Vasohibin inhibition improves myocardial relaxation in a rat model of heart failure with preserved ejection fraction.

Heart failure with preserved ejection fraction (HFpEF) is a complex syndrome associated with increased myocardial stiffness and cardiac filling abnormalities. Prior studies implicated increased α-tubulin detyrosination, which is catalyzed by the vasohibin enzymes, as a contributor to increased stabilization of the cardiomyocyte microtubule network (MTN) and stiffness in failing human hearts. We explored whether increased MTN detyrosination contributed to impaired diastolic function in the ZSF1 obese rat model of HFpEF and designed a small-molecule vasohibin inhibitor to ablate MTN detyrosination in vivo.

Microtubule destabilization with colchicine increases the work output of myocardial slices.

Cardiac microtubules have recently been implicated in mechanical dysfunction during heart failure. However, systemic intolerance and non-cardiac effects of microtubule-depolymerizing compounds have made it challenging to determine the effect of microtubules on myocardial performance. Herein, we leverage recent advancements in living myocardial slices to develop a stable working preparation that recapitulates the complexity of diastole by including early and late phases of diastolic filling.

Adult human cardiomyocyte mechanics in osteogenesis imperfecta.

Osteogenesis imperfecta (OI) is an extracellular matrix disorder characterized by defects in collagen-1 transport or synthesis, resulting in bone abnormalities. Although reduced collagen in OI hearts has been associated with reduced myocardial stiffness and left ventricular remodeling, its impact on cardiomyocyte (CM) function has not been studied. Here, we explore the tissue-level and CM-level properties of a heart from a deceased organ donor with OI type I.

Chronic activation of tubulin tyrosination in HCM mice and human iPSC-engineered heart tissues improves heart function.

Hypertrophic cardiomyopathy (HCM) is the most common cardiac genetic disorder caused by sarcomeric gene variants and associated with left ventricular (LV) hypertrophy and diastolic dysfunction. The role of the microtubule network has recently gained interest with the findings that -α-tubulin detyrosination (dTyr-tub) is markedly elevated in heart failure. Acute reduction of dTyr-tub by inhibition of the detyrosinase (VASH/SVBP complex) or activation of the tyrosinase (tubulin tyrosine ligase, TTL) markedly improved contractility and reduced stiffness in human failing cardiomyocytes, and thus poses a new perspective for HCM treatment.

Extracellular stiffness induces contractile dysfunction in adult cardiomyocytes via cell-autonomous and microtubule-dependent mechanisms.

The mechanical environment of the myocardium has a potent effect on cardiomyocyte form and function, yet an understanding of the cardiomyocyte responses to extracellular stiffening remains incomplete. We therefore employed a cell culture substrate with tunable stiffness to define the cardiomyocyte responses to clinically relevant stiffness increments in the absence of cell-cell interactions. When cultured on substrates magnetically actuated to mimic the stiffness of diseased myocardium, isolated rat adult cardiomyocytes exhibited a time-dependent reduction of sarcomere shortening, characterized by slowed contraction and relaxation velocity, and alterations of the calcium transient.

The microtubule cytoskeleton in cardiac mechanics and heart failure.

The microtubule network of cardiac muscle cells has unique architectural and biophysical features to accommodate the demands of the working heart. Advances in live-cell imaging and in deciphering the 'tubulin code' have shone new light on this cytoskeletal network and its role in heart failure. Microtubule-based transport orchestrates the growth and maintenance of the contractile apparatus through spatiotemporal control of translation, while also organizing the specialized membrane systems required for excitation-contraction coupling.

Transcriptional, Post-Transcriptional, and Post-Translational Mechanisms Rewrite the Tubulin Code During Cardiac Hypertrophy and Failure.

A proliferated and post-translationally modified microtubule network underlies cellular growth in cardiac hypertrophy and contributes to contractile dysfunction in heart failure. Yet how the heart achieves this modified network is poorly understood. Determining how the "tubulin code"-the permutations of tubulin isoforms and post-translational modifications-is rewritten upon cardiac stress may provide new targets to modulate cardiac remodeling.

Truncated titin proteins in dilated cardiomyopathy.

Truncating variants in (TTNtvs) are the most common known cause of nonischemic dilated cardiomyopathy (DCM), but how TTNtvs cause disease has remained controversial. Efforts to detect truncated titin proteins in affected human DCM hearts have failed, suggesting that disease is caused by haploinsufficiency, but reduced amounts of titin protein have not yet been demonstrated. Here, we leveraged a collection of 184 explanted posttransplant DCM hearts to show, using specialized electrophoretic gels, Western blotting, allelic phasing, and unbiased proteomics, that truncated titin proteins can quantitatively be detected in human DCM hearts.

Need for Speed: The Importance of Physiological Strain Rates in Determining Myocardial Stiffness.

The heart is viscoelastic, meaning its compliance is inversely proportional to the speed at which it stretches. During diastolic filling, the left ventricle rapidly expands at rates where viscoelastic forces impact ventricular compliance. In heart disease, myocardial viscoelasticity is often increased and can directly impede diastolic filling to reduce cardiac output.

Cochlear supporting cells require GAS2 for cytoskeletal architecture and hearing.

In mammals, sound is detected by mechanosensory hair cells that are activated in response to vibrations at frequency-dependent positions along the cochlear duct. We demonstrate that inner ear supporting cells provide a structural framework for transmitting sound energy through the cochlear partition. Humans and mice with mutations in GAS2, encoding a cytoskeletal regulatory protein, exhibit hearing loss due to disorganization and destabilization of microtubule bundles in pillar and Deiters' cells, two types of inner ear supporting cells with unique cytoskeletal specializations.

