bluuebunny/crossref_metadata_2025 huggingface dataset:
Bioactive sphingolipids in inflammation and cancer
Authors: Obeid Lina Marie
Published: June 2021

The bioactive sphingolipids ceramide, sphingosine, and sphingosine‐1‐phosphate (S1P) have recently emerged as important modulators of cell growth, cellular senescence, and programmed cell death. In order to study the roles of these lipids in cell regulation, it is important to understand their interconnected metabolic pathways. Ceramide, the backbone of sphingolipids is broken down by one of many ceramidases (CDAse) to generate sphingosine the precursor of S1P by the action of sphingosine kinase (SK). The enzymes involved in the breakdown of ceramide, and in the generation and breakdown of S1P all appear to be important regulated enzymes. Our laboratory has focused on studying the role of CDAse, SK, and its product S1P in inflammation and in cancer. We have recently implicated the SK1/ S1P pathway in mediating inflammatory responses in cells and most recently in vivo in a DSS model of colitis. In order to determine the mechanism of substrate generation for SK in inflammation we are utilizing a combination of CDAse inhibitors and KO mice. We demonstrate distinct roles for neutral and acid CDAses in regulation of ceramide/ S1P levels in the stromal and epithelial layers of intestine and consequently in the inflammatory response to DSS‐induced colitis. In addition, significant evidence has implicated bioactive sphingolipids in cancer progression and apoptosis. In probing the role of CDAses and SK in cancer we find distinct roles for the different CDAses and SK1 in colon cancer progression. These studies lend strong support for the role of bioactive lipids and their metabolizing enzymes in inflammation and cancer and make them attractive therapeutic targets for inflammation and cancer.
Targeted mutation of NaV1.4 causes paralysis in mouse as observed in attacks of Hyperkalemic Periodic Paralysis (HyperKPP)
Authors: Khogali Shiemaa , Hayward Lawrence J. , Renaud Jean‐Marc
Published: June 2021

The single point mutation M1592V on the skeletal muscle sodium channel, NaV1.4, causes human HyperKPP. For this specific point mutation, the onset of the paralytic attacks occurs between 5–10 years of age. In response to several known triggers, such attacks may then increase in frequency, duration and intensity until adolescence, but typically they diminish in mid‐ adulthood. By that time, fixed muscle weakness and a major shift toward type I and IIA fibers are observed in many muscles. The objective of this study was to determine if introducing a missense substitution corresponding to a human familial HyperKPP mutation (Met1592Val) into the mouse gene (mice(+/M1592V)) encoding the skeletal muscle voltage‐gated Na+ channel NaV1.4 also may predispose to paralytic attacks with changes in frequency and intensity. Paralysis of the hindlimb muscles were observed during the period of 6‐12 weeks postnatal. By 8 weeks of age, EDL muscle from mice(+/M1592V) had more than 2‐fold less type IIB and 2‐times more type IIA fibers when compared to EDL muscles of wild type mice. Finally, measurement of NaV1.4 content by immunohistochemistry showed a small decrease in protein content from 3 to 8 weeks of age followed by no further changes up to 16 weeks of age. More importantly, there was no difference in NaV1.4 protein content between wild type and mice(+/M1592V). We conclude that altered mouse NaV1.4 equivalent to the human M1592V mutation causes paralytic attacks during a postnatal window of 6–12 weeks and a shift toward type IIA fibers that is not associated with a change in NaV1.4 protein content.
Sphingomyelinase and ceramide increase reactive species and depress maximal skeletal muscle force in vitro
Authors: Ferreira Leonardo F , Smith Jeffrey D , Moylan Jennifer S , Reid Michael B
Published: June 2021

Activation of Sphingomyelinase (SMase) depresses maximal muscle force: an effect blunted by antioxidants. In non‐muscle cells, SMase catalyzes the breakdown of sphingomyelin into ceramide, which increases reactive oxygen and nitrogen species (i.e., oxidants). Thus, we tested three hypotheses: i) SMase increases ceramide levels in myocytes; ii) SMase and ceramide increase oxidants in myocytes; and iii) ceramide depresses skeletal muscle force. We performed experiments in differentiated mytubes and murine diaphragm. Myotubes were exposed to SMase (0.5 U/ml), C2‐ceramide (10 μM), C6‐ceramide (10 μM), or vehicle (CTRL) for 20 min at 37°C. Diaphragm fiber bundles were exposed to C6‐ceramide in vitro (20 μM, 30 min, 37°C). Our results show that SMase increased total ceramide levels (in pmol/nmol Pi: CTRL 1.96 ± 0.09, SMase 5.47 ± 0.36; p < 0.05). Oxidant‐stimulated fluorescence was increased by C2‐ceramide (17 ± 6%; p < 0.02), C6‐ceramide (25 ± 5%; p < 0.001), and SMase (35 ± 8%; p < 0.001). Reactive nitrogen species‐dependent fluorescence was unaffected by SMase (CTRL 179.4 ± 3.6 a.u., SMase 179.5 ± 3.8 a.u.). C6‐ceramide decreased maximal diaphragm force by 56 ± 10% (p < 0.05). We conclude that SMase increases reactive oxygen species in muscle cells. This effect appears to be mediated by ceramide and results in depression of maximal skeletal muscle force.

*Funding provided by NIH (R01 AR055974) and AHA‐GRA (09POST2020082)
Myofilament structure in muscle from tissue specific Bmal1 KO mice
Authors: Houtz Jessica , Campbell Kenneth , Esser Karyn
Published: June 2021

We have observed that skeletal muscle from the arrhythmic germline Bmal1 knock out mouse (Bmal1 KO) exhibits significant weakness defined by a reduction in muscle specific tension. Evaluation of electron micrographs (EMs) from cross‐sections of adult gastrocnemius muscles reveals obvious divergences from the normal hexagonal arrangement of thin and thick filaments in the Bmal1 KO mice.

