Maximum Respiration Rate Research Articles

PERM1 regulates mitochondrial energetics through O-GlcNAcylation in the heart

PERM1 was initially identified as a new downstream target of PGC-1α and ERRs that regulates mitochondrial bioenergetics in skeletal muscle. Subsequently, we and other groups demonstrated that PERM1 is also a positive regulator of mitochondrial bioenergetics in the heart. However, the exact mechanisms of regulatory functions of PERM1 remain poorly understood. O-GlcNAcylation is a post-translational modification of proteins that are regulated by two enzymes: O-GlcNAc transferase (OGT) that adds O-GlcNAc to proteins; O-GlcNAcase (OGA) that removes O-GlcNAc from proteins. O-GlcNAcylation is a powerful signaling mechanism mediating cellular responses to stressors and nutrient availability, which, among other targets, may influence cardiac metabolism. We hypothesized that PERM1 regulates mitochondrial energetics in cardiomyocytes through modulation of O-GlcNAcylation. We found that overexpression of PERM1 decreased the total levels of O-GlcNAcylated proteins, concomitant with decreased OGT and increased OGA expression levels. Luciferase gene reporter assay showed that PERM1 significantly decreases the promoter activity of Ogt without changing the promoter activity of Oga. The downregulation of OGT by PERM1 overexpression was mediated through its interaction with E2F1, a known transcription repressor of Ogt. A deliberate increase of O-GlcNAcylation through Oga silencing in cardiomyocytes decreased the basal and maximal mitochondrial respiration and ATP production rates, all of which were completely restored by PERM1 overexpression. Furthermore, excessive O-GlcNAcylation caused by the loss of PERM1 led to the increase of O-GlcNAcylated PGC-1α, a master regulator of mitochondrial bioenergetics, concurrent with the dissociation of PGC-1α from PPARα, a well-known transcription factor that regulates fatty acid β-oxidation. We conclude that PERM1 positively regulates mitochondrial energetics, in part, via suppressing O-GlcNAcylation in cardiac myocytes.

Effects of acute alcohol intoxication on the respiration and dehydrogenase activity of rat pancreatic acini

The exocrine function of pancreatic acini cells is a highly energy-intensive process. A cell always needs to maintain a stable level of ATP balancing between states of activation and rest. Low-energy is one of the possible mechanisms contributing to the development of pancreatic diseases. The most commonly encountered disease of the pancreas is acute pancreatitis. It is known that excessive alcohol consumption causes the development of pancreatitis. The pathogenesis of this disease is linked to the cellular loss of energy, but the mechanism of alcohol’s effect on the mitochondria in pancreatic acini is unclear. This study’s main aim is to assess the impact of acute alcohol administration on the mitochondrial function of rat pancreatic acini. Wistar rats were administered ethanol (6 g/kg body weight) by oral gavage for 3 h before the experiment. A suspension of isolated pancreatic acini was obtained following collagenase digestion. Respiration of isolated pancreatic acini was studied with a Clark electrode. The maximal respiration rate was studied at different concentrations of protonophore FCCP (0.5–2 μM) in solutions containing glucose combined with oxidative substrates (pyruvate and glutamine, monomethyl-succinate or dimethyl-α-ketoglutarate). Dehydrogenase activity was measured by colorimetric method. Ethanol administration caused a significant increase in the activity of pyruvate dehydrogenase. It was confirmed that FCCP induced an increase in the respiration rate of pancreatic acinar cells in each experimental group. The addition of 1.5 μM FCCP reduced the respiration rate of pancreatic acini during the oxidation of glucose and monomethyl succinate or dimethyl-α-ketoglutarate, but not during the oxidation of glucose, pyruvate and glutamine substrates. The administration of ethanol had no impact on the basal or FCCP-uncoupled respiration of isolated pancreatic acini. The observed data are consistent with the findings of other researchers. However, alcohol exposure is not sufficient to cause mitochondrial damage in pancreatic acinar cells. In conclusion, acute ethanol administration does not cause mitochondrial dysfunction in the pancreas of rats but causes an increase in pyruvate dehydrogenase activity.

PINK1-Mediated Mitochondrial Activity Confers Olaparib Resistance in Prostate Cancer Cells.

