Biology subjects

Baumert, P.

Publications and source records attributed to Baumert, P..

5 recordsLinked to original sources

bioRxiv2026

Plasma metabolite responses to an oral protein tolerance test differ between young and sarcopenic participants and suggest altered anabolic sensitivity

BackgroundSarcopenia is associated with anabolic resistance, a blunted muscle protein synthesis response to protein ingestion. Here, we hypothesized that anabolic resistance may be associated with a delayed postprandial decline in circulating plasma amino acids following protein ingestion. We therefore wanted to investigate whether an oral protein tolerance test (OPTT) combined with untargeted plasma metabolomics can detect age-related or sarcopenia-related differences in amino acid time courses consistent with altered postprandial amino acid handling, which could potentially reflect reduced anabolic sensitivity. Moreover, we investigated whether metabolites other than amino acids reacted to the OPTT. MethodsTwelve young healthy adults (controls: 22-28 years) and 12 older adults with clinically diagnosed probable or confirmed sarcopenia (70-91 years) ingested 20 g of whey protein after an overnight fast. We collected venous blood at baseline, 1 h, and 2 h post-ingestion and analyzed the samples by untargeted LC-HRMS plasma metabolomics. Linear mixed-effects models were fitted for 2,968 metabolic features with Benjamini-Hochberg FDR correction. For each category (branched-chain amino acid, essential amino acid [EAA], total amino acid) we summed the within-subject log2 fold changes (FC) of the constituent amino acids. This composite is reported as the summed log2FC Results201 metabolites were structurally annotated including 58 amino acid-related metabolites and 97 lipids. Fourteen of 17 proteinogenic amino acids increased significantly after protein ingestion (FDR<0.05). In young controls, essential amino acids rose more steeply at 1 h than in sarcopenic individuals (+10.06 {+/-} 1.05 vs. +7.84 {+/-} 1.58 summed log2FC) and declined more between 1 and 2 h (-4.93 {+/-} 1.29 vs. -0.20 {+/-} 2.27 summed log2FC). Leucine exemplified this pattern best, rising 1.74 log2FC in controls and declining to 0.96 at 2 h, while remaining elevated at 1.61 log2FC in the sarcopenic group at 2 h (p=0.009). Beyond amino acids, whey protein lowered circulating free fatty acids in both groups (FA 18:2, FA 18:1, FA 16:0; all FDR<0.05). Medium- and long-chain acylcarnitines (Car 8:0, Car14:2) declined postprandially in controls but remained elevated in sarcopenic individuals (p<0.05), suggesting altered postprandial lipid metabolism. ConclusionIn this proof-of-concept study, an OPTT showed that plasma EAAs declined more slowly from their postprandial peak in older adults with sarcopenia than in young adults, consistent with altered postprandial amino acid handling that may reflect anabolic resistance. Whey protein ingestion additionally modulates lipid and acylcarnitine metabolism in an age-dependent manner, suggesting broader alterations in postprandial metabolic regulation in older adults with sarcopenia.

physiology↗

bioRxiv2025

Sample-multiplexed FACS-preprocessing of PBMCs enables scalable scRNA-seq without compromising transcriptomic or cellular integrity

Efficient preprocessing of peripheral blood mononuclear cells (PBMCs) for single-cell RNA-Sequencing (scRNA-seq) is crucial to ensure high sample throughput while maintaining sample integrity. In particular, when enrichment of rare immune cell populations is necessary to enable their representative profiling among more common PBMCs, sample preprocessing may become a detrimental bottleneck. Here, we present an optimized fluorescence-activated cell sorting (FACS)-based preprocessing workflow designed to enrich rare immune cells while conserving overall PBMC composition. The protocol integrates dead cell removal, targeted rare cell enrichment, channel splitting, and hash-based sample multiplexing together with a new powerful yet lightweight demultiplexing tool (YAHD), improving throughput and cell yield, reducing batch effects, and preserving biological context. Validation across cryopreserved human PBMCs obtained from different scientifically relevant sources (clinical routine and laboratory setting) demonstrated improved sample viability and representation of rare subsets in the final scRNA-seq data. Thorough transcriptomic assessment confirmed non-concerning levels of stress induction and T cell activation as well as low technical variability, removing concerns around FACS-processing, cross-donor multiplexing and channel splitting. The presented approach enables scalable and biologically faithful PBMC preprocessing for scRNA-seq, advancing the study of immune heterogeneity in health and disease.

genomics↗

bioRxiv2022

Skeletal muscle hypertrophy rewires glucose metabolism in mice: an experimental investigation and systematic review

