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

Temporal and spatial expression of osteoactivin during fracture repair

Authors

Samir M. Abdelmagid, Mary F. Barbe, Michael Hadjiargyrou, Thomas A. Owen, Roshanak Razmpour, Saqib Rehman, Steven N. Popoff, Fayez F. Safadi

Abstract

We previously identified osteoactivin (OA) as a novel secreted osteogenic factor with high expression in developing long bones and calvaria, and that stimulates osteoblast differentiation and matrix mineralization in vitro. In this study, we report on OA mRNA and protein expression in intact long bone and growth plate, and in fracture calluses collected at several time points up to 21 days post-fracture (PF). OA mRNA and protein were highly expressed in osteoblasts localized in the metaphysis of intact tibia, and in hypertrophic chondrocytes localized in growth plate, findings assessed by in situ hybridization and immunohistochemistry, respectively. Using a rat fracture model, Northern blot analysis showed that expression of OA mRNA was significantly higher in day-3 and day-10 PF calluses than in intact rat femurs. Using in situ hybridization, we examined OA mRNA expression during fracture healing and found that OA was temporally regulated, with positive signals seen as early as day-3 PF, reaching a maximal intensity at day-10 PF, and finally declining at day-21 PF. At day-5 PF, which correlates with chondrogenesis, OA mRNA levels were significantly higher in the soft callus than in intact femurs. Similarly, we detected high OA protein immuno-expression throughout the reparative phase of the hard callus compared to intact femurs. Interestingly, the secreted OA protein was also detected within the newly made cartilage matrix and osteoid tissue. Taken together, these results suggest the possibility that OA plays an important role in bone formation and serves as a positive regulator of fracture healing.

Link to Article

http://dx.doi.org/10.1002/jcb.22702

Hypothalamic Suppression during Adolescence Varies By Bone Envelope

Authors

Saine, M.E.; Barbe, M.F.; Agah, M.R.; Yingling, V.R.

Abstract

The purpose of this study was to suppress estradiol levels in adolescent (post pubertal rats) using gonadotropin releasing hormone antagonist (GnRH-a) injections and determine the changes in bone structure and mechanical strength. In an IACUC approved study, female rats at 23 days of age were assigned to a baseline group (BL65) (n=10) sacrificed on day 65, a control group (C) (n=15) sacrificed on day 90, or an experimental group (AMEN) (n=9) sacrificed on day 90 that received daily injections of GnRH-a for a 25 day period from 65 to 90 days of age (2.5 mg/kg/dose). Body weights were similar on day 65 however, the AMEN group was significantly heavier than C (17%, p=.001) on day 90. In the AMEN rats relative to C, plasma estradiol levels were reduced by 36% (p=.0001), and plasma IGF-1 levels were 24 % higher (p=.003). In the femur, there was no change in periosteal bone apposition or total cross-sectional area. The marrow area increased by 13.7% (p=.05) resulting in a 7.8% decrease in relative cortical area (p=.012), and endocortical bone formation rate increased by 39.4% (p=.04). trabecular volume and number decreased by 51.5% (p=.0003) and 49.5% (p=.0003), respectively. The absolute peak moment of the tibiae and femurs were unchanged in the AMEN group relative to C, but were reduced by 8.8% (p=.03) and 7.5% (p=.09) respectively when normalized by body weight. Suppression of estradiol by 25 days of GnRH antagonist administration to 65-day old (post pubertal) rats, reduced trabecular volume and number by about 50%, increased endocortical bone turnover, and reduced relative cortical thickness without changing tibial and femoral total area. These changes in bone structure were associated with no change in absolute mechanical strength possibly due to increases in body weight or in IGF-1 concentrations.

Link to Article

http://dx.doi.org/10.1249/MSS.0b013e3181f56a2c

Contribution of Mineral to Bone Structural Behavior and Tissue Mechanical Properties

Authors

Eve Donnelly, Dan X. Chen, Adele L. Boskey, Shefford P. Baker and Marjolein C. H. van der Meulen

Abstract

Bone geometry and tissue material properties jointly govern whole-bone structural behavior. While the role of geometry in structural behavior is well characterized, the contribution of the tissue material properties is less clear, partially due to the multiple tissue constituents and hierarchical levels at which these properties can be characterized. Our objective was to elucidate the contribution of the mineral phase to bone mechanical properties across multiple length scales, from the tissue material level to the structural level. Vitamin D and calcium deficiency in 6-week-old male rats was employed as a model of reduced mineral content with minimal collagen changes. The structural properties of the humeri were measured in three-point bending and related to the mineral content and geometry from microcomputed tomography. Whole-cortex and local bone tissue properties were examined with infrared (IR) spectroscopy, Raman spectroscopy, and nanoindentation to understand the role of altered mineral content on the constituent material behavior. Structural stiffness (−47%) and strength (−50%) were reduced in vitamin D-deficient (−D) humeri relative to controls. Moment of inertia (−38%), tissue mineral density (TMD, −9%), periosteal mineralization (−28%), and IR mineral:matrix ratio (−19%) were reduced in −D cortices. Thus, both decreased tissue mineral content and changes in cortical geometry contributed to impaired skeletal load-bearing function. In fact, 97% of the variability in humeral strength was explained by moment of inertia, TMD, and IR mineral:matrix ratio. The strong relationships between structural properties and cortical material composition demonstrate a critical role of the microscale material behavior in skeletal load-bearing performance.

Link to Article

http://dx.doi.org/10.1007/s00223-010-9404-x

Effects of the Combination Treatment of Raloxifene and Alendronate on the Biomechanical Properties of Vertebral Bone

Authors

Tamim Diab, Jason Wang, Susan Reinwald, Robert E. Guldberg, David B. Burr

Abstract

Raloxifene (RAL) and alendronate (ALN) improve the biomechanical properties of bone by different mechanisms. The goal here was to investigate the effects of combination treatment of RAL and ALN on the biomechanical properties of vertebral bone. Six-month-old Sprague-Dawley rats (n=80) were randomized into 5 experimental groups (Sham, OVX, OVX+RAL, OVX+ALN, OVX+RAL+ALN; n=16/group). Following sacrifice, structural and derived material biomechanical properties of vertebral bodies were assessed. Density and dynamic histomorphometric measurements were made on cancellous bone. The results demonstrate that the structural biomechanical properties of vertebral bone are improved with the combination treatment. Stiffness and ultimate load of the OVX+RAL and OVX+ALN groups were significantly lower than sham, but the combination treatment with RAL+ALN was not significantly different than sham. Furthermore, the OVX+RAL+ALN group was the only agent-treated group in which the ultimate load was significantly higher than OVX (p<0.05). Cancellous bone fractional volume (BV/TVcanc) and mineral density (aBMD) were also improved with the combination treatment. BV/TVcanc of the OVX+RAL+ALN group was 6.7% and 8.7% greater than the OVX+RAL (p<0.05) and OVX+ALN (p<0.05) groups, respectively. aBMD of the OVX+RAL or OVX+ALN groups were not significantly different than OVX, but the combination treatment was significantly higher than OVX or OVX+RAL alone, and not significantly different from sham. Turnover rates of both the RAL+ALN and ALN alone groups were lower than the RAL alone group (p<0.05). We conclude that the combination treatment of raloxifene and alendronate has beneficial effects on bone volume, resulting in an improvement of the structural properties of vertebral bone.

Link to Article

http://dx.doi.org/10.1002/jbmr.197