Rebalancing α-Synuclein Clearance: Novel Therapeutic Frontiers in Parkinson's Disease.

Parkinson's disease (PD), the second most common neurodegenerative condition, develops because of abnormal protein misfolding and aggregation of α-synuclein with its subsequent intercellular spread. Such pathological changes lead to disruption of neuronal homeostasis and contribute to neuronal degeneration. During normal conditions, α-synuclein clearance is controlled by different types of lysosomal degradation, namely, macro autophagy, chaperone-mediated autophagy (CMA), micro autophagy, and the ubiquitin-proteasome system. Malfunction of these systems results in increased α-synuclein secretion due to exosome-dependent, direct, and damage-induced mechanisms, which, in turn, promotes enhanced intercellular propagation, inflammation, mitochondrial dysfunction, blood-brain barrier leakage, and neuronal cell death. Although several approaches targeting α-synuclein clearance have shown biological activity in preclinical or early clinical studies, consistent disease-modifying efficacy has not yet been established, owing to challenges including target specificity, blood brain barrier penetration, biological heterogeneity, and the limited sensitivity of clinical endpoints. Recent research indicates that successful treatment is more related to restoring the balance of these two processes than to manipulating one of them.In this review, it is proposed that a systems-level approach can be taken where PD is understood as a disease characterized by the imbalance in proteostasis. Potential treatment modalities include small molecules targeting lysosome function (ambroxol, rapamycin, TFEB activators), CMA enhancers, gene therapy, and antibodies against extracellular α-synuclein. Furthermore, new modalities like molecular glue degraders, allostery-based stabilization of α-synuclein tetramers, engineered decoy particles, and bispecific antibodies represent some other possible routes towards multimodal disease modification.