Physiopathologies cardiométaboliques associées à l'obésité : mécanismes sous-jacents et thérapie nutritionnelle

Le tractus digestif et le foie interagissent continuellement, non seulement à travers les connexions anatomiques, mais également par des liens physiologiques/fonctionnels. Le déséquilibre de l’axe intestin-foie apparait de plus en plus comme un facteur primordial dans les désordres cardiométaboliques, à savoir l’obésité, le syndrome métabolique, le diabète de type 2 et la stéatose hépatique non alcoolique (NAFLD), pour lesquels la prévalence demeure alarmante, les mécanismes moléculaires encore méconnus, et les traitements peu efficaces. L’hypothèse centrale du présent projet de recherche est que la combinaison d’anomalies génétiques et nutritionnelles affecte la sensibilité de l’insuline intestinale, ce qui conduit à une surproduction des chylomicrons, à une dyslipidémie, une insulinorésistance systémique et des répercussions sur le foie. Dans cet agencement, le foie développe une NAFLD progressive, impliquant plusieurs sentiers métaboliques intrinsèques et des mécanismes comprenant le stress oxydatif, l’inflammation et l’insulinorésistance. En revanche, des nutriments, comme les acides gras polyinsaturés (AGPI) n-3, peuvent présenter des effets bénéfiques en ciblant plusieurs circuits pathogéniques. L’objectif central de cette thèse consiste à : (i) Démontrer que des gènes codant pour les protéines intestinales clés associées au transport des lipides, comme c’est le cas du Sar1b GTPase, peuvent interagir avec l’environnement nutritionnel pour produire l’obésité et des dérangements cardiométaboliques, incluant la NAFLD ; (ii) Explorer les mécanismes hépatiques sous-jacents à la NAFLD; et (iii) Identifier les effets et les cibles thérapeutiques des AGPI n-3 sur la NAFLD. Ces objectifs seront soutenus par une prospection de la littérature scientifique disponible dans les champs du syndrome métabolique et de la NAFLD afin d’en disséquer les forces et les faiblesses au bénéfice de la communauté scientifique. À ces fins, nous avons utilisé des modèles animaux et cellulaires manipulés génétiquement, des animaux exposés de façon chronique à des diètes riches en lipides, des spécimens de tissus hépatiques obtenus durant la chirurgie bariatrique d’obèses morbides, et une cohorte d’adolescents obèses souffrant de NAFLD et qui seront traités avec les AGPI n-3. L’ensemble de nos expériences ont soutenu nos hypothèses et ont mis en évidence les concepts et mécanismes suivants : (i) L’abondance d’un gène crucial (notamment Sar1b GTPase) au niveau de l’intestin, en synergie avec une alimentation obésogène, perturbe l’homéostasie locale et mène à des dérangements cardiométaboliques, défiant même l’axe intestin-foie ; (ii) Les causes développementales de la NAFLD comprennent les dérangements du métabolisme des acides gras, du statut redox et inflammatoire, de la sensibilité à l’insuline, des sentiers métaboliques (lipogenèse, β-oxydation, gluconéogenèse) et de l’expression des facteurs de transcription; et (iii) Les AGPI n-3 représentent un robuste arsenal thérapeutique des dérangements cardiométaboliques, notamment la NAFLD, en agissant sur plusieurs cibles pathogéniques. Globalement, nos résultats montrent le rôle indéniable de l’intestin comme organe insulino-sensible interagissant de près avec les aliments et capable de déclencher des troubles métaboliques. Plusieurs mécanismes gouvernant les désordres métaboliques ont été dévoilés par nos travaux. En outre, nos études cliniques ont pointé la force thérapeutique des AGPI n-3 qui interviennent dans de nombreux processus de régulation métaboliques et notamment dans le stress oxydatif et l’inflammation.The digestive tract and liver interact continuously, not only through anatomical connections, but also through physiological / functional links. The imbalance of the intestine-liver axis is increasingly emerging as a key factor in cardiometabolic disorders (CMD), namely obesity, metabolic syndrome, type 2 diabetes, and non alcoholic fatty liver disease (NAFLD), for which prevalence remains alarmingly high, molecular mechanisms are poorly understood, and treatments are largely inefficient. The central hypothesis of this research project is that the combination of genetic and nutritional abnormalities affect intestinal insulin sensitivity, leading to overproduction of chylomicrons, dyslipidemia, systemic insulin resistance and dysregulated intestine-liver axis. In this situation, the liver develops progressive NAFLD, implicating several intrinsic metabolic pathways and mechanisms, including oxidative stress, inflammation and insulin resistance. In contrast, functional foods, such as omega-3 polyunsaturated fatty acids (n-3 PUFA), may have beneficial effects by targeting several pathogenic pathways. The central objective of this thesis is to: (i) Demonstrate that genes coding for key intestinal proteins associated with lipid transport, as is the case with Sar1b GTPase, can interact with the nutritional environment to produce obesity and CMD, including hepatic steatosis; (ii) explore the mechanisms underlying NAFLD; and (iii) identify the effects and therapeutic targets of n-3 PUFA. These objectives will be supported by a critical review on metabolic syndrome and NAFLD in order to dissect their strengths and weaknesses for the benefit of the scientific community. For these purposes, we used genetically engineered animal and cell models, chronic exposure of animals to high-fat diets, liver tissue specimens obtained during bariatric surgery of morbidly obese patients, and treatment of obese NAFLD adolescents with n-3 PUFA. All of our experiments supported our hypotheses and highlighted the following concepts and mechanisms: (i) The abundance of a crucial gene (notably Sar1b GTPase) in the intestine, in synergy with an obesogenic diet, disrupts local homeostasis and leads to CMD, challenging even the intestine-liver axis; (ii) Developmental causes of NAFLD include disturbances of fatty acid metabolism, redox and inflammatory status, insulin sensitivity, metabolic pathways (lipogenesis, β-oxidation, gluconeogenesis), and expression of transcription factors; and (iii) n-3 PUFA represent a robust therapeutic arsenal of CMD, including NAFLD, by acting on several pathogenic targets. Overall, our results show the undeniable role of the intestine, as an insulin-sensitive organ, interacting closely with obesogenic food, and capable of triggering CMD, including perturbations of the intestine-liver axis. Several mechanisms governing metabolic disorders have been unveiled by our work. In addition, our clinical studies have pointed to the therapeutic potential of n-3 PUFA involved in many regulatory processes, including oxidative stress and inflammation

