Institute of Medical Microbiology, University Hospital of Münster, Münster, Germany.
Department of Anaesthesiology and Intensive Care, Experimental and Clinical Haemostasis, University Hospital of Münster, Münster, Germany.
Microbiol Spectr. 2023 Jun 15;11(3):e0388622. doi: 10.1128/spectrum.03886-22. Epub 2023 Mar 30.
Invasion of host cells is an important feature of Staphylococcus aureus. The main internalization pathway involves binding of the bacteria to host cells, e.g., endothelial cells, via a fibronectin (Fn) bridge between S. aureus Fn binding proteins and αβ-integrin, followed by phagocytosis. The secreted extracellular adherence protein (Eap) has been shown to promote this cellular uptake pathway of not only S. aureus, but also of bacteria otherwise poorly taken up by host cells, such as Staphylococcus carnosus. The exact mechanisms are still unknown. Previously, we demonstrated that Eap induces platelet activation by stimulation of the protein disulfide isomerase (PDI), a catalyst of thiol-disulfide exchange reactions. Here, we show that Eap promotes PDI activity on the surface of endothelial cells, and that this contributes critically to Eap-driven staphylococcal invasion. PDI-stimulated β-integrin activation followed by increased Fn binding to host cells likely accounts for the Eap-enhanced uptake of S. aureus into non-professional phagocytes. Additionally, Eap supports the binding of S. carnosus to Fn-αβ integrin, thereby allowing its uptake into endothelial cells. To our knowledge, this is the first demonstration that PDI is crucial for the uptake of bacteria into host cells. We describe a hitherto unknown function of Eap-the promotion of an enzymatic activity with subsequent enhancement of bacterial uptake-and thus broaden mechanistic insights into its importance as a driver of bacterial pathogenicity. Staphylococcus aureus can invade and persist in non-professional phagocytes, thereby escaping host defense mechanisms and antibiotic treatment. The intracellular lifestyle of S. aureus contributes to the development of infection, e.g., in infective endocarditis or chronic osteomyelitis. The extracellular adherence protein secreted by S. aureus promotes its own internalization as well as that of bacteria that are otherwise poorly taken up by host cells, such as Staphylococcus carnosus. In our study, we demonstrate that staphylococcal uptake by endothelial cells requires catalytic disulfide exchange activity by the cell-surface protein disulfide isomerase, and that this critical enzymatic function is enhanced by Eap. The therapeutic application of PDI inhibitors has previously been investigated in the context of thrombosis and hypercoagulability. Our results add another intriguing possibility: therapeutically targeting PDI, i.e., as a candidate approach to modulate the initiation and/or course of S. aureus infectious diseases.
宿主细胞的入侵是金黄色葡萄球菌的一个重要特征。主要的内化途径涉及细菌通过金黄色葡萄球菌纤维连接蛋白（Fn）结合蛋白和αβ-整合素之间的纤维连接蛋白（Fn）桥与宿主细胞（如内皮细胞）结合，随后被吞噬。已发现分泌的细胞外黏附蛋白（Eap）不仅可促进金黄色葡萄球菌，还可促进宿主细胞摄取能力差的细菌（如肉葡萄球菌）的这种细胞摄取途径。确切的机制尚不清楚。先前，我们证明 Eap 通过刺激蛋白质二硫键异构酶（PDI）诱导血小板活化，PDI 是巯基-二硫键交换反应的催化剂。在这里，我们表明 Eap 可促进内皮细胞表面的 PDI 活性，并且这对于 Eap 驱动的葡萄球菌入侵至关重要。PDI 刺激β整合素激活，随后增加宿主细胞上 Fn 的结合，可能解释了 Eap 增强金黄色葡萄球菌进入非专业吞噬细胞的摄取。此外，Eap 支持肉葡萄球菌与 Fn-αβ整合素的结合，从而允许其进入内皮细胞。据我们所知，这是首次证明 PDI 对细菌进入宿主细胞至关重要。我们描述了 Eap 的一个以前未知的功能——促进具有随后增强细菌摄取能力的酶活性，从而拓宽了对其作为细菌致病性驱动因素的重要性的机制理解。金黄色葡萄球菌可以入侵并在非专业吞噬细胞中存活，从而逃避宿主防御机制和抗生素治疗。金黄色葡萄球菌的细胞内生活方式有助于感染的发展，例如在感染性心内膜炎或慢性骨髓炎中。金黄色葡萄球菌分泌的细胞外黏附蛋白可促进其自身内化以及宿主细胞摄取能力差的细菌内化，如肉葡萄球菌。在我们的研究中，我们证明了内皮细胞摄取葡萄球菌需要细胞表面蛋白二硫键异构酶的催化二硫键交换活性，并且 Eap 增强了这种关键的酶功能。PDI 抑制剂的治疗应用先前已在血栓形成和高凝状态的背景下进行了研究。我们的研究结果增加了另一种有趣的可能性：针对 PDI 的治疗性靶向，即作为调节金黄色葡萄球菌感染性疾病的起始和/或病程的候选方法。
