Authors:
Zou K, Huntsman HD, Valero MC, Adams J, Skelton J, De Lisio M, Jensen T, & Boppart MD
Summary:
Purpose - The α7β1 integrin is a transmembrane protein expressed in skeletal muscle that can link the actin cytoskeleton to the surrounding basal lamina. We have previously demonstrated that transgenic mice overexpressing the α7B integrin in skeletal muscle (MCK:α7B; α7Tg) mount an enhanced satellite cell and growth response to single or multiple bouts of eccentric exercise. Additionally, interstitial stem cells characterized as mesenchymal stem cells (MSCs) accumulate in α7Tg muscle (mMSCs) in the sedentary state and post-exercise. The results from these studies prompted us to determine the extent to which mMSCs underlie the beneficial adaptive responses observed in α7Tg skeletal muscle post-exercise.
Methods - mMSCs (Sca-1CD45) were isolated from α7Tg mice, dye-labeled, and intramuscularly injected into adult wild type recipient mice. Following injection of mMSCs or saline, mice remained sedentary (SED) or were subjected to eccentric exercise training (TR) (downhill running) on a treadmill (3X/week) for two or four weeks. Gastrocnemius-soleus complexes were collected 24 hours after the last bout of exercise.
Results - mMSCs did not directly fuse with existing fibers, however, mMSC injection enhanced Pax7 satellite cell number and myonuclear content compared to all other groups at two weeks post-exercise. Mean CSA, percentage of larger caliber fibers (>3000 μm) and grip strength were increased in mMSC/TR compared to Saline/SED and mMSC/SED at four weeks. mMSC transplantation did not enhance repair or growth in the absence of exercise.
Conclusion - The results from this study demonstrate that mMSCs contribute to beneficial changes in satellite cell expansion and growth in α7Tg muscle following eccentric exercise. Thus, MSCs that naturally accumulate in muscle following eccentric contractions may enhance the adaptive response to exercise.
Source:
Medicine & Science in Sports & Exercise; (06/05/14)