Russian scientists have developed a method to accurately verify the function of artificially grown retinal cells. This method will help more reliably test drugs for degenerative vision diseases and may be useful in the creation of bionic implants. MIPT researchers were the first in Russia to thoroughly measure the electrical activity of light-sensitive cells in three-dimensional retinal organoids and compile a kind of “electrical passport” for them.
Organoids are small, three-dimensional tissue models grown from reprogrammed human blood cells. First, the cells are returned to an embryonic-like state, then their development is directed so that they transform into retinal cells. After about six months, true photoreceptors—rods and cones—appear in the organoids, which capture light and convert it into a nerve signal. Such models allow the study of processes that are extremely difficult to investigate in a living human eye.
To ensure that the cultured cells not only look like photoreceptors but also function similarly, scientists developed a new method. Using a thin glass microelectrode, they gained access inside an individual cell and measured the movement of ions across its membrane. Simultaneously, the cells were illuminated with special dyes to accurately understand that the signal was coming specifically from the photoreceptor, and not from an adjacent neuron.
Experiments showed that the electrical activity of cells changes as the organoid matures. On day 80, the signal was still very weak; by day 130, it became noticeable, and after 150 days, it approached the levels of adult primate cells. Most photoreceptor-like cells did not exhibit typical nerve impulses, but some did produce action potentials. Scientists also recorded ionic currents whose characteristics almost matched the data for mammalian photoreceptors.
This method provides a quantitative way to check whether a new drug restores the function of light-sensitive cells. It can also help in the creation of retinal implants: developers will be able to take into account the real electrical characteristics and sensitivity thresholds of living photoreceptors to make stimulation more precise and safer.
In the future, scientists want to study signal transmission between photoreceptors and adjacent retinal cells. The research is published by Springer Nature Link in the book “Retinal Gene Therapy: Methods and Protocols”.