Pathogenic, Total Loss-of-Function DYRK1B Variants Cause Monogenic Obesity Associated With Type 2 Diabetes.

OBJECTIVE: Rare variants in DYRK1B have been described in some patients with central obesity, type 2 diabetes, and early-onset coronary disease. Owing to the limited number of conducted studies, the broader impact of DYRK1B variants on a larger scale has yet to be investigated. RESEARCH DESIGN AND METHODS: DYRK1B was sequenced in 9,353 participants from a case-control study for obesity and type 2 diabetes. Each DYRK1B variant was functionally assessed in vitro. Variant pathogenicity was determined using criteria from the American College of Medical Genetics and Genomics (ACMG). The effect of pathogenic or likely pathogenic (P/LP) variants on metabolic traits was assessed using adjusted mixed-effects score tests. RESULTS: Sixty-five rare, heterozygous DYRK1B variants were identified and were not associated with obesity or type 2 diabetes. Following functional analyses, 20 P/LP variants were pinpointed, including 6 variants that exhibited a fully inhibitory effect (P/LP-null) on DYRK1B activity. P/LP and P/LP-null DYRK1B variants were associated with increased BMI and obesity risk; however, the impact was notably more pronounced for the P/LP-null variants (effect of 8.0 ± 3.2 and odds ratio of 7.9 [95% CI 1.2-155]). Furthermore, P/LP-null variants were associated with higher fasting glucose and type 2 diabetes risk (effect of 2.9 ± 1.0 and odds ratio of 4.8 [95% CI 0.85-37]), while P/LP variants had no effect on glucose homeostasis. CONCLUSIONS: P/LP, total loss-of-function DYRK1B variants cause monogenic obesity associated with type 2 diabetes. This study underscores the significance of conducting functional assessments in order to accurately ascertain the tangible effects of P/LP DYRK1B variants.

Pathogenic monoallelic variants in GLIS3 increase type 2 diabetes risk and identify a subgroup of patients sensitive to sulfonylureas.

AIMS/HYPOTHESIS: GLIS3 encodes a transcription factor involved in pancreatic beta cell development and function. Rare pathogenic, bi-allelic mutations in GLIS3 cause syndromic neonatal diabetes whereas frequent SNPs at this locus associate with common type 2 diabetes risk. Because rare, functional variants located in other susceptibility genes for type 2 diabetes have already been shown to strongly increase individual risk for common type 2 diabetes, we aimed to investigate the contribution of rare pathogenic GLIS3 variants to type 2 diabetes. METHODS: GLIS3 was sequenced in 5471 individuals from the Rare Variants Involved in Diabetes and Obesity (RaDiO) study. Variant pathogenicity was assessed following the criteria established by the American College of Medical Genetics and Genomics (ACMG). To address the pathogenic strong criterion number 3 (PS3), we conducted functional investigations of these variants using luciferase assays, focusing on capacity of GLIS family zinc finger 3 (GLIS3) to bind to and activate the INS promoter. The association between rare pathogenic or likely pathogenic (P/LP) variants and type 2 diabetes risk (and other metabolic traits) was then evaluated. A meta-analysis combining association results from RaDiO, the 52K study (43,125 individuals) and the TOPMed study (44,083 individuals) was finally performed. RESULTS: Through targeted resequencing of GLIS3, we identified 105 rare variants that were carried by 395 participants from RaDiO. Among them, 49 variants decreased the activation of the INS promoter. Following ACMG criteria, 18 rare variants were classified as P/LP, showing an enrichment in the last two exons compared with the remaining exons (p<5×10-6; OR>3.5). The burden of these P/LP variants was strongly higher in individuals with type 2 diabetes (p=3.0×10-3; OR 3.9 [95% CI 1.4, 12]), whereas adiposity, age at type 2 diabetes diagnosis and cholesterol levels were similar between variant carriers and non-carriers with type 2 diabetes. Interestingly, all carriers with type 2 diabetes were sensitive to oral sulfonylureas. A total of 7 P/LP variants were identified in both 52K and TOPMed studies. The meta-analysis of association studies obtained from RaDiO, 52K and TOPMed showed an enrichment of P/LP GLIS3 variants in individuals with type 2 diabetes (p=5.6×10-5; OR 2.1 [95% CI 1.4, 2.9]). CONCLUSIONS/INTERPRETATION: Rare P/LP GLIS3 variants do contribute to type 2 diabetes risk. The variants located in the distal part of the protein could have a direct effect on its functional activity by impacting its transactivation domain, by homology with the mouse GLIS3 protein. Furthermore, rare P/LP GLIS3 variants seem to have a direct clinical effect on beta cell function, which could be improved by increasing insulin secretion via the use of sulfonylureas.

