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Cardiologie Cellulaire et Moléculaire U-446 INSERM, Châtenay-Malabry, France and
* Département de Physiologie, Faculté de Médecine, ULP, Strasbourg, France
1Correspondence: U-446 INSERM, Faculté de Pharmacie, 92 296 Châtenay-Malabry, France. E-mail: anne.garnier{at}cep.u-psud.fr
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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and its downstream transcription factors. A coordinate increase in PGC-1 and mRNA levels of proteins involved in degradation, fusion, and fission of mitochondria was observed associated with calcineurin activation. Despite decreased VO2 peak, in CHF patients skeletal muscles showed preserved Vmax in accordance with preserved markers and transcription factors of mitochondrial biogenesis and dynamics, with no calcineurin activation. The results provide strong support for a central role for PGC-1 and calcineurin activation in mitochondrial biogenesis in healthy and diseased human skeletal muscles.—Garnier, A., Fortin, D., Zoll, J., N’Guessan, B., Mettauer, B., Lampert, E., Veksler, V., Ventura-Clapier, R. Coordinated changes in mitochondrial function and biogenesis in healthy and diseased human skeletal muscle.
Key Words: endurance training • heart failure • mitochondrial function • mitochondrial biogenesis
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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, 2)
, but with an improvement of coupling and regulatory properties of mitochondrial respiration in human skeletal muscle (3
, 4)
. Conversely, in human chronic heart failure (CHF), decreased mitochondrial content has been described, but the bioenergetic status of skeletal muscle is becoming controversial. Morphological and biochemical studies have demonstrated altered mitochondrial volume and enzyme activity of the vastus lateralis muscle in CHF patients (5
, 6)
, but recent functional studies have shown preserved oxidative phosphorylation capacity in patients undergoing transplantation (7
, 8)
.
During the past decade, considerable progress has been made to identify the molecular basis of mitochondrial plasticity in mammalian tissues (for review, see refs 2
, 9
). The structural and functional adaptations of the mitochondrial network in challenged skeletal muscles result not only from changes in the mitochondrial protein expression and proper assembly but also in mitochondrial dynamics (see Fig. 4
). Mitochondrial biogenesis depends on the coordinated expression of the nuclear and mitochondrial genomes. Mitochondria have their own DNA (mtDNA), encoding 13 subunits of the oxidative phosphorylation system (OXPHOS). The remaining OXPHOX subunits as well as other mitochondrial proteins are encoded by the nucleus. Recently, a transcriptional coactivator termed peroxisome proliferator activated receptor gamma coactivator 1 (PGC-1) has emerged as a critical factor coordinating the activation of metabolic genes required for substrate utilization and mitochondrial biogenesis (10
, 11)
. These effects of PGC-1 could be explained via its interaction with several DNA binding transcription factors, such as the nuclear respiratory factors (NFRs), which in turn up-regulate the expression of nuclear genes encoding respiratory chain components, as well as the mitochondrial transcription factor A (mtTFA), a factor required for mtDNA replication and transcription (see Fig. 4
). In rodent skeletal muscles, exercise performed regularly induces an increase in PGC-1, coincidently with an increase in NRFs and mtTFA mRNA and/or protein expression (for a recent review, see ref 9
). Calcineurin, a calcium-sensitive phosphatase involved in the transcriptional response of skeletal muscle to endurance training through dephosphorylation and nuclear import of the myocyte enhancer factor (MEF) 2 and the nuclear transcription factor of activated T cell (NFAT) family (12
, 13)
, was recently proposed to control the expression of PGC-1 (14
15
16)
.
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In human skeletal muscle, the involvement of PGC-1 and its downstream transcription factors in adaptation to endurance training is still controversial (17
18
19
20
21)
and deserves further study. Mitochondria and bioenergetic processes play a key role in the pathophysiology of heart failure (22)
. In CHF, we recently showed that PGC-1 and its downstream transcription factors are decreased in skeletal muscle in experimental CHF (23)
, but nothing is known for humans. It remains to be established whether PGC-1 and its downstream cascade are altered in human skeletal muscle in accordance with training status and CHF and whether it can play a role in skeletal muscle oxidative capacity.
