AXL在狼疮性肾炎发病中的作用及调控靶点研究

Lupus nephritis (LN) is the most common and serious clinical feature of systemic lupus erythematosus (SLE). Abnormal structure or dysfunction of receptor tyrosine kinase (RTK) may be one of the pathogenesis of SLE, but the exact mechanism of AXL (one of the main members of RTK) in the pathogenesis of SLE is not clear. Our previous study showed: 1) the level of soluble AXL of SLE and LN patients in the serum is higher than the healthy control group.2) AXL expression levels on PBMCs negatively correlates with the levels of soluble AXL in the serum.3) The levels of soluble AXL in the spontaneous lupus mouse models are higher than the healthy control group, while the AXL expression on splenocytes and the surface of CD11b+ cells isolates from the lupus mouse models decreased. According to the literatures and our previous study, we hypothesize that AXL is the key RTK to control the proliferation and activation of immune cells in LN; sAXL acts as a decoy to trap the growth factor (Gas6) and inhibit the anti-inflammation signaling pathway mediated by Gas-AXL. To test the hypothesis, we will utilize the AXL-/- lupus mouse model to clarify the role of AXL and sAXL played in LN at the genetic level and protein level；We plan to use a novel microfluidic phosphopeptide array to scan possible phosphorylation targets downstream of AXL and validate the above results. The results of this study will help us to uncover what AXL and sAXL does in LN and supply us with potential novel treatment targets and strategy.

狼疮肾炎(LN) 是系统性红斑狼疮（SLE）患者常见的死亡原因。已知受体酪氨酸激酶（RTK）的功能异常参与SLE的发病；AXL是RTK的主要成员，以AXL及剪切产物sAXL形式存在。我们前期研究发现：1）SLE及LN患者sAXL水平高于正常人；2）SLE患者sAXL水平和外周血单核细胞表达的AXL水平呈反比；3）LN小鼠sAXL水平升高，脾细胞和CD11b+细胞表面的AXL表达下调。据此我们认为：AXL/sAXL调控异常在狼疮合并肾损伤的发病中起重要作用；其机制与sAXL抑制Gas6-AXL介导的抗炎信号通路相关。为此，拟利用AXL-/-的LN小鼠模型评价AXL/sAXL在LN发病中的关键作用；并用新型磷酸肽芯片确定AXL下游关键调控靶点。为探索sAXL分子及下游关键分子的阻断剂的联合治疗LN新方案提供实验依据。

系统性红斑狼疮（SLE）是一种抗体介导的自身免疫炎症，研究发现若干炎症信号通路参与SLE发病，对于这些信号通路的干预有望减轻红斑狼疮的病症。而狼疮肾损害是系统性红斑狼疮常见的并发症，及严重的器官损伤之一。AXL是一种细胞膜表面的酪氨酸激酶受体，通过对Axl酪氨酸激酶受体与其配体Gas6 相关的信号通路的干预，可以阻断免疫介导的炎症反应。因此我们提出假设：AXL可能在系统性红斑狼疮病人起到重要的作用，抑制AXL信号通路可改善狼疮肾炎的疾病进展。前期我们利用ELISA技术检测红斑狼疮病人、慢性肾脏病人、健康对照患者血清中sAXL的水平，证明狼疮患者血清中sAXL水平明显增高，并且血清中sAXL可作为红斑狼疮患者疾病活动的生物标志物；接着，我们采用MRL/lpr小鼠是模拟狼疮肾炎的动物模型，利用AXL抑制剂R428处理狼疮鼠来研究AXL在狼疮肾炎中的作用。ELISA技术证明狼疮鼠血清抗ds-DNA抗体明显增加，R428处理后血浆抗ds-DNA抗体减少；流式细胞术证明狼疮鼠脾细胞总数、脾B、边缘区B、滤泡中心B、T、CD4+T、CD8+T、DC、Mφ细胞数量明显增加，以及活化CD4、CD8也明显增加，而R428治疗后，免疫细胞数量有减少的趋势；病理切片提示，狼疮鼠肾小球系膜细胞及内皮细胞明显增生，R428处理后肾损伤减轻，肾病理评分降低。根据以上结果，证明抑制AXL受体，阻断AXL-Gas6信号通路可能减少狼疮肾炎的疾病进展。探索AXL在系统性红斑狼疮肾炎中的作用，为临床系统性红斑狼疮治疗提供新靶点，为改善狼疮病人肾脏受累情况提供可能。