GROWTH AND DIFFERENTIATION OF TRACHEAL EPITHELIAL PROGENITOR CELLS

The purpose of these studies was to determine whether both basal and s ecretory rat tracheal epithelial (RTE) cells served as multipotent epi thelial progenitors and whether both cell types gave rise to a similar ''poorly differentiated'' cell during the early phase of epithelial r egeneration in denuded tracheal grafts. Griffonia simplicifolia I (GSI ) lectin and flow cytometry were used for cell sorting. More than 98% of GSI-positive cells expressed plasma membrane alpha 1-3 terminal gal actose (Gal), and 95% contained keratin 14 (K14), phenotypic markers f or basal cells; <1% were secretory or ciliated cells. Less than 2% of the GSI-negative cells expressed Gal or K14, but this fraction contain ed 16% ciliated cells and 54-79% secretory cells, dependent on whether periodic acid-Schiff staining or binding of an antisecretory cell mon oclonal antibody (RTE 12) was used as the criterion. Equal numbers of viable cells from either fraction were inoculated into denuded trachea l grafts, which were studied on days 1-14. At 24 h, greater numbers of GSI-negative than -positive cells were found attached to the graft wa ll; the keratin staining pattern of the attached cells was similar to that of the parent cell populations, but monoclonal antibody-detectabl e secretory and ciliated cell epitopes, originally present in the GSI- negative fraction, were lost. 5-Bromo-2'-deoxyuridine uptake was not s een at 24 h, but by 48 h all epithelial cells from both fractions ente red the cell cycle. From 48 to 96 h, cells derived from either fractio n were ultrastructurally indistinguishable; they were poorly different iated and highly proliferative, and all expressed Gal and K14. A matur e epithelium evolved from the poorly differentiated cells in both sets of grafts, but secretory and ciliated cells appeared earlier in graft s inoculated with GSI-negative cells. The results strongly suggest tha t in this model of tracheal epithelial regeneration both basal and sec retory cells ''dedifferentiated'' into a similar highly proliferative phenotype from which a mucociliary epithelium ''redifferentiated.''