Mitochondrial biogenesis also depends on production or degradation of the various mitochondrial components in order to achieve proper assembly of subunits of mitochondrial and nuclear origin. This degradation process is mediated in part by protein-specific pathways involving intramitochondrial proteases such as the ATP-dependent Lon protease (LonP) (for a recent review, see ref 24
) (see Fig. 4
). The Lon protease seems to be expressed in all human tissues, but mRNA and protein levels are highest in heart, brain, liver, and skeletal muscle. A growing body of evidence suggests that the Lon protease may control mtDNA replication and gene expression by degrading regulatory proteins involved in replication and may play an important role in mitochondrial biogenesis (25)
. The expression level of Lon protease in human skeletal muscle during training interventions or CHF has never been assessed.
Despite a large body of literature on many aspects of mitochondrial function, little is known about interactions between the subsequent structural and functional adaptations of the mitochondria in challenged skeletal muscles and the dynamic nature of mitochondria. Life microscopy has revealed in mammalian cells that mitochondria are organized into dynamic tubular structures or networks and that the balance between continuous fission and fusion reactions regulates this dynamic (for a review, see ref 26
; Fig. 4
). Among the best-known proteins involved in mitochondrial dynamics and those highly expressed in human skeletal and heart muscles are mitofusin 2 (Mfn2), a mitochondrial transmembrane GTPase involved in fusion (27
, 28)
and dynamin-related protein 1 (Drp1), a GTPase with a domain structure similar to that of other dynamin family members involved in fission (29
30
31)
. Mitochondrial dynamic plays a significant role in vertebrate cells during cell division, differentiation, and development and could also be involved in the mitochondrial response to skeletal muscle challenge.
Insights into the molecular mechanisms of mitochondrial biogenesis are of uppermost interest in molecular medicine both for pathophysiological understanding and therapeutic perspectives. The aim of this study was thus to gain insight into the molecular mechanisms of mitochondrial biogenesis in human skeletal muscle challenged by physiological means (i.e., the response to different levels of physical activity) or during a pathophysiological process (i.e., altered exercise capacity and skeletal muscle bioenergetic damages in heart failure). We studied the expression of transcription factors of mitochondrial biogenesis and of protein markers of oxidative phosphorylation, calcineurin activation, mitochondrial protein degradation, and mitochondrial dynamics (by real time RT-PCR and enzymatic activity measurements), and correlated them to the functional assessment of muscle oxidative capacity (oxygen consumption rate of in situ mitochondria in muscle biopsy samples) and exercise capacities (VO2 peak assessments) of subjects. We explored a group of middle-aged volunteers with a wide range of fitness levels, from completely sedentary to extreme endurance capacity, and a group of patients with advanced heart failure compared with truly sedentary subjects.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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. They were compared with 10 CHF patients in NYHA class III to IV undergoing heart transplantation (Table 1
). The origin of CHF was nonischemic cardiomyopathy in seven patients and coronary disease in three. Their VO2 peak was severely reduced at 13.4±0.5 mL·min–1·kg–1. Medical therapy consisted of diuretics and angiotensin-converting enzyme (ACE) inhibitors. All subjects who volunteered for the study gave written informed consent before the study that had been approved by our institution’s ethics committee and conformed to the Declaration of Helsinki.
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Exercise testing consisted in a cycloergometric incremental symptom-limited test while measuring the VO2 and the carbon dioxide produced by means of a metabolic cart (Medical graphics, St Paul, Minnesota). In healthy subjects, the exercise test increments were designed (15–25 W·min–1) to exhaust the subject in 10 to 15 min and were performed within 2 wk of their biopsy. In CHF patients, exercise tests (10 W·min–1) were repeated every 3 months to assess urgency, the last pretransplantation values being taken for the study.
Skeletal muscle biopsy
Biopsy samples were obtained from the vastus lateralis muscle using the Bergström needle technique under general anesthesia at the time of cardiac transplantation in patients or local anesthesia in healthy subjects. One part was rapidly frozen for biochemical and molecular studies, the remaining tissue being immediately dissected into thin bundles of diameter 100–200 µm in an iced relaxing solution containing (in mM) EGTA-calcium buffer 10 (free Ca2+ concentration 100 nM), MgCl2 1, taurine 20, DTT 0.5, imidazole 20 (pH 7.1), MgATP 5, PCr 15 at ionic strength 160 (potassium methanesulfonate) and permeabilized for 30 min with 50 µg·mL–1 saponin for respiration studies.
