Attenuation of EMT in RPE cells and subretinal fibrosis by an RAR-γ agonist

Enhancing prosthetic vision by upgrade of a subretinal photovoltaic implant in situ

In patients with atrophic age-related macular degeneration, subretinal photovoltaic implant (PRIMA) provided visual acuity up to 20/440, matching its 100 µm pixels size. Next-generation implants with smaller pixels should significantly improve the acuity. This study in rats evaluates removal of a subretinal implant, replacement with a newer device, and the resulting grating acuity in-vivo. Six weeks after the initial implantation with planar and 3-dimensional devices, the retina was re-detached, and the devices were successfully removed. Histology demonstrated a preserved inner nuclear layer. Re-implantation of new devices into the same location demonstrated retinal re-attachment to a new implant. New devices with 22 µm pixels increased the grating acuity from the 100 µm capability of PRIMA implants to 28 µm, reaching the limit of natural resolution in rats. Reimplanted devices exhibited the same stimulation threshold as for the first implantation of the same implants in a control group. This study demonstrates the feasibility of safely upgrading the subretinal photovoltaic implants to improve prosthetic visual acuity.

Subretinal fibrosis secondary to neovascular age-related macular degeneration: mechanisms and potential therapeutic targets

Subretinal fibrosis is the end-stage sequelae of neovascular age-related macular degeneration. It causes local damage to photoreceptors, retinal pigment epithelium, and choroidal vessels, which leads to permanent central vision loss of patients with neovascular age-related macular degeneration. The pathogenesis of subretinal fibrosis is complex, and the underlying mechanisms are largely unknown. Therefore, there are no effective treatment options. A thorough understanding of the pathogenesis of subretinal fibrosis and its related mechanisms is important to elucidate its complications and explore potential treatments. The current article reviews several aspects of subretinal fibrosis, including the current understanding on the relationship between neovascular age-related macular degeneration and subretinal fibrosis; multimodal imaging techniques for subretinal fibrosis; animal models for studying subretinal fibrosis; cellular and non-cellular constituents of subretinal fibrosis; pathophysiological mechanisms involved in subretinal fibrosis, such as aging, infiltration of macrophages, different sources of mesenchymal transition to myofibroblast, and activation of complement system and immune cells; and several key molecules and signaling pathways participating in the pathogenesis of subretinal fibrosis, such as vascular endothelial growth factor, connective tissue growth factor, fibroblast growth factor 2, platelet-derived growth factor and platelet-derived growth factor receptor-β, transforming growth factor-β signaling pathway, Wnt signaling pathway, and the axis of heat shock protein 70-Toll-like receptors 2/4-interleukin-10. This review will improve the understanding of the pathogenesis of subretinal fibrosis, allow the discovery of molecular targets, and explore potential treatments for the management of subretinal fibrosis.

Cromolyn sodium reduces LPS-induced pulmonary fibrosis by inhibiting the EMT process enhanced by MC-derived IL-13

BACKGROUND

Sepsis is a systemic inflammatory response caused by infection. When this inflammatory response spreads to the lungs, it can lead to acute lung injury (ALI) or more severe acute respiratory distress syndrome (ARDS). Pulmonary fibrosis is a potential complication of these conditions, and the early occurrence of pulmonary fibrosis is associated with a higher mortality rate. The underlying mechanism of ARDS-related pulmonary fibrosis remains unclear.

METHODS

To evaluate the role of mast cell in sepsis-induced pulmonary fibrosis and elucidate its molecular mechanism. We investigated the level of mast cell and epithelial-mesenchymal transition(EMT) in LPS-induced mouse model and cellular model. We also explored the influence of cromolyn sodium and mast cell knockout on pulmonary fibrosis. Additionally, we explored the effect of MC-derived IL-13 on the EMT and illustrated the relationship between mast cell and pulmonary fibrosis.

RESULTS

Mast cell was up-regulated in the lung tissues of the pulmonary fibrotic mouse model compared to control groups. Cromolyn sodium and mast cell knockout decreased the expression of EMT-related protein and IL-13, alleviated the symptoms of pulmonary fibrosis in vivo and in vitro. The PI3K/AKT/mTOR signaling was activated in fibrotic lung tissue, whereas Cromolyn sodium and mast cell knockout inhibited this pathway.

CONCLUSION

The expression level of mast cell is increased in fibrotic lungs. Cromolyn sodium intervention and mast cell knockout alleviate the symptoms of pulmonary fibrosis probably via the PI3K/AKT/mTOR signaling pathway. Therefore, mast cell inhibition is a potential therapeutic target for sepsis-induced pulmonary fibrosis.

Decreased sialylation elicits complement-related microglia response and bipolar cell loss in the mouse retina

Sialylation plays an important role in self-recognition, as well as keeping the complement and innate immune systems in check. It is unclear whether the reduced sialylation seen during aging and in mice heterozygous for the null mutant of UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (Gne+/-), an essential enzyme for sialic acid biosynthesis, contributes to retinal inflammation and degeneration. We found a reduction of polysialic acid and trisialic acid expression in several retinal layers in Gne+/- mice at 9 months of age compared to Gne+/+ wildtype (WT) mice, which was associated with a higher microglial expression of the lysosomal marker CD68. Furthermore, the total number of rod bipolar cells was reduced in 12 months old Gne+/- mice in comparison to WT mice, demonstrating loss of these retinal interneurons. Transcriptome analysis showed up-regulation of complement, inflammation, and apoptosis-related pathways in the retinas of Gne+/- mice. Particularly, increased gene transcript levels of the complement factors C3 and C4 and the pro-inflammatory cytokine Il-1β were observed by semi-quantitative real-time polymerase chain reaction (sqRT-PCR) in 9 months old Gne+/- mice compared to WT mice. The increased expression of CD68, loss of rod bipolar cells, and increased gene transcription of complement factor C4, were all prevented after crossing Gne+/- mice with complement factor C3-deficient animals. In conclusion, our data show that retinal hyposialylation in 9 and 12 months old Gne+/- mice was associated with complement-related inflammation and lysosomal microglia response, as well as rod bipolar cells loss, which was absent after genetic deletion of complement factor C3.

The role of immune modulators in age-related macular degeneration

We provide an overview of the expanding literature on the role of cytokines and immune mediators in pathophysiology of age-related macular degeneration (AMD). Although many immunological mediators have been linked to AMD pathophysiology, the broader mechanistic picture remains unclear with substantial variations in the levels of evidence supporting these mediators. Therefore, we reviewed the literature considering the varying levels of supporting evidence. A Medical Subject Headings (MeSH) term-based literature research was conducted in September, 2023, consisting of the MeSH terms "cytokine" and "Age-related macular degeneration" connected by the operator "AND". After screening the publications by title, abstract, and full text, a total of 146 publications were included. The proinflammatory cytokines IL-1β (especially in basic research studies), IL-6, IL-8, IL-18, TNF-α, and MCP-1 are the most extensively characterised cytokines/chemokines, highlighting the role of local inflammasome activation and altered macrophage function in the AMD pathophysiology. Among the antiinflammatory mediators IL-4, IL-10, and TGF-β were found to be the most extensively characterised, with IL-4 driving and IL-10 and TGF-β suppressing disease progression. Despite the extensive literature on this topic, a profound understanding of AMD pathophysiology has not yet been achieved. Therefore, further studies are needed to identify potential therapeutic targets, followed by clinical studies.

The role of JNK signaling pathway in organ fibrosis

BACKGROUND

Fibrosis is a tissue damage repair response caused by multiple pathogenic factors which could occur in almost every apparatus and leading to the tissue structure damage, physiological abnormality, and even organ failure until death. Up to now, there is still no specific drugs or strategies can effectively block or changeover tissue fibrosis. JNKs, a subset of mitogen-activated protein kinases (MAPK), have been reported that participates in various biological processes, such as genetic expression, DNA damage, and cell activation/proliferation/death pathways. Increasing studies indicated that abnormal regulation of JNK signal pathway has strongly associated with tissue fibrosis.

AIM OF REVIEW

This review designed to sum up the molecular mechanism progresses in the role of JNK signal pathway in organ fibrosis, hoping to provide a novel therapy strategy to tackle tissue fibrosis.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Recent evidence shows that JNK signaling pathway could modulates inflammation, immunoreaction, oxidative stress and Multiple cell biological functions in organ fibrosis. Therefore, targeting the JNK pathway may be a useful strategy in cure fibrosis.

