Neurobiology Research Unit, University Hospital Copenhagen, Copenhagen, Denmark.
J Neurochem. 2012 Oct;123(1):73-83. doi: 10.1111/j.1471-4159.2012.07876.x. Epub 2012 Aug 16.
Long-term treatment with nicotine or selective α7 nicotinic acetylcholine receptor (nAChR) agonists increases the number of α7 nAChRs and this up-regulation may be involved in the mechanism underlying the sustained procognitive effect of these compounds. Here, we investigate the influence of type I and II α7 nAChR positive allosteric modulators (PAMs) on agonist-induced α7 nAChR up-regulation. We show that the type II PAMs, PNU-120596 (10 μM) or TQS (1 and 10 μM), inhibit up-regulation, as measured by protein levels, induced by the α7 nAChR agonist A-582941 (10 nM or 10 μM), in SH-EP1 cells stably expressing human α7 nAChR, whereas the type I PAMs AVL-3288 or NS1738 do not. Contrarily, neither type I nor II PAMs affect 10 μM nicotine-induced receptor up-regulation, suggesting that nicotine and A-582941 induce up-regulation through different mechanisms. We further show in vivo that 3 mg/kg PNU-120596 inhibits up-regulation of the α7 nAChR induced by 10 mg/kg A-582941, as measured by [(125)I]-bungarotoxin autoradiography, whereas 1 mg/kg AVL-3288 does not. Given that type II PAMs decrease desensitization of the receptor, whereas type I PAMs do not, these results suggest that receptor desensitization is involved in A-582941-induced up-regulation. Our results are the first to show an in vivo difference between type I and II α7 nAChR PAMs, and demonstrate an agonist-dependent effect of type II PAMs occurring on a much longer time scale than previously appreciated. Furthermore, our data suggest that nicotine and A-582941 induce up-regulation through different mechanisms, and that this confers differential sensitivity to the effects of α7 nAChR PAMs. These results may have implications for the clinical development of α7 nAChR PAMs.
长期使用尼古丁或选择性 α7 烟碱型乙酰胆碱受体 (nAChR) 激动剂会增加 α7 nAChR 的数量，这种上调可能与这些化合物持续的促认知作用的机制有关。在这里，我们研究了 I 型和 II 型 α7 nAChR 正变构调节剂 (PAMs) 对激动剂诱导的 α7 nAChR 上调的影响。我们表明，II 型 PAMs，PNU-120596（10 μM）或 TQS（1 和 10 μM），抑制由 α7 nAChR 激动剂 A-582941（10 nM 或 10 μM）诱导的蛋白水平上调，在稳定表达人 α7 nAChR 的 SH-EP1 细胞中，而 I 型 PAMs AVL-3288 或 NS1738 则没有。相反，I 型和 II 型 PAMs 都不影响 10 μM 尼古丁诱导的受体上调，这表明尼古丁和 A-582941 通过不同的机制诱导上调。我们进一步在体内表明，3 mg/kg PNU-120596 抑制由 10 mg/kg A-582941 诱导的 α7 nAChR 上调，如[(125)I]-金环毒素放射自显影所示，而 1 mg/kg AVL-3288 则没有。鉴于 II 型 PAMs 可减少受体的脱敏，而 I 型 PAMs 则不能，这些结果表明受体脱敏参与了 A-582941 诱导的上调。我们的结果首次表明 I 型和 II 型 α7 nAChR PAMs 之间存在体内差异，并证明了 II 型 PAMs 的激动剂依赖性效应发生在比以前认识到的更长的时间尺度上。此外，我们的数据表明，尼古丁和 A-582941 通过不同的机制诱导上调，这使得它们对 α7 nAChR PAMs 的作用具有不同的敏感性。这些结果可能对 α7 nAChR PAMs 的临床开发具有重要意义。
