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Insulin Signaling Regulation of Sortilin 1 and Glut4 Storage Vesicle Formation in NIH 3T3‐L1 Adipocytes and Mouse Adipose Tissue
Author(s) -
Li Jibiao,
Matye David,
Wang Yifeng,
Li Tiangang
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.307.2
Subject(s) - glut4 , 3t3 l1 , medicine , endocrinology , adipose tissue , glucose uptake , glucose transporter , insulin receptor , insulin , protein kinase b , chemistry , insulin resistance , biology , adipocyte , microbiology and biotechnology , signal transduction
Type‐II diabetes is associated with impaired insulin‐stimulated glucose uptake into the muscle and adipose tissues. Insulin regulates glucose uptake in adipocytes and muscle cells by promoting the plasma membrane translocation of the glucose transporter 4 (Glut4)‐containing storage vesicles, which is defective in type‐II diabetes. The intracellular trafficking receptor Sortilin 1 is an essential component of the Glut4 storage vesicles in adipocytes and mediates the insulin responsiveness of Glut4 translocation to the plasma membrane. Knockdown of Sortilin 1 impaired Glut4 storage vesicle formation and resulted in Glut4 degradation in NIH 3T3‐L1 cells. The objective of this study is to investigate the effect and molecular mechanism of insulin regulation of Sortilin 1 in differentiated 3T3‐L1 adipocytes and in mouse adipose tissue. Adipose Sortilin 1 and Glut4 protein levels were determined in obese and diabetic mice. The effects of insulin and insulin signaling inhibitors on Sortilin 1 mRNA and protein levels were determined in differentiated 3T3‐L1 adipocytes. The potential role of Sortilin 1 phosphorylation in mediating insulin regulation of Sortilin 1 was further investigated. Results showed that insulin induced Sortilin 1 protein, but not mRNA, in 3T3‐L1 adipocytes. Treatment of PI3K or AKT inhibitors decreased Sortilin 1 protein, but not mRNA in 3T3‐L1 cells. In addition, treatment of pro‐inflammatory cytokine TNFα impaired Insulin signaling and decreased Sortilin 1 protein in 3T3‐L1 adipocytes. Consistently, Sortilin 1 protein was down‐regulated in the white and brown adipose of obese and diabetic mice, which was partially restored after the administration of the insulin sensitizer metformin. In addition, intraperitoneal injection of a PI3K inhibitor in lean mice caused rapid downregulation of Sortilin 1 protein in the adipose tissue without alteration of Sortilin 1 mRNA levels. LC‐MS/MS analysis further revealed novel serine phosphorylation sites on Sortilin 1 protein. Additional mechanistic studies suggest that Sortilin 1 phosphorylation affects Sortilin1 protein trafficking function and stability, and potentially mediates insulin regulation of Sortilin 1. In conclusion, we have identified Sortilin 1 as a novel target of insulin signaling in adipose tissue, and suggest that insulin resistance may be responsible for the Sortilin 1 downregulation and impaired Glut4 storage vesicle formation in obesity and diabetes. Support or Funding Information American Diabetes Association, NIDDK