Network Of Muscle Cells Research Articles

Mechanical Loading Modulates AMPK and mTOR Signaling in Muscle Cells.

Skeletal muscle adaptation to exercise involves various phenotypic changes that enhance the metabolic and contractile functions. One key regulator of these adaptive responses is the activation of AMPK, which is influenced by exercise intensity. However, the mechanistic understanding of AMPK activation during exercise remains incomplete. In this study, we utilized an in vitro model to investigate the effects of mechanical loading on AMPK activation and its interaction with the mTOR signaling pathway. Proteomic analysis of muscle cells subjected to static loading (SL) revealed distinct quantitative protein alterations associated with RNA metabolism, with 10% SL inducing the most pronounced response compared to lower intensities of 5% and 2% as well as the control. Additionally, 10% SL suppressed RNA and protein synthesis while activating AMPK and inhibiting the mTOR pathway. We also found that SRSF2, necessary for pre-mRNA splicing, is regulated by AMPK and mTOR signaling, which, in turn, is regulated in an intensity-dependent manner by SL with the highest expression in 2% SL. Further examination showed that the ADP/ATP ratio was increased after 10% SL compared to the control and that SL induced changes in mitochondrial biogenesis. Furthermore, Seahorse assay results indicate that 10% SL enhances mitochondrial respiration. These findings provide novel insights into the cellular responses to mechanical loading and shed light on the intricate AMPK-mTOR regulatory network in muscle cells.

Caenorhabditis elegans SORB-1 localizes to integrin adhesion sites and is required for organization of sarcomeres and mitochondria in myocytes.

We have identified and characterized sorb-1, the only sorbin and SH3 domain-containing protein family member in Caenorhabditis elegans SORB-1 is strongly localized to integrin adhesion complexes in larvae and adults, including adhesion plaques and dense bodies (Z-disks) of striated muscles and attachment plaques of smooth muscles. SORB-1 is recruited to the actin-binding, membrane-distal regions of dense bodies via its C-terminal SH3 domains in an ATN-1(α-actinin)- and ALP-1(ALP/Enigma)-dependent manner, where it contributes to the organization of sarcomeres. SORB-1 is also found in other tissues known to be under mechanical stress, including stress fibers in migratory distal tip cells and the proximal gonad sheath, where it becomes enriched in response to tissue distention. We provide evidence for a novel role for sorbin family proteins: SORB-1 is required for normal positioning of the mitochondrial network in muscle cells. Finally, we demonstrate that SORB-1 interacts directly with two other dense body components, DEB-1(vinculin) and ZYX-1(zyxin). This work establishes SORB-1 as a bona fide sorbin family protein-one of the late additions to the dense body complex and a conserved regulator of body wall muscle sarcomere organization and organelle positioning.

Whole heart modeling - Spatiotemporal dynamics of electrical wave conduction and propagation.

Cardiac electrical activities are varying in both space and time. Human heart consists of a fractal network of muscle cells, Purkinje fibers, arteries and veins. Whole-heart modeling of electrical wave conduction and propagation involves a greater level of complexity. Our previous work developed a computer model of the anatomically realistic heart and simulated the electrical conduction with the use of cellular automata. However, simplistic assumptions and rules limit its ability to provide an accurate approximation of real-world dynamics on the complex heart surface, due to sensitive dependence of nonlinear dynamical systems on initial conditions. In this paper, we propose new reaction-diffusion methods and pattern recognition tools to simulate and model spatiotemporal dynamics of electrical wave conduction and propagation on the complex heart surface, which include (i) whole heart model; (ii) 2D isometric graphing of 3D heart geometry; (iii) reaction-diffusion modeling of electrical waves in 2D graph, and (iv) spatiotemporal pattern recognition. Experimental results show that the proposed numerical solution has strong potentials to model the space-time dynamics of electrical wave conduction in the whole heart, thereby achieving a better understanding of disease-altered cardiac mechanisms.

Testis follicles ultrastructure of three species of terrestrial isopods (Crustacea, Isopoda Oniscidea).

The aim of the research, carried out on three species of terrestrial isopods - Armadillidium granulatum, Halophiloscia hirsuta and Trichoniscus alexandrae - is to bring a first consistent contribution to the knowledge of the ultrastructural organization of the testis follicles. The testis follicles are seat of a remarkable dynamic activity of their cell components (somatic cells and germ cells) that results in a continuous variation, related to the trend of spermatogenesis, of their morphology, organization and of the relationships between the two cell populations. The somatic cells, known in literature as follicular cells, nurse cells or Sertoli cells, are arranged at the periphery of the follicle to form an epithelial layer of variable thickness resting on a thin basal lamina in turn surrounded by a discontinuous network of muscle cells. In A. granulatum and H. hirsuta, two types of Sertoli cells are present: a first type, the nurse cells, envelop the spermatids in cavities within their cytoplasm and through their secretion activity play a fundamental role in the formation of the spermatophores; moreover, they phagocytizes the residual cytoplasm of spermatids. A second type of Sertoli cells shows features that leave clearly identify its supporting role to the spermatophores in formation. In T. alexandrae, instead, only one type of Sertoli cells, the nurse cell, is present, whose features are widely superimposable to those observed in the other two species. Moreover, two septa of Sertoli cells depart from the periphery of the testis follicle to constitute an articulated compartmentalization of the follicle itself, probably targeted to realize at its inside a series of microenvironments functionally diversified in order to meets the needs of the different stages of the spermatogenic cycle.

