Search

Chronic HFD intake induces low-grade inflammation in the hypothalamus, which is characterized by proinflammatory cytokine overproduction. This process occurs, at least in part, via TLR4 activation by circulant saturated fatty acids. The TLR4 signaling in the brain is mediated by the TLR4 interactor with leucine-rich repeats (TRIL), an upstream accessory protein. Our main purpose was to determine the putative involvement of TRIL in diet-induced hypothalamic inflammation. We employed male, 8-12 week-old C57BL and POMCCRE mice fed on chow or HFD. The mRNA levels in the hypothalamus were measured by RT-PCR, western blot analyses was used for determination of protein content and immunofluorescence microscopy for evaluate the distribution of TRIL in arcuate nucleus (ARC) of hypothalamus and leptin signaling in POMC-expressing neurons. Finally, bilateral viral injections were performed to non-specific knockdown of TRIL in ARC using shRNA-based lentivirus and Cre-dependent AAV to knockdown TRIL specifically in POMC neurons. The non-specific knockdown of TRIL in the ARC of mice fed on HFD attenuated body weight gain despite no alterations in food intake, improved glucose homeostasis and increased energy expenditure. Moreover, nlrp3, il1β and hspa5 mRNA expression were decreased upon knockdown of TRIL. POMC-specific knockdown of TRIL reduced body fat with no changes in food intake or body weight gain in mice fed on HFD for 8 weeks. The inhibition of TRIL in POMC neurons resulted in a trend of improved leptin signaling in those neurons. We also found increased expression of thermogenic genes in the iBAT and improved fasting glucose. POMC-specific inhibition of TRIL in mice fed on HFD for long-term (24 weeks) did not prevent POMC loss or diminishes cleaved-caspase 3 in ARC. Collectively our results suggest that TRIL is involved in the TLR4-mediated early response to dietary fats and TRIL targeting counteract hypothalamic inflammation and partially restores metabolic homeostasis. Disclosure A. Moura-Assis: None. J. Junior: None. J.M. Gaspar: None. L. Velloso: None. P.S. Nogueira: None. Funding São Paulo Research Foundation (2016/01245-5)

On the basis of the recommendation of the American Diabetes Association’s Panel on Ethical Scientific Programs (ESP), the American Diabetes Association, the publisher of Diabetes , is issuing this expression of concern to alert readers to questions about the reliability of the data in the above-cited article. After readers of the journal contacted Diabetes about potentially duplicated images in the article, the ESP reviewed the following issues: Prada et al. FEBS Lett …

Mutation of tub gene in mice induces obesity, suggesting that tub could be an important regulator of energy balance. In the current study, we investigated whether insulin, leptin, and obesity can modulate Tub in vivo in hypothalamic nuclei, and we investigated possible consequences on energy balance, neuropeptide expression, and hepatic glucose metabolism. Food intake, metabolic characteristics, signaling proteins, and neuropeptide expression were measured in response to fasting and refeeding, intracerebroventricular insulin and leptin, and Tub antisense oligonucleotide (ASO). Tub tyrosine phosphorylation (Tub-p-tyr) is modulated by nutritional status. Tub is a substrate of insulin receptor tyrosine kinase (IRTK) and leptin receptor (LEPR)-Janus kinase 2 (JAK2) in hypothalamic nuclei. After leptin or insulin stimulation, Tub translocates to the nucleus. Inhibition of Tub expression in hypothalamus by ASO increased food intake, fasting blood glucose, and hepatic glucose output, decreased O(2) consumption, and blunted the effect of insulin or leptin on proopiomelanocortin, thyroid-releasing hormone, melanin-concentrating hormone, and orexin expression. In hypothalamus of mice administered a high-fat diet, there is a reduction in leptin and insulin-induced Tub-p-tyr and nuclear translocation, which is reversed by reducing protein tyrosine phosphatase 1B expression. These results indicate that Tub has a key role in the control of insulin and leptin effects on food intake, and the modulation of Tub may contribute to insulin and leptin resistance in DIO mice.

Type 2 diabetes (T2D) results from the combination of insulin resistance and a relative deficiency of insulin secretion (1,2). Over the last 20 years, clinical and experimental studies have advanced our understanding of the cause of insulin resistance, revealing the existence of subclinical inflammation in subjects with increased adiposity (3,4). Inflammatory cytokines produced in the context of this metabolic inflammation activate serine/threonine kinases that target proteins of the insulin signaling pathway, rendering them unresponsive to the insulin signal (5,6). Unfortunately, despite great advances obtained in the characterization of the pathophysiology of T2D, no anti-inflammatory approaches have been developed as therapeutic options for this disease. Excessive nutrient consumption, particularly fatty acids, is regarded as one of the main triggers of metabolic inflammation (7). Among the mechanisms identified as a link between dietary fats, inflammation, and insulin resistance, endoplasmic reticulum (ER) stress has received special attention; it occupies a pivotal position, as it simultaneously acts as a target and a trigger of a number of inflammatory and metabolic events that are closely related to insulin resistance (8,9). On the one hand, ER stress can be induced by either excessive nutrient load (10) or extracellular inflammatory signals (11); alternatively, the unfolded protein response generated to reestablish ER homeostasis can activate inflammatory signaling proteins, such as Jun NH2-terminal kinase (JNK) and inhibitory κB kinase (IKK), thereby inducing transcription of inflammatory genes, such as Tnfa and Il6 (10). A recent study provided an important advance in this field when it identified the double-stranded RNA–dependent kinase (PKR) as a protein that integrates inflammation, nutrient overload, and ER stress (12). PKR was originally described as an intracellular sensor of viral infection (13), whose activation leads to the simultaneous …

