Adult Human Retinal Pigment Epithelium Research Articles

Single-cell transcriptomics reveals maturation of transplanted stem cell–derived retinal pigment epithelial cells toward native state

Transplantation of stem cell-derived retinal pigment epithelial (RPE) cells is considered a viable therapeutic option for age-related macular degeneration (AMD). Several landmark Phase I/II clinical trials have demonstrated safety and tolerability of RPE transplants in AMD patients, albeit with limited efficacy. Currently, there is limited understanding of how the recipient retina regulates the survival, maturation, and fate specification of transplanted RPE cells. To address this, we transplanted stem cell-derived RPE into the subretinal space of immunocompetent rabbits for 1 mo and conducted single-cell RNA sequencing analyses on the explanted RPE monolayers, compared to their age-matched invitro counterparts. We observed an unequivocal retention of RPE identity, and a trajectory-inferred survival of all invitro RPE populations after transplantation. Furthermore, there was a unidirectional maturation toward the native adult human RPE state in all transplanted RPE, regardless of stem cell resource. Gene regulatory network analysis suggests that tripartite transcription factors (FOS, JUND, and MAFF) may be specifically activated in posttransplanted RPE cells, to regulate canonical RPE signature gene expression crucial for supporting host photoreceptor function, and to regulate prosurvival genes required for transplanted RPE's adaptation to the host subretinal microenvironment. These findings shed insights into the transcriptional landscape of RPE cells after subretinal transplantation, with important implications for cell-based therapy for AMD.

Transcriptional comparison of adult human primary Retinal Pigment Epithelium, human pluripotent stem cell-derived Retinal Pigment Epithelium, and ARPE19 cells.

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.

Inflammasome Activation in Retinal Pigment Epithelium from Human Donors with Age-Related Macular Degeneration.

Age-related macular degeneration (AMD), the leading cause of blindness in the elderly, is characterized by the death of retinal pigment epithelium (RPE) and photoreceptors. One of the risk factors associated with developing AMD is the single nucleotide polymorphism (SNP) found within the gene encoding complement factor H (CFH). Part of the innate immune system, CFH inhibits alternative complement pathway activation. Multi-protein complexes called inflammasomes also play a role in the innate immune response. Previous studies reported that inflammasome activation may contribute to AMD pathology. In this study, we used primary human adult RPE cell cultures from multiple donors, with and without AMD, that were genotyped for the Y402H CFH risk allele. We found complement and inflammasome-related genes and proteins at basal levels in RPE tissue and cell cultures. Additionally, treatment with rotenone, bafilomycin A, and ATP led to inflammasome activation. Overall, the response to priming and activation was similar, irrespective of disease state or CFH genotype. While these data show that the inflammasome is present and active in RPE, our results suggest that inflammasome activation may not contribute to early AMD pathology.

Intravitreal connective tissue growth factor neutralizing antibody or bevacizumab alone or in combination for prevention of proliferative vitreoretinopathy in an experimental model

