The role of matricellular proteins thrombospondin-1 and osteonectin during RPE cell migration in proliferative vitreoretinopathy

PURPOSE: To investigate the hypothesis that the Matricellular proteins thrombospondin 1 (TSP1), tenascin (TN) and Secreted Protein Acidic and Rich in Cysteine (SPARC) modulate the migration of RPE cells in the epiretinal membranes of proliferative vitreoretinopathy. METHODS: Ten PVR epiretinal membranes were studied by immunohistochemical methods in which aggregates of RPE cells were identified by their expression of a broad range of cytokeratins. RPE subsets containing migratory RPE cells were detected by immunoreactivity for the monoclonal antibody RGE53 (which detects an epitope on cytokeratin-18 on motile RPE cells). Co-localisation of the RPE subsets with the glycoproteins TSP-1, SPARC and TN was evaluated. RESULTS: Nineteen migratory RPE (RGE53 positive) subsets and 13 RPE (RGE53 negative) subsets were identified. All of the RGE53+ subsets colocalised with TSP1 and SPARC and 17 with TN. Ten of the RGE53- aggregates stained for TN, 6 for SPARC and 5 for TSP1. The association between the presence of RGE53+ cells in the RPE cell aggregates and TSP1 immunoreactivity in the aggregates was significant (p < 0.001), and there was a comparable significant association between RGE53+ cells and SPARC (p < 0.001). No such association was detected for RGE53+ cells and TN (p > 0.2). CONCLUSIONS: The findings support the concept that the migration of retinal pigment cells in epiretinal membranes is modulated by TSP1 and SPARC and thus that these two proteins ultimately may represent therapeutic targets in the management of the membranes.     

Matrix and the retinal pigment epithelium in proliferative retinal disease

In their normal state, RPE cells are strongly adherent to Bruch's membrane. Certain pathological conditions such as retinal detachment cause an injury-type response (probably augmented or induced by the local accumulation of a variety of substances which modulate cell behaviour) in which RPE begin to dissociate from the membrane. This RPE-Bruch's membrane separation may be mediated by proteins with counter-adhesive properties and proteolytic enzymes, partly derived from the RPE themselves. Concomitant with the RPE disassociation, the cells begin to lose tertiary differentiation characteristics and gain macrophage-like features.When the “free” RPE arrive at the surface of the neuroretina, they may attach to or create a provisional matrix. Some of the cells adopt a fibroblast-like phenotype. This phenotype is similar to that of the dermal fibroblast during cutaneous wound repair and the fibroblastic RPE synthesise the types of matrix components found in healing skin wounds. Many of these molecules in turn further modulate the activities of the cells via several families of cell surface receptors, while the RPE continue to remodel the new matrix with a range of proteolytic enzymes. The resulting tissue (or membrane) has many of the features of a contractile scar and is the hallmark of the condition known as proliferative vitreoretinopathy (PVR). Thus the development of PVR, and the resulting tractional distortion of the neuroretina, appears to be dependent on RPE-matrix interactions. The interactions present a number of potential therapeutic targets for the management of the disorder.     

Modulation of growth in retina-derived cells by extracellular matrices

Intravitreal membranes from patients with proliferative vitreoretinopathy (PVR) consist partly of retinal glial (RG) and retinal pigment epithelial (RPE) cells surrounded by varying amounts of extracellular matrix (ECM). The contribution of the ECM to the growth of PVR membranes is unknown. This study was undertaken to determine if proliferation in cultured RPE and RG cells is affected by different substrates, including some ECM materials which have been identified in PVR membranes. Substrates tested included type I collagen, basement membrane Matrigel, and poly-D-lysine, as well as uncharacterized cell type-specific matrices deposited by cultured RPE and RG cells. Proliferation was quantified by 3H-thymidine incorporation and radioautography 24 hours after plating and by cell counts after 14 days in the presence of serum. Relative to uncoated culture plastic, growth of RPE cells was inhibited by Matrigel, enhanced by poly-D-lysine, and unaffected by type I collagen. In contrast, growth in RG cells was inhibited by type I collagen and unaffected by the other substrates. Analysis of the timing of DNA synthesis after plating suggested that the substrates which affected RPE growth did so by altering the fraction of cycling cells rather than the cell cycle time. For the cell-derived matrices, heterotypic matrix (matrix produced by the other retinal cell type) enhanced the growth of both RPE and RG. The results suggest that the ECM may modify the growth of cells contributing to PVR membranes. Of note is that the cell-derived matrices reciprocally stimulated growth of RG and RPE cells, cell types which may interact in PVR membranes.     

