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

Omega-3 Attenuates Disrupted Neurotransmission and Partially Protects Metabolic Dysfunction Caused by Obesity in Wistar Rats

Omega-3 (n3) is a polyunsaturated fatty acid well known for its anti-inflammatory and neuroprotective properties. Obesity is linked to chronic inflammation that disrupts metabolism, the intestine physiology and the central nervous system functioning. This study aims to determine if n3 supplementation can interfere with the effects of obesity on the mitochondrial activity, intestinal barrier, and neurotransmitter levels in the brain of Wistar rats that received cafeteria diet (CAF). We examined adipose tissue, skeletal muscle, plasma, intestine, and the cerebral cortex of four groups: CT (control diet), CTn3 (control diet with n3 supplementation), CAF, and CAFn3 (CAF and n3). Diets were offered for 13 weeks, with n3 supplementation in the final 5 weeks. Adipose tissue Electron Transport Chain complexes I, II, and III showed higher activity in CAF groups, as did complexes III and IV in skeletal muscle. Acetate levels in plasma were reduced in CAF groups, and Lipopolysaccharide (LPS) was higher in the CAF group but reduced in CAFn3 group. Claudin-5 in the intestine was lower in CAF groups, with no n3 supplementation effect. In the cerebral cortex, dopamine levels were decreased with CAF, which was reversed by n3. DOPAC, a dopamine metabolite, also showed a supplementation effect, and HVA, a diet effect. Serotonin levels increased in the CAF group that received supplementation. Therefore, we demonstrate disturbances in mitochondria, plasma, intestine and brain of rats submitted to CAF and the potential benefit of n3 supplementation in endotoxemia and neurotransmitter levels.

Potential regulatory role of PGC-1α within the skeletal muscle during metabolic adaptations in response to high-fat diet feeding in animal models

High-fat diet (HFD) feeding in rodents has become an essential tool to critically analyze and study the pathological effects of obesity, including mitochondrial dysfunction and insulin resistance. Peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) regulates cellular energy metabolism to influence insulin sensitivity, beyond its active role in stimulating mitochondrial biogenesis to facilitate skeletal muscle adaptations in response to HFD feeding. Here, some of the major electronic databases like PubMed, Embase, and Web of Science were accessed to update and critically discuss information on the potential role of PGC-1α during metabolic adaptations within the skeletal muscle in response to HFD feeding in rodents. In fact, available evidence suggests that partial exposure to HFD feeding (potentially during the early stages of disease development) is associated with impaired metabolic adaptations within the skeletal muscle, including mitochondrial dysfunction and reduced insulin sensitivity. In terms of implicated molecular mechanisms, these negative effects are partially associated with reduced activity of PGC-1α, together with the phosphorylation of protein kinase B and altered expression of genes involving nuclear respiratory factor 1 and mitochondrial transcription factor A within the skeletal muscle. Notably, metabolic abnormalities observed with chronic exposure to HFD (likely during the late stages of disease development) may potentially occur independently of PGC-1α regulation within the muscle of rodents. Summarized evidence suggests the causal relationship between PGC-1α regulation and effective modulations of mitochondrial biogenesis and metabolic flexibility during the different stages of disease development. It further indicates that prominent interventions like caloric restriction and physical exercise may affect PGC-1α regulation during effective modulation of metabolic processes.

The BET inhibitor JQ1 targets fat metabolism and counteracts obesity

INTRODUCTION

Obesity, one of the most frequent health problems in the adult population, is a condition characterized by excessive white adipose tissue accumulation and accompanied by the increased risk to develop other disorders such as type II diabetes, cardiovascular disorders, physical disability, frailty and sarcopenia. Total fat mass frequently increases during aging, often coexisting with sarcopenia, thus resulting in an emerging condition defined sarcopenic obesity (SO). Our previous data demonstrated the relevant role of the bromo and extra-terminal domain (BET) proteins inhibitor JQ1 in attenuating inflammation and fibrosis in sarcopenic mice. Moreover, we preliminarily observed that JQ1 administration markedly reduces white adipose tissue mass, suggesting a potential role of BET proteins on visceral fat deposition during aging.

OBJECTIVES

Starting from those observations, the aim of this study was to investigate the ability of JQ1 to reduce adiposity in a chronic diet-induced obesity (DIO) mouse model mimicking the human metabolic syndrome.

METHODS

Male C57BL/6J mice were divided in subgroups, either fed a standard diet or a high fat diet for 22 or 12 weeks, treated over the last 14 days with JQ1 or with vehicle.

RESULTS

The results showed that JQ1 administration reduces fat mass, preserving skeletal muscle mass and function. A direct JQ1 lipolytic effect was demonstrated on mature adipocyte cultures. JQ1-mediated loss of adipose tissue mass was not associated with systemic inflammation or with lipid accumulation in muscle and liver. JQ1 administration did not impinge on skeletal muscle metabolism and oxidative capability, as shown by the lack of significant impact on mitochondrial mass and biogenesis.

CONCLUSION

In conclusion, the current data highlight a potential benefit of JQ1 administration to counteract obesity, suggesting epigenetic modulation as a prospective target in the treatment of obesity and sarcopenic obesity, despite the underlying multiorgan molecular mechanism is still not completely elucidated.

Alternating current electromagnetic field exposure lessens intramyocellular lipid accumulation due to high-fat feeding via enhanced lipid metabolism in mice

Long-term high-fat feeding results in intramyocellular lipid accumulation, leading to insulin resistance. Intramyocellular lipid accumulation is related to an energy imbalance between excess fat intake and fatty acid consumption. Alternating current electromagnetic field exposure has been shown to enhance mitochondrial metabolism in the liver and sperm. Therefore, we hypothesized that alternating current electromagnetic field exposure would ameliorate high-fat diet-induced intramyocellular lipid accumulation via activation of fatty acid consumption. C57BL/6J mice were either fed a normal diet (ND), a normal diet and exposed to an alternating current electromagnetic field (ND+EMF), a high-fat diet (HFD), or a high-fat diet and exposed to an alternating current electromagnetic field (HFD+EMF). Electromagnetic field exposure was administered 8 hrs/day for 16 weeks using an alternating current electromagnetic field device (max.180 mT, Hokoen, Utatsu, Japan). Tibialis anterior muscles were collected for measurement of intramyocellular lipids, AMPK phosphorylation, FAT/CD-36, and carnitine palmitoyltransferase (CPT)-1b protein expression levels. Intramyocellular lipid levels were lower in the HFD + EMF than in the HFD group. The levels of AMPK phosphorylation, FAT/CD-36, and CPT-1b protein levels were higher in the HFD + EMF than in the HFD group. These results indicate that alternating current electromagnetic field exposure decreases intramyocellular lipid accumulation via increased fat consumption.

Melatonin Alleviates the Impairment of Muscle Bioenergetics and Protein Quality Control Systems in Leptin-Deficiency-Induced Obesity

Leptin is critically compromised in the major common forms of obesity. Skeletal muscle is the main effector tissue for energy modification that occurs as a result of the effect of endocrine axes, such as leptin signaling. Our study was carried out using skeletal muscle from a leptin-deficient animal model, in order to ascertain the importance of this hormone and to identify the major skeletal muscle mechanisms affected. We also examined the therapeutic role of melatonin against leptin-induced muscle wasting. Here, we report that leptin deficiency stimulates fatty acid β-oxidation, which results in mitochondrial uncoupling and the suppression of mitochondrial oxidative damage; however, it increases cytosolic oxidative damage. Thus, different nutrient-sensing pathways are disrupted, impairing proteostasis and promoting lipid anabolism, which induces myofiber degeneration and drives oxidative type I fiber conversion. Melatonin treatment plays a significant role in reducing cellular oxidative damage and regulating energy homeostasis and fuel utilization. Melatonin is able to improve both glucose and mitochondrial metabolism and partially restore proteostasis. Taken together, our study demonstrates melatonin to be a decisive mitochondrial function-fate regulator in skeletal muscle, with implications for resembling physiological energy requirements and targeting glycolytic type II fiber recovery.

Acrolein induces mitochondrial dysfunction and insulin resistance in muscle and adipose tissues in vitro and in vivo

Type 2 diabetes mellitus (DM) is a common chronic condition characterized by persistent hyperglycemia and is associated with insulin resistance (IR) in critical glucose-consuming tissues, including skeletal muscle and adipose tissue. Oxidative stress and mitochondrial dysfunction are known to play key roles in IR. Acrolein is a reactive aldehyde found in the diet and environment that is generated as a fatty acid product through the glucose autooxidation process under hyperglycemic conditions. Our previous studies have shown that acrolein impairs insulin sensitivity in normal and diabetic mice, and this effect can be reversed by scavenging acrolein. This study demonstrated that acrolein increased oxidative stress and inhibited mitochondrial respiration in differentiated C2C12 myotubes and differentiated 3T3-L1 adipocytes. As a result, insulin signaling pathways were inhibited, leading to reduced glucose uptake. Treatment with acrolein scavengers, N-acetylcysteine, or carnosine ameliorated mitochondrial dysfunction and inhibited insulin signaling. Additionally, an increase in acrolein expression correlated with mitochondrial dysfunction in the muscle and adipose tissues of diabetic mice. These findings suggest that acrolein-induced mitochondrial dysfunction contributes to IR, and scavenging acrolein is a potential therapeutic approach for treating IR.

