Organoids as advanced three-dimensional models for studying brain development, neurodegeneration, and translational therapeutics

Abstract Organoids are stem cell-derived three-dimensional (3D) multicellular constructs that recapitulate key cytoarchitectural, molecular, and functional properties of their tissue of origin. Two fundamentally distinct strategies govern their generation: unguided approaches, which exploit intrinsic self-organization to produce regionally heterogeneous whole-brain-like structures, and guided approaches, which apply defined morphogenetic signals to generate region-specific tissues with high cellular purity and reproducibility. Understanding the trade-offs between these strategies is central to selecting appropriate models for basic discovery, disease modeling, or translational applications, and constitutes the organizing framework of the present review. We present a comprehensive and mechanistic overview of organoid technologies spanning the full spectrum of CNS models, including cerebral, midbrain-like, cerebellar, retinal, spinal cord, and blood–brain barrier organoids, as well as endoderm-derived liver, lung, and kidney systems relevant to translational neuropharmacology. Particular emphasis is placed on patient-derived and genetically engineered midbrain-like organoids (MLOs) as platforms for recapitulating Parkinson’s disease (PD) pathology, including selective dopaminergic neuronal vulnerability, α-synuclein aggregation and Lewy body-like formation, mitochondrial dysfunction, oxidative stress, and neuroinflammatory signaling within a human cellular context. The core stages of organoid generation stem cell source selection, biomimetic extracellular matrix establishment, spatiotemporal morphogen gradient modulation, and self-organization and maturation are systematically delineated alongside a critical evaluation of their respective limitations. Bioengineering advances including defined synthetic matrices, microfluidic perfusion, vascularization strategies, multi-lineage assembloids, and brain-on-a-chip platforms are discussed as approaches to enhance physiological relevance. A unified characterization and validation framework is presented, integrating histomorphology, immunophenotyping, electrophysiology, bulk and single-cell transcriptomics, and spatial omics. Challenges related to genomic stability, batch variability, incomplete maturation, and absence of non-neural lineages are critically examined. Emerging future directions including AI-assisted phenotyping, GMP-grade organoid production, and organoid-guided cell therapy are evaluated. Ethical and regulatory considerations pertaining to organoid sentience, germline modification, commercialization, and regulatory acceptance are addressed with reference to current international guidelines. Collectively, organoid platforms are redefining human tissue biology and hold transformative potential for precision medicine and next-generation regenerative therapeutics.