The benzoylphenylurea derivative BPU17 acts as an inhibitor of prohibitin and exhibits antifibrotic activity

Inflammation-induced choroidal neovascularization followed by the epithelial-mesenchymal transition (EMT) of retinal pigment epithelial cells (RPEs) is a cause of neovascular age-related macular degeneration (nAMD). RPE-derived myofibroblasts overproduce extracellular matrix, leading to subretinal fibrosis. We already have demonstrated that benzylphenylurea (BPU) derivatives inhibit the function of cancer-associated fibroblasts. Here, we investigated the anti-myofibroblast effects of BPU derivatives and examined such BPU activity on subretinal fibrosis. A BPU derivative, BPU17, exhibits the most potent anti-myofibroblast activity among dozens of BPU derivatives and inhibits subretinal fibrosis in a mouse model of retinal degeneration. Investigations with primary cultured RPEs reveal that BPU17 suppresses cell motility and collagen synthesis in RPE-derived myofibroblasts. These effects depend on repressing the serum response factor (SRF)/CArG-box-dependent transcription. BPU17 inhibits the expression of SRF cofactor, cysteine and glycine-rich protein 2 (CRP2), which activates the SRF function. Proteomics analysis reveals that BPU17 binds to prohibitin 1 (PHB1) and inhibits the PHB1-PHB2 interaction, resulting in mild defects in mitochondrial function. This impairment causes a decrease in the expression of CRP2 and suppresses collagen synthesis. Our findings suggest that BPU17 is a promising agent against nAMD and the close relationship between PHB function and EMT.

JR5558 mice are a reliable model to investigate subretinal fibrosis

Subretinal fibrosis is a major untreatable cause of poor outcomes in neovascular age-related macular degeneration. Mouse models of subretinal fibrosis all possess a degree of invasiveness and tissue damage not typical of fibrosis progression. This project characterises JR5558 mice as a model to study subretinal fibrosis. Fundus and optical coherence tomography (OCT) imaging was used to non-invasively track lesions. Lesion number and area were quantified with ImageJ. Retinal sections, wholemounts and Western blots were used to characterise alterations. Subretinal lesions expand between 4 and 8 weeks and become established in size and location around 12 weeks. Subretinal lesions were confirmed to be fibrotic, including various cell populations involved in fibrosis development. Müller cell processes extended from superficial retina into subretinal lesions at 8 weeks. Western blotting revealed increases in fibronectin (4 wk and 8 wk, p < 0.001), CTGF (20 wks, p < 0.001), MMP2 (12 wks and 20 wks p < 0.05), αSMA (12 wks and 20 wks p < 0.05) and GFAP (8 wk and 12 wk, p ≤ 0.01), consistent with our immunofluorescence results. Intravitreal injection of Aflibercept reduced subretinal lesion growth. Our study provides evidence JR5558 mice have subretinal fibrotic lesions that grow between 4 and 8 weeks and confirms this line to be a good model to study subretinal fibrosis development and assess treatment options.

Enhancing Prosthetic Vision by Upgrade of a Subretinal Photovoltaic Implant in situ

In patients with atrophic age-related macular degeneration, subretinal photovoltaic implant (PRIMA) provided visual acuity up to 20/440, matching its 100μm pixels size. Next-generation implants with smaller pixels should significantly improve the acuity. This study in rats evaluates removal of a subretinal implant, replacement with a newer device, and the resulting grating acuity in-vivo. Six weeks after the initial implantation with planar and 3-dimensional devices, the retina was re-detached, and the devices were successfully removed. Histology demonstrated a preserved inner nuclear layer. Re-implantation of new devices into the same location demonstrated retinal re-attachment to a new implant. New devices with 22μm pixels increased the grating acuity from the 100μm capability of PRIMA implants to 28μm, reaching the limit of natural resolution in rats. Reimplanted devices exhibited the same stimulation threshold as for the first implantation of the same implants in a control group. This study demonstrates the feasibility of safely upgrading the subretinal photovoltaic implants to improve prosthetic visual acuity.

RAR Inhibitors Display Photo-Protective and Anti-Inflammatory Effects in A2E Stimulated RPE Cells In Vitro through Non-Specific Modulation of PPAR or RXR Transactivation

N-retinylidene-N-retinylethanolamine (A2E) has been associated with age-related macular degeneration (AMD) physiopathology by inducing cell death, angiogenesis and inflammation in retinal pigmented epithelial (RPE) cells. It was previously thought that the A2E effects were solely mediated via the retinoic acid receptor (RAR)-α activation. However, this conclusion was based on experiments using the RAR "specific" antagonist RO-41-5253, which was found to also be a ligand and partial agonist of the peroxisome proliferator-activated receptor (PPAR)-γ. Moreover, we previously reported that inhibiting PPAR and retinoid X receptor (RXR) transactivation with norbixin also modulated inflammation and angiogenesis in RPE cells challenged in the presence of A2E. Here, using several RAR inhibitors, we deciphered the respective roles of RAR, PPAR and RXR transactivations in an in vitro model of AMD. We showed that BMS 195614 (a selective RAR-α antagonist) displayed photoprotective properties against toxic blue light exposure in the presence of A2E. BMS 195614 also significantly reduced the AP-1 transactivation and mRNA expression of the inflammatory interleukin (IL)-6 and vascular endothelial growth factor (VEGF) induced by A2E in RPE cells in vitro, suggesting a major role of RAR in these processes. Surprisingly, however, we showed that (1) Norbixin increased the RAR transactivation and (2) AGN 193109 (a high affinity pan-RAR antagonist) and BMS 493 (a pan-RAR inverse agonist), which are photoprotective against toxic blue light exposure in the presence of A2E, also inhibited PPARs transactivation and RXR transactivation, respectively. Therefore, in our in vitro model of AMD, several commercialized RAR inhibitors appear to be non-specific, and we propose that the phototoxicity and expression of IL-6 and VEGF induced by A2E in RPE cells operates through the activation of PPAR or RXR rather than by RAR transactivation.

Association between Oral Active-Matrix Metalloproteinase-8 Levels and Subretinal Fibrosis among Wet Age-Related Macular Degeneration Patients

PURPOSE

Periodontitis causes low-grade systemic inflammation and has been associated with elevated active-matrix metalloproteinase (aMMP-8) levels, blood-ocular barrier breakdown and a risk of wet age-related macular degeneration. To assess the association between aMMP-8 levels and macular status among patients with wet age-related macular degeneration (AMD).

METHODS

Patients on anti-VEGF treatment for wet AMD were enrolled for oral aMMP-8 rinse test in Mehiläinen Private Hospital, Helsinki, Finland. Macular status was examined from spectral-domain optical coherence tomography (SD-OCT) scans by a medical retina specialist and aMMP-8 levels were analyzed with chairside point-of-care oral rinse (PerioSafe®) test and real-time quantitated by a dentist using the ORALyzer®- reader with a 10 ng/ml cut-off for aMMP-8 activity.

RESULTS

Elevated aMMP-8 levels were found in 10 out of 32 patients. Age, gender, anti-VEGF (bevacizumab or aflibercept) distribution, cumulative number of anti-VEGF injections and treatment interval were comparable between patients with aMMP-8 levels below and above the point-of-care level. Macular status differed in regard to aMMP-8 activity; among patients with aMMP-8 levels below the point-of-care subretinal fibrosis was found in 6 out of 22 eyes, whereas among patients with aMMP-8 levels above the point-of-care subretinal fibrosis was found in 8 out of 10 eyes (p = 0.005). Respectively, the mean thickness of subretinal fibrosis at fovea was 19.5 ± 44.1 and 92.3 ± 78.3 µm (p = 0.018). No differences were found in the presence and in the area of geographic atrophy, or fluid distribution, whereas thicknesses of serous pigment epithelial detachment (65.5 ± 99.5 and 12.9 ± 27.9 µm, p = 0.038) and neuroretina (204.2 ± 57.8 µm and 143.0 ± 43.7 µm, p = 0.006) were greater in the eyes of patients with physiological aMMP-8 levels compared to those with elevated aMMP-8 levels.

CONCLUSION

Elevated aMMP-8 levels may account for subretinal fibrosis formation in wet AMD.

Molecular pathogenesis of subretinal fibrosis in neovascular AMD focusing on epithelial-mesenchymal transformation of retinal pigment epithelium

Age-related macular degeneration (AMD) is a leading cause of vision loss among elderly people in developed countries. Neovascular AMD (nAMD) accounts for more than 90% of AMD-related vision loss. At present, intravitreal injection of anti-vascular endothelial growth factor (anti-VEGF) is widely used as the first-line therapy to decrease the choroidal and retinal neovascularizations, and thus to improve or maintain the visual acuity of the patients with nAMD. However, about 1/3 patients still progress to irreversible visual impairment due to subretinal fibrosis even with adequate anti-VEGF treatment. Extensive literatures support the critical role of epithelial-mesenchymal transformation (EMT) of retinal pigment epithelium (RPE) in the pathogenesis of subretinal fibrosis in nAMD, but the underlying mechanisms still remain largely unknown. This review summarized the molecular pathogenesis of subretinal fibrosis in nAMD, especially focusing on the transforming growth factor-β (TGF-β)-induced EMT pathways. It was also discussed how these pathways crosstalk and respond to signals from the microenvironment to mediate EMT and contribute to the progression of nAMD-related subretinal fibrosis. Targeting EMT signaling pathways might provide a promising and effective therapeutic strategy to treat subretinal fibrosis secondary to nAMD.

