Influence on collagen metabolism of vitreous from eyes with proliferative vitreoretinopathy

Unexpected and Synergistical Effects of All-Trans Retinoic Acid and TGF-β2 on Biological Aspects of 2D and 3D Cultured ARPE19 Cells

Objectives: To study the effects of all-trans retinoic acid (ATRA) on TGF-β2-induced effects of human retinal pigment epithelium cells under normoxia and hypoxia conditions. Methods: Two-dimensionally (2D) and three-dimensionally (3D) cultured ARPE19 cells were subjected to cellular functional analyses by transepithelial electrical resistance (TEER) and an extracellular flux assay (2D), measurement of levels of reactive oxygen species (ROS), gene expression analyses of COL1, αSMA, Zo-1, HIF1α, and PGC1α (2D), and physical property analyses (3D). Results: Under a normoxia condition, treatment with 100 nM ATRA substantially decreased barrier function regardless of the presence of 5 ng/mL TGF-β2 in 2D ARPE19 monolayer cells. Under a hypoxia condition, treatment with ATRA conversely increased barrier function, but the effect was masked by a marked increase in effects induced by TGF-β2. Although ATRA alone did not affect cellular metabolism and ROS levels in 2D ARPE cells, treatment with ATRA under a hypoxia condition did not affect ROS levels but shifted cellular metabolism from mitochondrial respiration to glycolysis. The changes of cellular metabolism and ROS levels were more pronounced with treatment of both ATRA and TGF-β2 independently of oxygen conditions. Changes in mRNA expressions of some of the above genes suggested the involvement of synergistical regulation of cellular functions by TGF-β2 and hypoxia. In 3D ARPE spheroids, the size was decreased and the stiffness was increased by either treatment with TGF-β2 or ATRA, but these changes were unexpectedly modulated by both ATRA and TGF-β2 treatment regardless of oxygen conditions. Conclusions: The findings reported herein indicate that TGF-β2 and hypoxia synergistically and differentially induce effects in 2D and 3D cultured ARPE19 cells and that their cellular properties are significantly altered by the presence of ATRA.

TGF-β Isoforms and Local Environments Greatly Modulate Biological Nature of Human Retinal Pigment Epithelium Cells

To characterize transforming growth factor-β (TGF-β) isoform (TGF-β1~3)-b's biological effects on the human retinal pigment epithelium (RPE) under normoxia and hypoxia conditions, ARPE19 cells cultured by 2D (two-dimensional) and 3D (three-dimensional) conditions were subjected to various analyses, including (1) an analysis of barrier function by trans-epithelial electrical resistance (TEER) measurements; (2) qPCR analysis of major ECM molecules including collagen 1 (COL1), COL4, and COL6; α-smooth muscle actin (αSMA); hypoxia-inducible factor 1α (HIF1α); and peroxisome proliferator-activated receptor-gamma coactivator (PGC1α), a master regulator for mitochondrial respiration;, tight junction-related molecules, Zonula occludens-1 (ZO1) and E-cadherin; and vascular endothelial growth factor (VEGF); (3) physical property measurements of 3D spheroids; and (4) cellular metabolic analysis. Diverse effects among TGF-β isoforms were observed, and those effects were also different between normoxia and hypoxia conditions: (1) TGF-β1 and TGF-β3 caused a marked increase in TEER values, and TGF-β2 caused a substantial increase in TEER values under normoxia conditions and hypoxia conditions, respectively; (2) the results of qPCR analysis supported data obtained by TEER; (3) 3D spheroid sizes were decreased by TGF-β isoforms, among which TGF-β1 had the most potent effect under both oxygen conditions; (4) 3D spheroid stiffness was increased by TGF-β2 and TGF-β3 or by TGF-β1 and TGF-β3 under normoxia conditions and hypoxia conditions, respectively; and (5) the TGF-β isoform altered mitochondrial and glycolytic functions differently under oxygen conditions and/or culture conditions. These collective findings indicate that the TGF-β-induced biological effects of 2D and 3D cultures of ARPE19 cells were substantially diverse depending on the three TGF-β isoforms and oxygen levels, suggesting that pathological conditions including epithelial-mesenchymal transition (EMT) of the RPE may be exclusively modulated by both factors.

