Multilayered control of retinal stem/progenitor cell fate in the single-cell and organoid era: Developmental blueprints and regenerative opportunities

Metabolic Features of Mouse and Human Retinas: Rods versus Cones, Macula versus Periphery, Retina versus RPE.

Immunological Properties of Human Embryonic Stem Cell-Derived Retinal Pigment Epithelial Cells.

The identification of cells with properties of retinal progenitor cells (RPCs) in the adult human ciliary margin (CM) prompted a number of studies of their proliferative and differentiation potential. One of the remaining challenges is to find a feasible method of isolating RPCs from the patient's eye. In the human CM, only the iris pigment epithelium (IPE) is easily obtained by a minimally invasive procedure. In the light of recent studies questioning the existence of RPCs in the adult mammalian CM, we wanted to assess the potential of the adult human IPE as source of RPCs. The IPE were isolated from peripheral iridectomies during glaucoma surgery, and IPE and ciliary body (CB) epithelium were also isolated from post-mortem tissue. Cells were cultivated in sphere-promoting conditions or as monolayers. Whole-tissue samples, undifferentiated and differentiated cells were studied by immunocytochemistry, RT-PCR and transmission electron microscopy. The adult human IPE, like the CB, expressed markers of RPCs such as Pax6, Sox2 and Nestin in vivo. Both sphere-promoting and monolayer cultures preserved this phenotype. However, both IPE/CB cultures expressed markers of differentiated epithelial cells such as Claudin, microphtalmia-associated transcription factor (MITF) and Cytokeratin-19. Ultrastructurally, IPE spheres displayed epithelial-like junctions and contained mature melanosomes. After induced differentiation, IPE-derived cells showed only partial neuronal differentiation expressing β-III-tubulin, Map-2 and Rhodopsin, whereas no mature glial markers were found. Proliferative cells with some properties of RPCs can be isolated from the adult human IPE by peripheral iridectomies. Yet, many cells retain properties of differentiated epithelial cells and lack central properties of somatic stem cells.

Toward the Miracle of Retinal Reanimation

Characterization of Human Induced Pluripotent Stem Cell-Derived Retinal Pigment Epithelium Cell Sheets Aiming for Clinical Application

To explore the safety and efficacy of the allogeneic induced pluripotent stem cell (iPSC)-derived retinal pigment epithelium (RPE) strip transplantation for patients with RPE degeneration. Single-arm, open-label, interventional study. Three eyes from 3 patients clinically diagnosed with RPE impairment disease; 1 patient had dry age-related macular degeneration (AMD), and remaining 2 patients had MERTK-associated retinitis pigmentosa. Allogeneic iPSC-derived RPE strip transplantation was performed by a 25-gauge pars plana vitrectomy. The RPE strips were prepared by incubating iPSC-derived RPE cells in 2-mm-wide grooves in the mold. Artificial retinal detachment was generated using a 38-gauge subretinal cannula, and the RPE strips were injected into the retinal bleb using a 31-gauge cannula with the maximum graft dose limited to 2 strips. The reduction of RPE abnormal area by the engraftment of transplanted allogeneic iPSC-derived RPE cells, which was measured by analyzing fluorescein angiography with an automated evaluation program at pretransplantation and up to 52 weeks posttransplantation. The primary endpoint of reducing abnormal areas of RPE through the survival of the transplanted graft cells was achieved in all patients at 52 weeks posttransplantation. Visual function assessments confirmed significant vision-related quality of life improvement and potential retinal sensitivity restoration in 1 patient with dry AMD. The successful subretinal delivery of the iPSC-derived RPE strips was confirmed during and immediately after surgery. The engraftment of RPE cells migrated out from the strips was observed using polarization-sensitive OCT specifically and visualized as characteristic hexagonal cells via adaptive optics imaging in all patients. While no serious adverse events occurred, suspected immune reactions to graft cells and epiretinal membrane formation were observed in 1 patient each. A decrease in the RPE abnormal area by reliable delivery of allogeneic iPSC-derived RPE strips was achieved in all 3 cases with no serious adverse events. Further long-term studies and larger cohorts with better preoperative vision are warranted to evaluate the safety and efficacy of RPE strip transplantation. Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

