RPE epithelial-mesenchymal transition plays a critical role in the pathogenesis of proliferative vitreoretinopathy

Tenascin-C induces transdifferentiation of retinal pigment epithelial cells in proliferative vitreoretinopathy

Proliferation and transdifferentiation of the retinal pigment epithelium (RPE) are hallmarks of proliferative vitreoretinopathy (PVR); however, the critical regulators of this process remain to be elucidated. Here, we investigated the role of tenascin-C in PVR development. In vitro, exposure of human ARPE-19 (hRPE) cells to TGF-β2 increased tenascin-C expression. Tenascin-C was shown to be involved in TGF-β2-induced transdifferentiation of hRPE cells, which was inhibited by pretreatment with tenascin-C siRNA. In PVR mouse models, a marked increase in the expression of tenascin-C mRNA and protein was observed. Additionally, immunofluorescence analysis demonstrated a dramatic increase in the colocalization of tenascin-C with RPE65 or α-smooth muscle actin(α-SMA) in the epiretinal membranes of patients with PVR. There was also abundant expression of integrin αV and β-catenin in the PVR membranes. ICG-001, a β-catenin inhibitor, efficiently attenuated PVR progression in a PVR animal model. These findings suggest that tenascin-C is secreted by transdifferentiated RPE cells and promotes the development of PVR via the integrin αV and β-catenin pathways. Therefore, tenascin-C could be a potential therapeutic target for the inhibition of epiretinal membrane development associated with PVR.

Silencing the long noncoding RNA MALAT1 inhibits vitreous-induced epithelial-mesenchymal transition in RPE cells by regulating the PDGFRs/AKT axis

PURPOSE

Epithelial-mesenchymal transition (EMT) is a crucial pathological process that contributes to proliferative vitreoretinopathy (PVR), and research indicates that factors present in the vitreous that target cells play pivotal roles in regulating EMT. Experimental studies have confirmed that rabbit vitreous (RV) promotes EMT in human retinal pigment epithelial (RPE) cells. The long noncoding RNA (lncRNA) MALAT1 has been implicated in EMT in various diseases. Thus, this study aimed to investigate the involvement of lncRNA MALAT1 in vitreous-induced EMT in RPE cells.

METHODS

MALAT1 was knocked down in ARPE-19 cells by short hairpin RNA (shRNA) transfection. Reverse transcription PCR (RT‒PCR) was used to evaluate MALAT1 expression, and Western blotting analysis was used to measure the expression of EMT-related proteins. Wound-healing, Transwell, and cell contraction assays were conducted to assess cell migration, invasion, and contraction, respectively. Additionally, cell proliferation was assessed using the CCK-8 assay, and cytoskeletal changes were examined by immunofluorescence.

RESULTS

MALAT1 expression was significantly increased in ARPE-19 cells cultured with RV. Silencing MALAT1 effectively suppressed EMT and downregulated the associated factors snail1 and E-cadherin. Furthermore, silencing MALAT1 inhibited the RV-induced migration, invasion, proliferation, and contraction of ARPE-19 cells. Silencing MALAT1 also decreased RV-induced AKT and P53 phosphorylation.

CONCLUSIONS

In conclusion, lncRNA MALAT1 participates in regulating vitreous-induced EMT in human RPE cells; these results provide new insight into the pathogenesis of PVR and offer a potential direction for the development of antiproliferative drugs.

Multi-omics profiling of retinal pigment epithelium reveals enhancer-driven activation of RANK-NFATc1 signaling in traumatic proliferative vitreoretinopathy

During the progression of proliferative vitreoretinopathy (PVR) following ocular trauma, previously quiescent retinal pigment epithelial (RPE) cells transition into a state of rapid proliferation, migration, and secretion. The elusive molecular mechanisms behind these changes have hindered the development of effective pharmacological treatments, presenting a pressing clinical challenge. In this study, by monitoring the dynamic changes in chromatin accessibility and various histone modifications, we chart the comprehensive epigenetic landscape of RPE cells in male mice subjected to traumatic PVR. Coupled with transcriptomic analysis, we reveal a robust correlation between enhancer activation and the upregulation of the PVR-associated gene programs. Furthermore, by constructing transcription factor regulatory networks, we identify the aberrant activation of enhancer-driven RANK-NFATc1 pathway as PVR advanced. Importantly, we demonstrate that intraocular interventions, including nanomedicines inhibiting enhancer activity, gene therapies targeting NFATc1 and antibody therapeutics against RANK pathway, effectively mitigate PVR progression. Together, our findings elucidate the epigenetic basis underlying the activation of PVR-associated genes during RPE cell fate transitions and offer promising therapeutic avenues targeting epigenetic modulation and the RANK-NFATc1 axis for PVR management.

