Natural Sciences And Engineering Research Council Of Canada Research Articles

Time-restricted Eating to Improve Metabolic Health: Investigating the Mechanisms Underlying Glycolytic and Lipolytic actions

Time-restricted eating (TRE) is a behavioral intervention approach motivated by the emerging role of circadian rhythms in physiology and metabolism. In this approach, all caloric intake is restricted within a regular interval of less than 12 hours, with no overt attempt to reduce calories. We present a whole-body computational model of TRE that incorporates enzyme and substrate reactions as well as hormonal actions during fasting and postprandial states. The model is divided into seven compartments: brain, heart, skeletal muscle, gastrointestinal tract, liver, adipose tissue, and other tissues. We conducted simulations to test the hypothesis that TRE modulates whole-body glucose balance by improving postprandial hyperglycemia and hypertriglyceridemia, keeping these excursions to a minimum. We simulated different TRE schedules with meals varying in fat and carbohydrate content. Our results highlight the importance of chrono-pharmacological considerations in glycemic control: TRE modulates the interplay between glycogenolysis in the liver, lipolysis in adipose tissue and fatty acid oxidation in other organs to improve glucose control. The alternation of eating and fasting, in particular, could be manipulated to balance blood sugar levels. TRE simulations have also shown beneficial effects on the lipid front, such as lower triglyceride levels and improved lipolytic effciency, meaning the body is better able to use fat stores for fuel. This work was supported by the Canadian Institutes of Health Research (CIHR) and the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery award. 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.

Carbon Dioxide as a Novel Blood Pressure Therapy for Neurogenic Orthostatic Hypotension

BACKGROUND: On standing, people with neurogenic orthostatic hypotension (nOH) experience plummeting blood pressure (>20/10mmHg), crippling symptoms, and syncope. Current blood pressure therapies lack effcacy and have serious side effects. In healthy people, increased inspired CO2 increases blood pressure. This raises the tantalizing possibility that increased inspired CO2 may effectively treat nOH patients. OBJECTIVE: We aimed to understand if increased inspired CO2 can increase standing blood pressure in nOH. METHODS: Seventeen patients with nOH (F=5; 71±8 years) completed three randomized sit-to-stand tests with inspired CO2 maintained 0mmHg (0CO2), +5mmHg (+5CO2) or +10mmHg (+10CO2) relative to baseline. Respiratory and hemodynamics (blood pressure, heart rate, stroke volume, cardiac output, systemic vascular resistance) were continuously measured. Data are reported as mean ± SD. The change (stand-sit) in respiratory and hemodynamics between 0mmHg, +5mmHg and +10mmHg were compared using a repeated measures ANOVA with a Bonferroni correction. RESULTS: Inspired CO2 caused a dose-dependent increase in standing blood pressure (0CO2:-43±25mmHg; +5CO2:-22±26mmHg; +10CO2:-4±30mmHg; p<0.001). Blood pressure changes were predominantly facilitated by increased stroke volume (0CO2:-10±10mL; +5CO2:-5±10mL; +10CO2:0.1±10mL;p<0.001) and cardiac output (0CO2:-0.2±0.6L/min; +5CO2:0.2±0.5L/min; +10CO2:0.7±0.5L/min; p<0.001) as neither the changes in heart rate (p=0.2) nor systemic vascular resistance (p=0.6) were different across CO2 conditions. Breathing CO2 decreased the percentage of time that standing systolic blood pressure dropped ≥20mmHg (0CO2:75±35%; +5CO2:48±38%; +10CO2:32±37%; p<0.001) and fewer patients met the blood pressure criteria for orthostatic hypotension (p=0.02). CONCLUSION: Our data indicates increased inspired CO2 can increase standing blood pressure in nOH patients by increasing stroke volume and cardiac output. CO2 may offer a novel pressor therapy for patients with nOH. This work was supported by a University of Calgary Seed Funding (S.R.R). J.R.B is supported by a Canadian Institutes of Health Research (CIHR) Fellowship, a Libin Cardiovascular Institute Post-Doctoral Fellowship in Women’s Cardiovascular Health, the Natural Sciences and Engineering Research Council of Canada (NSERC) Brain CREATE Program, and a Canadian Cardiovascular Society Fellowship. S.I.R. is supported by the NSERC Brain CREATE Program, an Alberta Graduate Excellence Scholarship, and an Alberta Strategy for Patient Oriented SUPPORT Unit scholarship. A.V.I is supported by a CIHR Fellowship and an Achievers in Medical Science Postdoctoral Fellowship. 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.

