Rat liver GTP-binding proteins mediate changes in mitochondrial membrane potential and organelle fusion

Inferring mitochondrial and cytosolic metabolism by coupling isotope tracing and deconvolution

The inability to inspect metabolic activities within distinct subcellular compartments has been a major barrier to our understanding of eukaryotic cell metabolism. Previous work addressed this challenge by analyzing metabolism in isolated organelles, which grossly bias metabolic activity. Here, we describe a method for inferring physiological metabolic fluxes and metabolite concentrations in mitochondria and cytosol based on isotope tracing experiments performed with intact cells. This is made possible by computational deconvolution of metabolite isotopic labeling patterns and concentrations into cytosolic and mitochondrial counterparts, coupled with metabolic and thermodynamic modelling. Our approach lowers the uncertainty regarding compartmentalized fluxes and concentrations by one and three orders of magnitude compared to existing modelling approaches, respectively. We derive a quantitative view of mitochondrial and cytosolic metabolic activities in central carbon metabolism across cultured cell lines without performing cell fractionation, finding major variability in compartmentalized malate-aspartate shuttle fluxes. We expect our approach for inferring metabolism at a subcellular resolution to be instrumental for a variety of studies of metabolic dysfunction in human disease and for bioengineering.

Chronic eccentric arm cycling improves maximum upper-body strength and power

INTRODUCTION

Eccentric leg cycling (cycle ergometry adapted to impose muscle lengthening contractions) offers an effective exercise for restoring lower-body muscular function, maintaining health, and improving performance in clinical and athletic populations.

PURPOSE

We extended this model to the upper body and evaluated the effectiveness of a 7-week eccentric arm cycling (ECC_arm) intervention to improve upper-body muscular function. We also explored whether ECC_arm would alter arterial function.

METHODS

Participants performed ECC_arm (n = 9) or concentric arm cycling (CON_arm; n = 8) 3×/week while training intensity increased (5-20 min, 60-70% upper-body peak heart rate). Maximum elbow extensor strength, upper-body concentric power, and peripheral and central arterial stiffness were assessed before and after training.

RESULTS

During training, heart rates and perceived exertion did not differ between groups (~68% upper-body peak heart rate, ~12 Borg units, both P > 0.05), whereas power during ECC_arm was ~2× that for CON_arm (122 ± 43 vs. 59 ± 20 W, P < 0.01). Muscle soreness for ECC_arm was greater than CON_arm (P = 0.02), however, soreness was minimal for both groups (<0.50 cm). Following training, ECC_arm exhibited greater changes in elbow extensor strength (16 ± 10 vs. 1 ± 9%, P = 0.01) and upper-body power (6 ± 8 vs. -3 ± 7%, P < 0.01) compared to CON_arm. Peripheral and central arterial stiffness did not change for either group (both P > 0.05).

CONCLUSION

Upper-body eccentric exercise improved dynamic muscular function while training at low exertion levels. Results occurred with minimal soreness and without compromising arterial function. ECC_arm findings parallel eccentric leg cycling findings and indicate that eccentric cycle ergometry offers a robust model for enhancing upper-body muscular function. ECC_arm could have applications in rehabilitation and sport training.

Similar substrate oxidation rates in concentric and eccentric cycling matched for aerobic power output

This study investigated substrate oxidation in concentric and eccentric cycling matched for aerobic power output in the postprandial state. Energy expenditure, respiratory exchange ratio, and fat and carbohydrate oxidation rates were measured at rest and after 15, 30, and 45 min of eccentric and concentric cycling in 12 men. Absolute and relative aerobic power output and energy expenditure were similar during concentric and eccentric exercise. No effect of exercise modality was observed for substrate metabolism.

Measurement of technetium-99m sestamibi signals in rats administered a mitochondrial uncoupler and in a rat model of heart failure

Background

Many methods have been used to assess mitochondrial function. Technetium-99m sestamibi (^99mTc-MIBI), a lipophilic cation, is rapidly incorporated into myocardial cells by diffusion and mainly localizes to the mitochondria. The purpose of this study was to investigate whether measurement of ^99mTc-MIBI signals in animal models could be used as a tool to quantify mitochondrial membrane potential at the organ level.

Methods and Results

We analyzed ^99mTc-MIBI signals in Sprague-Dawley (SD) rat hearts perfused with carbonyl cyanide m-chlorophenylhydrazone (CCCP), a mitochondrial uncoupler known to reduce the mitochondrial membrane potential. ^99mTc-MIBI signals could be used to detect changes in the mitochondrial membrane potential with sensitivity comparable to that obtained by two-photon laser microscopy with the cationic probe tetramethylrhodamine ethyl ester (TMRE). We also measured ^99mTc-MIBI signals in the hearts of SD rats administered CCCP (4 mg/kg intraperitoneally) or vehicle. ^99mTc-MIBI signals decreased in rat hearts administered CCCP, and the ATP content, as measured by ³¹P magnetic resonance spectroscopy, decreased simultaneously. Next, we administered ^99mTc-MIBI to Dahl salt-sensitive rats fed a high-salt diet, which leads to hypertension and heart failure. The ^99mTc-MIBI signal per heart tissue weight was inversely correlated with heart weight, cardiac function, and the expression of atrial natriuretic factor, a marker of heart failure, and positively correlated with the accumulation of labeled fatty acid analog. The ^99mTc-MIBI signal per liver tissue weight was lower than that per heart tissue weight.

Conclusion

Measurement of ^99mTc-MIBI signals can be an effective tool for semiquantitative investigation of cardiac mitochondrial membrane potential in the SD rat model by using a chemical to decrease the mitochondrial membrane potential. The ^99mTc-MIBI signal per heart tissue weight was inversely correlated with the severity of heart failure in the Dahl rat model.

