Apolipoprotein F is reduced in humans with steatosis and controls plasma triglyceride-rich lipoprotein metabolism.

BACKGROUND: NAFLD affects nearly 25% of the global population. Cardiovascular disease (CVD) is the most common cause of death among patients with NAFLD, in line with highly prevalent dyslipidemia in this population. Increased plasma triglyceride (TG)-rich lipoprotein (TRL) concentrations, an important risk factor for CVD, are closely linked with hepatic TG content. Therefore, it is of great interest to identify regulatory mechanisms of hepatic TRL production and remnant uptake in the setting of hepatic steatosis. APPROACH AND RESULTS: To identify liver-regulated pathways linking intrahepatic and plasma TG metabolism, we performed transcriptomic analysis of liver biopsies from two independent cohorts of obese patients. Hepatic encoding apolipoprotein F ( APOF ) expression showed the fourth-strongest negatively correlation with hepatic steatosis and the strongest negative correlation with plasma TG levels. The effects of adenoviral-mediated human ApoF (hApoF) overexpression on plasma and hepatic TG were assessed in C57BL6/J mice. Surprisingly, hApoF overexpression increased both hepatic very low density lipoprotein (VLDL)-TG secretion and hepatic lipoprotein remnant clearance, associated a ~25% reduction in plasma TG levels. Conversely, reducing endogenous ApoF expression reduced VLDL secretion in vivo , and reduced hepatocyte VLDL uptake by ~15% in vitro . Transcriptomic analysis of APOF -overexpressing mouse livers revealed a gene signature related to enhanced ApoB-lipoprotein clearance, including increased expression of Ldlr and Lrp1 , among others. CONCLUSION: These data reveal a previously undescribed role for ApoF in the control of plasma and hepatic lipoprotein metabolism by favoring VLDL-TG secretion and hepatic lipoprotein remnant particle clearance.

Roux-en-Y gastric bypass induces hepatic transcriptomic signatures and plasma metabolite changes indicative of improved cholesterol homeostasis.

BACKGROUND & AIMS: Roux-en-Y gastric bypass (RYGB), the most effective surgical procedure for weight loss, decreases obesity and ameliorates comorbidities, such as non-alcoholic fatty liver (NAFLD) and cardiovascular (CVD) diseases. Cholesterol is a major CVD risk factor and modulator of NAFLD development, and the liver tightly controls its metabolism. How RYGB surgery modulates systemic and hepatic cholesterol metabolism is still unclear. METHODS: We studied the hepatic transcriptome of 26 patients with obesity but not diabetes before and 1 year after undergoing RYGB. In parallel, we measured quantitative changes in plasma cholesterol metabolites and bile acids (BAs). RESULTS: RYGB surgery improved systemic cholesterol metabolism and increased plasma total and primary BA levels. Transcriptomic analysis revealed specific alterations in the liver after RYGB, with the downregulation of a module of genes implicated in inflammation and the upregulation of three modules, one associated with BA metabolism. A dedicated analysis of hepatic genes related to cholesterol homeostasis pointed towards increased biliary cholesterol elimination after RYGB, associated with enhancement of the alternate, but not the classical, BA synthesis pathway. In parallel, alterations in the expression of genes involved in cholesterol uptake and intracellular trafficking indicate improved hepatic free cholesterol handling. Finally, RYGB decreased plasma markers of cholesterol synthesis, which correlated with an improvement in liver disease status after surgery. CONCLUSIONS: Our results identify specific regulatory effects of RYGB on inflammation and cholesterol metabolism. RYGB alters the hepatic transcriptome signature, likely improving liver cholesterol homeostasis. These gene regulatory effects are reflected by systemic post-surgery changes of cholesterol-related metabolites, corroborating the beneficial effects of RYGB on both hepatic and systemic cholesterol homeostasis. IMPACT AND IMPLICATIONS: Roux-en-Y gastric bypass (RYGB) is a widely used bariatric surgery procedure with proven efficacy in body weight management, combatting cardiovascular disease (CVD) and non-alcoholic fatty liver disease (NAFLD). RYGB exerts many beneficial metabolic effects, by lowering plasma cholesterol and improving atherogenic dyslipidemia. Using a cohort of patients undergoing RYGB, studied before and 1 year after surgery, we analyzed how RYGB modulates hepatic and systemic cholesterol and bile acid metabolism. The results of our study provide important insights on the regulation of cholesterol homeostasis after RYGB and open avenues that could guide future monitoring and treatment strategies targeting CVD and NAFLD in obesity.