Enzyme assay and mitochondrial respiration
After homogenization of frozen tissue samples in an ice-cold buffer (30 mg·mL–1) composed of (in mM) HEPES 5 (pH 8.7), EGTA 1, DTT 1, MgCl2 5, and Triton X-100 (0.1%), an incubation was performed for 60 min at 4°C to ensure complete enzyme extraction. The total activities of citrate synthase (CS), cytochrome c oxidase (COX), respiratory chain complex I, and creatine kinase (CK) were assayed (30°C, pH7.5) using spectrophotometry as described previously (23
, 32)
. CK isoenzymes were separated using agarose (1%) gel electrophoresis performed at 200V for 90 min; individual isoenzymes were resolved by incubating the gels with a coupled enzyme system.
Maximal oxidative capacity of human muscle fibers (Vmax) was studied in situ by measuring activity of the oxidative phosphorylation (OXPHOS) pathway in saponin-skinned muscle fibers (7)
. Respiratory rates were determined using a Clark electrode (Strathkelvin Instruments, Glasgow, UK) in a water-jacketed oxygraphic cell containing 3 mL of respiration solution (see below) at 22°C with continuous stirring. Respiration solution had the same composition as the relaxing solution except that MgATP and PCr were replaced by 5 mM glutamate, 2 mM malate as substrates, with 3 mM phosphate and 2 mg·mL–1 fatty acid-free bovine serum albumin. The ADP-stimulated respiration (VADP) above basal oxygen consumption (V0) was plotted as a function of [ADP] with or without creatine (20 mM). VADP was calculated using a nonlinear fitting of the Michaelis-Menten equation. Maximal respiration rate (Vmax) was (VADP+V0) and expressed as µmol O2·min–1·g–1 dry weight.
Real-time quantitative RT-PCR analysis
Transcript levels of nuclear encoded (COXVb) and mitochondrial encoded (COXI) subunits of the OXPHOS complex IV, 12S rRNA (12S rRNA), and gene products involved in mitochondrial protein expression (PGC-1, NRF-1, mtTFA), mitochondrial protein degradation (LonP), fusion (Mfn2), and fission (Drp1) were measured by real-time RT-PCR. We followed the mRNA expression of MCIP1 (myocyte-enriched calcineurin interacting protein 1), which accurately reflects the activated state of the calcineurin system (33)
.
Total muscle RNA was extracted using standard procedure. Oligo-dT first-strand cDNA was synthesized from 2 to 4 µg total RNA using SuperscriptTM II reverse transcriptase (InVitrogen, Cergy Pontoise, France). Real-time PCR was performed using the SYBR®Green technology on a LightCycler rapid thermal cycler (Roche Diagnostics, Meylan, France) as described (23)
. Forward and reverse primers (Table 2
) were each designed in a different exon of the target sequence, eliminating the possibility of amplifying genomic DNA. For the mitochondrial COXI and 12SrRNA genes, which were devoid of intronic sequences, we checked using the negative reverse transcription products that contamination of genomic DNA did not interfere with quantification. For each set of primers, a basic local alignment search tool (BLAST) search revealed that sequence homology was obtained only for the target gene.
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PCR amplification was performed in duplicate in a total reaction volume of 15 µL. The reaction mixture consisted of 1 µL diluted template, 1.5 µL the FastStart DNA Master SYBR Green I kit (10x), 3 mM MgCl2 (except for LonP, 4 mM), and 0.5 µM forward and reverse primers (except for PGC-1, 0.3 µM). After a 8 min activation of Taq polymerase, amplification was allowed to proceed from 30 to 40 cycles, each consisting of denaturation at 95°C for 10 s, annealing at 60°C (NRF-1, mtTFA, MCIP1, 12S rRNA, COXI, COXVb, Mfn2, GCB=glucocerebrosidase), or 58°C (PGC-1, LonP, Drp1) from 5 to 9 s and extension at 72°C from 5 to 19 s depending on the target gene. Amplification specificity was controlled by a melting curve analysis and a gel electrophoresis of the PCR product. Fivefold serial dilutions from a SED control total RNA were analyzed for each target gene and allowed to construct linear standard curves from which the concentrations of the test sample were calculated. Results were normalized to GCB transcription to compensate for variation in input RNA amounts and efficiency of reverse transcription, then corrected for the amount of RNA relative to muscle weight (23)
.
Statistics
Data are expressed as means ± SE. Linear regression analysis was used to determine the relations between parameters of mitochondrial function, gene expression, and dynamics among healthy subjects with different levels of physical activity. An unpaired Student’s t test was used to determine the effects of CHF compared with the SED group. Significance was taken as P 
0.05.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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.
