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From the Glaucoma Center, University of California San Diego, La Jolla, California.
| Abstract |
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METHODS. Human ciliary smooth muscle cell cultures were grown to confluence and treated for 24 hours with medium supplemented with latanoprost acid or vehicle. Total RNA was then isolated, and the expression of mRNAs for MMP-1, -2, -3, and -9 were determined using Taqman and energy-transfer real-time PCR analyses. All results were normalized according to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA in each sample.
RESULTS. Specificity and linearity of each real-time PCR assay were confirmed by electrophoresis and serial dilution analysis of oligonucleotides containing the amplicon sequence. Addition of latanoprost acid for 24 hours increased expression of MMP-1 by 3- to 13-fold in three of five primary ciliary muscle lines. Addition of 8, 40, and 200 nM latanoprost acid for 24 hours increased MMP-1 mRNA in a dose-dependent manner. Analysis of cultures exposed to 200 nM latanoprost acid for 4, 6, 12, or 24 hours revealed an increase and then a decline of MMP-1 mRNA, with peak expression at 6 to 12 hours after initiation of treatment. Parallel assessments of RNA from ciliary muscle cultures exposed to latanoprost acid for 24 hours revealed increased MMP-1, -3, and -9 mRNAs and reduced MMP-2 mRNA, when compared with RNA from vehicle-treated cultures.
CONCLUSIONS. Latanoprost acid induced a dose-dependent increase of MMP-1, -3, and -9 gene transcription in cultured human ciliary smooth muscle cells. These results are consistent with increased MMPs contributing to the increased uveoscleral outflow facility observed after topical latanoprost.
| Introduction |
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and of humans with latanoprost, a PG
analogue, lowers intraocular pressure and increases uveoscleral outflow
facility.1
2
Extracellular spaces among ciliary muscle
fiber bundles that also contain extracellular matrix molecules, such as
collagens, are a major component of the uveoscleral outflow
pathway.3
4
5
6
The PGF2
-induced
increase in uveoscleral outflow facility has been associated with
several changes in ciliary muscle, including expansion of the
extracellular spaces,7
reduction of
collagens,8
9
and increased matrix metalloproteinases
(MMPs).10
11
12
Reduced collagens and increased MMPs in
ciliary muscle also have been noted after treatment with
latanoprost.11
13
These studies support an association
between PG-mediated lowering of IOP and increased MMP expression. MMPs are neutral proteinases that specifically degrade extracellular matrix molecules.14 15 They can initiate degradation of collagen and other extracellular matrix components within ciliary muscle extracellular matrix.16 After such cleavage, the resultant collagen fragments unwind at body temperature17 and are then further degraded by MMPs and nonspecific extracellular proteases or by lysosomal enzymes after phagocytosis of the fragments.18 We have hypothesized previously that increased MMPs plays a pivotal role in the reduction of extracellular matrix in the ciliary muscle after PG treatment and the concomitant increase in uveoscleral outflow.19 Support for another possible role of MMPs, in normal regulation of uveoscleral outflow, comes from the observation of measurable MMP-1, -2, and -3 immunoreactivity in the iris, the ciliary muscle, choroid, and sclera of untreated normal human and primate eyes.20 21 22 However, little is known about how PGs, or PG analogues such as latanoprost influence MMP gene transcription.
Previous studies in various cell types have found that increases in MMP secretion in tissues typically are preceded by changes in corresponding MMP gene transcription.23 24 However, this is not always the case.25 26 The present study was therefore undertaken to characterize the induction of MMP-1, -2, -3, and -9 mRNAs in cultures of human ciliary smooth muscle cells after exposure to latanoprost acid, the biologically active form of latanoprost.
| Methods |
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To minimize dedifferentiation that can occur in high-passage primary cell lines, cultures were used in the present experiments that had been passaged five to seven times. Because the number of low-passage cells that can be generated from the ciliary muscle of a single pair of human donor eyes is limited, each experiment with a particular cell line was performed once.
Experimental Treatments of the Cultures
Stock solutions containing 10 mM latanoprost acid (Cayman
Chemical Co., Ann Arbor, MI) were prepared in ethanol and diluted to
appropriate test concentrations with DMEM/F12 nutrient mixture. The
vehicle control was DMEM/F12 nutrient mixture containing 0.1% ethanol
(the same concentration of ethanol as was present in the highest
agonist concentration experimental test media).