Tissue transglutaminase as a modifying enzyme of the extracellular matrix in PVR membranes

PURPOSE: Proliferative vitreoretinopathy (PVR) is characterized by the development of epi- and subretinal fibrocellular membranes containing modified retinal pigment epithelial (RPE) cells among others. In the present study, the role of transglutaminases in accumulation of extracellular matrix (ECM) proteins in these membranes was investigated. Transglutaminases are enzymes capable of cross-linking ECM proteins to proteolysis-resistant complexes. METHODS: PVR membranes were incubated with dansyl-cadaverine to demonstrate active transglutaminase. Localization of tissue transglutaminase (tTgase), its reaction product epsilon-(gamma-glutamyl)-lysine, and fibronectin was investigated immunohistochemically. Colocalization was studied with a confocal laser scanning microscope. PVR membranes were also analyzed by RT-PCR for the presence of tTgase mRNA. In vitro, RPE cells were treated with transforming growth factor-beta2 (TGF-beta2), basic fibroblast growth factor, interleukin-6, and interleukin-1beta. Their effect was studied using immunohistochemistry and Northern and Western blot analyses. RESULTS: Transglutaminase activity and expression of tTgase were present in all PVR membranes. Staining was most prominent at the rim of the membranes. The enzyme was colocalized with epsilon-(gamma-glutamyl)-lysine and fibronectin. No staining differences were found between epi- and subretinal membranes. Although native RPE cells contained only a basal level of tTgase mRNA, the expression and activity of tTgase was increased under culture conditions and further stimulated by TGF-beta2 treatment. CONCLUSIONS: The findings demonstrate that in PVR membranes tTgase is present and functionally active. The amount and activity of this enzyme appears to be related to the differentiation state of the RPE cells and their stimulation by TGF-beta2, a growth factor known to be increased in the vitreous of PVR. Intervention at this pathway may open a new approach for PVR prevention and therapy.     

Novel growth factors involved in the pathogenesis of proliferative vitreoretinopathy

AIMS: To determine whether hepatocyte growth factor (HGF) and connective tissue growth factor (CTGF) are expressed in human specimens of proliferative vitreoretinopathy (PVR) and to propose a model of PVR pathogenesis based upon the known activities of these growth factors.Methods Immunohistochemical methods (ABC Elite) were used to demonstrate the presence of HGF and CTGF in cryostat sections of five human PVR membranes. RESULTS: In each of the five PVR membranes, stromal cells were immunohistochemically positive for both HGF and CTGF. Based upon this information and the known actions of these growth factors, a model of PVR pathogenesis was developed. In this model, injury of the retina induces an inflammatory response that upregulates HGF expression inducing the formation of multilayered groups of migratory retinal pigment epithelial cells (RPE). These RPE, present in a provisional extracellular matrix, come in contact with vitreous containing TGF-beta. The TGF-beta is activated, upregulating expression of CTGF. Under the influence of TGF-beta and CTGF, RPE become myofibroblastic and fibrosis ensues. Retinal traction induces further detachment continuing the cycle of retinal injury. CONCLUSIONS: HGF and CTGF are expressed in PVR membranes and may play important roles in the pathogenesis of PVR. The expression and function of these growth factors should be critically examined in human PVR specimens, in in vitro cultures of RPE, and in animal models of PVR.     

Cultures of human retinal pigment epithelium. Modulation of extracellular matrix.