Intergenerational Hyperglycemia Impairs Mitochondrial Function and Follicular Development and Causes Oxidative Stress in Rat Ovaries Independent of the Consumption of a High-Fat Diet

We analyzed the influence of maternal hyperglycemia and the post-weaning consumption of a high-fat diet on the mitochondrial function and ovarian development of the adult pups of diabetic rats. Female rats received citrate buffer (Control-C) or Streptozotocin (for diabetes induction-D) on postnatal day 5. These adult rats were mated to obtain female pups (O) from control dams (OC) or from diabetic dams (OD), and they received a standard diet (SD) or high-fat diet (HFD) from weaning to adulthood and were distributed into OC/SD, OC/HFD, OD/SD, and OD/HFD. In adulthood, the OGTT and AUC were performed. These rats were anesthetized and euthanized for sample collection. A high percentage of diabetic rats were found to be in the OD/HFD group (OD/HFD 40% vs. OC/SD 0% p < 0.05). Progesterone concentrations were lower in the experimental groups (OC/HFD 0.40 ± 0.04; OD/SD 0.30 ± 0.03; OD/HFD 0.24 ± 0.04 vs. OC/SD 0.45 ± 0.03 p < 0.0001). There was a lower expression of MFF (OD/SD 0.34 ± 0.33; OD/HFD 0.29 ± 0.2 vs. OC/SD 1.0 ± 0.41 p = 0.0015) and MFN2 in the OD/SD and OD/HFD groups (OD/SD 0.41 ± 0.21; OD/HFD 0.77 ± 0.18 vs. OC/SD 1.0 ± 0.45 p = 0.0037). The number of follicles was lower in the OD/SD and OD/HFD groups. A lower staining intensity for SOD and Catalase and higher staining intensity for MDA were found in ovarian cells in the OC/HFD, OD/SD, and OD/HFD groups. Fetal programming was responsible for mitochondrial dysfunction, ovarian reserve loss, and oxidative stress; the association of maternal diabetes with an HFD was responsible for the higher occurrence of diabetes in female adult pups.

High-fat diet increases electron transfer flavoprotein synthesis and lipid respiration in skeletal muscle during exercise training in female mice

High-fat diet (HFD) and exercise remodel skeletal muscle mitochondria. The electron transfer flavoproteins (ETF) transfer reducing equivalents from β-oxidation into the electron transfer system. Exercise may stimulate the synthesis of ETF proteins to increase lipid respiration. We determined mitochondrial remodeling for lipid respiration through ETF in the context of higher mitochondrial abundance/capacity seen in female mice. We hypothesized HFD would be a greater stimulus than exercise to remodel ETF and lipid pathways through increased protein synthesis alongside increased lipid respiration. Female C57BL/6J mice (n = 15 per group) consumed HFD or low-fat diet (LFD) for 4 weeks then remained sedentary (SED) or completed 8 weeks of treadmill training (EX). We determined mitochondrial lipid respiration, RNA abundance, individual protein synthesis, and abundance for ETFα, ETFβ, and ETF dehydrogenase (ETFDH). HFD increased absolute and relative lipid respiration (p = 0.018 and p = 0.034) and RNA abundance for ETFα (p = 0.026), ETFβ (p = 0.003), and ETFDH (p = 0.0003). HFD increased synthesis for ETFα and ETFDH (p = 0.0007 and p = 0.002). EX increased synthesis of ETFβ and ETFDH (p = 0.008 and p = 0.006). Higher synthesis rates of ETF were not always reflected in greater protein abundance. Greater synthesis of ETF during HFD indicates mitochondrial remodeling which may contribute higher mitochondrial lipid respiration through enhanced ETF function.

The tissue-specific metabolic effects of the PPARα agonist ciprofibrate in insulin-resistant male individuals: a double-blind, randomized, placebo-controlled crossover study

OBJECTIVE

Insulin resistance is characterized by ectopic fat accumulation leading to cardiac diastolic dysfunction and nonalcoholic fatty liver disease. The objective of this study was to determine whether treatment with the peroxisome proliferator-activated receptor-α (PPARα) agonist ciprofibrate has direct effects on cardiac and hepatic metabolism and can improve insulin sensitivity and cardiac function in insulin-resistant volunteers.

METHODS

Ten insulin-resistant male volunteers received 100 mg/d of ciprofibrate and placebo for 5 weeks in a randomized double-blind crossover study. Insulin-stimulated metabolic rate of glucose (MRgluc) was measured using dynamic 18 F-fluorodeoxyglucose-positron emission tomography (18 F-FDG-PET). Additionally, cardiac function, whole-body insulin sensitivity, intrahepatic lipid content, skeletal muscle gene expression, 24-hour blood pressure, and substrate metabolism were measured.

RESULTS

Whole-body insulin sensitivity, energy metabolism, and body composition were unchanged after ciprofibrate treatment. Ciprofibrate treatment decreased insulin-stimulated hepatic MRgluc and increased hepatic lipid content. Myocardial net MRgluc tended to decrease after ciprofibrate treatment, but ciprofibrate treatment had no effect on cardiac function and cardiac energy status. In addition, no changes in PPAR-related gene expression in muscle were found.

CONCLUSIONS

Ciprofibrate treatment increased hepatic lipid accumulation and lowered MRgluc, without affecting whole-body insulin sensitivity. Furthermore, parameters of cardiac function or cardiac energy status were not altered upon ciprofibrate treatment.

The interactive effects of psychosocial stress and diet composition on health in primates

Social disadvantage and diet composition independently impact myriad dimensions of health. They are closely entwined, as social disadvantage often yields poor diet quality, and may interact to fuel differential health outcomes. This paper reviews effects of psychosocial stress and diet composition on health in nonhuman primates and their implications for aging and human health. We examined the effects of social subordination stress and Mediterranean versus Western diet on multiple systems. We report that psychosocial stress and Western diet have independent and additive adverse effects on hypothalamic-pituitary-adrenal and autonomic nervous system reactivity to psychological stressors, brain structure, and ovarian function. Compared to the Mediterranean diet, the Western diet resulted in accelerated aging, nonalcoholic fatty liver disease, insulin resistance, gut microbial changes associated with increased disease risk, neuroinflammation, neuroanatomical perturbations, anxiety, and social isolation. This comprehensive, multisystem investigation lays the foundation for future investigations of the mechanistic underpinnings of psychosocial stress and diet effects on health, and advances the promise of the Mediterranean diet as a therapeutic intervention on psychosocial stress.

Reduced glucose tolerance and insulin sensitivity after prolonged exercise in endurance athletes

AIM

The purpose of this study was to 1. investigate if glucose tolerance is affected after one acute bout of different types of exercise; 2. assess if potential differences between two exercise paradigms are related to changes in mitochondrial function; and 3. determine if endurance athletes differ from nonendurance-trained controls in their metabolic responses to the exercise paradigms.

METHODS

Nine endurance athletes (END) and eight healthy nonendurance-trained controls (CON) were studied. Oral glucose tolerance tests (OGTT) and mitochondrial function were assessed on three occasions: in the morning, 14 h after an overnight fast without prior exercise (RE), as well as after 3 h of prolonged continuous exercise at 65% of VO2 max (PE) or 5 × 4 min at ~95% of VO2 max (HIIT) on a cycle ergometer.

RESULTS

Glucose tolerance was markedly reduced in END after PE compared with RE. END also exhibited elevated fasting serum FFA and ketones levels, reduced insulin sensitivity and glucose oxidation, and increased fat oxidation during the OGTT. CON showed insignificant changes in glucose tolerance and the aforementioned measurements compared with RE. HIIT did not alter glucose tolerance in either group. Neither PE nor HIIT affected mitochondrial function in either group. END also exhibited increased activity of 3-hydroxyacyl-CoA dehydrogenase activity in muscle extracts vs. CON.

CONCLUSION

Prolonged exercise reduces glucose tolerance and increases insulin resistance in endurance athletes the following day. These findings are associated with an increased lipid load, a high capacity to oxidize lipids, and increased fat oxidation.

Nutritional Considerations for the Vegan Athlete

Accepting a continued rise in the prevalence of vegan-type diets in the general population is also likely to occur in athletic populations, it is of importance to assess the potential impact on athletic performance, adaptation, and recovery. Nutritional consideration for the athlete requires optimization of energy, macronutrient, and micronutrient intakes, and potentially the judicious selection of dietary supplements, all specified to meet the individual athlete's training and performance goals. The purpose of this review is to assess whether adopting a vegan diet is likely to impinge on such optimal nutrition and, where so, consider evidence based yet practical and pragmatic nutritional recommendations. Current evidence does not support that a vegan-type diet will enhance performance, adaptation, or recovery in athletes, but equally suggests that an athlete can follow a (more) vegan diet without detriment. A clear caveat, however, is that vegan diets consumed spontaneously may induce suboptimal intakes of key nutrients, most notably quantity and/or quality of dietary protein and specific micronutrients (eg, iron, calcium, vitamin B12, and vitamin D). As such, optimal vegan sports nutrition requires (more) careful consideration, evaluation, and planning. Individual/seasonal goals, training modalities, athlete type, and sensory/cultural/ethical preferences, among other factors, should all be considered when planning and adopting a vegan diet.

