Mice lacking neutral amino acid transporter B⁰AT1 (Slc6a19) have elevated levels of FGF21 and GLP-1 and improved glycaemic control

OBJECTIVE: Type 2 diabetes arises from insulin resistance of peripheral tissues followed by dysfunction of β-cells in the pancreas due to metabolic stress. Both depletion and supplementation of neutral amino acids have been discussed as strategies to improve insulin sensitivity. Here we characterise mice lacking the intestinal and renal neutral amino acid transporter B⁰AT1 (Slc6a19) as a model to study the consequences of selective depletion of neutral amino acids. METHODS: Metabolic tests, analysis of metabolite levels and signalling pathways were used to characterise mice lacking the intestinal and renal neutral amino acid transporter B⁰AT1 (Slc6a19). RESULTS: Reduced uptake of neutral amino acids in the intestine and loss of neutral amino acids in the urine causes an overload of amino acids in the lumen of the intestine and reduced systemic amino acid availability. As a result, higher levels of glucagon-like peptide 1 (GLP-1) are produced by the intestine after a meal, while the liver releases the starvation hormone fibroblast growth factor 21 (FGF21). The combination of these hormones generates a metabolic phenotype that is characterised by efficient removal of glucose, particularly by the heart, reduced adipose tissue mass, browning of subcutaneous white adipose tissue, enhanced production of ketone bodies and reduced hepatic glucose output. CONCLUSIONS: Reduced neutral amino acid availability improves glycaemic control. The epithelial neutral amino acid transporter B⁰AT1 could be a suitable target to treat type 2 diabetes.This work was supported by a sponsored research agreement with Sanofi-Aventis, Germany

Browning of White Adipose Tissue Uncouples Glucose Uptake from Insulin Signaling

<div><p>Presence of thermogenically active adipose tissue in adult humans has been inversely associated with obesity and type 2 diabetes. While it had been shown that insulin is crucial for the development of classical brown fat, its role in development and function of inducible brown-in-white (brite) adipose tissue is less clear. Here we show that insulin deficiency impaired differentiation of brite adipocytes. However, adrenergic stimulation almost fully induced the thermogenic program under these settings. Although brite differentiation of adipocytes as well as browning of white adipose tissue entailed substantially elevated glucose uptake by adipose tissue, the capacity of insulin to stimulate glucose uptake surprisingly was not higher in the brite state. Notably, in line with the insulin-independent stimulation of glucose uptake, our data revealed that brite recruitment results in induction of solute carrier family 2 (GLUT-1) expression in adipocytes and inguinal WAT. These results for the first time demonstrate that insulin signaling is neither essential for brite recruitment, nor is it improved in cells or tissues upon browning.</p></div

Brite adipose cells and tissues exhibit elevated glucose uptake independent of insulin stimulation, thereby enhancing glucose clearance from blood.

<p>(<b>A, B</b>) ³H-2-deoxy-D-glucose (3H-2DOG) uptake by primary inguinal white adipose tissue (iWAT) precursor cells (<b>A</b>) absolute or (<b>B</b>) relative to unstimulated basal uptake. Cells were differentiated into white (EtOH treated) or brite (cPGI₂ treated) adipocytes for 8 days and stimulated with different doses of Insulin for 20 minutes. (<b>C, D</b>) Intraperitoneal insulin (Ins) tolerance test (0.5 U/kg body weight insulin) of mice treated with CL316,243 (CL, 1 µg/g/day) or NaCl via s.c. implanted osmotic pumps for 10 days. (<b>C</b>) Absolute blood glucose levels and (<b>D</b>) levels relative to non-insulin-stimulated are shown. (<b>E, F</b>) 3H-2DOG uptake rate into inguinal or abdominal white (iWAT, aWAT) or brown (BAT) adipose tissue and heart of the same mice as in B, C. (<b>E</b>) Absolute uptake and (<b>F</b>) uptake relative to non-insulin-stimulated conditions is shown. Uptake rates were measured 45 minutes after intraperitoneal injection of insulin or vehicle. All values are expressed as means ± SEM, n = 3–6, #p<0.05, ##p<0.01, ###p<0.001 white vs. brite, *p<0.05, **p<0.01, ***p<0.001 no insulin vs. insulin stimulated.</p

Lack of insulin impairs differentiation but not browning capacity of primary pre-adipocytes.

