bluuebunny/crossref_metadata_2025 huggingface dataset:
Determinants of skeletal muscle work efficiency in patients with COPD
Authors: Layec Gwenael , Hart Corey R , Trinity Joel , Le Fur Yann , Jeong Eun‐Kee , Richardson Russell
Published: November 2023

Skeletal muscle work inefficiency plays a major role in limiting exercise capacity in patients with chronic Obstructive Pulmonary Disease (COPD). However, the physiological mechanisms responsible for this excessive energy demand from the exercising muscle of patients with COPD remains poorly understood. To address this gap in our knowledge, we measured the cost of muscle contraction (ATP cost) in the quadriceps of patients with moderate to severe COPD (n=11) and age‐matched sedentary controls (n=12) with phosphorus magnetic resonance spectroscopy (31P‐MRS) during 1) maximal intermittent contractions to elicit a metabolic demand from both cross‐bridge cycling and ion pumping and 2) a continuous maximal contraction to predominantly tax cross‐bridge cycling. In addition, muscle fiber type distribution was determined in the vastus lateralis using immunofluorescence analysis. The ATP cost of contraction for both the continuous (Control: 0.11 ± 0.07 mM.min−1.N m−1; COPD: 0.12 ± 0.07 mM.min−1.N m−1) and intermittent (Control: 0.24 ± 0.17 mM.min−1.N m−1; COPD: 0.24 ± 0.18 mM.min−1.N m−1) protocols were not significantly different between groups with or without normalization for muscle mass (P>0.05). Somewhat surprisingly, fiber type distribution was also not different between groups (Type I; Control: 41 ± 12 %; COPD: 40 ± 18 %; Type II; Control: 59 ± 12 %; COPD: 60 ± 18 % respectively P>0.05). Of note, this finding of similar fiber type composition in controls and COPD was partly the consequence of a relatively high proportion of type II fibers in the elderly controls. These, somewhat serendipitous, data reveal that excessive energy demand from ion pumping or myosin ATPase per se is not an obligatory component of the skeletal muscle work inefficiency in COPD and suggest that the previously documented elevated ATP cost of contraction in the locomotor muscles of these patients was likely mediated by a fiber type shift. In practical terms, these findings highlight the potential importance of developing effective therapeutic strategies to limit the likely deleterious consequences of a skeletal muscle fiber type shift in the lower limbs of patients with COPD.

Support or Funding Information

This work was funded in part by grants from the Flight Attendant Medical Research Institute (FAMRI), NIH National Heart, Lung, and Blood Institute (PO1 HL 091830, K99HL125756) and VA Merit grant E6910R.
Myosin phosphorylation‐mediated potentiation does not alter the economy of work performed in fast skeletal muscles
Authors: Gittings William , Bunda Jordan , Vandenboom Rene
Published: November 2023

The physiological role of myosin regulatory light chain (RLC) phosphorylation in fast skeletal muscle is unclear, as the resultant potentiation of contractile function comes with an undetermined energetic cost. We conducted in vitro experiments (25°C) to quantify contractile economy (i.e. energy cost/work performed) in potentiated extensor digitorum longus (EDL) muscles from wildtype and myosin light chain kinase knockout (skMLCK−/−) mice. Economy values were calculated as the ratio of total work performed to high‐energy phosphate consumption (HEPC) during a period of repeated isovelocity contractions that followed a potentiating stimulus (PS). The PS enhanced contractile parameters (concentric force and work) in both genotypes, although the effect was significantly greater in wildtype (1.38 ± 0.03 and 1.51 ± 0.03) vs. skMLCK−/− (1.10 ± 0.04 and 1.10 ± 0.05) muscles (P < 0.05, n = 8 for all data). During the experimental period of repetitive stimulation in the potentiated state, wildtype muscles performed ~58% more total work than skMLCK−/− muscles (94.05 ± 3.80 vs. 59.55 ± 4.10 J•kg−1; P < 0.001) without a statistical increase in HEPC (19.03 ± 3.37 vs. 16.02 ± 3.41 μmol~P; P = 0.27) or genotype difference in economy (5.74 ± 0.67 vs. 4.61 ± 0.71 J•kg−1μmol~P−1; P = 0.27). Importantly, when relative genotype differences were analyzed, the quantity of total work performed was ~3 fold greater than the increase in HEPC for wildtype muscles. Our results support the idea that myosin RLC phosphorylation‐mediated potentiation is a mechanism capable of augmenting sustained contractile function without significantly increasing energetic cost or decreasing economy.

Support or Funding Information

Natural Sciences & Engineering Research Council of Canada (NSERC): Discovery Grant (R. Vandenboom)
Increased Superoxide Dismutase‐2 in skeletal muscle in a rat model of preterm birth
Authors: Hokanson Elise S , Tetri Laura , Braun Rudolf K , Eldridge Marlowe W
Published: November 2023

Background

In the United States an estimated 12% of births are preterm, meaning a significant number of infants are at increased risk for hypertension, type‐2 diabetes, and insulin resistance later in life. After a preterm birth, a common intervention used is oxygen therapy in order to improve oxygen delivery to systemic tissues. Although acutely life sustaining, there may be adverse effects of oxygen therapy in the long term. Many metabolic alterations have been identified in adults born preterm, including increased risk of insulin resistance and metabolic syndrome. In these conditions, there have been alterations in uncoupling protein‐3 (UCP‐3) expression, a protein that aids in the release of energy from the mitochondria as heat, and superoxide dismutase one and two (SOD‐1 and SOD‐2) expression, which metabolize reactive oxygen species. We hypothesized that altered levels of uncoupling protein and antioxidants would be observed at one year of age in a rat model of prematurity.

Methods

Within 12 hours of their birth, we exposed Harlan Sprague‐Dawley (SD) rat pups for 14 days to either normoxia (NORM, 21% oxygen, n=12, 6 males) or hyperoxia (HYP, 85% oxygen, n=12, 6 males) in custom chambers. After the 14 days, the pups were aged out to one year of age in standard room air. The gastrocnemius muscles were then harvested and flash frozen in liquid nitrogen. Western blotting was used to observe the differences in UCP3, SOD1, and SOD2. Statistics were run by two way ANOVA with Tukey's post hoc analysis.

