CX3CR1 regulates gut microbiota and metabolism. A risk factor of type 2 diabetes.

OBJECTIVE: The intestinal microbiota to immune system crosstalk is a major regulator of metabolism and hence metabolic diseases. An impairment of the chemokine receptor CX3CR1, as a key regulator shaping intestinal microbiota under normal chow feeding, could be one of the early events of dysglycemia. METHODS: We studied the gut microbiota ecology by sequencing the gut and tissue microbiota. We studied its role in energy metabolism in CX3CR1-deficent and control mice using various bioassays notably the glycemic regulation during fasting and the respiratory quotient as two highly sensitive physiological features. We used antibiotics and prebiotics treatments, and germ free mouse colonization. RESULTS: We identify that CX3CR1 disruption impairs gut microbiota ecology and identified a specific signature associated to the genotype. The glycemic control during fasting and the respiratory quotient throughout the day are deeply impaired. A selected four-week prebiotic treatment modifies the dysbiotic microbiota and improves the fasting state glycemic control of the CX3CR1-deficent mice and following a glucose tolerance test. A 4 week antibiotic treatment also improves the glycemic control as well. Eventually, germ free mice colonized with the microbiota from CX3CR1-deficent mice developed glucose intolerance. CONCLUSIONS: CX3CR1 is a molecular mechanism in the control of the gut microbiota ecology ensuring the maintenance of a steady glycemia and energy metabolism. Its impairment could be an early mechanism leading to gut microbiota dysbiosis and the onset of metabolic disease.

Liraglutide targets the gut microbiota and the intestinal immune system to regulate insulin secretion.

AIMS: Liraglutide controls type 2 diabetes (T2D) and inflammation. Gut microbiota regulates the immune system and causes at least in part type 2 diabetes. We here evaluated whether liraglutide regulates T2D through both gut microbiota and immunity in dysmetabolic mice. METHODS: Diet-induced dysmetabolic mice were treated for 14 days with intraperitoneal injection of liraglutide (100 µg/kg) or with vehicle or Exendin 4 (10 µg/kg) as controls. Various metabolic parameters, the intestinal immune cells were characterized and the 16SrDNA gene sequenced from the gut. The causal role of gut microbiota was shown using large spectrum antibiotics and by colonization of germ-free mice with the gut microbiota from treated mice. RESULTS: Besides, the expected metabolic impacts liraglutide treatment induced a specific gut microbiota specific signature when compared to vehicle or Ex4-treated mice. However, liraglutide only increased glucose-induced insulin secretion, reduced the frequency of Th1 lymphocytes, and increased that of TReg in the intestine. These effects were abolished by a concomitant antibiotic treatment. Colonization of germ-free mice with gut microbiota from liraglutide-treated diabetic mice improved glucose-induced insulin secretion and regulated the intestinal immune system differently from what observed in germ-free mice colonized with microbiota from non-treated diabetic mice. CONCLUSIONS: Altogether, our result demonstrated first the influence of liraglutide on gut microbiota and the intestinal immune system which could at least in part control glucose-induced insulin secretion.

Lixisenatide requires a functional gut-vagus nerve-brain axis to trigger insulin secretion in controls and type 2 diabetic mice.

Endogenous glucagon-like peptide-1 (GLP-1) regulates glucose-induced insulin secretion through both direct ß-cell-dependent and indirect gut-brain axis-dependent pathways. However, little is known about the mode of action of the GLP-1 receptor agonist lixisenatide. We studied the effects of lixisenatide (intraperitoneal injection) on insulin secretion, gastric emptying, vagus nerve activity, and brain c-Fos activation in naive, chronically vagotomized, GLP-1 receptor knockout (KO), high-fat diet-fed diabetic mice, or db/db mice. Lixisenatide dose-dependently increased oral glucose-induced insulin secretion that is correlated with a decrease of glycemia. In addition, lixisenatide inhibited gastric emptying. These effects of lixisenatide were abolished in vagotomized mice, characterized by a delay of gastric emptying and in GLP-1 receptor KO mice. Intraperitoneal administration of lixisenatide also increased the vagus nerve firing rate and the number of c-Fos-labeled neurons in the nucleus tractus solitarius (NTS) of the brainstem. In diabetic mouse models, lixisenatide increased the firing rate of the vagus nerve when administrated simultaneously to an intraduodenal glucose. It increased also insulin secretion and c-Fos activation in the NTS. Altogether, our findings show that lixisenatide requires a functional vagus nerve and neuronal gut-brain-islets axis as well as the GLP-1 receptor to regulate glucose-induced insulin secretion in healthy and diabetic mice. NEW & NOTEWORTHY Lixisenatide is an agonist of the glucagon-like protein (GLP)-1 receptor, modified from exendin 4, used to treat type 2 diabetic patients. However, whereas the mode of action of endogenous GLP-1 is extensively studied, the mode of action of the GLP-1 analog lixisenatide is poorly understood. Here, we demonstrated that lixisenatide activates the vagus nerve and recruits the gut-brain axis through the GLP-1 receptor to decrease gastric emptying and stimulate insulin secretion to improve glycemia.

