Background

Retinol-binding protein 4 (RBP4) is elevated and associated with inflammation in metabolic diseases. Disruption of the retinol cascade and O-GlcNAcylation of the RBP4 receptor (STRA6) are found in diabetic kidneys.

Objectives

We investigated whether the disruption of the retinol cascade induces RBP4 overproduction and if O-linked GlcNAc modification targets RBPR2 and contributes to the disruption of retinol cascades in diabetic livers.

Methods

Western blot or immunohistochemistry for RBPR2, CRBP1, LRAT, RALDH, RARα, RARγ, RXRα, RBP4, GFAT, OGT, OGA and inflammatory markers, as well as ELISA for RBP4, were performed in livers of db/db and ob/ob mice and high glucose-cultured hepatocytes. Immunoprecipitation and dual fluorescence staining were used to explore O-GlcNAc-modified RBPR2 and RBP4 binding activity on RBPR2. Transfection of the CRBP1 gene was done to verify whether a disrupted retinol cascade induces RBP4 overproduction. OGT silencing was done to investigate the association of O-GlcNAcylation with the disruption of retinol cascade.

Results

Disruption of retinol cascade, RBP4 overproduction, O-GlcNAcylation of RBPR2, decreased RBP4 binding activity on RBPR2 and inflammation were found in livers of db/db and ob/ob mice and high glucose-cultured hepatocytes. CRBP1 gene transfection reversed the suppression of the cellular retinol cascade and simultaneously attenuated the RBP4 overproduction and inflammation in high glucose-treated hepatocytes. The silencing of OGT reversed the disruption of the cellular retinol cascade, RBP4 overproduction and inflammation induced by high glucose in hepatocytes.

Conclusions

This study indicates that the disruption of cellular retinol cascade is strongly associated with RBP4 overproduction and inflammation in diabetic livers. RBPR2 is one target for high glucose-mediated O-linked GlcNAc modification, which causes liver retinol dyshomeostasis.

中文翻译：

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维甲酸类稳态的破坏引起糖尿病中RBP4的过度生产：涉及O -GlcNAcylation

背景

视黄醇结合蛋白4（RBP4）升高并与代谢疾病中的炎症相关。在糖尿病肾中发现视黄醇级联的破坏和RBP4受体（STRA6）的O- GlcNAcy化。

目标

我们调查了视黄醇级联的破坏是否诱导了RBP4的过度生产，以及O-连接的GlcNAc修饰是否靶向RBPR2并有助于糖尿病肝脏中视黄醇级联的破坏。

方法

在db / db和ob / ob小鼠的肝脏中进行了RBPR2，CRBP1，LRAT，RALDH，RARα，RARγ，RXRα，RBP4，GFAT，OGT，OGA和炎性标志物的蛋白质印迹或免疫组化分析和高葡萄糖培养的肝细胞。使用免疫沉淀和双重荧光染色来研究O -GlcNAc修饰的RBPR2和RBP4对RBPR2的结合活性。进行了CRBP1基因的转染，以验证视黄醇级联的破坏是否诱导RBP4过度生产。进行了OGT沉默以研究O- GlcNAcylation与视黄醇级联反应的破坏。

结果

在db / db和ob / ob小鼠的肝脏和高葡萄糖培养的肝细胞中发现了视黄醇级联的破坏，RBP4的过度生产，RBPR2的O -GlcNAcy化，RBP4对RBPR2的结合活性降低和炎症。CRBP1基因转染逆转了细胞视黄醇级联的抑制作用，同时减弱了高糖处理的肝细胞中RBP4的过度产生和炎症。OGT的沉默逆转了细胞视黄醇级联的破坏，RBP4的过度产生以及肝细胞中高糖诱导的炎症。

结论

这项研究表明，糖尿病细胞肝脏中视黄醇级联的破坏与RBP4的过度产生和炎症密切相关。RBPR2是高葡萄糖介导的O-连接的GlcNAc修饰的靶标，其引起肝视黄醇动态失调。