Connective tissue growth factor (CTGF) is released by retinal pigment epithelial (RPE) cells and detectable in proliferative membranes (PrMs). This experimental study was performed to investigate the mRNA and protein levels of both CTGF and vascular endothelial growth factor A (VEGF-A) in a rabbit model of proliferative vitreoretinopathy (PVR). In addition, the effects of a single intravitreal injection of the safe dose of anti-CTGF or bevacizumab as monotherapy and in combination were evaluated. PVR was induced in the right eye of albino rabbits by intravitreal injection of cultured adult human RPE cells. Quantitative real-time reverse transcription PCR (qRT-PCR) and Western blot analysis of CTGF and VEGF-A were performed on whole eye tissue in the PVR model versus controls at different time points. In the next step, the PVR models were assigned to five groups. The monotherapy groups received a single intravitreal injection of 0.1 ml of anti-CTGF 100 μg/ml (final concentration of 6.6 μg/ml in the vitreous) or 0.03 ml of 25 mg/ml bevacizumab. In the combined group, the abovementioned amounts of anti-CTGF and bevacizumab were injected intravitreally from separate sites in one session. No antibody injection was performed in the control group. Intravitreal injection of 0.1 ml of control IgG (1 mg/ml of isotype matched) antibody was performed in the placebo group. After 2 weeks, histologic evaluation including, trichrome staining for collagen, immunostaining by anti-alpha-smooth muscle actin for myofibroblasts, and anti-collagen type-1 antibody on paraffin embedded anterior-posterior sections was done. In addition, fundus photography was performed for clinically equivalent PVR staging. Twenty-four hours following PVR induction, CTGF mRNA and protein levels increased five- and- three-fold compared to controls, respectively (P < 0.001). VEGF-A mRNA and protein levels decreased significantly after 72 h of PVR induction compared to controls (P < 0.05). Means of PrM thickness and myofibroblast cell counts significantly decreased in the anti-CTGF group (P < 0.001 and P < 0.05, respectively). The mean area of collagen type-1 fibers of PrM in the mono- and combination therapy groups that received intravitreal anti-CTGF was significantly reduced (P < 0.001); in addition, mild PVR (stage-1 and 2) formation occurred in comparison with moderate to severe PVR (stage-4 and higher) in other groups. In conclusion, we found that intravitreal injection of CTGF neutralizing antibody resulted in a reduction in PrM thickness, collagen fibers and myofibroblast density in the PVR model. CTGF inhibition may represent a potential therapeutic target for PVR.

SARS-CoV-2 infects human adult donor eyes and hESC-derived ocular epithelium.

The SARS-CoV-2 pandemic has caused unparalleled disruption of global behavior and significant loss of life. To minimize SARS-CoV-2 spread, understanding the mechanisms of infection from all possible routes of entry is essential. While aerosol transmission is thought to be the primary route of spread, viral particles have been detected in ocular fluid, suggesting that the eye may be a vulnerable point of viral entry. To this end, we confirmed SARS-CoV-2 entry factor and antigen expression in post-mortem COVID-19 patient ocular surface tissue and observed productive viral replication in cadaver samples and eye organoid cultures, most notably in limbal regions. Transcriptional analysis of ex vivo infected ocular surface cells and hESC-derived eye cultures revealed robust induction of NF-κB in infected cells as well as diminished type I/III interferon signaling. Together these data suggest that the eye can be directly infected by SARS-CoV-2 and implicate limbus as a portal for viral entry.

Surgical Transplantation of Human RPE Stem Cell-Derived RPE Monolayers into Non-Human Primates with Immunosuppression.

SummaryRecent trials of retinal pigment epithelium (RPE) transplantation for the treatment of disorders such as age-related macular degeneration have been promising. However, limitations of existing strategies include the uncertain survival of RPE cells delivered by cell suspension and the inherent risk of uncontrolled cell proliferation in the vitreous cavity. Human RPE stem cell-derived RPE (hRPESC-RPE) transplantation can rescue vision in a rat model of retinal dystrophy and survive in the rabbit retina for at least 1 month. The present study placed hRPESC-RPE monolayers under the macula of a non-human primate model for 3 months. The transplant was able to recover in vivo and maintained healthy photoreceptors. Importantly, there was no evidence that subretinally transplanted monolayers underwent an epithelial-mesenchymal transition. Neither gliosis in adjacent retina nor epiretinal membranes were observed. These findings suggest that hRPESC-RPE monolayers are safe and may be a useful source for RPE cell replacement therapy.

Epigenomic and Transcriptomic Changes During Human RPE EMT in a Stem Cell Model of Epiretinal Membrane Pathogenesis and Prevention by Nicotinamide.