Olaparib, a PARP inhibitor, is a targeted therapy used in treating various cancers including castration-resistant prostate cancer (CRPC). Despite its efficacy, resistance to Olaparib remains a significant challenge. Understanding the molecular mechanisms underpinning this resistance is crucial for developing more effective treatment strategies. This study focuses on elucidating the role of mitochondrial alterations and the PINK1 gene in conferring Olaparib resistance in CRPC cells. We investigated the transcriptomic and functional differences in mitochondrial activity between Olaparib-resistant (2B-OlapR, LN-OlapR) and treatment naïve prostate cancer (PCa) cells (C4-2B, LNCaP) in both castration sentitive and resistant settings. Through RNA sequencing and Gene Set Enrichment Analysis (GSEA), we identified significant enrichment of mitochondrial and oxidative phosphorylation-related gene sets in Olaparib Resistant derived cell lines. Resistant lines exhibited enhanced mitochondrial functionality including increased basal and maximal respiration rates, as well as elevated ATP production and spare respiratory capacity compared to parental cells. Subsequent investigations revealed a substantial increase in mitochondrial mass and electron transport chain complex I activity in Olaparib-resistant cells. Furthermore, overexpression of the PINK1 gene was observed in resistant cells, which was correlated with resistance to Olaparib and poor clinical outcomes in prostate cancer patients. Inhibition of PINK1 expression significantly reduced mitochondrial function and mass, impaired cell growth, and decreased resistance to Olaparib. These findings suggest that PINK1 plays a crucial role in modulating mitochondrial dynamics that confer therapeutic resistance, highlighting its potential as a therapeutic target for overcoming Olaparib resistance in PCa.

Chemotherapy effects on mitochondrial function in adipose tissue in oesophageal and gastroesophageal junction adenocarcinomas with or without associated cachexia: protocol for a prospective, comparative observational study (ChiFMeOE)

IntroductionCachexia is strongly associated with digestive cancers, particularly oesogastric cancer. Mitochondria in adipose tissue are involved in the regulation of metabolism and physiopathology of cancer cachexia in animal studies. Chemotherapeutic...

Autonomic regulation in athletic horses repetitively participating in two novice jumping classes on consecutive days.

Animal welfare is of great concern in equestrian sports and has been evaluated in athletic horses competing at different levels. However, the impact of consecutive days of jumping competition and the extent of resultant stress responses remains unclear. To address this point, the present study compared the changes in stress response via heart rate variability (HRV) in horses participating in two national jumping events on consecutive days. The study involved six experienced horses equipped with heart rate monitoring devices. HRV variables were measured before, during, and after jumping at 10-min intervals for 60 min on each competition day. Multiple HRV variables decreased to varying degrees on both days from warm-up until 30 min post-jumping. Meanwhile, the mean heart rate increased during jumping and returned to normal levels at 50 min post-jumping on the first day (for all intervals, p < 0.05-0.001), while it remained elevated beyond 60 min post-jumping on the second day (for all intervals, p < 0.01-0.001). Additionally, maximum heart rate and respiratory rate were higher on the second day than in the first round during the warm-up phase (p < 0.05 for both variables). The proportion of the HRV low-frequency band was higher during riding on the second day (p < 0.05), while the proportion of the high-frequency band was reduced during warm-up on the first day (p < 0.05) and during course riding on the second (p < 0.01). Meanwhile, the sympathetic nervous system index took longer to return to baseline on the second day than on the first. These results suggest that autonomic regulation differed in horses between jumping rounds on two consecutive days, with horses experiencing higher sympathetic activity and potentially increased stress in the second round. This information is important for riders, highlighting the need to be mindful of potential stress that could, at least in part, impact the welfare of horses participating in the same jumping competition on consecutive days.