Downhill walking to improve lower limb strength in healthy young adults

Walking is the most natural physical activity to maintain and improve fitness and health. Walking downhill is usefully adopted to plan training programmes to improve the strength, particularly in older adults. The present research was aimed to evaluate the influence of downhill walking on leg strength in young adult. A total of 32 females (age 26 ± 4 years; height 1.64 ± 0.05 m; body mass 57.6 ± 5.6 kg) were divided into four groups and they carried out an exercise intervention consisting of three sessions per week for 6 weeks, each lasting 30 minutes. Groups were defined at several workloads characterised by treadmill inclination (%) and walking speed (m · s(-1)): Level Walking at treadmill inclination 0% and walking speed 1.0; Uphill Walking at +20%, 0.75; Downhill Walking (DW) at -20%, 1.36; and Mixed Walking at +20%, 0.75 and -20%, 1.36 each lasting 15 minutes. Maximum voluntary contraction (MVC) developed by the Quadriceps Femoris and Endurance Time at 60% MVC were evaluated before and after experimental period. At the end of each session, Borg's scale and Visual Analogue Scale (VAS) were adopted in order to evaluate perception of rate exertion and pain. Statistical analysis showed significant only in MVC for DW in both right and left legs. Borg's scale and VAS described light activity free of pain. Present findings showed how an eccentric exercise, short lasting and at a low workload, can be useful in inducing improvements in leg strength.

Construction of an Isokinetic Eccentric Cycle Ergometer for Research and Training

Eccentric cycling serves a useful exercise modality in clinical, research, and sport training settings. However, several constraints can make it difficult to use commercially available eccentric cycle ergometers. In this technical note, we describe the process by which we built an isokinetic eccentric cycle ergometer using exercise equipment modified with commonly available industrial parts. Specifically, we started with a used recumbent cycle ergometer and removed all the original parts leaving only the frame and seat. A 2.2 kW electric motor was attached to a transmission system that was then joined with the ergometer. The motor was controlled using a variable frequency drive, which allowed for control of a wide range of pedaling rates. The ergometer was also equipped with a power measurement device that quantified work, power, and pedaling rate and provided feedback to the individual performing the exercise. With these parts along with some custom fabrication, we were able to construct an isokinetic eccentric cycle ergometer suitable for research and training. This paper offers a guide for those individuals who plan to use eccentric cycle ergometry as an exercise modality and wish to construct their own ergometer.

Eccentric exercise in rehabilitation: safety, feasibility, and application

This nonexhaustive mini-review reports on the application of eccentric exercise in various rehabilitation populations. The two defining properties of eccentric muscle contractions--a potential for high muscle-force production at an energy cost that is uniquely low--are revisited and formatted as exercise countermeasures to muscle atrophy, weakness, and deficits in physical function. Following a dual-phase implementation, eccentric exercise that induces rehabilitation benefits without muscle damage, thereby making it both safe and feasible in rehabilitation, is described. Clinical considerations, algorithms of exercise progression, and suggested modes of eccentric exercise are presented.

Isometric strength and steadiness adaptations of the knee extensor muscles to level and downhill treadmill walking in older adults

An ageing related decline in muscle strength and steadiness decreases quality of life and increases the risk for falls. Downhill treadmill walking (DTW) may enhance muscle strength and steadiness in older adults. Eighteen healthy older adults (age: 67 ± 4, body mass: 75 ± 14 kg) completed 12-weeks of level treadmill walking (LTW, 0 %, n = 8) or DTW (-10 %, n = 10) (30 min, 3 days per week) at a self-selected walking speed (re-adjusted in week 4 and 8). Maximal voluntary isometric force (MVIF) and electromyography (EMG) of the m. quadriceps femoris (QF) were measured at baseline, 4, 8 and 12 weeks. Steadiness of submaximal (5, 10 and 20 % MVIF) isometric contractions (i.e. coefficient of variation of the force signal) and EMG of QF were measured at baseline and 12 weeks. Baseline MVIF of LTW (340 ± 112 N) and DTW (368 ± 128 N) increased equally by 14 ± 6 and 5 ± 6 % (p < 0.05). Steadiness at 5 %MVIF improved following 12 weeks of LTW (baseline: 0.04 ± 0.01; 12 weeks: 0.03 ± 0.01) and DTW (baseline: 0.04 ± 0.02; 12 weeks: 0.03 ± 0.01 (p < 0.05). EMG root mean square of m. vastus lateralis during MVIF increased by 38 % following 12 weeks of LTW only (p < 0.05). The potential implications for an exercise modality, such as DTW, with a lower oxygen demand, to improve muscle strength could serve as a rehabilitative countermeasure for older adults.

Extensive paternal mtDNA leakage in natural populations of Drosophila melanogaster

Strict maternal inheritance is considered a hallmark of animal mtDNA. Although recent reports suggest that paternal leakage occurs in a broad range of species, it is still considered an exceptionally rare event. To evaluate the impact of paternal leakage on the evolution of mtDNA, it is essential to reliably estimate the frequency of paternal leakage in natural populations. Using allele-specific real-time quantitative PCR (RT-qPCR), we show that heteroplasmy is common in natural populations with at least 14% of the individuals carrying multiple mitochondrial haplotypes. However, the average frequency of the minor mtDNA haplotype is low (0.8%), which suggests that this pervasive heteroplasmy has not been noticed before due to a lack of power in sequencing surveys. Based on the distribution of mtDNA haplotypes in the offspring of heteroplasmic mothers, we found no evidence for strong selection against one of the haplotypes. We estimated that the rate of paternal leakage is 6% and that at least 100 generations are required for complete sorting of mtDNA haplotypes. Despite the high proportion of heteroplasmic individuals in natural populations, we found no evidence for recombination between mtDNA molecules, suggesting that either recombination is rare or recombinant haplotypes are counter-selected. Our results indicate that evolutionary studies using mtDNA as a marker might be biased by paternal leakage in this species.