To directly assess the role of MMP transcription changes in the ocular response to latanoprost, the ciliary smooth muscle cells were exposed to latanoprost acid. Test concentrations were 8, 40, 200, and 1000 nM. Previous investigation had shown that the average peak concentration of latanoprost in human anterior chamber aqueous after a standard clinical dose is approximately 100 nM, although concentrations as high as 200 nM have been observed (Sjostrand B, personal communication, May 2000). Therefore, the test concentrations encompassed the pharmacological range observed in aqueous humor with clinical doses. Treatments were initiated by exposing cultures to the test media and terminated by addition of the lysis buffer for RNA harvesting.
Reverse Transcriptase Reaction Conditions
Total RNA was harvested by using acid guanidine phenol
chloroform extraction, as described previously.29
30
To
assess the accuracy of the procedures, triplicate aliquots of total RNA
were used to produce cDNA in parallel reactions. First-strand cDNA was
synthesized using RNase H- reverse transcriptase
purified form Escherichia coli containing the pol gene of
Moloney murine leukemia virus (Superscript II; Gibco BRL). The 20 µL
reaction volume contained 1 to 5 µg total RNA, 0.5 µg oligo (dT),
50 mM Tris (pH 8.3 at room temperature), 75 mM KCl, 3 mM
MgCl2, 0.01 M dithiothreitol, 0.5 mM dNTPs, and
200 U reverse transcriptase. The reaction mixture was incubated at
42°C for 50 minutes and terminated by incubation at 70°C for 15
minutes.
Taqman Real-Time PCR
MMP-1 gene transcription in the treated ciliary muscle cells was
measured using a real-time polymerase chain reaction (PCR) system
(Taqman Real-Time PCR; PE-Applied Biosystems, Inc., Foster City,
CA).31
The protocol was exactly as described
previously,30
except that the primers and probe were
specific for MMP-1. Briefly, the probe, which contains both a
fluorophore and a quencher on opposite ends, was designed to bind
specifically to a region of the MMP-1 sequence between the primers.
During each PCR cycle, the bound probe was digested by the 5'-nuclease
activity of Taqman polymerase as the primers were extended. The
amount of fluorophore that remained unquenched during each cycle was
assessed by illuminating the reaction mixture with a laser beam and
measuring the resultant fluorescence. Expression of
glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in the same specimens
also was measured and used to normalize the MMP-1 results.
Primers and probe for MMP-1 and GAPDH are shown in Table 1
.
|
Reaction differences include the addition of a short oligonucleotide sequence, 5'-ACTGAACCTGACCGTACA-3', to the 5' end of the forward primer, inclusion of a hairpin configuration oligonucleotide primer containing the quenched fluorophore (Amplifluor Uniprimer; Intergen Co.), and elimination of the specific probe used in Taqman real-time PCR. The primers used for measuring the various MMP mRNAs are shown in Table 2 . Each determination of specific MMP mRNA amount was normalized according to GAPDH mRNA also present in each sample by using Taqman real-time PCR primers and probe.
|
Standard Curves
To evaluate linearity of the Taqman assay, a standard curve
was produced using a synthetic oligonucleotide generated according to
the sequence of the MMP-1 amplicon defined by the corresponding
primers. The concentration of RNA was determined by measuring optical
density (OD) at 260 nm and comparing this against an OD curve generated
by a serial dilution of purified calf liver RNA (Sigma, St. Louis, MO).
A serial dilution of the oligonucleotide was generated extending from
50 to 0.78 ng, and each dilution was assayed by Taqman real-time
PCR to determine CT. For the energy-transfer
real-time PCR assays, standard curves for MMP-1, -2, -3, and -9 and
GAPDH were generated using RNA from an MMP-secreting human melanoma
cell line (OCM1). A serial dilution of this RNA was made, and the
CT for MMP-1, -2, -3, and -9 in each dilution was
determined using the corresponding primers (Amplifluor
Uniprimers; Intergen Co.). The CT for GAPDH in
each of the OCM1 RNA dilutions also was assessed using Taqman
real-time PCR.
Analysis
The mean ± SD of the measurements for each RNA sample was
determined to evaluate the reproducibility of the measurements.
| Results |
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MMP-9 mRNA expression was increased in the ciliary muscle cultures from four of the five donors and unchanged in the remaining one after exposure to latanoprost acid (Fig. 6C) . This increase was biphasic in two of the responding cultures and increased linearly in the other two responding cultures.
