Mitochondrial Oxidative Enzyme Activity Research Articles

Investigation of mitochondrial oxidative phosforylation enzymes in hematological cancers

It is known that cancerous cells are different from normal cells in their structure and functions. It is aimed to determine whether there is a change in the activities of mitochondrial oxidative phosphorylation (OXPOS) respiratory enzymes, the main energy production site of cells, in various haematological cancers and to use the obtained data for therapeutic purposes. In this study, leukocyte mitochondria were isolated from blood samples obtained from patients with non-hodgkin lymphoma (NHL), hodgkin lemphoma (HL), chronic lymphocytic leukaemia (CLL), acute myelogenic leukaemia (AML), acute lymphocytic leukaemia (ALL), chronic myeloid leukaemia (CML), multiple myeloma and myelodysplastic syndrome (MDS) and controls. The enzyme activities of oxidative phosphorylation complexes I, II and IV were measured by spectrophotometric method. Enzyme activity results were statistically evaluated according to various criteria. Enzyme activities were evaluated according to gender, chemotherapy or not and disease groups. As a result of these statistical evaluations, no correlation was found between the type of haematological cancer and gender (p>0.05). The difference in mitochondrial oxidative complex enzyme activities between patients receiving chemotherapy and those not receiving chemotherapy was insignificant (p>0.05). When the enzyme activities of the control group and all haematological cancer cells studied were compared, the difference was found to be statistically significant (p<0.05). As a result, changes in the activities of OXPOS respiratory enzymes were found in various haematological cancers. The large number of therapies that specifically target mitochondria, the altered metabolic functions and dynamics of mitochondria in cancer cells make it a target for cancer therapeutics.

SIRT3 overexpression in rat muscle does not ameliorate peripheral insulin resistance.

Reduced expression of the NAD+-dependent deacetylase, SIRT3, has been associated with insulin resistance and metabolic dysfunction in humans and rodents. In this study, we investigated whether specific overexpression of SIRT3 in vivo in skeletal muscle could prevent high-fat diet (HFD)-induced muscle insulin resistance. To address this, we used a muscle-specific adeno-associated virus (AAV) to overexpress SIRT3 in rat tibialis and extensor digitorum longus (EDL) muscles. Mitochondrial substrate oxidation, substrate switching and oxidative enzyme activity were assessed in skeletal muscles with and without SIRT3 overexpression. Muscle-specific insulin action was also assessed by hyperinsulinaemic-euglycaemic clamps in rats that underwent a 4-week HFD-feeding protocol. Ex vivo functional assays revealed elevated activity of selected SIRT3-target enzymes including hexokinase, isocitrate dehydrogenase and pyruvate dehydrogenase that was associated with an increase in the ability to switch between fatty acid- and glucose-derived substrates in muscles with SIRT3 overexpression. However, during the clamp, muscles from rats fed an HFD with increased SIRT3 expression displayed equally impaired glucose uptake and insulin-stimulated glycogen synthesis as the contralateral control muscle. Intramuscular triglyceride content was similarly increased in the muscle of high-fat-fed rats, regardless of SIRT3 status. Thus, despite SIRT3 knockout (KO) mouse models indicating many beneficial metabolic roles for SIRT3, our findings show that muscle-specific overexpression of SIRT3 has only minor effects on the acute development of skeletal muscle insulin resistance in high-fat-fed rats.

Impaired fatigue resistance, sarcoplasmic reticulum function, and mitochondrial activity in soleus muscle of db/db mice.

