Skeletal Muscle Mitochondrial Density Research Articles

Acute resistance exercise training does not augment mitochondrial remodelling in master athletes or untrained older adults.

Background: Ageing is associated with alterations to skeletal muscle oxidative metabolism that may be influenced by physical activity status, although the mechanisms underlying these changes have not been unraveled. Similarly, the effect of resistance exercise training (RET) on skeletal muscle mitochondrial regulation is unclear. Methods: Seven endurance-trained masters athletes ([MA], 74 ± 3years) and seven untrained older adults ([OC]. 69 ± 6years) completed a single session of knee extension RET (6 x 12 repetitions, 75% 1-RM, 120-s intra-set recovery). Vastus lateralis muscle biopsies were collected pre-RET, 1h post-RET, and 48h post-RET. Skeletal muscle biopsies were analyzed for citrate synthase (CS) enzyme activity, mitochondrial content, and markers of mitochondrial quality control via immunoblotting. Results: Pre-RET CS activity and protein content were ∼45% (p < .001) and ∼74% greater in MA compared with OC (p = .006). There was a significant reduction (∼18%) in CS activity 48h post-RET (p < .05) in OC, but not MA. Pre-RET abundance of individual and combined mitochondrial electron transport chain (ETC) complexes I-V were significantly greater in MA compared with OC, as were markers of mitochondrial fission and fusion dynamics (p-DRP-1Ser616, p-MFFSer146, OPA-1 & FIS-1, p < .05 for all). Moreover, MA displayed greater expression of p-AMPKThr172, PGC1α, TFAM, and SIRT-3 (p < .05 for all). Notably, RET did not alter the expression of any marker of mitochondrial content, biogenesis, or quality control in both OC and MA. Conclusion: The present data suggest that long-term aerobic exercise training supports superior skeletal muscle mitochondrial density and protein content into later life, which may be regulated by greater mitochondrial quality control mechanisms and supported via superior fission-fusion dynamics. However, a single session of RET is unable to induce mitochondrial remodelling in the acute (1h post-RET) and delayed (48h post-RET) recovery period in OC and MA.

Interactions Between Statins, Exercise, and Health: A Clinical Update

Interactions Between Statins, Exercise, and Health: A Clinical Update

The Rate of Cellular Energy Production of Muscle Cells Is Attenuated By Carnitine Intracellular Deficiency Caused By Imatinib Treatment

