Inhibition of proteasome activity blocks the ability of TNF alpha to down-regulate G(i) proteins and stimulate lipolysis

Effects of physical exercise on muscle metabolism and meat quality characteristics of Mongolian sheep

The objective of this study was to investigate the effects of exercise training on muscle metabolism, fatty acid composition, carcass traits, and meat quality characteristics of Mongolian sheep. Fourteen Mongolian sheep were randomly divided into two groups (7 sheep in each) and placed in two adjacent livestock pens. One group of sheep was kept in the pen (Control [C] group) and the other group of sheep (Training [T] group) were driven away in a field to walk twice a day. The results showed a reduction in pH measured 45 min post mortem, L*, a*, and b* value, intramuscular fat, and carcass length, and an increase in the ultimate pH value and shear force in the meat of T group in comparison with that of C group (p < .050). Also, exercise training moderately affected the fatty acid composition of LT muscle. Compared with C group, the concentrations of myristoleic acid (C14:1) and stearic acid (C18:0) were increased (p < .050), while the concentrations of C20:3 n‐6, neurolic acid (C24:1), and n‐3 polyunsaturated fatty acid (PUFA) were decreased in T group (p < .050). Transcriptome analysis highlighted 621 genes differentially expressed in two groups, including 385 were up‐regulated (e.g., GLUT4 and PGC‐1α) and 236 were down‐regulated (e.g., PLIN1 and ACSL3) in T with respect to C group. Besides, considering these genes, a number of enrichment pathways related to muscle metabolic processes, involving carbohydrate metabolism, lipid metabolism, oxidation reduction process, and muscle tissue development, were highlighted. In conclusion, these results contributed to a better understanding of the possible biological and molecular processes underlying the effects of exercise training on muscle metabolism and meat quality in Mongolian sheep, and provide useful information for contributing to understand the phenotypic and functional differences in meat quality of sheep.

DOCK2 deficiency mitigates HFD-induced obesity by reducing adipose tissue inflammation and increasing energy expenditure

Obesity is the major risk factor for type 2 diabetes, cardiovascular disorders, and many other diseases. Adipose tissue inflammation is frequently associated with obesity and contributes to the morbidity and mortality. Dedicator of cytokinesis 2 (DOCK2) is involved in several inflammatory diseases, but its role in obesity remains unknown. To explore the function of DOCK2 in obesity and insulin resistance, WT and DOCK2-deficient (DOCK2^-/-) mice were given chow or high-fat diet (HFD) for 12 weeks followed by metabolic, biochemical, and histologic analyses. DOCK2 was robustly induced in adipose tissues of WT mice given HFD. DOCK2^-/- mice with HFD showed decreased body weight gain and improved metabolic homeostasis and insulin resistance compared with WT mice. DOCK2 deficiency also attenuated adipose tissue and systemic inflammation accompanied by reduced macrophage infiltration. Moreover, DOCK2^-/- mice exhibited increased expression of metabolic genes in adipose tissues with greater energy expenditure. Mechanistically, DOCK2 appeared to regulate brown adipocyte differentiation because increased preadipocyte differentiation to brown adipocytes in interscapular and inguinal fat was observed in DOCK2^-/- mice, as compared with WT. These data indicated that DOCK2 deficiency protects mice from HFD-induced obesity, at least in part, by stimulating brown adipocyte differentiation. Therefore, targeting DOCK2 may be a potential therapeutic strategy for treating obesity-associated diseases.

Molecular implications of adenosine in obesity

Adenosine has broad activities in organisms due to the existence of multiple receptors, the differential adenosine concentrations necessary to activate these receptors and the presence of proteins able to synthetize, degrade or transport this nucleoside. All adenosine receptors have been reported to be involved in glucose homeostasis, inflammation, adipogenesis, insulin resistance, and thermogenesis, indicating that adenosine could participate in the process of obesity. Since adenosine seems to be associated with several effects, it is plausible that adenosine participates in the initiation and development of obesity or may function to prevent it. Thus, the purpose of this review was to explore the involvement of adenosine in adipogenesis, insulin resistance and thermogenesis, with the aim of understanding how adenosine could be used to avoid, treat or improve the metabolic state of obesity. Treatment with specific agonists and/or antagonists of adenosine receptors could reverse the obesity state, since adenosine receptors normalizes several mechanisms involved in obesity, such as lipolysis, insulin sensitivity and thermogenesis. Furthermore, obesity is a preventable state, and the specific activation of adenosine receptors could aid in the prevention of obesity. Nevertheless, for the treatment of obesity and its consequences, more studies and therapeutic strategies in addition to adenosine are necessary.

