Caenorhabditis elegans碳酸氫鹽傳輸蛋白ABTS-1之功能探討

Abstract

砷是一種自然存在的毒性物質，其毒性危性危害了世界上許多的人，而在文獻中指出砷毒性可能會影響神經系統的病變，但是關於砷對神經系統的影響卻沒有太多的資料，而在目前的研究中，砷對神經系統的影響已經在線蟲中被研究。砷也是一種可以誘導產生活性氧分子的化學物質，我們在線蟲中發現一種依賴鈉離子來傳輸氯離子跟碳酸氫根離子的傳輸蛋白：ABTS-1，這個傳輸蛋白可以保護線蟲去抵抗砷所造成的毒性。此外，基因轉殖的線蟲abts-1::GFP也顯示出abts-1主要表達在蟲體的神經元以及皮下組織，但是在經過砷的暴露之後，在咽喉以及體壁肌肉細胞有更加明顯的表達；相反的，在短暫的暴露juglone誘導所產生的氧化壓力後，咽喉及體壁肌肉細胞的表達卻有明顯的下降，而基因轉殖線蟲在暴露砷之後，與未暴露的線蟲比較起來，其mRNA的表達也有顯著的上升。此外缺少abts-1的線蟲對於神經干擾物質aldicarb及levamisole造成的癱瘓也相當的敏感，若是環境中有砷的影響之下，癱瘓的速度會更加的明顯。另外，對於abts-1突變或者是基因表達被抑制的線蟲，比起正常的線蟲有著更長的生命；同樣的，我們發現在缺乏abts-1的線蟲對於氧化壓力有著較高的抵抗力，而這兩個影響可能都與胰島素信號通路的調控有關聯，砷造成的毒性可能藉由其他機制的傷害而非砷誘導的氧化壓力。最後，我們指出砷、胰島素信號通路以及碳酸氫鹽傳輸蛋白ABTS-1可能存在著相互影響的關係。

Arsenic poisoning affects millions of people worldwide. Although there is evidence to suggest that the nervous system is a target of arsenic, relatively little information is known regarding its effects on nervous system. The effects of arsenite on the nervous system in Caenorhabditis elegans were investigated in the present study. Arsenic is also a chemical which can induce the generation of reactive oxygen species. We found that abts-1, which encodes a Na+-dependent Cl－/HCO3－ transporter, is required to protect C. elegans from arsenite toxicity. The transgenic strain abts-1::GFP showed the expression of abts-1 is primarily on the neurons and the hypodernis, but stronger expression was also found in the pharynx and body wall muscle cells after exposure to arsenite. On the contrary, the level of GFP decreased after exposing to juglone. The mRNA expression of abts-1 in transgenic strain increased after arsenite exposure comparing to those unexposed animals. We showed that worms lacking of abts-1 is hypersensitive to the paralytic effects of the cholinesterase inhibitor, aldicarb, and the nicotinic acetylcholine receptor agonist, levamisole. Arsenic exposure can enhance the effect to aldicarb and levamisole in abts-1 mutant worms. Moreover, we showed that abts-1 mutants and RNAi-mediated abts-1 knockdown worms have an increase in life span comparing to wild-type worms, and the regulation between abts-1 and insulin signaling. We also showed that lacking of abts-1 can resist to juglone-induced oxidative stress, which might be regulated by insulin signaling pathway. It means that the function of abts-1 to protect C. elegans from arsenite toxicity is not by decreasing the arsenite-induced oxidative stress. Our results indicate the effects of arsenite, insulin/IGF-1 signaling, and the ABTS-1 bicarbonate transporter.