Osteoclast differentiation in ectopic bone formation induced by recombinant human bone morphogenetic protein 2 (rhBMP-2)

Abstract

Osteoclast differentiation in the process of ectopic bone formation induced by recombinant human bone morphogenetic protein 2 (rhBMP-2) was examined to clarify the relationship between osteoclast development and rhBMP-2-induced bone formation. A combination of rhBMP-2 with a porous microsphere (PMS) and blood clot was implanted subcutaneously on the bilateral chest muscles of rats. Tartrate-resistant acid phosphatase (TRAPase) activity, cathepsin K (cath K), and calcitonin receptor (CTR), as markers of osteoclasts and their precursors, were examined using enzyme and immunohistochemical analysis up to 7 days after implantation. Mononuclear cells positive for TRAPase, cath K, and CTR first appeared on day 3 in connective tissue surrounding the PMS after implantation of rhBMP-2. Simultaneously, alkaline phosphatase activity became detectable in mesenchymal cells in the connective tissue. Electron microscopy demonstrated some mononuclear cells with abundant mitochondria and poorly developed rough endoplasmic reticulum in the proximity of mesenchymal cells. However, there was no evidence of cartilage or bone matrix formation on day 3. Osteoclasts in various stages of development, classified by the pattern of immunoreactivity for cath K, were observed by day 7. The polarized intracellular distribution of cath K was found only in osteoclasts attached to bone matrix. In conclusion, we have demonstrated for the first time the appearance of osteoclast precursors before bone matrix formation induced by rhBMP-2, suggesting that bone matrix is not a prerequisite for osteoclast precursor recruitment. Furthermore, we suggest that differentiation into polarized functional osteoclasts is accomplished when the osteoclasts attach to the bone matrix.

Pressure and Distortion Regulate Human Mesenchymal Stem Cell Gene Expression

“…29 Osteoclast differentiation is thought to be initiated before the deposition of cartilage or bone matrix as calcitonin-binding cells appear before cartilage and bone formation in the area of ectopic bone formation induced by BMP. 25 Nell1 is a protein strongly present in cells of neural crest origin residing within the craniofacial complex. 10 It has been observed to be upregulated in abnormally fusing cranial sutures and is specific for osteochondral progenitor cells.…”

Novel Wnt Regulator NEL-Like Molecule-1 Antagonizes Adipogenesis and Augments Osteogenesis Induced by Bone Morphogenetic Protein 2

“…24,89 In support of this concept, mice homozygous for Nell1 deficiency exhibit reduced expression of the osteoclastogenesis inhibitor osteoprotegerin, 6 and the heterozygous Nell1-deficient mice that survive to adulthood manifest an osteoporotic phenotype. 39 Interestingly, BMP2 and Wnt signaling synergistically increase osteoprotegerin expression, 90 and ongoing studies will determine whether BMP2þNELL-1 can similarly induce osteoprotegerin and/or inhibit osteoclastogenesis.…”

“…19e21 Unfortunately, the high BMP2 concentrations required for osteogenesis in humans are associated with significant adverse effects, including an FDA warning of life-threatening cervical swelling, 22 ectopic bone formation (U.S. Food and Drug Administration, http://www.fda. gov/MedicalDevices/Safety/AlertsandNotices/PublicHealth Notifications/ucm062000.htm, last accessed September 28, 2011), 23 osteoclastogenesis, 24 and inconsistent bone formation. 25 Thus, improving the safety and efficacy of BMP2-based skeletal repair is crucial.…”

BMP‐2 regulation of PTHrP and osteoclastogenic factors during osteoblast differentiation of C2C12 cells

“…The opposite actions of BMP-2 enhancing OPG and inhibiting RANKL expression seem to be contradictory to those of promoting survival and resorption activity of mature osteoclast. Nevertheless these observations could partially explain the succession of events occurred when inducing ectopic bone formation in vivo with BMP-2 (Irie et al, 2003;Cowan et al, 2005). In these reports, the authors describe the appearance of active osteoclast cells in the connective tissue surrounding the BMP-2 implantation area, but always after new bone mass has been formed and needs to be remodeled.…”