Nuances of electrophoresis study of titin/connectin

Identification of Giant Isoforms of Obscurin in Rat Striated Muscles Using Polyclonal Antibodies

Using produced polyclonal antibodies specific to the N-terminal sequence (residues 61-298) of rat obscurin, we investigated the isoform composition of this protein in 4 striated muscles: myocardium of the left ventricle, diaphragm, skeletal m. gastrocnemius (containing mainly fast fibers), and m. soleus (containing mainly slow fibers). The m. gastrocnemius, m. soleus, and diaphragm were found to have 2 giant isoforms of obscurin: a smaller A-isoform and a larger B-isoform. Their molecular weights were ~870 and ~1150 kDa in the diaphragm and m. gastrocnemius and ~880 and ~1130 kDa in m. soleus, respectively. The B-isoform to A-isoform ratio was 1:3 in the diaphragm and m. soleus and 1:4 in the m. gastrocnemius. In the left-ventricular myocardium, A-isoform of obscurin with a molecular weight of ~880 kDa was found. No other obscurin isoforms or their fragments within the molecular weight range of 10 up to ~800 kDa were revealed in the investigated rat striated muscles. The antibodies produced are recommended for research into qualitative and quantitative changes of giant obscurin isoforms in rat striated muscles in the norm and during the development of pathological processes.

Changes in the Mechanical Properties of Fast and Slow Skeletal Muscle after 7 and 21 Days of Restricted Activity in Rats

Disuse muscle atrophy is usually accompanied by changes in skeletal muscle structure, signaling, and contractile potential. Different models of muscle unloading can provide valuable information, but the protocols of experiments with complete immobilization are not physiologically representative of a sedentary lifestyle, which is highly prevalent among humans now. In the current study, we investigated the potential effects of restricted activity on the mechanical characteristics of rat postural (soleus) and locomotor (extensor digitorum longus, EDL) muscles. The restricted-activity rats were kept in small Plexiglas cages (17.0 × 9.6 × 13.0 cm) for 7 and 21 days. After this, soleus and EDL muscles were collected for ex vivo mechanical measurements and biochemical analysis. We demonstrated that while a 21-day movement restriction affected the weight of both muscles, in soleus muscle we observed a greater decrease. The maximum isometric force and passive tension in both muscles also significantly changed after 21 days of movement restriction, along with a decrease in the level of collagen 1 and 3 mRNA expression. Furthermore, the collagen content itself changed only in soleus after 7 and 21 days of movement restriction. With regard to cytoskeletal proteins, in our experiment we observed a significant decrease in telethonin in soleus, and a similar decrease in desmin and telethonin in EDL. We also observed a shift towards fast-type myosin heavy chain expression in soleus, but not in EDL. In summary, in this study we showed that movement restriction leads to profound specific changes in the mechanical properties of fast and slow skeletal muscles. Future studies may include evaluation of signaling mechanisms regulating the synthesis, degradation, and mRNA expression of the extracellular matrix and scaffold proteins of myofibers.

Calpain-dependent degradation of cytoskeletal proteins as a key mechanism for a reduction in intrinsic passive stiffness of unloaded rat postural muscle

In mammals, prolonged mechanical unloading results in a significant decrease in passive stiffness of postural muscles. The nature of this phenomenon remains unclear. The aim of the present study was to investigate possible causes for a reduction in rat soleus passive stiffness after 7 and 14 days of unloading (hindlimb suspension, HS). We hypothesized that HS-induced decrease in passive stiffness would be associated with calpain-dependent degradation of cytoskeletal proteins or a decrease in actomyosin interaction. Wistar rats were subjected to HS for 7 and 14 days with or without PD150606 (calpain inhibitor) treatment. Soleus muscles were subjected to biochemical analysis and ex vivo measurements of passive tension with or without blebbistatin treatment (an inhibitor of actomyosin interactions). Passive tension of isolated soleus muscle was significantly reduced after 7- and 14-day HS compared to the control values. PD150606 treatment during 7- and 14-day HS induced an increase in alpha-actinin-2 and -3, desmin contents compared to control, partly prevented a decrease in intact titin (T1) content, and prevented a decrease in soleus passive tension. Incubation of soleus muscle with blebbistatin did not affect HS-induced reductions in specific passive tension in soleus muscle. Our study suggests that calpain-dependent breakdown of cytoskeletal proteins, but not a change in actomyosin interaction, significantly contributes to unloading-induced reductions in intrinsic passive stiffness of rat soleus muscle.

