Abstract

Objective: To examine fat biopsy samples from lean, insulin sensitive and obese, insulin resistant non-diabetic individuals for evidence of ER stress.

Research Design and Methods: Subcutaneous fat biopsies were obtained from the upper thighs of 6 lean and 6 obese non-diabetic subjects. Fat homogenates were used for proteomic (2-D gel and MALDI-TOF-TOF), Western blot, and RT-PCR analysis.

Results: Proteomic analysis revealed 19 differentially upregulated proteins in fat of obese subjects. Three of these proteins were the ER stress related unfolded protein response (UPR), proteins calreticulin (CRT), protein disulfide-isomerase A3 (PDI) and glutathione-S-transferase P. Western blotting revealed upregulation of several other UPR stress related proteins including calnexin (CNX), a membrane bound chaperone and phospho c-jun NH₂-terminal kinase 1 (JNK-1), a downstream effector protein of ER stress. RT-PCR analysis revealed upregulation of the spliced form of X box protein-1 (XBP-1s), a potent transcription factor and part of the proximal ER stress sensor, inositol requiring enzyme 1 (IRE 1) pathway.

Conclusion: These findings represent the first demonstration of UPR activation in subcutaneous adipose tissue of obese human subjects. As JNK can inhibit insulin action and activate proinflammatory pathways, ER stress activation of JNK may be a link between obesity, insulin resistance and inflammation.