Biology subjects

Engman, V.

Publications and source records attributed to Engman, V..

4 recordsLinked to original sources

bioRxiv2026

Molecular responsiveness to testosterone is uncoupled from skeletal muscle mass and strength in males aged 18 - 80 years

Objective Testosterone exerts wide-ranging physiological effects, including the regulation of anabolic processes in skeletal muscle. However, its role in skeletal muscle ageing remains unclear. This study aimed to establish the association between endogenous testosterone levels and skeletal muscle phenotype across the adult lifespan and determine whether ageing modulates this relationship. Methods Eighty-one healthy males aged 18-80 underwent comprehensive phenotypic assessment. Body composition and muscle morphology were assessed using dual-energy X-ray absorptiometry (DEXA) and peripheral quantitative computed tomography (pQCT). Muscle strength was estimated leg press one-repetition maximum (e1RM). Vastus lateralis biopsies were used to assess fibre type, sequence the transcriptome and establish primary myocytes. Cell lines from young (n=5) and older (n=7) donors were cultured and compared under control and testosterone-treated conditions for cellular phenotype. Results Ageing was associated with lower free testosterone, muscle mass and strength, altered type IIa fibre characteristics, and widespread transcriptional changes in skeletal muscle. Free, but not total, testosterone was strongly associated with the muscle transcriptome, although neither fraction was associated with muscle mass or strength. In primary myocytes, testosterone increased androgen receptor abundance and nuclear localisation and enriched pathways involved in protein translation. Conclusion Testosterone is biologically active in male skeletal muscle, with its free fraction strongly associated with the transcriptome; however, these molecular effects do not translate into differences in muscle mass or strength. Testosterone may therefore play a primary role in establishing the male muscle phenotype during puberty, before transitioning to a more ancillary role in adult skeletal muscle.

physiology↗

bioRxiv2026

Development and Validation of an LC-MS Method for Quantification of Sex Steroid Hormones in Skeletal Muscle

1Sex steroid hormones are not exclusively localised in the circulation and can be found in numerous extragonadal tissues, in concentrations unrelated to the circulating fraction. Existing methodology to measure intramuscular steroid hormone concentrations includes both immune-based assays and liquid chromatography-mass spectrometry (LC-MS), the gold standard for hormone measurements. To date, no LC-MS based methods validation has been published on the measurement of intramuscular sex steroid hormones, despite clear biological relevance. Here, we describe the development and validation of a simple, high-throughput LC-MS Orbitrap method for the measurement of 10 intramuscular sex steroid hormones, including pregnenolone, progesterone, dehydroepiandrosterone, androstenedione, testosterone, epitestosterone, dihydrotestosterone, oestrone, oestradiol, and oestriol. In brief, isotope labelled standards were added to 5-6 milligrams of lyophilised muscle tissue, homogenised and extracted with ethyl acetate. The extracts were dried down and sequentially derivatised with 1-methylimidazole-2-sulfonyl chloride and hydroxylamine hydrochloride to target both the phenolic hydroxyl groups and ketone groups. The limit of detection was 1.0 {+/-} 1.0 pg/mg (range 0.36 - 3.26 pg/mg), with a R2 > 0.99 for all analytes. Matrix effects were 90-110% for all analytes except for dihydrotestosterone (143.6%), and precision was <10 CV% for all analytes in the presence of a muscle matrix. Our method allows for 20-40 samples to be prepared in [~]4 h, with a sample data acquisition time of 13 minutes. Moreover, our method provides the opportunity for specific analysis of steroid hormone concentrations in skeletal muscle, allowing target tissue specificity instead of relying on proxy measures from the circulation.

biochemistry↗

bioRxiv2026

MetAR: A semi-automated meta-analysis of skeletal muscle androgen receptors association with age

BackgroundThe maintenance of skeletal muscle health plays a pivotal role in prolonging both the lifespan and healthspan. However, muscle mass and strength exhibit significant declines with age. Ageing is associated with a reduced muscle protein synthesis response to key anabolic stimuli, including the androgen hormone testosterone, termed anabolic resistance. Testosterone enacts its anabolic effects in muscle through androgen receptor (AR) mediated pathways. Emerging evidence suggests that AR availability may represent a rate-limiting factor in androgen signalling, with AR saturation occurring below physiological testosterone levels in some tissues. Prior research in rodents has reported age-related reductions in AR expression, suggesting changes in AR protein content may constitute a key component of anabolic resistance. However, reports of the effects of age on the human skeletal muscle AR are inconclusive and limited by small sample sizes. Therefore, this study aimed to characterise age-related changes in expression of the AR, its regulators and downstream target genes in human skeletal muscle. MethodsWe developed and used a novel R-based pipeline, MetAR, to perform reproducible meta-analyses of publicly available bulk RNA-Seq datasets from NCBI GEO and investigate associations between target gene expression and variables of interest without the need for high-performance computing. Eligible datasets included skeletal muscle samples from healthy adult males aged [≥]18 years, with an age range of [≥] 10 years and sample size [≥] 6. Raw counts data were downloaded, appraised and TMM normalised. Dataset-level associations between age and target gene expression were assessed using linear and generalised additive models (GAMs). Random-effects meta-analyses were performed, and heterogeneity, publication bias and leave-one-out sensitivity assessed. ResultsSixteen skeletal muscle bulk RNA-seq datasets (n = 364; age 18-92 years) were eligible for inclusion in the meta-analyses. AR expression was negatively associated with age ({beta} = -0.006 log2 TMM-CPM per year, p < 0.001) corresponding to a 4.4% decrease in expression per decade. Age was also associated with a significant reduction in expression of various regulators of AR stability, transcriptional activity and nuclear transport. Additionally, steroidogenic enzymes and key downstream targets of the AR, including genes encoding for key structural proteins and mitochondrial function were negatively associated with age. ConclusionsCollectively, these findings suggest a multi-faceted age-associated remodelling of AR expression, signalling and nuclear transport that may contribute to the development of anabolic resistance and consequent age-associated muscle loss.

physiology↗

bioRxiv2023

A 2-Hydroxybutyrate-mediated feedback loop regulates muscular fatigue

The metabolite 2-hydroxybutyrate (2HB) is produced by skeletal muscle acutely during exercise and persists for several hours in the blood post-exertion. We show here that 2HB directly inhibits branched- chain aminotransferase enzymes, and that this inhibition in turn triggers a SIRT4-dependent shift in the compartmental abundance of protein ADP-ribosylation. The 2HB-induced decrease in nuclear protein ADP-ribosylation leads to a C/EBP{beta} mediated transcriptional response in the branched-chain amino acid degradation pathway. This response to 2HB exposure leads to an improved oxidative capacity both in vitro and in vivo, with the latter mimicking the effects of exercise training on whole body metabolism. Thus, we show here that 2-HB production by skeletal muscle represents a novel mechanism for the modification of metabolism by exercise.

physiology↗