Brouwers B, Hesselink MK, Schrauwen Enhabced, Schrauwen-Hinderling VB Effects of Body composition tracking training on Enhabced lipid Healthy vegan eating in humans. Diluted HCl oxidafion added to stop the enzymatic reaction, and finally the optical density was measured at nm with readings at nm subtracted to account for optical imperfections in the plate. Skeletal muscle lipid content and insulin resistance: evidence for a paradox in endurance-trained athletes. Download PDF.

Enhanced lipid oxidation capacity -

Biochimica et biophysica acta , — Article CAS PubMed Google Scholar. Cytoplasmic lipid droplets: rediscovery of an old structure as a unique platform. Annals of the New York Academy of Sciences , — Article ADS CAS PubMed Google Scholar. Gao, Q. The lipid droplet-a well-connected organelle.

Frontiers in cell and developmental biology 3, 49 Article ADS PubMed PubMed Central Google Scholar. Badin, P. Altered skeletal muscle lipase expression and activity contribute to insulin resistance in humans.

Diabetes 60, — Article CAS PubMed PubMed Central Google Scholar. Samuel, V. Mechanisms for insulin resistance: common threads and missing links.

Cell , — van Loon, L. Increased intramuscular lipid storage in the insulin-resistant and endurance-trained state. Pflugers Arch , — DeFronzo, R. Skeletal muscle insulin resistance is the primary defect in type 2 diabetes. Diabetes care 32 Suppl 2, S— Wolins, N. Diabetes 55, — Dalen, K. LSDP5 is a PAT protein specifically expressed in fatty acid oxidizing tissues.

Bosma, M. Overexpression of PLIN5 in skeletal muscle promotes oxidative gene expression and intramyocellular lipid content without compromising insulin sensitivity. Pollak, N. Cardiac-specific overexpression of perilipin 5 provokes severe cardiac steatosis via the formation of a lipolytic barrier.

Journal of lipid research 54, — Wang, C. Perilipin 5 improves hepatic lipotoxicity by inhibiting lipolysis. Hepatology 61, — The lipid droplet coat protein perilipin 5 also localizes to muscle mitochondria.

Histochemistry and cell biology , — Wang, H. Perilipin 5, a lipid droplet-associated protein, provides physical and metabolic linkage to mitochondria. Journal of lipid research 52, — Harris, L. Perilipin 5-Driven Lipid Droplet Accumulation in Skeletal Muscle Stimulates the Expression of Fibroblast Growth Factor Diabetes 64, — Kase, E.

Primary defects in lipolysis and insulin action in skeletal muscle cells from type 2 diabetic individuals. Randle, P. The glucose fatty-acid cycle.

Its role in insulin sensitivity and the metabolic disturbances of diabetes mellitus. Lancet 1, — CAS PubMed Google Scholar. Regulation of skeletal muscle lipolysis and oxidative metabolism by the co-lipase CGI Journal of lipid research 53, — Billecke, N.

Perilipin 5 mediated lipid droplet remodelling revealed by coherent Raman imaging. Integrative biology: quantitative biosciences from nano to macro 7, — Article CAS Google Scholar. Pickersgill, L. Key role for ceramides in mediating insulin resistance in human muscle cells. The Journal of biological chemistry , — Mason, R.

PLIN5 deletion remodels intracellular lipid composition and causes insulin resistance in muscle. Molecular metabolism 3, — Bindesboll, C. Fatty acids regulate perilipin5 in muscle by activating PPARdelta. Amati, F. Skeletal muscle triglycerides, diacylglycerols, and ceramides in insulin resistance: another paradox in endurance-trained athletes?

Granneman, J. Interactions of perilipin-5 Plin5 with adipose triglyceride lipase. Goodpaster, B. Skeletal muscle lipid content and insulin resistance: evidence for a paradox in endurance-trained athletes.

The Journal of clinical endocrinology and metabolism 86, — Louche, K. Endurance exercise training up-regulates lipolytic proteins and reduces triglyceride content in skeletal muscle of obese subjects.

The Journal of clinical endocrinology and metabolism 98, — Shepherd, S. Sprint interval and traditional endurance training increase net intramuscular triglyceride breakdown and expression of perilipin 2 and 5.

