Hedgehog通过Gli介导调控巨噬细胞极化影响急性肾损伤的分子机制

Macrophages are important inflammatory cells in the process of acute renal injury (AKI), and can be polarized into inflammatory phenotype (M1) and promoting repair (M2) phenotype, which play critical roles in the process and prognosis of AKI. But how to start and regulate macrophage polarization in AKI remains unknown. Our previous studies have shown that M1 phenotype were the majority in early stage of AKI and M2 phenotype in later stage, and both of these polarizations are accompanied by the activation of the hedgehog signaling. Moreover, exogenous sonic hedgehog (Shh)-induced activation of the hedgehog signaling in cultured macrophages resulted in the polarization of M1 and M2 phenotype, suggesting a close relationship of hedgehog signaling and macrophage bidirectional polarization. Further study showed that the Gli, a downstream transcription factor of hedgehog signaling, may be crucial for macrophage to be polarized into different phenotypes. Moreover, Gli itself is differentially induced by hypoxia. Therefore, we hypothesized that different Gli molecules (Gli1/2/3) mediate hedgehog signaling to regulate M1 or M2 polarization in response to hypoxia, resulting in AKI inflammatory injury and repair. In this study, the effects of hypoxia-hedgehog-Gli signaling axis on macrophage polarization in AKI in vitro and in vivo and clinical samples were performed. In addition, whether the IRF4/5 was involved in macrophage polarization induced by hedgehog-Gli was investigated. This study clarifies the molecular mechanism that Gli-mediated hedgehog signaling regulates macrophage polarization in AKI, which can provide a new strategy for early intervention of AKI.

巨噬细胞是急性肾损伤（AKI）重要的炎症细胞，可极化为促炎型M1和修复型M2两种表型，影响AKI进程和预后。但AKI中如何启动和调控巨噬细胞极化不清楚。前期研究发现AKI早期巨噬细胞以M1为主，后期以M2为主，两者均伴有Hedgehog（HH）信号的活化；体外实验表明M1或M2的极化均与HH信号相关；深入研究显示信号下游Gli为诱导巨噬细胞向不同表型极化的关键，且受缺氧调控。就此我们提出假设：缺氧损伤引起不同Gli（Gli1/2/3）的活化，介导了HH信号对M1或M2极化的调控，进而影响AKI炎症损伤和修复。拟通过体内体外及临床样本，应用转基因、过表达等技术，研究AKI中缺氧-HH-Gli信号轴对巨噬细胞极化的作用；在此基础上，深入解析Gli影响巨噬细胞极化机制是否涉及IRF4/5的调控。本课题阐明HH信号通过Gli介导调控巨噬细胞极化影响AKI的作用机制，可为AKI早期干预提供新的策略。

急性肾损伤（AKI）是一种临床常见的危重病症，病死率较高，且目前尚无确实有效的治疗药物。因此，阐明AKI发病机制，进行早期干预是改善AKI预后的关键。巨噬细胞是AKI发生过程中重要的炎症细胞。巨噬细胞累积是诱导AKI发生的重要因素，同时巨噬细胞也具有组织保护作用。巨噬细胞在AKI中这种生物学效应差异与其表型异质性有关。在不同的微环境下，巨噬细胞能极化为诱导炎症损伤（M1型）或促进修复（M2型）两种截然不同的功能状态。然而，在损伤微环境中肾组织如何启动和调控巨噬细胞极化，进而影响AKI损伤修复进程和预后等科学问题尚不清楚。本研究通过构建单侧输尿管梗阻肾损伤（UUO）、缺血再灌注肾损伤（IRI）、胰腺炎肾损伤（PKI）等多种AKI模型，证实了AKI存在明显的巨噬细胞浸润。进一步研究发现，AKI早期浸润的巨噬细胞以M1型为主，M1型可诱导TNF-α高表达促进早期炎症损伤，而AKI后期以M2型为主，通过提高TGF-β1水平促进纤维增生性修复。深入研究表明：AKI早期，Hedgehog经Gli3活化IRF5，诱导M1型极化，发挥炎症损伤作用；AKI后期，Hedgehog经Gli1或Gli2活化IRF4，诱导M2型极化，发挥组织修复功能。不同的Gli分子也通过调控能量代谢途径，影响巨噬细胞极化方式。此外，研究也显示LPS诱导M1型巨噬细胞极化过程中的机制可能也涉及IL-8/STK11/MARK2信号途径。除了Hedgehog信号外，损伤后肾脏的上皮细胞和间质Notch1信号也被激活，通过靶向下游TGF-β1/Smad2/3信号，诱导肾小管上皮细胞表型转化，促进成纤维细胞转分化形成肌纤维母细胞表型，最终引起间质纤维化的发生发展。在此基础上，我们筛选了多种中草药成分。垂盆草提取物及其主要成分槲皮素均可通过NF-κB和IRF信号调控巨噬细胞极化，缓解AKI。此外，研究也发现白藜芦醇和白术内酯I等药物可通过调控增殖相关信号途径，从体内和体外抑制肌成纤维细胞表型和间质纤维化，因此具有拮抗AKI引起的间质纤维化作用。本研究一定程度上阐明AKI中炎症和纤维化机制，为今后AKI防治提供全新的治疗方案，同时也为炎症损伤时的脏器保护提供药物研发和治疗的理论基础。