CELLS CULTURED FROM THE GROWING TIP OF RED DEER ANTLER EXPRESS ALKALINE-PHOSPHATASE AND PROLIFERATE IN RESPONSE TO INSULIN-LIKE GROWTH-FACTOR-I

Deer antler growth provides a unique natural model of rapid and comple te bone regeneration. In this study, the distal antler tips of male re d deer (Centus elaphus) were collected post-mortem during the annual g rowth period (April-August), and an in vitro system established for th e culture of cells from three regions; the inner layer of the perichon drium, the reserve mesenchyme and the cartilage zone. Alkaline phospha tase (ALP) expression by cultured cells, as demonstrated by enzyme his tochemistry and biochemical assay, reflected the stage of cellular dif ferentiation. ALP activity was highest in cells cultured from the hype rtrophic cartilage region (3.6 +/- 0.2 mu mol/mu g cell protein/minute ), and lowest in undifferentiated mesenchymal cells (0.3 +/- 0.01 mu m ol/mu g cell protein/minute). ALP expression was lost with passage in culture. Levels of ALP activity in cultured cells correlated with the pattern and extent of enzyme expression in tissue sections as demonstr ated by histochemical staining. Insulin-like growth factor (IGF)-I (10 (-9)M-10(-7)M) was found to be mitogenic for cultured cells from all t hree zones as shown by increased incorporation of [H-3]thymidine into DNA. These results demonstrate that cells from three different regions of the antler tip can be maintained in culture, and that antler cells share certain phenotypic characteristics of growth plate chondrocytes . These data provide further evidence of a role for IGF-I in the regul ation of antler growth. Antler regrowth is a potentially useful model for the study of the factors that regulate bone formation.