Author(s): Dpp C, Schmutz S, Hoppeler H, Flck M
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Abstract This study investigated the use of the hindlimb suspension (HS) and reloading model of mice for the mapping of ultrastructural and gene expressional alterations underlying load-dependent muscular adaptations. Mice were hindlimb suspended for 7 days or kept as controls (n = 12). Soleus muscles were harvested after HS (HS7, n = 23) or after resuming ambulatory cage activity (reloading) for either 1 day (R1, n = 13) or 7 days (R7, n = 9). Using electron microscopy, a reduction in mean fiber area (-37\%) and in capillary-to-fiber ratio (from 1.83 to 1.42) was found for HS7. Subsequent reloading caused an increase in interstitial cells (+96\%) and in total capillary length (+57\%), whereas mean fiber area and capillary-to-fiber ratio did not significantly change compared with HS. Total RNA in the soleus muscle was altered with both HS (-63\%) and reloading (+108\% in R7 compared with control). This is seen as an important adaptive mechanism. Gene expression alterations were assessed by a muscle-specific low-density cDNA microarray. The transcriptional adjustments indicate an early increase of myogenic factors during reloading together with an overshoot of contractile (MyHC I and IIa) and metabolic (glycolytic and oxidative) mRNA amounts and suggest mechano-sensitivity of factors keeping the sarcomeres in register (desmin, titin, integrin-beta1). Important differences to published data from former rat studies were found with the mouse HS model for contractile and glycolytic enzyme expression. These species-specific differences need to be considered when transgenic mice are used for the elucidation of monogenetic factors in mechano-dependent muscle plasticity.
This article was published in Physiol Genomics
and referenced in Journal of Yoga & Physical Therapy