Osteoclast function in healthy subjects and in patients with Paget's disease

Osteoclasts, the bone resorbing cells, are important in normal bone remodel ing. Resorption of bone by osteoclasts is coupled to osteoblastic bone form ation. An increase in osteoclastic bone resorption relative to bone formati on is found in many conditions, which lead to a net loss of bone resulting in osteoporosis. Like osteoporosis, Paget's disease of the bone is also cha racterized by an increase in osteoclastic resorption. It is an important cl inical entity in our aging population, and the osteoclasts are the primary cells responsible for the characteristic bone lesions. Unlike osteoporosis, the profound increase in bone resorption is followed by excessive new bone formation. The study of the factors responsible for normal osteo elastic d ifferentiation, maturation and activation has been invaluable in understand ing the patho physiology of osteoporosis and Paget's disease. This review w ill focus on normal osteoclastic mor phology, the factors that affect osteo clast function and formation, and then contrast these with ab normalities o f osteoclasts in Paget's disease.