High-Frequency Repetitive Transcranial Magnetic Stimulation Attenuates Post-Stroke Brain Fibrosis by Increasing Brain-Derived Estrogen Levels: A Dual-Tracer PET/CT Study.

Abstract

Fibrotic scar formation after ischemic stroke limits neuroplasticity and functional recovery. While estradiol (E2) exerts anti-fibrotic effects, the mechanisms by which high-frequency repetitive transcranial magnetic stimulation (rTMS) promotes post-stroke recovery remain poorly understood. We investigated whether rTMS attenuates post-ischemic brain fibrosis via aromatase-dependent local E2 synthesis. Male Sprague-Dawley rats subjected to permanent middle cerebral artery occlusion received high-frequency rTMS starting post-stroke day 3. Fibrosis and metabolism were evaluated using longitudinal dual-tracer [¹⁸F]AlF-FAPI-42 and [¹⁸F]FDG PET/CT on days 3 and 14, alongside histological and biochemical assessments. The aromatase inhibitor letrozole was used to probe mechanistic dependence. Additionally, we retrospectively analyzed dual-tracer PET/CT data from 10 ischemic stroke patients. In rats, rTMS significantly reduced [¹⁸F]AlF-FAPI-42 uptake, decreased collagen deposition and fibrotic marker expression, increased [¹⁸F]FDG uptake, and improved neurological outcomes. rTMS also upregulated aromatase expression and elevated peri-infarct E2 levels; these anti-fibrotic and metabolic benefits were no longer observed under letrozole treatment. Brain E2 levels correlated negatively with [¹⁸F]AlF-FAPI-42 uptake and positively with motor performance. Corroborating the preclinical model, clinical imaging revealed elevated [¹⁸F]AlF-FAPI-42 uptake in the ischemic hemisphere of patients, which was inversely associated with [¹⁸F]FDG uptake. These findings demonstrate that high-frequency rTMS attenuates post-stroke fibrosis and promotes metabolic recovery partly through aromatase-dependent elevation of local E2. Furthermore, dual-tracer [¹⁸F]AlF-FAPI-42/[¹⁸F]FDG PET provides a novel, non-invasive method for monitoring fibrosis-metabolism coupling. The clinical findings highlight the translational relevance of this relationship, suggesting that tracking fibrotic remodeling could guide post-stroke rehabilitation.