Intramyocellular Triglyceride Research Articles

Intramyocellular Triglyceride Content During the Early Course of Type 1 and Type 2 Diabetes Mellitus.

Intramyocellular lipid content (IMCL) is elevated in insulin-resistant humans, but its changes over time and relationships with comorbidities remain unclear. We examined IMCL during the initial course of diabetes and its associations with complications. Participants of the German Diabetes Study (GDS) with recent-onset type 1 (n=132) or type 2 diabetes (n=139) and glucosetolerant controls (n=128) underwent 1H-magnetic resonance spectroscopy to measure IMCL and muscle volume, whole-body insulin sensitivity (hyperinsulinemic-euglycemic clamps; Mvalue) and cycling spiroergometry (VO2max). Subgroups underwent the same measurements after 5 years. At baseline, IMCL was ∼30% higher in type 2 diabetes than in other groups independently of age, sex, BMI and muscle volume. In type 2 diabetes, M-value was ∼36% and ∼62% lower compared to type 1 diabetes and controls, respectively. After 5 years, M-value decreased by ∼29% in type 1 and ∼13% in type 2 diabetes, whereas IMCL remained unchanged. The correlation of IMCL and M-value in type 2 diabetes at baseline was modulated by VO2max. IMCL also associated with microalbuminuria, Framingham risk score for cardiovascular disease and cardiac autonomic neuropathy. Changes in IMCL within 5 years after diagnosis do not mirror progression of insulin resistance in type 2 diabetes but associate with early diabetesrelated complications.

576-P: Local Muscle Microenvironment, Instead of Training Status, Affects Resting IMTG Turnover

Intramyocellular triglyceride (IMTG) level correlates with insulin resistance. Paradoxically, trained humans and obese, sedentary, insulin-resistant humans have high IMTG levels despite discrepant clinical phenotypes. We hypothesize that higher IMTG turnover in trained humans explains this paradox. Methods: Obese, insulin-resistant subjects [n=47, mean (SD), BMI:36.2 kg/m2(5.7), VO2max 25.4 ml/kg/min (5.7)] and lean trained subjects [n=15, BMI:22.2 kg/m2(1.8), VO2max 55ml/kg/min (10.1)] were fasted overnight. Two muscle biopsies (Bx) were acquired during a pulse-chase experiment using [U-13C]palmitate and [9-2H]palmitate infusions (6 h each), overlapping by 1 hour. Bx#1 was performed during the infusion overlap [last hour of 6 h [U-13C]palmitate infusion, 1 hour after starting [9-2H]palmitate. Bx#2 was performed at study conclusion [last hour of [9-2H]palmitate infusion, 6 hours after stopping [U-13C]palmitate]. Palmitate enrichment and concentration were measured. [9-2H]palmitate IMTG incorporation at Bx#1 and [U-13C] IMTG loss at Bx#2 indicated the interplay between plasma and muscle fatty acids. Results: Palmitate IMTG incorporation positively correlated between measures of IMTG turnover and negatively with insulin sensitivity. No correlation seen for VO2max/BMI. Conclusion: Muscle-level IMTG measures dictates higher resting IMTG turnover more than training related phenotype. Disclosure L.S.Chow: Research Support; Dexcom, Inc. A.Bantle: None. A.C.Alvear: None. D.G.Mashek: None. M.D.Jensen: Other Relationship; Novo Nordisk, Elsevier. Funding National Institutes of Health (R01DK098203)

Lower mitochondrial respiration does not lead to decreased fat oxidation in young African American women without obesity.

The prevalence of type 2 diabetes in African American women (AAW) is nearly twice that of White women. Lower insulin sensitivity and decreased mitochondrial function may be contributing factors. The purpose of this study was to compare fat oxidation in AAW and White women. Participants were 22 AAW and 22 White women, matched for age (18.7-38.3 years) and BMI (< 28 kg/m2). Participants completed two submaximal (50% VO2max) exercise tests with indirect calorimetry and stable isotope tracers to assess total, plasma, and intramyocellular triglyceride fat oxidation. The respiratory quotientduring the exercise test was nearly identical in AAW and White women (0.813 ± 0.008 vs. 0.810 ± 0.008, p=0.83). Although absolute total and plasma fat oxidation was lower in AAW, adjusting for the lower workload in AAW eliminated these racial differences. There was no racial difference in plasma and intramyocellular triglyceride source of fat for oxidation. No racial differences were observed in rates of ex vivo fat oxidation. Exercise efficiency was lower in AAW when adjusted to leg fat free mass. The data suggest that fat oxidation is not lower in AAW compared with White women, but additional studies are needed across exercise intensity, body weight, and age to confirm these results.

