Oestrogen-dependent satellite cell activation and proliferation following a running exercise occurs via the PI3K signalling pathway and not IGF-1

AimThe purpose of this study was to determine whether 17-estradiol (E2) enhances the activation, proliferation and differentiation of muscle satellite cells (SC) following eccentric exercise either via insulin-like growth factor-1 (IGF-1) or through phosphatidylinositol 3-kinase (PI3K) signalling. MethodsThis study used 64, 9-week-old, ovariectomized Sprague-Dawley rats that were divided into eight treatments groups based on oestrogen status (0.25mg oestrogen pellet or sham), exercise status (90min run @ 17mmin(-1), -13.5 degrees or unexercised) and PI3K signalling inhibition (0.7mgwortmanninkg(-1) body weight or DMSO control). ResultsSignificant increases in total SCs were found in both soleus and white gastrocnemius muscles (immunofluorescent co-localization of Pax7(+) nuclei) 72h following eccentric exercise (P<0.05). Oestrogen supplementation caused a further enhancement in total SCs in exercised rats (P<0.05). In animals where the PI3K pathway was inhibited, regardless of oestrogen or exercise status, there was no significant enhancement of SC number in both the soleus or white gastrocnemius muscles. Interestingly, oestrogen supplementation lowered muscle levels of IGF-1 with this effect being most prominent in the soleus muscle. While IGF-1 was increased following exercise (P<0.05), oestrogen supplementation abrogated this increase back to sedentary levels. ConclusionThese data suggest that the increase in SC population following exercise in oestrogen-supplemented females may be mediated via PI3K pathway signalling and not IGF-1.