The Journal of physiology , — Henriksson, J. Effect of training and nutrition on the development of skeletal muscle. Journal of sports sciences 13 Spec No , S25—30 Muscle fuel selection: effect of exercise and training.

Proc Nutr Soc 54, — Hunnicutt, J. Saturated fatty acid-induced insulin resistance in rat adipocytes. Diabetes 43, — Storlien, L. Influence of dietary fat composition on development of insulin resistance in rats. Relationship to muscle triglyceride and omega-3 fatty acids in muscle phospholipid.

Diabetes 40, — The interplay of protein kinase A and perilipin 5 regulates cardiac lipolysis. Sanders, M. Endogenous and Synthetic ABHD5 Ligands Regulate ABHD5-Perilipin Interactions and Lipolysis in Fat and Muscle.

Cell metabolism 22, — Kuramoto, K. Perilipin 5, a lipid droplet-binding protein, protects heart from oxidative burden by sequestering fatty acid from excessive oxidation.

Chabowski, A. Not only accumulation, but also saturation status of intramuscular lipids is significantly affected by PPARgamma activation. Acta Physiol Oxf , — Hancock, C.

High-fat diets cause insulin resistance despite an increase in muscle mitochondria. Proceedings of the National Academy of Sciences of the United States of America , — Oakes, N. Roles of Fatty Acid oversupply and impaired oxidation in lipid accumulation in tissues of obese rats.

J Lipids , Riou, M. Predictors of cardiovascular fitness in sedentary men. Article PubMed Google Scholar. Ukropcova, B. Dynamic changes in fat oxidation in human primary myocytes mirror metabolic characteristics of the donor.

The Journal of clinical investigation , — Bakke, S. Palmitic acid follows a different metabolic pathway than oleic acid in human skeletal muscle cells; lower lipolysis rate despite an increased level of adipose triglyceride lipase.

Laurens, C. Adipogenic progenitors from obese human skeletal muscle give rise to functional white adipocytes that contribute to insulin resistance. International journal of obesity 40, — Bourlier, V. Enhanced glucose metabolism is preserved in cultured primary myotubes from obese donors in response to exercise training.

Igal, R. Acylglycerol recycling from triacylglycerol to phospholipid, not lipase activity, is defective in neutral lipid storage disease fibroblasts. High-fat diet-mediated lipotoxicity and insulin resistance is related to impaired lipase expression in mouse skeletal muscle.

Endocrinology , — Coue, M. Defective Natriuretic Peptide Receptor Signaling in Skeletal Muscle Links Obesity to Type 2 Diabetes. Download references. The authors thank Justine Bertrand-Michel, Fabien Riols and Aurélie Batut Lipidomic Core Facility, INSERM, UMR [part of Toulouse Metatoul Platform] for lipidomic analysis, advice and technical assistance.

We also thank Cédric Baudelin and Xavier Sudre from the Animal Care Facility. Special thanks for all the participants for their time and invaluable cooperation.

The authors would also like to thank Josée St-Onge, Marie-Eve Riou, Etienne Pigeon, Erick Couillard, Guy Fournier, Jean Doré, Marc Brunet, Linda Drolet, Nancy Parent, Marie Tremblay, Rollande Couture, Valérie-Eve Julien, Rachelle Duchesne and Ginette Lapierre for their expert technical assistance in the LIME study.

DL is a member of Institut Universitaire de France. INSERM, UMR, Institute of Metabolic and Cardiovascular Diseases, Toulouse, France.

University of Toulouse, Paul Sabatier University, France. Department of Medicine, Laval University, Quebec City, Canada. Department of Kinesiology, Laval University, Quebec City, Canada. Department of Clinical Biochemistry, Toulouse University Hospitals, Toulouse, France.

You can also search for this author in PubMed Google Scholar. and C. researched data and edited the manuscript. wrote the manuscript. Cedric Moro is the guarantor of this work and, as such, had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

This work is licensed under a Creative Commons Attribution 4. Reprints and permissions. Sci Rep 6 , Download citation. Received : 07 September Accepted : 07 November Published : 06 December Anyone you share the following link with will be able to read this content:.

Sorry, a shareable link is not currently available for this article. Provided by the Springer Nature SharedIt content-sharing initiative. European Journal of Applied Physiology European Journal of Clinical Nutrition By submitting a comment you agree to abide by our Terms and Community Guidelines.