Introduction: Previous works identified that imatinib intake through the carnitine-specific OCTN2 (SLC22A5) transporter resulted in a significant decrease of carnitine intracellular concentrations in chronic myeloid leukemia (CML) and muscle cell lines. On contrary, even high doses of carnitine in preincubation did not influence imatinib cell intake capacity. Specifically performed inhibition of OCTN2 activity by vinorelbine resulted in block of carnitine cell intake, while imatinib intake was only slightly reduced (13-30%). This observation is in line with the knowledge that imatinib is transported also through other known SLC transporters. OCTN2 transporter is the major transporter for carnitine, an essential compound in cell energy metabolism. Presented work follows a hypothesis that non-equal competition between imatinib and carnitine intake through OCTN2 can lead to the carnitine intracellular deficiency, which can be in CML patients manifested by a disruption of skeletal muscle mitochondrial density and cause side effects like fatigue, muscle pain and cramps reported up to 80% of patients treated with imatinib (Kekale et al., 2015).Methods: Muscle cell HTB-153 (human rhabdomyosarcoma, ATCC HS 729), CML cell line KCL-22 (DSMZ ACC 519) were used for in vitro experiments. Intracellular concentration of imatinib, carnitine and metabolites were measured by chromatographic separation using XBridge Amide column (50x2.1mm, 3.5µm; Waters, Milford (MA), USA) and ZIC-pHILIC column (50x2.1mm, 5 µm; Merck, Darmstadt, Germany) coupled to tandem mass spectrometer (QTRAP 4000; Sciex, USA).Results: Carnitine, resp. L-carnitine transports long-chain fatty acids to mitochondria and its high rate is required especially in energetically demanding tissues such as skeletal and cardiac muscles. The concentrations of citric acid cycle (CAC) metabolites (citrate, malate, alpha-ketoglutarate, succinate, fumarate, 2-hydroxyglutarate, cis-aconitate), glycolysis (phosphoenolpyruvate, 3- phosphoglycerate, lactate), production of ATP, ADP and AMP were measured in HTB-153 cells 3 and 24 hours after imatinib treatment in vitro. The significant decrease of malate (CAC), lactate (glycolysis) and ATP levels were found at both time points after imatinib treatment compared to baseline. The same observations were found in KCL-22, which was used for comparison as BCR-ABL1 positive cell line. Additionally, significant decrease of succinate and 2-hydroxyglutarate (CAC) was detected in KCL-22 after imatinib treatment. Next, HTB-153 was incubated with imatinib (1-8 µM) for 24 hours and carnitine (8 µM) was supplied for last 3 hours of incubation, i.e., after 21 hours of imatinib treatment start. No significant changes were found in any metabolites of CAC and glycolysis. Production of ATP, ADP and AMP was not changed as well.Conclusions: Imatinib treatment of muscle (rhabdomyosarcoma) and CML cell lines caused a significant decrease of intracellular concentrations of carnitine. Significant decrease of ATP levels and of certain metabolites of CAC and glycolysis outlined that cells struggle from attenuated mitochondria energy production after imatinib treatment. This has not happened, if carnitine was supplied to the culture for final 3 hours of 24 hours incubation with imatinib. Observed data strongly support the hypothesis that decreased carnitine intake to the muscle cells due to competition with imatinib transport through OCTN2 attenuated mitochondria energy production. Interestingly, the clinical trial NCT03426722 (Chae H et al. 2019) showed that L-carnitine could effectively relieve imatinib-related muscle cramps and significantly increase QoL in patients with advanced gastrointestinal stromal tumor.Supported by GACR18-18407S, MZCR00023736 DisclosuresNo relevant conflicts of interest to declare.

Dysregulation of Skeletal Muscle Mitochondrial Function following Critical Illness: a Translational Approach

Bioenergetic failure is a significant clinical consequence of sepsis‐induced critical illness and is characterized by reduced skeletal muscle mitochondrial density, and mitochondrial dysfunction. Early activation of mitochondrial biogenesis is associated with survival and improved physical function in critically ill patients. Therefore, investigating mechanisms associated with early activation of mitochondrial biogenesis may improve targeting of future rehabilitative strategies. A rodent cecal‐ligation and puncture (CLP) model was used to mimic sepsis‐induced critical illness. The objective of the study was to determine whether CLP impaired genes implicated in mitochondrial function in the diaphragm. The CLP model involved ligation of 50% of the cecum below the ileocecal valve in adult C57BL6 mice, followed by needle puncture of the cecum resulting in mid‐grade sepsis. Mice survived for 48 hours or more, following injury. Diaphragm and limb muscles were harvested 24 hours following CLP (N=6) and following a sham CLP procedure (N=6). Gene expression of mef2c, myh1, and pgc1‐α, were significantly decreased in the diaphragm of CLP injured animals when compared to controls. In addition, ubiquitin ligases, murf1 and atrogin were increased in the diaphragm 24 hours after injury (p&lt; 0.01). Our results indicate that sepsis‐induced critical illness significantly impacts the expression of genes implicated in mitochondrial homeostasis and atrophy. Ongoing studies will identify whether CLP injury decreases skeletal muscle mitochondrial function.Support or Funding InformationNIH grants U54 GM104940 and Department of Physiology Funds.

Passive Heat Therapy in Sedentary Humans Improves Aerobic Capacity and Insulin Sensitivity via Increases in Skeletal Muscle Capillarisation and eNOS