Profil lipidique et statut des acides gras chez les patients avec trouble de déficit d'attention/hyperactivité (TDAH)

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Insight into Polyphenol and Gut Microbiota Crosstalk: Are Their Metabolites the Key to Understand Protective Effects against Metabolic Disorders?

Lifestyle factors, especially diet and nutrition, are currently regarded as essential avenues to decrease modern-day cardiometabolic disorders (CMD), including obesity, metabolic syndrome, type 2 diabetes, and atherosclerosis. Many groups around the world attribute these trends, at least partially, to bioactive plant polyphenols given their anti-oxidant and anti-inflammatory actions. In fact, polyphenols can prevent or reverse the progression of disease processes through many distinct mechanisms. In particular, the crosstalk between polyphenols and gut microbiota, recently unveiled thanks to DNA-based tools and next generation sequencing, unravelled the central regulatory role of dietary polyphenols and their intestinal micro-ecology metabolites on the host energy metabolism and related illnesses. The objectives of this review are to: (1) provide an understanding of classification, structure, and bioavailability of dietary polyphenols; (2) underline their metabolism by gut microbiota; (3) highlight their prebiotic effects on microflora; (4) discuss the multifaceted roles of their metabolites in CMD while shedding light on the mechanisms of action; and (5) underscore their ability to initiate host epigenetic regulation. In sum, the review clearly documents whether dietary polyphenols and micro-ecology favorably interact to promote multiple physiological functions on human organism

Efficacy of Polyphenols in the Management of Dyslipidemia: A Focus on Clinical Studies

Polyphenols (PLPs), phytochemicals found in a wide range of plant-based foods, have gained extensive attention in view of their antioxidant, anti-inflammatory, immunomodulatory and several additional beneficial activities. The health-promoting effects noted in animal models of various non-communicable diseases explain the growing interest in these molecules. In particular, in vitro and animal studies reported an attenuation of lipid disorders in response to PLPs. However, despite promising preclinical investigations, the effectiveness of PLPs in human dyslipidemia (DLP) is less clear and necessitates revision of available literature. Therefore, the present review analyzes the role of PLPs in managing clinical DLP, notably by dissecting their potential in ameliorating lipid/lipoprotein metabolism and alleviating hyperlipidemia, both postprandially and in long-term interventions. To this end, PubMed was used for article search. The search terms included polyphenols, lipids, triglycerides, cholesterol, LDL-cholesterol and /or HDL-cholesterol. The critical examination of the trials published to date illustrates certain benefits on blood lipids along with co-morbidities in participant’s health status. However, inconsistent results document significant research gaps, potentially owing to study heterogeneity and lack of rigor in establishing PLP bioavailability during supplementation. This underlines the need for further efforts in order to elucidate and support a potential role of PLPs in fighting DLP

