Microdamage repair and remodeling requires mechanical loading

Authors

Erik I Waldorff, Katya B Christenson, Laura A Cooney, Steven A Goldstein

Abstract

Bone remodeling is necessary to avoid microdamage accumulation, which could lead to whole-bone failure. Previous studies have shown that this bone-repair mechanism is triggered by osteocyte apoptosis. Through the use of a rodent hindlimb suspension model and tibial four-point bending model, the effects of disuse on microdamage remodeling was examined. At day 0, male rats were assigned to one of three groups: weight bearing (WB), hindlimb suspension (HS), or hindlimb suspension with daily intermittent weight bearing following damage-inducing loading (HW). Within each group, the rats were further divided into subgroups corresponding to three sacrifice time points [day 14 (WB and HS only), day 18, or day 35]. At day 14, animals were anesthetized, and their left tibiae underwent cyclic four-point bending to produce fatigue-induced microdamage. At sacrifice, the tibiae were examined using 3D micro-computed tomography (µCT), flow cytometry, and histologic and immunohistochemical stains. The results indicate that only the WB and HW groups had a significant increase in intracortical TRAP-positive resorption pits following damage induction, which was paralleled by a significant decrease in microdamage over time in combination with a shift in the osteoclast lineage owing to a decrease in monocytes. These results demonstrate that osteocyte apoptosis may be insufficient for repair of microdamage without the stimulation provided through physiologic loading. In addition, this potentially could have clinical implications for the current therapeutic paradigm for treating stress fractures, where extended non-weight bearing is employed.

Link to Article

http://dx.doi.org/10.1359/jbmr.091016

The characterization and optimization of injectable silicone resin particles in conjunction with dermal fibroblasts and growth factors: An in vitro study

Authors

Robert M. Crews, Jessica A. Jennings, Jonathan McCanless, Judith A. Cole, Joel D. Bumgardner, Warren O. Haggard

Abstract

Minimally invasive subdermal injection of liquid silicone has been used clinically to augment the soft tissue of the foot to mitigate high pressures that cause diabetic foot ulcers. However, implant migration has been a clinical issue. The objective of this study was to assess the effects of three specific concentrations of silicone resin particles (12 μm average diameter) in conjunction with either platelet-derived growth factor (PDGF-BB) or basic fibroblast growth factor (bFGF) on fibroblast cell proliferation, collagen synthesis, cell morphology, and migration through in vitro assays and a monolayer scratch wound model. PDGF and bFGF enhanced the proliferation of fibroblasts 5.7-fold and fivefold, respectively, while the addition of silicone particles had no significant effect on proliferation. Collagen production was increased approximately twofold with the addition of bFGF and the medium concentration of particles over bFGF without particles and the PDGF groups. The addition of silicone particles had no significant effect on collagen production compared with control groups without particles. Fibroblast migration was enhanced by the addition of both PDGF and bFGF compared to controls, although slower scratch wound closure rates were observed in the presence of particles compared to controls without particles. Cell morphology suggested that particles induced cellular aggregation encircling silicone particles postwounding as well as migration into the wound area. These results suggest that silicone particles in combination with a growth factor might enhance fibroblast aggregation and implant stability, and could promote connective tissue ingrowth and implant encapsulation in the soft tissue of the diabetic foot.

Link to Article

http://dx.doi.org/10.1002/jbm.b.31579

A rate-limiting role for DKK1 in bone formation and the remediation of bone loss in mouse and primate models of postmenopausal osteoporosis by an experimental therapeutic antibody

Authors

Helmut Glantschnig, Kevin Scott, Richard Hampton, Nan Wei, Paul McCracken, Pascale Nantermet, Jing Zhao, Salvatore Vitelli, Lingyi Huang, Peter Haytko, Ping Lu, John Fisher, Punam Sandhu, Jacquellynn Cook, Donald Williams, William Strohl, Osvaldo Flores, Donald Kimmel, Fubao Wang and An Zhiqiang

Abstract

Genetic studies have linked both osteoporotic and high bone mass (HBM) phenotypes to LDL-receptor related proteins (LRP 4/5/6). LRP are receptors for inhibitory Dickkopf-1 (DKK1) protein and treatment modalities that modulate LRP/DKK1 binding may therefore act as stimulators of bone mass accrual. Here we report that RH2-18, a fully human monoclonal anti-DKK1 antibody elicits systemic pharmacologic bone efficacy and new bone formation at endosteal bone surfaces in vivo in a mouse model of estrogen deficiency induced osteopenia. This was paralleled by partial-to-complete resolution of osteopenia (bone mineral density, BMD) at all skeletal sites investigated in femur and lumbar-vertebral bodies and the restoration of trabecular bone micro-architecture. Importantly, testing of RH2-18 in adult, osteopenic rhesus macaques demonstrated a rate limiting role of DKK1 at multiple skeletal sites and responsiveness to treatment. In conclusion, this study provides pharmacologic evidence for modulation of DKK1 bioactivity in the adult osteopenic skeleton as a viable approach to resolve osteopenia in animal models. Thus, data described here suggest that targeting DKK1 through means such as a fully-human anti-DKK1-antibody provides a potential bone-anabolic treatment for postmenopausal osteoporosis.

