The role of vasodilator-stimulated phosphoprotein (VASP) in the control of hepatic gluconeogenic gene expression.

During periods in which glucose absorption from the gastrointestinal (GI) tract is insufficient to meet body requirements, hepatic gluconeogenesis plays a key role to maintain normal blood glucose levels. The current studies investigated the role in this process played by vasodilatory-associated phosphoprotein (VASP), a protein that is phosphorylated in hepatocytes by cAMP/protein kinase A (PKA), a key mediator of the action of glucagon. We report that following stimulation of hepatocytes with 8Br-cAMP, phosphorylation of VASP preceded induction of genes encoding key gluconeogenic enzymes, glucose-6-phosphatase (G6p) and phosphoenolpyruvate carboxykinase (Pck1), and that VASP overexpression enhanced this gene induction.

Fat-specific protein 27α inhibits autophagy-dependent lipid droplet breakdown in white adipocytes.

Aims/introduction: Fat-specific protein 27 (FSP27) α is the major isoform of FSP27 in white adipose tissue (WAT), and is essential for large unilocular lipid droplet (LD) formation in white adipocytes. In contrast, FSP27β is abundantly expressed in brown adipose tissue (BAT), and plays an important role in small multilocular LD formation. In FSP27 KO mice in which FSP27α and β are both depleted, WAT is characterized by multilocular LD formation, and by increased mitochondrial abundance and energy expenditure, whereas BAT conversely manifests large oligolocular LDs and reduced energy expenditure.

Effects of Insulin Degludec and Insulin Glargine U300 on Day-to-Day Fasting Plasma Glucose Variability in Individuals with Type 1 Diabetes: A Multicenter, Randomized, Crossover Study (Kobe Best Basal Insulin Study 2).

Introduction: Administered basal insulin markedly influences the fasting plasma glucose (FPG) level of individuals with type 1 diabetes. Insulin degludec (IDeg) and insulin glargine U300 (IGlar U300) are now available as ultra-long-acting insulin formulations, but whether or how their glucose-stabilizing effects differ remains unclear. We will compare the effects of these basal insulins on parameters related to blood glucose control, with a focus on day-to-day glycemic variability, in individuals with type 1 diabetes treated with multiple daily injections.

Cell death-inducing DNA fragmentation factor A-like effector A and fat-specific protein 27β coordinately control lipid droplet size in brown adipocytes.

Adipose tissue stores neutral lipids and is a major metabolic organ involved in regulating whole-body energy homeostasis. Triacylglycerol is stored as unilocular large lipid droplets (LDs) in white adipocytes and as multilocular small LDs in brown adipocytes. Proteins of the cell death-inducing DNA fragmentation factor A-like effector (Cide) family include CideA, CideB, and fat-specific protein of 27 (FSP27).

Colonic Pro-inflammatory Macrophages Cause Insulin Resistance in an Intestinal Ccl2/Ccr2-Dependent Manner.

High-fat diet (HFD) induces low-grade chronic inflammation and insulin resistance. However, little is known about the mechanism underlying HFD-induced chronic inflammation in peripheral insulin-responsive tissues. Here, we show that colonic pro-inflammatory macrophages regulate insulin sensitivity under HFD conditions.

Negatively-charged residues in the polar carboxy-terminal region in FSP27 are indispensable for expanding lipid droplets.

FSP27 has an important role in large lipid droplet (LD) formation because it exchanges lipids at the contact site between LDs. In the present study, we clarify that the amino-terminal domain of FSP27 (amino acids 1-130) is dispensable for LD enlargement, although it accelerates LD growth. LD expansion depends on the carboxy-terminal domain of FSP27 (amino acids 131-239).

M2 Macrophage Polarization Mediates Anti-inflammatory Effects of Endothelial Nitric Oxide Signaling.

Endothelial nitric oxide (NO) signaling plays a physiological role in limiting obesity-associated insulin resistance and inflammation. This study was undertaken to investigate whether this NO effect involves polarization of macrophages toward an anti-inflammatory M2 phenotype. Mice with transgenic endothelial NO synthase overexpression were protected against high-fat diet (HFD)-induced hepatic inflammation and insulin resistance, and this effect was associated with reduced proinflammatory M1 and increased anti-inflammatory M2 activation of Kupffer cells.

