The role of gram-positive bacteria in pulp inflammation – NF-κB as a potential therapeutic target?

龋齿在世界范围内普遍存在。它通过细菌将碳水化合物转化为有机酸来破坏牙齿。革兰氏阳性菌起着关键作用，尤其是变形链球菌，其特点是能够合成大量的细胞外基质，这有利于生物膜的形成，并且即使在低ph下也能代谢各种碳水化合物。在龋齿病变中，微生物及其产物通过牙本质小管扩散到牙髓腔，导致牙髓炎症。脂质胆酸（LTA）固定在革兰氏阳性细菌（如变形链球菌）的细胞膜上，在深部腔中起着核心作用。通过与细胞膜上的TLR-2结合，它触发牙髓-牙本质界面的成牙细胞以及中心的成牙髓细胞的免疫反应。在细胞内，NF-κB信号级联被激活，导致各种趋化因子和细胞因子的分泌，从而调节炎症，恢复组织稳态。此外，牙髓反应形成第三牙本质，以保护自己免受微生物刺激。到目前为止，无症状牙齿或可逆性牙髓炎患者的龋齿治疗目标一直是去除大部分感染的牙本质并恢复牙齿。当临床症状表现为不可逆性牙髓炎时，不需要再进行重要的牙髓治疗，而必须开始进行根管治疗。然而，在未来，免疫调节疗法可能通过控制牙髓炎症和允许再生，为不可逆性牙髓炎提供一种替代牙髓切除的方法。因此，本项目的目的是研究临床建立的特异性作用于NF-κB信号通路的药物是否适用于牙髓炎症的治疗。为了解决这个首要问题，将设立五个具有具体目标的次级项目。第一个研究重点是与变形链球菌的新型共培养模型，并研究LTA是否分别通过TLR-2激活髓质-牙本质界面细胞和髓成纤维细胞诱导NF-κB核内易位。下面，我们将通过基因图谱研究两种细胞类型的防御反应，一方面研究细胞分化，另一方面研究免疫特性，特别是炎症小体和促炎细胞因子的激活。此外，细胞释放的抗菌分子可能会引发S. mutans的适应性反应，这将通过RNA测序进行分析。最后，将研究三种临床药物乙酰水杨酸、氢化可的松和他克莫司在牙髓-牙本质界面细胞和牙髓成纤维细胞中特异性控制炎症反应的潜力。

Dental caries has a significant prevalence worldwide. It destroys teeth by bacteria that convert carbohydrates into organic acids. Gram-positive ones play a key role, with Streptococcus mutans in particular being distinguished by its ability to synthesize large amounts of extracellular matrix, which favors biofilm formation, and its ability to metabolize a variety of carbohydrates even at low pH. In a caries lesion, the microorganisms and their products diffuse to the pulp cavity through dentinal tubules, leading to inflammation of the dental pulp. Lipoteichoic acid (LTA), which is anchored in the cell membrane of gram-positive bacteria like S. mutans, plays a central role in deep cavities. By binding to TLR-2 on cell membranes, it triggers immune responses in the odontoblasts at the pulp-dentin-interface as well as pulp fibroblasts in the center. Intracellularly, the NF-κB signaling cascade is activated, leading to the secretion of various chemokines and cytokines to modulate the inflammation and restore tissue homeostasis. Furthermore, the dental pulp reacts by forming tertiary dentin to shield itself from the microbial irritants. Until now, the goal of caries treatment in asymptomatic teeth or those with reversible pulpitis has been to remove most of the infected dentin and to restore the tooth. When clinical symptoms demonstrate irreversible pulpitis, vital pulp therapy is no longer indicated and root canal treatment must be initiated. In the future, however, immunomodulatory therapeutics may provide an alternative to pulp removal for irreversible pulpitis by controlling pulp inflammation and allowing regeneration. Therefore, the aim of the proposed project is to investigate, whether clinically established pharmacological agents acting specifically on the NF-κB signaling pathway would be suitable for the treatment of inflammatory conditions of the dental pulp. To address the overarching question, five subprojects with specific objectives will be established. The first focuses on a novel coculture model with S. mutans and investigates whether LTA induces intranuclear translocation of NF-κB via TLR-2 activation in cells of the pulp-dentin-interface and in pulp fibroblasts, respectively. In the following, the defense responses of both cell types are studied on the one hand on cell differentiation by genetic profiling, and on the other hand on the immunological properties, especially the activation of inflammasomes and proinflammatory cytokines. In addition, antimicrobial molecules released by the cells could trigger an adaptive response in S. mutans, which will be analyzed by RNA sequencing. Finally, the potential of three clinically established drugs, acetylsalicylic acid, hydrocortisone, and tacrolimus, will be investigated to specifically control the inflammatory response in cells of the pulp-dentin interface and in dental pulp fibroblasts.