Mitochondrial Oxidative Capacity Research Articles

Positive Association between NIRS‐derived measures of Microvascular Reactivity and Mitochondrial Capacity in the Quadriceps and Hamstrings

BACKGROUNDDelivery of oxygen to the mitochondria is essential for oxidative phosphorylation and the production of ATP during rest and during muscle contraction. Despite widespread application of near infrared spectroscopy (NIRS), to our knowledge it has not been used to evaluate whether oxygen delivery to the mitochondria, as assessed by post‐ischemic reoxygenation parameters, is related to the oxidative capacity of the muscle.PURPOSETo determine the relation between microvascular reactivity and mitochondrial oxidative capacity in the knee joint musculature using NIRS.METHODSBilateral measurements of the vastus lateralis (VL) and medial hamstring (MH) muscles were taken in 14 moderate to highly active healthy adults (7M/7F, age: 22 ± 3 yrs, BMI: 21.3 ± 3.5 kg/m2, physical activity levels: 4190 ± 1324 MET minutes/week). Two NIRS probes (Portamon, Artinis) were secured over the respective muscle bellies, which collected data during a 30 second bout of surface electrical stimulation that caused an increase in metabolism followed by brief arterial occlusions to determine the metabolic rate of the muscle over time. A final resting metabolism measurement was taken 5 minutes after the arterial occlusions to obtain the time to half recovery of metabolic rate (NIRS k), which is a valid estimate of mitochondrial oxidative capacity. Microvascular reactivity was measured as 1) the 10‐second reoxygenation slope of the oxygen saturation signal (StO2) and 2) the half time to peak oxygenation following 5 minutes of arterial occlusion in each muscle.RESULTSThere was a significant positive association between NIRS kand the reoxygenation slope in both the VL (r = 0.64, p = 0.025) and the MH (r = 0.53, p = 0.049) muscles. NIRS kvalues were also positively associated with the time to half peak oxygenation in the VL (r = 0.65, p = 0.021) and the MH (r = 0.60, p = 0.026) muscles. There were no differences between the VL and MH muscles for NIRS kvalues (Mean ± SD: 1.78 ± 0.24 vs. 1.78 ± 0.33, p = 0.99), 10‐second reoxygenation slope (2.16 ± 0.84 vs. 1.99 ± 0.96, p = 0.65), and half time to peak oxygenation (8.4s ± 1.6 vs. 9.1s ± 2.2, p = 0.38).CONCLUSIONOur results suggest that microvascular reactivity is positively associated with the mitochondrial capacity of the knee joint musculature in this sample of healthy adults. Whether these associations exist in different clinical populations warrants future investigation.

Liver energy homeostasis impacts hypothalamus gene expression and food intake regulation

Several neuronal populations within the hypothalamus are known to modulate feeding behavior in mammals. Specifically, the arcuate nucleus contains appetite‐suppressing neurons pro‐opiomelanocortin (POMC), and appetite‐stimulating neurons neuropeptide Y (NPY)/agouti‐related peptide (AgRP) neurons. These neurons receive peripheral signals through blood and peripheral vagal afferents fibers. However, it is not well understood how peripheral signals, such as liver energy metabolism, may impact these neuronal populations to modulate feeding behavior. Herein, we used a hepatocyte‐specific PGC1a heterozygous (LPGC1a) mouse model, with associated reductions in mitochondrial fatty acid oxidation and respiratory capacity, to assess the role of liver energy homeostasis in the expression of arcuate nucleus genes involved in food intake regulation, and acute feeding behavior after peripheral delivery of nutrient or peripheral satiation hormones. To assess the impact of liver energy changes on arcuate nucleus gene expression, we used a fasting/refeeding paradigm (16‐hour fast, 2‐hour food withdrawal, and 16‐hour fast with a 4‐hour refeed). We observed reductions in liver PGC1a mRNA expression in LPGC1a compared to wildtype (WT) during all fasting and refed states. LPGC1a mice had significantly lower liver ATP and increased AMP during a fasted state. Suggesting that during a fasted state, the LPGC1a mice struggle to maintain liver energy homeostasis. Furthermore, LPGC1a mice had significantly increased AgRP mRNA expression in the hypothalamus during a fast. Interestingly, POMC expression was lower in LPGC1a mice at 2hrs and refed compared to WT and showed no change across any of the energy states. Importantly, acute food intake following 2 hr food withdrawal was not inhibited by intraperitoneal glucose or GLP‐1 in LPGC1a mice. Together these results suggest that a reduced liver energy state modulates activity of hypothalamic POMC and AgRP neurons, potentially contributing to alterations in feeding behavior of LPGC1a mice previously observed.

