Gut-derived hormones, such as GLP-1, have been proposed to relay information to the brain to regulate appetite. GLP-1 receptor agonists, currently used for the treatment of type 2 diabetes (T2DM), improve glycemic control and stimulate satiety, leading to decreases in food intake and body weight. We hypothesized that food intake reduction after GLP-1 receptor activation is mediated through appetite-and reward-related brain areas. Obese T2DM patients and normoglycemic obese and lean individuals (n = 48) were studied in a randomized, crossover, placebocontrolled trial. Using functional MRI, we determined the acute effects of intravenous administration of the GLP-1 receptor agonist exenatide, with or without prior GLP-1 receptor blockade using exendin 9-39, on brain responses to food pictures during a somatostatin pancreatic-pituitary clamp. Obese T2DM patients and normoglycemic obese versus lean subjects showed increased brain responses to food pictures in appetite-and reward-related brain regions (insula and amygdala). Exenatide versus placebo decreased food intake and food-related brain responses in T2DM patients and obese subjects (in insula, amygdala, putamen, and orbitofrontal cortex). These effects were largely blocked by prior GLP-1 receptor blockade using exendin 9-39. Our findings provide novel insights into the mechanisms by which GLP-1 regulates food intake and how GLP-1 receptor agonists cause weight loss.The global rise in obesity and type 2 diabetes (T2DM) prevalence is a major public health problem (1,2). It has been hypothesized that excessive eating due to changes in central nervous system (CNS) satiety and reward responses to food underlies the development of obesity and T2DM, comparable to the role for altered CNS responses in drug addiction (3). Several studies in obese individuals have demonstrated increased CNS responses to visual food cues in areas involved in appetite and reward processing (insula, amygdala, orbitofrontal cortex [OFC], and striatum) (4-6), and this increased CNS food-cue responsiveness predicts future weight gain (7). The mechanisms underlying these alterations in CNS responses to food cues are not clear, but multiple metabolic and hormonal factors seem to be involved (8-10).Food ingestion activates the secretion of several gutderived mediators, including the incretin hormone GLP-1. GLP-1 stimulates meal-related insulin secretion, inhibits glucagon release, and delays gastric emptying, mechanisms that all contribute to its glucometabolic effects (11). In addition, several observations suggest that GLP-1 has a role in the regulation of food intake. Systemic administration of GLP-1 reduced food intake in rodent and human studies (12), and blocking the GLP-1 receptor with

Angiopoietin-like protein 8 (ANGPTL8) has been implicated in metabolic syndrome and reported to regulate adipose FA uptake through unknown mechanisms. Here, we studied how complex formation of ANGPTL8 with ANGPTL3 or ANGPTL4 varies with feeding to regulate lipoprotein lipase (LPL). In human serum, ANGPTL3/8 and ANGPTL4/8 complexes both increased postprandially, correlated negatively with HDL, and correlated positively with all other metabolic syndrome markers. ANGPTL3/8 also correlated positively with LDL-cholesterol and blocked LPL-facilitated hepatocyte VLDL-cholesterol uptake. LPL-inhibitory activity of ANGPTL3/8 was >100-fold more potent than that of ANGPTL3, and LPL-inhibitory activity of ANGPTL4/8 was >100-fold less potent than that of ANGPTL4. Quantitative analyses of inhibitory activities and competition experiments among the complexes suggested a model in which localized ANGPTL4/8 blocks the LPL-inhibitory activity of both circulating ANGPTL3/8 and localized ANGPTL4, allowing lipid sequestration into fat rather than muscle during the fed state. Supporting this model, insulin increased ANGPTL3/8 secretion from hepatocytes and ANGPTL4/8 secretion from adipocytes. These results suggest that low ANGPTL8 levels during fasting enable ANGPTL4-mediated LPL inhibition in fat tissue to minimize adipose FA uptake. During feeding, increased ANGPTL8 increases ANGPTL3 inhibition of LPL in muscle via circulating ANGPTL3/8, while decreasing ANGPTL4 inhibition of LPL in adipose tissue through localized ANGPTL4/8, thereby increasing FA uptake into adipose tissue. Excessive caloric intake may shift this system toward the latter conditions, possibly predisposing to metabolic syndrome.

Proprotein convertase subtilisin/kexin type 9 (PCSK9) has gained attention as a key regulator of serum low density lipoprotein cholesterol (LDL-C) levels. This novel protease causes the degradation of hepatic low density lipoprotein receptors. In humans, gain-of-function mutations in PCSK9 cause a form of familial hypercholesterolemia, whereas loss-of-function mutations result in significantly decreased LDL-C levels and cardiovascular risk. Previous studies have demonstrated that statins upregulate PCSK9 mRNA expression in cultured cells and animal models. In light of these observations, we studied the effect of atorvastatin on circulating PCSK9 protein levels in humans using a sandwich ELISA to quantitate serum PCSK9 levels in patients treated with atorvastatin or placebo for 16 weeks. We observed that atorvastatin (40 mg/day) significantly increased circulating PCSK9 levels by 34% compared with baseline and placebo and decreased LDL-C levels by 42%. These results suggest that the addition of a PCSK9 inhibitor to statin therapy may result in even further LDL-C decreases. The serum protease proprotein convertase subtilisin/ kexin type 9 (PCSK9) has gained tremendous attention as a potential key regulator of serum low density lipoprotein cholesterol (LDL-C) levels (1-3). PCSK9 is a protease made by the liver that acts to degrade hepatic low density lipoprotein receptors (LDLRs) (4-10). The mechanism by which PCSK9 degrades LDLRs is extremely complex and is only beginning to be understood. It was recently suggested that the protease itself does not have to be proteolytically active to cause degradation of the LDLR but rather binds to the LDLR and subsequently targets it for intracellular destruction within the hepatocyte (11-13). Regardless of the exact mechanism, the result of LDLR levels being decreased is that the liver has a decreased ability to bind LDL from the circulation and serum LDL-C levels increase. Therefore, mutations in PCSK9 can have dramatic effects on serum LDL-C levels in humans.Patients with gain-of-function mutations of PCSK9 manifest severe familial hypercholesterolemia and accompanying increased cardiovascular risk (14-17). These mutations in PCSK9 account for ?10-25% of familial dominant hypercholesterolemia cases that could not be explained by mutations in either the LDLR or apolipoprotein B (apoB) (14-17). In contrast, heterozygous subjects with loss-of-function mutations in PCSK9, including mutations that prevent the self-cleavage and secretion of the protein itself, have significantly decreased levels of serum LDL-C and dramatically decreased cardiovascular risk (18)(19)(20). Approximately 2% of African-Americans carry such mutations, with an accompanying 80-90% decreased risk of serious cardiovascular events (18). Recently, the first compound heterozygote for PCSK9 loss-of-function mutations was described. This subject, a healthy 32 year old female, had an extremely low serum LDL-C level of 14 mg/dl (20).Interestingly, statins have been shown to increase the activity/nuclear t...

