Aberrant Akt2 signaling in the RPE may contribute to retinal fibrosis process in diabetic retinopathy

Exosomes derived from human umbilical cord blood mesenchymal stem cells protect against blue light-induced damage to retinal pigment epithelial cells by inhibiting FGF2 expression

Age-related macular degeneration (AMD) is a debilitating retinal disorder that may lead to progressive vision loss. One contributing factor to AMD pathogenesis is excessive blue light (BL) exposure. In this study, we investigated the therapeutic potential of exosomes derived from human umbilical cord blood mesenchymal stem cells (hUCMSC-EXs) in addressing BL-induced damage to ARPE-19 human retinal pigment epithelial (RPE) cells and explored the underlying mechanisms. Our findings revealed that BL exposure induced morphological alterations in ARPE-19 cells, accompanied by a time-dependent decline in cell viability, increased apoptosis, heightened oxidative stress, and inflammatory responses; however, hUCMSC-EXs dose-dependently mitigated BL-induced ARPE-19 cell damage. Interestingly, hUCMSC-EXs were found to suppress the upregulation of fibroblast growth factor 2 (FGF2) in BL-exposed ARPE-19 cells. Furthermore, FGF2 overexpression partially counteracted the inhibitory effects of hUCMSC-EXs on FGF2 expression and compromised the protective benefits of hUCMSC-EXs against BL-induced ARPE-19 cell damage. In conclusion, our results suggest that hUCMSC-EXs shield ARPE-19 cells from BL-induced harm by inhibiting FGF2 expression.

ROS-responsive drug delivery system with enhanced anti-angiogenic and anti-inflammatory properties for neovascular age-related macular degeneration therapy

Neovascular age-related macular degeneration (nAMD) has become the leading cause of vision loss in people over 60 years old. Anti-vascular endothelial growth factor (anti-VEGF), the current first-line drug for the treatment of nAMD, suffers from poor patient compliance and fundus fibrosis scar formation. In addition to VEGF, oxidative stress and inflammation also play key roles in the pathological process of choroidal neovascularization (CNV). Therefore, combinational therapeutics with anti-angiogenic, reactive oxygen species (ROS)-scavenging and anti-inflammatory functions will broaden therapeutic effects and reduce side effects. The Yes-associated protein-1 (YAP) has proven to inhibit angiogenesis, inflammation, and subretinal fibrosis in CNV. Herein, verteporfin (VP), the inhibitor of YAP, was encapsulated into a polydopamine modified mesoporous silica nanoparticle (PMSN-VP NPs) and then conjugated with PLGA-PEG-PBA decorated cerium oxide nanoparticles (PPCeO2 NPs) to develop an integrated nano-drug delivery system. The PMSN-VP@PPCeO2 NPs exhibited ROS-responsive degradation and VP release behaviors, and our in vitro data revealed that the PMSN-VP@PPCeO2 NPs downregulated angiogenic-related and fibrosis-related gene expressions in human umbilical vein endothelial cells (HUVECs) and further showed excellent anti-oxidative and anti-inflammatory capacities in BV2 cells. More importantly, the PMSN-VP@PPCeO2 NPs significantly suppressed vascular leakage and macrophage infiltration in the laser-induced CNV lesions of mice. Overall, our findings demonstrated that the PMSN-VP@PPCeO2 NPs provided an effective therapeutic strategy for nAMD.

Klotho attenuates epithelial‑mesenchymal transition of retinal pigment epithelial cells in subretinal fibrosis by suppressing the ERK1/2 and Wnt/β‑catenin signaling pathways

