Intramyocellular Lipid Deposition Research Articles

Muscle-generated BDNF (brain derived neurotrophic factor) maintains mitochondrial quality control in female mice

ABSTRACT Mitochondrial remodeling is dysregulated in metabolic diseases but the underlying mechanism is not fully understood. We report here that BDNF (brain derived neurotrophic factor) provokes mitochondrial fission and clearance in skeletal muscle via the PRKAA/AMPK-PINK1-PRKN/Parkin and PRKAA-DNM1L/DRP1-MFF pathways. Depleting Bdnf expression in myotubes reduced fatty acid-induced mitofission and mitophagy, which was associated with mitochondrial elongation and impaired lipid handling. Muscle-specific bdnf knockout (MBKO) mice displayed defective mitofission and mitophagy, and accumulation of dysfunctional mitochondria in the muscle when they were fed with a high-fat diet (HFD). These animals also have exacerbated body weight gain, increased intramyocellular lipid deposition, reduced energy expenditure, poor metabolic flexibility, and more insulin resistance. In contrast, consuming a BDNF mimetic (7,8-dihydroxyflavone) increased mitochondrial content, and enhanced mitofission and mitophagy in the skeletal muscles. Hence, BDNF is an essential myokine to maintain mitochondrial quality and function, and its repression in obesity might contribute to impaired metabolism. Abbreviation: 7,8-DHF: 7,8-dihydroxyflavone; ACACA/ACC: acetyl Coenzyme A carboxylase alpha; ACAD: acyl-Coenzyme A dehydrogenase family; ACADVL: acyl-Coenzyme A dehydrogenase, very long chain; ACOT: acyl-CoA thioesterase; CAMKK2: calcium/calmodulin-dependent protein kinase kinase 2, beta; BDNF: brain derived neurotrophic factor; BNIP3: BCL2/adenovirus E1B interacting protein 3; BNIP3L/NIX: BCL2/adenovirus E1B interacting protein 3-like; CCL2/MCP-1: chemokine (C-C motif) ligand 2; CCL5: chemokine (C-C motif) ligand 5; CNS: central nervous system; CPT1B: carnitine palmitoyltransferase 1b, muscle; Cpt2: carnitine palmitoyltransferase 2; CREB: cAMP responsive element binding protein; DNM1L/DRP1: dynamin 1-like; E2: estrogen; EHHADH: enoyl-CoenzymeA hydratase/3-hydroxyacyl CoenzymeA dehydrogenase; ESR1/ER-alpha: estrogen receptor 1 (alpha); FA: fatty acid; FAO: fatty acid oxidation; FCCP: carbonyl cyanide-4-(trifluoromethoxy)phenylhydrazone; FFA: free fatty acids; FGF21: fibroblast growth factor 21; FUNDC1: FUN14 domain containing 1; HADHA: hydroxyacyl-CoA dehydrogenase trifunctional multienzyme complex subunit alpha; HFD: high-fat diet; iWAT: inguinal white adipose tissues; MAP1LC3A/LC3A: microtubule-associated protein 1 light chain 3 alpha; MBKO; muscle-specific bdnf knockout; IL6/IL-6: interleukin 6; MCEE: methylmalonyl CoA epimerase; MFF: mitochondrial fission factor; NTRK2/TRKB: neurotrophic tyrosine kinase, receptor, type 2; OPTN: optineurin; PA: palmitic acid; PARL: presenilin associated, rhomboid-like; PDH: pyruvate dehydrogenase; PINK1: PTEN induced putative kinase 1; PPARGC1A/PGC-1α: peroxisome proliferative activated receptor, gamma, coactivator 1 alpha; PRKAA/AMPK: protein kinase, AMP-activated, alpha 2 catalytic subunit; ROS: reactive oxygen species; TBK1: TANK-binding kinase 1; TG: triacylglycerides; TNF/TNFα: tumor necrosis factor; TOMM20: translocase of outer mitochondrial membrane 20; ULK1: unc-51 like kinase 1

Metformin in combination with genistein ameliorates skeletal muscle inflammation in high-fat diet fed c57BL/6 mice