From Obesity-Induced Low-Grade Inflammation to Lipotoxicity and Mitochondrial Dysfunction: Altered Multi-Crosstalk between Adipose Tissue and Metabolically Active Organs

Obesity is a major risk factor for several metabolic diseases, including type 2 diabetes, hyperlipidemia, cardiovascular diseases, and brain disorders. Growing evidence suggests the importance of inter-organ metabolic communication for the progression of obesity and the subsequent onset of related disorders. This review provides a broad overview of the pathophysiological processes that from adipose tissue dysfunction leading to altered multi-tissue crosstalk relevant to regulating energy homeostasis and the etiology of obesity. First, a comprehensive description of the role of adipose tissue was reported. Then, attention was turned toward the unhealthy expansion of adipose tissue, low-grade inflammatory state, metabolic inflexibility, and mitochondrial dysfunction as root causes of systemic metabolic alterations. In addition, a short spot was devoted to iron deficiency in obese conditions and the role of the hepcidin-ferroportin relationship in the management of this issue. Finally, different classes of bioactive food components were described with a perspective to enhance their potential preventive and therapeutic use against obesity-related diseases.

Association between skeletal muscle mitochondrial dysfunction and insulin resistance in patients with rheumatoid arthritis: a case-control study

BACKGROUND

Insulin resistance affects a substantial proportion of patients with rheumatoid arthritis (RA). Skeletal muscle mitochondrial dysfunction results in the accumulation of lipid intermediates that interfere with insulin signaling. We therefore sought to determine if lower oxidative phosphorylation and muscle mitochondrial content are associated with insulin resistance in patients with RA.

METHODS

This was a cross-sectional prospective study of RA patients. Matsuda index from the glucose tolerance test was used to estimate insulin sensitivity. Mitochondrial content was measured by citrate synthase (CS) activity in snap-frozen muscle samples. Mitochondrial function was measured by using high-resolution respirometry of permeabilized muscle fibers and electron transport chain complex IV enzyme kinetics in isolated mitochondrial subpopulations.

RESULTS

RA participants demonstrated lower insulin sensitivity as measured by the Matsuda index compared to controls [median 3.95 IQR (2.33, 5.64) vs. 7.17 (5.83, 7.75), p = 0.02]. There was lower muscle mitochondrial content among RA vs. controls [median 60 mU/mg IQR (45, 80) vs. 79 mU/mg (65, 97), p = 0.03]. Notably, OxPhos normalized to mitochondrial content was higher among RA vs. controls [mean difference (95% CI) = 0.14 (0.02, 0.26), p = 0.03], indicating a possible compensatory mechanism for lower mitochondrial content or lipid overload. Among RA participants, the activity of muscle CS activity was not correlated with the Matsuda index (ρ =  - 0.05, p = 0.84), but it was positively correlated with self-reported (IPAQ) total MET-minutes/week (ρ = 0.44, p = 0.03) and Actigraph-measured time on physical activity (MET rate) (ρ = 0.47, p = 0.03).

CONCLUSIONS

Mitochondrial content and function were not associated with insulin sensitivity among participants with RA. However, our study demonstrates a significant association between muscle mitochondrial content and physical activity level, highlighting the potential for future exercise interventions that enhance mitochondrial efficiency in RA patients.

GCMS fingerprints and phenolic extracts of Allium sativum inhibit key enzymes associated with type 2 diabetes

Objectives

Inhibition of carbohydrate digestion enzymes (α-amylase and α-glucosidase) has been reported in studies as a therapeutic approach for the management or treatment of type 2 diabetes mellitus, owing to its potential to decrease postprandial hyperglycemia. The anti-diabetic potential of Allium sativum (also known as garlic) against diabetes mellitus has been established. Therefore, in this study, we assessed the antidiabetic potential of A. sativum using in vitro enzyme assays after which we explored computational modelling approach using the quantified GC-MS identities to unravel the key bioactive compounds responsible for the anti-diabetic potential.

Methods

We used in vitro enzyme inhibition assays (α-amylase and α-glucosidase) to evaluate antidiabetic potential and subsequently performed gas chromatography-mass spectroscopy (GC-MS) to identify and quantify the bioactive compounds of the plant extract. The identified bioactive compounds were subjected to in silico docking and pharmacokinetic assessment.

Results

A. sativum phenolic extract showed high dose-dependent inhibition of α-amylase and α-glucosidase (p < 0.05). Interestingly, the extract inhibited α-glucosidase with a half maximal inhibitory concentration of 53.75 μg/mL, a value higher than that obtained for the standard acarbose. Docking simulation revealed that morellinol and phentolamine were the best binders of α-glucosidase, with mean affinity values of -7.3 and -7.1 kcal/mol, respectively. These compounds had good affinity toward active site residues of the enzyme, and excellent drug-like and pharmacokinetic properties supporting clinical applications.

Conclusions

Our research reveals the potential of A. sativum as a functional food for the management of type 2 diabetes, and suggests that morellinol and phentolamine may be the most active compounds responsible for this anti-diabetic prowess. Therefore these compounds require further clinical asessment to demonstrate their potential for drug development.

Evaluation of the Combined Administration of Chlorella fusca and Vibrio proteolyticus in Diets for Chelon labrosus: Effects on Growth, Metabolism, and Digestive Functionality

This study aimed to evaluate the combined effect of dietary Chlorella fusca and ethanol-inactivated Vibrio proteolyticus DCF12.2 (C + V diet) in Chelon labrosus juveniles, highlighting their nutritional, physiological, and morphological effects. The results showed that the combined dietary inclusion of C. fusca and V. proteolyticus significantly enhanced growth performance and feed utilization compared to the control group. The C + V diet increased the fish lipid quality index (FLQ), n-3 polyunsaturated fatty acids, and n-3/n-6 ratio, which might be beneficial in terms of human nutrition. The C + V diet considerably increased carbohydrate metabolic activity by statistically boosting plasma glucose. The dietary inclusion of C. fusca in conjunction with V. proteolyticus increased metabolic enzyme activity as well as intestinal absorption capacity compared to that found in the control group. In conclusion, the experimental diet was suitable for feeding C. labrosus, increasing their growth and the nutritional characteristics of the muscle and intestine, without causing tissue damage.

The impact of high-fat feeding and parkin overexpression on skeletal muscle mass, mitochondrial respiration, and H2O2 emission

Obesity is a major risk factor for developing various health problems, including insulin resistance and type 2 diabetes. Although controversial, accumulation of mitochondrial dysfunction, and notably an increase in mitochondrial reactive oxygen species (ROS) production, was proposed as a key contributor leading to obesity-induced insulin resistance. Here, our goal was to investigate whether Parkin overexpression, a key regulator of the removal of dysfunctional mitochondria through mitophagy, could confer protection against obesity-induced mitochondrial dysfunction. To this end, intramuscular injections of adeno-associated viruses (AAVs) were performed to overexpress Parkin in limb muscle of 6-mo-old mice fed a control diet (CD) or a high-fat diet (HFD) for 12 wk. An AAV-expressing the green fluorescent protein (GFP) was used as control. HFD increased fat mass, altered glycemia, and resulted in insulin resistance. Parkin overexpression resulted in an increase in muscle mass in both CD and HFD mice. In CD mice, Parkin overexpression increased maximal mitochondrial respiration and lowered H₂O₂ emission. HFD increased mitochondrial respiration and, surprisingly, also lowered H₂O₂ emission. Parkin overexpression did not significantly impact mitochondrial function in HFD mice. Taken altogether, our results indicate that Parkin overexpression positively impacts muscle and mitochondrial health under basal conditions and challenges the notion that intrinsic mitochondrial dysfunction is involved in the development of insulin resistance caused by high-fat feeding.

Metabolic dysfunctions promoted by AIN-93G standard diet compared with three obesity-inducing diets in C57BL/6J mice

Researchers from different fields have studied the causes of obesity and associated comorbidities, proposing ways to prevent and treat this condition by using a common animal model of obesity to create a profound energy imbalance in young adult rodents. However, to confirm the harmful effects of consuming a high-fat and hypercaloric diet, it is common to include normolipidic and normocaloric control groups in the experimental protocols. This study compared the effect of three experimental diets described in the literature - namely, a high-fat diet, a high-fat and high-sucrose diet, and a high-fat and high-fructose diet - to induce obesity in C57BL/6 J mice with the standard AIN-93G diet as a control. We hypothesize that the AIN diet formulation is not a good control in this type of experiment because this diet promotes weight gain and metabolic dysfunctions similar to the hypercaloric diet. The metabolic data of animals fed the AIN-93G diet were similar to those of the high-calorie groups (development of steatosis and hyperlipidemia). However, it is important to emphasize that the group fed a high-fat diet had a higher percentage of total fat (p = 0.0002) and abdominal fat (p = 0.013) compared to the other groups. Also, the high-fat group responded poorly to glucose and insulin tolerance tests, showing a picture of insulin resistance. As expected, the intake of the AIN-93G diet promotes metabolic alterations in the animals like the high-fat formulations. Therefore, although this diet continues to be used as the gold standard for growth and maintenance, it warrants a reassessment of its composition to minimize the metabolic changes observed in this study, thus updating its fitness as a normocaloric model of a standard rodent diet.

