Biology subjects

Schjerling, P.

Publications and source records attributed to Schjerling, P..

7 recordsLinked to original sources

bioRxiv2025

Spatially distinct ECM-producing fibroblasts and myonuclei orchestrate early adaptation to mechanical loading in the human muscle-tendon unit

Mechanical loading drives structural and functional improvements in muscle and tendon, protecting against injury at their interface - the myotendinous junction (MTJ) - and within the tendon matrix. However, the early cellular and molecular events that initiate these adaptations in humans remain poorly understood. To investigate this, we applied single nucleus RNA sequencing and in situ hybridization to map the acute transcriptional response of the human muscle-tendon unit to a single bout of eccentric resistance exercise, with a focus on extracellular matrix (ECM) regulation. We identified four transcriptionally distinct fibroblast subtypes expressing key ECM components, including COL1A1 and DCN. Three of these subtypes were localized to tendon and responded to exercise: two were spatially restricted to the collagen fascicles or the MTJ, while the third, enriched in the interfascicular matrix (IFM), exhibited the strongest response. This IFM population, marked by PDGFRA, upregulated PRG4 and VCAN, ECM genes linked to tissue lubrication and resilience. In parallel, exercise induced dynamic ECM regulation in myonuclei, particularly in a distinct subset of type II myonuclei at the MTJ that expanded in number and robustly upregulated COL22A1, a collagen essential for MTJ integrity. Together, these findings uncover a spatially organized, cell type-specific program of ECM remodeling in response to mechanical load, offering new insight into the early molecular events of human muscle-tendon adaptation.

cell biology↗

bioRxiv2024

Muscle Fibroblasts and Stem Cells Stimulate Motor Neurons in An Age and Exercise-Dependent Manner

Exercise preserves neuromuscular function in ageing through unknown mechanisms. Skeletal muscle fibroblasts (FIB) and stem cells (MuSC) are abundant in skeletal muscle and reside close to neuromuscular junctions, but their relative roles in motor neuron maintenance remain undescribed. Using direct co-cultures of embryonic rat motor neurons with either human MuSC or FIB, RNA sequencing revealed profound differential regulation of the motor neuron transcriptome, with FIB generally favoring neuron growth and cell migration and MuSC favoring production of ribosomes and translational machinery. Conditioned medium from FIB was superior to MuSC in preserving motor neurons and increasing their maturity. Lastly, we established the importance of donor age and exercise status and found an age-related distortion of motor neuron and muscle cell interaction that was fully mitigated by lifelong physical activity. In conclusion, we show that human muscle FIB and MuSC synergistically stimulate the growth and viability of motor neurons, which is further amplified by regular exercise.

physiology↗

bioRxiv2024

Fibre type differences in the organisation of mononuclear cells and myonuclei at the tips of human myofibres

The myotendinous junction (MTJ) is a weak link in the musculoskeletal system. Here, we isolated the tips of single myofibres from healthy human hamstring muscles for confocal microscopy (n=6) and RNAscope in situ hybridization (n=6) to gain insight into the profiles of cells and myonuclei in this region. A marked presence of mononuclear cells was observed coating the fibre tips, with a median of 29 (range 16-63) and 16 (9-23) cells per fibre for type I and II myofibres, respectively (p<0.05). The number and density of myonuclei gradually increased from the myofibre proper towards the tip (p<0.05), similarly for both fibre types, and a greater number of COL22A1-expressing nuclei was seen in type II vs type I myofibres (p<0.05). These divergent fibre type-specific characteristics of the MTJ reflect the respective demands for remodelling of the tendon and myofibre sides of the junction according to loading patterns. This insight refines our fundamental understanding of the human MTJ at the cell and structural levels. Summary statementAt the site of attachment to tendon, type I and II human myofibre tips display divergent numbers of mononuclear cells and COL22A1+ nuclei, changing our understanding of myotendinous junction biology.

physiology↗

bioRxiv2023

The mitochondrial mRNA stabilizing protein, SLIRP, regulates skeletal muscle mitochondrial structure and respiration by exercise-recoverable mechanisms

Summary and graphical abstractDecline in mitochondrial function associates with decreased muscle mass and strength in multiple conditions, including sarcopenia and type 2 diabetes. Optimal treatment could include improving mitochondrial function, however, there are limited and equivocal data regarding the molecular cues controlling muscle mitochondrial plasticity. Here we uncover the mitochondrial-mRNA-stabilizing protein SLIRP, in complex with LRPPRC, as a PGC-1 target that regulates mitochondrial structure, respiration, and mitochondrially-encoded-mRNA pools in skeletal muscle. Exercise training effectively counteracted mitochondrial defects induced by loss of LRPPRC/SLIRP, despite sustained low mitochondrially-encoded-mRNA pools, via increased mitoribosome translation capacity. In humans, exercise training robustly increased muscle SLIRP and LRPPRC protein content across exercise modalities and sexes, yet this increase was less prominent in subjects with type 2 diabetes. Our work identifies a mechanism of post-transcriptional mitochondrial regulation in skeletal muscle through mitochondrial mRNA stabilization. It emphasizes exercise as an effective approach to alleviate mitochondrial defects by possibly increasing mitoribosome capacity. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=142 SRC="FIGDIR/small/564600v2_ufig1.gif" ALT="Figure 1"> View larger version (61K): org.highwire.dtl.DTLVardef@1cdc6c5org.highwire.dtl.DTLVardef@b4cb1borg.highwire.dtl.DTLVardef@182871corg.highwire.dtl.DTLVardef@7462ea_HPS_FORMAT_FIGEXP M_FIG C_FIG

molecular biology↗

bioRxiv2023

Pantothenate Kinase 4 controls efficient skeletal muscle energy substrate metabolism via acetyl-CoA