Microbial community respiration kinetics and their dynamics in coastal seawater

Oxygen (O2) concentrations in coastal seawater have been declining for decades and models predict continued deoxygenation into the future. As O2 declines, metabolic energy use is progressively channelled from higher trophic levels into microbial community respiration, which in turn influences coastal ecology and biogeochemistry. Despite its critical role in deoxygenation and ecosystem functioning, the kinetics of microbial respiration at low O2 concentrations in coastal seawater remain uncertain and are mostly modeled based on parameters derived from laboratory cultures and a limited number of environmental observations. To explore microbial responses to declining O2, we measured respiration kinetics in coastal microbial communities in Hong Kong over the course of an entire year. We found the mean maximum respiration rate (Vmax) ranged between 560 ± 280 and 5930 ± 800 nmol O2 L−1 h−1, with apparent half-saturation constants (Km) for O2 uptake of between 50 ± 40 and 310 ± 260 nmol O2 L−1. These kinetic parameters vary seasonally in association with shifts in microbial community composition that were linked to nutrient availability, temperature, and biological productivity. In general, coastal communities in Hong Kong exhibited low affinities for O2, yet communities in the dry season had higher affinities, which may play a key role in shaping the relationship between community size, biomass, and O2 consumption rates through respiration. Overall, parameters derived from these experiments can be employed in models to predict the expansion of deoxygenated waters and associated effects on coastal ecology and biogeochemistry.

Effect of long-term ethanol consumption and a high-fat diet on mitochondrial respiration in rat pancreatic acinar cells and hepatocytes

Chronic alcohol consumption may cause pancreatitis and alcohol-related liver diseases. Both adaptation and damage of liver mitochondria in animals on chronic ethanol and high-fat diets were demonstrated. It is currently not clear if ethanol or its metabolites such as fatty acid ethyl esters can cause mitochondrial damage to the pancreas. The present study aimed to evaluate the effect of chronic ethanol administration in combination with a high-fat diet on mitochondrial respiration in both pancreatic acinar cells and hepatocytes of rats. Wistar male rats on a high-fat diet (35% calories) were administered ethanol (6 g/kg body weight) by oral gavage for 14 days. Pancreatic acini cells and hepatocytes were isolated with collagenase digestion. The respiration of isolated cells was studied with a Clark electrode. Ethanol administration to rats kept on a high-fat diet was followed by a rapid loss of animal weight during the first 5 days of the experiment and diminished secretory response of pancreatic acini to acetylcholine, however, no changes in acinar cells ultrastructure, basal, oligomycin-insensitive or FCCP-uncoupled respiration were found. Meanwhile ethanol caused a significant (~40%) increase in basal and maximal FCCP-uncoupled respiration rate of isolated hepatocytes. In conclusion, chronic ethanol administration to rats on a high-fat diet does not cause mitochondrial damage in the pancreas, while mitochondria of the liver adapt to ethanol by increasing respiration rate. Keywords: ethanol, hepatocytes, high fat diet, mitochondrial respiration, pancreatic acinar cells

Markers of Mitochondrial Function and DNA Repair Associated with Physical Function in Centenarians.

Mitochondrial dysfunction and genomic instability are key hallmarks of aging. The aim of this study was to evaluate whether maintenance of physical capacities at very old age is associated with key hallmarks of aging. To investigate this, we measured mitochondrial bioenergetics, mitochondrial DNA (mtDNA) copy number and DNA repair capacity in peripheral blood mononuclear cells from centenarians. In addition, circulating levels of NAD+/NADH, brain-derived neurotrophic factor (BDNF) and carbonylated proteins were measured in plasma and these parameters were correlated to physical capacities. Centenarians without physical disabilities had lower mitochondrial respiration values including ATP production, reserve capacity, maximal respiration and non-mitochondrial oxygen-consumption rate and had higher mtDNA copy number than centenarians with moderate and severe disabilities (p < 0.05). In centenarian females, grip strength had a positive association with mtDNA copy number (p < 0.05), and a borderline positive trend for activity of the central DNA repair enzyme, APE 1 (p = 0.075), while a negative trend was found with circulating protein carbonylation (p = 0.07) in the entire cohort. Lastly, a trend was observed for a negative association between BDNF and activity of daily living disability score (p = 0.06). Our results suggest that mechanisms involved in maintaining mitochondrial function and genomic stability may be associated with maintenance of physical function in centenarians.

