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

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.

Visible light induces matrix metalloproteinase-9 expression in rat eye

Up-regulation of matrix metalloproteinase-9 (MMP-9, gelatinase B) in the nervous system has been demonstrated when excitotoxicity-induced tissue remodeling and neuronal death occurs. Induction of MMP-9 by a natural stimulus has not been observed yet. Using RT-PCR and gelatin-zymography we demonstrated MMP-9 induction at transcriptional and protein levels in different structures of the rat eye following over-stimulation with white light. MMP-9 elevation occurred in the retina without reduction in photoreceptor number or major anatomical reorganization. A transient decrease in electroretinogram b-wave indicated the functional recovery. Retrobulbar injection of a broad-spectrum MMP-inhibitor GM6001, slowed the recovery rate of b-wave amplitude. Even room-light applied to dark-adapted awake animals induced MMP-9 increase in the retina, which suggests a role for MMP-9 in physiological functional plasticity of the nervous system, such as light adaptation. This is the first demonstration of MMP-9 induction by a sensory stimulus.

Retinal pigment epithelium produces matrix metalloproteinases after laser treatment

PURPOSE

To evaluate production of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) after panretinal photocoagulation (PRP) of human retinal pigment epithelium (RPE) explants.

METHODS

Treated explants were subjected to substrate zymography to differentiate MMP-2 from MMP-9 and dot immunoblot analysis to quantify MMP-3 and TIMP activity. Tritiated thymidine uptake by RPE cells was measured to document evidence of cellular division in the laser-treated versus control explants.

RESULTS

We detected MMP-2, MMP-3, and TIMP-1. MMP-2 and MMP-3 secretion increased to twice the control values. TIMP decreased until day 4 and then increased by day 6. Tritiated thymidine uptake increased 2.5-fold until day 6, returning to baseline by day 8.

CONCLUSION

PRP disturbs MMP/TIMP balance, inhibiting the initiation and maintenance required for active neovascularization. The efficacy of PRP may be due to changes in the expression pattern of metalloproteinases and inhibitors. This model elucidates the possible contribution of PRP to neovascularization regression by demonstrating the effect of laser on TIMP/MMP balance. The effects of PRP may be much more complex than currently understood and most likely involve more than vascular endothelial growth factor and other ischemia-related factors.

Expression of matrix metalloproteinases and their inhibitors in retinoblastoma

Tumor invasion is the critical step that could lead to metastasis in retinoblastoma (RB), a common childhood cancer. Matrix metalloproteinases (MMPs) degrade extracellular matrix, which is a crucial step involved in various stages of tumor progression, including tumor angiogenesis, tumor growth, and also local invasion and subsequent distant metastasis. We investigated the role of extracellular MMP inducer (EMMPRIN), MMP-2, MMP-9 and tissue inhibitor of metalloproteinases (TIMPs): TIMP-1, TIMP-2 in RB and correlated clinicopathologically. Among 60 tumors, EMMPRIN was expressed in 40 (64%), MMP-2 in 41 (66%), MMP-9 in 38 (61%), TIMP-1 in 35 (56%), and TIMP-2 in 33 (53%) tumors. EMMPRIN was positive (3+) in 13 (39%) out of 33 tumors with invasion and was positive (3+) in only 1 (3%) out of 29 tumors without invasion. MMP-2 (P<0.0001) and MMP-9 (P<0.0001) were significantly positive (3+) in 7 (21%) and 12 (36%) out of 33 tumors with invasion, whereas positive (3+) in 3 (10%) and faint (1+) in 10 (34%) tumors, respectively, out of 29 tumors without invasion. TIMP-1 (P<0.0001) and TIMP-2 (P=0.04) were significantly positive (3+) in 7 (21%) and 10 (30%), respectively out of 33 tumors with invasion, whereas positive (3+) in only 1 (3%) tumor each out of 29 tumors without invasion. Immunoblotting of tumors confirmed the presence of EMMPRIN, MMPs, and TIMPs. In conclusion, both MMPs and TIMPs may be involved RB invasion and EMMPRIN could play a role in up-regulation of MMP-2 in invasive RB.

