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Am J Physiol Endocrinol Metab 298: E1-E7, 2010. First published November 3, 2009; doi: 10.1152/ajpendo.00562.2009.--Autophagy is a major degradative pathway(s) by which intracellular components are delivered into the lysosomes. It is largely implicated in determining cell death and survival because it eliminates unnecessary, damaged, and/or potentially harmful cellular products and organelles and is an important source for nutrients and energy production under conditions of external nutrient deficiency. As such, autophagy has been suggested to contribute to the regulation of carbohydrate and protein metabolism during fasting. Recently, three papers implicated a role for autophagy in cellular lipid metabolism as well. This Perspectives article presents these novel findings in the context of prior studies on the role of autophagy and lysosomes in metabolic and energy regulation, discusses their points of agreement and opposing propositions, and outlines key outstanding questions. lipolysis; liquid droplet biogenesis and breakdown; liquid droplet-associated proteins; lysosomal proteolysis

Intraabdominal (IA) fat functionally differs from subcutaneous (SC) adipose tissue, likely contributing to its stronger association with obesity-induced morbidity and to differential response to medications. Drug-induced partial lipodystrophy, like in response to antiretroviral agents, is an extreme manifestation of the different response of different fat depots, with loss of SC but not IA. Investigating depot-specific adipocyte differences is limited by the low accessibility to IA fat and by the heterogenous cell population comprising adipose tissue. Here, we aimed at utilizing immortalized preadipocyte cell lines from IA (epididymal) or SC (inguinal) fat to investigate whether they differentially respond to the HIV protease inhibitor nelfinavir. Preadipocytes were readily amenable to adipogenesis, as evidenced by lipid accumulation, expression of adipose-specific genes, measurable lipolysis, and insulin responsiveness. Leptin secretion was higher by the SC line, consistent with known differences between IA and SC fat. As previously reported, nelfinavir inhibited adipogenesis downstream of C/EBP[beta], but similarly in both cell lines. In contrast, nelfinavir's capacity to diminish insulin signaling, decrease leptin secretion, enhance basal lipolysis, and decrease expression of the lipid droplet-associated protein perilipin occurred more robustly and/or at lower nelfinavir concentrations in the SC line. This was despite similar intracellular concentrations of nelfinavir (23.8 [+ or -] 5.6 and 33.6 [+ or -] 12.2 [micro]g/mg protein for inguinal and epididymal adipocytes, respectively, P = 0.46). The cell lines recapitulated depot-differential effects of nelfinavir observed in differentiated primary preadipocytes and with whole tissue explants. Thus, we report the use of fat depot-specific adipocyte cell lines for unraveling depot-differential responses to a drug causing partial lipodystrophy. nelfinavir; lipolysis; perilipin; intra-abdominal adipocytes; subcutaneous adipocytes

Increased oxidative stress is believed to be one of the mechanisms responsible for hyperglycemia-induced tissue damage and diabetic complications. In these studies, we undertook to characterize glucose uptake and oxidative stress in adipocytes of type 2 diabetic animals and to determine whether these promote the activation of PKC-[delta]. The adipocytes used were isolated either from C57Bl/6J mice that were raised on a high-fat diet (HF) and developed obesity and insulin resistance or from control animals. Basal glucose uptake significantly increased (8-fold) in HF adipocytes, and this was accompanied with upregulation of GLUT1 expression levels. Insulin-induced glucose uptake was inhibited in HF adipocytes and GLUT4 content reduced by 20% in these adipocytes. Reactive oxygen species (ROS) increased twofold in HF adipocytes compared with control adipocytes and were largely reduced with decreased glucose concentrations. At zero glucose, ROS levels were reduced to the normal levels seen in control adipocytes. The activity of PKC-[delta] increased twofold in HF adipocytes compared with control adipocytes and was further activated by [H.sub.2][O.sub.2]. Moreover, PKC-[delta] activity was inhibited in HF adipocytes either by glucose deprivation or by treatment with the antioxidant N-acetyl-L-cysteine. In summary, we propose that increased glucose intake in HF adipocytes increases oxidative stress, which in turn promotes the activation of PKC-[delta]. These consequential events may be responsible, at least in part, for development of HF diet-induced insulin resistance in the fat tissue. oxidative stress; protein kinase C-[delta]; insulin resistance; glucose metabolism; C57B1/6J mice

The stimulation of glucose transport, lipogenesis and glycogen synthase activity were analyzed in 3T3-L1 adipocyte cell lines to determine the effects of oxidant stress on adipocyte insulin resistance. Prolonged exposure of 3T3-L1 adipocyte cell lines to glucose oxidase increased the uptake of basal 2-deoxyglucose and enhanced basal lipoxygenase activity. However, basal lipoxygenase activity was significantly reduced by insulin stimulation in a dose-dependent manner.

A study using the L6 line of skeletal muscle cells was conducted to determine the effect of the iron chelators deferoxamine and bipyridyl on glucose transport and the expression of the GLUT-1 transmembrane glycoprotein in cultured muscle cells. The results show that L6 muscle cells responded to the reduction of iron availability due to iron chelators by enhancing GLUT-1 expression, which increased glucose transport. Furthermore, muscle cells adapted to reduced iron availability without losing their normal sensitivity to insulin.

Inhibition of oxidative phosphorylation and the electron transport chain as well as hypoxic conditions led to elevated glucose uptake by L6 muscle cells and 3T3-L1 fat cells to twicethe normal levels while quickly depleting intracellular adenosine triphosphate stores. It is postulated that the depletion of energy stores activate glucose transport by synthesis and/or translocation of carrier proteins. This increasesthe availability of substrates for anaerobic energy generation.