CXCR4-mediated chemoattraction of long bone and jaw osteoclast precursors

Bone is important to give the body support, but it also contains marrow that harbors mesenchymal stem cells and hematopoietic progenitors. An important chemoattractant for hematopoietic cell homing towards the bone marrow, CXCL12, was shown to inhibit expression of apoptosis related genes. Previously, it was shown that jaw osteoclast precursors express more anti-apoptotic genes than long bone osteoclast precursors. Also, jaw and long-bone marrow cells have a different osteoclastogenic potential. Here, we used time-lapse microscopy to follow long bone and jaw osteoclast precursors during three important steps of osteoclastogenesis, i.e. proliferation, migration, and fusion. Gene expression analyses were performed on markers of the different steps of osteoclastogenesis, and the directional migration of jaw and long-bone osteoclast precursors towards CXCL12 was studied. Long bone and jaw osteoclast precursors had similar rates of proliferation, random and directional migration, and fusion. Jaw osteoclast precursors expressed more CXCL12 and its receptors CXCR4 and CXCR7 than long bone osteoclast precursors. Therefore, we provide more evidence that osteoclast precursors are bone-site specific. Higher CXCL12 expression may explain the higher anti-apoptotic gene expression that was previously found in jaw cells than in long bone cells.