Changes in the expression and distribution of collagens in the outflow tissues and sclera due to decorin deficiency

Abstract

Purpose : Decorin is reduced in the outflow tissues of patients with primary open-angle glaucoma. Decorin deficiency in mice (Dcn^-/-) disrupts the homeostatic balance of growth factors in the anterior chamber angle by increasing the expression of TGF-β2 and CCN2/CTGF, leading to elevated intraocular pressure (IOP) and loss of optic nerve axons. In addition to the matricellular properties, DCN interacts with collagens and is involved in collagen fibrillogenesis. In the present study, we investigated the localization of DCN and various collagens in the outflow tissues and sclera of wild-type (WT) mice and whether Dcn deficiency affects their expression and localization.

Methods : Immunohistochemistry toward DCN and collagen (Col) type I, III, IV and VI was performed on sagittal sections of WT and Dcn^-/- mice (12 weeks). Double staining for Dcn and collagens was analyzed in the outflow tissues and the inner wall of Schlemm's canal (IWSC). Quantification was measured as mean fluorescence/µm² using Fiji/imageJ software. En face images were used for structural analysis of the outflow tissues. In addition, scleral wholemounts were used to evaluate the distribution of Dcn and collagens in WT and Dcn^-/-. Student’s t-test was used for statistical analysis.

Results : We detected Dcn and Col I, III, IV and VI in the outflow tissues and sclera of WT mice. Notably, we found co-localization of Dcn mainly with Col III and IV. In Dcn^-/-, we found an increase in mean fluorescence intensity/µm² for all collagens near the IWSC (Col I: 1.6±0.2, p<0.05; Col IV: 1.8±0.1, p<0.05; Col VI: 1.3 ±0.1, p<0.05), whereas in the entire outflow tissues Col III (1.2±0.1, p<0.05), IV (1.8±0.2, p<0.05) and VI (1.2±0.1, p<0.05) were significantly upregulated compared to WT. Structural analysis of en face images showed changes in distribution and organization of collagens, resulting in structural loss. Col III, IV, and VI showed disorganized fibrils and a more compact appearance in Dcn^-/-. In the Dcn^-/- scleral wholemounts, the orientation of collagen fibrils was markedly distorted and more amorphous vis-a-vis WT samples.

Conclusions : Our results suggest that Dcn is crucial for collagen fibril organization in the outflow tissues and the sclera. We propose that changes in collagen organization in the Dcn^-/- mice alter the biomechanical properties of these tissues thereby contributing to the elevated IOP and loss of axons.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.