Predominance of MMP-1 and MMP-2 in epiretinal and subretinal membranes of proliferative vitreoretinopathy

Matrix Metalloproteinases in Glaucoma: An Updated Overview

Matrix metalloproteinases (MMPs) are important regulators of the extracellular matrix (ECM) and are involved in many stages of cellular growth and development. An imbalance of MMP expression is also the basis of many diseases, including eye diseases, such as diabetic retinopathy (DR), glaucoma, dry eye, corneal ulcer, keratoconus. This paper describes the role of MMPs in the glaucoma and their role in the glaucomatous trabecular meshwork (TM), aqueous outflow channel, retina, and optic nerve (ON). This review also summarizes several treatments for glaucoma that target MMPs imbalance and suggests that MMPs may represent a viable therapeutic target for glaucoma.

Low-dose rosmarinic acid and thymoquinone accelerate wound healing in retinal pigment epithelial cells

PURPOSE

Thymoquinone (TQ) and rosmarinic acid (RA) are two biologically active compounds found in plants and that possess remarkable anti-oxidant and anti-inflammatory properties. The present study aimed to investigate the potential protective effects of RA and TQ, which have known anti-inflammatory and anti-oxidant effects, on retinal damage by establishing a wound healing model for retinal pigment epithelial cells (ARPE-19).

METHOD

To this end, IC50 doses of RA and TQ in ARPE-19 cells were calculated by MTT assay. Both agents were administered at IC50, IC50/2 and IC50/4 doses for wound healing assay, and wound closure percentages were analyzed. Since the best wound healing was found at IC50/4 dose (low dose) for both agents, other biochemical and molecular analyses were planned to be performed using these doses. Following low dose RA and TQ treatments, the cells were lysed and TGF-β1 and MMP-9 levels were analyzed by ELISA technique from the cell lysates obtained. In addition, the mRNA expression levels of TLR3, IFN-γ and VEGF were calculated by RT-PCR technique.

RESULTS

Low dose of RA and TQ dramatically increased wound healing. RA may have achieved this by increasing levels of MMP-9 and TLR-3. In contrast, the mRNA expression level of VEGF remained unchanged. TQ accelerated wound healing by increasing both the protein levels of TGF-β1 and MMP-9. Furthermore, low dose of TQ decreased both TLR3 and IFN-γ mRNA expression levels.

CONCLUSION

Low doses of RA and TQ were clearly demonstrated to have protective properties against possible damage to retinal pigment epithelial cells.

Matrix Metalloproteinases and Glaucoma

Matrix metalloproteinases (MMPs) are enzymes that decompose extracellular matrix (ECM) proteins. MMPs are thought to play important roles in cellular processes, such as cell proliferation, differentiation, angiogenesis, migration, apoptosis, and host defense. MMPs are distributed in almost all intraocular tissues and are involved in physiological and pathological mechanisms of the eye. MMPs are also associated with glaucoma, a progressive neurodegenerative disease of the eyes. MMP activity affects intraocular pressure control and apoptosis of retinal ganglion cells, which are the pathological mechanisms of glaucoma. It also affects the risk of glaucoma development based on genetic pleomorphism. In addition, MMPs may affect the treatment outcomes of glaucoma, including the success rate of surgical treatment and side effects on the ocular surface due to glaucoma medications. This review discusses the various relationships between MMP and glaucoma.

Matrix Metalloproteinases in Age-Related Macular Degeneration (AMD)

Age-related macular degeneration (AMD) is a complex, multifactorial and progressive retinal disease affecting millions of people worldwide. In developed countries, it is the leading cause of vision loss and legal blindness among the elderly. Although the pathogenesis of AMD is still barely understood, recent studies have reported that disorders in the regulation of the extracellular matrix (ECM) play an important role in its etiopathogenesis. The dynamic metabolism of the ECM is closely regulated by matrix metalloproteinases (MMPs) and the tissue inhibitors of metalloproteinases (TIMPs). The present review focuses on the crucial processes that occur at the level of the Bruch’s membrane, with special emphasis on MMPs, TIMPs, and the polymorphisms associated with increased susceptibility to AMD development. A systematic literature search was performed, covering the years 1990–2020, using the following keywords: AMD, extracellular matrix, Bruch’s membrane, MMPs, TIMPs, and MMPs polymorphisms in AMD. In both early and advanced AMD, the pathological dynamic changes of ECM structural components are caused by the dysfunction of specific regulators and by the influence of other regulatory systems connected with both genetic and environmental factors. Better insight into the pathological role of MMP/TIMP complexes may lead to the development of new strategies for AMD treatment and prevention.

Inflammatory and Fibrogenic Factors in Proliferative Vitreoretinopathy Development

Purpose

Proliferative vitreoretinopathy (PVR) occurs in 5%-10% of rhegmatogenous retinal detachment cases and is the principle cause for failure of retinal reattachment surgery. Although there are a number of surgical adjunctive agents available for preventing the development of PVR, all have limited efficacy. Discovering predictive molecular biomarkers to determine the probability of PVR development after retinal reattachment surgery will allow better patient stratification for more targeted drug evaluations.

Methods

Narrative literature review.

Results

We provide a summary of the inflammatory and fibrogenic factors found in ocular fluid samples during the development of retinal detachment and PVR and discuss their possible use as molecular PVR predictive biomarkers.

Conclusions

Studies monitoring the levels of the above factors have found that few if any have predictive biomarker value, suggesting that widening the phenotype of potential factors and a combinatorial approach are required to determine predictive biomarkers for PVR.

Translational Relevance

The identification of relevant biomarkers relies on an understanding of disease signaling pathways derived from basic science research. We discuss the extent to which those molecules identified as biomarkers and predictors of PVR relate to disease pathogenesis and could function as useful disease predictors. (http://www.umin.ac.jp/ctr/ number, UMIN000005604).

Higher aqueous levels of matrix metalloproteinases indicated visual impairment in patients with retina vein occlusion after anti-VEGF therapy

PURPOSE

To investigate the levels of matrix metalloproteinases (MMPs) in aqueous humour of patients with retinal vein occlusion (RVO) and the relationship between intraocular MMP levels and retinal lesion and visual prognosis.