Although the beneficial effects of metformin (MET) and genistein in ameliorating inflammation have been elucidated, their combined impacts on skeletal muscle inflammation have not been clearly understood. This study aimed to examine the possible preventive effect of MET in combination with genistein on skeletal muscle inflammation in high-fat diet (HFD) fed C57BL/6 mice. Fifty C57BL/6 male mice were fed on an HFD for 10 weeks. The mice were categorized into five groups, control, HFD, HFD + MET (0.23%), HFD + genistein (0.2%), and HFD + MET + genistein for 12 weeks. The results showed that treatment with MET and genistein, either alone or in combination, led to reduced weight gain, fasting blood glucose, plasma insulin, HOMA-IR levels, and Area Under the Curves (AUCs) in ipGTT. MET in combination with genistein demonstrated a decreasing effect on macrophages infiltration rate compared to genistein and MET groups alone. The expression of iNOS was reduced, whereas the expression of M2 macrophage markers was increased in combined treatment of MET and genistein. Furthermore, MET in combination with genistein reduced the expression of TNF-α, IL-1β, MCP-1, and IL-6 and increased the expression of IL-10 in comparison with genistein and MET groups alone. Plasma and skeletal muscle triglycerides and intra-myocellular lipid deposition were reversed by treatment with MET and genistein, alone or in combination. These results imply that the combination therapy of MET and genistein may have therapeutic potential for decreasing obesity-induced skeletal muscle inflammation in the HFD-fed model.

One-leg inactivity induces a reduction in mitochondrial oxidative capacity, intramyocellular lipid accumulation and reduced insulin signalling upon lipid infusion: a human study with unilateral limb suspension

Aims/hypothesisPhysical inactivity, low mitochondrial function, increased intramyocellular lipid (IMCL) deposition and reduced insulin sensitivity are common denominators of chronic metabolic disorders, like obesity and type 2 diabetes. Yet, whether low mitochondrial function predisposes to insulin resistance in humans is still unknown.MethodsHere we investigated, in an intervention study, whether muscle with low mitochondrial oxidative capacity, induced by one-legged physical inactivity, would feature stronger signs of lipid-induced insulin resistance. To this end, ten male participants (age 22.4 ± 4.2 years, BMI 21.3 ± 2.0 kg/m2) underwent a 12 day unilateral lower-limb suspension with the contralateral leg serving as an active internal control.ResultsIn vivo, mitochondrial oxidative capacity, assessed by phosphocreatine (PCr)-recovery half-time, was lower in the inactive vs active leg. Ex vivo, palmitate oxidation to 14CO2 was lower in the suspended leg vs the active leg; however, this did not result in significantly higher [14C]palmitate incorporation into triacylglycerol. The reduced mitochondrial function in the suspended leg was, however, paralleled by augmented IMCL content in both musculus tibialis anterior and musculus vastus lateralis, and by increased membrane bound protein kinase C (PKC) θ. Finally, upon lipid infusion, insulin signalling was lower in the suspended vs active leg.Conclusions/interpretationTogether, these results demonstrate, in a unique human in vivo model, that a low mitochondrial oxidative capacity due to physical inactivity directly impacts IMCL accumulation and PKCθ translocation, resulting in impaired insulin signalling upon lipid infusion. This demonstrates the importance of mitochondrial oxidative capacity and muscle fat accumulation in the development of insulin resistance in humans.Trial registrationClinicalTrial.gov NCT01576250.FundingPS was supported by a ‘VICI’ Research Grant for innovative research from the Netherlands Organization for Scientific Research (Grant 918.96.618).

Resveratrol alleviates obesity-induced skeletal muscle inflammation via decreasing M1 macrophage polarization and increasing the regulatory T cell population

Resveratrol was reported to inhibit inflammatory responses; however, the role of this polyphenol in obesity-induced skeletal muscle inflammation remains unknown. Mice fed a high fat diet (HFD) were treated with resveratrol for 16 weeks. Resveratrol treatment decreased macrophage infiltration into skeletal muscle of HFD-fed mice. Resveratrol also led to the polarization of macrophages to the M2 direction, as well as decreasing the expression of a number of M1 pro-inflammatory cytokines [tumor necrosis factor α (TNF-α), interleukin 1 β (IL-1β) and interleukin 6 (IL-6)]. In addition, increased infiltration of regulatory T cells (Treg cells) was found following resveratrol treatment in skeletal muscle of mice. Decreased intramyocellular lipid deposition was associated with reduced expression levels of toll-like receptors 2 (TLR2) and TLR4 in resveratrol treated mice. We also found that diminished inflammation in skeletal muscle following resveratrol treatment was accompanied by increasing phosphorylation of 5’-adenosine monophosphate-activated protein kinase (AMPK) and decreasing phosphorylation of p38 mitogen-activated protein kinase (MAPK) and c-Jun N-terminal kinase (JNK). Taken together, these findings suggest that resveratrol ameliorates inflammation in skeletal muscle of HFD-induced model of obesity. Therefore, resveratrol might represent a potential treatment for attenuation of inflammation in skeletal muscle tissue.