OBJECTIVESNegative associations have been reported in a sedentary Finnish population between sauna bathing and all‐cause mortality1, while a joint association of sauna bathing and cardiorespiratory fitness was seen on cardiovascular and all‐cause mortality in a more recent study2. These associations give scientific support to the ‘proverbial wisdom’ in Scandinavia that frequent sauna bathing has multiple health and fitness benefits. The first objective of the current study was to investigate the hypotheses that 1) passive heat therapy (PHT, as occurs in sauna bathing) similar to moderate intensity continuous exercise training (MICT) increases whole body insulin sensitivity and VO2max and that 2) this is the result of increases both in a) skeletal muscle capillarisation and endothelial specific eNOS content and b) mitochondrial, GLUT4 and IMTG content.METHODSTwenty young sedentary males (21 ± 1 years; Body Mass Index (BMI) 25 ± 1 kg/m2) were allocated to either 6 weeks of PHT (n=10; 40–50 min at 40°C in a heat chamber, 3 x per week) or MICT (n=10; time matched cycling at ~65% VO2peak). VO2peak and whole‐body insulin sensitivity were measured and muscle biopsies were taken from the vastus lateralis muscle pre and post the interventions. Immunofluorescence microscopy was used to assess changes in capillarisation measures and endothelial specific eNOS content, as described before 3 and skeletal muscle mitochondrial density, GLUT4 content and IMTG content as described elsewhere4.RESULTSPHT and MICT increased VO2peak (PHT 5%, MICT 7%; P&lt;0.05) and insulin sensitivity index (ISI, Matsuda) (PHT 15%, MICT 36%; P&lt;0.05). PHT and MICT both increased capillary density, capillary–fibre perimeter exchange index, and endothelial specific eNOS content (Table 1). However, unlike MICT (P&lt;0.05) PHT did not increase mitochondrial density (P=0.443), total GLUT4 content (P=0.217) and IMTG content (P=0.957).CONCLUSIONThis study is the first to show that 6 weeks PHT induces similar increases in aerobic capacity and whole‐body insulin sensitivity as a time matched traditional MICT intervention. The study also shows and that these improvements coincide with increases in skeletal muscle capillarisation and endothelial specific eNOS content similar in magnitude to MICT. As skeletal muscle mitochondrial density, GLUT4 content and IMTG concentration were not changed by PHT the data suggest that the microvascular adaptations alone are responsible for the observed effects. This leads to the conclusion that PHT (and sauna bathing) may be effective alternative interventions to achieve significant health benefits in the large and growing population of sedentary and elderly people unable to exercise or to chronically adhere to high physical activity levels.Support or Funding InformationNAThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Prior reproduction alters how mitochondria respond to an oxidative event.

An animal's pace of life is mediated by the physiological demands and stressors it experiences (e.g. reproduction) and one likely mechanism that underlies these effects is oxidative stress. Reproduction has been shown to increase or reduce oxidative stress under different conditions and to modify mitochondrial performance. We hypothesized that the changes associated with reproduction can alter how animals respond to future oxidative stressors. We tested this theory by comparing the organ-specific mitochondrial response in wild-derived female house mice. Specifically, we examined the effect of an oxidant (X-irradiation) on virgin mice and on mice that had reproduced. We measured liver and skeletal muscle mitochondrial density, respiratory performance, enzyme activity and oxidant production, as well as markers of oxidative damage to tissues. In the liver, prior reproduction prevented a radiation-induced reduction in mitochondrial density and increased mitochondrial respiratory performance. In skeletal muscle, prior reproduction resulted in a radiation-induced decline in mitochondrial density which could reduce the bioenergetic capacity of skeletal muscle mitochondria. Yet, electron transport chain complex I activity in skeletal muscle, which dropped after reproduction, returned to control levels following oxidant exposure. The results of this investigation indicate that prior reproduction alters the response of mitochondria to an oxidative challenge in an organ-specific manner. Such changes could have differential effects on future reproductive performance and risk of death.

