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(Investigative Ophthalmology and Visual Science. 2006;47:953-963.)
© 2006 by The Association for Research in Vision and Ophthalmology, Inc.
DOI:  10.1167/iovs.05-0516
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Analysis of Expression of Matrix Metalloproteinases and Tissue Inhibitors of Metalloproteinases in Human Ciliary Body after Latanoprost

Dong-Jin Oh,1,2 Jonathan L. Martin,1 Adrienne J. Williams,1 Rachel E. Peck,1 Corinna Pokorny,1 Paul Russell,3 David E. Birk,4 and Douglas J. Rhee1,2,4

1From the Laboratory for Molecular Ophthalmology, Wills Eye Hospital, Philadelphia, Pennsylvania; the 2Department of Ophthalmology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts; the 3Section on Aging and Ocular Disease, National Eye Institute, National Institutes of Health, Bethesda, Maryland; and the 4Department of Pathology, Anatomy and Cell Biology, Thomas Jefferson University, Philadelphia, Pennsylvania.


   Abstract
Top
 Abstract
Materials and Methods
 Results
 Discussion
 References
 
PURPOSE. To determine the effect of latanoprost on the expression of human matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) in the ciliary body.

METHODS. Total RNA was isolated, and qualitative RT-PCR was performed to detect the mRNA of MMPs and TIMPs in human ciliary body tissue and explant cultures of ciliary body smooth muscle (CBSM) cells. CBSM cell cultures were treated with vehicle control or latanoprost acid for 24 hours. Quantitative RT-PCR of cell cultures from five different donors was performed to determine relative changes in expression. GAPDH served as an endogenous control.

RESULTS. The mRNA of MMP-1, -2, -3, -11, -12, -14, -15, -16, -17, -19, and -24 as well as TIMP-1 to -4 were found in ciliary body tissue and CBSM cells. MMP-9 was present after latanoprost treatment. In control CBSM cells, the relative expression of MMP mRNA was MMP-2 and -14 > MMP-24 > MMP-1, -11, -15, -16, and -19 > MMP-3 and 17, > MMP-12. The relative expression of TIMP mRNA was TIMP-2 > TIMP-1 > TIMP-3 > TIMP-4. Latanoprost increased MMP-3 (in three of five cultures), MMP-17 (in four of five cultures), and TIMP-3 (in all five cultures); MMP-1, -2, -12, -14, -15, and -16 and TIMP-4 were downregulated.

CONCLUSIONS. The transcription of the genes for MMP-3 and -17 is increased by latanoprost treatment. MMP-9 is present after latanoprost treatment and may also mediate ECM changes. TIMP-3 is upregulated and may compensate for the increase in MMPs. These coordinated changes could be expected to mediate the latanoprost-induced alteration of ECM in the ciliary body.

In the United States, glaucoma is the second leading cause of irreversible visual impairment.1 2 3 The only rigorously validated treatment in humans is the lowering of intraocular pressure (IOP).4 5 6 7 8 9 Latanoprost is a most effective topical IOP-lowering medication.10 11 12

Latanoprost lowers IOP by increasing uveoscleral outflow up to 60%.13 14 15 16 17 The increased facility of outflow is believed to be the result of increased space around ciliary body smooth muscle (CBSM) cells caused by a PGF2{alpha} analogue–mediated alteration of the extracellular matrix (ECM) after 4 to 8 days of treatment.18 19 The increased ECM turnover in the ciliary body (CB) is thought to be the result of increased expression and release of matrix metalloproteinases (MMPs) by CBSM cells.

MMPs are zinc-dependent endopeptidases that are collectively capable of degrading many ECM components.20 To date, there are at least 21 unique MMPs divided into five subfamilies in humans: collagenases, stromelysins, gelatinases, membrane-type (MT)-MMPs, and miscellaneous others.21 Although there is significant substrate overlap, the subfamilies of MMPs are defined by the their ability to degrade certain ECM components. Five MMPs (i.e., MMP-1, -2, -3, -9, and -14) and three tissue inhibitors of matrix metalloproteinases (TIMPs; i.e., TIMP-1, -2, and -3) have been described in the CB, whereas only four MMPs (i.e., MMPs -1, -2, -3, and -9) and two TIMPs (i.e., TIMP-1 and -2) have been studied with regard to their response to latanoprost.22 23 24 25 26 MMPs can be regulated at transcription, translation, and activation and through inhibition at the active site by TIMPs. For most MMPs, with the notable exception of MMP-2, transcriptional regulation and kinetic inhibition by TIMPs predominate.20