Corrupted adipose tissue endogenous myelopoiesis initiates diet-induced metabolic disease.

Activation and increased numbers of inflammatory macrophages, in adipose tissue (AT) are deleterious in metabolic diseases. Up to now, AT macrophages (ATM) accumulation was considered to be due to blood infiltration or local proliferation, although the presence of resident hematopoietic stem/progenitor cells (Lin-/Sca+/c-Kit+; LSK phenotype) in the AT (AT-LSK) has been reported. By using transplantation of sorted AT-LSK and gain and loss of function studies we show that some of the inflammatory ATM inducing metabolic disease, originate from resident AT-LSK. Transplantation of AT-LSK sorted from high fat diet-fed (HFD) mice is sufficient to induce ATM accumulation, and to transfer metabolic disease in control mice. Conversely, the transplantation of control AT-LSK improves both AT-inflammation and glucose homeostasis in HFD mice. Our results clearly demonstrate that resident AT-LSK are one of the key point of metabolic disease, and could thus constitute a new promising therapeutic target to fight against metabolic disease.

Transfer of dysbiotic gut microbiota has beneficial effects on host liver metabolism.

Gut microbiota dysbiosis has been implicated in a variety of systemic disorders, notably metabolic diseases including obesity and impaired liver function, but the underlying mechanisms are uncertain. To investigate this question, we transferred caecal microbiota from either obese or lean mice to antibiotic-free, conventional wild-type mice. We found that transferring obese-mouse gut microbiota to mice on normal chow (NC) acutely reduces markers of hepatic gluconeogenesis with decreased hepatic PEPCK activity, compared to non-inoculated mice, a phenotypic trait blunted in conventional NOD2 KO mice. Furthermore, transferring of obese-mouse microbiota changes both the gut microbiota and the microbiome of recipient mice. We also found that transferring obese gut microbiota to NC-fed mice then fed with a high-fat diet (HFD) acutely impacts hepatic metabolism and prevents HFD-increased hepatic gluconeogenesis compared to non-inoculated mice. Moreover, the recipient mice exhibit reduced hepatic PEPCK and G6Pase activity, fed glycaemia and adiposity. Conversely, transfer of lean-mouse microbiota does not affect markers of hepatic gluconeogenesis. Our findings provide a new perspective on gut microbiota dysbiosis, potentially useful to better understand the aetiology of metabolic diseases.

Periodontitis induced by Porphyromonas gingivalis drives periodontal microbiota dysbiosis and insulin resistance via an impaired adaptive immune response.

OBJECTIVE: To identify a causal mechanism responsible for the enhancement of insulin resistance and hyperglycaemia following periodontitis in mice fed a fat-enriched diet. DESIGN: 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. RESULTS: 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. CONCLUSIONS: 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.

Triggering the adaptive immune system with commensal gut bacteria protects against insulin resistance and dysglycemia.

