[Show abstract][Hide abstract] ABSTRACT: Objective:
To identify a causal mechanism responsible for the enhancement of insulin resistance and hyperglycaemia following periodontitis in mice fed a fat-enriched diet.
We set-up a unique animal model of periodontitis in C57Bl/6 female mice by infecting the periodontal tissue with specific and alive pathogens like Porphyromonas gingivalis (Pg), Fusobacterium nucleatum and Prevotella intermedia. The mice were then fed with a diabetogenic/non-obesogenic fat-enriched diet for up to 3 months. Alveolar bone loss, periodontal microbiota dysbiosis and features of glucose metabolism were quantified. Eventually, adoptive transfer of cervical (regional) and systemic immune cells was performed to demonstrate the causal role of the cervical immune system.
Periodontitis induced a periodontal microbiota dysbiosis without mainly affecting gut microbiota. The disease concomitantly impacted on the regional and systemic immune response impairing glucose metabolism. The transfer of cervical lymph-node cells from infected mice to naive recipients guarded against periodontitis-aggravated metabolic disease. A treatment with inactivated Pg prior to the periodontal infection induced specific antibodies against Pg and protected the mouse from periodontitis-induced dysmetabolism. Finally, a 1-month subcutaneous chronic infusion of low rates of lipopolysaccharides from Pg mimicked the impact of periodontitis on immune and metabolic parameters.
We identified that insulin resistance in the high-fat fed mouse is enhanced by pathogen-induced periodontitis. This is caused by an adaptive immune response specifically directed against pathogens and associated with a periodontal dysbiosis.
[Show abstract][Hide abstract] ABSTRACT: Background:
Gut microbiota is now known to control glucose metabolism. Previous studies have shown that probiotics and prebiotics may improve glucose metabolism, but their effects have not been studied in combination with drug therapy. The aim of this study was to investigate whether probiotics and prebiotics combined with drug therapy affect diabetic outcomes.
Two different study designs were used to test gut microbiota modulating treatments with metformin (MET) or sitagliptin (SITA) in male C57Bl/6J mice. In Design 1, diabetes was induced with four-week feeding with a ketogenic, 72 kcal% fat diet with virtually no carbohydrates. Mice were then randomly divided into four groups (n = 10 in each group): (1) vehicle, (2) Bifidobacterium animalis ssp. lactis 420 (B420) (10(9) CFU/day), (3) MET (2 mg/mL in drinking water), or (4) MET + B420 (same doses as in the MET and B420 groups). After another 4 weeks, glucose metabolism was assessed with a glucose tolerance test. Fasting glucose, fasting insulin and HOMA-IR were also assessed. In Design 2, mice were fed the same 72 kcal% fat diet to induce diabetes, but they were simultaneously treated within their respective groups (n = 8 in each group): (1) non-diabetic healthy control, (2) vehicle, (3) SITA [3 mg/(kg*day)] (4) SITA with prebiotic polydextrose (PDX) (0.25 g/day), (5) SITA with B420 (10(9) CFU/day), and (6) SITA + PDX + B420. Glucose metabolism was assessed at 4 weeks, and weight development was monitored for 6 weeks.
In Design 1, with low-dose metformin, mice treated with B420 had a significantly lower glycemic response (area under the curve) (factorial experiment, P = 0.002) and plasma glucose concentration (P = 0.02) compared to mice not treated with B420. In Design 2, SITA + PDX reduced glycaemia in the oral glucose tolerance test significantly more than SITA only (area under the curve reduced 28 %, P < 0.0001). In addition, B420, PDX or B420+PDX, together with SITA, further decreased fasting glucose concentrations compared to SITA only (-19.5, -40 and -49 %, respectively, P < 0.01 for each comparison). The effect of PDX may be due to its ability to increase portal vein GLP-1 concentrations together with SITA (P = 0.0001 compared to vehicle) whereas SITA alone had no statistically significant effect compared to vehicle (P = 0.14).