Link to Article

http://dx.doi.org/10.1124/jpet.111.181404

Cerebroretinal microangiopathy with calcifications and cysts: Characterization of the skeletal phenotype

Authors

Sanna Toiviainen-Salo, Tarja Linnankivi, Anne Saarinen, Mervi K. Mäyränpää, Riitta Karikoski, Outi Mäkitie

Abstract

Cerebral cysts and calcifications with leukoencephalopathy and retinal vascular abnormalities are diagnostic hallmarks of cerebroretinal microangiopathy with calcifications and cysts (CRMCC). Previous studies have suggested that skeletal involvement is also common, but its characteristics remain unknown. This study aimed to assess the skeletal phenotype in CRMCC. All Finnish patients with features consistent with CRMCC and for whom radiographs were available were included. Clinical information pertinent to the skeletal phenotype was collected from hospital records, and all plain radiographs were reviewed for skeletal features. Bone mineral density (BMD) was measured by DXA. In one patient, bone biopsies were obtained for bone histology and histomorphometric analyses. The LRP5 gene was analyzed for mutations by direct sequencing. Our results show that the skeletal phenotype in CRMCC includes (1) compromised longitudinal growth pre- and postnatally, (2) generalized osteopenia or early onset low turnover osteoporosis with fragility fractures, and (3) metaphyseal abnormalities that may lead to limb deformities such as short femoral neck or genua valga. DXA measurements in three patients showed low BMD, and bone biopsies in the fourth patient with pathological fractures and impaired fracture healing showed low-turnover osteoporosis, with reduced osteoclast and osteoblast activity. Direct sequencing of all LRP5 coding exons and exon–intron boundaries in six patients with CRMCC revealed no putative mutations. We conclude that the CRMCC-associated bone disease is characterized by low BMD and pathological fractures with delayed healing, metaphyseal changes, and short stature pre- and postnatally. LRP5 is not a disease-causing gene in CRMCC.

Link to Article

http://dx.doi.org/10.1002/ajmg.a.33994

Analysis of osteoarthritis in a mouse model of the progeroid human DNA repair syndrome trichothiodystrophy

Authors

Sander M. Botter, Michel Zar, Gerjo J. V. M van Osch, Harry van Steeg, Martijn E. T. Dollé, Jan H. J. Hoeijmakers, Harrie Weinans, and Johannes P. T. M. van Leeuwen

Abstract

The increasing average age in developed societies is paralleled by an increase in the prevalence of many age-related diseases such as osteoarthritis (OA), which is characterized by deformation of the joint due to cartilage damage and increased turnover of subchondral bone. Consequently, deficiency in DNA repair, often associated with premature aging, may lead to increased pathology of these two tissues. To examine this possibility, we analyzed the bone and cartilage phenotype of male and female knee joints derived from 52- to 104-week-old WT C57Bl/6 and trichothiodystrophy (TTD) mice, who carry a defect in the nucleotide excision repair pathway and display many features of premature aging. Using micro-CT, we found bone loss in all groups of 104-week-old compared to 52-week-old mice. Cartilage damage was mild to moderate in all mice. Surprisingly, female TTD mice had less cartilage damage, proteoglycan depletion, and osteophytosis compared to WT controls. OA severity in males did not significantly differ between genotypes, although TTD males had less osteophytosis. These results indicate that in premature aging TTD mice age-related changes in cartilage were not more severe compared to WT mice, in striking contrast with bone and many other tissues. This segmental aging character may be explained by a difference in vasculature and thereby oxygen load in cartilage and bone. Alternatively, a difference in impact of an anti-aging response, previously found to be triggered by accumulation of DNA damage, might help explain why female mice were protected from cartilage damage. These findings underline the exceptional segmental nature of progeroid conditions and provide an explanation for pro- and anti-aging features occurring in the same individual.

Link to Article

http://dx.doi.org/10.1007/s11357-010-9175-3

Decreased Bone Formation and Osteopenia in Lamin A/C-Deficient Mice

Authors

Wei Li, Li Sze Yeo, Christopher Vidal, Thomas McCorquodale, Markus Herrmann, Diane Fatkin, Gustavo Duque

Abstract

Age-related bone loss is associated with changes in bone cellularity with characteristically low levels of osteoblastogenesis. The mechanisms that explain these changes remain unclear. Although recent in vitro evidence has suggested a new role for proteins of the nuclear envelope in osteoblastogenesis, the role of these proteins in bone cells differentiation and bone metabolism in vivo remains unknown. In this study, we used the lamin A/C null (Lmna−/−) mice to identify the role of lamin A/C in bone turnover and bone structure in vivo. At three weeks of age, histological and micro computed tomography measurements of femurs in Lmna−/− mice revealed a significant decrease in bone mass and microarchitecture in Lmna−/− mice as compared with their wild type littermates. Furthermore, quantification of cell numbers after normalization with bone surface revealed a significant reduction in osteoblast and osteocyte numbers in Lmna−/− mice compared with their WT littermates. In addition, Lmna−/− mice have significantly lower osteoclast number, which show aberrant changes in their shape and size. Finally, mechanistic analysis demonstrated that absence of lamin A/C is associated with increase expression of MAN-1 a protein of the nuclear envelope closely regulated by lamin A/C, which also colocalizes with Runx2 thus affecting its capacity as osteogenic transcription factor. In summary, these data clearly indicate that the presence of lamin A/C is necessary for normal bone turnover in vivo and that absence of lamin A/C induces low bone turnover osteopenia resembling the cellular changes of age-related bone loss.

Link to Article

http://dx.doi.org/10.1371/journal.pone.0019313