Comparison of genome-wide gene expression in suture- and alkali burn-induced murine corneal neovascularization

Purpose: Suture placement and alkali burn to the cornea are often used to induce inflammatory corneal neovascularization (CorNV) models in animals. This study compares the changes in genome-wide gene expression under these two CorNV conditions in mice. Methods: CorNV were induced in Balb/c mice by three interrupted 10-0 sutures placed at sites about 1 mm from the corneal apex, or by alkali burns that were 2 mm in size in the central area of the cornea. At the points in time when neovascularization progressed most quickly, some eyeballs were subjected to histological staining to examine CorNV and inflammatory cells infiltration, and some corneas were harvested to extract mRNA for microarray assay. After normalization and filtering, the microarray data were subject to statistical analysis using Significance Analysis of Microarray software, and interested genes were annotated using the Database for Annotation, Visualization, and Integrated Discovery (DAVID) program. The expression change of classical proangiogenic molecule like vascular endothelial growth factor (VEGF) and antiangiogenic molecule like pigment epithelium-derived factor (PEDF) was further verified using western blotting. Results: Suture placement induced CorNV in the areas between the suture and limbus, but did not affect the transparency of the yet unvasuclarized areas of the corneas. In contrast, alkali burn caused edema and total loss of transparency of the whole cornea. Histology showed that sutures only caused localized epithelial loss and inflammatory infiltration between the suture and limbus, but chemical burn depleted the whole epithelial layer of the central cornea and caused heavy cellular infiltration of the whole cornea. At day 5 after suture placement, 1,055 differentially expressed probes were identified, out of which 586 probes were upregulated and 469 probes were downregulated. At a comparable time point, namely on day 6 after the alkali burn to the corneas, 472 probes were upregulated and 389 probes were downregulated. Among these differentially expressed probes, a significant portion (530 probes in total, including 286 upregulated and 244 downregulated probes) showed a similar pattern of change in both models. Annotation (using DAVID) of the overlapping differential genes revealed that the significant enrichment gene ontology terms were "chemotaxis" and "immune response" for the upregulated genes, and "oxidation reduction" and "programmed cell death" for the downregulated genes. Some genes or gene families (e.g., S100A family or alpha-, beta-, or gamma-crystallin family) that had not been related to corneal pathogenesis or neovascularization were also revealed to be involved in CorNV. VEGF was upregulated and PEDF was stable as shown with western blotting. Conclusions: Sutures and alkali burn to the corneas produced types of damage that affected transparency differentially, but gene profiling revealed similar patterns of changes in gene expression in these two CorNV models. Further studies of the primary genes found to be involved in CorNV will supplement current understanding about the pathogenesis of neovascularization diseases.