Hypoxia Differently Affects TGF-β2-Induced Epithelial Mesenchymal Transitions in the 2D and 3D Culture of the Human Retinal Pigment Epithelium Cells

The hypoxia associated with the transforming growth factor-β2 (TGF-β2)-induced epithelial mesenchymal transition (EMT) of human retinal pigment epithelium (HRPE) cells is well recognized as the essential underlying mechanism responsible for the development of proliferative retinal diseases. In vitro, three-dimensional (3D) models associated with spontaneous O₂ gradients can be used to recapitulate the pathological levels of hypoxia to study the effect of hypoxia on the TGF-β2-induced EMT of HRPE cells in detail, we used two-dimensional-(2D) and 3D-cultured HRPE cells. TGF-β2 and hypoxia significantly and synergistically increased the barrier function of the 2D HRPE monolayers, as evidenced by TEER measurements, the downsizing and stiffening of the 3D HRPE spheroids and the mRNA expression of most of the ECM proteins. A real-time metabolic analysis indicated that TGF-β2 caused a decrease in the maximal capacity of mitochondrial oxidative phosphorylation in the 2D HRPE cells, whereas, in the case of 3D HRPE spheroids, TGF-β2 increased proton leakage. The findings reported herein indicate that the TGF-β2-induced EMT of both the 2D and 3D cultured HRPE cells were greatly modified by hypoxia, but during these EMT processes, the metabolic plasticity was different between 2D and 3D HRPE cells, suggesting that the mechanisms responsible for the EMT of the HRPE cells may be variable during their spatial spreading.

Suppression of PGC-1α Drives Metabolic Dysfunction in TGFβ2-Induced EMT of Retinal Pigment Epithelial Cells

PGC-1α, a key orchestrator of mitochondrial metabolism, plays a crucial role in governing the energetically demanding needs of retinal pigment epithelial cells (RPE). We previously showed that silencing PGC-1α induced RPE to undergo an epithelial-mesenchymal-transition (EMT). Here, we show that induction of EMT in RPE using transforming growth factor-beta 2 (TGFβ2) suppressed PGC-1α expression. Correspondingly, TGFβ2 induced defects in mitochondrial network integrity with increased sphericity and fragmentation. TGFβ2 reduced expression of genes regulating mitochondrial dynamics, reduced citrate synthase activity and intracellular ATP content. High-resolution respirometry showed that TGFβ2 reduced mitochondrial OXPHOS levels consistent with reduced expression of NDUFB5. The reduced mitochondrial respiration was associated with a compensatory increase in glycolytic reserve, glucose uptake and gene expression of glycolytic enzymes (PFKFB3, PKM2, LDHA). Treatment with ZLN005, a selective small molecule activator of PGC-1α, blocked TGFβ2-induced upregulation of mesenchymal genes (αSMA, Snai1, CTGF, COL1A1) and TGFβ2-induced migration using the scratch wound assay. Our data show that EMT is accompanied by mitochondrial dysfunction and a metabolic shift towards reduced OXPHOS and increased glycolysis that may be driven by PGC-1α suppression. ZLN005 effectively blocks EMT in RPE and thus serves as a novel therapeutic avenue for treatment of subretinal fibrosis.

Scanning Electron Microscopy and Energy Dispersive Spectroscopy Findings in Explanted Pmma and Hydrophilic Acrylic Intraocular Lenses

Purpose

To investigate the presence of calcium (Ca) aggregates influencing biocompatibility and the factors that affect calcium accumulation in explanted intraocular lenses (IOL) and to analyze the Ca distribution in an opacified hydrophilic acrylic lens.

