Interleukin-2 induces extracellular matrix synthesis and TGF-β2 expression in retinal pigment epithelial cells

SPI1-mediated macrophage polarization aggravates age-related macular degeneration

Objective

This study revealed a core regulator and common upstream mechanisms for the multifaceted pathological processes of age-related macular degeneration (AMD) and provided proof-of-concept for this new therapeutic target.

Methods

Comprehensive gene expression analysis was performed using RNA sequencing of eye cup from old mice as well as laser-induced choroidal neovascularization (CNV) mouse model. Through integrative analysis and protein-protein interaction (PPI) analysis, common pathways and key transcription factor was identified simultaneously engaged in age-related retinal degeneration and CNV, the two typical pathological process of AMD. Subsequently, the expression changes of Spi1, the key regulator, as well as the alternation of the downstream mechanisms were validated in both models through qRT-PCR, Elisa, flow cytometry and immunofluorescence. Further, we assessed the impact of Spi1 knockdown in vitro and in vivo using gene intervention vectors carried by adeno-associated virus or lentivirus to test its potential as a therapeutic target.

Results

Compared to corresponding controls, we found 1,939 and 1,319 genes differentially expressed in eye cups of old and CNV mice respectively. The integrative analysis identified a total of 275 overlapping DEGs, of which 150 genes were co-upregulated. PPI analysis verified a central transcription factor, SPI1. The significant upregulation of Spi1 expression was then validated in both models, accompanied by macrophage polarization towards the M1 phenotype. Finally, SPI1 suppression significantly inhibited M1 polarization of BMDMs and attenuated neovascularization in CNV mice.

Conclusion

This study demonstrates that SPI1 exerts a pivotal role in AMD by regulation of macrophage polarization and innate immune response, offering promise as an innovative target for treating AMD.

Role of immune inflammation regulated by macrophage in the pathogenesis of age-related macular degeneration

Age-related macular degeneration (AMD) can lead to irreversible impairment of visual function, and the number of patients with AMD has been increasing globally. The immunoinflammatory theory is an important pathogenic mechanism of AMD, with macrophages serving as the primary inflammatory infiltrating cells in AMD lesions. Its powerful immunoinflammatory regulatory function has attracted considerable attention. Herein, we provide an overview of the involvement of macrophage-regulated immunoinflammation in different stages of AMD. Additionally, we summarize novel therapeutic approaches for AMD, focusing on targeting macrophages, such as macrophage/microglia modulators, reduction of macrophage aggregation in the subretinal space, modulation of macrophage effector function, macrophage phenotypic alterations, and novel biomimetic nanocomposites development based on macrophage-associated functional properties. We aimed to provide a basis and reference for the further exploration of AMD pathogenesis, developmental influences, and new therapeutic approaches.

Role of reactive oxygen species in epithelial-mesenchymal transition and apoptosis of human lens epithelial cells

AIM

To investigate the role of reactive oxygen species (ROS) in epithelial-mesenchymal transition (EMT) and apoptosis of human lens epithelial cells (HLECs).

METHODS

Flow cytometry was used to assess ROS production after transforming growth factor β2 (TGF-β2) induction. Apoptosis of HLECs after H2O2 and TGF-β2 interference with or without ROS scavenger N-acetylcysteine (NAC) were assessed by flow cytometry. The corresponding protein expression levels of the EMT marker α-smooth muscle actin (α-SMA), the extracellular matrix (ECM), marker fibronectin (Fn), and apoptosis-associated proteins were detected by using Western blotting in the presence of an ROS scavenger (NAC). Wound-healing and Transwell assays were used to assess the migration capability of HLECs.

RESULTS

TGF-β2 stimulates ROS production within 8h in HLECs. Additionally, TGF-β2 induced HLECs cell apoptosis, EMT/ECM synthesis protein markers expression, and pro-apoptotic proteins production; nonetheless, NAC treatment prevented these responses. Similarly, TGF-β2 promoted HLECs cell migration, whereas NAC inhibited cell migration. We further determined that although ROS initiated apoptosis, it only induced the accumulation of the EMT marker α-SMA protein, but not COL-1 or Fn.

CONCLUSION

ROS contribute to TGF-β2-induced EMT/ECM synthesis and cell apoptosis of HLECs; however, ROS alone are not sufficient for EMT/ECM synthesis.

