Biology subjects

Bishop, D. J.

Publications and source records attributed to Bishop, D. J..

5 recordsLinked to original sources

bioRxiv2018

A physiological drop in pH decreases mitochondrial respiration, and AMPK and Akt signalling, in L6 myocytes

Exercise stimulates mitochondrial biogenesis and increases mitochondrial respiratory function and content. However, during high-intensity exercise muscle pH can decrease below pH 6.8 with a concomitant increase in lactate concentration. This drop in muscle pH is associated with reduced exercise-induced mitochondrial biogenesis, whilst increased lactate may act as a signaling molecule to affect mitochondrial biogenesis. Therefore, in this study we wished to determine the impact of altering pH and lactate concentration in L6 myotubes on genes and proteins known to be involved in mitochondrial biogenesis. We also examined mitochondrial respiration in response to these perturbations. Differentiated L6 myotubes were exposed to normal (pH 7.5), low (pH 7.0) or high pH (pH 8.0) media with and without 20 mM sodium L-lactate for 1 and 6 h. Low pH and 20 mM Sodium L-Lactate resulted in decreased Akt (Ser473) and AMPK (T172) phosphorylation at 1 h compared to controls, whilst at 6 h the nuclear localisation of HDAC5 was decreased. When the pH was increased both Akt (Ser473) and AMPK (T172) phosphorylation was increased at 1 h. Overall increased lactate decreased the nuclear content of HDAC5 at 6 h. Exposure to both high and low pH media significantly decreased basal mitochondrial respiration, ATP turnover, and maximum mitochondrial respiratory capacity. These data indicate that muscle pH affects several metabolic signalling pathways, including those required for mitochondrial function.

cell biology↗

bioRxiv2017

Repeated-ischaemic exercise enhances mitochondrial and ion transport gene adaptations in human skeletal muscle: Role of muscle redox state and AMPK

This study assessed the effect of repeated-ischaemic exercise on the mRNA content of PGC-1 (total, 11, and 14) and Na+,K+-ATPase (NKA; 1-3, {beta}1-3, and FXYD1) isoforms in human skeletal muscle, and studied some of the potential molecular mechanisms involved. Eight trained men (26 {+/-} 5 y and 57.4 {+/-} 6.3 mL{middle dot}kg-1{middle dot}min-1) completed three interval running sessions with (ISC) or without ischaemia (CON), or in hypoxia (HYP, ~3250 m), in a randomised, crossover fashion separated by 1 week. A muscle sample was collected from the dominant leg before (Pre) and after exercise (+0h, +3h) in all sessions to measure the mRNA content of PGC-1 and NKA isoforms, oxidative stress markers (i.e. catalase and HSP70 mRNA), muscle lactate, and phosphorylation of AMPK, ACC, CaMKII, and PLB protein in type I and II fibres. Muscle hypoxia (i.e. deoxygenated haemoglobin) was matched between ISC and HYP, which was higher than in CON (~90% vs. ~70%; p< 0.05). The levels of PGC-1 total, -11, -14, and FXYD1 mRNA increased in ISC only (p< 0.05). These changes were associated with increases in oxidative stress markers and higher p-ACCSer221/ACC in type I fibres, but were unrelated to muscle hypoxia, lactate, and CaMKII and PLB phosphorylation. These findings highlight that repeated-ischaemic exercise augments the skeletal muscle gene response related to mitochondrial biogenesis and ion transport in trained men. This effect seems attributable, in part, to increased oxidative stress and AMPK activation, whereas it appears unrelated to altered CaMKII signalling, and the muscle hypoxia and lactate accumulation induced by ischaemia.\n\nSummary in key pointsO_LIWe investigated if ischaemia would augment the exercise-induced mRNA response of PGC-1 and Na+,K+-ATPase (NKA) isoforms (1-3, {beta}1-3, and FXYD1), and examined whether this effect could be related to oxidative stress and fibre type-dependent AMPK and CaMKII signalling in the skeletal muscle of trained men.\nC_LIO_LIRepeated-ischaemic exercise increased the mRNA content of PGC-1 total, -11, and-14, and of the NKA regulatory subunit FXYD1, whereas exercise in systemic hypoxia or alone was without effect on these genes.\nC_LIO_LIThese responses to ischaemia were complemented by increased oxidative stress (as assessed by catalase and HSP70 mRNA) and ACC phosphorylation (an indicator of AMPK activation) in type I fibres. However, they were unrelated to CaMKII signalling, muscle hypoxia, and lactate accumulation.\nC_LIO_LIThus, repeated ischaemic exercise augments the muscle gene response associated with mitochondrial biogenesis and ion homeostasis in trained men. This effect seems partly attributable to promoted oxidative stress and AMPK activation.\nC_LI\n\nAbbreviations

physiology↗

bioRxiv2017

Regulation of Na+,K+-ATPase isoforms and phospholemman (FXYD1) in skeletal muscle fibre types by exercise training and cold-water immersion in men