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.

The activated form of gelatinase B/matrix metalloproteinase-9 is associated with diabetic vitreous hemorrhage

We aimed to investigate the presence and activation status of matrix metalloproteinase (MMP)-2 and MMP-9 in vitreous samples from proliferative diabetic retinopathy (PDR) patients. Paired vitreous and serum samples were obtained from patients undergoing vitrectomy for the treatment of rhegmatogenous retinal detachment (RD) (65 patients) and PDR (67 patients). PDR patients were diagnosed for the presence of hemorrhage and/or patent new vessels. Quantitative assays were performed for vitreous protein content, MMP-2, MMP-9, tissue inhibitor of metalloproteinases-1 (TIMP-1) and hemoglobin. Qualitative evaluation of the MMP-2 and MMP-9 activation status was performed by zymography. Vitreous samples contained proMMP-2 but levels were unselectively related to total protein content. ProMMP-9 and activated MMP-9 levels were significantly increased in PDR patients (p<0.001 for both comparisons). In addition, TIMP-1 levels were significantly increased in PDR patients (p=0.004) and functionally inhibited activation of MMP-9 in vitreous samples. None of the parameters significantly differed between PDR patients with patent new vessels and those with inactive disease. However, activated MMP-9 levels in vitreous samples of PDR patients with hemorrhage (75.7+/-106.3 scanning units per 2 microl) were significantly higher than those in PDR patients without hemorrhage (7.1+/-16.2 scanning units per 2 microl) (p<0.001) and strongly correlated with hemoglobin levels (r=0.7525; p<0.001). Activated MMP-9 was not detected in paired serum samples. We conclude that activated MMP-9 might be involved in hemorrhagic transformation in patients with PDR.

Elevated circulating levels of matrix metalloproteinase-9 in type 1 diabetic patients with and without retinopathy

OBJECTIVE

Tissue expression pattern of matrix metalloproteinases (MMPs) and their inhibitors TIMPs indicate that microvascular complications of diabetes mellitus are associated with extracellular matrix remodelling. We investigated whether circulating levels of MMP-9 and TIMP-1 are altered in diabetic retinopathy and whether they might serve as biological markers of ocular complications in type 1 diabetes.

RESEARCH DESIGN AND METHODS

We recruited 47 type 1 diabetic patients free of vascular complications (n=40) or with retinopathy (n=14). Patients with macroangiopathy, neuropathy and nephropathy were excluded. A group of nondiabetic control subjects (n=35) was also constituted for comparative purposes. Peripheral blood levels of MMP-9 and TIMP-1 were determined using immunoenzymatic assays.

RESULTS

Type 1 diabetic subjects exhibited significantly higher circulating levels of both MMP-9 and MMP-9/TIMP-1 ratio, as well as a tendency to increased serum TIMP-1 levels relative to nondiabetic controls (p<0.001). Diabetic patients with retinopathy also displayed elevated systemic values of MMP-9 and MMP-9/TIMP-1 ratio when compared to patients without retinopathy (p<0.05). Logistic regression analysis identified diabetes duration firstly (P<0.01), and MMP-9 serum levels secondly (P<0.01) as significant and independent variables associated with the existence of retinopathy.

CONCLUSIONS

Our data suggest that peripheral blood MMP-9 levels might serve as surrogate biomarkers of retinopathy in type 1 diabetic patients free of other vascular complications.

What role do extracellular matrix changes contribute to the cardiovascular disease burden of diabetes mellitus?

Matrix metalloproteinases (MMP) and their inhibitors (TIMP) are central factors in the control of extracellular matrix turnover. They are important in normal physiology and also during a range of pathological states. In this review, we have systematically identified clinical articles relevant to cardiovascular disease in diabetes from the last 10 years. Our aim was to outline the structure, function and regulation of metalloproteinases and their key roles in cardiomyopathy and vasculopathy in diabetes. We also explore the effects of drug intervention on both human subjects with diabetes and experimental animal models. The modulation of MMP and TIMP activity using drugs that affect the expression and function of these proteins may provide us with new ways to treat this serious and disabling disease, and we explore potential mechanisms and treatments.

