Human iPSC-Derived Brain Cells, Organoids, and Organoids-on-Chips: Advancing Neurological Disease Modeling to Improve Clinical Outcome.

Neurological disorders are the leading cause of overall disease and disability worldwide, affecting more than 3.4 billion people globally and over 180 million Americans. Yet there are no curative treatments available for any of the cardinal neurological diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis-frontotemporal dementia (ALS-FTD) and Huntington's disease (HD). Many compounds that demonstrate excellent activity in preclinical models fail in clinical trials. The most compelling reason for this failure is attributed to inherent limitations of rodent models that fail to replicate complex human biology. The transformation of patient-derived somatic cells into induced pluripotent stem cells (iPSCs) that can become functional human neurons is an emerging technology that is expected to revolutionize medical treatments and personal medicine. Here, we review the available evidence for the efficacy of iPSC-derived neurons, organoids, assembloids and organ-on-chip in models of AD, PD, ALS-FTD and HD. We focus on how these human-relevant iPSC-derived brain cells are crucial for understanding neurological disease pathogenesis and accelerating drug discovery. We also discuss the current limitations of this technology and how alternative models such as induced neurons (iNs) are generated by directly reprogramming fibroblasts that preserve age-associated epigenetic signatures and may serve as better models for neurological disorders.