[Magnetic resonance imaging T2 mapping could reflect disease status in patients with dermatomyositis or polymyositis].

This study aimed to explore the value of magnetic resonance imaging (MRI) T2 mapping in the assessment of dermatomyositis (DM) and polymyositis (PM). Thirty-three confirmed cases (myosin group) and eight healthy volunteers (healthy control group) at the Department of Rheumatology and Immunology, the First Affiliated Hospital of Kunming Medical University, from October 2016 to December 2017, were collected and analyzed. Multiple parameters of the myosin group were quantified, including creatine kinase (CK), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), complement C3, and complement C4. Disease status was evaluated using a panel of tools: myositis disease activity assessment tool-muscle (MDAAT-muscle), myositis disease activity assessment tool-whole (MDAAT-all), health assessment questionnaire (HAQ), medical outcomes study health survey short form-36 item (SF-36), hand muscle strength test (MMT-8) score, and MRI T2 mapping of muscle (22 muscles in the pelvis and thighs) T2 values. The results showed that in the myositis group, the measurements for CK, ESR, CRP, complement C3, and complement C4 were 457.2 (165.6, 1 229.2) IU/L, 20 (10, 42) mm/1h, 3.25 (2.38, 10.07) mg/L, 0.90 (0.83, 1.06) g/L, and 0.18 (0.14, 0.23) g/L, respectively. The scores for MMT-8, MDAAT-muscle, MDAAT-all, HAQ, and SF-36 were 57.12±16.23, 5.34 (4.00, 6.00), 34.63±12.62, 1.55 (0.66, 2.59), and 44.66±7.98, respectively. T2 values were significantly higher in all 22 muscles of the pelvis and thighs of patients with DM or PM compared with the healthy controls [(54.99±11.60)ms vs. (36.62±1.66)ms, P<0.001], with the most severe lesions in the satrorius, iliopsoas, piriformis, gluteus minimus, and gluteus medius muscles. The total muscle T2 value in the myositis group was positively correlated with CK, MDAAT-muscle, MDAAT-all, and HAQ (r=0.461, 0.506, 0.347, and 0.510, respectively, all P<0.05). There was a negative correlation between complement C4, SF-36, and MMT-8 scores (r=-0.424, -0.549, and -0.686, respectively, all P<0.05). Collectively, the findings from this study suggest that MRI T2 mapping can objectively reflect the disease status of DM and PM.

Unraveling the evolutionary origin of the complex Nuclear Receptor Element (cNRE), a cis-regulatory module required for preferential expression in the atrial chamber.

Cardiac function requires appropriate proteins in each chamber. Atria requires slow myosin to act as reservoirs, while ventricles demand fast myosin for swift pumping. Myosins are thus under chamber-biased cis-regulation, with myosin gene expression imbalances leading to congenital heart dysfunction. To identify regulatory inputs leading to cardiac chamber-biased expression, we computationally and molecularly dissected the quail Slow Myosin Heavy Chain III (SMyHC III) promoter that drives preferential expression to the atria. We show that SMyHC III gene states are orchestrated by a complex Nuclear Receptor Element (cNRE) of 32 base pairs. Using transgenesis in zebrafish and mice, we demonstrate that preferential atrial expression is achieved by a combinatorial regulatory input composed of atrial activation motifs and ventricular repression motifs. Using comparative genomics, we show that the cNRE might have emerged from an endogenous viral element through infection of an ancestral host germline, revealing an evolutionary pathway to cardiac chamber-specific expression.

The prevalence and clinical features of MYO7A-related hearing loss including DFNA11, DFNB2 and USH1B.

