Purpose: Glaucoma filtration surgery often fails because of the fibrotic reaction from Tenon's capsule fibroblasts (TCFs). This study examined whether the interaction of the opioid growth factor (OGF) [Met(5)]-enkephalin with its receptor (OGFr) is a regulator of TCF proliferation.
Methods: The presence of OGF and its receptor (OGFr) was determined in rabbit TCFs (RTCFs) by immunocytochemistry. The kinetics of OGFr were established in receptor binding assays. The ability of OGF to inhibit RTCF proliferation was assessed with dose-response, receptor mediation, and reversibility studies. Dependence on OGF and OGFr was ascertained by antibody neutralization and siRNA studies, respectively. The mechanism of action of the OGF-OGFr axis on survival (apoptosis, necrosis) and DNA synthesis of RTCFs was elucidated.
Results: OGF and OGFr were detected in RTCF cells, and specific and saturable binding to OGFr was recorded. Exogenous OGF had a dose-dependent, reversible, and receptor-mediated inhibitory effect on cell proliferation. Endogenous OGF was found to be constitutively produced and tonically active in cell replication, with neutralization of this peptide causing acceleration of cell proliferation. The silencing of OGFr by using siRNA technology stimulated cell replication, validating OGFr's integral role. The mechanism of OGF-OGFr action was not related to cell survival, but rather to DNA synthesis-specifically, the cyclin-dependent kinase inhibitory pathway. Knockdown of p16 or p21 eliminated OGF's inhibitory effect on growth.
Conclusions: The OGF-OGFr system is a native biological regulator of cell proliferation in RTCFs and may offer a means of improving the success of glaucoma filtration surgery in a safe and nontoxic manner.