Type 2 diabetes mellitus (T2DM) is characterized by reduced exercise tolerance due to increased fatigability in skeletal muscle. In this study, we investigated muscle fatigue resistance of soleus (SOL) muscle in obese type 2 diabetic model mice (db/db). No differences in muscle volume, absolute force, or specific force in SOL muscle were observed between db/db mice and control mice (db/+), while fatigue resistance evaluated by repeated tetanic contractions was significantly lower in db/db mice (30th tetani, db/+: 63.7 ± 4.7%, db/db: 51.3 ± 4.8%). The protein abundance related to Ca2+ release from the sarcoplasmic reticulum (SR) in SOL muscle was not different between db/db mice and db/+ mice, while SR Ca2+‐ATPase (Ca2+ reuptake to SR) protein was decreased in db/db mice compared to db/+ mice (db/+: 1.00 ± 0.17, db/db: 0.60 ± 0.04, relative units). In addition, mitochondrial oxidative enzyme activity (succinate dehydrogenase) was decreased in the SOL muscle of db/db mice (p < 0.05). These data suggest that fatigue resistance in slow‐twitch dominant muscle is impaired in mice with T2DM. Decreased mitochondrial oxidative enzyme activity and impairment of Ca2+ uptake to SR, or both might be involved in the mechanisms.

Exercise and metformin counteract altered mitochondrial function in the insulin-resistant brain.

Insulin resistance associates with increased risk for cognitive decline and dementia; however, the underpinning mechanisms for this increased risk remain to be fully defined. As insulin resistance impairs mitochondrial oxidative metabolism and increases ROS in skeletal muscle, we considered whether similar events occur in the brain, which - like muscle - is rich in insulin receptors and mitochondria. We show that high-fat diet-induced (HFD-induced) brain insulin resistance in mice decreased mitochondrial ATP production rate and oxidative enzyme activities in brain regions rich in insulin receptors. HFD increased ROS emission and reduced antioxidant enzyme activities, with the concurrent accumulation of oxidatively damaged mitochondrial proteins and increased mitochondrial fission. Improvement of insulin sensitivity by both aerobic exercise and metformin ameliorated HFD-induced abnormalities. Moreover, insulin-induced enhancement of ATP production in primary cortical neurons and astrocytes was counteracted by the insulin receptor antagonist S961, demonstrating a direct effect of insulin resistance on brain mitochondria. Further, intranasal S961 administration prevented exercise-induced improvements in ATP production and ROS emission during HFD, supporting that exercise enhances brain mitochondrial function by improving insulin action. These results support that insulin sensitizing by exercise and metformin restores brain mitochondrial function in insulin-resistant states.

Sirtuin 3 deficiency accelerates Angiotensin II-induced skeletal muscle atrophy

ABSTRACT Background: It has been reported that Angiotensin II (Ang II) induced skeletal muscle atrophy. However, the precise mechanisms remain elusive. Sirtuin 3 (SIRT3), an NAD-dependent deacetylase, plays a central role in maintaining cellular metabolic homeostasis. This work aims to determine the role of SIRT3-mediated cellular metabolism in skeletal muscle wasting. Methods and Results: Eight-week-old male wild-type (WT) and SIRT3 knockout (SIRT3 KO) mice were infused with Ang II or saline for 4 weeks. Ang II induces skeletal muscle atrophy by inducing expression of the muscle-enriched E3 ubiquitin ligase muscle RING-finger-1 (MuRF1) and atrogin-1, accompanied by a reduction in SIRT3 in skeletal muscle. SIRT3 deficiency accelerated Ang II-induced loss of lean mass and protein hyper-acetylation, while the activities of mitochondrial oxidative enzymes, such as complex I and complex V, were significantly decreased. Furthermore, SIRT3 deficiency accelerated the Ang II-induced shift from slow-twitch towards fast-twitch fibres. Similarly, the three major rate-limiting enzymes in the glycolytic pathway, hexokinase 2 (HK2), phosphofructokinase-1(PFK) and pyruvate kinase (PK), were upregulated in Ang II-treated SIRT3 KO mice. Conclusion: These studies indicate that SIRT3 deficiency augmented Ang II-induced fibre-type shifting and metabolic reprogramming.

Hypertension Editors' Picks Preeclampsia.

Hypertension Editors' Picks Preeclampsia.

