Disruption of the anterior–posterior rotator cuff force balance alters joint function and leads to joint damage in a rat model

Authors

Katherine E. Reuther, Stephen J. Thomas, Jennica J. Tucker, Joseph J. Sarver, Chancellor F. Gray, Sarah I. Rooney, David L. Glaser, Louis J. Soslowsky

Abstract

The rotator cuff assists in shoulder movement and provides dynamic stability to the glenohumeral joint. Specifically, the anterior–posterior (AP) force balance, provided by the subscapularis anteriorly and the infraspinatus and teres minor posteriorly, is critical for joint stability and concentric rotation of the humeral head on the glenoid. However, limited understanding exists of the consequences associated with disruption of the AP force balance (due to tears of both the supraspinatus and infraspinatus tendons) on joint function and joint damage. We investigated the effect of disrupting the APforce balance on joint function and joint damage in an overuse rat model. Twenty-eight rats underwent 4 weeks of overuse to produce a tendinopathic condition and were then randomized into two surgical groups: Detachment of the supraspinatus only or detachment of the supraspinatus and infraspinatus tendons. Rats were then gradually returned to their overuse protocol. Quantitative ambulatory measures including medial/lateral, propulsion, braking, and vertical forces were significantly different between groups. Additionally, cartilage and adjacent tendon properties were significantly altered. These results identify joint imbalance as a mechanical mechanism for joint damage and demonstrate the importance of preserving rotator cuff balance when treating active cuff tear patients.

Link To Article

http://dx.doi.org/10.1002/jor.22586

Differential Effects of Collagen Prolyl 3-Hydroxylation on Skeletal Tissues

Authors

Erica P. Homan, Caressa Lietman, Ingo Grafe, Jennifer Lennington, Roy Morello, Dobrawa Napierala, Ming-Ming Jiang, Elda M. Munivez, Brian Dawson, Terry K. Bertin, Yuqing Chen, Rhonald Lua, Olivier Lichtarge, Brendan H. L. Lee

Abstract

Mutations in the genes encoding cartilage associated protein (CRTAP) and prolyl 3-hydroxylase 1 (P3H1 encoded by LEPRE1) were the first identified causes of recessive Osteogenesis Imperfecta (OI). These proteins, together with cyclophilin B (encoded by PPIB), form a complex that 3-hydroxylates a single proline residue on the α1(I) chain (Pro986) and has cis/trans isomerase (PPIase) activity essential for proper collagen folding. Recent data suggest that prolyl 3-hydroxylation of Pro986 is not required for the structural stability of collagen; however, the absence of this post-translational modification may disrupt protein-protein interactions integral for proper collagen folding and lead to collagen over-modification. P3H1 and CRTAP stabilize each other and absence of one results in degradation of the other. Hence, hypomorphic or loss of function mutations of either gene cause loss of the whole complex and its associated functions. The relative contribution of losing this complex's 3-hydroxylation versus PPIase and collagen chaperone activities to the phenotype of recessive OI is unknown. To distinguish between these functions, we generated knock-in mice carrying a single amino acid substitution in the catalytic site of P3h1 (Lepre1H662A). This substitution abolished P3h1 activity but retained ability to form a complex with Crtap and thus the collagen chaperone function. Knock-in mice showed absence of prolyl 3-hydroxylation at Pro986 of the α1(I) and α1(II) collagen chains but no significant over-modification at other collagen residues. They were normal in appearance, had no growth defects and normal cartilage growth plate histology but showed decreased trabecular bone mass. This new mouse model recapitulates elements of the bone phenotype of OI but not the cartilage and growth phenotypes caused by loss of the prolyl 3-hydroxylation complex. Our observations suggest differential tissue consequences due to selective inactivation of P3H1 hydroxylase activity versus complete ablation of the prolyl 3-hydroxylation complex.