Microbial utilisation of maize rhizodeposits applied to agricultural soil at a range of concentrations

AbstractRhizodeposition fuels carbon (C) and nutrient cycling in soil. However, changes in the dynamics of microbial growth on rhizodeposits with increasing distance from the root is not well studied. This study investigates microbial growth on individual organic components of rhizodeposits and maize root‐derived exudates and mucilage from agricultural soil. By creating a gradient of substrate concentrations, we simulated reduced microbial access to rhizosphere C with increasing distance to the root surface. We identified distinct C‐thresholds for the activation of microbial growth, and these were significantly higher for rhizodeposits than singular, simple sugars. In addition, testing for stoichiometric constraints of microbial growth by supplementing nitrogen (N) and phosphorus (P) showed accelerated and increased microbial growth by activating a larger proportion of the microbial biomass. Early and late season exudates triggered significantly different microbial growth responses. The mineralization of early‐season exudates was induced at a high C‐threshold. In contrast, the mineralization of late‐season exudates showed ‘sugar‐like’ properties, with a low C‐threshold, high substrate affinity, and a reduced maximum respiration rate of microorganisms growing on the added substrate. Mucilage exhibited the highest C‐threshold for the activation of microbial growth, although with a short lag‐period and with an efficient mucilage degradation comparable to that of sugars. By determining kinetic parameters and turnover times for different root‐derived substrates, our data enable the upscaling of micro‐scale processes to the whole root system, allowing more accurate predictions of how rhizodeposition drives microbial C and nutrient dynamics in the soil.

Respirometric estimation of the oxygen consumption in nitrifying and sulfide oxidation bioprocesses

The design and optimization of wastewater treatment require information about its characteristics and biokinetic parameters. Specifically, determining the maximum respiration rate (rO2max) and the dissolved oxygen affinity constant (KO2) would enhance the plant’s aeration efficiency. Aeration is crucial in biological processes to ensure the biodegradation of NH4 + and H2 S. The estimation of rO2max and KO2 has commonly been performed by measuring and interpreting the dissolved oxygen concentration under well-defined conditions, known as respirometry. In this study, these parameters were measured using the static respirometry technique (absence of external aeration) for nitrification and sulfide oxidation processes. Additionally, a discussion was presented regarding the error in estimation if an oxygen transfer process (OTR) were present during the experiment.

Activation of innate immunity selectively compromises mitochondrial complex I, proline oxidation, and flight activity in the major arbovirus vector Aedes aegypti.

Aedes aegypti females are natural vectors of important arboviruses such as dengue, zika, and yellow fever. Mosquitoes activate innate immune response signaling pathways upon infection, as a resistance mechanism to fight pathogens and limit their propagation. Despite the beneficial effects of immune activation for insect vectors, phenotypic costs ultimately affect their fitness. However, the underlying mechanisms that mediate these fitness costs remain poorly understood. Given the high energy required to mount a proper immune response, we hypothesized that systemic activation of innate immunity would impair flight muscle mitochondrial function, compromising tissue energy demand and flight activity. Here, we investigated the dynamic effects of activation of innate immunity by intra-thoracic zymosan injection on A. aegypti flight muscle mitochondrial metabolism. Zymosan injection significantly increased defensin A expression in fat bodies in a time-dependent manner that compromised flight activity. Although oxidant levels in flight muscle were hardly altered, ATP-linked respiratory rates driven by mitochondrial pyruvate+proline oxidation were significantly reduced at 24 h upon zymosan injection. Oxidative phosphorylation coupling was preserved regardless of innate immune response activation along 24 h. Importantly, rotenone-sensitive respiration and complex I-III activity were specifically reduced 24 h upon zymosan injection. Also, loss of complex I activity compromised ATP-linked and maximal respiratory rates mediated by mitochondrial proline oxidation. Finally, the magnitude of innate immune response activation negatively correlated with respiratory rates, regardless of the metabolic states. Collectively, we demonstrate that activation of innate immunity is strongly associated with reduced flight muscle complex I activity with direct consequences to mitochondrial proline oxidation and flight activity. Remarkably, our results indicate a trade-off between dispersal and immunity exists in an insect vector, underscoring the potential consequences of disrupted flight muscle mitochondrial energy metabolism to arbovirus transmission.

