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

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.

Niosome-encapsulated auraptene reduced the mRNA expression of VEGF-A and PDGFs genes in human retina-derived RPE cell line

AIM

To evaluate the effect of auraptene (AUR) treatment in forms of free and encapsulated in niosome nanoparticles by investigating the mRNA expression level of vascular endothelium growth factor (VEGF)-A and platelet-derived growth factors (PDGFs) in human retinal pigment epithelium (RPE) cell line.

METHODS

Niosome nanocarriers were produced using two surfactants Span 60 and Tween 80. RPE cell line was treated with both free AUR and niosome-encapsulated. Optimum dosage of treatments was calculated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Expression of VEGF-A and PDGF-A, PDGF-B, PDGF-C, PDGF-D genes was measured after total RNA extraction and cDNA synthesis, using real-time polymerase chain reaction (RT-PCR).

RESULTS

The highest entrapment efficiency (EE) was achieved by Span 60:cholesterol (1:1) with 64.3%. The half maximal inhibitory concentration (IC50) of free and niosome-encapsulated AUR were 38.5 and 27.78 µg/mL, respectively. Release study revealed that niosomal AUR had more gradual delivery to the cells. RT-PCR results showed reduced expression levels of VEGF-A, PDGF-A, PDGF-B, PDGF-C, and PDGF-D after treatment with both free and niosomal AUR.

CONCLUSION

Niosomal formulation of Span 60: cholesterol (1:1) is an effective drug delivery approach to transfer AUR to RPE cells. VEGF-A, PDGF-A, PDGF-B, PDGF-C, and PDGF-D are four angiogenic factors, inhibiting which by niosomal AUR may be effective in age-related macular degeneration.

Pharmaceutical therapies targeting autophagy for the treatment of age-related macular degeneration

Age-related macular degeneration (AMD) is a major cause of irreversible vision loss in the elderly. Although new therapies have recently emerged, there are currently no ways of preventing the development of the disease. Changes in intracellular recycling processes. Changes in intracellular recycling processes, called autophagy, lead to debris accumulation and cellular dysfunction in AMD models and AMD patients. Drugs that enhance autophagy hold promise as therapies for slowing AMD progression in preclinical models; however, more studies in humans are required. While a definitive cure for AMD will likely hinge on a personalized medicine approach, treatments that enhance autophagy hold promise for slowing vision loss.

Age-Related Macular Degeneration: A Disease of Cellular Senescence and Dysregulated Immune Homeostasis

Age-related macular degeneration (AMD) is a degenerative ocular disease primarily affecting central vision in the elderly. Its pathogenesis is complex, involving cellular senescence and immune homeostasis dysregulation. This review investigates the interaction between these two critical biological processes in AMD pathogenesis and their impact on disease progression. Initially, cellular senescence is analyzed, with particular emphasis on retinal damage induced by senescent retinal pigment epithelial cells. Subsequently, the occurrence of immune homeostasis dysregulation within the retina and its mechanistic role in AMD areis explored. Furthermore, the paper also discusses in detail the interplay between cellular senescence and immune responses, forming a vicious cycle that exacerbates retinal damage and may influence treatment outcomes. In summary, a deeper understanding of the interrelation between cellular senescence and immune dysregulation is vital for the developing innovative therapeutic strategies for AMD.

Gene therapy for age-related macular degeneration: potential, feasibility, and pitfalls

PURPOSE OF REVIEW

The landscape for age-related macular degeneration (AMD) is rapidly changing with addition of biosimilars and now United States Food and Drug Administration (FDA) approved nonneovascular AMD (nnAMD) treatment options. These developments have inspired a burgeoning pipeline of gene therapy approaches focused on similar antivascular endothelial growth factors (VEGF) and complement related pathways. Historic and more recent setbacks in the gene therapy pipeline, including intraocular inflammatory reactions, have raised important concerns for adverse events related to AMD therapeutics both for gene and nongene approaches. The specific clinical profile of these therapeutics approaching later stage clinical trials are complex and under active investigation; however, these options hold promise to disrupt the current landscape and change management paradigms for one of the leading causes of vision loss worldwide.

RECENT FINDINGS

This review covers current gene therapy approaches for neovascular AMD (nAMD) and nnAMD. Intravitreal, suprachoroidal, and subretinal delivery routes are discussed with attention to technical procedure, capabilities for transgene delivery to target tissue, immunogenicity, and collateral effects. Suprachoroidal delivery is an emerging approach which may bridge some of the practical drawbacks for intravitreal and subretinal methods, though with less elaborated immunologic profile. In parallel to delivery modification, viral vectors have been cultivated to target specific cells, with promising enhancements in adeno-associated viral (AAV) vectors and persistent interest in alternate viral and nonviral delivery vectors. Ongoing questions such as steroid or immunosuppressive regimen and economic considerations from a payer and societal perspective are discussed.

SUMMARY

The present review discusses emerging gene therapy options which could foster new, more durable nAMD and nnAMD therapeutics. These options will need refinement with regards to route, vector, and dosage, and specialists must decipher the specific clinical risk benefit profile for individual patients. Ongoing concerns for immunogenicity or dosage related adverse events could stifle progress, while further vector development and refined delivery techniques have the potential to change the safety and efficacy of currently options in the pipeline.

Features Associated With Vision in Eyes With Subfoveal Fibrosis From Neovascular Age-Related Macular Degeneration

PURPOSE

To report the characteristics and correlation of visual acuity in eyes treated for neovascular age-related macular degeneration (nAMD) and developed fibrosis.

DESIGN

Case-control study.

METHODS

Three hundred fifty-six treatment-naive nAMD eyes that were treated for 12 months were included. Fibrosis was defined as present if well-defined hyperreflective material (HRM) were present between the neurosensory retina and the Bruch membrane on optical coherence tomography (OCT) that correlated with well-defined regions of yellowish pallor on fundus photography and/or staining on fluorescence angiography. OCT features of subfoveal fibrosis and the overlying retina were correlated with visual acuity at month 12.

RESULTS

Sixty-three eyes (20.3%) developed incident fibrosis at month 12. Compared with eyes that did not develop fibrosis, these eyes had lower baseline vision (49 vs 54 letters, P = .02) and more of them had type 2 macular neovascularization (15.0 vs 8.8%, P = .03), larger lesion area (29.6 vs 15.1 mm2, P = .02), and subretinal hemorrhage ≥4 disc diameters (44.4% vs 19.8%, P < .01). Visual acuity was worse in the incident fibrosis compared with the group that never developed fibrosis by month 12. (-1.4±17.1 versus +6.0±17.4 letters, P < .01). In 83 eyes that had subfoveal fibrosis, better vision was associated with intact ellipsoid zone-external limiting membrane complex (β coefficient 29.4, 95% CI 14.2-44.6, P < .01), whereas worse vision was associated with retinal pigment epithelium (RPE)-involving HRM, HRM above the RPE, and width of HRM (β coefficients -25.4 [95% CI -36.3 to -14.6], P < .01; -23.5 [95% CI -39.0 to -7.9], P < .01; and -3.8 [95% CI -7.2 to -0.4], P = .03, respectively).

CONCLUSION

Although fibrosis is associated with poorer visual outcome, preservation of external limiting membrane and level of fibrosis relative to the RPE are associated with visual outcomes.

Fibronectin binds integrin α5β1 to regulate macular neovascularization through the Wnt/β-catenin signaling pathway

Age-related macular degeneration (AMD) is a progressive, degenerative disease of the macula. The formation of macular neovascularization (MNV) and subretinal fibrosis of AMD is the most classic cause of the loss of vision in older adults worldwide. While the underlying causes of MNV and subretinal fibrosis remain elusive, the common feature of many common retinal diseases is changes the proportions of protein deposition in extracellular matrix (ECM) when compared to normal tissue. In ECM, fibronectin (FN) is a crucial component and plays a pivotal part not only in fibrotic diseases but also in the process of angiogenesis. The study aims to understand the role of ligand FN and its common integrin receptor α5β1 on MNV, and to understand the molecular mechanism involved. To study this, the laser-induced MNV mouse model and the rhesus macaque choroid-retinal endothelial cell line (RF/6A) chemical hypoxia mode were established, and the FN-α5β1 expression levels were detected by immunohistochemistry (IHC) and quantitative real-time PCR analysis (qRT-PCR). Fibronectin expression was silenced using small interfering RNA (siRNA) targeting FN. The tube formation and vitro scratch assays were used to assess the ability to form blood vessels and cell migration. To measure the formation of MNV, immunofluorescence, and Western blot assays were used. These results revealed that the expressions of FN and integrin α5β1 were distinctly increased in the laser-induced MNV mouse model and in the RF/6A cytochemically induced hypoxia model, and the expression tendency was identical. After the use of FN siRNA, the tube formation and migration abilities of the RF/6A cells were lower, the ability of endothelial cells to proliferate was confined and the scope of damage caused by the laser in animal models was significantly cut down. In addition, FN gene knockdown dramatically inhibited the expression of Wnt/β-catenin signal. The interaction of FN with the integrin receptor α5β1 in the constructed model, which may act through the Wnt/β-catenin signaling pathway, was confirmed in this study. In conclusion, FN may be a potential new molecular target for the prevention and treatment of subretinal fibrosis and MNV.