Methods

Surface irregularities and aggregates of 13 IOLs were studied with scanning electron microscopy, and their relative concentrations with energy dispersive spectroscopy (EDS). Relationships of distribution between Ca and silicone (Si) and nitrogen (N) and between N and Si and Na, and the influence of Si on Ca accumulation and the effect of differences in lens material on the distribution of N, and the effect of endophthalmitis on the distribution of Ca were evaluated statistically. EDS analyses were performed on the surface and cross-section of the opacified lens.

Results

The statistically significant relationships between the distribution of Ca and N, and between the distribution of N and Na, the significant effect of Si on the Ca accumulation, significant relationship between endophthalmitis and the Ca accumulation in the aggregates were shown. The EDS analysis of the opacified IOL, Ca and P peaks were shown from the whole surface, Ca, O peaks were determined from cross-sections over a 70–80 μm distance.

Conclusions

In the aggregates influencing IOL biocompatibility, presence of proteins was determined to be more important than the presence of Si regarding the distribution of Ca, while the presence of Si affected the accumulation of Ca. Opacification, caused by the Ca accumulation within the lens, was found to result from Ca penetrating from lens pores.

Regulation of cell-mediated collagen gel contraction in human retinal pigment epithelium cells by vascular endothelial growth factor compared with transforming growth factor-β2

BACKGROUND

To explore the potential role of vascular endothelial growth factor compared with transforming growth factor-β2 in the regulation of human retinal pigment epithelium cell-mediated collagen gel contraction.

METHODS

The retinal pigment epithelium cell mediated type I collagen gel contraction assay was performed to evaluate and compare the effect of vascular endothelial growth factor and transforming growth factor-β2. The number of viable retinal pigment epithelium cells in the gel and the expression of α-smooth muscle actin were analysed.

RESULTS

Both vascular endothelial growth factor and transforming growth factor-β2 caused a time dependent gel contraction, associated with over expression of α-smooth muscle actin in retinal pigment epithelium cells undergoing a fibroblast like transformation. The decrease in volume of the collagen gel and increase in α-smooth muscle actin expression were more significant in the transforming growth factor-β2-treated group than in vascular endothelial growth factor-treated group beginning at day 2, and the growth of retinal pigment epithelium cells was significantly more inhibited in the transforming growth factor-β2-treated group compared with the vascular endothelial growth factor-treated group after day 1 (P < 0.05). Transforming growth factor-β2 stimulation increased both vascular endothelial growth factor mRNA expression and secretion. The α-smooth muscle actin expression and the change in volume of collagen gel were significantly positively correlated in both experimental groups.

CONCLUSIONS

Both vascular endothelial growth factor and transforming growth factor-β2 can cause induction of retinal pigment epithelium cell-mediated collagen gel contraction in vitro via partial upregulation of α-smooth muscle actin expression.

Medical devices for the treatment of eye diseases

Development of intraocular drug delivery systems (DDSs) is urgently required for the treatment of eye diseases, especially in the posterior segment of the eye (the vitreous cavity, retina, and choroid), most of which are refractory to conventional pharmacologic approaches; eye drops and systemically administered drugs cannot achieve therapeutic drug concentrations in the posterior segment of the eye. Repeated intravitreal injections of anti-angiogenic agents are effective in the treatment of age-related macular degeneration, but there remain risks of serious side effects such as endophthalmitis associated with repeated injections. Intraocular DDSs may address these problems. Intraocular sustained drug release from implantable or injectable devices has been investigated to treat vitreoretinal diseases. A reservoir-type nonbiodegradable implant was first launched in the market in 1996 for the treatment of cytomegalovirus retinitis secondary to the acquired immunodeficiency syndrome, followed by clinical trials for a variety of potent devices to treat other challenging eye diseases. An injectable rod-shaped insert releasing a steroid is presently being assessed in a phase III trial to treat macular edema secondary to diabetic retinopathy or retinal vein occlusion. Thus various types of intraocular DDSs will be commercially available to treat vision-threatening intraocular diseases in the near future.