Intensified mitophagy in skeletal muscle with aging is downregulated by PGC-1alpha overexpression in vivo

Mitochondrial dysfunction plays an important role in the etiology of age-related muscle atrophy known as sarcopenia. PGC-1α is positioned at the center of crosstalk in regulating mitochondrial quality control, but its role in mitophagy in aged skeletal muscle is currently unclear. The present study investigated the effects of aging and PGC-1α overexpression via in vivo DNA transfection on key mitophagy protein markers, as well as mitochondrial dynamics related proteins, metabolic function and antioxidant capacity in mouse muscle. C57BL/6J mice at the age of 2 mo (young, Y; N = 14) and 24 mo (old, O; N = 14) were transfected in vivo with either PGC-1α DNA (OE, N = 7) or GFP (N = 7) into the tibialis anterior (TA) muscle followed by electroporation. PINK1 and Parkin protein contents were 3.6 and 1.4-fold higher (P < 0.01), whereas mitochondrial ubiquitination (Ub) increased 1.5-fold (P < 0.05), in O vs. Y mice. PGC-1 OE suppressed PINK and Parkin protein levels by 50–60% (P < 0.01), and decreased Ub by 20% (P < 0.05) in old mice. Aging significantly increased the protein content of LC3II (30%, P < 0.05), p62 (42%, P < 0.05), RheB (5.5-fold, P < 0.01), Beclin-1 (3-fold, P < 0.01) and Mfn2 (~4-fold, P < 0.01) in the TA muscle. However, these age-related increases in mitophagy markers were attenuated by PGC-1α OE. Furthermore, aging dramatically increased Fis-1 protein content by 14-fold (P < 0.01), along with a severe reduction of citrate synthase activity (64%, P < 0.01) and cytochrome c oxidase subunit IV (COXIV) protein content (85%, P < 0.01). PGC-1α OE mitigated the age effects on Fis-1 and Drp-1 (P < 0.05). Moreover, PGC-1α OE enhanced mitochondrial oxidative function and antioxidant enzyme activities, and decreased lipid peroxidation and inner membrane damage found in old mice (P < 0.01). In summary, our data demonstrate that mitophagy protein expression in skeletal muscle was enhanced at old age driven possibly by increased mitochondrial dysfunction, damage, and fission. PGC-1α OE was effective in ameliorating mitochondrial deficits but did not restore muscle fiber atrophy.

Role of Mitochondrial Dysfunction and Reactive Oxygen Species in Mediating Hypertension in the Reduced Uterine Perfusion Pressure Rat Model of Preeclampsia.

Placental ischemia is believed to be the initial event in the development of preeclampsia. Mitochondrial dysfunction is a cause of reactive oxygen species (ROS) generation and oxidative stress, however, there are not many studies examining the role of mitochondrial ROS in the pathology of preeclampsia. The purpose of this study was to not only examine the effect of placental ischemia on mitochondrial-mediated oxidative stress in reduced uterine perfusion pressure (RUPP) rat model of preeclampsia but to also examine the role of mitochondrial ROS in contributing to hypertension in response to placental ischemia. Female pregnant Sprague Dawley rats were used in this study. On gestational day 14, RUPP surgery was performed. On gestational day 19, blood pressure (mean arterial pressure) was measured, placentas and kidneys were collected from normal pregnant and RUPP rats and processed for mitochondrial respiration, ROS, and oxidative phosphorylation enzyme activities. Renal and placental complex activities, expressions and respiration rates were significantly reduced and mitochondrial ROS was increased in RUPP versus normal pregnant mitochondria. Mean arterial pressure was elevated in RUPP (n=6) compared with normal pregnant rats (n=5; 126±4 versus 103±4 mm Hg; P<0.05) and treatment with mitochondrial-specific antioxidants (MitoQ/MitoTEMPO) significantly reduced mean arterial pressure in RUPPs (n=5-10). Mitochondrial ROS was significantly elevated in endothelial cells incubated with RUPP serum compared from with normal pregnant rats, whereas serum from mito antioxidant-treated RUPP rats attenuated this response. Impaired mitochondrial function and vascular, placental, and renal mitochondrial ROS play an important role in hypertension and reduced fetal weight in response to placental ischemia during pregnancy.

