Neural organoids for disease phenotyping, drug screening and developmental biology studies

Abstract

Human induced pluripotent stem cells (hiPSCs) can theoretically yield limitless supplies of cells fated to any cell type that comprise the human organism, making them a new tool by which to potentially overcome caveats in current biomedical research. In vitro derivation of central nervous system (CNS) cell types has the potential to provide material for drug discovery and validation, safety and toxicity assays, cell replacement therapy and the elucidation of previously unknown disease mechanisms. However, current two-dimensional (2D) CNS differentiation protocols do not faithfully recapitulate the spatial organization of heterogeneous tissue, nor the cell-cell interactions, cell-extracellular matrix interactions, or specific physiological functions generated within complex tissue such as the brain. In an effort to overcome 2D protocol limitations, there have been advancements in deriving highly complicated 3D neural organoid structures. Herein we provide a synopsis of the derivation and application of neural organoids and discuss recent advancements and remaining challenges on the full potential of this novel technological platform.

Modeling Neurological Diseases With Human Brain Organoids

“…Conventional methods used in neurobiology might not be able to exploit the neuronal activity and network connectivity within the 3D architecture of brain organoids. The combination of advanced multi-level and high-throughput detection techniques which allow analysis of the whole or intact brain organoids, will greatly benefit phenotypic profiling of human brain organoid models and may help to further uncover mechanisms for disease pathogenesis (Mariani et al, 2015 ; Luo et al, 2016 ; Qian et al, 2016 ; Quadrato et al, 2016 ; Bershteyn et al, 2017 ; Hartley and Brennand, 2017 ; Renner et al, 2017 ; Xiang et al, 2017 ; Paşca, 2018 ). The brain organoid models could be potentially used in drug testing or screening, identification of new biomarkers or development of innovative diagnostics and therapeutics.…”

“…Owning to the missing of surrounding supportive tissue and body axes, brain organoids do not organize themselves into the same shape or pattern of the in vivo brain although they do develop discrete brain regions (Lancaster et al, 2013 ; Kelava and Lancaster, 2016a ). Axial patterning signals, which in turn affect the formation of different brain regions, could be applied to the organoids by mimicking endogenous developmental signaling gradients using controlled signal-releasing beads, or by culturing organoids on signaling molecules-coated scaffolds (Hartley and Brennand, 2017 ). Additionally, most protocols mainly depend on the ability of stem cells to self-organize into distinct brain structures.…”

Unprecedented Potential for Neural Drug Discovery Based on Self-Organizing hiPSC Platforms

“…This allows for in vitro modelling of the pathological phenotype via their differentiation to the affected cell types [18,19]. Further, organoids have enabled the characterization of disease in more complex cellular milieus and this is of great interest for drug screening in that they may allow movement away from animal models, and perhaps an accelerated, more effective drug screening process for an individual's disease [20,21].…”

Application of CRISPR/Cas9 to the study of brain development and neuropsychiatric disease

“…hiPSC-based models facilitate the study of normal developmental biology and disease mechanisms, and can serve as a component of drug-discovery platforms (Mertens et al, 2015; Brennand et al, 2015; Hartley and Brennand 2016; Xu et al, 2016). Expression of the four Yamanaka factors ( C-MYC, KLF4, OCT4, and SOX2) reprograms adult somatic cells into hiPSCs (Takahashi and Yamanaka, 2006; Takahashi et al, 2007; Yu et al, 2007), from which neurons can be differentiated by sequential treatment with growth factors or small molecules in a manner recapitulating neuronal development in vivo (Watanabe et al, 2005).…”

“…Second, because hiPSC-derived neurons most resemble fetal brain cells in temporal and spatial patterning (Mariani et al, 2012; Lancaster et al, 2013; Miller et al, 2013; Vera and Studer, 2015), they better model aspects of disease predisposition than the disease-state itself (Brennand et al, 2015). Even neural organoids (“brain balls”), which provide some three dimensional context to in vitro models (reviewed in Hartley and Brennand, 2016), still most resemble fetal, rather than adult, brain tissue (Pasca et al, 2015). Third, somatic mosaicism - differences in genomic content between cells from the same organism – occurs both in vivo and in hiPSC-based models (McConnell et al, 2013), and the extent to which cell-based models recapitulate the diversity of mosaicism detected in the human brain remains unclear.…”