Dual Role of Interleukin-6 in Regulating Insulin Sensitivity in Murine Skeletal Muscle

OBJECTIVE—Cytokines are elevated in various insulin-resistant states, including type 2 diabetes and obesity, although the contribution of interleukin-6 (IL-6) in the induction of these diseases is controversial

Resistencia a insulina en el músculo esquelético: conexión con la obesidad

Insulin resistance is an important contributor to the pathogenesis of type 2 diabetes and obesity is a risk factor for its development, due in part to the fact that adipose tissue secretes proteins called adipokines that may influence insulin sensitivity. Among these molecules, TNFa has been proposed as a link between obesity and insulin resistance because TNFa is overexpressed in adipose tissues of obese animals and humans, and obese mice lacking either TNFa or its receptor show protection for developing insulin resistance. The direct exposure to TNFa induced a state of insulin resistance on glucose uptake in myocytes and brown adipocytes, due to the activation of pro-inflammatory pathways that impair insulin-signaling at the level of the IRS proteins. In this regard the residue Ser307 in IRS-1 has been identified as a site for TNFa-inhibitory effects in myotubes, with being p38MAPK and IKK involved in the phosphorylation of this residue. Conversely, serine phosphorylation of IRS-2 mediated by TNFa activation of MAPKs was the mechanism found in brown adipocytes. The phosphatase PTP1B acts as a physiological negative regulator of insulin signaling by dephosphorylating the phosphotyrosine residues of the insulin receptor and IRS-1, and PTP1B expression is increased in muscle and white adipose tissue of obese and diabetic humans and rodents. Moreover, up-regulation of PTP1B expression has recently been found in cells treated with TNFa. Accordingly, myocytes and primary brown adipocytes deficient on PTP1B are protected against insulin resistance by this cytokine. Furthermore, down-regulation of PTP1B activity is also possible by the use of pharmacological agonists of nuclear receptors that restored insulin sensitivity in the presence of TNFa. In conclusion, the lack of PTP1B in muscle and brown adipocytes increase insulin sensitivity and glucose uptake and could confer protection against insulin resistance induced by adipokines.Key Words: Glucose uptake, LXR, PTP1B, TNFa, IL-6.Entre las complicaciones asociadas a la Obesidad, tiene una especial relevancia el desarrollo de resistencia a la insulina, siendo el primer eslabón de una amplia patología conocida como diabetes tipo 2. La Obesidad se considera como un estado crónico de inflamación de baja intensidad, como indican los niveles circulantes elevados de moléculas proinflamatorias. Se ha propuesto al TNFa como el nexo de unión entre adiposidad y desarrollo de resistencia a insulina ya que la mayoría de los pacientes con diabetes tipo 2 son obesos y tienen aumentada la expresión de TNFa en sus adipocitos, y los animales obesos deleccionados para la función del TNFa o su receptor no desarrollan resistencia a insulina. Las citocinas proinflamatorias producidas por los adipocitos y/o macrófagos activan quinasas de estrés, proinflamatorias y factores de transcripción que actúan sobre los tejidos periféricos (entre ellos el músculo y el propio tejido adiposo) produciendo resistencia a la acción de la insulina, que es un defecto en la señalización a varios niveles. En concreto, el TNFa activa la quinasa p38MAPK que fosforila en residuos de serina a los IRSs, bloqueando su fosforilación en tirosina en respuesta a la insulina, tanto en adipocitos marrones como en miocitos. Muy recientemente hemos observado que la fosfatasa PTP1B también está implicada en la resistencia a insulina por TNFa en ambos modelos. En la clínica se está utilizando actualmente el tratamiento con tiazolidindionas en pacientes con diabetes tipo 2. Otros agonistas de receptores nucleares empiezan a aparecer en la bibliografía como potenciales sensibilizadores a acción de la insulina, entre ellos el LXR, que puede antagonizar la señalización proinflamatoria en los propios adipocitos y/o en el músculo.Palabras clave: Transporte de glucosa, LXR, PTP1B, TNFa, IL-6

G Protein–Coupled Receptor Kinase 2 Plays a Relevant Role in Insulin Resistance and Obesity