Results

There were no differences observed in UCP3 protein expression or SOD1 protein expression (p=0.8). There is a trend towards higher expression of SOD2 expression in HYP rats (p=0.9). There was a trend towards higher expression of SOD2 in the HYP rats compared to NORM rats (38% higher, p=0.08).

Conclusions

No difference in UCP3 expression is indicative that the main mechanism of uncoupling in the skeletal muscle is unaltered, at least in expression, in this rat model of prematurity. SOD1 is the form of SOD present in the cytoplasm, and indicates that there may not be an increased need for antioxidants in the cytoplasm. However, the potentially higher level of SOD2, the mitochondrial form, in HYP rats indicates that there may be increased need for antioxidants in the mitochondria. Previous data has shown altered mitochondrial mass and function in the HYP rats, and this observation of greater expression of SOD2, a potent antioxidant, further supports the possibility of altered mitochondrial function in the HYP rats.

Support or Funding Information

NHLBI, R01 HL115061‐03, Suppl (Eldridge) & NHLBI, R01 HL115061 (Eldridge)
Carotid Artery Structure during and after Long‐Duration Space Flight
Authors: Lee Stuart M. C. , Martin David S. , Laurie Steven S. , Ribeiro L. Christine , Smith Scott M. , Zwart Sara R. , Stenger Michael B.
Published: November 2023

Space flight missions may expose astronauts to increased risk of oxidative stress and inflammatory damage induced by a variety of sources, including radiation, psychological stress, reduced physical activity, diminished nutritional status, and hyperoxic exposure during extravehicular activity. Given that evidence exists that these factors can accelerate the development of atherosclerosis, the purpose of this investigation is to determine whether long‐duration space flight (>4 months) on the International Space Station results in structural changes in the carotid artery.

METHODS

Carotid artery intima‐media thickness (cIMT) and diameter during systole (Ds) and diastole (Dd) were measured using standard ultrasound (VividQ, GE Healthcare) in 10 astronauts (9 M, 1 F) approximately 180 and 60 days before launch, at approximately 15 (FD15) and 60 days of flight (FD60), within two weeks before landing (R‐14), and within one week after landing. Pre‐ and post‐flight measures were obtained after the subjects had been supine for at least 20 min. Inflight measures were acquired by trained astronauts while being guided by an expert sonographer on the ground using telemedicine techniques. Carotid artery distensibility coefficient was calculated (cDC = (Ds2−Dd2)/(PP·Dd2); Gepner et al., Stroke 45: 48–53, 2014). Pre‐flight data were averaged to represent baseline. Results were analyzed using one‐way repeated measures ANOVA.

RESULTS

Carotid artery diameters during systole (Ds FD15: 7.6 ± 0.4; FD60: 7.6 ± 0.4; R‐14: 7.7 ± 0.4 mm; mean ± SD) and diastole (Dd FD15: 7.2± 0.3; FD60: 7.3 ± 0.4; R‐14: 7.3 ± 0.5 mm) were significantly greater during space flight than pre‐ (Ds: 7.3 ± 0.4; Dd: 6.9 ± 0.4 mm) and post‐flight (Ds: 7.4 ± 0.4; Dd: 7.1 ± 0.5 mm). There was a main effect of time on cIMT, but post‐hoc analyses did not reveal significant difference from pre‐flight (Pre: 0.58 ± 0.09 mm) at any time point (FD15: 0.58 ± 0.14; FD60: 0.54 ± 0.09; R‐14: 0.54 ± 0.09; Post: 0.62 ± 0.10 mm). Although pre‐flight cDC (0.0028 ± 0.0011/mmHg) was not different than in‐flight (FD15: 0.0023 ± 0.0011; FD60: 0.0020 ± 0.0008; R‐14: 0.0023 ± 0.0012/mmHg), post‐flight cDC (0.0019 ± 0.0010/mmHg) was significantly less than pre‐flight.

CONCLUSIONS

Although the carotid artery was distended chronically during space flight and cDC was decreased in the week after landing, in these astronauts pathological remodeling of this vessel was not evident.

Support or Funding Information

Supported by the NASA Human Research Program
Effects of Type 1 Diabetes on the Exercise Pressor Reflex in Rats
Authors: Stone Audrey J , Grotle Ann‐Katrin , Garcia Elizabeth A. , Harrison Michelle L.
Published: November 2023