Vasodilator-stimulated phosphoprotein protects against vascular inflammation and insulin resistance.

Among the pleotropic effects of endothelial nitric oxide (NO) is protection against vascular inflammation during high-fat diet (HFD) feeding. The current work investigated the role of the enzyme vasodilatory-stimulated phosphoprotein (VASP) as a downstream mediator of the anti-inflammatory effect of NO signaling in vascular tissue. Relative to mice fed a low-fat diet (LFD), levels of VASP Ser(239) phosphorylation, a marker of VASP activation, were dramatically reduced in aortic tissue of mice with obesity induced by consuming a HFD.

Recent advances in obesity-induced inflammation and insulin resistance.

It has been demonstrated in rodents and humans that chronic inflammation characterized by macrophage infiltration occurs mainly in adipose tissue or liver during obesity, in which activation of immune cells is closely associated with insulin sensitivity. Macrophages can be classified as classically activated (M1) macrophages that support microbicidal activity or alternatively activated (M2) macrophages that support allergic and antiparasitic responses. In the context of insulin action, M2 macrophages sustain insulin sensitivity by secreting IL-4 and IL-10, while M1 macrophages induce insulin resistance through the secretion of proinflammatory cytokines, such as TNFα.

VASP increases hepatic fatty acid oxidation by activating AMPK in mice.

Activation of AMP-activated protein kinase (AMPK) signaling reduces hepatic steatosis and hepatic insulin resistance; however, its regulatory mechanisms are not fully understood. In this study, we sought to determine whether vasodilator-stimulated phosphoprotein (VASP) signaling improves lipid metabolism in the liver and, if so, whether VASP's effects are mediated by AMPK. We show that disruption of VASP results in significant hepatic steatosis as a result of significant impairment of fatty acid oxidation, VLDL-triglyceride (TG) secretion, and AMPK signaling.

Apolipoprotein A-I attenuates palmitate-mediated NF-κB activation by reducing Toll-like receptor-4 recruitment into lipid rafts.

While high-density lipoprotein (HDL) is known to protect against a wide range of inflammatory stimuli, its anti-inflammatory mechanisms are not well understood. Furthermore, HDL's protective effects against saturated dietary fats have not been previously described. In this study, we used endothelial cells to demonstrate that while palmitic acid activates NF-κB signaling, apolipoprotein A-I, (apoA-I), the major protein component of HDL, attenuates palmitate-induced NF-κB activation.

Endothelial NO/cGMP/VASP signaling attenuates Kupffer cell activation and hepatic insulin resistance induced by high-fat feeding.

Objective: Proinflammatory activation of Kupffer cells is implicated in the effect of high-fat feeding to cause liver insulin resistance. We sought to determine whether reduced endothelial nitric oxide (NO) signaling contributes to the effect of high-fat feeding to increase hepatic inflammatory signaling and if so, whether this effect 1) involves activation of Kupffer cells and 2) is ameliorated by increased NO signaling.

Research Design And Methods: Effect of NO/cGMP signaling on hepatic inflammation and on isolated Kupffer cells was examined in C57BL/6 mice, eNos(-/-) mice, and Vasp(-/-) mice fed a low-fat or high-fat diet.

Reduced vascular nitric oxide-cGMP signaling contributes to adipose tissue inflammation during high-fat feeding.

Objective: Obesity is characterized by chronic inflammation of adipose tissue, which contributes to insulin resistance and diabetes. Although nitric oxide (NO) signaling has antiinflammatory effects in the vasculature, whether reduced NO contributes to adipose tissue inflammation is unknown. We sought to determine whether (1) obesity induced by high-fat (HF) diet reduces endothelial nitric oxide signaling in adipose tissue, (2) reduced endothelial nitric oxide synthase (eNOS) signaling is sufficient to induce adipose tissue inflammation independent of diet, and (3) increased cGMP signaling can block adipose tissue inflammation induced by HF feeding.

Reduced NO-cGMP signaling contributes to vascular inflammation and insulin resistance induced by high-fat feeding.

