Genetic and hormonal control of bone volume, architecture, and remodeling in XXY mice

Authors

Peter Y Liu, Robert Kalak, YanHe Lue, Yue Jia, Krista Erkkila, Hong Zhou, Markus J Seibel, Christina Wang, Ronald S Swerdloff, Colin R Dunstan

Abstract

Klinefelter syndrome is the most common chromosomal aneuploidy in men (XXY karyotype, 1 in 600 live births) and results in testicular (infertility and androgen deficiency) and nontesticular (cognitive impairment and osteoporosis) deficits. The extent to which skeletal changes are due to testosterone deficiency or arise directly from gene overdosage cannot be determined easily in humans. To answer this, we generated XXY mice through a four-generation breeding scheme. Eight intact XXY and 9 XY littermate controls and 8 castrated XXY mice and 8 castrated XY littermate controls were euthanized at 1 year of age. Castration occurred 6 months prior to killing. A third group of 9 XXY and 11 XY littermates were castrated and simultaneously implanted with a 1-cm Silastic testosterone capsule 8 weeks prior to sacrifice. Tibias were harvested from all three groups and examined by micro–computed tomography and histomorphometry. Blood testosterone concentration was assayed by radioimmunoassay. Compared with intact XY controls, intact androgen-deficient XXY mice had lower bone volume (6.8% ± 1.2% versus8.8% ± 1.7%, mean ± SD, p = .01) and thinner trabeculae (50 ± 4 µm versus 57 ± 5 µm, p = .007). Trabecular separation (270 ± 20 µm versus 270 ± 20 µm) or osteoclast number relative to bone surface (2.4 ± 1.0/mm2 versus 2.7 ± 1.5/mm2) did not differ significantly. Testosterone-replaced XXY mice continued to show lower bone volume (5.5% ± 2.4% versus 8.1% ± 3.5%, p = .026). They also exhibited greater trabecular separation (380 ± 69 µm versus 324 ± 62 µm, p = .040) but equivalent blood testosterone concentrations (6.3 ± 1.8 ng/mL versus 8.2 ± 4.2 ng/mL, p = .28) compared with testosterone-replaced XY littermates. In contrast, castration alone drastically decreased bone volume (p < .001), trabecular thickness (p = .05), and trabecular separation (p < .01) to such a great extent that differences between XXY and XY mice were undetectable. In conclusion, XXY mice replicate many features of human Klinefelter syndrome and therefore are a useful model for studying bone. Testosterone deficiency does not explain the bone phenotype because testosterone-replaced XXY mice show reduced bone volume despite similar blood testosterone levels.

Link to Article

http://dx.doi.org/10.1002/jbmr.104

Loss of skeletal mineralization by the simultaneous ablation of PHOSPHO1 and alkaline phosphatase function: A unified model of the mechanisms of initiation of skeletal calcification

Authors

Manisha C Yadav, Ana Maria Sper Simão, Sonoko Narisawa, Carmen Huesa, Marc D McKee, Colin Farquharson, José Luis Millán

Abstract

Endochondral ossification is a carefully orchestrated process mediated by promoters and inhibitors of mineralization. Phosphatases are implicated, but their identities and functions remain unclear. Alkaline phosphatase (TNAP) plays a crucial role promoting mineralization of the extracellular matrix by restricting the concentration of the calcification inhibitor inorganic pyrophosphate (PPi). Mutations in the TNAP gene cause hypophosphatasia, a heritable form of rickets and osteomalacia. Here we show that PHOSPHO1, a phosphatase with specificity for phosphoethanolamine and phosphocholine, plays a functional role in the initiation of calcification and that ablation of PHOSPHO1 and TNAP function prevents skeletal mineralization. Phospho1−/− mice display growth plate abnormalities, spontaneous fractures, bowed long bones, osteomalacia, and scoliosis in early life. Primary cultures of Phospho1−/− tibial growth plate chondrocytes and chondrocyte-derived matrix vesicles (MVs) show reduced mineralizing ability, and plasma samples from Phospho1−/− mice show reduced levels of TNAP and elevated plasma PPi concentrations. However, transgenic overexpression of TNAP does not correct the bone phenotype in Phospho1−/− mice despite normalization of their plasma PPi levels. In contrast, double ablation of PHOSPHO1 and TNAP function leads to the complete absence of skeletal mineralization and perinatal lethality. We conclude that PHOSPHO1 has a nonredundant functional role during endochondral ossification, and based on these data and a review of the current literature, we propose an inclusive model of skeletal calcification that involves intravesicular PHOSPHO1 function and Pi influx into MVs in the initiation of mineralization and the functions of TNAP, nucleotide pyrophosphatase phosphodiesterase-1, and collagen in the extravesicular progression of mineralization.

Link to Article

http://dx.doi.org/10.1002/jbmr.195

Age-related changes in iliac crest cortical width and porosity: a histomorphometric study

Authors

Shobna Vedi, Stephen Kaptoge, J. E. Compston

Abstract

Although age-related changes in cancellous bone structure in human are relatively well characterized, few studies have addressed changes in cortical bone. We have investigated age-related changes in iliac crest bone biopsy specimens from 54 normal subjects, 23 men and 31 women, aged 18–90 years. A significant decrease in cortical width and area was seen (P = 0.002 and < 0.001 respectively), with no difference between sexes. Haversian canal density increased significantly with age by approximately 9% per decade (P = 0.032) but Haversian canal area tended to be lower, resulting in no overall age-related difference in cortical porosity. Haversian canal area was significantly higher in the endosteal section than in the periosteal section of the cortex (P = 0.019) but the Haversian canal density was lower, resulting in similar overall porosity in the two sections. In conclusion, our results demonstrate an age-related decrease in iliac crest cortical width in men and women and an increase in Haversian canal density, but no overall change in cortical porosity.

