韩国汉阳大学Jiwon Shim研究组发现，果蝇免疫细胞通过PPO2蛋白相变运输氧气。该项研究成果于2024年6月26日在线发表在《自然》上。

研究人员描述了果蝇晶体细胞（被称为血细胞的髓细胞样免疫细胞）通过氧合丙酚氧化酶2（PPO2）蛋白来控制呼吸。晶体细胞引导血细胞在幼虫体壁的气管和血液循环之间移动，以收集氧气。在铜和中性pH值的帮助下，氧气被截留在晶体细胞中PPO2的晶体结构中。相反，当碳酸酐酶降低细胞内的pH值时，PPO2晶体会溶解，然后附着在气管上重新组合成晶体。

从生理学角度看，缺乏晶体细胞或PPO2的幼虫，或表达PPO2铜结合突变体的幼虫，在常氧条件下表现出缺氧反应，并且容易缺氧。这些缺氧表型可以通过高氧、表达节肢动物血蓝蛋白或阻止幼虫穴居活动以暴露其呼吸器官来挽救。因此，研究人员认为昆虫免疫细胞与气管系统合作，通过PPO2晶体的相变来储备和运输氧气，从而促进体内氧气平衡，其过程与脊椎动物的呼吸作用类似。

据介绍，长期以来，人们一直认为昆虫的呼吸完全依赖于复杂的气管系统，而没有循环系统或免疫细胞的辅助。

附：英文原文

Title: Drosophila immune cells transport oxygen through PPO2 protein phase transition

Author: Shin, Mingyu, Chang, Eunji, Lee, Daewon, Kim, Nayun, Cho, Bumsik, Cha, Nuri, Koranteng, Ferdinand, Song, Ji-Joon, Shim, Jiwon

Issue&Volume: 2024-06-26

Abstract: Insect respiration has long been thought to be solely dependent on an elaborate tracheal system without assistance from the circulatory system or immune cells1,2. Here we describe that Drosophila crystal cells—myeloid-like immune cells called haemocytes—control respiration by oxygenating Prophenoloxidase 2 (PPO2) proteins. Crystal cells direct the movement of haemocytes between the trachea of the larval body wall and the circulation to collect oxygen. Aided by copper and a neutral pH, oxygen is trapped in the crystalline structures of PPO2 in crystal cells. Conversely, PPO2 crystals can be dissolved when carbonic anhydrase lowers the intracellular pH and then reassembled into crystals in cellulo by adhering to the trachea. Physiologically, larvae lacking crystal cells or PPO2, or those expressing a copper-binding mutant of PPO2, display hypoxic responses under normoxic conditions and are susceptible to hypoxia. These hypoxic phenotypes can be rescued by hyperoxia, expression of arthropod haemocyanin or prevention of larval burrowing activity to expose their respiratory organs. Thus, we propose that insect immune cells collaborate with the tracheal system to reserve and transport oxygen through the phase transition of PPO2 crystals, facilitating internal oxygen homeostasis in a process that is comparable to vertebrate respiration.

DOI: 10.1038/s41586-024-07583-x

Source: https://www.nature.com/articles/s41586-024-07583-x