Development of a cellular model of human trabecular meshwork to evaluate the role of chemokine ligands in glaucoma

Abstract

Purpose: Trabecular meshwork (TM) is the main site of resistance of the aqueous humor (AH) and is implicated in the regulation of the AH outflow. TGF-b2 and dexamethasone are known to act on TM cells to induce glaucoma. We recently demonstrated that a CXCR3 antagonist can restore the trabecular function in a rat model of ocular hypertension obtained by episceral veins electro-coagulation. The purpose of this study was firstly to characterize an in vitro model of human TM in order to evaluate the involvement of CXCR3 chemokine receptor and its ligands (CXCL9, CXCL10 and CXCL11) in the biology of TM cells.

Methods: Primary human TM cells obtained from ScienCell were treated with either dexamethasone (100 nM) or TGF-b2 (10 ng/ml). Myocilin secretion, a-smooth muscle actin (a-SMA) expression and phosphorylation of myosin light chain (MLC) were investigated by western blotting. Collagen I and a-SMA immunolabelling were analyzed by quantitative immunocytochemistry (ICC). CXCR3, CXCL9, CXCL10 and CXCL11 mRNA expressions were measured using TaqMan assays by quantitative PCR. Immunolabelling of CXCR3 was also quantified by ICC and flow cytometry (FC).

Results: TGF-b2 treatment induced a myofibroblastic phenotype of TM cells characterized by a dose dependent effect on a-SMA up-regulation (24h), increase phosphorylation of MLC (24h) and collagen I secretion (96h). In addition, we observed that dexamethasone increased significantly myocilin secretion, a specific marker of the TM. In this in vitro model, a low expression of the isoform B of CXCR3 was measured by qPCR and correlated by ICC and FC. Furthermore, CXCL9, CXCL10 and CXCL11 were up-regulated 4h post-treatment with either TGF-b2 or dexamethasone. This transient increase of CXCL9, CXCL10 and CXCL11 was followed by a subsequent decrease of mRNA below the basal condition after 24h

Conclusions: This study characterizes an in vitro model of TM cells and demonstrates the presence of CXCR3 B isoform on TM cells. Moreover, the regulation of its ligands expression under known inducers of IOP increase (TGF-b2 and dexamethasone) suggests a role of CXCR3 signaling in the regulation of the AH outflow.

Keywords: 735 trabecular meshwork