Three-dimensional models for studying development and disease: moving on from organisms to organs-on-a-chip and organoids

Abstract

Human development and disease are challenging to study because of lack of experimental accessibility to in vivo systems and the complex nature of biological processes. For these reasons researchers turn to the use of model systems, ranging in complexity and scale from single cells to model organisms. While the use of model organisms is valuable for studying physiology and pathophysiology in an in vivo context and for aiding pre-clinical development of therapeutics, animal models are costly, difficult to interrogate, and not always equivalent to human biology. For these reasons, three-dimensional (3D) cell cultures have emerged as an attractive model system that contains key aspects of in vivo tissue and organ complexity while being more experimentally tractable than model organisms. In particular, organ-on-a-chip and organoid models represent orthogonal approaches that have been able to recapitulate characteristics of physiology and disease. Here, we review advances in these two categories of 3D cultures and applications in studying development and disease. Additionally, we discuss development of key technologies that facilitate the generation of 3D cultures, including microfluidics, biomaterials, genome editing, and imaging technologies.

Figure 1

Biological model systems. Model systems for studying human biological range from 2D cell culture to model organisms and lie on a spectrum in terms of their experimental tractability and physiological relevance.

Figure 2

Approaches in generating tissue and organ models. In a top-down approach individual components are incorporated into a system to mimic the in vivo tissue environment. Components include multiple cell types, biomaterial scaffolds and ECM, soluble cues, mechanical cues, and microfabricated elements to define spatial arrangement and structure. Organ-on-a-chip models are an example of using a top-down approach. In contrast, a bottom-up approach supplies fewer external cues and instead relies on cellular self-organization to generate tissues with in vivo-like structure and function. Typically PSCs are formed into aggregates and cultured in the presence of soluble and material cues to guide inherent self-organization and yield organoids.

Figure 3

Organoid examples. A: Optic cup organoids. (i–iv) Images show morphology and gene expression of optic cup structures at days 9 and 12. (i,ii) Formation of eye cup structures expressing Rx-GFP, indicating early retinal tissue, on day 9. (i,ii) The outer shell expressed markers resembling retinal epithelium progenitors, including Mitf (i) and accumulated pigment (ii). (iii) Expression of aPKC and laminin demonstrate apical-basal polarity. (iv) E11.5 mouse eye. (v) Schematic of optic cup formation. B: Cerebral organoids. (i) Schematic of protocol for cerebral organoid formation. (ii) Sectioning and staining of tissue shows the complex tissue morphology, with regions of neural progenitors (SOX2, red) and neurons (TUJ1, green) (arrow). Scale bars, 200 μm. C: Liver buds generated from human iPSCs. Images show presence of human iPSC hepatic endoderm (iPSC-HE) (green) and endothelial networks (red) inside liver buds. Scale bars, 100 μm. C: D: Intestinal organoids. On left, confocal image shows intestinal crypts grown for 3 weeks. Lgr-GFP+ stem cells (green) are located at the tips of crypt domains. Scale bar, 50 μm. On right, aschematic of a crypt organoid depicts thestructure. All figures reprinted by permission from Macmillan Publishers Ltd: Nature. Respectively: Eiraku et al, copyright 2011. Lancaster et al, copyright 2013. Takebe et al., copyright 2013. Sato et al, copyright 2013.

Figure 4

Organ-on-a-chip examples. A: Schematic shows the design of a human gut-on-a-chip. Human intestinal epithelial cells are cultured on an ECM-coated porous membrane and exposed to low levels of fluid shear stress. Side vacuum chambers are used to apply cyclic strain that mimics physiological peristaltic motions. Reproduced from Kim et al. with permission from The Royal Society of Chemistry. B: Schematics show the design of the liver-on-a-chip. Hepatocytes are cultured in a central channel, surrounded by small, closely spaced parallel channels that mimic the endothelial cell barrier. Two side channels deliver nutrients and drugs by diffusive to the central cell culture region. Reproduced from Lee et al. with permission from Wiley Periodicals. Copyright 2007, Wiley Periodicals, Inc. C: A human lung-on-a-chip models the alveolar-capillary interface. Alveolar epithelial cells and pulmonary microvascular endothelial cells are cultured on opposite sides of a PDMS membrane. Vacuum is applied to lateral side chambers to stretch the PDMS membrane and mimic physiological breathing. From Hung et al. Reprinted with permission from AAAS.D: Schematics show the design of a kidney duct model. Renal cells are cultured within the channel and exposed to fluid shear stress, osmotic gradients, and hormonal stimulation. Reproduced from Jang et al. with permission from The Royal Society of Chemistry.