Trabecular response to laser trabeculoplasty is mediated by a factor produced after treatment

Purpose. Laser trabeculoplasty (LTP) induces trabecular insert cell division and juxtacanalicular matrix metalloproteinase (MMP) expression. Treatment of 180 degrees produces responses for 360 degrees, thus implicating signal transmission by a soluble factor(s). To test this hypothesis, we evaluated trabecular responses to medium conditioned by LTP-treated human anterior segment explant cultures. Methods. Human anterior segment explants were given sham or clinical-parameter LTP treatments and allowed to condition culture medium for 8 hrs. This conditioned medium was then applied to fresh explants or trabecular cell cultures. ³H-thymidine incorporation into DNA or MMP protein or mRNA expression was then evaluated. Results. Trabecular insert cell division in explants is increased by exposure to 8-hr conditioned medium from LTP- but not sham-treated explants. Gelatinase B and stromelysin expression by trabecular cells exposed to LTP- but not sham-treatment medium were increased at 24-72 hrs. Alternative types of trabecular wounding did not mimic LTP-treatment. Hypotonic shock and sonication of trabecular meshworks did not release this LTP factor. Conclusion. The trabecular response to LTP involves the production rather than release of a factor(s), which can mediate both the trabecular insert cell division response and the MMP expression response by trabecular cells. This factor may have the potential to replace LTP-treatment as a therapy for glaucoma.