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Lysosomes coordinate cellular metabolism and growth upon sensing of essential nutrients, including cholesterol. Through bioinformatic analysis of lysosomal proteomes, we identified lysosomal cholesterol signaling (LYCHOS, previously annotated as G protein-coupled receptor 155), a multidomain transmembrane protein that enables cholesterol-dependent activation of the master growth regulator, the protein kinase mechanistic target of rapamycin complex 1 (mTORC1). Cholesterol bound to the amino-terminal permease-like region of LYCHOS, and mutating this site impaired mTORC1 activation. At high cholesterol concentrations, LYCHOS bound to the GATOR1 complex, a guanosine triphosphatase (GTPase)-activating protein for the Rag GTPases, through a conserved cytoplasm-facing loop. By sequestering GATOR1, LYCHOS promotes cholesterol- and Rag-dependent recruitment of mTORC1 to lysosomes. Thus, LYCHOS functions in a lysosomal pathway for cholesterol sensing and couples cholesterol concentrations to mTORC1-dependent anabolic signaling.

The protein tyrosine phosphatase Src homology region 2 domain-containing phosphatase-1 (SHP-1) plays an important role in modulating glucose and lipid homeostasis. We previously suggested a potential role of SHP-1 in the regulation of peroxisome proliferator-activated receptor γ2 (PPARγ2) expression and activity but the mechanisms were unexplored. PPARγ2 is the master regulator of adipogenesis, but how its activity is regulated by tyrosine phosphorylation is largely unknown. Here, we found that SHP-1 binds to PPARγ2 primarily via its N-terminal SH2-domain. We confirmed the phosphorylation of PPARγ2 on tyrosine-residue 78 (Y78), which was reduced by SHP-1 in vitro resulting in decreased PPARγ2 stability. Loss of SHP-1 led to elevated, agonist-induced expression of the classical PPARγ2 targets FABP4 and CD36, concomitant with increased lipid content in cells expressing PPARγ2, an effect blunted by abrogation of PPARγ2 phosphorylation. Collectively, we discovered that SHP-1 affects the stability of PPARγ2 through dephosphorylation thereby influencing adipogenesis. [ABSTRACT FROM AUTHOR]

Many people living with diabetes also have nonalcoholic fatty liver disease (NAFLD). Interleukin-6 (IL-6) is involved in both diseases, interacting with both membrane-bound (classical) and circulating (trans-signaling) soluble receptors. We investigated whether secretion of IL-6 trans-signaling coreceptors are altered in NAFLD by diabetes and whether this might associate with the severity of fatty liver disease. Secretion patterns were investigated with use of human hepatocyte, stellate, and monocyte cell lines. Associations with liver pathology were investigated in two patient cohorts: 1) biopsy-confirmed steatohepatitis and 2) class 3 obesity. We found that exposure of stellate cells to high glucose and palmitate increased IL-6 and soluble gp130 (sgp130) secretion. In line with this, plasma sgp130 in both patient cohorts positively correlated with HbA1c, and subjects with diabetes had higher circulating levels of IL-6 and trans-signaling coreceptors. Plasma sgp130 strongly correlated with liver stiffness and was significantly increased in subjects with F4 fibrosis stage. Monocyte activation was associated with reduced sIL-6R secretion. These data suggest that hyperglycemia and hyperlipidemia can directly impact IL-6 trans-signaling and that this may be linked to enhanced severity of NAFLD in patients with concomitant diabetes. Article Highlights: IL-6 and its circulating coreceptor sgp130 are increased in people with fatty liver disease and steatohepatitis. High glucose and lipids stimulated IL-6 and sgp130 secretion from hepatic stellate cells. sgp130 levels correlated with HbA1c, and diabetes concurrent with steatohepatitis further increased circulating levels of all IL-6 trans-signaling mediators. Circulating sgp130 positively correlated with liver stiffness and hepatic fibrosis. Metabolic stress to liver associated with fatty liver disease might shift the balance of IL-6 classical versus trans-signaling, promoting liver fibrosis that is accelerated by diabetes. [ABSTRACT FROM AUTHOR]