Characterization of one anastomosis gastric bypass and impact of biliary and common limbs on bile acid and postprandial glucose metabolism in a minipig model.

The alimentary limb has been proposed to be a key driver of the weight-loss-independent metabolic improvements that occur upon bariatric surgery. However, the one anastomosis gastric bypass (OAGB) procedure, consisting of one long biliary limb and a short common limb, induces similar beneficial metabolic effects compared to Roux-en-Y Gastric Bypass (RYGB) in humans, despite the lack of an alimentary limb. The aim of this study was to assess the role of the length of biliary and common limbs in the weight loss and metabolic effects that occur upon OAGB. OAGB and sham surgery, with or without modifications of the length of either the biliary limb or the common limb, were performed in Gottingen minipigs. Weight loss, metabolic changes, and the effects on plasma and intestinal bile acids (BAs) were assessed 15 days after surgery. OAGB significantly decreased body weight, improved glucose homeostasis, increased postprandial GLP-1 and fasting plasma BAs, and qualitatively changed the intestinal BA species composition. Resection of the biliary limb prevented the body weight loss effects of OAGB and attenuated the postprandial GLP-1 increase. Improvements in glucose homeostasis along with changes in plasma and intestinal BAs occurred after OAGB regardless of the biliary limb length. Resection of only the common limb reproduced the glucose homeostasis effects and the changes in intestinal BAs. Our results suggest that the changes in glucose metabolism and BAs after OAGB are mainly mediated by the length of the common limb, whereas the length of the biliary limb contributes to body weight loss.NEW & NOTEWORTHY Common limb mediates postprandial glucose metabolism change after gastric bypass whereas biliary limb contributes to weight loss.

A randomized placebo-controlled trial of elafibranor in patients with primary biliary cholangitis and incomplete response to UDCA.

BACKGROUND & AIMS: Patients with primary biliary cholangitis (PBC) who have an incomplete response to ursodeoxycholic acid remain at risk of disease progression. We investigated the safety and efficacy of elafibranor, a dual PPARα/δ agonist, in patients with PBC. METHODS: This 12-week, double-blind phase II trial enrolled 45 adults with PBC who had incomplete response to ursodeoxycholic acid (alkaline phosphatase levels ≥1.67-fold the upper limit of normal (ULN). Patients were randomly assigned to elafibranor 80 mg, elafibranor 120 mg or placebo. The primary endpoint was the relative change of ALP at 12 weeks (NCT03124108). RESULTS: At 12 weeks, ALP was reduced by -48.3±14.8% in the elafibranor 80 mg group (p <0.001 vs. placebo) and by -40.6±17.4% in the elafibranor 120 mg group (p <0.001) compared to a +3.2±14.8% increase in the placebo group. The composite endpoint of ALP ≤1.67-fold the ULN, decrease of ALP >15% and total bilirubin below the ULN was achieved in 67% patients in the elafibranor 80 mg group and 79% patients in the elafibranor 120 mg group, vs. 6.7% patients in the placebo group. Levels of gamma-glutamyltransferase decreased by 37.0±25.5% in the elafibranor 80 mg group (p <0.001) and 40.0±24.1% in the elafibranor 120 mg group (p <0.01) compared to no change (+0.2±26.0%) in the placebo group. Levels of disease markers such as IgM, 5'-nucleotidase or high-sensitivity C-reactive protein were likewise reduced by elafibranor. Pruritus was not induced or exacerbated by elafibranor and patients with pruritus at baseline reported less pruritic symptoms at the end of treatment. All possibly drug-related non-serious adverse events were mild to moderate. CONCLUSION: In this randomized phase II trial, elafibranor was generally safe and well tolerated and significantly reduced levels of ALP, composite endpoints of bilirubin and ALP, as well as other markers of disease activity in patients with PBC and an incomplete response to ursodeoxycholic acid. LAY SUMMARY: Patients with primary biliary cholangitis (a rare chronic liver disease) that do not respond to standard therapy remain at risk of disease progression toward cirrhosis and impaired quality of life. Elafibranor is a nuclear receptor agonist that we tested in a randomized clinical trial over 12 weeks. It successfully decreased levels of disease activity markers, including alkaline phosphatase. Thus, this study is the foundation for a larger prospective study that will determine the efficacy and safety of this drug as a second-line therapy. CLINICAL TRIAL REGISTRATION NUMBER: Clinical Trials.gov NCT03124108.

Sirt6 deletion in bone marrow-derived cells increases atherosclerosis - Central role of macrophage scavenger receptor 1.

