Inhibition of Endothelial Notch Signaling Impairs Fatty Acid Transport and Leads to Metabolic and Vascular Remodeling of the Adult Heart.

BACKGROUND: Nutrients are transported through endothelial cells before being metabolized in muscle cells. However, little is known about the regulation of endothelial transport processes. Notch signaling is a critical regulator of metabolism and angiogenesis during development. Here, we studied how genetic and pharmacological manipulation of endothelial Notch signaling in adult mice affects endothelial fatty acid transport, cardiac angiogenesis, and heart function. METHODS: Endothelial-specific Notch inhibition was achieved by conditional genetic inactivation of Rbp-jκ in adult mice to analyze fatty acid metabolism and heart function. Wild-type mice were treated with neutralizing antibodies against the Notch ligand Delta-like 4. Fatty acid transport was studied in cultured endothelial cells and transgenic mice. RESULTS: Treatment of wild-type mice with Delta-like 4 neutralizing antibodies for 8 weeks impaired fractional shortening and ejection fraction in the majority of mice. Inhibition of Notch signaling specifically in the endothelium of adult mice by genetic ablation of Rbp-jκ caused heart hypertrophy and failure. Impaired heart function was preceded by alterations in fatty acid metabolism and an increase in cardiac blood vessel density. Endothelial Notch signaling controlled the expression of endothelial lipase, Angptl4, CD36, and Fabp4, which are all needed for fatty acid transport across the vessel wall. In endothelial-specific Rbp-jκ-mutant mice, lipase activity and transendothelial transport of long-chain fatty acids to muscle cells were impaired. In turn, lipids accumulated in the plasma and liver. The attenuated supply of cardiomyocytes with long-chain fatty acids was accompanied by higher glucose uptake, increased concentration of glycolysis intermediates, and mTOR-S6K signaling. Treatment with the mTOR inhibitor rapamycin or displacing glucose as cardiac substrate by feeding a ketogenic diet prolonged the survival of endothelial-specific Rbp-jκ-deficient mice. CONCLUSIONS: This study identifies Notch signaling as a novel regulator of fatty acid transport across the endothelium and as an essential repressor of angiogenesis in the adult heart. The data imply that the endothelium controls cardiomyocyte metabolism and function.

Control of diabetic hyperglycaemia and insulin resistance through TSC22D4.

Obesity-related insulin resistance represents the core component of the metabolic syndrome, promoting glucose intolerance, pancreatic beta cell failure and type 2 diabetes. Efficient and safe insulin sensitization and glucose control remain critical therapeutic aims to prevent diabetic late complications Here, we identify transforming growth factor beta-like stimulated clone (TSC) 22 D4 as a molecular determinant of insulin signalling and glucose handling. Hepatic TSC22D4 inhibition both prevents and reverses hyperglycaemia, glucose intolerance and insulin resistance in diabetes mouse models. TSC22D4 exerts its effects on systemic glucose homeostasis-at least in part-through the direct transcriptional regulation of the small secretory protein lipocalin 13 (LCN13). Human diabetic patients display elevated hepatic TSC22D4 expression, which correlates with decreased insulin sensitivity, hyperglycaemia and LCN13 serum levels. Our results establish TSC22D4 as a checkpoint in systemic glucose metabolism in both mice and humans, and propose TSC22D4 inhibition as an insulin sensitizing option in diabetes therapy.

A liver stress-endocrine nexus promotes metabolic integrity during dietary protein dilution.

Dietary protein intake is linked to an increased incidence of type 2 diabetes (T2D). Although dietary protein dilution (DPD) can slow the progression of some aging-related disorders, whether this strategy affects the development and risk for obesity-associated metabolic disease such as T2D is unclear. Here, we determined that DPD in mice and humans increases serum markers of metabolic health. In lean mice, DPD promoted metabolic inefficiency by increasing carbohydrate and fat oxidation. In nutritional and polygenic murine models of obesity, DPD prevented and curtailed the development of impaired glucose homeostasis independently of obesity and food intake. DPD-mediated metabolic inefficiency and improvement of glucose homeostasis were independent of uncoupling protein 1 (UCP1), but required expression of liver-derived fibroblast growth factor 21 (FGF21) in both lean and obese mice. FGF21 expression and secretion as well as the associated metabolic remodeling induced by DPD also required induction of liver-integrated stress response-driven nuclear protein 1 (NUPR1). Insufficiency of select nonessential amino acids (NEAAs) was necessary and adequate for NUPR1 and subsequent FGF21 induction and secretion in hepatocytes in vitro and in vivo. Taken together, these data indicate that DPD promotes improved glucose homeostasis through an NEAA insufficiency-induced liver NUPR1/FGF21 axis.

