Tissue inhibitor of metalloproteinase 4 in aqueous humor of patients with primary open angle glaucoma, pseudoexfoliation syndrome and pseudoexfoliative glaucoma and its role in proteolysis imbalance
BMC Ophthalmology
Tissue inhibitor of metalloproteinase 4 in aqueous humor of patients with primary open angle glaucoma, pseudoexfoliation syndrome and pseudoexfoliative glaucoma and its role in proteolysis imbalance
Nikitas Fountoulakis 0 1
Georgios Labiris 0 1
Antonios Aristeidou 0 1
Andreas Katsanos 2
Ioannis Tentes 3
Alexandros Kortsaris 3
Vassilios P Kozobolis 0 1
0 Eye Institute of Thrace , Alexandroupolis , Greece
1 Department of Ophthalmology, Democritus University of Thrace , Alexandroupolis , Greece
2 Department of Ophthalmology, University of Ioannina , Ioannina , Greece
3 Department of Biochemistry, Democritus University of Thrace , Alexandroupolis , Greece
Background: To quantify the levels of tissue inhibitor of metalloproteinase 4 (TIMP4) and its ratios with free metalloproteinases (MMP) in the aqueous humor of patients with primary open angle glaucoma (POAG), pseudoexfoliation syndrome (PXS) and pseudoexfoliative glaucoma (PXG) and to evaluate a possible imbalance between MMPs and TIMPs in these samples. Methods: Free MMP2, MMP3, MMP9, TIMP1, TIMP2, TIMP4 concentrations and active levels of MMP2 and MMP3 were determined with immunoassay ELISA and activity assay kits in 168 aqueous samples. Results: TIMP4 was elevated in glaucoma patients(POAG: 0.95 0.49 PXG: 1.28 1.38 pg/ml. p < 0.001). POAG, PXS and PXG samples demonstrated higher MMP2, TIMP1 and TIMP2 concentrations (p < 0.001). Samples from the PXS and PXG groups had a lower total/active MMP2 ratio (p < 0.004 and p < 0.008 respectively). Stoichiometric analysis showed an overbalance of TIMPsover MMPs in both POAG & PXG groups,especially of TIMP4. Conclusion: TIMP4 elevation is a novel finding in glaucomatous eyes. A disregulation of extracellular matrix homeostasis is suggested in POAG, PXS and PXG.
Glaucoma; Pseudoexfoliation; Metalloproteinases; TIMP4; TIMP/MMP ratios
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Background
The most important risk factor for the development and
progression of glaucoma is the elevation of the intraocular
pressure (IOP) [1]. IOP regulation is directly associated
with aqueous humor outflow. Although the exact
mechanism has not been thoroughly elucidated, studies have shown
that the main resistance to the aqueous humour outflow is
located at the trabecular meshwork (TM), especially the
juxtacanalicular part directly underneath the inner wall of
Schlemms canal [2,3]. The special characteristics of the
extracellular matrix and the cell interactions in this region
can potentially determine the outflow facility [4].
In glaucoma, the normal architecture and function of
the juxtacanalicular TM is altered by the pathological
accumulation of connective tissue and the partial loss of
endothelial cells [5,6]. Other local factors such as the
expression of vasoconstrictive molecules and oxidative
stress may also be involved [7,8].
Pseudoexfoliation syndrome (PXS) is an age-related
systemic disorder characterized by the abnormal accumulation
of extracellular matrix (ECM) material in extraocular and
ocular tissues. The pseudoexfoliative material might
congest the outflow pathways of the TM contributing to the
elevation of the IOP and may be involved in the
development of pseudoexfoliative glaucoma (PXG) [9,10].
ECM remodeling is primarily controlled by
endogenous enzymes, known as matrix metalloproteinases
(MMPs). MMPs are a family of endopeptidases that
contain an active Zn2+ site which is responsible for their
enzymatic activity [11]. They are synthesized as
proenzymes and secreted as inactive molecules which are
activated in vivo by disruption of the cystein-Zn link
[11,12]. The regulation of the proteolytic activity of
MMP is mainly controlled by the presence of tissue
inhibitors of MMPs (TIMPs) which bind MMPs in a 1:1
stoichiometry [13]. Four TIMPs have been identified in
vertebrates which can inhibit the action of MMPs. All
TIMPs except TIMP3 are in soluble form [13,14]. In
biological fluids, MMPs are found either as free proforms,
activated enzymes or as complexes with TIMPs.
It is well documented that MMPs and TIMPs play an
important role in many ocular pathological processes,
including glaucoma [15]. In vitro and in vivo studies
have shown that MMPs in TM directly control outflow
resistance [16]. Their presence in aqueous humor has
also been established [17,18]. Moreover, the recently
identified TIMP4, which is associated with MMP
inhibition along with other biological processes such as
apoptosis [19], has never been traced or quantified in the
aqueous humor.
Within this context, the objectives of this study were:
a) to trace and estimate the levels of TIMP4 in the
aqueous humor, b) to investigate the ratios of TIMP4 to
other free MMPs and TIMPs in the aqueous humor, and
c) to investigate the potential imbalance of free forms of
MMPs and TIMPs in eyes with POAG, PXS and PXG.
Methods
Setting
This was a clinic-based, cross-sectional study. The protocol
adhered to the tenets of the Helsinki Declaration and
written informed consent was given by (...truncated)