The objective of this project is to address whether the structural pathology in muscle is the result of local or systemic loss of Bmal1. We have generated a striated muscle specific Bmal1 KO mouse and developed a computational tool for the quantitative analysis of myofilament architecture. Bmal1 is selectively eliminated in striated muscle by crossing the MCK‐Cre mouse with the floxed Bmal1 mouse. Muscle structure will be evaluated with newly developed image processing software that identifies bundles of actin (thin filaments) or myosin (thick filaments) in EMs of muscle cross‐sections. Preliminary programming detects myofilaments as intensity peaks in the gray‐scale image and categorizes them as thick or thin depending on the cross‐sectional area of the peaks. Cellular–level muscle function is assessed using permabilized single fiber mechanics. The results of this work will determine whether local muscle specific expression of Bmal1 is necessary for maintenance of adult skeletal muscle structure and function.
Skeletal Muscle Regulatory Responses to Increased Extracellular Lactate
Authors: Lindinger Michael I , Leung Matt , Moradi Jasmin , Shortreed Karin E , Hawke Thomas J
Published: June 2021

Mammalian skeletal muscle cells exhibit cell shrinkage followed by regulatory volume increase (RVI) in response to increases in extracellular osmolarity caused by addition of concentrated NaCl or sucrose. We hypothesized that increased extracellular sodium lactate would similarly result in a transient loss of cell volume, followed by RVI, and that the RVI would be more rapid and pronounced than that seen with NaCl due to entry of lactate into the cell. The present study measured the time course of change single fibre width in response to varied increases in extracellular NaCl or Na‐lactate. Adult mouse EDL single fibres were isolated using collagenase and incubated in DMEM prior to and during experimentation. Fibre images were obtained at 3–6 s intervals for up to 40 min. Fibre images were analyzed for width at 2 sites. Increased osmolarity resulted in a rapid decrease in fibre width, followed by RVI. The volume recovery was faster and more complete when [lactate] ≥20 mmol/L. There was a linear relationship between increases extracellular [lactate], cell shrinkage, and magnitude of RVI. It appears that the inward transport of lactate into skeletal muscle contributes, together with increased NKCC activity, to the RVI in mammalian skeletal muscle.

Supported by NSERC of Canada.
TWEAK/Fn14 system is a critical regulator of denervation‐induced skeletal muscle atrophy
Authors: Kumar Ashok , Bhatnagar Shephali , Mittal Ashwani , Glass David J
Published: June 2021

Skeletal muscle atrophy occurs in a variety of clinical settings, including disuse atrophy and denervation. Inflammatory cytokines are important mediators of muscle‐wasting in settings such as cancer cachexia; however, their role in denervation remains unknown. We demonstrate the cytokine TWEAK mediates skeletal muscle atrophy in response to denervation. Transgenic expression of TWEAK induced atrophy, fibrosis, fiber‐type switching, and the degradation of muscle proteins. Conversely, genetic ablation of TWEAK decreased the loss of muscle proteins and spared fiber cross‐sectional area, muscle mass and strength after denervation. Expression of the TWEAK receptor Fn14 was significantly increased in muscle upon denervation, demonstrating an unexpected “inside‐out” signaling pathway leading to atrophy. TWEAK activates NF‐kappa B, causing an increase in the expression of the E3 ubiquitin ligase MuRF1. This study reveals a novel mechanism of skeletal muscle atrophy, and indicates that the TWEAK/Fn14 system is an important target for preventing skeletal muscle wasting. This work was supported by a National Institute of Health grant (RO1 AG129623) to AK.
The effect of nNOS overexpression on intracellular ROS activities in skeletal muscle fibres at rest and following a period of contractile activity
Authors: Sakellariou Giorgos K , Palomero Jesus , Van Remmen Holly , Jackson Malcolm J
Published: June 2021

ROS serve as important signaling molecules and interact with multiple cell signaling and regulatory pathways to modulate changes in gene expression. The aim was to examine the effect of nNOS overexpression on ROS activities in skeletal muscle fibres at rest and following a period of contractile activity. To elucidate the roles of ROS, we examined their intracellular activities by using fluorescence microscopy. Mice overexpressing nNOS and age‐matched wild type (WT) mice were used in this study. Flexor digitorum brevis muscles were dissected and incubated in collagenase to isolate single muscle fibres. Fibres were plated on culture dishes and were loaded with DAF‐FM DA, DHE or DCFH DA, fluorescent probes for the assessment of nitric oxide (NO·) superoxide (O2·) and a general probe for ROS respectively. Contractile activity was induced by electrical stimulation. Control non‐stimulated fibres from the nNOS mice showed a higher rate of increase in DAF‐FM fluorescence compared with the WT group implying a higher NO· formation. Fibres from nNOS overexpressors showed a reduced ethidium fluorescence compared with fibres from WT mice at rest indicating a lower O2· generation. No differences were observed between groups following contractions. These results suggest that overexpression of nNOS can increase NO· ‘bioavailability’ in skeletal muscle cells and reduce O2· toxicity. Supported by the A Onassis Foundation (GR).
Exercise ability is determined by muscle ATP buffer content, not Pi or pH
Authors: Jeneson Jeroen Antonius , Schmitz Joep PJ , van Dijk Johannes H , Stegeman Dick F , Nicolay Klaas
Published: June 2021