The Role of Kidney Intercalated Cells in the Immune Response Against UTIs

Introduction: Urinary tract infections (UTIs) are among the most prevalent infections. About 3 in 5 women will experience UTIs in their lifetime, resulting from a bacterial infection caused by uropathogenic E. coli (UPEC). Ascending UPEC first adhere to the collecting ducts, where intercalated cells (ICs) are essential for raising an innate immune response activated by UPEC-outer membrane lipopolysaccharide (LPS). Interestingly, individuals with distal renal tubular acidosis (dRTA) who have a mutation on the gene encoding the kidney anion exchanger 1 (kAE1) have a decreased abundance of IC and are at a higher risk for UTIs. The cellular mechanisms contributing to this higher vulnerability to UTIs remain unclear. Objective and Hypothesis: To enhance our understanding of the immune response mechanisms of collecting duct cells in dRTA patients during UTIs, we hypothesize that the loss of intercalated cells (ICs) in dRTA results in an inadequate immune response against UPEC. Methods: Mouse inner medullary collecting duct cells (mIMCD3) and a mouse strain with a knock-in mutation for kAE1 dRTA (specifically, R607H, equivalent to human R589H) were utilized in the study. We identified and quantified innate immunity markers in mIMCD3 cells exposed to vehicle, UPEC or LPS using qRT-PCR and immunoblot. Primary IC were prepared by magnetic-activated cell sorting (MACS). Various incubation conditions, including exposure to vehicle, LPS, control K12 bacteria, and UPEC for different time intervals were assessed to determine the best experimental conditions. Transurethral UPEC inoculation procedures were also performed to validate results obtained in the in vitro approaches. Results: Experiments on mIMCD3 cells showed a significant increase in the innate immunity marker adrenomedullin (ADM) following exposure to UPEC or LPS, compared to the control group. After 17 h, exposing the primary MACS-enriched ICs to UPEC significantly increased the adrenomedullin protein abundance. UPEC transurethral infections in dRTA mice resulted in a higher bacterial load and increased IL-1β, IL-6, and TNF-α mRNA and protein levels compared to WT mice at 24 post-UTI. In the transgenic mice, ADM gene expression was not up-regulated to the same extent as in WT mice, but LCN2/NGAL gene expression was significantly higher. Conclusions: Our study suggests that the loss of IC in a dRTA mouse model results in higher inflammation and reduced immunity against UPEC exposure. Our research will unravel new therapeutic leads on the intracellular signaling pathway(s) and cellular changes that result in IC-mediated renal protection. The findings may contribute to the development of novel therapeutics for UTIs. Natural Sciences and Engineering Research Council of Canada (NSERC), the Canadian Institutes of Health Research (CIHR), University of Alberta Graduate Recruitment Scholarship (2023). 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.

Central α2-adrenergic mechanisms differentially affect baroreflex control of sympathetic and cardiovagal outflow

This study aimed to investigate the impact of central α2-adrenergic mechanisms on arterial baroreflex control of sympathetic and cardiovagal outflow in healthy humans. R-R interval (ECG), blood pressure (brachial arterial catheter), and muscle sympathetic nerve activity (MSNA; peroneal microneurography) were measured in eight healthy participants (5 females; 28±7 years). Sympathetic action potentials (AP) were extracted from the filtered MSNA neurogram (continuous wavelet transform) during a 5-minute baseline (BSL) and an intravenous dexmedetomidine infusion consisting of a loading dose (LD; 10 minutes at 0.225 μg/kg/hr) and a maintenance dose (MD; ~0.15 μg/kg/hr). Sympathetic AP baroreflex threshold gain was measured as the slope of the linear relationship between AP discharge probability and diastolic blood pressure. The linear relationship between R-R interval and systolic blood pressure (sequence technique) quantified cardiovagal baroreflex gain. Mixed-effects analyses and post-hoc t-tests were performed. Data are reported as mean ± SD. Dexmedetomidine reset the baroreflex threshold operating points for all sympathetic AP clusters downwards to lower firing probabilities (cluster 4; BSL: 20±6, LD: 13±8, MD: 6±5%, both p<0.01 vs. BSL) and leftwards to lower diastolic pressures (BSL: 72±9, LD: 69±8, MD: 65±10 mmHg, both p<0.01 vs. BSL). Dexmedetomidine reduced baroreflex threshold gain for the subpopulation of medium-sized sympathetic APs (cluster 4; BSL: -6.5±2.0, LD: -2.6±1.6, MD: -2.0±0.7 %/mmHg, both p<0.01 vs. BSL). Dexmedetomidine did not affect baroreflex threshold gain of small (cluster 1; BSL: -1.9±1.1, LD: -1.3±1.6, MD: -1.1±0.8 %/mmHg, both P>0.88 vs. BSL) or large AP clusters (cluster 9; BSL: -0.8±0.4, LD: -0.8±1.0, MD: -0.2±0.7 %/mmHg, both P>0.98 vs. BSL). Dexmedetomidine reset the cardiovagal baroreflex to lower systolic pressures but did not affect R-R interval (BSL: 1035±261, LD: 1025±308, MD: 1005±292ms, Main effect P=0.45) or gain (BSL: 24±11, LD: 30±20, MD: 26±25 ms/mmHg, Main effect P=0.63). These findings suggest that central α2-adrenergic mechanisms differentially affect arterial baroreflex control of sympathetic and cardiovagal outflow in humans by minimally affecting cardiovagal baroreflex gain but strongly affecting the baroreflex gain for the subpopulation of medium-sized sympathetic APs. This work was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) and the National Institutes of Health (NIH). 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.

