Nonmyocytes may contribute to regional adaptive changes during persistent atrial fibrillation (PsAF), favoring its perpetuation. We aimed to investigate the differential features of fibroblast and macrophage populations within individual-specific atrial regions associated with PsAF maintenance. The study was conducted in 2 pig models of PsAF with and without infarct-related substrate (N=27 and N=27, respectively) and further validated in humans with PsAF (N=20). Sham-operated pigs (N=9), healthy animals (N=4), and patients in sinus rhythm (N=7) were used as comparative controls. In pigs, in vivo high-density instantaneous frequency modulation maps were used to identify atrial regions associated with PsAF maintenance (drivers). Regional cellular composition and phenotypic states of fibroblast and myeloid lineages were determined using flow cytometry, single-cell RNA sequencing, immunohistochemistry, and proteomic analyses. The functional relevance of driver regions was further studied in patients with symptomatic PsAF undergoing ablation. Flow cytometry and single-cell RNA sequencing analyses were performed in tissue samples of the left atrial appendage in a complementary cohort of patients with PsAF undergoing thoracoscopic-guided ablation. PsAF terminated acutely in 12 of 14 pigs undergoing mapping and ablation of driver regions. In humans, driver ablation was associated with 90% AF-freedom (on/off antiarrhythmic drugs) after 2 years of follow-up. Samples from nonablated pigs revealed a phenotypic shift towards ACTA2 (actin alpha 2)-fibroblasts and PTX3 (pentraxin 3)-fibroblasts during PsAF. Although ACTA2-fibroblasts were highly preserved in human samples, paired comparisons in pig samples showed that PTX3-fibroblasts were enriched only in driver regions. PsAF also showed changes in myeloid cells towards inflammatory profiles. However, regional analysis revealed that, in both humans and pigs with PsAF, driver regions were enriched in cardiac resident macrophages with transcriptomic and proteomic profiles favoring cardiomyocyte homeostasis and cell survival. PsAF shows differential regional changes in fibroblast and myeloid populations with distinctive gene signatures in areas that drive the overall arrhythmia.

Many invertebrates have obliquely striated muscles, in which neighboring thin and thick filaments are staggered and aligned obliquely. This type of muscle allows force production over a wide range of lengths and is beneficial for soft-bodied animals. Unlike vertebrate cross-striated muscles, most of obliquely striated muscles lack distinct Z-lines and, instead, have dense bodies. Because the dense bodies are located in the middle of the I-bands and contain α-actinin, the dogma is that dense bodies are equivalent to the Z-lines anchoring the actin barbed ends. However, we show that the barbed ends of sarcomeric actin filaments in the nematode Caenorhabditis elegans body wall muscle are aligned linearly without converging at the dense bodies. Colocalization of F-actin and ATN-1/α-actinin was negatively correlated. CAP-1, an α-subunit of capping protein/CapZ, was linearly aligned without concentration at the dense bodies independently of ATN-1. Depletion of the capping protein subunit, CAP-1 or CAP-2, caused embryonic or larval lethality with severe actin disorganization in muscle, indicating that barbed-end regulation by capping protein is essential for sarcomere assembly. These results contradict the current view of the sarcomere organization in C. elegans muscle and suggest a new model of a linear Z-line-like arrangement of actin barbed ends.

Pseudo-acetylation of ACTC1 K326 and K328 promotes dysinhibition of reconstituted human cardiac thin filaments.

We propose the synchrotron self-Compton (SSC) scenario coupled with a filamentary jet model to reproduce the very-high-energy γ -ray emissions from Cen A. With reference to self-similarity of knot-like features in the jet, we assumed a nonuniform magnetic field associated with current filaments of various transverse sizes. For energetic electron production, the diffusive shock acceleration at sites distributed over the kiloparsec-scale jet was considered. We show that the maximum Lorentz factor of the electron steadily exceeds 10 8 due to suppression of synchrotron loss of the electrons trapped in the weak magnetic field of the thin filaments, and an inhomogeneous SSC scenario in the inner jet can predominantly contribute to establishment of the pronounced hardening of γ -ray flux detected by the High Energy Stereoscopic System (H.E.S.S.). It is also suggested that the spectral contribution from diffuse regions of the outer jet potentially amounts to the observed Fermi fluxes.