Failure to maintain power output during intense work is a property of skeletal muscle commonly known as muscle fatigue. The past years have witnessed a paradigm shift in the debate of its molecular basis. Accumulation of an ATP hydrolysis product, inorganic phosphate (Pi), has overtaken muscle acidification on the list of main culprits. Here, we employed in‐magnet bicycle ergometry (1), 31P nuclear magnetic resonance spectroscopy and multi‐channel surface electromyography to investigate this hypothesis in human subjects in vivo. The dissociation between maximal energetic depletion and maximal muscle acidification that is particular to two‐legged voluntary exercise (2) was exploited to design an in vivo experiment in which the muscle concentrations of Pi and H+ at the onset of bicycling exercise were manipulated quasi‐independently. It was found that the ability of a subject to exercise at supramaximal workload maintaining a pedalling frequency of 80 rpm was neither affected by low pH or high Pi but required a minimal muscle phosphocreatine concentration of 4.9 ± 0.3 mM.
Protective effect of methylprednisolone on ventilator‐induced diaphragm dysfunction is dose dependent
Authors: Maes Karen , Agten Anouk , Smuder Ashley , Powers Scott K , Decramer Marc , Gayan‐Ramirez Ghislaine
Published: June 2021

We previously showed that an acute high dose of corticosteroids (80 mg/kg) with controlled mechanical ventilation (CMV) prevented ventilator‐induced diaphragm dysfunction in rats. We examined whether administration of lower doses of methylprednisolone (5 and 30 mg/kg) would result into a similar protective effect. Rats were assigned to a control group (C) or to 24 h of CMV receiving an im injection of saline (CMV) or 5 (MP‐5) or 30 mg/kg (MP‐30) of methylprednisolone. Diaphragm force was decreased after CMV but was more depressed in MP‐5 while in MP‐30 it was similar to C. Atrophy was more severe in MP‐5 than after CMV while no atrophy was observed in MP‐30. Diaphragm calpain activity was increased after CMV and even more so in MP‐5, while it was similar to C in MP‐30. Caspase‐3 activity was increased after CMV and after MP‐5 and MP‐30. Expression of calpastatin, an endogenous inhibitor of calpain, was decreased in CMV and MP‐5 and similar to C in MP‐30. These data clearly show that the effects of corticosteroids during CMV are dose dependent and are related to calpain activity. The latter was upregulated at low doses and inhibited at high doses. These effects are probably mediated by calpastatin. Supported by Fonds voor Wetenschappelijk Onderzoek‐Vlaanderen and by AstraZeneca Pharmaceuticals
Effects of glutathione depletion on apoptotic signaling in slow and fast skeletal muscle of young and old rats
Authors: Lalonde Crystal Cassandra , Denniss Steven G. , Levy Andrew S. , Rush James W.E. , Quadrilatero Joe
Published: June 2021

Oxidative stress has been associated with aging and can also induce apoptosis. Glutathione is an antioxidant widely expressed in mammalian tissue; however, its role in skeletal muscle apoptosis is currently unclear. Young (34.85 ± 0.68 wks) and old (69.11 ± 3.61 wks) male Sprague‐Dawley rats were provided either drinking water alone or drinking water supplemented with L‐buthionine‐[S,R]‐sulfoximine (BSO) for 10 days. BSO treatment significantly (p<0.05) decreased reduced glutathione (GSH) content in white gastrocnemius (WG) and soleus muscle by 96% and 89%, respectively, compared to age‐matched controls. Furthermore, reactive oxygen species generation was significantly (p<0.05) elevated in soleus muscle of young and old BSO‐treated animals. Western blot analysis revealed that heat shock protein‐70 (Hsp70) protein expression was significantly (p<0.05) elevated in old soleus muscle; however, BSO treatment had no effect. There was also a trend towards increased CuZnSOD (p=0.08) protein levels in BSO‐treated animals compared to age‐matched controls. In addition, caspases‐3, ‐8, and ‐9 activity was significantly (p<0.05) increased in old soleus muscle compared to young animals. This data indicates that caspase‐mediated apoptotic signaling is elevated in skeletal muscle during aging, but may not be influenced by glutathione content. Research supported by NSERC of Canada.
Protein O‐GlcNAcylation Influences the Mammalian Circadian Clock
Authors: Young Martin E , Laczy Boglarka , Durgan David J , Chatham John C
Published: June 2021

Posttranslational modification of ser/thr residues of nucleocytoplasmic proteins by O‐linked‐N‐actetylglucosamine (O‐GlcNAc) is a rapid and reversible process regulating the function, activity, and stability of target proteins and is also a key nutrient sensing mechanism. The mammalian circadian clock is interlinked with cellular metabolism, and is sensitive to nutritional status. Uncontrolled streptozotocin‐induced diabetes results in increased total protein O‐GlcNAc levels, as well as a phase shift in the circadian clock; we hypothesized, therefore, that protein O‐GlcNAcylation may influence this clock mechanism. Using the heart as a model system, we report that acute augmentation of O‐GlcNAc levels in perfused rat hearts was associated with a rapid decrease in BMAL1 (critical clock component) and a reciprocal increase in PER2 (negative clock component) protein levels. We also show that O‐GlcNAc transferase and BMAL1 co‐immunoprecipitate with CLOCK, and that CLOCK is a target for O‐GlcNAcylation. Pharmacological activation of murine heart O‐GlcNAcylation led to rapid changes in clock gene expression. Collectively, these observations indicate that O‐GlcNAc status may directly regulate the circadian clock by altering degradation‐stability of clock proteins. Our findings may have important implications in understanding mechanistic links between mammalian clocks and energy metabolism.
Will stripping of the great saphenous vein for venous insufficiency also improve the rise in arterial leg blood flow during exercise?
Authors: Nadland Inger Helene , Wesche Jarlis , Sheriff Don , Toska Karin
Published: June 2021

Competent venous valves and the leg muscle pump are important for adequate return of blood to the heart. However, the role of this muscle pump for the rise in arterial blood flow to active skeletal muscle is incompletely understood. We have shown that the leg muscle pump does indeed increase muscle perfusion during upright exercise in healthy subjects (Nådland et al. Eup J appl physiol 2009), and that this mechanism is absent in patients with isolated insufficiency of the great saphenous vein (GSV) (FASEB J 23: 777.3, 2009). In the present study we investigated the muscle pump effect on the rise in muscle perfusion in these patients after treatment for GSV insufficiency, i.e. after stripping of the GSV (N=8).