METTL3-mediated m6A modification of HMGA2 mRNA promotes subretinal fibrosis and epithelial-mesenchymal transition

Subretinal fibrosis is a major cause of the poor visual prognosis for patients with neovascular age-related macular degeneration (nAMD). Myofibroblasts originated from retinal pigment epithelial (RPE) cells through epithelial-mesenchymal transition (EMT) contribute to the fibrosis formation. N6-Methyladenosine (m6A) modification has been implicated in the EMT process and multiple fibrotic diseases. The role of m6A modification in EMT-related subretinal fibrosis has not yet been elucidated. In this study, we found that during subretinal fibrosis in the mouse model of laser-induced choroidal neovascularization, METTL3 was upregulated in RPE cells. Through m6A epitranscriptomic microarray and further verification, high-mobility group AT-hook 2 (HMGA2) was identified as the key downstream target of METTL3, subsequently activating potent EMT-inducing transcription factor SNAIL. Finally, by subretinal injections of adeno-associated virus vectors, we confirmed that METTL3 deficiency in RPE cells could efficiently attenuate subretinal fibrosis in vivo. In conclusion, our present research identified an epigenetic mechanism of METTL3-m6A-HMGA2 in subretinal fibrosis and EMT of RPE cells, providing a novel therapeutic target for subretinal fibrosis secondary to nAMD.

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

Diabetic Retinopathy (DR) is a complication of diabetes that causes blindness in adults. Retinal fibrosis is closely associated with developing proliferative diabetic retinopathy (PDR). Clinical studies have shown that fibrotic membranes exhibit uncontrolled growth in PDR and contribute to retinal detachment from RPE cells, ultimately leading to vision loss. While anti-VEGF agents and invasive laser treatments are the primary treatments for PDR, retinal fibrosis has received minimal attention as a potential target for therapeutic intervention. Therefore, to investigate the potential role of Akt2 in the diabetes-induced retinal fibrosis process, we generated RPE-specific Akt2 conditional knockout (cKO) mice and induced diabetes in these mice and Akt2^fl/fl control mice by intraperitoneal injection of streptozotocin. After an 8-month duration of diabetes (10 months of age), the mice were euthanized and expression of tight junction proteins, epithelial-mesenchymal transition (EMT), and fibrosis markers were examined in the RPE. Diabetes induction in the floxed control mice decreased levels of the RPE tight junction protein ZO-1 and adherens junction proteins occludin and E-cadherin; these decreases were rescued in Akt2 cKO diabetic mice. Loss of Akt2 also inhibited diabetes-induced elevation of RNA and protein levels of the EMT markers Snail/Slug and Twist1 in the RPE as compared to Akt2^fl/fl diabetic mice. We also found that in Akt2 cKO mice diabetes-induced increase of fibrosis markers, including collagen IV, Connective tissue growth factor (CTGF), fibronectin, and alpha-SMA was attenuated. Furthermore, we observed that high glucose-induced alterations in EMT and fibrosis markers in wild-type (WT) RPE explants were rescued in the presence of PI3K and ERK inhibitors, indicating diabetes-induced retinal fibrosis may be mediated via the PI3K/Akt2/ERK signaling, which could provide a novel target for DR therapy.

Recent Advances in Transcription Factors Biomarkers and Targeted Therapies Focusing on Epithelial-Mesenchymal Transition

Transcription factors involve many proteins in the process of transactivating or transcribing (none-) encoded DNA to initiate and regulate downstream signals, such as RNA polymerase. Their unique characteristic is that they possess specific domains that bind to specific DNA element sequences called enhancer or promoter sequences. Epithelial-mesenchymal transition (EMT) is involved in cancer progression. Many dysregulated transcription factors-such as Myc, SNAIs, Twists, and ZEBs-are key drivers of tumor metastasis through EMT regulation. This review summarizes currently available evidence related to the oncogenic role of classified transcription factors in EMT editing and epigenetic regulation, clarifying the roles of the classified conserved transcription factor family involved in the EMT and how these factors could be used as therapeutic targets in future investigations.

Molecular mechanisms of TGFβ-mediated EMT of retinal pigment epithelium in subretinal fibrosis of age-related macular degeneration

Age-related macular degeneration (AMD) is one of the leading causes of blindness in the elderly, affecting the macula of the retina and resulting in vision loss. There are two types of AMD, wet and dry, both of which cause visual impairment. Wet AMD is called neovascular AMD (nAMD) and is characterized by the formation of choroidal neovascular vessels (CNVs) in the macula. nAMD can be treated with intravitreal injections of vascular endothelial growth factor (VEGF) inhibitors, which help improve vision. However, approximately half the patients do not achieve satisfactory results. Subretinal fibrosis often develops late in nAMD, leading to irreversible photoreceptor degeneration and contributing to visual loss. Currently, no treatment exists for subretinal fibrosis, and the molecular mechanisms of fibrous tissue formation following neovascular lesions remain unclear. In this review, we describe the clinical features and molecular mechanisms of macular fibrosis secondary to nAMD. Myofibroblasts play an essential role in the development of fibrosis. This review summarizes the latest findings on the clinical features and cellular and molecular mechanisms of the pathogenesis of subretinal fibrosis in nAMD and discusses the potential therapeutic strategies to control subretinal fibrosis in the future.

A Randomised Phase I Study to Assess the Safety, Tolerability and Pharmacokinetics of Palovarotene Ophthalmic Solution

BACKGROUND AND OBJECTIVE

Palovarotene, a selective retinoic acid receptor γ agonist, is under investigation for the treatment of dry eye disease. This study aimed to determine the ocular and systemic safety, tolerability and pharmacokinetics of palovarotene ophthalmic solution (PVO-OS) in healthy adults.

METHODS

This was a randomised, vehicle-controlled phase I study (NCT04762355; retrospectively registered). Participants received either PVO-OS (at 0.025, 0.05 or 0.10 mg/mL) or a vehicle (placebo-to-match PVO-OS) once-daily or twice-daily for seven consecutive days. Safety was assessed by ocular and systemic assessments. Blood samples for pharmacokinetic assessments were collected before and after dose administration.

RESULTS

Thirty-six participants were randomised to PVO-OS and 12 to the vehicle. Overall, 89 treatment-emergent ocular adverse events (TEOAEs) were reported by 22 participants (61.1%) receiving PVO-OS and ten TEOAEs were reported by five participants (41.7%) receiving the vehicle. Erythema, irritation and skin dryness of the eyelid were the most common TEOAEs in participants receiving PVO-OS. The incidence of TEOAEs and eyelid-related findings in the PVO-OS groups increased with ascending dose and frequency compared with participants treated with the vehicle. All TEOAEs were mild (96.6%) or moderate (3.4%) and resolved without sequelae. Plasma palovarotene concentrations were generally measurable for up to 3-4 h for 0.025 mg/mL and 0.05 mg/mL and up to 12 h for 0.10 mg/mL dose regimens, independent of the frequency of administration.

CONCLUSIONS

PVO-OS was generally well tolerated at doses up to and including 0.10 mg/mL twice daily. Similar pharmacokinetic profiles were observed for the once-daily and twice-daily regimens following multiple ascending doses of PVO-OS.

Role of Adrenomedullin 2/Intermedin in the Pathogenesis of Neovascular Age-Related Macular Degeneration

Adrenomedullin 2 (AM2; also known as intermedin) is a member of the adrenomedullin (AM) peptide family. Similarly to AM, AM2 partakes in a variety of physiological activities. AM2 has been reported to exert protective effects on various organ disorders; however, its significance in the eye is unknown. We investigated the role of AM2 in ocular diseases. The receptor system of AM2 was expressed more abundantly in the choroid than in the retina. In an oxygen-induced retinopathy model, physiological and pathologic retinal angiogenesis did not differ between AM2-knockout (AM2-/-) and wild-type mice. In contrast, in laser-induced choroidal neovascularization, a model of neovascular age-related macular degeneration, AM2-/- mice had enlarged and leakier choroidal neovascularization lesions, with exacerbated subretinal fibrosis and macrophage infiltration. Contrary to this, exogenous administration of AM2 ameliorated the laser-induced choroidal neovascularization-associated pathology and suppressed gene expression associated with inflammation, fibrosis, and oxidative stress, including that of VEGF-A, VEGFR-2, CD68, CTGF, and p22-phox. The stimulation of human adult retinal pigment epithelial (ARPE) cell line 19 cells with TGF-β2 and TNF-α induced epithelial-to-mesenchymal transition (EMT), whereas AM2 expression was also elevated. The induction of EMT was suppressed when the ARPE-19 cells were pretreated with AM2. A transcriptome analysis identified 15 genes, including mesenchyme homeobox 2 (Meox2), whose expression was significantly altered in the AM2-treated group compared with that in the control group. The expression of Meox2, a transcription factor that inhibits inflammation and fibrosis, was enhanced by AM2 treatment and attenuated by endogenous AM2 knockout in the early phase after laser irradiation. The AM2 treatment of endothelial cells inhibited endothelial to mesenchymal transition and NF-κB activation; however, this effect tended to be canceled following Meox2 gene knockdown. These results indicate that AM2 suppresses the neovascular age-related macular degeneration-related pathologies partially via the upregulation of Meox2. Thus, AM2 may be a promising therapeutic target for ocular vascular diseases.

