Biology subjects

Labeit, S.

Publications and source records attributed to Labeit, S..

6 recordsLinked to original sources

bioRxiv2026

Small-molecule targeting MuRF1 enhances functional exercise capacity in rats: an exploratory study

Maintenance of skeletal muscle function is essential for functional independence, quality of life and healthspan. Muscle RING-finger protein-1 (MuRF1) negatively regulates muscle function and mass through ubiquitination and degradation of muscle proteins. Accordingly, genetic and pharmacological inhibition of MuRF1 attenuates muscle wasting and weakness under catabolic stress. To explore the potential of MuRF1 inhibitors (e.g., MyoMed-205) to improve muscle health, we investigated here the long-term effects of MyoMed-205 on functional capacity and muscle physiology in rats under basal conditions. Wistar rats were randomized to control or MyoMed-205 groups and were followed for 4 or 8 weeks. Body weight, food and water intake, and exercise capacity were monitored weekly. At each endpoint, the soleus muscle was collected for histological analyses. MyoMed-205-treated rats showed normal basic survival-related behaviors and body growth. After 8 weeks, MyoMed-205-treated animals exhibited enhanced exercise capacity (speed (m/min): +45%, p = 0.01; endurance (min): +47%, p = 0.03; and distance covered (m): +87%, p = 0.04) compared with baseline performance. Conversely, no differences were found in soleus fiber type distribution, cross-sectional area, or lipid and collagen content. Our findings indicate that MyoMed-205 enhances functional exercise capacity independently of changes in soleus muscle structure in rats under basal conditions.

physiology↗

bioRxiv2025

Small-molecule inhibition of MuRF1 protects against disuse-induced diaphragmatic dysfunction: Underlying molecular mechanisms

BackgroundMechanical inactivity rapidly induces diaphragm muscle fibers contractile dysfunction and atrophy. Diaphragm weakness can impair respiratory function, quality of life, and increase risks of morbidity and mortality. Muscle RING-finger protein-1 (MuRF1) expression is upregulated during denervation and muscle inactivity, and is known to target key muscle proteins for degradation. We previously reported that the small-molecule targeting MuRF1 (MyoMed-205) protects against diaphragm contractile dysfunction and atrophy after 12 hours of unilateral diaphragm denervation (UDD) in rats. In this study, we investigated the mechanisms by which MyoMed-205 protects the diaphragm structure and function during early UDD in rats. MethodsMale Wistar rats were subjected to unilateral diaphragm denervation (UDD) for 12 hours. Immediately after UDD, rats received either a placebo (vehicle) or small-molecule targeting MuRF1 (MyoMed-205, 50 mg/kg bw), and outcomes were compared with Sham-operated controls. Diaphragm was used for histological, morphometric, transcriptomic (RNA-seq), and protein content (Western Blot) analysis. ResultsUDD induced diaphragm slow-(type I: p = 0.03) and fast-twitch (type IIa: p = 0.04; type IIb/x: p = 0.02) fibers atrophy after 12 hours, which was prevented by MyoMed-205 (p < 0.05). Mechanistically, UDD perturbed mechanisms involved with myofiber ultrastructure and contractility, mitochondrial function, proteolysis, and tissue remodeling in the diaphragm. MyoMed-205 enhanced the activation of mechanisms required for sarcomere integrity, calcium handling, antioxidant defense, chaperone-mediated unfolded protein response, and muscle growth. MyoMed-205 also mitigated intramuscular fat deposition and pro-fibrotic responses triggered by UDD. ConclusionSmall-molecule targeting MuRF1 (MyoMed-205) protects against diaphragm muscle contractile dysfunction and atrophy after 12 hours of UDD. Herein, we demonstrate that this protective effect involved augmented activation of signaling pathways controlling muscle structure and function, chaperone-mediated unfolded protein, and muscle growth, while mitigating intramuscular fat deposition and pro-fibrotic responses triggered by UDD at the transcriptional and/or protein level.

physiology↗

bioRxiv2025

The titin N2A-MARP signalosome constrains muscle longitudinal hypertrophy in response to stretch

Titin-based mechanosensing is a key driver of trophic signaling in muscle, yet the downstream pathways linking titin sensing to muscle remodeling remain poorly understood. To investigate these signaling mechanisms, we utilized unilateral diaphragm denervation (UDD), an in vivo model that induces titin-stiffness-dependent hypertrophy via mechanical stretch. Using UDD in rats and mice, we characterized the longitudinal hypertrophic response and distinguished stretch-induced signaling from denervation effects by performing global transcriptomic and proteomic analyses following UDD and bilateral diaphragm denervation (BDD) in rats. Our findings identified upregulation of titin-associated muscle ankyrin repeat proteins (MARPs). Subsequent phosphorylation enrichment mass spectrometry in mouse diaphragm highlighted the involvement of the N2A-element. UDD in MARP knockout (KO) mice resulted in enhanced longitudinal hypertrophy, with Western blot analysis revealing activation of the mTOR pathway. Furthermore, pharmacological inhibition of mTORC1 with rapamycin suppressed longitudinal hypertrophy, demonstrating that mTOR signaling regulates titin-mediated hypertrophic growth in a MARP-dependent manner. These findings establish MARPs as key modulators of titin-based mechanotransduction and highlight mTORC1 as a central regulator of longitudinal muscle hypertrophy.