Cytokines as drivers: Unraveling the mechanisms of epithelial-mesenchymal transition in COVID-19 lung fibrosis

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), like other viruses, can induce proliferation of myofibroblasts and even lead to fibrosis in the lung. Epithelial-mesenchymal transition (EMT) is thought to play an essential role in the pathogenesis of Coronavirus disease 19 (COVID-19). EMT is originally a critical process that regulates the development of different tissues in the embryo, but in inflammatory situations, EMT tries to be activated again to control inflammation or even heal inflammatory damage. However, in pathological situations, such as chronic viral infections (e.g., COVID-19) or pulmonary fibrosis initiation, this benign healing transforms into sinister nature, pushing the lung into the fibrotic process. Notably, the cytokines released by inflammatory cells and the chronic inflammatory microenvironment shared by fibrotic cells promote each other as critical factors in the induction of pathological EMT. In the induction of SARS-CoV-2 virus, cytokines are an essential mediator of EMT transformation, and a summary of whether COVID-19 patients, during the infection phase, have many persistent inflammatory mediators (cytokines) that are a causative factor of EMT has not yet appeared. The following common signaling drivers, including Transforming growth factor beta (TGF-β), cytokines, Notch signaling pathway, Wnt and hypoxia signaling pathways, drive the regulation of EMT. In this review, we will focus on 3 key EMT signaling pathways: TGF-β, Leucine zipper transcription factor like 1 (LZTFL1) and the common interleukin family expressed in the lung. TGF-β-induced SNAIL and LZTFL1 were identified as regulatory EMT in COVID-19. For cytokines, the interleukin family is a common inducer of EMT and plays an essential role in the formation of the microenvironment of fibrosis. We sought to demonstrate that cytokines act as "communicators" and build the "microenvironment" of fibrosis together with EMT as a "bridge" to induce EMT in fibrosis. The mechanisms utilized by these two pathways could serve as templates for other mesenchymal transformations and provide new potential therapeutic targets.

ADAMTS5 promotes neovascularization via autophagic degradation of PEDF in proliferative diabetic retinopathy

Proliferative diabetic retinopathy (PDR) adversely affects visual function. Extracellular matrix proteins (ECM) contribute significantly to the development of PDR. A Disintegrin and Metalloproteinase with Thrombospondin motifs 5 (ADAMTS5) is a member of ECM proteins. ADAMTS5 participates in angiogenesis and inflammation in diverse diseases. However, the role of ADAMTS5 in PDR remains elusive. Multiplex beam array technology was used to analyze vitreous humor of PDR patients and normal people. ELISA and Western blot were used to detect the expression of ADAMTS5, PEDF and autophagy related factors. Immunofluorescence assay was used to mark the expression and localization of ADAMTS5 and PEDF. The neovascularization was detected by tube formation test. Our results revealed that ADAMTS5 expression was increased in the vitreous humor of PDR patients and oxygen-induced retinopathy (OIR) mice retinas. Inhibiting ADAMTS5 alleviated pathological angiogenesis and upregulated PEDF expression in the OIR mice. In addition, ADAMTS5 inhibited PEDF secretion in ARPE-19 cells in vitro studies, thereby inhibiting the migration of HMEC-1. Mechanically, ADAMTS5 promoted the autophagic degradation of PEDF. Collectively, inhibition of ADAMTS5 during OIR suppresses pathological angiogenesis. Our study provides a new approach for resolving pathological angiogenesis in PDR.

Carbon dots enhance extracellular matrix secretion for dentin-pulp complex regeneration through PI3K/Akt/mTOR pathway-mediated activation of autophagy

Pulp injury is one of the most common clinical diseases, and severe cases are usually associated with the functional loss of the tooth, while the current clinical treatment modality is only a cavity filling procedure without the regeneration of the dentin-pulp complex, thus leading to a devitalized and brittle tooth. In this study, carbon dots (CDots) with excellent biocompatibility are prepared from ascorbic acid and polyethyleneimine via a hydrothermal method. The as-prepared CDots can enhance extracellular matrix (ECM) secretion of human dental pulp stem cells (DPSCs), giving rise to increased cell adhesion on ECM and a stronger osteogenic/odontogenic differentiation capacity of DPSCs. Further, the mechanism underlying CDots-enhanced ECM secretion is revealed by the transcriptome analysis, Western blot assay and molecular dynamics simulation, identifying that the pharmacological activities of CDots are originated from a reasonable activation of the autophagy, which is mediated by regulating phosphoinositide 3-kinase/protein kinase B/mammalian target of rapamycin signaling pathway. Based on the abundant CDots-induced ECM and thereby the reinforcement of the cell-ECM adhesion, an intact dental pulp stem cell sheet can be achieved, which in return promote in vivo the efficient regeneration of dentin-pulp complex as well as blood vessels.