SummaryEpithelial to mesenchymal transition (EMT) is a biological process involved in tissue morphogenesis and disease that causes dramatic changes in cell morphology, migration, proliferation, and gene expression. The retinal pigment epithelium (RPE), which supports the neural retina, can undergo EMT, producing fibrous epiretinal membranes (ERMs) associated with vision-impairing clinical conditions, such as macular pucker and proliferative vitreoretinopathy (PVR). We found that co-treatment with TGF-β and TNF-α (TNT) accelerates EMT in adult human RPE stem cell-derived RPE cell cultures. We captured the global epigenomic and transcriptional changes elicited by TNT treatment of RPE and identified putative active enhancers associated with actively transcribed genes, including a set of upregulated transcription factors that are candidate regulators. We found that the vitamin B derivative nicotinamide downregulates these key transcriptional changes, and inhibits and partially reverses RPE EMT, revealing potential therapeutic routes to benefit patients with ERM, macular pucker and PVR.

Metformin and rapamycin protect cells from vital dye-induced damage in retinal pigment epithelial cells and in vivo.

To evaluate the effect of autophagy inducers on damage caused by vital dye in adult human RPE (ARPE) cells and in a rat model. ARPE-19 cells were exposed to ICG or BBG (0.05mg/ml) with rapamycin (200nM) or metformin (2mM) for 30min and treated with or without 20μM chloroquine (CQ) to identify the protein levels of LC3 and SQSTM1 by immunoblotting. In vivo study was performed by injecting 10μl 0.05% ICG and 0.25% BBG into the subretinal space of the rat eyes, and/or co-treated them with metformin and rapamycin. The retinas were used to determine autophagy with the LC3-II level and apoptosis with terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL) assay. In this study, both ICG and BBG inhibited autophagy flux in adult human retinal pigment epithelium cells (ARPE-19), whereas only ICG consistently reduced autophagy in the retina of rats. Moreover, rapamycin and metformin induced autophagic flux in ARPE-19 cells and increased the LC3-II level in retinal tissues exposed to vital dyes. Both ICG and BBG increased apoptosis in the retina of rats. However, both rapamycin and metformin induced autophagy and reduced the apoptosis caused by vital dyes. Taken together, these results suggest that rapamycin and metformin may diminish vital dye-induced retinal damage in vivo through activation of autophagy.

Efficacy and safety of Resvega in diabetic macular edema: preliminary results of a pilot study

AbstractPurposeThe protective effects of resveratrol within the eye are extensive. It has been demonstrated to have anti‐oxidant, anti‐apoptotic, anti‐tumourogenic, anti‐inflammatory, anti‐angiogenic and vasorelaxant properties. Of note, resveratrol inhibits vascular endothelial growth factor (VEGF) expression in human adult retinal pigment epithelium cells. The purpose of this study was to examine the efficacy and safety of vitamin supplements with resveratrol (Resvega, Thea Laboratories) in patients with diabetic macular edema (DME).MethodsParticipants in this prospective, pilot study were 23 patients with DME, who were previously treated with anti‐VEGF injections. All patients presented mild DME, with good visual acuity (&gt;7/10) and central retinal thickness (CRT) 280–330 μm, where anti‐VEGF injection was not needed at the current time at the discretion of the physician. All participants received Resvega (2 tablets once/day) for 4 months. Visual acuity and CRT were assessed every month, while potential adverse events were recorded.ResultsThe visual acuity remained stable at the 4‐month follow‐up. The mean CRT increased slightly at month 4 post initiation of treatment compared to baseline, but the difference was not statistically significant. Four out of 23 patients (17.4%) needed additional anti‐VEGF injection at the end of the follow‐up due to worsening of macular edema. No adverse events were reported.ConclusionsResvega was found to be safe and effective in patients with DME, since it stabilized visual acuity and CRT in the short‐term follow‐up of 4 months. Long‐term studies are needed to confirm our results.

Sostdc1 is expressed in all major compartments of developing and adult mammalian eyes.