Loss of Estrogen‐Related Receptor Alpha (ESRRA) Impairs Neuronal Mitochondrial Function and Results in Disturbed Sleep and Neural Oscillatory Patterns

ESRRA is an orphan nuclear receptor enriched in metabolically active tissues and has been known to affect the transcription of a set of genes that regulate mitochondrial bioenergetics in peripheral organs. Of note, ESRRA is also abundantly expressed in the brain, but the functional role of brain ESRRA remains poorly understood. To test the role of ESRRA on energy metabolism in neurons, we performed the Seahorse assay in mouse primary cortical neurons with or without ESRRA expression and found that neurons lacking ESRRA have significantly reduced cellular respiration compared to control neurons, indicating that loss of ESRRA decreases mitochondrial oxidative capacity and thus neuronal energy production. We have previously reported that global ESRRA null (KO) displayed markedly reduced locomotor activity (home cage vibration plate p<0.05, wheel running p<0.001), suggesting that these mice do display an energy deficit as a result of this manipulation. Based on the commonly appreciated role of sleep in the replenishment of energy stores for normal brain function, we hypothesized that reduced brain energy levels caused by genetic loss of ESRRA would lead to hypersomnia and diminished neural oscillations, which may underlie hypolocomotion seen in ESRRA KO mice. To test this hypothesis, wireless electroencephalography/electromyography (EEG/EMG) devices were implanted in a cohort of ESRRA KO and wildtype (WT) mice and 24hr sleep state was recorded and scored. Sleep architecture analysis from 24‐hour wireless EEG/EMG recording revealed that ESRRA KO mice exhibit significantly increased non‐rapid eye movement (NREM) (p<0.05) sleep as well as disrupted circadian pattern of rapid eye movement (REM) (p<0.01) sleep compared to WT littermates. Power spectral analysis further revealed that high range gamma (40‐100Hz) (p<0.001) and alpha (9‐13Hz) (p<0.05) oscillations are significantly decreased while low range gamma (25‐40Hz) (p<0.05) and beta (13‐25Hz) (p<0.05) oscillations are increased in ESRRA KO mice. Our findings not only reveal a previously unappreciated role of ESRRA in regulating neuronal mitochondrial function, sleep‐wake cycle, and neural oscillations, but also support a novel concept that a single molecular cause of diminished brain energy levels can prolong sleep duration and results in aberrant REM sleep pattern.

2 deoxy-D-glucose augments the mitochondrial respiratory chain in heart

2-Deoxy-D-glucose (2DG) has recently received emergency approval for the treatment of COVID-19 in India, after a successful clinical trial. SARS-CoV-2 infection of cultured cells is accompanied by elevated glycolysis and decreased mitochondrial function, whereas 2DG represses glycolysis and stimulates respiration, and restricts viral replication. While 2DG has pleiotropic effects on cell metabolism in cultured cells it is not known which of these manifests in vivo. On the other hand, it is known that 2DG given continuously can have severe detrimental effects on the rodent heart. Here, we show that the principal effect of an extended, intermittent 2DG treatment on mice is to augment the mitochondrial respiratory chain proteome in the heart; importantly, this occurs without vacuolization, hypertrophy or fibrosis. The increase in the heart respiratory chain proteome suggests an increase in mitochondrial oxidative capacity, which could compensate for the energy deficit caused by the inhibition of glycolysis. Thus, 2DG in the murine heart appears to induce a metabolic configuration that is the opposite of SARS-CoV-2 infected cells, which could explain the compound’s ability to restrict the propagation of the virus to the benefit of patients with COVID-19 disease.

Sirt6 reprograms myofibers to oxidative type through CREB-dependent Sox6 suppression

Expanding the exercise capacity of skeletal muscle is an emerging strategy to combat obesity-related metabolic diseases and this can be achieved by shifting skeletal muscle fibers toward slow-twitch oxidative type. Here, we report that Sirt6, an anti-aging histone deacetylase, is critical in regulating myofiber configuration toward oxidative type and that Sirt6 activator can be an exercise mimetic. Genetic inactivation of Sirt6 in skeletal muscle reduced while its transgenic overexpression increased mitochondrial oxidative capacity and exercise performance in mice. Mechanistically, we show that Sirt6 downregulated Sox6, a key repressor of slow fiber specific gene, by increasing the transcription of CREB. Sirt6 expression is elevated in chronically exercised humans, and mice treated with an activator of Sirt6 showed an increase in exercise endurance as compared to exercise-trained controls. Thus, the current study identifies Sirt6 as a molecular target for reprogramming myofiber composition toward the oxidative type and for improving muscle performance.

