Adhesive substrates influence acid-productive activities of cultured rabbit osteoclasts: cultured osteoclasts with large vacuoles have enhanced acid-productive activities

Adhesive and bone resorptive activities of isolated osteoclasts from hen medullary bone

In the present study, osteoclasts were isolated from hen medullary bones at the formative and resorptive phases. The cells were cultured on glass culture dishes and bone slices. After culturing, the adhesion activity of the isolated osteoclasts with the substrates was estimated with a light microscope, and the surfaces of the bone slices were observed with a scanning electron microscope. The results showed that the adhesion activity of tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts is higher at the bone resorptive phase than at the bone formative phase, and this tendency in isolated osteoclasts was observed more frequently on the bone slices than on the glass culture dishes. Furthermore, scanning electron microscopy showed that the isolated osteoclasts in the bone resorptive phase adhered to the bone surface with developed-cytoplasmic projections and formed broad pits where collagen fibrils were exposed. On the other hand, isolated osteoclasts in the bone formative phase adhered to the bone slice with board-shaped cytoplasmic projections and did not form any pits. These results suggest that isolated osteoclasts in the bone resorptive phase have a high level of adhesion activity and actively resorb the bone, whereas isolated osteoclasts in the bone formative phase have a low level of adhesion activity and cease bone resorption. The procedure reported here is useful for studying the bone-resorptive mechanism of authentic osteoclasts.

Molecular aspects of osteoclast function

In this article we have overviewed recent important advances in understanding the molecular mechanisms involved in osteoclastic bone resorption. Specifically, new findings relating to osteoclast activation and the process of bone resorption are reviewed and a current overall model of how osteoclasts resorb bone is presented. Controversial research topics concerning the regulation of osteoclast activity are also critically discussed.