Systemic regulators of bone metabolism and local mediators, including cytokines, and leukotrienes, exert regulatory effects on the recruitment, differentiation, and physiology of cells participating in normal or pathological bone remodeling. Osteoclasts are specialized multinucleated cells responsible for removing the organic and inorganic components of bone matrix. Although it is generally accepted that the osteoclast originates from an early progenitor related to mononuclear phagocytes, the developmental relationship between circulating mononuclear cells, tissue macrophages, and osteoclast precursors is uncertain. Our working hypothesis proposes that osteoclast development is regulated through multiple external cues, some of which derive from osteoclasts. The integrated effects of these signals regulate osteoclast development and function. Bone remodeling pathologies may arise from inappropriate signals that affect osteoclast development or activity. Therefore, the specific aims of this application are to 1) further characterize and purify osteoblast-derived peptide factors influential in osteoclast cytodifferentiation, 2) further characterize and purify other osteoblast- secreted metabolites that may act independently or in concert with the osteoblast peptide factors identified in specific aim 1, 3) continue investigating the potential interactive role of the factors identified in specific aims 1 and 2 with a number of known cytokines, hormones, and matrix components for synergistic and/or antagonist actions on osteoclast development, 4) begin to determine the signal transduction mechanisms and pathways related to osteoblast factor induction of osteoclast cytodifferentiation, 5) clone osteoblast-derived peptide factors involved in osteoclast development and initiate molecular studies aimed at understanding the regulation of these factors. Highly purified chicken osteoclasts will be used to compare functional responses and to determine if the factors identified exert an influence on mature osteoclasts. Osteoblast factors will be purified and characterized using a combination of chromatographic procedures. Purified osteoblast factors will be tested for antigen induction and osteoclast precursor recruitment in the marrow or FLG 29.1 cell culture systems. Active components will be further analyzed for osteoclast development activity with the chick chorioallantoic membrane implant system. In vitro osteoclast development will be monitored by: a) ELISA and cDNA probing of osteoclast-specific antigens, b) changing levels of tartrate-resistant acid phosphatase, and c) acquisition of bone resorptive ability. These studies should expand our basic understanding of the cellular and molecular mechanisms of bone remodeling and potentially aid in devising therapeutic strategies for the skeletal osteopenia of periodontal disease, arthritis, osteoporosis, and other local or metabolic disorders of bone.