Skeletal Muscle Mitochondria Research Articles

EIF3 Associates with 80S Ribosomes to Promote Translation Elongation, Mitochondrial Homeostasis, and Muscle Health

eIF3, a multi-subunit complex with numerous functions in canonical translation initiation, is known to interact with 40S and 60S ribosomal proteins and translation elongation factors, but a direct involvement in translation elongation has never been demonstrated. We found that eIF3 deficiency reduced early ribosomal elongation speed between codons 25 and 75 on a set of ∼2,700 mRNAs encoding proteins associated with mitochondrial and membrane functions, resulting in defective synthesis of their encoded proteins. To promote elongation, eIF3 interacts with 80S ribosomes translating the first ∼60 codons and serves to recruit protein quality-control factors, functions required for normal mitochondrial physiology. Accordingly, eIF3e+/- mice accumulate defective mitochondria in skeletal muscle and show a progressive decline in muscle strength. Hence, eIF3 interacts with 80S ribosomes to enhance, at the level of early elongation, the synthesis of proteins with membrane-associated functions, an activity that is critical for mitochondrial physiology and muscle health.

Early adjustments in mitochondrial structure and function in skeletal muscle to high altitude: design and rationale of the first study from the Kilimanjaro Biobank.

The physiological acclimatisation and adaptation processes in skeletal muscle at high altitude are of high medical and social relevance not only to understand limitations in physical performance at high altitude but also to understand the consequences of hypoxemia and tissue hypoxia in critically ill patients. Of particular importance in these processes are the alterations in content and function of mitochondria and myoglobin. The majority of studies on oxygen delivery to the tissues and utilisation by the cellular metabolism at high altitude were performed after prolonged stay at high altitude and in altitude-adapted highlanders. However, these studies do not provide insight in the sequence of events during the physiological acclimatisation and adaptation processes. Therefore, it is important to identify the early alterations in structure and function of the major determinants of the oxygen transport via myoglobin and oxygen utilisation by the mitochondria in skeletal muscle at high altitude. To achieve this goal, it is of interest to collect, analyse and compare quadriceps muscle biopsies and venous blood samples of climbers, guides and porters before and after climbing Mount Kilimanjaro and in participants of the Kilimanjaro Marathon before and after the run. The samples will be carefully documented and stored in the Kilimanjaro Biobank and will be made available to other research groups.

Impact of nicotinamide riboside supplementation on skeletal muscle mitochondria and whole‐body glucose homeostasis: challenging the current hypothesis

Impact of nicotinamide riboside supplementation on skeletal muscle mitochondria and whole‐body glucose homeostasis: challenging the current hypothesis

MO045MITOCHONDRIAL DYSFUNCTION AND MUSCLE ENERGETICS IN CKD PATIENTS

Abstract Background and Aims Patients with chronic kidney disease (CKD) suffer from frailty and sarcopenia. Skeletal muscle mitochondria are important for physical function and could be a target to prevent frailty and sarcopenia. Method We tested the hypothesis that mitochondrial function worsens with the progression of CKD. We evaluated the interaction between mitochondrial function and co-existing comorbidities such as impaired physical performance, intermuscular adipose tissue (IMAT) infiltration, inflammation, and oxidative stress. We evaluated in-vivo thigh mitochondrial function using 31-phosphorus magnetic resonance spectroscopy to obtain the phosphocreatine (PCr) recovery constant, a measure of mitochondrial function. We measured physical performance using the six-minute walk test, IMAT infiltration and markers of inflammation in plasma. Results Sixty-three participants were studied including controls (n=21), patients with CKD not on maintenance hemodialysis (MHD; n=20), and patients on MHD (n=22). We found a prolonged PCr recovery constant in patients on MHD (53.3 (43.4, 70.1) seconds) and with CKD not on MHD (46.3 (40,0, 49.9) seconds) compared to controls (34.2 (28.8, 43.7) seconds) (p<0.001 between groups), Figure 1A-C. Mitochondrial dysfunction was associated with poor physical performance, greater IMAT, and increased markers of inflammation Figure 2A-C. Conclusion Mitochondrial function worsens with the progression of CKD and correlates with physical function, IMAT, inflammation, and oxidative stress. These data suggest that therapeutic approaches targeted at mitochondrial dysfunction and dynamics could prevent or treat frailty and sarcopenia in patients CKD.

