Functional assessment of cryopreserved clinical grade hESC-RPE cells as a qualified cell source for stem cell therapy of retinal degenerative diseases

The biosafety and efficiency of transplanting retinal pigment epithelial (RPE) cells derived from both human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) have been evaluated in phase I and phase II clinical trials. For further large-scale application, cryopreserved RPE cells must be used; thus, it is highly important to investigate the influence of cryopreservation and thawing on the biological characteristics of hESC-RPE cells and their post-transplantation vision-restoring function. Here, via immunofluorescence, qPCR, transmission electron microscopy, transepithelial electrical resistance, and enzyme-linked immunosorbent assays (ELISAs), we showed that cryopreserved hESC-RPE cells retained the specific gene expression profile, morphology, ultrastructure, and maturity-related functions of induced RPE cells. Additionally, cryopreserved hESC-RPE cells exhibited a polarized monolayer, tight junction, and gap junction structure and an in vitro nanoparticle phagocytosis capability similar to those of induced hESC-RPE cells. However, the level of pigment epithelium-derived factor (PEDF) secretion was significantly decreased in cryopreserved hESC-RPE cells. Royal College of Surgeons rats with cryopreserved hESC-RPE cells engrafted into the subretinal space exhibited a significant decrease in the b-wave amplitude compared with rats engrafted with induced hESC-RPE cells at 4 weeks post transplantation. However, the difference disappeared at 8 weeks and 12 weeks post operation. No significant difference in the outer nuclear layer (ONL) thickness was observed between the two groups. Our data showed that even after cryopreservation and thawing, cryopreserved hESC-RPE cells are still qualified as a donor cell source for cell-based therapy of retinal degenerative diseases.

IL-6-induced acetylation of E2F1 aggravates oxidative damage of retinal pigment epithelial cell line

Oxidative damage in retinal pigment epithelial cells (RPE) is considered to be a crucial pathogenesis of age-related macular degeneration (AMD). Although dysregulation of the DNA repair system has been found in RPE cells of AMD patients, the detailed molecular mechanisms of this dysregulation and their relationship with the intraocular microenvironment of AMD patients remain unclear. Here, we established an RPE model of H₂O₂-induced oxidative stress and found that Sirtuin 1 (Sirt1)-mediated deacetylation of E2F transcription factor 1 (E2F1) was required for oxidation resistance in RPE cells. Moreover, E2F1 induced the expression of the chromatin-binding protein, high mobility group AT-Hook 1 (HMGA1), which promoted the transcription of glucose 6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme of the pentose phosphate pathway, to increase NADPH level for antioxidant defense. Interrupting the E2F1/HMGA1/G6PD regulatory axis increased reactive oxygen species (ROS) levels, DNA damage, and apoptosis in RPE cells under oxidative stress. Notably, interleukin 6 (IL-6), an inflammatory cytokine that is known to be upregulated in the intraocular fluid of AMD patients, induced phosphorylation (S47) of Sirt1 by activating PI3K/AKT/mTOR signaling, thereby inhibiting Sirt1 activity and increasing the acetylation of E2F1. Specific inhibitors of PI3K/AKT/mTOR signaling decreased DNA damage and ROS while increasing NADPH in RPE cells. Collectively, our findings demonstrate that IL-6-induced acetylation of E2F1 impairs the antioxidant capacity of RPE cells by disturbing the pentose phosphate pathway, which elucidates a relationship between the intraocular microenvironment and RPE oxidative damage in AMD and provides a possible therapeutic target for AMD.