physiology↗

bioRxiv2023

Truncated titin is integrated into the human dilated cardiomyopathic sarcomere

Heterozygous (HET) truncating mutations in the TTN gene (TTNtv) encoding the giant titin protein are the most common genetic cause of dilated cardiomyopathy (DCM). However, the molecular mechanisms by which TTNtv mutations induce DCM are controversial. Here we investigated 127 clinically identified DCM human cardiac samples with next-generation sequencing (NGS), high-resolution gel electrophoresis, Western blot analysis and super-resolution microscopy in order to dissect the structural and functional consequences of TTNtv mutations. The occurrence of TTNtv was found to be 15% in the DCM cohort. Truncated titin proteins matching, by molecular weight, the gene-sequence predictions were detected in the majority of the TTNtv samples. The total amount of expressed titin, which includes the truncated fragments, was comparable in the TTNtv+ and TTNtv-samples, indicating that titin haploinsufficiency is not the leading cause of the molecular pathogenesis. Proteomic analysis of washed cardiac myofibrils and Stimulated Emission Depletion (STED) super-resolution microscopy of myocardial sarcomeres labeled with sequence-specific anti-titin antibodies revealed that truncated titin is structurally integrated in the sarcomere. Sarcomere lengthdependent anti-titin epitope position, shape and intensity analysis pointed at structural defects in the I/A junction and the M-band of TTNtv+ sarcomeres, which may contribute, via faulty mechanosensor function, to the development of manifest DCM.

biophysics↗

bioRxiv2021

The skeletal muscle circadian clock regulates sarcomere length homeostasis through titin splicing

Circadian rhythms are maintained by a cell autonomous, transcriptional-translational feedback loop known as the molecular clock. While previous research suggests a role of the molecular clock in regulating skeletal muscle structure and function, no mechanisms have connected the molecular clock to sarcomere filaments. Utilizing inducible, skeletal muscle specific, Bmal1 knockout (iMSBmal1-/-) mice, we showed that knocking out skeletal muscle clock function alters titin isoform expression using RNAseq, LC-MS, and SDS-VAGE. This alteration in titins spring length resulted in sarcomere length heterogeneity. We demonstrate the direct link between altered titin splicing and sarcomere length in vitro using U7 snRNPs that truncate the region of titin altered in iMSBmal1-/- muscle. We identified a mechanism whereby the skeletal muscle clock regulates titin isoform expression through transcriptional regulation of Rbm20, a potent splicing regulator of titin. Lastly, we used an environmental model of circadian rhythm disruption and identified significant down-regulation of Rbm20 expression. Our findings demonstrate the importance of the skeletal muscle circadian clock in maintaining titin isoform through regulation of RBM20 expression. Because circadian rhythm disruption is a feature of many chronic diseases, our results highlight a novel pathway that could be targeted to maintain skeletal muscle structure and function in a range of pathologies.

physiology↗

bioRxiv2019

Perturbation of the titin/MURF1 signaling complex is associated with hypertrophic cardiomyopathy in a fish model and in human patients.

Hypertrophic cardiomyopathy (HCM) is a hereditary disease characterized by cardiac hypertrophy with diastolic dysfunction. Gene mutations causing HCM have been found in about half of the patients, while the genetic etiology and pathogenesis remain unknown for many cases of HCM. To identify novel mechanisms underlying HCM pathogenesis, we generated a cardiovascular-mutant medaka fish non-spring heart (nsh), which showed diastolic dysfunction and hypertrophic myocardium. The nsh homozygotes had fewer myofibrils, disrupted sarcomeres and expressed pathologically stiffer titin isoforms. In addition, the nsh heterozygotes showed M-line disassembly that is similar to the pathological changes found in HCM. Positional cloning revealed a missense mutation in an immunoglobulin (Ig) domain located in the M-line-A-band transition zone of titin. Screening of mutations in 96 unrelated patients with familial HCM, who had no previously implicated mutations in known sarcomeric gene candidates, identified two mutations in Ig domains close to the M-line region of titin. In vitro studies revealed that the mutations found in both medaka fish and in familial HCM increased binding of titin to muscle-specific ring finger protein 1 (MURF1) and enhanced titin degradation by ubiquitination. These findings implicate an impaired interaction between titin and MURF1 as a novel mechanism underlying the pathogenesis of HCM.

developmental biology↗