Elsevier

Neuroscience

Volume 137, Issue 3, 2006, Pages 795-805
Neuroscience

Cellular neuroscience
Transgenic mice over-expressing human β-amyloid have functional nicotinic alpha 7 receptors

https://doi.org/10.1016/j.neuroscience.2005.10.007Get rights and content

Abstract

A potentially major factor in the development of Alzheimer’s disease is the enhanced production of soluble β-amyloid peptide fragments amyloid β peptide1–40 and amyloid β peptide1–42. These amyloid peptides are generated by cleavage of the amyloid-precursor protein and aggregate spontaneously to form amyloid plaques, which are a classical pathological hallmark in Alzheimer’s disease. Although the precise mechanisms are unknown, it is widely believed that amyloid peptides initiate the degenerative process, resulting in subsequent cognitive decline. One interaction of amyloid β peptide that may contribute to an impairment of cognition is its high affinity binding to the alpha 7 nicotinic receptor; a receptor shown to be important for cognition in a number of studies. There is some controversy, however, whether amyloid β peptide inhibits or activates this receptor. We have cloned and stably expressed the human alpha 7 receptor and investigated its interaction with amyloid β peptide using patch clamp electrophysiology. Human alpha 7 was activated in a concentration-dependent fashion by nicotine, acetylcholine and choline and potently inhibited by methyllycaconitine citrate. The responses were inwardly rectifying and exhibited rapid activation, desensitization and deactivation. Amyloid β peptide1–42 antagonized human α7 responses in a partially reversible fashion; no agonist effects of amyloid β peptide1–42 were detected. A similar inhibition of mouse alpha 7 was also observed. In addition, we have assessed the function of native alpha 7 receptors in hippocampal slices prepared from transgenic mice that over-express human amyloid. Despite this clear inhibition of recombinant receptors, hippocampal GABAergic interneurones in slices from β-amyloid over-expressing mice still possess alpha 7 receptor-mediated currents.

Section snippets

Cloning of human and mouse nicotinic α7 receptors

A human α7 nicotinic acetylcholine (ACh) receptor cDNA, corresponding to GenBank accession number U62436 (Elliott et al., 1996) with the exception of a single silent base pair substitution, was isolated from a human cerebellum library and subcloned into the PvuII site of the episomal vector pCEP4 (Invitrogen Ltd., Paisley, UK). The resulting expression construct was transfected into the rat pituitary tumor GH4C1 cell line (European Collection of Cell Cultures, Salisbury, UK) as described

Nicotinic α7 receptors expressed in GH4C1 cells

We initially characterized the basic response properties of the human α7 receptor using whole-cell patch clamp recordings (Vhold −74 mV) from GH4C1 cells stably expressing an appropriate construct. In response to 250 ms challenges with high concentrations of either ACh (300–1000μM) or nicotine (100μM), these cells typically exhibited rapidly and almost completely desensitizing inward currents, with an average amplitude of around 1 nA. Choline was also found to be an effective agonist albeit at

Discussion

In support of previous data reporting an inhibitory activity of Aβ peptide on both recombinant and native α7 receptors (Liu et al 2001, Pettit et al 2001, Tozaki et al 2002, Lee and Wang 2003), we have found that human Aβ1–42 can inhibit human α7 receptors stably expressed in a GH4C1 cell line. Given that AD, and the associated accumulation of Aβ, is a condition suffered by more than 20 million humans we feel these data are a useful extension to the previous important work performed on

Conclusions

In conclusion, we have confirmed that the human amyloid peptide is capable of inhibiting recombinant human and mouse α7 receptors. In contrast we are unable to identify a correlate of this inhibition in a transgenic mouse model of AD. Thus, we suggest that postsynaptic α7 receptors on hippocampal interneurones may be spared from any significant inhibition by excess Aβ. Furthermore, the fact that we never observe a complete block of α7 receptors by Aβ in the recombinant cell lines does suggest

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