Exploring the role of purinergic receptor P2RY1 in type 2 diabetes risk and pathophysiology: Insights from human functional genomics.

OBJECTIVE: Human functional genomics has proven powerful in discovering drug targets for common metabolic disorders. Through this approach, we investigated the involvement of the purinergic receptor P2RY1 in type 2 diabetes (T2D). METHODS: P2RY1 was sequenced in 9,266 participants including 4,177 patients with T2D. In vitro analyses were then performed to assess the functional effect of each variant. Expression quantitative trait loci (eQTL) analysis was performed in pancreatic islets from 103 pancreatectomized individuals. The effect of P2RY1 on glucose-stimulated insulin secretion was finally assessed in human pancreatic beta cells (EndoCßH5), and RNA sequencing was performed on these cells. RESULTS: Sequencing P2YR1 in 9,266 participants revealed 22 rare variants, seven of which were loss-of-function according to our in vitro analyses. Carriers, except one, exhibited impaired glucose control. Our eQTL analysis of human islets identified P2RY1 variants, in a beta-cell enhancer, linked to increased P2RY1 expression and reduced T2D risk, contrasting with variants located in a silent region associated with decreased P2RY1 expression and increased T2D risk. Additionally, a P2RY1-specific agonist increased insulin secretion upon glucose stimulation, while the antagonist led to decreased insulin secretion. RNA-seq highlighted TXNIP as one of the main transcriptomic markers of insulin secretion triggered by P2RY1 agonist. CONCLUSION: Our findings suggest that P2RY1 inherited or acquired dysfunction increases T2D risk and that P2RY1 activation stimulates insulin secretion. Selective P2RY1 agonists, impermeable to the blood-brain barrier, could serve as potential insulin secretagogues.

A novel pathogenic variant in MRAP2 in an obese patient with successful outcome of bariatric surgery.

Mutations in genes encoding proteins located in the leptin/melanocortin pathway have been identified in the rare cases of genetic obesities. Heterozygous variants of MRAP2, encoding a G coupled-protein receptor accessory protein implicated in energy control notably via the melanocortin-4 receptor, have been recently identified. A 24-year-old patient with early-onset severe obesity (body mass index [BMI]: 64 kg/m2) associated with hypertension, respiratory complications, nonalcoholic fatty liver disease, and type 2 diabetes was referred to our department. Sleeve gastrectomy was successful. A new heterozygous variant in MRAP2 (NM_138409.4: c.154G>C/p.G52R) variant was identified in the patient DNA. Functional assessment confirmed that this new variant was pathogenic. We report a new pathogenic loss-of-function mutation in MRAP2 in a patient suffering from a severe multicomplicated obesity. This confirms the metabolic phenotype in patients with this monogenic form of obesity. Longer follow-up will be necessary. Our finding will allow a personalized medicine.

Discovery, Structure-Activity Relationships, and In Vivo Activity of Dihydropyridone Agonists of the Bile Acid Receptor TGR5.

A novel series of potent agonists of the bile acid receptor TGR5 bearing a dihydropyridone scaffold was developed from a high-throughput screen. Starting from a micromolar hit compound, we implemented an extensive structure-activity-relationship (SAR) study with the synthesis and biological evaluation of 83 analogues. The project culminated with the identification of the potent nanomolar TGR5 agonist 77A. We report the GLP-1 secretagogue effect of our lead compound ex vivo in mouse colonoids and in vivo. In addition, to identify specific features favorable for TGR5 activation, we generated and optimized a three-dimensional quantitative SAR model that contributed to our understanding of our activity profile and could guide further development of this dihydropyridone series.

Contribution of heterozygous PCSK1 variants to obesity and implications for precision medicine: a case-control study.

