The uses of 3D human brain organoids for neurotoxicity evaluations: A review.

Neurotoxicity studies aim at understanding the toxic effects and mechanisms of toxicants to human central nervous systems (CNS). However, human brains are the most complex organs, whereas the most commonly used models, such as 2D cell cultures and animal brains, are probably too simple to predict the responses of human brains. Embryonic stem cells (ESCs) or induced pluripotent stem cells (iPSCs)-based 3D human brain organoids hold unprecedented promise for the understanding of neurodevelopment and brain disease development. This review summarizes recent advances of using 3D human brain organoids for neurotoxicity studies. Comparative studies showed that 3D human brain organoids could support the findings obtained by animal or cohort studies, indicating that 3D human brain organoids are reliable models to evaluate the developmental neurotoxicity. 3D human brain organoids have been used to understand the toxicological mechanisms by using both conventional toxicological methods to investigate the signaling pathway changes as well as single cell RNA-sequencing to understand the neuron diversity. Some studies also used brain organoids carrying gene mutations or with virus infections to understand the toxicological responses of brains under diseased conditions. Although there are still limitations associated, 3D human brain organoids are promising tools for future neurotoxicity studies.

Rapid and Efficient Invasion Assay of Glioblastoma in Human Brain Organoids.

Glioblastoma (GBM) possesses glioma stem cells (GSCs) that exhibit aggressive invasion behavior in the brain. Current preclinical GBM invasion assays using mouse brain xenografts are time consuming and less efficient. Here, we demonstrate an array of methods that allow rapid and efficient assaying of GSCs invasion in human brain organoids. The assays are versatile to characterize various aspects of GSCs, such as invasion, integration, and interaction with mature neurons of brain organoids. Tissue clearing and quantitative 3D imaging of GSCs in host organoids reveal that invasiveness is inversely correlated with the organoids' age. Importantly, the described invasion assays can distinguish the invasive behaviors of primary and recurrent GSCs. The assays are also amenable to test pharmacological agents. As an example, we show that GI254023X, an inhibitor of ADAM10, could prevent the integration of GSCs into the organoids.

Recent Zika Virus Isolates Induce Premature Differentiation of Neural Progenitors in Human Brain Organoids.

The recent Zika virus (ZIKV) epidemic is associated with microcephaly in newborns. Although the connection between ZIKV and neurodevelopmental defects is widely recognized, the underlying mechanisms are poorly understood. Here we show that two recently isolated strains of ZIKV, an American strain from an infected fetal brain (FB-GWUH-2016) and a closely-related Asian strain (H/PF/2013), productively infect human iPSC-derived brain organoids. Both of these strains readily target to and replicate in proliferating ventricular zone (VZ) apical progenitors. The main phenotypic effect was premature differentiation of neural progenitors associated with centrosome perturbation, even during early stages of infection, leading to progenitor depletion, disruption of the VZ, impaired neurogenesis, and cortical thinning. The infection pattern and cellular outcome differ from those seen with the extensively passaged ZIKV strain MR766. The structural changes we see after infection with these more recently isolated viral strains closely resemble those seen in ZIKV-associated microcephaly.