Orthopedics Research Trainee
Samantha Perez-Menendez, Xiaomeng You, Renee T Ormsby, Haley Cox, Kelly Tsang, Thomas L Andersen, and Julia F Charles
Dr. Julia F Charles
Research Category: Musculoskeletal/Orthopedics/Sports Medicine
We examined 3 murine models of severe ARO (Clcn7F318L/F318L, Slc4a2-/-, and CtskCre;Nfatc1fl/fl mice) using conventional histologic, immunohistochemistry and in situ hybridization investigations and micro-CT. OC depletion: OC depletion was achieved by either treating mice with the neutralizing antibody to RANKL, or genetically by crossing to CtskCre;Rankfl/fl mice. Radiation chimeras: Lethally irradiated wildtype mice were reconstituted with hematopoietic stem cells (HSC) from CtskCre;Nfatc1fl/fl or littermate controls and maintained on a low calcium diet.
Examination of ARO mouse long bones demonstrated osteopetrosis, runting and loss of normal bone morphology. Characterization of marrow fibrosis demonstrated proliferative early osteoblasts (Ki67+, RUNX2+ and SMA+). RANKL inhibition diminished fibrosis in ARO mice, demonstrating a role for OC in marrow fibrosis. Crossing Clcn7F318L/F318L and CtskCre;Nfatc1fl/fl onto an OC deficient genetic background (CtskCre;Rankfl/fl) eliminated both OC and marrow fibrosis. Finally, reconstitution of lethally irradiated wildtype mice with CtskCre;Nfatc1fl/fl HSC was sufficient to induce marrow fibrosis.
The coupling of osteoclastic bone resorption to osteoblastic bone formation is key to maintaining bone structure and function. Coupling is not fully understood but appears to require osteoclasts (OC). Dysregulated coupling is a feature of osteopetrosis, a family of diseases caused by mutations affecting OC resorptive function, where bone formation continues despite minimal resorptive activity. In severe autosomal recessive forms of osteopetrosis (ARO), marrow fibrosis resulting in failure is described in both patients and mouse models. We hypothesized that marrow fibrosis is a consequence of dysregulated coupling and therefore, dysfunctional OC are both necessary and sufficient for marrow fibrosis in ARO.