Ginger Root Extract Improves GI Health in Diabetic Rats by Improving Intestinal Integrity and Mitochondrial Function

Background Emerging research suggests hyperglycemia can increase intestinal permeability. Ginger and its bioactive compounds have been reported to benefit diabetic animals due to their anti-inflammatory and antioxidant properties. In this study, we revealed the beneficial effect of gingerol-enriched ginger (GEG) on intestinal health (i.e., barrier function, mitochondrial function, and anti-inflammation) in diabetic rats. Methods Thirty-three male Sprague Dawley rats were assigned to three groups: low-fat diet (control group), high-fat-diet (HFD) + streptozotocin (single low dose 35 mg/kg body weight (BW) after 2 weeks of HFD feeding) (DM group), and HFD + streptozotocin + 0.75% GEG in diet (GEG group) for 42 days. Glucose tolerance tests (GTT) and insulin tolerance tests (ITT) were conducted at baseline and prior to sample collection. Total pancreatic insulin content was determined by ELISA. Total RNA of intestinal tissues was extracted for mRNA expression using qRT-PCR. Results Compared to the DM group, the GEG group had improved glucose tolerance and increased pancreatic insulin content. Compared to those without GEG (DM group), GEG supplementation (GEG group) increased the gene expression of tight junction (Claudin-3) and antioxidant capacity (SOD1), while it decreased the gene expression for mitochondrial fusion (MFN1), fission (FIS1), biogenesis (PGC-1α, TFAM), mitophagy (LC3B, P62, PINK1), and inflammation (NF-κB). Conclusions Ginger root extract improved glucose homeostasis in diabetic rats, in part, via improving intestinal integrity and mitochondrial dysfunction of GI health.

Failure of diet-induced transcriptional adaptations in alpha-synuclein transgenic mice

Nutritional influences have been discussed as potential modulators of Parkinson's disease (PD) pathology through various epidemiological and physiological studies. In animal models, a high-fat diet (HFD) with greater intake of lipid-derived calories leads to accelerated disease onset and progression. The underlying molecular mechanisms of HFD-induced aggravated pathology, however, remain largely unclear. In this study, we aimed to further illuminate the effects of a fat-enriched diet in PD by examining the brainstem and hippocampal transcriptome of alpha-synuclein transgenic mice exposed to a life-long HFD. Investigating individual transcript isoforms, differential gene expression and co-expression clusters, we observed that transcriptional differences between wild-type (WT) and transgenic animals intensified in both regions under HFD. Both brainstem and hippocampus displayed strikingly similar transcriptomic perturbation patterns. Interestingly, expression differences resulted mainly from responses in WT animals to HFD, while these genes remained largely unchanged or were even slightly oppositely regulated by diet in transgenic animals. Genes and co-expressed gene groups exhibiting this dysregulation were linked to metabolic and mitochondrial pathways. Our findings propose the failure of metabolic adaptions as the potential explanation for accelerated disease unfolding under exposure to HFD. From the identified clusters of co-expressed genes, several candidates lend themselves to further functional investigations.

Linking Mitochondrial Function to Insulin Resistance: Focusing on Comparing the Old and the Young

Long-term intake of high-energy diet can lead to decreased insulin sensitivity and even insulin resistance, eventually leading to diabetes. Diabetes often occurs in middle-aged and elderly people. However, there is growing evidence that the incidence rate of young body is increasing over the years. This means that insulin resistance can be caused by excessive energy intake in both young and old people. In this study, high-fat diet (HFD) and normal diet were fed to rats of elderly experimental group (EE), elderly control group (EC), young experimental group (YE), and young control group (YC), respectively, for 8 weeks, by which insulin resistance model was obtained. Insulin sensitivity was measured, histopathology changes in liver and skeletal muscle tissues were observed, and mitochondrial fusion and division and cell senescence were detected in four groups of rats. The results showed that both young and elderly rats developed significant insulin resistance, fat deposition, decline of mitochondrial function and mitochondrial biosynthesis in liver and skeletal muscle, and cell aging after HFD feeding. In addition, the degree of mitochondrial dysfunction and aging in young rats was similar to that of aged rats fed a normal diet after HFD. This experiment provides a reference for an in-depth study of the regulatory mechanisms of cellular energy metabolism in this state.

Nicotinamide Riboside Supplementation to Suckling Male Mice Improves Lipid and Energy Metabolism in Skeletal Muscle and Liver in Adulthood

Nicotinamide riboside, an NAD⁺ precursor, has been attracting a lot of attention in recent years due to its potential benefits against multiple metabolic complications and age-related disorders related to NAD⁺ decline in tissues. The metabolic programming activity of NR supplementation in early-life stages is much less known. Here, we studied the long-term programming effects of mild NR supplementation during the suckling period on lipid and oxidative metabolism in skeletal muscle and liver tissues using an animal model. Suckling male mice received a daily oral dose of NR or vehicle (water) from day 2 to 20 of age, were weaned at day 21 onto a chow diet, and at day 90 were distributed to either a high-fat diet (HFD) or a normal-fat diet for 10 weeks. Compared to controls, NR-treated mice were protected against HFD-induced triacylglycerol accumulation in skeletal muscle and displayed lower triacylglycerol levels and steatosis degree in the liver and distinct capacities for fat oxidation and decreased lipogenesis in both tissues, paralleling signs of enhanced sirtuin 1 and AMP-dependent protein kinase signaling. These pre-clinical findings suggest that mild NR supplementation in early postnatal life beneficially impacts lipid and energy metabolism in skeletal muscle and liver in adulthood, serving as a potential preventive strategy against obesity-related disorders characterized by ectopic lipid accumulation.

Metabolic Flexibility and Its Impact on Health Outcomes

A metabolically flexible state exists when there is a rapid switch between glucose and fatty acids during the transition between the fed and fasting state. This flexibility in fuel choice serves to prevent hyperglycemia following a meal and simultaneously ensures an adequate amount of blood glucose is available for delivery to the brain and exclusively glycolytic tissues during fasting. The modern era is characterized by chronic overnutrition in which a mixture of fuels is delivered to the mitochondria in an unabated manner thereby uncoupling the feast and famine situation. The continuous influx of fuel leads to accumulation of reducing equivalents in the mitochondria and an increase in the mitochondrial membrane potential. These changes create a microenvironment fostering the generation of reactive oxygen species and other metabolites leading to deleterious protein modification, cell injury, and ultimately clinical disease. Insulin resistance may also play a primary role in this deleterious effect. The imbalance between mitochondrial energy delivery and use is made worse with a sedentary lifestyle. Maneuvers that restore energy balance across the mitochondria activate pathways that remove or repair damaged molecules and restore the plasticity characteristic of normal energy metabolism. Readily available strategies to maintain energy balance across the mitochondria include exercise, various forms of caloric restriction, administration of sodium-glucose cotransporter-2 inhibitors, cold exposure, and hypobaric hypoxia.

The combination of endurance exercise and SGTC (Salvia-Ginseng-Trigonella-Cinnamon) ameliorate mitochondrial markers' overexpression with sufficient ATP production in the skeletal muscle of mice fed AGEs-rich high-fat diet

BACKGROUND

Skeletal muscle mitochondria is one of the most important affected sites of T2DM and its molecular mechanism is yet to be elucidated. Some recent theories believed that mitochondrial markers are upregulated in response to high fat induced T2DM; however, the reasons and the affected factors are still uncertain. In this regard, we aimed to investigate the effect of high fat induced T2DM on mitochondrial markers of skeletal muscle, and an herbal component along with endurance exercise, as probable treatments, in AGE-rich high-fat diet (AGEs-HFD) induced T2DM mice.

METHODS

T2DM was induced by 16 weeks of AGEs-HFD consumption in male C57BL/6 mice, followed by 8 weeks of drugs ingestion and endurance exercise treatments (n = 6 in each group and total number of 42 mice). The herbal component was an aquatic extract of Salvia officinalis, Trigonella foenum-graecum, Panax ginseng, and Cinnamomum zeylanicum, termed "SGTC". We then examined the relative expression of several mitochondrial markers, including Ppargc1α, Tfam, and electron transport chain genes and ATP levels, in skeletal muscle samples.

RESULTS

T2DM was successfully induced according to morphological, biochemical, and molecular observations. All mitochondrial markers, including Ppargc1a, Tfam, Cpt2, and electron transport chain genes, were upregulated in T2DM group compared to controls with no significant changes in the ATP levels. Most mitochondrial markers were downregulated by drug treatment compared to T2DM, but the ATP level was not significantly altered. All mitochondrial markers were upregulated in exercised group compared to T2DM with mild increase in the ATP level. The Ex + SGTC group had moderate level of mitochondrial markers compared to T2DM, but the highest ATP production.

CONCLUSION

The highly significant overexpression of mitochondrial markers may be in response to free fatty acid overload. However, the lack of significant change in the ATP level may be a result of ROS generation due to electron leakage in the AGEsRAGE axis and electron transport chain. Almost all treatments ameliorate mitochondrial markers' overexpression. The SGTC appears to regulate this with its antioxidant properties. Instead, exercise upregulated mitochondrial markers efficiently; however, the most efficient results, i.e. the most ATP production among the treatments, were observed in the Ex + SGTC group.

Limited Metabolic Effect of the CREBRFR457Q Obesity Variant in Mice

The Arg457Gln missense variant in the CREBRF gene has previously been identified as driving excess body weight in Pacific/Oceanic populations. Intriguingly, Arg457Gln variant carriers also demonstrate paradoxical reductions in diabetes risk, indicating that the gene has a critical role in whole-body metabolism. To study the function of this variant in more detail, we generated mice on an FVB/N background with the Crebrf Arg458Gln variant knocked in to replace the endogenous Crebrf. The whole-body metabolic phenotype was characterized for male and female mice on a regular chow diet or an 8-week high-fat challenge. Regular assessment of body composition found that the Crebrf variant had no influence on total body weight or fat mass at any time point. Glucose tolerance tests demonstrated no obvious genotype effect on glucose homeostasis, with indirect calorimetry measures of whole-body energy expenditure likewise unaffected. Male chow-fed variant carriers displayed a trend towards increased lean mass and significantly reduced sensitivity to insulin administration. Overall, this novel mouse model showed only limited phenotypic effects associated with the Crebrf missense variant. The inability to recapitulate results of human association studies may invite reconsideration of the precise mechanistic link between CREBRF function and the risks of obesity and diabetes in variant allele carriers.

