Age independent expression of myocilin in the human trabecular meshwork

Glaucoma is a leading cause of blindness. Primary open-angle glaucoma, the most common form of glaucoma, is known to increase in prevalence with age. One of its major risk factors is an elevated intraocular pressure believed to be related to the trabecular meshwork (TM), a specialized tissue located at the chamber angle of the eye. Myocilin, a gene linked to open-angle glaucomas (OAG), has been found to be expressed in the TM and a broad range of other ocular and non-ocular tissues. The purpose of this study was to examine the distribution of myocilin protein and mRNA in the TM of normal human eyes to determine whether age-related changes exist. Studies with glaucomatous eyes were carried out concurrently. Immunoperoxidase staining experiments demonstrated positive immunoreactivity for myocilin protein in both the cells and beams in all regions of the TM. The staining intensity and the myocilin level as determined by dot blot assays were not correlated with the ages of donors ranging from 8 weeks to 93 years. Neither did myocilin mRNA, detected by in situ hybridization in cells throughout the TM and quantified by relative quantitative RT-PCR, vary with age. Myocilin mRNA and protein expression in diseased tissues was either comparable to that of normal tissues or reduced. This study represents the first in-depth investigation of myocilin expression in relation to age in the TM of human eyes. The results indicate an age independence, argue thus against a direct role of myocilin and reiterate the involvement of additional factors in the pathogenesis of glaucoma.