Immunohistochemical study of extracellular matrix components in epiretinal membranes of vitreoproliferative retinopathy and proliferative diabetic retinopathy

PURPOSE

The migration, proliferation, differentiation, and adhesion of cells and other cellular functions are influenced by the surrounding extracellular matrix in normal and wound healing conditions. The formation of epiretinal membranes, a wound healing process, is a serious complication of retinal diseases, the most important being proliferative diabetic retinopathy (PDR) and proliferative vitreoretinopathy (PVR). In the present study, the authors investigated the expression of various extracellular matrix components and in particular tenascin, fibronectin, laminin, collagen IV, and MMP-3 glycoprotein as well as the expression of glial fibrillary acidic protein in each type of epithelial membrane in order to elucidate the role of these molecules in the formation of these two types of membranes.

METHODS

The authors performed immunohistochemistry in 14 PVR and 14 PDR membranes, using antibodies against the above mentioned extracellular matrix components. Tenascin and fibronectin were observed as major components in the extracellular matrix, while laminin and collagen type IV were detected as minor components in both types of membranes. A higher fibronectin expression in PVR compared with PDR membranes was found (p=0.0035). A positive relationship of its expression with the proliferative activity (p=0.15) and collagen type IV expression (p<0.0001) was also observed.

RESULTS

Tenascin expression was positively correlated with glial fibrillary acidic protein positive cells in PDR membranes (p=0.04). Collagen type IV localized around vessels was observed with high levels in PDR membranes (p=0.0031).

CONCLUSIONS

The results indicated that the extracellular matrix components seem to be involved in PVR and PDR, contributing to tissue remodeling and perhaps by different pathogenetic pathways, which could reflect different stages of development in these two types of membranes.

Alterations in peripheral blood levels of TIMP-1, MMP-2, and MMP-9 in patients with type-2 diabetes

BACKGROUND AND AIM

In vivo and in vitro experimental findings indicate that the hyperglycemic diabetic milieu can induce altered expression of the matrix metalloproteinase (MMP) genes and contribute to imbalances in vascular matrix homeostasis. We examined the plasma levels of enzymes and inhibitors involved in extracellular matrix turnover.

METHODS

We measured the plasma concentrations of MMP-2, MMP-9, and tissue inhibitor of metalloproteinase 1 (TIMP-1) in 80 type-2 diabetic subjects without uremia and in 80 age-matched controls. In addition, we determined the plasma levels of intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1) and high sensitive(hs) C-reactive protein (CRP) in both groups.

RESULTS

Plasma MMP-2, TIMP-1, and hs-CRP concentrations were significantly elevated in diabetic patients as compared to the control subjects (p<0.05). Plasma levels of MMP-2, MMP-9, TIMP-1, VCAM-1, ICAM-1, and hs-CRP were found not to be significantly associated with age, duration of diabetes, blood pressure, or serum lipid concentrations.

CONCLUSIONS

Plasma MMP-2, TIMP-1 and hs-CRP concentrations were significantly increased in type-2 diabetic patients.

Matrix metalloproteinases and diabetic vascular complications

Diabetes mellitus (DM) is associated with an increased incidence of cardiovascular events and microvascular complications. These complications contribute to the morbidity and mortality associated with DM. There is increasing evidence supporting a role for matrix metalloproteinases (MMPs) and their inhibitors (tissue inhibitors of matrix metalloproteinases - TIMPs) in the atherosclerotic process. However, the relationship between MMPs/TIMPs and diabetic angiopathy is less well defined. Hyperglycemia directly or indirectly (eg, via oxidative stress or advanced glycation products) increases MMP expression and activity. These changes are associated with histologic alterations in large vessels. On the other hand, low proteolytic activity of MMPs contributes to diabetic nephropathy. Within atherosclerotic plaques an imbalance between MMPs and TIMPs may induce matrix degradation, resulting in an increased risk of plaque rupture. Furthermore, because MMPs enhance blood coagulability, MMPs and TIMPs may play a role in acute thrombotic occlusion of vessels and consequent cardiovascular events. Some drugs can inhibit MMP activity. However, the precise mechanisms involved are still not defined. Further research is required to demonstrate the causative relationship between MMPs/TIMPs and diabetic atherosclerosis. It also remains to be established if the long-term administration of MMP inhibitors can prevent acute cardiovascular events.