OBJECTIVE In obesity, an increased macrophage infiltration in adipose tissue occurs, contributing to low-grade inflammation and insulin resistance. Epidermal growth factor receptor (EGFR) mediates both chemotaxis and proliferation in monocytes and macrophages. However, the role of EGFR inhibitors in this subclinical inflammation has not yet been investigated. We investigated, herein, in vivo efficacy and associated molecular mechanisms by which PD153035, an EGFR tyrosine kinase inhibitor, improved diabetes control and insulin action. RESEARCH DESIGN AND METHODS The effect of PD153035 was investigated on insulin sensitivity, insulin signaling, and c-Jun NH2-terminal kinase (JNK) and nuclear factor (NF)-κB activity in tissues of high-fat diet (HFD)-fed mice and also on infiltration and the activation state of adipose tissue macrophages (ATMs) in these mice. RESULTS PD153035 treatment for 1 day decreased the protein expression of inducible nitric oxide synthase, tumor necrosis factor (TNF)-α, and interleukin (IL)-6 in the stroma vascular fraction, suggesting that this drug reduces the M1 proinflammatory state in ATMs, as an initial effect, in turn reducing the circulating levels of TNF-α and IL-6, and initiating an improvement in insulin signaling and sensitivity. After 14 days of drug administration, there was a marked improvement in glucose tolerance; a reduction in insulin resistance; a reduction in macrophage infiltration in adipose tissue and in TNF-α, IL-6, and free fatty acids; accompanied by an improvement in insulin signaling in liver, muscle, and adipose tissue; and also a decrease in insulin receptor substrate-1 Ser307 phosphorylation in JNK and inhibitor of NF-κB kinase (IKKβ) activation in these tissues. CONCLUSIONS Treatment with PD153035 improves glucose tolerance, insulin sensitivity, and signaling and reduces subclinical inflammation in HFD-fed mice.

OBJECTIVE—A high-protein diet (HPD) is known to promote the reduction of body fat, but the mechanisms underlying this change are unclear. AMP-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) function as majors regulators of cellular metabolism that respond to changes in energy status, and recent data demonstrated that they also play a critical role in systemic energy balance. Here, we sought to determine whether the response of the AMPK and mTOR pathways could contribute to the molecular effects of an HPD. RESEARCH DESIGN AND METHODS—Western blotting, confocal microscopy, chromatography, light microscopy, and RT-PCR assays were combined to explore the anorexigenic effects of an HPD. RESULTS—An HPD reduced food intake and induced weight loss in both normal rats and ob/ob mice. The intracerebroventricular administration of leucine reduced food intake, and the magnitude of weight loss and reduction of food intake in a leucine-supplemented diet are similar to that achieved by HPD in normal rats and in ob/ob mice, suggesting that leucine is a major component of the effects of an HPD. Leucine and HPD decrease AMPK and increase mTOR activity in the hypothalamus, leading to inhibition of neuropeptide Y and stimulation of pro-opiomelanocortin expression. Consistent with a cross-regulation between AMPK and mTOR to control food intake, our data show that the activation of these enzymes occurs in the same specific neuronal subtypes. CONCLUSIONS—These findings provide support for the hypothesis that AMPK and mTOR interact in the hypothalamus to regulate feeding during HPD in a leucine-dependent manner.

Obesity is associated with insulin resistance and a state of abnormal inflammatory response. The Toll-like receptor (TLR)4 has an important role in inflammation and immunity, and its expression has been reported in most tissues of the body, including the insulin-sensitive ones. Because it is activated by lipopolysaccharide and saturated fatty acids, which are inducers of insulin resistance, TLR4 may be a candidate for participation in the cross-talk between inflammatory and metabolic signals. Here, we show that C3H/HeJ mice, which have a loss-of-function mutation in TLR4, are protected against the development of diet-induced obesity. In addition, these mice demonstrate decreased adiposity, increased oxygen consumption, a decreased respiratory exchange ratio, improved insulin sensitivity, and enhanced insulin-signaling capacity in adipose tissue, muscle, and liver compared with control mice during high-fat feeding. Moreover, in these tissues, control mice fed a high-fat diet show an increase in IκB kinase complex and c-Jun NH2-terminal kinase activity, which is prevented in C3H/HeJ mice. In isolated muscles from C3H/HeJ mice, protection from saturated fatty acid–induced insulin resistance is observed. Thus, TLR4 appears to be an important mediator of obesity and insulin resistance and a potential target for the therapy of these highly prevalent medical conditions.