Abstract The supernova remnant (SNR) RCW86 is among the few SNRs with Balmer-emission lines containing broad and narrow spectral components that trace fast, nonradiative shocks in partially ionized gas. These are invaluable laboratories for collisionless shock physics, especially for poorly understood phenomena like electron-ion equilibration, and shock precursors. Here we present the first ∼0.3 pc spatial scale integral field unit observations of the southwestern RCW86 shock, obtained as part of the Sloan Digital Sky Survey-V Local Volume Mapper (LVM). The forward shock, clearly visible as thin filaments in narrowband images, exhibits broad component H α emission, indicating shock velocities varying from 500–900 km s −1 in the south to 1000–1500 km s −1 in the north. The varying velocity widths and broad-to-narrow intensity ratios show that electrons and ions have lower equilibration ( T e / T p → 0.1) in faster (>800 km s −1 ) shocks, in line with previous studies. The broad components are generally redshifted from the narrow components by ≲100 km s −1 , likely due to shock-obliquity or non-Maxwellian post-shock distributions. We observe high extinction-corrected Balmer-decrements of 3–5 in the narrow components, indicating that conversion of Ly β photons to H α is more efficient than Ly γ to H β . Upper limits on the He II λ 4686 in the southern shock are consistent with a moderate-to-high (30%–100%) neutral fraction in the preshock gas. We also find the first evidence of an intermediate H α component in RCW86, with ΔV(FWHM) = 193–207 km s −1 , likely due to a fast neutral precursor. We also briefly discuss the southwestern radiative shock, and lay out the exciting future of studying astrophysical shocks with LVM.

The IQGAP protein family-comprising IQGAP1, IQGAP2, and IQGAP3-exhibits structural similarity but fulfils distinct cellular functions. We previously demonstrated that IQGAP1 is recruited to Marburg virus (MARV)-induced inclusion bodies (IBs) and associates with motile nucleocapsids. To further elucidate the roles of IQGAP proteins in the MARV life cycle, we generated Huh-7 cell lines with single, combined, or triple knockouts (KOs) of IQGAP isoforms. Loss of IQGAP proteins consistently reduced cellular permissiveness to MARV infection and impaired multiple key viral processes: (i) transcription and replication efficiency was diminished predominantly by IQGAP3 KO; (ii) virus release was most notably reduced in IQGAP3 KO cells, whereas cell-to-cell spread was more strongly impaired in IQGAP1 KO cells; and (iii) although actin tails continued to form at nucleocapsids in triple KO cells, long distance nucleocapsid transport was altered, with reduced spatial displacement efficiency observed in both IQGAP1 KO and IQGAP3 KO cells. The expression of individual IQGAPs in triple KO cells demonstrated their functionality and ability to partially restore the phenotype of wild-type cells. These findings identify IQGAPs as critical host factors that support MARV transcription/replication, nucleocapsid transport, and viral spread, likely through modulation of actin dynamics.

Abstract Summation-by-Parts Finite-Difference (SBP-FD) methods are widely used to construct stable, high-order accurate spatial discretizations for hydrodynamics and continuum mechanics. This article presents a locally mass-conserving and monotonic SBP-FD scheme for a tracer advection equation in the flux form. Our approach reformulates the SBP-FD spatial discretization in a finite-volume manner, expressing it as the difference of fluxes across grid cell interfaces. These fluxes are limited using the Flux-Corrected Transport (FCT) method. The resulting scheme preserves monotonicity in terms of the tracer specific concentration – the ratio of tracer density to dry air density. Achieving this required modifications to the standard FCT limiter operating on tracer density. The proposed numerical scheme is evaluated using a standard suite of test cases relevant to atmospheric modelling, demonstrating accuracy comparable to state-of-the-art methods. For smooth tracer distributions, the scheme demonstrates second-order accuracy in the ℓ 2 -norm. Strict monotonicity is verified for discontinuous initial conditions and wind fields that severely deform the tracer into thin filaments, including divergent wind fields.