OBJECTIVE: Insulin resistance is associated with the pathogenesis of metabolic disorders as type 2 diabetes and obesity. Given the emerging role of signal transduction in these syndromes, we set out to explore the possible role that G protein-coupled receptor kinase 2 (GRK2), first identified as a G protein-coupled receptor regulator, could have as a modulator of insulin responses. RESEARCH DESIGN AND METHODS: We analyzed the influence of GRK2 levels in insulin signaling in myoblasts and adipocytes with experimentally increased or silenced levels of GRK2, as well as in GRK2 hemizygous animals expressing 50% lower levels of this kinase in three different models of insulin resistance: tumor necrosis factor-α (TNF-α) infusion, aging, and high-fat diet (HFD). Glucose transport, whole-body glucose and insulin tolerance, the activation status of insulin pathway components, and the circulating levels of important mediators were measured. The development of obesity and adipocyte size with age and HFD was analyzed. RESULTS: Altering GRK2 levels markedly modifies insulin-mediated signaling in cultured adipocytes and myocytes. GRK2 levels are increased by ∼2-fold in muscle and adipose tissue in the animal models tested, as well as in lymphocytes from metabolic syndrome patients. In contrast, hemizygous GRK2 mice show enhanced insulin sensitivity and do not develop insulin resistance by TNF-α, aging, or HFD. Furthermore, reduced GRK2 levels induce a lean phenotype and decrease age-related adiposity. CONCLUSIONS: Overall, our data identify GRK2 as an important negative regulator of insulin effects, key to the etiopathogenesis of insulin resistance and obesity, which uncovers this protein as a potential therapeutic target in the treatment of these disorders

PPP2R5C couples hepatic glucose and lipid homeostasis

In mammals, the liver plays a central role in maintaining carbohydrate and lipid homeostasis by acting both as a major source and a major sink of glucose and lipids. In particular, when dietary carbohydrates are in excess, the liver converts them to lipids via de novo lipogenesis. The molecular checkpoints regulating the balance between carbohydrate and lipid homeostasis, however, are not fully understood. Here we identify PPP2R5C, a regulatory subunit of PP2A, as a novel modulator of liver metabolism in postprandial physiology. Inactivation of PPP2R5C in isolated hepatocytes leads to increased glucose uptake and increased de novo lipogenesis. These phenotypes are reiterated in vivo, where hepatocyte specific PPP2R5C knockdown yields mice with improved systemic glucose tolerance and insulin sensitivity, but elevated circulating triglyceride levels. We show that modulation of PPP2R5C levels leads to alterations in AMPK and SREBP-1 activity. We find that hepatic levels of PPP2R5C are elevated in human diabetic patients, and correlate with obesity and insulin resistance in these subjects. In sum, our data suggest that hepatic PPP2R5C represents an important factor in the functional wiring of energy metabolism and the maintenance of a metabolically healthy state

Skeletal muscle myogenesis is regulated by G protein-coupled receptor kinase 2

This is a pre-copyedited, author-produced pdf of an article accepted for publication in Journal of Molecular Cell Biology following peer review. The version of record Journal of Molecular Cell Biology 6.4 (2014) is available online at: http://dx.doi.org/10.1093/jmcb/mju025G protein-coupled receptor kinase 2 (GRK2) is an important serine/threonine-kinase regulating different membrane receptors and intracellular proteins. Attenuation of Drosophila Gprk2 in embryos or adult flies induced a defective differentiation of somatic muscles, loss of fibers, and a flightless phenotype. In vertebrates, GRK2 hemizygous mice contained less but more hypertrophied skeletal muscle fibers than wild-type littermates. In C2C12 myoblasts overexpression of a GRK2 kinase-deficient mutant (K220R) caused precocious differentiation of cells into immature myotubes, which were wider in size and contained more fused nuclei, while GRK2 overexpression blunted differentiation. Moreover, p38MAPK and Akt pathways were activated at an earlier stage and to a greater extent in K220R-expressing cells or upon kinase downregulation, while the activation of both kinases was impaired in GRK2- overexpressing cells. The impaired differentiation and fewer fusion events promoted by enhanced GRK2 levels were recapitulated by a p38MAPK mutant, which was able to mimic the inhibitory phosphorylation of p38MAPK by GRK2, whereas the blunted differentiation observed in GRK2-expressing clones was rescued in the presence of a constitutively active upstream stimulator of the p38MAPK pathway. These results suggest that balanced GRK2 function is necessary for a timely and complete myogenic process.This work was supported by Grants BFU2008-04043 (to M.L. and S.F.-V.), SAF2012-3618 (to S.F.-V.), and SAF2011-23800 (to F.M.) from Ministerio de Economía y Competitividad, Spain; S2010/BMD-2332 (INDISNET) from Comunidad de Madrid, Spain (to F.M.); CIBER de Diabetes y Enfermedades Metabólicas Asociadas and The Cardiovascular Network (RD06- 0014/0037 and RD12/0042/0012) from Ministerio Sanidad y Consumo-Instituto Carlos III, Spain (to F.M.); UAM-Banco de Santander (to C.M.); BFU2010-14884 (to M.R.-G.). S.F.-V. is recipient of a ‘Miguel Servet’ tenure track program (CP10/00438) co-financed by the European Regional Development Fund (ERDF). We also acknowledge the support of COST Action BM0602 from the European Commission (to M.L.) and institutional support from Fundación Ramón Arece