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.

Influence of submacular hemorrhage at baseline on the long-term outcomes of aflibercept treatment for typical neovascular age-related macular degeneration and polypoidal choroidal vasculopathy

PURPOSE

To investigate the influence of submacular hemorrhage (SMH) at baseline on long-term visual outcomes of patients with typical age-related macular degeneration (tAMD) and polypoidal choroidal vasculopathy (PCV) treated with intravitreal aflibercept (IVA).

METHODS

In this retrospective study, eyes of treatment-naïve patients with tAMD and PCV who initiated IVA under a treat-and-extend regimen and were followed up for ≥ 5 years were classified into the tAMD-SMH ( +), tAMD-SMH (-), PCV-SMH ( +), and PCV-SMH (-) groups based on the presence of SMH at baseline. Best-corrected visual acuity (BCVA) changes and macular fibrosis and atrophy incidences were assessed.

RESULTS

This study included 127 eyes (127 patients), including 51 with tAMD and 76 with PCV; 18 eyes had SMH at baseline. In the tAMD-SMH ( +) group (n = 6), the mean logMAR BCVA significantly deteriorated from 0.59 ± 0.45 at baseline to 0.88 ± 0.47 at the final visit (P = 0.024). No significant BCVA changes were observed in the tAMD-SMH (-) (n = 45), PCV-SMH ( +) (n = 12), or PCV-SMH (-) (n = 64) groups (all P > 0.05). The tAMD-SMH ( +) group showed a significantly higher incidence of macular fibrosis at the final visit than did the tAMD-SMH (-) group (P = 0.042). There was no influence of baseline SMH on the macular fibrosis incidence in eyes with PCV and the macular atrophy incidence in eyes with tAMD and PCV.

CONCLUSION

The presence of SMH at baseline resulted in poorer long-term visual acuity in eyes with tAMD, even with aflibercept treatment. However, no such influence was observed in eyes with PCV.

First-Year Real-Life Experience with Intravitreal Faricimab for Refractory Neovascular Age-Related Macular Degeneration

Background: To evaluate the outcomes of intravitreal faricimab (IVF) for refractory neovascular age-related macular degeneration (nAMD) and investigate the impact of baseline optical coherence tomography, biomarkers for total IVF injections are needed. Methods: A retrospective analysis of 33 eyes of patients who completed one year (52 W) of treatment with IVF. The eyes received four IVF injections (6 mg/0.05 mL) as the upload phase. Thereafter, the treatment interval was extended to 8 or 12 weeks if disease activity was not recorded. The outcome measures included best-corrected visual acuity (BCVA), central macular thickness (CMT), subfoveal choroidal thickness (SFCT), and retinal fluid distribution. Results: A total of 33 eyes were included. CMT decreased significantly at 52 W (p < 0.01). BCVA and SFCT did not change significantly at 52 W (p > 0.05). The number of eyes with subretinal fluid decreased significantly at 52 W (p < 0.01). Complete fluid resolution was achieved in 20 eyes (60%). The total number of injections was significantly negatively correlated with the presence of hyperreflective dots at baseline (HRDs, p < 0.01) and SFCT at baseline (p < 0.01). Conclusions: IVF led to a significant reduction in CMT with stabilization of BCVA. The total number of injections was lower in eyes with HRDs and increased SFCT at baseline. This might provide clues regarding response to IVF for future studies.

Wnt5a/β-catenin-mediated epithelial-mesenchymal transition: a key driver of subretinal fibrosis in neovascular age-related macular degeneration

BACKGROUND

Neovascular age-related macular degeneration (nAMD), accounts for up to 90% of AMD-associated vision loss, ultimately resulting in the formation of fibrotic scar in the macular region. The pathogenesis of subretinal fibrosis in nAMD involves the process of epithelial-mesenchymal transition (EMT) occurring in retinal pigment epithelium (RPE). Here, we aim to investigate the underlying mechanisms involved in the Wnt signaling during the EMT of RPE cells and in the pathological process of subretinal fibrosis secondary to nAMD.

METHODS

In vivo, the induction of subretinal fibrosis was performed in male C57BL/6J mice through laser photocoagulation. Either FH535 (a β-catenin inhibitor) or Box5 (a Wnt5a inhibitor) was intravitreally administered on the same day or 14 days following laser induction. The RPE-Bruch's membrane-choriocapillaris complex (RBCC) tissues were collected and subjected to Western blot analysis and immunofluorescence to examine fibrovascular and Wnt-related markers. In vitro, transforming growth factor beta 1 (TGFβ1)-treated ARPE-19 cells were co-incubated with or without FH535, Foxy-5 (a Wnt5a-mimicking peptide), Box5, or Wnt5a shRNA, respectively. The changes in EMT- and Wnt-related signaling molecules, as well as cell functions were assessed using qRT-PCR, nuclear-cytoplasmic fractionation assay, Western blot, immunofluorescence, scratch assay or transwell migration assay. The cell viability of ARPE-19 cells was determined using Cell Counting Kit (CCK)-8.

RESULTS

The in vivo analysis demonstrated Wnt5a/ROR1, but not Wnt3a, was upregulated in the RBCCs of the laser-induced CNV mice compared to the normal control group. Intravitreal injection of FH535 effectively reduced Wnt5a protein expression. Both FH535 and Box5 effectively attenuated subretinal fibrosis and EMT, as well as the activation of β-catenin in laser-induced CNV mice, as evidenced by the significant reduction in areas positive for fibronectin, alpha-smooth muscle actin (α-SMA), collagen I, and active β-catenin labeling. In vitro, Wnt5a/ROR1, active β-catenin, and some other Wnt signaling molecules were upregulated in the TGFβ1-induced EMT cell model using ARPE-19 cells. Co-treatment with FH535, Box5, or Wnt5a shRNA markedly suppressed the activation of Wnt5a, nuclear translocation of active β-catenin, as well as the EMT in TGFβ1-treated ARPE-19 cells. Conversely, treatment with Foxy-5 independently resulted in the activation of abovementioned molecules and subsequent induction of EMT in ARPE-19 cells.

CONCLUSIONS

Our study reveals a reciprocal activation between Wnt5a and β-catenin to mediate EMT as a pivotal driver of subretinal fibrosis in nAMD. This positive feedback loop provides valuable insights into potential therapeutic strategies to treat subretinal fibrosis in nAMD patients.

Structure-Function Correlation of Retinal Fibrosis in Eyes with Neovascular Age-Related Macular Degeneration

Purpose: To assess retinal function in areas of presumed fibrosis due to neovascular age-related macular degeneration (nAMD), using multimodal imaging and structure-function correlation. Design: Cross-sectional observational study. Methods: 30 eyes of 30 consecutive patients with nAMD with a minimum history of one year of anti-vascular endothelial growth factor therapy were included. Each patient underwent microperimetry (MP), color fundus photography (CFP), standard spectral-domain-based OCT (SD-OCT), and polarization sensitive-OCT (PS-OCT) imaging. PS-OCT technology can depict retinal fibrosis based on its birefringence. CFP, SD-OCT, and PS-OCT were evaluated independently for the presence of fibrosis at the corresponding MP stimuli locations. MP results and morphologic findings in CFP, SD-OCT, and PS-OCT were co-registered and analyzed using mixed linear models. Results: In total, 1350 MP locations were evaluated to assess the functional impact of fibrosis according to a standardized protocol. The estimated means of retinal areas with signs of fibrosis were 12.60 db (95% confidence interval: 10.44-14.76) in CFP, 11.60 db (95% COI: 8.84-14.36) in OCT, and 11.02 db (95% COI 8.10-13.94) in PS-OCT. Areas evaluated as subretinal fibrosis in three (7.2 db) or two (10.1 db) modalities were significantly correlated with a lower retinal sensitivity than a subretinal fibrosis observed in only one (15.3 db) or none (23.3 db) modality (p < 0.001). Conclusions: CFP, SD-OCT and PS-OCT are all suited to detect areas of reduced retinal sensitivity related to fibrosis, however, a multimodal imaging approach provides higher accuracy in the identification of areas with low sensitivity in MP (i.e., impaired retinal function), and thereby improves the detection rate of subretinal fibrosis in nAMD.

