Du Xiaofeng, McManus Donald P, Cai Pengfei, Hu Wei, You Hong
Molecular Parasitology Laboratory, Infectious Diseases Division, QIMR Berghofer Medical Research Institute, Brisbane, Queensland, Australia.
School of Life Sciences, Fudan University, 2005 Songhu Road, Shanghai, 200438, China.
Parasit Vectors. 2017 Apr 14;10(1):181. doi: 10.1186/s13071-017-2095-7.
Previous studies have shown that insulin receptors in schistosomes, triggered by host insulin, play an important role in parasite growth, development and fecundity by regulating glucose metabolism. However, limited information is available on the recently identified endogenous insulin-like peptide (ILP) in blood flukes.
We isolated ILPs from Schistosoma japonicum (SjILP) and S. recognised (SmILP) and present results of their molecular and structural analysis. SjILP shares 63% amino acid identity with SmILP, but only 18% identity with human insulin. There is high cross immunological reactivity between the S. japonicum and S. mansoni ILPs as observed in western blots using an anti-SjILP polyclonal antibody. ADP binding/hydrolysis ability was observed in both SjILP and SmILP, but not in human insulin, suggesting a parasite-specific role for ILP compared with host insulin. Protein binding assays using the Octet-RED system showed SjILP binds S. japonicum IRs (SjIR1 and SjIR2) strongly. An anti-phospho antibody against extracellular signal-regulated kinase (Erk) recognised a 44-kDa target band in an extract of adult worms after stimulation by rSjILP in vitro, suggesting an important role for SjILP in activating SjIRs and in regulating downstream signal transduction. Immunolocalisation showed SjILP is located on the tegument and the underlying musculature, similar to that observed for SjIR1, but it is also present throughout the parenchyma of males and in the vitelline cells of females, the same locations as SjIR2 described in an earlier published study of ours. The same localisation of SjILP and the SjIRs is suggestive of an interaction between the insulin-like peptide and the IRs. In addition to binding host insulin, schistosomes also can express their own endogenous ILPs, which can activate the parasite insulin signal pathway, thereby playing a critical role in worm growth, development and fertility.
These findings shed new light on ILPs in schistosomes, providing further insight into the distinct and specialised functions of SjIR1 and 2 in S. japonicum and their interaction with host insulin.
先前的研究表明，血吸虫中的胰岛素受体在宿主胰岛素的触发下，通过调节葡萄糖代谢，在寄生虫的生长、发育和繁殖中发挥重要作用。然而，关于最近在血吸虫中发现的内源性胰岛素样肽（ILP）的信息有限。
我们从日本血吸虫（SjILP）和曼氏血吸虫（SmILP）中分离出ILP，并展示了它们的分子和结构分析结果。SjILP与SmILP的氨基酸同一性为63%，但与人类胰岛素的同一性仅为18%。在使用抗SjILP多克隆抗体的western印迹中观察到，日本血吸虫和曼氏血吸虫的ILP之间存在高度交叉免疫反应性。在SjILP和SmILP中均观察到ADP结合/水解能力，但在人类胰岛素中未观察到，这表明与宿主胰岛素相比，ILP具有寄生虫特异性作用。使用Octet-RED系统进行的蛋白质结合试验表明，SjILP与日本血吸虫胰岛素受体（SjIR1和SjIR2）强烈结合。一种针对细胞外信号调节激酶（Erk）的抗磷酸化抗体在体外受重组SjILP刺激后的成虫提取物中识别出一条44 kDa的目标条带，这表明SjILP在激活SjIRs和调节下游信号转导中起重要作用。免疫定位显示，SjILP位于体表和下方的肌肉组织上，这与SjIR1的情况相似，但它也存在于雄性的整个实质组织和雌性的卵黄细胞中，与我们之前发表的研究中描述的SjIR2的位置相同。SjILP和SjIRs的相同定位表明胰岛素样肽与胰岛素受体之间存在相互作用。除了结合宿主胰岛素外，血吸虫还可以表达自己的内源性ILP，其可以激活寄生虫胰岛素信号通路，从而在虫体生长、发育和繁殖力中起关键作用。
这些发现为血吸虫中的ILP提供了新的见解，进一步深入了解了SjIR1和2在日本血吸虫中的独特和特殊功能以及它们与宿主胰岛素的相互作用。