Codonopsis lanceolata ameliorates sarcopenic obesity via recovering PI3K/Akt pathway and lipid metabolism in skeletal muscle

BackgroundThe incidence of sarcopenic obesity, muscle atrophy induced by obesity, has steadily increased and is emerging as a health problem. Although the anti-obesity effect of Codonopsis lanceolata (CL) is known, its efficacy against sarcopenic obesity has not been studied. PurposeWe aimed to investigate the effect of CL on sarcopenic obesity and the changes in the related mechanisms to confirm the potential of CL as an effective natural therapeutic agent for sarcopenic obesity. MethodsC57BL/6 mice were fed a high-fat diet (HFD) for 9 weeks, and CL was administered for 6 weeks with HFD feeding. Body weight and grip strength were measured twice a week. After sacrifice, muscle fiber histological analysis, blood lipid analysis, muscle triglyceride extraction, western blot, and real-time PCR were performed. High-performance liquid chromatography (HPLC)-electrospray ionization (ESI)-mass spectrometry (MS) analysis and in vitro experiments using C2C12 cells were performed to verify the main and active compounds of CL. Confluent C2C12 cells were differentiated for 4 days, and then the main compound of CL was co-treated with palmitic acid for 24 h. ResultsCL reduced body weight, mass of three fat tissues (epididymal fat, mesenteric fat, and perirenal fat), adipocyte cross-sectional area (CSA), and improved insulin signaling. Simultaneously, CL improved grip strength, mass of three muscle tissues (quadriceps, gastrocnemius, and soleus), and muscle fiber CSA. These results were due to the recovery of both the phosphatidylinositol-3-kinase (PI3K)/ protein kinase B (Akt) signaling pathway and lipid metabolisms in skeletal muscle. Lipids accumulated in skeletal muscle interrupt the PI3K/Akt pathway, but CL reduced intramyocellular triglyceride concentration by restoring gene expression of factors related to triglyceride synthesis and fatty acid oxidation. Therefore, the activated PI3K/Akt pathway enhanced muscle protein synthesis by increasing phosphorylation of ribosomal protein S6 kinase 1 and eIF4E-binding protein 1 and suppressed muscle protein degradation by decreasing expression of muscle ring finger-1 and muscle atrophy F-box protein. In addition, tangshenoside I (TS) was verified as the main compound of CL by HPLC-ESI-MS analysis, and its efficacy of inhibiting myotube atrophy and lipid accumulation in myotubes was confirmed, verifying that TS is an active compound. ConclusionCL is an effective natural material for sarcopenic obesity that suppresses muscle atrophy by inhibiting the accumulation of lipids in skeletal muscle through restoration of impaired PI3K/Akt pathway and lipid metabolism.

Acute Effects Of A Single Bout Of Exercise On Intrahepatic And Intramyocellular Triglyceride In Obese Individuals With Nafld

High amounts of intrahepatic triglyceride (IHTG) and intramyocellular triglyceride (IMTG) are common metabolic complications associated in obese individuals with Non-alcoholic fatty liver disease (NAFLD). Caloric restriction is often prescribed to treat NAFLD, however, the effects of aerobic exercise in reducing IHTG and IMTG is unknown. PURPOSE: The aim of this study was to evaluate the effect of a single bout of the aerobic exercise on IHTG and IMTG content obese individuals with NAFLD. METHODS: Ten obese people (Means ± SD, Age 45.2 ± 5.2 years, BMI = 38.1 ± 4.6 kg/m2) with NAFLD performed a single bout of aerobic exercise (60 minutes at 50% of V02max) on a motor driven treadmill. Magnetic resonance spectroscopy was used to evaluate IHTG and IMTG content before and immediately after the exercise bout. IMTG was evaluated from the soleus muscle. Duel Energy X-ray Absorptiometry (DXA) was used to measure body weight and percent body fat. RESULTS: A single bout of aerobic exercise resulted in a significant (p < 0.05) decrease in IHTG from before (15.0 ± 1.8%) to after (12.2 ± 1.2%) the exercise bout. IMTG significantly (p < 0.05) decreased from before (3.2 ± 0.7%) to after (1.5 ± 0.8%) the single exercise bout. As expected there was no significant change in body weight (104.1 ± 3.2 kg and 103.9 ± 3.3 kg) or percent body fat (30.0 ± 2.0% and 30.2 ± 2.1%) before and after the exercise bout. CONCLUSION: Performing even a single bout of aerobic exercise reduces IHTG and IMTG obese persons with NAFLD.

