OBJECTIVE

Peripheral insulin resistance is linked to an increase in reactive oxygen species (ROS), leading in part to the production of reactive lipid aldehydes that modify the side chains of protein amino acids in a reaction termed protein carbonylation. The primary enzymatic method for lipid aldehyde detoxification is via glutathione S-transferase A4 (GSTA4) dependent glutathionylation. The objective of this study was to evaluate the expression of GSTA4 and the role(s) of protein carbonylation in adipocyte function.


RESEARCH DESIGN AND METHODS

GSTA4-silenced 3T3-L1 adipocytes and GSTA4-null mice were evaluated for metabolic processes, mitochondrial function, and reactive oxygen species production. GSTA4 expression in human obesity was evaluated using microarray analysis.


RESULTS

GSTA4 expression is selectively downregulated in adipose tissue of obese insulin-resistant C57BL/6J mice and in human obesity-linked insulin resistance. Tumor necrosis factor- treatment of 3T3-L1 adipocytes decreased GSTA4 expression, and silencing GSTA4 mRNA in cultured adipocytes resulted in increased protein carbonylation, increased mitochondrial ROS, dysfunctional state 3 respiration, and altered glucose transport and lipolysis. Mitochondrial function in adipocytes of lean or obese GSTA4-null mice was significantly compromised compared with wild-type controls and was accompanied by an increase in superoxide anion.


CONCLUSIONS

These results indicate that downregulation of GSTA4 in adipose tissue leads to increased protein carbonylation, ROS production, and mitochondrial dysfunction and may contribute to the development of insulin resistance and type 2 diabetes.

 

OBJECTIVE

It is becoming apparent that there is a strong link between taste perception and energy homeostasis. Recent evidence implicates gut-related hormones in taste perception, including glucagon-like peptide 1 and vasoactive intestinal peptide (VIP). We used VIP knockout mice to investigate VIP’s specific role in taste perception and connection to energy regulation.


RESEARCH DESIGN AND METHODS

Body weight, food intake, and plasma levels of multiple energy-regulating hormones were measured and pancreatic morphology was determined. In addition, the immunocytochemical profile of taste cells and gustatory behavior were examined in wild-type and VIP knockout mice.


RESULTS

VIP knockout mice demonstrate elevated plasma glucose, insulin, and leptin levels, with no islet β-cell number/topography alteration. VIP and its receptors (VPAC1, VPAC2) were identified in type II taste cells of the taste bud, and VIP knockout mice exhibit enhanced taste preference to sweet tastants. VIP knockout mouse taste cells show a significant decrease in leptin receptor expression and elevated expression of glucagon-like peptide 1, which may explain sweet taste preference of VIP knockout mice.


CONCLUSIONS

This study suggests that the tongue can play a direct role in modulating energy intake to correct peripheral glycemic imbalances. In this way, we could view the tongue as a sensory mechanism that is bidirectionally regulated and thus forms a bridge between available foodstuffs and the intricate hormonal balance in the animal itself.

 

OBJECTIVE

Diabetic dyslipoproteinemia is characterized by low HDL cholesterol and high triglycerides. We examined the association of lipoprotein particle size and concentration measured by nuclear magnetic resonance (NMR) spectroscopy with clinical type 2 diabetes.


RESEARCH DESIGN AND METHODS

This was a prospective study of 26,836 initially healthy women followed for 13 years for incident type 2 diabetes (n = 1,687). Baseline lipids were measured directly and lipoprotein size and concentration by NMR. Cox regression models included nonlipid risk factors (age, race, smoking, exercise, education, menopause, blood pressure, BMI, family history, A1C, and C-reactive protein). NMR lipoproteins were also examined after further adjusting for standard lipids.


RESULTS

Incident diabetes was significantly associated with baseline HDL cholesterol, triglycerides, and NMR-measured size and concentration of LDL, IDL, HDL, and VLDL particles. The associations of these particles differed substantially by size. Small LDLNMR and small HDLNMR were positively associated with diabetes (quintile 5 vs. 1 [adjusted hazard ratios and 95% CIs], 4.04 [3.21–5.09] and 1.84 [1.54–2.19], respectively). By contrast, large LDLNMR and large HDLNMR were inversely associated (quintile 1 vs. 5, 2.50 [2.12–2.95] and 4.51 [3.68–5.52], respectively). For VLDLNMR, large particles imparted higher risk than small particles (quintile 5 vs. 1, 3.11 [2.35–4.11] and 1.31 [1.10–1.55], respectively). Lipoprotein particle size remained significant after adjusting for standard lipids and nonlipid factors.