A semi-automated pipeline for quantifying drusen-like deposits in human induced pluripotent stem cell-derived retinal pigment epithelium cells

Adeno-associated viral vectors are showing great promise as gene therapy vectors for a wide range of retinal disorders. To date, evaluation of therapeutic approaches has depended almost exclusively on the use of animal models. With recent advances in human stem cell technology, stem cell-derived retina now offers the possibility to assess efficacy in human organoids in vitro. Here we test six adeno-associated virus (AAV) serotypes [AAV2/2, AAV2/9, AAV2/8, AAV2/8T(Y733F), AAV2/5, and ShH10] to determine their efficiency in transducing mouse and human pluripotent stem cell-derived retinal pigment epithelium (RPE) and photoreceptor cells in vitro. All the serotypes tested were capable of transducing RPE and photoreceptor cells in vitro. AAV ShH10 and AAV2/5 are the most efficient vectors at transducing both mouse and human RPE, while AAV2/8 and ShH10 achieved similarly robust transduction of human embryonic stem cell-derived cone photoreceptors. Furthermore, we show that human embryonic stem cell-derived photoreceptors can be used to establish promoter specificity in human cells in vitro. The results of this study will aid capsid selection and vector design for preclinical evaluation of gene therapy approaches, such as gene editing, that require the use of human cells and tissues.

The therapeutic potential of pluripotent stem cells is great as they promise to usher in a new era of medicine where cells or organs may be prescribed to replace dysfunctional tissue. At the forefront are efforts in the eye to develop this technology as it lends itself to in vivo monitoring and sophisticated non-invasive imaging modalities. In the retina, retinal pigment epithelium (RPE) is the most promising replacement cell as it has a single layer, is relatively simple to transplant, and is associated with several eye diseases. However, after transplantation, the cells may transform and cause complications. This transformation may be partially due to incomplete maturation. With the goal of learning how to mature RPE, we compared induced pluripotent stem cell-derived RPE (iPSC-RPE) cells with adult human primary RPE (ahRPE) cells and the immortalized human ARPE-19 line. We cultured ARPE-19, iPSC-RPE, and ahRPE cells for one month, and evaluated morphology, RPE marker staining, and transepithelial electrical resistance (TEER) as quality control indicators. We then isolated RNA for bulk RNA-sequencing and DNA for genotyping. We genotyped ahRPE lines for the top age-related macular degeneration (AMD) and proliferative vitreoretinopathy (PVR) risk allele polymorphisms. Transcriptome data verified that both adult and iPSC-RPE exhibit similar RPE gene expression signatures, significantly higher than ARPE-19. In addition, in iPSC-RPE, genes relating to stem cell maintenance, retina development, and muscle contraction were significantly upregulated compared to ahRPE. We compared ahRPE to iPSC-RPE in a model of epithelial-mesenchymal transition (EMT) and observed an increased sensitivity of iPSC-RPE to producing contractile aggregates in vitro which resembles incident reports upon transplantation. P38 inhibition was capable of inhibiting iPSC-RPE–derived aggregates. In summary, we find that the transcriptomic signature of iPSC-RPE conveys an immature RPE state which may be ameliorated by targeting “immature” gene regulatory networks.

An improved protocol for generation and characterization of human-induced pluripotent stem cell-derived retinal pigment epithelium cells

Retinoid Processing in Induced Pluripotent Stem Cell-Derived Retinal Pigment Epithelium Cultures.

