PTH receptor signaling in osteocytes governs periosteal bone formation and intra-cortical remodeling

Authors

Yumie Rhee, Matthew R. Allen, Keith Condon, Virginia Lezcano, Ana C. Ronda, Carlo Galli, Naomi Olivos, Giovanni Passeri, Charles A. O'Brien, Nicoletta Bivi, Lilian I. Plotkin, Teresita Bellido

Abstract

The periosteal and endocortical surfaces of cortical bone dictate the geometry and overall mechanical properties of bone. Yet, the cellular and molecular mechanisms that regulate activity on these surfaces are far from being understood. Parathyroid hormone (PTH) has profound effects in cortical bone, stimulating periosteal expansion and at the same time accelerating intra-cortical bone remodeling. We report herein that transgenic mice expressing a constitutive active PTH receptor in osteocytes (DMP1-caPTHR1 mice) exhibit increased cortical bone area and elevated rate of periosteal and endocortical bone formation. In addition, DMP1-caPTHR1 mice display marked increase in intra-cortical remodeling and cortical porosity. Crossing DMP1-caPTHR1 mice with mice lacking the Wnt co-receptor LDL related receptor 5 (LRP5) or with mice overexpressing the Wnt antagonist Sost in osteocytes (DMP1-Sost mice), reduced or completely abolished, respectively, the increased cortical bone area, periosteal BFR, and expression of osteoblast markers and Wnt target genes exhibited by the DMP1-caPTHR1 mice. In addition, DMP1-caPTHR1 lacking LRP5 or double transgenic DMP1-caPTHR1;DMP1-Sost mice exhibit exacerbated intra-cortical remodeling and osteoclast numbers, and markedly decreased expression of the RANK decoy receptor osteoprotegerin (OPG). Thus, whereas Sost downregulation and the consequent Wnt activation is required for the stimulatory effect of PTH receptor signaling on periosteal bone formation, the Wnt-independent increase in osteoclastogenesis induced by PTH receptor activation in osteocytes overrides the effect on Sost. These findings demonstrate that PTH receptor signaling influences cortical bone through actions on osteocytes and define the role of Wnt signaling in PTH receptor action. © 2010 American Society for Bone and Mineral Research

Link to Article

http://dx.doi.org/10.1002/jbmr.304

Smad signaling determines chondrogenic differentiation of bone-marrow derived mesenchymal stem cells: Inhibition of Smad 1/5/8P prevents terminal differentiation and calcification

Authors

Catharine A Hellingman, Esmeralda Blaney Davidson, Wendy Koevoet, Elly L Vitters, Wim B van den Berg, Gerjo van Osch, Peter M van der Kraan

Abstract

The aim of this study was to investigate the roles of Smad2/3 and Smad1/5/8 phosphorylation in TGF-β induced chondrogenic differentiation of bone-marrow derived mesenchymal stem cells (BMSCs) in order to assess whether specific targeting of different Smad signaling pathways offers possibilities to prevent terminal differentiation and mineralization of chondrogenically differentiated BMSCs. Terminally differentiated chondrocytes produced in-vitro by chondrogenic differentiation of BMSCs or studied ex-vivo during murine embryonic limb formation, stained positive for both Smad2/3P and Smad1/5/8P. Hyaline-like cartilage produced in vitro by articular chondrocytes or studied in ex-vivo articular cartilage samples that lacked expression for MMP13 and collagen X only expressed Smad2/3P. When either Smad2/3 or Smad1/5/8 phosphorylation was blocked in BMSC culture by addition of SB-505124 or dorsomorphin throughout culture, no collagen II expression was observed, indicating that both pathways are involved in early chondrogenesis. Distinct functions for these pathways were demonstrated when Smad signaling was blocked after the onset of chondrogenesis. Blocking Smad2/3P after the onset of chondrogenesis resulted in a halt in collagen II production. On the other hand, blocking Smad1/5/8P during this time period resulted in decreased expression of MMP13, collagen X and alkaline phosphatase while allowing collagen II production. Moreover, blocking Smad1/5/8P prevented mineralization. This indicates that while Smad2/3P is important for continuation of collagen II deposition, Smad1/5/8 phosphorylation is associated with terminal differentiation and mineralization.

