Abstract
Purpose: :
At both cellular and molecular level, the sites of action of muscarinic antagonists in myopia are unclear. In addition to the fibroblasts of the sclera, the retinal pigment epithelial cells (RPE) would be another possible target for these agents. The purpose of this study is to determine the role of muscarinic receptors (MRs), matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) on mouse RPE and their function in the onset and development of myopia in MR mutant mice.
Methods: :
On post-natal day 10, negative 10D spectacle lenses were placed over the right eyes of M1, M3 mutant and wild type mice (n = 18 mice from each strain). Refraction was measured by automated infrared photo-refraction and axial length was measured by AC-Master, OLCI at 2, 4, 6 weeks after induction. Expression of MRs, MMPs and TIMPs was detected by western blot and immunohistochemistry. Transcript levels of MRs, MMPs and TIMPs was quantified by real-time PCR.
Results: :
Using a MR mutant mice for experimental myopia, both the RPE tissue and RPE cultured cells were used to uncover RPE response to myopia. The expression of MRs, MMPs and TIMPs were compared between myopic induced MR mutants and myopic-induced wild type. The expression of MRs, MMPs and TIMPs in the RPE was differentially regulated upon the induction of myopia. Using PCR and immunohistochemical studies, the presence of all five MRs, MMP1, 2, 3, 9 and TIMP 1, 2, 3 were established in mouse RPE. Refractive state and axial length measurements for myopic-induced mouse showed M1 mutant mouse to be more myopic as compared to MR3 mutant mouse. Down-regulation of MMP-2, MMP-3 and TIMP-1 were observed in myopic-induced MR1 mutant mice but not in myopic-induced MR3 mutant mice. Up-regulation of TIMP-3 was observed in myopic-induced MR3 mutant mice.
Conclusions: :
Down-regulation of MMP-2, MMP-3 and TIMP-1 and up-regulation of TIMP-3 might play a role in preventing myopia progression. Up-regulation of TIMP-3 by MR3 antagonist might play a greater role in the prevention of myopia progression as compared to down-regulation of MMP-2, MMP-3 and TIMP-1 by M1 antagonist. Understanding the specific reaction of each receptor subtype to the muscarinic antagonists treatment could enable us to design or develop an effective and specific drug toward the prevention of myopia.
Keywords: myopia • retinal pigment epithelium • gene/expression