Mitigation of MAFLD in High Fat-High Sucrose-Fructose Fed Mice by a Combination of Genistein Consumption and Exercise Training

PURPOSE

Metabolic dysfunction-associated fatty liver disease (MAFLD) is fueled by escalations in both sedentary behavior and caloric intake and is noted in obese type 2 diabetic (T2DM) patients. This study aimed to examine the effects of exercise and the phytoestrogen genistein in mice fed a high fat (60% fat) high sugar (55% fructose with 45% sucrose), HFHS diet.

METHODS

Male C57BL/6J mice were assigned to five groups: HFHS, HFHS with genistein (600 mg/kg diet, HFHS+Gen), HFHS with moderate exercise (HFHS+Ex), and HFHS with combined genistein and moderate exercise (HFHS-Gen+Ex). Control lean mice were fed standard chow and water. Exercise consisted of 30-minute sessions of treadmill running five days/week for the 12-week study duration. Body weight was assessed weekly. Liver, kidney, fecal pellets and serum were extracted at the end of the study and maintained at -80°C.

RESULTS

After 12 weeks of treatment, mice in the HFHS group had the highest hepatic lipid content. Plasma levels of glucose, insulin, leptin, cholesterol, amylin, and total fat content were significantly elevated in HFHS mice compared to control mice. HFHS feeding increased protein expression of carnitine palmitoyltransferase 1b (CPT-1b isoform) in gastrocnemius, CPT1a, glucose transporter protein 2 (GLUT2), glucocorticoid receptor (GR), and fructose 1,6-bisphosphate 1 (FBP1) expression in liver. Exercise alone had minor effects on these metabolic abnormalities. Genistein alone resulted in improvements in body weight, fat content, amylin, insulin sensitivity, and liver histopathology, GR, FBP1, and acetyl-CoA carboxylase 1 (ACC1). Combination treatment resulted in additional metabolic improvements, including reductions in hepatic lipid content and lipid area, alanine transferase activity, CPT1b, and CPT1a.

CONCLUSION

Our results indicate that a HFHS diet is obesogenic, inducing metabolic perturbations consistent with T2DM and MAFLD. Genistein alone and genistein combined with moderate intensity exercise were effective in reducing MAFLD and the aberrations induced by chronic HFHS feeding.

Revisiting the contribution of mitochondrial biology to the pathophysiology of skeletal muscle insulin resistance

While the etiology of type 2 diabetes is multifaceted, the induction of insulin resistance in skeletal muscle is a key phenomenon, and impairments in insulin signaling in this tissue directly contribute to hyperglycemia. Despite the lack of clarity regarding the specific mechanisms whereby insulin signaling is impaired, the key role of a high lipid environment within skeletal muscle has been recognized for decades. Many of the proposed mechanisms leading to the attenuation of insulin signaling - namely the accumulation of reactive lipids and the pathological production of reactive oxygen species (ROS), appear to rely on this high lipid environment. Mitochondrial biology is a central component to these processes, as these organelles are almost exclusively responsible for the oxidation and metabolism of lipids within skeletal muscle and are a primary source of ROS production. Classic studies have suggested that reductions in skeletal muscle mitochondrial content and/or function contribute to lipid-induced insulin resistance; however, in recent years the role of mitochondria in the pathophysiology of insulin resistance has been gradually re-evaluated to consider the biological effects of alterations in mitochondrial content. In this respect, while reductions in mitochondrial content are not required for the induction of insulin resistance, mechanisms that increase mitochondrial content are thought to enhance mitochondrial substrate sensitivity and submaximal adenosine diphosphate (ADP) kinetics. Thus, this review will describe the central role of a high lipid environment in the pathophysiology of insulin resistance, and present both classic and contemporary views of how mitochondrial biology contributes to insulin resistance in skeletal muscle.

Exercise ameliorates insulin resistance and improves ASK1-mediated insulin signalling in obese rats

Increasing evidence reveals that physical exercise is an efficient therapeutical approach in the treatment of insulin resistance (IR) and related metabolic diseases. However, the potential beneficial effects of exercise on insulin resistance and its underlying mechanisms remain unclear. Recent findings elucidated the negative role of ASK1 in repressing the glucose uptake through JNK1‐IRS1‐Akt signalling in liver. Thus, a detailed investigation of the effect of ASK1‐mediated insulin signalling on exercise‐mediated improvement of insulin sensitivity and its underlying mechanism was implemented in this study. Using a high‐fat diet‐induced IR rat model of chronic or acute swimming exercise training, we here showed that body weight and visceral fat mass were significantly reduced after chronic exercise. Moreover, chronic exercise reduced serum FFAs levels and hepatic triglyceride content. Both chronic and acute exercise promoted glucose tolerance and insulin sensitivity. Meanwhile, both chronic and acute exercise decreased ASK1 phosphorylation and improved JNK1‐IRS1‐Akt signalling. Furthermore, exercise training decreased CFLAR, CREG and TRAF1 protein levels in liver of obese rats, which are positive regulator of ASK1 activity. These results suggested that swimming exercise demonstrated to be an effective ameliorator of IR through the regulation of ASK1‐mediated insulin signalling and therefore, could present a prospective therapeutic mean towards the treatment of IR and several metabolic diseases based on IR, containing NAFLD and type Ⅱ diabetes.

Mitochondrial phenotypes in purified human immune cell subtypes and cell mixtures

Using a high-throughput mitochondrial phenotyping platform to quantify multiple mitochondrial features among molecularly defined immune cell subtypes, we quantify the natural variation in mitochondrial DNA copy number (mtDNAcn), citrate synthase, and respiratory chain enzymatic activities in human neutrophils, monocytes, B cells, and naïve and memory T lymphocyte subtypes. In mixed peripheral blood mononuclear cells (PBMCs) from the same individuals, we show to what extent mitochondrial measures are confounded by both cell type distributions and contaminating platelets. Cell subtype-specific measures among women and men spanning four decades of life indicate potential age- and sex-related differences, including an age-related elevation in mtDNAcn, which are masked or blunted in mixed PBMCs. Finally, a proof-of-concept, repeated-measures study in a single individual validates cell type differences and also reveals week-to-week changes in mitochondrial activities. Larger studies are required to validate and mechanistically extend these findings. These mitochondrial phenotyping data build upon established immunometabolic differences among leukocyte subpopulations, and provide foundational quantitative knowledge to develop interpretable blood-based assays of mitochondrial health.

Skeletal muscle type-specific mitochondrial adaptation to high-fat diet relies on differential autophagy modulation

In obesity, skeletal muscle mitochondrial activity changes to cope with increased nutrient availability. Autophagy has been proposed as an essential mechanism involved in the regulation of mitochondrial metabolism. Still, the contribution of autophagy to mitochondrial adaptations in skeletal muscle during obesity is unknown. Here, we show that in response to high-fat diet (HFD) feeding, distinct skeletal muscles in mice exhibit differentially regulated autophagy that may modulate mitochondrial activity. We observed that after 4 and 40 weeks of high-fat diet feeding, OXPHOS subunits and mitochondrial DNA content increased in the oxidative soleus muscle. However, in gastrocnemius muscle, which has a mixed fiber-type composition, the mitochondrial mass increased only after 40 weeks of HFD feeding. Interestingly, fatty acid-supported mitochondrial respiration was enhanced in gastrocnemius, but not in soleus muscle after a 4-week HFD feeding. This increased metabolic profile in gastrocnemius was paralleled by preserving autophagy flux, while autophagy flux in soleus was reduced. To determine the role of autophagy in this differential response, we used an autophagy-deficient mouse model with partial deletion of Atg7 specifically in skeletal muscle (SkM-Atg7+/- mice). We observed that Atg7 reduction resulted in diminished autophagic flux in skeletal muscle, alongside blunting the HFD-induced increase in fatty acid-supported mitochondrial respiration observed in gastrocnemius. Remarkably, SkM-Atg7+/- mice did not present increased mitochondria accumulation. Altogether, our results show that HFD triggers specific mitochondrial adaptations in skeletal muscles with different fiber type compositions, and that Atg7-mediated autophagy modulates mitochondrial respiratory capacity but not its content in response to an obesogenic diet.

Dynamic regional alterations in mouse brain neuronal activity following short-term changes in energy balance

OBJECTIVE

Knowledge of the functional contribution to energy homeostatic control by different brain areas is limited. This study employed a systematic approach to identify brain regions specifically influenced by a positive energy balance.

METHODS

The c-fos expression was mapped throughout the mouse brain after varying durations (24 hours to up to 14 days) of high-fat diet (HFD) exposure or after reversal from a 7-day HFD to a chow diet. In parallel, the metabolic and behavioral impacts of these treatments were examined.

RESULTS

A HFD elicited rapid and pronounced compensatory responses which were, however, insufficient to overcome the impact of the positive energy balance. Rapid and dynamic responses of c-fos expression throughout the brain were seen over the course of HFD exposure, with some regions showing linear-like responses and some regions exhibiting biphasic responses. The switch from HFD to chow resulted in metabolic compensations mitigating the effects of the negative energy balance and a heightened preference for sweet taste. Interestingly, this diet switch led to a significant c-fos activation in the lateral hypothalamus, an area unresponsive to HFD intervention.

CONCLUSIONS

Plasticity exists in the extended brain networks facilitating rapid adaptations dependent on energy availability. Knowledge of these critical control points may provide novel antiobesity treatment targets.

