Osteoclast Deficiency Contributes to Temporomandibular Joint Ankylosed Bone Mass Formation

Authors

L.H. He, E. Xiao, D.H. Duan, Y.H. Gan, Y. Zhang

Abstract

Ankylosed bone mass in temporomandibular joint ankylosis (TMJA) is an important factor affecting mouth-opening limitation. However, the mechanism underlying the occurrence of ankylosed bone mass remains unknown. Research has shown that osteoblasts and osteoclasts maintain balance in bone remodeling. Thus, we hypothesized that aberrant osteoclastogenesis and osteogenesis may be involved in the occurrence of ankylosed bone mass in TMJA. In this study, we characterized the osteogenesis of bone marrow stem cells and the osteoclastogenesis of myelomonocyte in clinical specimens of TMJA and normal controls. Results showed that, compared with control bone marrow stem cells, TMJA bone marrow stem cells had lower proliferative and osteogenic capacities. The number of osteoclasts in the ankylosed bone mass group dramatically decreased, and myelomonocyte osteoclastogenic potential was impaired. The RANKL/OPG ratio of the ankylosed bone mass group was lower than that of the control group. Thus, our study suggests that osteoclast deficiency may be an important factor affecting bone mass ankylosis.

Optimizing tamoxifen-inducible Cre/loxp system to reduce tamoxifen effect on bone turnover in long bones of young mice

Authors

Zhendong A. Zhong, Weihua Sun, Haiyan Chen, Hongliang Zhang, Yu-an E. Lay, Nancy E. Lane, Wei Yao

Abstract

Abstract For tamoxifen-dependent Cre recombinase, also known as CreER recombinase, tamoxifen (TAM) is used to activate the Cre to generate time- and tissue-specific mouse mutants. TAM is a potent CreER system inducer; however, TAM is also an active selective estrogen receptor modulator (SERM) that can influence bone homeostasis. The purpose of this study was to optimize the TAM dose for Cre recombinase activation while minimizing the effects of TAM on bone turnover in young growing mice.

Methods To evaluate the effects of TAM on bone turnover and bone mass, 1-month-old male wild-type mice were intraperitoneally injected with TAM at 0, 1, 10 or 100 mg/kg/day for four consecutive days. The distal femurs were analyzed one month after the last TAM injection by microCT, mechanical test, and surface-based bone histomorphometry. Similar doses of TAM were used in Col1 (2.3 kb)-CreERT2; mT/mG reporter mice to evaluate the dose-dependent efficacy of Cre-ER activation in bone tissue.

Results A TAM dose of 100 mg/kg × 4 days significantly increased trabecular bone volume/total volume (BV/TV) of the distal femur, femur length, bone strength, and serum bone turnover markers compared to the 0 mg control group. In contrast, TAM doses ≤ 10 mg/kg did not significantly change any of these parameters compared to the 0 mg group, although a higher bone strength was observed in the 10 mg group. Surface-based histomorphometry revealed that the 100 mg/kg dose of TAM dose significantly increased trabecular bone formation and decreased periosteal bone formation at 1-week post-TAM treatment. Using the reporter mouse model Col1-CreERT2; mT/mG, we found that 10 mg/kg TAM induced Col1-CreERT2 activity in bone at a comparable level to the 100 mg/kg dose.

Conclusions TAM treatment at 100 mg/kg/day × 4 days significantly affects bone homeostasis, resulting in an anabolic bone effect on trabecular bone in 1-month-old male mice. However, a lower dose of TAM at 10 mg/kg/day × 4 days can yield similar Col1-CreERT2 induction efficacy with minimum effects on bone turnover in young male mice.

Link To Article

http://dx.doi.org/10.1016/j.bone.2015.07.034

Negative Skeletal Effects of Locally Produced Adiponectin

Authors

Marcia J. Abbott, Theresa M. Roth, Linh Ho, Liping Wang, Dylan O’Carroll, Robert A. Nissenson

Abstract

Epidemiological studies show that high circulating levels of adiponectin are associated with low bone mineral density. The effect of adiponectin on skeletal homeostasis, on osteoblasts in particular, remains controversial. We investigated this issue using mice with adipocyte-specific over-expression of adiponectin (AdTg). MicroCT and histomorphometric analysis revealed decreases (15%) in fractional bone volume in AdTg mice at the proximal tibia with no changes at the distal femur. Cortical bone thickness at mid-shafts of the tibia and at the tibiofibular junction was reduced (3–4%) in AdTg mice. Dynamic histomorphometry at the proximal tibia in AdTg mice revealed inhibition of bone formation. AdTg mice had increased numbers of adipocytes in close proximity to trabecular bone in the tibia, associated with increased adiponectin levels in tibial marrow. Treatment of BMSCs with adiponectin after initiation of osteoblastic differentiation resulted in reduced mineralized colony formation and reduced expression of mRNA of osteoblastic genes, osterix (70%), Runx2 (52%), alkaline phosphatase (72%), Col1 (74%), and osteocalcin (81%). Adiponectin treatment of differentiating osteoblasts increased expression of the osteoblast genes PPARγ (32%) and C/ebpα (55%) and increased adipocyte colony formation. These data suggest a model in which locally produced adiponectin plays a negative role in regulating skeletal homeostasis through inhibition of bone formation and by promoting an adipogenic phenotype.