CONCLUSIONS

In this prospective study of women, NMR lipoprotein size and concentrations were associated with incident type 2 diabetes and remained significant after adjustment for established risk factors, including HDL cholesterol and triglycerides.

 

OBJECTIVE

Maternal adiponectin levels are reduced and placental nutrient transporters are upregulated in obesity and gestational diabetes mellitus; however, the effects of adiponectin on placental function are unknown. We hypothesized that adiponectin regulates placental amino acid transport.


RESEARCH DESIGN AND METHODS

Human primary trophoblast cells were cultured and incubated with globular adiponectin (gAd) or full-length adiponectin (fAd) alone or in combination with insulin. System A and L amino acid transport and SNAT1, SNAT2, and SNAT4 isoform expression was measured. The activity of the AMP-activated protein kinase (AMPK), phosphatidylinositol 3 kinase–AKT, and peroxisome proliferator–activated receptor- (PPAR) signaling pathways was determined.


RESULTS

In the absence of insulin, gAd stimulated AMPK Thr172 phosphorylation, SNAT2 protein expression, and system A activity. This effect appeared to be mediated by interleukin-6 release and signal transducer and activator of transcription 3 (STAT3) signaling because gAd failed to stimulate system A in cells in which STAT3 had been silenced using small interfering RNA. fAd alone had no effect on system A activity or SNAT expression. Insulin increased AKT and insulin receptor substrate 1 (IRS-1) phosphorylation, system A activity, and SNAT2 expression. When combined with insulin, gAd did not affect system A activity or SNAT expression. In contrast, fAd abolished insulin-stimulated AKT Thr308 and IRS-1 Tyr612 phosphorylation, system A activity, and SNAT2 expression. Furthermore, fAd increased PPAR expression and PPAR (Ser21) phosphorylation.


CONCLUSIONS

In contrast to the insulin-sensitizing actions of adiponectin in liver and muscle reported in the literature, fAd attenuates insulin signaling in primary human trophoblast cells. As a result, fAd inhibits insulin-stimulated amino acid transport, which may have important implications for placental nutrient transport and fetal growth in pregnancy complications associated with altered maternal adiponectin levels.

 

OBJECTIVE

To identify, localize, and determine M1/M2 polarization of epidydimal adipose tissue (eAT) macrophages (s) during high-fat diet (HFD)-induced obesity.


RESEARCH DESIGN AND METHODS

Male C57BL/6 mice were fed an HFD (60% fat kcal) or low-fat diet (LFD) (10% fat kcal) for 8 or 12 weeks. eATMs (F4/80+ cells) were characterized by in vivo fluorescent labeling, immunohistochemistry, fluorescence-activated cell sorting, and quantitative PCR.


RESULTS

Recruited interstitial macrophage galactose-type C-type lectin (MGL)1+/CD11c and crown-like structure–associated MGL1/CD11c+ and MGL1med/CD11c+ eATMs were identified after 8 weeks of HFD. MGL1med/CD11c+ cells comprised ~65% of CD11c+ eATMs. CD11c+ eATMs expressed a mixed M1/M2 profile, with some M1 transcripts upregulated (IL-12p40 and IL-1β), others downregulated (iNOS, caspase-1, MCP-1, and CD86), and multiple M2 and matrix remodeling transcripts upregulated (arginase-1, IL-1Ra, MMP-12, ADAM8, VEGF, and Clec-7a). At HFD week 12, each eATM subtype displayed an enhanced M2 phenotype as compared with HFD week 8. CD11c+ subtypes downregulated IL-1β and genes mediating antigen presentation (I-a, CD80) and upregulated the M2 hallmark Ym-1 and genes promoting oxidative metabolism (PGC-1) and adipogenesis (MMP-2). MGL1med/CD11c+ eATMs upregulated additional M2 genes (IL-13, SPHK1, CD163, LYVE-1, and PPAR-). MGL1med/CD11c+ ATMs expressing elevated PGC-1, PPAR-, and Ym-1 transcripts were selectively enriched in eAT of obese mice fed pioglitazone for 6 days, confirming the M2 features of the MGL1med/CD11c+ eATM transcriptional profile and implicating PPAR activation in its elicitation.