Functional changes induced by caloric restriction in cardiac and skeletal muscle mitochondria.

Caloric restriction (CR) is widely known to increase life span and resistance to different types of injuries in several organisms. We have previously shown that mitochondria from livers or brains of CR animals exhibit higher calcium uptake rates and lower sensitivity to calcium-induced mitochondrial permeability transition (mPT), an event related to the resilient phenotype exhibited by these organs. Given the importance of calcium in metabolic control and cell homeostasis, we aimed here to uncover possible changes in mitochondrial calcium handling, redox balance and bioenergetics in cardiac and skeletal muscle mitochondria in response to six months of CR. Unexpectedly, we found that CR does not alter the susceptibility to mPT in muscle (cardiac or skeletal), nor calcium uptake rates. Despite the lack in changes in calcium transport properties, CR consistently decreased respiration in the presence of ATP synthesis in heart and soleus muscle. In heart, such changes were accompanied by a decrease in respiration in the absence of ATP synthesis, lower maximal respiratory rates and a reduced rate of hydrogen peroxide release. Hydrogen peroxide release was unaltered by CR in skeletal muscle. No changes were observed in inner membrane potentials and respiratory control ratios. Together, these results highlight the tissue-specific bioenergetic and ion transport effects induced by CR, demonstrating that resilience against calcium-induced mPT is not present in all tissues.

Comparative analysis of MACROD1, MACROD2 and TARG1 expression, localisation and interactome

The posttranslational modification ADP-ribosylation is involved in many cellular processes, with distinct roles for poly- and mono(ADP-ribosyl)ation (PAR- and MARylation, respectively). Reversibility of intracellular MARylation was demonstrated with the discovery of MACROD1, MACROD2 and TARG1, three macrodomain-containing enzymes capable of reversing MARylation of proteins and RNA. While the three enzymes have identical activities in vitro, their roles in cells are unclear and published data are partially contradictory, possibly due to a lack of validated reagents. We developed monoclonal antibodies to study these proteins and analysed their tissue distribution and intracellular localisation. MACROD1 is most prevalent in mitochondria of skeletal muscle, MACROD2 localises to nucleo- and cytoplasm and is found so far only in neuroblastoma cells, whereas the more ubiquitously expressed TARG1 is present in nucleoplasm, nucleolus and stress granules. Loss of MACROD1 or loss of TARG1 leads to disruption of mitochondrial or nucleolar morphology, respectively, hinting at their importance for these organelles. To start elucidating the underlying mechanisms, we have mapped their interactomes using BioID. The cellular localisation of interactors supports the mitochondrial, nucleolar and stress granule localisation of MACROD1 and TARG1, respectively. Gene ontology analysis suggests an involvement of MACROD1 and TARG1 in RNA metabolism in their respective compartments. The detailed description of the hydrolases’ expression, localisation and interactome presented here provides a solid basis for future work addressing their physiological function in more detail.

Lower oxygen consumption and Complex I activity in mitochondria isolated from skeletal muscle of fetal sheep with intrauterine growth restriction.

Fetal sheep with placental insufficiency-induced intrauterine growth restriction (IUGR) have lower hindlimb oxygen consumption rates (OCRs), indicating depressed mitochondrial oxidative phosphorylation capacity in their skeletal muscle. We hypothesized that OCRs are lower in skeletal muscle mitochondria from IUGR fetuses, due to reduced electron transport chain (ETC) activity and lower abundances of tricarboxylic acid (TCA) cycle enzymes. IUGR sheep fetuses (n = 12) were created with mid-gestation maternal hyperthermia and compared with control fetuses (n = 12). At 132 ± 1 days of gestation, biceps femoris muscles were collected, and the mitochondria were isolated. Mitochondria from IUGR muscle have 47% lower State 3 (Complex I-dependent) OCRs than controls, whereas State 4 (proton leak) OCRs were not different between groups. Furthermore, Complex I, but not Complex II or IV, enzymatic activity was lower in IUGR fetuses compared with controls. Proteomic analysis (n = 6/group) identified 160 differentially expressed proteins between groups, with 107 upregulated and 53 downregulated mitochondria proteins in IUGR fetuses compared with controls. Although no differences were identified in ETC subunit protein abundances, abundances of key TCA cycle enzymes [isocitrate dehydrogenase (NAD+) 3 noncatalytic subunit β (IDH3B), succinate-CoA ligase ADP-forming subunit-β (SUCLA2), and oxoglutarate dehydrogenase (OGDH)] were lower in IUGR mitochondria. IUGR mitochondria had a greater abundance of a hypoxia-inducible protein, NADH dehydrogenase 1α subcomplex 4-like 2, which is known to incorporate into Complex I and lower Complex I-mediated NADH oxidation. Our findings show that mitochondria from IUGR skeletal muscle adapt to hypoxemia and hypoglycemia by lowering Complex I activity and TCA cycle enzyme concentrations, which together, act to lower OCR and NADH production/oxidation in IUGR skeletal muscle.