Short-term GLP-1 receptor agonist exenatide ameliorates intramyocellular lipid deposition without weight loss in ob/ob mice.

Ectopic lipid deposition is closely associated with type 2 diabetes (T2D). Accumulating evidence shows that GLP-1 receptor agonists (GLP-1 RAs) improve obesity and liver steatosis. However, it remains unknown whether and how they ameliorate lipid deposition in skeletal muscle. This study aimed to investigate the effect of exenatide (a GLP-1 RA) on intramyocellular lipid deposition in the skeletal muscle of T2D models and its dependence on weight loss. Ob/ob mice and diet-induced obese (DIO) mice were treated with exenatide (24 nmol/kg), leptin (1 mg/kg), or saline control intraperitoneally once daily for 4 weeks. Phenotypic evaluations were performed during and after the intervention. PA-induced myoblast C2C12 cells were used as an in vitro model. The expression of key enzymes involved in lipid metabolism was assessed in the skeletal muscle of ob/ob mice and DIO mice. In ob/ob mice, 4-week exenatide treatment did not improve the body weight and fat mass, but modestly ameliorated intramyocellular lipid deposition and lipid profiles. In DIO mice, it remarkably alleviated the body weight, lipid profiles, and intramyocellular lipid deposition. In the skeletal muscle of these two models, exenatide treatment activated the AMP-activated protein kinase (AMPK) signaling pathway, stimulated lipid oxidation enzymes, and upregulated the insulin signaling pathway. In vitro, exendin-4 activated the AMPK signaling pathway and stimulated lipid metabolism to improve lipid accumulation in palmitate-induced myoblast C2C12 cells. Exenatide ameliorated intramyocellular lipid deposition without body weight reduction in ob/ob mice, but alleviated body weight and intramyocellular lipid deposition in DIO mice. The underlying mechanism included the activation of AMPK signaling pathway and improvement in insulin sensitivity, independent of weight loss in ob/ob mice.

A Novel Acetyl-CoA Carboxylase 2 Selective Inhibitor Improves Whole-Body Insulin Resistance and Hyperglycemia in Diabetic Mice through Target-Dependent Pathways.

Excess intramyocellular lipid (IMCL) deposition in skeletal muscle is closely associated with insulin resistance. Pharmacological inhibition of acetyl-CoA carboxylase (ACC) 2 offers a promising approach to treat insulin resistance through stimulation of mitochondrial fatty acid oxidation (FAO) and reduction of IMCL deposition. Previously reported experimental ACC2 inhibitors exhibited plasma glucose-lowering effects in diabetic rodents. However, their antidiabetic action may be potentially biased by off-target effects on triglyceride metabolism or by neurologic side effects. In this study, we investigated a safety profile, target dependency of its action, and antidiabetic efficacy of compound 2e, a novel olefin derivative potent ACC2 selective inhibitor. Four-day administration of suprapharmacological dose of compound 2e did not exhibit any obvious side effects in Sprague-Dawley rats. In db/db mice, single administration of compound 2e led to significantly elevated FAO and reduced IMCL deposition in skeletal muscle. In ACC2 knockout mice, treatment with pharmacological doses of compound 2e did not reduce plasma triglyceride levels, whereas A-908292, a previously reported ACC2 inhibitor, caused a significant triglyceride reduction, showing that compound 2e was devoid of off-target triglyceride-lowering activity. Chronic treatment of db/db mice with compound 2e improved hyperglycemia but did not decrease plasma triglyceride levels. Additionally, compound 2e showed significant improvements of whole-body insulin resistance in the clamp study and insulin tolerance test. Collectively, compound 2e demonstrated a good safety profile and significant antidiabetic effects through inhibition of ACC2-dependent pathways. These findings provide further evidence that selective inhibition of ACC2 is an attractive strategy against insulin resistance and type 2 diabetes. SIGNIFICANCE STATEMENT: This study shows that pharmacological inhibition of acetyl-CoA carboxylase (ACC) 2 leads to significant improvements in whole-body glucose homeostasis, independently of off-target metabolic pathways and toxicity, which were observed in previously reported ACC2 inhibitors. These findings support the concept that ACC2-selective inhibitors will be a novel remedy for treatment of type 2 diabetes.