If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate. Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Skip to main content Thank you for visiting nature. nature scientific reports articles article. Download PDF. Subjects Fat metabolism Pre-diabetes. Abstract Lipid droplets LD play a central role in lipid homeostasis by controlling transient fatty acid FA storage and release from triacylglycerols stores, while preventing high levels of cellular toxic lipids.

Introduction Cytosolic lipid droplets LD are important energy-storage organelles in most tissues 1. Results PLInN5 relates to oxidative capacity in mouse and human skeletal muscle Muscle PLIN5 content was measured in various types of skeletal muscles in the mouse Fig.

Figure 1. PLIN5 relates to oxidative capacity in mouse and human skeletal muscle. Full size image. Figure 2. Figure 3. PLIN5 overexpression facilitates lipid oxidation upon increased metabolic demand. Figure 4. PLIN5 exerts a protective role against palmitate-induced lipotoxicity. Figure 5. Figure 6.

PLIN5 knockdown in mouse skeletal muscle ameliorates insulin action under high-fat feeding. Discussion LD play a critical role in oxidative tissues to maintain appropriate fuel supply during periods of energy needs but also to buffer daily fluxes of FA to avoid cellular lipotoxicity.

Figure 7. Proposed mechanistic model of PLIN5 in skeletal muscle upon various metabolic states. Skeletal muscle primary cell culture Satellite cells from rectus abdominis of healthy male subjects age Overexpression of PLIN5 in human myotubes For overexpression experiments, adenoviruses expressing in tandem GFP and human PLIN5 hPLIN5 were used Vector Biolabs, Philadelphia, PA.

Tissue-specific [2- 3 H] deoxyglucose uptake in vivo Muscle-specific glucose uptake was assessed in response to an intraperitoneal bolus injection of 2-[1,2- 3 H N ]deoxy-D-Glucose PerkinElmer, Boston, Massachusetts 0.

Determination of neutral lipid and ceramide content Triacylglycerols and diacylglycerols were determined by gas chromatography, and ceramide and sphingomyelin species by high-performance liquid chromatography-tandem mass spectrometry after total lipid extraction as described elsewhere 45 , Statistical analyses All statistical analyses were performed using GraphPad Prism 5.

Additional Information How to cite this article : Laurens, C. References Fujimoto, T. Article CAS PubMed Google Scholar Fujimoto, T. Article ADS CAS PubMed Google Scholar Gao, Q. Article ADS PubMed PubMed Central Google Scholar Badin, P.

Article CAS PubMed PubMed Central Google Scholar Samuel, V. Article CAS PubMed PubMed Central Google Scholar van Loon, L. Article CAS PubMed Google Scholar DeFronzo, R. Article CAS PubMed PubMed Central Google Scholar Wolins, N.

Article CAS PubMed Google Scholar Dalen, K. Article CAS PubMed Google Scholar Bosma, M. Article CAS PubMed Google Scholar Pollak, N. Article CAS PubMed PubMed Central Google Scholar Wang, C. Article CAS PubMed Google Scholar Wang, H.

Article CAS PubMed PubMed Central Google Scholar Harris, L. Article CAS PubMed PubMed Central Google Scholar Kase, E. Article CAS PubMed Google Scholar Randle, P. CAS PubMed Google Scholar Badin, P. Article CAS PubMed PubMed Central Google Scholar Billecke, N. Article CAS Google Scholar Pickersgill, L.

Article CAS PubMed Google Scholar Mason, R. Article CAS PubMed PubMed Central Google Scholar Bindesboll, C. Article CAS PubMed PubMed Central Google Scholar Amati, F. Article CAS PubMed PubMed Central Google Scholar Granneman, J.

Article CAS PubMed Google Scholar Goodpaster, B. Article CAS PubMed Google Scholar Louche, K. Article CAS PubMed Google Scholar Shepherd, S. Article CAS PubMed Google Scholar Henriksson, J.

Article CAS PubMed Google Scholar Hunnicutt, J. Article CAS PubMed Google Scholar Storlien, L. Article CAS PubMed Google Scholar Sanders, M.

Article CAS PubMed PubMed Central Google Scholar Kuramoto, K. Article CAS PubMed PubMed Central Google Scholar Chabowski, A. Article CAS Google Scholar Hancock, C. Article ADS PubMed PubMed Central Google Scholar Oakes, N.