AIMS: Sirtuin 6 (Sirt6) is a NAD+-dependent deacetylase that plays a key role in DNA repair, inflammation and lipid regulation. Sirt6-null mice show severe metabolic defects and accelerated aging. Macrophage-foam cell formation via scavenger receptors is a key step in atherogenesis. We determined the effects of bone marrow-restricted Sirt6 deletion on foam cell formation and atherogenesis using a mouse model. METHODS AND RESULTS: Sirt6 deletion in bone marrow-derived cells increased aortic plaques, lipid content and macrophage numbers in recipient Apoe-/- mice fed a high-cholesterol diet for 12 weeks (n = 12-14, p < .001). In RAW macrophages, Sirt6 overexpression reduced oxidized low-density lipoprotein (oxLDL) uptake, Sirt6 knockdown enhanced it and increased mRNA and protein levels of macrophage scavenger receptor 1 (Msr1), whereas levels of other oxLDL uptake and efflux transporters remained unchanged. Similarly, in human primary macrophages, Sirt6 knockdown increased MSR1 protein levels and oxLDL uptake. Double knockdown of Sirt6 and Msr1 abolished the increase in oxLDL uptake observed upon Sirt6 single knockdown. FACS analyses of macrophages from aortic plaques of Sirt6-deficient bone marrow-transplanted mice showed increased MSR1 protein expression. Double knockdown of Sirt6 and the transcription factor c-Myc in RAW cells abolished the increase in Msr1 mRNA and protein levels; c-Myc overexpression increased Msr1 mRNA and protein levels. CONCLUSIONS: Loss of Sirt6 in bone marrow-derived cells is proatherogenic; hereby macrophages play an important role given a c-Myc-dependent increase in MSR1 protein expression and an enhanced oxLDL uptake in human and murine macrophages. These findings assign endogenous SIRT6 in macrophages an important atheroprotective role.

Bile acid alterations in nonalcoholic fatty liver disease, obesity, insulin resistance and type 2 diabetes: what do the human studies tell?

PURPOSE OF REVIEW: The purpose of this review is to discuss the influence of obesity, insulin resistance, type 2 diabetes (T2D), and nonalcoholic fatty liver disease (NAFLD) on bile acid metabolism and to analyze whether these findings reinforce current beliefs about the role of bile acids in the pathophysiology of these diseases. RECENT FINDINGS: Discordant results on plasma bile acid alterations in NAFLD patients have been reported. Obesity, insulin resistance, and T2D, common comorbidities of NAFLD, have been associated with bile acid changes, but the individual bile acid species variations differ between studies (summarized in this review), perhaps because of clinicobiological differences between the studied patient populations and the heterogeneity of statistical analyses applied. SUMMARY: The regulatory role of bile acids in metabolic and cellular homeostasis renders bile acids attractive candidates as players in the pathophysiology of NAFLD. However, considering the complex relationship between NAFLD, obesity, insulin resistance and T2D, it is difficult to establish clear and independent associations between bile acid alterations and these individual diseases. Though bile acid alterations may not drive NAFLD progression, signaling pathways activated by bile acids remain potent therapeutic targets for its treatment. Further studies with appropriate matching or adjustment for potential confounding factors are necessary to determine which pathophysiological conditions drive the alterations in bile acid metabolism.

Transcription profiling in the liver of undernourished male rat offspring reveals altered lipid metabolism pathways and predisposition to hepatic steatosis.

Clinical and animal studies have reported an association between low birth weight and the development of nonalcoholic fatty liver disease (NAFLD) in offspring. Using a model of prenatal maternal 70% food restriction diet (FR30) in the rat, we previously showed that maternal undernutrition predisposes offspring to altered lipid metabolism in adipose tissue, especially on a high-fat (HF) diet. Here, using microarray-based expression profiling combined with metabolic, endocrine, biochemical, histological, and lipidomic approaches, we assessed whether FR30 procedure sensitizes adult male offspring to impaired lipid metabolism in the liver. No obvious differences were noted in the concentrations of triglycerides, cholesterol, and bile acids in the liver of 4-mo-old FR30 rats whichever postweaning diet was used. However, several clues suggest that offspring's lipid metabolism and steatosis are modified by maternal undernutrition. First, lipid composition was changed (i.e., higher total saturated fatty acids and lower elaidic acid) in the liver, whereas larger triglyceride droplets were observed in hepatocytes of undernourished rats. Second, FR30 offspring exhibited long-term impact on hepatic gene expression and lipid metabolism pathways on a chow diet. Although the transcriptome profile was globally modified by maternal undernutrition, cholesterol and bile acid biosynthesis pathways appear to be key targets, indicating that FR30 animals were predisposed to impaired hepatic cholesterol metabolism. Third, the FR30 protocol markedly modifies hepatic gene transcription profiles in undernourished offspring in response to postweaning HF. Overall, FR30 offspring may exhibit impaired metabolic flexibility, which does not enable them to properly cope with postweaning nutritional challenges influencing the development of nonalcoholic fatty liver.