Sexual Dimorphism in Substrate Metabolism During Exercise

During aerobic exercise, women oxidize significantly more lipids and less carbohydrates than men. This sexual dimorphism in substrate metabolism has been attributed, in part, to the observed differences in epinephrine and glucagon levels between men and women during exercise. To identify the underpinning candidate physiological mechanisms for these sex differences, we developed a sex-specific multi-scale mathematical model that relates cellular metabolism in the organs to whole-body responses during exercise. We conducted simulations to test the hypothesis that sex differences in the exercise-induced changes to epinephrine and glucagon would result in the sexual dimorphism of hepatic metabolic flux rates via the glucagon-to-insulin ratio (GIR). Indeed, model simulations indicate that the shift towards lipid metabolism in the female model is primarily driven by the liver. The female model liver exhibits resistance to GIR-mediated glycogenolysis, which helps maintain hepatic glycogen levels. This decreases arterial glucose levels and promotes the oxidation of free fatty acids. Furthermore, in the female model, skeletal muscle relies on plasma free fatty acids as the primary fuel source, rather than intramyocellular lipids, whereas the opposite holds true for the male model. This work was supported by the Canadian Institutes of Health Research (CIHR) and the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery award. 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.

Mathematical Modeling of Magnesium Homeostasis in Male Rats

Magnesium (Mg2+) is an important cofactor for numerous biological processes, including protein synthesis, nucleic acid stability, and neuromuscular excitability. Extracellular magnesium is tightly regulated, with plasma [Mg2+] maintained relatively constant between 1.6 and 2.3 mg/dL under normal physiological conditions. Almost all of the body’s Mg2+ (approximately 99%) is either stored in bone or within cells (DOI: 10.1053/j.ackd.2018.01.003). A normal daily Mg2+ intake averages around 300 mg, about half of which is absorbed by the intestine. The kidneys reabsorb 95-98% of the filtered Mg2+ and excrete only 2-5% through urine. To understand the interplay between intestine, kidneys, and bones to maintain Mg2+ homeostasis, we developed a computational model of Mg2+ homeostasis for male rats and incorporated it with a male rat calcium (Ca2+) homeostasis model. Our model consists of five compartments: plasma, intestine, kidneys, bones, and parathyroid gland. The model also includes parathyroid hormone and vitamin D3 since they significantly regulate Mg2+ and Ca2+ homeostasis. We used this model to simulate three conditions: change in dietary Mg2+, change in dietary vitamin D3, and administration of proton-pump inhibitors. In the case of variation in dietary Mg2+, our model predicted that the body compensates mainly through decreasing (in case of low dietary Mg2+) and increasing (in case of high dietary Mg2+) urinary Mg2+ excretion and the Mg2+ content in the rapidly exchangeable bone pool. Change in dietary Mg2+ does not have any significant effect on Ca2+ homeostasis. On the other hand, change in dietary vitamin D3 has significant effect on both Mg2+ and Ca2+ homeostasis, with the effect being more pronounced for Ca2+ compared to Mg2+. Our model predicted significant changes in intestinal Mg2+ and Ca2+ absorption, PTH secretion, urinary Mg2+ and Ca2+ excretion, and Mg2+ and Ca2+ content in the rapidly exchangeable bone pool following change in dietary vitamin D3. Administration of proton pump inhibitors (PPIs) such as omeprazole, which are a class of medicine commonly used to reduce stomach acid production, affect Mg2+ and Ca2+ transport in the intestine. PPIs reduce intestinal Mg2+ and Ca2+ absorption by 3.5-fold and 40%, respectively. The body compensates for this huge drop in intestinal Mg2+ absorption by tapping into the Mg2+ stored in the rapidly exchangeable bone pool in addition to decreasing urinary Mg2+ excretion. By contrast, the body can compensate for the drop in intestinal Ca2+ absorption by only decreasing urinary Ca2+ excretion. Thus, this model can be used to understand the compensatory mechanisms adopted by the body to maintain Mg2+ and Ca2+ homeostasis under various pathophysiological conditions and drug administrations. This work was supported by the Canada 150 Research Chair program, National Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant, and Canada Institutes of Health Research (CIHR) Project Grant to Anita Layton. 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.

Culture Shock! Investigating the Importance of Physiological Tumour-Like Conditions on Cultured Cancer Cells

