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Posttranslational modifications in microtubules affect cytoskeletal mechanics and mechanotransduction. In this study, Coleman et al. show that acetylated α-tubulin affects cytoskeletal stiffness and viscoelastic resistance, thus revealing another regulator of striated muscle mechanotransduction.

Fazlollahi et al. show that contraction and relaxation remain tightly coupled in intact canine myocardium after exercise training and/or myocardial infarction. They postulate that the action of cardiac myosin binding protein C on actin and myosin may play a key role in this process.

Article

Stronczek et al. analyze the structure of the titin-N2A poly-Ig segment, a key signaling element in the sarcomere. They reveal a unique topography for the I81-I83 tandem, but they could not confirm the presence of Ca2+ binding sites in I81-I83 or the interaction of N2A with actin.

Cardiac myosin-binding protein C (cMyBP-C) is thought to regulate cardiac muscle and heart contraction. Hanft et al. show that cMyBP-C phosphorylation regulates length dependence of power output in murine permeabilized cardiac myocytes, which translates to in vivo Frank–Starling relationships.

Scellini et al. show that mavacamten, a preclinical inhibitor of sarcomeric myosins, has a fast and reversible mechanical action on skeletal and cardiac myofibers that is mediated by a shift of motor heads out of a force-generating cycle, with no effect on the kinetics of cardiac force development.

Rasicci et al. investigate the mechanochemical properties of distinct isoforms of cardiac myosin carrying the K104E regulatory light chain mutation, previously associated with hypertrophic cardiomyopathy. They demonstrate that the mutation does not affect the ATPase or motor properties of human cardiac myosin subfragment-1 (M2β-S1), but the mutation increases the sliding velocity and disrupts RLC incorporation in full-length α-cardiac myosin.

Mamidi et al. investigate the effect of cardiac myosin-binding protein C (cMyBPC) phosphorylation on the response to omecamtiv mecarbil (OM), a candidate heart failure therapy. They show that OM uncouples myocardial force dynamics from cMyBPC phosphorylation, suggesting important therapeutic constraints.

Review

This review focuses on thin filament regulatory mechanisms with emphasis on cardiac-specific mechanisms in the three-state model of sarcomere activation and on signaling cascades at the barbed and pointed ends.

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