For many of us, death will not be the end today. We don’t mean that in a metaphysical sense – and this isn’t an oddly tranquil preamble to herald the start of a zombie apocalypse – we’re talking about organ donation. Thanks to this life-saving procedure, many of us can literally pump iron, pose, and, um, poop long after we’re dead.
But as smart as our scientists are, there are some body parts that just don’t donate well. While organs like the kidneys or liver can be placed on ice for hours to slow damage from lack of oxygen, tissue from the central nervous system becomes non-viable in less than four minutes after death. And, frustratingly, it hasn’t been understood exactly why this happens and if it’s reversible. Until now.
“We were able to wake up photoreceptor cells in the human macula, which is the part of the retina responsible for our central vision and our ability to see fine detail and color,” explained Fatima Abbas, a postdoctoral fellow at the John A. Moran Eye Center of the University of Utah, in a statement. “In eyes taken up to five hours after the death of an organ donor, these cells responded to bright light, colored light, and even very faint flashes of light.”
Abbas is lead author of a new study, published this week in the journal Nature, aimed at figuring out how neurons die — and possible ways to revive them. Using the human retina as a model for the central nervous system, the team made a series of discoveries that they write “enable[e] transformative studies in the human central nervous system, Rais[e] Questions about the irreversibility of neuronal cell death and offer[e] new avenues for visual rehabilitation.”
Although the researchers managed to revive the photoreceptors, things did not look good, at least initially. “Until now, it has not been possible to get the cells in all the different layers of the central retina to communicate with each other in the way they normally do in a living retina,” explains study co-author Anne Hanneken, a retinal surgeon and specialist Scripps Research Associate Professor in the Department of Molecular Medicine at The Scripps Research Institute in San Diego.
The reason, they realized, was lack of oxygen. So they set out to find a way to overcome the damage caused by oxygen deprivation, with study co-author Frans Vinberg and Moran Eye Center colleague designing a special transport unit that would increase the supply of oxygen and other nutrients to the eyes from organ donors could recover within 20 minutes of death.
That wasn’t the only invention Vinberg brought to the experiment. He also developed a device that could stimulate these retinas to produce electrical activity and measure the output. This technique enabled the team to overcome another barrier: the first-ever recording of a ‘b-wave’ signal from the central retina of postmortem human eyes.
In living eyes, b-waves are a type of electrical signal associated with the health of the inner layers of the retina – so being able to stimulate them in postmortem eyes is really important. This means the layers of the macula were communicating with each other again, just as they were when we were alive, to help us see.
“We were able to get the retinal cells to talk to each other like they do in the living eye to mediate human vision,” explained Vinberg. “Previous studies have restored very limited electrical activity in the eyes of organ donors, but this has never been achieved in the macula, and never to the extent that we have now demonstrated.”
It might be a small result – after all, the macula is only about 5 millimeters (0.2 inch) in diameter – but the impact is huge. As it stands, death is a condition defined in part by the death of neurons, which so far has been shown to be irreversible. If neurons can indeed be brought back to life, it may force us to reconsider what counts as “dead” — and we may see the Grim Reaper held up longer than we already have.
Of course, even if that discovery eventually leads there, there are more pressing matters—as any eyeglass wearer can attest. And the team is confident that their results will also have great benefits for the future of vision research: “In the future, we will be able to use this approach to develop treatments to improve vision and light signaling in eyes with macular diseases, such as e.g. B. with age, to develop -related macular degeneration,” emphasized Hanneken.
The wealth of new results points to future researchers an opportunity to study neurodegenerative diseases throughout the body, not just the eyes, but their importance to vision research cannot be overstated. The study has already laid the groundwork for the revival of B-waves, and the team think they may have also uncovered the mechanism responsible for speed-limiting the speed of human central vision; The techniques also open the door to developing visual therapies using the working human eye, sparing researchers the ethical concerns of using non-human primates (and even more so human primates) or the scientific problems associated with using laboratory mice (which lack macula). are connected .)
Now they just need more eyes.
“The scientific community can now study human vision in ways that are simply not possible with laboratory animals,” Vinberg said. “We hope this will motivate organ donation societies, organ donors and eye banks by helping them understand the exciting new opportunities this type of research offers.”