Adaptation Of Mitochondrial Function Research Articles

Mitochondrial Elongation and OPA1 Play Crucial Roles during the Stemness Acquisition Process in Pancreatic Ductal Adenocarcinoma.

Simple SummaryPancreatic ductal adenocarcinoma (PDAC) is a highly lethal neoplasia and the currently used treatments are not effective in a wide range of patients. Presently, the evidence points out that cancer stem cells (CSCs) are key players during tumor development, metastasis, chemoresistance, and tumor relapse. The study of the metabolism of CSCs, specifically the mitochondrial alterations, could pave the way to the discovery of new therapeutical targets. In this study, we show that during progressive de-differentiation, pancreatic CSCs undergo changes in mitochondrial mass, dynamics, and function. Interestingly, the silencing of OPA1, a protein involved in mitochondrial fusion, significantly inhibits the formation of CSCs. These results reveal new insight into mitochondria and stemness acquisition that could be useful for the design of novel potential therapies in PDAC.Pancreatic ductal adenocarcinoma (PDAC) is the most common type of pancreatic cancer with an overall 5-year survival rate of less than 9%. The high aggressiveness of PDAC is linked to the presence of a subpopulation of cancer cells with a greater tumorigenic capacity, generically called cancer stem cells (CSCs). CSCs present a heterogeneous metabolic profile that might be supported by an adaptation of mitochondrial function; however, the role of this organelle in the development and maintenance of CSCs remains controversial. To determine the role of mitochondria in CSCs over longer periods, which may reflect more accurately their quiescent state, we studied the mitochondrial physiology in CSCs at short-, medium-, and long-term culture periods. We found that CSCs show a significant increase in mitochondrial mass, more mitochondrial fusion, and higher mRNA expression of genes involved in mitochondrial biogenesis than parental cells. These changes are accompanied by a regulation of the activities of OXPHOS complexes II and IV. Furthermore, the protein OPA1, which is involved in mitochondrial dynamics, is overexpressed in CSCs and modulates the tumorsphere formation. Our findings indicate that CSCs undergo mitochondrial remodeling during the stemness acquisition process, which could be exploited as a promising therapeutic target against pancreatic CSCs.

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

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

1816-P: Hepatic Mitochondrial Alterations in a Murine Model of Combined Diabetes and Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is tightly associated with obesity and type 2 diabetes. There is evidence that mitochondrial function is altered in both diseases. Here, we examined hepatic mitochondria during different stages of NAFLD in mice with experimental diabetes. Two-days old male C57BL/6j mice received 200 µg streptozotocin (STAM) or vehicle (CTRL). From 4 weeks on, they were on high-fat diet for either 4 w or 8 w to induce steatosis or nonalcoholic steatohepatitis (NASH). Liver histology was performed to quantify steatosis, inflammation and fibrosis. Mitochondrial respiration was assessed in liver tissues using high-resolution respirometry with different substrate protocols. Citrate synthase activity (CSA) served as a surrogate marker for mitochondrial content. Immunoblotting was used to quantify mitochondrial complexes. Compared to CTRL, STAM mice showed 140% and 54% higher blood glucose and liver/body weight. Hepatic steatosis increased from 2% to 15% at 4 w and decreased to 5% at 8 w. NAFLD activity score was 0.25 in CTRL and increased to 2.5 at 4 w and 8 w in STAM. STAM mice had lower CSA, indicating lower mitochondrial content at both time points, whereas complex III protein content was decreased only at 8 w. Of note, maximal uncoupled β-oxidation-associated respiration, normalized to CSA, was 1.7- and 2.7-fold higher in livers of STAM mice after 4 w and 8 w, respectively, as compared to CTRL. In conclusion, combined diabetes and NASH decreased mitochondrial content but resulted in greater maximal oxidative capacity per mitochondrion, possibly reflecting an adaptation of mitochondrial function during NAFLD progression in adult mice. Disclosure B. Dewidar: None. C. Englisch: None. D. Pesta: None. E. Rohbeck: None. C. Ress: None. I. Esposito: None. M. Roden: Advisory Panel; Self; Servier. Board Member; Self; Poxel SA. Consultant; Self; Eli Lilly and Company, Gilead Sciences, Inc., ProSciento, TARGET PharmaSolutions. Research Support; Self; Boehringer Ingelheim International GmbH, Novartis Pharma K.K., Sanofi US. Speaker’s Bureau; Self; Novo Nordisk A/S. Funding German Federal Ministry of Health and Ministry of Culture and Science of the State North Rhine-Westphalia; German Federal Ministry of Education and Research by the European Regional Development Fund (KomIT, EFRE-0400191); German Research Foundation (DFG; SFB 1116/2)