A Review of Current Trends with Type 2 Diabetes Epidemiology, Aetiology, Pathogenesis, Treatments and Future Perspectives

Type 2 diabetes (T2D), which has currently become a global pandemic, is a metabolic disease largely characterised by impaired insulin secretion and action. Significant progress has been made in understanding T2D aetiology and pathogenesis, which is discussed in this review. Extrapancreatic pathology is also summarised, which demonstrates the highly multifactorial nature of T2D. Glucagon-like peptide (GLP)-1 is an incretin hormone responsible for augmenting insulin secretion from pancreatic beta-cells during the postprandial period. Given that native GLP-1 has a very short half-life, GLP-1 mimetics with a much longer half-life have been developed, which are currently an effective treatment option for T2D by enhancing insulin secretion in patients. Interestingly, there is continual emerging evidence that these therapies alleviate some of the post-diagnosis complications of T2D. Additionally, these therapies have been shown to induce weight loss in patients, suggesting they could be an alternative to bariatric surgery, a procedure associated with numerous complications. Current GLP-1-based therapies all act as orthosteric agonists for the GLP-1 receptor (GLP-1R). Interestingly, it has emerged that GLP-1R also has allosteric binding sites and agonists have been developed for these sites to test their therapeutic potential. Recent studies have also demonstrated the potential of bi- and tri-agonists, which target multiple hormonal receptors including GLP-1R, to more effectively treat T2D. Improved understanding of T2D aetiology/pathogenesis, coupled with the further elucidation of both GLP-1 activity/targets and GLP-1R mechanisms of activation via different agonists, will likely provide better insight into the therapeutic potential of GLP-1-based therapies to treat T2D.

Lipids activate skeletal muscle mitochondrial fission and quality control networks to induce insulin resistance in humans

BACKGROUND AND AIMS

A diminution in skeletal muscle mitochondrial function due to ectopic lipid accumulation and excess nutrient intake is thought to contribute to insulin resistance and the development of type 2 diabetes. However, the functional integrity of mitochondria in insulin-resistant skeletal muscle remains highly controversial.

METHODS

19 healthy adults (age:28.4 ± 1.7 years; BMI:22.7 ± 0.3 kg/m²) received an overnight intravenous infusion of lipid (20% Intralipid) or saline followed by a hyperinsulinemic-euglycemic clamp to assess insulin sensitivity using a randomized crossover design. Skeletal muscle biopsies were obtained after the overnight lipid infusion to evaluate activation of mitochondrial dynamics proteins, ex-vivo mitochondrial membrane potential, ex-vivo oxidative phosphorylation and electron transfer capacity, and mitochondrial ultrastructure.

RESULTS

Overnight lipid infusion increased dynamin related protein 1 (DRP1) phosphorylation at serine 616 and PTEN-induced kinase 1 (PINK1) expression (P = 0.003 and P = 0.008, respectively) in skeletal muscle while reducing mitochondrial membrane potential (P = 0.042). The lipid infusion also increased mitochondrial-associated lipid droplet formation (P = 0.011), the number of dilated cristae, and the presence of autophagic vesicles without altering mitochondrial number or respiratory capacity. Additionally, lipid infusion suppressed peripheral glucose disposal (P = 0.004) and hepatic insulin sensitivity (P = 0.014).

CONCLUSIONS

These findings indicate that activation of mitochondrial fission and quality control occur early in the onset of insulin resistance in human skeletal muscle. Targeting mitochondrial dynamics and quality control represents a promising new pharmacological approach for treating insulin resistance and type 2 diabetes.

CLINICAL TRIAL REGISTRATION

NCT02697201, ClinicalTrials.gov.

Age-related susceptibility to insulin resistance arises from a combination of CPT1B decline and lipid overload

BACKGROUND

The skeletal muscle plays a central role in glucose homeostasis through the uptake of glucose from the extracellular medium in response to insulin. A number of factors are known to disrupt the normal response to insulin leading to the emergence of insulin resistance (IR). Advanced age and a high-fat diet are factors that increase the susceptibility to IR, with lipid accumulation in the skeletal muscle being a key driver of this phenomenon. It is debated, however, whether lipid accumulation arises due to dietary lipid overload or from a decline of mitochondrial function. To gain insights into the interplay of diet and age in the flexibility of muscle lipid and glucose handling, we combined lipidomics, proteomics, mitochondrial function analysis and computational modelling to investigate young and aged mice on a low- or high-fat diet (HFD).

RESULTS

As expected, aged mice were more susceptible to IR when given a HFD than young mice. The HFD induced intramuscular lipid accumulation specifically in aged mice, including C18:0-containing ceramides and diacylglycerols. This was reflected by the mitochondrial β-oxidation capacity, which was upregulated by the HFD in young, but not in old mice. Conspicuously, most β-oxidation proteins were upregulated by the HFD in both groups, but carnitine palmitoyltransferase 1B (CPT1B) declined in aged animals. Computational modelling traced the flux control mostly to CPT1B, suggesting a CPT1B-driven loss of flexibility to the HFD with age. Finally, in old animals, glycolytic protein levels were reduced and less flexible to the diet.

CONCLUSION

We conclude that intramuscular lipid accumulation and decreased insulin sensitivity are not due to age-related mitochondrial dysfunction or nutritional overload alone, but rather to their combined effects. Moreover, we identify CPT1B as a potential target to counteract age-dependent intramuscular lipid accumulation and thereby IR.

Mitostasis, Calcium and Free Radicals in Health, Aging and Neurodegeneration

Mitochondria play key roles in ATP supply, calcium homeostasis, redox balance control and apoptosis, which in neurons are fundamental for neurotransmission and to allow synaptic plasticity. Their functional integrity is maintained by mitostasis, a process that involves mitochondrial transport, anchoring, fusion and fission processes regulated by different signaling pathways but mainly by the peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α). PGC-1α also favors Ca²⁺ homeostasis, reduces oxidative stress, modulates inflammatory processes and mobilizes mitochondria to where they are needed. To achieve their functions, mitochondria are tightly connected to the endoplasmic reticulum (ER) through specialized structures of the ER termed mitochondria-associated membranes (MAMs), which facilitate the communication between these two organelles mainly to aim Ca²⁺ buffering. Alterations in mitochondrial activity enhance reactive oxygen species (ROS) production, disturbing the physiological metabolism and causing cell damage. Furthermore, cytosolic Ca²⁺ overload results in an increase in mitochondrial Ca²⁺, resulting in mitochondrial dysfunction and the induction of mitochondrial permeability transition pore (mPTP) opening, leading to mitochondrial swelling and cell death through apoptosis as demonstrated in several neuropathologies. In summary, mitochondrial homeostasis is critical to maintain neuronal function; in fact, their regulation aims to improve neuronal viability and to protect against aging and neurodegenerative diseases.

Decreased Glucocorticoid Signaling Potentiates Lipid-Induced Inflammation and Contributes to Insulin Resistance in the Skeletal Muscle of Fructose-Fed Male Rats Exposed to Stress

The modern lifestyle brings both excessive fructose consumption and daily exposure to stress which could lead to metabolic disturbances and type 2 diabetes. Muscles are important points of glucose and lipid metabolism, with a crucial role in the maintenance of systemic energy homeostasis. We investigated whether 9-week fructose-enriched diet, with and without exposure to 4-week unpredictable stress, disturbs insulin signaling in the skeletal muscle of male rats and evaluated potential contributory roles of muscle lipid metabolism, glucocorticoid signaling and inflammation. The combination of fructose-enriched diet and stress increased peroxisome proliferator-activated receptors-α and -δ and stimulated lipid uptake, lipolysis and β-oxidation in the muscle of fructose-fed stressed rats. Combination of treatment also decreased systemic insulin sensitivity judged by lower R-QUICKI, and lowered muscle protein content and stimulatory phosphorylations of insulin receptor supstrate-1 and Akt, as well as the level of 11β-hydroxysteroid dehydrogenase type 1 and glucocorticoid receptor. At the same time, increased levels of protein tyrosine phosphatase-1B, nuclear factor-κB, tumor necrosis factor-α, were observed in the muscle of fructose-fed stressed rats. Based on these results, we propose that decreased glucocorticoid signaling in the skeletal muscle can make a setting for lipid-induced inflammation and the development of insulin resistance in fructose-fed stressed rats.

The Alterations of Mitochondrial Function during NAFLD Progression-An Independent Effect of Mitochondrial ROS Production

The progression of non-alcoholic fatty liver (NAFL) into non-alcoholic steatohepatitis implicates multiple mechanisms, chief of which is mitochondrial dysfunction. However, the sequence of events underlying mitochondrial failure are still poorly clarified. In this work, male C57BL/6J mice were fed with a high-fat plus high-sucrose diet for 16, 20, 22, and 24 weeks to induce NAFL. Up to the 20th week, an early mitochondrial remodeling with increased OXPHOS subunits levels and higher mitochondrial respiration occurred. Interestingly, a progressive loss of mitochondrial respiration along "Western diet" feeding was identified, accompanied by higher susceptibility to mitochondrial permeability transition pore opening. Importantly, our findings prove that mitochondrial alterations and subsequent impairment are independent of an excessive mitochondrial reactive oxygen species (ROS) generation, which was found to be progressively diminished along with disease progression. Instead, increased peroxisomal abundance and peroxisomal fatty acid oxidation-related pathway suggest that peroxisomes may contribute to hepatic ROS generation and oxidative damage, which may accelerate hepatic injury and disease progression. We show here for the first time the sequential events of mitochondrial alterations involved in non-alcoholic fatty liver disease (NAFLD) progression and demonstrate that mitochondrial ROS are not one of the first hits that cause NAFLD progression.

