Biology subjects

Genders, A. J.

Publications and source records attributed to Genders, A. J..

6 recordsLinked to original sources

bioRxiv2022

Amyloid beta 42 alters cardiac metabolism and impairs cardiac function in obesity

There are epidemiological associations between obesity and type 2 diabetes, cardiovascular disease and Alzheimers disease. While some common aetiological mechanisms are known, the role of amyloid beta 42 (A{beta}42) in these diverse chronic diseases is obscure. Here we show that adipose tissue releases A{beta}42, which is increased from adipose tissue of obese mice and is associated with higher plasma A{beta}42. Increasing circulating A{beta}42 levels in non-obese mice had no effect on systemic glucose homeostasis but had obesity-like effects on the heart, including reduced cardiac glucose clearance and impaired cardiac function. These effects on cardiac function were not observed when circulating levels of the closely related A{beta}40 isoform were increased. Administration of an A{beta} neutralising antibody prevented obesity-induced cardiac dysfunction and hypertrophy. Furthermore, A{beta} neutralising antibody administration in established obesity prevented further deterioration of cardiac function. Multi-contrast transcriptomic analyses revealed that A{beta}42 impacted pathways of mitochondrial metabolism and exposure of cardiomyocytes to A{beta}42 inhibited mitochondrial function. These data reveal a role for systemic A{beta}42 in the development of cardiac disease in obesity and suggest that therapeutics designed for Alzheimers disease could be effective in combating obesity-induced heart failure.

physiology↗

bioRxiv2021

Exercise and training regulation of autophagy markers in human and rodent skeletal muscle.

Autophagy is a key intracellular mechanism by which cells degrade old or dysfunctional proteins and organelles. In skeletal muscle, evidence suggests that exercise increases autophagosome content and autophagy flux. However, the exercise-induced response seems to differ between rodents and humans, and little is known about how different exercise prescription parameters may affect these results. The present study utilised skeletal muscle samples obtained from four different experimental studies using rats and humans. Here we show that following exercise, in the soleus muscle of Wistar rats, there is an increase in LC3B-I protein levels (+ 109%) immediately after exercise, and a subsequent increase in LC3B-II protein levels (+ 97%) 3 hours into the recovery. Conversely, in human skeletal muscle, there is an immediate exercise-induced decrease in LC3B-II protein levels (- 24%), independent of whether exercise is performed below or above the maximal lactate steady state, which returns to baseline 3.5 hours following recovery, while no change in LC3B-I protein levels is observed. p62 protein levels did not change in neither rats nor humans following exercise. By employing an ex vivo autophagy flux assay previously used in rodents we demonstrate that the exercise-induced decrease in LC3B-II protein levels in humans does not reflect a decreased autophagy flux. Instead, effect size analyses suggest a modest-to-large increase in autophagy flux following exercise that lasts up to 24 hours. Our findings suggest that exercise-induced changes in autophagosome content markers differ between rodents and humans, and that exercise-induced decrease in LC3B-II protein levels do not reflect autophagy flux level.

molecular biology↗

bioRxiv2021

Methodological considerations when assessing mitochondrial respiration and biomarkers for mitochondrial content in human skeletal muscle

BackgroundThe assessment of mitochondrial respiration and mitochondrial content are two common measurements in the fields of skeletal muscle research and exercise science. However, to verify the validity of the observed changes in both mitochondrial respiration and mitochondrial content following an intervention such as exercise training, it is important to determine the reliability and reproducibility of the experimental design and/or techniques employed. We examined the repeatability of widely used methodologies for assessing mitochondrial respiration and mitochondrial content, respectively; the measurement of maximal mitochondrial oxidative phosphorylation in permeabilized muscle fibres using high-resolution respirometry, and the measurement of citrate synthase activity as a biomarker for mitochondrial content in a microplate with spectrophotometer. ResultFor mitochondrial respiration, the coefficient of variation for repeated measurements using muscle sampled from same biopsy decreased from 12.7% to 11% when measured in triplicate with outliers excluded, rather than in duplicate. The coefficient of variation was 9.7% for repeated muscle biopsies sampled across two separated days. For measurements of citrate synthase activity, the coefficient of variation was 3.5% of three technical repeats on the same plate, 10.2% for duplicate analyses using the same muscle lysate when conducted in the same day, and 30.5% when conducted four weeks apart. ConclusionWe have provided evidence for important technical considerations when measuring mitochondrial respiration with human skeletal muscle: 1) the relatively large technical variability can be reduced by increasing technical repeats and excluding outliers; 2) the biological variability and absolute mitochondrial respiration value of the participants should be considered when estimating the required sample size; 3) a new threshold of 15% for the increase in respiration rate after the addition of cytochrome c test for testing mitochondrial outer membrane integrity. When analysing citrate synthase activity, our evidence suggests it is important to consider the following: 1) all samples from the same study should be homogenized and measured at the same time using the same batch of freshly made chemical reagents; 2) biological variability should be considered when detecting small change in mitochondrial content; 3) the relative change should be used to compare the outcomes from different studies.

