A morphological study on the effect of Thrombospondin-1 on episcleral veins in a TSP-1 deficient mouse model
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Abstract
BACKGROUND: Untreated primary open-angle glaucoma (POAG) can lead to irreversible blindness. One of the primary risk factors is elevated intraocular pressure (IOP). Studies have shown that increased IOP can result from increased resistance in the drainage pathway or excess secretion of aqueous humor (AH). More extensive research has already been done on the trabecular meshwork (TM) and Schlemm’s Canal (SC), and shown novel changes in extracellular matrix composition, morphology, and gene expression in POAG eyes that may be correlated with the IOP increase seen in most POAG cases. Studies have shown that the distal outflow pathway structures, including episcleral veins (ESV) also plays a role in IOP regulation. A previous study showed that Thrombospondin-1 (TSP-1)-/- mice were resistant to dexamethasone induced IOP elevation and had lower IOP at baseline than WT mice. TSP-1 is a protein that has been studied for its antiangiogenic, vasoconstrictive, and extracellular matrix (ECM) remodeling effects. This study evaluated TSP-1’s effect on ESVs to test whether a lack of TSP-1 would affect the size [cross-sectional area (CSA)] of ESVs.
METHODS: 5 WT and 5 TSP-1-/- eyes from male mice were enucleated. All eyes were fixed and embedded in resin for sectioning. 4-6 µm sections were taken from superior and inferior regions from each eye and stained with 0.1% Toluidine blue solution. ESVs were identified using a light microscope and cross-sectional area (CSA) measurements were taken on ImageJ (NIH). Unpaired t-test was performed to analyze differences in CSA.
RESULTS: The average CSA of ESVs in the superior region of TSP-1-/- eyes (74.49 ± 14.74 µm2) was significantly reduced compared to the average CSA of ESVs in the superior region of WT eyes (133.13 ± 15.55 µm2) (p<0.05). The CSA of ESVs in the inferior region was smaller, but the results did not meet statistical significance.
CONCLUSIONS: TSP-1 increased the size of ESVs in the superior region but did not affect the size of ESVs in the inferior region significantly. The results in this study support a possible segmental variation that may affect TSP-1’s effect seen in ESVs.
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2024