TIMPs are kinetic inhibitors of MMP enzymatic activity and, in some cases, are involved in the activation of MMPs from their inactive zymogen form to their active form. TIMP-2, 3, and -4 can bind pro-MMP-2, whereas TIMP-1 and -3 can bind pro-MMP-9.27 Four mammalian TIMPs have been described. All four bind all known activated MMPs, although TIMP-1 poorly inhibits MMP-14, -15, -16, -19, and -24.27 28

In many tissues, the ratio of MMPs to TIMPs ultimately determines the rate of ECM turnover.29 30 31 32 33 34 35 36 37 Our long-term goal is to determine the MMP-to-TIMP ratios that are associated with the observed increased uveoscleral outflow. In this investigation, we determined the presence of transcripts of MMPs and TIMPs expressed at baseline and determined the relative changes in transcription after incubation with latanoprost in human CBSM cells, to ascertain which MMPs and TIMPs are critical in regulating outflow resistance.


   Materials and Methods
Top
 Abstract
 Materials and Methods
Results
 Discussion
 References
 
Tissue and Explant Culture
All ciliary bodies were dissected from human donor corneoscleral buttons harvested within 12 hours after death. The corneoscleral buttons were removed by the Lyons Eye Bank of Delaware Valley (Philadelphia, PA) and stored (Optisol-GS; Bausch & Lomb Surgical, Irvine, CA) in accordance with the guidelines set forth in the Declaration of Helsinki. We have shown the suitability of corneoscleral buttons for molecular biological studies.38 The CB tissue was dissected from the anterior segment and placed in –80°C for no longer than 2 weeks before isolation of RNA. We isolated CB tissue from 23 separate individuals ages, 23 to 84 years. Ages of the donors of the CB tissue samples to determinate the presence of MMPs and TIMPs were 26, 46, 49, 50, 51, 52, 54, 59, 60, 64, 66, 69, and 84 years. Explant cultures of CBSM cells from the CBs of separate donors, ages 23, 40, 43, 44, 46, 54, 60, 63, 64, 65, and 69, were used to determine the presence of transcripts of MMPs and TIMPs, and cultures from donors aged 23, 40, 52, 54, 56, 64, and 65 years were used for quantitative reverse transcription-polymerase chain reaction (qRT-PCR).

CBSM cells were cultured according to a previously published protocol.39 The cultures were maintained in Dulbecco’s modified Eagle’s medium (DMEM; BioWhittaker; Walkersville, MD) containing 20% fetal bovine serum, 1% L-glutamine (2 mM), and gentamicin (0.1 mg/mL; all from Gibco-Invitrogen, Carlsbad, CA) at 37°C in 10% CO2. Cell identity-confirmatory immunohistochemistry, labeling with anti-desmin and anti-smooth muscle actin antibodies, of our cultured cells was consistent with CBSM cells.39 All the cells used were from passage-4 cultures.

Latanoprost Incubation
Stock solutions of 10 mM latanoprost free acid (Cayman Chemical, Ann Arbor, MI) were prepared in ethanol and diluted to experimental concentrations with serum-free medium. CBSM cells (1 x 106) were plated into T-75 flasks and allowed to grow to confluence. Once confluent, the cultures were maintained for 1 week. The cells were then incubated with serum-free medium for 48 hours and then exposed to ethanol (0.06%, the vehicle control), 0.03, 0.3, and 30 µg/mL of latanoprost free acid for 24 hours. In studies of human uveal and cutaneous melanoma cell lines, concentrations of 10 µg/mL reliably showed changes in tyrosinase and cyclic AMP levels. We chose 30 µg/mL in the event that no trend was observed at 0.03 or 0.3 µg/mL, to see the trend at a dose far in excess of the pharmacological one.40 In practice, latanoprost is given as a 0.005% (50 µg/mL) topical solution, resulting in a peak aqueous concentration of latanoprost free acid of 78 nM (0.028 µg/mL, 28 ng/mL) 1 to 2 hours after administration (the half-life in aqueous humor is 2 to 3 hours).41 The cells were then scraped for RNA extraction.