Retinal pigment epithelial (RPE) cells undergoing epithelial‑mesenchymal transition (EMT) are a key factor in promoting the progression of subretinal fibrosis. The klotho protein and gene exert anti‑fibrotic effects in multiple fibrotic diseases. However, the mechanisms involved in the role of klotho are unclear in subretinal fibrosis. The aim of the present study was to explore the effects of klotho on subretinal fibrosis induced by laser photocoagulation in mice and EMT induced by TGF‑β1 in RPE cells and the underlying molecular mechanisms. In vitro, klotho overexpression or knockdown was performed in ARPE‑19 cells (adult retinal Pigment Epithelial‑19), then TGF‑β1 treatment was applied. Using western blotting, expression of epithelial markers (zonula occludens‑1), mesenchymal signs (α‑smooth muscle actin, α‑SMA, N‑cadherin, N‑cad and collagen I), and the ERK1/2 and Wnt/β‑catenin signaling pathways were assessed. The proliferative ability of ARPE‑19 cells was examined by CCK‑8 and EdU test, and the migratory ability was examined by wound healing and Transwell assays. Furthermore, to explore the underlying molecular pathway of klotho overexpression, RNA‑sequencing (seq) was performed. In vivo, photocoagulation was used to induce subretinal fibrosis in mice, which occurs as a result of choroidal neovascularization (CNV), then recombinant mouse klotho protein was administered intravitreally. Upregulation of epithelial and downregulation of mesenchymal markers demonstrated that klotho overexpression prevented TGF‑β1‑induced EMT; klotho knockdown resulted in the opposite effects. Additionally, klotho overexpression suppressed cell proliferation and migration and attenuated ERK1/2 and Wnt/β‑catenin signaling activated by TGF‑β1. RNA‑seq results demonstrated that several signaling pathways, including cellular senescence and the TNF signaling pathway, were associated with anti‑fibrotic effects of klotho overexpression. In vivo, subretinal fibrotic areas were attenuated following klotho treatment in laser‑induced CNV lesions, as illustrated by immunofluorescence and Masson staining of the mouse eyes. Western blotting results that the protein levels of mesenchymal markers were significantly downregulated and those of epithelial markers were upregulated. In summary, the present study suggested that klotho may have therapeutic value in management of fibrotic vitreoretinal disorders such as subretinal fibrosis.

Overexpressed Poldip2 Incurs Retinal Fibrosis via the TGF-β1/SMAD3 Signaling Pathway in Diabetic Retinopathy

Retinal fibrosis is one of the major features of diabetic retinopathy (DR). Our recent research has shown that Poldip2 can affect early DR through oxidative stress, but whether Poldip2 would regulate retinal fibrosis during DR development is still enigmatic. Here, diabetic Sprague-Dawley (SD) rats were induced with streptozotocin (STZ) and treated with adeno-associated virus serotype 9-polymerase-δ interacting protein 2 (Poldip2) shRNA, while human adult retinal pigment epithelial (ARPE-19) cells were treated with high glucose or Poldip2 siRNA. We identified that in STZ-induced DR rats and ARPE-19 cells treated with high glucose, the expression of Poldip2, transforming growth factor-β1 (TGF-β1), phosphorylated-SMAD3/SMAD3, MMP9, COL-1, FN, and CTGF increased while the expression of cadherin decreased. However, deleting Poldip2 inhibited the TGF-β1/SMAD3 signaling pathway and attenuated the above protein expression in vivo and in vitro. Mechanistically, we found that Poldip2 promotes the activation of SMAD3, facilitates its nuclear translocation through interacting with it, and significantly enhances the expression of fibrosis makers. Collectively, Poldip2 was identified is a novel regulator of DR fibrosis and is expected to become a therapeutic target for PDR.

ARTICLE HIGHLIGHTS

Apigenin suppresses epithelial-mesenchymal transition in high glucose-induced retinal pigment epithelial cell by inhibiting CBP/p300-mediated histone acetylation

Epithelial mesenchymal transition (EMT) is a critical process implicated in the pathogenesis of retinal fibrosis and the exacerbation of diabetic retinopathy (DR) within retinal pigment epithelium (RPE) cells. Apigenin (AP), a potential dietary supplement for managing diabetes and its associated complications, has demonstrated inhibitory effects on EMT in various diseases. However, the specific impact and underlying mechanisms of AP on EMT in RPE cells remain poorly understood. In this study, we have successfully validated the inhibitory effects of AP on high glucose-induced EMT in ARPE-19 cells and diabetic db/db mice. Notably, our findings have identified CBP/p300 as a potential therapeutic target for EMT in RPE cells and have further substantiated that AP effectively downregulates the expression of EMT-related genes by attenuating the activity of CBP/p300, consequently reducing histone acetylation alterations within the promoter region of these genes. Taken together, our results provide novel evidence supporting the inhibitory effect of AP on EMT in RPE cells, and highlight the potential of specifically targeting CBP/p300 as a strategy for inhibiting retinal fibrosis in the context of DR.