Leucine decreases intramyocellular lipid deposition in an mTORC1-independent manner in palmitate-treated C2C12 myotubes.

Higher intramyocellular lipid (IMCL) deposition in skeletal muscle is commonly observed in patients with obesity, resulting in mitochondrial damage. Palmitic acid, a saturated fatty acid, has been reported to induce obesogenic conditions in C2C12 myotubes. Leucine has been shown to improve obesity-related metabolic signatures; however, evidence for the effect of leucine on IMCL and the underlying mechanisms are still lacking. The objective of this study was to determine the effect of leucine on IMCL deposition and identify the potential mechanisms. Palmitate-treated C2C12 myotubes were used as an in vitro model of obesity. Two doses of leucine were used: 0.5 mM (postprandial physiological plasma concentration) and 1.5 mM (supraphysiological plasma concentration). Rapamycin was used to determine the role of mammalian target of rapamycin complex 1 (mTORC1) in leucine's regulation of lipid deposition in C2C12 myotubes. One-way ANOVA followed by Tukey's post hoc test was used to calculate differences between treatment groups. Our results demonstrate that leucine reduces IMCL deposition in an mTORC1-independent fashion. Furthermore, leucine acts independently of mTORC1 to upregulate gene expression related to fatty acid metabolism and works through both mTORC1-dependent and mTORC1-independent pathways to regulate mitochondrial biogenesis in palmitate-treated C2C12 myotubes. In agreement with increased mitochondrial biogenesis, increased mitochondrial content, circularity, and decreased autophagy are observed in the presence of 1.5 mM leucine. Taken together, the results indicate leucine reduces IMCL potentially through an mTORC1-independent pathway in palmitate-treated C2C12 myotubes.

1938-P: GLP-1 Receptor Agonist Ameliorates Intramyocellular Lipid Deposition without Weight Loss by Activating AMPK

Objective: Ectopic deposition of lipids is closely related with type 2 diabetes (T2D). Whether and how GLP-1 receptor agonists (GLP-1 RAs) ameliorate lipid deposition in skeletal muscle remain unknown. Here, we investigate the effect of GLP-1 RA exenatide on intramyocellular lipid deposition of skeletal muscle in T2D models and whether this process depends on weight loss. Methods: ob/ob mice and diet-induced obese (DIO) mice were treated with exenatide, leptin or saline control i.p. for four weeks. Systemic phenotypic evaluations were carried out during and after the intervention. An in vitro model used palmitate-treated myoblast C2C12 cells. The expression of key enzymes involved in lipid metabolism was assessed in skeletal muscle of ob/ob mice and DIO mice. Results: In ob/ob mice, body weight and fat mass were not improved by four-week exenatide treatment. However, intramyocellular lipid deposition and lipid profiles were still modestly ameliorated by exenatide. In DIO mice, body weight, lipid profiles and intramyocellular lipid were all remarkably alleviated by exenatide but not by leptin. In skeletal muscle of these two models, activated AMPK signaling pathway, stimulated lipid oxidative enzymes and improved insulin signaling pathway were observed by exenatide treatment. In vitro, exendin-4 activated AMPK signaling pathway and promoted lipid metabolism to improve lipid accumulation in palmitate-treated myoblast C2C12 cells, and inhibiting AMPK abolished this effect. Conclusion: Exenatide ameliorates intramyocellular lipid deposition before the weight loss effect appears in ob/ob mice. While both body weight and intramyocellular lipid are alleviated remarkably at the same time by exenatide in DIO mice. Thus, the effect of exenatide on ameliorating intramyocellular lipid deposition could be independent on weight loss by activating AMPK signaling pathway. Disclosure F. Xu: None. H. Cao: None. Z. Chen: None. H. Gu: None. W. Guo: None. B. Lin: None. J. Weng: None.