Combined effects of a ketogenic diet and exercise training alter mitochondrial and peroxisomal substrate oxidative capacity in skeletal muscle

Ketogenic diets (KDs) are reported to improve body weight, fat mass, and exercise performance in humans. Unfortunately, most rodent studies have used a low-protein KD, which does not recapitulate diets used by humans. Since skeletal muscle plays a critical role in responding to macronutrient perturbations induced by diet and exercise, the purpose of this study was to test if a normal-protein KD (NPKD) impacts shifts in skeletal muscle substrate oxidative capacity in response to exercise training (ExTr). A high fat, carbohydrate-deficient NPKD (16.1% protein, 83.9% fat, 0% carbohydrate) was given to C57BL/6J male mice for 6 wk, whereas controls (Con) received a low-fat diet with similar protein (15.9% protein, 11.9% fat, 72.2% carbohydrate). After 3 wk on the diet, mice began treadmill training 5 days/wk, 60 min/day for 3 wks. The NPKD increased body weight and fat mass, whereas ExTr negated a continued rise in adiposity. ExTr increased intramuscular glycogen, whereas the NPKD increased intramuscular triglycerides. Neither the NPKD nor ExTr alone altered mitochondrial content; however, in combination, the NPKD-ExTr group showed increases in PGC-1α and markers of mitochondrial fission/fusion. Pyruvate oxidative capacity was unchanged by either intervention, whereas ExTr increased leucine oxidation in NPKD-fed mice. Lipid metabolism pathways had the most notable changes as the NPKD and ExTr interventions both enhanced mitochondrial and peroxisomal lipid oxidation and many adaptations were additive or synergistic. Overall, these results suggest that a combination of a NPKD and ExTr induces additive and/or synergistic adaptations in skeletal muscle oxidative capacity.NEW & NOTEWORTHY A ketogenic diet with normal protein content (NPKD) increases body weight and fat mass, increases intramuscular triglyceride storage, and upregulates pathways related to protein metabolism. In combination with exercise training, a NPKD induces additive and/or synergistic activation of AMPK, PGC-1α, mitochondrial fission/fusion genes, mitochondrial fatty acid oxidation, and peroxisomal adaptations in skeletal muscle. Collectively, results from this study provide mechanistic insight into adaptations in skeletal muscle relevant to keto-adaptation.

Long-term programming of skeletal muscle and liver lipid and energy metabolism by resveratrol supplementation to suckling mice

Metabolic programming by dietary chemicals consumed in early life stages is receiving increasing attention. We here studied long-term effects of mild resveratrol (RSV) supplementation during lactation on muscular and hepatic lipid metabolism in adulthood. Newborn male mice received RSV or vehicle from day 2-20 of age, were weaned onto a chow diet on day 21, and were assigned to either a high-fat diet (HFD) or a normal-fat diet on day 90 of age for 10 weeks. RSV-treated mice showed in adulthood protection against HFD-induced triacylglycerol accumulation in skeletal muscle, enhanced muscular capacities for fat oxidation and mitochondria activity, signs of enhanced sirtuin 1 and AMP-dependent protein kinase signaling in muscle, and increased fat oxidation capacities and a decreased capacity for lipogenesis in liver compared with controls. Thus, RSV supplementation in early postnatal life may help preventing later diet-related disorders linked to ectopic lipid accumulation in muscle and liver tissues.

Genetically increasing flux through β-oxidation in skeletal muscle increases mitochondrial reductive stress and glucose intolerance

Elevated mitochondrial hydrogen peroxide (H₂O₂) emission and an oxidative shift in cytosolic redox environment have been linked to high-fat-diet-induced insulin resistance in skeletal muscle. To test specifically whether increased flux through mitochondrial fatty acid oxidation, in the absence of elevated energy demand, directly alters mitochondrial function and redox state in muscle, two genetic models characterized by increased muscle β-oxidation flux were studied. In mice overexpressing peroxisome proliferator-activated receptor-α in muscle (MCK-PPARα), lipid-supported mitochondrial respiration, membrane potential (ΔΨ_m), and H₂O₂ production rate (JH₂O₂) were increased, which coincided with a more oxidized cytosolic redox environment, reduced muscle glucose uptake, and whole body glucose intolerance despite an increased rate of energy expenditure. Similar results were observed in lipin-1-deficient, fatty-liver dystrophic mice, another model characterized by increased β-oxidation flux and glucose intolerance. Crossing MCAT (mitochondria-targeted catalase) with MCK-PPARα mice normalized JH₂O₂ production, redox environment, and glucose tolerance, but surprisingly, both basal and absolute insulin-stimulated rates of glucose uptake in muscle remained depressed. Also surprising, when placed on a high-fat diet, MCK-PPARα mice were characterized by much lower whole body, fat, and lean mass as well as improved glucose tolerance relative to wild-type mice, providing additional evidence that overexpression of PPARα in muscle imposes more extensive metabolic stress than experienced by wild-type mice on a high-fat diet. Overall, the findings suggest that driving an increase in skeletal muscle fatty acid oxidation in the absence of metabolic demand imposes mitochondrial reductive stress and elicits multiple counterbalance metabolic responses in an attempt to restore bioenergetic homeostasis.NEW & NOTEWORTHY Prior work has suggested that mitochondrial dysfunction is an underlying cause of insulin resistance in muscle because it limits fatty acid oxidation and therefore leads to the accumulation of cytotoxic lipid intermediates. The implication has been that therapeutic strategies to accelerate β-oxidation will be protective. The current study provides evidence that genetically increasing flux through β-oxidation in muscle imposes reductive stress that is not beneficial but rather detrimental to metabolic regulation.

Aging Influences the Metabolic and Inflammatory Phenotype in an Experimental Mouse Model of Acute Lung Injury

Increased age is a risk factor for poor outcomes from respiratory failure and acute respiratory distress syndrome (ARDS). In this study, we sought to define age-related differences in lung inflammation, muscle injury, and metabolism after intratracheal lipopolysaccharide (IT-LPS) acute lung injury (ALI) in adult (6 months) and aged (18-20 months) male C57BL/6 mice. We also investigated age-related changes in muscle fatty acid oxidation (FAO) and the consequences of systemic FAO inhibition with the drug etomoxir. Aged mice had a distinct lung injury course characterized by prolonged alveolar neutrophilia and lack of response to therapeutic exercise. To assess the metabolic consequences of ALI, aged and adult mice underwent whole body metabolic phenotyping before and after IT-LPS. Aged mice had prolonged anorexia and decreased respiratory exchange ratio, indicating increased reliance on FAO. Etomoxir increased mortality in aged but not adult ALI mice, confirming the importance of FAO on survival from acute severe stress and suggesting that adult mice have increased resilience to FAO inhibition. Skeletal muscles from aged ALI mice had increased transcription of key fatty acid metabolizing enzymes, CPT-1b, LCAD, MCAD, FATP1 and UCP3. Additionally, aged mice had increased protein levels of CPT-1b at baseline and after lung injury. Surprisingly, CPT-1b in isolated skeletal muscle mitochondria had decreased activity in aged mice compared to adults. The distinct phenotype of aged ALI mice has similar characteristics to the adverse age-related outcomes of ARDS. This model may be useful to examine and augment immunologic and metabolic abnormalities unique to the critically ill aged population.

Effects of Lifestyle Intervention in Tissue-Specific Lipidomic Profile of Formerly Obese Mice

Lipids are highly diverse in their composition, properties and distribution in different biological entities. We aim to establish the lipidomes of several insulin-sensitive tissues and to test their plasticity when divergent feeding regimens and lifestyles are imposed. Here, we report a proton nuclear magnetic resonance (1H-NMR) study of lipid abundance across 4 tissues of C57Bl6J male mice that includes the changes in the lipid profile after every lifestyle intervention. Every tissue analysed presented a specific lipid profile irrespective of interventions. Glycerolipids and fatty acids were most abundant in epididymal white adipose tissue (eWAT) followed by liver, whereas sterol lipids and phosphoglycerolipids were highly enriched in hypothalamus, and gastrocnemius had the lowest content in all lipid species compared to the other tissues. Both when subjected to a high-fat diet (HFD) and after a subsequent lifestyle intervention (INT), the lipidome of hypothalamus showed no changes. Gastrocnemius and liver revealed a pattern of increase in content in many lipid species after HFD followed by a regression to basal levels after INT, while eWAT lipidome was affected mainly by the fat composition of the administered diets and not their caloric density. Thus, the present study demonstrates a unique lipidome for each tissue modulated by caloric intake and dietary composition.

Physiological and pathophysiological concentrations of fatty acids induce lipid droplet accumulation and impair functional performance of tissue engineered skeletal muscle

Fatty acids (FA) exert physiological and pathophysiological effects leading to changes in skeletal muscle metabolism and function, however, in vitro models to investigate these changes are limited. These experiments sought to establish the effects of physiological and pathophysiological concentrations of exogenous FA upon the function of tissue engineered skeletal muscle (TESkM). Cultured initially for 14 days, C2C12 TESkM was exposed to FA-free bovine serum albumin alone or conjugated to a FA mixture (oleic, palmitic, linoleic, and α-linoleic acids [OPLA] [ratio 45:30:24:1%]) at different concentrations (200 or 800 µM) for an additional 4 days. Subsequently, TESkM morphology, functional capacity, gene expression and insulin signaling were analyzed. There was a dose response increase in the number and size of lipid droplets within the TESkM (p < .05). Exposure to exogenous FA increased the messenger RNA expression of genes involved in lipid storage (perilipin 2 [p < .05]) and metabolism (pyruvate dehydrogenase lipoamide kinase isozyme 4 [p < .01]) in a dose dependent manner. TESkM force production was reduced (tetanic and single twitch) (p < .05) and increases in transcription of type I slow twitch fiber isoform, myosin heavy chain 7, were observed when cultured with 200 µM OPLA compared to control (p < .01). Four days of OPLA exposure results in lipid accumulation in TESkM which in turn results in changes in muscle function and metabolism; thus, providing insight ito the functional and mechanistic changes of TESkM in response to exogenous FA.

