LONDON — The eyes of the scientific community are firmly fixed on London. Scientists at University College London Great Ormond Street Institute of Child Health (UCL GOS ICH) report they’ve grown miniature human eyes, making it much easier to study and understand the development and progression of blindness in the rare genetic disease known as Usher syndrome.
These 3D “mini eyes” are called organoids, and were grown using stem cells generated via skin samples donated by patients at Great Ormond Street Hospital for Children (GOSH).
In a healthy human eye, light-detecting rod cells are found in the back of the eye within the retina, which is responsible for processing images. In this latest research, study authors were actually able to provoke these rod cells to “organize themselves” into layers mimicking how they would be organized in the retina, thus creating a ‘mini eye’.
These mini eyes represent an enormous step forward in this field. Prior efforts using animal cells hadn’t been able to mimic the same sort of sight loss as that seen in Usher syndrome, the most common genetic cause of deafness and blindness. It’s estimated to impact three to ten in 100,000 people globally. Children diagnosed with Type 1 Usher syndrome are in many cases born very deaf, while their sight deteriorates at a much slower rate before blindness sets in around adulthood.
While cochlear implants can help mitigate hearing loss, there are currently no treatments for retinitis pigmentosa, considered the primary cause of vision loss associated with Usher syndrome. This new work, while preliminary, opens up exciting new possibilities towards understanding the condition and designing an effective future treatment that could help countless people retain their eyesight.
How are scientists using these ‘mini-eyes’ to improve medical treatments?
These newly created mini eyes will allow researchers to study light-sensing cells from the human eye at an individual level, and in more detail than ever before. More specifically, thanks to powerful single cell RNA-sequencing, this was the first time researchers have been able to view the tiny molecular changes in rod cells just before death.
Now, via these mini eyes, the research team discovered that Müller cells also appear involved in the development of Usher syndrome. Müller cells are usually responsible for metabolic and structural support of the retina. Cells taken from people with Usher syndrome abnormally displayed genes turned on for stress responses and protein breakdown. Reversing those developments may be key to stopping the progression of the disease.
Since the mini eyes were grown using cells donated both by patients with and without the genetic “fault” that is responsible for Usher syndrome, researchers were able to compare healthy cells with those that will lead to blindness. Forming a clearer understanding of these differences could yield pivotal clues as to what changes occur in the eye before a child’s vision begins to deteriorate. Consequently, this research could help locate the best targets for early treatment, which is crucial to providing the best possible health outcome.
“It’s difficult to study the inaccessible tiny nerve cells of the patient’s retina as they are so intricately connected and delicately positioned at the back of the eye. By using a small biopsy of skin, we now have the technology to reprogram the cells into stem cells and then create lab-grown retina with the same DNA, and therefore same genetic conditions, as our patients,” says first study author Dr. Yeh Chwan Leong in a media release.
The mini eyes aren’t limited to Usher syndrome research. Study authors explain these organoids can help plenty of researchers better understand other inherited conditions in which the death of rod cells in the eye occurs, such as forms of retinitis pigmentosa without deafness. Moreover, the technology used to grow disease models via human skin cells can be used for a number of other diseases.
Future research is already being planned that will create new mini eyes from more patient samples, and then use them to identify treatments. One day in the future it may be possible to edit a person’s DNA within specific eye cells to avoid blindness.
“We are very grateful to patients and families who donate these samples to research so that, together, we can further our understanding of genetic eye conditions, like Usher syndrome,” explains senior study author Professor Jane Sowden, Professor of Developmental Biology & Genetics at UCL. “Although a while off, we hope that these models can help us to one day develop treatments that could save the sight of children and young people with Usher syndrome.”
The study is published in Stem Cell Reports.