Type 1 diabetes (T1DM) is known to cause both peripheral and autonomic neuropathy through mechanisms affecting thinly myelinated afferents. These same afferents may also play a role in the exercise pressor reflex suggesting that T1DM could alter this reflex as well. The purpose of this study was to establish the effects of type 1 diabetes on the pressor and cardioaccelerator responses evoked by statically contracting the hindlimb muscles at different time points of the disease and identify possible mechanisms responsible for these changes. We injected (i.p.) 50 mg/kg of Streptozotocin (STZ) or the vehicle (CTL) in either sex and waited 1wk (STZ: BW=267±12 g, glucose=438±24 mg/dL, HbA1C=6.5±0.3%; CTL: BW=328±16 g, glucose=167±10 mg/dL, HbA1C=4.4±0.1%), 3wks (STZ: BW=293±10 g, glucose=465±22 mg/dL, HbA1C=10±0.3%; CTL: BW=329±22 g, glucose=212±26 mg/dL, HbA1C=4.8±0.4%), or 6wks (STZ: BW=380±16 g, glucose=546±35 mg/dL, HbA1C=12±0.4%) before performing experiments. In unanaesthetized, decerebrate rats, we statically contracted the hindlimb muscles for 30s and measured changes in mean arterial pressure (MAP) and heart rate (HR). We then injected either α,β‐methylene ATP (20μg/kg; 200μl), a P2X receptor agonist, or lactic acid (24mM; 200μl), an ASIC3 channel agonist, into the arterial supply of the hindlimb and measured the evoked pressor and cardioaccelerator responses for each group. We found that the pressor (STZ: ΔMAP=25±5 mmHg, n=4; CTL: ΔMAP=13±2 mmHg, n=7; p=0.01) but not cardioaccelerator (STZ: ΔHR=23±9 bpm, n=4; CTL: ΔHR=13±3 bpm, n=7; p=0.10) response to static contraction was exaggerated 1wk after injecting STZ. Likewise, the pressor (STZ: ΔMAP=32±5 mmHg, n=8; CTL: ΔMAP=17±3 mmHg, n=6; p=0.02) but not cardioaccelerator (STZ: ΔHR=22±5 bpm, n=8; CTL: ΔHR=15±2 bpm, n=6; p=0.27) response to static contraction was exaggerated 3wks after injecting STZ. Conversely, both the pressor (6wks STZ: ΔMAP=5±2 mmHg, n=7) and cardioaccelerator (6wks STZ: ΔHR=1±2 bpm, n=7) responses to static contraction were significantly attenuated 6wks after injecting STZ compared to 1wk (MAP: p=0.02; HR: p=0.01) and 3wks after injecting STZ (MAP: p<0.01; HR: p<0.01). The developed tensions from contraction were similar within each comparison. Furthermore, we found that injecting lactic acid, but not α,β‐methylene ATP, into the arterial supply of the hindlimb evoked a greater pressor (STZ: ΔMAP=31±5 mmHg, n=9; CTL: ΔMAP=20±3 mmHg, n=13; p=0.04) and cardioaccelerator (STZ: ΔHR=13±3 bpm, n=9; CTL: ΔHR=3±2 bpm, n=13; p<0.01) response 1wk after STZ injection compared to CTL. We conclude that the exercise pressor reflex is exaggerated in the early stages of T1DM but attenuated in the late stages of this disease. Additionally, ASIC3 channels but not P2X receptors may play a role in this exaggerated reflex 1wk after STZ injection.
ATP‐sensitive K+ Channel Inhibition via Glibenclamide Does Not Increase Lumbar or Renal Sympathetic Nerve Discharge in Healthy Rats
Authors: Colburn Trenton D , Holdsworth Clark T , Craig Jesse C , Hirai Daniel M , Montgomery Shawnee , Kenney Michael J , Musch Timothy I , Poole David C
Published: November 2023

ATP‐sensitive K+ (KATP) channels contribute to exercise‐induced hyperemia and O2 delivery in skeletal muscle. KATP channel inhibition via glibenclamide (GLI) increases mean arterial pressure (MAP) and reduces blood flow to the rat hindlimb during exercise: demonstrating greater reductions in oxidative compared to glycolytic muscles. Whether this control via KATP channels is mediated locally within skeletal muscle by decreased vascular hyperpolarization or alternatively by increased sympathetic nerve activity instigated within the rostral ventrolateral medulla (Guo et al. J. Pharmacol. Exp. Therapeut. 338:458–65, 2011) or other cardiovascular control centers is unknown. We hypothesized that KATP channel inhibition via intravascular infusion of GLI would increase MAP without increasing lumbar and renal sympathetic nerve discharge (SND). In 12 male anesthetized Sprague‐Dawley rats, lumbar (n=8) and renal (n=8) nerves were isolated for measurement of SND. Following 60 min stabilization after surgery, a bolus infusion of saline (CON) was administered via the femoral vein catheter and SND, MAP (n=12), and HR (n=12) were recorded for 10 min. This protocol was then used following a bolus infusion of GLI (5 mg kg−1 in ~1 mL heparinized saline). SND was calculated as percent change from baseline (ΔSND (%)). There were no significant changes in MAP, HR, or lumbar ΔSND (%) following CON (P > 0.05 for all) and only minute 8 exhibited marginally increased renal ΔSND (%) (P < 0.05). Compared to CON, GLI increased MAP (min 3–10), reduced lumbar ΔSND (%) (min 2–10; up to 47%), and reduced renal ΔSND (%) (min 2–9; up to 36%) (P < 0.05 for all). There were no significant changes in HR due to GLI (P > 0.05). These results demonstrate that KATP inhibition produces a decrease in both lumbar and renal SND likely related to increased MAP. Therefore, reductions in exercising muscle blood flow and O2 delivery following GLI do not result from enhanced sympathetic activity; supporting that vasomotor control via KATP channels is likely mediated by local vascular effects within skeletal muscle.

Support or Funding Information

NIH HL‐2‐108328
Lumbar Sympathetic Nerve Activity at Rest and During Muscle Contraction: Effects of Estrogen and Nitric Oxide
Authors: Just Timothy P , DeLorey Darren S
Published: November 2023

Efferent sympathetic nerve activity (SNA) is critical for the control of blood pressure and peripheral vascular resistance at rest and during exercise. Nitric oxide (NO) is known to have an inhibitory effect on efferent SNA and estrogen has been shown influence NO synthase (NOS) expression and NO bioavailability. Therefore, the purpose of this study was to investigate the hypothesis that estrogen status alters SNA at rest and during muscle contraction through an NO dependent mechanism. Female Sprague‐Dawley rats were randomly assigned to OI (n=10), OVX (n=9) or OVX‐E (n=8) groups. A bilateral ovariectomy was performed in OVX rats and a placebo or time‐release 17β‐estradiol pellet (OVX‐E) was implanted subcutaneously for 4 weeks. Rats were then anesthetized and instrumented for the measurement of blood pressure and lumbar SNA (LSNA) at rest and during hindlimb muscle contraction in control, NOS blockade (L‐NAME; 10 mg·kg−1 IV), and NOS blockade with normalization of blood pressure (hydralazine; 0.01–0.06 mg·kg−1·min−1 IV) conditions. In control conditions, MAP and LSNA were similar (p>0.05) in OI, OVX and OVX‐E rats at rest. LSNA increased in response to muscle contraction in all groups and LSNA was not different in OI, OVX and OVX‐E rats during muscle contraction. NOS blockade increased (p<0.05) MAP and decreased LSNA by similar magnitudes (p>0.05) in OI, OVX and OVX‐E rats at rest and during exercise. Infusion of hydralazine in the presence of NOS inhibition returned MAP to levels observed at rest and during muscle contraction in the control condition in all groups. LSNA was not different (p<0.05) in OI, OVX, OVX‐E rats at rest and during muscle contraction in the presence of NOS inhibition and hydralazine. These data suggest that estrogen status does not alter efferent sympathetic nerve activity directed to skeletal muscle at rest or during exercise. Furthermore, these data suggest that the effects of systemic NOS blockade on LSNA are not dependent on estrogen status.

