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Abstract #6613 Published in IGR 4-1
Effects of elevated intraocular pressure on outflow facility and TIGR/MYOC expression in perfused human anterior segments
Borras T; Rowlette LLS; Tamm ER; Gottanka J; Epstein DLInvestigative Ophthalmology and Visual Science 2002; 43: 33-40
PURPOSE: To investigate the effects of high intraocular pressure (h-IOP) on TIGR/MYOC expression, extracellular matrix (ECM) deposition, and outflow facility (C) in perfused human anterior segment cultures. METHODS: Anterior segments of 31 pairs of normal human eyes from postmortem donors were perfused at constant flow (3 μl/min). After reaching stable baseline, the flow of one eye from each of 31 pairs was raised to obtain a continuous pressure of 60-70 mmHg for a period of one hour (three pairs), six hours (ten pairs), 24 hours (two pairs), 48 hours (three pairs), and seven days (13 pairs). Sixteen of these pairs were used to study trabecular meshwork expression of TIGR/MYOC and stromelysin by Northern blot analysis hybridization. Nine pairs (one pair each at h-IOP for one, six, and 48 hours and six pairs at seven days) were fixed at pressure for analysis by electron microscopy. Eyes selected for C measurements fulfilled the inclusion criteria of C0 values between 0.06 and 0.4, intact RNA recovery and normal light microscopy morphology. Percent change of facility from the baseline (C/C0) was computed at six and 24 hours and two, four, and seven days from the long-term perfusion experiments (n = 9 h-IOP; n = 8 controls). RESULTS: No induction of TIGR/MYOC expression was observed after h-IOP for one and six hours. A slight induction was seen after 24 and 48 hours. At seven days, the treated eye of four of five pairs showed a clear induction, which was very pronounced in one of the pairs. In contrast, stromelysin expression was induced at six hours but not at seven days. Morphometric electron microscopy after seven days showed no significant difference in the amounts of fine fibrillar material or plaque material in the juxtacanalicular (JCT) region. The percent increase of C of the treated eye at six hours was 11.0% ± 4.6% compared with 3.7% ± 3.8% in the control eyes (p = 0.26). However, after longer time periods, the facility of the h-IOP eyes increased, whereas that of the contralateral eyes remained unchanged. This difference reached peak, significant values at four days (32.9% ± 8.4% versus 7.4% ± 7.6%, respectively; p = 0.04) and decreased to 8.9% ± 7.9% versus 1.1% ± 12.7% (p = 0.6) at seven days. CONCLUSIONS: Elevated IOP appears to cause a decrease in outflow pathway resistance at one to four days, and this effect seems to disappear with further time. In contrast, induction of TIGR/MYOC appears to be strongest at seven days. The authors speculate that this induction pattern might indicate a stress-related, rather than a possible homeostatic, role for the TIGR/MYOC protein.
Dr. T. Borras, Department of Ophthalmology, Duke University Medical Center, Durham, NC 27710, USA. borra001@mc.duke.edu
Classification:
2.5 Meshwork (Part of: 2 Anatomical structures in glaucoma)
3.4 Molecular genetics (Part of: 3 Laboratory methods)
