Chronic low-grade inflammation associated with obesity contributes to insulin resistance and type 2 diabetes. Helminth parasites are the strongest natural inducers of type 2 immune responses, and short-lived infection with rodent nematodes was reported to improve glucose tolerance in obese mice. Here, we investigated the effects of chronic infection (12 weeks) with Schistosoma mansoni, a helminth that infects millions of humans worldwide, on whole-body metabolic homeostasis and white adipose tissue (WAT) immune cell composition in high-fat diet-induced obese C57BL/6 male mice. Our data indicate that chronic helminth infection reduced body weight gain (262%), fat mass gain (289%), and adipocyte size; lowered whole-body insulin resistance (223%) and glucose intolerance (216%); and improved peripheral glucose uptake (+25%) and WAT insulin sensitivity. Analysis of immune cell composition by flow cytometry and quantitative PCR (qPCR) revealed that S. mansoni promoted strong increases in WAT eosinophils and alternatively activated (M2) macrophages. Importantly, injections with S. mansoni-soluble egg antigens (SEA) recapitulated the beneficial effect of parasite infection on whole-body metabolic homeostasis and induced type 2 immune responses in WAT and liver. Taken together, we provide novel data suggesting that chronic helminth infection and helminthderived molecules protect against metabolic disorders by promoting a T helper 2 (Th2) response, eosinophilia, and WAT M2 polarization.-Hussaarts, L., García-Tardón, N., van

Aim/hypothesisThe glucose-lowering drug metformin has been shown to activate hepatic AMP-activated protein kinase (AMPK), a master kinase regulating cellular energy homeostasis. However, the underlying mechanisms remain controversial and have never been investigated in primary human hepatocytes.MethodsHepatocytes isolated from rat, mouse and human livers were treated with various concentrations of metformin. Isoform-specific AMPKα abundance and activity, as well as intracellular adenine nucleotide levels and mitochondrial oxygen consumption rates were determined at different time points.ResultsMetformin dose- and time-dependently increased AMPK activity in rat and human hepatocytes, an effect associated with a significant rise in cellular AMP:ATP ratio. Surprisingly, we found that AMPKα2 activity was undetectable in human compared with rat hepatocytes, while AMPKα1 activities were comparable. Accordingly, metformin only increased AMPKα1 activity in human hepatocytes, although both AMPKα isoforms were activated in rat hepatocytes. Analysis of mRNA expression and protein levels confirmed that only AMPKα1 is present in human hepatocytes; it also showed that the distribution of β and γ regulatory subunits differed between species. Finally, we demonstrated that the increase in AMP:ATP ratio in hepatocytes from liver-specific Ampkα1/2 (also known as Prkaa1/2) knockout mice and humans is due to a similar and specific inhibition of the mitochondrial respiratory-chain complex 1 by metformin.Conclusions/interpretationActivation of hepatic AMPK by metformin results from a decrease in cellular energy status owing to metformin’s AMPK-independent inhibition of the mitochondrial respiratory-chain complex 1. The unique profile of AMPK subunits found in human hepatocytes should be considered when developing new pharmacological agents to target the kinase.Electronic supplementary materialThe online version of this article (doi:10.1007/s00125-011-2311-5) contains peer-reviewed but unedited supplementary material, which is available to authorised users.

Metformin is the first-line drug for the treatment of type 2 diabetes. Besides its well-characterized antihyperglycemic properties, metformin also lowers plasma VLDL triglyceride (TG). In this study, we investigated the underlying mechanisms in APOE*3-Leiden.CETP mice, a well-established model for human-like lipoprotein metabolism. We found that metformin markedly lowered plasma total cholesterol and TG levels, an effect mostly due to a decrease in VLDL-TG, whereas HDL was slightly increased. Strikingly, metformin did not affect hepatic VLDL-TG production, VLDL particle composition, and hepatic lipid composition but selectively enhanced clearance of glycerol tri[ 3 H]oleate-labeled VLDL-like emulsion particles into brown adipose tissue (BAT). BAT mass and lipid droplet content were reduced in metformin-treated mice, pointing to increased BAT activation. In addition, both AMP-activated protein kinase a1 (AMPKa1) expression and activity and HSL and mitochondrial content were increased in BAT.Furthermore, therapeutic concentrations of metformin increased AMPK and HSL activities and promoted lipolysis in T37i differentiated brown adipocytes. Collectively, our results identify BAT as an important player in the TG-lowering effect of metformin by enhancing VLDL-TG uptake, intracellular TG lipolysis, and subsequent mitochondrial fatty acid oxidation. Targeting BAT might therefore be considered as a future therapeutic strategy for the treatment of dyslipidemia.