An AMP-activated protein kinase-stabilizing peptide ameliorates adipose tissue wasting in cancer cachexia in mice.

Cachexia represents a fatal energy-wasting syndrome in a large number of patients with cancer that mostly results in a pathological loss of skeletal muscle and adipose tissue. Here we show that tumor cell exposure and tumor growth in mice triggered a futile energy-wasting cycle in cultured white adipocytes and white adipose tissue (WAT), respectively. Although uncoupling protein 1 (Ucp1)-dependent thermogenesis was dispensable for tumor-induced body wasting, WAT from cachectic mice and tumor-cell-supernatant-treated adipocytes were consistently characterized by the simultaneous induction of both lipolytic and lipogenic pathways. Paradoxically, this was accompanied by an inactivated AMP-activated protein kinase (Ampk), which is normally activated in peripheral tissues during states of low cellular energy. Ampk inactivation correlated with its degradation and with upregulation of the Ampk-interacting protein Cidea. Therefore, we developed an Ampk-stabilizing peptide, ACIP, which was able to ameliorate WAT wasting in vitro and in vivo by shielding the Cidea-targeted interaction surface on Ampk. Thus, our data establish the Ucp1-independent remodeling of adipocyte lipid homeostasis as a key event in tumor-induced WAT wasting, and we propose the ACIP-dependent preservation of Ampk integrity in the WAT as a concept in future therapies for cachexia.

Fasting-induced liver GADD45ß 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 "growth arrest and DNA damage-inducible" GADD45ß 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 GADD45ß in the coordination of liver fatty acid uptake, through cytoplasmic retention of FABP1, ultimately impacting obesity-driven hyperglycaemia. In summary, fasting stress-induced GADD45ß represents a liver-specific molecular event promoting adaptive metabolic function.

A Glyoxalase-1 Knockdown Does Not Have Major Short Term Effects on Energy Expenditure and Atherosclerosis in Mice.

Objective. Glyoxalase-1 is an enzyme detoxifying methylglyoxal (MG). MG is a potent precursor of advanced glycation endproducts which are regarded to be a key player in micro- and macrovascular damage. Yet, the role of Glo1 in atherosclerosis remains unclear. In this study, the effect of Glo1 on mouse metabolism and atherosclerosis is evaluated. Methods. Glo1 knockdown mice were fed a high fat or a standard diet for 10 weeks. Body weight and composition were investigated by Echo MRI. The PhenoMaster system was used to measure the energy expenditure. To evaluate the impact of Glo1 on atherosclerosis, Glo1(KD) mice were crossed with ApoE-knockout mice and fed a high fat diet for 14 weeks. Results. Glo1 activity was significantly reduced in heart, liver, and kidney lysates derived from Glo1(KD) mice. Yet, there was no increase in methylglyoxal-derived AGEs in all organs analyzed. The Glo1 knockdown did not affect body weight or body composition. Metabolic studies via indirect calorimetry did not show significant effects on energy expenditure. Glo1(KD) mice crossed to ApoE(-/-) mice did not show enhanced formation of atherosclerosis. Conclusion. A Glo1 knockdown does not have major short term effects on the energy expenditure or the formation of atherosclerotic plaques.

Mice lacking neutral amino acid transporter B(0)AT1 (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 ß-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 B(0)AT1 (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 B(0)AT1 (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 B(0)AT1 could be a suitable target to treat type 2 diabetes.

Brown adipose tissue harbors a distinct sub-population of regulatory T cells.

Regulatory T (Treg) cells are critical determinants of both immune responses and metabolic control. Here we show that systemic ablation of Treg cells compromised the adaptation of whole-body energy expenditure to cold exposure, correlating with impairment in thermogenic marker gene expression and massive invasion of pro-inflammatory macrophages in brown adipose tissue (BAT). Indeed, BAT harbored a unique sub-set of Treg cells characterized by a unique gene signature. As these Treg cells respond to BAT activation upon cold exposure, this study defines a BAT-specific Treg sub-set with direct implications for the regulation of energy homeostasis in response to environmental stress.

Browning of white adipose tissue uncouples glucose uptake from insulin signaling.

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.

Hepatic transforming growth factor-ß 1 stimulated clone-22 D1 controls systemic cholesterol metabolism.