BACKGROUND: Rare biallelic pathogenic mutations in PCSK1 (encoding proprotein convertase subtilisin/kexin type 1 [PC1/3]) cause early-onset obesity associated with various endocrinopathies. Setmelanotide has been approved for carriers of these biallelic mutations in the past 3 years. We aimed to perform a large-scale functional genomic study focusing on rare heterozygous variants of PCSK1 to decipher their putative impact on obesity risk. METHODS: This case-control study included all participants with overweight and obesity (ie, cases) or healthy weight (ie, controls) from the RaDiO study of three community-based and one hospital-based cohort in France recruited between Jan 1, 1995, and Dec 31, 2000. In adults older than 18 years, healthy weight was defined as BMI of less than 25·0 kg/m2, overweight as 25·0-29·9 kg/m2, and obesity as 30·0 kg/m2 or higher. Participants with type 2 diabetes had fasting glucose of 7·0 mmol/L or higher or used treatment for hyperglycaemia (or both) and were negative for islet or insulin autoantibodies. Functional assessment of rare missense variants of PCSK1 was performed. Pathogenicity clusters of variants were determined with machine learning. The effect of each cluster of PCSK1 variants on obesity was assessed using the adjusted mixed-effects score test. FINDINGS: All 13 coding exons of PCSK1 were sequenced in 9320 participants (including 7260 adults and 2060 children and adolescents) recruited from the RaDiO study. We detected 65 rare heterozygous PCSK1 variants, including four null variants and 61 missense variants that were analysed in vitro and clustered into five groups (A-E), according to enzymatic activity. Compared with the wild-type, 15 missense variants led to complete PC1/3 loss of function (group A; reference) and rare exome variant ensemble learner (REVEL) led to 15 (25%) false positives and four (7%) false negatives. Carrying complete loss-of-function or null PCSK1 variants was significantly associated with obesity (six [86%] of seven carriers vs 1518 [35%] of 4395 non-carriers; OR 9·3 [95% CI 1·5-177·4]; p=0·014) and higher BMI (32·0 kg/m2 [SD 9·3] in carriers vs 27·3 kg/m2 [6·5] in non-carriers; mean effect π 6·94 [SE 1·95]; p=0·00029). Clusters of PCSK1 variants with partial or neutral effect on PC1/3 activity did not have an effect on obesity or overweight and on BMI. INTERPRETATION: Only carriers of heterozygous, null, or complete loss-of-function PCSK1 variants cause monogenic obesity and, therefore, might be eligible for setmelanotide. In silico tests were unable to accurately detect these variants, which suggests that in vitro assays are necessary to determine the variant pathogenicity for genetic diagnosis and precision medicine purposes. FUNDING: Agence Nationale de la Recherche, European Research Council, National Center for Precision Diabetic Medicine, European Regional Development Fund, Hauts-de-France Regional Council, and the European Metropolis of Lille.

Erratum: Rémy et al. Modelling the Impact of Chronic Cigarette Smoke Exposure in Obese Mice: Metabolic, Pulmonary, Intestinal, and Cardiac Issues. Nutrients 2020, 12, 827.

The authors have requested that the following changes be made to their paper [...].

[Something new in the genetics of monogenic obesity and its insights into pathophysiology]. / Du nouveau dans la génétique des formes monogéniques d'obésité et son impact pour mieux en comprendre la physiopathologie.

Obesity is a complex, multifactorial disorder. About 5% of obese patients actually present with a monogenic form of obesity where only one mutation is sufficient to cause the disease. So far, the genes that have been found to be mutated in these monogenic forms play a key role in the leptin/melanocortin pathway which is mainly active in the hypothalamus and which regulates food intake and energy expenditure. Our laboratory has recently reported a novel monogenic form of obesity due to MRAP2 deficiency where, contrary to previously described monogenic forms of obesity, the carriers presented with hyperglycemia and hypertension in addition to obesity, suggesting that MRAP2 might play a pleiotropic role in metabolic tissues, in addition to its role in brain control of food intake and energy expenditure.