The extracellular matrix of retinal pigment epithelial (RPE) cells is an important component of the fibroelastic membranes formed in proliferative vitreoretinopathy (PVR). These membranes consist of cells intermingled with fibrillar proteins, such as elastin and collagen. Because RPE cells may be exposed to vitreous and serum-derived factors in conditions that lead to PVR, the effects of vitreous and serum on the deposition of fibrillar proteins by RPE cells were studied using radioactive labeling and indirect immunofluorescence techniques. The RPE cells, modulated by combined vitreous and serum into a fibrocytic-like appearance, deposited less fibroelastic proteins per cell. However, as a result of simultaneous cell proliferation, the total deposition of fibroelastic proteins per culture was increased. Indirect immunofluorescence studies suggest that it is type I collagen that is altered in the matrix of these modulated cell cultures. This information is important in pathologic conditions characterized by intraocular cell proliferation and fibroelastic membrane formation; these phenomena are seen in many vitreoproliferative disorders.     

增生性玻璃体视网膜病变膜剥离标本的免疫组化研究

目的 探讨不同增生性玻璃体视网膜病变(PVR)的增殖特征。方法采用5种特异性抗体对12例PVR膜样本进行免疫组织化学研究。结果成纤维细胞、神经胶质细胞为参与PVR膜的主要细胞成分,视网膜色素上皮细胞(RPE)、巨噬细胞、纤维连接蛋白和新生血管也参与了PVR的病理过程。结论新生血管主要参与了增生性视网膜血管病变的病理过程。增殖膜中增殖的细胞、细胞外基质和血管成分参与了PVR的病理过程并起着不同的作用。     

肝细胞生长因子受体在视网膜前膜及培养的人视网膜色素上皮细胞中的表达

目的 观察增生性玻璃体视网膜病变(proliferative vitreoretinopathy,PVR)C、D两级视网膜前膜 (epiretinal membranes, ERM)和培养的人视网膜色素上皮(retinal pigment epithelium, RPE)细胞中肝细胞生长因子受体（hepatocyte growth factor receptor, HGFR）的表达情况。 方法 采用免疫组织化学染色方法对15例复杂孔源性视网膜脱离患者玻璃体切割术中剥离的ERM以及培养的人RPE细胞中HGFR的表达情况进行观察。 结果 在6例PVR C级和9例PVR D级ERM标本中分别有5、7例呈HGFR阳性表达；培养的RPE细胞胞浆中HGFR呈阳性表达。 结论 肝细胞生长因子有可能参与了 PVR的病理过程。 (中华眼底病杂志, 2002, 18: 221-223)     

Proliferative vitreoretinopathy membranes. An immunohistochemical study

Proliferative vitreoretinopathy (PVR) is the leading cause of failure after retinal detachment surgery. Therefore, both the extracellular matrix and cellular components of preretinal membranes from 23 eyes with PVR were characterized immunohistochemically. The membrane stroma was composed primarily of types I, II, and III collagen. Laminin and both heparan sulfate proteoglycans and collagens types IV and V were co-distributed in discrete regions within the stroma. Glial and retinal pigment epithelial (RPE) cell populations were identified in these membranes using specific immunohistochemical markers as was a small but significant macrophage population. Double-labeling experiments indicated that RPE cells in these membranes expressed the class II histocompatibility antigen HLA-DR, although neither the RPE monolayer in situ nor cultured RPE cells was HLA-DR positive unless induced by gamma interferon. Only rare isolated vascular endothelial cells were detected in 5 of the 23 membranes.     

增生性玻璃体视网膜病变的发病机制及治疗研究进展

增生性玻璃体视网膜病变（proliferative vitreoretinopathy,PVR）是孔源性视网膜脱离手术常见的并发症,它是一种由多种细胞成分、玻璃体、细胞外基质以及大量自分泌或旁分泌的细胞因子的混合作用构成的复杂病理反应.胶质细胞、视网膜色素上皮细胞、视网膜色素上皮衍生细胞、成纤维细胞、成纤维细胞样细胞和巨噬细胞被认为在PVR产生的过程中起重要作用.较之PVR中固定成分和细胞组分,细胞因子如色素上皮细胞衍生因子、单核细胞趋化蛋白1、血管内皮生长因子、肿瘤坏死因子α及其受体和血小板衍生生长因子及其受体也不容忽视.PVR相关的细胞生物学和细胞因子机制仍需进一步阐明.在PVR形成之前进行临床干预将是防治本病的研究方向.5-氟尿嘧啶、低分子量肝素、柔红霉素、13顺式维甲酸等对PVR预防和治疗的临床有效性试验研究结果不尽相同.     

