Biology subjects

Gabriel, B. M.

Publications and source records attributed to Gabriel, B. M..

7 recordsLinked to original sources

bioRxiv2026

No Effect of Exercise Timing on Daily Glycaemia Despite Shifts in Acute Glucose Dynamics in Participants with Normal Glucose Tolerance: A Randomised Crossover Trial

Exercise is a well-established modulator of glucose regulation, but whether the time of day it is performed matters for healthy, free-living adults remains unresolved. In a randomised crossover trial, 29 healthy adults completed a single 30-minute bout of moderate-intensity exercise in the morning (07:00-10:00) and in the evening (16:00-19:00), with continuous glucose monitoring and wrist-worn activity tracking used to capture responses over an 8-day free-living protocol. Evening exercise produced a significantly greater acute reduction in blood glucose (P < 0.001) compared to morning exercise, but this did not translate into consistent differences in overall daily mean glycaemic exposure, whether measured over the calendar day or over a window aligned with exercise onset. Evening exercise was linked to greater within-day glycaemic variability than morning exercise, with the clearest evidence coming from the circadian-aligned analysis (day x timing interaction, SD: P = 0.00939; CV: P = 0.00766). Appetite rose after exercise in both conditions, with no difference by time of day. Taken together, these results show that exercise timing does not change how much glucose exposure a healthy adult accumulates over a day, but it does change the shape of the glucose response around the exercise bout itself, a distinction only visible when glucose is examined at a finer temporal resolution than daily averages allow.

physiology↗

bioRxiv2025

Live cell GLUT4 translocation assay reveals Per3 as a novel regulator of circadian insulin sensitivity in skeletal muscle cells.

Type 2 Diabetes (T2D) is a growing global health concern, with skeletal muscle playing a central role in its pathology due to its role in postprandial glucose disposal. Insulin resistance in skeletal muscle often precedes T2D diagnosis and is linked to impaired GLUT4 trafficking. Additionally, circadian disruptions are increasingly recognized as contributors to metabolic dysfunction. We have shown that skeletal muscle cells from T2D donors exhibit disrupted CLOCK/BMAL1 rhythms, impairing mitochondrial oxidative function. To investigate circadian insulin sensitivity, we developed a high-throughput, live-cell assay for GLUT4 translocation, allowing us to explore novel regulators of metabolic rhythmicity in skeletal muscle. In this study, we analysed circadian insulin sensitivity in skeletal muscle using transcriptomics, PheWAS, and GLUT4-HiBiT assays. L6 and human myocytes were cultured, transfected, and assessed via our novel live-cell, circadian GLUT4 translocation assay. Circadian rhythms were analysed (JTK_CYCLE), and siRNA knockdowns targeted key genes, with glucose uptake measured using the Uptake-Glo assay in human myocytes. Skeletal muscle cells from individuals with T2D exhibited disrupted circadian rhythms, with altered rhythmicity in ARNTL, HOXB5, PER3, and TSSK6 (p<0.05). Public database analysis revealed significant associations between these genes and T2D (p=0.0001-0.03). Our high-sensitivity, live-cell assay demonstrated a 120% increase in GLUT4 translocation at 40 nM insulin (p<0.001). Circadian rhythmicity in GLUT4 translocation was evident at physiological insulin levels (5 & 30 nM). PER3/Per3 knockdown significantly reduced GLUT4 translocation (p<0.001) and glucose uptake in human muscle cells (p<0.01), while Arntl knockdown caused a moderate reduction (p<0.01) in GLUT4 translocation. Per3 silencing also abolished circadian rhythmicity in GLUT4 translocation (p<0.01). These findings establish PER3/Per3 as a key regulator of circadian GLUT4 translocation and insulin sensitivity, linking its dysregulation to metabolic impairments in T2D. Additionally, this study presents a novel live-cell GLUT4 translocation assay that is highly sensitive and capable of performing time-course or circadian experiments in the same group of cells. The sensitivity of this assay, coupled with reduced variation that is possible from using live-cells in time-course assays make it a powerful new tool for the discovery of GLUT4 translocation regulators. In this study, we have identified Per3 as a novel regulator of GLUT4 translocation in skeletal muscle cells.

cell biology↗

bioRxiv2024

Downregulation of NR4A3 During Inactivity Alters Glucose Metabolism and Impairs Translation in Human Skeletal Muscle

The transcription factor NR4A3 is regulated by exercise and a potent modulator of skeletal muscle metabolism. We report here that physical inactivity decreased skeletal muscle NR4A3 levels, concomitant with mitochondrial function and proteostasis pathways. Silencing of NR4A3 in myotubes decreased glucose oxidation and increased lactate production. This coincided with greater signalling downstream of AMPK and elevated rates of fatty acid oxidation. While NR4A3 silencing reduced protein synthesis, mTORC1 signalling, and ribosomal transcription, overexpression of the canonical NR4A3 protein isoform augmented translation and cellular protein content. Moreover, restoration of NR4A3 levels rescued glucose oxidation in NR4A3-silenced myotubes and restored phosphorylation of mTORC1 substrates. NR4A3 depletion reduced myotube area and altered the abundance of contractile elements. Thus, downregulation of NR4A3 has adverse effects on skeletal muscle metabolism, myotube size, and contractile apparatus by directing mTORC1 signalling and ribosomal biogenesis. Our data demonstrate that NR4A3 controls skeletal muscle atrophy associated with physical inactivity.