Long-term effects in bone mineral density after different bariatric procedures in patients with type 2 diabetes: outcomes of a randomized clinical trial

There is scant evidence of the long-term effects of bariatric surgery on bone mineral density (BMD). We compared BMD changes in patients with severe obesity and type 2 diabetes (T2D) 5 years after randomization to metabolic gastric bypass (mRYGB), sleeve gastrectomy (SG) and greater curvature plication (GCP). We studied the influence of first year gastrointestinal hormone changes on final bone outcomes. Forty-five patients, averaging 49.4 (7.8) years old and body mass index (BMI) 39.4 (1.9) kg/m(2), were included. BMD at lumbar spine (LS) was lower after mRYGB compared to SG and GCP: 0.89 [0.82;0.94] vs. 1.04 [0.91;1.16] vs. 0.99 [0.89;1.12],p= 0.020. A higher percentage of LS osteopenia was present after mRYGB 78.6% vs. 33.3% vs. 50.0%, respectively. BMD reduction was greater in T2D remitters vs. non-remitters. Weight at fifth year predicted BMD changes at the femoral neck (FN) (adjustedR(2): 0.3218;p= 0.002), and type of surgery (mRYGB) and menopause predicted BMD changes at LS (adjustedR(2): 0.2507;p< 0.015). In conclusion, mRYGB produces higher deleterious effects on bone at LS compared to SG and GCP in the long-term. Women in menopause undergoing mRYGB are at highest risk of bone deterioration. Gastrointestinal hormone changes after surgery do not play a major role in BMD outcomes

Enhanced fatty acid oxidation in adipocytes and macrophages reduces lipid-induced triglyceride accumulation and inflammation

Lipid overload in obesity and type 2 diabetes is associated with adipocyte dysfunction, inflammation, macrophage infiltration, and decreased fatty acid oxidation (FAO). Here, we report that the expression of carnitine palmitoyltransferase 1A (CPT1A), the rate-limiting enzyme in mitochondrial FAO, is higher in human adipose tissue macrophages than in adipocytes and that it is differentially expressed in visceral vs. subcutaneous adipose tissue in both an obese and a type 2 diabetes cohort. These observations led us to further investigate the potential role of CPT1A in adipocytes and macrophages. We expressed CPT1AM, a permanently active mutant form of CPT1A, in 3T3-L1 CARΔ1 adipocytes and RAW 264.7 macrophages through adenoviral infection. Enhanced FAO in palmitate-incubated adipocytes and macrophages reduced triglyceride content and inflammation, improved insulin sensitivity in adipocytes, and reduced endoplasmic reticulum stress and ROS damage in macrophages. We conclude that increasing FAO in adipocytes and macrophages improves palmitate-induced derangements. This indicates that enhancing FAO in metabolically relevant cells such as adipocytes and macrophages may be a promising strategy for the treatment of chronic inflammatory pathologies such as obesity and type 2 diabetes

Downregulation of G protein-coupled receptor kinase 2 levels enhances cardiac insulin sensitivity and switches on cardioprotective gene expression patterns

G protein-coupled receptor kinase 2 (GRK2) has recently emerged as a negative modulator of insulin signalling. GRK2 downregulation improves insulin sensitivity and prevents systemic insulin resistance (IR). Cardiac GRK2 levels are increased in 5 human heart failure, while genetically inhibiting GRK2 leads to cardioprotection in mice. However, the molecular basis underlying the 6 deleterious effects of GRK2 up-regulation and the beneficial effects of its inhibition in the heart are not fully understood. Therefore, 7 we have explored the interconnections among a systemic IR status, GRK2 dosage and cardiac insulin sensitivity in adult (9 month-old) animals. GRK2+/- mice display enhanced cardiac insulin sensitivity and mild heart hypertrophy with preserved systolic function. Cardiac gene expression is reprogrammed in these animals, with increased expression of genes related to physiological hypertrophy, while the expression of genes related to pathological hypertrophy or to diabetes/obesity co-morbidities is repressed. Notably, we find that cardiac GRK2 levels increase in situations where IR develops, such as in ob/ob mice or after high fat diet feeding. Our data suggest that GRK2 downregulation/inhibition can help maintain cardiac function in the face of co-morbidities such as IR, diabetes or obesity by sustaining insulin sensitivity and promoting a gene expression reprogramming that confers cardioprotection.Grants from Ministerio de Educación y Ciencia (SAF2011-23800), Fundación para la Investigación Médica Aplicada (FIMA) and UTE project CIMA, The Cardiovascular Network of Ministerio Sanidad y Consumo-Instituto Carlos III (RD06-0014/0037 and RD12/0042/0012), Comunidad de Madrid (S2010/BMD-2332) and EFSD-Novo Nordisk to F.M and UAM Grupo Santander to C.M and Wood-Whelan Research Fellowship from IUBMB to E.L. We also acknowledge institutional support from Fundación Ramón Arece

