Aggregation Mechanisms of PolyQ-containing Proteins: Structure and Cytotoxicity of the Metastable Intermediate Species

不溶性纤维聚集是多聚谷氨酰胺(PolyQ)重复性疾病的主要组织学特征，但其在疾病病理中的作用仍存在争议。以下三个假设可以解释文献中报道的毒性与体内聚集形成之间相关性较差的情况：1)具有不同毒性的多个亚稳态物种的有序组装途径；2)具有不同稳定性和毒性的各种瞬时物种的多个竞争性聚集途径；以及3)各种内部(如多聚Q侧翼序列)和分子间因素(如老化、应激反应)可以改变聚集途径(S)。为了验证这些假设，我们提出了新的体内实验，允许直接映射亨廷顿蛋白(Huntingtin，Htt)外显子1编码片段(Htt)的外显子1编码片段(Htt)的聚集途径中出现的聚集物种的结构(例如，涉及聚集核心、灵活区域的序列)和特征(在途径上或途径外)。此外，使用广泛的体内和体外方法，我们的目标是确定亚稳态聚集体的结构和支配聚集体形态的分子相互作用，它们在细胞环境中的传播和它们的毒性特性。结构和细胞毒性之间的联系将是我们进一步主要目标的机制基础：开发不利于有毒物种形成的策略。因此，主要的焦点将是探索一种自然进化的机制，渗透压补偿反应，以及不同类型的渗透调节物质如何重塑多聚Q蛋白的聚集途径，并促进非淀粉样变性、无毒的非途径物种的形成。

Insoluble fibrillar aggregates are the major histophological feature of polyglutamine (polyQ)-repeat diseases however their role in the disease pathology is still controversial. Following three hypotheses could explain the reported in the literature poor correlation between toxicity and aggregate formation in vivo: 1) a sequential assembly pathway with multiple metastable species with different toxicity, 2) multiple competing aggregation pathways with various transient species with different stability and toxicity, and 3) various intra- (e.g., polyQ-flanking sequences) and intermolecular factors (e.g., aging, stress response) could alter the aggregation pathway(s). To test these hypotheses, we propose new in vivo experiments allowing to directly map the structure (e.g., sequences involved in the aggregate core, flexible regions) and the character (on- or off- pathway) of the aggregate species emerging in the aggregation pathway of the exon 1 encoded fragment of huntingtin (Htt) with expanded polyglutamine stretch. In addition, using a broad spectrum of in vivo and ex vivo approaches we aim to determine the structure of the metastable aggregates and the molecular interactions governing aggregate morphology, their propagation in the cellular context and their toxic properties. The link between the structure and cytotoxicity will be the mechanistic foundation for our further major goal: to develop strategies to disfavor the formation of the toxic species. Thereby, the main focus will be to explore a naturally evolved mechanism, the osmocompensatory response, and how different types of osmolytes can re-shape the aggregation pathway of polyQ proteins and promote the formation of non-amyloidogenic, non-toxic off-pathway species.