Molecular mechanisms of ischemia-reperfusion injury in brain: pivotal role of the mitochondrial membrane potential in reactive oxygen species generation

Stroke and circulatory arrest cause interferences in blood flow to the brain that result in considerable tissue damage. The primary method to reduce or prevent neurologic damage to patients suffering from brain ischemia is prompt restoration of blood flow to the ischemic tissue. However, paradoxically, restoration of blood flow causes additional damage and exacerbates neurocognitive deficits among patients who suffer a brain ischemic event. Mitochondria play a critical role in reperfusion injury by producing excessive reactive oxygen species (ROS) thereby damaging cellular components, and initiating cell death. In this review, we summarize our current understanding of the mechanisms of mitochondrial ROS generation during reperfusion, and specifically, the role the mitochondrial membrane potential plays in the pathology of cerebral ischemia/reperfusion. Additionally, we propose a temporal model of ROS generation in which posttranslational modifications of key oxidative phosphorylation (OxPhos) proteins caused by ischemia induce a hyperactive state upon reintroduction of oxygen. Hyperactive OxPhos generates high mitochondrial membrane potentials, a condition known to generate excessive ROS. Such a state would lead to a "burst" of ROS upon reperfusion, thereby causing structural and functional damage to the mitochondria and inducing cell death signaling that eventually culminate in tissue damage. Finally, we propose that strategies aimed at modulating this maladaptive hyperpolarization of the mitochondrial membrane potential may be a novel therapeutic intervention and present specific studies demonstrating the cytoprotective effect of this treatment modality.

The motor-learning process of older adults in eccentric bicycle ergometer training

This study describes the motor-learning process of older individuals during the course of a training intervention on a motor-driven eccentric bicycle ergometer. Seventeen women and 16 men (64 ± 6 yr) took part in a 10-wk training program. Uniformity of force production and consistency of timing were used to describe their motor performance. The results suggested that participants improved the coefficient of variation of peak force during the intervention (measured at the 2nd, 4th, 6th, 8th, 10th, 12th, and the 18th training sessions). They reached a fairly constant level of motor performance around the 12th training session (5 wk). Age and sex affected improvements in the early phases of the learning process to an extent, but the differences diminished by the end of the intervention. These results suggest that the force control of continuous eccentric muscle contractions improves as a result of training in older adults.

Assessing mitochondrial redox status by flow cytometric methods: vascular response to fluid shear stress

Mitochondria are an important source of superoxide production contributing to physiological and pathological responses, including vascular oxidative stress that is relevant to cardiovascular diseases. Vascular oxidative stress is intimately linked with pro-inflammatory states and atherosclerosis. Oxidized low-density lipoprotein (OxLDL) modulates intracellular redox status and induces apoptosis in endothelial cells. Hemodynamic, specifically, fluid shear stress imparts both biomechanical and metabolic effects on vasculature. Mitochondria are an important source of superoxide production contributing to vascular oxidative stress with relevance to cardiovascular diseases. We hereby present biophysical and biochemical approaches, including fluorescence-activated cell sorting, to assess the dynamics of vascular redox status.

Does eccentric endurance training improve walking capacity in patients with coronary artery disease? A randomized controlled pilot study

Objective: To examine the effect of eccentric endurance training on exercise capacities in patients with coronary artery disease.

Design: Randomized parallel group controlled study.

Setting: Cardiac rehabilitation unit, Dijon University Hospital.

Participants: Fourteen patients with stable coronary artery disease after percutaneous coronary intervention.

Intervention: Patients followed 15 sessions of training (1 session per day, 3 days a week), either in the concentric group, following a standard programme, or in the eccentric group, performing eccentric resistance exercises using both lower limbs on a specifically designed ergometer.

Main outcomes measured: Symptom-limited Vo2, peak workload, isometric strength of leg extensor and ankle plantar flexors, distance covered during the 6-minute walk test and time to perform the 200-m fast walk test in both groups, before and after the training period.

Results: Patients did not report any adverse effects and were highly compliant. All measured parameters improved in eccentric and concentric group, except for 200-m fast walk test: symptom-limited Vo2 (+14.2% versus +4.6%), peak workload (+30.8% versus +19.3%), 6-minute walk test distance walked (+12.6% versus +10.1%) and leg extensor strength (+7% versus +13%) improved to a similar degree in both groups (P<0.01); ankle plantar flexor strength improved in both groups with a significantly greater increase in the eccentric group (+17% versus +7%, P<0.05).

Conclusion: Patients with stable coronary artery disease can safely engage in eccentric endurance training, which appears to be as efficient as usual concentric training, with reduced oxygen consumption.

Different response to eccentric and concentric training in older men and women

Sarcopenia is the age-related loss of muscle mass and strength and has been associated with an increased risk of falling and the development of metabolic diseases. Various training protocols, nutritional and hormonal interventions have been proposed to prevent sarcopenia. This study explores the potential of continuous eccentric exercise to retard age-related loss of muscle mass and function. Elderly men and women (80.6 +/- 3.5 years) were randomized to one of three training interventions demanding a training effort of two sessions weekly for 12 weeks: cognitive training (CT; n = 16), conventional resistance training (RET; n = 23) and eccentric ergometer training (EET; n = 23). Subjects were tested for functional parameters and body composition. Biopsies were collected from M. vastus lateralis before and after the intervention for the assessment of fiber size and composition. Maximal isometric leg extension strength (MEL: +8.4 +/- 1.7%) and eccentric muscle coordination (COORD: -43 +/- 4%) were significantly improved with EET but not with RET (MEL: +2.3 +/- 2.0%; COORD: -13 +/- 3%) and CT (MEL: -2.3 +/- 2.5%; COORD: -12 +/- 5%), respectively. We observed a loss of body fat (-5.0 +/- 1.1%) and thigh fat (-6.9 +/- 1.5%) in EET subjects only. Relative thigh lean mass increased with EET (+2.5 +/- 0.6%) and RET (+2.0 +/- 0.3%) and correlated negatively with type IIX/type II muscle fiber ratios. It was concluded that both RET and EET are beneficial for the elderly with regard to muscle functional and structural improvements but differ in their spectrum of effects. A training frequency of only two sessions per week seems to be the lower limit for a training stimulus to reveal measurable benefits.