A specific gut microbiota signature is associated with an enhanced GLP-1 and GLP-2 secretion and improved metabolic control in patients with type 2 diabetes after metabolic Roux-en-Y gastric bypass

ObjectiveTo determine changes in incretins, systemic inflammation, intestinal permeability and microbiome modifications 12 months after metabolic RYGB (mRYGB) in patients with type 2 diabetes (T2D) and their relationship with metabolic improvement.Materials and methodsProspective single-center non-randomized controlled study, including patients with class II-III obesity and T2D undergoing mRYGB. At baseline and one year after surgery we performed body composition measurements, biochemical analysis, a meal tolerance test (MTT) and lipid test (LT) with determination of the area under the curve (AUC) for insulin, C-peptide, GLP-1, GLP-2, and fasting determinations of succinate, zonulin, IL-6 and study of gut microbiota.ResultsThirteen patients aged 52.6 ± 6.5 years, BMI 39.3 ± 1.4 kg/m2, HbA1c 7.62 ± 1.5% were evaluated. After mRYGB, zonulin decreased and an increase in AUC after MTT was observed for GLP-1 (pre 9371 ± 5973 vs post 15788 ± 8021 pM, P&lt;0.05), GLP-2 (pre 732 ± 182 vs post 1190 ± 447 ng/ml, P&lt;0.001) and C- peptide, as well as after LT. Species belonging to Streptococaceae, Akkermansiacea, Rickenellaceae, Sutterellaceae, Enterobacteriaceae, Oscillospiraceae, Veillonellaceae, Enterobacterales_uc, and Fusobacteriaceae families increased after intervention and correlated positively with AUC of GLP-1 and GLP-2, and negatively with glucose, HbA1c, triglycerides and adiposity markers. Clostridium perfringens and Roseburia sp. 40_7 behaved similarly. In contrast, some species belonging to Lachnospiraceae, Erysipelotricaceae, and Rumnicocaceae families decreased and showed opposite correlations. Higher initial C-peptide was the only predictor for T2D remission, which was achieved in 69% of patients.ConclusionsPatients with obesity and T2D submitted to mRYGB show an enhanced incretin response, a reduced gut permeability and a metabolic improvement, associated with a specific microbiota signature

Role of adipose tissue GLP-1R expression in metabolic improvement after bariatric surgery in patients with type 2 diabetes

We aimed to explore the relationship between GLP-1 receptor (GLP-1R) expression in adipose tissue (AT) and incretin secretion, glucose homeostasis and weight loss, in patients with morbid obesity and type 2 diabetes undergoing bariatric surgery. RNA was extracted from subcutaneous (SAT) and visceral (VAT) AT biopsies from 40 patients randomized to metabolic gastric bypass, sleeve gastrectomy or greater curvature plication. Biochemical parameters, fasting plasma insulin, glucagon and area under the curve (AUC) of GLP-1 following a standard meal test were determined before and 1 year after bariatric surgery. GLP-1R expression was higher in VAT than in SAT. GLP-1R expression in VAT correlated with weight (r = -0.453, p = 0.008), waist circumference (r = -0.494, p = 0.004), plasma insulin (r = -0.466, p = 0.007), and systolic blood pressure (BP) (r = -0.410, p = 0.018). At 1 year, GLP-1R expression in VAT was negatively associated with diastolic BP (r = -0.361, p = 0.039) and, following metabolic gastric bypass, with the increase of GLP-1 AUC, (R-2 = 0.46, p = 0.038). Finally, GLP-1R in AT was similar independently of diabetes outcomes and was not associated with weight loss after surgery. Thus, GLP-1R expression in AT is of limited value to predict incretin response and does not play a role in metabolic outcomes after bariatric surgery