ABSTRACT
The existence of α7ß2 nicotinic acetylcholine receptors (nAChRs) has recently been demonstrated in both the rodent and human brain. Since α7-containing nAChRs are promising drug targets for schizophrenia and Alzheimer's disease, it is critical to determine whether α7ß2 nAChRs are present in the human brain, in which brain areas, and whether they differ functionally from α7 nAChR homomers. We used α-bungarotoxin to affinity purify α7-containing nAChRs from surgically excised human temporal cortex, and found that α7 subunits co-purify with ß2 subunits, indicating the presence of α7ß2 nAChRs in the human brain. We validated these results by demonstrating co-purification of ß2 from wild-type, but not α7 or ß2 knock-out mice. The pharmacology and kinetics of human α7ß2 nAChRs differed significantly from that of α7 homomers in response to nAChR agonists when expressed in Xenopus oocytes and HEK293 cells. Notably, α7ß2 heteromers expressed in HEK293 cells display markedly slower rise and decay phases. These results demonstrate that α7 subunits in the human brain form heteromeric complexes with ß2 subunits, and that human α7ß2 nAChR heteromers respond to nAChR agonists with a unique pharmacology and kinetic profile. α7ß2 nAChRs thus represent an alternative mechanism for the reported clinical efficacy of α7 nAChR ligands.
Subject(s)
Cerebral Cortex/metabolism , Receptors, Nicotinic/metabolism , alpha7 Nicotinic Acetylcholine Receptor/metabolism , Animals , Cerebral Cortex/pathology , Gene Expression Regulation/drug effects , HEK293 Cells , Humans , Mice , Mice, Inbred C57BL , Mice, Knockout , Nicotinic Agonists/pharmacology , Nicotinic Antagonists/pharmacology , Oocytes/drug effects , Oocytes/metabolism , Patch-Clamp Techniques , Receptors, Nicotinic/deficiency , Receptors, Nicotinic/genetics , Xenopus laevis/growth & development , Xenopus laevis/metabolism , alpha7 Nicotinic Acetylcholine Receptor/deficiency , alpha7 Nicotinic Acetylcholine Receptor/geneticsABSTRACT
The Ly-6 superfamily of proteins, which affects diverse processes in the immune system, has attracted renewed attention due to the ability of some Ly-6 proteins to bind to and modulate the function of neuronal nicotinic acetylcholine receptors (nAChRs). However, there is a scarcity of knowledge regarding the distribution and developmental regulation of these proteins in the brain. We use protein cross-linking and synaptosomal fractions to demonstrate that the Ly-6 proteins Lynx1 and Ly6H are membrane-bound proteins in the brain, which are present on the cell surface and localize to synaptic compartments. We further estimate the amount of Lynx1 in the rat cortex using known amounts of a heterologously expressed soluble Lynx1 variant (ws-Lynx1) to be approximately 8.6 ng/µg total protein, which is in line with the concentrations of ws-Lynx1 required to affect nAChR function. In addition, we demonstrate that Lynx1 and Ly6H are expressed in cultured neurons, but not cultured micro- or astroglial cultures. In addition, Lynx1, but not Ly6H was detected in the CSF. Finally, we show that the Ly-6 proteins Lynx1, Lynx2, Ly6H, and PSCA, display distinct expression patterns during postnatal development in the rat frontal cortex and hippocampus at the mRNA and protein level, and that this is paralleled to some degree by the expression of the nAChR subunits α2, α4, α7 and ß2. Our results demonstrate a developmental pattern, localization, and concentration of Ly-6 proteins in the brain, which support a role for these proteins in the modulation of signaling at synaptic membranes.
