Renal Research Institute and Departments of Medicine, Pharmacology, and Physiology, New York Medical College, Touro University, Valhalla, New York.
Department of Nephrology and Rheumatology, Göttingen University , Göttingen , Germany.
Am J Physiol Heart Circ Physiol. 2018 Mar 1;314(3):H484-H496. doi: 10.1152/ajpheart.00548.2017. Epub 2017 Nov 3.
Syndecan-4 (Synd4) is a member of the membrane-spanning, glycocalyx-forming proteoglycan family. It has been suggested that Synd4 participates in renal fibrosis. We compared wild-type and fibrosis-prone endothelial sirtuin 1-deficient (Sirt1) mice, the latter being a model of global endothelial dysfunction. We performed mass spectrometry analysis, which revealed that Synd4 was highly enriched in the secretome of renal microvascular endothelial cells obtained from Sirt1 mice upon stimulation with transforming growth factor-β; notably, all detectable peptides were confined to the ectodomain of Synd4. Elevated Synd4 was due to enhanced NF-κB signaling in Sirt1 mice, while its shedding occurred as a result of oxidative stress in Sirt1 deficiency. Synd4 expression was significantly enhanced after unilateral ureteral obstruction compared with contralateral kidneys. Furthermore, hyperplasia of renal myofibroblasts accompanied by microvascular rarefaction and overexpression of Synd4 were detected in Sirt1 mice. The ectodomain of Synd4 acted as a chemoattractant for monocytes with higher levels of macrophages and higher expression levels of Synd4 in the extracellular matrix of Sirt1 mice. In vitro, ectodomain application resulted in generation of myofibroblasts from cultured renal fibroblasts, while in vivo, subcapsular injection of ectodomain increased interstitial fibrosis. Moreover, the endothelial glycocalyx was reduced in Sirt1 mice, highlighting the induction of Synd4 occurring in parallel with the depletion of its intact form and accumulation of its ectodomain in Sirt1 mice. On the basis of our experimental results, we propose that it is the Synd4 ectodomain per se that is partially responsible for fibrosis in unilateral ureteral obstruction, especially when it is combined with endothelial dysfunction. NEW & NOTEWORTHY Our findings suggest that endothelial dysfunction induces the expression of syndecan-4 via activation of the NF-κB pathway. Furthermore, we show that syndecan-4 is shed to a greater amount because of increased oxidative stress in dysfunctional endothelial cells and that the release of the syndecan-4 ectodomain leads to tubulointerstitial fibrosis.
硫酸乙酰肝素蛋白聚糖 4（Syndecan-4，Synd4）是一种跨膜糖蛋白聚糖家族成员，它参与了肾纤维化的形成。我们比较了野生型和易发生纤维化的内皮组织蛋白酶 SIRT1 缺陷（Sirt1）小鼠，后者是一种内皮功能障碍的全身性模型。我们进行了质谱分析，结果显示 Synd4 在转化生长因子-β刺激的 Sirt1 小鼠肾脏微血管内皮细胞的分泌组中高度富集；值得注意的是，所有可检测到的肽都局限于 Synd4 的细胞外结构域。在 Sirt1 小鼠中，NF-κB 信号的增强导致 Synd4 升高，而 Synd4 的脱落则是由于 Sirt1 缺乏导致的氧化应激。与对侧肾脏相比，单侧输尿管梗阻后 Synd4 的表达显著增加。此外，在 Sirt1 小鼠中检测到肾肌成纤维细胞增生，伴有微血管稀疏和 Synd4 过度表达。 Synd4 的细胞外结构域作为一种趋化因子，吸引单核细胞，导致 Sirt1 小鼠中巨噬细胞增多，细胞外基质中 Synd4 表达水平升高。在体外，细胞外结构域的应用导致培养的肾成纤维细胞生成肌成纤维细胞，而在体内，细胞外结构域的囊下注射增加了间质纤维化。此外，Sirt1 小鼠的内皮糖萼减少，突出了 Synd4 的诱导与完整形式的消耗以及其细胞外结构域在 Sirt1 小鼠中的积累同时发生。基于我们的实验结果，我们提出，正是 Synd4 的细胞外结构域本身部分导致了单侧输尿管梗阻中的纤维化，尤其是当它与内皮功能障碍相结合时。本研究的新颖之处在于，我们发现内皮功能障碍通过激活 NF-κB 通路诱导 Syndecan-4 的表达。此外，我们还表明，由于功能失调的内皮细胞中氧化应激的增加， Syndecan-4 的脱落量增加，并且 Syndecan-4 细胞外结构域的释放导致肾小管间质纤维化。