This study was conducted in order to study Sostdc1 expression in rat and human developing and adult eyes. Using the yeast signal sequence trap screening method, we identified the Sostdc1 cDNA encoding a protein secreted by the adult rat retinal pigment epithelium. We determined by in situ hybridization, RT-PCR, immunohistochemistry, and western blot analysis Sostdc1 gene and protein expression in developing and postnatal rat ocular tissue sections. We also investigated Sostdc1 immunohistolocalization in developing and adult human ocular tissues. We demonstrated a prominent Sostdc1 gene expression in the developing rat central nervous system (CNS) and eyes at early developmental stages from E10.5days postconception (dpc) to E13dpc. Specific Sostdc1 immunostaining was also detected in most adult cells of rat ocular tissue sections. We also identified the rat ocular embryonic compartments characterized by a specific Sostdc1 immunohistostaining and specific Pax6, Sox2, Otx2, and Vsx2 immunohistostaining from embryonic stages E10.5 to E13dpc. Furthermore, we determined the localization of SOSTDC1 immunoreactivity in ocular tissue sections of developing and adult human eyes. Indeed, we detected SOSTDC1 immunostaining in developing and adult human retinal pigment epithelium (RPE) and neural retina (NR) as well as in several developing and adult human ocular compartments, including the walls of choroidal and scleral vessels. Of utmost importance, we observed a strong SOSTDC1 expression in a pathological ocular specimen of type 2 Peters' anomaly complicated by retinal neovascularization as well in the walls ofother pathological extra-ocular vessels. CONCLUSION: As rat Sostdc1 and human SOSTDC1 are dual antagonists of the Wnt/β-catenin and BMP signaling pathways, these results underscore the potential crucial roles of these pathways and their antagonists, such as Sostdc1 and SOSTDC1, in developing and adult mammalian normal eyes as well as in syndromic and nonsyndromic congenital eye diseases.

P38 inhibition reverses TGF\u03b21 and TNF\u03b1-induced contraction in a model of proliferative vitreoretinopathy

Proliferative vitreoretinopathy (PVR) is a metaplasia in the vitreous of the eye manifested by the transformation of retinal pigment epithelial (RPE) cells and the development of contracting epiretinal membranes (ERM), which lead to retinal detachment and vision loss. While TGFβ1 and TNFα have been associated with PVR, here we show that these cytokines act synergistically to induce an aggressive contraction phenotype on adult human (ah)RPE. Connected RPE detach upon contraction and form motile membranes that recruit more cells. TGFβ1 and TNFα (TNT)-induced contracting membranes uniquely express muscle and extracellular rearrangement genes. Whole transcriptome RNA sequencing of patient-dissected PVR membranes showed activation of the p38-MAPK signaling pathway. Inhibition of p38 during TNT treatment blocks ahRPE transformation and membrane contraction. Furthermore, TNT-induced membrane contractility can be reversed by p38 inhibition after induction. Therefore, targeting the p38-MAPK pathway may have therapeutic benefits for patients with PVR even after the onset of contracting ERMs.

Differentiation of adult human retinal pigment epithelial cells into dopaminergic-like cells in vitro and in the recipient monkey brain

BackgroundCell therapy is proposed to be a potential treatment for Parkinson’s disease (PD). Although fetal retinal pigment epithelial (RPE) cells have been tested in trials for treating PD patients, controversy has been raised over the issue of whether such cells can be reprogrammed into dopamine-producing cells for therapeutic efficacy. Here, we aim to investigate whether adult human RPE cells can be reprogrammed into dopamine-producing cells both in vitro and in the recipient monkey brain.MethodsThe RPE layer was isolated from frozen posterior eyeball tissue after penetrating keratoplasty surgery. The tumorigenicity of RPE cells was examined by G-banding and a tumor formation assay in nude mice. Immunogenicity was measured using a one-way mixed lymphocyte reaction (MLR) assay. Dopamine-production in chemically reprogrammed RPE cells was measured by HPLC. Finally, RPE cells were grafted into the brains of monkeys with MPTP-induced PD in order to investigate the potential of such cells treating PD patients in the future.ResultsRPE cell lines have been successively established from adult human eye tissues. Such cells can be chemically reprogrammed into dopamine-producing cells in vitro. Moreover, after being grafted into the brain caudate putamen of monkeys with MPTP-induced PD, RPE cells became tyrosine hydroxylase-positive cells, and recipient PD monkeys showed significant improvement of clinical conditions.ConclusionsThis preclinical study using a primate model indicates that human adult RPE cells could be a potential cell source for the treatment of PD in the future.