Link to Article

http://dx.doi.org/10.1111/j.1469-7580.2011.01356.x

Biofunctionalization of titanium implants with a biomimetic active peptide (P-15) promotes early osseointegration

Authors

R. Lutz, S. Srour, J. Nonhoff, T. Weisel, C. J. Damien, K. A. Schlegel

Abstract

The early stages of peri-implant bone formation play an essential role in the osseointegration and long-term success of dental implants. By incorporating bioactive coatings, this biofunctionalization of implant surfaces may enhance the attachment of the implant to the surrounding bone and stimulate bone regeneration. Material and methods: To demonstrate faster osseointegration, the surfaces of dental implants were grit-blasted and acid-etched. They were then coated with hydroxyapatite (HA) and experimental implants were further coated with a biomimetic active peptide (P-15) in one of two concentrations. These biofunctionalized samples and controls with no peptide were placed in the forehead region of 12 adult pigs. Six animals were evaluated for a period of 14 or 30 days. Histomorphometric analysis demonstrated that the implants with the high concentration of P-15 had significantly higher percentage of bone-to-implant contact (BIC) at 14 (P=0.018) and 30 (P=0.015) days compared with the other groups. Both concentrations of P-15 showed increased peri-implant bone density compared to the control group at 30 days. Biofunctionalization of the implant surface with a biomimetic active peptide leads to significantly increased BIC rates at 14 and 30 days and higher peri-implant bone density at 30 days.

Link to Article

http://dx.doi.org/10.1111/j.1600-0501.2009.01904.x

Blockade of transforming growth factor-beta (TGFβ) signaling inhibits osteoblastic tumorigenesis by a novel human prostate cancer cell line

Authors

Sweta Mishra, Yuping Tang, Long Wang, Linda deGraffenried, I-Tien Yeh, Sherry Werner, Dean Troye, John A. Copland, Lu-Zhe Sun

Abstract

The skeleton is the most common site of prostate cancer metastasis, which often results in osteoblastic lesions. The role of transforming growth factor-beta (TGFβ) signaling in prostate cancer-induced osteoblastic metastasis is not clear. We investigated the role of TGFβ signaling in prostate cancer-induced bone metastasis using a novel human prostate cancer cell line, PacMetUT1. We injected PacMetUT1/Luc-GFP cells in male nude mice by intracardiac and intratibia injections and then investigated the effect of TGFβ signaling abrogation on osteoblastic tumor growth and incidence in vivo by using fluorescence and bioluminescence imaging analysis and quantifying bone and tumor volume by histomorphometry analysis. Osteoclasts were counted using TRAP assay. Osteoblastic bone metastasis in skull, rib, and femur was detected after 10–16 weeks of intracardiac injection of the PacMetUT1 cells. Stable knockdown of TGFβ1 with an shRNA resulted in decreased tumor incidence and bone formation when the cells were directly injected into the tibiae. Systemic administration of either a small inhibitor of TGFβ type I receptor kinase or a pan TGFβ binding protein (BGERII) also decreased bone tumor growth and osteoblastic bone formation in vivo after 7 weeks of treatment. Our results for the first time indicate that blockade of TGFβ signaling in the PacMetUT1 model significantly inhibits osteoblastic bone formation and tumor incidence. Thus, TGFβ signaling pathway may be a viable target for the prevention and treatment of prostate cancer-induced bone metastasis

Link to Article

http://dx.doi.org/10.1002/pros.21361

Osteoarthritis induction leads to early and temporal subchondral plate porosity in the tibial plateau of mice: An in vivo micro CT study

Authors

Sander M. Botter, Gerjo J.V.M van Osch, Stefan Clockaerts, Jan H. Waarsing, Harrie Weinans, Johannes P.T.M. van Leeuwen

Abstract

In osteoarthritis (OA) changes occur both in cartilage and subchondral bone. The subchondral bone plate facilitates normal crosstalk between articular cartilage and trabecular subchondral bone, and adaptive changes in the plate due to OA may therefore disturb crosstalk homeostasis. To investigate these changes over time we examined the cartilage-subchondral bone interface using a combined approach of histology and in vivo micro CT. Male C57Bl/6 mice (n=8), aged 16 weeks, received intra-articular injections with collagenase in one joint to induce instability-related OA and saline into the contralateral knee joint (controls). At 2, 4, 6, 10 and 14 weeks post-injection, changes in the tibial subchondral bone plate and subchondral trabeculae were analyzed. At two weeks post-injection, collagenase injected joints had significantly more cartilage damage and osteophytosis than control joints. Osteoclast activity directly underneath the subchondral bone plate was significantly elevated (Oc.S./BS controls: 7.60± 0.81%; OA: 11.07± 0.79%), causing the plate to become thinner and creating a large increase in subchondral bone plate porosity (cumulative porosity volume controls: 0.05e-3 ± 0.04e-3 mm3; OA: 2.52e-3 ± 0.69e-3 mm3). At four weeks post-injection, the previously formed perforations disappeared, coinciding with a significant rise in osteoblast activity in the subchondral trabecular bone (bone formation rate controls: 0.30± 0.03, OA: 0.62± 0.13 μm2/μm3*day). The current study provides for the first time quantitative longitudinal data on the dynamic changes in the subchondral bone plate after OA induction. The development of plate perforations may enhance mutual interaction between subchondral trabeculae, bone marrow cells and the articular cartilage in OA.

Link to Article

http://dx.doi.org/10.1002/art.30307