MATERIALS AND METHODS

52 RVO patients, including 23 with central retinal vein occlusion (CRVO) and 29 with branch retinal vein occlusion (BRVO) and 20 participants with senile cataract were enrolled in this study. Retinal lesions were examined by fundus colour photography, fluorescein fundus angiography and optical coherence tomographic angiography. Sixty microliters of aqueous humour were collected during intravitreal anti-Vascular Endothelial Growth Factor (VEGF) injection or cataract surgery. The aqueous levels of MMP-1, MMP-2, MMP-7, MMP-9 and MMP-10 were measured using the Luminex xMAP multiplex assay. The relationship between MMP levels and clinical presentations was analysed by Pearson correlation test.

RESULTS

The aqueous humour levels of MMP-1, MMP-2, MMP-7 and MMP-9, but not MMP10 in RVO patients were significantly higher than those in people with cataract after adjusting for age. Further analysis of RVO subgroups showed that the aqueous humour level of MMP2 in CRVO was significantly higher than that in BRVO. The aqueous humour levels of MMP-1 and MMP-2 were positively correlated with superficial capillary plexus vessel density (SVD), whereas the aqueous humour levels of MMP-1 and MMP-7 were negatively correlated with visual improvement following treatment. No correlation between aqueous humour levels of MMP and disease duration and central retinal thickness was observed.

CONCLUSIONS

RVO eyes had significantly higher intraocular levels of MMP-1, MMP-2, MMP-7 and MMP-9 than cataract eyes and the level of MMP2 appears to be related to the area of occlusion. Intraocular levels of MMP may positively affect SVD and negatively impact visual function in RVO.

Kaempferol suppresses cell migration through the activation of the ERK signaling pathways in ARPE-19 cells

Kaempferol is a flavonoid with anticancer and anti-metastasis activity in different cancer-cell lines. However, the underlying mechanisms by which kaempferol acts on human retinal pigment epithelial (ARPE-19) cells remain unclear. In this study, we demonstrated that kaempferol inhibited migration and invasion in ARPE-19 cells at non-toxic dosages. We discovered that kaempferol obviously reduced the enzyme activity and protein expression of matrix metalloproteinase-2 by increasing the phosphorylated levels of extracellular signal-regulated kinases 1/2 (ERK1/2) signaling pathways. Additionally, ERK1/2-specific inhibitor PD98059 significantly reversed kaempferol's inhibitory effects on migration and expression of MMP-2 in ARPE-19 cells. Overall, our results are the first to demonstrate that kaempferol is capable of inhibiting cell migration by targeting ERK1/2 signaling in human retinal pigment epithelial cells.

Polarized Secretion of Matrix Metalloproteinases and Their Inhibitors by Retinal Pigment Epithelium Derived from Induced Pluripotent Stem Cells During Wound Healing

PURPOSE

To characterize the secretion of matrix metalloproteinases (MMPs) and tissue inhibitors of matrix metalloproteinases (TIMPs) by induced pluripotent stem cell-derived retinal pigment epithelium (iPS-RPE) during wound healing. We hypothesize that iPS-RPE secretes mediators of tissue remodeling such as MMPs and TIMPs to promote migration and proliferation of cells during wound healing.

METHODS

iPS-RPE was grown on transwells until fully confluent and pigmented. The monolayers were scratched to induce a wound. Conditioned media were collected from the apical and basolateral sides of the transwells every 72 h for 12 days. The media were analyzed by multiplex ELISA assays to detect secreted MMPs and TIMPs. Activity assays were performed to detect the active form of MMP-2 in conditioned media.

RESULTS

MMP-2 and TIMP-1, -2, -3, and -4 were detected in conditioned media from iPS-RPE. The proteins were found to be secreted in a polarized manner. The apical secretion and activation of MMP-2 was elevated from days 3 to 12 after wounding. TIMP-1, -2, -3, and -4 were detected in conditioned media from both the apical and basolateral sides of wounded cells. Apical secretion of all 4 TIMPs increased within 3 days after wounding.

CONCLUSIONS

These results indicate that iPS-RPE secretes MMP-2 and all 4 TIMPs in a polarized manner. After wounding, apical secretion of MMP-2 was higher compared to control. Apical secretion of all 4 TIMPs increased compared to control, while only TIMP-1 showed increased basolateral secretion compared to control.

IGF-1R Regulates the Extracellular Level of Active MMP-2, Pathological Neovascularization, and Functionality in Retinas of OIR Mouse Model

In ischemic proliferative diseases such as retinopathies, persistent hypoxia leads to the release of numerous neovascular factors that participate in the formation of abnormal vessels and eventually cause blindness. The upregulation and activation of metalloproteinases (MMP-2 and MMP-9) represent a final common pathway in this process. Although many regulators of the neovascular process have been identified, the complete role of the insulin-like growth factor 1 (IGF-1) and its receptor (IGF-1R) appears to be significantly more complex. In this study, we used an oxygen-induced retinopathy (OIR) mouse model as well as an in vitro model of hypoxia to study the role of MMP-2 derived from Müller glial cells (MGCs) and its relation with the IGF-1/IGF-1R system. We demonstrated that MMP-2 protein expression increased in P17 OIR mice, which coincided with the active phase of the neovascular process. Also, glutamine synthetase (GS)-positive cells were also positive for MMP-2, whereas IGF-1R was expressed by GFAP-positive cells, indicating that both proteins were expressed in MGCs. In addition, in the OIR model a single intravitreal injection of the IGF-1R blocking antibody (αIR3) administered at P12 effectively prevented pathologic neovascularization, accelerated physiological revascularization, and improved retinal functionality at P17. Finally, in MGC supernatants, the blocking antibody abolished the IGF-1 effect on active MMP-2 under normoxic and hypoxic conditions without affecting the extracellular levels of pro-MMP-2. These results demonstrate, for the first time, that the IGF-1/IGF-1R system regulates active MMP-2 levels in MGCs, thus contributing to MEC remodeling during the retinal neovascular process.

Effect of bradykinin on TGF-β1-induced retinal pigment epithelial cell proliferation and extracellular matrix secretion

Background

To evaluate the effect of bradykinin (BK) on TGF-β1-induced retinal pigment epithelial (RPE) cell proliferation and extracellular matrix secretion and to elucidate the relationship between BK and the Erk/Akt signaling pathway.

