Apolipoprotein E-Derived Peptides Block α7 Neuronal Nicotinic Acetylcholine Receptors Expressed inXenopusOocytes

Abstract

For decades, the pathology of Alzheimer's disease has been associated with dysfunction of cholinergic signaling; however, the cellular mechanisms by which nicotinic acetylcholine receptor (nAChR) function is impaired in Alzheimer's disease are as yet unknown. The most significant genetic risk factor for the development of Alzheimer's disease is inheritance of the ⑀4 allele of apolipoprotein E (apoE). Recent data have demonstrated the ability of apoE-derived peptides to inhibit nAChRs in rat hippocampus. In the current study, the functional interaction between nAChRs and apoE-derived peptides was investigated in Xenopus oocytes expressing selected nAChRs. Both a 17-amino acid peptide fragment, apoE [133][134][135][136][137][138][139][140][141][142][143][144][145][146][147][148][149] , and an eight-amino acid peptide, apoE 141-148 , were able to maximally block acetylcholine (ACh)-mediated peak current responses for homomeric ␣7 nAChRs. ApoE peptide inhibition was dose-dependent and voltage-and activity-independent. The current findings suggest that apoE peptides are noncompetitive for acetylcholine and do not block functional ␣-bungarotoxin binding. ApoE peptides had a significantly decreased ability to inhibit ACh-mediated peak current responses for ␣4␤2 and ␣2␤2 nAChRs. Amino acid substitutions in the apoE peptide sequence suggest that the arginines are critical for peptide blockade of the ␣7 nAChR. The current data suggest that apoE fragments can disrupt nAChR signaling through a direct blockade of ␣7 nAChRs. These results may be useful in elucidating the mechanisms underlying memory loss and cognitive decline seen in Alzheimer's disease as well as aid in the development of novel therapeutics using apoE-derived peptides.

Structural Determinates for Apolipoprotein E-Derived Peptide Interaction with the α7 Nicotinic Acetylcholine Receptor

“…As previously reported (Gay et al, 2006), the eight-aminoacid peptide apoE 141-148 (3 M, near maximal inhibition) significantly reduced the amplitude of wild-type ␣7 nAChR-mediated responses by 78 Ϯ 3% (Table 1, Fig. 2A).…”

“…Previous studies indicated that a synthetic apoE peptide, containing the low-density lipoprotein receptor binding region, can inhibit ␣7 nAChR-mediated ACh-induced currents through a direct interaction. In addition, previous functional data suggest that this peptide/receptor interaction is noncompetitive with ␣-BgTx blockade and possibly ACh gating of the receptor (Gay et al, 2006). Direct binding experiments using ␣-BgTx were carried out to determine whether apoE 141-148 binds competitively with the toxin.…”

“…It had been demonstrated (Gay et al, 2006) that when the two positively charged lysines (at positions 143 and 146) of apoE 141-148 were substituted with leucines (which will be referred to as apoE 141-148 2K/2L), this new peptide was able to inhibit ACh-induced current responses similarly to apoE [141][142][143][144][145][146][147][148] . However, this change dramatically decreased the rate of block (Gay et al, 2006). In the current study, we tested the ability of apoE 141-148 2K/2L to inhibit the ␣7-W55A nAChR.…”

“…In addition, treatment with apoE mimetic peptides reduces the clinical symptoms of experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis, as well as reducing demyelination and inflammation (Li et al, 2006). We have demonstrated that apoE-derived peptides can inhibit nAChRs expressed on interneurons in rat hippocampal slices, as well as ␣7 receptors expressed in Xenopus laevis oocytes, indicating a possible direct interaction between apoE and nAChRs (Klein and Yakel, 2004;Gay et al, 2006).…”

Nicotinic Acetylcholine Receptor Signalling: Roles in Alzheimer's Disease and Amyloid Neuroprotection

“…An APOE-derived peptide blocks nAChRs on rat hippocampal slices with a submicromolar affinity, and this action is dependent on an arginine-rich segment of the APOE peptide (Klein and Yakel, 2004). Block of heterologously expressed ␣7 nAChRs is greater than that for ␣4␤2 or ␣2␤2 nAChRs (Gay et al, 2006). This block of ␣7 receptors is abolished when ␣7 Trp55 is mutated to alanine, providing strong evidence that it results from a direct interaction between the peptide and the receptors (Gay et al, 2007), and the effects of other substitutions of Trp55 suggests that this interaction is hydrophobic.…”