Beat‐to‐beat femoral artery blood flow (Ultrasound Doppler) was recorded continuously during calf exercise in supine and 30 degree head up tilted (HUT) positions. Because arterial and venous pressures in the legs increase with the height of a hydrostatic column, any muscle pump effect is more pronounced in an upright position. Thus the rise in blood flow from rest to exercise in the supine and in the 30 degree HUT positions was compared.

The rise in femoral flow within 15 seconds of the start of exercise was 0.20 and 0.28 L/min above rest in the supine and HUT positions, respectively.

These results indicate GSV stripping can improve the leg muscle pump effect on the rise in arterial leg blood flow during muscle work in these patients.
Regional blood flow responses of facial skin to cycling exercise
Authors: Shimizu Miku , Someya Nami , Hayashi Naoyuki
Published: June 2021

We investigated blood flow (BF) responses in the face (whole face, circumoculars, nose, lip and bucca) during exercise. After a 5‐min baseline period, seven subjects performed 30 min of cycling exercise at mild intensity (110—120 bpm). BF in the target regions were measured for 4 s every 5 min using laser speckle flowgraphy. During the measurements, the subject remained still and with their face in a fixed expression. We calculated skin blood flow in each of the regions indicated above. BF did not show any significant change from the baseline in any of the target regions during exercise, and there was no significant difference in BF among the regions. We calculated the coefficients of variation (CV) of values obtained from the baseline and during exercise in each target region of each subject. The CV of the circumocular (11±10%) was significantly greater than those of the nose (6±6%) and whole face (6±6%). These findings suggested that BF in the circumocular is susceptible to exercise even though there was no apparent consistency in the observed responses, and that the influence of exercise on BF in the facial skin differs among regions. Supported by JSPS Grant 21650180.
Habitual exercise is associated with reduced arterial stiffness in systemic lupus erythematosus
Authors: Barnes Jill Nicole , Nualnim Nantinee , Sugawara Jun , Tanaka Hirofumi
Published: June 2021

Chronic, systemic inflammation has been implicated in the pathogenesis of cardiovascular disease and a potential underlying mechanism for vascular dysfunction often seen in individuals with systemic lupus erythematosus (SLE). Currently, it is unknown whether the favorable effect of habitual exercise observed in healthy adults can be extended to individuals with SLE. As an initial step to address this, we performed a cross‐sectional study to determine the association between habitual exercise, inflammatory markers, and arterial stiffness. We studied 41 adults, aged 33±11yr (15 healthy controls, 12 sedentary SLE, 14 exercising SLE). Age, BMI, and metabolic risk factors were not different between the 3 groups. Carotid arterial compliance was lower, and augmentation index and inflammatory markers (CRP, IL‐12, TNF‐α) were higher in sedentary SLE patients compared with healthy controls, but were not different between exercising SLE patients and healthy controls. In the pooled population, carotid arterial compliance was inversely associated with TNF‐α (p<0.01), and augmentation index was positively associated with CRP and ICAM‐1 (both p<0.05). These results indicate that habitual exercise is associated with a favorable effect on central arterial stiffness in individuals with SLE and the beneficial results may be mediated by the effect on inflammatory markers.
Blood flow patterns during aerobic and resistance exercise
Authors: Gurovich Alvaro Natalio , Braith Randy W.
Published: June 2021

Blood flow (BF)‐induced shear stress regulates endothelial function. BF pattern is defined as either antegrade or retrograde. However, the presence of turbulent flow, quantified by Reynolds number (Re), is another important BF characteristic not normally assessed in vivo. Aerobic (AX) and resistance (RX) exercise have been shown to improve endothelial function, although Re combined with BF pattern has not yet been characterized during exercise. We hypothesized that shear rate (SR) and Re would increase in a dose‐dependent manner during AX and RX. High‐resolution ultrasound imaging and Doppler BF velocity (V) of the brachial and femoral arteries was performed in 8 young, healthy men during rest and bouts of AX and RX at 40 and 70% of VO2max and 1‐RM, respectively. Microhematocrit measurement was used to determine blood density (ρ) and viscosity (μ). Re was calculated using Re=V·artery diameter·ρ/μ. Results show a dose‐dependent increase in antegrade and retrograde SR during AX and RX in both brachial and femoral arteries. Re also increases in a dose‐dependent manner in both antegrade and retrograde BF patterns throughout AX and RX. These preliminary findings suggest that characterization of BF pattern during exercise must include both BF direction and BF turbulence. Including turbulence when defining BF patterns provides a better understanding of the mechanical effects of exercise on endothelial function.
Renal lactate uptake during exercise in humans
Authors: Volianitis Stefanos , Dawson Ellen A , Dalsgaard Mads K , Yoshiga Chie C , Clemmesen Jens O , Secher Niels H , Olsen Niels V , Nielsen Henning B
Published: June 2021