BackgroundProliferating cancer cells shift their metabolism toward glycolysis even in the presence of oxygen to especially generate glycolytic intermediates as substrates for anabolic reactions. We hypothesize that a similar metabolic remodeling occurs during skeletal muscle hypertrophy. MethodsWe used mass spectrometry in hypertrophying C2C12 myotubes in vitro and plantaris mice muscle in vivo and assessed metabolomic changes and the incorporation of [U-13C6]glucose tracer. We performed enzyme inhibition of the key serine synthesis pathway enzyme phosphoglycerate dehydrogenase (Phgdh) for further mechanistic analysis and conducted a systematic review to align any changes in metabolomics during muscle growth with published findings. Finally, UK Biobank was used to link the findings to population level. ResultsThe metabolomics analysis in myotubes revealed IGF-1 induced altered metabolite concentrations in anabolic pathways such as in the pentose phosphate (ribose-5-phosphate/ribulose-5-phosphate: +40%; p=0.01) and serine synthesis pathway (serine: - 36.8%; p=0.009). Like the hypertrophy-stimulation with IGF-1 in myotubes in vitro, the concentration of the dipeptide L-carnosine was decreased by 26.6% (p=0.001) during skeletal muscle growth in vivo. However, phosphorylated sugar (glucose-6-phosphate, fructose-6-phosphate or glucose-1-phosphate) decreased by 32.2% (p=0.004) in the overloaded muscle in vivo, while increased in the IGF-1 stimulated myotubes in vitro. The systematic review revealed that 10 metabolites linked to muscle hypertrophy were directly associated with glycolysis and its interconnected anabolic pathways. We demonstrated that labelled carbon from [U-13C6]glucose is increasingly incorporated by [~]13% (p=0.001) into the non-essential amino acids in hypertrophying myotubes, which is accompanied by an increased depletion of media serine (p=0.006). The inhibition of Phgdh suppressed muscle protein synthesis in growing myotubes by 58.1% (p<0.001) highlighting the importance of the serine synthesis pathway for maintaining muscle size. Utilizing data from the UK Biobank (n=450,243), we then discerned genetic variations linked to the serine synthesis pathway (PHGDH and PSPH) and to its downstream enzyme (SHMT1), revealing their association with appendicular lean mass in humans (p<5.0e-8). ConclusionUnderstanding the mechanisms that regulates skeletal muscle mass will help in developing effective treatments against muscle weakness. Our results provide evidence for metabolic rewiring of glycolytic intermediates into anabolic pathways during muscle growth, such as in the serine synthesis.

molecular biology↗

bioRxiv2019

DNA methylation across the genome in aged human skeletal muscle tissue and muscle stem cells: The role of HOX genes and physical activity

Skeletal muscle tissue demonstrates global hypermethylation with aging. However, methylome changes across the time-course of differentiation in aged human muscle derived stem cells, and larger coverage arrays in aged muscle tissue have not been undertaken. Using 850K DNA methylation arrays we compared the methylomes of young (27 {+/-} 4.4 years) and aged (83 {+/-} 4 years) human skeletal muscle and that of young/aged muscle stem cells over several time points of differentiation (0, 72 hours, 7, 10 days). Aged muscle tissue was hypermethylated compared with young tissue, enriched for; pathways-in-cancer (including; focal adhesion, MAPK signaling, PI3K-Akt-mTOR signaling, p53 signaling, Jak-STAT signaling, TGF-beta and notch signaling), rap1-signaling, axon-guidance and hippo-signalling. Aged muscle stem cells also demonstrated a hypermethylated profile in pathways; axon-guidance, adherens-junction and calcium-signaling, particularly at later timepoints of myotube formation, corresponding with reduced morphological differentiation and reductions in MyoD/Myogenin gene expression compared with young cells. While young cells showed little alteration in DNA methylation during differentiation, aged cells demonstrated extensive and significantly altered DNA methylation, particularly at 7 days of differentiation and most notably in the focal adhesion and PI3K-AKT signalling pathways. While the methylomes were vastly different between muscle tissue and isolated muscle stem cells, we identified a small number of CpG sites showing a hypermethylated state with age, in both muscle and tissue and stem cells (on genes KIF15, DYRK2, FHL2, MRPS33, ABCA17P). Most notably, differential methylation analysis of chromosomal regions identified three locations containing enrichment of 6-8 CpGs in the HOX family of genes altered with age. With HOXD10, HOXD9, HOXD8, HOXA3, HOXC9, HOXB1, HOXB3, HOXC-AS2 and HOXC10 all hypermethylated in aged tissue. In aged cells the same HOX genes (and additionally HOXC-AS3) displayed the most variable methylation at 7 days of differentiation versus young cells, with HOXD8, HOXC9, HOXB1 and HOXC-AS3 hypermethylated and HOXC10 and HOXC-AS2 hypomethylated. We also determined that there was an inverse relationship between DNA methylation and gene expression for HOXB1, HOXA3 and HOXC-AS3. Finally, increased physical activity in young adults was associated with oppositely regulating HOXB1 and HOXA3 methylation compared with age. Overall, we demonstrate that a considerable number of HOX genes are differentially epigenetically regulated in aged human skeletal muscle and muscle stem cells and increased physical activity may help prevent age-related epigenetic changes in these HOX genes.

physiology↗

bioRxiv2019

Neuromuscular fatigue and recovery after strenuous exercise depends on skeletal muscle size and stem cell characteristics

Hamstring muscle injury is highly prevalent in sports involving repeated maximal sprinting. Although neuromuscular fatigue is thought to be a risk factor, the mechanisms underlying the fatigue response to repeated maximal sprints are unclear. Here, we show that repeated maximal sprints induce neuromuscular fatigue accompanied with a prolonged strength loss in hamstring muscles. The immediate hamstring strength loss was linked to both central and peripheral fatigue, while prolonged strength loss was associated with indicators of muscle damage. The kinematic changes immediately after sprinting likely protected fatigued hamstrings from excess elongation stress, while larger hamstring muscle physiological cross-sectional area and lower myoblast:fibroblast ratio appeared to protect against fatigue/damage and improve muscle recovery within the first 48 h after sprinting. We have therefore identified novel mechanisms that likely regulate the fatigue/damage response and initial recovery following repeated maximal sprinting in humans.

physiology↗