Exercise training results in depot-specific adaptations to adipose tissue mitochondrial function

We assessed differences in mitochondrial function in gluteal (gSAT) and abdominal subcutaneous adipose tissue (aSAT) at baseline and in response to 12-weeks of exercise training; and examined depot-specific associations with body fat distribution and insulin sensitivity (SI). Obese, black South African women (n = 45) were randomized into exercise (n = 23) or control (n = 22) groups. Exercise group completed 12-weeks of aerobic and resistance training (n = 20), while the control group (n = 15) continued usual behaviours. Mitochondrial function (high-resolution respirometry and fluorometry) in gSAT and aSAT, SI (frequently sampled intravenous glucose tolerance test), body composition (dual-energy X-ray absorptiometry), and ectopic fat (MRI) were assessed pre- and post-intervention. At baseline, gSAT had higher mitochondrial respiratory capacity and hydrogen peroxide (H2O2) production than aSAT (p < 0.05). Higher gSAT respiration was associated with higher gynoid fat (p < 0.05). Higher gSAT H2O2 production and lower aSAT mitochondrial respiration were independently associated with lower SI (p < 0.05). In response to training, SI improved and gynoid fat decreased (p < 0.05), while H2O2 production reduced in both depots, and mtDNA decreased in gSAT (p < 0.05). Mitochondrial respiration increased in aSAT and correlated with a decrease in body fat and an increase in soleus and hepatic fat content (p < 0.05). This study highlights the importance of understanding the differences in mitochondrial function in multiple SAT depots when investigating the pathophysiology of insulin resistance and associated risk factors such as body fat distribution and ectopic lipid deposition. Furthermore, we highlight the benefits of exercise training in stimulating positive adaptations in mitochondrial function in gluteal and abdominal SAT depots.

Placental mitochondria adapt developmentally and in response to hypoxia to support fetal growth

Mitochondria respond to a range of stimuli and function in energy production and redox homeostasis. However, little is known about the developmental and environmental control of mitochondria in the placenta, an organ vital for fetal growth and pregnancy maintenance in eutherian mammals. Using respirometry and molecular analyses, the present study examined mitochondrial function in the distinct transport and endocrine zones of the mouse placenta during normal pregnancy and maternal inhalation hypoxia. The data show that mitochondria of the two zones adopt different strategies in modulating their respiration, substrate use, biogenesis, density, and efficiency to best support the growth and energy demands of fetoplacental tissues during late gestation in both normal and hypoxic conditions. The findings have important implications for environmentally induced adaptations in mitochondrial function in other tissues and for compromised human pregnancy in which hypoxia and alterations in placental mitochondrial function are associated with poor outcomes like fetal growth restriction.

Near infrared spectroscopy-guided exercise training for claudication in peripheral arterial disease.

Supervised treadmill exercise for claudication in peripheral arterial disease is effective but poorly tolerated because of ischemic leg pain. Near infrared spectroscopy allows non-invasive detection of muscle ischemia during exercise, allowing for characterization of tissue perfusion and oxygen utilization during training. We evaluated walking time, muscle blood flow, and muscle mitochondrial capacity in patients with peripheral artery disease after a traditional pain-based walking program and after a muscle oxygen-guided walking program. Patients with peripheral artery disease trained thrice weekly in 40-minute-long sessions for 12 weeks, randomized to oxygen-guided training ( n = 8, age 72 ± 9.7 years, 25% female) versus traditional pain-based training ( n = 10, age 71.6 ± 8.8 years, 20% female). Oxygen-guided training intensity was determined by maintaining a 15% reduction in skeletal muscle oxygenation by near infrared spectroscopy rather than relying on symptoms of pain to determine exercise effort. Pain free and maximal walking times were measured with a 12-minute Gardner treadmill test. Gastrocnemius mitochondrial capacity and blood flow were measured using near infrared spectroscopy. Baseline pain-free walking time was similar on a Gardner treadmill test (2.5 ± 0.9 vs. 3.6 ± 1.0 min, p = 0.5). After training, oxygen-guided cohorts improved similar to pain-guided cohorts (pain-free walking time 6.7 ± 0.9 vs. 6.9 ± 1.1 min, p < 0.01 for change from baseline and p = 0.97 between cohorts). Mitochondrial capacity improved in both groups but more so in the pain-guided cohort than in the oxygen-guided cohort (38.8 ± 8.3 vs. 14.0 ± 9.3, p = 0.018). Resting muscle blood flow did not improve significantly in either group with training. Oxygen-guided exercise training improves claudication comparable to pain-based training regimens. Adaptations in mitochondrial function rather than increases in limb perfusion may account for functional improvement. Increases in mitochondrial oxidative capacity may be proportional to the degree of tissue hypoxia during exercise.