The Cori cycle is critical for lactate metabolism during exercise as attenuated lactate elimination contributes to the arterial lactate accumulation. We evaluated renal lactate elimination by measuring the arterial‐renal venous (a‐v) lactate difference at rest, following infusion of sodium lactate (0.5 mM) and during moderate cycling that elicited a heart rate of 123 ± 9 b·min−1(mean ± SEM) combined with sodium lactate infusion in nine healthy men. At rest, the a‐v oxygen content and the a‐v lactate differences were 0.8 ± 0.2 mM and 0.02 ± 0.02 mM, respectively. Following infusion of sodium lactate the arterial lactate and the a‐v lactate difference were elevated to 6.5 ± 0.4 mM (P < 0.05) and 0.2 ± 0.3 mM (P < 0.05), respectively. During exercise with sodium lactate infusion arterial lactate reached 7.1 ± 1.1 mM (P < 0.05) and the a‐v oxygen content difference increased to 2.6 ± 0.8 mM (P < 0.05), indicating a 70% reduction of renal blood flow. The a‐v lactate difference increased to 0.5 ± 0.8 mM but was not significantly different from the pre‐exercise level and lactate uptake was not different during exercise than at rest with sodium lactate infusion suggesting that renal lactate uptake is driven by the lactate arterial concentration. In conclusion, during moderate exercise renal lactate extraction increases as renal blood flow is reduced by 70% and lactate uptake is maintained.
Dexamethasone negative side effects on insulin signaling is prevented by Exercise Training: role of IRS‐1 and p‐AKT
Authors: Dionísio Thiago José , de Andrade Louzada Juliana Cavalcante , Viscelli Bruno Alvares , Dionísio Evandro José , Martuscelli Aline Mio , Boaqueiro José Roberto , Santos Carlos Ferreira , Amaral Sandra Lia
Published: June 2021

Dexamethasone (Dexa) is widely used as treatment of chronic inflammatory diseases, however high doses of glucocorticoids cause reduction in skeletal muscle insulin‐dependent glucose uptake. Exercise training (T) causes opposite effects. This study investigated whether physical exercise could prevent the side effects of Dexa in the skeletal muscle insulin‐dependent glucose uptake. Rats underwent a training period where they were either submitted to a running protocol (8 weeks) or kept sedentary. After this T period, the animals underwent Dexa treatment (1 mg/kg/day, i.p., 10 days) concomitant with T. An ipGTT was performed and the area under the glucose curve (AUC) was calculated. Western blot analysis was performed to identify IRS‐1 and p‐AKT protein expression in the tibialis anterior (TA) muscle. The AUC was 39% higher for Dexa‐treated rats, which was attenuated by T. Dexa significantly reduced IRS‐1 (−58%) and p‐AKT (−48%) protein expression in the TA muscle. On the other hand, T increased protein expression of IRS‐1 (112%) and p‐AKT (93%). T completely blocked the reduction of IRS‐1, and also inhibited the p‐AKT protein expression reductions in the trained group. Therefore, T prevented the Dexa‐reductions of IRS‐1 and p‐AKT protein expression in the skeletal muscle and may be a good strategy to prevent Dexa‐induced peripheral insulin resistance. Financial support: FAPESP
An evaluation of endurance and combined endurance and resistance training on fitness and C‐reactive protein
Authors: Daray Laura A. , Henagan Tara , Zanovec Michael , Earnest Conrad P. , Johnson Lisa G. , Winchester Jason B. , Tuuri Georgianna , Stewart Laura K.
Published: June 2021

This study was designed to determine whether endurance or endurance + resistance training affects C‐reactive protein (CRP) levels and if these changes were related to alterations in fitness and/or body composition. Fifty‐eight adults aged 18–24 yrs were assigned to one of three groups: 1) endurance training (E), 2) endurance + resistance training (ER), or 3) active control (AC). The E and ER groups completed 15 weeks of endurance training. The ER group performed 15 weeks of resistance training in addition to endurance training. The AC group maintained their usual exercise routine. Pre/post measures included: a 1.5 mile run, 8 rep max (ER group only) on bench and leg presses, height, weight, waist and hip circumference, DXA, and plasma CRP (ELISA). At baseline, no significant differences were observed between groups. In the E group only, estimated VO2 max significantly increased 12.45% (P < 0.05) and total percent body fat decreased 1.7% (P < 0.05). In the ER group only, plasma CRP concentrations decreased, but not significantly (P = 0.16). Only the ER group entered the low risk category (< 1mg/L) with an average CRP value of 0.99mg/L. Combined endurance and resistance training may be an effective modality for reducing plasma CRP in young adults. However, improvements in aerobic capacity and total percent body fat did not appear to affect changes in CRP in this cohort. FUNDING: Louisiana State University
Effects of exercise and corticotrophin‐releasing factor 2 receptor agonist on skeletal muscle of mdx mice
Authors: Ogborn Daniel I , Crane Justin D , Hall Julie E , Hettinga Bart P , Isfort Robert J , Tarnopolsky Mark A
Published: June 2021

Exercise and corticotrophin‐releasing factor 2 receptor (CRF2R) agonist treatment improves skeletal muscle function, however the potential synergistic transcriptional effects of both treatments in dystrophic muscle are not characterized. Mdx (C57BL/10ScSn‐Dmdmdx) and WT (C57BL/6) mice were treated with placebo (PL) or CRF2R agonist and remained sedentary or performed treadmill exercise (EX; 3x/week, 30 minutes at 8–12m/min) for 12 weeks. RNA from tibialis anterior was prepared for gene array analysis using the Affymetrix Mouse 430 array and functional cluster analysis was performed on differentially expressed (DE) genes using DAVID. The Mdx genotype had 224 DE genes, many associated with muscle differentiation and development of the actin cytoskeleton and extracellular matrix. Exercise resulted in 79 DE genes, primarily those involved in transcriptional regulation and circadian rhythms, whereas the CRF2R‐agonist produced 122 DE genes, many involved in chromatin remodeling. The combination of exercise and CRF2R‐agonist resulted in 87 DE genes compared to MDX‐PL‐EX mice, influencing genes involved in protein transport and neuronal nitric oxide synthase (nNOS). These results indicate that the effects of exercise and CRF2R agonist treatment are not identical and that combination treatment may result in a favorable transcriptional signature that holds therapeutic potential. (Funded by P&G)
Endurance Training‐mediated Differential Regulation of miRNAs in Skeletal Muscle of Lean and Obese Men
Authors: Samjoo Imtiaz , Safdar Adeel , Hamadeh Mazen , Akhtar Mahmood , Raha Sandeep , Timmons James , Tarnopolsky Mark
Published: June 2021