Support or Funding Information

Natural Sciences and Engineering Research Council of Canada (NSERC), Canadian Foundation for Innovation, and Alberta Advanced Education and Technology.
Combined Influences of Subsystolic Regional Circulatory Occlusion and Pedal Rate on the Exercise Pressor Reflex in Healthy Adults
Authors: Villarraga Nico , Van Iterson Erik H. , Randall Nicholas , Ziegler Briana , Olson Thomas P.
Published: November 2023

Introduction

The contribution of metabolic vs mechanical stimuli related to the group III/IV afferent‐mediated exercise pressor reflex (EPR) remains incompletely understood. High pedal frequency during cycling increases type II muscle fiber recruitment and may contribute to increased anaerobically‐mediated metabolic byproduct accumulation. This may lead to an augmented rise in systolic blood pressure (SBP) and, hence, EPR in humans. Thus, we hypothesized, 1) Mean arterial pressure (MAP) will be increased during exercise with SubRCO vs without NoRCO irrespective of pedal frequency, and 2) MAP will be augmented further during exercise with SubRCO at high pedal frequencies.

Methods

Healthy adults (N=13; 46% men; age 36±19 yr; BMI 24±4 kg/m2) participated in 2 study visits, each consisting of 2 sessions of fixed load (20 W) recumbent cycle ergometry with bilateral upper thigh pressure tourniquets for 8 min at a fixed pedal frequency of 35 (LOW) or 100 (HIGH) rpm (randomized). Cuffs remained at 0 mm Hg for the first 3 min (CTL), and were then randomized to 0 mm Hg (NoRCO) or 90 mm Hg (SubRCO) for the final 5 min of exercise. SBP and diastolic blood pressure (DBP) were measured via manual sphygmomanometry at the end of CTL and end‐exercise (END). MAP was calculated as (SBP + 2 * DBP)/3.

Results

There were no between or within condition differences at CTL for MAP (P>0.05). In contrast, for between SubRCO and NoRCO differences at END, MAP was increased in SubRCO vs NoRCO in both HIGH (106±12 vs 92±13 mm Hg, respectively) and LOW (94±9 vs 85±8 mm Hg, respectively) (P<0.05). At END, MAP was increased in HIGH vs LOW within both SubRCO and NoRCO (P<0.01). Within both NoRCO (129 ± 18 vs 117 ± 11 mm Hg) and SubRCO (125 ± 15 vs 113 ± 10 mm Hg) at CTL, SBP was increased in HIGH vs LOW, respectively (P<0.01). At CTL, there were no between SBP NoRCO vs SubRCO differences in HIGH or LOW. Within SBP differences for NoRCO (134 ± 19 vs 113 ± 11 mm Hg) and SubRCO (147 ± 20 vs 127 ± 12 mm Hg) in HIGH vs LOW persisted to END, respectively (P<0.01). SBP increased at END vs CTL within SubRCO for both HIGH and LOW (P<0.02), but not within NoRCO (P>0.05). Lastly, SBP increased in SubRCO vs NoRCO at END in both HIGH and LOW (both P<0.01). There were no differences for DBP at any time point (P>0.05).

Conclusion

These data support our hypothesis that, independent of pedal frequency, SubRCO provokes increased MAP during fixed‐load submaximal exercise as a function of increased SBP. However, high pedal rate accompanied by SubRCO results in exaggerated SBP‐mediated increased MAP. These data contribute to an improved understanding of the stimuli that activate group III/IV afferents during exercise in humans.

Support or Funding Information

NHLBI RO1 HL126638; AHA 16POST30260021
Functional Sympatholysis is Impaired in End‐stage Renal Disease
Authors: Downey Ryan , Lee Ho Lim , Liao Peizhou , DaCosta Dana , Park Jeanie
Published: November 2023

Chronic renal failure patients have reduced exercise tolerance contributing to increased cardiovascular risk. Reflex activation of sympathetic nervous activity (SNA) during exercise increases cardiac output and vasoconstricts nonworking skeletal muscle. However, within exercising skeletal muscle, local metabolites, such as nitric oxide, are generated that oppose SNA‐mediated vasoconstriction to preserve blood flow and oxygenation within the working muscle, termed functional sympatholysis. We hypothesized that chronic kidney disease (CKD) and end‐stage renal disease (ESRD) patients requiring chronic hemodialysis have impaired functional sympatholysis resulting in reduced oxygenation of exercising muscle which could contribute to exercise dysfunction. Muscle oxygen tissue saturation index (TSI) was measured in 33 subjects (13 Controls, 10 CKD, 10 ESRD) using near‐infrared spectroscopy (NIRS) positioned over the flexor digitorum profundus muscle in the forearm. Changes in muscle TSI were calculated as a percentage of total labile signal (TLS) defined as muscle TSI at the point of maximum deoxygenation during arterial occlusion. Lower‐body negative pressure (LBNP) was applied at −20 mmHg to induce an increase in SNA without causing arterial blood pressure changes. Continuous measurements were made at baseline, during LBNP, and during LBNP with concomitant rhythmic handgrip exercise performed at 30% of maximum voluntary contraction. Baseline muscle TSI was significantly lower in ESRD compared to controls and CKD (Control, 68.25±1.25%; CKD, 67.88±1.10%; ESRD, 61.80±1.74%; p=0.004). There was a reduction in muscle TSI in all groups during SNS activation induced by LBNP at rest. When compared to muscle TSI changes during LBNP at rest, the reduction in muscle TSI was significantly ameliorated during LBNP with handgrip exercise in controls (−15.20±3.05% vs. −5.01±2.62%, p=0.013), suggesting intact functional sympatholysis. Similarly, in CKD, compared to LBNP at rest, there was a trend towards improvement in the reduction in muscle TSI during LBNP with concomitant exercise (−15.74±7.66% vs. 2.26±4.28, p=0.062). However, there was no significant improvement in muscle TSI changes with concomitant exercise in ESRD (−11.94±2.04% vs. −6.25±1.82%, p=0.169). These data suggest that controls without kidney disease, and those with CKD not yet requiring renal replacement therapy have intact functional sympatholysis. However, ESRD patients on chronic hemodialysis have impaired functional sympatholysis that could contribute to exercise tolerance. Further studies are needed to elucidate the mechanisms underlying impaired functional sympatholysis in ESRD.