Lmods (leiomodins) are critical for the assembly and maintenance of thin filaments in striated muscles by allowing thin filament elongation at the pointed ends. Lmod2's elongation function has been linked to both actin-binding sites (ABSs) 2 and 3, while the existence and function of an N-terminal ABS1 has been debated. To elucidate the little-known role of Lmod2's ABS1, we created a mutant (F64D/L69D/W72D/W73D: Lmod2-quadruple mutant) predicted to decrease the binding of ABS1 to actin. We analyzed the effect of the mutations using several in vitro, cellular, and in vivo assays. By disrupting the interaction of Lmod2 ABS1 with actin in isolated cardiomyocytes and in mice, we engineered a super Lmod2 that results in remarkably longer thin filaments. Structural analysis determined that ABS1 of Lmod2 binds to actin through a disordered region and an amphipathic α-helix. Analysis of the mutated ABS1 revealed that the helix is destroyed, and binding to actin is maintained only in the N-terminal disordered region of Lmod2 ABS1. These discoveries support a model of controlled thin filament pointed end elongation by Lmod2 and provide the first direct evidence of, as well as the structural and functional mechanistic basis for, Lmod2's physiological leaky cap activity.

ABSTRACT Filaments are crucial components of the cosmic web, representing the extensive and aligned distributions of galaxies and gas. Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), we report the detection of a filament in the Ursa Major supergroup using atomic-hydrogen (H i) observations. This filament consists of sixteen various types of galaxies and five starless gas clumps, spanning a length of approximately 0.9 Mpc. Notably, it is extremely thin, with a thickness comparable to the diameter of a galaxy. We observed a galaxy-filament spin alignment and a velocity gradient within the filament. These findings strongly suggest a cold accretion flow along the filament, potentially contributing to the formation and growth of the galaxies. The thin filament, as a small group, is likely to be merged into the Ursa Major supergroup in the context of hierarchical structure formation.

Functionally relevant protein dynamics monitored by time-resolved quasielastic neutron scattering.

Integrating transcriptomics and network pharmacology to investigate YangxinDingji Capsule alleviates myocardial injury in tachyarrhythmia rat.

We study the behaviour of a thin fluid filament (a rivulet) flowing in an air-filled Hele-Shaw cell. Transverse and longitudinal deformations can propagate on this rivulet, although both are linearly attenuated in the parameter range we use. On this seemingly simple system, we impose an external acoustic forcing, homogeneous in space and harmonic in time. When the forcing amplitude exceeds a given threshold, the rivulet responds nonlinearly, adopting a peculiar pattern. We investigate the dance’ of the rivulet both experimentally using spatiotemporal measurements, and theoretically using a model based on depth-averaged Navier–Stokes equations. The instability is due to a three-wave resonant interaction between waves along the rivulet, the resonance condition fixing the pattern wavelength. Although the forcing is additive, the amplification of transverse and longitudinal waves is effectively parametric, being mediated by the linear response of the system to the homogeneous forcing. Our model successfully explains the mode selection and phase-locking between the waves, it notably allows us to predict the frequency dependence of the instability threshold. The dominant spatiotemporal features of the generated pattern are understood through a multiple-scale analysis.

Abstract Background Paediatric hypertrophic cardiomyopathy (HCM) presents with variable phenotypic expression, influenced by the underlying genetic background. This study aimed to assess genotype-phenotype correlations using cardiac magnetic resonance (CMR) imaging at diagnosis in a cohort of paediatric patients. Methods 126 patients aged ≤18 years with sarcomeric or nonsyndromic familial HCM underwent CMR at diagnosis. Patients were categorized into four groups based on genetic findings: MYBPC3 (n=44), MYH7 (n=47), thin filament variants (TNNT2, TNNI3, or ACTC1) (n=19), and genotype-negative (n=16). Morphological and functional parameters were compared among groups. Results Median age was 12 [IQR 10-15] years without significant difference between genotype (p=0.474). Patients with MYH7 mutations were more frequently obstructive compared to other genotypes (p=0.024). There was a trend towards higher prevalence of late gadolinium enhancement (LGE) in patients with thin filament variants and MYH7 (p=0.078). Genotype-negative patients exhibited higher left ventricular ejection fraction (LVEF) and cardiac output (LVCO) compared to other groups (p=0.017 and p=0.048, respectively). Conversely, patients with MYBPC3 mutations had larger indexed left ventricular end-systolic volume (LVESVi) (p=0.022). Conclusion This study highlights distinct CMR-derived phenotypic differences across genetic subgroups in paediatric HCM. MYH7 mutations were associated with a higher prevalence of left ventricular outflow tract obstruction, thin filament variants with increased fibrosis, while genotype-negative patients had higher LVEF. These findings may contribute to improved risk stratification and tailored management in paediatric HCM.