Little is understood about the fibre type-dependent regulation of Na+,K+-ATPase (NKA) isoforms by exercise training in humans. The main aim of this study was therefore to assess the impact of a period of repeated exercise sessions on NKA-isoform protein abundance in different skeletal muscle fibre types in men. Post-exercise cold-water immersion (CWI) has been reported to increase oxidative stress, which may be one mechanism underlying increases in NKA-isoform expression. Thus, a second aim was to evaluate the effect of CWI on training-induced modulation of NKA-isoform abundance. Vastus lateralis muscle biopsies were obtained from nineteen men at rest before (Pre) and after (Post) six weeks of intense interval cycling, with training sessions followed by passive rest (CON, n=7) or CWI (10{degrees}C; COLD, n=5). Training increased (p<0.05) the abundance of NKA1 and NKA{beta}3 in both type I and type II fibres, NKA{beta}1 in type II fibres, but was without effect on NKA2 and NKA3 (p>0.05). Furthermore, training decreased FXYD1 protein content in type I fibres, which abolished its fibre type-specific expression detected at Pre (p<0.05). CWI was without impact on the responses to training (p>0.05). These results highlight that NKA isoforms are regulated in a fibre type-dependent fashion in response to intense training in humans. This may partly explain the improvement in muscle Na+/K+ handling after a period of intense training. CWI may be performed without adversely or favourably affecting training-induced changes in NKA-isoform abundance.\n\nSummary in key pointsO_LIIt is unclear how Na+,K+-ATPase (NKA) isoforms are regulated in different skeletal muscle fibre types by exercise training in humans, and the effect on phospholemman (FXYD1) protein abundance in different fibre types remains to be elucidated. We investigated the impact of six weeks of training on NKA-isoform protein abundance (1-3, {beta}1-3 and FXYD1) in type I and II muscle fibres in men.\nC_LIO_LIWe show that intense interval training selectively increases the protein content of NKA 1 and {beta}3 in both fibre types, {beta}1 in type II fibres, and decreases FXYD1 in type I fibres.\nC_LIO_LIThese results suggest the favourable impact of intense training on human muscle Na+/K+ regulation could be attributable, in part, to fibre type-dependent modulation of NKA-isoform abundance.\nC_LIO_LIGiven that cold exposure has been shown to modulate cellular redox state, which has been linked to increased NKA expression, we also investigated the effect of exercise training plus cold-water immersion (CWI) on the fibre type-specific responses of NKA isoforms and FXYD1. We found that CWI was without effect on the responses to training.\nC_LI\n\nAbbreviationsAMPK{beta}2, 5 AMP-activated protein kinase subunit {beta}2; CaMKII, Ca2+-calmodulin-dependent protein kinase isoform 2; COLD, cold-water immersion group; CON, control group; Ct, cycle threshold; CV, coefficient of variation; CWI, cold-water immersion; EDL, extensor digitorum longus; FXYD1, phospholemman isoform 1; HSP70, heat-shock protein 70; GXT, graded exercise test; K+, potassium; Km, Michaelis-Menten constant; MHC, myosin heavy chain; Na+, sodium; NF-1, neurofibromatosis type 1; NKA, Na+,K+-ATPase; ROS, reactive oxygen species; SDS-PAGE, sodium dodecyl sulphate polyacrylamide gel electrophoresis; SERCA1, sarco/endoplasmic reticulum Ca2+-ATPase isoform 1; VO2peak, maximum oxygen uptake.

physiology↗

bioRxiv2017

Post-exercise cold-water immersion increases Na+,K+-ATPase α2-isoform mRNA content in parallel with elevated Sp1 expression in human skeletal muscle

We investigated the effect of a session of sprint-interval exercise on the mRNA content of NKA isoforms (1-3, {beta}1-3) and FXYD1 in human skeletal muscle. To explore some of the cellular stressors involved in this regulation, we evaluated the association between these mRNA responses and those of the transcription factors Sp1, Sp3 and HIF-1. Given cold exposure perturbs muscle redox homeostasis, which may be one mechanism important for increases in NKA-isoform mRNA, we also explored the effect of post-exercise cold-water immersion (CWI) on the mRNA responses. Muscle was sampled from nineteen men before (Pre) and after (+0h, +3h) exercise plus passive rest (CON, n=10) or CWI (10{degrees}C; COLD, n=9). In COLD, exercise increased NKA2 and Sp1 mRNA (+0h, p<0.05). These genes remained unchanged in CON (p>0.05). In both conditions, exercise increased NKA1, NKA{beta}3 and HIF-1 mRNA (+3h; p <0.05), decreased NKA{beta}2 mRNA (+3h; p<0.05), whereas NKA3, NKA{beta}1, FXYD1 and Sp3 mRNA remained unchanged (p>0.05). These human findings highlight 1) sprint-interval exercise increases the mRNA content of NKA 1 and {beta}3, and decreases that of NKA {beta}2, which may relate, in part, to exercise-induced muscle hypoxia, and 2) post-exercise CWI augments NKA2 mRNA, which may be associated with promoted Sp1 activation.

physiology↗

bioRxiv2017

Ribosome biogenesis adaptation and mTORC1 signalling in human skeletal muscle following concurrent training compared with resistance training alone

1.Combining endurance training with resistance training (RT) may attenuate skeletal muscle hypertrophic adaptation versus RT alone; however, the underlying mechanisms are unclear. We investigated changes in markers of ribosome biogenesis, a process linked with skeletal muscle hypertrophy, following concurrent training versus RT alone. Twenty-three males underwent eight weeks of RT, either performed alone (RT group, n = 8), or combined with either high-intensity interval training (HIT+RT group, n = 8), or moderate-intensity continuous training (MICT+RT group, n = 7). Muscle samples (vastus lateralis) were obtained before training, and immediately before, 1 h and 3 h after the final training session. Training-induced changes in basal expression of the 45S ribosomal RNA (rRNA) precursor (45S pre-rRNA), and 5.8S and 28S mature rRNAs, were greater with concurrent training versus RT. However, during the final training session, RT further increased both mTORC1 (p70S6K1 and rps6 phosphorylation) and 45S pre-rRNA transcription-related signalling (TIF-1A and UBF phosphorylation) versus concurrent training. These data suggest that when performed in a training-accustomed state, RT induces further increases mTORC1 and ribosome biogenesis related signalling in human skeletal muscle versus concurrent training; however, changes in ribosome biogenesis markers were more favourable following a period of short-term concurrent training versus RT performed alone.

physiology↗