Pathogenic LMNA variants disrupt cardiac lamina-chromatin interactions and de-repress alternative fate genes.

Pathogenic mutations in LAMIN A/C (LMNA) cause abnormal nuclear structure and laminopathies. These diseases have myriad tissue-specific phenotypes, including dilated cardiomyopathy (DCM), but how LMNA mutations result in tissue-restricted disease phenotypes remains unclear. We introduced LMNA mutations from individuals with DCM into human induced pluripotent stem cells (hiPSCs) and found that hiPSC-derived cardiomyocytes, in contrast to hepatocytes or adipocytes, exhibit aberrant nuclear morphology and specific disruptions in peripheral chromatin.

Processivity and Velocity for Motors Stepping on Periodic Tracks.

Processive molecular motors enable cargo transportation by assembling into dimers capable of taking several consecutive steps along a cytoskeletal filament. In the well-accepted hand-over-hand stepping mechanism, the trailing motor detaches from the track and binds the filament again in the leading position. This requires fuel consumption in the form of ATP hydrolysis and coordination of the catalytic cycles between the leading and the trailing heads.

Depletion of Vasohibin 1 Speeds Contraction and Relaxation in Failing Human Cardiomyocytes.

Rationale: Impaired myocardial relaxation is an intractable feature of several heart failure (HF) causes. In human HF, detyrosinated microtubules stiffen cardiomyocytes and impair relaxation. Yet the identity of detyrosinating enzymes have remained ambiguous, hindering mechanistic study and therapeutic development.

Microtubules Increase Diastolic Stiffness in Failing Human Cardiomyocytes and Myocardium.

Background: Diastolic dysfunction is a prevalent and therapeutically intractable feature of heart failure (HF). Increasing ventricular compliance can improve diastolic performance, but the viscoelastic forces that resist diastolic filling and become elevated in human HF are poorly defined. Having recently identified posttranslationally detyrosinated microtubules as a source of viscoelasticity in cardiomyocytes, we sought to test whether microtubules contribute meaningful viscoelastic resistance to diastolic stretch in human myocardium.

Cardiac microtubules in health and heart disease.

Unlabelled: Cardiomyocytes are large (∼40,000 µm), rod-shaped muscle cells that provide the working force behind each heartbeat. These highly structured cells are packed with dense cytoskeletal networks that can be divided into two groups—the contractile (i.e.

Microtubules Provide a Viscoelastic Resistance to Myocyte Motion.

Background: Microtubules (MTs) buckle and bear load during myocyte contraction, a behavior enhanced by post-translational detyrosination. This buckling suggests a spring-like resistance against myocyte shortening, which could store energy and aid myocyte relaxation. Despite this visual suggestion of elastic behavior, the precise mechanical contribution of the cardiac MT network remains to be defined.

Suppression of detyrosinated microtubules improves cardiomyocyte function in human heart failure.

Detyrosinated microtubules provide mechanical resistance that can impede the motion of contracting cardiomyocytes. However, the functional effects of microtubule detyrosination in heart failure or in human hearts have not previously been studied. Here, we utilize mass spectrometry and single-myocyte mechanical assays to characterize changes to the cardiomyocyte cytoskeleton and their functional consequences in human heart failure.

The Antiparallel Dimerization of Myosin X Imparts Bundle Selectivity for Processive Motility.

Myosin X is an unconventional actin-based molecular motor involved in filopodial formation, microtubule-actin filament interaction, and cell migration. Myosin X is an important component of filopodia regulation, localizing to tips of growing filopodia by an unclear targeting mechanism. The native α-helical dimerization domain of myosin X is thought to associate with antiparallel polarity of the two amino acid chains, making myosin X the only myosin that is currently considered to form antiparallel dimers.

Network confinement and heterogeneity slows nanoparticle diffusion in polymer gels.

Nanoparticle (NP) diffusion was measured in polyacrylamide gels (PAGs) with a mesh size comparable to the NP size, 21 nm. The confinement ratio (CR), NP diameter/mesh size, increased from 0.4 to 3.

Competitive Adsorption of Polyelectrolytes onto and into Pellicle-Coated Hydroxyapatite Investigated by QCM-D and Force Spectroscopy.

A current effort in preventive dentistry is to inhibit surface attachment of bacteria using antibacterial polymer coatings on the tooth surface. For the antibacterial coatings, the physisorption of anionic and cationic polymers directly onto hydroxyapatite (HA) and saliva-treated HA surfaces was studied using quartz crystal microbalance, force spectroscopy, and atomic force microscopy. First, single species adsorption is shown to be stronger on HA surfaces than on silicon oxide surfaces for all polymers (i.

Intracellular nanoparticle dynamics affected by cytoskeletal integrity.

The cell interior is a crowded chemical space, which limits the diffusion of molecules and organelles within the cytoplasm, affecting the rates of chemical reactions. We provide insight into the relationship between non-specific intracellular diffusion and cytoskeletal integrity. Quantum dots entered the cell through microinjection and their spatial coordinates were captured by tracking their fluorescence signature as they diffused within the cell cytoplasm.

Detyrosinated microtubules buckle and bear load in contracting cardiomyocytes.

The microtubule (MT) cytoskeleton can transmit mechanical signals and resist compression in contracting cardiomyocytes. How MTs perform these roles remains unclear because of difficulties in observing MTs during the rapid contractile cycle. Here, we used high spatial and temporal resolution imaging to characterize MT behavior in beating mouse myocytes.