AMPK signaling inhibits the differentiation of myofibroblasts: impact on age-related tissue fibrosis and degeneration

Disruption of the extracellular matrix (ECM) and an accumulation of fibrotic lesions within tissues are two of the distinctive hallmarks of the aging process. Tissue fibroblasts are mesenchymal cells which display an impressive plasticity in the regulation of ECM integrity and thus on tissue homeostasis. Single-cell transcriptome studies have revealed that tissue fibroblasts exhibit a remarkable heterogeneity with aging and in age-related diseases. Excessive stress and inflammatory insults induce the differentiation of fibroblasts into myofibroblasts which are fusiform contractile cells and abundantly secrete the components of the ECM and proteolytic enzymes as well as many inflammatory mediators. Detrimental stresses can also induce the transdifferentiation of certain mesenchymal and myeloid cells into myofibroblasts. Interestingly, many age-related stresses, such as oxidative and endoplasmic reticulum stresses, ECM stiffness, inflammatory mediators, telomere shortening, and several alarmins from damaged cells are potent inducers of myofibroblast differentiation. Intriguingly, there is convincing evidence that the signaling pathways stimulated by the AMP-activated protein kinase (AMPK) are potent inhibitors of myofibroblast differentiation and accordingly AMPK signaling reduces fibrotic lesions within tissues, e.g., in age-related cardiac and pulmonary fibrosis. AMPK signaling is not only an important regulator of energy metabolism but it is also able to control cell fate determination and many functions of the immune system. It is known that AMPK signaling can delay the aging process via an integrated signaling network. AMPK signaling inhibits myofibroblast differentiation, e.g., by suppressing signaling through the TGF-β, NF-κB, STAT3, and YAP/TAZ pathways. It seems that AMPK signaling can alleviate age-related tissue fibrosis and degeneration by inhibiting the differentiation of myofibroblasts.

Single-cell sequencing reveals an important role of SPP1 and microglial activation in age-related macular degeneration

Purpose

To investigate the role of senescence-related cytokines (SRCs) in the pathophysiology of age-related macular degeneration (AMD).

Design

The whole study is based on single-cell and bulk tissue transcriptomic analysis of the human neuroretinas with or without AMD. The transcriptomic data of human neuroretinas was obtained from Gene-Expression Omnibus (GEO) database.

Methods

For single-cell transcriptomic analysis, the gene expression matrix goes through quality control (QC) filtering, being normalized, scaled and integrated for downstream analysis. The further analyses were performed using Seurat R package and CellChat R package. After cell type annotation, the expression of phenotype and functional markers of microglia was investigated and cell-cell communication analysis was performed. For bulk tissue transcriptomic analysis, GSE29801 dataset contains the transcriptomic data of human macular neuroretina (n = 118) from control group and AMD patients. The expression of SPP1 in control and AMD subtypes were compared by Student's t-test. In addition, the AMD macular neuroretina were classified into SPP1-low and SPP1-high groups according to the expression level of SPP1. The differentially expressed genes between these two groups were subsequently identified and the pathway enrichment analysis for these genes was further conducted.

Results

Secreted phosphoprotein 1, as an SRC, was revealed to be highly expressed in microglia of AMD neuroretina and the SPP1-receptor signaling was highly activated in AMD neuroretina. In addition, SPP1 signaling was associated with the pro-inflammatory phenotype and phagocytic state of microglia. SPP1 expression was elevated in macular neuroretina with late dry and wet AMD and the inflammatory pathways were found to be activated in SPP1-high AMD macular neuroretina.

Conclusion

Our findings indicated that SPP1 and microglial activation might play an important role in the pathophysiology of AMD. Therefore, SPP1 might serve as a potential therapeutic target for AMD. More in vitro and in vivo studies are required to confirm the results and the therapeutic effect of SPP1-targeting strategy.

The endoplasmic reticulum: Homeostasis and crosstalk in retinal health and disease

The endoplasmic reticulum (ER) is the largest intracellular organelle carrying out a broad range of important cellular functions including protein biosynthesis, folding, and trafficking, lipid and sterol biosynthesis, carbohydrate metabolism, and calcium storage and gated release. In addition, the ER makes close contact with multiple intracellular organelles such as mitochondria and the plasma membrane to actively regulate the biogenesis, remodeling, and function of these organelles. Therefore, maintaining a homeostatic and functional ER is critical for the survival and function of cells. This vital process is implemented through well-orchestrated signaling pathways of the unfolded protein response (UPR). The UPR is activated when misfolded or unfolded proteins accumulate in the ER, a condition known as ER stress, and functions to restore ER homeostasis thus promoting cell survival. However, prolonged activation or dysregulation of the UPR can lead to cell death and other detrimental events such as inflammation and oxidative stress; these processes are implicated in the pathogenesis of many human diseases including retinal disorders. In this review manuscript, we discuss the unique features of the ER and ER stress signaling in the retina and retinal neurons and describe recent advances in the research to uncover the role of ER stress signaling in neurodegenerative retinal diseases including age-related macular degeneration, inherited retinal degeneration, achromatopsia and cone diseases, and diabetic retinopathy. In some chapters, we highlight the complex interactions between the ER and other intracellular organelles focusing on mitochondria and illustrate how ER stress signaling regulates common cellular stress pathways such as autophagy. We also touch upon the integrated stress response in retinal degeneration and diabetic retinopathy. Finally, we provide an update on the current development of pharmacological agents targeting the UPR response and discuss some unresolved questions and knowledge gaps to be addressed by future research.

A quantitative sonoelastography evaluation of ocular and periocular elasticity after intravitreal ranibizumab injection

PURPOSE

We evaluated changes in ocular and periocular elasticity by ultrasound (US) elastography in intravitreal ranibizumab-treated eyes and the healthy fellow eyes of patients with neovascular AMD.

METHODS

The study was performed on 52 eyes of 26 volunteers who ranged in age from 59 to 89 (mean 72±7.78) years old. The study group consisted of the patients with neovascular AMD treated with intravitreal ranibizumab. The fellow eyes (without choroidal neovascularization) of the study group were selected as the control group. All patients were examined with sonoelastography before intravitreal injection and at 1day, 1week, and 1month after intravitreal injection. All images were acquired with a Toshiba Aplio 500 ultrasound system (Tokyo, Japan) including software with a combined autocorrelation method and a multifrequency linear probe. The elastography values of the anterior vitreous (AV), posterior vitreous (PV), retina-choroid-sclera complex (RCS), retrobulbar fat tissue (RF), optic nerve head (ONH) and retrobulbar optic nerve (RON) were measured in each eye.

RESULTS

There were 13 male (50%) and 13 female (50%) participants in our study. Anterior vitreous, posterior vitreous, RCS, retrobulbar fat tissue, ONH, and RON US elastography values were similar in both groups (P˃0.05 for all). On the other hand, there was a positive correlation between the difference between baseline and 1-month PV sonoelastography values and age (r=0.47, P=0.035).

CONCLUSION

A single dose intravitreal Ranibizumab (Lucentis®, Genentech, USA) injection does not alter the elasticity of ocular and periocular structures.