Cardiac contraction is driven by double-headed myosin cycling on cardiac thin filaments, where troponin-tropomyosin regulates myosin access to actin. Prior research used a single-headed myosin bound to bare actin, thereby limiting insight into coordination between myosin heads and the influence of troponin-tropomyosin on actomyosin interactions. Here, we report a high-resolution structure of the native cardiac rigor cross-bridge formed by heavy meromyosin bound to the thin filament. We show that direct communication between the two bound heads, uneven interactions between the heads and tropomyosin, and spatial constraints imposed by troponin govern myosin placement along the thin filament. Additionally, the two heads display non-equivalent motor-light chain interactions, yielding distinct lever-arm conformations indicative of asymmetric intramolecular strain. Together, these findings provide a structural framework for how the two myosin heads coordinate and how the components of the thin filament are integrated into force generation by active cross-bridges.

Myosin motor-heads projecting from muscle thick filaments interact cyclically with actin-based thin filament tracks, thereby driving inter-filament sliding that powers muscle contraction. Here, controlled recruitment of myosin heads from thick filaments leads pre-powerstroke myosin to bind weakly to actin. Myosin then isomerizes into strongly bound post-powerstroke conformations on actin, thus producing crossbridge motion in active muscles. In striated muscles, this process is regulated by a steric mechanism involving coiled-coil tropomyosin controlling access to myosin-binding sites on actin. Biochemical and structural studies suggest the regulatory mechanism involves tropomyosin occupying three average configurations on the actin thin filament, dependent on Ca2+, troponin, and myosin binding. Once Ca2+-activation of muscle occurs, tropomyosin pivots away from a troponin subunit-I (TnI) imposed B-state (myosin-blocking) position to a C-state position on actin, allowing initial weak myosin-binding to actin. The thin filament reconfiguration only partially relieves tropomyosin-troponin imposed steric inhibition of the myosin binding. However, the initial weak myosin-binding causes further tropomyosin translocation to an M-state position as myosin transitions from its pre-powerstroke to its post-powerstroke conformation, thereby fully activating the thin filament and resulting in contraction. This review summarizes the evolving structural evidence that has accumulated over many years, and which has shaped our current understanding of the troponin-tropomyosin steric regulatory mechanism that governs muscle contractility.

Cardiac thin filament mutations in TNNI3 are associated with up to 3% of hypertrophic (HCM) cardiomyopathy cases and contribute to severe restrictive (RCM) and dilated (DCM) cardiomyopathy caseloads. As such, thin filament cardiomyopathy mediated by TNNI3 mutations is an orphan disease with unmet therapeutic need. Gene therapy is one approach to addressing orphan disease but has been restricted to the repletion of protein deficiency. Based on the best available knowledge, TNNI3 gene therapy has never been applied in the context of a functional mutant protein. Described here is the viral gene therapy rescue at a 4-month endpoint of an experimental murine Tnni3 mutation resulting in slow-onset dilated cardiomyopathy (DCM) with cardiac failure at 12-18months. Mutant mice treated with AAV encoding wild-type (WT) human TNNI3 at 1.0E+14 vg/kG prevented the onset of DCM pathology. This work describes the first adeno-associated virus (AAV) gene therapy replacement of functional mutated Tnni3 protein. The results suggest a broader application of gene therapy for gene replacement.