Brain insulin response and peripheral metabolic changes in a Tau transgenic mouse model.

Accumulation of hyper-phosphorylated and aggregated Tau proteins is a neuropathological hallmark of Alzheimer's Disease (AD) and Tauopathies. AD patient brains also exhibit insulin resistance. Whereas, under normal physiological conditions insulin signaling in the brain mediates plasticity and memory formation, it can also regulate peripheral energy homeostasis. Thus, in AD, brain insulin resistance affects both cognitive and metabolic changes described in these patients. While a role of Aß oligomers and APOE4 towards the development of brain insulin resistance emerged, contribution of Tau pathology has been largely overlooked. Our recent data demonstrated that one of the physiological function of Tau is to sustain brain insulin signaling. We postulated that under pathological conditions, hyper-phosphorylated/aggregated Tau is likely to lose this function and to favor the development of brain insulin resistance. This hypothesis was substantiated by observations from patient brains with pure Tauopathies. To address the potential link between Tau pathology and brain insulin resistance, we have evaluated the brain response to insulin in a transgenic mouse model of AD-like Tau pathology (THY-Tau22). Using electrophysiological and biochemical evaluations, we surprisingly observed that, at a time when Tau pathology and cognitive deficits are overt and obvious, the hippocampus of THY-Tau22 mice exhibits enhanced response to insulin. In addition, we demonstrated that the ability of i.c.v. insulin to promote body weight loss is enhanced in THY-Tau22 mice. In line with this, THY-Tau22 mice exhibited a lower body weight gain, hypoleptinemia and hypoinsulinemia and finally a metabolic resistance to high-fat diet. The present data highlight that the brain of transgenic Tau mice exhibit enhanced brain response to insulin. Whether these observations are ascribed to the development of Tau pathology, and therefore relevant to human Tauopathies, or unexpectedly results from the Tau transgene overexpression is debatable and discussed.

Hepatic PPARα is critical in the metabolic adaptation to sepsis.

BACKGROUND & AIMS: Although the role of inflammation to combat infection is known, the contribution of metabolic changes in response to sepsis is poorly understood. Sepsis induces the release of lipid mediators, many of which activate nuclear receptors such as the peroxisome proliferator-activated receptor (PPAR)α, which controls both lipid metabolism and inflammation. We aimed to elucidate the previously unknown role of hepatic PPARα in the response to sepsis. METHODS: Sepsis was induced by intraperitoneal injection of Escherichia coli in different models of cell-specific Ppara-deficiency and their controls. The systemic and hepatic metabolic response was analyzed using biochemical, transcriptomic and functional assays. PPARα expression was analyzed in livers from elective surgery and critically ill patients and correlated with hepatic gene expression and blood parameters. RESULTS: Both whole body and non-hematopoietic Ppara-deficiency in mice decreased survival upon bacterial infection. Livers of septic Ppara-deficient mice displayed an impaired metabolic shift from glucose to lipid utilization resulting in more severe hypoglycemia, impaired induction of hyperketonemia and increased steatosis due to lower expression of genes involved in fatty acid catabolism and ketogenesis. Hepatocyte-specific deletion of PPARα impaired the metabolic response to sepsis and was sufficient to decrease survival upon bacterial infection. Hepatic PPARA expression was lower in critically ill patients and correlated positively with expression of lipid metabolism genes, but not with systemic inflammatory markers. CONCLUSION: During sepsis, Ppara-deficiency in hepatocytes is deleterious as it impairs the adaptive metabolic shift from glucose to FA utilization. Metabolic control by PPARα in hepatocytes plays a key role in the host defense against infection. LAY SUMMARY: As the main cause of death in critically ill patients, sepsis remains a major health issue lacking efficacious therapies. While current clinical literature suggests an important role for inflammation, metabolic aspects of sepsis have mostly been overlooked. Here, we show that mice with an impaired metabolic response, due to deficiency of the nuclear receptor PPARα in the liver, exhibit enhanced mortality upon bacterial infection despite a similar inflammatory response, suggesting that metabolic interventions may be a viable strategy for improving sepsis outcomes.