Metformin regulates the LIN28B‑mediated JNK/STAT3 signaling pathway through miR‑140‑3p in subretinal fibrosis

Subretinal fibrosis (SF) is an important cause of submacular neovascularization that leads to permanent vision loss, but has no effective clinical treatment. The present study examined the influence of metformin on SF, and investigated whether the mechanism involves the microRNA (miR)-140-3p/LIN28B/JNK/STAT3-mediated regulation of oxidative stress, angiogenesis and fibrosis-associated indicators. A mouse model of laser-induced SF was established. In addition, an ARPE-19 fibrotic cell model was established using TGF-β1. A Cell Counting Kit-8 assay was used to examine cell viability. Flow cytometry was used to measure reactive oxygen species levels, and western blotting was used to detect the levels of proteins associated with epithelial-mesenchymal transition (EMT), signaling and fibrosis. The levels of superoxide dismutase, malondialdehyde, glutathione-peroxidase and catalase were measured using kits. Scratch assays and Transwell assays were used to assess cell migration and invasion, respectively, and reverse transcription-quantitative PCR was used to determine the levels of miR-140-3p and LIN28B. Dual-luciferase assays were used to verify the targeting relationship between miR-140-3p and LIN28B, and coimmunoprecipitation was used to confirm the interaction between LIN28B and JNK. Masson staining and hematoxylin and eosin staining were used to examine collagenous fibers and the histopathology of eye tissue. In ARPE-19 cells induced by TGF-β1, metformin promoted miR-140-3p expression and inhibited LIN28B expression and JNK/STAT3 pathway activation, thereby inhibiting oxidative stress, EMT and fibrosis in ARPE-19 cells. The overexpression of LIN28B or treatment with the JNK/STAT3 agonist anisomycin partially reversed the inhibitory effect of metformin on oxidative stress and fibrosis in ARPE-19 cells. The dual-luciferase reporter assay and coimmunoprecipitation assay showed that miR-140-3p targeted the 3' untranslated region of LIN28B mRNA and inhibited LIN28B expression. LIN28B targeted and bound to JNK and regulated the JNK/STAT3 pathway. Therefore, it may be concluded that metformin can promote miR-140-3p expression, inhibit LIN28B and then inhibit the JNK/STAT3 pathway to alleviate SF.

Assessment of Inner Blood-Retinal Barrier: Animal Models and Methods

Proper functioning of the neural retina relies on the unique retinal environment regulated by the blood-retinal barrier (BRB), which restricts the passage of solutes, fluids, and toxic substances. BRB impairment occurs in many retinal vascular diseases and the breakdown of BRB significantly contributes to disease pathology. Understanding the different molecular constituents and signaling pathways involved in BRB development and maintenance is therefore crucial in developing treatment modalities. This review summarizes the major molecular signaling pathways involved in inner BRB (iBRB) formation and maintenance, and representative animal models of eye diseases with retinal vascular leakage. Studies on Wnt/β-catenin signaling are highlighted, which is critical for retinal and brain vascular angiogenesis and barriergenesis. Moreover, multiple in vivo and in vitro methods for the detection and analysis of vascular leakage are described, along with their advantages and limitations. These pre-clinical animal models and methods for assessing iBRB provide valuable experimental tools in delineating the molecular mechanisms of retinal vascular diseases and evaluating therapeutic drugs.

Clinical Correlation of Retinal Fluid Fluctuation Represented by Fluctuation Index in Wet Age-Related Macular Degeneration: TOWER Study Report 2

Purpose

To explore outcomes and biomarkers associated with retinal fluid instability represented by a new parameter in neovascular age-related macular degeneration (nAMD).

Methods

Patients with treatment-naïve nAMD receiving anti-vascular endothelial growth factor (VEGF) injections for a duration of 1 to 3 years were consecutively reviewed. Fluctuation Index (FI) of each eye, calculated by averaging the sum of differences in 1-mm central subfield thickness between each follow-up from months 3 to 24, was arranged into ascending order from the lowest to the highest and split equally into low, moderate, and high fluctuation groups. Outcomes were analyzed at 24 months.

Results

Of 558 eyes, FI values showed a negative correlation with a degree-response gradient with 24-month visual improvement. After controlling for baseline best-corrected visual acuity and potential confounders, eyes with low fluctuation gained more Early Treatment Diabetic Retinopathy Study letters than those in the moderate and high fluctuation group (Δ, 10.1 and 14.0 letters, respectively). Significant best-corrected visual acuity improvement from baseline to month 24 (11.8 letters) was observed exclusively in the low fluctuation group despite the indifference in the number of injections and types of anti-VEGF drug used among groups. Patients presenting with central subfield thickness of ≥405 µm or intraretinal fluid coinciding with subretinal fluid showed a significant association with foveal thickness instability during the maintenance phase.

Conclusions

Apart from the central subfield thickness values, unstable macular thickening represented by the FI was associated with some baseline features and may contribute to substandard visual outcomes.

Translational Relevance

FI may be a valuable tool for assessing therapeutic adequacy in the treatment of nAMD.

[Role of vitreous in the pathogenesis of neovascular age-related macular degeneration]

Age-related changes in vitreous molecular and anatomic morphology begin early in life and involve two major processes: vitreous liquefaction and weakening of vitreo-retinal adhesion. An imbalance in these two processes results in anomalous posterior vitreous detachment (PVD), which comprises, among other conditions, vitreo-macular adhesion (VMA) and traction (VMT). VMA is more common in patients with neovascular age-related macular degeneration (nAMD) than age-matched control patients, with the site of posterior vitreous adherence to the inner retina correlating with location of neovascular complexes. The pernicious effects of an attached posterior vitreous on age-related macular degeneration (AMD) progression involve mechanical forces, enhanced fluid influx and inflammation in and between the retinal layers, hypoxia leading to an accumulation of vascular endothelial growth factor (VEGF) and other stimulatory cytokines, and probably an infiltration of hyalocytes. It has been shown that vitrectomy not only mitigates progression to end-stage AMD, but existing choroidal neovascularization regresses after surgery. Thus, surgical PVD induction during vitrectomy or by pharmacologic vitreolysis may be considered in non-responders to anti-VEGF treatment with concomitant VMA.

Clinical features and associated factors of intraocular inflammation following intravitreal brolucizumab as switching therapy for neovascular age-related macular degeneration

PURPOSE

The aim of this study is to explore the clinical features and associated factors of intraocular inflammation (IOI) following intravitreal brolucizumab (IVBr) administration for neovascular age-related macular degeneration (nAMD).

METHODS

This retrospective study included 87 eyes from 87 Japanese patients with nAMD who were followed up for 5 months after the initial administration of IVBr as switching therapy. Clinical pictures of IOI post-IVBr and changes in best corrected visual acuity (BCVA) at 5 months were evaluated between eyes with and without IOI (non-IOI). The association between IOI and baseline factors (age, sex, BCVA, hypertension, and/or arteriosclerotic changes in the fundus, subretinal hyperreflective material [SHRM], and macular atrophy) was evaluated.

RESULTS

Of the 87 eyes, 18 (20.6%) developed IOI and 2 (2.3%) developed retinal artery occlusion. There were 9 (50%) cases of posterior or pan-uveitis among eyes with IOI. The mean interval from initial IVBr administration to IOI was 2 months. The mean changes in logMAR BCVA at 5 months were significantly worse in IOI eyes than in non-IOI eyes (0.09 ± 0.22 vs. - 0.01 ± 0.15, P = 0.03). There were 8 (44.4%) and 7 (10.1%) cases of macular atrophy and 11 (61.1%) and 13 (18.8%) cases of SHRM in the IOI and non-IOI groups, respectively. SHRM and macular atrophy were significantly associated with IOI (P = 0.0008 and P = 0.002, respectively).

CONCLUSION

In IVBr therapy for nAMD, eyes with SHRM and/or macular atrophy should be observed more meticulously, given the increased risk of developing IOI, which is associated with insufficient BCVA gain.

Effect of N-oleoyl dopamine on myofibroblast trans-differentiation of retinal pigment epithelial cells

Retinal pigment epithelial (RPE) cells contribute to several clinical conditions resulting in retinal fibrotic scars. Myofibroblast trans-differentiation of RPE cells is a critical step in the process of retinal fibrosis. In this study, we investigated the effects of N-oleoyl dopamine (OLDA), a newer endocannabinoid with a structure distinct from classic endocannabinoids, on TGF-β2-induced myofibroblast trans-differentiation of porcine RPE cells. Using an in vitro collagen matrix contraction assay, OLDA was found to inhibit TGF-β2 induced contraction of collagen matrices by porcine RPE cells. This effect was concentration-dependent, with significant inhibition of contraction observed at 3 μM and 10 μM. OLDA did not affect the proliferation of porcine RPE cells. Immunocytochemistry showed that at 3 μM, OLDA decreased incorporation of α-SMA in the stress fibers of TGF-β2-treated RPE cells. In addition, western blot analysis showed that 3 μM OLDA significantly downregulated TGF-β2-induced α-SMA protein expression. Taken together these results demonstrate that OLDA inhibits TGF-β induced myofibroblast trans-differentiation of RPE cells. It has been established that classic endocannabinoid such as anandamide, by activating the CB1 cannabinoid receptor, promote fibrosis in multiple organ systems. In contrast, this study demonstrates that OLDA, an endocannabinoid with a chemical structure distinct from classic endocannabinoids, inhibits myofibroblast trans-differentiation, an important step in fibrosis. Unlike classic endocannabinoids, OLDA has weak affinity for the CB1 receptor. Instead, OLDA acts on non-classic cannabinoid receptors such as GPR119, GPR6, and TRPV1. Therefore, our study indicates that the newer endocannabinoid OLDA and its non-classic cannabinoid receptors could potentially be novel therapeutic targets for treating ocular diseases involving retinal fibrosis and fibrotic pathologies in other organ systems.

