秀麗隱桿線蟲中微量無機四價硒有益效應之調控分析

Regulatory analyses of the beneficial effects by trace amount of selenite in Caenorhabditis elegans

李汶軒(Wen-Hsuan Li)

指導教授 ： 廖秀娟

國立臺灣大學/生物資源暨農學院/生物環境系統工程學研究所/博士(2014年)

https://doi.org/10.6342/NTU.2014.11200

摘要

作為一微量必需元素，硒參與許多重要之細胞反應，且在維持良好健康上極其重要。雖然硒之許多有益效應皆已被發現，其所參與之調控機制至今仍不明確。故本論文以Caenorhabditis elegans (C. elegans)作為模式生物，探討微量元素硒對生物體的有益效應及其調控機制，包括以下3個研究目標：(1) 微量無機四價硒的抗氧化活性及相關機制；(2) 微量無機四價硒對神經毒物(鉛)所誘導毒性之保護能力；及(3) 微量無機四價硒對人類致病菌(綠膿桿菌P. aerugonisa)所造成之免疫反應與相關調節機制。
根據研究目標1的研究結果顯示，微量無機四價硒(0.01 μM)暴露之C. elegans相較於未暴露之控制組，於氧化壓力與高溫壓力下具有較高之存活率。進一步的研究顯示，微量無機四價硒對C. elegans所造成之顯著壓力抗性可歸因於其自由基去除力。本研究亦發現此壓力抗性之現象於C. elegans之daf-16轉錄因子突變株中不存在。再者，無機四價硒可影響C. elegans細胞內DAF-16的分佈，並可提升超氧化物歧化酶(SOD-3)和熱擊蛋白(HSP-16.2)之mRNA表達。此外，0.01 μM硒亦可提升基因轉殖C. elegans中之SOD-3綠色螢光蛋白與HSP-16.2綠色螢光蛋白表達，但是此影響可透過於C. elegans中以daf-16 RNA干擾而消失。最後，不像野生株N2，無機四價硒所提供之氧化壓力抗性，無法發生於缺乏硒蛋白TRXR-1之C. elegans或trxr-1突變株，並佐以daf-16 RNA干擾之C. elegans中存在。此結果說明，微量無機四價硒於C. elegans之抗氧化效應，需透過DAF-16和TRXR-1蛋白進行調控。
研究目標2則探討無機四價硒在C. elegans中抵抗重金屬鉛所誘導神經毒性之保護潛力。結果顯示，微量無機四價硒(0.01 μM)的暴露，可以緩和高濃度鉛的毒害(100 μM)對於C. elegansn所造成之移動行為衰退(frequencies of body bends、head thrashes和reversal)。在鉛暴露前，以無機四價硒的補充可以顯著的降低C. elegans體內鉛所誘導之活性氧程度。最後，微量無機四價硒可以保護AFD感受神經元免於鉛誘導之毒性。本研究結果說明，微量無機四價硒透過其抗氧化特性而具有保護特性以對抗鉛誘導之神經毒性。
在研究目標3中，以C. elegans對於綠膿桿菌PA14之反應來探討微量無機四價硒於生物體之免疫效應。研究結果發現，在PA14感染情況下，相較於無暴露之控制組，微量硒暴露之C. elegans具有顯著增加的存活率。微量無機四價硒對於PA14之quorum sensing與其他致病因子並無影響，此結果說明硒於C. elegans之病原菌抗性並非來自於硒對綠膿桿菌之影響。研究結果更進一步顯示，微量無機四價硒可增強C. elegans自然免疫中關鍵基因的表達。此外，研究亦發現無機四價硒所引起之病原菌抵抗力不存在於skn-1突變株。再者，在PA14感染下，硒可以影響C. elegans細胞內SKN-1/Nrf轉錄因子之分佈，以及提升其下游目標基因(gst-4和gcs-1)之mRNA表達。本研究證明，微量無機四價硒可經由調控SKN-1訊息傳遞路徑和影響C. elegans之自然免疫，而使C. elegans可抵抗綠膿桿菌PA14之感染。
本研究論文結果顯示，微量的無機四價硒可以： (1) 透過DAF-16轉錄因子與TRXR-1硒蛋白，調節C. elegans之抗氧化反應以抵抗氧化壓力；(2) 透過抗氧化活性，使C. elegans得以抵抗鉛所誘導之神經毒性；及(3) 經由SKN-1轉錄因子與提升C. elegans之免疫抗性用，以抵抗綠膿桿菌之感染。由本論文的研究結果顯示，微量元素無機四價硒經由調控壓力相關或免疫相關基因的活化，提供C. elegans在抗氧化防禦系統、神經系統、與免疫系統之有益效應。