Fat in flames: influence of cytokines and pattern recognition receptors on adipocyte lipolysis

Adipose tissue has the largest capacity to store energy in the body and provides energy through the release of free fatty acids during times of energy need. Different types of immune cells are recruited to adipose tissue under various physiological conditions, indicating that these cells contribute to the regulation of adipose tissue. One major pathway influenced by a number of immune cells is the release of free fatty acids through lipolysis during both physiological (e.g., cold stress) and pathophysiological processes (e.g., obesity, type 2 diabetes). Adipose tissue expansion during obesity leads to immune cell infiltration and adipose tissue remodeling, a homeostatic process that promotes inflammation in adipose tissue. The release of proinflammatory cytokines stimulates lipolysis and causes insulin resistance, leading to adipose tissue dysfunction and systemic disruptions of metabolism. This review focuses on the interactions of cytokines and other inflammatory molecules that regulate adipose tissue lipolysis during physiological and pathophysiological states.

Three-dimensional spheroid cell model of in vitro adipocyte inflammation

To improve treatment of obesity, a contributing factor to multiple systemic and metabolic diseases, a better understanding of metabolic state and environmental stress at the cellular level is essential. This work presents development of a three-dimensional (3D) in vitro model of adipose tissue displaying induced lipid accumulation as a function of fatty acid supplementation that, subsequently, investigates cellular responses to a pro-inflammatory stimulus, thereby recapitulating key stages of obesity progression. Three-dimensional spheroid organization of adipose cells was induced by culturing 3T3-L1 mouse preadipocytes on an elastin-like polypeptide-polyethyleneimine (ELP-PEI)-coated surface. Results indicate a more differentiated phenotype in 3D spheroid cultures relative to two-dimensional (2D) monolayer analogues based on triglyceride accumulation, CD36 and CD40 protein expression, and peroxisome proliferator-activated receptor-γ (PPAR-γ) and adiponectin mRNA expression. The 3T3-L1 adipocyte spheroid model was then used to test the effects of a pro-inflammatory microenvironment, namely maturation in the presence of elevated fatty acid levels followed by acute exposure to tumor necrosis factor alpha (TNF-α). Under these conditions, we demonstrate that metabolic function was reduced across all cultures exposed to TNF-α, especially so when pre-exposed to linoleic acid. Further, in response to TNF-α, enhanced lipolysis, monitored as increased extracellular glycerol and fatty acids levels, was observed in adipocytes cultured in the presence of exogenous fatty acids. Taken together, our 3D spheroid model showed enhanced adipogenic differentiation and presents a platform for elucidating the key phenotypic responses that occur in pro-inflammatory microenvironments that characterize obesogenic states.

Regulation of adipocyte lipolysis

In adipocytes the hydrolysis of TAG to produce fatty acids and glycerol under fasting conditions or times of elevated energy demands is tightly regulated by neuroendocrine signals, resulting in the activation of lipolytic enzymes. Among the classic regulators of lipolysis, adrenergic stimulation and the insulin-mediated control of lipid mobilisation are the best known. Initially, hormone-sensitive lipase (HSL) was thought to be the rate-limiting enzyme of the first lipolytic step, while we now know that adipocyte TAG lipase is the key enzyme for lipolysis initiation. Pivotal, previously unsuspected components have also been identified at the protective interface of the lipid droplet surface and in the signalling pathways that control lipolysis. Perilipin, comparative gene identification-58 (CGI-58) and other proteins of the lipid droplet surface are currently known to be key regulators of the lipolytic machinery, protecting or exposing the TAG core of the droplet to lipases. The neuroendocrine control of lipolysis is prototypically exerted by catecholaminergic stimulation and insulin-induced suppression, both of which affect cyclic AMP levels and hence the protein kinase A-mediated phosphorylation of HSL and perilipin. Interestingly, in recent decades adipose tissue has been shown to secrete a large number of adipokines, which exert direct effects on lipolysis, while adipocytes reportedly express a wide range of receptors for signals involved in lipid mobilisation. Recently recognised mediators of lipolysis include some adipokines, structural membrane proteins, atrial natriuretic peptides, AMP-activated protein kinase and mitogen-activated protein kinase. Lipolysis needs to be reanalysed from the broader perspective of its specific physiological or pathological context since basal or stimulated lipolytic rates occur under diverse conditions and by different mechanisms.