Support or Funding Information

Supported by NIH HL‐098744, NIH DK‐00756, NIH GM‐000680, VA Merit I01CX001065, and Satellite Healthcare, a not‐for‐profit renal care provider.
Effect of endurance training on the centrally‐induced muscle vasodilatation during one‐legged cycling
Authors: Asahara Ryota , Matsukawa Kanji , Shintaku Takahiro
Published: November 2023

Our laboratory has reported that central command contributes to increased blood flow in the non‐contracting vastus lateralis (VL) muscle during voluntary one‐legged cycling exercise in sedentary subjects. The present study aimed to examine whether the muscle vasodilator response is affected by endurance training. Seven trained athletes and seven sedentary men performed voluntary or passive one‐legged cycling exercise and mental imagery of the voluntary exercise for 1 min. Exercise intensity was set at 35% of the maximal voluntary exercise. The relative changes in oxygenated‐hemoglobin concentration (Oxy‐Hb) of the gluteus medius (GM) and VL muscles in the non‐exercising leg were measured as index of muscle tissue blood flow with near‐infrared spectroscopy. In both groups, the Oxy‐Hb of the GM and VL muscles increased at the start period of voluntary one‐legged cycling. The increases in Oxy‐Hb of the muscles were significantly greater in trained athletes than in sedentary subjects. In contrast, the Oxy‐Hb of the GM and VL muscles was unchanged at the start period of passive one‐legged cycling, suggesting that the initial increases in Oxy‐Hb of both leg muscles during the voluntary exercise were not derived from a feedback by limb mechanosensitive afferents. The Oxy‐Hb of both muscles also increased during mental‐imagery of voluntary one‐legged cycling and the responses were greater in the athletes as compared to the sedentary subjects. Taken together, it is likely that the muscle vasodilator effect by central command is augmented by endurance training.
PGC‐1α Upregulates Mitochondrial Sirtuins and Reduces Protein Acetylation in Skeletal Muscle of Old Mice.
Authors: Kang Choung Hun , Yeo Dongwook , Ji Li Li
Published: November 2023

Mitochondrial dysfunction in skeletal muscle may contribute to decreased muscle mass, metabolic function and force generation during aging termed sarcopenia. Peroxisome proliferator‐activated receptor gamma coactivator 1‐alpha (PGC‐1α) and sirtuins are two groups of master regulators for mitochondrial biogenesis, dynamics and homeostasis. The purpose of the study was to investigate the effect of aging and PGC‐1α overexpression (OE) on sirtuin gene expressions, protein acetylation and mitochondrial function in mouse skeletal muscle. Male C57BL mice at the age of 6 mo (young, Y; N=8), 12 mo (middle‐aged, M; N=8), and; and 24 mo (old, O; N=8) were transfected in vivo with either PGC‐1α DNA or GFP into the tibialis anterior (TA) muscle of one of their hindlimbs. Sirt1 mRNA expression was increased by 19% in M (P<0.05), but decreased by 15% in O (P<0.05), compared to Y, whereas PGC‐1α OE had no effect. Sirt3 mRNA level was lowered in M (28%, P<0.01) and O (56%, P<0.01) vs. Y; however, the level was restored by PGC‐1α by 24% (P<0.05), 53% (P<0.01) and 50% (P<0.01) in Y, M, and O group, respectively. Further, Sirt5 mRNA level was reduced by ~60% in both M and O (P<0.01), but increased with PGC‐1α by 26% (P<0.05), 35% (P<0.05) and 60% (P<0.01) in Y, M and O, respectively. Sirt6 mRNA level was not affected by aging or PGC‐1α OE. Total cytoplasmic protein acetylation was 1.2‐fold higher in O vs. Y (P<0.05), with no effect of PGC‐1α OE. Mitochondrial protein acetylation was increased 1.7‐fold in O vs. Y (P<0.01), and suppressed by 22–28% (P<0.05), in all age groups by PGC‐1α OE. Citrate synthase (CS) activity in M and O was 28 and 58% lower (P<0.01), respectively, than that in Y. PGC‐1α OE increased CS activity by 14% (P<0.05), 26% (P<0.05) and 62% (P<0.01) in Y, M and O, respectively. These data would suggest that aging reduces sirtuin family gene expression, whereas PGC‐1α OE can ameliorate mitochondrial function in older muscle by upregulating mitochondrial isoform Sirt3 and Sirt5 possibly due to their canonical role in promoting mitochondrial biogenesis.
Orphan nuclear hormone receptor Small Heterodimer Partner plays a protective role in diet‐induced islet dysfunction
Authors: Park Jung Eun , Lee Mikang , Lee Yoon‐Kwang
Published: November 2023

