Deletion of SPARC Enhances Retinal Vaso-Obliteration in Mouse Model of Oxygen-Induced Retinopathy.

Abstract

BACKGROUND Secreted Protein Acidic and Rich in Cysteine (SPARC) is a matricellular protein which is implicated in regulation of angiogenesis. PURPOSE To characterize the changes in SPARC expression and effect of its deletion in a mouse model Oxygen Induced Retinopathy (OIR). MATERIALS AND METHODS Wild type (wt) and SPARC-deficient mice were subjected to high oxygen (75%) for 5 days (p7-p12) before room air for additional 5 days (p12-p17). Retinas from both groups were flat mounted and retinal vessels were labeled with Isolectin-B4. Areas of Retinal Neovascularization (RNV) and vaso-obliteration were measured by Image-J and normalized to total retinal areas. SPARC expression was analyzed in both groups at p14 and p17 in retinal homogenates and sections by Western Blotting (WB) and immunofluorescence respectively. Human Retinal Endothelial Cells (HRECs) were exposed to hypoxia (1% O2) for 6 hours then SPARC was measured in cell lysate and condition medium by WB and ELISA. Moreover, HRECs were treated with VEGF or SPARC to study their mutual regulatory effect. RESULTS SPARC-deficient mice demonstrated significant increase in the vaso-obliteration (p=0.03) and modest increase in RNV compared to the wt control. Retinal levels of SPARC was significantly decreased during OIR at p14 (p=0.01) and partially restored to normal level by p17. Moreover, hypoxia significantly reduced SPARC expression and secretion in HRECs (p=0.001). We noticed a mutual positive regulatory feedback between SPARC and VEGF. CONCLUSION SPARC deletion enhances ischemic retinopathy, thus modulation of SPARC expression could be a novel therapeutic approach to prevent pathological RNV.