Article CAS PubMed PubMed Central Google Scholar Riou, M. Article PubMed Google Scholar Ukropcova, B. Article CAS PubMed PubMed Central Google Scholar Bakke, S. Article CAS PubMed Google Scholar Laurens, C.

Article CAS PubMed Google Scholar Bourlier, V. Diabetes 1 August ; 56 8 : — A reduced capacity for mitochondrial fatty acid oxidation in skeletal muscle has been proposed as a major factor leading to the accumulation of intramuscular lipids and their subsequent deleterious effects on insulin action.

Here, we examine markers of mitochondrial fatty acid oxidative capacity in rodent models of insulin resistance associated with an oversupply of lipids.

Several markers of muscle mitochondrial fatty acid oxidative capacity were measured, including 14 C-palmitate oxidation, palmitoyl-CoA oxidation in isolated mitochondria, oxidative enzyme activity citrate synthase, β-hydroxyacyl CoA dehydrogenase, medium-chain acyl-CoA dehydrogenase, and carnitine palmitoyl-transferase 1 , and expression of proteins involved in mitochondrial metabolism.

Enzyme activity and mitochondrial protein expression were also examined in muscle from other rodent models of insulin resistance. Furthermore, oxidative enzyme activity and protein expression of peroxisome proliferator—activated receptor γ coactivator PGC -1α, uncoupling protein UCP 3, and mitochondrial respiratory chain subunits were significantly elevated in fat-fed animals.

These findings suggest that high lipid availability does not lead to intramuscular lipid accumulation and insulin resistance in rodents by decreasing muscle mitochondrial fatty acid oxidative capacity.

Insulin resistance, which represents an impaired ability for insulin to exert its effects on glucose and lipid homeostasis, is a key metabolic defect associated with obesity and type 2 diabetes. The factors underlying the development of insulin resistance are not fully elucidated; however, there is substantial literature linking lipid accumulation in skeletal muscle to reduced insulin sensitivity 1.

Specifically, potent lipid metabolites, including fatty acyl CoAs, diacylglycerols, and ceramides, whose concentrations correlate with intramuscular triglyceride levels, have been shown to antagonize the metabolic actions of insulin in skeletal muscle 1. Several mechanisms may be responsible for lipid accumulation in skeletal muscle.

In humans 2 and rodents 3 , 4 , dysregulated insulin action has been linked with an increased uptake of fatty acids into muscle, suggesting that an increased availability of fatty acids contributes to excess muscle lipid. There is also a growing body of evidence suggesting that defective muscle mitochondrial metabolism, and a subsequent impaired ability to oxidize fatty acids, may be a causative factor in the accumulation of intramuscular lipid and the development of insulin resistance.

In muscle from obese insulin-resistant humans, the activity of enzymes of oxidative metabolism and fatty acid utilization are reduced 5. Muscle mitochondria from subjects with insulin resistance or type 2 diabetes are reduced in size and number and have diminished activity of proteins in the respiratory chain 6 — 8.

These defects appear to be particularly pronounced in the subsarcolemmal mitochondria, which are considered to be most the important site for muscle fatty acid oxidation 7. In vivo functional studies using magnetic resonance spectroscopy have also demonstrated reduced mitochondrial oxidative and phosphorylation capacities in skeletal muscle from insulin-resistant elderly subjects 9 , from patients with type 2 diabetes 10 , and from insulin-resistant offspring of patients with type 2 diabetes Consistent with the observed defects in mitochondrial metabolism in insulin resistance and type 2 diabetes, some 12 , 13 , but not all 6 , 14 , studies have shown reduced expression of peroxisome proliferator—activated receptor PPAR γ coactivator PGC -1α, a transcriptional coactivator that is a key regulator of mitochondrial biogenesis and fatty acid oxidation in skeletal muscle It must be noted, however, that the results of many of the abovementioned studies are correlative and it still remains to be determined whether reduced fatty acid metabolism in muscle mitochondria is an innate characteristic or whether it is secondary to other metabolic irregularities such as increased lipid availability.

Rodent models, both genetic and dietary, are commonly used to examine the mechanisms underlying the development of insulin resistance in humans. In many of these animal models, such as high-fat—fed rodents and those with an absence of leptin signaling e.