Neuroprotection by quercetin via mitochondrial function adaptation in traumatic brain injury: PGC‐1α pathway as a potential mechanism

The aim of this study was to investigate the neuroprotective effects of quercetin in mouse models of traumatic brain injury (TBI) and the potential role of the PGC‐1α pathway in putative neuroprotection. Wild‐type mice were randomly assigned to four groups: the sham group, the TBI group, the TBI+vehicle group and the TBI+quercetin group. Quercetin, a dietary flavonoid used as a food supplement, significantly reduced TBI‐induced neuronal apoptosis and ameliorated mitochondrial lesions. It significantly accelerated the translocation of PGC‐1α protein from the cytoplasm to the nucleus. In addition, quercetin restored the level of cytochrome c, malondialdehyde and superoxide dismutase in mitochondria. Therefore, quercetin administration can potentially attenuate brain injury in a TBI model by increasing the activities of mitochondrial biogenesis via the mediation of the PGC‐1α pathway.

Supramolecular structure of dietary fat in early life modulates expression of markers for mitochondrial content and capacity in adipose tissue of adult mice

BackgroundPrevious studies have shown that early life nutrition can modulate the development of white adipose tissue and thereby affect the risk on obesity and metabolic disease later in life. For instance, postnatal feeding with a concept infant milk formula with large, phospholipid coated lipid droplets (Concept, Nuturis®), resulted in reduced adiposity in adult mice. The present study investigated whether differences in cell energy metabolism, using markers of mitochondrial content and capacity, may contribute to the observed effects.MethodsC57Bl/6j male mice were exposed to a rodent diet containing the Concept (Concept) or standard (CTRL) infant milk formula from postnatal day 16 until postnatal day 42, followed by a western style diet challenge until postnatal day 98. Markers for mitochondrial content and capacity were analyzed in retroperitoneal white adipose tissue and gene expression of metabolic markers was measured in both retroperitoneal white adipose tissue and muscle tibialis (M. tibialis) at postnatal day 98.ResultsIn retroperitoneal white adipose tissue, the Concept group showed higher citrate synthase activity and mitochondrial DNA expression compared to the CTRL group (p < 0.05). In addition, protein expression of mitochondrial cytochrome c oxidase subunit I of the oxidative phosphorylation pathway/cascade was increased in the Concept group compared to CTRL (p < 0.05). In the M. tibialis, gene expression of uncoupling protein 3 was higher in the Concept compared to the CTRL group. Other gene and protein expression markers for mitochondrial oxidative capacity were not different between groups.ConclusionPostnatal feeding with large, phospholipid coated lipid droplets generating a different supramolecular structure of dietary lipids enhances adult gene and protein expression of specific mitochondrial oxidative capacity markers, indicative of increased substrate oxidation in white adipose tissue and skeletal muscle. Although functional mitochondrial capacity was not measured, these results may suggest that adaptations in mitochondrial function via early feeding with a more physiological structure of dietary lipids, could underlie the observed beneficial effects on later life adiposity.

Mitochondrial DNA: The Alternative Molecular Marker for Cancer Detection and Treatment

Mitochondrion being an organelle plays a major role in many metabolic and bio synthetic pathways. Cancer is strongly associated with changes in cellular metabolism, with a characteristic metabolic shift toward aerobic glycolysis in transformed cells. The recent resurgence of interest in the study of mitochondria has come into the light due to recognition of the fact that the genetic or metabolic alterations in this organelle are causative or contributing factors in a variety of human diseases including cancer. A variety of mitochondrial dna mutations are caused by oxidative damage via ROS that are generated either endogenously during oxidative phosphorylation or by exogenous sources and other mutagens. The ability of adaptation of mitochondrial function has been recognized as crucial to the changes that occur in cancer cells. Due to the presence of this unique property of abundance and homoplasmic nature of mitochondria it makes mt DNA an attractive molecular marker of cancer. These alterations in mitochondrial structure and function might prove clinically useful either as markers for the early detection of cancer or as unique molecular sites against which novel and selective chemotherapeutic agents might be targeted. This review suggests that mitochondrion is one such target.