Lack of platelet-activating factor receptor protects mice against diet-induced adipose inflammation and insulin-resistance despite fat pad expansion

OBJECTIVE

The role of platelet-activating factor (PAF) on diet-induced inflammatory and metabolic dysfunction is unknown. The effects of diet-induced metabolic and inflammatory dysfunction in mice with deletion of the PAF receptor (PAFR(-/-) ) were evaluated in this study.

METHODS

Wild-type and PAFR(-/-) mice were fed chow (WT-C and PAFR(-/-) -C) or high-refined carbohydrate-containing diet (WT-HC and PAFR(-/-) -HC). PAFR(-/-) - RESULTS: HC mice gained more weight and adiposity than PAFR(-/-) -C and WT-HC mice. Lipogenesis increased and hormone-sensitive lipase expression decreased in PAFR(-/-) -HC compared to WT-HC mice. WT-HC mice had impaired glucose tolerance and insulin sensitivity compared to WT-C mice. In contrast, glucose tolerance and insulin sensitivity in PAFR(-/-) -HC mice were similar to that of lean littermates. PAFR(-/-) -HC mice expressed significantly more peroxisome proliferator-activator receptor gamma (PPARγ) than PAFR(-/-) -C and WT-C mice. Resistin increased in WT-HC mice compared to WT-C mice. However, the levels of resistin were 35% lower in PAFR(-/-) -HC mice than WT-HC mice. PAFR(-/-) presented with less HC diet-induced adipose tissue inflammation than WT mice. Adipocytes isolated from PAFR(-/-) mice incubated in media containing normal or high levels of glucose secreted less interleukin-6 and tumor necrosis factor alpha and presented lower rate of lipolysis than WT mice.

CONCLUSION

PAFR deficiency resulted in less inflammation in adipose tissue and improvement in glucose homeostasis when fed the HC diet. The higher adiposity observed in PAFR(-/-) mice fed HC diet could be owing to the maintenance of insulin sensitivity, decreased adipocyte lipolysis rate, high lipogenesis and PPARγ expression, and lower inflammatory milieu in adipose tissue.

Expression of the GTP-binding protein Gαs in human myometrial cells is regulated by ubiquitination and protein degradation: involvement of proteasomal inhibition by trichostatin A

In this study, we show that myometrial transcriptional complexes consisting of Sp1, Sp3, histone deacetylase (HDAC)1/2, RbAp48, and mSin3A are recruited to 4 out of the 6 Sp1-4 sites within the Gαs promoter. Moreover disruption in the binding of these complexes via mithramycin administration results in a substantial decrease in expression of Gαs proteins in myometrial cell cultures. In many instances, these transcriptional regulatory complexes repress expression of genes having a high CG content within their promoter region. This repression can be attenuated by inhibition of HDAC activity by the class I/II HDAC inhibitor trichostatin A (TSA) resulting in increased gene transcription. However, although a substantial increase in Gαs protein levels was observed upon administration of TSA to primary cultures of human myometrial cells, this was not preceded by an increase in messenger RNA (mRNA) and thus an elevation in gene transcription. Importantly the increase in Gαs protein levels occurred via ubiquitination and inhibition of proteasomal activity, indicating that this pathway is also involved in regulating Gαs protein expression during pregnancy and parturition.

Regulation of adipose tissue lipolysis revisited

Human obesity and its complications are an increasing burden in developed and underdeveloped countries. Adipose tissue mass and the mechanisms that control it are central to elucidating the aetiology of obesity and insulin resistance. Over the past 15 years tremendous progress has been made in several avenues relating to adipose tissue. Knowledge of the lipolytic machinery has grown with the identification of new lipases, cofactors and interactions between proteins and lipids that are central to the regulation of basal and stimulated lipolysis. The dated idea of an inert lipid droplet has been appropriately revamped to that of a dynamic and highly-structured organelle that in itself offers regulatory control over lipolysis. The present review provides an overview of the numerous partners and pathways involved in adipose tissue lipolysis and their interaction under various metabolic states. Integration of these findings into whole adipose tissue metabolism and its systemic effects is also presented in the context of inflammation and insulin resistance.

Tumor necrosis factor-alpha modulates human in vivo lipolysis

CONTEXT

Low-grade systemic inflammation is a feature of most lifestyle-related chronic diseases. Enhanced TNF-alpha concentrations have been implicated in the development of hyperlipidemia.

OBJECTIVE

We hypothesized that an acute elevation of TNF-alpha in plasma would cause an increase in lipolysis, increasing circulatory free fatty acid (FFA) levels.