Whether defects in mitochondrial fatty acid metabolism are present in skeletal muscle of these animals is, however, not clear. Studies 3 , 16 — 20 have shown mitochondrial fatty acid oxidation and the activity of oxidative enzymes are elevated in muscle of fat-fed rats and obese Zucker rats.

Equally, however, several recent studies 21 — 24 in rodent models of insulin resistance have reported deficits in a variety of markers of mitochondrial metabolism in muscle. Therefore, the aim of the current study was to determine whether high lipid availability contributes to insulin resistance, in part, through a decreased mitochondrial fatty acid oxidative capacity in skeletal muscle.

D; Research Diets, New Brunswick, NJ. Rats were fed the standard or high-fat diet ad libitum for a period of 4 weeks. Vincent's Hospital Animal Experimentation Ethics Committee, following guidelines issued by the National Health and Medical Research Council of Australia.

were performed in overnight-fasted mice. Blood samples were obtained from the tail tip at the indicated times, and glucose levels were measured using a glucometer AccuCheck II; Roche, New South Wales, Castle Hill, Australia.

Serum measurements were performed on blood collected from the chest cavity and centrifuged at 14, g for 10 min to obtain the serum.

Insulin concentrations were measured using a sensitive radioimmunoassay kit Linco Research, St. Louis, MO. The concentration of nonesterified fatty acids was determined using a colorimetric kit Wako Pure Chemical Industries, Osaka, Japan.

Oxygen consumption rate V o 2 was measured using an eight-chamber indirect calorimeter Oxymax series; Columbus Instruments, Columbus, OH with an airflow of 0.

Studies were commenced after 2 h of acclimation to the metabolic chamber 20 × 10 × V o 2 was measured in individual mice at min intervals over a h period under a consistent environmental temperature 22°C. During the study, mice had ad libitum access to food and water.

Fat and lean body mass was measured using dual-energy X-ray absorptiometry Lunar PIXImus2 mouse densitometer; GE Healthcare in accordance with the manufacturer's instructions. Palmitate and glutamate oxidation were measured in muscle homogenates using a modified method of that described by Kim et al.

For assessment of substrate oxidation, 50 μl of muscle homogenate was incubated with μl reaction mixture pH 7. Substrates were 0. For palmitate incubations, 14 C counts present in the acid-soluble fraction were also measured and combined with the CO 2 values to give the total palmitate oxidation rate.

Protein content in the homogenates were measured using the Bradford method protein assay kit; Bio-Rad Laboratories, Regents Park, Australia. Mitochondria were isolated from the quadriceps muscle as described by Bruce et al.

Oxygen consumption was measured at 30°C in a Clark-type oxygen electrode Strathkelvin Instruments, Motherwell, Scotland. For each assay 0. Protein content of the mitochondrial preparations were measured as described above.

Citrate synthase, β-hydroxyacyl CoA dehydrogenase βHAD , and medium-chain acyl-CoA dehydrogenase MCAD were determined at 30°C, as described previously 28 , 29 , using a Spectra Max microplate spectrophotometer Molecular Devices, Sunnyvale, CA. Carnitine palmitoyl-transferase CPT -1 activity was measured at 30°C in isolated mitochondria and corrected to muscle wet weight based on recovery rates of citrate synthase Enzyme activities are presented as units per gram wet weight, where units are defined as micromoles per minute.

Powdered muscle samples were resuspended in radioimmunoprecipitation assay buffer PBS, pH 7. Equal amounts of tissue lysates 10 μg protein were resolved by SDS-PAGE and immunoblotted with appropriate antibodies against PGC-1α Chemicon International, Temecula, CA , uncoupling protein UCP 3 Affinity Bioreagents, Golden, CO , cytochrome oxidase complex IV subunit 1 Invitrogen, Victoria, Australia , and an antibody cocktail that recognizes several subunits of the mitochondrial respiratory chain MS; Mitosciences, Eugene, OR.

Immunolabeled bands were quantitated by densitometry. Data are presented as means ± SE. An unpaired Student's t test was used for comparison of relevant groups.

Table 1 shows the body mass, fat mass, and oxygen consumption measured in 5 and 20 weeks fat-fed mice along with their standard diet controls. Mice fed a high-fat diet for 5 weeks weighed the same as their standard diet—fed controls; however, they displayed a 2. At the week time point, fat-fed mice weighed on average 4.

