Progranulin的抗炎症作用及机制研究

The major hypothesis of the proposal is that progranulin (PGRN) is an important controller of systemic inflammation and tissue stability in a substantial part through its ability to modulate IL-10 production. Specifically, we believe that this important regulatory pathway is structured hierarchically in the following order: PGRN→CCAAT/enhancer-binding protein (C/EBP)→IL-10. To test the hypothesis we will investigate (i) how PGRN regulates C/EBPα activity towards IL-10 promoter, (ii) the molecular mechanisms whereby the transcription factor C/EBPα targeted by PGRN stimulates IL-10 gene expression at the transcriptional level, and (iii) the mechanisms of PGRN-regulated systemic inflammatory responses and their IL-10-dependency via C/EBPα. Finally we will also assess if compensating the IL-10 deficit in PGRN-deficient mice can ease their susceptibility to microbial-induced septic shock; and whether administration of recombinant PGRN can protect mice from sepsis-induced lethality. The long-term objective of this application is to gain insights into how the host regulates immune responses to inflammatory assaults, such as microbes and trauma, and to lay the foundation for developing better therapies for systemic inflammation-related maladies. The current project focuses on the cellular and molecular mechanisms whereby PGRN regulates the synthesis of IL-10 in macrophages in vitro and protects the host in systemic inflammatory disorders. The proposed studies will provide greater understanding of the novel role and mechanism of PGRN in the systemic inflammatory response syndrome and aid in the development of innovative strategies for effective interventions in sepsis, restoration of tissue homeostasis, and reestablishment of impaired immunological competency.

炎症反应对机体清除外源感染和维持正常器官功能是十分重要的。然而许多常见病却因炎症控制失调而引起，因而充分了解促使体内炎症消退的机理对基础医学和临床医学都十分重要。本课题将探讨调控炎症的一个新机理:一个分布广泛的分泌蛋白progranulin (PGRN)如何通过激活转录因子C/EBPα诱导IL-10来控制炎症反应。我们首创了grn基因敲除小鼠并发现其控制炎症的能力严重受损。其巨噬细胞产生过多促炎症因子但IL-10水平明显降低。PGRN功能缺失小鼠在注射LPS后更容易引起败血性休克和死亡。因此PGRN是一个新发现的抗炎症因子。我们将探讨PGRN如何通过激活C/EBPα而调控il10基因转录的分子机制、如何影响il10基因转录过程中染色体重塑和组蛋白修饰以及能否用PGRN来缓解微生物败血性休克反应。本课题将加深我们对PGRN抗炎分子机制的了解，从而为使用PGRN作为抗炎药物奠定基础。

前粒蛋白（progranulin, PGRN）是广泛表达的多向性蛋白，参与不同的生物过程，包括细胞增殖，神经元发育和伤口愈合。然而，PGRN对调节病原体诱导的系统性炎症反应所涉及的机制尚不清楚。我们2016年的研究显示PGRN缺陷小鼠显示在多微生物败血症和内毒素血症的模型中增加的死亡率，具有增加的炎症细胞因子的组织水平并降低IL-10产生。相反，施用rPGRN降低PGRN缺陷小鼠对LPS诱导的易感性内毒素休克，并以TNFR依赖性方式增强LPS-活化巨噬细胞的IL-10产生。分子分析揭示转录因子C/EBPa在PGRN调节的IL-10表达中的直接作用。 C/EBPa缺陷巨噬细胞响应LPS产生较少的IL-10。此外，在造血细胞中C/EBPa缺陷的小鼠是高度的易受LPS诱导的败血性休克的影响。最后，由PGRN缺陷细胞产生的IL-10缺陷主要是由于通过E3泛素轭合酶E6AP和蛋白酶体介导的降解降低C/EBPa蛋白稳定性。这项研究提供了第一个证据表明PGRN是系统性炎症反应的重要调节因子。PGRN的作用是通过调节C/EBPa，IL-10和泛素-蛋白酶体蛋白水解途径的水平和活性来进行的。该研究结果对人类PGRN功能不全及其突变相关的全身和器官特异性炎症疾病有着深刻影响。