Altered expression of mitochondrial electron transport chain proteins and improved myocardial energetic state during late ischemic preconditioning

Comparative Serum Proteome Analysis Indicates a Negative Correlation between a Higher Immune Level and Feed Efficiency in Pigs

Identifying and verifying appropriate biomarkers is instrumental in improving the prediction of early-stage pig production performance while reducing the cost of breeding and production. The main factor that affects the production cost and environmental protection cost of the pig industry is the feed efficiency of pigs. This study aimed to detect the differentially expressed proteins in the early blood index determination serum between high-feed efficiency and low-feed efficiency pigs and to provide a basis for further identification of biomarkers using the isobaric tandem mass tag and parallel reaction monitoring approach. In total, 350 (age, 90 ± 2 d; body weight, 41.20 ± 4.60 kg) purebred Yorkshire pigs were included in the study, and their serum samples were obtained during the early blood index determination. The pigs were then arranged based on their feed efficiency; 24 pigs with extreme phenotypes were grouped as high-feed efficiency and low-feed efficiency, with 12 pigs in each group. A total of 1364 proteins were found in the serum, and 137 of them showed differential expression between the groups with high- and low-feed efficiency, with 44 of them being upregulated and 93 being downregulated. PRM (parallel reaction monitoring) was used to verify 10 randomly chosen differentially expressed proteins. The proteins that were differentially expressed were shown to be involved in nine pathways, including the immune system, digestive system, human diseases, metabolism, cellular processing, and genetic information processing, according to the KEGG and GO analyses. Moreover, all of the proteins enriched in the immune system were downregulated in the high-feed efficiency pigs, suggesting that a higher immune level may not be conducive to improving feed efficiency in pigs. This study provides insights into the important feed efficiency proteins and pathways in pigs, promoting the further development of protein biomarkers for predicting and improving porcine feed efficiency.

Importance of Mitochondria in Cardiac Pathologies: Focus on Uncoupling Proteins and Monoamine Oxidases

On the one hand, reactive oxygen species (ROS) are involved in the onset and progression of a wide array of diseases. On the other hand, these are a part of signaling pathways related to cell metabolism, growth and survival. While ROS are produced at various cellular sites, in cardiomyocytes the largest amount of ROS is generated by mitochondria. Apart from the electron transport chain and various other proteins, uncoupling protein (UCP) and monoamine oxidases (MAO) have been proposed to modify mitochondrial ROS formation. Here, we review the recent information on UCP and MAO in cardiac injuries induced by ischemia-reperfusion (I/R) as well as protection from I/R and heart failure secondary to I/R injury or pressure overload. The current data in the literature suggest that I/R will preferentially upregulate UCP2 in cardiac tissue but not UCP3. Studies addressing the consequences of such induction are currently inconclusive because the precise function of UCP2 in cardiac tissue is not well understood, and tissue- and species-specific aspects complicate the situation. In general, UCP2 may reduce oxidative stress by mild uncoupling and both UCP2 and UCP3 affect substrate utilization in cardiac tissue, thereby modifying post-ischemic remodeling. MAOs are important for the physiological regulation of substrate concentrations. Upon increased expression and or activity of MAOs, however, the increased production of ROS and reactive aldehydes contribute to cardiac alterations such as hypertrophy, inflammation, irreversible cardiomyocyte injury, and failure.

Uncoupling Proteins in Striated Muscle Tissue: Known Facts and Open Questions

Significance: Uncoupling proteins (UCPs) are a family of proteins that allow proton leakage across the inner mitochondrial membrane. Although UCP1, also known as thermogenin, is well known and important for heat generation in brown adipose tissue, striated muscles express two distinct members of UCP, namely UCP2 and UCP3. Unlike UCP1, the main function of UCP2 and UCP3 does not appear to be heat production. Recent Advances: Interestingly, UCP2 is the main isoform expressed in cardiac tissues, whereas UCP3 is the dominant isoform in skeletal muscles. In the past years, researchers have started to investigate the regulation of UCP2 and UCP3 expression in striated muscles. Furthermore, concepts about the proposed functions of UCP2 and UCP3 in striated muscles are developed but are still a matter of debate. Critical Issues: Potential functions of UCP2 and UCP3 in striated muscles include a role in protection against mitochondria-dependent oxidative stress, as transporter for pyruvate, fatty acids, and protons into and out of the mitochondria, and in metabolic sensing. In this context, the different isoform expression of UCP2 and UCP3 in the skeletal and cardiac muscle may be related to different metabolic requirements of the two organs. Future Directions: The level of expression of UCP2 and UCP3 in striated muscles changes in different disease stages. This suggests that UCPs may become drug targets for therapy in the future. Antioxid. Redox Signal. 37, 324-335.