We measured energy expenditure and food intake, as changes in either of these parameters may have contributed to the increased adiposity observed in the fat-fed animals. As expected, the respiratory exchange ratio was significantly lower in the fat-fed animals, reflecting the difference in diet between the two groups Table 1.

To determine whether the increased adiposity in the fat-fed mice was associated with reduced insulin action, we examined whole-body glucose clearance during an intraperitoneal glucose tolerance test Fig. At both the 5- and week time point, high-fat feeding resulted in a significant impairment in glucose clearance Fig.

Fat-fed mice displayed higher circulating insulin levels after both 5 weeks 0. High-fat feeding also resulted in a significant increase in circulating nonesterified fatty acid levels compared with standard diet—fed controls at both the 5-week 0.

To determine the effect of the high-fat regime on muscle fatty acid oxidative capacity, we measured the palmitate oxidation rate in tissue homogenates.

Recently, it has been suggested that a reduced ratio of complete measured as CO 2 production to incomplete measured as acid-soluble metabolites fatty acid oxidation may be important in high-fat diet—induced insulin resistance 23 ; however, we observed no difference in this ratio between standard diet—and fat-fed mice in our assays 5 weeks: 2.

We also measured glutamate oxidation and found no significant difference between standard diet—and fat-fed animals at either the 5-week 96 ± 8 vs. As a further measure of fatty acid oxidative capacity, we measured oxygen consumption in isolated mitochondria, with palmitoyl-CoA as the substrate.

Similar to the homogenate oxidations, there was no significant difference in mitochondrial respiration when glutamate was used as an alternative substrate data not shown. We also measured the activity of a range of enzymes associated with fatty acid utilization and oxidative capacity, including βHAD, MCAD, CPT-1, and citrate synthase.

Consistent with the results observed in the homogenate oxidations and mitochondrial respiration measurements, there was a significant increase in the activity of all of these enzymes in muscle from 5 and 20 weeks fat-fed mice compared with standard diet controls Table 2.

Our data suggested an increase in mitochondrial content in skeletal muscle of mice fed a high-fat diet. Accordingly, we examined the protein expression of several subunits of the respiratory chain, both nuclear kDa subunit of complex II, core protein 2 subunit of complex III, and the α subunit of complex V and mitochondrial ND6 subunit of complex I and subunit 1 of complex IV encoded, as well as the expression of PGC-1α, given its important role in the regulation of mitochondrial biogenesis and fatty acid oxidation In muscle from mice fed the high-fat diet for 5 or 20 weeks, there was increased protein expression of all subunits from the respiratory chain compared with standard diet—fed controls Fig.

Additionally, we determined the protein expression of UCP3 because although its precise function has yet to be determined, it has been suggested to be a potentially important protein for the regulation of fatty acid transport, and metabolism and its expression is increased during periods of elevated fatty acid oxidation 30 , There was a 1.

We also examined protein expression of PGC-1α, UCP3, and respiratory chain subunits complex I and complex III and found elevated protein levels in muscle from the insulin-resistant animals Fig.

Inappropriate lipid deposition in skeletal muscle is recognized as an important factor associated with insulin resistance 1. Recent studies 7 — 9 , 12 , 13 in humans have suggested that aberrant mitochondrial fatty acid metabolism may be associated with intramuscular lipid accumulation in conditions of reduced insulin action.

Many of these studies, however, have been conducted in subjects with well-established insulin resistance, and whether defects in muscle mitochondrial metabolism are a cause or correlate of insulin resistance remains to be clarified.

In the current study, we examined markers of mitochondrial fatty acid metabolism in skeletal muscle from rodents, in which insulin resistance is associated with an oversupply of lipids. Despite this, we observed increased fatty acid oxidative capacity; higher activity of βHAD, MCAD, CPT1, and citrate synthase; and elevated protein expression of PGC-1α, UCP3, and mitochondrial respiratory chain subunits in skeletal muscle from these animals.

Collectively, our findings suggest that mitochondrial fatty acid oxidative capacity is increased in skeletal muscle from insulin-resistant rodents. Insulin resistance is associated with elevated fatty acid levels in the circulation.