Table 3
and Fig. 1
, Fig. 2
clearly show that PGC-1 is a key component in mitochondrial adaptation to exercise training as it significantly correlated with all measured parameters. PGC-1 gene expression significantly correlated with exercise performance (P=0.032). It was strongly related to Vmax (P=0.002), a measurement of muscle OXPHOS activity. In addition, we found a significant linear relation between PGC-1 gene expression (P<0.01)/VO2 peak and the mRNA content of the transcription factors NRF-1 and mtTFA, which act downstream of PGC-1 and regulate the expression of mitochondrial proteins. Accordingly, the transcript levels of mitochondrial encoded COXI subunit and 12S rRNA, as well as of nuclear encoded COXVb subunit, were significantly coupled to the training status of healthy subjects (VO2 peak), muscle OXPHOS activity (except for 12S rRNA), and PGC-1 gene expression. MCIP1, a marker for calcineurin activation highly correlated with PGC-1 mRNA level and muscle OXPHOS activity (Table 3
, Fig. 1
).
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Results revealed that the transcript levels of gene products involved in mitochondrial protein degradation (LonP) and mitochondrial dynamics (Mfn2, Drp1) correlated closely with muscle OXPHOS activity (P<0.05) and with PGC-1 mRNA content (P<0.01) (Table 3)
.
Mitochondrial function, protein expression/degradation, and dynamics in subjects with chronic heart failure
While all subjects showed no significant differences in age or height, the SED group was heavier than the CHF group (Table 1)
. By design, the percentages of predicted VO2 peak markedly differed among groups: < 50% of predicted values in CHF patients and close to the predicted values in the SED group. Exercise capacity, assessed by the VO2 peak, was reduced by 50% in the CHF group.
Only the activities of CS, total CK, MM-CK, and MB-CK were significantly depressed (–40% to –60%) in CHF patients compared with the SED group (Table 4
). However, muscle OXPHOX activity, measured by oxygen consumption, and activity of complex I and IV (COX) of the respiratory chain were similar in CHF patients and SED controls (Table 4)
despite the much lower exercise capacity of CHF patients.
|
The real-time quantitative RT-PCR analysis revealed no significant difference in the mRNA levels of PGC-1, NRF-1, mtTFA, and MCIP1 between CHF patients and SED subjects (Fig. 3
). No significant change was ob-served in the transcript levels of mitochondrial encoded COXI subunit and 12S rRNA, or of nuclear encoded COXVb subunit in skeletal muscle of CHF patients (Table 4)
.
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Transcript levels of gene products implicated in mitochondrial protein degradation (LonP) and mitochondrial dynamics by fusion (Mfn2) and fission (Drp1) reactions were unchanged in CHF human skeletal muscle (Table 4)
.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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and its downstream transcription factors (NRF-1, mtTFA). We observed a significant correlation between muscle OXPHOS activity and PGC-1 expression on the one hand and gene expression of LonP, involved in mitochondrial degradation, as well as of Mfn2 and Drp1, involved respectively in fusion and fission reactions of tubular mitochondrial networks on the other. These results suggest that mitochondrial adaptation to endurance training in humans is associated with calcineurin and PGC-1 activation, which induce coordinated expression of mitochondrial metabolic proteins and of factors of mitochondrial dynamics. 2) In CHF, although some metabolic alterations appeared as depressed CS and CK activities, muscle oxidative capacity, complex I, and COX activities were similar to those of SED subjects despite lower exercise capacity. Accordingly, we could not detect a change in the transcript levels of mitochondrial encoded COXI subunit and 12S rRNA, of nuclear encoded COXVb subunit, or in the transcript levels of gene products implicated in mitochondrial protein expression (PGC-1, NRF-1, mtTFA), mitochondrial protein degradation (LonP), fusion (Mfn2), and fission (Drp1), or in calcineurin activation in CHF muscle. All these results suggest that PGC-1 is at the crossroad of regulation of mitochondrial network in human normal and diseased muscle.
Mitochondrial function, protein expression/degradation, and dynamics in healthy subjects with different training status
The adaptive response of human and animal skeletal muscles to endurance training is well documented and includes not only quantitative mitochondrial changes such as an increase in mitochondrial density and activities of enzymes involved in oxidative metabolism (for a recent review, see ref 2
), but also quantitative and qualitative changes in muscle respiration rate and improvement of coupling and regulatory properties of respiration (4)
. Increases in Vmax and CS activity confirm previous data, and the strong correlation between Vmax and VO2 peak are in line with the fact that muscle OXPHOS activity is a key component of endurance capacity.
