Identification of keratocyte-like cells differentiated from circulating bone marrow-derived cells in the mouse cornea

Bone marrow (BM)-derived stem cells have the potential to differentiate into multiple lineages of tissue resident cells. BM-derived cells have been detected in the mouse cornea, but most of these cells were found to be CD45 ⁺ or CD11b⁺ immunocompetent cells. Although some BM-derived cells in the cornea were negative for these cell surface markers, it has remained unclear whether cells of BM origin can differentiate into corneal resident cells. To address this issue, we subjected wild-type mice that had been exposed to a lethal dose of radiation to intravenous injection with BM cells from green fluorescent protein (GFP) transgenic mice. Two months after cell transplantation, fluorescence microscopy revealed the presence of numerous GFP⁺ cells throughout the cornea, with intense GFP fluorescence being apparent around the limbal region. Immunohistofluorescence analysis of corneal cross-sections revealed that most of the BM-derived GFP⁺ cells expressed CD45 or CD11b, although a few GFP⁺ cells were negative for these markers. Immunostaining of individual cells isolated from the corneal stroma, however, showed that a small proportion (~1 %) of GFP⁺ BM-derived cells expressed the keratocyte-specific proteoglycan keratocan. Our results suggest that BM-derived cells introduced intravenously are able to differentiate into resident cells of the corneal stroma.