Methods

The effects of BK on TGF-β1-induced RPE cell proliferation were examined via CCK-8 assay. Cell culture supernatant collagen I concentrations were measured via ELISA. Fibronectin (Fn), matrix metalloproteinase-2 (MMP-2) and MMP-9 mRNA and protein expression levels were measured via q-PCR and Western blotting, respectively. Changes in Akt/Erk phosphorylation induced by BK and HOE-140 were evaluated via Western blotting.

Results

TGF-β1 stimulated ARPE-19 cell proliferation, which was inhibited by BK, whose effects were inhibited by HOE-140. BK inhibited TGF-β1-induced collagen I, Fn and MMP-2 secretion in RPE cells, and these effects were inhibited by HOE-140. BK also inhibited TGF-β1-induced Akt phosphorylation in RPE cells, and these effects were blocked by HOE-140. BK had no significant effect on Erk-mediated signaling.

Conclusions

The findings from this study indicate that BK could be novel therapeutic targets for the treatment of PVR.

Spontaneous release of epiretinal membrane in a young weight-lifting athlete by presumed central rupture and centrifugal pull

This patient presented for surgery at the age of 32 years, 14 months after his initial complaint of metamorphopsia and visual loss in the right eye. Past tests demonstrated a whitish epiretinal membrane (ERM) with translucent stress lines over a thickened macula. Visual acuity was found on last presentation to be normal with minimal alteration on Amsler grid testing. A torn ERM was found in the center with left-over ERM temporally and rolled-over ERM nasally at the site of the epicenter with no posterior vitreous detachment. Visual recovery occurred gradually over several days 2 months prior to presentation apparently following heavy weight-lifting with a sensation of severe eye pressure. Sequential funduscopy and optical coherence tomography scans demonstrated the peeling of an ERM accompanied by normalization of foveal thickness. Valsalva maneuver had put excessive tension on ERM which tore in its center at the weakest line with gradual contraction of the ERM away from the fovea towards the peripapillary area. This is a new mechanism of self-separation of ERM induced by Valsalva. ERM in young subjects is subject to rupture and subsequent separation by tangential traction. There are three mechanisms for spontaneous separation of ERM: 1) posterior vitreous detachment with pulling of ERM by detaching vitreous (most common in adults); 2) the contracting forces of the immature ERM become stronger than its adhesions to the retina resulting in slow tangential traction on the edges of the ERM and gradual separation from the edges towards the center (remodeling common in youngsters); and 3) acute tearing of ERM at its weakest central point and retraction of part of the membrane towards the epicenter (current case report).

Retinal MMP-12, MMP-13, TIMP-1, and TIMP-2 expression in murine experimental retinal detachment

PURPOSE

Matrix metalloproteinases (MMPs) and their inhibitors play a role in the pathobiology of retinal detachment (RD) and proliferative vitreoretinopathy (PVR). Proliferative vitreoretinopathy is facilitated by chronic retinal detachment and involves excessive deposition of extracellular matrix (ECM) proteins. Matrix metalloproteinase-2 and -13 are important modulators of the ECM which have not been evaluated in RD. The purpose of this study was to investigate the retinal expression of select MMPs, including MMP-12, MMP-13, and associated inhibitors in a murine model of retinal detachment.

METHODS

Transient or chronic retinal detachments (RDs) were induced by subretinal injection of either saline (SA) or hyaluronic acid (HA) in C57BL/6 mice. To confirm that the HA-RD model has features consistent with PVR-like changes, glial activation and subretinal fibrosis were evaluated with immunofluorescence, dilated fundus examination, and spectral-domain optical coherence tomography (SD-OCT). Gene expression was quantified by qRT-PCR. Proteins were assayed by immunoblot and immunohistochemistry.

RESULTS

Hyaluronic acid RD eyes developed gliosis and subretinal fibrosis on dilated exam, SD-OCT, and immunofluorescence analysis. Gene expression of Mmp-12 and Mmp-13, and Timp-1 was strongly upregulated at all time points in RD compared with controls. Timp-2, Mmp-2, and Mmp-9 expression was modest. Hyaluronic acid RDs exhibited more MMP and TIMP expression than SA-RDs. MMP-12, -13, and TIMP-1 proteins were elevated in RDs compared with controls. Immunohistochemistry revealed moderate to strong MMP-13 levels in subretinal space macrophages.

CONCLUSIONS

Fibrosis can develop in the HA-RD model. There is an upregulation of select MMPs that may modulate the wound healing process following RD.

Comparison of interleukin-6 and matrix metalloproteinase expression in the subretinal fluid and the vitreous during proliferative vitreoretinopathy: correlations with extent, duration of RRD and PVR grade

INTRODUCTION

The full extent of IL-6 involvement in PVR pathophysiology has not yet been comprehensively investigated. The aim of this study was the comparison of the IL-6 effect on MMP expression between SRF and the vitreous in the context of RRD complicated by PVR.

MATERIALS AND METHODS

Thirty-one SRF samples from 31 eyes of 31 consecutive patients suffering from RRD with PVR were collected during treatment by scleral buckling. Twenty-eight vitreous samples from 28 eyes of 28 RRD patients with PVR were collected during surgical management with pars plana vitrectomy (PPV). Enzyme Linked Immunosorbent Assay was employed for the measurement of MMP-1, -3, -8 and TIMP-1 concentrations (in ng/ml). MMP gelatinolytic activity was determined with the use of gelatin zymography analysis using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE).

RESULTS

Correlation analysis in the SRF revealed a significant correlation between MMP-1/IL6 and RRD duration. Regression analysis in the SRF revealed a significant correlation between the MMP-9/IL-6 and RRD extent. In the same fluid, with respect to PVR grade, ANOVA revealed a significant relationship with the proMMP-2/IL-6, MMP-2/IL6 and TIMP-1/IL-6 ratios. Graphical representation of the results revealed that, between the SRF and vitreous groups, significant peak values were observed for all MMP/IL-6 and TIMP-1/IL-6 ratios included in this study with the exception of the MMP-2/IL-6 ratio.

CONCLUSIONS

It appears that there is a significant correlation between the presence of IL-6 and MMP/TIMP ratio in the SRF, indicating that IL-6 may contribute to the increased MMP/TIMP ratio during PVR.