Regular exercise of sufficient and prolonged intensity (endurance training) stimulates mitochondrial biogenesis in skeletal muscle and a contribution of transcriptional events in the orchestration of mitochondrial plasticity has been recently proposed. Expression of mitochondrial proteins from nuclear and mitochondrial genomes is coordinated and involves the transcriptional coactivator PGC-1 and its downstream transcription factors NRF-1 and mtTFA (10
, 11)
(Fig. 4
). The tissue expression of PGC-1 gene strongly correlates with the level of oxidative capacity, being highly expressed in human and rodents cardiac and oxidative muscles and to a lower extent in glycolytic muscles (14
, 23
, 34
, 35)
. A direct cause and effect relationship between PGC-1 expression and mitochondrial content and function has been established by PGC-1 gene overexpression in skeletal muscle cells (36
, 37)
and cardiac myocytes (38)
and by up- or down-regulation of PGC1- expression in mouse heart (39
, 40)
. An acute or prolonged exercise-induced increase in PGC-1, coincident with increases in NRFs and mtTFA mRNA and/or protein expression, has been demonstrated in rodent skeletal muscles (35
, 37
, 41
42
43)
. In the present study, we demonstrate that PGC-1 significantly correlated with the training status of healthy subjects. Moreover, PGC-1 was associated with an enhanced expression of mitochondrial transcripts either encoded by the mitochondrial and nuclear genomes. This is in line with the effects of a 16 wk aerobic exercise program on mitochondrial genes and genes involved in mitochondrial biogenesis (20)
while shorter program duration showed an increase in PGC-1 expression that was not always associated with an up-regulation of its downstream transcription factors NRF-1 and mtTFA expression (16
17
18
19
, 21)
. This discrepancy may be related to the duration of physical training and to the fact that we examined volunteers engaged in long-term physical activity.
Our results demonstrate that mitochondrial protein degradation could participate in the mitochondrial adaptation to long-term physical training. In fact, gene expression of the LonP involved in the protein-specific pathway of degradation followed muscle OXPHOS activity and PGC-1 mRNA level. Our results thus add support to the proposal that the LonP participates in the physiological regulation of mitochondrial biogenesis. Its precise physiological role remains to be established, but an increase in LonP expression could be involved in the proper assembly of mitochondrial complexes by eliminating nonassembled subunits (25)
.
In the present study, we followed the transcript level of two GTPase proteins that act in opposing fusion (Mfn2) and fission (Drp1) pathways to maintain the dynamic of tubular mitochondrial networks (Fig. 4)
. Recent data suggest that proteins that participate in mitochondrial dynamics may be relevant to mitochondrial function in allowing exchanges of soluble matrix proteins and modulating mitochondrial size and morphology (31
, 44)
. Our results show in human skeletal muscle a coordinated increase in muscle OXPHOS activity and mRNA levels of Mfn2 and Drp1 in accordance with the training status of healthy subjects. This suggests that mitochondrial dynamics may participate to the adaptations of mitochondrial function to long-term physical activity by increasing the balance between fusion and fission reactions.
The fact that the mRNA content of mitochondrial enzymes and proteins involved in mitochondrial dynamics and protein assembly correlates with PGC-1 expression suggests that this transcription factor could coordinately regulate their expression in conjunction with its downstream transcription factors NRFs and mtTFA.
One of the signaling pathways involved in the remodeling of skeletal muscle in response to increased activity is activation by calcineurin of NFAT- and MEF2-dependent modulation of gene expression. Recent data suggest that the transcriptional coactivator PGC-1 drives the formation of slow-twitch muscle fibers and that calcineurin potentiates the effects of PGC-1 (14)
. Moreover, recent in vitro studies have shown that the PGC-1 promoter is regulated by the calcium signaling pathway involving calcineurin, resulting in stable induction of PGC-1 contributing to muscle fiber type determination (15)
. We thus examined whether this pathway could account for mitochondrial biogenesis related to physical activity in human skeletal muscle. We used MCIP1 as a marker of calcineurin activation as expression of this protein is rapidly and robustly regulated by calcineurin and thus is recognized as the best marker of calcineurin activation in vivo (33)
. The results show that MCIP1 expression strongly correlated with PGC-1 expression and oxidative capacity. This result is in accordance with recent data showing that MCIP1 and PGC-1 expression are increased in response to prolonged exercise in humans (16)
. Altogether this strongly supports that calcineurin activation plays a significant role in adaptation to increased activity and mitochondrial biogenesis in human skeletal muscle as well.