Stage specificity of novel growth factor expression during development of proliferative vitreoretinopathy

OBJECTIVE: To compare the relative levels of connective tissue growth factor (CTGF), platelet-derived growth factor alpha (PDGF-AA), and hepatocyte growth factor (HGF) in glial and retinal pigment epithelial (RPE) cells of epiretinal membranes from proliferative vitreoretinopathy (PVR). METHODS: A total of 37 PVR membranes, of various stages, underwent fluorescent immunohistochemisty and confocal laser scanning microscopy to localize CTGF, HGF, and PDGF-AA in RPE and glial cells. RESULTS: Numerous RPE, and relatively fewer glial cells, were found in all stages of PVR. CTGF immunoreactivity increased from early to late stage PVR and was principally expressed by RPE cells in early stage, and by glial cells in late stage PVR. HGF, expressed by both RPE and glial cells, was principally expressed in mid-stage PVR. PDGF-AA, expressed by both cell types, demonstrated a uniform level of staining throughout all stages of PVR. CONCLUSIONS: RPE and glial cells contribute to the expression of CTGF, HGF, and PDGF-AA during PVR, but with specific developmental patterns. PDGF-AA is expressed uniformly throughout all stages of PVR, while HGF expression peaks during mid stage, and CTGF expression is highest during late stage PVR. These results allow for the development of stage-specific therapeutics for PVR that may allow targeting of the early proliferative and/or the late tractional stages of PVR.     

Human retinal pigment epithelial cell cultures: phenotypic modulation by vitreous and macrophages

In proliferative vitreoretinopathy (PVR), retinal pigment epithelial (RPE) cells migrate into the vitreous, where they may acquire a fibroblast-like morphology. Such cells may eventually form contractile periretinal membranes, resulting in traction retinal detachment. Among the environmental influences that could cause this change in RPE phenotype, exposure to vitreous and to macrophages is most obvious, as macrophages are invariably found in epiretinal membranes and precede membrane formation in experimental traction retinal detachment. We initiated studies to define modulation of cultured RPE cell morphology by exposure to vitreous or to macrophage-conditioned media. Vitreous, serum, and albumin alone had no effect on the epithelial appearance of RPE cells in vitro. However, macrophage-conditioned media and vitreous-serum or vitreous-albumin mixtures induced a reversible fibroblast-like appearance in these cells. These findings show that macrophages produce a morphoplastic substance for RPE cells, and suggest that vitreous also contains a factor(s) that affects RPE cell shape, and that requires mediation by serum components.     

Keratinocyte transglutaminase in proliferative vitreoretinopathy

PURPOSE: Proliferative vitreoretinopathy (PVR) is an excessive wound-healing process and the major complication in rhegmatogenous retinal detachment. The present study was designed to investigate the expression of keratinocyte transglutaminase (kTgase) in PVR membranes and retinal pigment epithelial (RPE) cells and to evaluate its expression in response to growth factors known to be increased in PVR disease. METHODS: Distribution of kTgase and its relation to fibronectin have been investigated immunohistochemically. PVR membranes and native and cultured RPE cells were analyzed by RT-PCR for the presence of kTgase mRNA. In vitro, RPE cells were treated with transforming growth factor (TGF)-beta2, basic fibroblast growth factor, interleukin-6, and interleukin-1beta. Expression of kTgase was studied by Northern and Western blot analysis. The effect of connective tissue growth factor (CTGF) silencing on the TGF-beta2-modulated expression of kTgase was investigated by transfection with CTGF small interfering (si)RNA before TGF-beta2 treatment. RESULTS: mRNA expression of kTgase was present in all PVR membranes. Immunohistochemical staining for kTgase showed an inhomogeneous pattern with localized accumulation and little colocalization with fibronectin. Although native RPE cells contained only a basal level of kTgase mRNA, the expression of kTgase was increased under culture conditions and was further enhanced by TGF-beta2 treatment. Silencing of CTGF expression did not attenuate the TGF-beta2-mediated induction of kTgase. CONCLUSIONS: The findings demonstrate that kTgase is present in PVR membranes. Its amount is related to the differentiation state of RPE cells and stimulation by TGF-beta2. TGF-beta2-mediated increase seems to be independent of CTGF.     

