Deciphering the role of Plasmodium falciparum plasmepsin 2/3 amplifications in mutant pfcrt-driven piperaquine resistance

项目摘要 对青蒿素类复方疗法-抗疟原虫的一线疗法-的耐药性正在出现 恶性疟原虫（Pf）疟疾是一个主要的公共卫生问题。对哌喹（PPQ）和二氢- 青蒿素目前已席卷东南亚，治疗失败率高达87%。越来越多地使用 这种组合在非洲增加了PPQ耐药性在非洲大陆传播的威胁， 付出了最沉重的代价因此，迫切需要了解PPQ耐药性的机制基础， 与其他研究一起关注突变PfKelch 13介导的青蒿素抗性。最近的研究 PPQ耐药与编码两个Pf的浆蛋白酶2/3（pfpm 2/3）扩增相关 血红蛋白酶，以及最近出现的Pf氯喹抗性转运蛋白（PfCRT）突变。 这些PfCRT突变使PPQ能够在寄生虫的消化系统中从其血红素靶点流出， 液泡，总是出现在扩增的pfpm 2/3遗传背景，表明这些重要的作用 扩增。在目标1中，我们将检验pfpm 2/3扩增增加PPQ水平的假设 抗性，利用在两个PPQ抗性突变体中表达一系列pfpm 2/3拷贝数的同基因克隆， pfcrt柬埔寨分离株。利用CRISPR/Cas9介导的基因编辑，我们将取代内源性 单拷贝和多拷贝pfpm 2/3克隆中的突变pfcrt等位基因与亲本PPQ敏感性pfcrt Dd 2等位基因，和 评估这些扩增是否可以单独介导PPQ耐受性表型。我们还将测试 pfpm 2/3扩增补偿血红蛋白（Hb）衍生的替代非排他性假设 由突变PfCRT引起的肽积累缺陷，从而恢复寄生虫适应性。我们的研究也将 确定pfpm 2/3拷贝数在调节消化空泡形态和Hb来源的 肽水平。对于目标2，有证据表明PfPM 2/3与Pf血红素解毒蛋白一起起作用 （PfHDP）作为疟原虫色素（Hz）形成复合物（HFC）的一部分。我们将探讨pfpm 2/3 扩增增加了HFC介导的Hb向Hz的转化。我们假设pfpm 2/3扩增 增加Hb降解并导致降低PPQ对血红素解毒抑制。使用血红素分馏 在pfpm 2/3单拷贝和多拷贝克隆中，我们将定量Hb、游离血红素和Hz，并评估它们是否 通过PFPM 2/3扩增改变相对水平。我们还将产生可控的TetR-DOZI- 在具有单拷贝或多拷贝pfpm 2/3的寄生虫中，基于pfhdp的条件性敲低，并测试这些条件性敲低是否 敲低调节PPQ抗性和血红素水平。这些结果将明确评估 pfpm 2/3扩增至PPQ抗性。机制性见解还将指导减轻PPQ的策略 通过靶向Hz形成的介体来研究耐药性，并告知PfHDP作为新型药物靶标的适用性。

Project Summary Emerging resistance to artemisinin-based combination therapies, the first-line treatment against Plasmodium falciparum (Pf) malaria, poses a major public health problem. Resistance to piperaquine (PPQ) and dihydro- artemisinin has now swept across Southeast Asia, with treatment failures as high as 87%. The increasing use of this combination in Africa adds to the threat of PPQ resistance spreading across this continent, where malaria exerts its heaviest toll. There is thus an urgent need to understand the mechanistic basis of PPQ resistance, alongside other studies focused on mutant PfKelch13-mediated artemisinin resistance. Recent studies have associated PPQ resistance with the amplification of plasmepsins 2/3 (pfpm 2/3) that encode two Pf hemoglobinases, as well as recently emerged mutations in the Pf chloroquine resistance transporter (PfCRT). These PfCRT mutations, which enable the efflux of PPQ away from its heme target in the parasite’s digestive vacuole, always occur on an amplified pfpm 2/3 genetic background, indicating an important role for these amplifications. In Aim 1 we will test the hypothesis that pfpm 2/3 amplifications augment levels of PPQ resistance, utilizing isogenic clones that express a range of pfpm 2/3 copy numbers in two PPQ-resistant, mutant pfcrt Cambodian isolates. Leveraging CRISPR/Cas9-mediated gene editing, we will replace the endogenous mutant pfcrt allele in single and multicopy pfpm 2/3 clones with the parental PPQ-sensitive pfcrt Dd2 allele, and assess whether these amplifications alone can mediate a PPQ tolerance phenotype. We will also test the alternate, non-exclusive hypothesis that pfpm 2/3 amplifications compensate for a hemoglobin (Hb)-derived peptide accumulation defect caused by mutant PfCRT and thereby restore parasite fitness. Our studies will also determine the contribution of pfpm 2/3 copy number in regulating digestive vacuole morphology and Hb-derived peptide levels. For Aim 2, evidence suggests that PfPM 2/3 functions with the Pf heme detoxification protein (PfHDP) as part of the hemozoin (Hz) formation complex (HFC). We will explore the hypothesis that pfpm 2/3 amplifications increase the HFC-mediated conversion of Hb to Hz. We postulate that pfpm 2/3 amplifications increase Hb degradation and result in reduced PPQ inhibition of heme detoxification. Using heme fractionation assays, we will quantify Hb, free heme and Hz in single and multicopy pfpm 2/3 clones and assess whether their relative levels are altered by pfpm 2/3 amplifications. We will also generate translationally controlled TetR-DOZI- based conditional knockdowns of pfhdp in parasites with single or multicopy pfpm 2/3 and test whether these knockdowns modulate PPQ resistance and heme levels. These results will definitively assess the contribution of pfpm 2/3 amplifications to PPQ resistance. Mechanistic insights will also guide strategies to mitigate PPQ resistance by targeting the mediators of Hz formation, and inform the suitability of PfHDP as a novel drug target.