The localization of CD44 and moesin in osteoclasts after calcitonin administration in mouse tibiae

We investigated the immunohistochemical localization of CD44, hyaluronate receptor, and moesin, of the ezrinradixin-moesin (ERM) family, in osteoclasts after calcitonin adminstration using confocal laser scanning microscopy and transmission electron microscopy to clarify the role of CD44 and moesin in their cytoskeletal organization and cell polarity. We also elucidated the localization of osteopontin (OPN) to confirm its possible role in cell-matrix recognition via CD44. In untreated mice, intense immunoreactivities for CD44 and moesin were detected on the basolateral plasma membrane of osteoclasts. Rhodamine-phalloidin reactivity was seen in a bandlike pattern on the region of contact between osteoclasts and bone and was also detected moderately along their basolateral plasma membrane. At 30 min after calcitonin administration, osteoclasts did not show either clear zones or ruffled borders. The bandlike reactivity of rhodamine-phalloidin in the contact region was diminished, although labeling was seen along osteoclasts. CD44 and moesin were colocalized along their plasma membranes, including the region facing the bone surface. Electron microscopic observation revealed that the microvillus processes in the contacting region with bone surface, as well as the basolateral plasma membrane, showed immunoreactivities to CD44 and moesin. At 60 min, some osteoclasts attached to bone and showed a bandlike pattern of rhodamine-phalloidin. On the other hand, OPN was localized under CD44-positive cytoplasmic processes and the clear zone of osteoclasts. These findings suggest that calcitonin effects on the cell polarity of osteoclasts and the CD44-moesin-actin filament system in osteoclasts plays an imporant role in cell polarity and cell-matrix recognition.