RNA Isolation
RNA was extracted (RNAqueous-4PCR kit; Ambion, Austin, TX) in accordance with the manufacturer’s protocol. Briefly, the tissue (or cell pellet) was lysed with a guanidinium thiocyanate-containing buffer to inactivate RNase and then homogenized. Total RNA was isolated using a spin column (i.e., a silica-gel membrane). The RNA was then treated with DNase I for 25 minutes in a 37°C water bath, to remove DNA contaminants. Purity and concentration of the RNA was tested by spectrophotometry (BioMate 5 Spectrophotometer; Thermo Spectronic, Madison, WI).

RT-PCR and Sequencing of PCR Product
To determine the presence of MMPs and TIMPs, qualitative RT-PCR was performed on total RNA isolated from CB tissue and untreated explant cultures of CBSM cells (SuperScript One-Step RT-PCR with the Platinum Taq System; Invitrogen) in accordance with the manufacturer’s protocol. RT-PCR was initially performed with oligonucleotide primers previously published in the literature (Table 1) specific to the mRNA of the MMP or TIMP of interest. Two tubes were run in parallel, with the second tube containing only polymerase (Platinum Taq; Invitrogen), to assure that the source of the RT-PCR product was mRNA. For each reaction, 100 ng of template RNA was used (200 µM dNTP, 1.2 mM Mg, each primer 0.2 µM). Amplification was performed on a thermocycler (model 2700; Applied Biosystems, Inc. [ABI], Foster City, CA). The parameters were as follows: cDNA synthesis 50°C for 25 minutes, denaturation at 94°C for 2 minutes, amplification for 40 cycles of 94°C for 15 seconds, annealing for 20 seconds, and extension at 72°C for 45 seconds. A final extension of 72°C for 10 minutes was run after the 40 cycles. The mRNA concentration for MMPs in CB tissue is low, and so reamplification was performed with a PCR Reagent System (Invitrogen).


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  		TABLE 1. Primer Sequences and Expected PCR Products Sizes of Human MMPs and TIMPs

 
Ten percent of the RT-PCR product was used as the DNA template for the PCR reaction. PCR conditions were as follows: incubation at 94°C for 2 minutes, followed by amplification at 94°C for 30 seconds, annealing for 30 seconds, and extension at 72°C for 30 seconds for 35 cycles. A final extension was run at 72°C for 7 minutes. This reamplification was not necessary for cultures of CBSM cells. Gel electrophoresis of the PCR products was performed on a 2% agarose gel (E-gel; Invitrogen).

When the single correct band size was located, the bands were cut from the gel and purified (Gel Extraction Kit; Qiagen, Valencia, CA). DNA sequencing was then performed at the core facility of Thomas Jefferson University to confirm that the product obtained was representative of the specific MMP or TIMP. Results from the sequencing were analyzed with the BLAST program (http://www.ncbi.nlm.nih.gov/BLAST/ provided in the public domain by National Center for Biotechnology Information [NCBI], Bethesda, MD). If a band was not present, then RT-PCR was attempted with at least three to four primer sets designed by an online primer design program (e.g., Primer3: http://www.genome.wi.mit.edu/cgi-bin/primer/primer3_www.cgi).

qRT-PCR: Primer-Probe Design
For the gene of interest, the DNA sequence (GenBank; NCBI, Bethesda, MD) was used to create a primer–probe combination (Primer Express; ABI, Foster City, CA; Table 2 ). RT-PCR was performed with these primers, as described in the prior section. The PCR products (between 75 and 150 bp in length) were run on a 4% agarose gel (E-gel; Invitrogen) with a 25-bp DNA ladder (Invitrogen). DNA sequencing of the amplicons verified the specificity of the primers, as described earlier. This served as a second confirmation as to the presence of mRNA of the MMP or TIMP of interest.


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  		TABLE 2. Sequences of the Primers and of Human MMPs and TIMPs for Quantitative RT-PCR and Their PCR Product Sizes

 
Quantitative RT-PCR was performed (Prism 7000; ABI) with mastermix (TaqMan One Step RT-PCR; ABI) with GAPDH as an endogenous control (ABI). The thermocycling conditions were performed in three stages: one was cDNA synthesis of 48°C for 30 minutes; two was denaturation at 95°C for 10 minutes; and three was 40 cycles of 95°C for 15 seconds followed by annealing at 60°C for 1 minute. Results were then quantified (Prism 7000 SDS Software; ABI). We used 20 or 30 ng of total RNA to compare expression levels of MMPs and TIMPs.