Metabolic inflexibility in skeletal muscle (SkM) is closely linked to metabolic diseases. Exercise improves metabolic flexibility, rendering it a valuable discovery tool of mechanisms promoting efficient metabolism of glucose and lipids. We herein discover pantothenate kinase 4 (PanK4) as a conserved exercise target with high abundance in SkM. We go on to show that murine muscle Pank4 is dysregulated with high-fat diet feeding, and identify human PANK4 variants that associate with glycemic control and body mass index traits, indicating important roles of PanK4 in glucose metabolism and growth. Consistent with the latter, germline deletion of PanK4 reduces circulating IGF-1 and stunts growth in mice. Deletion specifically in mouse SkM reveals that PanK4 facilitates fatty acid oxidation by acting as a regulator of SkM acetyl-CoA, a key node in metabolism of both glucose and lipids. Consequently, without PanK4, elevated SkM acetyl-CoA levels allosterically gridlock key enzymes required for efficient lipid and glucose utilization, and these SkM metabolic perturbations manifest in whole-body insulin resistance. As proof of principle, we show that an increase in muscle PanK4 lowers SkM acetyl-CoA and increases SkM glucose utilization. Our findings identify PanK4 as a novel regulator of SkM energy substrate metabolism, warranting inclusion in comprehensive strategies against metabolic disease.

physiology↗

bioRxiv2022

Distinct myofibre domains of the human myotendinous junction revealed by single nucleus RNA-seq

The myotendinous junction (MTJ) is a specialized domain of the multinucleated myofibre, faced with the challenge of maintaining robust cell-matrix contact with the tendon under high mechanical stress and strain. Here, we profiled 24,161 nuclei in semitendinosus muscle-tendon samples from 3 healthy males by single nucleus RNA-sequencing (snRNA-seq), alongside spatial transcriptomics, to gain insight into the genes characterizing this specialization in humans. We identified a cluster of MTJ myonuclei, represented by 47 enriched transcripts, of which the presence of ABI3BP, ABLIM1, ADAMTSL1, BICD1, CPM, FHOD3, FRAS1 and FREM2 was confirmed at the MTJ at the protein level by immunofluorescence. Four distinct subclusters of MTJ myonuclei were apparent and segregated into two COL22A1-expressing subclusters and two lacking COL22A1 but with a clear fibre type profile expressing MYH7 or MYH1/2. Our findings reveal distinct myonuclei profiles of the human MTJ, a weak link in the musculoskeletal system, which is selectively affected in pathological conditions, from muscle strains to muscular dystrophies.

molecular biology↗

bioRxiv2019

The role of p-21 activated kinases (PAKs) in glucose homeostasis and skeletal muscle glucose uptake

ObjectiveSkeletal muscle glucose uptake is essential for maintaining whole-body glucose homeostasis and accounts for the majority of glucose disposal in response to insulin. The group I p21-activated kinase (PAK) isoforms PAK1 and PAK2 are activated in response to insulin in skeletal muscle. Interestingly, PAK1/2 signalling is impaired in insulin-resistant mouse and human skeletal muscle and PAK1 has been suggested to be required for insulin-stimulated GLUT4 translocation. However, the relative contribution of PAK1 and PAK2 to insulin-stimulated glucose uptake in mature skeletal muscle is unresolved. The aim of the present investigation was to determine the requirement for PAK1 and PAK2 in whole-body glucose homeostasis and insulin-stimulated glucose uptake in skeletal muscle. MethodsGlucose uptake was measured in isolated skeletal muscle incubated with a pharmacological inhibitor (IPA-3) of group I PAKs and in muscle from whole-body PAK1 knockout (KO), muscle-specific PAK2 (m)KO and double whole-body PAK1 and muscle-specific PAK2 knockout mice. ResultsThe whole-body respiratory exchange ratio was largely unaffected by lack of PAK1 and/or PAK2. Whole-body glucose tolerance was mildly impaired in PAK2 mKO, but not PAK1 KO mice. IPA-3 partially reduced (-20%) insulin-stimulated glucose uptake in mouse soleus muscle. In contrast to a previous study of GLUT4 translocation in PAK1 KO mice, PAK1 KO muscles displayed normal insulin-stimulated glucose uptake in vivo and in isolated muscle. On the contrary, glucose uptake was slightly reduced in response to insulin in glycolytic extensor digitorum longus muscle lacking PAK2, alone (-18%) or in combination with PAK1 KO (-12%). ConclusionsInsulin-stimulated glucose uptake partly relies on PAK2, but not PAK1, in mouse skeletal muscle. Thus, the present study challenges that group I PAKs, and especially PAK1, are major regulators of whole-body glucose homeostasis and insulin-stimulated glucose uptake in skeletal muscle.

cell biology↗