444 Influence of temperament on skeletal muscle mitochondrial capacity of Brahman cows

To investigate a potential relationship between animal temperament and mitochondrial function, 5-yr-old Brahman cows were stratified into one of three temperament groups based on herdsman scores: T1 (n = 4; calm), T2 (n = 4; normal), or T3 (n = 4; temperamental). The cows were processed at the departmental meats lab and samples from the longissimus dorsi (LD) and semitendinous muscles were collected. All samples were assessed for mitochondrial density (via citrate synthase activity) and function (via cytochrome c oxidase activity); samples from the LD were also evaluated for mitochondrial capacity utilizing high-resolution respirometry. Data were analyzed using the MIXED procedure of SAS (9.4). Relative to mg of tissue (integrative mitochondrial capacity), temperamental cattle (T3) had greater state 3 oxidative phosphorylation capacity with complex I substrates (PCI), PCI plus complex II substrates (PCI+II), maximum electron transport capacity (ECI+II), and ECII than T1 (P = 0.009, P = 0.03, P = 0.02, and P = 0.04 for PCI, PCI+II, ECI+II, and ECII, respectively) or T2 (P = 0.03, P = 0.02, P = 0.03, and P = 0.03 for PCI, PCI+II, ECI+II, and ECII, respectively). Temperamental cattle (T3) also had a higher fractional control ratio of PCI+II (0.890 ± 0.023) than T2 (0.780 ± 0.025; P = 0.02), with T1 being intermediate (0.814 ± 0.023). This indicates a greater contribution of complex II to oxidative phosphorylation and energy production in temperamental animals, the effects of which are unknown at this time. Temperamental animals (T3) also had the greatest citrate synthase activity across muscle groups (9.49 ± 0.70 nmol/min*mg tissue) compared to T1 (6.44 ± 0.68; P = 0.009) or T2 (5.29 ± 0.59; P = 0.0008), indicating greater skeletal muscle mitochondrial density in T3. Intrinsic mitochondrial capacity (relative to CS activity) and cytochrome c oxidase activity (mitochondrial function) were not different between muscles, nor between temperament groups. Research is needed to clarify the significance of different patterns of energy production in temperamental cattle. Further, skeletal muscle mitochondrial capacity may be a useful early indicator of animal performance and carcass quality at harvest. High-resolution respirometry data from longissimus dorsi muscles between calm (T1), normal (T2), and temperamental (T3) Brahman cows P = state 3 oxidative phosphorylation; CI = pyruvate + malate + glutamate; CI+II = pyruvate + malate + glutamate + succinate; E = electron transport system capacity. High-resolution respirometry data from longissimus dorsi muscles between calm (T1), normal (T2), and temperamental (T3) Brahman cows P = state 3 oxidative phosphorylation; CI = pyruvate + malate + glutamate; CI+II = pyruvate + malate + glutamate + succinate; E = electron transport system capacity.

Skeletal Muscle Mitochondrial Density and Quality in Untrained and Endurance‐Trained Humans

Skeletal Muscle Mitochondrial Density and Quality in Untrained and Endurance‐Trained Humans

IL-15Rα deficiency in skeletal muscle alters respiratory function and the proteome of mitochondrial subpopulations independent of changes to the mitochondrial genome

Interleukin-15 receptor alpha knockout (IL15RαKO) mice exhibit a greater skeletal muscle mitochondrial density with an altered mitochondrial morphology. However, the mechanism and functional impact of these changes have not been determined. In this study, we characterized the functional, proteomic, and genomic alterations in mitochondrial subpopulations isolated from the skeletal muscles of IL15RαKO mice and B6129 background control mice. State 3 respiration was greater in interfibrillar mitochondria and whole muscle ATP levels were greater in IL15RαKO mice supporting the increases in respiration rate. However, the state 3/state 4 ratio was lower, suggesting some degree of respiratory uncoupling. Proteomic analyses identified several markers independently in mitochondrial subpopulations that are associated with these functional alterations. Next Generation Sequencing of mtDNA revealed a high degree of similarity between the mitochondrial genomes of IL15RαKO mice and controls in terms of copy number, consensus coding and the presence of minor alleles, suggesting that the functional and proteomic alterations we observed occurred independent of alterations to the mitochondrial genome. These data provide additional evidence to implicate IL-15Rα as a regulator of skeletal muscle phenotypes through effects on the mitochondrion, and suggest these effects are driven by alterations to the mitochondrial proteome.