SUBJECTS AND METHODS

Using a randomized controlled, crossover design, healthy young male individuals (n = 10) received recombinant human (rh) TNF-alpha (700 ng/m(-2).h(-1)) for 4 h, and energy metabolism was evaluated using a combination of tracer dilution methodology and arterial-venous differences over the leg.

RESULTS

Plasma TNF-alpha levels increased from 0.7 +/- 0.04 to 16.7 +/- 1.8 pg/ml, and plasma IL-6 increased from 1.0 +/- 0.2 to 9.2 +/- 1.0 pg/ml (P < 0.05) after 4-h rhTNF-alpha infusion. Here, we demonstrate that 4-h rhTNF-alpha infusion increases whole body lipolysis by 40% (P < 0.05) with a concomitant increase in FFA clearance, with no changes in skeletal muscle FFA uptake, release, or oxidation. Of note, systemic glucose turnover and lactate and catecholamine levels were unaffected by rhTNF-alpha infusion.

CONCLUSION

This study demonstrates that a relatively low dose of rhTNF-alpha induces systemic lipolysis and that the skeletal muscle fat metabolism is unaffected.

Calpain is required for the rapid, calcium-dependent repair of wounded plasma membrane

Mammalian cells require extracellular calcium ion to undergo rapid plasma membrane repair seconds after mechanical damage. Utilizing transformed fibroblasts from calpain small subunit knock-out (Capns1-/-) mouse embryos, we now show that the heterodimeric, typical subclass of calpains is required for calcium-mediated survival after plasma membrane damage caused by scraping a cell monolayer. Survival of scrape-damaged Capns1-/- cells was unaffected by calcium in the scraping medium, whereas more Capns1+/+ cells survived when calcium was present. Calcium-mediated survival was increased when Capns1-/- cells were scraped in the presence of purified m- or mu-calpain. Survival rates of scraped Capns1+/+, HFL-1, or Chinese hamster ovary cells were decreased by the calpain inhibitor, calpeptin, or the highly specific calpain inhibitor protein, calpastatin. Capns1-/- cells failed to reseal following laser-induced membrane disruption, demonstrating that their decreased survival after scraping resulted, at least in part, from failed membrane repair. Proteomic and immunologic analyses demonstrated that the known calpain substrates talin and vimentin were exposed at the cell surface and processed by calpain following cell scraping. Autoproteolytic activation of calpain at the scrape site was evident at the earliest time point analyzed and appeared to precede proteolysis of talin and vimentin. The results indicate that conventional calpains are required for calcium-facilitated survival after plasma membrane damage and may act by localized remodeling of the cortical cytoskeleton at the injury site.

Importance of TNFalpha and neutral lipases in human adipose tissue lipolysis

Catecholamines and natriuretic peptides stimulate human adipocyte lipolysis through an increase in cAMP and cGMP levels, resulting in phosphorylation and activation of hormone-sensitive lipase. A defect in hormone-sensitive lipase expression might contribute to the resistance to catecholamine-induced lipolysis observed in obesity. The respective roles and regulation of hormone-sensitive lipase and adipose triglyceride lipase in spontaneous and hormone-stimulated lipolysis remain to be determined. Tumor necrosis factor alpha stimulates triglyceride hydrolysis by multiple intracellular pathways acting on insulin signaling, G proteins and perilipins, and might contribute to enhanced plasma fatty acid levels in obesity. Characterization of the lipolytic pathways might provide novel strategies to decrease free fatty acid production and reverse insulin resistance and other obesity-related metabolic complications.

Effects of tumor necrosis factor-alpha on the 26S proteasome and 19S regulator in skeletal muscle of severely scalded mice

The negative nitrogen balance after burns is an important factor in the rehabilitation and treatment of burn injury. It is known that the 26s protesome system plays a key role in the protein breakdown of skeletal muscle in some pathological situations, including burns, although the mechanism of which remains poorly understood. The present study surveyed the effect of tumor necrosis factor-alpha (TNF-alpha) on the 26S proteasome sysytem after burn injury, which is thought to be principally responsible for the proteolysis. The means of immuno-precipitation-deduction and enzyme-linked immunosorbent assay were used to test the change of activities and contents of 26S proteasome and 19S regulator in skeletal muscle of mice inflicted with 30% TBSA third-degree burns. The genes expression of 19S regulator's subunits Psmc2, Psmc5, Psmd1, and Psmd2 were examined by the use of reverse-transcription polymerase chain reaction. The results showed that TNF-alpha and burn can markedly increased the activities and contents of 26S proteasome and 19S regulator in mice skeletal muscle. In addition, the expression levels of the 19S regulator's subunits also were remarkably increased. The monoclonal antibody to TNF-alpha obviously can diminish the increment of the activities and contents of 26S proteasome and 19S regulator as much as the expression levels of the 19S regulator's subunits. The results suggested that TNF-alpha can activate the 26S proteasome system in skeletal muscle, thus enhancing the degradation of protein, which is associated with the development of negative nitrogen balance after scald.

