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Diet-induced obesity and its serious consequences such as diabetes, cardiovascular disease, and cancer are rapidly becoming a major global health threat. Therefore, understanding the cellular and molecular mechanisms by which dietary fat causes obesity and diabetes is of paramount importance in order to identify preventive and therapeutic strategies. Increased dietary fat intake results in high plasma levels of triglyceride-rich lipoproteins (TGRL). Tissue uptake of TGRL has been shown to promote glucose intolerance. We generated mice with an adipocyte-specific inactivation of the multifunctional receptor LDL receptor-related protein-1 (LRP1) to determine its role in mediating the effects of TGRL on diet-induced obesity and diabetes. Knockout mice displayed delayed postprandial lipid clearance, reduced body weight, smaller fat stores, lipid-depleted brown adipocytes, improved glucose tolerance, and elevated energy expenditure due to enhanced muscle thermogenesis. We further demonstrated that inactivation of adipocyte LRP1 resulted in resistance to dietary fat-induced obesity and glucose intolerance. These findings identify LRP1 as a critical regulator of adipocyte energy homeostasis, where functional disruption leads to reduced lipid transport, increased insulin sensitivity, and muscular energy expenditure. IntroductionThe chronic consumption of meals rich in fat and carbohydrates is a major causative factor of obesity and diabetes. The prevailing view on the mechanism by which these dietary factors contribute to obesity and diabetes is that when energy intake surpasses expenditure, the excess calories are deposited as fat in adipose tissues and its subsequent mobilization to nonadipose tissues causes insulin resistance that ultimately leads to type 2 diabetes (1-3). High fat and carbohydrate intake also leads to plasma lipid abnormalities, including high plasma levels of nonesterified fatty acids (NEFAs) and triglyceride-rich lipoproteins (TGRL) as well as reduced plasma levels of HDL (2, 3). Numerous past studies have shown that elevated plasma NEFA levels directly induce insulin resistance and thus play a causative role in the pathogenesis of obesity-related diabetes (1,4,5). However, only sporadic attention has been paid to the role of TGRL in obesity and diabetes. The TGRL are generally thought of primarily as triglyceride carriers in the circulation, delivering substrates to tissues where lipoprotein lipase-catalyzed (LpL-catalyzed) hydrolysis liberates NEFAs prior to their uptake by cells through CD36 and other pathways (6). It is important to note that TGRL as well as lipase-hydrolyzed TGRL remnants can also be internalized by cells directly via whole-particle uptake and provide triglyceride-derived fatty acids via mechanisms mediated by LDL receptor family member proteins (7). Results showing

Insulin stimulates the translocation of intracellular GLUT4 to the plasma membrane where it functions in adipose and muscle tissue to clear glucose from circulation. The pathway and regulation of GLUT4 trafficking are complicated and incompletely understood and are likely to be contingent upon the various proteins other than GLUT4 that comprise and interact with GLUT4-containing vesicles. Moreover, not all GLUT4 intracellular pools are insulin-responsive as some represent precursor compartments, thus posing a biochemical challenge to the purification and characterization of their content. To address these issues, we immunodepleted precursor GLUT4-rich vesicles and then immunopurified GLUT4 storage vesicle (GSVs) from primary rat adipocytes and subjected them to semi-quantitative and quantitative proteomic analysis. The purified vesicles translocate to the cell surface almost completely in response to insulin, the expected behavior for bona fide GSVs. In total, over 100 proteins were identified, about 50 of which are novel in this experimental context. LRP1 (low density lipoprotein receptorrelated protein 1) was identified as a major constituent of GSVs, and we show it interacts with the lumenal domains of GLUT4 and other GSV constituents. Its cytoplasmic tail interacts with the insulin-signaling pathway target, AS160 (Akt substrate of 160 kDa). Depletion of LRP1 from 3T3-L1 adipocytes reduces GLUT4 expression and correspondingly results in decreased insulin-stimulated 2-[ 3 H]deoxyglucose uptake. Furthermore, adipose-specific LRP1 knock-out mice also exhibit decreased GLUT4 expression. These findings suggest LRP1 is an important component of GSVs, and its expression is needed for the formation of fully functional GSVs.The insulin-dependent translocation of GLUT4 from intracellular membranes to the cell surface is a well studied paradigm for the effects of signal transduction on membrane trafficking, and this process is of considerable physiological relevance for the regulation of glucose homeostasis, as dysregulation of this process plays a role in insulin resistance and type 2 diabetes mellitus (1). Only about half of the intracellular GLUT4 translocates to the plasma membrane in response to insulin (2-5) suggesting that more than one GLUT4-containing compartment exists. In addition, kinetic analyses of GLUT4 trafficking are consistent with the interpretation that GLUT4 traffics through multiple intracellular compartments (6 -8). These and other data have led to the concept that an ultimate target of insulin signaling is a subpopulation of translocating GLUT4-containing membranes that are commonly referred to as GLUT4 storage vesicles (GSVs) 3 (9, 10). The focus of many groups over the years has been on how these GSVs form, what their protein composition is, and how insulin communicates with them and stimulates their translocation to the cell surface.GLUT4-containing vesicles have been purified and their protein composition analyzed by a number of investigators, first by conventional protein sequencing (11, 12)...