Targeting the gut microbiota with inulin-type fructans: preclinical demonstration of a novel approach in the management of endothelial dysfunction.

OBJECTIVE: To investigate the beneficial role of prebiotics on endothelial dysfunction, an early key marker of cardiovascular diseases, in an original mouse model linking steatosis and endothelial dysfunction. DESIGN: We examined the contribution of the gut microbiota to vascular dysfunction observed in apolipoprotein E knockout (Apoe-/-) mice fed an n-3 polyunsaturated fatty acid (PUFA)-depleted diet for 12 weeks with or without inulin-type fructans (ITFs) supplementation for the last 15 days. Mesenteric and carotid arteries were isolated to evaluate endothelium-dependent relaxation ex vivo. Caecal microbiota composition (Illumina Sequencing of the 16S rRNA gene) and key pathways/mediators involved in the control of vascular function, including bile acid (BA) profiling, gut and liver key gene expression, nitric oxide and gut hormones production were also assessed. RESULTS: ITF supplementation totally reverses endothelial dysfunction in mesenteric and carotid arteries of n-3 PUFA-depleted Apoe-/- mice via activation of the nitric oxide (NO) synthase/NO pathway. Gut microbiota changes induced by prebiotic treatment consist in increased NO-producing bacteria, replenishment of abundance in Akkermansia and decreased abundance in bacterial taxa involved in secondary BA synthesis. Changes in gut and liver gene expression also occur upon ITFs suggesting increased glucagon-like peptide 1 production and BA turnover as drivers of endothelium function preservation. CONCLUSIONS: We demonstrate for the first time that ITF improve endothelial dysfunction, implicating a short-term adaptation of both gut microbiota and key gut peptides. If confirmed in humans, prebiotics could be proposed as a novel approach in the prevention of metabolic disorders-related cardiovascular diseases.

Bile Acid Control of Metabolism and Inflammation in Obesity, Type 2 Diabetes, Dyslipidemia, and Nonalcoholic Fatty Liver Disease.

Bile acids are signaling molecules that coordinately regulate metabolism and inflammation via the nuclear farnesoid X receptor (FXR) and the Takeda G protein-coupled receptor 5 (TGR5). These receptors activate transcriptional networks and signaling cascades controlling the expression and activity of genes involved in bile acid, lipid and carbohydrate metabolism, energy expenditure, and inflammation by acting predominantly in enterohepatic tissues, but also in peripheral organs. In this review, we discuss the most recent findings on the inter-organ signaling and interplay with the gut microbiota of bile acids and their receptors in meta-inflammation, with a focus on their pathophysiologic roles in obesity, type 2 diabetes, dyslipidemia, and nonalcoholic steatohepatitis, and their potential therapeutic applications.

Cholesterol uptake disruption, in association with chemotherapy, is a promising combined metabolic therapy for pancreatic adenocarcinoma.

The malignant progression of pancreatic ductal adenocarcinoma (PDAC) is accompanied by a profound desmoplasia, which forces proliferating tumor cells to metabolically adapt to this new microenvironment. We established the PDAC metabolic signature to highlight the main activated tumor metabolic pathways. Comparative transcriptomic analysis identified lipid-related metabolic pathways as being the most highly enriched in PDAC, compared with a normal pancreas. Our study revealed that lipoprotein metabolic processes, in particular cholesterol uptake, are drastically activated in the tumor. This process results in an increase in the amount of cholesterol and an overexpression of the low-density lipoprotein receptor (LDLR) in pancreatic tumor cells. These findings identify LDLR as a novel metabolic target to limit PDAC progression. Here, we demonstrate that shRNA silencing of LDLR, in pancreatic tumor cells, profoundly reduces uptake of cholesterol and alters its distribution, decreases tumor cell proliferation, and limits activation of ERK1/2 survival pathway. Moreover, blocking cholesterol uptake sensitizes cells to chemotherapeutic drugs and potentiates the effect of chemotherapy on PDAC regression. Clinically, high PDAC Ldlr expression is not restricted to a specific tumor stage but is correlated to a higher risk of disease recurrence. This study provides a precise overview of lipid metabolic pathways that are disturbed in PDAC. We also highlight the high dependence of pancreatic cancer cells upon cholesterol uptake, and identify LDLR as a promising metabolic target for combined therapy, to limit PDAC progression and disease patient relapse.