Screening and optimization of potential injection vehicles for storage of retinal pigment epithelial stem cell before transplantation.

Retinal pigment epithelial (RPE) cells are highly specialized neural cells that have several functions essential for vision. Progressive deterioration of RPE cells in elderly individuals can result in visual impairment and ultimately the blinding disease age-related macular degeneration. Subretinal transplantation of stem cell-derived RPE cell suspensions is being explored as a strategy to recover the damaged retina and improve vision. This approach may be improved by developing a vehicle that increases postinjection cell viability and distribution and integration of RPE cells. In this study, Food and Drug Administration-approved natural polymers, including alginate, methylcellulose, and hyaluronic acid (HA), were examined for performance as cell vehicles for adult human RPE stem cells (RPESCs). We compared the effect of RPESC storage as a cell suspension in these delivery vehicles for 1-96hr at different temperatures on subsequent cell performance in a cell culture model. RPESC survival, attachment, distribution, proliferation, and differentiation into RPE cells were monitored by microscopy over the course of 8weeks. Our in vitro results demonstrate that RPESC suspension in a 0.2% HA solution promotes better initial cell distribution, proliferation, cobblestone formation, and expression of RPE cell markers (microphthalmia-associated transcription factor and orthodenticle homeobox 2) after 96hr of storage. These data suggest that HA addition to the vehicle can significantly enhance RPESC performance in vitro and is a promising strategy to pursue an improved delivery vehicle supporting in vivo RPE cell transplantation.

Antiangiogenic cytokines as potential new therapeutic targets for resveratrol in diabetic retinopathy.

Diabetes mellitus (DM) affects >350 million people worldwide. With many complications that can reduce the patient’s quality of life, vision loss is one of the most debilitating disorders it can cause. Active research in the field of diabetes includes microvascular complications in diabetic retinopathy (DR). Disturbances in the balance of pro-angiogenesis and anti-angiogenesis factors can lead to the progression of DR. The retinal pigment epithelium (RPE) is the outermost layer of the retina, and it is essential in maintaining the visual function. The RPE produces and secretes growth factors as well as protective agents which maintain structural integrity of the retina. Small natural molecules, such as resveratrol, may influence neurotrophic factors of the retina. The pigment epithelium-derived factor (PEDF) and thrombospondin-1 (TSP-1) are secreted by RPE cells. These two proteins inhibit angiogenesis and inflammation in RPE cells. An alteration of their production contributes to various eye diseases. There is a critical balance between two important factors secreted on opposite sides of the RPE: at the basal side, vascular endothelial growth factor (VEGF; acts on the choroidal endothelium) and, on the apical side, PEDF (acts on neurons and photoreceptors). Resveratrol inhibits VEGF expression in human adult RPE cells and limits the development of proliferative vitreoretinopathy, by attenuating transforming growth factor-β2-induced wound closure and cell migration. Possible new mechanisms could include PEDF and TSP-1 expression alterations under physiological and pathological conditions. Resveratrol is currently of interest due to its capacity to influence the cell’s secretory activity. Some limitations arise from its low bioavailability. Several drug delivery systems are currently tested, promising to improve tissue concentrations. This article reviews biological pathways involved in the pathogenesis of DR that could be influenced by resveratrol. A study of these pathways could identify new potential targets for the reduction of diabetic complications.

Microtubule-Associated Protein 1 Light Chain 3 (LC3) Isoforms in RPE and Retina.

Microtubule-associated protein 1 light chain 3 (MAP1LC3), a human homologue of yeast Atg8, is an essential component of autophagy. LC3 plays a critical role in hybrid degradation pathways in which some but not all components of autophagy are coupled with phagocytosis in a process known as LC3-associated phagocytosis (LAP). LC3 exists as three highly homologous isoforms in human (LC3A, LC3B, and LC3C) with two of these (LC3A and LC3B) in mouse. LC3B predominated in both fetal and adult human retinal pigment epithelium (RPE) relative to LC3A and LC3C, while in mouse RPE and neural retina, LC3A and LC3B were expressed at approximately equivalent levels. In situ hybridization studies localized LC3A and LC3B transcripts in the retina and RPE. LC3B protein was detected in C57Bl6/J RPE and retinal lysates and was absent in the LC3BKO mouse.