Link To Article

http://dx.doi.org/10.1371/journal.pone.0134290

Rescue of the abnormal skeletal phenotype in Ts65Dn Down syndrome mice using genetic and therapeutic modulation of trisomic Dyrk1a

Authors

Joshua D. Blazek, Irushi Abeysekera, Jiliang Li and Randall J. Roper

Abstract

Trisomy 21 causes skeletal alterations in individuals with Down syndrome (DS) but the causative trisomic gene and a therapeutic approach to rescue these abnormalities are unknown. Individuals with DS display skeletal alterations including reduced bone mineral density, modified bone structure and distinctive facial features. Due to peripheral skeletal anomalies and extended longevity, individuals with DS are increasingly more susceptible to bone fractures. Understanding the genetic and developmental origins of DS skeletal abnormalities would facilitate the development of therapies to rescue these and other deficiencies associated with DS. DYRK1A is found in three copies in individuals with DS and Ts65Dn DS mice and has been hypothesized to be involved in many Trisomy 21 phenotypes including skeletal abnormalities. Return of Dyrk1a copy number to normal levels in Ts65Dn mice rescued the appendicular bone abnormalities, suggesting that appropriate levels of DYRK1A expression are critical for the development and maintenance of the DS appendicular skeleton. Therapy using the DYRK1A inhibitor EGCG improved Ts65Dn skeletal phenotypes. These outcomes suggest that the osteopenic phenotype associated with DS may be rescued postnatally by targeting trisomic Dyrk1a.

Link To Article

http://dx.doi.org/10.1093/hmg/ddv284

Mechanical loading causes site-specific anabolic effects on bone following exposure to ionizing radiation

Authors

Yasaman Shirazi-Fard, Joshua S. Alwood, Ann-Sofie Schreursl, Alesha B. Castillo, Ruth K. Globus

Abstract

During spaceflight, astronauts will be exposed to a complex mixture of ionizing radiation that poses a risk to their health. Exposure of rodents to ionizing radiation on Earth causes bone loss and increases osteoclasts in cancellous tissue, but also may cause persistent damage to stem cells and osteoprogenitors. We hypothesized that ionizing radiation damages skeletal tissue despite a prolonged recovery period, and depletes the ability of cells in the osteoblast lineage to respond at a later time. The goal of the current study was to test if irradiation prevents bone accrual and bone formation induced by an anabolic mechanical stimulus. Tibial axial compression was used as an anabolic stimulus after irradiation with heavy ions. Mice (male, C57BL/6J, 16 weeks) were exposed to high atomic number, high energy (HZE) iron ions (56Fe, 2 Gy, 600 MeV/ion) (IR, n = 5) or sham-irradiated (Sham, n = 5). In vivo axial loading was initiated 5 months post-irradiation; right tibiae in anesthetized mice were subjected to an established protocol known to stimulate bone formation (cyclic 9N compressive pulse, 60 cycles/day, 3 day/wk for 4 weeks). In vivo data showed no difference due to irradiation in the apparent stiffness of the lower limb at the initiation of the axial loading regimen. Axial loading increased cancellous bone volume by microcomputed tomography and bone formation rate by histomorphometry in both sham and irradiated animals, with a main effect of axial loading determined by two-factor ANOVA with repeated measure. There was no effect of radiation in cancellous bone microarchitecture and indices of bone formation. At the tibia diaphysis, results also revealed a main effect of axial loading in structure. Furthermore, irradiation prevented axial loading-induced stimulation of bone formation rate at the periosteal surface of cortical tissue. In summary, axial loading stimulated the net accrual of cancellous and cortical mass and increased cancellous bone formation rate despite prior exposure to ionizing radiation, in this case, HZE particles. Our findings suggest that mechanical stimuli may prove an effective treatment to improve skeletal structure following exposure to ionizing radiation.

Link To Article

http://dx.doi.org/10.1093/hmg/ddv284

Hdac3-Deficiency Increases Marrow Adiposity and Induces Lipid Storage and Glucocorticoid Metabolism in Osteo-Chondroprogenitor Cells

Authors

Meghan E. McGee-Lawrence, Lomeli R. Carpio, Ryan J. Schulze, Jessica L. Pierce, Mark A. McNiven, Joshua N. Farr, Sundeep Khosla, Merry Jo Oursler, and Jennifer J. Westendorf

Abstract

Bone loss and increased marrow adiposity are hallmarks of aging skeletons. Conditional deletion of histone deacetylase (Hdac) 3 in murine osteo-chondroprogenitor cells causes osteopenia and increases marrow adiposity, even in young animals, but the origins of the increased adiposity are unclear. To explore this, bone marrow stromal cells (BMSCs) from Hdac3-depleted and control mice were cultured in osteogenic medium. Hdac3-deficient cultures accumulated lipid droplets in greater abundance than control cultures and expressed high levels of genes related to lipid storage (Fsp27/Cidec, Plin1) and glucocorticoid metabolism (Hsd11b1) despite normal levels of Pparγ2. Approximately 5% of the lipid containing cells in the wildtype cultures expressed the master osteoblast transcription factor Runx2, but this population was 3-fold greater in the Hdac3-depleted cultures. Adenoviral expression of Hdac3 restored normal gene expression, indicating that Hdac3 controls glucocorticoid activation and lipid storage within osteoblast lineage cells. HDAC3 expression was reduced in bone cells from postmenopausal as compared to young women, and in osteoblasts from aged as compared to younger mice. Moreover, phosphorylation of S424 in Hdac3, a posttranslational mark necessary for deacetylase activity, was suppressed in osseous cells from old mice. Thus, concurrent declines in transcription and phosphorylation combine to suppress Hdac3 activity in aging bone, and reduced Hdac3 activity in osteo-chondroprogenitor cells contributes to increased marrow adiposity associated with aging.

Link To Article

http://dx.doi.org/10.1002/jbmr.2602