Relative Quantitation
For relative quantitation normalized to GAPDH, an endogenous control, standard curves were prepared for both MMPs and GAPDHs and TIMPs and GAPDHs. Standard curves for MMP-1, -2, -14, -15, -16, -19, and -24 and their counterpart GAPDHs were constructed using a serial dilution of total RNA with a range of 0.2, 0.5, 1, 2, 5, 10, and 20 ng (Fig. 1A) . Standard curves for MMP-3, -11, and -17 and their counterpart GAPDHs were constructed with a serial dilution of total RNA with a range of 0.1, 0.2, 0.5, 1, 2, 5, 10, and 20 ng (Fig. 1B) . Standard curves for MMP-12 and its counterpart GAPDH were constructed with a serial dilution of total RNA of the cultured CBSM cells, using a range of 5, 10, 20, 40, and 80 ng (Fig. 1C) . Standard curves for TIMPs and their counterpart GAPDHs were constructed with a serial dilution of total RNA of the cultured trabecular meshwork endothelial cells, with a range of 0.2, 0.5, 1, 2, 5, 10, and 20 ng for TIMP-1, -2, and -3 and with a range of 2.5, 5, 10, 20, 40, and 80 ng for TIMP-4 (Fig. 1D) . Using three CT levels (i.e., threshold cycle, defined as the fractional cycle number at which the amount of amplified target reaches a fixed threshold) for each input amount of dilution, standard curve equations for MMPs, TIMPs, and their counterpart GAPDHs were generated (Table 3) . The comparative {Delta}CT method was used for relative quantitation of those genes whose absolute value of the slope of log input versus {Delta}CT was less than 0.1 (Table 3) . The relative standard curve method was used for genes that did not satisfy the criteria. The coefficient of variation (CV) was used for data reproducibility. Reproducibility of standard curves of GAPDHs obtained from those cell lines used for different genes was as follows: 4.45 to 5.57 of CV (%) for HT-1080, 2.27 to 3.61 of CV (%) for CCF-STTG1, and 0.98 to 2.38 of CV (%) for cultured TM endothelial cells. All triplicates of CTs used for the experiment showed much less than 1% CV (Table 3) . According to the manufacturer’s protocol, triplicates showing less than 2% CV are accepted for this assay (ABI).


Figure 1
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  		FIGURE 1. Relative standard curves of MMPs and relative efficiency plots of TIMPs for relative quantitation. To evaluate validation of the comparative {Delta}CT method in PCR, (A) standard curves for MMP-1, -2, -12, -14, -15, -16, -19, and -24 and GAPDH were generated with total RNA from HT-1080 cells (human fibrosarcoma cell line; ATCC, Manassas, VA), (B) standard curves for MMP-3, -11, and -17 and GAPDH were generated with total RNA from CCF STTG1 cells (human astrocytoma; ATCC), (C) standard curves for MMP-12 and GAPDH and their {Delta}CT plots were generated with total RNA from hCBSM cells and (D) relative efficiency plots for TIMPs were generated with total RNA from human trabecular meshwork endothelial cells. The mRNA expression level of MMPs and TIMPs in the control and latanoprost-treated cultures was calculated with the comparative {Delta}CT method, in which the absolute value of the slope of log input versus {Delta}CT is < 0.1. However, the relative standard curve method was used for genes that did not satisfy the criteria. Each point in a linear line is the average of triplicate results.

 

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  		TABLE 3. Equations for Standard Curves and {Delta}CT of MMPs and TIMPs

 

   Results
Top
 Abstract
 Materials and Methods
 Results
Discussion
 References
 
mRNA Expression of MMPs and TIMPs
Eleven of 21 MMPs were expressed in the CB tissue and the cultures of CBSM cells (Table 4) as determined by qualitative RT-PCR and subsequent DNA sequence confirmation (Fig. 2) . MMP-9 was not detected, but a very small amount was observed when CBSM cells were treated with latanoprost in quantitative RT-PCR. All four TIMPs were expressed by qualitative RT-PCR, and their subsequent DNA sequences were confirmed.