The tumour microenvironment (TME) is complex and dynamic, characterized by poor vascularization, limited nutrient availability, hypoxia, and an acidic pH. This environment plays a critical role in cancer progression, driving hallmark changes in cancer cell metabolism, morphology, proliferation, and motility. Although mammalian cell culture is a foundational tool for investigating cancer cell biology in vitro, standard cell culture practices fall short of replicating the in vivo conditions of tumours. Recently, ‘physiologic’ cell culture media that closely resemble human plasma (e.g., Plasmax, HPLM) have been developed, along with more frequent adoption of physiological oxygen conditions (2-8% O2) rather than standard atmosphere (~18% O2). Although an improvement, these conditions are not representative of all in vivo cellular environments, particularly that of the TME. Considering the tight regulatory capacity of cancer cells to sense and respond to changes in metabolic availability, we hypothesized that alterations in nutrient and oxygen availability, even if within the physiological range, may subtly rewire the metabolism in cultured cancer cells. This may necessitate further refinement of cell-specific physiologic culture conditions to better maintain the in vivo biology of cells. In this study, we directly address this hypothesis by describing the development of a tumour microenvironment-like medium (TMEM) based on metabolomic profiling of murine pancreatic ductal adenocarcinoma tumour interstitial fluid from relevant literature. We found that murine pancreatic ductal adenocarcinoma (KPCY) cells cultured under TME-like conditions (TMEM, pH 7.0, 1.5% O2) exhibited increased glucose uptake and lactate production rates compared to those cultured under healthy plasma-like conditions (Mouse Plasma-like Medium, pH 7.4, 5% O2), despite lower initial glucose concentrations in TMEM (2.3 mM vs. 4.4 mM in Mouse Plasma-like Medium). Moreover, cell proliferation rates were lower in TMEM, suggesting an overall reduction in ATP consumption fueling cell division. Seahorse Extracellular Flux Analysis is being performed to determine effects on cellular bioenergetics. Metabolomic amino acid uptake using LCMS is also being performed to further assess the effect of TMEM on nutrient utilization. Using RNA-sequencing, we showed that culture in TMEM increased expression of genes associated with angiogenesis, amino acids biosynthesis, cell migration, and endothelial-to-mesenchymal transition. Migration assays confirmed increased motility in KPCY cells cultured in TMEM. Taken together, these results demonstrate that growth in a medium designed to simulate the TME alters KPCY cell biology in ways that are relevant to their pathology, which highlights the significance of maintaining TME-like conditions in culture. This research was funded by a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant from JAS and a NSERC Canadian Graduate Student (Masters) Grant awarded to GLG. 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.

Systematic Assessment of Electrode Wettability for Vanadium Redox Flow Batteries

Vanadium redox flow batteries (VRFBs) are a promising energy storage technology due to their advantages such as long-life cycle and scalability. In these systems, porous electrodes such as carbon paper and carbon felts have been used because of their desirable properties such as good acid resistance and low cost. However, these materials may have poor reversibility and wettability, which can negatively affect the system performance. Recently, different activation methods have been proposed to enhance physico-chemical properties and overcome these limitations. Among different methods, surface treatments have been commonly used in the literature [1-5] since they can introduce desirable functional groups (e.g., oxygen, nitrogen) and enhance electrochemically active surface area (ECSA), which is believed to be the main mechanisms for electrode performance improvement. Although it is suggested that higher electrode performance can be achieved by enhancing wetted or active surface area [6], there is still a disparity in how to assess relevant wetting properties, since wettability assessment is often neglected and performance assessment is usually done based on VRFB cycling test results, which is costly and time consuming.Static contact angle (CA) is commonly used to characterize electrode wettability and evaluate the effect of different treatments on the electrode surface. However, this technique offers a limited understanding and superficial analysis, since samples are either classified as hydrophobic or hydrophilic, showing no correlation to electrochemical performance. Moreover, CA measurements are not adequate for porous electrodes, since porosity and surface roughness can impact on contact angle results. In the present work, we propose to use the method of standard porosimetry (MSP) and cyclic voltammetry (CV) to evaluate the impact of surface treatments on electrode wettability from a complete physical (pore size distribution), chemical (functional group density), and electrochemical (electrochemically active surface area) perspective. These tools offer richer information than basic CA measurements and only take a few hours to be performed, thus reducing the assessment time and cost compared to VRFB assembly and cycling tests.Preliminary results show that both MSP and CV techniques can provide useful information regarding physical and chemical properties that can correlate electrode wettability to electrochemical performance. While MSP results can provide electrode morphology (pore size distribution, porosity, specific and wetted surface area), CV measurements can provide surface chemistry information (functional groups density) and electrochemically active surface area (capacitance). Thus, both tools can be used synergistically to investigate how different treatments impact both physical and chemical properties and how wetting properties impact electrode performance. Achieving high performance is essential to increase system energy density and decrease both capital and operational cost, making VRFBs more competitive and suitable for grid-scale storage of renewable energy, having positive environmental impacts and facilitating sustainable transition. Acknowledgements This research was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC), Canada Foundation for Innovation (CFI), British Columbia Knowledge Development Fund (BCKDF), Western Economic Diversification Canada (WD), Canada Research Chairs (CRC), and the National Research Council of Canada (NRC). Technical support from Elizabeth Fisher and Jonas Stoll is also acknowledged.

High Durability of Pemion® Proton Exchange Membranes in Cross-Pressure Accelerated Mechanical Stress Tests

