Roles of PPAR delta in lipid absorption and metabolism: a new target for the treatment of type 2 diabetes.

Peroxisome proliferator-activated receptors (PPARs) are lipid-activated transcription factors exerting several functions in development and metabolism. PPARalpha, activated by polyunsaturated fatty acids and fibrates, is implicated in regulation of lipid metabolism, lipoprotein synthesis and metabolism and inflammatory response in liver and other tissues. PPARgamma plays important roles in regulation of proliferation and differentiation of several cell types, including adipose cells. Its activation by thiazolidinediones results in insulin sensibilization and antidiabetic action. Until recently, the physiological functions of PPARdelta remain elusive. The utilization of specific agonists and of appropriate cellular and animal models revealed that PPARdelta has an important role in metabolic adaptation of several tissues to environmental changes. Treatment of obese animals by specific PPARdelta agonists results in normalization of metabolic parameters and reduction of adiposity. The nuclear receptor appeared to be implicated in the regulation of fatty acid burning capacities of skeletal muscle and adipose tissue by controlling the expression of genes involved in fatty acid uptake, beta-oxidation and energy uncoupling. PPARdelta is also implicated in the adaptive metabolic response of skeletal muscle to endurance exercise by controlling the number of oxidative myofibers. Given the results obtained with animal models, PPARdelta agonists may have therapeutic usefulness in metabolic syndrome by increasing fatty acid consumption in skeletal muscle and adipose tissue.

The very high cardiovascular risk in heterozygous familial hypercholesterolemia: Analysis of 734 French patients.

BACKGROUND: Heterozygous familial hypercholesterolemia (heFH) is a genetic disease causing high levels of low-density lipoprotein cholesterol (LDL-C). Although this population is at high cardiovascular (CV) risk, the risk is variable within patients depending on additional risk factors. CV disease risk groups have been defined by the Nouvelle Société Francophone d'Athérosclérose (NSFA) and by the National Lipid Association recommendations. OBJECTIVES: The study aimed to describe a sample of French heFH patients, comparing patients at very high risk (VHR) and patients at high risk in terms of demographic and clinical characteristics as well as biological measurements and disease management. METHODS: Cross-sectional retrospective analysis on 734 patients hospitalized after 2005 in 5 academic centers. RESULTS: When considering NSFA classification, 550 (74.9%) patients belonged to the VHR group. Most patients in the VHR group presented more than 1 risk factor, the most prevalent ones being Lp(a) > 50 mg/dL and smoking. Patients in the VHR group were older (50.6 vs 45.0 years old, P = .0002), and presented a higher body mass index (25.5 kg/m(2) vs 23.3 kg/m(2), P < .0001). The proportion of patients with carotid arterial plaque was higher in the VHR group (59.8% vs 48.6%, P = .06). Total cholesterol (2.41 g/L on average) and LDL-C (1.65 g/L on average) were not found to be significantly different. Maximum level of lipid-lowering treatments were used in 34% of cases in the VHR group, significantly higher than 16% in the high-risk group (P = .001). Very similar results were found when using the National Lipid Association recommendations. CONCLUSION: This study provides a detailed description of French heFH patients according to their CV risk. Patients with very high CV risk had usually more advanced carotid plaques and were treated with heavier lipid-lowering drugs although their LDL-C level remained similar. This highlights the significant burden of this population.

Novel mutations of the PCSK9 gene cause variable phenotype of autosomal dominant hypercholesterolemia.

