Disembodied human tear glands that cry sound like something out of a sci-fi movie. But in the Netherlands, functional tear glands that don't attach to anyone's eyes (or emotions) are starring in their own real-life drama.
Researchers from the Hubrecht Institute and UMC Utrecht used stem cells to grow tiny tear glands in a petri dish that mimic the real thing. They hope these so-called organoids can serve as models for studying how the cells in human tear glands produce tears. The ultimate goal: to better understand and treat conditions such as dry eye disease or the autoimmune disorder Sjögren's syndrome, as well as cancers of the tear gland.
"Hopefully in the future, this type of organoid may even be transplantable to patients with nonfunctioning tear glands," says Marie Bannier-Hélaouët, a doctoral candidate at the Hubrecht Institute for developmental biology and stem cell research. She co-authored a study published Tuesday in the journal Cell Stem Cell that details the project.
Organoids are built in vitro, in 3D suspension, from a small number of stem cells that eventually multiply to form something resembling a real organ, such as a mini-brain, bladder, or, in this case, the glands located inside the upper eyelid.
Tear, or lacrimal, glands continuously supply fluid that's wiped across the surface of the eye every time we blink and then drains into small holes in the corners of our upper and lower lids before traveling down our tear ducts to the nose. In addition to displaying emotion, the fluid is essential to the eye's health, lubricating the cornea and helping ward off bacteria. Tear gland dysfunction can be annoying, causing scratching, stinging or burning sensations and sensitivity to light. But it can also be serious, leading to corneal abrasions or ulcerations or even blindness in the most severe cases.
Tear glands are made up of several kinds of cells. The lab-grown glands out of the Netherlands are made up of just one type, ductal, and cry in response to chemical stimuli such as noradrenaline, a neurotransmitter that sends a message from our neurons to our tear glands.
"Our eyes are always wet, as are the tear glands in a dish," Bannier-Hélaouët says of the artificial glands. Bannier-Hélaouët works in molecular biologist Hans Clevers' lab, which focuses on creating organoids for disease modeling and has previously re-created snake venom glands and mice tear glands.
It's not like you'd walk into Clevers' lab and see big tear-shaped drops floating in jars. The cells shed tears on the inside of the organoid, called the lumen. This causes the organoid to swell up like a balloon, with the size indicating how much tear production and secretion is going on.
This isn't the first time scientists have created human eye components from stem cells. In 2018, a team from John Hopkins University created eyeball parts in hopes of better understanding how and why we developed "trichromatic vision" -- the ability to see in red, blue and green.
The Dutch researchers acknowledge limitations to their tear gland, as it's comprised of just one of the main cell types found in the gland. They say they'd eventually like to grow a full tear gland from the broader array of cells that make it up, gaining an even more robust understanding of how we form tears.