Resting skeletal muscle PNPLA2 (ATGL) and CPT1B are associated with peak fat oxidation rates in men and women but do not explain observed sex differences

What is the central question of this study? What is the relationship between proteins in skeletal muscle and adipose tissue determined at rest and at peak rates of fat oxidation in men and women? What is the main finding and its importance? The resting contents of proteins in skeletal muscle involved in triglyceride hydrolysis and mitochondrial lipid transport were more strongly associated with peak fat oxidation rates than proteins related to lipid transport or hydrolysis in adipose tissue. Although females displayed higher relative rates of fat oxidation than males, this was not explained by the proteins measured in this study, suggesting that other factors determine sex differences in fat metabolism. We explored key proteins involved in fat metabolism that might be associated with peak fat oxidation (PFO) and account for sexual dimorphism in fuel metabolism during exercise. Thirty-six healthy adults [15 women; 40±11years of age; peak oxygen consumption 42.5±9.5ml(kg body mass)-1 min-1 ; mean±SD] completed two exercise tests to determine PFO via indirect calorimetry. Resting adipose tissue and/or skeletal muscle biopsies were obtained to determine the adipose tissue protein content of PLIN1, ABHD5 (CGI-58), LIPE (HSL), PNPLA2 (ATGL), ACSL1, CPT1B and oestrogen receptorα (ERα) and the skeletal muscle protein content of FABP 3 (FABPpm), PNPLA2 (ATGL), ACSL1, CTP1B and ESR1 (ERα). Moderate strength correlations were found between PFO [in milligrams per kilogram of fat-free mass (FFM) per minute] and the protein content of PNPLA2 (ATGL) [rs =0.41 (0.03-0.68), P<0.05] and CPT1B [rs =0.45 (0.09-0.71), P<0.05] in skeletal muscle. No other statistically significant bivariate correlations were found consistently. Females had a greater relative PFO than males [7.1±1.9 vs. 4.5±1.3 and 7.3±1.7 vs. 4.8±1.2mg(kg FFM)-1 min-1 in the adipose tissue (n=14) and skeletal muscle (n=12) subgroups, respectively (P<0.05)]. No statistically significant sex differences were found in the content of these proteins. The regulation of PFO might involve processes relating to intramyocellular triglyceride hydrolysis and mitochondrial fatty acid transport, and adipose tissue is likely to play a more minor role than muscle. Sex differences in fat metabolism are likely to be attributable to factors other than the resting content of proteins in skeletal muscle and adipose tissue relating to triglyceride hydrolysis and fatty acid transport.

Molecular Mechanisms Underpinning The Regulation Of Peak Fat Oxidation Rates During Exercise

