When patients lose some organ function due to disease or injury, it would be ideal to simply regrow the lost organ. But organogenesis is complex and tightly regulated, involving special stem cells that are fated to become specific tissues. And with the exception of some organs such as hair follicles, those precursor cells are only present during early development.
The alternative is to use embryonic stem cells or induced pluripotent stem cells, which can transform into many types of cells to create an organoid, or a simplified three-dimensional tissue resembling the structure of a real organ. Growing functional organoids in the lab would enable patients with failing organs to recover at least some of the original organs’ function.
Researchers led by Kenji Mishima of Showa University and Takashi Tsuji of the RIKEN Center for Biodynamic Systems Research have recreated salivary gland tissue, which can be damaged by Sjogren’s syndrome or by radiation therapy for cancer. These glands develop from an early structure called the oral ectoderm, but the actual process is not fully understood.
Organ development happens through a complex process of chemical signaling and changes in gene expression, so the researchers explored what the important changes were. They identified two transcription factors, Sox9 and Foxc1, as key to the differentiation of stem cells into salivary gland tissue. They also identified a pair of signaling chemicals, FGF7 and FGF10, that induce cells into expressing those transcription factors to differentiate into salivary gland tissue.
To create a salivary gland organoid, the researchers used a cocktail of chemicals that allowed the formation of the oral ectoderm. Next, they used this mix to induce the embryonic stem cells to form the ectoderm and then used viral vectors to get the cells to express both Sox9 and Foxc1. Adding the two chemicals to the mix induced the cells to form tissue that genetic analysis revealed was very similar to actual developing salivary glands in the embryo.
Finally, the researchers implanted the organoids into mice without saliva glands and tested them by feeding the mice citric acid. When the organoids were transplanted with mesenchymal tissue, another embryonic tissue that allows the glands to attach to other tissues, the implanted tissues were found to be properly connected to the nerve tissue and secreted a substance that was remarkably similar to real saliva in response to the stimulation.
“It was incredibly exciting to see that the tissues we created actually functioned in a living mammal. This is an important proof of concept that organoids are a valid alternative to actual organs,” said Mishima.
“We continue to work to develop functional tissues to replace the functions of various organs, and we hope that these experiments will soon find their way into the clinic and help patients suffering from a variety of disorders,” said Tsuji.
The study, “Generation of Orthotopically Functional Salivary Gland from Embryonic Stem Cells,” was published by Nature Communications.