The increased capacity for fatty acid oxidation observed in skeletal muscle of insulin-resistant rodents in the current study is potentially a compensatory response to elevated fatty acid substrate availability. Mice with muscle-specific overexpression of lipoprotein lipase, which increases fatty acid influx into skeletal muscle, display extensive mitochondrial proliferation Fatty acids have also been shown to increase PGC-1α expression in muscle cells 33 and β-cells 34 , and this is associated with increased mitochondrial metabolism 33 , The fatty acid subtype appears to be important 33 , as palmitate alone reduces PGC-1α expression 36 ; however, this may be related to its activation of inflammatory pathways that are known to impact on PGC-1α expression The coordinated increase in the activity of β-oxidation and trichloroacetic cycle enzymes, along with the increased expression of respiratory chain subunits observed in the current study, suggest that PGC-1α is in part mediating the increase in fatty acid oxidative capacity and mitochondrial content by coactivating its known binding partners estrogen-related receptor α, PPARα, PPARδ, and nuclear respiratory factor-1 Mechanistically elevated fatty acid could stimulate PGC-1α expression and increase fatty acid oxidative capacity via a number of pathways.

Fatty acids are known ligands for the PPAR family of nuclear hormone receptors, and part of the increase in fatty acid oxidative capacity in the current study may be related to direct activation of PPARα or PPARδ by fatty acids.

In skeletal muscle, activation of PPARδ has been shown to increase expression of PGC-1α PGC-1α is also known to coactivate PPARδ 39 , resulting in a feed-forward loop that stabilizes PGC-1α protein expression and drives the transcription of genes associated with fatty acid metabolism Other studies in insulin-resistant rodents have reported reduced expression of PGC-1α and other markers of mitochondrial metabolism in muscle 21 — The reason for the disparity in results is unclear but may be related to methodological factors such as diet composition, the length of high-fat feeding, or the particular muscle groups examined i.

Furthermore, it must also be noted that many studies in rodents and humans have only examined mRNA expression for PGC-1α, and as PGC-1α is known to be posttranslationally modified, its gene expression may not always correlate with protein levels Despite our findings of elevated fatty acid oxidative capacity in insulin-resistant rodents, increased intramuscular lipid is a characteristic feature of these animal models 1 , 4.

Excess lipid storage may be in part related to a greater increase in the efficiency of fatty acid uptake, as it has been observed in insulin-resistant rodents that there is increased clearance of fatty acid into muscle 3 , 4. We did not directly measure fatty acid uptake in our animals; however, adipose mass and circulating nonesterified fatty acids levels were elevated in fat-fed mice Table 1 , and the increased UCP3 protein in all of our rodent models is consistent with an increased influx of fatty acid into muscle 30 , 31 , Skeletal muscle is quantitatively an important tissue for whole-body fat oxidation, and lipid overload in muscle may be linked to the reduction in muscle mass observed in insulin resistance Table 1 ; [ 42 ].

Another factor to be considered is that our ex vivo measurements represent the capacity of enzymes and fatty acid oxidation pathways under favorable conditions of substrate availability, and in vivo, regulatory factors such as elevated levels of malonyl-CoA 43 or reduced activity of adiponectin and leptin signaling pathways 44 might contribute to ectopic deposition of lipids in muscle.

The proposed causative role for mitochondrial dysfunction in the development of insulin resistance is yet to be definitively demonstrated.

Several studies 7 — 9 , 12 , 13 have reported defects in various markers of mitochondrial metabolism and biogenesis in skeletal muscle from subjects with obesity, insulin resistance, and type 2 diabetes. These results may be confounded by various disease factors; however, investigations demonstrating mitochondrial defects in first-degree relatives of patients with type 2 diabetes 6 , 11 , 12 suggest that mitochondrial dysfunction may be among the earliest defects that predisposes these subjects to lipid accumulation and insulin resistance, as opposed to increased lipid availability leading to decreased mitochondrial function and then insulin resistance.

Studies in humans in which lipid availability has been experimentally altered have provided inconclusive results in this respect. Acute oversupply of lipids, via lipid infusion, has been shown to reduce gene expression for PGC-1α and mitochondrial respiratory chain components in muscle 45 , However, 1 week of pharmacological reduction of plasma free fatty acids and subsequently intramuscular acyl-CoA concentrations in insulin-resistant subjects also reduced gene expression of PGC-1α and other mitochondrial markers in muscle Dietary studies in humans are also equivocal with high-fat feeding studies reporting increases 48 , decreases 24 , or no change 49 in various markers of muscle mitochondrial metabolism.

