Insulin resistance in muscle, adipocytes and liver is a gateway to a number of metabolic diseases. Here, we show a selective deficiency in mitochondrial coenzyme Q (CoQ) in insulin-resistant adipose and muscle tissue. This defect was observed in a range of in vitro insulin resistance models and adipose tissue from insulin-resistant humans and was concomitant with lower expression of mevalonate/CoQ biosynthesis pathway proteins in most models. Pharmacologic or genetic manipulations that decreased mitochondrial CoQ triggered mitochondrial oxidants and insulin resistance while CoQ supplementation in either insulin-resistant cell models or mice restored normal insulin sensitivity. Specifically, lowering of mitochondrial CoQ caused insulin resistance in adipocytes as a result of increased superoxide/hydrogen peroxide production via complex II. These data suggest that mitochondrial CoQ is a proximal driver of mitochondrial oxidants and insulin resistance, and that mechanisms that restore mitochondrial CoQ may be effective therapeutic targets for treating insulin resistance.

Background: We searched for novel regulators of insulin-stimulated glucose transport in adipocytes.Results: Tumor suppressor candidate 5 (TUSC5) colocalized with GLUT4, and manipulation of TUSC5 expression levels affected insulin-regulated glucose transport.Conclusion: TUSC5 is a novel regulator of insulin-stimulated glucose transport.Significance: TUSC5 contributes to insulin-sensitizing effects of PPARγ agonists in adipocytes.

Background: Insulin resistance is an early risk factor for metabolic disease. Results: Using various insulin resistance models, insulin regulation of glucose metabolism was universally blunted, whereas other actions (protein synthesis and anti-lipolysis) were unimpaired. Conclusion: Insulin resistance is selective for glucose metabolism in adipocytes. Significance: Chronic hyperactivation of unaffected insulin action pathways in the context of the metabolic syndrome likely contributes to disease progression.

Insulin and exercise stimulate glucose uptake into skeletal muscle via different pathways. Both stimuli converge on the translocation of the glucose transporter GLUT4 from intracellular vesicles to the cell surface. Two Rab guanosine triphosphatases-activating proteins (GAPs) have been implicated in this process: AS160 for insulin stimulation and its homolog, TBC1D1, are suggested to regulate exercise-mediated glucose uptake into muscle. TBC1D1 has also been implicated in obesity in humans and mice. We investigated the role of TBC1D1 in glucose metabolism by generating TBC1D1 2/2 mice and analyzing body weight, insulin action, and exercise. TBC1D12/2 mice showed normal glucose and insulin tolerance, with no difference in body weight compared with wild-type littermates. GLUT4 protein levels were reduced by ∼40% in white TBC1D1 2/2 muscle, and TBC1D1 2/2 mice showed impaired exercise endurance together with impaired exercise-mediated 2-deoxyglucose uptake into white but not red muscles. These findings indicate that the RabGAP TBC1D1 plays a key role in regulating GLUT4 protein levels and in exercise-mediated glucose uptake in nonoxidative muscle fibers.