PURPOSE: The molecular regulation of peak fat oxidation (PFO) during exercise remains poorly characterized. The aim of this study was to examine the relationship between the content of key proteins involved in adipose tissue and skeletal muscle fat metabolism with PFO. METHODS: Thirty-six healthy men and women adults [15 females; mean (SD) age 40 (11) years; V̇O2peak 42.5 (9.5) mL·kg BM-1·min-1; body fat %: 21.8 (8.2) %] completed two incremental exercise tests (separated by 7-28 days) to determine PFO via indirect calorimetry. A DEXA scan and adipose tissue and/or skeletal muscle biopsies were obtained 2-7 days after the second exercise test to determine the protein content of PLIN1, CGI-58, ATGL, HSL, ACSL1, and oestrogen receptor α (ERα) in adipose tissue, and FABPpm, ATGL, ACSL1, CTP1b and ERα in skeletal muscle. Sex comparisons were performed on sub-groups of males and females matched for aerobic capacity relative to fat free mass and classifications of the physical activity level index and fat mass index (n = 14 and 12 for adipose tissue and skeletal muscle comparison sub-groups, respectively). RESULTS: Moderate strength correlations were found between PFO (mg·kg FFM-1·min-1) and the protein content of ATGL [r = 0.41 (0.05 - 0.68), p < 0.05] and CPT1b [r = 0.41 (0.05 - 0.68), p < 0.05] in skeletal muscle. No other statistically significant bivariate correlations were found between PFO and the content of proteins in adipose tissue or skeletal muscle. Females had a greater PFO compared to males when expressed relative to fat-free mass [mean (SD): 7.1 (1.9) and 7.3 (1.7) vs 4.5 (1.3) and 4.8 (1.2) mg·kg FFM-1·min-1 in the adipose tissue and skeletal muscle-sub-groups, respectively, p < 0.05]. No statistically significant sex differences were found in the content of any of the measured proteins involved in lipid metabolism in adipose tissue or skeletal muscle. CONCLUSIONS: The molecular regulation of PFO may primarily lie within skeletal muscle rather than adipose tissue, involving processes relating to intramyocellular triglyceride hydrolysis (ATGL) and mitochondrial fatty acid transport (CPT1b). Future studies should explore alternative molecular mechanisms that may account for sexual dimorphism in exercise fuel metabolism.

ALTERATIONS OF LIPID LEVELS MAY INDUCE THE INSULIN RESISTANCE IN TYPE TWO DIABETES MELLITUS: A SYSTEMIC REVIEW

Diabetes mellitus (DM) is not one disorder; it represents a series of metabolic conditions related to hyperglycemia and caused by defects in hormone secretion and hormone action. Exposure to chronic hyperglycemia may result in microvascular complications in the retina (diabetic retinopathy), kidney (diabetic nephropathy), neuron (diabetic-neuropathy), skin, foot, and cardiac complications (stroke, hypertension…etc.). International Diabetes Federation estimates that 1.1 million children and adolescents aged 14–19 years have type one DM. Without interventions to halt the increase in diabetes, there will be at least 629 million people living with diabetes by 2045. In the body, white adipose tissue is the leading site for the storage of excess energy produced from the food intake in large quantities, of the development of insulin resistance (IR) and type 2 DM by the over intake of fatty acid in the body. It results in the accumulation of fatty acyl co-A (FA-CoA) within the myocytes. It leads to improper signaling of the insulin and reduces the level in the myocytes and pancreases beta cells. It combines with genetically reduces the expression of peroxisome proliferator-activated receptor-gamma (PPAR-γ) coactivator-1, initiates the inflammation process by the activation of the tumor necrotic factor alpha and protein kinase C. These alterations lead to further increase the intramyocellular FA-CoA and triglycerides. The sequence of events may develop mitochondrial dysfunction in the sarcolemma outer layers. Finally improves IR also with increasing intramyocellular lipids. This concept might be helpful to those who are pursuing endocrinology specialization, nursing staff, pharmacists, and other medical departments.

Novel metabolic disorders in skeletal muscle of Lipodystrophic Bscl2/Seipin deficient mice

Bscl2−/− mice recapitulate many of the major metabolic manifestations in Berardinelli-Seip congenital lipodystrophy type 2 (BSCL2) individuals, including lipodystrophy, hepatosteatosis, muscular hypertrophy, and insulin resistance. Metabolic defects in Bscl2−/− mice with regard to glucose and lipid metabolism in skeletal muscle have never been investigated. Here, we identified Bscl2−/− mice displayed reduced intramyocellular triglyceride (IMTG) content but increased glycogen storage predominantly in oxidative type I soleus muscle (SM). These changes were associated with increased incomplete fatty acid oxidation and glycogen synthesis. Interestingly, SM in Bscl2−/− mice demonstrated a fasting duration induced insulin sensitivity which was further confirmed by hyperinsulinemic-euglycemic clamp in SM of overnight fasted Bscl2−/− mice but reversed by raising circulating NEFA levels through intralipid infusion. Furthermore, mice with skeletal muscle-specific inactivation of BSCL2 manifested no changes in muscle deposition of lipids and glycogen, suggesting BSCL2 does not play a cell-autonomous role in muscle lipid and glucose homeostasis. Our study uncovers a novel link between muscle metabolic defects and insulin resistance, and underscores an important role of circulating NEFA in regulating oxidative muscle insulin signaling in BSCL2 lipodystrophy.