This study proposes that combining probiotics and/or prebiotics with antidiabetic drugs improves glycemic control and insulin sensitivity in mice. Mechanisms could be related to incretin secretion.
[Show abstract][Hide abstract] ABSTRACT: Alterations of the gut microbiota and mucosal barrier are linked with metabolic diseases. Our aim was to investigate the potential benefit of the potential probiotic Bifidobacterium animalis ssp. lactis 420 in reducing high-fat diet-induced body weight gain and diabetes in mice. In the obesity model, C57Bl/6J mice were fed a high-fat diet (60 energy %) for 12 weeks, and gavaged daily with B. lactis 420 (109 cfu) or vehicle. In the diabetes model, mice were fed a high-fat, ketogenic diet (72 energy % fat) for 4 weeks, with a 6-week subsequent treatment with B. lactis 420 (108-1010 cfu/day) or vehicle, after which they were analysed for body composition. We also analysed glucose tolerance, plasma lipopolysaccharide and target tissue inflammation using only one of the B. lactis 420 groups (109 cfu/day). Intestinal bacterial translocation and adhesion were analysed in a separate experiment using an Escherichia coli gavage. Body fat mass was increased in both obese (10.7±0.8 g (mean ± standard error of mean) vs. 1.86±0.21 g, P<0.001) and diabetic mice (3.01±0.4 g vs. 1.14±0.15 g, P<0.001) compared to healthy controls. Treatment with B. lactis 420 significantly decreased fat mass in obese (7.83 ± 0.67 g, P=0.007 compared to obese with vehicle) and diabetic mice (1.89 ± 0.16 g, P=0.02 for highest dose). This was reflected as reduced weight gain and improved glucose tolerance. Furthermore, B. lactis 420 decreased plasma lipopolysaccharide levels (P<0.001), liver inflammation (P=0.04), and E. coli adhesion in the distal gut (P<0.05). In conclusion, B. lactis 420 reduces fat mass and glucose intolerance in both obese and diabetic mice. Reduced intestinal mucosal adherence and plasma lipopolysaccharide suggest a mechanism related to reduced translocation of gut microbes.
[Show abstract][Hide abstract] ABSTRACT: Polycystic ovarian syndrome is a common endocrine disorder in females of reproductive age and is believed to have a developmental origin in which gestational androgenization programs reproductive and metabolic abnormalities in offspring. During gestation, both male and female fetuses are exposed to potential androgen excess. We determined the consequences of developmental androgenization in male mice exposed to neonatal testosterone (NTM). Adult NTM displayed hypogonadotropic hypogonadism with decreased serum testosterone and gonadotropins. Hypothalamic KiSS1 neurons are believed to be critical in the onset of puberty and are the target of leptin. Adult NTM showed lower hypothalamic Kiss1 expression and a failure of leptin to upregulate Kiss1 expression. NTM displayed an early reduction in lean mass, decreased locomotor activity and decreased energy expenditure. They developed a delayed increase in subcutaneous white adipose tissue. Thus, excessive neonatal androgenization disrupts reproduction and energy homeostasis and predisposes to hypogonadism and obesity in adult male mice.
Full-text · Article · Oct 2013 · Journal of Endocrinology
[Show abstract][Hide abstract] ABSTRACT: Circulating lipopolysaccharide-binding protein (LBP) is an acute-phase reactant known to be increased in obesity. We hypothesised that LBP is produced by adipose tissue (AT) in association with obesity.
LBP mRNA and LBP protein levels were analysed in AT from three cross-sectional (n = 210, n = 144 and n = 28) and three longitudinal (n = 8, n = 25, n = 20) human cohorts; in AT from genetically manipulated mice; in isolated adipocytes; and in human and murine cell lines. The effects of a high-fat diet and exposure to lipopolysaccharide (LPS) and peroxisome proliferator-activated receptor (PPAR)γ agonist were explored. Functional in vitro and ex vivo experiments were also performed.