Downregulation of Uncoupling Protein 2(UCP2) Mediated by MicroRNA-762 Confers Cardioprotection and Participates in the Regulation of Dynamic Mitochondrial Homeostasis of Dynamin Related Protein1 (DRP1) After Myocardial Infarction in Mice

Acute myocardial infarction (MI) is one of the leading causes of death in the world, and its pathophysiological mechanisms have not been fully elucidated. The purpose of this study was to investigate the role and mechanism of uncoupling protein 2 (UCP2) after MI in mouse heart. Here, we examined the expression and role of UCP2 in mouse heart 4 weeks after MI. The expression of UCP2 was detected by RT-PCR and western blotting. Cardiac function, myocardial fibrosis, and cardiomyocyte apoptosis were assessed by echocardiography and immunohistochemistry. Phosphatase dynamin-related protein1 (P-DRP1) and myocardial fibrosis-related proteins were measured. Cardiomyocytes were exposed to hypoxia for 6 h to mimic the model of MI. Mdivi, an inhibitor of P-DRP1, was used to inhibit DRP1-dependent mitochondrial fission. Mitochondrial superoxide, membrane potential, oxygen consumption rate, and cardiomyocyte apoptosis were detected after hypoxia. It is shown mitochondrial superoxide, membrane potential, oxygen consumption rate, and cardiomyocyte apoptosis were dependent on the level of P-DRP1. UCP2 overexpression reduced cardiomyocyte apoptosis (fibrosis), improved cardiac function and inhibit the phosphorylation of DRP1 and the ratio of P-DRP1/DRP1. However, inhibition of DRP1 by mdivi did not further reduce cell apoptosis rate and cardiac function in UCP2 overexpression group. In addition, bioinformatics analysis, luciferase activity, and western blot assay proved UCP2 was a direct target gene of microRNA-762, a up-regulated microRNA after MI. In conclusion, UCP2 plays a protective role after MI and the mechanism is involved in microRNA-762 upstream and DRP1-dependent mitochondrial fission downstream.

Intracellular ATP Concentration and Implication for Cellular Evolution

Crystalline lens and striated muscle exist at opposite ends of the metabolic spectrum. Lens is a metabolically quiescent tissue, whereas striated muscle is a mechanically dynamic tissue with high-energy requirements, yet both tissues contain millimolar levels of ATP (>2.3 mM), far exceeding their underlying metabolic needs. We explored intracellular concentrations of ATP across multiple cells, tissues, species, and domains to provide context for interpreting lens/striated muscle data. Our database revealed that high intracellular ATP concentrations are ubiquitous across diverse life forms including species existing from the Precambrian Era, suggesting an ancient highly conserved role for ATP, independent of its widely accepted view as primarily "metabolic currency". Our findings reinforce suggestions that the primordial function of ATP was non-metabolic in nature, serving instead to prevent protein aggregation.

Ischemic Preconditioning: Improved Cycling Performance Despite Nocebo Expectation

PURPOSE

Ischemic preconditioning (IPC) through purposeful circulatory occlusion may enhance exercise performance. The value of IPC for improving performance is controversial owing to challenges with employing effective placebo controls. This study examines the efficacy of IPC versus a deceptive sham protocol for improving performance to determine whether benefits of IPC are attributable to true physiological effects. It was hypothesized that IPC would favorably alter performance more than a sham treatment and that physiological responses to exercise would be affected only after IPC treatment.

METHODS

In a randomized order, 16 participants performed incremental exercise to exhaustion on a cycle ergometer in control conditions and after sham and IPC treatments. Participants rated their belief as to the efficacy of each treatment compared with control.

RESULTS

Time to exhaustion was greatest after IPC (control = 1331 [270] s, IPC = 1429 [300] s, sham = 1343 [255] s, P = .02), despite negative performance expectations after IPC and positive expectation after sham. Maximal aerobic power remained unchanged after both SHAM and IPC (control = 42.0 [5.2], IPC = 41.7 [5.5], sham = 41.6 [5.5] mL·kg-1·min-1, P = .7), as did submaximal lactate concentration (control = 8.9 [2.6], sham = 8.0 [1.9], IPC = 7.7 [2.1] mmol, P = .1) and oxygen uptake (control = 37.8 [4.8], sham = 37.5 [5.3], IPC = 37.5 [5.5] mL·kg-1·min-1, P = .6).

CONCLUSIONS

IPC before cycling exercise provides an ergogenic benefit that is not attributable to a placebo effect from positive expectation and that was not explained by traditionally suggested mechanisms.

Recovery of hibernating myocardium using stem cell patch with coronary bypass surgery

OBJECTIVE

This study aims to investigate the utility of mesenchymal stem cells (MSCs) applied as an epicardial patch during coronary artery bypass graft (CABG) to target hibernating myocardium; that is, tissue with persistently decreased myocardial function, in a large animal model.