Link To Article

http://dx.doi.org/10.1371/journal.pgen.1004121

A closer look at the immediate trabecula response to combined parathyroid hormone and alendronate treatment

Authors

Allison R. Altman, Wei-Ju Tseng, Chantal M.J. de Bakker, Beom Kang Huh, Abhishek Chandra, Ling Qin, X. Sherry Liu

Abstract

Daily injections of parathyroid hormone (PTH) are the only FDA-approved anabolic treatment for osteoporosis; however PTH is only clinically approved for treatment periods of up to 24 months. To enhance its anabolic effect, combining PTH with anti-resorptive therapy was proposed and expected to maximize the effectiveness of PTH. The current study aimed to elucidate structural mechanisms through which combination therapy can further improve bone strength over a limited treatment window of 12 days, to more closely examine the early phase of the anabolic window. We examined 30 female rats treated with either vehicle (Veh), alendronate (ALN), PTH, or both PTH and ALN (PTH + ALN). Standard and individual trabecula segmentation (ITS)-based microstructural analyses were performed using in vivo micro-computed tomography. We found an increase in BV/TV in all treatments with the highest in the PTH + ALN group. Tb.Th* increased in both PTH and PTH + ALN groups well beyond that of the Veh or ALN group. SMI decreased in all treatments with PTH + ALN having the greatest tendency toward plate-like structures. ITS confirmed the trend toward more plate-like structures with increased plate Tb.N and increased plate-to-rod ratio that was most pronounced in the PTH + ALN group. Using image-based finite element analysis, we demonstrated that stiffness increased in all treatment groups, again with the largest increase in the PTH + ALN group, indicating the resulting structural implications of increased plate-like structure. Static and dynamic bone histomorphometry and a serum resorption marker confirmed that PTH + ALN significantly increased bone formation activities and suppressed bone resorption activities. Overall the results indicate that PTH + ALN treatment has an additive effect due to a preferential increase in plate-like structures.

Link To Article

http://dx.doi.org/10.1016/j.bone.2014.01.008

First Mouse Model for Combined Osteogenesis Imperfecta and Ehlers-Danlos Syndrome

Authors

Frieda Chen Ph.D., Ruolin Guo Ph.D., Shousaku Itoh D.D.S., Ph.D., Luisa Moreno Ph.D., Esther Rosenthal, Tanya Zappitelli, Ralph A. Zirngibl Ph.D., Ann Flenniken Ph.D., William Cole M.D., Marc Grynpas Ph.D., Lucy R. Osborne Ph.D., Wolfgang Vogel Ph.D., Lee Adamson Ph.D., Janet Rossant Ph.D., Jane E. Aubin Ph.D.

Abstract

Using a genome-wide N-ethyl-N-nitrosourea (ENU)-induced dominant mutagenesis screen in mice, we identified a founder with low bone mineral density (BMD). Mapping and sequencing revealed a T to C transition in a splice donor of the collagen alpha1 type I (Col1a1) gene resulting in the skipping of exon 9 and a predicted 18 amino acid deletion within the N-terminal region of the triple helical domain of Col1a1. Col1a1Jrt/+ mice were smaller in size, had lower BMD associated with decreased bone volume/tissue volume (BV/TV) and reduced trabecular number and furthermore exhibited mechanically weak and brittle, fracture-prone bones, a hallmark of Osteogenesis Imperfecta (OI). Several markers of osteoblast differentiation were upregulated in mutant bone and histomorphometry showed that the proportion of trabecular bone surfaces covered by activated osteoblasts (Ob.S/BS and N.Ob/BS) was elevated but bone surfaces undergoing resorption (Oc.S/BS and N.Oc/BS) were not. The number of bone marrow stromal osteoprogenitors (CFU-ALP) was unaffected, but mineralization was decreased in cultures from young Col1a1Jrt/+ versus +/+ mice. Total collagen and type I collagen content of matrices deposited by Col1a1Jrt/+ dermal fibroblasts in culture was ∼40% and 30% respectively that of +/+ cells, suggesting that mutant collagen chains exerted a dominant negative effect on type I collagen biosynthesis. Mutant collagen fibrils were also markedly smaller in diameter than +/+ fibrils in bone, tendon and extracellular matrices deposited by dermal fibroblasts in vitro. Col1a1Jrt/+ mice also exhibited traits associated with Ehlers-Danlos syndrome (EDS): their skin had reduced tensile properties, tail tendon appeared more frayed and a third of the young adult mice had noticeable curvature of the spine. Col1a1Jrt/+ is the first reported model of combined OI/EDS and will be useful for exploring aspects of OI and EDS pathophysiology and treatment.