Our early study found that deficiency of small heterodimer partner (SHP, NR0B2) protected the mice from diet‐induced obesity due to increased fatty acid oxidation but exacerbated glucose tolerance due to impaired glucose‐stimulated insulin secretion upon a 6‐month western diet regimen. Current study explored potential roles of SHP in the development of glucose intolerance furthermore. We assessed islet function using illumina beadchip array and morphometric measurement of pancreatic sections. Beadchip array revealed that many exocrine specific genes (for example, CUB and Zona Pellucida‐Like Domains (cuzd1), pancreas specific transcription factor 1a (ptf1a), trypsin 4 (try4) and pancreatic carboxyl ester lipase (cel) etc.) were markedly down‐regulated in the islets of SHP null mice in either chow or western diet‐fed condition. However, expression of major genes involved in insulin secretion and islet function were similar between WT and SHP null mice. Results from quantitative real‐time PCR analysis agreed with majority of beadchip array results except Glut2, which was decreased in SHP null islets. Corroborating with impaired insulin secretion and lower Glut2 mRNA level, glucose‐stimulated Ca2+ influx was greatly diminished in SHP null islets. Islet size was also decreased in SHP null mice fed either diet. The observed diabetic phenotype and pancreatic exocrine insufficiency in whole body SHP−/−mice was recapitulated in the pancreas specific SHPKO (PSHPKO) mice, where SHP deletion is confirmed in both endocrine and exocrine tissues. Interestingly the lean phenotype was reproduced only in liver‐specific SHPKO mice but not in PSHPKO mice. Even though detailed underlying molecular mechanisms for the observed phenotypes by SHP deletion remain to be elucidated, current data suggest that SHP plays distinctive and tissue‐specific role in the development of obesity and diabetes.

Support or Funding Information

This work had been supported by the National Institutes of Health 344 Grant R01DK093774 (to YKL)
Short‐term Metformin and Exercise Training Effects on Strength, Aerobic Capacity, Glycemic Control and Mitochondrial Function in Burn Children
Authors: Rivas Eric , Porter Craig , Herndon David N. , Suman Oscar E.
Published: November 2023

Metformin (M) has been shown to attenuate hyperglycemia and exercise (EX) has been shown to improve strength and aerobic exercise capacity in severely burn patients. However, it is unknown if the combination of M+EX can further improve these outcome measures and if EX alone will improve glycemic control in burn populations. This project tested the hypothesis that 6‐weeks of exercise training combined with short‐term administration of metformin (EX+M) compared to exercise alone (EX) would synergistically improve aerobic and strength exercise capacity, while improving mitochondrial respiration and glucose tolerance. Eight burned children (4 male) received EX after discharge while nine burned children (6 male) received M at 72–96 h post‐ admission with EX at discharge. Prior to EX, both groups had similar physical characteristics (means±SD; 15 ± 2y, 157.1±7cm, 50.1±11 kg, 34.7±6 lean body mass, LBM, 46±15% total body surface area burned; P>0.05), peak strength (peak torque 1.6±0.5 N‐M·KgLBM; P>0.05) peak aerobic capacity (VO2peak; 34.6±8 mlO2·kgLBM·min; P>0.05) and metabolic characteristics (fasting glucose 110.4±16 mg·dL and insulin 20.6±11 pmol·L, 75g oral glucose tolerance, OGTT, AUC for glucose 17776±3245 mg·dL·min and AUC insulin 8451±6043 pmol·L·min, 1878±151 kcal/24h resting energy expenditure, REE, and resting heart rate, HR 129±13 bpm; P>0.05). At PreEX time, mitochondrial respiration (pmol·sec·mg) was attenuated for each state: leak (−5.9±5) states 2 (−22.5±3) and 3 (−42.4±13), and oxphos (−58.9±19) in the M compared to the EX+M (each, P ≤0.02). Post‐burn injury EX training (started 1.4±0.6 mo postburn; P=0.33) and completed exercise sessions (30±11 days; P=0.71) was similar between groups. EX improved strength (change from preEX, Δ1.6±0.6 N‐M·KgLBM), VO2peak (Δ9±7 mlO2·kgLBM) and reduced fasting glucose (Δ19.3±13 mg·dL) and glucose AUC for the 75g OGTT (Δ3402±3674 mg·dL·min) in both groups (each, P ≤0.03). EX+M significantly reduced REE (Δ539±480 kcal/24h, P<0.01) while E alone did not (P=0.68). Both, EX+M and EX reduced resting HR (Δ30±23bpm; P≤0.02). EX+M increased mitochondrial respiration for each state (P≤0.05) to similar levels as EX alone (each P>0.05). These data indicate that short‐term metformin combined with exercise provides no further improvement beyond that of exercise alone in terms of strength, exercise capacity, and glycemic control. Most importantly, for the first time we show that short‐term exercise training improved glycemic control in burn patients. However, it remains unknown if a longer (1‐year administration) M treatment is needed to improve the hyperglycemia/insulinemia state in burn patients.

Support or Funding Information

This study was supported in part or totally by awards from: NIH P50‐GM060338, NIH R01‐GM56687, R01 HD049471, SHC 84080, 71008, 84090, and NIDILRR 90DP0043‐01‐00.
Polyphenolics Protect Renal Fibroblasts from the Harmful Effects of Hyperglycemia‐Stimulated Advanced Glycation End Products
Authors: Harris Janay M. , Blount Mitsi A.
Published: November 2023