The contribution of the immune system to genitourinary fibrosis

Fibrotic diseases of the genitourinary tract are devastating and incompletely understood pathologies. These diseases include urethral and ureteral strictures, retroperitoneal fibrosis, and Peyronie's disease. They can contribute to obstructive uropathy and sexual dysfunction. Poor understanding of the pathophysiology of these diseases severely limits our ability to prevent and treat them. Genitourinary fibrotic diseases likely represent related pathologies that share common underlying mechanisms involving wound healing in response to injury. These diseases share the common feature of extracellular matrix abnormalities-such as collagen deposition, transforming growth factor-β accumulation, and dysregulation of collagen maturation-leading to abnormal tissue stiffness. Given the association of many of these diseases with autoimmunity, a systemic pro-inflammatory state likely contributes to their associated fibrogenesis. Herein, we explore the immunologic contribution to fibrogenesis in several fibrotic diseases of the genitourinary system. Better understanding how the immune system contributes to fibrosis in these diseases may improve prevention and therapeutic strategies and elucidate the functions of immunologic contributors to fibrosis in general.

Cytokines possibly involved in idiopathic epiretinal membrane progression after uncomplicated cataract surgery

Epiretinal membrane (ERM) is a common retinal fibrotic disorder disease causing visual impairment and metamorphopsia. Recently, increasing attention has been devoted to ERM progression after uncomplicated cataract surgery. Cytokines, which play a role in diverse physiological and pathological activities in eyes, are suggested to be involved in these postoperative changes. However, few studies have investigated the post-cataract surgery cytokine expression changes in ERM eyes and their roles in the postoperative changes. The purpose of this study was to evaluate the aqueous levels of cytokines in eyes with idiopathic epiretinal membrane (iERM) both pre- and post-cataract surgery, and their correlations with postoperative iERM progression. In this study, aqueous humor (AH) samples were collected from iERM eyes (n = 25) and non-iERM eyes (n = 23) from 48 patients (48 eyes) undergoing uncomplicated cataract surgery preoperatively and 20 h postoperatively. Samples were analyzed for 48 cytokines with multiplex bead-based immunoassay. Correlations between cytokine level changes (postoperation vs. preoperation) and three-month postoperative best-corrected visual acuity (BCVA) and optical coherence tomography measure changes were evaluated in iERM eyes. We found that in iERM eyes, the levels of 4 cytokines exhibited significant elevations when compared with those in the controls (all p ≤ 0.0015) preoperatively. Postoperatively, the concentrations of 21 cytokines were higher than the preoperative levels in iERM eyes (all p ≤ 0.0015), among which GRO-α, IL-8, and MCP-3 levels showed more pronounced changes than the controls. Additionally, in iERM eyes, IL-4 level changes showed moderate positive correlations with MV (r = 0.492, p = 0.028) and MT (r = 0.481, p = 0.032) changes. LogMAR changes were positively correlated with IL-1α (r = 0.553, p = 0.011), IL-12(P40) (r = 0.544, p = 0.013), and MCP-3 (r = 0.588, p = 0.006) level changes. No significant cytokine-level-change differences were found between eyes with and without postoperative cystoid macular edema development. In conclusion, cataract surgery will bring great alterations to the specific intraocular cytokine microenvironment inherently in eyes with iERM. Many fibrotic and inflammatory cytokines showing elevated levels or relationships with clinical characteristics are suggested to be involved in the pathogenesis and post-cataract surgery progression of iERM; however, further investigations are needed to discern their real roles.

The effect of systemic levels of TNF-alpha and complement pathway activity on outcomes of VEGF inhibition in neovascular AMD

Background/Objectives

Systemic levels of pro-inflammatory cytokines and activated complement components affect the risk and/or progression of neovascular age-related macular degeneration (AMD). This study investigated the effect of serum pro-inflammatory cytokine levels and complement pathway activity on the clinical response to vascular endothelial growth factor (VEGF) inhibition in neovascular AMD.