Induction of proliferative vitreoretinopathy by a unique line of human retinal pigment epithelial cells

BACKGROUND: The most widely used models of proliferative vitreoretinopathy (PVR) rely on injection of cells into the vitreous of animals. Using retinal pigment epithelial (RPE) cells from human PVR membranes may produce a more accurate model of human PVR. We performed a study to determine whether human RPE cells derived from a single epiretinal membrane (ERM) are capable of inducing the same disease in the rabbit eye, and whether the induced ERMs had cellular components similar to those of human PVR membranes. METHODS: Cells were harvested from a human ERM obtained at surgery for PVR. RPE cells were cultured from the membrane and injected into the right eye of 24 New Zealand albino rabbits. The left eyes served as controls. The eyes were examined by indirect ophthalmoscopy over 4 weeks. The enucleated eyes were then examined by means of microscopy and histochemical analysis. RESULTS: By day 7, PVR had developed in all but 1 of the 24 experimental eyes, with 8 progressing to localized tractional retinal detachment. By day 21, localized tractional retinal detachment had developed in 17 eyes; 1 eye progressed to extensive tractional retinal detachment by day 28. Immunostaining showed that mostly RPE cells, but also myofibroblasts, glial cells and collagen, were present in the newly formed rabbit PVR membranes. INTERPRETATION: Human RPE cells cultured from a PVR membrane appear to be capable of inducing PVR in rabbits. The resultant ERMs are similar to those formed in human PVR and consist mainly of RPE cells.     

IL-10 and antibodies to TGF-beta2 and PDGF inhibit RPE-mediated retinal contraction

PURPOSE: Retinal pigment epithelial (RPE) cells are believed to play a pivotal role in the formation and contraction of epiretinal membranes in proliferative vitreoretinopathy (PVR). In the present study, an organ culture method was used that mimics the contractile stage of PVR, to investigate the contribution of a variety of growth factors in human RPE cell-mediated contraction of the retina. METHODS: Cultured human RPE cells were seeded onto bovine retinal explants. After attachment, cultures received one of the following exogenous growth factors: platelet-derived growth factor (PDGF)-AB, PDGF-BB, basic fibroblast growth factor (bFGF), transforming growth factor (TGF)-beta1, TGF-beta2, or interleukin (IL)-10; or a neutralizing antibody to PDGF and/or TGF-beta2. Control explants were either untreated or received a null antibody. Contraction was assessed by image analysis and expressed as percentage reduction in retinal area. RESULTS: RPE cells produced a more than 50% contraction of the retina after 7 days in untreated samples. PDGF and TGF-beta2 stimulated RPE-mediated contraction by a further 20% at 100 ng/ml. IL-10 decreased contraction by 63%, whereas the other growth factors gave rise to similar contraction to untreated controls. Neutralizing antibodies against PDGF and TGF-beta2 reduced RPE-mediated contraction by up to 70% in comparison with untreated controls. The neutralizing antibodies also inhibited the effects of exogenous PDGF and TGF-beta2 on RPE-mediated contraction of the retina (P < 0.01). CONCLUSIONS: These findings confirm a role for both PDGF and TGF-beta2 in RPE cell-mediated contraction of the retina. Such contraction can be inhibited by neutralizing antibodies against PDGF and TGF-beta2, which, together with IL-10, are putative candidates for therapeutic intervention in PVR.     

