Diverse osteoclastogenesis of bone marrow from mandible versus long bone

Mandibles (MB) and maxillae possess unique metabolic and functional properties and demonstrate discrete responses to homeostatic, mechanical, hormonal, and developmental stimuli. Osteogenic potential of bone marrow stromal cells (BMSCs) differs between MB versus long bones (LB). Furthermore, MB- versus LB-derived osteoclasts (OCs) have disparate functional properties. This study explores the osteoclastogenic potential of rat MB versus LB marrow in vitro and in vivo under basal and stimulated conditions.

Bone marrow from rat MB and LB was cultured in osteoblastic or osteoclastic differentiation media. Tartrate-resistant acid phosphatase (TRAP) staining, resorption pit assays, and real-time polymerase chain reaction were performed. Additionally, osmotic mini-pumps were implanted in animals, mandibles and tibiae were isolated, and multinucleated cells (MNCs) were measured.

MB versus LB marrow cultures that were differentiated with receptor activator of nuclear factor-κB ligand (RANKL) and macrophage colony-stimulating factor produced more TRAP(+) MNCs and greater resorptive area. To explore MB versus LB BMSC-supported osteoclastogenesis, confluent BMSCs were cultured with parathyroid hormone (PTH), 1,25-dihydroxyvitamin D3 (1,25D3), or PTH+1,25D3. 1,25D3- or PTH+1,25D3-treated LB BMSCs expressed significantly higher RANKL and lower osteoprotegerin (OPG) mRNA and increased RANKL:OPG ratio. When whole marrow was cultured with PTH+1,25D3, more TRAP(+) MNCs were seen in LB versus MB cultures. Ultimately, rats were infused with PTH+1,25D3, and MB versus tibia MNCs were measured. Hormonal stimulation increased osteoclastogenesis in both MB and tibiae. However, higher TRAP(+) MNC numbers were observed in tibiae versus MB under basal and hormonal stimulation.

Collectively, these data illustrate differences of both osteoclastogenic potential and OC numbers of MB versus LB marrow.