Polymer electrolyte membrane fuel cells (PEMFC) are the dominant technology for hydrogen-powered fuel cell electric vehicles in clean transportation systems. To be suitable for commercialization and applicability in real-world use-cases, light and heavy-duty fuel cell vehicles require lifetimes of over 8,000 and 30,000 hours, respectively [1]. Hence, enhancing the durability of all fuel cell components, particularly the proton exchange membrane (PEM), is of great importance.Recently, fuel cell membranes based on hydrocarbon (HC) chemistries have become increasingly common in the literature [2]. Materials with polyaromatic backbones, tunable electrochemical properties, and low reactant permeability are increasingly seen as potential alternatives to incumbent perfluorosulfonic acid (PFSA) materials [2]. Additionally, as restrictions on the use of fluorinated materials in various industries continue to grow, the importance of HC chemistries will as well. Sulfo-phenylated polyphenylenes (sPPPs) are a particular class of HC materials that show promise [3]. However, the phase separation between hydrophilic and hydrophobic domains within sPPPs may not be as discrete as in PFSAs [3], requiring higher ion exchange capacity (IEC) values than PFSAs to achieve similar protonic conductivity. High IEC typically results in greater material hydrophilicity, which can render membranes dimensionally unstable in a fuel cell [4].State-of-the-art commercial PEMs are now manufactured as thin films (≤ 18 µm), offering small ohmic loss and therefore high fuel cell performance. To improve dimensional stability and eliminate the risks of electrical shorting, PEMs are commonly mechanically reinforced using a porous, inert, and non-ionic substrate, such as expanded polytetrafluoroethylene (ePTFE). In a work by Miyake et al. [5], sulfonated polyphenylene-based ionomer membranes with flexible polyethylene mechanical reinforcement were prepared and the results indicated promising mechanical properties and improved longevity in RH cycling tests. However, there is still a lack of data about the fatigue durability of HC membranes in the literature, and evaluating and comparing the mechanical durability of numerous PEMs with a mechanical reinforcement layer in a traditional wet-dry cycling accelerated stress test would be a time-consuming and thus costly process [6].In our previous work, [7] we combined constant pressure differential across an ePTFE-reinforced perfluorosulfonic acid (PFSA) ionomer membrane with in-situ RH cycles (ΔP-AMST) to simulate the actual mechanical stresses in the fuel cell environment, while accelerating the durability testing for reinforced PEMs. In this study, ΔP-AMST is used to benchmark the fatigue lifetime curves for Pemion® membranes and compare it with a commercial reinforced PFSA-based PEM. The test temperature was set to 90 °C, and dry and wet (90% RH) phases were 60s and 30s, respectively. The hardware and semi-MEA specifications used for the test are shown in Figure 1a-c. A semitransparent polycarbonate spacer plate with 20 mm thickness and a circular aperture (25.4 mm) in the middle was used to allow free expansion of the membrane (Figure 1d). The cathode side was pressurized to create a cross pressure between the two sides and intensify the stress on the membrane during the RH cycling process. The ultimate failure of the membrane is shown in Figure 1e. The radial stress at the center of the deformed membrane is estimated by Hencky’s solution, as reported in our previous work [7]. Figure 1f demonstrates the estimated nominal stress on the membranes as a function of their lifetimes in terms of RH cycles. According to the fatigue S-N curves, reinforced Pemion® membranes afford longer lifetime than incumbent PFSA materials if the membrane edges are well protected. In addition, the impact of IEC on the fatigue durability of Pemion® membranes is investigated and the results are evaluated against stress of dehydration and dynamic mechanical analysis measurements. Acknowledgements This project was financially supported by Natural Sciences and Engineering Research Council of Canada (NSERC), Ionomr Innovations Inc, Canada Foundation for Innovation (CFI), British Columbia Knowledge Development Fund (BCKDF), Western Economic Diversification Canada (WD), and Canada Research Chairs (CRC).

Grooved Electrodes for High Power Density Fuel Cells

Proton exchange membrane fuel cells (PEMFCs) are a promising alternative to internal combustion engines, owing to their intrinsic power density, decoupled energy storage and generation, and relatively short refueling time. However, challenges related to cost, performance, and durability continue to prevent wide adoption of PEMFCs.1 Development of alternative electrode structures, which can enable smaller and less expensive PEMFCs with higher power and lower precious metal content, provides a promising path to overcome these challenges.2 Here, we report grooved electrodes, where the transport pathways of H+ and O2 were partitioned. Specifically, H+ are transported through electrode ridges with optimized ionomer content, and O2 is transported through the grooves that separate the electrode ridges. The grooved electrodes made with commercial electrode materials enhanced the performance up to 50%, and the enhancement becomes greater after accelerated durability tests. We verify via electrochemical impedance analyses, limiting current measurements, and multiphysics modeling that the enhancement is due to improved H+ and O2 transport. The work also demonstrates that the electrodes can be further improved by optimizing the electrode geometry, proven via machine learning investigations. These results inform next generation electrode designs for enhanced PEMFC performance and durability. Acknowledgement: This work was supported by the Hydrogen and Fuel Cell Technologies Office (HFTO), Office of Energy Efficiency and Renewable Energy, US Department of Energy (DOE) through the Million Mile Fuel Cell Truck (M2FCT) consortia, technology managers G. Kleen and D. Papageorgopoulos. Financial support for this work from the Laboratory Directed Research and Development (LDRD) program at Los Alamos National Laboratory (LANL) is gratefully acknowledged (Projects 2020200DR and 20210915PRD2). ChungHyuk Lee acknowledges the support of the Natural Sciences and Engineering Research Council of Canada (NSERC).