The effect of muscle-damaging exercise on blood and skeletal muscle oxidative stress: magnitude and time-course considerations

The aim of this article is to present the effects of acute muscle-damaging exercise on oxidative stress/damage of animal and human tissues using a quantitative approach and focusing on the time-course of exercise effects. The reviewed studies employed eccentric contractions on a dynamometer or downhill running. The statistical power of each study to detect a 20% or 40% post-exercise change compared with pre-exercise value in each oxidative stress/damage biomarker was calculated. Muscle-damaging exercise can increase free radical levels and augment oxidation of lipids, proteins, glutathione and possibly DNA in the blood. In contrast, the effect of muscle-damaging exercise on concentration of antioxidants in the blood, except for glutathione, was little. Muscle-damaging exercise induces oxidative stress/damage in skeletal muscle, even though this is not fully supported by the original statistical analysis of some studies. In contrast, muscle-damaging exercise does not appear to affect--at least to similar extent as the oxidative stress/damage markers--the levels of antioxidants in skeletal muscle. Based on the rather limited data available, the oxidative stress response of skeletal muscle to exercise was generally independent of muscle fibre type. Most of the changes in oxidative stress/damage appeared and were sustained for days after muscle-damaging exercise. The major part of the delayed oxidative stress/damage production that follows muscle-damaging exercise probably comes from phagocytic cells that are activated and recruited to the site of the initial damage. A point that emerged and potentially explains much of the lack of consensus among studies is the low statistical power of many of them. In summary, muscle-damaging exercise can increase oxidative stress/damage in blood and skeletal muscle of rats and humans that may persist for and/or appear several days after exercise.

The prevention and treatment of exercise-induced muscle damage

Exercise-induced muscle damage (EIMD) can be caused by novel or unaccustomed exercise and results in a temporary decrease in muscle force production, a rise in passive tension, increased muscle soreness and swelling, and an increase in intramuscular proteins in blood. Consequently, EIMD can have a profound effect on the ability to perform subsequent bouts of exercise and therefore adhere to an exercise training programme. A variety of interventions have been used prophylactically and/or therapeutically in an attempt to reduce the negative effects associated with EIMD. This article focuses on some of the most commonly used strategies, including nutritional and pharmacological strategies, electrical and manual therapies and exercise. Long-term supplementation with antioxidants or beta-hydroxy-beta-methylbutyrate appears to provide a prophylactic effect in reducing EIMD, as does the ingestion of protein before and following exercise. Although the administration of high-dose NSAIDs may reduce EIMD and muscle soreness, it also attenuates the adaptive processes and should therefore not be prescribed for long-term treatment of EIMD. Whilst there is some evidence that stretching and massage may reduce muscle soreness, there is little evidence indicating any performance benefits. Electrical therapies and cryotherapy offer limited effect in the treatment of EIMD; however, inconsistencies in the dose and frequency of these and other interventions may account for the lack of consensus regarding their efficacy. Both as a cause and a consequence of this, there are very few evidence-based guidelines for the application of many of these interventions. Conversely, there is unequivocal evidence that prior bouts of eccentric exercise provide a protective effect against subsequent bouts of potentially damaging exercise. Further research is warranted to elucidate the most appropriate dose and frequency of interventions to attenuate EIMD and if these interventions attenuate the adaptation process. This will both clarify the efficacy of such strategies and provide guidelines for evidence-based practice.

Regulation of oxidative phosphorylation, the mitochondrial membrane potential, and their role in human disease

Thirty years after Peter Mitchell was awarded the Nobel Prize for the chemiosmotic hypothesis, which links the mitochondrial membrane potential generated by the proton pumps of the electron transport chain to ATP production by ATP synthase, the molecular players involved once again attract attention. This is so because medical research increasingly recognizes mitochondrial dysfunction as a major factor in the pathology of numerous human diseases, including diabetes, cancer, neurodegenerative diseases, and ischemia reperfusion injury. We propose a model linking mitochondrial oxidative phosphorylation (OxPhos) to human disease, through a lack of energy, excessive free radical production, or a combination of both. We discuss the regulation of OxPhos by cell signaling pathways as a main regulatory mechanism in higher organisms, which in turn determines the magnitude of the mitochondrial membrane potential: if too low, ATP production cannot meet demand, and if too high, free radicals are produced. This model is presented in light of the recently emerging understanding of mechanisms that regulate mammalian cytochrome c oxidase and its substrate cytochrome c as representative enzymes for the entire OxPhos system.

Effects of early progressive eccentric exercise on muscle structure after anterior cruciate ligament reconstruction

BACKGROUND

Thigh muscle atrophy is a major impairment that occurs early after reconstruction of the anterior cruciate ligament and persists for several years. Eccentric resistance training has the potential to induce considerable gains in muscle size and strength that could prove beneficial during postoperative rehabilitation. The purpose of this study was to evaluate the effects of progressive eccentric exercise on thigh muscle structure following reconstruction of the anterior cruciate ligament.

METHODS

Beginning three weeks after reconstruction of the anterior cruciate ligament, forty patients were randomly assigned to a program involving either twelve weeks of eccentric exercises or a standard rehabilitation protocol. Patients were matched by surgical procedure, sex, and age. The final series consisted of two cohorts of twenty patients each who had been treated with one of two types of graft (semitendinosus-gracilis or bone-patellar tendon-bone), with ten patients treated with each of the two rehabilitation protocols in each graft cohort. To evaluate changes in muscle structure, magnetic resonance images of the involved and uninvolved thighs were acquired before and after training. The volume and peak cross-sectional area of the quadriceps, hamstrings, and gracilis and the distal portion of the gluteus maximus were calculated from these images.

