Estradiol changes mitochondrial morphology into complexity in response to exercise

Abstract

Mitochondria in mammalian cells undergo morphological remodeling via dynamic fusion (maintaining functional mitochondria) and fission (removing dysfunctional mitochondria) events to adapt to external exercise‐associated stimulation and functional needs. The purpose of this investigation was to determine the effect of acute exercise on the mitochondrial morphology of skeletal muscle within the phases of the menstrual cycle. Twenty‐four female Wistar‐Imamichi rats (15‐week‐old) were divided into four groups: low level of estradiol + sedentary (LE + S), low level of estradiol + acute treadmill exercise (LE + Ex), high level of estradiol + sedentary (HE + S) and high level of estradiol + acute treadmill exercise (T+ Ex). Vaginal smears for all animals were used to determine the menstrual cycle phase. The acute treadmill exercise in LE + Ex and HE + Ex groups involved a treadmill run at 60% V(■)O2 max for 120 min. Upon completion of each intervention, the red portion of the gastrocnemius muscle was dissected. Approximately 900 intermyofibrillar mitochondria were analyzed by transmission electron microscopy. We estimated the shapes and sizes of sampled mitochondria using ImageJ software based on measurements of surface area, perimeter, aspect ratio (AR), form factor (FF), circularity, and roundness. The mitochondrial shapes and sizes did not differ between the LE + S and HE + S groups. Mitochondrial morphological changes were also absent in the LE rats (LE + S vs. LE + Ex), whereas indicators of the fusion event were present after the acute treadmill exercise in HE rats (HE + S vs. HE + Ex), i.e., increased surface area (+20%), perimeter (+31%), AR (+29%), and FF (+42%), as well as decreased circularity (−22%) and roundness (−16%). In conclusion, mitochondrial adaptations in HE rats in response to exercise may be due to fusion.