Resistance exercise training increases skeletal muscle mitochondrial respiration in chronic obstructive pulmonary disease

AbstractBackgroundChronic obstructive pulmonary disease (COPD) is associated with skeletal muscle mitochondrial dysfunction. Resistance exercise training (RT) is a training modality with a relatively small pulmonary demand that has been suggested to increase skeletal muscle oxidative enzyme activity in COPD. Whether a shift into a more oxidative profile following RT also translates into increased mitochondrial respiratory capacity in COPD is yet to be established.MethodsThis study investigated the effects of 13 weeks of RT on m. vastus lateralis mitochondrial capacity in 11 persons with moderate COPD [45% females, age: 69 ± 4 years (mean ± SD), predicted forced expiratory volume in 1 s (FEV1): 56 ± 7%] and 12 healthy controls (75% females, age: 66 ± 5 years, predicted FEV1: 110 ± 16%). RT was supervised and carried out two times per week. Leg exercises included leg press, knee extension, and knee flexion and were performed unilaterally with one leg conducting high‐load training (10 repetitions maximum, 10RM) and the other leg conducting low‐load training (30 repetitions maximum, 30RM). One‐legged muscle mass, maximal muscle strength, and endurance performance were determined prior to and after the RT period, together with mitochondrial respiratory capacity using high‐resolution respirometry and citrate synthase (CS) activity (a marker for mitochondrial volume density). Transcriptome analysis of genes associated with mitochondrial function was performed.ResultsResistance exercise training led to similar improvements in one‐legged muscle mass, muscle strength, and endurance performance in COPD and healthy individuals. In COPD, mitochondrial fatty acid oxidation capacity and oxidative phosphorylation increased following RT (+13 ± 22%, P = 0.033 and +9 ± 23%, P = 0.035, respectively). Marked increases were also seen in COPD for mitochondrial volume density (CS activity, +39 ± 35%, P = 0.001), which increased more than mitochondrial respiration, leading to lowered intrinsic mitochondrial function (respiration/CS activity) for complex‐1‐supported respiration (−12 ± 43%, P = 0.033), oxidative phosphorylation (−10 ± 42%, P = 0.037), and electron transfer system capacity (−6 ± 52%, P = 0.027). No differences were observed between 10RM and 30RM RT, nor were there any adaptations in mitochondrial function following RT in healthy controls. RT led to differential expression of numerous genes related to mitochondrial function in both COPD and healthy controls, with no difference being observed between groups.ConclusionsThirteen weeks of RT resulted in augmented skeletal muscle mitochondrial respiratory capacity in COPD, accompanied by alterations in the transcriptome and driven by an increase in mitochondrial quantity rather than improved mitochondrial quality.

Accuracy and precision of 31P-MRS assessment for evaluating the effect of melatonin-pretreated mitochondria transferring on liver fibrosis of rats

This study examined the reliability of 31phosphorus-magnetic resonance spectroscopy (31P-MRS) to measure parameters of liver metabolic function in the intact animals. These parameters can help us to evaluate the severity and prognosis of liver fibrosis. In addition, 31P-MRS was also used to examine the protective effects of melatonin on liver mitochondria. An animal model of liver fibrosis was established via intraperitoneal administration of thioacetamide (TAA) to rats. Rats were scanned at baseline, week 3 and 6 after TAA treatment, respectively, to measure the longitudinal changes of phosphorus metabolite levels by 31P-MRS at 9.4 T. The results showed a consistent decline in the levels of phosphorus metabolites (inorganic phosphate, α-ATP, γ-ATP and NADH) in rats with fibrosis. Impaired mitochondrial respiration capacity, collagen accumulation and the extent of fibrosis in liver were markedly associated with decreased concentrations of phosphorus metabolites. Melatonin-pretreated mitochondria transferring efficiently prevented TAA-induced liver damage mainly by restoring mitochondrial function. In conclusion, the levels of phosphorus metabolites could serve as the indicators of mitochondrial oxidative capacity and thus provides a novel tool to evaluate mitochondrial integrity in the in vivo condition by using 31P-MRS in the setting of liver fibrosis.