Disturbances in lipid homeostasis are hallmarks of severe metabolic disorders and their long-term complications, including obesity, diabetes, and atherosclerosis. Whereas elevation of triglyceride (TG)-rich very-low-density lipoproteins (VLDL) has been identified as a risk factor for cardiovascular complications, high-density lipoprotein (HDL)-associated cholesterol confers atheroprotection under obese and/or diabetic conditions. Here we show that hepatocyte-specific deficiency of transcription factor transforming growth factor ß 1-stimulated clone (TSC) 22 D1 led to a substantial reduction in HDL levels in both wild-type and obese mice, mediated through the transcriptional down-regulation of the HDL formation pathway in liver. Indeed, overexpression of TSC22D1 promoted high levels of HDL cholesterol in healthy animals, and hepatic expression of TSC22D1 was found to be aberrantly regulated in disease models of opposing energy availability. The hepatic TSC22D1 transcription factor complex may thus represent an attractive target in HDL raising strategies in obesity/diabetes-related dyslipidemia and atheroprotection.

Transcriptional cofactor TBLR1 controls lipid mobilization in white adipose tissue.

Lipid mobilization (lipolysis) in white adipose tissue (WAT) critically controls lipid turnover and adiposity in humans. While the acute regulation of lipolysis has been studied in detail, the transcriptional determinants of WAT lipolytic activity remain still largely unexplored. Here we show that the genetic inactivation of transcriptional cofactor transducin beta-like-related 1(TBLR1) blunts the lipolytic response of white adipocytes through the impairment of cAMP-dependent signal transduction. Indeed, mice lacking TBLR1 in adipocytes are defective in fasting-induced lipid mobilization and, when placed on a high-fat-diet, show aggravated adiposity, glucose intolerance, and insulin resistance. TBLR1 levels are found to increase under lipolytic conditions in WAT of both human patients and mice, correlating with serum free fatty acids (FFAs). As a critical regulator of WAT cAMP signaling and lipid mobilization, proper activity of TBLR1 in adipocytes might thus represent a critical molecular checkpoint for the prevention of metabolic dysfunction in subjects with obesity-related disorders.

Effects of increased renal tubular vascular endothelial growth factor (VEGF) on fibrosis, cyst formation, and glomerular disease.

The role of vascular endothelial growth factor (VEGF) in renal fibrosis, tubular cyst formation, and glomerular diseases is incompletely understood. We studied a new conditional transgenic mouse system [Pax8-rtTA/(tetO)(7)VEGF], which allows increased tubular VEGF production in adult mice. The following pathology was observed. The interstitial changes consisted of a ubiquitous proliferation of peritubular capillaries and fibroblasts, followed by deposition of matrix leading to a unique kind of fibrosis, ie, healthy tubules amid a capillary-rich dense fibrotic tissue. In tubular segments with high expression of VEGF, cysts developed that were surrounded by a dense network of peritubular capillaries. The glomerular effects consisted of a proliferative enlargement of glomerular capillaries, followed by mesangial proliferation. This resulted in enlarged glomeruli with loss of the characteristic lobular structure. Capillaries became randomly embedded into mesangial nodules, losing their filtration surface. Serum VEGF levels were increased, whereas endogenous VEGF production by podocytes was down-regulated. Taken together, this study shows that systemic VEGF interferes with the intraglomerular cross-talk between podocytes and the endocapillary compartment. It suppresses VEGF secretion by podocytes but cannot compensate for the deficit. VEGF from podocytes induces a directional effect, attracting the capillaries to the lobular surface, a relevant mechanism to optimize filtration surface. Systemic VEGF lacks this effect, leading to severe deterioration in glomerular architecture, similar to that seen in diabetic nephropathy.

Sulfated glycosphingolipid as mediator of phagocytosis: SM4s enhances apoptotic cell clearance and modulates macrophage activity.

Sulfoglycolipids are present on the surface of a variety of cells. The sulfatide SM4s is increased in lung, renal, and colon cancer and is associated with an adverse prognosis, possibly due to a low immunoreactivity of the tumor. As macrophages significantly contribute to the inflammatory infiltrate in malignancies, we postulated that SM4s may modulate macrophage function. We have investigated the effect of SM4s on the uptake of apoptotic tumor cells, macrophage cytokine profile, and receptor expression. Using flow cytometry and microscopic analyses, we found that coating apoptotic murine carcinoma cells from the colon and kidney with SM4s promoted their phagocytosis by murine macrophages up to 3-fold ex vivo and in vivo. This increased capacity was specifically inhibited by preincubation of macrophages with oxidized or acetylated low density lipoprotein and maleylated albumin, indicating involvement of scavenger receptors in this interaction. The uptake of SM4s-coated apoptotic cells significantly enhanced macrophage production of TGF-beta1, expression of P-selectin, and secretion of IL-6. These data suggest that SM4s within tumors may promote apoptotic cell removal and alter the phenotype of tumor-associated macrophages.

Novel class of glycosphingolipids involved in male fertility.