增生性玻璃体视网膜病变增生膜再塑型机制的研究

目的 观察不同病程增生性玻璃体视网膜病变（PVR）增生膜中不同细胞成分、细胞外基质（ECM）、基质金属蛋白酶（MMPs）及其抑制剂（TIMPs）随病程变化的规律，探讨PVR增生膜的再塑型机制。 方法 病程2个月至8年的孔源性视网膜脱离伴PVR患者的增生膜手术标本16例，用免疫组织化学方法标记增生膜中视网膜色素上皮（RPE）细胞、胶质细胞等不同的细胞成分，纤维连接蛋白（FN）、层粘连蛋白（l aminin）、Ⅰ～Ⅳ型胶原等不同ECM成分，以及MMPs（MMP2、MMP9）和TIMP1，分析不同病程PVR增生膜中各标记成分的变化以及与病程的相关性。 结果 随PVR病程延长，增生膜中RPE细胞、MMP2、FN表达逐渐减少(P=0.014，P=0.001，P=0.008)， 胶质细胞、Ⅰ、Ⅲ型胶原逐渐增多（P=0.022，P=0.001，P=0.008)，层粘连蛋白和Ⅱ、Ⅳ型胶原均有表达，但不随病程变化。RPE细胞、MMP2、纤维连接蛋白的表达与病程呈负相关，胶质细胞、Ⅰ、Ⅲ型胶原的表达与病程呈正相关；MMP2与FN变化呈正相关。MMP9、TIMP1始终都有表达，但不随病程变化。 结论 在PVR增生膜形成和发展的过程中，增生膜中的RPE细胞、胶质细胞、FN、Ⅰ、Ⅲ型胶原、MMP2参与了PVR的再塑型过程。 (中华眼底病杂志， 2006， 22： 308-312）     

血管内皮生长因子及上皮-间充质转化在增生性玻璃体视网膜病变发病中的作用

增生性玻璃体视网膜病变(PVR)是一种发生在孔源性视网膜脱离(RRD)自然病程中或复位手术后的严重并发症,常常导致患者视力丧失。目前,临床缺乏有效的治疗方法。PVR病理特征是多种细胞在细胞因子的作用下发生的过度炎症反应和异常增生,最终在视网膜表面形成增殖膜及进一步的牵拉性视网膜脱离(TRD)。对PVR发病机制的深入研究将有助于为其治疗寻找有前景的分子靶标。近年研究发现,血管内皮生长因子(VEGF)及视网膜色素上皮(RPE)细胞的上皮-间充质转化(EMT)在PVR发病中发挥着重要作用。本文就VEGF及RPE细胞EMT在PVR发病中的作用,以及二者的相互联动机制进行了总结,以期为PVR的治疗和临床研究提供新的思路。     

增生性玻璃体视网膜病变过程中细胞外基质作用的研究进展

国内外多项有关增生性玻璃体视网膜病变(PVR)的研究结果表明,细胞外基质(ECM)的多种成分参与了PVR的形成,包括ECM结构蛋白、黏附蛋白、抗黏附蛋白、基质金属蛋白酶及其组织抑制因子等.其中,结构蛋白包括胶原、弹力纤维蛋白等,是视网膜前、后及玻璃体腔内形成增生膜的主要的非细胞成分,可以促进增生膜的收缩;黏附蛋白包括纤维连接蛋白、玻璃体连接蛋白、层黏连蛋白等,能促进增生膜中细胞与基质间的黏附,增进视网膜色素上皮的黏附、移行及分化功能等;抗黏附蛋白包括血小板反应蛋白-1、骨连接蛋白、韧连接蛋白等,可促进视网膜色素上皮的移行,促使增生膜再塑形;基质金属蛋白酶及组织抑制因子能降解多种ECM,增加增生膜中血管内皮通透性,促进新生血管的形成等.笔者就其目前国内外有关增生性玻璃体视网膜病变增生膜的研究结果予以综述,以供同道参考.(中华眼科杂志,2008,44:759-763)     

uPA, tPA and PAI-1 mRNA expression in periretinal membranes

PURPOSE: Formation of periretinal membranes occurs in proliferative vitreoretinopathy (PVR) and proliferative diabetic retinopathy (PDR) and includes cell migration, proliferation, extracellular matrix formation and tissue contraction, processes in which plasminogen activation (PA) system is involved. METHODS: Twenty PVR, PDR or pucker membranes were examined to identify the cells with cell specific markers and to detect the expression of urokinase (uPA), tissue-type plasminogen activator (tPA) or plasminogen activator inhibitor-1 (PAI-1) by in situ hybridization and by immunohistochemistry. RESULTS: In PVR, uPA, tPA and PAI-1 were expressed by retinal pigment epithelial (RPE) cells, macrophages or retinal glial cells. In PDR, PA components were also expressed by endothelial cells. Semiquantitative analysis in in situ hybridization and immunohistochemistry results demonstrated no notable differences in uPA, tPA or PAI-1 expression between PDR and PVR membranes. CONCLUSIONS: We conclude that local proteolytic activation is involved in extracellular matrix production both in diabetic and non-diabetic membranes.