Unloading of juvenile muscle results in a reduced muscle size 9 wk after reloading

Abstract

The role of satellite cells and DNA unit size in determining muscle size was examined by inhibiting postnatal skeletal muscle development by using hindlimb suspension. Satellite cell mitotic activity and DNA unit size were determined in the soleus muscles from hindlimb-suspended and age-matched weight-bearing rats before the initiation of hindlimb suspension, at the conclusion of a 28-day hindlimb-suspension period, 2 wk after reloading, and 9 wk after reloading. The body weights of hindlimb-suspended rats were significantly (P < 0.05) less than those of weight-bearing rats at the conclusion of hindlimb suspension, but they were the same (P > 0. 05) as those of weight-bearing rats 9 wk after reloading. The soleus muscle weight, soleus muscle weight-to-body weight ratio, myofiber diameter, nuclei per millimeter, and DNA unit size for the hindlimb-suspended rats were significantly (P < 0.05) smaller than for the weight-bearing rats at all recovery times. Satellite cell mitotic activity was significantly (P < 0.05) higher in the soleus muscles from hindlimb-suspended rats 2 wk after reloading, but it was the same (P > 0.05) as in weight-bearing rats 9 wk after reloading. Juvenile soleus muscles failed to achieve normal muscle size 9 wk after reloading because there was incomplete compensation for the hindlimb-suspension-induced interruptions in myonuclear accretion and DNA unit size expansion.

Are Human and Mouse Satellite Cells Really the Same?

“…However, satellite cells do not seem to be involved in muscle hypertrophy mediated by this pathway (Amthor et al 2009). In rodent models of unloading-induced muscle atrophy, satellite cells initially become activated (Ferreira et al 2006), but eventually decrease in number (Schultz et al 1994;Mozdziak et al 2000;Hawke and Garry 2001;Jejurikar et al 2002;Jejurikar and Kuzon 2003), and those that remain are dysfunctional (Mitchell and Pavlath 2004). These studies have implications not only for repair and maintenance of skeletal muscle during periods of immobilization but also for using satellite cells to repair muscle that is already affected by disuse atrophy as, for example, in muscular dystrophies.…”

Role(s) of Mechanical Load and Satellite Cells in The Regulation of The Size of Soleus Muscle Fiber in Rats

“…Unloading of muscle fibers caused down-regulation of the number and mitotic activity (Darr and Schultz, 1989;Mozdziak et al, 1998Mozdziak et al, , 2000Mozdziak et al, and 2001 of satellite cells. In contrast, up-regulation of these parameters was induced by re-loading of muscle fibers .…”

“…Satellite cells have been shown to serve as a source of new myonuclei during regeneration after a muscle injury (McGeachie and Allbrook, 1978;Schultz et al, 1985;Snow, 1977) and during functional overload (Dangott et al, 2000;McCormick and Schultz, 1994;Snow, 1990). In contrast, hindlimb unloading down-regulates the satellite cell mitotic activity (Darr and Schultz, 1989;Mozdziak et al, 1998Mozdziak et al, , 2000Mozdziak et al, and 2001Schultz et al, 1994). The mechanisms underlying the modulation of satellite cells in response to various loading conditions are still unclear.…”

Células satélites musculares

“…7c) Atrofia muscular -a atrofia muscular conduz à diminuição do número de mionúcleos, podendo ser secundária a desnervação, nutrição deficiente ou imobilização do músculo. Em um modelo com ratos pré-púberes, a imobilização de um músculo levou à diminuição do número e da capacidade proliferativa das CS, alterando irreversivelmente a remodelação muscular, fato que não ocorreu em animais adultos, nos quais as CS proliferaram e repopularam o músculo atrófico (57) . Quando sofrem desnervação, as CS aumentam em número na fase aguda, para, depois, numa fase crônica, ocorrer um decrésci-mo significativo das mesmas.…”