In vitro generation of equine osteoclasts from bone marrow cells using a novel culture system

We report on preliminary results of a novel in vitro culture system designed to generate equine osteoclasts in large numbers. Osteoclast generation, as determined by the expression of tartrate resistant acid phosphatase (TRAP) and ability to resorb bone, was enhanced in equine bone marrow cultures supplemented with fibroblastic cell (L929) conditioned medium (L929-CM). Bone marrow was collected from a total of 12 horses and ponies and TRAP-positive cells with bone resorbing ability were generated in significant numbers in the last seven. TRAP-positive mononuclear cells appeared after three days in culture and steadily increased in number and size up to seven days when multinuclear TRAP-positive cells started to appear. L929-CM caused a significant increase in the number of TRAP-positive mononuclear cells generated after four and seven days, after which time the number of TRAP-positive cells decreased. The development of this in vitro system provides a reproducible means of generating large numbers of equine osteoclasts necessary for the study of bone remodelling and endochondral ossification in the horse.