Visualizing melanosomes, lipofuscin, and melanolipofuscin in human retinal pigment epithelium using serial block face scanning electron microscopy

To assess serial section block-face scanning electron microscopy (SBFSEM) for retinal pigment epithelium (RPE) ultrastructure, we determined the number and distribution within RPE cell bodies of melanosomes (M), lipofuscin (L), and melanolipofuscin (ML).Eyes of 4 Caucasian donors (16M, 32F, 76F, 84M) with unremarkable maculas were sectioned and imaged using an SEM fitted with an in-chamber automated ultramicrotome. Aligned image stacks were generated by alternately imaging an epoxy resin block face using backscattered electrons, then removing a 125 nm-thick layer. Series of 249-499 sections containing 5–24 nuclei were examined per eye. Trained readers manually assigned boundaries of individual cells and x,y,z locations of M, L, and ML. A Density Recovery Profile was computed in three dimensions for M, L, and ML.The number of granules per RPE cell body in 16M, 32F, 76F, and 84M eyes, respectively, was 465 ± 127 (mean ± SD), 305 ± 92, 79 ± 40, and 333 ± 134 for L; 13 ± 9; 6 ± 7, 131 ± 55, and 184 ± 66 for ML; and 29 ± 19, 24 ± 12, 12 ± 7, and 7 ± 3 for M. Granule types were spatially organized, with M near apical processes. The effective radius, a sphere of decreased probability for granule occurrence, was 1 μm for L, ML, and M combined. In conclusion, SBFEM reveals that adult human RPE has hundreds of L, LF, and M and that granule spacing is regulated by granule size alone. When obtained for a larger sample, this information will enable hypothesis testing about organelle turnover and regulation in health, aging, and disease, and elucidate how RPE-specific signals are generated in clinical optical coherence tomography and autofluorescence imaging.

Differential expression of TYRP1 in adult human retinal pigment epithelium and uveal melanoma cells

Uveal melanoma (UM) is the most frequently occurring primary intraocular malignancy in adults. Tyrosinase (TYR) is a copper-containing enzyme and a type I membrane protein that is involved in the generation of melanin, the main pigment in vertebrates. TYR-related protein 1 (TYRP1) is regarded to have a crucial role in the immunotherapy of melanoma. As biomarkers, the TYR-related proteins, TYRP1 and TYRP2, exhibit specific expression in melanocytes, while also contributing to melanin synthesis within melanosomes. In the present study, the differential expression of TYRP1 was investigated at the mRNA, protein and morphological levels in four human UM cell lines (SP6.5, OM431, OCM1 and OCM290) and the human retinal pigment epithelium (RPE) cell line, using polymerase chain reaction, western blotting, immunocytochemistry and immunofluorescence staining. It was found that SP6.5 cells expressed the highest level of TYRP1, in comparison to SP6.5 OCM1 and OM431 cells, which produced less TYRP1, and OCM290 cells, which produced almost no TYRP1. No TYRP1 protein expression was identified in the RPE cell line. These findings indicate the potential use of TYRP1 in the development of therapy for UM.

Cytotoxicity considerations and electrically tunable release of dexamethasone from polypyrrole for the treatment of back-of-the-eye conditions.