Deficiency of PKD2L1 (TRPP3) Exacerbates Pathological Cardiac Hypertrophy by Augmenting NCX1-Mediated Mitochondrial Calcium Overload

High salt intake is one independent risk factor for cardiac hypertrophy. Polycystic kidney disease 2-like 1 (PKD2L1, also called TRPP3) acts as a sour sensor in taste cells, and its possible role in the cardiovascular system is unknown. Here, we report that knockout of PKD2L1 exacerbated high-salt diet (HSD)-induced cardiac hypertrophy and fibrosis, accompanied by cardiac dysfunction and reduced cardiac mitochondrial oxidative phosphorylation and enzyme activity. Furthermore, knockdown of PKD2L1 led to more serious mitochondrial Ca2+ overload and reduced Ca2+ uptake in cardiomyocytes onhigh salt loading. Mechanistically, PKD2L1 deficiency increased p300-mediated acetylation of histone 3 lysine 27 on the promoter of sodium/calcium exchange 1 (NCX1) by repressing AMP-activated protein kinase (AMPK) activity, resulting in NCX1 overexpression and mitochondrial Ca2+ overload. These results reveal an inhibitory effect ofPKD2L1 on cardiac hypertrophy and provide amechanistic insight into the link between mitochondrial Ca2+ homeostasis and cardiac hypertrophy.

Obesity-induced discrepancy between contractile and metabolic phenotypes in slow- and fast-twitch skeletal muscles of female obese Zucker rats.

A clear picture of skeletal muscle adaptations to obesity and related comorbidities remains elusive. This study describes fiber-type characteristics (size, proportions, and oxidative enzyme activity) in two typical hindlimb muscles with opposite structure and function in an animal model of genetic obesity. Lesser fiber diameter, fiber-type composition, and histochemical succinic dehydrogenase activity (an oxidative marker) of muscle fiber types were assessed in slow (soleus)- and fast (tibialis cranialis)-twitch muscles of obese Zucker rats and compared with age (16 wk)- and sex (females)-matched lean Zucker rats (n = 16/group). Muscle mass and lesser fiber diameter were lower in both muscle types of obese compared with lean animals even though body weights were increased in the obese cohort. A faster fiber-type phenotype also occurred in slow- and fast-twitch muscles of obese rats compared with lean rats. These adaptations were accompanied by a significant increment in histochemical succinic dehydrogenase activity of slow-twitch fibers in the soleus muscle and fast-twitch fiber types in the tibialis cranialis muscle. Obesity significantly increased plasma levels of proinflammatory cytokines but did not significantly affect protein levels of peroxisome proliferator-activated receptors PPARγ or PGC1α in either muscle. These data demonstrate that, in female Zucker rats, obesity induces a reduction of muscle mass in which skeletal muscles show a diminished fiber size and a faster and more oxidative phenotype. It was noteworthy that this discrepancy in muscle's contractile and metabolic features was of comparable nature and extent in muscles with different fiber-type composition and antagonist functions.NEW & NOTEWORTHY This study demonstrates a discrepancy between morphological (reduced muscle mass), contractile (shift toward a faster phenotype), and metabolic (increased mitochondrial oxidative enzyme activity) characteristics in skeletal muscles of female Zucker fatty rats. It is noteworthy that this inconsistency was comparable (in nature and extent) in muscles with different structure and function.

New amino acid-Schiff base derived from s-allyl cysteine and methionine alleviates carbon tetrachloride-induced liver dysfunction

