The Exercise-CTSS-AD Axis: a novel framework for understanding exercise-induced neuroprotection in Alzheimer's...

Disease-modifying therapies for Alzheimer's disease (AD) targeting amyloid-β and tau have consistently failed, highlighting the urgent need for innovative therapeutic strategies. Cathepsin S (CTSS), a lysosomal cysteine protease upregulated in AD, functions as a "multifaceted disruptor" that interconnects neuroinflammation, blood-brain barrier (BBB) dysfunction, and Aβ metabolic dysregulation. Although exercise is a validated non-pharmacological intervention that mitigates AD pathology, its multi-target molecular mechanisms remain elusive. Here, we propose and substantiate the "Exercise-CTSS-AD Axis" hypothesis, positing that exercise confers neuroprotection by suppressing CTSS through synergistic anti-inflammatory, anti-aging, and metabolic regulatory pathways. Exercise-induced myokines and clearance of senescent cells inhibit CTSS transcription, while AMPK-TFEB axis activation enhances lysosomal function to repress CTSS enzymatic activity. This systemic CTSS suppression preserves BBB integrity, ameliorates microglia-driven neuroinflammation, and restores Aβ homeostasis by reducing production and enhancing clearance. Our framework provides a unifying molecular explanation for the pleiotropic benefits of exercise, positions CTSS as a quantifiable biomarker for personalized exercise regimens, and supports an innovative combinatorial strategy: "Exercise + low-dose CTSS inhibitors" as a disease-modifying therapy for AD.