The titin N2A-MARP signalosome constrains muscle longitudinal hypertrophy in response to stretch.

Titin-based mechanosensing is a key driver of trophic signaling in muscle, yet the downstream pathways linking titin sensing to muscle remodeling remain poorly understood. To investigate these signaling mechanisms, we utilized unilateral diaphragm denervation (UDD), an in vivo model that induces titin-stiffness-dependent hypertrophy via mechanical stretch. Using UDD in rats and mice, we characterized the longitudinal hypertrophic response and distinguished stretch-induced signaling from denervation effects by performing global transcriptomic and proteomic analyses following UDD and bilateral diaphragm denervation (BDD) in rats.

Glycerol storage increases passive stiffness of muscle fibers through effects on titin extensibility.

To study the physiological and pathological mechanisms of muscle, it is crucial to store muscle samples in ways that preserve their properties. Glycerol is commonly used for storage, as it stabilizes muscle proteins, slows enzymatic activity, and minimizes degradation. However, previous studies validating glycerol storage have not examined its effects on passive properties.

An ovary-intact postmenopausal HFpEF mouse model; menopause is more than just estrogen deficiency.

The incidence of heart failure with preserved ejection fraction (HFpEF) in women significantly increases following menopause. This trend cannot solely be attributed to chronological aging, as evidenced by the more gradual increase in prevalence among men, suggesting that menopause is a provocative event for HFpEF. However, the underlying mechanisms remain elusive and challenging to investigate in human subjects; moreover, an attempt to create HFpEF in ovariectomized (OVX) mice was unsuccessful.

Importance of N2BA Titin in Maintaining Cardiac Homeostasis and Its Role in Dilated Cardiomyopathy.

Background: TTN (titin) is the third myofilament type of the cardiac sarcomere and performs important functions that include generating passive tension. Changes in TTN expression are associated with cardiac dysfunction, and TTN is one of the main genes linked to dilated cardiomyopathy (DCM). DCM is frequently associated with changes in the expression of N2BA (compliant cardiac TTN isoform), 1 of the 2 major TTN isoforms found in the heart (the other isoform being the N2B [stiff cardiac TTN isoform]).

Pathomechanisms of Monoallelic variants in TTN causing skeletal muscle disease.

Pathogenic variants in the titin gene (TTN) are known to cause a wide range of cardiac and musculoskeletal disorders, with skeletal myopathy mostly attributed to biallelic variants. We identified monoallelic truncating variants (TTNtv), splice site or internal deletions in TTN in probands with mild, progressive axial and proximal weakness, with dilated cardiomyopathy frequently developing with age. These variants segregated in an autosomal dominant pattern in 7 out of 8 studied families.

Characterization of NEB pathogenic variants in patients reveals novel nemaline myopathy disease mechanisms and omecamtiv mecarbil force effects.

Nebulin, a critical protein of the skeletal muscle thin filament, plays important roles in physiological processes such as regulating thin filament length (TFL), cross-bridge cycling, and myofibril alignment. Pathogenic variants in the nebulin gene (NEB) cause NEB-based nemaline myopathy (NEM2), a genetically heterogeneous disorder characterized by hypotonia and muscle weakness, currently lacking curative therapies. In this study, we examined a cohort of ten NEM2 patients, each with unique pathogenic variants, aiming to understand their impact on mRNA, protein, and functional levels.

Titin's cardiac-specific N2B element is critical to mechanotransduction during volume overload of the heart.

The heart has the ability to detect and respond to changes in mechanical load through a process called mechanotransduction. In this study, we focused on investigating the role of the cardiac-specific N2B element within the spring region of titin, which has been proposed to function as a mechanosensor. To assess its significance, we conducted experiments using N2B knockout (KO) mice and wildtype (WT) mice, subjecting them to three different conditions: 1) cardiac pressure overload induced by transverse aortic constriction (TAC), 2) volume overload caused by aortocaval fistula (ACF), and 3) exercise-induced hypertrophy through swimming.

Comprehensive phenotypic characterization of an allelic series of zebrafish models of NEB-related nemaline myopathy.

Nemaline myopathy (NM) is a rare congenital neuromuscular disorder characterized by muscle weakness and hypotonia, slow gross motor development, and decreased respiratory function. Mutations in at least twelve genes, all of each encode proteins that are either components of the muscle thin filament or regulate its length and stability, have been associated with NM. Mutations in Nebulin (NEB), a giant filamentous protein localized in the sarcomere, account for more than 50% of NM cases.

Characterization of mutations in patients reveals novel nemaline myopathy disease mechanisms and omecamtiv mecarbil force effects.