Elevated aqueous humour tissue inhibitor of matrix metalloproteinase-1 and connective tissue growth factor in pseudoexfoliation syndrome

BACKGROUND/AIMS

Pseudoexfoliation syndrome (PXF) was recently found to be associated with increased expression of transforming growth factor beta(1) (TGFbeta(1)) in the aqueous humour. As concern has been raised regarding anti-TGFbeta therapy, which can potentially disrupt the maintenance of anterior chamber associated immune deviation, the authors explored the levels of tissue inhibitor of matrix metalloproteinase-1 (TIMP-1), matrix metalloproteinase-9 (MMP-9), and connective tissue growth factor (CTGF) in aqueous humour to determine if these may represent alternative therapeutic targets.

METHODS

Aqueous humour samples were collected from patients who underwent routine cataract surgery. All patients were categorised into three main groups-PXF, uveitis, and control. The PXF group was further subcategorised into three grades based on the density of the exfoliative material observed on biomicroscopy, as well as the presence or absence of glaucoma. TIMP-1, MMP-9, and CTGF levels were measured using specific enzyme immunoassays (ELISA).

RESULTS

Eyes with PXF had significantly higher aqueous humour TIMP-1 concentration (n = 56, mean (SE), 9.76 (1.10) ng/ml) compared with controls (n = 112, 5.73 (0.43) ng/ml, p<0.01). Similarly, the CTGF level in PXF eyes (n = 36, 4.38 (0.65) ng/ml) was higher than controls (n = 29, 2.35 (0.46) ng/ml, p<0.05). Further, the CTGF concentration in the PXF glaucoma group is significantly higher compared with PXF eyes without glaucoma (6.03 (1.09) ng/ml v 2.73 (0.45) ng/ml, p<0.01). The MMP-9 levels were low and below detection limit in all PXF and control samples with no statistical difference between groups.

CONCLUSION

A raised TIMP-1 level and a low MMP-9 level in aqueous humour of PXF eyes may imply a downregulation in proteolytic activity. The increased CTGF concentration supports the proposed fibrotic pathology of PXF. Regulation of MMP/TIMP expression and anti-CTGF therapy may offer potential therapeutic avenues for controlling PXF associated ocular morbidity.

The effects of glucose on the expression of MMP and TIMP in cultured retinal pigment epithelial cells

This study evaluated the effects of glucose in human retinal pigment epithelial (RPE) cells to investigate the cause of diabetic retinal complications. Human RPE cells were cultured in media containing 5.5 mM, 11.0 mM, and 16.5 mM D-glucose. The present study performed proliferation and migration assays, and conducted western blotting for the protein expression, as well as RT-PCR for the mRNA expression, of MMP-2 and -9, and TIMP-1 and -2. The results of the western blotting analysis showed that increasing glucose concentration significantly increased the expression of MMP-2 and -9, but significantly decreased the expression of TIMP-1 and -2. Moreover, the RT-PCR results indicated significant increases in the mRNA expression of MMP-2 and -9, as well as of TIMP-1 and -2, by raising glucose concentration. This study provides fundamental data for future research on the mechanism of retinal complication in diabetic patients.

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.

Expression of ADAMTS metalloproteinases in the retinal pigment epithelium derived cell line ARPE-19: transcriptional regulation by TNFalpha