Diabetes mellitus is the most common metabolic disease and a leading cause of kidney failure. Chronic hyperglycemia leads to non‐enzymatic glycation of proteins to form advanced glycation end products (AGEs), a major culprit in the progression of diabetic nephropathy (DN). AGEs promote DN by inducing secretion of cytokines and growth factors, as well as mediate tubulointerstitial fibrosis, via the receptor for AGEs (RAGE). Herbs and spices contain high concentrations of polyphenolics which block AGE formation. The aim of this study was to determine if a mixture of culinary spices with high phenolic content could reduce AGE promotion of DN in renal fibroblasts. Cloves, cinnamon and Jamaican allspice were ground into a fine powder and extracted with 50% ethanol to extract phenolic content. The resulting extract (SPICE) was used to treat rat kidney fibroblasts (NRK‐49F) that were serum starved and treated with either mannitol (control) or glucose for 24 hours. Glucose only‐treated fibroblasts have elevated RAGE mRNA expression compared to control‐untreated fibroblasts, but SPICE treatment lowered RAGE expression in fibroblasts exposed to high glucose. Similarly, SPICE/glucose‐treated fibroblasts had lower IL‐6 and VEGF mRNA expression compared to glucose‐treated fibroblasts. Hyperglycemia‐mediated alterations in matrix metalloproteinases (MMPs) and their naturally occurring specific inhibitors (TIMPs) contribute to renal injury in DN. Glucose‐treated fibroblasts had elevated MMP9 and lowered TIMP1 expression compared to untreated cells; however, SPICE treatment of glucose‐treated fibroblasts dampened MMP9 and increased TIMP1 expression. MMP2 was and lowered by high glucose treatment of fibroblasts while TIMP2 was elevated; however, the addition of SPICE returned MMP2 and TIMP2 expression to basal levels. In summary, polyphenolics reduce RAGE expression in renal fibroblasts subjected to hyperglycemia which likely explains the dampened expression of IL‐6 and VEGF, factors known to be upregulated by AGE and harmful in DN progression. Polyphenolics also reverse the hyperglycemia‐mediated alterations in MMPs and TIMPs in kidney fibroblasts that are known to promote renal interstitial fibrosis in DN. Collectively, dietary consumption of biological polyphenolics may prove to be an effective treatment for advancing DN.
Maternal Treatment of Renovascular Hypertensive Rats with Hydrogen Sulfide Inhibited Hypertension in Offspring
Authors: Wu Yuming , Guo Qi , Feng Xiaohong , Xue Hongmei
Published: November 2023

Aim

Recently, Hydrogen sulfide (H2S) has been demonstrated to be a powerful vasodilator of the placental vasculature and can improve intrauterine growth restriction. In this study, we tested the fetal programming effect of H2S on renovascular hypertensive rats (RVH), a rat model of secondary hypertension.

Methods

Maternal hypertensive rats were treated with H2S (56 μmol/Kg per day) during pregnancy and lactation periods and the offspring without H2S after weaning. Another treatment group was maternal hypertensive rats treated without H2S and the offspring with H2S (56 μmol/Kg per day) after weaning till 16 weeks old. Blood pressure was measured non‐invasively by tail cuff plethysmography in conscious offsprings. Baroreflex sensitivity was induced by angiotensin II (Ang II), phenylephrine (PHE), and sodium nitroprusside (SNP) in conscious rats. The cardiac autonomic tonus was tested by atropine and propranolol during two consecutive days in a reverse order. Western blot was used to check the expression of protein in central.

Results

(1) The blood pressure in male offspring of renovascular hypertensive rats was higher than normal SD rats, even up to borderline hypertension. Although the blood pressure of female offspring was higher than that of normal rats, but it did not reach the critical hypertension. (2) Baroreflex sensitivity induced by Ang II and PHE in the offspring of renovascular hypertension decreased. (3) The sympathetic system in the offspring of renovascular hypertension was activated and the autonomic nervous system was imbalance. (4) Ang II /AT1R pathway, in nucleus tractus solitarius (NTS) and rostral ventrolateral medulla (RVLM), was activated in offspring of renovascular hypertensive rats and the downstream level of oxidative stress and inflammation‐related protein was also increased. The expression of cystathionine beta synthase (CBS), which was an endogenous generating enzyme of H2S, decreased in male offspring but increased in female, and there were differences between male and female offspring. (5) Both maternal and offspring treatment with H2S could improve the above effects.

Conclusion

These long‐lasting improved effects of H2S were accompanied by downregulating central Ang II/AT1R pathway in offspring.

Support or Funding Information

This study was supported by the grants from the National Natural Science Foundation of China [Grant 31671185, 31171098], the Specialized Research Fund for the Doctoral Program of Higher Education of China [NO. 20121323110008], the Program for New Century Excellent Talents in University from the Education Ministry of China Grant NCET‐07‐0252.
Salinity‐Dependent Expression of ncc‐like 2 in the Gill and Opercular Epithelium of Euryhaline Killifish
Authors: Doud James , Popovski Christine , Ritter Eleanore , Tipsmark Christian , Breves Jason
Published: November 2023

Atlantic killifish (Fundulus heteroclitus) can tolerate abrupt changes in environmental salinity because of their ability to rapidly adjust the activities of ionocytes in the gill and opercular epithelium. Salinity acclimation responses often entail the coordinated and dynamic expression of genes encoding effectors of ion transport. For example, exposure to seawater (SW) induces elevated gene transcription of Na+/K+/2Cl− cotransporter (nkcc) and cystic fibrosis transmembrane regulator (cftr) in support of the ion‐extrusion capacities of SW‐type ionocytes. On the other hand, it has not been fully resolved how freshwater (FW)‐type ionocytes in teleosts, including F. heteroclitus, actually mediate ion uptake at the sub‐cellular level. A recently characterized Na+/Cl− cotransporter (Ncc) has been proposed as a conduit for the uptake of Na+ and Cl− across the apical surface of FW‐type ionocytes in a subset of teleosts. To examine whether killifish employ an Ncc‐dependent ion‐uptake pathway, we first identified a putative ncc‐like 2 in F. heteroclitus that was highly expressed in the gill and opercular epithelium. Transfer of killifish from SW to FW elicited an increase in ncc‐like 2 levels in both gill and opercular epithelium in parallel with reductions in nkcc and cftr levels. On the other hand, transfer from FW to SW resulted in a marked reduction in ncc‐like 2 levels concurrent with increases in nkcc and cftr. We will describe the distribution of Ncc‐like 2 immunoreactivity in the gill and operculum epithelium by employing an anti‐killifish Ncc‐like 2 antibody. We propose that ncc‐like 2‐expressing ionocytes support the capacity of F. heteroclitus to acclimate to freshwater environments.