Autosomal dominant hypercholesterolemia (ADH) is a frequent (1/500) monogenic inherited disorder characterized by isolated elevation of LDL leading to premature cardiovascular disease. ADH is known to result from mutations at two main loci: LDLR (encoding the low density lipoprotein receptor), and APOB (encoding apolipoprotein B100), its natural ligand. We previously demonstrated that ADH is also caused by mutations of the PCSK9 (proprotein convertase subtilisin/kexin type 9) gene that encodes Narc-1 (neural apoptosis-regulated convertase 1). However, the role of this novel disease locus as a cause of hypercholesterolemia remains unclear. In the present study, we analysed the PCSK9 coding region and intronic junctions in 130 adult or pediatric patients with ADH, previously found as being non LDLR/non APOB mutation carriers. Four novel heterozygous missense variations were found: c.654A>T (p.R218S), c.1070G>A (p.R357H), c.1405C>T (p.R469W), and c.1327G>A (p.A443T). All mutations were absent in 340 normolipidemic controls. Except for the A443T, all mutations are nonconservative and modify a highly conserved residue. Segregation with hypercholesterolemia is incomplete in one pedigree. Type and severity of hyperlipidemia and of cardiovascular disease could vary among subjects from the same family. Finally, the proband carrying the R357H mutation exhibited very high plasma cholesterol during pregnancy, whereas the proband carrying the p.R469W mutation exhibited a severe phenotype of hypercholesterolemia in combination with a LDLR mutation resulting from a frameshift at residue F382 (1209delC). These observations suggest that variations in PCSK9 are a rare cause of non LDLR/non APOB ADH (approximately 2.3%) and that additional environmental or genetic factors may contribute to the phenotype caused by PCSK9 missense mutations in humans.

Peroxisome proliferator-activated receptor delta controls muscle development and oxidative capability.

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors exerting several functions in development and metabolism. The physiological functions of PPARdelta remain elusive. By using a CRE-Lox recombination approach, we generated an animal model for muscle-specific PPARdelta overexpression to investigate the role of PPARdelta in this tissue. Muscle-specific PPARdelta overexpression results in a profound change in fiber composition due to hyperplasia and/or shift to more oxidative fiber and, as a consequence, leads to the increase of both enzymatic activities and genes implicated in oxidative metabolism. These changes in muscle are accompanied by a reduction of body fat mass, mainly due to a large reduction of adipose cell size. Furthermore, we demonstrate that endurance exercise promotes an accumulation of PPARdelta protein in muscle of wild-type animals. Collectively, these results suggest that PPARdelta plays an important role in muscle development and adaptive response to environmental changes, such as training exercise. They strongly support the idea that activation of PPARdelta could be beneficial in prevention of metabolic disorders, such as obesity or type 2 diabetes.

Roles of peroxisome proliferator-activated receptor delta (PPARdelta) in the control of fatty acid catabolism. A new target for the treatment of metabolic syndrome.

Peroxisome proliferator-activated receptors (PPARs) are lipid-activated transcription factors playing important regulatory functions in development and metabolism. PPARalpha and PPARgamma are the most extensively examined and characterized, mainly because they are activated by marketed hypolipidemic and insulin sensitizer compounds, such as fibrates and thiazolidinediones. It has been established that the third member of the family, PPARdelta is implicated in developmental regulations, but until recently, its role in metabolism remained unclear. The availability of specific PPARdelta agonists and of appropriate cellular and animal models revealed that PPARdelta plays a crucial role in fatty acid metabolism in several tissues. Treatment of obese animals with PPARdelta agonists results in normalization of metabolic parameters and reduction of adiposity. Activation of the nuclear receptor promotes fatty acid burning in skeletal muscle and adipose tissue by upregulation of fatty acid uptake, beta-oxidation and energy uncoupling. PPARdelta is also involved in the adaptive metabolic responses of skeletal muscle to environmental changes, such as long-term fasting or physical exercise, by controlling the number of oxidative myofibers. These observations strongly suggest that PPARdelta agonists may have therapeutic usefulness in metabolic syndrome by increasing fatty acid consumption and decreasing obesity.

Hormonal contraception in women at risk of vascular and metabolic disorders: guidelines of the French Society of Endocrinology.