RESULTS

The volume and peak cross-sectional area of the quadriceps and gluteus maximus, in both the involved and the uninvolved thighs and in the patients treated with each type of graft, improved significantly more in the eccentric-exercise group (p < 0.001). The magnitude of the volume change was more than twofold greater in that group. No significant differences in any hamstring or gracilis structural measurements were observed between the rehabilitation groups. However, the volume and peak cross-sectional area of the gracilis were markedly reduced, compared with the pretraining values, in the patients who had undergone reconstruction with the semitendinosus-gracilis graft.

CONCLUSIONS

Eccentric resistance training implemented three weeks after reconstruction of the anterior cruciate ligament can induce structural changes in the quadriceps and gluteus maximus that greatly exceed those achieved with a standard rehabilitation protocol. The success of this intervention can be attributed to the gradual and progressive exposure to negative work through eccentric exercise, ultimately leading to production of high muscle force.

High-intensity resistance training amplifies muscle hypertrophy and functional gains in persons with Parkinson's disease

Strength deficits in persons with Parkinson's disease (PD) have been identified as a contributor to bradykinesia. However, there is little research that examines the effect of resistance training on muscle size, muscle force production, and mobility in persons with PD. The purpose of this exploratory study was to examine, in persons with PD, the changes in quadriceps muscle volume, muscle force production, and mobility as a result of a 12-week high-force eccentric resistance training program and to compare the effects to a standard-care control. Nineteen individuals with idiopathic PD were recruited and consented to participate. Matched assignment for age and disease severity resulted in 10 participants in the eccentric group and 9 participants in the control group. All participants were tested prior to and following a 12-week intervention period with testing and training conducted at standardized times in their medication cycle. The eccentric group performed high-force quadriceps contractions on an eccentric ergometer 3 days a week for 12 weeks. The standard-care group exercise program encompassed standard exercise management of PD. The outcome variables were quadriceps muscle volume, muscle force, and mobility measures (6-minute walk, stair ascent/descent time). Each outcome variable was tested using separate one-way analyses of covariance on the difference scores. Muscle volume, muscle force, and functional status improvements occurred in persons with PD as a result of high-force eccentric resistance training. The eccentric group demonstrated significantly greater difference scores for muscle structure, stair descent, and 6-minute walk (P < 0.05). Magnitude of effect size estimators for the eccentric group consistently exceeded those in the standard-care group for all variables. To our knowledge, this is the first clinical trial to investigate and demonstrate the effects of eccentric resistance training on muscle hypertrophy, strength, and mobility in persons with PD. Additional research is needed to determine the anatomical and neurological mechanisms of the observed strength gains and mobility improvements.

Gene expression in working skeletal muscle

A number of molecular tools enable us to study the mechanisms of muscle plasticity. Ideally, this research is conducted in view of the structural and functional consequences of the exercise-induced changes in gene expression. Muscle cells are able to detect mechanical, metabolic, neuronal and hormonal signals which are transduced over multiple pathways to the muscle genome. Exercise activates many signaling cascades--the individual characteristic of the stress leading to a specific response of a network of signaling pathways. Signaling typically results in the transcription of multiple early genes among those of the well known for and jun family, as well as many other transcription factors. These bind to the promoter regions of downstream genes initiating the structural response of muscle tissue. While signaling is a matter of minutes, early genes are activated over hours leading to a second wave of transcript adjustments of structure genes that can then be effective over days. Repeated exercise sessions thus lead to a concerted accretion of mRNAs which upon translation results in a corresponding protein accretion. On the structural level, the protein accretion manifests itself for instance as an increase in mitochondrial volume upon endurance training or an increase in myofibrillar proteins upon strength training. A single exercise stimulus carries a molecular signature which is typical both for the type of stimulus (i.e. endurance vs. strength) as well as the actual condition of muscle tissue (i.e. untrained vs. trained). Likewise, it is clearly possible to distinguish a molecular signature of an expressional adaptation when hypoxic stress is added to a regular endurance exercise protocol in well-trained endurance athletes. It therefore seems feasible to use molecular tools to judge the properties of an exercise stimulus much earlier and at a finer level than is possible with conventional functional or structural techniques.

Early application of negative work via eccentric ergometry following anterior cruciate ligament reconstruction: a case report

STUDY DESIGN

Case report.

OBJECTIVES

To present a progressively increasing negative-work exercise program via eccentric ergometry early after anterior cruciate ligament reconstruction (ACL-R) and to suggest the potential of negative work to amplify the return of quadriceps size and strength.

CASE DESCRIPTION

The patient was a 26-year-old highly active recreational athlete who sustained an ACL tear while skiing in January 2004 and then again while skiing in February 2005. This individual underwent an arthroscopically assisted ACL-R with a double-loop semitendinosusgracilis autograft initially, then a patellar tendon autograft following his ACL graft rupture. Beginning within 3 weeks after surgery, a progressive negative-work exercise program was initiated using an eccentric ergometer. The patient completed 31 training sessions of 5 to 30 minutes in duration over a 12-week period following the ACL-R and 33 training sessions of the same frequency and duration following the ACL revision.

OUTCOMES

Following ACL-R, quadriceps volume increased 28% (involved lower extremity) and 14% (uninvolved lower extremity) during the 12-week training program. Following revision, quadriceps volume returned to similar levels at the same postoperative period as those achieved after the initial surgery (2% less on the involved side and 2% greater on the uninvolved side). Quadriceps strength, 15 weeks after ACL-R, exceeded preoperative measures by an average of 20% (involved) and 14% (uninvolved). Quadriceps strength after ACL revision exceeded all previous measures.

DISCUSSION

This case report suggests that if gradually and progressively applied, negative work via eccentric ergometry can be both safe and efficacious early after ACL-R. Eccentric exercise may mitigate the prevalent muscle size and strength deficits commonly observed after ACL-R. The results of this case suggest a need for continued research with early negative work interventions following ACL-R.

Simultaneous quantitative measurement and automated analysis of mitochondrial morphology, mass, potential, and motility in living human skin fibroblasts

BACKGROUND

Understanding the interdependence of mitochondrial and cellular functioning in health and disease requires detailed knowledge about the coupling between mitochondrial structure, motility, and function. Currently, no rapid approach is available for simultaneous quantification of these parameters in single living cells.

