Orthodontic mini-implant diameter does not affect in-situ linear microcrack generation in the mandible or the maxilla

Authors

Sean Shih-Yao Liu, Enrique Cruz-Marroquin, Jun Sun, Kelton T. Stewart, Matthew R. Allen

Abstract

Microdamage reduces bone mechanical properties and thus could contribute to implant failure. The objective of this study was to investigate whether the diameter of mini-implants affects linear microcrack generation and whether this differs between the mandible and the maxilla because of their contrasting cortical thicknesses. Maxillary and mandibular quadrants of 5 dogs were randomly assigned to receive, in situ, no pilot drilling or mini-implant insertion (control), pilot drilling only without mini-implants, or pilot drilling plus a mini-implant of 1 of 3 diameters: 1.4 mm (n = 18), 1.6 mm (n = 18), and 2.0 mm (n = 18). Linear microcracks were assessed on basic fuchsin-stained sections by using epifluorescence microscopy. Pilot drilling without mini-implant insertion produced significantly higher linear microcrack burdens in the mandible compared with the maxilla. In the both the mandible and the maxilla, all implants produced higher linear microcrack burdens than did the controls, yet there were no differences between the 3 implant diameters. Neither the diameter of the mini-implant nor the site of insertion (mandible vs maxilla) had a significant effect on the amount of linear microdamage adjacent to the implant when the implants were inserted after pilot drilling in situ.

Link to Article

http://dx.doi.org/10.1016/j.ajodo.2012.07.014

Low-dose Risedronate Sodium Protects Bone Cells after Abrupt Oestrogen Withdrawal

Authors

Wang, G.; Zhu, Z.; Lei, C.; Li, M.; Liu, F.; Mao, Y.; Yu, Z.; Liu, M.; Zhao, X.; Tang, T

Abstract

To investigate the effects of low-dose risedronate sodium on the in vitro cellular profile of osteoblasts, adipocytes, osteocytes and osteoclasts in a rat model of abrupt oestrogen deficiency. Oestrogen deficiency was induced by ovariectomy in 24 female rats. The rats were treated with low-dose (0.24 μg/kg) or high-dose (2.4 μg/kg) risedronate sodium for 4 days presurgery, continuing every 3 days until 15 days postsurgery. Osteogenic and adipogenic differentiation were determined in cultured bone marrow cells by alkaline phosphatase and Oil Red O staining, respectively, and by osteogenic and adipogenic gene expression. Osteoclast formation was measured in bone marrow cells stimulated with macrophage colony-stimulating factor and receptor activator of nuclear factor κB ligand, and stained with tartrate-resistant acid phosphatase. Osteocyte apoptosis was assessed by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labelling assay and B-cell lymphoma-2 (Bcl-2) immunohistochemistry. Low-dose risedronate sodium enhanced osteoblast differentiation, suppressed adipocyte differentiation and osteoclast formation, and reduced osteocyte apoptosis through regulation of Bcl-2 and Bcl-2-associated X protein. Low-dose risedronate sodium may have clinical benefit in protecting against bone loss after abrupt oestrogen deficiency.

Link to Article

http://www.ingentaconnect.com/content/field/jimr/2012/00000040/00000005/art00015

β-catenin promotes bone formation and suppresses bone resorption in postnatal growing mice

