Department of Anesthesiology and Intensive Care Medicine, Charité Campus Benjamin Franklin, Freie Universität Berlin, Berlin, Germany.
PLoS One. 2013 Nov 27;8(11):e79121. doi: 10.1371/journal.pone.0079121. eCollection 2013.
While humans and most animals respond to µ-opioid receptor (MOR) agonists with analgesia and decreased aggression, in the naked mole rat (NMR) opioids induce hyperalgesia and severe aggression. Single nucleotide polymorphisms in the human mu-opioid receptor gene (OPRM1) can underlie altered behavioral responses to opioids. Therefore, we hypothesized that the primary structure of the NMR MOR may differ from other species. Sequencing of the NMR oprm1 revealed strong homology to other mammals, but exposed three unique amino acids that might affect receptor-ligand interactions. The NMR and rat oprm1 sequences were cloned into mammalian expression vectors and transfected into HEK293 cells. Radioligand binding and 3'-5'-cyclic adenosine monophosphate (cAMP) enzyme immunoassays were used to compare opioid binding and opioid-mediated cAMP inhibition. At normalized opioid receptor protein levels we detected significantly lower [3H]DAMGO binding to NMR compared to rat MOR, but no significant difference in DAMGO-induced cAMP inhibition. Strong DAMGO-induced MOR internalization was detectable using radioligand binding and confocal imaging in HEK293 cells expressing rat or NMR receptor, while morphine showed weak or no effects. In summary, we found minor functional differences between rat and NMR MOR suggesting that other differences e.g. in anatomical distribution of MOR underlie the NMR's extreme reaction to opioids.
当人类和大多数动物对 μ 阿片受体 (MOR) 激动剂产生镇痛和减少攻击性反应时，裸鼹鼠 (NMR) 中的阿片类药物却会引起痛觉过敏和严重的攻击性反应。人类 μ 阿片受体基因 (OPRM1) 的单核苷酸多态性可能导致对阿片类药物的行为反应发生改变。因此，我们假设 NMR MOR 的主要结构可能与其他物种不同。对 NMR oprm1 的测序结果显示，其与其他哺乳动物具有很强的同源性，但暴露了三个可能影响受体-配体相互作用的独特氨基酸。NMR 和大鼠 oprm1 序列被克隆到哺乳动物表达载体中，并转染到 HEK293 细胞中。放射性配体结合和 3'-5'-环磷酸腺苷 (cAMP) 酶免疫测定用于比较阿片类药物结合和阿片类药物介导的 cAMP 抑制作用。在归一化的阿片受体蛋白水平上，我们检测到与大鼠 MOR 相比，NMR 中 [3H]DAMGO 的结合显著降低，但 DAMGO 诱导的 cAMP 抑制没有显著差异。在表达大鼠或 NMR 受体的 HEK293 细胞中，使用放射性配体结合和共聚焦成像检测到 DAMGO 诱导的强烈 MOR 内化，而吗啡表现出较弱或没有作用。总之，我们发现大鼠和 NMR MOR 之间存在较小的功能差异，这表明其他差异，例如 MOR 在解剖分布上的差异，是 NMR 对阿片类药物产生极端反应的基础。