Quantification of muscle triglyceride synthesis rate requires an adjustment for total triglyceride content

Intramyocellular triglyceride (imTG) in skeletal muscle plays a significant role in metabolic health, and an infusion of [13C16]palmitate can be used to quantitate the in vivo fractional synthesis rate (FSR) and absolute synthesis rate (ASR) of imTGs. However, the extramyocellular TG (emTG) pool, unless precisely excised, contaminates the imTG pool, diluting the imTG-bound tracer enrichment and leading to underestimation of FSR. Because of the difficulty of excising the emTGs precisely, it would be advantageous to be able to calculate the imTG synthesis rate without dissecting the emTGs from each sample. Here, we tested the hypothesis that the ASR of total TGs (tTGs), a combination of imTGs and emTGs, calculated as "FSR × tTG pool," reasonably represents the imTG synthesis. Muscle lipid parameters were measured in nine healthy women at 90 and 170 min after the start of [13C16]palmitate infusion. While the measurements of tTG content, enrichment, and FSR did not correlate (P > 0.05), those of the tTG ASR were significantly correlated (r = 0.947, P < 0.05). These results demonstrate that when imTGs and emTGs are pooled, the resulting underestimation of imTG FSR is balanced by the overestimation of the imTG content. We conclude that imTG metabolism is reflected by the measurement of the tTG ASR.

Changes in markers for cardio-metabolic disease risk after only 1-2 weeks of a high saturated fat diet in overweight adults.

PurposeDiets high in saturated fat acids (SFA) have been linked with cardio-metabolic disease risk. The purpose of this study was to determine whether only 1–2 weeks of a high SFA diet could impact disease risk factors in overweight adults who normally eat a relatively low proportion of SFA (i.e., <40% of dietary fat).MethodsTwelve overweight (BMI: 27±1 kg/m2) young adults were studied before and after a 2-week diet that increased the proportion of SFA (<40% to 60% of dietary fat), while maintaining their daily intake of total fat, carbohydrate, protein, and calories. Insulin resistance, blood pressure, plasma markers of liver damage, total plasma cholesterol concentrations, and fatty acid profile within plasma and skeletal muscle lipid pools were assessed before and after the intervention.ResultsTotal plasma cholesterol concentration increased (148±5 vs. 164±8 mg/dl; P<0.05) after only one week, due exclusively to an increase in LDL-cholesterol (78±4 vs. 95±7 mg/dl; P<0.05). After two weeks, plasma aspartate amino transferase (AST) concentration increased (P<0.05) but we found no change in insulin resistance, or resting blood pressure. The diet increase the proportion of SFA in plasma (35±1% vs. 39±2%; P<0.05) and the intramyocellular triglyceride pool (32±1% vs. 37±1%; P<0.05) suggesting the fatty acids in these pools may readily exchange.ConclusionsAlthough blood lipids remain within normal clinical range, increasing saturated fat in diet for only 2 weeks raises plasma markers of cardiovascular risk (LDL-cholesterol) and liver damage (AST). In overweight, but healthy-young adults SFA accumulate in plasma and muscle after only 1–2 weeks of dietary increase.

Effects of Diet/Exercise and Pioglitazone on the Association between Fitness and Intramyocellular FFA Trafficking