Liver X Receptor Regulates Triglyceride Absorption Through Intestinal Down-regulation of Scavenger Receptor Class B, Type 1.

BACKGROUND & AIMS: Reducing postprandial triglyceridemia may be a promising strategy to lower the risk of cardiovascular disorders associated with obesity and type 2 diabetes. In enterocytes, scavenger receptor class B, type 1 (SR-B1, encoded by SCARB1) mediates lipid-micelle sensing to promote assembly and secretion of chylomicrons. The nuclear receptor subfamily 1, group H, members 2 and 3 (also known as liver X receptors [LXRs]) regulate genes involved in cholesterol and fatty acid metabolism. We aimed to determine whether intestinal LXRs regulate triglyceride absorption. METHODS: C57BL/6J mice were either fed a cholesterol-enriched diet or given synthetic LXR agonists (GW3965 or T0901317). We measured the production of chylomicrons and localized SR-B1 by immunohistochemistry. Mechanisms of postprandial triglyceridemia and SR-B1 regulation were studied in Caco-2/TC7 cells incubated with LXR agonists. RESULTS: In mice and in the Caco-2/TC7 cell line, LXR agonists caused localization of intestinal SR-B1 from apical membranes to intracellular organelles and reduced chylomicron secretion. In Caco-2/TC7 cells, LXR agonists reduced SR-B1-dependent lipidic-micelle-induced Erk phosphorylation. LXR agonists also reduced intracellular trafficking of the apical apolipoprotein B pool toward secretory compartments. LXR reduced levels of SR-B1 in Caco-2/TC7 cells via a post-transcriptional mechanism that involves microRNAs. CONCLUSION: In Caco-2/TC7 cells and mice, intestinal activation of LXR reduces the production of chylomicrons by a mechanism dependent on the apical localization of SR-B1.

Rapid and body weight-independent improvement of endothelial and high-density lipoprotein function after Roux-en-Y gastric bypass: role of glucagon-like peptide-1.

BACKGROUND: Roux-en-Y gastric bypass (RYGB) reduces body weight and cardiovascular mortality in morbidly obese patients. Glucagon-like peptide-1 (GLP-1) seems to mediate the metabolic benefits of RYGB partly in a weight loss-independent manner. The present study investigated in rats and patients whether obesity-induced endothelial and high-density lipoprotein (HDL) dysfunction is rapidly improved after RYGB via a GLP-1-dependent mechanism. METHODS AND RESULTS: Eight days after RYGB in diet-induced obese rats, higher plasma levels of bile acids and GLP-1 were associated with improved endothelium-dependent relaxation compared with sham-operated controls fed ad libitum and sham-operated rats that were weight matched to those undergoing RYGB. Compared with the sham-operated rats, RYGB improved nitric oxide (NO) bioavailability resulting from higher endothelial Akt/NO synthase activation, reduced c-Jun amino terminal kinase phosphorylation, and decreased oxidative stress. The protective effects of RYGB were prevented by the GLP-1 receptor antagonist exendin9-39 (10 µg·kg(-1)·h(-1)). Furthermore, in patients and rats, RYGB rapidly reversed HDL dysfunction and restored the endothelium-protective properties of the lipoprotein, including endothelial NO synthase activation, NO production, and anti-inflammatory, antiapoptotic, and antioxidant effects. Finally, RYGB restored HDL-mediated cholesterol efflux capacity. To demonstrate the role of increased GLP-1 signaling, sham-operated control rats were treated for 8 days with the GLP-1 analog liraglutide (0.2 mg/kg twice daily), which restored NO bioavailability and improved endothelium-dependent relaxations and HDL endothelium-protective properties, mimicking the effects of RYGB. CONCLUSIONS: RYGB rapidly reverses obesity-induced endothelial dysfunction and restores the endothelium-protective properties of HDL via a GLP-1-mediated mechanism. The present translational findings in rats and patients unmask novel, weight-independent mechanisms of cardiovascular protection in morbid obesity.

The Sirt1 activator SRT3025 provides atheroprotection in Apoe-/- mice by reducing hepatic Pcsk9 secretion and enhancing Ldlr expression.