LBP synthesis and release was demonstrated to increase with adipocyte differentiation in human and mouse AT, isolated adipocytes and human and mouse cell lines (Simpson-Golabi-Behmel syndrome [SGBS], human multipotent adipose-derived stem [hMAD] and 3T3-L1 cells). AT LBP expression was robustly associated with inflammatory markers and increased with metabolic deterioration and insulin resistance in two independent cross-sectional human cohorts. AT LBP also increased longitudinally with weight gain and excessive fat accretion in both humans and mice, and decreased with weight loss (in two other independent cohorts), in humans with acquired lipodystrophy, and after ex vivo exposure to PPARγ agonist. Inflammatory agents such as LPS and TNF-α led to increased AT LBP expression in vivo in mice and in vitro, while this effect was prevented in Cd14-knockout mice. Functionally, LBP knockdown using short hairpin (sh)RNA or anti-LBP antibody led to increases in markers of adipogenesis and decreased adipocyte inflammation in human adipocytes.
Collectively, these findings suggest that LBP might have an essential role in inflammation- and obesity-associated AT dysfunction.
[Show abstract][Hide abstract] ABSTRACT: Metabolic endotoxemia triggers inflammation, targets cells from the stroma-vascular fraction of adipose depots, and metabolic disease. To identify these cells we here infused mice with lipopolysaccharides and showed by FACS analyses and BrdU staining that the number of small subcutaneous adipocytes, preadipocytes and macrophages increased in wild type but not in CD14-knockout (KO) mice. This mechanism was direct since in CD14KO mice grafted subcutaneously and simultaneously with fat pads from CD14KO and wild-type mice the concentration of cytokine mRNA was increased in the wild-type fat pad only. Conversely, the mRNA concentration of genes involved in glucose and lipid metabolism and the number of large adipocytes was reduced. Eventually, a pretreatment with LPS enhanced HFD-induced metabolic diseases. Altogether, these results show that metabolic endotoxemia increases the proliferation of preadipocytes through a CD14-dependent mechanism directly, without recruiting CD14-positive cells from non-adipose depot origin. This mechanism could precede the onset of metabolic diseases.
Full-text · Article · Aug 2013 · Molecular Metabolism
[Show abstract][Hide abstract] ABSTRACT: The beneficial metabolic actions of estrogen-based therapies are mainly mediated by estrogen receptor-α (ERα), a nuclear receptor which regulates gene transcription through two activation functions (AFs), AF-1 and AF-2. Using mouse models deleted electively for ERαAF-1 (ERαAF-1(0)) or ERαAF-2 (ERαAF-2(0)), we determined their respective roles in the actions of estrogens on body composition and glucose homeostasis, either under normal diet or in response to a high-fat diet. ERαAF-2(0) males and females developed accelerated weight gain, massive adiposity, severe insulin resistance and glucose intolerance, quite reminiscent to the phenotype observed in mice deleted for the entire ERα protein (ERα(-/-)). In striking contrast, ERαAF-1(0) and wild-type mice shared a similar metabolic phenotype. Accordingly, 17β-estradiol administration regulated key metabolic genes in insulin-sensitive tissues and conferred a strong protection against high-fat diet-induced metabolic disturbances in wild-type and ERαAF-1(0) ovariectomized mice, while these actions were totally abrogated in ERαAF-2(0) and ERα(-/-) mice. Thus, whereas both AFs have been previously shown to contribute to endometrial and breast cancer cell proliferation, the protective effect of estrogens against obesity and insulin resistance depends on ERαAF-2 but not on ERαAF-1, thereby delineating new options for selective modulation of ERα.