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The low-density lipoprotein receptor-related protein LRP1 is a cell surface receptor with functions in diverse physiological pathways, including lipid metabolism. Here we show that LRP1-deficient fibroblasts accumulate high levels of intracellular cholesterol and cholesteryl-ester when stimulated for adipocyte differentiation. We demonstrate that LRP1 stimulates a canonical Wnt5a signaling pathway that prevents cholesterol accumulation. Moreover, we show that LRP1 is required for lipolysis and stimulates fatty acid synthesis independently of the noradrenergic pathway, through inhibition of GSK3␤ and its previously unknown target acetyl-CoA carboxylase (ACC). As a result of ACC inhibition, mature LRP1-deficient adipocytes of adult mice are hypotrophic, and lower uptake of fatty acids into adipose tissue leads to their redistribution to the liver. These results establish LRP1 as a novel integrator of adipogenic differentiation and fat storage signals.The number of adipocytes in an organism is determined by a tightly regulated differentiation process of fibroblast-like preadipocytes (1, 2). Fat cell differentiation (adipogenesis) is controlled by hormonal-induced coordinated expression and activation of two main groups of transcription factors, the CCAAT/enhancer-binding protein (C/EBP) family and peroxisome proliferator-activated receptor ␥ (PPAR␥) 4 (2). PPAR␥, a member of the nuclear hormone receptors superfamily, is a crucial component of this cascade, as adipogenesis is impaired in PPAR␥-deficient mesenchymal stem cells (3). Activation of PPAR␥ induces the expression of lipogenic genes, such as adipocyte fatty acid-binding protein (422/aP2) (4), CD36 and lipoprotein lipase (LPL) (5). Accumulation of intracellular triglyceride (TG) droplets ultimately gives rise to the morphologically distinct fat cell (2). During periods of caloric restriction, TGs stored in adipocytes are catabolized into glycerol and fatty acids, to provide energy. Mobilization of lipids involves the sequential activation of hormone-sensitive lipase (HSL) and adipose triglyceride lipase (ATGL) (6), two lipolytic enzymes responsible for more than 95% of the TG hydrolase activity in the adipose tissues of mammals (7). The low-density lipoprotein receptor-related protein 1 (LRP1) is a multifunctional cell surface receptor. Two NPXY motifs in the intracellular domain (ICD) serve as docking sites for several cytoplasmic adaptor proteins including Shc, Disabled-1, JIP1, PSD-95, CED-6/GULP, ARH, and Fe65, which control intracellular trafficking, as well as signaling events (8). LRP1 interacts with and mediates endocytosis of more than 40 unrelated ligands ranging from viruses to protease/protease inhibitor complexes, cytokines, and growth factors (9). In the liver, LRP1 and the LDL receptor (LDLr) share the endocytosis and subsequent degradation of TG-rich very-low-density lipoproteins and chylomicron remnants. However, endocytosis and clearance of macromolecules is only one function of LRP1. There is now substantial evidence that LRP1 also serves ...

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Flap endonuclease 1 (FEN1) is a key enzyme in maintaining genomic stability and protecting against carcinogenesis. This study investigated whether functional variations in FEN1 gene are associated with DNA damage and lung cancer risk. Thirty DNA samples were sequenced to identify variants and function of the variants was examined by a set of biochemical assays. DNA damage levels were detected by comet assays in a cohort of 303 coke-oven workers and 297 controls. The association with lung cancer risk was examined in two independent case-control panels consisted of a total 1,840 lung cancer patients and 1,958 controls. We identified two single nucleotide polymorphisms (SNPs) located in the FEN1 promoter c.-69G>A (rs174538:G>A) and 3'-untranslational region c.4150G>T (rs4246215:G>T) that were associated with reduced FEN1 expression. Among coke-oven workers, DNA damage levels were significantly higher in the -69GG or GA carriers compared with the -69AA carriers. The -69GG or 4150GG carriers had a significantly increased risk for developing lung cancer compared with the -69AA or 4150TT carriers. These results highlight FEN1 as an important gene in human carcinogenesis and genetic polymorphisms in FEN1 confer susceptibility to lung cancer.

Summary Background Limited research has been published on current Helicobacter pylori infection rate in asymptomatic children in China. Aim To assess current Helicobacter pylori infection rate, distribution characteristics and risk factors in Chinese asymptomatic children. Methods A prospective, cross‐sectional, population‐based study was performed from 2009 to 2011 in three cities of China. Helicobacter pylori infection was diagnosed by a stool antigen test. Multi‐stage cluster random sampling was used to select asymptomatic children including neonates. Socioeconomic details were obtained through a standardised questionnaire. Results Among total of 3491 children (0–18 years), the global infection rate was 6.8% and there were no significant differences between genders. Age specific infection rate between regions was significantly different (P < 0.05). The infection rate significantly increased with age (P for trend <0.01). It was low during the newborn (0.6%) to preschool period and was significantly increased in high school students (13.5%) (P < 0.01). Multivariable regression indicated that hand sanitisation, individually served meals, higher education level of mother, above average living space and residence in urban areas were significantly protective against infection (OR 0.749, 0.698, 0.720, 0.838 and 0.770 respectively). Conversely, consuming meals in unsanitised conditions, sharing towels, receiving pre‐chewed food from the mother, artificial feeding and family history of gastrointestinal disease were significantly associated with the risk of infection (OR 1.200, 1.965, 2.002, 1.071 and 2.093 respectively). Conclusions Helicobacter pylori infection rate increases with age in Chinese asymptomatic children and is common after 10 years of age. The rate of infection is related to socioeconomic status.