關鍵字

硒 ； C. elegans ； 抗氧化 ； 神經保護 ； 免疫 ； DAF-16轉錄因子 ； TRXR-1硒蛋白 ； SKN-1轉錄因子

並列摘要

Selenium (Se), an essential trace element, is involved in many important cell processes and is vital for health. Although several beneficial effects of Se have been described, the associated regulatory mechanisms by Se remain further eluciared. The goal of this dissertion is to investigate the beneficial effects of Se and its associated regulatory mechanisms in Caenorhabditis elegans. There are 3 specific aims in this study: (1) the antioxidant activities of selenite (Se(IV)) and its related mechanisms; (2) the neuroprotective activities of (Se(IV)) against the neurotoxin (i.e., lead); and (3) the effects of (Se(IV)) on immune systems against human pathogen Pseudomonas aeruginosa PA14 and its related mechanisms.
For specific aim 1, trace amount of Se(IV)-treated (0.01 μM) C. elegans showed an increased survival under oxidative stress and thermal stress compared to untreated controls. Further studies demonstrated that the significant stress resistance of Se(IV) on C. elegans could be attributable to its in vivo free radical-scavenging ability. The oxidative and thermal stress resistance phenotypes by Se(IV) were also found to be absent from the forkhead transcription factor daf-16 mutant worms. Moreover, Se(IV) influenced the subcellular distribution of DAF-16 in C. elegans. Furthermore, Se(IV) increased mRNA levels of stress-resistance-related proteins, including superoxide dismutase-3 and heat shock protein-16.2. Additionally, Se(IV) (0.01 μM) upregulated expressions of transgenic C. elegans carrying sod-3::green fluorescent protein (GFP) and hsp-16.2::GFP, whereas this effect was abolished by feeding daf-16 RNA interference in C. elegans. Finally, unlike the wild-type N2 worms, the oxidative stress resistance phenotypes by Se(IV) were both absent from the C. elegans selenoprotein trxr-1 mutant worms and trxr-1 mutants feeding with daf-16 RNA interference. These findings suggest that the antioxidant effects of Se(IV) in C. elegans are mediated via DAF-16 and TRXR-1.
For specific aim 2, the study investigated the protective potential of selenite (IV) against lead (Pb(II))-induced neurotoxicity in C. elegans. The results showed that Se(IV) (0.01 μM) pretreatment ameliorated the decline of locomotion behaviors (frequencies of body bends, head thrashes, and reversal ) of C. elegans that are damaged by Pb(II) (100 μM) exposure. The intracellular ROS level of C. elegans induced by Pb(II) exposure was significantly lowered by Se(IV) supplementation prior to Pb exposure. Finally, Se(IV) protects AFD sensory neurons from Pb(II)-induced toxicity. Our study suggests that Se(IV) has protective activities against Pb(II)-induced neurotoxicity through its antioxidant property.
For specific aim 3, the immune effects of Se(IV) were investigated by examining the responses of C. elegans to P. aerugonisa PA14 strain. Se(IV)-treated C. elegans showed increased survival under PA14 infection compared with untreated controls. The significant pathogen resistance of Se(IV) on C. elegans might not be attributable to the effects of Se(IV) on PA14 as Se(IV) showed no effect on bacterial quorum-sensing and virulence factors of PA14. This study showed that Se(IV) enhanced the expression of a gene pivotal for the innate immunity in C. elegans. The study found that the pathogen-resistant phenotypes contributed by Se(IV) was absent from the skn-1 mutant worms. Moreover, Se(IV) influenced the subcellular distribution of SKN-1/Nrf in C. elegans upon PA14 infection. Furthermore, Se(IV) increased mRNA levels of SKN-1 target genes (gst-4 and gcs-1). This study found evidence of Se(IV) protecting C. elegans against P. aeruginosa PA14 infection by exerting effects on the innate immunity of C. elegans that is likely to be mediated via regulation of a SKN-1-dependent signaling pathway.
In conclusion, results in this dissertion showed that trace amount of Se(IV) can: (1) protect C. elegans from oxidative stress via DAF-16 and TRXR-1; (2) provide protection against lead-induced neurotoxicity in C. elegans; and (3) enhance immune responses against P. aeruginosa PA14 infection via SKN-1 in C. elegans. This dissertion demonstrates that (Se(IV)) modulates activation of stress-related or immune-related genes to offer beneficial effects on C. elegans in antioxidant defense systems, nerve systems, and immune systems.

並列關鍵字

Selenium ； Caenorhabditis elegans ； antioxidant ； neuroprotective ； immune ； DAF-16 ； TRXR-1 ； SKN-1

參考文獻

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