physiology↗

bioRxiv2021

Disrupted circadian core-clock oscillations in Type 2 Diabetes are linked to altered rhythmic mitochondrial metabolism

Circadian rhythms are generated by an auto-regulatory feedback loop composed of transcriptional activators and repressors. Disruption of circadian rhythms contributes to Type 2 diabetes (T2D) pathogenesis. We elucidated whether altered circadian rhythmicity of clock genes is associated with metabolic dysfunction in T2D. Transcriptional cycling of core clock genes ARNTL, CLOCK, CRY1 and NR1D1 was altered in skeletal muscle from individuals with T2D and this was coupled with reduced number and amplitude of cycling genes and disturbed circadian oxygen consumption. Mitochondrial associated genes were enriched for differential circadian amplitudes in T2D, and positively correlated with insulin sensitivity. ChIP- sequencing identified CLOCK and BMAL1 binding to circadian mitochondrial genes associated with insulin sensitivity, implicating regulation by the core clock. Mitochondria disruption altered core-clock gene expression and free-radical production, phenomena that were restored by resveratrol treatment. We identify bi-directional communication between mitochondrial function and rhythmic gene expression, processes which are disturbed in diabetes.

physiology↗

bioRxiv2021

Circadian Transcriptomic and Epigenomic Remodeling in Response to Lipid Overload and Human Obesity

Obesity and elevated circulating lipids may impair metabolism by disrupting the molecular circadian clock. We tested the hypothesis that lipid-overload may interact with the circadian clock and alter the rhythmicity of gene expression through epigenomic mechanisms in skeletal muscle. Palmitate reprogrammed the circadian transcriptome in myotubes without altering the rhythmic mRNA expression of core clock genes. Genes with enhanced cycling in response to palmitate were associated with post-translational modification of histones. Cycling of histone 3 lysine 27 acetylation (H3K27ac), a marker of active gene enhancers, was modified by palmitate treatment. Chromatin immunoprecipitation and sequencing confirmed that palmitate exposure altered the cycling of DNA regions associated with H3K27ac. Overlap of mRNA and DNA regions associated with H3K27ac and pharmacological inhibition of histone acetyl transferases revealed novel cycling genes associated with lipid exposure of primary human myotubes. Palmitate exposure disrupts transcriptomic rhythmicity and modifies enhancers through changes in histone H3K27 acetylation in a circadian manner. Thus, histone acetylation is responsive to lipid-overload and redirects the circadian chromatin landscape leading to reprogramming of circadian genes in skeletal muscle.

physiology↗

bioRxiv2020

Myotube hypertrophy is associated with cancer-like metabolic reprogramming and limited by PHGDH

Muscle fiber size and oxidative metabolism are inversely related, suggesting that a glycolytic metabolism may offer a growth advantage in muscle fibers. However, the mechanisms underlying this advantage remains unknown. Nearly 100 years ago, Warburg reported that cancer cells take up more glucose to produce glycolytic intermediates for anabolic reactions such as amino acid-protein synthesis. The aim of this study was to test whether glycolysis contributes to anabolic signalling responses and hypertrophy in post-mitotic muscle cells. Skeletal muscle hypertrophy was induced in vitro by treating mouse C2C12 myotubes with IGF-1. 14C glucose was added to differentiation medium and radioactivity in isolated protein was measured. We exposed differentiated C2C12 and primary mouse myotubes, to 2-deoxyglucose (2DG) and PHGDH siRNA upon which we assessed myotube diameter and signaling pathways involved in the regulation of muscle fiber size. Here, we present evidence that, hypertrophying C2C12 myotubes undergo a cancer-like metabolic reprogramming. First, IGF-1-induced C2C12 myotube hypertrophy increases shunting of carbon from glucose into protein. Second, reduction of glycolysis through 2-deoxy-D-glucose (2DG) lowers C2C12 and primary myotube size 16-40%. Third, reducing the cancer metabolism-associated enzyme PHGDH decreases C2C12 and primary myotube size 25-52%, whereas PHGDH overexpression increases C2C12 myotube size {approx}20%. Fourth, the muscle hypertrophy-promoting kinase AKT regulates PHGDH expression. Together these results suggest that glycolysis is important for hypertrophying C2C12 myotubes by reprograming their metabolism similar to cancer cells.

molecular biology↗

bioRxiv2019

Transcriptomic Profiling of Skeletal Muscle Adaptations to Exercise and Inactivity

The molecular mechanisms underlying the response to exercise and inactivity are not fully understood. We propose an innovative approach to profile the skeletal muscle transcriptome to exercise and inactivity using 66 published datasets. Data collected from human studies of aerobic and resistance exercise, including acute and chronic exercise training, were integrated using meta-analysis methods (www.metamex.eu). Gene ontology and pathway analyses reveal selective pathways activated by inactivity, aerobic versus resistance and acute versus chronic exercise training. We identified NR4A3 as one of the most exercise- and inactivity-responsive genes, and established a role for this nuclear receptor in mediating the metabolic responses to exercise-like stimuli in vitro. The meta-analysis (MetaMEx) also highlights the differential response to exercise in individuals with metabolic impairments. MetaMEx provides the most extensive dataset of skeletal muscle transcriptional responses to different modes of exercise and an online interface to readily interrogate the database.

physiology↗