Intraocular mRNA delivery with endogenous MmPEG10-based virus-like particles

Virus-like particles (VLP) are a promising tool for intracellular gene delivery, yet their potential in ocular gene therapy remains underexplored. In this study, we bridged this knowledge gap by demonstrating the successful generation and application of vesicular stomatitis virus glycoprotein (VSVG)-pseudotyped mouse PEG10 (MmPEG10)-VLP for intraocular mRNA delivery. Our findings revealed that PEG10-VLP can efficiently deliver GFP mRNA to adult retinal pigment epithelial cell line-19 (ARPE-19) cells, leading to transient expression. Moreover, we showed that MmPEG10-VLP can transfer SMAD7 to inhibit epithelial-mesenchymal transition (EMT) in RPE cells effectively. In vivo experiments further substantiated the potential of these vectors, as subretinal delivery into adult mice resulted in efficient transduction of retinal pigment epithelial (RPE) cells and GFP reporter gene expression without significant immune response. However, intravitreal injection did not yield efficient ocular expression. We also evaluated the transduction characteristics of MmPEG10-VLP following intracameral delivery, revealing transient GFP protein expression in corneal endothelial cells without significant immunotoxicities. In summary, our study established that VSVG pseudotyped MmPEG10-based VLP can transduce mitotically inactive RPE cells and corneal endothelial cells in vivo without triggering an inflammatory response, underscoring their potential utility in ocular gene therapy.

Effect of adalimumab as an anti-inflammatory agent on gene expression of retinal pigment epithelial cells

Adalimumab (ADA) is an anti-inflammatory antibody that has FDA approval as a systemic medication for treating noninfectious uveitis. It is also provisionally being investigated as an intravitreal injection for various retinal conditions. This study aimed to assess the effect of ADA on apoptotic, inflammatory, and fibrogenesis gene expression at mRNA and protein levels in retinal pigment epithelial (RPE) cells. RPEs were treated with serial concentrations of ADA (0.5x, x, 2x, and 4x; [x = 250 µg/mL]) for 24 hours. MTT assay was done and the mRNA and protein expressions were quantified using real-time PCR and ELISA assay, respectively. The mRNA levels of IL-1b and IL-6 were significantly increased in ADA-treated RPEs at 0.5x and x concentrations. However, the increase in cytokine secretion was observed only in IL-1b at x concentration. TGF-β was significantly upregulated in the 0.5x and 4x doses of ADA both at mRNA and protein levels. MTT assay, along with an unchanged BCL-2/BAX ratio confirmed the safety of ADA on RPEs at all studied concentrations. In conclusion, despite its safety, the 2x concentration of ADA was the only dose that did not ignite the expression of any of the studied inflammatory and fibrogenesis genes. This dosage, which is roughly equal to 2 mg intravitreal dose in a clinical setting, might be referred to as a reference starting point for future in-vivo studies in ocular conditions.

Effects of dopamine D2 receptor antagonists on retinal pigment epithelial/choroid complex metabolism in form-deprived myopic guinea pigs

The retinal pigment epithelial (RPE)/choroid complex regulates myopia development, but the precise pathogenesis of myopia remains unclear. We aimed to investigate the changes in RPE/choroid complex metabolism in a form deprivation myopia model after dopamine D2 receptor (D2R) modulation. Guinea pigs were randomly divided into normal (NC), form deprivation myopia (FDM), and FDM treated with dopamine D2R antagonist groups. Differential metabolites were screened using SIMCA-P software and MetaboAnalyst metabolomics analysis tool. Functions of differential metabolites were analyzed using KEGG enrichment pathways. Relative to the NC group, 38 differential metabolites were identified, comprising 29 increased metabolites (including nicotinic acid, cytosine, and glutamate) and 9 decreased metabolites, of which proline exhibited the largest decrease. Pathway analysis revealed regulation of arginine/proline and aspartate/glutamate metabolism. Intravitreal D2R antagonist injection increased proline concentrations and activated arginine/proline and purine metabolism pathways. In sum, D2R antagonists alleviated the myopia trend of refractive biological parameters in form deprivation myopic guinea pigs, suggesting the involvement of dopamine D2R signaling in myopia pathogenesis. The RPE/choroid may provide glutamate to the retina by activating proline metabolism via metabolic coupling with the retina. Dopamine D2R antagonism may modulate proline/arginine metabolic pathways in the RPE/choroid and regulate metabolism, information presentation, and myopia.