METHODS

Hibernating myocardium was induced in juvenile swine (n = 12) using a surgically placed constrictor on the left anterior descending artery, causing stenosis without infarction. After 12 weeks, single-vessel CABG was performed using left internal thoracic artery to left anterior descending artery graft. During CABG, an epicardial patch was applied to the hibernating myocardium region consisting either of MSCs grown onto a polyglactin mesh (n = 6), or sham polyglactin mesh without MSCs (n = 6). Four weeks after CABG and patch placement, cardiac magnetic resonance imaging was performed and cardiac tissue was examined by gross inspection, including coronary dilators for vessel stenosis and patency, electron microscopy, protein assays, and proteomic analysis.

RESULTS

CABG + MSC myocardium showed improvement in contractile function (78.24% ± 19.6%) compared with sham patch (39.17% ± 5.57%) during inotropic stimulation (P < .05). Compared with sham patch control, electron microscopy of CABG + MSC myocardium showed improvement in mitochondrial size, number, and morphology; protein analysis similarly showed increases in expression of the mitochondrial biogenesis marker peroxisome proliferator-activated receptor gamma coactivator 1-alpha (0.0022 ± 0.0009 vs 0.023 ± 0.009) (P < .01) along with key components of the electron transport chain, including succinate dehydrogenase (complex II) (0.06 ± 0.02 vs 0.14 ± 0.03) (P < .05) and adenosine triphosphate synthase (complex V) (2.7 ± 0.4 vs 4.2 ± 0.26) (P < .05).

CONCLUSIONS

In hibernating myocardium, placement of a stem cell patch during CABG shows promise in improving myocardial function by improving mitochondrial morphology and function.

CoQ10 enhances PGC1α and increases expression of mitochondrial antioxidant proteins in chronically ischemic swine myocardium

Background

Expression of mitochondrial proteins is reduced within hibernating myocardium (HM). It is unclear whether dietary supplementation with CoQ₁₀ can increase expression of mitochondrial electron transport chain (ETC) and antioxidant proteins within this tissue. In a swine model of HM, we tested whether dietary administration of CoQ₁₀ for four weeks enhances the expression of ETC and antioxidant proteins within the mitochondria via increased PGC1α signaling.

Methods

12 swine were instrumented with a fixed constrictor around the LAD artery to induce gradual stenosis. At three months, transthoracic ECHO was performed to confirm the presence of a wall motion abnormality in the anterior wall. Animals were then randomly assigned to receive daily dietary supplements of either CoQ₁₀ (10 mg/kg/day) or placebo for four weeks. At this time, animals underwent a final ECHO and terminal procedure. Expression of nuclear-bound PGC1α (Western blots) and mitochondrial proteins (Tandem Mass Tag) were determined.

Results

Mitochondrial and nuclear membranes were isolated from the LAD region. Nuclear-bound PGC1α levels were > 200-fold higher with administration of four weeks of CoQ₁₀ treatment (p = 0.016). Expression of ETC proteins was increased in those animals that received CoQ₁₀. Compared with mitochondria in the LAD region from placebo-treated pigs, CoQ₁₀-treated pigs had higher levels of Complex I (p = 0.03), Complex IV (p = 0.04) and Complex V (p = 0.028) peptides.

Conclusions

Four weeks of dietary CoQ₁₀ in HM pigs enhances active, nuclear-bound PGC1α and increases the expression of ETC proteins within mitochondria of HM tissue.

Proteomic analysis of the response of porcine adrenal gland to heat stress

Heat stress (HS) and its associated pathologies are major challenges facing the pig industry in southern China, and are responsible for large economic losses. However, the molecular mechanisms governing the abnormal secretion of HS-responsive hormones, such as glucocorticoids, are not fully understood. The goal of this study was to investigate differentially expressed proteins (DEPs) in the adrenal glands of pigs, and to elucidate changes in the immune neuroendocrine system in pigs following HS. Through a functional proteomics approach, we identified 1202 peptides, corresponding to 415 proteins. Of these, we found 226 DEPs between heat-stressed and control porcine adrenal gland tissue; 99 of these were up-regulated and 127 were down-regulated in response to HS. These DEPs included proteins involved in substrate transport, cytoskeletal changes, and stress responses. Ingenuity Pathway Analysis was used to identify the subcellular characterization, functional pathway involvement, regulatory networks, and upstream regulators of the identified proteins. Functional network and pathway analyses may provide insights into the complexity and dynamics of HS-host interactions, and may accelerate our understanding of the mechanisms of HS.

