Distribution of SPARC protein (osteonectin) in normal and wounded feline cornea

The purpose of this study was to determine the distribution of SPARC protein, also known as osteonectin or BM-40, in normal and wounded cat cornea. Indirect immunohistochemistry was used to study the distribution of SPARC protein. The following types of corneal wounds were performed: -5.0-dioptric excimer laser photorefractive keratectomy, mechanical keratectomy, and epithelial scrape wounds. The cats (n = 9) were killed 1-30 days after the operation and corneas prepared for immunohistochemistry using polyclonal rabbit anti-murine SPARC antibody and avidin-biotin complex. Weak immunoreaction for SPARC protein was observed in the cytoplasm of epithelial and endothelial cells but not in the keratocytes of both normal and wounded corneas. Unwounded extracellular matrix was negative in the control cornea. Following experimental wounding, an intense immunoreaction for SPARC appeared transiently at the basal aspect of the basal epithelial cells of multilayered, recently healed epithelium. The SPARC immunoreaction began from the wound edge but was not observed subjacent to the flattened single-layered epithelial cells of the leading edge. The immunoreaction for SPARC was found on Days 1-6 following wounding and subsequently withdrew. The transient appearance of SPARC under the healing corneal epithelium suggests its involvement in the regulation of epithelial cell migration or shape during the healing process.