The MYO7A gene is known to be responsible for both syndromic hearing loss (Usher syndrome type1B:USH1B) and non-syndromic hearing loss including autosomal dominant and autosomal recessive inheritance (DFNA11, DFNB2). However, the prevalence and detailed clinical features of MYO7A-associated hearing loss across a large population remain unclear. In this study, we conducted next-generation sequencing analysis for a large cohort of 10,042 Japanese hearing loss patients. As a result, 137 patients were identified with MYO7A-associated hearing loss so that the prevalence among Japanese hearing loss patients was 1.36%. We identified 70 disease-causing candidate variants in this study, with 36 of them being novel variants. All variants identified in autosomal dominant cases were missense or in-frame deletion variants. Among the autosomal recessive cases, all patients had at least one missense variant. On the other hand, in patients with Usher syndrome, almost half of the patients carried biallelic null variants (nonsense, splicing, and frameshift variants). Most of the autosomal dominant cases showed late-onset progressive hearing loss. On the other hand, cases with autosomal recessive inheritance or Usher syndrome showed congenital or early-onset hearing loss. The visual symptoms in the Usher syndrome cases developed between age 5-15, and the condition was diagnosed at about 6-15 years of age.

F-actin architecture determines the conversion of chemical energy into mechanical work.

Mechanical work serves as the foundation for dynamic cellular processes, ranging from cell division to migration. A fundamental driver of cellular mechanical work is the actin cytoskeleton, composed of filamentous actin (F-actin) and myosin motors, where force generation relies on adenosine triphosphate (ATP) hydrolysis. F-actin architectures, whether bundled by crosslinkers or branched via nucleators, have emerged as pivotal regulators of myosin II force generation. However, it remains unclear how distinct F-actin architectures impact the conversion of chemical energy to mechanical work. Here, we employ in vitro reconstitution of distinct F-actin architectures with purified components to investigate their influence on myosin ATP hydrolysis (consumption). We find that F-actin bundles composed of mixed polarity F-actin hinder network contraction compared to non-crosslinked network and dramatically decelerate ATP consumption rates. Conversely, linear-nucleated networks allow network contraction despite reducing ATP consumption rates. Surprisingly, branched-nucleated networks facilitate high ATP consumption without significant network contraction, suggesting that the branched network dissipates energy without performing work. This study establishes a link between F-actin architecture and myosin energy consumption, elucidating the energetic principles underlying F-actin structure formation and the performance of mechanical work.

Myosin XI, a model of its conserved role in plant cell tip growth.

In eukaryotic cells, organelle and vesicle transport, positioning, and interactions play crucial roles in cytoplasmic organization and function. These processes are governed by intracellular trafficking mechanisms. At the core of that trafficking, the cytoskeleton and directional transport by motor proteins stand out as its key regulators. Plant cell tip growth is a well-studied example of cytoplasm organization by polarization. This polarization, essential for the cell's function, is driven by the cytoskeleton and its associated motors. This review will focus on myosin XI, a molecular motor critical for vesicle trafficking and polarized plant cell growth. We will center our discussion on recent data from the moss Physcomitrium patens and the liverwort Marchantia polymorpha. The biochemical properties and structure of myosin XI in various plant species are discussed, highlighting functional conservation across species. We further explore this conservation of myosin XI function in the process of vesicle transport in tip-growing cells. Existing evidence indicates that myosin XI actively organizes actin filaments in tip-growing cells by a mechanism based on vesicle clustering at their tips. A hypothetical model is presented to explain the essential function of myosin XI in polarized plant cell growth based on vesicle clustering at the tip. The review also provides insight into the in vivo localization and dynamics of myosin XI, emphasizing its role in cytosolic calcium regulation, which influences the polymerization of F-actin. Lastly, we touch upon the need for additional research to elucidate the regulation of myosin function.

Preparation of an injectable and photocurable carboxymethyl cellulose/hydroxyapatite composite and its application in cranial regeneration.