Effect of Ischemic Preconditioning on the Recovery of Cardiac Autonomic Control From Repeated Sprint Exercise

Repeated sprint exercise (RSE) acutely impairs post-exercise heart rate (HR) recovery (HRR) and time-domain heart rate variability (i. e., RMSSD), likely in part, due to lactic acidosis-induced reduction of cardiac vagal reactivation. In contrast, ischemic preconditioning (IPC) mediates cardiac vagal activation and augments energy metabolism efficiency during prolonged ischemia followed by reperfusion. Therefore, we investigated whether IPC could improve recovery of cardiac autonomic control from RSE partially via improved energy metabolism responses to RSE. Fifteen men team-sport practitioners (mean ± SD: 25 ± 5 years) were randomly exposed to IPC in the legs (3 × 5 min at 220 mmHg) or control (CT; 3 × 5 min at 20 mmHg) 48 h, 24 h, and 35 min before performing 3 sets of 6 shuttle running sprints (15 + 15 m with 180° change of direction and 20 s of active recovery). Sets 1 and 2 were followed by 180 s and set 3 by 360 s of inactive recovery. Short-term HRR was analyzed after all sets via linear regression of HR decay within the first 30 s of recovery (T30) and delta from peak HR to 60 s of recovery (HRR60s). Long-term HRR was analyzed throughout recovery from set 3 via first-order exponential regression of HR decay. Moreover, RMSSD was calculated using 30-s data segments throughout recovery from set 3. Energy metabolism responses were inferred via peak pulmonary oxygen uptake (V˙O2peak), peak carbon dioxide output (V˙O2peak), peak respiratory exchange ratio (RERpeak), first-order exponential regression of V˙O2 decay within 360 s of recovery and blood lactate concentration ([Lac-]). IPC did not change T30, but increased HRR60s after all sets (condition main effect: P = 0.03; partial eta square (η²_p) = 0.27, i.e., large effect size). IPC did not change long-term HRR and RMSSD throughout recovery, nor did IPC change any energy metabolism parameter. In conclusion, IPC accelerated to some extent the short-term recovery, but did not change the long-term recovery of cardiac autonomic control from RSE, and such accelerator effect was not accompanied by any IPC effect on surrogates of energy metabolism responses to RSE.

Uncoupling Protein 2 in Cardiovascular Health and Disease

Uncoupling protein 2 (UCP2) belongs to the family of mitochondrial anion carrier proteins. It uncouples oxygen consumption from ATP synthesis. UCP2 is ubiquitously expressed in most cell types to reduce oxidative stress. It is tightly regulated at the transcriptional, translational, and post-translational levels. UCP2 in the cardiovascular system is being increasingly recognized as an important molecule to defend against various stress signals such as oxidative stress in the pathology of vascular dysfunction, atherosclerosis, hypertension, and cardiac injuries. UCP2 protects against cellular dysfunction through reducing mitochondrial oxidative stress and modulation of mitochondrial function. In view of the different functions of UCP2 in various cell types that contribute to whole body homeostasis, cell type-specific modification of UCP2 expression may offer a better approach to help understanding how UCP2 governs mitochondrial function, reactive oxygen species production and transmembrane proton leak and how dysfunction of UCP2 participates in the development of cardiovascular diseases. This review article provided an update on the physiological regulation of UCP2 in the cardiovascular system, and also discussed the involvement of UCP2 deficiency and associated oxidative stress in the pathogenesis of several common cardiovascular diseases. Drugs targeting UCP2 expression and activity might serve another effective strategy to ameliorate cardiovascular dysfunction. However, more detailed mechanistic study will be needed to dissect the role of UCP2, the regulation of UCP2 expression, and the cellular responses to the changes of UCP2 expression in normal and stressed situations at different stages of cardiovascular diseases.

Study of respiratory chain dysfunction in heart disease

The relentlessly beating heart has the greatest oxygen consumption of any organ in the body at rest reflecting its huge metabolic turnover and energetic demands. The vast majority of its energy is produced and cycled in form of ATP which stems mainly from oxidative phosphorylation occurring at the respiratory chain in the mitochondria. A part from energy production, the respiratory chain is also the main source of reactive oxygen species and plays a pivotal role in the regulation of oxidative stress. Dysfunction of the respiratory chain is therefore found in most common heart conditions. The pathophysiology of mitochondrial respiratory chain dysfunction in hereditary cardiac mitochondrial disease, the aging heart, in LV hypertrophy and heart failure, and in ischaemia-reperfusion injury is reviewed. We introduce the practicing clinician to the complex physiology of the respiratory chain, highlight its impact on common cardiac disorders and review translational pharmacological and non-pharmacological treatment strategies.