physiology↗

bioRxiv2020

Changes in insulin resistance do not occur in parallel with changes in mitochondrial content and function in male rats

Aims/hypothesisTo investigate if there is a causal relationship between changes in insulin resistance and mitochondrial respiratory function and content in rats fed a high fat diet (HFD) with or without concurrent exercise training. We hypothesised that provision of a high fat diet (HFD) would increase insulin resistance and decrease mitochondrial characteristics (content and function), and that exercise training would improve both mitochondrial characteristics and insulin resistance in rats fed a HFD. MethodsMale Wistar rats were given either a chow diet or a high fat diet (HFD) for 12 weeks. After 4 weeks of the dietary intervention, half of the rats in each group began eight weeks of interval training. In vivo glucose and insulin tolerance was assessed, as was ex vivo glucose uptake in epitrochlearis muscle. Mitochondrial respiratory function was assessed in permeabilised soleus and white gastrocnemius (WG) muscles. Mitochondrial content was determined by measurement of citrate synthase (CS) activity and protein expression of components of the electron transport system (ETS). ResultsHFD rats had impaired glucose and insulin tolerance. HFD did not change CS activity in the soleus; however, it did increase CS activity in WG (Chow 5.9 {+/-} 0.5, HFD 7.2 {+/-} 0.7 mol h-1 kg protein-1). Protein expression of components of the ETS and mitochondrial respiratory function (WG Chow 65.2 {+/-} 8.4, HFD 88.6 {+/-} 8.7 pmol O2 s-1 mg-1) were also increased by HFD. Exercise training improved glucose and insulin tolerance in the HFD rats. Exercise training did not alter CS activity in either muscle. Mitochondrial respiratory function was increased with exercise training in the chow fed animals in soleus muscle, but not in WG. This exercise effect was absent in the HFD animals. Mitochondrial characteristics did not consistently correlate with insulin or glucose tolerance. Conclusions/interpretationHFD induced insulin resistance, but it did not negatively affect any of the measured mitochondrial characteristics. Exercise training improved insulin resistance, but without changes in mitochondrial respiration and content. The lack of an association between mitochondrial characteristics and insulin resistance was reinforced by the absence of strong correlations between these measures. Our results suggest that defects in mitochondrial respiration and content are not responsible for insulin resistance in HFD rats.

physiology↗

bioRxiv2020

Exercise mitigates sleep-loss-induced changes in glucose tolerance, mitochondrial function, sarcoplasmic protein synthesis, and circadian rhythms.

Sleep loss has emerged as a risk factor for the development of impaired glucose tolerance. The mechanisms underpinning this observation are unknown; however, both mitochondrial dysfunction and circadian misalignment have been proposed. Given that exercise improves glucose tolerance, mitochondrial function, and alters circadian rhythms, we investigated whether exercise may counteract the effects induced by inadequate sleep. We report that sleeping 4 hours per night, for five nights, reduced glucose tolerance, with novel observations of associated reductions in mitochondrial function, sarcoplasmic protein synthesis, and measures of circadian rhythmicity; however, incorporating three sessions of high-intensity interval exercise (HIIE) during this period mitigates these effects. These data demonstrate, for the first time, a sleep loss-induced concomitant reduction in a range of physiological processes linked to metabolic function. These same effects are not observed when exercise is performed during a period of inadequate sleep, supporting the use of HIIE as an intervention to mitigate the detrimental physiological effects of sleep loss.Competing Interest StatementThe authors have declared no competing interest.View Full Text

physiology↗

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↗