Vitreous humor proteome: unraveling the molecular mechanisms underlying proliferative and neovascular vitreoretinal diseases

Proliferative diabetic retinopathy (PDR), proliferative vitreoretinopathy (PVR), and neovascular age-related macular degeneration (nAMD) are among the leading causes of blindness. Due to the multifactorial nature of these vitreoretinal diseases, omics approaches are essential for a deeper understanding of the pathophysiologic processes underlying the evolution to a proliferative or neovascular etiology, in which patients suffer from an abrupt loss of vision. For many years, it was thought that the function of the vitreous was merely structural, supporting and protecting the surrounding ocular tissues. Proteomics studies proved that vitreous is more complex and biologically active than initially thought, and its changes reflect the physiological and pathological state of the eye. The vitreous is the scenario of a complex interplay between inflammation, fibrosis, oxidative stress, neurodegeneration, and extracellular matrix remodeling. Vitreous proteome not only reflects the pathological events that occur in the retina, but the changes in the vitreous itself play a central role in the onset and progression of vitreoretinal diseases. Therefore, this review offers an overview of the studies on the vitreous proteome that could help to elucidate some of the pathological mechanisms underlying proliferative and/or neovascular vitreoretinal diseases and to find new potential pharmaceutical targets.

Retinoic acid promotes fibrinolysis and may regulate polyp formation

BACKGROUND

Patients with aspirin-exacerbated respiratory disease (AERD) regularly exhibit severe nasal polyposis. Studies suggest that chronic rhinosinusitis with nasal polyps (CRSwNP) is characterized by excessive fibrin deposition associated with a profound decrease in epithelial tissue plasminogen activator (tPA). Retinoids, including vitamin A and its active metabolite retinoic acid (RA), are necessary for maintaining epithelial function and well-known inducers of tPA in endothelial cells.

OBJECTIVES

This study sought to determine whether endogenous retinoids are involved in NP pathophysiology and disease severity in patients with CRSwNP and AERD.

METHODS

NP tissue was collected from patients with AERD or CRSwNP, and concentrations of retinoids and fibrinolysis markers were measured using ELISA. Normal human bronchial epithelial cells were stimulated alone or in combination with RA and IL-13 for 24 hours.

RESULTS

This study observed lower retinoid levels in nasal polyps of patients with AERD than those with CRSwNP or healthy controls (P < .01). Levels of the fibrin-breakdown product d-dimer were the lowest in AERD polyps (P < .01), which is consistent with lower tPA expression (P < .01). In vitro, all-trans RA upregulated tPA levels in normal human bronchial epithelial cells by 15-fold and reversed the IL-13-induced attenuation of tPA expression in cultured cells (P < .01).

CONCLUSIONS

RA, a potent inducer of epithelial tPA in vitro, is reduced in tissue from patients with AERD, a finding that may potentially contribute to decreased levels of tPA and fibrinolysis in AERD. RA can induce tPA in epithelial cells and can reverse IL-13-induced tPA suppression in vitro, suggesting the potential utility of RA in treating patients with CRSwNP and/or AERD.

Induced retinal pigment epithelial cells with anti-epithelial-to-mesenchymal transition ability delay retinal degeneration

The hostile microenvironment of the retina in patients with age-related macular degeneration (AMD) may trigger epithelial-to-mesenchymal transition (EMT) of grafted retinal pigment epithelial (RPE) cells, thus attenuating the therapeutic outcome. Here, we transformed human dedifferentiated induced pluripotent stem cell-derived RPE (iPSC-RPE) cells into induced RPE (iRPE) cells using a cocktail of four transcription factors (TFs)-CRX, MITF-A, NR2E1, and C-MYC. These critical TFs maintained the epithelial property of iRPE cells by regulating the expression of bmp7, forkhead box f2, lin7a, and pard6b, and conferred resistance to TGF-β-induced EMT in iRPE cells by targeting ppm1a. The iRPE cells with Tet-on system-regulated c-myc expression exhibited EMT resistance and better therapeutic function compared with iPSC-RPE cells in rat AMD model. Our study demonstrates that endowing RPE cells with anti-EMT property avoids the risk of EMT after cells are grafted into the subretinal space, and it may provide a suitable candidate for AMD treatment.

Morphologic and Microvascular Differences Between Macular Neovascularization With and Without Subretinal Fibrosis

Purpose

To evaluate morphologic and microvascular differences between eyes with and without subretinal fibrosis (SF) caused by neovascular age-related macular degeneration (nAMD).

Methods

Patients with nAMD with a minimum history of 12 months of anti-VEGF treatment were prospectively included in this cross-sectional study. Patients were imaged using standard imaging, swept-source optical coherence tomography angiography for quantitative microvascular analysis and polarization-sensitive OCT as an ancillary method for automated SF segmentation. The presence of reticular pseudodrusen, hyperreflective foci (HRF), and outer retinal tubulation (ORT) were also evaluated.

Results

Sixty eyes of 60 participants (37 female) with nAMD and a mean 3.1 (±2.7)-year history of anti-VEGF treatment were included, 20 (33%) of which were diagnosed with SF. Eyes with SF had a higher prevalence of ORT (P < 0.001) and a lower prevalence of HRF (P = 0.004) than eyes without SF. Fifty eyes were analyzed quantitatively for microvascular biomarkers. Eyes with SF had a larger greatest vascular caliber (P = 0.001) and greatest linear diameter (P = 0.042), a larger microvascular neovascularization (MNV) area (P = 0.026), larger vessel area (P = 0.037), higher number of vessel junctions (P = 0.025), longer total vessel length (P = 0.027), higher number of vessel endpoints (P = 0.007), and higher endpoint density (P = 0.047).

Conclusions

This multimodal imaging approach demonstrated in vivo microvascular and morphological differences in eyes with and without SF. Eyes with SF tend to have larger MNV lesions with thicker vessels and are often associated with the presence of ORT.

Translational Relevance

This study points out imaging biomarkers in patients with SF, which may help identifying high-risk patients.

Subretinal fibrosis in neovascular age-related macular degeneration: current concepts, therapeutic avenues, and future perspectives

Age-related macular degeneration (AMD) is a progressive, degenerative disease of the human retina which in its most aggressive form is associated with the formation of macular neovascularization (MNV) and subretinal fibrosis leading to irreversible blindness. MNVs contain blood vessels as well as infiltrating immune cells, myofibroblasts, and excessive amounts of extracellular matrix proteins such as collagens, fibronectin, and laminin which disrupts retinal function and triggers neurodegeneration. In the mammalian retina, damaged neurons cannot be replaced by tissue regeneration, and subretinal MNV and fibrosis persist and thus fuel degeneration and visual loss. This review provides an overview of subretinal fibrosis in neovascular AMD, by summarizing its clinical manifestations, exploring the current understanding of the underlying cellular and molecular mechanisms and discussing potential therapeutic approaches to inhibit subretinal fibrosis in the future.

Blockade of mTORC1-NOX signaling pathway inhibits TGF-β1-mediated senescence-like structural alterations of the retinal pigment epithelium

The retinal pigment epithelium (RPE) undergoes characteristic structural changes and epithelial-mesenchymal transition (EMT) during normal aging, which are exacerbated in age-related macular degeneration (AMD). Although the pathogenic mechanisms of aging and AMD remain unclear, transforming growth factor-β1 (TGF-β1) is known to induce oxidative stress, morphometric changes, and EMT as a senescence-promoting factor. In this study, we examined whether intravitreal injection of TGF-β1 into the mouse eye elicits senescence-like morphological alterations in the RPE and if this can be prevented by suppressing mammalian target of rapamycin complex 1 (mTORC1) or NADPH oxidase (NOX) signaling. We verified that intravitreal TGF-β1-induced stress fiber formation and EMT in RPE cells, along with age-associated morphometric changes, including increased variation in cell size and reduced cell density. In RPE cells, exogenous TGF-β1 increased endogenous expression of TGF-β1 and upregulated Smad3-ERK1/2-mTORC1 signaling, increasing reactive oxygen species (ROS) production and EMT. We demonstrated that inhibition of the mTORC1-NOX4 pathway by pretreatment with 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR), an activator of AMP-dependent protein kinase, or GKT137831, a NOX1/4 inhibitor, decreased ROS generation, prevented stress fiber formation, attenuated EMT, and improved the regularity of the RPE structure in vitro and in vivo. These results suggest that intravitreal TGF-β1 injection could be used as a screening model to investigate the aging-related structural and functional changes to the RPE. Furthermore, the regulation of TGF-β-mTORC1-NOX signaling could be a potential therapeutic target for reducing pathogenic alterations in aged RPE and AMD.