Thermo-Mechanical Stability of Hydrocarbon-Based Pemion® Proton Exchange Membranes

Considering the environmental concerns about the disposal of perfluorosulfonic acid (PFSA) membranes as well as the growing interest in higher temperature operability of polymer electrolyte membrane fuel cells (PEMFCs), non-fluorinated hydrocarbon-based proton exchange membranes (PEMs) with aromatic backbones have become an increasingly active area of research. Low reactant cross-over, tunable electrochemical properties, and differentiated chemistries and potentially safer and cost-reducing synthesis procedures, are additional favourable features of hydrocarbon-based PEMs for prospective use in PEMFCs [1]. Vulnerable linking units, however, are known to be the main disadvantages of these polymers in the oxidative environment of fuel cells. During PEMFC operation, destructive radical species such as hydroxyl (HO•) are produced, causing polymer degradation and thinning in the membrane [2]. Recently, sulfo-phenylated polyphenylenes (sPPPs) have shown outstanding oxidative stability due to a polymer backbone comprising only aryl-aryl bonds, with mitigated chemical degradation in ex-situ and in-situ durability studies [3, 4]. Another concern is regarding the thermo-mechanical stability of PEMs. Thus, a systematic thermo-mechanical stability study is required to confirm the potential of sPPP-based PEMs to replace conventional PFSAs, especially for high temperature PEMFC, i.e., 110-120 °C.The present research objective is to assess the thermo-mechanical stability of a commercial reinforced hydrocarbon-based PEM, Pemion® (PF1-HLF8-15-X, 15 µm thick, reinforced), as well as a mechanically-reinforced PFSA-based reference membrane, across a wide range of temperature (30-120 °C) and relative humidity (RH) (10-90%) conditions that includes the crucial high temperature window of interest for future PEMFCs [6]. To this end, a comprehensive design of experiment yielded 19 tensile tests at various hygrothermal conditions with dynamic mechanical analyzer (DMA 850; TA Instruments) equipped with an external environmental chamber accessory (TA Instruments, RH Accessory). Important mechanical properties such as Young’s modulus, ultimate tensile stress, yield stress, maximum elongation at break, strain hardening, and modulus of resilience were extracted and discussed as well. Datapoints were fitted for empirical model development and mechanical properties were estimated for high temperature and RH conditions beyond the capability of the instrument. This method can be employed to assess if the mechanical properties of membrane materials can be retained at higher temperatures, regardless of polymer chemistry and type. Storage modulus and loss modulus were separately measured in a dynamic mode to observe the impact of temperature on the mechanical response of the hydrophobic backbone and hydrophilic ionic clusters, respectively.Overall, Pemion® demonstrates tough tensile properties in the stress-strain tests due to its sterically encumbered polyphenylene backbone (Figure 1a), whereas the reference PFSA (Figure 1b) shows elastomer-like behavior with much lower Young’s modulus, yield stress, and strain hardening (slope of the curve in the plastic deformation region). Figure 1c-f show the main viscoelastic properties extracted from the tensile tests at room (30 °C, 50% RH) and high temperature fuel cell conditions (110 °C, 50% RH). The modulus of elasticity and strain hardening of Pemion® membrane are almost temperature-independent, whereas these properties for the reinforced PFSA material undergo a significant decay at high-temperature ambience. Pemion® maintains good yielding strength even at high temperature and RH conditions (110-120 °C and 80% RH). Nevertheless, small mechanical stress values as low as 1 MPa can cause spontaneous yielding in the PFSA reference material above 110 °C. The modulus of resilience for the reinforced PFSA is also predicted to be zero at elevated hygrothermal conditions (i.e., 90 °C and 70% RH). This is interpreted as an approach to the material’s glass transition condition, where it loses its mechanical integrity and therefore, is potentially unsuitable for higher temperature PEMFC operation. Moreover, the dynamic mechanical thermal analysis revealed that Pemion® retains its robustness at hygrothermal ambience close to high-temperature PEMFCs, i.e., 110-120 °C and 40-50% RH, whereas the backbone of the PFSA material gradually loses its strength. Acknowledgements This project was financially supported by Natural Sciences and Engineering Research Council of Canada (NSERC), Ionomr Innovations Inc, Canada Foundation for Innovation (CFI), British Columbia Knowledge Development Fund (BCKDF), Western Economic Diversification Canada (WD), and Canada Research Chairs (CRC).

ECR Spotlight – Yangfan Zhang

ECR Spotlight is a series of interviews with early-career authors from a selection of papers published in Journal of Experimental Biology and aims to promote not only the diversity of early-career researchers (ECRs) working in experimental biology during our centenary year but also the huge variety of animals and physiological systems that are essential for the ‘comparative’ approach. Yangfan Zhang is an author on ‘ Energetics of collective movement in vertebrates’, published in JEB. Yangfan is a Natural Sciences and Engineering Research Council of Canada (NSERC) post-doctoral research fellow in the lab of George V. Lauder at Harvard University, USA, investigating environmental effects on respiratory phenotype and the bioenergetics of specific locomotion gaits, to ultimately expand the potential of tracking field metabolic rate in fish in the light of ecology and evolution.