NOS-dependent effects of plantar mechanical stimulation on mechanical characteristics and cytoskeletal proteins in rat soleus muscle during hindlimb suspension

The study was aimed at investigating the mechanisms and structures which determine mechanical properties of skeletal muscles under gravitational unloading and plantar mechanical stimulation (PMS). We hypothesized that PMS would increase NO production and prevent an unloading-induced reduction in skeletal muscle passive stiffness. Wistar rats were hindlimb suspended and subjected to a daily PMS and one group of stimulated animals was also treated with nitric oxide synthase (NOS) inhibitor (L-NAME). Animals received mechanical stimulation of the feet for 4 h a day throughout 7-day hindlimb suspension (HS) according to a scheme that mimics the normal walking of the animal. Seven-day HS led to a significant reduction in soleus muscle weight by 25%. However, PMS did not prevent the atrophic effect induced by HS. Gravitational unloading led to a significant decrease in maximum isometric force and passive stiffness by 38% and 31%, respectively. The use of PMS prevented a decrease in the maximum isometric strength of the soleus muscle. At the same time, the passive stiffness of the soleus in the PMS group significantly exceeded the control values by 40%. L-NAME (NOS inhibitor) administration attenuated the effect of PMS on passive stiffness and maximum force of the soleus muscle. The content of the studied cytoskeletal proteins (α-actinin-2, α-actinin-3, desmin, titin, nebulin) decreased after 7-day HS, but this decrease was successfully prevented by PMS in a NOS-dependent manner. We also observed significant decreases in mRNA expression levels of α-actinin-2, desmin, and titin after HS, which was prevented by PMS. The study also revealed a significant NOS-dependent effect of PMS on the content of collagen-1a, but not collagen-3a. Thus, PMS during mechanical unloading is able to maintain soleus muscle passive tension and force as well as mRNA transcription and protein contents of cytoskeletal proteins in a NOS-dependent manner.

Amyloid Aggregates of Smooth-Muscle Titin Impair Cell Adhesion

Various amyloid aggregates, in particular, aggregates of amyloid β-proteins, demonstrate in vitro and in vivo cytotoxic effects associated with impairment of cell adhesion. We investigated the effect of amyloid aggregates of smooth-muscle titin on smooth-muscle-cell cultures. The aggregates were shown to impair cell adhesion, which was accompanied by disorganization of the actin cytoskeleton, formation of filopodia, lamellipodia, and stress fibers. Cells died after a 72-h contact with the amyloid aggregates. To understand the causes of impairment, we studied the effect of the microtopology of a titin-amyloid-aggregate-coated surface on fibroblast adhesion by atomic force microscopy. The calculated surface roughness values varied from 2.7 to 4.9 nm, which can be a cause of highly antiadhesive properties of this surface. As all amyloids have the similar structure and properties, it is quite likely that the antiadhesive effect is also intrinsic to amyloid aggregates of other proteins. These results are important for understanding the mechanisms of the negative effect of amyloids on cell adhesion.

Predominant synthesis of giant myofibrillar proteins in striated muscles of the long-tailed ground squirrel Urocitellus undulatus during interbout arousal

Molecular mechanisms underlying muscle-mass retention during hibernation have been extensively discussed in recent years. This work tested the assumption that protein synthesis hyperactivation during interbout arousal of the long-tailed ground squirrel Urocitellus undulatus should be accompanied by increased calpain-1 activity in striated muscles. Calpain-1 is known to be autolysed and activated in parallel. Western blotting detected increased amounts of autolysed calpain-1 fragments in the heart (1.54-fold, p < 0.05) and m. longissimus dorsi (1.8-fold, p < 0.01) of ground squirrels during interbout arousal. The total protein synthesis rate determined by SUnSET declined 3.67-fold in the heart (p < 0.01) and 2.96-fold in m. longissimus dorsi (p < 0.01) during interbout arousal. The synthesis rates of calpain-1 substrates nebulin and titin in muscles did not differ during interbout arousal from those in active summer animals. A recovery of the volume of m. longissimus dorsi muscle fibres, a trend towards a heart-muscle mass increase and a restoration of the normal titin content (reduced in the muscles during hibernation) were observed. The results indicate that hyperactivation of calpain-1 in striated muscles of long-tailed ground squirrels during interbout arousal is accompanied by predominant synthesis of giant sarcomeric cytoskeleton proteins. These changes may contribute to muscle mass retention during hibernation.

High-yield skeletal muscle protein recovery from TRIzol after RNA and DNA extraction

Extraction of DNA, RNA and protein from the same sample would allow for direct comparison of genomic, transcriptomic and proteomic information. Commercially available kits exhibit poor protein yield and the TRIzol^® reagent produces a protein pellet that is extremely difficult to solubilize. In response to these limitations, this study presents an optimized method for the extraction of protein from the organic phase of TRIzol that allows for higher yield recovery of skeletal muscle protein compared with direct homogenization in a common protein lysis buffer. The presented method is inexpensive, simple and fast, requires no additional treatment of the protein pellet for dissolution, and is compatible with downstream western blot applications.

Scientists analyze DNA, RNA and protein using separate kits and techniques that do not allow for effective analysis of all three macromolecules from the same sample. Simultaneous extraction kits and techniques are limited by poor protein yield after nucleic acid isolation. We present a fast, effective, inexpensive and high-yield method of recovering protein (including large proteins such as titin) from tissue using the TRIzol reagent after RNA and DNA recovery.