Background: Intramyocellular (im) triglycerides (TG) are increased in athletes, but also insulin resistant (IR) adults. To elucidate this discrepancy, we studied FFA storage in imTG and im oleyl-carnitine (OC) concentrations in IR humans pre and post 2 methods of insulin sensitization (IS) in the context of fitness (VO2max). Methods: 39 adults (BMI 28-36 kg/m2) were given a diet/exercise program (DE; 11.7 ± 3.2 kg weight loss) or 30 mg/day pioglitazone (PI) for ∼19 weeks. Blood and muscle samples were taken before and after a 6 hour [U-13C]oleate infusion with either a euglycemic, hyperinsulinemic clamp (n=20) or saline infusion. Plasma oleate storage in imTG (nmol FFA/g muscle/hr) was calculated. Results: Quantative IS was similar in DE and PI groups. VO2max increased post DE (44 ± 1 to 46 ± 2 ml/kgFFM/min†), but not PI (45 ± 1 ml/kgFFM/min pre and post PI). At baseline, oleate storage in imTG during clamps correlated with VO2max (r=0.51*), but the δVO2max with treatment did not correlate with the δoleate storage in imTG. Following IS, VO2max correlated with imOC (r=0.46*); the latter was true for men (m) (r=0.89*), but not women (r=0.32), and for DE (m: r=0.97*) but not PI (m: r=0.70, p=0.18). δ VO2max correlated with δimOC (m: r=0.92*, f: r=0.57†), both post WL (r=0.91*) and PI (r=0.96*).Summary: In IR adults, IS influences the associations between fitness and markers of imFFA oxidation and storage in imTG during hyperinsulinemia. These relationships are more apparent in men and exaggerated post-IS. Conclusion: Fitness in men regulates imFFA trafficking towards storage and oxidation. *p&amp;lt;0.05; †p=NS. Disclosure S. Shadid: None. M.D. Jensen: Other Relationship; Self; Novo Nordisk A/S. Consultant; Self; Novo Nordisk A/S.

VLDL triglyceride accumulation in skeletal muscle and adipose tissue in type 2 diabetes.

Insulin resistance is closely linked to accumulation of lipid outside adipose tissue (ectopic fat storage). VLDL particles transport lipids from the liver to peripheral tissues. However, whether abnormalities in VLDL-triglyceride storage in muscle and adipose tissue exist in type 2 diabetes has previously been unknown, primarily because of methodological difficulties. Here, we review recent research on VLDL-triglyceride storage. In a recent study, men with type 2 diabetes had increased skeletal muscle VLDL-triglyceride storage compared to weight-matched nondiabetic men, potentially leading to intramyocellular triglyceride accumulation. In contrast, studies of adipose tissue VLDL-triglyceride storage have shown similar storage capacity in men with and without diabetes, both in the postabsorptive and the postprandial period. In the initial submission, studies have failed to show associations between lipoprotein lipase activity, considered the rate-limiting step in storage of lipids from lipoproteins, and VLDL-TG storage in both muscle and adipose tissue. Differences in muscle VLDL-triglyceride storage may lead to ectopic fat storage and contribute to the development of type 2 diabetes, whereas the ability to store VLDL-triglyceride in adipose tissue is preserved in type 2 diabetes.

Double diabetes: the cardiovascular implications of combining type 1 with type 2 diabetes

Double diabetes: the cardiovascular implications of combining type 1 with type 2 diabetes

Increased VLDL-TG Fatty Acid Storage in Skeletal Muscle in Men With Type 2 Diabetes.

Lipoprotein lipase (LPL) activity is considered the rate-limiting step of very-low-density-lipoprotein triglycerides (VLDL-TG) tissue storage, and has been suggested to relate to the development of obesity as well as insulin resistance and type 2 diabetes. The objective of the study was to assess the relationship between the quantitative storage of VLDL-TG fatty acids and LPL activity and other storage factors in muscle and adipose tissue. In addition, we examine whether such relations were influenced by type 2 diabetes. We recruited 23 men (12 with type 2 diabetes, 11 nondiabetic) matched for age and body mass index. Postabsorptive VLDL-TG muscle and subcutaneous adipose tissue (abdominal and leg) quantitative storage was measured using tissue biopsies in combination with a primed-constant infusion of ex vivo triolein labeled [1-14C]VLDL-TG and a bolus infusion of ex vivo triolein labeled [9,10-3H]VLDL-TG. Biopsies were analyzed for LPL activity and cellular storage factors. VLDL-TG storage rate was significantly greater in men with type 2 diabetes compared with nondiabetic men in muscle tissue (P = 0.02). We found no significant relationship between VLDL-TG storage rate and LPL activity or other storage factors in muscle or adipose tissue. However, LPL activity correlated with fractional VLDL-TG storage in abdominal fat (P = 0.04). Men with type 2 diabetes have increased VLDL-TG storage in muscle tissue, potentially contributing to increased intramyocellular triglyceride and ectopic lipid deposition. Neither muscle nor adipose tissue storage rates were related to LPL activity. This argues against LPL as a rate-limiting step in the postabsorptive quantitative storage of VLDL-TG.

