Biology subjects

Kuehn, M. N.

Publications and source records attributed to Kuehn, M. N..

5 recordsLinked to original sources

bioRxiv2026

Myosin binding protein-C limits strain induced cross-bridge detachment in response to rapid stretch in cardiac and skeletal muscle

Myosin binding protein-C (MyBP-C) consists of a family of regulatory proteins expressed in sarcomeres of cardiac, fast and slow twitch skeletal muscles. The 3 MyBP-C paralogs expressed in each muscle type are encoded by separate genes but maintain a similar structure. Given the overall similarity in structure and localization of each of paralog, it is assumed that MyBP-C expressed in different muscles have similar functional effects. Here we directly tested this assumption by making use of our cut and paste approach to remove and replace N-terminal regions of MyBP-C in sarcomeres of different muscle types. We found that the different MyBP-C paralogs similarly slowed cross-bridge cycling kinetics, increased Ca2+ sensitivity of tension, and damped force oscillations. However, responses to a rapid stretch in actively contracting fibers, taken as indices of cross-bridge detachment and attachment kinetics, differed in each muscle type and responses depended on the presence or absence of a given paralog of MyBP-C. Altered responses to stretch were most evident for fast MyBP-C where loss of MyBP-C in psoas muscle resulted in transient responses to stretch that resembled those found in cardiomyocytes. Replacement of cardiac MyBP-C with fast MyBP-C in cardiomyocytes led to responses similar to psoas muscle. In separate X-ray diffraction experiments we also found that loss of MyBP-C in Ca2+-activated psoas muscle increased lattice disorder, reduced the ordering of myosin heads, and decreased thin filament length. Taken together, these results indicate that the different MyBP-C paralogs exert both common and unique effects on myosin cross-bridge kinetics. Significance StatementMyBP-C is a family of regulatory proteins found in muscle sarcomeres, where they regulate contraction and relaxation. Mutations in all MyBP-C paralogs cause disease in skeletal and cardiac muscles. We used a powerful "cut and paste" strategy to selectively remove MyBP-C from slow-twitch, fast-twitch, and cardiac muscle to show that each MyBP-C effects cross-bridge behavior similarly, though to varying degrees. Each MyBP-C had a notable effect on transient responses to rapid stretch, where MyBP-C was found to limit strain-induced cross-bridge detachment, especially in fast-twitch muscles. Strain-induced cross-bridge detachment is critical for rapid filling of the left ventricle in diastole and for sustained contraction in skeletal muscle. MyBP-C paralogs appear adapted to meet the mechanical demands of each muscle type.

physiology↗

bioRxiv2025

Piperine activates the thick filament of resting rat skeletal muscle, enhancing dynamic contractility in a fiber-type-dependent manner

The myosin-containing thick filament has recently been shown to alter its resting activation level in response to multiple diseases and therapeutics. Changes in thick filament resting activation level are caused by myosin heads transitioning between OFF and ON conformational states. Functionally, this modulation of thick filament activation level is a key regulatory step in muscle contraction and a promising therapeutic target. The availability of resting ON-state myosin heads governs dynamic contractility, which is critical to physical function and well-being. At present, there is a lack of compounds favouring this ON-state in resting skeletal muscle. Piperine is a molecule known to bind to myosin and increase submaximal isometric contractility in fast and slow skeletal muscle. Yet, effects on dynamic contractility and the underlying mechanism responsible for the observed effects in skeletal muscles remain unclear. Here, we used fibre small-angle X-ray diffraction and intact-muscle ex vivo contractility experiments to determine the effects of piperine on resting myosin structure and dynamic contractility in fast and slow rat muscles. X-ray diffraction data suggest that piperine promotes an OFF-to-ON transition of myosin in resting skeletal muscle, increasing the availability of myosin heads for force generation. Functionally, piperine substantially enhanced dynamic contractility in both muscle types, with greater improvements in slow muscle during maximal activation. These findings establish piperine as a tool to probe thick-filament activation in skeletal muscle, highlighting fibre-type-specific effects of thick-filament activation on the recruitment of the contractile reserve capacity. Key Points- Piperine is a compound known to bind to skeletal muscle myosin and enhance isometric contractility in fast and slow muscles, but the underlying molecular mechanisms and effects on dynamic contractile function remain unknown. - We show that piperine increases the activation level of the myosin-containing thick filament in resting fast and slow skeletal muscle, which may explain the effect of piperine on contractile function. - Piperine substantially increases the maximal contractile power of both fast and slow skeletal muscles at low-frequency activation; however, it only enhances the maximal power in slow skeletal muscle at high-frequency activation. - Our data reveal potentiation of dynamic contractility with fibre-type-dependent magnitudes in response to piperine-induced activation of the resting thick filament, a phenomenon that requires further investigation and may ultimately be exploited in the treatment of diseases characterised by muscle weakness. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=127 SRC="FIGDIR/small/689918v2_ufig1.gif" ALT="Figure 1"> View larger version (36K): org.highwire.dtl.DTLVardef@1ff3672org.highwire.dtl.DTLVardef@4f809forg.highwire.dtl.DTLVardef@1857404org.highwire.dtl.DTLVardef@83d958_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGraphical abstractC_FLOATNO Abstract figure legend: We investigated the effects of piperine on 1) the activation level of the resting thick filament and 2) dynamic contractility in fibres and intact slow (soleus) and fast (extensor digitorum longus, EDL) rat muscles, respectively. The activation level of the resting thick filament was assessed pre- and post-piperine incubation using small-angle X-ray diffraction. Dynamic contractility was assessed at submaximal and maximal activation levels by constructing low- and high-frequency force-velocity curves and corresponding power curves using an ex vivo contraction setup. The setup allows for simultaneous experiments on the effects of piperine and vehicle treatment in contralateral muscles. We found that piperine increased the activation level of the resting thick filament by favouring the ON-myosin state in fibres from both muscle types. In whole muscle preparations, piperine also induced substantial increases in dynamic contractility, especially in slow soleus muscle. C_FIG