Interleukin-6 and matrix metalloproteinase expression in the subretinal fluid during proliferative vitreoretinopathy: correlation with extent, duration of RRD and PVR grade

PURPOSE

To investigate interleukin (IL)-6 protein levels in the subretinal fluid (SRF) of patients with rhegmatogenous retinal detachment (RRD) complicated by proliferative vitreoretinopathy (PVR); to correlate the IL-6 levels with matrix metalloproteinases (MMP)-1, -2, -3, -8, -9 and tissue inhibitor of metalloproteinases (TIMP)-1 with respect to RRD extent, duration and PVR grade.

METHODS

Thirty-one SRF samples from 31 eyes of 31 patients with RRD complicated with PVR and five SRF samples from five eyes of five patients suffering from RRD not complicated with PVR were collected during treatment by scleral buckling. Enzyme-Linked Immunosorbent Assay was employed for the measurement of IL-6, MMP-1, -3, -8 and TIMP-1 levels while the enzymatic activity of MMP-2 and MMP-9 was assessed by gelatin zymography.

RESULTS

Protein levels of IL-6 (p=0.050), MMP-1 (p=0.001), MMP-3 (p=0.005), MMP-8 (p=0.003), TIMP-1 (p=0.001) as well as enzymatic activity of proMMP-2 (p=0.001), MMP-2 (p=0.023) and MMP-9 (p=0.015), were significantly higher in the SRF of PVR patients compared to controls. IL-6 levels correlated significantly with TIMP-1 (r=0.528, p=0.035). Regarding clinical parameters of the detachment, IL-6 levels correlated with RRD extent (r=0.592, p=0.016), but not with RRD duration (p=0.857) and PVR grade (p=0.594). Regression analysis revealed positive correlations between IL-6 and MMP-2.

CONCLUSIONS

There was a significant correlation between IL-6 and TIMP-1 levels in the SRF of PVR patients. The findings of this study are in agreement with relevant studies concerning IL-6 involvement in the modulation of MMP expression and are indicative of IL-6 and MMP activity during PVR, mainly that of MMP-2 and TIMP-1.

Transcriptomic analysis of human retinal detachment reveals both inflammatory response and photoreceptor death

BACKGROUND

Retinal detachment often leads to a severe and permanent loss of vision and its therapeutic management remains to this day exclusively surgical. We have used surgical specimens to perform a differential analysis of the transcriptome of human retinal tissues following detachment in order to identify new potential pharmacological targets that could be used in combination with surgery to further improve final outcome.

METHODOLOGY/PRINCIPAL FINDINGS

Statistical analysis reveals major involvement of the immune response in the disease. Interestingly, using a novel approach relying on coordinated expression, the interindividual variation was monitored to unravel a second crucial aspect of the pathological process: the death of photoreceptor cells. Within the genes identified, the expression of the major histocompatibility complex I gene HLA-C enables diagnosis of the disease, while PKD2L1 and SLCO4A1 -which are both down-regulated- act synergistically to provide an estimate of the duration of the retinal detachment process. Our analysis thus reveals the two complementary cellular and molecular aspects linked to retinal detachment: an immune response and the degeneration of photoreceptor cells. We also reveal that the human specimens have a higher clinical value as compared to artificial models that point to IL6 and oxidative stress, not implicated in the surgical specimens studied here.

CONCLUSIONS/SIGNIFICANCE

This systematic analysis confirmed the occurrence of both neurodegeneration and inflammation during retinal detachment, and further identifies precisely the modification of expression of the different genes implicated in these two phenomena. Our data henceforth give a new insight into the disease process and provide a rationale for therapeutic strategies aimed at limiting inflammation and photoreceptor damage associated with retinal detachment and, in turn, improving visual prognosis after retinal surgery.

Adipokine levels in subretinal fluid from patients with rhegmatogenous retinal detachment

Adipokines have recently emerged as a novel group of mediators with important roles in inflammatory and immune responses and in the process of wound healing. This study investigated the involvement of several adipokines in the future development of proliferative vitreoretinopathy (PVR) following reattachment surgery for rhegmatogenous retinal detachment (RRD). A multiplex immunoassay was used to measure 6 different adipokines in 75 subretinal fluid samples collected during reattachment surgery for primary RRD. Twenty-one patients who developed a redetachment due to postoperative PVR after scleral buckling surgery (PVR group) were compared with age-, sex-, and storage-time-matched RRD samples from 54 patients with an uncomplicated postoperative course (RRD group). Levels of adiponectin (P = 0.006), cathepsin S (P = 0.001), and leptin (P = 0.041) were significantly elevated in the PVR group as compared to the RRD group. Levels of tissue inhibitor of metalloproteinase (TIMP)-1 were significantly lower in the PVR group than in the RRD group (P = 0.044). After correction for diabetes, body mass index (BMI), macular involvement, and preoperative PVR, the association between postoperative PVR development and adiponectin, cathepsin S, and TIMP-1 remained statistically significant (P < 0.05), whereas the significant correlation between PVR and elevated leptin levels was lost (P = 0.068). There were no significant differences in levels of chemerin (P = 0.351) and adipsin (P = 0.915). Of all adipokines investigated, multivariate logistic regression analysis showed that adiponectin was the exclusive predictor of the development of postoperative PVR after scleral buckling surgery (P = 0.003). Our findings indicate that, at the time of surgery for primary RRD, an altered expression of certain adipokines is associated with the future development of postoperative PVR.

Correlation of matrix metalloproteinase levels with the grade of proliferative vitreoretinopathy in the subretinal fluid and vitreous during rhegmatogenous retinal detachment

PURPOSE

We investigated the activity of matrix metalloproteinase (MMP)-2 and -9 and their latent pro-forms (proMMP-2, -9), and protein levels of MMP-1, -3, -8 and tissue inhibitor of MMPs (TIMP)-1 in the subretinal fluid (SRF) and vitreous of patients with rhegmatogenous retinal detachment (RRD). Potential correlations with proliferative vitreoretinopathy (PVR) grade were determined.

METHODS

Thirty-seven SRF and 32 vitreous samples from RRD patients and nine vitreous samples from human organ donors (controls), were collected and assayed for MMP-1, -3, -8/TIMP-1 levels using enzyme-linked immunosorbent assay (ELISA), and for proMMP-2, -9, MMP-2, -9 activity employing gelatine zymography.