Luteolin inhibits subretinal fibrosis and epithelial-mesenchymal transition in laser-induced mouse model via suppression of Smad2/3 and YAP signaling

BACKGROUND

Subretinal fibrosis (SF) accounts for vision loss in patients with neovascular age-related macular degeneration (nAMD) even treated with adequate intravitreal injection of anti-vascular endothelial growth factor (anti-VEGF) drugs. Currently, there is no treatment available to prevent or treat SF caused by nAMD.

PURPOSE

This study aims to investigate the potential effects of luteolin on SF and epithelial-mesenchymal transition (EMT) as well as the underlying molecular pathways both in vivo and in vitro.

METHODS

Seven-week-old male C57BL/6J mice were employed to establish laser-induced choroidal neovascularization (CNV) and SF. One day after the laser induction, luteolin was administered intravitreally. SF and CNV were assessed with the immunolabeling of collagen type I (collagen I) and isolectin B4 (IB4), respectively. RPE65 and α-SMA colocalization in the lesions was used to evaluate the extent of EMT in retinal pigment epithelial (RPE) cells by using immunofluorescence. In vitro, luteolin was administered to TGFβ1-treated primary human RPE (phRPE) cells. RT-qPCR, Western blot and immunofluorescence were employed to evaluate the change of EMT-related molecules, epithelial markers, and relevant signaling pathways. The functional changes associated with EMT were investigated using the scratch assay, Transwell migration assay, and collagen gel contraction assay. CCK-8 was used to determine the cell viability of phRPE cells.

RESULTS

On day 7 and 14 after laser induction in mice, intravitreal injection of luteolin dramatically decreased the immunolabeled sizes of both collagen I and IB4, as well as the amount of colocalized double immunostaining of α-SMA and RPE65 in laser-induced SF lesions. In vitro, TGFβ1-treated phRPE cells demonstrated increased cell migration and contraction capacity, accompanied with considerable overexpression of fibronectin, α-SMA, N-cadherin and vimentin, as well as downregulation of E-cadherin and ZO-1. The above changes were largely inhibited by luteolin co-incubation. Mechanistically, luteolin could evidently decrease the phosphorylation of Smad2/3, whereas increase the phosphorylation of YAP in TGFβ1-treated phRPE cells.

CONCLUSION

This study demonstrates that luteolin exhibits the anti-fibrotic effect in a laser-induced mouse model by inhibiting EMT of RPE cells via deactivating Smad2/3 and YAP signaling, which provides a potential natural compound for the prevention and treatment of SF and fibrosis-related diseases.

Animal model of subretinal fibrosis without active choroidal neovascularization

Subretinal fibrosis can occur during neovascular age-related macular degeneration (nAMD) and consequently provokes progressing deterioration of AMD patient's vision. Intravitreal anti-vascular endothelial growth factor (VEGF) injections decrease choroidal neovascularization (CNV), however, subretinal fibrosis remains principally unaffected. So far, no successful treatment nor established animal model for subretinal fibrosis exists. In order to investigate the impact of anti-fibrotic compounds on solely fibrosis, we refined a time-dependent animal model of subretinal fibrosis without active choroidal neovascularization (CNV). To induce CNV-related fibrosis, wild-type (WT) mice underwent laser photocoagulation of the retina with rupture of Bruch's membrane. The lesions volume was assessed with optical coherence tomography (OCT). CNV (Isolectin B4) and fibrosis (type 1 collagen) were separately quantified with confocal microscopy of choroidal whole-mounts at every time point post laser induction (day 7-49). In addition, OCT, autofluorescence and fluorescence angiography were carried out at designated timepoints (day 7, 14, 21, 28, 35, 42, 49) to monitor CNV and fibrosis transformation over time. From 21 to 49 days post laser lesion leakage in the fluorescence angiography decreased. Correspondingly, Isolectin B4 decreased in lesions of choroidal flat mounts and type 1 collagen increased. Fibrosis markers, namely vimentin, fibronectin, alpha-smooth muscle actin (α-SMA) and type 1 collagen were detected at different timepoints of tissue repair in choroids and retinas post laser. These results prove that the late phase of the CNV-related fibrosis model enables screening of anti-fibrotic compounds to accelerate the therapeutic advancement for the prevention, reduction, or inhibition of subretinal fibrosis.

Zinc Supplementation Induced Transcriptional Changes in Primary Human Retinal Pigment Epithelium: A Single-Cell RNA Sequencing Study to Understand Age-Related Macular Degeneration

Zinc supplementation has been shown to be beneficial to slow the progression of age-related macular degeneration (AMD). However, the molecular mechanism underpinning this benefit is not well understood. This study used single-cell RNA sequencing to identify transcriptomic changes induced by zinc supplementation. Human primary retinal pigment epithelial (RPE) cells could mature for up to 19 weeks. After 1 or 18 weeks in culture, we supplemented the culture medium with 125 µM added zinc for one week. RPE cells developed high transepithelial electrical resistance, extensive, but variable pigmentation, and deposited sub-RPE material similar to the hallmark lesions of AMD. Unsupervised cluster analysis of the combined transcriptome of the cells isolated after 2, 9, and 19 weeks in culture showed considerable heterogeneity. Clustering based on 234 pre-selected RPE-specific genes divided the cells into two distinct clusters, we defined as more and less differentiated cells. The proportion of more differentiated cells increased with time in culture, but appreciable numbers of cells remained less differentiated even at 19 weeks. Pseudotemporal ordering identified 537 genes that could be implicated in the dynamics of RPE cell differentiation (FDR < 0.05). Zinc treatment resulted in the differential expression of 281 of these genes (FDR < 0.05). These genes were associated with several biological pathways with modulation of ID1/ID3 transcriptional regulation. Overall, zinc had a multitude of effects on the RPE transcriptome, including several genes involved in pigmentation, complement regulation, mineralization, and cholesterol metabolism processes associated with AMD.

Experimental Models to Study Epithelial-Mesenchymal Transition in Proliferative Vitreoretinopathy

Proliferative vitreoretinal diseases (PVDs) encompass proliferative vitreoretinopathy (PVR), epiretinal membranes, and proliferative diabetic retinopathy. These vision-threatening diseases are characterized by the development of proliferative membranes above, within and/or below the retina following epithelial-mesenchymal transition (EMT) of the retinal pigment epithelium (RPE) and/or endothelial-mesenchymal transition of endothelial cells. As surgical peeling of PVD membranes remains the sole therapeutic option for patients, development of in vitro and in vivo models has become essential to better understand PVD pathogenesis and identify potential therapeutic targets. The in vitro models range from immortalized cell lines to human pluripotent stem-cell-derived RPE and primary cells subjected to various treatments to induce EMT and mimic PVD. In vivo PVR animal models using rabbit, mouse, rat, and swine have mainly been obtained through surgical means to mimic ocular trauma and retinal detachment, and through intravitreal injection of cells or enzymes to induce EMT and investigate cell proliferation and invasion. This review offers a comprehensive overview of the usefulness, advantages, and limitations of the current models available to investigate EMT in PVD.

Old age promotes retinal fibrosis in choroidal neovascularization through circulating fibrocytes and profibrotic macrophages

BACKGROUND

Retinal fibrosis affects 40-70% of neovascular age-related macular degeneration patients. This study investigated the effect of ageing on subretinal fibrosis secondary to choroidal neovascularization and the mechanism of action.