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  		TABLE 4. The Relative the mRNA Expression Levels of MMPs and TIMPs in Cultures of Human CBSM Cells and the Effect of Latanoprost Acid on Their Expression at the Pharmacologic Concentration of 0.03 µg/mL

 

Figure 2
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  		FIGURE 2. Qualitative RT-PCR results with primers developed by Primer Express (ABI). DNA ladders were run concurrently to verify DNA size. The gel was imaged, and the expected band sizes for the corresponding MMPs and TIMPs were recorded (Table 2) . (A) Qualitative RT-PCR for MMPs in CBSM cells cultured from a 40-year-old donor. Odd-numbered lanes correspond to the no-template control. Lane 2: MMP-1; lane 4: MMP-2; lane 6: MMP-3; lane 8: MMP-11; lane 10: MMP-12; lane 12: MMP-14; lane 14: MMP-15; lane 16: MMP-16; lane 18: MMP-17; lane 20: MMP-19; and lane 22: MMP-24. All PCR DNA products were sequenced. (B) Qualitative RT-PCR for TIMPs in CBSM cells cultured from a 40-year-old donor. Odd-numbered lanes correspond to the no-template control. Lane 2: TIMP-1; lane 4: TIMP-2; lane 6: TIMP-3; and lane 8: TIMP-4. (A, B) Unnumbered left column: 25-bp DNA ladder.

 
In the cultured CBSM cells, the relative level of expression of the 11 MMPs and four TIMPs was determined by the CT values in the control group. MMP-2 and -14 had very high expression levels with CTs of 24 to 26 at 20 ng of total RNA (MMP-2 ≥ MMP-14); MMP-24 had high expression levels with a CT of 26 to 29; and MMP-1, -11, -15, -16, and -19 had intermediate expression levels, with CTs of 29 to 32. MMP-3 and -17 had low expression levels, MMP-3 with a CT of 34 to 35 and MMP-17 with a CT of 33, and MMP-12 had a very low expression level with a CT of 39. The CTs of GAPDH were 21 to 22 at the same total RNA concentration (20 ng).

TIMP-2 appeared to be expressed at a higher level than the other TIMPs. At 20 ng of total RNA, TIMP-2 had a CT of 26 to 27. TIMP-1 also had a high expression level, showing a CT of 27 to 28, and TIMP-3 had an intermediate expression level with a CT of 29 to 30. TIMP-4 had a low expression level showing a CT of 32 to 36. The CT of GAPDH was 22 to 23 at the same total RNA concentration.

Changes in mRNA Expression of MMPs by Latanoprost Acid
Cultures of CBSM cells derived from five to six eyes of different donors were exposed to vehicle control (0.06% ethanol), 0.03, 0.3, or 30 µg/mL of latanoprost free acid.

A change of more than 10% in expression between the control and experimental levels was defined as an alteration of expression. Relative efficiencies of target and reference genes were considered equal if the absolute value of the slope of log input versus {Delta}CT was less than 0.1. Thus, the relative quantitation method classified 10% variability as unchanged, according to the manufacturer’s instructions. There was substantial individual variability among the donors tested, which had been encountered in previous studies of MMP and TIMP expression with latanoprost in CB.49 Therefore, the ultimate determination of the effect of latanoprost on expression of an individual MMP or TIMP was determined by the trend of the majority (>60%) of the samples at a concentration of 0.03 µg/mL (Table 4) . The trend at the other latanoprost concentrations was determined in the same way (Fig. 1) .

Collagenases.
Of the three known collagenases, collagenase-1 (MMP-1) was the only detected enzyme in this subfamily. At a pharmacologic level (0.03 µg/mL) of latanoprost, the expression of MMP-1 decreased an average of 18% in all five donors. As the concentration of latanoprost increased to suprapharmacologic doses, two of five donors showed a further dose-dependent decrease in expression (Fig. 3A) .


Figure 3
Figure 3
Figure 3
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  		FIGURE 3. Changes in mRNA expressions of (A–D) MMPs, (E–G) MT-MMPs, and (H–K) TIMPs in hCBSM cells treated with latanoprost. In response to latanoprost at the therapeutic level (0.03 µg/mL), in cultures of hCBSM cells, MMP-3, MMP-17, and TIMP-3 were upregulated, whereas MMP-1, -2, -12, -14, -15, and -16 and TIMP-4 were downregulated. Fifteen to 50 ng total RNA was used, according to the expression levels of the MMPs.

 
Gelatinases.
Of the two gelatinases, only gelatinase A (MMP-2) was detected. The expression of MMP-2 in three donors decreased an average of 16% in response to 0.03 µg/mL of latanoprost, and as the concentration of latanoprost increased, a tendency toward decreased expression was observed (Fig. 3B) . The other two donors showed no changes in expression at 0.03 µg/mL.