MicroRNAs (miRNAs) are evolutionarily conserved small non‐coding RNA species involved in post‐transcriptional gene regulation. In skeletal muscle, an acute bout of endurance exercise differentially alters miRNA species that regulate transcriptional networks involved in mitochondrial biogenesis, glucose and fatty acid metabolism, and muscle remodeling. The purpose of this study was to assess the expressional profile of targeted miRNAs following 3‐mo of endurance training in sedentary lean and obese men (N=5/group). The expression of miR‐ 100, 144, 190, 424, 668, and 923 was measured in the vastus lateralis before and after the program. Basal expression of miR‐424 was 160% greater (P<0.02), whereas miR‐144 was reduced by 77% (P=0.06) in the obese compared to the lean group. Endurance training significantly increased the expression of miR‐424 in both groups (P<0.01). Interestingly, the expression of miR‐144 in the obese was normalized to lean controls post endurance training (P=0.06). No changes were observed in miR‐100, 190, 668, and 923. We conclude that investigation of these molecules and their genetic targets may potentially identify new pathways involved in the pathology of complex metabolic diseases, improving our understanding of metabolic disorders and influence future approaches to the treatment of obesity. Research supported by CIHR.
Improved assessment of the global transcriptional response to endurance exercise in human skeletal muscle
Authors: Crane Justin , Ogborn Daniel , Abadi Arkan , Melov Simon , Hubbard Alan , Tarnopolsky Mark
Published: June 2021

Endurance exercise is a potent stimulus for mitochondrial biogenesis and cellular metabolism. While the molecular events surrounding an acute bout of endurance exercise have been previously evaluated using small‐scale approaches, recent advances in gene microarray technology have substantially improved the number of gene targets available for investigation. Therefore, the purpose of this study was to examine the global mRNA response to a single bout of endurance exercise. Eleven healthy, young men (age 22±1 yrs, VO2peak 46±2 ml·kg−1·min−1) were recruited for this investigation. Muscle samples were acquired prior to and at 30 mins and 3 hours following an exhaustive cycling protocol. At 30 mins post‐exercise 404 genes were differentially expressed from rest (P<0.05), while at 3h 846 genes were significantly altered (P<0.05). When clustered by biological function, the greatest enrichment of genes at 30 mins occurred in those relating to developmental processes, cell differentiation, DNA binding, negative regulation of cellular processes, and primary metabolic processes. At 3h, functional annotation revealed clusters related to developmental processes, signal transduction, anatomical structure development, DNA binding and the regulation of apoptosis. To date, these data provide the most comprehensive transcriptional approach regarding the acute effects of endurance exercise. (Supported by NSERC Canada).
Skeletal muscle protein synthesis is elevated after moderate‐intensity aerobic exercise
Authors: Reidy Paul , Konopka Adam , Trappe Todd , Harber Matthew
Published: June 2021

The acute influence of aerobic exercise on muscle protein turnover is not well defined. The purpose of this study was to examine the influence of moderate intensity aerobic exercise on muscle protein synthesis in the fasted and fed states. Eight recreationally active males (23±2yr, 74±3kg, VO2max: 52±2 ml·kg−1·min−1) performed 60min of cycle ergometry at 72±1% VO2max on two occasions in a counter‐balanced design. Trials differed only in a post‐exercise nutritional intervention. Subjects ingested a non‐caloric placebo (FAST) beverage or a beverage containing (per kg body weight): 5kcal, 0.83g carbohydrate, 0.37g protein and 0.28g fat (FED) immediately and 1h after exercise. Mixed muscle protein synthesis (FSR) was assessed at rest and following exercise with the use of an L‐[ring D5]‐phenylalanine infusion combined with muscle biopsies at 2 and 6h post‐exercise. Mixed muscle FSR was higher (P<0.05) after exercise in both FAST (0.112 ± 0.010%·h−1) and FED (0.129 ± 0.014 %·h−1) trials as compared to rest (0.071 ± 0.005 %·h−1). These data demonstrate that a moderate intensity, non‐exhaustive bout of aerobic exercise stimulates skeletal muscle FSR in the fasted state. Additionally, post‐exercise feeding did not further enhance FSR after aerobic exercise.

Supported by a grant from the Gatorade Sports Science Institute
Quantification of the in vivo production of nitric oxide within the nucleus tractus solitarius during activation of the skeletal muscle mechanoreflex
Authors: Leal Anna K , Cherry Brandon H , Murphy Megan N , Squiers John J , Smith Scott A
Published: June 2021

During exercise, the skeletal muscle mechanoreflex (MMR) evokes increases in blood pressure. Sensory information from the MMR is processed in the nucleus tractus solitarius (NTS). Pharmacological data suggest that MMR function is modulated by the production of nitric oxide (NO) in the NTS. Due to the instability and short half‐life of NO, direct quantification of NO production in the NTS during activation of the MMR has yet to be reported. We recently quantified the in vivo production of NO within the NTS (at rest) using the molecular probe 1,2‐diaminoanthraquinone (DAA). DAA reacts with NO to form a water‐insoluble red‐fluorescent precipitate that can be quantified by microscopic analysis of fixed tissue. The purpose of this study was to determine the changes in NO production in the NTS during MMR activation using the DAA method. Using microdialysis, DAA (100 μg/mL) was delivered bilaterally to the NTS of Sprague‐Dawley rats (n=6) for 15 min at rest or during stimulation of the MMR via passive stretch of hindlimb skeletal muscle. Animals were then fixed and brainstem tissue harvested. As compared to rest, MMR activation significantly enhanced fluorescence by 156±8% and 114±11% within the NTS ipsilateral and contralateral to the stretched muscle, respectively. The data provide direct evidence that NO production is augmented within the NTS in response to stimulation of the MMR. Supported by HL‐094075 and HL‐088422.
Novel Methods to Investigate Multi‐fiber Nerve Recordings
Authors: Burgess Don Edward , Verberne Anthony J.M. , Sartor Daniela M.
Published: June 2021

