National Fisheries Research & Development Institute, #707 Eulwang dong, Jung-gu, Incheon, Republic of Korea.
BMC Immunol. 2011 Dec 30;12:70. doi: 10.1186/1471-2172-12-70.
The prophenoloxidase-activating (PO activating) system plays an important role in the crustacean innate immunity, particularly in wound healing and pathogen defense. A key member of this system is prophenoloxidase-activating enzyme (PPAE), which is the direct activator of prophenoloxidase (proPO). Despite their importance in crustacean PO activating system, the studies on them remain limited.
Here we report on a PPAE of white shrimp, Litopenaeus vannamei (lvPPAE1), which showed 94% similarity to PPAE1 of Penaeus monodon. We found that lvPPAE1 in fluid hemocytes was down regulated after challenge by Vibrio harveyi but was enhanced when shrimps were exposed to a bacteria-rich environment for long-term. In vivo gene silence of lvPPAE1 by RNAi can significantly reduce the phenoloxidase activity (PO) and increase the susceptibility of shrimps to V. harveyi. Although lvPPAE1 was down-regulated in fluid hemocytes by Vibrio challenge, its expression increased significantly in gill after bacteria injection, which is the primary bacteria-clearance tissue.
Suppressed expression in fluid hemocytes and enhanced expression in gill indicates selectively enhanced expression at the bacterial clearance site. This is a novel feature for PPAE expression. The results will contribute to our understanding of the PO activating system in crustaceans.
酚氧化酶原激活（PO 激活）系统在甲壳动物先天免疫中起着重要作用，特别是在伤口愈合和病原体防御方面。该系统的一个关键成员是酚氧化酶原激活酶（PPAE），它是酚氧化酶原（proPO）的直接激活剂。尽管它们在甲壳动物 PO 激活系统中很重要，但对它们的研究仍然有限。
本研究报告了凡纳滨对虾（Litopenaeus vannamei）的一种 PPAE（lvPPAE1），它与斑节对虾（Penaeus monodon）的 PPAE1 具有 94%的相似性。我们发现，在受到哈维弧菌（Vibrio harveyi）挑战后，体液血细胞中的 lvPPAE1 下调，但当虾长期暴露在富含细菌的环境中时，其表达增强。通过 RNAi 沉默 lvPPAE1 基因可显著降低酚氧化酶活性（PO）并增加虾对哈维弧菌的易感性。尽管 lvPPAE1 在受到弧菌挑战后在体液血细胞中下调，但在细菌注射后其在鳃中的表达显著增加，鳃是主要的细菌清除组织。
在体液血细胞中表达受抑制，在鳃中表达增强，表明在细菌清除部位选择性增强表达。这是 PPAE 表达的一个新特征。这些结果将有助于我们理解甲壳动物的 PO 激活系统。