Link to Article

http://dx.doi.org/10.1089/ten.TEA.2010.0043

The ARF Tumor Suppressor Regulates Bone Remodeling and Osteosarcoma Development in Mice

Authors

Daniel A. Rauch, Michelle A. Hurchla, John C. Harding, Hongju Deng, Lauren K. Shea, Mark C. Eagleton, Stefan Niewiesk, Michael D. Lairmore, David Piwnica-Worms, Thomas J. Rosol, Jason D. Weber, Lee Ratner, Katherine N. Weilbaecher

Abstract

The ARF tumor suppressor regulates p53 as well as basic developmental processes independent of p53, including osteoclast activation, by controlling ribosomal biogenesis. Here we provide evidence that ARF is a master regulator of bone remodeling and osteosarcoma (OS) development in mice. Arf-/- mice displayed increased osteoblast (OB) and osteoclast (OC) activity with a significant net increase in trabecular bone volume. The long bones of Arf-/- mice had increased expression of OB genes while Arf-/- OB showed enhanced differentiation in vitro. Mice transgenic for the Tax oncogene develop lymphocytic tumors with associated osteolytic lesions, while Tax+Arf-/- mice uniformly developed spontaneous OS by 7 months of age. Tax+Arf-/- tumors were well differentiated OS characterized by an abundance of new bone with OC recruitment, expressed OB markers and displayed intact levels of p53 mRNA and reduced Rb transcript levels. Cell lines established from OS recapitulated characteristics of the primary tumor, including the expression of mature OB markers and ability to form mineralized tumors when transplanted. Loss of heterozygosity in OS tumors arising in Tax+Arf+/- mice emphasized the necessity of ARF-loss in OS development. Hypothesizing that inhibition of ARF-regulated bone remodeling would repress development of OS, we demonstrated that treatment of Tax+Arf-/- mice with zoledronic acid, a bisphosphonate inhibitor of OC activity and repressor of bone turnover, prevented or delayed the onset of OS. These data describe a novel role for ARF as a regulator of bone remodeling through effects on both OB and OC. Finally, these data underscore the potential of targeting bone remodeling as adjuvant therapy or in patients with genetic predispositions to prevent the development of OS.

Link to Article

http://dx.doi.org/10.1371/journal.pone.0015755

Histologic evaluation of root response to intrusion in mandibular teeth in beagle dogs

Authors

Juan I. Ramirez-Echave, Peter H. Buschang, Roberto Carrillo, P. Emile Rossouw, William W. Nagy, Lynne A. Opperman

Abstract

The purpose of this article was to histologically evaluate root resorption and repair after orthodontic intrusion with different force magnitudes and fixed anchorage. A randomized split-mouth repeated-measure design was used. Intrusive forces were applied for 98 days to the mandibular second, third, and fourth premolars of 8 mature beagle dogs. Two miniscrew implants were used as anchorage to apply constant intrusive forces of 50, 100, or 200 g per tooth. Demineralized sections of each tooth were stained and histologically studied for root resorption. Multilevel statistical procedures were used to evaluate the results. Root resorption was present in all teeth, independent of the force applied. Significant differences were found between root regions, with the apices and the interradicular regions the most affected and with dentin involvement at the furcation. There was cementum repair in 24.14% of the lacunae. Light constant intrusive forces between 50 and 200 g showed no significant differences in the amount of resorption produced. Resorption was more frequently seen at the level of the apices and the furcation. Orthodontically induced root resorption is not clinically significant after application of continuous intrusive forces between 50 and 200 g. Moreover, there is no relationship between root resorption, the position of posterior mandibular teeth in the arch, and the amount of intrusive force applied.