The anti-inflammatory effect of exercise

Regular exercise offers protection against all-cause mortality, primarily by protection against cardiovascular disease and Type 2 diabetes mellitus. The latter disorders have been associated with chronic low-grade systemic inflammation reflected by a two- to threefold elevated level of several cytokines. Adipose tissue contributes to the production of TNF-α, which is reflected by elevated levels of soluble TNF-α receptors, IL-6, IL-1 receptor antagonist, and C-reactive protein. We suggest that TNF-α rather than IL-6 is the driver behind insulin resistance and dyslipidemia and that IL-6 is a marker of the metabolic syndrome, rather than a cause. During exercise, IL-6 is produced by muscle fibers via a TNF-independent pathway. IL-6 stimulates the appearance in the circulation of other anti-inflammatory cytokines such as IL-1ra and IL-10 and inhibits the production of the proinflammatory cytokine TNF-α. In addition, IL-6 enhances lipid turnover, stimulating lipolysis as well as fat oxidation. We suggest that regular exercise induces suppression of TNF-α and thereby offers protection against TNF-α-induced insulin resistance. Recently, IL-6 was introduced as the first myokine, defined as a cytokine that is produced and released by contracting skeletal muscle fibers, exerting its effects in other organs of the body. Here we suggest that myokines may be involved in mediating the health-beneficial effects of exercise and that these in particular are involved in the protection against chronic diseases associated with low-grade inflammation such as diabetes and cardiovascular diseases.

Adenylate cyclase regulation via proteasome-mediated modulation of Galphas levels

The adenylate cyclase (AC)/cyclic AMP (cAMP)/cAMP-dependent protein kinase pathway controls many biological phenomena. The ubiquitin/proteasome system, controlling the levels of many proteins, modulates important cellular processes such as cell cycle and cell growth. Here we describe a novel mechanism for AC regulation by proteasome pathway. Pharmacological inhibition of proteasome function in human osteosarcoma U2OS cells results in up-regulation of AC activity, increase of levels of alpha subunit of heterotrimeric stimulatory GTP-binding proteins (alphas) and, remarkably, also in preventing of beta-adrenergic receptor-mediated down-regulation of alphas protein levels. Accumulation of alphas protein is also accompanied by the appearance of polyubiquitinated alphas species. Our results: (1) identify alphas protein as a novel proteasome substrate in mammalian cells; (2) indicate that proteasome might play a physiological role in controlling AC/cAMP mediated pathways by modulating the levels of Galphas protein; (3) suggest a role for the proteasome also in controlling alphas-mediated signaling pathways other than those affecting AC complex.

Desensitization of the inhibitory effect of norepinephrine on insulin secretion from pancreatic islets of exercise-trained rats

The effect of exercise training (9 weeks of running) on norepinephrine-induced inhibition of insulin secretion was examined in rat islets. Insulin secretions from islets in the presence of glucose (> or =5.5 mmol/L) were significantly lower in trained (TR) than in control rats (CR). Norepinephrine inhibited 5.5 mmol/L glucose-stimulated insulin secretions and cyclic adenosine monophosphate (cAMP) contents in a dose-dependent manner in CR. Norepinephrine (10 micromol/L)-induced inhibition of insulin secretion was reversed by the blockade of the alpha(2)-adrenergic receptor in CR, but not in TR. Exercise training substantially shifted the dose-dependent curve for clonidine-induced inhibition of insulin secretions and that of cAMP contents to the right. Exercise training did not alter the density of the alpha(2)-adrenergic receptor either per islet or per protein of islet crude membrane. However, exercise training significantly reduced the protein expression of G alpha i-2 without change in G alpha i-2 mRNA. In CR but not in TR, norepinephrine significantly inhibited insulin secretions elicited by a combination of high glucose, a protein kinase C activator, and an adenylate cyclase activator under Ca(2+)-free conditions. Thus, exercise training appears to provoke a decreased expression of G alpha i-2 protein. This, at least in part, results in loss of the inhibitory effect of norepinephrine either on cAMP content or on insulin secretion at the post-calcium events in stimulus-secretion coupling, which, in turn, leads to the blunted inhibitory effects of norepinephrine on insulin secretion.