Robustness of Stochastic Optimal Control to Approximate Diffusion Models Under Several Cost Evaluation Criteria

In control theory, typically a nominal model is assumed based on which an optimal control is designed and then applied to an actual (true) system. This gives rise to the problem of performance loss because of the mismatch between the true and assumed models. A robustness problem in this context is to show that the error because of the mismatch between a true and an assumed model decreases to zero as the assumed model approaches the true model. We study this problem when the state dynamics of the system are governed by controlled diffusion processes. In particular, we discuss continuity and robustness properties of finite and infinite horizon α-discounted/ergodic optimal control problems for a general class of nondegenerate controlled diffusion processes as well as for optimal control up to an exit time. Under a general set of assumptions and a convergence criterion on the models, we first establish that the optimal value of the approximate model converges to the optimal value of the true model. We then establish that the error because of the mismatch that occurs by application of a control policy, designed for an incorrectly estimated model, to a true model decreases to zero as the incorrect model approaches the true model. We see that, compared with related results in the discrete-time setup, the continuous-time theory lets us utilize the strong regularity properties of solutions to optimality (Hamilton–Jacobi–Bellman) equations, via the theory of uniformly elliptic partial differential equations, to arrive at strong continuity and robustness properties. Funding: The research of S. Yüksel was partially supported by the Natural Sciences and Engineering Research Council of Canada (NSERC).

Responsive polymer thin films

Responsive polymer thin films

Central alpha-2 adrenergic mechanisms affect human sympathetic neuronal discharge strategies

The central neural mechanisms affecting sympathetic neuronal discharge strategies supporting homeostatic adjustments in human muscle sympathetic nerve activity (MSNA) remain unclear. This study investigated the hypothesis that central alpha-2 adrenergic mechanisms affect sympathetic action potential (AP) discharge, recruitment, and latency patterns within human MSNA (peroneal nerve microneurography and continuous wavelet transform). An alpha-2 adrenergic agonist (dexmedetomidine) was infused in eight healthy male and female participants (5 females; 28 ± 7years). Data were recorded during a 5-minute resting control condition, a 10-minute intravenous dexmedetomidine loading dose (0.225 μg/kg), and a dexmedetomidine maintenance dose (~0.1 μg/kg/hr). Data are reported as mean (SD) for the 5-minute control condition and 2-minutes of the dexmedetomidine infusion when MSNA bursting activity was demonstrably reduced. Two-tailed paired t-tests were performed. Dexmedetomidine reduced mean pressure (92 ± 7 to 80 ± 8 mmHg; P < 0.01) but did not affect heart rate (61 ± 13 to 60 ± 14 bpm; P = 0.75). Dexmedetomidine reduced integrated MSNA burst frequency (14 ± 6 to 4 ± 3 bursts/min; P < 0.01), sympathetic AP frequency (75 ± 46 to 16 ± 14 AP/min; P < 0.01), APs per burst (5 ± 1 to 4 ± 1 AP/burst; P = 0.01), AP clusters per burst (3.5 ± 0.7 to 3.0 ± 0.7 clusters/burst; P = 0.03), and de-recruited the largest AP clusters (12 ± 3 to 7 ± 2 AP clusters; P < 0.01). Despite de-recruiting large AP clusters with short conduction times, dexmedetomidine elicited shorter sympathetic AP conduction times (1.18 ± 0.12 to 1.14 ± 0.13 s; P = 0.03). Six participants performed a Valsalva Maneuver (20 s, 40 mmHg mouth pressure) during the control condition and during the dexmedetomidine maintenance dose. Data are reported as mean (SD) change (Δ) from the 2-minute period preceding the Valsalva Maneuver to the Valsalva Maneuver for each condition. During the control condition, Valsalva Maneuver increased AP frequency (Δ 311 ± 317 AP/min; P = 0.048), recruited larger previously silent AP clusters (Δ 2 ± 1 AP clusters; P < 0.01), and elicited shorter AP conduction times (Δ ‑0.09 ± 0.07 s; P = 0.02). Compared to the control condition, Valsalva Maneuver performed during the dexmedetomidine maintenance dose condition elicited lesser increases in AP frequency (Δ 116 ± 189 AP/min; P vs. control = 0.02) and lesser recruitment of larger previously silent AP clusters (Δ 0 ± 1 AP clusters; P vs. control = 0.02). Dexmedetomidine did not affect the latency reduction elicited by Valsalva Maneuver (Δ ‑0.07 ± 0.14 s; P vs. control = 0.61). These data suggest that human central alpha-2 adrenergic mechanisms affect: i) sympathetic postganglionic neuronal discharge and recruitment patterns, and ii) synaptic delays within the sympathetic neurocircuitry influencing AP latency. This work was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) and the National Institutes of Health (NIH). This is the full abstract presented at the American Physiology Summit 2023 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.

