Coexpression and Regulation of Interleukin 1 Type I and Type II Receptors in Trabecular Meshwork

Abstract

Abstract: : Purpose: Interleukin 1 (IL–1) signaling in the trabecular meshwork (TM) increases aqueous humor outflow. This signaling may be mediated by the IL–1 type I receptor (IL–1RI) and suppressed by the IL–1 type II receptor (IL–1RII). Studies were conducted to identify these receptors in both human and porcine TM cells and to determine if IL–1 or tumor necrosis factor (TNF) modulate TM receptor levels. Methods: Human and porcine TM cells were grown in standard conditions, serum–starved for 48 hours, and then treated with IL–1α (5 ng/ml) or TNFα (5 ng/ml) for 12, 24 or 48 hours. The presence of IL–1RI and IL–1RII was evaluated using immunocytochemistry and western immunoblotting. Results:IL–1RI and IL–1RII are coexpressed on both human and porcine TM cells. TNFα treatment, and, to a lesser extent, IL–1α treatment, caused downregulation of the 80 kDa IL–1RI protein. This downregulation was greatest at 48 hours, as compared with 12 or 24 hours. An additional 120 kDa band recognized by the IL–1RI antibody was upregulated in both human and porcine cultures in response to these same cytokines. The presence of IL–1RII was comparable to that of IL–1RI in untreated cells. Both IL–1RI and IL–1RII were identified using immunocytostaining to be constitutively expressed on both porcine and human TM cells. Conclusions: TM cells have strong constitutive expression of both IL–1 type I and type II receptors. The presence of these receptors on TM cells supports our hypothesis that an IL–1 autocrine loop in the TM exists and has roles in uveitis and surgically induced inflammation (trabeculoplasty or incisional). The significance of downregulation of the 80 kDa IL–1RI, in conjunction with the upregulation of the 120 kDa protein suggests an interesting regulatory mechanism for this autocrine feedback loop. We speculate that specific induced changes in receptor concentration may alter the subsequent effects that these receptors have on matrix metalloproteinases and aqueous outflow.

Keywords: cytokines/chemokines • receptors • outflow: trabecular meshwork