Researchers in The Netherlands have grown their tear glands in a lab – and then made them cry. Don’t worry, this isn’t the result of evil scientists with too much time on their hands: the cluster of cells were created to help understand eye diseases.
Using stem cells and a cocktail of growth factors, experts at University Medical Centre Utrecht were able to build tear ‘organoids’. These are essentially a three-dimensional collection of cells designed to resemble miniature versions of tear glands (also called lacrimal glands).
Mimicking the wetness of the human eye, these petri-dish organoids were also suspended in liquid.
Scientists soon discovered that the glands reacted to same chemical stimuli humans use to produce tears. But, as the organoids lacked ducts to secrete this liquid, they swelled up like balloons and some ruptured. Once transplanted into mice, however, the organoids eventually developed duct-like structures.
"Further experiments revealed that different cells in the tear gland make different components of tears. And these cells respond differently to tear-inducing stimuli," said Dr Yorick Post, another researcher on the project.
Read more about the science of crying:
Tear glands aren’t only useful to convey emotions in humans, but they also lubricate the eye, providing a protective layer of liquid over the cornea. This means unhealthy glands can lead to serious medical problems.
"Dysfunction of the tear gland, for example in Sjögren's syndrome, can have serious consequences including dryness of the eye or even ulceration of the cornea. This can, in severe cases, lead to blindness," Dr Rachel Kalmann, ophthalmologist and researcher on the project, explained.
It’s hoped the development of the tear organoids can help the testing of new drugs, and help scientists understand how cancers in the gland first form.
"Hopefully in the future, this type of organoids may even be transplantable to patients with non-functioning tear glands," added PhD student Marie Bannier-Hélaouët, who worked on the project.
This isn’t the first time that scientists have sculpted sections of the human eye using stem cells. In 2018, a team from Johns Hopkins University grew human retinas in petri-dishes to help investigate how our colour vision developed.
Reader Q&A: Why do humans cry?
Asked by: Luke Azzopardi, Malta
Either for emotional reasons, or to wash away irritants such as dust, grit, insects and ‘lachrymatory agents’ – chemicals that make you cry. When an onion is cut, its enzymes mix with sulphoxides and sulphenic acids to produce a gas called propanethiol S-oxide, which reacts with tears to form sulphuric acid. This irritation alerts brain systems that then tell the lacrimal glands to stimulate tears to wash it away. These are called ‘reflex tears’ and are also provoked by coughing and yawning.
Emotional tears are different, containing more prolactin, adrenocorticotropic hormone and encephalin (a natural painkiller). Part of the brain’s limbic system, including the hypothalamus, control emotional responses including fear, anger and grief, and can signal the lacrimal glands to produce tears.
The really difficult question is why emotional humans cry at all. The reason may be social. Blurred vision and sobbing provide a social signal of weakness and neediness, and crying can bring groups together – for example, when a family is in a state of grief.
Read more about the science of tears: