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

尽管在20016-2000年期间取得了最近的进展，但进展停滞不前，疟疾仍然是一种毁灭性的疾病，每年导致约40.5万人死亡，2.28亿人感染。恶性疟原虫是导致疟疾最致命的寄生虫，当雌性蚊子在叮咬感染者时摄取称为雄配子体和雌配子体的特殊寄生虫细胞时，恶性疟原虫就会传播。这些配子体无法控制蚊子何时叮咬，因此，为了最大限度地增加它们传播的机会，它们在人类血液中处于“静止”(即休眠)状态长达22天。大多数抗疟疾药物对静止的配子体无效，因此使疾病(和耐药基因)得以逃逸并在整个人群中传播。细胞静止是一个对所有生命都至关重要的过程。作为对不利环境或特定信号的反应，细胞可能会停止生长，并在一段时间内处于静止状态。当条件变得更有利时，静止的细胞就会退出休眠，恢复正常的程序化生长。细胞通过许多不同的方法进行静止，然而细胞内发生的维持它们存活的共同过程：1.减少或有效的能量产生；2.资源生产从生长所需的转移到生存所必需的；3.有效的损伤和修复机制。我假设，干扰配子体静止机制将对它们的传染性产生灾难性的影响，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细胞静止的新的传播阻断抗疟疾疗法。我的研究重点是静止的配子细胞如何调节它们的能量产生。蚊子体内的寄生虫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，这是在细胞中被称为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是必不可少的，但在人类体内则不那么重要。配子细胞必须准备好在瞬间“开启”线粒体的呼吸。然而，太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，从而限制配子体的寿命，降低其传播的机会。因此，配子细胞似乎有几种机制来控制它们的能量产生。据推测，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。或者，可以通过用效率较低的替代品取代参与这一过程的关键酶(制造细胞所需材料的蛋白质)来减少能量产生。我已经确定了四种由配子细胞制造的酶，它们可能与这种控制有关。为了研究这些蛋白质所起的作用，我将对寄生虫进行基因改造，使其缺乏这些蛋白质，并观察这对配子细胞和蚊子传播的影响。这将涉及到用寄生虫喂活蚊子。我还将使用一种名为代谢组学的技术来追踪寄生虫对葡萄糖的利用在突变寄生虫中是如何受到影响的，代谢组学是一种分离和识别细胞制造的个别化学物质的技术。为了确定对维持配子细胞处于静止状态很重要的其他蛋白质，我将在配子细胞内新生成的蛋白质上贴上化学“标签”，这将使我能够“捕获”它们，并使用一种名为质谱学的技术来识别它们。通过在雄配子体和雌配子体上分别使用这种方法，我将确定配子体如何保持静止是否存在性别差异。最后，我将研究干扰配子细胞能量代谢如何影响它们自我修复的能力。最终，我的研究将确定新疗法可能针对静止途径中的哪些步骤。

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.