Adaptations of skeletal muscle mitochondria to exercise training.

Mitochondrial volume density (Mito(VD)) is composed of two distinct mitochondrial subpopulations--intermyofibrillar mitochondria (Mito(IMF)) and subsarcolemmal mitochondria (Mito(SS)). With exercise training, Mito(VD) may increase by up to 40% and is, for the most part, related to an increase in Mito(IMF). Exercise-induced adaptations in mitochondrial function depend on the intensity of training and appear to be explained predominately by an increased expression of mitochondrial enzymes that facilitate aerobic metabolism. Although mitochondrial content often increases with training, it seems that mitochondrial adaptations are not needed to facilitate maximal oxygen uptake, whereas such adaptations are of greater importance for endurance capacity.

Mitochondrial Markers for Cancer: Relevance to Diagnosis, Therapy, and Prognosis and General Understanding of Malignant Disease Mechanisms

Cancer cells display changes that aid them to escape from cell death, sustain their proliferative powers, and shift their metabolism toward glycolytic energy production. Mitochondria are key organelles in many metabolic and biosynthetic pathways, and the adaptation of mitochondrial function has been recognized as crucial to the changes that occur in cancer cells. This paper zooms in on the pathologic evaluation of mitochondrial markers for diagnosing and staging of human cancer and determining the patients’ prognoses.

Regulation of hepatic mitochondrial metabolism in response to a high fat diet: a longitudinal study in rats

Mitochondrial dysfunctions have been detected in non-alcoholic steatohepatitis, but less information exists regarding adaptation of mitochondrial function during the initiation of hepatic steatosis. This study aimed to determine in rat liver the sequence of mitochondrial and metabolic adaptations occurring during the first 8 weeks of a moderate high fat diet (HFD). Sprague-Dawley rats were fed a HFD during 2, 4, and 8 weeks. Mitochondrial oxygen consumption, respiratory chain complexes activity, and oxidative phosphorylation efficiency were assessed in isolated liver mitochondria. Gene expression related to fat metabolism and mitochondrial biogenesis were determined. Results were compared to data collected in a group of rats sacrificed before starting the HFD feeding. After 2 and 4 weeks of HFD, there was a development of fatty liver and a concomitant increase the expression of mitochondrial glycerol-3-phosphate acyltransferase (mtGPAT) and peroxisome proliferator-activated receptor γ. Higher serum β-hydroxybutyrate levels and enhanced hepatic pyruvate dehydrogenase kinase 4 expression suggested increased fatty acid oxidation. However, mitochondrial respiration and respiratory chain activity were normal. After 8 weeks of HFD, lower accumulation of liver triglycerides was associated with reduced expression of mtGPAT. At this time, oxygen consumption with palmitoyl-L: -carnitine was decreased whereas oxidative phosphorylation efficiency (ATP/O) with succinate was enhanced. Hepatic levels of mtDNA were unchanged whatever the time points. This longitudinal study in rats fed a HFD showed that hepatic lipid homeostasis and mitochondrial function can adapt to face the increase in fatty acid availability.

Aldehyde stress and up-regulation of Nrf2-mediated antioxidant systems accompany functional adaptations in cardiac mitochondria from mice fed n−3 polyunsaturated fatty acids