Stromelysins.
Of the three known stromelysins, stromelysin-1 and -3 (MMP-3 and -11, respectively) mRNAs were detected. At 0.03 µg/mL of latanoprost, three of five donors showed approximately 30% more MMP-3 mRNA expression, which further increased at 0.3 µg/mL; 30 µg/mL of latanoprost decreased the expression below baseline levels in two of these three donors. In the two other donors, the relative expression was within 10% of control in one, and there was a consistent decrease in expression at all concentrations in the other (Fig. 3C) .

MMP-11 expression was not observed to change in three donors at 0.03 µg/mL of latanoprost, but as the concentration of latanoprost increased, there was a decrease in expression (Fig. 3C) . One donor showed an increase and the other a decrease of expression at all doses leading us to conclude that the expression of MMP-11 is unchanged by latanoprost.

Membrane-Type Matrix Metalloproteinases.
At 0.03 µg/mL, the expression of MT1-MMP (MMP-14) was consistently decreased in three donors an average of 20%, whereas the two other donors had a consistent increase. Higher doses tended not to change the trends observed at 0.03 µg/mL (Fig. 3E) .

At 0.03 µg/mL, the expression of MT2-MMP (MMP-15) decreased in three donors an average of 35%. The decreased expression in these four donors continued at higher concentrations of latanoprost. The other donor showed a dose-dependent increase in expression (Fig. 3E) .

The expression of MT3-MMP (MMP-16) decreased an average of 20%, in three donors at all concentrations of latanoprost. In the remaining two donors, MMP-16 expression increased in one and remained unchanged in the other at 0.03 µg/mL. At higher concentrations of latanoprost, the expression of MMP-16 was less than 10% different from baseline in the remaining two (Fig. 3G) .

Only MT4-MMP (MMP-17) showed a consistent dose-dependent increase in expression in response to latanoprost in four of five donors and was unchanged in the remaining one (Fig. 3G) . At 0.03 µg/mL, the average increase was 23%.

At 0.03 µg/mL, the expression of MT5-MMP (MMP-24) in two donors decreased. The expression in one donor was unchanged, and in the remaining two donors expression increased, leading us to conclude that the expression of MMP-24 is unchanged. As the concentration of latanoprost increased, no trends were elucidated (Fig. 3F) .

Miscellaneous MMPs.
Metalloelastase (MMP-12) had an average decrease of 24% in expression in four of five donors at 0.03 µg/mL. The expression in the remaining donor increased at 0.03 µg/mL of latanoprost (Fig. 3D) . The cultures from five donors were tested and MMP-12 was detected at a level too low to provide useful data for the quantitative RT-PCR assay in two of these donors; therefore, CBSM cell cultures from two additional donors were tested. At higher concentrations, MMP-12 showed a trend toward a dose-dependent decline.

At 0.03 µg/mL, the expression of RASI-1 (MMP-19) decreased in two donors, was unchanged in two, and increased in the remaining donor. Higher concentrations of latanoprost did not change the trend at 0.03 µg/mL (Fig. 3D) leading us to conclude that MMP-19 expression was unchanged by latanoprost.

In summary, MMP-3 and MMP-17 tended to have an increase in mRNA expression in response to latanoprost, whereas MMP-1, -2, -12, -14, -15, and -16 decreased. There was high variability in the responses of mRNA expression of MMPs to latanoprost among donors.

Tissue Inhibitors of Matrix Metalloproteinases.
The expression of TIMP-1 did not change in three of the five donors (Fig. 3H) at 0.03 µg/mL. In the remaining two, levels were elevated in one and decreased in the other. At higher concentrations of latanoprost, no trend was observed.

At 0.03 µg/mL, TIMP-2 expression was unchanged in two of the five donors. The expression in two other donors increased (Fig. 3I) and expression decreased in the remaining one. As the concentration of latanoprost increased, no trend was detectable.

TIMP-3 expression increased an average of 32% in all five donors at 0.03 µg/mL. The increase in expression continued in four of five donors at 0.3 µg/mL (Fig. 3J) . At 30 µg/mL, TIMP-3 was downregulated.

The expression of TIMP-4 did not change in three of the five donors at 0.03 µg/mL, but decreased in the remaining two (Fig. 3K) . At 0.3 µg/mL, TIMP-4 expression decreased in four of the five donors and in all five donors at 30 µg/mL.

In response to pharmacologic doses of latanoprost, TIMP-3 transcription increased, whereas the transcription of TIMPs-1, -2, and -4 was not observed to change.