Skeletal muscle miR-34a/SIRT1:AMPK axis is activated in experimental and human non-alcoholic steatohepatitis.

Non-alcoholic fatty liver disease (NAFLD) pathogenesis associates with intramyocellular lipid deposition and mitochondrial dysfunction. microRNAs (miRs), including pro-apoptotic miR-34a, are modulated during disease progression in liver tissue and plasma. We aimed to investigate the functional role of the miR-34a/SIRT1:AMP-activated protein kinase (AMPK) pathway in modulating local mitochondrial dysfunction in the skeletal muscle of human and experimental non-alcoholic steatohepatitis. Muscle biopsies were obtained from morbid obese NAFLD patients undergoing bariatric surgery. C57BL/6N mice were fed different NAFLD-inducing diets and C2C12 muscle cells incubated with palmitic acid (PA) in the presence or absence of an AMPK activator, or upon miR-34a functional modulation. Several muscle miRNAs, including miR-34a, were found increased with human NAFLD progression. Activation of the miR-34a/SIRT1:AMPK pathway, concomitant with impairment in insulin signalling mediators and deregulation of mitochondrial-shaping proteins, was evident in C2C12 cells incubated with PA, as well as in the skeletal muscle of all three diet-induced NAFLD mice models. Functional studies established the association between miR-34a- and PA-induced muscle cell deregulation. Of note, activation of AMPK almost completely prevented miR-34a- and PA-induced cellular stress. In addition, the miR-34a/SIRT1:AMPK pathway and mitochondrial dynamics dysfunction were also found amplified in muscle of human NAFLD. Finally, muscle miR-34a expression and mitofusin 2 (Mfn2) protein levels correlated with hallmarks of NAFLD and disease progression. Our results indicate that activation of the miR-34a/SIRT1:AMPK pathway leads to mitochondrial dynamics dysfunction in skeletal muscle of human and experimental NAFLD, representing an appealing prospective target in metabolic syndrome. KEY MESSAGES: Skeletal muscle microRNAs are modulated during NAFLD progression. Palmitic acid-induced muscle cell dysfunction occurs, at least in part, through activation of the miR-34a/SIRT1:AMPK pathway. miR-34a/SIRT1:AMPK activation associates with mitochondria dynamics dysfunction in human NAFLD.

Transgenic animal model for studying the mechanism of obesity-associated stress urinary incontinence.

To study and compare the function and structure of the urethral sphincter in female Zucker lean (ZL) and Zucker fatty (ZF) rats and to assess the viability of ZF fats as a model for female obesity-associated stress urinary incontinence (SUI). Two study arms were created: a ZL arm including 16-week-old female ZL rats (ZUC-Leprfa 186; n = 12) and a ZF arm including 16-week-old female ZF rats (ZUC-Leprfa 185; n = 12). I.p. insulin tolerance testing was carried out before functional study. Metabolic cages, conscious cystometry and leak point pressure (LPP) assessments were conducted. Urethral tissues were harvested for immunofluorescence staining to check intramyocellular lipid (IMCL) and sphincter muscle (smooth muscle and striated muscle) composition. The ZF rats had insulin resistance, a greater voiding frequency and lower LPP compared with ZL rats (P < 0.05), with more IMCL deposition localized in the urethral striated muscle fibres of the ZF rats (P < 0.05). The thickness of the striated muscle layer and the ratio of striated muscle to smooth muscle were lower in ZF than in ZL rats. Obesity impairs urethral sphincter function via IMCL deposition and leads to atrophy and distortion of urethral striated muscle. The ZF rats could be a consistent and reliable animal model in which to study obesity-associated SUI.

Myopathy, muscle atrophy and tongue lipid composition in MuSK myasthenia gravis.

