Histochemical assessment for osteoblastic activity coupled with dysfunctional osteoclasts in c-src deficient mice.

Since osteoblastic activities are believed to be coupled with osteoclasts, we have attempted to his-tologically verify which of the distinct cellular circumstances, the presence of osteoclasts themselves or bone resorption by osteoclasts, is essential for coupled osteoblastic activity, by examining c-fos(-/-) or c-src(-/-) mice. Osteopetrotic c-fos deficient (c-fos(-/-)) mice have no osteoclasts, while c-src deficient (c-src(-/-)) mice, another osteopetrotic model, develop dysfunctional osteoclasts due to a lack of ruffled borders. c-fos(-/-) mice possessed no tartrate-resistant acid phosphatase (TRAPase)-reactive osteoclasts, and showed very weak tissue nonspecific alkaline phosphatase (TNALPase)-reactive mature osteoblasts. In contrast, c-src(-/-) mice had many TNALPase-positive osteoblasts and TRAPase-reactive osteoclasts. Interestingly, the parallel layers of TRAPase-reactive/osteopontin- positive cement lines were observed in the superficial region of c-src(-/-) bone matrix. This indicates the possibility that in c-src(-/-) mice, osteoblasts were activated to deposit new bone matrices on the surfaces that osteoclasts previously passed along, even without bone resorption. Transmission electron microscopy demonstrated cell-to-cell contacts between mature osteoblasts and neighboring ruffled border-less osteoclasts, and osteoid including many mineralized nodules in c-src(-/-) mice. Thus, it seems likely that osteoblastic activities would be maintained in the presence of osteoclasts, even if they are dysfunctional.