RESULTS

ProMMP-2, -9, MMP-1, -3, -9, TIMP-1 were significantly higher in the SRF and vitreous of RRD patients compared to the vitreous of organ donors. MMP-8 levels were higher in RRD patients' SRF. Regarding PVR grade, MMPs and TIMP-1 were differentially present in SRF and vitreous. PVR grade correlated significantly with the levels of MMP-2 in SRF, while proMMP-2, MMP-1, -2, -3, -8, -9 and TIMP-1 levels correlated with PVR grade in the vitreous.

CONCLUSION

MMP/TIMP-1 levels are elevated in SRF and vitreous during RRD. Significant correlations between PVR grade and MMP-2 in SRF and proMMP-2, MMP-1, -2, -3, -8, -9 and TIMP-1 levels in vitreous were revealed. Investigation of MMP activity in vitreous may provide more valid conclusions compared to SRF pertaining to the role of the MMPs during RRD. The observations of the present study suggest a possible role for MMPs and TIMP-1 in PVR pathophysiology.

Interleukin-6 and the matrix metalloproteinase response in the vitreous during proliferative vitreoretinopathy

PURPOSE

To investigate the levels of IL-6 in the vitreous of patients with RRD complicated with PVR and correlate the IL-6 levels with matrix metalloproteinase (MMP)-1,-2,-3,-8,-9 and tissue inhibitor of metalloproteinases (TIMP)-1 with respect to RRD extent, duration and PVR grade.

DESIGN

Cohort study.

PARTICIPANTS

Twenty-eight vitreous samples from 28 eyes of 28 patients with RRD complicated with PVR.

METHODS

Institutional study. Twenty-eight vitreous samples from 28 eyes of 28 patients with RRD complicated with PVR were collected during pars plana vitrectomy (PPV) and were compared to vitreous control samples. IL-6, MMP-1,-3,-8 and TIMP-1 levels were measured using ELISA while enzymatic activity of MMP-2, and -9 was determined employing gelatin zymography.

RESULTS

Protein IL-6 (p=0.030), MMP-1 (p=0.003), MMP-3 (p=0.003), TIMP-1 (p=0.001) levels as well as enzymatic activity of proMMP-9 (p=0.013), MMP-9 (p=0.017) and proMMP-2 (p=0.010), were significantly increased in PVR patients as compared to controls. IL-6 levels correlated with MMP-1 (p=0.002), proMMP-2 (p=0.006), MMP-3 (p=0.001) and TIMP-1 (p=0.006). Regression analysis revealed positive correlations between IL-6 and all MMPs and TIMP-1.

CONCLUSIONS

Taking into account the previously established effect of interleukins in MMP activity, the findings of this study suggest a role of IL-6 in MMP stimulation during PVR development.

Mechanical force enhances MMP-2 activation via p38 signaling pathway in human retinal pigment epithelial cells

BACKGROUND

Rhegmatogenous retinal detachment and proliferative vitreoretinopathy (PVR) are eye diseases that are characterized by mechanical stress involving stretching of the retinal pigment epithelial (RPE) cells by the vitreous or the hyperplastic membranes. Here, we assessed whether mechanical force could change the expression of matrix metalloproteinases (MMPs) in RPE cells via the mitogen-activated protein kinase (MAPK) pathway.

METHODS

Collagen-coated magnetite beads and magnetic fields were used to apply tensile forces to cultured RPE cells at focal adhesions. Activation of the MAPK, including extracellular signal-regulated protein kinase (ERK), c-jun N-terminal kinase (JNK), and p38 were determined over a time course from 5 to 30 min by Western-blot analysis. Activation of p38 was also tested using immunofluorescence staining. The mRNA levels of MMP-2, MMP-9, tissue inhibitor of MMP (TIMP)-2 and fibronectin (FN) were analyzed by RT-PCR. Active MMP-2 and MMP-9 were demonstrated by zymography. MMP-2 secretion was evaluated by enzyme immunoassay.

RESULTS

Stimulation of RPE cells with mechanical stress did not change the total protein expression of the MAPK proteins ERK, JNK, and p38. However, of the three kinases, only active p38 showed an increased protein expression which was also shown by a 2.8-fold increase in immunofluorescence staining at 5 min following mechanical stress stimulation. This increase in active p38 expression was blocked by treating the cells with the p38 inhibitor SB203580. FN mRNA increased 2.4-fold at 15 min and MMP-2 mRNA increased 2.1-fold at 4 h. MMP-2 secretion increased 1.5-fold at 4 h and 1.9-fold at 12 h. The expression of MMP-2 and FN, and the activation and secretion of MMP-2, were inhibited in the presence of SB203580. The mRNA expression of MMP-9 and TIMP-2 did not change throughout.

CONCLUSIONS

This study shows that mechanical stress upregulates MMP-2 and FN expression through activation of the p38 pathway. The increase in MMP-2 levels evoked by mechanical force may contribute to the remodeling of the extracellular matrix around RPE cells, weakening the interlinkage and membrane attachment between RPE cells, and facilitate cellular migration.

Involvement of Müller glial cells in epiretinal membrane formation

BACKGROUND

Proliferative retinopathies are considered to represent maladapted retinal wound repair processes driven by growth factor- and cytokine-induced overstimulation of proliferation, migration, extracellular matrix production and contraction of retinal cells. The formation of neovascular membranes represents an attempt to reoxygenize non-perfused retinal areas. Müller glial cells play a crucial role in the pathogenesis of proliferative retinopathies. This review summarizes the present knowledge regarding the role of Müller cells in periretinal membrane formation, especially in the early steps of epiretinal membrane formation, which involve an interaction of inflammatory and glial cells, and gives a survey of the factors which are suggested to be implicated in the induction of Müller cell gliosis and proliferation.

CONCLUSIONS

Alterations in the membrane conductance of Müller cells suggest that Müller cells may alter their phenotype into progenitor-like cells in the course of proliferative retinopathies; transdifferentiated Müller cells may have great impact for the development of new cell-based therapies.