Of mice and men (and muscle mitochondria)

Of mice and men (and muscle mitochondria)

Role of Skeletal Muscle Mitochondrial Density on Exercise‐Stimulated Lipid Oxidation

Reduced skeletal muscle mitochondrial density is proposed to lead to impaired muscle lipid oxidation and increased lipid accumulation in sedentary individuals. We assessed exercise-stimulated lipid oxidation by imposing a prolonged moderate-intensity exercise in men with variable skeletal muscle mitochondrial density as measured by citrate synthase (CS) activity. After a 2-day isoenergetic high-fat diet, lipid oxidation was measured before and during exercise (650 kcal at 50% VO(2)max) in 20 healthy men with either high (HI-CS = 24 ± 1; mean ± s.e.) or low (LO-CS = 17 ± 1 nmol/min/mg protein) muscle CS activity. Vastus lateralis muscle biopsies were obtained before and immediately after exercise. Respiratory exchange data and blood samples were collected at rest and throughout the exercise. HI-CS subjects had higher VO(2)max (50 ± 1 vs. 44 ± 2 ml/kg fat free mass/min; P = 0.01), lower fasting respiratory quotient (RQ) (0.81 ± 0.01 vs. 0.85 ± 0.01; P = 0.04) and higher ex vivo muscle palmitate oxidation (866 ± 168 vs. 482 ± 78 nmol/h/mg muscle; P = 0.05) compared to LO-CS individuals. However, whole-body exercise-stimulated lipid oxidation (20 ± 2 g vs. 19 ± 1 g; P = 0.65) and plasma glucose, lactate, insulin, and catecholamine responses were similar between the two groups. In conclusion, in response to the same energy demand during a moderate prolonged exercise bout, reliance on lipid oxidation was similar in individuals with high and low skeletal muscle mitochondrial density. This data suggests that decreased muscle mitochondrial density may not necessarily impair reliance on lipid oxidation over the course of the day since it was normal under a high-lipid oxidative demand condition. Twenty-four-hour lipid oxidation and its relationship with mitochondrial density need to be assessed.

Skeletal muscle mitochondrial density, gene expression, and enzyme activities in human heart failure: minimal effects of the disease and resistance training

Impaired skeletal muscle energetics could adversely affect physical and metabolic function in patients with heart failure (HF). The effect of HF on aspects of mitochondrial structure and function, independent of muscle disuse and other disease-related confounding factors, however, is unclear. Moreover, no study has evaluated whether resistance exercise training, a modality that increases functional capacity, might derive its benefits through modulation of mitochondrial structure and function. Thirteen HF patients and 14 age- and physical activity-matched controls were evaluated for skeletal muscle mitochondrial size/content, gene expression, and enzyme activity before and after an 18-wk resistance exercise-training program. At baseline, HF patients and controls had similar mitochondrial fractional areas, although HF patients had larger average mitochondrion size (P < 0.05) and a trend toward a reduced number of mitochondria (P ≤ 0.10). No differences in the expression of transcriptional regulators or cytochrome oxidase subunits or the activity of mitochondrial and cytosolic enzymes were noted. Relationships among transcriptional regulators suggested that networks controlling mitochondrial content and gene expression are intact. Resistance training increased (P < 0.01) mitochondrial transcription factor A expression in patients and controls, and this increase was related to improvements in muscle strength (P = 0.05). Training did not, however, alter mitochondrial size/content, enzyme activities, or expression of other transcriptional regulators. In conclusion, our results suggest that the HF syndrome has minimal effects on skeletal muscle mitochondrial biology when the confounding effects of muscle disuse and other disease-related factors are removed. Moreover, the beneficial effects of resistance training on physical function in HF patients and controls are likely not related to alterations in mitochondrial biology.

Enzyme inducing antiepileptic drugs are associated with mitochondrial proliferation and increased cytochrome c oxidase activity in muscle of children with epilepsy