Pharmacologic inhibitors of MEK are important anti-cancer drugs but can result in MEK inhibitor-Associated Retinopathy (MEKAR) in which vision is lost due to serous retinal detachments that form via an unknown mechanism. We hypothesized that the cause of this side effect is drug-induced dysfunction of retinal pigment epithelial (RPE) cells. To test this hypothesis, we used human induced pluripotent stem cell-derived RPE cells. We treated mature, hiPSC-derived RPE cells with selumetinib and measured impacts on RPE-specific function, structure, and gene expression. Selumetinib increases the ability of hiPSC-derived RPE to internalize bovine rod outer segments (1.9 vs 3.0, p=0.0024). It also decreases expression of aquaporin 1 during the first 10 days of treatment (2.7 vs 1.1, p=0.0015). It has no effect on the ability of hiPSC-derived RPE to maintain membrane integrity. Selumetinib alters gene expression of hiPSC-derived RPE, with significant changes in genes involved in transport of ions and small molecules regulating cell volume and lysosomal acidification. Selumetinib may lead to subretinal fluid accumulation by both increasing secretions into this space and decreasing outflow.

BackgroundTransplantation of human pluripotent stem cell-derived retinal pigment epithelium (RPE) is an urgently needed treatment for the cure of degenerative diseases of the retina. The transplanted cells must tolerate cellular stress caused by various sources such as retinal inflammation and regain their functions rapidly after the transplantation. We have previously shown the maturation level of the cultured human embryonic stem cell-derived RPE (hESC-RPE) cells to influence for example their calcium (Ca2+) signaling properties. Yet, no comparison of the ability of hESC-RPE at different maturity levels to tolerate cellular stress has been reported.MethodsHere, we analyzed the ability of the hESC-RPE populations with early (3 weeks) and late (12 weeks) maturation status to tolerate cellular stress caused by chemical cell stressors protease inhibitor (MG132) or hydrogen peroxide (H2O2). After the treatments, the functionality of the RPE cells was studied by transepithelial resistance, immunostainings of key RPE proteins, phagocytosis, mitochondrial membrane potential, Ca2+ signaling, and cytokine secretion.ResultsThe hESC-RPE population with late maturation status consistently showed improved tolerance to cellular stress in comparison to the population with early maturity. After the treatments, the early maturation status of hESC-RPE monolayer showed impaired barrier properties. The hESC-RPE with early maturity status also exhibited reduced phagocytic and Ca2+ signaling properties, especially after MG132 treatment.ConclusionsOur results suggest that due to better tolerance to cellular stress, the late maturation status of hESC-RPE population is superior compared to monolayers with early maturation status in the transplantation therapy settings.

In vitro disease modeling of oculocutaneous albinism type 1 and 2 using human induced pluripotent stem cell-derived retinal pigment epithelium

The purpose of this study was to characterize the secretion profile of induced pluripotent stem cell-derived retinal pigment epithelium (iPS-RPE) during wound healing. iPS-RPE was used to develop an in vitro wound healing model. We hypothesized that iPS-RPE secretes cytokines and growth factors which act in an autocrine manner to promote migration and proliferation of cells during wound healing. iPS-RPE was grown in transwells until fully confluent and pigmented. The monolayers were scratched to induce a wound. Levels of Ki-67, β-catenin, e-cadherin, n-cadherin, and S100A4 expression were analyzed by immunofluorescent labeling. Cell culture medium samples were collected from both the apical and basolateral sides of the transwells every 72 hours for 21 days. The medium samples were analyzed using multiplex ELISA to detect secreted growth factors and cytokines. The effects of conditioned medium on collagen gel contraction, cell proliferation, and migration were measured. iPS-RPE underwent epithelial-mesenchymal transition (EMT) during wound healing as indicated by the translocation of β-catenin to the nucleus, cadherin switch, and expression of S100A4. GRO, GM-CSF, MCP-1, IL-6, and IL-8 were secreted by both the control and the wounded cell cultures. VEGF, FGF-2, and TGFβ expression were detected at higher levels after wounding than those in control. The proteins were found to be secreted in a polarized manner. The conditioned medium from wounded monolayers promoted collagen gel contraction, as well as proliferation and migration of ARPE 19 cells. These results indicate that after the monolayer is wounded, iPS-RPE secretes proteins into the culture medium that promote increased proliferation, contraction, and migration.