All-trans retinoic acid remodels extracellular matrix and suppresses laminin-enhanced contractility of cultured human retinal pigment epithelial cells

All-trans retinoic acid (atRA) has been reported to inhibit the proliferation of retinal pigment epithelial (RPE) cells and used in treatment of proliferative vitreoretinopathy (PVR) in animal model. This study aimed at examining the effectiveness of atRA in inhibiting the extracellular matrix (ECM) biosynthesis by RPE cells and the RPE cell-mediated collagen gel contraction. Cultured RPE cells were treated with atRA and the expression of four ECM proteins (collagen types I, III, IV and laminin beta1) was profiled. The results indicated that atRA treatment up-regulated de novo synthesis of collagen type I, but decreased that of laminin beta1 in a dose-dependent manner. Moreover, the effect of atRA on RPE cell contraction was evaluated by measuring the area of collagen gel where RPE cells populated. Treatment with atRA significantly inhibited RPE cell-mediated collagen gel contraction. Addition of exogenous laminin nonapeptide into gels promoted RPE cell contraction, while atRA reversed the laminin-enhanced contractility. atRA treatment significantly suppressed the gene expression of integrin beta3 but not alphaV subunit, and effectively inhibited the tyrosine phosphorylation of integrin beta3 at residue 747 in RPE cells grown on laminin-coated dish, suggesting that atRA may suppress the RPE contractility through either inhibiting integrin beta3 expression or abrogating the integrin beta3-mediated signaling. In conclusion, atRA pharmacologically possesses a tissue-remodeling capacity and inhibits contractility of RPE cells. Therefore, atRA might be potentially a therapeutic agent for certain ocular disorders such as PVR.

Correlation of the extent and duration of rhegmatogenous retinal detachment with the expression of matrix metalloproteinases in the vitreous

BACKGROUND

Investigation of the activity of matrix metalloproteinase (MMP)-2 and -9 and protein levels of MMP-1, -3, -8, and the tissue inhibitor of MMPs (TIMP)-1 in the vitreous of patients with rhegmatogenous retinal detachment (RRD) and establishment of potential correlations of MMPs with clinical parameters.

METHODS

Thirty-two vitreous samples from patients with RRD and 9 vitreous samples from human organ donors (controls) were assayed for MMP-1,-3, -8, and TIMP-1 levels using enzyme-linked immunosorbent assay and MMP-2 and -9 activity employing gelatin zymography.

RESULTS

MMP-1, MMP-3, proMMP-2, proMMP-9, MMP-9, and TIMP-1 were higher in vitreous from patients with RRD as compared to organ donors. Overall, MMPs and TIMPs were differentially expressed in vitreous from RRD with respect to the duration and extent of RRD. Regression analysis for all data indicated that a model consisting of MMP-2 and TIMP-1 could estimate the extent of RRD.

CONCLUSION

Levels of MMPs and TIMP-1 studied are elevated in vitreous during RRD. MMP-2 and TIMP-1 may have a more prominent and persistent role than other MMPs in the wound healing process of the retina during RRD. A regression model consisting of MMP-2 and TIMP-1 may prove to be of potential use in providing information for the evaluation of the extent of RRD.

Expression of matrix metalloproteinases in the subretinal fluid correlates with the extent of rhegmatogenous retinal detachment

BACKGROUND

We investigated the activity of matrix metalloproteinase (MMP)-2 and -9 and the protein levels of MMP-1, -3, -8 and the tissue inhibitor of MMPs (TIMP)-1 in the subretinal fluid (SRF) of patients with rhegmatogenous retinal detachment (RRD) and establishment of potential correlations with clinical parameters.

METHODS

Thirty-seven SRF from RRD patients and nine vitreous samples from the human eye of organ donors (controls) were collected and assayed for MMP-1,-3,-8 and TIMP-1 levels using ELISA and for MMP-2 and -9 activity employing gelatin zymography.

RESULTS

MMP-1, MMP-3, MMP-8, proMMP-2, proMMP-9, MMP-9 and TIMP-1 levels were higher in SRF compared with vitreous fluid. Overall, MMPs and TIMPs were differentially expressed in SRF with respect to duration and extent of RRD, as well as to stage of proliferative vitreoretinopathy. Regression analysis for all data indicated that a model consisting of MMP-3, MMP-8 and proMMP-9 could estimate the extent of RRD.

CONCLUSIONS

MMPs and TIMP-1 levels are elevated in SRF during RRD. A regression model consisting of MMP-3, MMP-8 and proMMP-9 may be proved to be of potential use in providing information for evaluation of the extent of RRD.

Upregulation of RAGE and its ligands in proliferative retinal disease

We sought to study the presence of the receptor for advanced glycation endproducts (RAGE) and its ligands, advanced glycation endproducts (AGEs), S100/calgranulins and amphoterin (high mobility group box 1 protein; HMGB1), in the vitreous cavity and epiretinal membranes (ERMs) of eyes of patients with proliferative diabetic retinopathy (PDR) and proliferative vitreoretinopathy (PVR). Undiluted vitreous specimens were collected from 30 eyes of 30 patients undergoing pars plana vitrectomy for repair of retinal detachment (RD) secondary to PDR (n = 15) or PVR (n = 15). The vitreous samples obtained from 10 eyes undergoing macular hole repair were used as controls. Epiretinal membranes were obtained from eight eyes with PDR and from 10 eyes with PVR. The levels of AGEs in the vitreous were measured using ELISA. The vitreous levels of soluble RAGE (sRAGE), S100/calgranulins and amphoterin were measured using Western blot analyses. The localization of RAGE and its ligands in ERMs was determined with immunohistochemistry. The vitreous levels of sRAGE were significantly increased in both PDR and PVR (p < or = 0.05) compared to control vitreous. In both PDR and PVR, the vitreous levels of AGEs (p < or = 0.01), S100/calgranulins (p < or = 0.05), and amphoterin (p < or = 0.01) were also elevated compared to control eyes. Expression of RAGE was detected in six of eight ERMs from eyes with PDR and eight of 10 ERMs from eyes with PVR. Many cells expressing RAGE also expressed vimentin, suggesting a glial cell origin. Ligands for RAGE were also detected in ERMs, with AGEs detected in five eyes with PDR and eight eyes with PVR. Similarly, S100 and amphoterin ERM expression was observed in six eyes with PDR; these ligands were also expressed in ERMs from eyes with PVR (8 and 7 cases, respectively). We conclude that RAGE and its ligands are increased in the vitreous cavity of eyes with PDR and PVR and are present in ERMs of eyes with these proliferative retinal disorders. These findings suggest a role for the proinflammatory RAGE axis in the pathogenesis of proliferative retinal diseases.

rd1 mouse retina shows imbalance in cellular distribution and levels of TIMP-1/MMP-9, TIMP-2/MMP-2 and sulfated glycosaminoglycans

BACKGROUND

The rd1 mouse retina displays fast degeneration of photoreceptors resulting in a depletion of almost all rod photoreceptors by postnatal day 21 (PN21). To evaluate the role of proteinases in the pathophysiology of this animal model of retinitis pigmentosa, C3H rd1 and congenic wild-type (wt) mice retinas were analyzed.