Unlike a high-fat diet model, mitochondrial ROS production does not appear to contribute to bed rest-induced insulin resistance.

Unlike a high-fat diet model, mitochondrial ROS production does not appear to contribute to bed rest-induced insulin resistance.

Basic biochemical characterization of cytosolic enzymes in thymidine nucleotide synthesis in adult rat tissues: implications for tissue specific mitochondrial DNA depletion and deoxynucleoside-based therapy for TK2-deficiency

BackgroundDeficiency in thymidine kinase 2 (TK2) or p53 inducible ribonucleotide reductase small subunit (p53R2) is associated with tissue specific mitochondrial DNA (mtDNA) depletion. To understand the mechanisms of the tissue specific mtDNA depletion we systematically studied key enzymes in dTMP synthesis in mitochondrial and cytosolic extracts prepared from adult rat tissues.ResultsIn addition to mitochondrial TK2 a cytosolic isoform of TK2 was characterized, which showed similar substrate specificity to the mitochondrial TK2. Total TK activity was highest in spleen and lowest in skeletal muscle. Thymidylate synthase (TS) was detected in cytosols and its activity was high in spleen but low in other tissues. TS protein levels were high in heart, brain and skeletal muscle, which deviated from TS activity levels. The p53R2 proteins were at similar levels in all tissues except liver where it was ~ 6-fold lower. Our results strongly indicate that mitochondria in most tissues are capable of producing enough dTTP for mtDNA replication via mitochondrial TK2, but skeletal muscle mitochondria do not and are most likely dependent on both the salvage and de novo synthesis pathways.ConclusionThese results provide important information concerning mechanisms for the tissue dependent variation of dTTP synthesis and explained why deficiency in TK2 or p53R2 leads to skeletal muscle dysfunctions. Furthermore, the presence of a putative cytosolic TK2-like enzyme may provide basic knowledge for the understanding of deoxynucleoside-based therapy for mitochondrial disorders.

Unbiased Proteomics Supports a Key Role for Mitochondria in Skeletal Muscle of Highly Functioning Octogenarians

IntroductionSkeletal muscle mass and function decline with aging, and more precipitously after the age 75 y. To help provide insights into biologically relevant mechanisms for preserving muscle mass and function in advanced age, in this study we performed proteomics on skeletal muscle of world class octogenarian track and field athletes in comparison to healthy octogenarian non‐athletes.MethodsMuscle cross‐sectional area by MRI and a vastus lateralis muscle biopsy were performed in 15 octogenarian world class track and field athletes (8 of whom were world record holders in their discipline at the time of testing) and 14 non‐athlete age‐ and sex‐matched non‐athlete controls. From these subjects, a portion of muscle from a subset of 12 master athletes (MA mean age 81.19 ± 5.1 y) and 12 non‐athlete controls (NA mean age 80.94 ± 4.5 y) was used for liquid‐chromatography mass spectrometry to generate quantitative tandem mass tag proteomics data. In addition, we measured mtDNA copy number, COX/SDH histochemistry to identify respiratory compromised fibers, and Western blot of mitochondrial inner and outer membrane proteins.ResultsMuscle cross‐sectional area was higher in MA. Tandem mass spectrometry identified over 6000 proteins, and significant differences in abundance were found between NA controls and MA for more than 800 proteins. A pathway analysis revealed that pathways involved in mitochondria (e.g., TCA cycle, respiratory electron transport, cristae formation, sirtuins) were higher in MA, while proteins in pathways involved in the spliceosome and nuclear pore were downregulated in MA. Finally, 8 mtDNA‐encoded proteins that were included in the analysis were elevated in MA versus NA. These proteomics data are consistent with phenotypic data showing MA have higher mtDNA copy number, fewer respiratory chain compromised muscle fibers, and an increased ratio of ETC subunits (inner mitochondrial membrane proteins) relative to VDAC (outer mitochondrial membrane protein), suggesting an increase in cristae formation.ConclusionOur data underscore that mitochondrial pathways are key to maintaining a high level of physical function in advanced age. With the current study design we cannot determine the degree to which these differences are attributable to the physical activity habits of MA, but it is likely to play a role.Support or Funding InformationCIHR (MOP 125986 to RTH)NIA Intramural Research program