Moreover, it should be kept in mind that our results were obtained at rest and thus reflects the mean training status of the subjects. We have previously suggested that PGC-1 may set the oxidative capacity of muscle as its basal level of expression correlates with the oxidative capacity of different muscles types in health and diseases (23)
. This proposal is reinforced by the present observations in healthy human subjects having different fitness levels. The graded level of activation of calcineurin reflected in MCIP1 expression could be the upstream signal responsible for the graded expression of PGC-1. The molecular basis of a stable expression of genes characteristic of oxidative muscle fibers by an autoregulatory loop between PGC-1 and components of calcium-signaling pathway have been recently provided by Handschin et al. (15)
.
Mitochondrial function, protein expression/degradation and dynamics in subjects with chronic heart failure
In the skeletal muscle of patients with severe CHF, oxidative capacity and complex I, COX and mi-CK activities did not differ from that of truly sedentary controls, consistent with a previous report of our group (7)
. In contrast, activities of enzymes involved in energy transfer (MM- and MB-CK) and the Krebs cycle enzyme CS were depressed in the CHF group. However, OXPHOS pathway rather than the Krebs cycle appear to be the rate-controlling step in mitochondrial respiration in muscle (45)
, explaining that skeletal muscle oxidative capacity is preserved in CHF. Accordingly, neither gene products involved in the regulation of mitochondrial protein expression (PGC-1, NRF-1, mtTFA), nor calcineurin activation (MCIP1) nor mitochondrial proteins (COXI, COXVb) and 12S rRNA expression differed in CHF patients from sedentary subjects, in line with maintained muscle OXPHOS activity. Transcript levels of gene implicated in mitochondrial protein degradation (LonP) and in mitochondrial dynamics by fusion (Mfn2) and fission (Drp1) reactions were unchanged in CHF skeletal muscle. These results allow to establish that muscle OXPHOS activity, OXPHOS enzymes expression/degradation and mitochondrial dynamics, are again closely linked to calcineurin activation and to the expression of PGC-1 and its downstream transcription factors NRFs and mtTFA. The decreased CS and MM-CK activities in CHF patients and the lower correlation between CS activity and PGC-1 mRNA level in healthy subjects suggest that additional factors (or events) control the expression of these enzymes, factors that may be altered in CHF.
Whatsoever, preserved mitochondrial function and OXPHOS protein expression in skeletal muscle of CHF patients are in contrast with previous results in humans (5
, 6)
and results obtained in animal models of heart failure (23
, 32)
. However, our results agree with a recent study in humans showing that exercise limitation in CHF was not related to impaired skeletal muscle oxidative capacity (8)
. These authors hypothesized that the low VO2 peak observed in CHF patients may be at least in part the result of fiber atrophy, but decreased oxygen delivery could be involved. It is necessary here to emphasize that nowadays patients receive new therapies that may improve muscle function. Whether drug treatment of heart failure might have been protective against dysfunction of mitochondrial protein expression and function remains an open question. All patients were given therapy with ACE inhibitors. ACE inhibitors have been shown to protect skeletal muscle from structural alterations in models of CHF (46)
, and to improve abnormal myosin heavy chain profile (47)
and leg oxygen consumption as well as skeletal muscle blood flow at exercise (48)
in patients. Whether ACE inhibitors therapy may have been protective for mitochondrial biogenesis deserve further research in this direction.
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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and its downstream transcription factors (NRF1 and mtTFA). These factors are maintained elevated and correlate with exercise capacity of the subjects, oxidative capacities of the vastus lateralis muscle and expression of mitochondrial proteins. Moreover we show for the first time that markers of the mitochondrial network dynamics (protein involved in fusion and fission) are up-regulated and correlate with the expression of the transcription coactivator PGC-1. These results add strong support to the proposal that calcineurin and PGC-1 may orchestrate mitochondrial biogenesis and scale muscle oxidative capacities. The important and novel finding is that despite decreased exercise capacity of heart failure patients, the skeletal muscle of these patients exhibit preserved mitochondrial biogenesis transcription cascade and expression of mitochondrial markers of oxidative phosphorylation, and of mitochondrial degradation and dynamics, in line with their preserved muscle oxidative capacity albeit some bioenergetic defects still mark this pathology.
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ACKNOWLEDGMENTS |
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Received for publication June 16, 2004. Accepted for publication September 2, 2004.
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