MATERIAL AND METHODS

The cellular localization and levels of proteins, matrix metalloproteinases (MMPs), their endogenous inhibitors (TIMPs), total sulfated glycosaminoglycans (sGAG) and nature of saccharides in rd1 and wt retinal extracts were compared.

RESULTS

MMP-2/TIMP-2 and MMP-9/TIMP-1 were predominantly localized in the interphotoreceptor matrix (IPM) of both genotypes, but MMP-2/TIMP-2 also appeared in the Muller cell fibers of rd1 retina. In rd1 retinal extracts the levels of total proteins were lower and those of active MMP-9, MMP-2, TIMP-1 and total sGAG were higher than those of wt extracts. Despite an increase in TIMP-1, active MMP-9/MMP-2 were disproportionately elevated in rd1 compared to wt retina. With increasing age, MMPs in wt retinas were decreased but were increased in rd1. The sialylation of proteoglycans in PN2 and PN7 rd1 retinas was lower, and galactosylation was higher than that in wt retinas.

CONCLUSIONS

MMP-9/MMP-2 and TIMP-1/TIMP-2 are associated with IPM, possibly after secretion by retinal pigmented epithelial cells. In degenerating rd1 retina, MMP-2/TIMP-2 are associated with the Muller cell fibers, which apparently play a central role in modifying the balance between MMPs and TIMPs. Elevated sGAG and proteolysis due to an imbalance in the levels of TIMPs and active MMP-9/MMP-2 in rd1 retina possibly contribute to retinal degeneration in the rd1 mouse.

The activation of IL-8 receptors in cultured guinea pig Müller glial cells is modified by signals from retinal pigment epithelium

Interleukin 8 (IL-8, CXCL8) is a pro-inflammatory chemokine which attracts neutrophils to sites of inflammation via an activation of the G-protein-coupled receptors, CXCR1 and CXCR2. However, both IL-8 and IL-8 receptors are widely expressed in various tissues and cell types, and have been suggested to be involved in other functions such as angiogenesis, tumor growth, or brain pathology. We examined the expression of IL-8 and IL-8 receptors in highly enriched primary cultures of guinea pig Muller glial cells. Immunoreactivity for CXCL8, CXCR1 and CXCR2 was observed in all cultured Muller cells. The expression of CXCL8 was confirmed by PCR, and the secretion of the CXCL8 protein from Muller cells was revealed by ELISA. Western blots showed prominent bands at approximately 40 kDa by using antibodies specific for human CXCR1 and CXCR2, and the expression of a putative CXCR2 receptor in Muller cells was confirmed by PCR. Furthermore, cultured Muller cells responded to application of recombinant human IL-8 with an increase of the cytosolic Ca(2+) concentration. If supernatants of cultured human retinal pigment epithelium (RPE) cells were applied to the Muller cell cultures, no obvious changes were observed in the CXCL8, CXCR1 and CXCR2 expression but (i) Muller cell proliferation was stimulated, and (ii) there was an increased number of CXCL8-responsive Muller cells and the amplitudes of the evoked calcium responses were enhanced. It is concluded that Muller glial cells may participate in the inflammatory response(s) of the retina during ocular diseases, and that this contribution may be modified by interactions with RPE cells.

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.

Growth factors and protein kinase C inhibitors as novel therapies for the medical management diabetic retinopathy

Diabetic retinopathy is a leading cause of acquired visual loss. Current treatment modalities are not effective in all cases and may have side effects. Investigation of the biochemical basis of diabetic retinopathy suggests that future treatments may reverse or halt the progression of diabetic retinopathy, or actually prevent the development of diabetic retinopathy. Pharmacological manipulation of protein kinase C and various growth factors may form the basis of future treatments for diabetic retinopathy.

Temporal and spatial expression of matrix metalloproteinases during wound healing of human corneal tissue

Our understanding of MMP expression during corneal repair has previously relied upon animal models, isolated human biopsy specimens and cell culture studies. The aim of this study was to determine the temporal and spatial expression of matrix metalloproteinases following wounding of cultured human corneal tissue. Human corneas were cultured and cut into six pieces. The epithelium was removed with a corneal brush. The tissue was then re-cultured and tissue pieces were fixed up to 7 days post-wounding. Matrix metalloproteinases were detected by in situ hybridisation and immunohistochemistry. Intracellular laminin-5, a marker of migratory epithelial cells, was located immunohistologically. In the time scale studied tissue series from nine corneas achieved coverage of the stroma with epithelial cells and partial repair of damaged basement membrane, demonstrated by the Periodic acid-Schiff reaction and haematoxylin and eosin counter-staining. By day 3, migrating epithelial cells and stromal cells beneath the wounded area expressed collagenase-1 (MMP-1). Stromelysin-1 (MMP-3) was expressed only by fibroblast-like stromal cells. Stromelysin-2 (MMP-10) was detected in migrating epithelial cells and remained when the stroma was surrounded by a monolayer of epithelial cells. By day 7, development of multi-layered epithelium around the tissue coincided with cessation of MMP expression in both epithelial and stromal cells, except for MMP-9, which remained in epithelial basal cells. Tissue inhibitor of matrix metalloproteinase-1 was mainly associated with stromal cells and was reduced upon formation of a multi-layered epithelium. This study demonstrates matrix metalloproteinase expression in epithelial and fibroblast-like cells following wounding of human corneal tissue in culture where the cells remain in contact with their natural matrices.