Phosphatidylcholine (PC) is synthesized through the Kennedy pathway, but more than 50% of PC is remodeled through the Lands cycle, i.e. the deacylation and reacylation of PC to attain the final and proper fatty acids within PC. The reacylation step is catalyzed by lysophosphatidylcholine acyltransferase (LPCAT), and we report here the identification of a novel LPCAT, which we named LPCAT3. LPCAT3 belongs to the membrane-bound O-acyltransferase (MBOAT) family and encodes a protein of 487 amino acids with a calculated molecular mass of 56 kDa. Membranes from HEK293 cells overexpressing LPCAT3 showed significantly increased LPCAT activity as assessed by thin layer chromatography analysis with substrate preference toward unsaturated fatty acids. LPCAT3 is localized within the endoplasmic reticulum and is primarily expressed in metabolic tissues including liver, adipose, and pancreas. In a human hepatoma Huh7 cells, RNA interference-mediated knockdown of LPCAT3 resulted in virtually complete loss of membrane LPCAT activity, suggesting that LPCAT3 is primarily responsible for hepatic LPCAT activity. Furthermore, peroxisome proliferator-activated receptor ␣ agonists dosedependently regulated LPCAT3 in liver in a peroxisome proliferator-activated receptor ␣-dependent fashion, implicating a role of LPCAT3 in lipid homeostasis. Our studies identify a long-sought enzyme that plays a critical role in PC remodeling in metabolic tissues and provide an invaluable tool for future investigations on how PC remodeling may potentially impact glucose and lipid homeostasis.

This article is available online at http://www.jlr.org Proprotein convertase subtilisin kexin type 9 (PCSK9) has been recognized as a key regulator of serum low density lipoprotein cholesterol (LDL-C) levels ( 1-7 ). PCSK9 is a protease made and secreted by the liver into the plasma, which then binds to and degrades hepatic LDL receptors (LDLR) (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). The mechanism by which PCSK9 degrades LDLR is complex. Recent studies suggest that after self-cleavage and secretion, PCSK9 does not have to be enzymatically active to cause degradation of the LDLR ( 19-21 ). Rather, PCSK9 binds to the LDLR and subsequently targets it for lysosomal destruction within the hepatocyte ( 8,(19)(20)(21). This concept of how PCSK9 acts to decrease hepatic LDLR levels is supported by recent fi ndings that disruption of the binding of PCSK9 to the LDLR using anti-PCSK9 antibody results in preserved LDLR and decreased [22][23][24].Several different PCSK9 mutations have been reported in humans. Patients with gain-of-function mutations of PCSK9 present with severe familial hypercholesterolemia and accompanying increased cardiovascular risk (25)(26)(27)(28)(29). In contrast, individuals with loss-of-function mutations in PCSK9, including mutations which prevent the selfcleavage and secretion of the protein, have signifi cantly decreased levels of serum LDL-C and lower cardiovascular risk (30)(31)(32). Approximately 3% of African-Americans are heterozygous for such mutations ( 30 ). Of note, a compound heterozygote for PCSK9 loss-of-function mutations was recently described. The subject, a healthy 32-year-old female, had a serum LDL-C level of 14 mg/dl ( 32 ). A second Abstract Proprotein convertase subtilisin kexin type 9 (PCSK9) is a key regulator of serum LDL-cholesterol (LDL-C) levels. PCSK9 is secreted by the liver into the plasma and binds the hepatic LDL receptor (LDLR), causing its subsequent degradation. We fi rst demonstrated that a moderate dose of atorvastatin (40 mg) increases PCSK9 serum levels, suggesting why increasing statin doses may have diminished effi cacy with regard to further LDL-C lowering. Since that initial observation, at least two other groups have reported statin-induced PCSK9 increases. To date, no analysis of the effect of high-dose atorvastatin (80 mg) on PCSK9 over time has been conducted. Therefore, we studied the time course of atorvastatin (80 mg) in human subjects. We measured PCSK9 and lipid levels during a 2-week lead-in baseline period and every 4 weeks thereafter for 16 weeks. We observed that atorvastatin (80 mg) caused a rapid 47% increase in serum PCSK9 at 4 weeks that was sustained throughout 16 weeks of dosing. Importantly, while PCSK9 levels were highly correlated with total cholesterol (TC), LDL-C, and triglyceride (TG) levels at baseline, atorvastatin (80 mg) completely abolished all of these correlations. Together, these results further suggest an explanation for why increasing doses of statins fail to achieve proportional LDL-C lowering. Abbreviations: HDL-...