physiology↗

bioRxiv2024

Mavacamten facilitates myosin head ON-to-OFF transitions and shortens thin filament length in relaxed skeletal muscle

The first-in-its-class cardiac drug mavacamten reduces the proportion of so-called ON-state myosin heads in relaxed sarcomeres, altering contraction performance. However, mavacamten is not completely specific to cardiac myosin and can also affect skeletal muscle myosin, an important consideration since mavacamten is administered orally and so will also be present in skeletal tissue. Here, we studied the effect of mavacamten on skeletal muscle structure using small-angle X-ray diffraction. Mavacamten treatment reduced the proportion of ON myosin heads but did not eliminate the molecular underpinnings of length-dependent activation, demonstrating similar effects to those observed in cardiac muscle. These findings provide valuable insights for the potential use of mavacamten as a tool to study muscle contraction across striated muscle.

physiology↗

bioRxiv2023

Remodelling of Skeletal Muscle Myosin Metabolic States in Hibernating Mammals

Hibernation is a period of metabolic suppression utilized by many small and large mammal species to survive during winter periods. As the underlying cellular and molecular mechanisms remain incompletely understood, our study aimed to determine whether skeletal muscle myosin and its metabolic efficiency undergo alterations during hibernation to optimize energy utilization. We isolated muscle fibers from small hibernators, Ictidomys tridecemlineatus and Eliomys quercinus and larger hibernators, Ursus arctos and Ursus americanus. We then conducted loaded Mant-ATP chase experiments alongside X-ray diffraction to measure resting myosin dynamics and its ATP demand. In parallel, we performed multiple proteomics analyses. Our results showed a preservation of myosin structure in U. arctos and U. americanus during hibernation, whilst in I. tridecemlineatus and E. quercinus, changes in myosin metabolic states during torpor unexpectedly led to higher levels in energy expenditure of type II, fast-twitch muscle fibers at ambient lab temperatures (20{degrees}C). Upon repeating loaded Mant-ATP chase experiments at 8{degrees}C (near the body temperature of torpid animals), we found that myosin ATP consumption in type II muscle fibers was reduced by 77-107% during torpor compared to active periods. Additionally, we observed Myh2 hyper-phosphorylation during torpor in I. tridecemilineatus, which was predicted to stabilize the myosin molecule. This may act as a potential molecular mechanism mitigating myosin-associated increases in skeletal muscle energy expenditure during periods of torpor in response to cold exposure. Altogether, we demonstrate that resting myosin is altered in hibernating mammals, contributing to significant changes to the ATP consumption of skeletal muscle. Additionally, we observe that it is further altered in response to cold exposure and highlight myosin as a potentially contributor to skeletal muscle non-shivering thermogenesis.

physiology↗

bioRxiv2023

Titin-based force regulates cardiac myofilament structures mediating length-dependent activation

The Frank-Starling law states that the hearts stroke volume increases with greater preload due to increased venous return, allowing the heart to adapt to varying circulatory demands. Molecularly, increasing preload increases sarcomere length (SL), which alters sarcomere structures that are correlated to increased calcium sensitivity upon activation. The titin protein, spanning the half-sarcomere, acts as a spring in the I-band, applying a SL-dependent force suggested to pull against and alter myofilaments in a way that supports the Frank-Starling effect. To evaluate this, we employed the titin cleavage (TC) model, where a tobacco-etch virus protease recognition site is inserted into distal I-band titin and allows for rapid, specific cleavage of titin in an otherwise-healthy sarcomere. Here, we evaluated the atomic-level structures of amyopathic cardiac myofilaments following 50% titin cleavage under passive stretch conditions using small-angle X-ray diffraction, which measures these structures under near-physiological (functional) conditions. We report that titin-based forces in permeabilized papillary muscle regulate both thick and thin myofilament structures clearly supporting titins role in the Frank-Starling mechanism.

physiology↗