The structural basis for intermitochondrial communications is fundamentally different in cardiac and skeletal muscle.

What is the topic for this review? This review summarizes recent discoveries in mitochondrial development and morphology studied with electron microscopy. What advances does it highlight? Although mitochondria are generally considered to be isolated from each other, this review highlights recently discovered evidence for the presence of intermitochondrial communication structures in cardiac and skeletal muscle, in animal models and humans. Within striated muscles, the means of intermitochondrial exchange and the reaction of mitochondria to external stimuli are uniquely dependent on the tissue, and we clearly differentiate between nanotunnels, the active protrusion of cardiac mitochondria, and the connecting ducts of skeletal muscle derived from fusion-fission and elongation events. This review focuses on recent discoveries in skeletal and cardiac muscles indicating that mitochondria behave as an interactive cohort with inter-organelle communication and specific reactions to stress signals. Our new finding is that intermitochondrial communications in cardiac and skeletal muscles rely on two distinct methods. In cardiac muscle, mitochondria are discrete entities and are fairly well immobilized in a structural context. The organelles have developed a unique method of communication, via nanotunnels, which allow temporary connection from one mitochondrion to another over distances of up to several micrometres, without overall movement of the individual organelles and loss of their identity. Skeletal muscle mitochondria, in contrast, are dynamic. Through fusion, fission and elongation, they form connections that include constrictions and connecting ducts (distinct from nanotunnels) and lose individual identity in the formation of extensive networks. Connecting elements in skeletal muscle are distinct from nanotunnels in cardiac muscle.

Subpopulation-specific differences in skeletal muscle mitochondria in humans with obesity: insights from studies employing acute nutritional and exercise stimuli.

Mitochondria from skeletal muscle of humans with obesity often display alterations with respect to their morphology, proteome, biogenesis, and function. These changes in muscle mitochondria are considered to contribute to metabolic abnormalities observed in humans with obesity. Most of the evidence describing alterations in muscle mitochondria in humans with obesity, however, lacks reference to a specific subcellular location. This is despite data over the years showing differences in the morphology and function of subsarcolemmal (found near the plasma membrane) and intermyofibrillar (nested between the myofibrils) mitochondria in skeletal muscle. Recent studies reveal that impairments in mitochondrial function in obesity with respect to the subcellular location of the mitochondria in muscle are more readily evident following exposure of the skeletal muscle to physiological stimuli. In this review, we highlight the need to understand skeletal muscle mitochondria metabolism in obesity in a subpopulation-specific manner and in the presence of physiological stimuli that modify mitochondrial function in vivo. Experimental approaches employed under these conditions will allow for more precise characterization of impairments in skeletal muscle mitochondria and their implications in inducing metabolic dysfunction in human obesity.

Alterations in mitochondrial functions and morphology in muscle and non-muscle tissues in type 1 diabetes: implications for metabolic health.