Myasthenia gravis (MG) associated with anti-muscle-specific tyrosine kinase (MuSK) antibodies differs in many aspects from typical presentation of acetylcholine receptor (AChR)-positive MG. Myopathy and muscle atrophy are observed in MuSK-positive MG patients, unlike AChR-positive patients with MG. That is why the aim of this study was to assess the presence of myopathy and muscle atrophy as well as the tongue lipid composition in our cohort of MuSK-positive MG patients. Clinical examination, electromyography (EMG) and proton magnetic resonance spectroscopy were performed in 31 MuSK-positive and 28 AChR-positive MG patients. Myopathic EMG was more frequent in MuSK compared to AChR MG patients. In AChR MG patients, myopathic EMG in facial muscles was more frequent after long-term corticosteroid treatment, which was not the case with MuSK-positive MG patients. Facial and/or tongue muscle atrophy was registered in 23 % of MuSK MG patients. Longer disease duration was observed in patients with clinical signs of tongue and/or facial muscle atrophy compared to those with normal tongue muscle. Intramyocellular lipid deposition in the tongue was present in 85.2 % of MuSK and 20 % of AChR MG patients. Female MuSK MG patients had more frequently electrophysiological signs of myopathy on the facial muscles and signs of intramyocellular lipid deposition in the tongue, compared to male patients with MuSK-positive MG. Myopathy, muscle atrophy and intramyocellular lipid deposition in the tongue are more frequent in MuSK-positive compared to AChR-positive MG patients.

Effect of Cafeteria Diet Feeding on Soleus Intramyocellular Lipid of Wistar Rats

Background: The presence of lipid besides muscle fibres facilitates the energy supply for exercise, but it is also indicative of insulin resistance in the untrained. Muscle lipid is associated with increased dietary energy: hyperlipidic diets induce an increase in intramyocellular lipid deposition in skeletal muscle. Methods: In the present study we analyzed the changes in soleus (a red-fibre muscle) intracellular muscle content under a hyperlipidic (cafeteria) diet in Wistar rats. We also analyzed in parallel the mitochondrial content a relative index of energy output capability. Results: Cafeteria diet-fed rats contained more lipid and mitochondria per unit of muscle section area than controls. Conclusions: The correlation found in the increases of muscle lipid and mitochondria hit at this increase as an adaptation of muscle to oxidize excess energy substrates under conditions of excess energy availability, probably contributing to adaptive thermogenesis. doi:10.4021/jem63w

Effect of Cafeteria Diet Feeding on Soleus Intramyocellular Lipid of Wistar Rats

Background: The presence of lipid besides muscle fibres facilitates the energy supply for exercise, but it is also indicative of insulin resistance in the untrained. Muscle lipid is associated with increased dietary energy: hyperlipidic diets induce an increase in intramyocellular lipid deposition in skeletal muscle. Methods: In the present study we analyzed the changes in soleus (a red-fibre muscle) intracellular muscle content under a hyperlipidic (cafeteria) diet in Wistar rats. We also analyzed in parallel the mitochondrial content a relative index of energy output capability. Results: Cafeteria diet-fed rats contained more lipid and mitochondria per unit of muscle section area than controls. Conclusions: The correlation found in the increases of muscle lipid and mitochondria hit at this increase as an adaptation of muscle to oxidize excess energy substrates under conditions of excess energy availability, probably contributing to adaptive thermogenesis. J Endocrinol Metab. 2012;2(1):21-25 doi: https://doi.org/10.4021/jem63w

Skeletal Muscle Phosphodiester Content Relates to Body Mass and Glycemic Control

BackgroundAging and insulin resistance have been related to reduced mitochondrial function and oxidative stress. Muscular phosphodiesters (PDE) are comprised of metabolites of phospholipid breakdown and may reflect membrane damage. We aimed to test the hypothesis that myocellular PDE are increased in patients with type 2 diabetes (T2D) and correlate inversely with mitochondrial ATP turnover.MethodsA Cross-sectional study in the Clinical Research Facility of an University hospital was performed. 10 nonobese middle-aged patients with T2D, 10 healthy humans matched for sex, age and physical activity index (CONm) and 18 young healthy humans (CONy) were included. Myocellular PDE and unidirectional flux through ATP synthase (fATP) were measured with 31P magnetic resonance spectroscopy (MRS). Intramyocellular (IMCL) and hepatocellular lipid deposition (HCL) were quantified with 1H MRS. Insulin sensitivity (Rd) was assessed from hyperinsulinemic-euglycemic clamp tests in 10 T2D, 10 CONm and 11 CONy.ResultsDuring fasting, T2D and CONm had 1.5 fold greater PDE than CONy (2.8±0.2, 2.5±0.2, 1.7±0.1 mmol/l, P = 0.004). Stimulation by insulin did not affect PDE in any group. PDE correlated negatively with Rd (r = −0.552, p<0.005) and fATP (r = −0.396, p<0.05) and positively with age (r = 0.656, p<0.001) and body mass (r = 0.597, p<0.001). PDE also related positively to HbA1c (r = 0.674, p<0.001) and fasting plasma glucose (r = 0.629, p<0.001) within T2D and across all participants.ConclusionsMuscular PDE concentrations associate with age, lower resting mitochondrial activity and insulin resistance, which is determined mainly by body mass and glycemia.