We developed novel methods to investigate responses of neuronal populations within a multi‐fiber sympathetic nerve recording. We applied these methods to analyze the relationship between barosensitive RVLM medullospinal neurons marked by their response to systemic administration of the gastrointestinal hormone cholecystokinin (CCK) and splanchnic and lumbar sympathetic nerve activity (SNA). In addition to the standard analysis of Spike‐Triggered Averaging (STA) of SNA, we used Spike2 software to identify spike‐like structures within the sympathetic nerve recording (SND). We then calculated cross‐correlograms between apparent “spikes” in SND and RVLM neuronal discharges. Also, we calculated a STA of RVLM mean frequency triggered by the identified “spikes”. These novel analyses yielded consistent results with the standard STA of SNA and detected sympathetic nerve discharges driven only by the fast pathway. We find statistically significant peaks (p<0.001) in the cross‐correlogram between CCK inhibited neurons and “spikes” driven by the fast pathway (n=5). The time‐delay between RVLM neuronal discharges and the fast burst of SNA in splanchnic nerves is 52 +/− 2ms. The corresponding delay for lumbar nerves is 78+/− 4ms. These novel analyses may serve as a tool to study differential behavior of populations of neurons that drive sympathetic vasomotor nerve activity. Supported by R01 NS39774, HL091440
Neuregulin‐1/erbB signaling in rostral ventrolateral medulla of brainstem is involved in blood pressure regulation alteration of major neurotransmitters
Authors: Matsukawa Ryuichi , Hirooka Yoshitaka , Nishihara Masaaki , Ito Koji , Kishi Takuya , Sunagawa Kenji
Published: June 2021

Background

Neuregulin‐1 (NRG‐1) is a multifunctional modulator that acts through epidermal growth factor family of tyrosine kinase receptors, including erbB2‐4. In the central nervous system, NRG‐1/erbB pathway has been shown to affect both glutamatergic and GABAergic function. However, it is totally unknown if this signaling pathway is involved in central blood pressure regulation. Therefore, we determined if NRG‐1/erbB signaling in the rostral ventrolateral medulla (RVLM) contributes to blood pressure regulation by altering the major neurotranmsiiters' function.

Methods and Results

In anesthetized male Wistar rats, we microinjected NRG‐1β(0.025 pmol), erbB2‐receptor antagonist (AG825: 1.0 pmol) into the RVLM. NRG‐1 decreased mean arterial pressure (MAP) and heart rate (HR) ΔMAP −23.2 ± 1.8 mmHg, Δ HR −40.7 ± 5.5 bpm, n=5), while AG825 increased MAP and HR (Δ MAP 19.2 ± 2.9 mmHg, ΔHR 16.8 ± 1.2 bpm, n=4). Pre‐microinjection of NMDA receptor antagonist (AP‐5) into the RVLM attenuated the AG825 induced‐pressor response (6.5 ± 1.2 mmHg). Pre‐microinjection of GABAA receptor antagonist (bicuculine) into the RVLM attenuated the NRG‐1β induced‐depressor response (−4.3 ± 2.5 mmHg).

Conclusion

NRG‐1/erbB signaling in the RVLM contributes to AP and HR regulation via the modulation of both glutamatergic and GABAergic function. This pathway in the RVLM is involved in neural control of blood pressure.
Photostimulation of Channelrhodopsin‐2 expressing ventral medullary astrocytes increases sympathetic nerve activity and blood pressure in rats
Authors: Marina Nephtali , Figueiredo Melina , Tang Feige , Kasparov Sergey , Gourine Alexander
Published: June 2021

Astrocytes play an important role in the control of complex central nervous functions by regulating synaptic strength and information processing. Here we explored the potential role of ventral medullary astrocytes in the regulation of central sympathetic tone and blood pressure (BP). Adult rats received bilateral microinjections in the rostral ventrolateral medulla (RVLM) of AVV‐sGFAP‐ChR2(H134R)‐Katushka1.3, an adenovirus that expresses channelrhodopsin‐2 (ChR2) under the control of the astrocyte‐specific promoter GFAP. 7–14 days later, strong ChR2 expression was detected in ventral medullary astrocytes located in close proximity to tyrosine hydroxilase‐immunoreactive RVLM neurons. Unilateral stimulation with blue light (445 nm) increased BP (20.7 mmHg, n=11) and renal nerve sympathetic discharge (SND; 28.7 %, n=11). Application of the ATP receptor antagonist MRS 2179 (200 μM) on the ventral medullary surface decreased baseline SND (15%) and BP (7.5%). Photostimulation after ATP receptor blockade produced signtificantly smaller responses in SND (12.5%) and BP (5%).

CONCLUSIONS

Activation of ventral medullary astrocytes increases sympathetic activity and blood pressure at least in part via ATP‐dependent mechanisms. This is the first demonstration that astroglia may play an active role in shaping the patterns of central sympathetic outflow.
Purinergic signaling is altered in rostral ventrolateral medulla after chronic intermittent hypoxia in rats
Authors: Zoccal Daniel Breseghello , Huidobro‐Toro Juan Pablo , Machado Benedito Honorio
Published: June 2021