METHODS

Subretinal fibrosis was induced in young (2.5-month) and aged (15-16-month) C57BL/6J mice using the two-stage laser protocol. Five and 30 days later, eyes were collected and stained for CD45 and collagen-1 and observed by confocal microscopy. Fibrocytes (CD45+collagen-1+) were detected in the bone marrow (BM), blood and fibrotic lesions by flow cytometry and confocal microscopy, respectively. BM-derived macrophages (BMDMs) were cultured from young and aged mice with or without TGF-β1 (10 ng/mL) treatment. The expression of mesenchymal marker αSMA (Acta2), fibronectin (Fn1) and collagen-1 (Col1a1) was examined by qPCR and immunocytochemistry, whereas cytokine/chemokine production was measured using the Luminex multiplex cytokine assay. BM were transplanted from 22-month (Ly5.2) aged mice into 2.5-month (Ly5.1) young mice and vice versa. Six weeks later, subretinal fibrosis was induced in recipient mice and eyes were collected for evaluation of fibrotic lesion size.

RESULTS

Under normal conditions, the number of circulating fibrocytes (CD45+collagen-1+) and the expression levels of Tgfb1, Col1a1, Acta2 and Fn1 in BMDMs were significantly higher in aged mice compared to young mice. Induction of subretinal fibrosis significantly increased the number of circulating fibrocytes, enhanced the expression of Col1a1, Acta2 and Fn1 and the production of soluble urokinase plasminogen activator surface receptor (suPAR) but decreased the production of CXCL10 in BMDMs. BMDMs from aged subretinal fibrosis mice produced significantly higher levels of VEGF, angiopoietin-2 and osteopontin than cells from young subretinal fibrosis mice. The subretinal fibrotic lesion in 15-16-month aged mice was 62% larger than that in 2.5-month young mice. The lesion in aged mice contained a significantly higher number of fibrocytes compared to that in young mice. The number of circulating fibrocytes positively correlated with the size of subretinal fibrotic lesion. Transplantation of BM from aged mice significantly increased subretinal fibrosis in young mice.

CONCLUSIONS

A retina-BM-blood-retina pathway of fibrocyte/macrophage recruitment exists during retinal injury. Ageing promotes subretinal fibrosis through higher numbers of circulating fibrocytes and profibrotic potential of BM-derived macrophages.

Review of Fibrosis in Neovascular Age-Related Macular Degeneration

PURPOSE

To report the diagnosis and definitions, epidemiology, risk factors, and visual outcomes of fibrosis in neovascular age-related macular degeneration (nAMD).

DESIGN

Systematic review and meta-analysis.

METHODS

The review was performed using the Cochrane Handbook and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Observational studies and randomized controlled trials were included.

RESULTS

Identification of fibrosis is challenging. Optical coherence tomography angiography and polarization-sensitive optical coherence tomography represent novel options in multimodal imaging. The prevalence of fibrosis at baseline, 12, 24, and 60 months was 13%, 32%, 36%, and 56%, respectively. Approximately 60% of the fibrosis burden in nAMD at 5 years was present in the first year of treatment. Fibrosis development was highest in the first 12 months and slowed down over time. The risk factors of fibrosis included classic choroidal neovascularization (CNV), intra-retinal fluid, hemorrhage, hyperreflective material, CNV lesion size, and retinal thickness. Sub-retinal fluid and pigment epithelial detachment may be protective. Treatment-associated factors included disease activity and time to diagnosis. At baseline, the best corrected visual acuity in eyes with fibrosis was poorer than in eyes without fibrosis (-18.50 letters); this difference became larger at 12 months despite treatment (-26.86 letters).

CONCLUSIONS

There is a need to identify effective treatment strategies for fibrosis and to closely monitor at-risk patients. More studies involving multimodal imaging are required to clarify the definitions and grading criteria for fibrosis.

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.

The role of the gut microbiome in eye diseases

The gut microbiome is a complex ecosystem of microorganisms and their genetic entities colonizing the gastrointestinal tract. When in balanced composition, the gut microbiome is in symbiotic interaction with its host and maintains intestinal homeostasis. It is involved in essential functions such as nutrient metabolism, inhibition of pathogens and regulation of immune function. Through translocation of microbes and their metabolites along the epithelial barrier, microbial dysbiosis induces systemic inflammation that may lead to tissue destruction and promote the onset of various diseases. Using whole-metagenome shotgun sequencing, several studies have shown that the composition and associated functional capacities of the gut microbiome are associated with age-related macular degeneration, retinal artery occlusion, central serous chorioretinopathy and uveitis. In this review, we provide an overview of the current knowledge about the gut microbiome in eye diseases, with a focus on interactions between the microbiome, specific microbial-derived metabolites and the immune system. We explain how these interactions may be involved in the pathogenesis of age-related macular degeneration, retinal artery occlusion, central serous chorioretinopathy and uveitis and guide the development of new therapeutic approaches by microbiome-altering interventions for these diseases.

MiR-302d inhibits TGFB-induced EMT and promotes MET in primary human RPE cells

PURPOSE

Transforming growth factor-beta (TGFB)-mediated epithelial-mesenchymal transition (EMT) plays a crucial role in the pathogenesis of retinal fibrosis, which is one of the leading causes of impaired vision. Current approaches to treating retinal fibrosis focus, among other things, on inhibiting the TGFB signaling pathway. Transient expression of microRNAs (miRNAs) is one way to inhibit the TGFB pathway post-transcriptionally. Our previous study identified the miRNA miR-302d as a regulator of multiple TGFB-related genes in ARPE-19 cells. To further explore its effect on primary cells, the effect of miR-302d on TGFB-induced EMT in primary human retinal pigment epithelium (hRPE) was investigated in vitro.

METHODS

hRPE cells were extracted from patients receiving enucleation. Transfection of hRPE cells with miR-302d was performed before or after TGFB1 stimulation. Live-cell imaging, immunocytochemistry staining, Western blot, and ELISA assays were utilized to identify the alterations of cellular morphology and EMT-related factors expressions in hRPE cells.

RESULTS

hRPE cells underwent EMT by TGFB1 exposure. The transfection of miR-302d inhibited the transition with decreased production of mesenchymal markers and increased epithelial factors. Meanwhile, the phosphorylation of SMAD2 activated by TGFB1 was suppressed. Moreover, miR-302d expression promoted TGFB1-induced fibroblast-like hRPE cells to revert towards an epithelial stage. As confirmed by ELISA, miR-302d reduced TGFB receptor 2 (TGFBR2) and vascular endothelial growth factor A (VEGFA) levels 48 hours after transfection.

CONCLUSIONS

The protective effect of miR-302d might be a promising approach for ameliorating retinal fibrosis and neovascularization. MiR-302d suppresses TGFB-induced EMT in hRPE cells via downregulation of TGFBR2, even reversing the process. Furthermore, miR-302d reduces the constitutive secretion of VEGFA from hRPE cells.

The Architecture of Macular Neovascularizations Predicts Treatment Responses to Anti-VEGF Therapy in Neovascular AMD

Introduction: Anti-VEGF therapy is an effective option for improving and stabilizing the vision in neovascular age-related macular degeneration (nAMD). However, the response to treatment is markedly heterogeneous. The aim of this study was therefore to analyze the vascular characteristics of type 1,2, and 3 macular neovascularizations (MNV) in order to identify biomarkers that predict treatment response, especially with regard to changes in intraretinal and subretinal fluid. Materials and Methods: Overall, 90 treatment-naive eyes with nAMD confirmed by optic coherence tomography (OCT), fluorescein angiography, and OCT angiography (OCTA) were included in this retrospective study. The MNV detected by OCTA were subjected to quantitative vascular analysis by binarization and skeletonization of the vessel using ImageJ. We determined their area, total vascular length (sumL), fractal dimension (FD), flow density, number of vascular nodes (numN), and average vascular diameter (avgW). The results were correlated with the treatment response to the initial three injections of anti-VEGF and the changes in intraretinal (IRF) and subretinal fluid (SRF) and the occurrence of pigment epithelial detachements (PED). Results: All patients found to have no subretinal or intraretinal fluid following the initial three injections of anti-VEGF showed a significantly smaller MNV area (p < 0.001), a lower sumL (p < 0.0005), and lesser FD (p < 0.005) before treatment than those who still exhibited signs of activity. These parameters also showed a significant influence in the separate analysis of persistent SRF (p < 0.005) and a persistent PED (p < 0.05), whereas we could not detect any influence on changes in IRF. The vascular parameters avgW, numN, and flow density showed no significant influence on SRF/IRF or PED changes. Conclusions: The size, the total vessel length, and the fractal dimension of MNV at baseline are predictors for the treatment response to anti-VEGF therapy. Therefore, particularly regarding the development of new classes of drugs, these parameters could yield new insights into treatment response.