Acute exercise alters Gαi2 protein expressions through the ubiquitin–proteasome proteolysis pathway in rat adipocytes

The effects of acute exercise on the protein expressions of heterotrimeric G protein alpha subunits were examined in rat adipocytes. Galphai2 protein expression was significantly reduced 0 and 3h after exercise but increased 24h after exercise, without alterations in Galphai2 mRNA expressions. The protein expressions of other alpha subunits, Galphas, Galphai1, and Galphai3, were not influenced. Both the 26S proteasome activity and polyubiquitination of Galphai2 protein were significantly increased 0 and 3h after exercise. Whereas, proteasome activity was decreased, and the polyubiquitination of Galphai2 protein was returned to the control level 24h after exercise. The reductions in Galphai2 protein expressions 0 and 3h after exercise were completely prevented by the injection either of a proteasome inhibitor or of a beta-adrenergic receptor blocker prior to exercise. Thus, acute exercise altered the expression of Galphai2 protein via mechanisms which involve the coupling of beta-adrenergic receptors to an agonist with subsequent ubiquitin-proteasome-dependent proteolysis.

Heterotrimeric G protein subunits are located on rat liver endosomes

Background

Rat liver endosomes contain activated insulin receptors and downstream signal transduction molecules. We undertook these studies to determine whether endosomes also contain heterotrimeric G proteins that may be involved in signal transduction from G protein-coupled receptors.

Results

By Western blotting G_sα, G_iα1,2, G_iα3 and G_β were enriched in both canalicular (CM) and basolateral (BLM) membranes but also readily detectable on three types of purified rat liver endosomes in the order recycling receptor compartment (RRC) > compartment for uncoupling of receptor and ligand (CURL) > multivesicular bodies (MVB) >> purified secondary lysosomes. Western blotting with antibodies to Na, K-ATPase and to other proteins associated with plasma membranes and intracellular organelles indicated this was not due to contamination of endosome preparations by CM or BLM. Adenylate cyclase (AC) was also identified on purified CM, BLM, RRC, CURL and MVB. Percoll gradient fractionation of liver postnuclear supernatants demonstrated co-occurrence of endosomes and heterotrimeric G protein subunits in fractions with little plasma membrane markers. By confocal microscopy, punctate staining for G_sα, G_iα3 and G_β corresponded to punctate areas of endocytosed Texas red-dextran in hepatocytes from control and cholera toxin-treated livers.

Conclusion

We conclude that heterotrimeric G protein subunits as well as AC likely traffic into hepatocytes on endosome membranes, possibly generating downstream signals spatially separate from signalling generated at the plasma membrane, analogous to the role(s) of internalized insulin receptors.

Stimulation of lipolysis by tumor necrosis factor-alpha in 3T3-L1 adipocytes is glucose dependent: implications for long-term regulation of lipolysis

Tumor necrosis factor-alpha (TNF-alpha) and hyperglycemia both impair insulin sensitivity in vivo. This may be secondary to stimulation of adipose tissue lipolysis and consequent increased circulating free fatty acids (FFAs). Here we report that neither TNF-alpha nor glucose alone has a pronounced effect on lipolysis in 3T3-L1 adipocytes. However, the combination of TNF-alpha plus glucose markedly stimulates lipolysis. Glucose does not affect the ability of isoproterenol to stimulate lipolysis. Alternative substrates such as acetate, pyruvate, and lactate do not allow the TNF-alpha effect. Mannose was almost as effective as glucose; fructose was marginally effective, but galactose was ineffective. The effectiveness of the sugars corresponded with production of lactate, i.e., the cells readily produced lactate from glucose or mannose, slightly from fructose, and not at all from galactose. The ability of TNF-alpha to phosphorylate extracellular signal-regulated kinase 1 (ERK1) and ERK2 and to downregulate perilipin (which has been implicated in the lipolytic effect of TNF-alpha) was not affected by glucose. We conclude that the lipolytic action of TNF-alpha is influenced by glucose in 3T3-L1 adipocytes. The findings suggest that glucose metabolism is required for the lipolytic response to TNF-alpha but not for early signaling events. These findings suggest novel mechanisms by which TNF-alpha and hyperglycemia raise FFA levels and induce insulin resistance.