Inhibition of epithelial-mesenchymal transition in retinal pigment epithelial cells by a retinoic acid receptor-α agonist

Epithelial-mesenchymal transition (EMT) in retinal pigment epithelial (RPE) cells plays a key role in proliferative retinal diseases such as age-related macular degeneration by contributing to subretinal fibrosis. To investigate the potential role of retinoic acid receptor-α (RAR-α) signaling in this process, we have now examined the effects of the RAR-α agonist Am580 on EMT induced by transforming growth factor-β2 (TGF-β2) in primary mouse RPE cells cultured in a three-dimensional type I collagen gel as well as on subretinal fibrosis in a mouse model. We found that Am580 inhibited TGF-β2-induced collagen gel contraction mediated by RPE cells. It also attenuated the TGF-β2-induced expression of the mesenchymal markers α-smooth muscle actin, fibronectin, and collagen type I; production of pro-matrix metalloproteinase 2 and interleukin-6; expression of the focal adhesion protein paxillin; and phosphorylation of SMAD2 in the cultured RPE cells. Finally, immunofluorescence analysis showed that Am580 suppressed both the TGF-β2-induced translocation of myocardin-related transcription factor-A (MRTF-A) from the cytoplasm to the nucleus of cultured RPE cells as well as subretinal fibrosis triggered by laser-induced photocoagulation in a mouse model. Our observations thus suggest that RAR-α signaling inhibits EMT in RPE cells and might attenuate the development of fibrosis associated with proliferative retinal diseases.

Adrenomedullin-Receptor Activity-Modifying Protein 2 System Ameliorates Subretinal Fibrosis by Suppressing Epithelial-Mesenchymal Transition in Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a leading cause of visual impairment. Anti-vascular endothelial growth factor drugs used to treat AMD carry the risk of inducing subretinal fibrosis. We investigated the use of adrenomedullin (AM), a vasoactive peptide, and its receptor activity-modifying protein 2, RAMP2, which regulate vascular homeostasis and suppress fibrosis. The therapeutic potential of the AM-RAMP2 system was evaluated after laser-induced choroidal neovascularization (LI-CNV), a mouse model of AMD. Neovascular formation, subretinal fibrosis, and macrophage invasion were all enhanced in both AM and RAMP2 knockout mice compared with those in wild-type mice. These pathologic changes were suppressed by intravitreal injection of AM. Comprehensive gene expression analysis of the choroid after LI-CNV with or without AM administration revealed that fibrosis-related molecules, including Tgfb, Cxcr4, Ccn2, and Thbs1, were all down-regulated by AM. In retinal pigment epithelial cells, co-administration of transforming growth factor-β and tumor necrosis factor-α induced epithelial-mesenchymal transition, which was also prevented by AM. Finally, transforming growth factor-β and C-X-C chemokine receptor type 4 (CXCR4) inhibitors eliminated the difference in subretinal fibrosis between RAMP2 knockout and wild-type mice. These findings suggest the AM-RAMP2 system suppresses subretinal fibrosis in LI-CNV by suppressing epithelial-mesenchymal transition.

Transcriptome Landscape of Epithelial to Mesenchymal Transition of Human Stem Cell-Derived RPE

Purpose

RPE injury often induces epithelial to mesenchymal transition (EMT). Although RPE-EMT has been implicated in a variety of retinal diseases, including proliferative vitroretinopathy, neovascular and atrophic AMD, and diabetic retinopathy, it is not well-understood at the molecular level. To contribute to our understanding of EMT in human RPE, we performed a time-course transcriptomic analysis of human stem cell-derived RPE (hRPE) monolayers induced to undergo EMT using 2 independent, yet complementary, model systems.

Methods

EMT of human stem cell-derived RPE monolayers was induced by either enzymatic dissociation or modulation of TGF-β signaling. Transcriptomic analysis of cells at different stages of EMT was performed by RNA-sequencing, and select findings were confirmed by reverse transcription quantitative PCR and immunostaining. An ingenuity pathway analysis (IPA) was performed to identify signaling pathways and regulatory networks associated with EMT.

Results

Proteocollagenolytic enzymatic dissociation and cotreatment with TGF-β and TNF-α both induce EMT in human stem cell-derived RPE monolayers, leading to an increased expression of mesenchymal factors and a decreased expression of RPE differentiation-associated factors. Ingenuity pathway analysis identified the upstream regulators of the RPE-EMT regulatory networks and identified master switches and nodes during RPE-EMT. Of particular interest was the identification of widespread dysregulation of axon guidance molecules during RPE-EMT progression.

Conclusions

The temporal transcriptome profiles described here provide a comprehensive resource of the dynamic signaling events and the associated biological pathways that underlie RPE-EMT onset. The pathways defined by these studies may help to identify targets for the development of novel therapeutic targets for the treatment of retinal disease.

The HIF-1α/p53/miRNA-34a/Klotho axis in retinal pigment epithelial cells promotes subretinal fibrosis and exacerbates choroidal neovascularization

Wet age‐related macular degeneration (wAMD), characterized by choroidal neovascularization (CNV), is a leading cause of irreversible vision loss among elderly people in developed nations. Subretinal fibrosis, mediated by epithelial‐mesenchymal transition (EMT) of retinal pigment epithelium (RPE) cells, leads to unsuccessful anti‐vascular endothelial growth factor (VEGF) agent treatments in CNV patients. Under hypoxic conditions, hypoxia‐inducible factor‐1α (HIF‐1α) increases the stability and activation of p53, which activates microRNA‐34a (miRNA‐34a) transcription to promote fibrosis. Additionally, Klotho is a target gene of miRNA‐34a that inhibits fibrosis. This study aimed to explore the role of the HIF‐1α/p53/miRNA‐34a/Klotho axis in subretinal fibrosis and CNV. Hypoxia‐induced HIF‐1α promoted p53 stability, phosphorylation and nuclear translocation in ARPE‐19 cells (a human RPE cell line). HIF‐1α‐dependent p53 activation up‐regulated miRNA‐34a expression in ARPE‐19 cells following hypoxia. Moreover, hypoxia‐induced p53‐dependent miRNA‐34a inhibited the expression of Klotho in ARPE‐19 cells. Additionally, the HIF‐1α/p53/miRNA‐34a/Klotho axis facilitated hypoxia‐induced EMT in ARPE‐19 cells. In vivo, blockade of the HIF‐1α/p53/miRNA‐34a/Klotho axis alleviated the formation of mouse laser‐induced CNV and subretinal fibrosis. In short, the HIF‐1α/p53/miRNA‐34a/Klotho axis in RPE cells promoted subretinal fibrosis, thus aggravating the formation of CNV.

Geographic Atrophy: Confocal Scanning Laser Ophthalmoscopy, Histology, and Inflammation in the Region of Expanding Lesions

Purpose

To describe the pathology of AMD in eyes with geographic atrophy (GA) using confocal scanning laser ophthalmoscopy (SLO) blue light autofluorescence (BAF), and near-infrared (IR) AF and to correlate it with the histology and immunohistochemistry analysis at the margins of the GA lesion.

Methods

Enucleated, fixed eyes from seventeen donors with GA were imaged and analyzed by BAF-SLO, IRAF-SLO, and by fundus macroscopy (FM). Tissue from the margins of the GA lesions was cut and processed for resin embedding and histology or cryosectioning and fluorescence in the green and far-red channels, and immunohistochemistry to assess markers of inflammation. Isolated DNA from donors was genotyped for single nucleotide polymorphisms (SNPs) previously shown to be risk factors for the development and progression of AMD.

Results

Around the leading edge of the GA lesions we observed hypertrophic RPE cells with cytoplasm filled with granules fluorescent both in the far-red and green-red channels; abundant microglia and macrophage; deposition of complement factor H (CFH) in Bruch's membrane (BM) and increased membrane attack complex (MAC) on RPE cells.

Conclusions

Fluorescence imaging of cryosections of RPE cells around the leading edge of the GA lesions suggest that IRAF-SLO visualizes mostly melanin-related compounds. In addition, medium-size GA atrophy displayed the most significant changes in inflammation markers.

