Three-dimensional midbrain organoids: a next-generation tool for Parkinson's disease modelling and drug discovery.

Parkinson's disease (PD), a progressive neurodegenerative disorder marked by dopaminergic (DA) neuron loss and Lewy body formation, lacks therapies to halt neurodegeneration. Current models, including 2D cultures and animal studies, fail to fully recapitulate human midbrain complexity, underscoring the need for advanced human-relevant disease modelling systems. Midbrain organoids (MOs), three-dimensional (3D) stem cell-derived neuronal structures mimicking midbrain architecture, have emerged as transformative tools for modelling PD. These organoids replicate key pathological hallmarks and enable disease mechanistic studies and drug screening for PD. Recent advances of research in MOs include genetic modelling of PD-linked mutations (e.g., LRRK2, GBA1, DNAJC6), optogenetics-assisted α-synuclein (α-syn) protein aggregation systems, and high-throughput drug testing platforms. MOs also show promise for cell replacement therapy, with successful integration and functional recovery in animal PD models. However, challenges such as batch variability, limited vascularization, incomplete neuronal maturation, and high costs hinder reproducibility and scalability. Future directions focus on integrating vascular networks, microglia co-cultures, automated workflows, and assembloid technologies to enhance pathophysiological relevance and translational potential in PD. By addressing these limitations, research in MOs could revolutionize PD research, offering critical insights into disease mechanisms and accelerating therapeutic discovery for PD patients.