The recent Hollywood trend of adapting much beloved movies from two-dimensional (2D) into 3-dimensional (3D) offerings hasn’t met with the expected fanfare and applause. However, strategies which have adapted pluripotent stem cell (PSC) differentiation strategies from 2D to 3D have created some masterpieces of epic proportions.
Differentiating PSCs as adherent cell monolayers is a commonly used and easy to control 2D strategy for creating a specific cell type, or set of cell types. More recently, researchers are crafting differentiation strategies in 3D to mimic in vivo development processes in order to create mini-organs, or organoids, which resemble mature human tissues and sometimes consisting of a multitude of different cell types.
Differentiating PSCs in a 3D extracellular matrix scaffold or as 3D cell aggregates has seen success; various groups have created tissues which resemble the inner ear , brain , kidney , retina , thyroid , pituitary gland , and liver , in the last 4 years alone.
The great hope is to use these 3D constructs to model development and disease/disorders, to test drugs and therapies, and even generate replacement tissues. These findings are only enhanced by the inclusion of iPSCs which bring patient and disease specificity to these created tissues.
As scientists continue to push the pace of innovative research in stem cell biology, and regenerative medicine as a whole, we want to keep you up to date with some of the recent exciting studies following this trend.
Going with the Gut: Generating Gastric and Intestinal Organoids
Stem cell researchers from the Cincinnati Children’s Hospital Medical Center, Ohio, USA are getting a little bit gutsy these days; especially those from the laboratory of James M. Wells and Michael A Helmrath where researchers recently used 3D differentiation strategies to create “miniature stomachs”, or to be precise, gastric and intestinal organoids from human (h)PSCs.
In one study, researchers used factors which aid the development of the gastro-intestinal tract in vivo (FGF, WNT, BMP, retinoic acid and EGF) and a 3D extracellular matrix support to coax hPSCs to form rice-grain sized gastric organoids which passed through molecular and morphogenetic stages resembling developing mouse stomach tissue. Differentiating cells formed structures containing mucous secreting cells as well as other gastric endocrine cells and displayed evidence of a stem cell niche.
The authors also “infected” the organoids with the Helicobacter pylori bacterium, well-known to cause ulceration of the stomach lining and cancer, in order to study the consequences of this action. In the future they hope to be able to increase organoid size for the treatment of ulcers and other stomach defects.
A second related study utilised a similar 3D hPSC differentiation protocol, using Activin A, FGF4 and WNT3A to promote hindgut spheroid formation before implantation into a 3D extracellular matrix, to promote intestinal organoid formation. This technique created an immature organoid, which the group then engrafted under the kidney capsule in mouse to “mature” in vivo for 6 weeks. This generated a much larger organoid which displayed vast anatomical similarities to native human intestine, including the formation of a supportive layer of mesenchyme, important for the development and function of intestinal tissues.
The organoids also displayed excellent functional characteristics; physiological cues emitted by the mouse following removal of part of the intestine stimulated the engrafted intestinal organoids suggesting that they may be useful in replacement therapies, while permeability and peptide uptake studies suggested that the organoid also possessed the digestive abilities. Tasty!
Both strategies pass through an endodermal stage, endoderm being one of the three germ layers in the embryo, and tweaking these differentiation strategies could potentially generate other endodermal tissues, such as the lungs, liver, pancreas and bladder.
Perhaps most exciting of all the recent reports is that from the group of Elly Tanaka at the Center for Regenerative Therapies, Dresden, Germany, who for the first time have created a 3D piece of the spinal cord from mouse ESCs, bringing the dream of rebuilding broken spines firmly into reality.
The simple protocol involved seeding single mouse ESCs in a 3D culture substrate and exposing them to a simple neural differentiation medium to form a neuroepithelial “cyst”. The addition of retinoic acid then transformed these cysts into structures similar to the embryonic neural tube, the precursor to the central nervous system, which comprises the brain and spinal cord.
Hopefully this research will advance, and translate to human PSCs and from there to the clinic.
The message is clear for stem cell biologists; the extra dimension can make all the difference, read these enthralling new studies here: McCracken KW et al, Nature, 2014, Watson CL et al, Nature Medicine, 2014, and Meinhardt A et al, Stem Cell Reports, 2014.
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- Lancaster MA, Renner M, Martin CA, et al. Cerebral organoids model human brain development and microcephaly. Nature 2013;501:373-379.
- Xia Y, Nivet E, Sancho-Martinez I, et al. Directed differentiation of human pluripotent cells to ureteric bud kidney progenitor-like cells. Nat Cell Biol 2013;15:1507-1515.
- Nakano T, Ando S, Takata N, et al. Self-formation of optic cups and storable stratified neural retina from human ESCs. Cell Stem Cell 2012;10:771-785.
- Antonica F, Kasprzyk DF, Opitz R, et al. Generation of functional thyroid from embryonic stem cells. Nature 2012;491:66-71.
- Suga H, Kadoshima T, Minaguchi M, et al. Self-formation of functional adenohypophysis in three-dimensional culture. Nature 2011;480:57-62.
- Takebe T, Sekine K, Enomura M, et al. Vascularized and functional human liver from an iPSC-derived organ bud transplant. Nature 2013;499:481-484.