17β-estradiol mitigates ovariectomy-induced defects in mitochondrial bioenergetics and redox balance after VML injury in female mice

Volumetric muscle loss (VML) is characterized by an irrecoverable loss of skeletal muscle mass, persistent functional deficits, and metabolic dysfunction. A disrupted cellular redox homeostasis is one attribute of this metabolic dysfunction and can lead to excessive reactive oxygen species (ROS) emissions and chronic oxidative stress. The primary objective of this study was to define the role of ovarian hormones, specifically 17β-estradiol (17β-E2), in driving mitochondrial bioenergetic and redox balance after VML injury. Female C57BL/6J mice were randomized into experimental and control groups (VML-sham OVX, VML-OVX, and VML-OVX-E2). A time course of ROS emissions and antioxidant buffering capacity (AoxBC) for VML-injured muscles was established across the first 60 days post-injury (dpi) in ovary-intact females. Ovariectomy (OVX) was performed prior to injury to deplete ovarian hormones, and 17β-E2 was administered via continuous-release pellets to investigate the effects of hormone loss and repletion on ROS emissions and mitochondrial bioenergetics. The long-term effects of 17β-E2 were evaluated to determine whether restoring redox led to sustained redox balance long-term. Transcriptomic analyses were conducted to explore molecular mechanisms of 17β-E2 benefit after VML. In intact females, ROS emissions were greater during the first 14-dpi, but AoxBC recovered more rapidly than previously observed in males. OVX exacerbated VML-induced metabolic dysfunction, resulting in less AoxBC, greater ROS emissions, and an early suppression of mitochondrial gene networks. 17β-E2 repletion attenuated ROS emissions and improved AoxBC at 7-dpi, and led to greater mitochondrial respiratory capacity, conductance, and bioenergetic efficiency out to 60-dpi. Chronic 17β-E2 depletion resulted in impaired glucose tolerance and greater adiposity, which were mitigated by 17β-E2 treatment. Transcriptomic analyses suggest that 17β-E2 contributes to resolving inflammation and enforcing a temporal decoupling of cellular expansion and mitochondrial maturation after VML injury.