BACKGROUND:Microvascular complications are the major outcome of type 2 diabetes progression, and the underlying mechanism remains to be determined.METHODS:High-throughput RNA sequencing was performed using human monocyte samples from controls and diabetes. The transgenic mice expressing human CTSD (cathepsin D) in the monocytes was constructed using CD68 promoter. In vivo 2-photon imaging, behavioral tests, immunofluorescence, transmission electron microscopy, Western blot analysis, vascular leakage assay, and single-cell RNA sequencing were performed to clarify the phenotype and elucidate the molecular mechanism.RESULTS:Monocytes expressed high-level CTSD in patients with type 2 diabetes. The transgenic mice expressing human CTSD in the monocytes showed increased brain microvascular permeability resembling the diabetic microvascular phenotype, accompanied by cognitive deficit. Mechanistically, the monocytes release nonenzymatic pro-CTSD to upregulate caveolin expression in brain endothelium triggering caveolae-mediated transcytosis, without affecting the paracellular route of brain microvasculature. The circulating pro-CTSD activated the caveolae-mediated transcytosis in brain endothelial cells via its binding with low-density LRP1 (lipoprotein receptor-related protein 1). Importantly, genetic ablation of CTSD in the monocytes exhibited a protective effect against the diabetes-enhanced brain microvascular transcytosis and the diabetes-induced cognitive impairment.CONCLUSIONS:These findings uncover the novel role of circulatory pro-CTSD from monocytes in the pathogenesis of cerebral microvascular lesions in diabetes. The circulatory pro-CTSD is a potential target for the intervention of microvascular complications in diabetes.

中文翻译：

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单核细胞释放组织蛋白酶 D 前体驱动糖尿病患者的血脑转胞吞作用

背景：微血管并发症是2型糖尿病进展的主要结果，其潜在机制仍有待确定。方法：使用来自对照和糖尿病的人单核细胞样本进行高通量RNA测序。使用CD68启动子构建在单核细胞中表达人CTSD（组织蛋白酶D）的转基因小鼠。通过体内2光子成像、行为测试、免疫荧光、透射电镜、Western blot分析、血管渗漏分析和单细胞RNA测序来阐明表型并阐明分子机制。 结果：单核细胞高水平表达CTSD 2 型糖尿病患者。在单核细胞中表达人类 CTSD 的转基因小鼠表现出类似于糖尿病微血管表型的脑微血管通透性增加，并伴有认知缺陷。从机制上讲，单核细胞释放非酶促 CTSD 前体，上调脑内皮细胞中小窝蛋白的表达，从而触发小窝介导的转胞吞作用，而不影响脑微血管系统的细胞旁途径。循环中的前 CTSD 通过与低密度 LRP1（脂蛋白受体相关蛋白 1）结合，激活脑内皮细胞中小窝介导的转胞吞作用。重要的是，单核细胞中 CTSD 的基因消融对糖尿病增强的脑微血管转胞吞作用和糖尿病引起的认知障碍具有保护作用。 结论：这些发现揭示了单核细胞循环前 CTSD 在脑微血管发病机制中的新作用糖尿病的病变。循环pro-CTSD是干预糖尿病微血管并发症的潜在靶点。