Very low-density lipoprotein receptor (VLDLR) is a multifunctional transmembrane protein. Beyond the function of the full-length VLDLR in lipid transport, the soluble ectodomain of VLDLR (sVLDLR) confers anti-inflammatory and antiangiogenic roles in ocular tissues through inhibition of canonical Wnt signaling. However, it remains unknown how sVLDLR is shed into the extracellular space. In this study, we present the first evidence that a disintegrin and metalloprotease 17 (ADAM17) is responsible for sVLDLR shedding in human retinal pigment epithelium cells using pharmacological and genetic approaches. Among selected proteinase inhibitors, an ADAM17 inhibitor demonstrated the most potent inhibitory effect on sVLDLR shedding. siRNA-mediated knockdown or CRISPR/Cas9-mediated KO of ADAM17 diminished, whereas plasmid-mediated overexpression of ADAM17 promoted sVLDLR shedding. The amount of shed sVLDLR correlated with an inhibitory effect on the Wnt signaling pathway. Consistent with these in vitro findings, intravitreal injection of an ADAM17 inhibitor reduced sVLDLR levels in the extracellular matrix in the mouse retina. In addition, our results demonstrated that ADAM17 cleaved VLDLR only in cells coexpressing these proteins, suggesting that shedding occurs in a cis manner. Moreover, our study demonstrated that aberrant activation of Wnt signaling was associated with decreased sVLDLR levels, along with downregulation of ADAM17 in ocular tissues of an age-related macular degeneration model. Taken together, our observations reveal the mechanism underlying VLDLR cleavage and identify a potential therapeutic target for the treatment of disorders associated with dysregulation of Wnt signaling.

中文翻译：

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ADAM17 介导视网膜上皮中可溶性 VLDL 受体片段的胞外域脱落。

极低密度脂蛋白受体 (VLDLR) 是一种多功能跨膜蛋白。除了全长 VLDLR 在脂质转运中的功能之外，VLDLR 的可溶性胞外域 (sVLDLR) 通过抑制经典 Wnt 信号传导在眼组织中赋予抗炎和抗血管生成作用。然而，sVLDLR 如何进入细胞外空间仍然未知。在这项研究中，我们提出了第一个证据，即使用药理学和遗传学方法，解整合素和金属蛋白酶 17 (ADAM17) 是人视网膜色素上皮细胞中 sVLDLR 脱落的原因。在选定的蛋白酶抑制剂中，ADAM17 抑制剂表现出对 sVLDLR 脱落最有效的抑制作用。siRNA 介导的击倒或 CRISPR/Cas9 介导的 ADAM17 KO 减弱，而质粒介导的 ADAM17 过表达促进了 sVLDLR 脱落。脱落的 sVLDLR 量与对 Wnt 信号通路的抑制作用相关。与这些体外研究结果一致，玻璃体内注射 ADAM17 抑制剂降低了小鼠视网膜细胞外基质中的 sVLDLR 水平。此外，我们的结果表明 ADAM17 仅在共表达这些蛋白质的细胞中切割 VLDLR，表明脱落以顺式方式发生。此外，我们的研究表明，Wnt 信号的异常激活与 sVLDLR 水平降低以及年龄相关性黄斑变性模型眼组织中 ADAM17 的下调有关。综合起来，