Plasma levels of soluble tumor necrosis factor-α receptors are related to total and LDL-cholesterol in lean, but not in obese subjects

BACKGROUND: Tumor necrosis factor-α (TNFα) is a mediator of insulin resistance. Plasma levels of soluble TNFα receptors (sTNFR1 and sTNFR2) probably reflect paracrine action of the cytokine. TNFα is also a regulator of lipid metabolism, however, data about impact of obesity on the relationships between TNFα and plasma lipids remain controversial. AIM: The purpose of the present study was to examine the associations of TNFα system with plasma lipids in lean and obese subjects with normal glucose metabolism. METHODS: We examined 63 subjects, 33 lean (BMI<25 kg × m(-2)) and 30 with marked overweight or obesity (BMI>27.8 kg × m(-2)). Anthropometric and biochemical parameters were measured. Oral glucose tolerance test and euglycemic hyperinsulinemic clamp were also performed. RESULTS: Obese subjects were markedly more insulin resistant and had higher levels of both TNFα receptors. Total (TC) and LDL-cholesterol (LDL-C), triglycerides (TG) and non-esterified fatty acids (NEFA) were also higher in the obese group. In obese subjects, both receptors were significantly related to TG and HDL-cholesterol (HDL-C), while sTNFR2 was also associated with NEFA. All those correlations disappeared after controlling for insulin sensitivity. In lean subjects, both receptors were related to TC, HDL-C and LDL-C. In that group, sTNFR1 predicted values of all those parameters independently of BMI, plasma glucose and insulin, and insulin sensitivity. CONCLUSION: We conclude that TNFα receptors are associated with plasma lipids in different way in lean and in obese subjects. TNFα system is probably important in determining cholesterol levels in lean subjects, while in obese this effect might be masked by other metabolic abnormalities

The Role of Skeletal Muscle Sphingolipids in the Development of Insulin Resistance

Insulin resistance is an important risk factor for type 2 diabetes, obesity, cardiovascular disease, polycystic ovary syndrome and other diseases. The most important stage in the development of insulin resistance is impairment of insulin-stimulated skeletal muscle glucose uptake. There is evidence that intramyocellular lipids might be responsible for this process through inhibition of insulin signaling. One of the important intracellular lipid pools is associated with the sphingomyelin signaling pathway. The second messenger in this pathway is ceramide. In vitro data indicate that ceramide inhibits insulin signaling, mainly through inactivation of protein kinase B. In vivo data suggest that ceramide accumulation within muscle cells might be associated with the development of insulin resistance. In this review, we discuss both in vitro and in vivo evidence for the role of muscle ceramide in the impairment of insulin action with particular focus on the question whether findings from animal studies are applicable to humans. We describe problems that are unresolved so far and topics of potential interest for future research

Profiling of circulating microRNAs reveals common microRNAs linked to type 2 diabetes that change with insulin sensitization

International audienceOBJECTIVE: This study sought to identify the profile of circulating microRNAs (miRNAs) in type 2 diabetes (T2D) and its response to changes in insulin sensitivity. RESEARCH DESIGN AND METHODS: The circulating miRNA profile was assessed in a pilot study of 12 men: 6 with normal glucose tolerance (NGT) and 6 T2D patients. The association of 10 circulating miRNAs with T2D was cross-sectionally validated in an extended sample of 45 NGT vs. 48 T2D subjects (65 nonobese and 28 obese men) and longitudinally in 35 T2D patients who were recruited in a randomized, double-blinded, and placebo-controlled 3-month trial of metformin treatment. Circulating miRNAs were also measured in seven healthy volunteers before and after a 6-h hyperinsulinemic-euglycemic clamp and insulin plus intralipid/heparin infusion. RESULTS: Cross-sectional studies disclosed a marked increase of miR-140-5p, miR-142-3p, and miR-222 and decreased miR-423-5p, miR-125b, miR-192, miR-195, miR-130b, miR-532-5p, and miR-126 in T2D patients. Multiple linear regression analyses revealed that miR-140-5p and miR-423-5p contributed independently to explain 49.5% (P \textless 0.0001) of fasting glucose variance after controlling for confounders. A discriminant function of four miRNAs (miR-140-5p, miR-423-5p, miR-195, and miR-126) was specific for T2D with an accuracy of 89.2% (P \textless 0.0001). Metformin (but not placebo) led to significant changes in circulating miR-192 (49.5%; P = 0.022), miR-140-5p (-15.8%; P = 0.004), and miR-222 (-47.2%; P = 0.03), in parallel to decreased fasting glucose and HbA1c. Furthermore, while insulin infusion during clamp decreased miR-222 (-62%; P = 0.002), the intralipid/heparin mixture increased circulating miR-222 (163%; P = 0.015) and miR-140-5p (67.5%; P = 0.05). CONCLUSIONS: This study depicts the close association between variations in circulating miRNAs and T2D and their potential relevance in insulin sensitivity

Autophagy-regulating TP53INP2 mediates muscle wasting and is repressed in diabetes

A precise balance between protein degradation and synthesis is essential to preserve skeletal muscle mass. Here, we found that TP53INP2, a homolog of the Drosophila melanogaster DOR protein that regulates autophagy in cellular models, has a direct impact on skeletal muscle mass in vivo. Using different transgenic mouse models, we demonstrated that muscle-specific overexpression of Tp53inp2 reduced muscle mass, while deletion of Tp53inp2 resulted in muscle hypertrophy. TP53INP2 activated basal autophagy in skeletal muscle and sustained p62-independent autophagic degradation of ubiquitinated proteins. Animals with muscle-specific overexpression of Tp53inp2 exhibited enhanced muscle wasting in streptozotocin-induced diabetes that was dependent on autophagy; however, TP53INP2 ablation mitigated experimental diabetes-associated muscle loss. The overexpression or absence of TP53INP2 did not affect muscle wasting in response to denervation, a condition in which autophagy is blocked, further indicating that TP53INP2 alters muscle mass by activating autophagy. Moreover, TP53INP2 expression was markedly repressed in muscle from patients with type 2 diabetes and in murine models of diabetes. Our results indicate that TP53INP2 negatively regulates skeletal muscle mass through activation of autophagy. Furthermore, we propose that TP53INP2 repression is part of an adaptive mechanism aimed at preserving muscle mass under conditions in which insulin action is deficient.We thank the Advanced Digital Microscopy Facility (IRB Barcelona), the Biostatistics/Bioinformatics Unit (IRB Barcelona), the Functional Genomics Facility (IRB Barcelona), the Unit of Electron Cryo-Microscopy (Scientific and Technological Centers, Universitat de Barcelona), V. Lukesova, J.M. Seco, I. Castrillón, and J.C. Monasterio for technological assistance. D. Sala was the recipient of a FPU fellowship from the “Ministerio de Educación y Cultura,” Spain. V. Ribas was supported by a postdoctoral fellowship from the Instituto de Salud Carlos III (Ministerio de Economía y Competitividad, Spain). This study was supported by research grants from the MINECO (SAF2008-03803), grant 2009SGR915 from the “Generalitat de Catalunya,” CIBERDEM (“Instituto de Salud Carlos III”), FIS-PS09/01267 and FIS-PI13/025 from “Instituto de Salud Carlos III,” Spain, SB/CP2013-0167/16642 from Association Française contre les Myopathies (AFM), Interreg IV-B-Sudoe-Feder (DIOMED, SOE1/P1/E178), and UDA-POIG.01.03.01-00-128/08 from the Innovative Economy Program 2007-2013, partially financed by the European Union within the European Regional Development Fund. A. Zorzano was the recipient of a Science Intensification Award from the University of Barcelona