Delta-Opioid Receptors Attenuate TNF-α-Induced MMP-2 Secretion From Human ONH Astrocytes

PURPOSE. We examined the signaling mechanisms involved in delta-opioid-receptor agonist, SNC-121-mediated attenuation of TNF-alpha-induced matrix metalloproteinase-2 (MMP-2) secretion from human optic nerve head (ONH) astrocytes. METHODS. Human ONH astrocytes were treated with SNC-121 (1 mu mol/L) for 15 minutes followed by TNF-alpha (25 ng/mL) treatment for 6 or 24 hours. Cells were pretreated with inhibitors of p38 mitogen-activated protein (MAP) kinase (SB-203580) or NF-kappa B (Helenalin) prior to TNF-alpha treatment. Changes in phosphorylation and expression of p38 MAP kinase, I kappa B alpha, NF-kappa B, and MMP-2 were measured by Western blotting. Translocation of NF-kappa B was determined by immunocytochemistry. RESULTS. TNF-alpha treatment increased MMP-2 secretion from ONH astrocytes to 236% +/- 17% and 142% +/- 8% at 6 and 24 hours, respectively; while SNC-121 treatment reduced MMP-2 secretion to 149% +/- 11% and 108% +/- 7% at 6 and 24 hours, respectively. The SNC-121-mediated inhibitory response was blocked by the delta-opioid-receptor antagonist naltrindole. TNF-alpha treatment resulted in a sustained phosphorylation of p38 MAP kinase up to 24 hours (226% +/- 15% over control levels), which was reduced to 150% +/- 20% by SNC-121 treatment. TNF-alpha treatment increased the expression of NF-kappa B to 179% +/- 21% and 139% +/- 6% at 6 and 24 hours, respectively, which was significantly blocked by SNC-121 treatment. Furthermore, TNF-alpha-induced MMP-2 secretion was blocked by 100% and 78% in the presence of SB-203580 and Helenalin, respectively. CONCLUSIONS. Evidence is provided that SNC-121 attenuated TNF-alpha-induced MMP-2 secretion from ONH astrocytes. Data also supported the idea that p38 MAP kinase and NF-kappa B played central roles in TNF-alpha-induced MMP-2 secretion, and both were negatively regulated by SNC-121.