[Show abstract][Hide abstract] ABSTRACT: Among women, the polycystic ovarian syndrome (PCOS) is considered a form of metabolic syndrome with reproductive abnormalities. Women with PCOS show increased sympathetic tone, visceral adiposity with enlarged adipocytes, hypoadiponectinemia, insulin resistance, glucose intolerance, increased inactive osteocalcin and hypertension. Excess fetal exposure to androgens has been hypothesized to play a role in the pathogenesis of PCOS. Previously, we showed that neonatal exposure to the androgen testosterone (NT) programs leptin resistance in adult female mice. Here, we studied the impact of NT on lean and adipose tissues, sympathetic tone in cardiometabolic tissues and the development of metabolic dysfunction in mice. Neonatally androgenized adult female mice (NTF) displayed masculinization of lean tissues with increased cardiac and skeletal muscle as well as kidney masses. NTF mice showed increased and dysfunctional white adipose tissue with increased sympathetic tone in both visceral and subcutaneous fat, as well as increased number of enlarged and insulin resistant adipocytes that displayed altered expression of developmental genes and hypoadiponectinemia. NTF exhibited dysfunctional brown adipose tissue with increased mass and decreased energy expenditure. They also displayed decreased undercarboxylated and active osteocalcin and were predisposed to obesity during chronic androgen excess. NTF showed increased renal sympathetic tone associated with increased blood pressure and they developed glucose intolerance and insulin resistance. Thus, developmental exposure to testosterone in female mice programs features of cardiometabolic dysfunction as can be observed in women with PCOS including increased sympathetic tone, visceral adiposity, insulin resistance, pre-diabetes and hypertension.
[Show abstract][Hide abstract] ABSTRACT: When energy is needed, white adipose tissue (WAT) provides fatty acids (FAs) for use in peripheral tissues via stimulation of fat cell lipolysis. FAs have been postulated to play a critical role in the development of obesity-induced insulin resistance, a major risk factor for diabetes and cardiovascular disease. However, whether and how chronic inhibition of fat mobilization from WAT modulates insulin sensitivity remains elusive. Hormone-sensitive lipase (HSL) participates in the breakdown of WAT triacylglycerol into FAs. HSL haploinsufficiency and treatment with a HSL inhibitor resulted in improvement of insulin tolerance without impact on body weight, fat mass, and WAT inflammation in high-fat-diet-fed mice. In vivo palmitate turnover analysis revealed that blunted lipolytic capacity is associated with diminution in FA uptake and storage in peripheral tissues of obese HSL haploinsufficient mice. The reduction in FA turnover was accompanied by an improvement of glucose metabolism with a shift in respiratory quotient, increase of glucose uptake in WAT and skeletal muscle, and enhancement of de novo lipogenesis and insulin signalling in liver. In human adipocytes, HSL gene silencing led to improved insulin-stimulated glucose uptake, resulting in increased de novo lipogenesis and activation of cognate gene expression. In clinical studies, WAT lipolytic rate was positively and negatively correlated with indexes of insulin resistance and WAT de novo lipogenesis gene expression, respectively. In obese individuals, chronic inhibition of lipolysis resulted in induction of WAT de novo lipogenesis gene expression. Thus, reduction in WAT lipolysis reshapes FA fluxes without increase of fat mass and improves glucose metabolism through cell-autonomous induction of fat cell de novo lipogenesis, which contributes to improved insulin sensitivity.
[Show abstract][Hide abstract] ABSTRACT: Lactoferrin is considered an epithelial protein present in different gland secretions. Administration of exogenous lactoferrin is also known to modulate adipogenesis and insulin action in human adipocytes. Here, we aimed to investigate lactoferrin gene expression (real-time polymerase chain reaction) and protein (enzyme-linked immunosorbent assay) levels in human (n=143) and mice adipose tissue samples, in adipose tissue fractions and during human preadipocyte and 3T3-L1 cell line differentiation, evaluating the effects of inducers (rosiglitazone) and disruptors (inflammatory factors) of adipocyte differentiation. Lactoferrin (LTF) gene and protein were detectable at relatively high levels in whole adipose tissue and isolated adipocytes in direct association with low-density lipoprotein-related protein 1 (LRP1, its putative receptor). Obese subjects with type 2 diabetes and increased triglycerides had the lowest levels of LTF gene expression in subcutaneous adipose tissue. Specifically, LTF gene expression was significantly increased in adipocytes, mainly from lean subjects, increasing during differentiation in parallel to adipogenic genes and gene markers of lipid droplets. The induction or disruption of adipogenesis led to concomitant changes (increase and decrease, respectively) of lactoferrin levels during adipocyte differentiation also in parallel to gene markers of adipogenesis and lipid droplet development. The administration of lactoferrin led to autopotentiated increased expression of the LTF gene. The decreased lactoferrin mRNA levels in association with obesity and diabetes were replicated in mice adipose tissue. In conclusion, this is the first observation, to our knowledge, of lactoferrin gene expression in whole adipose tissue and isolated adipocytes, increasing during adipogenesis and suggesting a possible contribution in adipose tissue physiology through LRP1.