ADAMTS (A Disintegrin-like And Metalloprotease domain with ThromboSpondin type I motifs) are multidomain proteins with demonstrated metalloproteinase functionality and have potential roles in embryonic development, angiogenesis and cartilage degradation. We present here investigations of ADAMTS expression in an ocular cell type, ARPE-19, with a view to implicating them in retinal matrix turnover. Expression analysis was undertaken using a combination of reverse transcription polymerase chain reaction (RT-PCR) and Northern blotting experiments, which together detected the expression of mRNAs for several ADAMTS proteins, all of which have active site motifs characteristic of matrix metalloproteases (MMPs). These included ADAMTS1, ADAMTS2, ADAMTS3, ADAMTS5, ADAMTS6, ADAMTS7 and ADAMTS9. The expression of mRNA isoforms for ADAMTS7 and ADAMTS9 were also detected. Following stimulation with TNFalpha, ADAMTS1, ADAMTS6 and both ADAMTS9 transcripts expressed in ARPE-19 cells showed a potent upregulation. The expression of ADAMTS genes in ARPE-19 cells and the transcriptional stimulation of some family members by TNFalpha may implicate them in inflammatory eye disease and the compromise of retinal matrix structure, which is evident in age-related macular degeneration (ARMD) and other retinal pathologies.

Evidence for a matrix metalloproteinase induction/activation system in arterial vasculature and decreased synthesis and activity in diabetes

Pathological remodeling characterized by extracellular matrix (ECM) deposition contributes to the diabetic vascular complications. Matrix metalloproteinases (MMPs) regulate ECM turnover. However, the expression profile of the MMP system in diabetic human tissue remains unknown. The objectives of this study were 1) to identify a local MMP induction/activation system that exists in arterial vasculature and 2) to determine how the MMP system may be altered in diabetes. Internal mammary artery specimens were obtained from patients who did (n = 14) and did not (n = 14) have diabetes and were undergoing coronary artery bypass grafting surgery. ECM inducer protein (EMMPRIN); membrane-type MMP (MT-MMP); and MMP-1, -2, and -9 were quantified by immunoblotting and densitometric scanning (pixels). Pro-MMP-1 and MMP-2 levels were decreased from 952 +/- 120 and 1,081 +/- 508 pixels, respectively, in nondiabetic tissue to 398 +/- 62 and 249 +/- 42 pixels in the diabetic tissue (P < 0.05). Both EMMPRIN and MT-MMP expression and total MMP activity were decreased by twofold in diabetic patients (P < 0.05). These results demonstrated for the first time that an MMP induction and activation system exists in human arterial vasculature and that it is downregulated in diabetes. Decreased MMP activity may contribute to increased collagen deposition and pathological remodeling in diabetes.

Matrix metalloproteinase-9 contributes to choroidal neovascularization

Age-related macular degeneration (AMD) is the primary cause of irreversible photoreceptors loss in adult patients and current therapies are limited. Increased levels of matrix metalloproteinases (MMPs) have been documented in neovascularization of severe ocular pathologies such as AMD and proliferative diabetic retinopathy. We report here that MMP-9 (gelatinase B) expression is induced and temporally regulated in the course of experimental choroidal neovascularization. We used transgenic mice expressing beta-galactosidase reporter gene under the dependence of MMP-9 promoter and RT-PCR analysis on choroidal neovascular structures microdissected from serial sections by laser pressure catapulting to show that MMP-9 expression is up-regulated concomitantly with the appearance of inflammatory cells in the subretinal lesion. In mice deficient in MMP-9 expression the development of choroidal neovascularization induced by laser photocoagulation still occurred, but at a reduced level.

Matrix metalloproteinase-9-dependent exposure of a cryptic migratory control site in collagen is required before retinal angiogenesis

Retinal neovascularization is a leading cause of human blindness. However, little is known concerning the molecular mechanisms controlling retinal neovascularization in vivo. Here we provide evidence that exposure of a collagen type IV cryptic epitope detected by monoclonal antibody (mAb) HUIV26, delineates sites of vascular bud formation and represents one of the earliest structural remodeling events required before vessel out-growth. Exposure of these cryptic sites was inhibited in matrix metalloproteinase (MMP)-9-deficient but not MMP-2-deficient mice implicating MMP-9 in their exposure. Retinal endothelial cell interactions with the HUIV26 epitopes induced endothelial cell migration, which was blocked by mAb HUIV26. Importantly, subcutaneous administration of mAb HUIV26 potently inhibited retinal angiogenesis in vivo. Taken together, these findings suggest a novel mechanism in which MMP-9 facilitates exposure of HUIV26 cryptic sites, thereby promoting retinal endothelial cell migration and neovascularization in vivo.

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.