Eccentric training enhances the αB-crystallin binding to the myofibrils and prevents skeletal muscle weakness in adjuvant-induced arthritis rat

Skeletal Muscle Heat Shock Protein Content and the Repeated Bout Effect

The "Repeated Bout Effect" (RBE) occurs when a skeletal muscle is preconditioned with a few lengthening contractions (LC) prior to exposing the muscle to a greater number of LC. The preconditioning (PC) results in significantly less damage and preservation of force. Since it takes only a few LC to increase muscle heat shock protein (HSP) content, it was of interest to examine the relationship between HSPs and the RBE. To do this, one tibialis anterior (TA) muscle from Sprague-Dawley rats (n = 5/group) was preconditioned with either 0, 5, or 15 lengthening contractions (LC) and exposed to a treatment of 60 LC 48 h later. Preconditioning TA muscles with 15 LC, but not 5 LC, significantly elevated muscle αB-crystallin (p < 0.05), HSP25 (p < 0.05), and HSP72 content (p < 0.001). These preconditioned TA muscles also showed a significantly (p < 0.05) reduced loss of active torque throughout the subsequent 60 LC. While there was a trend for all preconditioned muscles to maintain higher peak torque levels throughout the 60 LC, no significant differences were detected between the groups. Morphologically, preconditioned muscles appeared to show less discernible muscle fiber damage. In conclusion, an elevated skeletal muscle HSP content from preconditioning may contribute to the RBE.

Desmin and its molecular chaperone, the αB-crystallin: How post-translational modifications modulate their functions in heart and skeletal muscles?

Maintenance of the highly organized striated muscle tissue requires a cell-wide dynamic network through protein-protein interactions providing an effective mechanochemical integrator of morphology and function. Through a continuous and complex trans-cytoplasmic network, desmin intermediate filaments ensure this essential role in heart and in skeletal muscle. Besides their role in the maintenance of cell shape and architecture (permitting contractile activity efficiency and conferring resistance towards mechanical stress), desmin intermediate filaments are also key actors of cell and tissue homeostasis. Desmin participates to several cellular processes such as differentiation, apoptosis, intracellular signalisation, mechanotransduction, vesicle trafficking, organelle biogenesis and/or positioning, calcium homeostasis, protein homeostasis, cell adhesion, metabolism and gene expression. Desmin intermediate filaments assembly requires αB-crystallin, a small heat shock protein. Over its chaperone activity, αB-crystallin is involved in several cellular functions such as cell integrity, cytoskeleton stabilization, apoptosis, autophagy, differentiation, mitochondria function or aggresome formation. Importantly, both proteins are known to be strongly associated to the aetiology of several cardiac and skeletal muscles pathologies related to desmin filaments disorganization and a strong disturbance of desmin interactome. Note that these key proteins of cytoskeleton architecture are extensively modified by post-translational modifications that could affect their functional properties. Therefore, we reviewed in the herein paper the impact of post-translational modifications on the modulation of cellular functions of desmin and its molecular chaperone, the αB-crystallin.

Influence of 4 weeks of downhill running on calcium sensitivity of rat single muscle fibers

Improved Ca2+ sensitivity has been suggested as a mechanism behind enhancements in muscle mechanical function following eccentric training. However, little is known regarding the effects of eccentric training on single muscle fiber Ca2+ sensitivity. Adult male Sprague-Dawley rats (sacrificial age ~18 weeks; mass = 400.1 ± 34.8 g) were assigned to an eccentric training (n = 5) or sedentary control group (n = 6). Eccentric training consisted of 4 weeks of weighted downhill running 3×/week at a 15° decline and 16 m/min for 35 min per day in 5-min bouts. After sacrifice, vastus intermedius single muscle fibers were dissected, chemically permeabilized, and stored until testing. Fibers (n = 63) were isolated, and standard Ca2+ sensitivity, force, rate of force redevelopment (ktr ), and active instantaneous stiffness tests were performed using [Ca2+ ] ranging from 7.0 to 4.5. Following all mechanical testing, fiber type was determined using SDS-PAGE. There was no difference in pCa50 (i.e., [Ca2+ ] needed to elicit half of maximal force) between groups or between fiber types. However, when comparing normalized force across pCa values, fibers from the control group produced greater forces than fibers from the trained group at lower Ca2+ concentrations (p < 0.05), and this was most evident for Type I fibers (p = 0.002). Type II fibers produced faster (p < 0.001) ktr than Type I fibers, but there were no differences in absolute force, normalized force, or other measures of mechanical function between fibers from the trained and control groups. These findings indicate that eccentric training does not appear to improve single muscle fiber Ca2+ sensitivity.

Exercise-driven exacerbation of inflammation: contribution of animal models of rheumatoid arthritis and spondyloarthritis

PURPOSE

To describe the observations of studies that have explored the effects of exercise on inflammation and tissue remodeling in animal models of inflammatory arthropathies including Rheumatoid Arthritis and Spondyloarthritis.