Obstructive sleep apnea syndrome is a highly prevalent disease resulting in transient respiratory arrest and chronic intermittent hypoxia (cIH). cIH is associated with insulin resistance and impaired metabolic homeostasis in rodents and humans, but the exact underlying mechanisms remain unclear. In the current study, we investigated the effects of 2 weeks of cIH (1-min cycle, fraction of inspired oxygen 21-5%, 8 h/day) on whole-body insulin sensitivity and glucose tolerance in lean mice. Although food intake and body weight were reduced compared with normoxia, cIH induced systemic insulin resistance in a hypoxia-inducible factor 1-independent manner and impaired insulin signaling in liver, white adipose tissue, and skeletal muscle. Unexpectedly, cIH improved whole-body glucose tolerance independently of changes in body weight and glucose-induced insulin response. This effect was associated with elevated phosphorylation of Thr172-AMPK and Ser237-TBC1 domain family member 1 (TBC1D1) in skeletal muscle, suggesting a tissue-specific AMPK-dependent increase in TBC1D1-driven glucose uptake. Remarkably, although food intake, body weight, and systemic insulin sensitivity were still affected, the improvement in glucose tolerance by cIH was abolished in muscle-specific AMPKα1α2-deficient mice. We conclude that cIH impairs insulin sensitivity while improving whole-body glucose tolerance by promoting specific activation of the skeletal muscle AMPK pathway.

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We have determined the primary structure of a mutant insulin receptor of a leprechaun patient born from a consanguineous marriage. A characteristic feature of leprechaunism is an extreme resistance to insulin. In this patient the insulin resistance seems to result from an observed lack of insulin binding to intact cells. Solubilizanion of cells in non-ionic detergents leads to the appearance of insulin receptors which can bind insulin. However, the insulin-stimulated autophosphorylation of the receptor's : subunit is markedly reduced. Cloning and sequencing of cDNA derived from insulin receptor mRNA of this patient revealed a leucine-to-proline mutation at position 233 in the a subunit. By means of DNA amplification we found that the patient is homozygous for this mutation and that the parents and two grandparents from the consanguineous line are heterozygous. The heterozygous individuals all show decreased insulin binding to cultured fibroblasts. In addition, they are mildly insulin resistant in vivo. These observations show a linkage between the leucine-to-proline mutation and the observed insulin resistance in this family. We therefore conclude that the mutation in the homozygous form is responsible for the extreme insulin resistance in the leprechaun patient. The mutation for the first time characterizes a region in the insulin receptor which seems to be involved in transmitting the insulin binding signal to the tyrosine kinase domain.

Recent reports have attributed an immunoregulatory role to the mammalian target of rapamycin (mTOR), a key serine/threonine protein kinase integrating input from growth factors and nutrients to promote cell growth and differentiation. In the present study, we investigated the role of the mTOR pathway in Th2 induction by human monocyte-derived dendritic cells (moDCs). Using a co-culture system of human lipopolysaccharide (LPS)-matured moDCs and allogeneic naive CD4(+) T cells, we show that inhibition of mTOR by the immunosuppressive drug rapamycin reduced moDC maturation and promoted Th2 skewing. Next, we investigated whether antigens from helminth parasites, the strongest natural inducers of Th2 responses, modulate moDCs via the mTOR pathway. In contrast to rapamycin, neither Schistosoma mansoni-soluble egg antigens (SEA) nor its major immunomodulatory component omega-1 affected the phosphorylation of S6 kinase (S6K) and 4E-binding protein 1 (4E-BP1), downstream targets of mTORC1. Finally, we found that the effects of rapamycin and SEA/omega-1 on Th2 skewing were additive, suggesting two distinct underlying molecular mechanisms. We conclude that conditioning human moDCs to skew immune responses towards Th2 can be achieved via an mTOR-dependent and -independent pathway triggered by rapamycin and helminth antigens, respectively.

Obesity in humans is often associated with metabolic inflexibility, but the underlying molecular mechanisms remain incompletely understood. The aim of the present study was to investigate how adaptation to prolonged fasting affects energy/nutrient-sensing pathways and metabolic gene expression in skeletal muscle from lean and obese individuals. Twelve lean and 14 nondiabetic obese subjects were fasted for 48 h. Whole body glucose/lipid oxidation rates were determined by indirect calorimetry, and blood and skeletal muscle biopsies were collected and analyzed. In response to fasting, body weight loss was similar in both groups, but the decrease in plasma insulin and leptin and the concomitant increase in growth hormone were significantly attenuated in obese subjects. The fasting-induced shift from glucose toward lipid oxidation was also severely blunted. At the molecular level, the expression of insulin receptor-β (IRβ) was lower in skeletal muscle from obese subjects at baseline, whereas the fasting-induced reductions in insulin signaling were similar in both groups. The protein expression of mitochondrial respiratory chain components, although not modified by fasting, was significantly reduced in obese subjects. Some minor differences in metabolic gene expression were observed at baseline and in response to fasting. Surprisingly, fasting reduced AMPK activity in lean but not in obese subjects, whereas the expression of AMPK subunits was not affected. We conclude that whole body metabolic inflexibility in response to prolonged fasting in obese humans is associated with lower skeletal muscle IRβ and mitochondrial respiratory chain content as well as a blunted decline of AMPK activity.