Proton magnetic resonance spectroscopy of the intrinsic tongue muscles in patients with myasthenia gravis with different autoantibodies

Objective To assess lipid composition of the intrinsic tongue muscles in patients with myasthenia gravis (MG). Methods This study included 15 MG patients with antibodies against muscle-specific kinase (MuSK), 15 matched MG patients with antibodies against acetylcholine receptor (AChR) and 15 matched healthy subjects. Middle posterior region of the tongue was analyzed by single voxel point-resolved proton magnetic resonance spectroscopy (MRS) using 1.5 T MRI scanner. Results MRS obtained from subject with AChR MG showed a broad resonance arising from methylene groups of lipids (PMN) with no observable shoulder attributed to methyl groups (PML). Full-width at half maximum (FWHM) of PMN + PML peak showed higher value in patients with AChR MG in comparison to healthy subjects and MuSK MG patients (p < 0.05). In patients with MuSK MG, the shape and FWHM of PMN + PML peak was similar as in healthy subjects (p > 0.05), with tendency toward increased ratio between PMN and resonance from vinyl protons of lipids (PV). In both AChR and MuSK MG, total creatine resonance (creatine + phosphocreatine, CP) was almost absent with significant increase of PMN/CP ratio in comparison to healthy subjects (p < 0.05). Conclusion MRS is useful in revealing muscle lipid composition in MG. In patients with AChR MG, MRS showed increased lipid content in the tongue muscles due to the lipid migration from intra- to extramyocellular space. Finding in patients with MuSK MG might reflect intramyocellular lipid deposition in the tongue. CP decrease in tongue muscles indicated impairment of oxidative metabolism in both AChR MG and MuSK MG.

Activation of Wnt/β-Catenin Signaling Increases Insulin Sensitivity through a Reciprocal Regulation of Wnt10b and SREBP-1c in Skeletal Muscle Cells

BackgroundIntramyocellular lipid accumulation is strongly related to insulin resistance in humans, and we have shown that high glucose concentration induced de novo lipogenesis and insulin resistance in murin muscle cells. Alterations in Wnt signaling impact the balance between myogenic and adipogenic programs in myoblasts, partly due to the decrease of Wnt10b protein. As recent studies point towards a role for Wnt signaling in the pathogenesis of type 2 diabetes, we hypothesized that activation of Wnt signaling could play a crucial role in muscle insulin sensitivity.Methodology/Principal FindingsHere we demonstrate that SREBP-1c and Wnt10b display inverse expression patterns during muscle ontogenesis and regeneration, as well as during satellite cells differentiation. The Wnt/β-catenin pathway was reactivated in contracting myotubes using siRNA mediated SREBP-1 knockdown, Wnt10b over-expression or inhibition of GSK-3β, whereas Wnt signaling was inhibited in myoblasts through silencing of Wnt10b. SREBP-1 knockdown was sufficient to induce Wnt10b protein expression in contracting myotubes and to activate the Wnt/β-catenin pathway. Conversely, silencing Wnt10b in myoblasts induced SREBP-1c protein expression, suggesting a reciprocal regulation. Stimulation of the Wnt/β-catenin pathway i) drastically decreased SREBP-1c protein and intramyocellular lipid deposition in myotubes; ii) increased basal glucose transport in both insulin-sensitive and insulin-resistant myotubes through a differential activation of Akt and AMPK pathways; iii) restored insulin sensitivity in insulin-resistant myotubes.Conclusions/SignificanceWe conclude that activation of Wnt/β-catenin signaling in skeletal muscle cells improved insulin sensitivity by i) decreasing intramyocellular lipid deposition through downregulation of SREBP-1c; ii) increasing insulin effects through a differential activation of the Akt/PKB and AMPK pathways; iii) inhibiting the MAPK pathway. A crosstalk between these pathways and Wnt/β-catenin signaling in skeletal muscle opens the exciting possibility that organ-selective modulation of Wnt signaling might become an attractive therapeutic target in regenerative medicine and to treat obese and diabetic populations.