What is the topic of this review? Evidence of impaired mitochondrial functions and/or morphology in people with type 1 diabetes across various organ systems. What advances does it highlight? Impairments to mitochondrial functions and morphology may be a primary mechanism underlying the pathophysiology of various complications in people with type 1 diabetes. We recently made the observation that there are significant alterations to the ultrastructure and functions of mitochondria in skeletal muscle of people with type 1 diabetes (T1D). These alterations are proposed to lead to decreased energy production in skeletal muscle during exercise and thus may contribute to the impaired aerobic exercise capacity reported in some people with T1D. This Symposium Review summarizes the evidence that similar alterations also occur in the mitochondria present in organ systems outside skeletal muscle in people with T1D, and that this may contribute to the development and progression of the known complications of T1D, which eventually lead to the reported premature mortality.

Skeletal muscle metabolism in sea-acclimatized king penguins. II. Improved efficiency of mitochondrial bioenergetics.

At fledging, juvenile king penguins (Aptenodytes patagonicus) must overcome the tremendous energetic constraints imposed by their marine habitat, including during sustained extensive swimming activity and deep dives in cold seawater. Both endurance swimming and skeletal muscle thermogenesis require high mitochondrial respiratory capacity while the submerged part of dive cycles repeatedly and greatly reduces oxygen availability, imposing a need for solutions to conserve oxygen. The aim of the present study was to determine in vitro whether skeletal muscle mitochondria become more 'thermogenic' to sustain heat production or more 'economical' to conserve oxygen in sea-acclimatized immature penguins (hereafter 'immatures') compared with terrestrial juveniles. Rates of mitochondrial oxidative phosphorylation were measured in permeabilized fibers and mitochondria from the pectoralis muscle. Mitochondrial ATP synthesis and coupling efficiency were measured in isolated muscle mitochondria. The mitochondrial activities of respiratory chain complexes and citrate synthase were also assessed. The results showed that respiration, ATP synthesis and respiratory chain complex activities in pectoralis muscles were increased by sea acclimatization. Furthermore, muscle mitochondria were on average 30-45% more energy efficient in sea-acclimatized immatures than in pre-fledging juveniles, depending on the respiratory substrate used (pyruvate, palmitoylcarnitine). Hence sea acclimatization favors the development of economical management of oxygen, decreasing the oxygen needed to produce a given amount of ATP. This mitochondrial phenotype may improve dive performance during the early marine life of king penguins, by extending their aerobic dive limit.

Mitochondrial abundance and function in muscle from beef steers with divergent residual feed intakes

The objective of this study was to evaluate the relationship between muscle mitochondrial function and residual feed intake (RFI) in growing beef cattle. A 56-day feeding trial was conducted with 81 Angus × Hereford steers (initial BW = 378 ± 43 kg) from the University of California Sierra Foothills Research Station (Browns Valley, CA, USA). All steers were individually fed the same finishing ration (metabolizable energy = 3.28 Mcal/kg DM). Average daily gain (ADG), DM intake (DMI) and RFI were 1.82 ± 0.27, 8.89 ± 1.06 and 0.00 ± 0.55 kg/day, respectively. After the feeding trial, the steers were categorized into high, medium and low RFI groups. Low RFI steers consumed 13.6% less DM (P < 0.05) and had a 14.1% higher G : F ratio (P < 0.05) than the high RFI group. No differences between RFI groups were found in age, ADG or BW (P > 0.10). The most extreme individuals from the low and high RFI groups were selected to assess mitochondrial function (n = 5 low RFI and n = 6 high RFI). Mitochondrial respiration was measured using an oxygraph (Hansatech Instruments Ltd., Norfolk, UK). State 3 and State 4 respiration rates were similar between both groups (P > 0.10). Respiratory control ratios (RCRs, i.e., State 3 : State 4 oxygen uptakes) declined with animal age and were greater in low RFI steers (4.90) as compared to high RFI steers (4.26) when adjusted for age by analysis of covariance (P = 0.003). Mitochondrial complex II activity levels per gram of muscle were 42% greater in low RFI steers than in high RFI steers (P = 0.004). These data suggest that skeletal muscle mitochondria have greater reserve respiratory capacity and show greater coupling between respiration and phosphorylation in low RFI than in high RFI steers.

Physical and Functional Cross Talk Between Endo-Sarcoplasmic Reticulum and Mitochondria in Skeletal Muscle.

