Elsevier

Neuroscience

Volume 110, Issue 2, 12 March 2002, Pages 199-211
Neuroscience

Intracellular accumulation of β-amyloid1–42 in neurons is facilitated by the α7 nicotinic acetylcholine receptor in Alzheimer’s disease

https://doi.org/10.1016/S0306-4522(01)00460-2Get rights and content

Abstract

Amyloid β1–42, a major component of amyloid plaques, binds with exceptionally high affinity to the α7 nicotinic acetylcholine receptor and accumulates intracellularly in neurons of Alzheimer’s disease brains. In this study, we investigated the possibility that this binding plays a key role in facilitating intraneuronal accumulation of amyloid β1–42. Consecutive section immunohistochemistry and digital imaging were used to reveal the spatial relationship between amyloid β1–42 and the α7 receptor in affected neurons of Alzheimer’s disease brains. Results showed that neurons containing substantial intracellular accumulations of amyloid β1–42 invariably express relatively high levels of the α7 receptor. Furthermore, this receptor is highly co-localized with amyloid β1–42 within neurons of Alzheimer’s disease brains. To experimentally test the possibility that the binding interaction between exogenous amyloid β1–42 and the α7 receptor facilitates internalization and intracellular accumulation of amyloid β1–42 in Alzheimer’s disease brains, we studied the fate of exogenous amyloid β1–42 and its interaction with the α7 receptor in vitro using cultured, transfected neuroblastoma cells that express elevated levels of this receptor. Transfected cells exhibited rapid binding, internalization and accumulation of exogenous amyloid β1–42, but not amyloid β1–40. Furthermore, the rate and extent of amyloid β1–42 internalization was related directly to the α7 receptor protein level, since (1) the rate of amyloid β1–42 accumulation was much lower in untransfected cells that express much lower levels of this receptor and (2) internalization was effectively blocked by α-bungarotoxin, an α7 receptor antagonist. As in neurons of Alzheimer’s disease brains, the α7 receptor in transfected cells was precisely co-localized with amyloid β1–42 in prominent intracellular aggregates. Internalization of amyloid β1–42 in transfected cells was blocked by phenylarsine oxide, an inhibitor of endocytosis.

We suggest that the intraneuronal accumulation of amyloid β1–42 in Alzheimer’s disease brains occurs predominantly in neurons that express the α7 receptor. In addition, internalization of amyloid β1–42 may be facilitated by the high-affinity binding of amyloid β1–42 to the α7 receptor on neuronal cell surfaces, followed by endocytosis of the resulting complex. This provides a plausible explanation for the selective vulnerability of neurons expressing the α7 receptor in Alzheimer’s disease brains and for the fact that amyloid β1–42 is the dominant amyloid β peptide species in intracellular accumulations and amyloid plaques.

Section snippets

Tissue samples

Post-mortem brain tissues (entorhinal cortex and hippocampus) from patients with clinically diagnosed sporadic AD (n=62, age range=72–78) and control tissues from normal, age-matched, neurologically normal (n=20, age range=69–76) individuals were obtained from the Harvard Brain Tissue Resource Center (HBTRC, Belmont, MA, USA) and Analytical Biological Services (Wilmington, DE, USA) and fixed in a 10% neutral buffered formalin solution. The HBTRC is supported in part by a Public Health Service

1–42 accumulates intracellularly in AD brains and is abundant in APs

Immunohistochemistry using three different Aβ42-specific antibodies revealed that APs were the most prominent Aβ42-positive feature in AD brains (Fig. 1A), but were generally lacking in most age-matched control brains (Fig. 1B). APs were also conspicuously absent from the molecular layer of the entorhinal cortex of AD brains, which contains primarily the dendritic trees of pyramidal neurons and is largely devoid of their associated perikarya (Fig. 1A). In addition to APs, Aβ42 was highly

Discussion

Recent work has suggested that Aβ42 first accumulates intracellularly, rather than extracellularly, and that pyramidal neurons are primary targets in the entorhinal cortex and hippocampus of AD brains (Gouras et al., 2000, D’Andrea et al., 2001). Furthermore, we have provided strong evidence that Aβ42-burdened cells eventually undergo lysis in AD brains and that each neuronal lysis event may correspond to the formation of a single AP (D’Andrea et al., 2001, Wang et al., 2001). Since pyramidal

Conclusions

Although binding of Aβ peptides to the α7nAChR may also alter calcium ion influx and acetylcholine release, our results point to an important role for the α7nAChR in facilitating the entry and intraneuronal accumulation of Aβ42 via endocytosis. Thus, the interaction of these two proteins may represent a key step in the pathogenesis of AD. This study demonstrates that the neuronal expression of the α7nAChR is strongly correlated with the rate and extent of Aβ42 accumulation. The high-affinity

Acknowledgements

The authors wish to thank Dr. Daniel H.S. Lee for the use of the transfected SK-N-MC cells. This work was supported in part by a grant from the National Institute on Aging (AG00925).

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