Ankle-Brachial Index and Energy Production in People Without Peripheral Artery Disease: The BLSA.

BackgroundLower ankle‐brachial index (ABI) values within the 0.90 to 1.40 range are associated with poorer mitochondrial oxidative capacity of thigh muscles in cross‐sectional analyses. Whether ABI decline is associated with greater declines in thigh muscle oxidative capacity with aging is unknown.Method and ResultsWe analyzed data from 228 participants (100 men) of the BLSA (Baltimore Longitudinal Study of Aging), aged 39 to 97 years, with an ABI between 0.9 and 1.40 at baseline and at follow‐up (mean follow‐up period of 2.8 years). We examined mitochondrial oxidative capacity of the left thigh muscle, by measuring the postexercise phosphocreatine recovery rate constant (kPCr) from phosphorus‐31 magnetic resonance spectroscopy. Greater kPCr indicated higher mitochondrial oxidative capacity. Although kPCr was available on the left leg only, ABI was measured in both legs. Longitudinal rates of change (Change) of left and right ABI and kPCr of the left thigh muscle were estimated using linear mixed effects models, and their association was analyzed by standardized multiple linear regressions. In multivariate analysis including sex, age, baseline kPCr, both left and right baseline ABI, and ABI change in both legs, (kPCr)Change was directly associated with ipsilateral (left) (ABI)Change (standardized [STD]‐β=0.14; P=0.0168) but not with contralateral (right) (ABI)Change (P=0.22). Adjusting for traditional cardiovascular risk factors, this association remained significant (STD‐β=0.18; P=0.0051). (kPCr)Change was steeper in White race participants (STD‐β=0.16; P=0.0122) and body mass index (STD‐β=0.13; P=0.0479). There was no significant association with current smoking status (P=0.63), fasting glucose (P=0.28), heart rate (P=0.67), mean blood pressure (P=0.78), and low‐density lipoprotein (P=0.75), high‐density lipoprotein (P=0.82), or triglycerides (P=0.15).ConclusionsIn people without peripheral arterial disease, greater decline in ABI over time, but not baseline ABI, was associated with faster decline in thigh mitochondrial oxidative capacity in the ipsilateral leg. Further studies are needed to examine whether early interventions that improve lower extremity muscle perfusion can improve and prevent the decline of muscle energetics.

Inhibition of mitoNEET attenuates LPS-induced inflammation and oxidative stress

MitoNEET (mitochondrial protein containing Asn–Glu–Glu–Thr (NEET) sequence) is a 2Fe–2S cluster-containing integral membrane protein that resides in the mitochondrial outer membrane and participates in a redox-sensitive signaling and Fe–S cluster transfer. Thus, mitoNEET is a key regulator of mitochondrial oxidative capacity and iron homeostasis. Moreover, mitochondrial dysfunction and oxidative stress play critical roles in inflammatory diseases such as sepsis. Increased iron levels mediated by mitochondrial dysfunction lead to oxidative damage and generation of reactive oxygen species (ROS). Increasing evidence suggests that targeting mitoNEET to reverse mitochondrial dysfunction deserves further investigation. However, the role of mitoNEET in inflammatory diseases is unknown. Here, we investigated the mechanism of action and function of mitoNEET during lipopolysaccharide (LPS)-induced inflammatory responses in vitro and in vivo. Levels of mitoNEET protein increased during microbial or LPS-induced sepsis. Pharmacological inhibition of mitoNEET using mitoNEET ligand-1 (NL-1) decreased the levels of pro-inflammatory cytokines such as IL-1β, IL-6, and TNF-α in animal models of sepsis, as well as LPS-induced inflammatory responses by macrophages in vitro. Inhibition of mitoNEET using NL-1 or mitoNEET shRNA abrogated LPS-induced ROS formation and mitochondrial dysfunction. Furthermore, mitochondrial iron accumulation led to generation of LPS-induced ROS, a process blocked by NL-1 or shRNA. Taken together, these data suggest that mitoNEET could be a key therapeutic molecule that targets mitochondrial dysfunction during inflammatory diseases and sepsis.

Transcription Factor Movement and Exercise-Induced Mitochondrial Biogenesis in Human Skeletal Muscle: Current Knowledge and Future Perspectives.