A lesson from the oxidative metabolism of hibernator heart: Possible strategy for cardioprotection

In the present study we hypothesized that myocardial adaptive phenotype in mammalian hibernation involves rearrangement of mitochondria bioenergetic pathways providing protective pattern in states of reduced metabolism and low temperature. European ground squirrels (Spermophilus citellus) were exposed to low temperature (4 ± 1 °C) and then divided into two groups: (1) animals that fell into torpor (hibernating group) and (2) animals that stayed active and euthermic for 1, 3, 7, 12, or 21 days (cold-exposed group). Protein levels of selected components of the electron transport chain and ATP synthase in the heart increased after prolonged cold acclimation (mainly from day 7-21 of cold exposure) and during hibernation. Peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) was also upregulated under both cold exposure and hibernating conditions. The phosphorylation state (Thr172) of 5'-AMP-activated protein kinase α increased early in cold exposure (at day 1 and 3) along with increased protein levels of phosphofructokinase and pyruvate dehydrogenase, whereas hypoxia inducible factor 1α protein levels showed no changes in response to cold exposure or hibernation. Hibernation also resulted in protein upregulation of three antioxidant defense enzymes (manganese and copper/zinc superoxide dismutases and glutathione peroxidase) and thioredoxin in the heart. Cold-exposed and hibernation-related phenotypes of the heart are characterized by improved molecular basis for mitochondrial energy-producing and antioxidant capacities that are achieved in a controlled manner. The recapitulation of such adaptive mechanisms found in hibernators could have broad application for myocardial protection from ishemia/reperfusion to improve hypothermic survival and cold preservation of hearts from non-hibernating species, including humans.

Respiratory gas exchange as a new aid to monitor acidosis in endotoxemic rats: relationship to metabolic fuel substrates and thermometabolic responses

This study introduces the respiratory exchange ratio (RER; the ratio of whole‐body CO₂ production to O₂ consumption) as an aid to monitor metabolic acidosis during the early phase of endotoxic shock in unanesthetized, freely moving rats. Two serotypes of lipopolysaccharide (lipopolysaccharide [LPS] O55:B5 and O127:B8) were tested at shock‐inducing doses (0.5–2 mg/kg). Phasic rises in RER were observed consistently across LPS serotypes and doses. The RER rise often exceeded the ceiling of the quotient for oxidative metabolism, and was mirrored by depletion of arterial bicarbonate and decreases in pH. It occurred independently of ventilatory adjustments. These data indicate that the rise in RER results from a nonmetabolic CO₂ load produced via an acid‐induced equilibrium shift in the bicarbonate buffer. Having validated this new experimental aid, we asked whether acidosis was interconnected with the metabolic and thermal responses that accompany endotoxic shock in unanesthetized rats. Contrary to this hypothesis, however, acidosis persisted regardless of whether the ambient temperature favored or prevented downregulation of mitochondrial oxidation and regulated hypothermia. We then asked whether the substrate that fuels aerobic metabolism could be a relevant factor in LPS‐induced acidosis. Food deprivation was employed to divert metabolism away from glucose oxidation and toward fatty acid oxidation. Interestingly, this intervention attenuated the RER response to LPS by 58%, without suppressing other key aspects of systemic inflammation. We conclude that acid production in unanesthetized rats with endotoxic shock results from a phasic activation of glycolysis, which occurs independently of physiological changes in mitochondrial oxidation and body temperature.

Effect of Ischemic Preconditioning on Endurance Performance Does Not Surpass Placebo

PURPOSE

Recent studies have reported ischemic preconditioning (IPC) can acutely improve endurance exercise performance in athletes. However, placebo and nocebo effects have not been sufficiently controlled, and the effect on aerobic metabolism parameters that determine endurance performance (e.g., oxygen cost of running, lactate threshold, and maximal oxygen uptake [V˙O2max]) has been equivocal. Thus, we circumvented limitations from previous studies to test the effect of IPC on aerobic metabolism parameters and endurance performance in well-trained runners.

METHODS

Eighteen runners (14 men/4 women) were submitted to three interventions, in random order: IPC; sham intervention (SHAM); and resting control (CT). Subjects were told both IPC and SHAM would improve performance compared to CT (i.e., similar placebo induction), and IPC would be harmless despite circulatory occlusion sensations (i.e., nocebo avoidance). Next, pulmonary ventilation and gas exchange, blood lactate concentration, and perceived effort were measured during a discontinuous incremental test on a treadmill. Then, a supramaximal test was used to verify the V˙O2max and assess endurance performance (i.e., time to exhaustion).

RESULTS

Ventilation, oxygen uptake, carbon dioxide output, lactate concentration, and perceived effort were similar among IPC, SHAM, and CT throughout the discontinuous incremental test (P > 0.05). Oxygen cost of running, lactate threshold, and V˙O2max were also similar among interventions (P > 0.05). Time to exhaustion was longer after IPC (mean ± SEM, 165.34 ± 12.34 s) and SHAM (164.38 ± 11.71 s) than CT (143.98 ± 12.09 s; P = 0.02 and 0.03, respectively), but similar between IPC and SHAM (P = 1.00).

CONCLUSIONS

IPC did not change aerobic metabolism parameters, whereas improved endurance performance. The IPC improvement, however, did not surpass the effect of a placebo intervention.

