Grander Clinic, Kaohsiung, Taiwan; School of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan.
The Graduate Institute of Animal Vaccine Technology, National Pingtung University of Science and Technology, Pingtung, Taiwan; General Research Service Center, National Pingtung University of Science and Technology, Pingtung, Taiwan.
Metabolism. 2020 Dec;113:154403. doi: 10.1016/j.metabol.2020.154403. Epub 2020 Oct 14.
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.
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.
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.
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.
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.
视黄醇结合蛋白 4（RBP4）在代谢性疾病中升高并与炎症有关。在糖尿病肾脏中发现视黄醇级联和 RBP4 受体（STRA6）的 O-GlcNAc 糖化作用被破坏。
我们研究了视黄醇级联的破坏是否会导致 RBP4 过度产生，以及 O-连接的 GlcNAc 修饰是否靶向 RBPR2 并导致糖尿病肝脏中视黄醇级联的破坏。
在 db/db 和 ob/ob 小鼠的肝脏以及高葡萄糖培养的肝细胞中，通过 Western blot 或 RBPR2、CRBP1、LRAT、RALDH、RARα、RARγ、RXRα、RBP4、GFAT、OGT、OGA 和炎症标志物的免疫组织化学染色，以及 RBP4 的 ELISA 进行检测。免疫沉淀和双荧光染色用于探索 O-GlcNAc 修饰的 RBPR2 和 RBP4 与 RBPR2 的结合活性。转染 CRBP1 基因以验证视黄醇级联的破坏是否导致 RBP4 过度产生。沉默 OGT 以研究 O-GlcNAc 糖化与视黄醇级联破坏的关系。
在 db/db 和 ob/ob 小鼠的肝脏以及高葡萄糖培养的肝细胞中发现，视黄醇级联的破坏、RBP4 过度产生、RBPR2 的 O-GlcNAc 糖化、RBP4 与 RBPR2 的结合活性降低以及炎症。CRBP1 基因转染逆转了高葡萄糖处理的肝细胞中细胞视黄醇级联的抑制，同时减轻了 RBP4 过度产生和炎症。OGT 沉默逆转了高葡萄糖诱导的肝细胞中细胞视黄醇级联、RBP4 过度产生和炎症的破坏。
本研究表明，细胞视黄醇级联的破坏与糖尿病肝脏中 RBP4 过度产生和炎症密切相关。RBPR2 是高葡萄糖介导的 O-连接 GlcNAc 修饰的靶标之一，导致肝脏视黄醇稳态失调。
