Can malaria transmission be prevented through catastrophic failure of gametocyte quiescence?

尽管2000年至2016年期间取得了进展，但进展停滞不前，疟疾仍然是一种破坏性疾病，每年造成约40.5万人死亡，感染2.28亿人。恶性疟原虫是导致最致命形式疟疾的寄生虫，当雌性蚊子在叮咬被感染者的同时摄入被称为雄性和雌性配子体的特殊寄生虫细胞时，这种寄生虫就会传播。这些配子细胞无法控制蚊子何时叮咬，因此，为了最大限度地提高它们的传播机会，它们在人类血液中“休眠”（即休眠）长达22天。大多数抗疟疾药物对静止配子体无效，从而使疾病（和耐药基因）逃逸并在人群中传播。细胞静止是一个对所有生命都至关重要的过程。为了应对不利的环境或特定的信号，细胞可以停止生长，并在一段时间内处于静止状态。当条件变得更加有利时，静止的细胞就会退出这种休眠状态，恢复正常的程序性生长。细胞通过许多不同的方法来实现静止，但在细胞内发生共同的过程来保持它们的存活：减少或有效的能源产生；2. 资源生产从增长所需转向生存所需；3. 有效的损坏和修复机制。我推测，干扰配子体静止机制将对它们的传染性产生灾难性影响，使它们无法传播给蚊子。研究这些过程将有助于设计和发现针对配子体静止的新的传输阻断抗疟疾疗法。我的研究重点是静止配子体如何调节它们的能量产生。蚊子体内的寄生阶段通过消耗葡萄糖来产生能量，这一过程被称为线粒体呼吸，这一过程是在细胞中一个叫做线粒体的特殊部分进行的。线粒体呼吸对于寄生虫在蚊子体内的生存至关重要，但在人类体内则不那么重要。配子体必须随时准备“开启”线粒体呼吸。然而，过多不必要的线粒体呼吸对细胞是有害的，因为它会产生有毒的“自由基”，可以杀死细胞，从而限制配子细胞的寿命，降低其传播的机会。因此，配子体似乎有几种机制来控制它们的能量产生。据推测，其中一种机制是在葡萄糖被消耗之前将其从线粒体转移到细胞外。另一种方法是，用效率较低的替代品替换过程中涉及的关键酶（制造细胞所需物质的蛋白质），从而减少能量的产生。我已经确定了配子体产生的四种酶，它们可能负责这种控制。为了研究这些蛋白质的作用，我将对寄生虫进行基因改造，使其缺乏这些蛋白质，并观察这对配子体和蚊子传播的影响。这包括将寄生虫喂给活蚊子。我还将使用一种叫做代谢组学的技术来追踪突变寄生虫对葡萄糖的使用是如何受到影响的，这种技术可以分离并识别细胞产生的单个化学物质。为了识别对维持配子细胞处于静止状态很重要的其他蛋白质，我将用化学“标签”标记配子细胞内新生成的蛋白质，这将使我能够“捕获”它们并使用一种称为质谱的技术来识别它们。通过对雄性和雌性配子细胞分别使用这种方法，我将确定配子细胞保持静止的方式是否存在性别差异。最后，我将研究破坏配子体能量代谢如何影响其自我修复能力。最终，我的研究将确定静止途径中的哪些步骤可以被新的治疗方法所靶向。

Despite recent gains in 2000-20016, progress has stalled and malaria is still a devastating disease, killing ~405,000 people each year and infecting 228 million. Plasmodium falciparum, the parasite causing the most deadly form of malaria spreads when a female mosquito ingests specialised parasite cells called male and female gametocytes whilst biting an infected person. These gametocytes have no control over when a mosquito might bite, therefore, to maximise their chances of transmission they become "quiescent" (i.e. dormant) for up to 22 days in human blood. Most antimalarial drugs are not effective against quiescent gametocytes thus allowing the disease (and drug resistance genes) to escape and spread throughout the population. Cellular quiescence is a process that is fundamental to all of life. In response to an unfavourable environment or a specific signal, cells can stop growing and become quiescent for a period of time. When conditions become more favourable, quiescent cells then exit this dormancy and resume their normal programmed growth. Cells carry out quiescence by a number of different methods, however common processes occur within the cell to keep them alive: 1. Reduced or efficient energy generation; 2. A shift in resource production from those needed for growth, to those necessary for survival; 3. Efficient damage and repair mechanisms.I hypothesise that interfering with gametocyte quiescence mechanisms will have catastrophic effects on their infectiousness, leaving them unable to transmit to mosquitoes. Studying these processes will help the design and discovery of new transmission-blocking antimalarial therapies targeting gametocyte quiescence.My fellowship focuses on how quiescent gametocytes regulate their energy production. Parasite stages in the mosquito generate energy by consuming glucose in a process called mitochondrial respiration, which is carried out in a specialised part of the cell called the mitochondrion. Mitochondrial respiration is essential for the parasite to survive in the mosquito but less important whilst it is in the human. Gametocytes must be ready to "switch on" mitochondrial respiration at a moment's notice. However, too much unwanted mitochondrial respiration is damaging for cells as it produces toxic "free radicals" that can kill the cell and thus would limit the lifespan of the gametocyte and lower its chances of transmission. Therefore, gametocytes appear to have several mechanisms to control their energy generation. It is hypothesised that one mechanism is to divert glucose away from the mitochondrion and out of the cell before it has been consumed. Alternatively, energy production could be reduced by replacing key enzymes (proteins that manufacture materials needed by the cell) involved in the process with less efficient alternatives. I have identified four enzymes made by gametocytes that may be responsible for this control. To study the role these play, I will genetically modify the parasite to lack these proteins and observe how this affects gametocytes and mosquito transmission. This will involve feeding parasites to live mosquitoes. I will also trace how glucose use by the parasite is affected in the mutant parasites using a technique called metabolomics which separates and identifies individual chemicals made by the cell. To identify additional proteins important for maintaining gametocytes in their quiescent state, I will label newly made proteins within the gametocyte with a chemical "tag" which will allow me to "capture" them and identify them using a technique called mass spectroscopy. By using this approach on male and female gametocytes individually, I will determine whether there is a sex difference in how gametocytes maintain quiescence. Finally, I will study how disrupting gametocyte energy metabolism impacts their ability to repair themselves.Ultimately, my research will identify which steps in the quiescence pathway could by targeted by new therapeutics.