Thus, the effect of elevated lipid availability on muscle mitochondrial oxidative capacity in humans remains to be clarified.

In summary, our study demonstrates that fatty acid oxidative capacity and protein expression of PGC-1α and mitochondrial respiratory chain subunits are upregulated in skeletal muscle of a variety of rodent models of insulin resistance.

We suggest that these changes likely represent a homeostatic response to attempt to compensate for elevated availability of lipids in these animals. We therefore conclude that increased lipid availability is unlikely to lead to lipid accumulation and insulin resistance via a specific effect to diminish mitochondrial fatty acid oxidative capacity.

C : Incremental areas under the curve as an indicator of glucose clearance in the standard diet—and fat-fed animals.

Data represent the means ± SE of 10—11 mice for panels A — C and 3—5 mice for panel D. standard diet—fed controls. A : Palmitate oxidation rate in muscle homogenates.

B : ADP-stimulated respiration rate in isolated muscle mitochondria, with palmitoyl-CoA as substrate. Data represent the means ± SE of 5—6 mice. Immunoblots for markers of mitochondrial metabolism and biogenesis in skeletal muscle from 5 and 20 weeks standard diet SD —and fat-fed mice.

Equal amounts of muscle lysates 10 μg protein were resolved by SDS-PAGE and immunoblotted with specific antibodies for PGC-1α, UCP3, and mitochondrial respiratory chain subunits. SD, standard diet. Data are means ± SE of 6—11 animals per group.

V o 2 and RER respiratory exchange ratio represents the average values recorded over a h period. Activity of enzymes of fatty acid utilization and oxidative capacity in standard diet—and fat-fed mice.

Data are means ± SE of 5—6 animals per group. Activities are expressed as units per gram wet weight. Citrate synthase, βHAD, and MCAD activities were determined directly in muscle homogenates, while CPT-1 activity was determined in isolated mitochondria and is expressed per gram wet weight based on recovery rates of citrate synthase Activity of enzymes of fatty acid utilization and oxidative capacity in rodent models of insulin resistance.

Data are means ± SE of 5—7 animals per group. org on 29 May DOI: The costs of publication of this article were defrayed in part by the payment of page charges. Section solely to indicate this fact. This work was supported by the National Health and Medical Research Council of Australia NHMRC , the Diabetes Australia Research Trust DART , and the Rebecca L.

Cooper Medical Research Foundation. and C. are supported by Peter Doherty Fellowships and G. by a Research Fellowship from the NHMRC. The contribution of Dr. Bronwyn Hegarty, Andrew Hoy, Donna Wilks, and Ron Enriquez to specific methodological and technical aspects of the study is gratefully acknowledged.

We thank the Biological Testing Facility at the Garvan Institute for their help with animal care.

Fatty acids Healthy vegan eating an important energy source during exercise. Lopid Enhanced lipid oxidation capacity and substrate Enhanced lipid oxidation capacity are determinants of the lipdi Healthy vegan eating absolute contribution of fatty acids and glucose to total Healthy vegan eating expenditure. Endurance-trained Enhanced lipid oxidation capacity have Enhwnced high oxidative capacity, while, in insulin-resistant individuals, fat oxidation is compromised. Fatty acids that are oxidised during exercise originate from the circulation white adipose tissue lipolysisas well as from lipolysis of intramyocellular lipid droplets. Moreover, hepatic fat may contribute to fat oxidation during exercise. Nowadays, it is clear that myocellular lipid droplets are dynamic organelles and that number, size, subcellular distribution, lipid droplet coat proteins and mitochondrial tethering of lipid droplets are determinants of fat oxidation during exercise. Nigel LilidClinton Enhanced lipid oxidation capacity. BruceSusan M. EnyancedMindful productivity tips L. HoehnTrina So Enhanced lipid oxidation capacity, Michael S. RolphGregory J. Cooney; Excess Lipid Availability Increases Mitochondrial Fatty Acid Oxidative Capacity in Muscle : Evidence Against a Role for Reduced Fatty Acid Oxidation in Lipid-Induced Insulin Resistance in Rodents.

Video

Mechanism of Lipid Peroxidation