Significance: The physiological relevance of contacts between the sarcoplasmic reticulum (SR), a specialized domain of the endoplasmic reticulum (ER) in skeletal muscle, and mitochondria is still not clear. Recent Advances: An extensive close proximity of these two organelles is a late developmental event, which suggests that it does not have an essential function. Critical Issues: The intimate association of SR/mitochondria develops during murine postnatal differentiation and the recovery of denervated atrophic muscle, which suggests that this is a highly regulated process with a specific function. Analyses of mouse models for muscle diseases suggest that impaired ER/SR-mitochondrial contacts may be due to ER stress and lead to defective bioenergetics and insulin signaling. Future Directions: Future studies are necessary to identify the molecular determinants weakening insulin signaling upon impairment of ER/mitochondrial contacts in skeletal muscles as well as to analyze the distance between SR/ER and mitochondria in muscle diseases associated with ER stress.

Quantification of Mitochondrial Oxidative Phosphorylation in Metabolic Disease: Application to Type 2 Diabetes.

Type 2 diabetes (T2D) is a growing health concern with nearly 400 million affected worldwide as of 2014. T2D presents with hyperglycemia and insulin resistance resulting in increased risk for blindness, renal failure, nerve damage, and premature death. Skeletal muscle is a major site for insulin resistance and is responsible for up to 80% of glucose uptake during euglycemic hyperglycemic clamps. Glucose uptake in skeletal muscle is driven by mitochondrial oxidative phosphorylation and for this reason mitochondrial dysfunction has been implicated in T2D. In this review we integrate mitochondrial function with physiologic function to present a broader understanding of mitochondrial functional status in T2D utilizing studies from both human and rodent models. Quantification of mitochondrial function is explained both in vitro and in vivo highlighting the use of proper controls and the complications imposed by obesity and sedentary lifestyle. This review suggests that skeletal muscle mitochondria are not necessarily dysfunctional but limited oxygen supply to working muscle creates this misperception. Finally, we propose changes in experimental design to address this question unequivocally. If mitochondrial function is not impaired it suggests that therapeutic interventions and drug development must move away from the organelle and toward the cardiovascular system.

P734Research on the mechamism of renal sympathetic denervation in the treatment of insulin resistance

Abstract Background Insulin resistance is the main pathogenesis of type 2 diabetes. In order to better control the blood glucose of diabetic patients, the key is to improve the insulin sensitivity. With the in-depth study on the mechanism of insulin resistance, sympathetic nerve is an important part of it, but the specific mechanism is not clear. Objective This experiment aims to observe the effects of RDN on insulin resistance and skeletal muscle mitochondrial function in spontaneous diabetes ZDF rats. Methods 6 SPF healthy male ZDF (fa/+) rats were selected as control group, 12 healthy males ZDF (fa/fa) rats were randomly divided into sham group and RDN group. In the sham group and RDN group, the rats were treated with sham operation or bilateral renal sympathetic denervation respectively. Insulin sensitivity was tested in all rats with Hyperinsulinemic-euglycemic clamp test 2 weeks after RDN. The skeletal muscle ATPsyn, COXIV, UCP3 and SOD2 were tested by Western-blot method. Results The result showed that 2 weeks after RDN, the blood glucose level of the RDN group decreased significantly (P=0.000) when compared with the sham group. The glucose infusion rate (GIR) in sham and RDN group decreased significantly when compared with the control group (P=0.000). After RDN, the GIR in RDN group increased significantly. ATPsyn, COXIV which were the key enzyme of oxidative metabolism in skeletal muscle mitochondria decreased significantly in the sham and RDN group when compared with control group (P=0.001). However, parameters improved dramatically after RDN (P=0.001). Table 1. Comparision of Baseline in each group 2 weeks after RDN Control (n=6) Sham (n=6) RDN (n=6) Pa Pb Pc Weight (g) 311.1±8.5 410.8±10.7 377.9±15.3 0.000 0.001 0.002 BBG (mmol/L) 5.97±0.16 21.42±1.45 7.91±0.54 0.000 0.001 0.000 BISN (ng/mL) 100.67±4.18 162.17±3.13 134.67±2.50 0.000 0.001 0.001 TG (mmol/L) 2.71±0.28 6.90±0.24 4.88±0.23 0.000 0.001 0.002 TC (mmol/L) 2.38±0.17 6.98±0.15 5.40±0.09 0.000 0.000 0.000 HDL-C (mmol/L) 7.92±0.44 2.95±0.22 5.35±0.19 0.000 0.000 0.000 LDL-C (mmol/L) 3.72±0.37 4.12±0.17 3.98±0.17 0.001 0.000 0.000 aCompared with Control Group and Sham Group. bCompared with RDN Group and Sham Group. cCompared with Sham Group and RDN Group. Relative results Conclusion Our results showed that RDN improved the insulin sensitivity in diabetes rats. The mechanism may be related to the decrease of oxidative stress and function improvement in skeletal muscle mitochondrial by RDN.