Objective: Diet-induced obesity (DIO) in mice causes vascular inflammation and insulin resistance that are accompanied by decreased endothelial-derived NO production. We sought to determine whether reduced NO-cGMP signaling contributes to the deleterious effects of DIO on the vasculature and, if so, whether these effects can be blocked by increased vascular NO-cGMP signaling.

Methods And Results: By using an established endothelial cell culture model of insulin resistance, exposure to palmitate, 100 micromol/L, for 3 hours induced both cellular inflammation (activation of IKK beta-nuclear factor-kappaB) and impaired insulin signaling via the insulin receptor substrate-phosphatidylinositol 3-kinase pathway.

An increase in the circulating concentration of monocyte chemoattractant protein-1 elicits systemic insulin resistance irrespective of adipose tissue inflammation in mice.

Chronic inflammation in adipose tissue is thought to be important for the development of insulin resistance in obesity. Furthermore, the level of monocyte chemoattractant protein-1 (MCP-1) is increased not only in adipose tissue but also in the circulation in association with obesity. However, it has remained unclear to what extent the increased circulating level of MCP-1 contributes to insulin resistance.

The t-SNAREs syntaxin4 and SNAP23 but not v-SNARE VAMP2 are indispensable to tether GLUT4 vesicles at the plasma membrane in adipocyte.

SNARE proteins (VAMP2, syntaxin4, and SNAP23) have been thought to play a key role in GLUT4 trafficking by mediating the tethering, docking and subsequent fusion of GLUT4-containing vesicles with the plasma membrane. The precise functions of these proteins have remained elusive, however. We have now shown that depletion of the vesicle SNARE (v-SNARE) VAMP2 by RNA interference in 3T3-L1 adipocytes inhibited the fusion of GLUT4 vesicles with the plasma membrane but did not affect tethering of the vesicles to the membrane.

Activation of NF-kappaB by palmitate in endothelial cells: a key role for NADPH oxidase-derived superoxide in response to TLR4 activation.

Objective: We investigated whether NADPH oxidase-dependent production of superoxide contributes to activation of NF-kappaB in endothelial cells by the saturated free fatty acid palmitate.

Methods And Results: After incubation of human endothelial cells with palmitate at a concentration known to induce cellular inflammation (100 mumol/L), we measured superoxide levels by using electron spin resonance spectroscopy and the spin trap 1-hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine (CMH). Palmitate exposure induced a >2-fold increase in superoxide levels, an effect associated with activation of NF-kappaB signaling as measured by phospho-IkappaBalpha, NF-kappaB activity, IL-6, and ICAM expression.

FSP27 contributes to efficient energy storage in murine white adipocytes by promoting the formation of unilocular lipid droplets.

White adipocytes are unique in that they contain large unilocular lipid droplets that occupy most of the cytoplasm. To identify genes involved in the maintenance of mature adipocytes, we expressed dominant-negative PPARgamma in 3T3-L1 cells and performed a microarray screen. The fat-specific protein of 27 kDa (FSP27) was strongly downregulated in this context.

Increased insulin action in SKIP heterozygous knockout mice.

Insulin controls glucose homeostasis and lipid metabolism, and insulin impairment plays a critical role in the pathogenesis of diabetes mellitus. Human skeletal muscle and kidney enriched inositol polyphosphate phosphatase (SKIP) is a member of the phosphatidylinositol 3,4,5-trisphosphate phosphatase family (T. Ijuin et al.

MCP-1 contributes to macrophage infiltration into adipose tissue, insulin resistance, and hepatic steatosis in obesity.

Adipocytes secrete a variety of bioactive molecules that affect the insulin sensitivity of other tissues. We now show that the abundance of monocyte chemoattractant protein-1 (MCP-1) mRNA in adipose tissue and the plasma concentration of MCP-1 were increased both in genetically obese diabetic (db/db) mice and in WT mice with obesity induced by a high-fat diet. Mice engineered to express an MCP-1 transgene in adipose tissue under the control of the aP2 gene promoter exhibited insulin resistance, macrophage infiltration into adipose tissue, and increased hepatic triglyceride content.