OBJECTIVE: To demonstrate that glycemia and insulin resistance are controlled by a mechanism involving the adaptive immune system and gut microbiota crosstalk. METHODS: We triggered the immune system with microbial extracts specifically from the intestinal ileum contents of HFD-diabetic mice by the process of immunization. 35 days later, immunized mice were fed a HFD for up to two months in order to challenge the development of metabolic features. The immune responses were quantified. Eventually, adoptive transfer of immune cells from the microbiota-immunized mice to naïve mice was performed to demonstrate the causality of the microbiota-stimulated adaptive immune system on the development of metabolic disease. The gut microbiota of the immunized HFD-fed mice was characterized in order to demonstrate whether the manipulation of the microbiota to immune system interaction reverses the causal deleterious effect of gut microbiota dysbiosis on metabolic disease. RESULTS: Subcutaneous injection (immunization procedure) of ileum microbial extracts prevented hyperglycemia and insulin resistance in a dose-dependent manner in response to a HFD. The immunization enhanced the proliferation of CD4 and CD8 T cells in lymphoid organs, also increased cytokine production and antibody secretion. As a mechanism explaining the metabolic improvement, the immunization procedure reversed gut microbiota dysbiosis. Finally, adoptive transfer of immune cells from immunized mice improved metabolic features in response to HFD. CONCLUSIONS: Glycemia and insulin sensitivity can be regulated by triggering the adaptive immunity to microbiota interaction. This reduces the gut microbiota dysbiosis induced by a fat-enriched diet.

Periodontal dysbiosis linked to periodontitis is associated with cardiometabolic adaptation to high-fat diet in mice.

Periodontitis and type 2 diabetes are connected pandemic diseases, and both are risk factors for cardiovascular complications. Nevertheless, the molecular factors relating these two chronic pathologies are poorly understood. We have shown that, in response to a long-term fat-enriched diet, mice present particular gut microbiota profiles related to three metabolic phenotypes: diabetic-resistant (DR), intermediate (Inter), and diabetic-sensitive (DS). Moreover, many studies suggest that a dysbiosis of periodontal microbiota could be associated with the incidence of metabolic and cardiac diseases. We investigated whether periodontitis together with the periodontal microbiota may also be associated with these different cardiometabolic phenotypes. We report that the severity of glucose intolerance is related to the severity of periodontitis and cardiac disorders. In detail, alveolar bone loss was more accentuated in DS than Inter, DR, and normal chow-fed mice. Molecular markers of periodontal inflammation, such as TNF-α and plasminogen activator inhibitor-1 mRNA levels, correlated positively with both alveolar bone loss and glycemic index. Furthermore, the periodontal microbiota of DR mice was dominated by the Streptococcaceae family of the phylum Firmicutes, whereas the periodontal microbiota of DS mice was characterized by increased Porphyromonadaceae and Prevotellaceae families. Moreover, in DS mice the periodontal microbiota was indicated by an abundance of the genera Prevotella and Tannerella, which are major periodontal pathogens. PICRUSt analysis of the periodontal microbiome highlighted that prenyltransferase pathways follow the cardiometabolic adaptation to a high-fat diet. Finally, DS mice displayed a worse cardiac phenotype, percentage of fractional shortening, heart rhythm, and left ventricle weight-to-tibia length ratio than Inter and DR mice. Together, our data show that periodontitis combined with particular periodontal microbiota and microbiome is associated with metabolic adaptation to a high-fat diet related to the severity of cardiometabolic alteration.

Probiotic B420 and prebiotic polydextrose improve efficacy of antidiabetic drugs in mice.

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. METHODS: 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. RESULTS: 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). CONCLUSIONS: 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.

The Gut Microbiota Regulates Intestinal CD4 T Cells Expressing RORγt and Controls Metabolic Disease.

A high-fat diet (HFD) induces metabolic disease and low-grade metabolic inflammation in response to changes in the intestinal microbiota through as-yet-unknown mechanisms. Here, we show that a HFD-derived ileum microbiota is responsible for a decrease in Th17 cells of the lamina propria in axenic colonized mice. The HFD also changed the expression profiles of intestinal antigen-presenting cells and their ability to generate Th17 cells in vitro. Consistent with these data, the metabolic phenotype was mimicked in RORγt-deficient mice, which lack IL17 and IL22 function, and in the adoptive transfer experiment of T cells from RORγt-deficient mice into Rag1-deficient mice. We conclude that the microbiota of the ileum regulates Th17 cell homeostasis in the small intestine and determines the outcome of metabolic disease.

Developmental androgen excess disrupts reproduction and energy homeostasis in adult male mice.

