6-Month PROJECT UPDATE
We are excited to share the interim progress report of our project. This project’s primary goal is to determine the criteria and protocols for generating and maintaining viable macula patches from human donor eyes. The ultimate goal is to generate patches of the macula that, in the future, could be used to restore vision in blind type 1 diabetic patients. A first step to achieve this goal is to be able to recover patches of the human macula that can generate and transmit light signals from photoreceptors, the sensory neurons in the retina, all the way to ganglion cells, the output neurons in the retina that project their axons to the visual centers of the brain for visual perception. To do this, we have assembled a team that currently involves research scientists, clinicians, eye banks, and organ donor society. With this team, we have determined how time from death to eye recovery, cause of death, postmortem light exposure, hypoxia, and acidosis contribute to our ability to restore light-evoked responses in the retina and specifically in the human macula. We have established conditions for the ex vivo eyes. Normal retinal light signaling can be maintained for at least 20 hours, and ongoing experiments are expected to extend this time window significantly. Our results demonstrate that we can restore light-evoked photoreceptor responses under certain conditions when eyes are recovered 0.5 – 4 hours postmortem. However, the transmission of light signals from photoreceptors to second-order neurons is often compromised even in the eyes recovered just 30 minutes after death. Using mice in our experiments have demonstrated postmortem hypoxia as the driving force for this apparent irreversible loss of light signal transmission in the retina. Ongoing investigations are testing if conditioning of mice to hypoxia before death or postconditioning of the eyes using drugs to induce hypoxia signaling pathways could promote the revival of the light signal transmission in the postmortem eyes. On the other hand, in pigs, we are conducting experiments to determine the maximal time window from death to enucleation, still allowing a robust restoration of light signal transmission in the retina. Based on these experiments, our organ donor experiments’ criteria and protocols will be modified to establish a method for producing fully functional human macular patches.
One of the major complications in type 1 diabetes (T1D) is vision impairment. Diabetic retinopathy is the leading cause of blindness among working-age adults, and accounts for a high degree of disability and long-term morbidity. Current approaches to treat diabetic retinopathy have limited success to restore vision when the retina is damaged. We are investigating the feasibility and technical challenges associated with the far-reaching concept of retinal cell replacement, a future goal that we believe has the potential to improve vision to blind T1D’s.
We envision a retinal cell replacement program consisting of several stages with multi-disciplinary and multi-institutional clinicians and scientists. For this project, we want to address 2 phases: Phase 1 consists of maintaining the viability of retinal tissue in postmortem eyes. Phase 2 consists of identifying conditions that allow cells to integrate into the retina.
Over the past three years, we have generated preliminary data that supports the feasibility of Phase 1. With a multidisciplinary team consisting of representatives from regional eye banks, organ donor programs, visual chemists, electrophysiologists and clinicians, we have succeeded in developing the techniques for maintaining or reviving the viability of macular and peripheral retinal tissue in postmortem human eyes. Initially, we found the neuronal viability in the human macula from donor eyes was compromised. We attributed the poor outcomes to multiple obstacles, including prolonged death-enucleation times. To solve these problems, we adopted a novel approach, using human organ donor eyes.
Dr. Hanneken became a registered organ donor research recipient and established a collaboration with LifeSharing, a major organ donor Society in San Diego and Imperial Valley. She harvested human organ donor eyes at the time that the transplant team was procuring heart and lung tissues, which overcame multiple obstacles. The responses with human organ donor eye tissues were significantly better, particularly in the outer retina where photoreceptor responses could be measured with good electrical amplitudes. However, there are still challenges and technical factors that reduce viability, particularly in the inner retina function.
In this project, we will use sophisticated approaches to examine the timing and the harvesting conditions of the human eye donor to optimize neuronal survival and/or revival of retinal neurons. These results are expected to establish criteria and protocols for potential retinal cell replacement capable of generating and transmitting light-evoked signals from photoreceptors all the way to the retinal ganglion cells, which are the output neurons of the retina.