CONCLUSIONS

These results 1) redefine the phenotypic potential of CD11c+ eATMs and 2) suggest previously unappreciated phenotypic and functional commonality between murine and human ATMs in the development of obesity and its complications.

 

OBJECTIVE

Type 1 diabetes is a chronic endocrine disorder in which enteroviruses, such as coxsackie B viruses and echoviruses, are possible environmental factors that can trigger or accelerate disease. The development or acceleration of type 1 diabetes depends on the balance between autoreactive effector T-cells and regulatory T-cells. This balance is particularly influenced by dendritic cells (DCs). The goal of this study was to investigate the interaction between enterovirus-infected human pancreatic islets and human DCs.


RESEARCH DESIGN AND METHODS

In vitro phagocytosis of human or porcine primary islets or Min6 mouse insuloma cells by DCs was investigated by flow cytometry and confocal analysis. Subsequent innate DC responses were monitored by quantitative PCR and Western blotting of interferon-stimulated genes (ISGs).


RESULTS

In this study, we show that both mock- and coxsackievirus B3 (CVB3)-infected human and porcine pancreatic islets were efficiently phagocytosed by human monocyte–derived DCs. Phagocytosis of CVB3-infected, but not mock-infected, human and porcine islets resulted in induction of ISGs in DCs, including the retinoic acid–inducible gene (RIG)-I–like helicases (RLHs), RIG-I, and melanoma differentiation–associated gene 5 (Mda5). Studies with murine Min6 insuloma cells, which were also efficiently phagocytosed, revealed that increased ISG expression in DCs upon encountering CVB-infected cells resulted in an antiviral state that protected DCs from subsequent enterovirus infection. The observed innate antiviral responses depended on RNA within the phagocytosed cells, required endosomal acidification, and were type I interferon dependent.


CONCLUSIONS

Human DCs can phagocytose enterovirus-infected pancreatic cells and subsequently induce innate antiviral responses, such as induction of RLHs. These responses may have important consequences for immune homeostasis in vivo and may play a role in the etiology of type 1 diabetes.

 

OBJECTIVE

The aim of the study was to elucidate the cellular mechanism underlying the suppression of glucose-induced insulin secretion in mice fed a high-fat diet (HFD) for 15 weeks.


RESEARCH DESIGN AND METHODS

C57BL6J mice were fed a HFD or a normal diet (ND) for 3 or 15 weeks. Plasma insulin and glucose levels in vivo were assessed by intraperitoneal glucose tolerance test. Insulin secretion in vitro was studied using static incubations and a perfused pancreas preparation. Membrane currents, electrical activity, and exocytosis were examined by patch-clamp technique measurements. Intracellular calcium concentration ([Ca2+]i) was measured by microfluorimetry. Total internal reflection fluorescence microscope (TIRFM) was used for optical imaging of exocytosis and submembrane depolarization-evoked [Ca2+]i. The functional data were complemented by analyses of histology and gene transcription.


RESULTS

After 15 weeks, but not 3 weeks, mice on HFD exhibited hyperglycemia and hypoinsulinemia. Pancreatic islet content and β-cell area increased 2- and 1.5-fold, respectively. These changes correlated with a 20–50% reduction of glucose-induced insulin secretion (normalized to insulin content). The latter effect was not associated with impaired electrical activity or [Ca2+]i signaling. Single-cell capacitance and TIRFM measurements of exocytosis revealed a selective suppression (>70%) of exocytosis elicited by short (50 ms) depolarization, whereas the responses to longer depolarizations were (500 ms) less affected. The loss of rapid exocytosis correlated with dispersion of Ca2+ entry in HFD β-cells. No changes in gene transcription of key exocytotic protein were observed.


CONCLUSIONS

HFD results in reduced insulin secretion by causing the functional dissociation of voltage-gated Ca2+ entry from exocytosis. These observations suggest a novel explanation to the well-established link between obesity and diabetes.

 
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