title: Effects of receptor activator of NFkappaB (RANK) signaling blockade on fracture healing.
abstract: As dominant regulators of osteoclastogenesis and bone resorption, receptor activator of NFkappaB (RANK), receptor activator of NFkappaB ligand, and OPG have been identified as ideal drug targets for the treatment of metabolic bone disease. One concern regarding the therapeutic use of RANK signaling inhibitors is their effect on fracture healing. Therefore we tested if uncoupling and osteoclast depletion via RANK blockade affects callus formation, maturation and matrix remodeling, as well as union rates in a mouse tibia fracture model. Low dose (1 mg/kg i.p.) RANK:Fc therapy had no effect on callus formation, matrix maturation and remodeling, and resulted in 100% bony union by day 28. High dose RANK:Fc treatment (10 mg/kg i.p.) effectively eliminated osteoclasts at the fracture site on day 14, with no significant effects on fracture healing. When therapy was discontinued, normal numbers of osteoclasts were observed at the fracture site by day 28. However, continuous therapy resulted in a large osteopetrotic callus consisting of both mineralized and unmineralized matrix that was void of osteoclasts, but bony union was unaffected at day 28. We also evaluated this process in the complete absence of RANK signaling using RANK -/- mice. These animals exhibited significant radiographic and histologic evidence of callus formation, indicating that RANK signaling is not required for fracture callus formation. However, only 33% of RANK -/- animals formed bony unions compared to 100% of the osteopetrotic control mice. This defect was most likely a result of decreased blood flow, as evidenced by fewer blood vessels in the RANK -/- animals. Together, these data imply that osteoclast depletion via inhibition of RANK signaling is a viable option for the treatment of pathological bone loss since no adverse effects on fracture healing are observed when therapy is discontinued.
authors.affiliation: Department of Microbiology and Immunology, University of Rochester Medical Center, Rochester, NY 14642, USA.
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Flick
authors.forename: Jason M
authors.initials: JM
authors.lastname: Weaver
authors.forename: Michael
authors.initials: M
authors.lastname: Ulrich-Vinther
authors.forename: Faruk
authors.initials: F
authors.lastname: Abuzzahab
authors.forename: Xinping
authors.initials: X
authors.lastname: Zhang
authors.forename: William C
authors.initials: WC
authors.lastname: Dougall
authors.forename: Dirk
authors.initials: D
authors.lastname: Anderson
authors.forename: Regis J
authors.initials: RJ
authors.lastname: O'Keefe
authors.forename: Edward M
authors.initials: EM
authors.lastname: Schwarz
mesh_terms: D000818:Animals; D002146:Bony Callus / Q000378:metabolism; D016466:CHO Cells; D006224:Cricetinae; D017102:Fracture Healing / Q000187:drug effects / Q000502:physiology*; D006023:Glycoproteins / Q000037:antagonists & inhibitors* / Q000235:genetics* / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D008817:Mice, Mutant Strains; D016328:NF-kappa B / Q000378:metabolism*; D010006:Osteoblasts / Q000502:physiology; D010010:Osteoclasts / Q000502:physiology; D053244:Osteoprotegerin; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors* / Q000235:genetics*; D018124:Receptors, Tumor Necrosis Factor; D011994:Recombinant Proteins / Q000494:pharmacology; D012039:Regional Blood Flow; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D013978:Tibial Fractures / Q000378:metabolism*
chemical_list: D006023:Glycoproteins; D016328:NF-kappa B; D053244:Osteoprotegerin; D018160:Receptors, Cytoplasmic and Nuclear; D018124:Receptors, Tumor Necrosis Factor; D011994:Recombinant Proteins; C506031:Tnfrsf11b protein, mouse