Ischemic Preconditioning and Repeated Sprint Swimming: A Placebo and Nocebo Study

PURPOSE

Ischemic preconditioning (IPC) has been shown to improve performance of exercises lasting 10-90 s (anaerobic) and more than 90 s (aerobic). However, its effect on repeated sprint performance has been controversial, placebo effect has not been adequately controlled, and nocebo effect has not been avoided. Thus, the IPC effect on repeated sprint performance was investigated using a swimming task and controlling placebo/nocebo effects.

METHODS

Short-distance university swimmers were randomized to two groups. One group (n = 15, 24 ± 1 yr [mean ± SEM]) was exposed to IPC (ischemia cycles lasted 5 min) and control (CT) (no ischemia); another (n = 15, 24 ± 1 yr) to a placebo intervention (SHAM) (ischemia cycles lasted 1 min) and CT. Seven subjects crossed over groups. Subjects were informed IPC and SHAM would improve performance compared with CT and would be harmless despite circulatory occlusion sensations. The swimming task consisted of six 50-m all-out efforts repeated every 3 min.

RESULTS

IPC, in contrast with SHAM, reduced worst sprint time (IPC, 35.21 ± 0.73 vs CT, 36.53 ± 0.72 s; P = 0.04) and total sprints time (IPC, 203.7 ± 4.60 vs CT, 206.03 ± 4.57 s; P = 0.02), moreover augmented swimming velocity (IPC, 1.45 ± 0.03 vs CT, 1.44 ± 0.03 m·s; P = 0.049). Six of seven subjects who crossed over groups reduced total sprints time with IPC versus SHAM (delta = -3.95 ± 1.49 s, P = 0.09). Both IPC and SHAM did not change blood lactate concentration (P = 0.20) and perceived effort (P = 0.22).

CONCLUSION

IPC enhanced repeated sprint swimming performance in university swimmers, whereas a placebo intervention did not.

Ubiquinol-cytochrome c reductase core protein 1 may be involved in delayed cardioprotection from preconditioning induced by diazoxide

This study aimed to use long-term diazoxide treatment to establish a loss-of-cardioprotection model and then perform proteomics analysis to explore which proteins of mitochondrial inner membrane (MIM) are potentially involved in delayed cardioprotection. Rats received 1 to 8 weeks of diazoxide treatments (20 mg•kg-1•d-1) to establish a loss-of-cardioprotection model in different groups. Detection of serum cTnI levels and cell apoptosis assays in heart tissue were performed. Then, rats MIM after 0, 4 and 6 weeks of diazoxide treatment was isolated and proteomics analysis was performed. An invitro model of H9C2 cells was performed to explore the effects of targeted protein on delayed cardioprotection. The effect of delayed cardioprotection by diazoxide preconditioning disappeared when diazoxide treatments were given for six weeks or longer. Ubiquinol-cytochrome c reductase core protein 1 (UQCRC1) was identified in the proteomics analysis. UQCRC1 expression was upregulated by diazoxide treatment in H9C2 cells, and UQCRC1 down-regulation could increase the lactate dehydrogenase release and apoptosis rate after injury induced by oxygen glucose deprivation. These results showed that UQCRC1 might contribute to the loss-of-cardioprotection model induced by long-term diazoxide treatment and play a role in delayed cardioprotection.

Molecular Bases of Brain Preconditioning

Preconditioning of the brain induces tolerance to the damaging effects of ischemia and prevents cell death in ischemic penumbra. The development of this phenomenon is mediated by mitochondrial adenosine triphosphate-sensitive potassium (KATP+) channels and nitric oxide signaling (NO). The aim of this study was to investigate the dynamics of molecular changes in mitochondria after ischemic preconditioning (IP) and the effect of pharmacological preconditioning (PhP) with the KATP+-channels opener diazoxide on NO levels after ischemic stroke in rats. Immunofluorescence-histochemistry and laser-confocal microscopy were applied to evaluate the cortical expression of electron transport chain enzymes, mitochondrial KATP+-channels, neuronal and inducible NO-synthases, as well as the dynamics of nitrosylation and nitration of proteins in rats during the early and delayed phases of IP. NO cerebral content was studied with electron paramagnetic resonance (EPR) spectroscopy using spin trapping. We found that 24 h after IP in rats, there is a two-fold decrease in expression of mitochondrial KATP+-channels (p = 0.012) in nervous tissue, a comparable increase in expression of cytochrome c oxidase (p = 0.008), and a decrease in intensity of protein S-nitrosylation and nitration (p = 0.0004 and p = 0.001, respectively). PhP led to a 56% reduction of free NO concentration 72 h after ischemic stroke simulation (p = 0.002). We attribute this result to the restructuring of tissue energy metabolism, namely the provision of increased catalytic sites to mitochondria and the increased elimination of NO, which prevents a decrease in cell sensitivity to oxygen during subsequent periods of severe ischemia.

