Loss of ovarian function and estrogen therapy remodel the brain's synaptic and metabolic proteome

Menopause is linked to cognitive decline and reduced brain metabolism, while estrogen (E2) therapy has been shown to mitigate these effects. Understanding the molecular mechanisms by which ovarian hormones and E2 influence neuroprotection is essential for developing strategies to maintain brain health in women. In this study, we examined how the loss of ovarian hormones, with or without E2 treatment, affects the brain proteome and mitochondrial energy production in aged female C57BL/6J mice (36-40 weeks). The mice underwent sham or ovariectomy (OVX) surgery and were fed a high-fat diet for 10 weeks; six weeks after surgery, OVX mice received either sesame oil or E2 treatment for four weeks. Proteomic analysis of brain homogenates revealed 4,992 proteins regulated by E2, with pathway analysis showing increased signaling proteins related to synaptogenesis. OVX reduced proteins involved in synaptic function, branched-chain amino acid and ketone metabolism, the TCA cycle, and oxidative phosphorylation (Complexes I, IV, and V), while E2 restored protein expression within these pathways. Despite alterations in OxPhos proteins, basal and state 3 mitochondrial respiration remained unchanged, although notable impairments to Complex IV enzymatic activity were apparent in OVX, but not following E2 replacement. Overall, these results indicate that E2 supports brain health by maintaining proteins crucial for synaptic integrity and metabolism, and by reducing the decline in mitochondrial bioenergetics associated with menopause.