METHODS

A search was performed at Pubmed, Scopus and Web of Science databases from 2010 to 2021. The selected articles were classified into those who reported positive and negative effects of exercise, and the characteristics of their experimental designs, including the animal model, the study groups, the exercise intervention and the evaluation techniques, were detailed.

RESULTS

Thirteen original articles that met the selection criteria were included. The effects of exercise on the joint biology of mice with inflammatory arthritis were controversial. Although exercise benefits have been observed in some experimental designs, the majority of them have shown that exercise leads to exacerbation of inflammation, tissue remodeling, and processes associated with arthritis such as oxidative stress and hypoxia.

CONCLUSION

Further research is necessary as the existing guidelines do not consider the negative effects of the exercise evidenced in animal models. The potential risks of exercise for patients should be considered.

Alpha B-Crystallin in Muscle Disease Prevention: The Role of Physical Activity

HSPB5 or alpha B-crystallin (CRYAB), originally identified as lens protein, is one of the most widespread and represented of the human small heat shock proteins (sHSPs). It is greatly expressed in tissue with high rates of oxidative metabolism, such as skeletal and cardiac muscles, where HSPB5 dysfunction is associated with a plethora of human diseases. Since HSPB5 has a major role in protecting muscle tissues from the alterations of protein stability (i.e., microfilaments, microtubules, and intermediate filament components), it is not surprising that this sHSP is specifically modulated by exercise. Considering the robust content and the protective function of HSPB5 in striated muscle tissues, as well as its specific response to muscle contraction, it is then realistic to predict a specific role for exercise-induced modulation of HSPB5 in the prevention of muscle diseases caused by protein misfolding. After offering an overview of the current knowledge on HSPB5 structure and function in muscle, this review aims to introduce the reader to the capacity that different exercise modalities have to induce and/or activate HSPB5 to levels sufficient to confer protection, with the potential to prevent or delay skeletal and cardiac muscle disorders.

Eccentric Resistance Training Ameliorates Muscle Weakness in a Mouse Model of Idiopathic Inflammatory Myopathies

OBJECTIVE

High-force eccentric contractions (ECCs) have traditionally been excluded from rehabilitation programs that include patients with idiopathic inflammatory myopathies (IIMs) due to unverified fear of causing muscle damage and inflammation. In an IIM animal model that used mice with experimental autoimmune myositis (EAM), we undertook this study to investigate whether ECC training can safely and effectively be used to counteract muscle weakness in IIM.

METHODS

EAM was induced in BALB/c mice by immunization with 3 injections of myosin emulsified in Freund's complete adjuvant. Controls (n = 12) and mice with EAM (n = 12) were exposed to either an acute bout of 100 ECCs or 4 weeks of ECC training (20 ECCs every other day). To induce ECCs, plantar flexor muscles were electrically stimulated while the ankle was forcibly dorsiflexed.

RESULTS

Less cell damage, as assessed by Evans blue dye uptake, was observed in the muscles of mice with EAM, compared to controls, after an acute bout of 100 ECCs (P < 0.05). Maximum Ca²⁺ -activated force was decreased in skinned gastrocnemius muscle fibers from mice with EAM, and this was accompanied by increased expression of endoplasmic reticulum (ER) stress proteins, including Gsp78 and Gsp94 (P < 0.05). ECC training prevented the decrease in force and the increase in ER stress proteins and also enhanced the expression and myofibrillar binding of small heat-shock proteins (HSPs) (P < 0.05), which can stabilize myofibrillar structure and function.

CONCLUSION

ECC training protected against the reduction in myofibrillar force-generating capacity in an IIM mouse model, and this occurred via inhibition of ER stress responses and small HSP-mediated myofibrillar stabilization.

Masseter response to long-term experimentally induced anterior crossbite in Sprague-Dawley rats

OBJECTIVE

To detect the long-term response to unilateral anterior crossbite (UAC) in masticatory muscles and in molecular biomarkers of peripheral blood leukocytes.

DESIGN

Fifty-six six-week-old Sprague-Dawley rats were used. The gene-fold changes in peripheral blood leukocytes were detected by the microarray analysis to compare the rats that received 20-week UAC treatment with age-matched controls (n = 4). Muscle atrophy-related gene Fbxo32 was selected based on the data of the microarray analysis verified by using real-time PCR. The remaining 36 rats were randomly separated in the UAC and control groups at 12 and 20 weeks (n = 12). The protein expression of Fbxo32 and the muscle injury and myogenesis-related markers, αB-crystallin and desmin, were detected in the masseter and lateral pterygoid muscles by western blot assay.

RESULTS

In the 20-week UAC group, the masseter muscle weight was lower than that in the age-matched control group, and the expression level of Fbxo32 gene in peripheral blood leukocytes was increased according to the microarray analysis confirmed by real-time PCR detection. The increased protein expression levels of Fbxo32 were detected in the masseter in the 20-week UAC group, and the protein expression levels of desmin and αB-crystallin were decreased at this time point. No similar changes were detected in the lateral pterygoid muscle.

CONCLUSIONS

Masseter atrophy is induced by long-term stimulation of UAC. The increased expression of the Fbxo32 gene in peripheral blood leukocytes may be a candidate biological marker of masseter atrophy.