Limited bone regeneration, uncontrollable degradation rate, mismatched defect zone and poor operability have plagued the reconstruction of irregular bone defect by tissue-engineered materials. A combination of biomimetic scaffolds with hydroxyapatite has gained great popularity in promoting bone regeneration. Therefore, we designed an injectable, photocurable and in-situ curing hydrogel by methacrylic anhydride -modified carboxymethyl cellulose (CMC-MA) loading with spherical hydroxyapatite (HA) to highly simulate the natural bony matrix and match any shape of damaged tissue. The prepared carboxymethyl cellulose-methacrylate/ hydroxyapatite(CMC-MA/HA) composite presented good rheological behavior, swelling ratio and mechanical property under light illumination. Meanwhile, this composite hydrogel promoted effectively proliferation, supported adhesion and upregulated the osteogenic-related genes expression of MC3T3-E1 cells in vitro, as well as the activity of the osteogenic critical protein, Integrin α1, ß1, Myosin 9, Myosin 10, BMP-2 and Smad 1 in Integrin/BMP-2 signal pathway. Together, the composite hydrogels realized promotion of bone regeneration, deformity improvement, and the enhanced new bone strength in skull defect. It also displayed a good histocompatibility and stability of subcutaneous implantation in vivo. Overall, this study laid the groundwork for future research into developing a novel biomaterial and a minimally invasive therapeutic strategies for reconstructing bone defects and contour deficiencies.

Long non-coding RNA MLLT4 antisense RNA 1 induces autophagy to inhibit tumorigenesis of cervical cancer through modulating the myosin-9/ATG14 axis.

The regulatory mechanism of long non-coding RNAs (lncRNAs) in autophagy is as yet not well established. In this research, we show that the long non-coding RNA MLLT4 antisense RNA 1 (lncRNA MLLT4-AS1) is induced by the MTORC inhibitor PP242 and rapamycin in cervical cells. Overexpression of MLLT4-AS1 promotes autophagy and inhibits tumorigenesis and the migration of cervical cancer cells, whereas knockdown of MLLT4-AS1 attenuates PP242-induced autophagy. Mass spectrometry, RNA fluorescence in situ hybridization (RNA-FISH), and immunoprecipitation assays were performed to identify the direct interactions between MLLT4-AS1 and other associated targets, such as myosin-9 and autophagy-related 14(ATG14). MLLT4-AS1 was upregulated by H3K27ac modification with PP242 treatment, and knockdown of MLLT4-AS1 reversed autophagy by modulating ATG14 expression. Mechanically, MLLT4-AS1 was associated with the myosin-9 protein, which further promoted the transcription activity of the ATG14 gene. In conclusion, we demonstrated that MLLT4-AS1 acts as a potential tumor suppressor in cervical cancer by inducing autophagy, and H3K27ac modification-induced upregulation of MLLT4-AS1 could cause autophagy by associating with myosin-9 and promoting ATG14 transcription.

Combined effects of high-intensity ultrasound treatment and hydrogen peroxide addition on the thermal stabilities of myofibrillar protein emulsions at low ionic strengths.

In this study, the effects of high-intensity ultrasound (HIU) treatment combined with hydrogen peroxide (H2O2) addition on the thermal stability of myofibrillar protein (MP)-stabilized emulsions in low-salt conditions were investigated. Results showed that compared to using either HIU or H2O2 treatment alone, HIU treatment combined with H2O2 was most effective in enhancing the physical stability of emulsions. Moreover, the emulsion stabilized by MPs co-treated with HIU and H2O2 exhibited the most uniform distribution, highest absolute zeta potential, and optimal rheological properties upon heating. This combination effect during heating was caused by the inhibition of disulfide bond cross-linking of myosin heads by H2O2 and the dissociation of filamentous myosin structures using the HIU treatment. In addition, the results of oxidative stability analysis indicated that the addition of H2O2 increased the content of oxidation products; however, the overall influence on the oxidative stability of emulsions was not significant. In conclusion, the combination of HIU and H2O2 treatment is a promising approach to suppress heat-induced MP aggregation and improve the thermal stability of corresponding emulsions.

The Janus-faced functions of Apolipoproteins L in membrane dynamics.

