Impact of the cytoprotective chaperone HSP25/27 on the structural integrity and autophagic degradation of chlamydial compartments

衣原体是一种专性细胞内细菌，可引起性传播疾病、眼部感染和非典型肺炎。所有已知的衣原体物种都经历了一个独特的两相发育周期，该周期发生在一个非酸化的膜结合液泡中，称为包涵体。衣原体以宿主细胞骨架为靶标，调节其细胞内生存的各个方面，如包涵体的结构稳定性和生理维持。为此，细菌用一网细胞骨架细丝包围它们的液泡，这些细胞骨架细丝充当结构上稳定细菌室的支架。因此，宿主细胞防御机制的激活受到限制，因为防止了包涵体内容物泄漏到细胞质中。我们最近证明了衣原体感染的免疫和非免疫细胞能够分解包涵体，导致细菌的胞浆释放。随后，衣原体通过自噬被杀死和降解，导致衣原体抗原的加工，并将其展示给T细胞进行免疫监控。此外，我们发现，感染诱导的宿主细胞伴侣HSP25/27的表达，调节细胞骨架细丝的重塑，似乎在破坏和降解衣原体间隔方面发挥了关键作用。因此，对衣原体感染细胞中HSP25/27介导的过程的详细阐明对于了解包涵体是如何在宿主细胞中受到攻击以及哪些细胞机制被用来破坏细菌室是至关重要的。我们的主要目标是揭开HSP25/27影响的分子和细胞过程，并评估这些过程如何决定衣原体感染的结果。我们将利用生物化学、显微镜、细胞生物学和分子生物学中最先进的方法来从功能上表征感染诱导的HSP25/27，并试图识别宿主细胞和病原体衍生的HSP25/27相互作用伙伴。我们还将探索HSP25/27如何影响细菌细胞骨架效应器蛋白，以及它如何破坏持久和多产包涵体的完整性以及它们与宿主细胞骨架的相互作用。此外，我们将评估衣原体基因的表达伴随着包涵体的分解。我们工作的另一个重点将解决衣原体隔间解体和随后的降解之间的功能合作。在这里，我们将集中在NOD1/2(核苷酸结合寡聚化结构域1/2)途径和HMGB1(高迁移组盒1)控制的HSP25/27表达和自噬过程。我们对细胞保护性HSP25/27及其对细菌室的影响的研究将有助于深入了解衣原体的细胞内生命周期，并开发针对衣原体感染的新的治疗策略。

Chlamydiae are obligate intracellular bacteria that cause sexually transmitted disease, ocular infections, and atypical pneumonia. All known chlamydia species undergo a unique biphasic developmental cycle that takes place within a non-acidified membrane-bound vacuole, termed inclusion. Chlamydiae target the host cytoskeleton to regulate diverse aspects of their intracellular survival such as the structural stability and physiological maintenance of their inclusions. To this end, the bacteria surround their vacuole with a mesh of cytoskeletal filaments, which serve as a scaffold structurally stabilizing the bacterial compartment. As a consequence, the activation of host cell defense mechanisms is limited as leakage of inclusion contents into the cytosol is prevented. We recently demonstrated that chlamydia-infected immune and non-immune cells are able to break down inclusions resulting in the cytosolic release of bacteria. Subsequently, chlamydiae are killed and degraded via autophagy leading to the processing of chlamydial antigens and their display to T cells for immunosurveillance. Moreover, we found that the infection-induced expression of the host cell chaperone HSP25/27, which regulates the remodeling of cytoskeletal filaments, seems to play a critical role in disrupting and degrading chlamydial compartments. Therefore, the detailed elucidation of HSP25/27-mediated processes in chlamydia-infected cells is crucial to understand how inclusions are attacked in host cells and which cellular machinery is used to destroy the bacterial compartments. Our key goal is to unravel the molecular and cellular processes that HSP25/27 impacts and to assess how these processes determine the outcome of chlamydial infections. We will utilize advanced state-of-the-art methods in biochemistry, microscopy, cell biology, and molecular biology to functionally characterize infection-induced HSP25/27 and attempt to identify both host cellular and pathogen-derived HSP25/27 interaction partners. We will also explore how HSP25/27 affects bacterial cytoskeleton effector proteins, and how it disrupts the integrity of persistent and productive inclusions as well as their interaction with the host cytoskeleton. Moreover, we will assess the chlamydial gene expression accompanying inclusion breakdown. Another focus of our work will address the functional cooperation between the disintegration of chlamydial compartments and their subsequent degradation. Here, we will concentrate on NOD1/2 (Nucleotide-Binding Oligomerization Domain 1/2)-pathways and on HMGB1 (High Mobility Group Box 1)-controlled processes of HSP25/27 expression and autophagy. Our studies on cytoprotective HSP25/27 and its effects on bacterial compartments will aid the deeper understanding of the intracellular life cycle of chlamydia and the development of novel therapeutic strategies against chlamydial infections.