類鐸受體訊息傳遞路徑參與調控瓢體蟲前端再生之研究

Abstract

受傷時為了避免嚴重感染，免疫系統及發炎反應扮演相當重要的角色，現今的研究者主張免疫系統的發展和再生能力的減弱是互為權衡下的結果，然而，關於受傷所引發的發炎反應是否真的與再生能力有相互調控之關係的研究至今依然相當有限，本研究旨在闡明並釐清類鐸受體訊息傳遞路徑(TLRs signailing pathway)如何參與並調控具有全身再生能力之淡水生環節動物瓢體蟲Aeolosoma viride前端再生，首先我詳細描述瓢體蟲前端及尾端再生的形態學變化，如芽體(blastema)、嘴以及尾板(pygidium)的形成，接著亦證實此過程是透過變形再生(epimorphosis)包含大規模的細胞增生以及極少數的細胞遷移所完成。另一方面為了使用瓢體蟲為模式研究類鐸受體訊息傳遞路徑參與再生的過程，此路徑中古老且保守的TLR、MyD88以及TNF同源基因亦從瓢體蟲中被鑑定及分析，並分別命名為Avi-TLR-a、Avi-TLR-b、Avi-MyD88-a、Avi-MyD88-i、Avi-TNF-1及Avi-TNF-2，這些基因於瓢體蟲切除頭部後大多先降低其表現量而後才又回升至未受損傷時的水平，其中只有缺少標準MyD88蛋白質序列中的TIR domain，Avi-MyD88-i，於傷口形成後立即大量提升其基因表現量並維持直至再生完成。此外使用抗生素及病原相關分子模式(PAMP)中的聚肌胞苷酸(poly I:C)進行再生實驗，亦證實可透過促進或抑制細胞增生達到調控再生成功與否的結果，使用聚肌胞苷酸可於再生過程中進行前發炎細胞激素的雙向調控，其一為透過Avi-TLR-a、Avi-MyD88-a及Avi-TNF-1的增加，其二為Avi-TLR-b、Avi-MyD88-i及Avi-TNF-2的基因表現量減少進而抑制了瓢體蟲的再生能力，再者，此雙向調控可被類鐸受體訊息傳遞路徑之抑制劑C34所恢復，利用RNA干擾減少Avi-MyD88-i表現後亦導致瓢體蟲減緩其再生速度，這些結果指出透過類鐸受體訊息傳遞路徑引發的發炎反應於再生過程中需要被正確且確實的調控，而本研究也支持了互為權衡下的免疫系統及再生能力之理論。

The immune system and inflammatory responses associated with injury to prevent deadly infection have been implicated as critical roles during wound healing and regeneration. Nowadays, some scientists have proposed that immune system has been trade-off with the capacity of regeneration in animals. However, the involvement and regulation of injury-induced inflammatory responses with regeneration remains poorly understood in invertebrates. The aim of this study is to unravel the involvement of toll-like receptors (TLRs) signaling pathway in the regeneration of Aeolosoma viride, a 3 mm long freshwater annelid with an exceptional whole body regenerative ability. I detailedly described the sequential morphological events during the process of regeneration, such as wound healing and the formation of blastema, mouth, and pygidium after amputation. Massive proliferation and the absence of cell migration indicated that the animal regenerates primarily through epimorphosis. On the other hand, the homologous genes with TLR, myeloid differentiation primary response 88 (MyD88) and tumor necrosis factor (TNF) of the ancient and conserved TLRs signaling pathway were characterized in A. viride, namely Avi-TLR-a, Avi-TLR-b, Avi-MyD88-a, Avi-MyD88-i, Avi-TNF-1 and Avi-TNF-2. The expression level of most these genes were reduced after head amputation then back to normal, but that of Avi-MyD88-I, that deficiency of toll/interleukin-1 receptor (TIR) domain, induced immediately and kept in higher level. Moreover, the inverse regulation of regeneration using either antibiotic cocktail or poly I:C, the one of PAMPs were demonstrated through increasing or suppression of cell proliferation. The opposite modulation of poly I:C affected on inflammatory responses of pro-inflammatory cytokine production have been confirmed by two directions of TLR signaling pathway in this worm. One way is to increase transcript levels of Avi-TLR-a, Avi-MyD88-a and Avi-TNF-1, the other way is to decrease gene expression of Avi-TLR-b, Avi-MyD88-i and Avi-TNF-2 during wound healing at regenerative tissues. Furthermore, this two regulations of TLR signaling pathway can be rescued by the inhibitor of TLR, C34. Also, the inhibitory effect of regeneration was showed by knockdown of Avi-MyD88-i. These results indicated the necessary management of inflammatory responses from TLR signaling pathway during A. viride regeneration. Summary, the modulation of TLR signaling pathway in this study supported the trade-off theory between immunity and regeneration.