The functions of human Apolipoproteins L (APOLs) are poorly understood, but involve diverse activities like lysis of bloodstream trypanosomes and intracellular bacteria, modulation of viral infection and induction of apoptosis, autophagy, and chronic kidney disease. Based on recent work, I propose that the basic function of APOLs is the control of membrane dynamics, at least in the Golgi and mitochondrion. Together with neuronal calcium sensor-1 (NCS1) and calneuron-1 (CALN1), APOL3 controls the activity of phosphatidylinositol-4-kinase-IIIB (PI4KB), involved in both Golgi and mitochondrion membrane fission. Whereas secreted APOL1 induces African trypanosome lysis through membrane permeabilization of the parasite mitochondrion, intracellular APOL1 conditions non-muscular myosin-2A (NM2A)-mediated transfer of PI4KB and APOL3 from the Golgi to the mitochondrion under conditions interfering with PI4KB-APOL3 interaction, such as APOL1 C-terminal variant expression or virus-induced inflammatory signalling. APOL3 controls mitophagy through complementary interactions with the membrane fission factor PI4KB and the membrane fusion factor vesicle-associated membrane protein-8 (VAMP8). In mice, the basic APOL1 and APOL3 activities could be exerted by mAPOL9 and mAPOL8, respectively. Perspectives regarding the mechanism and treatment of APOL1-related kidney disease are discussed, as well as speculations on additional APOLs functions, such as APOL6 involvement in adipocyte membrane dynamics through interaction with myosin-10 (MYH10).

Lmod2 is necessary for effective skeletal muscle contraction.

Muscle contraction is a regulated process driven by the sliding of actin-thin filaments over myosin-thick filaments. Lmod2 is an actin filament length regulator and essential for life since human mutations and complete loss of Lmod2 in mice lead to dilated cardiomyopathy and death. To study the little-known role of Lmod2 in skeletal muscle, we created a mouse model with Lmod2 expressed exclusively in the heart but absent in skeletal muscle. Loss of Lmod2 in skeletal muscle results in decreased force production in fast- and slow-twitch muscles. Soleus muscle from rescued Lmod2 knockout mice have shorter thin filaments, increased Lmod3 levels, and present with a myosin fiber type switch from fast myosin heavy chain (MHC) IIA to the slower MHC I isoform. Since Lmod2 regulates thin-filament length in slow-twitch but not fast-twitch skeletal muscle and force deficits were observed in both muscle types, this work demonstrates that Lmod2 regulates skeletal muscle contraction, independent of its role in thin-filament length regulation.

The non-muscle actinopathy-associated mutation E334Q in cytoskeletal γ-actin perturbs interaction of actin filaments with myosin and ADF/cofilin family proteins.

Various heterozygous cytoskeletal γ-actin mutations have been shown to cause Baraitser-Winter cerebrofrontofacial syndrome, non-syndromic hearing loss, or isolated eye coloboma. Here, we report the biochemical characterization of human cytoskeletal γ-actin carrying mutation E334Q, a mutation that leads to a hitherto unspecified non-muscle actinopathy. Following expression, purification, and removal of linker and thymosin ß4 tag sequences, the p.E334Q monomers show normal integration into linear and branched actin filaments. The mutation does not affect thermal stability, actin filament nucleation, elongation, and turnover. Model building and normal mode analysis predict significant differences in the interaction of p.E334Q filaments with myosin motors and members of the ADF/cofilin family of actin-binding proteins. Assays probing the interactions of p.E334Q filaments with human class 2 and class 5 myosin motor constructs show significant reductions in sliding velocity and actin affinity. E334Q differentially affects cofilin-mediated actin dynamics by increasing the rate of cofilin-mediated de novo nucleation of actin filaments and decreasing the efficiency of cofilin-mediated filament severing. Thus, it is likely that p.E334Q-mediated changes in myosin motor activity, as well as filament turnover, contribute to the observed disease phenotype.

Cell-particles interaction - selective uptake and transport of microdiamonds.

Diamond particles have recently emerged as novel agents in cellular studies because of their superb biocompatibility. Their unique characteristics, including small size and the presence of fluorescent color centers, stimulate many important applications. However, the mechanism of interaction between cells and diamond particles-uptake, transport, and final localization within cells-is not yet fully understood. Herein, we show a novel, to the best of our knowledge, cell behavior wherein cells actively target and uptake diamond particles rather than latex beads from their surroundings, followed by their active transport within cells. Furthermore, we demonstrate that myosin-X is involved in cell-particle interaction, while myosin-II does not participate in particle uptake and transport. These results can have important implications for drug delivery and improve sensing methods that use diamond particles.