Polarized Cytokine Release Triggered by P2X7 Receptor from Retinal Pigmented Epithelial Cells Dependent on Calcium Influx

Cytokine release from non-inflammatory cells is a key step in innate immunity, and agonists triggering cytokine release are central in coordinating responses. P2X7 receptor (P2X7R) stimulation by extracellular ATP is best known to active the NLRP3 inflammasome and release IL-1β, but stimulation also leads to release of other cytokines. As cytokine signaling by retinal pigmented epithelial (RPE) cells is implicated in retinal neurodegeneration, the role of P2X7R in release of cytokine IL-6 from RPE cells was investigated. P2X7R stimulation triggered IL-6 release from primary mouse RPE, human iPS-RPE and human ARPE-19 cells. IL-6 release was polarized, with predominant rise across apical membranes. IL-6 release was inhibited by P2X7R antagonists A438079, A839977, and AZ10606120, but not the NRTI lamivudine (3TC), P2X1R antagonist NF279, or P2Y1R antagonist MRS2179. P2X7R-mediated IL-6 release required extracellular Ca²⁺ and was blocked by Ca²⁺ chelator BAPTA. IL-6 release and Ca²⁺ elevation occurred rapidly, consistent with vesicular IL-6 staining in unstimulated cells. P2X7R stimulation did not trigger IL-1β release in these unprimed cells. P2X7R-mediated IL-6 release was enhanced in RPE cells from the ABCA4^−/− mouse model of retinal degeneration. In summary, P2X7R stimulation triggers rapid Ca²⁺-dependent IL-6 release across the apical membrane of RPE cells.

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.

Mesenchymal stem cells reverse EMT process through blocking the activation of NF-κB and Hedgehog pathways in LPS-induced acute lung injury

Acute lung injury (ALI) is a pulmonary disorder, which can result in fibrosis of the lung tissues. Recently, mesenchymal stem cell (MSC) has become a novel therapeutic method for ALI. However, the potential mechanism by which MSC regulates the progression of ALI remains blurry. The present study focused on investigating the mechanism underneath MSC-reversed lung injury and fibrosis. At first, we determined that coculture with MSC led to the inactivation of NF-κB signaling and therefore suppressed hedgehog pathway in LPS-treated MLE-12 cells. Besides, we confirmed that MSC-exosomes were responsible for the inhibition of EMT process in LPS-treated MLE-12 cells through transmitting miRNAs. Mechanism investigation revealed that MSC-exosome transmitted miR-182-5p and miR-23a-3p into LPS-treated MLE-12 cells to, respectively, target Ikbkb and Usp5. Of note, Usp5 interacted with IKKβ to hamper IKKβ ubiquitination. Moreover, co-inhibition of miR-182-5p and miR-23a-3p offset the suppression of MSC on EMT process in LPS-treated MLE-12 cells as well as in LPS-injured lungs of mice. Besides, the retarding effect of MSC on p65 nuclear translocation was also counteracted after co-inhibiting miR-182-5p and miR-23a-3p, both in vitro and in vivo. In summary, MSC-exosome transmitted miR-23a-3p and miR-182-5p reversed the progression of LPS-induced lung injury and fibrosis through inhibiting NF-κB and hedgehog pathways via silencing Ikbkb and destabilizing IKKβ.

Retinal pigment epithelium transcriptome analysis in chronic smoking reveals a suppressed innate immune response and activation of differentiation pathways

Cigarette smoking, a powerful mixture of chemical oxidants, is the strongest environmental risk factor for developing age-related macular degeneration (AMD), the most common cause of blindness among the elderly in western societies. Despite intensive study, the full impact of smoking on the retinal pigment epithelium (RPE), a central cell type involved in AMD pathobiology, remains unknown. The relative contribution of the known dysfunctional pathways to AMD, at what stage they are most pathogenic, or whether other processes are relevant, is poorly understood, and furthermore, whether smoking activates them, is unknown. We performed global RNA-sequencing of the RPE from C57BL/6J mice exposed to chronic cigarette smoke for 6 months to identify potential pathogenic and cytoprotective pathways. The RPE transcriptome induced by chronic cigarette smoking exhibited a mixed response of marked suppression of the innate immune response including type I and II interferons and upregulation of cell differentiation and morphogenic gene clusters, suggesting an attempt by the RPE to maintain its differentiated state despite smoke-induced injury. Given that mice exposed to chronic smoke develop early features of AMD, these novel findings are potentially relevant to the transition from aging to AMD.

Nanoscopic Approach to Study the Early Stages of Epithelial to Mesenchymal Transition (EMT) of Human Retinal Pigment Epithelial (RPE) Cells In Vitro

The maintenance of visual function is supported by the proper functioning of the retinal pigment epithelium (RPE), representing a mosaic of polarized cuboidal postmitotic cells. Damage factors such as inflammation, aging, or injury can initiate the migration and proliferation of RPE cells, whereas they undergo a pseudo-metastatic transformation or an epithelial to mesenchymal transition (EMT) from cuboidal epithelioid into fibroblast-like or macrophage-like cells. This process is recognized as a key feature in several severe ocular pathologies, and is mimicked by placing RPE cells in culture, which provides a reasonable and well-characterized in vitro model for a type 2 EMT. The most obvious characteristic of EMT is the cell phenotype switching, accompanied by the cytoskeletal reorganization with changes in size, shape, and geometry. Atomic force microscopy (AFM) has the salient ability to label-free explore these characteristics. Based on our AFM results supported by the genetic analysis of specific RPE differentiation markers, we elucidate a scheme for gradual transformation from the cobblestone to fibroblast-like phenotype. Structural changes in the actin cytoskeletal reorganization at the early stages of EMT lead to the development of characteristic geodomes, a finding that may reflect an increased propensity of RPE cells to undergo further EMT and thus become of diagnostic significance.

Nanoceria Particles Are an Eligible Candidate to Prevent Age-Related Macular Degeneration by Inhibiting Retinal Pigment Epithelium Cell Death and Autophagy Alterations

Retinal pigment epithelium (RPE) dysfunction and degeneration underlie the development of age-related macular degeneration (AMD), which is the leading cause of blindness worldwide. In this study, we investigated whether cerium oxide nanoparticles (CeO₂-NPs or nanoceria), which are anti-oxidant agents with auto-regenerative properties, are able to preserve the RPE. On ARPE-19 cells, we found that CeO₂-NPs promoted cell viability against H₂O₂-induced cellular damage. For the in vivo studies, we used a rat model of acute light damage (LD), which mimics many features of AMD. CeO₂-NPs intravitreally injected three days before LD prevented RPE cell death and degeneration and nanoceria labelled with fluorescein were found localized in the cytoplasm of RPE cells. CeO₂-NPs inhibited epithelial-mesenchymal transition of RPE cells and modulated autophagy by the down-regulation of LC3B-II and p62. Moreover, the treatment inhibited nuclear localization of LC3B. Taken together, our study demonstrates that CeO₂-NPs represent an eligible candidate to counteract RPE degeneration and, therefore, a powerful therapy for AMD.

Targeting the Notch and TGF-β signaling pathways to prevent retinal fibrosis in vitro and in vivo

Rationale: The Notch and transforming growth factor-β (TGFβ) signaling pathways are two intracellular mechanisms that control fibrosis in general but whether they play a major role in retinal fibrosis is less clear. Here we study how these two signaling pathways regulate Müller cell-dominated retinal fibrosis in vitro and in vivo.

Methods: Human MIO-M1 Müller cells were treated with Notch ligands and TGFβ1, either alone or in combination. Western blots were performed to study changes in γ-secretase proteases, Notch downstream effectors, endogenous TGFβ1, phosphorylated Smad3 (p-Smad3) and extracellular matrix (ECM) proteins. We also studied the effects of RO4929097, a selective γ-secretase inhibitor, on expression of ECM proteins after ligand stimulation. Müller cell viability was studied by AlamarBlue and cytotoxicity by lactate cytotoxicity assays. Finally, we studied changes in Notch and TGFβ signaling and tested the effect of intravitreal injections of the Notch pathway inhibitor RO4929097 on retinal fibrosis resulted from Sodium iodate (NaIO₃)-induced retinal injury in mice. We also studied the safety of intravitreal injections of RO4929097 in normal mice.

Results: Treatment of Müller cells with Notch ligands upregulated γ-secretase proteases and Notch downstream effectors, with increased expression of endogenous TGFβ1, TGFβ receptors and p-Smad3. TGFβ1 upregulated the expression of proteins associated with both signaling pathways in a similar manner. Notch ligands and TGFβ1 had additive effects on overexpression of ECM proteins in Müller cells which were inhibited by RO4929097. Notch and TGFβ ligands stimulated Müller cell proliferation which was inhibited by RO4929097 without damaging the cells. NaIO₃-induced retinal injury activated both Notch and TGFβ signaling pathways in vivo. Intravitreal injection of RO4929097 prevented Müller cell gliosis and inhibited overexpression of ECM proteins in this murine model. We found no safety concerns for up to 17 days after an intravitreal injection of RO4929097.

Conclusions: Inhibiting Notch signaling might be an effective way to prevent retinal fibrosis. This study is of clinical significance in developing a treatment for preventing fibrosis in proliferative vitreoretinopathy, proliferative diabetic retinopathy and wet age-related macular degeneration.