Cyclic stretch reveals a mechanical role for intermediate filaments in a desminopathic cell model

Mechanics is now recognized as crucial in cell function. To date, the mechanical properties of cells have been inferred from experiments which investigate the roles of actin and microtubules ignoring the intermediate filaments (IFs) contribution. Here, we analyse myoblasts behaviour in the context of myofibrillar myopathy resulting from p.D399Y desmin mutation which disorganizes the desmin IF network in muscle cells. We compare the response of myoblasts expressing either mutated or wild-type desmin to cyclic stretch. Cells are cultivated on supports submitted to periodic uniaxial stretch of 20% elongation amplitude and 0.3 Hz frequency. We show that during stretching cycles, cells expressing mutated desmin reduce their mean amplitude both for the elongation and spreading area compared to those expressing wild-type desmin. Even more unexpected, the reorientation angles are altered in the presence of p.D399Y desmin. Yet, at rest, the whole set of those parameters are similar for the two cell populations. Thus, we demonstrate that IFs affect the mechanical properties and the dynamics of cell reorientation. Since these processes are known due to actin cytoskeleton, these results suggest the IFs implication in mechanics signal transduction. Further studies may lead to better understanding of their contribution to this process.

Circumferential alignment of muscle cells in the tunica media of the human brain artery.

Our purpose was to measure how structurally coordinated is the network of muscle cells in the brain artery. Vessels from 7 autopsies were fixed with glutaraldehyde and formalin at physiologic pressure. We embedded each artery alongside a block of liver, formed into a rectangular prism, prepared it for light microscopy and stained the sections with haematoxylin and eosin (HE). The angle of cutting the arterial segments was determined with the aid of the block of liver tissue as a Cartesian reference. We measured the directional alignment of vascular smooth muscle using the centrally located nucleus as a vector of orientation. The end coordinates of the profiles of the nuclei (appearing dark with the HE stain) were recorded on a digitizer tablet, and analysis was done as suggested by a previous modelling study. The method provides an average alignment from the collective measurements on the hundreds of nuclei in each histological section. Data from 10 arteries (approximately 22,000 nuclei) from 17 sections showed that brain arteries have highly oriented medial muscle cells aligned circumferentially (average magnitude of 1.3 +/- [SD] 1.5 degrees from true cross section), with a helical variation (along the artery) of +/- 7.9 degrees and a variation in the spiral direction of +/- 5.4 degrees, i.e. a three-dimensional variation from nucleus to nucleus of +/- 10 degrees.

The Structure and Function of the Cutaneous Glands in Helix aspersa

ABSTRACT The glands discharging ‘slime’ on to the surface of the mantle collar and foot of Helix aspersa have been investigated histologically and histochemically on chemically fixed and frozen-dried material. All the glands are unicellular; they lie in the connective tissue and discharge by pores passing between the epidermal cells; some are club-shaped, others are polygonal with a distinct and usually long duct. At least 8 different kinds of gland are found: 4 extruding various kinds of mucus, one protein, one calcium carbonate granules, one a pigmented secretion containing a flavone, and one releasing fatglobules. The histology of the mantle collar is very similar to that of the dorsal and lateral surfaces of the foot except that the glands in the mantle are usually larger. All kinds of secretion are extruded from these parts. The glands of the sole of the foot are mostly of a distinct kind and produce mucus combined with protein. The mechanism of discharge is discussed: some of the gland cells are enclosed in a network of muscle-fibres which are thought to be concerned in the removal of the secretion, in other cases no fibres have been found and it seems likely that changes in pressure in the haemocoel are involved. The composition of the slime changes from colourless and viscous to yellow and watery when the animal is irritated. It is usually slightly alkaline, is not distasteful to man, and does not inhibit the growth of micro-organisms. The mucous component acts as a lubricant, and on the sole for adhesion. The calcium carbonate granules and the protein may be concerned in defence, while the flavone is a waste-product varying with the amount of green food eaten. The epiphragm is formed by the secretion of part of the mantle collar and is probably dissolved away by a protein-splitting enzyme which has been demonstrated in the slime.