Significance of hydrogen sulfide in sepsis-induced myocardial injury in rats

Sepsis-induced myocardial injury is a detrimental disorder for intensive care medicine due to its high rates of morbidity and mortality. Data suggest that nuclear factor (NF)-κB serves a critical role in the pathogenesis of myocardial injury. Hydrogen sulfide (H₂S) serves an important role in the physiology and pathophysiology of regulatory mechanisms, particularly during an inflammatory reaction. However, the relationship between NF-κB and H₂S in sepsis-induced myocardial injury is not well understood, and the underlying mechanisms remain unclear. In the present study, 60 male Sprague Dawley rats were randomly divided into the following six groups: A sham group, cecal ligation and puncture (CLP) group, sham + propargylglycine (PAG) group, CLP + PAG group, sham + sodium hydrosulfide (NaHS) group and CLP + NaHS group, with 10 rats in each group. The rats in all groups were sacrificed 12 h after surgery for sample collection. Compared with the sham group, it was observed that the concentrations of Creatine Kinase-MB (CK-MB) and cardiac troponin I (cTnI) in the serum, and pathological scores of myocardial tissue were significantly increased in the CLP, CLP + NaHS and CLP + PAG groups (P<0.05). The pathological scores and concentrations of CK-MB and cTnI were significantly higher in the CLP + PAG group (P<0.05) and significantly lower in the CLP + NaHS group (P<0.05) when compared with the CLP group. The expression of cystathionine-γ-lyase (CSE) mRNA and content of interleukin (IL)-10 were significantly higher in the CLP group compared with the CLP + PAG group (P<0.05), while the expression of myocardial NF-κB and content of tumor necrosis factor (TNF)-α in the CLP group were significantly lowered compared with the CLP + PAG group (P<0.05). The expression of NF-κB and content of TNF-α were significantly increased in the CLP group when compared with the CLP + NaHS group (P<0.05), while the content of myocardial IL-10 in the CLP group was significantly lower than in the CLP + NaHS group (P<0.05). In conclusion, H₂S acted as an anti-inflammatory cytokine and biomarker in sepsis-induced myocardial injury. Furthermore, H₂S may downregulate the NF-κB subunit p65 to mediate inflammatory responses. The present data suggest that myocardial injury in sepsis may be relieved through the regulation of H₂S expression, and provide an experimental basis for the treatment of sepsis patients presenting with myocardial injury. In addition, myocardial injury in sepsis may be identified by monitoring changes in the expression of H₂S.

iTRAQ-based proteomic analysis reveals key proteins affecting muscle growth and lipid deposition in pigs

Growth rate and meat quality, two economically important traits in pigs, are controlled by multiple genes and biological pathways. In the present study, we performed a proteomic analysis of longissimus dorsi muscle from six-month-old pigs from two Chinese native mini-type breeds (TP and DSP) and two introduced western breeds (YY and LL) using isobaric tag for relative and absolute quantification (iTRAQ). In total, 4,815 peptides corresponding to 969 proteins were detected. Comparison of expression patterns between TP-DSP and YY-LL revealed 288 differentially expressed proteins (DEPs), of which 169 were up-regulated and 119 were down-regulated. Functional annotation suggested that 28 DEPs were related to muscle growth and 15 to lipid deposition. Protein interaction network predictions indicated that differences in muscle growth and muscle fibre between TP-DSP and YY-LL groups were regulated by ALDOC, ENO3, PGK1, PGK2, TNNT1, TNNT3, TPM1, TPM2, TPM3, MYL3, MYH4, and TNNC2, whereas differences in lipid deposition ability were regulated by LPL, APOA1, APOC3, ACADM, FABP3, ACADVL, ACAA2, ACAT1, HADH, and PECI. Twelve DEPs were analysed using parallel reaction monitoring to confirm the reliability of the iTRAQ analysis. Our findings provide new insights into key proteins involved in muscle growth and lipid deposition in the pig.

Pioglitazone increases PGC1-α signaling within chronically ischemic myocardium

The peroxisome proliferator-activated receptor (PPAR)-γ drug pioglitazone (PIO) has been shown to protect tissue against oxidant stress. In a swine model of chronic myocardial ischemia, we tested whether PIO increases PGC1-α signaling and the expression of mitochondrial antioxidant peptides. Eighteen pigs underwent a thoracotomy with placement of a fixed constrictor around the LAD artery. At 8 weeks, diet was supplemented with either PIO (3 mg/kg) or placebo for 4 weeks. Regional myocardial function and blood flow were determined at the time of the terminal study. PGC1-α expression was quantified from nuclear membranes by gels and respiration, oxidant stress markers and proteomics by iTRAQ were determined from isolated mitochondria. In the chronically ischemic LAD region, wall thickening from the PIO and control groups was 42 ± 6 and 45 ± 5 %, respectively (NS) with no intergroup differences in basal blood flow (0.72 ± 0.04 versus 0.74 ± 0.04 ml/min g, respectively; NS). In the PIO group, the expression of nuclear bound PGC1-α was higher (11.3 ± 2.6 versus 4.4 ± 1.4 AU; P < 0.05) and the content of mitochondrial antioxidant peptides including superoxide dismutase 2, aldose reductase, glutathione S-transferase and thioredoxin reductase were greater than controls. Although isolated mitochondria from the PIO group showed lower state 3 respiration (102 ± 13 versus 161 ± 22 nmol/min mg; P < 0.05), no differences in oxidant stress were noted by protein carbonyl (1.7 ± 0.7 versus 1.1 ± 0.1 nmol/mg). Chronic pioglitazone does not reduce regional myocardial blood flow or function in a swine model of chronic myocardial ischemia, but may have an important role in increasing expression of antioxidant proteins through PGC1-α signaling.