Link To Article

http://dx.doi.org/10.1002/jbmr.2177

Evolution of mesoporous bioactive glass scaffold implanted in rat femur based on 45Ca labelling, tracing and histological analysis

Authors

Baiyan Sui, Gaoren Zhong, and Jiao Sun

Abstract

Mesoporous bioactive glass (MBG) as a biodegradable scaffold with a nanostructure has attracted significant attention. However, the in vivo evolution of MBG, which includes in-situ degradation, the local effect induced by degradation and the disposition of degradation products, remains unclear. In this study, we performed in situ labelling and synthesis of MBG scaffold for the first time using 45CaCl2. The obtained 45Ca-MBG scaffolds possessed as mesoporous-macroporous cross-linked structure. These 45Ca-MBG scaffolds were implanted in critical-sized rat femur defects (3×3 mm) for 1 day and for 1, 4, 8 and 12 weeks and analyzed by isotopic quantitative tracing. The results illustrated MBG scaffolds gradually degraded over time and persisted at a local level of approximately 9.63% at week 12. This finding suggests that only a very small amount of MBG-released calcium ions may have been transformed into calcium components of the new bone matrix. The research also confirmed that the active ingredients derived from the degradation of MBG scaffolds could actively regulate the mRNA expression levels of osteoblast-related genes in rat bone marrow-derived mesenchymal stem cells (rBMSCs) and promote bone regeneration in vivo. Moreover, through isotopic tracing of the entire body, 45Ca, which disappeared in situ after implantation, could be detected in the heart, lungs, spleen, kidneys, intestines and brain via the blood and mainly accumulated in distal bone tissue, including the radius and cranium. However, 45Ca radioactivity in the body tissues significantly decreased or disappeared after 12 weeks. Systemic toxicological studies on MBG scaffolds demonstrated the degradation products that spread to major organs did not cause abnormal histopathological changes. The above discoveries comprehensively address crucial issues regarding the application of MBG in vivo, and these findings provide a scientific basis for introducing a material with mesoporous structure into clinical applications.

Link To Article

http://dx.doi.org/10.1021/am4056886

Induced ablation of Bmp1 and Tll1 produces osteogenesis imperfecta in mice

Authors

Alison M. Muir, Yinshi Ren, Delana Hopkins Butz, Nicholas A. Davis, Robert D. Blank, David E. Birk, Se-Jin Lee, David Rowe, Jian Q. Feng and Daniel S. Greenspan

Abstract

Osteogenesis imperfecta (OI), or brittle bone disease, is most often caused by dominant mutations in the collagen I genes COL1A1/COL1A2, whereas rarer recessive OI is often caused by mutations in genes encoding collagen I-interacting proteins. Recently, mutations in the gene for the proteinase bone morphogenetic 1 (BMP1) were reported in two recessive OI families. BMP1 and the closely related proteinase mammalian tolloid-like 1 (mTLL1) are co-expressed in various tissues, including bone, and have overlapping activities that include biosynthetic processing of procollagen precursors into mature collagen monomers. However, early lethality of Bmp1- and Tll1-null mice has precluded use of such models for careful study of in vivo roles of their protein products. Here we employ novel mouse strains with floxed Bmp1 and Tll1 alleles to induce postnatal, simultaneous ablation of the two genes, thus avoiding barriers of Bmp1−/− and Tll1−/− lethality and issues of functional redundancy. Bones of the conditionally null mice are dramatically weakened and brittle, with spontaneous fractures—defining features of OI. Additional skeletal features include osteomalacia, thinned/porous cortical bone, reduced processing of procollagen and dentin matrix protein 1, remarkably high bone turnover and defective osteocyte maturation that is accompanied by decreased expression of the osteocyte marker and Wnt-signaling inhibitor sclerostin, and by marked induction of canonical Wnt signaling. The novel animal model presented here provides new opportunities for in-depth analyses of in vivo roles of BMP1-like proteinases in bone and other tissues, and for their roles, and for possible therapeutic interventions, in OI.

Link To Article

http://dx.doi.org/10.1093/hmg/ddu013