TITLE: Du nouveau dans la génétique des formes monogéniques d'obésité et son impact pour mieux en comprendre la physiopathologie. ABSTRACT: L'obésité est une maladie complexe multifactorielle. Chez environ 5 % des individus obèses, il existe des formes monogéniques d'obésité pour laquelle une seule mutation est suffisante pour entraîner la maladie. Jusqu'à présent, les gènes mutés identifiés dans ces formes monogéniques sont impliqués dans la voie leptine/mélanocortine, principalement active au niveau de l'hypothalamus et régissant la satiété. Récemment, notre laboratoire a décrit une nouvelle forme monogénique d'obésité. Elle est due à une déficience du gène MRAP2 (melanocortin-2 receptor accessory protein 2) pour laquelle, contrairement aux formes précédemment décrites, on retrouve chez les porteurs une hyperglycémie et une hypertension, suggérant que MRAP2 joue un rôle biologique général dans les tissus métaboliques en plus de son rôle dans l'hypothalamus.

Influenza infection rewires energy metabolism and induces browning features in adipose cells and tissues.

Like all obligate intracellular pathogens, influenza A virus (IAV) reprograms host cell's glucose and lipid metabolism to promote its own replication. However, the impact of influenza infection on white adipose tissue (WAT), a key tissue in the control of systemic energy homeostasis, has not been yet characterized. Here, we show that influenza infection induces alterations in whole-body glucose metabolism that persist long after the virus has been cleared. We report depot-specific changes in the WAT of IAV-infected mice, notably characterized by the appearance of thermogenic brown-like adipocytes within the subcutaneous fat depot. Importantly, viral RNA- and viral antigen-harboring cells are detected in the WAT of infected mice. Using in vitro approaches, we find that IAV infection enhances the expression of brown-adipogenesis-related genes in preadipocytes. Overall, our findings shed light on the role that the white adipose tissue, which lies at the crossroads of nutrition, metabolism and immunity, may play in influenza infection.

Modelling the Impact of Chronic Cigarette Smoke Exposure in Obese Mice: Metabolic, Pulmonary, Intestinal, and Cardiac Issues.

Unhealthy lifestyle choices, such as bad eating behaviors and cigarette smoking, have major detrimental impacts on health. However, the inter-relations between obesity and smoking are still not fully understood. We thus developed an experimental model of high-fat diet-fed obese C57BL/6 male mice chronically exposed to cigarette smoke. Our study evaluated for the first time the resulting effects of the combined exposure to unhealthy diet and cigarette smoke on several metabolic, pulmonary, intestinal, and cardiac parameters. We showed that the chronic exposure to cigarette smoke modified the pattern of body fat distribution in favor of the visceral depots in obese mice, impaired the respiratory function, triggered pulmonary inflammation and emphysema, and was associated with gut microbiota dysbiosis, cardiac hypertrophy and myocardial fibrosis.

Loss-of-function mutations in MRAP2 are pathogenic in hyperphagic obesity with hyperglycemia and hypertension.

The G-protein-coupled receptor accessory protein MRAP2 is implicated in energy control in rodents, notably via the melanocortin-4 receptor1. Although some MRAP2 mutations have been described in people with obesity1-3, their functional consequences on adiposity remain elusive. Using large-scale sequencing of MRAP2 in 9,418 people, we identified 23 rare heterozygous variants associated with increased obesity risk in both adults and children. Functional assessment of each variant shows that loss-of-function MRAP2 variants are pathogenic for monogenic hyperphagic obesity, hyperglycemia and hypertension. This contrasts with other monogenic forms of obesity characterized by excessive hunger, including melanocortin-4 receptor deficiency, that present with low blood pressure and normal glucose tolerance4. The pleiotropic metabolic effect of loss-of-function mutations in MRAP2 might be due to the failure of different MRAP2-regulated G-protein-coupled receptors in various tissues including pancreatic islets.

Cdkn2a/p16Ink4a regulates fasting-induced hepatic gluconeogenesis through the PKA-CREB-PGC1α pathway.

Type 2 diabetes (T2D) is hallmarked by insulin resistance, impaired insulin secretion, and increased hepatic glucose production. The worldwide increasing prevalence of T2D calls for efforts to understand its pathogenesis in order to improve disease prevention and management. Recent genome-wide association studies have revealed strong associations between the CDKN2A/B locus and T2D risk. The CDKN2A/B locus contains genes encoding cell cycle inhibitors, including p16(Ink4a), which have not yet been implicated in the control of hepatic glucose homeostasis. Here, we show that p16(Ink4a) deficiency enhances fasting-induced hepatic glucose production in vivo by increasing the expression of key gluconeogenic genes. p16(Ink4a) downregulation leads to an activation of PKA-CREB-PGC1α signaling through increased phosphorylation of PKA regulatory subunits. Taken together, these results provide evidence that p16(Ink4a) controls fasting glucose homeostasis and could as such be involved in T2D development.