In response to exercise, the oxidative capacity of mitochondria within skeletal muscle increases through the coordinated expression of mitochondrial proteins in a process termed mitochondrial biogenesis. Controlling the expression of mitochondrial proteins are transcription factors—a group of proteins that regulate messenger RNA transcription from DNA in the nucleus and mitochondria. To fulfil other functions or to limit gene expression, transcription factors are often localised away from DNA to different subcellular compartments and undergo rapid movement or accumulation only when required. Although many transcription factors involved in exercise-induced mitochondrial biogenesis have been identified, numerous conflicting findings and gaps exist within our knowledge of their subcellular movement. This review aims to summarise and provide a critical analysis of the published literature regarding the exercise-induced movement of transcription factors involved in mitochondria biogenesis in skeletal muscle.

Impact of exercise training on muscle mitochondria modifications in older adults: a systematic review of randomized controlled trials.

Previous evidence showed that cellular aging is a multifactorial process that is associated with decline in mitochondrial function. Physical exercise has been proposed as an effective and safe therapeutical intervention to improve the mitochondria network in the adult myocytes. The aim of this systematic review of randomized controlled trials (RCTs) was to assess the exercise-induced muscle mitochondria modifications in older adults, underlining the differences related to different exercise modalities. On November 28th, 2021, five databases (PubMed, Scopus, Web of Science, Cochrane, and PEDro) were systematically searched for RCTs to include articles with: healthy older people as participants; physical exercise (endurance training (ET), resistance training (RT), and combined training (CT)) as intervention; other different exercise modalities or physical inactivity as comparator; mitochondrial modifications (quality, density and dynamics, oxidative, and antioxidant capacity) as outcomes. The quality assessment was performed according to the PEDro scale; the bias risk was evaluated by Cochrane risk-of-bias assessment tool. Out of 2940 records, 6 studies were included (2 assessing ET, 2 RT, 1 CT, and 1 both ET and RT). Taken together, 164 elderly subjects were included in the present systematic review. Significant positive effects were reported in terms of mitochondrial quality, density, dynamics, oxidative and antioxidant capacity, even though with different degrees according to the exercise type. The quality assessment reported one good-quality study, whereas the other five studies had a fair quality. The overall low quality of the studies on this topic indicate that further research is needed. RT seems to be the most studied physical exercise modality improving mitochondrial density and dynamics, while ET have been related to mitochondrial antioxidant capacity improvements. However, these exercise-induced specific effects should be better explored in older people.

Disruption of neuromedin B receptor improves mitochondrial oxidative phosphorylation capacity in gastrocnemius muscle of female mice.

Neuromedin B (NB), a bombesin-like peptide, exerts its specific actions by binding to the neuromedin B receptor (NBR), a G protein-coupled receptor. Female NBR-knockout (NBR-KO) mice exhibit resistance to diet-induced obesity, without hyperphagia, suggesting possible increase in energy expenditure. Skeletal muscle (SM) is crucial for whole body energy homeostasis, however, the presence of NB-NBR signaling and its effects in SM are unknown. Here, we show that male and female wild type express Nmbr and Nmb mRNA in SM, with higher levels in females. Female NBR-KO gastrocnemius showed increased Myh7 mRNA level, which characterizes type I fibers (oxidative profile). Their permeabilized gastrocnemius fibers, studied by high-resolution respirometry, exhibited higher consumption of O2 coupled to ATP synthesis and unaltered uncoupled respiration. NBR-KO gastrocnemius had higher protein levels of ATP-synthase and Nduf9 mRNA, corresponding to mitochondrial complex I subunit. NBR-KO gastrocnemius exhibited slight increase in mitochondria number, increased thickness of Z line at electron microscopy, and unaltered mitochondrial dynamics markers. Therefore, in the females' gastrocnemius, a predominantly glycolytic SM, the NBR absence promotes changes that favor mitochondrial oxidative phosphorylation capacity. In addition, in L6 myocytes, NB treatment (5 μg/mL/16 h) promoted lower O2 consumption coupled to ATP synthesis, suggesting direct action at SM cells. Altogether, the study reinforces the hypothesis that inhibition of NB-NBR signaling enhances the capacity for oxidative phosphorylation of white SM, encouraging future studies to elucidate their contribution on other types of SM and whole body energy expenditure, which may lead to a new target to drug development for obesity treatment.NEW & NOTEWORTHY This study describes neuromedin B (NB) and NB receptor as new regulators of skeletal muscle mitochondrial function. The white skeletal muscle mitochondrial oxidative phosphorylation capacity was increased by NB receptor genetic disruption in female mice. These findings may contribute to the resistance to diet-induced obesity, previously found in these mice, which requires future studies. Thus, investigations are necessary to clarify if blockade of NB receptor may be an approach to develop drugs to combat obesity.

