SGK1 is a Central Regulator of P. gingivalis-Induced Inflammation

描述（由申请方提供）：牙龈卟啉单胞菌（牙龈卟啉单胞菌）是一种革兰氏阴性厌氧菌，是牙周炎的病原体。 评估宿主对牙龈卟啉单胞菌的炎症反应的研究已经证明，Toll样受体（TLR）-2是参与识别牙龈卟啉单胞菌的LPS和各种其他微生物相关分子模式的主要TLR。 然而，潜在的细胞信号传导途径，特别是细胞内调节分子，调节牙龈卟啉单胞菌（TLR 2）介导的炎症反应尚未完全理解。利用siRNA和Cre/loxP系统，我们首次鉴定了血清和糖皮质激素诱导的激酶1（SGK 1）抑制牙龈卟啉单胞菌介导的先天免疫细胞炎症反应。 SGK 1是一种普遍存在的丝氨酸/苏氨酸激酶，属于AGC激酶家族（蛋白激酶A、-G和-C家族），可被PI 3激酶激活。 尽管PI 3 K-Akt-GSK 3-<$通路已被证明在TLR介导的炎症反应中发挥关键的调节作用，但SGK 1在TLR介导的免疫反应中的功能作用完全未知。 因此，本文提出的研究旨在鉴定和表征SGK 1如何调节P. gingvalis诱导的炎症介质，以及描述TLR如何参与SGK 1的磷酸化和激活。我们假设SGK 1是一种关键激酶，通过调节Forkhead box蛋白O 1（FoxO 1）及其下游CCAAT/增强子结合蛋白β（C/EBP-β）的激活，在牙龈卟啉单胞菌刺激后控制先天免疫细胞的炎症。这一假设进一步证实了（i）预测磷酸化位点（ii）我们的初步数据显示牙龈卟啉单胞菌刺激磷酸化激活SGK 1并消除FoxO 1与BMDC中C/EBP-1启动子的结合;和（iii）我们最近的出版物证明PDK 2抑制介导FoxO 1核隔离并增强先天免疫细胞中TLR 4介导的炎症反应（15）。这些观察结果为SGK 1通过TLR 2-SGK 1-FoxO 1-C/EBP-γ轴调节牙龈卟啉单胞菌介导的炎症反应提供了强有力的理论依据。 具体目标将确定SGK 1作为牙龈卟啉单胞菌介导的炎症反应的内源性抑制剂的作用，并描述SGK 1如何响应牙龈卟啉单胞菌刺激而被激活，以及确定SGK 1是否通过改变FoxO 1及其下游C/EBP-1的活性来负调节牙龈卟啉单胞菌诱导的促炎细胞因子产生。该项目的成功完成将导致分离出一种新的和潜在的关键信号通路（TLR 2-PI 3 K-SGK 1-FoxO 1-C/EBP-<$），并极大地帮助理解宿主炎症反应是如何被调节的，这将为开发免疫调节疗法铺平道路，该疗法应具有远远超出口腔的相关性。

DESCRIPTION (provided by applicant): Porphyromonas gingivalis (P. gingivalis) is a Gram-negative anaerobic bacterium and a causative agent of periodontitis. Studies assessing the host inflammatory response to P. gingivalis have demonstrated that Toll-like receptor (TLR)-2 is the predominant TLR involved in the recognition of LPS and various other microbe-associated molecular patterns of P. gingivalis. However, the underlying cell-signaling pathways, especially the intracellular regulatory molecules, regulating the P. gingivalis (TLR2)-mediated inflammatory response are not fully understood. Using siRNA and Cre/loxP system, we have, for the first time, identified that serum- and glucocorticoid-inducible kinase 1 (SGK1) suppresses P. gingivalis-mediated inflammatory responses in innate immune cells. SGK1 is a ubiquitous serine/theronine kinase belonging to AGC kinase family (Protein kinase A, -G and -C family) and can be activated by PI3 kinase. Whereas the PI3K-Akt-GSK3-¿ pathway has been demonstrated to play a critical regulatory role in TLR-mediated inflammatory responses, the functional role of SGK1 in TLR-mediated immune responses is entirely unknown. Therefore, the studies proposed here are intend to identify and characterize how SGK1 regulates P. gingvalis induced inflammatory mediators, as well as to delineate how the TLRs are involved in the phosphorylation and activation of SGK1. We hypothesize SGK1 is a critical kinase that controls inflammation of innate immune cells upon stimulation with P. gingivalis by regulating activation of Forkhead box protein O1 (FoxO1) and its downstream CCAAT/enhancer-binding protein beta (C/EBP-¿). This hypothesis is further substantiated by (i) the prediction of phosphorylation sites (by the software NetworKIN) identified FoxO1 as the optimum substrate of SGK1; (ii) our preliminary data showing that P. gingivalis stimulation phospho-activates SGK1 and abolishes the binding of FoxO1 to the promoter of C/EBP-¿ in BMDC; and (iii) our recent publication demonstrating that PDK2 inhibition mediates FoxO1 nuclear sequestration and enhances TLR4 mediated inflammatory responses in innate immune cells (15). These observations provide a strong rationale for SGK1 in modulating P. gingivalis mediated inflammatory response via the TLR2-SGK1-FoxO1-C/EBP-¿ axis. The specific aims will establish the role for SGK1 as an endogenous inhibitor of the P. gingivalis-mediated inflammatory response and delineate how SGK1 is activated in response to P. gingivalis stimulation, as well as determine if SGK1 negatively regulates P. gingivalis induced pro-inflammatory cytokines production via modification of the activity of FoxO1 and its downstream C/EBP-¿ . Successful completion of this project will result in the isolation a novel and potentiall critical signaling pathway (TLR2-PI3K-SGK1-FoxO1-C/EBP-¿ ) and greatly aid in the understanding of how the host inflammatory response is being regulated, which will pave the way for the development of immunoregulatory therapeutics that should have relevance well beyond the oral cavity.