In spite of the tremendous stride in modern medicine, conventional drugs used in the hepatotoxic management are mostly inadequate. The present study aims in the synthesis of novel Schiff base compound derived using s-allyl cystiene and methionine. The newly synthesized compound, 2-((2-((2-(allylthio)-1-carboxyethyl)imino)ethylidene)amino)-4-(methylthio)butanoic acid (ACEMB) was characterized using UV–visible spectrophotometer, FTIR, 1HNMR, and GC-MS. ACEMB showed potent in vitro antioxidant property. Chronic administration of ACEMB prior to CCl4 intoxication: i) attenuated the leakage of liver injury markers, such as, enzymes (AST, ALT, GGT, ALP and LDH) and biomolecules (bilirubin) into the blood circulation; ii) normalized the concentration of total proteins, albumin and globulin to control level; and iii) protected the liver against dyslipidemia. These effects of ACEMB show the preservation of endoplasmic reticulum function against CCl4 toxicity in the liver. The protective effect of ACEMB was due to its antioxidant property, which was revealed by reduced oxidative stress (TBARS and HP) and enhanced functions of the endogenous antioxidative system (SOD, catalase, GPx, GST, GSH, vitamin E and C) against CCl4 intoxication. Also, ACEMB protected the functional activities of the various mitochondrial tricarboxylic acid cycle and oxidative phosphorylation enzymes. The biochemical alterations are in concurrence with the histological observations, wherein ACEMB pretreatment prevented the vacuolation, degeneration of nuclei and necrosis of hepatocytes. In addition, in silico analysis reveals the interaction of ACEMB in the active site of cytochrome P450. ACEMB mediates hepatoprotective effect by substituting itself as an antioxidant and decreasing oxidative stress, thereby diminishing the intracellular organelle dysfunction against CCl4 toxicity in the liver.

Long-term, but not short-term high-fat diet induces fiber composition changes and impaired contractile force in mouse fast-twitch skeletal muscle.

In this study, we investigated the effects of a short‐term and long‐term high‐fat diet (HFD) on morphological and functional features of fast‐twitch skeletal muscle. Male C57BL/6J mice were fed a HFD (60% fat) for 4 weeks (4‐week HFD) or 12 weeks (12‐week HFD). Subsequently, the fast‐twitch extensor digitorum longus muscle was isolated, and the composition of muscle fiber type, expression levels of proteins involved in muscle contraction, and force production on electrical stimulation were analyzed. The 12‐week HFD, but not the 4‐week HFD, resulted in a decreased muscle tetanic force on 100 Hz stimulation compared with control (5.1 ± 1.4 N/g in the 12‐week HFD vs. 7.5 ± 1.7 N/g in the control group; P < 0.05), whereas muscle weight and cross‐sectional area were not altered after both HFD protocols. Morphological analysis indicated that the percentage of type IIx myosin heavy chain fibers, mitochondrial oxidative enzyme activity, and intramyocellular lipid levels increased in the 12‐week HFD group, but not in the 4‐week HFD group, compared with controls (P < 0.05). No changes in the expression levels of calcium handling‐related proteins and myofibrillar proteins (myosin heavy chain and actin) were detected in the HFD models, whereas fast‐troponin T‐protein expression was decreased in the 12‐week HFD group, but not in the 4‐week HFD group (P < 0.05). These findings indicate that a long‐term HFD, but not a short‐term HFD, impairs contractile force in fast‐twitch muscle fibers. Given that skeletal muscle strength largely depends on muscle fiber type, the impaired muscle contractile force by a HFD might result from morphological changes of fiber type composition.

Sarcopenia, age, atrophy, and myopathy: Mitochondrial oxidative enzyme activities.

We studied mitochondrial impairment as a factor in the pathologic equivalent of sarcopenia, muscle fiber atrophy associated with increased age. Mitochondrial oxidative enzyme activities and coenzyme Q10 levels were measured in frozen human proximal limb muscles with combined age and atrophy, age alone, atrophy alone, denervation, immune myopathies, and mitochondrial disorders with ophthalmoplegia. Sarcopenia (age and atrophy) had reduced mean activities of mitochondrial Complexes I, II, and II+III, with severe reduction of Complex I activity in 54% of patients. Atrophy, and specific denervation atrophy, had similar patterns of changes. Age alone had moderately reduced Complex I activity. Mitochondrial myopathies had mildly lower Complex IV activity. Immune myopathies had unchanged enzyme activities. Mitochondrial oxidative enzyme activities, especially Complex I, but also Complexes II and II+III, are reduced in muscles with the pathologic equivalent of sarcopenia. Individually, atrophy and age have different patterns of oxidative enzyme changes. Muscle Nerve 56: 122-128, 2017.