Short-Term Adaptations in Skeletal Muscle Mitochondrial Oxidative Capacity and Metabolic Pathways to Breaking up Sedentary Behaviors in Overweight or Obese Adults.

Breaking up sedentary behavior with short-frequent bouts of physical activity (PA) differentially influences metabolic health compared with the performance of a single-continuous bout of PA matched for total active time. However, the underlying mechanisms are unknown. We compared skeletal muscle mitochondrial respiration (high-resolution respirometry) and molecular adaptations (RNA sequencing) following 4-day exposure to breaks vs. energy-matched single-continuous PA bout in inactive adults with overweight/obesity. Participants (9M/10F, 32.2 ± 6.4 years, 30.3 ± 3.0 kg/m2) completed three 4-day interventions of a randomized cross-over study: SED, sedentary control; MICRO, 5 min brisk walking each hour for 9 h; ONE: 45 min/d continuous brisk walking bout. Fasted muscle biopsies were collected on day 5. Mitochondrial coupling in the presence of lipid-associated substrates was higher after ONE (4.8 ± 2.5) compared to MICRO (3.1 ± 1.1, p = 0.02) and SED (2.3 ± 1.0, p = 0.001). Respiratory rates did not differ across groups with carbohydrate-associated substrates. In pathways associated with muscle contraction transcription signaling, ONE and MICRO similarly enhanced Oxidative Phosphorylation and Sirtuin Signaling expression (p < 0.0001, for both). However, ONE (p < 0.001, for all), but not MICRO, had greater pathway enrichment, including Ca++, mTOR, AMPK, and HIF1α signaling, than SED. Although breaking up sedentary behavior triggered skeletal muscle molecular adaptations favoring oxidative capacity, it did not improve mitochondrial function over the short term.

Time-restricted feeding during the inactive phase abolishes the daily rhythm in mitochondrial respiration in rat skeletal muscle.

Shift-workers show an increased incidence of type 2 diabetes mellitus (T2DM). A possible mechanism is the disruption of the circadian timing of glucose homeostasis. Skeletal muscle mitochondrial function is modulated by the molecular clock. We used time-restricted feeding (TRF) during the inactive phase to investigate how mistimed feeding affects muscle mitochondrial metabolism. Rats on an ad libitum (AL) diet were compared to those that could eat only during the light (inactive) or dark (active) phase. Mitochondrial respiration, metabolic gene expressions, and metabolite concentrations were determined in the soleus muscle. Rats on AL feeding or dark-fed TRF showed a clear daily rhythm in muscle mitochondrial respiration. This rhythm in mitochondrial oxidative phosphorylation capacity was abolished in light-fed TRF animals and overall 24h respiration was lower. The expression of several genes involved in mitochondrial biogenesis and the fission/fusion machinery was altered in light-fed animals. Metabolomics analysis indicated that light-fed animals had lost rhythmic levels of α-ketoglutarate and citric acid. Contrastingly, lipidomics showed that light-fed animals abundantly gained rhythmicity in levels of triglycerides. Furthermore, while the RER shifted entirely with the food intake in the light-fed animals, many measured metabolic parameters (e.g., activity and mitochondrial respiration) did not strictly align with the shifted timing of food intake, resulting in a mismatch between expected metabolic supply/demand (as dictated by the circadian timing system and light/dark-cycle) and the actual metabolic supply/demand (as dictated by the timing of food intake). These data suggest that shift-work impairs mitochondrial metabolism and causes metabolic inflexibility, which can predispose to T2DM.