Na/K-ATPase α1/Src Signaling Regulates Mitochondrial Metabolic Function and ROS Production in Human iPSC-derived Cardiomyocytes

Through an isoform specific mechanism, the Na/K-ATPase (NKA) α1 polypeptide-mediated regulation of Src kinase has emerged as a novel regulator of mitochondrial function in various cell types. Mitochondrial metabolism ensures adequate myocardial performance and adaptation to physiological demand. It is also a critical cellular determinant of cardiac repair and remodeling. To investigate the importance of the proposed NKA/Src regulatory signaling on cardiac mitochondrial metabolic function independently from the classic Na/K-ATPase enzymatic function, we used a gene targeting approach in cardiomyocytes. Human induced pluripotent stem cells (hiPSC) expressing a Src-signaling null mutant (A420P) form of NKA α1 were generated using CRISPR/Cas9-mediated genome editing. NKA isoform protein expression and enzymatic activity remained unchanged. However, baseline levels of Src and ERK1/2 phosphorylation were decreased by 55% and 80%, respectively in the A420P hiPSC (n=3, p&lt;0.05). Both the WT and A420P hiPSC differentiated into cardiomyocytes (iCM) as assessed by morphology, spontaneous cell contraction, marker gene expression, and subcellular striations. Cell metabolism assessed by Seahorse extracellular flux analysis revealed significant reductions in basal and maximal rates of mitochondrial respiration (50%), spare respiratory capacity (50%), ATP production (60%), and coupling effciency (20%) (n=4, p&lt;0.05). ROS production was monitored in live cells by measuring the oxidation of the CM-H2DCFDA dye using a fluorescence microscope. The slope of the ROS production rate curve was dramatically reduced in A420P iCM (80%, n=3, p&lt;0.05). Protein carbonylation levels, analyzed by ELISA as markers of oxidative damage, were also decreased in A420P iCM (n=4, p&lt;0.05). Taken together, these data provide genetic evidence for a role of NKA α1/Src in the tonic stimulation of basal mitochondrial metabolism and ROS production in human cardiac myocytes. This has potential significance in cardiometabolic diseases and suggests that targeting the NKA α1/Src signaling axis may offer a novel approach to address mitochondrial dysfunction. NIH Grant R15 HL145666, NIH Grant P20GM103434 to the West Virginia IDeA Network of Biomedical Research Excellence, and American Heart Association Postdoctoral Fellowship — 22POST917776 — to Marco T. Pessoa. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Efficient estimation of gas exchange and respiration kinetics in apple using pathlength-resolved GASMAS

Optimization of controlled atmosphere (CA) storage of pome fruit crucially depends on understanding of respiratory gas exchange. Different fruit properties are involved in describing gas transfer and respiration kinetics, which can vary between cultivars, fruit batches and individual fruit. Determination of these properties currently requires a combination of different time-consuming techniques and data analysis procedures. This study introduces a more efficient single method for O2 gas exchange characterization of fruit based on the non-destructive pathlength-resolved GASMAS (gas in scattering media absorption spectroscopy) technique. GASMAS was used to measure the absolute intercellular O2 concentration in fruit of different apple cultivars (Malus x domestica Borkh.) with distinct porosity including 'Jonagold', 'Braeburn', and 'Nicoter'. To resolve the ambiguity between variation in pathlength and O2 concentration inherent to GASMAS, the pathlength travelled through pores cavities was quantified through a second GASMAS measurement at the absorption line of H2O vapour. Dynamic experiments were then performed in which the fruit was subjected to varying external O2 concentrations while measuring the internal O2 response. The observed dynamic profiles of external and internal O2 concentration were fitted with a lumped -respiration model to estimate the effective mass transfer coefficient, maximum respiration rate and Michaelis Menten constant of intact fruit. The model showed a good fit (R2>0.95) with the measured data and reliable estimates for the model parameters. The proposed method provides a novel and more efficient way to estimate the gas exchange properties of fruit that are essential for optimizing CA storage conditions. Future challenges for the proposed method are with applications to other gasses such as CO2 and ethylene.

Comparison of the efficacy for early warning systems in predicting obstetric critical illness