Exercise training counteracts urothelial carcinoma-induced alterations in skeletal muscle mitochondria phospholipidome in an animal model

Cancer associated body wasting is the cause of physical disability, reduced tolerance to anticancer therapy and reduced survival of cancer patients and, similarly to cancer, its incidence is increasing. There is no cure for this clinical condition, and the pathophysiological process involved is largely unknown. Exercise training appears as the gold standard non-pharmacological therapy for the management of this wasting syndrome. Herein we used a lipidomics approach based on liquid chromatography coupled with high-resolution mass spectrometry (LC-HR-MS) to study the effect of exercise in the modulation of phospholipids profile of mitochondria isolated from gastrocnemius muscle of a pre-clinical model of urothelial carcinoma-related body wasting (BBN induced), submitted to 13 weeks of treadmill exercise after diagnosis. Multivariate analysis showed a close relationship between the BBN exercise group and both control groups (control sedentary and control exercise), while the BBN sedentary group was significantly separated from the control groups and the BBN exercise group. Univariate statistical analysis revealed differences mainly in phosphatidylserine (PS) and cardiolipin (CL), although some differences were also observed in phosphatidylinositol (PI, LPI) and phosphatidylcholine (PC) phospholipids. PS with shorter fatty acyl chains were up-regulated in the BBN sedentary group, while the other species of PS with longer FA and a higher degree of unsaturation were down-regulated, but the BBN exercise group was mostly similar to control groups. Remarkably, exercise training prevented these alterations and had a positive impact on the ability of mitochondria to produce ATP, restoring the healthy phospholipid profile. The remodelling of mitochondria phospholipid profile in rats with urothelial carcinoma allowed confirming the importance of the lipid metabolism in mitochondria dysfunction in cancer-induced skeletal muscle remodelling. The regulation of phospholipid biosynthetic pathways observed in the BBN exercise group supported the current perspective that exercise is an adequate therapeutic approach for the management of cancer-related muscle remodeling.

Skeletal muscle mitochondrial function and exercise capacity are not impaired in mice with knockout of STAT3.

Signal transducer and activator of transcription 3 (STAT3) was recently found to be localized to mitochondria in a number of tissues and cell types, where it modulates oxidative phosphorylation via interactions with the electron transport proteins, complex I and complex II. Skeletal muscle is densely populated with mitochondria although whether STAT3 contributes to skeletal muscle oxidative capacity is unknown. In the present study, we sought to elucidate the contribution of STAT3 to mitochondrial and skeletal muscle function by studying mice with muscle-specific knockout of STAT3 (mKO). First, we developed a novel flow cytometry-based approach to confirm that STAT3 is present in skeletal muscle mitochondria. However, contrary to findings in other tissue types, complex I and complex II activity and maximal mitochondrial respiratory capacity in skeletal muscle were comparable between mKO mice and floxed/wild-type littermates. Moreover, there were no genotype differences in endurance exercise performance, skeletal muscle force-generating capacity, or the adaptive response of skeletal muscle to voluntary wheel running. Collectively, although we confirm the presence of STAT3 in skeletal muscle mitochondria, our data establish that STAT3 is dispensable for mitochondrial and physiological function in skeletal muscle.NEW & NOTEWORTHY Whether signal transducer and activator of transcription 3 (STAT3) can regulate the activity of complex I and II of the electron transport chain and mitochondrial oxidative capacity in skeletal muscle, as it can in other tissues, is unknown. By using a mouse model lacking STAT3 in muscle, we demonstrate that skeletal muscle mitochondrial and physiological function, both in vivo and ex vivo, is not impacted by the loss of STAT3.