The objective of this study was to investigate the role of 17β-estradiol (E2) in modulating mitochondrial bioenergetics and reactive oxygen species (ROS) homeostasis following acute and chronic volumetric muscle loss (VML) injury in female mice. The central hypothesis was that the loss of ovarian hormones would lessen mitochondrial bioenergetic efficiency causing greater ROS production and that E2 replacement would rescue this phenotype in the context of VML. Female C57BL/6J mice were divided into three groups: VML+Sham surgery (VML), VML+Ovariectomized (OVX)+Placebo pellets (VML+OVX+Placebo), and VML+OVX+Estradiol (E2) pellets (VML+OVX+E2) and skeletal muscle was analyzed at 3-, 7-, and 60-day post-injury (dpi). At 12 weeks of age, sham or OVX surgery was performed, followed by either placebo or E2 pellet implantation in OVX cohorts. Two weeks after surgery, unilateral VML surgery was conducted on the hindlimb plantar flexors (gastrocnemius, soleus, plantaris muscles). At 3- and 7-dpi, antioxidant buffering capacity (AoxBC, balance between ROS production and ROS emission), and mitochondrial transcriptomics were evaluated. At 60-dpi, mitochondrial respiration (JO 2 ) and AoxBC were measured. The loss of ovarian hormones led to lower mitochondrial AoxBC when either carb- or fat-substrates were supplied (p≤0.02) at 3- and 7-dpi. A hallmark gene set enrichment analysis (GSEA) following bulk RNA sequencing revealed that oxidative phosphorylation was among the top-3 pathways modulated by the loss of ovarian hormones and E2 replacement. A focused mitochondrial-pathway GSEA showed a robust and temporal regulation of the mitochondrial transcriptome at 3- and 7-dpi for both VML+OVX+Placebo and VML+OVX+E2. At 60-dpi, both carb- and fat-mediated JO 2 were 30% and 44% lower in the VML+OVX+Placebo group (p≤0.008) compared to VML; however, both carb- and fat-mediated JO 2 was 49% and 92% greater in VML+OVX+E2 muscle fibers compared to the VML+OVX+Placebo fibers (p≤0.001). Both carb- and fat-mediated AoxBC were 27% and 40% less, respectively, in the VML+OVX+Placebo compared to the VML mice (p≤0.001); however, they were 40% and 61% greater in the VML+OVX+E2 muscle fiber bundles relative to the VML+OVX+Placebo fibers (p≤0.001). Our findings demonstrated that VML injury led to significant impairments in mitochondrial bioenergetics, increased ROS production, and diminished antioxidant defenses. OVX exacerbates VML-induced decrease in antioxidant defense, whereas E2 replacement mitigated these disruptions, improving mitochondrial bioenergetics and AoxBC under ovarian hormone-deficient conditions following VML injury. RNA sequencing and gene set enrichment analysis revealed key shifts in mitochondrial maintenance, oxidative phosphorylation, and metabolic pathways, highlighting the crucial role of E2 in mitochondrial adaptation following traumatic injury in female mice. These findings suggest the therapeutic potential of hormone therapy in restoring metabolic homeostasis and redox balance following traumatic muscle injury, particularly in naturally or surgically estrogen-deficient conditions. Funding: NIH R01 AR078903. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.
Heo et al. (Fri,) studied this question.