The method of high-yield protein extraction from TRIzol after RNA and DNA isolation involves replacing chloroform with bromochloropropane. Instead of producing a tightly packed protein pellet using isopropanol, the protein in the organic phase is precipitated using ethanol and water. Complete dissolution of the resulting protein pellet is achieved using a sodium dodecyl sulfate-urea buffer that allows solubilization of large protein species.

[Early changes of energy metabolism, isoformic content and level of titin phosphorylation at diastolic dysfunction]

RELEVANCE

 Diastolic dysfunction occurring at hypertension, obesity, diabetes, or treatment with doxorubicin tends to prevail in all patterns of chronic heart failure. Lack of effective therapy forces to look more into the metabolic processes in cardiomyocytes.

OBJECTIVE

 Assess energy metabolism in cardiomyocytes and changes in titin, a giant myofibril protein that responsible for their elasticity.

MATERIAL AND METHODS

 The study model was cardiomyopathy occurring after the 4-week administration of doxorubicin (2 mg/kg weekly). Diastolic dysfunction was identified by echocardiography and catheterization with the simultaneous measurement of pressure and volume of the left ventricle (LV).

RESULTS

 The levels of adenine nucleotides and phosphocreatine in the heart of animals treated with doxorubicin differed little from the normal values, but lactate levels were increased manifold. A 50% increase in the level of titin phosphorylation was detected, which correlated (r = 0,94) with a nearly twofold increase in the share of a more elastic N2BA-isoform of this protein.

CONCLUSION

This form of diastolic dysfunction involves the activation of anaerobic metabolism and increased stretching of myofibrils facilitating LV filling.

Effect of L-Arginine on Titin Expression in Rat Soleus Muscle After Hindlimb Unloading

Nitric oxide (NO), produced by NO-synthases via L-arginine oxidation, is an essential trigger for signaling processes involved in structural and metabolic changes in muscle fibers. Recently, it was shown that L-arginine administration prevented the decrease in levels of the muscle cytoskeletal proteins, desmin and dystrophin, in rat soleus muscle after 14 days of hindlimb unloading. Therefore, in this study, we investigated the effect of L-arginine administration on the degree of atrophy changes in the rat soleus muscles under unloading conditions, and on the content, gene expression, and phosphorylation level of titin, the giant protein of striated muscles, able to form a third type of myofilaments—elastic filaments. A 7-day gravitational unloading [hindlimb suspension (HS) group] resulted in a decrease in the soleus weight:body weight ratio (by 31.8%, p < 0.05), indicating muscle atrophy development. The content of intact titin (T1) decreased (by 22.4%, p < 0.05) and the content of proteolytic fragments of titin (T2) increased (by 66.7%, p < 0.05) in the soleus muscle of HS rats, compared to control rats. The titin gene expression and phosphorylation level of titin between these two groups were not significantly different. L-Arginine administration under 7-day gravitational unloading decreased the degree of atrophy changes and also prevented the decrease in levels of T1 in the soleus muscle as compared to HS group. Furthermore, L-arginine administration under unloading resulted in increased titin mRNA level (by 76%, p < 0.05) and decreased phosphorylation level of T2 (by 28%, p < 0.05), compared to those in the HS group. These results suggest that administration of L-arginine, the NO precursor, under unloading decreased the degree of atrophy changes, increased gene expression of titin and prevented the decrease in levels of T1 in the rat soleus muscle. The results can be used to search for approaches to reduce the development of negative changes caused by gravitational unloading in the muscle.

Cellular and molecular signatures of alcohol-induced myopathy in women

Alcoholic myopathy is characterized by the reduction in cross-sectional area (CSA) of muscle fibers and impaired anabolic signaling. The goal of the current study was to investigate the causes and compare the changes in CSA and fiber type composition with the modifications of anabolic and catabolic signaling pathways at the early stages of chronic alcohol consumption in women. Skeletal muscle samples from 5 female patients with alcohol abuse (AL; 43 ± 5 yr old; alcohol abuse duration 5,6 ± 0,6 yr) were compared with the muscle from the control group of 8 healthy women (C; 35 ± 4 yr old). The average daily dose of alcohol consumption was 110 ± 10 ml of pure ethanol. In women patients, a significant decrease in CSA of type I and II muscle fibers, titin and nebulin content, plasma IGF-1 level and total IRS-1, p-Akt and p-4E-BP1 in vastus lateralis was found in comparison with the control group. The p-AMPK level was found to be increased versus the control group. In women patients with chronic alcoholic myopathy 1) both fast and slow muscle fibers are subjected to atrophy; 2) impairments in IGF-I-dependent signaling and pathways controlling translation initiation (AMPK/mTOR/4E-BP1), but not translation elongation, are observed; 3) the level of calpain-1 and ubiquitinated proteins increases, unlike E3 ligases content.