METHODS

Human skin fibroblasts were pulse-loaded with the mitochondria-selective fluorescent cation rhodamine 123. Next, mitochondria were visualized using video-rate (30 Hz) confocal microscopy and real-time image averaging. To highlight the mitochondria, the acquired images were binarized using a novel image processing strategy.

RESULTS

Our approach enabled rapid and simultaneous quantification of mitochondrial morphology, mass, potential, and motility. It was found that acute inhibition of mitochondrial complex I (NADH:ubiquinone oxidoreductase) by means of rotenone transiently reduced mitochondrial branching, area, and potential. In contrast, mitochondrial motility was permanently reduced.

CONCLUSIONS

We present and validate a novel approach for rapid, unbiased, and simultaneous quantification of multiple mitochondrial parameters in living cells. Because this method is automated, large numbers of cells can be analyzed in a short period of time.

Induction of mitochondrial fusion by cysteine-alkylators ethacrynic acid and N-ethylmaleimide

Mitochondrial fusion and fission are important aspects of eukaryotic cell function that permit the adoption of varied mitochondrial morphologies depending upon cellular physiology. We previously observed that ethacrynic acid (EA) induced mitochondrial fusion in cultured BSC-1 and CHO/wt cells. However, the mechanism responsible for it was not clear since EA has a number of known cellular effects including glutathione (GSH) depletion and alkylation of cysteine residues. To gain insight, we have tested the effects of a variety of compounds on EA induced cellular toxicity and mitochondrial fusion. N-acetyl cysteine (NAC), a GSH precursor, was found to abrogate both the toxic and fusion-inductive effects, whereas diethylmaleate (dEM), a GSH depletor, potentiated both these effects in a dose-dependent manner. However, treatment with dEM alone, which depleted GSH to the same degree as EA, did not induce mitochondrial fusion. These results indicate that although detoxification of EA via formation of GSH conjugates is dependant upon GSH levels, the depletion of GSH by EA is not responsible for its effect on mitochondrial fusion. Dihydro-EA (DH-EA), a saturated EA analogue, lacked EA's toxicity and effect on fusion, indicating that the alpha,beta-unsaturated ketone is central to its observed effects. N-ethylmaleimide (NEM), another well-known cysteine-alkylator, also induced mitochondrial fusion at near toxic concentrations. These data suggests that cysteine-alkylation is the causative factor for fusion and toxicity. In live BSC-1 cells, EA induced fusion of mitochondria occurred very rapidly (<20 min), which suggests that it is inducing fusion by modifying certain critical cysteine residue(s) in proteins involved in the process.

Widespread Recombination in Published Animal mtDNA Sequences1

Mitochondrial DNA (mtDNA) recombination has been observed in several animal species, but there are doubts as to whether it is common or only occurs under special circumstances. Animal mtDNA sequences retrieved from public databases were unambiguously aligned and rigorously tested for evidence of recombination. At least 30 recombination events were detected among 186 alignments examined. Recombinant sequences were found in invertebrates and vertebrates, including primates. It appears that mtDNA recombination may occur regularly in the animal cell but rarely produces new haplotypes because of homoplasmy. Common animal mtDNA recombination would necessitate a reexamination of phylogenetic and biohistorical inference based on the assumption of clonal mtDNA transmission. Recombination may also have an important role in producing and purging mtDNA mutations and thus in mtDNA-based diseases and senescence.

Eccentric Cycle Exercise: Training Application of Specific Circulatory Adjustments

PURPOSE

Despite identical oxygen uptake (VO2), enhanced heart rate (HR) and cardiac output (Q) responses have been reported in eccentric (ECC) versus concentric (CON) cycle exercise. The aim of this study was to describe the specific circulatory adjustments (HR and stroke volume (SV)) to incremental ECC cycle exercise in order to: 1) determine the HR values leading to identical VO2 in ECC and CON cycling; and 2) estimate the interindividual variability of this HR correspondence between the two exercise modes, with emphasis upon rehabilitation and training purposes.

METHODS

Eight healthy male subjects (age, 28 +/- 2 yr) participated in this study. They performed CON and ECC cycle incremental exercises (power output increases of 50 W every 3 min). Breath-by-breath gas exchange analysis and beat-by-beat thoracic impedancemetry were used to determine VO2 and Q, respectively.

RESULTS

At the same metabolic power (VO2 of 1.08 +/- 0.05 L x min(-1) in CON vs 1.04 +/- 0.06 L x min in ECC), SV was not different, but HR was 17% higher in ECC (P < 0.01), leading to a 27% enhanced Q (P < 0.01). Q and HR net adjustments (exercise minus resting values) in ECC versus CON muscle involvement demonstrated important interindividual variability with coefficients of variation amounting to 32% and 30%, respectively.

CONCLUSION

In practice, if a given level of VO2 is to be reached, ECC HR has to be set above the CON one. Taking into account the interindividual variability of the circulatory adjustments in ECC versus CON muscle involvement, a precise HR correspondence can be established individually from the VO2/HR relationship obtained using ECC incremental testing, allowing prescription of accurate target HR for rehabilitation or training purposes.

Comparison of heart-rate and blood-pressure increases during isokinetic eccentric versus isometric exercise in older adults

The authors compared heart-rate and blood-pressure responses to typical isometric (ISO) and isokinetic (90 degrees /s) eccentric (ECC) resistance-training protocols in older adults. Twenty healthy older adults (74 +/- 5 years old) performed randomly ordered ISO and isokinetic ECC exercise (3 sets of 10 repetitions) at a target intensity of 100 % of their peak ISO torque value. Heart rate and systolic (SBP) and diastolic (DBP) blood pressures were recorded continuously, and mean arterial pressure (MAP) and rate-pressure product (RPP) were calculated. ECC peak torque (139 +/- 33 N. m) was significantly greater than ISO peak torque (115 +/- 26 N. m; p <.001). All variables increased significantly (p <.001) during both ISO and ECC exercise. Changes in SBP, DBP, MAP, and RPP were significantly greater during ISO exercise than during ECC exercise (p <.001). Clinically, an isokinetic ECC exercise program enables older adults to work at the same torque output with less cardiovascular stress than ISO exercise.

