Biology subjects

Hepple, R. T.

Publications and source records attributed to Hepple, R. T..

4 recordsLinked to original sources

bioRxiv2026

Mitochondrial Permeability Transition in Skeletal Muscle Phenocopies Muscle Alterations seen in Cancer Cachexia and other Wasting Conditions

Skeletal muscle in wasting conditions often exhibits atrophy, mitochondrial respiratory dysfunction, and fragmentation of the acetylcholine receptor (AChR) cluster at the endplate. The accompanying alterations of mitochondrial morphology suggest mitochondria may be involved in muscle pathology in these conditions. To address this gap, we tested an established pathological mechanism in ischemia-reperfusion injury and neurodegeneration but poorly studied in skeletal muscle: mitochondrial permeability transition (mPT). We tested if mPT recapitulated phenotypes common in wasting conditions, whether tumor-conditioned media (TCM) could promote mPT, and compared differentially expressed genes (DEGs) induced by mPT with DEGs observed in a mouse model of pancreatic cancer cachexia. Inducing mPT in mouse skeletal muscle bundles progressively altered mitochondrial cristae morphology, culminating in breach of the outer mitochondrial membrane. Inducing mPT in mouse muscle fibers increased mROS and Caspase 3 activity and caused atrophy. Inducing mPT caused a complex I mitochondrial respiratory impairment, increased lysosome-mitochondrion co-localization, and fragmented the AChR cluster at the muscle endplate. The Ca2+ threshold for mPT, mitochondrial calcein colocalization and mitochondrial membrane potential were reduced by TCM in skeletal muscle or C2C12 myoblasts, respectively. Knockout of the mPT-regulating protein CypD attenuated the reduction in Ca2+ threshold for mPT by TCM. Inhibitors of mPT attenuated atrophy with TCM in C2C12 and human primary myotubes. Finally, there was overlap between the DEGs of mPT and diaphragm muscle in a mouse model of pancreatic cancer cachexia during the muscle wasting phase. We conclude that mPT should be explored as a therapeutic target in muscle wasting disorders.

physiology↗

bioRxiv2026

MicroRNA regulatory targets of VO2peak in older adult participants of the Study of Muscle Mobility and Aging (SOMMA)

Skeletal muscle aging (sarcopenia) is associated with reduced peak oxygen consumption (VO peak) during exercise, a key determinant of physical function and overall health. However, the molecular mechanisms linking muscle aging to low VO peak remain poorly understood. We aimed to identify miRNA signatures and miRNA-gene regulatory networks associated with VO peak in older adults. Using small RNA and mRNA sequencing, we analyzed skeletal muscle from 72 SOMMA participants (70-79 years old) with low or high VO peak (n = 18/group) and from 36 participants spanning the full VO peak spectrum. Differential expression was assessed using LIMMA, with pathway and network analyses performed using Ingenuity Pathway Analysis (IPA) and Weighted Gene Co-expression Network Analysis (WGCNA). We detected 1,408 miRNAs and 16,210 genes; among these, 14 miRNAs and 2,018 genes were differentially expressed (FDR < 0.05). The 14 miRNAs regulated 142 genes, and expression of 10 miRNAs inversely correlated with 50 genes enriched in mitochondrial, sirtuin-1, and nitric oxide signaling pathways. Regression analyses identified 21 miRNAs and 1,744 genes significantly correlated with VO peak after adjusting for age and sex. WGCNA revealed 10 co-expression modules associated with VO peak, with the cyan module showing the strongest correlation and enrichment for nitric oxide signaling genes. These findings highlight novel miRNA-mediated molecular pathways potentially contributing to low VO peak and skeletal muscle aging in older adults. Future studies will further investigate these miRNA-gene interactions to uncover therapeutic targets for preserving muscle function with age.

molecular biology↗

bioRxiv2025

MicroRNA signatures of VO2peak in older adult participants of the Study of Muscle, Mobility and Aging

BackgroundPeak oxygen consumption during exercise (VO2peak), is a direct measure of cardiorespiratory fitness (CF), a key indicator of physical function and overall health. However, the molecular changes that underpin VO2peak variation are not clear. Our objective is to understand the miRNA signatures that relate to VO2peak variation, which could provide insights to novel mechanisms that contribute to low VO2peak. MethodsWe used small RNA sequencing to analyze serum samples from 72 participants (70-79 yrs old, 53% female) of the Study of Muscle, Mobility and Aging (SOMMA). We analyzed samples from individuals with low or high VO2peak (N=18/group) as well as samples from 36 randomly selected participants spanning the entire spectrum of VO2peak. We used LIMMA analysis package for regression analysis and to identify differentially expressed miRNAs. We used receiver operating characteristic curve analysis to evaluate the Area Under the Curve (AUC) and sensitivity and specificity rates. ResultsWe identified 1,055 miRNAs expressed in all serum samples. Expression of 65 miRNAs differed between participants with low and high VO2peak (p < 0.05). After p-value adjustment, expression of 5 miRNAs (miR-1301-3p, -431-5p, -501-5p, -519a-3p, and -18a-3p) remained significantly different (FDR = 0.05). The five miRNAs had AUC ranging from 0.77 to 0.84. The optimal sensitivity and specificity ranged from 70 to 80% and 80 to 90%, respectively. After adjustment for age and sex covariates, 46 miRNAs significantly correlated with VO2peak (p < 0.05) and miR-519a-3p remained significant based on adjusted of p-values. ConclusionsWe identified a miRNA signature of VO2peak in older individuals that might provide insights to novel mechanisms that drive low VO2peak. Future studies will validate the findings in a larger, longitudinal study cohort.

molecular biology↗

bioRxiv2021

Chronic Aryl Hydrocarbon Receptor Activity Phenocopies Smoking-induced Skeletal Muscle Impairment

BackgroundCOPD patients exhibit skeletal muscle atrophy, denervation, and reduced mitochondrial oxidative capacity. Whilst chronic tobacco smoke exposure is implicated in COPD muscle impairment, the mechanisms involved are ambiguous. The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that activates detoxifying pathways with numerous exogenous ligands, including tobacco smoke. Whereas transient AHR activation is adaptive, chronic activation can be toxic. On this basis, we tested the hypothesis that chronic smoke-induced AHR activation causes adverse muscle impact. MethodsWe used clinical patient muscle samples, and in vitro (C2C12 myotubes) and in vivo models (mouse), to perform gene expression, mitochondrial function, muscle and neuromuscular junction morphology, and genetic manipulations (adeno-associated virus-mediated gene transfer). Results16 weeks tobacco smoke exposure in mice caused: muscle atrophy, neuromuscular junction degeneration, and reduced oxidative capacity. Similarly, smoke exposure reprogrammed the muscle transcriptome, with down-regulation of mitochondrial and neuromuscular junction genes. In mouse and human patient specimens, smoke exposure increased muscle AHR signaling. Mechanistically, experiments in cultured myotubes demonstrated that smoke condensate activated the AHR, caused mitochondrial impairments, and induced an AHR-dependent myotube atrophy. Finally, to isolate the role of AHR activity, expression of a constitutively active AHR mutant without smoke exposure caused atrophy and mitochondrial impairments in cultured myotubes, and muscle atrophy and neuromuscular junction degeneration in mice. ConclusionsThese results establish that chronic AHR activity, as occurs in smokers, phenocopies the atrophy, mitochondrial impairment and neuromuscular junction degeneration caused by chronic tobacco smoke exposure.

physiology↗