No preview · Article · Jan 2013 · The Journal of nutritional biochemistry
[Show abstract][Hide abstract] ABSTRACT: Endoplasmic reticulum (ER) stress has been implicated in the development of type 2 diabetes, via effects on obesity, insulin resistance and pancreatic beta cell health. C/EBP homologous protein (CHOP) is induced by ER stress and has a central role in apoptotic execution pathways triggered by ER stress. The aim of this study was to characterise the role of CHOP in obesity and insulin resistance.
Metabolic studies were performed in Chop ( -/- ) and wild-type C57Bl/6 mice, and included euglycaemic-hyperinsulinaemic clamps and indirect calorimetry. The inflammatory state of liver and adipose tissue was determined by quantitative RT-PCR, immunohistology and macrophage cultures. Viability and absence of ER stress in islets of Langerhans was determined by electron microscopy, islet culture and quantitative RT-PCR.
Systemic deletion of Chop induced abdominal obesity and hepatic steatosis. Despite marked obesity, Chop ( -/- ) mice had preserved normal glucose tolerance and insulin sensitivity. This discrepancy was accompanied by lower levels of pro-inflammatory cytokines and less infiltration of immune cells into fat and liver.
These observations suggest that insulin resistance is not induced by fat accumulation per se, but rather by the inflammation induced by ectopic fat. CHOP may play a key role in the crosstalk between excessive fat deposition and induction of inflammation-mediated insulin resistance.
[Show abstract][Hide abstract] ABSTRACT: Mitochondria are dynamic organelles that play a key role in energy conversion. Optimal mitochondrial function is ensured by a quality-control system tightly coupled to fusion and fission. In this connection, mitofusin 2 (Mfn2) participates in mitochondrial fusion and undergoes repression in muscle from obese or type 2 diabetic patients. Here, we provide in vivo evidence that Mfn2 plays an essential role in metabolic homeostasis. Liver-specific ablation of Mfn2 in mice led to numerous metabolic abnormalities, characterized by glucose intolerance and enhanced hepatic gluconeogenesis. Mfn2 deficiency impaired insulin signaling in liver and muscle. Furthermore, Mfn2 deficiency was associated with endoplasmic reticulum stress, enhanced hydrogen peroxide concentration, altered reactive oxygen species handling, and active JNK. Chemical chaperones or the antioxidant N-acetylcysteine ameliorated glucose tolerance and insulin signaling in liver-specific Mfn2 KO mice. This study provides an important description of a unique unexpected role of Mfn2 coordinating mitochondria and endoplasmic reticulum function, leading to modulation of insulin signaling and glucose homeostasis in vivo.