Association study of the platelet collagen receptor glycoprotein VI gene with rheumatoid arthritis.

OBJECTIVES: Beyond their role in haemostasis, platelets can actively contribute to immunity. The activation of the platelet collagen receptor glycoprotein VI (GPVI) promotes the release of small extracellular vesicles called microparticles. These microparticles are found in the joint bathing fluid of patients with rheumatoid arthritis (RA) and are thought to amplify inflammation. The gene coding for GPVI is localised on chromosome 19q13.4 and contains different single nucleotide polymorphisms (SNPs). Five non-synonymous SNPs define the major and minor haplotypes of GPVI. The minor haplotype is associated with higher risk of cardiovascular incidents. In this study, we examined whether this minor haplotype is also associated with RA. METHODS: Allelic discrimination of the SNPs reported to define these haplotypes encoding SKTQH and PEALN protein isoforms, ie rs1613662, rs1654416, rs2304167, rs1654413 and rs1671152, was performed in 399 RA patients and their two parents, all of Western European ethnicity. Statistical analysis relied on the transmission disequilibrium test by the use of the FBAT programme. Haplotypes were also estimated by the FBAT programme. RESULTS: We observed no statistically significant transmission disequilibrium for the SNPs tested. The major haplotype TAAC, which encodes the SKTQH isoform, was identified in 78% of our cohort individuals, and the CGGA haplotype which encodes the PEALN isoform was identified in 8% of our individuals. We observed no association of these haplotypes of the GPVI gene with RA. CONCLUSIONS: This demonstrates that the SNPs tested within the GPVI gene are not associated with RA susceptibility and/or severity, suggesting that platelet GPVI may contribute to arthritis independently of its gene polymorphism.

Hepatoprotective effects of the dual peroxisome proliferator-activated receptor alpha/delta agonist, GFT505, in rodent models of nonalcoholic fatty liver disease/nonalcoholic steatohepatitis.

UNLABELLED: Nonalcoholic fatty liver disease (NAFLD) covers a spectrum of liver damage ranging from simple steatosis to nonalcoholic steatohepatitis (NASH), fibrosis, and cirrhosis. To date, no pharmacological treatment is approved for NAFLD/NASH. Here, we report on preclinical and clinical data with GFT505, a novel dual peroxisome proliferator-activated receptor alpha/delta (PPAR-α/δ) agonist. In the rat, GFT505 concentrated in the liver with limited extrahepatic exposure and underwent extensive enterohepatic cycling. The efficacy of GFT505 was assessed in animal models of NAFLD/NASH and liver fibrosis (Western diet [WD]-fed human apolipoprotein E2 [hApoE2] transgenic mice, methionine- and choline-deficient diet-fed db/db mice, and CCl4 -induced fibrosis in rats). GFT505 demonstrated liver-protective effects on steatosis, inflammation, and fibrosis. In addition, GFT505 improved liver dysfunction markers, decreased hepatic lipid accumulation, and inhibited proinflammatory (interleukin-1 beta, tumor necrosis factor alpha, and F4/80) and profibrotic (transforming growth factor beta, tissue inhibitor of metalloproteinase 2, collagen type I, alpha 1, and collagen type I, alpha 2) gene expression. To determine the role of PPAR-α-independent mechanisms, the effect of GFT505 was assessed in hApoE2 knock-in/PPAR-α knockout mice. In these mice, GFT505 also prevented WD-induced liver steatosis and inflammation, indicating a contribution of PPAR-α-independent mechanisms. Finally, the effect of GFT505 on liver dysfunction markers was assessed in a combined analysis of four phase II clinical studies in metabolic syndrome patients. GFT505 treatment decreased plasma concentrations of alanine aminotransferase, gamma-glutamyl transpeptidase, and alkaline phosphatase. CONCLUSION: The dual PPAR-α/δ agonist, GFT505, is a promising liver-targeted drug for treatment of NAFLD/NASH. In animals, its protective effects are mediated by both PPAR-α-dependent and -independent mechanisms.

Activation of intestinal peroxisome proliferator-activated receptor-α increases high-density lipoprotein production.