AIMS: The deacetylase sirtuin 1 (Sirt1) exerts beneficial effects on lipid metabolism, but its roles in plasma LDL-cholesterol regulation and atherosclerosis are controversial. Thus, we applied the pharmacological Sirt1 activator SRT3025 in a mouse model of atherosclerosis and in hepatocyte culture. METHODS AND RESULTS: Apolipoprotein E-deficient (Apoe(-/-)) mice were fed a high-cholesterol diet (1.25% w/w) supplemented with SRT3025 (3.18 g kg(-1) diet) for 12 weeks. In vitro, the drug activated wild-type Sirt1 protein, but not the activation-resistant Sirt1 mutant; in vivo, it increased deacetylation of hepatic p65 and skeletal muscle Foxo1. SRT3025 treatment decreased plasma levels of LDL-cholesterol and total cholesterol and reduced atherosclerosis. Drug treatment did not change mRNA expression of hepatic LDL receptor (Ldlr) and proprotein convertase subtilisin/kexin type 9 (Pcsk9), but increased their protein expression indicating post-translational effects. Consistent with hepatocyte Ldlr and Pcsk9 accumulation, we found reduced plasma levels of Pcsk9 after pharmacological Sirt1 activation. In vitro administration of SRT3025 to cultured AML12 hepatocytes attenuated Pcsk9 secretion and its binding to Ldlr, thereby reducing Pcsk9-mediated Ldlr degradation and increasing Ldlr expression and LDL uptake. Co-administration of exogenous Pcsk9 with SRT3025 blunted these effects. Sirt1 activation with SRT3025 in Ldlr(-/-) mice reduced neither plasma Pcsk9, nor LDL-cholesterol levels, nor atherosclerosis. CONCLUSION: We identify reduction in Pcsk9 secretion as a novel effect of Sirt1 activity and uncover Ldlr as a prerequisite for Sirt1-mediated atheroprotection in mice. Pharmacological activation of Sirt1 appears promising to be tested in patients for its effects on plasma Pcsk9, LDL-cholesterol, and atherosclerosis.

Bariatric surgery, lipoprotein metabolism and cardiovascular risk.

PURPOSE OF REVIEW: To summarize recent epidemiological, preclinical and clinical studies on the effects of Roux-en-Y-gastric bypass (RYGBP) surgery on cardiovascular risk factors and the underlying mechanisms. RECENT FINDINGS: Although RYGBP has mechanical effects on the gastrointestinal tract, the reduced gastric pouch and intestinal calorie absorption cannot fully explain the metabolic improvements. SUMMARY: Obesity predisposes to cardiovascular risk factors such as dyslipidemia, type 2 diabetes, nonalcoholic fatty liver disease and hypertension. In contrast to the limited success of pharmacological and lifestyle interventions, RYGBP induces sustained weight loss, metabolic improvements and decreases morbidity/mortality. In line, RYGBP reduces cardiovascular risk factors. Although the mechanisms are not entirely understood, RYGBP induces complex changes in the gut affecting other organs through endocrine and metabolic signals from the intestine to all key metabolic organs, which can link RYGBP and decreased cardiovascular risk. Here, we discuss the roles of changes in lipid absorption and metabolism, bile acid metabolism, gut hormones and the microbiote as potential mechanisms in the decreased cardiovascular risk and metabolic improvement after RYGBP.

The transrepressive activity of peroxisome proliferator-activated receptor alpha is necessary and sufficient to prevent liver fibrosis in mice.

UNLABELLED: Nonalcoholic fatty liver disease (NAFLD) is increasingly prevalent and strongly associated with central obesity, dyslipidemia, and insulin resistance. According to the multiple-hit model of NAFLD pathogenesis, lipid accumulation drives nonalcoholic steatohepatitis (NASH) initiation by triggering oxidative stress, lipotoxicity, and subsequent activation of hepatic inflammatory responses that may progress, in predisposed individuals, to fibrosis and cirrhosis. While there is an unmet therapeutical need for NASH and fibrosis, recent preclinical studies showed that peroxisome proliferator-activated receptor (PPAR)-α agonism can efficiently oppose these symptoms. To dissect the relative contribution of antisteatotic versus anti-inflammatory PPAR-α activities in counteracting dietary-induced liver fibrosis, we used a PPAR-α mutant lacking its DNA-binding-dependent activity on fatty acid metabolism. Liver-specific expression of wild-type or a DNA-binding-deficient PPAR-α in acute and chronic models of inflammation were used to study PPAR-α's anti-inflammatory versus metabolic activities in NASH and fibrosis. Pharmacologically activated PPAR-α inhibited hepatic inflammatory responses and the transition from steatosis toward NASH and fibrosis through a direct, anti-inflammatory mechanism independent of its lipid handling properties. CONCLUSION: The transrepression activity of PPAR-α on chronic liver inflammation is sufficient to prevent progression of NASH to liver fibrosis. Dissociated PPAR-α agonists, selectively modulating PPAR-α transrepression activity, could thus be an option to prevent NASH and fibrosis progression.

