Mechanical loading regulates the expression of tenascin-C in the myotendinous junction and tendon but does not induce de novo synthesis in the skeletal muscle

Abstract

Tenascin-C is a hexabrachion-shaped matricellular protein with a very restricted expression in normal musculoskeletal tissues, but it is expressed abundantly during regenerative processes of these tissues and embryogenesis. To examine the importance of mechanical stress for the regulation of tenascin-C expression in the muscle-tendon unit, the effects of various states of mechanical loading (inactivity by cast-immobilization and three-varying intensities of subsequent re-activity by treadmill running) on the expression of tenascin-C were studied using immunohistochemistry and mRNA in situ hybridization at the different locations of the muscle-tendon unit of the rat gastrocnemius muscle, the Achilles tendon complex. This muscle-tendon unit was selected as the study site, because the contracting activity of the gastrocnemius-soleus muscle complex, and thus the mechanical loading-induced stimulation, is easy to block by cast immobilization. Tenascin-C was expressed abundantly in the normal myotendinous and myofascial junctions, as well as around the cells and the collagen fibers of the Achilles tendon. Tenascin-C expression was not found in the normal skeletal muscle, although it was found in blood vessels within the muscle tissue. Following the removal of the mechanical loading-induced stimulation on the muscle-tendon unit by cast immobilization for 3 weeks, the immonoreactivity of tenascin-C substantially decreased or was completely absent in the regions expressing tenascin-C normally. Restitution of the mechanical loading by removing the cast and allowing free cage activity for 8 weeks resulted in an increase in tenascin-C expression, but it could not restore the expression of tenascin-C to the normal level (in healthy contralateral leg). In response to the application of a more strenuous mechanical loading stimulus after the removal of the cast (after 8 weeks of low- and high-intensity treadmill running), the expression of tenascin-C was markedly increased and reached the level seen in the healthy contralateral limb. Tenascin-C was abundantly expressed in myotendinous and myofascial junctions and in the Achilles tendon, but even the most strenuous mechanical loading (high-intensity treadmill running) could not induce the expression of tenascin-C in the skeletal muscle. This was in spite of the marked immobilization-induced atrophy of the previously immobilized skeletal muscle,which had been subjected to intensive stress during remobilization. mRNA in situ hybridization analysis confirmed the immunohistochemical results for the expression of tenascin-C in the study groups. In summary, this study shows that mechanical loading regulates the expression of tenascin-C in an apparently dose-dependent fashion at sites of the muscle-tendon unit normally expressing tenascin-C but can not induce de novo synthesis of tenascin-C in the skeletal muscle without accompanying injury to the tissue. Our results suggest that tenascin-C provides elasticity in mesenchymal tissues subjected to heavy tensile loading.

Age-related changes in structure and extracellular matrix protein expression levels in rat tendons

“…While PRG4, Eln, SDF1, and TGFb1 were clearly localized to the tendon side of the MTJs, CTGF was localized to the ends of the skeletal muscle fibers embedded into tendons. It is well known that muscle fibers secrete specialized proteins at the MTJs (Law et al 1994;Jarvinen et al 2003;Welser et al 2009), but to our knowledge, the present study is the first to show that tenocytes located in close proximity to the MTJs also participate in defining structural composition of the MTJs by increased deposition of the specific proteins.…”

“…A number of proteins are reported to be specifically expressed or to show increased levels at the MTJs (Law et al 1994;Jarvinen et al 2003;Welser et al 2009). Consistent with previous reports (Turner et al 1991;Frenette and Tidball 1998;Koch et al 2004), we confirmed paxillin, talin, and collagen XXII localization to the muscle side of the MTJs.…”

Propriedades mecânicas do músculo gastrocnêmio de ratas, imobilizado e posteriormente submetido a diferentes protocolos de alongamento

“…Sendo assim, a postura de alongamento do músculo gastrocnêmio, adotada pelos animais em posição de repouso, gera um estímulo tensional com resposta semelhante à do alongamento muscular aplicado uma vez ao dia. Järvinen et al (25) não encontraram diferença significativa na porcentagem de tecido conectivo intramuscular de músculos de animais liberados pós-imobilização quando comparados com aqueles de animais treinados em esteira, sugerindo que ambas as atividades foram capazes de restaurar os valores às condições controle. Por outro lado, Mattiello-Sverzut et al (26) , seguindo protocolo de imobilização e alongamento similar ao aqui aplicado, encontraram aumento significativo na quantidade de tecido conjuntivo de músculo sóleo de animais alongados (10 séries de 15 segundos) pós-imobilização quando comparados com o de animais liberados.…”

Mechano-regulated Tenascin-C orchestrates muscle repair

“…TNC is expressed only in actively remodeling musculoskeletal tissue, subject to high mechanical stress (3). This expression is loaddependent and reversible (4)(5)(6). Microdamage may contribute to the mechano-regulation of TNC expression (6).…”

“…This expression is loaddependent and reversible (4)(5)(6). Microdamage may contribute to the mechano-regulation of TNC expression (6).…”