Abstract
Abstract: :
Purpose: Trabecular meshwork (TM) and ciliary muscle cells possess smooth muscle–like properties that have been hypothesized to be involved in the regulation of aqueous outflow facility. The purpose of this study was to investigate the effects of cholesterol lowering statin drugs, which are known to influence the Rho pathway, on cell shape, contractile properties, cytoskeletal integrity in TM and ciliary muscle cells, and aqueous outflow through the TM. Methods: Porcine primary trabecular meshwork (PTM) and ciliary muscle cells (PCM) were cultured and treated with lovastatin or compactin at concentrations of 25 µM and 50 µM. Effects on actin stress fibers (phalloidin staining) and focal adhesion formation (vinculin) were evaluated by immunofluorescence staining. Urea/glycerol polyacrylamide gel electrophoresis and Western blot analysis were utilized to investigate the effects of statins on myosin light chain (MLC) phosphorylation. Changes in cell shape were recorded using the phase contrast microscope. A constant flow organ culture perfusion system was used to measure outflow facility in perfused porcine eye anterior segments. Results: PTM cells treated with lovastatin and compactin demonstrated dramatic changes in cell shape, with cells becoming rounded and separated from each other. These morphological changes were found to be reversible upon drug withdrawal. Within 24 hours of drug administration, there was evidence of actin depolymerization and loss of focal adhesions. Supplementation of cell culture media containing lovastatin with geranylgeranyl pyrophosphate completely reversed the changes in cell shape and cytoskeletal organization. Lovastatin and compactin also induced marked reduction in MLC phosphorylation indicative of cellular relaxation. Similar changes in cell shape, cytoskeletal organization and MLC phosphorylation were observed in PCM cells treated with statins. In an ongoing study, perfusion of porcine eye anterior chambers with 100 µM lovastatin caused a 48% drop in intraocular pressure at 72 hours, as compared to a 22% reduction in IOP in control eyes. Conclusions: These data demonstrate that statins (lovastatin and compactin) induce cellular relaxation in TM and ciliary muscle cells via effects on cell shape, actin cytoskeletal integrity and MLC phosphorylation. These effects of statins appear to involve the isoprenylation of small GTP–binding proteins such as Rho GTPase. Furthermore, these statins demonstrated the ability to decrease IOP in an organ culture perfusion model indicating their potential use in glaucoma therapy.
Keywords: trabecular meshwork • outflow: trabecular meshwork • pharmacology