Loss of ovarian function prevents exercise-induced activation of hepatic mitophagic flux.

Abstract

Exercise effectively treats metabolic dysfunction-associated steatotic liver disease (MASLD) by enhancing hepatic mitochondria energy metabolism. However, the efficiency of exercise in treating MASLD in postmenopausal women may be reduced. Previously, we showed acute treadmill exercise activates hepatic mitophagy, the selective degradation of low-functioning mitochondria. Mitophagic flux is differentially regulated in female mice compared with males, possibly by estrogen. Here, we tested if loss of ovarian function via ovariectomy (OVX), which reduces estrogen, drives MASLD, and compromised hepatic mitochondrial energetics, would blunt activation of hepatic mitophagy induced by exercise. Following OVX, 12- to 15-wk-old female mice were placed on a low-fat diet (LFD) or high-fat diet (HFD) for 4 wk to induce MASLD, after which half of the mice performed a single acute bout of treadmill exercise to exhaustion or remained sedentary. Two hours post exercise, isolated hepatic mitochondria were examined via Western blotting and proteomics for accumulation of known mitophagy proteins. After exercise, reduced basal mitophagic flux in LFD-fed OVX was restored to levels found in sham mice. However, exercise possessed blunted capacity to promote mitochondrial recruitment of DRP1 (regulator of fission) and accumulation mitophagy-associated proteins (E3-ubiquitin ligase, ubiquitin, autophagy adaptor proteins, and autophagosome cargo receptors) in OVX versus sham mice on HFD. Mitochondrial H₂O₂ production, which putatively activates mitophagy, was elevated following exercise in all conditions except OVX + HFD. In summary, OVX reduces mitophagic flux, blunting the stimulatory effects of exercise on these factors. The impaired regulation of mitophagy following the cessation of ovarian function likely contributes to the pathogenesis of MASLD post menopause.NEW & NOTEWORTHY Loss of ovarian function reduces hepatic mitochondrial respiratory capacity, but mechanisms are unknown. Here, we leverage exercise-induced hepatic mitophagy activation to determine if loss of ovarian function impairs mitochondrial quality control mechanisms. Our data reveal that loss of ovarian function reduces both ubiquitin-mediated hepatic mitophagy and mitochondrial recruitment of Drp1 (mitochondrial fission protein) following acute exercise. These impairments to hepatic mitophagy coincided with alterations in hepatic mitochondrial respiratory capacity and mitochondrial-derived H₂O₂ production.