Effect of gender on lipid-induced insulin resistance in obese subjects

In obese subjects, chronically elevated plasma concentrations of non-esterified fatty acids (NEFAs) exert a marked risk to contract insulin resistance and subsequently type 2 diabetes. When NEFA is acutely increased due to i.v. infusion of lipid, glucose disposal during a hyperinsulinemic-euglycemic clamp is reduced. This effect has been explained by a NEFA-induced decrease in skeletal muscle insulin sensitivity caused by accumulation of the lipid intermediates such as ceramide and diacylglycerol in the myocytes. However, neither the lipid-induced reduction of glucose disposal nor the intramyocellular lipid deposition has been compared directly in obese females and males. We studied eight obese females and eight obese males (body mass index (BMI): 32.6+/-1.4 and 32.8+/-0.8 respectively, non significant (NS)) matched for cardiorespiratory fitness relative to lean body mass (43.7+/-1.6 and 47.6+/-1.3 ml/kg min respectively, NS). Each subject underwent two hyperinsulinemic-euglycemic clamps with infusion of lipid or saline respectively. Furthermore, the subjects exercised during the last half an hour of each clamp. The lipid-induced reduction in glucose disposal during the clamp was similar in females and males (46+/-10 and 60+/-4% respectively, NS). However, whole-body insulin sensitivity as well as non-oxidative glucose disposal was higher in obese females compared with obese males both during lipid and saline infusion (P<0.001 and P=0.01 respectively). Muscle ceramide, triacylglycerol (TAG), diacylglycerol (DAG), and glycogen content were similar between sexes and remained unchanged during the clamp and when exercise was superimposed. The lipid-induced inhibition of glucose disposal is similar in obese females and males. However, obese females are more insulin sensitive compared with obese males (both during saline and lipid infusion), which is not due to differences in the concentration of the muscle lipid intermediates such as ceramide and DAG.

Fat distribution and storage: how much, where, and how?

Obesity does not necessarily imply disease and similarly obese individuals may manifest obesity-related morbidity or seemingly be in reasonably good health. Recent studies have shown that patterns of lipid partitioning are a major determinant of the metabolic profile and not just obesity per se. The underlying mechanisms and clinical relevance of lipid deposition in the visceral compartment and in insulin-sensitive tissues are described. Increased intramyocellular lipid deposition impairs the insulin signal transduction pathway and is associated with insulin resistance. Increased hepatic lipid deposition is similarly associated with the majority of the components of the insulin resistance syndrome. The roles of increased circulating fatty acids in conditions of insulin resistance and the typical pro-inflammatory milieu of specific obesity patterns are provided. Insights into the patterns of lipid storage within the cell are provided along with their relation to changes in insulin sensitivity and weight loss.

The “Obese Insulin-Sensitive” Adolescent: Importance of Adiponectin and Lipid Partitioning

There is a wide interindividual variation in peripheral insulin sensitivity at any given body mass index or percent body fat among obese adolescents with normal glucose tolerance. The goals of this study were to determine whether variability in insulin sensitivity is associated with differences in patterns of lipid partitioning or substrate use under fasting and hyperinsulinemic conditions. We compared 14 obese insulin-resistant adolescents with 14 obese insulin-sensitive controls, pair matched for age, gender, pubertal stage and body composition. Insulin sensitivity was assessed by the hyperinsulinemic-euglycemic clamp, intramyocellular lipid content by (1)H-nuclear magnetic resonance and visceral fat by magnetic resonance imaging. Obese insulin-sensitive subjects had lower intramyocellular (1.64 +/- 0.68 vs.2.26 +/- 0.62% of water peak, P = 0.017) and visceral lipid deposition (45 +/- 23 vs. 77 +/- 52 cm(2), P = 0.04) and a higher level of adiponectin, compared with their obese-resistant counterparts (8.8 +/- 3.6 vs. 6.5 +/- 1.8 mug/dl, P = 0.015). Glycerol fluxes were similar between the two obese groups yet occurred in the face of different concentrations of insulin. Intramyocellular lipid and visceral fat were negatively related to insulin sensitivity. Obese insulin-sensitive adolescents are characterized by lower lipid deposition in the intramyocellular and visceral compartments and greater levels of adiponectin, despite similar degree of adiposity.