Hormonal contraceptive methods are widely used in France, including not only oral estrogen-progestin combinations but also non-oral estrogen-progestin delivery methods (patches, vaginal rings), as well as oral forms, implants and intra-uterine devices that deliver only a progestin. Hormonal contraception has only a modest impact on lipid and carbohydrate metabolism, but estrogen-progestin contraceptives have been linked to a variety of vascular risks. Overall, the risk of venous thrombosis is multiplied by a factor of about 4, depending on age, the compounds used, and other risk factors (including biological thrombophilia and a personal history of thrombosis), whereas the risk of arterial events is only increased in women with risk factors. Available data suggest there is no excess risk with progestin-based contraceptives, but far fewer studies have been conducted. At the initiative of the French Society of Endocrinology, an expert group met in 2010 in order to reach a consensus on the use of hormonal contraceptive methods in women with vascular or metabolic risk factors, based on available data and international guidelines published by WHO in 2009 and subsequently adapted to the United States context. The following text, intentionally limited to hormonal contraception, is intended to serve as a guide when prescribing in specific clinical situations, such as a family or personal history of arterial or venous thromboembolism, or the existence of cardiovascular risk factors (hypertension, smoking, diabetes, dyslipidemia, obesity).

Roles of peroxisome proliferator-activated receptor delta in skeletal muscle function and adaptation.

PURPOSE OF THE REVIEW: Peroxisome proliferator-activated receptors mediate the transcriptional effects of fatty acids and fatty acid metabolites and regulate many physiological functions including development and metabolism. The roles of peroxisome proliferator-activated receptor alpha and gamma isotypes have been well established, while the functions of the third member of the family, peroxisome proliferator-activated receptor delta, remained unclear until very recently. This review focuses on the physiological functions of the nuclear receptor and especially on its roles in the control of fatty acid metabolism. RECENT FINDINGS: We review very recent data demonstrating that peroxisome proliferator-activated receptor delta plays a central role in the regulation of fatty acid oxidation in several tissues, such as skeletal muscle and adipose tissue, and also that the nuclear receptor is involved in cholesterol metabolism. SUMMARY: Use of potent and specific peroxisome proliferator-activated receptor delta agonists and appropriate transgenic animal models revealed the importance of this nuclear receptor in regulation of fatty acid catabolism in skeletal muscle and other tissues. It also indicated the potential of peroxisome proliferator-activated receptor delta as a therapeutic target in pathologies such as metabolic syndrome. However, the effects of peroxisome proliferator-activated receptor delta activation in atherosclerosis and the control of cell proliferation remain to be established.

Intronic mutations outside of Alu-repeat-rich domains of the LDL receptor gene are a cause of familial hypercholesterolemia.

Familial hypercholesterolemia (FH), a frequent monogenic condition complicated by premature cardiovascular disease, is characterized by high allelic heterogeneity at the low-density lipoprotein receptor ( LDLR) locus. Despite more than a decade of genetic testing, knowledge about intronic disease-causing mutations has remained limited because of lack of available genomic sequences. Based on the finding from bioinformatic analysis that Alu repeats represent 85% of LDLR intronic sequences outside exon-intron junctions, we designed a strategy to improve the exploration of genomic regions in the vicinity of exons in 110 FH subjects from an admixed population. In the first group of 42 patients of negative mutation carriers, as previously established by former screening strategies (denaturing gradient gel electrophoresis, DNA sequencing with former primers overlapping splice-sites, Southern Blotting), about half ( n=22) were found to be carriers of at least one heterozygous mutation. Among a second group of 68 newly recruited patients, 27% of mutation carriers ( n=37) had a splicing regulatory mutation. Overall, out of the 54 mutations identified, 13 were intronic, and 18 were novel, out of which nearly half were intronic. Two novel intronic mutations (IVS8-10G-->A within the polypyrimidine tract and IVS7+10G-->A downstream of donor site) might create potential aberrant splice sites according to neural-network computed estimation, contrary to 31 common single nucleotide variations also identified at exon-intron junctions. This new strategy of detecting the most likely disease-causing LDLR mutations outside of Alu-rich genomic regions reveals that intronic mutations may have a greater impact than previously reported on the molecular basis of FH.