Melatonin as a Guardian of Mitochondria: Mechanisms and Therapeutic Potential in Neurodegenerative Diseases

Mitochondrial dysfunction is a key early pathological process in neurodegenerative diseases (NDs), leading to oxidative stress, impaired energy metabolism, and neuronal apoptosis prior to the onset of clinical symptoms. Although mitochondria represent important therapeutic targets, effective interventions targeting mitochondrial function remain limited. This review summarizes current evidence regarding the mechanisms by which melatonin protects mitochondria and evaluates its therapeutic relevance, with a primary focus on Alzheimer's disease, Parkinson's disease, and Huntington's disease-the major protagonists of NDs-while briefly covering other NDs such as amyotrophic lateral sclerosis, multiple sclerosis, and prion diseases. Melatonin selectively accumulates in neuronal mitochondria and exerts neuroprotection through multiple pathways: (1) direct scavenging of reactive oxygen species (ROS); (2) transcriptional activation of antioxidant defenses via the SIRT3 and Nrf2 pathways; (3) regulation of mitochondrial dynamics through DRP1 and OPA1; and (4) promotion of PINK1- and Parkin-mediated mitophagy. Additionally, melatonin exhibits context-dependent pleiotropy: under conditions of mild mitochondrial stress, it restores mitochondrial homeostasis; under conditions of severe mitochondrial damage, it promotes pro-survival autophagy by inhibiting the PI3K/AKT/mTOR pathway, thereby conferring stage-specific therapeutic advantages. Overall, melatonin offers a sophisticated mitochondria-targeting strategy for the treatment of NDs. However, successful clinical translation requires clarification of receptor-dependent signaling pathways, development of standardized dosing strategies, and validation in large-scale randomized controlled trials.