ObjectiveTo validate the accuracy of four early warning scores for early identification of women at risk. MethodsThis was a retrospective study of pregnant women admitted in obstetrics Critical Care Unit (ICU). Capacity of the Modified Obstetric Early Warning Score (MOEWS), ICNARC Obstetric Early Warning Score (OEWS), Maternal Early Obstetric Warning System (MEOWS chart), and Maternal Early Warning Trigger (MEWT) were compared in predicting severe maternal morbidity. Area under receiver operator characteristic (AUROC) curve was used to evaluate the predictive performance of scoring system. ResultsA total of 352 pregnant women were enrolled and 290 were identified with severe maternal morbidity. MOEWS was more sensitive than MEOWS chart, ICNARC OEWS and MEWT (96.9 % vs. 83.4 %, 66.6 % and 44.8 %). MEWT had the highest specificity (98.4 %), followed by MOEWS (83.9 %), ICNARC OEWS (75.8 %) and MEOWS chart (48.4 %). AUROC of MOEWS, ICNARC OEWS, MEOWS chart, and MEWT for prediction of maternal mortality were 0.91 (95 % CI: 0.874–0.945), 0.765(95 % CI: 0.71–0.82), 0.657(95 % CI: 0.577–0.738), and 0.716 (95 % CI, 0.659–0.773) respectively. MOEWS had the highest AUCs in the discrimination of serious complications in hypertensive disorders, cardiovascular disease, obstetric hemorrhage and infection. For individual vital signs, maximum diastolic blood pressure (DBP), maximum systolic blood pressure (SBP), maximum respiratory rate (RR) and peripheral oxygen saturation (SPO2) demonstrated greater predictive ability. ConclusionMOEWS is more accurate than ICNARC OEWS, MEOWS chart, and MEWT in predicting the deterioration of women. The prediction ability of DBP, SBP, RR and SPO2 are more reliable.

BDE-99 stimulates generation of aberrant brown/beige adipocytes

Adipose tissue compromises one of the principal depots where brominated flame retardants (BFR) accumulate in vivo, yet whether BFR disturb thermogenic brown/beige adipocytes is still not referred to date. Herein, effects of BDE-99, a major congener of polybrominated diphenyl ethers (PBDEs) detected in humans, on brown/beige adipocytes were explored for the first time, aiming to provide new knowledge evaluating the obesogenic and metabolic disrupting effects of BFR. Our results firstly demonstrated that exposure to BDE-99 during the lineage commitment period significantly promoted C3H10T1/2 MSCs differentiating into brown/beige adipocytes, evidenced by the increase of brown/beige adipocyte marker UCP1, Cidea as well as mitochondrial membrane potential and basal respiration rate, which was similar to pharmacological PPARγ agonist rosiglitazone. Unexpectedly, the mitochondrial maximal respiration rate of BDE-99 stimulated brown/beige adipocytes was not synchronously enhanced and resulted in a significant reduction of mitochondrial spare respiration capacity (SRC) compared to control or rosiglitazone stimulated adipocytes, indicating a deficient energy-dissipating capacity of BDE-99 stimulated thermogenic adipocytes. Consistently with compromised mitochondrial SRC, lipidomic analysis further revealed that the lipids profile of mitochondria derived from BDE-99 stimulated brown/beige adipocytes were quite different from control or rosiglitazone stimulated cells. In detail, BDE-99 group contains more free fatty acid (FFA) and lyso-PE in mitochondria. In addition to energy metabolism, our results also demonstrated that BDE-99 stimulated brown/beige adipocytes were deficient in endocrine, which secreted more adverse adipokine named resistin, coinciding with comparable beneficial adipokine adiponectin compared with that of rosiglitazone. Taken together, our results showed for the first time that BDE-99 stimulated brown/beige adipocytes were aberrant in energy metabolism and endocrine, which strongly suggests that BDE-99 accumulated in human adipose tissue could interfere with brown/beige adipocytes to contribute to the occurrence of obesity and relevant metabolic disorders.

The influence of low resistance respiratory muscle training on pulmonary function and high intensity exercise performance

Background/objectivesRespiratory muscle training (RMT) was recognized as an effective means to improve respiratory muscle (RM) strength and enhance exercise performance. The purpose of this study was to examine the effect of low-intensity RMT on RM strength, pulmonary function, and performance. MethodsFourteen healthy active adults were assigned randomly to either a training or placebo group. The training group completed six weeks of RMT, which consisted of a first week, 1 set of 15 min/d, 5 d/wk at 10–25% of maximal inspiratory pressure (PImax), and the remaining 5 weeks, 2 sets of 15 min/d, 5 d/wk, at 30% PImax. The placebo group followed the same protocol but with almost no additional ventilatory resistance. Measurement of RM strength and endurance, spirometry, and endurance exercise performance were obtained before and after the RMT program. ResultsIn the training group, PImax (+14%) and maximal expiratory pressure (PEmax, +27%), forced vital capacity (FVC, +3.6%), maximal oxygen uptake (VO2max, +11%), and time to exhaustion (Tlim90%, +25%) increased significantly from baseline values (P < 0.05). No significant changes were observed in the placebo group. Also, no significant interaction in maximum voluntary ventilation (MVV12), minute ventilation (VE), and respiratory rate (RR) were detected. ConclusionsThese data suggest that low-intensity RMT is an effective tool to improve RM strength, pulmonary elastic properties and endurance exercise performance.