MTORC2 and AMPK differentially regulate muscle triglyceride content via Perilipin 3

ObjectiveWe have recently shown that acute inhibition of both mTOR complexes (mTORC1 and mTORC2) increases whole-body lipid utilization, while mTORC1 inhibition had no effect. Therefore, we tested the hypothesis that mTORC2 regulates lipid metabolism in skeletal muscle. MethodsBody composition, substrate utilization and muscle lipid storage were measured in mice lacking mTORC2 activity in skeletal muscle (specific knockout of RICTOR (Ric mKO)). We further examined the RICTOR/mTORC2-controlled muscle metabolome and proteome; and performed follow-up studies in other genetic mouse models and in cell culture. ResultsRic mKO mice exhibited a greater reliance on fat as an energy substrate, a re-partitioning of lean to fat mass and an increase in intramyocellular triglyceride (IMTG) content, along with increases in several lipid metabolites in muscle. Unbiased proteomics revealed an increase in the expression of the lipid droplet binding protein Perilipin 3 (PLIN3) in muscle from Ric mKO mice. This was associated with increased AMPK activity in Ric mKO muscle. Reducing AMPK kinase activity decreased muscle PLIN3 expression and IMTG content. AMPK agonism, in turn, increased PLIN3 expression in a FoxO1 dependent manner. PLIN3 overexpression was sufficient to increase triglyceride content in muscle cells. ConclusionsWe identified a novel link between mTORC2 and PLIN3, which regulates lipid storage in muscle. While mTORC2 is a negative regulator, we further identified AMPK as a positive regulator of PLIN3, which impacts whole-body substrate utilization and nutrient partitioning.

Single Bout Of Aerobic Exercise Reduces Intrahepatic And Intramyocellular Triglyceride In Obese Individuals With Nafld

High amounts of intrahepatic triglyceride (IHTG) and intramyocellular triglyceride (IMTG) are common metabolic complications associated in obese individuals with Non-alcoholic fatty liver disease (NAFLD). Caloric restriction is often prescribed to treat NAFLD, however, the effects of aerobic exercise in reducing IHTG and IMTG is unknown. PURPOSE: The aim of this study was to evaluate the effect of a single bout of the American College of Sports Medicine physical activity guidelines for adults on IHTG and IMTG content obese individuals with NAFLD. METHODS: Ten obese people (Mean ± SD, Age 45.2±5.2 years, BMI=38.1±4.6 kg/m2) with NAFLD performed a single bout of aerobic exercise (30 minutes at 50% of V02max) on a motor driven treadmill. Magnetic resonance spectroscopy was used to evaluate IHTG and IMTG content before and immediately after the exercise bout. IMTG was evaluated from the soleus muscle. Duel Energy X-ray Absorptiometry (DXA) was used to measure body weight and percent body fat. RESULTS: A single bout of aerobic exercise resulted in a significant (p<0.05) decrease in IHTG from before (16.0 ± 2.8%) to after (14.2 ± 2.2%) the exercise bout. IMTG significantly (p<0.05) decreased from before (2.2 ± 0.9%) to after (1.3 ± 0.7%) the single exercise bout. As expected there was no significant change in body weight (103.1±4.2 kg and 102.9±4.2 kg) or percent body fat (38.9±2.1% and 39.2±2.1%) before and after the exercise bout. CONCLUSION: Performing even a single bout of physical activity as recommended by the ACSM reduces IHTG and IMTG obese persons with NAFLD.

Exercise and Weight Loss Improve Muscle Mitochondrial Respiration, Lipid Partitioning, and Insulin Sensitivity After Gastric Bypass Surgery.

