Primary Isolation and Culture of Chicken Osteoclasts

Bone is a dynamic tissue that is continually remodeled throughout life. Such remodeling is carried out by the coordinated actions of two bone cell types: bone-resorbing osteoclasts (OCs) which are uniquely capable of dissolving and removing a small volume of bone, and bone-forming osteoblasts that subsequently fill in these lacunae or pits with new bone tissue. Whereas osteoblasts originate from mesenchymal cell precursors, OCs derive from hematopoietic precursors related to monocytic cells that are present both in the bone marrow and peripheral circulation. In response to specific hormonal or local signals provided by osteoblasts, stromal cells, or other cells within the bone marrow microenvironment, OCs precursors fuse and differentiate into large multinucleated cells expressing characteristic morphological features, membrane polarization, adhesion molecules, ion pumps, enzyme activities, and antigenic profiles (1 –3 ). Most importantly, they develop a capacity for bone pit resorption, the unique and defining functional attribute of OCs. Bone resorption and formation are normally carefully balanced processes in adults. However, in various diseases or pathological conditions, an imbalance exists such that the number of OCs, number of resorption sites initiated, and/or rates of remodeling are altered, thereby resulting in either too much or too little bone turnover. Excessive bone loss occurs in many clinically relevant disorders that affect millions of people, including postmenopausal osteoporosis, rheumatoid arthritis, periodontal disease, tumor-associated osteolysis, and orthopedic implant loosening (4 –7 ).