Polycystic ovary 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. In this study, 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 gonadotropin concentrations. Hypothalamic KiSS1 neurons are believed to be critical to the onset of puberty and are the target of leptin. Adult NTM exhibited 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 displayed a delayed increase in subcutaneous white adipose tissue amounts. Thus, excessive neonatal androgenization disrupts reproduction and energy homeostasis and predisposes to hypogonadism and obesity in adult male mice.

Metabolic endotoxemia directly increases the proliferation of adipocyte precursors at the onset of metabolic diseases through a CD14-dependent mechanism.

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.

Prevention of obesity and insulin resistance by estrogens requires ERα activation function-2 (ERαAF-2), whereas ERαAF-1 is dispensable.

The beneficial metabolic actions of estrogen-based therapies are mainly mediated by estrogen receptor α (ERα), a nuclear receptor that regulates gene transcription through two activation functions (AFs): AF-1 and AF-2. Using mouse models deleted electively for ERαAF-1 (ERαAF-1°) or ERαAF-2 (ERαAF-2°), we determined their respective roles in the actions of estrogens on body composition and glucose homeostasis in response to either a normal diet or a high-fat diet (HFD). ERαAF-2° males and females developed accelerated weight gain, massive adiposity, severe insulin resistance, and glucose intolerance--quite reminiscent of the phenotype observed in mice deleted for the entire ERα protein (ERα(-/-)). In striking contrast, ERαAF-1° and wild-type (wt) mice shared a similar metabolic phenotype. Accordingly, 17ß-estradiol administration regulated key metabolic genes in insulin-sensitive tissues and conferred a strong protection against HFD-induced metabolic disturbances in wt and ERαAF-1° ovariectomized mice, whereas these actions were totally abrogated in ERαAF-2° 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 ERαAF-1, thereby delineating new options for selective modulation of ERα.

A role for adipocyte-derived lipopolysaccharide-binding protein in inflammation- and obesity-associated adipose tissue dysfunction.

AIMS/HYPOTHESIS: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS/INTERPRETATION: Collectively, these findings suggest that LBP might have an essential role in inflammation- and obesity-associated AT dysfunction.

Developmental androgen excess programs sympathetic tone and adipose tissue dysfunction and predisposes to a cardiometabolic syndrome in female mice.

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, prediabetes, and hypertension.

Partial inhibition of adipose tissue lipolysis improves glucose metabolism and insulin sensitivity without alteration of fat mass.

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.

Study of lactoferrin gene expression in human and mouse adipose tissue, human preadipocytes and mouse 3T3-L1 fibroblasts. Association with adipogenic and inflammatory markers.

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.

Mitofusin 2 (Mfn2) links mitochondrial and endoplasmic reticulum function with insulin signaling and is essential for normal glucose homeostasis.

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.

Reduction of heart failure by pharmacological inhibition or gene deletion of protein tyrosine phosphatase 1B.

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.

Metabolic adaptation to a high-fat diet is associated with a change in the gut microbiota.

OBJECTIVE: The gut microbiota, which is considered a causal factor in metabolic diseases as shown best in animals, is under the dual influence of the host genome and nutritional environment. This study investigated whether the gut microbiota per se, aside from changes in genetic background and diet, could sign different metabolic phenotypes in mice. METHODS: The unique animal model of metabolic adaptation was used, whereby C57Bl/6 male mice fed a high-fat carbohydrate-free diet (HFD) became either diabetic (HFD diabetic, HFD-D) or resisted diabetes (HFD diabetes-resistant, HFD-DR). Pyrosequencing of the gut microbiota was carried out to profile the gut microbial community of different metabolic phenotypes. Inflammation, gut permeability, features of white adipose tissue, liver and skeletal muscle were studied. Furthermore, to modify the gut microbiota directly, an additional group of mice was given a gluco-oligosaccharide (GOS)-supplemented HFD (HFD+GOS). RESULTS: Despite the mice having the same genetic background and nutritional status, a gut microbial profile specific to each metabolic phenotype was identified. The HFD-D gut microbial profile was associated with increased gut permeability linked to increased endotoxaemia and to a dramatic increase in cell number in the stroma vascular fraction from visceral white adipose tissue. Most of the physiological characteristics of the HFD-fed mice were modulated when gut microbiota was intentionally modified by GOS dietary fibres. CONCLUSIONS: The gut microbiota is a signature of the metabolic phenotypes independent of differences in host genetic background and diet.