Methods

Sixty-five patients with a new diagnosis of neovascular AMD were observed over a six-month period in a single-centre, longitudinal cohort study. At each visit, the visual acuity score (VAS), central macular thickness (CMT), serum levels of CRP, pro-inflammatory cytokines (TNF-α, IL-1β, IL-2, IL-6 and IL-8), and complement pathway activity were measured. Participant DNA samples were sequenced for six complement pathway single nucleotide polymorphisms (SNPs) associated with AMD.

Results

A statistically significant difference in VAS was observed for serum levels of TNF-α only: there was a gain in VAS (from baseline) of 1.37 for participants below the 1st quartile of mean concentration compared to a reduction of 2.71 for those above the 3rd quartile. Statistical significance was maintained after Bonferroni correction (P value set at <0.006). No significant differences in CMT were observed. In addition, statistically significant differences, maintained after Bonferroni correction, were observed in serum complement activity for participants with the following SNPs: CFH region (rs1061170), SERPING1 (rs2511989) and CFB (rs641153). Serum complement pathway components did not significantly affect VAS.

Conclusions

Lower serum TNF-α levels were associated with an increase in visual acuity after anti-VEGF therapy. This suggests that targeting pro-inflammatory cytokines may augment treatment for neovascular AMD.

Lipoxin A4 inhibits ovalbumin-induced airway inflammation and airway remodeling in a mouse model of asthma

Asthma is a chronic respiratory disease, which is characterized by airway inflammation, remodeling and airway hyperresponsiveness. Airway remodeling is caused by long-term inflammation of the airways. Lipoxin A4 (LXA4) is a natural eicosanoid with powerful anti-inflammatory properties, and has been shown to serve a critical role in orchestrating pulmonary inflammation and airway hyper-responsiveness in asthmatic mice. However, its effect on airway remodeling is unknown. Female BALB/c mice were used to establish a mouse model of asthma which were sensitized and challenged by ovalbumin (OVA). LXA4 was intranasally administrated prior to the challenge. The results of our study indicated that LXA4 suppressed the OVA-induced inflammatory cell infiltration and T helper type 2 (Th2) cytokines secretion in the mouse model of asthma. Characteristics of airway remodeling, such as thickening of the bronchial wall and smooth muscle, overdeposition of collagen, and overexpression of α-smooth muscle actin (α-SMA) and collagen-I were reversed by LXA4. Furthermore, LXA4 suppressed the aberrant activation of the signal transducer and activator of transcription 3 (STAT3) pathway in the lung tissues of asthmatic mice. In conclusion, these findings demonstrated that LXA4 alleviated allergic airway inflammation and remodeling in asthmatic mice, which may be related to the inhibition of STAT3 pathway.

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

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

Yes-associated protein is essential for proliferative vitreoretinopathy development via the epithelial-mesenchymal transition in retinal pigment epithelial fibrosis

This study was aim to investigate whether the progression of proliferative vitreoretinopathy (PVR) depended on the activation of Yes‐associated protein (YAP) and the subsequent epithelial‐mesenchymal transition (EMT) of retinal pigment epithelial (RPE) cell. The effect of YAP activation on retinal fibrosis in a PVR mouse model and in human ARPE‐19 cells in vitro was studied. After treated with transforming growth factor‐β2(TGF‐β2), the expressions of fibrogenic molecules, YAP activation and the TGF‐β2‐Smad signalling pathway in ARPE‐19 cells were detected by Western blot and immunocytochemical analyses. The effect of YAP on change in fibrosis and EMT was tested by knockdown experiment using verteporfin (YAP inhibitor). YAP was upregulated in the PVR mouse model and during TGF‐β2–induced RPE cell EMT. In an in vivo study, verteporfin attenuated PVR progression in a mouse model. Additionally, YAP knockdown retained phenotype of RPE cells and ameliorated TGF‐β2–induced migration, gel contraction and EMT in vitro. YAP knockdown inhibited the TGF‐β2–induced upregulation of connective tissue growth factor (CTGF), smooth muscle actin (SMA‐α) and fibronectin. YAP was essential for the TGF‐β2–induced nuclear translocation and phosphorylation of Smad2/3. Our work provides direct evidence that YAP is an essential regulator of EMT and profibrotic responses in PVR and indicates that YAP inhibition could be a potential target in PVR therapeutic intervention.