Nebulin, a critical protein of the skeletal muscle thin filament, plays important roles in physiological processes such as regulating thin filament length (TFL), cross-bridge cycling, and myofibril alignment. Mutations in the nebulin gene ( ) cause NEB-based nemaline myopathy (NEM2), a genetically heterogeneous disorder characterized by hypotonia and muscle weakness, currently lacking therapies targeting the underlying pathological mechanisms. In this study, we examined a cohort of ten NEM2 patients, each with unique mutations, aiming to understand their impact on mRNA, protein, and functional levels.

RBM20 mutation is a high genetic risk factor for premature death through RNA-protein condensates.

Dilated cardiomyopathy (DCM) is a heritable and genetically heterogenous disease often idiopathic and a leading cause of heart failure with high morbidity and mortality. DCM caused by RNA binding motif protein 20 (RBM20) mutations is diverse and needs a more complete mechanistic understanding. RBM20 mutation S637G (S639G in mice) is linked to severe DCM and early death in human patients.

The number of Z-repeats and super-repeats in nebulin greatly varies across vertebrates and scales with animal size.

Nebulin is a skeletal muscle protein that associates with the sarcomeric thin filaments and has functions in regulating the length of the thin filament and the structure of the Z-disk. Here we investigated the nebulin gene in 53 species of birds, fish, amphibians, reptiles, and mammals. In all species, nebulin has a similar domain composition that mostly consists of ∼30-residue modules (or simple repeats), each containing an actin-binding site.

Nebulin and Lmod2 are critical for specifying thin-filament length in skeletal muscle.

Regulating the thin-filament length in muscle is crucial for controlling the number of myosin motors that generate power. The giant protein nebulin forms a long slender filament that associates along the length of the thin filament in skeletal muscle with functions that remain largely obscure. Here nebulin's role in thin-filament length regulation was investigated by targeting entire super-repeats in the gene; nebulin was either shortened or lengthened by 115 nm.

Titin splicing regulates cardiotoxicity associated with calpain 3 gene therapy for limb-girdle muscular dystrophy type 2A.

Limb-girdle muscular dystrophy type 2A (LGMD2A or LGMDR1) is a neuromuscular disorder caused by mutations in the calpain 3 gene (). Previous experiments using adeno-associated viral (AAV) vector-mediated calpain 3 gene transfer in mice indicated cardiac toxicity associated with the ectopic expression of the calpain 3 transgene. Here, we performed a preliminary dose study in a severe double-knockout mouse model deficient in calpain 3 and dysferlin.

Fine mapping titin's C-zone: Matching cardiac myosin-binding protein C stripes with titin's super-repeats.

Titin is largely comprised of serially-linked immunoglobulin (Ig) and fibronectin type-III (Fn3) domains. Many of these domains are arranged in an 11 domain super-repeat pattern that is repeated 11 times, forming the so-named titin C-zone in the A-band region of the sarcomere. Each super-repeat is thought to provide binding sites for thick filament proteins, such as cMyBP-C (cardiac myosin-binding protein C).

Downsizing the molecular spring of the giant protein titin reveals that skeletal muscle titin determines passive stiffness and drives longitudinal hypertrophy.

Unlabelled: Titin, the largest protein known, forms an elastic myofilament in the striated muscle sarcomere. To establish titin's contribution to skeletal muscle passive stiffness, relative to that of the extracellular matrix, a mouse model was created in which titin's molecular spring region was shortened by deleting 47 exons, the model. RNA sequencing and super-resolution microscopy predicts a much stiffer titin molecule.

Plant responses to Agrobacterium tumefaciens and crown gall development.

Agrobacterium tumefaciens causes crown gall disease on various plant species by introducing its T-DNA into the genome. Therefore, Agrobacterium has been extensively studied both as a pathogen and an important biotechnological tool. The infection process involves the transfer of T-DNA and virulence proteins into the plant cell.

DNA methylation mediated control of gene expression is critical for development of crown gall tumors.

Crown gall tumors develop after integration of the T-DNA of virulent Agrobacterium tumefaciens strains into the plant genome. Expression of the T-DNA-encoded oncogenes triggers proliferation and differentiation of transformed plant cells. Crown gall development is known to be accompanied by global changes in transcription, metabolite levels, and physiological processes.

Regulation of plant cytosolic glyceraldehyde 3-phosphate dehydrogenase isoforms by thiol modifications.

Cytosolic NAD-dependent glyceraldehyde 3-P dehydrogenase (GAPDH; GapC; EC 1.2.1.