   Discussion
Top
 Abstract
 Materials and Methods
 Results
 Discussion
References
 
mRNA Expression of MMPs and TIMPs
To date, this is the most comprehensive analysis of MMP and TIMP mRNA expression in human CB. The presence of mRNA and protein of MMP-1, -2, -3, and -9 have been described in human CB.22 23 24 25 49 50 51 TIMP-1 and -2 have been described at the mRNA and protein levels, whereas TIMP-3 and -4 proteins have been found in the CB.24 26 51 We found the mRNA of eight other MMPs and TIMP-4. To assure the validity of our expression pattern of MMPs and TIMPs, we used oligonucleotide primers previously validated in the literature and confirmed the DNA sequence of the PCR products. We tested both tissues and explant cultures of CBSM cells. A second set of primers (those for the quantitative RT-PCR) also confirmed the expression of these genes in the CBSM cells.

The presence of nearly all known MT-MMPs points to their importance in the functioning of CBSM cells and uveoscleral outflow. All MT-MMPs can degrade ECM components and can be competitively inhibited by TIMPs.52 MT1-MMP, along with TIMP-2, is involved in the activation of MMP-2 (gelatinase A) and MMP-13.52 53 54 55 56

We could not detect expression of MMP-9, gelatinase B, in untreated or control samples, but it was induced by latanoprost at a very low level. In immunolabeling studies of human CBSM cell cultures and monkey CB tissue treated with control or latanoprost, Ocklind23 was unable to find MMP-9. However, expression of MMP-9 in CB has been described at both the RNA42 and protein22 24 51 levels. Weinreb and Lindsey49 found the mRNA of MMP-9 in control samples of CBSM cells. The protein of MMP-9 has been described at low levels in other studies. Using an immunohistochemical study to map the distribution of MMP-1, -2, -3, and -9 and the four TIMPs in the anterior uvea, Lan et al.,51 described MMP-9 as having moderate staining in the CB. El Shabrawi et al.,24 using CB explant organ cultures, reported that MMP-9 was barely detectable in the medium of their control cultures, and was undetectable in dexamethasone-treated cultures. In their immunohistochemical studies, they found diffuse staining throughout the CB, but much less than that found for MMP-2 and -3.24 In the zymogram in the study by Weinreb et al.,22 MMP-9 activity was barely above background. In their Western blot analysis, a band at approximately 95 kDa was present, but was clearly weaker than the bands for the other three MMPs studied. The predominance of the band at 95 rather than 82 kDa indicated that the protein is primarily inactive.22 If MMP-9 is expressed, it is probably expressed at extremely low levels with low activity and could vary from one individual to another. However, it appeared to be inducible with latanoprost in our studies.

Changes in MMPs and TIMPs to Latanoprost
Most of the MMPs are either downregulated or unchanged in response to latanoprost at pharmacologic concentrations. Based on the consistent increase in mRNA expression of MMP-3 (stromelysin-1) and MMP-17 (MT4-MMP), it seems that these two enzymes are important for the latanoprost-induced increase in ECM degradation. Both of these are expressed at low amounts in control samples. In trabecular meshwork, MMP-3 is involved in the ECM-mediated decrease in outflow resistance to both tert-butylhydroquinone and argon laser.57 58 MMP-3 may have a similar role as an effector of ECM degradation in CB after latanoprost treatment. Little is known about MMP-17. Through association with syndecan-1 on the cell surface, MMP-17 activates aggrecanase-1 (ADAMTS4), the active form of which associates with syndecan-1 through chondroitin sulfate and heparin sulfate.59 60 61 MMP-17 can activate TNF-{alpha}.62 63 64 It is unclear whether MMP-17 can activate MMP-2 (pro-gelatinase A).62 63 Aggrecanase-1 degrades glycosaminoglycans, and its upregulation is associated with increased ECM degradation.59 60 61 It is possible that by activating aggrecanase-1, MMP-17 helps further ECM turnover in CB in response to latanoprost.

