Enhanced Satellite Cell Activity in Aging Skeletal Muscle after Manual Acupuncture-Induced Injury

Abstract

Skeletal muscle injury stimulates normally quiescent resident satellite (stem) cells to re-enter the cell cycle and execute the myogenic program to restore muscle structure and function. Previously, we reported that manual acupuncture needling of the tibialis anterior (TA) (ST36 = Zusanli) muscle of young male rats produced focal injury and morphological changes that accompanied the presence of activated satellite cells (SC) 72 hours post-needling. To investigate whether aging TA muscle responds in a similar fashion to acupuncture needling, 17-month-old female rats were subjected to a single insertion and manual manipulation of an acupuncture needle. At 72 hours’ post-needling, hematoxylin staining of the TA revealed increased mononuclear cell infiltration that was indicative of localized injury. Moreover, this was accompanied by a four-fold increase in the expression of proliferating cell nuclear antigen within cells of needled tissues. Heightened immunofluorescence for MyoD was found within SC in the needled muscle, which correlated with a 6- and 10-fold increase in two MyoD isoforms (~38 and 42 kDa, respectively), when analyzed by Western blotting. An additional 56 kDa MyoD immunoreactive species was observed in both needled and control muscle of the aging rats. The present study in pre-senile female rats, in conjunction with our previous study in young male rats, suggests that muscle remodeling and restructuring after injury may constitute the initial cellular and molecular mechanisms that underlie the benefits associated with acupuncture throughout the life-span.