Pathobiology of epiretinal and subretinal membranes: possible roles for the matricellular proteins thrombospondin 1 and osteonectin (SPARC)

Epiretinal and subretinal membranes are fibrocellular proliferations which form on the surfaces of the neuroretina as a sequel to a variety of ocular diseases. When these proliferations complicate rhegmatogenous retinal detachment (a condition known as proliferative vitreoretinopathy or PVR), the membranes often contain numerous retinal pigment epithelial (RPE) cells and a variety of extracellular proteins. The extracellular proteins include adhesive proteins like collagen, laminin and fibronectin. In addition, several matricellular proteins with potential counter-adhesive functions are present in the membranes. Two such matricellular proteins, thrombospondin 1 and osteonectin (or SPARC: Secreted Protein Acidic and Rich in Cysteine), tend to be co-distributed with the RPE cells in PVR membranes. By virtue of their counter-adhesive properties, thrombospondin 1 and SPARC may reduce RPE cell-matrix adhesion and so permit key RPE cellular activities (for example, migration or shape change) in periretinal membrane development. Furthermore, within a 'cocktail' containing other proteins such as the metalloproteinases and growth factors like the scatter factor/hepatocyte growth factor family, matricellular proteins may play a role in the RPE cell dissociation from Bruch's membrane, which characterises early PVR.

Differential expression of matrix metalloproteinases 2 and 9 by glial Müller cells: response to soluble and extracellular matrix-bound tumor necrosis factor-alpha

Glial Müller cells are known to undergo functional and morphological changes during retinal proliferative disorders, but very little is known of the contribution of these cells to extracellular matrix deposition during retinal wound healing and gliosis. This study constitutes the first demonstration that retinal Müller cells express two major matrix metalloproteinases (MMPs), gelatinase A (MMP-2) and gelatinase B (MMP-9), implicated in cell migration and matrix degradation. Although mRNA and gelatinolytic activity of MMP-2 remained unchanged in cultured Müller cells, basal levels of MMP-9 mRNA observed after subculture at 24 hours, markedly declined after 48 or 72 hours. This correlated with the expression of MMP-9 gelatinolytic activity that peaked at 24 hours, but gradually decreased at 48 and 72 hours. Tumor necrosis factor-alpha, in both a soluble form or bound to collagen and fibronectin, increased MMP-9 mRNA and gelatinolytic activity, but not MMP-2 expression, and its effect could be blocked by anti-tumor necrosis factor-alpha antibodies. The results suggest that Müller cells may aid in the local control of extracellular matrix deposition during retinal proliferative disorders, and that interaction of these cells with matrix-bound cytokine may influence their pathological behavior. Control of Müller cell production of MMP-9 may constitute an important target for the design of new therapeutic approaches to treat and prevent retinal proliferative disease.

MMPs in the eye: emerging roles for matrix metalloproteinases in ocular physiology

Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes that function to maintain and remodel tissue architecture. Their substrates represent an astounding variety of extracellular matrix components, secreted cytokines and cell surface molecules, and they have been implicated in a wide range of processes and diseases. To date MMPs have been found in virtually every tissue of the eye under conditions of health and disease. Although their functions in vivo remain poorly understood, it is clear they impact on essentially every aspect of eye physiology. This chapter reviews the expanding literature on MMPs in the eye and attempts to place it in the context of basic MMP biology. A general overview of MMP functions is presented first, and then the discussion moves to examples of possible MMP roles in two eye structures. For the cornea, we present recent work on the roles of MMPs during various aspects of wound healing. For the retina, we describe the activities of MMPs in specific disease states from which common principles may emerge.

Matrix metalloproteinases: a role in the contraction of vitreo-retinal scar tissue

The most common cause of failure of retinal reattachment surgery is formation of fibrocellular contractile membranes on both surfaces of the neuroretina. This intraocular fibrosis, known as proliferative vitreoretinopathy, results in a blinding tractional retinal detachment because of the contractile nature of the membrane. Contractility is a cell-mediated event that is thought to be dependent on locomotion and adhesion to the extracellular matrix. Interactions between cells and the extracellular matrix can be influenced by matrix metalloproteinases (MMPs) and we investigated the role of MMPs in two in vitro models (two- and three-dimensional) of human retinal pigment epithelial (RPE) cell-mediated contraction. MMP activity was detected using enzyme-linked immunosorbent assays and zymography techniques that revealed MMP-1, -2, -3, and -9 positivity during the collagen matrix contraction assays. RPE-populated collagen matrix contraction (three-dimensional) was inhibited using a cocktail of anti-MMP antibodies and with Galardin (a broad-spectrum MMP inhibitor). Galardin inhibition was dose-dependent, reversible, and dependent on cell number. MMP inhibitors had no effect on contraction when RPEs were seeded on two-dimensional collagen matrices or on cellular adhesion to collagen type I. Our results suggest that MMP activity may be required for three-dimensional but not two-dimensional RPE-collagen matrix contraction.

Matrix metalloproteinases and their natural inhibitors in fibrovascular membranes of proliferative diabetic retinopathy

AIM

To examine epiretinal membranes of proliferative diabetic retinopathy (PDR) for the presence of selective matrix metalloproteinases (MMPs) and their natural inhibitors (TIMPs), in order to determine whether neovascularisation and fibrosis, characteristic of this complication of diabetes mellitus, are associated with specific anomalies of MMP or TIMP expression.

METHODS

The presence of selected MMPs and TIMPs was investigated in 24 fibrovascular epiretinal membranes of PDR, and the findings compared with that observed in 21 avascular epiretinal membranes of proliferative vitreoretinopathy (PVR) and five normal retinas. Specimens were examined for deposition of interstitial collagenase (MMP-1), stromelysin-1 (MMP-3), gelatinase A (MMP-2), gelatinase B (MMP-9), and three tissue inhibitors of metalloproteinases (TIMP-1, TIMP-2, and TIMP-3).

RESULTS

The results showed that unlike normal retina, which constitutively expresses MMP-1 and TIMP-2, a large proportion of PDR membranes (> 62%) stained for MMP-1, MMP-2, MMP-3, MMP-9, TIMP-1, TIMP-2, and TIMP-3. There were no differences in the expression of these molecules when compared with PVR membranes. A characteristic staining for MMP-9 was observed within the perivascular matrix of PDR membranes, and there was a significant increase in TIMP-2 expression by PDR membranes (p= 0.036) when compared with PVR membranes.

CONCLUSIONS

The findings that MMPs involved in degradation of fibrovascular tissue matrix, as well as TIMP-1 and TIMP-2, are found in a large proportion of PDR membranes, and that their expression does not differ from that of PVR membranes, suggest the existence of common pathways of extracellular matrix degradation in pathological processes leading to retinal neovascularisation and fibrosis.