A consistent increase in TIMP-3 mRNA expression in response to latanoprost was found. TIMP-3 is the only TIMP that is sequestered in ECM to heparin-sulfate containing proteoglycans and possibly chondroitin-sulfate containing proteoglycans.65 66 67 TIMP-3 is unique in its ability to inhibit TNF-{alpha}-converting enzyme (TACE) and its ability to inhibit strongly not only MMPs but several ADAMs (a disintegrin and metalloproteinase) and ADAMTS (ADAM with thrombospondin motifs).66 67 68 69 70 TIMP-3 has also been hypothesized to function in a tissue-specific fashion as part of an acute response to remodeling stimuli and regulating ECM remodeling during the folding of epithelia.71 72 73 TIMP-3 is an excellent inhibitor of MT1-MMP and MT2-MMP.37 74 Mutations in TIMP-3 causes Sorsby’s fundus dystrophy.75 Although TIMP-3 overexpression can cause apoptosis in some cancer cell lines, there has been no evidence that apoptosis occurs in CB in response to latanoprost treatment.76 77 78 Because TIMP-3’s functions are primarily believed to be inhibitory, the upregulation of TIMP-3 may be part of a regulatory reaction to balance the latanoprost-induced increase in MMPs. However, it is also possible that its increase facilitates activation of the MMP zymogens, since TIMP-3 can bind pro-MMP-9.27

MMP-2 and -14 were the most highly expressed MMPs in the CBSM, and both were downregulated in response to latanoprost. Thus, our results do not support that these enzymes are primarily responsible for latanoprost-mediated ECM turnover. However, further study comparing the relative levels of zymogen (i.e., pro-MMP-2) versus active MMP-2 and -14 are needed to determine the importance of MMP-2, since it is primarily regulated at activation.

We observed variability in the response to latanoprost among cultures from different donors similar to other studies of MMP-1, -2, -3, and -9 transcription after latanoprost incubation.49 The source of this variation is unknown, but it could represent normal human variations of a mRNA that is present in very low amounts under normal conditions, donor medication history, variability inherent in the analysis methods, and normal genetic variation in response to latanoprost.79 Clinically, there are some patients whose IOPs do not lower in response to latanoprost treatment.80 In our study, latanoprost altered at least some of the MMPs and TIMPs in all cell lines. There was no apparent age-dependent pattern of response. The absence of a nonresponder may simply reflect our small sample size or indicate that the cause of clinical nonresponse is at a level beyond transcription in the CB.

Weinreb and Lindsey49 found MMP-1 increased (in all five donors at 6 hours, but decreased at 24 hours), MMP-2 decreased (in three of five donors), MMP-3 increased (in three of five donors), and MMP-9 increased (in four of five donors) in response to latanoprost. Our results are consistent with regards to MMP-1, -2 and -3 at 24 hours.

In the other study examining the transcriptional activity of TIMP-1 and -2 after latanoprost, Anthony et al.26 found that TIMP-1 was upregulated at 24 hours, which we did not find. They also found that TIMP-2 was mildly elevated at 6 hours and was unchanged at 24 hours, which agrees with our results. At 6 hours, the elevation was 6% to 11%, which would have been interpreted as unchanged with our criteria.26 At the protein level, El Shabawri et al.24 found no change in either TIMP-1 or -2 after latanoprost or dexamethasone treatment.

Our results indicated that MMP-3, -9, and -17 may be responsible for the alteration in the ECM with latanoprost treatment. TIMP-3 was the only TIMP consistently altered by latanoprost. Examination of MMP/TIMP mRNA expression at only one time point is a limitation of this study. In addition, latanoprost-mediated changes in MMP and TIMP activity may be regulated by posttranscriptional events during biosynthesis and by extracellular activation, kinetic inhibition, and degradation. However, in the CB, latanoprost appears to shift the balance of MMPs and TIMPs toward greater levels of MMPs, resulting in the observed changes in the ECM.


   Footnotes
 
Supported by EY 13997 (DJR), Pfizer Ophthalmics, American Glaucoma Society Clinician-Scientist Fellowship (Allergan), and unrestricted funds from Research to Prevent Blindness, New York, New York.

Submitted for publication April 26, 2005; revised July 11, August 16, and October 20, 2005; accepted January 5, 2006.

Disclosure: D.-J Oh, None; J.L. Martin, None; A.J. Williams, None; R.E. Peck, None; C. Pokorny, None; P. Russell, None; D.E. Birk, None; D.J. Rhee, Pfizer Ophthalmics (F), Allergan (F)

The publication costs of this article were defrayed in part by page charge payment. This article must therefore be marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

Corresponding author: Douglas J. Rhee, Department of Ophthalmology, Massachusetts Eye and Ear Infirmary, 243 Charles Street; Boston, MA 02114; dougrhee{at}aol.com.


   References
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 Abstract
 Materials and Methods
 Results
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 References
 

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