Mice require testicular glycosphingolipids (GSLs) for proper spermatogenesis. Mutant mice strains deficient in specific genes encoding biosynthetic enzymes of the GSL pathway including Galgt1 (encoding GM2 synthase) and Siat9 (encoding GM3 synthase) have been established lacking various overlapping subsets of GSLs. Although male Galgt1-/- mice are infertile, male Siat9-/- mice are fertile. Interestingly, GSLs thought to be essential for male spermatogenesis are not synthesized in either of these mice strains. Hence, these GSLs cannot account for the different phenotypes. A novel class of GSLs was observed composed of eight fucosylated molecules present in fertile but not in infertile mutant mice. These GSLs contain polyunsaturated very long chain fatty acid residues in their ceramide moieties. GSLs of this class are expressed differentially in testicular germ cells. More importantly, the neutral subset of this new GSL class strictly correlates with male fertility. These data implicate polyunsaturated, fucosylated GSLs as essential for spermatogenesis and male mouse fertility.

Chemokines bind to sulfatides as revealed by surface plasmon resonance.

Chemokines bind to sulfated cell surface glycosaminoglycans and thereby modulate signaling mediated by G-protein-coupled seven-transmembrane domain chemokine receptors. Similar to glycosaminoglycans, sulfated oligosaccharides are also exposed on the cell surface by sulfatides, a class of glycosphingolipids. We have now identified sulfated glycosphingolipids (sulfatides) as novel binding partners for chemokines. Using surface plasmon resonance (SPR), the binding of proinflammatory and homeostatic chemokines to glycosphingolipids, in particular sulfatides, was investigated. Chemokines were immobilized while glycosphingolipids or additional phospholipids incorporated into liposomes were applied as soluble analytes. A specific affinity of the chemokines MCP-1/CCL2, IL-8/CXCL8, SDF-1alpha/CXCL12, MIP-1alpha/CCL3 and MIP-1beta/CCL4 to the sulfatides SM4s, SM3, SM2a and SB2, SB1a was detected. No significant interactions with the chemokines were observed for gangliosides, neutral glycosphingolipids or phospholipids. Chemokine receptors have been associated with the detergent-insoluble fraction supposed to contain 'rafts', i.e., glycosphingolipid enriched microdomains of the cell surface. Accordingly, the data suggest that early chemokine receptor signaling may take place in the vicinity of sulfated glycosphingolipids on the cell surface, whereby these sulfatides could modulate the chemokine receptor-mediated cell activation signal.

Common cholesteryl ester transfer protein gene polymorphisms and the effect of atorvastatin therapy in type 2 diabetes.

OBJECTIVE: The cholesteryl ester transfer protein (CETP) plays a key role in the remodeling of triglyceride (TG)-rich and HDL particles. Sequence variations in the CETP gene may interfere with the effect of lipid-lowering treatment in type 2 diabetes. RESEARCH DESIGN AND METHODS: We performed a 30-week randomized double-blind placebo-controlled trial with atorvastatin 10 mg (A10) and 80 mg (A80) in 217 unrelated patients with diabetes. RESULTS: CETP TaqIB and A-629C polymorphisms were tightly concordant (P < 0.001). At baseline, B1B1 carriers had lower plasma HDL cholesterol (0.99 +/- 0.2 vs. 1.11 +/- 0.2 mmol/l, P < 0.05), higher CETP mass (2.62 +/- 0.8 vs. 2.05 +/- 0.4 mg/l, P < 0.001), and slightly increased, though not significant, plasma TGs (2.7 +/- 1.05 vs. 2.47 +/- 0.86, P = 0.34) compared with B2B2 carriers. Atorvastatin treatment significantly reduced CETP mass dose-dependently by 18% (A10) and 29% (A80; both vs. placebo P < 0.001, A10-A80 P < 0.001). CETP mass and activity were strongly correlated (r = 0.854, P < 0.0001). CETP TaqIB polymorphism appeared to modify the effect of atorvastatin on HDL cholesterol elevation (B1B1 7.2%, B1B2 6.1%, B2B2 0.5%; P < 0.05), TG reduction (B1B1 39.7%, B1B2 38.4%, B2B2 18.4%; P = 0.08), and CETP mass reduction (B1B1 32.1%, B1B2 29.6%, B2B2 21.9%; P = 0.27, NS). Similar results were obtained for the A-629C polymorphism. CONCLUSIONS: In conclusion, the B1B1/CC carriers of the CETP polymorphisms have a more atherogenic lipid profile, including low HDL, and they respond better to statin therapy. These results favor the hypothesis that CETP polymorphisms modify the effect of statin treatment and may help to identify patients who will benefit most from statin therapy.