Expression of uncoupling protein-2 remains increased within hibernating myocardium despite successful coronary artery bypass grafting at 4 wk post-revascularization

BACKGROUND

We have previously shown that mitochondrial uncoupling protein-2 (UCP-2) is increased in a swine model of hibernating myocardium (HM). Although UCP-2 reduces oxidant stress, it can promote inefficiency of the electron transport chain. In this study, we tested whether UCP-2 remains increased in revascularized HM (RHM) after coronary artery bypass grafting (CABG).

METHODS

Seven swine underwent thoracotomy with placement of a constrictor on the left anterior descending artery (LAD). Twelve weeks later, a left internal mammary artery graft was placed on the distal LAD. Four weeks post-CABG, computed tomography angiography documented patent grafts and function. At the terminal study, blood flow to the LAD and remote territories were assessed during high dose dobutamine and mitochondria isolated from both regions for analysis. Comparisons were made to a group of swine with HM who underwent constrictor placement without bypass grafting (n = 4).

RESULTS

During dobutamine infusion, RHM demonstrated lower blood flows (2.44 ± 0.23 versus 3.43 ± 0.30 mL/min/g; P < 0.05) and reduced wall thickening (33 ± 9% versus 52 ± 13%; P < 0.05) compared with remote regions. RHM had lower respiratory control indices (3.7 ± 0.3 versus 4.3 ± 0.4; P < 0.05) with persistently increased UCP-2 content.

CONCLUSIONS

Despite patent grafts, RHM demonstrates a submaximal response to dobutamine infusion and increased mitochondrial UCP-2 expression. These data support the notion that recovery of the mitochondria in RHM is delayed early post-CABG and may contribute to impaired oxygen consumption and contractile reserve during catecholamine challenges.

Organ protective mechanisms common to extremes of physiology: a window through hibernation biology

Supply and demand relationships govern survival of animals in the wild and are also key determinants of clinical outcomes in critically ill patients. Most animals' survival strategies focus on the supply side of the equation by pursuing territory and resources, but hibernators are able to anticipate declining availability of nutrients by reducing their energetic needs through the seasonal use of torpor, a reversible state of suppressed metabolic demand and decreased body temperature. Similarly, in clinical medicine the majority of therapeutic interventions to care for critically ill or trauma patients remain focused on elevating physiologic supply above critical thresholds by increasing the main determinants of delivery of oxygen to the tissues (cardiac output, perfusion pressure, hemoglobin concentrations, and oxygen saturation), as well as increasing nutritional support, maintaining euthermia, and other general supportive measures. Techniques, such as induced hypothermia and preconditioning, aimed at diminishing a patient's physiologic requirements as a short-term strategy to match reduced supply and to stabilize their condition, are few and underutilized in clinical settings. Consequently, comparative approaches to understand the mechanistic adaptations that suppress metabolic demand and alter metabolic use of fuel as well as the application of concepts gleaned from studies of hibernation, to the care of critically ill and injured patients could create novel opportunities to improve outcomes in intensive care and perioperative medicine.

The breathing heart - mitochondrial respiratory chain dysfunction in cardiac disease

The relentlessly beating heart has the greatest oxygen consumption of any organ in the body at rest reflecting its huge metabolic turnover and energetic demands. The vast majority of its energy is produced and cycled in form of ATP which stems mainly from oxidative phosphorylation occurring at the respiratory chain in the mitochondria. Apart from energy production, the respiratory chain is also the main source of reactive oxygen species and plays a pivotal role in the regulation of oxidative stress. Dysfunction of the respiratory chain is therefore found in most common heart conditions. The pathophysiology of mitochondrial respiratory chain dysfunction in hereditary cardiac mitochondrial disease, the ageing heart, in LV hypertrophy and heart failure, and in ischaemia-reperfusion injury is reviewed. We introduce the practising clinician to the complex physiology of the respiratory chain, highlight its impact on common cardiac disorders and review translational pharmacological and non-pharmacological treatment strategies.