Biology subjects

Garnham, A.

Publications and source records attributed to Garnham, A..

24 records · Page 2Linked to original sources

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↗

bioRxiv2020

Interpretation of exercise-induced changes in human skeletal muscle mRNA expression depends on the timing of the post-exercise biopsies

AimExercise elicits a range of adaptive responses in skeletal muscle that include changes in mRNA expression. To better understand the health benefits of exercise training, it is essential to investigate the underlying molecular mechanisms of skeletal muscle adaptations to exercise. However, most studies have assessed the molecular events at a few convenient time points within a short time frame post exercise, and the variations of gene expression kinetics have not been addressed systematically. MethodMuscle biopsies were collected from nine participants at baseline and six time points (0, 3, 9, 24, 48, and 72 h) following a session of high-intensity interval exercise. We assessed the mRNA content of 23 gene isoforms from the muscle samples. ResultThe temporal patterns of target gene expression were highly variable and the mRNA contents detected were largely dependent on the muscle sample timing. The maximal levels of mRNA content of all tested target genes were observed between 3 to 48 h post exercise. ConclusionOur findings highlight a critical gap in knowledge regarding the molecular response to exercise, where the use of a few time points within a short period after exercise has led to an incomplete understanding of the molecular responses to exercise. The timing of muscle sampling for individual studies needs to be carefully chosen based on existing literature and preliminary analysis of the molecular targets of interest. We propose that a comprehensive time-course analysis on the exercise-induced transcriptional response in humans will significantly benefit the field of exercise molecular biology.

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↗

bioRxiv2020

The effect of acute sleep deprivation on skeletal muscle protein synthesis and the hormonal environment

Chronic sleep loss is a potent catabolic stressor, increasing the risk of metabolic dysfunction and loss of muscle mass and function. To provide mechanistic insight into these clinical outcomes, we sought to determine if acute sleep deprivation blunts skeletal muscle protein synthesis and promotes a catabolic environment. Healthy young adults (N=13; 7 male, 6 female) were subjected to one night of total sleep deprivation (DEP) and normal sleep (CON) in a randomized cross-over design. Anabolic and catabolic hormonal profiles, skeletal muscle fractional synthesis rate and markers of muscle protein degradation were assessed across the following day. Acute sleep deprivation reduced muscle protein synthesis by 18% (CON: 0.072 {+/-} 0.015 vs. DEP: 0.059 {+/-} 0.014 %*h-1, p=0.040). In addition, it increased plasma cortisol by 21% (p=0.030) and decreased plasma testosterone, but not IGF-1, by 22% (p=0.029). A single night of total sleep deprivation is sufficient to induce anabolic resistance and a pro-catabolic environment. These acute changes may represent mechanistic precursors driving the metabolic dysfunction and body composition changes associated with chronic sleep deprivation.

physiology↗

bioRxiv2019

Vasoactive intestinal peptide confers anticipatory mucosal immunity by regulating ILC3 activity

ILC3-mediated IL-22 cytokine production is critical for the maintenance of immune homeostasis in the gastrointestinal tract. Here, we show that group 3 ILC (ILC3) constitutive function is not constant across the day but instead oscilliates between active and resting phases. Coordinate responsiveness of ILC3 in the intestine depended on food-induced expression of the neuronal hormone vasoactive intestinal peptide (VIP). Intestinal ILC3 expressed high levels of the G protein-coupled receptor, VIPR2, and activation via enteric neuronal VIP markedly enhanced IL-22 production and conferred gut protection. Conversely, deficiency of VIPR2 signalling led to impaired production of IL-22 by ILC3 and increased susceptibility to inflammatory gut disease. As such, intrinsic cellular rhythms synergise with the cyclic patterns of food intake to drive IL-22 thereby syncronizing intestinal epithelial protection via the ILC3 VIP-VIPR2 pathway.

immunology↗

bioRxiv2019

Toxoplasma gondii bradyzoites induce transcriptional changes to host cells and prevent IFNγ-mediated cell death

Toxoplasma gondii, the causative agent of toxoplasmosis, lies dormant for life and is a reservoir for disease reactivation, causing blindness, encephalitis and congenital birth defects. Acute-stage tachyzoites extensively manipulate their host cell by exporting a repertoire of proteins across the parasitophorous vacuolar membrane (PVM). This interferes with the hosts transcriptional program, allowing for persistence during immune attack. It is unknown how bradyzoites persist and what role host manipulation plays in latency. Here we show that bradyzoite-containing host cells have a unique transcriptional landscape when compared to tachyzoite infection. We demonstrate that many of these changes are dependent parasite protein export. Furthermore, we show that bradyzoite effector proteins protect host cells from IFN{gamma}-mediated cell death, thus highlighting the functional importance of host manipulation. Together, our work provides the first understanding of how Toxoplasma sets up latency to persist in its host.

microbiology↗