Takayuki Nagasaki, PhD

A goal of our research is to understand wound healing in the cornea at a molecular and cellular level for better management of injuries and diseases of the cornea and also to improve ketorefractive surgery, a procedure that has become popular in recent years. Therefore, we are studying movements of all types of cells in the cornea.

Cell movement is integral to both homeostasis of normal tissues and healing of damaged tissues, and we hope to 1) describe movements of individual cells in detail under both conditions and 2) understand molecular regulation of such movements in the cornea. We approach the problems of cell movement in the mouse cornea with both conventional histological methods and a real-time video microscopic observation of living cells. The latter procedure was developed using a standard fluorescence microscope and continuously improving its technical details. To date we have successfully documented and analyzed movements of corneal epithelial cells, corneal stromal cells, leukocytes that infiltrate the corneal stroma after an injury, and also capillary sprout formation during neovascularization induced by cauterization.

Our interests also extend to some basic cell biological questions of cell movement in three dimensional tissue environment such as the corneal stroma. This is an area that has not been explored well and many basic questions remain unanswered, such as adhesion and de-adhesion of a cell to extracellular matrix components during movement, an extracellular source of driving force, intracellular force generation for a movement, a role of cell-cell contact, etc. The corneal stroma is technically an ideal tissue to address these questions because of its transparency, avascularity, simple collagen lamellar structures, and ease of access with microscopy. Taking full advantage of findings from tissue culture studies, we hope to gain insight on molecular mechanisms of cell movement in a living tissue. In addition, our recent study of corneal epithelial cell movement (Nagasaki and Zhao, 2003, IOVS, 44:558) prompted us to ask a question concerning epithelial stem cells. Overwhelming evidence now suggests that corneal epithelial stem cells are located in a limbal area but a positive identification of stem cells has not been achieved due to a lack of a definitive molecular marker. We are taking advantage of our ability to track individual epithelial cells of the cornea to try to identify and study behavior of epithelial stem cells and their immediate progeny, or transient amplifying cells, at the limbus. It has been long known that when the corneal epithelium is scraped off the cornea, underlying stromal cells degenerate within hours. We have shown recently that the tears contain molecules that are cytotoxic to the stromal cells in the mouse (Zhao et al., 2001, IOVS 42:1743), and determined the major source of such molecules to be lacrimal glands. Our goals of this project are to 1) identify the molecular nature of the cytotoxic activity in the tears and 2) investigate its physiological role.

For further details and up-to-date information, see the following web page: http://www.columbia.edu/~tn4/research/