Striated muscle is composed of overlapping arrays of thick myosin filaments and thin actin filaments. The thick filaments are composed of myosin molecules, which are hexamers of two heavy chains and two pairs of light chains. The heavy chain has an N-terminal head domain and a C-terminal helical rod domain. The latter dimerises to form a two-stranded coiled-coil rod. The distal two-thirds of these rods aggregate in parallel to form the filament backbone, while the heads lie on the surface to facilitate interactions with actin. The molecules aggregate in an antiparallel manner in the centre of the A-band to form the so-called bare zone. The proximal one-third of the rod can swivel and thereby allow the myosin heads to interact with actin. The atomic structure of the head, determined in the 1990s, was a major milestone in the muscle field. Over the next threedecades, great strides were made in cryo-electron microscope technology and software. This led to the high-resolution structure of the insect flight muscle thick filament, showing the structure of the myosin tails at 6Å resolution and the structure of the heads. There has been great excitement recently with the high-resolution structures of relaxed cardiac muscle thick filaments showing details of all the important players: three types of myosin crowns and the paths of their tails, the structure and interactions of cMyBP-C and the structure of two unique forms of titin and its role in filament assembly. Hypertrophic cardiomyopathy, which resultsfrom mutations in sarcomeric proteins, especially myosin and cMyBP-C, is a major health burden and insight gained from the new studies will help to devise new therapies.

Dose-response to lead-induced alterations in right atrial and ventricular myocardial contractility in adult rats.

Cardiac contractility is regulated by the Ca2+ sensitivityof thin filaments, largely controlled by troponin I (TnI). Phosphorylationof TnI at Ser23/24 and the green tea catechin (−)-epigallocatechin-3-gallate(EGCG) both reduce thin filament Ca2+ responsiveness, yetthe underlying structural mechanisms remain incompletely defined.Here, we integrate in vitro motility assays with AlphaFold 3 modelingand molecular dynamics (MD) simulations to characterize the effectsof TnI phosphorylation and EGCG on the troponin complex. Motilityassays using reconstituted thin filaments showed that TnI Ser23/24phosphorylation reduced maximum sliding velocity (Vmax) by −49 ± 7% and shifted pCa50 by −3 ± 2%. EGCG caused a greater decrease in Vmax (−58 ± 8%) and a larger pCa50 shift (−8 ± 4%), consistent with desensitizationto Ca2+ in both cases. Structural models generated viaAlphaFold 3 predict that Ser23/24 phosphorylation induces an α-helicalconformation that repositions the TnI N-terminal extension away fromthe Troponin C (TnC) N-lobe. On/off time analyses from MD simulationsshowed rapid transitions (∼0.18 ps on, ∼0.16 ps off),consistent with transient, functionally meaningful interactions atthe TnI-TnC interface of unphosphorylated TnI. Docking simulationsidentified a probable EGCG binding site at the interface between theTnC C-lobe (residues 120–161) and TnI’s IT-arm and upstreamunstructured region (residues 34–71), stabilized by hydrogenbonds to both subunits. MD simulations revealed recurrent, short-livedhydrogen bonding between TnI and TnC. Together, these findings supportan allosteric desensitization model where phosphorylation modulatesthe TnI-TnC N-lobe interaction, while EGCG binding could modify conformationalchanges at the TnC C-lobe and contigous TnI domains. These insightsmay guide small-molecule design to modulate Ca2+ sensitivityin cardiac disease.

During tetanic contractions of fast motor units (MUs), an early increase in force (boost) is followed by a slight decline to a plateau (sag). This boost is present at the onset of activity but disappears during rhythmically repeated contractions at short intervals; however, it may be restituted after a period of rest. Nevertheless, background of the boost, especially the minimum time required to restore this effect is unknown, and the present study aimed to address this gap. The functional isolation of a single MU was achieved by splitting the L5 or L4 ventral roots into thin filaments, which were electrically stimulated with rectangular electrical pulses. We recorded series of three 504 ms tetanic contractions (triplets) evoked at 35 Hz repeated once per second, with the boost visible in the first tetanus. The triplets were evoked at progressively shorter time intervals, ranging from 90 to 2 s. The boost in successive triplets reduced when the intervals became critically short. The reduction of boost was estimated by the decrease in sag amplitude following the peak force associated with the boost. In fast fatigue-resistant MUs, the sag amplitude decreased by 25% at an average interval of 29.80 s and by 50% at an interval of 16.84 s. For fast fatigable MUs, the interval required to restitute the studied effect was longer: a 25% reduction in sag corresponded to an interval of 82.29 s, and a 50% reduction corresponded to 54.07 s. The results suggest that the physiological basis for the restitution of initial force (boost) is the kinetics of muscle energy status recovery following initial exercise.