Estradiol (E2) is the primary circulating sex hormone in females of reproductive age and plummets following menopause, which coincides with an accelerated reduction in age-related skeletal muscle contractile function in otherwise healthy females. Evidence from pre-clinical models suggest that E2 deficiency impairs mitochondrial respiration (MiR) and increases the production of reactive oxygen species. This metabolic phenotype is rescued with exogenous E2, highlighting its impact on intramyocellular conditions. Although the effects of E2 depletion have been studied extensively in pre-clinical models, its role in human skeletal muscle, and its independent contribution for age-related contractile dysfunction remains largely unclear. Therefore, our objective is to further understand how E2 impacts skeletal muscle mitochondrial function and oxidative damage independent of age. To accomplish this in humans, we leverage recruitment of younger females with high and low E2 levels, secondary to hormonal contraceptive use, that we will compare to post-menopausal females with age-related depletion of E2. We hypothesize that E2 will have protective effects on mitochondrial respiration (MiR) and myofibrillar protein oxidation levels regardless of age group. METHODS: To test this hypothesis, we compared MiR in 3 cohorts; young females using progesterone-only contraceptives (HCs; E2 suppressed), young eumenorrheic females (Eu; high E2) and post-menopausal (PM; E2 depleted) older adults. Skeletal muscle biopsies from the vastus lateralis of each participant were obtained. Tissue was separated and prepared for mitochondrial function and oxidation assays. Mitochondrial function was assessed via high-resolution respirometry (O2K; Oroboros Instruments, Innsbruck Austria). Briefly, muscle bundles were dissected in MiR05 buffer with or without dithiothreitol (DTT), a disulfide reducing agent shown to reduce oxidant damage in striated muscle. Muscle bundles were then chemically permeabilized for 30 minutes, blotted, weighed, and immediately placed in the O2K containing 2 mL of MiR05 buffer. Carbohydrate-supported metabolism was assessed by measuring maximal respiration for complex I (PI), maximal respiration for complex I and II (PI+II), leak respiration at maximal capacity (LI+II), and maximal electron transfer capacity (E). Oxidative damage was assessed by measuring levels of myosin heavy chain (MHC) carbonylation with an Oxyblot protein oxidation detection kit and normalized to protein content, determined by ponceau red staining. RESULTS: Preliminary data for mitochondrial function (n = 2 per group) revealed Eu females have higher MiR at PI+II, LI+II and E than HC and PM females. Regression analyses indicated trends toward a positive association between E2 and PI+II (R2 = 0.46, p = 0.14), and E2 and E (R2 = 0.66, p = 0.05) in the presence of DTT. Additionally, preliminary analyses of myofibrillar protein oxidation (n = 1 per group) revealed that Eu females have lower levels of protein oxidation than HC and PM, with overall greater differences observed in MHC II isoform. DISCUSSION: Preliminary results are consistent with our hypotheses that E2 protects mitochondrial function and prevents MHC oxidation. Further studies will provide statistical power to test our hypotheses and investigate whether mitochondrial abundance or dysfunction is the primary driver oxidative impairments with low E2. FUNDING: Wu Tsai Human Performance Alliance and Achievement Rewards for College Scientists (ARCS), Oregon 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.
Ortiz-Delatorre et al. (Fri,) studied this question.