Biology subjects

Seto, J. T.

Publications and source records attributed to Seto, J. T..

4 recordsLinked to original sources

bioRxiv2024

alpha-Actinin-3 deficiency protects from the effects of acute cold exposure through altered skeletal muscle Ca2+ and OXPHOS signaling.

Summary / AbstractA nonsense polymorphism in the ACTN3 gene (R577X, rs1815739) results in the loss of the fast skeletal muscle fiber protein -actinin-3 in an estimated 1.5 billion humans worldwide. Homozygosity for this common polymorphism (ACTN3 577XX) does not cause disease but is detrimental to sprint performance in elite athletes. Recently, we reported that ACTN3 577XX humans and Actn3 knockout mice show improved cold tolerance. This was not due to an increase in brown adipose tissue activity or a greater muscle shivering response, but was associated with an increased abundance of slow myosin heavy chain muscle fibers in XX individuals, which in turn increased muscle tone to improve cold tolerance. Using the Actn3 knockout mouse we have now analyzed the molecular and physiological impacts of acute cold exposure (4{degrees}C, for 5 hours) on skeletal muscle. In addition, we used statistical inference of publicly available archaic (Neanderthal and Denisovan) and modern human DNA data to estimate the age of the ACTN3 X-allele and to identify a novel haplotype associated with this variant that provides support for genetic selection in some populations of modern humans. Our results indicate that skeletal muscle of Actn3 knockout mice exhibit higher mitochondrial oxidative phosphorylation abundance and activity than wild-type controls. Following acute cold exposure, we identified reductions in gene ontology pathways associated with metabolism and protein breakdown, which impact muscle mass loss and improved muscle fatigue resistance. Together this provides further evidence for improved cold tolerance in Actn3 knockout mice and ACTN3 577XX individuals. Furthermore, we confirm that the X-allele first appeared in modern humans [~]135,000 years ago, with this variant increasing in frequency in European and Asian populations from as early as 42,000 years ago, which aligns with modern human migration out of Africa. Taken together these data provide additional molecular and functional evidence for a protective advantage of -actinin-3 deficiency following cold exposure, highlighting the importance of skeletal muscle in mammalian thermogenesis and its potential role in the evolution of modern-day humans.

cell biology↗

bioRxiv2024

ACTN3 genotype influences androgen response in skeletal muscle

AbstractAndrogens are vital for the maintenance of muscle mass and their anabolic effects are primarily exerted through the androgen receptor (AR). Accumulating evidence in humans and mice suggests that circulating androgens, AR and androgen response are influenced by ACTN3 (- actinin-3), also known as "the gene for speed". One in 5 people worldwide are -actinin-3 deficient due to homozygous inheritance of a common null polymorphism (577X) in ACTN3. In this study, we show that -actinin-3 deficiency decreases baseline AR in skeletal muscles of mice and humans, in both males and females, and that AR expression directly correlates with ACTN3 in a dosage dependent manner. We further demonstrate in Actn3 knockout mice that - actinin-3 deficiency increases muscle wasting induced by androgen deprivation and reduces the muscle hypertrophic response to dihydrotestosterone and this is mediated by differential activation of pathways regulating amino acid metabolism, intracellular transport, MAPK signalling, autophagy, mitochondrial activity and calcineurin signalling. Gene set enrichment and protein analyses indicate that the absence of -actinin-3 results in a failure to coactivate many of these pathways in response to changes in androgens, and relies on leveraging mitochondrial remodelling and calcineurin signalling to restore muscle homeostasis. We further identified 7 genes that are androgen sensitive and -actinin-3-dependent in expression, and whose functions correspond to these processes. Our results highlight the pivotal role of - actinin-3 in various processes associated with the regulation of protein turnover and muscle mass, and suggest that ACTN3 genotype is a genetic modifier of androgen action in skeletal muscle.

genetics↗

bioRxiv2024

Modern Insights into Muscle Glycogen Phosphorylase Activity

Recent identification of new human muscle glycogen phosphorylation sites has renewed interest in understanding human variations in the regulation of glycogen metabolism and glucose homeostasis. This paper presents a detailed method for the measurement of glycogen phosphorylase (GPh) activity in skeletal muscle. Our approach incorporates modifications to existing radiolabelling assays, optimizing specificity and sensitivity while enabling the assessment of both active and total enzyme activity levels. The utilization of radioisotope tracers and scintillation counting ensures accurate quantification of GPh activity, which we use to validate a previously published reduction in GPh activity in an Actn3 deficient mouse model. Moreover, we introduce a step-by-step guide for data acquisition, highlight the use of appropriate homogenization, discuss the need for allosteric activators/inhibitors and the importance of assay optimization to record a GPh activity assay for skeletal muscle. In conclusion, our refined method not only contributes to a deeper understanding of glycogen metabolism in muscle tissue but also provides a framework for future investigations, underscoring its role in advancing research on glycogen utilization and glucose homeostasis. NEW & NOTEWORTHYThe study optimizes the glycogen phosphorylase radiolabelled activity assay, unveiling nuances in muscle homogenization, sample dilution, and caffeine inclusion. The research introduces standardized conditions, enhancing assay reliability and reproducibility across mouse strains to reveal sex specific variations in GPh activity and underscore novel distinctions in an Actn3 deficient mouse model. These findings advance our understanding of muscle glycogen metabolism, offering a crucial tool for researchers and facilitating meaningful inter-laboratory comparisons.

biochemistry↗

bioRxiv2020

ACTN3 genotype influences skeletal muscle mass regulation and response to dexamethasone

Homozygosity for the common ACTN3 null polymorphism (ACTN3 577X) results in -actinin-3 deficiency in ~20% of humans worldwide and is linked to reduced sprint and power performance in both elite athletes and the general population. -Actinin-3 deficiency is also associated with reduced muscle mass and strength, increased risk of sarcopenia in the elderly, and altered response to muscle wasting induced by denervation and immobilisation. ACTN3 genotype is also a disease modifier for Duchenne muscular dystrophy (DMD), with -actinin-3 deficiency associated with slower disease progression. Here we show that -actinin-3 plays a key role in the regulation of protein synthesis and breakdown signalling in skeletal muscle, and its influence on muscle mass begins during early postnatal muscle development. Actn3 genotype also influences the skeletal muscle response to the glucocorticoid dexamethasone. Following acute dexamethasone exposure, transcriptomic analyses by RT-qPCR and RNA-sequencing show reduced atrophy signalling (Mstn, Tmem100, mRas, Fbxo32, Trim63) and anti-inflammatory response in -actinin-3 deficient mice compared to wild-type. -Actinin-3 deficiency also protects against muscle wasting following prolonged daily treatment with dexamethasone in female, but not male mice. In combination, these data suggest that ACTN3 R577X is a pharmacogenetic variant influencing the anti-inflammatory and muscle wasting response to glucocorticoid therapy.

genetics↗