Nano-Graphene Oxide-Promoted Epithelial-Mesenchymal Transition of Human Retinal Pigment Epithelial Cells through Regulation of Phospholipase D Signaling

Nano-graphene oxide (Nano-GO) is an extensively studied multifunctional carbon nanomaterial with attractive applications in biomedicine and biotechnology. However, few studies have been conducted to assess the epithelial-to-mesenchymal transition (EMT) in the retinal pigment epithelium (RPE). We aimed to determine whether Nano-GO induces EMT by regulating phospholipase D (PLD) signaling in human RPE (ARPE-19) cells. The physicochemical characterization of Nano-GO was performed using a Zetasizer, X-ray diffraction, Fourier-transform infrared spectroscopy, and transmission electron microscopy. RPE cell viability assays were performed, and the migratory effects of RPE cells were evaluated. RPE cell collagen gel contraction was also determined. Intracellular reactive oxygen species (ROS) levels were determined by fluorescence microscopy and flow cytometry. Immunofluorescence staining and western blot analysis were used to detect EMT-related protein expression. Phospholipase D (PLD) enzymatic activities were also measured. Nano-GO significantly enhanced the scratch-healing ability of RPE cells, indicating that the RPE cell migration ability was increased. Following Nano-GO treatment, the RPE cell penetration of the chamber was significantly promoted, suggesting that the migratory ability was strengthened. We also observed collagen gel contraction and the generation of intracellular ROS in RPE cells. The results showed that Nano-GO induced collagen gel contraction and intracellular ROS production in RPE cells. Moreover, immunofluorescence staining and western blot analysis revealed that Nano-GO significantly regulated key molecules of EMT, including epithelial-cadherin, neural-cadherin, α-smooth muscle actin, vimentin, and matrix metalloproteinases (MMP-2 and MMP-9). Interestingly, Nano-GO-induced RPE cell migration and intracellular ROS production were abrogated in PLD-knockdown RPE cells, indicating that PLD activation played a crucial role in the Nano-GO-induced RPE EMT process. We demonstrate for the first time that Nano-GO promotes RPE cell migration through PLD-mediated ROS production. We provide preliminary evidence to support the hypothesis that Nano-GO has adverse health effects related to RPE damage.

Triamcinolone acetonide modulates TGF‑β2‑induced angiogenic and tissue‑remodeling effects in cultured human retinal pigment epithelial cells

Transforming growth factor-β2 (TGF-β2) has been implicated in the pathogenesis of proliferative vitreoretinopathy (PVR) and proliferative diabetic retinopathy (PDR), due to its ability to stimulate the overproduction of pro-angiogenic factors, such as vascular endothelial growth factor (VEGF), and remodeling of the extracellular matrix (ECM). Although intravitreal triamcinolone acetonide (TA) is clinically useful in the treatment of PVR and PDR, its molecular mechanism has yet to be fully elucidated. The present study investigated whether TA treatment altered TGF-β2-driven biological effects on the behavior of cultured human retinal pigment epithelial (RPE) cells, in order to determine which signaling pathway may be essential for the pharmacological action of TA. The R-50 human RPE cell line was treated with TA in the presence of TGF-β2, followed by analyses of cell viability and contraction using cell viability and collagen gel contraction assays. VEGF mRNA expression and protein production were measured using reverse transcription-quantitative PCR and ELISA, respectively. The phosphorylation status of signaling mediators and the protein expression of type I collagen (COL1A1), α-smooth muscle actin (α-SMA), and ECM-remodeling enzymes, including MMP-2 and MMP-9, were analyzed using western blotting. The gelatinolytic activity of MMPs was detected using gelatin zymography. TA treatment exhibited no prominent cytotoxicity but markedly antagonized TGF-β2-induced cytostatic effects on RPE cell viability and TGF-β2-enhanced contractility in collagen gels. In the context of TGF-β2-related signaling, TA significantly attenuated TGF-β2-elicited Smad2, extracellular-regulated kinase (ERK)1/2 and p38 mitogen-activated protein kinase (MAPK) phosphorylation. Moreover, TA markedly mitigated TGF-β2-induced VEGF upregulation through ablation of p38 signaling activity. TA also partially attenuated TGF-β2-elicted expression of COL1A1, α-SMA, MMP-2, and MMP-9, but only suppressed TGF-β2-induced MMP-9 gelatinolytic activity. Mechanistically, the MEK/ERK signaling pathway may have a critical role in the TGF-β2-induced upregulation of COL1A1, α-SMA and MMP-9. In conclusion, TA may be considered a useful therapeutic agent for treating TGF-β2-associated intraocular angiogenesis and tissue remodeling, the underlying mechanism of which may involve the ERK and p38 MAPK signaling pathways.