We investigated the mechanisms whereby peroxisome proliferator-activated receptor-[gamma], (PPAR[gamma]) agonism affects glucose and lipid metabolism in brown adipose tissue (BAT) by studying the impact of PPAR[gamma] activation on BAT glucose uptake and metabolism, lipogenesis, and mRNA levels plus activities of enzymes involved in triacylglycerol (TAG) synthesis. Interscapular BAT of rats treated or not with rosiglitazone (15 mg x [kg.sup.-1] x [day.sup.-1], 7 days) was evaluated in vivo for glucose uptake and lipogenesis and in vitro for glucose metabolism, gene expression, and activities of glycerolphosphate acyltransferase (GPAT), phosphatidate phosphatase-1 (PAP or lipin-1), and diacylglycerol acyltransferase (DGAT). Rosiglitazone increased BAT mass without affecting whole tissue glucose uptake. BAT glycogen content (-80%), its synthesis from glucose (-50%), and mRNA levels of UDP-glucose pyrophosphorylase (-40%), which generates UDP-linked glucose for glycogen synthesis, were all reduced by rosiglita-zone. In contrast, BAT TAG-glycerol synthesis in vivo and glucose incorporation into TAG-glycerol in vitro were stimulated by the agonist along with the activities and mRNA levels of glycerol 3-phosphate-generating phosphoenolpyruvate carboxykinase and glycerokinase. Furthermore, rosiglitazone markedly increased the activities of GPAT and DGAT but not those of lipin-l-mediated PAP-l, enzymes involved in the sequential acylation of glycerol 3-phosphate and TAG synthesis. Because an adequate supply of fatty acids is essential for BAT nonshivering thermogenesis, the enhanced ability of BAT to synthesize TAG under PPAR[gamma] activation may constitute an important mechanism by which lipid substrates are stored in preparation for an eventual thermogenic activation. glycogen; glycerokinase; phosphoenolpyruvate carboxykinase; glycerolphosphate acyltransferase; lipin; diacylglycerol acyltransferase; peroxisome proliferator-activated receptor-[gamma]

Peroxisome proliferator-activated receptor-[gamma] (PPAR[gamma]) agonism potently reduces circulating triglycerides (TG) in rodents and more modestly so in humans. This study aimed to quantify in vivo the relative contribution of hepatic VLDL-TG secretion and tissue-specific TG clearance to such action. Rats were fed an obesogenic diet, treated with the PPAR[gamma] full agonist COOH (30 mg x [kg.sup.-1] x [day.sup.-1] for 3 wk, and studied in both the fasted and refed (fat-free) states. Hepatic VLDL-TG secretion rate was not affected by chronic COOH in the fasted state and was only modestly decreased (-30%) in refed rats. In contrast, postprandial VLDL-TG clearance was increased 2.6-fold by COOH, which concomitantly stimulated adipose tissue TG-derived lipid uptake and one of its major determinants, lipoprotein lipase (LPL) activity, in a highly depot-specific manner. TG-derived lipid uptake and LPL were indeed strongly increased in subcutaneous inguinal white adipose tissue and in brown adipose tissue, independently of the nutritional state, whereas of the three visceral fat depots examined (epididymal, retroperitoneal, mesenteric) only the latter responded consistently to COOH. Robust correlations (0.5 < r < 0.9) were observed between TG-derived lipid uptake and LPL in adipose tissues. The agonist did not increase LPL in muscle, and its enhancing action on postprandial muscle lipid uptake appeared to be mediated by post-LPL processes involving increased expression of fatty acid binding/transport proteins (aP2, likely in infiltrated adipocytes, FAT/CD36, and FATP-I). The study establishes in a diet-induced obesity model the major contribution of lipid uptake by specific, metabolically safe adipose depots to the postprandial hypotriglyceridemic action of PPAR[gamma] agonism, and suggests a key role for LPL therein. PPAR[gamma] agonist; white adipose tissue; brown adipose tissue; triglyceride secretion; triglyceride clearance

Acylation-stimulating protein (ASP), a lipogenic hormone, stimulates triglyceride (TG) synthesis and glucose transport upon activation of C5L2, a G protein-coupled receptor. ASP-deficient mice have reduced adipose tissue mass due to increased energy expenditure despite increased food intake. The objective of this study was to evaluate the blocking of ASP-C5L2 interaction via neutralizing antibodies (anti-ASP and anti-C5L2-L1 against C5L2 extracellular loop 1). In vitro, anti-ASP and anti-C5L2-Ll blocked ASP binding to C5L2 and efficiently inhibited ASP stimulation of TG synthesis and glucose transport. In vivo, neither anti-ASP nor anti-C5L2-Ll altered body weight, adipose tissue mass, food intake, or hormone levels (insulin, leptin, and adiponectin), but they did induce a significant delay in TG clearance [P < 0.0001,2-way repeated-measures (RM) ANOVA] and NEFA clearance (P < 0.0001, 2-way RM ANOVA) after a fat load. After treatment with either anti-ASP or anti-C5L2-L1 antibody there was no change in adipose tissue AMPK activity, but neutralizing antibodies decreased perirenal TG mass (-38.4% anti-ASP, 18.8% anti-C5L2, P < 0.01-0.001) and perirenal LPL activity (-75.6% anti-ASP, -72.5% anti-C5L2, P < 0.05). In liver, anti-C5L2-L1 decreased TG mass (-42.8%, P < 0.05), whereas anti-ASP increased AMPK activity (+34.6%, P < 0.001). In the muscle, anti-C5L2-L1 significantly increased TG mass (+128.0%, P < 0.05), LPL activity (+226.1%, P < 0.001), and AMPK activity (+71.1%, P < 0.01). In addition, anti-ASP increased LPL activity (+ 164.4, P < 0.05) and AMPK activity (+53.9%, P < 0.05) in muscle. ASP/C5L2-neutralizing antibodies effectively block ASP-C5L2 interaction, altering lipid distribution and energy utilization. lipoprotein lipase; adenosine 5'-monophosphate-activated protein kinase; dietary fat partitioning; fatty acid reesterification; C3adesArg

