SPARC Deficiency Results in Improved Surgical Survival in a Novel Mouse Model of Glaucoma Filtration Surgery

Abstract

Glaucoma is a disease frequently associated with elevated intraocular pressure that can be alleviated by filtration surgery. However, the post-operative subconjunctival scarring response which blocks filtration efficiency is a major hurdle to the achievement of long-term surgical success. Current application of anti-proliferatives to modulate the scarring response is not ideal as these often give rise to sight-threatening complications. SPARC (secreted protein, acidic and rich in cysteine) is a matricellular protein involved in extracellular matrix (ECM) production and organization. In this study, we investigated post-operative surgical wound survival in an experimental glaucoma filtration model in SPARC-null mice. Loss of SPARC resulted in a marked (87.5%) surgical wound survival rate compared to 0% in wild-type (WT) counterparts. The larger SPARC-null wounds implied that aqueous filtration through the subconjunctival space was more efficient in comparison to WT wounds. The pronounced increase in both surgical survival and filtration efficiency was associated with a less collagenous ECM, smaller collagen fibril diameter, and a loosely-organized subconjunctival matrix in the SPARC-null wounds. In contrast, WT wounds exhibited a densely packed collagenous ECM with no evidence of filtration capacity. Immunolocalization assays confirmed the accumulation of ECM proteins in the WT but not in the SPARC-null wounds. The observations in vivo were corroborated by complementary data performed on WT and SPARC-null conjunctival fibroblasts in vitro. These findings indicate that depletion of SPARC bestows an inherent change in post-operative ECM remodeling to favor wound maintenance. The evidence presented in this report is strongly supportive for the targeting of SPARC to increase the success of glaucoma filtration surgery.

Current concepts on primary open-angle glaucoma genetics: a contribution to disease pathophysiology and future treatment

“…112 It distributes throughout the TM and it has been considered to have an important role in IOP regulation. 113 SPARC has also been detected in the iris of POAG patients, 114 while Seet et al 115 have found that SPARC deficiency in mice resulted in improved surgical survival in a mouse model of glaucoma filtration surgery. Aroca-Aguilar et al 116 reported an interaction between recombinant MYOC and SPARC.…”

Validation of the Glaucoma Filtration Surgical Mouse Model for Antifibrotic Drug Evaluation

“…We have developed a mouse model of GFS which can be employed to investigate the postoperative subconjunctival scarring response (21). To ascertain that the murine model is relevant to the clinical setting, we applied MMC in the mouse model and examined the postoperative surgical responses.…”

“…Careful slit lamp, anterior segmentoptical coherence tomography (AS-OCT) and in vivo confocal microscopic examinations on subconjunctival blebs were performed at postoperative day 2, and weekly thereafter for a total of 4 wks as described previously (21). A bleb was judged to have failed if the surgical site appeared flat by slit lamp analysis.…”

“…All animals from each group were subjected to slit lamp and AS-OCT analyses. In vivo confocal microscopy was performed on two animals from each group as described previously (21).…”

“…Mice were euthanized on day 28 after surgery, and the eyes were enucleated for immediate fixation and processing as described (21). Five-μm sections were stained with hematoxylin and eosin to visualize tissue morphology.…”