To evaluate the effects of epilepsy-related factors associated with mitochondrial pathology and function in skeletal muscle of children with suspected mitochondrial disorders. This case-control study evaluated patients and age-matched controls with muscle biopsies at Cincinnati Children's Hospital Medical Center obtained between January, 2000 and December, 2008. A total of 65 epilepsy patients and 65 age-matched controls met the inclusion criteria. No significant clinical, pathological, or biochemical differences were found between the epilepsy and control groups. Treatment resistance was associated with decreased electron transport chain (ETC) complex II+III activity compared to treatment-responsive patients. Only patients receiving enzyme inducer antiepileptic drugs (AEDs) had ETC complex activities equivalent to or greater than other study groups. Robust regression modeling found a significant effect between percentage of myofibers with subsarcolemmal mitochondrial aggregates (SSMA) and ETC complex IV activity for the enzyme inducer AED group. Least squares regression showed that only complex IV/citrate synthase ratio was strongly correlated with SSMA percentage for the enzyme inducer AED group. As far as we can determine this is the first study to show an association between enzyme inducer AED treatment and enhanced ETC complex IV activity. In skeletal muscle mitochondrial density, assessed by SSMA percentage, and ETC complex IV activity are positively correlated in patients receiving enzyme inducer AED treatment.

Metabolic adaptation of skeletal muscle to high altitude hypoxia: how new technologies could resolve the controversies

In most tissues of the body, cellular ATP production predominantly occurs via mitochondrial oxidative phosphorylation of reduced intermediates, which are in turn derived from substrates such as glucose and fatty acids. In order to maintain ATP homeostasis, and therefore cellular function, the mitochondria require a constant supply of fuels and oxygen. In many disease states, or in healthy individuals at altitude, tissue oxygen levels fall and the cell must meet this hypoxic challenge to maintain energetics and limit oxidative stress. In humans at altitude and patients with respiratory disease, loss of skeletal muscle mitochondrial density is a consistent finding. Recent studies that have used cultured cells and genetic mouse models have elucidated a number of elegant adaptations that allow cells with a diminished mitochondrial population to function effectively in hypoxia. This article reviews these findings alongside studies of hypoxic human skeletal muscle, putting them into the context of whole-body physiology and acclimatization to high-altitude hypoxia. A number of current controversies are highlighted, which may eventually be resolved by a systems physiology approach that considers the time-or tissue-dependent nature of some adaptive responses. Future studies using high-throughput metabolomic, transcriptomic, and proteomic technologies to investigate hypoxic skeletal muscle in humans and animal models could resolve many of these controversies, and a case is therefore made for the integration of resulting data into computational models that account for factors such as duration and extent of hypoxic exposure, subjects' backgrounds, and whether data have been acquired from active or sedentary individuals. An integrated and more quantitative understanding of the body's metabolic response to hypoxia and the conditions under which adaptive processes occur could reveal much about the ways that tissues function in the very many disease states where hypoxia is a critical factor.

Effects of Physical Activity and Weight Loss on Skeletal Muscle Mitochondria and Relationship With Glucose Control in Type 2 Diabetes

Reduced mitochondrial capacity in skeletal muscle occurs in type 2 diabetic patients and in those at increased risk for this disorder, but the extent to which mitochondrial dysfunction in type 2 diabetic patients is remediable by physical activity and weight loss intervention is uncertain. We sought to address whether an intervention of daily moderate-intensity exercise combined with moderate weight loss can increase skeletal muscle mitochondrial content in type 2 diabetic patients and to address the relationship with amelioration of insulin resistance and hyperglycemia. Muscle biopsies were obtained before and after a 4-month intervention to assess mitochondrial morphology, mitochondrial DNA content, and mitochondrial enzyme activities. Glucose control, body composition, aerobic fitness, and insulin sensitivity were measured. In response to a weight loss of 7.1 +/- 0.8% and a 12 +/- 1.6% improvement in Vo(2max) (P < 0.05), insulin sensitivity improved by 59 +/- 21% (P < 0.05). There were significant increases in skeletal muscle mitochondrial density (by 67 +/- 17%, P < 0.01), cardiolipin content (55 +/- 17%, P < 0.01), and mitochondrial oxidation enzymes. Energy expenditure during physical activity correlated with the degree of improvement in insulin sensitivity (r = 0.84, P < 0.01), and, in turn, improvement in mitochondrial content was a strong correlate of intervention-induced improvement in A1C and fasting plasma glucose. Intensive short-term lifestyle modifications can restore mitochondrial content and functional capacity in skeletal muscle in type 2 diabetic patients. The improvement in the oxidative capacity of skeletal muscle may be a key component mediating salutary effects of lifestyle interventions on hyperglycemia and insulin resistance.