Eccentric muscle contractions: their contribution to injury, prevention, rehabilitation, and sport

Muscles operate eccentrically to either dissipate energy for decelerating the body or to store elastic recoil energy in preparation for a shortening (concentric) contraction. The muscle forces produced during this lengthening behavior can be extremely high, despite the requisite low energetic cost. Traditionally, these high-force eccentric contractions have been associated with a muscle damage response. This clinical commentary explores the ability of the muscle-tendon system to adapt to progressively increasing eccentric muscle forces and the resultant structural and functional outcomes. Damage to the muscle-tendon is not an obligatory response. Rather, the muscle can hypertrophy and a change in the spring characteristics of muscle can enhance power; the tendon also adapts so as to tolerate higher tensions. Both basic and clinical findings are discussed. Specifically, we explore the nature of the structural changes and how these adaptations may help prevent musculoskeletal injury, improve sport performance, and overcome musculoskeletal impairments.

Eccentric exercise in coronary patients: central hemodynamic and metabolic responses

PURPOSE

With lengthening (eccentric) muscle contractions, the magnitude of locomotor-muscle mass and strength increase has been demonstrated to be greater compared with shortening (concentric) muscle contractions. In healthy subjects, energy demand and heart rate responses with eccentric exercise are small relative to the amount of muscle force produced. Thus, eccentric exercise may be an attractive alternative to resistance exercise for patients with limited cardiovascular exercise tolerance.

METHODS

We tested the cardiovascular tolerance of eccentric exercise in 13 coronary patients (ages 40-66) with preserved and/or mild reduced left ventricular function. Patients were randomly assigned to either an eccentric (ECC; N = 7) or a concentric (CON; N = 6) training group and trained for 8 wk. Training workload was increased progressively (from week 1 to 5) to an intensity equivalent to 60% [OV0312]O(2peak).

RESULTS

On average, maximum power output achieved with ECC was fourfold compared with CON (357 +/- 96 W vs 97 +/- 21 W; P < 0.005), whereas measures of oxygen uptake and blood lactate were significantly lower (P < 0.05 each), and ratings of perceived exertion were similar for ECC and CON. During a 20-min session of ECC and CON, central hemodynamics was measured by means of right heart catheterization. During ECC, responses of mean arterial blood pressure, systemic vascular resistance, pulmonary capillary pressure, cardiac index, and stroke work of the left ventricle on average were in the normal range of values and similar to those observed during CON. Compared with baseline, after 8 wk of training, echocardiographic left ventricular function was unchanged.

CONCLUSION

The results indicate uncoupling of skeletal muscle load and cardiovascular stress during ECC. For low-risk patients with coronary heart disease without angina, inducible ischemia, or left ventricular dysfunction, ECC can be recommended as a safe new approach to perform high-load muscular exercise training with minimal cardiovascular stress.

The regulation of mitochondrial physiology by organelle-associated GTP-binding proteins

Recent studies have shown that GTP-binding proteins can modulate mitochondrial membrane fusion and fission. Furthermore, GTP-binding proteins can regulate the binding of ribosomes to the mitochondrial membrane and may facilitate the import of proteins through contact points between inner and outer mitochondrial membranes. Mitochondrial GTP-binding proteins therefore appear to have the potential to modulate physiological function of the organelle and may also be involved in cellular processes such as cellular transformation. A beginning has been made on the characterization of mitochondrial GTP-binding proteins and the DNA sequence of one protein has become newly available. Future studies are needed to determine whether GTP-binding proteins are interacting with cell signalling molecules such as protein kinases in the mitochondria.

Exercise-induced muscle damage and the potential protective role of estrogen

Exercise-induced muscle damage is a well documented phenomenon that often follows unaccustomed and sustained metabolically demanding activities. This is a well researched, but poorly understood area, including the actual mechanisms involved in the muscle damage and repair cycle. An integrated model of muscle damage has been proposed by Armstrong and is generally accepted. A more recent aspect of exercise-induced muscle damage to be investigated is the potential of estrogen to have a protective effect against skeletal muscle damage. Estrogen has been demonstrated to have a potent antioxidant capacity that plays a protective role in cardiac muscle, but whether this antioxidant capacity has the ability to protect skeletal muscle is not fully understood. In both human and rat studies, females have been shown to have lower creatine kinase (CK) activity following both eccentric and sustained exercise compared with males. As CK is often used as an indirect marker of muscle damage, it has been suggested that female muscle may sustain less damage. However, these findings may be more indicative of the membrane stabilising effect of estrogen as some studies have shown no histological differences in male and female muscle following a damaging protocol. More recently, investigations into the potential effect of estrogen on muscle damage have explored the possible role that estrogen may play in the inflammatory response following muscle damage. In light of these studies, it may be suggested that if estrogen inhibits the vital inflammatory response process associated with the muscle damage and repair cycle, it has a negative role in restoring normal muscle function after muscle damage has occurred. This review is presented in two sections: firstly, the processes involved in the muscle damage and repair cycle are reviewed; and secondly, the possible effects that estrogen has upon these processes and muscle damage in general is discussed. The muscle damage and repair cycle is presented within a model, with particular emphasis on areas that are important to understanding the potential effect that estrogen has upon these processes.

