<b>GAS6/AXL signaling pathway contributes to PLA2R overexpression in membranous nephropathy</b>

Phospholipase A2 receptor, PLA2R, is the most frequently targeted auto-antigen in membranous nephropathy(MN).However, the precise mechanisms PLA2R plays in the development and progression of the disease remain to be elucidated. From the microarray data ofthe NEPTUNE study, we found that AXL, a tyrosine protein kinase receptor,was expressed and elevatedin podocytesin patients with MN . We used in situ hybridization,immunofluorescence and immunogold analysesand provided direct evidences that AXL was localized in podocytes and elevated in renal biopsies from patients wtih MN. Furthermore, the ELISA and immunohistochemical analysesrevealed that the expression level of AXL was enhanced and correlated with poor renal outcomes in patients with MN. Notably, upon the stimulation with GAS6, the ligand of AXL, the level of PLA2R was upregulated in cultured human podocytesin vitrodue to delayed degradation while the knockout of AXL reversed the effect. Last, co-immunoprecipitationand Bio-Layer Interferometry analysesdemonstrated that AXL interacted directly withPLA2R. In conclusion, the present study shows that AXLis localized in podocytes and the increase in membranous nephropathy is correlated with the level of PLA2R. AXL could be used as a biomarker in the pathogenesis of membranous nephropathy.磷脂酶A2受体（Phospholipase A2 receptor, PLA2R）是膜性肾病（membranous nephropathy, MN）中最常见的靶向自身抗原。然而，PLA2R在该病发生与进展中的精确机制仍有待阐明。我们从NEPTUNE研究的微阵列数据中发现，酪氨酸蛋白激酶受体AXL在膜性肾病患者的足细胞中表达且水平升高。我们通过原位杂交、免疫荧光及免疫金分析，直接证实AXL定位于足细胞，且在膜性肾病患者的肾活检组织中表达上调。进一步的酶联免疫吸附试验（Enzyme-Linked Immunosorbent Assay, ELISA）与免疫组化分析显示，AXL的表达水平升高与膜性肾病患者较差的肾脏预后相关。值得注意的是，在AXL的配体GAS6刺激下，体外培养的人足细胞中PLA2R的水平因降解延迟而上调，而AXL基因敲除可逆转这一效应。此外，免疫共沉淀与生物层干涉测量法（Bio-Layer Interferometry）分析证实，AXL可与PLA2R直接相互作用。综上，本研究表明AXL定位于足细胞，其在膜性肾病中的表达升高与PLA2R水平相关，AXL可作为膜性肾病发病机制中的生物标志物。