A Linkage between Angiogenesis and Inflammation in Neovascular Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is the leading cause of visual impairment in the aging population with a limited understanding of its pathogenesis and the number of patients are all the time increasing. AMD is classified into two main forms: dry and neovascular AMD (nAMD). Dry AMD is the most prevalent form (80–90%) of AMD cases. Neovascular AMD (10–20% of AMD cases) is treated with monthly or more sparsely given intravitreal anti-vascular endothelial growth factor inhibitors, but unfortunately, not all patients respond to the current treatments. A clinical hallmark of nAMD is choroidal neovascularization. The progression of AMD is initially characterized by atrophic alterations in the retinal pigment epithelium, as well as the formation of lysosomal lipofuscin and extracellular drusen deposits. Cellular damage caused by chronic oxidative stress, protein aggregation and inflammatory processes may lead to advanced geographic atrophy and/or choroidal neovascularization and fibrosis. Currently, it is not fully known why different AMD phenotypes develop. In this review, we connect angiogenesis and inflammatory regulators in the development of nAMD and discuss therapy challenges and hopes.

RO4929097, a Selective γ-Secretase Inhibitor, Inhibits Subretinal Fibrosis Via Suppressing Notch and ERK1/2 Signaling in Laser-Induced Mouse Model

Purpose

This study aimed to explore whether RO4929097 (RO), a specific γ-secretase inhibitor, could inhibit the subretinal fibrosis in laser-induced mouse model and the relevant molecular mechanisms.

Methods

Male C57BL/6J mice were used to produce choroidal neovascularization (CNV) and subretinal fibrosis by laser photocoagulation, and RO was administered intravitreally 1 day after laser induction. The sizes of CNV and subretinal fibrosis were measured and quantified in both 2D and 3D constructions. The ARPE-19 cell line and primary human RPE (phRPE) cells were treated with TGFβ1, in combination with or without RO, to examine Notch related molecules, epithelial mesenchymal transition (EMT), cell viability, migration, and contractile function, as well as the crosstalk between Notch and other EMT relevant signaling pathways.

Results

Intravitreal injection of RO reduced the sizes of both CNV and subretinal fibrosis in laser-induced young and old mice at day 7 and day 14 after laser induction. Moreover, EMT and Notch activation in RPE-choroid complexes from laser-induced mice were significantly attenuated by RO. In vitro, TGFβ1 activated Notch signaling and induced EMT in ARPE-19 cells, accompanied by enhanced EMT-related function, which were inhibited by RO. The inhibition of RO on EMT was further confirmed in TGFβ1-treated phRPE cells. Blockage of Notch signaling by RO could inhibit ERK1/2 signaling; whereas ERK1/2 inhibition had no effect on Notch. The action of RO was independent of Smad2/3 or p38, and co-inhibition of Notch and Smad2/3 showed synergistic effect on EMT inhibition.

Conclusions

RO exerts its antifibrotic effect by directly inhibiting Notch signaling and indirectly suppressing ERK1/2 signaling. Targeting Notch signaling might provide a therapeutic strategy in prevention and treatment of subretinal fibrosis in neovascular age-related macular degeneration (nAMD).

YAP is critical to inflammation, endothelial-mesenchymal transition and subretinal fibrosis in experimental choroidal neovascularization

Subretinal fibrosis causes local damage to the retina and irreversible vision loss, as the final stage of neovascular age-related macular degeneration (nAMD). More recently, the endothelial-to-mesenchymal transition (EndoMT) has been considered one of the most significant sources of myofibroblasts in subretinal fibrosis, though the underpinning molecular mechanisms remain unclear. In this study, a series of experiments were performed to test the hypothesis that Yes-associated protein (YAP) may be involved in EndoMT and subretinal fibrosis. We demonstrated that transforming growth factor (TGF)-β2 stimulation induces YAP dephosphorylation (activated) and nuclear transcription in human umbilical vein endothelial cells (HUVECs) by increasing reactive oxygen species (ROS) levels. Moreover, TGF-β2-mediated EndoMT and proinflammatory cytokine production in HUVECs were reduced by ROS clearance or YAP knockdown. Furthermore, the severity of subretinal fibrosis was markedly relieved by intravitreal administration of a small interfering RNA targeting YAP in the mouse laser-induced choroidal neovascularization (CNV) model. Our findings provide novel insights into a previously unknown effect of YAP on the EndoMT process and reveal YAP as a potential target for suppressing CNV-related subretinal fibrosis and protect vision.

Single-Cell Protein and Transcriptional Characterization of Epiretinal Membranes From Patients With Proliferative Vitreoretinopathy

Purpose

Proliferative vitreoretinopathy (PVR) remains an unresolved clinical challenge and can lead to frequent revision surgery and blindness vision loss. The aim of this study was to characterize the microenvironment of epiretinal PVR tissue, in order to shed more light on the complex pathophysiology and to unravel new treatment options.

Methods

A total of 44 tissue samples were analyzed in this study, including 19 epiretinal PVRs, 13 epiretinal membranes (ERMs) from patients with macular pucker, as well as 12 internal limiting membranes (ILMs). The cellular and molecular microenvironment was assessed by cell type deconvolution analysis (xCell), RNA sequencing data and single-cell imaging mass cytometry. Candidate drugs for PVR treatment were identified in silico via a transcriptome-based drug-repurposing approach.

Results

RNA sequencing of tissue samples demonstrated distinct transcriptional profiles of PVR, ERM, and ILM samples. Differential gene expression analysis revealed 3194 upregulated genes in PVR compared with ILM, including FN1 and SPARC, which contribute to biological processes, such as extracellular matrix (ECM) organization. The xCell and IMC analyses showed that PVR membranes were composed of macrophages, retinal pigment epithelium, and α-SMA-positive myofibroblasts, the latter predominantly characterized by the co-expression of immune cell signature markers. Finally, 13 drugs were identified as potential therapeutics for PVR, including aminocaproic acid and various topoisomerase-2A inhibitors.

Conclusions

Epiretinal PVR membranes exhibit a unique and complex transcriptional and cellular profile dominated by immune cells and myofibroblasts, as well as a variety of ECM components. Our findings provide new insights into the pathophysiology of PVR and suggest potential targeted therapeutic options.

TGF-β promotes pericyte-myofibroblast transition in subretinal fibrosis through the Smad2/3 and Akt/mTOR pathways

Subretinal fibrosis remains a major obstacle to the management of neovascular age-related macular degeneration. Choroidal pericytes were found to be a significant source of subretinal fibrosis, but the underlying mechanisms of pericyte-myofibroblast transition (PMT) remain largely unknown. The goal of this study was to explore the role and potential mechanisms by which PMT contributes to subretinal fibrosis. Choroidal neovascularization (CNV) was induced by laser photocoagulation in transgenic mice with the collagen1α1-green fluorescent protein (Col1α1-GFP) reporter, and recombinant adeno-associated virus 2 (rAAV2)-mediated TGF-β2 (rAAV2-TGF-β2) was administered intravitreally to further induce PMT. Primary mouse choroidal GFP-positive pericytes were treated with TGF-β2 in combination with siRNAs targeting Smad2/3, the Akt inhibitor MK2206 or the mTOR inhibitor rapamycin to examine cell proliferation, migration, and differentiation into myofibroblasts. The involvement of the Akt/mTOR pathway in PMT in subretinal fibrosis was further investigated in vivo. Intraocular TGF-β2 overexpression induced GFP-positive pericyte infiltration and PMT in subretinal fibrosis, which was mimicked in vitro. Knockdown of Smad2/3 or inhibition of Akt/mTOR decreased cell proliferation, PMT and migration in primary mouse pericytes. Combined inhibition of Smad2/3 and mTOR showed synergistic effects on attenuating α-smooth muscle actin (α-SMA) expression and cell proliferation. In mice with laser-induced CNV, the administration of the Akt/mTOR inhibitors suppressed pericyte proliferation and alleviated the severity of subretinal fibrosis. Our results showed that PMT plays a pivotal role in subretinal fibrosis, which was induced by TGF-β2 through the Smad2/3 and Akt/mTOR pathways. Thus, inhibiting PMT may be a novel strategy for the treatment of subretinal fibrosis.

The identification of a new cell type that plays a crucial role in causing fibrosis under the retina could improve treatment of eye disease. Effective treatments exist for diseases that cause impairment and loss of vision in elderly people, but success can be limited by the development of subretinal fibrosis. Jingfa Zhang at Shanghai Jiao Tong University, China, and co-workers used mice with laser-induced retinal damage to explore how subretinal fibrosis may result from transition of pericytes, multi-functional cells in the capillaries, into myofibroblasts, cells associated with fibrosis. The overexpression of a growth factor called TGF-β2 induced pericytes to infiltrate the subretinal area and pericyte-myofibroblast transition via two signalling pathways. Inhibiting these pathways may help to treat subretinal fibrosis, and one option is the use of inhibitors of AKT/mTOR which may slow the ageing process.

