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

Balancing mechanical strength with bioactivity in chitosan–calcium phosphate 3D microsphere scaffolds for bone tissue engineering: air- vs. freeze-drying processes

Authors

D.T. Nguyen, J.D. McCanless, M.M. Mecwan, A.P. Noblett, W.O. Haggard, R.A. Smith & J.D. Bumgardner

Abstract

The objective of this study was to evaluate the potential benefit of 3D composite scaffolds composed of chitosan and calcium phosphate for bone tissue engineering. Additionally, incorporation of mechanically weak lyophilized microspheres within those air-dried (AD) was considered for enhanced bioactivity. AD microsphere, alone, and air- and freeze-dried microsphere (FDAD) 3D scaffolds were evaluated in vitro using a 28-day osteogenic culture model with the Saos-2 cell line. Mechanical testing, quantitative microscopy, and lysozyme-driven enzymatic degradation of the scaffolds were also studied. FDAD scaffold showed a higher concentration (p < 0.01) in cells per scaffold mass vs. AD constructs. Collagen was 31% greater (p < 0.01) on FDAD compared to AD scaffolds not evident in microscopy of microsphere surfaces. Alternatively, AD scaffolds demonstrated a superior threefold increase in compressive strength over FDAD (12 vs. 4 MPa) with minimal degradation. Inclusion of FD spheres within the FDAD scaffolds allowed increased cellular activity through improved seeding, proliferation, and extracellular matrix production (as collagen), although mechanical strength was sacrificed through introduction of the less stiff, porous FD spheres.

Link to Article

http://dx.doi.org/10.1080/09205063.2012.735099

Inflammatory arthritis increases mouse osteoclast precursors with myeloid suppressor function

Authors

Julia F. Charles, Lih-Yun Hsu, Erene C. Niemi, Arthur Weiss, Antonios O. Alipranti and Mary C. Nakamura

Abstract

Increased osteoclastic bone resorption leads to periarticular erosions and systemic osteoporosis in RA patients. Although a great deal is known about how osteoclasts differentiate from precursors and resorb bone, the identity of an osteoclast precursor (OCP) population in vivo and its regulatory role in RA remains elusive. Here, we report the identification of a CD11b–/loLy6Chi BM population with OCP activity in vitro and in vivo. These cells, which can be distinguished from previously characterized precursors in the myeloid lineage, display features of both M1 and M2 monocytes and expand in inflammatory arthritis models. Surprisingly, in one mouse model of RA (adoptive transfer of SKG arthritis), cotransfer of OCP with SKG CD4+ T cells diminished inflammatory arthritis. Similar to monocytic myeloid-derived suppressor cells (M-MDSCs), OCPs suppressed CD4+ and CD8+ T cell proliferation in vitro through the production of NO. This study identifies a BM myeloid precursor population with osteoclastic and T cell–suppressive activity that is expanded in inflammatory arthritis. Therapeutic strategies that prevent the development of OCPs into mature bone-resorbing cells could simultaneously prevent bone resorption and generate an antiinflammatory milieu in the RA joint.

Link to Article

http://dx.doi.org/10.1172/JCI60920

Hydrogen water consumption prevents osteopenia in ovariectomized rats

Authors

Ji-Dong Guo, Li Li, Ya-Min Shi, Hua-Dong Wang, Shu-Xun Hou

Abstract

Accumulating evidence indicates an important role of oxidative stress in the progression of osteoporosis. Recently, it was demonstrated that hydrogen gas, as a novel antioxidant, could selectively reduce hydroxyl radicals and peroxynitrite anion to exert potent therapeutic antioxidant activity. The aim of the present work was to investigate the effect of hydrogen water (HW) consumption on ovariectomy-induced osteoporosis. Ovariectomized rats were fed with HW (1.3 ± 0.2 mg·L−1) for 3 months. Then, blood was collected and femur and vertebrae were removed for evaluation of the effect of HW on bone. HW consumption in ovariectomized rats had no significant effect on oestrogen production, but prevented the reduction of bone mass including bone mineral content and bone mineral density in femur and vertebrae, and preserved mechanical strength including ultimate load, stiffness, and energy, and bone structure including trabecular bone volume fraction, trabecular number, and trabecular thickness in femur, and preserved mechanical strength including ultimate load and stiffness, and bone structure including trabecular bone volume fraction and trabecular number in vertebrae. In addition, treatment with HW abated oxidative stress and suppressed IL-6 and TNF-α mRNA expressions in femur of ovariectomized rats; treatment with HW increased femur endothelial NOS activity and enhanced circulating NO level in ovariectomized rats. HW consumption prevents osteopenia in ovariectomized rats possibly through the ablation of oxidative stress induced by oestrogen withdrawal.

Link to Article

http://dx.doi.org/10.1111/bph.12036