New research into organoids can help airway levels reach maturity. Injecting these improved air passageway models into mice can help detect lung diseases quicker and enable pre-clinic drug testing. The researchers worked on improving organoids that were previously developed and did not have mucus producing cells known as goblets or a number of other secretory cells.
The researchers noted that that these shortcomings can be overcome by using a combination of synthetic “scaffolds” and in vivo growth in mice. Organoids are three-dimensional organ buds grown in vitro and have proved to be an excellent testing model to examine biological processes over the years.
In the most basic sense, organoid models include three dimensional (3D) cell cultures that closely resemble the in vivo organ or tissue from which they were derived.
Microbiologists have long been able to synthesize mature airway epithelia in vitro by extracting airway cells from patients and cadavers and growing them in culture. These epithelia have been used for a variety of scientific purposes, from fundamental cellular biology and cancer genetics to clinical diagnosis and pharmacological testing.
Over the past few years, scientists have been trying to use human pluripotent stem cells, master cells that can reproduce any of the types of cells that are found in the body, to produce mature airway epithelia.
Since these epithelial cells are available in real people, potentially with a complete medical record, the question arises as to why there is any interest in using pluripotent stem cells to manufacture these epithelial cells.
The answer lies in the fact that human epithelial cells grown in culture have severe limitations: they are quite unpredictable; they only contain a limited range of cell types; and it is not possible to introduce targeted genetic mutations in them, despite several labs working to overcome these shortcomings.
Since growing pluripotent stem cells to mature airway epithelia has the potential of allowing researchers to study the how a disease develops and progresses over time, they can enable a disease to be monitored more closely.
Moreover, the use of pluripotent stem cell lines will make it possible to introduce a specific alternative gene and study its effects by comparing these cell lines to otherwise genetically similar sample cells.
Reproducible growth of epithelia with these advantages has the potential to improve disease modeling, to facilitate drug discovery across a variety of lung diseases, and to provide a limitless supply of cells for toxicology testing, and even has potential for developing regenerative medicinal options.
However, while there have been numerous cases of methods for manufacturing mature airway epithelia from pluripotent stem cells, the cells in these epithelia have tended to resemble embryonic and neonatal cells rather than fully developed adult cells.
The airways and lungs are derived from an area in the developing embryo called the anterior foregut endoderm. A typical technique for developing mature epithelia from stem cells involves starting with pluripotent stem cells and manipulating them to become endoderm cells, then anterior foregut endoderm cells, then lung progenitor cells, which can transform to form into any type of lung cell, and finally, develop into different types of airway epithelial cells.
Working on improving their previous work, by using a combination of synthetic “scaffolds” and in vivo growth in mice, the scientists managed to overcome most of the shortcomings of mature epithelial cells.
It has become a common procedure to implant immature organoids or cells derived from pluripotent stem cells in mice who have a compromised immune system. The growth of the cells in this in vivo environment, usually in the kidney capsule or in fatty tissue adjacent to the stomach or epididymis, helps organoids to grow, possibly due to the favorable levels of nutrients, oxygen and good circulation conditions.
The scientists began by taking human lung organoids that had been grown in a basement membrane substrate, called Matrigel, and inserting them directly into the mice. Although human epithelia were recovered from these initial transplants, they rarely contained lung cells.
The scientists fixed this problem by synthesizing the epithelia on synthetic polymer scaffolds, which is also used to culture pancreatic cells and in certain medical devices. Due to the size of the scaffolds, the only suitable transplantation site was the fat pad adjacent to the epididymis.
After the scaffolds had been extracted from the mice, which was usually after 8 to 15 weeks of growth in vivo, the organoids had on many occasions grown into tubes that were similar to adult airway passages and, they contained an overall high probability of mature cell types than had been produced before. Importantly, this latter finding was validated by detailed comparison to human fetal and adult airways.
If the scientists managed to uncover more about the underlying mechanism behind the maturation process, it might be possible to produce mature epithelia in vitro for experiments involved in advanced drug manufacturing techniques.
It will also be crucial to figure out whether mature alveoli, the lung cells that are involved in the exchange of oxygen and carbon dioxide, can be synthesized from pluripotent stem cells in a similar fashion using the same techniques. Detailed research is required to assess how the maturation of cells in vivo is impacted by different kinds of scaffolds.
Advantages Of Organoids Over Traditional Techniques
The three dimensional structure of organoid systems reproduce the complex spatial morphology of a differentiated epithelium to allow structurally similar cell-cell and cell-matrix interactions.
Ideally, the physical, cellular, and molecular characteristics of 3D organoid models mean that they are most likely to physiologically respond similarly with in vivo differentiated epithelia. Compared with traditional two dimensional (2D) cell culture models that often bear little physical, molecular, or physiological similarity to their tissue of origin, organoids are far superior.