., & Hofmann-Apitius, M. (2018). BEL Commons: an environment for exploration and analysis of networks encoded in Biological Expression Language. Database, 2018(3), 1–11.