<p>(<b>A</b>) Heatmap showing differential mRNA expression between confluent primary inguinal white adipose tissue (iWAT) precursor cells differentiated for 24 h with white (EtOH treated) or brite (cPGI₂ treated) differentiation cocktail and between absence or presence of insulin (Ins) in the medium. Higher and lower expression is displayed in red and blue, respectively. (n = 3). (<b>B</b>) mRNA expression of UCP-1 and CIDEA or (<b>C</b>) FABP4 and RETN in primary iWAT precursor cells differentiated into white (EtOH treated) or brite (cPGI₂ treated) adipocytes for 8 days with insulin present in the differentiation medium for the indicated timepoints (n = 3). All values in bar graphs are expressed as means ± SEM, #p<0.05, ##p<0.01, ###p<0.001 white (EtOH treated) vs. brite (cPGI₂ treated) cells, *p<0.05, **p<0.01, ***p<0.001 normal conditions vs. insulin deprived conditions.</p

Comparison of different methods to investigate postprandial lipaemia

Postprandial hyperlipidaemia has been associated with coronary artery disease (CAD). We investigated which of the generally used methods to test postprandial lipaemia differentiated best between patients with premature CAD (50 +/- 4 years, n=20) and healthy controls. Furthermore, the effects of rosuvastatin 40 mg/day on postprandial parameters were assessed. Standardised oral fat-loading tests (OFLT) and ambulant self-measurements of daylong capillary triglycerides (TGc) were performed. Total responses of individual lipoproteins, plasma TG (TGp) and remnant-like particle cholesterol (RLP-C) were estimated as area under the curve (AUC). Most AUCs were highest in untreated patients and reached control levels after rosuvastatin. From all AUCs, RLP-C-AUC was best associated to TGp-AUC in untreated patients and controls (adjusted R(2)=0.84, beta=0.92, P <0.001). From all parameters of postprandial lipaemia, TGc-AUC differentiated best between untreated patients and controls (adjusted R(2)=0.48, beta=0.70, p <0.0001) and between patients on and off-treatment (adjusted R(2)=0.34, beta=0.60, p <0.0001). Our findings indicate that the real-life TG load, instead of metabolic ward testing, is the best parameter of postprandial lipaemia to identify patients with premature coronary sclerosis and to evaluate postprandial effects of statin treatmen

Fasting-induced liver GADD45&beta; restrains hepatic fatty acid uptake and improves metabolic health.

Recent studies have demonstrated that repeated short-term nutrient withdrawal (i.e. fasting) has pleiotropic actions to promote organismal health and longevity. Despite this, the molecular physiological mechanisms by which fasting is protective against metabolic disease are largely unknown. Here, we show that, metabolic control, particularly systemic and liver lipid metabolism, is aberrantly regulated in the fasted state in mouse models of metabolic dysfunction. Liver transcript assays between lean/healthy and obese/diabetic mice in fasted and fed states uncovered &quot;growth arrest and DNA damage-inducible&quot; GADD45&beta; as a dysregulated gene transcript during fasting in several models of metabolic dysfunction including ageing, obesity/pre-diabetes and type 2 diabetes, in both mice and humans. Using whole-body knockout mice as well as liver/hepatocyte-specific gain- and loss-of-function strategies, we revealed a role for liver GADD45&beta; in the coordination of liver fatty acid uptake, through cytoplasmic retention of FABP1, ultimately impacting obesity-driven hyperglycaemia. In summary, fasting stress-induced GADD45&beta; represents a liver-specific molecular event promoting adaptive metabolic function

Diet-dependent function of the extracellular matrix proteoglycan Lumican in obesity and glucose homeostasis.

Objective: Extracellular matrix remodeling is required for adipose expansion under increased caloric intake. In turn, inhibited expandability due to aberrant collagen deposition promotes insulin resistance and progression towards the metabolic syndrome. An emerging role for the small leucine-rich proteoglycan Lumican in metabolically driven nonalcoholic fatty liver disease sparks an interest in further understanding its role in diet-induced obesity and metabolic complications.Methods: Whole body ablation of Lumican (Lum(-/-)) gene and adeno-associated virus-mediated over-expression were used in combination with control or high fat diet to assess energy balance, glucose homeostasis as well as adipose tissue health and remodeling.Results: Lumican was found to be particularly enriched in the stromal cells isolated from murine gonadal white adipose tissue. Likewise murine and human visceral fat showed a robust increase in Lumican as compared to fat from the subcutaneous depot. Lumican null female mice exhibited moderately increased fat mass, decreased insulin sensitivity and increased liver triglycerides in a diet-dependent manner. These changes coincided with inflammation in adipose tissue and no overt effects in adipose expandability, i.e. adipocyte formation and hypertrophy. Lumican over-expression in visceral fat and liver resulted in improved insulin sensitivity and glucose clearance.Conclusions: These data indicate that Lumican may represent a functional link between the extracellular matrix, glucose homeostasis, and features of the metabolic syndrome. (C) 2018 The Authors. Published by Elsevier GmbH