Evidence demonstrates that exogenous nitric oxide (NO) and the NO produced by inducible nitric oxide synthase (iNOS) can induce insulin resistance in muscle. Here, we investigated whether this insulin resistance could be mediated by S-nitrosation of proteins involved in early steps of the insulin signal transduction pathway. Exogenous NO donated by S-nitrosoglutathione (GSNO) induced in vitro and in vivo S-nitrosation of the insulin receptor β subunit (IRβ) and protein kinase B/Akt (Akt) and reduced their kinase activity in muscle. Insulin receptor substrate (IRS)-1 was also rapidly S-nitrosated, and its expression was reduced after chronic GSNO treatment. In two distinct models of insulin resistance associated with enhanced iNOS expression—diet-induced obesity and the ob/ob diabetic mice—we observed enhanced S-nitrosation of IRβ/IRS-1 and Akt in muscle. Reversal of S-nitrosation of these proteins by reducing iNOS expression yielded an improvement in insulin action in both animal models. Thus, S-nitrosation of proteins involved in insulin signal transduction is a novel molecular mechanism of iNOS-induced insulin resistance.

The above-cited article has been retracted by the American Diabetes Association, the publisher of Diabetes. This article was previously the subject of an expression of concern in the March 2015 issue of the journal (Diabetes 2015;64:1068–1070. DOI: 10.2337/db15-ec03). As noted in the March 2015 expression of concern, the American Diabetes Association asked the corresponding author’s institution, the University of Campinas, to review the following issues with the article

Growth hormone (GH) and IGFs have a long distinguished history in diabetes, with possible participation in the development of renal complications. The implicated effect of GH in diabetic end-stage organ damage may be mediated by growth hormone receptor (GHR) or postreceptor events in GH signal transduction. The present study investigates the effects of diabetes induced by streptozotocin (STZ) on renal GH signaling. Our results demonstrate that JAK2, insulin receptor substrate (IRS)-1, Shc, ERKs, and Akt are widely distributed in the kidney, and after GH treatment, there is a significant increase in phosphorylation of these proteins in STZ-induced diabetic rats compared with controls. Moreover, the GH-induced association of IRS-1/phosphatidylinositol 3-kinase, IRS-1/growth factor receptor bound 2 (Grb2), and Shc/Grb2 are increased in diabetic rats as well. Immunohistochemical studies show that GH-induced p-Akt and p-ERK activation is apparently more pronounced in the kidneys of diabetic rats. Administration of G120K-PEG, a GH antagonist, in diabetic mice shows inhibitory effects on diabetic renal enlargement and reverses the alterations in GH signal transduction observed in diabetic animals. The present study demonstrates a role for GH signaling in the pathogenesis of early diabetic renal changes and suggests that specific GHR blockade may present a new concept in the treatment of diabetic kidney disease.

The above-cited article has been retracted by the American Diabetes Association, the publisher of Diabetes . This article was previously the subject of an expression of concern in the March 2015 issue of the journal (Diabetes 2015;64:1068–1070. DOI: 10.2337/db15-ec03). As noted in the March 2015 expression of concern, the American Diabetes Association asked the corresponding author’s institution, the University of Campinas, to review the following issue with the …

Glutamic acid decarboxylase (GAD) is a major islet cell autoantigen in insulin-dependent diabetes mellitus (IDDM), and autoantibodies are found in high frequencies in patients with recent-onset IDDM, stiff-man syndrome (SMS), and autoimmune polyendocrine syndrome type I (APS I). Antigens in autoimmune disorders are often enzymes, and autoantibody binding frequently inhibit their activity. In this study, we examined the reactivity of anti-GAD–containing sera from 7 patients with IDDM, 4 patients with SMS, and 5 patients with APS I. All sera immunoprecipitated GAD from [35S]methionine-labeled rat islet lysates and the sera from patients with SMS and APS I, but none of the IDDM patients’ sera, identified the GAD protein in Western blots. Two of four SMS patients’ sera and 5 of 5 APS I patients’ sera, in contrast to 0 of 7 IDDM patients’ sera, inhibited the enzymatic activity of GAD. When the various sera were tested with the GAD65 and GAD67 isoforms, produced separately by transient expression in COS cells, the enzymatic activity of GAD65 was inhibited by sera from patients with SMS and APS I, whereas no effect on the GAD67 activity was observed. Taken together, the results demonstrate that the GAD autoantibodies in these three disorders display marked differences in epitope recognition and indicate that, during the development of the diseases, the autoantigen is being presented to the immune system through separate pathogenetic mechanisms.