Organoids are miniature organs that can be grown in the lab from a person’s stem cells. They can be used to model diseases, and in the future could be used to test drugs or even replace damaged tissue in patients.
But currently organoids are very difficult to grow in a standardized and controlled way, which is key to designing and using them. EPFL scientists have now solved the problem by developing a patent-pending “hydrogel” that provides a fully controllable and tunable way to grow organoids. The breakthrough is published in Nature.
Organoids need a 3D scaffold
Growing organoids begins with stem cells — immature cells that can grow into any cell type of the human body and that play key roles in tissue function and regeneration. To form an organoid, the stem cells are grown inside three-dimensional gels that contain a mix of biomolecules that promote stem cell renewal and differentiation.
The role of these gels is to mimic the natural environment of the stem cells, which provides them with a protein- and sugar-rich scaffold called the “extracellular matrix”, upon which the stem cells build specific body tissues. The stem cells stick to the extracellular matrix gel, and then “self-organize” into miniature organs like retinas, kidneys, or the gut. These tiny organs retain key aspects of their real-life biology, and can be used to study diseases or test drugs before moving on to human trials.
But the current gels used for organoid growth are derived from mice, and have problems. First, it is impossible to control their makeup from batch to batch, which can cause stem cells to behave inconsistently. Second, their biochemical complexity makes them very difficult to fine-tune for studying the effect of different parameters (e.g. biological molecules, mechanical properties, etc.) on the growth of organoids. Finally, the gels can carry pathogens or immunogens, which means that they are not suitable for growing organoids to be used in the clinic.
A hydrogel solution
The lab of Matthias Lütolf at EPFL’s Institute of Bioengineering has developed a synthetic “hydrogel” that eschews the limitations of conventional, naturally derived gels. The patent-pending gel is made of water and polyethylene glycol, a substance used widely today in various forms, from skin creams and toothpastes to industrial applications and, as in this case, bioengineering.
Nikolce Gjorevski, the first author of the study, and his colleagues used the hydrogel to grow stem cells of the gut into a miniature intestine. The functional hydrogel was not only a goal in and of itself, but also a means to identify the factors that influence the stem cells’ ability to expand and form organoids. By carefully tweaking the hydrogel’s properties, they discovered that separate stages of the organoid formation process require different mechanical environments and biological components.
One such factor is a protein called fibronectin, which helps the stem cells attach to the hydrogel. Lütolf’s lab found that this attachment itself is immensely important for growing organoids, as it triggers a whole host of signals to the stem cell that tell it to grow and build an intestine-like structure. The researchers also discovered an essential role for the mechanical properties, i.e. the physical stiffness, of the gel in regulating intestinal stem cell behavior, shedding light on how cells are able to sense, process and respond to physical stimuli. This insight is particularly valuable – while the influence of biochemical signals on stem cells is well-understood, the effect of physical factors has been more mysterious.
Because the hydrogel is man-made, it is easy to control its chemical composition and key properties, and ensure consistency from batch to batch. And because it is artificial, it does not carry any risk of infection or triggering immune responses. As such, it provides a means of moving organoids from basic research to actual pharmaceutical and clinical applications in the future.
Lütolf’s lab is now researching other types of stem cells in order to extend the capacities of their hydrogel into other tissues.
Learn more: Taking miniature organs from lab to clinic
By coating tiny gel beads with lung-derived stem cells and then allowing them to self-assemble into the shapes of the air sacs found in human lungs, researchers at the Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research at UCLA have succeeded in creating three-dimensional lung “organoids.” The laboratory-grown lung-like tissue can be used to study diseases including idiopathic pulmonary fibrosis, which has traditionally been difficult to study using conventional methods.
“While we haven’t built a fully functional lung, we’ve been able to take lung cells and place them in the correct geometrical spacing and pattern to mimic a human lung,” said Dr. Brigitte Gomperts, an associate professor of pediatric hematology/oncology and the study’s lead author.
Idiopathic pulmonary fibrosis is a chronic lung disease characterized by scarring of the lungs. The scarring makes the lungs thick and stiff, which over time results in progressively worsening shortness of breath and lack of oxygen to the brain and vital organs. After diagnosis, most people with the disease live about three to five years. Though researchers do not know what causes idiopathic pulmonary fibrosis in all cases, for a small percentage of people it runs in their families. Additionally, cigarette smoking and exposure to certain types of dust can increase the risk of developing the disease.
To study the effect of genetic mutations or drugs on lung cells, researchers have previously relied on two-dimensional cultures of the cells. But when they take cells from people with idiopathic pulmonary fibrosis and grow them on these flat cultures, the cells appear healthy. “Scientists have really not been able to model lung scarring in a dish,” said Gomperts, who is a member of the UCLA Broad Stem Cell Research Center. The inability to model idiopathic pulmonary fibrosis in the laboratory makes it difficult to study the biology of the disease and design possible treatments.
Gomperts and her colleagues started with stem cells created using cells from adult lungs. They used those cells to coat sticky hydrogel beads, and then they partitioned these beads into small wells, each only 7 millimeters across. Inside each well, the lung cells grew around the beads, which linked them and formed an evenly distributed three-dimensional pattern. To show that these tiny organoids mimicked the structure of actual lungs, the researchers compared the lab-grown tissues with real sections of human lung.
“The technique is very simple,” said Dan Wilkinson, a graduate student in the department of materials science and engineering and the paper’s first author. “We can make thousands of reproducible pieces of tissue that resemble lung and contain patient-specific cells.”
Moreover, when Wilkinson and Gomperts added certain molecular factors to the 3-D cultures, the lungs developed scars similar to those seen in the lungs of people who have idiopathic pulmonary fibrosis, something that could not be accomplished using two-dimensional cultures of these cells.
Using the new lung organoids, researchers will be able to study the biological underpinnings of lung diseases including idiopathic pulmonary fibrosis, and also test possible treatments for the diseases. To study an individual’s disease, or what drugs might work best in their case, clinicians could collect cells from the person, turn them into stem cells, coax those stem cells to differentiate into lung cells, then use those cells in 3-D cultures. Because it’s so easy to create many tiny organoids at once, researchers could screen the effect of many drugs. “This is the basis for precision medicine and personalized treatments,” Gomperts said.