ARL2 and BART enter mitochondria and bind the adenine nucleotide transporter

The ADP-ribosylation factor-like 2 (ARL2) GTPase and its binding partner binder of ARL2 (BART) are ubiquitously expressed in rodent and human tissues and are most abundant in brain. Both ARL2 and BART are predominantly cytosolic, but a pool of each was found associated with mitochondria in a protease-resistant form. ARL2 was found to lack covalent N-myristoylation, present on all other members of the ARF family, thereby preserving the N-terminal amphipathic alpha-helix as a potential mitochondrial import sequence. An overlay assay was developed to identify binding partners for the BART.ARL2.GTP complex and revealed a specific interaction with a protein in bovine brain mitochondria. Purification and partial microsequencing identified the protein as an adenine nucleotide transporter (ANT). The overlay assay was performed on mitochondria isolated from five different tissues from either wild-type or transgenic mice deleted for ANT1. Results confirmed that ANT1 is the predominant binding partner for the BART.ARL2.GTP complex and that the structurally homologous ANT2 protein does not bind the complex. Cardiac and skeletal muscle mitochondria from ant1(-)/ant1(-) mice had increased levels of ARL2, relative to that seen in mitochondria from wild-type animals. We conclude that the amount of ARL2 in mitochondria is subject to regulation via an ANT1-sensitive pathway in muscle tissues.

Gene therapy by mitochondrial transfer

Mitochondrial DNA (mtDNA) is highly susceptible to mutation. Novel approaches such as those involving cytoplast fusion and mitochondrial microinjection are essential for gene therapy of diseases caused by these mutations, due to the non-Mendelian genetics of these diseases. In this fusion method, mtDNA in the cytoplast is transferred into mutant cells via the formation of cybrids; once inside the cell the mtDNA complement the defect correctly and safely. The genes in cloned animals are composed of nuclear DNA (nDNA) of a mature tissue and mtDNA from an oocyte. Recent advances in transmitochondrial mice depends on the microinjection of mitochondria into the oocyte. Here we present data on in vitro gene therapy using human mtDNA, cybrid formation and microinjection.

Tumor necrosis factor-alpha inhibits aquaporin 5 expression in mouse lung epithelial cells

Aquaporin 5 (AQP5), the major water channel expressed in alveolar, tracheal, and upper bronchial epithelium, is significantly down-regulated during pulmonary inflammation and edema. The mechanisms that underlie this decrease in AQP5 levels are therefore of considerable interest. Here we show that AQP5 expression in cultured lung epithelial cells is decreased 2-fold at the mRNA level and 10-fold at the protein level by the proinflammatory cytokine tumor necrosis factor alpha (TNF-alpha). Treatment of murine lung epithelial cells (MLE-12) with TNF-alpha results in a concentration- and time-dependent decrease in AQP5 mRNA and protein expression. Activation of the p55 TNF-alpha receptor (TNFR1) with an agonist antibody is sufficient to cause decreased AQP5 expression, demonstrating that the TNF-alpha effect is mediated through TNFR1. Inhibition of nuclear factor kappaB (NF-kappaB) translocation to the nucleus blocks the effect of TNF-alpha on AQP5 expression, indicating that activation of NF-kappaB is required, whereas inhibition of extracellular signal-regulated or p38 mitogen-activated protein kinases showed no effect. These data show that TNF-alpha decreases AQP5 mRNA and protein expression and that the molecular pathway for this effect involves TNFR1 and activated NF-kappaB. The ability of inflammatory cytokines to decrease aquaporin expression may help explain the connection between inflammation and edema.

Yeast mitochondrial dynamics: fusion, division, segregation, and shape

Mitochondria are essential organelles found in virtually all eukaryotic cells that play key roles in a variety of cellular processes. Mitochondria show a striking heterogeneity in their number, location, and shape in many different cell types. Although the dynamic nature of mitochondria has been known for decades, the molecules and mechanisms that mediate these processes are largely unknown. Recently, several laboratories have isolated and analyzed mutants in the yeast Saccharomyces cerevisiae defective in mitochondrial fusion and division, in the segregation of mitochondria to daughter cells, and in the establishment and maintenance of mitochondrial shape. These studies have identified several proteins that appear to mediate different aspects of mitochondrial morphogenesis. Although it is clear that many additional components have yet to be identified, some of the newly discovered proteins raise intriguing possibilities for how the processes of mitochondrial division, fusion, and segregation occur. Below we summarize our current understanding of the molecules known to be required for yeast mitochondrial dynamics.

Electrical coupling and plasticity of the mitochondrial network

Kinetic fluorescence imaging and the potentiometric probe tetramethylrhodamine methyl ester (TMRM) were used to evoke and detect changes in membrane potential (delta Psi(m)) of individual mitochondria in living cells. As a combined effect of preferential TMRM accumulation in mitochondria, and of TMRM photoactivation, individual organelles displayed sharp transient depolarizations caused by local reactive oxygen species (ROS)-mediated gatings of the mitochondrial permeability transition pore (PTP). In COS-7 cells, such directed repetitive gatings of the PTP gave rise to stochastic delta Psi(m)flickering at the level of individual organelles, but also to prominent synchronous delta Psi(m)transitions in whole subgroups of the mitochondrial population, indicative of the existence of an underlying electrically coupled mitochondrial network. In single cells, this network could comprise as much as 65% of the total mitochondrial population, a nd exhibited a high plasticity with mitochondrial units spontaneously connecting to and disconnecting from the coupled structure within seconds. These results indicate that in resting cells, the mitochondrial network is a dynamic proton-conducting structure capable to commute and coordinate electrical signals generated by the PTP.

Homogeneous longitudinal profiles and synchronous fluctuations of mitochondrial transmembrane potential

This study reports for the first time (a) the longitudinal profile of the transmembrane potential (mDeltapsi) of single mitochondria using a Nernstian fluorescent probe and (b) the distribution of mDeltapsi fluctuations of mitochondria undergoing permanent depolarization. Our findings show that (1) mitochondria in different energetic conditions coexist in the same cell, (2) mDeltapsi is rather homogeneous along the entire length of single mitochondria, (3) mDeltapsi is not influenced by the surrounding cytoplasmic environment and (4) mDeltapsi fluctuations occur simultaneously in groups of mitochondria connected in a network. Taken together, these findings provide further evidence for a functional relationship between mitochondrial arrangement and energetic condition.