miRNA‑124 regulates palmitic acid‑induced epithelial‑mesenchymal transition and cell migration in human retinal pigment epithelial cells by targeting LIN7C

The present study revealed that palmitic acid (PA) treatment induced epithelial-mesenchymal transition (EMT) of retinal pigment epithelial (RPE) cells, which are involved in the progression of proliferative vitreoretinopathy (PVR). ARPE-19 cells were treated with PA followed by miRNA screening and EMT marker detection using qRT-PCR. Then, miR-124 mimic or inhibitor was transfected into ARPE-19 cells to explore the role of miR-124 on the EMT of ARPE-19 cells using transwell assay. The underlying mechanism of miRNA were predicted by bioinformatics method and confirmed by luciferase activity reporter assay. Furthermore, gain-of-function strategy was also used to explore the role of LIN7C in the EMT of ARPE-19 cells. The expression of miRNA or mRNA expression was determined by qRT-PCR and the protein expression was determined using western blot assay. The result presented that PA reduced the expression of E-cadherin/ZO-1 whilst increasing the expression of fibronectin/α-SMA. In addition, PA treatment enhanced the expression of microRNA (miR)-124 in ARPE-19 cells. Overexpression of miR-124 enhanced PA-induced upregulation of E-cadherin and ZO-1 expression and downregulation of fibronectin and α-SMA. Moreover, miR-124 mimic also enhanced the migration of ARPE-19 cells induced by PA treatment. Inversely, miR-124 inhibitor presented opposite effect on PA-induced EMT and cell migration in ARPE-19 cells. Luciferase activity reporter assay confirmed that Lin-7 homolog C (LIN7C) was a direct target of miR-124 in ARPE-19 cells. Overexpression of LIN7C was found to suppress the migration ability and expression of fibronectin and α-SMA, while increasing expression of E-cadherin and ZO-1; miR-124 mimic abrogated the inhibitive effect of LIN7C on the EMT of ARPE-19 cells and PA further enhanced this abolishment. Collectively, these findings suggest that miR-124/LIN7C can modulate EMT and cell migration in RPE cells, which may have therapeutic implications in the management of PVR diseases.

Downregulation of FEM1C enhances metastasis and proliferation in colorectal cancer

Background

Feminization-1 (FEM-1) is considered a substrate recognition subunit of CUL2-RING E3 ubiquitin ligase complexes, which refers to sex determination by modulating TRA-1 stability in C. elegans. The function of mammalian orthologous gene of FEM-1 remains to be elucidated.

Methods

The expression of FEM1C in colorectal cancer (CRC) cells was interfered by small interference RNA (siRNA) transfection, and Cell counting kit-8 (CCK-8) assay, colony formation assay and transwell assay were performed. In order to estimate the function on metastasis, stable knockdown FEM1C cells were used to established liver and lung metastasis models. In addition, the expression of FEM1C in normal tissues, adenomas and tumor tissues were analyzed, and the relationship between FEM1C expression level and prognosis was analyzed by Kaplan-Meier method.

Results

Here, we report that the elimination of FEM1C, one of the members of FEM-1, significantly promoted the migration and invasion of colorectal cancer (CRC) cells in vitro and promoted liver and lung metastases in vivo. It also showed that the removal of FEM1C improved the proliferation ability of CRC cells. In particular, the cell shape changed from epithelial to fibroblast-like morphology. The tight cell monolayer was transformed into a dispersed distribution. Furthermore, it was demonstrated that FEM1C is down-regulated in tissues of CRC compared to normal tissues, and the high expression of FEM1C positively correlates with a good prognosis in patients with CRC. GSEA analysis showed that EMT signatures was enriched in FEM1C knockdown groups.

Conclusions

Down-regulation of FEM1C promotes proliferation and metastasis, and FEM1C may be a tumor suppressor in the development of CRC.