Effects of different music on HEK293T cell growth and mitochondrial functions

Background: Mitochondria are considered a portal to receive, process and integrate external energy and information to maintain cellular homeostasis. Previous studies demonstrated that mitochondrial function and antioxidant capacity of in-vitro cultured mammalian cells is modified by different energetic stimuli including electromagnetic energy, acoustic energy, external Qi and subtle energy emitted by written texts in relatively short time frames. Thus, individual cells can act as a rapid and sensitive biological sensor and act as a platform to evaluate and understand the subtle effect of different biophysical stimuli. Regarding acoustic energy, several different types of music have been reported to produce beneficial effects on human health.Objective: To compare eastern and western music styles on cell function at the biochemical level to understand the underlying mechanisms involved.Methods In this study, we compared the effects of Chinese five-element music with two types of western music (heavy-metal and classical) on mitochondrial function, oxidative capacity and growth using HEK293T cells (human embryonic kidney cells).Results: Unlike rock and classical music, exposing cells to five-element music produced several beneficial physiological effects, including statistically significant increases in the production of adenosine triphosphate (ATP) by 17%, glutathione (GSH) by 21% and cell growth rates (14%), as well as a significant reduction in the reactive oxygen species (ROS) by 13%. For the group treated with classical music, there was only a trend toward increased GSH (8%), although the increased growth rates (14%) did reach significance. In sharp contrast, the cells treated with heavy-metal music responded with an opposite and significant 16% increase in ROS and a significant 11% reduction in cell viability.Conclusions: This study revealed the dramatically different and even opposite effects of different styles of music on specific biochemical measures in cultured human cells. These results help explain the underlying biochemical mechanisms of the effects of the different types of music.

Skeletal muscle energetics in patients with moderate to advanced kidney disease.

Sarcopenia, defined as decrease in muscle function and mass, is common in patients with moderate to advanced chronic kidney disease (CKD) and is associated with poor clinical outcomes. Muscle mitochondrial dysfunction is proposed as one of the mechanisms underlying sarcopenia. Patients with moderate to advanced CKD have decreased muscle mitochondrial content and oxidative capacity along with suppressed activity of various mitochondrial enzymes such as mitochondrial electron transport chain complexes and pyruvate dehydrogenase, leading to impaired energy production. Other mitochondrial abnormalities found in this population include defective beta-oxidation of fatty acids and mitochondrial DNA mutations. These changes are noticeable from the early stages of CKD and correlate with severity of the disease. Damage induced by uremic toxins, oxidative stress, and systemic inflammation has been implicated in the development of mitochondrial dysfunction in CKD patients. Given that mitochondrial function is an important determinant of physical activity and performance, its modulation is a potential therapeutic target for sarcopenia in patients with kidney disease. Coenzyme Q, nicotinamide, and cardiolipin-targeted peptides have been tested as therapeutic interventions in early studies. Aerobic exercise, a well-established strategy to improve muscle function and mass in healthy adults, is not as effective in patients with advanced kidney disease. This might be due to reduced expression or impaired activation of peroxisome proliferator-activated receptor-gamma coactivator 1α, the master regulator of mitochondrial biogenesis. Further studies are needed to broaden our understanding of the pathogenesis of mitochondrial dysfunction and to develop mitochondrial-targeted therapies for prevention and treatment of sarcopenia in patients with CKD.

A roadmap for the characterization of energy metabolism in human cardiomyocytes derived from induced pluripotent stem cells

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) are an increasingly employed model in cardiac research and drug discovery. As cellular metabolism plays an integral role in determining phenotype, the characterization of the metabolic profile of hiPSC-CM during maturation is crucial for their translational application. In this study we employ a combination of methods including extracellular flux, 13C-glucose enrichment and targeted metabolomics to characterize the metabolic profile of hiPSC-CM during their maturation in culture from 6 weeks, up to 12 weeks. Results show a progressive remodeling of pathways involved in energy metabolism and substrate utilization along with an increase in sarcomere regularity. The oxidative capacity of hiPSC-CM and particularly their ability to utilize fatty acids increased with time. In parallel, relative glucose oxidation was reduced while glutamine oxidation was maintained at similar levels. There was also evidence of increased coupling of glycolysis to mitochondrial respiration, and away from glycolytic branch pathways at later stages of maturation. The rate of glycolysis as assessed by lactate production was maintained at both stages but with significant alterations in proximal glycolytic enzymes such as hexokinase and phosphofructokinase. We observed a progressive maturation of mitochondrial oxidative capacity at comparable levels of mitochondrial content between these time-points with enhancement of mitochondrial network structure. These results show that the metabolic profile of hiPSC-CM is progressively restructured, recapitulating aspects of early post-natal heart development. This would be particularly important to consider when employing these cell model in studies where metabolism plays an important role.