Age-related macular degeneration (AMD) and diabetic macular edema (DME) are common causes of blindness in people aged over 55years. Current treatment involves frequent intravitreal administration of corticosteroids such as dexamethasone. The aim of this research was to formulate an electrically controlled delivery system for dexamethasone. Polypyrrole (PPy) was polymerized with dexamethasone sodium phosphate (Dex-P) through two approaches. Firstly, conventional films (CFs) of PPy were electropolymerized by applying a constant current density of 2mA/cm2 for 4min. Secondly, for the first time, we report drug-loaded ethanol-washed films (EWFs). EWFs were prepared in the same manner as CFs, except ethanol washing steps were introduced in the middle and at the end of PPy electropolymerization. The ethanol washing removed unbound PPy oligomers resulting in the formation of smooth surfaces with two distinct layers when viewed in cross-section. The EWFs showed superior electrochemical activity compared to CFs. Sustained release was observed from both CFs and EWFs with bursts of release triggered by electrical stimulation. The EWFs were initially more responsive to the electrical trigger, offering future opportunities to fine tune release. The cytotoxicity of aqueous extracts collected from both films was evaluated on human adult retinal pigment epithelium (ARPE-19) cells using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay with negligible toxicity observed. The results suggest PPy-Dex-P films are highly suitable for the development of electro-responsive implants for the treatment of AMD and DME.

Reduced Expression of Cytoskeletal and Extracellular Matrix Genes in Human Adult Retinal Pigment Epithelium Cells Exposed to Simulated Microgravity

Background/Aims: Microgravity (µg) has adverse effects on the eye of humans in space. The risk of visual impairment is therefore one of the leading health concerns for NASA. The impact of µg on human adult retinal epithelium (ARPE-19) cells is unknown. Methods: In this study we investigated the influence of simulated µg (s-µg; 5 and 10 days (d)), using a Random Positioning Machine (RPM), on ARPE-19 cells. We performed phase-contrast/fluorescent microscopy, qRT-PCR, Western blotting and pathway analysis. Results: Following RPM-exposure a subset of ARPE-19 cells formed multicellular spheroids (MCS), whereas the majority of the cells remained adherent (AD). After 5d, alterations of F-actin and fibronectin were observed which reverted after 10d-exposure, suggesting a time-dependent adaptation to s-µg. Gene expression analysis of 12 genes involved in cell structure, shape, adhesion, migration, and angiogenesis suggested significant changes after a 10d-RPM-exposure. 11 genes were down-regulated in AD and MCS 10d-RPM-samples compared to 1g, whereas FLK1 was up-regulated in 5d- and 10d-RPM-MCS-samples. Similarly, TIMP1 was up-regulated in 5d-RPM-samples, whereas the remaining genes were down-regulated in 5d-RPM-samples. Western blotting revealed similar changes in VEGF, β-actin, laminin and fibronectin of 5d-RPM-samples compared to 10d, whereas different alterations of β-tubulin and vimentin were observed. The pathway analysis showed complementing effects of VEGF and integrin β-1. Conclusions: These findings clearly show that s-µg induces significant alterations in the F-actin-cytoskeleton and cytoskeleton-related proteins of ARPE-19, in addition to changes in cell growth behavior and gene expression patterns involved in cell structure, growth, shape, migration, adhesion and angiogenesis.

Subretinal implantation of human stem cell‐derived RPE on ultrathin carriers in rabbits

SummaryTransplantation of retinal pigment epithelium (RPE) is being developed as a cell replacement therapy for age‐related macular degeneration (AMD). Human embryonic and adult human RPE stem cells (hESC and hRPESC, resp.) are known potential sources that are currently being pursued towards the clinic. Polarized monolayers of SC‐derived RPE were shown to grow on biostable polyester (PET) membranes. They were found to be similar to fetal hRPE monolayers and to have near‐native characteristics. Stamped pieces of RPE monolayers on the carrier were loaded into a custom‐designed surgical instrument and transplanted subretinally in the rabbit, a large‐eyed animal model. Compared to fetal and hRPESC derived RPE, hESC‐RPE xenografts showed better preservation of the neural retina overlying the implant. Histology obtained 4 weeks after implantation confirmed a continuous polarized human RPE monolayer on PET. We demonstrate that the xeno‐RPE monolayer implant survived well and retained its polarization. Moreover, our initial data suggest a distinctly advantageous tolerance of hESC derived RPE xenografts in rabbit subretinal space.