Role of Epithelial-Mesenchymal Transition in Retinal Pigment Epithelium Dysfunction

Retinal pigment epithelial (RPE) cells maintain the health and functional integrity of both photoreceptors and the choroidal vasculature. Loss of RPE differentiation has long been known to play a critical role in numerous retinal diseases, including inherited rod-cone degenerations, inherited macular degeneration, age-related macular degeneration, and proliferative vitreoretinopathy. Recent studies in post-mortem eyes have found upregulation of critical epithelial-mesenchymal transition (EMT) drivers such as TGF-β, Wnt, and Hippo. As RPE cells become less differentiated, they begin to exhibit the defining characteristics of mesenchymal cells, namely, the capacity to migrate and proliferate. A number of preclinical studies, including animal and cell culture experiments, also have shown that RPE cells undergo EMT. Taken together, these data suggest that RPE cells retain the reprogramming capacity to move along a continuum between polarized epithelial cells and mesenchymal cells. We propose that movement along this continuum toward a mesenchymal phenotype be defined as RPE Dysfunction. Potential mechanisms include impaired tight junctions, accumulation of misfolded proteins and dysregulation of several key pathways and molecules, such as TGF-β pathway, Wnt pathway, nicotinamide, microRNA 204/211 and extracellular vesicles. This review synthesizes the evidence implicating EMT of RPE cells in post-mortem eyes, animal studies, primary RPE, iPSC-RPE and ARPE-19 cell lines.

Spectral-Domain Optical Coherence Tomography Analysis of Fibrotic Lesions in Neovascular Age-Related Macular Degeneration

PURPOSE

To describe the spectral-domain optical coherence tomography (OCT) features of fibrotic lesions associated with neovascular age-related macular degeneration (nAMD) and to outline the progression pathways from initial macular choroidal neovascular lesions (CNVs) to fibrosis.

METHODS

Patients with nAMD were retrospectively included when macular subretinal fibrosis was present. Fibrosis was categorized using spectral-domain OCT with respect to retinal pigment epithelium (RPE) in 836 spectral-domain OCT slices from 44 eyes of 39 patients. In addition, in 47 distinct eyes, 4181 spectral-domain OCT slices were retrospectively reviewed to longitudinally assess progression from the initial lesion to the final fibrosis.

RESULTS

Cross-sectional analysis classified fibrosis on spectral-domain OCT slices, as type A if located underneath the RPE, as type B if located above the RPE, and as type C if the remaining RPE was undistinguishable. The longitudinal analysis series revealed 3 progression pathways from the original CNV: 1) progression to type A, followed by RPE erosion and subretinal hyperreflective material, then type B and type C fibroglial lesion (FGL; 17/47 eyes); 2) progression to type B then type C FGL (17/47 eyes); and 3) persistence of type A with development of a flat, fibroatrophic lesion (13/47 eyes). Subretinal hyperreflective material, macular hemorrhage, or RPE tear occurred in 14 of 47, 13 of 47, and 10 of 47 eyes, respectively.

CONCLUSION

This spectral-domain OCT analysis identified various patterns of macular fibrosis in eyes with nAMD. Three pathways of progression to fibrosis were described including the well-established pathway of type 2 CNV progression to FGL and the progression of type 1 fibrovascular CNV to FGL or fibroatrophic lesion.

Integrated bioinformatics analysis of aberrantly-methylated differentially-expressed genes and pathways in age-related macular degeneration

Background

Age-related macular degeneration (AMD) represents the leading cause of visual impairment in the aging population. The goal of this study was to identify aberrantly-methylated, differentially-expressed genes (MDEGs) in AMD and explore the involved pathways via integrated bioinformatics analysis.

Methods

Data from expression profile GSE29801 and methylation profile GSE102952 were obtained from the Gene Expression Omnibus database. We analyzed differentially-methylated genes and differentially-expressed genes using R software. Functional enrichment and protein–protein interaction (PPI) network analysis were performed using the R package and Search Tool for the Retrieval of Interacting Genes online database. Hub genes were identified using Cytoscape.

Results

In total, 827 and 592 genes showed high and low expression, respectively, in GSE29801; 4117 hyper-methylated genes and 511 hypo-methylated genes were detected in GSE102952. Based on overlap, we categorized 153 genes as hyper-methylated, low-expression genes (Hyper-LGs) and 24 genes as hypo-methylated, high-expression genes (Hypo-HGs). Four Hyper-LGs (CKB, PPP3CA, TGFB2, SOCS2) overlapped with AMD risk genes in the Public Health Genomics and Precision Health Knowledge Base. KEGG pathway enrichment analysis indicated that Hypo-HGs were enriched in the calcium signaling pathway, whereas Hyper-LGs were enriched in sphingolipid metabolism. In GO analysis, Hypo-HGs were enriched in fibroblast migration, membrane raft, and coenzyme binding, among others. Hyper-LGs were enriched in mRNA transport, nuclear speck, and DNA binding, among others. In PPI network analysis, 23 nodes and two edges were established from Hypo-HGs, and 151 nodes and 73 edges were established from Hyper-LGs. Hub genes (DHX9, MAPT, PAX6) showed the greatest overlap.

Conclusion

This study revealed potentially aberrantly MDEGs and pathways in AMD, which might improve the understanding of this disease.

The Regulation of NFE2L2 (NRF2) Signalling and Epithelial-to-Mesenchymal Transition in Age-Related Macular Degeneration Pathology

Age-related macular degeneration (AMD) is a mounting cause of loss of sight in the elderly in the developed countries, a trend enhanced by the continual ageing of the population. AMD is a multifactorial and only partly understood, malady. Unfortunately, there is no effective treatment for most AMD patients. It is known that oxidative stress (OS) damages the retinal pigment epithelium (RPE) and contributes to the progression of AMD. We review here the potential importance of two OS-related cellular systems in relation to AMD. First, the nuclear factor erythroid 2-related factor 2 (NFE2L2; NRF2)-mediated OS response signalling pathway is important in the prevention of oxidative damage and a failure of this system could be critical in the development of AMD. Second, epithelial-to-mesenchymal transition (EMT) represents a change in the cellular phenotype, which ultimately leads to the fibrosis encountered in RPE, a characteristic of AMD. Many of the pathways triggering EMT are promoted by OS. The possible interconnections between these two signalling routes are discussed here. From a broader perspective, the control of NFE2L2 and EMT as ways of preventing OS-derived cellular damage could be potentially valuable in the therapy of AMD.

Inhibitory effect of nintedanib on VEGF secretion in retinal pigment epithelial cells induced by exposure to a necrotic cell lysate

Necrosis is a form of cell death that results in rupture of the plasma membrane and the release of cellular contents, and it can give rise to sterile inflammation in the retina and other tissues. The secretion of vascular endothelial growth factor (VEGF) by retinal pigment epithelial (RPE) cells contributes to retinal homeostasis as well as to pathological angiogenesis. We have now examined the effect of a necrotic cell lysate prepared from human RPE cells (NLR) on the release of VEGF by healthy RPE cells. We found that NLR markedly increased the release of VEGF from RPE cells and that this effect was attenuated by nintedanib, a multiple receptor tyrosine kinase inhibitor, whereas it was unaffected by inhibitors of NF-κB signaling or of caspase-1. NLR also induced the phosphorylation of extracellular signal-regulated kinase (Erk) and signal transducer and activator of transcription 3 (Stat3) in a manner sensitive to inhibition by nintedanib, although inhibitors of Erk and Stat3 signaling pathways did not affect NLR-induced VEGF secretion. In addition, nintedanib attenuated the development of choroidal neovascularization in mice. Our results have thus shown that a necrotic lysate of RPE cells induced VEGF secretion from healthy RPE cells and that this effect was mediated by receptor tyrosine kinase signaling. They therefore suggest that VEGF secretion by healthy RPE cells is a potential therapeutic target for retinal diseases associated with sterile inflammation and pathological angiogenesis.

Inhibitor of growth 4 (ING4) inhibits hypoxia-induced EMT by decreasing HIF-1α and snail in HK2 cells

Renal fibrosis is a common mechanism that leads to all kidney diseases and Epithelial-mesenchymal transition (EMT) is considered as one of the potential mechanisms of renal fibrosis. Inhibitor of growth 4 (ING4) was reported to involve in several diseases; especially it was negatively correlated with lung fibrogenesis parameters. However, the role of ING4 and underlying mechanisms in EMT are still unknown. In this study, we used a UUO rat model to mimic renal fibrosis, which was examined by Masson and HE staining analysis. To explore the effects of ING4 on hypoxia-induced EMT, HK2 cells were treated with hypoxia to induce EMT and ING4 was over-expressed in hypoxia-treated HK2 cells by transfection of pEGFP-N1-ING4. MTT assay was used to describe the cell viability of HK2 cells under the hypoxic condition. The expression levels of ING4, hypoxia-inducible factor-1α (HIF-1α), and EMT markers (E-cadherin, N-cadherin and vimentin) were examined in vivo and in vitro by western blot, qRT-PCR, immunohistochemical staining or Immunofluorescence. Our results showed that, in a UUO rat model, ING4 was decreased and EMT was developed with reduction in E-cadherin and increase in N-cadherin and vimentin, suggesting a significant association between ING4 expression and EMT. Under hypoxia, E-cadherin was down-regulated and N-cadherin and vimentin were up-regulated, indicating that hypoxia induced EMT in HK2 cells. Nonetheless, changes in the expression of EMT biomarkers were inhibited by over-expression of ING4. Moreover, over-expressing ING4 decreased the expression of HIF-1α and snail in HK2 cells. These findings suggest that ING4 may inhibit hypoxia-induced EMT via decreasing HIF-1α and snail in HK2 cells, indicating the potential of ING4 as a therapeutic target for renal fibrosis.

