Stem-cell-derived organoids that swell up with tears could shed light on the biology of crying and dry-eye disease, suggests a study publishing March 16 in the journal Cell Stem Cell. Although regenerative therapies using human tear-gland organoids will not be possible anytime soon, these researchers have demonstrated that the organoids can engraft, integrate, and produce mature tear products upon transplantation into mouse tear glands.
"We hope that scientists will use our model to identify new treatment options for patients with tear-gland disorders by either testing new drugs on a patient's organoids or expanding healthy cells and, one day, using them for transplantation," says senior study author Hans Clevers (@HansClevers) of the Hubrecht Institute.
The tear gland, or lacrimal gland, secretes the watery layer of the tear film and is essential for lubricating and protecting the eye. Dysfunction in tear production or secretion can lead to dry-eye disease or Sjögren's syndrome--a poorly understood autoimmune disease that causes dry eyes and dry mouth. Currently, treatment options for patients with disorders of the lacrimal gland include eye drops, tear-duct plugs, and surgery.
"What struck us is that at least 5% of the adult population is estimated to have dry-eye disease, which is most of the time related to a defect of tear production by the tear gland," says co-first study author Yorick Post of the Hubrecht Institute. "But treatment options are limited because there was no complete understanding of the biology and no reliable, long-term in vitro model to study the tear gland."
To overcome this hurdle, the researchers generated 3D mouse and human lacrimal-gland organoids derived from adult stem cells by adapting a protocol they previously used for other organs. The organoids could be expanded over multiple months and recapitulated structural, transcriptional, and functional features of the lacrimal-gland epithelium--tissue that secretes most of the tear fluid. Remarkably, the organoids swelled up like a balloon after being exposed to the neurotransmitter noradrenaline, which triggers tear secretion.
"The challenge was to get the organoids to cry, as this is a hallmark of the lacrimal gland," says co-first study author Marie Bannier-Hélaouët of the Hubrecht Institute. "We had to modify the cocktail of factors the organoids are grown in so that they would become the mature cells that we have in our tear glands and that are capable of crying."
The researchers leveraged the mouse organoids to explore the role of Pax6--the master control gene for eye development--in adult tear glands. By using CRISPR/Cas9 genome editing to delete Pax6, they discovered that the gene is an important contributor to the maturation of adult lacrimal-gland epithelial cells. These particular organoids could provide valuable insights into potential treatments for Sjögren's syndrome because PAX6 deficiency has been observed in the eye tissue of these patients.
Using single-cell mRNA sequencing, the researchers also examined poorly understood cellular features and origins of tear components in the lacrimal gland. Their single-cell atlas revealed new tear components and demonstrated that ductal and acinar cells in the human lacrimal gland secrete a different repertoire of tear components.
To test the potential of the organoids for regenerative medicine, the researchers then transplanted human organoid cells into mouse lacrimal glands. Two weeks later, the human organoid cells formed duct-like structures that remained in the lacrimal gland for at least two months. Engrafted organoids appeared to self-organize, and some cells were proliferating up to two months after transplantation. Moreover, the researchers detected tear proteins inside the ducts formed by the transplanted cells.
The beneficial effects of organoid transplantation will need to be validated in mouse models of dry eye disease. Future studies could also focus on modeling Sjögren's syndrome by incorporating immune cells into the organoids. "Patient-derived organoids open up new avenues to study lacrimal gland diseases in a personalized fashion," Clevers says. "But there is still a long way to go before these mini-organoids can be used for regenerative therapies."
This work was supported by a grant from the Leducq Foundation, a NWO-ZonW grant, an ERC Advanced Grant, a VENI grant from NWO-ZonMW, and the gravitation program CancerGenomiCs.nl from the Netherlands Organisation for Scientific Research (NWO). H.C. is the inventor on several patents related to organoid technology; his full disclosure is given at https://www.uu.nl/staff/JCClevers/.
Cell Stem Cell, Bannier-Hélaouët et al.: "Exploring the human lacrimal gland using organoids and single-cell sequencing" https://www.cell.com/cell-stem-cell/fulltext/S1934-5909(21)00075-8
Cell Stem Cell (@CellStemCell), published by Cell Press, is a monthly journal that publishes research reports describing novel results of unusual significance in all areas of stem cell research. Each issue also contains a wide variety of review and analysis articles covering topics relevant to stem cell research ranging from basic biological advances to ethical, policy, and funding issues. Visit: http://www.cell.com/cell-stem-cell. To receive Cell Press media alerts, contact firstname.lastname@example.org.
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