Full-text · Article · Mar 2012 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: Protein tyrosine phosphatase 1B (PTP1B) regulates tyrosine kinase receptor-mediated responses, and especially negatively influences insulin sensitivity, thus PTP1B inhibitors (PTP1Bi) are currently evaluated in the context of diabetes. We recently revealed another important target for PTP1Bi, consisting in endothelial protection. The present study was designed to test whether reduction of PTP1B activity may be beneficial in chronic heart failure (CHF). We evaluated the impact of either a 2 month pharmacological inhibition, or a gene deletion of PTP1B (PTP1B(-/-)) in CHF mice (2 months post-myocardial infarction). PTP1Bi and PTP1B deficiency reduced adverse LV remodeling, and improved LV function, as shown by the increased LV fractional shortening and cardiac output (measured by echocardiography), the increased LV end systolic pressure, and the decreased LV end diastolic pressure, at identical infarct sizes. This was accompanied by reduced cardiac fibrosis, myocyte hypertrophy and cardiac expression of ANP. In vitro vascular studies performed in small mesenteric artery segments showed a restored endothelial function (i.e. improved NO-dependent, flow-mediated dilatation, increased eNOS phosphorylation) after either pharmacological inhibition or gene deletion. PTP1B(-/-) CHF also displayed an improved insulin sensitivity (assessed by euglycemic-hyperinsulinemic clamp studies), when compared to wild-type CHF associated with an increased insulin mediated mesenteric artery dilation. Thus, chronic pharmacological inhibition or gene deletion of PTP1B improves cardiac dysfunction and cardiac remodeling in the absence of changes in infarct size. Thus this enzyme may be a new therapeutic target in CHF. Diabetic patients with cardiac complications may potentially benefit from PTP1B inhibition via two different mechanisms, reduced diabetic complications, and reduced heart failure.
Full-text · Article · Mar 2012 · Journal of Molecular and Cellular Cardiology
[Show abstract][Hide abstract] ABSTRACT: Introduction
La maladie parodontale (MP) est définie comme une maladie infectieuse bactérienne bucco-dentaire multifactorielle à manifestation inflammatoire locale à bas bruit. Or, une des principales causes de l’insulinorésistance chez les diabétiques est la réaction inflammatoire métabolique. Des données récentes de la littérature démontrent le rôle causal de la flore intestinale dans l’induction de l’inflammation métabolique. Ainsi, nous suggérons que l’infection buccale caractérisant la MP puisse être considérée comme un facteur de risque initiant ou aggravant l’inflammation et ainsi l’insulinorésistance et le développement du diabète de type 2.
Matériels et méthodes
Nous avons identifié par RT-PCR qu’un régime gras induisait un changement de flore buccale qui correspondait à une augmentation de la proportion de Prevotella intermedia et Fusobacterium nucleatum dans le microbiote parodontal. Pour évaluer l’impact de ces bactéries parodonto-pathogènes en tant que facteur de risque du diabète, des souris ont initialement été colonisées par cette microflore sous-gingivale pathogène puis après un mois nourries avec un régime normal (NCD) ou riche en lipides diabétogène (HFD) et affiliées dans quatre groupes: NCD (n = 6), NCD + MP (n = 6), HFD (n = 19) et HFD + MP (n = 17). Le phénotype diabétique a été évalué en effectuant un test de tolérance oral au glucose et un clamp hyperinsulinémique euglycémique. La lyse osseuse alvéolaire mandibulaire a été évaluée par tomodensitométrie et les cytokines inflammatoires du foie, du tissu adipeux, du muscle et du tissu parodontal ont été quantifiées par RT-PCR. La pression artérielle fut mesurée à la queue à l’aide du système CODA®.
La colonisation bactérienne a induit une lyse osseuse mandibulaire (p < 0, 0001) ce qui caractérise l’induction d’une MP. La MP amplifie la pression systolique chez les souris diabétiques (p = 0,021). La résistance à l’insuline induite par le régime gras était majorée par l’infection du tissu parodontal. Cette observation suggérait que la MP représentait un facteur de risque du développement du diabète car la résorption osseuse alvéolaire est corrélée avec la tolérance au glucose, la sensibilité à l’insuline (p = 0, 037), et l’hypertension artérielle, par rapport aux souris témoins.
Ainsi, la modification du microbiote parodontal associée à l’inflammation du parodonte peut être considérée comme un facteur de risque de déséquilibre de l’homéostasie du glucose et plus largement du syndrome métabolique. Nos résultats montrent que l’état parodontal peut représenter un nouvel axe de traitement des maladies métaboliques.
No preview · Article · Mar 2012 · Diabetes & Metabolism