Authors

Jianquan Chen, Fanxin Long

Abstract

Genetic studies in the mouse have demonstrated multiple roles for β-catenin in the skeleton. In the embryo, β-catenin is critical for the early stages of osteoblast differentiation. Postnatally, β-catenin in mature osteoblasts and osteocytes indirectly suppresses osteoclast differentiation. However, a direct role for β-catenin in regulating osteoblast number and/or function specifically in the postnatal life has not been demonstrated. Addressing this knowledge gap is important because LRP5, a co-receptor for WNT signaling proposed to function through β-catenin, controls osteoblast number and function in postnatal mice or humans. To overcome the neonatal lethality caused by embryonic deletion of β-catenin in early-stage osteoblast-lineage cells, we utilize Osx-CreERT2 to remove β-catenin in Osx-expressing cells by administering tamoxifen (TM) temporarily to postnatal mice. Lineage-tracing experiments in the long bones demonstrate that Osx-CreERT2 targets predominantly osteoblast-lineage cells on the bone surface, but also transient progenitors that contribute to bone marrow stromal cells and adipocytes. Deletion of β-catenin by this strategy greatly reduces the bone formation activity of the targeted osteoblasts. However, the targeted osteoblasts rapidly turn over and are replaced by an excessive number of non-targeted osteoblasts, causing an unexpected increase in bone formation, but an even greater increase in osteoclast number and activity produces a net effect of severe osteopenia. With time, the mutant mice also exhibit a marked increase in bone marrow adiposity. Thus, β-catenin in postnatal Osx-lineage cells critically regulates bone homeostasis by promoting osteoblast activity and suppressing osteoblast turnover, while restraining osteoclast and marrow fat formation.

Link to Article

http://dx.doi.org/10.1002/jbmr.1834

Decorin expression is important for age-related changes in tendon structure and mechanical properties

Authors

Andrew A. Dunkman, Mark R. Buckley, Michael J. Mienaltowski, Sheila M. Adams, Stephen J. Thomas, Lauren Satchell, Akash Kumar, Lydia Pathmanathan, David P. Beason, Renato V. Iozzo, David E. Birk, Louis J. Soslowsky

Abstract

The aging population is at an increased risk of tendon injury and tendinopathy. Elucidating the molecular basis of tendon aging is crucial to understanding the age-related changes in structure and function in this vulnerable tissue. In this study, the structural and functional features of tendon aging are investigated. In addition, the roles of decorin and biglycan in the aging process were analyzed using transgenic mice at both mature and aged time points. Our hypothesis is that the increase in tendon injuries in the aging population is the result of altered structural properties that reduce the biomechanical function of the tendon and consequently increase susceptibility to injury. Decorin and biglycan are important regulators of tendon structure and therefore, we further hypothesized that decreased function in aged tendons is partly the result of altered decorin and biglycan expression. Biomechanical analyses of mature (day 150) and aged (day 570) patellar tendons revealed deteriorating viscoelastic properties with age. Histology and polarized light microscopy demonstrated decreased cellularity, alterations in tenocyte shape, and reduced collagen fiber alignment in the aged tendons. Ultrastructural analysis of fibril diameter distributions indicated an altered distribution in aged tendons with an increase of large diameter fibrils. Aged wild type tendons maintained expression of decorin which was associated with the structural and functional changes seen in aged tendons. Aged patellar tendons exhibited altered and generally inferior properties across multiple assays. However, decorin-null tendons exhibited significantly decreased effects of aging compared to the other genotypes. The amelioration of the functional deficits seen in the absence of decorin in aged tendons was associated with altered tendon fibril structure. Fibril diameter distributions in the decorin-null aged tendons were comparable to those observed in the mature wild type tendon with the absence of the subpopulation containing large diameter fibrils. Collectively, our findings provide evidence for age-dependent alterations in tendon architecture and functional activity, and further show that lack of stromal decorin attenuates these changes.

Link to Article

http://dx.doi.org/10.1016/j.matbio.2012.11.005

TULA-2, a novel histidine phosphatase, regulates bone remodeling by modulating osteoclast function

Authors

Steven H. Back, Naga Suresh Adapala, Mary F. Barbe, Nick C. Carpino, Alexander Y. Tsygankov, Archana Sanjay