Macrophage elastase (MMP12) critically contributes to the development of subretinal fibrosis

Background

Macular subretinal fibrosis is the end-stage complication of neovascular age-related macular degeneration (nAMD). We previously developed a mouse model of two-stage laser-induced subretinal fibrosis that mimics closely the dynamic course of macular fibrosis in nAMD patients. This study was aimed to understand the molecular mechanism of subretinal fibrosis.

Methods

Subretinal fibrosis was induced in C57BL/6J mice using the two-stage laser-induced protocol. Twenty days later, eyes were collected and processed for RNA sequencing (RNA-seq) analysis. DESeq2 was used to determine the differentially expressed genes (DEGs). Gene Ontology (GO) and KEGG were used to analyze the enriched pathways. The expression of the selected DEGs including Mmp12 was verified by qPCR. The expression of MMP12 in subretinal fibrosis of mouse and nAMD donor eyes was examined by immunofluorescence and confocal microscopy. The expression of collagen 1, αSMA and fibronectin and cytokines in bone marrow-derived macrophages from control and subretinal fibrosis mice were examined by qPCR, immunocytochemistry and Luminex multiplex cytokine assay. The MMP12 specific inhibitor MMP408 was used to evaluate the effect of MMP12 on TGFβ-induced macrophage-to-myofibroblast transition (MMT) in vitro and its role in subretinal fibrosis in vivo.

Results

RNA-seq analysis of RPE-choroid from subretinal fibrosis eyes uncovered 139 DEGs (fold change log2(fc) ≥ 0.5, FDR < 0.05), including 104 up-regulated and 35 were down-regulated genes. The top 25 enrichment GO terms were related to inflammation, blood vessels/cardiovascular development and angiogenesis. One of the most significantly upregulated genes, Mmp12, contributed to 12 of the top 25 GO terms. Higher levels of MMP12 were detected in subretinal fibrotic lesions in nAMD patients and the mouse model, including in F4/80⁺ or Iba1⁺ macrophages. BMDMs from subretinal fibrosis mice expressed higher levels of MMP12, collagen-1, αSMA and fibronectin. MMP408 dose-dependently suppressed TGFβ-induced MMT in BMDMs. In vivo treatment with MMP408 (5 mg/kg) significantly reduced subretinal fibrosis accompanied by reduced F4/80⁺ macrophage infiltration.

Conclusions

MMP12 critically contributes to the development of subretinal fibrosis, partially through promoting MMT.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02433-x.

The Role of Osteopontin in Microglia Biology: Current Concepts and Future Perspectives

The innate immune landscape of the central nervous system (CNS), including the brain and the retina, consists of different myeloid cell populations with distinct tasks to fulfill. Whereas the CNS borders harbor extraparenchymal CNS-associated macrophages whose main duty is to build up a defense against invading pathogens and other damaging factors from the periphery, the resident immune cells of the CNS parenchyma and the retina, microglia, are highly dynamic cells with a plethora of functions during homeostasis and disease. Therefore, microglia are constantly sensing their environment and closely interacting with surrounding cells, which is in part mediated by soluble factors. One of these factors is Osteopontin (OPN), a multifunctional protein that is produced by different cell types in the CNS, including microglia, and is upregulated in neurodegenerative and neuroinflammatory conditions. In this review, we discuss the current literature about the interaction between microglia and OPN in homeostasis and several disease entities, including multiple sclerosis (MS), Alzheimer’s and cerebrovascular diseases (AD, CVD), amyotrophic lateral sclerosis (ALS), age-related macular degeneration (AMD) and diabetic retinopathy (DR), in the context of the molecular pathways involved in OPN signaling shaping the function of microglia. As nearly all CNS diseases are characterized by pathological alterations in microglial cells, accompanied by the disturbance of the homeostatic microglia phenotype, the emergence of disease-associated microglia (DAM) states and their interplay with factors shaping the DAM-signature, such as OPN, is of great interest for therapeutical interventions in the future.

Transcriptional and Distributional Profiling of Microglia in Retinal Angiomatous Proliferation

Macular neovascularization type 3, formerly known as retinal angiomatous proliferation (RAP), is a hallmark of age-related macular degeneration and is associated with an accumulation of myeloid cells, such as microglia (MG) and infiltrating blood-derived macrophages (MAC). However, the contribution of MG and MAC to the myeloid cell pool at RAP sites and their exact functions remain unknown. In this study, we combined a microglia-specific reporter mouse line with a mouse model for RAP to identify the contribution of MG and MAC to myeloid cell accumulation at RAP and determined the transcriptional profile of MG using RNA sequencing. We found that MG are the most abundant myeloid cell population around RAP, whereas MAC are rarely, if ever, associated with late stages of RAP. RNA sequencing of RAP-associated MG showed that differentially expressed genes mainly contribute to immune-associated processes, including chemotaxis and migration in early RAP and proliferative capacity in late RAP, which was confirmed by immunohistochemistry. Interestingly, MG upregulated only a few angiomodulatory factors, suggesting a rather low angiogenic potential. In summary, we showed that MG are the dominant myeloid cell population at RAP sites. Moreover, MG significantly altered their transcriptional profile during RAP formation, activating immune-associated processes and exhibiting enhanced proliferation, however, without showing substantial upregulation of angiomodulatory factors.

Deciphering the Molecular Signature of Human Hyalocytes in Relation to Other Innate Immune Cell Populations

Purpose

Hyalocytes are the tissue-resident innate immune cell population of the vitreous body with important functions in health and vitreoretinal disease. The purpose of this study is to gain new insights into the biology and function of human hyalocytes in comparison to other innate immune cells.

Methods

The present study applies fluorescence-activated cell sorting and RNA sequencing to compare the transcriptional profiles of human hyalocytes, retinal microglia (rMG) and classical, intermediate, and non-classical monocytes isolated from the same patients. Immunohistochemistry was applied for morphological characterization of human hyalocytes.

Results

Pairwise analysis indicates distinct differences between hyalocytes and monocytes, whereas a high degree of similarity to rMG is apparent, with comparable expression levels of established microglia markers, such as TREM2, P2RY12, and TMEM119. Among the top expressed genes in hyalocytes, SPP1, CD74, and C3, were significantly upregulated when compared with monocytes. Despite the high level of similarity of hyalocytes and rMG, ten highly expressed genes in hyalocytes compared to microglia were identified, among them FOS, DUSP1, and EGR2.

Conclusions

This study reveals a high degree of similarity between hyalocytes and retinal microglia. Nevertheless, hyalocytes exhibit some expression differences that may adapt them to the specific needs of the vitreous and provide the basis for deciphering the multiple roles of this fascinating cell population in health and vitreoretinal diseases.

Immunosenescence in Choroidal Neovascularization (CNV)-Transcriptional Profiling of Naïve and CNV-Associated Retinal Myeloid Cells during Aging

Immunosenescence is considered a possible factor in the development of age-related macular degeneration and choroidal neovascularization (CNV). However, age-related changes of myeloid cells (MCs), such as microglia and macrophages, in the healthy retina or during CNV formation are ill-defined. In this study, Cx3cr1-positive MCs were isolated by fluorescence-activated cell sorting from six-week (young) and two-year-old (old) Cx3cr1^GFP/+ mice, both during physiological aging and laser-induced CNV development. High-throughput RNA-sequencing was performed to define the age-dependent transcriptional differences in MCs during physiological aging and CNV development, complemented by immunohistochemical characterization and the quantification of MCs, as well as CNV size measurements. These analyses revealed that myeloid cells change their transcriptional profile during both aging and CNV development. In the steady state, senescent MCs demonstrated an upregulation of factors contributing to cell proliferation and chemotaxis, such as Cxcl13 and Cxcl14, as well as the downregulation of microglial signature genes. During CNV formation, aged myeloid cells revealed a significant upregulation of angiogenic factors such as Arg1 and Lrg1 concomitant with significantly enlarged CNV and an increased accumulation of MCs in aged mice in comparison to young mice. Future studies need to clarify whether this observation is an epiphenomenon or a causal relationship to determine the role of immunosenescence in CNV formation.