The effect of prinomastat (AG3340), a potent inhibitor of matrix metalloproteinase, on a new animal model of epiretinal membrane

PURPOSE

To develop a simple epiretinal membrane (ERM) animal model and evaluate the efficacy of prinomastat (AG3340), a synthetic inhibitor of matrix metalloproteinase.

METHODS

This experiment was carried out on 18 eyes of nine Brown Norway rats. Preretinal hemorrhage was induced bilaterally using diode laser focused deeply on choroidal blood vessels. One day later, AG3340 was injected intravitreally in the right eyes while the left eyes received equal amounts of vehicle. The developed epiretinal membrane was measured in disk areas and compared between groups.

RESULTS

Clinically, preretinal hemorrhage showed a slow clearance persisting for 8 to 10 weeks. ERM was well established around 12 weeks. Histologically, ERMs consist of fibroblast and glial cells embedded in collagen-rich extracellular matrix infiltrated by macrophages. Seventy-five percent of the hemorrhagic laser burns in the control group developed ERM, whereas only 25% of the hemorrhagic laser burns in treated group developed ERM (P = 0.01). The total surface area of developed ERM was 3.66 DD in treated eyes versus 25.45 DD in control eyes (P = 0.049). The mean surface area of ERM per eye was 0.52 disk areas +/- 1.05 in treated eyes versus 3.18 +/- 3.07 in control eyes.

CONCLUSION

We demonstrated that ERM can be induced on rat retina by simple hemorrhagic retinal laser coagulation. This new animal model could be used for future evaluation of different medical treatment modalities for proliferating ERM. Furthermore, AG3340 demonstrated an inhibitory effect on ERM formation in this new rat model.

Drug delivery systems for vitreoretinal diseases

The eye has an environment that is specific unto itself in terms of pharmacokinetics: the inner and outer blood-retinal barriers separate the retina and the vitreous from the systemic circulation and vitreous body, which physiologically has no cellular components, occupies the vitreous cavity, an inner space of the eye, and reduces practical convection of molecules. Considering this, development of a drug delivery system (DDS) is becoming increasingly important in the treatment of vitreoretinal diseases not only to facilitate drug efficacy but also to attenuate adverse effects. The DDS has three major goals: enhances drug permeation (e.g., iontophoresis and transscleral DDS), controls release of drugs (e.g., microspheres, liposomes, and intraocular implants), and targets drugs (e.g., prodrugs with high molecular weight and immunoconjugates). Comprehensive knowledge of these should lead to development of innovative treatment modalities.

Gene transfer of soluble TGF-beta type II receptor inhibits experimental proliferative vitreoretinopathy

This study was conducted to investigate a method of gene therapy for proliferative vitreoretinopathy (PVR) by inhibiting type beta transforming growth factor (TGF-beta). PVR was induced in pigmented rabbits by intravitreal injection of 50 000 rabbit conjunctival fibroblasts after vitrectomy. Subsequently, the eyes received an intravitreal application of adenovirus vector encoding a soluble type II TGF-beta receptor (AdTbeta-ExR, n = 10) or adenoviral vector expressing beta-galactosidase (AdLacZ) (n = 10) or balanced salt solution (BSS) (n = 6). The eyes were examined ophthalmoscopically for 28 days after surgery, and the clinical stage of PVR was evaluated on a scale of zero to five. Histological examinations were performed on the treated eyes on day 28. All control eyes injected with AdLacZ or BSS developed PVR, characterized by retinal detachment and the formation of intravitreal membranes within 7 days. The eyes injected with AdTbeta-ExR also developed features of PVR, but the average severity from day 5 to day 28 was significant lower than in the control eyes (P < 0.05). TGF-beta plays an important role in PVR progression in a PVR model, and prevention of TGF-beta signaling could be therapeutically useful.