Dictionary of immune responses to 86 cytokines in vivoat single-cell resolution

Abstract Cytokines mediate cell-cell communication in the immune system and represent important therapeutic targets. A myriad of studies have underscored their central role in immune function, yet we lack a global view of the cellular responses of each immune cell type to each cytokine. To address this gap we created the Immune Dictionary – a compendium of single-cell transcriptomic profiles of over 20 cell types in response to each of 86 cytokines in murine lymph nodes in vivo, representing over 1,500 cytokine-cell type combinations. A cytokine-centric view of the dictionary revealed that most cytokines induced highly cell type-specific responses. For example, the inflammatory cytokine IL-1β induced distinct gene programs in almost every cell type. A cell type-centric view of the dictionary identified multiple cytokine-driven cellular polarization states in each immune cell type, including previously uncharacterized states such as an IL-18-induced polyfunctional NK cell state. Based on the dictionary, we developed companion software, Immune Response Enrichment Analysis (IREA), for assessing cytokine activities and immune cell polarization from gene expression data, and applied it to reveal cytokine networks in tumors following immune checkpoint blockade therapy. Our dictionary generates new hypotheses for cytokine functions, illuminates pleiotropic effects of cytokines, expands our knowledge of activation states of each immune cell type, and provides a framework to deduce the roles of specific cytokines and cell-cell communication networks in any immune response. This work was supported by the NIH Grant RM1HG006193 and an Adelson Medical Research Foundation Grant to N.H. This work was also supported by a Natural Sciences and Engineering Research Council of Canada (NSERC) Doctoral Fellowship, Whitaker Health Sciences Fund Fellowship, and Wellington and Irene Loh Fund Fellowship to A.C., and NCI Research Specialist Award (R50CA251956) to S.L.

Sarcolipin ablation decreases whole body VO2 in young female nice

The sarco(endo)plasmic reticulum calcium (Ca 2+ ) ATPase (SERCA) pump is a major regulator of cytosolic Ca 2+ in striated muscle. Sarcolipin (SLN) reduces SERCA-mediated Ca 2+ pumping efficiency and is a key regulator of muscle metabolism and contractile function. With SERCA activity comprising approximately 12% of whole-body metabolic rate, the inefficient SERCA Ca 2+ cycling promoted by SLN would be predicted to increase metabolic rate. Although SLN is involved in adaptive diet-induced thermogenesis and overexpression of SLN increases metabolic rate and protects against diet-induced obesity, we found previously that SLN ablation had no effect on whole body metabolic rate or body composition in male mice that were fed a standard chow diet. However, unpublished work from our lab indicates that SLN expression in mouse soleus is significantly higher in females compared with males. Therefore, the purpose of this study was to investigate the effects of SLN ablation on body composition and metabolic rate of female mice. Adult (4-6mo) female wild type (WT) and SLN knockout (KO) mice (n=4 per group) were used to collect anthropometric measures (adiposity and body weight) and were housed in a comprehensive lab animal monitoring system (CLAMS) over a 48-hour period to assess daily whole body VO2 and total cage activity. With SLN ablation, total whole body VO 2 (ml/kg/hr) was lower (p<0.05) in the KO females (3534 ± 95.1) compared to WT females (5080 ± 98.8), with no differences (p>0.05) found for total cage activity (counts) (WT, 14935.42 ± 1799.6 vs. KO, 11860.83 ± 679.48), body weight (grams) (WT, 20.97 ± 0.76 vs. KO, 22.18 ± 0.80), or adiposity (arbitrary units) (WT, 5.18 ± 1.71 vs. KO, 2.12 ± 0.36). These results showing that high levels of endogenous muscle SLN expression in female mice influence whole-body metabolism even under chow-fed conditions, demonstrate a potential important sex difference in whole body physiology and metabolism. Natural Sciences and Engineering Research Council of Canada (NSERC) [grant number 311922-05 (to A.R.T.)] This is the full abstract presented at the American Physiology Summit 2023 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.

Imaging Chronic Active Lesions in Multiple Sclerosis: a Consensus Statement from the North America Imaging in Multiple Sclerosis Cooperative (P11-3.009)

Imaging Chronic Active Lesions in Multiple Sclerosis: a Consensus Statement from the North America Imaging in Multiple Sclerosis Cooperative (P11-3.009)

They mostly come at night: Predation on sleeping insects by introduced candy-striped spiders in North America.

They mostly come at night: Predation on sleeping insects by introduced candy-striped spiders in North America.

Polynomial Upper Bounds on the Number of Differing Columns of Δ-Modular Integer Programs

We study integer-valued matrices with bounded determinants. Such matrices appear in the theory of integer programs (IPs) with bounded determinants. For example, an IP can be solved in strongly polynomial time if the constraint matrix is bimodular: that is, the determinants are bounded in absolute value by two. Determinants are also used to bound the [Formula: see text] distance between IP solutions and solutions of its linear relaxation. One of the first to quantify the complexity of IPs with bounded determinants was Heller, who identified the maximum number of differing columns in a totally unimodular matrix. Each extension of Heller’s bound to general determinants has been superpolynomial in the determinants or the number of equations. We provide the first column bound that is polynomial in both values. For integer programs with box constraints, our result gives the first [Formula: see text] distance bound that is polynomial in the determinants and the number of equations. Our result can also be used to derive a bound on the height of Graver basis elements that is polynomial in the determinants and the number of equations. Furthermore, we show a tight bound on the number of differing columns in a bimodular matrix; this is the first tight bound since Heller. Our analysis reveals combinatorial properties of bimodular IPs that may be of independent interest. Funding: J. Lee was supported in part by the Office of Naval Research [Grant N00014-21-1-2135] and the Air Force Office of Scientific Research [Grant FA9550-19-1-0175]. J. Paat was supported by a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant [Grant RGPIN-2021-02475].