Sequence Alignment-Based Prediction of Myosin 7A: Structural Implications and Protein Interactions.

Myosin, a superfamily of motor proteins, obtain the energy they require for movement from ATP hydrolysis to perform various functions by binding to actin filaments. Extensive studies have clarified the diverse functions performed by the different isoforms of myosin. However, the unavailability of resolved structures has made it difficult to understand the way in which their mechanochemical cycle and structural diversity give rise to distinct functional properties. With this study, we seek to further our understanding of the structural organization of the myosin 7A motor domain by modeling the tertiary structure of myosin 7A based on its primary sequence. Multiple sequence alignment and a comparison of the models of different myosin isoforms and myosin 7A not only enabled us to identify highly conserved nucleotide binding sites but also to predict actin binding sites. In addition, the actomyosin-7A complex was predicted from the protein-protein interaction model, from which the core interface sites of actin and the myosin 7A motor domain were defined. Finally, sequence alignment and the comparison of models were used to suggest the possibility of a pliant region existing between the converter domain and lever arm of myosin 7A. The results of this study provide insights into the structure of myosin 7A that could serve as a framework for higher resolution studies in future.

Triggered contraction of self-assembled micron-scale DNA nanotube rings.

Contractile rings are formed from cytoskeletal filaments during cell division. Ring formation is induced by specific crosslinkers, while contraction is typically associated with motor protein activity. Here, we engineer DNA nanotubes and peptide-functionalized starPEG constructs as synthetic crosslinkers to mimic this process. The crosslinker induces bundling of ten to hundred DNA nanotubes into closed micron-scale rings in a one-pot self-assembly process yielding several thousand rings per microliter. Molecular dynamics simulations reproduce the detailed architectural properties of the DNA rings observed in electron microscopy. Theory and simulations predict DNA ring contraction - without motor proteins - providing mechanistic insights into the parameter space relevant for efficient nanotube sliding. In agreement between simulation and experiment, we obtain ring contraction to less than half of the initial ring diameter. DNA-based contractile rings hold promise for an artificial division machinery or contractile muscle-like materials.

Distribution and appearance of myosin, dystrophin, and collagen IV in strabismus-affected extraocular muscle tissue compared with control tissue.

OBJECTIVE: Extraocular muscles have complex development processes. The present study aimed to analyze the presence of myosin, dystrophin, and collagen IV in the strabismus-affected extraocular muscle. METHODS: This research was an observational case-control study. Myosin, dystrophin, and collagen IV were detected by histological and immunohistochemical analyses of extraocular muscle samples from concomitant strabismus patients and controls. A semi-quantitative grading method and statistical analysis were used. RESULTS: In the strabismus-affected extraocular muscle, morphological analysis demonstrated different-sized muscle fibers. Immature muscle fibers and an increased amount of connective tissue were also noted. Strong positive correlations were identified between myosin and collagen IV and between dystrophin and collagen IV. CONCLUSIONS: The presence of newly formed muscle fibers, increased connective tissue, and variable diameters of skeletal striated muscle fibers indicate the decreased quality of extraocular muscles in strabismus cases. Reduced levels of myosin and dystrophin and a near absence of collagen IV in strabismus-affected skeletal striated muscle fibers characterized the muscular dystrophy of strabismus. Adjuvant therapy aimed at normalizing the metabolism of these muscles may be appropriate alongside concomitant strabismus treatment.

Myosin-binding protein C regulates the sarcomere lattice and stabilizes the OFF states of myosin heads.

