Functional evidence for physiological mechanisms to circumvent neurotoxicity of cardenolides in an adapted and a non-adapted hawk-moth species
Functional evidence for physiological mechanisms to circumvent neurotoxicity of cardenolides in an adapted and a non-adapted hawk-moth species
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DOI：
10.1098/rspb.2012.3089
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发表时间：
2013-05-22
影响因子：
4.7
通讯作者：
Dobler, Susanne
中科院分区：
文献类型：
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作者：
Petschenka, Georg;Pick, Christian;Dobler, Susanne
由于Cardenolide专门抑制Na+K+-ATPase，以含有Cardenolide的植物为食的昆虫需要绕过这种有毒影响。一些昆虫，如帝王蝶，依赖于靶点不敏感，而另一些适应隆起内酯的鳞翅目动物，如夹竹桃天蛾，具有高度敏感的Na+K+-ATPase。然而，该物种的幼虫和相关的六分叶蝉对注射的万寿菊内酯不敏感。通过对这两个物种的神经索进行放射活性结合分析，我们证明了神经组织周围的神经膜对一种极性腰果内酯(哇巴因)具有扩散屏障的作用。相比之下，对于像地高辛这样的非极性洋地黄内酯来说，主动外排载体限制了进入神经索的途径。这种屏障可以被代谢抑制剂和P-糖蛋白(PGPs)的特异性抑制剂维拉帕米消除。这支持了PGP样转运蛋白参与了主动的卡氏内酯-外膜屏障。组织特异性逆转录聚合酶链式反应证实了3个Pgp样基因在家蚕神经索中的表达，免疫组织化学进一步证实了Pgp在神经外膜中的表达。因此，我们的结果表明，鳞翅目昆虫的神经膜对极性的卡丹内酯具有扩散屏障作用，对非极性的卡丹内酯则提供了一种活性屏障。这可能解释了为什么在一些鳞翅目幼虫体内观察到对Cardenolide的高抗性，尽管它们对Na+K+-ATPase高度敏感。
Because cardenolides specifically inhibit the Na+K+-ATPase, insects feeding on cardenolide-containing plants need to circumvent this toxic effect. Some insects such as the monarch butterfly rely on target site insensitivity, yet other cardenolide-adapted lepidopterans such as the oleander hawk-moth, Daphnis nerii, possess highly sensitive Na+K+-ATPases. Nevertheless, larvae of this species and the related Manduca sexta are insensitive to injected cardenolides. By radio-active-binding assays with nerve cords of both species, we demonstrate that the perineurium surrounding the nervous tissue functions as a diffusion barrier for a polar cardenolide (ouabain). By contrast, for non-polar cardenolides such as digoxin an active efflux carrier limits the access to the nerve cord. This barrier can be abolished by metabolic inhibitors and by verapamil, a specific inhibitor of P-glycoproteins (PGPs). This supports that a PGP-like transporter is involved in the active cardenolide-barrier of the perineurium. Tissue specific RT-PCR demonstrated expression of three PGP-like genes in hornworm nerve cords, and immunohistochemistry further corroborated PGP expression in the perineurium. Our results thus suggest that the lepidopteran perineurium serves as a diffusion barrier for polar cardenolides and provides an active barrier for non-polar cardenolides. This may explain the high in vivo resistance to cardenolides observed in some lepidopteran larvae, despite their highly sensitive Na+K+-ATPases.