Possible Role of Non-Muscle Alpha-Actinins in Muscle Cell Mechanosensitivity

Abstract

The main hypothesis suggested that changes in the external mechanical load would lead to different deformations of the submembranous cytoskeleton and, as a result, dissociation of different proteins from its structure (induced by increased/decreased mechanical stress). The study subjects were fibers of the soleus muscle and cardiomyocytes of Wistar rats. Changes in external mechanical conditions were reconstructed by means of antiorthostatic suspension of the animals by their tails for 6, 12, 18, 24 and 72 hours. Transversal stiffness was measured by atomic force microscopy imaging; beta-, gamma-actin, alpha-actinin 1 and alpha-actinin 4 levels in membranous and cytoplasmic fractions were quantified by Western blot analysis; expression rates of the corresponding genes were studied using RT-PCR. Results: In 6 hours, alpha-actinin 1 and alpha-actinin 4 levels decreased in the membranous fraction of proteins of cardiomyocytes and soleus muscle fibers, respectively, but increased in the cytoplasmic fraction of the abovementioned cells. After 6–12 hours of suspension, the expression rates of beta-, gamma-actin, alpha-actinin 1 and alpha-actinin 4 were elevated in the soleus muscle fibers, but the alpha-actinin 1 expression rate returned to the reference level in 72 hours. After 18–24 hours, the expression rates of beta-actin and alpha-actinin 4 increased in cardiomyocytes, while the alpha-actinin 1 expression rate decreased in soleus muscle fibers. After 12 hours, the beta- and gamma-actin content dropped in the membranous fraction and increased in the cytoplasmic protein fractions from both cardiomyocytes and soleus muscle fibers. The stiffness of both cell types decreased after the same period of time. Further, during the unloading period the concentration of nonmuscle actin and different isoforms of alpha-actinins increased in the membranous fraction from cardiomyocytes. At the same time, the concentration of the abovementioned proteins decreased in the soleus muscle fibers.

Loss of melusin is a novel, neuronal NO synthase/FoxO3‐independent master switch of unloading‐induced muscle atrophy

“…Although both nNOS and melusin are costamere proteins, unloading‐induced, mitochondrial‐derived oxidative stress initiates nNOS redistribution in the sarcoplasm, whereas it does not appear involved in melusin protein decrease. A short unloading bout induces also disorganization in the lipid‐ordered phase of sarcolemma, detachment of cytoskeletal components, such as the non‐muscle α‐actinin isoform 4, and loss of function of α 2 Na‐K‐ATPase pump . It remains to be determined whether any of these unloading‐induced perturbations would act upstream or downstream melusin loss from costameres and catabolism.…”

The Development Of Drosophila Melanogaster under Different Duration Space Flight and Subsequent Adaptation to Earth Gravity

“…Our results corroborate our previous results obtained from mice in model experiments and after the space flight of the Bion-M1 biological satellite (2013, Russia); the increase in the external mechanical stress (gravity) decreases the alpha-actinin-1 content (leading to the reduced content of another isoform, alpha-actinin-4) in the membrane fraction of proteins and an increase in the cytoplasmic fraction after 6 hours, subsequent (after 12 hours) to the reduced expression of the corresponding gene level [25,26,27,28,29]. These results allowed us to assume that different deformations of the cortical cytoskeleton are the primary mechanical sensor of the increase and decrease in the external mechanical stress, resulting in the separation of various actin-binding proteins and, consequently, the triggering of different signalling pathways [30].…”

Modeling of the Primary Acts of the Interaction between a Cell and an External Mechanical Field

“…We consider the actin-binding proteins alpha-actinin-4 and alpha-actinin-1 as a "sensitive" protein and its antagonist, respectively, and beta-actin as a protein of microfilaments of the submembrane cytoskeleton because its content dominates over the content of gamma-actin in this cell type [28] (Figure 1(a)).…”

“…However, these strains are fundamentally different with increasing and decreasing loads. The first result is the dissociation of various actin-binding proteins from the cortical cytoskeleton: alpha-actinin-4 with a load decrease and alpha-actinin-1 with an increase [10] [27] [28]. With further development of this process, the deformation leads to the destruction of the structure and, at subsequent early stages of exposure, to an initial decrease in stiffness, which correlates with the content of actin non-muscle isoforms in the membrane fraction, which form the cortical cytoskeleton [29].…”