Blocking connexin43 hemichannels prevents TGF-β2 upregulation and epithelial-mesenchymal transition in retinal pigment epithelial cells

Epithelial-mesenchymal transition (EMT) occurs when polarised epithelial cells change to a mesenchymal phenotype. EMT plays a role in several chronic conditions, including ocular diseases with retinal pigment epithelium (RPE) EMT associated with retinal diseases such as diabetic retinopathy (DR). Here, EMT results in breakdown of the blood-retinal barrier (BRB) leading to sub-retinal fluid deposition and retinal detachment. Previous studies have shown that blocking connexin43 (Cx43) hemichannels can protect against RPE BRB breakdown, but the underlying mechanism is unknown. To determine whether open Cx43 hemichannels may enable EMT of RPE cells and thus result in BRB breakdown, ARPE-19 cells were either challenged with high glucose plus the inflammatory cytokines IL-1β and TNF-α (HG + Cyt) to simulate DR or treated with the Cx43 hemichannel blocker tonabersat alongside the HG + Cyt challenge. HG + Cyt induced a morphological change in RPE cells to a fibroblastic phenotype with a corresponding decrease in epithelial zonular occludens-1 and an increase in the fibroblastic marker α-SMA. The HG + Cyt challenge also induced loss of transepithelial electrical resistance while increasing dye passage between RPE cells. All of these changes were significantly reduced with tonabersat treatment, which also prevented HG + Cyt-induced transforming growth factor-β2 (TGF-β2) release. In conclusion, Cx43 hemichannel block with tonabersat attenuated both TGF-β2 release and RPE EMT under disease-mimicking conditions, offering the potential to ameliorate the progression of EMT-associated retinal diseases.

Advantages of nanofibrous membranes for culturing of primary RPE cells compared to commercial scaffolds

PURPOSE

Dysfunction of the retinal pigment epithelium (RPE) causes numerous forms of retinal degeneration. RPE replacement is a modern option to save vision. We aimed to test the results of transplanting cultured RPEs on biocompatible membranes.

METHODS

We cultivated porcine primary RPE cells isolated from cadaver eyes from the slaughterhouse on two types of membranes: commercial polyester scaffolds Transwell (Corning Inc., Kenneburg, ME, USA) with 0.4 µm pore size and prepared Poly (L-lactide-co-DL-lactide) (PDLLA) nanofibrous membranes with an average pore size of 0.4 µm.

RESULTS

Five types of assays were used for the analysis: immunocytochemistry (ICC), phagocytosis assay, Western blotting, real-time qPCR (RT-qPCR) and electron microscopy. RT-qPCR demonstrated that RPEs cultured on nanofibrous membranes have higher expressions of BEST1 (bestrophin 1), RLBP1 (retinaldehyde-binding protein 1), RPE65 (retinal pigment epithelium-specific 65 kDa protein), PAX6 (transcription factor PAX6), SOX9 (transcription factor SOX9), DCT (dopachrome tautomerase) and MITF (microphthalmia-associated transcription factor). ICC of the RPEs cultured on nanofibrous membranes showed more intensive staining of markers such as BEST1, MCT1 (monocarboxylate transporter 1), Na⁺ /K⁺ ATPase, RPE65 and acetylated tubulin in comparison with commercial ones. Additionally, the absence of α-SMA proved the stability of the RPE polarization state and the absence of epithelial-to-mesenchymal transition. RPE possessed high phagocytic activity. Electron microscopy of both membranes confirmed a confluent layer of RPE cells and their genuine morphological structure, which was comparable to native RPEs.

CONCLUSIONS

Retinal pigment epitheliums cultured on polylactide nanofibrous membranes improved the final quality of the cell product by having better maturation and long-term survival of the RPE monolayer compared to those cultured on commercial polyester scaffolds. PDLLA-cultured RPEs are a plausible source for the replacement of non-functioning RPEs during cell therapy.

Proteomic and phosphoproteomic analyses identify liver-related signaling in retinal pigment epithelial cells during EMT

Epithelial-mesenchymal transition (EMT) of the retinal pigment epithelium (RPE) is associated with several blinding retinal diseases. Using proteomics and phosphoproteomics studies of human induced pluripotent stem cell-derived RPE monolayers with induced EMT, we capture kinase/phosphatase signaling cascades 1 h and 12 h after induction to better understand the pathways mediating RPE EMT. Induction by co-treatment with transforming growth factor β and tumor necrosis factor alpha (TGNF) or enzymatic dissociation perturbs signaling in many of the same pathways, with striking similarity in the respective phosphoproteomes at 1 h. Liver hyperplasia and hepatocyte growth factor (HGF)-MET signaling exhibit the highest overall enrichment. We also observe that HGF and epidermal growth factor signaling, two cooperative pathways inhibited by EMT induction, regulate the RPE transcriptional profile.