AIMS: Peroxisome proliferator-activated receptor (PPAR)-α is a transcription factor controlling lipid metabolism in liver, heart, muscle, and macrophages. Peroxisome proliferator-activated receptor-α activation increases plasma HDL cholesterol and exerts hypotriglyceridaemic actions via the liver. However, the intestine expresses PPAR-α, produces HDL and chylomicrons, and is exposed to diet-derived PPAR-α ligands. Therefore, we examined the effects of PPAR-α activation on intestinal lipid and lipoprotein metabolism. METHODS AND RESULTS: The impact of PPAR-α activation was evaluated in term of HDL-related gene expression in mice, ex vivo in human jejunal biopsies and in Caco-2/TC7 cells. Apolipoprotein-AI/HDL secretion, cholesterol esterification, and trafficking were also studied in vitro. In parallel to improving plasma lipid profiles and increasing liver and intestinal expression of fatty acid oxidation genes, treatment with the dual PPAR-α/δ ligand GFT505 resulted in a more pronounced increase in plasma HDL compared with fenofibrate in mice. GFT505, but not fenofibrate, increased the expression of HDL production genes such as apolipoprotein-AI and ATP-binding cassette A1 transporter in murine intestines. A similar increase was observed upon PPAR-α activation of human biopsies and Caco-2/TC7 cells. Additionally, HDL secretion by Caco-2/TC7 cells increased. Moreover, PPAR-α activation decreased the cholesterol esterification capacity of Caco-2/TC7 cells, modified cholesterol trafficking, and reduced apolipoprotein-B secretion. CONCLUSION: Peroxisome proliferator-activated receptor-α activation reduces cholesterol esterification, suppresses chylomicron, and increases HDL secretion by enterocytes. These results identify the intestine as a target organ of PPAR-α ligands with entero-hepatic tropism to reduce atherogenic dyslipidaemia.

Cell-derived microparticles in atherosclerosis: biomarkers and targets for pharmacological modulation?

Cardiovascular diseases remain an important cause of morbi-mortality. Atherosclerosis, which predisposes to cardiovascular disorders such as myocardial infarction and stroke, develops silently over several decades. Identification of circulating biomarkers to evaluate cardiovascular event risk and pathology prognosis is of particular importance. Microparticles (MPs) are small vesicles released from cells upon apoptosis or activation. Microparticles are present in blood of healthy individuals. Studies showing a modification of their concentrations in patients with cardiovascular risk factors and after cardiovascular events identify MPs as potential biomarkers of disease. Moreover, the pathophysiological properties of MPs may contribute to atherosclerosis development. In addition, pharmacological compounds, used in the treatment of cardiovascular disease, can reduce plasma MP concentrations. Nevertheless, numerous issues remain to be solved before MP measurement can be applied as routine biological tests to improve cardiovascular risk prediction. In particular, prospective studies to identify the predictive values of MPs in pathologies such as cardiovascular diseases are needed to demonstrate whether MPs are useful biomarkers for the early detection of the disease and its progression.

PPARα activation differently affects microparticle content in atherosclerotic lesions and liver of a mouse model of atherosclerosis and NASH.

BACKGROUND: Atherosclerosis and non-alcoholic fatty liver disease (NAFLD) are complex pathologies characterized by lipid accumulation, chronic inflammation and extensive tissue remodelling. Microparticles (MPs), small membrane vesicles produced by activated and apoptotic cells, might not only be biomarkers, but also functional actors in these pathologies. The apoE2-KI mouse is a model of atherosclerosis and NAFLD. Activation of the nuclear receptor PPARα decreases atherosclerosis and components of non-alcoholic steatohepatitis (NASH) in the apoE2-KI mouse. OBJECTIVES: (1) To determine whether MPs are present in atherosclerotic lesions, liver and plasma during atherosclerosis and NASH progression in apoE2-KI mice, and (2) to study whether PPARα activation modulates MP concentrations. METHODS: ApoE2-KI mice were fed a Western diet to induce atherosclerosis and NASH. MPs were isolated from atherosclerotic lesions, liver and blood and quantified by flow cytometry. RESULTS: An increase of MPs was observed in the atherosclerotic lesions and in the liver of apoE2-KI mice upon Western diet feeding. PPARα activation with fenofibrate decreased MP levels in the atherosclerotic lesions in a PPARα-dependent manner, but did not influence MP concentrations in the liver. CONCLUSION: Here we report that MPs are present in atherosclerotic lesions and in the liver of apoE2-KI mice. Their concentration increased during atherosclerosis and NASH development. PPARα activation differentially modulates MP levels in a tissue-specific manner.