Diets replete with n-3 PUFAs (polyunsaturated fatty acids) are known to have therapeutic potential for the heart, although a specifically defined duration of the n-3 PUFA diet required to achieve these effects remains unknown, as does their mechanism of action. The present study was undertaken to establish whether adaptations in mitochondrial function and stress tolerance in the heart is evident following short- (3weeks) and long- (14weeks) term dietary intervention of n-3 PUFAs, and to identify novel mechanisms by which these adaptations occur. Mitochondrial respiration [mO2 (mitochondrial O2)], H2O2 emission [mH2O2 (mitochondrial H2O2)] and Ca2+-retention capacity [mCa2+ (mitochondrial Ca2+)] were assessed in mouse hearts following dietary intervention. Mice fed n-3 PUFAs for 14weeks showed significantly lower mH2O2 and greater mCa2+ compared with all other groups. However, no significant differences were observed after 3weeks of the n-3 PUFA diet, or in mice fed on an HFC (high-fat control) diet enriched with vegetable shortening, containing almost no n-3 PUFAs, for 14weeks. Interestingly, expression and activity of key enzymes involved in antioxidant and phase II detoxification pathways, all mediated by Nrf2 (nuclear factor E2-related factor 2), were elevated in hearts from mice fed the n-3 PUFA diet, but not hearts from mice fed the HFC diet, even at 3weeks. This increase in antioxidant systems in hearts from mice fed the n-3 PUFA diet was paralleled by increased levels of 4-hydroxyhexenal protein adducts, an aldehyde formed from peroxidation of n-3 PUFAs. The findings of the present study demonstrate distinct time-dependent effects of n-3 PUFAs on mitochondrial function and antioxidant response systems in the heart. In addition, they are the first to provide direct evidence that non-enzymatic oxidation products of n-3 PUFAs may be driving mitochondrial and redox-mediated adaptations, thereby revealing a novel mechanism for n-3 PUFA action in the heart.

Molecular basis for an attenuated mitochondrial adaptive plasticity in aged skeletal muscle

Our intent was to investigate the mechanisms driving the adaptive potential of subsarcolemmal (SS) and intermyofibrillar (IMF) mitochondria in young (6 mo) and senescent (36 mo) animals in response to a potent stimulus for organelle biogenesis. We employed chronic electrical stimulation (10 Hz, 3 h/day, 7 days) to induce contractile activity of skeletal muscle in 6 and 36 mo F344XBN rats. Subsequent to chronic activity, acute stimulation (1 Hz, 5 min) in situ revealed greater fatigue resistance in both age groups. However, the improvement in endurance was significantly greater in the young, compared to the old animals. Chronic muscle use also augmented SS and IMF mitochondrial volume to a greater extent in young muscle. The molecular basis for the diminished organelle expansion in aged muscle was due, in part, to the collective attenuation of the chronic stimulation-evoked increase in regulatory proteins involved in mediating mitochondrial protein import and biogenesis. Furthermore, adaptations in mitochondrial function were also blunted in old animals. However, chronic contractile activity evoked greater reductions in mitochondrially-mediated proapoptotic signaling in aged muscle. Thus, mitochondrial plasticity is retained in aged animals, however the magnitude of the changes are less compared to young animals due to attenuated molecular processes regulating organelle biogenesis.

The effects of temperature and thermal acclimation upon the osmotic properties and nonelectrolyte permeability of liver and gill mitochondria from rainbow trout (Salmo gairdneri).

Thermal acclimation of rainbow trout (Salmo gairdneri) taken from 20 degrees C to 7 degrees C resulted in adaptation of mitochondrial function, as evidenced by increases in the specific activities of NADH- and succinate-cytochrome c reductase of 1.93- and 2.7-fold respectively. Mitochondria from both gill and liver obeyed the Boyle-van't Hoff relationship in the range from 400 to 60 mosM. Thermal acclimation had no effect on the osmotic properties of liver mitochondria, whereas gill mitochondria from cold-acclimated trout were more sensitive to osmotic swelling than mitochondria from warm-acclimated individuals. The non-electrolyte permeability of liver mitochondria was assessed by optically monitoring mitochondrial swelling rates in isosmotic solutions of urea, glycerol, mannitol and glucose. Two parameters of mitochondrial swelling were determined: (a) initial swelling rates, d(1/A)dt, and (b) swelling constants, ks, derived from the time required to swell a fixed volume. Regardless of the assay temperature or the permeant employed, liver mitochondria from cold-acclimated trout exhibited greater initial swelling rates than mitochondria from warm-acclimated trout, indicating properties of temperature-compensated permeability. The apparent ranking of nonelectrolyte permeabilities was urea greater than glycerol greater than mannitol greater than glucose. ks values for urea and glycerol from cold-acclimated trout were greater than values typical of warm-acclimated populations; however ks values for glucose and mannitol were not influenced by thermal acclimation. Regardless of the permeant considered, activation energies for ks values were 3- to 5-fold greater than those for initial swelling rates. The time course of mitochondrial swelling consists of two components, an initial rapid swelling phase characterized by a half-life of 3-12 seconds, and a slower swelling phase characterized by a half life of 1-6 minutes. Initial swelling rates, which approximate the rapid swelling component, are considered to be the least ambiguous index of permeability, whereas ks values are more complex and strongly influenced by the slower swelling component.