Fatty Acids Play a Critical Role in Mitochondrial Oxidative Phosphorylation in Effector T Cells in Graft-versus-Host Disease.

Although the role of aerobic glycolysis in activated T cells has been well characterized, whether and how fatty acids (FAs) contribute to donor T cell function in allogeneic hematopoietic stem cell transplantation is unclear. Using xenogeneic graft-versus-host disease (GVHD) models, this study demonstrated that exogenous FAs serve as a crucial source of mitochondrial respiration in donor T cells in humans. By comparing human T cells isolated from wild-type NOD/Shi-scid-IL2rγnull (NOG) mice with those from MHC class I/II-deficient NOG mice, we found that donor T cells increased extracellular FA uptake, the extent of which correlates with their proliferation, and continued to increase FA uptake during effector differentiation. Gene expression analysis showed the upregulation of a wide range of lipid metabolism-related genes, including lipid hydrolysis, mitochondrial FA transport, and FA oxidation. Extracellular flux analysis demonstrated that mitochondrial FA transport was required to fully achieve the mitochondrial maximal respiration rate and spare respiratory capacity, whereas the substantial disruption of glucose supply by either glucose deprivation or mitochondrial pyruvate transport blockade did not impair oxidative phosphorylation. Taken together, FA-driven mitochondrial respiration is a hallmark that differentiates TCR-dependent T cell activation from TCR-independent immune response after hematopoietic stem cell transplant.

It’s not just the heart: respiratory limitations to constant-load exercise in adult Fontan patients and potential implications for rehabilitation

Introduction Congenital heart defects may require surgical intervention such as the Fontan procedure that connects the systemic venous return to the pulmonary arteries. Although this procedure has increased survival, it results in reduced exercise capacity; which is reduced not only due to cardiovascular factors, but respiratory limitations as well. However, there is a lack of evidence outlining ventilatory limitations during constant-load exercise, which better represents exercise in cardiac rehabilitation programs and non-laboratory based exercise. Therefore, the aim of the present study was to compare responses to constant-load exercise in adult Fontan patients with those of healthy well-matched controls. Methods 14 adult Fontan patients (5F, 27 ± 6yrs) were recruited with 14 healthy matched controls. Participants performed forced vital capacity (FVC), as well as maximal inspiratory and and expiratory pressure assessments (MIP and MEP, respectively). Patients performed an incremental cycling test (ICT) to exhaustion to determine peak work rate. Following a period of recovery, patients performed a constant-load cycling test (CLCT) at 70% of peak ICT work rate until exhaustion. Healthy subjects reproduced the exercise of their matched patient. Cardiorespiratory variables and heart rate (HR) were measured using a metabolic cart and a 12-lead electrocardiogram, respectively. Participants were asked to rate their perception of breathlessness and respiratory exertion via a visual analogue scale every 2 min and at peak exercise. Patients without cardiac pacemakers underwent involuntary assessments of respiratory muscle contractility via phrenic (n = 8) nerve magnetic stimulation before and following exercise to quantify respiratory muscle fatigue. Results Patients showed significantly reduced FVC, MIP and MEP compared to controls (all p &lt; 0.025). Patients’ time-to-exhaustion during the CLCT was 7.1 ± 3.3 min. During CLCT vs. the ICT, patients reached maximal HR, respiratory rate (fR), breathlessness, respiratory exertion, and leg exertion. End-exercise V̇O2 during the CLCT did not reach ICT values, with a mean difference of 1.5 ml/kg/min (p = 0.017). Controls did not reach peak ICT responses during the CLCT. During the CLCT, patients displayed significantly elevated minute ventilation (V̇E; mean difference = 21.5 L/min), fR (mean difference = 13.8 breaths-per-minute), breathlessness (mean difference = 3.4 points), and respiratory exertion (mean difference = 2.3 points), along with significantly decreased ventilatory reserve (V̇E/maximal voluntary ventilation; mean difference = 27.5%; all p &lt; 0.002). Following the CLCT, Fontan patients showed a larger decrease in involuntary respiratory muscle contractility (15 ± 12% vs. 2 ± 11%). Finally, a decreased ventilatory reserve was significantly correlated with decreased MIP (r = 0.723, p = 0.003) and MEP (r = 0.623, p = 0.042). Discussion/Conclusion Fontan patients had a lower-than-expected time-to-exhausiton, in part due to their abnormal ventilatory response. First, the increased pulmonary restriction in the Fontan patients likely led to increased V̇E driven by a high fR during exercise. Second, Fontan patients showed decreased ventilatory reserve - which was significantly associated with respiratory muscle weakness. Third, patients showed significantly increased respiratory muscle fatigue following exercise. Collectively, these factors likely contributed to the increased breathlessness and respiratory exertion in patients, leading to increased exercise limitation. Given this, and the fact that patients reached near maximal physiological responses during the CLCT, it’s possible that patients may benefit more from aerobic training at less than 70% of peak word rate, or from interval-training with significant recovery time.