Targeting matrix stiffness-induced activation of retinal pigment epithelial cells through the RhoA/YAP pathway ameliorates proliferative vitreoretinopathy

The purpose of this study was to investigate whether excessive extracellular matrix (ECM) deposition-induced mechanical matrix stiffness plays a key role in promoting retinal pigment epithelial (RPE) cell activation and the subsequent development of proliferative vitreoretinopathy (PVR). Human ARPE-19 cells were cultured on either 50 kappa (stiff) or 0.5 kappa (soft) gel-coated coverslips. Reverse and knockdown experiments were carried out to establish a model of matrix stiffness-induced activation in ARPE-19 cells in vitro. A PVR mouse model was established by the intravitreal injection of dispase. The effects of RhoA/YAP signalling blockade on matrix stiffness-induced ARPE-19 cell activation and PVR-induced retinal fibrosis were determined by using a combination of the Yes-associated protein (YAP) inhibitor verteporfin and the RhoA inhibitor C3 exoenzyme. Matrix stiffness stimulated YAP nuclear translocation and expression in ARPE-19 cells. The effect of YAP activation was dependent on F-actin cytoskeleton polymerization and RhoA activity, forming the RhoA/YAP signalling pathway. Upstream pharmacological blockade of RhoA by C3 exoenzyme or downstream blockade of YAP by verteporfin reduced the invasion, migration, and MMP expression of ARPE-19 cells and collagen gel contraction. Furthermore, blockade of RhoA/YAP signalling reduced PVR-induced retinal fibrogenesis and inhibited the TGF-β/Smad pathway in vivo. RhoA/YAP signalling modulates matrix stiffness-induced activation of ARPE-19 cells. Targeting this signalling pathway could alleviate PVR-induced retinal fibrosis and suggests attractive novel therapeutic strategies for intervening in the progression of PVR.

Proline metabolism and transport in retinal health and disease

The retina is one of the most energy-demanding tissues in the human body. Photoreceptors in the outer retina rely on nutrient support from the neighboring retinal pigment epithelium (RPE), a monolayer of epithelial cells that separate the retina and choroidal blood supply. RPE dysfunction or cell death can result in photoreceptor degeneration, leading to blindness in retinal degenerative diseases including some inherited retinal degenerations and age-related macular degeneration (AMD). In addition to having ready access to rich nutrients from blood, the RPE is also supplied with lactate from adjacent photoreceptors. Moreover, RPE can phagocytose lipid-rich outer segments for degradation and recycling on a daily basis. Recent studies show RPE cells prefer proline as a major metabolic substrate, and they are highly enriched for the proline transporter, SLC6A20. In contrast, dysfunctional or poorly differentiated RPE fails to utilize proline. RPE uses proline to fuel mitochondrial metabolism, synthesize amino acids, build the extracellular matrix, fight against oxidative stress, and sustain differentiation. Remarkably, the neural retina rarely imports proline directly, but it uptakes and utilizes intermediates and amino acids derived from proline catabolism in the RPE. Mutations of genes in proline metabolism are associated with retinal degenerative diseases, and proline supplementation is reported to improve RPE-initiated vision loss. This review will cover proline metabolism in RPE and highlight the importance of proline transport and utilization in maintaining retinal metabolism and health.

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.

Discovery of microRNA expression profiles involved in regulating TGF-2 expression in the tears of dry eye patients

BACKGROUND

To date, the difference in microRNA expression profiles in tears of dry eye patients and healthy people has not been reported. In current study, we evaluated the significance of microRNAs and transforming growth factor beta2 (TGF-β2) in distinguishing dry eye.