Interplay of endothelial-mesenchymal transition, inflammation, and autophagy in proliferative diabetic retinopathy pathogenesis

Background

Assessment and validation of endothelial-mesenchymal transition (EndoMT) in the retinal endothelium of patients with proliferative diabetic retinopathy (PDR) at the level of retinal and vitreous specimens, and preliminary discussion of its regulatory mechanisms.

Methods

Transcriptome sequencing profiles of CD31+ cells from 9 retinal fibrovascular mem-branes (FVMs) and 4 postmortem retinas were downloaded from GEO databases to analyze EndoMT-related differentially expressed genes (DEGs). Then, 42 PDR patients and 34 idiopathic macular holes (IMH) patients were enrolled as the PDR and control groups, respectively. Vitreous humor (VH) samples were collected, and the expression of EndoMT-related proteins was quantified by enzyme-linked immunosorbent assay.

Results

A total of 5845 DEGs were identified, and we subsequently focused on the analysis of 24 EndoMT-related marker genes, including the trigger of EndoMT, endothelial genes, mesenchymal genes, transcription factors, inflammatory factors, and autophagy markers. Six of these genes were selected for protein assay validation in VH, showing increased mesenchymal marker (type I collagen α 2 chain, COL1A2) and decreased endothelial marker (VE-cadherin, CDH5) accompanied by increased TGFβ, IL-1β, LC3B and P62 in PDR patients. In addition, anti-VEGF therapy could enhance EndoMT-related phenotypes.

Conclusions

EndoMT may underlie the pathogenesis of PDR, and the induction and regulation correlate with autophagy defects and the inflammatory response.

Mechanistic insights into the alterations and regulation of the AKT signaling pathway in diabetic retinopathy

In the early stages of diabetic retinopathy (DR), diabetes-related hyperglycemia directly inhibits the AKT signaling pathway by increasing oxidative stress or inhibiting growth factor expression, which leads to retinal cell apoptosis, nerve proliferation and fundus microvascular disease. However, due to compensatory vascular hyperplasia in the late stage of DR, the vascular endothelial growth factor (VEGF)/phosphatidylinositol 3 kinase (PI3K)/AKT cascade is activated, resulting in opposite levels of AKT regulation compared with the early stage. Studies have shown that many factors, including insulin, insulin-like growth factor-1 (IGF-1), VEGF and others, can regulate the AKT pathway. Disruption of the insulin pathway decreases AKT activation. IGF-1 downregulation decreases the activation of AKT in DR, which abrogates the neuroprotective effect, upregulates VEGF expression and thus induces neovascularization. Although inhibiting VEGF is the main treatment for neovascularization in DR, excessive inhibition may lead to apoptosis in inner retinal neurons. AKT pathway substrates, including mammalian target of rapamycin (mTOR), forkhead box O (FOXO), glycogen synthase kinase-3 (GSK-3)/nuclear factor erythroid 2-related factor 2 (Nrf2), and nuclear factor kappa-B (NF-κB), are a research focus. mTOR inhibitors can delay or prevent retinal microangiopathy, whereas low mTOR activity can decrease retinal protein synthesis. Inactivated AKT fails to inhibit FOXO and thus causes apoptosis. The GSK-3/Nrf2 cascade regulates oxidation and inflammation in DR. NF-κB is activated in diabetic retinas and is involved in inflammation and apoptosis. Many pathways or vital activities, such as the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) and mitogen-activated protein kinase (MAPK) signaling pathways, interact with the AKT pathway to influence DR development. Numerous regulatory methods can simultaneously impact the AKT pathway and other pathways, and it is essential to consider both the connections and interactions between these pathways. In this review, we summarize changes in the AKT signaling pathway in DR and targeted drugs based on these potential sites.