CSIRO Animal, Food and Health Sciences, 306 Carmody Rd., St. Lucia, Brisbane QLD 4067, Australia ; School of Veterinary Science, University of Queensland, Gatton QLD 4341, Australia.
School of Veterinary Science, University of Queensland, Gatton QLD 4341, Australia.
Int J Parasitol Drugs Drug Resist. 2013 Feb 1;3:51-8. doi: 10.1016/j.ijpddr.2013.01.002. eCollection 2013 Dec.
The mechanism of resistance to the anthelmintic levamisole in parasitic nematodes is poorly understood, although there is some evidence implicating changes in expression of nicotinic acetylcholine receptor (nAChR) subunit genes. Hence, in order to define levamisole resistance mechanisms in some Australian field-derived isolates of Haemonchus contortus we examined gene expression patterns and SNPs in nAChR subunit genes, as well as expression levels for P-glycoprotein (P-gp) and receptor ancillary protein genes, in various life stages of one levamisole-sensitive and three levamisole-resistant isolates of this species. Larvae of two isolates showed high-level resistance to levamisole (resistance ratios at the IC50 > 600) while the third isolate showed a degree of heterogeneity, with a resistance factor of only 1.1-fold at the IC50 alongside the presence of a resistant subpopulation. Transcription patterns for nAChR subunit genes showed a great degree of variability across the different life stages and isolates. The most consistent observation was the down-regulation of Hco-unc-63a in adults of all resistant isolates. Transcription of this gene was also reduced in the L3 stage of the two most resistant isolates, highlighting its potential as a resistance marker in the readily accessible free-living stages. There was down regulation of all four Hco-unc-29 paralogs in adults of one resistant isolate. There were no consistent changes in expression of P-gps or ancillary protein genes across the resistant isolates. The present study has demonstrated a complex pattern of nAChR subunit gene expression in H. contortus, and has highlighted several instances where reduced expression of subunit genes (Hco-unc-63a, Hco-unc-29) may be associated with the observed levamisole resistance. The data also suggests that it will be difficult to detect resistance using gene transcription-based methods on pooled larval samples from isolates containing only a resistant subpopulation due to the averaging of gene expression data across the whole population.
抗蠕虫药左旋咪唑在寄生性线虫中的耐药机制尚不清楚，尽管有一些证据表明烟碱型乙酰胆碱受体（nAChR）亚基基因的表达发生了变化。因此，为了确定一些澳大利亚田间分离的捻转血矛线虫对左旋咪唑的耐药机制，我们检查了 nAChR 亚基基因的基因表达模式和 SNP，以及 P-糖蛋白（P-gp）和受体辅助蛋白基因的表达水平，在该物种的三个左旋咪唑敏感和三个左旋咪唑耐药分离株的各个生活阶段。两个分离株的幼虫对左旋咪唑表现出高水平的耐药性（IC50 处的耐药比值>600），而第三个分离株表现出一定程度的异质性，IC50 处的耐药因子仅为 1.1 倍，同时存在耐药亚群。nAChR 亚基基因的转录模式在不同的生活阶段和分离株之间表现出很大的变异性。最一致的观察结果是所有耐药分离株的成虫中 Hco-unc-63a 的下调。两个最耐药的分离株的 L3 阶段也降低了该基因的转录，这突出了它作为易于获得的自由生活阶段的耐药标记的潜力。一个耐药分离株的成虫中所有四个 Hco-unc-29 基因都下调。在耐药分离株中，P-gp 或辅助蛋白基因的表达没有一致的变化。本研究表明，捻转血矛线虫的 nAChR 亚基基因表达存在复杂模式，并强调了几个亚基基因（Hco-unc-63a、Hco-unc-29）表达降低可能与观察到的左旋咪唑耐药有关的实例。数据还表明，由于整个种群的基因表达数据的平均化，使用仅包含耐药亚群的分离株的幼虫混合样本进行基因转录为基础的方法很难检测到耐药性。
