Epithelial Ion Channels and Eye Disease

In the epithelial tissue of the eye, researchers have found cellular components that were previously thought to exist only in electrically active tissues, such as those in nerves and in the heart. They found that these components are involved in the renewal of sensory cells in the retina, which is adjacent neural tissue. The study was published today in BMC Biology.

“These proteins, voltage-gated sodium channels, are typically responsible for generating electrical signals in the nerve cells,” says senior author Soile Nymark from Tampere University. “Therefore, it is exciting to think of what they could do in the epithelial tissue, which is traditionally considered electrically inactive.”

In order for our vision to work properly, retinal sensory cells need to be constantly renewed, and this renewal requires the operation of a strictly controlled and multistep phagocytosis process in the retinal pigment epithelium. In this process, part of the retinal sensory cell is detached and enclosed within the adjacent epithelium. The epithelial tissue then metabolizes these detached parts of the sensory cells in a controlled manner and thus maintains normal functioning of the retina.

The present discovery reveals how the ion channel proteins responsible for the electrical signaling of neurons influence the phagocytosis process. This process is impaired in many retinal degenerative diseases, the most important example being age-related macular degeneration (AMD). The mechanisms and causes of these diseases can now be studied in the light of the new findings, which could lead to new opportunities for the development of curative treatments.

Our present understanding of epithelial tissue function is strongly based on cell biological studies. In the present study, the researchers investigated the epithelial tissue of the eye by utilizing techniques that have traditionally been used to determine the electrical communication of nerve cells.

“This perspective enabled our new observation and highlights that the major role of electrical phenomena and the underlying ion channels in the functioning of epithelial tissue may not yet be fully understood,” Nymark points out.

In the future, the multidisciplinary project will focus in particular on the role of the newly discovered ion channels in the communication between epithelial cells.

Image: Cells of the retinal pigment epithelium. An epithelial cell is in the middle with microvilli (golden), voltage-gated sodium channels (white), and the photoreceptor cells of the retina (blue) made fluorescent and imaged with a high-resolution confocal microscope. The size of the image is 38 x 38 micrometers (one micrometer is one-thousandth of a millimeter). Image courtesy of Julia Johansson and Teemu Ihalainen, Tampere University.