Evidence that Metalloproteinases Mediate Adenosine A1–Induced Increase in Outflow Facility

Abstract

Abstract: : Purpose: Studies have shown that the activation of adenosine A–1 receptors lower intraocular pressure, in large part, by increasing pressure–dependent outflow facility. The purpose of this study was to investigate the role of matrix metalloproteinases (MMP) in adenosine A–1 agonist–induced increases in outflow facility. Methods: The effects of adenosine A–1 agonist, cyclohexyladenosine (CHA), on MMP secretion were evaluated in primary cultures of bovine trabecular meshwork cells. The secretion of MMPs were determined by Western blotting. The effects of CHA and the nonselective MMP inhibitor, GM–6001, on outflow facility were evaluated in isolated bovine anterior segments, perfused at a constant pressure of 10 mmHg. Results: The addition of CHA (100 nM) to cultured trabecular cells produced a significant increase in the secretion of MMP–2 within 30 minutes, and reached a maximum by 2 hours. No changes in the secretion of MMP–3 or MMP–9 were observed in these experiments. The administration of CHA (100 nM) to perfused anterior segments produced a 26% increase in outflow facility over basal levels. This response was relatively slow to develop with no significant change in outflow facility until after 40 minutes of CHA infusion. The peak response to CHA infusion occurred between 2 and 3 hours following CHA administration. In anterior segments perfused with the MMP inhibitor, GM–6001, no significant change in baseline facility was measured when compared to non–treated controls. However, pretreatment with GM–6001 blocked the increase in outflow facility induced by CHA (100 nM). Conclusions: These studies demonstrate that the adenosine A–1 agonist, CHA, stimulates the secretion of MMP–2 from bovine trabecular meshwork cells. In the perfused bovine anterior segment the administration of CHA significantly increased outflow facility, and this response was blocked by pre–treatment with the nonselective MMP inhibitor, GM6001. Taken together, these data support the idea that increases in outflow facility and resulting reduction in IOP induced by adenosine A–1 agonists involve the secretion and activation of MMPs within the outflow pathway.

Keywords: adenosine • outflow: trabecular meshwork • receptors: pharmacology/physiology