Peroxisome proliferator-activated receptor-alpha gene level differently affects lipid metabolism and inflammation in apolipoprotein E2 knock-in mice.

OBJECTIVE: Peroxisome proliferator-activated receptor-α (PPARα) is a ligand-activated transcription factor that controls lipid metabolism and inflammation. PPARα is activated by fibrates, hypolipidemic drugs used in the treatment of dyslipidemia. Previous studies assessing the influence of PPARα agonists on atherosclerosis in mice yielded conflicting results, and the implication of PPARα therein has not been assessed. The human apolipoprotein E2 knock-in (apoE2-KI) mouse is a model of mixed dyslipidemia, atherosclerosis, and nonalcoholic steatohepatitis (NASH). The aim of this study was to analyze, using homo- and heterozygous PPARα-deficient mice, the consequences of quantitative variations of PPARα gene levels and their response to the synthetic PPARα agonist fenofibrate on NASH and atherosclerosis in apoE2-KI mice. METHODS AND RESULTS: Wild-type (+/+), heterozygous (+/-), and homozygous (-/-) PPARα-deficient mice in the apoE2-KI background were generated and subjected to a Western diet supplemented with fenofibrate or not supplemented. Western diet-fed PPARα-/- apoE2-KI mice displayed an aggravation of liver steatosis and inflammation compared with PPARα+/+ and PPARα+/- apoE2-KI mice, indicating a role of PPARα in liver protection. Moreover, PPARα expression was required for the fenofibrate-induced protection against NASH. Interestingly, fenofibrate treatment induced a similar response on hepatic lipid metabolism in PPARα+/+ and PPARα+/- apoE2-KI mice, whereas, for a maximal antiinflammatory response, both alleles of the PPARα gene were required. Surprisingly, atherosclerosis development was not significantly different among PPARα+/+, PPARα+/-, and PPARα-/- apoE2-KI mice. However, PPARα gene level determined both the antiatherosclerotic and vascular antiinflammatory responses to fenofibrate in a dose-dependent manner. CONCLUSIONS: These results demonstrate a necessary but quantitatively different role of PPARα in the modulation of liver metabolism, inflammation, and atherogenesis.

Human atherosclerotic plaque alternative macrophages display low cholesterol handling but high phagocytosis because of distinct activities of the PPARγ and LXRα pathways.

RATIONALE: A crucial step in atherogenesis is the infiltration of the subendothelial space of large arteries by monocytes where they differentiate into macrophages and transform into lipid-loaded foam cells. Macrophages are heterogeneous cells that adapt their response to environmental cytokines. Th1 cytokines promote monocyte differentiation into M1 macrophages, whereas Th2 cytokines trigger an "alternative" M2 phenotype. OBJECTIVE: We previously reported the presence of CD68(+) mannose receptor (MR)(+) M2 macrophages in human atherosclerotic plaques. However, the function of these plaque CD68(+)MR(+) macrophages is still unknown. METHODS AND RESULTS: Histological analysis revealed that CD68(+)MR(+) macrophages locate far from the lipid core of the plaque and contain smaller lipid droplets compared to CD68(+)MR(-) macrophages. Interleukin (IL)-4-polarized CD68(+)MR(+) macrophages display a reduced capacity to handle and efflux cellular cholesterol because of low expression levels of the nuclear receptor liver x receptor (LXR)α and its target genes, ABCA1 and apolipoprotein E, attributable to the high 15-lipoxygenase activity in CD68(+)MR(+) macrophages. By contrast, CD68(+)MR(+) macrophages highly express opsonins and receptors involved in phagocytosis, resulting in high phagocytic activity. In M2 macrophages, peroxisome proliferator-activated receptor (PPAR)γ activation enhances the phagocytic but not the cholesterol trafficking pathways. CONCLUSIONS: These data identify a distinct macrophage subpopulation with a low susceptibility to become foam cells but high phagocytic activity resulting from different regulatory activities of the PPARγ-LXRα pathways.