In contrast, to MMP-1, -3, and -9, MMP-2 mRNA expression was reduced in the ciliary muscle cultures from three of the five donors and unchanged in the other two after exposure to latanoprost acid (Fig. 6D) . In each responding culture line, the overall trend was greater reduction with increasing latanoprost acid concentration.
| Discussion |
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The time course of MMP-1 mRNA induction was consistent with its accounting for the increased MMP-1 secretion observed after exposure of ciliary muscle cells to latanoprost acid. Zymographic analysis found no MMP-1 protein difference in the medium from ciliary muscle cells treated with latanoprost acid for 12 hours or the medium from vehicle-treated cultures.11 However, marked increases were observed after treatment for 24 or 72 hours. In the present study, increased MMP-1 mRNA was observed at 6 or 12 hours after exposure to latanoprost acid. Thus, the induction of MMP-1 mRNA preceded the increase in MMP-1 protein secretion.
Although increases in MMP-1, -3, and -9 mRNAs were seen in most of the
cultures treated overnight with 200 nM latanoprost acid, there was a
portion of cell lines in which there was no detectable response. This
was probably not the result of choosing GAPDH to serve as a reference
for mRNA loading in the real-time PCR measurements. In previous
experiments that directly compared the amount of cardiac myocyte mRNA
loaded in real-time PCR measurements, the investigators observed that
the ratio of GAPDH mRNA to total mRNA was the same in cells exposed to
control medium or to 1 µM PGF2
, a treatment
known to induce myocyte hypertrophy.33
At the same time,
transcription of genes for c-Fos and atrial natriuretic factor in these
cells were increased 35-fold and 800-fold, respectively. However, a
doubling of total mRNA per cell in the treated cultures was noted. If
an increase in total mRNA per cell occurred in the present cultures, it
would have resulted in an underestimation of transcription induction by
latanoprost acid. Unlike cardiac myocytes, however, no change was noted
in the appearance or survival of cultured human ciliary smooth muscle
cells exposed to 10 µM PGF2
, a concentration
10 times higher than that used in the present study.34
Therefore, the present increases in mRNA measurements relative to
GAPDH mRNA in the treated cultures is likely either to directly
reflect or to underestimate the increase in MMP mRNA copies per cell.
The observation that MMP-1, -3, and -9 mRNAs increased, whereas MMP-2
mRNA decreased in latanoprost acid-treated ciliary muscle cells
suggests there is a different mechanism of gene regulation for MMP-2
than for MMP-1, -3, and -9 in these cells. The basis of this difference
may be due in part to the presence of several regulatory element types
in the MMP-1, -3, and -9 promoters that are absent from the MMP-2
promoter.24
35
The physiological significance of this
promoter difference is supported by the increased MMP-1, -3, and -9
secretion and decreased MMP-2 secretion by corneal fibroblasts exposed
to the AP-1 regulatory element activator phorbol myristate
acetate. Similar results were observed in human cervical
smooth muscle cells exposed to TNF
,36
a cytokine
that also activates AP-1.37
Therefore, it is plausible
that these promoter differences are important for the differences
in MMP mRNA induction.
The significance of the differential MMP-2 gene regulation to MMP-2
protein secretion may be different in ciliary muscle cells than in
corneal fibroblasts. Zymographic analysis of medium from human ciliary
muscle cell cultures exposed to various PGs, including PG
F2
and latanoprost acid, have found increased
secretion of MMP-1, -3, and -9, as well as MMP-2.11
13
Stimulated increases in MMP-2 secretion that are not accompanied by
increases in MMP-2 mRNA have been demonstrated in macrophages and
vascular tumor cells.25
26
In the latter case, it was also
shown that this secreted MMP-2 originated from intracellular stores.
Further experiments are needed to determine whether this applies to
ciliary muscle cells or whether MMP-2 mRNA induction by PGs is merely
delayed, compared with the induction of MMP-1, -3, and -9 mRNAs. This
latter possibility is supported by the increased MMP-2 immunoreactivity
observed in paraffin sections of monkey ciliary muscle after 5 days of
daily treatment with PGF2
-isopropyl
ester.12
In conclusion, this study has provided evidence that the increased MMPs seen in ciliary muscle cells after latanoprost acid treatment reflects increased transcription of MMP-1, -3, and -9 mRNAs. These observations are consistent with a role for increased MMPs in the regulation of uveoscleral outflow.
| Acknowledgements |
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| Footnotes |
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Submitted for publication June 29, 2001; revised November 2, 2001; accepted November 5, 2001.
Commercial relationships policy: N.
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: Robert N. Weinreb, UCSD Glaucoma Center, 9500 Gilman Drive, La Jolla, CA 92093-0946; weinreb{at}eycenter.ucsd.edu
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increases uveoscleral outflow in the cynomolgus monkey Exp Eye Res 49,389-402[Medline][Order article via Infotrieve]
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-isopropyl ester treatment Arch Ophthalmol 1(19),1165-1170
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in human ciliary smooth muscle cells Invest Ophthalmol Vis Sci 35,242-250This article has been cited by other articles:
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