Muscle contraction is produced via the interaction of myofilaments and is regulated so that muscle performance matches demand. Myosin-binding protein C (MyBP-C) is a long and flexible protein that is tightly bound to the thick filament at its C-terminal end (MyBP-CC8C10), but may be loosely bound at its middle- and N-terminal end (MyBP-CC1C7) to myosin heads and/or the thin filament. MyBP-C is thought to control muscle contraction via the regulation of myosin motors, as mutations lead to debilitating disease. We use a combination of mechanics and small-angle X-ray diffraction to study the immediate and selective removal of the MyBP-CC1C7 domains of fast MyBP-C in permeabilized skeletal muscle. We show that cleavage leads to alterations in crossbridge kinetics and passive structural signatures of myofilaments that are indicative of a shift of myosin heads towards the ON state, highlighting the importance of MyBP-CC1C7 to myofilament force production and regulation.

Moonwalking molecular machines: Unraveling the choreography of myosin filament assembly.

We have made tremendous progress in identifying the machines that shape the architecture of actin filaments. However, we know less about the mechanisms mediating myosin assembly at the supramolecular level. In this issue, Quintanilla et al. (https://doi.org/10.1083/jcb.202305023) provide important new insights into this process.

Force and kinetics of fast and slow muscle myosin determined with a synthetic sarcomere-like nanomachine.

Myosin II is the muscle molecular motor that works in two bipolar arrays in each thick filament of the striated (skeletal and cardiac) muscle, converting the chemical energy into steady force and shortening by cyclic ATP-driven interactions with the nearby actin filaments. Different isoforms of the myosin motor in the skeletal muscles account for the different functional requirements of the slow muscles (primarily responsible for the posture) and fast muscles (responsible for voluntary movements). To clarify the molecular basis of the differences, here the isoform-dependent mechanokinetic parameters underpinning the force of slow and fast muscles are defined with a unidimensional synthetic nanomachine powered by pure myosin isoforms from either slow or fast rabbit skeletal muscle. Data fitting with a stochastic model provides a self-consistent estimate of all the mechanokinetic properties of the motor ensemble including the motor force, the fraction of actin-attached motors and the rate of transition through the attachment-detachment cycle. The achievements in this paper set the stage for any future study on the emergent mechanokinetic properties of an ensemble of myosin molecules either engineered or purified from mutant animal models or human biopsies.

Myosin-5 varies its step length to carry cargo straight along the irregular F-actin track.

Molecular motors employ chemical energy to generate unidirectional mechanical output against a track while navigating a chaotic cellular environment, potential disorder on the track, and against Brownian motion. Nevertheless, decades of nanometer-precise optical studies suggest that myosin-5a, one of the prototypical molecular motors, takes uniform steps spanning 13 subunits (36 nm) along its F-actin track. Here, we use high-resolution interferometric scattering microscopy to reveal that myosin takes strides spanning 22 to 34 actin subunits, despite walking straight along the helical actin filament. We show that cumulative angular disorder in F-actin accounts for the observed proportion of each stride length, akin to crossing a river on variably spaced stepping stones. Electron microscopy revealed the structure of the stepping molecule. Our results indicate that both motor and track are soft materials that can adapt to function in complex cellular conditions.

Exploring the Super-Relaxed State of Human Cardiac ß-Myosin by Molecular Dynamics Simulations.

Human ß-cardiac myosin plays a critical role in generating the mechanical forces necessary for cardiac muscle contraction. This process relies on a delicate dynamic equilibrium between the disordered relaxed state (DRX) and the super-relaxed state (SRX) of myosin. Disruptions in this equilibrium due to mutations can lead to heart diseases. However, the structural characteristics of SRX and the molecular mechanisms underlying pathogenic mutations have remained elusive. To bridge this gap, we conducted molecular dynamics simulations and free energy calculations to explore the conformational changes in myosin. Our findings indicate that the size of the phosphate-binding pocket can serve as a valuable metric for characterizing the transition from the DRX to SRX state. Importantly, we established a global dynamic coupling network within the myosin motor head at the residue level, elucidating how the pathogenic mutation E483K impacts the equilibrium between SRX and DRX through allosteric effects. Our work illuminates molecular details of SRX and offers valuable insights into disease treatment through the regulation of SRX.