PGC-1α overexpression via local transfection attenuates mitophagy pathway in muscle disuse atrophy

Loss of mitochondrial structural and functional integrity plays a critical role in the pathogenesis of muscle disuse atrophy. Peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α) has been suggested to modulate autophagy–lysosome pathway (mitophagy) during muscle atrophy, but clear evidence is still lacking. In the current study, we tested the hypothesis that overexpression of PGC-1α via in vivo transfection would ameliorate mitophagy in mouse tibialis anterior muscle subjected to two weeks of immobilization (IM), followed by remobilization (RM). While mitochondrial biogenesis and antioxidant enzymes are decreased, all autophagic and mitophagic protein markers such as Beclin-1, Bnip3, PINK1, parkin, Mul1 and the LC3II/LC3I ratio were increased in IM–RM muscle together with activation of FoxO pathway. Overexpression of PGC-1α significantly increased mitochondrial DNA proliferation and oxidative enzyme activity, whereas it mitigated oxidative stress and mitochondrial ubiquination in IM–RM muscle. Protein contents of PINK1, parkin and Mul1 in mitochondria decreased by approximately 50% with PGC-1α treatment. Furthermore, PGC-1α overexpression suppressed FoxO1 and FoxO3 activation along with a decreased LC3II/LC3I ratio. Importantly, PGC-1α attenuated IM–RM-induced ubiquination and degradation of mitofusion protein Mfn2. Muscle apoptotic tendency, measured by Bax/Bcl2 ratio and caspase-3 activity, were elevated with IM–RM, but unaffected by PGC-1α. We conclude that overexpression of PGC-1α by in vivo transfection can inhibit activation of mitophagy pathway in the atrophying muscle caused by immobilization.

Mitochondrial protein synthesis is increased in oxidative skeletal muscles of rats with cardiac cachexia

Since cardiac cachexia could be associated with alterations in muscular mitochondrial metabolism, we hypothesized that the expected alterations in the activities of mitochondrial oxidative enzymes could be associated with changes in mitochondrial protein synthesis in oxidative skeletal muscles. Cardiac cachexia was provoked in male rats by the ligation of the left coronary artery. Six cachectic and 6 control rats were age-paired, and their food intake was observed. The synthesis of mitochondrial proteins was measured by [1-13C]-valine infusion in soleus, tibilais, myocardium, and liver. Muscles (soleus, gastrocnemius, and tibialis anterior), heart, kidneys, liver, and visceral adipose tissue were weighed. Mitochondrial cytochrome c oxydase IV as well as citrate synthase and myosin ATPase activities were measured. As expected, decreased food intake was observed in the cachectic group. Heart, kidney, and liver weights were higher in the cachectic group, while the visceral adipose tissue weight was lower (P < .01). No changes in muscle weights were observed. Soleus mitochondrial proteins fractional synthesis rate was higher in the cachectic group (P = .054). Cytochrome c oxydase IV activity was reduced (P = .009) and increased (P = .038) in the soleus and liver of the cachectic rats, respectively. No change in citrate synthase activity was observed. Myosin ATPase activity was reduced in the gastrocnemius of the cachectic group (P < .01). Mitochondrial protein synthesis is increased in the soleus of rats with cardiac cachexia, suggesting a compensatory mechanism of the impaired oxidative mitochondrial function. Further work should assess whether the mitochondrial protein synthesis is altered in chronic heart failure patients with cardiac cachexia, and whether this is the cause or the consequence of cachexia.

