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Naseem Akhter, Shahid Husain; Blocking of TNF-α-Induced Signaling Events by -Opioid Agonist in the Optic Nerve. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1962.
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Current study examined if enhancement of Δ-opioidergic activity opposes the production of TNF-α within the optic nerve against glaucomatous injury. Moreover, studies also determined if TNF-α-induced secretion of MMP-2, MMP-3, or NF-kB expression in optic nerve head (ONH) astrocytes is blocked by Δ-opioid-receptor activation.
Brown Norway rats were used to elevate intraocular pressure (IOP) by injecting 50µL of 2M hypertonic saline into the circumferential limbal veins. IOP was recorded as the average of 6-8 consecutive measurements prior to surgery (baseline IOP) and weekly after treatment, using a calibrated Tonolab tonometer. Immediately after saline injections, animals were treated daily with Δ-opioid-receptor agonist, SNC-121 (1mg/kg; i.p.), for 7 days. Retinas were collected at 3, 7, and 42 days post injury. Primary cultures of human ONH astrocytes were isolated and purified by immunopanning. Cells were treated with SNC-121 (1μM), 15 minutes prior to TNF-α (25 ng/mL) treatment for 6 hours. The expression of TNF-α, MMP-2, MMP-3, and NF-kB was determined by Western blotting.
In ocular hypertensive eyes, expression of TNF-α was significantly (P<0.05) up-regulated in the optic nerve when measured between 3-42 days post injury. TNF-α production was completely inhibited when animals were treated with the selective Δ-opioid-receptor agonist, SNC-121. To dissect out the TNF-α-induced signaling mechanisms, ONH astrocytes were treated with TNF-α for 6 hours in the presence or absence of 1μM SNC-121, followed by analysis of MMP-2, MMP-3, and NF-ΚB expression. TNF-α treatment increased the secretion of MMP-2 and MMP-3 by 870±215 and 588±168%, respectively, at 6 hours when compared with controls. The MMP-2 and MMP-3 secretion was reduced to 171±8 and 238±48%, respectively, at 6 hours, when cells were pre-incubated with 1μM SNC-121. Additionally, TNF-α increases NF-kB (p65) expression by 61±5%, which was inhibited significantly (P<0.05) in the presence of SNC-121.
These data provide evidence that TNF-α is produced from glial cells in the early phase of glaucomatous injury, and remain significantly elevated during disease progression. Mechanistic data in ONH astrocytes provide clues that Δ-opioid-receptor activation opposes the secretion of MMP-2 and MMP-3 by inhibiting the upstream regulator transcription factor, NF-kB (p65).
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