Alterations in purinergic signaling was evaluated in the rostral ventrolateral medulla (RVL), a critical region controlling respiratory and sympathetic activities, of juvenile rats (P19–21) submitted to chronic intermittent hypoxia (CIH, 6% O2 for 40 s, every 9 min, 8 h/day; n=8) or normoxia (control, n=8) for 10 days. On the 11th day using the in situ working heart‐brainstem preparation, changes in thoracic sympathetic (tSN), abdominal (Abd) and phrenic nerve (PN) activities were recorded in response to ATP microinjections (1, 10 and 50 mM) into the RVL. In separate groups of control and CIH rats, P2X1, P2X3, P2X4 and P2Y2 receptor expressions were examined in RVL punches by immunoblotting. ATP into the RVL evoked similar Abd responses in both groups. However, significant (P<0.01) larger increases in tSN were observed in CIH than in controls. Furthermore, the recovery of the ATP‐induced apneic responses occurred earlier in CIH than in control rats (P<0.05), although the responses reached similar magnitudes. Consonant to the functional changes, the expression of P2X3 and P2X4, but not P2X1 or P2Y2, increased 20% (P<0.05) in CIH rats. Altogether, these findings indicate that purinergic mechanisms are up‐regulated in the RVL of rats submitted to CIH, which may contribute to the respiratory‐sympathetic dysfunctions observed in this experimental model. Supported by FAPESP, CNPq, FONDAP 13980001, MIFAB and PFB‐12.
Intermittent Hypoxia in Rats Increases expression of AP‐1 target genes in the median preoptic nucleus
Authors: Knight W David , Mifflin Steve , Cunningham J. Thomas
Published: June 2021

Intermittent hypoxia (IH) is an animal model of hypoxemia similar to obstructive sleep apnea. In addition to hypertension and sympathoexcitation, IH increases FosB expression and angiotensin II signaling in several brain regions including the median preoptic nucleus (MnPO). Inhibition of FosB or angiotensin II reduces IH‐induced hypertension. Rats were subjected to one week of exposure to IH during the light phase. IH increased arterial pressure (Base: 103±4 IH: 108±4, mmHg). After IH, animals were anesthetized and the MnPO was dissected using stainless steel punches. MnPO total RNA was isolated, reverse transcribed, and PCR arrays were performed on a list of selected genes containing AP‐1 response elements because FosB is a component of the AP‐1 transcription factor complex. IH increased FosB expression by 75%. Further, both endothelial and neuronal nitric oxide synthases (NOS) were upregulated by 40–60%. Consistent with increased angiotensin signaling in IH, expression of both angiotensin converting enzyme types I and II were increased by approximately 50%. Lastly, the antioxidant enzyme peroxiredoxin 2, a putative response to increased oxidative stress, is increased by 62%. These data indicate that IH increases a host of genes that may be responsible for the increased blood pressure seen during IH and in downstream fashion to FosB/AP‐1 regulated gene expression. Supported by PO1 HL‐88052.
Intrathoracic neurons modify myocardial ischemia‐induced sudden cardiac death
Authors: Ardell Jeffrey L , Southerland E. Marie , Armour J. Andrew
Published: June 2021

To determine if cardiac sympathetic intrathoracic reflexes represent a risk factor for ischemia‐induced sudden cardiac death (SCD) and, if so, whether targeting them reduces that risk. Left ventricular (LV) interstitial fluid (ISF) norepinephrine (NE) levels were assessed by microdialysis in anesthetized canines during transient coronary artery occlusion (CAO). Responses in animals with intact neuroaxes were compared to those in which the intrathoracic component of the cardiac neuronal hierarchy was surgically disconnected from central neurons vs those with intact neuroaxis that underwent spinal cord stimulation (SCS; T1‐T3 spinal level). In intact preparations, animals exhibiting enhanced NE ISF levels with increased dispersion between ischemic and border zone were at increased risk for SCD. Following intrathoracic neuronal decentralization, CAO induced NE release was reduced ~20% and uniform across the ischemic to border zones. Following intrinsic cardiac neuronal decentralization, CAO induced NE release occurred only in ischemic tissue. SCS also reduced CAO‐induced NE release (~60% vs control). Risk for CAO‐induced SCD was 42% in control, 8% following decentralization and 10% with SCS. These data demonstrate that stabilization of intrathoracic nervous system by such means reduces the potential for ischemia‐induced SCD while maintaining regulatory function. HL71830
Chronic administration of angiotensin II (AngII) to rats consuming a high salt diet causes mesenteric vasoconstriction by increasing sympathetic tone
Authors: Kuroki Marcos Takuya , Guzman Pilar Ariza , Fink Gregory D , Osborn John W
Published: June 2021

We previously reported that AngII induced hypertension in rats consuming a high salt diet is accompanied by a sustained decrease in mesenteric vascular conductance (MVC). We tested the hypothesis that this vasoconstrictor response is mediated by increased sympathetic tone. Rats (n=5) were fed a high (2%) NaCl diet and instrumented for measurement of mean arterial pressure (MAP) and superior mesenteric artery blood flow (SMABF) during 4 days of control, and 14 days of AngII infusion (150ng/kg/min, sc). The contribution of sympathetic tone to MAP and MVC (SMABF/MAP) was assessed during control, and days 3, 7, and 13 of AngII by ganglionic blockade (hexamethonium; 20mg/kg, iv). MAP increased from a control level of 102±2 mmHg to 133±4, 141±4, and 140±12 on days 3, 7, and 13 of AngII. MVC decreased from 0.108±0.008 mL/mmHg·min during control to 0.065±0.004, 0.076±0.009, and 0.09±0.01 over the same time course. The decrease in MAP to ganglionic blockade was similar during control (−39±3) and on Day 3 (−37±12), but then increased significantly on Day 7 (−68±8) and Day 13 (−81±12) of AngII. The increase in MVC to ganglionic blockade was 0.04±0.01 during control and was 0.01±0.01 on Day 3, but then increased on Day 7 (0.06±0.01) and Day 13 (0.064±0.007) of AngII. We conclude that mesenteric vasoconstriction in AngII‐salt induced hypertension is mediated, in part, by a delayed increase in sympathetic tone (HL076312).