Link to Article

http://dx.doi.org/10.1016/j.ajodo.2009.07.014

Skeletal effects of whole-body vibration in adult and aged mice

Authors

Michelle A. Lynch, Michael D. Brodt, Matthew J. Silva

Abstract

Low-amplitude, whole-body vibration (WBV) may be anabolic for bone. Animal studies of WBV have not evaluated skeletal effects in aged animals. We exposed 75 male BALB/c mice (7 month/young-adult; 22 month/aged) to 5 weeks of daily WBV (15 min/day, 5 day/wk; 90 Hz sine wave) at acceleration amplitudes of 0 (sham), 0.3, or 1.0 g. Whole-body bone mineral content (BMC) increased with time in 7 month (p < 0.001) but not 22 month (p = 0.34) mice, independent of WBV (p = 0.60). In 7 month mice, lower-leg BMC increased with time in 0.3 and 1.0 g groups (p < 0.005) but not in the sham group (p = 0.09), indicating a positive WBV effect. In 22 month mice, there were no changes with time in lower-leg BMC (p = 0.11). WBV did not affect tibial trabecular or cortical bone structure (by µCT), dynamic indices of trabecular or cortical bone formation, trabecular osteoclast surface, or the mass of the reproductive fat pad (p > 0.05). Each of these outcomes was diminished in 7 month versus 22 month animals (p < 0.05). In summary, 5 weeks of daily exposure to low-amplitude WBV had no skeletal effects in aged male mice. The potential of WBV to enhance bone mass in age-related osteoporosis is not supported in this preclinical study.

Link to Article

http://dx.doi.org/10.1002/jor.20965

Suberoylanilide hydroxamic acid (SAHA; vorinostat) causes bone loss by inhibiting immature osteoblasts

Authors

Meghan E. McGee-Lawrence and Angela L. McCleary-Wheeler and Frank J. Secreto and David F. Razidlo and Minzhi Zhang and Bridget A. Stensgard and Xiaodong Li and Gary S. Stein and Jane B. Lian and Jennifer J. Westendorf

Abstract

Histone deacetylase (Hdac) inhibitors are used clinically to treat cancer and epilepsy. Although Hdac inhibition accelerates osteoblast maturation and suppresses osteoclast maturation in vitro, the effects of Hdac inhibitors on the skeleton are not understood. The purpose of this study was to determine how the pan-Hdac inhibitor, suberoylanilide hydroxamic acid (SAHA; a.k.a. vorinostat or ZolinzaTM) affects bone mass and remodeling in vivo. Male C57BL/6 mice received daily SAHA (100 mg/kg) or vehicle injections for 3 to 4 weeks. SAHA decreased trabecular bone volume fraction and trabecular number in the distal femur. Cortical bone at the femoral midshaft was not affected. SAHA reduced serum levels of P1NP, a bone formation marker, and also suppressed tibial mRNA levels of type I collagen, osteocalcin and osteopontin, but did not alter Runx2 or osterix transcripts. SAHA decreased histological measures of osteoblast number but interestingly increased indices of osteoblast activity including mineral apposition rate and bone formation rate. Neither serum (TRAcP 5b) nor histological markers of bone resorption were affected by SAHA. P1NP levels returned to baseline in animals which were allowed to recover for 4 weeks after 4 weeks of daily SAHA injections, but bone density remained low. In vitro, SAHA suppressed osteogenic colony formation, decreased osteoblastic gene expression, induced cell cycle arrest, and caused DNA damage in bone marrow-derived adherent cells. Collectively, these data demonstrate that bone loss following treatment with SAHA is primarily due to a reduction in osteoblast number. Moreover, these decreases in osteoblast number can be attributed to the deleterious effects of SAHA on immature osteoblasts, even while mature osteoblasts are resistant to the harmful effects and demonstrate increased activity in vivo, indicating that the response of osteoblasts to SAHA is dependent upon their differentiation state. These studies suggest that clinical use of SAHA and other Hdac inhibitors to treat cancer, epilepsy or other conditions may potentially compromise skeletal structure and function.

Link to Article

http://dx.doi.org/10.1016/j.bone.2011.01.007