A review of the multi-level adaptations for maximizing aerobic dive duration in marine mammals: from biochemistry to behavior

Marine mammals exhibit multi-level adaptations, from cellular biochemistry to behavior, that maximize aerobic dive duration. A dive response during aerobic dives enables the efficient use of blood and muscle oxygen stores, but it is exercise modulated to maximize the aerobic dive limit at different levels of exertion. Blood volume and concentrations of blood hemoglobin and muscle myoglobin are elevated and serve as a significant oxygen store that increases aerobic dive duration. However, myoglobin is not homogeneously distributed in the locomotory muscles and is highest in areas that produce greater force and consume more oxygen during aerobic swimming. Muscle fibers are primarily fast and slow twitch oxidative with elevated mitochondrial volume densities and enhanced oxidative enzyme activities that are highest in areas that produce more force generation. Most of the muscle mitochondria are interfibriller and homogeneously distributed. This reduces the diffusion distance between mitochondria and helps maintain aerobic metabolism under hypoxic conditions. Mitochondrial volume densities and oxidative enzyme activities are also elevated in certain organs such as liver, kidneys, and stomach. Hepatic and renal function along with digestion and assimilation continue during aerobic dives to maintain physiological homeostasis. Most ATP production comes from aerobic fat metabolism in carnivorous marine mammals. Glucose is derived mostly from gluconeogenesis and is conserved for tissues such as red blood cells and the central nervous system. Marine mammals minimize the energetic cost of swimming and diving through body streamlining, efficient, lift-based propulsive appendages, and cost-efficient modes of locomotion that reduce drag and take advantage of changes in buoyancy with depth. Most dives are within the animal's aerobic dive limit, which maximizes time underwater and minimizes recovery time at the surface. The result of these adaptations is increased breath-hold duration and enhanced foraging ability that maximizes energy intake and minimizes energy output while making aerobic dives to depth. These adaptations are the long, evolutionary legacy of an aquatic lifestyle that directly affects the fitness of marine mammal species for different diving abilities and environments.

In vivo imaging of intracellular Ca2+ after muscle contractions and direct Ca2+ injection in rat skeletal muscle in diabetes

The effects of muscle contractions on the profile of postcontraction resting intracellular Ca2+ ([Ca2+]i) accumulation in Type 1 diabetes are unclear. We tested the hypothesis that, following repeated bouts of muscle contractions, the rise in resting [Ca2+]i evident in healthy rats would be increased in diabetic rats and that these changes would be associated with a decreased cytoplasmic Ca2+ -buffering capacity. Adult male Wistar rats were divided randomly into diabetic (DIA; streptozotocin, ip) and healthy control (CONT) groups. Four weeks later, animals were anesthetized and spinotrapezius muscle contractions (10 sets of 50 contractions) were elicited by electrical stimulation (100 Hz). Ca2+ imaging was achieved using Fura-2 AM in the spinotrapezius muscle in vivo (i.e., circulation intact). The ratio (340/380 nm) was determined from fluorescence images following each set of contractions for estimation of [Ca2+]i. Also, muscle Ca2+ buffering was studied in individual myocytes microinjected with 2 mM Ca2+ solution. After muscle contractions, resting [Ca2+]i in DIA increased earlier and more rapidly than in CONT (P < 0.05 vs. precontraction). Peak [Ca2+]i in response to the Ca2+ injection was significantly higher in CONT (25.8 ± 6.0% above baseline) than DIA (10.2 ± 1.1% above baseline). Subsequently, CONT [Ca(2+)]i decreased rapidly (<15 s) to plateau 9-10% above baseline, whereas DIA remained elevated throughout the 60-s measurement window. No differences in SERCA1 and SERCA2 (Ca2+ uptake) protein levels were evident between CONT and DIA, whereas ryanodine receptor (Ca2+ release) protein level and mitochondrial oxidative enzyme activity (succinate dehydrogenase) were decreased in DIA (P < 0.05). In conclusion, diabetes impairs resting [Ca2+]i homeostasis following muscle contractions. Markedly different responses to Ca2+ injection in DIA vs. CONT suggest fundamentally deranged Ca2+ handling.