Both Roux-en-Y gastric bypass (RYGB) surgery and exercise can improve insulin sensitivity in individuals with severe obesity. However, the impact of RYGB with or without exercise on skeletal muscle mitochondria, intramyocellular lipids, and insulin sensitivity index (SI) is unknown. We conducted a randomized exercise trial in patients (n = 101) who underwent RYGB surgery and completed either a 6-month moderate exercise (EX) or a health education control (CON) intervention. SI was determined by intravenous glucose tolerance test. Mitochondrial respiration and intramyocellular triglyceride, sphingolipid, and diacylglycerol content were measured in vastus lateralis biopsy specimens. We found that EX provided additional improvements in SI and that only EX improved cardiorespiratory fitness, mitochondrial respiration and enzyme activities, and cardiolipin profile with no change in mitochondrial content. Muscle triglycerides were reduced in type I fibers in CON, and sphingolipids decreased in both groups, with EX showing a further reduction in a number of ceramide species. In conclusion, exercise superimposed on bariatric surgery–induced weight loss enhances mitochondrial respiration, induces cardiolipin remodeling, reduces specific sphingolipids, and provides additional improvements in insulin sensitivity.

Glycemic Control, Skeletal Muscle Glucose Uptake And Lipid Metabolism In Mice With Skeletal Muscle Foxo1 Overexpression

Previous research has indicated a possible role for Forkhead Box protein O1 (FoxO1) in the pathogenesis of type 2 diabetes through its purported role in affecting whole body glycemic control and lipid metabolism. However, the literature indicating such a relationship is limited and has primarily relied on in vitro models. PURPOSE: The purpose of the present study was to use in vivo and ex vivo methodology to examine the role of FoxO1 on whole body glycemic control, skeletal muscle glucose metabolism and lipid metabolism. METHODS: Transgenic mice with skeletal muscle-specific overexpression of FoxO1 were subjected to intraperitoneal glucose tolerance testing (IPGTT) with concomitant plasma insulin analysis followed by ex vivo examination of skeletal muscle insulin stimulated glucose uptake, intramyocellular triglyceride (IMTG) storage and fatty acid oxidation. RESULTS: IPGTT and plasma insulin analysis revealed no differences between FoxO1 transgenic and wildtype (WT) mice. Likewise, basal level skeletal muscle protein expression levels of phosphoinositide kinase-3 (PI3K) and serine473 phosphorylated Akt (pAkt473) were not different between mouse strains. Additionally, FoxO1 did not exhibit any impairment in insulin stimulated glucose uptake. However, IMTG and fatty acid oxidation capacity was significantly (p<0.05) reduced in FoxO1 transgenic mice. CONCLUSION: These findings indicate that in vivo skeletal muscle FoxO1 overexpression does not impede whole body glycemic control or skeletal muscle insulin action. However, it does appear to reduce IMTG while impairing skeletal muscle lipid oxidation capacity.

ATGL-mediated triglyceride turnover and the regulation of mitochondrial capacity in skeletal muscle.

Emerging evidence indicates that skeletal muscle lipid droplets are an important control point for intracellular lipid homeostasis and that regulating fatty acid fluxes from lipid droplets might influence mitochondrial capacity. We used pharmacological blockers of the major triglyceride lipases, adipose triglyceride lipase (ATGL) and hormone-sensitive lipase, to show that a large proportion of the fatty acids that are transported into myotubes are trafficked through the intramyocellular triglyceride pool. We next tested whether increasing lipolysis from intramyocellular lipid droplets could activate transcriptional responses to enhance mitochondrial and fatty acid oxidative capacity. ATGL was overexpressed by adenoviral and adenoassociated viral infection in C2C12 myotubes and the tibialis anterior muscle of C57Bl/6 mice, respectively. ATGL overexpression in C2C12 myotubes increased lipolysis, which was associated with increased peroxisome proliferator-activated receptor (PPAR)-∂ activity, transcriptional upregulation of some PPAR∂ target genes, and enhanced mitochondrial capacity. The transcriptional responses were specific to ATGL actions and not a generalized increase in fatty acid flux in the myotubes. Marked ATGL overexpression (20-fold) induced modest molecular changes in the skeletal muscle of mice, but these effects were not sufficient to alter fatty acid oxidation. Together, these data demonstrate the importance of lipid droplets for myocellular fatty acid trafficking and the capacity to modulate mitochondrial capacity by enhancing lipid droplet lipolysis in vitro; however, this adaptive program is of minor importance when superimposing the normal metabolic stresses encountered in free-moving animals.