摘要

最近引起了全球范围内对环境中微塑料污染增加的担忧。已经充分研究了通过生物群（包括淡水浮游动物）摄取微塑料，然而，尽管淡水食物网中存在关键物种，但响应于微塑料的浮游动物的分子响应（例如氧化防御）仍处于初期阶段。硫氧还蛋白（TRx）系统通过消除过量产生活性氧（ROS）而在细胞抗氧化防御中具有重要功能。因此，有必要研究硫氧还蛋白还原酶（TRxR）的作用，因为它触发了TRx催化级联反应。本研究首次在Daphnia magna（Dm-TRxR）中鉴定出TRxR，发现全长cDNA长1862 bp，含有1821 bp的开放阅读框。同源比对显示存在保守的催化结构域CVNVGC和位于N-和C-末端部分的选择性半胱氨酸（SeCys）残基（U）。随后，在暴露于四种（1.25-μm）聚苯乙烯（PS）微珠浓度：0（对照）后，通过定量实时PCR的方法研究Dm-TRxR与通透酶，精氨酸激酶（AK）的表达， 2,4和8毫克L-1，持续10天。暴露于2,4 mg L-1 PS后，Dm-TRxR，通透酶和AK mRNA显着上调，但在8 mg L-1 PS存在下则下降。基因表达结果表明，微弹性暴露可显着调节氧化防御，能量产生和物质细胞外运输。总的来说，本研究将提高我们对微弹性污染对浮游动物的生物学影响的认识，并为淡水环境研究建立微塑料机械和生化反应的基础。

Global scale concerns regarding rise in microplastics pollution in the environment have recently aroused. Ingestion of microplastics by biota, including freshwater zooplankton has been well studied, however, despite keystone species in freshwater food webs, the molecular response (e.g. oxidative defense) of zooplankton in response to microplastics is still in its infancy. The thioredoxin (TRx) system has a vital function in cellular antioxidative defense via eliminating the excessive generation of reactive oxygen species (ROS). Therefore, it is necessary to investigate the effects of thioredoxin reductase (TRxR), due to its triggering the TRx catalysis cascade. The present study identified TRxR in Daphnia magna (Dm-TRxR) for the first time, and found that the full-length cDNA was 1862 bp long, containing an 1821-bp open reading frame. Homologous alignments showed the presence of conserved catalytic domain CVNVGC and the seleocysteine (SeCys) residue (U) located in the N- and C- terminal portions. Subsequently, the expression of Dm-TRxR, together with permease, arginine kinase (AK), was investigated by approach of quantitative real-time PCR after exposure to four (1.25-μm) polystyrene (PS) microbeads concentrations: 0 (control), 2, 4 and 8 mg L-1 for 10 days. Dm-TRxR, permease and AK mRNA were significantly upregulated after exposure to 2, 4 mg L-1 of PS, but then declined in the presence of 8 mg L-1 PS. The gene expression results suggested that oxidative defense, energy production and substance extra cellular transportation were significantly regulated by microplastic exposure. Collectively, the present study will advance our knowledge regarding the biological effects of microplastic pollution on zooplankton, and builds a foundation for freshwater environmental studies on mechanistic and biochemical responses to microplastics.

https://www.ncbi.nlm.nih.gov/pubmed/30639982