Repression of Smad4 by MicroRNA-1285 moderates TGF-β-induced epithelial-mesenchymal transition in proliferative vitreoretinopathy

The purpose of this study was to assess whether microRNA (miR)-1285 can suppress the epithelial-mesenchymal transition (EMT) in retinal pigment epithelial cells. Expression of miR-1285 was evaluated using quantitative real-time polymerase chain reaction (RT-qPCR). The features of EMT were assessed using Western blotting, immunocytochemical staining, scratch wound healing tests, modified Boyden chamber assay, and collagen gel contraction assay. A rabbit model of proliferative vitreoretinopathy (PVR) was used for in vivo testing, which involved the induction of PVR by injection of transfected ARPE cells into the vitreous chamber. Luciferase reporter assay was performed to identify the putative target of miR-1285. The expression of miR-1285 was downregulated in ARPE-19 cells treated with transforming growth factor (TGF)-β. Overexpression of miR-1285 led to upregulation of zonula occludens-1, downregulation of α-smooth muscle actin and vimentin, cell migration and cell contractility-all EMT features-in the TGF-β2-treated ARPE-19 cells. The reporter assay indicated that the 3' untranslated region of Smad4 was the direct target of miR1285. PVR progression was alleviated in the miR-1285 transfected rabbits. In conclusion, overexpression of miR-1285 attenuates TGF-β2-induced EMT in a rabbit model of PVR, and the effect of miR-1285 in PVR is dependent on Smad4. Further research is warranted to develop a feasible therapeutic approach for the prevention and treatment of PVR.

PI3K/AKT/mTOR signaling participates in insulin-mediated regulation of pathological myopia-related factors in retinal pigment epithelial cells

BACKGROUND

Insulin positively correlates with the length of the eye axis and is increased in the vitreous and serum of patients with pathological myopia (PM). How insulin influences the physiological process of retinal pigment epithelial (RPE) cells in PM remains unclear. This study aimed to explore the effect of insulin on the ultrastructure and function of RPE cells and the role of PI3K/AKT/mTOR signaling involved in the development of PM.

METHODS

The ARPE-19 cells were treated with different concentrations of insulin to analyze the cell morphology, cell viability, the protein level of insulin receptor β, and the mRNA and protein levels of and PM-related factors (TIMP-2, MMP-2, bFGF, and IGF-1). The ultrastructure of APRE-19 cells was also observed after insulin treatment. Besides, the PI3K/AKT/mTOR signaling was studied with or without the PI3K inhibitor LY294002 in ARPE-19 cells.

RESULTS

Insulin enhanced the cell viability of ARPE-19 cells and caused the endoplasmic reticulum to expand and vesiculate, suggesting increased secretion of growth factors and degeneration in ARPE-19 cells. Furthermore, the insulin receptor β was stimulated with insulin treatment, subsequently, the phosphorylation of AKT and mTOR was positively activated, which was adversely suppressed in the presence of LY294002. The secretion of TIMP-2 and bFGF was significantly decreased, and the secretion of MMP-2 and IGF-1 was highly elevated with insulin treatment depending on the concentration in ARPE-19 cells. Furthermore, the effect of insulin on PM-related proteins was restored with the addition of LY294002.

CONCLUSIONS

Our results indicated that insulin regulated the secretion of PM-related factors via the PI3K/AKT/mTOR signaling pathway in retinal pigment epithelial cells, and thus probably promoted the development of PM through transducing regulation signals from retina to choroid and sclera.

Polarity and epithelial-mesenchymal transition of retinal pigment epithelial cells in proliferative vitreoretinopathy

Under physiological conditions, retinal pigment epithelium (RPE) is a cellular monolayer composed of mitotically quiescent cells. Tight junctions and adherens junctions maintain the polarity of RPE cells, and are required for cellular functions. In proliferative vitreoretinopathy (PVR), upon retinal tear, RPE cells lose cell-cell contact, undergo epithelial-mesenchymal transition (EMT), and ultimately transform into myofibroblasts, leading to the formation of fibrocellular membranes on both surfaces of the detached retina and on the posterior hyaloids, which causes tractional retinal detachment. In PVR, RPE cells are crucial contributors, and multiple signaling pathways, including the SMAD-dependent pathway, Rho pathway, MAPK pathways, Jagged/Notch pathway, and the Wnt/β-catenin pathway are activated. These pathways mediate the EMT of RPE cells, which play a key role in the pathogenesis of PVR. This review summarizes the current body of knowledge on the polarized phenotype of RPE, the role of cell-cell contact, and the molecular mechanisms underlying the RPE EMT in PVR, emphasizing key insights into potential approaches to prevent PVR.