Armed with an ability to morph into a myriad of cell types, stem cells have taken centre stage in regenerative treatments that replace diseased cells with healthy ones. Such strategies hold a promise for treating a range of conditions such as age-related macular degeneration (AMD), where ageing retinal pigment epithelial (RPE) cells cause progressive vision loss.
While data from early clinical trials suggest that stem cell-derived RPEs are safe and feasible for use in patients with AMD, it’s not as clear what makes these cells thrive—or fail to do so—after their move from a sterile plate to a living organ.
“There are knowledge gaps about how RPE cell heterogeneity impacts transplant outcomes, and how these cells evolve and adapt at a single-cell level once they’re in the eye,” said Xinyi Su, Senior Principal Investigator at A*STAR’s Institute of Molecular and Cell Biology (IMCB). “To improve cell-based AMD treatments, we need to know what makes those cells survive, integrate and function better post-transplant: which genes are expressed, the patterns of that expression, and how the recipient retina interacts with all of it.”
Post-transplantation outcomes for RPE cells have remained a grey area because traditional imaging and histological techniques don’t provide insights at a molecular level on how transplanted cells are faring, Su added.
Together with co-corresponding author Tim Xiaoming Hu, Su and IMCB colleagues collaborated with researchers from the Singapore Eye Research Institute; the Yong Loo Lin School of Medicine, National University of Singapore; and the Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, in a high-resolution study of the fate of transplanted RPE cells in an in vivo rabbit model.
The team first surgically transplanted RPE cells derived from human pluripotent stem cells (hPSC) into rabbit eyes. Using cutting-edge single-cell RNA sequencing technology and computational dataset integration, the team looked for changes in gene expression patterns in individual RPE cells between those on a petri dish and those transplanted in the rabbit eye.
When the team compared transplanted cells against hPSC-derived RPE cells kept in vitro for the same duration, the former was not only more uniform, but showed gene expression profiles that much more closely resembled healthy, native adult RPE cells. “We showed that these transplanted cells evolve to become functionally closer to their counterparts in the adult human eye,” said Su.
They also identified boosted activity levels in key transcription factors such as FOS, JUND and MAFF in transplanted cells, which targeted genes essential to the RPE cells’ ability to help maintain a healthy retina and support the survival of photoreceptor cells responsible for vision.
According to Su, RPE cells that display this distinct gene expression profile can be induced and selectively isolated in culture to enhance their efficacy once transplanted. “In the longer term, we hope to move forward with FDA-approved manufacturing processes for these ‘superior’ RPE cells as an AMD treatment product,” said Su.
The A*STAR-affiliated researchers contributing to this research are from the Institute of Molecular and Cell Biology (IMCB).