Emerging roles of transforming growth factor β signaling in wet age-related macular degeneration

Age-related macular degeneration (AMD) is one of the major causes of irreversible blindness among aging populations in developed countries and can be classified as dry or wet according to its progression. Wet AMD, which is characterized by angiogenesis on the choroidal membrane, is uncommonly seen but more severe. Controlling or completely inhibiting the factors that contribute to the progression of events that lead to angiogenesis may be an effective strategy for treating wet AMD. Emerging evidence has shown that transforming growth factor-β (TGF-β) signaling plays a significant role in the progression of wet AMD. In this review, we described the roles of and changes in TGF-β signaling in the development of AMD and discussed the mechanisms of the TGF-β superfamily in choroidal neovascularization (CNV) and wet AMD, including the modulation of angiogenesis-related factors, inflammation, vascular fibrosis, and immune responses, as well as cross-talk with other signaling pathways. These remarkable findings indicate that TGF-β signaling is a potential target for wet AMD treatment.

GEP100/ARF6 regulates VEGFR2 signaling to facilitate high-glucose-induced epithelial-mesenchymal transition and cell permeability in retinal pigment epithelial cells

Cell permeability and epithelial-mesenchymal transition (EMT) were found to be enhanced in diabetic retinopathy, and the aim of this study was to investigate the underlying mechanism. ARPE-19 cell line or primary retinal pigment epithelial (RPE) cells were cultured under high or normal glucose conditions. Specific shRNAs were employed to knock down ADP-ribosylation factor 6 (ARF6), GEP100, or VEGF receptor 2 (VEGFR2) in ARPE-19 or primary RPE cells. Cell migration ability was measured using Transwell assay. Western blotting was used to measure indicated protein levels. RPE cells treated with high glucose showed increased cell migration, paracellular permeability, EMT, and expression of VEGF. Knockdown of VEGFR2 inhibited the high-glucose-induced effects on RPE cells via inactivation of ARF6 and MAPK pathways. Knockdown ARF6 or GEP100 led to inhibition of high-glucose-induced effects via inactivation of VEGFR2 pathway. Knockdown of ARF6, but not GEP100, decreased high-glucose-induced internalization of VEGFR2. High-glucose enhances EMT and cell permeability of RPE cells through activation of VEGFR2 and ARF6/GEP100 pathways, which form a positive feedback loop to maximize the activation of VEGF/VEGFR2 signaling.

Myofibroblasts in macular fibrosis secondary to neovascular age-related macular degeneration - the potential sources and molecular cues for their recruitment and activation

Age-related macular degeneration (AMD) is the leading cause of blindness in the elderly in developed countries. Neovascular AMD (nAMD) accounts for 90% of AMD-related vision loss. Although intravitreal injection of VEGF inhibitors can improve vision in nAMD, approximately 1/3 of patients do not benefit from the therapy due to macular fibrosis. The molecular mechanism underlying the transition of the neovascular lesion to a fibrovascular phenotype remains unknown. Here we discussed the clinical features and risk factors of macular fibrosis secondary to nAMD. Myofibroblasts are key cells in fibrosis development. However, fibroblasts do not exist in the macula. Potential sources of myofibroblast precursors, the molecular cues in the macular microenvironment that recruit them and the pathways that control their differentiation and activation in macular fibrosis were also discussed. Furthermore, we highlighted the challenges in macular fibrosis research and the urgent need for better animal models for mechanistic and therapeutic studies.

A Role for βA3/A1-Crystallin in Type 2 EMT of RPE Cells Occurring in Dry Age-Related Macular Degeneration

Purpose

The RPE cells have a major role in the development of dry age-related macular degeneration (AMD). We present novel evidence that βA3/A1-crystallin, encoded by the Cryba1 gene, a protein known to be important for lysosomal clearance in the RPE, also has a role in epithelial-to-mesenchymal transition (EMT) of RPE cells.

Methods

RPE from dry AMD globes, genetically engineered mice lacking Cryba1 globally or specifically in the RPE, spontaneous mutant rats (Nuc1) with a loss-of-function mutation in Cryba1, and the melanoma OCM3 cell line were used. Spatial localization of proteins was demonstrated with immunofluorescence, gene expression levels were determined by quantitative PCR (qPCR), and protein levels by Western blotting. Cell movement was evaluated using wound healing and cell migration assays. Co-immunoprecipitation was used to identify binding partners of βA3/A1-crystallin.

Results

βA3/A1-crystallin is upregulated in polarized RPE cells compared to undifferentiated cells. Loss of βA3/A1-crystallin in murine and human RPE cells resulted in upregulation of Snail and vimentin, downregulation of E-cadherin, and increased cell migration. βA3/A1-crystallin binds to cortactin, and loss of βA3/A1-crystallin resulted in increased P-cortactin^Y421. The RPE from AMD samples had increased Snail and vimentin, and decreased E-cadherin, compared to age-matched controls.

Conclusions

We introduced a novel concept of dry AMD initiation induced by lysosomal clearance defects in the RPE and subsequent attempts by RPE cells to avoid the resulting stress by undergoing EMT. We demonstrate that βA3/A1-crystallin is a potential therapeutic target for AMD through rejuvenation of lysosomal dysfunction and potentially, reversal of EMT.

Tranilast inhibits TGF-β-induced collagen gel contraction mediated by human corneal fibroblasts

AIM

To determine if tranilast affects human corneal fibroblast (HCFs) contraction.

METHODS

HCFs cultured in a three-dimensional type I collagen gel were treated with or without transforming growth factor beta (TGF-β) or tranilast. Gel diameter was measured as an indicator for collagen contraction. Immunoblot was performed to evaluate myosin light chain (MLC) and paxillin phosphorylation. Confocal microscopy was employed to examine the focal adhesions and actin stress fiber formation. Immunoblot analysis and gelatin zymography were performed to detect tissue inhibitors of metalloproteinases and matrix metalloproteinases (MMPs) in supernatant.

RESULTS

The inhibitory effect of tranilast on HCFs-mediated collagen gel contraction induced by TGF-β was dose-dependent. The significant effect of tranilast was started from 100 µmol/L and maximized at 300 µmol/L. The peak effect of 300 µmol/L tranilast also relied on the duration of treatment, which showed statistical significance from day 2. TGF-β-induced paxillin and MLC phosphorylation, stress fiber formation, focal adhesions, and MMP-1, MMP-2, and MMP-3 secretion in HCFs were also inhibited by tranilast.

CONCLUSION

Tranilast suppresses the HCFs-cultured collagen gel contraction induced by TGF-β. It attenuates actin stress fibers formation, focal adhesions, and the secretion of MMPs, with these actions likely contributing to the inhibitory effect on HCF contractility. By attenuating the contractility of corneal fibroblasts, tranilast treatment may inhibit corneal scarring.

Protective effect of retinoic acid receptor α on hypoxia-induced epithelial to mesenchymal transition of renal tubular epithelial cells associated with TGF-β/MMP-9 pathway

Retinoic acid receptor α (RARα), a member of family of the nuclear retinoic acid receptors (RARs), plays an essential role in various chronic kidney diseases (CKD). Renal tubular epithelial to mesenchymal transition (EMT) is a common mechanism of progression of renal interstitial fibrosis (RIF). Hypoxia has been extensively considered as one of major inducers of renal tubular EMT. However, the effects of RARα on hypoxia-induced EMT have not yet been described so far. The aim of the present study was to explore the roles and potential mechanisms of RARα in hypoxia-induced EMT of renal tubular epithelial cells (RTECs). Our results showed that expression of RARα in RTECs subjected to hypoxia significantly was reduced, accompanied by decreased expression level of the epithelial marker E-cadherin, and increased expression levels of the mesenchymal markers α-smooth muscle actin (α-SMA) and vimentin, in accord with EMT. Meanwhile, hypoxia could cause RTECs to obviously express TGF-β and matrix metalloproteinase-9 (MMP-9). Furthermore, using lentivirus-based delivery vectors to overexpress RARα in RTECs, we demonstrated that RARα alleviated hypoxia-induced EMT of RTECs and downregulated the expression levels of TGF-β and MMP-9. In a word, RARα protects RTECs against EMT induced by hypoxia associated with TGF-β/MMP-9 pathway.