Growth and photosynthetic physiology of holopelagic Sargassum (Phaeophyceae) under laboratory conditions

SummarySpecies of holopelagic Sargassum are responsible for Caribbean golden tides, commonly known as ‘Sargassum events’. These events mainly comprise Sargassum fluitans and Sargassum natans I, which are exposed to high levels of irradiance, but also self‐shading within their floating masses. In this study, we grew S. fluitans and S. natans I and acclimated them to low‐light conditions at 23°C in the laboratory to explore their responses to increasing light intensities. Photosynthesis, respiration, growth, and pigment content were evaluated over 3 weeks. S. fluitans and S. natans I photoacclimate to higher irradiances by decreasing their chlorophyll a and c contents. An increase in maximum photosynthesis and respiration rates was observed under high light, although differences occurred in the saturation irradiance and the initial slope of the photosynthesis versus irradiance curve. These adjustments were reflected in S. fluitans daily growth (from 2% to 7% d−1 at low to high light, respectively) and tissue nitrogen content (1.6–2.7%) but were absent in S. natans I (~1% d−1). The photosynthetic physiology of S. fluitans under these conditions suggests lower light requirements without compromising growth; however, under high light a higher photosynthetic performance was observed. Combining physiological and growth studies in holopelagic Sargassum species will serve as a baseline to understand and explain the success and overgrowth of these species along the Caribbean coast.

The Na/K-ATPase α1/Src Signaling Axis Regulates Mitochondrial Metabolic Function and Redox Signaling in Human iPSC-Derived Cardiomyocytes.

Na/K-ATPase (NKA)-mediated regulation of Src kinase, which involves defined amino acid sequences of the NKA α1 polypeptide, has emerged as a novel regulatory mechanism of mitochondrial function in metazoans. Mitochondrial metabolism ensures adequate myocardial performance and adaptation to physiological demand. It is also a critical cellular determinant of cardiac repair and remodeling. To assess the impact of the proposed NKA/Src regulatory axis on cardiac mitochondrial metabolic function, we used a gene targeting approach in human cardiac myocytes. Human induced pluripotent stem cells (hiPSC) expressing an Src-signaling null mutant (A420P) form of the NKA α1 polypeptide were generated using CRISPR/Cas9-mediated genome editing. Total cellular Na/K-ATPase activity remained unchanged in A420P compared to the wild type (WT) hiPSC, but baseline phosphorylation levels of Src and ERK1/2 were drastically reduced. Both WT and A420P mutant hiPSC readily differentiated into cardiac myocytes (iCM), as evidenced by marker gene expression, spontaneous cell contraction, and subcellular striations. Total NKA α1-3 protein expression was comparable in WT and A420P iCM. However, live cell metabolism assessed functionally by Seahorse extracellular flux analysis revealed significant reductions in both basal and maximal rates of mitochondrial respiration, spare respiratory capacity, ATP production, and coupling efficiency. A significant reduction in ROS production was detected by fluorescence imaging in live cells, and confirmed by decreased cellular protein carbonylation levels in A420P iCM. Taken together, these data provide genetic evidence for a role of NKA α1/Src in the tonic stimulation of basal mitochondrial metabolism and ROS production in human cardiac myocytes. This signaling axis in cardiac myocytes may provide a new approach to counteract mitochondrial dysfunction in cardiometabolic diseases.