METHODS

A total of 138 patients with dry eye from October 2017 to October 2018 were selected. During the same period, 138 healthy persons were collected. All patients were followed up for 12 months through outpatient, telephone or medical records and the time of corneal injury was recorded.

RESULTS

Compared with healthy people, TGF-β2 concentrations in dry eye patients were significantly decreased (P < 0.05). Array analysis, predictive software and dual-luciferase reporter assays showed that miR-450b-5p, miR-1283 and miR-3671 can target TGF-β2 expression. Tear miR-450b-5p, miR-1283 and miR-3671 concentrations were significantly higher in dry eye patients than healthy people. A logistic regression model combining miR-450b-5p, miR-1283, miR-3671 and TGF-β2 was performed. This model presented a high discriminating value (AUC: 0.907, 0.876-0.939, P < 0.001) than any single indicator, and the sensitivity and specificity were 77.7% and 92.7%, respectively. Compared with the low miR-450b-5p, low miR-1283, low miR-3671 and high TGF-β2 groups, the high miR-450b-5p, high miR-1283, high miR-3671 and low TGF-β2 groups had a significantly higher probability of corneal injury (TGF-β2: χ² = 5.762, P = 0.016; miR-450b-5p: χ² = 13.267, P < 0.001; miR-1283: χ² = 19.431, P < 0.001; miR-3671: χ² = 8.131, P = 0.004).

CONCLUSION

Current model combining tear miR-450b-5p, miR-1283, miR-3671 and TGF-β2 had important values in the identification of dry eye and was of great value in evaluating the risk of corneal injury.

The Role of Inflammation in Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a blinding eye disease which incidence gradually increases with age. Inflammation participates in AMD pathogenesis, including choroidal neovascularization and geographic atrophy. It is also a kind of self-protective regulation from injury for the eyes. In this review, we described inflammation in AMD pathogenesis, summarized the roles played by inflammation-related cytokines, including pro-inflammatory and anti-inflammatory cytokines, as well as leukocytes (macrophages, dendritic cells, neutrophils, T lymphocytes and B lymphocytes) in the innate or adaptive immunity in AMD. Possible clinical applications such as potential diagnostic biomarkers and anti-inflammatory therapies were also discussed. This review overviews the inflammation as a target of novel effective therapies in treating AMD.

Interleukin-2 induces extracellular matrix synthesis and TGF-β2 expression in retinal pigment epithelial cells

Macular fibrosis is a vital obstacle of vision acuity improvement of age‐related macular degeneration patients. This study was to investigate the effects of interleukin 2 (IL‐2) on epithelial‐mesenchymal transition (EMT), extracellular matrix (ECM) synthesis and transforming growth factor β2 (TGF‐β2) expression in retinal pigment epithelial (RPE) cells. 10 μg/L IL‐2 was used to induce fibrosis in RPE cells for various times. Western blot was used to detect the EMT marker α‐smooth muscle actin (α‐SMA), ECM markers fibronectin (Fn) and type 1 collagen (COL‐1), TGF‐β2, and the activation of the JAK/STAT3 and NF‐κB signaling pathway. Furthermore, JAK/STAT3 and NF‐κB signaling pathways were specifically blocked by WP1066 or BAY11‐7082, respectively, and the expression of α‐SMA, COL‐1, Fn and TGF‐β2 protein were detected. Wound healing and Transwell assays were used to measure cell migration ability of IL‐2 with or without WP1066 or BAY11‐7082. After induction of IL‐2, the expressions of Fn, COL‐1, TGF‐β2 protein were significantly increased, and this effect was correlated with IL‐2 treatment duration, while α‐SMA protein expression did not change significantly. Both WP1066 and BAY11‐7082 could effectively downregulate the expression of Fn, COL‐1 and TGF‐β2 induced by IL‐2. What's more, both NF‐κB and JAK/STAT3 inhibitors could suppress the activation of the other signaling pathway. Additionally, JAK/STAT3 inhibitor WP1066 and NF‐κB inhibitor BAY 11‐7082 could obviously decrease RPE cells migration capability induced by IL‐2. IL‐2 promotes cell migration, ECM synthesis and TGF‐β2 expression in RPE cells via JAK/STAT3 and NF‐κB signaling pathways, which may play an important role in proliferative vitreoretinopathy.