Using Brain Organoids to Explore Human Neurobiology

Abstract One of the major challenges in neuroscience is understanding how the human brain develops into a highly organized and functionally integrated organ, because many developmental processes cannot be investigated directly in humans and are not fully recapitulated in animal models. Brain organoids derived from human pluripotent stem cells have emerged as powerful three-dimensional (3D) experimental models that recapitulate key features of human neurodevelopment, including regional patterning, cellular diversification, and neural circuit assembly. Recent advances in long-term organoid culture, organoid bioengineering, vascularization, assembloid technology, transplantation, multi-omics, and artificial intelligence have substantially expanded the applications of brain organoids to investigate human neurodevelopment, model neurological disorders, support drug discovery, and advance therapeutic development. Integration of single-cell and spatial multi-omics with computational approaches has enabled robust molecular benchmarking, assessment of developmental fidelity, and evaluation of organoid reproducibility, facilitating direct comparison with primary human fetal brain tissue. However, current organoid systems remain limited owing to incomplete cellular and tissue complexity, inter-organoid variability, limited vascularization, limited functional maturation, and incomplete physiological integration. Continued advances in tissue engineering, computational biology, and standardized differentiation protocols are expected to enhance the biological fidelity and translational utility of brain organoids for basic and translational neuroscience, as well as mechanistic and translational research. Graphical Abstract Human Pluripotent Stem Cell-Derived Brain Organoids: From Directed Differentiation to Biomedical Applications. The graphic presented represents a summary of the overall workflow used for creating, characterizing, and medical uses of the brain organoids derived from stem cells. To create brain organoids, scientists utilize stem cells, and through controlling developmental signaling pathway processes bring forth the organoids that are organ-specific and exhibit distinct features of formation of human body. Depending on the technique that was used for creating organoids, different kinds of organoids can be generated, including, for instance, the organoids of the dorsal forebrain (one can also name it as the cortex), organoid of the ventral forebrain, organoids of different parts of the brain like stipular, hypothalamic, retinal, mesencephalic, rhombic, cerebellar, and spinal organoids. There are many methods that help with providing enough information about organoids. The methods used mostly can be characterized by their efficiency, using approaches that enable scientists to know more about cell heterogeneity through using scRNA-seq, understanding the tissue structure through the use of spatial transcriptomics, learning about neuron functioning through utilizing electroactivity tests and calcium imaging, and obtaining other information through applying multiple omics. Organ identity becomes interactive with many branches of science without exception, mostly forming large platform for research and applications in the field of neuroscience. But still, the process of applying brain-based approaches for research development requires the solution of some issues that need to be attended and solved. Most of the issues emerged can be explained by a lack of blood vessels, partial immune system efficiency, limitations in cell functioning, and variability of protocols. Summarizing the graphic provided, it is evident that it represents a detailed process of brain organoid research and its application. The information provided for making the above-mentioned graphic was based on numerous scientific works that deal with the issue of the generation of organoids and the general overview of the development, usage, and creation process of this material. Abbreviations: AI, artificial intelligence; hPSC, human pluripotent stem cell; scRNA-seq, single-cell RNA sequencing.