MicroRNA Expression in the Glaucomatous Retina

Abstract

Purpose: MicroRNAs are small, endogenous noncoding RNAs that modulate posttranscriptional gene expression. Although the contribution of microRNAs to the pathogenesis of glaucomatous damage is unknown, supporting evidence from central nervous system (CNS) research suggests they may play a role. It was therefore hypothesized that microRNAs known to be altered in CNS injury are also altered in experimental glaucoma.

Methods: Intraocular pressure (IOP) was elevated in rats by unilateral injection of hypertonic saline and IOP monitored for 5 weeks. After rats were killed, retrobulbar optic nerve sections were graded for damage. MicroRNA was extracted from whole retinae of eyes with advanced nerve damage (n = 8) and from normal, noninjected control eyes (n = 8). Quantitative PCRs were performed using a panel of 17 microRNAs, reported from CNS research to be implicated in mechanisms also linked to glaucomatous damage. Computationally and experimentally derived gene targets were identified for the differentially expressed microRNAs. These were then integrated with existing gene array data. Functional interpretation was performed using the Molecular Signatures Database and DAVID Functional Annotation Clustering.

Results: Eight microRNAs were significantly downregulated in glaucomatous retinae compared with controls (miR-181c, miR-497, miR-204, let-7a, miR-29b, miR-16, miR106b, and miR-25); miR-27a was significantly upregulated. Enrichment of targets associated with extracellular matrix/cell proliferation, immune system, and regulation of apoptosis were observed. Cholesterol homeostasis and mTORC-1 pathways showed reduced expression.

Conclusions: MicroRNAs are differentially expressed in retinae of eyes with advanced glaucomatous damage compared with normal controls. Integrating microRNA with gene expression data may improve understanding of the complex biological responses produced by chronically elevated IOP.

Figure 1

(A) Mean/maximum IOP of control eyes and those with experimental glaucoma over the duration of the experiment. Error bars represent ± SD. (B) Cumulative IOP profile of control and experimental eyes over the duration of the experiment.

Figure 2

Biological interpretations of differential microRNA expression in retinae with advanced glaucomatous damage. (A) Reduced expression of proapoptotic microRNAs (miR-16, miR-497, miR-29b, and let 7-a) would aim to reduce apoptotic cell death. Increased expression of the antiapoptotic miR-27a would also enhance this effect. These changes in the microRNA signature are suggestive of a protective shift to limit apoptosis. (B) Reduced expression of several microRNAs (miR-106b, miR25, and miR-204) is associated with enhanced TGF-β signaling and a reduction in let-7a expression is also known to enhance cell proliferation. These changes in the MicroRNA signature within glaucomatous retina are consistent with extensive ECM remodeling.