Tissue Distribution and Regulation of the Small Sar1b GTPase in Mice

Background/Aims: Sar1b GTPase (Sar1b) represents an obligatory component of COPII vesicles that bud from the endoplasmic reticulum to transport proteins to the Golgi apparatus. Its genetic mutations lead to a severe disorder known as chylomicron retention disease. Despite growing knowledge on Sar1b, little is known about it tissue distribution and regulation, which constitute the aims of the present study. We aimed to determine the Sar1b tissue distribution and modulation by a high-fat diet and gene forcing using transgenic mice in comparison to wild-type mice. Methods: The expression pattern of Sar1b was studied in different organs of wild-type and Sar1b transgenic mice by qRT-PCR and Western blot. The effect of transgenesis and insulin resistance induced by a 12-week high-fat diet on Sar1b gene expression was also assessed by qRT-PCR. Results: Evaluation of Sar1b mRNA revealed the skeletal muscle as the tissue with the highest Sar1b expression, followed by the heart and liver, the organs composing the digestive tract, the brain and finally the lung and the adipose tissue. Sar1b protein expression levels follow a similar pattern among the organs, except for its lower expression in the heart. While the high-fat diet did not exert any significant alterations, Sar1b transgenic mice displayed higher gene expression in the liver, ileum, jejunum, proximal and distal colon compared to wild-type mice. Conclusion: Our study supports the importance of Sar1b in organs involved in lipid transport and/or calcium trafficking such as the liver, intestine, skeletal muscle and heart

Intestinal cholesterol transport proteins: an update and beyond.

International audiencePURPOSE OF REVIEW: Various studies have delineated the causal role of dietary cholesterol in atherogenesis. Strategies have thus been developed to minimize cholesterol absorption, and cholesterol transport proteins found at the apical membrane of enterocytes have been extensively investigated. This review focuses on recent progress related to various brush-border proteins that are potentially involved in alimentary cholesterol transport. RECENT FINDINGS: Molecular mechanisms responsible for dietary cholesterol and plant sterol uptake have not been completely defined. Growing evidence, however, supports the concept that several proteins are involved in mediating intestinal cholesterol transport, including SR-BI, NPC1L1, CD36, aminopeptidase N, P-glycoprotein, and the caveolin-1/annexin-2 heterocomplex. Other ABC family members (ABCA1 and ABCG5/ABCG8) act as efflux pumps favoring cholesterol export out of absorptive cells into the lumen or basolateral compartment. Several of these cholesterol carriers influence intracellular cholesterol homeostasis and are controlled by transcription factors, including RXR, LXR, SREBP-2 and PPARalpha. The lack of responsiveness of NPC1L1-deficient mice to ezetimibe suggests that NPC1L1 is likely to be the principal target of this cholesterol-lowering drug. SUMMARY: The understanding of the role, genetic regulation and coordinated function of proteins mediating intestinal cholesterol transport may lead to novel ways of treating cardiovascular disease

CFTR silencing in pancreatic β-cells reveals a functional impact on glucose-stimulated insulin secretion and oxidative stress response

Cystic fibrosis (CF)-related diabetes (CFRD) has become a critical complication that seriously affects the clinical outcomes of CF patients. Although CFRD has emerged as the most common nonpulmonary complication of CF, little is known about its etiopathogenesis. Additionally, whether oxidative stress (OxS), a common feature of CF and diabetes, influences CFRD pathophysiology requires clarification. Aim: The objective of this study is to shed light on the role of CFTR in combination with OxS in insulin secretion from pancreatic β-cells. Methods: CFTR silencing was accomplished in MIN6 cells by stable expression of small hairpin RNAs and glucose-induced insulin secretion was evaluated in the presence/absence of the pro-oxidant system iron/ascorbate (Fe/Asc) along with or without the antioxidant Trolox. Results: insulin output from CFTR-silenced MIN6 cells was significantly reduced at basal and at different glucose concentrations compared with control Mock cells. Furthermore, CFTR silencing rendered MIN6 cells more sensitive to OxS as evidenced by both increased lipid peroxides and weakened antioxidant defense, especially following incubation with Fe/Asc. The decreased insulin secretion in CFTR-silenced MIN6 cells was associated with high levels of NF-κB (the major participant in inflammatory responses), raised apoptosis and diminished ATP production in response to the Fe/Asc challenge. These defects were alleviated by the addition of Trolox, thereby pointing out the role of OxS in aggravating the effects of CFTR deficiency. Conclusions: Our findings indicate that CFTR deficiency with OxS may contribute to endocrine cell dysfunction and insulin secretion, which at least in part may explain the development of CFRD