High fat intake with monounsaturated fatty acids, but not n6 polyunsaturated fatty acid, increases activity of key mitochondrial oxidative enzymes in the heart

Evidence suggests that a high fat intake may be beneficial for cardiovascular health, though optimal dietary fatty acid composition is unclear. In this study, we compare the effects of a standard low fat diet (STD, 15% energy from fat) to high fat diets (40% energy from fat) comprised of monounsaturated fat (MUFA, oleate (18:1)), n6 polyunsaturated fat (PUFA, linoleic acid (18:2n6)), or saturated fat (SAT, palmitate and stearate (16:0 and 18:0)). Male rats (n=13–14/group) were fed the STD diet until 16 weeks of age and then assigned to dietary treatment for 15 weeks. Cardiac function was assessed by echocardiography and left ventricle (LV) pressure measurements and was unaffected by diet. Mitochondria were isolated from the LV and show no impact of dietary treatment on mitochondrial yield or respiration with lipid and nonlipid substrates. Mitochondrial oxidative enzyme activity in whole tissue dramatically increased with MUFA compared to STD. Citrate synthase activity increased from 105±15 μmol/g/min in STD to 157±14 in MUFA (P&lt;0.05 vs STD and PUFA), with no significant effect in PUFA (107±9) or SAT (130±11). Similar changes occurred with aconitase and long chain acyl‐CoA dehydrogenase activities. In summary, a high fat diet did not adversely impact cardiac function, increased activity of mitochondrial oxidative enzymes of the TCA cycle and fatty acid oxidation, and did not affect mitochondrial function.

Seasonal upregulation of catabolic enzymes and fatty acid transporters in the flight muscle of migrating hoary bats, Lasiurus cinereus

The high energy density of fat, and limited capacity for carbohydrate storage suggest that migrating bats should fuel endurance flights with fat, as observed in migrating birds. Yet, cursorial mammals are unable to support high intensity exercise with fat stores. We hypothesized that migratory bats and birds have converged on similar physiological mechanisms to fuel endurance flight with fat. We predicted bats would seasonally upregulate fatty acid transport and oxidation pathways when migration demands were high. We studied seasonal variation in mitochondrial oxidative enzyme activities and fatty acid transport protein expression in the flight muscle of hoary bats (Lasiurus cinereus). Carnitine palmitoyl transferase, 3-hydroxyacyl-CoA dehydrogenase and citrate synthase activity increased during migration. There were no changes in expression of fatty acid translocase or plasma membrane fatty acid binding protein. Heart-type fatty acid binding protein expression increased 5-fold in migrating females, but did not vary seasonally in males. An aerial insectivore lifestyle, and the coincidence of migration and pregnancy may explain differences in transporter expression compared to previously studied birds. Overall, our results are consistent with seasonal upregulation of lipid metabolism and aerobic capacity, and confirm that migration poses distinct physiological challenges for bats.

Skeletal muscle mitochondrial dysfunction during chronic obstructive pulmonary disease: central actor and therapeutic target

Muscle dysfunction is a common complication and an important prognostic factor in chronic obstructive pulmonary disease (COPD). As therapeutic strategies are still needed to treat this complication, gaining more insight into the process that leads to skeletal muscle decline in COPD appears to be an important issue. This review focuses on mitochondrial involvement in limb skeletal muscle alterations (decreased muscle mass, strength, endurance and power and increased fatigue) in COPD. Mitochondria are the main source of energy for the cells; they are involved in production of reactive oxygen species and activate an important pathway that leads to apoptosis. In COPD patients, skeletal muscles are characterized by decreased mitochondrial density and biogenesis, impaired activity and coupling of mitochondrial respiratory chain complexes, increased mitochondrial production of reactive oxygen species and, possibly, increased apoptosis. Of particular interest, a sedentary lifestyle, hypoxia, hypercapnia, tobacco smoking, corticosteroid therapy and, possibly, inflammation participate in this mitochondrial dysfunction, which is accessible to conventional therapies, such as exercise and tobacco cessation, as well as, potentially, to more innovative approaches, such as antioxidant treatment and supplementation with polyunsaturated fatty acids.