Support or Funding Information

Supported by Start‐Up funds to J.P.B.
Expression and Function of an Animal MEP/Amt Ammonia Transporter, AeAmt2 in the Larvae of the Mosquito, Aedes aegypti
Authors: Durant Andrea Claire , Donini Andrew
Published: November 2023

The mosquito Aedes aegypti is the primary vector of zika, dengue and chikungunya viruses. Larvae are commonly found in freshwater habitats; however, it was shown that ammonia rich septic tanks in the Caribbean also serve as habitats for larval development and adult emergence which can explain the prevalence of disease during the dry season. Since ammonia (NH3/NH4+) is toxic to animals an understanding of how the larvae of A. aegypti can survive in septic tanks is important. Our previous studies showed that A. aegypti possess two Rhesus‐like proteins, AeRh50‐1, AeRh50‐2, and a MEP/Amt transporter, AeAmt1. Those studies demonstrated that these ammonia transporters are expressed in the anal papillae, finger like sacs that surround the anus and actively transport ions, where they play a role in ammonia excretion. This study reports on a fourth ammonia transporter in A. aegypti, a MEP/Amt transporter, AeAmt2. The AeAmt2 is expressed in the anal papillae epithelium where it is co‐localized with the V‐type H+‐ATPase on the apical (water facing) membrane. To elucidate the function of AeAmt2 in anal papillae, larvae were treated for double stranded RNA knockdown of AeAmt2 and ammonia fluxes were recorded at the anal papillae with the scanning ion selective electrode technique (SIET). The effects of AeAmt2 knockdown on larvae were assessed by tracking survival over time and measuring the ammonia and proton (pH) levels of the hemolymph with ion selective microelectrodes. Ammonia excretion is a vital physiological process in all animals and this study further elucidates ammonia excretion mechanisms of larval disease vector mosquitoes, which is of particular significance given their ability to inhabit areas of high environmental ammonia.

Support or Funding Information

National Sciences and Engineering Research Council of Canada
Antibodies Against Sodium‐Dependent Cation Chloride Cotransporters in the Yellow Fever Mosquito Aedes aegypti
Authors: Viel Kenyatta CMF , DeBrosse Adrienne C. , Riley Grace F. , Piermarini Peter M. , Gillen Christopher M.
Published: November 2023

Sodium‐dependent cation‐chloride cotransporters (CCCs) participate in ion secretion and absorption across animal phyla. The genome of the yellow fever mosquito Aedes aegypti has three genes with sequence similarity to vertebrate sodium‐dependent CCCs. One of these sequences (AAEL006180) codes for a protein with 50% identity to the human secretory Na‐K‐Cl cotransporter NKCC1 and 70% identity to a Drosophila melanogaster Na‐K‐Cl cotransporter with a role in secretion by Malpighian tubules. The other two of these sequences (AAEL009888 and AAEL009886) code for proteins with approximately 40% identity to the human Na‐K‐Cl cotransporter NKCC1 and approximately 55% identity to uncharacterized proteins in Drosophila and other insects. To begin evaluating the role of the proteins coded for by AAEL009888 and AAEL009886, we conducted experiments to determine their developmental and tissue expression patterns. Polyclonal antibodies were developed by injecting two rabbits with two peptide sequences from each paralog. Antiserum from both rabbits reacted with proteins in larvae, adult male, and adult female whole body tissues, as well as in adult Malpighian tubules and larval anal papillae, with the most prominent bands above 150 kDa size markers on 7.5% SDS‐PAGE gels. To develop paralog‐specific antibodies, we affinity purified the antiserum against peptides from either the AAEL009888 or AAEL009886 sequences. We confirmed specificity of these antibodies with peptide competition experiments on dot blots. Similar to the unpurified serum, the affinity purified antibodies reacted with proteins above 150 kDa on Western blots of lysates and membrane preps from whole body samples of larvae and adults. We are testing the effectiveness of the affinity purified antibodies on Western blots of isolated tissue samples and on formalin‐fixed paraffin‐embedded sections of larvae.

Support or Funding Information

NSF‐IOS‐1557230
Do ion‐motive pumps contribute to cold‐acclimation in Drosophila?
Authors: Yerushalmi Gil , MacMillan Heath , Donini Andrew
Published: November 2023

At low temperatures Drosophila, like most insects, lose the ability to regulate ion and water flux across the gut epithelia, which leads to a lethal accumulation of K+ in the hemolymph. Cold‐acclimation can mitigate or entirely prevent these ion imbalances, but the physiological mechanisms that facilitate these plastic changes are not understood. This study assessed the activity of Na+/K+‐ATPase (NKA), and V‐Type H+ ATPase (VA) in the primary ionoregulatory tissues of Drosophila (the gut and the Malpighian tubules) to test whether modulation of their activity is a potential mechanism of cold‐acclimation. Upon adult emergence, D. melanogaster females were subjected to seven days at 25°C (warm acclimation) or 10°C (cold acclimation). Cold‐acclimation reduced the critical thermal minimum (CTmin), sped up recovery from chill coma, and improved survival following prolonged cold stress, suggesting that cold acclimation may be mitigating ion imbalance resulting from cold in our flies. We then quantified both NKA and VA activity in the hindgut, midgut, and the Malpighian tubules of warm‐ and cold‐acclimated flies. Using Ramsay assays, Malpighian tubule fluid secretion rates were compared for warm and cold acclimated flies, and the Na+ and K+ concentrations of secreted fluid were measured with ion‐selective microelectrodes. The scanning ion‐selective electrode technique was used to measure the Na+ and K+ flux across the midgut and hindgut epithelia of warm and cold acclimated flies. The effects of cold acclimation on ionomotive pump activity, Malpighian tubule function and ion fluxes across the Drosophila gut are presented. This study sheds light on the underlying physiological mechanisms that facilitate changes that mitigate the loss of ion balance upon a cold stress.

Support or Funding Information

NSERC Discovery Grant to Andrew DoniniBanting Postdoctoral Fellowship to Heath MacMillan