Phenotypic Discovery of SB1501, an Anti-obesity Agent, through Modulating Mitochondrial Activity

Obesity has become a pandemic that threatens the quality of life and discovering novel therapeutic agents that can reverse obesity and obesity-related metabolic disorders are necessary. Here, we aimed to identify new anti-obesity agents using a phenotype-based approach. We performed image-based high-content screening with a fluorogenic bioprobe (SF44), which visualizes cellular lipid droplets (LDs), to identify initial hit compounds. A structure-activity relationship study led us to yield a bioactive compound SB1501, which reduces cellular LDs in 3T3-L1 adipocytes without cytotoxicity. SB1501 induced the expression of gene products that regulate mitochondrial biogenesis and fatty acid oxidation in 3T3-L1 adipocytes. Daily treatment with SB1501 improved the metabolic states of db/db mice by reducing body fat mass, adipose tissue mass, food intake, and increasing glucose tolerance. The anti-obesity effect of SB1501 may result from perturbation of the PGC-1α-UCP1 regulatory axis in inguinal white adipose tissue and brown adipose tissue. These data suggest the therapeutic potential of SB1501 as an anti-obesity agent via modulating mitochondrial activities.

Atorvastatin impairs liver mitochondrial function in obese Göttingen Minipigs but heart and skeletal muscle are not affected

Statins lower the risk of cardiovascular events but have been associated with mitochondrial functional changes in a tissue-dependent manner. We investigated tissue-specific modifications of mitochondrial function in liver, heart and skeletal muscle mediated by chronic statin therapy in a Göttingen Minipig model. We hypothesized that statins enhance the mitochondrial function in heart but impair skeletal muscle and liver mitochondria. Mitochondrial respiratory capacities, citrate synthase activity, coenzyme Q10 concentrations and protein carbonyl content (PCC) were analyzed in samples of liver, heart and skeletal muscle from three groups of Göttingen Minipigs: a lean control group (CON, n = 6), an obese group (HFD, n = 7) and an obese group treated with atorvastatin for 28 weeks (HFD + ATO, n = 7). Atorvastatin concentrations were analyzed in each of the three tissues and in plasma from the Göttingen Minipigs. In treated minipigs, atorvastatin was detected in the liver and in plasma. A significant reduction in complex I + II-supported mitochondrial respiratory capacity was seen in liver of HFD + ATO compared to HFD (P = 0.022). Opposite directed but insignificant modifications of mitochondrial respiratory capacity were seen in heart versus skeletal muscle in HFD + ATO compared to the HFD group. In heart muscle, the HFD + ATO had significantly higher PCC compared to the HFD group (P = 0.0323). In the HFD group relative to CON, liver mitochondrial respiration decreased whereas in skeletal muscle, respiration increased but these changes were insignificant when normalizing for mitochondrial content. Oral atorvastatin treatment in Göttingen Minipigs is associated with a reduced mitochondrial respiratory capacity in the liver that may be linked to increased content of atorvastatin in this organ.

GPR10 gene deletion in mice increases basal neuronal activity, disturbs insulin sensitivity and alters lipid homeostasis

G-protein-coupled receptor GPR10 is expressed in brain areas regulating energy metabolism. In this study, the effects of GPR10 gene deficiency on energy homeostasis in mice of both sexes fed either standard chow or a high-fat diet (HFD) were studied, with a focus on neuronal activation of PrRP neurons, and adipose tissue and liver metabolism. GPR10 deficiency in males upregulated the phasic and tonic activity of PrRP neurons in the nucleus of the solitary tract. GPR10 knockout (KO) males on a standard diet displayed a higher body weight than their wild-type (WT) littermates due to an increase in adipose tissue mass; however, HFD feeding did not cause weight differences between genotypes. Expression of lipogenesis genes was suppressed in the subcutaneous adipose tissue of GPR10 KO males. In contrast, GPR10 KO females did not differ in body weight from their WT controls, but showed elevated expression of lipid metabolism genes in the liver and subcutaneous adipose tissue compared to WT controls. An attenuated non-esterified fatty acids change after glucose load compared to WT controls suggested a defect in insulin-mediated suppression of lipolysis in GPR10 KO females. Indirect calorimetry did not reveal any differences in energy expenditure among groups. In conclusion, deletion of GPR10 gene resulted in changes in lipid metabolism in mice of both sexes, however in different extent. An increase in adipose tissue mass observed in only GPR10 KO males may have been prevented in GPR10 KO females owing to a compensatory increase in the expression of metabolic genes.

Mitochondrial Dysfunction in Obesity and Reproduction

Mounting evidence suggests a role for mitochondrial dysfunction in the pathogenesis of many diseases, including type 2 diabetes, aging, and ovarian failure. Because of the central role of mitochondria in energy production, heme biosynthesis, calcium buffering, steroidogenesis, and apoptosis signaling within cells, understanding the molecular mechanisms behind mitochondrial dysregulation and its potential implications in disease is critical. This review will take a journey through the past and summarize what is known about mitochondrial dysfunction in various disorders, focusing on metabolic alterations and reproductive abnormalities. Evidence is presented from studies in different human populations, and rodents with genetic manipulations of pathways known to affect mitochondrial function.

Short-Term High-Fat Feeding Does Not Alter Mitochondrial Lipid Respiratory Capacity but Triggers Mitophagy Response in Skeletal Muscle of Mice

Lipid overload of the mitochondria is linked to the development of insulin resistance in skeletal muscle which may be a contributing factor to the progression of type 2 diabetes during obesity. The targeted degradation of mitochondria through autophagy, termed mitophagy, contributes to the mitochondrial adaptive response to changes in dietary fat. Our previous work demonstrates long-term (2-4 months) consumption of a high-fat diet increases mitochondrial lipid oxidation capacity but does not alter markers of mitophagy in mice. The purpose of this study was to investigate initial stages of mitochondrial respiratory adaptations to high-fat diet and the activation of mitophagy. C57BL/6J mice consumed either a low-fat diet (LFD, 10% fat) or high-fat diet (HFD, 60% fat) for 3 or 7 days. We measured skeletal muscle mitochondrial respiration and protein markers of mitophagy in a mitochondrial-enriched fraction of skeletal muscle. After 3 days of HFD, mice had lower lipid-supported oxidative phosphorylation alongside greater electron leak compared with the LFD group. After 7 days, there were no differences in mitochondrial respiration between diet groups. HFD mice had greater autophagosome formation potential (Beclin-1) and greater activation of mitochondrial autophagy receptors (Bnip3, p62) in isolated mitochondria, but no difference in downstream autophagosome (LC3II) or lysosome (Lamp1) abundance after both 3 and 7 days compared with the LFD groups. In cultured myotubes, palmitate treatment decreased mitochondrial membrane potential and hydrogen peroxide treatment increased accumulation of upstream mitophagy markers. We conclude that several days of high-fat feeding stimulated upstream activation of skeletal muscle mitophagy, potentially through lipid-induced oxidative stress, without downstream changes in respiration.

Endurance Runners with Intramyocellular Lipid Accumulation and High Insulin Sensitivity Have Enhanced Expression of Genes Related to Lipid Metabolism in Muscle

Context: Endurance-trained athletes have high oxidative capacities, enhanced insulin sensitivities, and high intracellular lipid accumulation in muscle. These characteristics are likely due to altered gene expression levels in muscle. Design and setting: We compared intramyocellular lipid (IMCL), insulin sensitivity, and gene expression levels of the muscle in eight nonobese healthy men (control group) and seven male endurance athletes (athlete group). Their IMCL levels were measured by proton-magnetic resonance spectroscopy, and their insulin sensitivity was evaluated by glucose infusion rate (GIR) during a euglycemic–hyperinsulinemic clamp. Gene expression levels in the vastus lateralis were evaluated by quantitative RT-PCR (qRT-PCR) and microarray analysis. Results: IMCL levels in the tibialis anterior muscle were approximately 2.5 times higher in the athlete group compared to the control group, while the IMCL levels in the soleus muscle and GIR were comparable. In the microarray hierarchical clustering analysis, gene expression patterns were not clearly divided into control and athlete groups. In a gene set enrichment analysis with Gene Ontology gene sets, “RESPONSE TO LIPID” was significantly upregulated in the athlete group compared with the control group. Indeed, qRT-PCR analysis revealed that, compared to the control group, the athlete group had 2–3 times higher expressions of proliferator-activated receptor gamma coactivator-1 alpha (PGC1A), adiponectin receptors (AdipoRs), and fatty acid transporters including fatty acid transporter-1, plasma membrane-associated fatty acid binding protein, and lipoprotein lipase. Conclusions: Endurance runners with higher IMCL levels have higher expression levels of genes related to lipid metabolism such as PGC1A, AdipoRs, and fatty acid transporters in muscle.