Probing a Highly Homogeneous and Highly Functional 3-Dimensional Human Cortical Spheroid High Throughput and High Content Screening Platform With Known Neurotoxic Profile Compounds

The human cerebral cortex is organized in a complex 3-dimensional (3D) structure comprising different neural cell types. The coordinated work of these different cell types is key for brain function and homeostasis. Recently, much work has been focused on obtaining 3D brain organoids in an attempt to better recapitulate the brain development/function in vitro. However, current protocols may lead to variable organoid size and function, making the use of these powerful tools impractical in an investigative toxicology setting. Here we describe the development of a highly homogenous human induced Pluripotent Stem ell (hiPSC)-derived cortical spheroid screening platform in 384 well format, composed of cortical neurons and astrocytes. Immunofluorescence analysis indicated that these derived neurons and astrocytes display key markers of cellular identity as well as maturity, such as synaptic proteins and glutamate transporters. Viability assays carried out with compounds with known mechanism of action indicated scalability and feasibility of the assays, with results comparable to a standard 2D model employing the same culture composition. Kinetic, high trhoughput calcium flux analysis performed in a in a Fluorometric Imaging Plate Reader (FLIPR) highlighted that the spheroids present quantifiable, robust and uniform spontaneous calcium oscillations, measured. The calcium signal was modified with excitatory and inhibitory modulators coherently and in a highly reproducible fashion, confirming the presence of a functionally integrated glutamatergic/GABAergic circuit. High speed confocal imaging confirmed homogenous calcium oscillations at the cellular level, whereas multielectrode array (MEA) analysis demonstrated robust synchronous neurophysiological activity at the network level. Additionally, these cortical spheroids are amenable to immunostaining in suspension, enabling scalable high content image-based assays focused on key protein markers. Altogether, the developed 3D cortical spheroid platform can be easily implemented as a reliable high throughput screening platform to investigate complex cortical phenotypes in vitro, as a reliable high-throughput screening platform for toxicology studies, disease modeling and drug testing.

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