Glucose sensing O-GlcNAcylation pathway regulates the nuclear bile acid receptor farnesoid X receptor (FXR).

UNLABELLED: Bile acid metabolism is intimately linked to the control of energy homeostasis and glucose and lipid metabolism. The nuclear receptor farnesoid X receptor (FXR) plays a major role in the enterohepatic cycling of bile acids, but the impact of nutrients on bile acid homeostasis is poorly characterized. Metabolically active hepatocytes cope with increases in intracellular glucose concentrations by directing glucose into storage (glycogen) or oxidation (glycolysis) pathways, as well as to the pentose phosphate shunt and the hexosamine biosynthetic pathway. Here we studied whether the glucose nonoxidative hexosamine biosynthetic pathway modulates FXR activity. Our results show that FXR interacts with and is O-GlcNAcylated by O-GlcNAc transferase in its N-terminal AF1 domain. Increased FXR O-GlcNAcylation enhances FXR gene expression and protein stability in a cell type-specific manner. High glucose concentrations increased FXR O-GlcNAcylation, hence its protein stability and transcriptional activity by inactivating corepressor complexes, which associate in a ligand-dependent manner with FXR, and increased FXR binding to chromatin. Finally, in vivo fasting-refeeding experiments show that FXR undergoes O-GlcNAcylation in fed conditions associated with increased direct FXR target gene expression and decreased liver bile acid content. CONCLUSION: FXR activity is regulated by glucose fluxes in hepatocytes through a direct posttranslational modification catalyzed by the glucose-sensing hexosamine biosynthetic pathway.

Screening strategy to generate cell specific recombination: a case report with the RIP-Cre mice.

Conditional gene knockout technology is a powerful tool to study the function of a gene in a specific tissue, organ or cell lineage. The most commonly used procedure applies the Cre-LoxP strategy, where the choice of the Cre driver promoter is critical to determine the efficiency and specificity of the system. However, a considered choice of an appropriate promoter does not always protect against the risk of unwanted recombination and the consequent deletion of the gene in other tissues than the desired one(s), due to phenomena of non-specific activation of the Cre transgene. Furthermore, the causes of these phenomena are not completely understood and this can potentially affect every strain of Cre-mice. In our study on the deletion of a same gene in two different tissues, we show that the incidence rate of non-specific recombination in unwanted tissues depends on the Cre driver strain, ranging from 100%, rendering it useless (aP2-Cre strain), to ~5%, which is still compatible with their use (RIP-Cre strain). The use of a simple PCR strategy conceived to detect this occurrence is indispensable when producing a tissue-specific knockout mouse. Therefore, when choosing the Cre-driver promoter, researchers not only have to be careful about its tissue-specificity and timing of activation, but should also include a systematical screening in order to exclude mice in which atypical recombination has occurred and to limit the unnecessary use of laboratory animals in uninterpretable experiments.

Hepatic trans-Golgi action coordinated by the GTPase ARFRP1 is crucial for lipoprotein lipidation and assembly.

The liver is a major organ in whole body lipid metabolism and malfunctioning can lead to various diseases including dyslipidemia, fatty liver disease, and type 2 diabetes. Triglycerides and cholesteryl esters are packed in the liver as very low density lipoproteins (VLDLs). Generation of these lipoproteins is initiated in the endoplasmic reticulum and further maturation likely occurs in the Golgi. ADP-ribosylation factor-related protein 1 (ARFRP1) is a small trans-Golgi-associated guanosine triphosphatase (GTPase) that regulates protein sorting and is required for chylomicron lipidation and assembly in the intestine. Here we show that the hepatocyte-specific deletion of Arfrp1 (Arfrp1(liv-/-)) results in impaired VLDL lipidation leading to reduced plasma triglyceride levels in the fasted state as well as after inhibition of lipoprotein lipase activity by Triton WR-1339. In addition, the concentration of ApoC3 that comprises 40% of protein mass of secreted VLDLs is markedly reduced in the plasma of Arfrp1(liv-/-) mice but accumulates in the liver accompanied by elevated triglycerides. Fractionation of Arfrp1(liv-/-) liver homogenates reveals more ApoB48 and a lower concentration of triglycerides in the Golgi compartments than in the corresponding fractions from control livers. In conclusion, ARFRP1 and the Golgi apparatus play an important role in lipoprotein maturation in the liver by influencing lipidation and assembly of proteins to the lipid particles.