Evaluation of muscle-specific and metabolism regulating microRNAs in a chronic swimming rat model

Making benefit from the epigenetic effects of environmental factors such as physical activity may result in a considerable improvement in the prevention of chronic civilization diseases. In our chronic swimming rat model, the expression levels of such microRNAs were characterized, that are involved in skeletal muscle differentiation, hypertrophy and fine-tuning of metabolism, which processes are influenced by chronic endurance training, contributing to the metabolic adaptation of skeletal muscle during physical activity. After chronic swimming, the level of miR-128a increased significantly in EDL muscles, which may influence metabolic adaptation and stress response as well. In SOL, the expression level of miR-15b and miR-451 decreased significantly after chronic swimming, which changes are opposite to their previously described increment in insulin resistant skeletal muscle. MiR-451 also targets PGC-1α mRNA, whiches expression level significantly increased in SOL muscles, resulting in enhanced biogenesis and oxidative capacity of mitochondria. In summary, the microRNA expression changes that were observed during our experiments suggest that chronic swim training contributes to a beneficial metabolic profile of skeletal muscle.

Impact of acute exercise on peripheral blood mononuclear cells nutrient sensing and mitochondrial oxidative capacity in healthy young adults.

Regular exercise is associated with changes in peripheral blood mononuclear cell (PBMC) proportions that have enhanced effector functions in young and old adults; however, the effects of acute exercise on PBMC nutrient sensors and metabolic function in active young adults is unknown. To fill this gap, activation status and nutrient‐sensing mechanisms of PBMCs isolated from 21 healthy active adults (20–35 yr; 36.5 ± 6.3 V̇O2peak) were characterized before and after 30 min of moderate‐to‐vigorous cycling (65%–75% V̇O2peak). In addition, changes in PBMC mitochondrial respiratory function in response to exercise were assessed using high‐resolution respirometry. There was an increase in the number of activated CD69+/CD4 (79% increase) and CD69+/CD8 (166% increase) T‐cells in response to the acute bout of exercise, while the nutrient‐sensing mechanisms remained unchanged. PBMC mitochondrial respiration did not increase on a cell‐per‐cell basis, however, mitochondrial oxidative capacity (OXPHOS) increased at the tissue level (18.6 pmol/(s*ml blood) versus 29.3 pmol/(s*ml blood); p < 0.05) in response to acute exercise. Thus, this study shows that acute exercise preferentially mobilizes activated T‐cells while concomitantly increasing PBMC mitochondrial oxidative capacity at the tissue level, rather than acutely changing mitochondrial oxidative capacity at the cellular level in young adults.

Chronic aryl hydrocarbon receptor activity phenocopies smoking-induced skeletal muscle impairment.

BackgroundChronic obstructive pulmonary disease (COPD) patients exhibit skeletal muscle atrophy, denervation, and reduced mitochondrial oxidative capacity. Whilst chronic tobacco smoke exposure is implicated in COPD muscle impairment, the mechanisms involved are ambiguous. The aryl hydrocarbon receptor (AHR) is a ligand‐activated transcription factor that activates detoxifying pathways with numerous exogenous ligands, including tobacco smoke. Whereas transient AHR activation is adaptive, chronic activation can be toxic. On this basis, we tested the hypothesis that chronic smoke‐induced AHR activation causes adverse muscle impact.MethodsWe used clinical patient muscle samples, and in vitro (C2C12 myotubes) and in vivo models (mouse), to perform gene expression, mitochondrial function, muscle and neuromuscular junction morphology, and genetic manipulations (adeno‐associated virus‐mediated gene transfer).ResultsSixteen weeks of tobacco smoke exposure in mice caused muscle atrophy, neuromuscular junction degeneration, and reduced oxidative capacity. Similarly, smoke exposure reprogrammed the muscle transcriptome, with down‐regulation of mitochondrial and neuromuscular junction genes. In mouse and human patient specimens, smoke exposure increased muscle AHR signalling. Mechanistically, experiments in cultured myotubes demonstrated that smoke condensate activated the AHR, caused mitochondrial impairments, and induced an AHR‐dependent myotube atrophy. Finally, to isolate the role of AHR activity, expression of a constitutively active AHR mutant without smoke exposure caused atrophy and mitochondrial impairments in cultured myotubes, and muscle atrophy and neuromuscular junction degeneration in mice.ConclusionsThese results establish that chronic AHR activity, as occurs in smokers, phenocopies the atrophy, mitochondrial impairment, and neuromuscular junction degeneration caused by chronic tobacco smoke exposure.