Tissue-specific alterations in 11[beta]-hydroxysteroid dehydrogenase (HSD) type 1 activity, which amplifies glucocorticoid action, are thought to contribute to some of the metabolic complications of obesity. The present study tested whether hypertriglyceridemia is one such complication by investigating the effects of an ll[beta]-HSD1 inhibitor (compound A, 3 mg x [kg.sup.-1] x [day.sup.-1], 21 days) on triglyceride (TG) metabolism in a rat model of diet-induced obesity. The dose of compound A used did not affect food intake or final body weight. Compound A improved fasting triglyceridemia (-42%) through a robust reduction (-41%) in hepatic TG secretion rate, without change in plasma TG clearance rate. Uptake of TG-derived fatty acids was, however, increased in oxidative tissues, including red gastrocnemius (+47%), heart (+39%), and brown adipose tissue (BAT, +46%) at the expense of the liver, with a concomitant increase in plasma membrane fatty acid-binding protein. Lipid oxidation products were increased in red gastrocnemius (+35%) and heart (+33%), as were levels of uncoupling protein 1 mRNA in BAT (+48%), and carnitine palmitoyltransferase 1 activity tended to be increased in some oxidative tissues. These findings demonstrate that pharmacological inhibition of 11[beta]-HSD1 at a dose that does not affect food intake improves triglyceridemia by reducing hepatic very low density lipoprotein-TG secretion, with a shift in the pattern of TG-derived fatty acid uptake toward oxidative tissues, in which lipid accumulation is prevented by increased lipid oxidation. 11[beta]-hsd1 inhibitor; glucocorticoids; diet-induced obesity; triglycerides; lipid metabolism; lipid partitioning; lipid oxidation.

Excess caloric intake can lead to insulin resistance. The underlying reasons are complex but likely related to ectopic lipid deposition in nonadipose tissue. We hypothesized that the inability to appropriately [...]

Agonists of the peroxisome proliferator-activated receptor [gamma] (PPAR[gamma]) are insulin sensitizers that potently improve lipemia in rodents. This study aimed to determine the contribution of lipid secretion vs. clearance and the involvement of white adipose tissue (WAT) and brown adipose tissue (BAT) in the rapid hypolipidemic action of PPAR-y agonism. Male rats were treated with rosiglitazone (RSG; 15 mg*[kg.sup.-1]*[day.sup.-1]) for 1 to 4 days, and determinants of lipid metabolism were assessed postprandially. Serum triglycerides (TG) were lowered (-54%) after 3 days of RSG treatment, due to accelerated clearance from blood without contribution of changes in secretion rates. Both BAT and WAT were the major sites of RSG action on TG clearance, the increase in TG-derived fatty acid (FA) uptake reaching threefold in BAT and 60-90% in WAT depots. Accelerated TG clearance was associated with increased lipoprotein lipase (LPL) activity mostly in BAT. Serum nonesterified FA were lowered (-20%) by a single dose of RSG, an effect associated with increased expression levels of FA binding/transport (fatty acid binding protein-4), esterification (diacylglycerol acyltransferase-1), and recycling glycerol kinase and phosphoenolpyruvate carboxykinase enzymes in BAT and WAT, suggesting FA trapping. After 4 days of RSG treatment, nonesterified fatty acid (NEFA) uptake was also stimulated in both BAT (2.5-fold) and WAT (40%). These findings demonstrate the causal involvement of increased efficiency of LPL-mediated TG clearance and reveal the important contribution of TG-derived and albumin-bound FA uptake by BAT in the rapid hypolipidemic action of PPAR[gamma] agonism in the rat. triglycerides; triglyceride secretion; triglyceride clearance; lipoprotein lipase; nonesterified fatty acids