OBJECTIVEPeripheral insulin resistance is linked to an increase in reactive oxygen species (ROS), leading in part to the production of reactive lipid aldehydes that modify the side chains of protein amino acids in a reaction termed protein carbonylation. The primary enzymatic method for lipid aldehyde detoxification is via glutathione S-transferase A4 (GSTA4) dependent glutathionylation. The objective of this study was to evaluate the expression of GSTA4 and the role(s) of protein carbonylation in adipocyte function.RESEARCH DESIGN AND METHODSGSTA4-silenced 3T3-L1 adipocytes and GSTA4-null mice were evaluated for metabolic processes, mitochondrial function, and reactive oxygen species production. GSTA4 expression in human obesity was evaluated using microarray analysis.RESULTSGSTA4 expression is selectively downregulated in adipose tissue of obese insulin-resistant C57BL/6J mice and in human obesity-linked insulin resistance. Tumor necrosis factor-α treatment of 3T3-L1 adipocytes decreased GSTA4 expression, and silencing GSTA4 mRNA in cultured adipocytes resulted in increased protein carbonylation, increased mitochondrial ROS, dysfunctional state 3 respiration, and altered glucose transport and lipolysis. Mitochondrial function in adipocytes of lean or obese GSTA4-null mice was significantly compromised compared with wild-type controls and was accompanied by an increase in superoxide anion.CONCLUSIONSThese results indicate that downregulation of GSTA4 in adipose tissue leads to increased protein carbonylation, ROS production, and mitochondrial dysfunction and may contribute to the development of insulin resistance and type 2 diabetes.

SUMMARY Polyglutamine (polyQ) stretches exceeding a threshold length confer a toxic function on proteins that contain them and cause at least nine neurological disorders. The basis for this toxicity threshold is unclear. Although polyQ expansions render proteins prone to aggregate into inclusion bodies (IBs), IB formation may be a neuronal coping response to more toxic forms of polyQ. The exact structure of these more toxic forms is unknown. Here we show that monoclonal antibody (mAb) 3B5H10 recognizes a species of polyQ protein in situ that strongly predicts neuronal death. The epitope selectively appears among some of the many low-molecular weight conformational states expanded polyQ assumes and disappears in higher molecular-weight aggregated forms, such as IBs. These results suggest that protein monomers and possibly small oligomers containing expanded polyQ stretches can adopt a conformation that is recognized by 3B5H10 and is toxic or closely related to a toxic species.