Abstract

Bone is a dynamic tissue that depends on the intricate relationship between protein tyrosine kinases (PTK) and protein tyrosine phosphatases (PTP) for maintaining homeostasis. PTKs and PTPs act like molecular on and off switches and help modulate differentiation and the attachment of osteoclasts to bone matrix regulating bone resorption. The protein T cell ubiquitin ligand-2 (TULA-2), which is abundantly expressed in osteoclasts, is a novel histidine phosphatase. Our results show that of the two family members, only TULA-2 is expressed in osteoclasts and that its expression is sustained throughout the course of osteoclast differentiation, suggesting that TULA-2 may play a role during early as well late stages of osteoclast differentiation. Skeletal analysis of mice that do not express TULA or TULA-2 proteins (DKO mice) revealed that there was a decrease in bone volume due to increased osteoclast numbers and function. Furthermore, in vitro experiments indicated that bone marrow precursor cells from DKO mice have an increased potential to form osteoclasts. At the molecular level, the absence of TULA-2 in osteoclasts results in increased Syk phosphorylation at the Y352 and Y525/526 residues and activation of phospholipase C gamma 2 (PLCγ2) upon engagement of immune-receptor-tyrosine-based-activation-motif (ITAM)—mediated signaling. Furthermore, expression of a phosphatase-dead TULA-2 leads to increased osteoclast function. Taken together, these results suggest that TULA-2 negatively regulates osteoclast differentiation and function.

Link to Article

http://dx.doi.org/10.1007/s00018-012-1203-2

In vivo overexpression of tissue-nonspecific alkaline phosphatase increases skeletal mineralization and affects the phosphorylation status of osteopontin

Authors

Sonoko Narisawa, Manisha C. Yadav, José Luis Millán

Abstract

Functional ablation of tissue-nonspecific alkaline phosphatase (TNAP) (Alpl-/- mice) leads to hypophosphatasia, characterized by rickets/osteomalacia attributable to elevated levels of extracellular inorganic pyrophosphate, a potent mineralization inhibitor. Osteopontin (OPN) is also elevated in the plasma and skeleton of Alpl-/- mice. Phosphorylated OPN is known to inhibit mineralization, however, the phosphorylation status of the increased OPN found in Alpl-/- mice is unknown. Here, we generated a transgenic mouse line expressing human TNAP under control of an osteoblast-specific Col1a1 promoter (Col1a1-Tnap). The transgene is expressed in osteoblasts, periosteum, and cortical bones, and plasma levels of TNAP in mice expressing Col1a1-Tnap are 10-20 times higher than those of wild-type mice. The Col1a1-Tnap animals are healthy and exhibit increased bone mineralization by microCT analysis. Crossbreeding of Col1a1-Tnap transgenic mice to Alpl-/- mice rescues the lethal hypophosphatasia phenotype characteristic of this disease model. Osteoblasts from [Col1a1-Tnap] mice mineralize better than non-transgenic controls and osteoblasts from [Col1a1-Tnap+/-; Alpl-/-] mice are able to mineralize to the level of Alpl+/- heterozygous osteoblasts, while Alpl-/- osteoblasts show no mineralization. We found that the increased levels of OPN in bone tissue of Alpl-/- mice are comprised of phosphorylated forms of OPN while WT and [Col1a1-Tnap+/-; Alpl-/-] mice had both phosphorylated and dephosphorylated forms of OPN. OPN from [Col1a1-Tnap] osteoblasts were more phosphorylated than non-transgenic control cells. Titanium dioxide-liquid chromatography and tandem mass spectrometry analysis revealed that OPN peptides derived from Alpl-/- bone and osteoblasts yielded a higher proportion of phosphorylated peptides than samples from WT mice, and at least two phosphopeptides, p(S174FQVS178DEQY182PDAT186DEDLT191)SHMK and FRIp(S299HELES304S305S306S307)EVN, with one non-localized site each, appear to be preferred sites of TNAP action on OPN. Our data suggest that the pro-mineralization role of TNAP may be related not only to its accepted pyrophosphatase activity but also to its ability to modify the phosphorylation status of OPN.

Link to Article

http://dx.doi.org/10.1002/jbmr.1901